JP2006232667A - Low thermal expansion ceramic and member for device for manufacturing semiconductor using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lightweight ceramic having a low thermal expansion coefficient and high stiffness, which is most suitable for a material of various devices including an aligner used in a semiconductor manufacturing process or the like, components and tools, and its manufacturing method. <P>SOLUTION: The low thermal expansion ceramic comprises β-eucryptite represented by the general formula: LiAlSiO<SB>4</SB>of 95-99 wt% and magnesia of 1-5 wt%. The void rate of the low thermal expansion ceramic is less than 0.1% by volume and the average void diameter is less than 2 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a lightweight, high-rigidity, low thermal expansion ceramic suitable for use in semiconductor manufacturing processes and the like, and a semiconductor manufacturing apparatus suitable for members such as an XY stage for an exposure apparatus, an electrostatic chuck and its structural parts, and a mirror. Related to parts.

In recent years, along with the high integration of semiconductor electronic circuit components such as LSI, circuit line widths and circuit design rules have been rapidly miniaturized, and circuit line widths are becoming smaller from 0.35 μm to 0.10 μm. Further, with respect to an exposure apparatus for forming an electronic circuit having a fine circuit line width on a Si wafer, structurally high accuracy and high positional accuracy are required. In the Y stage, positioning accuracy of less than 10 nm is required, and in order to improve product quality, yield, and high throughput, reduction of alignment error of the exposure apparatus is regarded as a major element technology.

Conventionally, in the manufacturing process of semiconductor electronic circuit components such as LSI as described above, a susceptor, vacuum chuck, electrostatic chuck, insulating ring and other treatments for supporting or holding the silicon wafer in the process of forming wiring on the silicon wafer. As ceramic materials for tools and the like, alumina ceramics and silicon nitride ceramics have been widely used because they are relatively inexpensive and chemically stable. Also, conventionally, alumina ceramics, silicon nitride ceramics, and the like have been used as materials for the XY stage of the exposure apparatus.

In recent years, it has been proposed to use cordierite ceramics as various parts and jigs for semiconductor manufacturing by utilizing the low thermal expansion property of cordierite ceramics (Japanese Patent Laid-Open No. 1-191422, Japanese Patent Publication No. 6). -97675). According to Japanese Patent Laid-Open No. 1-191422, it is described that the stress of the membrane is controlled by producing a reinforcing ring that adheres to a mask substrate for X-ray exposure using SiO ₂ , invar, and cordierite ceramics. ing. Japanese Patent Publication No. 6-97675 discloses the use of alumina ceramics or cordierite ceramics as an electrostatic chuck substrate on which a silicon wafer is placed.

Conventionally, cordierite ceramics and lithium aluminosilicate ceramics (LiAlSiO ₄ , hereinafter referred to as LAS) are known as low thermal expansion ceramics. For cordierite ceramics, raw material powders containing cordierite powder or MgO powder, Al ₂ O ₃ powder, and SiO ₂ powder forming cordierite ceramics, rare earth oxides, CaO, SiO ₂ , MgO as sintering aids And the like, and after forming into a predetermined shape, it is known to produce by baking at a temperature of 1000 to 1400 ° C. (see Japanese Patent Publication No. 57-3629 and Japanese Patent Application Laid-Open No. Hei 2-229760).

Among the LAS ceramics, β-spodumene is known to be produced by forming into a predetermined shape using natural raw materials and then firing at a temperature of 1100 to 1400 ° C. (Japanese Patent Publication No. 53-9605). And Japanese Patent Publication No. 56-164070). Further, _Al 2 _{O 3} is 25 to 70 wt%, SiO ₂ 25 to 70 wt%, _Al Li ₂ O is 1 to 5% by weight and impurities 5 wt% or less _{2 O 3 · SiO 2 · Li} 2 There has been proposed an O-based low-expansion thermal spray material, which is used as a repair material for a coke oven and can form a fine thermal spray film having excellent mechanical strength (see Japanese Patent Laid-Open No. 63-25280). .
JP-A-1-191422 Japanese Patent Publication No. 6-97675 Japanese Patent Publication No.57-3629 JP-A-2-229760 Japanese Patent Publication No.53-9605 Japanese Patent Publication No. 56-164070 JP-A 63-25280

