JP2005047769A - Highly cleaned ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly cleaned ceramic by which the contamination of a wafer is reduced. <P>SOLUTION: The highly cleaned ceramic has ≥98.5% relative density, ≤3% defective area on a mirror polished surface, ≤1.0 pieces/mm<SP>2</SP>particle transfer rate in the transfer to the silicon wafer, and ≤1×10<SP>12</SP>atom/cm<SP>2</SP>in total of transfer rate of each metal of Cr, Fe, Ni, and Cu. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ceramic with high cleanliness that is suitably used mainly as a component of a semiconductor manufacturing apparatus.

  In semiconductor manufacturing apparatuses, the same silicon materials and ceramic materials as quartz materials and silicon wafers are widely used for parts exposed to high temperature atmospheres, corrosive gas atmospheres, and vacuum atmospheres. Quartz materials and silicon materials are limited in parts used due to properties such as strength and rigidity, thermal expansion, and restrictions on manufacturing parts such as molding and processing, but ceramic materials are lightweight, highly rigid, and high It has characteristics such as strength and low thermal expansion, and there are few restrictions on manufacturing parts (see, for example, Patent Document 1).

  However, since the ceramic member is manufactured by a powder metallurgy technique, the structure includes pores in the matrix, and dust derived from the manufacturing process may remain in the pores. Further, particles may accumulate in the pores in the actual use process. For this reason, there is a problem that dust or the like accumulated in the pores of components such as an electrostatic chuck and a conveying member that are in direct contact with the silicon wafer is transferred to the silicon wafer and the silicon wafer is contaminated.

Recently, the design rules regarding the manufacture of semiconductor devices have been refined, and the allowable contamination of silicon wafers, for example, the size and number of fine particles (particles), and the amount of metal contamination have been extremely severely limited. For this reason, the transfer of particles, etc., which has not been a hindrance from ceramic parts to silicon wafers, has become a major problem under new design rules, and there is a need for ceramic parts with higher cleanliness. ing.
JP 2000-191370 A

  This invention is made | formed in view of such a situation, and it aims at providing the highly clean ceramics which reduce the contamination of a silicon wafer.

  As a result of repeated studies to solve the above problems, the present inventor has an adverse effect on semiconductor devices by strictly controlling the raw material purity and manufacturing conditions so that the amount of particle transfer and the transfer amount of a specific metal is below a specific value. It has been found that highly clean ceramics can be obtained without giving any resistance.

That is, according to the present invention, the relative density is 98.5% or more, the area of defects on the mirror-polished surface is 3% or less, and the amount of transferred particles by silicon wafer transfer after mirror-polishing and cleaning is 1. There is provided a highly clean ceramic characterized in that the number of metal transfer of Cr / Fe / Ni / Cu is 1 × 10 ¹² atoms / cm ² or less in total of 0 pieces / mm ² or less.

  Since the highly clean ceramic of the present invention has very few defects such as pores, contamination of the silicon wafer due to such defects is suppressed. This improves the quality and reliability of the semiconductor device.

Hereinafter, the present invention will be described in detail.
Silicon wafers are contaminated by contact between ceramic parts used in semiconductor manufacturing equipment and silicon wafers, so-called wafer transfer is the transfer of particles to which fine particles such as organic and inorganic particles adhere, and the adhesion of metal impurities. Or metal transfer impregnated with metal components.

The parts using the highly clean ceramics according to the present invention have high purity and high density, and when the mirror polishing process is performed, the defect area of the mirror polishing surface is 3% or less. In addition, when the wafer transfer is performed after the cleaning process, which is the final process in the manufacturing process, the ceramic component has a particle transfer amount of 1.0 piece / mm ² or less, and Cr, Fe, Ni , Cu metal transfer amount can be suppressed to 1 × 10 ¹² atoms / cm ² or less in total. Since the ceramic parts have such high cleanliness, contamination of the silicon wafer due to wafer transfer can be suppressed to an extremely low level.

  In order to keep particle transfer low, it is particularly effective to reduce the pore area and pore volume of the contact surface of the ceramic part with the silicon wafer, that is, to make the structure of the ceramic part dense. For this reason, the relative density of the ceramic component according to the present invention is set to 98.5% or more. As shown in the examples described later, when the relative density is less than 98.5%, neither particle transfer nor metal transfer reaches a desirable level.

  In order to keep the metal transfer low, it is preferable to use a high-purity raw material for the production of ceramic parts. In addition, it is effective to make the structure of the ceramic parts dense. Specifically, a high-purity powder having a purity of 99.9% (3N) or higher is used for the production of ceramic parts according to the present invention, and the molding conditions and firing conditions are appropriately set according to the characteristics of the raw material powder. Determined. In addition, by using a high-purity jig or the like used for firing, mixing of impurities into the fired sample during the firing process or the like can be prevented, and metal transfer can be further reduced.

  In order to obtain ceramics (sintered body) having high density, it is important to produce a compact with a uniform density using raw material powder with high surface activity and to perform a sintering process with suppressed grain growth. . This is because when the grain growth is promoted, the frequency of particle dropout (droplet removal) increases in the subsequent mirror polishing, and the pore area / volume increases. Therefore, by reducing the pores by densification of the structure by firing treatment, and by preventing grain growth defects by suppressing grain growth, the mirror polished surface when the ceramic component is mirror polished The defect area can be 3% or less.

