JP2011093803A - Method for manufacturing gallium nitride-based compound semiconductor single crystal - Google Patents
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本発明は、光デバイス，電子デバイスなどの半導体デバイスの製造に用いられる窒化ガリウム系化合物半導体単結晶の製造方法に関するものである。 The present invention relates to a method for manufacturing a gallium nitride-based compound semiconductor single crystal used for manufacturing semiconductor devices such as optical devices and electronic devices.
窒化ガリウム系化合物半導体（例えば、ＩｎxＧａyＡｌ1-x-yＮ）（０≦ｘ，ｙ；ｘ+ｙ≦１）は、禁制帯幅が広く、短波長発光素子，耐環境素子として期待され、広く研究されてきた。 Gallium nitride-based compound semiconductors (for example, In x Ga y Al 1-xy N) (0 ≦ x, y; x + y ≦ 1) have a wide forbidden bandwidth and are expected as short-wavelength light-emitting elements and environment-resistant elements. Have been studied extensively.
しかしながら、この窒化ガリウム系の化合物半導体においては、未だ大型のバルク結晶が得られないため、異種結晶（例えばサファイアα−Ａｌ2Ｏ3）上へのヘテロエピタキシーによってＧａＮ等の薄膜単結晶を形成したものが基板として用いられてきた。 However, in this gallium nitride-based compound semiconductor, since a large bulk crystal cannot be obtained yet, a thin-film single crystal such as GaN is formed by heteroepitaxy on a different crystal (for example, sapphire α-Al 2 O 3 ). Things have been used as substrates.
ところが、サファイアに代表されるように、多くの場合、基板に用いられる異種結晶とその上に成長される窒化ガリウム系化合物半導体薄膜との格子不整合性が大きく、欠陥や熱歪みなどが発生し易いため、窒化ガリウム系化合物薄膜単結晶は品質的に問題を抱えるものであった。 However, as represented by sapphire, in many cases, the lattice mismatch between the dissimilar crystal used for the substrate and the gallium nitride compound semiconductor thin film grown thereon is large, resulting in defects and thermal strain. Therefore, the gallium nitride compound thin film single crystal has a problem in quality.
そこで、窒化ガリウム系化合物半導体のヘテロエピタキシー用に、種々の優れた特性を備える異種結晶基板の材料の一つとして希土類Ｇａペロブスカイトに代表される希土類１３（３Ｂ）族ペロブスカイトを用いる窒化ガリウム系化合物半導体単結晶の成長方法および窒化ガリウム系化合物半導体装置が提案されている（特許文献１）。
この希土類１３（３Ｂ）族ペロブスカイトの基板を用いると、例えばＮｄＧａＯ3を基板として用い、その基板上にＧａＮをエピタキシャル成長させる場合には、格子不整合を１．２％程度とすることができた。この格子不整合性は、サファイアやその代替品として用いられるＳｉＣを基板とした場合と比較しても非常に小さく、窒化ガリウム系化合物半導体単結晶のヘテロエピタキシーに適していると考えられる。
Therefore, a gallium nitride compound semiconductor using a rare earth 13 (3B) group perovskite represented by a rare earth Ga perovskite as one of the materials of a heterogeneous crystal substrate having various excellent characteristics for hetero epitaxy of a gallium nitride compound semiconductor. A single crystal growth method and a gallium nitride compound semiconductor device have been proposed (Patent Document 1).
When this rare earth 13 (3B) group perovskite substrate was used, for example, when NdGaO 3 was used as the substrate and GaN was epitaxially grown on the substrate, the lattice mismatch could be reduced to about 1.2%. This lattice mismatch is very small as compared with the case of using sapphire or SiC used as a substitute for the substrate as a substrate, and is considered suitable for heteroepitaxy of a gallium nitride-based compound semiconductor single crystal.
しかし、希土類１３（３Ｂ）族ペロブスカイトを窒化ガリウム系化合物半導体のヘテロエピタキシー用の基板として用いる場合において、例えばＮｄＧａＯ3を基板として窒化ガリウム系化合物半導体単結晶をエピタキシャル成長させると、基板とエピタキシャル層との熱膨張係数の差によって生じる熱歪みに起因して、成長終了後の冷却時に基板およびエピタキシャル層の双方が小片状に砕けて破壊されてしまい、歩留まりを大幅に低下させる問題を生じる場合があった。 However, when the rare earth 13 (3B) group perovskite is used as a heteroepitaxial substrate for a gallium nitride compound semiconductor, for example, when a gallium nitride compound semiconductor single crystal is epitaxially grown using NdGaO 3 as a substrate, the substrate and the epitaxial layer Due to the thermal strain caused by the difference in thermal expansion coefficient, both the substrate and the epitaxial layer may be broken into pieces and destroyed during cooling after the growth, resulting in a problem of greatly reducing the yield. It was.
