JP2007169118A - Silicon nitride sintered compact, and member for semiconductor manufacturing unit and member for liquid crystal manufacturing unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon nitride sintered compact having a practically large mechanical strength and a small coefficient of thermal expansion, and small grinding resistance. <P>SOLUTION: This silicon nitride sintered compact is mainly composed of β-Si<SB>3</SB>N<SB>4</SB>, and it contains 5-30 vol% Si<SB>2</SB>N<SB>2</SB>O (silicon oxynitride) and 1-10 vol% β-RE<SB>2</SB>Si<SB>2</SB>O<SB>7</SB>(RE is an element in the group III of the periodical table). The sintered compact keeps a strong mechanical strength due to a composition composed mainly of β-Si<SB>3</SB>N<SB>4</SB>, and has a small grinding resistance due to a composition having 5-30 vol% Si<SB>2</SB>N<SB>2</SB>O and also has a small coefficient of thermal expansion of the grain boundary layer and a small residual stress in the sintered compact due to a composition having the range of 1-10 vol% β-RE<SB>2</SB>Si<SB>2</SB>O<SB>7</SB>, and further the sintered compact exhibits excellent processability allowing a smooth grinding process and the working of high dimensional accuracy due to its small grinding force. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a silicon nitride-based sintered body, and particularly to a silicon nitride-based sintered body having a small grinding resistance and excellent workability, a member for a semiconductor manufacturing apparatus, and a member for a liquid crystal manufacturing apparatus using the same.

  A silicon nitride sintered body is used as a member for a substrate processing apparatus used in a semiconductor manufacturing process or a liquid crystal panel manufacturing process, for example, a reticle stage for an exposure apparatus, a wafer stage, or a positioning mirror. These members are required to have the following characteristics.

  First, it is required to have a sufficiently large mechanical strength for practical use so that cracking and chipping do not occur even when mechanical stress is applied in a semiconductor manufacturing process or a liquid crystal panel manufacturing process. Secondly, these members are manufactured through grinding using a grindstone or the like in order to increase the dimensional accuracy, and the grinding resistance is reduced by increasing the amount of grinding per unit time and reducing the manufacturing cost. Small things are required. Thirdly, since it is driven by friction drive using an ultrasonic motor, it is necessary to reduce the dimensional change of the member even when the member temperature changes due to the heat generated by the friction drive or the temperature change around the member. The sintered body is required to have a small coefficient of thermal expansion. In particular, when the thermal expansion of the grain boundary phase increases, the residual stress in the sintered body increases and the grinding resistance during grinding increases, so that the thermal expansion coefficient of the grain boundary phase is required to be small.

As these silicon nitride sintered bodies, for example, Patent Document 1 discloses at least one disilicate phase of Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase, and Yb ₂ Si ₂ O ₇ phase, oxynitriding Since it is composed of a silicon (Si ₂ N ₂ O) phase, a β-Si ₃ N ₄ phase, and spherical SiC fine particles having an average particle size of 0.05 μm or less, one that can improve oxidation resistance and thermal shock resistance at high temperatures. It is shown.

In Patent Document 2, since Si ₂ N ₂ O and RE ₂ Si ₂ O ₇ crystals are precipitated at the grain boundaries, and the average grain size of the crystals is 0.3 μm or less, the mechanical strength is high. A silicon nitride sintered body is shown.
JP 2004-59346 A JP-A-6-287065

  However, although the silicon nitride sintered bodies of Patent Documents 1 and 2 have a sufficiently large mechanical strength, they have the following problems.

Since the silicon nitride sintered body of Patent Document 1 tends to shrink larger than the crystal of β-Si ₃ N ₄ and silicon oxynitride in the cooling process of firing, the crystal composed of γ-type disilicate phase is γ-type. The crystal composed of the disilicate phase strongly restrains the β-Si ₃ N ₄ or Si ₂ N ₂ O crystal to increase the residual stress, resulting in a problem that the grinding resistance increases. Furthermore, since SiC particles are crystal nuclei, a γ-type disilicate phase having a large thermal expansion coefficient is easily generated as a grain boundary phase, and a β-type disilicate phase having a low thermal expansion coefficient is difficult to generate. There was a problem that the thermal expansion coefficient could not be made sufficiently small.

  As a result, when these silicon nitride sintered bodies are used as members for semiconductor or liquid crystal panel manufacturing equipment, the member undergoes dimensional changes due to heat generated by friction drive of an ultrasonic motor or the like, or temperature changes around the member. It had the problem of occurring. Further, the thermal expansion coefficient of the grain boundary phase is large, the residual stress in the sintered body is increased, and the grinding resistance is liable to increase.

In addition, the silicon nitride sintered body of Patent Document 2 has a small grinding resistance because it contains a small amount of Si ₂ N ₂ O (silicon oxynitride) and a large amount of γ-RE ₂ Si ₂ O _7. There was a problem. In addition, since the sintered body contains a large amount of γ-RE ₂ Si ₂ O ₇ having a large thermal expansion coefficient as a grain boundary phase, the thermal expansion coefficient of the sintered body becomes large, and when used as a member for a semiconductor or liquid crystal panel manufacturing apparatus In addition, similar to Patent Document 1, there is a problem in that a dimensional change occurs in the member due to heat generated by friction drive of an ultrasonic motor or the like and a temperature change around the member. The content of γ-RE ₂ Si ₂ O _{7 in} the silicon nitride sintered body is high between the phase transition temperature Tt at which the y-type transitions to the β-type and the melting point temperature of the grain boundary phase. It is thought that it originates in having been produced. In particular, in the process of producing a silicon nitride-based sintered body, if the temperature drop rate is slowed during cooling, a large amount of γ-RE ₂ Si ₂ O ₇ crystals are generated. There was a problem that was particularly likely to become large.

