JP2006232563A - METHOD FOR SYNTHESIZING n-TYPE SEMICONDUCTOR DIAMOND THIN FILM - Google Patents
METHOD FOR SYNTHESIZING n-TYPE SEMICONDUCTOR DIAMOND THIN FILM Download PDFInfo
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本発明は、ＣＶＤ法による欠陥のないダイヤモンド合成法に関する。詳しくは、これまで困難であったｎ型半導体ダイヤモンド薄膜の合成法に関する。さらに詳しくは、リンドープによるｎ型ダイヤモンド薄膜の合成法に関する。さらにまた、詳しくは、リンドープｎ型ダイヤモンド薄膜の合成において、不要な欠陥の生成を抑制することで、電気的特性、光学的特性を向上させ、電子放出素子、紫外線ディテクター、紫外線発光素子、高速ハイパワートランジスタ等、エレクトロニクス分野において利用が期待されるｎ型半導体薄膜の合成法に関する。 The present invention relates to a defect-free diamond synthesis method by CVD. Specifically, the present invention relates to a method for synthesizing an n-type semiconductor diamond thin film, which has been difficult until now. More specifically, the present invention relates to a method for synthesizing an n-type diamond thin film by phosphorus doping. More specifically, in the synthesis of a phosphorus-doped n-type diamond thin film, generation of unnecessary defects is suppressed to improve electrical characteristics and optical characteristics, and electron emission elements, ultraviolet detectors, ultraviolet light emitting elements, high-speed high-speed The present invention relates to a method for synthesizing an n-type semiconductor thin film expected to be used in the field of electronics such as a power transistor.
ダイヤモンドは、古くから宝石としての価値は勿論、高い硬度、高い熱伝導、速い音速といった他の材料にはない数々の特性を有し、この特性を利用して様々な分野に使用されてきた。近年では、ダイヤモンドの電気的、半導体特性に注目が集まっている。ダイヤモンドは、５．５ｅＶと広いバンドギャップをもつワイドギャップ半導体として知られていることから、シリコン半導体に代わる次世代型半導体としての利用が期待されている。高い破壊電界や電子・正孔の高い移動度はＳｉと比べて極めて優れ、シリコン半導体と並ぶ汎用性デバイスとしては勿論、宇宙環境等極限環境での高速・パワーデバイスとしての機能を発揮し、その面での開発が進むものと期待されている。また、広いバンドギャップに対応した紫外線発光素子として利用研究も盛んになされ、すでに強い励起子発光に成功したとの報告も寄せられている（非特許文献１）。 Diamonds have long been used in various fields by utilizing these properties, as well as other properties such as high hardness, high heat conduction, and fast sound speed, as well as gem value. In recent years, attention has been focused on the electrical and semiconductor properties of diamond. Since diamond is known as a wide gap semiconductor having a wide band gap of 5.5 eV, it is expected to be used as a next-generation semiconductor that replaces a silicon semiconductor. High breakdown electric field and high mobility of electrons and holes are extremely superior to Si, and as a versatile device along with silicon semiconductors, it functions as a high-speed and power device in extreme environments such as the space environment. It is expected that development in terms of development will proceed. In addition, research on use as an ultraviolet light-emitting device corresponding to a wide band gap has been actively conducted, and it has been reported that strong exciton light emission has already been achieved (Non-patent Document 1).
何れにしても、今後、ハイパワーデバイスを含めた各種電子デバイスとして利用するにおいては、ｐ型、ｎ型導電性の実現が必須である。通常、ダイヤモンドは、ｐ型特性を有するものについてはすでに天然にも産していることが確認されており、また、ホウ素をドープすることによって容易に合成し、入手する合成方法も確立されている。しかし、ｎ型導電性のダイヤモンドについては、天然には存在が確認されておらず、合成することも非常に困難であった。 In any case, p-type and n-type conductivity must be realized for future use as various electronic devices including high-power devices. In general, it has been confirmed that diamond having p-type characteristics has already been naturally produced, and a synthesis method for easily synthesizing and obtaining boron by doping with boron has been established. . However, the existence of n-type conductive diamond has not been confirmed in nature, and it has been very difficult to synthesize it.
