Title: Ceramic substrate for a semiconductor production/inspection device
Abstract: The present invention provides a ceramic substrate which can keep a sufficiently large breakdown voltage even if the pore diameter of its maximum pore is 50 μm or less to be larger than that of conventional ceramic substrates, can give a large fracture toughness value because of the presence of pores, can resist thermal impact, and can give a small warp amount at high temperature. The ceramic substrate of the present invention is a ceramic substrate for a semiconductor-producing/examining device having a conductor formed on a surface of the ceramic substrate or inside the ceramic substrate, wherein: the substrate is made of a non-oxide ceramic containing oxygen; and the pore diameter of the maximum pore thereof is 50 μm or less.
Patent Number: 6,891,263 Issued on 05/10/2005 to Hiramatsu, et al.
| Inventors:
|
Hiramatsu; Yasuji (Gifu, JP);
Ito; Yasutaka (Gifu, JP)
|
| Assignee:
|
Ibiden Co., Ltd. (Ogaki, JP)
|
| Appl. No.:
|
926297 |
| Filed:
|
February 7, 2001 |
| PCT Filed:
|
February 7, 2001
|
| PCT NO:
|
PCTJP01/00866
|
| 371 Date:
|
December 26, 2001
|
| 102(e) Date:
|
December 26, 2001
|
| PCT PUB.NO.:
|
WO0158828 |
| PCT PUB. Date:
|
August 16, 2001 |
Foreign Application Priority Data
| Feb 07, 2000[JP] | 2000-029279 |
| Current U.S. Class: |
257/703; 118/724; 118/725; 219/444.1; 219/544; 219/553; 257/700; 257/705; 257/E23.077 |
| Intern'l Class: |
H01L 023/06; H01L023/10; H01L023/15 |
| Field of Search: |
257/43,703,700,629,705
219/444.1,544,553
118/724-725
29/599
|
References Cited [Referenced By]
U.S. Patent Documents
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| 5294574 | Mar., 1994 | Riedel et al.
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| 5310453 | May., 1994 | Fukasawa et al.
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| 5408574 | Apr., 1995 | Deevi et al.
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| 5473137 | Dec., 1995 | Queriaud et al.
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| 5756215 | May., 1998 | Sawamura et al.
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| 5843589 | Dec., 1998 | Hoshiya et al.
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| 5965193 | Oct., 1999 | Ning et al.
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| 5998321 | Dec., 1999 | Katsuda et al.
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| 6025579 | Feb., 2000 | Tanaka et al.
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| 6086990 | Jul., 2000 | Sumino et al.
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| 6176140 | Jan., 2001 | Autenrieth et al.
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| 6182340 | Feb., 2001 | Bishop.
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| 6183875 | Feb., 2001 | Ning et al.
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| 6272002 | Aug., 2001 | Mogi et al.
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| 6465763 | Oct., 2002 | Ito et al.
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| 6475606 | Nov., 2002 | Niwa.
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| 6507006 | Jan., 2003 | Hiramatsu et al.
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| 2002/0010073 | Jan., 2002 | Beall et al.
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| Foreign Patent Documents |
| 3-255625 | Nov., 1991 | JP.
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| 5-8140 | Jan., 1993 | JP.
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| 6-48837 | Feb., 1994 | JP.
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| 7-94576 | Apr., 1995 | JP.
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| 8-133840 | May., 1996 | JP.
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| 9-165264 | Jun., 1997 | JP.
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| 9-283608 | Oct., 1997 | JP.
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| 10-275524 | Oct., 1998 | JP.
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| 10-279359 | Oct., 1998 | JP.
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| 11-67886 | Mar., 1999 | JP.
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| 11-100270 | Apr., 1999 | JP.
| |
| 11-168134 | Jun., 1999 | JP.
| |
| 2000/-143349 | May., 2000 | JP.
| |
Primary Examiner: Zarabian; Amir
Assistant Examiner: Soward; Ida M.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Claims
1. A ceramic heater for a semiconductor-producing/examining device, the ceramic
heater comprising
a ceramic substrate having a disc form including two opposing surfaces; and
a resistance heating element on one of the two opposing surfaces of the ceramic
substrate or inside the ceramic substrate, wherein
the ceramic substrate comprises a non-oxide ceramic containing 0.05 to 5% by
weight of oxygen; and
the non-oxide ceramic has a maximum pore diameter of 5 μm or less.
2. The ceramic heater according to claim 1, wherein said non-oxide ceramic is
a nitride ceramic.
3. The ceramic heater according to claim 1, wherein said non-oxide ceramic is
a carbide ceramic.
4. The ceramic heater according to claim 1, wherein said ceramic substrate has
a porosity of 5% or less.
5. The ceramic heater according to claim 1, wherein said ceramic substrate is
capable of use within the temperature range of 100 to 700 C.
6. The ceramic heater according to claim 1, wherein said ceramic substrate has
a thickness of 25 mm or less, and a diameter of 200 mm or more.
7. The ceramic heater according to claim 1, wherein said ceramic substrate has
a plurality of through holes into which lifter pins for a semiconductor wafer are
capable of being inserted.
8. The ceramic heater according to claim 1, wherein said ceramic substrate contains
oxygen in an amount of 0.1 to 5% by weight.