  In view of the above problems, an object of the present invention is to provide a silicon nitride sintered body having a practically sufficiently large mechanical strength and a small thermal expansion coefficient and a small grinding resistance.

The silicon nitride-based sintered body of the present invention contains β-Si ₃ N ₄ as a main component, Si ₂ N ₂ O (silicon oxynitride) in an amount of 5% by volume to 30% by volume, and β-RE ₂ Si _2. O ₇ (RE is a Group 3 element of the Periodic Table) is contained in a range of 1% by volume to 10% by volume, respectively.

  The RE is at least one of Er, Yb, and Lu.

  A member for a semiconductor manufacturing apparatus according to the present invention is used in a semiconductor manufacturing apparatus for processing a semiconductor wafer placed in a processing chamber, and is made of the silicon nitride sintered body.

  The member for a liquid crystal manufacturing apparatus according to the present invention is used in a liquid crystal manufacturing apparatus used in a process for manufacturing a liquid crystal panel, and is characterized by comprising the silicon nitride sintered body.

According to the silicon nitride sintered body of the present invention, β-Si ₃ N ₄ is the main component, Si ₂ N ₂ O (silicon oxynitride) is 5% by volume to 30% by volume, and β-RE _2. Since Si ₂ O ₇ (RE is a Group 3 element of the Periodic Table) is contained in a range of 1% by volume to 10% by volume, β-Si ₃ N ₄ as a main component has a sufficiently large mechanical strength. The grinding resistance can be reduced by containing Si ₂ N ₂ O in the range of 5% by volume or more and 30% by volume or less while being held, and β-RE ₂ Si ₂ O ₇ (RE is a periodic table) The thermal expansion coefficient of the grain boundary phase can be reduced by containing the Group 3 element) in the range of 1% by volume or more and 10% by volume or less. As a result, since the residual stress in the sintered body can be reduced, grinding can be performed smoothly, and a sintered body having excellent workability capable of performing processing with high dimensional accuracy because of low grinding resistance is obtained. be able to.

  Hereinafter, the best mode for carrying out the present invention will be described.

The silicon nitride-based sintered body of the present invention contains β-Si ₃ N ₄ as a main component, Si ₂ N ₂ O (silicon oxynitride) in an amount of 5% by volume to 30% by volume, and β-RE ₂ Si _2. Each of them contains O ₇ (RE is a Group 3 element of the Periodic Table) in a range of 1% by volume to 10% by volume.

Β-Si ₃ N ₄ constituting the main component has an effect of increasing mechanical strength, Si ₂ N ₂ O has an effect of reducing grinding resistance, and β-RE ₂ Si ₂ O ₇ has an effect of reducing the thermal expansion coefficient. Each of which is made of a polycrystalline sintered body containing crystals of β-Si ₃ N ₄ , Si ₂ N ₂ O and β-RE ₂ Si ₂ O ₇ , having a mechanical strength of 500 MPa or more and a thermal expansion coefficient of 1.5 × 10 ⁻⁶ / K or less.

The fact that β-Si ₃ N ₄ is the main component is that the surface of the silicon nitride sintered body or the polished surface of the present invention is observed at a high magnification, and the area ratio of silicon nitride crystals in the observed surface is 50% or more. Can be confirmed.

Next, it is important for the silicon nitride sintered body of the present invention to contain Si ₂ N ₂ O in a range of 5% by volume to 30% by volume, and the sintered body is ground by a grindstone or the like. At this time, since Si ₂ N ₂ O functions to promote the destruction of the grain boundaries of the sintered body, the grinding resistance received by the grindstone or the like can be reduced.

Specifically, the fracture toughness value of the sintered body mainly composed of β-Si ₃ N ₄ is about 6 MPa · m ^1/2 , whereas the sintered body mainly composed of Si ₂ N ₂ O The fracture toughness value is as small as about 4 MPa · m ^1/2 . Thereby, when a local stress is applied to the silicon nitride sintered body containing Si ₂ N ₂ O by a grindstone or the like, the crystal made of Si ₂ N ₂ O is broken and easily scraped, so that the grinding resistance is reduced. It is considered a thing. When Si ₂ N ₂ O is less than 5% by volume, the grinding resistance increases due to a lack of fracture sources in the sintered body during grinding. On the other hand, when it exceeds 30% by volume, β-Si ₃ N ₄ Since the content is lowered, the mechanical strength is reduced, and when stress is applied to the sintered body, the crystal of Si ₂ N ₂ O tends to be a fracture source, so that it is considered that the mechanical strength is further reduced. Furthermore, it is more preferable to contain Si ₂ N ₂ O in the range of 8% by volume or more and 18% by volume or less, and it is possible to reduce the grinding resistance and further increase the bending mechanical strength.

  The grinding resistance is to detect a grinding resistance (N) when performing grinding processing such as drilling on a sintered body under a certain condition by using a crystal piezoelectric dynamometer.

