U.S. patent application number 11/013691 was filed with the patent office on 2005-05-05 for ceramic heater for semiconductor manufacturing and inspecting equipment.
This patent application is currently assigned to IBIDEN CO., LTD.. Invention is credited to Ito, Atsushi, Ito, Yasutaka.
Application Number | 20050092733 11/013691 |
Document ID | / |
Family ID | 26598832 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050092733 |
Kind Code |
A1 |
Ito, Yasutaka ; et
al. |
May 5, 2005 |
Ceramic heater for semiconductor manufacturing and inspecting
equipment
Abstract
A ceramic heater for a semiconductor producing/examining device
including a ceramic substrate having a heating surface for
receiving a semiconductor wafer, a heating device for generating
heat sufficient for producing/examining the semiconductor wafer and
formed on the heating surface or inside the ceramic substrate, and
a temperature measuring device for measuring a temperature of the
heating surface and pressed against the ceramic substrate.
Inventors: |
Ito, Yasutaka; (Gifu,
JP) ; Ito, Atsushi; (Gifu, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
IBIDEN CO., LTD.
Gifu
JP
|
Family ID: |
26598832 |
Appl. No.: |
11/013691 |
Filed: |
December 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11013691 |
Dec 17, 2004 |
|
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10111980 |
Jun 27, 2002 |
|
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10111980 |
Jun 27, 2002 |
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PCT/JP01/07455 |
Aug 30, 2001 |
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Current U.S.
Class: |
219/444.1 |
Current CPC
Class: |
H01L 21/67109 20130101;
H01L 21/67248 20130101 |
Class at
Publication: |
219/444.1 |
International
Class: |
F27B 005/14; H05B
003/68 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 2000 |
JP |
2000-261474 |
Aug 30, 2000 |
JP |
2000-261475 |
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. A ceramic heater for a semiconductor producing/examining device,
comprising: a ceramic substrate having a heating surface configured
to receive a semiconductor wafer; at least one heating device
configured to generate heat sufficient for producing/examining the
semiconductor wafer and formed on the heating surface or inside the
ceramic substrate; and a temperature measuring device configured to
measure a temperature of the heating surface and pressed against
the ceramic substrate.
2. The ceramic heater for a semiconductor producing/examining
device according to claim 1, further comprising a plate having a
thermal conductivity higher than a thermal conductivity of the
ceramic substrate, the plate being interposed between the ceramic
substrate and temperature measuring device.
3. The ceramic heater for a semiconductor producing/examining
device according to claim 1, wherein the temperature measuring
device is pressed by force of 1.times.10.sup.-6 to 20 Kg.
4. The ceramic heater for a semiconductor producing/examining
device according to claim 1, wherein the temperature measuring
device is pressed against a surface of the ceramic substrate on an
opposite side of the heating surface.
5. The ceramic heater for a semiconductor producing/examining
device according to claim 1, wherein the temperature measuring
device comprises a thermocouple and a sheath housing the
thermocouple.
6. The ceramic heater for a semiconductor producing/examining
device according to claim 5, wherein the temperature measuring
device is pressed against a surface of the ceramic substrate on an
opposite side of the heating surface.
7. A ceramic heater for a semiconductor producing/examining device,
comprising: a ceramic substrate having a heating surface configured
to receive a semiconductor wafer; heat generating means for
generating heat sufficient for producing/examining the
semiconductor wafer; and temperature measuring means for measuring
a temperature of the heating surface, wherein the heat generating
means is formed on the heating surface or inside the ceramic
substrate, and the temperature measuring means is pressed against
the ceramic substrate.
Description
TECHNICAL FIELD
[0001] The present invention relates to a ceramic heater for a
semiconductor producing/examining device, which can be for heating
a variety of objects, and more particularly to a ceramic heater for
a semiconductor producing/examining device, which can be preferably
used for drying, sputtering and the like of a silicon wafer and the
like in the semiconductor industry, and which has an excellent
temperature evenness of a heating face thereof.
BACKGROUND ART
[0002] A semiconductor product is produced through several steps
including a step of forming a photosensitive resin as an etching
resist on a silicon wafer to perform etching for the silicon wafer.
This photosensitive resin is liquid-state, so that it is applied
onto a surface of the silicon wafer by using a spin coater and the
like. However, the photosensitive resin must be dried after
applying, and thus the silicon wafer applied with the resin is
placed on a heater and heated for drying. Conventionally, a heater
used for such a purpose is made of a metal, for example, a heater
in which a heating element is arranged on a back face of an
aluminum plate has been employed as the heater made of metal.
[0003] However, such a heater made of metal has the following
problems. First, the thickness of the substrate must be as thick as
about 15 mm since the substrate is made of metal. This is because,
in a thin metal plate, a bend or a strain is generated because of
thermal expansion resulting from heating so that a semiconductor
wafer put on the metal plate is damaged or inclined. However, if
the thickness of the substrate is made thick, the heater becomes
heavy and bulky.
[0004] At the time of heating, the heating temperature is
controlled by changing the voltage or amperage applied to the
heating elements. However, since the metal plate is thick, the
temperature of the substrate does not follow the change in the
voltage or amperage promptly. Thus, the temperature thereof cannot
be easily controlled. Thus, as disclosed in JP Kokoku Hei No.
8-8247, there are suggested techniques of performing the
temperature-control of a nitride ceramic with which a resistance
heating element is formed, by measuring the temperature in the
vicinity of the resistance heating element.
[0005] Inventors of the present invention also tried to heat a
silicon wafer employing the technique, however at that time, a
problem of occurrence of temperature distribution on the surface of
the heater took place. Therefore, inventors of the present
invention have made enthusiastic investigations of causes of the
temperature distribution and consequently, found that a reason for
the occurrence of the temperature distribution in spite of
temperature control is the fact that: a surface roughness of the
ceramic substrate contacting a thermocouple is high and thus the
contact of the thermocouple and a temperature measurement element
becomes a point contact, so that the heat of the ceramic substrate
cannot sufficiently be transmitted to the thermocouple to result in
erroneous measurement result by the thermocouple.
[0006] Further, also a problem such that the thermocouple attached
to the ceramic substrate became easy to be dropped during a long
time use took place. The thermocouple is normally fixed on the
surface of the ceramic substrate using a solder or an inorganic
adhesive material or fixed in the inside of a bottomed hole formed
on the bottom face of the ceramic substrate, and if the
thermocouple is dropped, a heater becomes uncontrollable, resulting
in occurrence of fires and serious incidents.
SUMMARY OF THE INVENTION
[0007] Thus, inventors of the present invention have carried out
further investigations to solve such problems and, with respect to
a solution for the problem of the occurrence of the temperature
distribution of the heater surface, found out that the
above-mentioned problem can be solved by making the surface of the
ceramic substrate smooth to have the surface roughness Ra of 5
.mu.m or less, particularly preferably 2 .mu.m or less, by
polishing the face of the ceramic substrate contacting the
thermocouple or further forming an insulating layer on the surface
of the above-mentioned ceramic substrate.
[0008] Further, with respect to the problem that the temperature
measurement element of the thermocouple drops during a long time
use, the cause is found out that it is owing to the deterioration
of a fixing member such as the solder, the inorganic adhesive, and
the like by heating. Therefore, at the time of installation of the
temperature measurement element in the ceramic substrate, if the
temperature measurement element is pushed against and fixed on the
ceramic substrate by physical force not by a conventional adhesion
or fixation, the problem owing to the thermal deterioration is
supposed to be solved and thus the present invention is
completed.
[0009] The present invention is completed based on the
above-mentioned findings, and an object thereof is to provide: a
ceramic heater for a semiconductor producing/examining device,
excellent in the response to a thermocouple and scarcely causing
the temperature distribution; and a ceramic heater for a
semiconductor producing/examining device, excellent in durability
and capable of heating an object to be heated such as a
semiconductor wafer with even temperature.
[0010] That is, a ceramic heater for a semiconductor
producing/examining device of a first aspect of the present
invention is a ceramic heater comprising: a ceramic substrate; and
a heating element formed on the surface of the ceramic substrate or
inside of the ceramic substrate, wherein a temperature measurement
element is formed while being brought into contact with the
above-mentioned ceramic substrate and the surface roughness Ra of
the ceramic substrate brought into contact with the above-mentioned
temperature measurement element is Ra.ltoreq.5 .mu.m, desirably
Ra.ltoreq.2 .mu.m.
[0011] In the first aspect of the ceramic heater for the
semiconductor producing/examining device of the present invention,
if the temperature measurement element such as a thermocouple is
brought into contact with the ceramic substrate having a surface
roughness Ra.ltoreq.2 .mu.m, the above-mentioned temperature
measurement element and the above-mentioned ceramic substrate are
brought into almost face contact with each other, so that heat is
sufficiently transmitted to the temperature measurement element
from the ceramic substrate to make the accurate temperature
measurement of the ceramic substrate possible. Incidentally, in the
first aspect of the present invention, inthe case an insulating
layer is formed on the surface of the ceramic substrate, the
surface roughness of the ceramic substrate means the surface
roughness of the insulating layer surface.
[0012] If Ra>2 .mu.m, the contact with the temperature
measurement element becomes a point contact, so that the heat is
not sometimes transmitted sufficiently to make the accurate
temperature measurement impossible.
[0013] However, in the case Ra is from 2 to 5 .mu.m, the contact
surface area can be assured to some extent by transversely laying
the temperature measurement element to increase the contact area,
so that the temperature measurement error can be corrected.
However, if Ra exceeds 5 .mu.m, it is found out difficult to
accurately control the temperature by any means.
[0014] To keep the surface roughness Ra.ltoreq.5 .mu.m, preferably
Ra.ltoreq.2 .mu.m, a method for polishing the surface of the
ceramic substrate or forming an insulating layer with a higher
volume resistivity than that of the ceramic substrate on the
surface of the ceramic substrate are desirable.
[0015] The surface roughness Ra of the ceramic substrate is
preferably to be higher than 0.001 .mu.m. If the substrate is too
smooth, the temperature measurement element slips and becomes
difficult to be brought into contact with the surface of the
ceramic substrate.
[0016] The surface roughness Ra is, particularly, optimum in a
range from 0.05 to 1 .mu.m.
[0017] The method for adjusting the surface roughness of the
ceramic substrate surface is carried out by, for example,
simultaneously polishing both faces using a diamond grind stone
with a roughness of #100 to #1,000 while applying a load of 0.1 to
50 kg/cm.sup.2 from both faces. The rotation speed of the grind
stone is preferably 50 to 300 rpm. Further, for the surface
finishing, polishing is preferably carried out using a diamond
paste (particle size of 0.1 to 5 .mu.m) and a cloth in
combination.
[0018] A concaved portion may be formed in the ceramic substrate
and the temperature measurement element may be put in the concaved
portion. In the case the inside of the concaved portion is ground
and polished, a rod-like grind stone and a polishing material may
be used.
[0019] Further, in the above-mentioned ceramic heater for a
semiconductor producing/examining device of the first aspect of the
present invention, the above-mentioned ceramic substrate and the
above-mentioned temperature measurement element are desirably
brought into contact with each other through a heat transmission
plate having a higher thermal conductivity than that of the
above-mentioned ceramic substrate. Because the contact surface area
with the temperature measurement element can be widened by the
existence of the heat transmission plate and the temperature of the
ceramic substrate can be measured more accurately.
[0020] Further, the above-mentioned temperature measurement element
is desirable to be fixed while being brought into contact with the
ceramic substrate and further desirable to be pressed on the
above-mentioned ceramic substrate. Because it can reliably brought
into contact with the surface of the ceramic substrate and the heat
transmission from the ceramic substrate can be better performed. As
the method for pressing the temperature measurement element on the
ceramic substrate, a method using a spring and the like is
preferable.
[0021] Next, a second aspect of the present invention will be
described.
[0022] A ceramic heater for a semiconductor producing/examining
device of a second aspect of the present invention is a ceramic
heater comprising: a ceramic substrate; and a resistance heating
element formed on the surface of the ceramic substrate or inside of
the ceramic substrate, wherein the resistance heating element is
pressed on the above-mentioned ceramic substrate.
[0023] The ceramic heater for the semiconductor producing/examining
device according to the second aspect of the present invention, the
temperature measurement element is pressed on the ceramic substrate
using a mechanical means but not brought into contact with the
ceramic substrate without using a solder, an inorganic adhesive
material and the like, and therefore any problem attributed to
thermal deterioration of a solder or an inorganic adhesive material
used for the contact and consequent dropping of the temperature
measurement element does not take place.
[0024] Further, even if the ceramic substrate is expanded by
heating or contracted by cooling, since the temperature measurement
element is pushed only by physical force, the size change can be
absorbed to suppress generation of the thermal stress and the like,
thus preventing dropping of the temperature measurement element.
Consequently, any problem that the heater becomes uncontrollable
and fires take place is not caused and thus the ceramic heater for
the semiconductor producing/examining device is provided with a
high safe property.
[0025] The above-mentioned ceramic substrate and the temperature
measurement element are preferably brought into contact with each
other through a heat transmission plate having a higher thermal
conductivity than that of the above-mentioned ceramic substrate.
That is in order to increase the response and the measurement
accuracy. Especially, a dent is formed in the heat transmission
plate and the thermocouple is fitted in the dent to be fixed, so
that the response and the measurement accuracy can be improved and
the thermocouple can firmly be fixed as well.
