JP2004296640A - GROWTH METHOD OF GaN SEMICONDUCTOR LAYER, SEMICONDUCTOR SUBSTRATE MANUFACTURING METHOD USING THE SAME, AND METHOD OF MANUFACTURING SEMICONDUCTOR DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of growing a GaN semiconductor layer of high quality at a high speed through a hydride vapor growth method. <P>SOLUTION: In a process of feeding V material gas containing a nitrogen element and group III material gas formed of a compound containing Ga and halogen to the surface of a substrate, a group V/III ratio specified by the ratio of the feed flow rate of the group III material gas to that of the group V material gas is set at 0.1 to below 10. As shown by a curve (a) in the graph, the group V/III ratio is set at about 5 to 9. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３０】
各ＮＯ．の出典は以下のとおりである。
ＮＯ．１ Ｈｗａ−Ｍｏｋ Ｋｉｍ ｅｔ ａｌ， ＩＰＡＰ Ｃｏｎｆ． Ｓｅｒｉｅｓ １ ｐｐ．４９−５２
ＮＯ．２ Ｓｕｎｇ． Ｓ． Ｐａｒｋ ｅｔ ａｌ， ＩＰＡＰ Ｃｏｎｆ． Ｓｅｒｉｅｓ １ ｐｐ．６０−６３
ＮＯ．３ Ｋ．Ｍｏｔｏｋｉ ｅｔ ａｌ， Ｊｐｎ．Ｊ．Ａｐｐｌ．Ｐｈｙｓ． Ｖｏｌ．４０（２００１）ｐｐ．Ｌ１４０−１４３．
ＮＯ．４ Ｙ．Ｏｓｈｉｍａ ｅｔ ａｌ， ｐｈｙｓ．ｓｔａｔ．ｓｏｌｉ．（ａ） １９４， Ｎｏ． ２， ５５４−５５８（２００２）．
ＮＯ．５ Ｄ．Ｍａｒｔｉｎ ｅｔ ａｌ， ｐｈｙｓ．ｓｔａｔ．ｓｏｌｉ．（ａ） １９４， Ｎｏ． ２， ５２０−５２３（２００２）．
ＮＯ．６ Ａ．Ｕｓｕｉ ｅｔ ａｌ， Ｊｐｎ．Ｊ．Ａｐｐｌ．Ｐｈｙｓ． Ｖｏｌ．３６（１９９７）ｐｐ．Ｌ８９９−Ｌ９０２．
表中、Ｖ／ＩＩＩ比が範囲で示されているものは、文献に記載されたＶ／ＩＩＩの値が一定の範囲をもって記載されていることを示す。
【００３１】
いずれの文献発表値もＶ／ＩＩＩ比が１０以上となっている。本発明では、これに比べて顕著に低いＶ／ＩＩＩ比としている。こうした低いＶ／ＩＩＩ比を実現するためには、ＩＩＩ族原料ガスの供給量を増大させることが必要となるが、従来のＨＶＰＥ成長装置では実現困難であった。前述の図１１に代表される従来の成長装置では、ＩＩＩ族原料ガスの供給量を増大させようとしてハロゲンガスを過剰に供給してもＩＩＩ族原料のハロゲン化反応が追いつかず、ＩＩＩ族原料ガスの供給量を顕著に増大させることが困難である。また、このようにＩＩＩ族元素と充分に反応しない状態でハロゲンガスの流量を増大させると、成長速度が低下したり半導体層の膜質が低下したりするという問題が生じる。基板表面で成長の逆反応が進行し、形成された半導体層がハロゲンガスによりエッチングされるためである。
【００３２】
本発明で規定する低いＶ／ＩＩＩ比で良好な層成長を実現するためには、
（ｉ）ＩＩＩ族元素をハロゲン化して基板表面に供給する方式において、ハロゲン化反応を促進する、
（ｉｉ）Ｖ族元素の分解率を向上させる、
（ｉｉｉ）基板表面における成長の逆反応を抑制する、
といった手法を組み合わせることが有効となる。こうした手法は、成長装置の構造を工夫することにより実現される。
【００３３】
たとえば、（ｉ）については、以下の構造を採用することが有効となる。すなわち、成長室、成長室内に基板を保持する基板保持部、成長室内にＩＩＩ族原料ガスを供給する第一のガス供給部、成長室内にＶ族原料ガスを供給する第二のガス供給部、を備える成長装置において、第一のガス供給部の上流側に、ＩＩＩ族元素のハロゲン化物を生成するハロゲン化物生成室を備える構造とする。このハロゲン化物生成室は、ハロゲンガス供給部と、ＩＩＩ族元素含有化合物を設置するソースボードとを含む。そして、ハロゲンガス供給部から供給されるハロゲンガスは、ハロゲン化物生成室内で滞留するように構成する。こうすることにより、ハロゲンガスとＩＩＩ族元素含有化合物との反応が促進され、ハロゲンガス流量を低減させ低いＶ／ＩＩＩで良好な成長を行うことが可能となる。
【００３４】
（ｉｉ）については、成長室全体を加熱する加熱部材を設けた上で、成長室の上流側からＶ族元素ガスを供給するようにし、成長室内におけるＶ族元素の滞在時間を長くして分解を促進することが有効である。さらに、成長室内を２つの室に区画し、Ｖ族元素の滞在時間をより長くすることも有効である。
【００３５】
（ｉｉｉ）については、基板温度をたとえば１０６０℃以上の高温に維持することが有効である。こうすることにより、低いＶ／ＩＩＩによる成長速度促進効果がより顕著に発現する。また、このようにすれば、得られるＧａＮ系半導体層の平坦性が顕著に向上する。ここで、成長室全体をこのような高温にすると、Ｖ族元素ガスの分解の制御が困難になるため、かかる構成を採用する場合は、上記したように成長室内を２つの室に区画することが好ましい。
【００３６】
以下、こうした構成を備える成長装置について説明する。図５は上記（ｉ）〜（ｉｉｉ）を実現する成長装置の一例である。ここでは、ＨＶＰＥによるＧａＮ成長を行う装置を例に挙げて説明する。
【００３７】
この成長装置は、成長の行われる反応管１１と、反応管１１にＶ族原料ガスを供給するＶ族原料ガス導入管２８と、反応管１１にＩＩＩ族原料ガスを供給するＩＩＩ族ハロゲン化物供給管１２と、反応管１１の内部に配置され被処理基板を保持する基板ホルダ２０とを備えている。
【００３８】
ハロゲン化物生成室３６は、塩化ガリウムを生成し、これを、ＩＩＩ族ハロゲン化物供給管１２を介して基板ホルダ２０上のＧａＮ基板３８表面に供給する。ハロゲン化物生成室３６は、ハロゲンガス供給管２９およびドーピングガス供給管３０を備えるとともに、Ｇａソース１４を収容するソースボード１５を含んでいる。ハロゲンガス供給管２９の供給口は、ＩＩＩ族ハロゲン化物供給管１２の上流側に位置し、供給された塩素ガスはＩＩＩ族ハロゲン化物供給管１２内で滞留するようになっている。これにより、揮発したＧａソース１４と接触する時間が長く確保される。このため、Ｇａの塩化反応が促進され、塩素ガスの流量を増大させた場合でも、塩化ガリウムの生成効率は低下しない。導入された塩素の大部分は塩化ガリウムになり、未反応塩素の残存は微量にとどまる。
【００３９】
反応管１１は遮蔽板３１により２つの室に区画されている。図中左側に位置する室では、Ｖ族原料ガス導入管２８から供給されたアンモニアが滞留し、分解が促進される。この室の周囲には電気炉１６が配置され、室内はたとえば８００〜９００℃程度の温度に維持される。図中右側に位置する成長領域３５には、ＧａＮ基板３８を保持する基板ホルダ２０が配置され、この室内でＧａＮの成長が行われる。この室の周囲には電気炉１７が配置され、室内はたとえば１０００〜１２００℃程度の温度に維持される。
【００４０】
Ｖ族原料ガス導入管２８から供給されたアンモニアは、図中左側の室で滞留し分解した後、遮蔽板３１の間隙を介して図中右側の室に流入する。この室内に配置されたＧａＮ基板３８表面において、アンモニア分解物と塩化ガリウムとが反応し、ＧａＮ基板３８表面にＧａＮが堆積する。
【００４１】
基板ホルダ２０は、回転軸２４およびモータ２６からなる回転駆動手段により、成長の間、回転運動している。このように基板３８を回転させながら成長ガスを供給することにより、基板面内におけるＧａＮ層の膜質および厚みの均一化を図ることができる。なお、ＧａＮ層中に不純物を導入する場合は、ドーピングガス供給管３０により適宜ドーピングガスを供給する。
【００４２】
以上説明した装置によれば、低いＶ／ＩＩＩ比を安定的に実現するとともに、こうした条件下でも未反応塩素や未分解Ｖ族原料ガスを低減し、良質なＧａＮ系半導体層を高速で成長させることができる。
【００４３】
【実施例】
実施例１
本実施例における成長プロセスを、図１に基づいて説明する。まず、洗浄したＧａＮ基板１１１を用意した後（図１（ａ））、その表面にＧａＮ層１１２をＨＶＰＥにより成長させた（図１（ｂ））。成長にあたっては、前述した図５のＨＶＰＥ成長装置を用いた。以下、この装置を用いた成長プロセスについて図５を参照して説明する。
【００４４】
まず、ＧａＮ基板１１１を有機溶剤による超音波洗浄し、８０℃程度の温度の硝酸に浸し表面処理を行った後、流水洗浄した。つづいて、洗浄したＧａＮ基板を図５の装置の基板ホルダ２０に取り付け、遮蔽板３１によって区画された図中右側の成長領域３５にセットした。
【００４５】
次いで反応管１１内のＧａソース１４領域と成長領域３５を、それぞれ電気炉１６、１７を用いて昇温した。ＧａＮ基板３８のセットされた成長領域３５が６００℃付近の温度になったところで、３００〜３０００ｃｃ／ｍｉｎでＮＨ_３ガスを供給してＧａＮ基板３８表面の分解を抑えた。
【００４６】
