JP4122548B2

JP4122548B2 - Method for producing silicon carbide single crystal

Info

Publication number: JP4122548B2
Application number: JP28222397A
Authority: JP
Inventors: 勇山本; 邦雄小巻; 幸太郎矢野; 直樹小柳; 茂弘西野
Original assignee: Showa Denko KK
Current assignee: Showa Denko KK
Priority date: 1997-10-15
Filing date: 1997-10-15
Publication date: 2008-07-23
Anticipated expiration: 2017-10-15
Also published as: JPH11116398A

Description

【０００１】
【発明の属する技術分野】
本発明は炭化珪素原料を昇華させ炭化珪素単結晶を製造する方法に係わり、結晶欠陥の少ない品質安定性に優れた炭化珪素単結晶を高い歩留まりで製造する方法に関する。
炭化珪素（ＳｉＣ）は熱的、化学的に非常に安定であり且つ電子エネルギ−バンドギャップが広い特徴があり、高温高圧下でも使用可能な耐環境素子材料、耐放射線素子材料、パワ−素子材料や短波長発光素子材料として期待されている。
【０００２】
【従来の技術】
半導体材料として期待されている炭化珪素単結晶は炭化珪素粉末を原料とする昇華法で通常作製される。一般的に昇華法においては原料炭化珪素粉末と単結晶の種結晶を対向させて黒鉛製ルツボ内に配置し、不活性雰囲気中で２０００〜２４００℃に加熱する。加熱により炭化珪素原料の分解、昇華により発生した昇華蒸気は成長領域に到達し、成長温度に保持された種結晶表面に結晶方位を揃えて析出し、単結晶としてエピタキシャル成長する。一般的に反応容器として用いられる黒鉛製ルツボの内壁と昇華ガスとの相互作用や黒鉛壁よりの炭素等の昇華によりガス組成は原料から発生した状態からズレを生じる。そして昇華ガス成分は変動し易く、それが成長単結晶の結晶性に大きく影響する。これらの結晶成長過程中の昇華ガス成分の変動を抑制補正する方法としてＳｉ成分、又はＣ成分の内の一つを添加する事が行われている。例えばＳｉ分を過剰に原料に混合する特公昭５１−２９５１８、Ｓｉ₃ Ｎ₄ を加える特開平６−１６９８がある。又珪素成分ガスと炭素成分ガスを導入する事を併用する特開平７−８２０９０が提案されている。しかし結晶品質及び安定性が十分とは言えず更なる改良が要望されている。又大型結晶の要請も根強く存在する。
不純物濃度制御の観点から従来技術で用いられている黒鉛製ルツボは大きな不純物混入源の一つである。ルツボ壁からの不純物混入を防ぐ方法として雰囲気ガス流を反応室内壁への接触を避ける様に流す特開平５−３０６１９９が提案されているが、その効果は十分とは言えない。
【０００３】
【発明が解決しようとする課題】
原料粉末からの分解、昇華ガスとしてはＳｉＣの他に主にＳｉ，Ｓｉ₂ Ｃ，ＳｉＣ₂ 等が生成し、これらの昇華ガスの分圧は黒鉛ルツボを使用すると黒鉛ルツボ内壁との反応、取り込み、及び反応系からの成分間の不均一性により昇華時の状態から変動する。昇華ガス成分の変動はいわゆる昇華過程の逆反応と考えられる結晶析出過程で化学量論比の変動、更にはインクル−ジョン、不純物元素、結晶欠陥として結晶中に取り込まれ易くなる。
一方基板は成長温度に保持され、一般に原料温度よりは低いが、基板近傍又は基板と接して黒鉛材が存在すると基板のエッチング等が起こり、基板結晶にダメージを与えることが知られている。
【０００４】
また昇華ガス成分比の変動は前述の種々の昇華ガス中の化学種からＳｉＣとして結晶化する過程で必然的に各々の反応パスが異なる。そのため種基板結晶と異なる多型を持つ結晶が成長する誘因ともなる。その結果、得られた単結晶は結晶欠陥、多型混入の多い品質の低いものとなる。
