U.S. patent application number 10/535986 was filed with the patent office on 2006-09-07 for metal heater.
This patent application is currently assigned to IBIDEN CO., LTD.. Invention is credited to Kazutaka Mashima.
Application Number | 20060199135 10/535986 |
Document ID | / |
Family ID | 32397744 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060199135 |
Kind Code |
A1 |
Mashima; Kazutaka |
September 7, 2006 |
Metal heater
Abstract
The present invention aims to provide a metal heater that hardly
causes dispersion in the temperature of a semiconductor wafer or
the like upon heating, and heats it quickly without causing warping
and sagging in its metal plate. The present invention provides a
metal heater which includes metal plates and a heating element,
wherein the number of said metal plates is a plural number, the
heating element is sandwiched between the metal plates, and the
thickness of a metal plate on a heating face side is the same as or
larger than the thickness of a metal plate on a side opposite to
said heating face side.
Inventors: |
Mashima; Kazutaka; (GIFU,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
IBIDEN CO., LTD.
1, KANDACHO 2-CHOME, OGAKI-SHI
GIFU
JP
503-8004
|
Family ID: |
32397744 |
Appl. No.: |
10/535986 |
Filed: |
November 25, 2003 |
PCT Filed: |
November 25, 2003 |
PCT NO: |
PCT/JP03/14963 |
371 Date: |
February 15, 2006 |
Current U.S.
Class: |
432/214 |
Current CPC
Class: |
H01L 21/67109 20130101;
H01L 21/67103 20130101; H05B 3/12 20130101; H05B 3/72 20130101 |
Class at
Publication: |
432/214 |
International
Class: |
C21B 9/00 20060101
C21B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 2002 |
JP |
2002-340858 |
Dec 5, 2002 |
JP |
2002-353849 |
Dec 5, 2002 |
JP |
2002-354431 |
Claims
1. A metal heater comprising a metal plate and a heating element,
wherein the number of said metal plates is a plural number, said
heating element is sandwiched between said metal plates, and the
thickness of a metal plate on a heating face side is the same as or
larger than the thickness of a metal plate on a side opposite to
said heating face side.
2. The metal heater according to claim 1, wherein said heating
element is divided into two or more portions.
3. A metal heater comprising a plurality of metal plates and a
heating element, said heating element sandwiched between said metal
plates, wherein said plurality of metal plates are made of the same
material.
4. The metal heater according to claim 3, wherein said plurality of
metal plates comprises a copper-aluminum alloy.
5. A metal heater comprising a plurality of metal plates and a
heating element, with said heating element sandwiched between said
metal plates, wherein a convex portion for supporting an object to
be heated is placed on a heating face opposing the object to be
heated, of said metal plate corresponding to an area on which said
heating element is formed.
6. The metal heater according to claim 5, wherein the area on which
said heating element is formed has a diameter of 250 mm or more,
and the number of convex portions is 6 or more.
7. The metal heater according to claim 5, wherein the area on which
said heating element is formed has a diameter of 200 to 250 mm, and
the number of said convex portions is 5 or more.
8. The metal heater according to any of claims 5 to 7, wherein said
heating element is divided into two or more portions.
Description
TECHNICAL FIELD
[0001] The present invention relates to a metal heater that is
mainly used in the semiconductor industry and optical industry.
BACKGROUND ART
[0002] With respect to an etching device, and a semiconductor
producing/examining device including a chemical vapor deposition
device or the like, metal heaters having substrates of a metal
material such as stainless steel have been used.
[0003] FIG. 4 is a cross-sectional view that schematically shows a
metal heater having a structure that has been conventionally
used.
[0004] In this metal heater 450, a heater 453 in which a nichrome
wire 452 is sandwiched between silicon rubbers 461 is provided to
an aluminum plate 451 having a thickness of 15 mm.
SUMMARY OF THE INVENTION
[0005] However, metal heaters with such structures have the
following problems.
[0006] Metal plates to be used for the metal heaters are needed to
have a thickness to a certain extent. It is because if the metal
plates are thin, the rigidity are low and the metal plates are
warped and sagged since the metal plates are pushed from the
surrounding because of thermal expansion attributed to heating or
there is a difference of thermal expansion coefficients between
supporting cases and metal plates.
[0007] If such warping, sagging and the like occurs in the metal
plates, a semiconductor wafer placed on the metal plates cannot be
heated evenly, so that a dispersion of temperature or a damage in
the semiconductor wafer is generated in some cases.
[0008] However, if the metal plates are made thick, the heat
capacity of the metal plates is increased, and in the case of
heating or cooling an object to be heated, the temperature of the
heating faces of the metal plates cannot promptly follow the change
of the voltage or the electric current applied to the heating
elements, and there has been a problem that temperature control
becomes difficult.
[0009] Further, there has been a problem that it takes a long time
(a long recovery time) to recover the previous temperature of the
heating face and productivity reduces in the case a semiconductor
wafer is placed on the metal plate and the temperature of the
heating face of the metal plate abruptly drops.
[0010] Further, such metal heaters may have, in the case
temperature is increased, an overshoot phenomenon that the
temperature temporarily goes over the set temperature. If the
overshoot phenomenon occurs, it takes further longer time to bring
the temperature of the heating faces of the metal plates to the set
temperature.
[0011] Additionally, along with the recent tendency of enlargement
of the diameter of semiconductor wafers and the like, and other
reasons, metal heaters with a larger diameter are desired. With the
enlargement of the diameter of the metal plates, the uneven
temperature distribution in the metal plates themselves tends to
occur, and accordingly, the above temperature evenness of the
semiconductor wafer is further deteriorated.
[0012] In view of the above-mentioned problems, the present
inventor has made extensive research efforts for the purpose of
obtaining a metal heater which has a comparatively fast
temperature-rising speed and a comparatively short recovery time,
hardly causes temperature change in a semiconductor wafer and the
like upon heating, and is free from warping and sagging in metal
plates, and found that, by: sandwiching a heating element between a
plurality of metal plates; and making the thickness of a metal
plate on a heating face side larger than the thickness of a metal
plate on the opposite side, it becomes possible to ensure the
flatness of the heating face and consequently to maintain the
temperature of the heating face in an even level; thus, a first
aspect of the present invention has been completed.
[0013] In other words, a metal heater according to a first aspect
of the present invention comprises a metal plate and a heating
element. Herein, the number of the metal plates is a plural number,
the heating element is sandwiched between the metal plates, and the
thickness of a metal plate on a heating face side is the same as or
larger than the thickness of a metal plate on a side opposite to
said heating face side.
[0014] The metal heater according to the first aspect of the
present invention comprises the plurality of metal plates, and the
heater is sandwiched between the metal plates. The metal heater
having this structure makes it possible to more quickly heat an
object to be heated, such as a semiconductor wafer or the like, in
comparison with a metal heater that is formed by a single metal
plate with a heater placed on a side opposite to the heating face
side of the metal plate, and also to shorten the recovery time.
[0015] Since the metal heater according to the first aspect of the
present invention is designed so that the thickness of the metal
plate on the heating face side is the same as or larger than the
thickness of a metal plate on the side opposite to said heating
face side, it becomes possible to improve the flatness of the
heating face upon heating and, also, to evenly heat the entire
semiconductor wafer.
[0016] The reason therefor will be briefly described below.
[0017] In the metal heater according to the first aspect of the
present invention, since the thickness of the metal plate on the
heating face side is made larger, the mechanical strength becomes
higher, making the metal plate less likely to have warping and the
like upon heating. Therefore, upon heating, the flatness of the
heating face is improved.
[0018] Moreover, in the case where the thickness of the metal plate
on the heating face side is made larger, the thermal capacity of
the metal plate on the side opposite to said heating face side is
made relatively smaller than the thermal capacity of the metal
plate on the heating face side. For this reason, the metal plate on
the side opposite to said heating face side is made less likely to
have accumulation of heat in comparison with the metal plate on the
heating face side. Therefore, even in the case where
ordinary-temperature silicon wafers are successively placed on the
heating face so as to carry out a continuous process, heat
conduction hardly occurs from the metal plate on the side opposite
to said heating face side to the metal plate on the heating face
side. Of course, temperature change hardly occurs in the metal
plate on the heating face side due to an overshoot phenomenon
caused by the heat conduction from the metal plate on the side
opposite to said heating face side to the metal plate on the
heating face side. Therefore, it becomes possible to easily control
the temperature of the metal plate on the heating face side, and
consequently to maintain the heating treatment temperature at a
constant level.
[0019] The metal heater according to the first aspect of the
present invention may have a structure in which another metal plate
is further attached to the heating element placed on the metal
plate, that is, a structure in which a heating element is
sandwiched between two metal plates or a structure in which heating
elements are sandwiched among three or more metal plates.
[0020] In the case where the metal heater according to the first
aspect of the present invention comprises three or more metal
plates, the thickness of the metal plate on the heating face side
refers to the thickness of metal plates located above the heater of
the uppermost layer, and the thickness of the metal plate on the
side opposite to said heating face side refers to the total
thickness of the metal plates located below the heater on the
uppermost layer.
[0021] FIG. 3 shows a structure of a metal heater comprising three
metal plates. Herein, FIG. 3 shows only the metal plate and the
heater.
[0022] In the case of the metal heater as shown in FIG. 3, the
thickness of the metal plate on the heating face side refers to a
thickness a of a metal plate A located above a heater A of the
uppermost layer. Moreover, the thickness of the metal plate on the
side opposite to the heating face side refers to a total thickness
b+c of a metal plate B and a metal plate C located below the heater
A on the uppermost layer.
[0023] In the following, a metal heater having a structure in which
a heater is sandwiched between two metal plates will be mainly
described according to the first aspect of the present invention.
Here, in the case where the metal heater has the structure having
two metal plates as described above, the metal plate on the heating
face side is referred to as an upper metal plate, and the metal
plate on the side opposite to said heating face side is referred to
as a lower metal plate.
[0024] In the metal heater according to the first aspect of the
present invention, the lower limit of the thickness of the upper
metal plate is desirably 3 mm.
[0025] If the thickness of the upper metal plate is less than 3 mm,
the distance between the heating element and the heating face
becomes too short; thus, the pattern of the heating element is
reflected to the temperature distribution of the heating face. As a
result, it becomes difficult to evenly heat an object to be heated
such as a semiconductor wafer or the like in some cases. In
contrast, if the thickness of the upper metal plate is within the
above-mentioned range, the pattern of the heating element is not
reflected to the temperature distribution of the heating face so
that it becomes possible to evenly heat the object to be
heated.
[0026] Moreover, if the thickness of the substrate is within the
above-mentioned range, the metal heater is allowed to have superior
mechanical strength without occurrence of warping, sagging and the
like, making it possible to positively ensure the flatness of the
heating face.
[0027] Furthermore, the lower limit of the thickness of the upper
metal plate is more desirably 5 mm.
[0028] The upper limit of the thickness of the upper metal plate is
desirably 50 mm. The thickness of the upper metal plate exceeding
50 mm sometimes makes it difficult for the temperature of the
heating face of the metal plate to follow change in a voltage and
an amount of current to be applied to the heating element, failing
to quickly heat the object to be heated, such as a semiconductor
wafer or the like, and when the semiconductor wafer is placed on
the heating face, time (recovery time) taken to bring the decreased
temperature back to the previous temperature takes longer to cause
a prolonged working time and the subsequent reduction in
productivity.
[0029] The upper limit of the thickness of the upper metal plate is
more desirably 30 mm.
[0030] Moreover, in the case of the above-mentioned structure, the
upper limit of the thickness of the lower metal plate is desirably
50 mm, more desirably 30 mm, and the lower limit thereof is
desirably 1 mm, more desirably 3 mm.
[0031] Furthermore, the ratio of the thickness of the upper metal
plate and the thickness of the lower metal plate (thickness of
upper metal plate/thickness of lower metal plate) is desirably 1 to
10. When the ratio exceeds 10, the thermal capacity of the upper
metal plate becomes too high, sometimes failing to quickly heat the
object to be heated. Moreover, when the thermal capacity of the
upper metal plate becomes too high, the temperature difference
between the outermost circumference of the heating face and the
vicinity of the center portion becomes too large, sometimes causing
reduction in the temperature evenness on the heating face.
[0032] The ratio of the thickness of the upper metal plate and the
thickness of the lower metal plate is optimally larger than 1 and
10 or less. If the ratio of the thickness of the upper metal plate
and the thickness of the lower metal plate is within the
above-mentioned range, it becomes possible to provide superior
temperature evenness on the heating face in a steady state.
[0033] In the metal heater according to the first aspect of the
present invention, the heater is sandwiched between the upper metal
plate and the lower metal plate, and the heating element is formed
inside the heater. A circuit constituting the heating element is
desirably divided into two or more portions.
[0034] In the case where the circuit constituting the heating
element is divided into two or more portions, it becomes possible
to carry out a precise temperature controlling operation on the
outermost circumference of the metal heater, the part of which is
more likely to have a temperature drop, and consequently to
suppress dispersion in the temperature of the metal heater.
[0035] Moreover, in the metal heater according to the first aspect
of the present invention, all the diameters of the metal plates and
the heater are desirably the same. This arrangement makes it
possible to evenly transmit heat from the heater to the heating
face of the metal plate.
[0036] In the case where a heat insulating ring or the like is
interposed between the metal plate and the supporting case, the
diameters of the metal plates may be made different from one
another.
[0037] In the metal heater according to the first aspect of the
present invention, the diameter of the metal plates is desirably
200 mm or more. As the diameter of the metal heater becomes larger,
the temperature of the semiconductor wafer tends to become uneven
upon heating; therefore, in such a large diameter, the structure of
the first aspect of the present invention is allowed to function
more effectively. Moreover, a substrate having such a large
diameter makes it possible to receive a semiconductor wafer having
a large diameter.
[0038] In particular, the diameter of the metal plates is desirably
12 inches (300 mm) or more. This size is mainly used for
semiconductor wafers in the next generation.
[0039] In the metal plates constituting the metal heater according
to the first aspect of the present invention, flatness on the
surface thereof is desirably 50 .mu.m or less. In the case where a
semiconductor wafer is heated by using the metal heater according
to the first aspect of the present invention, since the distance
between the semiconductor wafer and the metal plate is maintained
at an almost constant level, the entire semiconductor wafer can be
evenly heated. Here, the flatness on the surface of the metal plate
is more desirably 30 .mu.m or less.
[0040] In order to realize a metal heater that is superior in
flatness, it is necessary to prevent the metal plate from curving
due to pressure imposed from the side faces upon thermal expansion
of the metal plate. For this reason, it is desirable to maintain a
space between each of the side faces of the metal plate and the
supporting case (bottom plate) so that each of the side faces is
not made in contact with the metal plate.
[0041] The material of the above-mentioned metal plates desirably
has superior thermal conductivity with high rigidity, and is less
likely to be deformed even when thermally expanded so that, upon
completion of the machining processes of the metal plate, the metal
plate is desirably allowed to have a superior flatness.
[0042] With respect to the material of the metal plates
constituting the metal heater according to the first aspect of the
present invention, examples thereof include aluminum, an aluminum
alloy, copper, a copper alloy, stainless, inconel, steel and the
like. Among these, an aluminum alloy is desirably used, and an
aluminum-copper alloy is more desirably used. Since the
aluminum-copper alloy has high mechanical strength, neither warping
nor distortion takes place due to applied heat even when the
thickness of the metal plate is made thinner. For this reason, the
metal plate can be made thinner and lighter. Moreover, since the
aluminum-copper alloy is also superior in thermal conductivity, the
temperature of the heating face is allowed to follow temperature
change in the heating element when it is used as the metal plate.
In other words, the temperature of the heating element is changed
by varying the voltage and current value so that the heating face
temperature of the upper metal plate can be controlled.
[0043] In the metal heater according to the first aspect of the
present invention, the material of the upper metal plate and the
material of the lower metal plate are desirably the same. This
makes it possible to prevent occurrence of deformations such as
warping, sagging and the like in the upper metal plate due to a
difference in thermal expansion coefficients of the materials, and
consequently to positively ensure the flatness of the heating
face.
[0044] Moreover, with respect to the aluminum-copper alloy, other
materials such as magnesium, manganese, silicon, zinc and the like
may be added thereto in addition to aluminum and copper. This is
because, it becomes possible to further improve various functions,
such as workability, corrosion resistance and low expansion
property.
[0045] In the case where aluminum, an aluminum alloy or the like is
used as the material of the metal plate, the surface of the metal
plate is desirably subjected to an alumite treatment.
