JP2000247732A - Low-resistance ceramic, its production and member for semiconductor producing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low-resistance ceramic having both low resistance and low thermal expansion. SOLUTION: Mixed powder comprising cordierite as a main component and 1-20 wt.%, calculated as oxide, of rare earth element or its molding product is baked in a reducing atmosphere, containing at least carbon, under <=0.2 atmospheric pressure of oxygen partial pressure or embedded in carbon powder and baked to give a dense low-resistance ceramic having 0.01-2.0 wt.% carbon, <=107 Ω.cm volume specific resistance, <=1×10-6/ deg.C coefficient of thermal expansion at 10-40 deg.C and >=95% relative density. The ceramic is applied to a member for a semiconductor producing apparatus to control charging properties of the member and to prevent an undesirable influence by static charge in semiconductor production.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structural member for a vacuum apparatus, a susceptor, a vacuum chuck, a stage in a lapping machine or an exposure apparatus, a mirror for measuring a stage position, a supporting member thereof, and various types of semiconductor manufacturing processes. The present invention relates to a low-resistance ceramic having excellent antistatic properties, mainly a cordierite suitable for a member that comes into contact with a semiconductor wafer, such as a jig, and a method of manufacturing the same, and a member for a semiconductor manufacturing apparatus.

[0002]

2. Description of the Related Art Conventionally, cordierite-based sintered bodies have been known as low thermal expansion ceramics,
It is applied to honeycombs and refractories. This cordierite-based sintered body is generally made of cordierite powder or MgO, Al ₂ O ₃ ,
It is made by mixing SiO ₂ powder, adding a rare earth element oxide, SiO ₂ , CaO, MgO, etc. as a sintering aid to this, shaping it into a predetermined shape, and firing at a temperature of 1000 to 1400 ° C. It is done (Japanese Patent Publication No. 57-362)
9, JP-A-2-229760).

On the other hand, in a process of manufacturing a semiconductor device such as an LSI, in a process of forming wiring on a silicon wafer, a susceptor for supporting or holding the wafer, a vacuum chuck, an electrostatic chuck, a lapping machine, an insulating ring or other So far, alumina and silicon nitride have been widely used because they are relatively inexpensive and chemically stable. Also, ceramics such as alumina and silicon nitride have been conventionally used as an XY table of an exposure apparatus.

Recently, low-thermal-expansion ceramics such as cordierite have been applied to parts for semiconductor manufacturing equipment as disclosed in Japanese Patent Application Laid-Open No. 1-1191422 and Japanese Patent Publication No. 6-976.
No. 75. According to Japanese Patent Application Laid-Open No. 1-1191422, it is proposed that a reinforcing ring to be bonded to a mask substrate in an X-ray mask is formed of cordierite in addition to SiO ₂ , invar and the like to control the stress of the membrane. Japanese Patent Publication No. 6-97675 proposes using an alumina or cordierite-based sintered body as a base for an electrostatic chuck on which a wafer is placed.

In recent years, with high integration in LSIs and the like, circuit miniaturization has been rapidly advanced, and the line width thereof has been becoming highly precise to a submicron order level. High precision is required for an exposure apparatus for forming a high-precision circuit on a Si wafer. For example, a stage member of the exposure apparatus requires a positioning accuracy of 100 nm (0.1 μm) or less. At present, errors have a great effect on improving product quality and yield.

[0006]

However, ceramics such as alumina and silicon nitride which have been generally used for semiconductor manufacturing equipment have a smaller coefficient of thermal expansion than metals, but have a coefficient of thermal expansion at 10 to 40 ° C. 5.2 each
× a 10 ^-6 /℃,1.5×10 ^-6 / ℃, will be modified number when ambient temperature changes 0.1 ℃ 100nm (0.1μm) occurs, precise steps such as exposure In this case, this change becomes a serious problem, and the accuracy of conventional ceramics is low, resulting in a decrease in productivity.

On the other hand, the cordierite-based sintered body has a coefficient of thermal expansion of about 0.2 × 10 ⁻⁶ / ° C., which is lower than that of alumina or silicon nitride. The problem of exposure accuracy is solved to some extent. However, only the cordierite of the related art having a high volume resistivity of 10 ¹⁴ Ω · cm or more has been obtained. When various parts are manufactured from such high-resistance materials, static electricity is gradually accumulated in the parts, so that dust and the like easily adhere to the parts, and the plasma generation device has an effect on the generation of plasma. In particular, a member that comes into contact with a semiconductor wafer has a fatal problem of destroying a semiconductor by electrostatic discharge.

