JP4585359B2 - Method for producing silicon carbide single crystal - Google Patents
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- 239000013078 crystal Substances 0.000 title claims description 238
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims description 78
- 229910010271 silicon carbide Inorganic materials 0.000 title claims description 77
- 238000004519 manufacturing process Methods 0.000 title claims description 17
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 46
- 238000000034 method Methods 0.000 claims description 34
- 239000007789 gas Substances 0.000 claims description 26
- 229910052757 nitrogen Inorganic materials 0.000 claims description 23
- 238000000859 sublimation Methods 0.000 claims description 12
- 230000008022 sublimation Effects 0.000 claims description 12
- 238000001953 recrystallisation Methods 0.000 claims description 11
- 239000000654 additive Substances 0.000 claims description 8
- 230000000996 additive effect Effects 0.000 claims description 8
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 4
- 229910052782 aluminium Inorganic materials 0.000 claims description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 4
- 229910052796 boron Inorganic materials 0.000 claims description 4
- 230000007423 decrease Effects 0.000 claims description 2
- 239000012535 impurity Substances 0.000 description 47
- 235000012431 wafers Nutrition 0.000 description 35
- 230000007547 defect Effects 0.000 description 28
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 23
- 229910002804 graphite Inorganic materials 0.000 description 22
- 239000010439 graphite Substances 0.000 description 22
- 239000002994 raw material Substances 0.000 description 20
- 239000000843 powder Substances 0.000 description 12
- 239000000758 substrate Substances 0.000 description 12
- 239000010453 quartz Substances 0.000 description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 10
- 238000005229 chemical vapour deposition Methods 0.000 description 9
- 239000011261 inert gas Substances 0.000 description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 6
- 239000004065 semiconductor Substances 0.000 description 6
- 239000000126 substance Substances 0.000 description 5
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 4
- 238000004854 X-ray topography Methods 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 238000005530 etching Methods 0.000 description 4
- 238000003384 imaging method Methods 0.000 description 4
- 230000003287 optical effect Effects 0.000 description 4
- 229910052710 silicon Inorganic materials 0.000 description 4
- 239000010409 thin film Substances 0.000 description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- 229910052786 argon Inorganic materials 0.000 description 3
- 238000005520 cutting process Methods 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
- 229910001873 dinitrogen Inorganic materials 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 125000004433 nitrogen atom Chemical group N* 0.000 description 3
- 239000010703 silicon Substances 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 238000001069 Raman spectroscopy Methods 0.000 description 2
- 150000001721 carbon Chemical group 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 238000012790 confirmation Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000002019 doping agent Substances 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 230000006911 nucleation Effects 0.000 description 2
- 238000010899 nucleation Methods 0.000 description 2
- 230000000149 penetrating effect Effects 0.000 description 2
- JLTRXTDYQLMHGR-UHFFFAOYSA-N trimethylaluminium Chemical compound C[Al](C)C JLTRXTDYQLMHGR-UHFFFAOYSA-N 0.000 description 2
- WXRGABKACDFXMG-UHFFFAOYSA-N trimethylborane Chemical compound CB(C)C WXRGABKACDFXMG-UHFFFAOYSA-N 0.000 description 2
- 230000000007 visual effect Effects 0.000 description 2
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- 125000004429 atom Chemical group 0.000 description 1
- 125000004432 carbon atom Chemical group C* 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
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- -1 for example Substances 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 150000002829 nitrogen Chemical class 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
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- 230000005855 radiation Effects 0.000 description 1
- 230000002040 relaxant effect Effects 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- 238000001771 vacuum deposition Methods 0.000 description 1
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Description
本発明は、半導体素子作製用基板として好適な、欠陥の少ない結晶性に優れた高品質炭化珪素単結晶の製造方法に関する。 The present invention relates to a method for producing a high-quality silicon carbide single crystal excellent in crystallinity with few defects, which is suitable as a substrate for manufacturing a semiconductor element.
炭化珪素(SiC)は、耐熱性及び機械的強度も優れ、放射線に強い等の物理的、化学的性質から、耐環境性半導体材料として注目されている。SiCは、化学組成が同じでも、多数の異なった結晶構造を取る結晶多形(ポリタイプ)構造を持つ代表的物質である。ポリタイプとは、結晶構造においてSiとCの結合した分子を一単位として考えた場合、この単位構造分子が結晶のc軸方向([0001]方向)に積層する際の周期構造が異なることにより生じる。代表的なポリタイプとしては、6H、4H、15R又は3Cがある。ここで、最初の数字は積層の繰り返し周期を示し、アルファベットは結晶系(Hは六方晶系、Rは菱面体晶系、Cは立方晶系)を表す。各ポリタイプは、それぞれ物理的、電気的特性が異なり、その違いを利用して各種用途への応用が考えられている。例えば、6Hは、近年、青色から紫外にかけての短波長光デバイス用基板として用いられ、4Hは、高周波高耐圧電子デバイス等の基板ウェハとしての応用が考えられている。 Silicon carbide (SiC) is also attracting attention as an environmentally resistant semiconductor material because of its excellent heat resistance and mechanical strength and physical and chemical properties such as resistance to radiation. SiC is a typical substance having a crystal polymorphic (polytype) structure having many different crystal structures even though the chemical composition is the same. The polytype is based on the difference in the periodic structure when this unit structure molecule is stacked in the c-axis direction ([0001] direction) of the crystal when the molecule in which the Si and C are bonded is considered as one unit Arise. Typical polytypes include 6H, 4H, 15R or 3C. Here, the first number indicates the repetition period of the lamination, and the alphabet represents a crystal system (H is a hexagonal system, R is a rhombohedral system, and C is a cubic system). Each polytype has different physical and electrical characteristics, and application to various uses is considered using the difference. For example, 6H is recently used as a substrate for short-wavelength optical devices from blue to ultraviolet, and 4H is considered to be used as a substrate wafer for high-frequency, high-voltage electronic devices.
しかしながら、大面積を有する高品質のSiC単結晶を、工業的規模で安定に供給し得る結晶成長技術は、未だ確立されていない。それゆえ、SiCは、上述のような多くの利点及び可能性を有する半導体材料にもかかわらず、その実用化が阻まれていた。 However, a crystal growth technique that can stably supply a high-quality SiC single crystal having a large area on an industrial scale has not yet been established. Therefore, practical use of SiC has been hindered despite the semiconductor material having many advantages and possibilities as described above.
