JP2012066943A - Substrate for forming nitride semiconductor, and nitride semiconductor - Google Patents

Substrate for forming nitride semiconductor, and nitride semiconductor Download PDF

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JP2012066943A
JP2012066943A JP2010210417A JP2010210417A JP2012066943A JP 2012066943 A JP2012066943 A JP 2012066943A JP 2010210417 A JP2010210417 A JP 2010210417A JP 2010210417 A JP2010210417 A JP 2010210417A JP 2012066943 A JP2012066943 A JP 2012066943A
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nitride semiconductor
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germanium
boron
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JP5439675B2 (en
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Takeshi Sato
剛 佐藤
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Silicon Technology Co Ltd
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Abstract

PROBLEM TO BE SOLVED: To provide a silicon wafer-based substrate which is suitable for forming a nitride semiconductor and is low in cost; and to provide a substrate for forming a nitride semiconductor which reduces the occurrence of a curvature and crack, which are caused by differences in lattice constant and thermal expansion coefficient between materials, even if a nitride semiconductor epitaxial layer whose film is large in thickness is grown, the substrate being excellent in mechanical strength and thermal strength.SOLUTION: In a silicon wafer, boron and germanium are doped at a specific concentration. For a ratio in concentration of the boron to the germanium, the concentration of the germanium is controlled preferably to be 5-8 times as much as that of the boron.

Description

本発明は、窒化物半導体形成用基板に関し、詳しくは、基板上に窒化物半導体皮膜を形成した場合にも、該皮膜に生じる反りと応力を低減でき、良好な窒化物半導体を与える窒化物半導体形成用基板に関する。   The present invention relates to a substrate for forming a nitride semiconductor, and more specifically, even when a nitride semiconductor film is formed on the substrate, the warp and stress generated in the film can be reduced, and a nitride semiconductor that provides a good nitride semiconductor is provided. The present invention relates to a forming substrate.

化合物半導体として、例えばGaN、AlNに代表される窒化物半導体は、シリコン半導体と比較して、高移動度、発光特性、高バンドギャップ、高絶縁破壊電界等を有するので、電子デバイス(例えば高周波・高出力デバイス)、及び光デバイス(例えばレーザーダイオード、発光ダイオード)への使用が注目されている。
しかしながら、窒化物半導体のバルク結晶成長はコスト、技術的な面で問題があるため、シリコン基板上に窒化物半導体単結晶をヘテロエピタキシャル成長させた窒化物系化合物半導体に研究が加速されている。
As compound semiconductors, for example, nitride semiconductors typified by GaN and AlN have higher mobility, light emission characteristics, higher band gaps, higher breakdown electric fields, and the like than silicon semiconductors. High power devices) and optical devices (eg laser diodes, light emitting diodes) are attracting attention.
However, since bulk crystal growth of nitride semiconductors has problems in terms of cost and technology, research has been accelerated on nitride compound semiconductors obtained by heteroepitaxially growing a nitride semiconductor single crystal on a silicon substrate.

通常、窒化物半導体を用いた電子デバイスは、例えばシリコンカーバイド(SiC)、サファイヤ、ZnO又はシリコンからなる基板を用いて作製されている。特に、シリコンからなる基板は大口径のものが安価で入手できるため、電子デバイス用の基板として非常に有効である。
しかしながら、シリコンとGaNなどの窒化物半導体では格子定数および熱膨張係数に非常に大きな差があるため、シリコン基板上に窒化物半導体層を直接エピタキシャル成長させると、窒化物半導体層に大きな引張り歪みが内在することになり、窒化物半導体層をエピタキシャル成長させたエピタキシャル基板全体に凹形状の反りが発生したり結晶性が悪化したりする原因となる。さらに内在する歪みが大きいと窒化物半導体層中にクラックが発生する。
Usually, an electronic device using a nitride semiconductor is manufactured using a substrate made of, for example, silicon carbide (SiC), sapphire, ZnO, or silicon. In particular, a substrate made of silicon is very effective as a substrate for an electronic device because a large-diameter substrate can be obtained at a low price.
However, since there is a very large difference in lattice constant and thermal expansion coefficient between silicon and nitride semiconductors such as GaN, when a nitride semiconductor layer is directly epitaxially grown on a silicon substrate, a large tensile strain is inherent in the nitride semiconductor layer. As a result, the entire epitaxial substrate on which the nitride semiconductor layer is epitaxially grown may cause a concave warp or deteriorate crystallinity. Further, if the inherent strain is large, cracks are generated in the nitride semiconductor layer.

このようにシリコン基板上の窒化物半導体のエピタキシャル成長は、各々が格子定数、熱膨張係数が異なるヘテロエピタキシャル成長のため、成膜後の反り、クラックが大きく、結晶欠陥が少なく且つ厚い窒化物半導体エピタキシャル層を成長させることは、シリコン基板使用上の大きな問題点であった。   As described above, the nitride semiconductor epitaxial growth on the silicon substrate is heteroepitaxial growth with different lattice constants and thermal expansion coefficients, so that the nitride semiconductor epitaxial layer has a large warp, large cracks, few crystal defects, and a large thickness after film formation. It has been a big problem in using a silicon substrate.