Moreover, the silicon nitride sintered body of the present invention contains β-RE ₂ Si ₂ O ₇ in a range of 1% by volume to 10% by volume. RE ₂ Si ₂ O ₇ has types such as α, β, γ, δ, and y. Among them, β-RE ₂ Si ₂ O _7, which is β-type RE ₂ Si ₂ O _7, is β-Si _3. It exists mainly as a grain boundary phase at the grain boundary of the crystal of N ₄ , and β-RE ₂ Si ₂ O ₇ is smaller than the thermal expansion coefficient of RE ₂ Si ₂ O ₇ of types such as α, γ, δ, and y. Therefore, by including β-RE ₂ Si ₂ O ₇ in the range of 1 volume% or more and 10 volume% or less, the thermal expansion coefficient of the silicon nitride-based sintered body is 1.5 × 10 ⁻⁶ / K or less. Since the residual stress can be reduced by reducing the size, the grinding resistance can be further reduced. When the residual stress is reduced, the grinding resistance can be reduced because the stress at which the grain boundary phase β-RE ₂ Si ₂ O ₇ tries to constrain the β-Si ₃ N ₄ crystals is small. This is probably because the β-Si ₃ N ₄ crystals are easily broken by a grindstone or the like when the sintered body is ground.

When the content of β-RE ₂ Si ₂ O ₇ is less than 1% by volume, the silicon nitride sintered body cannot be made dense, and fine cracks are generated in the silicon nitride sintered body during grinding. Likely to happen. On the other hand, if it exceeds 10% by volume, the grinding resistance decreases, but the thermal expansion coefficient exceeds 1.5 × 10 ⁻⁶ / K, and the residual stress tends to increase, so that the grinding resistance can be sufficiently reduced. Can not. Furthermore, it is more preferable that the content of β-RE ₂ Si ₂ O ₇ is in the range of 4% by volume to 8% by volume, and the thermal expansion coefficient is 1.35 × 10 ⁻⁶ / K or less, A sintered body with a smaller thermal expansion coefficient can be obtained.

Moreover, RE in β-RE ₂ Si ₂ O ₇ may be any element of Group 3 of the periodic table, but among them, it is preferable to select at least one of Er, Yb, and Lu.

Thereby, the thermal expansion coefficient can be further reduced to 1.3 × 10 ⁻⁶ / K or less. This is because Er, Yb, and Lu are elements having a small ionic radius among the Group 3 elements of the Periodic Table, and thus have strong bonds with other constituent atoms (Si, O, N). The thermal expansion coefficient can be further reduced by reducing lattice vibration and volume expansion due to energy. In particular, when RE is Er and the content of β-Er ₂ Si ₂ O ₇ is in the range of 4% by volume to 8% by volume, the thermal expansion coefficient is further 1.27 × 10 ⁻⁶ / K or less. And can be made smaller.

  Furthermore, the silicon nitride sintered body of the present invention preferably has a relative density of 99% or more. By setting the relative density to 99% or more, not only the thermal expansion coefficient can be reduced and the grinding resistance can be reduced, but also the mechanical strength can be improved. For example, the point bending strength at room temperature can be further increased to 600 MPa or more. A silicon nitride sintered body having a relative density of 99% or more is pressurized at a gas pressure of 1 to 200 MPa by a high pressure GPS (Gas Pressure Sintering) method or a hot isostatic press (HIP) method described later. It can manufacture by the method of baking.

  Here, a method for measuring each characteristic of the silicon nitride sintered body of the present invention will be described.

The presence of β-Si ₃ N ₄ , Si ₂ N ₂ O, and β-RE ₂ Si ₂ O ₇ contained in the silicon nitride of the present invention is determined by X-ray diffraction using a powder obtained by pulverizing a sintered body. Measure with For example, the sintered body is pulverized to a particle size of # 200 mesh or less, and X-ray diffraction is performed with Cu-Kα rays (λ = 1.54056Å). β-Si ₃ N ₄ is No. of JCPDS-ICDD (Joint Committee for Powder Diffraction Studies-International Center for Diffraction Data). 33-1160, Si ₂ N ₂ O, JCPDS-ICDD No. 47-1627 and β-RE ₂ Si ₂ O ₇ are JCPDS-ICDD No. The data of 38-0440 can be used for identification. In the case where the sintered body contains α-RE ₂ Si ₂ O ₇ or γ-RE ₂ Si ₂ O ₇ , α-RE ₂ Si ₂ O ₇ is JCPDS-ICDD No. 38-0223 and γ-RE ₂ Si ₂ O ₇ are JCPDS-ICDD No. It can be identified using the data of 48-1623. In addition, although JCPDS-ICDD of these α, β, and γ-RE ₂ Si ₂ O ₇ has Y as RE, it can be substituted when RE is Er, Yb, and Lu. For JCPDS-ICDD in which RE is other than Y, Er, Yb, and Lu, a known X-ray diffraction pattern can be referred to.