従来、研究室程度の規模では、例えば、昇華再結晶法(レーリー法)でSiC単結晶を成長させ、半導体素子の作製が可能なサイズのSiC単結晶を得ていた。しかしながら、この方法では、得られた単結晶の面積が小さく、その寸法及び形状を高精度に制御することは困難である。また、SiCが有する結晶多形及び不純物キャリア濃度の制御も容易ではない。また、化学気相成長法(CVD法)を用いて、珪素(Si)等の異種基板上にヘテロエピタキシャル成長させることにより、立方晶の炭化珪素単結晶を成長させることも行われている。この方法では、大面積の単結晶は得られるが、基板との格子不整合が約20%もあること等により、多くの欠陥(〜107cm−2)を含むSiC単結晶しか成長させることができず、高品質のSiC単結晶を得ることは容易でない。 Conventionally, on a laboratory scale scale, for example, a SiC single crystal was grown by a sublimation recrystallization method (Rayleigh method) to obtain a SiC single crystal of a size capable of producing a semiconductor element. However, with this method, the area of the obtained single crystal is small, and it is difficult to control its size and shape with high accuracy. Moreover, it is not easy to control the crystal polymorphism and impurity carrier concentration of SiC. In addition, a cubic silicon carbide single crystal is grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using a chemical vapor deposition method (CVD method). In this method, a single crystal having a large area can be obtained, but only a SiC single crystal including many defects (−10 7 cm −2 ) is grown due to a lattice mismatch with the substrate of about 20%. It is not easy to obtain a high-quality SiC single crystal.
これらの問題点を解決するために、SiC単結晶{0001}ウェハを種結晶として用いて昇華再結晶を行う、改良型のレーリー法が提案されている(非特許文献1)。この方法では、種結晶を用いているため結晶の核形成過程が制御でき、また、不活性ガスにより雰囲気圧力を100Pa〜15kPa程度に制御することにより、結晶の成長速度等を再現性良くコントロールできる。図1を用いて、改良レーリー法の原理を説明する。種結晶となるSiC単結晶と原料となるSiC結晶粉末は、坩堝(通常黒鉛)の中に収納され、アルゴン等の不活性ガス雰囲気中(133〜13.3kPa)、2000〜2400℃に加熱される。この際、原料粉末に比べ種結晶がやや低温になるように、温度勾配が設定される。原料は、昇華後、濃度勾配(温度勾配により形成される)により、種結晶方向へ拡散、輸送される。単結晶成長は、種結晶に到着した原料ガスが種結晶上で再結晶化することにより実現される。この際、結晶の抵抗率は、不活性ガスからなる雰囲気中に不純物ガスを添加する、あるいは、SiC原料粉末中に不純物元素あるいはその化合物を混合することにより、SiC単結晶構造中のシリコン又は炭素原子の位置を不純物元素にて置換させる(ドーピング)ことで、制御可能である。SiC単結晶中の置換型不純物として代表的なものに、窒素(n型)、ホウ素、アルミニウム(p型)がある。キャリア型及び濃度を制御しながら、SiC単結晶を成長させることができる。 In order to solve these problems, an improved Rayleigh method has been proposed in which sublimation recrystallization is performed using a SiC single crystal {0001} wafer as a seed crystal (Non-patent Document 1). In this method, since the seed crystal is used, the nucleation process of the crystal can be controlled, and by controlling the atmospheric pressure to about 100 Pa to 15 kPa with an inert gas, the growth rate of the crystal can be controlled with good reproducibility. . The principle of the improved Rayleigh method will be described with reference to FIG. The SiC single crystal as a seed crystal and the SiC crystal powder as a raw material are stored in a crucible (usually graphite) and heated to 2000 to 2400 ° C. in an inert gas atmosphere such as argon (133 to 13.3 kPa). The At this time, the temperature gradient is set so that the seed crystal has a slightly lower temperature than the raw material powder. After sublimation, the raw material is diffused and transported in the direction of the seed crystal by a concentration gradient (formed by a temperature gradient). Single crystal growth is realized by recrystallization of the source gas that has arrived at the seed crystal on the seed crystal. At this time, the resistivity of the crystal is determined by adding an impurity gas in an atmosphere composed of an inert gas, or by mixing an impurity element or a compound thereof in the SiC raw material powder, thereby adding silicon or carbon in the SiC single crystal structure. It can be controlled by substituting the impurity position with an impurity element (doping). Typical substitutional impurities in the SiC single crystal include nitrogen (n-type), boron, and aluminum (p-type). A SiC single crystal can be grown while controlling the carrier type and concentration.
現在、上記の改良レーリー法で作製したSiC単結晶から口径2インチ(50mm)から3インチ(75mm)のSiC単結晶ウェハが切り出され、エピタキシャル薄膜成長、デバイス作製に供されている。 Currently, SiC single crystal wafers having a diameter of 2 inches (50 mm) to 3 inches (75 mm) are cut out from the SiC single crystal produced by the above-described improved Rayleigh method, and are used for epitaxial thin film growth and device production.
上記したように、成長結晶の抵抗率の制御は、成長時の不活性ガスからなる雰囲気中に不純物ガスを添加するか、あるいは、SiC原料粉末中に不純物元素あるいはその化合物を混合することにより、SiC単結晶構造中のシリコン又は炭素原子の位置を不純物元素にて置換させる(ドーピング)ことで行われる。特に、不純物ガスを添加する場合、通常は、成長開始時より、目的とする不純物元素濃度が得られるように不純物ガスを導入し、成長中は一定の導入量を保ちながら結晶成長を行う。 As described above, the resistivity of the grown crystal is controlled by adding an impurity gas in an atmosphere of an inert gas during growth, or by mixing an impurity element or a compound thereof in the SiC raw material powder. This is performed by replacing the position of silicon or carbon atoms in the SiC single crystal structure with an impurity element (doping). In particular, when an impurity gas is added, the impurity gas is usually introduced from the start of growth so as to obtain a target impurity element concentration, and crystal growth is performed while maintaining a constant introduction amount during the growth.
ここで、発明者は、以下の知見を得た。即ち、目的とする不純物元素濃度が得られるように不純物ガスを導入した際、種結晶として用いるSiC単結晶基板の不純物濃度と成長させる単結晶の不純物濃度が著しく異なる場合に、成長結晶中に各種転位欠陥あるいは種結晶と異なるポリタイプの発生に伴うマイクロパイプ欠陥(大型の螺旋転位の一種であり、転位により生じる大きい歪みを緩和するために、転位の芯が空洞化して発生するものと考えられている)の発生により、結晶性が劣化する。 Here, the inventor obtained the following knowledge. That is, when an impurity gas is introduced so as to obtain a target impurity element concentration, when the impurity concentration of the SiC single crystal substrate used as a seed crystal and the impurity concentration of the single crystal to be grown are significantly different, Micropipe defects associated with the generation of dislocation defects or polytypes different from seed crystals (a type of large-scale screw dislocations, which are thought to occur due to the dislocation cores becoming hollow in order to relieve large strain caused by dislocations. The crystallinity is degraded.