[0026] The above-mentioned temperature measurement element can
generally be pushed against the ceramic substrate, using elastic
force of an elastic body. Practically, an elastic body such as a
coil spring, a leaf spring and the like are used. Examples of the
ceramic heater for the semiconductor producing/examining device
using a coil spring is illustrated in FIGS. 4 to 9 and examples of
the ceramic heater for the semiconductor producing/examining device
using a leaf spring is illustrated in FIGS. 10 to 12.
[0027] As described above, the temperature measurement element is
installed in the ceramic substrate while being brought into contact
with the ceramic substrate and the surface roughness Ra of the
ceramic substrate being brought into contact with the temperature
measurement element is preferably Ra.ltoreq.5 .mu.m, more desirably
Ra.ltoreq.2 .mu.m.
[0028] If the temperature measurement element such as a
thermocouple is brought into contact with the ceramic substrate
having a surface roughness Ra.ltoreq.2 .mu.m, the above-mentioned
temperature measurement element and the above-mentioned ceramic
substrate are brought into almost face contact with each other, so
that heat is sufficiently transmitted to the temperature
measurement element from the ceramic substrate to make the accurate
temperature measurement of the ceramic substrate possible. If
Ra>2 .mu.m, the contact with the temperature measurement element
becomes a point contact, so that the heat sometimes does not
sufficiently transmit to make the accurate temperature measurement
impossible. However, in the case Ra is from 2 to 5 .mu.m, the
contact surface area can be assured to some extent by transversely
laying the temperature measurement element to increase the contact
area, so that the temperature measurement error can be
corrected.
[0029] To keep the surface roughness Ra at 2 .mu.m or less, it is
preferable to keep the surface roughness Ra at 2 .mu.m or less by
polishing the surface of the ceramic substrate or forming an
insulating layer on the surface of the ceramic substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a bottom plane view schematically showing one
example of a ceramic heater of the present invention.
[0031] FIG. 2(a) is a block diagram schematically showing a ceramic
heater of a first aspect of the present invention in which a
heating element is formed on a bottom face of a ceramic substrate,
and FIG. 2(b) is a partially enlarged sectional view showing a part
at which a thermocouple of the above-mentioned ceramic heater is
installed.
[0032] FIG. 3 is a block diagram schematically showing a ceramic
heater of a first aspect of the present invention in which a
heating element is provided inside of the ceramic substrate.
[0033] FIG. 4 is a sectional view schematically showing one example
of a contact structure of a temperature measurement element of the
ceramic heater of the present invention.
[0034] FIG. 5 is a sectional view showing a structure of a
sheath-type thermocouple.
[0035] FIG. 6 is a sectional view schematically showing a structure
of a hot plate unit of the present invention.
[0036] FIG. 7 is a sectional view schematically showing an example
of a contact structure of a temperature measurement element in the
ceramic heater of the present invention.
[0037] FIG. 8(a) is a block diagram schematically showing a ceramic
heater of a second aspect of the present invention in which a
heating element is formed on a bottom face of a ceramic substrate,
and FIG. 8(b) is a partially enlarged sectional view showing a part
at which a thermocouple of the above-mentioned ceramic heater is
installed.
[0038] FIG. 9 is a block diagram schematically showing a ceramic
heater of a second aspect of the present invention in which a
heating element is provided inside of a ceramic substrate.
[0039] FIG. 10 is a sectional view schematically showing one
example of a contact structure of a temperature measurement element
in a ceramic heater of the present invention.
[0040] FIG. 11 is a sectional view schematically showing one
example of a contact structure of a temperature measurement element
in a ceramic heater of the present invention.
[0041] FIG. 12 is a sectional view schematically showing one
example of a contact structure of a temperature measurement element
in a ceramic heater of the present invention.
[0042] FIG. 13 is a sectional view schematically showing one
example of a contact structure of a temperature measurement element
in a ceramic heater of a comparative example.
EXPLANATION OF SYMBOLS
[0043] 10, 20 ceramic heater
[0044] 11, 21 ceramic substrate
[0045] 11a, 21a heating face
[0046] 11b, 21b bottom face
[0047] 12, 22 heating element
[0048] 13 terminal pin
[0049] 14 temperature measurement part
[0050] 15, 25 through hole
[0051] 16 lifter pin
[0052] 19 silicon wafer
[0053] 24 metal covering layer
[0054] 27, 44, 64, 74 temperature measurement element
(thermocouple)
[0055] 28 conductor-filled through hole
[0056] 23, 29 control unit
[0057] 21, 30 memory unit
[0058] 22, 31 computation unit
[0059] 32 socket
[0060] 45 spring
[0061] 60, 75 leaf spring
[0062] 65, 75 bolt
[0063] 66 presser plate
[0064] S sheath
DETAILED DESCRIPTION OF THE INVENTION
[0065] A ceramic heater for a semiconductor producing/examining
device of a first aspect of the present invention is a ceramic
heater comprising a ceramic substrate and a heating element formed
on the surface of the ceramic substrate or inside of the ceramic
substrate, wherein a temperature measurement element is formed
while being brought into contact with the ceramic substrate and the
surface roughness Ra of the ceramic substrate is Ra.ltoreq.5 .mu.m,
desirably Ra.ltoreq.2 .mu.m.
[0066] Hereinafter, the ceramic heater for the semiconductor
producing/examining device of the first aspect of the present
invention will be described along with its embodiment.
[0067] In the following description, the ceramic heater for the
semiconductor producing/examining device is sometimes referred
simply as to a ceramic heater.
[0068] As the insulating layer to be employed for the first aspect
of the present invention, an oxide ceramic is preferable and
practically, for example, silica, alumina, mullite, cordierite,
beryllia and the like can be used.
[0069] The oxide ceramic has a volume resistivity higher than a
nitride ceramic or a carbide ceramic and therefore is particularly
advantageous for the insulating layer.
[0070] Such an insulating layer may be formed: by applying a sol
solution produced by hydrolysis polymerization of an alkoxide to a
ceramic substrate by spin coating and drying and firing the sol; or
by sputtering, CVD, and the like. Also, the surface of the ceramic
substrate may be subjected to oxidation treatment to form an oxide
layer and the oxide layer may be used as the insulating layer. In
addition, as an insulating layer 500, an alumina plate, a quarts
plate, and the like may be used.
[0071] In the first aspect of the present invention, in order to
adjust the surface roughness Ra of the ceramic substrate being
brought into contact with a temperature measurement element to be
Ra.ltoreq.5 .mu.m, desirably Ra.ltoreq.2 .mu.m, the surface of the
ceramic substrate is ground to be smoothed, or an insulating layer
having the surface roughness Ra.ltoreq.5 .mu.m, preferably
Ra.ltoreq.2 .mu.m is formed.
[0072] The thickness of the above-mentioned insulating layer is
preferably 0.1 to 3000 .mu.m. If it is less than 0.1 .mu.m, the
layer does not function as an insulating layer and if it exceeds
3000 .mu.m, the response of a temperature measurement element is
deteriorated in the case the temperature measurement element is
installed.
[0073] The insulating layer may be formed on the whole surface of
the ceramic substrate. In this case, a heating element can be
formed on the insulating layer. Also, the insulating layer may be
formed only in the portion where the temperature measurement
element is brought into contact. For example, as shown in FIG. 5, a
thermocouple 44 is housed in a sheath S made of a stainless steel
and an insulating powder 46 such as alumina, silica, magnesia and
the like is filled therein and the resulting sheath S as a whole
may be pushed against the surface of the ceramic substrate 11
coated with the insulating layer 50 by a spring 45 as shown in FIG.
4. In this case, a projected part 48 is formed on the side face of
the sheath S and a spring 45 is installed between the projected
part 48 and a plate-like body 41, which is the bottom plate or the
intermediate bottom plate. The spring may be a coil spring as shown
in FIG. 4 or a leaf spring.
[0074] Further, at that time, the sheath S containing a temperature
measurement element such as the thermocouple 44 and the like
therein may be fitted and fixed in an alumina pipe P so as to be
brought into contact with the ceramic substrate 11 and as shown in
FIG. 4, a heat transmission plate 42 made of a metal plate and the
like may be interposed between the sheath S containing the
thermocouple 44 and the insulating layer 500 to increase the
thermal conductivity between them. As the metal plate, aluminum, a
stainless steel, nickel, copper, a noble metal and the like may be
used.
[0075] Further, as shown in FIG. 4, in order to make the contact
surface area of the heat transmission plate 42 and the sheath S
large, a dent (concave portion) having the similar shape to that of
the tip end of the sheath S is preferable to be formed in the heat
transmission plate 42.
[0076] For the sheath S, other than metals, a ceramic such as
alumina may be used. However, to avoid deterioration of the
response of the temperature measurement element by the existence of
the sheath S, the thickness and the material thereof are required
to be controlled and selected.
[0077] The ceramic heater of the first aspect of the present
invention is made possible to accurately measure the temperature of
an object to be heated by employing the above-mentioned means and
by carrying out control based on the temperature measurement
results, the heat generating state of the heating element can
properly be controlled and accordingly, a whole body of a variety
of objects to be heated such as a silicon wafer and the like can
and evenly be heated. That is, in the ceramic heater of the first
aspect of the present invention, the temperature measurement
element and the ceramic substrate are brought into face-contact
with each other and therefore, the accurate temperature measurement
of the ceramic substrate is made possible; and by controlling the
heat generating state of the heating element based on the
temperature measurement result, an object to be heated can evenly
be heated.
[0078] The above-mentioned ceramic substrate and the temperature
measurement element may be brought into contact with each other
through a heat transmission plate made of: the above-mentioned
metal plate; nitride ceramic; or carbide ceramic and the like. Such
a heat transmission plate made of a metal plate and the like has a
high thermal conductivity and thus is capable of improving the
response of the thermocouple. Also, as mentioned above, a dent may
be formed in the heat transmission plate 42 to enlarge the contact
surface area with the thermocouple and accordingly, the response
can further be improved.
[0079] The above-mentioned temperature measurement element is
preferable to be fixed in the above-mentioned ceramic substrate
while being brought into contact with the ceramic substrate.
Practically, as shown in FIG. 2(b), it is preferable to be attached
to and fixed on the substrate by a protection member 600 made of
heat resistant resin or a ceramic.
[0080] Also, as shown in FIG. 4, using an elastic body such as a
spring 45, the temperature measurement element may be brought into
contact with the ceramic substrate by being pushed against the
surface of the ceramic substrate or, as shown in FIG. 7, being
pushed against the bottom face of a concave portion formed in face
of the ceramic substrate at the opposed side to the heating face by
an elastic body.
[0081] FIG. 7 is a sectional view schematically showing a contact
structure of the above-mentioned thermocouple.
[0082] A concave portion 95 is formed on a opposed side face to the
heating face of the ceramic substrate 91, and the thermocouple 94
housed in the sheath 96 is pushed against the bottom face of this
concave portion 95 by the spring 93, which is an elastic body fixed
to the plate-like body 81, through the aluminum plate 92, so that
the ceramic substrate 91 and the thermocouple 94 are brought into
contact with each other.
[0083] The contact structure as shown in FIG. 4 and FIG. 7 can
absorb the size change owing to the thermal expansion and
contraction and therefore is advantageous.
[0084] The temperature measurement element may be brought into
contact with the ceramic substrate surface as it is and also may be
covered with a sheath and brought into contact transversely (FIG.
7).
[0085] Further, as shown in FIG. 7, it may be pushed by a member of
such as a metal and the like having a high thermal
conductivity.
[0086] The ceramic substrate holding a heating element and made of
a nitride ceramic or a carbide ceramic has a thermal expansion
coefficient smaller than that of metal and mechanical strength
remarkably higher than that of metal. Accordingly, even if the
ceramic substrate is made thin in the thickness, it is not warped
or distorted by heating. As a result, the ceramic substrate can be
made thin and light by weight. Further, since the thermal
conductivity of the ceramic substrate is high and the ceramic
substrate itself is thin, the surface temperature of the ceramic
substrate can quickly follow the temperature change of the heating
element. That is, by changing the temperature of the heating
element by changing the voltage and the electric current value, the
surface temperature of the ceramic substrate can properly be
controlled.
[0087] The ceramic heater of the first aspect of the present
invention, as mentioned above, is a ceramic heater in which a
heating element is formed on the surface or inside of a ceramic
substrate. Firstly, the ceramic heater will be schematically
described by using FIGS. 1 and 2.
[0088] FIG. 1 is a bottom plane view schematically showing one
example of a ceramic heater of the first aspect of the present
invention.
[0089] FIG. 2(a) is a block diagram schematically showing a ceramic
heater of a first aspect of the present invention in which a
heating element is formed on a bottom face of a ceramic substrate,
and FIG. 2(b) is a partially enlarged sectional view showing a
vicinity of a part at which a thermocouple of the above-mentioned
ceramic heater is installed. Noted that FIG. 2(a) shows a part of a
cross-section of the ceramic substrate shown in FIG. 1.
[0090] As shown in FIG. 1, the ceramic substrate 11 is formed to be
a disk-like shape and the heating element 12 is formed into a
concentric pattern at the bottom face 11b of the ceramic substrate
11 since heating has to be carried out so as to keep the
temperature even on the whole heating face (the face opposite to
the illustrated bottom face) 11a of the ceramic substrate 11.