[0046] This alumite treatment makes it possible to improve the
corrosion resistance of the metal plate and, also, to harden the
surface thereof; thus, the metal plate is made less likely to have
scratches and the like. Moreover, even when used in actual
semiconductor producing/examining processes, the metal plate is
made less likely to have corrosion due to a resist solution,
corrosive gases and the like.
[0047] Moreover, a hard alumite treatment can be carried out by
performing an anodic oxide coating treatment at a lower
temperature, a higher voltage, and a higher current density
compared with a common alumite treatment. Such a hard alumite
treatment enables to obtain a harder and thinner coating.
[0048] Here, the thickness of the coat film is desirably set to 1
.mu.m or more. In the case of the hard alumite treatment, the
thickness of the coat film can be set to 3 .mu.m or more.
[0049] In the metal heater according to the first aspect of the
present invention, the outer rim of an area on which the heating
element is formed is desirably located at a position within 25% of
the diameter of the metal plate from the circumference of the metal
plate. Since heat radiation takes place from the peripheral edge of
the metal plate, the circumferential portion of the metal plate
normally has a temperature drop in comparison with the center
portion of the metal plate; thus, the temperature of the heating
face tends to become uneven. However, in the metal heater according
to the first aspect of the present invention, since the heating
element is also disposed at such a peripheral portion, a
semiconductor wafer or the like, that is, the object to be heated
can be evenly heated without dispersion in temperature.
[0050] Moreover, the heating element is desirably divided into two
or more portions.
[0051] If the heating element is divided into two or more portions,
the respective heating elements can be temperature-controlled in a
separate manner so that the temperature of the heating face can be
maintained at a more even level. More specifically, for example, by
preparing the heating element pattern formed on the outermost
circumference as a complex divided pattern, a precise temperature
controlling operation can be carried out on the outermost
circumference of the metal heater that tends to have a temperature
drop; thus, it becomes possible to suppress dispersion in the
temperature of the heating face.
[0052] In the metal heater according to the first aspect of the
present invention, a wafer guide ring may be placed at a side face
of the metal plate, or it may be placed at the peripheral edge or
the surface of the heating face of the metal plate.
[0053] In the case where the metal heater is attached to a
supporting case and used, a gas flow is generated from the metal
plate side toward a semiconductor wafer placed on the metal heater;
thus, this gas flow tends to make it difficult to maintain the
evenness in temperature of the semiconductor wafer. However, the
provision of the wafer guide ring can prevent the gas flow toward
the semiconductor wafer; therefore, it becomes possible to further
ensure the evenness in temperature of the semiconductor wafer.
[0054] In view of the above-mentioned problems, the present
inventor has made extensive research efforts for the purpose of
obtaining a metal heater which has a comparatively fast
temperature-rising speed and a comparatively short recovery time,
and can evenly heat an object to be heated such as a semiconductor
wafer or the like, without causing warping and sagging in its metal
plate, and found that, by: sandwiching a heating element between a
plurality of metal plates; and forming these metal plates from the
same material, it becomes possible to ensure the flatness of the
heating face and consequently to maintain the temperature of the
heating face at an even level; thus, a second aspect of the present
invention has been completed.
[0055] That is, a metal heater according to a second aspect of the
present invention comprises a plurality of metal plates and a
heating element, with the heating element sandwiched between the
metal plates. Herein, the plurality of metal plates are made of the
same material.
[0056] The metal heater according to the second aspect of the
present invention comprises the plurality of metal plates, and the
heater is sandwiched between the metal plates. In comparison with a
metal heater that is formed by a single metal plate with a heater
provided on the face on the side opposite to the heating face side
of the metal plate, since the metal heater having this structure
makes the thickness of the metal plate located on the heating face
side of the heater thinner than the above-mentioned single metal
plate, it becomes possible to more quickly heat an object to be
heated, such as a semiconductor wafer or the like, and also to
shorten the recovery time.
[0057] In the metal heater according to the second aspect of the
present invention, since the plurality of metal plates are made of
the same material, even when the temperature of the metal heater is
raised or lowered, the plurality of the metal plates are expanded
or shrunk at the same ratio. Therefore, even when these metal
plates are secured with securing screws, neither warping nor
sagging occurs in the metal plate on the heating face side of the
heater so that it becomes possible to maintain the flatness of the
heating face upon heating and, also, to make the distance between
the semiconductor wafer and the heating face constant; thus, the
entire semiconductor wafer can be heated evenly.
[0058] In the metal heater according to the second aspect of the
present invention, with respect to the plurality of metal plates,
the thickness of the metal plate (upper metal plate) on the heating
face side of the heater is desirably made larger than the thickness
of the metal plate (lower metal plates) on the opposite side.
[0059] Moreover, in the case where the thickness of the metal plate
on the heating face side is made larger, the thermal capacity of
the metal plate on the side opposite to the heating face side is
made relatively smaller than the thermal capacity of the metal
plates on the heating face side. For this reason, the metal plate
on the side opposite to the heating face side is made less likely
to have accumulation of heat in comparison with the metal plate on
the heating face side. Therefore, even in the case where
ordinary-temperature silicon wafers are successively placed on the
heating face so as to carry out a continuous process, heat
conduction hardly occurs from the metal plate on the side opposite
to the heating face side to the metal plate on the heating face
side. Of course, temperature change hardly occurs in the metal
plate on the heating face side due to an overshoot phenomenon
caused by the heat conduction from the metal plate on the side
opposite to the heating face side to the metal plate on the heating
face side. Therefore, it becomes possible to easily control the
temperature of the metal plate on the heating face side, and
consequently to maintain the heating treatment temperature at a
constant level.
[0060] The metal heater according to the second aspect of the
present invention may have a structure in which another metal plate
is further attached to the heating element placed on the metal
plate, that is, a structure in which a heating element is
sandwiched between two metal plates, or a structure in which
heating elements are sandwiched among three or more metal plates.
In the case where the metal heater according to the second aspect
of the present invention has three or more metal plates, the
thickness of the metal plate on the heating face side (upper metal
plate) and the thickness of the metal plate on the side opposite to
the heating face side (lower metal plate) are defined in the same
manner as those of the first aspect of the present invention.
[0061] In the following, a metal heater having a structure in which
a heater is sandwiched between two metal plates will be mainly
described according to the second aspect of the present
invention.
[0062] In metal heater according to the second aspect of the
present invention, the lower limit of the thickness of the upper
metal plate is desirably 3 mm. The reason therefor is the same as
that described in the first aspect of the present invention.
Moreover, the lower limit of the thickness of the upper metal plate
is more desirably 5 mm.
[0063] The upper limit of the thickness of the upper metal plate is
desirably 50 mm. The reason therefor is the same as that described
in the first aspect of the present invention. The upper limit of
the thickness of the upper metal plate is more desirably 30 mm.
[0064] Moreover, in the case of the above-mentioned structure, the
upper limit of the thickness of the lower metal plate is desirably
50 mm, more desirably 30 mm, and the lower limit thereof is
desirably 1 mm, more desirably 3 mm.
[0065] Furthermore, the ratio of the thickness of the upper metal
plate and the thickness of the lower metal plate (thickness of
upper metal plate/thickness of lower metal plate) is desirably 1 to
10. The reason therefor is the same as that described in the first
aspect of the present invention. In particular, the ratio is
optimal in a case exceeding 1. Thus, it becomes possible to provide
superior temperature evenness on the heating face in a steady
state.
[0066] In the metal heater according to the second aspect of the
present invention, the heater is sandwiched between the upper metal
plate and the lower metal plate, with the heating element formed
inside the heater. In the same manner as the first aspect of the
present invention, a circuit constituting the heating element is
desirably divided into two or more portions, and all the diameters
of the plurality of metal plates and the heater are desirably the
same. In the case where a heat insulating ring or the like is
interposed between the metal plate and the supporting case, the
diameters of the metal plates may be made different from one
another.
[0067] In the metal heater according to the second aspect of the
present invention, the diameter of the metal plates is desirably
200 mm or more, more desirably 12 inches (300 mm) or more. The
reason therefor is the same as that described in the first aspect
of the present invention.
[0068] In the metal plates constituting the metal heater according
to the second aspect of the present invention, the flatness on the
surface thereof is desirably 50 .mu.m or less, more desirably 30
.mu.m or less. The reason therefor is the same as that described in
the first aspect of the present invention.
[0069] In order to realize a metal heater that is superior in
flatness, it is necessary to prevent the metal plate from curving
due to pressure imposed from the side faces upon thermal expansion
of the metal plate. For this reason, it is desirable to maintain a
space between each of the side faces of the metal plate and the
supporting case (bottom plate) so that each of the side faces is
not made in contact with the metal plate.
[0070] In the second aspect of the present invention, the plurality
of metal plates are made of the same material, and the material of
the metal plates desirably has a superior thermal conductivity with
high rigidity, and is less likely to be deformed even when
thermally expanded so that, upon completion of the machining
processes of the metal plates themselves, each metal plate is
desirably allowed to have a superior flatness. With respect to the
material of the metal plates, for example, the same materials and
the like as in the first aspect of the present invention may be
used.
[0071] With respect to the material of the metal plates
constituting the metal heater according to the second aspect of the
present invention, an aluminum alloy is desirably used, and an
aluminum-copper alloy is more desirably used, for the same reason
as that described in the first aspect of the present invention. In
the same manner as the first aspect of the present invention, with
respect to the aluminum-copper alloy, other materials such as
magnesium, manganese, silicon, zinc and the like may be added
thereto in addition to aluminum and copper.
[0072] In the case where aluminum, an aluminum alloy or the like is
used as the material of the metal plate, the surface of the metal
plate is desirably subjected to an alumite treatment as in the same
manner described in the first aspect of the present invention.
[0073] Here, after the alumite treatment, the thickness of the coat
film is desirably 1 .mu.m or more, and in the case of the hard
alumite treatment, the thickness of the coat film may be set to 3
.mu.m or more.
[0074] In the metal heater according to the second aspect of the
present invention, the peripheral edge of an area on which the
heating element is formed is desirably located at a position within
25% of the diameter of the metal plate from the periphery of the
metal plate.
[0075] Moreover, the heating element is desirably divided into two
or more portions. In the metal heater according to the second
aspect of the present invention, a wafer guide ring may be placed
at a side face of the metal plate, or it may be placed at the
peripheral edge or the surface of the heating face of the metal
plate. The reason therefor is the same as that described in the
first aspect of the present invention.
[0076] In the metal heater according to the second aspect of the
present invention, a convex portion for supporting an object to be
heated is desirably placed on the heating face opposing the object
to be heated of the metal plate corresponding to an area on which a
heating element is formed. Thus, it becomes possible to make a
semiconductor wafer or the like, that is, the object to be heated,
less likely to have sagging and, also, to make the distance between
the semiconductor wafer or the like and the heating face of the
metal plate constant so that the entire semiconductor wafer or the
like can be heated evenly.
[0077] In the second aspect of the present invention, the terms "a
convex portion for supporting an object to be heated is placed
corresponding to an area on which a heating element is formed" and
"an area on which a heating element is formed" are used under the
same definitions as those of a third aspect of the present
invention, which will be described later.
[0078] With respect to the number of the above-mentioned convex
portions, if the diameter of the area on which a heating element is
formed is 250 mm or more and less than 300 mm, the number is
desirably 6 or more. If the diameter of the area on which a heating
element is formed is 200 mm or more and less than 250 mm, the
number is desirably 5 or more. If the diameter of the area on which
a heating element is formed is 300 mm or more, the number is
desirably 7 or more. The reason therefor is the same as that which
will be described in the third aspect of the present invention.
[0079] With respect to the upper limit of the number of the convex
portions formed on the heating face of the metal plate, although
not particularly limited, if the diameter of the area on which a
heating element is formed is 250 mm or more and less than 300 mm,
the number is desirably 20 or less. If the diameter of the area on
which a heating element is formed is 200 mm or more and less than
250 mm, the number is desirably 15 or less. The reason therefor is
the same as that which will be described in the third aspect of the
present invention.
[0080] Moreover, with respect to positions at which the convex
portions are formed, for example, the same layout as that which
will be described in the third aspect of the present invention
later may be used.
[0081] The positions at which the convex portions are formed are
desirably widely dispersed on the metal plate, with the positions
being rotation-symmetrical with respect to the center. The reason
therefor is the same as that which will be described in the third
aspect of the present invention.
[0082] In the case where the convex portions are placed on the
metal plate in a biased manner and/or the convex portions are
placed with irregular intervals, a portion having a wide interval
between the convex portions is formed, and in such a portion, the
semiconductor wafer tends to have sagging; as a result, the
distance between the semiconductor wafer and the metal plate tends
to become uneven, making it difficult to evenly heat the
semiconductor wafer.
[0083] With respect to a method for placing the convex portions on
the heating face of the metal plate, the same method as that used
for the following third aspect of the present invention may be
used.
[0084] With respect to a method for securing supporting pins into
the concave portions, the same method as that used for the
following third aspect of the present invention may be used.
[0085] With respect to the metal heater according to the second
aspect of the present invention, those metal heaters in which the
diameter of the area on which the heating element is formed is 250
mm or more, with six or more supporting pins placed on the heating
face of the metal plate may be optimally used. Moreover, at least
one supporting pin is desirably placed in the center of the area in
which the heating element is formed.
[0086] With respect to the shape of the supporting pin, for
example, a pinnacle shape with a cone on the tip, a pinnacle shape
with a pyramid on the tip, a semi-spherical shape or the like may
be desirably used. Here, in the case where the shape of the
supporting pin other than the tip is a cylindrical shape, the
diameter thereof is desirably 1 to 10 mm. Moreover, the height of
the cylindrical-shaped portion of the supporting pin is desirably 1
to 10 mm. The reason therefor is the same as that which will be
described in the third aspect of the present invention.
[0087] In the case where the supporting pin has a head portion
shaped like a nail, the head portion is desirably formed into a
shape and a size that are suitably fitted to each concave portion.
The reason therefor is the same as that which will be described in
the third aspect of the present invention.
[0088] The supporting pins are desirably made of ceramics, and in
consideration of abrasion resistance to silicon wafers with
comparatively little thermal deformation, productivity, costs and
the like, oxide ceramic materials such as alumina, silica and the
like are desirably used.
[0089] In the above-mentioned metal heater, the supporting pins are
desirably designed so as to protrude from the heating face of the
metal plate with the same height. The reason therefor is the same
as that which will be described in the third aspect of the present
invention.
[0090] The height at which the supporting pin protrudes from the
metal plate is desirably 5 to 5000 .mu.m, that is, in a state where
the object to be heated is held so as to be apart from the heating
face of the metal plate by 5 to 5000 .mu.m. The reason therefor is
the same as that which will be described in the third aspect of the
present invention.
[0091] The distance between the object to be heated and the heating
face of the metal plate is desirably 5 to 500 .mu.m, more desirably
20 to 200 .mu.m.
[0092] The diameters of the concave portion in which the supporting
pin is placed and the through hole used for the supporting pin are
desirably 1 to 10 mm. Moreover, the depth of each concave portion
is desirably 1 to 10 mm. The reason therefor is the same as that
which will be described in the third aspect of the present
invention.
[0093] In view of the above-mentioned problems, the present
inventor has made extensive research efforts for the purpose of
obtaining a metal heater which is superior in temperature evenness
in surface in transition period, has a comparatively short recovery
time, and can evenly heat an object to be heated such as a
semiconductor wafer, without causing sagging in the object to be
heated upon heating, and found that by: sandwiching a heating
element between a plurality of metal plates; and providing convex
portions on a heating face opposing the object to be heated of the
metal plate corresponding to an area on which the heating element
is formed, it becomes possible to evenly heat the object to be
heated, without causing any sagging in the semiconductor wafer;
thus, the third aspect of the present invention has been
completed.
[0094] That is, a metal heater according to the third aspect of the
present invention comprises a plurality of metal plates and a
heating element, with the heating element sandwiched between the
metal plates. Herein, a convex portion for supporting an object to
be heated is placed on a heating face opposing the object to be
heated of the metal plate corresponding to an area on which the
heating element is formed.
[0095] The metal heater according to the third aspect of the
present invention comprises the plurality of metal plates, and the
heater is sandwiched between the metal plates. In comparison with a
metal heater that is formed by a single metal plate with a heater
provided on the face on the side opposite to the heating face side
of the metal plate, since the metal heater having this structure
makes the thickness of the metal plate located on the heating face
side of the heater thinner than the above-mentioned single metal
plate, it becomes possible to more quickly heat an object to be
heated, such as a semiconductor wafer or the like, and also to
shorten the recovery time.
