U.S. patent application number 10/604514 was filed with the patent office on 2004-09-30 for wafer holder for semiconductor manufacturing device and semiconductor manufacturing device in which it is installed.
This patent application is currently assigned to SUMITOMO ELECTRIC INDUSTRIES, LTD.. Invention is credited to Hashikura, Manabu, Nakata, Hirohiko, Natsuhara, Masuhiro.
Application Number | 20040188321 10/604514 |
Document ID | / |
Family ID | 32984891 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040188321 |
Kind Code |
A1 |
Natsuhara, Masuhiro ; et
al. |
September 30, 2004 |
WAFER HOLDER FOR SEMICONDUCTOR MANUFACTURING DEVICE AND
SEMICONDUCTOR MANUFACTURING DEVICE IN WHICH IT IS INSTALLED
Abstract
Wafer holder and semiconductor manufacturing equipment in which
the holder is installed, the wafer holder having a wafer-carrying
surface, wherein incidence of warping and cracking when the wafer
holder is heated is slight. In the wafer holder having a
wafer-carrying surface, electrical circuitry consisting of one or
more sinter laminae is formed on the face or in the interior of the
wafer holder; and by rendering pores present in the circuitry, the
incidence of warping and cracking can be made very slight. The
electrical circuitry is preferably any of an electrode circuit for
an electrostatic chuck, a resistive-heating-element circuit, an
RF-power electrode circuit, and a high-voltage-generating electrode
circuit.
Inventors: |
Natsuhara, Masuhiro;
(Itami-shi, JP) ; Nakata, Hirohiko; (Itami-shi,
JP) ; Hashikura, Manabu; (Itami-shi, JP) |
Correspondence
Address: |
JUDGE PATENT FIRM
RIVIERE SHUKUGAWA 3RD FL.
3-1 WAKAMATSU-CHO
NISHINOMIYA-SHI, HYOGO
662-0035
JP
|
Assignee: |
SUMITOMO ELECTRIC INDUSTRIES,
LTD.
5-33 Kitahama 4-chome Chuo-ku
Osaka-shi
JP
|
Family ID: |
32984891 |
Appl. No.: |
10/604514 |
Filed: |
July 28, 2003 |
Current U.S.
Class: |
206/713 |
Current CPC
Class: |
H01L 21/67103 20130101;
H01L 21/6831 20130101 |
Class at
Publication: |
206/713 |
International
Class: |
B65D 085/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 2003 |
JP |
JP-2003-079324 |
Claims
What is claimed is:
1. A wafer holder for semiconductor manufacturing equipment, the
wafer holder having a surface for carrying wafers and comprising a
layer of electrical circuitry composed of one or more sinter
laminae, formed either on the face or in the interior of the wafer
holder, said circuit layer having porosity in that pores are
present therein.
2. A wafer holder as set forth in claim 1, wherein: said circuit
layer is as its main constituent one or more metals selected from
tungsten, molybdenum and tantalum; and said porosity is 0.1% or
more.
3. A wafer holder as set forth in claim 1, wherein: said circuit
layer is as its main constituent one or more metals selected from
silver, vanadium and platinum; and said porosity is 2% or more.
4. A wafer holder as set forth in claim 2, wherein said electrical
circuitry any of an electrode circuit for an electrostatic chuck, a
resistive-heating-element circuit, an RF-power electrode circuit,
and a high-voltage-generating electrode circuit.
5. A wafer holder as set forth in claim 3, wherein said electrical
circuitry any of an electrode circuit for an electrostatic chuck, a
resistive-heating-element circuit, an RF-power electrode circuit,
and a high-voltage-generating electrode circuit.
6. Semiconductor manufacturing equipment wherein the wafer holder
set forth in claim 1 is installed.
7. Semiconductor manufacturing equipment wherein the wafer holder
set forth in claim 2 is installed.
8. Semiconductor manufacturing equipment wherein the wafer holder
set forth in claim 3 is installed.
9. Semiconductor manufacturing equipment wherein the wafer holder
set forth in claim 4 is installed.
10. Semiconductor manufacturing equipment wherein the wafer holder
set forth in claim 5 is installed.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to wafer holders employed in
semiconductor manufacturing devices such as plasma-assisted CVD,
low-pressure CVD, metal CVD, dielectric-film CVD, ion-implantation,
etching, Low-K film heat treatment, and degassing heat treatment
device, and furthermore to process chambers and semiconductor
manufacturing devices in which the wafer holders are installed.
[0003] 2. Description of the Background Art
[0004] Conventionally, in semiconductor manufacturing procedures
various processes such as film deposition processes and etching
processes are carried out on semiconductor substrates that are the
processed objects. Ceramic susceptors that retain such
semiconductor substrates in order to heat them are used in the
processing devices in which the processes on the semiconductor
substrates are carried out.
[0005] Japanese Pat. App. Pub. No. H04-78138 for example discloses
a conventional ceramic susceptor of this sort. The ceramic
susceptor includes: a heater part made of ceramic, into which a
resistive heating element is embedded and that is provided with a
wafer-heating surface, arranged within a chamber; a columnar
support part that is provided on a surface apart from the
wafer-heating surface of the heating section and that forms a
gastight seal between it and the chamber; and electrodes connected
to the resistive heating element and leading outside the chamber so
as essentially not to be exposed to the chamber interior space.