For this purpose, conventionally, a method of forming a low-resistance coating on the surface of a conventional cordierite ceramic made of an insulating material in order to prevent electrification has been adopted. However, when a low-resistance coating is formed, the adhesiveness is deteriorated due to the difference in the coefficient of thermal expansion between the ceramic and the coating. As the film thickness increases, the coating tends to peel off. There was a problem of causing the occurrence of nation.

Accordingly, an object of the present invention is to provide a low-resistance ceramic having low resistance and low thermal expansion characteristics, and a method for producing the same. Another object of the present invention is to provide a member for a semiconductor manufacturing apparatus which has non-charging properties due to low resistance, has low thermal expansion characteristics, and comes into contact with a semiconductor wafer such as a vacuum chuck. It is.

[0010]

Means for Solving the Problems As a result of intensive studies on the above-mentioned problems, the present inventors have fired a molded body containing cordierite as a main component under a reducing atmosphere containing carbon. By impregnating with carbon or firing a molded body containing a carbon source in an inert atmosphere or a non-oxidizing atmosphere to suppress volatilization of carbon, a ceramic having low resistance and low thermal expansion can be obtained. This led to the present invention.

That is, the low-resistance ceramic of the present invention contains cordierite as a main component, 1 to 20% by weight of a rare earth element in terms of oxide, and 0.01 to 2.0% by weight of carbon. , A coefficient of thermal expansion of 1 × 10 ⁻⁶ / ° C. or less at 10 to 40 ° C., a relative density of 95% or more, and a volume resistivity at room temperature of 10 ⁷ Ω · cm or less. According to such ceramics, it is desirable that a silicate crystal phase of a rare earth element exists at the grain boundary of the cordierite crystal.

Further, according to the present invention, such a low-resistance ceramic is used as a member for a semiconductor manufacturing apparatus such as a vacuum chuck.

As a method for producing such a low-resistance ceramic, a mixed powder or a compact containing cordierite powder as a main component, a rare earth element oxide in an amount of 1 to 20% by weight, and a carbon source is produced with an oxygen partial pressure of 0%. 1100-145 in an inert atmosphere or a non-oxidizing atmosphere of 2 atm or less
Baking at a temperature of 0 ° C., the carbon content is 0.01 to
The method is characterized by obtaining a ceramic having 2.0% by weight and a relative density of 95% or more. In such a production method, it is preferable that the firing be performed under a pressure of 100 kg / cm ² or more.

In another production method, cordierite is used as a main component, and a rare earth element oxide is contained in an amount of 1 to 20% by weight.
In a reducing atmosphere containing carbon having an oxygen partial pressure of 0.2 atm or less.
Sintering at a temperature of ° C., and impregnating the molded body with carbon from the atmosphere to obtain a ceramic having a carbon content of 0.01 to 2.0% by weight and a relative density of 95% or more. In particular, it is preferable that the baking is performed with a carbon powder placed around the molded body, and that the baking is performed under a pressure of 100 kg / cm ² or more.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION
The cordierite is mainly composed of a cordierite-based composite oxide represented by 2MgO.2Al ₂ O ₃ .5SiO ₂ , and the cordierite crystals exist as crystal particles having an average particle diameter of 1 to 10 μm. , A coefficient of thermal expansion of 1 × 10 ⁻⁶ / ° C. or less at 10 to 40 ° C., especially 0.5 × 10 ⁻⁶ /
° C. or less, and a low-density material having a relative density of 95% or more, especially 97% or more, and a volume resistivity at room temperature of 10 ⁷ Ω · cm or less, particularly 10 ³ Ω · cm or less. It has characteristics.

The reason why the coefficient of thermal expansion is limited to 1 × 10 ⁻⁶ / ° C. or less is that when the coefficient of thermal expansion is larger than this, the dimensional change due to temperature change becomes large. In addition, misalignment or the like during exposure processing is likely to occur. On the other hand, if the volume resistivity is larger than 10 ⁷ Ω · cm, the chargeability is increased, and the material is unsuitable as a non-chargeable member. On the other hand, if the relative density is lower than 95%, contamination due to deposits on the pores is caused.

Having the above characteristics, the low-resistance ceramic of the present invention contains carbon in an amount of 0.01 to 2.0.
It is important that the content is 0% by weight, preferably 0.02 to 1.0% by weight. If the carbon content is less than 0.01% by weight, low resistance characteristics of 10 ⁷ Ω · cm or less cannot be obtained, and if the carbon content exceeds 2.0% by weight, the thermal expansion coefficient is 1 × 10 5 ^-6 / ° C and a dense body cannot be obtained.

