JP2005314217A - Silicon carbide single crystal and method for manufacturing the same - Google Patents
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- 239000013078 crystal Substances 0.000 title claims abstract description 155
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims abstract description 98
- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 97
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 39
- 238000000034 method Methods 0.000 title claims abstract description 15
- 239000002994 raw material Substances 0.000 claims abstract description 113
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 85
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims abstract description 69
- 229910052796 boron Inorganic materials 0.000 claims abstract description 68
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 62
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 45
- 239000010703 silicon Substances 0.000 claims abstract description 43
- 238000010438 heat treatment Methods 0.000 claims abstract description 20
- 239000002245 particle Substances 0.000 claims abstract description 12
- 238000000859 sublimation Methods 0.000 claims abstract description 9
- 230000008022 sublimation Effects 0.000 claims abstract description 9
- 238000001953 recrystallisation Methods 0.000 claims abstract description 8
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 43
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 28
- 229910052757 nitrogen Inorganic materials 0.000 claims description 14
- 239000011261 inert gas Substances 0.000 claims description 7
- 238000012545 processing Methods 0.000 claims description 4
- 238000002156 mixing Methods 0.000 claims description 3
- 238000005498 polishing Methods 0.000 claims description 3
- 239000012535 impurity Substances 0.000 abstract description 34
- 239000000203 mixture Substances 0.000 abstract description 7
- 229920002994 synthetic fiber Polymers 0.000 abstract 1
- 235000012431 wafers Nutrition 0.000 description 23
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 22
- 239000000843 powder Substances 0.000 description 20
- 229910002804 graphite Inorganic materials 0.000 description 17
- 239000010439 graphite Substances 0.000 description 17
- 239000007789 gas Substances 0.000 description 15
- 229910052786 argon Inorganic materials 0.000 description 11
- 238000001036 glow-discharge mass spectrometry Methods 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 238000003786 synthesis reaction Methods 0.000 description 5
- 238000011109 contamination Methods 0.000 description 4
- 229910052736 halogen Inorganic materials 0.000 description 4
- 150000002367 halogens Chemical class 0.000 description 4
- 239000004065 semiconductor Substances 0.000 description 4
- 239000000758 substrate Substances 0.000 description 4
- 238000004458 analytical method Methods 0.000 description 3
- 239000003575 carbonaceous material Substances 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000005485 electric heating Methods 0.000 description 3
- 150000002500 ions Chemical group 0.000 description 3
- 230000009257 reactivity Effects 0.000 description 3
- 239000007858 starting material Substances 0.000 description 3
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000002210 silicon-based material Substances 0.000 description 2
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 1
- PPWPWBNSKBDSPK-UHFFFAOYSA-N [B].[C] Chemical compound [B].[C] PPWPWBNSKBDSPK-UHFFFAOYSA-N 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 230000006837 decompression Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000011812 mixed powder Substances 0.000 description 1
- 229910052754 neon Inorganic materials 0.000 description 1
- GKAOGPIIYCISHV-UHFFFAOYSA-N neon atom Chemical compound [Ne] GKAOGPIIYCISHV-UHFFFAOYSA-N 0.000 description 1
- 238000007517 polishing process Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
Abstract
Description
本発明は、結晶中の不純物、特に硼素濃度が小さい炭化珪素単結晶、およびその安定製造を可能にする方法に関するものである。本発明の高純度炭化珪素単結晶より、加工、および研磨工程を経て製造される炭化珪素単結晶ウェハは、主として各種の半導体電子デバイス、あるいはそれらの基板として用いられる。 The present invention relates to a silicon carbide single crystal having a low concentration of impurities in the crystal, particularly boron, and a method that enables stable production thereof. A silicon carbide single crystal wafer manufactured from the high-purity silicon carbide single crystal of the present invention through processing and polishing steps is mainly used as various semiconductor electronic devices or their substrates.
炭化珪素（ＳｉＣ）は、優れた半導体特性を有しており、従来材であるシリコン（Ｓｉ）やガリウム砒素（ＧａＡｓ）等と比較して、特に耐熱性及び機械的強度等が格段に優れること等から、パワーデバイスや高周波デバイス等の各種半導体デバイス用ウェハ材料として注目されている。ＳｉＣ単結晶ウェハを用いたデバイスとして、ＧａＮ系青色発光ダイオードやショットキーバリアダイオード等が既に商品化されており、また、他にも、ＧａＮ系高周波デバイス、及びＭＯＳＦＥＴに代表される低損失パワーデバイス用の基板材料として試作に供されている。 Silicon carbide (SiC) has excellent semiconductor characteristics, and particularly has excellent heat resistance and mechanical strength compared to conventional materials such as silicon (Si) and gallium arsenide (GaAs). Therefore, it has been attracting attention as a wafer material for various semiconductor devices such as power devices and high-frequency devices. GaN-based blue light-emitting diodes and Schottky barrier diodes have already been commercialized as devices using SiC single crystal wafers. Besides, GaN-based high-frequency devices and low-loss power devices represented by MOSFETs It is used for trial production as a substrate material.
デバイス応用に当たっては、用途に応じてウェハ材料の電気伝導度特性を制御する必要がある。そのためにはＳｉやＧａＡｓ等の従来半導体製造で行われているように、結晶中の不純物濃度を極力抑えた、高純度な単結晶を製造できる技術を確立することが必要であり、単結晶ウェハの電気伝導特性の精密制御を可能にする上で重要な基盤技術となっている。特に、ドナーあるいはアクセプターとなりえる不純物元素については、単結晶の電気伝導度特性に及ぼす影響が大きく、ドープ量、あるいは不純物としての混入量を精密に管理する必要がある。ＳｉＣ単結晶の場合、上記不純物に該当する代表元素の１つとして硼素が挙げられる。ＳｉＣ単結晶のポリタイプにもよるが硼素はＳｉＣ結晶の約２．５〜３．０電子ボルト（ｅＶ）におよぶ大きな禁制帯の中で、価電子帯直上約０．２〜０．３ｅＶ程度の比較的浅い位置にアクセプター準位を形成するため、室温でも容易にイオン化され易く、硼素原子から結晶中に放出されるホールがキャリアーとなって、電気伝導度を押し上げる作用を及ぼす。このため、高周波デバイス用途等のように、ＳｉＣ単結晶ウェハとして極力小さな電気伝導度が要求される場合には、結晶中の不純物硼素濃度が高くならないような製造上の工夫が求められる。 In device applications, it is necessary to control the electrical conductivity characteristics of the wafer material according to the application. For this purpose, it is necessary to establish a technology capable of producing a high-purity single crystal with the impurity concentration in the crystal suppressed as much as possible in the conventional production of semiconductors such as Si and GaAs. It is an important basic technology to enable precise control of the electrical conduction characteristics of In particular, an impurity element that can be a donor or an acceptor has a large influence on the electrical conductivity characteristics of a single crystal, and it is necessary to precisely control the doping amount or the amount of impurities mixed therein. In the case of a SiC single crystal, boron is one of the representative elements corresponding to the impurities. Although it depends on the polytype of the SiC single crystal, boron is about 0.2 to 0.3 eV directly above the valence band in the large forbidden band of about 2.5 to 3.0 electron volts (eV) of the SiC crystal. Since the acceptor level is formed at a relatively shallow position of the film, it is easily ionized even at room temperature, and the holes emitted from the boron atoms into the crystal serve as carriers and have an effect of increasing electrical conductivity. For this reason, when an electric conductivity as small as possible is required as a SiC single crystal wafer as in a high-frequency device application, etc., a device for manufacturing that does not increase the impurity boron concentration in the crystal is required.