[0091] The heating element 12 is composed by connecting a pair of
mutually neighboring two concentric heaters to be one line and
connecting terminal pins 13 to be input and output terminals in
both ends. Further, at the portion near the center, through holes
15 to insert lifter pins 16 into for holding various kinds of
objects to be heated, such as a silicon wafer and the like, are
formed and further thermocouples 27 are fixed in the temperature
measurement parts 14a to 14i using protection members 600.
[0092] The thickness of the ceramic substrate in the ceramic heater
of the first aspect of the present invention is preferably 50 mm or
less, more desirably 25 mm or less.
[0093] If the thickness of the ceramic substrate exceeds 25 mm, the
heat capacity of the ceramic substrate increases and especially, in
case that heating and cooling is carried out by installing a
temperature control means, the temperature following property is
deteriorated owing to the high heat capacity in some cases.
[0094] The optimum thickness of the ceramic substrate is 5 mm or
less. Incidentally, the thickness is preferable to be not thinner
than 1.5 mm.
[0095] If it is thinner than 1.5 mm, the strength is decreased and
the substrate becomes easy to be broken, whereas if it thicker than
5 mm, it becomes difficult to transmit heat to result in decrease
of heating efficiency.
[0096] With respect to the material of the ceramic substrate 11, a
variety of ceramics with high thermal conductivity can be used, yet
a nitride ceramic or a carbide ceramic is desirable.
[0097] Examples of the above-mentioned nitride ceramic include
aluminum nitride, silicon nitride, boron nitride, titanium nitride
and the like. They may be used alone or in combination of two or
more of them. Examples of the carbide ceramic include silicon
carbide, zirconium carbide, titanium carbide, tantalum carbide,
tungsten carbide and the like. They may be used alone or in
combination of two or more of them. Among them, aluminum nitride is
most preferable. The reason for that is because it has the highest
thermal conductivity as high as 180 W/m.cndot.K and is excellent in
the temperature following property and accordingly, although it
tends to cause unevenness of the temperature distribution, such a
problem can be avoided by employing the arrangement and formation
structure of the first aspect of the present invention for the
temperature measurement element 27.
[0098] Also, as shown in FIG. 2, an insulating layer 500 is formed
on the bottomface 11b of the ceramic substrate 11 and a temperature
measurement element such as a thermocouple 27 and the like is
brought into contact with the insulating layer 500 to measure the
temperature of the ceramic substrate 11. In the case of bringing
the temperature measurement element such as the thermocouple 27
into contact with the ceramic substrate, as shown in FIGS. 2, 3 it
may be fixed using a protection member 600 made of a heat resistant
resin or ceramic, and a temperature measurement element such as a
thermocouple 44 installed in a sheath S also may be brought into
contact with the bottom face 11b of the ceramic substrate 11
through sheath S by using a spring 45 as shown in FIG. 4.
[0099] Examples of such a temperature measurement element include a
thermocouple, a platinum temperature measurement resistor, a
thermistor and the like. Further, the above-mentioned thermocouple
includes, for example, as listed up in JIS-C-1602 (1980), K-type,
R-type, S-type, E-type, J-type, T-type thermocouples and the like.
Among them, the K-type thermocouple is preferable. The size of the
joining part of the thermocouple and the ceramic plate is
preferably larger than the diameter of a strand and 0.5 mm or less.
That is because in the case the joining part is large, the heat
capacity is increased and the response is deteriorated.
Incidentally, it is difficult to make the size smaller than the
diameter of the strand.
[0100] Such temperature measurement elements as described above are
to be fixed in the temperature measurement portions 14a to 14i and
sealed with a heat resistant resin or a protection member 600, and
at that time, both ways may be used. As the above-mentioned heat
resistant resin, for example, thermosetting resin, especially,
epoxy resin, polyimide resin, bismaleimide-triazine resin, and the
like can be exemplified. These resin materials may be used alone or
in combination with two or more of them. Further, as the ceramic,
alumina sol and silica sol and the like may be used and these
ceramic sol materials are dried to be gel so as to fix the
temperature measurement element. Other than such a manner of fixing
the thermocouple, as described in the description of FIG. 4, the
method may be a manner of contacting the temperature measurement
element directly.
[0101] The heating element in the above-mentioned ceramic heater,
as shown in FIGS. 1 and 2, may be formed on the bottom face 11b of
the ceramic substrate 11 and, as shown in FIG. 3, also may be
formed inside of the ceramic substrate 21. In the former case, as
shown in FIG. 2, the opposed face is desirable to be the heating
face 11a where an object to be heated such as a silicon wafer and
the like is heated and in the latter case of the heating element
being formed inside, as shown in FIG. 3, the heating element is
preferable to be installed eccentrically from the center in the
thickness direction of the ceramic substrate and the face remote
from the heating element is desirable to be the heating face 21a.
In the first aspect of the present invention, by setting the
setting position of the heating element in such a manner, during
transmission of the heat generated from the heating element, the
heat is diffused to the whole ceramic substrate and the temperature
distribution in the face where an object to be heated (for example
a silicon wafer) to be heated is made even and as a result, the
temperature in each portion of the object to be heated can be made
even.
[0102] Further, referring to the setting position of the ceramic
material, as shown in FIG. 3, in the case the heating element 22
(22x, 22y) of the first aspect of the present invention is
installed inside thereof and eccentrically out of the center, the
position is preferable to be near to the face (bottom face) on the
opposite to the heating face 21a of the ceramic substance 21 and at
a point exceeding 50% and up to 99% to the distance from the
heating face 21a to the bottom face 21b. That is because if it is
less than 50%, the position is too near to the heating face to
cause uneven temperature distribution and on the contrary, if it
exceeds 99%, the ceramic substrate 11 itself warps to result in
distortion of an object to be heated such as a silicon wafer.
[0103] Further, in the case the heating element 22 is formed inside
of the ceramic substrate 21, the layer forming the heating element
may be formed in a plurality of separate layers but not to be a
single layer. In such a case, the patterns of the respective layers
are preferably formed in a manner that heating element 22 is formed
in any layer as to supplement the patterns one another when
observed from the direction at rectangular angles to the heating
face so that the patterns of the heating element 11 seem to exist
in the whole region when observed from the upper side of the
heating face. As such a structure, for example, a staggered
arrangement can be exemplified.
[0104] Regarding the arrangement pattern (shape) of the
above-mentioned heating element, other than the concentric circle
as shown in FIG. 1, for example, a spiral, an eccentric circle, a
curved line and the like can be exemplified, yet the concentric
arrangement is preferable. Further, in the case of the concentric
pattern, as shown in FIG. 1, the heating element is preferable to
be divided into 2 or more circuits, and further preferable to be
divided into 2 to 10 circuits. That is because the heat radiation
quantity can be changed by controlling the electric power to be
applied to the respective circuits and thus the temperature of the
heated face of a silicon wafer and the like can be adjusted by
dividing the circuits.
[0105] The cross-sectional shape of the heating element is not
particularly limited and may be rectangular or elliptical, however
it is preferable to be flat as shown in FIG. 2 and FIG. 3. That is
because the flat shape is convenient for radiating heat toward the
heating face and scarcely causes temperature distribution on the
heating face. The aspect ratio (width of the heating
element/thickness of the heating element) of the cross-section in
that case is preferably 10 to 5000. Adjustment within in the range
makes the resistance value of the heating element high and also
assures the evenness of the temperature on the heating face.
[0106] The reason for that is because in the case the thickness of
the heating element is made to be constant, if the aspect ratio is
too small than the above-mentined range, the heat transmission
quantity in the direction to the wafer heating face is small and
the heat distribution approximately similar to the heating element
pattern is caused on the heating face, whereas if the aspect ratio
is too high, the temperature immediately above the center of the
heating element becomes high and consequently, the heat
distribution approximately similar to the heating element pattern
is caused on the heating face. Accordingly, taking the temperature
distribution into consideration, the aspect ratio of the
cross-section is preferably 10 to 5000.
[0107] In the case the heating element is formed on the surface of
the ceramic substrate, the aspect ratio of the cross-section is
preferably 10 to 2000 and in the case the heating element is formed
inside of the ceramic substrate, aspect ratio of the cross-section
is preferably 200 to 5000. As it is so, the heating element has a
higher aspect ratio in the case of formation inside of the ceramic
substrate and it is attributed to that because installation of the
heating element inside makes the distance between the heating face
and the heating element short and the evenness of the surface
temperature is deteriorated, the heating element itself is needed
to be flat.
[0108] The practical thickness of the heating element, as shown in
FIG. 1, is desirably 1 to 30 .mu.m, more preferably 1 to 10 .mu.m,
in the case the heating element 12 is formed on the surface of the
ceramic substrate 11. As shown in FIG. 3, it is preferably 1 to 50
.mu.m in the case the heating element 12 is formed inside of the
ceramic substrate 11. Further, the width of the heating element is
preferably 0.1 to 20 mm, more preferably 0.1 to 5 mm in the case
the heating element 12 is formed on the surface of the ceramic
substrate 11. The thickness is preferably 5 to 20 .mu.m in the case
the heating element 22 is formed inside of the ceramic substrate
21.
[0109] The heating element is provided with a resistance value and
a heating capability changeable depending on the width and the
thickness and both cases that the heating element is formed inside
and on the surface, the above-mentioned ranges are respectively
most practical. The resistance value is increased more if heating
element becomes thinner in the thickness and in the width. As
described above, both of the thickness and the width of the heating
element are increased in the case of installation inside of the
ceramic substrate as compared with those in the case of
installation on the surface.
[0110] That is because: if the heating element is installed inside
of the ceramic substrate, the distance between the heating face and
the heating element becomes short and the evenness of the surface
temperature is deteriorated and therefore the width of the heating
element itself is needed to be widened. And also, owing to the
installation of the heating element inside, it is no need to take
the adhesion to the a nitride ceramic and the like into
consideration, thus a high melting point metal such as tungsten,
molybdenum and the like and carbides of tungsten, molybdenum and
the like can be used and it makes the resistance value increase
possible and accordingly the thickness may be thickened for the
purpose to prevent disconnection. As a result, the heating element
12 is preferable to have a thickness and a width in the
above-mentioned ranges.
[0111] Formation of the heating element on the surface of the
ceramic substrate in the first aspect of the present invention is
preferably carried out by a method involving steps of forming a
conductor containing paste layer with a specified pattern by
applying a metal particle-containing conductor containing paste to
the surface of the ceramic substrate and then firing the pattern to
sinter the metal particle on the surface of the ceramic substrate.
The sintering of the metal is sufficient if each metal particle
itself and the metal particle and the ceramic are melted and
adhered with others. In that case, the conductor containing paste
is not particularly limited, however it is preferable to contain
the metal particle or a conductive ceramic for assuring the
conductivity and, besides them, resin, a solvent, a thickener, a
metal oxide and the like.
[0112] The above-mentioned metal particle is preferably of noble
metals (gold, silver, platinum, palladium), lead, tungsten,
molybdenum, nickel and the like. They may be used alone or in
combination with two or more of them. Because these metals are
relatively difficult to be oxidized and have sufficient resistance
values to radiate heat. The above-mentioned conductive ceramic
includes, for example, carbides of tungsten and molybdenum. They
may be used alone or in combination with two or more of them.
[0113] The particle diameter of these metal particle and the
conductive ceramic particle is preferably 0.1 to 100 .mu.m. That is
because if it is smaller than 0.1 .mu.m, they are too fine and easy
to be oxidized and contrary, if it exceeds 100 .mu.m, sintering
becomes difficult to result in increase of the resistance value.
The shape of the above-mentioned metal particle may be spherical or
scaly. In the case such metal particles are employed, mixtures of
those with spherical shape and those with scaly shape may be
employed. In the case the above-mentioned metal particle is a
mixture of those with spherical shape and those with scaly shape,
metal oxides mixed among metal particles are easy to be held to
assure the adhesion of the heating element 12 to the nitride
ceramic and the like and increase the resistance value and
therefore it is advantageous.
[0114] The resin to be employed for the conductor containing paste
includes, for example, epoxy resin, phenol resin and the like. The
solvent is, for example, isopropyl alcohol and the like. The
thickener may be cellulose and the like. The conductor containing
paste is desirable, as described above, to contain the metal oxide
together with the metal particle to make the heating element 12 be
a sintered material of the metal particle and the metal oxide. By
sintering the metal oxide and the metal particle as described, a
nitride ceramic or a carbide ceramic, which is the ceramic
substrate, is firmly bonded to the metal particle.
[0115] The technological reason for improvement of the adhesion of
the metal particle to the nitride ceramic or carbide ceramic caused
by adding the metal oxide as described is not made clear, yet it is
supposedly attributed to that the metal particle surface, the
surface of the nitride ceramic and carbide ceramic is slightly
oxidized and oxide films are formed and these oxide films are
united through the metal oxide by sintering to result in firm
adhesion of the metal particle to the nitride ceramic and carbide
ceramic.
[0116] The above-mentioned metal oxide is preferably selected from
group consisting of, for example, lead oxide, zinc oxide, silica,
boron oxide (B.sub.2O.sub.3), alumina, yttria, titania and the
like. That is because these oxides can improve the adhesion
property of the metal particle to the nitride ceramic and carbide
ceramic without increasing the resistance value of the heating
element.