9. The ceramic heater according to claim 1, wherein said ceramic substrate comprises
an alkali metal oxide, an alkali earth metal oxide, or a rare earth element oxide.
10. The ceramic heater according to claim 1, wherein an electrostatic electrode
or an RF electrode is embedded inside the ceramic substrate.
11. The ceramic heater according to claim 1, wherein said heating element is
a Peltier device.
12. The ceramic heater according to claim 1, wherein said heating element is
selected from the group consisting of a conductive ceramic, a metal foil, a metal
sintered a metal wire.
13. The ceramic heater according to claim 1, wherein a chuck top conductor layer
is formed on the surface of said ceramic substrate.
14. The ceramic heater according to claim 1, wherein said ceramic substrate contains BN.
Description
FIELD OF THE INVENTION
The present invention relates to a ceramic substrate for a semiconductor-producing/examining
device, used mainly in the semiconductor industry, particularly to a ceramic substrate
which has a high breakdown voltage, is superior in the capability of absorbing
a silicon wafer when used as an electrostatic chuck, and is also superior in temperature-rising
and temperature-falling property when used as a hot plate (ceramic heater) or a
ceramic plate for a wafer prober.
BACKGROUND ART
Semiconductors are very important products necessary in various industries.
A semiconductor chip is produced, for example, by slicing a silicon monocrystal
into a given thickness to produce a silicon wafer, and then forming plural integrated
circuits and the like on this silicon wafer.
In the process for producing this semiconductor chip, a silicon wafer put on
an
electrostatic chuck is subjected to various treatments such as etching and CVD
to form a conductor circuit, an element and the like. At this time, corrosive gas
such as gas for deposition or gas for etching is used; therefore, it is necessary
to protect an electrostatic electrode layer from corrosion by the gas. Also, since
it is necessary to induce adsorption power, the electrostatic electrode layer is
usually coated with a ceramic dielectric film and the like.
SUMMARY OF THE INVENTION
As this ceramic dielectric film, a nitride ceramic has been conventionally used.
Hitherto, however, the dielectric film has been formed by sintering without addition
of an oxide and the like. Therefore, almost all of pores made inside the dielectric
film interconnect with each other, and the number of open pores is also large.
If such pores are present and the volume resistivity of the dielectric layer decreases
at high temperature, electrons easily fly or jump over the air in the pores by
application of a voltage so that the so-called spark is caused. Therefore, unless
the pore diameter of the maximum pore is made small, there remains a problem that
the sufficient breakdown voltage of the ceramic dielectric film cannot be easily
kept at a high level.
For example, JP Kokai Hei 5-8140discloses an electrostatic chuck, using a nitride
whose pore diameter is made very small so that the pore diameter of the maximum
pore is made to 5 μm or less.
It has been found out that such a problem is caused in not only an electrostatic
chuck but also a ceramic substrate for a semiconductor-producing/examining device,
wherein a conductor is formed on a surface of the ceramic substrate or inside the
ceramic substrate.
As a result of eager investigation for solving the above-mentioned problem, the
inventors have newly found out that by adding an oxide to a nitride ceramic and
firing the resultant product, sintering can be advanced so that interconnecting
pores are not practically generated and independent pores are formed, and that
by incorporating the oxide into boundaries between particles of the ceramic, a
sufficient breakdown voltage at high temperature can be ensured even if the diameter
of the pores is large.
That is, the present invention is a ceramic substrate for a semiconductor-producing/examining
device having a conductor formed on a surface of the ceramic substrate or inside
the ceramic substrate,
- wherein:
- the substrate is made of a non-oxide ceramic containing oxygen; and
- the pore diameter of the maximum pore thereof is 50 μm or less.
The non-oxide ceramic is preferably a nitride ceramic or a carbide ceramic.
The ceramic substrate preferably contains oxygen in an amount of 0.05 to 10%
by weight.
The ceramic substrate preferably has a porosity of 5% or less.
The ceramic substrate is preferably used within the temperature range of 100
to 700° C.
The ceramic substrate preferably has a thickness of 25 mm or less, and a diameter
of 200 mm or more.
The ceramic substrate preferably has a plurality of through holes into which
lifter pins for a semiconductor wafer will be inserted.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view that schematically illustrates one example of an
electrostatic chuck according to the present invention.
FIG. 2 is a sectional view taken along A—A line of the electrostatic
chuck illustrated in FIG. 1.
FIG. 3 is a sectional view taken along B—B line of the electrostatic
chuck illustrated in FIG. 1.
FIG. 4 is a sectional view that schematically illustrates one example of an
electrostatic chuck according to the present invention.
FIG. 5 is a sectional view that schematically illustrates one example of an
electrostatic chuck according to the present invention.
FIG. 6 is a sectional view that schematically illustrates one example of an
electrostatic chuck according to the present invention.
FIGS. 7(
a) to (
d) are sectional views that schematically
illustrate a part of a process for producing an electrostatic chuck according to
the present invention.
FIG. 8 is a horizontal sectional view that schematically illustrates a shape
of an electrostatic electrode constituting an electrostatic chuck according to
the present invention.
FIG. 9 is a horizontal sectional view that schematically illustrates a shape
of an electrostatic electrode constituting an electrostatic chuck according to
the present invention.
FIG. 10 is a sectional view that schematically illustrates the state that an
electrostatic chuck according to the present invention is fitted into a supporting case.
FIG. 11 is a sectional view that schematically illustrates a wafer prober according
to the present invention.
FIG. 12 is a sectional view that schematically illustrates a guard electrode
of the wafer prober according to the present invention.
FIG. 13 is a sectional view that schematically illustrates a hot plate according
to the present invention.
EXPLANATION OF SYMBOLS
101, 201, 301, 401 electrostatic chuck
1 ceramic substrate
2, 22, 32a, 32b chuck positive
electrostatic layer
3, 23, 33a, 33b chuck negative
electrostatic layer
2a, 3a semicircular part
2b, 3b comb-teeth-shaped part
4 ceramic dielectric film
5 resistance heating element
6, 18 external terminal pin
7 metal wire
8 Peltier device
9 silicon wafer
11 bottomed hole
12 through hole
13, 14 blind hole
15 resistance heating element
150 metal layer
16, 17 conductor-filled through hole
41 supporting case
42 coolant outlet
43 inhalation duct
44 coolant inlet
45 heat insulator
DETAILED DISCLOSURE OF THE INVENTION
The ceramic substrate for a semiconductor-producing/examining device of the present
invention is a ceramic substrate for a semiconductor-producing/examining device
having a conductor formed on a surface of the ceramic substrate or inside the ceramic substrate,
- wherein:
- the substrate is made of a non-oxide ceramic containing oxygen; and
- the pore diameter of the maximum pore thereof is 50 μm or less.
In the ceramic substrate of the present invention, pores are not present at all
or, if pores are present, the pore diameter of the maximum pore thereof is 50 μm
or less.
In the case that no pores are present, the breakdown voltage at high temperature
is particularly high. Conversely, if pores are present, the fracture toughness
value becomes high. Therefore, which design is selected is decided under the consideration
of required properties.
The reason why the fracture toughness value becomes high by the presence of the
pores is unclear, but it is presumed that the development of cracks is stopped
by the pores.
In the ceramic substrate of the present invention, it is preferred to use: a
nitride
ceramic or a carbide ceramic, which are containing oxygen. By incorporating oxygen,
sintering can be advanced and interconnecting pores are not practically generated.
Thus, independent pores are formed. Therefore, corrosive gas does not erode the
conductor. Electrons do not easily fly or jump inside the pores in the case of
the independent pores compared to the case of interconnecting pores.
Furthermore, by incorporating the oxide into the boundaries between
particles of the ceramic, a sufficient breakdown voltage at high temperature can
be ensured even if the pore diameter becomes large.
In the ceramic substrate of the present invention, it is necessary that the pore
diameter of the maximum pore is 50 μm or less. If the pore diameter of the
maximum pore is over 50 μm, high breakdown voltage property cannot be ensured
at 100 to 700° C., particularly high temperatures of 200° C. or higher.
The pore diameter of the maximum pore is desirably 10 μm or less. This
is because a warp amount at 100 to 700° C., particularly at 200° C. or
higher, becomes small.
The porosity and the pore diameter of the maximum pore are adjusted by pressing
time, pressure and temperature at the time of sintering. However, for nitride ceramics,
they are adjusted by additives such as SiC and BN. Since SiC or BN obstructs sintering,
pores can be introduced.
At the measurement of the pore diameter of the maximum pore, 5 samples are prepared.
The surfaces thereof are ground into mirror planes. With an electron microscope,
ten points on the surface are photographed with 2000 to 5000 magnifications. The
maximum pore diameters are selected from the photos obtained by the photographing,
and the average of the 50 shots is defined as the pore diameter of the maximum pore.
The ceramic substrate desirably contains oxygen in an amount of 0.05 to 10% by
weight, and particularly desirably in an amount of 0.1 to 5% by weight. If the
amount thereof is below 0.1% by weight, the sufficient breakdown voltage may not
be maintained. Conversely, if the amount is over 5% by weight, the high breakdown
voltage property of the oxide at high temperature becomes poor so that the breakdown
voltage of the ceramic substrate may drop, as well. If the oxygen amount is over
5% by weight, the thermal conductivity may drop so that the temperature-rising
and temperature-falling property may becomes poor.
In the ceramic substrate, the porosity thereof is desirably 5% or less. If the
porosity is over 5%, the number of the pores increases and the pore diameter of
the pores becomes too large. As a result, the pores interconnect easily with each
other so that the breakdown voltage drops.
The porosity is measured by Archimedes' method. According to this method, a sintered
product is crushed into pieces, and the crushed pieces are put into an organic
solvent or mercury to measure the volume thereof. Then the true specific gravity
of the pieces is obtained from the weight and the measured volume thereof, and
the porosity is calculated from the true specific gravity and apparent specific gravity.
The ceramic substrate is desirably used within the temperature range of 100 to
700° C. Within such a temperature range, the breakdown voltage drops. Thus,
the structure of the present invention is especially profitable.
In the ceramic substrate, its warp amount at 100 to 700° C. is desirably
small. This is because in the case that the ceramic substrate is used as a heater
or an electrostatic chuck, a semiconductor wafer can be uniformly heated. In the
case that the warp amount is large, the semiconductor wafer does not adhere closely
to a heating surface of heater so that the semiconductor wafer cannot be uniformly
heated. In this case, if the semiconductor wafer is heated in the manner that the
semiconductor wafer and the heating surface are apart from each other, the distance
between the semiconductor wafer and the heating surface becomes uneven so that
the semiconductor wafer cannot be uniformly heated.
