JP4255168B2 - Nitride semiconductor manufacturing method and light emitting device - Google Patents

Description

表１の実験結果から、貫通転位密度は、第１、第２のマスクパターンによらず、マスク被覆率が増加するに連れて、貫通転位密度が減少する傾向に有る。ただし、マスク被覆率が８０％以上になると、逆に貫通転位密度が増加し始める。一般に、マスク直上に成長した窒化物半導体結晶は結晶成長軸方向（基板表面に対して垂直方向）から、マスクストライプ方向と垂直な方向に微傾斜角度を持って成長する。特に、マスク被覆率が大きくなる（マスク幅が大きくなる）と、この微傾斜角度が大きくなる。この事から、前述のマスク被覆率が８０％以上になると、前記微傾斜角度が大きくなり、両側のマスク開口部から結晶成長してきた窒化物半導体結晶がマスク直上で会合するときに、空洞部を形成し、その事が新たな貫通転位の発生要因になっているものと考えられる。
【００８０】
また、マスク被覆率が、約８０％よりも上回ると、ラテラル成長速度が急激に遅くなるために、該マスクを被覆することが困難になり（空洞部の発生要因となる）、完全に該マスクを被覆するためには厚膜を積層しなければならない。さらに、マスク被覆率が９０％以上になると、厚膜を積層しても完全にマスクを埋没させることは困難となる。本発明者らの実験結果では、マスク被覆率９０％において、窒化物半導体膜を５０μｍまで積層したが、埋没しなかった。
【００８１】
表１で示した９０％のマスク被覆率は、第１、第２のマスクパターンによらず、マスクパターンを被覆することができなかった。これらマスクパターンの中央部は、窒化物半導体膜で覆われておらず、マスク方向に対して平行方向に空洞の溝が形成されていた。表１の第１と第２のマスクパターンのどちらかが、マスク被覆率９０％である窒化物半導体膜の貫通転位密度を調べてみると、１０⁶ｃｍ^-2台〜１０⁷ｃｍ^-2台のものが存在した。これは完全にマスクが被覆されていないために、その分だけ貫通転位が減少したものと考えられる。
【００８２】
さらに、表１をみると、第１のマスクパターンのマスク被覆率Ａ％、第２のマスクパターンのマスク被覆率Ｂ％のときの貫通転位密度と、第１のマスクパターンのマスク被覆率Ｂ％、第２のマスクパターンのマスク被覆率Ａ％のときの貫通転位密度とを比較したところ、後者の貫通転位密度の方が高かった。ここで、前記Ａ，Ｂは数値であり、Ａ＜Ｂの大小関係を有する。これは、第１のマスクパターン直上に積層した第１層目の窒化物半導体膜厚が、第１のマスクパターンのマスク被覆率に比べて前記微傾斜角度を十分に解消できるほど、厚くなかったためだと考えられる。すなわち、第１層目での微傾斜角度が十分に解消されることなく、第２のマスクパターンを形成したために、さらに微傾斜角度が大きくなり、空洞部の発生を容易にし、第２層目の窒化物半導体膜中の貫通転位密度が低減し難くなったからである。従って、貫通転位密度を効率良く低減するためには、第１層目の窒化物半導体膜厚を十分に厚くして、前記微傾斜角度（空洞部）の発生を抑制するか、第１のマスクパターンのマスク被覆率を小さくして、第２のマスクパターンのマスク被覆率を大きくする必要が有る。本発明者らの実験結果によれば、第１のマスクパターンと第２のマスクパターンとの間の、第１層目の窒化物半導体膜の厚みが、１０μｍ以上になると、徐々に微傾斜角度が緩和し始めた。しかしながら、前者の窒化物半導体膜厚を十分に厚くする方法は、生産性を考えると得策ではない。
【００８３】
以上の実験結果から、第１と第２のマスクパターンを利用して貫通転位密度を効率良く低減するためには、第１、第２のマスクパターンのマスク被覆率が、それぞれ約２０％から８０％（貫通転位密度約１０⁷ｃｍ^-2台以下、完全な被覆膜）が好ましい。より好ましくは、第１、第２のマスクパターンの被覆率が約５０％以上８０％以下（貫通転位密度約１０⁵ｃｍ^-2台以下）である。さらに好ましくは、６０％以上７０％以下（貫通転位密度約１０⁴ｃｍ^-2台以下）である。また、第１のマスクパターンのマスク被覆率Ａ％、第２のマスクパターンのマスク被覆率Ｂ％との関係がＡ≦Ｂであることが好ましい。加えて、生産性を考慮した場合、第１、第２のマスパターンのマスク被覆率が同一であることが望ましい。この事によって、第１、第２層目の窒化物半導体膜の選択成長様式が同一になるため、選択成長の制御制、再現性が良く、また、同一の生産プロセスを適用することができるため、歩留まりも向上する。
【００８４】
第１、第２のマスクパターンの、各々のマスク被覆率については、約６０％〜７０％のときが最も貫通転位密度が低かった。このことは、各々の第ｎ番目のマスクパターンについても同じであった（ｎ≧１）。
【００８５】
本発明の実施の形態で示した第１と第２のマスクパターンは、互いに１２０度回転した方向に形成した場合であるが、実施の形態３で記述した、互いに９０度回転した方向であっても同様の効果が得られた。また、第１と第２のマスクパターンとの間の角度が、上記で指定した角度（１２０度または９０度）から±１０度以内のズレであれば、本質的な相違は無く、本発明の実施の形態と同様な効果が得られた。さらに、詳細に調べた結果、第１と第２のマスクパターンが平行でない限り、本発明の実施の形態と同様な効果が得られた。これは、上記で述べたように、各々のマスクパターンのマスク被覆率に対する貫通転位密度の特性は変わっておらず、第１と第２のマスクパターンで、どれだけ窒化物半導体膜を被覆できたかに依存しているためだと考えられる。
【００８６】
（実施の形態７）
本実施の形態は、発明の実施の形態で述べた第１と第２のマスクパターンのマスク被覆率がそれぞれ、７０％、７０％の場合について、平坦な第２層目の窒化物半導体膜上に形成した窒化物半導体レーザについて述べる。窒化物半導体レーザの作製方法については、実施の形態５と同様の手法で作製した。レーザ発振寿命を調べたところ、発振波長４１０ｎｍで、レーザ出力４０ｍＷ一定下、雰囲気温度５０℃で１２００時間以上であった。
【００８７】
また、第１と第２のマスクパターンのマスク被覆率が、それぞれ６０％以上７０％以下であれば、本実施の形態と同様のレーザ発振寿命が得られた。これは、窒化物半導体レーザ素子を構成している窒化物半導体結晶の貫通転位密度が大きく低減したことによって、レーザの利得損失が大幅に改善されたためである。このことから、本手法を用いれば、光ディスクシステムにおける記録用高出力レーザが作製できる。
【００８８】
上記第１と第２のマスクパターンのマスク被覆率が、それぞれ６０％以上７０％以下であれば、第１と第２のマスクパターンのマスク被覆率が異なっていても構わない。発明の実施の形態で記述したように、好ましくは、第１のマスクパターンのマスク被覆率Ａ％、第２のマスクパターンのマスク被覆率Ｂ％との関係がＡ≦Ｂである。
【００８９】
（実施の形態８）
本実施の形態は、発明の実施の形態で述べた第１と第２のマスクパターンのマスク被覆率がそれぞれ、５０％、５０％の場合について、平坦な第２層目の窒化物半導体膜上に形成した窒化物半導体レーザについて述べる。窒化物半導体レーザの作製方法については、実施の形態５と同様の手法で作製した。レーザ発振寿命を調べたところ、発振波長４１０ｎｍで、レーザ出力１０ｍＷ一定下、雰囲気温度５０℃で２０００時間以上であった。
【００９０】
上記では第１と第２のマスクパターンのマスク被覆率がそれぞれ、５０％、５０％の場合について述べたが、第１と第２のマスクパターンのマスク被覆率がそれぞれ５０％以上８０％以下であれば、本実施の形態と同様のレーザ発振寿命が得られた。これは、窒化物半導体レーザ素子を構成している窒化物半導体結晶の貫通転位密度が低減したことによって、レーザの利得損失が改善されたためである。このことから、本手法を用いれば、光ディスクシステムにおける再生用に必要なレーザ出力が十分に確保された。さらに、実施の形態７で示したように、第１と第２のマスクパターンのマスク被覆率がそれぞれ、６０％以上７０％以下であればさらなる効果が得られる。
【００９１】
尚、上記第１と第２のマスクパターンのマスク被覆率が、それぞれ５０％以上８０％以下であれば、第１と第２のマスクパターンのマスク被覆率が異なっていても構わない。発明の実施の形態で記述したように、好ましくは、第１のマスクパターンのマスク被覆率Ａ％、第２のマスクパターンのマスク被覆率Ｂ％との関係がＡ≦Ｂである。
【００９２】
（実施の形態９）
本実施の形態は、発明の実施の形態で述べた第１と第２のマスクパターンのマスク被覆率がそれぞれ、３０％、３０％の場合について、平坦な第２層目の窒化物半導体膜上に形成した窒化物半導体レーザについて述べる。窒化物半導体レーザの作製方法については、実施の形態５と同様の手法で作製した。レーザ発振寿命を調べたところ、発振波長４１０ｎｍで、レーザ出力５ｍＷ一定下、雰囲気温度５０℃で１８００時間以上であった。
【００９３】
このようにそれぞれのマスクの被覆率が３０％の場合でも、実施の形態８よりは寿命は短いが、充分実用化できる寿命を達成することができた。また、第１と第２のマスクパターンのマスク被覆率が、それぞれ２０％以上８０％以下であれば、本実施の形態と同様のレーザ発振寿命が得られた。これは、窒化物半導体レーザ素子を構成している窒化物半導体結晶の貫通転位密度が低減したことによって、レーザの利得損失が改善されたためである。このことから、本手法を用いれば、光ディスクシステムにおける再生用レーザが作製できる。また、第１と第２のマスクパターンのマスク被覆率がそれぞれ、５０％以上８０％以下であれば実施の形態８の効果が、さらに６０％以上７０％以下であれば実施の形態７で示す効果が得られる。
【００９４】
つまり、上記第１と第２のマスクパターンのマスク被覆率が、それぞれ２０％以上８０％以下であれば、第１と第２のマスクパターンのマスク被覆率が異なっていても構わない。発明の実施の形態で記述したように、好ましくは、第１のマスクパターンのマスク被覆率Ａ％、第２のマスクパターンのマスク被覆率Ｂ％との関係がＡ≦Ｂである。
【００９５】
【発明の効果】
上述したように、本発明による窒化ガリウム結晶は、成長抑制効果のある物質と窒化物半導体膜を交互に積層させることによって、歪みが殆どなくかつ貫通転位密度が１０⁴ｃｍ^-2以下と極めて小さい結晶が得られた。このような結晶を用いて作製した窒化ガリウム半導体レーザは信頼性が高くかつ極めて歩留まりよく生産できた。
【図面の簡単な説明】
【図１】本発明の実施の形態１又は２で示した第１工程完了後の製造工程図である。
【図２】本発明の実施の形態１又は２で示した第２工程完了後の上面からの透視図である。
【図３】本発明の実施の形態１又は２で示した第２工程完了後の断面図である。
【図４】本発明の実施の形態１で示した第３工程完了後の透視図及び断面図である。
【図５】本発明の実施の形態３で示した製造方法での透視図及び断面図である。
【図６】本発明の実施の形態４で示した厚膜窒化物半導体の製造方法を示す断面図である。
【図７】本発明に係る窒化物半導体を用いた半導体レーザダイオードデバイスの断面図である。
【図８】選択成長方法による第１の従来例である。
【図９】選択成長方法による第２の従来例である。
【符号の説明】
１００、２００、４００ サファイア基板
１０１、２０１、４０１ ＧａＮ層