[0096] In the metal heater according to the third aspect of the
present invention, since convex portions for supporting an object
to be heated are placed on the heating face opposing the object to
be heated of the metal plate corresponding to the area in which the
heating element is formed, it becomes possible to make the
semiconductor wafer or the like, that is, the object to be heated,
less likely to have sagging. Consequently, it is possible to make
the distance between the semiconductor wafer or the like and the
heating face of the metal plate constant; thus, the entire
semiconductor wafer can be heated evenly.
[0097] In the third aspect of the present invention, the term, "a
convex portion for supporting an object to be heated is placed
corresponding to an area on which a heating element is formed",
refers to a structure in which an appropriate number of convex
portions are placed at appropriate positions on the heating face of
the metal plate corresponding to the size of the area on which the
heating element of the metal plate is formed and the size of the
semiconductor wafer to be heated.
[0098] Here, the term, "an area on which a heating element is
formed", is defined as follows: when the heating element pattern
formed on the metal plate is perpendicularly shifted onto the
heating face of the metal plate, the area corresponds to an inner
area of the minimum circle that includes all of the heating element
pattern.
[0099] With respect to the number of the convex portions, if the
diameter of the area on which a heating element is formed is 250 mm
or more and less than 300 mm, the number is desirably 6 or more. If
the number of the convex portions is less than 6, the interval
between the convex portions becomes too wide; as a result, the
semiconductor wafer tends to have sagging to cause dispersion in
the distance between the semiconductor wafer and the metal plate,
and the subsequent difficulty in evenly heating the entire
semiconductor wafer. If the diameter of the area on which a heating
element is formed is 200 mm or more and less than 250 mm, the
number of the convex portions is desirably 5 or more. If the
diameter of the area on which a heating element is formed is 300 mm
or more, the number thereof is desirably 7 or more.
[0100] With respect to the upper limit of the number of the convex
portions formed on the heating face of the metal plate, although
not particularly limited, if the diameter of the area on which a
heating element is formed is 250 mm or more and less than 300 mm,
the number is desirably 20 or less. This arrangement is prepared
from the viewpoints of avoiding complex manufacturing processes, of
cutting manufacturing costs, and of maintaining the temperature of
the heating face in a more even level. In the case where the
diameter of the area on which a heating element is 200 mm or more
and less than 250 mm, the number of the convex portions is
desirably set to 15 or less.
[0101] Moreover, with respect to positions at which the convex
portions are formed, for example, a layout in which on an area
forming a comparatively circumferential portion of the metal plate,
a plurality of convex portions are placed on circumferences of
concentric circles of the metal plate with equal intervals, with a
single supporting pin attached to the center of the metal plate,
may be used, or another layout in which on an area forming a
comparatively circumferential portion of the metal plate, a
plurality of supporting pins are respectively placed on
circumferences of concentric circles of the protruding metal plate
as well as on circumferences of concentric circles corresponding to
the inner circumference thereof, with a single supporting pin
attached to the center of the metal plate, may be used.
[0102] The positions at which the convex portions are formed are
desirably widely dispersed on the metal plate, with the positions
being rotation-symmetrical with respect to the center. The reason
therefor is as follows. By providing the convex portions at the
above-mentioned positions, upon heating a semiconductor wafer, the
semiconductor wafer is made free from sagging, and the distance
between the semiconductor wafer and the metal plate is made almost
constant so that the heating process is carried out on the
semiconductor wafer evenly.
[0103] In the case where the convex portions are placed on the
metal plate in a biased manner and/or the convex portions are
placed with irregular intervals, a portion having a wide interval
between the convex portions is formed, and in such a portion, the
semiconductor wafer tends to have sagging; as a result, the
distance between the semiconductor wafer and the metal plate tends
to become uneven, making it difficult to evenly heat the
semiconductor wafer.
[0104] For example, each of the convex portions may be placed on
the heating face of the metal plate by forming a concave portion on
the heating face of the metal place and inserting a supporting pin
in the concave portion so as to secure the convex portion therein,
or may be attached onto the heating face by forming a through hole
in the metal plate and inserting a supporting pin in the through
hole so as to secure the convex portion therein. Here, the through
hole for the supporting pin and the concave portion may be formed
in combination.
[0105] By using these methods, the supporting pin can be secured
onto the metal plate comparatively easily.
[0106] With respect to a method for fixedly securing the supporting
pin in the concave portion, for example, a method in which a
supporting pin having a head portion like a nail is inserted to a
concave portion formed as a cylindrical-shaped hollow portion
formed in the heating face of the metal plate with the head portion
placed on the metal plate side, and a spring having a C-shape is
fitted to the concave portion in a manner so as to surround the
supporting pin so that the supporting pin is fixedly secured
thereon by using the spring force, may be used.
[0107] By using such a method, the supporting pin is positively
secured thereon without coming off from the metal plate.
[0108] With respect to the metal heater according to the third
aspect of the present invention, those metal heaters in which the
diameter of the area on which the heating element is formed is set
to 250 mm or more, with six or more supporting pins being attached
to the heating face of the metal plate may be optimally used.
Moreover, at least one supporting pin is desirably placed in the
center of the area on which the heating element is formed.
[0109] With respect to the shape of the supporting pin, for
example, a pinnacle shape with a cone on the tip, a pinnacle shape
with a pyramid on the tip, a semi-spherical shape or the like may
be desirably used. When a semiconductor wafer is placed on the
supporting pins having such a shape, the semiconductor wafer is
supported through point contacts, making the semiconductor wafer
free from formation of hot spots and the like.
[0110] Here, in the case where the shape of the supporting pin
other than the tip is a cylindrical shape, the diameter thereof is
desirably 1 to 10 mm. Upon placing the semiconductor wafer, the
diameter of less than 1 mm tends to fail to provide a stable
supporting function as the supporting pin, while the diameter
exceeding 10 mm tends to cause hot spots and the like on the
semiconductor wafer.
[0111] Moreover, the height of the cylindrical-shaped portion of
the supporting pin is desirably 1 to 10 mm. The height of less than
1 mm tends to fail to positively secure the supporting pin onto the
heating face of the metal plate, while the height exceeding 10 mm
tends to fail to evenly heat the semiconductor wafer.
[0112] In the case where the supporting pin has a head portion
shaped like a nail, the head portion is desirably formed into a
shape and a size that are suitably fitted to each concave portion.
When the head portion is too small in comparison with the size of
the concave portion, the supporting pin becomes unstable.
[0113] The supporting pins are desirably made of ceramics, and in
consideration of abrasion resistance to silicon wafers with
comparatively little thermal deformation, productivity and costs,
oxide ceramic materials such as alumina, silica and the like are
desirably used.
[0114] In the above-mentioned metal heater, the supporting pins are
desirably designed so as to protrude from the heating face of the
metal plate with the same height. In the case where all the heights
by which the supporting pins protrude are made the same, upon
placing a semiconductor wafer, the semiconductor wafer is made in
parallel with the heating face of the metal plate, and since all
the supporting pins are allowed to support the semiconductor wafer,
no sagging occurs. Consequently, the distance between the
semiconductor wafer and the metal plate is maintained in an even
level so that the semiconductor wafer can be evenly heated. In
contrast, when the heights by which the supporting pins protrude
are different from one another, the semiconductor wafer tends to
tilt, or those supporting pins having short heights are not made in
contact with the semiconductor wafer to cause sagging.
Consequently, dispersion tend to occur in the distance between the
semiconductor wafer and the metal plate, making it difficult to
evenly heat the semiconductor wafer.
[0115] The height at which the supporting pin protrudes from the
heating face of the metal plate is desirably 5 to 5000 .mu.m, that
is, in a state in which the object to be heated is apart from the
heating face of the metal plate by 5 to 5000 .mu.m. The height of
less than 5 .mu.m tends to make the temperature of the
semiconductor wafer uneven due to influences from the temperature
distribution of the metal plate, and might cause the wafer to come
into contact with the metal plate. The height exceeding 5000 .mu.m
makes it difficult to raise the temperature of the semiconductor
wafer to cause a temperature drop, in particular, on the peripheral
portion of the semiconductor wafer.
[0116] The distance between the object to be heated and the heating
face of the metal plate is desirably 5 to 500 .mu.m, more desirably
20 to 200 .mu.m.
[0117] The diameters of the concave portion in which the supporting
pin is placed and the through hole for the supporting pin are
desirably 1 to 10 mm. The diameter of less than 1 mm tends to fail
to positively secure the supporting pin, while the diameter
exceeding 10 mm tends to cause cooling spots.
[0118] Moreover, the depth of each concave portion is desirably 1
to 10 mm. The depth of less than 1 mm might cause the supporting
pins to come off, while the depth exceeding 10 mm tends to cause
cooling spots.
[0119] In the metal heater according to the third aspect of the
present invention, with respect to the plurality of metal plates,
the thickness of the metal plate (upper metal plate) on the heating
face side of the heater is desirably made larger than the thickness
of the metal plate (lower metal plates) on the opposite side. The
reason therefor is the same as that in the metal heater according
to the second aspect of the present invention.
[0120] The metal heater according to the third aspect of the
present invention may have a structure in which another metal plate
is further attached to the heating element placed on the metal
plate, that is, a structure in which a heating element is
sandwiched between two metal plates, or a structure in which
heating elements are sandwiched among three or more metal plates.
In the case where the metal heater according to the third aspect of
the present invention has three or more metal plates, the thickness
of the metal plate on the heating face side (upper metal plate) and
the thickness of the metal plate on the side opposite to the
heating face side (lower metal plate) are defined in the same
manner as those of the first aspect of the present invention.
[0121] In the following, a metal heater in which a heater is
sandwiched between two metal plates will be mainly described
according to the third aspect of the present invention.
[0122] In metal heater according to the third aspect of the present
invention, the lower limit of the thickness of the upper metal
plate is desirably 1 mm. In the case where the thickness of the
upper metal plate is less than 1 mm, the distance between the
heating element and the heating face becomes too short; thus, the
pattern of the heating element is reflected to the temperature
distribution of the heating face. As a result, it becomes difficult
to evenly heat an object to be heated such as a semiconductor wafer
or the like in some cases. In contrast, when the thickness of the
upper metal plate is within the above-mentioned range, the pattern
of the heating element is not reflected to the temperature
distribution of the heating face so that it becomes possible to
evenly heat the object to be heated.
[0123] Moreover, when the thickness of the substrate is within the
above-mentioned range, the metal heater is allowed to have superior
mechanical strength without occurrence of warping, sagging and the
like in the metal plate, making it possible to positively ensure
the flatness of the heating face.
[0124] Furthermore, the lower limit of the thickness of the upper
metal plate is more desirably 5 mm.
[0125] The upper limit of the thickness of the upper metal plate is
desirably 50 mm. The thickness of the upper metal plate exceeding
50 mm sometimes makes it difficult for the temperature of the
heating face of the metal plate to follow a voltage to be applied
to the heating element and change in the amount of electric
current, failing to quickly heat an object to be heated, such as a
semiconductor wafer or the like, and when the semiconductor wafer
is placed on the heating face, time (recovery time) taken to bring
the decreased temperature back to the previous temperature takes
longer to cause a prolonged working time and the subsequent
reduction in productivity.
[0126] In the above-mentioned structure, the upper limit of the
thickness of the lower metal plate is desirably set to 50 mm, more
desirably 30 mm, and the lower limit thereof is desirably 1 mm,
more desirably 3 mm.
[0127] Moreover, the ratio of the thickness of the upper metal
plate and the thickness of the lower metal plate (thickness of
upper metal plate/thickness of lower metal plate) is desirably 1 to
10. The reason therefor is the same as that described in the first
aspect of the present invention. In particular, the ratio exceeding
1 is optimally used. Thus, it becomes possible to provide superior
temperature evenness on the heating face in steady state.
[0128] In the metal heater according to the third aspect of the
present invention, the heater is sandwiched between the upper metal
plate and the lower metal plate, and the heating element is formed
inside the heater. In the same manner as the first aspect of the
present invention, a circuit constituting the heating element is
desirably divided into two or more portions, and all the diameters
of the plurality of metal plates and the heater are desirably the
same. In the case where a heat insulating ring or the like is
interposed between the metal plate and the supporting case, the
diameters of the metal plates may be made different from one
another.
[0129] In the metal heater according to the third aspect of the
present invention, the diameter of the metal plates is desirably
200 mm or more, more desirably 12 inches (300 mm) or more. The
reason therefor is the same as that described in the first aspect
of the present invention.
[0130] In the metal plates constituting the metal heater according
to the third aspect of the present invention, the flatness on the
surface thereof is desirably 50 .mu.m or less, more desirably 30
.mu.m or less. The reason therefor is the same as that described in
the first aspect of the present invention.
[0131] In order to realize a metal heater that is superior in its
flatness, it is necessary to prevent the metal plate from curving
due to pressure imposed from the side faces upon thermal expansion
of the metal plate. For this reason, it is desirable to maintain a
space between each of the side faces of the metal plate and the
supporting case (bottom plate) so that the side faces is not made
in contact with the metal plate.
[0132] In the third aspect of the present invention, the plurality
of metal plates are desirably made of the same material. Moreover,
the material of the metal plates desirably has a superior thermal
conductivity with high rigidity, and is less likely to be deformed
even when thermally expanded so that, upon completion of the
machining processes of the metal plates themselves, the metal
plates are desirably allowed to have a superior flatness. With
respect to the material of the metal plates, for example, the same
material as that used in the first aspect of the present invention,
and the like are proposed.
[0133] Also in the third aspect of the present invention, an
aluminum alloy is desirably used, and an aluminum-copper alloy is
more desirably used in the same manner as the first aspect of the
present invention. Moreover, with respect to the aluminum-copper
alloy, other materials such as magnesium, manganese, silicon, zinc
and the like may be added thereto.
[0134] In the case where aluminum, an aluminum alloy or the like is
used as the material of the metal plate, the surface of the metal
plate is desirably subjected to an alumite treatment in the same
manner as the first aspect of the present invention.
[0135] In the case of the alumite treatment, the thickness of the
coat film is desirably 1 .mu.m or more, and in the case of a hard
alumite treatment, the thickness of the coat film may be set to 3
.mu.m or more.
[0136] In the metal heater according to the third aspect of the
present invention, the peripheral edge of an area in which the
heating element is formed is desirably located at a position within
25% of the diameter of the metal plate from the periphery of the
metal plate.
[0137] Moreover, the heating element is desirably divided into two
or more portions. In the metal heater according to the third aspect
of the present invention, a wafer guide ring may be placed at a
side face of the metal plate, or it may be placed at the peripheral
edge or the surface of the heating face of the metal plate. The
reason therefor is the same as that described in the first aspect
of the present invention.
[0138] The metal heater according to the third aspect of the
present invention may be used as a heater module or the like by
fixedly securing an optical waveguide such as quartz or the like
thereon. In this case, the optical waveguide may be supported by
convex portions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0139] FIG. 1 is a cross-sectional view that schematically shows
one example of a metal heater according to a first aspect of the
present invention.
[0140] FIG. 2 is a horizontal cross-sectional view of a heater that
constitutes a part of the metal heater shown in FIG. 1.
[0141] FIG. 3 is a cross-sectional view that schematically shows a
metal plate and the heater of the metal heater according to the
first aspect of the present invention.
[0142] FIG. 4(a) is a cross-sectional view that schematically shows
another example of a conventional metal heater, and FIG. 4(b) is a
plan view of FIG. 4(a).
[0143] FIG. 5(a) is a cross-sectional view that schematically shows
one example of a metal heater according to a second aspect of the
present invention. FIG. 5(b) schematically shows a method by which
a heating element and a conductive line are joined to each other by
caulking using a joining foil in the metal heater shown in FIG.
5(a).
[0144] FIG. 6(a) is a cross-sectional view that schematically shows
one example of a metal heater according to a third aspect of the
present invention. FIG. 6(b) schematically shows a method by which
a heating element and a conductive line are joined to each other by
caulking using a joining foil in the metal heater shown in FIG.
6(a).
[0145] FIG. 7 is a plan view that shows the metal heater shown in
FIG. 6(a).
[0146] FIG. 8 shows a three dimensional shape of a part of a metal
heater heating face according to Example 1 at ordinary
temperature.
[0147] FIG. 9 shows a three dimensional shape of a part of a metal
heater heating face in according with Example 1 at 140.degree.
C.
[0148] FIG. 10 shows a three dimensional shape of a part of a metal
heater heating face according to Test Example 1 at 140.degree.
C.
[0149] FIG. 11 shows a three dimensional shape of a part of a metal
heater heating face according to Example 8 at ordinary
temperature.
[0150] FIG. 12 shows a three dimensional shape of a part of a metal
heater heating face in according with Example 8 at 140.degree.
C.
[0151] FIG. 13 shows a three dimensional shape of a part of a metal
heater heating face according to Test Example 3 at 140.degree.