The warp amount in the case that the temperature of the ceramic substrate is
raised up to 100 to 700° C. and then returned to ambient temperature (25°
C.) (that is, the difference between the warp amounts before and after the temperature-rising)
is desirably 7 μm or less.
The ceramic substrate of the present invention can be used to produce/examine
a semiconductor, and can be used as an electrostatic chuck, a hot plate (ceramic
heater), a ceramic plate for a wafer prober (which is referred to merely as a wafer
prober, hereinafter), and the like.
The thickness of the ceramic substrate of the present invention is desirably
50 mm or less, and particularly desirably 25 mm or less. If the thickness of the
ceramic substrate is over 25 mm, the thermal capacity of the ceramic substrate
becomes large. Particularly when a temperature controlling means is set up to heat
or cool the substrate, temperature-following property may become poor due to the
large thermal capacity.
This is also because: the problem about the warp resulting from the presence
of the pores, which is to be solved by the ceramic substrate of the present invention,
is not practically caused in thick ceramic substrates having a thickness of more
than 25 mm. Particularly, 5 mm or less is optimal. Incidentally, the thickness
is desirably 1 mm or more.
The diameter of the ceramic substrate of the present invention is desirably 200
mm or more. It is particularly desirable that the diameter is 12 inches (300 mm)
or more. This is because such semiconductor wafers will become main currents of
the next-generation silicon wafers. This is also because a problem about warp at
high temperature ranges, which is to be solved by the present invention, is not
practically caused in the ceramic substrate having a diameter of 200 mm or less.
The ceramic substrate desirably has a plurality of through holes into which lifter
pins for a semiconductor wafer will be inserted. With the presence of the through
holes, strain at the time of processing is released in the case that Young's modulus
is lowered particularly at high temperature. As a result, warp is easily generated.
It can be considered that this is a structure for which the present invention exhibits
the best advantageous effect.
Examples of the nitride ceramic constituting the ceramic substrate of the
present invention include metal nitride ceramics, such as aluminum nitride, silicon
nitride, boron nitride and titanium nitride.
In the ceramic substrate of the present invention, it is desired that the ceramic
substrate contains a sintering aid.
The sintering aid that can be used may be an alkali metal oxide, an alkali earth
metal oxide or a rare earth element oxide. Among these sintering aids, CaO, Y
2O
3,
Na
2O, Li
2O and Rb
2O are particularly preferred.
Alumina may be used. The content of these sintering aids is desirably from 0.1
to 20% by weight.
In the ceramic substrate of the present invention, the ceramic substrate desirably
contains 5 to 5000 ppm of carbon.
The ceramic substrate can be blackened by incorporating carbon. Thus, when the
substrate is used as a heater, radiant heat can be sufficiently used.
Carbon may be amorphous or crystalline. When amorphous carbon is used, a drop
in the volume resistivity at high temperature can be prevented. When crystalline
carbon is used, a drop in the thermal conductivity at high temperature can be prevented.
Therefore, crystalline carbon and amorphous carbon may be used together dependently
on the purpose. The carbon content is preferably from 50 to 2000 ppm.
When carbon is contained in the ceramic substrate, carbon is preferably contained
in the manner that its brightness will be N6 or less as a value based on
the rule of JIS Z 8721. The ceramic having such a brightness is superior in radiant
heat capacity and covering-up property.
The brightness N is defined as follows: the brightness of ideal black is made
to 0; that of ideal white is made to 10; respective colors are divided into 10
parts in the manner that the brightness of the respective colors is recognized
stepwise between the brightness of black and that of white at equal intensity intervals;
and the resultant parts are indicated by symbols N0 to N10, respectively.
Actual brightness is measured by comparison with color chips corresponding
to N0 to N10. One place of decimals in this case is made to 0 or 5.
In the ceramic substrate of the present invention, a silicon wafer is put on a
wafer-putting surface of the ceramic substrate in the state that they contact each
other. Besides, the silicon wafer may be supported by lifter pins and the like
and held in the state that a given interval is kept between the silicon wafer and
the ceramic substrate, as illustrated in FIG. 13.
FIG. 13 is a partially enlarged sectional view that schematically illustrates
a ceramic heater, which is an example of the ceramic substrate of the present invention.
In FIG. 13, lifter pins 96 are inserted into through holes 95 to
support a silicon wafer 99. By moving the lifter pins 96 up and down,
it is possible to receive the silicon wafer 99 from a carrier machine, put
the silicon wafer 99 on a ceramic substrate 91, or heat the silicon
wafer 99 in the state that the silicon wafer 99 is supported. Heating
elements 92 are formed on a bottom surface 91
a of the ceramic
substrate 91, and metal covering layers 92
a are deposited
on the surface of the heating elements 92. A bottomed hole 94 is
also made. A thermocouple is inserted therein.
The silicon wafer 99 is heated on the side of a wafer-heating surface
91
b.