目下のところ、デバイス製造に適した大口径を有するＳｉＣ単結晶インゴットは、改良レーリー法を基本とする昇華再結晶法によって、製造されることが一般的になっている（非特許文献１）。この昇華再結晶法の基本は、（１）ＳｉＣ単結晶ウェハを種結晶として使用し、主として黒鉛からなる坩堝中に、原料となるＳｉＣ結晶粉末を充填、（２）アルゴン等の不活性ガス雰囲気中（１３３Ｐａ〜１３．３ｋＰａ）にて、約２０００〜２４００℃以上の高温に加熱、（３）原料粉末に比べ種結晶が低温側となる温度勾配が形成されるように種結晶及び原料粉末を配置、となっており、これにより原料から発生した昇華ガスが、種結晶方向へ拡散・輸送され、種結晶上で再結晶化することにより、単結晶成長が実現、の３点から構成される。 At present, SiC single crystal ingots having a large diameter suitable for device manufacture are generally manufactured by a sublimation recrystallization method based on the improved Rayleigh method (Non-patent Document 1). The basics of this sublimation recrystallization method are (1) using a SiC single crystal wafer as a seed crystal, filling a crucible mainly made of graphite with SiC crystal powder as a raw material, and (2) an inert gas atmosphere such as argon. Medium (133 Pa to 13.3 kPa) and heated to a high temperature of about 2000 to 2400 ° C. As a result, the sublimation gas generated from the raw material is diffused and transported in the direction of the seed crystal, and recrystallized on the seed crystal, thereby realizing single crystal growth. .
このような製造方法に立脚し、前述の観点から、結晶中の不純物硼素濃度を極力低減するためには、その製造プロセスの随所に亘って、硼素混入の可能性を注意深く逐一駆除する製造上の配慮が必要であり、その詳細は製造ノウハウとなっている。
ＳｉＣ結晶の代表的な不純物である硼素は、前述のようにアクセプター準位を形成するために、結晶中に大量に混入すると電気伝導度が大幅に増加する。したがって、ＳｉＣ単結晶ウェハとして低い電気伝導度が要求される場合には、ＳｉＣ結晶中の硼素濃度を１×１０１７ｃｍ−３以下、望ましくは１×１０１６ｃｍ−３以下にする必要がある。しかしながら、一般的に硼素濃度が極度に抑えられたＳｉＣ単結晶を、昇華再結晶法によって製造することは容易ではない。原料中の硼素濃度で、成長結晶中の硼素濃度が決定される傾向が強い。また、一度結晶中に取り込まれた硼素はその化学的性質も類似しているため、ＳｉＣ中に既に混入した硼素の除去は極めて困難である。したがって、硼素濃度が小さい結晶を製造するためには、硼素濃度の低い原料を使用する必要がある。 As described above, boron, which is a typical impurity of a SiC crystal, forms an acceptor level, so that the electrical conductivity increases greatly when mixed in the crystal in a large amount. Therefore, when low electrical conductivity is required for the SiC single crystal wafer, the boron concentration in the SiC crystal needs to be 1 × 10 17 cm −3 or less, preferably 1 × 10 16 cm −3 or less. . However, it is generally not easy to produce a SiC single crystal with a very low boron concentration by the sublimation recrystallization method. There is a strong tendency that the boron concentration in the grown crystal is determined by the boron concentration in the raw material. Further, since boron once taken into the crystal has similar chemical properties, it is very difficult to remove boron already mixed in SiC. Therefore, in order to produce a crystal having a low boron concentration, it is necessary to use a raw material having a low boron concentration.
このような場合、単結晶の電気伝導度制御が難しくなり、特に高周波デバイス応用に重要な低電気伝導度ＳｉＣ単結晶ウェハを、安定的にかつ歩留まり良く製造することが困難になる。かかる事情から硼素不純物を低減できる、工業的に有望な高純度ＳｉＣ単結晶、及びその製造方法が強く望まれていた。 In such a case, it becomes difficult to control the electrical conductivity of the single crystal, and it becomes difficult to manufacture a low electrical conductivity SiC single crystal wafer, which is particularly important for high-frequency device applications, stably and with a high yield. Under such circumstances, an industrially promising high-purity SiC single crystal capable of reducing boron impurities and a method for producing the same have been strongly desired.
本発明は、上記事情に鑑みてなされたものであり、硼素不純物の低い高純度ＳｉＣ単結晶、及びその製造方法を提供するものである。 The present invention has been made in view of the above circumstances, and provides a high-purity SiC single crystal having a low boron impurity and a method for producing the same.
本発明は、硼素不純物の低い高純度ＳｉＣ単結晶、高純度ＳｉＣ単結晶ウェハ及びその製造方法を提供するものであって、
（１）種結晶を用いた昇華再結晶法により作製される炭化珪素単結晶製造方法において、少なくとも１ｐｐｍ以下の硼素濃度の炭素原料、及び、該炭素原料の硼素濃度より低い硼素濃度を有するシリコンを出発原料とし、出発原料の混合体もしくは一度加熱し反応させ得られた炭化珪素を含む反応体を炭化珪素単結晶の原料として用いることを特徴とする高純度炭化珪素単結晶の製造方法、
（２）前記炭素原料の硼素濃度が０．１ｐｐｍ以下である（１）に記載の高純度炭化珪素単結晶の製造方法、
（３）前記炭素原料の硼素濃度が０．０５ｐｐｍ以下である請求項（１）に記載の高純度炭化珪素単結晶の製造方法、
（４）前記シリコン原料の硼素濃度が０．０１ｐｐｍ以下である（１）に記載の高純度炭化珪素単結晶の製造方法、
（５）前記炭素原料の平均粒径が３００μｍ以下である（１）〜（４）のいずれかに記載の高純度炭化珪素単結晶の製造方法、
（６）炭素原料として、出発原料の混合および反応させる前に少なくとも炭素原料を一旦、圧力１．３Ｐａ以下の不活性ガス雰囲気下で温度１４００℃以上に保持する高温熱処理を施した（１）〜（５）のいずれかに記載の高純度炭化珪素単結晶の製造方法。
The present invention provides a high-purity SiC single crystal having a low boron impurity, a high-purity SiC single crystal wafer, and a method for producing the same.
