JP3631976B2 - Method for growing silicon carbide single crystal - Google Patents
Method for growing silicon carbide single crystal Download PDFInfo
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- JP3631976B2 JP3631976B2 JP2001134822A JP2001134822A JP3631976B2 JP 3631976 B2 JP3631976 B2 JP 3631976B2 JP 2001134822 A JP2001134822 A JP 2001134822A JP 2001134822 A JP2001134822 A JP 2001134822A JP 3631976 B2 JP3631976 B2 JP 3631976B2
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- silicon carbide
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Description
【0001】
【発明の属する技術分野】
本発明は、炭化珪素単結晶に係り、詳しくは、炭化珪素種結晶上に炭化珪素単結晶を成長させてなる炭化珪素単結晶に関するものである。
【0002】
【従来の技術】
炭化珪素単結晶は、高周波用半導体基板、発光素子用基板、耐環境用デバイス、パワーデバイス等の半導体デバイス用の材料として有用であり、その製造方法としては種々の方法が用いられている。炭化珪素は、常圧での液相が存在せず、シリコン単結晶の引き上げ法のような液相からの結晶化が困難であり、従来はSi2C、SiC2,Si等の気相からの結晶化である昇華法による製造が一般的であった。
【0003】
昇華法には、珪砂等の固体の二酸化珪素源とコークス等の固体の炭素源とを高温加熱し、発生した蒸気と炭素源との反応により炭化珪素単結晶を製造するアチソン法や、黒鉛坩堝内で炭化珪素単結晶を再結晶化するレーリー法、改良レーリー法等がある。アチソン法は、得られる単結晶の大きさが小さい上、半導体デバイス用としては純度が低く、レーリー法や改良レーリー法は、炭化珪素の化学量論的組成のガスが存在しないことから、再結晶化の機構は複雑であり、制御が困難であるという問題がある。
【0004】
気相からの結晶成長は、原子や分子が種結晶表面に供給されて結晶が1層毎に成長するため、いずれの方法も単結晶の成長速度が1mm/時間程度と、シリコンの引き上げ法による成長速度の100mm/時間に比べて著しく遅く、収率も悪いという問題点がある。炭化珪素単結晶の主流の製法としては昇華再結晶法が用いられていた(例えば、特許第3087065号公報)。
【0005】
【発明が解決しようとする課題】
昇華再結晶法は固体の炭化珪素を原料とする気相法であり、マイクロパイプ等の貫通孔が発生し易い点で難点があった。本発明の目的は、従来では困難とされていた液相からの結晶化を実現させることにより、マイクロパイプ等の貫通孔の発生が解消された炭化珪素単結晶を得る点にある。
【0006】
【課題を解決するための手段】
本発明は、炭化珪素単結晶において、珪素含有液状化合物と炭素含有液状化合物とナトリウム化合物とを均一に混合させて乾燥、粉砕、及び炭化処理が施された原料粉を、略大気圧の不活性ガス雰囲気中に加熱状態で保持された炭化珪素種結晶表面に向けて供給し、原料粉中の二酸化珪素が炭化珪素種結晶表面において軟化されて流動する液状二酸化珪素を炭化珪素種結晶表面に密着させ、炭化珪素種結晶表面において液状二酸化珪素を炭素によって還元することにより、炭化珪素単結晶を炭化珪素種結晶表面に成長させてなることを特徴とする炭化珪素種結晶である。
【0007】
本発明においては、二酸化珪素と炭素が超微粒子として互いに均一に混合されて、しかも適量のナトリウムが含まれるため、この原料が種結晶表面において加熱されると原料粉中の二酸化珪素が先ず液状化して種結晶表面に液状膜を形成し、その後に、その液状膜中で二酸化珪素と炭素とが反応して炭化珪素に変換されるので、マイクロパイプ等の貫通孔の無い単結晶が育成できるようになる。ナトリウムを含まない原料では、軟化流動して液状膜ができる以前に原料粉中で炭化珪素の合成が進むため、種結晶表面にエピタキシャルに成長し難く、粉体を焼結した層が種結晶表面に付着する。
【0008】
【発明の実施の形態】
本発明に使用される珪素含有化合物としては、二酸化珪素超微粒子又は珪素アルコキシドが望ましい。二酸化珪素超微粒子の種類、粒子形状等の構成は特に限定されず、例えば種類としてはフュームドシリカ等が挙げられる。珪素アルコキシドとしては、例えばSi(OC2H5)4、Si(OCH3)4、又はこれらの重縮合物が挙げられる。粒径は、1μm以下、望ましくは100nm以下が良い。
【0009】
本発明に使用される炭素含有化合物としては、炭素超微粒子又は熱分解により炭素に変換できる、例えばフェノール樹脂が望ましい。炭素超微粒子の種類、粒子形状等の構成は特に限定されず、例えば種類としてはチャンネルブラックやファーネスブラック等のカーボンブラックが挙げられる。粒径は1μm以下、好ましくは100nm以下がよい。
【0010】
本発明に使用されるナトリウム化合物としては、常温で水等の溶媒に溶解・混合し易いNaOH、NaCl、Na2CO3等が望ましい。炭化珪素種結晶の表面温度は1700〜2300℃に設定されているのが望ましい。
【0011】
珪素含有化合物と炭素含有化合物とナトリウム化合物との混合液は、これに含有される二酸化珪素の重量の0.1〜2.0重量%のナトリウムが含まれることになるように、ナトリウム化合物の混合量を設定するのが望ましい。