本発明は上述のような問題を解決すべく案出されたものであり、成長終了後の冷却時に基板やエピタキシャル層の破壊を防止することのでき、エピタキシャル層の形状を保ったまま基板から剥離することのできる窒化ガリウム系化合物半導体単結晶の製造方法を提供することを主目的とするものである。 The present invention has been devised to solve the above-mentioned problems, and can prevent the substrate and the epitaxial layer from being destroyed during cooling after the growth is completed, and can be peeled off from the substrate while maintaining the shape of the epitaxial layer. The main object of the present invention is to provide a method for producing a gallium nitride compound semiconductor single crystal that can be used.
上記目的を達成するために、発明（１）は、単結晶基板上に窒化ガリウム系化合物半導体の結晶をエピタキシャル成長させた後、降温速度を毎分５℃以下、好ましくは毎分２℃以下の条件で冷却するようにしたものである。 In order to achieve the above object, the invention (1) is based on the condition that, after epitaxially growing a crystal of a gallium nitride compound semiconductor on a single crystal substrate, the temperature decreasing rate is 5 ° C. or less, preferably 2 ° C. or less. It is made to cool with.
これにより、窒化ガリウム系化合物半導体の結晶をエピタキシャル成長させた後の冷却工程における降温速度を小さくし、急激な熱衝撃を回避することにより窒化ガリウム系化合物半導体の単結晶のエピタキシャル層と単結晶基板との熱膨張係数の差に起因する熱歪を抑制することができ、基板やエピタキシャル層の破壊を防止することができる。 Thereby, the temperature drop rate in the cooling step after epitaxially growing the crystal of the gallium nitride compound semiconductor is reduced, and a sudden thermal shock is avoided, thereby the single crystal epitaxial layer and the single crystal substrate of the gallium nitride compound semiconductor It is possible to suppress thermal strain caused by the difference in thermal expansion coefficient between the substrates and the substrate and the epitaxial layer.
また、発明（２）は、単結晶基板上に窒化ガリウム系化合物半導体の結晶をエピタキシャル成長させる方法において、上記単結晶基板の厚さを、３００μｍ以下、好ましくは１００μｍ以下と薄くしたものである。 The invention (2) is a method of epitaxially growing a gallium nitride compound semiconductor crystal on a single crystal substrate, wherein the thickness of the single crystal substrate is reduced to 300 μm or less, preferably 100 μm or less.
これにより、単結晶基板とエピタキシャル層（窒化ガリウム系化合物半導体の結晶）との熱膨張係数の差に起因する熱歪みをエピタキシャル層が破壊しない程度に小さくすることができ、窒化ガリウム系化合物半導体の結晶を破壊することなく得ることができる。 As a result, the thermal strain due to the difference in thermal expansion coefficient between the single crystal substrate and the epitaxial layer (gallium nitride compound semiconductor crystal) can be reduced to such an extent that the epitaxial layer does not break down. It can be obtained without destroying the crystals.
さらに、発明（３）は、単結晶基板上に窒化ガリウム系化合物半導体の結晶をエピタキシャル成長させる方法において、成長させた窒化ガリウム系化合物半導体結晶の厚さを、１００μｍ以上、好ましくは３００μｍ以上と厚くしたものである。 Further, in the invention (3), in the method of epitaxially growing a gallium nitride compound semiconductor crystal on a single crystal substrate, the thickness of the grown gallium nitride compound semiconductor crystal is increased to 100 μm or more, preferably 300 μm or more. Is.
これにより、エピタキシャル層（窒化ガリウム系化合物半導体の結晶）の強度が、単結晶基板とエピタキシャル層との熱膨張係数の差に起因する熱歪みによっても破壊されない程度に強化することができ、窒化ガリウム系化合物半導体結晶の破壊を未然に防止することができる。 As a result, the strength of the epitaxial layer (gallium nitride compound semiconductor crystal) can be strengthened to such an extent that it is not destroyed by thermal strain caused by the difference in thermal expansion coefficient between the single crystal substrate and the epitaxial layer. Breakage of the system compound semiconductor crystal can be prevented beforehand.
なお、上記方法は適宜組み合わせて用いることができ、相乗効果により成長させた上記窒化ガリウム系化合物半導体結晶を破壊することなく単結晶基板から剥離させて窒化ガリウム系化合物半導体の結晶を歩留まりよく得ることができる。 Note that the above methods can be used in appropriate combinations, and the gallium nitride compound semiconductor crystal grown by a synergistic effect is peeled off from the single crystal substrate without breaking, thereby obtaining a gallium nitride compound semiconductor crystal with high yield. Can do.
具体的には、上記発明（１）＋発明（２），発明（１）＋発明（３），発明（２）＋発明（３），発明（１）＋発明（２）＋発明（３）等の組み合わせである。 Specifically, Invention (1) + Invention (2), Invention (1) + Invention (3), Invention (2) + Invention (3), Invention (1) + Invention (2) + Invention (3) Etc. are combinations.
また、上記単結晶基板は、１種類また２種類以上の希土類元素を含む希土類１３（３Ｂ）族ペロブスカイトの結晶とすることができる。また、上記希土類元素は、Ａｌ，Ｇａ，Ｉｎの少なくとも一つとしてもよい。 The single crystal substrate may be a rare earth 13 (3B) group perovskite crystal containing one kind or two or more kinds of rare earth elements. The rare earth element may be at least one of Al, Ga, and In.
このようにして製造した良質の窒化ガリウム系化合物半導体単結晶を用いることにより、熱的，化学的に安定な高性能の青色発光ダイオードや半導体レーザ等の半導体装置を作成することが可能となる。 By using the high-quality gallium nitride compound semiconductor single crystal thus manufactured, it is possible to produce a semiconductor device such as a high-performance blue light-emitting diode or semiconductor laser that is thermally and chemically stable.
本発明は、単結晶基板上に窒化ガリウム系化合物半導体の結晶をエピタキシャル成長させた後、降温速度を毎分５℃以下、好ましくは毎分２℃以下の条件で冷却するようにしたので、窒化ガリウム系化合物半導体の結晶をエピタキシャル成長させた後の冷却工程における降温速度を小さくし、急激な熱衝撃を回避することにより窒化ガリウム系化合物半導体の単結晶のエピタキシャル層と単結晶基板との熱膨張係数の差に起因する熱歪みによる破壊を防止することができるという効果がある。
また、単結晶基板上に窒化ガリウム系化合物半導体の結晶をエピタキシャル成長させる方法において、上記単結晶基板の厚さを、３００μｍ以下、好ましくは１００μｍ以下と薄くすることにより、単結晶基板とエピタキシャル層（窒化ガリウム系化合物半導体の結晶）との熱膨張係数の差に起因する熱歪みをエピタキシャル層が破壊しない程度に小さくすることができ、窒化ガリウム系化合物半導体の結晶を破壊することなく得ることができるという効果がある。
In the present invention, after a gallium nitride compound semiconductor crystal is epitaxially grown on a single crystal substrate, the temperature drop rate is 5 ° C./min or less, preferably 2 ° C./min or less. The thermal expansion coefficient between the single crystal epitaxial layer and the single crystal substrate of the gallium nitride compound semiconductor is reduced by reducing the temperature drop rate in the cooling step after epitaxially growing the crystal of the semiconductor compound semiconductor and avoiding a sudden thermal shock. There is an effect that it is possible to prevent breakage due to thermal distortion caused by the difference.
In the method of epitaxially growing a gallium nitride compound semiconductor crystal on a single crystal substrate, the thickness of the single crystal substrate is reduced to 300 μm or less, preferably 100 μm or less, so that the single crystal substrate and the epitaxial layer (nitride) The thermal strain caused by the difference in thermal expansion coefficient from the crystal of the gallium compound semiconductor) can be reduced to such an extent that the epitaxial layer does not break, and can be obtained without destroying the gallium nitride compound semiconductor crystal. effective.
さらに、単結晶基板上に窒化ガリウム系化合物半導体の結晶をエピタキシャル成長させる方法において、成長させた窒化ガリウム系化合物半導体結晶の厚さを、１００μｍ以上、好ましくは３００μｍ以上と厚くすることにより、エピタキシャル層（窒化ガリウム系化合物半導体の結晶）の強度が、単結晶基板とエピタキシャル層との熱膨張係数の差に起因する熱歪みによっても破壊されない程度に強化することができ、窒化ガリウム系化合物半導体結晶の破壊を未然に防止することができるという効果がある。
なお、上記方法は適宜組み合わせて用いることができ、相乗効果により成長させた上記窒化ガリウム系化合物半導体結晶を破壊することなく単結晶基板から剥離させて窒化ガリウム系化合物半導体の結晶を歩留まりよく得ることができるという効果を期待できる。
Further, in the method of epitaxially growing a gallium nitride compound semiconductor crystal on a single crystal substrate, the thickness of the grown gallium nitride compound semiconductor crystal is increased to 100 μm or more, preferably 300 μm or more, thereby forming an epitaxial layer ( The strength of the gallium nitride compound semiconductor crystal) can be strengthened to such an extent that it cannot be destroyed by thermal strain caused by the difference in thermal expansion coefficient between the single crystal substrate and the epitaxial layer. There is an effect that can be prevented.