C.
[0152] FIG. 14 is a graph that shows a relationship between a wafer
temperature and time in the vicinity of 100.degree. C. when a metal
heater according to Example 12 is used.
[0153] FIG. 15 is a graph that shows a relationship between a wafer
temperature and time in the vicinity of 120 to 130.degree. C. when
the metal heater according to Example 12 is used.
[0154] FIG. 16 is a graph that shows a relationship between a wafer
temperature and time in the vicinity of 140.degree. C. when the
metal heater according to Example 12 is used.
[0155] FIG. 17 is a graph that shows a relationship between a wafer
temperature and time in the vicinity of 100.degree. C. when the
metal heater according to Example 16 is used.
[0156] FIG. 18 is a graph that shows a relationship between a wafer
temperature and time in the vicinity of 120 to 130.degree. C. when
the metal heater according to Example 16 is used.
[0157] FIG. 19 is a graph that shows a relationship between a wafer
temperature and time in the vicinity of 140.degree. C. when the
metal heater according to Example 16 is used.
[0158] FIG. 20 shows a three dimensional shape of a part of a metal
heater heating face according to Example 12 at ordinary
temperature.
[0159] FIG. 21 shows a three dimensional shape of a part of a metal
heater heating face in according with Example 12 at 140.degree.
C.
[0160] FIG. 22 shows a three dimensional shape of a part of a metal
heater heating face according to Comparative Example 2 at
140.degree. C.
EXPLANATION OF SYMBOLS
[0161] 410, 510, 610 Metal heater [0162] 411, 511, 611 Upper metal
plate [0163] 411a, 511a, 611a Heating face [0164] 412, 512, 612
Heater [0165] 414, 514, 614 Bottomed hole [0166] 415, 515, 615
Through hole [0167] 416, 516, 616 Temperature measuring element
[0168] 417, 517, 617 Metal plate securing screw [0169] 418, 518,
618 Supporting pin [0170] 419, 519, 619 Semiconductor wafer [0171]
420, 520, 620 Supporting case [0172] 421, 521, 621 Lower metal
plate [0173] 422, 522, 622 Pressing plate [0174] 423, 523, 623 Heat
shielding plate [0175] 424, 524, 624 Conductive line [0176] 425
Heating element [0177] 525, 625 Supporting plate [0178] 426 Mica
plate [0179] 627 Spring [0180] 628 Concave portion [0181] 529, 629
Stainless foil [0182] 530, 630 Stainless foil for connection [0183]
531, 631 Attaching member [0184] 532, 632 Barrier ring
DETAILED DISCLOSURE OF THE INVENTION
[0185] In the following, description will be given of metal heaters
according to the first to third aspects of the present invention in
succession.
[0186] First, an embodiment of the first aspect of the present
invention will be described.
[0187] The metal heater according to the first aspect of the
present invention is a metal heater comprising a metal plate and a
heating element. Herein, the number of the metal plates is a plural
number, the heating element is sandwiched between the metal plates,
and the thickness of a metal plate on a heating face side is the
same as or larger than the thickness of a metal plate on a side
opposite to the heating face side.
[0188] Referring to the drawings, description will be given of a
metal heater in which a heater is sandwiched between two metal
plates as one example of the metal heater according to the first
aspect of the present invention.
[0189] FIG. 1 is a cross-sectional view that schematically shows
the metal heater of this type, and FIG. 2 is a horizontal
cross-sectional view of a heater that constitutes a part of the
metal heater shown in FIG. 1.
[0190] In this metal heater 410, a heater 412 is sandwiched between
an upper metal plate 411 and a lower metal plate 421, each of which
has a disk shape, and the upper metal plate 411, the heater 412 and
the lower metal plate 421 are fixedly secured to, and tightly bound
to one another through metal plate securing screws 417 so that heat
from the heater 412 is suitably transmitted to the upper metal
plate 411.
[0191] Moreover, the thickness of the upper metal plate 411 is made
larger than the thickness of the lower metal plate 421. Therefore,
as has been described already, the flatness of the heating face is
maintained, and the temperature of the heating face is equalized so
that the object to be heated can be evenly heated.
[0192] By securing the metal plate using the metal plate securing
screws 417, the thickness of the metal plate becomes substantially
large so that the flatness of the heating face is further
improved.
[0193] The metal heater 410 according to the first aspect of the
present invention makes it possible to realize a flatness of 50
.mu.m or less on a heating face 411a of the upper metal plate 411.
By realizing such a flatness, upon heating a semiconductor wafer,
the distance between the semiconductor wafer and the metal plate is
made almost constant so that the heating process is carried out on
the entire semiconductor wafer evenly.
[0194] In the metal heater 410 according to the first aspect of the
present invention, the side faces of the upper metal plate 411, the
heater 412 and the lower metal plate 421 are not made in tightly
contact with a supporting case 420, and secured in a non-contact
state. With this structure, the metal plate can be prevented from
being curved due to pressure from the side faces when the upper
metal plate 411 has been thermally expanded, and upon heating an
object to be heated, heat released from the metal plate and the
like is reduced so that an object to be heated can be heated more
quickly in comparison with the case in which the side faces of the
upper metal plate 411, the heater 412 and the lower metal plate 421
are made in tightly contact with the supporting case 420. In this
case, an air layer is allowed to function as a heat insulating
material.
[0195] Moreover, the metal heater 410 has a structure in which the
metal plate securing screws 417 do not penetrate supporting case
420, and are only allowed to penetrate the upper metal plate 411,
the heater 412 and the lower metal plate 421, and designed to
secure these members. With this structure, it becomes possible to
prevent deformation in the upper metal plate 411 due to a
difference in thermal expansion coefficients between the upper
metal plate 411 and the supporting case 420, and also to reduce
heat released from the upper metal plate 411 and the like upon
heating an object to be heated so that the object to be heated can
be heated quickly.
[0196] A heat shielding plate 423 is placed on the bottom portion
of the supporting case 420 so that it becomes possible to prevent
heat, released from the upper metal plate 411 and the lower metal
plate 421, from conducting to the device. Here, a barrier ring 428
is placed on the peripheral edge of the supporting case 420. The
provision of the barrier ring 428 makes it possible to prevent
outside gases from flowing therein to cause a temperature change in
the heating face 411a.
[0197] Moreover, a bottomed hole 414 is formed in the metal heater
410, and a temperature measuring element 416 configured to measure
the temperature of the upper metal plate 411 is inserted into the
bottomed hole 414, and sealed with an inorganic adhesive or the
like (not shown) to be secured therein.
[0198] In the metal heater 410, supporting pins 418, each having a
pinnacle-like tip, are placed on the heating face, and the
semiconductor wafer 419 is supported through the supporting pins
418 so that the semiconductor wafer 419 can be heated with a fixed
distance kept from the heating face of the upper metal plate
411.
[0199] In the metal heater according to the first aspect of the
present invention, with respect to the number of the supporting
pins, although not particularly limited, it is desirably set to six
or more in the case where, for example, the diameter of the metal
plate is 12 inches (300 mm) or more. When the number of the
supporting pins is six or more, a clearance between the heating
face and the semiconductor wafer is accurately maintained so that
it becomes possible to easily maintain the evenness of temperature
on the heating face in transition period.
[0200] Moreover, the metal heater 410 is also provided with through
holes 415 each of which penetrates the upper metal plate 411, the
heater 412, the lower metal plate 421 and the supporting case 420,
and by inserting pillar-shaped lifter pins and the like through the
through holes 415, a semiconductor wafer 419, that is, the object
to be heated is supported with a fixed distance kept from the
heating face 411a of the upper metal plate 411 so that the
semiconductor wafer 419 can be properly transported.
[0201] Here, the heater 412 is connected to a conductive line 424,
and the conductive line 424 is led outside from a through hole
formed in the supporting case 420 and the heat shielding plate 423,
and connected to a power supply or the like (not shown).
[0202] In the metal heater 410 shown in FIG. 1, a part of the
heating element 425 made of a metal foil such as stainless foil or
the like is exposed down to the lower side of the through hole
formed in the lower metal plate 421 so that one end of the
conductive line 424 is wrapped with the exposed foil (hereinafter,
referred to as foil for connection), and an attaching member 427
made of metal having a caulking portion (not shown) is then
attached thereto; thus, the caulking portion of the attaching
member 427 is caulked so that the heating element 425 and the
conductive line 424 are connected to each other.
[0203] Alternatively, the conductive line 424 may be connected to a
heating element placed inside the heater 412 on the side face of
the heater 412.
[0204] Moreover, in the metal heater 410, the upper metal plate
411, the heater 412 and the lower metal plate 421 are secured
through the metal plate fixing screws 417. Here, the metal plate
fixing screws 417 are attached in a manner so as to penetrate the
heater 412 and the lower metal plate 421 and so as not to penetrate
the upper metal plate 411.
[0205] As described above, in the case where the upper metal plate
411 and the like are secured through the metal plate securing
screws 417, the length of the portion of each metal plate securing
screw 417 inserted into the upper metal plate 411 is desirably set
to 3/4 or less of the thickness of the upper metal plate.
[0206] When the length of the portion of each metal plate securing
screw 417 inserted into the upper metal plate 411 is longer than
3/4 of the thickness of the upper metal plate 411, the temperature
of a portion right above each metal plate securing screw 417 of the
heating face of the metal plate becomes higher in comparison with
the temperature of its peripheral portion, failing to evenly heat
an object to be heated.
[0207] Moreover, the metal heater 410 has a structure in which the
screw head of each metal plate securing screw 417 is embedded in
the lower metal plate 421. Therefore, the upper metal plate 411,
the heater 412 and the lower metal plate 421 can be firmly secured
inside the supporting case 420 more positively so that the upper
metal plate 411 is allowed to have a structure that is less likely
to result in a deformation such as warping, sagging and the
like.
[0208] The heater 412 has a circular shape in its plan view in the
same manner as the upper metal plate 411 and the lower metal plate
421, and the heating element 425, constituted by closed circuits,
is arranged in the heater 412 so as to heat the entire heating face
411a of the upper metal plate 411 to an even temperature. With
respect to the heating element 425, as shown in FIG. 2, a heating
element, of a pattern in which a winding line is repeatedly placed
in a ring shape on the periphery of a heater to form a closed
circuit, and a heating element, of a pattern in which a winding
line is repeatedly placed inside thereof in a manner so as to form
a part of a concentric circle to form a closed circuit, are
arranged.
[0209] Moreover, although not shown in the figures, the heater 412
has a structure in which the heating element 425 is sandwiched by
two mica plates and secured therein, and upon current application,
the heating element 425 heats the mica plates so that an object to
be heated is heated by secondary radiation from the mica
plates.
[0210] In the metal heater 410 of the first aspect of the present
invention, the peripheral edge of the heating element 425 formed
inside the heater 412 is desirably located at a position within 25%
of the diameter of the metal plate 411 from the periphery of the
metal plate 411. Normally, the temperature on the peripheral
portion of the metal plate 411 tends to become uneven due to heat
radiation from the surface of the peripheral portion of the metal
plate 411; however, in the metal heater 410 according to the first
aspect of the present invention, since the heating element is also
disposed at the peripheral portion, a semiconductor wafer or the
like, that is, the object to be heated can be evenly heated without
dispersion in temperature.
[0211] With respect to the material, shape and the like of the
metal heater forming the first aspect of the present invention and
the manufacturing method of the metal heater according to the first
aspect of the present invention, detailed description will be given
later.
[0212] In the following, description will be given of an embodiment
according to the second aspect of the present invention.
[0213] The metal heater according to the second aspect of the
present invention is a metal heater comprising a plurality of metal
plates and a heating element, the heating element sandwiched
between the metal plates. Herein, the plurality of metal plates are
made of the same material. Referring to the drawings, description
will be given of a metal heater in which a heater is sandwiched
between two metal plates as one example of the metal heater
according to the second aspect of the present invention.
[0214] FIG. 5(a) is a cross-sectional view that schematically shows
such a metal heater, and FIG. 5(b) schematically shows a method by
which a heating element and a conductive line are joined to each
other by caulking using a joining foil in the metal heater shown in
FIG. 5(a).
[0215] In this metal heater 510, a heater 512 is sandwiched between
an upper metal plate 511 and a lower metal plate 521, each of which
has a disk shape, and the upper metal plate 511, the heater 512 and
the lower metal plate 521 are fixedly secured to, and tightly bound
to one another through metal plate securing screws 517 so that heat
from the heater 512 is suitably transmitted to the upper metal
plate 511.
[0216] Moreover, the thickness of the upper metal plate 511 is made
larger than the thickness of the lower metal plate 521. Therefore,
as has been described already, the flatness of the heating face is
maintained, and the temperature of the heating face is made even so
that the object to be heated can be evenly heated.
[0217] By securing the metal plate using the metal plate securing
screws 517, the thickness of the metal plate becomes substantially
large so that the flatness of the heating face is further
improved.
[0218] The upper metal plate 511, the heater 512 and the lower
metal plate 521, fixedly secured to one another through the metal
plate securing screws 517 are supported by a supporting plate 525
placed on the bottom face of a supporting case 520 having a
cylinder shape with a bottom, and in this structure, portions other
than the contact portion to the supporting plate 525 do not contact
with the supporting case 520. Moreover, a heat shielding plate 523
for shielding heat is provided below the supporting case 520.
Moreover, a barrier ring 532 is placed on the peripheral edge of
the supporting case 520. By providing the barrier ring, it becomes
possible to prevent outside gases from flowing therein, and
consequently to prevent temperature change in the heating face
511a.
[0219] With the above-mentioned structure, the metal heater 510
according to the second aspect of the present invention makes it
possible to realize a flatness of 50 .mu.m or less on the heating
face 511a of the upper metal plate 511. By realizing such a
flatness, upon heating a semiconductor wafer, the distance between
the semiconductor wafer and the metal plate can be made almost
constant so that the entire semiconductor wafer can be heated to an
even temperature.
[0220] The metal heater 510 according to the second aspect of the
present invention may be provided with a wafer guide ring 526 on
the peripheral edge portion of the heating face 511a so as to
prevent temperature change due to a gas flowing therein from
outside.
[0221] In the metal heater 510 according to the second aspect of
the present invention, the side faces of the upper metal plate 511,
the heater 512 and the lower metal plate 521 are not made in
tightly contact with the supporting case 520, and secured in a
non-contact state, and the lower metal plate 521 also does not
directly contact with the bottom face of the supporting case 520,
and is supported by a supporting plate 525. With this arrangement
in which the side faces of the upper metal plate 511, the heater
512 and the lower metal plate 521 are not made in contact with the
supporting case 520, the upper metal plate 511 can be prevented
from being curved due to pressure from the side faces when the
upper metal plate 511 has been thermally expanded. Moreover, the
upper metal plate 511, the heater 512 and the lower metal plate 521
are supported only through the supporting plate 525, without
contacting with any other portions; thus, upon heating an object to
be heated, heat released from the metal plate and the like is
reduced so that an object to be heated can be heated more quickly
in comparison with the case in which the side faces of the upper
metal plate 511, the heater 512 and the lower metal plate 521 are
made in tightly contact with the supporting case 520. In this case,
an air layer is allowed to function as a heat insulating layer.
[0222] Here, the upper metal plate 511, the heater 512, the upper
metal plate 521 and the like, as they are, may be placed on the
bottom face of the supporting case 520, without providing the
supporting member 525 on the bottom face of the supporting case
520.
[0223] After the heating process, the upper metal plate 511, the
heater 512 and the lower metal plate 521 sometimes need to be
cooled quickly, and in such a case, for example, a cooling pipe or
the like is connected to the bottom plate of the supporting case
520, with cooled air or the like introduced into the supporting
case 520, so that it becomes possible to carry out a quick cooling
process.
[0224] Moreover, the metal heater 510 has a structure in which the
metal plate securing screws 517 do not penetrate supporting case
520, and are allowed to penetrate only the upper metal plate 511,
the heater 512 and the lower metal plate 521, and designed to
secure these members. With this structure, it becomes possible to
prevent deformation in the upper metal plate 511 due to a
difference in thermal expansion coefficients between the upper
metal plate 511 and the supporting case 520, and also to reduce
heat released from the upper metal plate 511 and the like upon
heating an object to be heated so that the object to be heated can
be heated quickly.
[0225] A heat shielding plate 523 is placed on the bottom portion
of the supporting case 520 so that it becomes possible to prevent
heat, released from the upper metal plate 511 and the lower metal
plate 521, from transferring to the device.
[0226] Moreover, a bottomed hole 514 is formed in the metal heater
510, and a temperature measuring element 516 used for measuring the
temperature of the upper metal plate 511 is embedded in the
bottomed hole 514.