The content of β-RE ₂ Si ₂ O ₇ can be measured, for example, as follows when RE is Er. First, a method for measuring by an X-ray diffraction method using a calibration curve will be described. SiO ₂ powder, Er ₂ O ₃ powder, and Si ₃ N ₄ powder were mixed so as to be 64 mol%, 32 mol%, and 4 mol%, respectively, and pressed to produce a green compact, and the green compact obtained Is put in a crucible made of BN (boron nitride), kept in a nitrogen atmosphere of 900 kPa at 1800 ° C. for 1 hour, further cooled to 800 ° C. within 2 hours, and then cooled to room temperature, the Er—Si—O—N system Amorphous material is obtained. When this amorphous material was heat-treated at 110 ° C. for 5 hours at 1300 ° C., JCPDS-ICDD No. A compound is obtained in which the β-Er ₂ Si ₂ O ₇ crystal peak identified at 38-0440 is approximately 100%. The compound was pulverized, the powder and _β-Si 3 _{N 4} powder of this compound, the content of the compound _{(β-Er 2 Si 2 O} 7) and various changes between 0 and 100 vol%, the powder X Line diffraction is performed, and a calibration curve showing the relationship between the peak intensity of the obtained X-ray diffraction and the content of β-Er ₂ Si ₂ O ₇ is created. Here, the peak intensities used for the calibration curve are the (021) plane assigned diffraction peak intensity I _{(E2S) of} β-Er ₂ Si ₂ O _{7 and} the diffraction peak intensity I of the β-Si ₃ N ₄ (200) plane. _(SN) . An example of the result of the calibration curve thus obtained is shown in FIG.

As shown in FIG. 1, the content of β-Er ₂ Si ₂ O _{7 in} the sintered body is determined by X-ray diffraction of the powder of the sintered body, and (200) plane attributed X-ray of β-Si ₃ N _4. The ratio I _(E2S) / I _(SN) of the diffraction peak intensity and the (021) plane assigned X-ray diffraction peak intensity of β-RE ₂ Si ₂ O ₇ was determined, and the content of β-Er ₂ Si ₂ O ₇ was obtained from FIG. The amount can be measured. When RE is an element other than Er, the content of β-RE ₂ Si ₂ O ₇ can be measured by the same method.

Further, the content of β-RE ₂ Si ₂ O ₇ can be determined by observing the sintered body using a transmission electron microscope in addition to the above-described method using the calibration curve, and identifying the crystal structure of each observed crystal. The area ratio (%) of β-RE ₂ Si ₂ O ₇ occupying the area of the observation surface can be regarded as volume% for convenience.

The content of Si ₂ N ₂ O can be measured, for example, as follows.

The mirror surface obtained by polishing the sintered body is observed with a scanning electron microscope (SEM) and an X-ray microanalyzer (EPMA) at a magnification of about 1000 to 10,000 times, preferably about 5,000 times. Then, since the crystal of Si ₂ N ₂ O contains more O (oxygen) than the crystal of β-Si ₃ N ₄ , the crystal of Si ₂ N ₂ O can be specified when observed with EPMA. Here, when the mirror surface is observed with a field of view of 50 μm × 50 μm or more with SEM and EPMA, and the SEM photograph and EPMA photograph are taken, the ratio (%) of the area of the crystal of Si ₂ N ₂ O in the observed area is Can be sought. The ratio (%) of the area of Si ₂ N ₂ O obtained in this way is taken as the content (volume%) of Si ₂ N ₂ O for convenience.

  The mechanical strength is obtained by measuring the bending strength, and can be measured, for example, according to JIS (Japanese Industrial Standard) R1601 (1995). Make more than one. A load tester is used to apply a load to the test piece, measure the maximum load until breakage, and calculate the bending strength.

  Further, the thermal conductivity is measured in a 23 ° C. environment by a laser flash method in accordance with JIS R1611-1997. The thermal expansion coefficient referred to in the present invention is a thermal expansion coefficient at room temperature, specifically, a thermal expansion coefficient in the range of 0 to 50 ° C., and is particularly preferably specified as a thermal expansion coefficient at 23 ° C. Specifically, for example, the thermal expansion coefficient is measured as follows. The sample for measuring the thermal expansion coefficient is obtained by processing the silicon nitride sintered body of the present invention or processing this to a length of 15 to 16 mm, and chamfering both ends in the length direction into an R shape. Next, using a laser thermal dilatometer manufactured by Vacuum Riko Co., Ltd., using a laser while heating the sample continuously in He gas at a temperature rising rate of about 1 ° C./min in the range of 0 to 50 ° C. The length of the sample is measured, and the coefficient of thermal expansion at 23 ° C. is measured according to the measurement according to ASTM (The American Society of Testing and Materials) E 289 (Standard Test Method for Linear Thermal Expansion of Rigid Solids with Interferometry).

  For the measurement of grinding resistance, a grinding resistance measurement sample made of a disk-shaped silicon nitride sintered body having a diameter of 80 mm and a thickness of 10 mm was prepared, and one of the samples was placed on a VM4II vertical machining center manufactured by Osaka Kiko Co., Ltd. The main surface of is fixed. Next, a core drill with an outer diameter of 5 mm, electrodeposited with # 120 diamond, is attached to the vertical machining center, and while pouring water into the drill, the drill rotates at 2000 rpm and feed rate is 2 mm / min. Open and process. During this processing, the grinding resistance (N) in the longitudinal direction of the drill is detected by a quartz piezoelectric dynamometer TYPE 9254 manufactured by KISTLER.

  Next, a method for manufacturing the silicon nitride sintered body of the present invention will be described.