Note that the above methods can be used in appropriate combinations, and the gallium nitride compound semiconductor crystal grown by a synergistic effect is peeled off from the single crystal substrate without breaking, thereby obtaining a gallium nitride compound semiconductor crystal with high yield. You can expect the effect that you can.
ここで、本発明の実施形態について説明する。なお、本実施形態では、希土類ガリウムペロブスカイトの一種としてＮｄＧａＯ3の単結晶基板の（０１１）面上に窒化ガリウム系化合物半導体としてのＧａＮ単結晶を成長させる場合について述べる。また、ＧａＮの成長方法としては、ハイドライドＶＰＥ法を用いることができるが、これに限定されるものではない。 Here, an embodiment of the present invention will be described. In this embodiment, a case where a GaN single crystal as a gallium nitride compound semiconductor is grown on a (011) plane of a single crystal substrate of NdGaO 3 as a kind of rare earth gallium perovskite will be described. Further, as a method for growing GaN, a hydride VPE method can be used, but it is not limited to this.
（第１の実施形態）本実施形態は、窒化ガリウム系化合物半導体の結晶成長工程終了後の冷却工程における降温速度を毎分５℃以下、好ましくは毎分２℃以下とする場合の実施形態の一例であり、上記降温速度を毎分１．３℃にした場合について述べる。 (First Embodiment) This embodiment is an embodiment in which the temperature drop rate in the cooling step after the crystal growth step of the gallium nitride compound semiconductor is 5 ° C. or less, preferably 2 ° C. or less per minute. As an example, the case where the temperature drop rate is 1.3 ° C. per minute will be described.
本実施形態では、まず、厚さ３５０μｍの（０１１）面ＮｄＧａＯ3単結晶基板を有機洗浄および酸洗浄した後、乾燥させ、ハイドライドＶＰＥ（ＨＶＰＥ）装置にセットした。 In this embodiment, first, a (011) plane NdGaO 3 single crystal substrate having a thickness of 350 μm was subjected to organic cleaning and acid cleaning, and then dried and set in a hydride VPE (HVPE) apparatus.
次いで、窒素ガスを流しながら、基板部の温度を６００℃に、Ｇａ原料の温度を８５０℃に昇温して保持した。 Next, while flowing nitrogen gas, the temperature of the substrate portion was raised to 600 ° C. and the temperature of the Ga raw material was raised to 850 ° C. and held.
そして、Ｇａ原料の上流側から窒素（Ｎ2）ガスで希釈されたＨＣｌガスを流し、同時にＧａ原料をバイパスして基板の直上近傍にＮＨ3ガスを流して、基板の表面に第１のＧａＮ層の薄膜を１０分間成長させた。これにより得られた第１のＧａＮ層の薄膜の厚さは約０．１μｍであった。なお、この第１のＧａＮ層は、ＮｄＧａＯ3の単結晶基板が高温下でＮＨ3により分解されるのを防ぐ目的で形成されるものである。 Then, HCl gas diluted with nitrogen (N 2 ) gas is allowed to flow from the upstream side of the Ga source, and simultaneously, NH 3 gas is allowed to flow immediately above the substrate while bypassing the Ga source, so that the first GaN is formed on the surface of the substrate. A thin film of layers was grown for 10 minutes. The thickness of the thin film of the 1st GaN layer obtained by this was about 0.1 micrometer. The first GaN layer is formed for the purpose of preventing the NdGaO 3 single crystal substrate from being decomposed by NH 3 at a high temperature.
続いて、基板部の温度を１０００℃に昇温，保持して、第２のＧａＮ層の薄膜を３０分間成長させた。その後、降温速度毎分１．３℃で室温まで冷却してＧａＮ層を成長させた単結晶基板をＨＶＰＥ装置から取り出した。なお、第２のＧａＮ層と第１のＧａＮ層とを合わせたＧａＮ層全体の厚さは約５０μｍである。 Subsequently, the temperature of the substrate portion was raised to 1000 ° C. and held, and a thin film of the second GaN layer was grown for 30 minutes. Thereafter, the single crystal substrate on which the GaN layer was grown by cooling to room temperature at a temperature drop rate of 1.3 ° C. per minute was taken out from the HVPE apparatus. The total thickness of the GaN layer including the second GaN layer and the first GaN layer is about 50 μm.
このＧａＮ層に粘着テープを貼付するなどして単結晶基板から剥離させたところ、小片に破壊されることなく剥がすことができ、ＧａＮの単結晶として得ることができた。 When the GaN layer was peeled off from the single crystal substrate by sticking an adhesive tape or the like, it could be peeled off without being broken into small pieces and obtained as a single crystal of GaN.