１０２、２０２、４０２ 第１のマスクパターン
１０４、２０３、４０４ 第１層目のＧａＮ膜
１０５、２０６ 第１のマスクパターンの開口部
１０６、２０４、４０６ 第２のマスクパターン
１０７、２０５、４０７ 第２層目のＧａＮ膜
１０８ 第１と第２のマスクパターン直上部分
１０９ 第１のマスクパターンの開口部から成長した第２層目のＧａＮ膜の局部
１１０ 第１のマスクパターン直上の第２層目のＧａＮ膜の局部
１１１、４１１ 第３のマスクパターン
１１２、４１２ 第３層目のＧａＮ膜
１１３ 第１のマスクパターンの開口部から成長した第３層目のＧａＮ膜の局部
３００ 窒化物半導体
３０１ 最表面
３０２ 厚膜ＧａＮ
３０３ 第ｎのマスクパターン
４１３ ｎ−ＧａＮコンタクト層
４１４ ｎ−Ａｌ_0.1Ｇａ_0.9Ｎクラッド層
４１５ ｎ−ＧａＮ光ガイド層
４１６ 多重量子井戸構造活性層
４１７ Ａｌ_0.2Ｇａ_0.8Ｎ蒸発防止層＊
４１８ ｐ−ＧａＮ光ガイド層
４１９ ｐ−Ａｌ_0.1Ｇａ_0.9Ｎ型クラッド層
４２０ ｐ−ＧａＮ型コンタクト層
４２１ ｐ型電極
４２２ ｎ型電極
４２３ ＳｉＯ₂絶縁膜
５００、６００ サファイア基板
５０１、６０２ ＳｉＯ₂マスク
５０２、６０３ ＳｉＯ₂マスク開口部
５０３ ＧａＮ膜
５０４ ＳｉＯ₂マスク直上のＧａＮ
６０１ ＭＯＶＰＥ法で成長したＧａＮ膜
６０４ ＨＶＰＥ法で成長したＧａＮ膜[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a nitride semiconductor and a light emitting device manufactured by the method.
[0002]
[Prior art]
Gallium nitride (GaN) -based semiconductors are applied to light emitting devices for short wavelengths and electronic devices operating at high temperature and high speed. In realizing such a semiconductor element, characteristics of a crystal layer or a substrate serving as a base for manufacturing the element are important. Conventionally, sapphire and SiC have been used as substitute substrates, and a GaN layer formed thereon has been applied as a base for these device structures.
[0003]
However, GaN crystals formed in this way have 10⁹-10^Tencm^-2A crystal defect of the base occurs. In addition, when the thickness of the GaN layer exceeds 10 μm, there is a problem that crystal cracks and lattice strain of the GaN layer increase.
[0004]
Among the above problems, as a solution for reducing crystal cracks and lattice defects, FIG. 1 (1997) p265 shows a first conventional example. In FIG. 8, 500 is a sapphire substrate, 501 is SiO.₂Mask, 502 is SiO₂Reference numeral 503 denotes a GaN film grown by MOVPE (metal organic vapor phase epitaxy). In the present embodiment, SiO is such that crystal growth starts from the opening.₂By using the growth suppression effect (selective growth) by the pattern, SiO₂Only in the GaN film 504 directly above, a defect density of 10^Five-10⁶cm^-2Is obtained and SiO₂The defect density was reduced by about four orders of magnitude compared to crystals that did not use patterns.
[0005]
9 is the 58th JSAP Scientific Lecture Proceedings 2p-Q-15, No. 1 (1997) p266 is a second conventional example. In FIG. 9, 600 is a sapphire substrate, 601 is a GaN film grown by the MOVPE method, and 602 is SiO.₂Mask, 603 is SiO₂A mask opening 604 is a GaN film grown by HVPE (hydride vapor phase epitaxy). Also in this embodiment, a defect density of 6 × 10 is formed in the vicinity of the surface of the GaN film 604 grown by the HVPE method.⁷cm^-2As a result, the defect density was reduced by about three orders of magnitude compared to the conventionally obtained crystal. By using such a GaN single crystal film shown in the conventional example as a growth substrate for a GaN-based semiconductor device, high performance of the electronic device is expected.
[0006]
[Problems to be solved by the invention]
Conventional SiO₂By applying the vapor phase growth technique on the mask, 10^Five-10⁷cm^-2Although the crystal defects can be reduced to the extent, the quality of the GaN single crystal obtained by the above-mentioned conventional example is still high enough to obtain highly reliable semiconductor lasers, LEDs, and electronic devices such as FETs. It was not enough. That is, in any of the conventional examples described above, SiO₂Although the lattice strain in the direction perpendicular to the stripes of the masks 501 and 602 is reduced, the lattice strain in the direction parallel to the stripes is reduced to SiO 2.₂Lattice distortion almost equivalent to that when the mask is not used remains. In such a GaN layer having a lattice strain specified in one direction, an anisotropic lattice strain remains in the GaN layer.
[0007]
Furthermore, in order to ensure sufficient reliability of the semiconductor laser, the defect density is the same as that of other III-V group semiconductor substrates such as GaAs.^Fourcm^-2Table, more preferably 1 × 10^Fourcm^-2The following crystal defect density is required, but the GaN thick film layer produced by the conventional technique is at most 10^Fivecm^-2Another problem was the large number of crystal defects.
[0008]
Such a light emitting device manufactured on a GaN layer having lattice distortion and many crystal defects has low reliability. For example, in the case of a semiconductor laser device, it is about 900 hours in continuous oscillation under a 3 mW output condition at room temperature. Only the lifetime of was confirmed.
[0009]
Further, in the GaN substrate in which the GaN layer is grown to a thickness of about 50 μm and the sapphire substrate is removed from the back surface, the lattice strain having the above anisotropy or 10^Fivecm^-2Residual crystal defects on the base are not alleviated and are problematic as in the GaN layer described above.
[0010]
[Means for Solving the Problems]
  According to the present invention, an nth (where n is a positive number of 1 or more) mask pattern made of a material having a growth suppressing effect and a nitride semiconductor film are formed so as to cover the nth mask pattern above the substrate. The process is the n-th process, and the nitride semiconductor film is formed on the nitride semiconductor film formed by the n-th process so as to cover the (n + 1) th mask pattern and the (n + 1) th mask pattern made of a material having a growth suppressing effect. Process to be performed with the (n + 1) th processEach of the mask patterns includes a plurality of stripe-shaped masks parallel to each other, and the nth mask pattern and the (n + 1) th mask pattern are in a twisted relationship with each other.It is characterized by that. For example, a first layer nitride semiconductor film is formed on the first mask pattern manufactured in the first step, and then the second mask pattern and the second layer nitride semiconductor film in the second step are formed. Are formed in the same manner as in the first step. By sequentially performing these series of steps up to the n-th step, crystal strain in the nitride semiconductor film in each step (strain due to lattice constant difference between substrate and nitride semiconductor crystal or difference in thermal expansion coefficient) is reduced. Further, dislocations generated from the substrate interface do not appear on the growth crystal surface. In the present invention, since n is an integer of 1 or more, the above process is formed at least in the second process.
[0011]
  In addition,The nitride semiconductor film crystal directly over the mask pattern is difficult to grow directly on the mask pattern due to selective growth, and is formed by lateral growth in the direction perpendicular to the stripe direction of the mask pattern from the opening of the mask pattern Is done.
[0012]
Accordingly, the nitride semiconductor film on the upper part of the (n + 1) th mask pattern grown in the direction perpendicular to the stripe direction of the (n + 1) th mask pattern has a very weak interatomic bond with the (n + 1) th mask pattern, so that the lattice distortion is reduced. Although not generated, in the direction parallel to the stripe direction, the lattice strain from the underlying layer in the nth step and after is inherited by the nitride semiconductor film on the n + 1th mask pattern. The same applies to thermal strain.
[0013]
In the above invention, since the mutual mask patterns are in a twisted relationship position, the influence of the distortion from the underlying layer can be eliminated not only in one direction but also in various directions. The relaxation of the strain has an effect of suppressing the occurrence of edge dislocation which is one of dislocations.
[0014]
The present invention relates to an angle difference of 120 degrees between the direction of the nth mask pattern and the stripe direction of the (n + 1) th mask pattern. Since nitride semiconductors mainly have a wurtzite structure, there are three types of equivalent directions. These three directions have an angle difference of 120 degrees from each other. By forming the directions of the mask patterns produced by the above steps at an angle of 120 degrees with each other, these mask patterns have mutually equivalent selection characteristics, and distortion can be eliminated by an equivalent strain relaxation action.
[0015]
  The present invention relates to the fact that the stripe direction of the nth mask pattern and the stripe direction of the (n + 1) th mask pattern have an angle difference of 90 degrees. the aboveWhen the angle difference is 120 degreesIn contrast, the stripe directions of these mask patterns are not equivalent to each other, and it is not possible to expect the equivalent selectivity and equivalent strain relaxation action as described above. However, since the stripe directions of the mask pattern are 90 degrees with each other, the effect of strain relaxation is great.
[0016]
The present invention relates to the relationship that the stripe width of the nth mask pattern is such that the stripe width of the (n + 1) th mask pattern ≧ the stripe width of the nth mask pattern.
[0017]
According to the present invention, the stripe width of the mask pattern increases as the number of steps increases (as n increases), so that the nitride semiconductor film produced by each step penetrates from the substrate toward the crystal stacking direction. The dislocation density can be reduced. The mask pattern according to the present invention is SiO₂Or SiN_xTherefore, the growth suppressing effect is sufficient.
[0018]
The present invention relates to the fact that the stripe direction of the mask pattern is the <1-100> or <11-20> direction of a nitride semiconductor crystal. When the stripe direction of the mask pattern is formed to be <1-100>, the nitride semiconductor film formed by the MOVPE method in particular is greatly laterally grown along the <11-20> direction perpendicular to the stripe direction. The mask pattern can be buried with a nitride semiconductor film in a thin film stack. Also, depending on the growth conditions, there is a feature that threading dislocations hardly appear on the mask pattern. From these characteristics, the <1-100> stripe direction is a very important direction in selective growth (lateral growth).
[0019]
When the stripe direction of the mask pattern is <11-20>, the lateral growth of the nitride semiconductor crystal grows along the <1-100> direction. However, the lateral growth rate is slower than in the <1-100> stripe direction. In addition, threading dislocations that have entered from the mask opening are bent in the direction of the mask, and meet at the center of the mask and extend again in the crystal growth direction. This is because more threading dislocations are generated in the upper part of the mask than in the case where the stripe direction of the mask pattern is the <1-100> direction. However, new dislocations do not occur immediately above the mask, but threading dislocations that have penetrated from the mask opening diffused, resulting in the same effect of reducing the threading dislocation density as in the <1-100> direction. There is. In the present invention, by selecting the stripe direction of the mask pattern in the <1-100> or <11-20> direction, the lateral growth is promoted to efficiently fill the mask pattern, reducing the threading dislocation density and reducing the strain. Realize the effect.
[0020]
In the present invention, the stripe directions of the first mask pattern, the second mask pattern, and the third mask pattern are [1-100], [10-10], and [01-10] directions of the nitride semiconductor crystal. Related to the combination of The stripe direction of one mask pattern in the first to third steps is set to <1-100>, and the stripe direction of the other mask pattern is formed so as to have an angle difference of 120 ° from the <1-100> direction. In a nitride semiconductor, it has an equivalent strain relaxation effect and promotes lateral growth of the strain to efficiently fill the mask pattern, so that the threading dislocation density can be reduced and the strain relaxation effect can be maximized. it can.
[0021]
In the present invention, the nitride semiconductor film crystal laminated in the n-th step is made of Al._xIn_yGa_zN (x + y + z = 1; 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). The crystal is a material suitable for this growth method because of anisotropy of growth rate (lateral growth).
[0022]
The present invention relates to the nitride semiconductor film laminated by the nth step or the nitride semiconductor film laminated on the nitride semiconductor layer having a thickness of 5 μm or more. The threading dislocations generated from the substrate are blocked by the mask portion, and enter the nitride semiconductor film grown as it is from the opening portion of the mask. However, by depositing a nitride semiconductor film of 5 μm or more, the mask pattern can be covered with the GaN film, and threading dislocations that could not be shielded can be reduced by the deposited film thickness.
[0023]
According to the present invention, a nitride semiconductor structure including a substrate is formed by using the nitride semiconductor manufacturing method, and at least the substrate is removed from the nitride semiconductor structure, thereby at least part of the nitride semiconductor structure. Is a nitride semiconductor substrate. In the prior art, it was difficult to supply a nitride semiconductor substrate having a size suitable for device production and good surface morphology. However, with the above manufacturing method, a nitride semiconductor substrate that satisfies the requirements for device production by a simple method can be obtained. It becomes possible to supply. Further, the crystal growth method according to the above process has a strain relaxation effect in addition to the reduction of threading dislocation density. This distortion is caused by a difference in thermal expansion coefficient other than the difference in lattice constant between the substrate and the nitride semiconductor crystal. For example, it is known that when a thick-film nitride semiconductor is grown directly on a sapphire substrate, a crack is generated in the temperature lowering process after the completion of crystal growth due to the difference in thermal expansion coefficient, and the crack is generated at about 20 μm. It has been. However, by using the crystal growth method according to the present invention, it is possible to form a thick nitride semiconductor film on a sapphire substrate without generating cracks.
[0024]
The present invention relates to the case where the n + 1th mask pattern covers the substrate as a whole when the first to n + 1th steps are performed using the crystal growth method. By carrying out the above method, the dislocations generated from the opening of the first mask pattern formed immediately above the substrate or the nitride semiconductor film crystal-grown on the substrate are generated in the n number of steps. The mask pattern is shielded by any mask pattern. As a result, the threading dislocation density reaching the final surface of the nitride semiconductor film on the (n + 1) th mask pattern is extremely reduced.
[0025]
  The method for manufacturing a nitride semiconductor according to the present invention is characterized in that mask coverages (mask width / pitch) of the first and second mask patterns are 20% to 80%, respectively.The mask coverage of the first mask pattern is preferably less than or equal to the mask coverage of the second mask pattern. As the substrate, a sapphire substrate, GaN substrate, SiC substrate, spinel substrate, MgO substrate, Si substrate, or GaAs substrate can be preferably used.
[0026]
According to the present invention, light formed on a nitride semiconductor layer after the nth step or a nitride semiconductor film laminated on the nitride semiconductor layer after the nth step is manufactured using the crystal growth method. The present invention relates to a light-emitting element having an active layer that emits light. The crystal growth method enables a light-emitting element having an active layer that emits light with less lattice distortion and crystal defects, and an extremely excellent light emitting efficiency and reliability are formed.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
With reference to FIG. 1A, the crystal growth method of the first embodiment will be described. FIG. 1A shows a cross-sectional view of the formed nitride semiconductor.
[0028]
First, trimethylgallium (TMG) and ammonia (NH) are placed on a sapphire substrate 100 having a C-plane as a surface, which is installed in a predetermined growth furnace._Three) Is used as a raw material to grow the GaN layer 101 to a thickness of 2 μm.
[0029]
Next, in order to form a first mask pattern, a 100 nm thick SiO 2 film is formed on the GaN layer 101 by sputtering as a film made of a growth-inhibiting substance.₂A film was formed. SiO₂The film forming method is not limited to the sputtering method, and other methods such as a CVD method, an EB vapor deposition method, and a vacuum vapor deposition method may be used. Moreover, as a growth inhibitory substance, SiO₂Besides Al₂O_ThreeTiO₂Oxides such as SiN_xBut you can. Next, SiO 2 is formed by a normal photoresist method.₂The film was a first mask pattern 102 having a periodic stripe shape with a stripe width (w) of 7 μm and a pitch (d) of 10 μm. FIG. 1B shows a top view of the nitride semiconductor formed. As shown in FIG. 1B, the direction of the stripe is the [1-100] direction of the GaN crystal.
[0030]
Next, the first layer GaN film 104 is grown by the MOVPE method using the first mask-patterned substrate. Trimethylgallium (TMG) and ammonia (NH) in a predetermined growth furnace_Three) Was used as a raw material to grow a first GaN film 104 having a thickness of 5 μm at a growth temperature of 1050 ° C., and the first step was completed. The GaN film 104 of the first layer starts growing from the opening 105 of the first mask pattern and has a growth rate in the horizontal direction from the direction perpendicular to the substrate surface, particularly in the <11-20> direction with respect to the GaN crystal. Due to the fast anisotropy, it grew smoothly over almost the entire surface of the sapphire substrate.
[0031]
Since the first layer of the GaN film 104 in the upper part of the mask pattern grown in the direction perpendicular to the stripe direction of the mask pattern has a very weak interatomic bond with the mask pattern (not epitaxially grown from the mask) However, in the direction parallel to the stripe direction, the GaN layer 101 remains lattice strain due to the difference in lattice constant from the sapphire substrate, and the lattice strain is inherited in the first GaN film 104 as well. It is. Lattice strain and threading dislocation density are not sufficiently relaxed only by such a first step, and when a semiconductor laser is formed on the first-layer GaN film 104 in which these are inherent, continuous room temperature oscillation is 900 hours. It was about. This oscillation lifetime value did not satisfy the reliability as a production device.
[0032]
As for the thermal strain (crack), the GaN crystal and the mask pattern have very small interatomic bonds immediately above the mask pattern, and are not easily affected by thermal strain from the underlying layer (sapphire substrate). The GaN crystal at the upper part of the opening of the mask pattern is strongly affected by thermal strain from the underlayer (sapphire substrate).
[0033]
The threading dislocation density of the GaN film 104 of the first layer is about 10 immediately above the first mask pattern.^Four-10^Fivecm^-2However, it is about 10 above the mask opening.⁷-10⁸cm^-2It was an order. In the conventional example, the laser element is formed avoiding such a place, but it is insufficient in terms of reliability and yield.
[0034]
Next, the surface of the first GaN film 104 is SiO.₂A second mask pattern 106 made of was formed. In the formation of the second mask pattern 106, a 100 nm-thick SiO 2 film formed by the same method as the first mask pattern 102 is used.₂The film is subjected to normal photolithography and etching, and a periodic SiO having a stripe width of 8 μm and a pitch of 10 μm.₂A second mask pattern 106 made of Further, in a state where the stripe direction of the second mask pattern 106 is observed from above the wafer, it is set to the [01-10] direction of the GaN crystal so as to form an angle of 120 ° with the stripe of the first mask pattern. . A top view of the semiconductor element at this time is shown in FIG. FIG. 2 shows a mask pattern when seen through for explanation.
[0035]
The stripe width of the second mask pattern 106 was 1 μm wider than the stripe width of the first mask pattern 102 so as to cover the underlying GaN crystal surface wider than the first mask pattern 102.
[0036]
Subsequently, a second GaN film 107 is grown on the entire surface of the substrate by MOCVD on the first GaN film 104 on which the second mask pattern 106 is formed, and the second step is completed. did. The growth conditions at this time are a substrate temperature of 1050 ° C., and growth materials are TMG and NH._ThreeWas used. The layer thickness of the second GaN film 107 was about 5 μm. The second layer GaN film 107 thus formed grew uniformly over the entire surface of the wafer including above the second mask pattern 106, and the surface thereof became almost flat. FIG. 3A is a sectional view taken along the line aa ′ in the direction parallel to the second mask pattern in this state, and FIG. 3B is a sectional view taken along the line bb ′ in the direction parallel to the first mask pattern. Show. However, the b-b ′ cross section is a cross section of the missing portion of the first mask pattern 102, and the first mask pattern 102 cannot be observed in FIG.
[0037]
In the second-layer GaN film 107 grown in the second step, the lattice strain in the direction perpendicular to the stripe direction of the second mask pattern 106 is similar to that in the first step. This is reduced compared to the case where no pattern exists. On the other hand, the lattice strain in the direction parallel to the stripe direction of the second mask pattern was almost the same as that of the underlying GaN film 104 of the first layer. Here, in the first GaN film 104, the lattice strain in the vertical direction of the first mask pattern 102 has already been reduced in the first step. As a result, the lattice strain was relaxed in two directions, ie, a direction perpendicular to the stripe of the first mask pattern and a direction perpendicular to the stripe of the second mask pattern.
[0038]
The threading dislocation density of the second-layer GaN film 107 produced in the second step is about 10 in the portion 108 immediately above the first and second mask patterns.^Threecm^-2The crystallinity was greatly improved. Further, the local threading dislocation density of the second-layer GaN film grown from the opening of the first mask pattern is about 10 in the lateral growth by the second mask pattern 106.^Fivecm^-2It was an order. Further, the threading dislocation density of the local portion 110 of the GaN film immediately above the first mask pattern is about 10^Fourcm^-2It was an order.
[0039]
Further, as a third step, a GaN crystal was grown on the second-layer GaN film 107 using the same periodic stripe mask as in the first and second steps. First, a 100 nm thick SiO 2 film is formed on the surface of the second GaN film 107 by the same method as in the first step.₂A film was formed and processed into a periodic stripe shape having a width of 8 μm and a period of 10 μm using a normal photolithography technique and an etching technique to form a third mask pattern 111. The stripe direction of the third mask pattern 111 is arranged to have an angle of 120 ° with respect to both of the stripe directions of the first and second mask patterns. That is, it is the [−1010] direction with respect to the GaN crystal. A top view of the semiconductor element at this time is shown in FIG. FIG. 4A shows a mask pattern as seen through from the upper surface for the sake of explanation.
[0040]
Next, a third GaN film 112 having a thickness of 5 μm is grown on the second GaN film 107 having the third mask pattern 111 on the surface in the same manner as in the first and second steps. The third step was completed. The third-layer GaN film 112 was also grown uniformly on the entire surface so as to cover the third mask pattern 111 made of SiO 2, and the surface thereof showed a substantially flat single film. Further, in the third layer GaN film 112 formed in the third step, the lattice strain in the direction perpendicular to the stripe of the third mask pattern 111 is further reduced as compared with the second layer GaN film 107. It was done. FIG. 4B shows a structural diagram of the a-a ′ cross section.
[0041]
As described above, the third-layer GaN film 112 located on the outermost surface produced through the three steps is grown on the three types of mask patterns 102, 106, and 111 that form an angle with each other by 120 °. Thus, the effect of reducing the lattice strain in the direction perpendicular to the stripe direction of the mask pattern was accumulated for each step. Therefore, in the third-layer GaN film 112 on the outermost surface, the strain is reduced isotropically by the three types of mask patterns having the same angle as each other. As a result, the third layer has almost no strain in any in-plane direction. The GaN film 112 of the eye was realized.
[0042]
In the present embodiment, the stripe direction of the first mask pattern is [1-100], the stripe direction of the second mask pattern is [01-10], and the stripe direction of the third mask pattern is [10-10]. However, the present invention is not limited to this, and the stripe directions of the first, second, and third mask patterns are <1-100> directions, and each stripe direction has an angle difference of 120 °. In this case, there is an effect that there is almost no distortion in any in-plane direction.
[0043]
When the threading dislocation density on the surface of the third layer GaN film 112 was examined, most of the threading dislocations extending straight upward from the sapphire substrate 100 were covered by one of the masks by the first to third mask patterns. It was possible to prevent the film from extending upward from the mask. Therefore, the threading dislocation density on the surface of the third-layer GaN film 112 is 10^Threecm^-2To 10^Fourcm^-2And more than an order of magnitude less than that of the prior art. In addition, there are some regions that are not covered by the three types of masks, such as the local portion 113 of the third-layer GaN film grown from the opening of the first mask pattern, but the ratio of the total area is The threading dislocations did not increase especially in this region, as small as less than 10%. This is because threading dislocations extending upward from the sapphire substrate 100 diffuse to the left and right in the step of forming a GaN film of 15 μm or more in total, and on the surface of the third layer GaN film 112 formed in the third step, It is thought that threading dislocations were distributed almost uniformly.
[0044]
In the first embodiment, the first mask pattern, the second mask pattern, and the third mask pattern have the same thickness and the same growth suppressing material (SiO 2).₂However, it may be composed of different film thicknesses and different growth suppressing materials. In particular, if the growth suppressing materials for these mask patterns are the same, the growth furnace is not changed from the viewpoint of productivity, and the same growth suppressing effect can be obtained, so that the growth controllability is good. As for the nitride semiconductor growth method, in addition to the MOVPE method, an HVPE method or an MBE (molecular beam epitaxial) method may be used.
[0045]
[Embodiment 2]
The second embodiment according to the present invention evaluates the characteristics of the GaN film 107 formed in the second step of the first embodiment as a base when using it as the base of the device. That is, in the first embodiment, the mask formation and the crystal growth on the mask are repeated three times, but here, the effect of the present invention when it is completed twice will be described. In this case, since the first and second mask patterns are formed in a direction having an angle of 120 °, the lattice distortion in two directions perpendicular to the stripe direction of the two mask patterns is reduced. However, some lattice distortion remains in the direction that bisects the angle at which both mask patterns form 120 ° (that is, in the left-right direction of the paper in FIG. 2).
[0046]
Further, the threading dislocation density of the second-layer GaN film 107 located immediately above the first mask pattern and the second mask pattern is 10^Threecm^-2The threading dislocation density in the local portion 109 of the second GaN film grown from the opening of the first mask pattern is 10^Fivecm^-2Met. The average threading dislocation density over the entire surface of the second-layer GaN film 107 is 3 × 10.^Fourcm^-2Thus, it was confirmed that the threading dislocations were reduced by about one digit compared to the conventional example. Regarding the distortion, as described in the first embodiment, the relaxation effect is obtained by performing the process up to the second process of the present invention as compared with the conventional example (only the first process).
[0047]
[Embodiment 3]
The third embodiment is a modification of the second embodiment, and an angular difference between the stripe direction of the first mask pattern formed in the first step and the stripe direction of the second mask pattern formed in the second step. Is the same as Embodiment 2 except that the angle is 90 degrees. FIG. 5A shows a top view of the GaN film fabricated according to the third embodiment. However, FIG. 5A shows a mask pattern when seen through from the upper surface for explanation. As shown in FIG. 5A, the stripe directions of the first mask pattern 202 and the second mask pattern 204 are at an angle of 90 degrees with each other, and the <11-20> direction with respect to the GaN crystal, respectively. It is formed along the <1-100> direction. The stripe directions of the first and second mask patterns are preferably formed along the <1-100> direction and the <11-20> direction, respectively, but are not limited to this direction.
[0048]
FIG. 5B is a cross-sectional view taken along the line aa ′ in FIG. First, a C-plane sapphire substrate 200 is placed in a MOVPE growth reactor, and trimethylgallium (TMG) and ammonia (NH_Three) Was used as a raw material, and the GaN layer 201 was grown to a thickness of 2 μm. Next, in order to form a first patterned mask, an EB (electron beam) deposition method is used as a growth inhibitor on the GaN layer 201 to form a 100 nm thick SiO.₂A film was formed. Next, the SiO 2 is formed by a normal photoresist method.₂The film was formed into a periodic stripe pattern having a stripe width of 3 μm and a pitch of 7 μm, and a first mask pattern 202 was formed. As shown in FIG. 5A, the stripe direction of the first mask pattern 202 is the <11-20> direction of the GaN crystal.
[0049]
Using the substrate with the first mask pattern, a first-layer GaN film 203 was grown by the MOVPE method. Trimethylgallium (TMG) and ammonia (NH) in a predetermined growth furnace_Three) Was used as a raw material to grow a first GaN film 203 having a thickness of 10 μm at a growth temperature of 1050 ° C., and the first step was completed. The first-layer GaN film 203 started growing from the opening 206 of the first mask pattern, and laterally grown in a direction parallel to the substrate surface. Although the lateral growth rate is slower than the <1-100> direction which is the stripe direction of the mask pattern of the first or second embodiment, the first mask pattern is covered by laminating the GaN film 203 having a thickness of 10 μm. Grow smoothly.
[0050]
The threading dislocation density of the first-layer GaN film 203 is about 10 immediately above the first mask pattern 202.⁶cm^-2However, it is about 10 above the opening 206 of the first mask pattern.⁷cm^-2It was an order. Compared with the <1-100> direction of the stripe direction of the mask pattern, the threading dislocation density immediately above the mask pattern was about 1 to 2 digits. The direction in which the strain relaxation occurs is perpendicular to the stripe direction of the mask pattern, as in the first and second embodiments.
[0051]
Next, a second mask pattern 204 was formed on the first GaN film 203. With the same EB method as the formation of the first mask pattern 202, SiO with a thickness of 100 nm₂A periodic stripe pattern having a stripe width of 5 μm and a pitch of 7 μm was formed by a photoresist method. At this time, the stripe direction of the second mask pattern 204 is the <1-100> direction as shown in FIG. The stripe width of the second mask pattern 204 is 2 μm larger than that of the first mask pattern 202.
[0052]
Next, in the MOVPE growth furnace, trimethylgallium (TMG) and ammonia (NH_Three) Was used as a raw material to grow a second GaN film 205 having a thickness of 5 μm at a growth temperature of 1050 ° C., and the second step was completed. The GaN film 205 grown in this way grew uniformly over the entire wafer surface.
[0053]
The overall threading dislocation density of the second GaN film 205 is 10^Fivecm^-2The order was slightly lower than that of the conventional example. Regarding strain (including thermal strain) relaxation, the direction of strain generated in the first mask pattern 202 is the strain relaxation direction with respect to the second mask pattern 204. Similarly, the direction of distortion generated in the second mask pattern 204 is the distortion relaxation direction of the first mask pattern 202. Therefore, the third embodiment has a greater effect of removing distortion than the first and second embodiments. In the third embodiment, the second step is performed. However, the third mask pattern is formed on the second GaN film so as to cover the portion that cannot be shielded by the first and second mask patterns. Then, a third GaN film may be formed on the layer 205 (up to the third step). As a result, the threading dislocation density is about 10 above.^Fivecm^-210 orders from^Fourcm^-2Can be reduced to the order of.
[0054]
[Embodiment 4]
The purpose of the fourth embodiment is to form a thick GaN film on a GaN film containing a mask pattern having a growth suppressing effect. In the prior art, since a GaN substrate having an appropriate size and good surface morphology for the purpose of producing a nitride semiconductor device has not been supplied, a crack-free GaN substrate is obtained by carrying out the fourth embodiment. It is to provide.
[0055]
FIG. 6A shows a cross-sectional view of a nitride semiconductor structure in which the thick GaN layers produced in the fourth embodiment are stacked. Reference numeral 300 represents a nitride semiconductor (for example, a GaN film) including a substrate that is repeatedly manufactured up to the n-th step using the method for forming a GaN film described in the first to third embodiments. Reference numeral 301 denotes an n-th layer nitride semiconductor film (for example, a GaN film) manufactured in the n-th step. Reference numeral 302 denotes a thick GaN film manufactured by the HVPE method. The thick film GaN 302 may use the MOVPE method in addition to the HVPE method. As shown in FIG. 6A, the nitride semiconductor structure includes a nitride semiconductor 300 including a substrate and a thick film GaN 302.
[0056]
In the fourth embodiment, the GaN film produced in the first embodiment will be described as an example of the nitride semiconductor 300 having the nth step. The nitride semiconductor 300 including the sapphire substrate manufactured in the first embodiment was set in the HVPE apparatus. Next, NH is used as a group V gas for crystal growth of the thick film GaN 302._ThreeGas and carrier H₂As for the group III gas, a group III gas which is a reaction product of Ga and HCl gas by supplying HCl gas onto the Ga metal previously held at a temperature of about 850 ° C. in the HVPE apparatus. Chloride and carrier H₂The gas mixed with the gas was sent to the HVPE growth furnace in which the nitride semiconductor 300 was set, and the thick film GaN 302 was grown to 350 μm. The thick film GaN 302 grew smoothly, and when the surface was observed with an optical microscope, no cracks were generated. In this way, a nitride semiconductor structure could be formed.
[0057]
The threading dislocation density of the thick film GaN 302 produced in the fourth embodiment is about 10^Three-10^Fourcm^-2It was almost the same as that of the GaN film, which is the nitride semiconductor 300 manufactured in the first embodiment, or slightly decreased. The distortion is the same as in the first embodiment.
[0058]
In the fourth embodiment, the outermost surface 301 of the nitride semiconductor (for example, GaN film) 300 including the substrate manufactured by the nth process is the nth nitride semiconductor film (for example, GaN) manufactured by the nth process. However, as shown in FIG. 6B, the thick film GaN 302 may be formed directly on the nth mask pattern 303 using the HVPE method. For example, when the nitride semiconductor 300 shown in FIG. 6B is the first embodiment, it is directly above the third mask pattern. When the nitride semiconductor 300 is the second and third embodiments, it is directly above the second mask pattern. Thick film GaN is formed. The crystallinity characteristics are the same as in the fourth embodiment.
[0059]
The semiconductor structure including the sapphire substrate manufactured in Embodiment 4 can be used as a new substrate. Further, the sapphire substrate can be peeled off by polishing, etching or thermal strain, and used as a complete GaN substrate. When used as a complete GaN substrate, the thick film GaN 302 may be used as a substrate, or not only the sapphire substrate may be removed, but also a material obtained by polishing or etching a part of the nitride semiconductor structure may be used. As an example in this case, an n-th layer nitride semiconductor film that forms the outermost surface may be used as a substrate.
[0060]
[Embodiment 5]
FIG. 7 shows an LD element structure manufactured according to the fifth embodiment. GaN 400 to 412 in FIG. 7 are exactly the same as those 100 to 112 described in the first embodiment.
[0061]
In this figure, 413 is an n-GaN contact layer, 414 is n-Al._0.1Ga_0.9N-type cladding layer, 415 is an n-GaN light guide layer, 416 is 5 layers of In_0.2Ga_0.8N quantum well layer and 6 layers of In_0.05Ga_0.95Multiple quantum well structure active layer composed of N barrier layer, 417 is Al_0.2Ga_0.8N evaporation prevention layer, 418 is p-GaN light guide layer, 419 is p-Al_0.1Ga_0.9N-type cladding layer, 420 is a p-GaN contact layer, 421 is a p-type electrode, 422 is an n-type electrode, and 423 is SiO₂It is an insulating film.
[0062]
In the present invention, the surface of the sapphire substrate 400 may have other plane orientations such as a-plane, r-plane, and m-plane. Further, not only a sapphire substrate but also a GaN substrate, SiC substrate, spinel substrate, MgO substrate, Si substrate, and GaAs substrate can be used. In particular, in the case of a GaN substrate, since a difference in lattice constant with a gallium nitride-based semiconductor material deposited on the substrate is smaller than that of a sapphire substrate, a good crystalline film can be obtained. There is an advantage that the vessel can be easily formed. The n-type cladding layer 414 and the p-type cladding layer 419 are made of Al._0.1Ga_0.9An AlGaN ternary mixed crystal having an Al composition other than N may be used. In this case, when the Al composition is increased, the energy gap difference and the refractive index difference between the active layer and the clad layer increase, and carriers and light are confined in the active layer, thereby further reducing the oscillation threshold current and improving the temperature characteristics. . Further, if the Al composition is reduced to such an extent that the confinement of carriers and light is maintained, the mobility of carriers in the cladding layer increases, so that there is an advantage that the element resistance of the semiconductor laser element can be reduced. Further, this clad layer may be a quaternary mixed crystal semiconductor containing a small amount of other elements, and the n-type clad layer 414 and the p-type clad layer 419 may not have the same composition of mixed crystals.
[0063]
The light guide layers 415 and 418 are made of a material whose energy gap has a value between the energy gap of the quantum well layer constituting the multiple quantum well structure active layer 416 and the energy gap of the cladding layers 414 and 419. Other materials such as InGaN, AlGaN ternary mixed crystal, etc. may be used regardless of GaN. Further, it is not necessary to dope the donor or acceptor over the entire optical guide layer, only a part of the multiple quantum well structure active layer 416 side may be non-doped, and further the entire optical guide layer may be non-doped. In this case, there is an advantage that the number of carriers present in the light guide layer is reduced, light absorption by free carriers is reduced, and the oscillation threshold current can be further reduced.
[0064]
In constituting the multi-quantum well structure active layer 416_0.2Ga_0.8N quantum well layer and In_0.05Ga_0.95The composition of the N barrier layer may be set according to the required laser oscillation wavelength. If it is desired to increase the oscillation wavelength, the In composition of the quantum well layer should be increased, and if it is desired to be shortened, the In composition of the quantum well layer should be decreased. To do. Further, the quantum well layer and the barrier layer may be a quaternary or higher mixed crystal semiconductor containing a trace amount of other elements in the InGaN ternary mixed crystal. Furthermore, the barrier layer may simply be GaN.
[0065]
In the fifth embodiment, Al is in contact with the multiple quantum well structure active layer 416._0.2Ga_0.8The N evaporation preventing layer 417 is formed in order to prevent In in the multiple quantum well structure active layer 416 from evaporating while reaching the growth temperature of the p-GaN light guide layer. Therefore, any material that protects the active layer of the multiple quantum well structure can be used as the evaporation preventing layer 417, and AlGaN ternary mixed crystals or GaN having other Al compositions may be used. The evaporation prevention layer 417 may be doped with Mg. In this case, the p-GaN light guide layer 418 or the p-Al_0.1Ga_0.9There is an advantage that holes are easily injected from the N-type cladding layer 419. Further, when the In composition of the quantum well layer constituting the multi-quantum well structure active layer is small, the change in the In composition of the active layer due to In evaporation is small even without forming the evaporation prevention layer 417. Even if the prevention layer 417 is not laminated, the characteristics of the gallium nitride based semiconductor laser device of the fifth embodiment are not impaired.
[0066]
Next, the gallium nitride based semiconductor laser manufacturing method will be described with reference to FIG. In the following description, the case where the MOVPE method is used is shown, but any growth method capable of epitaxially growing GaN may be used, and other crystal growth methods such as MBE and HVPE can also be used.
[0067]
First, trimethylgallium (TMG) and ammonia (NH) were placed on a substrate that was installed in a predetermined growth furnace and manufactured in the first embodiment._Three) And silane gas (SiH)_Four) Is used as a raw material, and a 3 μm thick Si-doped n-GaN contact layer 413 is grown at a growth temperature of 1050 ° C. Further, trimethylaluminum (TMA) was subsequently added to the raw material, and the 0.4 μm Si-doped n-AI was maintained at a growth temperature of 1050 ° C._0.1Ga_0.9An N-type cladding layer 414 is grown. Subsequently, TMA is removed from the raw material, and a Si-doped n-GaN optical guide layer 415 having a thickness of 0.1 μm is grown at a growth temperature of 1050 ° C.
[0068]
Next, the growth temperature is lowered to 750 ° C., and TMG and NH_Three, And trimethylindium (TMI) as a raw material, In_0.05Ga_0.95N barrier layer (thickness 3 nm) / In_0.2Ga_0.8After five periods of growth of the N quantum well layer (thickness 2 nm), In_0.05Ga_0.95An N barrier layer (thickness 3 nm) is grown to produce a multiple quantum well structure active layer (total thickness 28 nm) 416. Continue with TMG, TMA and NH_ThreeIs used as a raw material, and the growth temperature remains at 750 ° C. and the thickness is 30 nm._0.2Ga_0.8An N evaporation preventing layer 417 is grown.
[0069]
Next, the growth temperature is again increased to 1050 ° C., and TMG and NH_Three, And bisethylcyclopentadienylmagnesium (EtCp₂A Mg-doped p-GaN optical guide layer 418 having a thickness of 0.1 μm is grown using Mg) as a raw material. Subsequently, TMA was added to the raw material, and the growth temperature remained at 1050 ° C., and 0.4 μm Mg-doped p-Al_0.1Ga_0.9An N-type cladding layer 419 is grown. Subsequently, TMA is removed from the raw material, and a 0.5 μm-thick Mg-doped p-GaN contact layer 420 is grown while maintaining the growth temperature at 1050 ° C., thereby completing an epitaxial wafer having a gallium nitride-based LD structure. To do. Thereafter, the wafer is annealed in a nitrogen gas atmosphere at 800 ° C. to reduce the resistance of the Mg-doped p-type layer.
[0070]
Further, by using normal photolithography and dry etching technology, etching is performed from the outermost surface of the p-GaN contact layer 420 in a stripe shape having a width of 200 μm until the n-GaN contact layer 413 is exposed, thereby producing a mesa structure. To do. Next, using the same photolithography and dry etching techniques as described above, the remaining p-GaN type contact layer 420, p-Al_0.1Ga_0.9The N-type cladding layer 419 is etched. At this time, the stripe-shaped ridge structure may be 3 μm or more away from both ends of the 200 μm-width mesa structure, and in the fifth embodiment, 10 μm away from the end of the mesa structure on the side where the n-type electrode 422 is formed. A striped ridge structure was formed there. If the striped ridge structure is arranged so as to be close to the n-type electrode 422 in this way, the electrical resistance of the element is reduced and the operating voltage is reduced. Further, since the etching is stopped so as not to reach the multi-quantum well structure active layer 416 during this dry etching, the etching damage to the active layer is suppressed, and the reliability is lowered and the oscillation threshold current is reduced. The increase is prevented.
[0071]
Subsequently, 200 nm thick SiO2 is formed on the side surface of the ridge and the p-type layer surface other than the ridge.₂An insulating film 423 is formed as a current blocking layer. This SiO₂A p-type electrode 421 made of nickel and gold is formed on the surfaces of the insulating film 423 and the p-type contact layer 420, and an n-type electrode 422 made of titanium and aluminum is formed on the surface of the n-GaN type contact layer 413 exposed by etching. Thus, a gallium nitride LD wafer is completed.
[0072]
Thereafter, the wafer is cleaved in a direction perpendicular to the stripe direction of the ridge to form a laser resonance surface, and further divided into individual chips. Then, each chip is mounted on the stem, and each electrode and the lead terminal are connected by wire bonding to complete a gallium nitride based semiconductor LD element.
[0073]
The semiconductor LD device fabricated as described above has good LD characteristics with an oscillation wavelength of 410 nm and an oscillation threshold of 50 mA. Further, due to the reduction of crystal defects, the LD element was extremely reliable at 900 hours (60 ° C.). In addition, the ratio of LD elements that seemed to be deteriorated by crystal defects was extremely reduced, and an element yield of 80% or more was obtained.
[0074]
In the fifth embodiment, the thicknesses of the quantum well layer and the barrier constituting the multi-quantum well structure active layer 416 are 2 nm and 3 nm, respectively. However, the thicknesses of the quantum well layer and the barrier layer are 10 nm or less. For example, regardless of the fifth embodiment, the same effect can be obtained with other layer thicknesses. The number of quantum well layers in the multiple quantum well structure 416 may be four or three, or a single quantum well structure active layer.
[0075]
Further, in the fifth embodiment, since sapphire, which is an insulator, is used as a substrate, an n-type electrode 422 is formed on the surface of the n-GaN contact layer 413 exposed by etching, but has n-type conductivity. If GaN, SiC, Si, GaAs or the like is used, an n-type electrode may be formed on the back surface of the substrate. In this case, the striped mesa structure having a width of 200 μm may be separated from both ends of the semiconductor laser element chip by 3 μm or more. Also, the p-type and n-type configurations may be reversed.
[0076]
Furthermore, GaN produced by the crystal growth method of the present invention can be applied to the production of GaN FETs and AlGaN / GaN HEMT elements as power devices that handle large currents, so-called devices in the field of hard electronics. When a nitride semiconductor is applied to a power device, the crystal growth method of the present invention is particularly advantageous because thermal strain due to heat generated by a large current is superimposed on strain inherent in the device and greatly adversely affects device reliability. is there.
[0077]
(Embodiment 6)
In the embodiment of the present invention, the effect of reducing the threading dislocation density of the nitride semiconductor film formed by using the first and second mask patterns will be described. The second layer nitride semiconductor film forming method using the first and second mask patterns described in the present embodiment is the same as in the second embodiment.
[0078]
Table 1 is a table showing the relationship between the threading dislocation density of the nitride semiconductor film formed according to the second embodiment according to the mask coverage of the first mask pattern and the mask coverage of the second mask pattern. . Here, the mask coverage is expressed in w / d using a mask width (w) and a pitch (d).
[0079]
[Table 1]

From the experimental results shown in Table 1, the threading dislocation density tends to decrease as the mask coverage increases regardless of the first and second mask patterns. However, when the mask coverage is 80% or more, the threading dislocation density starts to increase. In general, a nitride semiconductor crystal grown immediately above a mask grows from the crystal growth axis direction (perpendicular to the substrate surface) with a slight inclination angle in a direction perpendicular to the mask stripe direction. In particular, when the mask coverage is increased (the mask width is increased), the fine inclination angle is increased. For this reason, when the mask coverage is 80% or more, the fine inclination angle is increased, and when the nitride semiconductor crystals grown from the mask openings on both sides meet just above the mask, the cavity is formed. This is considered to be the cause of new threading dislocations.
[0080]
Further, if the mask coverage is higher than about 80%, the lateral growth rate is drastically decreased, so that it becomes difficult to cover the mask (causes generation of a cavity), and the mask is completely removed. In order to coat the film, a thick film must be laminated. Furthermore, when the mask coverage is 90% or more, it is difficult to completely embed the mask even if thick films are stacked. According to the experiment results of the present inventors, the nitride semiconductor film was laminated up to 50 μm at a mask coverage of 90%, but it was not buried.
[0081]
The mask coverage of 90% shown in Table 1 could not cover the mask pattern regardless of the first and second mask patterns. The central portion of these mask patterns is not covered with the nitride semiconductor film, and a hollow groove is formed in a direction parallel to the mask direction. When the threading dislocation density of the nitride semiconductor film in which either the first or second mask pattern in Table 1 has a mask coverage of 90% is examined, 10⁶cm^-210 to 10⁷cm^-2There was a table. This is thought to be because threading dislocations were reduced by that amount because the mask was not completely covered.
[0082]
Further, referring to Table 1, the threading dislocation density when the mask coverage A% of the first mask pattern and the mask coverage B% of the second mask pattern and the mask coverage B% of the first mask pattern are obtained. When the threading dislocation density at the mask coverage A% of the second mask pattern was compared, the latter threading dislocation density was higher. Here, A and B are numerical values and have a magnitude relationship of A <B. This is because the nitride semiconductor film thickness of the first layer stacked immediately above the first mask pattern was not so thick that the fine tilt angle could be sufficiently eliminated compared to the mask coverage of the first mask pattern. It is thought that. That is, since the second mask pattern is formed without sufficiently eliminating the fine tilt angle in the first layer, the fine tilt angle is further increased, and the generation of the cavity is facilitated. This is because it is difficult to reduce the threading dislocation density in the nitride semiconductor film. Therefore, in order to efficiently reduce the threading dislocation density, the nitride semiconductor film thickness of the first layer is made sufficiently thick to suppress the occurrence of the fine tilt angle (cavity) or the first mask. It is necessary to reduce the mask coverage of the pattern and increase the mask coverage of the second mask pattern. According to the experimental results of the present inventors, when the thickness of the first-layer nitride semiconductor film between the first mask pattern and the second mask pattern becomes 10 μm or more, the slight inclination angle gradually increases. Began to relax. However, the former method of sufficiently increasing the thickness of the nitride semiconductor is not a good idea in view of productivity.
[0083]
From the above experimental results, in order to efficiently reduce the threading dislocation density using the first and second mask patterns, the mask coverage of the first and second mask patterns is about 20% to 80%, respectively. % (Threading dislocation density of about 10⁷cm^-2Substrate, complete coating film) is preferred. More preferably, the coverage of the first and second mask patterns is about 50% to 80% (threading dislocation density of about 10^Fivecm^-2Or less). More preferably, it is 60% or more and 70% or less (threading dislocation density of about 10^Fourcm^-2Or less). The relationship between the mask coverage A% of the first mask pattern and the mask coverage B% of the second mask pattern is preferably A ≦ B. In addition, when productivity is considered, it is desirable that the mask coverages of the first and second mass patterns are the same. As a result, the selective growth modes of the first and second nitride semiconductor films become the same, so that the selective growth control system and reproducibility are good, and the same production process can be applied. Yield is also improved.
[0084]
About each mask coverage of the 1st, 2nd mask pattern, the threading dislocation density was the lowest when it was about 60%-70%. This was the same for each nth mask pattern (n ≧ 1).
[0085]
The first and second mask patterns shown in the embodiment of the present invention are cases where they are formed in directions rotated by 120 degrees with respect to each other. The same effect was obtained. If the angle between the first and second mask patterns is within ± 10 degrees from the angle specified above (120 degrees or 90 degrees), there is no essential difference. The same effect as the embodiment was obtained. Furthermore, as a result of detailed examination, as long as the first and second mask patterns are not parallel, the same effect as in the embodiment of the present invention was obtained. As described above, the characteristics of the threading dislocation density with respect to the mask coverage of each mask pattern has not changed, and how much the nitride semiconductor film can be covered with the first and second mask patterns. It is thought that it is because it depends on.
[0086]
(Embodiment 7)
In the present embodiment, when the mask coverages of the first and second mask patterns described in the embodiment of the invention are 70% and 70%, respectively, on the flat second-layer nitride semiconductor film The nitride semiconductor laser formed in Section 1 will be described. The nitride semiconductor laser was manufactured by the same method as in the fifth embodiment. When the laser oscillation lifetime was examined, it was 1200 hours or more at an oscillation wavelength of 410 nm, a constant laser output of 40 mW, and an ambient temperature of 50 ° C.
[0087]
Further, when the mask coverages of the first and second mask patterns were 60% or more and 70% or less, the same laser oscillation lifetime as that of the present embodiment was obtained. This is because the gain loss of the laser is greatly improved by greatly reducing the threading dislocation density of the nitride semiconductor crystal constituting the nitride semiconductor laser element. For this reason, by using this method, a high-power laser for recording in an optical disk system can be produced.
[0088]
As long as the mask coverage of the first and second mask patterns is 60% or more and 70% or less, the mask coverage of the first and second mask patterns may be different. As described in the embodiment of the invention, the relationship between the mask coverage A% of the first mask pattern and the mask coverage B% of the second mask pattern is preferably A ≦ B.
[0089]
(Embodiment 8)
In the present embodiment, when the mask coverages of the first and second mask patterns described in the embodiment of the invention are 50% and 50%, respectively, on the flat second-layer nitride semiconductor film The nitride semiconductor laser formed in Section 1 will be described. The nitride semiconductor laser was manufactured by the same method as in the fifth embodiment. When the laser oscillation lifetime was examined, it was 2000 hours or longer at an oscillation wavelength of 410 nm, a constant laser output of 10 mW, and an ambient temperature of 50 ° C.
[0090]
In the above description, the mask coverages of the first and second mask patterns are 50% and 50%, respectively. However, the mask coverages of the first and second mask patterns are 50% to 80%, respectively. If so, a laser oscillation lifetime similar to that of the present embodiment was obtained. This is because the gain loss of the laser is improved by reducing the threading dislocation density of the nitride semiconductor crystal constituting the nitride semiconductor laser element. From this, the laser output necessary for reproduction in the optical disk system was sufficiently secured by using this method. Further, as shown in the seventh embodiment, if the mask coverages of the first and second mask patterns are 60% or more and 70% or less, further effects can be obtained.
[0091]
Note that the mask coverages of the first and second mask patterns may be different as long as the mask coverages of the first and second mask patterns are 50% or more and 80% or less, respectively. As described in the embodiment of the invention, the relationship between the mask coverage A% of the first mask pattern and the mask coverage B% of the second mask pattern is preferably A ≦ B.
[0092]
(Embodiment 9)
In the present embodiment, when the mask coverages of the first and second mask patterns described in the embodiment of the invention are 30% and 30%, respectively, on the flat second-layer nitride semiconductor film The nitride semiconductor laser formed in Section 1 will be described. The nitride semiconductor laser was manufactured by the same method as in the fifth embodiment. When the laser oscillation lifetime was examined, it was 1800 hours or longer at an oscillation wavelength of 410 nm, a constant laser output of 5 mW, and an ambient temperature of 50 ° C.
[0093]
Thus, even when the coverage of each mask was 30%, the lifetime was shorter than that of the eighth embodiment, but a lifetime that could be sufficiently put into practical use could be achieved. Further, when the mask coverages of the first and second mask patterns were 20% or more and 80% or less, the same laser oscillation lifetime as that of the present embodiment was obtained. This is because the gain loss of the laser is improved by reducing the threading dislocation density of the nitride semiconductor crystal constituting the nitride semiconductor laser element. Therefore, by using this method, a reproducing laser in the optical disk system can be produced. Further, if the mask coverage of the first and second mask patterns is 50% or more and 80% or less, the effect of the eighth embodiment is shown. An effect is obtained.
[0094]
That is, as long as the mask coverage of the first and second mask patterns is 20% or more and 80% or less, the mask coverage of the first and second mask patterns may be different. As described in the embodiment of the invention, the relationship between the mask coverage A% of the first mask pattern and the mask coverage B% of the second mask pattern is preferably A ≦ B.
[0095]
【The invention's effect】
As described above, the gallium nitride crystal according to the present invention has almost no distortion and a threading dislocation density of 10 by alternately laminating a material having a growth suppressing effect and a nitride semiconductor film.^Fourcm^-2Very small crystals were obtained: Gallium nitride semiconductor lasers manufactured using such crystals were highly reliable and could be produced with extremely high yield.
[Brief description of the drawings]
FIG. 1 is a manufacturing process diagram after completion of a first process shown in Embodiment 1 or 2 of the present invention;
FIG. 2 is a perspective view from the top after completion of the second step shown in the first or second embodiment of the present invention.
FIG. 3 is a cross-sectional view after completion of the second step shown in Embodiment 1 or 2 of the present invention.
FIGS. 4A and 4B are a perspective view and a cross-sectional view after the completion of the third step shown in the first embodiment of the present invention. FIGS.
5A and 5B are a perspective view and a cross-sectional view in the manufacturing method shown in Embodiment 3 of the present invention.
FIG. 6 is a cross sectional view showing a method for manufacturing the thick film nitride semiconductor shown in the fourth embodiment of the present invention.
FIG. 7 is a cross-sectional view of a semiconductor laser diode device using a nitride semiconductor according to the present invention.
FIG. 8 is a first conventional example by a selective growth method.
FIG. 9 is a second conventional example by a selective growth method.
[Explanation of symbols]
100, 200, 400 Sapphire substrate
101, 201, 401 GaN layer
102, 202, 402 First mask pattern
104, 203, 404 First layer GaN film
105, 206 Openings of the first mask pattern
106, 204, 406 Second mask pattern
107, 205, 407 Second layer GaN film
108 Immediately above the first and second mask patterns
109 Local portion of the second-layer GaN film grown from the opening of the first mask pattern
110 Local portion of the second-layer GaN film immediately above the first mask pattern
111, 411 Third mask pattern
112, 412 Third layer GaN film
113 Local portion of the third-layer GaN film grown from the opening of the first mask pattern
300 Nitride semiconductor
301 outermost surface
302 Thick GaN
303 nth mask pattern
413 n-GaN contact layer
414 n-Al_0.1Ga_0.9N clad layer
415 n-GaN optical guide layer
416 Active layer with multiple quantum well structure
417 Al_0.2Ga_0.8N evaporation prevention layer *
418 p-GaN optical guide layer
419 p-Al_0.1Ga_0.9N-type cladding layer
420 p-GaN type contact layer
421 p-type electrode
422 n-type electrode
423 SiO₂Insulation film
500, 600 Sapphire substrate
501, 602 SiO₂mask
502, 603 SiO₂Mask opening
503 GaN film
504 SiO₂GaN just above the mask
601 GaN film grown by MOVPE method
604 GaN film grown by HVPE method

Claims (15)

An nth step of forming an nth (where n is a positive number of 1 or more) mask pattern made of a material having a growth suppressing effect and a nitride semiconductor film so as to cover the nth mask pattern above the substrate; The (n + 1) th step of forming a (n + 1) th mask pattern made of a material having a growth suppressing effect and a (n + 1) th mask pattern on the nitride semiconductor film formed in the (n) th step so as to cover the n + 1th mask pattern. It has a door,
Each of the mask patterns includes a plurality of striped masks parallel to each other,
A method of manufacturing a nitride semiconductor, wherein the nth mask pattern and the (n + 1) th mask pattern are twisted with each other . 2. The method of manufacturing a nitride semiconductor according to claim 1, wherein the stripe direction of the nth mask pattern and the stripe direction of the (n + 1) th mask pattern have an angle difference of 120 degrees. 2. The method of manufacturing a nitride semiconductor according to claim 1, wherein the stripe direction of the nth mask pattern and the stripe direction of the (n + 1) th mask pattern have an angle difference of 90 degrees. Stripe width of the n + 1 of the mask pattern, a nitride semiconductor method of manufacturing according to any of claims 1 to 3, characterized in that at least the stripe width of the mask pattern of the n. It said substance SiO ₂ having a growth inhibiting effect, or a nitride semiconductor method of manufacturing according to any one of claims 1 to 4, characterized in that a SiN _x. The stripe direction of the mask pattern of the n is, the nitride semiconductor crystal <1-100> direction or <11-20> nitride according to any one of claims 1 to wherein the 5 to be a direction semiconductor Manufacturing method. The stripe directions of the first mask pattern, the second mask pattern, and the third mask pattern are combinations of [1-100], [10-10], and [01-10] directions of the nitride semiconductor crystal. The method for producing a nitride semiconductor according to claim 2 . Characterized in that it is a; (0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1 x + y + z = 1) nitride was deposited by the n steps semiconductor film crystal Al _x In _y Ga _z N nitride semiconductor method of manufacturing according to any one of claims 1 to 7. The nitride semiconductor film laminated by the nth step or the nitride semiconductor film laminated on the nitride semiconductor layer laminated by the nth step has a thickness of 5 μm or more. nitride semiconductor method of manufacturing according to any of claims 1 to 8, characterized in that it. By the forming of the nitride semiconductor structure including a substrate with a nitride semiconductor manufacturing method according to any one of claims 1 to 9, removing at least said substrate from said nitride semiconductor structure, a nitride semiconductor A method for manufacturing a nitride semiconductor, wherein a part of the structure is a nitride semiconductor substrate. Above a substrate, when brought into the crystal growth to the n + 1 steps, nitride according to any one of claims 1 to 10, the n + 1 of the mask pattern from the first mask pattern, characterized in that the overall covering the substrate Semiconductor manufacturing method. The nitriding according to any one of claims 1 to 6 , wherein mask coverages defined by mask width / pitch of the first and second mask patterns are 20% to 80%, respectively. A method for manufacturing a semiconductor. Characterized in that it has an active layer for emitting any light, which is formed above the nitride semiconductor film of the n steps which is manufactured using the manufacturing method of the nitride semiconductor according to the claims 1 to 12 Light emitting element. The method for manufacturing a nitride semiconductor according to any one of claims 1 to 12 , wherein the substrate is a sapphire substrate, a GaN substrate, a SiC substrate, a spinel substrate, an MgO substrate, a Si substrate, or a GaAs substrate. The method for producing a nitride semiconductor according to claim 12 , wherein the mask coverage of the first mask pattern is equal to or less than the mask coverage of the second mask pattern.

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