【0012】
二酸化珪素含有化合物及び炭素含有化合物の供給量の比率は適宜選択できる。二酸化珪素含有化合物、炭素含有化合物のいずれも2種以上のものを混合して使用しても良い。又、二酸化珪素含有化合物、炭素含有化合物は、必要に応じて、本発明の作用を阻害しない範囲で、前処理を施したり他の成分を微量添加しても良い。
【0013】
次に、本発明が想起された考察過程を概略説明する。
【0014】
従来SiCの合成には下記の2段階反応が主として用いられてきた。
SiO2(s)+C(s)→SiO(g)+CO(g) (1)
SiO(g)+2C(s)→SiC(s)+CO(g) (2)
しかし(1)は固体間の接触点で起こる反応であり反応速度の制御が困難であり、合成されるSiCの粒径分布も広くなり、異常に大きな粒子が生成される事を防ぐことが困難であった。そこで近年では粒径分布の狭い、サイズの揃ったSiC微粒子を合成するために、二酸化珪素と炭素を極力微小な(例えば数nm程度の)粒子とし、極めて均一に混合された原料粉として調整し、この原料粉に熱エネルギーを与える事によって互いに隣接して存在する二酸化珪素超微粒子と炭素超微粒子に下記の直接反応(3)を起こさせてSiC微粒子を合成する事が研究されている。
SiO2(s,l)+3C(s)→SiC(s)+2CO(g) (3)
【0015】
炭化珪素セラミックの焼結は、原料の炭化珪素粉が微粒子であるほど容易であるが、1μm程度以上の炭化珪素粉の焼結には硼素、アルミニウム等の焼結助剤が必要である。
炭化珪素単結晶の育成を炭化珪素種結晶と炭化珪素微粒子を燒結する過程と見なすと、粒子径が少なくとも1μmより小さく、望ましくは100nmより小さな炭化珪素の超微粒子を炭化珪素種結晶表面に密着させて必要な温度に加熱しなければならない。
【0016】
炭化珪素超微粒子の合成は0014に述べた方法によって可能であるが、そのような微粒子の炭化珪素を炭化珪素種結晶表面に供給して加熱しても炭化珪素種結晶の上に炭化珪素の多結晶体が形成され、炭化珪素種結晶が成長することはなかった。これは炭化珪素微粒子と炭化珪素種結晶表面の相互作用が弱く、炭化珪素微粒子同士の焼結による粒子成長が優先的に進行するためと考えられる。
【0017】
上記の問題を解決するためには炭化珪素種結晶表面に密着した状態で炭化珪素微粒子を発生させ、炭化珪素微粒子同士が合体して粒子成長が起こる前に炭化珪素微粒子を炭化珪素種結晶表面に合体させなければならない。これを実現するために、本発明の育成法においては、0011において述べたように複合原料粉に適宜の量のナトリウムを添加する事により、複合原料粉中の二酸化珪素の軟化点温度を低下させ、(3)式で示される炭化珪素の合成反応が進行する以前に、炭化珪素種結晶表面に、複合原料粉中の二酸化珪素による液状膜を形成させ、引き続きその液状膜の中で(3)式の反応により炭化珪素の超微粒子を合成すると同時に表面エネルギーの作用により炭化珪素種結晶表面にエピタキシャルに合体させる事を試み、これに成功した。
【0018】
炭化珪素種結晶表面に複合原料粉を供給する手段としては、キャリアガスを用いる、自由落下させる、静電気力を利用する等が考えられるが0017に述べたように合成された炭化珪素の超微粒子が表面エネルギーの作用により炭化珪素種結晶表面にエピタキシャルに合体される速度を超えて供給すると超微粒子同士が合体して粒成長が進行し、単結晶化が困難となり多結晶となるので本発明の方法による炭化珪素単結晶の成長速度は炭化珪素種結晶表面に炭化珪素の超微粒子が取り込まれる速度により定まる。
【0019】
【実施例】
−実施例1−
本発明の炭化珪素単結晶を得るための製造装置の一例として、図1に示すような製造装置を用いて炭化珪素単結晶の製造を行った。図1の製造装置は、耐熱容器として円筒形で密閉状のカーボン外囲器2を、誘導加熱コイル1内に配置したものであり、カーボン外囲器2内に配置された試料受台3の上に、単結晶を作るための反応容器4が置かれている。反応容器4内の底には炭化珪素の種結晶6が投入されるとともに、不活性ガスの一例であるアルゴンガスが入れられた状態で蓋5が装着される。
【0020】
混合液は、二酸化珪素含有化合物としてメチルシリケート118g(含有二酸化珪素=60g)と、炭素含有化合物としてフェノール94g(含有炭素=36g)と、NaOH1gとを、適宜の量の水を加えてよく攪拌して混合した後に、脱水、乾燥してから粉砕し、約300℃で炭化処理して原料粉を作成する。この原料粉7を、大気圧のアルゴンガス中で1700〜2300℃に加熱された種結晶6上に供給することにより、エピタキシャルに成長した炭化珪素を得ることができた。
【0021】
【発明の効果】
本発明の炭化珪素単結晶は、炭化珪素種結晶の表面に液状膜を形成し、その後にその液状膜中における二酸化珪素と炭素との反応によって炭化珪素に変換されるので、炭化珪素種結晶表面上にマイクロパイプ等の貫通孔の無い炭化珪素単結晶が成長できるようになった。
【図面の簡単な説明】
【図1】図1は、本発明の炭化珪素単結晶を得るための製造装置の一例を示す概要図。
【符号の説明】
1 誘導加熱コイル
2 カーボン外囲器
3 試料受台
4 反応容器
5 蓋
6 種結晶
7 原料粉[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a silicon carbide single crystal, and more particularly to a silicon carbide single crystal obtained by growing a silicon carbide single crystal on a silicon carbide seed crystal.
[0002]
[Prior art]
Silicon carbide single crystal is useful as a material for semiconductor devices such as a high-frequency semiconductor substrate, a light-emitting element substrate, an environment-resistant device, and a power device, and various methods are used as its manufacturing method. Silicon carbide does not have a liquid phase at normal pressure and is difficult to crystallize from a liquid phase such as a pulling method of a silicon single crystal. Conventionally, silicon carbide is from a gas phase such as Si 2 C, SiC 2 , and Si. Production by the sublimation method, which is crystallization of, was common.
[0003]
In the sublimation method, a solid silicon dioxide source such as silica sand and a solid carbon source such as coke are heated at a high temperature, and a silicon carbide single crystal is produced by a reaction between the generated vapor and the carbon source, or a graphite crucible. Among them, there are a Rayleigh method for recrystallizing a silicon carbide single crystal, an improved Rayleigh method, and the like. In the Atchison method, the size of the single crystal obtained is small, and the purity is low for semiconductor devices. The Rayleigh method and the modified Rayleigh method are recrystallized because there is no gas with a stoichiometric composition of silicon carbide. There is a problem that the mechanism of conversion is complicated and difficult to control.
[0004]
In the crystal growth from the gas phase, atoms and molecules are supplied to the seed crystal surface and the crystal grows in each layer. Therefore, in either method, the growth rate of the single crystal is about 1 mm / hour, and the silicon pulling method is used. There is a problem that the growth rate is remarkably slow and the yield is poor as compared with the growth rate of 100 mm / hour. A sublimation recrystallization method has been used as a main production method of a silicon carbide single crystal (for example, Japanese Patent No. 3087065).
[0005]
[Problems to be solved by the invention]
The sublimation recrystallization method is a vapor phase method using solid silicon carbide as a raw material, and has a drawback in that through holes such as micropipes are easily generated. An object of the present invention is to obtain a silicon carbide single crystal in which generation of through-holes such as micropipes is eliminated by realizing crystallization from a liquid phase, which has been conventionally difficult.
