Applying SiC Nanoparticles to Functional Ceramics for Semiconductor Manufacturing Process

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1 Key Engineering Materials Online: ISSN: , Vol. 403, pp doi: / Trans Tech Publications, Switzerland Applying SiC Nanoparticles to Functional Ceramics for Semiconductor Manufacturing Process Mikio Konishi Sumitomo Osaka Cement Co., Ltd. 585, Toyotomi-cho, Funabashi-shi, Chiba , JAPAN Keywords: SiC, Al 2 O 3, Nanoparticles, Thermal Plasma, Nano-composite, Semiconductor Process Abstract. SiC nanoparticles are synthesized by r.f. thermal plasma chemical vapour deposition using a chemical system of SiH 4 -C 2 H 4 -H 2 -Ar. The average particle size is about 30 nm, and its shape is nearly spherical. The product is β-sic and high pure with total metal impurity of less than 1 ppm. High pure and fully densified SiC body can be made by hot-pressing the sub-micron sized SiC powder added SiC nanoparticles without any sintering additives. They show electrical conductivity, high thermal conductivity and better properties of thermal shock resistance and chemical resistance compared with conventional SiC ceramics. Furthermore, Al 2 O 3 -SiC nano-composite can be made by using SiC nanoparticles easily. These functional ceramics from nanoparticles are the most promising materials for the semiconductor manufacturing process. Up to now, various sintered parts, such as heater, susceptor, pulse heat tool, shower plate and electrical static chuck, etc. have been developed and widely used in the semiconductor industry. Introduction SiC has high potential in applications for high temperature structural materials because of its good properties of mechanical strength, chemical resistance, decomposition temperature. Furthermore highly purified SiC ceramics is applied to the components in semiconductor manufacturing process. SiC is a typical material, which is difficult to sinter because of its covalent bonding character. Nanoparticles are expected to decrease the sintering temperature and to be densified without sintering aids. SiC nanoparticles have been prepared in recent years by various methods [1]-[5]. In spite of many attempts, pure SiC have not yet been reported to be densified without the use of additives. We succeeded in sintering high pure and densified SiC by using the SiC nanoparticles, which was produced by the r.f. thermal plasma CVD method using the chemical system of SiH 4 C 2 H 4 H 2 Ar, without additives [6]. In this paper the properties of SiC nanoparticles, high pure SiC ceramics and Al 2 O 3 -SiC nano-composite are described together with its application to various products in the semiconductor industry. Synthesis and Properties of SiC Nanoparticle SiC nanoparticles are produced by r.f. thermal plasma CVD method in a pilot plant scale. A schematic diagram of this apparatus is drawn in Figure 1. Plasma working gas and sheath gas are Ar and H 2. Reactants of SiH 4 and C 2 H 4 are injected into the thermal plasma under reduced pressure, and decomposed into atoms or ions by heating above 6000 K in thermal plasma and these activated chemical species recombined in the temperature zone below 3000 K to nucleate SiC. The products are collected in the bag filters behind the reactor. The production yield is higher than 95 %. The mean particle size is about 30nm with a size distribution of 5 80 nm, and its shape is nearly spherical. A micrograph of SiC nanoparticles is shown in Figure 2. The product powder has a poly type of β-sic and pure in the crystal phase, containing no other SiC poly type or free Si. The oxygen content of the product powder is typically wt.% which is nearly equal to that of commercial SiC powders with sub-micron sized particles at room temperature. Oxygen exists on the surface of All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/05/16,10:21:30)

2 202 SiAlONs and Non-oxides Raw Gas Sheath Gas Plasma Torch Plasma Gas Cooling Water Work Coil Cooling Water Reaction Chamber Filter, Exhaust Collection Container Figure 1. Thermal Plasma CVD Apparatus Figure 2. Micrograph of SiC Nanoparticles nanoparticles and as absorbed H 2 O. However the oxidization level of nanoparticles increased drastically with increasing temperature. Table 1 shows metal impurity levels obtained for the product powder by neutron activation analysis. SiC nanoparticles are ultra high pure with metal impurity on the ppb level. Chracteristics of Functional Ceramics from SiC Nanoparticles High pure SiC ceramics is produced by hot-pressing of a commercial SiC powder with SiC nanoparticles without sintering additives. The commercially available SiC powders with average particle size in the sub-micron range are made by Acheson process or SiO 2 reduction method. β-sic powder added sintering additives, such as B or Al, are known to be transformed to α-phase during hot-pressing at temperatures of higher than 2273K. In our process, pressure retards the transformation of β-sic powder because of densification without sintering additives. On the otherhand Al 2 O 3 -SiC nano-composite can be obtained by hot-pressing of Al 2 O 3 powder with a small quantity of SiC nanoparticles. This composite has nano structure as shown in Figure 3 and fine grains by the pinning effect of SiC nanoparticles [7]. The properties of SiC and Al 2 O 3 -SiC are shown in Table 1. The density of SiC is near to theoretical density of kg/m 3. It is especially noted t h a t S i C s h o w s h i g h t h e r m a l SiC nanoparticles conductivity of 200 W/m K is much higher than current SiC and AlN which Al 2 O 3 grain 500 nm is known as high thermal conductive ceramics. In general, it is said that the Figure 3. TEM Photograpf of Al 2 O 3 -SiC Nano-composite