[0117] The relative mixing ratios of the above-mentioned respective
oxides such as lead oxide, zinc oxide, silica, boron oxide
(B.sub.2O.sub.3), alumina, yttria, titania and the like are
preferably to be adjusted within the respective ranges in the
weight ratio; lead oxide 1 to 10, silica 1 to 30, boron oxide 5 to
50, zinc oxide 20 to 70, alumina 1 to 10, yttria 1 to 50, and
titania 1 to 50; to the extent the total amount thereof does not
exceed 100 parts by weight in the case the total amount of the
metal oxides is set to be 100 parts by weight. The adhesion to
particularly to the nitride ceramic can be improved by adjusting
the amounts of the metal oxides within these ranges. The addition
amount of the above-mentioned metal oxides to the metal particle is
preferably not lower than 0.1% by weight and less than 10% by
weight. The area resistivity of the heating element 12 formed using
such a conductor containing paste is preferably 0.1 to 10
.OMEGA./.quadrature.. If the area resistivity is less than 0.1
.OMEGA./.quadrature., in order to assure the heat radiation
quantity, the width of the heating element pattern has to be as
extremely thin as 0.1 to 1 mm and accordingly, slight defects of
the pattern causes disconnection or changes of the resistance
value, whereas if the area resistivity exceeds 10
.OMEGA./.quadrature., the width of the heating element pattern has
to be widened and the heat radiation quantity can not be assured
and accordingly, the degree of option of the pattern design is
narrowed to make it difficult to keep the temperature even on the
heating face.
[0118] In the case the heating element 12 is formed on the surface
of the ceramic substrate 11, a metal covering layer 24 (reference
to FIG. 2) is desirable to be formed on the surface portion of the
heating element 12. That is because the resistance value of the
metal sintered body inside can be prevented from changing. In that
case, the thickness of the metal covering layer is preferably 0.1
to 10 .mu.m. The metal to be employed for the metal covering layer
is not particularly limited if it is non-oxidative metal and
practically, gold, silver, palladium, platinum, and nickel can be
exemplified. They may be used alone and in combination of two or
more of them.
[0119] Among them, nickel is preferable since the heating element
12 requires terminals to be connected with a power source and at
the time of attachment of the terminals, which are attached to the
heating element 12 through a solder, nickel can prevent thermal
diffusion of the solder. An example of the connection terminal
includes a terminal pin 13 made of Kovar.
[0120] In the case the heating element 22 is formed inside of the
ceramic substrate 21, since the heating element surface is not
oxidized, the coating is not required. In the case the heating
element 22 is formed inside of the ceramic substrate 21, some
portion of the heating element may be exposed to the surface and
conductor-filled through holes to connect the heating element may
be formed in the connection terminal parts and the connection
terminals may be connected and fixed in the conductor-filled
through holes. At that time, the solder for connecting the
connection terminal to be employed may be alloys such as
silver-lead, lead-tin, bismuth-tin. The thickness of the solder
layer is preferably 0.1 to 50 .mu.m. This is because it is
sufficient range for assuring the connection by the solder.
[0121] Incidentally, in the ceramic heater of the first aspect of
the present invention, other than that a semiconductor wafer is to
be placed on the heating face of the ceramic substrate while being
brought into contact with the heating face, the semiconductor wafer
is supported by supporting pins or supporting balls to hold the
semiconductor wafer at a constant distance from the ceramic
substrate in some cases. The separation distance is preferably 5 to
5000 .mu.m.
[0122] The semiconductor wafer can be received from a carrier
machine, and placed on the ceramic substrate, or heated while being
supported by lifter pins by moving the lifter pins up and down.
[0123] The diameter of the ceramic substrate of the first aspect of
the present invention is preferably 200 mm or more. Particularly,
12 inch (300 mm) or more is preferable, because it will be main
stream of a semiconductor wafer of the next generation.
[0124] Further, the outer shape of the above-mentioned ceramic
substrate is preferable to be equal to or lager than the
semiconductor wafer. Heating may be carried out in the state that
the semiconductor wafer and the ceramic substrate does not contact
each other.
[0125] FIG. 6 shows a sectional view schematically showing the
structure of the ceramic heater with the above-mentioned structure
and housed in the supporting case. In this ceramic heater 10, the
ceramic substrate is formed similarly to the ceramic substrate
shown in FIGS. 1, 2, that is, an insulating layer, which is not
shown, is formed on the surface (bottom face) of the ceramic
substrate 11 and the heating element 12 is formed on the insulating
layer.
[0126] In the inside of the supporting case 51, a plurality of
bolt-shaped supporting columns 56 are stood and inserted into
springs 53 and an intermediate bottom plate 52 is supported by the
springs 53. To the heating element 12, power supply terminals 54
inserted into the springs 55 are pushed by the springs 55 placed on
the intermediate bottom plate 52 to be connected with the heating
element; and to the power supply terminals 54, conductive wires 58
are connected and the conductive wires are led out to the outside
of the supporting case 51.
[0127] The thermocouples 44 housed in sheaths S are placed on the
intermediate bottom plate 52 and pushed against the heat
transmission plate 42 by the springs 45 into which the sheaths S
are inserted. The heat transmission plate 42 is provided with dents
having the same shape with that of the tip end of the sheaths and
accordingly the thermocouple 44 are brought into contact with the
ceramic substrate 11 through the heat transmission plate 42.
[0128] The supporting columns 56 are inserted in through holes
formed in the peripheral part of the ceramic substrate 11 and the
position of the ceramic substrate in the horizontal direction is
fixed by them. On the other hand, the power supply terminals 54 are
connected to the heating element 12 of the ceramic substrate and
the sheaths S are brought into contact with the portion where the
heat transmission plate 42 is arranged and the ceramic substrate 11
is pushed upward by the sheaths S and the power supply terminals
54. The head parts 56a of the supporting columns 56 are made to be
T-shape and the ceramic substrate 11 pushed up by the sheaths S is
engaged with the head parts 56a and fixed.
[0129] Further, cooling medium supply ports 59 are formed in the
bottom plate 51a of the supporting case 51 and also openings 510
are formed to introduce a liquid, a gas, practically, water, an
inert gas, air and the like, which is a cooling medium, through the
cooling medium supply ports 59 and discharge it out of the openings
510 for cooling the ceramic substrate 11. Also, by formation of the
openings 510, the reflection amount of the radiation heat can be
suppressed.
[0130] Next, the manufacture method of the ceramic heater,
particularly, the ceramic heater having a heating element on the
bottom face of a ceramic substrate (that is, the ceramic heater
with the structure shown in FIGS. 1 and 2) will be described along
with FIGS. 1, 2.
[0131] A. Manufacture Method of Ceramic Heater Having Heating
Element Formed on the Bottom Face of Ceramic Substrate
[0132] (1) Manufacture of Ceramic Substrate
[0133] After a slurry is produced by mixing the above-mentioned
nitride ceramic or carbide ceramic such as aluminum nitride with a
sintering aid such as yttria and the like, a binder and the like
based on the necessity and the slurry is granulated by a method of
spray dry to produce a granular powder and the obtained granular
powder is filled in a die and molded to be a flat plate to obtain a
raw formed body (a green sheet). Successively, based on the
necessity, the raw formed body is processed by drilling to form
through holes 15 to insert lifter pins for supporting a silicon
wafer. After production of the ceramic substrate, the
above-mentioned processing treatment may be carried out.
[0134] Next, the raw formed body is sintered by heating and firing
to produce a plate-like body made of a ceramic. After that, the
plate-like body is processed into a given shape to manufacture a
ceramic substrate 11, and may be processed into a shape to be used
as it is after firing. Heating and firing is carried out under the
pressurizing condition so that manufacture of the ceramic substrate
11 free from pores is made possible. The heating and firing is
carried out at a sintering temperature or higher and particularly
in the case of the nitride ceramic or the carbide ceramic, it is
1000 to 2500.degree. C. Further, an oxide ceramic film 500 is
formed on the surface. Practically, the method to be employed
includes: a sol-gel method of applying a sol solution containing
ethyl silicate, water, and an acid, drying it and firing at
1000.degree. C. or more; a method of applying a glass paste and
firing it at 1000.degree. C. or more; and a method of firing the
surface of the ceramic substrate at 1000.degree. C. or more in air
to form an oxide film. A plate made of an oxide ceramic, for
example, an alumina plate and a silica plate may be laminated.
[0135] After that, the ceramic substrate was ground with a diamond
grind stone or polished with a diamond paste to adjust the surface
roughness to Ra.ltoreq.5 .mu.m, desirably Ra.ltoreq.2 .mu.m.
[0136] (2) Step of Printing Conductor Containing Paste to Ceramic
Substrate
[0137] As described above, the conductor containing paste is a
fluid material containing generally a metal particle, resin, and a
solvent and having a high viscosity. The conductor containing paste
is printed on portions to form the heating element by a screen
printing and the like to form a conductor containing paste layer.
Since the heating element has to keep the whole body of the ceramic
substrate at an even temperature, it is preferable to form a
concentric pattern as shown in FIG. 1. The conductor containing
paste layer is preferable to be have a rectangular and flat cross
sectional shape as a heating element 12 after firing.
[0138] (3) Firing of Conductor Containing Paste Layer
[0139] The conductor containing paste layer printed on the bottom
face of the ceramic substrate 11 is heated and fired to remove the
resin and the solvent and at the same time sinter the metal
particle and bake it on the bottom face of the substrate 11 to form
the heating element 12. The temperature of the heating and firing
is preferably 500 to 1000.degree. C. If the above-mentioned metal
oxide is added to the conductor containing paste, the metal
particle, the ceramic substrate, and the metal oxide are sintered
and integrated, so that the adhesion property of the heating
element and the ceramic substrate is improved.
[0140] (4) Formation of Metal Covering Layer
[0141] It is preferable to form the metal covering layer 24 on the
surface of the heating element 12. The metal covering layer 24 can
be formed by a variety of means such as electroplating, electroless
plating, sputtering and the like, yet in consideration of mass
productivity, the electroless plating is optimum.
[0142] (5) Attachment of Terminal
[0143] Terminals (terminal pins 13) for connection with an electric
power source are attached to the end parts of the pattern of the
heating element 12 by a solder and further, as shown in FIG. 4,
using springs, the temperature measurement elements are brought
into contact with the ceramic substrate through sheaths and the
heat transmission plate to complete the manufacture of the ceramic
heater.
[0144] The above-mentioned manufacture method of the ceramic heater
is a manufacture method of a ceramic heater comprising a ceramic
substrate and a heating element formed on the bottom face of the
ceramic substrate and therefore, next a manufacture method of the
ceramic heater comprising a ceramic substrate and a heating element
formed inside of the ceramic substrate will be described.
[0145] B. Manufacture Method of Ceramic Heater Having Heating
Element Formed in Inside of Ceramic Substrate
[0146] (1) Manufacture of Ceramic Substrate
[0147] At first, a paste is produced by mixing a powder of the
nitride ceramic or carbide ceramic with a binder and a solvent and
formed in a sheet-like state by a doctor blade method to obtain a
green sheet. The thickness of the green sheet is preferably 0.1 to
5 mm.
[0148] In this case, aluminum nitride, silicon carbide and the like
may be used for the ceramic powder and based on the necessity, a
sintering aid of such as yttria and the like may be added. The
binder is preferably at least one kind of binders selected from a
group consisting of an acrylic-based binder, ethyl cellulose, butyl
cellosolve, and polyvinyl alcohol. Further, the solvent is
preferably at least one kind of binders selected from a group
consisting of .alpha.-terpineol and glycol.
[0149] Next, based on the necessity, portions to be through holes
to insert the lifter pins into for supporting an object to be
heated such as a silicon wafer and the like and portion to be
conductor-filled through holes for connecting the heating element
to external terminal pins are formed. This processing may be
carried out after the formation of green sheet laminate body, which
will be described later, or after the production of the sintered
body.
[0150] (2) Step of Printing Conductor Containing Paste to Green
Sheet
[0151] The conductor containing paste containing a metal or a
conductive ceramic is printed on the green sheet. In the conductor
containing paste, the metal particle or the conductive ceramic
particle is contained. The metal particle is preferably a tungsten
particle or a molybdenum particle and the average particle diameter
of the metal particle is preferably 0.1 to 5 .mu.m. This is because
if the average particle diameter is smaller than 0.1 .mu.m or
larger than 5 .mu.m, the conductor containing paste is difficult to
be printed. Such a conductor containing paste include a composition
(paste) containing, for example, 85 to 87 parts by weight of the
metal particle or a conductive ceramic particle; 1.5 to 10 parts by
weight of at least one kind of binders selected from a group
consisting of an acrylic-based binder, ethyl cellulose, butyl
cellosolve, and polyvinyl alcohol; and 1.5 to 10parts by weight of
at least one kind of solvents selected from a group consisting of
.alpha.-terpineol and glycol.