特許文献1には、シリコンエピタキシャル層を形成するためのシリコンウェーハとして、ボロンとゲルマニウムとが添加されたシリコン単結晶インゴットをスライスして作製されたシリコンウェーハが開示されている。
しかしながら、該文献に開示されているシリコンウェーハは、あくまでもシリコンエピタキシャル層を形成するための基板を提供するものであり、GaN等の窒化物半導体層を形成した際には、依然として反りが大きく生じ、窒化物半導体形成用基板としては不適であることから、窒化物半導体層形成に使用できる窒化物半導体形成用基板が強く要望されている。
Patent Document 1 discloses a silicon wafer produced by slicing a silicon single crystal ingot to which boron and germanium are added as a silicon wafer for forming a silicon epitaxial layer.
However, the silicon wafer disclosed in this document only provides a substrate for forming a silicon epitaxial layer, and when a nitride semiconductor layer such as GaN is formed, warping still occurs greatly. Since it is not suitable as a substrate for forming a nitride semiconductor, a substrate for forming a nitride semiconductor that can be used for forming a nitride semiconductor layer is strongly desired.

特開2004−175658号公報JP 2004-175658 A

本発明の目的は、窒化物半導体形成用基板を提供することである。   An object of the present invention is to provide a nitride semiconductor forming substrate.

具体的にはGaN等の窒化物半導体形成に好適な、シリコンウェーハをベースとした安価な形成用基板を提供することである。また、格子欠陥の少なくかつ厚膜の窒化物半導体エピタキシャル層を成長させた場合でも、反り、クラックの発生が低減され、機械的強度や、熱的強度に優れた窒化物半導体形成用基板を提供することである。   Specifically, it is an object to provide an inexpensive formation substrate based on a silicon wafer, which is suitable for forming a nitride semiconductor such as GaN. In addition, even when a nitride semiconductor epitaxial layer with a large number of lattice defects and a large thickness is grown, the generation of a warp and cracks is reduced, and a substrate for forming a nitride semiconductor having excellent mechanical strength and thermal strength is provided. It is to be.

本発明者らは、鋭意検討した結果、ボロンとゲルマニウムとが特定濃度でドープされており、好ましくはボロンとゲルマニウムの濃度比において、ゲルマニウム濃度をボロンの濃度の5〜8倍と制御したシリコンウェーハを準備し、窒化物半導体層としてGaN層を形成した所、著しく反り量が低減でき、良好な特性の窒化物半導体を提供できることを見出し、本発明の完成に至った。   As a result of intensive studies, the present inventors have determined that boron and germanium are doped at a specific concentration, and preferably a silicon wafer in which the germanium concentration is controlled to be 5 to 8 times the boron concentration in the concentration ratio of boron and germanium. Was prepared, and a GaN layer was formed as a nitride semiconductor layer. As a result, it was found that the amount of warpage can be significantly reduced and a nitride semiconductor having good characteristics can be provided, and the present invention has been completed.

すなわち本発明は、以下に示すものである。   That is, the present invention is as follows.

第1の発明は、窒化物半導体を形成するための半導体基板であって、
シリコン中に、ボロン及びゲルマニウムがドープされてなり、
ボロン及びゲルマニウムの濃度をそれぞれ[B]atoms/cm、[Ge]atoms/cmとしたときに、
以下の条件、
2.5×1018≦[Ge]≦2.5×1020
4.0×1016≦[B]≦4.0×1019
を満たすことを特徴とする窒化物半導体形成用基板である。
A first invention is a semiconductor substrate for forming a nitride semiconductor,
Boron and germanium are doped in silicon,
When the concentrations of boron and germanium are [B] atoms / cm 3 and [Ge] atoms / cm 3 , respectively.
The following conditions,
2.5 × 10 18 ≦ [Ge] ≦ 2.5 × 10 20 ,
4.0 × 10 16 ≦ [B] ≦ 4.0 × 10 19 ,
The nitride semiconductor forming substrate is characterized in that:

第2の発明は、さらに、5[B]≦[Ge]≦8[B]を満たすことを特徴とする第1の発明に記載の窒化物半導体形成用基板である。   The second invention is the nitride semiconductor forming substrate according to the first invention, further satisfying 5 [B] ≦ [Ge] ≦ 8 [B].

第3の発明は、1.5×1019≦[Ge]≦2.2×1020
3.0×1018≦[B]≦2.7×1019
であることを特徴とする第2の発明に記載の窒化物半導体形成用基板である。
The third invention is 1.5 × 10 19 ≦ [Ge] ≦ 2.2 × 10 20 ,
3.0 × 10 18 ≦ [B] ≦ 2.7 × 10 19 ,
The nitride semiconductor forming substrate according to the second invention, characterized in that:

第4の発明は、
窒素雰囲気中において800℃×4時間の熱処理を施し、
その後、酸素雰囲気中において1000℃×16時間の熱処理を施した後、
ウェーハ内部の酸素析出物密度が1.0×10個/cm以上、かつ2.0×1010個/cm未満であることを特徴とする第1から第3の発明のいずれかにひとつに記載の窒化物半導体形成用基板である。
The fourth invention is:
Heat treatment at 800 ° C. for 4 hours in a nitrogen atmosphere,
Thereafter, after heat treatment at 1000 ° C. for 16 hours in an oxygen atmosphere,
The oxygen precipitate density inside the wafer is 1.0 × 10 7 pieces / cm 3 or more and less than 2.0 × 10 10 pieces / cm 3. It is a nitride semiconductor formation substrate described in one.