In the case that a ceramic substrate for a semiconductor-producing/examining
device
of the present invention is used as a ceramic heater, a semiconductor wafer and
the heating-surface can be kept away from each other. The separation distance therebetween
is desirably 50 to 5000 μm. The present invention is particularly profitable
for the case that such separation is present. This is because the warp amount of
the ceramic substrate at high temperature is small so that the distance between
the semiconductor wafer and the heating-surface becomes uniform.
In the case that the ceramic substrate of the present invention is used as a
hot
plate (ceramic heater), the conductor is a heating element, and may be a metal
layer with the thickness of about 0.1 to 100 μm or may be a heating wire.
In the case that the ceramic substrate is used as an electrostatic chuck, the conductor
is an electrostatic electrode, and an RF electrode or a heating element may be
formed as a conductor: below the electrostatic electrode and inside the ceramic
substrate. In the case that the ceramic substrate is used as a wafer prober, a
chuck top conductor layer is formed as a conductor on the surface and guard electrodes,
and ground electrodes are formed as conductors inside.
The ceramic substrate of the present invention is desirably used at 100°
C. or higher, optimally 200° C. or higher.
The following will describe the present invention, giving: an electrostatic chuck
and a wafer prober, which have a function as a hot plate, as examples.
In an electrostatic chuck according to the present invention, electrostatic electrodes
are formed on a ceramic substrate. A ceramic dielectric film covering the electrostatic
electrodes is made of a non-oxide ceramic, such as a nitride ceramic or a carbide
ceramic, containing oxygen. Its porosity is 5% or less, and the pore diameter of
its maximum pore is 50 μm or less. Therefore, the pores in this dielectric
film are composed of pores independently on each other. Accordingly, it does not
happen that gas and so on which cause a drop in the breakdown voltage penetrate
through the ceramic dielectric film to corrode the electrostatic electrode and
lower the breakdown voltage of the ceramic dielectric film even at high temperature.
By setting the thickness of the ceramic dielectric film to 50 to 5000 μm,
a sufficient breakdown voltage can be ensured without lowering chucking power.
FIG. 1 is a vertical sectional view that schematically shows an electrostatic
chuck which is an embodiment of the ceramic substrate of the present invention.
FIG. 2 is a sectional view taken on A—A line of the electrostatic chuck
shown in FIG. 1. FIG. 3 is a sectional view taken along B—B line
of the electrostatic chuck shown in FIG. 1.
In this electrostatic chuck 101, an electrostatic electrode layer composed
of a chuck positive electrostatic layer 2 and a chuck negative electrostatic
layer 3 is formed on the surface of a ceramic substrate 1 in a circular
form as viewed from the above. A ceramic dielectric film 4 made of a nitride
ceramic containing oxygen is formed to cover this electrostatic electrode layer.
A silicon wafer 9 is put on the electrostatic chuck 101 and is grounded.
As shown in FIG. 2, the chuck positive electrostatic layer 2 is composed
of a semicircular part 2
a and a comb-teeth-shaped part 2
b.
The chuck negative electrostatic layer 3 is also composed of a semicircular
part 3
a and a comb-teeth-shaped part 3
b. These chuck
positive electrostatic layer 2 and chuck negative electrostatic layer 3
are arranged opposite to each other so that the comb-teeth-shaped parts 2
b
and 3
b cross each other. The + side and the - side of a direct
power source are connected to the chuck positive electrostatic layer 2 and
chuck negative electrostatic layer 3, respectively. Thus, a direct current
V
2 is applied thereto.
In order to control the temperature of the silicon wafer 9, resistance
heating elements 5 in the form of concentric circles as viewed from the
above, as shown in FIG. 3, are set up inside the ceramic substrate 1. External
terminal pins 6 are connected and fixed to both ends of the resistance heating
elements 5, and a voltage V
1 is applied thereto. Bottomed holes
11 into which temperature-measuring elements will be inserted and through
holes 12 through which lifter pins (not illustrated) that support the silicon
wafer 9 and move it up and down penetrate, are formed in the ceramic substrate
1, as shown in FIG. 3 but not shown in FIGS. 1, 2. The resistance
heating elements 5 may be formed on the bottom surface of the ceramic substrate.
When this electrostatic chuck 101 is caused to work, a direct voltage V
2
is applied to the chuck positive electrostatic layer 2 and the chuck
negative electrostatic layer 3. In this way, the silicon wafer 9
is adsorbed and fixed to the chuck positive electrostatic layer 2 and the
chuck negative electrostatic layer 3 through the ceramic dielectric film
4 by electrostatic action of these electrodes. The silicon wafer 9
is fixed onto the electrostatic chuck 101 in this way, and subsequently
the silicon wafer 9 is subjected to various treatments such as CVD.
The electrostatic chuck according to the present invention has a structure as
illustrated in FIGS. 1 to 3. The following will successively describe the
respective members of the above-mentioned electrostatic chuck and other embodiments
of the electrostatic chuck according to the present invention in detail.
The ceramic dielectric film used in the electrostatic chuck according to the
present invention preferably made of a nitride ceramic containing oxygen, and the
pore diameter of its maximum pore is 50 μm or less. Its thickness is preferably
50 to 1500 μm, and its porosity is 5% or less.
Examples of the nitride ceramic include metal nitride ceramics, such as
aluminum nitride, silicon nitride, boron nitride and titanium nitride. Among these
nitride ceramics, aluminum nitride is most preferred. This is because its breakdown
voltage is high and its thermal conductivity is highest, that is, 180 W/m·K.
