JP2010037156A - Method for producing group iii nitride compound semiconductor and gallium nitride self-supporting substrate - Google Patents

Method for producing group iii nitride compound semiconductor and gallium nitride self-supporting substrate Download PDF

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JP2010037156A
JP2010037156A JP2008202903A JP2008202903A JP2010037156A JP 2010037156 A JP2010037156 A JP 2010037156A JP 2008202903 A JP2008202903 A JP 2008202903A JP 2008202903 A JP2008202903 A JP 2008202903A JP 2010037156 A JP2010037156 A JP 2010037156A
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group iii
compound semiconductor
nitride compound
iii nitride
sapphire substrate
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JP4985579B2 (en
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Yasuhide Yakushi
康英 薬師
Shiro Yamazaki
史郎 山崎
Seiji Nagai
誠二 永井
Shinyuki Sato
峻之 佐藤
Takahiro Sonoyama
貴広 園山
Koji Okuno
浩司 奥野
Koichi Goshonoo
浩一 五所野尾
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Toyoda Gosei Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To produce a group III nitride compound semiconductor having the major face forming a minute off-angle with the m-plane. <P>SOLUTION: A concavo-convex pattern is formed on a sapphire substrate 10 and only the faces 10c-1 having the same normal vector direction in the c-plane or side faces making an angle of not more than 20 degrees with the c-plane are exposed while other faces are covered with an epitaxially grown mask 20 comprising SiO<SB>2</SB>(3.A). The method is carried out at normal pressure while maintaining a high V/III ratio in a period from when a GaN layer 30 starts to grow (3.B) until the layer buries grooves (3.C). In the period from when the grooves are buried until the top face of the convex portion is covered and flattened (3.D), the process is carried out under reduced pressure while controlling the V/III ratio to be low (by reducing the supplying amount of ammonia to 1/5). After the convex portion is mostly covered and flattened (3.E), the process is carried out at normal pressure while controlling the V/III ratio to be high (by resuming the original supply amount of ammonia). Thus, a GaN film having the major face as a flat surface forming the minute off-angle with the m-plane can be formed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

本発明は、III族窒化物系化合物半導体の製造方法に関する。本願においてIII族窒化物系化合物半導体とは、ＡｌxＧａyＩｎ1-x-yＮ（ｘ、ｙ、ｘ＋ｙはいずれも０以上１以下）で示される半導体、及び、ｎ型化／ｐ型化等のために任意の元素を添加したものを含む。更には、III族元素及びＶ族元素の組成の一部を、Ｂ又はＴｌ、或いは、Ｐ、Ａｓ、Ｓｂ又はＢｉで置換したものをも含むものとする。 The present invention relates to a method for producing a group III nitride compound semiconductor. In the present application, the group III nitride compound semiconductor is a semiconductor represented by Al x Ga y In 1-xy N (where x, y, and x + y are all 0 or more and 1 or less), n-type / p-type, etc. For which any element is added. Furthermore, it is intended to include those in which a part of the composition of the group III element and the group V element is substituted with B or Tl, or P, As, Sb or Bi.

緑色、青色、或いは紫外線発光素子として、III族窒化物系化合物半導体発光素子が広く使用されている。また、III族窒化物系化合物半導体を用いたＨＥＭＴ等も多数提案されている。これらは、通常、サファイア、シリコン、又は炭化ケイ素のような異種基板上に、III族窒化物系化合物半導体をエピタキシャル成長させて形成されたものである。III族窒化物系化合物半導体は、ｃ軸方向に積層するエピタキシャル成長が結晶性が良く、また最も速い成長が得られる。
特許文献１は、III族窒化物系化合物半導体の主面としてｃ面とは異なる面を形成するための技術についての、本出願人による先行出願の公開公報である。
特開２００６−０３６５６１号公報 Group III nitride compound semiconductor light emitting devices are widely used as green, blue, or ultraviolet light emitting devices. Many HEMTs using Group III nitride compound semiconductors have also been proposed. These are usually formed by epitaxially growing a group III nitride compound semiconductor on a dissimilar substrate such as sapphire, silicon, or silicon carbide. Group III nitride compound semiconductors have good crystallinity for epitaxial growth stacked in the c-axis direction, and the fastest growth is obtained.
Patent Document 1 is a publication of a prior application filed by the present applicant regarding a technique for forming a surface different from the c-plane as a main surface of a group III nitride compound semiconductor.
JP 2006-036561 A

しかし、III族窒化物系化合物半導体は、ｃ軸方向にピエゾ電界が生じることが指摘されている。これにより、例えば多重量子井戸構造の発光層において、電子とホールの高濃度部分が異なる結果を生じ、発光効率の低下が生じるとされている。
本発明者らは、III族窒化物系化合物半導体の主面としてｃ面とは異なる面を形成するための技術として新たな着想から本発明を完成させた。 However, it has been pointed out that a group III nitride compound semiconductor generates a piezoelectric field in the c-axis direction. As a result, for example, in a light emitting layer having a multiple quantum well structure, the result is that the high-concentration portions of electrons and holes are different, and the light emission efficiency is reduced.
The present inventors have completed the present invention from a new idea as a technique for forming a surface different from the c-plane as the main surface of a group III nitride compound semiconductor.

請求項１に係る発明は、サファイア基板上にIII族窒化物系化合物半導体をエピタキシャル成長させる、III族窒化物系化合物半導体の製造方法において、
サファイア基板の主面の法線ベクトルが、ａ軸からｃ軸方向に０．２度以上５度以下回転させた方向であり、
サファイア基板にｃ面又はｃ面と成す角が２０度以下の側面を有する凹凸を形成し、
当該側面のうち、法線ベクトルの向きが同じで、当該法線ベクトルとサファイア基板のａ軸との成す角の大きい方の側面のみが露出するように、他のサファイア基板の表面をIII族窒化物系化合物半導体がエピタキシャル成長しないマスク材料により覆い、
マスク材料により覆われていない、サファイア基板の露出したｃ面又はｃ面と成す角が２０度以下の側面からIII族窒化物系化合物半導体をエピタキシャル成長させることにより、主面が、ｍ面と０．２度以上５度以下の角を成すIII族窒化物系化合物半導体結晶を得ることを特徴とするIII族窒化物系化合物半導体の製造方法である。 The invention according to claim 1 is a method for producing a group III nitride compound semiconductor in which a group III nitride compound semiconductor is epitaxially grown on a sapphire substrate.
The normal vector of the main surface of the sapphire substrate is a direction rotated from 0.2 degrees to 5 degrees in the c-axis direction from the a-axis,
Forming concavo-convex having a c-plane or a c-plane or a side face with an angle of 20 degrees or less on the sapphire substrate,
The surface of the other sapphire substrate is group III-nitrided so that only the side with the larger normal angle between the normal vector and the a-axis of the sapphire substrate is exposed. Cover with a mask material that does not grow epitaxially compound semiconductors,
By epitaxially growing a group III nitride compound semiconductor from an exposed c-plane of the sapphire substrate or an angle formed with the c-plane that is not covered by the mask material and having an angle of 20 degrees or less, the main surface becomes the m-plane and 0. A method for producing a group III nitride compound semiconductor comprising obtaining a group III nitride compound semiconductor crystal having an angle of 2 degrees or more and 5 degrees or less.

ここにおいて、ｃ面又はｃ面と成す角が２０度以下の側面のうちの法線ベクトルの向きが同じ面のみが露出するとは、次のことを意味する。
例えばサファイア基板に凹凸を設けて凹凸の側面としてｃ面を形成する場合に、表裏の関係にあるｃ面からは、III族窒化物系化合物半導体が成長するが、サファイア基板の凹凸の表側の側面から成長するIII族窒化物系化合物半導体と、サファイア基板の凹凸の裏側の側面から成長するIII族窒化物系化合物半導体とは、成長方向が１８０度異なる。すると、例えば凹凸を覆うようにまで成長させても、それらサファイア基板の凹凸の表側の側面から成長したIII族窒化物系化合物半導体と、サファイア基板の凹凸の裏側の側面から成長したIII族窒化物系化合物半導体とは、結晶成長しても界面に極性の異なる不連続面が残ってしまう。
そこで、サファイア基板の凹凸の表側の側面と裏側の側面のうち一方のみを露出させる。これをサファイア基板の凹凸全てで行うものである。こうすることで、凹凸を覆うようにまで成長させたのち、異なる側面から成長した結晶の接合面は極性が同じとなるので、不連続面とならない。
また、凹凸の側面のうち、その法線ベクトルが同じで、当該法線ベクトルとサファイア基板のａ軸との成す角の大きい方の側面とは、次のことを意味する。図１に示す通り、主面の法線ベクトルがａ軸からδ（ｄｅｇ）＞０だけｃ軸側に反時計回りに傾いているとする。角度表示を反時計回りを正とし、凹凸の２つの側面の法線ベクトルが主面の方線ベクトルに対して対称に、９０−θ（ｄｅｇ）と−９０＋θ（ｄｅｇ）であるとする。ａ軸と成す角は各々９０−θ＋δ（ｄｅｇ）と−９０＋θ＋δ（ｄｅｇ）である。これらのうち、絶対値が大きい方は、９０−θ＋δ（ｄｅｇ）である。これはθの符号が正負いずれであっても成立する。 Here, the fact that only the surface having the same direction of the normal vector in the c-plane or the side surface having an angle of 20 degrees or less formed with the c-plane is exposed means the following.
For example, when a sapphire substrate is provided with unevenness to form a c-plane as the side surface of the unevenness, a group III nitride compound semiconductor grows from the c-plane having a front-back relationship. The group III nitride compound semiconductor that grows from the surface of the sapphire substrate and the group III nitride compound semiconductor that grows from the side surface on the back side of the unevenness of the sapphire substrate have a growth direction different by 180 degrees. Then, for example, even if it grows so as to cover the unevenness, the group III nitride compound semiconductor grown from the front side surface of the sapphire substrate and the group III nitride grown from the back surface side of the sapphire substrate unevenness With a compound compound semiconductor, even if crystals grow, discontinuous surfaces with different polarities remain at the interface.
Therefore, only one of the front side surface and the back side surface of the sapphire substrate is exposed. This is performed with all the irregularities of the sapphire substrate. In this way, after growing so as to cover the unevenness, the crystal bonding surfaces grown from different side surfaces have the same polarity, and thus do not become discontinuous surfaces.
Moreover, the side surface with the same normal vector among the side surfaces of the unevenness, and the side surface with the larger angle formed by the normal vector and the a-axis of the sapphire substrate means the following. As shown in FIG. 1, it is assumed that the normal vector of the main surface is tilted counterclockwise from the a-axis to the c-axis side by δ (deg)> 0. Assume that the angle display is positive in the counterclockwise direction, and the normal vectors of the two side surfaces of the unevenness are 90−θ (deg) and −90 + θ (deg) symmetrically with respect to the normal vector of the main surface. The angles formed with the a-axis are 90−θ + δ (deg) and −90 + θ + δ (deg), respectively. Of these, the one with the larger absolute value is 90−θ + δ (deg). This is true regardless of whether the sign of θ is positive or negative.

請求項２に係る発明は、マスク材料により覆われていない、サファイア基板の凹凸の露出した側面は、ｃ面と成す角が０．５度以下であることを特徴とする。
請求項３に係る発明は、 III族窒化物系化合物半導体の形成においては、８００度未満の温度でバッファ層を形成したのち、１０００度以上の温度で単結晶層を形成することを特徴とする。
請求項４に係る発明は、バッファ層はマスク材料を形成する前に形成されることを特徴とする。
請求項５に係る発明は、III族窒化物系化合物半導体は、窒化ガリウム（ＧａＮ）であることを特徴とする。
請求項６に係る発明は、エピタキシャル成長は、トリメチルガリウムとアンモニアを用いた有機金属気相成長法（ＭＯＶＰＥ）により行うものであり、アンモニア供給量のトリメチルガリウムの供給量に対するＶ／III比について、凹凸の凹部を埋めるまではＶ／III比を高く、凹凸の凸部をエピタキシャル成長膜が覆いつくすまではＶ／III比を低く、凹凸の凸部をエピタキシャル成長膜が覆いつくした以降はＶ／III比を高くすることを特徴とする。
請求項７に係る発明は、請求項６に記載のIII族窒化物系化合物半導体の製造方法によるエピタキシャル成長の後、更にハライド気相成長法により厚さ２００μｍ以上に窒化ガリウム単結晶を成長させ、その後冷却する際に劈開を生じさせてサファイア基板と分離することを特徴とする窒化ガリウム自立基板の製造方法である。 The invention according to claim 2 is characterized in that an angle formed between the concavo-convex exposed side surface of the sapphire substrate, which is not covered with a mask material, and the c-plane is 0.5 degrees or less.
The invention according to claim 3 is characterized in that, in the formation of the group III nitride compound semiconductor, the single crystal layer is formed at a temperature of 1000 ° C. or higher after forming the buffer layer at a temperature of less than 800 ° C. .
The invention according to claim 4 is characterized in that the buffer layer is formed before the mask material is formed.
The invention according to claim 5 is characterized in that the group III nitride compound semiconductor is gallium nitride (GaN).
In the invention according to claim 6, the epitaxial growth is performed by metal organic vapor phase epitaxy (MOVPE) using trimethylgallium and ammonia, and the V / III ratio of the ammonia supply amount to the trimethylgallium supply amount is uneven. The V / III ratio is high until the recesses are filled, the V / III ratio is low until the epitaxial growth film covers the uneven projections, and the V / III ratio is increased after the epitaxial growth film covers the projections. It is characterized by being raised.
The invention according to claim 7 is a method in which after the epitaxial growth by the method for producing a group III nitride compound semiconductor according to claim 6, a gallium nitride single crystal is further grown to a thickness of 200 μm or more by a halide vapor phase growth method, and thereafter A method of manufacturing a gallium nitride free-standing substrate, wherein cleavage is caused to separate from a sapphire substrate when cooling.

サファイア基板に凹凸を設けて、ｃ面又はｃ面と成す角が２０度以下の側面のうちの法線ベクトルの向きが同じ面のみを露出させる。この際、当該側面はサファイア基板の低指数面ではないので、結局サファイア基板のｃ面が微細な段差を伴って露出するステップ状の面となる。すると、そこにエピタキシャル成長するIII族窒化物系化合物半導体は、当該ステップ毎に、サファイア基板のｃ面に形成した形になる。即ち、階段状に露出したサファイア基板のｃ面に平行となるように、III族窒化物系化合物半導体のｃ面が形成される。
ここで用いるサファイア基板は、主面がａ面からわずかにオフしているので、形成されるIII族窒化物系化合物半導体のｍ面が、サファイア基板のａ面に平行に形成されることになる。
こうして、用いるサファイア基板の主面と平行なIII族窒化物系化合物半導体の表面は、＋ｃ面がステップの側面となる方向へオフしたｍ面となる。この方向にオフが形成されると、主面にほぼ平行な横方向の成長が大幅に促進され、平坦性の極めて優れたｍ面のエピタキシャル成長層を形成することができる。 An uneven surface is provided on the sapphire substrate, and only the surface having the same direction of the normal vector among the side surfaces having an angle of 20 degrees or less formed with the c surface or the c surface is exposed. At this time, since the side surface is not a low index surface of the sapphire substrate, the c-plane of the sapphire substrate eventually becomes a stepped surface that is exposed with a fine step. Then, the group III nitride compound semiconductor epitaxially grown thereon is formed on the c-plane of the sapphire substrate at each step. That is, the c-plane of the group III nitride compound semiconductor is formed so as to be parallel to the c-plane of the sapphire substrate exposed stepwise.
Since the main surface of the sapphire substrate used here is slightly off from the a-plane, the m-plane of the group III nitride compound semiconductor to be formed is formed parallel to the a-plane of the sapphire substrate. .
Thus, the surface of the group III nitride compound semiconductor parallel to the main surface of the sapphire substrate to be used is an m-plane that is turned off in the direction in which the + c plane becomes the side surface of the step. When OFF is formed in this direction, lateral growth substantially parallel to the main surface is greatly promoted, and an m-plane epitaxial growth layer with extremely excellent flatness can be formed.

例えば本発明により、III族窒化物系化合物半導体を厚膜結晶として得て、サファイア基板から分離すれば、厚さ方向がｃ軸方向とほぼ直角の、ほとんど無極性のＧａＮ基板が得られる。III族窒化物系化合物半導体はｍ面で劈開し易いので、例えば厚膜結晶を形成後、室温まで冷やす際にサファイア基板との界面近傍に劈開が生じ、厚膜の自立基板を得ることができる（請求項７）。
また、ｍ面からわずかにオフした主面を有するIII族窒化物系化合物半導体膜又はIII族窒化物系化合物半導体基板が得られるので、この上に、更にIII族窒化物系化合物半導体層を積層することで、積層方向（膜厚方向）に歪の生じない半導体素子等を容易に形成することが可能となる。
更には、公知の方法により、より厚膜にIII族窒化物系化合物半導体を結晶成長させることにより、ｍ面からわずかにオフした主面を有する、III族窒化物系化合物半導体の厚膜基板（自立基板）を得ることも可能となる。 For example, according to the present invention, when a group III nitride compound semiconductor is obtained as a thick film crystal and separated from the sapphire substrate, an almost nonpolar GaN substrate having a thickness direction substantially perpendicular to the c-axis direction can be obtained. Since group III nitride compound semiconductors are easy to cleave in the m-plane, for example, when a thick film crystal is formed and then cooled to room temperature, cleavage occurs in the vicinity of the interface with the sapphire substrate, and a thick self-supporting substrate can be obtained. (Claim 7).
Further, a group III nitride compound semiconductor film or a group III nitride compound semiconductor substrate having a main surface slightly off from the m-plane can be obtained, and a group III nitride compound semiconductor layer is further laminated thereon. By doing so, it is possible to easily form a semiconductor element or the like that does not cause distortion in the stacking direction (film thickness direction).
Further, a group III nitride compound semiconductor thick film substrate having a main surface slightly off from the m-plane by crystal growth of a group III nitride compound semiconductor in a thicker film by a known method ( It is also possible to obtain a self-supporting substrate).

オフ角が０．２度未満であると、横方向の成長が促進されず、平坦性が悪化したり、隣あうエピタキシャル成長部分が完全に合体せずに隙間（ボイド）が残ってしまう。一方、オフ角が５度を越えると、主面がｍ面から大きく異なる面となる。例えばこのような半導体膜に更にエピタキシャル成長を繰り返して半導体素子を形成すると、積層した各層の厚さ方向にｃ軸方向のピエゾ電界の影響が大きくなる。   If the off angle is less than 0.2 degrees, lateral growth is not promoted, flatness is deteriorated, and adjacent epitaxial growth portions are not completely combined, and voids remain. On the other hand, when the off-angle exceeds 5 degrees, the main surface becomes a surface that differs greatly from the m-plane. For example, when a semiconductor element is formed by repeating epitaxial growth on such a semiconductor film, the influence of the piezoelectric field in the c-axis direction increases in the thickness direction of each stacked layer.

用いるサファイア基板について、主面のオフ方向は、ｍ軸を中心とした回転により得られるものである。ｃ軸を中心とした回転は０．５度未満で良い。これにより、サファイア基板のｍ軸が主面と略平行となるので、その上に本発明により形成されるIII族窒化物系化合物半導体については、そのａ軸が略主面と平行となる。   For the sapphire substrate used, the off direction of the main surface is obtained by rotation about the m-axis. The rotation around the c-axis may be less than 0.5 degrees. Thereby, since the m-axis of the sapphire substrate is substantially parallel to the main surface, the a-axis of the group III nitride compound semiconductor formed thereon according to the present invention is substantially parallel to the main surface.

サファイア基板面に、凹凸を形成する方法は、任意の加工方法を用いることができる。例えばエッチングマスクを用いたエッチングにより凹凸を形成すると良い。サファイア基板に形成する凹凸は、欲しいｃ面又はｃ面と２０度以下の角度を成す面以外の面を形成しないことが望ましいので、例えばサファイア基板のｍ軸に平行な多数のストライプ状に溝を形成すると良い。
この場合、エッチングにより形成される凹部の幅が１〜１０μｍ、エッチングされずに残る凸部の幅が１〜１０μｍ、凹部と凸部の高低差が１〜１０μｍ程度とすると好適である。溝部が狭すぎると、結晶原料が到達しにくくなり、また、狭い領域でのエピタキシャル成長では良質な結晶が望めない。一方、凸部の幅が広すぎると、凸部を覆うまでに時間がかかり、完全に平坦化するのが困難となる。
エピタキシャル成長の際に形成する、ｃ面又はｃ面と２０度以下の角度を成す面以外の面を覆うマスク材料は、III族窒化物系化合物半導体がエピタキシャル成長しない任意の材料を用いることができる。例えばＳｉＯ2が簡易に用いることができる。形成方法も任意であるが、ＳｉＯ2を用いる場合、電子線蒸着又はプラズマＣＶＤにより精度良くマスクを形成できる。 An arbitrary processing method can be used as a method of forming irregularities on the sapphire substrate surface. For example, the unevenness may be formed by etching using an etching mask. It is desirable that the irregularities formed on the sapphire substrate do not form a desired c-plane or a plane other than a plane that forms an angle of 20 degrees or less with the c-plane. It is good to form.
In this case, it is preferable that the width of the concave portion formed by etching is 1 to 10 μm, the width of the convex portion remaining without being etched is 1 to 10 μm, and the height difference between the concave portion and the convex portion is about 1 to 10 μm. If the groove is too narrow, the crystal raw material is difficult to reach, and high-quality crystals cannot be expected by epitaxial growth in a narrow region. On the other hand, if the width of the convex portion is too wide, it takes time to cover the convex portion, and it becomes difficult to completely flatten the convex portion.
As the mask material that covers the surface other than the c-plane or a plane that forms an angle of 20 degrees or less with the c-plane formed during the epitaxial growth, any material that does not allow the group III nitride compound semiconductor to grow epitaxially can be used. For example, SiO 2 can be easily used. Although the formation method is also arbitrary, when SiO 2 is used, the mask can be formed with high accuracy by electron beam evaporation or plasma CVD.

Ｖ／III比を高くするとは、例えばアンモニアとトリメチルガリウムのモル比を８００以上、より好ましくは１０００以上とすると良い。
Ｖ／III比を低くするとは、例えばアンモニアとトリメチルガリウムのモル比を６００以下、より好ましくは３００以下とすると良い。 To increase the V / III ratio, for example, the molar ratio of ammonia and trimethylgallium is 800 or more, more preferably 1000 or more.
To lower the V / III ratio, for example, the molar ratio of ammonia to trimethylgallium is 600 or less, more preferably 300 or less.

以下、図を用いて本発明の具体的な一実施例について説明する。
主面が、ａ面と１度のオフ角を成すサファイア基板１０を用意し、その長手方向がｍ軸方向に平行なストライプ状の凹凸を形成した。図２．Ａに示すように、サファイア基板１０に垂直なエッチングにより、溝部の底１０ｖが形成され、エッチングされなかった凸部の表面１０ｔと、表裏の関係にある、法線ベクトルの向きが１８０度異なる２つの側面１０ｃ−１及び１０ｃ−２が形成された。ここで、紙面に垂直な方向がｍ軸である。
このうち、側面１０ｃ−１及び１０ｃ−２からは、サファイアのｃ軸方向に、III族窒化物系化合物半導体の＋ｃ軸が一致するように、III族窒化物系化合物半導体がエピタキシャル成長しうるものである。側面１０ｃ−１及び１０ｃ−２からのエピタキシャル成長を共存させると、ｃ軸方向に極性を有するIII族窒化物系化合物半導体が異なる方向から成長するため、接合面が不連続面となり、好ましくない。
ここで、側面１０ｃ−１の法線ベクトルが、図１で示したａ軸と９０−θ＋δ（ｄｅｇ）の角度を成し、側面１０ｃ−２の法線ベクトルが、図１で示したａ軸と−９０＋θ＋δ（ｄｅｇ）の角度を成すことに着目すると、ａ軸と法線ベクトルの成す角の絶対値の大きい側面１０ｃ−１を用いる方が好適である。これは形成されるIII族窒化物系化合物半導体の＋ｃ軸方向が、サファイア基板１０の主面に対して、サファイア基板１０内部から外部への向きであるのに対し、側面１０ｃ−２は、形成されるIII族窒化物系化合物半導体の＋ｃ軸方向が、サファイア基板１０の主面に対して、サファイア基板１０外部から内部への向きである。ここにおいて、側面１０ｃ−２からのIII族窒化物系化合物半導体のエピタキシャル成長の際には、成長が最も著しいｃ面は、ストライプ状の凹部にもぐり込む形となり、凸部より高い位置に形成される可能性がない。一方、側面１０ｃ−１からのIII族窒化物系化合物半導体のエピタキシャル成長の際には、成長が最も著しいｃ面は、少なくともその一部がストライプ状の凸部より高い位置に到達し、その後、言わば横方向である＋ｃ軸方向の成長により凸部を迅速に覆うことが可能となる。
このように、III族窒化物系化合物半導体の＋ｃ軸方向の成長を期待するため、側面１０ｃ−１は露出させ、側面１０ｃ−２はマスクで覆うことが好ましい。
図２．Ａで、ストライプ状の凸部の幅、凹部の幅を共に２μｍとした。即ち、４μｍ周期のストライプとなる。凸部上面と凹部底面の高低差は２μｍとした。
溝の角度、即ち表裏の関係にある２つの側面１０ｃ−１及び１０ｃ−２は、ａ面と１度のオフ角を成すサファイア基板１０の主面に対し垂直に形成した。この角度は、正確な９０度（即ちｃ面と１度のオフ角を成す面）でなくて良く、７０度以上１１０度以下であれば良い。即ちサファイア基板のａ面に対し、２つの側面１０ｃ−１及び１０ｃ−２は、６９度以上１１１度以下（ｍ軸の回りの回転角でもある）でよい。
エッチングの際にマスクとしてＳｉＯ2を用いる場合は、８０〜９０度に制御可能である。 Hereinafter, a specific embodiment of the present invention will be described with reference to the drawings.
A sapphire substrate 10 having a main surface forming an off angle of 1 degree with the a-plane was prepared, and striped irregularities whose longitudinal direction was parallel to the m-axis direction were formed. FIG. As shown in A, the bottom 10v of the groove is formed by etching perpendicular to the sapphire substrate 10, and the direction of the normal vector, which is in the relation of the front and back, is 180 degrees different from the surface 10t of the unetched convex portion 2 Two side surfaces 10c-1 and 10c-2 were formed. Here, the direction perpendicular to the paper surface is the m-axis.
Among these, from the side surfaces 10c-1 and 10c-2, the group III nitride compound semiconductor can be epitaxially grown so that the + c axis of the group III nitride compound semiconductor coincides with the c-axis direction of sapphire. is there. If the epitaxial growth from the side surfaces 10c-1 and 10c-2 coexists, the group III nitride compound semiconductor having polarity in the c-axis direction grows from different directions, so that the bonding surface becomes a discontinuous surface, which is not preferable.
Here, the normal vector of the side surface 10c-1 forms an angle of 90-θ + δ (deg) with the a axis shown in FIG. 1, and the normal vector of the side surface 10c-2 is the a axis shown in FIG. Note that it is preferable to use the side surface 10c-1 having a large absolute value of the angle formed by the a-axis and the normal vector. This is because the + c-axis direction of the group III nitride compound semiconductor to be formed is directed from the inside of the sapphire substrate 10 to the outside with respect to the main surface of the sapphire substrate 10, whereas the side surface 10c-2 is formed. The + c-axis direction of the group III nitride compound semiconductor is the direction from the outside to the inside of the sapphire substrate 10 with respect to the main surface of the sapphire substrate 10. Here, in the case of the epitaxial growth of the group III nitride compound semiconductor from the side surface 10c-2, the c-plane where the growth is most remarkable is formed in a shape of a stripe-shaped recess and can be formed at a position higher than the protrusion. There is no sex. On the other hand, during the epitaxial growth of the group III nitride compound semiconductor from the side surface 10c-1, the c-plane where growth is most remarkable reaches a position where at least a part thereof is higher than the stripe-shaped convex portion. The convex portion can be covered quickly by the growth in the + c-axis direction which is the lateral direction.
Thus, in order to expect the growth of the group III nitride compound semiconductor in the + c-axis direction, it is preferable that the side surface 10c-1 is exposed and the side surface 10c-2 is covered with a mask.
FIG. In A, the width of the stripe-shaped convex part and the width of the concave part were both 2 μm. That is, the stripe has a period of 4 μm. The height difference between the top surface of the convex portion and the bottom surface of the concave portion was 2 μm.
The two side surfaces 10c-1 and 10c-2 having a groove angle, that is, a front-back relationship, were formed perpendicular to the main surface of the sapphire substrate 10 having an off angle of 1 degree with respect to the a-plane. This angle does not have to be an exact 90 degrees (that is, a plane that forms an off angle of 1 degree with the c-plane), and may be 70 degrees or more and 110 degrees or less. That is, the two side surfaces 10c-1 and 10c-2 may be 69 degrees or more and 111 degrees or less (also a rotation angle around the m-axis) with respect to the a-plane of the sapphire substrate.
When SiO 2 is used as a mask during etching, it can be controlled to 80 to 90 degrees.

次に、ＳｉＯ2から成るエピ成長マスク２０を電子線（ＥＢ）蒸着により形成した。この際、図２．Ｂの太い矢印に示す通り、ＳｉＯ2の蒸着方向が、サファイア基板１０の主面に垂直な方向から、側面１０ｃ−２に当たる方向まで、掃引されるようにサファイア基板１０の向きを回転させると良い。この際、側面１０ｃ−１にはＳｉＯ2から成るエピ成長マスク２０が形成されないようにした。こうして凹凸加工を施したサファイア基板１０の、面１０ｔ、１０ｖ及び１０ｃ−２に厚さ５００ｎｍのＳｉＯ2から成るエピ成長マスク２０が蒸着された（図２．Ｂ）。
次に、露出すべき側面１０ｃ−１に一部付着する異物を、フッ酸を添加した希硝酸溶液で処理した。例えば、市販のフッ酸、濃硫酸及び水を３：２：２００の比率で混合すると良い。こうして、サファイア基板１０のｃ面と成す角が２０度以下の凹凸の側面１０ｃ−１以外がＳｉＯ2から成るエピ成長マスク２０で覆われたエピタキシャル成長基板が得られた（図２．Ｃ）。 Next, an epitaxial growth mask 20 made of SiO 2 was formed by electron beam (EB) evaporation. At this time, FIG. As indicated by the thick arrow B, the direction of the sapphire substrate 10 may be rotated so that the SiO 2 deposition direction is swept from the direction perpendicular to the main surface of the sapphire substrate 10 to the direction corresponding to the side surface 10c-2. . At this time, the epitaxial growth mask 20 made of SiO 2 was not formed on the side surface 10c-1. An epi-growth mask 20 made of SiO 2 having a thickness of 500 nm was deposited on the surfaces 10t, 10v, and 10c-2 of the sapphire substrate 10 thus subjected to uneven processing (FIG. 2.B).
Next, the foreign matter partially adhering to the side surface 10c-1 to be exposed was treated with a diluted nitric acid solution to which hydrofluoric acid was added. For example, commercially available hydrofluoric acid, concentrated sulfuric acid, and water may be mixed at a ratio of 3: 2: 200. In this way, an epitaxial growth substrate was obtained in which the surface other than the uneven side surface 10c-1 having an angle of 20 degrees or less with the c-plane of the sapphire substrate 10 was covered with the epitaxial growth mask 20 made of SiO 2 (FIG. 2.C).

サファイア基板１０のｃ面と成す角（ｍ軸の回りの回転角）が２０度以下の凹凸の側面１０ｃ−１以外がＳｉＯ2から成るエピ成長マスク２０で覆われたエピタキシャル成長基板をＭＯＣＶＤ装置に装着した（図３．Ａ、図２．Ｃの再掲）。
エピタキシャル成長は、基本的には次の通りに実行した。まず、サファイア基板１０の表面を１１００℃でベークした。次に基板温度を６００℃として、ＧａＮから成る低温バッファ層を形成した。この後、１１００℃でＧａＮ層３０を形成した。 An epitaxial growth substrate in which an angle formed with the c-plane of the sapphire substrate 10 (rotational angle about the m-axis) is 20 degrees or less, except for the uneven side surface 10c-1, which is covered with an epitaxial growth mask 20 made of SiO 2 is mounted on the MOCVD apparatus. (Reposted in FIG. 3.A and FIG. 2.C).
Epitaxial growth was basically performed as follows. First, the surface of the sapphire substrate 10 was baked at 1100 ° C. Next, the substrate temperature was set to 600 ° C., and a low-temperature buffer layer made of GaN was formed. Thereafter, the GaN layer 30 was formed at 1100 ° C.

ＧａＮ層３０の形成は次のようにした。まず、サファイア基板１０のｃ面と成す角が２０度以下の凹凸の側面１０ｃ−１からＧａＮ層３０が成長を開始してから（図３．Ｂ）、溝部を埋める迄（図３．Ｃ）は、常圧で、Ｖ／III比を高く保った。即ち、アンモニアを７．５Ｌ／分（３３６ｍｍｏｌ／分）、トリメチルガリウムを２８５μｍｏｌ／分、Ｖ／III比を１１８０とした。
溝部が埋まり、凸部の上面がほぼ覆われて平坦化する（図３．Ｄ）までは、減圧で、Ｖ／III比を低く（アンモニアの供給量を１／５と）した。即ち、アンモニアを１．５Ｌ／分（６７ｍｍｏｌ／分）、トリメチルガリウムを２８５μｍｏｌ／分、Ｖ／III比を２３６とした。
凸部の上面がほぼ覆われて平坦化した後（図３．Ｅ）は、常圧で、Ｖ／III比を高くした（アンモニアの供給量を元に戻した）。即ち、アンモニアを７．５Ｌ／分（３３６ｍｍｏｌ／分）、トリメチルガリウムを２８５μｍｏｌ／分、Ｖ／III比を１１８０とした。
こうして得られた結晶はストライプ状の凹凸が完全に覆われ、主面が、ｍ面と１度のオフ角を成す平坦な面であるＧａＮ膜が形成できた。得られた結晶表面の平坦性をＡＦＭで促成したところ、ＲＭＳが１．０ｎｍであった。
尚、図３．Ｄ及び図３．Ｅでは、ＧａＮ層３０の成長面である表面に大きなステップがある記載をしているが、これは、ＧａＮ層３０の成長面の微細構造が、ステップ状であることを示しているものである。即ち、サファイア基板１０に設けた凹凸と、ＧａＮ層３０のステップとは、その大きさの関係が図３．Ｄ及び図３．Ｅに示されたものではない。
あくまでも、ＧａＮ層３０の成長面がｍ面から１度のオフ角を成すため、その微細構造はｍ面と、幅の狭い＋ｃ面の段差の繰り返しであることを示しているに過ぎない。図３．Ｄ及び図３．Ｅは、言わばデフォルメした図である。 The GaN layer 30 was formed as follows. First, after the growth of the GaN layer 30 from the uneven side surface 10c-1 whose angle formed with the c-plane of the sapphire substrate 10 is 20 degrees or less (FIG. 3.B), the groove is filled (FIG. 3.C). Kept the V / III ratio high at normal pressure. That is, ammonia was 7.5 L / min (336 mmol / min), trimethylgallium was 285 μmol / min, and the V / III ratio was 1180.
The V / III ratio was lowered (ammonia supply amount was 1/5) under reduced pressure until the groove portion was filled and the upper surface of the convex portion was almost covered and flattened (FIG. 3.D). That is, ammonia was 1.5 L / min (67 mmol / min), trimethylgallium was 285 μmol / min, and the V / III ratio was 236.
After the upper surface of the convex portion was almost covered and flattened (FIG. 3.E), the V / III ratio was increased at normal pressure (the supply amount of ammonia was restored). That is, ammonia was 7.5 L / min (336 mmol / min), trimethylgallium was 285 μmol / min, and the V / III ratio was 1180.
The crystal thus obtained was completely covered with stripe-shaped irregularities, and a GaN film in which the main surface was a flat surface having an off angle of 1 degree with the m-plane could be formed. When the flatness of the obtained crystal surface was promoted by AFM, the RMS was 1.0 nm.
FIG. D and FIG. E describes that there is a large step on the growth surface of the GaN layer 30, which indicates that the microstructure of the growth surface of the GaN layer 30 is stepped. . That is, the size relationship between the unevenness provided on the sapphire substrate 10 and the step of the GaN layer 30 is shown in FIG. D and FIG. Not shown in E.
To the last, the growth surface of the GaN layer 30 forms an off angle of 1 degree from the m-plane, so that the fine structure merely shows that the step between the m-plane and the narrow + c-plane is repeated. FIG. D and FIG. E is a deformed figure.

上記実施例によれば、４μｍ間隔に形成された側面１０ｃ−１を核（成長開始領域）として横方向成長によりエピ成長マスク２０上部をも覆うようにエピタキシャル成長される。エピ成長マスク２０上部で、隣り合う２つの側面１０ｃ−１からのエピタキシャル結晶が合体する周期も４μｍ間隔となる。
即ち、本発明によれば側面１０ｃ−１のみをエピタキシャル成長の核とするので、基板面全体として極性の揃った、高品質の結晶が得られる。 According to the above embodiment, the epitaxial growth is performed so as to cover the upper part of the epi-growth mask 20 by lateral growth with the side surface 10c-1 formed at intervals of 4 μm as nuclei (growth start region). The period at which the epitaxial crystals from the two adjacent side surfaces 10c-1 merge together at the upper portion of the epi growth mask 20 is also 4 μm apart.
That is, according to the present invention, since only the side surface 10c-1 is used as the nucleus for epitaxial growth, a high-quality crystal having the same polarity as the entire substrate surface can be obtained.

主面が、ａ軸からｃ軸方向へ３度回転させた方向の法線ベクトルであるサファイア基板１０を用い、凹凸を形成した際、一方の側面１０ｃ−１がほぼ正確なｃ面となるように加工した。即ち、当該側面１０ｃ−１とサファイア基板の主面の成す角度は８７度とした。この他は実施例１と同様に６００℃でＧａＮから成る低温バッファ層を形成し、１１００℃でＧａＮ層３０を形成した。
ＧａＮ層３０の表面は完全に平坦化した。表面の高低をＡＦＭ画像で評価したところ、ＲＭＳは０．８ｎｍと算出された。 When the sapphire substrate 10 whose main surface is a normal vector in the direction rotated by 3 degrees from the a-axis to the c-axis is used to form irregularities, the one side surface 10c-1 becomes a substantially accurate c-plane. It was processed into. That is, the angle formed by the side surface 10c-1 and the main surface of the sapphire substrate was 87 degrees. Other than this, a low-temperature buffer layer made of GaN was formed at 600 ° C. as in Example 1, and a GaN layer 30 was formed at 1100 ° C.
The surface of the GaN layer 30 was completely planarized. When the height of the surface was evaluated with an AFM image, the RMS was calculated to be 0.8 nm.

〔比較例〕
比較のため、ａ面から０度以上０．５度以下ｃ軸方向に回転させた方向を主面の法線ベクトルとするサファイア基板を用い、実施例１と同様にストライプ状の凹凸を形成して、図２．Ａの側面１０ｃ−２、即ちｃ面からの法線ベクトルの方向がサファイア基板１０の主面に対して外部から内部への方向である側面を露出させるようにしてマスクを形成した。この他は実施例１と同様にＧａＮをエピタキシャル成長させたところ、ストライプ状の凹凸を完全に覆うことはできなかった。また、その表面の高低をＡＦＭ画像で評価したところ、ＲＭＳは５ｎｍ以上であった。 [Comparative Example]
For comparison, a sapphire substrate having a normal vector of the main surface that is rotated in the c-axis direction from 0 degrees to 0.5 degrees from the a plane is used to form striped irregularities as in Example 1. FIG. The mask was formed such that the side surface 10c-2 of A, that is, the side surface in which the direction of the normal vector from the c surface was the direction from the outside to the inside with respect to the main surface of the sapphire substrate 10, was exposed. Other than this, when GaN was epitaxially grown in the same manner as in Example 1, the stripe-shaped irregularities could not be completely covered. Moreover, when the height of the surface was evaluated by the AFM image, RMS was 5 nm or more.

実施例１で得られた、サファイア基板１０上に形成したＧａＮ層３０の上に、更にＨＶＰＥ法により厚膜ＧａＮを形成した。即ち、Ｖ族原料にはアンモニア（ＮＨ3)を、III族原料にはＧａとＨＣｌとを反応させて得られたＧａＣｌを用い、基板温度１１００℃でＧａＮを２５０μｍ成長させた。供給量は、ＨＣｌを５０ｓｃｃｍ(標準立方センチメートル)、ＮＨ3を２０００ｓｃｃｍとし、キャリアガス（Ｎ2）を５０００ｓｃｃｍとした。
結晶成長後、２００分かけて室温まで冷却したところ、厚膜ＧａＮ層とサファイア基板１０とが分離し、ｍ面からわずかにオフした面を主面とする厚膜のＧａＮ基板が得られた。これは、冷却中に、厚膜ＧａＮ層とサファイア基板１０との界面がストライプ状の凹凸であるために熱膨張係数差に基づく応力が集中し、その付近でＧａＮ層のｍ面を劈開面として分離したものである。得られたＧａＮ基板は割れや細かいクラックが生ぜず、高品位の結晶であった。 On the GaN layer 30 formed on the sapphire substrate 10 obtained in Example 1, a thick film GaN was further formed by HVPE. That is, ammonia (NH 3 ) was used as a group V material, and GaCl obtained by reacting Ga and HCl was used as a group III material, and GaN was grown to 250 μm at a substrate temperature of 1100 ° C. The supply amount was 50 sccm (standard cubic centimeter) for HCl, 2000 sccm for NH 3 , and 5000 sccm for the carrier gas (N 2 ).
After crystal growth, when cooled to room temperature over 200 minutes, the thick GaN layer and the sapphire substrate 10 were separated, and a thick GaN substrate having a main surface slightly off from the m-plane was obtained. This is because during the cooling, the interface between the thick GaN layer and the sapphire substrate 10 is striped unevenness, so stress based on the difference in thermal expansion coefficient is concentrated, and the m-plane of the GaN layer is cleaved in the vicinity. Separated. The obtained GaN substrate was a high-quality crystal without cracks or fine cracks.

本発明により、III族窒化物系化合物半導体素子を形成するための、主面がｃ面でないIII族窒化物系化合物半導体膜が提供される。   According to the present invention, there is provided a group III nitride compound semiconductor film whose main surface is not c-plane for forming a group III nitride compound semiconductor element.

本発明における、サファイア基板の主面の法線と、形成した凹凸の法線と、サファイアのａ軸及びｃ軸との関係を示す説明図。Explanatory drawing which shows the relationship between the normal line of the main surface of a sapphire substrate in this invention, the normal line of the formed unevenness | corrugation, and the a-axis and c-axis of sapphire. 実施例に係るＧａＮ層３０の製造方法を示す工程図の前半（断面図）。The first half (sectional drawing) of the process figure which shows the manufacturing method of the GaN layer 30 which concerns on an Example. 実施例に係るＧａＮ層３０の製造方法を示す工程図の後半（断面図）。The latter half (sectional drawing) of the process figure which shows the manufacturing method of the GaN layer 30 which concerns on an Example.

符号の説明Explanation of symbols

１０：主面がａ面とオフ角を成すサファイア基板
１０ｔ：サファイア基板１０に形成された凹凸の上面
１０ｖ：サファイア基板１０に形成された凹凸の底面
１０ｃ−１：エピタキシャル成長に用いる、サファイア基板１０に形成された凹凸の側面
１０ｃ−２：エピタキシャル成長に用いない、サファイア基板１０に形成された凹凸の側面
２０：ＳｉＯ2から成るエピ成長マスク
３０：ＧａＮ層 10: Sapphire substrate whose principal surface forms an off-angle with the a-plane 10t: Top surface of uneven surface formed on sapphire substrate 10 v: Bottom surface of uneven surface formed on sapphire substrate 10 10c-1: Sapphire substrate 10 used for epitaxial growth Formed uneven side surface 10c-2: Unused side surface formed on sapphire substrate 10 not used for epitaxial growth 20: Epi growth mask made of SiO 2 30: GaN layer

Claims (7)

サファイア基板上にIII族窒化物系化合物半導体をエピタキシャル成長させる、III族窒化物系化合物半導体の製造方法において、
前記サファイア基板の主面の法線ベクトルが、ａ軸からｃ軸方向に０．２度以上５度以下回転させた方向であり、
前記サファイア基板にｃ面又はｃ面と成す角が２０度以下の側面を有する凹凸を形成し、
当該側面のうち、その法線ベクトルが同じで、当該法線ベクトルと前記サファイア基板のａ軸との成す角の大きい方の側面のみが露出するように、他の前記サファイア基板の表面をIII族窒化物系化合物半導体がエピタキシャル成長しないマスク材料により覆い、
前記マスク材料により覆われていない、前記サファイア基板の露出したｃ面又はｃ面と成す角が２０度以下の側面からIII族窒化物系化合物半導体をエピタキシャル成長させることにより、主面が、ｍ面と０．２度以上５度以下の角を成すIII族窒化物系化合物半導体結晶を得ることを特徴とするIII族窒化物系化合物半導体の製造方法。 In a method for producing a group III nitride compound semiconductor, wherein a group III nitride compound semiconductor is epitaxially grown on a sapphire substrate,
The normal vector of the principal surface of the sapphire substrate is a direction rotated from 0.2 degrees to 5 degrees in the c-axis direction from the a-axis,
Forming concavo-convex having a c-plane or a side with an angle of 20 degrees or less formed on the sapphire substrate;
Among the side surfaces, the surface of the other sapphire substrate is group III so that the normal vector is the same and only the side surface with the larger angle formed by the normal vector and the a-axis of the sapphire substrate is exposed. Cover with a mask material that nitride compound semiconductor does not grow epitaxially,
By epitaxially growing a group III nitride compound semiconductor from an exposed c-plane of the sapphire substrate or an angle formed with the c-plane that is not covered by the mask material and having an angle of 20 degrees or less, the main surface is the m-plane. A method for producing a Group III nitride compound semiconductor, comprising obtaining a Group III nitride compound semiconductor crystal having an angle of 0.2 degrees to 5 degrees. 前記マスク材料により覆われていない、前記サファイア基板の凹凸の露出した側面は、ｃ面と成す角が０．５度以下であることを特徴とする請求項１に記載のIII族窒化物系化合物半導体kの製造方法。 2. The group III nitride compound according to claim 1, wherein an angle formed between a c-plane and an exposed side surface of the sapphire substrate that is not covered with the mask material is 0.5 degrees or less. 3. Manufacturing method of semiconductor k. 前記III族窒化物系化合物半導体の形成においては、８００度未満の温度でバッファ層を形成したのち、１０００度以上の温度で単結晶層を形成することを特徴とする請求項１又は請求項２に記載のIII族窒化物系化合物半導体の製造方法。 3. The formation of the group III nitride compound semiconductor includes forming a buffer layer at a temperature of less than 800 ° C. and then forming a single crystal layer at a temperature of 1000 ° C. or more. A method for producing a group III nitride compound semiconductor as described in 1. 前記バッファ層は前記マスク材料を形成する前に形成されることを特徴とする請求項３に記載のIII族窒化物系化合物半導体の製造方法。 4. The method for producing a group III nitride compound semiconductor according to claim 3, wherein the buffer layer is formed before forming the mask material. 前記III族窒化物系化合物半導体は、窒化ガリウム（ＧａＮ）であることを特徴とする請求項１乃至請求項４のいずれか１項に記載のIII族窒化物系化合物半導体の製造方法。 The method for producing a group III nitride compound semiconductor according to any one of claims 1 to 4, wherein the group III nitride compound semiconductor is gallium nitride (GaN). 前記エピタキシャル成長は、トリメチルガリウムとアンモニアを用いた有機金属気相成長法（ＭＯＶＰＥ）により行うものであり、
アンモニア供給量のトリメチルガリウムの供給量に対するＶ／III比について、
前記凹凸の凹部を埋めるまでは前記Ｖ／III比を高く、
前記凹凸の凸部をエピタキシャル成長膜が覆いつくすまでは前記Ｖ／III比を低く、
前記凹凸の凸部をエピタキシャル成長膜が覆いつくした以降は前記Ｖ／III比を高くすることを特徴とする請求項５に記載のIII族窒化物系化合物半導体の製造方法。 The epitaxial growth is performed by metal organic vapor phase epitaxy (MOVPE) using trimethylgallium and ammonia,
Regarding the V / III ratio of ammonia supply to trimethylgallium supply,
The V / III ratio is increased until the concave and convex portions are filled,
The V / III ratio is low until the epitaxially grown film covers the uneven portions.
6. The method for producing a group III nitride compound semiconductor according to claim 5, wherein the V / III ratio is increased after the convex and concave portions are covered with the epitaxial growth film. 請求項６に記載のIII族窒化物系化合物半導体の製造方法による前記エピタキシャル成長の後、更にハライド気相成長法により厚さ２００μｍ以上に窒化ガリウム単結晶を成長させ、その後冷却する際に劈開を生じさせて前記サファイア基板と分離することを特徴とする窒化ガリウム自立基板の製造方法。 After the epitaxial growth by the method for producing a group III nitride compound semiconductor according to claim 6, a gallium nitride single crystal is further grown to a thickness of 200 μm or more by a halide vapor phase growth method and then cleaved when cooled. And separating the sapphire substrate from the sapphire substrate.
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JP2003209062A (en) * 2002-01-17 2003-07-25 Sony Corp Crystal growth method of compound semiconductor layer and semiconductor element
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