本発明は上記の欠点をなくし、インクルージョン、不純物元素、結晶欠陥の少ない炭化珪素単結晶を得ることを目的とする。
【０００５】
【課題を解決するための手段】
本発明者らは原料の昇華組成のズレや変動要因及びこれらが生成する単結晶に与える影響等について鋭意検討した結果、炭化珪素原料を収容するルツボとして特定のものを使用することで目的を達成できる事を確認して本発明を完成させた。
即ち、本発明は昇華再結晶法で炭化珪素基板上に炭化珪素単結晶を製造する方法において、炭化珪素原料を収容するルツボとして内面が耐熱性金属炭化物で被覆されたルツボを使用することを特徴とする方法である。
【０００６】
【発明の実施の形態】
本発明で使用されるルツボは内面が耐熱性金属炭化物で被覆されている。この金属炭化物は、融点又は分解温度が１９００℃以上のものが好ましい。具体的には金属炭化物としてＴａＣ、ＺｒＣ、ＮｂＣ、Ｔａ₂ Ｃ，ＴｉＣ、Ｎｂ₂ Ｃ、ＭｏＣ、ＷＣ、Ｍｏ₂ Ｃ等から選ばれた材質で、又それら複数の材質を組み合わせて用いる事ができる。
これらの炭化物を構成する元素状金属は耐熱性があっても結晶成長過程中に除々に炭化反応を起こし、その際にガス組成に変動を来たすので望ましくない。
【０００７】
ルツボは内面が上記炭化物で被覆されていればよく、ルツボの基材は上記炭化物を構成する金属元素や黒鉛であってもよい。
金属炭化物の被覆は、基材が金属である場合そのルツボを炭化処理して行う事が出来る。具体的にはルツボ内に高純度黒鉛粉末を充填し不活性ガス雰囲気中か真空中での加熱処理をするか又はルツボ内に炭化水素等の炭素化合物を導入して加熱処理を行うことで達成することが出来る。
また基材が黒鉛であるルツボの場合はルツボの内面を電子ビーム加熱蒸着法等を用い、先ず金属元素を層状に蒸着させた後上記炭化処理法により炭化物内面層を形成させることができる。
【０００８】
金属炭化物の被膜の厚さは、炭化珪素単結晶の製造中に基材の金属や黒鉛等と昇華ガスの反応を防ぐに必要な厚さがあればよく、一般的には１０μｍ以上あればよい。
上述の金属炭化物の反応ルツボを用いれば、原料粉末からの分解、昇華ガスの主なものはＳｉＣ，Ｓｉ，Ｓｉ₂ Ｃ，ＳｉＣ₂ 等であるが、黒鉛ルツボ、金属ルツボを用いる場合と異なり、これらの昇華ガスの内壁との相互作用、反応系からの成分間の均一性が維持され、分解昇華時の状態からの変動を著しく抑制することができる。又成長温度に保持されたＳｉＣ単結晶基板は炭素材が接したり、近傍にあるために起こるダメージも本発明のルツボを用いればほとんど抑止することができる。その結果、いわば分解昇華過程の逆反応と考えられる結晶析出過程では化学量論比の変動、インクル−ジョン、不純物元素混入、結晶欠陥、多型混入等の結晶性マイナス要因を大幅に低減でき、高品位のＳｉＣ単結晶を種基板結晶上にエピタキシャル成長させることが出来る。
【０００９】
原料のＳｉＣはアチソン法による砥粒グレイドを用いる事が出来るが、高純度化を行った微粉で、昇華反応面積を得るため粒度は細目が好ましい。又多孔質の圧粉体、焼結体として用いても良い。
一方、β−ＳｉＣは高純度のものがシランガスと炭化水素ガスの水素雰囲気中でのＣＶＤで比較的容易に調製でき、高純度原料として適しているが、一般にサブミクロンの極微粉であるため、原料の充填密度を稼ぐために圧粉体のかたちで用いるのが望ましい。
本発明によるルツボ材質を用いて良質で大面積の更に大きな単結晶バルクを得るためには原料ＳｉＣが配置された部分にＳｉＣ原料を間欠的又は連続的に供給すれば、ルツボ内壁と昇華ガスとの相互作用が極めて少ない事より昇華領域に滞留する原料の分解昇華バランスが良く、時間安定性良く単結晶の成長を持続させることができる。
【００１０】
原料の供給システムの構成は、例えば上述の金属炭化物の金属成分でルツボ及び原料フィダー等を構築した後炭化処理により内面を炭化する事で比較的容易に行うことができる。
原料のＳｉＣを結晶合成中に間欠的又は連続的に供給するにはルツボの原料部分に接続され、不活性ガス圧をルツボ内圧と等しく保った供給管に連続又は間欠的に原料フィーダーより粉体又は圧粉、焼結粒の形態で搬入すればよい。