(1) In a silicon carbide single crystal manufacturing method produced by a sublimation recrystallization method using a seed crystal, a carbon raw material having a boron concentration of at least 1 ppm or less and silicon having a boron concentration lower than the boron concentration of the carbon raw material A method for producing a high-purity silicon carbide single crystal, characterized by using as a starting material, a mixture of starting materials or a reactant containing silicon carbide obtained by heating and reacting as a starting material for a silicon carbide single crystal,
(2) The method for producing a high-purity silicon carbide single crystal according to (1), wherein the boron concentration of the carbon raw material is 0.1 ppm or less,
(3) The method for producing a high-purity silicon carbide single crystal according to (1), wherein the boron concentration of the carbon raw material is 0.05 ppm or less.
(4) The method for producing a high-purity silicon carbide single crystal according to (1), wherein the boron concentration of the silicon raw material is 0.01 ppm or less,
(5) The method for producing a high-purity silicon carbide single crystal according to any one of (1) to (4), wherein an average particle size of the carbon raw material is 300 μm or less,
(6) As a carbon raw material, at least the carbon raw material was once subjected to high-temperature heat treatment for maintaining the temperature at 1400 ° C. or higher in an inert gas atmosphere having a pressure of 1.3 Pa or lower before mixing and reacting the starting raw materials (1) to (5) The manufacturing method of the high purity silicon carbide single crystal according to any one of (5).
（７）（１）〜（６）のいずれかに１項に記載の製造方法により得られる炭化珪素単結晶であって、単結晶中の硼素濃度が１×１０１７ｃｍ−３以下であることを特徴とする高純度炭化珪素単結晶、
（８）前記炭化珪素単結晶中の硼素濃度が１×１０１６ｃｍ−３以下である（７）記載の高純度炭化珪素単結晶、
（９）前記炭化珪素単結晶中の窒素濃度が５×１０１６ｃｍ−３以下である（７）又は（８）に記載の高純度炭化珪素単結晶、
（１０）炭化珪素単結晶のポリタイプが３Ｃ、４Ｈ又は６Ｈである（７）〜（９）のいずれか１項に記載の高純度炭化珪素単結晶、
（１１）（７）〜（１０）のいずれか１項に記載の炭化珪素単結晶を加工、研磨してなる高純度炭化珪素単結晶ウェハ、
（１２）前記単結晶ウェハの口径が５０ｍｍ以上である（１１）に記載の高純度炭化珪素単結晶ウェハ、
である。
(7) A silicon carbide single crystal obtained by the manufacturing method according to any one of (1) to (6), wherein a boron concentration in the single crystal is 1 × 10 17 cm −3 or less. High-purity silicon carbide single crystal, characterized by
(8) The high-purity silicon carbide single crystal according to (7), wherein a boron concentration in the silicon carbide single crystal is 1 × 10 16 cm −3 or less,
(9) The high-purity silicon carbide single crystal according to (7) or (8), wherein the nitrogen concentration in the silicon carbide single crystal is 5 × 10 16 cm −3 or less,
(10) The high-purity silicon carbide single crystal according to any one of (7) to (9), wherein the polytype of the silicon carbide single crystal is 3C, 4H, or 6H,
(11) A high-purity silicon carbide single crystal wafer formed by processing and polishing the silicon carbide single crystal according to any one of (7) to (10),
(12) The high-purity silicon carbide single crystal wafer according to (11), wherein the diameter of the single crystal wafer is 50 mm or more,
It is.
本発明によれば、少なくとも１ｐｐｍ以下の硼素濃度の炭素原料、及び該炭素原料の硼素濃度より低い硼素濃度を有するシリコン原料の混合体を加熱合成して得られる炭化珪素を含む合成原料体を炭化珪素単結晶の原料として採用することで、ＳｉＣ単結晶中の硼素濃度が１×１０１７ｃｍ−３以下である高純度ＳｉＣ単結晶の製造が可能になる。また、炭素原料の粒径を３００μｍ以下にすることでシリコン原料との反応性を確保し、結果として高純度ＳｉＣ単結晶の効率的な製造が可能になる。このような高純度ＳｉＣ単結晶ウェハを用いれば、電気的特性に優れた高耐圧・耐環境性電子デバイスを歩留まり良く作製することが可能になる。 According to the present invention, a synthetic raw material body containing silicon carbide obtained by heat synthesis of a carbon raw material having a boron concentration of at least 1 ppm or less and a silicon raw material having a boron concentration lower than the boron concentration of the carbon raw material is carbonized. By adopting the silicon single crystal as a raw material, it is possible to produce a high-purity SiC single crystal having a boron concentration in the SiC single crystal of 1 × 10 17 cm −3 or less. Moreover, the reactivity with a silicon raw material is ensured by making the particle size of a carbon raw material into 300 micrometers or less, As a result, efficient manufacture of a high purity SiC single crystal is attained. By using such a high-purity SiC single crystal wafer, it becomes possible to manufacture a high withstand voltage / environment resistant electronic device having excellent electrical characteristics with high yield.