The ceramic contains 1 to 20% by weight, especially 5 to 15% by weight of a rare earth element in terms of oxide.
Is desirable. Cordierite 1
Even if it is 00% by weight or a certain degree of densification is possible, its firing temperature is high and its firing temperature range is ± 5%.
It is difficult to stably produce a dense body because it is very narrow at ℃. On the other hand, when the rare earth element is contained in an amount of 1% by weight or more, it reacts with the cordierite component at the time of firing to form a liquid phase, thereby exhibiting an effect of enhancing sinterability. Since the temperature can be expanded to about ± 25 ° C., mass productivity can be improved. Therefore, if the amount of the rare earth element is less than 1% by weight, the sinterability decreases, and if it exceeds 20% by weight, the coefficient of thermal expansion increases, and characteristics of 1.0 × 10 ⁻⁶ / ° C. or less cannot be achieved.

Examples of rare earth elements contained in ceramics include Y, Yb, Lu, Er, Ce, Nd, and Sm. Among them, Y, Yb,
Yb is preferably contained.

The rare earth element exists at the grain boundary of the cordierite crystal, and the rare earth element is RE ₂ O.
It is desirable to present as silicate compound crystalline phase, such as ₃ · SiO ₂ or RE ₂ O ₃ · 2SiO _2. This is to achieve low thermal expansion by crystallization of the grain boundary phase.

In order to produce the low-resistance ceramic as described above, first, 1 to 20% by weight of a rare earth oxide powder having an average particle size of 10 μm or less is added to a cordierite powder having an average particle size of 10 μm or less. Add in proportions. In some cases, a carbon powder or an organic compound which can be converted into carbon after pyrolysis is added to prepare a starting material composition. At this time,
It is desirable that the cordierite powder and the rare earth element oxide powder used have an average particle size of 10 μm or less in order to enhance sinterability.

According to the method of the present invention, as a first method, first, a starting material composition containing cordierite powder as a main component, 1 to 20% by weight of a rare earth element oxide and a carbon source is sufficiently prepared. The powder is sufficiently mixed by a ball mill or the like to produce a mixed powder. In some cases, the mixed powder is formed into a predetermined shape by a desired molding means, for example, a die press, a cold isostatic press, an extrusion molding, or the like, into an arbitrary shape.

The carbon source blended at this time includes:
An organic resin such as a carbon powder or a phenol resin capable of generating carbon by heat treatment is used.

Then, the mixed powder or the compact is subjected to an inert atmosphere or a non-oxidizing atmosphere such as Ar or N ₂ having an oxygen partial pressure of 0.2 atm or less, particularly 0.1 atm or less, and even 0.05 atm or less. It is fired at a temperature of 1100 to 1450 ° C. in an atmosphere to densify it to a relative density of 95% or more. If the oxygen partial pressure of the atmosphere at this time exceeds 0.2 atm, the carbon contained in the mixed powder or the compact is volatilized, and finally 0.01 to 2.0% by weight in the ceramics.
Is difficult to survive. When the firing temperature is 1
If the temperature is lower than 100 ° C., a dense ceramic cannot be produced. If the temperature exceeds 1500 ° C., cordierite is melted.

In particular, in order to promote densification, 100 kg / cm ² at the time of firing by hot press firing or the like.
It is desirable to bake under the above pressure. In that case, densification can be performed at a firing temperature of 1100 to 1400 ° C.

In a second production method, a molded product containing cordierite as a main component and a rare earth element oxide at a ratio of 1 to 20% by weight is used.
In particular, baking is performed at a temperature of 1100 to 1450 ° C. in a reducing atmosphere containing carbon of 0.1 atm or less, further 0.05 atm or less, and carbon is impregnated into the molded body from the atmosphere. The reducing atmosphere containing carbon at this time can be formed by storing the compact in a sagger made of carbon and firing it, or by arranging carbon powder around the compact, but impregnation into the compact In order to carry out the process efficiently, it is most desirable to arrange a carbon powder around the molded body, and furthermore, bury the molded body in the carbon powder and fire it.

In order to promote the densification, it is desirable that the compact is buried in carbon powder by hot press firing or the like and fired under a pressure of 100 kg / cm ² or more. In that case, densification can be performed at a firing temperature of 1100 to 1400 ° C.

In this manner, a ceramic having a carbon content of 0.01 to 2.0% by weight and a relative density of 95% or more can be finally obtained. The maximum void diameter on the mirror surface can be reduced to 5 μm or less.

Further, in order to further densify the ceramics produced as described above, 900 to 1400 in a pressurized atmosphere of 1000 atm or more by Ar or N _2.
It is also possible to perform hot isostatic pressure treatment (HIP treatment) at a temperature of ° C.