[0152] (3) Green Sheet Lamination Step
[0153] Green sheets having no printing of the conductor containing
paste are laminated on the upper and the lower side of the green
sheet bearing the printing of the conductor containing paste. In
this case, the number of the green sheets to be laminated on the
upper side is controlled to be larger than the number of the green
sheets to be laminated on the lower side in order to make a formed
position of the heating element prejudised in the direction to the
bottom face. Practically, the number of the green sheets to be
laminated on the upper side is preferably 20 to 50 sheets and the
number of the green sheets to be laminated on the lower side is 5
to 20 sheets.
[0154] (4) Firing Step of Green Sheet Laminated Body
[0155] The green sheet laminated body is heated and pressurized to
sinter the green sheets and the conductor containing paste layer
inside. The heating temperature is preferably 1000 to 2000.degree.
C. and the pressurizing pressure is preferably 100 to 200
kg/cm.sup.2. Heating is carried out in an inert gas atmosphere. The
inert gas to be employed includes argon, nitrogen and the like.
[0156] Further, a film 500 of an oxide ceramic is formed on the
surface. Practically, the method to be employed includes a sol-gel
method of applying a sol solution containing ethyl silicate, water,
and an acid, drying it and firing it at 1000.degree. C. or more, a
method of applying a glass paste and firing it at 1000.degree. C.
or more, a method of firing the surface of the ceramic substrate at
1000.degree. C. or more in the air to form an oxide film. A plate
made of an oxide ceramic, for example, an alumina plate and a
silica plate may be laminated.
[0157] After that, the ceramic substrate is ground with a diamond
grind stone or polished with a diamond paste to adjust the surface
roughness to be Ra.ltoreq.5 .mu.m, preferably Ra.ltoreq.2
.mu.m.
[0158] Further, terminals are connected to the conductor-filled
through holes to be connected with the heating element inside
thereof and heated to carry out reflow. The heating temperature is
preferably 200 to 500.degree. C. Further, the thermocouples as
temperature measurement elements are fixed by heat resistant resin
or a ceramic or brought into contact by springs as shown in FIG. 4
to complete manufacture of the ceramic heater.
[0159] The ceramic heater of the first aspect of the present
invention is characterized in that the heating element is formed on
the surface or the inside of the ceramic plate and temperature
measurement elements are attached and fixed by the heat resistant
resin or the ceramic or by being pushed by springs and the like,
and yet it is desirable to further install control unit for
supplying electric power to the above-mentioned heating element, a
memory unit for storing the temperature data measured by the
above-mentioned temperature measuring element, and a computation
unit for computing the necessary electric power for the
above-mentioned heating element from the above-mentioned
temperature data to obtain a ceramic heater apparatus.
[0160] By adopting the installation as mentioned above, the
measurement results of the temperature are stored in the memory
unit, and based on the stored temperature data, the computation
unit computes the voltage to be applied to the heating element for
even heating and based on the computation results, the controlled
voltage is applied to the heating element from the control unit, so
that the whole body of an object to be heated such as a silicon
wafer can evenly be heated.
[0161] Further, the nitride ceramic and carbide ceramic have a
smaller thermal expansion coefficient than a metal and
significantly high mechanical strength than a metal, so that the
ceramic substrate can be made thin and light. Further, the ceramic
substrate has a high thermal conductivity and the ceramic substrate
itself is thin, so that the surface temperature of the ceramic
substrate can promptly follow the temperature change of the heating
element.
[0162] FIG. 3 shows a ceramic heater apparatus equipped with the
control unit for supplying electric power to the heating element, a
memory unit for storing the temperature data measured by the
above-mentioned temperature measureing element, and a computation
unit for computing the necessary electric power for the
above-mentioned heating element from the above-mentioned
temperature data and in the figure, the ceramic heater is a shown
as the partial cross-sectional view and the other facilities
installed in the ceramic heater are shown in block line
figures.
[0163] Different from the case of FIG. 1, in the ceramic heater
shown in the figure, the heating element 22 (22x, 22y) is formed
inside thereof and is not composed of pairs of double concentric
circles but composed of concentric circles composed of single
circles. The heating elements 22x, 22y are connected to the
terminal pins 13 formed on the bottom faces through the
conductor-filled through holes 28. Further, to the terminal pins
13, sockets 32 are attached and the sockets 32 are connected to the
control unit 29 having an electric power source.
[0164] Further, the thermocouples 27 are fixed in the ceramic
substrate 21. The thermocouples 27 are connected to the memory unit
30 so as to measure the temperature at the respective thermocouples
27 for every given interval and store the data. The memory unit 30
is connected to the control unit 29 and also to the computation
unit 31, and based on the data stored in the memory unit 30, the
computation unit 31 computes the voltage values and the like for
the control and based on the computation result, the control unit
29 applies given voltage to the heating element 22 to make the
temperature of the heating face 21a even.
[0165] Further, a plurality of through holes 25 (in the figure,
only one) are formed in the ceramic substrate 21. The lifter pins
16 are inserted into the through holes 25 and an object to be
heated, e.g., a silicon wafer 19, is to be placed on the lifter
pins 16. By moving the lifter pins 16 up and down, the silicon
wafer 19 is made possible to be transported to an un-illustrated
carrier machine or received from the carrier machine. The
respective members composing the ceramic heater 10 and temperature
measurement elements formed in the substrate 11 are similarly
constituted to those of the ceramic heater of FIG. 1, except the
points particularly described above and thus their detailed
description is omitted.
[0166] Next, the operation of the ceramic heater of the first
aspect of the present invention will be described with the
reference to the ceramic heater of FIG. 3 having the structure
where the heating element is buried in the ceramic substrate.
[0167] At first, when electric power is applied to the ceramic
heater 10 by operating the control unit 29, the temperature of the
ceramic heater 21 itself increases and the surface temperature of
the outer circumferential part becomes slightly low. The
thermocouples 27 measure the change of the temperature and the data
of the measured temperature is once stored in the memory unit
30.
[0168] After that, the measured temperature data is transmitted to
the computation unit 31 and in the computation unit 31, the
temperature difference .DELTA.T among the respective measurement
points is computed and further the data .DELTA.W necessary to make
the temperature on the heating face 21a even is computed. For
example, if the temperature difference .DELTA.T exists between the
heating element 22x and the heating element 22y and the temperature
is lower in the heating element 22x, the electric power data
.DELTA.W so as to make .DELTA.T 0 is computed and transmitted to
the control unit 29 and based on the data, electric power is
applied to the heating element 22x to increase the temperature
thereof.
[0169] Regarding the electric power calculation algorithm, it is
most convenient to employ a computation method for computing the
electric power necessary for temperature increase based on the
specific heat of the ceramic substrate 21 and the weight of the
heating region and a correction coefficient attributed to the
heating element pattern may be added. Also, previously a
temperature increase test is carried out for specified heating
element patterns to previously obtain the function among the
temperature measurement positions, the loaded electric power, and
the temperature, and the electric power to apply may be computed
from the function. The voltage for application corresponding to the
electric power computed in the computation unit 31 and the time are
transmitted to the control unit 29 and in the control unit 29,
electric power is applied to each heating element 22 based on the
values.
[0170] The ceramic heater shown in FIG. 1 and FIG. 2(a), similarly
to the ceramic heater shown in FIG. 3, is a ceramic heater equipped
with: a control unit for supplying electric power to the heating
element; a memory unit for storing the temperature data measured by
the above-mentioned temperature measuring element; and a
computation unit for computing the necessary electric power for the
above-mentioned heating element from the above-mentioned
temperature data. And unlike the case of heating element in FIG. 3,
the heating element is not embedded in the ceramic substrate but
installed on the bottom face of the ceramic substrate. FIG. 2(b) is
a partially enlarged sectional view of some portion of the ceramic
heater, particularly the temperature measurement element. In the
surrounding of the heating elements 12x, 12y formed on the bottom
face 11b of the ceramic substrate 11, a metal covering layer 24 is
formed and terminal pins 13 are connected to and fixed to the
heating elements 12x and 12y through the metal covering layer 24.
Sockets 32 are attached to the terminal pins 13 and the sockets 32
are connected to the control unit 23 having an electric power
source. Other than that, the ceramic heater is composed similarly
to the ceramic heater shown in FIG. 3.
[0171] Operation of the ceramic heater 10 shown in FIG. 1 and FIG.
2 is also similar to the ceramic heater shown in FIG. 3 and the
temperatures at two thermocouples 27 are measured for every given
interval and the data are stored in memory unit 21, and based on
the data, the computation unit 22 computes the voltage values and
the like for the control, and based on the computation results, the
control unit 23 applies given voltage to the heating elements 12x,
12y to make the temperature of the whole heating face 11a even.
[0172] Next, the ceramic heater for a semiconductor
producing/examining device according to the second aspect of the
present invention will be described along with an embodiment of the
present invention.
[0173] The ceramic heater for a semiconductor producing/examining
device according to the second aspect of the present invention is a
ceramic heater comprising a ceramic heater and a heating element
formed on the surface of the ceramic substrate or inside of the
ceramic substrate, and is characterized in that temperature
measurement elements are pressed on the above-mentioned ceramic
substrate.
[0174] The insulating layer to be used for the second aspect of the
present invention is same as that used in the first aspect of the
present invention.
[0175] In the second aspect of the present invention, the surface
roughness Ra of the ceramic substrate being brought into contact
with the temperature measurement elements is preferably Ra.ltoreq.5
.mu.m, more preferably Ra.ltoreq.2 .mu.m. Therefore, similarly to
the case of the first aspect of the present invention, the surface
of the ceramic substrate is made smooth by grinding or forming an
insulating layer with the roughness Ra.ltoreq.5 .mu.m.
[0176] The properties of the above-mentioned insulating layer such
as the size and the thickness, are same as those of the first
aspect of the present invention.
[0177] In this specification, the fact that the roughness of the
surface of the ceramic substrate is adjusted to be Ra.ltoreq.5
.mu.m includes that the roughness Ra of the surface of the
insulating layer is adjusted to be 2 .mu.m or less.
[0178] The temperature measurement elements are preferable to be
pushed by a force of 1.times.10.sup.-6 to 20 kg. If the pressing
force is less than 1.times.10.sup.-6 (9.8.times.10.sup.-6 N), the
contact of the temperature measurement elements and the ceramic
substrate is not sufficient and the response at the time of
measurement is inferior and the controllability of the temperature
of the heating face of the ceramic substrate is decreased and
accordingly, the temperature distribution of the heating face
becomes wide to result in difficulty of even heating of a silicon
wafer.
[0179] If the pressing force exceeds 20 kg (196 N), the ceramic
substrate is warped and in the case of heating in the state the
heating face and the silicon wafer are brought into contact with
each other, the heating face and the silicon wafer are not
sufficiently brought into contact with each other and on the other
hand, in the case of heating in the state the heating face and the
silicon wafer are distanced from each other, the distance between
the heating face and the silicon wafer is not constant and
accordingly the semiconductor wafer cannot be heated at an even
temperature.
[0180] Note that the pressing force is measured by a
gravimeter.
[0181] Similarly to the first aspect of the present invention, the
insulating layer may be formed on the whole ceramic substrate or
only on the portions where the temperature measurement elements
contact. In the case the insulating layer is formed on the whole
ceramic substrate, the heating element may be formed on the
insulating layer.
[0182] Similarly to the first aspect of the present invention, in
the second aspect of the present invention, for instance as shown
in FIG. 5, a thermocouple 44 may be housed in a sheath S made of a
stainless steel and an insulating powder 46 such as alumina,
silica, magnesia and the like is sealed therein and the resulting
sheath S as a whole may be pressed on the surface of the ceramic
substrate 11 bearing the insulating layer 500 by the force of a
spring 45 as shown in FIG. 4. In this case, a projection 48 may be
formed on the side face of the sheath S and the spring 45 is
installed between the projection 48 and the plate-like body 41
which is either the bottom plate or an intermediate bottom plate.
The spring 45 may be like a coil or a leaf as shown in FIG. 4.
[0183] In this case, the sheath S housing the temperature
measurement element such as the thermocouple 44 may be fitted and
fixed in an alumina pipe so as to be brought into contact with the
ceramic substrate 11 and also as shown in FIG. 4, a heat
transmission plate 42 made of a metal plate and the like may be
interposed between the sheath S containing the thermocouple 44 and
the insulating layer 500 to increase the thermal conductivity. As
the metal plate, aluminum, a stainless steel, nickel, copper, a
noble metal and the like may be used.
[0184] Further, as shown in FIG. 4, in order to make the contact
surface area of the heat transmission plate 42 and the sheath S
large, a dent (concave portion) having the similar shape to that of
the tip end of the sheath S is preferable to be formed in the heat
transmission plate 42.
[0185] For the sheath S, other than metals, a ceramic such as
alumina may be used. However, to avoid deterioration of the
response of the temperature measurement element by the existence of
sheath S, the thickness and the material thereof are required to be
controlled and selected.
[0186] As shown in FIG. 10, the sheath S housing the temperature
measurement element such as the thermocouple 44 may be fitted and
fixed in a leaf spring 60 made of a metal such as Kovar, a steel
and the like and pressed on the ceramic substrate 11 through a heat
transmission plate 42. The shape of the leaf spring 62 is not
particularly limited, yet as shown in FIG. 10, the leaf spring 60
which is bent so as to have a cross-section approximately like
numeral "2"-shape and have through hole to insert the sheath S into
may be employed.
[0187] Further, as shown in FIG. 11, the temperature measurement
element (thermocouple) 64 may be sandwiched between a presser plate
66 and the ceramic substrate 11 and fastened by a bolt 65 to be
fixed.