上記事情を鑑み、発明者らは、昇華再結晶法において硼素が低い、高純度ＳｉＣ単結晶を製造する方法を探索する中で、特に原料粉の製造プロセスに注目し、製造プロセスと硼素混入について詳しく調査した。その結果、硼素元素混入の主たる原因は主に原料自身にあることを突き止めた。したがって、発明者らは、硼素不純物の小さい結晶を製造するためには、使用する原料自身に含まれる硼素濃度が小さいことが必要であるとの結論を持つに至った。そのような原料を製造する方法として、硼素濃度の極めて小さな高純度炭素及びシリコンを用いればよい。しかしながら、一般に良く知られているように、炭素中には１ｐｐｍ以上の硼素が含まれていることが多く、これらの硼素は除去が困難である。そのため、例えば、硼素混入の少ない厳選した炭素材を、ハロゲンガス雰囲気下で２０００℃以上の高温を数週間にわたる長時間処理する等、極端な純化処理することで、硼素濃度の低減された炭素原料として利用可能となる。また、炭素原料は、上述のような炭素元素が主たる構成となることが、不純物低減上や合成後のＳｉＣ収率の上で好ましいが、全部又は一部に高純度炭化水素化合物を用いることも可能である。 In view of the above circumstances, the inventors, in search of a method for producing a high-purity SiC single crystal with low boron in the sublimation recrystallization method, pay particular attention to the production process of raw material powder, and about the production process and boron incorporation. We investigated in detail. As a result, it was found that the main cause of the boron element contamination is mainly the raw material itself. Therefore, the inventors have come to the conclusion that in order to produce a crystal having a small boron impurity, it is necessary that the concentration of boron contained in the raw material used is small. As a method for producing such a raw material, high purity carbon and silicon having a very low boron concentration may be used. However, as is generally well known, carbon often contains 1 ppm or more of boron, which is difficult to remove. Therefore, for example, a carbon raw material with a reduced boron concentration can be obtained by subjecting a carefully selected carbon material with little boron contamination to an extreme purification treatment, such as a high temperature of 2000 ° C. or higher for several weeks in a halogen gas atmosphere. Will be available as The carbon raw material is preferably composed mainly of carbon elements as described above in terms of impurity reduction and SiC yield after synthesis, but high purity hydrocarbon compounds may be used for all or part of the carbon raw material. Is possible.
一方、シリコン原料としては、少なくともシリコン原料の不純物濃度を炭素原料の不純物濃度よりも低くすることで、高純度化炭素原料の不純物濃度を上げることなく、ＳｉＣ原料粉を合成できる点で好ましい。さらに、不純物低減上、好ましくはシリコン単結晶用の原料となる超高純度シリコン・チップが挙げられる。 On the other hand, the silicon raw material is preferable in that the SiC raw material powder can be synthesized without increasing the impurity concentration of the highly purified carbon raw material by making the impurity concentration of the silicon raw material lower than the impurity concentration of the carbon raw material. Further, in order to reduce impurities, an ultra-high purity silicon chip that is preferably a raw material for a silicon single crystal is used.
硼素濃度が原子数密度で１×１０１７ｃｍ−３以下、望ましくは１×１０１６ｃｍ−３以下である高純度ＳｉＣ単結晶を製造する条件として、ＳｉＣ原料粉の合成に使用するシリコン原料は、炭素原料の硼素不純物濃度以下とし、炭素原料の硼素濃度は少なくとも１ｐｐｍ以下、好ましくは０．１ｐｐｍ以下、更に望ましくは０．０５ｐｐｍ以下である必要がある。硼素不純物濃度が１ｐｐｍを越える炭素原料を使用すると、ＳｉＣ結晶中への硼素混入濃度が過大となり、不純物濃度で１×１０１７ｃｍ−３を越えるために電気伝導制御が困難になる。結晶中の硼素不純物濃度を１×１０１６ｃｍ−３以下とするには、硼素不純物濃度が０．０５ｐｐｍ以下である炭素原料を使用することが望まれる。また、シリコン原料は、具体的には少なくとも０．５ｐｐｍ以下、好ましくは０．０１ｐｐｍ以下、下限としては特に設けないが、工業上比較的容易に利用できる範囲で超高純度シリコン原料の純度から判断して０．００１ｐｐｂまでの範囲とすることで、結晶中の硼素不純物濃度を１×１０１７ｃｍ−３以下、望ましくは１×１０１６ｃｍ−３以下の高純度ＳｉＣ単結晶製造が実現できる。 As a condition for producing a high-purity SiC single crystal having a boron concentration of 1 × 10 17 cm −3 or less, preferably 1 × 10 16 cm −3 or less in terms of atomic number density, a silicon raw material used for synthesis of SiC raw material powder is The boron impurity concentration of the carbon raw material should be lower than the boron concentration, and the boron concentration of the carbon raw material should be at least 1 ppm or lower, preferably 0.1 ppm or lower, more desirably 0.05 ppm or lower. If a carbon raw material having a boron impurity concentration exceeding 1 ppm is used, the boron concentration in the SiC crystal becomes excessive, and the impurity concentration exceeds 1 × 10 17 cm −3 , making it difficult to control electrical conduction. In order to set the boron impurity concentration in the crystal to 1 × 10 16 cm −3 or less, it is desirable to use a carbon raw material having a boron impurity concentration of 0.05 ppm or less. Further, the silicon raw material is specifically at least 0.5 ppm or less, preferably 0.01 ppm or less, and there is no particular lower limit, but it is judged from the purity of the ultra-high purity silicon raw material within a range that can be used relatively easily industrially. By making the range up to 0.001 ppb, it is possible to produce a high-purity SiC single crystal having a boron impurity concentration in the crystal of 1 × 10 17 cm −3 or less, preferably 1 × 10 16 cm −3 or less.
また、炭素とシリコンとの使用比率は、通常、モル比でＣ：Ｓｉ＝１：０．９〜１：１．１とするが、望ましくはＣ：Ｓｉ＝１：０．９〜１：１である。さらに、上記の点に加えて、加熱時に炭素とシリコンとの反応速度を確保して工業的生産性をもたらしめるためには、これら原料粉の粒径に留意する必要がある。これら背景を踏まえた検討の結果、シリコン原料の粒径より、むしろ炭素原料の粒径のみをある程度細かくすることで、ＳｉＣ原料合成時の反応性が高く、不純物混入量の増加も低減できることが明らかになった。また、十分な反応が進行しない場合、原料粉中にシリコン原料の残存もしくはシリコン濃度の高い領域の残存を引き起こす。シリコン濃度の高い領域が残存すると、ＳｉＣ単結晶成長の昇温時に種結晶の上に好ましくないシリコン濃度の高い付着物が着き易く、この領域を基点として多結晶化する等の結晶性を著しく損なう可能性がある。このような不具合を引き起こさないためにも、炭素原料の平均粒径で３００μｍ以下とすることが好ましい。但し、過度な微細粒を用いると、大気中に含まれる窒素等の不純物元素を吸着し易くなることから、平均粒径は少なくとも１００ｎｍ以上が好ましく、より好ましくは１μｍ以上である。 Further, the use ratio of carbon to silicon is usually C: Si = 1: 0.9 to 1: 1.1 in terms of molar ratio, but preferably C: Si = 1: 0.9 to 1: 1. It is. Furthermore, in addition to the above points, it is necessary to pay attention to the particle size of these raw material powders in order to ensure the reaction rate between carbon and silicon during heating and to bring about industrial productivity. As a result of studies based on these backgrounds, it is clear that by reducing the particle size of the carbon material rather than the silicon material to some extent, the reactivity at the time of synthesizing the SiC material is high and the increase in the amount of impurities mixed can be reduced. Became. Further, if the reaction does not proceed sufficiently, the silicon raw material remains in the raw material powder or the region having a high silicon concentration remains. If a region with a high silicon concentration remains, an unfavorable silicon-concentrated deposit easily attaches to the seed crystal when the temperature of the SiC single crystal growth is raised, and the crystallinity such as polycrystallization with this region as a base point is significantly impaired. there is a possibility. In order not to cause such a problem, the average particle size of the carbon raw material is preferably 300 μm or less. However, when excessive fine particles are used, it becomes easy to adsorb impurity elements such as nitrogen contained in the atmosphere. Therefore, the average particle size is preferably at least 100 nm, more preferably 1 μm or more.