この転位欠陥発生の原因としては、種結晶と成長結晶とで、結晶中の不純物濃度の著しい差により、両者の格子定数が異なることにより発生する歪が原因と考えられる。一般的に、結晶成長の基板と成長させる結晶との格子定数が異なる場合、両者の格子定数差により生じる歪エネルギ−を緩和させる目的で、両者間に両者の格子定数の中間の格子定数を持つ結晶(通称バッファ層と呼ばれる)を挿入することで、歪エネルギ−を低減させて、成長結晶における転位発生等の結晶性劣化を抑制させることが行われている。 The cause of the occurrence of this dislocation defect is considered to be the strain generated by the difference in lattice constant between the seed crystal and the grown crystal due to a significant difference in impurity concentration in the crystal. In general, when the crystal growth substrate and the crystal to be grown have different lattice constants, they have a lattice constant intermediate between both of them for the purpose of relaxing the strain energy caused by the difference between the two. By inserting a crystal (commonly referred to as a buffer layer), strain energy is reduced, and crystallinity deterioration such as dislocation generation in a grown crystal is suppressed.
通常、バッファ層を用いる場合、例えば、種結晶あるいは結晶成長用基板としての種結晶と成長結晶との格子定数差は、数%以上である。 Usually, when a buffer layer is used, for example, the difference in lattice constant between a seed crystal or a seed crystal as a crystal growth substrate and the grown crystal is several percent or more.
これに対して、炭化ケイ素単結晶中で、不純物、例えば、窒素がド−プされる場合、窒素原子は、結晶中にて炭素原子の位置を置換して、結晶内に組み込まれる。このとき、単結晶における原子同士の結合は、正四面体配置となっており、例えば、Paulingの「化学結合論」(非特許文献2)によれば、炭素原子の半径が0.077nmであるのに対して、窒素は0.070nmであり、この差は0.007nmと小さい。さらに、実際に結晶内にド−プされる原子密度は、多い場合でも1020cm−3と、全体に対して凡そ0.1%に留まる。このことから概算すると、窒素原子を不純物としてド−プした場合の格子定数差(例えば、4Hポリタイプの格子定数は、a軸方向にて0.3076nm)は、0.000025%となる。この値は非常に小さく、格子定数差による歪エネルギ−も同様に小さいと予想した場合、成長結晶における転位発生等は発生し難いと予想される。 On the other hand, when an impurity, for example, nitrogen is doped in a silicon carbide single crystal, the nitrogen atom is incorporated into the crystal by replacing the position of the carbon atom in the crystal. At this time, the bonds between atoms in the single crystal are in a tetrahedral arrangement. For example, according to Pauling's “chemical bond theory” (Non-patent Document 2), the radius of the carbon atom is 0.077 nm. On the other hand, nitrogen is 0.070 nm, and this difference is as small as 0.007 nm. Furthermore, even if the atomic density actually doped in the crystal is large, it is 10 20 cm −3 , which is about 0.1% of the whole. Approximate from this, the difference in lattice constant when nitrogen atoms are doped as impurities (for example, the lattice constant of 4H polytype is 0.3076 nm in the a-axis direction) is 0.000025%. When this value is very small and the strain energy due to the difference in lattice constant is also expected to be small, it is expected that the occurrence of dislocations in the grown crystal is unlikely to occur.
しかしながら、上記したように、発明者が得た知見として、実際に昇華再結晶法による2000℃以上の高温下におけるSiC単結晶成長においては、前述したような不純物濃度の違いによっても、成長結晶における転位発生等、成長結晶の結晶性が劣化することが確認された。
このため、昇華再結晶法によるSiC単結晶成長では、窒素を初めとする不純物元素の成長結晶における濃度変化について、種結晶における同濃度からの変化率をより細かく制御することが、種結晶と異なる所望の不純物濃度を持つ高品質炭化珪素を得る上で非常に重要となることが明らかになった。 For this reason, in SiC single crystal growth by the sublimation recrystallization method, the concentration change in the growth crystal of impurity elements such as nitrogen differs from the seed crystal in that the change rate from the same concentration in the seed crystal is more finely controlled. It has become clear that it is very important in obtaining high-quality silicon carbide having a desired impurity concentration.
この知見より、従来と同様に成長開始時より所望の不純物濃度を持つ成長結晶を得る不純物ガス流量を設定して成長させる場合、結晶欠陥を発生させないためには、常に目的とする不純物濃度と同じ不純物濃度を持つ種結晶基板を使用する必要があることとなる。しかしながら、この場合、毎回目的とする不純物濃度に合わせた種結晶を準備することは大変面倒であり、工業的な見地からも生産性の点で問題がある。また、厳密な意味では、不純物の違いによって結晶成長の安定性が異なることもあり、例えば、窒素をある範囲の濃度で添加した成長において、常に最高品質の結晶成長が再現性良く得られる場合、種結晶には、常にこの窒素濃度を有する最高品質の種結晶を利用できることが望ましい。このような理由から、どのような不純物濃度を有する種結晶でも常に使用できるようになることが望ましく、同時に成長中に目的とする不純物濃度まで濃度を変化させ、かつ濃度変化による結晶欠陥発生を抑制できる技術が必要となった。 From this finding, when the growth is performed with the impurity gas flow rate to obtain a growth crystal having a desired impurity concentration from the start of growth as in the conventional case, the same impurity concentration as the target is always used in order not to generate crystal defects. It is necessary to use a seed crystal substrate having an impurity concentration. However, in this case, it is very troublesome to prepare a seed crystal according to the target impurity concentration every time, and there is a problem in terms of productivity from an industrial point of view. In a strict sense, the stability of crystal growth may differ depending on the difference in impurities.For example, in the case of growth in which nitrogen is added in a certain concentration range, the highest quality crystal growth is always obtained with good reproducibility. It is desirable that the highest quality seed crystal having this nitrogen concentration can always be used for the seed crystal. For these reasons, it is desirable to be able to use a seed crystal having any impurity concentration at all times. At the same time, the concentration is changed to the target impurity concentration during growth, and the generation of crystal defects due to the concentration change is suppressed. A technology that can be used is necessary.
そこで、本発明は、上記の従来技術での問題を解決し、欠陥の少ない結晶性に優れた炭化珪素単結晶ウェハを取り出せる炭化珪素単結晶の製造方法を提供することを目的とする。 Accordingly, the present invention is to solve the problems of the above prior art, and an object thereof is to provide a manufacturing how silicon carbide single crystal can be extracted the silicon carbide single crystal wafer having excellent low crystallinity defect.
本発明は、
(1) 結晶上に炭化珪素単結晶インゴットを成長させる工程を包含する、昇華再結晶法による炭化珪素単結晶の製造方法であって、結晶成長中の不活性雰囲気中の添加ガス流量を変化させて、成長結晶中の添加元素濃度が種結晶から成長結晶中で種結晶中と同じ濃度から、結晶成長方向に対し、1%/100μm以上200%/100μm以下の濃度変化率の範囲内にて漸増あるいは漸減して所望の濃度まで変化させることを特徴とする炭化珪素単結晶の製造方法、
(2) 前記濃度変化率が、結晶成長方向に対し5%/100μm以上、100%/100μm以下の範囲内である(1)記載の炭化珪素単結晶の製造方法、
(3) 前記添加元素が、窒素、ホウ素、アルミニウムのいずれか1種である(1)記載の炭化珪素単結晶の製造方法、
である。
The present invention
(1) A method for producing a silicon carbide single crystal by a sublimation recrystallization method, comprising a step of growing a silicon carbide single crystal ingot on a crystal, wherein an additive gas flow rate in an inert atmosphere during crystal growth is changed. The concentration of the additive element in the growth crystal is within the range of the concentration change rate from 1% / 100 μm to 200% / 100 μm with respect to the crystal growth direction from the same concentration as in the seed crystal from the seed crystal. A method of producing a silicon carbide single crystal, characterized by gradually increasing or decreasing the concentration to a desired concentration;
(2) The method for producing a silicon carbide single crystal according to (1), wherein the concentration change rate is in the range of 5% / 100 μm or more and 100% / 100 μm or less with respect to the crystal growth direction,
(3) The method for producing a silicon carbide single crystal according to (1), wherein the additive element is any one of nitrogen, boron, and aluminum ,
It is.