[0227] Here, in the metal heater 510, supporting pins 518, each
having a pinnacle-like tip, are placed on the heating face, and the
semiconductor wafer 519 is supported through the supporting pins
518 so that the semiconductor wafer 519 can be supported with a
fixed distance kept from the heating face of the upper metal plate
511, so as to be heated.
[0228] In the metal heater according to the second aspect of the
present invention, with respect to the number of the supporting
pins, although not particularly limited, it is desirably six or
more in the case where, for example, the diameter of the metal
plate is 12 inches (300 mm) or more. The reason therefor is the
same as that described in the metal heater according to the first
aspect of the present invention.
[0229] Moreover, the metal heater 510 is provided with through
holes 515 each of which penetrates the upper metal plate 511, the
heater 512, the lower metal plate 521 and the supporting case 520,
and by inserting pillar-shaped lifter pins and the like through the
through holes 515, a semiconductor wafer 519, that is, the object
to be heated is supported with a fixed distance kept from the
heating face 51a of the upper metal plate 511 so that the
semiconductor wafer 519 can be properly transported.
[0230] Here, the heater 512 is connected to a conductive line 524,
and the conductive line 524 is led outside from a through hole
formed in the supporting case 520 and the heat shielding plate 523,
and connected to a power supply or the like (not shown).
[0231] In the metal heater 510 shown in FIG. 5, the through hole is
formed in the lower metal plate 521, and the conductive line 524 is
inserted into the through hole; however, the conductive line 524
may be connected to a heating element placed inside the heater on
the side face of the heater 512.
[0232] Moreover, in the metal heater 510, the upper metal plate
511, the heater 512 and the lower metal plate 521 are fixedly
secured by the metal plate securing screws 517. Here, the metal
plate securing screws 517 are attached in a manner so as to
penetrate the heater 512 and the lower metal plate 521, and so as
not to penetrate the upper metal plate 511.
[0233] As described above, in the case where the upper metal plate
511 and the like are secured through the metal plate securing
screws 517, the length of the portion of each metal plate securing
screw 517 inserted into the upper metal plate 511 is desirably 3/4
or less of the thickness of the upper metal plate.
[0234] When the length of the portion of each metal plate securing
screw 517 inserted into the upper metal plate 511 is longer than
3/4 of the thickness of the upper metal plate 511, the temperature
of a portion right above each metal plate securing screw 517 of the
heating face of the metal plate becomes higher than the temperature
of its peripheral portion, failing to evenly heat an object to be
heated.
[0235] The heater 512 has a circular shape in its plan view in the
same manner as the upper metal plate 511 and the lower metal plate
521, and the heating element 525, constituted by closed circuits,
is arranged in the heater 512 so as to heat the entire heating face
511a of the upper metal plate 511 to an even temperature.
[0236] In the heater 512, as shown in FIG. 2, a heating element, of
a pattern in which a winding line is repeatedly placed in a ring
shape on the periphery of the heater 512 to form a closed circuit,
and a heating element, of a pattern in which a winding line is
repeatedly placed inside thereof in a manner so as to form a part
of a concentric circle to form a closed circuit, are arranged.
[0237] Moreover, although not shown in the figures, the heater 512
has a structure in which the heating element is sandwiched between
two mica plates and secured therein, and upon current application,
the heating element heats the mica plates so that an object to be
heated can be heated by secondary radiation from the mica plates.
The heating element may be formed by a stainless foil.
[0238] In the metal heater 510 according to the second aspect of
the present invention, the peripheral edge of the heating element
formed inside the heater 512 is desirably located at a position
within 25% of the diameter of the metal plate 511 from the
periphery of the metal plate 511. Normally, the temperature on the
peripheral portion of the metal plate 511 tends to become uneven
due to heat radiation from the surface of the peripheral portion of
the metal plate 511; however, in the metal heater 510 according to
the second aspect of the present invention, since the heating
element is also disposed at the peripheral portion, a semiconductor
wafer or the like, that is, the object to be heated can be evenly
heated without dispersion in temperature.
[0239] With respect to the material, shape and the like of the
metal heater forming the second aspect of the present invention and
the manufacturing method of the metal heater according to the
second aspect of the present invention, detailed description will
be given later.
[0240] In the following, description will be given of an embodiment
according to the third aspect of the present invention.
[0241] The metal heater according to the third aspect of the
present invention is a metal heater comprising a plurality of metal
plates and a heating element, with the heating element sandwiched
between the metal plates. Herein, a convex portion for supporting
an object to be heated is placed on a heating face opposing the
object to be heated of the metal plate corresponding to an area on
which the heating element is formed.
[0242] Referring to the drawings, description will be given of a
metal heater in which a heater is sandwiched between two metal
plates as one example of the metal heater according to the third
aspect of the present invention.
[0243] FIG. 6(a) is a cross-sectional view that schematically shows
such a metal heater, and FIG. 6(b) schematically shows a method by
which a heating element and a conductive line are joined to each
other by caulking using a joining foil in the metal heater shown in
FIG. 6(a). Moreover, FIG. 7 is a plan view that shows the metal
heater of FIG. 6(a). Here, in FIG. 7, the heating element is
indicated by a broken line.
[0244] In a metal heater 610, each of supporting pins 618 having a
tip portion like a nail is inserted into each of concave portions
628 prepared as cylinder shaped hollow sections formed on the upper
metal plate 611, and a C-shaped spring 627 is fitted to each
concave portion 628 so as to contact therewith in a manner so as to
enclose the supporting pin 618 so that the supporting pin 618 is
fixedly secured to the heating face 611a of the upper metal plate
611.
[0245] Here, in the present embodiment, the supporting pin is
placed on the heating face of the metal plate by using a means
shown in FIG. 6; however, with respect to the means for placing the
supporting pin on the heating face of the metal plate, not limited
to the means shown in FIG. 6, for example, a method in which a
supporting pin having a screw portion is engaged with a concave
portion in which thread grooves are formed.
[0246] Moreover, as shown in FIG. 2, on the heating face 611a of
the upper metal plate 611, eight supporting pins 618 are placed on
circumferences of concentric circles of the upper metal plate 611
and one supporting pin 618 is placed on the center portion of the
upper metal plate 611 at an area located on a comparatively
peripheral portion of the upper metal plate 611; thus, the total
nine supporting pins 618 are placed thereon. Here, the supporting
pins located on the same circumference are placed so as to have the
same interval, in order to prevent sagging in the semiconductor
wafer 619.
[0247] Here, the other structures are the same as those of the
metal heater 510 according to the second aspect of the present
invention shown in FIG. 5; therefore, the description thereof is
omitted.
[0248] The metal heater 610 according to the third aspect of the
present invention, which has the above-mentioned structure, makes
it possible to realize a flatness of 50 .mu.m or less on the
heating face 611a of the upper metal plate 611. By realizing such a
flatness, upon heating a semiconductor wafer, the distance between
the semiconductor wafer and the metal plate is made almost constant
so that the entire semiconductor wafer can be heated to have an
even temperature.
[0249] The metal heater 610 according to the third aspect of the
present invention may be provided with a wafer guide ring 626 on
the peripheral edge portion of the heating face 611a so as to
prevent temperature changes due to a gas flowing therein from
outside, or may be provided with a barrier ring 632 thereon.
[0250] The metal heater 610 according to the third aspect of the
present invention is different from a conventional metal heater 450
shown in FIGS. 4(a) and 4(b) in the following points.
[0251] First, as described above, the metal heater 610 has the
structure in which the total nine supporting pins 618 are placed on
the heating face 611a of the upper metal plate 611, while the metal
heater 450 has a structure in which the total five supporting pins
458 are placed on the heating face 451a of the metal plate 451;
thus, the numbers of the supporting pins are different from each
other. Therefore, since the metal heater 610 has a narrower gap
between the supporting pins 618, it becomes possible to make the
semiconductor wafer 619 less likely to sagging. For this reason,
the distance between the semiconductor wafer 619 and the heating
face 611a of the upper metal plate 611 is made almost constant so
that the heating process can be carried out on the entire
semiconductor wafer 619 evenly.
[0252] Moreover, in the metal heater 610, the side faces of the
upper metal plate 611, the heater 612 and the lower metal plate 621
are not made in tightly contact with the supporting case 620, and
secured in a non-contact state, and the lower metal plate 621 is
not made in direct contact with the bottom face of the supporting
case 620 either, and supported by a supporting plate 625. With this
structure in which the side faces of the upper metal plate 611, the
heater 612 and the lower metal plate 621 are kept in a non-contact
state with the supporting case 620, the upper metal plate 611 can
be prevented from being curved due to pressure from the side faces
when the upper metal plate 611 has been thermally expanded. In the
case of the structure in which the upper metal plate 611, the
heater 612 and the lower metal plate 621 are supported only through
the supporting plate 625, with no other portions made in contact
therewith, upon heating an object to be heated, heat released from
the metal plate and the like is reduced so that an object to be
heated can be heated more quickly in comparison with the case in
which the side faces of the upper metal plate 611, the heater 612
and the lower metal plate 621 are made in tightly contact with the
supporting case 620. In this case, an air layer is allowed to
function as a heat insulating layer.
[0253] Here, the upper metal plate 611, the heater 612 and the
lower metal plate 621, as they are, may be placed on the bottom
face of the supporting case 620, without providing the supporting
member 625 on the bottom face of the supporting case 620.
[0254] After the heating process, the upper metal plate 611, the
heater 612 and the lower metal plate 621 sometimes need to be
cooled quickly, and in such a case, for example, a cooling pipe or
the like is connected to the bottom plate of the supporting case
620, with cooled air or the like introduced into the supporting
case 620, so that it becomes possible to carry out a quick cooling
process.
[0255] Moreover, the metal heater 610 has a structure in which the
metal plate securing screws 617 do not penetrate the supporting
case 620, and are allowed to penetrate only the upper metal plate
611, the heater 612 and the lower metal plate 621, and designed to
secure these members. With this structure, it becomes possible to
prevent deformation in the upper metal plate 611 due to a
difference in thermal expansion coefficients between the upper
metal plate 611 and the supporting case 620, and also to reduce
heat released from the upper metal plate 611 and the like upon
heating an object to be heated so that the object to be heated can
be heated quickly.
[0256] In the metal heater 610 according to the third aspect of the
present invention, the peripheral edge of the heating element 625
formed inside the heater 612 is desirably located at a position
within 25% of the diameter of the metal plate 611 from the
periphery of the metal plate 611. The reason therefor is the same
as described in the first aspect of the present invention.
[0257] With respect to the material, shape and the like of the
metal heater forming the third aspect of the present invention and
the manufacturing method of the metal heater according to the third
aspect of the present invention, detailed description will be given
later.
[0258] In the following, description will be given of the
materials, shapes and the like of the metal heaters according to
the first to third aspects of the present invention. Here, since
the materials, shapes and the like of the metal heaters according
to the first to third aspects of the present invention are almost
the same, the description thereof will be given all together.
[0259] With respect to each of the metal heaters according to the
first to third aspects of the present invention, the metal plate is
provided with bottomed holes formed on the side opposite to the
heating face side on which an object to be heated is placed, toward
the heating face, and the bottom of each bottomed hole is formed
relatively closer to the heating face from the heating element, and
a temperature measuring element (not shown), such as a thermocouple
or the like is desirably provided on the bottomed hole.
[0260] Moreover, the distance between the bottom of the bottomed
hole and the heating face is desirably between 0.1 mm and 1/2 of
the thickness of the metal plate. Thus, the temperature measuring
place is made closer to the heating face from the heating element
so that it becomes possible to measure the temperature of the
semiconductor wafer more accurately.
[0261] The distance between the bottom of the bottomed hole and the
heating face of less than 0.1 mm causes heat radiation, resulting
in a distribution of temperature on the heating face; in contrast,
the distance exceeding 1/2 of the thickness makes the metal plate
more likely to be influenced from the temperature of the heating
element, resulting in a failure in temperature control, and the
subsequent distribution of temperature on the heating face.
[0262] The diameter of the bottomed hole is desirably 0.3 to 5 mm.
The reason therefor is because, when the diameter is too large, the
heat radiating property becomes too high, while, when the diameter
is too small, the machining property becomes too low; thus, it
becomes impossible to evenly maintain the distance from the heating
face.
[0263] With respect to the temperature measuring element, for
example, a thermocouple, a platinum temperature measuring resistor,
a thermistor and the like may be used. With respect to the
thermocouple, for example, as listed in JIS-C-1602 (1980), K-type,
R-type, B-type, S-type, E-type, J-type and T-type thermocouples may
be used. Among these, the K-type thermocouples are more desirably
used.
[0264] The size of the coupling portion of the thermocouple is set
to the same as the diameter of an element wire, or greater than the
diameter thereof, and is desirably 0.5 mm or less. The coupling
portion that is greater than this tends to cause a great thermal
capacity and the subsequent reduction in responsivity. Here, it is
difficult to make the coupling portion smaller than the diameter of
an element wire.
[0265] The temperature measuring element may be bonded to the
bottom of the bottomed hole by using gold alloy, silver alloy or
the like, or may be sealed with a heat resistant resin after having
been inserted into the bottomed hole, or both of the
above-mentioned methods may be used in combination.
[0266] With respect to the heat resistant resin, examples thereof
include thermosetting resins, in particular, epoxy resin, polyimide
resin, bismaleimide-triazine resin and the like. Each of these
resins may be used alone, or two or more resins of these may be
used in combination.
[0267] With respect to the gold alloy, at least one kind selected
from the group consisting of Au (37 to 80.5% by weight)--Cu (63 to
19.5% by weight) alloy and Au (81.5 to 82.5% by weight)--Ni (18.5
to 17.5% by weight) alloy is desirably used. These alloys have
melting temperatures of 900.degree. C. or more, and hardly melt
even at a high-temperature range.
[0268] With respect to the silver alloy, for example, Ag--Cu-based
alloys may be used.
[0269] With respect to the heater, a mica heater as shown in FIG.
2, a silicon rubber heater or the like may be used. Moreover, a
heater in which a heating element line is simply formed on an
insulating seal may also be used.
[0270] With respect to the mica heater, a heater in which a heating
element such as a nichrome wire or the like, formed into an
optional pattern, is sandwiched by mica plates serving as
insulating members may be used. Moreover, with respect to the
silicon rubber heater, a heater in which a heating element such as
a nichrome wire or the like, formed into an optional pattern, is
sandwiched by silicon rubber plates serving as insulating members
may be used.
[0271] With respect to the heating element to heat the heater, not
limited by the above-mentioned nichrome wire, another metal line,
such as a tungsten line, a molybdenum line and the like, and the
like may be used as long as it generates heat upon applying a
voltage.
[0272] Moreover, with respect to the heating element, in addition
to the metal line, metal foil may be used. With respect to the
metal foil, a heating element in which nickel foil, stainless foil
or the like is etched into a pattern is desirably used. The
patterned metal foils may be bonded to each other by using a resin
film or the like.
[0273] With respect to the insulating member used for coating the
heating element, not limited to the above-mentioned mica plate and
silicon rubber, for example, a material, such as fluororesin,
polyimide resin, polybenzoimidazole (PBI) or the like, may be used
as long as it is capable of preventing short-circuiting and of
withstanding high temperatures, and a material in which fibers made
from ceramics or the like are formed into a mat shape may also be
used.
[0274] In the case where the metal heater has a structure in which
the heater is sandwiched between metal plates, a plurality of the
heaters may be provided. In this case, with respect to the patterns
of the respective layers, heating elements are desirably formed in
any of the layers so as to compensate for one another, and the
pattern is desirably formed in any of areas, when viewed from above
the heating face. Examples of such a structure include a staggered
structure.
[0275] Moreover, with respect to the pattern of the heating element
in the metal heaters according to the first to third aspects of the
present invention, not limited to the pattern as shown in FIG. 2
and the like, for example, patterns, such as a concentric circle
pattern, a spiral pattern, an eccentric circular pattern and the
like, maybe used. Moreover, a combined pattern of them may be
used.
[0276] The heating element is desirably divided into two or more
parts, as described above.
[0277] Moreover, the area resistivity of the heating element is
desirably 0.1 to 10.OMEGA./. When the area resistivity exceeds
10.OMEGA./, the diameter of the heating element needs to be made
extremely smaller in order to ensure a desired quantity of heat
generation, and, for this reason, even a slight chip or the like
tends to cause disconnection or dispersion in resistance value.
Moreover, in the case where the area resistivity is less than
0.1.OMEGA./, the diameter of the heating element needs to be made
larger so as to ensure a sufficient quantity of heat generation;
thus, the degree of freedom in designing the pattern of the heating
element is lowered, and it becomes difficult to evenly control the
temperature of the heating face.