１９８０年代にＣＶＤ法によるダイヤモンドの合成実験に成功したとの報告がなされて以来、この報告を契機にＣＶＤ法によるダイヤモンドの各種応用研究が一段と盛んになり、その中にはｎ型ダイヤモンドを得る研究も行われてきた。しかしながら、近年になるまでｎ型ダイヤモンドの合成については、決定的な成果を得ることができなかった。このような状況の中で、１９９７年、本発明者らの属している独立行政法人物質・材料研究所の前身である無機材料研究所において、プラズマＣＶＤ法によるダイヤモンドの合成において、リンをドープすることにより、ｎ型ダイヤモンドを得ることに初めて成功し、その成果を特許出願（特許文献１参照）し、論文にも発表した（非特許文献２）。この成功によって、ｎ型特性の実現可能性については一応の目途がつけられ、これを契機にｎ型ダイヤモンドに関する特許出願がいくつかなされている。 Since it was reported in the 1980s that a diamond synthesis experiment was successful by CVD, various reports on the application of diamond by CVD have become more active, and research into obtaining n-type diamonds has been included. Has also been done. However, until recently, definitive results have not been obtained for the synthesis of n-type diamond. Under such circumstances, in 1997, the inorganic material research institute, which is the predecessor of the National Institute for Materials Science, to which the present inventors belong, was doped with phosphorus in the synthesis of diamond by the plasma CVD method. As a result, we succeeded in obtaining n-type diamond for the first time, and applied for a patent (see Patent Document 1) and published it in a paper (Non-Patent Document 2). With this success, the feasibility of n-type characteristics has been temporarily set, and several patent applications relating to n-type diamond have been filed.
すなわち、ダイヤモンド半導体中に、Ｓｅ、Ｓ、Ｂｒ、Ｉなどの炭素原子より電気陰性度が大きく、且つイオン化ポテンシャルが炭素原子同士の単結合のそれ（１３．８３１ｅＶ）以下で、５価以上の原子をドナー原子として添加することによってｎ型ダイヤモンドを合成する手法（特許文献２）、あるいは、気相成長法、スパッタリング法によりダイヤモンドを合成させる際に、ｎ型ドーパントであるＮ、Ｐ、またはＡｓとｐ型ドーパントであるＨを同時にドーピングすることにより結晶中にドナー・アクセプター対を形成させて低抵抗のｎ型ダイヤモンドを合成する手法（特許文献３）、さらに、30Ｓｉ含有ダイヤモンドに中性子を照射し、30Ｓｉ（ｎ，γ）31Ｓｉ→31Ｐの核変換反応によりダイヤモンド
中にＰを含有させることによって、ｎ型ダイヤモンドを合成する手法（特許文献４）が提案されている。
That is, in a diamond semiconductor, an atom having a higher electronegativity than that of carbon atoms such as Se, S, Br, and I, and having an ionization potential of not more than that of a single bond between carbon atoms (13.831 eV) and having a valence of 5 or more. N-type diamond is synthesized by adding n as a donor atom (Patent Document 2), or when synthesizing diamond by a vapor phase growth method or a sputtering method, N-type dopants N, P, or As and A method of synthesizing a low-resistance n-type diamond by simultaneously forming a p-type dopant H to form a donor-acceptor pair in the crystal (Patent Document 3), and further irradiating 30 Si-containing diamond with neutrons , to be contained P to diamond by 30 Si (n, γ) transmutation reaction 31 Si → 31 P Te, a technique for synthesizing an n-type diamond (Patent Document 4) have been proposed.