Ceramics such as alumina ceramics and silicon nitride ceramics that have been generally used for various devices, parts, and jigs used in semiconductor manufacturing processes are lighter in weight, have a smaller coefficient of thermal expansion, and have higher rigidity. . The specific gravity of each is lightweight, 3.8 for alumina ceramics and 3.2 for silicon nitride ceramics. However, lighter weight has been required to reduce the motor load and suppress vibrations by reducing the weight of the exposure apparatus and the weight of the drive system member such as the XY stage. On the other hand, the thermal expansion coefficient at 10 to 40 ° C., which is the operating temperature zone of the exposure apparatus, is about 5.0 × 10 ⁻⁶ / ° C. for alumina ceramics and about 1.5 × 10 ⁻⁶ / ° C. for silicon nitride ceramics. In order to reduce the thermal deformation at the time of exposure along with the miniaturization of circuit design rules, those having a lower coefficient of thermal expansion have been required.

In contrast, cordierite-based ceramics have a thermal expansion coefficient of 0.2 × 10 ⁻⁶ / ° C. or lower, and have a lower thermal expansion coefficient than alumina ceramics and silicon nitride ceramics. However, in terms of rigidity, alumina ceramics are about 350 GPa (gigapascal) and silicon nitride ceramics are about 300 GPa, whereas porous cordierite ceramics are as low as 70 to 90 GPa. When cordierite ceramics are used in an exposure apparatus or the like, there is a concern that the Si wafer positioning time may increase due to the occurrence of resonance due to deformation or a decrease in natural frequency. In recent reports, dense cordierite ceramics have a specific gravity of 2.7 and a Young's modulus of 130 to 140 GPa, and are expected for measures against deformation and improvement of the natural frequency. However, although the specific gravity is smaller than that of alumina ceramic or silicon nitride ceramic, further reduction in specific gravity is desired to reduce the weight of the exposure apparatus and the weight of the member.

The β-spodumene of LAS ceramics has a specific gravity of 2.0 to 2.4, a coefficient of thermal expansion of 0.3 × 10 ^{−6 to} 2.7 × 10 ⁻⁶ / ° C., and the porcelain has pores. The value is as low as 3 × 10 ⁻⁶ to −1.0 × 10 ⁻⁶ / ° C., but the Young's modulus is as low as 60 to 80 GPa. The low coefficient of thermal expansion of LAS ceramics is attributed to the anisotropy in the crystal axis direction and the presence of microcracks associated therewith. Microcracks are often seen as the anisotropy in the crystal axis direction increases. A method for suppressing microcracks is to determine the critical grain size of microcracks and to control the ceramic crystal within the critical grain size.

As described above, characteristics such as light weight, low thermal expansion coefficient, and high rigidity are required as materials for exposure apparatuses and the like. In particular, ceramics having light weight and low thermal expansion as compared with metals are desirable, and the composition of rigidity is compositional. Although it is conceivable to cope with the design and the like, there has never been a ceramic that satisfies both of these characteristics.

Therefore, the present invention has been completed in view of the above circumstances, and the object thereof is optimal as a material for various apparatuses such as an exposure apparatus used in a semiconductor manufacturing process, components, and jigs, and is lightweight. It is to provide a ceramic having a low thermal expansion coefficient and a high rigidity, and a manufacturing method thereof.

The low thermal expansion ceramic of the present invention is characterized by containing 95 to 99% by weight of β-eucryptite represented by the general formula LiAlSiO ₄ and 1 to 5% by weight of magnesia.

  The low thermal expansion ceramic of the present invention is characterized in that the void ratio is less than 0.1% by volume.

  Furthermore, the low thermal expansion ceramic of the present invention is characterized in that an average void diameter is less than 2 μm.

Furthermore, in the low thermal expansion ceramic of the present invention, β-eucryptite represented by the general formula LiAlSiO ₄ is Li ₂ O: Al ₂ O ₃ : SiO ₂ = 12.5: 40. 5:47, and the variation in weight% is a component composition within 1% by weight.

