JPH11100275A - Low thermal expansion ceramic and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the ceramis having low thermal expansion as well as high stiffness, and to provide the method for preparing it. SOLUTION: The ceramics consisting of silicon nitride, wherein >=80% of the silicon nitride is α-type, and having a relative density of >=95%, a high young's modulus of >=200 GPa at room temp., and a low thermal expansion coefficient of <=1×10<-6> in the temp. range of 10-40 deg.C, is obtained by sintering the green body comprising 10-50 wt.% of cordierite, 0.5-10 wt.% of the oxides of rare-earth elements, and a residual amount of silicon nitride containing >=80% of an α-type, under inert atmosphere at 1,300-1,700 deg.C. It is possible to improve accuracy in forming highly fine circuit, quality of the product and productivity by applying the low thermal expansion ceramics to the parts for preparing semiconductors, e.g. the stage for an aligner etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a vacuum device structure,
The present invention relates to a low thermal expansion ceramic mainly composed of silicon nitride and cordierite suitable for a susceptor, an electrostatic chuck, a stage, a jig in a semiconductor manufacturing process, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Cordierite-based sintered bodies are conventionally known as ceramics having a low thermal expansion, and include filters,
It is applied to honeycombs and refractories. The cordierite-based sintered body is mixed with cordierite powder or MgO, Al ₂ O ₃ , and SiO ₂ powder that forms cordierite, and as a sintering aid, a rare earth element oxide or SiO ₂ , CaO, MgO, etc., molded into a predetermined shape, and fired at a temperature of 1000 to 1400 ° C. (JP-B-57-3629, 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, an electrostatic chuck, an insulating ring, or other jigs, etc. So far, alumina and silicon nitride have been relatively inexpensive,
It is widely used because it is chemically stable. Also,
Conventionally, ceramics such as alumina and silicon nitride have been used as an XY table of an exposure apparatus.

Recently, it has been proposed to use cordierite as a component of semiconductor manufacturing equipment by utilizing its low thermal expansion property, as disclosed in JP-A-1-191422 and Japanese Patent Publication No. 6-97675.
It is proposed in the issue. According to Japanese Patent Application Laid-Open No. 1-191422, it is proposed that a reinforcing ring 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.

In Japanese Patent Publication No. 6-97675, it is proposed to use an alumina or cordierite-based sintered body as a base for an electrostatic chuck on which a wafer is mounted.

[0006]

In recent years, with high integration in LSIs and the like, circuit miniaturization has been rapidly advanced,
The line width is also being refined to a submicron order. High accuracy is required for an exposure apparatus for forming a high-precision circuit on a Si wafer. For example, a stage member of an exposure apparatus requires a 100 nm (0.
At present, a positioning accuracy of 1 μm or less is required, and a positioning error of exposure has a great influence on improvement of product quality and yield.

Ceramics such as alumina and silicon nitride which have been generally used for manufacturing semiconductors have a smaller coefficient of thermal expansion than metals, but each have a coefficient of thermal expansion of 5.2 × 10 ^-6 / 10 to 40 ° C. ° C, 1.5 × 10 ^-6 / ° C, and several hundred nm when the ambient temperature changes by 0.1 ° C.
(0.1 .mu.m), and this change becomes a serious problem in precise processes such as exposure, and the conventional ceramics have low accuracy and lower 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, like the stage of an exposure apparatus,
In the case where the support on which the Si wafer is mounted moves at a high speed to the position where the exposure processing is performed, the support itself after the movement is still vibrating even after stopping at a predetermined position. However, there is a problem that the exposure accuracy decreases when the exposure process is performed. This is more remarkable as the width of the wiring formed by exposure becomes narrower, and has been a fatal problem in forming a fine wiring circuit.

Since such vibrations are caused by low rigidity of the members themselves, high rigidity, that is, high Young's modulus is required for these members.

Accordingly, an object of the present invention is to provide a low-thermal-expansion ceramic having low thermal expansion itself and high rigidity, and a method for producing the same.
It is another object of the present invention to provide a semiconductor manufacturing component that does not easily generate vibration even when driven at a high speed, such as a stage.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above-mentioned problems and found that cordierite is compounded with silicon nitride particles having a high Young's modulus, especially α-silicon nitride particles at a predetermined ratio. Found that the Young's modulus can be significantly increased without impairing the low thermal expansion characteristics,
The present invention has been reached.