一方、一般的に炭素粉体の粒径が小さくなると、炭素表面への窒素吸着が発生し、結晶中の窒素不純物濃度の増加を引き起こすことが明らかになった。しかしながら、この問題点は、通常、１．３Ｐａ以下、好ましくは１．３×１０−１Ｐａ以下（ただし、下限は、工業的に比較的容易に到達できる圧力であり、例えば、１×１０−２Ｐａとする）の不活性ガス（ここで、不活性ガスとは、アルゴン、ヘリウム、ネオン、もしくはこれらの混合ガスをいう。）流中で通常、１４００℃以上、望ましくは２０００℃以上で、ただし、上限は、工業的に比較的容易に実施できる温度であり、例えば、２６００℃とする、少なくとも５時間以上、望ましくは２０時間程度熱処理することで、炭素原料中の窒素不純物を減少させることができる。また、ＳｉＣ原料合成時に用いる坩堝容器として黒鉛坩堝を用いる場合は、坩堝から高温時に発生する窒素不純物も懸念されることから、同様な熱処理を、炭素原料の熱処理と同時もしくは別々に行うことで、窒素不純物混入を防ぐことができる。加えて、ＳｉＣ単結晶成長時に用いる黒鉛坩堝も、同様な熱処理を行うことが望ましい。更に窒素不純物混入を抑制するには、混合体を加熱合成する直前にも下記のような加熱減圧処理条件で行うことが好ましい。加熱減圧処理とは、坩堝容器に入れた混合体を、１．３Ｐａ以下、好ましくは１．３×１０−１Ｐａ以下（ただし、下限は、工業的に比較的容易に到達できる圧力であり、例えば、１×１０−２Ｐａとする）の不活性ガス流中で、通常、９００℃以上１１００℃以下で、好ましくは１１００℃において少なくとも０．５時間以上、望ましくは２時間程度熱処理することを指す。この加熱減圧処理後に、アルゴン等の不活性ガスで大気圧水準（例えば，５０ｋＰａ以上１２０ｋＰａ以下）まで圧力を戻すことで、原料の加熱合成処理を行うことが可能である。加熱合成処理の温度は、通常、１４００℃以上２６００℃以下とする。また、このような熱処理を行うことで、ＳｉＣ結晶中への窒素不純物混入濃度も低減され、窒素不純物濃度で５×１０１６ｃｍ−３を越えなくなり、電気伝導制御がさらに容易になる。 On the other hand, it has been clarified that generally when the particle size of carbon powder is reduced, nitrogen adsorption occurs on the carbon surface, causing an increase in nitrogen impurity concentration in the crystal. However, this problem is usually 1.3 Pa or less, preferably 1.3 × 10 −1 Pa or less (however, the lower limit is a pressure that can be reached relatively easily industrially, for example, 1 × 10 − 2 Pa) inert gas (wherein the inert gas refers to argon, helium, neon, or a mixed gas thereof) is usually 1400 ° C. or higher, preferably 2000 ° C. or higher. However, the upper limit is a temperature that can be carried out relatively easily industrially, for example, to reduce nitrogen impurities in the carbon raw material by heat treatment at 2600 ° C. for at least 5 hours or more, preferably about 20 hours. Can do. In addition, when using a graphite crucible as a crucible container used at the time of SiC raw material synthesis, there is a concern about nitrogen impurities generated at high temperatures from the crucible. Nitrogen impurity contamination can be prevented. In addition, it is desirable that the graphite crucible used at the time of SiC single crystal growth be subjected to the same heat treatment. Further, in order to suppress the mixing of nitrogen impurities, it is preferable to carry out under the following heat and pressure treatment conditions immediately before the mixture is heated and synthesized. Heating and decompression treatment is a mixture put in a crucible container, 1.3 Pa or less, preferably 1.3 × 10 −1 Pa or less (however, the lower limit is a pressure that can be reached relatively easily industrially, Heat treatment in an inert gas flow (for example, 1 × 10 −2 Pa), usually at 900 ° C. or more and 1100 ° C. or less, preferably at 1100 ° C. for at least 0.5 hours, desirably about 2 hours. Point to. After this heat-depressurization treatment, the raw material can be heat-synthesized by returning the pressure to an atmospheric pressure level (for example, 50 kPa to 120 kPa) with an inert gas such as argon. The temperature of the heat synthesis treatment is usually 1400 ° C. or higher and 2600 ° C. or lower. Further, by performing such a heat treatment, the concentration of nitrogen impurities in the SiC crystal is also reduced, and the nitrogen impurity concentration does not exceed 5 × 10 16 cm −3 , and electric conduction control is further facilitated.
高純度ＳｉＣ単結晶は、現在デバイス応用が有望視されている３Ｃ、４Ｈ及び６Ｈポリタイプのいずれにおいても有効である。また、結晶の口径が大型化すると、使用するＳｉＣ原料も増加するため、本発明は大口径ＳｉＣ単結晶成長に効果的であり、特に、口径が５０ｍｍ以上の場合に大きな効果が得られる。単結晶ウェハの口径としては、通常、５０ｍｍ以上である。上限としては、工業的に到達できれば特に制限はされないが、通常、３００ｍｍである。そのような結晶から、通常の加工及び研磨プロセスを経て製造される単結晶ウェハは、高純度ＳｉＣ単結晶ウェハの歩留まりが高いため、製造コストの大幅削減が可能になり、安価で高純度かつ高品質なウェハ供給が可能になる。 High-purity SiC single crystals are effective in any of the 3C, 4H and 6H polytypes that are currently promising for device applications. Moreover, since the SiC raw material to be used increases when the diameter of the crystal increases, the present invention is effective for growing a large-diameter SiC single crystal, and a great effect is obtained particularly when the diameter is 50 mm or more. The diameter of the single crystal wafer is usually 50 mm or more. The upper limit is not particularly limited as long as it can be industrially reached, but is usually 300 mm. Single crystal wafers manufactured from such crystals through normal processing and polishing processes have a high yield of high-purity SiC single crystal wafers, which can greatly reduce manufacturing costs, and are inexpensive, high-purity, and high-quality. Quality wafer supply becomes possible.