Furthermore, the low thermal expansion ceramic of the present invention is characterized in that the coefficient of thermal expansion is −0.4 × 10 ⁻⁶ / ° C. or more and 0.1 × 10 ⁻⁶ / ° C. or less.

  In the low thermal expansion ceramic of the present invention, the magnesia is characterized in that the average particle size of the raw material powder is 0.5 μm or more and 0.7 μm or less.

  The member for a semiconductor manufacturing apparatus of the present invention is formed using the low thermal expansion ceramic.

The present invention includes 95 to 99% by weight of β-eucryptite represented by the chemical formula LiAlSiO ₄ and 1 to 5% by weight of magnesia, so that the coefficient of thermal expansion is −0.4 × 10 ^{−6 to} 0.1. × 10 ⁻⁶ / ° C., Young's modulus of 110 to 120 GPa, specific gravity of 2.2 to 2.4, lightweight, low thermal expansion coefficient and high rigidity ceramic can be obtained. The low thermal expansion ceramic of the present invention includes various devices and parts for semiconductor manufacturing that perform exposure processing on a semiconductor wafer to form an ultrafine electronic circuit, such as an XY stage and its parts, a vacuum chuck, By using it for electrostatic chucks, mirrors, etc., it has excellent dimensional stability against temperature changes, and the effects of deformation and vibration are substantially eliminated.

  Furthermore, the present invention is an LAS-based ceramic having a particularly low specific gravity among low thermal expansion ceramics, and a β-eucryptite having a lower coefficient of thermal expansion is further sintered, preferably further subjected to hot pressing (processing). By densifying by the pressure firing method, the generation of microcracks can be suppressed, and a low rigidity and high rigidity material can be obtained. Further, by adding a predetermined amount of magnesia to β-eucryptite, it is possible to maintain a low coefficient of thermal expansion and densify β-eucryptite.

The low thermal expansion ceramic of the present invention is a LAS-based ceramic having light weight and low thermal expansion characteristics, and is particularly composed of a composite oxide represented by the general formula LiAlSiO ₄ known as β-eucryptite. The low thermal expansion ceramic contains 1 to 5% by weight of MgO as a sintering aid. The thermal expansion coefficient of MgO itself is 13 × 10 ^{−6 to} 14 × 10 ⁻⁶ / ° C. in the evaluation temperature range of 20 to 1000 ° C., and when the added amount exceeds 5 wt%, the thermal expansion is caused by an increase in the liquid phase content. The rate increases. Further, when the addition amount is less than 1% by weight, β-eucryptite is not densified. In the case of a sintering aid other than MgO, the sintering temperature rises and is accompanied by grain growth, and has a strong tendency to generate microcracks. The low thermal expansion ceramic of the present invention may contain a small amount of impurities in addition to β-eucryptite and MgO.

In the low thermal expansion ceramic of the present invention, it is preferable that the void ratio (porosity) is less than 0.1 volume% and the average void diameter is less than 2 μm. The light reflectance of the product surface is lowered. When the average void diameter is 2 μm or more, sufficient light reflection characteristics for positioning cannot be obtained when positioning a Si wafer or the like with light when used in a semiconductor manufacturing apparatus. More preferably, the maximum void diameter is less than 3 μm.

The lightweight low thermal expansion ceramic of the present invention is produced by the following steps [1] to [3].

[1] A raw material powder prepared in a weight percent ratio of Li ₂ O: Al ₂ O ₃ : SiO ₂ = 12.5: 40.5: 47 is used. By increasing or decreasing each component, mullite generation and cristobalite generation are observed in the crystal. In this case, since the coefficient of thermal expansion increases, it is preferable to suppress variation in the weight% ratio within 1% by weight. And the specific surface area of 12 to 95 to 99% by weight of LAS raw material powder having an average particle size of 5 to 7 μm at the composition ratio produced by the alkoxide method.
Add 1 to 5% by weight of MgO powder having an average particle size of 0.5 to 0.7 μm and ˜14 m ² / g.

[2] After blending the LAS raw material powder and the MgO powder, they are pulverized and mixed so as to have an average particle size of less than 1 μm using a vibration mill or the like, and formed into a predetermined shape.