第5の発明は、
ウェーハ中の酸素濃度(ASTM F−121 1979)が9×1017atoms/cm以上、かつ14×1017atoms/cm以下であることを特徴とする第1から第4の発明のいずれかひとつに記載の窒化物半導体形成用基板である。
The fifth invention is:
Any one of the first to fourth inventions, wherein the oxygen concentration (ASTM F-121 1979) in the wafer is 9 × 10 17 atoms / cm 3 or more and 14 × 10 17 atoms / cm 3 or less. It is a nitride semiconductor formation substrate described in one.

第6の発明は、第1から第5の発明のいずれかひとつに記載の半導体形成用基板上に、窒化物半導体薄膜を形成してなることを特徴とする窒化物半導体である。   A sixth invention is a nitride semiconductor comprising a nitride semiconductor thin film formed on the semiconductor forming substrate according to any one of the first to fifth inventions.

本発明の窒化物半導体形成用基板は、厚膜の窒化物半導体層を形成した際にも、反りならびにクラックが低減された、窒化物半導体用基板を提供することができる。
また、本発明の窒化物半導体は、厚膜の窒化物半導体層が形成されており、窒化物系半導体からなる電子デバイスとして極めて有用である。
The substrate for forming a nitride semiconductor of the present invention can provide a substrate for a nitride semiconductor with reduced warpage and cracks even when a thick nitride semiconductor layer is formed.
In addition, the nitride semiconductor of the present invention has a thick nitride semiconductor layer formed and is extremely useful as an electronic device made of a nitride semiconductor.

以下、本発明をより詳細に説明する。   Hereinafter, the present invention will be described in more detail.

本発明の窒化物半導体形成用基板は、シリコンウェーハにゲルマニウム及びボロンが含有されていることを特徴としている。
シリコンウェーハ中に、ゲルマニウムとボロンとがドープされていることで、上層にGaN等の窒化物半導体層を形成した際にも耐熱衝撃性に優れ、反りやクラックの生じない強靭なシリコンウェーハとなる。
The nitride semiconductor forming substrate of the present invention is characterized in that germanium and boron are contained in a silicon wafer.
The silicon wafer is doped with germanium and boron, so that even when a nitride semiconductor layer such as GaN is formed on the upper layer, it is excellent in thermal shock resistance and becomes a tough silicon wafer free from warping or cracking. .

(基板)
本発明の窒化物半導体形成用基板は、ボロンとゲルマニウムとがドープされたシリコン基板である。
本発明のボロンとゲルマニウムとがドープされたシリコン基板は、その上に形成する窒化物半導体層の格子定数差による格子歪ならびに熱膨張率差により生じる熱応力歪に伴う反りやクラックを低減し、得られる基板から製造される窒化物半導体からなる電子デバイスの歩留まり向上に資する。
(substrate)
The substrate for forming a nitride semiconductor of the present invention is a silicon substrate doped with boron and germanium.
The silicon substrate doped with boron and germanium of the present invention reduces warpage and cracks due to lattice stress due to the lattice constant difference of the nitride semiconductor layer formed thereon and thermal stress strain caused by the difference in thermal expansion coefficient, This contributes to improving the yield of electronic devices made of nitride semiconductors manufactured from the obtained substrate.

(ボロン)
本発明の窒化物半導体形成用基板中にドープされるボロンの濃度としては、ボロン濃度を[B]atoms/cmとすると、
4.0×1016≦[B]≦4.0×1019であり、より好ましくは、3.0×1018≦[B]≦2.7×1019を満たすものである。
シリコン中にボロンを上記濃度にてドーピングすることで、シリコン結晶中の転位を抑制することができる。
そして、本発明の窒化物半導体用基板であるシリコン基板は、さらにゲルマニウムを共存させることで、シリコン単結晶の機械的強度が高まり、極めて強靭なシリコン単結晶が得られる。
(boron)
As the concentration of boron doped in the nitride semiconductor formation substrate of the present invention, when the boron concentration is [B] atoms / cm 3 ,
4.0 × 10 16 ≦ [B] ≦ 4.0 × 10 19 , more preferably 3.0 × 10 18 ≦ [B] ≦ 2.7 × 10 19 .
By doping boron at the above concentration in silicon, dislocations in the silicon crystal can be suppressed.
The silicon substrate, which is a substrate for a nitride semiconductor according to the present invention, further increases the mechanical strength of the silicon single crystal by coexisting germanium, thereby obtaining an extremely tough silicon single crystal.

(ゲルマニウム)
ここで、好適なゲルマニウム濃度としては、ゲルマニウムの濃度を[Ge]atoms/cmとすると、
2.5×1018≦[Ge]≦2.5×1020であり、より好ましくは、1.5×1019≦[Ge]≦2.2×1020を満たすものである。
(germanium)
Here, as a suitable germanium concentration, if the germanium concentration is [Ge] atoms / cm 3 ,
2.5 × 10 18 ≦ [Ge] ≦ 2.5 × 10 20 , more preferably 1.5 × 10 19 ≦ [Ge] ≦ 2.2 × 10 20 .

(ゲルマニウムとボロンの濃度関係)
ここで、[B]で示されるボロン濃度と、[Ge]で示されるゲルマニウム濃度とは、以下の関係式(1)で示される。
5[B]≦[Ge]≦8[B]・・・(1)
ここで、ゲルマニウム濃度をボロン濃度の5倍以上とすることは、窒化物半導体層を形成するためのシリコン基板に極めて重要なことである。
すなわちゲルマニウムの濃度が5倍に満たない場合、シリコン基板中に形成されるGe−酸素−Bコンプレックスの形成が生じにくくなり、熱的強度や転位固着効果が低下し、窒化物半導体層形成時の格子定数差による格子歪ならびに熱膨張率差により生じる熱応力歪によって、基板に反りが生じやすくなる。
また、ゲルマニウム濃度がボロン濃度に対して8倍を超える場合、ゲルマニウムが非常に高価なことから、製造コストが高くなる他に、得られるシリコン基板中の格子ひずみ差が大きくなり、熱的強度や転位固着効果が低下してしまうため、基板の反りが大きくなる場合がある。
従って、ゲルマニウム濃度に対するボロン濃度の適正な比は、ボロン濃度1に対し、ゲルマニウムが5〜8の濃度であり、より好ましくは、6〜8である。
(Concentration relationship between germanium and boron)
Here, the boron concentration indicated by [B] and the germanium concentration indicated by [Ge] are represented by the following relational expression (1).
5 [B] ≦ [Ge] ≦ 8 [B] (1)
Here, it is extremely important for the silicon substrate for forming the nitride semiconductor layer that the germanium concentration is 5 times or more the boron concentration.
That is, when the concentration of germanium is less than 5 times, the formation of a Ge-oxygen-B complex formed in the silicon substrate is difficult to occur, the thermal strength and the dislocation fixing effect are lowered, and the nitride semiconductor layer is not formed. The substrate is likely to warp due to the lattice strain due to the lattice constant difference and the thermal stress strain caused by the difference in thermal expansion coefficient.
In addition, when the germanium concentration exceeds 8 times the boron concentration, germanium is very expensive, so that the manufacturing cost is increased and the lattice strain difference in the obtained silicon substrate is increased, the thermal strength and Since the dislocation fixing effect is lowered, the warpage of the substrate may be increased.
Therefore, the appropriate ratio of the boron concentration to the germanium concentration is 5 to 8 and more preferably 6 to 8 for germanium with respect to 1 for boron concentration.

(酸素濃度)
ボロンとゲルマニウムとがドープされたシリコンウェーハについては、酸素濃度にも大きく影響を受ける。本発明のウェーハ中の酸素濃度については、9×1017〜14×1017atoms/cm(ASTM F−121 1979)の範囲であることが好ましい。
該酸素濃度が9×1017atoms/cm未満の場合、機械的強度が低下するとともに、Ge−酸素−Bコンプレックスの形成が不十分となってしまい、十分な反り抑制効果が得られない場合がある。
一方、14×1017atoms/cmを超える場合、ウェーハ中の酸素析出物密度が多くなる場合があり、得られる半導体基板の機械的強度が劣り、反りが大きくなる場合がある。
(Oxygen concentration)
The silicon wafer doped with boron and germanium is greatly affected by the oxygen concentration. The oxygen concentration in the wafer of the present invention is preferably in the range of 9 × 10 17 to 14 × 10 17 atoms / cm 3 (ASTM F-121 1979).
When the oxygen concentration is less than 9 × 10 17 atoms / cm 3 , the mechanical strength is lowered and the formation of the Ge-oxygen-B complex is insufficient, and a sufficient warpage suppressing effect cannot be obtained. There is.
On the other hand, if it exceeds 14 × 10 17 atoms / cm 3 , the density of oxygen precipitates in the wafer may increase, and the mechanical strength of the resulting semiconductor substrate may be inferior and warpage may be increased.

(窒化物半導体形成用基板の製造方法)
本発明の窒化物半導体基板は以下の方法で製造することができる。
シリコン融液に、所定量のボロン及びゲルマニウムをドープし、CZ法等の通常の単結晶成長法を用いてシリコン単結晶を育成する。
得られたシリコン単結晶からシリコンウェーハをスライスし、各スライスドウェーハに対して、公知の方法で面取り、ラップ、酸エッチング、鏡面研磨等の各工程を施してシリコンウェーハを作製する。
(Manufacturing method of substrate for forming nitride semiconductor)
The nitride semiconductor substrate of the present invention can be manufactured by the following method.
A silicon melt is doped with a predetermined amount of boron and germanium, and a silicon single crystal is grown using a normal single crystal growth method such as a CZ method.
A silicon wafer is sliced from the obtained silicon single crystal, and each sliced wafer is subjected to various processes such as chamfering, lapping, acid etching, and mirror polishing by a known method to produce a silicon wafer.

(窒化物半導体の製造方法)
本発明のボロンとゲルマニウムとがドープされたシリコンウェーハ上に、窒化物半導体薄膜を成長、形成させるには、公知の技術を用いることができ、特に限定されない。公知の技術としては、常圧有機金属気相成長法(MOCVD法)、分子線エピタキシー法(MBE法)、ハイドライド気相成長法(HVPE法)、昇華法、液相成長法等が挙げられる。
また、本発明のボロンとゲルマニウムとがドープされたシリコンウェーハは、種々の窒化物半導体薄膜を成長、形成させることが可能であるが、バッファー層として、AlN、AlGaN等の窒化物化合物系半導体層を、公知の技術を用いて形成させ、次に、これらの窒化物化合物系半導体層にて形成されたバッファー層上に、公知の技術を用いてGaN層等の窒化物化合物系半導体層を成長させることが好ましい。
本発明のボロンとゲルマニウムとがドープされたシリコンウェーハは、その上部にGaN層を形成した際にも、格子定数差から生じる格子歪、及び熱膨張率差により生じる応力歪を低減し、窒化物系半導体からなる電子デバイス製造の際に、様々な熱履歴を繰り返しても反りが生じにくく、クラック及び格子歪を低減し、窒化物半導体の歩留まり向上に寄与する。
(Nitride semiconductor manufacturing method)
In order to grow and form a nitride semiconductor thin film on a silicon wafer doped with boron and germanium of the present invention, a known technique can be used, and there is no particular limitation. Known techniques include atmospheric pressure metalorganic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), sublimation, liquid phase epitaxy, and the like.
The silicon wafer doped with boron and germanium according to the present invention can grow and form various nitride semiconductor thin films, but as a buffer layer, a nitride compound semiconductor layer such as AlN or AlGaN can be used. Then, a nitride compound semiconductor layer such as a GaN layer is grown on the buffer layer formed of these nitride compound semiconductor layers using a known technique. It is preferable to make it.
The silicon wafer doped with boron and germanium of the present invention reduces the lattice strain caused by the lattice constant difference and the stress strain caused by the difference in thermal expansion coefficient even when the GaN layer is formed on the silicon wafer, and nitride. When an electronic device made of a semiconductor is manufactured, even if various thermal histories are repeated, warpage is unlikely to occur, cracks and lattice strain are reduced, and the yield of nitride semiconductors is improved.

(評価方法)
(ボロン、ゲルマニウム、酸素濃度の測定)
ボロン濃度、ゲルマニウム濃度および酸素濃度の測定方法としては、以下の方法で測定する。
ボロン、ゲルマニウムの濃度および酸素濃度の測定は、2次イオン質量分析装置(SIMS)を使用して測定できる。
(酸素析出物密度の測定法)
(1)酸素析出物を評価する方法として、本発明のボロンとゲルマニウムとがドープされたシリコンウェーハを作製した後、窒素雰囲気中において800℃で4時間の熱処理を施し、その後、さらに酸素雰囲気中において1000℃で16時間の熱処理を実施する。
(2)評価熱処理で形成された熱酸化膜をHF:HO=1:1のエッチング液で除去する。
(3)ウェーハを劈開して、ジルトルエッチング液(組成:HF:CrO3(5M)=1:1)を用いて該ウェーハの選択エッチングを行う。
(4)倍率500〜1000倍の光学顕微鏡を用いて、ウェーハ劈開面の酸素析出物を観察し、単位体積あたりの酸素析出物の個数を計測する。
この評価方法にて、酸素析出物が2.0×1010個/cmを超える場合、シリコンウェーハ中の酸素析出物の形成密度が過多となり、機械的強度が低下し、ウェーハの反りが大きくなる場合がある。
本評価方法にて酸素析出物密度(個/cm)の下限としては1.0×10以上であることが好ましい。これ以下の酸素析出物密度であると、シリコン単結晶基板中に必然的に形成され、シリコン単結晶基板の機械的強度を向上させると考えられているGe−酸素−Bコンプレックスの形成が生じにくくなり、十分な反り抑制効果が得られない場合がある。
(反りの測定方法)
レーザー測長器により、シリコンウェーハの厚み方向において、ウェーハ同一面上におけるウェーハの中心部と外周部の高低差を測定した値を反り量とする。
(Evaluation methods)
(Measurement of boron, germanium, oxygen concentration)
As a method for measuring the boron concentration, the germanium concentration, and the oxygen concentration, the following methods are used.
The concentration of boron and germanium and the oxygen concentration can be measured using a secondary ion mass spectrometer (SIMS).
(Measurement method of oxygen precipitate density)
(1) As a method for evaluating oxygen precipitates, a silicon wafer doped with boron and germanium of the present invention was prepared, and then heat treatment was performed at 800 ° C. for 4 hours in a nitrogen atmosphere, and then in an oxygen atmosphere. Heat treatment is performed at 1000 ° C. for 16 hours.
(2) The thermal oxide film formed by the evaluation heat treatment is removed with an etching solution of HF: H 2 O = 1: 1.
(3) The wafer is cleaved and the wafer is selectively etched using a Zirtor etchant (composition: HF: CrO 3 (5M) = 1: 1).
(4) Using an optical microscope with a magnification of 500 to 1000, the oxygen precipitates on the wafer cleavage plane are observed, and the number of oxygen precipitates per unit volume is measured.
In this evaluation method, when the number of oxygen precipitates exceeds 2.0 × 10 10 pieces / cm 3 , the formation density of the oxygen precipitates in the silicon wafer becomes excessive, the mechanical strength decreases, and the warpage of the wafer increases. There is a case.
In this evaluation method, the lower limit of the oxygen precipitate density (pieces / cm 3 ) is preferably 1.0 × 10 7 or more. If the oxygen precipitate density is less than this, formation of a Ge-oxygen-B complex that is inevitably formed in the silicon single crystal substrate and is considered to improve the mechanical strength of the silicon single crystal substrate is difficult to occur. Therefore, there is a case where a sufficient warp suppressing effect cannot be obtained.
(Measurement method of warpage)
A value obtained by measuring the height difference between the central portion and the outer peripheral portion of the wafer on the same surface in the thickness direction of the silicon wafer by the laser length measuring device is defined as a warp amount.