Ｇａソース１４の温度として８６０℃、成長領域の温度が９００℃〜１０６０℃の所定の温度に達したところで、Ｇａソース１４上にＨＣｌガスを供給して、塩化ガリウム（ＧａＣｌ）を生成して成長領域３５に供給した。成長領域３５に供給されたＧａＣｌガスとＮＨ_３ガスが反応し、成長領域３５で図１（ｂ）のように、ＧａＮ基板１１１表面にＧａＮ層１１２が成長する。所定の膜厚にＧａＮ層１１２を形成させた後、Ｇａソース１４上に供給したＨＣｌガスを停止し、電気炉１６、および１７の電源を切断し、反応管１１全体を降温した。ＮＨ_３ガスの供給は、成長領域３５の温度が６００℃前後の温度になるまで続行した。成長領域３５の温度が常温になってからＧａＮ基板を反応管１１から取り出し、基板ホルダ２０から外した。
【００４７】
上記の方法により、２５０μｍ／ｈｒ以上の成長速度を実現することができた。得られたＧａＮ層は、欠陥が少なく、また、ウエハ面内における厚みおよび膜質の均一性に優れるものであった。
【００４８】
次に、ＧａＮ層の高速成長を実現するため、成長領域３５の温度（成長温度）、ＮＨ_３ガス供給量、Ｇａソース１４上に供給するＨＣｌガス供給量、およびキャリアガス中のＨ_２ガスの割合を変えて、成長速度に対するこれらの条件依存性を詳細に調べた。ＨＣｌガス流量は、３０〜２５０ｃｃ／ｍｉｎの範囲で変化させ、また、成長時のＨ_２ガスの割合は、１％〜１００％の範囲で変化させた。
【００４９】
図６に、成長領域３５の温度を１０６０℃として、キャリアガス中のＨ_２ガスの割合（体積分率）を変化させたときの成長速度の変化を示す。キャリアガスは、窒素と水素の混合ガスとした。図中（ａ）の■印が、ＨＣｌガス供給量９０ｃｃ／ｍｉｎでの成長速度を示し、（ｂ）の●印は、ＨＣｌガス供給量が５０ｃｃ／ｍｉｎでの成長速度を示す。Ｖ／ＩＩＩ比は、（ａ）では、７．４、（ｂ）では１２であった。
【００５０】
ＧａＮ層の成長速度は、（ａ）の成長条件では、Ｈ_２ガスの割合が７％付近で最大になり、（ｂ）の条件では、１８％で付近で最大になることが判った。ＧａＮ層の成長速度は、ＨＣｌガス供給量やＮＨ_３ガスの供給量を変えると、成長速度の最大になるためのＨ_２ガスの割合が変わり、ＨＣｌ流量が多くなると成長温度の最大値は、Ｈ_２の割合が少ない領域にシフトした。
【００５１】
図７に、ＨＣｌガス供給量に対するＧａＮ層の成長速度の変化を示す。このときＮＨ_３ガス供給量は１０００ｃｃ／ｍｉｎと一定とした。ＨＣｌガス流量の増加とともに成長速度が増加し、ＨＣｌガス供給量が１１０ｃｃ／ｍｉｎ以上で２５０μｍ／ｈ以上の成長速度が実現できることが判る。このとき、ＮＨ_３ガスとＨＣｌガスの供給量（Ｖ／ＩＩＩ）比は、１０未満であった。
【００５２】
次に、図８に、ＮＨ_３ガスとＨＣｌガスの供給量比（Ｖ／ＩＩＩ比）をほぼ一定とし、ＨＣｌガスの供給量を変えたときの成長速度の変化を示す。（ａ）の●印は、Ｖ／ＩＩＩ比が５〜９での成長速度で、（ｂ）の▲印は、Ｖ／ＩＩＩ比が１５〜２０での成長速度である。これらの成長条件は以下のとおりである。
【００５３】
ａ：図５の成長装置を使用。Ｖ／ＩＩＩ５〜９、成長温度１１００℃
ｂ：図１１の成長装置を使用。Ｖ／ＩＩＩ１５〜２０、成長温度１０５０℃
（ａ）、（ｂ）ともにＨＣｌガス流量が７０ｃｃ／ｍｉｎまでは、ＨＣｌ流量に比例して成長速度はほぼ同様に増加した。しかしながらＧａＣｌガス流量が９０ｃｃ／ｍｉｎ以上になると両者の間に成長速度に違いが現れた。（ｂ）では、ＨＣｌガス供給量を１５０ｃｃ／ｍｉｎに増加しても成長速度は、ほとんど大きくならなかったが、（ａ）では、ＨＣｌガス供給量の増加で、さらに成長速度は大きくなり、１５０ｃｃ／ｍｉｎでは３２０μｍ／ｈに達した。
【００５４】
以上のことから、Ｖ／ＩＩＩ比を１０未満、より好ましくは９以下とすることにより、成長速度の飽和の問題を有効に解決し、成長速度が顕著に向上することが確認された。
【００５５】
次に、図９に、９００℃〜１０６０℃の成長温度で、成長速度の変化を調べた結果を示す。ＨＣｌガス供給量を１５０ｃｃ／ｍｉｎ、ＮＨ_３ガス供給量を１０００ｃｃ／ｍｉｎ（Ｖ／ＩＩＩ比：６．７）とした。この実験から成長温度の上昇とともに成長速度が増加することがわかった。このように成長速度が温度とともに増加するという現象は、反応速度の温度依存性を反映していると考えることができる。ハイドライドＶＰＥにおいては通常、成長表面でのＣｌ離脱に関与する反応が最も遅いことが知られているので、ＧａＮの成長においても同様な表面反応が全体の成長速度を律速していると考えることができる。この図から１０００℃程度以上の温度で２５０μｍ／ｈを実現できることが判った。成長温度が１０２０℃以上では、鏡面性に優れたＧａＮ層が成長した。特に１０６０℃以上では、優れた鏡面性を有するＧａＮ層が安定的に得られた。１０００℃以下の温度では、成長したＧａＮ層表面には凹凸が目立つ結果となった。
【００５６】
また、ＮＨ_３およびＨＣｌのガス供給量の比を変えて成長速度を測定した結果を図１０に示す。成長温度は１０６０℃、キャリアガス中の水素分圧は８．３とした。グラフの横軸がＶ／ＩＩＩ比となる。Ｖ／ＩＩＩ比１０未満の領域で、成長速度が顕著に向上することが明らかになった。
【００５７】
本実施例で述べたように、本発明の方法を用いることで、ＧａＮで従来報告されている成長速度に比べて、約２倍以上の速い成長速度で、膜厚均一性が高く、鏡面性に優れたＧａＮ膜を作製できることがわかった。高速の成長速度が実現できたことで、３００μｍの厚さのＧａＮ結晶を約１時間程度で成長させることができ、ＧａＮ自立基板の作製が容易になった。
【００５８】
本実施例では、基板としてＧａＮ基板を用いたが、この他に、サファイア基板、ＧａＡｓ基板、Ｓｉ基板、ＳｉＣ基板等の格子定数や熱膨張係数の異なる基板結晶を用いてもよく、全面成長ばかりでなく、選択成長や島状ＧａＮ膜、微粒核のＧａＮ、Ａｌ_１−ＸＧａ_ＸＮ、Ｉｎ_１−ＸＧａ_ＸＮであっても同様な効果が得られる。
【００５９】
また、ＧａＮ膜２２の成長中にＳｉ、Ｍｇ、Ｃ、Ｏ等の不純物を添加することで、ｎ型やｐ型の導電性を持つＧａＮ膜２２を作製することができる。
【００６０】
さらに、本実施例では、石英製反応管を用いて１０６０℃の成長温度までの成長速度を調べたが、反応管として１０６０℃以上の温度に耐えることが可能であれば、さらに速い速度でＧａＮ膜を作製することができる。
【００６１】
実施例２
本実施例について、図２を参照して説明する。成長装置は図５に示したものを用いた。
【００６２】
まず、実施例１と同様にＧａＮ基板１２１を有機洗浄した後、８０℃程度の硝酸液に１０分間浸し、さらに ８０℃の温度のリン酸＋硫酸混合液に２０分間浸してエッチングを行い、流水洗浄して成長表面処理を行う（図２（ａ））。
【００６３】
つづいて、洗浄した１２１を図５の装置における反応管１１内の基板ホルダ２０に取り付け、遮蔽板３１によって区画された図中右側の成長領域３５にセットした。
【００６４】
反応管１１内をＮ_２ガスで置換してからＮ_２ガスとＨ_２ガスの混合ガスを供給する。流量としてＮ_２は、１３００ｃｃ／ｍｉｎ、Ｈ_２は、６５０ｃｃ／ｍｉｎである。また、Ｖ族原料ガス導入管６７から３３００ｃｃ／ｍｉｎのＮ_２ガスを供給した。
【００６５】
反応管１１内のＧａソース１４領域と成長領域３５は、それぞれ電気炉１６、１７を用いて昇温した。成長領域３５が６００℃付近の温度になったところで、１５００ｃｃ／ｍｉｎでＮＨ_３ガスを供給して１２１表面の分解を抑えた。
【００６６】
Ｇａソース１４の温度を８５０℃、成長領域３５の温度を１０６０℃に昇温し、温度が安定した後、Ｇａソース１４上にＨＣｌガスを供給した。ＨＣｌガス流量を１６０ｃｃ／ｍｉｎとして、１０時間、ＧａＮ膜１２２の成長を行った（図２（ｂ））。Ｖ／ＩＩＩ比は９．４であった。この成長中、ハロゲンガス供給管２９よりＳｉＨ_２Ｃｌ_２ガスを０．００２ｃｃ／ｍｉｎで供給し、Ｓｉ不純物の添加を行った。所定の時間ＧａＮ膜１２２を成長させた後、電気炉１６、１７の電源を切断して、反応管１１全体を降温する。成長領域３５の温度が６００℃前後の温度になるまでＮＨ_３ガスの供給を続ける。反応管温度が常温付近になったところでＧａＮ基板１２１を反応管１１より取り出し、基板ホルダ２０から外した。
【００６７】
ＧａＮ基板１２１に成長したＧａＮ膜１２２の膜厚を調べたところ、３．２ｍｍの厚さに成長していることがわかった。ＧａＮ膜１２２表面は、平坦でかつ鏡面であった（図２（ｃ））。また、ホール測定により室温のキャリア濃度を測定したところ、ｎ型の導電性を示し、キャリア濃度は１〜１．５×１０^１８／ｃｍ^−３、移動度は、１６０ｃｍ^２／Ｖ・ｓであった。
【００６８】
さらに、ＧａＮ膜１２２の表面の転位密度を測定したところ、１×１０^５／ｃｍ^２の値が得られた。また、この形成したＧａＮ膜１２２をワイヤカッター等により切断し、０．４ｍｍの厚さのＧａＮ膜１２２を５枚得た。切断したＧａＮ膜１２２表面を鏡面研磨して、基板となるＧａＮ結晶１２２を作製することができた（図２（ｄ）、（ｅ））。
【００６９】
実施例３
本発明の第３の実施例を図３の概略図を参照して説明する。図３（ａ）は、厚さ２μｍのＧａＮ膜１３１を成長させた４インチ口径（直径）のＡ面サファイア基板１３２上にＳｉＯ_２膜を形成して、リソグラフィ技術とドライエッチング技術を用いてストライプ状の周期構造を作製した状態を示す。ＧａＮ膜１３１が露出した開口部１３４の幅は３μｍで、ＳｉＯ_２によるマスク１３３の幅は６μｍである。ストライプ方向は、ＧａＮ膜１３１に対し、＜１１−２０＞方向である。
【００７０】
この状態の基板を、図５のＨＶＰＥ装置の基板ホルダ２０に取り付け、成長領域３５にセットする。反応管１１内をＮ_２ガスで置換してから、ＩＩＩ族ハロゲン化物供給管１２とＶ族原料ガス導入管２８からＮ_２ガスを供給する。流量はそれぞれ、２４００ｃｃ／ｍｉｎ、３６００ｃｃ／ｍｉｎである。また、Ｖ族原料ガス導入管２８からはＨ_２ガスを６００ｃｃ／ｍｉｎ供給した。反応管１１内のＧａソース１４領域と成長領域３５を電気炉１６、１７で昇温する。成長領域３５の温度が６００℃になったところで１２００ｃｃ／ｍｉｎのＮＨ_３ガスを供給して基板表面の分解を抑えた。
【００７１】