[0006]
[Means for Solving the Problems]
The present invention relates to a raw material powder obtained by uniformly mixing a silicon-containing liquid compound, a carbon-containing liquid compound, and a sodium compound in a silicon carbide single crystal, followed by drying, pulverization, and carbonization treatment. Supply to the silicon carbide seed crystal surface that is heated in the gas atmosphere, and the silicon dioxide in the raw material powder is softened on the surface of the silicon carbide seed crystal and flows into the silicon carbide seed crystal surface. The silicon carbide seed crystal is characterized in that a silicon carbide single crystal is grown on the silicon carbide seed crystal surface by reducing liquid silicon dioxide with carbon on the silicon carbide seed crystal surface.
[0007]
In the present invention, silicon dioxide and carbon are uniformly mixed with each other as ultrafine particles, and an appropriate amount of sodium is contained. Therefore, when this raw material is heated on the seed crystal surface, the silicon dioxide in the raw material powder first liquefies. A liquid film is formed on the surface of the seed crystal, and then silicon dioxide and carbon react with each other in the liquid film to be converted into silicon carbide, so that a single crystal without a through hole such as a micropipe can be grown. become. For raw materials that do not contain sodium, the synthesis of silicon carbide proceeds in the raw material powder before it softens and flows to form a liquid film, so it is difficult to grow epitaxially on the seed crystal surface, and the powder-sintered layer is the seed crystal surface. Adhere to.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The silicon-containing compound used in the present invention is preferably silicon dioxide ultrafine particles or silicon alkoxide. The configuration of the silicon dioxide ultrafine particles, such as the type and particle shape, is not particularly limited, and examples thereof include fumed silica. Examples of the silicon alkoxide include Si (OC 2 H 5 ) 4 , Si (OCH 3 ) 4 , and polycondensates thereof. The particle size is 1 μm or less, preferably 100 nm or less.
[0009]
The carbon-containing compound used in the present invention is preferably carbon ultrafine particles or, for example, a phenol resin that can be converted to carbon by thermal decomposition. The configuration of the type and shape of the ultrafine carbon particles is not particularly limited, and examples thereof include carbon black such as channel black and furnace black. The particle size is 1 μm or less, preferably 100 nm or less.
[0010]
As the sodium compound used in the present invention, NaOH, NaCl, Na 2 CO 3 and the like which are easily dissolved and mixed in a solvent such as water at normal temperature are desirable. The surface temperature of the silicon carbide seed crystal is desirably set to 1700 to 2300 ° C.
[0011]
The mixed solution of the silicon-containing compound, the carbon-containing compound, and the sodium compound contains a mixture of sodium compounds so that 0.1 to 2.0% by weight of sodium is contained in the silicon dioxide contained therein. It is desirable to set the amount.
[0012]
The ratio of the supply amounts of the silicon dioxide-containing compound and the carbon-containing compound can be appropriately selected. Two or more silicon dioxide-containing compounds and carbon-containing compounds may be mixed and used. Further, the silicon dioxide-containing compound and the carbon-containing compound may be subjected to pretreatment or other components may be added in small amounts as long as they do not hinder the action of the present invention.
[0013]
Next, the consideration process in which the present invention has been recalled will be outlined.
[0014]
Conventionally, the following two-stage reaction has been mainly used for the synthesis of SiC.
SiO 2 (s) + C (s) → SiO (g) + CO (g) (1)
SiO (g) + 2C (s) → SiC (s) + CO (g) (2)
However, (1) is a reaction that occurs at the point of contact between solids, it is difficult to control the reaction rate, the particle size distribution of the synthesized SiC is wide, and it is difficult to prevent the generation of abnormally large particles. Met. Therefore, in recent years, in order to synthesize SiC fine particles with a narrow particle size distribution and uniform size, silicon dioxide and carbon are made as fine as possible (for example, about several nanometers) and adjusted as a raw material powder mixed extremely uniformly. Research has been conducted on synthesizing SiC fine particles by applying the following direct reaction (3) to the silicon dioxide ultrafine particles and carbon ultrafine particles existing adjacent to each other by applying thermal energy to the raw material powder.
SiO 2 (s, l) + 3C (s) → SiC (s) + 2CO (g) (3)
[0015]
Sintering of silicon carbide ceramic is easier as the raw material silicon carbide powder is finer, but sintering of silicon carbide powder of about 1 μm or more requires a sintering aid such as boron or aluminum.
