JPH11130520A - Low thermally expandable ceramic and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low thermally expandable ceramic having both a low thermal expansion and high rigidity and to provide a method for producing the ceramic. SOLUTION: A molded article obtained by compounding 80-92 wt.% of cordierite with 8-20 wt.% of an oxide of rare earth element (RE) is baked in vacuum at 1,300-1,500 deg.C, cooled at 10 deg.C/min cooling rate to 1,000 deg.C to give a low thermally expandable ceramic comprising cordierite as a main phase and a crystal phase of the formula RE2 O3 .2SiO2 precipitated on the boundary, having <=0.5×10<-6> / deg.C coefficient of thermal expansion and >=120 GPa Young modulus at >=95% relative humidity at 10-40 deg.C, suitable for especially a part of semiconductor producing apparatus such as a stage for an exposure device, 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 cordierite suitable for a susceptor, an electrostatic chuck, a stage, a jig in a semiconductor manufacturing process, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, cordierite-based sintered bodies have been conventionally known as low thermal expansion ceramics, and have been applied to filters, honeycombs, refractories, and the like. The cordierite-based sintered body is made of cordierite powder or MgO, Al ₂ O ₃ ,
By mixing SiO ₂ powder, adding a rare earth element oxide, SiO ₂ , CaO, MgO, etc. as a sintering aid thereto, forming the mixture into a predetermined shape, and firing at a temperature of 1000 to 1400 ° C. Produced (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, 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 part for semiconductor manufacturing equipment by utilizing its low thermal expansion property, as disclosed in JP-A-1-191422 and JP-B-6-9767.
No. 5 is proposed. 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.

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 semiconductor manufacturing equipment have a smaller coefficient of thermal expansion than metals, but have a coefficient of thermal expansion of 5.2 × 10 ^{-6 at} 10 to 40 ° C. / ° C, 1.5 × 10 ^-6 / ° C
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 steps 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 present inventors have conducted intensive studies on the above-mentioned problems, and as a result, obtained a composite of cordierite with a rare earth element oxide at a predetermined ratio, and the addition of the above-mentioned particles at the grain boundaries of cordierite crystals. The present inventors have found that the sinterability can be increased and the Young's modulus can be increased without impairing the low thermal expansion characteristics by causing the rare-earth element oxide to be present as a specific crystal phase.

That is, the low thermal expansion ceramic of the present invention comprises:
80 to 92% by weight of cordierite, rare earth element (R
E) containing 8 to 20% by weight of an oxide, having a relative density of 95% or more, and at the grain boundaries of cordierite crystals,
The method is characterized in that a disilicate crystal phase represented by RE ₂ O ₃ · 2SiO ₂ is precipitated. Further, as a method for producing low thermal expansion ceramics, cordierite powder is 80 to 92% by weight, Rare earth element (RE)
A molded body containing 8 to 20% by weight of an oxide of
After firing at a temperature of 1300-1500 ° C, 1000 ° C
, At a cooling rate of 10 ° C./min or less.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The low thermal expansion ceramic of the present invention is a cordierite having a general formula of 2MgO.2Al ₂ O _3.
· 5SiO are those mainly composed of a composite oxide represented by _2, the average particle size is present as 1~10μm crystal grains. This cordierite is present in the sintered body at a ratio of 80 to 92% by weight, preferably 85 to 90% by weight.

Further, the sintered body contains a rare earth element oxide as an auxiliary component in an amount of 8 to 20% by weight, particularly 10 to 15% by weight. Rare earth oxides
It reacts with the components of cordierite during firing, exhibits the effect of increasing the sinterability from generating a liquid phase, and has a high Young's modulus itself, so by including these, from the examples described later, As is apparent, the Young's modulus of the sintered body can be increased to 120 GPa or more, particularly 130 GPa or more.

By the addition of such a rare earth element oxide, the relative density of the sintered body can be increased to 95% or more, particularly to 96% or more. If the amount of the sintering aid is less than 8% by weight, the sinterability is not sufficient, and it is necessary to perform sintering at a high temperature, or the relative density cannot be increased to 95% or more. On the other hand, if it exceeds 20% by weight, the coefficient of thermal expansion becomes large, and characteristics of 0.5 × 10 ⁻⁶ / ° C. or less cannot be achieved.

In the sintered body, a rare earth element (RE) oxide added as a sintering aid to the grain boundaries of the cordierite crystal particles is represented by RE ₂ O ₃ .2SiO _2. By being present as a disilicate crystal phase,
It is possible to prevent the coefficient of thermal expansion of the ceramic from increasing. That is, as compared with the case where the rare-earth element oxide exists as an amorphous phase at the grain boundary, the crystalline phase, particularly the disilicate phase represented by RE ₂ O ₃ .2SiO ₂ , has a denser atomic arrangement. This has the effect of improving the Young's modulus of the entire sintered body and lowering the coefficient of thermal expansion. In addition, as the rare earth element to be used, in particular, Y, Y
Elements such as b, Er or Ce are desirable.

As described above, in order to precipitate a disilicate crystal phase at a grain boundary, it is necessary to contain a relatively large amount of a rare earth element oxide. Therefore, the content of the rare earth element oxide is limited to the above ratio. If the content is less than 8% by weight, the precipitation of the disilicate crystal phase cannot be expected, and as a result, the Young's modulus of the ceramics cannot be increased, If the content is more than 20% by weight, the amount of cordierite that reacts increases, and a different phase is precipitated, the coefficient of thermal expansion of the ceramics increases, and the cordierite does not exhibit excellent low thermal expansion characteristics. The coefficient of thermal expansion of the ceramic of the present invention is 0.5 × at 10 to 40 ° C.
It is desirably 10 ⁻⁶ / ° C. or less, especially 0.4 × 10 ⁻⁶ / ° C. or less.