その後、このＧａＮ単結晶を検査したところ、全体としては表面に異常成長が見られない平坦な鏡面のエピタキシャル膜であり、Ｘ線回折法による観察では良好な膜質の（０００１）面の単結晶であることが確認された。なお、若干の反りがみられる場合があったが実用上問題の無い程度であり、ＧａＮチップとして最大２０ｍｍ×３０ｍｍをとることが可能であった（表１の結果（ｂ）参照）。 After that, when this GaN single crystal was inspected, it was a flat mirror surface epitaxial film with no abnormal growth on the surface as a whole, and it was a (0001) plane single crystal with good film quality as observed by X-ray diffraction method. It was confirmed that there was. Although some warping was observed, there was no problem in practical use, and it was possible to take a maximum of 20 mm × 30 mm as a GaN chip (see the result (b) in Table 1).
なお、表１は、ＧａＮ層の厚さ，降温速度，剥離したＧａＮ単結晶の反りの程度，得られたＧａＮチップの最大のサイズを示す表である。 Table 1 is a table showing the thickness of the GaN layer, the temperature drop rate, the degree of warpage of the peeled GaN single crystal, and the maximum size of the obtained GaN chip.
上記表１の結果（ｂ）のような成果は、ＧａＮ層をエピタキシャル成長させた後の冷却工程における降温速度を毎分１．３℃と小さくすることにより、急激な熱衝撃を回避することができたため、ＧａＮ単結晶のエピタキシャル層とＮｄＧａＯ3単結晶基板との熱膨張係数の差に起因する熱歪みを抑制することができ、それによりＧａＮ単結晶の破壊を防止することができたものと推論することができる。 Results such as the result (b) in Table 1 above can avoid a rapid thermal shock by reducing the cooling rate in the cooling step after epitaxially growing the GaN layer to 1.3 ° C./min. Therefore, it is inferred that the thermal strain caused by the difference in thermal expansion coefficient between the epitaxial layer of the GaN single crystal and the NdGaO 3 single crystal substrate can be suppressed, thereby preventing the destruction of the GaN single crystal. can do.
なお、対比のため、上記と同様の条件で、ＧａＮ層育成後の降温速度のみを毎分１２℃と変更して実験したところ、基板からＧａＮ層を剥離する時点でＧａＮ層は破壊されてしまうか、あるいは破壊せずに剥離できた場合にも反りが大きかった。そのため、ＧａＮチップの最大サイズも７ｍｍ×４ｍｍと小さく（表１の結果（ａ）参照）実用上は難点を有するものであった。 For comparison, an experiment was conducted by changing only the temperature drop rate after growing the GaN layer to 12 ° C. per minute under the same conditions as described above, and the GaN layer was destroyed when the GaN layer was peeled from the substrate. The warpage was also great when the film could be peeled without breaking. Therefore, the maximum size of the GaN chip is also as small as 7 mm × 4 mm (see the result (a) in Table 1), which has a practical difficulty.
（第２の実施形態）本実施形態は、成長させる窒化ガリウム系化合物半導体結晶の厚さを、１００μｍ以上、好ましくは３００μｍ以上とする場合の実施形態の一例であり、上記厚さを１００μｍと３００μｍにした場合について述べる。 (Second Embodiment) This embodiment is an example of the embodiment in which the thickness of the gallium nitride compound semiconductor crystal to be grown is 100 μm or more, preferably 300 μm or more. The thickness is 100 μm and 300 μm. We will describe the case.
本実施形態では、厚さ３５０μｍの（０１１）面ＮｄＧａＯ3単結晶基板を有機洗浄および酸洗浄した後、乾燥させ、ハイドライドＶＰＥ（ＨＶＰＥ）装置にセットした。 In this embodiment, a (011) plane NdGaO 3 single crystal substrate having a thickness of 350 μm was subjected to organic cleaning and acid cleaning, and then dried and set in a hydride VPE (HVPE) apparatus.
次いで、窒素ガスを流しながら、基板部の温度を６００℃に、Ｇａ原料の温度を８５０℃に昇温して保持した。 Next, while flowing nitrogen gas, the temperature of the substrate portion was raised to 600 ° C. and the temperature of the Ga raw material was raised to 850 ° C. and held.
そして、Ｇａ原料の上流側から窒素（Ｎ2）ガスで希釈されたＨＣｌガスを流し、同時にＧａ原料をバイパスして基板の直上近傍にＮＨ3ガスを流して、基板の表面に第１のＧａＮ層の薄膜を１０分間成長させた。これにより得られた第１のＧａＮ層の薄膜の厚さは約０．１μｍであった。 Then, HCl gas diluted with nitrogen (N 2 ) gas is allowed to flow from the upstream side of the Ga source, and simultaneously, NH 3 gas is allowed to flow immediately above the substrate while bypassing the Ga source, so that the first GaN is formed on the surface of the substrate. A thin film of layers was grown for 10 minutes. The thickness of the thin film of the 1st GaN layer obtained by this was about 0.1 micrometer.