[3] Specific gravity 2.2-2.4, coefficient of thermal expansion −0.4 × 10 ^{−6 to} 0.1 × by sintering at 1000 to 1200 ° C., preferably 1040 to 1130 ° C. in an air atmosphere. A lightweight and highly rigid low thermal expansion ceramic with 10 ⁻⁶ / ° C. and Young's modulus of 110 to 120 GPa can be produced. In addition, after forming a raw material powder composed of LAS raw material powder and MgO powder into a predetermined shape, it is sintered at 900-1000 ° C. in an air atmosphere at a relative density of 90% or higher, and then heated at 1100-1200 ° C., 100 atmospheric pressure or higher. By pressure firing, it can be densified to a porosity of less than 0.1% and an average void diameter of less than 2 μm. If the temperature during the pressure firing is less than 1100 ° C., the porcelain is not sufficiently densified, and if it exceeds 1200 ° C., the porcelain starts melting and a good porcelain cannot be obtained. Moreover, if the pressure is less than 100 atm, the void reduction effect cannot be obtained.

The low thermal expansion ceramic thus obtained has a specific gravity as small as 2.2 to 2.4 compared to silicon nitride ceramics, cordierite ceramics, and KZP (potassium zirconium phosphate), and alumina ceramics and silicon nitrides. Compared with ceramics, the coefficient of thermal expansion is −0.4 × 10 ^{−6 to} 0.1 × 10 ⁻⁶ / ° C. and the coefficient of thermal expansion is substantially 0 or a value in the vicinity of 0. Further, among low thermal expansion materials such as cordierite ceramics, Young's modulus is as high as 110 to 120 GPa. Furthermore, as an exposure apparatus for manufacturing semiconductors, etc., it has excellent surface smoothness and surface coating properties, light weight, low thermal expansion and high rigidity characteristics with a void ratio of less than 0.1% by volume and an average void diameter of less than 2 μm.

Thus, the present invention is optimal as a material for various apparatuses such as exposure apparatuses used in semiconductor manufacturing processes, components, and jigs, and can obtain a lightweight, low thermal expansion coefficient and high rigidity ceramic. it can.

The present invention is not limited to the above embodiment, and various modifications may be made without departing from the scope of the present invention.

Example 1 With respect to β-eucryptite powder having an average particle size of 5.5 μm, MgO powder having a specific surface area of 12.6 m ² / g and an average particle size of 0.6 μm was added at 0 wt%, 1 wt%, 2% by weight, 3% by weight, 4% by weight, 5% by weight, and 6% by weight are respectively mixed to prepare raw material powders, which are mixed by a vibration mill for 72 hours, granulated, dried and then dried. A test piece was formed by press molding. Eight types of test pieces having different average particle diameters and MgO addition amounts of the raw material powder were further fired in the air at different firing temperatures, and ceramic porcelains were produced and evaluated. Among these, No. obtained was a dense body having a porosity of less than 0.1%. The characteristics evaluation was performed on the baked products of 3, 4 and 5 at 1040 ° C. The evaluation results are shown in Table 2. In Table 1, w
t% means weight%, vol% means volume%, and the average particle diameter of the raw material powder was measured by the microtrack method.

As shown in Table 1, NO. No. 1 LAS raw material powder having an average particle diameter of 1.8 μm and MgO of 2 wt% had a void ratio of 2.1 vol% or higher at any firing temperature, and a dense body was not obtained. NO. 2 having an average particle size of 0.7 μm and MgO of 0 wt%, the void ratio was 2.6% by volume or more at any firing temperature, and a dense body was not obtained. NO. 3 having an average particle diameter of 0.7 μm and MgO of 1 wt%, the void ratio was less than 0.1% by volume at the firing temperatures of 1040 ° C. and 1130 ° C., and a dense body was obtained. NO. 4 having an average particle size of 0.7 μm and MgO of 2 wt%, the void fraction was less than 0.1% by volume at 1040 ° C. and 1130 ° C., and a dense body was obtained.