[0006] Although the invention serves to remedy the contamination
and poor thermal efficiency that had been seen with heaters made of
metal--heaters prior to the invention--it does not touch upon
warping of or cracking in ceramic susceptors. Wafers are processed
at high temperatures in semiconductor manufacturing equipment,
however, which means that the ceramic susceptors are heated to high
temperatures. Given the circumstances, a problem has been that
warping in the ceramic susceptor, arising in the thermal
characteristics of its electrical circuitry, will occur, leading to
breaches in between the wafer and the wafer-retaining face and
making it improbable that the temperature of the wafer face will be
uniform. Should the temper of the wafer face turn out to be
non-uniform, in situations where a film-deposition process is
performed, irregularities in the thickness and quality of the thin
film formed on the wafer face will appear; in situations in which
an etching process is carried out, trouble such as fluctuations in
the etching speed will occur.
[0007] In this regard, Japanese Pat. App. Pub. No. 2001-302330
discloses a technique for resolving the problems of warping and
cracking in ceramic substrates. The invention has it that by
strictly controlling the thickness of both the ceramic substrate
and the electrical circuitry, warping and cracking in the ceramic
substrate can be prevented. Nevertheless, with strict control of
the thickness of the ceramic substrate and the electrical circuitry
layer meaning higher costs, it has been difficult to realize
inexpensive ceramic susceptors. As to electrical circuits,
moreover, there are various kinds; and depending on what they are
targeted for, there are various circuit patterns. For example, with
resistive heating element circuits, the configuration would be a
coil; with RF electrode circuits, the configuration would be a
continuous single-ply sheet. Thus, wherein a plurality of
electrical circuits that differ in configuration is formed on the
face and in the interior of the wafer holder, on account of their
configurations, the respective circuits will give rise to
differences in the extent to which they cause the wafer holder to
expand thermally.
[0008] By the same token, a difference in extent of thermal
expansion also arises between the circuits and the wafer-holder
ceramic, since there is a difference between them in thermal
expansion coefficient. The result is that internal stress caused by
the differences in degree of thermal expansion is produced in the
wafer holder, giving rise to warping and cracking. With methods as
in Japanese Pat. App. Pub. No. 2001-302330 of strictly controlling
the thickness of the ceramic substrate and the electrical
circuitry, in cases where as just mentioned several electrical
circuits are fashioned in a wafer holder, costs end up going even
higher.
SUMMARY OF INVENTION
[0009] The present invention has been brought about to address the
foregoing issues. In particular, an object of the present invention
is to realize for semiconductor manufacturing equipment a wafer
holder in which incidence of warping and cracking is slight when
heated to high temperatures, and semiconductor manufacturing
equipment in which the wafer holder is installed.
[0010] In a wafer holder having a wafer-carrying surface according
to the present invention, an electrical circuit layer consisting of
one or more sinter laminae is formed on the face or in the interior
of the wafer holder, which is characterized in that pores are
present in the circuit layer. It is preferable that the main
constituent of the circuit layer be one or more metals selected
from tungsten, molybdenum and tantalum, and that the porosity
thereof be 0.1% or more. It is alternatively preferable that the
main constituent of the circuit layer be one or more metals
selected from silver, vanadium and platinum, and that the porosity
thereof be 2% or more.
[0011] Also preferable is that the electrical circuitry be any one,
or a plurality, of: an electrode circuit for an electrostatic
chuck, a resistive-heating-element circuit, an RF-power electrode
circuit, and a high-voltage-generating electrode circuit; more
preferable is that the circuitry include at least a
resistive-heating-element circuit.
[0012] In a semiconductor manufacturing device in which a wafer
holder as in the foregoing is installed, inasmuch as incidence of
warping and cracking in the wafer holder is slight, the temperature
of a wafer that is being processed proves to be more uniform than
what has been conventional, making for better-throughput
manufacturing of semiconductors.
[0013] From the following detailed description in conjunction with
the accompanying drawings, the foregoing and other objects,
features, aspects and advantages of the present invention will
become readily apparent to those skilled in the art.
BRIEF DESCRIPTION OF DRAWINGS
[0014] The FIGURE illustrates one example of the sectional
structure of a wafer holder according to the present invention.
DETAILED DESCRIPTION
[0015] The present inventors discovered that imparting pores in
electrical circuitry made of a sinter, formed on the face or in the
interior of the wafer holder, and controlling the porosity thereof
makes for preventing warping and cracking in the wafer holder.
[0016] The electrical circuitry may be circuits such as an
electrostatic-chuck electrode circuit for electrostatically
chucking wafers, a resistive-heating-element circuit (heater
circuit) for heating the wafer holder, or an RF electrode circuit
for generating plasma, and furthermore may be a high-voltage
circuit for ion-beam irradiation. While the circuitry preferably is
equipped at least with a resistive-heating-element circuit, it may
be equipped with a resistive-heating-element circuit and at the
same time another circuit--for example, so as to be equipped with a
resistive-heating-eleme- nt circuit 2 and an RF electrode circuit 3
as illustrated in the figure.
[0017] Conventionally it has been maintained that the more
densified the circuitry, formed by calcining an ordinary metal
powder, the better it is. On the contrary, it was discovered that
imparting pores (or bubbles, voids, cavities, etc.) to the
circuitry is effective for absorbing the aforementioned differences
in degree of thermal expansion to prevent warping and cracking in
the wafer holder.