That is, the low thermal expansion ceramic of the present invention comprises:
It comprises cordierite in an amount of 10 to 50% by weight and a rare earth element oxide in an amount of 0.5 to 10% by weight, the balance being composed of silicon nitride having an α-type content of 95% or more. The Young's modulus at room temperature is 200G
Pa or more and the coefficient of thermal expansion at 10 to 40 ° C. is 1 ×
It has a low coefficient of thermal expansion of 10 ⁻⁶ / ° C. or less. Such a ceramic contains 10 to 50% by weight of cordierite, 0.5 to 10% by weight of a rare-earth element oxide, and a balance formed of silicon nitride having an α-type content of 80% or more. It is manufactured by firing at a temperature of 1300 to 1700 ° C. in a gas atmosphere.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The low thermal expansion ceramics of the present invention, cordierite is 2MgO.2Al ₂ O ₃ .5S
It is mainly composed of a composite oxide represented by iO ₂ and silicon nitride, and both cordierite and silicon nitride exist as crystal particles having an average particle size of 1 to 10 μm. This cordierite is present in the sintered body at a rate of 10 to 50% by weight, preferably 20 to 40% by weight. In addition, the sintered body contains at least one selected from rare earth element oxides as an auxiliary component in a proportion of 0.5 to 10% by weight, particularly 2 to 6% by weight. The remainder of the cordierite and the rare earth element oxide of this sintered body is made of silicon nitride, and is desirably present in the sintered body at a ratio of 50 to 89.5% by weight, particularly 60 to 80% by weight.

Cordierite is an important component for lowering the thermal expansion of the sintered body.
If the amount is less than 50% by weight, the coefficient of thermal expansion increases, and if the amount of cordierite is more than 50% by weight, the Young's modulus decreases.

Further, silicon nitride accounts for 8% of the total amount of silicon nitride.
It is important that 0% or more, particularly 90% or more, is α-type. By leaving the α-type silicon nitride, the Young's modulus can be improved as compared with the case of β-type silicon nitride while having a low coefficient of thermal expansion. Therefore, the content of α-type silicon nitride is 80%.
%, The desired high Young's modulus cannot be obtained.

Further, the rare-earth element oxide reacts with a part of cordierite, acts as a sintering aid, and enables sintering at a low temperature. It is possible to prevent the transition to silicon nitride. Therefore, when the amount of the rare earth element oxide is less than 0.5% by weight, densification is hindered, and the sintering temperature must be increased. As a result, the α-β transition of silicon nitride is promoted, and as a result, the Young The rate will be low. When the amount of the rare earth element oxide is more than 10% by weight, the coefficient of thermal expansion of the sintered body increases, and the cordierite does not exhibit excellent low thermal expansion characteristics. Note that the rare earth element oxide exists as a glass phase or a crystal phase at the grain boundaries of crystal grains of cordierite or silicon nitride.

The low thermal expansion ceramic of the present invention comprises:
The relative density is 95% or more, particularly 97% or more;
It has excellent properties such that the coefficient of thermal expansion at 40 ° C. is 1 × 10 ⁻⁶ / ° C. or less, particularly 0.7 × 10 ⁻⁶ / ° C. or less, and the Young's modulus at room temperature is 200 GPa or more, particularly 220 GPa or more. Have

In order to produce a sintered body as described above, cordierite powder having an average particle size of 10 μm or less is used
% By weight, particularly 20 to 40% by weight, containing 0.5 to 10% by weight, especially 2 to 6% by weight of the rare earth element oxide powder, and silicon nitride powder having α-type content of 80% or more. Weigh and mix as needed. After blending each component in the above ratio, thoroughly mixed by a ball mill or the like, desired molding means into a predetermined shape, for example, a mold press, cold isostatic press, after molding into an arbitrary shape by extrusion, etc., Bake.

The sintering is performed at a temperature of 1300 to 1700 ° C., preferably 1400 to 1600 ° C. for about 1 to 10 hours in a vacuum or in an atmosphere of an inert gas such as Ar or N ₂ to obtain a relative density of 95% or more. Especially 97% by weight
It can be densified as described above. The temperature at this time is 13
If the temperature is lower than 00 ° C., densification cannot be achieved. If the temperature exceeds 1700 ° C., the molded body is melted or α-β transition is promoted. In addition, firing in an oxidizing atmosphere such as air oxidizes silicon nitride compounded as a sub-component, and does not exhibit the effect of increasing the Young's modulus.