本発明によれば、種結晶を用いた改良型レーリー法により、所望の不純物濃度を有し且つ良質のSiC単結晶を、再現性良く成長させることができる。このような結晶から切り出したSiC単結晶ウェハを用いれば、高周波動作特性に優れた半導体素子や、電力損失の極めて小さい高性能の電力制御用半導体素子を作製することができる。 According to the present invention, a high-quality SiC single crystal having a desired impurity concentration can be grown with good reproducibility by an improved Rayleigh method using a seed crystal. By using a SiC single crystal wafer cut out from such a crystal, it is possible to manufacture a semiconductor element having excellent high-frequency operating characteristics and a high-performance power control semiconductor element with extremely low power loss.
本発明の製造方法では、結晶成長時の不純物添加用ガス流量を所定時間にわたり漸増又は漸減させて、所望の不純物濃度が得られるまで制御することにより、結晶中に結晶性の劣化した領域(各種転位、結晶粒界、マイクロパイプ欠陥等の存在する領域)が極めて少なく、所望の不純物濃度を有した高品質単結晶SiCインゴットを製造することができる。 In the manufacturing method of the present invention, the gas flow rate for impurity addition during crystal growth is gradually increased or decreased over a predetermined time and controlled until a desired impurity concentration is obtained, so that a region where crystallinity has deteriorated in the crystal (various types) A region in which dislocations, crystal grain boundaries, micropipe defects and the like are present) is extremely small, and a high-quality single crystal SiC ingot having a desired impurity concentration can be manufactured.
初めに、昇華再結晶法について説明する。昇華再結晶法は、2000℃を超える高温においてSiC粉末を昇華させ、その昇華ガスを低温部に再結晶化させることにより、SiC結晶を製造する方法である。この方法で、SiC単結晶からなる種結晶を用いて、SiC単結晶を製造する方法は、特に改良レーリー法と呼ばれ、バルク状のSiC単結晶の製造に利用されている。改良レーリー法では、種結晶を用いているため結晶の核形成過程が制御でき、また、不活性ガスにより雰囲気圧力を100Pa〜15kPa程度に制御することにより、結晶の成長速度等を再現性良くコントロールできる。図1を用いて、改良レーリー法の原理を説明する。種結晶となるSiC単結晶と原料となるSiC結晶粉末(通常、Acheson法で作製された研磨材を洗浄・前処理したものが使用される)は、坩堝(通常黒鉛製)の中に収納され、アルゴン等の不活性ガス雰囲気中(133Pa〜13.3kPa)、2000〜2400℃に加熱される。この際、原料粉末に比べ種結晶がやや低温になるように、温度勾配が設定される。原料は、昇華後、濃度勾配(温度勾配により形成される)により、種結晶方向へ拡散、輸送される。単結晶成長は、種結晶に到着した原料ガスが種結晶上で再結晶化することにより実現される。 First, the sublimation recrystallization method will be described. The sublimation recrystallization method is a method for producing SiC crystals by sublimating SiC powder at a high temperature exceeding 2000 ° C. and recrystallizing the sublimation gas into a low temperature part. In this method, a method for producing an SiC single crystal using a seed crystal composed of an SiC single crystal is called an improved Rayleigh method, and is used for producing a bulk SiC single crystal. The modified Rayleigh method uses a seed crystal to control the nucleation process of the crystal, and the atmosphere pressure is controlled to about 100 Pa to 15 kPa with an inert gas to control the crystal growth rate with good reproducibility. it can. The principle of the improved Rayleigh method will be described with reference to FIG. The SiC single crystal used as a seed crystal and the SiC crystal powder used as a raw material (usually used after cleaning and pretreatment of an abrasive prepared by the Acheson method) are stored in a crucible (usually made of graphite). In an inert gas atmosphere such as argon (133 Pa to 13.3 kPa), it is heated to 2000 to 2400 ° C. At this time, the temperature gradient is set so that the seed crystal has a slightly lower temperature than the raw material powder. After sublimation, the raw material is diffused and transported in the direction of the seed crystal by a concentration gradient (formed by a temperature gradient). Single crystal growth is realized by recrystallization of the source gas that has arrived at the seed crystal on the seed crystal.
上記した昇華再結晶法において、作製する単結晶への不純物ド−ピングは、結晶成長中にアルゴン等の不活性ガス雰囲気中に添加ガスの形(窒素原子なら窒素ガス、アルミニウムならトリメチルアルミニウム(Al(CH3)3)、ボロンならトリメチルボロン(B(CH3)3)で、所定量導入することで実施される。しかしながら、いずれの元素についても、成長に使用する種結晶における添加密度に対して、より高密度、あるいは低密度を有する成長結晶を実現するためには、添加ガス流量を増減させる必要がある。 In the above-described sublimation recrystallization method, impurity doping into a single crystal to be produced is performed in the form of an additive gas in an inert gas atmosphere such as argon during crystal growth (nitrogen gas for nitrogen atoms, trimethylaluminum for aluminum (Al (CH 3 ) 3 ), trimethylboron (B (CH 3 ) 3 ) in the case of boron is introduced by introducing a predetermined amount, however, for any element, the addition density in the seed crystal used for growth Thus, in order to realize a growth crystal having a higher density or a lower density, it is necessary to increase or decrease the additive gas flow rate.
結晶品質に最も影響を及ぼすものは、最高濃度を示すドーパントであるので、複数元素が含まれる場合では、最高濃度を示す元素を含有するガスで制御すればよい。 What has the greatest influence on the crystal quality is the dopant that exhibits the highest concentration. Therefore, when a plurality of elements are included, the dopant may be controlled with a gas containing the element that exhibits the highest concentration.