以下に、本発明の実施例について説明する。 Examples of the present invention will be described below.
（実施例１）
炭素原料として、ハロゲンガス中で２０００℃以上の熱処理を行った高純度炭素粉体を、シリコン原料として、シリコン単結晶引き上げ用純度９９．９９９９９９９９９％のシリコンチップを用いた。炭素原料及びシリコン原料の硼素濃度は、ＧＤＭＳ（グロー放電質量分析）測定でそれぞれ０．１１ｐｐｍ、０．００１ｐｐｍ以下であった。シリコンチップは、主に数ｍｍから十数ｍｍの大きさであり、高純度炭素粉体の平均粒度は４５μｍであった。これら炭素原料及びシリコン原料をそれぞれ６５．９ｇ及び１５４．１ｇに秤量し、軽く混練した後に黒鉛容器に入れた。黒鉛容器は、予め０．０１３Ｐａのアルゴンガス減圧下で高周波加熱炉で約２２００℃に加熱し、１４時間保持する処理を行っておいた。シリコン原料及び炭素原料の混合体の入った黒鉛容器を電気加熱炉に入れ、一旦０．０１Ｐａまで真空引きした後、純度として９９．９９９９％以上のアルゴンガスで置換して、炉内圧力を８０ｋＰａとした。この炉内圧力を調整しながら１４２０℃に昇温した後に、その温度で２時間維持した。さらに、引き続いて１８５０℃まで加熱し、その温度で２時間維持した後、室温へ降温した。得られた原料粉の一部を粉砕し、Ｘ線回折測定を行った。ＳｉＣのメインピーク強度を１００％とした場合、炭素（Ｃ）の強度比は３．０％であり、珪素（Ｓｉ）の強度比は０．２％以下であった。
Example 1
As a carbon raw material, a high-purity carbon powder subjected to a heat treatment at 2000 ° C. or higher in a halogen gas was used, and as a silicon raw material, a silicon chip having a purity for pulling a silicon single crystal of 99.99999999999% was used. The boron concentrations of the carbon raw material and silicon raw material were 0.11 ppm and 0.001 ppm or less, respectively, as measured by GDMS (glow discharge mass spectrometry). The silicon chip was mainly several mm to several tens of mm in size, and the average particle size of the high purity carbon powder was 45 μm. These carbon raw material and silicon raw material were weighed to 65.9 g and 154.1 g, respectively, and lightly kneaded and then put into a graphite container. The graphite container was previously heated to about 2200 ° C. in a high-frequency heating furnace under reduced pressure of 0.013 Pa of argon gas and held for 14 hours. A graphite container containing a mixture of silicon raw material and carbon raw material is put into an electric heating furnace, once evacuated to 0.01 Pa, and then replaced with argon gas having a purity of 99.9999% or more, and the pressure in the furnace is 80 kPa. It was. The temperature was raised to 1420 ° C. while adjusting the pressure in the furnace, and then maintained at that temperature for 2 hours. Further, it was subsequently heated to 1850 ° C., maintained at that temperature for 2 hours, and then cooled to room temperature. A part of the obtained raw material powder was pulverized and subjected to X-ray diffraction measurement. When the main peak intensity of SiC was 100%, the intensity ratio of carbon (C) was 3.0%, and the intensity ratio of silicon (Si) was 0.2% or less.
得られた原料粉を使用し、種結晶を用いる通常の昇華再結晶法によって、直径５０ｍｍ、ポリタイプが４Ｈである単結晶を作製した。図１に、使用した成長炉及び坩堝等々の概略図を示す。黒鉛坩堝（３）中にＳｉＣ原料（２）を充填し、その上部対向面にポリタイプが４Ｈ型の単結晶種結晶基板（１）を据え付けてあり、黒鉛坩堝を高周波コイル（７）により加熱させて、原料粉末を昇華させ、種結晶基板上に結晶成長させる方法である。雰囲気ガスとして、純度として９９．９９９９％以上のアルゴンガスを、種結晶にはポリタイプが４Ｈ型を使用した。黒鉛坩堝は、予め０．０１Ｐａのアルゴンガス減圧下で、高周波加熱炉で約２２００℃に加熱し、２０時間保持する処理を行っている。この黒鉛坩堝に前述の原料粉を充填し、種結晶を所定の位置に装着して、炉内圧力を１．３×１０３Ｐａに調整し、約２０００℃以上の高温状態にして結晶成長を実施した。このときの結晶成長速度は約１ｍｍ／時である。このように得られた単結晶（結晶Ａ）を成長方向に垂直な面内に平行にスライス切断し、種結晶から５ｍｍ、１０ｍｍ、１５ｍｍの位置から、厚さ約０．６ｍｍのウェハを切り出した。さらに、各ウェハのほぼ中心位置から１２ｍｍ角の正方形試料を切り出し、二次イオン質量分析装置（ＳＩＭＳ）により、結晶中の硼素濃度を決定した。表１中の結晶Ａ欄にその分析結果を示す。また、比較例として、炭素原料としてＧＤＭＳ測定で硼素濃度２．６ｐｐｍの市販炭素粉体を用いて製造された結晶Ｂについても、炭素粉体以外はすべて同一条件で作製し、評価を実施した。 Using the obtained raw material powder, a single crystal having a diameter of 50 mm and a polytype of 4H was produced by an ordinary sublimation recrystallization method using a seed crystal. FIG. 1 shows a schematic view of the growth furnace and crucible used. A graphite crucible (3) is filled with SiC raw material (2), and a single crystal seed crystal substrate (1) with a polytype of 4H is installed on the upper facing surface, and the graphite crucible is heated by a high frequency coil (7). In this method, the raw material powder is sublimated and crystal is grown on the seed crystal substrate. An argon gas having a purity of 99.9999% or more was used as the atmosphere gas, and a 4H polytype was used as the seed crystal. The graphite crucible is preliminarily heated to about 2200 ° C. in a high-frequency heating furnace under a reduced pressure of 0.01 Pa of argon gas and held for 20 hours. This graphite crucible is filled with the above-mentioned raw material powder, the seed crystal is mounted at a predetermined position, the pressure in the furnace is adjusted to 1.3 × 10 3 Pa, and the crystal is grown at a high temperature of about 2000 ° C. or higher. Carried out. The crystal growth rate at this time is about 1 mm / hour. The single crystal (crystal A) thus obtained was sliced and cut in parallel in a plane perpendicular to the growth direction, and a wafer having a thickness of about 0.6 mm was cut from the seed crystal at positions of 5 mm, 10 mm, and 15 mm. . Further, a 12 mm square sample was cut from the approximate center position of each wafer, and the boron concentration in the crystal was determined by a secondary ion mass spectrometer (SIMS). The analysis results are shown in the crystal A column of Table 1. In addition, as a comparative example, all of the crystals B produced using a commercially available carbon powder having a boron concentration of 2.6 ppm by GDMS measurement as a carbon raw material were produced under the same conditions and evaluated.