The nitride ceramic contains oxygen. For this reason, the sintering of the nitride
ceramic advances easily. Thus, even if pores are contained therein, the pores become
independent on each other. Therefore, the breakdown voltage is improved for the
above-mentioned reason.
Usually, raw material powder of the nitride ceramic is heated in oxygen
or in the air, or the raw material powder of the nitride ceramic is mixed with
a metal oxide and then the mixture is fired, in order to incorporate oxygen into
the nitride ceramic.
Examples of the metal oxide include yttria (Y
2O
3),
alumina (Al
2O
3), rubidium oxide (Rb
2O), lithium
oxide (Li
2O), and calcium oxide (CaCO
3).
The added amount of these metal oxides is preferably 0.1 to 10 parts by weight
per 100 parts by weight of the nitride ceramic.
The porosity of the ceramic dielectric film is desirably 5% or less. It is also
desirable that its thickness is 50 to 5000 μm and the pore diameter of its
maximum pore is 50 μm or less.
If the thickness of the ceramic dielectric film is below 50 μm, the film
thickness is too thin to obtain sufficient breakdown voltage. Thus, when a silicon
wafer is put on the film and is adsorbed thereon, the ceramic dielectric film may
undergo dielectric breakdown. On the other hand, if the thickness of the ceramic
dielectric film is over 5000 μm, the distance between the silicon wafer and
the electrostatic electrodes becomes large so that the capability of adsorbing
the silicon wafer becomes poor. The thickness of the ceramic dielectric film is
more preferably 100 to 1500 μm.
If the porosity is over 5%, the number of the pores increases and the pore diameter
becomes too large. As a result, the pores interconnect easily with each other.
In the ceramic dielectric film having such a structure, the breakdown voltage drops.
If the pore diameter of the maximum pore is over 50 μm, the sufficient
breakdown
voltage cannot be maintained at high temperature even if the oxide is present in
the boundaries between the particles. In the case that the pores are present, the
porosity is more preferably 0.001 to 3% and the pore diameter of the maximum pore
is more preferably 0.1 to 10 μm.
The ceramic dielectric film desirably contains 50 to 5000 ppm of carbon. This
is because the electrode pattern set inside the electrostatic chuck can be hidden
and high radiant heat can be obtained. As the volume resistivity is lower, the
capability of adsorbing a silicon wafer becomes high at low temperature.
The reason why in the electrostatic chuck of the present invention a considerable
number of the pores may be present in the ceramic dielectric film is that the pores
can cause an improvement in the fracture toughness value and the resistance to
thermal impact.
Examples of the electrostatic electrodes formed on the ceramic substrate
include a sintered body of a metal or a conductive ceramic; and a metal foil. As
the metal sintered body, at least one selected from tungsten and molybdenum is
preferred. The metal foil is preferably made of the same material as the metal
sintered body. These metals are not relatively liable to be oxidized and have a
sufficient conductivity for electrodes. As the conductive ceramic, at least one
selected from carbides of: tungsten; and molybdenum can be used.
FIGS. 8,9 are horizontal sectional views, each of which schematically
shows an electrostatic electrode in another electrostatic chuck. In an electrostatic
chuck 20 shown in FIG. 8, a chuck positive electrostatic layer 22
and a chuck negative electrostatic layer 23 in a semicircular form are formed
inside a ceramic substrate 1. In an electrostatic chuck shown in FIG. 9,
chuck positive electrostatic layers 32
a and 32
b and
chuck negative electrostatic layers 33
a and 33
b, each
of which has a shape obtained by dividing a circle into 4 parts, are formed inside
a ceramic substrate 1. The two chuck positive electrostatic layers 22
a
and 22
b and the two chuck negative electrostatic layers 33
a
and 33
b are formed to cross, respectively.
In the case that an electrode having a form that an electrode in the shape of
a circle or the like is divided is formed, the number of divided pieces is not
particularly limited and may be 5 or more. Its shape is not limited to a fan-shape.
The ceramic substrate used in the electrostatic chuck according to the present
invention is preferably made of nitride ceramic, or carbide ceramic.
Examples of the nitride ceramic include aluminum nitride, silicon nitride,
boron nitride and titanium nitride.
Examples of the carbide ceramic include silicon carbide, boron carbide,
titanium carbide, and tungsten carbide.
The ceramic dielectric film and the ceramic substrate are desirably made of the
same material. This is because the nitride ceramic has a high thermal conductivity
and can satisfactorily conduct heat generated in the resistance heating elements.
This is also because in the case that the ceramic dielectric film and the ceramic
substrate are made of the same material, the electrostatic chuck can easily be
produced by laminating green sheets in the same manner and then firing the lamination
under the same conditions.
Among the nitride ceramics, aluminum nitride is most preferred since its thermal
conductivity is highest, that is, 180 W/m·K.
The ceramic substrate desirably contains 50 to 5000 ppm of carbon. This is because
high radiant heat can be obtained. As the carbon, either of crystalline which can
be detected by X-ray diffraction or amorphous which cannot be detected thereby
may be used. Both of the crystalline and the amorphous may be used.