更に一段の高品位化を行うには一旦成長させた単結晶から切り出した種結晶を新たに配置して同様の条件で運転を繰り返せば、結晶欠陥が更に低減したより高品位の単結晶を成長させ得る。
その他加熱装置、温度条件等は従来公知の昇華再結晶法と同様でよい。即ち、加熱装置としては高周波加熱装置を用いることができ、温度は原料ゾーンが２０００〜２４００℃、基板が１８００〜２３００℃である。
【００１１】
詳しい説明を概略図と実施例によって以下に行う。
図１にルツボ内の配置の例を概略図で示す。
図１において１は内面を炭化タンタルで被覆したＴａ製ルツボ、２は炭化珪素種結晶、３は原料ＳｉＣ粉末、４は原料粉末供給管（一部のみ図示）、５は成長単結晶、６は供給原料ガイド板である。
【００１２】
【実施例】
Ｔａ製ルツボ１２０×４６φ（肉厚０．５ｍｍ）の炭化処理を先ず、Ｔａルツボに高純度黒鉛粉末を６８ｇ充填し、これを収容出来る大きさの黒鉛ルツボ中で２Ｅ−３の真空中で３０分、脱気した後７６０ｔｏｒｒのアルゴン雰囲気中で２３００℃で５時間処理を行った。処理後のルツボ内壁は均一に金色化していた。このルツボ壁のＸ線分析ではＴａ₂ ＣとＴａＣとＴａのピークを観測した（ここでは原料の連続供給を行わず、従ってルツボには図１の４，６は設置されていない）。
【００１３】
６Ｈ−ＳｉＣ単結晶（０００１）面を成長面とした種結晶２５０ｍｍ径、厚さ１．５ｍｍを上述の内壁を炭化処理したＴａルツボの蓋の中央に機械的に保持して設置した。ルツボ内に図１の様に高純度化した工業用グリ−ンＳｉＣ４００メッシュを２２０ｇ収容した。ルツボを黒鉛製外套管に収容し、更にその外側に断熱材を配し石英管内にセットした。これを高周波加熱炉を用いて原料温度を２３００℃、種結晶温度を２２５０℃にアルゴン雰囲気圧を１００ｔｏｒｒとし、５時間運転を行った。この時点で結晶先端部は円形に近い断面形状で４５．３ｍｍの径で高さ１０．６ｍｍであった。この結晶の成長方向の断面を切断、研磨により磨き出し、顕微鏡観察を行った結果、インクル−ジョンは皆無であり、結晶欠陥密度は１．３Ｅ２／ｃｍ² であった。又イオンエッチングにより電子顕微鏡試料を作製し、高分解能観察の結果、界面、成長端部とも６Ｈ−ＳｉＣの格子間隔を有することが確認されエピタキシャル成長が保たれていることがわかった。
【００１４】
［比較例］
実施例のルツボを黒鉛ルツボに換えた以外全ての条件を実施例と同一にして単結晶の成長を行った。成長結晶サイズは実施例の場合よりも体積が約３割方小さかつた。結晶断面の顕微鏡観察ではインクル−ジョンが散見され、また欠陥密度は実施例の場合の約３倍の水準であった。更に電子顕微鏡の高分解能観察では４Ｈタイプと希に１５Ｒの混入が見られた。又積層欠陥も多数観察された。
【００１５】
【発明の効果】
昇華再結晶法で原料の炭化珪素より炭化珪素基板上に単結晶を成長させるに際し、内面を耐熱性金属炭化物で被覆したルツボを用いる事で、安定して結晶欠陥の少ない高品位のＳｉＣ単結晶をＳｉＣ種基板上に効率良くエピタキシャル成長させることができる。又大型結晶も容易に成長できる。
【図面の簡単な説明】
【図１】本発明のルツボを用いて炭化珪素単結晶を成長させた状態を示す断面図である。
【符号の説明】
１内面を炭化タンタルで被覆したタンタル製ルツボ
２炭化珪素種結晶
３原料ＳｉＣ粉末
４原料粉末供給管
５成長単結晶
６供給原料ガイド板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a silicon carbide single crystal by sublimating a silicon carbide raw material, and relates to a method for producing a silicon carbide single crystal excellent in quality stability with few crystal defects at a high yield.