Ｇａソース１４の温度を８５０℃、成長領域３５の温度を１０４０℃に昇温し、温度が安定した後、Ｇａソース１４上にＨＣｌガスを供給した。ＨＣｌガス流量を１７０ｃｃ／ｍｉｎとして、１時間、ＧａＮ膜１３２の成長を行った（図３（ｂ））。Ｖ／ＩＩＩ比は７．１であった。所定の時間ＧａＮ膜１３２を成長させた後、電気炉１６、１７の電源を切断して、反応管１１全体を降温する。成長領域３５の温度が６００℃前後の温度になるまでＮＨ_３ガスの供給を続ける。反応管温度が常温付近になったところで基板を反応管１１より取り出し、基板ホルダ２０から外す。
【００７２】
成長したＧａＮ膜１３５の膜厚を調べたところ、３３０μｍ厚さであった。ＧａＮ膜１３５の表面は鏡面で、平坦性に優れていた。
【００７３】
また、成長したＧａＮ膜の厚さ分布を調べたところ、±３％以下で、膜厚分布に関しても良好な結果が得られた。これは、表面反応律速領域で成長を行うことで、気相中のガス濃度の部分があまり成長速度に大きく影響しないことによるものと考えられる。本実施例のように４インチという大きな基板を用いても膜厚均一性に優れたＧａＮ膜が得られることが確認された。
【００７４】
次に、サファイア基板１３２を除去して単体のＧａＮ膜１３５を得た（図３（ｃ））。サファイア基板１３１の除去は、レーザ照射による剥離や、リン酸＋硫酸混合液のよるサファイア基板の溶解、または研磨等の方法を用いることができる。またサファイア基板１３２を除去したＧａＮ膜１３５の裏面は、２４０℃前後の温度のリン酸＋硫酸混合液によるエッチングや、研磨等により平坦化することができる。
【００７５】
実施例４
本実施例では、本発明によるＨＶＰＥ成長を利用してＧａＮ層を形成し、半導体レーザを作製、評価した例を示す。まず製造方法について図４を参照して説明する。基板材料としては、２００μｍの厚さの（１１１）面シリコン（Ｓｉ）基板を用いる。このＳｉ基板４１上に有機金属化学気相成長法（ＭＯＣＶＤ）により、厚さ０．１μｍ程度のＡｌＮ層４２と０．３μｍのＧａＮ層４３を形成する。次に、ＧａＮ層４３上に０．５μｍの厚さのＳｉＯ_２膜を形成し、リソグラフィーとウエットエッチングで、ストライプ状のマスク４４と開口部４５をＧａＮ膜４３の＜１１−２０＞方向に形成する。続いて、図５に示したＨＶＰＥ装置を用いて、ＧａＮ膜４３が露出している開口部４５から成長を行いＧａＮ膜４６を形成する。
成長手順は次の通りである。洗浄したＳｉ基板４１を基板ホルダ２０に取り付け、成長領域３５にセットする。反応管１１内をＮ_２ガスで置換する。ＩＩＩ族ハロゲン化物供給管１２へＨ_２ガスとＮ_２ガスの混合ガスを供給する。ガス流量は、それぞれ７００ｃｃ／ｍｉｎ、２０００ｃｃ／ｍｉｎとした。また、Ｖ族原料ガス導入管２８からＮ_２ガスを４１００ｃｃ／ｍｉｎで供給した。反応管１１内のＧａソース１４領域と成長領域３５を電気炉１６、１７を用いて昇温する。成長領域３５が６００℃に上昇したところで、Ｖ族原料ガス導入管２８から１０００ｃｃ／ｍｉｎでＮＨ_３ガスを供給して、ＧａＮ膜４１の表面の分解を押さえた。Ｇａソース１４の温度が８５０℃、成長領域３５の温度が１０２０℃に達し、温度が安定したところで、Ｇａソース１４上にＨＣｌガスを１２０ｃｃ／ｍｉｎで供給し、開口部４５からＧａＮ膜４６を成長させた（図４（ｂ））。なお、ＧａＮ膜４６の成長中、ハロゲンガス供給管２９よりＳｉＨ_２Ｃｌ_２ガスを供給し、Ｓｉのドーピングを行った。
【００７６】
２時間の成長後、Ｇａソース１４上に供給したＨＣｌガスの供給を停止して、電気炉１６、１７の電源を切断して、反応管１１全体を降温する。成長領域３５の温度が６００℃に下がるまでＮＨ_３ガスの供給を続けた。常温になってから、成長結晶を取り出す。図４（ｂ）のＧａＮ膜４６の膜厚は５３０μｍであった。引き続いてＳｉ基板４１を硝酸と弗酸の混合液でエッチングして除去し、ＧａＮ膜４６の裏面を研磨して３００μｍ程度の厚さとし、ＧａＮ自立基板を得た（図４（ｃ））。
【００７７】
このＧａＮ基板上に窒化物系半導体レーザ構造（ＬＤ）を有機金属化学気相成長法を用いて作製した。ＧａＮ基板表面を有機洗浄した後、１００℃の温度の硝酸に３０分間浸し、流水洗浄後Ｎ_２ブローにより乾燥させる。この基板をＭＯＣＶＤ装置にセットし、ＮＨ_３ガスを供給しながら１０５０℃の温度に昇温する。温度が安定してからＳｉを添加した１．５μｍ厚のｎ型ＧａＮ膜４７、Ｓｉを添加した０．３５μｍ厚のｎ型Ａｌ_０．１５Ｇａ_０．８５Ｎクラッド層４８、Ｓｉを添加した０．１μｍ厚のＧａＮ光ガイド膜４９を形成した。次いでＧａＮ膜４６の温度を７５０℃に降温した後、厚さ２．５ｎｍのアンドープＩｎ_０．２Ｇａ_０．８Ｎ量子井戸と厚さ５ｎｍのアンドープＩｎ_０．０５Ｇａ_０．９５Ｎ障壁層からなる３周期の多重量子井戸からなる活性層５０、Ｍｇを添加した２０ｎｍ厚のｐ型Ａｌ_０．２Ｇａ_０．８Ｎクラッド層５１を形成し、再び、ＧａＮ膜４６を１０５０℃の温度の昇温して、Ｍｇを添加した０．１μｍの厚さのｐ型ＧａＮ光ガイド層５２、Ｍｇを添加した０．４μｍの厚さのｐ型Ａｌ_０．１Ｇａ_０．９Ｎクラッド層５３、Ｍｇを添加した０．５５μｍの厚さのｐ型ＧａＮコンタクト層５４を順次形成した。成長終了後降温し、成長結晶をＭＯＣＶＤ装置より取り出し、裏面を研磨や溶液エッチングにより除去して１２０μｍ程度の厚さとして、ｐ型ＧａＮコンタクト層５４上に６０ｎｍ厚のパラジウム（Ｐｄ）と０．３μｍ厚の金（Ａｕ）のｐ型電極５５を形成した。最後に 裏面に３０ｎｍ厚のチタン（Ｔｉ）および０．３μｍ厚のアルミニウム（Ａｌ）からなるｎ型電極５６を形成した（図４（ｄ））。次に、ＧａＮのへき開方向であるｍ面でへき開して、レーザ構造の共振器ミラー面を形成した。作製したＬＤでは、１０，０００時間を超す素子寿命が再現性良く得られた。
【００７８】
以上述べたように本発明によるＧａＮ結晶を基板として用いることで、信頼性の高い窒化物系半導体レーザや、発光ダイオード等の発光素子、さらには電界効果トランジスタ等の電子デバイスを得ることができた。
【００７９】
【発明の効果】
以上説明したように本発明によれば、ＨＶＰＥにおいてＶ／ＩＩＩを低く規定しているため、良質なＧａＮ系半導体層を高速で成長させることができる。
【図面の簡単な説明】
【図１】実施例に係るＧａＮ系半導体層の成長方法を示す図である。
【図２】実施例に係るＧａＮ系半導体基板の製造方法を示す図である。
【図３】実施例に係るＧａＮ系半導体基板の製造方法を示す図である。
【図４】実施例に係るＧａＮ系半導体レーザの製造方法を示す図である。
【図５】実施例で用いたＨＶＰＥ装置の概略構造を示す図である。
【図６】水素分圧とＧａＮ系半導体の成長速度との関係を示す図である。
【図７】ハロゲン供給速度とＧａＮ系半導体の成長速度との関係を示す図である。
【図８】Ｖ／ＩＩＩ比とＧａＮ系半導体の成長速度との関係を示す図である。
【図９】成長温度とＧａＮ系半導体の成長速度との関係を示す図である。
【図１０】Ｖ／ＩＩＩ比とＧａＮ系半導体の成長速度との関係を示す図である。
【図１１】従来のＨＶＰＥ装置の概略構造を示す図である。
【符号の説明】
１１ 反応管
１２ ＩＩＩ族原料ガス供給管
１４ Ｇａソース
１５ ソースボート
１６ 電気炉
１７ 電気炉
２０ 基板ホルダ
２４ 回転軸
２５ 噴出口
２６ モータ
２８ Ｖ族原料ガス導入管
２９ ハロゲンガス供給管
３０ ドーピングガス供給管
３１ 遮蔽板
３２ 排気口
３５ 成長領域
３６ ハロゲン化物生成室
４１ Ｓｉ基板
４２ ＡｌＮ層
４３ ＧａＮ層
４４ マスク
４５ 開口部
４６ ＧａＮ膜
４７ ｎ型ＧａＮ膜
４８ ｎ型Ａｌ_０．１５Ｇａ_０．８５Ｎクラッド層
４９ ＧａＮ光ガイド膜
５０ 活性層
５１ ｐ型Ａｌ_０．２Ｇａ_０．８Ｎクラッド層
５２ ｐ型ＧａＮ光ガイド層
５３ ｐ型Ａｌ_０．１Ｇａ_０．９Ｎクラッド層
５４ ｐ型ＧａＮコンタクト層
５５ ｐ型電極
５６ ｎ型電極
１１１ ＧａＮ基板
１１２ ＧａＮ層
１２１ ＧａＮ基板
１２２ ＧａＮ膜
１３１ ＧａＮ膜
１３２ ＧａＮ膜
１３３ マスク
１３４ 開口部
１３５ ＧａＮ膜[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for growing a GaN-based semiconductor layer using hydride vapor phase epitaxy, a method for manufacturing a semiconductor substrate using the same, and a method for manufacturing a semiconductor device.
[0002]
[Prior art]
Gallium nitride-based semiconductors have a large band gap and a direct transition between bands, and are therefore expected to be applied to short-wavelength light-emitting devices and electronic devices. In order to obtain such an element, it is necessary to form an element structure by epitaxially growing a gallium nitride-based semiconductor on a substrate. However, when there is no underlying substrate whose lattice constant matches that of gallium nitride, a substrate made of a different material such as sapphire or SiC is widely used for growth. However, when gallium nitride is grown on a dissimilar material substrate, many defects are introduced into the gallium nitride-based semiconductor layer due to a difference in lattice constant and a difference in thermal expansion coefficient, which causes a reduction in the device structure. .