[0188] Further, as shown in FIG. 12, one side of a leaf spring 76
is fixed by a bolt 75 and the like and the temperature measurement
element (thermocouple) 74 is attached to the other end to be
pressed.
[0189] Since the second aspect of the present invention employs the
above-mentioned means, no fixing member such as an adhesive and the
like is required and as a result, there is no probability of
occurrence of the thermal deterioration of the fixing member and
therefore the temperature measurement element does not fall
attributed to the deterioration. Also, different from the fixation
method using an adhesive, in the manufacturing process, any problem
such as inferior contact with the ceramic substrate does not take
place and accurate temperature measurement of an object to be
heated is made possible and based on the temperature measurement
results, the heating state of the heating element can properly be
adjusted to make the even heating of the whole body of a variety of
objects to be heated possible.
[0190] The above-mentioned ceramic substrate and the temperature
measurement element composing the ceramic heater of the second
aspect of the present invention may be brought into contact with
each other through a heat transmission plate made of a material
such as a nitride ceramic and the like, a carbide ceramic and the
like other than the above-mentioned metal plate. The heat
transmission plate of such a metal plate and the like has a high
thermal conductivity and is capable of improving the response to
the thermocouple. Also, as described above, if the contact surface
area with the thermocouple is made wide by forming a dent in the
heat transmission plate 42, the response can further be
improved.
[0191] Further, the ceramic substrate holding the heating element
and made of the nitride ceramic and carbide ceramic has a smaller
thermal expansion coefficient than a metal and significantly high
mechanical strength than a metal, so that even if the ceramic
substrate can be made thin and light in weight, it is not warped or
distorted by heating. Further, the ceramic substrate has a high
thermal conductivity and the ceramic substrate itself is thin, so
that the surface temperature of the ceramic substrate can promptly
follow the temperature change of the heating element. That is, the
surface temperature of the ceramic substrate can accurately be
controlled by changing the temperature of the heating element by
changing the voltage and current values.
[0192] As described above, the ceramic heater of the second aspect
of the present invention is a ceramic heater comprising a ceramic
substrate and a heating element on the surface of the ceramic
substrate or inside of the ceramic substrate. The summary of the
ceramic heater will be described along with FIG. 8.
[0193] FIG. 8(a) is a block diagram schematically showing a ceramic
heater of a second aspect of the present invention and FIG. 8(b) is
a sectional view showing the part having a temperature measurement
element.
[0194] The bottom face view of the ceramic heater shown in FIG. 8
is approximately same as the one described in FIG. 1, so that here
the description is omitted. FIG. 8(a) shows some portion of the
cross-section of the ceramic substrate shown in FIG. 1.
[0195] FIG. 8 is approximately same as FIG. 2, except the contact
structure of the ceramic substrate 11 and the thermocouple 27.
Accordingly, same reference numerals are assigned to the
constituent elements corresponding to those in the above-mentioned
FIG. 2.
[0196] As shown in FIG. 8, terminal pins 13 to be input and output
terminals are connected to both ends of the heating element 12.
Through holes 15 to insert lifter pins 16 into for holding a
variety of objects to be heated such as a silicon wafer on the
heating face are formed near the center portion and in the
temperature measurement portions 14a to 14i, sheaths S housing the
thermocouples 27 therein are pushed against the bottom face 11b of
the ceramic substrate 11 using springs 17 and brought into contact
with the bottom face 11b.
[0197] As shown in FIG. 8(b), the springs 17 are disposed in the
insides of cylindrical bodies 180 uprightly stood in the
intermediate bottom plate 18 and the sheaths S are inserted into
the springs 17 and the springs 17 push up the projections formed on
the side faces of the sheaths S, so that the sheaths S are brought
into contact with the insulating layer 500 formed on the ceramic
substrate 11.
[0198] The shape (the thickness and the diameter) and the material
(raw material) of the ceramic substrate composing the ceramic
heater of the second aspect of the present invention are similar to
those of the first aspect of the present invention and already
described and therefore description here is omitted.
[0199] As shown in FIG. 8, the insulating layer 500 is formed on
the bottom face 11b of the ceramic substrate 11 and the temperature
measurement elements such as thermocouples 27 are brought into
contact with the insulating layer 500 to measure the temperature of
the ceramic substrate 11.
[0200] The temperature measurement elements to be employed in the
ceramic heater of the second aspect of the present invention are
similar to those of the first aspect of the present invention and
already described and therefore description here is omitted. The
above-mentioned temperature measurement elements are arranged in
the temperature measurement portions 14a to 14i and, as described
above, pushed against the bottom face 11b of the ceramic substrate
11 using the elastic bodies such as the springs 17.
[0201] Similarly to the first aspect of the present invention, the
heating element of the above-mentioned ceramic heater may be formed
on the bottom face 11b of the ceramic substrate 11, as shown in
FIG. 8, or inside of the ceramic substrate 21, as shown in FIG. 9.
The formation position of the heating element 22 in the case the
heating element 22 is formed inside of the substrate 21 is same as
that in the first aspect of the present invention and already
described and therefore description here is omitted.
[0202] The shape, the material, and the formation method of the
above-mentioned heating element are similar to those of the first
aspect of the present invention and already described and therefore
description here is omitted.
[0203] In the ceramic heater of the second aspect of the present
invention, other than the case of mounting a semiconductor wafer
while bringing the wafer into contact with the heating face of the
ceramic substrate, the semiconductor wafer may be supported and
heating may be carried out as the semiconductor wafer is being
supported with a constant distance kept from the ceramic substrate.
The distance is desirably 5 to 5000 .mu.m.
[0204] The semiconductor wafer can be received from the conveyor,
placed on the ceramic substrate, and also heated by longitudinally
moving the lifter pin.
[0205] The ceramic heater of the second aspect of the present
invention with the above-mentioned structure is generally used
while being housed in a supporting case. The situation of the
ceramic heater of the second aspect of the present invention which
is housed in the supporting case is same as shown in FIG. 6. FIG. 6
is already described and therefore description here is omitted.
[0206] The manufacturing method of the ceramic heater of the second
aspect of the present invention, particularly, the ceramic heater
comprising a ceramic substrate and a heating element formed on the
bottom face of the ceramic substrate (that is, the ceramic heater
with the structure shown in FIGS. 1 and 8) is similar to the
above-mentioned A. of the first aspect of the present invention,
except that the surface roughness adjustment of the ceramic
substrate is not necessary and is already described and therefore
description here is omitted.
[0207] Also, the manufacturing method of the ceramic heater
comprising a ceramic substrate and a heating element formed inside
of the ceramic substrate is similar to the above-mentioned B. of
the second aspect of the present invention, except the surface
roughness adjustment of the ceramic substrate is not necessary and
is already described and therefore description here is omitted.
[0208] The ceramic heater of the second aspect of the present
invention is characterized in that the heating element is formed on
the surface or the inside of the ceramic substrate and the
temperature measurement elements are installed and fixed by pushing
them by springs and similarly to the first aspect of the present
invention, other than these, control unit for supplying electric
power to the above-mentioned heating element, a memory unit for
storing the temperature data measured by the above-mentioned
temperature measurement elements, and a computation unit for
computing the necessary electric power for the above-mentioned
heating element from the above-mentioned temperature data are
preferable to be installed to obtain a ceramic heater
apparatus.
[0209] FIG. 9 shows the ceramic heater apparatus comprising the
ceramic substrate, control unit for supplying electric power to the
heating element, a memory unit for storing the temperature data
measured by the above-mentioned temperature measurement elements,
and a computation unit for computing the necessary electric power
for the above-mentioned heating element from the above-mentioned
temperature data. In this figure, the ceramic heater is shown as a
partial cross-sectional view and the facilities other than the
elements of the ceramic heater are shown as block line figures. The
FIG. 9 is similar to FIG. 3 except the contact structure of the
ceramic substrate 21 and the thermocouples 27. Therefore, the same
reference numerals are assigned to the constituent components in
FIG. 9 which are corresponding in FIG. 3.
[0210] Different from that in FIG. 8, the ceramic heater shown in
the figure, the heating element 22 (22x, 22y) is embedded inside of
the ceramic substrate 21 and also different from that in FIG. 8,
the heating element 22 (22x, 22y) is not composed of pairs of
double concentric circles but composed of concentric circles
composed of single circles. The heating elements 22x, 22y are
connected to the terminal pins 13 formed on the bottom faces
through the conductor-filled through holes 28. Further, to the
terminal pins 13, sockets 32 are attached and the sockets 32 are
connected to the control unit 29 having an electric power
source.
[0211] Further, the sheaths S housing the thermocouples 27 therein
are fixed in the ceramic substrate 21 while being brought into
contact with the ceramic substrate. The thermocouples 27 are
connected to the memory unit 30 so as to measure the temperature at
the respective thermocouples 27 for every given interval and store
the data. The memory unit 30 is connected to the control unit 29
and also to the computation unit 31 and based on the data stored in
the memory unit 30, the computation unit 31 computes the voltage
values and the like for the control and based on the computation
result, the control unit 29 applies given voltage to the heating
element 22 to make the temperature of the heating face 21a
even.
[0212] Regarding the respective members composing the ceramic
heater 20 and the temperature measurement elements formed in the
ceramic substrate 21, the members other than those particularly
described above are similarly constituted to those of the ceramic
heater shown in FIG. 8 and already described and therefore
description here is omitted.
[0213] Further, the operation of the ceramic heaters of the second
aspect of the present invention shown in FIG. 8 and FIG. 9 is also
similar to that described for the above-mentioned first aspect of
the present invention and already described and therefore
description here is omitted.
BEST MODE FOR CARRYING OUT THE INVENTION
[0214] Hereinafter, the present invention will be described further
in detail along with examples of the present invention, yet it is
no need to say that the present invention is not at all limited to
these examples and it is therefore comprehended that the claims
will cover any modifications or embodiments as fall within the true
scope of the present invention.
EXAMPLE 1
Manufacture of Ceramic Heater Made of Aluminum Nitride (Reference
to FIG. 1)
[0215] (1) A composition containing 100 parts by weight of an
aluminum nitride powder (the average particle diameter: 1.1 .mu.m),
4 parts by weight of yttria (the average particle diameter: 0.4
.mu.m), 12 parts by weight of an acrylic binder, and an alcohol was
spray dried to produce a granular powder.
[0216] (2) Next, the obtained granular powder was filled in a die
and molded to be a flat plate to obtain a raw formed body (a green
sheet). The raw formed body was processed by drilling to form
through holes 15 to insert lifter pins for a silicon wafer.
[0217] (3) On completion of the processing, the raw formed body was
hot pressed at 1800.degree. C. and a pressure of 200 kg/cm.sup.2 to
obtain a 3 mm thick aluminum nitride plate-like body. Next, a disk
with a diameter of 12 inch (300 mm) was cut out of the plate-like
body to obtain a plate-like body made of ceramic (a ceramic
substrate) 11. Further, a glass paste (G-5177 produced by Shouei
Chemical Products Co., Ltd.) was applied to the surface and heated
to 1000.degree. C. to form a 2 .mu.m-thick SiO.sub.2 film.
[0218] The ceramic substrate 11 was ground with a diamond grind
stone of #220 at 1 kg/cm.sup.2 load and polished with a polishing
cloth (Malto Co.) and a diamond paste (particle diameter of 0.5
.mu.m) to adjust the surface roughness to Ra=0.01 .mu.m.
Incidentally, the measurement of the surface roughness was carried
out by a probe type surface roughness meter (Surfcom 920A, Tokyo
Precision Co.).
[0219] (4) On the ceramic substrate 11 obtained as described
above-mentioned (3), a conductor containing paste was printed by
screen printing. The printed pattern was made to be a concentric
pattern as shown in FIG. 1. As the conductor containing paste,
Sorbest PS603D produced by Tokuriki Chemical Research Co., Ltd.
used to form a plated through hole of a printed circuit board was
used. The conductor containing paste was a silver-lead paste and
contained 7.5 parts by weight of metal oxides consisting of lead
oxide (5% by weight), zinc oxide (55% by weight), silica (10% by
weight) boron oxide (25% by weight) and alumina (5% by weight) in
100 parts by weight of Ag. The silver particle had an average
particle diameter 4.5 .mu.m and a scaly shape.
[0220] (5) Next, the ceramic substrate 11 bearing the printed
conductor containing paste was heated and fired at 780.degree. C.
to sinter silver and lead in the conductor containing paste and
simultaneously bake them on the ceramic substrate 11 to form a
heating element 12. The silver-lead heating element 12 had a
thickness of 5 .mu.m, a width of 2.4 mm and an area resistivity of
7.7 m.OMEGA./.quadrature..
[0221] (6) Next, the ceramic substrate 11 produced as described in
(5) was immersed in an electroless nickel plating bath of an
aqueous solution containing 80 g/L of nickel sulfate, 24 g/L of
sodium hypophosphite, 12 g/L of sodium acetate, 8 g/L of boric
acid, and 6 g/L of ammonium chloride to deposit a 1 .mu.m-thick
metal covering layer (nickel layer) 24 on the surface of the
silver-lead heating element 12.