[0021]

EXAMPLE To a cordierite powder having an average particle diameter of 3 μm, a silicon nitride powder having an average particle diameter of 1 μm was added at a ratio shown in Table 1. Further, as a sintering aid component, Y ₂ O ₃ ,
After blending each powder of Yb ₂ O ₃ , Er ₂ O ₃ , and CeO _{2 at} the ratios shown in Table 1, mixing them with a ball mill for 24 hours,
Molding was performed at a pressure of t / cm ² . Then, the compact was placed in a silicon carbide sagger and fired under the conditions shown in Table 1.

The obtained sintered body is polished and 3 × 4 × 15 m
The sample was ground to a size of m, and the coefficient of thermal expansion of the sample up to 10 to 40 ° C. was measured. The Young's modulus at room temperature was measured by the ultrasonic pulse method. The relative density was calculated by the Archimedes method.

The results are shown in Table 1.

The content of α-type silicon nitride (α / α + β) in the sintered body was determined by X-ray diffraction measurement as α-Si ₃ N ₄
Of (102) and the total peak intensity of the (210) was divided by the peak intensity X ₁ in 2, β-Si ₃ of N ₄ (10
A value obtained by dividing the total peak intensity of 1) and (210) by 2 is defined as a peak intensity X ₂ , and an intensity ratio ΔX ₁ / (X ₁ +
X ₂ )｝ 100 (%).

[0025]

[Table 1]

As is clear from the results shown in Table 1, the sample No. 25 which is a conventional cordierite sintered body obtained by adding a rare earth element oxide to cordierite has a coefficient of thermal expansion of 0.2.
Very low thermal expansion of × 10 ^-6 / ° C, but Young's modulus of 1
It is as low as 20 GPa.

On the other hand, according to the present invention, the Young's modulus can be increased to 200 GPa or more by adding cordierite, silicon nitride and rare earth element oxide at a predetermined ratio, and the thermal expansion of 10 to 40 ° C. Rate 1 × 1
0 ⁻⁶ / ° C. or less.

However, in Sample No. 1 having a cordierite content of less than 10% by weight, the coefficient of thermal expansion was high, and
Sample No. 7 having more than 0% by weight had a low Young's modulus.

The rare earth element oxide content is 0.5% by weight.
Sample No. 20 having a lower Young's modulus
In the sample No. 24 having more than the weight%, the coefficient of thermal expansion was high. Sample No. 8 in which the α-type content in silicon nitride was less than 80% had a low Young's modulus.

Further, with respect to the firing temperature, the sample No. 12 lower than 1300 ° C. cannot be densified,
In sample No. 16 higher than 700 ° C., α-Si ₃ N ₄
The transition from to β-Si ₃ N ₄ progressed, the amount of α-Si ₃ N ₄ decreased, and the Young's modulus decreased.

[0031]

As described above in detail, the low thermal expansion ceramic of the present invention can increase rigidity, that is, Young's modulus, while maintaining excellent low thermal expansion characteristics of cordierite. As a result, by using this low thermal expansion ceramic as a part for semiconductor manufacturing such as performing exposure processing on a wafer for forming a fine circuit, for example, a stage for an exposure apparatus, it can be used even for a temperature change of an atmosphere. There is no change in dimensions, excellent accuracy can be obtained, and a decrease in accuracy due to vibration can be prevented, so that the quality and mass productivity of semiconductor device manufacturing can be improved.

Claims (3)

[Claims] 1. A silicon nitride containing 10 to 50% by weight of cordierite and 0.5 to 10% by weight of a rare-earth element oxide, the balance being silicon nitride having an α-type content of 80% or more, and a relative density of Is 95% or more. 2. Young's modulus at room temperature is 200 GPa or more.
2. The low thermal expansion ceramic according to claim 1, wherein the coefficient of thermal expansion at 0 to 40 [deg.] C. is 1 * 10 <^-6> or less. 3. A molded article comprising 10 to 50% by weight of cordierite, 0.5 to 10% by weight of a rare earth element oxide, and the remainder comprising silicon nitride having an α-type content of 80% or more, A method for producing low thermal expansion ceramics, comprising firing at a temperature of 1300 to 1700C in an inert gas atmosphere.