Silicon carbide (SiC) has the characteristics that it is very stable thermally and chemically and has a wide electron energy band gap, and can be used even under high temperature and high pressure. Environment-resistant element material, radiation-resistant element material, power element material And is expected as a material for short wavelength light emitting devices.
[0002]
[Prior art]
A silicon carbide single crystal expected as a semiconductor material is usually produced by a sublimation method using silicon carbide powder as a raw material. In general, in the sublimation method, a raw material silicon carbide powder and a single crystal seed crystal are placed facing each other in a graphite crucible and heated to 2000 to 2400 ° C. in an inert atmosphere. Sublimation vapor generated by decomposition and sublimation of the silicon carbide raw material by heating reaches the growth region, precipitates with the crystal orientation aligned on the surface of the seed crystal held at the growth temperature, and grows epitaxially as a single crystal. Generally, the gas composition deviates from the state generated from the raw material due to the interaction between the inner wall of a graphite crucible used as a reaction vessel and the sublimation gas, or the sublimation of carbon or the like from the graphite wall. The sublimation gas component tends to fluctuate, which greatly affects the crystallinity of the grown single crystal. As a method for suppressing and correcting the fluctuation of the sublimation gas component during the crystal growth process, one of Si component and C component is added. For example, Japanese Patent Publication No. 51-29518, in which Si content is excessively mixed with the raw material, and Japanese Patent Laid-Open No. 6-1698 in which Si ₃ N ₄ is added. Japanese Patent Laid-Open No. 7-82090 has been proposed which uses both introduction of silicon component gas and carbon component gas. However, crystal quality and stability are not sufficient, and further improvements are desired. There is also a strong demand for large crystals.
The graphite crucible used in the prior art from the viewpoint of impurity concentration control is one of the large impurity contamination sources. Japanese Patent Laid-Open No. 5-306199 has been proposed as a method for preventing impurity contamination from the crucible wall to flow an atmospheric gas flow so as to avoid contact with the reaction chamber wall, but the effect is not sufficient.
[0003]
[Problems to be solved by the invention]
Decomposition from raw material powder, sublimation gas mainly produces Si, Si ₂ C, SiC ₂ etc. in addition to SiC, and the partial pressure of these sublimation gases is the reaction and incorporation with the inner wall of graphite crucible. , And non-uniformity between components from the reaction system will vary from the sublimation state. The fluctuation of the sublimation gas component is likely to be incorporated into the crystal as a change in the stoichiometric ratio in the crystal precipitation process, which is considered to be a reverse reaction of the so-called sublimation process, and further as an inclusion, impurity element, and crystal defect.
On the other hand, it is known that the substrate is maintained at the growth temperature and generally lower than the raw material temperature, but if a graphite material is present in the vicinity of or in contact with the substrate, etching of the substrate occurs and damages the substrate crystal.
[0004]
Further, the change in the sublimation gas component ratio inevitably differs in each reaction path in the process of crystallizing as SiC from the above-mentioned chemical species in the various sublimation gases. Therefore, it is also an incentive to grow a crystal having a polymorphism different from that of the seed substrate crystal. As a result, the obtained single crystal has a low quality with many crystal defects and polymorphs.
An object of the present invention is to obtain a silicon carbide single crystal that eliminates the above-mentioned drawbacks and has few inclusions, impurity elements, and crystal defects.