以下、本発明について実施例を挙げ、より詳細に説明する。
なお、本発明は、本実施例により何ら限定されるものでない。
EXAMPLES Hereinafter, an Example is given and this invention is demonstrated in detail.
In addition, this invention is not limited at all by this Example.

実施例1〜6
シリコン融液に、ボロン及びゲルマニウムをドープし、CZ法により6インチの<111>シリコン単結晶を成長させ、このシリコン単結晶から、ジルトルエッチングによって検出されるシリコンウェーハ内部の酸素析出物を1.0×10個/cm以上、かつ2.0×1010個/cm未満、さらにウェーハ中の酸素濃度(ASTM F−121 1979)を9×1017atoms/cm以上、かつ14×1017atoms/cm以下となる鏡面シリコンウェーハを、公知の加工方法によって厚さ625μmとして作製した。
Examples 1-6
Boron and germanium are doped into the silicon melt, and a 6-inch <111> silicon single crystal is grown by the CZ method. From this silicon single crystal, oxygen precipitates inside the silicon wafer detected by Zirtor etching are 1 0.0 × 10 7 pieces / cm 3 or more and less than 2.0 × 10 10 pieces / cm 3 , and the oxygen concentration (ASTM F-121 1979) in the wafer is 9 × 10 17 atoms / cm 3 or more and 14 A mirror silicon wafer having a thickness of ≦ 10 17 atoms / cm 3 or less was produced with a thickness of 625 μm by a known processing method.

ボロン及びゲルマニウムのドープ量を制御しながら種々変え、表1に示すボロン濃度及びゲルマニウム濃度に変えた以外同様にウェーハを準備し、それぞれ実施例1〜6とした。
各シリコンウェーハの鏡面側となる主面に、バッファー層としてAlN層を形成し、次に窒化物半導体層として、GaN層を有機金属気相成長法により高温下で成長させ、計4〜6μm程度の窒化物半導体層を形成させた。
成長後に室温まで降温し、主面に生じた反り量をレーザー測長器により測定した。
結果を表1に示す。
Various changes were made while controlling the doping amounts of boron and germanium, and wafers were prepared in the same manner except that the boron concentration and the germanium concentration shown in Table 1 were changed to Examples 1 to 6, respectively.
An AlN layer is formed as a buffer layer on the mirror surface of each silicon wafer, and then a GaN layer is grown as a nitride semiconductor layer at a high temperature by metal organic vapor phase epitaxy. The nitride semiconductor layer was formed.
After the growth, the temperature was lowered to room temperature, and the amount of warpage generated on the main surface was measured with a laser length meter.
The results are shown in Table 1.

比較例1〜6
ボロンとゲルマニウムの濃度を表1に示すものに変化させた比較用ウェーハを準備し、それぞれ比較例1〜6とした。各ウェーハについて実施例と同様にGaN層を形成した後、反りを評価した。結果を表1に示す。
Comparative Examples 1-6
Comparative wafers in which the concentrations of boron and germanium were changed to those shown in Table 1 were prepared and used as Comparative Examples 1 to 6, respectively. After forming a GaN layer for each wafer in the same manner as in the example, the warpage was evaluated. The results are shown in Table 1.