[0018] In particular, if the circuitry is the usual densified
material, when it has expanded thermally internal stress will be
produced, and warping will arise, by just that difference with the
ceramic in the extent of its thermal expansion. If, however, pores
are present in the circuitry, the pores presumably absorb the
difference in thermal expansion, mitigating the internal stress.
Mitigating the internal stress would be what can prevent the
occurrence of warping. It will be realized that the occurrence of
warping can be prevented inasmuch as the internal stress is
mitigated.
[0019] Wherein the main constituent of the circuitry is made one or
more metals selected from tungsten, molybdenum and tantalum, the
porosity should be 0.1% or more. Likewise, wherein the main
constituent of the circuitry is made one or more metals selected
from silver, vanadium and platinum, the porosity should be 2% or
more.
[0020] That a difference in porosity will appear depending on what
the metal substance is in the circuitry reflects the disparity in
how great the difference between the thermal expansion coefficient
of the metal and of the ceramic is. Wherein the main constituent is
made tungsten, molybdenum and tantalum, whose differences in
thermal expansion coefficient with ceramics are slight, the effects
described above will be brought out if the porosity is at least
0.1%. Wherein the main constituent of the circuitry is made one or
more metals selected from silver, vanadium and platinum, whose
differences in thermal expansion coefficient with ceramics are
great, if the porosity is not made a considerable 2% or more, the
effects will not appear.
[0021] While the effects according to the present invention can be
gained if the porosity is a predetermined amount as just stated or
greater, since the electrical resistance of the circuitry will
become too high if the porosity is too large, it should be made
some 40% or less.
[0022] Insofar as the substances for a wafer holder according to
the present invention are insulative ceramics, they are not
particularly restricted, but aluminum nitride (AlN) is preferable
for its high thermal conductivity and superior corrosion
resistance. In the following, a method according to the present
invention of manufacturing a wafer holder in a AlN instance will be
described in detail.
[0023] An AlN raw-material powder whose specific surface area is
2.0 to 5.0 m.sup.2/g is preferable. The sinterability of the
aluminum nitride declines if the specific surface area is less than
2.0 m.sup.2/g. Handling proves to be a problem if on the other hand
the specific surface area is over 5.0 m.sup.2/g, because the powder
coherence becomes extremely strong. Furthermore, the quantity of
oxygen contained in the raw-material powder is preferably 2 wt. %
or less. In sintered form, its thermal conductivity deteriorates if
the oxygen quantity is in excess of 2 wt. %. It is also preferable
that the amount of metal impurities contained in the raw-material
powder other than aluminum be 2000 ppm or less. The thermal
conductivity of the powder in sintered form deteriorates if the
amount of metal impurities exceeds this range. In particular, the
content respectively of Group IV elements such as Si, and elements
of the iron family, such as Fe, which have a serious worsening
effect on the thermal conductivity of the sinter, is advisably 500
ppm or less.
[0024] Because AlN is not a readily sinterable material, adding a
sintering promoter to the AlN raw-material powder is advisable. The
sintering promoter added preferably is a rare-earth element
compound. Since rare-earth element compounds react with aluminum
oxides or aluminum oxynitrides present on the surface of the
particles of the aluminum nitride powder, acting to promote
densification of the aluminum nitride and to eliminate oxygen being
a causative factor that worsens the thermal conductivity of an
aluminum nitride sinter, they enable the thermal conductivity of
aluminum sinters to be improved.
[0025] Yttrium compounds, whose oxygen-eliminating action is
particularly pronounced, are preferable rare-earth element
compounds. The amount added is preferably 0.01 to 5 wt. %. If less
than 0.01 wt. %, producing ultrafine sinters is problematic, along
with which the thermal conductivity of the sinters deteriorates.
Added amounts in excess of 5 wt. % on the other hand lead to
sintering promoter being present at the grain boundaries in an
aluminum nitride sinter, and consequently, if the aluminum nitride
sinter is employed under a corrosive atmosphere, the sintering
promoter present along the grain boundaries gets etched, becoming a
source of loosened grains and particles. More preferably the amount
of sintering promoter added is 1 wt. % or less. If less than 1 wt.
% sintering promoter will no longer be present even at the grain
boundary triple points, which improves the corrosion
resistance.
[0026] To characterize the rare-earth compounds further: oxides,
nitrides, fluorides, and stearic oxide compounds may be employed.
Among these oxides, being inexpensive and readily obtainable, are
preferable. By the same token, stearic oxide compounds are
especially suitable since they have a high affinity for organic
solvents, and if the aluminum nitride raw-material powder,
sintering promoter, etc. are to be mixed together in an organic
solvent, the fact that the sintering promoter is a stearic oxide
compound will heighten the miscibility.
[0027] Next, the aluminum nitride raw-material powder, sintering
promoter as a powder, a predetermined volume of solvent, a binder,
and further, a dispersing agent or a coalescing agent added as
needed, are mixed together. Possible mixing techniques include
ball-mill mixing and mixing by ultrasound. Mixing can thus produce
a raw material slurry.
[0028] The obtained slurry can be molded, and by sintering the
molded product, an aluminum nitride sinter can be produced.
Co-firing and post-metallization are two possible methods as a way
of doing this.