In the electrostatic chuck according to the present invention, a temperature
controlling
means such as a resistance heating element is usually set up, as illustrated in
FIG. 1. This is because it is necessary to conduct CVD treatment and so
on while heating of the silicon wafer put on the electrostatic chuck and so on,
are performed.
The temperature controlling means may be a Peltier device (reference to FIG.
6) as well as the resistance heating element 5 illustrated in FIG. 3.
The resistance heating element may be set up inside the ceramic substrate or may
be set up on the bottom surface of the ceramic substrate. In the case that the
resistance heating element is set up, an inlet for blowing a coolant, such as air,
as cooling means may be made in a supporting case into which the electrostatic
chuck is to be fitted.
A plurality of layers of the resistance heating elements may be set inside the
ceramic substrate. In this case, the patterns of the respective layers may be formed
to complement them mutually. The pattern, when being viewed from the heating surface,
is desirably formed on any one of the layers. For example, a structure having a
staggered arrangement is desirable.
Examples of the resistance heating element include a sintered body of a
metal or a conductive ceramic; a metal foil; and a metal wire. As the metal sintered
body, at least one selected from tungsten and molybdenum is preferred. This is
because these metals are not relatively liable to be oxidized and have a sufficiently
large resistivity to generate heat.
As the conductive ceramic, at least one selected from carbides of: tungsten;
and
molybdenum may be used.
In the case that the resistance heating element is formed on the bottom surface
of the ceramic substrate, it is desired to use, as the metal sintered body, a noble
metal (gold, silver, palladium or platinum), or nickel. Specifically, silver, silver-palladium
and the like may be used.
As the metal particles used in the metal sintered body, spherical or scaly particles,
or a mixture of spherical particles and scaly particles can be used.
A metal oxide may be added to the metal sintered body. The metal oxide is used
in order to let the ceramic substrate closely adhere to particles of the metal.
The reason why the adhesion between the ceramic substrate and the metal particles
is improved by the metal oxide is unclear, but would be as follows: an oxide film
is slightly formed on the surface of the metal particles and a noxide film is formed
on the surface of the ceramic substrate in the case that the ceramic substrate
is made of a non-oxide ceramic as well as an oxide ceramic. It can be therefore
considered that these oxide films are sintered and integrated with each other,
through the metal oxide, on the surface of the ceramic substrate so that the metal
particles and the ceramic substrate adhere closely to each other.
A preferred example of the metal oxide is at least one selected from lead oxide,
zinc oxide, silica, boron oxide (B
2O
3) alumina, yttria, and
titania. These oxides make it possible to improve adhesiveness between the metal
particles and the ceramic substrate without increasing the resistivity of the resistance
heating element too much.
The amount of the metal oxide is desirably 0.1 part or more by weight and is
below 10 parts by weight per 100 parts by weight of the metal particles. The use
of the metal oxide within this range makes it possible to improve the adhesion
between the metal particles and the ceramic substrate without making the resistivity large.
When the total amount of the metal oxides is set to 100 parts by weight, the
weight ratio of lead oxide, zinc oxide, silica, boron oxide (B
2O
3),
alumina, yttria and titania is as follows: 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. The ratio is preferably adjusted within the scope that the total
amount of these oxides is not over 100 parts by weight. This is because in these
ranges it is possible to improve adhesiveness to the ceramic substrate.
In the case that the resistance heating element is set up on the bottom surface
of the ceramic substrate, the surface of the resistance heating element 15
is desirably covered with a metal layer 150 (reference to FIG. 4).
The resistance heating element 15 is a sintered body of the metal particles.
Thus, when the resistance heating element 15 is exposed, it is easily oxidized.
The oxidization causes a change in the resistivity. Thus, by covering the surface
with the metal layer 150, the oxidization can be prevented.
The thickness of the metal layer 150 is desirably 0.1 to 10 μm.
In this range, it is possible to prevent the oxidization of the resistance heating
element without changing the resistivity of the resistance heating element.
The metal used for the covering is any non-oxidizable metal. Specifically, at
least one selected from gold, silver, palladium, platinum and nickel is preferred.
Among these metals, nickel is more preferred. This is because of the following:
the resistance heating element needs to have a terminal for connection to a power
source. This terminal is attached to the resistance heating element through solder.
Nickel prevents thermal diffusion of the solder. As the connecting terminal, a
terminal pin made of Kovar can be used.
In the case that the resistance heating element is inside the heater plate, the
surface of the resistance heating element is not oxidized. Therefore, no covering
is necessary. In the case that the resistance heating element is inside the heater
plate, a part of the surface of the resistance heating element may be exposed.
As the metal foil used as the resistance heating element, a resistance heating
element patterned by the etching of a nickel foil or a stainless steel foil and
the like method is desirable.
The patterned metal foils may be put together with a resin film or the like.
Examples of the metal wire include a tungsten wire and a molybdenum wire.
In the case that the Peltier device is used as the temperature controlling means,
both heating and cooling can be attained by changing the direction along which
an electric current passes. Thus, this case is advantageous.
As shown in FIG. 6, the Peltier device 8 is formed by connecting p type
and n type thermoelectric elements 81 in series and then jointing the resultant
to a ceramic plate 82.
Examples of the Peltier device include silicon/germanium, bismuth/antimony,
and lead/tellurium materials.