[0003]
Under these circumstances, a technology using a substrate made of a gallium nitride-based semiconductor as a base substrate for epitaxial growth has been studied. In order to manufacture a substrate made of a gallium nitride based semiconductor, a method of growing a thick gallium nitride on a sapphire substrate, removing the sapphire substrate, and using the thick gallium nitride semiconductor layer as a substrate for crystal growth is widely used. Are known. In performing such a process, it is important to grow high-quality gallium nitride at a high speed.
[0004]
The hydride vapor phase epitaxy (HVPE) is a growth method that meets such demands. HVPE supplies a group V source gas containing a nitrogen element and a group III source gas made of a compound containing Ga and halogen to the surface of a substrate to grow a gallium nitride based semiconductor layer.
[0005]
Patent Literature 1 describes a conventional representative HVPE apparatus and a growth method. Hereinafter, description will be made with reference to FIG.
[0006]
The crystal growth apparatus 101 shown in FIG. 11 includes a resistance heater 104 on the outer periphery, a crystal growth vessel 108 sealed by a flange 110, a first introduction pipe 103 for introducing HCl gas, ₃ It comprises a second introduction pipe 102 for introducing a gas and a substrate holder 105 arranged in a crystal growth vessel 108. A gas exhaust port 107 is formed in a side surface of the crystal growth vessel 108, and a raw material mounting portion 109 is provided in the first introduction pipe 103, and a Ga raw material is disposed in this portion.
[0007]
Using this growth apparatus, a GaN layer is grown as follows. First, NdGaO having the (011) plane as a growth plane ₃ After cleaning the substrate 106, it is placed on the substrate holder 105. Then, from the first introduction pipe or the second introduction pipe, N ₂ Is heated by the resistance heater 4 until the temperature of the substrate 106 reaches 620 ° C. Next, HCl is introduced from the first introduction pipe 103 and reacted with the Ga metal arranged in the raw material mounting section 109 to introduce GaCl into the crystal growth vessel 108 and simultaneously introduce NHCl. ₃ Is introduced through the second introduction pipe 2, and both the source gases are NdGaO ₃ The reaction is performed on the substrate to form a GaN protective layer of about 100 nm. Next, the temperature of the substrate 106 was increased to 1000 ° C., and GaCl generated from Ga metal and HCl, NH 3 ₃ And N ₂ NdGaO using carrier gas ₃ HCl and NH in the crystal growth vessel 108 while being supplied on the substrate. ₃ While adjusting the gas flow rate of GaN, the GaN compound semiconductor ₃ Grow on substrate. Thus, a GaN compound semiconductor crystal is obtained.
[0008]
However, such conventional HVPE growth has a problem that even at a high growth rate, the growth is limited to at most about 100 μm / hr, and it takes time to grow. When a gallium nitride layer is formed at such a growth rate, not only the yield decreases, but also it is difficult to obtain a gallium nitride layer having sufficiently good film quality. In addition, during the layer growth process, the growth rate may be non-uniform in the wafer surface, resulting in non-uniform film quality and thickness. Further, when the growth process is performed using a large number of substrates, there is a problem that variations in layer growth between the substrates occur.
[0009]
[Patent Document 1]
JP-A-2002-305155
[0010]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and has as its object to provide a method capable of growing a high-quality GaN-based semiconductor layer at a high speed by a hydride vapor phase epitaxy method.
[0011]
Another object of the present invention is to improve the uniformity of the thickness of the growth layer in the plane of the wafer.
[0012]
Another object of the present invention is to provide a GaN-based semiconductor layer grown on a large-diameter wafer, to make the thickness of the grown layer uniform on the wafer surface and to eliminate warpage of the substrate caused by stress distribution in the substrate. It is in.
[0013]
[Means for Solving the Problems]
According to the present invention, there is provided a method for growing a GaN-based semiconductor layer on a substrate by hydride vapor phase epitaxy, comprising a group V source gas containing a nitrogen element and a group III source gas containing a compound containing Ga and halogen. Wherein the V / III ratio defined by the ratio of the supply flow rate of the group V source gas to the supply flow rate of the group III source gas is set to 0.1 or more and less than 10. The method for growing a GaN-based semiconductor layer described above is provided.
[0014]
According to the present invention, a GaN-based semiconductor layer having good film quality can be grown at a remarkably high growth rate as compared with the related art. If the supply amount of the group III source gas is increased, the growth reaction of the GaN-based semiconductor is kinetically accelerated. However, in the case of growing a GaN-based semiconductor, the growth rate saturates at a constant value even when the supply amount of the group III source gas is increased due to the surface reaction rate control on the growth surface. Therefore, in the present invention, the V / III ratio is set to 0.1 or more and less than 10, which is lower than the conventional method. According to the study of the present inventors, this promotes the surface reaction and shifts the saturation point of the growth rate to a higher speed side. The present invention realizes a high growth rate of, for example, 250 μm / hr or more by setting the V / III ratio.
[0015]
The low V / III ratio defined in the present invention is difficult to achieve in a conventional HVPE growth apparatus because the supply amount of the group III source gas is limited. In fact, as can be seen in Table 1 below, the V / III ratio in GaN growth by HVPE published by academic societies and papers is set to a value of 10 or more, and the HVPE with the V / III ratio in the above range is obtained. Had no reported cases. On the other hand, the present inventors have achieved the above V / III ratio by improving the group III raw material board of the HVPE growth apparatus, and have completed the present invention. This point will be described in detail in the embodiment section.
[0016]
In the method for growing a GaN-based semiconductor layer, the growth temperature of the GaN-based semiconductor layer may be set to be 1000 ° C. or more and 1300 ° C. or less. According to this configuration, the surface reaction on the substrate growth surface is promoted, the problem of the saturation of the growth rate is effectively solved, and the growth rate promoting effect by adopting a low V / III ratio is more stably obtained.
[0017]
In the method of growing a GaN-based semiconductor layer, a carrier gas containing 5 to 20% by volume of hydrogen may be used when supplying the group V source gas and the group III source gas to the substrate surface. According to this configuration, the surface reaction on the substrate growth surface is promoted, the problem of the saturation of the growth rate is effectively solved, and the growth rate promoting effect by adopting a low V / III ratio is more stably obtained. The carrier gas component other than hydrogen is, for example, nitrogen or the like.
[0018]
Further, in the above-mentioned method for growing a GaN-based semiconductor layer, the growth rate of the GaN-based semiconductor layer can be set to 250 μm / hr or more. By performing the growth at such a high growth rate, high productivity is obtained, and the uniformity of the film quality and thickness of the GaN-based semiconductor layer in the substrate surface is improved.
[0019]
In the method for growing a GaN-based semiconductor layer according to the present invention, a halogen gas is introduced into a chamber in which Ga or a Ga-containing compound is disposed, and while the supplied halogen gas is retained in the chamber, the vapor of the Ga or Ga-containing compound and the halogen are introduced. A gas may be reacted with the gas to generate the group III source gas including a compound containing Ga and halogen, and the group III source gas may be supplied to the substrate surface. By doing so, the reaction between the halogen and the group V element is promoted, and the low V / III defined by the present invention can be stably realized. Further, generation of unreacted halogen gas can be effectively suppressed.
[0020]
In the present invention, the “GaN-based semiconductor layer” includes GaN, AlGaN, AlGaInN, and the like.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention can be suitably applied to a technique for forming a gallium nitride substrate having a large diameter exceeding 2 inches, for example.
[0022]
When a large-area gallium nitride substrate is formed, it is desired that film growth proceeds uniformly at each point on the base substrate. Normally, when a growth is performed using such a large-area base substrate, the growth rate or the composition often fluctuates due to fluctuations in the growth gas, temperature distribution, and other factors. In this regard, according to the present invention, the growth gas is sufficiently supplied to the surface of the underlying substrate, and the reaction on the surface of the underlying substrate is controlled by the surface reaction, and the reaction is dynamically controlled. Under these circumstances, non-uniformity in film thickness due to unevenness in the concentration of the growth gas and the like is significantly reduced. As a result, the growth rate of gallium nitride at each point on the base substrate becomes almost uniform, and a gallium nitride layer having a uniform thickness and a flat surface can be obtained. Therefore, the problem of substrate warpage, which has conventionally been a problem, is effectively solved.
[0023]
Specifically, a large-area gallium nitride substrate can be suitably obtained by epitaxially growing a gallium nitride layer using a sapphire A-plane substrate by the method already extended. It is known that the growth of gallium nitride on the sapphire A plane is C-axis growth, and it is possible to use the same growth technique as when growing on the sapphire C plane.
[0024]
The gallium nitride substrate obtained by the method of the present invention has significantly reduced dislocation density and good substrate properties such as mobility as compared with a conventional gallium nitride substrate. This is considered to be due to the fact that the dislocation propagation in the layer growth direction is effectively suppressed because the layer growth rate is high.
[0025]
The method according to the present invention can be suitably applied to a method for manufacturing a semiconductor substrate. In other words, in the method of manufacturing a semiconductor substrate for obtaining a GaN-based semiconductor substrate composed of a GaN-based semiconductor layer by growing the GaN-based semiconductor layer on the substrate and then removing the substrate from the GaN-based semiconductor layer, The growth method according to the present invention can be adopted as the growth method for (1). By doing so, a GaN-based semiconductor substrate with few defects can be obtained with high productivity.
[0026]
Further, the method according to the present invention can be suitably applied to a method for manufacturing a semiconductor device. That is, in a method for manufacturing a semiconductor device including a step of forming an active layer having a GaN-based semiconductor layer on a substrate, the growth method according to the present invention can be employed as a method for growing a GaN-based semiconductor layer. In this way, a high quality active layer with few defects can be manufactured with high productivity.
[0027]
Hereinafter, preferred embodiments of the present invention will be described. In the following description, the term “V / III ratio” in this specification indicates a value based on a molar ratio. In each of the embodiments, the HVPE growth of the GaN-based semiconductor is performed at normal pressure. Further, since the group III source gas and the group V source gas are supplied at the same pressure and temperature, their flow ratios show the same value regardless of whether they are based on the flow velocity ratio or on the molar ratio basis.
[0028]
The present invention achieves a high growth rate by making the V / III ratio lower than that of the conventional HVPE. Table 1 shows the growth conditions and growth rates of GaN by HVPE published in the literature.
[0029]
[Table 1]

[0030]
Each NO. The source is as follows.
NO. 1 Hwa-Mok Kim et al, IPAP Conf. Series 1 pp. 49-52
NO. 2 Sung. S. Park et al, IPAP Conf. Series 1 pp. 60-63
NO. 3 K. Motoki et al, Jpn. J. Appl. Phys. Vol. 40 (2001) pp. L140-143.
NO. 4 Y. Oshima et al, phys. stat. soli. (A) 194, No. 2, 554-558 (2002).
NO. 5 D. Martin et al, phys. stat. soli. (A) 194, No. 2, 520-523 (2002).
NO. 6 A. Usui et al, Jpn. J. Appl. Phys. Vol. 36 (1997) pp. L899-L902.
In the table, those in which the V / III ratio is shown in the range indicate that the value of V / III described in the literature is described in a certain range.
[0031]
The V / III ratio is 10 or more in any of the literature published values. In the present invention, the V / III ratio is significantly lower than this. In order to realize such a low V / III ratio, it is necessary to increase the supply amount of the group III source gas, but it has been difficult to realize the conventional HVPE growth apparatus. In the conventional growth apparatus typified by FIG. 11 described above, the halogenation reaction of the group III source material cannot catch up even if the halogen gas is excessively supplied to increase the supply amount of the group III source gas. It is difficult to remarkably increase the supply amount. In addition, when the flow rate of the halogen gas is increased without sufficiently reacting with the group III element, there arises a problem that the growth rate is reduced and the film quality of the semiconductor layer is reduced. This is because a reverse reaction of the growth proceeds on the substrate surface and the formed semiconductor layer is etched by the halogen gas.
[0032]
In order to achieve good layer growth at a low V / III ratio defined in the present invention,
(I) promoting halogenation reaction in a method in which a group III element is halogenated and supplied to a substrate surface;
(Ii) improving the decomposition rate of group V elements,
(Iii) suppressing a reverse reaction of growth on the substrate surface;
It is effective to combine such methods. Such a technique is realized by devising the structure of the growth apparatus.
[0033]
For example, for (i), it is effective to adopt the following structure. That is, a growth chamber, a substrate holding unit that holds a substrate in the growth chamber, a first gas supply unit that supplies a group III source gas into the growth chamber, a second gas supply unit that supplies a group V source gas into the growth chamber, And a halide generation chamber for generating a halide of a group III element upstream of the first gas supply unit. The halide generation chamber includes a halogen gas supply unit and a source board for installing a group III element-containing compound. The halogen gas supplied from the halogen gas supply unit is configured to stay in the halide generation chamber. By doing so, the reaction between the halogen gas and the group III element-containing compound is promoted, and the flow rate of the halogen gas can be reduced to achieve good growth at a low V / III.
[0034]
Regarding (ii), after providing a heating member for heating the entire growth chamber, a group V element gas is supplied from the upstream side of the growth chamber, and the residence time of the group V element in the growth chamber is lengthened to decompose. It is effective to promote Further, it is also effective to divide the growth chamber into two chambers to make the residence time of the group V element longer.
[0035]
Regarding (iii), it is effective to maintain the substrate temperature at a high temperature of, for example, 1060 ° C. or higher. By doing so, the growth rate promoting effect of low V / III is more remarkably exhibited. Further, in this case, the flatness of the obtained GaN-based semiconductor layer is significantly improved. Here, if the entire growth chamber is set to such a high temperature, it becomes difficult to control the decomposition of the group V element gas. Therefore, when such a configuration is adopted, the growth chamber is divided into two chambers as described above. Is preferred.
[0036]
Hereinafter, a growth apparatus having such a configuration will be described. FIG. 5 shows an example of a growth apparatus for realizing the above (i) to (iii). Here, an apparatus for performing GaN growth by HVPE will be described as an example.
[0037]
The growth apparatus includes a reaction tube 11 in which growth is performed, a group V source gas introduction tube 28 for supplying a group V source gas to the reaction tube 11, and a group III halide supply for supplying a group III source gas to the reaction tube 11. The apparatus includes a tube 12 and a substrate holder 20 arranged inside the reaction tube 11 for holding a substrate to be processed.
[0038]
The halide generation chamber 36 generates gallium chloride and supplies it to the surface of the GaN substrate 38 on the substrate holder 20 via the group III halide supply pipe 12. The halide generation chamber 36 includes a halogen gas supply pipe 29 and a doping gas supply pipe 30 and includes the source board 15 that houses the Ga source 14. The supply port of the halogen gas supply pipe 29 is located on the upstream side of the group III halide supply pipe 12, and the supplied chlorine gas stays in the group III halide supply pipe 12. Thus, a long contact time with the volatilized Ga source 14 is ensured. For this reason, the chlorination reaction of Ga is promoted, and even when the flow rate of chlorine gas is increased, the production efficiency of gallium chloride does not decrease. Most of the introduced chlorine becomes gallium chloride, and the remaining unreacted chlorine remains in a trace amount.
[0039]
The reaction tube 11 is divided into two chambers by a shielding plate 31. In the chamber located on the left side in the figure, the ammonia supplied from the group V source gas introduction pipe 28 stays, and the decomposition is promoted. An electric furnace 16 is arranged around the room, and the room is maintained at a temperature of, for example, about 800 to 900 ° C. A substrate holder 20 for holding a GaN substrate 38 is arranged in a growth region 35 located on the right side in the figure, and GaN is grown in this chamber. An electric furnace 17 is arranged around the room, and the room is maintained at a temperature of, for example, about 1000 to 1200 ° C.
[0040]
Ammonia supplied from the group V source gas introduction pipe 28 stays in the left chamber in the drawing and is decomposed, and then flows into the right chamber in the drawing through the gap of the shielding plate 31. On the surface of the GaN substrate 38 placed in this chamber, the ammonia decomposition product reacts with gallium chloride, and GaN is deposited on the surface of the GaN substrate 38.
[0041]
The substrate holder 20 is rotationally moved during growth by a rotation driving means including a rotation shaft 24 and a motor 26. By supplying the growth gas while rotating the substrate 38 in this manner, the film quality and thickness of the GaN layer in the substrate surface can be made uniform. When introducing impurities into the GaN layer, a doping gas is appropriately supplied through the doping gas supply pipe 30.
[0042]
According to the apparatus described above, a low V / III ratio can be stably realized, unreacted chlorine and undecomposed group V source gas are reduced even under such conditions, and a high-quality GaN-based semiconductor layer is grown at high speed. be able to.
[0043]
【Example】
Example 1
The growth process in this embodiment will be described with reference to FIG. First, after preparing a washed GaN substrate 111 (FIG. 1A), a GaN layer 112 was grown on the surface by HVPE (FIG. 1B). For the growth, the HVPE growth apparatus shown in FIG. 5 was used. Hereinafter, a growth process using this apparatus will be described with reference to FIG.
[0044]
First, the GaN substrate 111 was subjected to ultrasonic cleaning with an organic solvent, immersed in nitric acid at a temperature of about 80 ° C. to perform surface treatment, and then washed with running water. Subsequently, the cleaned GaN substrate was attached to the substrate holder 20 of the apparatus shown in FIG. 5, and was set in the growth area 35 on the right side in the figure defined by the shielding plate 31.
[0045]
Next, the temperature of the Ga source 14 region and the growth region 35 in the reaction tube 11 was raised using electric furnaces 16 and 17, respectively. When the growth region 35 on which the GaN substrate 38 is set reaches a temperature near 600 ° C., the NH 3 is supplied at 300 to 3000 cc / min. ₃ The decomposition of the surface of the GaN substrate 38 was suppressed by supplying the gas.
[0046]
When the temperature of the Ga source 14 reaches 860 ° C. and the temperature of the growth region reaches a predetermined temperature of 900 ° C. to 1060 ° C., HCl gas is supplied onto the Ga source 14 to generate gallium chloride (GaCl). It was supplied to the area 35. GaCl gas and NH supplied to the growth region 35 ₃ The gas reacts, and a GaN layer 112 grows on the surface of the GaN substrate 111 in the growth region 35 as shown in FIG. After forming the GaN layer 112 to a predetermined thickness, the HCl gas supplied on the Ga source 14 was stopped, the power of the electric furnaces 16 and 17 was cut off, and the temperature of the entire reaction tube 11 was lowered. NH ₃ The gas supply was continued until the temperature of the growth region 35 reached a temperature around 600 ° C. After the temperature of the growth region 35 reached room temperature, the GaN substrate was taken out of the reaction tube 11 and removed from the substrate holder 20.
[0047]
By the above method, a growth rate of 250 μm / hr or more could be realized. The obtained GaN layer had few defects and was excellent in uniformity of thickness and film quality in the wafer plane.
[0048]
Next, in order to realize high-speed growth of the GaN layer, the temperature of the growth region 35 (growth temperature), NH ₃ Gas supply amount, HCl gas supply amount supplied on the Ga source 14, and H in the carrier gas. ₂ The dependence of these conditions on the growth rate was investigated in detail by changing the gas ratio. The HCl gas flow rate is changed in the range of 30 to 250 cc / min. ₂ The ratio of the gas was changed in the range of 1% to 100%.
[0049]
FIG. 6 shows that the temperature of the growth region 35 is 1060 ° C. ₂ The change in the growth rate when the gas ratio (volume fraction) is changed is shown. The carrier gas was a mixed gas of nitrogen and hydrogen. In the figure, a mark in (a) indicates the growth rate when the HCl gas supply rate is 90 cc / min, and a mark in (b) indicates the growth rate when the HCl gas supply rate is 50 cc / min. The V / III ratio was 7.4 in (a) and 12 in (b).
[0050]
The growth rate of the GaN layer is H under the growth condition (a). ₂ It was found that the gas ratio reached a maximum near 7%, and under the condition (b), the gas ratio reached a maximum near 18%. The growth rate of the GaN layer depends on the supply rate of HCl gas and NH3. ₃ By changing the gas supply, H is required to maximize the growth rate. ₂ When the gas ratio changes and the HCl flow rate increases, the maximum value of the growth temperature becomes H ₂ Was shifted to an area where the ratio was small.
[0051]
FIG. 7 shows a change in the growth rate of the GaN layer with respect to the supply amount of the HCl gas. At this time, NH ₃ The gas supply was constant at 1000 cc / min. It can be seen that the growth rate increases with an increase in the flow rate of the HCl gas, and a growth rate of 250 μm / h or more can be realized when the supply rate of the HCl gas is 110 cc / min or more. At this time, NH ₃ The supply ratio (V / III) of gas and HCl gas was less than 10.
[0052]
Next, FIG. ₃ The change in the growth rate when the supply ratio of the HCl gas is changed while the supply ratio of the gas and the HCl gas (V / III ratio) is made substantially constant is shown. (A) indicates the growth rate when the V / III ratio is 5 to 9, and (b) indicates the growth rate when the V / III ratio is 15 to 20. These growth conditions are as follows.
[0053]
a: The growth apparatus of FIG. 5 was used. V / III 5-9, growth temperature 1100 ° C
b: The growth apparatus of FIG. 11 was used. V / III 15-20, growth temperature 1050 ° C
In both cases (a) and (b), the growth rate increased substantially in proportion to the HCl flow rate up to the HCl gas flow rate of 70 cc / min. However, when the flow rate of the GaCl gas became 90 cc / min or more, a difference appeared in the growth rate between the two. In (b), even if the supply rate of HCl gas was increased to 150 cc / min, the growth rate hardly increased, but in (a), the growth rate further increased due to the increase in the supply rate of HCl gas, and the growth rate increased to 150 cc. / Min reached 320 μm / h.
[0054]
From the above, it was confirmed that by setting the V / III ratio to less than 10, more preferably 9 or less, the problem of the saturation of the growth rate was effectively solved, and the growth rate was significantly improved.
[0055]
Next, FIG. 9 shows a result of examining a change in growth rate at a growth temperature of 900 ° C. to 1060 ° C. HCl gas supply at 150 cc / min, NH ₃ The gas supply was 1000 cc / min (V / III ratio: 6.7). From this experiment, it was found that the growth rate increased with the growth temperature. Such a phenomenon that the growth rate increases with temperature can be considered to reflect the temperature dependence of the reaction rate. It is known that the reaction involved in Cl elimination at the growth surface is usually the slowest in hydride VPE, so it can be considered that the same surface reaction controls the overall growth rate in GaN growth. it can. From this figure, it was found that 250 μm / h can be realized at a temperature of about 1000 ° C. or higher. At a growth temperature of 1020 ° C. or higher, a GaN layer having excellent mirror surface properties was grown. In particular, at 1060 ° C. or higher, a GaN layer having excellent specularity was stably obtained. At a temperature of 1000 ° C. or less, the surface of the grown GaN layer had conspicuous irregularities.
[0056]
Also, NH ₃ FIG. 10 shows the result of measuring the growth rate while changing the ratio of the gas supply amounts of HCl and HCl. The growth temperature was 1060 ° C., and the hydrogen partial pressure in the carrier gas was 8.3. The horizontal axis of the graph is the V / III ratio. It was found that the growth rate was significantly improved in the region where the V / III ratio was less than 10.
[0057]
As described in the present embodiment, the use of the method of the present invention provides a film thickness uniformity and a high specularity at a growth rate that is about twice or more as fast as the growth rate conventionally reported for GaN. It was found that an excellent GaN film could be produced. By realizing a high growth rate, a GaN crystal having a thickness of 300 μm can be grown in about 1 hour, and the production of a GaN free-standing substrate has been facilitated.
[0058]
In this embodiment, a GaN substrate is used as a substrate. Alternatively, a substrate crystal having a different lattice constant or thermal expansion coefficient such as a sapphire substrate, a GaAs substrate, a Si substrate, or a SiC substrate may be used. Instead, selective growth, island-like GaN film, nucleated GaN, Al _1-X Ga _X N, In _1-X Ga _X Similar effects can be obtained with N.
[0059]
In addition, by adding impurities such as Si, Mg, C, and O during the growth of the GaN film 22, the GaN film 22 having n-type or p-type conductivity can be manufactured.
[0060]
Further, in this example, the growth rate up to a growth temperature of 1060 ° C. was examined using a quartz reaction tube. However, if the reaction tube can withstand a temperature of 1060 ° C. or higher, GaN is grown at a higher speed. A membrane can be made.
[0061]
Example 2
This embodiment will be described with reference to FIG. The growth apparatus shown in FIG. 5 was used.
[0062]
First, after the GaN substrate 121 is organically washed in the same manner as in Example 1, it is immersed in a nitric acid solution at about 80 ° C. for 10 minutes, and further immersed in a mixed solution of phosphoric acid and sulfuric acid at a temperature of 80 ° C. for 20 minutes to perform etching. After cleaning, a growth surface treatment is performed (FIG. 2A).
[0063]
Subsequently, the washed 121 was attached to the substrate holder 20 in the reaction tube 11 in the apparatus shown in FIG. 5, and was set in the growth area 35 on the right side in the figure defined by the shielding plate 31.
[0064]
N inside the reaction tube 11 ₂ After replacing with gas, N ₂ Gas and H ₂ Supply gas mixture. N as flow rate ₂ Is 1300cc / min, H ₂ Is 650 cc / min. In addition, 3300 cc / min. ₂ Gas was supplied.
[0065]
The temperature of the Ga source 14 region and the growth region 35 in the reaction tube 11 was raised using electric furnaces 16 and 17, respectively. When the temperature of the growth region 35 reaches about 600 ° C., the NH 3 is increased to 1500 cc / min. ₃ A gas was supplied to suppress the decomposition of the 121 surface.
[0066]
The temperature of the Ga source 14 was raised to 850 ° C., the temperature of the growth region 35 was raised to 1060 ° C., and after the temperature was stabilized, HCl gas was supplied onto the Ga source 14. The GaN film 122 was grown for 10 hours at an HCl gas flow rate of 160 cc / min (FIG. 2B). The V / III ratio was 9.4. During this growth, the SiH was supplied through the halogen gas supply pipe 29. ₂ Cl ₂ A gas was supplied at 0.002 cc / min to add Si impurities. After growing the GaN film 122 for a predetermined time, the power of the electric furnaces 16 and 17 is turned off, and the temperature of the entire reaction tube 11 is decreased. NH 3 until the temperature of the growth region 35 becomes about 600 ° C. ₃ Continue to supply gas. The GaN substrate 121 was taken out of the reaction tube 11 when the temperature of the reaction tube reached about room temperature, and was removed from the substrate holder 20.
[0067]
When the thickness of the GaN film 122 grown on the GaN substrate 121 was examined, it was found that the GaN film 122 had grown to a thickness of 3.2 mm. The surface of the GaN film 122 was flat and mirror-finished (FIG. 2C). When the carrier concentration at room temperature was measured by Hall measurement, it showed n-type conductivity and the carrier concentration was 1 to 1.5 × 10 ¹⁸ / Cm ^-3 , Mobility is 160cm ² / V · s.
[0068]
Furthermore, when the dislocation density on the surface of the GaN film 122 was measured, ⁵ / Cm ² Was obtained. The formed GaN film 122 was cut by a wire cutter or the like to obtain five GaN films 122 having a thickness of 0.4 mm. The cut surface of the GaN film 122 was mirror-polished to produce a GaN crystal 122 serving as a substrate (FIGS. 2D and 2E).
[0069]
Example 3
A third embodiment of the present invention will be described with reference to the schematic diagram of FIG. FIG. 3 (a) shows a 4-inch diameter (diameter) A-plane sapphire substrate 132 on which a 2 μm thick GaN film 131 is grown. ₂ This shows a state in which a film is formed and a stripe-shaped periodic structure is formed by using a lithography technique and a dry etching technique. The width of the opening 134 exposing the GaN film 131 is 3 μm, ₂ The width of the mask 133 is 6 μm. The stripe direction is a <11-20> direction with respect to the GaN film 131.
[0070]
The substrate in this state is mounted on the substrate holder 20 of the HVPE apparatus in FIG. N inside the reaction tube 11 ₂ After replacing with a gas, the group III halide supply pipe 12 and the group V source gas introduction pipe 28 ₂ Supply gas. The flow rates are 2400 cc / min and 3600 cc / min, respectively. Further, H gas is introduced from the group V source gas introduction pipe 28. ₂ Gas was supplied at 600 cc / min. The temperature of the Ga source 14 region and the growth region 35 in the reaction tube 11 is increased by electric furnaces 16 and 17. When the temperature of the growth region 35 reaches 600 ° C., 1200 cc / min NH ₃ The gas was supplied to suppress the decomposition of the substrate surface.
[0071]
The temperature of the Ga source 14 was raised to 850 ° C., the temperature of the growth region 35 was raised to 1040 ° C., and after the temperature was stabilized, HCl gas was supplied onto the Ga source 14. The GaN film 132 was grown for 1 hour at an HCl gas flow rate of 170 cc / min (FIG. 3B). The V / III ratio was 7.1. After growing the GaN film 132 for a predetermined time, the power of the electric furnaces 16 and 17 is turned off, and the temperature of the entire reaction tube 11 is lowered. NH 3 until the temperature of the growth region 35 becomes about 600 ° C. ₃ Continue to supply gas. When the temperature of the reaction tube becomes close to room temperature, the substrate is taken out of the reaction tube 11 and removed from the substrate holder 20.
[0072]
When the thickness of the grown GaN film 135 was examined, it was 330 μm. The surface of the GaN film 135 was a mirror surface and was excellent in flatness.
[0073]
In addition, when the thickness distribution of the grown GaN film was examined, it was ± 3% or less, and good results were obtained with respect to the film thickness distribution. It is considered that this is because the growth in the surface reaction controlled region does not greatly affect the growth rate due to the gas concentration in the gas phase. It was confirmed that a GaN film having excellent film thickness uniformity could be obtained even with a substrate as large as 4 inches as in this example.
[0074]
Next, the sapphire substrate 132 was removed to obtain a single GaN film 135 (FIG. 3C). The removal of the sapphire substrate 131 can be performed by a method such as separation by laser irradiation, dissolution of the sapphire substrate with a mixed solution of phosphoric acid and sulfuric acid, or polishing. Further, the back surface of the GaN film 135 from which the sapphire substrate 132 has been removed can be planarized by etching with a mixed solution of phosphoric acid and sulfuric acid at a temperature of about 240 ° C., polishing, or the like.
[0075]
Example 4
In this embodiment, an example in which a GaN layer is formed by using HVPE growth according to the present invention, and a semiconductor laser is manufactured and evaluated will be described. First, the manufacturing method will be described with reference to FIG. As a substrate material, a (111) plane silicon (Si) substrate having a thickness of 200 μm is used. An AlN layer 42 having a thickness of about 0.1 μm and a GaN layer 43 having a thickness of about 0.3 μm are formed on the Si substrate 41 by metal organic chemical vapor deposition (MOCVD). Next, a 0.5 μm thick SiO 2 is formed on the GaN layer 43. ₂ A film is formed, and a stripe-shaped mask 44 and an opening 45 are formed in the <11-20> direction of the GaN film 43 by lithography and wet etching. Subsequently, by using the HVPE apparatus shown in FIG. 5, growth is performed from the opening 45 where the GaN film 43 is exposed, and a GaN film 46 is formed.