成長方向において不純物濃度を変化させる場合、それまで成長した結晶と新たに成長する結晶との間で、不純物濃度差による結晶格子間隔の差に起因した歪が発生する。この歪のエネルギ−は、不純物濃度差が大きいほど増加する。このため、不純物濃度変化率(不純物濃度勾配)が急峻な場合、結晶成長が進行して結晶厚さが増加し(歪のエネルギ−は厚さに比例する) 、歪のエネルギ−が臨界値を越えた時点で、成長結晶中に転位等の各種欠陥が発生し、結晶性が劣化してしまう。これを防ぐためには、歪のエネルギ−が上記した欠陥発生を誘発する臨界値以下に保たれるように、成長方向における不純物濃度変化率を所定の値以下に保つ必要がある。 When the impurity concentration is changed in the growth direction, distortion due to the difference in crystal lattice spacing due to the impurity concentration difference occurs between the crystal grown so far and the newly grown crystal. The strain energy increases as the impurity concentration difference increases. For this reason, when the impurity concentration change rate (impurity concentration gradient) is steep, crystal growth proceeds and the crystal thickness increases (the strain energy is proportional to the thickness), and the strain energy reaches a critical value. When it exceeds, various defects such as dislocations occur in the grown crystal and the crystallinity deteriorates. In order to prevent this, it is necessary to keep the impurity concentration change rate in the growth direction below a predetermined value so that the strain energy is kept below the critical value that induces the above-described defect generation.
本発明では、結晶成長中の不純物濃度の成長方向における変化率を制御することにより、成長結晶表面における歪エネルギ−を欠陥発生につながる臨界値以下に抑えることで、結晶成長時における結晶欠陥発生を抑制する。この場合、実際に結晶成長を実施して確認したところでは、欠陥を発生させずに結晶成長が実施できる濃度変化率の上限値としては、結晶成長方向に対する一定距離における平均として200%/100μmである。一方、下限値としては、工業的見地より、極端に成長速度を低下させることは欠陥発生抑制には有効であっても、極めて生産性が悪化するために、実際には適用できないため、結晶成長方向に対し少なくとも1%/100μm以上の変化率が必要である。上限値及び下限値としては前記したとおりであるが、実際に適用するに当って、より望ましい範囲としては、5〜100%/100μmの範囲である。この濃度勾配条件を維持しながら、所望の濃度まで不純物濃度を変化させることにより、成長中に新たな結晶欠陥を発生させずに、種結晶と同様の良好な結晶性を有した成長結晶を得ることができる。 In the present invention, by controlling the rate of change in the growth direction of the impurity concentration during crystal growth, the strain energy on the surface of the grown crystal is suppressed to a critical value or less that leads to the occurrence of defects, thereby preventing the occurrence of crystal defects during crystal growth. Suppress. In this case, when the crystal growth is actually confirmed, the upper limit value of the concentration change rate at which the crystal growth can be performed without generating defects is 200% / 100 μm as an average at a fixed distance with respect to the crystal growth direction. is there. On the other hand, as the lower limit, from an industrial point of view, even though it is effective to suppress the occurrence of defects, extremely reducing the growth rate is extremely difficult to apply, so it cannot be actually applied. A change rate of at least 1% / 100 μm or more with respect to the direction is required. The upper limit value and the lower limit value are as described above, but in actual application, a more desirable range is a range of 5 to 100% / 100 μm. While maintaining this concentration gradient condition, by changing the impurity concentration to a desired concentration, a grown crystal having good crystallinity similar to the seed crystal is obtained without generating new crystal defects during the growth. be able to.
また、このようにして得られた結晶性良好な成長結晶から取り出した種結晶を使用して、成長時に結晶の口径が拡大するような構造を有する坩堝を用いることにより、種結晶口径より大口径の成長結晶を得ることができる。この手法を繰り返すことにより、口径として50mm〜300mmまでの口径を有する炭化珪素単結晶を得ることができる。
さらにこれらの単結晶を切断、研磨加工を施すことにより、50mm以上300mm以下の口径を有する炭化珪素単結晶ウェハを取り出せる。
In addition, by using a seed crystal taken out from a crystal having good crystallinity obtained in this way, and using a crucible having a structure in which the diameter of the crystal expands during growth, the diameter is larger than the seed crystal diameter. Can be obtained. By repeating this method, a silicon carbide single crystal having a diameter of 50 mm to 300 mm can be obtained.
Further, by cutting and polishing these single crystals, a silicon carbide single crystal wafer having a diameter of 50 mm or more and 300 mm or less can be taken out.
また、これらの単結晶ウェハ上に化学気相蒸着法(CVD法)を用いることでSiC単結晶薄膜をエピタキシャル成長させることにより、炭化珪素単結晶エピタキシャルウェハを作製することができる。このエピタキシャルウェハは、基板として用いた炭化珪素単結晶ウェハの良好な結晶性を継承しており、電子デバイスを作製した際に優れた特性を発揮するデバイスを得ることができる。 Moreover, a silicon carbide single crystal epitaxial wafer can be produced by epitaxially growing a SiC single crystal thin film on these single crystal wafers by using a chemical vapor deposition method (CVD method). This epitaxial wafer inherits the good crystallinity of the silicon carbide single crystal wafer used as the substrate, and a device that exhibits excellent characteristics when an electronic device is produced can be obtained.
以下に、本発明の実施例について述べる。 Examples of the present invention will be described below.
(実施例1)
先ず、図2に示す単結晶成長装置について、簡単に説明する。結晶成長は、SiC結晶粉末2を昇華させ、種結晶として用いたSiC単結晶1上で再結晶化させることにより行われる。種結晶のSiC単結晶1は、高純度黒鉛製坩堝3の蓋4の内面に取り付けられる。原料のSiC結晶粉末2は、高純度黒鉛製坩堝3の内部に充填されている。このような黒鉛製坩堝3は、二重石英管5の内部に、黒鉛の支持棒6により設置される。黒鉛製坩堝3の周囲には、熱シールドのための黒鉛製フェルト7が設置されている。二重石英管5は、真空排気装置により高真空排気(10−3Pa以下)することができ、かつ、内部雰囲気をガス流量調節計10を通って導入されるArガスにより圧力制御することができる。各種ド−ピングガス(窒素、トリメチルアルミニウム、トリメチルボロン)も、ガス流量調節計10を通して導入することができる。また、二重石英管5の外周には、ワークコイル8が設置されており、高周波電流を流すことにより黒鉛製坩堝3を加熱し、原料及び種結晶を所望の温度に加熱することができる。坩堝温度の計測は、坩堝上部及び下部を覆うフェルトの中央部に直径2〜4mmの光路を設け坩堝上部及び下部からの光を取り出し、二色温度計を用いて行う。坩堝下部の温度を原料温度、坩堝上部の温度を種温度とする。
Example 1
First, the single crystal growth apparatus shown in FIG. 2 will be briefly described. Crystal growth is performed by sublimating SiC crystal powder 2 and recrystallizing on SiC single crystal 1 used as a seed crystal. The seed crystal SiC single crystal 1 is attached to the inner surface of the lid 4 of the high-purity graphite crucible 3. The raw material SiC crystal powder 2 is filled in a high-purity graphite crucible 3. Such a graphite crucible 3 is installed inside a double quartz tube 5 by a support rod 6 made of graphite. Around the graphite crucible 3, a graphite felt 7 for heat shielding is installed. The double quartz tube 5 can be highly evacuated (10 −3 Pa or less) by an evacuation apparatus, and the internal atmosphere can be pressure controlled by Ar gas introduced through the gas flow rate controller 10. it can. Various doping gases (nitrogen, trimethylaluminum, trimethylboron) can also be introduced through the gas flow controller 10. In addition, a work coil 8 is provided on the outer periphery of the double quartz tube 5, and the graphite crucible 3 can be heated by flowing a high-frequency current to heat the raw material and the seed crystal to a desired temperature. The temperature of the crucible is measured using a two-color thermometer by providing an optical path having a diameter of 2 to 4 mm at the center of the felt covering the upper and lower parts of the crucible, and extracting light from the upper and lower parts of the crucible. The temperature at the bottom of the crucible is the raw material temperature, and the temperature at the top of the crucible is the seed temperature.