The disilicate crystal phase is a crystal phase formed by a reaction between a rare earth element oxide and the SiO ₂ component in cordierite, and the cordierite crystal phase is not necessarily of the general formula 2MgO.2Al ₂ O. ₃ · 5SiO
₂ , not MgO, Al ₂ O ₃ ,
Since the solid solution source is large for each component of SiO ₂ , for example, residual MgO, Al ₂
O ₃ may form a solid solution in the cordierite crystal to form a cordierite crystal phase having a non-stoichiometric composition.

In order to produce the above ceramics, a rare earth element oxide powder having an average particle diameter of 10 μm or less is added to a cordierite powder having an average particle diameter of 10 μm or less at a ratio of 8 to 20% by weight. I do.

After the respective components are blended in the above ratio, they are sufficiently mixed by a ball mill or the like, and formed into a desired shape by a desired molding means, for example, a die press, a cold isostatic press, an extrusion molding or the like. After molding, firing is performed.

The sintering can be performed at a temperature in the range of 1300 to 1500 ° C., preferably 1350 to 1450 ° C. for about 1 to 10 hours, so that the relative density can be increased to 98% or more. If the temperature at this time is lower than 1300 ° C., densification cannot be performed, and if it exceeds 1500 ° C., the molded body is melted.

In the present invention, RE ₂ O ₃
In order to precipitate a crystal phase of 2SiO ₂ , it is necessary to cool at an average cooling rate of 10 ° C./min or less, especially 5 ° C./min or less from the firing temperature to a temperature range of 1000 ° C. after the above firing. It is. If the cooling rate in this temperature range is higher than 10 ° C./min, it is difficult to precipitate a disilicate crystal phase at the grain boundaries. Note that the annealing temperature range may be extended from the firing temperature to a range of 1000 ° C. or less.

[0024]

EXAMPLE For cordierite powder having an average particle size of ₃ μm, Y ₂ O ₃ , Yb ₂ O ₃ and Er having an average particle size of 1 μm were used.
After mixing the powders of ₂ O ₃ and CeO _{2 at} the ratios shown in Tables 1 and 2, they were mixed in a ball mill for 24 hours, and then 1 t / cm ²
Molding was performed under the following pressure. Then, the molded body was placed in a silicon carbide sagger and fired under the conditions shown in Tables 1 and 2 at 1000 ° C.
The average cooling rate was changed as shown in Tables 1 and 2, and various ceramics were produced.

The obtained ceramic is polished and 3 × 4 ×
Grinding to a size of 15mm, this ceramic 1
The coefficient of thermal expansion from 0 to 40 ° C was measured. The Young's modulus at room temperature was measured by the ultrasonic pulse method. The results are shown in Tables 1 and 2.

[0026]

[Table 1]

[0027]

[Table 2]

[0028] As seen in Tables 1, based on the present invention, it was added to the cordierite a rare earth oxide at a predetermined ratio, by precipitating the crystal phase of RE ₂ O ₃ · 2SiO _2, thermal expansion 0.5 × 10 ^-6 / ° C.
The following was achieved, and the Young's modulus could be increased to 120 GPa or more, and the Young's modulus tended to increase as the amount of addition increased.

However, the amount of these rare earth element oxides is 8
The sample No. 1 having less than 95% by weight did not achieve a relative density of 95% or more, had a Young's modulus lower than 120 GPa, and had a coefficient of thermal expansion higher than 0.5 × 10 ^-6 / ° C. . Further, in sample No. 17 exceeding 20% by weight,
Although the Young's modulus was high, the coefficient of thermal expansion was larger than 0.5 × 10 ⁻⁶ / ° C.

Further, the firing temperature is 1300 ° C.
Sample No. 3, which was lower than that, could not be densified and a relative density of 95% or more was not achieved. In the case of Sample No. 9 in which the firing temperature was higher than 1500 ° C., the molded body was melted and ceramics could not be produced.

As for the cooling rate, Sample No. 1 in which the cooling rate up to 1000 ° C. is higher than 10 ° C./min.
In ₃ , 14, 22, 27 and 32, RE ₂ O ₃ 2Si
O ₂ crystal phase does not precipitate, resulting in low Young's modulus,
In addition, the thermal expansion coefficient was large. Therefore, it is understood that the precipitation of the crystal phase of RE ₂ O ₃ .2SiO _{2 at} the grain boundary is important for increasing the Young's modulus and reducing the thermal expansion.

[0032]

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 equipment such as performing exposure processing on a wafer for forming a fine circuit, for example, an exposure equipment stage, etc. Also, 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 (2)

[Claims] 1. A cordierite containing 80 to 92% by weight of a rare earth element (RE) oxide at a ratio of 8 to 20% by weight, a relative density of 95% or more, and a grain boundary of a cordierite crystal, A low thermal expansion ceramic, wherein a disilicate crystal phase represented by RE ₂ O ₃ .2SiO ₂ is precipitated. 2. A cordierite powder comprising 80 to 92% by weight,
After sintering a molded body in which an oxide of a rare earth element (RE) is blended at a rate of 8 to 20% by weight at a temperature of 1300 to 1500 ° C, it is cooled to 1000 ° C at a cooling rate of 10 ° C / min or less. A method for producing a low-thermal-expansion ceramic, comprising: