JP3653622B2 - Method for evaluating compound semiconductor epitaxial wafer including GaAs-AlGaAs superlattice structure layer - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、ＧａＡｓ−ＡｌＧａＡｓ超格子構造層を含む化合物半導体エピタキシャルウェハの評価方法に関し、特にウェハ表面にレーザー光線を照射し、その照射されたレーザー光線がウェハ表面で反射される際の散乱光の量を測定することによって、エピタキシャル成長層の結晶性の評価を行う方法に関する。
【０００２】
【従来の技術】
レーザーダイオードや発光ダイオード等の半導体発光素子、及びＦＥＴやＨＥＭＴ等の電子デバイスの作製にあたっては、一般に、ＧａＡｓ基板上に超格子構造をしたバッファー層が形成され、さらにその上に化合物半導体結晶層がエピタキシャル成長されてなる化合物半導体エピタキシャルウェハ、あるいはＩｎＰやＧａＩｎＰ等の半導体基板上に化合物半導体結晶層がエピタキシャル成長されてなるウェハが使用される。
【０００３】
従来、このようなエピタキシャルウェハの結晶性を評価する際には、レーザー光線等を励起源として用いてウェハのフォトルミネッセンス（ｐｈｏｔｏｌｕｍｉｎｅｓｃｅｎｃｅ）を測定する、所謂ＰＬ法が採用されている。このＰＬ法により測定された発光スペクトルの発光ピークの半値幅に基づいて、エピタキシャル層の結晶性の良否の情報が得られる。
【０００４】
ＰＬ法では、一般に、結晶性のより正確な情報を得るために、試料（ウェハ）を劈開して適当な大きさにし、それを液体窒素等を満たしたガラス製のデュワー等の中に入れて、液体窒素温度（７７Ｋ）以下の低温で測定を行っている。
【０００５】
また、例えば、ＧａＡｓ単結晶基板上にＧａＡｓ−ＡｌＧａＡｓ超格子層をエピタキシャル成長させ、さらにその上に１層もしくは２層以上のＧａＡｓ層等をエピタキシャル成長させてなる化合物半導体エピタキシャルウェハについて、ＧａＡｓ−ＡｌＧａＡｓ超格子層のフォトルミネッセンスを測定する場合には、超格子層上のエピタキシャル層の影響をなくすために、そのエピタキシャル層をエッチングにより除去してから測定を行っている。
【０００６】
ところで、ＰＬ法以外に、ウェハ表面に照射したレーザー光線の微小な散乱光を測定することにより、ウェハ表面の状態を評価する方法がある。具体的には、測定対象であるウェハの表面を、レーザー光線を照射しながら走査し、ウェハ表面の粗さや微小欠陥や微小な異物に起因して散乱されたレーザー光線の散乱量を測定する。そして、得られた散乱量に基づいて、ウェハ表面の異物やヘイズの大きさ、及びそれらの分布等の情報を得る。ここで、ヘイズとは、表面の不規則性または微細パーティクルであり、そのサイズが光線の波長と比較して非常に小さいが、表面の広範囲に及んでいるもののことである。このヘイズの測定では、ウェハ表面からの散乱光を、ウェハ表面に入射する光の１００万分率（ｐｐｍ）で表した値（これをヘイズ（ｈａｚｅ）という）が測定結果として得られる。具体的には、基板の反射率をＲ0 、表面粗さ（ＲＭＳ）をσ及び入射光の波長をλで表すと、ｈａｚｅは次の（１）式で表される。
ｈａｚｅ＝Ｒ0 （４πσ／λ）2 ×１０6 ・・・・（１）
ヘイズの測定を行う際に使用される機器としては、例えば、テンコールインスツルメンツ社（Ｔｅｎｃｏｒ Ｉｎｓｔｒｕｍｅｎｔｓ）製の表面評価装置Ｓｕｒｆｓｃａｎ４５００がある。このＳｕｒｆｓｃａｎ４５００では、レーザー光源として、波長６３２８オングストロームのＨｅ−Ｎｅレーザーが用いられている。
【０００７】
【発明が解決しようとする課題】
しかしながら、上記従来のＰＬ法は、破壊検査法の一種であり、測定対象である超格子層の上に積層された他のエピタキシャル層を除去したり、デュワー等の中に入れられる大きさにウェハを劈開したりしなければならず、手間がかかるだけでなく、ウェハの製品としての歩留まりが低下するという問題があった。
【０００８】
また、上記従来のＰＬ法では、冷却しながら測定を行うため、測定装置が複雑な構成になってしまうという問題もあった。
【０００９】
また、上述したヘイズの測定によるウェハ表面の評価方法には、次のような問題があることが本発明者らにより明らかとされた。すなわち、この評価方法により、エピタキシャル成長層を有する化合物半導体ウェハ表面の測定を行った場合、通常、測定値（すなわち、ｈａｚｅ）が約２０ｐｐｍ以上であれば肉眼による表面状態の観察時にウェハ表面に曇りが認められる。しかし、エピタキシャル成長層にＧａＡｓ−ＡｌＧａＡｓ超格子層が含まれている場合には、ｈａｚｅが数十ｐｐｍに達しているにもかかわらず、ウェハ表面に曇りが観察されない場合がある。例えば、ＧａＡｓ−ＡｌＧａＡｓ超格子層が含まれているウェハについて本発明者らが行った実験によれば、ｈａｚｅが２ｐｐｍより小さい値のウェハでは、表面に曇りがなく、原子間力顕微鏡（ＡＦＭ，Ａｔｏｍｉｃ Ｆｏｒｃｅ Ｍｉｃｒｏｓｃｏｐｅ）による表面粗さ（視野：１μｍ角）は１．５５６１ｎｍであった。また、ｈａｚｅが３６ｐｐｍのウェハでは、表面に曇りがなく、ＡＦＭによる表面粗さ（視野：１μｍ角）は１．４７３１ｎｍであった。それと同程度であるｈａｚｅ３６ｐｐｍのウェハでは、表面に曇りがあり、ＡＦＭによる表面粗さ（視野：１μｍ角）は１０．２１９ｎｍであった。つまり、ヘイズの測定結果と実際のウェハの表面状態との間に規則性が認められないことがわかった。
【００１０】
本発明は、上記事情に鑑みなされたもので、基板上にエピタキシャル成長された化合物半導体層、特にＧａＡｓ−ＡｌＧａＡｓ超格子構造層を含むエピタキシャル成長層の結晶性に関する情報を、レーザー光線を用いたヘイズの測定を行うことにより、ウェハを破壊することなく簡便に得ることができる化合物半導体エピタキシャルウェハの評価方法を提供することを目的とする。
【００１１】
【課題を解決するための手段】
上記目的を達成するために、本発明者らは、ＧａＡｓ−ＡｌＧａＡｓ超格子構造層を含むエピタキシャル成長層を有するウェハについて、ヘイズの測定を行い、鋭意検討した結果、図１に示すように、得られたｈａｚｅの値と、液体窒素温度（７７Ｋ）におけるＧａＡｓ−ＡｌＧａＡｓ超格子構造層からのＰＬ発光のピークの半値幅（ＦＷＨＭ）との間に密接な相関関係があることを見出した。
【００１２】
本発明は、上記知見に基づきなされたもので、基板上にエピタキシャル成長された化合物半導体層を有する化合物半導体エピタキシャルウェハの表面の一部にレーザー光線を照射し、その照射部位を走査させながら、ウェハ表面で散乱された散乱光を検出し、その検出結果と、予め求めておいた、ウェハ表面での散乱光の検出値とエピタキシャル成長層のフォトルミネッセンス（ＰＬ）の発光ピークの半値幅との間の相関関係に基づいて、前記化合物半導体層の結晶性の評価を行うことを特徴とするものである。
【００１３】
この発明によれば、化合物半導体エピタキシャルウェハの表面の散乱光を測定することによって、基板上に形成されたエピタキシャル成長層の、液体窒素温度（７７Ｋ）におけるＰＬ発光ピークの半値幅を推定することができる。
【００１４】
また、上記発明において、前記基板はＧａＡｓでできており、かつ前記エピタキシャル成長層はＧａＡｓ−ＡｌＧａＡｓ超格子構造層を含むようになっていてもよい。そうすれば、化合物半導体エピタキシャルウェハの表面の散乱光を測定することによって、ＧａＡｓ−ＡｌＧａＡｓ超格子構造層を含むエピタキシャル成長層の、液体窒素温度（７７Ｋ）におけるＰＬ発光ピークの半値幅を推定することができる。
【００１５】
【発明の実施の形態】
まず、ＧａＡｓ基板上に、所望の積層構造をなすように、１または２以上の化合物半導体結晶層がエピタキシャル成長されてなる化合物半導体エピタキシャルウェハを作製する。エピタキシャル成長される化合物半導体結晶層は、例えば、ＧａＡｓ−ＡｌＧａＡｓ超格子構造層上にさらに化合物半導体結晶層が積層されたものである。
【００１６】
作製されたウェハについて、テンコールインスツルメンツ社（Ｔｅｎｃｏｒ Ｉｎｓｔｒｕｍｅｎｔｓ）製のＳｕｒｆｓｃａｎ４５００等の表面評価装置を用いて、例えば室温にてヘイズの測定を行い、上記（１）式よりｈａｚｅの値を求める。Ｓｕｒｆｓｃａｎ４５００では、光源としてＨｅ−Ｎｅレーザー（波長：６３２８オングストローム）が用いられているが、これに限らず、光源として、例えばＡｒレーザー（波長：５１４５オングストローム）やＹＡＧレーザー（波長：１０６００オングストローム）を用いてもよい。
【００１７】
次いで、同ウェハを適当な大きさとなるように劈開し、エッチング処理を行った後、液体窒素温度（７７Ｋ）にてＰＬ測定を行い、ＰＬ発光のピークの半値幅を求める。
【００１８】
ｈａｚｅの値とＰＬ発光ピークの半値幅とに基づいて、それらの間の相関関係（図１参照）を求める。
【００１９】
以上のようにして予めｈａｚｅの値とＰＬ発光ピークの半値幅との関係が求まったら、実際に製造されたウェハについて、ＰＬ測定を行わずに、例えば室温にてヘイズの測定を行う。そして、先に求めた、ｈａｚｅの値とＰＬ発光ピークの半値幅との相関関係（図１参照）に基づいて、得られた製品としてのウェハのｈａｚｅの値からＰＬ発光ピークの半値幅を求め、ウェハの良否を判断する。
【００２０】
あるいは、ｈａｚｅの値とＰＬ発光ピークの半値幅との相関関係が求まった時点で、その相関関係に基づいて、ウェハの良否の臨界となるＰＬ発光ピークの半値幅（製品の仕様等により決まる）からウェハの良否の臨界となるｈａｚｅの値を求めておき、製品として製造されたウェハについて、ＰＬ測定を行わずに、室温にてヘイズの測定を行い、ウェハの良否を判断するようにしてもよい。
【００２１】
上記実施形態によれば、例えばＧａＡｓ−ＡｌＧａＡｓ超格子構造層を含む所望の積層構造をなすエピタキシャル成長層を有する化合物半導体エピタキシャルウェハについて、予め、例えば図１に示すように、ｈａｚｅの値とＰＬ発光ピークの半値幅との相関関係を求めておくことによって、以後作製されたウェハについてヘイズの測定を行うことにより、エピタキシャル成長層のＰＬ発光ピークの半値幅を推定することができるので、実際にＰＬ法を行わずに済み、ウェハを破壊することなく、簡便にエピタキシャル成長層の結晶性を評価することができる。従って、結晶性の評価に要する時間が著しく短縮されるとともに、非破壊検査であるため、エピタキシャルウェハの歩留まりが向上する。
【００２２】
【実施例】
電子デバイス作製用のＧａＡｓ基板上に、ＭＢＥ（分子線エピタキシー）法によりＧａＡｓよりなるバッファー層を成長させ、さらにその上にＧａＡｓ−ＡｌＧａＡｓ超格子構造層を成長させた。ＧａＡｓ−ＡｌＧａＡｓ超格子構造層は、厚さ１５ｎｍのＡｌＧａＡｓ層（ＡｌＡｓ組成が０．２８程度のもの）と厚さ５ｎｍのＧａＡｓ層とからなるヘテロ構造を１周期とし、これを全部で２０周期分積層した構造とした。そして、その超格子構造層上に、さらに厚さ３００ｎｍのＧａＡｓ層を成長させた後、その上に厚さ６００ｎｍ程度で、Ｓｉをドナーとするｎ型のＧａＡｓ層を成長させてエピタキシャルウェハを作製した。
【００２３】
このエピタキシャルウェハに対して、テンコールインスツルメンツ社（Ｔｅｎｃｏｒ Ｉｎｓｔｒｕｍｅｎｔｓ）製のＳｕｒｆｓｃａｎ４５００を用い、室温でウェハ表面からの散乱光を測定した。レーザー光源は、Ｈｅ−Ｎｅレーザー（波長：６３２８オングストローム）であった。ウェハ表面で散乱された光は、Ｓｕｒｆｓｃａｎ４５００の電子倍増管により検出され、その検出された散乱光の強度に基づいて、上記（１）式より、ｈａｚｅの値を算出した。
【００２４】
次に、散乱光を測定したウェハを劈開して７ｍｍ角程度の大きさのチップとした。そのチップの表面の前記ｎ型のＧａＡｓ層を、ウェットエッチングにより除去した。その際、フッ酸系エッチャント（ＨＦ：Ｈ2 Ｏ2 ：Ｈ2 Ｏ＝１：１：１０）を用いた。なお、アンモニア系エッチャント（ＮＨ4 ＯＨ：Ｈ2 Ｏ2 ：Ｈ2 Ｏ＝３：１：１４６）を用いてもよい。エッチング後、チップを水洗及び乾燥させ、液体窒素温度（７７Ｋ）にてＡｒレーザー（波長：５１４５オングストローム）を光源として、ＰＬ測定を行った。測定された、ＧａＡｓ−ＡｌＧａＡｓ超格子構造層からの発光ピークの波長は、７７００〜７８００オングストローム程度であった。
【００２５】
以上のようにして得られたｈａｚｅの値とＰＬ発光ピークの半値幅との関係を図１に示す。図１より、ＰＬ発光ピークの半値幅（ＦＷＨＭ）とｈａｚｅの値との間には、次の（２）式で表されるような良好な一次線形の相関関係があることがわかった。
（ＦＷＨＭ）＝０．０３７７×（ｈａｚｅ）＋４．５２２、Ｒ2 ＝０．７６２４・・・・（２）
従って、図１及び式（２）より、ｈａｚｅの値が大きくなるほどＰＬ発光ピークの半値幅が大きくなり、ＧａＡｓ−ＡｌＧａＡｓ超格子構造層の結晶性が悪化することがわかった。
【００２６】
図１及び式（２）を用いることにより、例えば、電子デバイス作製用の化合物半導体エピタキシャルウェハのＧａＡｓ−ＡｌＧａＡｓ超格子構造層の結晶性の良否の判断基準として、７７ＫにおけるＧａＡｓ−ＡｌＧａＡｓ超格子構造層からのＰＬ発光ピークの半値幅が５ｍｅＶ以下であると仮定すれば、ｈａｚｅの値は１０ｐｐｍ以下であればよいことがわかり、ＰＬ測定に代わって、ウェハを破壊することなく、室温でヘイズの測定を行うことによって、ＧａＡｓ−ＡｌＧａＡｓ超格子構造層の結晶性の良否を判断することができることがわかった。
【００２７】
なお、上記実施例では、ＧａＡｓ基板上のＧａＡｓ−ＡｌＧａＡｓ超格子構造層上に、さらにＧａＡｓ層が積層されたＧａＡｓエピタキシャルウェハの評価について説明したが、本発明は、これに限らず、他の構造のエピタキシャルウェハの評価にも適用可能であるのはいうまでもない。
【００２８】
【発明の効果】
本発明によれば、化合物半導体エピタキシャルウェハの表面の散乱光を測定することによって、基板上に形成されたエピタキシャル成長層の、液体窒素温度（７７Ｋ）におけるＰＬ発光ピークの半値幅を推定することができるので、実際にＰＬ法を行わずに済み、ウェハを破壊することなく、簡便にエピタキシャル成長層の結晶性を評価することができる。従って、結晶性の評価に要する時間が著しく短縮されるとともに、非破壊検査であるため、エピタキシャルウェハの歩留まりが向上する。
【００２９】
また、本発明によれば、化合物半導体エピタキシャルウェハの表面の散乱光を測定することによって、ＧａＡｓ基板上に形成されたＧａＡｓ−ＡｌＧａＡｓ超格子構造層を含むエピタキシャル成長層の、液体窒素温度（７７Ｋ）におけるＰＬ発光ピークの半値幅を推定することができるので、実際にＰＬ法を行わずに済み、ＧａＡｓ基板上にＧａＡｓ−ＡｌＧａＡｓ超格子構造層を含むエピタキシャル成長層が形成されてなるウェハを破壊することなく、簡便にエピタキシャル成長層の結晶性を評価することができる。従って、ＧａＡｓ−ＡｌＧａＡｓ超格子構造層を含むエピタキシャル成長層の結晶性評価に要する時間が著しく短縮されるとともに、非破壊検査であるため、エピタキシャルウェハの歩留まりが向上する。
【図面の簡単な説明】
【図１】ＧａＡｓ−ＡｌＧａＡｓ超格子構造層を含むエピタキシャル成長層を有するウェハのｈａｚｅの値と、７７ＫにおけるＧａＡｓ−ＡｌＧａＡｓ超格子構造層からのＰＬ発光のピークの半値幅との間の関係の一例を示す特性図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for evaluating a compound semiconductor epitaxial wafer including a GaAs-AlGaAs superlattice structure layer, and in particular, irradiates a laser beam on the wafer surface, and reduces the amount of scattered light when the irradiated laser beam is reflected on the wafer surface. The present invention relates to a method for evaluating crystallinity of an epitaxially grown layer by measurement.
[0002]
[Prior art]
In fabricating semiconductor light emitting devices such as laser diodes and light emitting diodes, and electronic devices such as FETs and HEMTs, a buffer layer having a superlattice structure is generally formed on a GaAs substrate, and a compound semiconductor crystal layer is further formed thereon. A compound semiconductor epitaxial wafer obtained by epitaxial growth or a wafer obtained by epitaxial growth of a compound semiconductor crystal layer on a semiconductor substrate such as InP or GaInP is used.
[0003]
Conventionally, when evaluating the crystallinity of such an epitaxial wafer, a so-called PL method has been adopted in which photoluminescence of the wafer is measured using a laser beam or the like as an excitation source. Based on the half-value width of the emission peak of the emission spectrum measured by the PL method, information on the crystallinity of the epitaxial layer can be obtained.
[0004]
In the PL method, in general, in order to obtain more accurate information on crystallinity, a sample (wafer) is cleaved to an appropriate size and placed in a glass dewar filled with liquid nitrogen or the like. The measurement is performed at a low temperature below the liquid nitrogen temperature (77K).
[0005]
Further, for example, a compound semiconductor epitaxial wafer obtained by epitaxially growing a GaAs-AlGaAs superlattice layer on a GaAs single crystal substrate and further epitaxially growing one or more GaAs layers on the GaAs-AlGaAs superlattice layer. When measuring the photoluminescence of a layer, in order to eliminate the influence of the epitaxial layer on the superlattice layer, the measurement is performed after removing the epitaxial layer by etching.
[0006]
In addition to the PL method, there is a method for evaluating the state of the wafer surface by measuring the minute scattered light of the laser beam applied to the wafer surface. Specifically, the surface of the wafer to be measured is scanned while irradiating a laser beam, and the scattering amount of the laser beam scattered due to the roughness of the wafer surface, minute defects, and minute foreign matter is measured. Then, based on the obtained scattering amount, information such as the size of foreign matter and haze on the wafer surface and their distribution is obtained. Here, haze is irregularity or fine particles on the surface, and its size is very small compared to the wavelength of light, but extends over a wide range of the surface. In this haze measurement, a value obtained by expressing the scattered light from the wafer surface in parts per million (ppm) of light incident on the wafer surface (this is referred to as haze) is obtained as a measurement result. Specifically, when the reflectance of the substrate is represented by R 0 , the surface roughness (RMS) is represented by σ, and the wavelength of incident light is represented by λ, haze is represented by the following equation (1).
haze = R 0 (4πσ / λ) 2 × 10 6 (1)
As an apparatus used when measuring haze, for example, there is a surface evaluation device Surfscan 4500 manufactured by Tencor Instruments. In the Surfscan 4500, a He-Ne laser having a wavelength of 6328 angstroms is used as a laser light source.
[0007]
[Problems to be solved by the invention]
However, the above-mentioned conventional PL method is a kind of destructive inspection method, and removes other epitaxial layers stacked on the superlattice layer to be measured, or allows the wafer to be of a size that can be placed in a dewar or the like. In addition to being troublesome, there is a problem that the yield of the wafer as a product is reduced.
[0008]
In addition, the conventional PL method has a problem that the measurement apparatus has a complicated configuration because the measurement is performed while cooling.
[0009]
Further, the present inventors have revealed that the above-described method for evaluating a wafer surface by measuring haze has the following problems. That is, when the surface of a compound semiconductor wafer having an epitaxially grown layer is measured by this evaluation method, usually, if the measured value (that is, haze) is about 20 ppm or more, the wafer surface becomes cloudy when the surface state is observed with the naked eye. Is recognized. However, when the epitaxial growth layer includes a GaAs-AlGaAs superlattice layer, cloudiness may not be observed on the wafer surface even though the haze reaches several tens of ppm. For example, according to an experiment conducted by the present inventors on a wafer including a GaAs-AlGaAs superlattice layer, a wafer having a haze value of less than 2 ppm has no cloudiness on the surface, and an atomic force microscope (AFM, The surface roughness (field of view: 1 μm square) according to Atomic Force Microscope was 1.5561 nm. Further, the wafer having a haze of 36 ppm had no cloudiness on the surface, and the surface roughness (field of view: 1 μm square) by AFM was 1.4731 nm. The wafer with haze of 36 ppm, which is comparable to that, had cloudiness on the surface, and the surface roughness (view field: 1 μm square) by AFM was 10.219 nm. That is, it was found that no regularity was observed between the measurement result of haze and the actual surface state of the wafer.
[0010]
The present invention has been made in view of the above circumstances, and information on crystallinity of a compound semiconductor layer epitaxially grown on a substrate, particularly an epitaxially grown layer including a GaAs-AlGaAs superlattice structure layer, is measured by measuring a haze using a laser beam. An object of the present invention is to provide a method for evaluating a compound semiconductor epitaxial wafer that can be easily obtained without destroying the wafer.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have conducted a haze measurement on a wafer having an epitaxially grown layer including a GaAs-AlGaAs superlattice structure layer, and as a result of earnest investigation, as shown in FIG. It was found that there is a close correlation between the value of haze and the half width (FWHM) of the peak of PL emission from the GaAs-AlGaAs superlattice structure layer at liquid nitrogen temperature (77 K).
[0012]
The present invention has been made on the basis of the above knowledge, and a part of the surface of a compound semiconductor epitaxial wafer having a compound semiconductor layer epitaxially grown on a substrate is irradiated with a laser beam, and the irradiated portion is scanned on the wafer surface. The scattered scattered light is detected, and the correlation between the detection result and the half-value width of the emission peak of the photoluminescence (PL) of the photoluminescence (PL) of the epitaxial growth layer obtained in advance is obtained. Based on the above, the crystallinity of the compound semiconductor layer is evaluated.
[0013]
According to this invention, the half-value width of the PL emission peak at the liquid nitrogen temperature (77 K) of the epitaxial growth layer formed on the substrate can be estimated by measuring the scattered light on the surface of the compound semiconductor epitaxial wafer. .
[0014]
In the above invention, the substrate may be made of GaAs, and the epitaxial growth layer may include a GaAs-AlGaAs superlattice structure layer. Then, the half-value width of the PL emission peak at the liquid nitrogen temperature (77 K) of the epitaxial growth layer including the GaAs-AlGaAs superlattice structure layer can be estimated by measuring the scattered light on the surface of the compound semiconductor epitaxial wafer. it can.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
First, a compound semiconductor epitaxial wafer in which one or more compound semiconductor crystal layers are epitaxially grown on a GaAs substrate so as to form a desired laminated structure is manufactured. The compound semiconductor crystal layer to be epitaxially grown is, for example, a compound semiconductor crystal layer further stacked on a GaAs-AlGaAs superlattice structure layer.
[0016]
About the produced wafer, haze is measured, for example at room temperature using surface evaluation apparatuses, such as Surfscan 4500 by Tencor Instruments, and the value of haze is calculated | required from said (1) Formula. In the Surfscan 4500, a He-Ne laser (wavelength: 6328 angstrom) is used as a light source. However, the present invention is not limited to this, and an Ar laser (wavelength: 5145 angstrom) or a YAG laser (wavelength: 10600 angstrom) is used as the light source. May be.
[0017]
Next, the wafer is cleaved to an appropriate size, etched, and then subjected to PL measurement at a liquid nitrogen temperature (77 K) to determine the half-value width of the PL emission peak.
[0018]
Based on the value of haze and the half-value width of the PL emission peak, a correlation between them (see FIG. 1) is obtained.
[0019]
When the relationship between the value of haze and the half-value width of the PL emission peak is obtained in advance as described above, haze measurement is performed on the actually manufactured wafer, for example, at room temperature without performing PL measurement. Then, based on the correlation between the value of haze and the half-value width of the PL emission peak obtained earlier (see FIG. 1), the half-value width of the PL emission peak is obtained from the value of the wafer as the obtained product. The quality of the wafer is judged.
[0020]
Alternatively, when the correlation between the value of haze and the half-value width of the PL emission peak is obtained, the half-value width of the PL emission peak, which is the criticality of wafer quality, is determined based on the correlation (determined by the product specifications, etc.) Then, the haze value that is the criticality of the wafer quality is obtained from the wafer, and for the wafer manufactured as a product, the haze measurement is performed at room temperature without performing the PL measurement to judge the wafer quality. Good.
[0021]
According to the above-described embodiment, for example, as shown in FIG. 1, the value of haze and the PL emission peak are preliminarily obtained for a compound semiconductor epitaxial wafer having an epitaxially grown layer having a desired laminated structure including a GaAs-AlGaAs superlattice structure layer. The half-width of the PL emission peak of the epitaxially grown layer can be estimated by measuring the haze of the wafer produced thereafter, by calculating the correlation with the half-width of the The crystallinity of the epitaxially grown layer can be easily evaluated without performing the process and without destroying the wafer. Therefore, the time required for the evaluation of crystallinity is remarkably shortened and the yield of the epitaxial wafer is improved because of non-destructive inspection.
[0022]
【Example】
A buffer layer made of GaAs was grown on a GaAs substrate for manufacturing an electronic device by MBE (molecular beam epitaxy) method, and a GaAs-AlGaAs superlattice structure layer was further grown thereon. The GaAs-AlGaAs superlattice structure layer has a heterostructure consisting of an AlGaAs layer having a thickness of 15 nm (with an AlAs composition of about 0.28) and a GaAs layer having a thickness of 5 nm as one period, and this is a total of 20 periods. A laminated structure was obtained. Then, after a GaAs layer having a thickness of 300 nm is further grown on the superlattice structure layer, an epitaxial wafer is fabricated by growing an n-type GaAs layer having a thickness of about 600 nm and using Si as a donor. did.
[0023]
The epitaxial wafer was measured for scattered light from the wafer surface at room temperature using a Surfscan 4500 manufactured by Tencor Instruments. The laser light source was a He—Ne laser (wavelength: 6328 Å). The light scattered on the wafer surface was detected by an electron multiplier tube of Surfscan 4500, and the value of haze was calculated from the above equation (1) based on the intensity of the detected scattered light.
[0024]
Next, the wafer from which the scattered light was measured was cleaved to obtain a chip having a size of about 7 mm square. The n-type GaAs layer on the surface of the chip was removed by wet etching. At that time, a hydrofluoric acid-based etchant (HF: H 2 O 2 : H 2 O = 1: 1: 10) was used. An ammonia-based etchant (NH 4 OH: H 2 O 2 : H 2 O = 3: 1: 146) may be used. After etching, the chip was washed with water and dried, and PL measurement was performed at a liquid nitrogen temperature (77 K) using an Ar laser (wavelength: 5145 angstrom) as a light source. The measured wavelength of the emission peak from the GaAs-AlGaAs superlattice structure layer was about 7700-7800 angstroms.
[0025]
The relationship between the haze value obtained as described above and the half-value width of the PL emission peak is shown in FIG. From FIG. 1, it was found that there is a good first-order linear correlation represented by the following equation (2) between the half-value width (FWHM) of the PL emission peak and the value of haze.
(FWHM) = 0.0377 × (haze) +4.522, R 2 = 0.7624 (2)
Therefore, from FIG. 1 and formula (2), it was found that as the haze value increases, the half-value width of the PL emission peak increases, and the crystallinity of the GaAs-AlGaAs superlattice structure layer deteriorates.
[0026]
By using FIG. 1 and formula (2), for example, a GaAs-AlGaAs superlattice structure layer at 77K can be used as a criterion for determining the crystallinity of the GaAs-AlGaAs superlattice structure layer of a compound semiconductor epitaxial wafer for manufacturing an electronic device. Assuming that the half-value width of the PL emission peak from 5 is 5 meV or less, it is understood that the haze value should be 10 ppm or less. Instead of PL measurement, haze measurement is performed at room temperature without destroying the wafer. It was found that the crystallinity of the GaAs-AlGaAs superlattice structure layer can be judged by performing the above.
[0027]
In the above embodiment, the evaluation of the GaAs epitaxial wafer in which the GaAs layer is further laminated on the GaAs-AlGaAs superlattice structure layer on the GaAs substrate has been described. However, the present invention is not limited to this, and other structures are also described. Needless to say, the present invention can also be applied to the evaluation of epitaxial wafers.
[0028]
【The invention's effect】
According to the present invention, the half width of the PL emission peak at the liquid nitrogen temperature (77 K) of the epitaxial growth layer formed on the substrate can be estimated by measuring the scattered light on the surface of the compound semiconductor epitaxial wafer. Therefore, the PL method is not actually performed, and the crystallinity of the epitaxial growth layer can be easily evaluated without destroying the wafer. Therefore, the time required for the evaluation of crystallinity is remarkably shortened and the yield of the epitaxial wafer is improved because of non-destructive inspection.
[0029]
Further, according to the present invention, by measuring the scattered light on the surface of the compound semiconductor epitaxial wafer, the epitaxial growth layer including the GaAs-AlGaAs superlattice structure layer formed on the GaAs substrate is measured at a liquid nitrogen temperature (77 K). Since the half-value width of the PL emission peak can be estimated, it is not necessary to actually perform the PL method, and without destroying the wafer in which the epitaxial growth layer including the GaAs-AlGaAs superlattice structure layer is formed on the GaAs substrate. The crystallinity of the epitaxial growth layer can be easily evaluated. Therefore, the time required for evaluating the crystallinity of the epitaxial growth layer including the GaAs-AlGaAs superlattice structure layer is remarkably shortened, and the yield of the epitaxial wafer is improved because the nondestructive inspection is performed.
[Brief description of the drawings]
FIG. 1 shows an example of the relationship between the haze value of a wafer having an epitaxial growth layer including a GaAs-AlGaAs superlattice structure layer and the half-value width of the peak of PL emission from the GaAs-AlGaAs superlattice structure layer at 77K. FIG.
Claims (2)
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| JP13641597A JP3653622B2 (en) | 1997-05-27 | 1997-05-27 | Method for evaluating compound semiconductor epitaxial wafer including GaAs-AlGaAs superlattice structure layer |
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| JP13641597A JP3653622B2 (en) | 1997-05-27 | 1997-05-27 | Method for evaluating compound semiconductor epitaxial wafer including GaAs-AlGaAs superlattice structure layer |
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| JP7467816B2 (en) * | 2021-06-24 | 2024-04-16 | ベイジン トンメイ クリスタル テクノロジー カンパニー リミテッド | Method and setup for detecting surface haze of a material |
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| JP3098670B2 (en) * | 1994-03-14 | 2000-10-16 | 三菱マテリアル株式会社 | Method for controlling polishing surface roughness of semiconductor wafer for bonding |
| JP2932238B2 (en) * | 1994-06-10 | 1999-08-09 | 株式会社ジャパンエナジー | Evaluation method of compound semiconductor |
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