3 Key Engineering Materials Vol thermal energy is transmitted Table 1. Properties of Functional Ceramics from SiC Nanoparticles by photon vibrations. For p o l yc r ys t a l l i n e s u c h a s Material SiC Al2O3-SiC ceramics, the harmony of these Density [kg/m 3 ] vibrations is disturbed by 4-point Bending Strength [MPa] impurities, defects and grain boundaries, etc. Therefore the Vickers Hardness SiC materials made from the Resistivity [Ω m] nanoparticles is considered to Relative Dielectric Constant (1MHz) - 17 h a v e a m u c h l o w e r Dielectric Loss tan δ (1MHz) concentration of impurities in the grains and the grain Break Down Voltage [kv/mm] boundaries. Furthermore this SiC with a β phase shows a low Thermal Expansion [K -1 ] electrical resistance ( Thermal Conductivity [W/m K] Ω m), and can be applied as electrical conductive ceramics. Specific Heat [kj/kg K] Almost all current electrical conductive SiC are composites of SiC and the electrical conductive materials, such as TiC, TaC and ZrC, etc. These materials have a significant problem in that oxidation resistance and chemical stability are deteriorated by electrical conductive components. On the other hand this monolithic SiC has unique characteristics combined with electrical conductivity and the physical, mechanical and thermal properties of pure SiC. This SiC sintered body can be easily machined by electrical discharge machining. Electrical discharge machining has been used for the complex shaping of components to very high tolerance. Accordingly this good electrical discharge machinability of it can break through the shape restriction and the high cost of diamond abrasive machining for the hot-pressed SiC. Electrical discharge machining has been used for the complex shaping of components to very high tolerance. Accordingly this good electrical discharge machinability of it can break through the shape restriction and the high cost of diamond abrasive Susceptor Edge Ring Shower Plate Heater Pulse Heat Tool Electrical Static Chucks Figure 4. Appearance of Functional Ceramic Products for Semiconductor Process

4 204 SiAlONs and Non-oxides machining for the hot-pressed SiC. The resistivity of Al 2 O 3 -SiC nano-composite is decreased to 10 8 Ω m from the insulation of Al 2 O 3. Moreover its wear resistance, mechanical properties and thermal conductivity are improved as compared with monolithic Al 2 O 3. In the case of using SiC nanoparticles, the marked effects of its complex are shown with a small quantiy of less than 10 vol.%. Applying to the Components in Semiconductor Manufacturing Process. The sintered products of SiC and Al 2 O 3 -SiC made from SiC nanoparticles have been applied to a wide variety fields including semiconductor process parts and mechanical and structural components because of its high purity, good mechanical strength, high thermal conductivity and excellent resistance to wear and chemical corrosion. In particular, the extremely high purity of these materials make them well suited for use in the semiconductor industry. Figure 3 shows appearance of these semiconductor process parts. SiC heater for single-wafer processes has been used in semiconductor manufacturing processes such as CVD, annealing and degassing. Another application for the heater is SiC pulse heat tool in flip chip bonding process. This tool performs extremely rapid heating (200 K/sec) and cooling (100 K/sec), and can make the throughputs and cycle times of assembly for MCM (Multi Chip Module) and BAG (Ball Array Grid) faster. Other current semiconductor applications are wafer support parts such as susceptors, edge rings and lift pins for CVD, epitaxial growth process and RTP (Rapid Thermal Process). Electrical static chucks have a function of chucking and de-chucking a wafer by electrical static force and recently has been used in many semiconductor manufacturing processes, such as plasma etching, CVD and PVD. The products made from Al 2 O 3 -SiC nano-composite have advantages of little contamination of wafer, low particle generation and long product life in fluorine plasma. Therefore it is expected that electrical static chucks are widely applied in high technology industries. Conclusions We have reviewed the properties of SiC nanoparticles manufactured by r.f. thermal plasma CVD method and the characteristics and the applications of its sintered parts. The high surface activity of SiC nanoparticle is considered the significant driving force in the sintering processes of SiC and Al 2 O 3 -SiC nano-composite. From the results of our development, it is verified that high purity and uniform microstructure obtained from nanoparticles can improve the quality and the reliability of sintered materials, and furthermore find up new character. References [1] Y. Okabe, K. Miyachi, J. Hojo and A. Kato, Chem. Soc. Jpn. (1981), p1363 [2] M. Ohkochi and Y. Ando, J. Ceram. Soc. Jpn 94 (1986), p26 [3] M. Asuwa and M. Yamamoto, Proceedings of the Ceramic Society of Japan Annual Meeting, 3G10 (Ceramic Society of Japan, Tokyo, 1986), p.421 [4] P. Pavlovic, P. Stefanovic, S. Boskovic and E. kostic, VDI. Berichte. NR. (1995), p1166 [5] E. Borsella, S. Botti, S. Martelli, A. Donato, C.A. Nannetti, G. D Alessandro and E. Scafe, Fourth Euro Ceram. Vol.1 (1995), p105 [6] K. Kijima, H. Noguchi and M. Konishi, Jpn. Patent 1,757,508. (1993) [7] Y. Jeong, A. Nakahira, E. D. Morgan and K. Niihara, J. Am. Ceram. Soc., 80, 797 (1997)

5 SiAlONs and Non-oxides / Applying SiC Nanoparticles to Functional Ceramics for Semiconductor Manufacturing Process /