In addition, NO. 5 having an average particle size of 0.7 μm and MgO 3 wt%, the void fraction was less than 0.1 vol% at 1040 ° C. and 1130 ° C., and a dense body was obtained. NO. When the average particle size of No. 6 was 0.7 μm and MgO was 4 wt%, the void ratio was less than 0.1 vol% at 1040 ° C., and a dense body was obtained. NO. 7 having an average particle diameter of 0.7 μm and MgO of 5 wt%, the void fraction was less than 0.1 volume% at 1040 ° C., and a dense body was obtained. NO. With an average particle diameter of 0.7 μm and MgO 6 wt%, the void ratio was 0.8 vol% or higher at any firing temperature, and a dense body was not obtained.

As shown in Table 2, in accordance with the present invention, 1 to 3% by weight of MgO powder having a specific surface area of 12.6 m ² / g and an average particle size of 0.6 μm was added to β-eucryptite powder, resulting in an average particle size of 0 By using raw material powder pulverized to 0.7 μm and firing at 1040 ° C. in an air atmosphere, specific gravity 2.3, coefficient of thermal expansion −0.4 × 10 ^{−6 to} 0.1 × 10 ⁻⁶ / ° C. A dense ceramic having a Young's modulus of 110 to 120 GPa and a porosity of less than 0.1% by volume could be obtained. Further, it is possible to further reduce the weight by making the raw material powder into a hollow body.

Example 2 With respect to β-eucryptite powder having an average particle size of 5.5 μm, MgO powder having a specific surface area of 12.6 m ² / g and an average particle size of 0.6 μm was 2% by weight and 5% by weight. The raw material powders were prepared by mixing each in proportions, and these were mixed for 72 hours by a vibration mill, then granulated, dried, and then formed into test specimens by dry press molding. Then, after baking at a baking temperature of 1000 ° C., HP (pressure baking) treatment was performed. As the HP conditions, two types of pressures of 100 atm and 300 atm were used, and firing was performed at 1000 ° C., 1100 ° C., 1200 ° C., and 1300 ° C., respectively, and a total of 8 types of HP treatments were performed. The average void ratio (porosity) and average void diameter were evaluated for these, and the results are shown in Table 3. The average void fraction and average void diameter are measured by taking 10 views of the surface or cross-section of the test piece with a magnification of 100 or 1000 using an optical microscope, assuming that the void is spherical, and performing image processing to occupy the void. The average void fraction was approximately derived from the area, and the average void diameter was determined by observing each void diameter and taking the average value.

When the applied pressure was 100 atm, the treatment temperature was 1100 to 1200 ° C., the average void ratio was less than 0.1% by volume, and the average void diameter was 1.2 to 1.8 μm. The β-eucryptite melted at 1300 ° C. At 300 atmospheres, the processing temperature was 1100 to 1200 ° C., the average void ratio was less than 0.1% by volume, and the average void diameter was 1.0 to 1.9 μm. The β-eucryptite melted at 1300 ° C. Accordingly, it was found that ceramic porcelain having an average void fraction of less than 0.1% by volume and an average void diameter of less than 2 μm can be obtained in the range of 1100 ° C. to 1200 ° C.

Claims (7)

A low thermal expansion ceramic comprising 95 to 99% by weight of β-eucryptite represented by the general formula LiAlSiO ₄ and 1 to 5% by weight of magnesia. 2. The low thermal expansion ceramic according to claim 1, wherein the void ratio is less than 0.1% by volume. 3. The low thermal expansion ceramic according to claim 1, wherein an average void diameter is less than 2 μm. Β-eucryptite represented by the general formula LiAlSiO ₄ is Li ₂ O: Al ₂ O ₃ : SiO ₂ = 12.5: 40.5: 47 in a weight% ratio, and the variation in the weight% is 1 The low thermal expansion ceramic according to any one of claims 1 to 3, wherein the component composition is within a weight percent. 5. The low thermal expansion ceramic according to claim 1, wherein the thermal expansion coefficient is −0.4 × 10 ⁻⁶ / ° C. or more and 0.1 × 10 ⁻⁶ / ° C. or less. The low thermal expansion ceramic according to any one of claims 1 to 5, wherein the magnesia has an average particle size of a raw material powder of 0.5 µm or more and 0.7 µm or less. A component for a semiconductor manufacturing apparatus, which is formed using the low thermal expansion ceramic according to any one of claims 1 to 5.