[0029] Post-metallization will be described first. Granules are
prepared from the slurry by means of a technique such as
spray-drying. The granules are inserted into a predetermined mold
and subject to press-molding. The pressing pressure therein
desirably is 0.1 t/cm.sup.2 or more. With pressure less than 0.1
t/cm.sup.2, in most cases sufficient strength in the molded mass
cannot be produced, making it liable to break in handling.
[0030] Although the density of the molded mass will differ
depending on the amount of binder contained and on the amount of
sintering promoter added, preferably it is 1.5 g/cm.sup.3 or more.
Densities less than 1.5 g/cm.sup.3 would mean a relatively large
distance between particles in the raw-material powder, which would
hinder the progress of the sintering. At the same time, the molded
mass density preferably is 2.5 g/cm.sup.3 or less. Densities of
more than 2.5 g/cm.sup.3 would make it difficult to eliminate
sufficiently the binder from within the molded mass in a degreasing
process of a subsequent step. It would consequently prove difficult
to produce an ultrafine sinter as described earlier.
[0031] Next, heating and degreasing processes are carried out on
the molded mass within a non-oxidizing atmosphere. Carrying out the
degreasing process under an oxidizing atmosphere such as air would
degrade the thermal conductivity of the sinter, because the AlN
powder would become superficially oxidized. Preferable
non-oxidizing ambient gases are nitrogen and argon. The heating
temperature in the degreasing process is preferably 500.degree. C.
or more and 1000.degree. C. or less. With temperatures of less than
500.degree. C., surplus carbon is left remaining within the
laminate following the degreasing process because the binder cannot
sufficiently be eliminated, which interferes with sintering in the
subsequent sintering step. On the other hand, at temperatures of
more than 1000.degree. C., the ability to eliminate oxygen from the
oxidized coating superficially present on the surface of the AlN
powder deteriorates, such that the amount of carbon left remaining
is too little, degrading the thermal conductivity of the
sinter.
[0032] The amount of carbon left remaining within the molded mass
after the degreasing process is preferably 1.0 wt. % or less. If
carbon in excess of 1.0 wt. % remains, it will interfere with the
sintering, which would mean that ultrafine sinters could not be
produced.
[0033] Next, sintering is carried out. The sintering is carried out
within a non-oxidizing nitrogen, argon, or like atmosphere, at a
temperature of 1700 to 2000.degree. C. Therein the moisture
contained in the ambient gas such as nitrogen that is employed is
preferably -30.degree. C. or less given in dew point. If it were to
contain more moisture than this, the thermal conductivity of the
sinter would likely be degraded, because the AlN would react with
the moisture within the ambient gas during sintering and form
nitrides. Another preferable condition is that the volume of oxygen
within the ambient gas be 0.001 vol. % or less. A larger volume of
oxygen would lead to a likelihood that the AlN would oxidize,
impairing the sinter thermal conductivity.
[0034] As another condition during sintering, the jig employed is
suitably a boron nitride (BN) molded part. Inasmuch as the jig as a
BN molded part will be sufficiently heat resistant against the
sintering temperatures, and superficially will have solid
lubricity, when the laminate contracts during sintering, friction
between the jig and the laminate will be lessened, which will
enable sinters to be produced with little distortion.
[0035] The obtained sinter is subjected to processing according to
requirements. In cases where a conductive paste is to be
screen-printed onto the sinter in a succeeding step, the surface
roughness is preferably 5 .mu.m or less in Ra. If over 5 .mu.m, in
screen printing to form circuits, defects such as blotting or
pinholes in the pattern are liable to arise. More suitable is a
surface roughness of 1 .mu.m or less in Ra.
[0036] In polishing to the abovementioned surface roughness,
although cases in which both sides of the sinter are screen printed
are a matter of course, even in cases where screen printing is
effected on one side only the polishing process is best carried out
on the face on the side opposite the screen-printing face. This is
because polishing only the screen-printing face would mean that
during screen printing, the sinter would be supported on the
unpolished face, and in that situation burrs and debris would be
present on the unpolished face, destabilizing the fixedness of the
sinter such that the circuit pattern by the screen printing might
not be drawn well.
[0037] Furthermore, at this point the thickness uniformity
(parallelism) between the processed faces is preferably 0.5 mm or
less. Thickness uniformity exceeding 0.5 mm can lead to large
fluctuations in the thickness of the conductive paste during screen
printing. Particularly suitable is a thickness uniformity of 0.1 mm
or less. Another preferable condition is that the planarity of the
screen-printing face be 0.5 mm or less. If the planarity exceeds
0.5 mm, in that case too there can be large fluctuations in the
thickness of the conductive paste during screen printing.
Particularly suitable is a planarity of 0.1 mm or less.
[0038] Screen printing is used to spread a conductive paste and
form the electrical circuits onto a sinter having undergone the
polishing process. The conductive paste can be obtained by mixing
together with a metal powder an oxide powder, a binder, and a
solvent according to requirements. The metal powder is preferably
tungsten (W), molybdenum (Mo) or tantalum (Ta), since their thermal
expansion coefficients match those of ceramics.
[0039] Adding the oxide powder to the conductive paste is also to
enhance the strength with which it bonds to AlN. The oxide powder
preferably is an oxide of Group IIa or Group IIIa elements, or is
Al.sub.2O.sub.3, SiO.sub.2, or a like oxide. Yttrium oxide is
especially preferable because it has very good wettability with
AlN. The amount of such oxides added is preferably 0.1 to 30 wt. %.