[0005]
[Means for Solving the Problems]
As a result of intensive investigations on deviations and fluctuation factors in the sublimation composition of the raw material and the effect of these on the single crystal produced, the present inventors achieved the object by using a specific crucible containing the silicon carbide raw material. The present invention was completed after confirming that it was possible.
That is, the present invention is a method for producing a silicon carbide single crystal on a silicon carbide substrate by a sublimation recrystallization method, wherein a crucible whose inner surface is coated with a refractory metal carbide is used as a crucible containing a silicon carbide raw material. It is a method.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The inner surface of the crucible used in the present invention is coated with a refractory metal carbide. This metal carbide preferably has a melting point or decomposition temperature of 1900 ° C. or higher. Specifically, it is possible to use a material selected from TaC, ZrC, NbC, Ta ₂ C, TiC, Nb ₂ C, MoC, WC, Mo ₂ C, etc. as a metal carbide, or a combination of these materials. .
Even though the elemental metal constituting these carbides has heat resistance, it gradually undergoes a carbonization reaction during the crystal growth process, and the gas composition changes at that time, which is not desirable.
[0007]
The crucible is only required to have the inner surface coated with the carbide, and the base material of the crucible may be a metal element or graphite constituting the carbide.
When the base material is a metal, the metal carbide can be coated by carbonizing the crucible. Specifically, high purity graphite powder is filled in the crucible and heat treatment is performed in an inert gas atmosphere or in a vacuum, or a carbon compound such as hydrocarbon is introduced into the crucible and heat treatment is performed. I can do it.
Further, when the base material is a crucible made of graphite, the inner surface of the crucible can be formed by using an electron beam heating vapor deposition method or the like.
[0008]
The thickness of the metal carbide coating may be as long as it is necessary to prevent the reaction between the metal, graphite, etc. of the base material and the sublimation gas during the production of the silicon carbide single crystal, and generally 10 μm or more. .
If the above-mentioned metal carbide reaction crucible is used, decomposition from the raw material powder, the main sublimation gas is SiC, Si, Si ₂ C, SiC ₂ or the like, but unlike the case of using a graphite crucible, a metal crucible, Interaction with these inner walls of the sublimation gas and uniformity among components from the reaction system are maintained, and fluctuations from the state during decomposition sublimation can be remarkably suppressed. Further, the SiC single crystal substrate maintained at the growth temperature can be hardly suppressed by using the crucible of the present invention because the carbon material is in contact with or near the SiC material. As a result, in the crystal precipitation process, which is considered to be the reverse reaction of the decomposition and sublimation process, the negative factors of crystallinity such as fluctuation of stoichiometry, inclusion, impurity element contamination, crystal defect, polymorphism contamination, etc. can be greatly reduced. A high quality SiC single crystal can be epitaxially grown on a seed substrate crystal.
[0009]
As the raw material SiC, an abrasive grade by the Atchison method can be used. However, the fine particle size is preferably fine in order to obtain a sublimation reaction area with a highly purified fine powder. Further, it may be used as a porous green compact or a sintered body.
On the other hand, β-SiC is highly pure and can be prepared relatively easily by CVD in a hydrogen atmosphere of silane gas and hydrocarbon gas, and is suitable as a high purity raw material. It is desirable to use it in the form of a green compact in order to increase the packing density of the raw material.
In order to obtain a large single crystal bulk having a high quality and a large area using the crucible material according to the present invention, if the SiC raw material is intermittently or continuously supplied to the portion where the raw material SiC is disposed, the inner wall of the crucible, the sublimation gas, From the fact that the interaction is extremely small, the decomposition and sublimation balance of the raw material staying in the sublimation region is good, and the growth of the single crystal can be sustained with good time stability.
[0010]
The configuration of the raw material supply system can be relatively easily performed by, for example, constructing a crucible and a raw material feeder with the metal components of the metal carbide described above and then carbonizing the inner surface by carbonization.
In order to supply raw material SiC intermittently or continuously during crystal synthesis, it is connected to the raw material part of the crucible, and is continuously or intermittently powdered from the raw material feeder in a supply pipe maintaining the inert gas pressure equal to the crucible internal pressure. Or it may carry in with the form of a compact and a sintered grain.