Further, the ceramics prepared as described above are heat-treated at 1100 to 1400 ° C. in a non-oxidizing atmosphere to promote crystallization of the grain boundaries of cordierite crystals, whereby the above-mentioned rare earth element Can be precipitated.

The low resistivity ceramic has a volume resistivity at room temperature of 10 ⁷ Ω · cm or less.
Thermal expansion coefficient at 10 to 40 ° C. 1 × 10 ⁻⁶ / ° C. or less,
Provided that the relative density satisfies the characteristic of 95% or more,
In addition to the cordierite component and the rare-earth element compound, it may contain unavoidable impurities in production and other components for improving sinterability and characteristics. For example, W, Mo, N
oxides such as i, Fe, Zr, and Sr;

The low-resistance ceramics of the present invention thus produced can be used as a member for a semiconductor manufacturing apparatus, for example, a member in a vacuum apparatus used for manufacturing a semiconductor element, a susceptor, a vacuum chuck, an electrostatic chuck, or the like. It is suitably used for a stage in a lapping machine or an exposure apparatus, a mirror for measuring the position of a stage, or a supporting member thereof, and various jigs in a semiconductor manufacturing process. In particular, it is most suitably used for a vacuum chuck or the like that requires non-charging properties.

[0033]

EXAMPLES (Example 1) Purity of 99% or more, average particle size of 3
μm cordierite powder, average particle size is 1μm
Of the rare earth element oxide powders of Y ₂ O ₃ , Yb ₂ O ₃ , Er ₂ O ₃ , and CeO ₂ were mixed at a ratio shown in Table 1 and then mixed for 24 hours by a ball mill. After the mixture is press-molded, the compact is buried in carbon powder (C baked), or the carbon powder is placed around the compact in a carbon sagger (around C) and the conditions in Table 1 are applied. Non-pressure firing (P
LS) or the compact was buried in carbon powder in a carbon press mold and fired by hot press (HP) under the conditions shown in Table 1.

The relative density of the obtained ceramic was measured by the Archimedes method. Further, the ceramic was polished and ground to a size of 3 × 4 × 15 mm, and the coefficient of thermal expansion of the ceramic up to 10 to 40 ° C. was measured. In addition, the volume resistivity at room temperature was measured. The mirror-polished surface of the ceramic was observed with a scanning electron microscope, and the maximum void diameter was measured. The results are shown in Table 1.

[0035]

[Table 1]

As shown in Table 1, based on the present invention,
By sintering a compact containing a predetermined amount of cordierite and a rare earth element oxide at a temperature of 1300 to 1450 ° C. by burying and burning carbon, a low resistivity having a relative density of 95% or more and a volume resistivity of 10 ⁷ Ω · cm or less is obtained. Ceramics could be produced.

However, in Sample No. 15 in which the firing temperature exceeded 1450 ° C., a part of the sample was melted and the firing temperature was 90 ° C.
In sample No. 11 at 0 ° C., densification was not possible to a relative density of 95% or more. In sample No. 21 in which carbon was not buried at the time of firing, the amount of carbon was reduced to 0.
At least 0.1% by weight could not be contained, and the volume resistivity at room temperature did not fall below 10 ⁷ Ω · cm. Sample No. 6 in which the amount of the rare earth element oxide added was more than 20% by weight could not achieve a thermal expansion characteristic of 1.0 × 10 ⁻⁶ / ° C. or less, and the amount of the rare earth element oxide was less than 1% by weight. Sample N
In Comparative Example No. 1, it was not possible to densify to a relative density of 95% or more, and the sinterable temperature range was very narrow at ± 5 ° C. Sample No. 16-1 pressurized to 100 kg / cm ² or more during firing
In No. 9, the maximum void diameter could be reduced to 5 μm or less.

Example 2 An average particle size of 1 μm was compared with a cordierite powder having a purity of 99% or more and an average particle size of 3 μm.
After mixing each of the rare earth element oxide powders of Y ₂ O ₃ , Yb ₂ O ₃ , Er ₂ O ₃ , and CeO _{2 with} a phenol resin capable of producing carbon by carbonization at a ratio shown in Table 2 in terms of carbon, The mixture was mixed in a ball mill for 24 hours. After press-molding the mixed powder, the compact was fired without pressure (PLS) under the conditions shown in Table 2. The mixed powder was subjected to hot press firing (HP) under the conditions shown in Table 2. In the non-pressurized firing, the molded body was placed in a carbon sagger, and in the hot press firing, a carbon press mold was used. Then, the same evaluation as in Example 1 was performed.