さらにまた、炭素源からのＣＶＤ法により形成されたｐ型ダイヤモンド薄膜を不活性ガスに曝すことで低抵抗のｎ型電気伝導性を有するｎ型ダイヤモンド半導体に変換する手法による提案（特許文献５）もされている。 Furthermore, a proposal based on a technique of converting a p-type diamond thin film formed by a CVD method from a carbon source into an n-type diamond semiconductor having low resistance n-type conductivity by exposing it to an inert gas (Patent Document 5). It has also been.
以上述べたｎ型半導体ダイヤモンドの合成手法の中には、興味を引く、重要な示唆に富んだ提案もあるが、その何れもＣＶＤ成長段階でのｎ型特性の発現を阻む要因について本質的に解明するには程遠く、結晶成長段階での不要な欠陥の基本的抑制と、この欠陥に起因する電気的、光学的特性の低下を抑制する手法の確立には遠いものであった。そのため、現在に至るも、ｎ型特性を十分に有してなるものを安定して、得ることは困難な状況にある。 Among the n-type semiconductor diamond synthesis methods described above, there are interesting and important suggestion proposals, all of which are essentially related to the factors that hinder the development of n-type characteristics at the CVD growth stage. It was far from elucidating, and it was far from establishing a basic method for suppressing unnecessary defects at the crystal growth stage and a method for suppressing deterioration of electrical and optical characteristics caused by these defects. Therefore, until now, it is difficult to stably obtain a product having sufficient n-type characteristics.
本発明は、このような状況に鑑み、ＣＶＤ法による欠陥のないダイヤモンドの合成方法を提供しようというものである。とりわけ、ｎ型特性が確実に向上したダイヤモンドの合成方法を提供しようというものである。すなわち、本発明の目的は、プラズマＣＶＤ法によるダイヤモンド、特にリンをドープしたｎ型ダイヤモンド薄膜の合成において、不要な欠陥の生成を抑制し、これによって、リンドープｎ型ダイヤモンド薄膜の電気的特性、光学的特性の向上を図ろうと言うものである。 In view of such circumstances, the present invention intends to provide a method for synthesizing diamond free from defects by the CVD method. In particular, the object is to provide a method for synthesizing diamond with improved n-type characteristics. That is, the object of the present invention is to suppress the generation of unnecessary defects in the synthesis of diamond, particularly phosphorus-doped n-type diamond thin films by plasma CVD, thereby reducing the electrical characteristics and optical properties of phosphorus-doped n-type diamond thin films. It aims to improve the physical characteristics.
そのため本発明者らにおいては、プラズマＣＶＤ法によるダイヤモンド合成、特に、リンをドープするｎ型ダイヤモンド薄膜の合成法を検討し、合成条件と欠陥との関係について仔細に検討した結果、前記欠陥は、薄膜を生成させる基板材料に大きく依存し、支配されているとの知見を得た。すなわち、先行技術によるダイヤモンドの合成においては、基板材料はダイヤモンドを機械研磨によって、特定方位の表面を高精度に平滑に処理し、その後、酸洗処理、純水にてリンスして付着物を取り除き、薄膜生成面を清浄にしてその上にダイヤモンドをエピタキシャル成長させ、ダイヤモンド薄膜を得ているが、こうして得られた薄膜をカソードルミネッセンス法でその表面の状態を観察すると、バンドＡという転位に関係した欠陥が試料の相当数において生じていることが確認された。この観察によって、機械研磨による平滑処理では結果的に欠陥を誘発する、例えば、表面キズだけではなく、表面からの観察では、特定し得ない内部的キズをも含めた欠陥誘発要因を表面近傍に残し、これがダイヤモンド結晶に欠陥を生成させる原因の一つになっていると考え、機械研磨に代わる方法として酸、アルカリ等各種化学的表面処理を試みた。 Therefore, in the present inventors, as a result of examining diamond synthesis by plasma CVD method, in particular, a synthesis method of n-type diamond thin film doped with phosphorus, and carefully examining the relationship between synthesis conditions and defects, the defects are: We obtained the knowledge that it is largely dependent on and governed by the substrate material that produces the thin film. In other words, in the synthesis of diamond according to the prior art, the substrate material is processed by smoothing the surface of a specific orientation with high precision by mechanical polishing of the diamond, and then rinsed with pickling and pure water to remove deposits. The thin film formation surface was cleaned and diamond was epitaxially grown thereon to obtain a diamond thin film. When the surface state of the thin film thus obtained was observed by the cathodoluminescence method, defects related to dislocations called band A were obtained. Was observed in a considerable number of samples. This observation results in defects caused by smoothing by mechanical polishing.For example, not only surface flaws, but also surface flaws, including internal flaws that cannot be identified by observation from the surface. Remainingly, this is considered to be one of the causes for generating defects in the diamond crystal, and various chemical surface treatments such as acid and alkali were tried as an alternative to mechanical polishing.