  Conventionally, in order to reduce pores on the surface of ceramic parts, surface film-forming treatment by CVD, PVD, etc., pore-filling treatment by CVI, etc. have been performed. There is a problem that the product cost of the ceramic parts is remarkably increased because it is easily peeled off and the processing cost is high.

  Processing of the sintered body, which is one of the manufacturing steps of the ceramic component, may be performed by a known polishing process using an abrasive suitable for the ceramic material, or a cutting process or a grinding process using a normal diamond grindstone. Also, there is no particular limitation on the method of cleaning the sample after such processing, but for example, after removing the wax for fixing the sample used during the processing and removing grinding waste, acid / alkali is used. Next, it is preferable to wash with functional water such as RCA chemical solution, hydrogen water-added ultrapure water or ozone water-added ultrapure water used in the silicon wafer cleaning process in the semiconductor device manufacturing process. Cleaning conditions with such RCA chemicals and various functional waters may be the same as those generally used for silicon wafers.

Under the new design rules that have recently advanced higher density and higher integration, ceramic parts used in semiconductor manufacturing equipment are required to have stricter transfer conditions than before. When wafer transfer is performed after such a cleaning process, the particle transfer amount is suppressed to 1.0 particles / mm ² or less, and the total metal transfer amounts of Cr, Fe, Ni, and Cu are 1 × 10 ¹² atoms. It was considered necessary to have the wafer transfer characteristic of being suppressed to / cm ² or less. Through the manufacturing process described above, a ceramic part that satisfies such conditions can be obtained. Of course, it is needless to say that such ceramic parts can be sufficiently used in current semiconductor manufacturing apparatuses.

  The evaluation of the amount of transferred particles is obtained, for example, by vacuum-transferring a mirror-polished ceramic component onto a silicon wafer and measuring the particles on the wafer transfer surface with a particle counter. The metal transfer amount is preferably performed using a total reflection fluorescent X-ray apparatus (TREX).

Next, examples of the present invention will be described. Raw material powders of various ceramic materials shown in Table 1 having a purity of 99.9% or more are prepared. Each of these raw material powders was preformed by a uniaxial press with a φ50 mold, and thereafter, cold isostatic pressing (CIP) was performed to produce the molded body. The compact is formed in an oxidizing atmosphere in the case of oxide ceramics, in an argon (Ar) atmosphere in the case of silicon carbide (SiC), and in a nitrogen (N ₂ ) atmosphere in the case of silicon nitride (Si ₃ N ₄ ). Each was fired at a predetermined temperature for 2 hours to obtain a ceramic sintered body.

  About the obtained ceramic sintered compact, the bulk density was measured by the Archimedes method, and the relative density was calculated | required by calculation. Next, the ceramic sintered body was subjected to surface grinding using a diamond grindstone, and further, one surface of the ground surface was mirror-finished using diamond abrasive grains so that the surface roughness was Ra 10 nm. Such grinding and polishing processing is performed so that the size of the test piece after processing becomes φ33 or more, and the polished surface is observed with an electron microscope, and a defect portion (exposed to the surface) in a vertical and horizontal 200 μm field of view is observed. The area of vacancies, etc.) was determined.

Next, a predetermined cleaning process such as an acid / alkali process or a pure water rinse process was performed on the sample after the polishing process to obtain a test piece. In a clean room, the test piece and the silicon wafer are brought into close contact with each other by a vacuum adsorption method to adsorb and transfer particles and metal impurities. Thereafter, the test piece is separated from the silicon wafer, and particles on the adsorption surface of the silicon wafer are collected by a particle counter. The amount of metal transferred was measured with TREX. Here, the particle transfer amount and the metal transfer amount are evaluated by measuring the number of particles in the φ20 region inside the suction hole, and normalizing this measured value by the suction area, and passing 1.0 piece / mm ² or less (that is, Can be used in semiconductor manufacturing equipment). For the same region, the total amount of metal transfer of Cr, Fe, Ni, and Cu was 1 × 10 ¹² atoms / cm ² or less for the same region.

  Such evaluation results are shown in Table 1. As shown in Examples 1 to 5, in order to keep the particle transfer amount and the metal transfer amount below the reference value, the relative density is 98.5% or more and the defect area is 3% or less. I know that there is. On the other hand, when the relative density was less than 98.5% and the defect area was more than 3%, the particle transfer amount and the metal transfer amount could not be made below the reference value.

  As described above, the highly clean ceramic of the present invention can be suitably used as a component for a semiconductor manufacturing apparatus. In particular, it is suitably used as a member for holding a silicon wafer as a part for a plasma processing chamber that requires heat resistance, high mechanical strength, and corrosion resistance. The highly clean ceramics of the present invention can be used not only as a semiconductor manufacturing apparatus but also as a part for various processing apparatuses that require cleanliness for a target object manufactured in a clean room.

Claims (1)

The relative density is 98.5% or more, the area of the defect on the mirror-polished surface is 3% or less, and the amount of transferred particles by silicon wafer transfer after the mirror-polishing treatment and the washing treatment is 1.0 piece / mm ² or less, and , Cr, Fe, Ni, Cu metal transfer amount is 1 × 10 ¹² atoms / cm ² or less in total.