[0278] With respect to the means for connecting the heating element
to a power supply, as shown in FIG. 1, a part of the heating
element made of metal foil is exposed to form a connecting foil,
and one end of the conductive line is wrapped with the connecting
foil, with an attaching member having a caulking portion attached
to this portion, so that the connection is made by caulking the
caulking portion, or conductive lines may be attached to the both
ends of the heating element through soldering or the like so that
the connection to the power supply or the like may be made through
these conductive lines, or terminals may be attached to the two
ends of the heating element so that the connection to the power
supply or the like may be made through these terminals.
[0279] Here, the terminals are desirably attached to the heating
element through soldering, brazing, crimping, caulking or the like.
The terminals are desirably attached through soldering because
nickel prevents thermal diffusion of solder. With respect to the
connecting terminals, for example, external terminals made of Kovar
may be used.
[0280] With respect to the solder used for connecting the
connecting terminals, an alloy, such as a silver-lead alloy, a
lead-tin alloy, a bismuth-tin alloy and the like, may be used. The
thickness of the solder layer is preferably 0.1 to 50 .mu.m. This
range makes it possible to sufficiently ensure connection through
soldering.
[0281] Moreover, in the metal heater according to the first to
third aspects of the present invention, an intermediate plate may
be interposed between the metal plate and the heater. By
interposing such an intermediate plate, heat generated by the
heating element can be transmitted to the metal plate in a further
even state.
[0282] With respect to the material of the intermediate plate,
ametal having a superior thermal conductivity is desirably used,
and, for example, copper, a copper alloy or the like may be
used.
[0283] In the metal heater shown in FIG. 1, the side face of the
metal plate and the supporting case are in a non-contact state;
however, in the case where these members are made in contact with
each other, a heat insulating ring is desirably interposed between
the side face of the metal plate and the supporting case. Since
heat is released from the peripheral portion of the metal plate, it
becomes possible to prevent temperature dispersion from occurring
on the heating face of the metal plate.
[0284] The supporting case and the heat shielding plate may be
integrally formed, or the heat shielding plate may be coupled and
secured to the supporting case. Desirably, the supporting case and
the heat shielding plate are integrally formed. Thus, it becomes
possible to ensure the strength of the entire metal heater.
[0285] The supporting case desirably has a cylinder shape, and the
heat shielding plate desirably has a disk shape. Moreover, the
thickness of the supporting case and that of the heat shielding
plate are desirably 0.1 to 5 mm. The thickness of less than 0.1 mm
causes insufficient strength, and the thickness exceeding 5 mm
makes the thermal capacity greater.
[0286] The supporting case and the heat shielding plate are
desirably made of a metal, such as SUS, aluminum, inconel
(nickel-based alloy containing 16% of chrome and 7% of iron) or the
like, so as to allow easy machining and superior mechanical
properties and ensure sufficient strength in the entire metal
heater.
[0287] In the case where the supporting case and the heat shielding
plate are not prepared as an integral part, the heat shielding
plate may be made of a material, such as a heat resistant resin, a
ceramic plate, a composite plate formed by blending heat-resistant
organic fibers and inorganic fibers into these materials, or the
like, that has a thermal conductivity that is not so high, and is
superior in heat resistance, so as to achieve a superior heat
shielding property.
[0288] Moreover, a coolant introducing pipe may be attached to the
supporting case or the heat shielding plate. By introducing a
coolant or the like used for forcibly cooling the metal heater, the
metal heater can be quickly cooled. Moreover, a through hole for
discharging the introduced coolant or the like for forcible cooling
may be formed in the supporting case or the heat shielding
plate.
[0289] In the following, description will be given of a
manufacturing method of the metal heaters according to the first to
third aspects of the present invention.
(1) Manufacturing Processes of Metal Plate
[0290] A plate-shaped member, made of a material such as an
aluminum-copper alloy or the like, is machined at outer diameter
portion by using an NC lathe and formed into a disk shape, and this
plate-shaped member is then subjected to an end-face machining
process, a surface machining process and a rear-face machining
process in succession.
[0291] In this case, the thickness of the plate-shaped member to
form an upper metal plate is made larger than the thickness of a
plate-shaped member to form a lower metal plate.
[0292] Next, each of parts to be through holes into which lifter
pins for supporting a semiconductor wafer are inserted, each of
concave portions on which supporting pins are placed and each of
parts to be bottomed holes in which a temperature measuring
element, such as a thermocouple, is embedded are formed by using a
machining center (MC) or the like. Moreover, after bottomed holes
have been formed at predetermined positions, thread grooves are
formed in the bottomed holes so that screw holes through which
metal plate securing screws are inserted are formed.
[0293] In particular, in the case where the metal heater according
to the third aspect of the present invention is manufactured, the
concave portions for placing the supporting pins are formed in a
manner so as to widely spread the supporting pins on the metal
plate as well as place them with equal intervals. With respect to
the layout thereof, for example, as shown in FIG. 7, a plurality of
supporting pins 618 are placed on circumferences of concentric
circles of the metal plate at equal intervals, with a single
supporting pin 618 placed in the center portion of the metal plate.
With this arrangement, upon heating the semiconductor wafer, the
semiconductor wafer is made free from sagging so that the distance
of a semiconductor wafer and a metal plate is made even; thus, the
semiconductor wafer can be evenly heated.
[0294] Moreover, the plate-shaped member to form the upper metal
plate is subjected to a surface grinding process by using a rotary
grinding machine so that the upper metal plate and the lower metal
plate are manufactured. By carrying out this surface grinding
process, the flatness of the surface of the metal plate can be set
to about 20 to 30 .mu.m.
[0295] Furthermore, a wafer guide ring for suppressing an ambient
gas (for example, air or the like) flow may be formed on the upper
metal plate, if necessary. The above-mentioned wafer guide ring
maybe made of, for example, an aluminum-copper alloy, SUS or the
like. Moreover, a barrier ring may be formed on the uppermost
portion of the supporting case for the same purpose.
[0296] By providing the wafer guide ring and the barrier ring, the
ambient gas flows inside and outside the heating area are
intervened so that the object to be heated can be evenly
heated.
[0297] Next, the upper metal plate and the lower metal plate are
subjected to an alumite treatment so that oxide coat films are
formed on the surfaces of the upper metal plate and the lower metal
plate. By carrying out this treatment, the corrosion resistance of
the metal plate is improved with a harder surface; therefore, the
metal plate becomes less likely to have scratches or the like.
Moreover, even when the metal plate is used during actual
semiconductor producing and examining processes, the metal plate
becomes less likely to receive corrosion due to a resist solution,
corrosive gases and the like.
[0298] With respect to the alumite treatment (anode oxidation
coating treatment), for example, a sulfate method, an oxalate
method or the like may be used, and the oxalate method is desirably
used. Thus, it becomes possible to prevent surface pinholes from
occurring after the treatments.
(2) Placement of Heater
[0299] A heater, formed by sandwiching a heating element such as a
nichrome wire processed into a predetermined pattern, a metal foil
like a stainless foil, or the like between ceramic plates such as
mica plates or the like, is placed between the upper metal plate
and the lower metal plate, and after metal plate securing screws
have been inserted through screw holes formed in the lower metal
plate and the heater, the lower metal plate and the heater are
fastened into an integral part by tightening the screws.
[0300] Here, since the entire heater needs to be set to an even
temperature in the heating element, a pattern or the like which is
basically formed by repeatedly placing a winding line in a ring
shape or repeatedly drawing a winding line in a manner so as to
form a part of each of concentric circles is preferably used.
[0301] Moreover, an intermediate plate, made of a material having
superior thermal conductivity such as copper or the like, may be
sandwiched between the metal plate and the heater. With this
arrangement, heat radiated from the heater can be transmitted to
the upper metal plate in a further even state.
(3) Attachment of Supporting Case
[0302] A device in which the metal plate and the heater are
integrally formed in this manner is supported in a cylinder-shaped
supporting case shown in FIG. 1 and secured therein.
[0303] A heat shielding plate, made from the same material as the
supportin gcase, is placed on the bottom face of the supporting
case, and through holes, which allow a temperature measuring
element, a conductive line and the like to pass, are formed in the
supporting case.
[0304] In the metal heaters according to the first to third aspects
of the present invention, as shown in FIG. 1, the side faces of the
metal plate and the heater are desirably supported and secured in
the supporting case in a non-contact state therewith.
[0305] This structure is prepared because the peripheral portion of
the heating face of the metal plate tends to have a low temperature
due to released heat from the side faces of the metal plate and the
heater.
[0306] In the case where the side faces of the metal plate and the
heater are supported and secured in the supporting case in a
contact state therewith, a heat insulating ring made of polyimide
resin, fluororesin or the like is desirably interposed between the
metal plate and the supporting case.
(4) Connection to Power Supply or the Like
[0307] Terminals (external terminals) for use in connection to a
power supply are attached to both ends of the heating element
provided in the heater through a brazing material or solder, or by
using a mechanical attaching method (attaching means) such as crimp
screwing, caulking or the like, so that the heater is connected to
an external power supply or the like; thus, the manufacturing
processes of the metal heater are completed. Here, in the case
where the metal heater according to the third aspect of the present
invention is manufactured, after supporting pins formed on the
heating face of the metal plate have been inserted, the supporting
pins are secured by using springs or the like to complete the
manufacturing processes of the metal heater.
BEST MODE FOR CARRYING OUT THE INVENTION
[0308] In the following, description will be given of the first to
third aspects of the present invention by way of examples in
detail.
[0309] The following examples exemplify a case in which a metal
heater for heating a semiconductor wafer is used; however, the
first to third aspects of the present invention may be applied to a
heater for temperature adjustment for an optical waveguide.
EXAMPLE 1
[0310] Manufacturing of metal heater (see FIGS. 1 and 2)
[0311] (1) A plate-shaped member, made of an aluminum-copper alloy
(A2219 (JIS-H4000)), was machined at outer-diameter portion by
using an NC lathe (manufactured by Washino Machinery Co., Ltd.) and
formed into a disk shape, and this plate-shaped member was then
subjected to an end-face machining process, a surface machining
process and a rear-face machining process so that a disk-shaped
member for an upper metal plate and a disk-shaped member for a
lower metal plate were manufactured.
[0312] Next, each of parts to be through holes 415 to which lifter
pins used for supporting a semiconductor wafer 419 are inserted,
each of concave portions in which supporting pins 418 are placed
and each of parts to be a bottomed hole 414 in which a temperature
measuring element 416 is embedded were formed by using a machining
center (Hitachi Seiki Co., Ltd.).
[0313] Here, the through holes 415 were formed at three positions,
and the concave portions for placing the supporting pins 418 were
formed at nine positions.
[0314] After the bottomed holes or the through holes had been
formed at predetermined positions in the same manner, thread
grooves were formed in the bottomed holes or the through holes so
that screw holes through which metal plate securing screws 17 are
inserted were formed in the disk shape.
[0315] Here, the screw holes were formed in the upper metal plate
and the plate-shaped member with a depth of 3/4 of the thickness
thereof.
[0316] (2) Next, the disk member for the upper metal plate,
manufactured through the processes of (1), was subjected to a
surface grinding process on its surface on the heating face side by
using a rotary grinding machine (manufactured by Okamoto Machine
Tool Works, Ltd.) so that an upper metal plate 411 having a
thickness of 15 mm and a diameter of 330 mm and a lower metal plate
421 having a thickness of 5 mm and a diameter of 330 mm were
obtained.
[0317] Moreover, a barrier ring 428 for suppressing a gas flow
toward a semiconductor wafer that is an object to be heated was
placed on a side face of the upper metal plate 411 by using the
above-mentioned method.
[0318] In other words, the peripheral edge portion of the
supporting case was made higher than the upper face (heating face)
of the upper metal plate so that the barrier ring was formed.
[0319] Here, in this example, the thickness of the upper metal
plate 411 was made larger than the thickness of the lower metal
plate 421.
[0320] (3) Next, the upper metal plate 411 and the lower metal
plate 421 were subjected to an alumite treatment under conditions
of 10% H.sub.2SO.sub.4 electrolytic solution, a voltage of 10 V, a
current density of 0.8 A/dm.sup.2 and a liquid temperature of
20.degree. C. so that an oxide coat film having a thickness of 15
.mu.m was formed on each of the surfaces of the upper metal plate
411 and the lower metal plate 421.
[0321] (4) A heating element 425, made of a stainless foil having a
thickness of 200 .mu.m on which a winding wire shown in FIG. 2 is
placed in a repeated pattern to form a ring shape and a winding
wire is repeatedly placed in a pattern so as to form a part of each
of concentric circles, was sandwiched between two mica plates 426
having a thickness of 0.3 mm to obtain a heater 412 having a
diameter of 330 mm.
[0322] Here, in the heater 412, the heating element 425 was formed
so that the outer rim of the heating element was placed at a
position within 25% of the diameter of the upper metal plate 411
from the periphery of the upper metal plate 411, and the total
number of the circuits of the heating element 425 was set to
four.
[0323] Moreover, parts to be through holes 415, a part to be the
bottomed hole 414 and parts to be screw holes through which metal
plate securing screws 417 are inserted were preliminary formed in
the mica plate 426.
[0324] Thereafter, the heater 12 was sandwiched between the upper
metal plate 411 and the lower metal plate 421 manufactured through
the processes of (1) to (3), and after the metal plate securing
screws 417 had been inserted through the screw holes formed in the
lower metal plate 421 and the heater 412, the securing screws were
tightened so that the upper metal plate 411, the lower metal plate
421 and the heater 412 were combined into an integral part.
[0325] (5) Next, a supporting case 420 having a cylinder shape as
shown in FIG. 1, made of SUS, was manufactured, and after parts to
be the through holes 415, a part to be the bottomed hole 414 and a
through hole through which the conductive wire 424 is inserted had
been formed in the bottom face of the supporting case 420, a heat
shielding plate 423 having a disk shape, made of SUS, was placed on
the bottom portion of the supporting case 420.
[0326] Moreover, the upper metal plate 411 to which the heater 412
and the lower metal plate 421 had been attached, manufactured in
the process (4), was placed inside the supporting case 420 in which
the heat shielding plate 423 had been placed, and fixedly secured
therein so that the side faces of the upper metal plate 411, the
heater 412 and the lower metal plate 621 were kept in no-contact
with the supporting case 420.
[0327] Here, in the metal heater in this example, the screw head of
each metal plate securing screw 417 was designed to be embedded
into the lower metal plate 421 so that the bottom face of the lower
metal plate 421 was made in contact with the inner face of the
supporting case 420.
[0328] (6) After a temperature measuring element 416 made of a
platinum temperature measuring resistor for use in controlling
temperatures had been inserted into the bottomed hole 414, the
bottomed hole 414 was sealed by using an inorganic adhesive (Aron
ceramic, made by Toagosei Co., Ltd.) . Moreover, supporting pins
418 were placed in the concave portions formed on the heating face
of the upper metal plate 411.
[0329] (7) Next, the conductive wire 424 was wrapped by a
connecting foil taken out of the stainless foil serving as the
heating element provided in the heater 412, and a metallic
attaching member was attached thereto, and this was then caulked so
that the connecting foil and the conductive wire 424 were connected
to each other and secured with each other. Thus, the heating
element provided in the heater 412 was connected to an external
power supply or the like so that a metal heater 410 was
obtained.
EXAMPLE 2
Manufacturing of Metal Heater
[0330] The same processes as those of Example 1 were carried out
except that the thickness of the upper metal plate 411 was set to
20 mm and that the thickness of the lower metal plate 421 was set
to 5 mm so that a metal heater was manufactured.
EXAMPLE 3
Manufacturing of Metal Heater
[0331] The same processes as those of Example 1 were carried out
except that the thickness of the upper metal plate 411 was set to
25 mm and that the thickness of the lower metal plate 421 was set
to 10 mm so that a metal heater was manufactured.
EXAMPLE 4
Manufacturing of Metal Heater
[0332] The same processes as those of Example 1 were carried out
except that the thickness of the upper metal plate 411 was set to
40 mm and that the thickness of the lower metal plate 421 was set
to 5 mm so that a metal heater was manufactured.
EXAMPLE 5
[0333] The same processes as those of Example 1 were carried out
except that the thickness of the upper metal plate 411 was set to
20 mm and that the thickness of the lower metal plate 421 was set
to 20 mm so that a metal heater was manufactured.
EXAMPLE 6
[0334] The same processes as those of Example 1 were carried out
except that the thickness of the upper metal plate 411 was set to
36 mm and that the thickness of the lower metal plate 421 was set
to 3 mm so that a metal heater was manufactured.