Examples of the electrostatic chuck according to the present invention include:
the electrostatic chuck 101 having a structure wherein the chuck positive
electrostatic layer 2 and the chuck negative electrostatic layer 3
are arranged between the ceramic substrate 1 and the ceramic dielectric
film 4 and the resistance heating elements 5 are set up inside the
ceramic substrate 1, as shown in FIG. 1; the electrostatic chuck 201
having a structure wherein the chuck positive electrostatic layer 2 and
the chuck negative electrostatic layer 3 are arranged between the ceramic
substrate 1 and the ceramic dielectric film 4 and the resistance
heating elements 15 are disposed on the bottom surface of the ceramic substrate
1, as shown in FIG. 4; the electrostatic chuck 301 having a structure
wherein the chuck positive electrostatic layer 2 and the chuck negative
electrostatic layer 3 are arranged between the ceramic substrate 1
and the ceramic dielectric film 4 and the metal wire 7, which is
a resistance heating element, is embedded in the ceramic substrate 1, as
shown in FIG. 5; and the electrostatic chuck 401 having a structure wherein
the chuck positive electrostatic layer 2 and the chuck negative electrostatic
layer 3 are arranged between the ceramic substrate 1 and the ceramic
dielectric film 4 and the Peltier device 8 composed of the thermoelectric
element 81 and the ceramic plate 82 is formed on the bottom surface
of the ceramic substrate 1, as shown in FIG. 6.
As shown in FIGS. 1 to 6, in the electrostatic chuck according to the present
invention the chuck positive electrostatic layer 2 and the chuck negative
electrostatic layer 3 are arranged between the ceramic substrate 1
and the ceramic dielectric film 4 and the resistance heating element 5
or the metal wire 7 is formed inside the ceramic substrate 1. Therefore,
connecting units (conductor-filled through holes) 16,17 are necessary
for connecting these to external terminal pins. The conductor-filled through holes
16,17 are made by filling therein with a high melting point metal
such as tungsten paste or molybdenum paste, or a conductive ceramic such as tungsten
carbide or molybdenum carbide.
The diameter of the connecting units (conductor-filled through holes) 16,17
is desirably from 0.1 to 10 mm. This is because disconnection can be prevented
and further cracks or strains can be prevented.
The conductor-filled through holes are used as connecting pads to connect external
terminal pins 6,18 (reference to FIG. 7(
d)).
The connecting thereof is performed with solder or brazing material. As the brazing
material, brazing silver, brazing palladium, brazing aluminum, or brazing gold
is used. Brazing gold is desirably Au—Ni alloy. Au—Ni alloy is superior
in adhesiveness to tungsten.
The ratio of Au/Ni is desirably [81.5 to 82.5 (% by weight)]/[18.5 to 17.5 (%
by weight)].
The thickness of the Au—Ni layer is desirably from 0.1 to 50 μm.
This is because this range is a range sufficient for keeping connection. If Au—Cu
alloy is used at a high temperature of 500 to 1000° C. and at a high vacuum
of 10
-6 to 10
-5 Pa, the Au—Cu alloy deteriorates.
However, Au—Ni alloy does not cause such a deterioration and is profitable.
When the total amount of the Au—Ni alloy is regarded as 100 parts by weight,
the amount of impurities therein is desirably below 1 part by weight.
If necessary, in the ceramic substrate of the present invention a thermocouple
may be buried in the bottomed hole 11 in the ceramic substrate 1.
This is because the thermocouple makes it possible to measure the temperature of
the resistance heating element and, on the basis of the resultant data, voltage
or electric current is changed so that the temperature can be controlled.
The size of the connecting portion of metal wires of the thermocouple is desirably
the same as the original diameter of the respective metal wires or larger, and
is preferably 0.5 mm or less. Such a structure makes the thermal capacity of the
connecting portion small, and causes a temperature to be correctly and rapidly
converted to a current value. For this reason, temperature controllability is improved
so that the temperature distribution of the heated surface of the semiconductor
wafer becomes small.
Examples of the thermocouple include K, R, B, S, E, J and T type thermocouples,
described in JIS-C-1602 (1980).
FIG. 10 is a sectional view that schematically shows a supporting case 41
into which the electrostatic chuck of the present invention, having a structure
as described above, is fitted.
The electrostatic chuck 101 is fitted into the supporting case 41
through a heat insulator 45. Coolant outlets 42 are formed in the
supporting case 11, and a coolant is blown from a coolant inlet 44
and goes outside from an inhalation duct 43 after passing through the coolant
outlet 42. By the act of this coolant, the electrostatic chuck 101
can be cooled.
The following will describe one example of the process for producing an electrostatic
chuck according to the present invention by referring to sections shown in FIGS. 7.
(1) First, ceramic powder of a nitride ceramic is mixed with a binder and
a solvent to obtain a green sheet 50.
As the ceramic powder, there may be used, for example, aluminum nitride powder.
If necessary, a sintering aid such as yttria may be added.
One or several green sheets 50′ laminated on the green sheet on
which an electrostatic electrode layer printed units 51 that will be described
later are formed are layers which will be a ceramic dielectric film 4; therefore,
the sheets 50′ are made to be sheets wherein oxide powder is mixed
with nitride powder.
Usually, the raw material of the ceramic dielectric film 4 and that
of the ceramic substrate 1 are desirably the same. This is because, in many