If the amount is less than 0.1 wt. %, the bonding strength between
AlN and the metal layer being the circuit that has been formed
deteriorates.
[0040] On the other hand, amounts in excess of 30 wt. % make the
electrical resistance of the circuit metal layer high.
[0041] The metal powder may also have as its main constituent one
or more selected from silver, vanadium and platinum.
[0042] Ag system metals such as Ag--Pd or Ag--Pt are, to be
specific, preferable. In that case the electrical resistance can be
controlled by adjusting the content of the vanadium (Pd) or
platinum (Pt). Oxide powder can also be added, likewise as the case
with the tungsten, etc. In this case, the amount added of such
oxides is preferably 1 wt. % or more, 30 wt. % or less.
[0043] A predetermined circuit pattern is fashioned by screen
printing a paste prepared by mixing the metal powders together and
adding a binder and a solvent. Therein, the thickness of the
conductive paste is preferably 5.mu.m or more and 100 .mu.m or less
in terms of it post-drying thickness. If the thickness were less
than 5 .mu.m the electrical resistance would be too high and the
bonding strength decline. Likewise, if in excess of 100 .mu.m the
bonding strength would deteriorate in that case too.
[0044] Also preferable is that in the patterns for the circuits
that are formed, in the case of the heater circuit (resistive
heating element circuit), the pattern spacing be 0.1 mm or more.
With a spacing of less than 0.1 mm, shorting will occur when
current flows in the resistive heating element and, depending on
the applied voltage and the temperature, leakage current is
generated. Particularly in cases where the circuit is employed at
temperatures of 500.degree. C. or more, the pattern spacing
preferably should be 1 mm or more; more preferable still is that it
be 3 mm or more.
[0045] After the conductive paste is degreased, baking follows.
Degreasing is carried out within a non-oxidizing nitrogen, argon,
or like atmosphere. The degreasing temperature is preferably
500.degree. C. or more. At less than 500.degree. C., elimination of
the binder from the conductive paste is inadequate, leaving behind
carbon in the metal layer that during baking will form carbides
with the metal and consequently raise the electrical resistance of
the metal layer.
[0046] The baking is suitably done within a non-oxidizing nitrogen,
argon, or like atmosphere at, in the case of W, Mo or Ta, a
temperature of 1500.degree. C. or more. At temperatures of less
than 1500.degree. C., the post-baking electrical resistance of the
metal layer turns out too high because the baking of the metal
powder within the paste does not proceed to the grain growth stage.
A further baking parameter is that the baking temperature should
not surpass the firing temperature of the ceramic produced. If the
conductive paste is baked at a temperature beyond the firing
temperature of the ceramic, dispersive volatilization of the
sintering promoter incorporated within the ceramic sets in, and
moreover, grain growth in the metal powder within the conductive
paste is accelerated, impairing the bonding strength between the
ceramic and the metal layer.
[0047] In the case of Ag-system metals, furthermore, the baking
temperature is preferably 700.degree. C. to 1000.degree. C. As far
as the baking atmosphere is concerned, the baking can be carried
out in air or in nitrogen. In this case the foregoing degreasing
process can be omitted.
[0048] If the baking temperature is made high, the porosity of the
electrical circuitry is decreased; it becomes greater if the baking
is done at a lower temperature. Moreover, the porosity can also be
adjusted depending on the amount of the binder and solvent added.
Irrespective of the way in which the porosity is adjusted, effects
according to the present invention are not influenced.
[0049] In order to ensure that the metal layer is electrically
isolated, an insulative coating can be formed on the metal layer.
Preferably the insulative coating substance is the same substance
as the ceramic on which the metal layer is formed. Problems such as
post-sintering warpage arising from the difference in thermal
expansion coefficient will occur if the ceramic and insulative
coating substances differ significantly. For example, in a case
where the ceramic is AlN, a predetermined amount of an
oxide/carbide of a Group IIa element or a Group IIIa element can be
added to and mixed together with AlN powder, a binder and a solvent
added and the mixture rendered into a paste, and the paste can be
screen-printed to spread it onto the metal layer.
[0050] In that case, the amount of sintering promoter added
preferably is 0.01 wt. % or more. With an amount less than 0.01 wt.
% the insulative coating does not densify, making it difficult to
secure electrical isolation of the metal layer. It is further
preferable that the amount of sintering promoter not exceed 20 wt.
%. Surpassing 30 wt. % leads to excess sintering promoter invading
the metal layer, which can end up altering the metal-layer
electrical resistance. Although not particularly limited, the
spreading thickness preferably is 5 .mu.m or more. This is because
securing electrical isolation proves to be problematic at less than
5 .mu.m.
[0051] Further according to the present method, the ceramic as
substrates can be laminated according to requirements. Lamination
may be done via an adhesive agent. The adhesive agent--being a
compound of Group IIa or Group IIIa elements, and a binder and
solvent, added to an aluminum oxide powder or aluminum nitride
powder and made into a paste--is spread onto the bonding surface by
a technique such as screen printing. The thickness of the applied
adhesive agent is not particularly restricted, but preferably is 5
.quadrature.m or more. Bonding defects such as pin-holes and
bonding irregularities are liable to arise in the adhesive layer
with thicknesses of less than 5 .mu.m.