Considering the growth of silicon carbide single crystal as a process of sintering silicon carbide seed crystals and silicon carbide fine particles, ultrafine particles of silicon carbide having a particle diameter of at least smaller than 1 μm, preferably smaller than 100 nm, are preferably adhered to the surface of the silicon carbide seed crystals. Must be heated to the required temperature.
[0016]
Silicon carbide ultrafine particles can be synthesized by the method described in 0014. Even if silicon carbide of such fine particles is supplied to the surface of the silicon carbide seed crystal and heated, a large amount of silicon carbide is deposited on the silicon carbide seed crystal. Crystals were formed, and silicon carbide seed crystals did not grow. This is presumably because the interaction between the silicon carbide fine particles and the surface of the silicon carbide seed crystal is weak, and the particle growth by sintering of the silicon carbide fine particles proceeds preferentially.
[0017]
In order to solve the above problem, silicon carbide fine particles are generated in close contact with the surface of the silicon carbide seed crystal, and the silicon carbide fine particles are put on the silicon carbide seed crystal surface before the silicon carbide fine particles coalesce and particle growth occurs. Must be merged. In order to realize this, in the growing method of the present invention, as described in 0011, an appropriate amount of sodium is added to the composite raw material powder to lower the softening point temperature of silicon dioxide in the composite raw material powder. Before the synthesis reaction of silicon carbide represented by the formula (3) proceeds, a liquid film of silicon dioxide in the composite raw material powder is formed on the surface of the silicon carbide seed crystal, and subsequently in the liquid film (3) We succeeded in synthesizing ultrafine particles of silicon carbide by the reaction of the formula and at the same time epitaxially coalescing with the surface of the silicon carbide seed crystal by the action of surface energy.
[0018]
As a means for supplying the composite raw material powder to the surface of the silicon carbide seed crystal, it is possible to use carrier gas, free fall, use of electrostatic force, etc. Since the ultrafine particles coalesce with each other when supplied at a rate exceeding the rate of being epitaxially coalesced to the surface of the silicon carbide seed crystal by the action of surface energy, the grain growth proceeds, making it difficult to form a single crystal, resulting in a polycrystal. The growth rate of the silicon carbide single crystal due to is determined by the rate at which ultrafine silicon carbide particles are taken into the surface of the silicon carbide seed crystal.
[0019]
【Example】
Example 1
As an example of a manufacturing apparatus for obtaining the silicon carbide single crystal of the present invention, a silicon carbide single crystal was manufactured using a manufacturing apparatus as shown in FIG. The manufacturing apparatus of FIG. 1 has a cylindrical and sealed
[0020]
The mixed solution was prepared by adding 118 g of methyl silicate as a silicon dioxide-containing compound (containing silicon dioxide = 60 g), 94 g of phenol (containing carbon = 36 g) as a carbon-containing compound, and 1 g of NaOH and adding an appropriate amount of water and stirring well. After mixing, dehydration, drying, pulverization, and carbonization at about 300 ° C. produce raw material powder. By supplying this
[0021]
【The invention's effect】
The silicon carbide single crystal of the present invention forms a liquid film on the surface of the silicon carbide seed crystal, and then is converted to silicon carbide by the reaction of silicon dioxide and carbon in the liquid film. A silicon carbide single crystal having no through-hole such as a micropipe can be grown thereon.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of a production apparatus for obtaining a silicon carbide single crystal of the present invention.
[Explanation of symbols]
1
Claims (6)
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Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN102803583A (en) * | 2009-06-11 | 2012-11-28 | 日本碍子株式会社 | Method for growing single crystal of group III metal nitride and reaction vessel for use in same |
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EP1739211A4 (en) | 2004-12-28 | 2008-01-23 | Matsushita Electric Ind Co Ltd | METHOD FOR PRODUCING SILICON CARBIDE (SiC) SINGLE CRYSTAL AND SILICON CARBIDE (SiC) SINGLE CRYSTAL OBTAINED BY SUCH METHOD |
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CN102803583A (en) * | 2009-06-11 | 2012-11-28 | 日本碍子株式会社 | Method for growing single crystal of group III metal nitride and reaction vessel for use in same |
CN102803583B (en) * | 2009-06-11 | 2015-11-25 | 日本碍子株式会社 | The cultural method of group III metal nitride single crystal and the reaction vessel for the method |
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