First, a compact containing Si ₃ N ₄ powder and RE ₂ O ₃ powder is heated in air at 600 to 800 ° C. for 1 to 5 hours, and a part of the Si ₃ N ₄ powder contained in the compact is oxidized. An oxidized molded body is produced. Subsequently, the oxidized compact was densified to a relative density of 96% or more at 1700 to 2000 ° C. in nitrogen gas containing SiO gas, and then cooled to 800 ° C. or less within 8 hours, and then into 800 to 1000 ° C. nitrogen gas. Hold for 0.1 to 5 hours, and further hold at 1200 to 1500 ° C. for 1 hour or more. By this manufacturing method, a silicon nitride-based firing having a mechanical strength sufficient for practical use, a thermal expansion coefficient as small as 1.5 × 10 ⁻⁶ / K or less, and a grinding resistance measured by the above method as small as 400 N or less. A knot can be produced.

  The method for producing the silicon nitride sintered body of the present invention is specifically as follows.

(A) As a starting material powder, a RE ₂ O ₃ powder made of an oxide of a Group 3 element such as silicon nitride powder, Er ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ is prepared. Preferably, Al ₂ O ₃ powder, WO ₃ powder, and SiO ₂ powder are further prepared. The silicon nitride powder prepared here is preferably a silicon nitride raw material having a high α conversion rate because it is superior in sinterability, but may be a silicon nitride powder having a zero α conversion rate. The silicon nitride powder may contain Si oxide as an impurity. The RE ₂ O ₃ powder preferably has a purity of 99% or more. The particle size of the primary raw material powder is preferably a median diameter _{D 50} is 0.5 to 30 m.

(B) The powder prepared in the above (a) is made into silicon nitride powder 60 to 99 mol%, RE ₂ O ₃ powder 1 to 40 mol%, and known methods such as a rotary mill, a vibration mill, a bead mill, etc. And then wet-mixed and pulverized to produce a slurry. Preferably, the silicon nitride powder is 95 to 80 mol%, the RE ₂ O ₃ powder is 1 to 5 mol%, and the SiO ₂ powder is 4 to 15 mol%. Particularly preferably, SiO ₂ powder (and SiO ₂ powder were prepared, a total of one oxygen content in the silicon nitride powder were considered SiO ₂ powder as converted to SiO _2), silicon nitride powder, and when the _RE 2 _{O 3} total 100 parts by mass of the powder, further _Al 2 _{O 3} powder 2.5 parts by weight, mixed WO ₃ powder 0.3 to 5 parts by weight, and ground. As the grinding media, those of silicon nitride, zirconia, and alumina can be used, but silicon nitride media that is a material that is less affected by contamination as impurities is preferable. In order to improve the sinterability, it is preferable to finely pulverize the pulverized particle size D ₅₀ to 1 μm or less. Further, after the primary raw material powder is finely pulverized in advance, it may be wet mixed and pulverized by a mill. Moreover, it is preferable to add a dispersant before pulverization for the purpose of lowering the viscosity of the resulting slurry.

  (C) The obtained wet slurry is dried to produce a dry powder. Prior to this drying, it is preferable to remove foreign matter as much as possible by passing the slurry through a mesh finer than # 200 and further removing iron using magnetic force. Moreover, 1-10 mass% of organic binders, such as paraffin wax, PVA (polyvinyl alcohol), PEG (polyethylene glycol), and PEO (polyethylene oxide), may be added to the slurry and mixed. In this case, it is preferable because generation of cracks and cracks of the molded body can be suppressed. As a method for drying the slurry, the slurry may be put in a container and heated and dried, or may be dried by a spray dryer, or may be dried by another method.

  (D) The dry powder is formed into a desired shape having a relative density of 45 to 60% by using a known molding method, for example, a powder pressure molding method using a mold or an isotropic pressure molding method using hydrostatic pressure. To do.

(E) The molded body is heated in air at 600 to 800 ° C. for 1 to 5 hours to produce an oxidized molded body in which a part of the Si ₃ N ₄ powder contained in the molded body is oxidized. When the molded body contains an organic binder, the organic binder is degreased by heating to 500 to 900 ° C. in nitrogen, and further heated in air at 600 to 800 ° C. for 1 to 5 hours. In order to improve the sinterability and produce a dense silicon nitride sintered body, the carbon content after degreasing is preferably 0.01% by weight or less.

  (F) The oxidized molded body is fired using a firing furnace as follows.

  A firing furnace or the like heated by a graphitic resistance heating element is used as the firing furnace, and the oxidized formed body is placed in the firing furnace. Preferably, it mounts in the container for baking which can surround the whole oxidation molded object. Here, when the oxidized molded body is placed in a firing furnace, a firing plate for placing the oxidized molded body, or a firing container for placing the oxidized molded body and surrounding the oxidized molded body ( These are hereinafter referred to as firing jigs).

  Suppresses the evaporation of Si components contained in the oxidized molded body during firing, and scatters foreign matter that may adhere to the oxidized molded body from the atmosphere in the firing furnace, etc. (for example, from a graphite heating element or a carbon heat insulating material) In order to prevent adhesion of carbon pieces or other small pieces of heat insulating material made of an inorganic material incorporated in the firing furnace, the material of the firing jig may be silicon nitride, silicon carbide, or the like. It is preferable to use a material such as a composite, and it is preferable to surround the entire oxidized molded body with a firing jig.