Figure 2012066943
Figure 2012066943

表1によれば、ボロン濃度が、4.0×1016atoms/cm未満、ゲルマニウム濃度が、2.5×1018atoms/cm未満、ボロン濃度[B]とゲルマニウム濃度[Ge]が、5[B]>[Ge]のいずれかの場合、ウェーハ主面に生じる反りが大きくなることがわかる。 According to Table 1, the boron concentration is less than 4.0 × 10 16 atoms / cm 3 , the germanium concentration is less than 2.5 × 10 18 atoms / cm 3 , and the boron concentration [B] and the germanium concentration [Ge] are It can be seen that in any of 5 [B]> [Ge], the warpage occurring on the main surface of the wafer increases.

また、ボロン濃度が、4.0×1019atoms/cm超、ゲルマニウム濃度が、2.5×1020atoms/cm超、ボロン濃度[B]とゲルマニウム濃度[Ge]が、8[B]<[Ge]のいずれかの場合においても、ウェーハ主面に生じる反りが同様に大きくなることがわかる。 The boron concentration is more than 4.0 × 10 19 atoms / cm 3 , the germanium concentration is more than 2.5 × 10 20 atoms / cm 3 , and the boron concentration [B] and the germanium concentration [Ge] are 8 [B ] <[Ge] It can be seen that the warpage generated on the main surface of the wafer is similarly increased.

ボロン濃度が、4.0×1016〜4.0×1019atoms/cm、かつゲルマニウム濃度が、2.5×1018〜2.5×1020atoms/cm、かつボロン濃度[B]とゲルマニウム濃度[Ge]が、5[B]≦[Ge]≦8[B]を満たす場合には、ウェーハ主面における反りが効果的に抑制され、優れた機械的強度、強いては反り抑制効果を有していることが確認された。 The boron concentration is 4.0 × 10 16 to 4.0 × 10 19 atoms / cm 3 , the germanium concentration is 2.5 × 10 18 to 2.5 × 10 20 atoms / cm 3 , and the boron concentration [B ] And the germanium concentration [Ge] satisfy 5 [B] ≦ [Ge] ≦ 8 [B], warpage on the wafer main surface is effectively suppressed, and excellent mechanical strength, and thus warpage suppression. It was confirmed to have an effect.

実験例1
濃度3.0×1018〜2.7×1019atoms/cmのボロンと、濃度1.5×1019〜2.2×1020atoms/cmのゲルマニウムについて、ボロン濃度[B]とゲルマニウム濃度[Ge]が、5[B]≦[Ge]≦8[B]を満たすようにドープし、CZ法により6インチの<111>シリコン単結晶を成長させた。
Experimental example 1
For boron with a concentration of 3.0 × 10 18 to 2.7 × 10 19 atoms / cm 3 and germanium with a concentration of 1.5 × 10 19 to 2.2 × 10 20 atoms / cm 3 , the boron concentration [B] A germanium concentration [Ge] was doped so as to satisfy 5 [B] ≦ [Ge] ≦ 8 [B], and a 6-inch <111> silicon single crystal was grown by the CZ method.

その際、シリコン単結晶を作製する際の酸素濃度を9×1017atoms/cm〜14×1017atoms/cmとしたもの、および14×1017atoms/cm超の酸素濃度で作製したものをそれぞれ準備した。 At that time, the oxygen concentration at the time of manufacturing the silicon single crystal is set to 9 × 10 17 atoms / cm 3 to 14 × 10 17 atoms / cm 3 , and the oxygen concentration is higher than 14 × 10 17 atoms / cm 3. Prepared each one.

これらのシリコン単結晶から、ジルトルエッチングによって検出されるシリコンウェーハ内部の酸素析出物密度が1.0×10個/cmから1.0×1011個/cmとなる鏡面シリコンウェーハが得られた。 From these silicon single crystals, a mirror-surface silicon wafer in which the density of oxygen precipitates inside the silicon wafer detected by Zirtor etching is 1.0 × 10 7 pieces / cm 3 to 1.0 × 10 11 pieces / cm 3 is obtained. Obtained.

公知の加工方法によって厚さ625μmのシリコンウェーハを作製し、各シリコンウェーハの鏡面側となる主面に、実施例1〜6と同様に窒化物半導体層を形成した後、反りを評価した。   A silicon wafer having a thickness of 625 μm was prepared by a known processing method, and a nitride semiconductor layer was formed on the main surface on the mirror surface side of each silicon wafer in the same manner as in Examples 1 to 6, and then warpage was evaluated.

図1は、シリコンウェーハ内部の酸素析出物密度と、GaN層形成後のウェーハ主面における反り量の関係を示すものである。
シリコン単結晶を作製する際の酸素濃度を9×1017atoms/cm〜14×1017atoms/cmで作製したウェーハ(図1中、○でプロットしたもの)は、反り量が少ない一方、14×1017atoms/cm超の酸素濃度で作製したもの(図1中、×でプロットしたもの)は相対的に反り量が著しく増加した。
FIG. 1 shows the relationship between the oxygen precipitate density inside a silicon wafer and the amount of warpage on the wafer main surface after the GaN layer is formed.
Wafers produced with a silicon single crystal having an oxygen concentration of 9 × 10 17 atoms / cm 3 to 14 × 10 17 atoms / cm 3 (plotted with a circle in FIG. 1) have a small amount of warpage. Those produced at an oxygen concentration of more than 14 × 10 17 atoms / cm 3 (plotted with x in FIG. 1) showed a significant increase in the amount of warpage.