次に、この結晶成長装置を用いたSiC単結晶の製造について実施例を説明する。先ず、種結晶として、口径50mmの(0001)面を有した六方晶系のSiC単結晶ウェハを用意した。同種結晶のマイクロパイプ欠陥密度は5個/cm2以下と非常に小さく結晶性良好であり、ド−ピング元素としての窒素の濃度は1×1019cm−3であった。次に、種結晶1を黒鉛製坩堝3の蓋4の内面に取り付けた。黒鉛製坩堝3の内部には、アチソン法により作製したSiC結晶原料粉末を充填した。次いで、SiC原料を充填した黒鉛製坩堝3を、蓋4で閉じ、黒鉛製フェルト7で被覆した後、黒鉛製支持棒6の上に乗せ、二重石英管5の内部に設置した。そして、石英管の内部を真空排気した後、ワークコイルに電流を流し、原料温度を2000℃まで上げた。その後、雰囲気ガスとして高純度Arガス(純度99.9995%)を流入させ、石英管内圧力を約80kPaに保ちながら、原料温度を目標温度である2400℃まで上昇させた。成長圧力である1.3kPaには約30分かけて減圧し、その後、約20時間成長を続けた。この成長時間中、成長開始時には窒素流量を0.5×10−6m3/sec(同流量にて、成長結晶中の窒素濃度が種結晶中濃度と同等の1×1019cm−3となることから、この流量を用いた)とし、成長開始後窒素流量を一定速度で増加させ、5時間で5.0×10−6m3/sec (同流量にて、成長結晶中の窒素濃度は2×1020cm−3となる)まで増加させた。その後は、5.0×10−6m3/sec一定とし、成長終了時まで保った。この際の坩堝内の温度勾配は15℃/cmであった。成長速度は約0.8mm/時であり、種結晶中の窒素濃度に対する成長結晶中での濃度変化率としては、50%/100μm(=2000%/(0.8mm/時×5時間))であった。得られた結晶の口径は51mmで、高さは16mm程度であった。 Next, an example of manufacturing a SiC single crystal using this crystal growth apparatus will be described. First, a hexagonal SiC single crystal wafer having a (0001) plane with a diameter of 50 mm was prepared as a seed crystal. The micropipe defect density of the same type crystal was as small as 5 pieces / cm 2 or less and good crystallinity, and the concentration of nitrogen as a doping element was 1 × 10 19 cm −3 . Next, the seed crystal 1 was attached to the inner surface of the lid 4 of the graphite crucible 3. The inside of the graphite crucible 3 was filled with SiC crystal raw material powder produced by the Atchison method. Next, the graphite crucible 3 filled with the SiC raw material was closed with the lid 4 and covered with the graphite felt 7, and then placed on the graphite support rod 6 and installed inside the double quartz tube 5. And after evacuating the inside of a quartz tube, the electric current was sent through the work coil and the raw material temperature was raised to 2000 degreeC. Thereafter, high-purity Ar gas (purity 99.9995%) was introduced as the atmospheric gas, and the raw material temperature was raised to the target temperature of 2400 ° C. while maintaining the pressure in the quartz tube at about 80 kPa. The growth pressure was reduced to 1.3 kPa over about 30 minutes, and then the growth was continued for about 20 hours. During this growth time, the nitrogen flow rate is 0.5 × 10 −6 m 3 / sec at the start of growth (at the same flow rate, the nitrogen concentration in the growth crystal is 1 × 10 19 cm −3, which is equivalent to the concentration in the seed crystal). Therefore, after the start of growth, the nitrogen flow rate was increased at a constant rate, and 5.0 × 10 −6 m 3 / sec over 5 hours (at the same flow rate, the nitrogen concentration in the grown crystal) Is increased to 2 × 10 20 cm −3 ). Thereafter, the pressure was kept constant at 5.0 × 10 −6 m 3 / sec and kept until the end of growth. The temperature gradient in the crucible at this time was 15 ° C./cm. The growth rate is about 0.8 mm / hour, and the concentration change rate in the growth crystal with respect to the nitrogen concentration in the seed crystal is 50% / 100 μm (= 2000% / (0.8 mm / hour × 5 hours)). Met. The diameter of the obtained crystal was 51 mm, and the height was about 16 mm.
こうして得られた炭化珪素単結晶をラマン散乱により分析したところ、種結晶と同一ポリタイプを有する六方晶系のSiC単結晶が、全面に渡り成長したことを確認できた。結晶性を測定する目的で、成長した単結晶インゴットの最上部(成長終了近傍に成長した部分)から厚さ1.0mmのウェハを切り出した。ウェハを直接光学顕微鏡にて観察したところ、貫通中空欠陥密度が10/cm2以下と、種結晶と同等の低密度を有していることが確認できた。さらに確認するために、520℃に溶融した水酸化カリウム溶液中で5分間エッチングを施した。このエッチング処理を行うと、貫通中空欠陥は六角状エッチピットとして観察できる。ウェハついて、エッチピット数密度を調べたところ、目視観察と同様の数密度の貫通中空欠陥が検出された。また、種結晶と同等の高品質結晶が得られているかを確認するため、予め測定していた種結晶のX線トポグラフ撮影デ−タと、成長した結晶から切り出したウェハのX線トポグラフ撮影デ−タを比較したところ、種結晶と同等の高品質を有し、成長に起因して新たに欠陥が発生していないことが確認できた。 When the silicon carbide single crystal thus obtained was analyzed by Raman scattering, it was confirmed that a hexagonal SiC single crystal having the same polytype as the seed crystal was grown over the entire surface. For the purpose of measuring the crystallinity, a wafer having a thickness of 1.0 mm was cut out from the uppermost portion of the grown single crystal ingot (the portion grown near the end of growth). When the wafer was directly observed with an optical microscope, it was confirmed that the through-hole defect density was 10 / cm 2 or less, which was as low as the seed crystal. For further confirmation, etching was performed in a potassium hydroxide solution melted at 520 ° C. for 5 minutes. When this etching process is performed, the penetrating hollow defects can be observed as hexagonal etch pits. When the number density of etch pits on the wafer was examined, through-hole defects having the same number density as in the visual observation were detected. In addition, in order to confirm whether a high-quality crystal equivalent to the seed crystal is obtained, the X-ray topography imaging data of the seed crystal measured in advance and the X-ray topography imaging data of the wafer cut out from the grown crystal are obtained. As a result of comparison, it was confirmed that the product had the same high quality as the seed crystal and no new defects were generated due to the growth.