その結果、溶液に浸漬する表面処理法ではさほどの効果は確認されなかった。これに対して、ダイヤモンド基板を各種気体、例えば酸素、水素等雰囲気ガスの存在下で試料表面に高周波プアズマを照射する反応性イオンエッチングを施してなるものが、ＣＶＤ法によるダイヤモンド成長基板材料として好ましいことを知見した。特に、リンをドープするｎ型ダイヤモンド薄膜の合成方法において顕著な作用効果が奏せられ、この反応性エッチングしたダイヤモンドを基板として使用することによって、この基板上に生成したダイヤモンド薄膜結晶は、欠陥が抑制され、ｎ型半導体特性、光学特性が向上したダイヤモンド薄膜が得られる等の顕著な作用効果が奏せられることを見出したものである。本発明は、この知見に基づいてなされたものであり、その構成は、以下、（１）〜（５）に記載の通りである。
（１） プラズマＣＶＤ法によるダイヤモンド薄膜の合成方法において、ダイヤモンド基板を反応性イオンによってエッチング処理し、この処理面に炭素源を含む原料ガスを供給し、プラズマにより原料ガスを分解・析出するＣＶＤ法により欠陥のない高品質ダイヤモンド薄膜を生成させることを特徴とする、ダイヤモンド薄膜の合成方法。
（２） 前記炭素源を含む原料ガスにはｎ型ドープ元素を添加し、得られる欠陥のない高品質ダイヤモンド薄膜がｎ型特性を有するダイヤモンド薄膜である、（１）記載のダイヤモンド薄膜の合成方法。
（３） 前記ｎ型ドープ元素がリンである、（２）記載のダイヤモンド薄膜の合成方法。（４） 前記反応性イオンが、酸素、水素、ハロゲンガス、または、ハロゲンを含む反応性ガスの１種または２種以上のガスによるイオンである、（１）ないし（３）の何れか１項に記載のダイヤモンド薄膜の合成方法。
（５） 前記エッチング処理し、ダイヤモンド薄膜が生成させるダイヤモンド基板面が｛１１１｝面である、（１）ないし（４）の何れか１項に記載のダイヤモンド薄膜の合成方法。
As a result, a significant effect was not confirmed by the surface treatment method immersed in the solution. On the other hand, it is preferable as a diamond growth substrate material by CVD that a diamond substrate is subjected to reactive ion etching in which a sample surface is irradiated with high-frequency plasma in the presence of various gases such as oxygen, hydrogen and the like. I found out. In particular, the method for synthesizing an n-type diamond thin film doped with phosphorus has a remarkable effect. By using this reactive etched diamond as a substrate, the diamond thin film crystal formed on this substrate has defects. It has been found that remarkable effects such as obtaining a diamond thin film with suppressed n-type semiconductor characteristics and optical characteristics can be obtained. This invention is made | formed based on this knowledge, and the structure is as following (1)-(5).
(1) In a method of synthesizing a diamond thin film by plasma CVD, a diamond substrate is etched by reactive ions, a source gas containing a carbon source is supplied to the treated surface, and the source gas is decomposed and deposited by plasma. A method for synthesizing a diamond thin film characterized in that a high-quality diamond thin film having no defects is produced by the above-described method.
(2) The method for synthesizing a diamond thin film according to (1), wherein an n-type doping element is added to the source gas containing the carbon source, and the resulting defect-free high-quality diamond thin film is a diamond thin film having n-type characteristics. .
(3) The method for synthesizing a diamond thin film according to (2), wherein the n-type doping element is phosphorus. (4) The reactive ion according to any one of (1) to (3), wherein the reactive ion is an ion of one or more kinds of oxygen, hydrogen, halogen gas, or a reactive gas containing halogen. A method for synthesizing a diamond thin film according to 1.
(5) The method for synthesizing a diamond thin film according to any one of (1) to (4), wherein a diamond substrate surface that is etched to generate a diamond thin film is a {111} plane.
本発明は、ＣＶＤ法によるリンをドープするダイヤモンド薄膜の合成方法において、使用するダイヤモンド基板を反応性イオンエッチング処理することにより、欠陥のない高品質のダイヤモンド薄膜を安定して得ることができるという、優れた効果が奏せられる。特に、ｎ型ダイヤモンド薄膜を狙いとする場合、本発明は、良好なｎ型特性を発現する薄膜を、再現性を以って提供することができる極めて優れた格別の特有な作用効果が期待でき、これによって、今後、ダイヤモンドの半導体特性、電気的特性、光学的特性を利用した各種デバイス設計、電子放出素子、紫外線発光素子、高周波ハイパワートランジスタなどへの利用が急速に進むものと期待される。 In the method of synthesizing a phosphorous-doped diamond thin film by CVD, the present invention can stably obtain a high-quality diamond thin film having no defects by subjecting the diamond substrate to be used to reactive ion etching. Excellent effect is achieved. In particular, when aiming at an n-type diamond thin film, the present invention can be expected to have a very excellent special effect that can provide a thin film exhibiting good n-type characteristics with reproducibility. As a result, it is expected that the device will be rapidly used in various device designs, electron-emitting devices, ultraviolet light-emitting devices, high-frequency high-power transistors, etc. that utilize the semiconductor properties, electrical properties, and optical properties of diamond. .
以下、図面及び実験を基礎にした実施例にもとづいて本発明を具体的に説明する。ただしこれらの実施例は、本発明のあくまでも一つの実施例を開示するものにすぎず、本発明はこの実施例によって限定されるものではない。 Hereinafter, the present invention will be described in detail based on examples based on the drawings and experiments. However, these examples merely disclose one example of the present invention, and the present invention is not limited to this example.
本発明は、以下に示す下地表面処理の効果を確かめる１から５の実験に基づいて具体的に説明し、これによって実施例とする。その概要は、ダイヤモンド基板を用い、このダイヤモンド基板を次に記載する各工程に供し、１から５の順番によって処理し、使用し、あるいは評価した。
１．反応性イオンエッチング（ＲＩＥ）による表面改質処理工程
２．熱混酸処理による汚染除去工程
３．リンドープダイヤモンド薄膜気相成長工程
４．カソードルミネッセンス評価試験
５．半導体特性評価試験
The present invention will be specifically described on the basis of experiments 1 to 5 for confirming the effects of the substrate surface treatment described below. The outline was that a diamond substrate was used, and this diamond substrate was subjected to each step described below, and processed, used or evaluated in the order of 1 to 5.
1. 1. Surface modification treatment step by reactive ion etching (RIE) 2. Decontamination process by hot mixed acid treatment 3. Phosphorus-doped diamond thin film vapor phase growth step 4. Cathodoluminescence evaluation test Semiconductor characteristic evaluation test
１．反応性イオンエッチング（ＲＩＥ）による表面改質処理工程
先ず、高周波プラズマを用いた反応性イオンエッチング（ＲＩＥ）により高圧合成単結晶ダイヤモンドの｛１１１｝研磨面を処理した。用いた反応ガスは、（ａ）酸素、（ｂ）水素、（ｃ）酸素およびＣＦ4混合ガスでそれぞれ行った。実験条件は表１に示すとおり
である。それ以外にも、Ａｒを使用したが、表面の改質に結びつく結果を得ることができなかった。ハロゲンガスも炭素と反応しうることから、本発明を実施するのに有効なガスであるが、装置の材質をいためること、扱いに慎重な取り扱いが必要である、といった点で好ましいとは言えず、上記表１に記載するガスが、好ましいガスとして挙げられる。エッチング深さは、処理時間によって調整した。この表面改質処理条件と、エッチング深さを表１にまとめて示す。その結果、（ａ）〜（ｃ）の何れの条件の場合においても表面粗さは、反応性イオンエッチング前と後とでは変わらなかった。
1. Surface modification treatment step by reactive ion etching (RIE) First, the {111} polished surface of high-pressure synthetic single crystal diamond was treated by reactive ion etching (RIE) using high-frequency plasma. The reaction gases used were (a) oxygen, (b) hydrogen, (c) oxygen and CF 4 mixed gas. The experimental conditions are as shown in Table 1. In addition to that, Ar was used, but a result related to surface modification could not be obtained. Since halogen gas can also react with carbon, it is an effective gas for carrying out the present invention. However, it cannot be said that it is preferable in that the material of the apparatus is distorted and handling with care is required. The gases listed in Table 1 are listed as preferred gases. The etching depth was adjusted according to the processing time. The surface modification treatment conditions and the etching depth are summarized in Table 1. As a result, the surface roughness did not change before and after the reactive ion etching under any of the conditions (a) to (c).
２．熱混酸処理による汚染除去工程
反応性イオンエッチング処理後、すべての試料は金属および有機物による汚染を除去するために熱混酸処理された。熱混酸はＨＮＯ3＋Ｈ2ＳＯ4またはＮａＣｌＯ3＋ＨＮＯ3で
ある。処理温度は２００℃、処理時間は３０分から２時間処理した。
2. Decontamination process by hot mixed acid treatment After reactive ion etching, all samples were hot mixed acid treated to remove contamination by metals and organics. The hot mixed acid is HNO 3 + H 2 SO 4 or NaClO 3 + HNO 3 . The treatment temperature was 200 ° C., and the treatment time was 30 minutes to 2 hours.
３．リンドープダイヤモンド薄膜気相成長（ＣＶＤ）工程
処理試料表面および未処理表面に同一条件でリンドープダイヤモンド薄膜を成長させ、比較した。用いた方法はマイクロ波プラズマＣＶＤである。合成実験は、表２に示す条件で行った。ＣＶＤ実験の際は必ずＲＩＥ処理下地および未処理下地に同時にダイヤモンド成長を行い、この処理による効果を明確にした。
４．カソードルミネッセンス評価試験
カソードルミネッセンスによる特性評価は、トプコン製３５０型走査型電子顕微鏡にフォトンデザイン製分光器を接続した装置を用いて行った。試料は室温および−１９０℃に冷却した。
２０ｋＶ、４０ｎＡの電子ビームを試料に照射し、発生したルミネッセンス光を凹面鏡で集光し、分光器にて分光して、発光分布、発光スペクトルを記録した。
その結果の一例を図１、２に示すが、上記３種類のＲＩＥでは違いが、観測されず、ほぼ同一の結果が得られた。これに対して、ＲＩＥ処理しない試料（ａ）とＲＩＥ処理した試料（ｂ）とでは顕著な違いが観測された。すなわち、ＲＩＥ処理しない試料（ａ）では、明るい筋が無数に観測された（図１（ａ））。この筋はバンドＡとよばれる欠陥の発光であり、機械研磨基板表面に欠陥を誘発するキズのような要因が存在することを暗に示しているに対し、ＲＩＥ処理した試料（ｂ）においては、このような欠陥に起因する筋は消えていることが観測された（図１（ｂ））。すなわち、基板をイオンエッチングすることで、バンドＡに基づく欠陥を発生させる原因となる要因、例えば研磨傷が除去される、と言うことがいえる。図の中に明るさの違うゾーンがみられるが、これは基板自身の発光強度の不均一性によるもので、ダイヤモンド薄膜自身の特性とは無関係である。さらにまた、これを発光スペクトルで調査すると、ＲＩＥ処理しない試料（ａ）と酸素によるＲＩＥ処理した試料（ｂ）とを比べると、励起子発光ピークを基準にして、エッチング処理した方はバンドＡ発光が小さくなっていることがわかる。これによっても、イオンエッチングすることで、バンドＡに基づく欠陥を解消ないし、抑制する効果があることが理解される。
4). Cathodoluminescence evaluation test The characteristic evaluation by cathodoluminescence was carried out using an apparatus in which a photon design spectrometer was connected to a Topcon 350 type scanning electron microscope. The sample was cooled to room temperature and -190 ° C.