続いて、基板部の温度を１０００℃に昇温，保持して、第２のＧａＮ層の薄膜を６０分間成長させた。その後、降温速度毎分１．３℃で室温まで冷却してＧａＮ層を成長させた単結晶基板をＨＶＰＥ装置から取り出した。 Subsequently, the temperature of the substrate portion was raised to 1000 ° C. and held, and a thin film of the second GaN layer was grown for 60 minutes. Thereafter, the single crystal substrate on which the GaN layer was grown by cooling to room temperature at a temperature drop rate of 1.3 ° C. per minute was taken out from the HVPE apparatus.
この場合に、第２のＧａＮ層と第１のＧａＮ層とを合わせたＧａＮ層全体の厚さは約１００μｍであった。 In this case, the total thickness of the GaN layer including the second GaN layer and the first GaN layer was about 100 μm.
このＧａＮ層に粘着テープを貼付するなどして単結晶基板から剥離させたところ、小片に破壊されることなく剥がれ、ＧａＮの単結晶として得ることができた。その後、このＧａＮ単結晶を検査したところ、全体としては表面に異常成長が見られない平坦な鏡面のエピタキシャル膜であり、Ｘ線回折法による観察では良好な膜質の（０００１）面の単結晶であることが確認された。また、反りも観察されず平坦性も良好であり、ＧａＮチップとして最大２０ｍｍ×３０ｍｍをとることが可能であった（表２の結果（ｃ）参照）。 When the GaN layer was peeled off from the single crystal substrate by attaching an adhesive tape or the like, it was peeled off without being broken into small pieces, and a GaN single crystal could be obtained. After that, when this GaN single crystal was inspected, it was a flat mirror surface epitaxial film with no abnormal growth on the surface as a whole, and it was a (0001) plane single crystal with good film quality as observed by X-ray diffraction method. It was confirmed that there was. Further, no warping was observed and the flatness was good, and it was possible to take a maximum of 20 mm × 30 mm as a GaN chip (see the result (c) in Table 2).
なお、表２は、ＧａＮ層の厚さ，降温速度，剥離したＧａＮ単結晶の反りの程度，得られたＧａＮチップの最大のサイズを示す表である。 Table 2 shows the thickness of the GaN layer, the temperature drop rate, the degree of warpage of the peeled GaN single crystal, and the maximum size of the obtained GaN chip.
また、第２のＧａＮ層の薄膜の成長時間を延ばして、第２のＧａＮ層と第１のＧａＮ層とを合わせたＧａＮ層全体の厚さを約３００μｍとする実験を行ったところ、やはり小片に破壊されることなく基板から剥がすことができ、ＧａＮの単結晶として得ることができた。このＧａＮ単結晶についても検査したところ、全体としては表面に異常成長が見られない平坦な鏡面のエピタキシャル膜であり、Ｘ線回折法による観察でも良好な膜質の（０００１）面の単結晶であることが確認された。また、反りも観察されず平坦性も良好であった（表２の結果（ｄ）参照）。この場合には、ＧａＮチップとして、用いた基板の大きさに相当する直径５０ｍｍをとることが可能であった。また、ＮｄＧａＯ3単結晶基板としては、最大４０ｍｍ×３０ｍｍのものを用いることができ、ＧａＮ単結晶の大面積化に有効であることを確認できた。 In addition, when the growth time of the thin film of the second GaN layer was extended and the total thickness of the GaN layer including the second GaN layer and the first GaN layer was about 300 μm, an experiment was performed. Can be peeled off from the substrate without being broken, and can be obtained as a single crystal of GaN. When this GaN single crystal was also inspected, it was a flat mirror surface epitaxial film with no abnormal growth on the surface as a whole, and was a (0001) plane single crystal with good film quality even when observed by X-ray diffraction. It was confirmed. Further, no warpage was observed and the flatness was good (see the result (d) in Table 2). In this case, it was possible to take a diameter of 50 mm corresponding to the size of the substrate used as the GaN chip. Further, as the NdGaO 3 single crystal substrate, a substrate having a maximum of 40 mm × 30 mm can be used, and it was confirmed that it is effective for increasing the area of the GaN single crystal.
このような結果は、成長させたＧａＮ結晶の厚さを、１００μｍ以上と厚くしたことにより、ＧａＮのエピタキシャル層の強度を、ＮｄＧａＯ3単結晶基板とエピタキシャル層との熱膨張係数の差に起因する熱歪みによっても破壊されない程度に強化することができたので、窒化ガリウム系化合物半導体結晶の破壊を未然に防止することができたものと推論することができる。 Such a result is attributed to the difference in thermal expansion coefficient between the NdGaO 3 single crystal substrate and the epitaxial layer by increasing the thickness of the grown GaN crystal to 100 μm or more. It can be inferred that the gallium nitride compound semiconductor crystal could be prevented from being broken because it could be strengthened to such an extent that it could not be destroyed by thermal strain.
（第３の実施形態）本実施形態は、単結晶基板の厚さを、３００μｍ以下、好ましくは１００μｍ以下とする場合の実施形態の一例であり、単結晶基板の厚さを１００μｍとし、窒化ガリウム系化合物半導体の結晶成長工程終了後の冷却工程における降温速度を毎分１２℃、成長させる窒化ガリウム系化合物半導体結晶の厚さを１００μｍと３００μｍにした場合について述べる。 (Third Embodiment) This embodiment is an example of an embodiment in which the thickness of the single crystal substrate is 300 μm or less, preferably 100 μm or less. The thickness of the single crystal substrate is 100 μm, and gallium nitride is used. A case will be described in which the temperature drop rate in the cooling step after the completion of the crystal growth step of the compound compound semiconductor is 12 ° C. per minute and the thickness of the gallium nitride compound semiconductor crystal to be grown is 100 μm and 300 μm.
本実施形態では、厚さ１００μｍの（０１１）面ＮｄＧａＯ3単結晶基板を有機洗浄および酸洗浄した後、乾燥させ、ハイドライドＶＰＥ（ＨＶＰＥ）装置にセットした。 In this embodiment, a (011) plane NdGaO 3 single crystal substrate having a thickness of 100 μm was subjected to organic cleaning and acid cleaning, and then dried and set in a hydride VPE (HVPE) apparatus.
次いで、窒素ガスを流しながら、基板部の温度を６００℃に、Ｇａ原料の温度を８５０℃に昇温して保持した。 Next, while flowing nitrogen gas, the temperature of the substrate portion was raised to 600 ° C. and the temperature of the Ga raw material was raised to 850 ° C. and held.
そして、Ｇａ原料の上流側から窒素（Ｎ2）ガスで希釈されたＨＣｌガスを流し、同時にＧａ原料をバイパスして基板の直上近傍にＮＨ3ガスを流して、基板の表面に第１のＧａＮ層の薄膜を１０分間成長させた。これにより得られた第１のＧａＮ層の薄膜の厚さは約０．１μｍであった。 Then, HCl gas diluted with nitrogen (N 2 ) gas is allowed to flow from the upstream side of the Ga source, and simultaneously, NH 3 gas is allowed to flow immediately above the substrate while bypassing the Ga source, so that the first GaN is formed on the surface of the substrate. A thin film of layers was grown for 10 minutes. The thickness of the thin film of the 1st GaN layer obtained by this was about 0.1 micrometer.
続いて、基板部の温度を１０００℃に昇温，保持して、第２のＧａＮ層の薄膜を３０分間成長させた。その後、降温速度毎分１２℃で室温まで冷却してＧａＮ層を成長させた単結晶基板をＨＶＰＥ装置から取り出した。 Subsequently, the temperature of the substrate portion was raised to 1000 ° C. and held, and a thin film of the second GaN layer was grown for 30 minutes. Thereafter, the single crystal substrate on which the GaN layer was grown by cooling to room temperature at 12 ° C. per minute was taken out from the HVPE apparatus.
この場合に、第２のＧａＮ層と第１のＧａＮ層とを合わせたＧａＮ層全体の厚さは約１００μｍであった。 In this case, the total thickness of the GaN layer including the second GaN layer and the first GaN layer was about 100 μm.
このＧａＮ層に粘着テープを貼付するなどして単結晶基板から剥離させたところ、小片に破壊されることなく剥がれ、ＧａＮの単結晶として得ることができた。その後、このＧａＮ単結晶を検査したところ、全体としては表面に異常成長が見られない平坦な鏡面のエピタキシャル膜であり、Ｘ線回折法による観察では良好な膜質の（０００１）面の単結晶であることが確認された。なお、若干の反りがみられる場合があったが実用上問題の無い程度であった（表３の結果（ｅ）参照）。 When the GaN layer was peeled off from the single crystal substrate by attaching an adhesive tape or the like, it was peeled off without being broken into small pieces, and a GaN single crystal could be obtained. After that, when this GaN single crystal was inspected, it was a flat mirror surface epitaxial film with no abnormal growth on the surface as a whole, and it was a (0001) plane single crystal with good film quality as observed by X-ray diffraction method. It was confirmed that there was. Although some warping was observed, there was no practical problem (see the result (e) in Table 3).
なお、表３は、ＧａＮ層の厚さ，降温速度，剥離したＧａＮ単結晶の反りの程度を示す表である。 Table 3 is a table showing the thickness of the GaN layer, the temperature drop rate, and the degree of warpage of the separated GaN single crystal.
