JP4186603B2 - Single crystal gallium nitride substrate, method for manufacturing single crystal gallium nitride substrate, and base substrate for gallium nitride growth - Google Patents

Description

【００８３】
外周部Ｒの幅Ｒｗには下限があり、１ｍｍ以上でなければならない。１ｍｍ以下であると補強効果が少なくてクラックが発生したり破断したりする。外周部Ｒの幅Ｒｗが大きい方が補強効果は大きい。
【００８４】
しかし外周部Ｒは無駄になる部分だから、あまり広いのは望ましくない。ウエハの直径にもよるが、経済性から外周部Ｒの幅Ｒｗは２０ｍｍ以下である。つまりＲｗ＝１〜２０ｍｍである。
【００８５】
外周部Ｒのより好ましい幅Ｒｗは２ｍｍ〜５ｍｍである。
中央部Ｑの方はランダム面積比Ｍが低い方がよい。ランダム面積比Ｍが低いと劈開性が強く現れる。劈開面があれば劈開面に沿ってチップを自然劈開することができるし、劈開した平行な面を共振器のミラー面として有効利用できる。その点でサファイヤ基板にヘテロエピタキシャル成長して形成したものよりも有利である。中央部Ｑはランダム面積比Ｍが低い方が良い。そのためには中央部Ｑのランダム面積比Ｍｑは１０％以下とする。より好ましくは０〜１％のランダム面積比Ｍｑとする。そのように外周部Ｒと中央部Ｑとが相補的な性質をもつため破損、クラック、破断などが起こらず、かつ劈開性のある窒化ガリウム単結晶とすることができる。中央部Ｑと外周部Ｒの相補性が本発明の本質である。
【００８６】
そのように本発明の窒化ガリウム単結晶は中央部Ｑと外周部Ｒの同心二重構造を有する。基板上での違いはランダム面積比Ｍである（Ｍｑ＜０．１＜Ｍｒ）。そのような違いを生じさせるために本発明は特別な形状の複合マスクを出発基板の上に形成し、その上から窒化ガリウムを気相エピタキシャル成長させる。
【００８７】
本発明で用いる複合マスクは、開口部と被覆部がある周期Ｔで規則正しく繰り返す周期の長い大パターンと、大パターンの開口部においてある短い周期で繰り返す窓からなるラテラルオーバーグロース用の小パターンを組み合わせたものである。大パターンは開口部と被覆部があり、被覆部はそのままであるが、開口部にはさらに小パターンを設けるのである。小パターンはすでに説明したラテラルオーバーグロース用のパターンである。ラテラルオーバーグロース用パターンだから連続被覆部にある間隔で窓を設け開口部としたものである。
【００８８】
大パターンは外周部Ｒでも中央部Ｑでも同じである。だから大パターンの周期Ｔは外周部Ｒも中央部Ｑも同一である。
【００８９】
違いを出すために本発明は、小パターンの窓の間隔に工夫をこらしている。つまりラテラルオーバーグロースのマスクである小パターンの窓Ｗの間隔Ｓが中央部Ｑと外周部Ｒで異なる。それによってエピタキシャル成長した窒化ガリウムの欠陥集合領域Ｈの不規則部分と規則部分の面積の広さを相違させている。
外周部Ｒでの窓間隔Ｓｒの方が広くてＳｒ＝０．３μｍ〜６μｍである。
中央部Ｑでの窓間隔Ｓｑの方が狭くてＳｑ＝０．１μｍ〜３μｍである。
【００９０】
【表２】

【００９１】
【表３】

【００９２】
比較例のマスクを図１３に、本発明で用いる内外二重マスクを図１４、１５に示す。
［Ａ．ランダム型内外二重マスク（図１３）］
これはＥＬＯ（小パターン）だけを内外二重構造にしたものである。中央部Ｑ（内側）での窓の直径、間隔が狭く、外周部Ｒ（外側）での窓の直径、間隔が広い。規則性のある大パターン（開口部＋被覆部）が存在しないので、これを下地基板上に形成してＧａＮをファセット成長させても規則性のある欠陥集合領域Ｈを作り出すことができない。欠陥集合領域Ｈは図５のようにランダム分布する。これは本発明のためには用いることができないが小パターンが基本的な内外二重構造をもつものであるので図示している。
【００９３】
［Ｂ．ドット型内外二重マスク（図１４）］
これは、ドット型大パターンの開口部に、ＥＬＯ（小パターン）を内外二重構造にして設けた複合マスクである。ＥＬＯマスク（小パターン）が内外二重構造であるのは先例と同じだがドット型大パターンを持っている点でＡと相違する。ＥＬＯ（小パターン）パターンは、中央部Ｑ（内側）での窓の直径、間隔が狭く、外周部Ｒ（外側）での窓の直径、間隔が広い。規則性のあるドット型大パターン（開口部＋被覆部）が存在するので、これを下地基板上に形成してＧａＮをファセット成長させるとドット上に規則性配列する欠陥集合領域Ｈとそれに隣接する低欠陥単結晶領域Ｕを作り出すことができる。それだけでなく一部に不規則に分布する欠陥集合領域Ｈとそれに隣接する低欠陥単結晶領域Ｕをも生成することができる。これは本発明のＧａＮ製造のために用いることができるマスクである。大パターンは内外共通だが小パターンが内外に二重の構造をもつ。
【００９４】
［Ｃ．ストライプ型内外二重マスク（図１５）］
これは、ストライプ型大パターンの開口部に、ＥＬＯ（小パターン）を内外二重構造にして設けた複合マスクである。ＥＬＯマスク（小パターン）が内外二重構造であるのは先例と同じだがストライプ型大パターンを持っている点でＡと相違する。ＥＬＯ（小パターン）パターンは、中央部Ｑ（内側）での窓の直径、間隔が狭く、外周部Ｒ（外側）での窓の直径、間隔が広い。規則性のあるドット型大パターン（開口部＋被覆部）が存在するので、これを下地基板上に形成してＧａＮをファセット成長させるとストライプ状に規則性配列する欠陥集合領域Ｈとそれに隣接する低欠陥単結晶領域Ｕを作り出すことができる。それだけでなく一部に不規則に分布する欠陥集合領域Ｈとそれに隣接する低欠陥単結晶領域Ｕをも生成することができる。これは本発明のＧａＮ製造のために用いることができるマスクである。大パターンは内外共通だが小パターンが内外に二重の構造をもつ。
【００９５】
【実施例】
規則配置した開口部、遮蔽部よりなる大パターンと、大パターンの開口部に内外で相違する小パターン（ＥＬＯ）とを有する複合マスクをＧａＡｓ基板上に形成した。マスクの上からＨＶＰＥ法によってＧａＮエピタキシャル層を成長させた。キャリヤガスとして水素ガス（Ｈ_２）を用いた。原料ガスとしては、塩化水素ガス（ＨＣｌ）とアンモニアガス（ＮＨ_３）を用いた。
【００９６】
初めに低温の成長温度（５３０℃）で約８０ｎｍ厚みのＧａＮバッファ層を形成した。ＧａＮバッファ層成長条件は以下のようである。
［バッファ層成長条件］
ガス流量 ５Ｌ （流速１００ｃｍ／分）
Ｇａ分圧 ２．５×１０^−３ａｔｍ （０．３３Ｐａ）
ＮＨ_３分圧 ０．１２ａｔｍ （１６Ｐａ）
成長温度 ５３０℃
成長時間 ２０分
成長膜厚 ８０ｎｍ
【００９７】
その後１０３０℃まで昇温して、その上に以下の条件で、ＧａＮエピ層を約３ｍｍ（３０００μｍ）成長させた。
【００９８】
［エピ層成長条件］
ガス流量 ５Ｌ （流速１００ｃｍ／分）
Ｇａ分圧 １．６×１０^−２ａｔｍ （２．１Ｐａ）
ＮＨ_３分圧 ０．２ａｔｍ （２７Ｐａ）
成長温度 １０３０℃
成長時間 ３０時間
成長膜厚 ３０００μｍ（３ｍｍ）
【００９９】
これによってＧａＮ／ＧａＡｓの試料を得た。それを王水でエッチングしてＧａＡｓ基板とマスクを除去した。自立した（フリースタンディング）単結晶窒化ガリウム基板を得た。これを加工、研磨して平坦なＧａＮ単結晶基板の１４種類のサンプル（試料１〜試料１４）を作製した。同じ条件の各試料はそれぞれ数十枚〜数百枚あった。
【０１００】
試料１〜１４の外周部Ｒと中央部Ｑの境界を調べ外周部Ｒの幅Ｒｗを測定した。 ＧａＮ単結晶基板サンプル（試料１〜試料１４）の中央部Ｑの規則配列する欠陥集合領域Ｈｇ_ｑとその周辺の低欠陥単結晶領域Ｕｇ_ｑの面積を測定し合計面積Ｇを求めた。同様に中央部Ｑで不規則分布する欠陥集合領域Ｈｆ_ｑとその周辺の低欠陥単結晶領域Ｕｆ_ｑの合計面積Ｆを求めた。Ｆを（Ｆ＋Ｇ）で割って中央部Ｑでのランダム面積比Ｍｑを求めた。
【０１０１】
同様に試料１〜試料１４の外周部Ｒの規則配列する欠陥集合領域Ｈｇ_ｒとその周辺の低欠陥単結晶領域Ｕｇ_ｒの面積を測定し合計面積Ｇを求めた。外周部Ｒで不規則分布する欠陥集合領域Ｈｆ_ｒとその周辺の低欠陥単結晶領域Ｕｆ_ｒの合計面積Ｆを求めた。Ｆを（Ｆ＋Ｇ）で割って外周部Ｒでのランダム面積比Ｍｒを求めた。
【０１０２】
中央部Ｑにクラックが発生しているかどうかを調べた。一つでもクラックが発生していれば、それはクラック発生基板とし、全くクラックがない基板をクラック非発生基板とした。同じ試料番号について数十〜数百の試料があるので、それぞれの全体数でクラック発生基板の数を割ってクラック発生頻度Ｋを求めた。
【０１０３】
表４にそれぞれの試料１〜１４について中央部Ｑランダム面積比Ｍｑ（％）、外周部Ｒランダム面積比Ｍｒ（％）、外周部Ｒの幅Ｒｗ（ｍｍ）、クラック発生頻度Ｋ（％）を示す。
【０１０４】
【表４】

【０１０５】
［試料１（Ｍｑ＝１００％、Ｍｒ＝１００％、Ｋ＝０％、Ｒｗ＝０）］
これは内外二重構造をもたない。本発明の実施例ではない。図１０に示すような大パターンをもたず小パターンだけのマスク、つまり一様な細かい窓配置をもつラテラルオーバーグロース用のマスクを用いファセット成長させてＧａＮ結晶を形成したものである。内外ともに欠陥集合領域Ｈが不規則分布している。これはラテラルオーバーグロース（ＥＬＯ）マスクだけでファセット成長させると欠陥集合領域Ｈがランダム分布するということを示している。基板全体一様にランダム面積比Ｍが１００％であり、それは堅牢である。クラックは発生しない。その点では最も優れたものであるが中央部Ｑで劈開性がないからレーザ素子、ＬＥＤ素子の基板としては適しない。
【０１０６】
［試料２（Ｍｑ＜１％、Ｍｒ＜１％、Ｋ＝９０％、Ｒｗ＝０）］
これも内外二重構造をもたない。これも本発明の実施例でない。規則配置した開口部と被覆部からなる大パターンと、その開口部に細かい一様窓配置をもつ小パターン（ＥＬＯ）をもつ複合マスクをＧａＡｓ基板に形成してＨＶＰＥ法によってＧａＮを成長させたものである。小パターンの間隔が内外一様であるから内外の二重構造が発生しない。外周部Ｒでもランダム面積比Ｍが１％以下であり欠陥集合領域Ｈが規則正しく並び劈開性がある。それだけに弱くてクラック発生頻度Ｋが９０％となっている。一様マスクによる手法で作製されたものは破損し易く弱いということである。
【０１０７】
［試料３（Ｍｑ＜１％、Ｍｒ＝１００％、Ｋ＝９０％、Ｒｗ＝０．１ｍｍ）］
これは内外二重構造をもつ比較例である。内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付けて、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えば図１４のようなドット型に種Ｅを設けた複合マスクを用いる。あるいは図１５のようなストライプ型に種Ｅを平行に設けた複合マスクを用いる。
【０１０８】
クラック発生頻度は９０％というように高い。それは外周部Ｒが狭すぎるからである。外周部Ｒの幅はＲｗ＝０．１ｍｍである。それが狭すぎて補強効果が不十分だということである。それと外周部Ｒのランダム面積比Ｍが１００％というのがかえって良くないということを示唆している。
【０１０９】
［試料４（Ｍｑ＜１％、Ｍｒ＝１００％、Ｋ＝７０％、Ｒｗ＝４ｍｍ）］
これも内外二重構造をもつ比較例である。内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付けて、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えば図１４のようなドット型に種Ｅを設けた複合マスクを用いる。あるいは図１５のようなストライプ型に種Ｅを平行に設けた複合マスクを用いる。
【０１１０】
クラック発生頻度は７０％というようになお高い。クラック発生頻度が７０％でも使えるが、より低い比率の方が望ましい。
外周部ＲはＲｗ＝４ｍｍであって充分な広さをもっている。
【０１１１】
外周部Ｒのランダム面積比Ｍｒ＝１００％で、１％以下の中央部Ｑのランダム面積比Ｍｑというように違いすぎるので、組織の状態、成長速度、反りなどが内外で大きく異なり内外の境界に大きな応力が発生し、それがクラックを誘引しているのであろう。試料４は内外のランダム面積比Ｍの違いが余りに大きすぎてもいけないということを意味する。
【０１１２】
しかし外周部Ｒのランダム面積比Ｍｒ＝１００％が全く禁止されるということではない。中央部Ｑでのランダム面積比Ｍｑが１０％というように大きければクラック発生頻度はより低くなって実用的なものになる。
【０１１３】
［試料５（Ｍｑ＜１％、Ｍｒ＝８０％、Ｋ＝９０％、Ｒｗ＝０．１ｍｍ）］
これも内外二重構造をもつ比較例である。試料３、４と同様に、内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付け、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えばドット型に種Ｅを設けた複合マスク（図１４）、或いはストライプ型に種Ｅを平行に設けた（図１５）複合マスクを用いる。
【０１１４】
クラック発生頻度は９０％というようになお高い。それは外周部Ｒの幅がＲｗ＝０．１ｍｍというように狭いから補強効果が弱いためである。外周部Ｒの幅をもっと広くすれば実用的なクラック発生頻度に下がるであろう。
【０１１５】
［試料６（Ｍｑ＜１％、Ｍｒ＝８０％、Ｋ＝３０％、Ｒｗ＝４ｍｍ）］
これが内外二重構造をもつ実施例である。試料３〜５と同様に、内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付け、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えばドット型に種Ｅを設けた複合マスク（図１４）、或いはストライプ型に種Ｅを平行に設けた（図１５）複合マスクを用いる。
【０１１６】
クラック発生頻度は３０％というように低くなっている。それは外周部Ｒの幅がＲｗ＝４ｍｍというように広くて補強効果が強く現れるためである。４ｍｍでもよいが外周部Ｒの幅をもっと広くすれば、さらにクラック発生頻度が下がる。
【０１１７】
これは３０％のクラック発生頻度で実用的な意味がある。試料４と比較すると外周部Ｒでのランダム面積比Ｍｒが１００％から８０％に下がり内外でのランダム面積比Ｍの差が２０％低下しているところに違いがある。内外のランダム面積比Ｍがあまり大きいと、成長速度が違い、結晶組織も異なり、内外境界に内部応力が強く発生して、それがクラックの発生をかえって促す。
ということは、さらに内外のランダム面積比Ｍｑ、Ｍｒの差を下げた方が良いだろうということを示唆する。
【０１１８】
［試料７（Ｍｑ＜１％、Ｍｒ＝５０％、Ｋ＝９０％、Ｒｗ＝０．１ｍｍ）］
これも内外二重構造をもつ比較例である。試料３〜６と同様に、内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付け、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えばドット型に種Ｅを設けた複合マスク（図１４）、或いはストライプ型に種Ｅを平行に設けた（図１５）複合マスクを用いる。
【０１１９】
試料６の意味する所に従って外周部Ｒのランダム面積比Ｍを５０％に下げている。しかし、クラック発生頻度は９０％というようになお高い。それは外周部Ｒの幅がＲｗ＝０．１ｍｍというように狭いから補強効果が弱いためである。外周部Ｒの幅をもっと広くすれば、より実用的なクラック発生頻度に下がるであろう。
【０１２０】
［試料８（Ｍｑ＜１％、Ｍｒ＝５０％、Ｋ＝１０％、Ｒｗ＝４ｍｍ）］
これも内外二重構造をもつ実施例である。試料３〜７と同様に、内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付け、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えばドット型に種Ｅを設けた複合マスク（図１４）、或いはストライプ型に種Ｅを平行に設けた（図１５）複合マスクを用いる。
【０１２１】
試料６の意味する所に従って外周部Ｒのランダム面積比Ｍを５０％に下げている。外周部Ｒの幅もＲｗ＝４ｍｍというように広くしている。クラック発生頻度は１０％というように極めて低い。
【０１２２】
試料４、試料６と比較すると、外周部Ｒのランダム面積比Ｍｒが５０％であって、内外のランダム面積比Ｍの差が５０％以下に減っている。それが成長速度の差を緩和し、内部組織の差異を減じ、境界での内部応力を減少させクラック発生を抑制しているのであろう。試料４、６と比較して、外周部Ｒのランダム面積比Ｍｒは７０％以下であることが良いということがわかる。
【０１２３】
外周部Ｒのランダム面積比Ｍｒが７０％〜１００％であっても、中央部Ｑのランダム面積比Ｍが１０％に近いと差異は減少するのでクラック発生は減る。
それでは外周部Ｒのランダム面積比Ｍｒの許される下限はどのぐらいであろうか、ということが問題になる。
【０１２４】
［試料９（Ｍｑ＜１％、Ｍｒ＝３０％、Ｋ＝９０％、Ｒｗ＝０．１ｍｍ）］
内外二重構造をもつ比較例である。試料３〜８と同様に、内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付け、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えばドット型に種Ｅを設けた複合マスク（図１４）、或いはストライプ型に種Ｅを平行に設けた（図１５）複合マスクを用いる。
【０１２５】
試料８の示唆に従って外周部Ｒのランダム面積比Ｍを３０％に下げている。しかし、クラック発生頻度は９０％というようになお高い。それは外周部Ｒの幅がＲｗ＝０．１ｍｍというように狭くて補強効果が弱いためである。外周部Ｒの幅をもっと広くすれば、より実用的なクラック発生頻度に下がるであろう。そこでＲｗを増やしてみた。
【０１２６】
［試料１０（Ｍｑ＜１％、Ｍｒ＝３０％、Ｋ＝１０％、Ｒｗ＝４ｍｍ）］
内外二重構造をもつ実施例である。試料３〜９と同様に、内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付け、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えばドット型に種Ｅを設けた複合マスク（図１４）、或いはストライプ型に種Ｅを平行に設けた（図１５）複合マスクを用いる。
【０１２７】
試料８、９の示唆に従って外周部Ｒのランダム面積比Ｍを３０％に下げ外周部Ｒの幅をＲｗ＝４ｍｍに増やしている。クラック発生頻度は１０％というように充分に低い。それは外周部Ｒの幅がＲｗ＝４ｍｍというように広くて補強効果があるということと、外周部Ｒでのランダム面積比Ｍが３０％であって内外のランダム面積比Ｍの差が小さくて、内外成長速度差、結晶組織差が小さくて境界に強い応力が生じないためであろう。外周部Ｒランダム面積比Ｍｒが３０％というように低くても良いというこがわかった。さらに外周部Ｒのランダム面積比Ｍｒを下げ、その効果を調べる。
【０１２８】
［試料１１（Ｍｑ＜１％、Ｍｒ＝１０％、Ｋ＝９０％、Ｒｗ＝０．１ｍｍ）］
内外二重構造をもつ比較例である。内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付け、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えばドット型に種Ｅを設けた複合マスク（図１４）、或いはストライプ型に種Ｅを平行に設けた（図１５）複合マスクを用いる。
【０１２９】
試料８〜１０の示唆に従って外周部Ｒのランダム面積比Ｍｒを１０％に下げている。クラック発生頻度は９０％というように極めて高い。それは外周部Ｒの幅がＲｗ＝０．１ｍｍというように狭くて補強効果が弱いためか、ランダム面積比Ｍｒ＝１０％が低いためかわからない。そこでＲｗを増やしてみた。
【０１３０】
［試料１２（Ｍｑ＜１％、Ｍｒ＝１０％、Ｋ＝４０％、Ｒｗ＝４ｍｍ）］
内外二重構造をもつ実施例である。内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付け、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えばドット型に種Ｅを設けた複合マスク（図１４）、或いはストライプ型に種Ｅを平行に設けた（図１５）複合マスクを用いる。
【０１３１】
試料８〜１１の示唆に従って外周部Ｒのランダム面積比Ｍｒを１０％に下げ、外周部Ｒの幅をＲｗ＝４ｍｍに増やしている。クラック発生頻度は４０％というように高くなる。４０％のクラック発生頻度でも使うことはできるが不満が残る。
【０１３２】
外周部Ｒの幅はＲｗ＝４ｍｍであるから充分であろう。試料８、１０と比較すると、外周部Ｒのランダム面積比Ｍｒ＝１０％が低すぎるということがわかる。ということは、外周部Ｒのランダム面積比Ｍｒは３０％以上であることが望ましいということがわかる。試料６、８、１０、１２から外周部Ｒの好ましいランダム面積比Ｍｒの範囲が３０％〜７０％だということがわかる。
【０１３３】
それは中央部Ｑのランダム面積比Ｍｑが１％以下で小さく内外の差異が強調されるからである。中央部Ｑのランダム面積比Ｍｑが１０％に近いときは、外周部Ｒのランダム面積比Ｍｒを７０〜１００％にすることもできる。
【０１３４】
［試料１３（Ｍｑ＜１％、Ｍｒ＝５％、Ｋ＝９０％、Ｒｗ＝０．１ｍｍ）］
内外二重構造をもつ比較例である。内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付け、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えばドット型に種Ｅを設けた複合マスク（図１４）、或いはストライプ型に種Ｅを平行に設けた（図１５）複合マスクを用いる。
【０１３５】
外周部Ｒのランダム面積比Ｍｒをさらに５％に下げている。クラック発生頻度は９０％というように極めて高い。それは外周部Ｒの幅がＲｗ＝０．１ｍｍというように狭くて補強効果が弱いためか、ランダム面積比Ｍｒ＝５％が低いためであろう。
【０１３６】
［試料１４（Ｍｑ＜１％、Ｍｒ＝５％、Ｋ＝５０％、Ｒｗ＝４ｍｍ）］
内外二重構造をもつ比較例である。内外ともに規則配置した開口部と被覆部とよりなる大パターンと、大パターンの開口部に細かい窓が等間隔で並ぶラテラルオーバーグロース（ＥＬＯ）用の小パターンを含む複合マスクをＧａＡｓ下地基板に付け、その上にＨＶＰＥ法でＧａＮを成長させたものである。複合マスクは例えばドット型に種Ｅを設けた複合マスク（図１４）、或いはストライプ型に種Ｅを平行に設けた（図１５）複合マスクを用いる。
【０１３７】
外周部Ｒのランダム面積比Ｍｒを５％に下げている。クラック発生頻度は５０％というように極めて高い。外周部Ｒの幅がＲｗ＝４ｍｍであって充分であるのにクラック発生頻度が５０％なのであるから、外周部Ｒのランダム面積比Ｍｒ＝５％というのが低すぎるのである。試料１２と試料１４を比較して、外周部Ｒのランダム面積比Ｍｒは１０％以上なければならないという事がわかる。
【０１３８】
【発明の効果】
以上の実施例の試料８および試料１０において、ウエハ中央部のクラック発生を１０％にまで抑えることができた。従来の、外周部・中央部の区別をもたないウエハではウエハプロセスにおいて熱応力などにより劈開面に平行なクラックが入り、ウエハが破断することもあったが、本発明では外周部のランダム面積比Ｍｒを中央部のランダム面積比Ｍｑより多くすることにより外周部からのクラック発生を抑制することができ、ウエハ破断を防ぐごとができる。
【０１３９】
本発明の方法で成長させたウエハの中央部を使用して、その上にＧａＮ、ＩｎＧａＮ、ＡｌＧａＮ薄膜などをエピタキシャル成長させ、劈開面を利用してチップに切り出した後、レーザデバイスとすることができる。極めて歩留まりが良いＧａＮウエハの製造が可能となる。
【図面の簡単な説明】
【図１】 ラテラルオーバーグロース法を説明するための図。（１）は基板、（２）は基板の上にマスクを設けたもの、（３）は開口部に結晶核が発生したもの、（４）は開口部にＧａＮ薄膜が形成された状態、（５）は開口部から角錐状に成長したＧａＮ結晶と転位、（６）は開口部からマスクの上へと横向きに成長したＧａＮ結晶、（７）は隣接開口部から横向き成長した結晶が合体して転位が減少している状態、（８）は合体したあと平坦なＣ面を維持しながらＣ面成長している状態を示している。
【図２】 基板上に規則正しい配置で種Ｅを設けて、その上にＧａＮをファセット成長させるとファセットピットが種Ｅからのびてゆき種Ｅの直上部は閉鎖欠陥集合領域Ｈとなり、その廻りは正六角形状のファセットピットになり、ピットとピットの間は平坦なＣ面となって成長することを説明するためのファセット成長するＧａＮ結晶の一部拡大平面図。
【図３】 基板上に規則正しい配置で種Ｅを設けて、その上にＧａＮをファセット成長させるとファセットピットが種Ｅからのびてゆき種Ｅの直上部は閉鎖欠陥集合領域Ｈとなり、ファセットの下には欠陥が少なく単結晶である単結晶低転位随伴領域Ｚが成長し、平坦なＣ面の下には欠陥が少なく単結晶であり高抵抗の単結晶低転位余領域Ｙが成長してゆくことを説明するための断面図。
【図４】 基板の上に規則正しい配置で種Ｅを設けたマスクの上にＧａＮをファセット成長させ閉鎖欠陥集合領域が規則正しく分布するドット型単結晶ＧａＮを成長させたときのＧａＮ結晶の閉鎖欠陥集合領域分布を示すための平面図。
【図５】 基板の上にランダムな配置で種Ｅを設け、あるいは種を全く設けずに基板の上にＧａＮをファセット成長させ閉鎖欠陥集合領域がランダムに分布するランダム型単結晶ＧａＮを成長させたときのＧａＮ結晶の閉鎖欠陥集合領域のランダム分布を示すための平面図。
【図６】 平行な複数の閉鎖欠陥集合領域Ｈをファセット成長によって発生させるために基板の上に形成する平行な被覆部をもつストライプ状のマスクの平面図。
【図７】 図６のストライプ被覆部マスクを用いてファセット成長させたときのＧａＮ結晶の表面に現れる平行な複数の閉鎖欠陥集合領域Ｈとその両側に発生する平行な単結晶低転位随伴領域Ｚ、単結晶低転位余領域Ｙを示すＧａＮ結晶の平面図。
【図８】 図６のストライプ被覆部マスクを用いてファセット成長させたときのＧａＮ結晶の表面に現れる平行な複数の閉鎖欠陥集合領域Ｈとその両側に発生する平行な単結晶低転位随伴領域Ｚ、単結晶低転位余領域Ｙを示すＧａＮ結晶の縦断面図。
【図９】 図６のような平行ストライプのマスクをＧａＡｓ基板上に被覆しＧａＮを結晶成長させ、図７、８のような平行に延びる欠陥集合領域Ｈとその両側にあって平行に延びる低欠陥単結晶領域Ｕ（単結晶低転位随伴領域Ｚ＋単結晶低転位余領域Ｙ）を生成した場合、劈開性が強いので、エッチング、研磨、ウエハプロセスにおいてストライプと直交する方向に割れてしまう事があるということを示すための成長ＧａＮ基板の平面図。
【図１０】 短い一定間隔で規則正しく並べられた同等の細かい窓Ｗをもつラテラルオーバーグロース用小パターンを全面に形成したＥＬＯマスクの平面図。
【図１１】 規則正しく格子状に欠陥集合領域Ｈが発生するよう格子状（ドット型）に長い周期で規則正しく被覆部（種Ｅ）と開口部が並ぶファセット成長用大パターンと、その開口部に短い一定間隔で規則正しく並べられた同等の細かい窓Ｗをもつラテラルオーバーグロース用小パターンを含む複合マスクの平面図。
【図１２】 規則正しく平行ストライプ状に欠陥集合領域Ｈが発生するよう平行ストライプ状に長い周期で規則正しく被覆部（種Ｅ）と開口部が並ぶファセット成長用大パターンと、その開口部に短い一定間隔で規則正しく並べられた同等の細かい窓Ｗをもつラテラルオーバーグロース用小パターンを含む複合マスクの平面図。
【図１３】 外周部Ｒでは少し広い一定間隔で規則正しく並べられた同等の細かい窓をもち中央部Ｑでは少し狭い一定間隔で規則正しく並べられた同等の細かい窓をもつ内外二重ラテラルオーバーグロース用小パターンを形成した二重ＥＬＯマスクの平面図。
【図１４】 規則正しく格子状に欠陥集合領域Ｈが発生するよう格子状（ドット型）に長い周期で規則正しく被覆部（種Ｅ）と開口部が並ぶファセット成長用大パターンと、その開口部に外周部Ｒでは少し広い一定間隔で規則正しく並べられた同等の細かい窓をもち中央部Ｑでは少し狭い一定間隔で規則正しく並べられた同等の細かい窓をもつ内外二重ラテラルオーバーグロース用小パターンを含み本発明で用いられる複合マスクの平面図。
【図１５】 規則正しく平行ストライプ状に欠陥集合領域Ｈが発生するよう平行ストライプ状に長い周期で規則正しく被覆部（種Ｅ）と開口部が並ぶファセット成長用大パターンと、その開口部に外周部Ｒでは少し広い一定間隔で規則正しく並べられた同等の細かい窓をもち中央部Ｑでは少し狭い一定間隔で規則正しく並べられた同等の細かい窓をもつ内外二重ラテラルオーバーグロース用小パターンを含み本発明で用いられる複合マスクの平面図。
【図１６】 ファセット成長したＧａＮ結晶において不規則に分布する欠陥集合領域Ｈとそれに隣接する低欠陥単結晶領域Ｕ（単結晶低転位随伴領域Ｚ＋単結晶低転位余領域Ｙ）を含む部分をＣＬ（カソードルミネセンス）観察したものの平面図。多様な寸法形状でランダムに分布する欠陥集合領域Ｈとそれに接する低欠陥単結晶領域Ｕが見える。低欠陥単結晶領域Ｕの位置、寸法、形状も不規則である。この図に現れたものは全て不規則に分布する欠陥集合領域Ｈｆ、低欠陥単結晶領域Ｕｆであるから不規則分布領域の面積Ｆに算入される。
【図１７】 図１６の１７−１７断面図。多様な位置、寸法、形状の欠陥集合領域Ｈｆと低欠陥単結晶領域Ｕｆ（単結晶低転位随伴領域Ｚ＋単結晶低転位余領域Ｙ）は垂直方向には大体一定であるが水平方向にはランダムである。
【図１８】 ファセット成長したＧａＮ結晶において不規則に分布した欠陥集合領域Ｈ、低欠陥単結晶領域Ｕと、（ストライプ状に）規則的に配列した欠陥集合領域Ｈ、低欠陥単結晶領域Ｕとの境界部分の構造をＣＬで見た平面図。平行で幅が一様な規則正しいストライプ構造が終り楔型の境界から不規則に分布する欠陥集合領域Ｈと低欠陥単結晶領域Ｕが存在するという明白な構造の変化を示す。楔型の境界の上の部分が規則分布領域の面積Ｇに算入される。楔型の境界から下の部分が不規則分布領域の面積Ｆに算入される。ランダム面積比Ｍというのは全面積（Ｆ＋Ｇ）によって、不規則領域の面積Ｆを割ったものとして定義される。Ｍ＝Ｆ／（Ｆ＋Ｇ）。
【図１９】 図１８の１９−１９断面図。
【図２０】 図１８の２０ー２０断面図。
【図２１】ＥＬＯマスクの窓の間隔Ｓを中央部Ｑと外周部Ｒで異ならせることによって不規則に分布する欠陥集合領域Ｈと規則的に配列する欠陥集合領域Ｈの比率を中央部Ｑと外周部Ｒで異なるものにしている本発明において、間隔Ｓと窓Ｗの定義を説明する図。外周部Ｒでは間隔Ｓｒ、窓Ｗｒが大きく、中央部Ｑでは間隔Ｓｑ、窓Ｗｑが小さくなっている。
【符号の説明】
２ 基板
３ マスク
４ 窓
５ ＧａＮ結晶核
６ 膜状ＧａＮ結晶
７ 錘状ＧａＮ結晶
８ ファセット面
９ 頂面
２０ 衝合面
２１ マスク
２２ マスク
２３ 上面
２４ マスク
２５ 遮蔽部
２６ 開口部
２７ 被覆部
Ｈ 閉鎖欠陥集合領域
Ｅ 種
Ｚ 単結晶低転位随伴領域
Ｙ 単結晶低転位余領域
Ｑ 中心部
Ｒ 外周部
Ｕ 低欠陥単結晶領域
Ｓ マスクの窓間隔
Ｗ 窓[0001]
BACKGROUND OF THE INVENTION
The present invention relates to single crystal gallium nitride (GaN), a method for producing single crystal gallium nitride, and a base substrate with a mask for growing gallium nitride.
InGaN-based light-emitting diodes (LEDs) and laser diodes (LDs) are useful as blue light-emitting elements and have a proven record. They generate blue using the wide band gap of GaN. InGaN-LEDs are already widely used, and InGaN-LD will be commercially available in the near future. The notation InGaN represents the composition of the active layer. InGaN-LD is an LD that emits light using InGaN, which is a ternary mixed crystal, as an active layer. The prefix does not indicate a board. The same thing is sometimes written as GaN-LD. The basic crystal is GaN, and mixed crystals of InGaN, AlGaN, etc. are laminated so that they are expressed as such.
[0002]
Since a good n-type GaN substrate cannot be produced even now, all practical InGaN light-emitting elements are heteroepitaxially grown on sapphire substrates such as thin films of n-type, p-type GaN, InGaN, AlGaN, etc. It is.
[0003]
Since an InGaN / sapphire LD has a sapphire substrate and is not cleaved, it is necessary to mechanically cut the chip, polish the resonator surface, and finish the flat parallel surface with high accuracy. It significantly reduces the laser manufacturing yield. That will increase the cost of InGaN / Sapphire-LD.
[0004]
I think that InGaN-LD should also be fabricated on an n-type GaN substrate. Manufacturing an n-type GaN single crystal substrate is very difficult. The applicant has so far concentrated his efforts to develop a manufacturing technique for a GaN single crystal substrate.
[0005]
If a GaN single crystal substrate (GaN wafer) can be manufactured, when a thin film such as GaN, InGaN, or AlGaN is grown on the GaN single crystal substrate, thermal distortion does not occur, the chip can be separated by natural cleavage, and the laser resonator surface is It can be produced by natural cleavage.
[0006]
However, at present, there is no method for producing a GaN substrate that is excellent in cleavage and does not generate cracks. It is extremely difficult to manufacture a GaN single crystal with few defects. It is even more difficult to produce a GaN single crystal substrate that is cleaved and robust. Cleavage and robustness are contradictory properties that are difficult to achieve.
[0007]
The present invention relates to a method of manufacturing a gallium nitride single crystal substrate that is excellent in cleavage property suitable for manufacturing a laser resonator and has a good yield without cracks during the manufacturing.
[0008]
[Prior art]
The applicant has made numerous inventions for producing single crystal gallium nitride (GaN) substrates. Since the present invention uses these techniques, some of them will be described. What is described here is an idea for epitaxial dislocation overgrowth using an epitaxial lateral overgrowth method (ELO), a facet growth method, and a closed defect set.
[0009]
(1) Japanese Patent Application 2000-519462
A mask layer forming step of forming a mask layer having a plurality of opening windows spaced apart on a GaAs substrate, and an epitaxial layer growth step of growing an epitaxial layer made of GaN on the mask layer are provided. This is a method of manufacturing a single crystal gallium nitride substrate.
[0010]
At this time, GaN nuclei are formed in the openings of the mask layer, and these GaN nuclei gradually grow laterally in the lateral direction on the mask layer. Since the defects in the GaN nucleus do not spread when the GaN nucleus grows laterally, it is possible to form a single crystal gallium nitride substrate with greatly reduced crystal defects. This is called an epitaxial lateral overgrowth method and is well known in GaN production.
[0011]
Many other documents are known about ELO grown on sapphire substrates. In either case, the ELO method is applied on a sapphire substrate. In the case of a sapphire substrate, an InGaN light emitting device is fabricated with the substrate attached. A sapphire substrate cannot be removed from a sample grown with a GaN-based thin film. A device with a sapphire substrate attached. Therefore, the difficult work of dicing hard sapphire is required.
[0012]
The applicant uses a (111) crystal of GaAs for the substrate. When a GaAs substrate is used, there is a possibility that a GaN self-standing single crystal film is formed by growing a thick GaN film and removing the GaAs base substrate. Therefore, the purpose of using GaAs as a base substrate is not to make an InGaN light emitting device with GaAs, but to make a single crystal substrate of GaN itself. The single crystal substrate serves as a starting substrate for manufacturing an InGaN-based light emitting device, and is intended to replace the sapphire substrate.
[0013]
The mask is, for example, a window having a regular hexagonal shape with a diameter of 1 to 2 μm, a circle, a square, a belt, or the like placed at 6-fold symmetrical positions at intervals of 1 to 2 μm. Since the mask acts to suppress the growth of GaN, GaN nucleates independently within each window. Nuclei are generated with the window surface as the C-plane. The GaN thin film filling the window further grows in the c-axis direction and extends to the same height as the window. Dislocations extend longitudinally with growth. Since it grows over the mask beyond the window, the growth is in the horizontal direction (a-axis, b-axis, d-axis directions). Since the dislocation is in the same direction as the growth direction, the extension direction of the dislocation is also in the horizontal direction. This is lateral overgrowth. GaN extended from the adjacent window collides just at the bisector of the window. At that time, since the dislocations collide head-on at 180 degrees, the dislocations cancel each other here and are greatly reduced. After that, the growth direction is again upward (c-axis direction). Dislocations also grow upward with upward growth.
[0014]
The lateral overgrowth will be described with reference to FIG. FIG. 1A is a cross-sectional view of the surface of the substrate 2. The substrate 2 is a single crystal substrate such as GaAs or sapphire. SiN, SiO on the substrate 2 as shown in FIG. ₂ A thin mask 3 made of AlN or the like is formed. GaN hardly grows on the mask. In other words, it has a growth deterrent effect. The mask 3 is regularly provided with a large number of openings 4 (windows). The substrate surface is exposed from the opening 4. A thin film of GaN is formed by HVPE, MOCVD, MOC, sublimation or the like.
[0015]
As shown in FIG. 1 (3), GaN crystal nuclei 5 are formed in isolation only on the substrate 2 in the opening 4. As the growth proceeds further, the island-shaped crystal nuclei coalesce inside the window 4 as shown in FIG. The thickness of the mask is as thin as about 80 nm to 100 nm. The surface of the thin film crystal 6 is a C plane and grows in the c-axis direction. Eventually, the GaN crystal 6 becomes the same thickness as the mask 3. Further, the growth of GaN progresses, but it does not readily grow on the mask, and gradually accumulates on the crystal on the opening 4. Then, the GaN crystal 7 grows in a spindle shape. The surface of the conical GaN crystal 7 is a crystal orientation plane with a certain low plane index. This is called the facet plane. Facet is a broad term that means the crystal face of a gemstone that was originally cut, but here it is used in a narrower sense.
[0016]
A facet is a word that refers to a crystal plane other than the C plane that appears on the surface in the case of C-plane growth. The crystal plane is a plane expressed by the Miller index (integer), not a random plane. When the C plane is grown, the C plane itself is one of the crystal planes, but only the C plane is excluded and the crystal plane that actually appears on the surface is called a facet. These are {−1101} plane, {2-1-12} plane and the like. Usually, crystal growth is performed with a surface (mirror surface) perpendicular to the crystal direction. When growing while maintaining the C-plane, it is called C-plane growth. When growing in the c-axis direction while holding a facet other than the C-plane on the surface, this is called facet growth and is distinguished from C-plane (mirror) growth.
[0017]
Growing crystals grow in layers in a direction parallel to the plane. Dislocation D is indicated by vertical lines in the crystal. A GaN crystal contains a large number of dislocations and extends in the longitudinal direction. The growth in FIG. 1 (5) is not C-plane growth but facet growth. When the mask opening is full, it cannot be raised any higher, so the GaN crystal extends laterally onto the mask.
[0018]
FIG. 1 (6) shows such a state in the middle. The front end of the facet surface 8 of the crystal extending in the lateral direction advances over the mask. Eventually it will come into contact with anything extending from the adjacent window. Each is the state of FIG. 1 (6). This is also facet growth because it grows on the facet surface 8. However, it is facet growth for a short time and is basically C-plane growth. The top surface 9 of the crystal is a flat surface. V-grooves are formed between adjacent crystals. Dislocations bend and extend in this direction. V-grooves formed between adjacent windows are gradually distorted. As shown in FIG. 1 (7), the crystals extending from both collide at the abutting surface 20. Since dislocations collide with each other at the abutting surface 20, some disappear, and the dislocation density temporarily decreases. That is the advantage of the lateral overgrowth method (ELO).
[0019]
After that, it grows upward. The dislocation D extends upward. The upper surface 23 is a flat C surface. So it is C-plane growth. That is, most of the ELO methods employ C-plane growth. This is shown in FIG. Thereafter, when a thick crystal is grown and the substrate 2 and the mask 3 are removed, a GaN single crystal free-standing film is obtained. It is a GaN single crystal substrate. The GaN lateral overgrowth method (ELO) as shown in FIG. 1 is well known.
[0020]
That alone does not reduce the dislocation density sufficiently. It is still difficult to use an InGaN-LED or InGaN-laser substrate. A free-standing GaN film substrate is expensive and cannot replace a proven sapphire substrate. Further, a lower dislocation is desired.
[0021]
(2) Japanese Patent Application No. 2001-284323 (facet growth method)
Forming pits consisting of facet surfaces on the growth surface during crystal growth, always holding the closed defect assembly region H, which is a collection of defects, at the bottom of the pits, and allowing dislocations to be captured in the closed defect assembly region This reduces the dislocations in the surrounding low dislocation single crystal portion U (single crystal low dislocation associated region Z and single crystal low dislocation residual region Y).
[0022]
It is a very delicate growth method. The closed defect gathering region H is forcibly created in the crystal and the defects are concentrated there. The term “closed” is used in the sense that the defect gathering region H is closed and the defect does not re-diffuse. The other portions have fewer defects due to the generation of the defect accumulation region H, and can be a GaN substrate suitable as a laser substrate. It is a story after the end of lateral overgrowth.
[0023]
After lateral overgrowth (ELO), GaN grows in the vertical direction (c-axis direction), but does not grow while holding a smooth flat C-plane, but has a growth surface that is an inclined facet. The facet surface grows upward (c-axis direction) while facing the oblique direction, so that the defects are swept and pushed to the central part to collect the defects at a high density in the central part. That is the closed defect gathering region H. The closed defect gathering region H is called a closed defect gathering region H because the defects are gathered at a high density and the crystal part is closed.
[0024]
A device for such a low dislocation density will be described with reference to FIGS. FIG. 2 is a plan view of a part of the crystal surface, and FIG. 3 is a 3-3 cross-sectional view thereof. A hexagonal pit P (concave portion) has a hexagonal shape. That is the facet F ₁ , F ₂ ... F ₆ And a closed defect gathering region H at the center. When a seed (shielding layer) E is formed on the substrate 2 and GaN is facet grown thereon, a closed defect gathering region H in which defects are condensed at a high density is grown following the seed E. The portion that grows after the surrounding facet plane F is a high-quality single crystal with low resistivity and few dislocations. It occurs adjacent to and concomitant with the closed defect collection region H. Therefore, the present inventor named the high-quality single crystal region as a single crystal low dislocation associated region Z. That is because it appears along with the closed defect assembly region and is low dislocation and single crystal. It is a facet grown part, not C-plane growth.
[0025]
A portion of a flat surface exists between the adjacent pits P, P. The flat surface portion has as its surface a C plane parallel to the original substrate surface. It is also a single crystal and low dislocation. However, it was not faceted under the facet, but C-face. It is distinguished from the single crystal low dislocation associated region Z having a high electric resistance and faceted growth. The single crystal low dislocation associated region Z is generated along with the closed defect assembly region H, but the C-plane grown portion is generated outside the single crystal low dislocation associated region Z as a remaining region. Let's call it Y. The single crystal low dislocation associated region Z and the single crystal low dislocation residual region Y are collectively referred to as a low defect single crystal region U, and both are low-dislocation portions of the single crystal centered on the defect assembly region H (U = Z + Y ). Hereinafter, the closed defect gathering region H may be simply referred to as the defect gathering region H.
[0026]
As described in the explanation of the lateral overgrowth method (ELO), a large dislocation density is generated in GaN. Decrease slightly with lateral overgrowth (10 ¹⁰ cm ^-3 -10 ⁸ cm ^-3 ) Is still too much. Dislocations extend upward with growth. F to maintain facet growth ₁ , F ₂ The dislocations are distributed to the left and right and gather at the boundary. Furthermore, when faceted, dislocations gathered at the boundary will gather at the center. Since dislocations gather at the center, it becomes a closed defect gathering region H. The upward funnel-shaped pits collect the dislocations as such.
[0027]
Dislocations do not disappear easily. However, since it aggregates in the center, the dislocation density in the other part decreases. In the central closed defect gathering region H, single crystals, inversion crystals, and grain boundaries exist at high density. It is a mass of dislocations. The single crystal low dislocation associated region Z under the adjacent facet plane F immediately after the dislocation is removed from the outside becomes low dislocation. When the single crystal low dislocation associated region Z becomes low dislocation, the dislocation of the adjacent single crystal low dislocation residual region is gradually drawn and enters the pit P. The dislocations are aggregated from the boundary line to the stop line by being swept to the facet surface in the pit P. Therefore, the dislocation density in the remaining single crystal low dislocation associated region Z and single crystal low dislocation residual region Y is 10 ⁶ cm ^-3 -10 ⁵ cm ^-3 Reduce to.
[0028]
An HZY structure is formed concentrically around the isolated closed defect gathering region H. If the seed E is prepared on the substrate in advance, a closed defect gathering region H is formed at the same location as the seed E. In order to make the structure of HZY regularly as shown in FIG. 2, the seed E should be formed regularly on the substrate 2 first. The dot type is a group in which the seeds E are regularly arranged in this manner to produce a set of closed defect collecting regions H having the same pattern.
[0029]
From the beginning to form the closed defect collection region H, SiO on the GaAs substrate ₂ In other words, seeds of different materials such as SiN, Pt, and Mo are placed. Since GaN is difficult to grow on different materials, the growth is delayed, which becomes the position of the facet pit. That is, facet pits are generated from seeds of different materials. The facet pits sweep the dislocations as described above and pull the dislocations into the inside, and form the closed defect gathering region H described above at the center. Therefore, first, the position of the closed defect gathering region H can be specified by the position of the different kind of material arranged on the GaAs substrate.
[0030]
Therefore, if the arrangement of the first isolated seed (circle, square) is made random, the closed defect assembly region H is distributed in a random arrangement in the crystal. This is called a random type.
[0031]
If the distribution of the first isolated species is regularly arranged in the vertical and horizontal directions on the substrate, the GaN grown thereon has the closed defect gathering region H having the same regularity. Such a closed defect gathering region H that is regularly isolated is called a dot type. Dots are called dots because the planar shape of the closed defect collection region is an isolated point (circle, square, or regular hexagon). There is no sense that it is regularly arranged in itself, but here, what is regularly arranged is called a dot type.
[0032]
FIG. 4 shows the arrangement of the seed E on the substrate 2 for producing the GaN of the dot mask. If the seed E is regularly formed in the vertical and horizontal directions and faceted, the concentric HZY structure centered on the closed defect gathering region H is generated on the seed E. The mask includes a covering portion and an opening portion. In this example, the covering portion is seed E, and the opening portion is a portion without seed E. Since the seed E on the base substrate and the defect gathering region H in the GaN crystal match, the dot-like E in FIG. 4 can be regarded as the distribution of the closed defect gathering region H.
[0033]
FIG. 5 shows a mask in which seeds E having different dimensions are randomly arranged. A GaN crystal having defect collection regions H distributed randomly can be formed by a random mask. Even in such a case, a concentric HZY structure is formed around the defect assembly region H. Therefore, FIG. 5 is a plan view of the random mask, but it can also be said to be a plan view showing the distribution of the defect collection region H of the GaN crystal grown using the random mask. Since the mask covering portion (seed E) and the defect gathering region H have almost the same dimensions and the position is determined by the seed E, there is such correspondence.
[0034]
However, the distribution of the random defect gathering region H can be generated only by an ELO mask having no seeds and a fine window. When GaN is grown on a GaAs substrate with an ELO mask while maintaining facet growth conditions, a GaN crystal having defect collection regions H with a random distribution as shown in FIG. 5 is formed. Even in this case, the facet growth condition is indispensable only with the ELO mask.
[0035]
The GaN crystal is transparent. The closed defect assembly region H, the single crystal low dislocation residual region Y, and the single crystal low dislocation associated region Z cannot be distinguished as they are. It is a distinction that is visible for the first time by CL (cathodoluminescence).
[0036]
If the seed E is simply used as a mask, the story is simple, but actually it is used in conjunction with lateral overgrowth. Then, there are two types of masks, which is complicated. Lateral overgrowth masks have small holes and a short period, but facet grown seed masks are large and widely spaced. The ELO mask has windows and intervals of about 1 to 2 μm. The mask for generating the defect collecting region H has a covering portion and an opening portion arranged with a period of several tens μm to several hundreds μm. Therefore, there is a difference of several tens to several hundred times in terms of dimensions.
[0037]
A mask which is a seed for facet growth includes a covering portion and an opening portion. This means that an ELO mask is provided in the opening.
A facet growth mask is called a large mask, and an ELO mask is called a small mask. That is, the small mask is complementarily provided in the opening of the large mask.
[0038]
FIG. 11 shows an example of such a double structure mask 22. The dot type mask 22 has a double periodicity. A number of small regular hexagonal windows are the windows (ELO openings) 4 that appear in FIG. It consists of a very narrow window 4 and a narrow covering 3 with a diameter of 1 μm to 2 μm and 1 μm to 2 μm. A window 4 and a covering portion 3 for lateral overgrowth provided at a small pitch and at a position six times symmetrical.
[0039]
On the other hand, the large covering portions 27 (E) regularly exist with a large period. The covering portion 27 is a seed E of the closed defect gathering region H. The covering portion 27 (type E) has a large diameter of 10 μm to 50 μm and a period of 100 μm to 400 μm. A large pattern opening means a wide area other than the covering 27. The large pattern opening is covered by the ELO pattern and is no longer an opening, but it is an opening from the standpoint of a large pattern. The large pattern opening and covering are formed in accordance with the size of the light emitting device such as LD or LED formed on the substrate. Therefore, what is necessary is just to change the magnitude | size and pitch (period) suitably with the target device.
[0040]
In FIG. 11, in order to easily distinguish the mask for lateral overgrowth, which is a small pattern, and the seed (E) of the closed defect gathering region H, the seed E is written only in four vertical and horizontal directions. As shown in FIG. 4, a large number of seeds 23 (E) are formed vertically and horizontally on the substrate. The ELO windows are actually finer and there are more on the underlying substrate. Here, the window is also drawn large, but the seed pattern (large pattern) is provided with a period of several tens to several hundred times the period of the window of ELO (small pattern). Here, since the mask material for the lateral overgrowth shielding portion 3 and the material for the seed E of the closed defect gathering region H are the same, the figure is complicated. However, it may be a heterogeneous material.
[0041]
It has been found that the shielding part 3 should be stronger than the seed E and should have an action of suppressing GaN crystal growth. On the other hand, if the action of the seed E to suppress crystal growth is too strong, the closed defect assembly region H cannot be formed sufficiently, and even if it can be formed, it may be cut off in the middle.
[0042]
So the lateral overgrowth shield 3 is SiO ₂ As a dielectric such as SiN, the seed E of the closed defect assembly region H is a metal such as Pt, Pd, or Ni.
[0043]
However, even if the seed E is not forcibly produced, if the facet growth is maintained (without the C-plane growth), the closed defect gathering region H occurs spontaneously somewhere. If a closed defect gathering region H is generated somewhere, it is maintained and extends vertically, so that a concentric structure of HZY is also formed around the closed defect gathering region H. Where it occurs, it depends on chance. Therefore, the distribution of the concentric HZY structure centered on the closed defect gathering region H is random.
[0044]
FIG. 5 can be said to be an example of the distribution of the closed defect gathering region H generated by chance. The closed defect gathering region H occurs accidentally when the free energy is non-uniform, and its size and distribution are determined by chance. However, the same can be obtained by forming the seed E having a random distribution as shown in FIG. 5 on the substrate 2 and performing facet growth.
[0045]
The closed defect gathering region H sometimes disappears with or without the seed E. When it becomes C-plane growth instead of facet growth, such a closed defect gathering region H once disappears and aggregates, dislocations are unrolled and scattered around. Again, the surrounding crystals become high dislocations. Since it is troublesome, it is necessary to monitor the GaN crystal with great care to maintain facet growth. Facet growth is performed at a relatively low temperature compared to C-plane growth. Always observe the facet pits and if there are signs that the pits disappear, the temperature is lowered to strengthen the facet growth conditions.
[0046]
Such facet growth that maintains dislocation aggregation is key. It grows in the c-axis direction but is not C-plane growth. It is facet growth instead of C-plane. A closed defect gathering region H is formed at the bottom of the facet pit. Immediately therearound is a portion grown following the facet plane, which is a single crystal low dislocation associated region Z. That is because the portion is a single crystal, has low dislocations, and is accompanied by the closed defect assembly region H. This is a good single crystal and a useful part as a laser substrate.
[0047]
The single crystal low dislocation associated region Z grows in the c-axis direction but is not C-plane growth. However, since the closed defect gathering region H and the surrounding single crystal low dislocation associated region Z grow in a cylindrical shape (correctly, a regular hexagonal column or a regular dodecagonal column), there is always a portion left behind. It cannot be facet grown and it becomes C-plane growth. The C-plane grown portion is single crystal and has low dislocations, but is slightly different from the single crystal low dislocation associated region Z because it is C-plane grown. It has the feature that resistivity is higher than anything else. This is because it grows in the C plane, and is a portion left behind from a cylinder or the like, so it will be referred to as a single crystal low dislocation residual region Y. The single crystal low dislocation residual region Y is also low dislocation but high in resistivity.
[0048]
The reason why such a difference can be made is that the facet surface is doped with oxygen, which becomes an n-type impurity and has low resistance, but the C surface is not doped with oxygen and has high resistance. It is. Although there is no direct relationship with the present invention, the difference between the single crystal low dislocation residual region Y and the single crystal low dislocation associated region Z is described and what is the cause.
[0049]
Z and Y may be collectively referred to as a low defect single crystal region U. The low defect single crystal region U is associated with the defect assembly region H, and the area becomes a problem in the present invention. In this case, the area is the sum of the defect assembly region H and the low defect single crystal region U associated therewith. Is the area.
[0050]
Facet face F ₁ , F ₂ , F ₃ , F ₄ , F ₅ , F ₆ Is a {1-101} plane or a {2-1-12} plane. Here, {1-101} in curly brackets is a set representation of a surface, and six symmetrical individual representations (1-101), (-1101), (01-11), (0-111), ( 10-11) and (-1011). Similarly, {2-1-12} in curly brackets means six symmetrical individual expressions (-1-122), (11-22), (1-2-12), (-1212), (2 -1-12) and (-2111). When both plane orientations coexist, it becomes a dodecahedron pyramid shape.
[0051]
(3) Japanese Patent Application No. 2001-311018 (Stripe type)
This also creates a parallel stripe-shaped defect gathering region H at a predetermined position in the crystal, grows it while maintaining the facet plane F around it, propagates the defect, and converges to the closed defect gathering region H. This is the same as described above. The difference is SiO ₂ , SiN, Pt, Mo and the like are arranged in a parallel strip shape (stripe), and the closed defect gathering region H is also generated in a parallel strip shape.
[0052]
FIG. 6 shows a mask for creating a stripe structure. The mask 24 comprises a number of parallel shields (species E) 25 and a number of parallel openings 26 existing therebetween. In this figure, the extending direction of the shielding part 25 and the opening part 26 is the x direction. The crystal orientation of the substrate determines the orientation of the GaN crystal grown on it. The orientation of the stripe-shaped shielding part 25 (type E) is selected and formed on the substrate 2 so that a cleavage plane {1-100} is formed in a direction perpendicular to the stripe. GaN is facet grown on the substrate 2 and the mask 24. As shown in FIG. 7, parallel closed defect gathering regions H are formed on the shielding part 25. A large number of single crystal low dislocation associated regions Z and single crystal low dislocation residual regions Y parallel to both sides of the defect assembly region H are generated. It is a stripe corresponding to the stripe mask. FIG. 8 is a cross-sectional view of the same, and it can be seen that a defect collecting region H, a single crystal low dislocation associated region Z, and a single crystal low dislocation residual region Y are grown perpendicular to the substrate surface. In FIG. 7, FIG. 6 is rotated by 90 degrees, and the x direction is upward.
[0053]
Facet surfaces are formed on both sides of the shield 25 (type E). It is no longer a regular hexagon or a dodecagon. As shown in the cross-sectional view of FIG. The facet surface pits P do not have a pyramid shape but become parallel V grooves. A closed defect gathering region H extends on the parallel seed 25 (shield E). A single crystal low dislocation associated region Z continuously grows under the inclined wall facet F of the V groove. A narrow flat surface which is a boundary between adjacent V grooves is a C plane. The portion where the C-plane grows is a single crystal low dislocation residual region Y. Depending on the facet growth conditions and the interval between the shielding portions 25, the single crystal low dislocation residual region Y that grows C-plane may not be formed. As shown in FIG. 7, the single crystal low dislocation residual region Y and the single crystal low dislocation associated region Z can be made parallel.
[0054]
As a result, the closed defect gathering region H, the single crystal low dislocation associated region Z, and the single crystal low dislocation residual region Y are regularly arranged in parallel, such as HZYZHZYZHZYZHZYZ. Defects are concentrated and accumulated in the belt-like H portion. The single crystal low dislocation associated regions Z on both sides are single crystals, have low resistance, and low dislocations. It is optimal as a laser substrate. By determining the width of the stripe in accordance with the width of the laser, a group of lasers can be taken from one stripe. And if it cuts in the site | part of H and it is made not to use the part, it will be said that the defect was effectively eliminated. If the width of the laser is 400 μm, the width of the ZYZ portion sandwiched between H and H may be about 450 μm or 500 μm. FIG. 6 shows such a stripe type mask 24. This is a mask in which a large number of linear covering portions 25 are provided in parallel as seed E. When GaN is grown, a closed defect gathering region H grows on the straight covering portion 25.
[0055]
The cleavage plane of GaN is the {1-100} plane, but if any of them is orthogonal to the stripe, the laser chip can be separated by natural cleavage. Since it becomes a resonator surface, there is an advantage that a flat smooth surface can be easily formed.
[0056]
A structure in which the closed defect gathering region H, the single crystal low dislocation residual region Y, and the single crystal low dislocation associated region Z are arranged in parallel is called a stripe type. In the dot type, isolated defect gathering regions H are regularly arranged two-dimensionally, and in the stripe type, a large number of linear defect gathering regions H are regularly arranged in parallel. Those having no regularity in the distribution of the defect gathering region H are called random types.
[0057]
[Problems to be solved by the invention]
Here, a method for manufacturing three types of GaN single crystals using the closed defect assembly region H was introduced. Regarding the distribution of closed defect gathering regions, the conventional example (2) proposes a dot type and a random type. (3) proposes a stripe type.
[0058]
The faceted GaN crystal has three different sites,
Closed defect gathering region H
Single crystal low dislocation associated zone Z
Single crystal low dislocation residual region Y
[0059]
Is a single crystal. The single crystal low dislocation residual region Y + single crystal low dislocation associated region Z is a single crystal (low defect single crystal region U), but the closed defect assembly region H is not. However, it is sufficient if the closed defect gathering region H is not used as a laser substrate.
[0060]
Each of the above applications proposes a method of reducing dislocations using the distribution of closed defect gathering regions due to facet growth. Depending on the distribution of the closed defect gathering region H, it is simply called a random type, a dot type, or a stripe type. The dot type and random type have a single crystal single crystal low dislocation associated region Z and a single crystal low dislocation residual region Y concentrically around the closed defect gathering region H. A regular distribution is called a dot type, and a random distribution is called a random type. Both are concentric structures of HZY. The stripe type has a continuous structure of HZYZH. Both are clever GaN, but still have difficulties. State it.
[0061]
[1. Disadvantages of stripe type]
(3) It is formed from a linear defect collecting region H having a width of Japanese Patent Application No. 2001-311018 and linear low defect single crystal regions Z and Y having a width formed by facet surfaces on both sides thereof. In the GaN growth method (stripe type), the cleavage property is remarkably improved. Such a region may be intentionally formed in a parallel strip shape such as HZYZHZY... And a laser may be produced by a wafer process so that the laser chip is placed in the ZYZ portion. The laser can be regularly formed so that the central portion of the laser (active layer: stripe) does not reach H. When the wafer process is finished, the wafer is scribed in a direction (cleavage plane) perpendicular to the ZYZ side, and the H portion is also cut and cut into chips. The cavity surface of the laser becomes the cleavage plane. It is a particularly useful property when cutting out a laser chip. Furthermore, it is convenient that the resonator surface can be cleaved.
[0062]
Although there are such advantages, there is a problem that the crystal is weak, and cracks are likely to occur in the crystal substrate in the substrate removal, polishing, and wafer processes after growth. The stripe type easily cracks in the direction perpendicular to the stripe. This is shown in FIG. The black background portion is a closed defect gathering region H, and there are a single crystal low dislocation associated region Z and a single crystal low dislocation residual region Y on both sides thereof (the single crystal low dislocation residual region Y may not exist). The cleavage plane exists so as to be orthogonal to the stripe. For this reason, cracks 30 parallel to the cleavage plane often occur. The crack 30 is orthogonal to the stripe. The wafer may break due to the crack 30. The crack 30 is a long one extending over the entire diameter. There may be one or more than two.
[0063]
GaN is essentially a hard and brittle crystal. In the case of the stripe type, cracks are generated from the outer periphery of the GaN substrate due to thermal stress generated during cooling after crystal growth and stress generated during GaN substrate processing. Sometimes it breaks. Sometimes it breaks when it is grown, cooled and polished.
[0064]
In severe cases, cracks may occur on the wafer surface just by growing a single crystal and cooling. In that case, a round wafer itself cannot be manufactured in the first place. Even if it becomes a GaN wafer, when the laser device is manufactured by the wafer process, it breaks due to thermal stress.
[0065]
If it is so brittle and easily broken, a GaN, InGaN, AlGaN thin film or the like can be epitaxially grown on it and cut into a chip to make a laser device. Therefore, the yield is extremely bad.
[0066]
[2. Disadvantages of dot type and random type]
(2) In the growth method of Japanese Patent Application No. 2001-284323, stress concentrates on the core S where defects are gathered, but this core exists on the GaN substrate randomly or regularly. Since the closed defect gathering area and facet distribution are not linear, the cleavage plane is not uniform. A closed defect assembly region H, a single crystal low dislocation residual region Y, and a single crystal low dislocation associated region Z exist asymmetrically with respect to the cleavage plane, and stress is applied asymmetrically to the closed defect assembly region. Since asymmetrical stress is applied to the cleavage, it will not be cleaved cleanly and the cut will be jagged. In other words, there was a problem of poor cleavage.
[0067]
The cleaved surface of GaN is a {1-100} plane, and the one produced by that method is a single crystal as a whole, but the closed defect assembly region H is not a single crystal. The closed defect assembly region H may be polycrystalline, or even a single crystal may have its orientation reversed from another part. Anyway, in the closed defect gathering region H, the lattice structure is not continuous with the adjacent single crystal. Discontinuous. Therefore, even if it tries to cleave along a certain cleavage plane, if there is a closed defect gathering region on the extension line and the cutting line collides with it, it cannot be cleaved cleanly. Since the lattice is discontinuous in the closed defect gathering region, it is not continuously cleaved. Sometimes it is impossible to cut at that part. It may be cut around the closed defect gathering area.
[0068]
Then, the cleavage plane does not become a beautiful cut surface even if it is cleaved. It becomes jagged or breaks diagonally from the closed defect gathering area. Therefore, the random type and the dodd type have the disadvantage that cleavage is incomplete. This is inconvenient for a laser substrate.
[0069]
On the other hand, it was also a crystal that is less prone to cracking. Since a crack is a beautiful phenomenon of cutting at a cleavage plane, a crystal in which a closed defect gathering region is randomly distributed collides with the closed defect gathering region at some point, which prevents the cleavage. . Therefore, even if a crack is to be generated, it is immediately stopped by the closed defect gathering region H. So it won't break. That is, the random type and the dot type are strong against mechanical and thermal shocks and do not break easily, and are robust and robust in polishing and other wafer processing and are not broken. This is a significant advantage of the dot type and random type.
[0070]
As described above, the stripe type is excellent in cleavage but is brittle and easily cracks. The random type and dot type are robust and cannot crack, but are inferior in cleavage.
[0071]
It is a first object of the present invention to provide a method for producing a strong GaN wafer that has excellent cleavage properties and does not suffer from cracks and fractures.
It is a second object of the present invention to provide a method of manufacturing a GaN wafer that allows a large number of laser chips to be fabricated thereon and cut into chips by cleavage.
[0072]
[Means for Solving the Problems]
The single crystal gallium nitride substrate of the present invention has a large periodic pattern in which the opening and the covering part are regularly repeated and the outer peripheral part R and the central part Q are the same. For lateral overgrowth (Sr> Sq) having a window Wr that periodically repeats at a constant interval Sr narrower than the period of the large pattern and a window Wq that repeats periodically at a constant interval Sq shorter than Sr (Sr> Sq) ELO) A complex mask having a small pattern is formed in the outer peripheral portion R and the central portion Q of the surface of the starting substrate crystal, and gallium nitride is vapor-grown while maintaining facets, thereby randomly distributed defect collection regions Hf. And a low-defect single crystal region Uf adjacent thereto, a regularly arranged defect assembly region Hg and a low-defect single crystal region Ug adjacent thereto are grown, and irregular The total irregular area F of the distributed defect assembly region Hf and its adjacent low defect single crystal region Uf is equal to the total regular area G of the regularly arranged defect assembly region Hg and its adjacent low defect single crystal region Ug. The random area ratio M occupying the total area (G + F), which is the sum of the regular areas F, is lower in the central portion Q than in the outer peripheral portion R (Mq <Mr), and when the predetermined thickness is reached, the growth is stopped, It is manufactured by removing the starting substrate and the mask.
[0073]
The random area ratio Mq at the central portion Q is 10% or less (Mq ≦ 0.1). More desirably, the random area ratio Mq at the central portion Q is set to 0 to 1% (0 ≦ Mq ≦ 0.01).
[0074]
The random area ratio Mr at the outer peripheral portion R is preferably 10% or more (Mr ≧ 0.1). More preferably, the random area ratio Mr at the outer peripheral portion R is set to 30% to 70% (0.3 ≦ Mr ≦ 0.7).
[0075]
The random area ratio M is the ratio of the area of the defect gathering region H having an irregular distribution and the portion of the low defect single crystal region U associated therewith to the entire area. If this is large, the cleavage property decreases and the strength increases. When the random area ratio M is low, the cleaving property becomes clear, which is suitable for element isolation and laser resonator formation.
[0076]
The outer peripheral portion R increases the random area ratio M to increase the strength. The random area ratio M at the outer peripheral portion R is 10% or more. More preferably, it is 30% to 70%. Since the outer peripheral portion R has a high random area ratio M, it is robust and does not break. Therefore, the outer peripheral portion R having a high random area ratio M has a reinforcing effect. The outer peripheral portion R reinforces the central portion Q. The outer peripheral portion R has a reinforcing effect, but sacrifices the cleaving property, so that a high-performance optical element such as a laser cannot be produced therefrom. In other words, it is useless in terms of the substrate of the optical element, but it has an active role of reinforcing the central portion Q, so that is sufficient.
[0077]
On the other hand, the random area ratio M is low in the central portion Q, and is set to 10% or less. Preferably it is 1% or less. Since the random area ratio M is low, cleavage is strong and chip separation by natural cleavage becomes possible, and a laser resonator mirror can be formed by a cleavage plane. Lasers and light emitting diodes can be formed in the center Q of the wafer with good yield. If it is as it is, there is a possibility of cracks, cracks, breaks, etc. during polishing, transport, and wafer process. Such internal and external complementarity is a feature of the present invention.
[0078]
By making the interval S of the window of the ELO mask different between the central portion Q and the outer peripheral portion R, the ratio of the irregularly distributed defect collecting regions H to the regularly arranged defect collecting regions H is the central portion Q and the outer peripheral portion R. It is different. The definition of the interval S will be described with reference to FIG. In FIG. 21, the window is a regular hexagon and has an ELO pattern in which a regular hexagonal window is positioned at the corner of a set of regular triangles. However, the shape of the window is arbitrary, such as a circle, a square, a regular triangle, or a belt. Thus, the symmetry of the window arrangement is not limited to the six-fold rotational symmetry. 4-fold rotational symmetry, 3-fold rotational symmetry, 2-fold rotational symmetry, and the like may be used.
[0079]
In FIG. 21, the arrangement of the ELO windows W in the outer peripheral portion R is such that the windows with larger dimensions on the upper side are regularly arranged. The interval S is the distance from the edge of the adjacent window. That alone does not determine the window arrangement. A parameter indicating the size of the window is required. The window diameter W is also a parameter. The window interval Sr and the window diameter Wr at the outer peripheral portion R are larger than the window interval Sq and the window diameter Wq at the central portion Q. Sr> Sq, Wr> Wq. The diameter W is approximately equal to the spacing S. The window interval has been expressed so far as Sr> Sq. More specifically, the window interval and the window diameter are wide at the outer peripheral portion R and narrow at the central portion Q.
[0080]
Sr, Wr = 0.3 μm to 6 μm
Sq, Wq = 0.1 μm to 3 μm
When best
Sr, Wr = 2 μm
Sq, Wq = 1 μm
It is.
[0081]
DETAILED DESCRIPTION OF THE INVENTION
The central portion Q of the gallium nitride substrate of the present invention is a crystal having regularity and good cleaving properties, and the central portion Q is reinforced by the peripheral portion R as an irregular and excellent crystal in the peripheral portion R. It is. Since the central portion Q of the gallium nitride wafer has good cleavage and good regularity, it can be used for manufacturing a light emitting device, and the outer peripheral portion R has a reinforcing action, and the wafer is broken and cracks occur in the polishing process and the wafer process. To prevent. Table 1 shows definitions of the defect gathering region H, the low defect single crystal region U, the random area ratio M, and the like in the outer peripheral portion R and the central portion Q, and a comparison between the width and the narrowness.
[0082]
[Table 1]

[0083]
The width Rw of the outer peripheral portion R has a lower limit and must be 1 mm or more. If it is 1 mm or less, the reinforcing effect is small, and cracks are generated or broken. The reinforcement effect is larger when the width Rw of the outer peripheral portion R is larger.
[0084]
However, since the outer peripheral portion R is a wasteful portion, it is not desirable that the outer peripheral portion R be too wide. Although it depends on the diameter of the wafer, the width Rw of the outer peripheral portion R is 20 mm or less for economic reasons. That is, Rw = 1 to 20 mm.
[0085]
A more preferable width Rw of the outer peripheral portion R is 2 mm to 5 mm.
It is better that the central area Q has a lower random area ratio M. When the random area ratio M is low, the cleaving property appears strongly. If there is a cleavage plane, the chip can be naturally cleaved along the cleavage plane, and the parallel plane that has been cleaved can be effectively used as the mirror surface of the resonator. In this respect, it is more advantageous than that formed by heteroepitaxial growth on a sapphire substrate. The central part Q should have a lower random area ratio M. For this purpose, the random area ratio Mq of the central portion Q is set to 10% or less. More preferably, the random area ratio Mq is 0 to 1%. As described above, the outer peripheral portion R and the central portion Q have complementary properties, so that a gallium nitride single crystal that does not cause breakage, cracks, breakage, and the like and that is cleaved can be obtained. Complementarity between the central portion Q and the outer peripheral portion R is the essence of the present invention.
[0086]
Thus, the gallium nitride single crystal of the present invention has a concentric double structure of the central portion Q and the outer peripheral portion R. The difference on the substrate is the random area ratio M (Mq <0.1 <Mr). In order to make such a difference, the present invention forms a specially shaped composite mask on the starting substrate, and vapor-phase epitaxially grows gallium nitride thereon.
[0087]
The composite mask used in the present invention is a combination of a large pattern with a long period that repeats regularly in a period T with an opening and a covering part, and a small pattern for lateral overgrowth that consists of a window that repeats with a short period in a large pattern opening. It is a thing. The large pattern has an opening portion and a covering portion, and the covering portion is left as it is, but a further small pattern is provided in the opening portion. The small pattern is a pattern for the lateral overgrowth already described. Since it is a pattern for lateral overgrowth, windows are provided at intervals in the continuous covering portion to form openings.
[0088]
The large pattern is the same at the outer peripheral portion R and the central portion Q. Therefore, the period T of the large pattern is the same for the outer peripheral portion R and the central portion Q.
[0089]
In order to make a difference, the present invention devised a small pattern window interval. That is, the interval S between the small pattern windows W which are lateral overgrowth masks is different between the central portion Q and the outer peripheral portion R. Thereby, the area of the irregular portion and the regular portion of the defect gathering region H of the epitaxially grown gallium nitride is made different.
The window interval Sr at the outer peripheral portion R is wider, and Sr = 0.3 μm to 6 μm.
The window interval Sq at the central portion Q is narrower and Sq = 0.1 μm to 3 μm.
[0090]
[Table 2]

[0091]
[Table 3]

[0092]
FIG. 13 shows the mask of the comparative example, and FIGS. 14 and 15 show the inner and outer double masks used in the present invention.
[A. Random type inner / outer double mask (Fig. 13)]
In this case, only the ELO (small pattern) has an internal / external double structure. The window diameter and interval at the center Q (inside) are narrow, and the window diameter and interval at the outer periphery R (outside) are wide. Since there is no large regular pattern (opening + cover), even if it is formed on the base substrate and GaN is facet grown, the regular defect collection region H cannot be created. The defect collection region H is randomly distributed as shown in FIG. This is illustrated because the small pattern has a basic internal / external double structure which cannot be used for the present invention.
[0093]
[B. Dot-type inner / outer double mask (Figure 14)]
This is a composite mask in which ELO (small pattern) is provided in an inner / outer double structure in the opening of a large dot pattern. The ELO mask (small pattern) has an internal / external double structure, which is the same as the previous example, but differs from A in that it has a dot-type large pattern. The ELO (small pattern) pattern has a narrow window diameter and interval at the central portion Q (inside) and a wide window diameter and interval at the outer peripheral portion R (outside). Since there is a regular dot-shaped large pattern (opening portion + covering portion), when this is formed on the underlying substrate and GaN is facet grown, it is adjacent to the defect collection region H that is regularly arranged on the dot and the defect gathering region H. A low defect single crystal region U can be created. In addition, it is possible to generate a defect gathering region H that is irregularly distributed in part and a low defect single crystal region U adjacent thereto. This is a mask that can be used for the GaN production of the present invention. The large pattern is common to the inside and outside, but the small pattern has a double structure inside and outside.
[0094]
[C. Striped inner / outer double mask (Figure 15)]
This is a composite mask in which ELO (small pattern) is provided in an inner / outer double structure in the opening of a stripe-type large pattern. The ELO mask (small pattern) has an internal / external double structure, which is the same as the previous example, but differs from A in that it has a stripe-type large pattern. The ELO (small pattern) pattern has a narrow window diameter and interval at the central portion Q (inside) and a wide window diameter and interval at the outer peripheral portion R (outside). Since there is a regular dot-shaped large pattern (opening portion + covering portion), when this is formed on the base substrate and GaN is facet grown, it is adjacent to the defect gathering region H which is regularly arranged in stripes and adjacent to it. A low defect single crystal region U can be created. In addition, it is possible to generate a defect gathering region H that is irregularly distributed in part and a low defect single crystal region U adjacent thereto. This is a mask that can be used for the GaN production of the present invention. The large pattern is common to the inside and outside, but the small pattern has a double structure inside and outside.
[0095]
【Example】
A composite mask having a large pattern of regularly arranged openings and shielding parts and a small pattern (ELO) that differs between the inside and outside of the large pattern openings was formed on a GaAs substrate. A GaN epitaxial layer was grown on the mask by HVPE. Hydrogen gas (H ₂ ) Was used. Source gases include hydrogen chloride gas (HCl) and ammonia gas (NH ₃ ) Was used.
[0096]
First, a GaN buffer layer having a thickness of about 80 nm was formed at a low growth temperature (530 ° C.). The growth conditions for the GaN buffer layer are as follows.
[Buffer layer growth conditions]
Gas flow 5L (flow rate 100cm / min)
Ga partial pressure 2.5 × 10 ^-3 atm (0.33Pa)
NH ₃ Partial pressure 0.12 atm (16 Pa)
Growth temperature 530 ° C
Growth time 20 minutes
Growth thickness 80nm
[0097]
Thereafter, the temperature was raised to 1030 ° C., and a GaN epilayer was grown thereon by about 3 mm (3000 μm) under the following conditions.
[0098]
[Epitaxial layer growth conditions]
Gas flow 5L (flow rate 100cm / min)
Ga partial pressure 1.6 × 10 ^-2 atm (2.1 Pa)
NH ₃ Partial pressure 0.2atm (27Pa)
Growth temperature 1030 ° C
Growth time 30 hours
Growth thickness 3000μm (3mm)
[0099]
As a result, a sample of GaN / GaAs was obtained. It was etched with aqua regia to remove the GaAs substrate and mask. A self-standing (free standing) single crystal gallium nitride substrate was obtained. This was processed and polished to prepare 14 types of samples (Sample 1 to Sample 14) of a flat GaN single crystal substrate. There were tens to hundreds of samples under the same conditions.
[0100]
The boundary between the outer peripheral portion R and the central portion Q of the samples 1 to 14 was examined, and the width Rw of the outer peripheral portion R was measured. GG single crystal substrate samples (sample 1 to sample 14) at the center Q of the defect arrangement region Hg regularly arranged _q And its low-defect single crystal region Ug _q The total area G was determined. Similarly, the defect collection region Hf irregularly distributed in the central portion Q _q And the low-defect single crystal region Uf around it _q The total area F was determined. F was divided by (F + G) to obtain a random area ratio Mq at the central portion Q.
[0101]
Similarly, the defect collecting region Hg regularly arranged on the outer peripheral portion R of the samples 1 to 14 _r And its low-defect single crystal region Ug _r The total area G was determined. Defect collection region Hf that is irregularly distributed in outer periphery R _r And the low-defect single crystal region Uf around it _r The total area F was determined. F was divided by (F + G) to obtain a random area ratio Mr at the outer peripheral portion R.
[0102]
It was investigated whether a crack occurred in the central portion Q. If even one crack was generated, it was regarded as a crack-generating substrate, and a substrate having no cracks was determined as a non-cracking substrate. Since there are several tens to several hundreds of samples for the same sample number, the crack generation frequency K was determined by dividing the number of crack generation substrates by the total number of each.
[0103]
Table 4 shows the central portion Q random area ratio Mq (%), the outer peripheral portion R random area ratio Mr (%), the width Rw (mm) of the outer peripheral portion R, and the crack occurrence frequency K (%) for each sample 1-14. Show.
[0104]
[Table 4]

[0105]
[Sample 1 (Mq = 100%, Mr = 100%, K = 0%, Rw = 0)]
This does not have an internal / external double structure. It is not an embodiment of the present invention. A GaN crystal is formed by facet growth using a mask having only a small pattern without a large pattern as shown in FIG. 10, that is, a lateral overgrowth mask having a uniform fine window arrangement. The defect gathering regions H are irregularly distributed both inside and outside. This indicates that when the facet growth is performed only with the lateral overgrowth (ELO) mask, the defect collection regions H are randomly distributed. The random area ratio M is 100% uniformly throughout the substrate, which is robust. Cracks do not occur. Although it is the most excellent in that respect, it is not suitable as a substrate for a laser element or an LED element because there is no cleavage at the central portion Q.
[0106]
[Sample 2 (Mq <1%, Mr <1%, K = 90%, Rw = 0)]
This also has no internal / external double structure. This is not an example of the present invention. A GaN substrate grown by HVPE with a composite mask having a large pattern consisting of regularly arranged openings and coverings and a small pattern (ELO) with a small uniform window arrangement in the openings on a GaAs substrate. It is. Since the intervals of the small patterns are uniform inside and outside, there is no double structure inside and outside. Even in the outer peripheral portion R, the random area ratio M is 1% or less, and the defect gathering regions H are regularly arranged and cleaved. Therefore, it is weak and the crack occurrence frequency K is 90%. Those manufactured by the uniform mask method are easily damaged and weak.
[0107]
[Sample 3 (Mq <1%, Mr = 100%, K = 90%, Rw = 0.1 mm)]
This is a comparative example having an internal / external double structure. A composite mask containing a large pattern consisting of openings and coverings arranged regularly both inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the large pattern openings, is attached to the GaAs substrate. Then, GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which a seed E is provided in a dot shape as shown in FIG. 14 is used. Alternatively, a composite mask in which a seed E is provided in parallel in a stripe type as shown in FIG.
[0108]
The crack occurrence frequency is as high as 90%. This is because the outer peripheral portion R is too narrow. The width of the outer peripheral portion R is Rw = 0.1 mm. It is too narrow and the reinforcing effect is insufficient. In addition, it is suggested that the random area ratio M of the outer peripheral portion R is not 100%.
[0109]
[Sample 4 (Mq <1%, Mr = 100%, K = 70%, Rw = 4 mm)]
This is also a comparative example having an internal / external double structure. A composite mask containing a large pattern consisting of openings and coverings arranged regularly both inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the large pattern openings, is attached to the GaAs substrate. Then, GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which a seed E is provided in a dot shape as shown in FIG. 14 is used. Alternatively, a composite mask in which a seed E is provided in parallel in a stripe type as shown in FIG.
[0110]
The cracking frequency is still as high as 70%. Although it can be used even if the crack occurrence frequency is 70%, a lower ratio is desirable.
The outer peripheral portion R is Rw = 4 mm and has a sufficient width.
[0111]
Since the random area ratio Mr of the outer peripheral portion R is 100% and the random area ratio Mq of the central portion Q of 1% or less is too different, the state of the organization, the growth rate, the warp, etc. are greatly different inside and outside, and at the inner and outer boundaries A large amount of stress is generated, which may be causing the crack. Sample 4 means that the difference in the internal and external random area ratio M should not be too large.
[0112]
However, the random area ratio Mr = 100% of the outer peripheral portion R is not prohibited at all. If the random area ratio Mq at the central portion Q is as large as 10%, the frequency of occurrence of cracks becomes lower and becomes practical.
[0113]
[Sample 5 (Mq <1%, Mr = 80%, K = 90%, Rw = 0.1 mm)]
This is also a comparative example having an internal / external double structure. Similar to Samples 3 and 4, it includes a large pattern consisting of openings and coverings regularly arranged on the inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the large pattern openings. A composite mask is attached to a GaAs base substrate, and GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which the seed E is provided in the dot type (FIG. 14) or a composite mask in which the seed E is provided in parallel in the stripe type (FIG. 15) is used.
[0114]
The cracking frequency is still as high as 90%. This is because the reinforcing effect is weak because the width of the outer peripheral portion R is as narrow as Rw = 0.1 mm. If the width of the outer periphery R is made wider, the frequency of occurrence of practical cracks will be lowered.
[0115]
[Sample 6 (Mq <1%, Mr = 80%, K = 30%, Rw = 4 mm)]
This is an embodiment having an internal / external double structure. Similar to Samples 3 to 5, including a large pattern of openings and coverings regularly arranged on both the inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the openings of the large pattern A composite mask is attached to a GaAs base substrate, and GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which the seed E is provided in the dot type (FIG. 14) or a composite mask in which the seed E is provided in parallel in the stripe type (FIG. 15) is used.
[0116]
The crack occurrence frequency is as low as 30%. This is because the outer peripheral portion R is wide such that Rw = 4 mm and the reinforcing effect appears strongly. Although it may be 4 mm, if the width of the outer peripheral portion R is made wider, the frequency of occurrence of cracks is further reduced.
[0117]
This has a practical meaning with a crack occurrence frequency of 30%. Compared with Sample 4, the difference is that the random area ratio Mr at the outer peripheral portion R decreases from 100% to 80%, and the difference in the random area ratio M between the inside and outside is reduced by 20%. If the internal / external random area ratio M is too large, the growth rate is different, the crystal structure is also different, and an internal stress is strongly generated at the internal / external boundary, which promotes the generation of cracks.
This suggests that it would be better to further reduce the difference between the internal and external random area ratios Mq and Mr.
[0118]
[Sample 7 (Mq <1%, Mr = 50%, K = 90%, Rw = 0.1 mm)]
This is also a comparative example having an internal / external double structure. Similar to Samples 3 to 6, including a large pattern of openings and coverings regularly arranged on both the inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the openings of the large pattern A composite mask is attached to a GaAs base substrate, and GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which the seed E is provided in the dot type (FIG. 14) or a composite mask in which the seed E is provided in parallel in the stripe type (FIG. 15) is used.
[0119]
According to the meaning of the sample 6, the random area ratio M of the outer peripheral portion R is lowered to 50%. However, the crack occurrence frequency is still as high as 90%. This is because the reinforcing effect is weak because the width of the outer peripheral portion R is as narrow as Rw = 0.1 mm. If the width of the outer peripheral portion R is made wider, the frequency of occurrence of cracks will be lowered.
[0120]
[Sample 8 (Mq <1%, Mr = 50%, K = 10%, Rw = 4 mm)]
This is also an embodiment having an internal / external double structure. Similar to Samples 3 to 7, including a large pattern of openings and coverings regularly arranged on both the inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the openings of the large pattern A composite mask is attached to a GaAs base substrate, and GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which the seed E is provided in the dot type (FIG. 14) or a composite mask in which the seed E is provided in parallel in the stripe type (FIG. 15) is used.
[0121]
According to the meaning of the sample 6, the random area ratio M of the outer peripheral portion R is lowered to 50%. The width of the outer peripheral portion R is also widened such that Rw = 4 mm. The occurrence frequency of cracks is as low as 10%.
[0122]
Compared with Sample 4 and Sample 6, the random area ratio Mr of the outer peripheral portion R is 50%, and the difference between the inner and outer random area ratio M is reduced to 50% or less. This may alleviate the difference in growth rate, reduce the difference in internal structure, reduce the internal stress at the boundary, and suppress the generation of cracks. It can be seen that the random area ratio Mr of the outer peripheral portion R is preferably 70% or less as compared with Samples 4 and 6.
[0123]
Even if the random area ratio Mr of the outer peripheral portion R is 70% to 100%, the difference is reduced when the random area ratio M of the central portion Q is close to 10%, so that the occurrence of cracks is reduced.
Then, what is the allowable lower limit of the random area ratio Mr of the outer peripheral portion R becomes a problem.
[0124]
[Sample 9 (Mq <1%, Mr = 30%, K = 90%, Rw = 0.1 mm)]
This is a comparative example having an internal / external double structure. Similar to Samples 3 to 8, including a large pattern composed of openings and coverings arranged regularly both inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the large pattern openings. A composite mask is attached to a GaAs base substrate, and GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which the seed E is provided in the dot type (FIG. 14) or a composite mask in which the seed E is provided in parallel in the stripe type (FIG. 15) is used.
[0125]
According to the suggestion of the sample 8, the random area ratio M of the outer peripheral portion R is lowered to 30%. However, the crack occurrence frequency is still as high as 90%. This is because the width of the outer peripheral portion R is so narrow that Rw = 0.1 mm and the reinforcing effect is weak. If the width of the outer peripheral portion R is made wider, the frequency of occurrence of cracks will be lowered. So I tried increasing Rw.
[0126]
[Sample 10 (Mq <1%, Mr = 30%, K = 10%, Rw = 4 mm)]
This is an embodiment having an internal / external double structure. Similar to Samples 3 to 9, including a large pattern consisting of openings and coverings regularly arranged on the inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the openings of the large pattern A composite mask is attached to a GaAs base substrate, and GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which the seed E is provided in the dot type (FIG. 14) or a composite mask in which the seed E is provided in parallel in the stripe type (FIG. 15) is used.
[0127]
According to the suggestion of Samples 8 and 9, the random area ratio M of the outer peripheral portion R is lowered to 30% and the width of the outer peripheral portion R is increased to Rw = 4 mm. The crack occurrence frequency is sufficiently low such as 10%. That is, the width of the outer peripheral portion R is as wide as Rw = 4 mm and has a reinforcing effect, and the random area ratio M at the outer peripheral portion R is 30%, and the difference between the inner and outer random area ratio M is small. This is probably because the inner and outer growth rate differences and crystal structure differences are small and no strong stress is generated at the boundaries. It was found that the outer peripheral portion R random area ratio Mr may be as low as 30%. Further, the random area ratio Mr of the outer peripheral portion R is lowered and the effect is examined.
[0128]
[Sample 11 (Mq <1%, Mr = 10%, K = 90%, Rw = 0.1 mm)]
This is a comparative example having an internal / external double structure. A composite mask containing a large pattern consisting of openings and coverings arranged regularly both inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the large pattern openings, is attached to the GaAs substrate. GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which the seed E is provided in the dot type (FIG. 14) or a composite mask in which the seed E is provided in parallel in the stripe type (FIG. 15) is used.
[0129]
The random area ratio Mr of the outer peripheral portion R is lowered to 10% according to the suggestion of the samples 8 to 10. The occurrence frequency of cracks is extremely high as 90%. This is not known because the width of the outer peripheral portion R is so narrow that Rw = 0.1 mm and the reinforcing effect is weak, or because the random area ratio Mr = 10% is low. So I tried increasing Rw.
[0130]
[Sample 12 (Mq <1%, Mr = 10%, K = 40%, Rw = 4 mm)]
This is an embodiment having an internal / external double structure. A composite mask containing a large pattern consisting of openings and coverings arranged regularly both inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the large pattern openings, is attached to the GaAs substrate. GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which the seed E is provided in the dot type (FIG. 14) or a composite mask in which the seed E is provided in parallel in the stripe type (FIG. 15) is used.
[0131]
According to the suggestion of Samples 8 to 11, the random area ratio Mr of the outer peripheral portion R is lowered to 10%, and the width of the outer peripheral portion R is increased to Rw = 4 mm. The crack occurrence frequency is as high as 40%. Although it can be used even with a crack occurrence frequency of 40%, dissatisfaction remains.
[0132]
The width of the outer peripheral portion R will be sufficient because Rw = 4 mm. Compared with samples 8 and 10, it can be seen that the random area ratio Mr = 10% of the outer peripheral portion R is too low. This means that the random area ratio Mr of the outer peripheral portion R is desirably 30% or more. From the samples 6, 8, 10, and 12, it can be seen that the preferable range of the random area ratio Mr of the outer peripheral portion R is 30% to 70%.
[0133]
This is because the random area ratio Mq of the central portion Q is 1% or less and the difference between inside and outside is emphasized. When the random area ratio Mq of the central portion Q is close to 10%, the random area ratio Mr of the outer peripheral portion R can be set to 70 to 100%.
[0134]
[Sample 13 (Mq <1%, Mr = 5%, K = 90%, Rw = 0.1 mm)]
This is a comparative example having an internal / external double structure. A composite mask containing a large pattern consisting of openings and coverings arranged regularly both inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the large pattern openings, is attached to the GaAs substrate. GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which the seed E is provided in the dot type (FIG. 14) or a composite mask in which the seed E is provided in parallel in the stripe type (FIG. 15) is used.
[0135]
The random area ratio Mr of the outer peripheral portion R is further lowered to 5%. The occurrence frequency of cracks is extremely high as 90%. This is probably because the width of the outer peripheral portion R is so narrow that Rw = 0.1 mm and the reinforcing effect is weak, or the random area ratio Mr = 5% is low.
[0136]
[Sample 14 (Mq <1%, Mr = 5%, K = 50%, Rw = 4 mm)]
This is a comparative example having an internal / external double structure. A composite mask containing a large pattern consisting of openings and coverings arranged regularly both inside and outside, and a small pattern for lateral overgrowth (ELO) in which fine windows are arranged at equal intervals in the large pattern openings, is attached to the GaAs substrate. GaN is grown thereon by the HVPE method. As the composite mask, for example, a composite mask in which the seed E is provided in the dot type (FIG. 14) or a composite mask in which the seed E is provided in parallel in the stripe type (FIG. 15) is used.
[0137]
The random area ratio Mr of the outer peripheral portion R is lowered to 5%. The frequency of occurrence of cracks is extremely high, such as 50%. Since the width of the outer peripheral portion R is sufficient and Rw = 4 mm and the crack occurrence frequency is 50%, the random area ratio Mr = 5% of the outer peripheral portion R is too low. Comparing sample 12 and sample 14, it can be seen that the random area ratio Mr of the outer peripheral portion R must be 10% or more.
[0138]
【The invention's effect】
In Sample 8 and Sample 10 of the above examples, the occurrence of cracks at the center of the wafer could be suppressed to 10%. In conventional wafers that have no distinction between the outer peripheral part and the central part, cracks parallel to the cleaved surface may occur due to thermal stress in the wafer process, and the wafer may break. By making the ratio Mr larger than the random area ratio Mq in the central portion, it is possible to suppress the occurrence of cracks from the outer peripheral portion and to prevent wafer breakage.
[0139]
Using the central portion of the wafer grown by the method of the present invention, a GaN, InGaN, AlGaN thin film, or the like is epitaxially grown on the wafer and cut into a chip using the cleavage plane. . It becomes possible to manufacture a GaN wafer with a very good yield.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a lateral overgrowth method. (1) is a substrate, (2) is a substrate provided with a mask, (3) is a crystal nucleus generated in the opening, (4) is a state in which a GaN thin film is formed in the opening, 5) is a dislocation with a GaN crystal grown in a pyramid shape from the opening, (6) is a GaN crystal grown laterally from the opening onto the mask, and (7) is a crystal grown laterally from the adjacent opening. (8) shows a state in which the C-plane is grown while maintaining a flat C-plane after merging.
FIG. 2 shows that when seed E is provided in a regular arrangement on a substrate and GaN is facet grown thereon, the facet pits extend from seed E, and the immediately upper part of seed E becomes a closed defect gathering region H. FIG. 5 is a partially enlarged plan view of a facet-grown GaN crystal for explaining that it becomes a regular hexagonal facet pit and grows as a flat C-plane between pits.
3] When seed E is provided in a regular arrangement on the substrate and GaN is facet grown on it, facet pits extend from seed E, and the upper part of seed E becomes a closed defect gathering region H. Single crystal low dislocation associated region Z, which is single crystal with few defects, grows, and single crystal low dislocation residual region Y, with few defects and single crystal, grows under the flat C-plane. Sectional drawing for demonstrating this.
FIG. 4 shows a closed defect set of GaN crystal when facet-grown GaN is grown on a mask having seeds E arranged in a regular arrangement on a substrate to grow dot-type single crystal GaN in which closed defect set regions are regularly distributed. The top view for showing field distribution.
FIG. 5: Species E is randomly arranged on the substrate, or GaN is facet grown on the substrate without any seed, and random single crystal GaN in which closed defect gathering regions are randomly distributed is grown. The top view for showing the random distribution of the closed defect gathering area | region of a GaN crystal at the time.
FIG. 6 is a plan view of a striped mask having parallel covering portions formed on a substrate in order to generate a plurality of parallel closed defect gathering regions H by facet growth.
7 shows a plurality of parallel closed defect gathering regions H appearing on the surface of a GaN crystal when facet grown using the stripe covering portion mask of FIG. 6, and parallel single crystal low dislocation associated regions Z occurring on both sides thereof. FIG. 3 is a plan view of a GaN crystal showing a single crystal low dislocation residual region Y.
8 shows a plurality of parallel closed defect gathering regions H appearing on the surface of a GaN crystal when facet grown using the stripe covering portion mask of FIG. 6 and parallel single crystal low dislocation associated regions Z occurring on both sides thereof. FIG. 3 is a longitudinal sectional view of a GaN crystal showing a single crystal low dislocation residual region Y.
9 is a GaAs substrate coated with a parallel stripe mask as shown in FIG. 6 and crystal growth of GaN. As shown in FIGS. When the defect single crystal region U (single crystal low dislocation associated region Z + single crystal low dislocation residual region Y) is generated, the cleavage property is strong, and therefore, in the etching, polishing, and wafer processes, it may break in the direction perpendicular to the stripe. The top view of the growth GaN substrate for showing that there exists.
FIG. 10 is a plan view of an ELO mask in which a small pattern for lateral overgrowth having equal fine windows W regularly arranged at short regular intervals is formed on the entire surface.
FIG. 11 shows a large facet growth pattern in which a covering portion (seed E) and openings are regularly arranged in a lattice pattern (dot type) with a long period so that defect gathering regions H are regularly formed in a lattice shape, and short in the openings. The top view of the composite mask containing the small pattern for lateral overgrowth with the equivalent fine window W arranged regularly at regular intervals.
FIG. 12 shows a large facet growth pattern in which covering portions (seed E) and openings are regularly arranged in a long period in parallel stripes so that defect gathering regions H are regularly formed in parallel stripes, and short constant intervals in the openings. The top view of the composite mask containing the small pattern for lateral overgrowth with the equivalent fine window W regularly arranged in order.
FIG. 13 The inner and outer double lateral overgrowth small have the same fine windows regularly arranged at a slightly wide constant interval at the outer peripheral portion R and the same fine windows regularly arranged at a slightly narrow constant interval at the central portion Q. The top view of the double ELO mask in which the pattern was formed.
FIG. 14 shows a large pattern for facet growth in which covering portions (seed E) and openings are regularly arranged in a lattice pattern (dot type) in a long cycle so that defect gathering regions H are formed in a regular lattice shape, and an outer periphery in the opening portion. The portion R includes a small pattern for inner and outer double lateral overgrowth having an equal fine window regularly arranged at a slightly wide constant interval, and the central portion Q having an equivalent fine window regularly arranged at a slightly narrow constant interval. The top view of the composite mask used by.
FIG. 15 shows a large facet growth pattern in which covering portions (seed E) and openings are regularly arranged in a long period in parallel stripes so that defect collecting regions H are regularly formed in parallel stripes, and an outer peripheral portion R in the openings. In the present invention, the center Q includes a small pattern for inner and outer double lateral overgrowth having an equal fine window regularly arranged at a constant interval slightly wider and an equal fine window regularly arranged at a constant interval slightly narrower at the center Q. FIG.
FIG. 16 shows a portion including a defect gathering region H randomly distributed in a facet grown GaN crystal and a low defect single crystal region U (single crystal low dislocation associated region Z + single crystal low dislocation residual region Y) adjacent thereto. (Cathodeluminescence) Plan view of what was observed. A defect collection region H randomly distributed in various dimensions and a low defect single crystal region U in contact therewith can be seen. The position, size and shape of the low defect single crystal region U are also irregular. All appearing in this figure are irregularly distributed defect gathering regions Hf and low-defect single crystal regions Uf, and are therefore included in the area F of the irregularly distributed regions.
17 is a cross-sectional view taken along line 17-17 in FIG. 16; Defect assembly regions Hf of various positions, sizes, and shapes and low defect single crystal regions Uf (single crystal low dislocation associated regions Z + single crystal low dislocation residual regions Y) are generally constant in the vertical direction but random in the horizontal direction. It is.
FIG. 18 shows irregularly distributed defect assembly regions H and low defect single crystal regions U in a facet grown GaN crystal, and regularly arranged defect assembly regions H and low defect single crystal regions U (in the form of stripes). The top view which looked at the structure of the boundary part of this in CL. This shows a clear structural change in which a regular stripe structure having a uniform width and a uniform width ends, and there are defect collection regions H and low defect single crystal regions U that are irregularly distributed from the wedge-shaped boundary. The portion above the wedge-shaped boundary is included in the area G of the regular distribution region. The portion below the wedge-shaped boundary is included in the area F of the irregular distribution region. The random area ratio M is defined as the area F of the irregular region divided by the total area (F + G). M = F / (F + G).
FIG. 19 is a cross-sectional view taken along line 19-19 in FIG. 18;
20 is a cross-sectional view taken along line 20-20 in FIG.
FIG. 21 shows the ratio of the defect gathering regions H distributed irregularly and the defect gathering regions H regularly arranged by differentiating the window spacing S of the ELO mask between the central part Q and the outer peripheral part R; The figure explaining the definition of the space | interval S and the window W in this invention made different by the outer peripheral part R. FIG. In the outer peripheral portion R, the interval Sr and the window Wr are large, and in the central portion Q, the interval Sq and the window Wq are small.
[Explanation of symbols]
2 Substrate
3 Mask
4 windows
5 GaN crystal nucleus
6 Film-like GaN crystal
7 Conical GaN crystal
8 Facet surface
9 Top surface
20 Collision surface
21 Mask
22 Mask
23 Top view
24 mask
25 Shielding part
26 opening
27 Covering part
H Close defect area
E species
Z single crystal low dislocation associated region
Y single crystal low dislocation residual region
Q center
R Outer periphery
U Low defect single crystal region
S Mask window interval
W window

Claims (17)

  A plurality of regularly arranged defect collection regions Hg having a peripheral portion R and a central portion Q, and a low defect single crystal region Ug adjacent thereto, a plurality of irregularly distributed defect collection regions Hf, and a low defect adjacent thereto The total area of the irregularly distributed defect assembly region Hf and the low defect single crystal region Uf adjacent thereto including the single crystal region Uf is F, and the area of the regular array defect assembly region Hg and the low defect single crystal region Ug adjacent thereto is F. Is defined as G, and a random area ratio M = F / (F + G) is defined as a value for the entire area (F + G) of the irregular area F, and the outer peripheral portion R is larger than the random area ratio Mq in the central portion Q. A single crystal gallium nitride substrate characterized in that the random area ratio Mr is higher (Mr> Mq).   The single crystal gallium nitride substrate according to claim 1, wherein a width Rw of the outer peripheral portion R is 1 to 20 mm.   The single crystal gallium nitride substrate according to claim 2, wherein the width Rw of the outer peripheral portion R is 2 mm to 5 mm.   The single-crystal gallium nitride substrate according to any one of claims 1 to 3, wherein the random area ratio Mq at the central portion Q is 0 to 10%.   The single-crystal gallium nitride substrate according to any one of claims 1 to 3, wherein the random area ratio Mq at the central portion Q is 0 to 1%.   6. The single crystal gallium nitride substrate according to claim 1, wherein the random area ratio Mr at the outer peripheral portion R is 10% to 100%.   The single crystal gallium nitride substrate according to any one of claims 1 to 5, wherein a random area ratio Mr at the outer peripheral portion R is 30% to 70%.   The opening and the covering portion regularly repeat and have a large periodic pattern in which the outer peripheral portion R and the central portion Q are the same. A composite mask having a small pattern for lateral overgrowth (Sr> Sq) having a window Wr that periodically repeats at a certain interval Sq shorter than Sr in the central portion Q. Formed on the outer peripheral portion R and the central portion Q of the surface of the crystal, and a gallium nitride crystal is grown on the composite mask while maintaining facets by a vapor phase synthesis method, and is adjacent to the regularly arranged defect gathering region Hg. After growing a gallium nitride crystal composed of the low defect single crystal region Ug, the irregularly distributed defect aggregation region Hf and the adjacent low defect single crystal region Uf, and reaching a predetermined thickness The crystal growth is stopped, the substrate and the mask are removed to form a self-supporting gallium nitride wafer, the total area of the irregularly distributed defect aggregate region Hf and the adjacent low defect single crystal region Uf is F, and the regularly distributed defect aggregate region The total area of Hg and the low-defect single crystal region Ug adjacent thereto is defined as G, and the random area ratio M = F / (F + G) is defined as the value of the irregular region area F with respect to the total area (F + G). The random area ratio Mq at is lower than the random area ratio Mr at the outer peripheral portion R, and the outer peripheral portion R has a reinforcing action to prevent cracking and breakage at the central portion Q. A method for manufacturing a single crystal gallium nitride substrate.   The spacing Sq of the small pattern for lateral overgrowth at the central portion Q is 0.1 to 3 μm, and the spacing Sr of the small pattern for lateral overgrowth at the outer peripheral portion R is larger than Sq and 0.3 μm. The method for producing a single crystal gallium nitride substrate according to claim 8, wherein the thickness is ˜6 μm.   A value (Sr−Sq) obtained by subtracting the window spacing Sr of the lateral overgrowth small pattern at the outer peripheral portion R by the window spacing Sq of the lateral overgrowth small pattern at the center Q is 0.2 μm to 3 μm. The method for producing a single crystal gallium nitride substrate according to claim 8, wherein   A value (Sr−Sq) obtained by subtracting the window spacing Sr of the lateral overgrowth small pattern at the outer peripheral portion R by the window spacing Sq of the lateral overgrowth small pattern at the central portion Q is 0.5 μm to 1. The method for producing a single crystal gallium nitride substrate according to claim 10, wherein the method is 5 μm.   The space Sq between the windows of the small patterns for lateral overgrowth at the central portion Q is 1 μm, and the space between the windows for lateral overgrowth at the outer peripheral portion R is 2 μm. A method for manufacturing a single crystal gallium nitride substrate.   The method for producing a single crystal gallium nitride substrate according to any one of claims 8 to 12, wherein a width Rw of the outer peripheral portion R is 1 to 20 mm.   14. The single-crystal gallium nitride substrate according to claim 8, wherein the growth rate in the outer peripheral portion minus the growth rate in the central portion is 50% or less of the outer peripheral growth rate. Method. Similarly, the outer peripheral portion R and the central portion Q have a large periodic pattern in which the opening portion and the covering portion are regularly repeated with a wide period, and the large pattern opening portion is narrower in the outer peripheral portion R than the period of the periodic large pattern. Lateral overgrowth has a window Wr that repeats periodically at intervals Sr of 0.3 to 6 μm and has a window Wq that repeats periodically at intervals Sq of 0.1 μm to 3 μm shorter than Sr in the central portion Q (Sr> Sq). A base substrate for growing gallium nitride, wherein a composite mask having a small pattern is formed on an outer peripheral portion R and a central portion Q of a surface of a substrate crystal.   The periodic large pattern in which the opening and the covering portion are regularly repeated with a wide period is composed of a plurality of parallel stripe-like covering portions arranged at a constant interval with a constant width and an opening portion therebetween. The base substrate for gallium nitride growth according to claim 15.   A large periodic pattern in which the opening and the covering part are regularly repeated with a wide period is an isolated polygonal or circular covering part arranged in a two-dimensional manner with a rotational symmetry at regular intervals, and the opening between them. The gallium nitride growth base substrate according to claim 15, wherein the gallium nitride growth base substrate is made of.

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