When the entire oxidized molded body is fired by being surrounded by a firing jig, a powder containing Si and / or its oxide to suppress evaporation of Si components from the oxidized molded body, or an oxidized molded body of this powder Is preferably placed in a firing jig. In the process of densification to be described later, such Si oxide is obtained, for example, as Si—O gas, which evaporates in the firing jig and prevents the Si component from evaporating from the oxidized molded body. Variations in the composition of the sintered body are suppressed, and β-Er ₂ Si ₂ O ₇ can be generated particularly stably in the sintered body in the reheating treatment step (j) described later.

(G) The oxidized molded body placed on the firing jig is placed in a firing furnace and fired at 1700 to 2000 ° C. to be densified to a relative density of 96% or more. Here, the relative density is a value obtained by dividing the density obtained by the Archimedes method by the theoretical powder density. By this firing, Si ₂ N ₂ O crystals are generated in the range of 5% by volume to 30% by volume.

  For densification to a relative density of 96% or higher, more specifically, firing is performed by the following method.

The temperature is raised in nitrogen gas and maintained at a maximum temperature of 1700-2000 ° C. Preferably, the temperature is maintained at a temperature at which a liquid phase is generated, for example, 1500 ° C. or more and less than 1700 ° C. before reaching the maximum temperature. When the maximum temperature is less than 1800 ° C., the nitrogen partial pressure may be about atmospheric pressure, but when the maximum temperature is 1800 ° C. or more, the nitrogen partial pressure is increased to about 1 MPa to suppress the decomposition reaction of Si ₃ N _4. preferable. In order to further promote the densification, it is preferable to pressurize with a higher pressure gas when the open porosity becomes 5% or less. As this pressurization method, it is preferable to use a method of pressurizing at a gas pressure of 1 to 200 MPa by a high pressure GPS (Gas Pressure Sintering) method or a hot isostatic press (HIP) method, and relative to this. The density can be particularly increased to 99% or more.

  (H) Cool to 800 ° C. or less within 8 hours. Thereby, the grain boundary can be sufficiently amorphized. The reason for cooling to 800 ° C. or lower within 8 hours is as follows.

Crystal nuclei of RE ₂ Si ₂ O ₇ are generated at 800 to 1000 ° C., and the crystal nuclei can be grown by further raising the temperature to 1000 to 1650 ° C. When cooling to a temperature of 800 ° C. or less within 8 hours, if it exceeds 8 hours, during the cooling, other than RE ₂ Si ₂ O ₇ , for example, RE ₅ (Si ₄ ) ₃ N (apatite phase) is easily crystallized, Since the crystal nuclei of RE ₂ Si ₂ O ₇ cannot be sufficiently generated in the step (i) described later, the content of β-RE ₂ Si ₂ O ₇ is in the range of 3% by volume to 20% by volume. It is because it becomes impossible. Preferably, the cooling time is within 4 hours.

(I) Hold at 800 to 1000 ° C. for 0.1 to 5 hours in nitrogen gas. By this holding, the crystal nuclei of RE ₂ Si ₂ O ₇ can be sufficiently generated at the grain boundaries of β-Si ₃ N ₄ crystals. When the temperature is lower than 800 ° C. or higher than 1000 ° C., or when the holding time is shorter than 0.1 hour, the crystal nuclei of RE ₂ Si ₂ O ₇ are not sufficiently formed, and therefore β in the step (j) described later. The silicon nitride based sintered body containing the content of -RE ₂ Si ₂ O ₇ in the range of 3 vol% or more and 20 vol% or less cannot be produced. In particular, when the retention time is less than 0.1 hour, many crystal nuclei other than RE ₂ Si ₂ O ₇ (eg, RE ₅ (Si ₄ ) ₃ N (apatite phase)) are generated, and the thermal expansion coefficient is large. The problem of becoming may also arise. Further, when the holding time exceeds 5 hours, the amorphous grain boundary phase existing at the grain boundary of the β-Si ₃ N ₄ crystal is softened, and the sintered body is greatly deformed. It becomes a bad silicon nitride sintered body, and it becomes difficult to produce an industrially usable silicon nitride sintered body.

(J) Hold at 1200 to 1500 ° C. for 1 hour or longer. Thus, the step (i) generated _RE 2 crystal nuclei of _Si 2 _{O 7} is transferred to the _β-RE 2 _Si 2 _{O 7,} the growing, the content of _β-RE 2 _Si 2 _{O 7} is 3 vol% As described above, a silicon nitride-based sintered body containing 20% by volume or less can be obtained. Holding temperature is the content of _β-RE 2 _Si 2 _{O 7} is less than 3% by volume less than 1200 ° C.. Holding temperature is high, the _γ-RE 2 _Si 2 _{O 7} next than 1500 ° C., the content of _β-RE 2 _Si 2 _{O 7} is less than 3% by volume. When the holding time is less than 1 hour, the content of β-RE ₂ Si ₂ O ₇ is less than 3% by volume. By containing the content of β-RE ₂ Si ₂ O ₇ in the range of 5% by volume or more and 10% by volume or less, a silicon nitride sintered body having a smaller thermal expansion coefficient and a larger thermal conductivity is manufactured. For this purpose, the holding time is preferably 2 to 24 hours.

  In addition, although the said process (i) and (j) may be performed continuously with the said process (h) and may be performed intermittently, it is for generation | occurrence | production of the chip | tip by an operator's handling, and manufacturing cost reduction. It is preferable to carry out continuously. In addition, the holding in the above (i) and (j) means the total time spent in a predetermined temperature range. For example, the holding time, the temperature rising time, and the temperature falling time are set as the holding time. included.