[0052] The ceramic substrates onto which the adhesive agent has
been spread are degreased within a non-oxidizing atmosphere at a
temperature of 500.degree. C. or more. The ceramic substrates are
thereafter bonded to one another by stacking the ceramic substrates
together, applying a predetermined load to the stack, and heating
it within a non-oxidizing atmosphere. The load preferably is 0.05
kg/cm.sup.2 or more. With loads of less than 0.05 kg/cm.sup.2
sufficient adhesive strength will not be obtained, and otherwise
defects in the joint will likely occur.
[0053] Although the heating temperature for bonding is not
particularly restricted as long as it is a temperature at which the
ceramic substrates adequately bond to one another via the adhesive
layers, preferably it is 1500.degree. C. or more. At less than
1500.degree. C. adequate adhesive strength proves difficult to
gain, such that defects in the bond are liable to arise. Nitrogen
or argon is preferably employed for the non-oxidizing atmosphere
during the degreasing and boding just discussed.
[0054] A ceramic laminated sinter that serves as a wafer holder
thus can be produced as in the foregoing. As far as the electrical
circuits are concerned, it should be understood that if they are
heater circuits for example, then a molybdenum coil can be
utilized, and in the electrostatic-chuck electrode and RF electrode
cases, molybdenum or tungsten mesh can be, without employing
conductive paste.
[0055] In this case, the molybdenum coil or the mesh can be built
into the AlN raw-material powder, and the wafer holder can be
fabricated by hot pressing. While the temperature and atmosphere in
the hot press may be on par with the AlN sintering temperature and
atmosphere, the hot press desirably applies a pressure of 10
kg/cm.sup.2 or more. With pressure of less than 10 kg/cm.sup.2, the
wafer holder might not exhibit its capabilities, because gaps arise
between the AlN and the molybdenum coil or the mesh.
[0056] Co-firing will now be described. The earlier-described
raw-material slurry is molded into a sheet by doctor blading. The
sheet-molding parameters are not particularly limited, but the
post-drying thickness of the sheet advisably is 3 mm or less. The
sheet thickness surpassing 3 mm leads to large shrinkage in the
drying slurry, raising the probability that fissures will be
generated in the sheet.
[0057] A metal layer of predetermined form that serves as an
electrical circuit is formed onto the abovementioned sheet using a
technique such as screen printing to spread onto it a conductive
paste. The conductive paste utilized can be the same as that which
was descried under the post-metallization method. Nevertheless, not
adding an oxide powder to the conductive paste does not hinder the
cofiring method.
[0058] Subsequently, sheets that have undergone circuit formation
are laminated with sheets that have not. Lamination is by setting
the sheets each into position to stack them together. Therein,
according to requirements, a solvent is spread on between sheets.
In the stacked state, the sheets are heated as may be necessary. In
cases where the stack is heated, the heating temperature is
preferably 150.degree. C. or less. Heating to temperatures in
excess of this greatly deforms the laminated sheets. Pressure is
then applied to the stacked-together sheets to unitize them. The
applied pressure is preferably within a range of from 1 to 100 MPa.
At pressures less than 1 MPa, the sheets are not adequately
unitized and can peel apart during subsequent processes. Likewise,
if pressure in excess of 100 MPa is applied, the extent to which
the sheets deform becomes too great.
[0059] This laminate undergoes a degreasing process as well as
sintering, in the same way was with the post-metallization method
described earlier. Parameters such as the temperature in degreasing
and sintering and the amount of carbon are the same as with
post-metallization. In the previously described screen printing of
a conductive paste onto sheets, a wafer holder having a plurality
of electrical circuits can be readily fabricated by printing heater
circuits, electrostatic-chuck electrodes, etc. respectively onto a
plurality of sheets and laminating them. In this way a ceramic
laminated sinter that serves as a wafer holder can be produced.
[0060] The obtained ceramic laminated sinter is subject to
processing according to requirements. Routinely with semi-conductor
manufacturing devices, in the sintered state the ceramic laminated
sinter often cannot be gotten into the precision demanded. The
planarity of the wafer-carrying surface as an example of processing
precision is preferably 0.5 mm or less; moreover 0.1 mm or less is
particularly preferable. The planarity surpassing 0.5 mm is apt to
give rise to gaps between the wafer and the wafer holder, keeping
the heat of the wafer holder from being uniformly transmitted to
the wafer and making likely the generation of temperature
irregularities in the wafer.
[0061] A further preferable condition is that the surface roughness
of the wafer-carrying surface be 5 .quadrature.m in Ra. If the
roughness is over 5 .quadrature.m in Ra, grains loosened from the
AlN due to friction between the wafer holder and the wafer can grow
numerous. Particles loosened in that case become contaminants that
have a negative effect on processes, such as film deposition and
etching, on the wafer. Furthermore, then, a surface roughness of 1
.mu.m or less in Ra is ideal.
[0062] A wafer holder base part can thus be fabricated as in the
foregoing. Furthermore, a shaft is attached to the wafer holder.
Although the shaft substance is not particularly limited as long as
its thermal expansion coefficient is not appreciably different from
that of the wafer-holder ceramic, the difference in thermal
expansion coefficient between the shaft substance and the wafer
holder preferably is 5.times.10.sup.-6 K or less.