EXAMPLE 7
[0335] The same processes as those of Example 1 were carried out
except that the thickness of the upper metal plate 411 was set to
50 mm and that the thickness of the lower metal plate 421 was set
to 5 mm so that a metal heater was manufactured.
TEST EXAMPLE 1
[0336] The same processes as those of Example 1 were carried out
except that in the processes of (1) to (3) in Example 1, the
thickness of the upper metal plate was set to 5 mm and that the
thickness of the lower metal plate was set to 20 mm so that a metal
heater was manufactured. In this test example, the thickness of the
lower metal plate was made larger than the thickness of the upper
metal plate.
TEST EXAMPLE 2
[0337] The same processes as those of Example 1 were carried out
except that in the process of (5) of Example 1, the supporting case
420 was manufactured in such a manner that the inner diameter of
the supporting case 420 was made almost the same as the diameter
(330 mm) of the upper metal plate 411, the heater 412 and the lower
metal plate 411 are placed and fixedly secured inside the
supporting case 420 with the side faces thereof being made in
tightly contact with the supporting case 420; thus, a metal heater
was manufactured.
COMPARATIVE EXAMPLE 1
[0338] A metal heater in which an intermediate plate made of copper
and a heater were placed on the bottom face of a metal plate was
manufactured. The thickness of the metal plate was 55 mm, and the
pattern of the heating element was the same as that of Example
1.
[0339] A current was applied to each of the metal heaters according
to Examples 1 to 7, Test Examples 1 and 2 and Comparative Example 1
to raise the temperature; thus, evaluation was made on each of the
following points: (1) temperature evenness in surface in steady
state, (2) temperature evenness in surface in transition period,
(3) measurements on flatness; (4) overshoot amount. The results
thereof are shown in Table 1.
[0340] The respective evaluating processes were carried out by
using the following methods.
(1) Temperature Evenness in Surface in Steady State
[0341] After the temperature of the metal heater had been raised to
140.degree. C., a wafer with a temperature sensor equipped with a
thermocouple was placed on the heating face of the metal heater so
that the distribution of temperature on the heating face was
measured. The distribution of temperature was indicated by a
maximum value of a temperature difference between the highest
temperature and the lowest temperature during the temperature
rise.
(2) Temperature Evenness in Surface in Transition Period
[0342] The wafer with a temperature sensor was heated from ordinary
temperature to 140.degree. C. by the metal heater so that the
distribution of temperature in surface of the wafer with a
temperature sensor was measured. The distribution of temperature
was measured at 100.degree. C., 120.degree. C. and 130.degree. C.
respectively, and indicated by a maximum value of a temperature
difference between the highest temperature and the lowest
temperature.
(3) Measurements on Flatness
[0343] The flatness on the heating face of the metal plate was
measured at ordinary temperature as well as at 140.degree. C. by a
laser displacement gauge (made by Keyence Corporation).
(4) Overshoot Amount
[0344] The overshoot amount (the value obtained by subtracting the
set temperature (140.degree. C.) from the maximum temperature
during the process) in the case where 20 silicon wafers were
processed at 140.degree. C. was measured.
[0345] Here, with respect to the evaluation of (3) measurements on
flatness, a three-dimensional shape of a part of the heating face
of the metal heater according to Example 1 at ordinary temperature
is shown in FIG. 8; a three-dimensional shape of a part of the
heating face of the metal heater according to Example 1 at
140.degree. C. is shown in FIG. 9; and a three-dimensional shape of
a part of the heating face of the metal heater according to Test
Example 1 at 140.degree. C. is shown in FIG. 10. TABLE-US-00001
TABLE 1 Thickness of Distribution of Distribution of metal plate
temperature in temperature in Overshoot amount (mm) surface in
surface in Flatness (.mu.m) (.degree. C.) Upper Lower steady state
transition period At after processing metal metal (.degree. C.)
(.degree. C.) ordinary 20 wafers at plate plate 140.degree. C.
100.degree. C. 120.degree. C. 130.degree. C. temperature
140.degree. C. 140.degree. C.) Example 1 15 5 0.17 5.37 2.38 2.01
29 30 0.30 Example 2 20 5 0.24 5.38 2.80 1.51 29 30 0.35 Example 3
25 10 0.19 5.45 2.22 1.76 29 29 0.33 Example 4 40 5 0.25 4.80 2.24
1.64 28 29 0.31 Example 5 20 20 0.31 4.16 2.53 1.96 28 35 0.35
Example 6 36 3 0.32 4.20 2.53 1.95 28 36 0.30 Example 7 50 5 0.27
4.98 2.62 1.97 28 29 0.30 Test 5 20 0.44 9.56 6.66 5.10 37 47 1.32
Example 1 Test 15 5 0.36 4.78 2.67 2.13 40 53 0.35 Example 2
Comparative 55 0 0.42 5.58 3.66 2.36 44 56 0.32 Example 1
As shown in Table 1, the metal heaters according to Examples 1 to 7
had an even temperature on the heating face of the upper metal
plate in steady state as well as in transition period. This is
presumably because the thickness of the metal plate on the heating
face side is large so that heat transmitted to the metal plate is
sufficiently dispersed to prevent the pattern of the heating
element from being reflected to the heating face.
[0346] Moreover, as shown in Table 1 as well as in FIGS. 8 and 9,
since the flatness in the metal heaters of Examples 1 to 4 is 50
.mu.m or less, the distance between the upper metal plate and the
sensor wafer becomes less likely to have dispersion to provide an
even heating process.
[0347] This is presumably because, since the metal heaters
according to Examples 1 to 4 have a structure in which the lower
metal plate having a fixed thickness is placed on the bottom face
of the heater, thermal radiation released from the heater is made
even.
[0348] Furthermore, in the metal heaters of Examples 5 and 6, the
temperature evenness of the heating face in steady state is
inferior to that of the metal heaters of Examples 1 to 4; however,
the temperature evenness of the heating face in transition period
is superior to that of the metal heaters of Examples 1 to 4.
[0349] In contrast, in the case of the metal heaters according to
Test Examples 1 and 2, the temperature of the heating face of the
upper metal plate was uneven in steady state as well as in
transition period. This is presumably because the thickness of the
upper metal plate is thin; thus, warping and sagging occur in the
metal plate due to thermal expansion during the heating
process.
[0350] Moreover, in the metal heater according to Comparative
Example 1, since the heater is placed on the bottom face of the
metal plate without the lower metal plate, the flatness of the
heating face becomes inferior; thus, the temperature on the heating
face becomes uneven.
[0351] With respect to the overshoot amount, the measured results
of the metal heater according to Test Example 1 gave values greater
than those of the measured results of the other metal heaters. This
is presumably because, since the thickness of the lower metal plate
is larger than the thickness of the upper metal plate with the
thermal capacity of the lower metal plate being relatively greater
than the thermal capacity of the upper metal plate, heat is
accumulated in the lower metal plate to cause heat conduction from
the lower metal plate to the upper metal plate and the subsequent
overshooting phenomenon due to the heat conduction.
EXAMPLE 8
Manufacturing of Metal Heater (see FIG. 5)
[0352] (1) A plate-shaped member, made of an aluminum-copper alloy
(A2219 (JIS-H4000)), was machined at outer-diameter portion by
using an NC lathe (made by Washino Machinery Co., Ltd.) and formed
into a disk shape, and this disk-shaped member was then subjected
to an end-face machining process, a surface machining process and a
rear-face machining process so that a disk-shaped member for an
upper metal plate and a disk-shaped member for a lower metal plate
were manufactured.
[0353] Next, each of parts to be through holes 515 to which lifter
pins for supporting a semiconductor wafer 519 are inserted, each of
concave portions in which supporting pins 518 are placed and a part
to be a bottomed hole 514 in which a temperature measuring element
516 is embedded were formed in these disk members by using a
machining center (Hitachi Seiki Co., Ltd.).
[0354] Here, the through holes 515 were formed at three positions,
and the concave portions used for placing the supporting pins 518
were formed at nine positions.
[0355] After the bottomed holes or the through holes had been
formed at predetermined positions in the same manner, thread
grooves were formed in the bottomed holes or the through holes so
that screw holes through which metal plate securing screws 517 are
inserted were formed in the disk members.
[0356] Here, the screw holes were formed in the upper metal plate
and the plate-shaped member with a depth of 3/4 of the thickness
thereof.
[0357] (2) Next, the disk member for the upper metal plate,
manufactured through the processes of (1), was subjected to a
surface grinding process on its surface on the heating face side by
using a rotary grinding machine (made by Okamoto Machine Tool
Works, Ltd.) so that an upper metal plate 511 having a thickness of
15 mm and a diameter of 330 mm and a lower metal plate 521 having a
thickness of 5 mm and a diameter of 330 mm were obtained.
[0358] Moreover, a barrier ring for a wafer that is an object to be
heated was formed on the side face of the upper metal plate 511 by
using the following method.
[0359] In other words, the outer rim portion of the supporting case
was made higher than the upper face of the heating face of the
upper metal plate so that the barrier ring 532 was formed.
[0360] Here, in this example, the thickness of the upper metal
plate 511 was made larger than the thickness of the lower metal
plate 521.
[0361] (3) Next, the upper metal plate 511 and the lower metal
plate 521 were subjected to an alumite treatment under conditions
of 10% H.sub.2SO.sub.4 electrolytic solution, a voltage of 10 V, a
current density of 0.8 A/dm.sup.2 and a liquid temperature of
20.degree. C. so that an oxide coat film having a thickness of 15
.mu.m was formed on each of the surfaces of the upper metal plate
511 and the lower metal plate 521.
[0362] (4) A heating element, made of a stainless foil having a
thickness of 200 .mu.m on which a winding wire is placed in a
repeated pattern to form a ring shape and a winding wire is
repeatedly placed in a pattern so as to form a part of each of
concentric circles as shown in FIG. 2, was sandwiched between two
mica plates having a thickness of 0.3 mm to obtain a heater 512
having a diameter of 330 mm.
[0363] Here, in the heater 512, the heating element was formed so
that the outer rim of the heating element was placed at a position
within 25% of the diameter of the upper metal plate 511 from the
periphery of the upper metal plate 511, and the total number of the
circuits of the heating element was set to four.
[0364] Moreover, parts to be through holes 515, a part to be the
bottomed hole 514 and parts to be screw holes through which metal
plate securing screws 517 are inserted were preliminary formed in
the mica plate 526.
[0365] Thereafter, the heater 512 was sandwiched between the upper
metal plate 511 and the lower metal plate 521 manufactured through
the processes of (1) to (3), and after the metal plate securing
screws 517 had been inserted through the screw holes formed in the
lower metal plate 521 and the heater 512, the securing screws were
tightened so that the upper metal plate 511, the lower metal plate
521 and the heater 512 were combined into an integral part.
[0366] (5) Next, a supporting case 520 having a cylinder shape with
a bottom as shown in FIG. 5, made of SUS, was manufactured, and a
supporting plate 525 was placed on the bottom face of the
supporting case 520 and parts to be the through holes 515, a part
to be the bottomed hole 514 and a through hole through which the
conductive wire 524 was inserted had been formed in the bottom face
of the supporting case 520, a heat shielding plate 523 having a
disk shape, made of SUS, was placed on the bottom portion of the
supporting case 520.
[0367] Moreover, the upper metal plate 511 to which the heater 512
and the lower metal plate 521 had been attached, manufactured in
the process (4), was placed inside the supporting case 520 on which
the heat shielding plate 523 had been placed through the supporting
plate 525, and fixedly secured therein.
[0368] (6) After a temperature measuring element 516 made of a
platinum temperature measuring resistor for use in controlling
temperatures had been inserted into the bottomed hole 514, the
bottomed hole 514 was sealed by using an inorganic bonding agent
(Aron ceramic, made by Toagosei Co., Ltd.) serving as a sealing
material. Moreover, supporting pins 518 were placed in the concave
portions formed on the heating face of the upper metal plate
511.
[0369] (7) Next, the conductive wire 524 was wrapped by a
connecting stainless foil 530 taken out of the stainless foil 529
serving as the heating element attached to the heater 512, and this
was then caulked with an attaching member 531 attached thereto so
that the conductive wire 524 was attached to the connecting
stainless foil 530, and connected to an external power supply or
the like; thus, a metal heater 510 was obtained.
EXAMPLE 9
Manufacturing of Metal Heater
[0370] The same processes as those of Example 8 were carried out
except that the thickness of the upper metal plate 511 was set to
20 mm and that the thickness of the lower metal plate 521 was set
to 5 mm so that a metal heater was manufactured.
EXAMPLE 10
Manufacturing of Metal Heater
[0371] The same processes as those of Example 8 were carried out
except that the thickness of the upper metal plate 511 was set to
25 mm and that the thickness of the lower metal plate 521 was set
to 10 mm so that a metal heater was manufactured.
EXAMPLE 11
Manufacturing of Metal Heater
[0372] The same processes as those of Example 8 were carried out
except that the thickness of the upper metal plate 511 was set to
40 mm and that the thickness of the lower metal plate 521 was set
to 5 mm so that a metal heater was manufactured.
TEST EXAMPLE 3
[0373] The same processes as those of Example 8 were carried out
except that the lower metal plate was made of copper so that a
metal heater was manufactured. In this test example, the thickness
of the upper metal plate was made larger than the thickness of the
lower metal plate.
[0374] A current was applied to each of the metal heaters according
to Examples 8 to 11 and Test Example 3 to raise the temperature;
thus, evaluation was made on each of the following points: (1)
temperature evenness in surface in steady state, (2) temperature
evenness in surface in transition period, (3) measurements on
flatness; (4) overshoot amount. The results thereof are shown in
Table 2. Here, the same evaluation method as the method of Example
1 was used.
[0375] Moreover, in the evaluation of the measurements on the
flatness (5), a three dimensional shape of a part of a metal heater
heating face of Example 8 at ordinary temperature is shown in FIG.
11, a three dimensional shape of a part of a metal heater heating
face of Example 8 at 140.degree. C. is shown in FIG. 12, and a
three dimensional shape of a part of a metal heater heating face of
Test Example 3 at 140.degree. C. is shown in FIG. 13.
TABLE-US-00002 TABLE 2 Thickness of Distribution of Distribution of
metal plate temperature in temperature in Overshoot amount (mm)
surface in surface in Flatness (.mu.m) (.degree. C.) Upper Lower
steady state transition period At after processing metal metal
(.degree. C.) (.degree. C.) ordinary 20 wafers at plate plate
140.degree. C. 100.degree. C. 120.degree. C. 130.degree. C.
temperature 140.degree. C. 140.degree. C.) Example 8 15 5 0.17 5.37
2.38 1.62 29 30 0.31 Example 9 20 5 0.24 5.38 2.80 1.51 29 30 0.34
Example 10 25 10 0.19 5.45 2.22 1.76 29 29 0.32 Example 11 40 5
0.25 4.80 2.24 1.64 28 29 0.35 Test 20 5 0.52 4.48 3.33 1.86 28 40
0.30 Example 3 Comparative 55 0 0.42 5.58 3.66 2.36 44 56 0.32
Example 1
[0376] As shown in Table 2, the metal heaters according to Examples
8 to 11 had an even temperature on the heating face of the upper
metal plate in steady state as well as in transition period. This
is presumably because, since the material of the metal plate on the
heating face side as well as on the opposite side was the same, the
thermal expansion coefficient was equal so that no warping occurs
even upon a temperature rise; thus, no dispersion occurs in the
distance between the wafer and the heating face, making it possible
to carry out an even heating process.
[0377] In contrast, in the case of the metal heater according to
Test Example 3, since the materials of the upper metal plate and
the lower metal plate are different from each other, the thermal
expansion coefficients are different from each other, with the
result that a deformation occurs upon heating to cause dispersion
in the temperature of the heating face.
[0378] Moreover, the metal heaters according to Examples 8 to 11
have superior temperature evenness on the heating face in steady
state as well as in transition period, in comparison with the metal
heater according to the above-mentioned Comparative Example 1.
[0379] With respect to the overshoot amount, all the metal heaters
according to Examples 8 to 11, Test Example 3 and Comparative
Example 1 had almost the same measured results.
EXAMPLE 12
Manufacturing of Metal Heater (see FIGS. 6(a) and 6(b), and FIG.
7)
[0380] (1) A plate-shaped member, made of an aluminum-copper alloy
(A2219 (JIS-H4000)), was machined at outer diameter portion by
using an NC lathe (made by Washino Machinery Co., Ltd.) and formed
into a disk shape, and this disk-shaped member was then subjected
to an end-face machining process, a surface machining process and a
rear-face machining process so that a disk-shaped member for an
upper metal plate and a disk-shaped member for a lower metal plate
were manufactured.