  Further, by replacing a part of the starting silicon nitride powder with silicon powder, it becomes easy to improve the relative density in the step (g), and shrinkage at the time of firing the molded body can be suppressed. Thus, the dimensional accuracy of the obtained silicon nitride based sintered body can be improved. When a part of the starting silicon nitride powder is replaced with silicon powder, before reaching the maximum temperature in the step (g), the nitrogen partial pressure is from 1000 to 1400 ° C. in an atmosphere of 50 kPa to 1.1 MPa. For 5 hours or more.

  As described above, the silicon nitride sintered body of the present invention has a sufficiently large mechanical strength in practical use, a small thermal expansion coefficient, and a small grinding resistance. Therefore, when the silicon nitride sintered body of the present invention is used as a member for a substrate processing apparatus used in a semiconductor manufacturing process or a liquid crystal panel manufacturing process, for example, a reticle stage for an exposure apparatus, a wafer stage, a wafer positioning mirror The following effects can be achieved.

  That is, first, even when mechanical stress is applied in a semiconductor manufacturing process or a liquid crystal panel manufacturing process, no cracks or chips are generated. Secondly, even when the member temperature changes due to the heat generated by friction drive using an ultrasonic motor or the temperature change around the member, the dimensional change of the member can be made extremely small, enabling highly accurate fine wiring. It becomes. Third, since the grinding resistance is small, grinding can be performed with high dimensional accuracy, so that the dimensional accuracy of the obtained member can be increased. Thus, the silicon nitride sintered body of the present invention can be suitably used as a member for a semiconductor / liquid crystal manufacturing apparatus.

  Next, examples of the present invention will be described.

In order to obtain various silicon nitride sintered bodies, silicon nitride powder (average particle size 10 μm, β conversion rate 100%, oxygen content 0.9 mass%, Fe impurity content 0.3 mass%, Al impurity content 0.2 Mass%), as shown in Table 1, various Group 3 element oxides RE ₂ O ₃ powder (average particle size of 5 to 10 μm), SiO ₂ powder (average particle size of about 2 μm) so as to have the composition shown in Table 1. Weighed.

The addition amount of the SiO ₂ powder was prepared as follows so that the content in terms of SiO ₂ in the obtained sintered body was the amount shown in Table 1.

Oxygen contained in the silicon nitride powder is deemed to contain as SiO _2, by converting the amount of oxygen 0.9 mass% SiO _2, 1.7 mass with oxygen in terms of SiO ₂ in the silicon nitride powder % Is assumed to be included. SiO ₂ (mol%) shown in Table 1 is the total amount of the SiO ₂ amount (1.7% by mass) assumed to be contained in the silicon nitride powder and the weighed SiO ₂ powder. See also, for each sample, the silicon nitride powder, and the SiO ₂ powder _RE 2 _{O 3} powder and SiO ₂ powder (weighed and SiO ₂ powder which is the same as the oxygen content in the silicon nitride powder to SiO ₂ when the total 100 parts by mass of the total) and those without further _Al 2 _{O 3} powder 2 parts by weight were weighed WO ₃ powder 0.5 parts by weight.

Pure water is added to each weighed powder, mixed and pulverized in a ball mill using a silicon nitride medium so that the particle size D ₅₀ is 0.9 μm, and the resulting slurry is deironed and then PVA (polyvinyl alcohol). ), 100 parts by mass of PEG (polyethylene glycol), 2 parts by mass of each was added and mixed, and dried and granulated with a spray dryer to prepare granulated powder.

  The obtained granulated powder was isostatically pressed at a pressure of 800 KPa by a hydrostatic pressure method, and formed into an outer shape of 60 mm and a thickness of 30 mm to produce a molded body. This molded body was subjected to nitrogen gas at 800 ° C. for 5 hours. PVA and PEG were degreased by heating, and further oxidized in the air at the temperature and holding time shown in Table 1 to produce an oxidized molded body.

The entire oxidized molded body thus obtained was placed and enclosed in a silicon nitride container. At this time, the green compact containing the SiO ₂ powder was placed in the container so as to be 0.1 g per 1 cm ³ of volume in the container.

  The oxide molded body was set in a firing furnace while being placed in a silicon nitride container, held at 1650 ° C. for 10 hours and 1750 ° C. for 10 hours in a nitrogen partial pressure of 110 kPa, and then at 1850 ° C. in a nitrogen partial pressure of 900 kPa. Was sintered for 10 hours, cooled from the maximum temperature to 800 ° C. in the time shown in Table 1, and further cooled to room temperature to obtain a sintered body. The density of the obtained sintered body was measured by the Archimedes method. As a result, it was found that the relative density of all the samples was 96% or more.

  Next, the obtained sintered body was placed in a container made of silicon nitride, heated to 800 ° C. at 5 ° C./min in a nitrogen partial pressure of 110 kPa, and the time shown in Table 1 from 800 ° C. to 1000 ° C. The sample was further heated from 1000 ° C. to 1200 ° C. at a rate of 10 ° C./min, continuously raised from 1200 ° C. to 1500 ° C. for the time shown in Table 1, and then cooled to room temperature to obtain a sample of the present invention. It was.