[0222] (7) To the portions where terminals for assuring the
connection with an electric power source, a silver-lead solder
paste (Tanaka Noble Metals. Co.) was applied by screen printing to
form a solder layer.
[0223] Then, terminal pins 13 made of Kovar were attached on the
solder layer and the solder was heated for reflow at 420.degree. C.
to attach the terminal pins 13 to the surface of the heating
element 12.
[0224] (8) Thermocouples for temperature control were fixed by
polyimide resin and the resin was cured at 190.degree. C. for 2
hours to obtain a ceramic heater 10.
EXAMPLE 2
Manufacture of Ceramic Heater Made of Silicon Carbide
[0225] A ceramic heater made of silicon carbide was manufactured in
the same manner as Example 1, except that silicon carbide with an
average particle diameter of 1.0 .mu.m was used and the sintering
temperature was 1900.degree. C. and further, the obtained ceramic
substrate surface was fired at 1500.degree. C. for 2 hours to form
a 1 .mu.m-thick SiO.sub.2 layer on the surface.
[0226] The substrate was ground with a diamond grind stone of #220
at 1 kg/cm.sup.2 load and polished with a polishing cloth (Malto
Co.) and a diamond paste (particle diameter of 0.25 .mu.m) to
adjust the surface roughness to Ra=0.008 .mu.m.
[0227] To the substrate, sheaths S housing thermocouples 44 as
shown in FIG. 4 were pushed with springs 45.
EXAMPLE 3
Manufacture of Ceramic Heater Containing Heating Element Inside
(Reference to FIG. 3)
[0228] (1) Using a paste produced by mixing an aluminum nitride
powder (the average particle diameter: 1.1 .mu.m produced by
Tokuyama), 4 parts by weight of yttria (the average particle
diameter: 0.4 .mu.m), 11.5 parts by weight of an acrylic binder,
0.5 parts by weight of a dispersant, and 53 parts by weight of
alcohol consisting of 1-butanol and ethanol, forming was carried
out by a doctor blade method to obtain a 0.47 mm green sheet.
[0229] (2) Successively, after the green sheet was dried at
80.degree. C. for 5 hours, portions to be through holes 15 with
diameters of 1.8 mm, 3.0 mm, and 5.0 mm to insert silicon wafer
lifter pins into and portions to be conductor-filled through holes
for connection with terminal pins were formed by punching.
[0230] (3) Next, a conductor containing paste A was produced by
mixing 100 parts by weight of a tungsten carbide particle with an
average particle diameter of 1 .mu.m, 3.0 parts by weight of an
acrylic binder, 3.5 parts by weight of .alpha.-terpineol solvent,
and 0.3 parts by weight of a dispersant.
[0231] Further, a conductor containing paste B was produced by
mixing 100 parts by weight of a tungsten carbide particle with an
average particle diameter of 1 .mu.m, 1.9 parts by weight of an
acrylic binder, 3.7 parts by weight of .alpha.-terpineol solvent,
and 0.2 parts by weight of a dispersant.
[0232] (4) Using the conductor containing paste A, printing on the
green sheet was carried out by a screen printing to form a
conductor containing paste layer. The printed pattern was made to
be a concentric pattern as shown in FIG. 1. Further, the through
holes for forming conductor-filled through holes for connection
with terminal pins were filled with the conductor containing paste
B. On the green sheet finished for the above-mentioned treatment,
37 green sheets and 13 sheets with no printing with the tungsten
paste were laminated on the upper side (heating face) and on the
lower side, respectively, and laminated at 130.degree. C. and 80
kg/cm.sup.2 pressure.
[0233] (5) The laminated body obtained in such a manner was
degreased at 600.degree. C. for 5 hours in nitrogen gas and hot
pressed at 1890.degree. C. and 150 kg/cm.sup.2 pressure for 3 hours
to obtain a 3 mm-thick aluminum nitride plate-like body. The
obtained plate-like body was cut into a disk-like shape with a
diameter of 300 mm to obtain a plate-like body made of a ceramic
containing a heating element with a thickness of 6 .mu.m and a
width of 10 mm inside.
[0234] A sol solution produced by hydrolysis polymerization of a
mixed solution containing 25 parts by weight of tetraethyl
silicate, 37.6 parts by weight of ethanol, and 0.3 parts by weight
of hydrochloric acid by stirring for 24 hours was applied by a spin
coating, dried at 80.degree. C. for 5 hours, and fired at
1000.degree. C. for 1 hour to form an insulating layer 500 of a 2
.mu.m-thick SiO.sub.2 film on the surface of the ceramic substrate
11.
[0235] (6) Next, the ceramic substrate was ground with a diamond
grind stone of #220 at 1 kg/cm.sup.2 load to adjust the surface
roughness to Ra=0.6 .mu.m.
[0236] (7) After that, some portions of the through holes for
conductor-filled through holes were hollowed out to form concave
portions and using a gold braze of Ni-Au, terminal pins made of
Kovar were connected by conducting heating and reflowing of the
braze at 700.degree. C. Incidentally, the connection of the
terminal pins is preferable to have a supporting structure of
three-point support with tungsten supports. Because such a
structure can assure the connection reliability.
[0237] (8) Further, a plurality of thermocouples for temperature
control were fixed by silica sol and the silica sol was dried at
100.degree. C. for 1 hour to complete production of a ceramic
heater.
EXAMPLE 4
[0238] A ceramic heater was produced in this example in an
approximately same manner as Example 3, except the following
different points. That is, after a ceramic substrate bearing an
insulating layer was obtained in the step (5), the substrate was
ground with a diamond grind stone of #120 at 1 kg/cm.sup.2 load to
adjust the surface roughness to Ra=1.0 .mu.m.
[0239] Further, a heat transmission plate 42 made of a 1 mm-thick
aluminum plate was installed in the installation points of the
thermocouples and further through the heat transmission plate 42,
as shown in FIG. 4, sheaths S containing the thermocouple 44 were
brought into contact with the surface of the ceramic substrate by
springs 45.
EXAMPLE 5
[0240] A ceramic heater was produced in this example in an
approximately same manner as Example 1, except the following
different points. That is, after a ceramic substrate bearing an
insulating layer was obtained in the step (3), the substrate was
ground with a diamond grind stone of #220 at 1 kg/cm.sup.2 load and
successively polished with a polishing cloth (Malto Co.) and a
diamond paste (particle diameter of 0.1 .mu.m) to adjust the
surface roughness to Ra=0.0008 .mu.m.
EXAMPLE 6
[0241] A ceramic heater was produced in this example in an
approximately same manner as Example 1, except the following
different points. That is, after a ceramic substrate bearing an
insulating layer was obtained in the step (3), the substrate was
ground with a diamond grind stone of #100 at 1 kg/cm.sup.2 load to
adjust the surface roughness to Ra=1.5 .mu.m.
EXAMPLE 7
[0242] A ceramic heater was produced in this example in an
approximately same manner as Example 1, except the following
different points. That is, after a ceramic substrate bearing an
insulating layer was obtained in the step (3), the substrate was
ground with a diamond grind stone of #80 at 1 kg/cm.sup.2 load to
adjust the surface roughness to Ra=2.0 .mu.m.
EXAMPLE 8
[0243] A ceramic heater was produced in this example in an
approximately same manner as Example 1, except the following
different points. That is, after a ceramic substrate bearing an
insulating layer was obtained in the step (3), the substrate was
subjected to drilling in the face opposed to the face of the
substrate for heating an object to be heated such as a
semiconductor wafer and the like to form concave portions with a
diameter of 10 mm and further ground with a rod-like diamond grind
stone of #100 at 1 kg/cm.sup.2 load to adjust the surface roughness
to Ra=1.5 .mu.m.
[0244] Further, sheath-type thermocouples obtained by sheathing
K-type thermocouples together with magnesia and alumina in sheaths
made of a stainless steel were transversely set and fixed on the
bottom faces of the concave portions as shown in FIG. 7 while being
pressed by the aluminum plate and springs.
EXAMPLE 9
[0245] A ceramic heater was produced in this example in an
approximately same manner as Example 1, except the following
different points. That is, after a ceramic substrate bearing an
insulating layer was obtained in the step (3), the substrate was
subjected to drilling on the face opposed to the face of the
substrate for heating an object to be heated such as a
semiconductor wafer and the like to form concave portions with a
diameter of 10 mm and further ground with a rod-like diamond grind
stone of #50 at 1 kg/cm.sup.2 load to adjust the surface roughness
to Ra=3 .mu.m.
[0246] Further, sheath-type thermocouples obtained by sheathing
K-type thermocouples together with magnesia and alumina in sheaths
made of a stainless steel were transversely set and fixed on the
bottom faces of the concave portions as shown in FIG. 7 while being
pushed by the aluminum plate and springs.
EXAMPLE 10
[0247] A ceramic heater was produced in this example in an
approximately same manner as Example 1, except the following
different points. That is, after a ceramic substrate bearing an
insulating layer was obtained in the step (3), the substrate was
subjected to drilling in the face opposed to the face of the
substrate for heating an object to be heated such as a
semiconductor wafer and the like to form concave portions with a
diameter of 10 mm and further ground with a rod-like diamond grind
stone of #30 at 1 kg/cm.sup.2load to adjust the surface roughness
to Ra=5 .mu.m.
[0248] Further, sheath-type thermocouples obtained by sheathing
K-type thermocouples together with magnesia and alumina in sheaths
made of a stainless steel were transversely set and fixed on the
bottom faces of the concave portions as shown in FIG. 7 while being
pushed by the aluminum plate and springs.
EXAMPLE 11
[0249] A ceramic heater was produced in an approximately same
manner as Example 1, except that no surface polishing was carried
out. The surface roughness Ra of the obtained ceramic heater was
2.2 .mu.m.
COMPARATIVE EXAMPLE 1
[0250] A ceramic heater was produced in this example in an
approximately same manner as Example 1, except the following
different points. That is, after a ceramic substrate bearing an
insulating layer was obtained in the step (3), the substrate was
subjected to drilling in the face opposed to the face of the
substrate for heating an object to be heated such as a
semiconductor wafer and the like to form concave portions with a
diameter of 10 mm. At the time of drilling, the surface roughness
Ra was 5.5 .mu.m.
[0251] Further, sheath-type thermocouples obtained by sheathing
K-type thermocouples together with magnesia and alumina in sheaths
made of a stainless steel were transversely set and fixed on the
bottom faces of the concave portions as shown in FIG. 7 while being
pushed by the aluminum plate and springs.
[0252] <Performance Test>
[0253] The difference between the highest temperature and the
lowest temperature of the ceramic substrates of Example 1 to 11 and
Comparative Example 1 was investigated in the case that temperature
thereof was increased to 250.degree. C.
[0254] The equipment employed for the performance test was a
temperature control apparatus (E5ZE manufactured by Omron) equipped
with: a control unit having a power source; a computation unit. The
ceramic heaters produced in the respective examples were
controlled. Further, after the temperature increase to 250.degree.
C., a silicon wafer at 25.degree. C. was placed on each heating
face and the time taken until the temperature thereof recovered to
250.degree. C. was measured.
[0255] The results were shown in the following Table 1.
1TABLE 1 Temperature difference between the Surface highest Time
required roughness of temperature for recovering ceramic and the
lowest to original substrate temperature temperature (.mu.m)
(.degree. C.) (second) Example 1 0.01 0.5 35 Example 2 0.008 0.3 35
Example 3 0.6 0.5 35 Example 4 1.0 0.5 35 Example 5 0.0008 1.0 45
Example 6 1.5 0.6 35 Example 7 2.0 0.8 38 Example 8 1.5 (bottom 0.3
35 face of concave portion) Example 9 3.0 (bottom 0.6 35 face of
concave portion) Example 10 5.0 (bottom 0.8 38 face of concave
portion) Example 11 2.2 2.0 60 Comparative 5.5 6.5 80 Example 1
[0256] As being made clear from the above results shown in Table 1,
if Ra was lower than 0.001 .mu.m, it is considered that the contact
surface area with a thermocouple became too small, and thus the
response of the thermocouple deteriorated.
[0257] In Example 4, the thermocouples were brought into contact
through the aluminum plate and Ra was high, yet the respond was not
found deteriorating.
[0258] Further, in Examples 8 to 10, the contact surface area was
increased by making the thermocouples sheath-type and set
transversely, the contact surface area was widened to make more
accurate temperature measurement possible, so that the difference
between the highest temperature and the lowest temperature was
narrowed.
[0259] In the case the contact surface area was widened by making
the thermocouples sheath-type and set transversely, the temperature
control was possible if Ra was up to 5 .mu.m.
EXAMPLE 12
Manufacture of Ceramic Heater Made of Aluminum Nitride (Reference
to FIG. 1)
[0260] (1) A composition containing 100 parts by weight of an
aluminum nitride powder (the average particle diameter: 1.1 .mu.m),
4 parts by weight of yttria (the average particle diameter: 0.4
.mu.m), 12 parts by weight of an acrylic binder, and an alcohol was
spray dried to produce a granular powder.
[0261] (2) Next, the obtained granular powder was filled in a die
and molded to be a flat plate to obtain a raw formed body (a green
sheet). The raw formed body was processed by drilling to form
through holes 15 to insert lifter pins for a silicon wafer.