本発明の低硼素炭素原料を用いた結晶Ａでは、結晶のほぼ全体積に亘って硼素濃度が１×１０１６ｃｍ−３を下回っているが、結晶Ｂでは、全体積に亘って１×１０１７ｃｍ−３を越えている。このように、本発明の製造方法を採用することにより、結晶のほぼ全体積に亘って１×１０１６ｃｍ−３以下である高純度なＳｉＣを得ることができる。 In the crystal A using the low boron carbon raw material of the present invention, the boron concentration is lower than 1 × 10 16 cm −3 over almost the entire volume of the crystal, but in the crystal B, 1 × 10 6 over the entire volume. It exceeds 17 cm −3 . Thus, by adopting the production method of the present invention, it is possible to obtain high-purity SiC that is 1 × 10 16 cm −3 or less over almost the entire volume of the crystal.
（実施例２）
炭素原料として、ハロゲンガス中で２０００℃以上の温度で加熱する熱処理を行った高純度炭素粉体を、シリコン原料として、シリコン単結晶引き上げ用純度９９．９９９９９９９９９％のシリコンチップを用いた。炭素原料及びシリコン原料の硼素濃度は、ＧＤＭＳ（グロー放電質量分析）測定でそれぞれ０．１３ｐｐｍ、０．００１ｐｐｍ以下であった。シリコンチップは、主に数ｍｍから十数ｍｍの大きさであり、高純度炭素は、粉体の平均粒度が異なる２種類の粉体（平均粒径６３μｍ（炭素原料Ｉ）及び５００μｍ（炭素原料ＩＩ））を用いた。これら炭素原料及びシリコン原料をそれぞれ７４．９ｇ及び１７５．１ｇに秤量し、軽く混練した後に、黒鉛容器に入れた。黒鉛容器は、予め０．０１３Ｐａのアルゴンガス減圧下で、高周波加熱炉で約２２００℃に加熱し、１４時間保持する高温熱処理を行った。シリコン原料及び炭素原料の混合体の入った黒鉛容器を電気加熱炉に入れ、０．０１Ｐａまで真空引きした後、純度として９９．９９９９％以上のアルゴンガスで置換して、炉内圧力を８０ｋＰａとした。この炉内圧力を調整しながら、１４２０℃に昇温した後に、その温度で２時間維持した。さらに、引き続いて１８５０℃まで加熱し、その温度で２時間維持した後、室温へ降温した。
(Example 2)
As a carbon raw material, a high-purity carbon powder subjected to heat treatment in a halogen gas at a temperature of 2000 ° C. or higher was used, and a silicon chip having a purity for pulling a silicon single crystal of 99.99999999999% was used as a silicon raw material. The boron concentrations of the carbon material and silicon material were 0.13 ppm and 0.001 ppm or less, respectively, as measured by GDMS (glow discharge mass spectrometry). Silicon chips mainly have a size of several mm to several tens of mm, and high-purity carbon is composed of two types of powders (average particle size 63 μm (carbon raw material I) and 500 μm (carbon raw material) II)) was used. These carbon raw material and silicon raw material were weighed to 74.9 g and 175.1 g, respectively, and lightly kneaded, and then placed in a graphite container. The graphite container was preliminarily heated to about 2200 ° C. in a high-frequency heating furnace under a reduced pressure of 0.013 Pa of argon gas and subjected to high-temperature heat treatment for 14 hours. A graphite container containing a mixture of silicon raw material and carbon raw material is put into an electric heating furnace, evacuated to 0.01 Pa, and then replaced with argon gas having a purity of 99.9999% or more, and the pressure in the furnace is set to 80 kPa. did. While adjusting the pressure in the furnace, the temperature was raised to 1420 ° C. and then maintained at that temperature for 2 hours. Further, it was subsequently heated to 1850 ° C., maintained at that temperature for 2 hours, and then cooled to room temperature.
炭素原料Ｉ又は炭素原料ＩＩから得られた原料粉体（それぞれ原料粉Ｉ及び原料粉ＩＩとする）を粉砕し、Ｘ線回折強度比により、合成されたＳｉＣのメインピーク強度を１００％としたときの残留するＳｉ、Ｃの相対強度比を比較した。表２にその結果を示す。 The raw material powder obtained from the carbon raw material I or the carbon raw material II (respectively referred to as the raw material powder I and the raw material powder II) was pulverized, and the main peak intensity of synthesized SiC was set to 100% by the X-ray diffraction intensity ratio. The relative strength ratio of the remaining Si and C was compared. Table 2 shows the results.
３００μｍ以下の炭素原料を用いた原料粉Ｉでは、ＳｉＣに対するＸ線強度比が、原料粉ＩＩと比較して大きく、本発明である３００μｍ以下の炭素原料を用いることで、ＣとＳｉとの反応が促進され、ＳｉＣが効率的に合成されていることが示されている。 In the raw material powder I using a carbon raw material of 300 μm or less, the X-ray intensity ratio to SiC is larger than that of the raw material powder II. By using the carbon raw material of 300 μm or less according to the present invention, the reaction between C and Si It is shown that SiC is synthesized efficiently.
得られた原料粉Ｉを使用し、実施例１と同様な条件で結晶成長を実施した。このようにして得られた単結晶（結晶Ｉ）と、原料粉ＩＩから同様な方法で製造した単結晶（結晶ＩＩ）とを成長方向に垂直な面内に平行にスライス切断し、種結晶から５ｍｍ、１０ｍｍ、１５ｍｍの位置から厚さ約０．６ｍｍのウェハを切り出した。さらに、各ウェハのほぼ中心位置から１２ｍｍ角の正方形試料を切り出し、二次イオン質量分析装置（ＳＩＭＳ）により結晶中の硼素濃度を決定した。表３にその分析結果を示す。このように、３００μｍ以下の炭素原料粉を採用することにより、シリコン原料との反応性を確保し、結果として高純度ＳｉＣ単結晶の効率的な製造が可能になることが確認できた。 Using the obtained raw material powder I, crystal growth was performed under the same conditions as in Example 1. The single crystal (crystal I) thus obtained and the single crystal (crystal II) produced by the same method from the raw material powder II are sliced and cut in parallel in a plane perpendicular to the growth direction. A wafer having a thickness of about 0.6 mm was cut out from positions of 5 mm, 10 mm, and 15 mm. Further, a 12 mm square sample was cut from the approximate center position of each wafer, and the boron concentration in the crystal was determined by a secondary ion mass spectrometer (SIMS). Table 3 shows the analysis results. Thus, it was confirmed that by adopting a carbon raw material powder of 300 μm or less, the reactivity with the silicon raw material was ensured, and as a result, it was possible to efficiently produce a high-purity SiC single crystal.