[0063] If the difference in thermal expansion coefficient exceeds
5.times.10.sup.-6 K, cracks can arise adjacent the joint between
the wafer holder and the shaft when it is being attached; but even
if cracks do not arise when the two are joined, splitting and
cracking can occur in the joint in that it is put through heating
cycling in the course of being repeatedly used. For cases in which
the wafer holder is AlN, for example, the shaft substance is
optimally AlN; but silicon nitride, silicon carbide, or mullite can
be used.
[0064] Mounting is joining via an adhesive layer. The adhesive
layer constituents preferably are composed of AlN and
Al.sub.2O.sub.3, as well as rare-earth oxides. These constituents
are preferable because of their favorable wettability with ceramics
such as the AlN that is the substance of the wafer holder and the
shaft, which makes the joint strength relatively high, and readily
produces a gastight joint surface. The planarity of the respective
joining faces of the shaft and wafer holder to be joined preferably
is 0.5 mm or less. Planarity greater than this makes gaps liable to
occur in the joining faces, impeding the production of a joint
having adequate gastightness. A planarity of 0.1 mm or less is more
suitable. Here, still more suitable is a planarity of the wafer
holder joining faces of 0.02 mm or less. Likewise, the surface of
the respective joining faces preferably is 5 .mu.m or less in Ra.
Surface roughness exceeding this would then also mean that gaps are
liable to occur in the joining faces. A surface roughness of 1
.mu.m or less in Ra is still more suitable.
[0065] Subsequently, electrodes are attached to the wafer holder.
The attaching can be done according to publicly known techniques.
For example, the side of the wafer holder opposite its
wafer-retaining face, may be spot faced through to the electrical
circuits, and metallization carried out on the circuit, or without
metallizing, electrodes of molybdenum, tungsten, etc. may be
connected to it directly using an active metal brazing material.
The electrodes can thereafter be plated as needed to improve their
resistance to oxidation. In this way, a wafer holder for
semiconductor manufacturing devices can be fabricated.
[0066] Moreover, semiconductor wafers can be processed on a wafer
holder according to the present invention, assembled into a
semiconductor manufacturing device. Inasmuch as incidence of
warping and cracking when heating is kept under control,
manufacturing conditions are stabilized, making better-throughput
processing of semiconductor wafers possible. Keeping warping and
cracking under control makes it possible to gain stabilized
characteristics in terms of the films formed and the heating
processes.
Embodiments
[0067] Embodiment 1
[0068] A slurry was prepared by mixing 99 parts by weight aluminum
nitride powder and 1 part by weight Y.sub.2O.sub.3 powder, and
blending into the mixture 10 parts by weight polyvinyl butyral as a
binder and 5 parts by weight dibutyl phthalate as a solvent. Here,
an aluminum nitride powder having a mean particle diameter of 0.6
.mu.m and a specific surface area of 3.4 m.sup.2/g was utilized.
The slurry was rendered into granules using a spray dryer; and the
granules were inserted into a mold and molded, degreased at
850.degree. C., and then sintered at 1900.degree. C. Here the
atmosphere when degreasing and sintering was made a nitrogen
atmosphere. The top and bottom sides as well as the perimeter of
the sinters were processed to produce 345 mm outer diameter, 5 mm
thickness AlN sinters.
[0069] In addition, a tungsten paste was prepared by adding ethyl
cellulose as a binder and butyl Carbitol.TM. as a solvent to, and
mixing together with: 98.8 weight % of a tungsten powder whose mean
particle diameter was 2.0 .quadrature.m, 0.6 weight % Y
.sub.2O.sub.3, and 0.6 weight % Al.sub.2O.sub.3. A pot mill and a
triple-roller mill were used for mixing. This tungsten paste was
formed into a pattern for a heater circuit by screen-printing the
paste onto the AlN sinters.
[0070] Electrical circuits of differing porosity were prepared by
degreasing at 800.degree. C. under a nitrogen atmosphere the AlN
sinters printed with the heater circuits, and then baking them at
temperatures of from 1800.degree. C. to 1900.degree. C. as set
forth in Table I. Wafer holders were prepared by stacking a
plurality of layers of AlN sinters not fashioned with electrical
circuitry on the AlN sinters on which the heater circuit was
formed, and laminating the stack together using a
Al2O3-Y.sub.2O.sub.3--AlN as a bonding agent. A polishing process
was performed on the wafer-retaining face of the wafer holders so
that it would be 1 .quadrature.m or less in Ra, and on the
shaft-joining face so that it would be 5 .quadrature.m or less in
Ra. The wafer holders were also processed to true their outer
diameter. The dimensions of the post-processing wafer holders were
340 mm outside diameter and 16 mm thickness.
[0071] A shaft made of AlN, 80 mm in outside diameter, 60 mm inside
diameter, and 300 mm in length was then mounted onto the face on
the side of the wafer holders opposite the wafer-retaining face.
The bonding agent was 50% Al.sub.2O-30% Y.sub.2O.sub.3-20% AlN.
[0072] The heater circuits in the wafer holders were partially
exposed by spot-facing through the surface on the side opposite the
wafer-retaining face, up to the heater circuit. Electrodes made of
molybdenum were connected directly to the exposed portions of the
heater circuits utilizing an active metal brazing material. The
wafer holders were heated by passing current through the
electrodes, and the isothermal ratings and change in the form of
the wafer holders were measured.