A sample was cut out from the obtained sample, and the crystal phase by X-ray diffraction method using the method described in the embodiment, the content of β-RE ₂ Si ₂ O ₇ , Si at a magnification of 5000 times using SEM and EPMA The content of ₂ N ₂ O was measured, and as the characteristics of each sample, the three-point bending strength, the thermal expansion coefficient at 23 ° C., and the maximum value of the grinding resistance during drilling using a drill were measured.

Next, a comparative example was carried out in the same manner as in the examples except that the conditions for the oxidation treatment and the heat treatment conditions after sintering (cooling time to 800 ° C., time for 800 to 1000 ° C., time for 1200 to 1500 ° C.) were changed. A sample of was prepared. The results are shown in Table 1.

As is apparent from Table 1, the sample No. 2-8, 11-17, the content of Si ₂ N ₂ O is 5% by volume or more and 30% by volume or less, and the content of β-RE ₂ Si ₂ O ₇ is 1% by volume or more and 10% by volume or less. The thermal expansion coefficient at 23 ° C. can be reduced to 1.5 × 10 ⁻⁶ / K or less while maintaining the three-point bending strength as large as 522 MPa or more. As a result, the grinding resistance can be reduced to 395 N or less. A sintered body with high workability could be obtained.

When the content of _β-RE 2 _Si 2 _{O 7} are the same, among _β-RE 2 _Si 2 _{O 7} containing, RE is Er, Yb, samples consisting of either Lu (No.4, 5,7,11,12,16,17) has a particularly small thermal expansion coefficient and a grinding resistance of 376 N or less, compared with the sample (No. 2, 13-15) in which RE is Y. did it.

On the other hand, among the samples of comparative examples having compositions outside the scope of claims of the present invention, heat treatment at 800 ° C. or higher is not performed, there is no crystal phase at the grain boundaries, and the grain boundaries are amorphous. Sample No. containing no Er ₂ Si ₂ O ₇ No. 1 had a very large thermal expansion coefficient at room temperature of 1.62 × 10 ⁻⁶ / K and a grinding resistance of as large as 410 N. Further, as long as 30 hours to a heat treatment time at 1200 to 1500 ° C., the content of _β-Er 2 _Si 2 _{O 7} in the grain boundary is large and 15% Sample No. No. 9 had a bending strength as small as 462 MPa and a thermal expansion coefficient at room temperature as large as 1.45 × 10 ⁻⁶ / K, so that the grinding resistance increased to 418 N.

Further, the cooling time from the firing temperature to 800 ° C. was as long as 12 hours, the apatite phase was precipitated at the grain boundaries even after heat treatment, and no sample No. 6 containing no β-disilicate was obtained. No. 10 had a large thermal expansion coefficient at room temperature of 1.52 × 10 ⁻⁶ / K and a grinding resistance of 434 N. Furthermore, the oxidation treatment is not performed, the heat treatment time at 1200 to 1500 ° C. is shortened to 0.5 hours, the content of Si ₂ N ₂ O is 0.5% by volume, and the content of β-Er ₂ Si ₂ O ₇ Sample No. with an amount of 0.5% by volume. 18 had a large thermal expansion coefficient of 1.55 × 10 ⁻⁶ / K and a grinding resistance of 460 N. Oxidation treatment was performed at 500 ° C., an atmosphere containing no SiO during the heat treatment, Si ₂ N ₂ O, β-Er ₂ Si ₂ O ₇ not contained, and sample No. containing borastite. 19 had a large thermal expansion coefficient of 1.51 × 10 ⁻⁶ / K and a grinding resistance of 490 N. Sample No. with an oxidation treatment temperature of 900 ° C. or higher and a high Si ₂ N ₂ O content of 36% by volume. No. 20 has a thermal expansion coefficient of 1.60 × 10 ⁻⁶ / K. Sample No. 21 with an oxidation treatment temperature of 500 ° C. and a low Si ₂ N ₂ O content of 3% by volume had a high grinding resistance of 450 N.

  In Table 1, “there is an SiO-containing atmosphere” means that the green compact is placed in a container during firing, and no SiO-containing atmosphere means that the green compact is in the container. Indicates no placement.

  The silicon nitride sintered body of the present invention is suitable for a substrate processing apparatus member used in a semiconductor manufacturing process or a liquid crystal panel manufacturing process, for example, a reticle stage or sample stage for an exposure apparatus, a wafer stage, a positioning mirror, etc. Used for. Moreover, it is used suitably also for various industrial equipment components, for example, components for molten aluminum that require thermal shock resistance.

It is a calibration curve used for measurement of the content of β-Er ₂ Si ₂ O ₇ .

Claims (4)

β-Si ₃ N ₄ as a main component, Si ₂ N ₂ O (silicon oxynitride) at 5 volume% or more and 30 volume% or less, and β-RE ₂ Si ₂ O ₇ (RE is Group 3 of the periodic table) Element) in a range of 1% by volume or more and 10% by volume or less, respectively. The silicon nitride based sintered body according to claim 1, wherein the RE is at least one of Er, Yb, and Lu. A member for a semiconductor manufacturing apparatus, which is used in a semiconductor manufacturing apparatus for performing a process on a semiconductor wafer placed in a processing chamber and is made of the silicon nitride sintered body according to claim 1. A member for a liquid crystal manufacturing apparatus, which is used in a liquid crystal manufacturing apparatus used in a process for manufacturing a liquid crystal panel and is made of the silicon nitride based sintered body according to claim 1.

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