In order to further improve the quality, if a seed crystal cut out from a single crystal once grown is newly placed and the operation is repeated under the same conditions, a higher-quality single crystal with further reduced crystal defects is grown. Can be.
Other heating devices, temperature conditions, and the like may be the same as those of a conventionally known sublimation recrystallization method. That is, a high-frequency heating device can be used as the heating device, and the temperature is 2000 to 2400 ° C. for the raw material zone and 1800 to 2300 ° C. for the substrate.
[0011]
A detailed description is given below by means of schematic diagrams and examples.
FIG. 1 is a schematic view showing an example of arrangement in the crucible.
In FIG. 1, 1 is a Ta crucible whose inner surface is coated with tantalum carbide, 2 is a silicon carbide seed crystal, 3 is a raw material SiC powder, 4 is a raw material powder supply pipe (only a part is shown), 5 is a grown single crystal, 6 is It is a feedstock guide plate.
[0012]
【Example】
First, the Ta crucible 120 × 46φ (thickness 0.5 mm) is carbonized. First, 68 g of high-purity graphite powder is filled in the Ta crucible, and the graphite crucible having a size capable of accommodating this is 30 in a vacuum of 2E-3. After degassing for 5 minutes, treatment was performed at 2300 ° C. for 5 hours in an argon atmosphere of 760 torr. The inner wall of the crucible after the treatment was uniformly gold. In the crucible wall X-ray analysis, Ta ₂ C, TaC, and Ta peaks were observed (here, the raw materials were not continuously supplied, and therefore the crucibles 4 and 6 in FIG. 1 were not installed).
[0013]
A seed crystal having a diameter of 250 mm and a thickness of 1.5 mm with a 6H—SiC single crystal (0001) plane as a growth surface was mechanically held and installed at the center of the lid of the Ta crucible whose inner wall was carbonized. In the crucible, 220 g of industrially purified SiC 400 mesh with high purity as shown in FIG. 1 was accommodated. The crucible was housed in a graphite mantle tube, and a heat insulating material was further arranged outside the crucible tube and set in the quartz tube. This was operated for 5 hours using a high-frequency heating furnace at a raw material temperature of 2300 ° C., a seed crystal temperature of 2250 ° C. and an argon atmosphere pressure of 100 torr. At this time, the tip of the crystal had a cross-sectional shape close to a circle, a diameter of 45.3 mm, and a height of 10.6 mm. As a result of cutting and polishing the cross section in the crystal growth direction and observing under a microscope, there was no inclusion and the crystal defect density was 1.3E2 / cm ² . Also, an electron microscope sample was prepared by ion etching, and as a result of high-resolution observation, it was confirmed that both the interface and the growth edge had 6H—SiC lattice spacing, and epitaxial growth was maintained.
[0014]
[Comparative example]
Single crystals were grown under the same conditions as in the example except that the crucible in the example was replaced with a graphite crucible. The growth crystal size was about 30% smaller in volume than in the example. In the microscopic observation of the crystal cross section, an inclusion was scattered and the defect density was about three times that in the example. Furthermore, in high-resolution observation with an electron microscope, 15R was rarely mixed with the 4H type. Many stacking faults were also observed.
[0015]
【The invention's effect】
When a single crystal is grown on a silicon carbide substrate from the raw material silicon carbide by the sublimation recrystallization method, a high-quality SiC single crystal with stable and few crystal defects is used by using a crucible whose inner surface is coated with a refractory metal carbide. Can be efficiently epitaxially grown on the SiC seed substrate. Large crystals can also be easily grown.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a state in which a silicon carbide single crystal is grown using a crucible of the present invention.
[Explanation of symbols]
1 Tantalum crucible whose inner surface is coated with tantalum carbide 2 Silicon carbide seed crystal 3 Raw material SiC powder 4 Raw material powder supply tube 5 Growing single crystal 6 Feed material guide plate

Claims

In a method for producing a silicon carbide single crystal on a silicon carbide substrate by a sublimation recrystallization method, a tantalum crucible whose inner surface is coated with tantalum carbide is used as a crucible for containing a silicon carbide raw material. How to manufacture.

The method for producing a silicon carbide single crystal according to claim 1 , wherein the tantalum carbide coating has a thickness of 10 μm or more.