[0073] Measurement of isothermal ratings was by setting a 12-inch
wafer temperature gauge on the wafer-retaining faces and measuring
the difference between the maximum and minimum temperatures. At
that time, the power was adjusted so that the maximum temperature
of the wafer temperature gauge would be 700.degree. C. In addition,
for change in form the wafer holders, not carrying the wafer
temperature gauge, were heated to 700.degree. C. and the difference
in height (displacement differential) between the center and the
periphery of the wafer-retaining face was measured using a laser
displacement meter. Measurement also of the porosity of the heater
circuits that were the electrical circuitry was carried out by
slicing through the heater circuits, and observing the
cross-sections with an electron microscope under 2000.times.
magnification. The results are set forth in Table I.
1TABLE I Bake temp. Pore proportion Temp. No. (.degree. C.) (%)
diff.(.degree. C.) Displacement (.quadrature.m) 1 1800 2.0 6 70 2
1850 0.5 8 80 3 1870 0.1 14 95 4 1900 0.05 21 120
[0074] In very one of the test samples, with respect to the center
of the wafer-retaining face the periphery was high--i.e., the
wafer-retaining face deformed into a concave shape--and the wafer
temperature gauge temperature for the center was lowest.
[0075] Embodiment 2
[0076] Wafer holders made of AlN, 340 mm outside diameter and 16 mm
thickness, were prepared in the same manner as in Embodiment 1.
Either molybdenum (Mo) paste or tantalum (Ta) paste was utilized,
however, for the heater circuits that were the electrical
circuitry. The oxides, binder and solvent within the pastes were
made likewise as with Embodiment 1. The heater-circuit porosity,
the temperature differential at 700.degree. C., and the
displacement were measured in the same manner as in Embodiment 1.
The results are set forth in Table II.
2TABLE II Bake Pore Heater-circuit temp. proportion Temp. diff.
Displacement No. substance (.degree. C.) (%) (.degree. C.)
(.quadrature.m) 5 Mo 1800 1.9 7 75 6 Mo 1840 0.4 9 85 7 Mo 1860 0.1
14 95 8 Mo 1890 0.03 25 130 9 Ta 1800 2.0 7 75 10 Ta 1840 0.6 10 85
11 Ta 1860 0.2 16 100 12 Ta 1880 0.04 30 145
[0077] As is evident from Tables I and II, in cases in which W, Mo
or Ta was utilized for the electrical circuitry, if the porosity of
the circuitry was made 0.1% or more, displacement exceeding 100
.mu.m did not appear in the wafer holders, even heated to
700.degree. C., and the temperature differential was within
20.degree. C. But with porosity of less than 0.1%, displacement
differentials exceeding 100 .quadrature.m occurred; moreover, the
temperature differentials were large, exceeding 20.degree. C., such
that uniform temperature distribution could not be obtained.
[0078] Embodiment 3
[0079] Wafer holders made of AlN, 340 mm outside diameter and 16 mm
thickness, were prepared in the same manner as in Embodiment 1.
Either 90 weight % Ag-10 weight % Pd (substance A) or 92 weight %
Ag-8 weight % Pt (substance B) was utilized, however, for the
heater circuits; and the heater-circuit baking temperature was
varied from 850.degree. C. to 900.degree. C. as set forth in Table
III. The porosity, the temperature differential at 500.degree. C.,
and the displacement were measured in the same manner as in
Embodiment 1. The results are set forth in Table III.
3TABLE III Bake Pore Heater-circuit temp. proportion Temp. diff.
Displacement No. substance (.degree. C.) (%) (.degree. C.)
(.quadrature.m) 13 A 850 5.0 3 40 14 A 870 2.2 7 80 15 A 890 1.6 13
115 16 B 850 3.9 4 55 17 B 870 2.0 6 75 18 B 890 1.5 12 105
[0080] As is evident from Table III, in cases in which an Ag system
metal was utilized for the electrical circuitry, if the porosity of
the circuitry was made 2% or more, significant deformation in the
wafer holders when heated did not occur, and uniform temperature
distribution could be obtained. But it was clear that in cases in
which the porosity was less than 2.0%, deformation became
appreciable and temperature distribution proved to be large.
[0081] Embodiment 4
[0082] Wafer holders No. 1 and No. 4 of Embodiment 1 were in
stalled into film-deposition equipment, wherein tungsten films were
deposited onto 12-inch silicon wafers. The result was that while in
the case in which wafer holder No. 1 was utilized, fluctuation in
the thickness of the tungsten film was a favorable 10% or less, in
the case in which No. 4 was utilized, the fluctuation in the
thickness of the tungsten film was a poor 20% approximately.
[0083] According to the present invention as given in the
foregoing, in a wafer holder having a wafer-carrying surface, an
electrical circuit layer consisting of one or more sinter laminae
is formed on the face or in the interior of the wafer holder; and
by rendering pores present in the circuit layer, the wafer holder
can be made so that deformation such as warping and cracking does
not occur when the wafer holder is heated. Utilizing a wafer holder
of this sort enables the realization of semiconductor manufacturing
equipment superior in isothermal rating and stabilized in
manufacturing conditions.
[0084] Only selected embodiments have been chosen to illustrate the
present invention. To those skilled in the art, however, it will be
apparent from the foregoing disclosure that various changes and
modifications can be made herein without departing from the scope
of the invention as defined in the appended claims. Furthermore,
the foregoing description of the embodiments according to the
present invention is provided for illustration only, and not for
limiting the invention as defined by the appended claims and their
equivalents.
* * * * *