For sample No. 42, a compact containing cordierite, a rare earth element oxide and a carbon source was embedded in carbon powder and fired under the conditions shown in Table 2, and similarly evaluated.

[0040]

[Table 2]

As shown in Table 2, based on the present invention,
A raw material powder containing a predetermined amount of cordierite, a rare-earth element oxide and a carbon source is fired at a temperature of 1100 to 1450 ° C. in a carbon atmosphere having an oxygen partial pressure of 0.1 atm or less to obtain a relative density of 95% or more and an electric resistance of Is 10 ⁷ Ω
Properties of less than cm were achieved.

However, in Sample No. 36, in which the firing temperature exceeds 1450 ° C., a part of the sample is melted and the firing temperature is 90 °.
In Sample No. 32 at a temperature lower than 0 ° C., densification did not proceed. Sample No. 27, in which the amount of the rare earth oxide added was more than 20% by weight, had a large thermal expansion coefficient of 1.0 × 10
^-6 / ° C. or less cannot be achieved, and in Sample No. 22 in which the amount of rare earth element oxide is less than 1% by weight, the densification is insufficient and the sinterable temperature range is extremely narrow at ± 5 ° C. there were. Sample N pressed to 100 kg / cm ² or more during firing
In o.37 to 40, the maximum void diameter could be reduced to 5 μm or less.

[0043]

As described in detail above, the low-resistance ceramic of the present invention can realize a low resistance of not more than 10 ⁷ Ω · cm while maintaining the excellent low thermal expansion characteristics of cordierite. . As a result, this low-thermal-expansion ceramic is used as an exposure apparatus for performing an exposure process for forming a fine circuit on the surface of a Si wafer, various members such as a vacuum apparatus, in particular, a vacuum chuck that contacts a semiconductor wafer. As a result, there is no change in dimensions even when the temperature of the atmosphere changes, and it also affects the prevention of dust adhesion and the generation of plasma due to charging of the member surface, and can be destroyed by static electricity when it comes into contact with a semiconductor wafer. Therefore, the quality and mass productivity at the time of manufacturing the semiconductor element can be improved.

Claims (9)

[Claims] 1. A method comprising a cordierite as a main component, a rare earth element in an amount of 1 to 20% by weight in terms of an oxide, and carbon in an amount of 0.01 to
2.0% by weight and 10-40 ° C
Coefficient of thermal expansion at 1 × 10 ⁻⁶ / ° C. or less, relative density 95
% And a volume resistivity at room temperature of 10 ⁷ Ω · cm or less. 2. The low-resistance ceramic according to claim 1, wherein a silicate crystal phase of a rare earth element exists at a grain boundary of the cordierite crystal. 3. A mixed powder or molded product containing cordierite powder as a main component, 1 to 20% by weight of a rare earth element oxide and a carbon source or an inert atmosphere having an oxygen partial pressure of 0.2 atm or less. 1100-14 in oxidizing atmosphere
Calcined at a temperature of 50 ° C. to have a carbon content of 0.01 to
A method for producing a low-resistance ceramic, comprising obtaining a ceramic having 2.0% by weight and a relative density of 95% or more. 4. The method according to claim 3, wherein the firing is performed under a pressure of 100 kg / cm ² or more. 5. A molded body containing cordierite as a main component and a rare earth element oxide in a proportion of 1 to 20% by weight is placed in a reducing atmosphere containing carbon having an oxygen partial pressure of 0.2 atm or less. Sintering at a temperature of about 1450 ° C. to impregnate carbon into the compact from the atmosphere to obtain a ceramic having a carbon content of 0.01 to 2.0% by weight and a relative density of 95% or more. Manufacturing method of resistance ceramics. 6. The method for producing a low-resistance ceramic according to claim 5, wherein the firing is performed by arranging carbon powder around the molded body. 7. The method according to claim 5, wherein the firing is performed under a pressure of 100 kg / cm ² or more. 8. A composition mainly comprising cordierite, 1 to 20% by weight of a rare earth element oxide and 0.01 to 2.0% of carbon.
A ceramic having a thermal expansion coefficient of 1 × 10 ⁻⁶ / ° C. or less at 10 to 40 ° C., a relative density of 95% or more, and a volume resistivity at room temperature of 10 ⁷ Ω · cm or less at 10 to 40 ° C. A member for a semiconductor manufacturing apparatus characterized by the above-mentioned. 9. The member for a semiconductor manufacturing apparatus according to claim 8, comprising a member that contacts at least the semiconductor wafer.