このウェハの抵抗率を測定するため、ウェハを12mm角に切り出し、洗浄した後、真空蒸着によりニッケル電極(直径1mmの円形)を四隅に形成した。この電極を付けたウェハ片を用いて、ホ−ル測定を実施し、ウェハの抵抗率を求めたところ、0.009Ωcmと言う低抵抗率を有することを確認した。 In order to measure the resistivity of the wafer, the wafer was cut into 12 mm squares, washed, and then nickel electrodes (circular with a diameter of 1 mm) were formed at the four corners by vacuum deposition. Hole measurement was performed using the wafer piece to which this electrode was attached, and when the resistivity of the wafer was determined, it was confirmed that it had a low resistivity of 0.009 Ωcm.
こうして得られた結晶性良好な結晶を切断、加工して作製したウェハに化学気相蒸着法(CVD法)を用いることでSiC単結晶薄膜をエピタキシャル成長させることにより、炭化珪素単結晶エピタキシャルウェハを作製した。同エピタキシャルウェハの結晶性について調べるために、前記した溶融水酸化カリウム溶液中にてエピタキシャルウェハ表面のエッチングを実施した。その結果、基板である炭化珪素単結晶ウェハが有していた良好な結晶品質を継承していることが確認された。 A silicon carbide single crystal epitaxial wafer is produced by epitaxially growing a SiC single crystal thin film by using a chemical vapor deposition method (CVD method) on a wafer produced by cutting and processing the crystal having good crystallinity thus obtained. did. In order to investigate the crystallinity of the epitaxial wafer, the surface of the epitaxial wafer was etched in the molten potassium hydroxide solution described above. As a result, it was confirmed that the good crystal quality of the silicon carbide single crystal wafer as the substrate was inherited.
これに対して、成長開始時より最終的に必要な流量となる5.0×10−6m3/secを流して結晶成長を行った場合、結晶の厚さが1mm程度に達したところで種結晶(六方晶形)と異なる原子配置(三方晶形)を有する3Cポリタイプが発生し、そこから多結晶又は異種ポリタイプが発生した結果により結晶粒界、マイクロパイプ欠陥等が発生して結晶性が劣化した。種結晶と成長結晶との不純物濃度が著しく異なることによる歪が、結晶が成長し厚さが増加するにつれて大きくなり、結晶性の劣化を引き起こしているものと推定された。 On the other hand, when the crystal growth is carried out at a flow rate of 5.0 × 10 −6 m 3 / sec, which is the final required flow rate from the start of the growth, the seed is reached when the crystal thickness reaches about 1 mm. A 3C polytype having a different atomic arrangement (trigonal form) than a crystal (hexagonal form) is generated, and as a result of the generation of a polycrystal or a heterogeneous polytype, crystal grain boundaries, micropipe defects, etc. occur, resulting in crystallinity. Deteriorated. It was estimated that the distortion due to the markedly different impurity concentration between the seed crystal and the grown crystal increased as the crystal grew and the thickness increased, causing deterioration of crystallinity.
(実施例2)
実施例1と同様にして、種結晶として、(0001)面を有した六方晶系のSiC単結晶1を用意した。同種結晶のマイクロパイプ欠陥密度は5個/cm2以下と非常に小さく結晶性良好であり、ド−ピング元素としての窒素の濃度は1×1019cm−3であった。次に、種結晶1を黒鉛製坩堝3の蓋4の内面に取り付けた。黒鉛製坩堝3の内部には、CVD法により得られた高純度SiC結晶粉末2(高抵抗率を実現するために、不純物の少ない高純度原料が必要)を充填した。次いで、SiC原料を充填した黒鉛製坩堝3を、蓋4で閉じ、黒鉛製フェルト7で被覆した後、黒鉛製支持棒6の上に乗せ、二重石英管5の内部に設置した。そして、石英管の内部を真空排気した後、ワークコイルに電流を流し、原料温度を2000℃まで上げた。その後、雰囲気ガスとして高純度Arガス(純度99.9995%)を流入させ、石英管内圧力を約80kPaに保ちながら、原料温度を目標温度である2400℃まで上昇させた。成長圧力である1.3kPaには約30分かけて減圧し、その後、約20時間成長を続けた。この際の坩堝内の温度勾配は15℃/cmで、成長速度は約0.75mm/時であった。得られた結晶の口径は51mmで、高さは15mm程度であった。この成長時間中、成長開始時には窒素流量を0.5×10−6m3/sec(同流量にて成長結晶中の窒素濃度が種結晶中濃度と同等の1×1019cm−3となることからこの流量を用いた)とし、成長開始後、窒素流量を一定速度で低減させ、5時間で0m3/sec(バルブ閉の状態)まで低減させた。窒素流量を0m3/sec(アンド−プ)とした際に得られる成長結晶中の窒素濃度は1×1018cm−3となるため、成長結晶中での濃度変化率は26.7%/100μm(=1000%/(0.75mm/時×5時間))であった。
(Example 2)
In the same manner as in Example 1, a hexagonal SiC single crystal 1 having a (0001) plane was prepared as a seed crystal. The micropipe defect density of the same type crystal was as small as 5 pieces / cm 2 or less and good crystallinity, and the concentration of nitrogen as a doping element was 1 × 10 19 cm −3 . Next, the seed crystal 1 was attached to the inner surface of the lid 4 of the graphite crucible 3. The graphite crucible 3 was filled with high-purity SiC crystal powder 2 obtained by a CVD method (a high-purity raw material with few impurities is necessary to achieve high resistivity). Next, the graphite crucible 3 filled with the SiC raw material was closed with the lid 4 and covered with the graphite felt 7, and then placed on the graphite support rod 6 and installed inside the double quartz tube 5. And after evacuating the inside of a quartz tube, the electric current was sent through the work coil and the raw material temperature was raised to 2000 degreeC. Thereafter, high-purity Ar gas (purity 99.9995%) was introduced as the atmospheric gas, and the raw material temperature was raised to the target temperature of 2400 ° C. while maintaining the pressure in the quartz tube at about 80 kPa. The growth pressure was reduced to 1.3 kPa over about 30 minutes, and then the growth was continued for about 20 hours. At this time, the temperature gradient in the crucible was 15 ° C./cm, and the growth rate was about 0.75 mm / hour. The diameter of the obtained crystal was 51 mm, and the height was about 15 mm. During this growth time, at the start of growth, the nitrogen flow rate is 0.5 × 10 −6 m 3 / sec (at the same flow rate, the nitrogen concentration in the grown crystal becomes 1 × 10 19 cm −3 , which is equivalent to the concentration in the seed crystal). Therefore, after the start of growth, the nitrogen flow rate was reduced at a constant rate and decreased to 0 m 3 / sec (valve closed state) in 5 hours. Since the nitrogen concentration in the grown crystal obtained when the nitrogen flow rate is 0 m 3 / sec (andop) is 1 × 10 18 cm −3 , the concentration change rate in the grown crystal is 26.7% / 100 μm (= 1000% / (0.75 mm / hour × 5 hours)).