また、第２のＧａＮ層の薄膜の成長時間を延ばして、第２のＧａＮ層と第１のＧａＮ層とを合わせたＧａＮ層全体の厚さを約３００μｍとする実験をおこなったところ、やはり小片に破壊されることなく基板から剥がすことができ、ＧａＮの単結晶として得ることができた。このＧａＮ単結晶についても検査したところ、全体としては表面に異常成長が見られない平坦な鏡面のエピタキシャル膜であり、Ｘ線回折法による観察でも良好な膜質の（０００１）面の単結晶であることが確認された。また、反りも観察されず平坦性も良好であった（表３の結果（ｆ）参照）。 Further, when the growth time of the thin film of the second GaN layer was extended and the total thickness of the GaN layer including the second GaN layer and the first GaN layer was about 300 μm, an experiment was performed. Can be peeled off from the substrate without being broken, and can be obtained as a single crystal of GaN. When this GaN single crystal was also inspected, it was a flat mirror surface epitaxial film with no abnormal growth on the surface as a whole, and was a (0001) plane single crystal with good film quality even when observed by X-ray diffraction. It was confirmed. Further, no warpage was observed and the flatness was good (see the result (f) in Table 3).
このような結果は、ＮｄＧａＯ3単結晶基板の厚さを、１００μｍと薄くしたことにより、ＮｄＧａＯ3単結晶基板とＧａＮのＧａＮのエピタキシャル層との熱膨張係数の差に起因する熱歪みをエピタキシャル層が破壊しない程度に小さくすることができたので、ＧａＮ結晶を破壊することなく得ることができたものと推論することができる。 Such a result shows that the thickness of the NdGaO 3 single crystal substrate is reduced to 100 μm, so that the thermal strain caused by the difference in thermal expansion coefficient between the NdGaO 3 single crystal substrate and the GaN epitaxial layer of GaN is reduced to the epitaxial layer. Therefore, it can be inferred that the GaN crystal could be obtained without destroying it.
このように上記第１から第３の実施形態によれば、成長させた窒化ガリウム系化合物半導体結晶（ＧａＮ単結晶）を破壊することなく単結晶基板から剥離させて窒化ガリウム系化合物半導体の結晶を歩留まりよく得ることができ、生産性を向上させて窒化ガリウム系化合物半導体結晶の製造コストを低減することができる。 As described above, according to the first to third embodiments, the grown gallium nitride compound semiconductor crystal (GaN single crystal) is peeled off from the single crystal substrate without destroying the gallium nitride compound semiconductor crystal. It can be obtained with a good yield, and the productivity can be improved and the manufacturing cost of the gallium nitride compound semiconductor crystal can be reduced.
また、上述のようにハイドライドＶＰＥ法等を用いる場合には、成長速度が速いため短時間で容易に窒化ガリウム系化合物半導体結晶の厚膜を得ることができ、さらに、結晶のエピタキシャル成長過程で不純物をドーピングすることにより、導電性の窒化ガリウム系化合物半導体単結晶を製造することも可能である。 Further, when the hydride VPE method or the like is used as described above, since the growth rate is high, a thick film of a gallium nitride compound semiconductor crystal can be easily obtained in a short time, and impurities can be added during the epitaxial growth process of the crystal. Conducting gallium nitride compound semiconductor single crystals can be produced by doping.
なお、上記実施形態では、希土類ガリウムペロブスカイトとしてＮｄＧａＯ3単結晶基板を用い、ＧａＮ単結晶を成長させる場合について説明したが、これに限られるものではなく、その他の１または２種類以上の希土類元素を含む希土類１３（３Ｂ）族ペロブスカイトの単結晶基板上にＧａＮ以外の窒化ガリウム系化合物半導体単結晶を成長させる場合にも適用することができる。また、上記希土類元素は、Ａｌ，Ｇａ，Ｉｎの少なくとも一つとすることができる。 In the above embodiment, a case where a NdGaO 3 single crystal substrate is used as a rare earth gallium perovskite and a GaN single crystal is grown has been described. However, the present invention is not limited to this, and other one or more kinds of rare earth elements are used. The present invention can also be applied to the case where a gallium nitride compound semiconductor single crystal other than GaN is grown on a rare earth 13 (3B) group perovskite single crystal substrate. The rare earth element may be at least one of Al, Ga, and In.
また、本実施形態では、不活性ガスとしてＮ2ガスを用いる場合について述べたがこれに限定されずその他の不活性ガスを用いることも可能である。 In this embodiment, the case where N 2 gas is used as the inert gas has been described. However, the present invention is not limited to this, and other inert gases can also be used.
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| US9531154B2 (en) | 2014-07-14 | 2016-12-27 | Disco Corporation | Lift-off method |
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