（実施例３）
炭素原料として、ハロゲンガス中で２０００℃以上の熱処理を行った高純度炭素粉体を、シリコン原料として、シリコン単結晶引き上げ用純度９９．９９９９９９９９９％のシリコンチップを用いた。炭素原料は、単結晶成長に用いる黒鉛坩堝と共に、予め０．０１３Ｐａのアルゴンガス減圧下、高周波加熱炉で約２２００℃に加熱し、１５時間保持する処理を行っておいた。事前処理後の炭素原料及びシリコン原料の硼素濃度は、ＧＤＭＳ（グロー放電質量分析）測定でそれぞれ０．１１ｐｐｍ、０．００１ｐｐｍ以下であった。シリコンチップは、主に数ｍｍから十数ｍｍの大きさであり、高純度炭素粉体の平均粒度は９２μｍであった。これら炭素原料及びシリコン原料をそれぞれ６５．９ｇ及び１５４．１ｇに秤量し、軽く混練した後に、混合粉を先述の黒鉛坩堝に充填した。シリコン原料及び炭素原料の混合体の入った黒鉛容器を電気加熱炉に入れ、一旦０．０１Ｐａまで真空引きした後、純度として９９．９９９９％以上のアルゴンガスで置換して炉内圧力を８０ｋＰａとした。この炉内圧力を調整しながら、１４２０℃まで加熱し、２時間維持した後に、更に１９００℃まで加熱し、３時間維持し、降温した。
(Example 3)
As a carbon raw material, a high-purity carbon powder subjected to a heat treatment at 2000 ° C. or higher in a halogen gas was used, and as a silicon raw material, a silicon chip having a purity for pulling a silicon single crystal of 99.99999999999% was used. The carbon raw material was previously heated together with a graphite crucible used for single crystal growth under a reduced pressure of 0.013 Pa of argon gas to about 2200 ° C. in a high-frequency heating furnace and held for 15 hours. The boron concentrations in the carbon raw material and silicon raw material after the pretreatment were 0.11 ppm and 0.001 ppm or less, respectively, as measured by GDMS (glow discharge mass spectrometry). The silicon chip was mainly a size of several mm to several tens of mm, and the average particle size of the high purity carbon powder was 92 μm. These carbon raw material and silicon raw material were weighed to 65.9 g and 154.1 g, respectively, and lightly kneaded, and then the mixed powder was filled in the graphite crucible described above. A graphite container containing a mixture of silicon raw material and carbon raw material is put into an electric heating furnace, and after evacuating to 0.01 Pa, the purity is replaced with argon gas of 99.9999% or more, and the pressure in the furnace is set to 80 kPa. did. While adjusting the pressure in the furnace, it was heated to 1420 ° C. and maintained for 2 hours, and further heated to 1900 ° C., maintained for 3 hours, and cooled.
得られた原料粉Ｅを使用し、実施例１と同様な条件で結晶成長を実施した。このように得られた単結晶（結晶Ｅ）を成長方向に垂直な面内に平行にスライス切断し、種結晶から５ｍｍ、１０ｍｍ、１５ｍｍの位置から厚さ約０．６ｍｍのウェハを切り出した。さらに、各ウェハのほぼ中心位置から１２ｍｍ角の正方形試料を切り出し、二次イオン質量分析装置（ＳＩＭＳ）により結晶中の窒素濃度及び硼素濃度を決定した。また、比較例として、炭素原料を予め熱処理しなかった炭素粉体を用いて製造された結晶Ｆについても、同様な評価を実施した。 Crystal growth was carried out under the same conditions as in Example 1 using the obtained raw material powder E. The single crystal (crystal E) thus obtained was sliced and cut in parallel in a plane perpendicular to the growth direction, and a wafer having a thickness of about 0.6 mm was cut from the seed crystal at positions of 5 mm, 10 mm, and 15 mm. Further, a 12 mm square sample was cut out from the approximate center position of each wafer, and the nitrogen concentration and boron concentration in the crystal were determined by a secondary ion mass spectrometer (SIMS). Moreover, the same evaluation was implemented also about the crystal F manufactured using the carbon powder which did not heat-process a carbon raw material previously as a comparative example.
表４にその分析結果を示す。結晶Ｅ及び結晶Ｆいずれの試料においても、硼素濃度は１×１０１６ｃｍ−３以下となる高純度なＳｉＣ結晶が得られたことがわかる。加えて、本発明の事前熱処理した炭素原料を用いた結晶Ｅでは、ほぼ全面に亘って窒素濃度が５×１０１６ｃｍ−３を下回っているが、結晶Ｆでは、５×１０１６ｃｍ−３を越えている。本発明の製造方法を採用することにより、窒素不純物濃度も十分に低減できることが示された。 Table 4 shows the analysis results. It can be seen that high purity SiC crystals having a boron concentration of 1 × 10 16 cm −3 or less were obtained in both the crystals E and F samples. In addition, in the crystal E using the pre-heat-treated carbon raw material of the present invention, the nitrogen concentration is almost lower than 5 × 10 16 cm −3 over the entire surface, but in the crystal F, 5 × 10 16 cm −3. Is over. It was shown that the nitrogen impurity concentration can be sufficiently reduced by employing the manufacturing method of the present invention.
１ 種結晶（ＳｉＣ単結晶）、
２ ＳｉＣ原料、
３ 黒鉛坩堝、
４ 二重石英管（水冷式）、
５ 断熱材、
６ 真空排気装置、
７ 高周波加熱コイル、
８ 高周波加熱炉。
1 seed crystal (SiC single crystal),
2 SiC raw material,
3 graphite crucible,
4 Double quartz tube (water-cooled),
5 Insulation,
6 vacuum exhaust system,
7 high frequency heating coil,
8 High-frequency heating furnace.
Claims (12)
度炭化珪素単結晶の製造方法。 The method for producing a high-purity silicon carbide single crystal according to claim 1, wherein the carbon raw material has an average particle size of 300 μm or less.
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