それぞれのシリコンウェーハについて、窒素雰囲気中において800℃×4時間の熱処理を施し、その後、酸素雰囲気中において1000℃×16時間の熱処理を施した後、上記段落0027に示した評価方法にて酸素析出物密度を測定した酸素析出物密度と反り量には明らかに関係がみられ、GaN層形成後のウェーハ主面における反り量を抑制するためには、酸素析出物密度を2.0×1010個/cm未満に留めることが望ましいことがわかった。 Each silicon wafer was heat-treated at 800 ° C. for 4 hours in a nitrogen atmosphere, and then heat-treated at 1000 ° C. for 16 hours in an oxygen atmosphere, and then subjected to oxygen precipitation by the evaluation method shown in paragraph 0027 above. There is a clear relationship between the oxygen precipitate density measured for the object density and the amount of warpage. In order to suppress the amount of warpage on the main surface of the wafer after forming the GaN layer, the oxygen precipitate density is set to 2.0 × 10 10. It has been found desirable to stay below < 3 / cm 3 .

基板酸素析出物密度とGaN層形成後の反り量との関係を示した図。The figure which showed the relationship between a board | substrate oxygen precipitate density and the curvature amount after GaN layer formation.

本発明の窒化物半導体形成用基板は、窒化物半導体層を形成する際の、反りを低減し、クラックを抑制することができる。   The nitride semiconductor forming substrate of the present invention can reduce warpage and suppress cracks when forming a nitride semiconductor layer.

また本発明によれば、窒化物半導体形成用基板は厚膜の窒化物半導体層の形成が可能であり、窒化物系半導体からなる電子デバイスとして極めて有用である。   Further, according to the present invention, the nitride semiconductor forming substrate can form a thick nitride semiconductor layer, and is extremely useful as an electronic device made of a nitride-based semiconductor.

Claims (6)

窒化物半導体を形成するための半導体基板であって、
シリコン中に、ボロン及びゲルマニウムがドープされてなり、
ボロン及びゲルマニウムの濃度をそれぞれ[B]atoms/cm、[Ge]atoms/cmとしたときに、
以下の条件、
2.5×1018≦[Ge]≦2.5×1020
4.0×1016≦[B]≦4.0×1019
を満たすことを特徴とする窒化物半導体形成用基板。
A semiconductor substrate for forming a nitride semiconductor,
Boron and germanium are doped in silicon,
When the concentrations of boron and germanium are [B] atoms / cm 3 and [Ge] atoms / cm 3 , respectively.
The following conditions,
2.5 × 10 18 ≦ [Ge] ≦ 2.5 × 10 20 ,
4.0 × 10 16 ≦ [B] ≦ 4.0 × 10 19 ,
A nitride semiconductor forming substrate characterized in that:
さらに、5[B]≦[Ge]≦8[B]を満たすことを特徴とする請求項1に記載の窒化物半導体形成用基板。   The nitride semiconductor forming substrate according to claim 1, further satisfying 5 [B] ≦ [Ge] ≦ 8 [B]. 1.5×1019≦[Ge]≦2.2×1020
3.0×1018≦[B]≦2.7×1019
であることを特徴とする請求項2に記載の窒化物半導体形成用基板。
1.5 × 10 19 ≦ [Ge] ≦ 2.2 × 10 20 ,
3.0 × 10 18 ≦ [B] ≦ 2.7 × 10 19 ,
The substrate for forming a nitride semiconductor according to claim 2, wherein:
窒素雰囲気中において800℃×4時間の熱処理を施し、
その後、酸素雰囲気中において1000℃×16時間の熱処理を施した後、
ウェーハ内部の酸素析出物密度が1.0×10個/cm以上、かつ2.0×1010個/cm未満であることを特徴とする請求項1から請求項3のいずれかひとつに記載の窒化物半導体形成用基板。
Heat treatment at 800 ° C. for 4 hours in a nitrogen atmosphere,
Thereafter, after heat treatment at 1000 ° C. for 16 hours in an oxygen atmosphere,
The oxygen precipitate density inside the wafer is 1.0 × 10 7 pieces / cm 3 or more and less than 2.0 × 10 10 pieces / cm 3. The nitride semiconductor forming substrate according to 1.
ウェーハ中の酸素濃度(ASTM F−121 1979)が9×1017atoms/cm以上、かつ14×1017atoms/cm以下であることを特徴とする請求項1から請求項4のいずれかひとつに記載の窒化物半導体形成用基板。 5. The oxygen concentration (ASTM F-121 1979) in a wafer is 9 × 10 17 atoms / cm 3 or more and 14 × 10 17 atoms / cm 3 or less. The substrate for forming a nitride semiconductor according to one. 請求項1から請求項5のいずれかひとつに記載の半導体形成用基板上に、窒化物半導体薄膜を形成してなることを特徴とする窒化物半導体。   A nitride semiconductor, comprising a nitride semiconductor thin film formed on the semiconductor forming substrate according to claim 1.
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