こうして得られた炭化珪素単結晶をラマン散乱により分析したところ、種結晶と同一ポリタイプを有する六方晶系のSiC単結晶が全面に渡り成長したことを確認できた。結晶性を測定する目的で、成長した単結晶インゴットの最上部(成長終了近傍に成長した部分)から厚さ1.0mmのウェハを切り出した。ウェハを直接光学顕微鏡にて観察したところ、貫通中空欠陥密度が10/cm2以下と、種結晶と同等の低密度を有していることが確認できた。さらに確認するために、520℃に溶融した水酸化カリウム溶液中で5分間エッチングを施した。このエッチング処理を行うと、貫通中空欠陥は六角状エッチピットとして観察できる。ウェハついてエッチピット数密度を調べたところ、目視観察と同様の数密度の貫通中空欠陥が検出された。また、種結晶と同等の高品質結晶が得られているかを確認するため、予め測定していた種結晶のX線トポグラフ撮影デ−タと、成長した結晶から切り出したウェハのX線トポグラフ撮影デ−タを比較したところ、種結晶と同等の高品質を有し、成長に起因して新たに欠陥が発生していないことが確認できた。 When the silicon carbide single crystal thus obtained was analyzed by Raman scattering, it was confirmed that a hexagonal SiC single crystal having the same polytype as the seed crystal grew over the entire surface. For the purpose of measuring the crystallinity, a wafer having a thickness of 1.0 mm was cut out from the uppermost portion of the grown single crystal ingot (the portion grown near the end of growth). When the wafer was directly observed with an optical microscope, it was confirmed that the through-hole defect density was 10 / cm 2 or less, which was as low as the seed crystal. For further confirmation, etching was performed in a potassium hydroxide solution melted at 520 ° C. for 5 minutes. When this etching process is performed, the penetrating hollow defects can be observed as hexagonal etch pits. When the etch pit number density of the wafer was examined, through-hole defects having the same number density as in the visual observation were detected. In addition, in order to confirm whether a high-quality crystal equivalent to the seed crystal is obtained, the X-ray topography imaging data of the seed crystal measured in advance and the X-ray topography imaging data of the wafer cut out from the grown crystal are obtained. As a result of comparison, it was confirmed that the product had the same high quality as the seed crystal and no new defects were generated due to the growth.
このウェハの抵抗率測定については、誘電緩和現象を利用することで、絶縁性の大きな試料の電気抵抗率を算出する「誘電緩和法」を用いて測定したところ、5×105Ωcmと言う高抵抗率を有することを確認した。 With respect to the resistivity measurement of this wafer, the dielectric relaxation phenomenon was used to measure the electrical resistivity of a sample having a large insulation, and the measurement was performed using a “dielectric relaxation method”. As a result, the wafer resistivity was as high as 5 × 10 5 Ωcm. It was confirmed to have resistivity.
こうして得られた結晶性良好な結晶を切断、加工して作製したウェハに化学気相蒸着法(CVD法)を用いることでSiC単結晶薄膜をエピタキシャル成長させることにより、炭化珪素単結晶エピタキシャルウェハを作製した。同エピタキシャルウェハの結晶性について調べるために、前記した溶融水酸化カリウム溶液中にてエピタキシャルウェハ表面のエッチングを実施した。その結果、基板である炭化珪素単結晶ウェハが有していた良好な結晶品質を継承していることが確認された。 A silicon carbide single crystal epitaxial wafer is produced by epitaxially growing a SiC single crystal thin film by using a chemical vapor deposition method (CVD method) on a wafer produced by cutting and processing the crystal having good crystallinity thus obtained. did. In order to investigate the crystallinity of the epitaxial wafer, the surface of the epitaxial wafer was etched in the molten potassium hydroxide solution described above. As a result, it was confirmed that the good crystal quality of the silicon carbide single crystal wafer as the substrate was inherited.
これに対して、成長開始時より、最終目的濃度が得られる窒素ガス流量である0m3/sec(窒素ガスバルブ閉、窒素を全く流さない状態)の条件にて成長した場合、結晶の厚さが1mm程度に達したところで種結晶(六方晶形)と異なる原子配置(三方晶形)を有する3Cポリタイプが発生し、そこから多結晶が発生、又は異種ポリタイプが発生した結果により、結晶粒界、マイクロパイプ欠陥等が発生して結晶性が劣化した。種結晶と成長結晶との不純物濃度が著しく異なることによる歪が、結晶が成長し厚さが増加するにつれて大きくなり、結晶性の劣化を引き起こしているものと推定された。 On the other hand, when the growth is performed under the condition of 0 m 3 / sec (the nitrogen gas valve is closed and no nitrogen is flown at all), which is the nitrogen gas flow rate at which the final target concentration is obtained, from the start of the growth, When reaching about 1 mm, a 3C polytype having an atomic arrangement (trigonal crystal) different from the seed crystal (hexagonal crystal) is generated, from which polycrystals are generated or heterogeneous polytypes are generated. The crystallinity deteriorated due to micropipe defects. It was estimated that the distortion due to the markedly different impurity concentration between the seed crystal and the grown crystal increased as the crystal grew and the thickness increased, causing deterioration of crystallinity.
1 種結晶(SiC単結晶)
2 SiC結晶粉末原料
3 坩堝(黒鉛あるいはタンタル等の高融点金属)
4 黒鉛製坩堝蓋
5 二重石英管
6 支持棒
7 黒鉛製フェルト(断熱材)
8 ワークコイル
9 高純度Arガス配管
10 高純度Arガス及び不純物ガス用マスフローコントローラ
11 真空排気装置。
1 Seed crystal (SiC single crystal)
2 SiC crystal powder raw material 3 Crucible (high melting point metal such as graphite or tantalum)
4 Graphite crucible lid 5 Double quartz tube 6 Support rod 7 Graphite felt (heat insulation)
8 Work coil 9 High purity Ar gas piping 10 Mass flow controller for high purity Ar gas and impurity gas 11 Vacuum exhaust system.
Claims (3)
以下の範囲内である請求項1記載の炭化珪素単結晶の製造方法。 The concentration change rate is 5% / 100 μm or more, 100% / 100 μm with respect to the crystal growth direction.
The method for producing a silicon carbide single crystal according to claim 1, which is within the following range.
珪素単結晶の製造方法。 The method for producing a silicon carbide single crystal according to claim 1, wherein the additive element is any one of nitrogen, boron, and aluminum.
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US11566344B2 (en) | 2020-06-16 | 2023-01-31 | Senic Inc. | Silicon carbide ingot, wafer, method for producing a silicon carbide ingot, and method for manufacturing a wafer |
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