[0381] Next, each of parts to be through holes 615 to which lifter
pins used for supporting a semiconductor wafer 619 are inserted,
each of parts to be concave portions 628 in which supporting pins
618 are placed and a part to be a bottomed hole 614 in which a
temperature measuring element 616 is embedded were formed in this
disk-shaped member by using a machining center (Hitachi Seiki Co.,
Ltd.).
[0382] Here, the through holes 615 were formed at three positions,
and the concave portions used for placing the supporting pins 618
were formed at nine positions. With respect to the layout of the
positions, as shown in FIG. 6(a), eight supporting pins were placed
on circumferences of concentric circles of the upper metal plate
with equal intervals, and a single supporting pin was placed in the
center portion of the upper metal plate.
[0383] After the bottomed holes or the through holes had been
formed at predetermined positions in the same manner, thread
grooves were formed in the bottomed holes or the through holes so
that screw holes through which metal plate securing screws 617 are
inserted were formed in the disk member.
[0384] Here, the screw holes were formed in the upper metal plate
and the plate-shaped member with a depth of 3/4 of the thickness
thereof.
[0385] (2) Next, the disk member for the upper metal plate,
manufactured through the processes of (1), was subjected to a
surface grinding process on its surface on the heating face side by
using a rotary grinding machine (manufactured by Okamoto Machine
Tool Works, Ltd.) so that an upper metal plate 611 having a
thickness of 15 mm and a diameter of 330 mm and a lower metal plate
621 having a thickness of 5 mm and a diameter of 330 mm were
obtained.
[0386] Moreover, a barrier ring for a wafer that is an object to be
heated was formed on the side face of the upper metal plate 611 by
using the following method. In other words, the outer rim portion
of the supporting case was made higher than the upper face of the
heating face of the upper metal plate so that the barrier ring 632
was formed.
[0387] Here, in this example, the thickness of the upper metal
plate 611 was made larger than the thickness of the lower metal
plate 621.
[0388] (3) Next, the upper metal plate 611 and the lower metal
plate 621 were subjected to an alumite treatment under conditions
of 10% H.sub.2SO.sub.4 electrolytic solution, a voltage of 10 V, a
current density of 0.8 A/dm.sup.2 and a liquid temperature of
20.degree. C. so that an oxide coat film having a thickness of 15
.mu.m was formed on each of the surfaces of the upper metal plate
611 and the lower metal plate 621.
[0389] (4) A heating element, made of a stainless foil having a
thickness of 200 .mu.m on which, as shown in FIG. 7, a winding wire
is repeatedly placed in a repeated pattern to form a ring shape and
a winding wire is repeatedly placed in a pattern so as to form a
part of each of concentric circles, was sandwiched between two mica
plates having a thickness of 0.3 mm to obtain a heater 612 having a
diameter of 330 mm.
[0390] Here, in the heater 612, the heating element was formed so
that the area including the heating element had a diameter of 320
mm, and the total number of the circuits of the heating element was
set to four.
[0391] Moreover, parts to be through holes 615, a part to be the
bottomed hole 614 and parts to be screw holes through which metal
plate securing screws 617 are inserted were preliminary formed in
the mica plate 626.
[0392] Thereafter, the heater 612 was sandwiched between the upper
metal plate 611 and the lower metal plate 621 manufactured through
the processes of (1) to (3), and after the metal plate securing
screws 617 had been inserted through the screw holes provided in
the lower metal plate 621 and the heater 612, the securing screws
were tightened so that the upper metal plate 611, the lower metal
plate 621 and the heater 612 were combined into an integral
part.
[0393] (5) Next, a supporting case 620 having a cylinder shape with
a bottom as shown in FIG. 6(a), made of SUS, was manufactured, and
a supporting plate 625 was placed on the bottom face of this
supporting case 620; then, after parts to be the through holes 615,
apart to be the bottomed hole 614 and a through hole through which
the conductive wire 624 is inserted had been formed in the bottom
face of the supporting case 620, a heat shielding plate 623 having
a cylinder shape, made of SUS, was placed on the bottom portion of
the supporting case 620.
[0394] Moreover, the upper metal plate 611 to which the heater 612
and the lower metal plate 621 had been attached, manufactured in
(4), was placed inside the supporting case 620 in which the heat
shielding plate 623 had been placed, and fixedly secured therein
through the supporting plate 625.
[0395] (6) After a Pt temperature measuring element 616 made of a
Pt temperature measuring resistor for use in controlling
temperatures had been inserted into the bottomed hole 614, the
bottomed hole 614 was sealed by using an inorganic bonding agent
(Aron ceramic, made by Toagosei Co., Ltd.). Moreover, supporting
pins 618 having a shape as shown in FIG. 6(a), made of alumina,
were inserted into nine concave portions 628 formed on the heating
face of the upper metal plate 611, and a spring 627 having a
C-shape was fitted to each concave portion 628 in a manner so as to
surround each supporting pin 618 so that the supporting pins were
fixedly secured onto the heating face 611a of the upper metal plate
611.
[0396] (7) Next, the conductive wire 624 was wrapped by a
connecting stainless foil 630 taken out of a stainless foil 629
serving as the heating element provided in the heater 612, and an
attaching member 631 was attached thereto, and this was then
caulked so that the conductive wire 624 was attached to the
connecting stainless foil 630, and connected to an external power
supply or the like; thus, a metal heater 610 was obtained.
EXAMPLE 13
Manufacturing of Metal Heater
[0397] The same processes as those of Example 12 were carried out
except that the thickness of the upper metal plate 611 was set to
20 mm and that the thickness of the lower metal plate 621 was set
to 5 mm, with the number of pins set to six in total, one in the
center and five on the same circumference on the periphery thereof,
so that a metal heater was manufactured.
EXAMPLE 14
Manufacturing of Metal Heater
[0398] The same processes as those of Example 12 were carried out
except that the thickness of the upper metal plate 611 was set to
25 mm and that the thickness of the lower metal plate 621 was set
to 10 mm, with the number of pins set to nineteen in total, one in
the center, six on the same circumference on the periphery thereof,
and twelve on the same circumference located outside thereof, so
that a metal heater was manufactured.
EXAMPLE 15
Manufacturing of Metal Heater
[0399] The same processes as those of Example 12 were carried out
except that the thickness of the upper metal plate 611 was set to
40 mm and that the thickness of the lower metal plate 621 was set
to 5 mm so that a metal heater was manufactured.
EXAMPLE 16
[0400] The same processes as those of Example 12 were carried out
except that in the process (2) of Example 12, five concave portions
for placing supporting pins were formed on the surface on the
heating face side of the circular plate member for the upper metal
plate and that in the process (6) thereof, supporting pins were
placed in the five concave portions formed on the heating face of
the upper metal plate so that a metal heater was manufactured. In
Example 16, total five supporting pins were placed on the heating
face of the upper metal plate with a layout in which four
supporting pins were placed on circumferences of concentric circles
of the upper metal plate with equal intervals, with a single
supporting pin placed in the center of the upper metal plate.
EXAMPLE 17
[0401] In this example, the same processes as those of Example 12
were carried out except that the heater had a diameter of 220 mm,
and that the number of pins was set to five in total, that is, one
in the center and four on the same circumference on the periphery
thereof; thus, a metal heater was manufactured.
EXAMPLE 18
[0402] In this example, the same processes as those of Example 12
were carried out except that the heater had a diameter of 220 mm,
and that the number of pins was set to fifteen in total, that is,
one in the center, four on the same circumference on the periphery
thereof and ten on the same circumference outside thereof; thus, a
metal heater was manufactured.
TEST EXAMPLE 4
[0403] In this test example, the same processes as those of Example
12 were carried out except that the number of pins was set to four
in total, that is, one in the center and three on the same
circumference on the periphery thereof so that a metal heater was
manufactured.
TEST EXAMPLE 5
[0404] In this test example, the same processes as those of Example
17 were carried out except that three supporting pins were placed
on circumferences of concentric circles of the upper metal plate
with equal intervals so that a metal heater was manufactured.
COMPARATIVE EXAMPLE 2
[0405] A metal heater in which an intermediate plate made of copper
and a heater were placed on the bottom face of a metal plate was
manufactured. The thickness of the metal plate was 55 mm, and the
pattern of the heating element was the same as that of Example 12,
without any supporting pins.
[0406] A current was applied to each of the metal heaters according
to Examples 12 to 18, Test Examples 4 and5and Comparative Example 2
to raise the temperature; thus, evaluation was made on each of the
following points: (1) temperature evenness in surface in steady
state, (2) temperature evenness in surface in transition period,
(3) measurements on flatness; (4) overshoot amount. The results
thereof are shown in Table 3. Here, the same evaluation method as
that of Example 1 was used.
[0407] Here, with respect to the evaluation of (2) temperature
evenness in surface in transition period, the relationship between
the temperature and time at each of measuring points of the wafer
with a temperature sensor, obtained when measurements are carried
out by using the metal heater according to Example 12, is shown in
each of FIGS. 14 to 16, and the relationship between the
temperature and time at each of measuring points of the wafer with
a temperature sensor, obtained when measurements are carried out by
using the metal heater according to Example 16, is shown in each of
FIGS. 17 to 19.
[0408] FIGS. 14 and 17 show the relationship between the
temperature and time in the vicinity of 100.degree. C.; FIGS. 15
and 18 show the relationship between the temperature and time in
the vicinity of 120 to 130.degree. C.; and FIGS. 16 and 19 show the
relationship between the temperature and time in the vicinity of
140.degree. C.
[0409] Moreover, with respect to (3) measurements on flatness, a
three-dimensional shape of a part of the heating face of the metal
heater according to Example 12 at ordinary temperature is shown in
FIG. 20; a three-dimensional shape of a part of the heating face of
the metal heater according to Example 12 at 140.degree. C. is shown
in FIG. 21; and a three-dimensional shape of a part of the heating
face of the metal heater according to Comparative Example 2 at
140.degree. C. is shown in FIG. 22. TABLE-US-00003 TABLE 3
Thickness of Distribution of Distribution of metal plate
temperature in temperature in Overshoot amount (mm) surface in
surface in Flatness (.mu.m) (.degree. C.) Upper Lower steady state
transition period At after processing metal metal (.degree. C.)
(.degree. C.) ordinary 20 wafers at plate plate 140.degree. C.
100.degree. C. 120.degree. C. 130.degree. C. temperature
140.degree. C. 140.degree. C. Example 12 15 5 0.17 5.37 2.38 2.01
29 30 0.30 Example 13 20 5 0.24 5.38 2.80 1.51 29 30 0.33 Example
14 25 10 0.19 5.45 2.22 1.76 29 29 0.32 Example 15 40 5 0.25 4.80
2.24 1.64 28 29 0.35 Example 16 15 5 0.38 17.30 12.19 7.53 29 30
0.31 Example 17 15 15 0.18 5.31 2.30 2.00 29 30 0.34 Example 18 15
15 0.19 5.20 2.75 1.86 29 30 0.33 Test 15 5 0.25 11.90 8.20 5.20 30
33 0.30 Example 4 Test 15 15 0.29 12.67 10.00 5.75 29 30 0.35
Example 5 Comparative 55 0 1.31 20.00 15.30 9.38 44 56 0.34 Example
2
[0410] As shown in Table 3 as well as in FIGS. 14 to 16, the metal
heaters according to Examples 12 to 15 had an even temperature on
the heating face of the upper metal plate in steady state as well
as in transition period. This is presumably because, since the
thickness of the metal plate on the heating face side is higher
than a certain value, heat, transmitted through the metal plate, is
sufficiently dispersed so that the pattern of the heating element
is not reflected to the heating face.
[0411] Moreover, the fact that the temperature is maintained in an
even level, in particular, in transition period is because, since
the interval between the supporting pins is narrow, no sagging
occurs in the sensor wafer so that no dispersion occurs in the
distance between the heating face of the upper metal plate and the
sensor wafer.
[0412] Since the metal heaters according to examples 12 to 15 are
allowed to have a flatness of 50 .mu.m or less, as shown in Table 3
as well as in FIGS. 20 and 21, no dispersion occurs in the distance
between the upper metal plate and the sensor wafer, making it
possible to carry out an even heating process.
[0413] Furthermore, in the metal heaters according to examples 12
to 15, since the lower metal plate having a certain thickness is
placed on the bottom face of the heater, thermal radiation released
from the heater is made even.
[0414] In contrast, in the case of the metal heater according to
Example 16, in transition period, the temperature on the heating
face of the upper metal plate became uneven as shown in Table 3 and
FIGS. 17 to 19. The reason that dispersion occur in the temperature
of the heating face is because, since the interval between the
supporting pins is wider, slight sagging occurs in the sensor
wafer, with the result that slight dispersion occur in the distance
between the heating face of the upper metal plate and the sensor
wafer. In this case, however, the temperature on the heating face
of the upper metal plate is maintained in an almost even level in
steady state, causing no serious problems in practical use.
[0415] Moreover, in the metal heaters according to Examples 17 and
18, as shown in Table 3, the temperature on the heating face of the
upper metal plate is maintained in an even level in steady state as
well as in transition period. This is presumably because, since a
sufficient number of supporting pins are arranged on the heating
face, the clearance between the heating face and the semiconductor
wafer is precisely maintained without any sagging in the
semiconductor wafer; thus, it becomes possible to easily ensure the
evenness in the temperature of the heating face, in particular, the
evenness in the temperature of the heating face in transition
period.
[0416] As shown in Table 3, in the case of the metal heater
according to Test Example 4, the temperature on the heating face of
the upper metal plate becomes uneven in transition period, in
comparison with the metal heater according to Example 12. Moreover,
in the case of the metal heater according to Test Example 5, as
shown in Table 3, the temperature on the heating face of the upper
metal plate becomes uneven in transition period, in comparison with
the metal heater according to Example 17. The reason that
dispersion occur in the temperature on the heating face in
transition period is because, since the interval between the
supporting pins is wide, slight sagging occurs in the sensor wafer
to cause slight dispersion in the distance between the heating face
of the upper metal plate and the sensor wafer.
[0417] As shown in Table 3, in the case of the metal heater
according to Comparative Example 2, the temperature on the heating
face of the upper metal plate is uneven in steady state as well as
in transition period. The reason that dispersion occur in the
temperature on the heating face is presumably because big
undulation occurs to cause dispersion in the distance between the
metal plate and the sensor wafer.
[0418] With respect to the overshoot amount, all the measured
results of the metal heaters according to Examples 8 to 11, Test
Example 3 and Comparative Example 1 are almost the same.
INDUSTRIAL APPLICABILITY
[0419] As described above, the metal heater according to the first
aspect of the present invention makes it possible to more quickly
heat an object to be heated, such as a semiconductor wafer or the
like, in comparison with a metal heater that is formed by a single
metal plate with a heater placed on the side opposite to the
heating face side of the metal plate.
[0420] Moreover, since the metal heater according to the first
aspect of the present invention is designed so that the thickness
of the metal plate on the heating face side is the same as, or
larger than the thickness of a metal plate on the side opposite to
the heating face side, the flatness of the heating face is improved
at the time of heating, and the temperature evenness is also
improved so that it becomes possible to evenly heat the entire
semiconductor wafer.
[0421] As described above, the metal heater according to the second
aspect of the present invention makes it possible to more quickly
heat an object to be heated, such as a semiconductor wafer or the
like, in comparison with a metal heater that is formed by a single
metal plate with a heater placed on the side opposite to the
heating face side of the metal plate.
[0422] Moreover, since the metal heater according to the second
aspect of the present invention is designed so that a plurality of
metal plates constituting the metal heater are made from the same
material, the flatness of the heating face is improved at the time
of heating, and the distance between the semiconductor wafer and
the object to be heated can be made constant so that it becomes
possible to heat the semiconductor wafer or the like evenly.
[0423] As described above, the metal heater according to the third
aspect of the present invention makes it possible to more quickly
heat an object to be heated, such as a semiconductor wafer or the
like, in comparison with a metal heater that is formed by a single
metal plate with a heater placed on the side opposite to the
heating face side of the metal plate.
[0424] Moreover, since the metal heater according to the third
aspect of the present invention is designed so that a convex
portion for supporting an object to be heated is placed on the
heating face opposing the object to be heated of the metal plate
corresponding to an area on which a heating element is formed, it
is possible to make a semiconductor wafer or the like, that is, the
object to be heated, less likely to generate sagging; thus, the
distance between the semiconductor wafer or the like and the
heating face of the metal plate can be made constant so that it
becomes possible to heat the semiconductor wafer or the like
evenly.
* * * * *