[0262] (3) On completion of the processing, the raw formed body was
hot pressed at 1800.degree. C. and a pressure of 200 kg/cm.sup.2 to
obtain a 3 mm thick aluminum nitride plate-like body. Next, a disk.
with a diameter of 12 inch (300 mm) was cut out of the plate-like
body (a ceramic substrate) 11. Further, a glass paste (G-5177
produced by Shouei Chemical Products Co., Ltd.) was applied to the
surface and heated to 1000.degree. C. to form a 2 .mu.m
thick-SiO.sub.2 film.
[0263] The ceramic substrate 11 was ground with a diamond grind
stone of #220 at 1 kg/cm.sup.2 load and polished with a polishing
cloth (Malto Co.) and a diamond paste (particle diameter of 0.5
.mu.m) to adjust the surface roughness to Ra=0.01 .mu.m.
Incidentally, the measurement of the surface roughness was carried
out by a probe type surface roughness meter (Surfcom 920A, Tokyo
Precision Co.).
[0264] (4) On the ceramic substrate 11 obtained as described above
(3), a conductor containing paste was printed by screen printing.
The printed pattern was made to be a concentric pattern as shown in
FIG. 1. As the conductor containing paste, Sorbest PS603D produced
by Tokuriki Chemical Research Co.,Ltd. used for a plated through
hole was used. The conductor containing paste was a silver-lead
paste and contained 7.5 parts by weight of metal oxides consisting
of lead oxide (5% by weight), zinc oxide (55% by weight), silica
(10% by weight), boron oxide (25% by weight), and alumina (5% by
weight) in 100 parts by weight of Ag. The silver particle had an
average particle diameter 4.5 .mu.m and a scaly shape.
[0265] (5) Next, the ceramic substrate 11 bearing the printed
conductor containing paste was heated and fired at 780.degree. C.
to sinter silver and lead in the conductor containing paste and
simultaneously bake them on the ceramic substrate 11 to form a
heating element 12. The silver-lead heating element 12 had a
thickness of 5 .mu.m, a width of 2.4 mm and an area resistivity of
7.7 m.OMEGA./.quadrature..
[0266] (6) Next, the ceramic substrate 11 produced as described in
(5) was immersed in an electroless nickel plating bath of an
aqueous solution containing 80 g/L of nickel sulfate, 24 g/L of
sodium hypophosphite, 12 g/L of sodium acetate, 8 g/L of boric
acid, and 6 g/L of ammonium chloride to deposit a 1 .mu.m-thick
metal covering layer (nickel layer) 24 on the surface of the
silver-lead heating element 12.
[0267] (7) To the portions where terminals for assuring the
connection with an electric power source, a silver-lead solder
paste (Tanaka Noble Metals.Co) was applied by screen printing to
form a solder layer. Then, terminal pins 13 made of Kovar were
attached on the solder layer and the solder was heated for reflow
at 420.degree. C. to attach the terminal pins 12 to the surface of
the heating element 12.
[0268] (8) Thermocouples (sheath-type thermocouple shown in FIG. 4)
for temperature control were brought into contact with the bottom
face of the ceramic substrate 11 through a heat transmission plate
42 made of a 2 mm-thick aluminum nitride plate in which dents were
formed. In this case, as shown in FIG. 6, coil springs 45 were
placed so as to insert the sheaths S containing the thermocouples 4
on an intermediate bottom plate 52 and pushed the sheaths with a
force of 2 kg to push up the projections formed on the sheaths S by
the coil spring 45, so that the sheath-type thermocouples were
brought into contact with the bottom face 11b of the ceramic
substrate 11 through the heat transmission plate 42 and thus the
production of the ceramic heater 10 was completed.
EXAMPLE 13
Manufacture of Ceramic Heater Made of Silicon Carbide
[0269] A ceramic heater made of silicon carbide was manufactured in
the same manner as Example 12, except that silicon carbide with an
average particle diameter of 1.0 .mu.m was used and the sintering
temperature was 1900.degree. C. and further, the obtained ceramic
substrate surface was fired at 1500.degree. C. for 2 hours to form
a 1 .mu.m-thick SiO.sub.2 layer on the surface.
[0270] The substrate was ground with a diamond grind stone of #220
at 1 kg/cm.sup.2 load and polished with a polishing cloth (Malto
Co.) and a diamond paste (particle diameter of 0.25 .mu.m) to
adjust the surface roughness to Ra=0.008 .mu.m.
[0271] Next, as shown FIG. 7, using leaf springs 60 made of Kovar,
sheaths S housing the thermocouples 44 were pushed against the
bottom face 11b of the ceramic substrate 11 by a force of 1 kg
through the heat transmission plate 42 made of a 2 mm-thick
aluminum plate in which dents were formed.
EXAMPLE 14
Manufacture of Ceramic Heater Containing Heating Element Inside
(Reference to FIG. 9)
[0272] (1) Using a paste produced by mixing an aluminum nitride
powder (the average particle diameter: 1.1 .mu.m produced by
Tokuyama), 4 parts by weight of yttria (the average particle
diameter: 0.4 .mu.m), 11.5 parts by weight of an acrylic binder,
0.5 parts by weight of a dispersant, and 53 parts by weight of
alcohol consisting of 1-butanol and ethanol, forming was carried
out by a doctor blade method to obtain a 0.47 mm green sheet.
[0273] (2) Successively, after the green sheet was dried at
80.degree. C. for 5 hours, portions to be through holes 15 with
diameters of 1.8 mm, 3.0 mm, and 5.0 mm to insert silicon wafer
lifter pins into and portions to be conductor-filled through holes
for connection with terminal pins were formed by punching.
[0274] (3) Next, a conductor containing paste A was produced by
mixing 100 parts by weight of a tungsten carbide particle with an
average particle diameter of 1 .mu.m, 3.0 parts by weight of an
acrylic binder, 3.5 parts by weight of .alpha.-terpineol solvent,
and 0.3 parts by weight of a dispersant.
[0275] Further, a conductor containing paste B was produced by
mixing 100 parts by weight of a tungsten carbide particle with an
average particle diameter of 1 .mu.m, 1.9 parts by weight of an
acrylic binder, 3.7 parts by weight of .alpha.-terpineol solvent,
and 0.2 parts by weight of a dispersant.
[0276] (4) Using the conductor containing paste A, printing on the
green sheet was carried out by a screen printing to form a
conductor containing paste layer. The printed pattern was made to
be a concentric pattern as shown in FIG. 1. Further, the through
holes for forming conductor-filled through holes for connection
with terminal pins were filled with the conductor containing paste
B. On the green sheet finished for the above-mentioned treatment,
37 green sheets and 13 green sheets with no printing with the
tungsten paste were laminated on the upper side (heating face) and
on the lower side, respectively, and laminated at 130.degree. C.
and 80 kg/cm.sup.2 pressure.
[0277] (5) The laminated body obtained in such a manner was
degreased at 600.degree. C. for 5 hours in nitrogen gas and hot
pressed at 1890.degree. C. and 150 kg/cm.sup.2 pressure for 3 hours
to obtain a 3 mm-thick aluminum nitride plate body. The obtained
plate-like body was cut into a disk-like shape with a diameter of
300 mm to obtain a plate-like body made of a ceramic containing a
heating element with a thickness of 6 .mu.m and a width of 10 mm
inside thereof.
[0278] A sol solution produced by hydrolysis polymerization of a
mixed solution containing 25 parts by weight of tetraethyl
silicate, 37.6 parts by weight of ethanol, and 0.3 parts by weight
of hydrochloric acid by stirring for 24 hours was applied by a spin
coating, dried at 80.degree. C. for 5 hours, and fired at
1000.degree. C. for 1 hour to form an insulating layer 500 of a 2
.mu.m-thick SiO.sub.2 film on the surface of the ceramic substrate
11.
[0279] (6) Next, the ceramic substrate was ground with a diamond
grind stone of #220 at 1 kg/cm.sup.2load to adjust the surface
roughness to Ra=0.6 .mu.m.
[0280] (7) After that, some portions of the through holes for
conductor-filled through holes were hollowed out to form concave
portions and using a gold braze of Ni-Au, terminal pins made of
Kovar were connected by conducting heating and reflowing of the
braze at 700.degree. C. Incidentally, the connection of the
terminal pins is preferable to have a supporting structure of
three-point support with tungsten supports. Because such a
structure can assure the connection reliability.
[0281] (8) Further, as shown in FIG. 6, by coil springs 45 arranged
on an intermediate bottom plate 52, sheaths S housing the
thermocouples 44 were pushed against and brought into contact with
the bottom face of the ceramic substrate 11 by 2 kg force through
the heat transmission plate 42 made of a 2 mm-thick aluminum plate
in which dents were formed and thus the production of the ceramic
heater 10 was completed.
EXAMPLE 15
[0282] This example was similar to Example 12, however different
from Example 12 in a point that, as shown in FIG. 12, the
thermocouples 74 were fixed by leaf springs 76 made of a stainless
steel and bolts 75. The pressing force was 8 mg (8.times.10.sup.-6
kg)
EXAMPLE 16
[0283] This example was similar to Example 12, however different
from Example 12 in a point that, as shown in FIG. 11, the
thermocouples 64 were fixed by presser plates 66 made of a
stainless steel and bolts 65. The pressing force was 15 kg.
EXAMPLE 17
[0284] This example was similar to Example 12, however different
from Example 12 in a point that, as shown in FIG. 11, the
thermocouples 64 were fixed by presser plates 66 made of a
stainless steel and bolts 65. The pressing force was 25 kg.
EXAMPLE 18
[0285] This example was similar to Example 12, however different
from Example 12 in a point that, as shown in FIG. 7, the substrate
was subjected to drilling on the face opposed to the wafer heating
face to form concave portions 95 with a diameter of 10 mm and
sheath-type thermocouples obtained by sheathing thermocouples 94
together with MgO and Al.sub.2O.sub.3 powder in sheaths 96 made of
a stainless steel were pushed through aluminum plates 92 by springs
93 arranged on the intermediate bottom plate 81 and pushed against
and fixed on the bottom face formed in the concave portions 95 of
the ceramic substrate 91. The pressing force was 1 kg.
COMPARATIVE EXAMPLE 2
[0286] A ceramic heater was produced in approximately same manner
as Example 12, however that thermocouples were fixed on the surface
of the ceramic substrate using an inorganic adhesive (Aron Ceramic
produced by Toagosei Chemical Industry Co., Ltd.) was the different
point from Example 12.
COMPARATIVE EXAMPLE 3
[0287] A ceramic heater was produced in approximately same manner
as Example 12, however that sheaths S housing the thermocouples 84
were stood in pipes 85 of the bottom plate 52 to only keep contact
with the ceramic substrate 11 was the different point. Although the
accurate measurement was difficult, the pressing force was supposed
to be 0.8 mg (0.8.times.10.sup.-6 kg) or less.
[0288] <Performance Test>
[0289] The ceramic heaters of Examples 12 to 18 and Comparative
Examples 2, 3 were heated to 250.degree. C. and occurrence of
dropping of the thermocouples after leaving them for 1000 hours was
investigated.
[0290] Further, ceramic heaters of Examples 12 to 18 and
Comparative Examples 2, 3 were heated to 200.degree. C. and a
silicon wafer was heated at a distance of 150 .mu.m from the
heating face and the difference between the highest temperature and
the lowest temperature of the silicon wafer was measured by a
thermo-viewer.
[0291] The results were shown in the following Table 2.
2 TABLE 2 Presence or Temperature Pressing force absence of
difference* (kg) dropping (.degree. C.) Example 12 2 Absence 0.2
Example 13 1 Absence 0.5 Example 14 2 Absence 0.3 Example 15 8
.times. 10.sup.-6 Absence 0.8 Example 16 15 Absence 0.8 Example 17
25 Absence 5.0 Example 18 1 Absence 0.1 Comparative -- Presence 0.5
Example 2 Comparative <0.8 .times. 10.sup.-6 Absence 5.0 Example
3 Note) *Temperature difference: temperature difference between the
highest temperature and the lowest temperature.
[0292] As a result, in the ceramic heaters of Examples 12 to 18, no
dropping of the thermocouples took place, whereas the ceramic
heater of Comparative Example 2, the thermocouple dropped. Further,
as the case of Examples 12 to 18 and Comparative Example 3, in the
case the temperature measurement elements were pressed on and
fixed, being different from that in the case of only being pressed
on, they did not drop. However, in the case the thermocouple was
firmly pressed on (Example 17) or kept so as to have only a contact
(Comparative Example 3), temperature correction was supposed to be
necessary. In the case that the thermocouples were pushed by a
force of 1.times.10.sup.-6 to 20 kg, such correction was supposed
to be unnecessary.
INDUSTRIAL APPLICABILITY
[0293] As described above, according to the ceramic heater for a
semiconductor producing/examining device of the first aspect of the
present invention, accurate temperature measurement of an object to
be heated is made possible and the whole body of a silicon wafer is
made possible to be heated evenly by adjusting the heating state of
the heating element based on the temperature measurement
result.
[0294] Also, by the ceramic heater for a semiconductor
producing/examining device of the second aspect of the present
invention, the temperature measurement element does not drop and
safety for a long duration can be retained and also, it is made
possible to accurately measure temperature thereof, so that the
whole body of a silicon wafer is made possible to be heated evenly
by adjusting the heating state of the heating element based on the
temperature measurement result.
* * * * *