The growth procedure is as follows. The cleaned Si substrate 41 is mounted on the substrate holder 20 and set in the growth region 35. N inside the reaction tube 11 ₂ Replace with gas. H to group III halide supply pipe 12 ₂ Gas and N ₂ Supply gas mixture. The gas flow rates were 700 cc / min and 2000 cc / min, respectively. Further, N gas is introduced from the group V source gas introduction pipe 28. ₂ Gas was supplied at 4100 cc / min. The temperature of the Ga source 14 region and the growth region 35 in the reaction tube 11 is increased using electric furnaces 16 and 17. When the growth region 35 rises to 600 ° C., the NH 3 gas is introduced at 1000 cc / min. ₃ By supplying the gas, the decomposition of the surface of the GaN film 41 was suppressed. When the temperature of the Ga source 14 reaches 850 ° C. and the temperature of the growth region 35 reaches 1020 ° C. and the temperature is stabilized, HCl gas is supplied onto the Ga source 14 at 120 cc / min to grow the GaN film 46 from the opening 45. (FIG. 4B). During the growth of the GaN film 46, the SiH was supplied from the halogen gas supply pipe 29. ₂ Cl ₂ A gas was supplied to dope Si.
[0076]
After the growth for 2 hours, the supply of the HCl gas supplied on the Ga source 14 is stopped, the power of the electric furnaces 16 and 17 is turned off, and the temperature of the entire reaction tube 11 is lowered. Until the temperature of the growth region 35 drops to 600 ° C. ₃ Gas supply was continued. After reaching room temperature, the grown crystal is taken out. The thickness of the GaN film 46 in FIG. 4B was 530 μm. Subsequently, the Si substrate 41 was removed by etching with a mixed solution of nitric acid and hydrofluoric acid, and the back surface of the GaN film 46 was polished to a thickness of about 300 μm to obtain a GaN free-standing substrate (FIG. 4C).
[0077]
On this GaN substrate, a nitride-based semiconductor laser structure (LD) was fabricated by using a metal organic chemical vapor deposition method. After GaN substrate surface is organically washed, it is immersed in nitric acid at a temperature of 100 ° C. for 30 minutes. ₂ Dry by blowing. This substrate is set in the MOCVD apparatus, and NH ₃ The temperature is raised to 1050 ° C. while supplying gas. After the temperature is stabilized, 1.5 μm thick n-type GaN film 47 to which Si is added, 0.35 μm thick n-type Al to which Si is added _0.15 Ga _0.85 An N cladding layer 48 and a GaN light guide film 49 with a thickness of 0.1 μm to which Si was added were formed. Next, after the temperature of the GaN film 46 is lowered to 750 ° C., the undoped In _0.2 Ga _0.8 N quantum well and 5 nm thick undoped In _0.05 Ga _0.95 Active layer 50 composed of three periods of multiple quantum wells composed of an N barrier layer, p-type Al of 20 nm thickness doped with Mg _0.2 Ga _0.8 The N-cladding layer 51 is formed, the GaN film 46 is heated again at a temperature of 1050 ° C., and the Mg-added p-type GaN optical guide layer 52 having a thickness of 0.1 μm and the Mg-added 0.4 μm Thickness of p-type Al _0.1 Ga _0.9 An N-clad layer 53 and a p-type GaN contact layer 54 having a thickness of 0.55 μm to which Mg was added were sequentially formed. After completion of the growth, the temperature is lowered, the grown crystal is taken out from the MOCVD apparatus, and the back surface is removed by polishing or solution etching to a thickness of about 120 μm, and palladium (Pd) having a thickness of 60 nm and 0.3 μm A thick gold (Au) p-type electrode 55 was formed. Finally, an n-type electrode 56 made of titanium (Ti) having a thickness of 30 nm and aluminum (Al) having a thickness of 0.3 μm was formed on the back surface (FIG. 4D). Next, cleavage was performed at the m-plane, which is the cleavage direction of GaN, to form a resonator mirror surface having a laser structure. In the manufactured LD, a device life exceeding 10,000 hours was obtained with good reproducibility.
[0078]
As described above, by using the GaN crystal according to the present invention as a substrate, a highly reliable nitride-based semiconductor laser, a light-emitting element such as a light-emitting diode, and an electronic device such as a field-effect transistor could be obtained. .
[0079]
【The invention's effect】
As described above, according to the present invention, V / III is specified to be low in HVPE, so that a high-quality GaN-based semiconductor layer can be grown at high speed.
[Brief description of the drawings]
FIG. 1 is a view showing a method of growing a GaN-based semiconductor layer according to an example.
FIG. 2 is a diagram illustrating a method of manufacturing a GaN-based semiconductor substrate according to an example.
FIG. 3 is a diagram illustrating a method of manufacturing a GaN-based semiconductor substrate according to an example.
FIG. 4 is a diagram illustrating a method of manufacturing a GaN-based semiconductor laser according to an example.
FIG. 5 is a diagram showing a schematic structure of an HVPE apparatus used in an example.
FIG. 6 is a diagram showing a relationship between a hydrogen partial pressure and a growth rate of a GaN-based semiconductor.
FIG. 7 is a diagram showing a relationship between a halogen supply rate and a growth rate of a GaN-based semiconductor.
FIG. 8 is a diagram showing a relationship between a V / III ratio and a growth rate of a GaN-based semiconductor.
FIG. 9 is a diagram showing a relationship between a growth temperature and a growth rate of a GaN-based semiconductor.
FIG. 10 is a diagram showing a relationship between a V / III ratio and a growth rate of a GaN-based semiconductor.
FIG. 11 is a diagram showing a schematic structure of a conventional HVPE apparatus.
[Explanation of symbols]
11 Reaction tube
12 Group III source gas supply pipe
14 Ga source
15 source boat
16 Electric furnace
17 Electric furnace
20 Substrate holder
24 rotating shaft
25 spout
26 motor
28 Group V source gas inlet pipe
29 Halogen gas supply pipe
30 Doping gas supply pipe
31 Shield plate
32 exhaust port
35 Growth area
36 Halide production room
41 Si substrate
42 AlN layer
43 GaN layer
44 Mask
45 opening
46 GaN film
47 n-type GaN film
48 n-type Al _0.15 Ga _0.85 N cladding layer
49 GaN light guide film
50 Active layer
51 p-type Al _0.2 Ga _0.8 N cladding layer
52 p-type GaN optical guide layer
53 p-type Al _0.1 Ga _0.9 N cladding layer
54 p-type GaN contact layer
55 p-type electrode
56 n-type electrode
111 GaN substrate
112 GaN layer
121 GaN substrate
122 GaN film
131 GaN film
132 GaN film
133 mask
134 opening
135 GaN film

Claims (8)

A method for growing a GaN-based semiconductor layer on a substrate by hydride vapor phase epitaxy,
Supplying a group V source gas containing a nitrogen element and a group III source gas made of a compound containing Ga and halogen to the substrate surface,
A method for growing a GaN-based semiconductor layer, wherein a V / III ratio defined by a ratio of a supply flow rate of the group V source gas to a supply flow rate of the group III source gas is set to 0.1 or more and less than 10. The method for growing a GaN-based semiconductor layer according to claim 1,
A method for growing a GaN-based semiconductor layer, wherein the growth temperature of the GaN-based semiconductor layer is 1000 ° C. or more and 1300 ° C. or less. The method for growing a GaN-based semiconductor layer according to claim 1 or 2,
A method for growing a GaN-based semiconductor layer, comprising using a carrier gas containing 5 to 20% by volume of hydrogen when supplying a group V source gas and a group III source gas to a substrate surface. The method for growing a GaN-based semiconductor layer according to claim 1,
A method for growing a GaN-based semiconductor layer, wherein the growth rate of the GaN-based semiconductor layer is 250 μm / hr or more. The method for growing a GaN-based semiconductor layer according to any one of claims 1 to 4,
A halogen gas is introduced into a chamber in which Ga or a Ga-containing compound is arranged, and the vapor of the Ga or Ga-containing compound reacts with the halogen gas while the supplied halogen gas stays in the room, and a compound containing Ga and halogen is contained. A method for growing a GaN-based semiconductor layer, comprising: generating the group III source gas comprising: and supplying the group III source gas to the substrate surface. The method for growing a GaN-based semiconductor layer according to any one of claims 1 to 5,
A method for growing a GaN-based semiconductor layer, wherein the substrate is a wafer having a size exceeding 2 inches in diameter. A method for manufacturing a semiconductor substrate, comprising: after growing a GaN-based semiconductor layer on a substrate, removing the substrate from the GaN-based semiconductor layer to obtain a GaN-based semiconductor substrate including the GaN-based semiconductor layer;
A method for manufacturing a semiconductor substrate, comprising: forming the GaN-based semiconductor layer by the growth method according to claim 1. A method for manufacturing a semiconductor device, comprising a step of forming an active layer having a GaN-based semiconductor layer on a substrate,
A method for manufacturing a semiconductor device, comprising: forming the GaN-based semiconductor layer by the growth method according to claim 1.

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