The sample was irradiated with an electron beam of 20 kV and 40 nA, and the generated luminescence light was collected with a concave mirror and dispersed with a spectroscope to record the emission distribution and emission spectrum.
An example of the results is shown in FIGS. 1 and 2, but no difference was observed in the above three types of RIE, and almost the same results were obtained. On the other hand, a remarkable difference was observed between the sample (a) not subjected to RIE treatment and the sample (b) subjected to RIE treatment. That is, countless bright streaks were observed in the sample (a) not subjected to the RIE treatment (FIG. 1 (a)). This streak is the light emission of a defect called band A, which implies that there is a flaw-like factor that induces a defect on the surface of the mechanically polished substrate, whereas in the RIE-treated sample (b) It was observed that the streaks due to such defects disappeared (FIG. 1 (b)). In other words, it can be said that by causing the substrate to be ion-etched, a factor that causes a defect based on the band A, such as a polishing flaw, is removed. There are zones with different brightness in the figure, but this is due to the non-uniformity of the emission intensity of the substrate itself and is not related to the properties of the diamond thin film itself. Furthermore, when this is examined with an emission spectrum, when the sample (a) not subjected to RIE treatment and the sample (b) subjected to RIE treatment with oxygen are compared, the one subjected to the etching treatment based on the exciton emission peak is the band A emission. It can be seen that is smaller. Also by this, it is understood that the ion etching has an effect of eliminating or suppressing the defect based on the band A.
５．半導体特性評価試験
ホール効果測定により各種ＲＩＥ処理下地および未処理下地表面に成長したリンドープダイヤモンド薄膜の電気特性を評価した。測定には東陽テクニカＡＣ磁場ホール効果測定装置（ＲｅｓｉＴｅｓｔ８３１０）を用い、室温から６００℃の温度範囲で比抵抗、ホール係数の測定を行い、電気伝導度、電子濃度、電子移動度の温度依存性を詳細に評価した。酸素を用いたＲＩＥで２００ｎｍエッチングした試料においてＣＶＤ成長によるリンドープ薄膜は電子移動度の向上、電気伝導度の向上が確認された。ＲＩＥを行わない基板を用いた場合に比べて、移動度は１．６倍、電気伝導率は２．５〜６倍程度増大した。水素および混合ガス（酸素＋ＣＦ4）でのＲＩＥでも同様の結果が得られた。
5. Semiconductor characteristic evaluation test The electrical characteristics of phosphorus-doped diamond thin films grown on various RIE-treated and untreated foundation surfaces were evaluated by Hall effect measurement. For measurement, Toyo Technica AC magnetic field Hall effect measuring device (ResiTest 8310) is used to measure the specific resistance and Hall coefficient in the temperature range from room temperature to 600 ° C, and the temperature dependence of electric conductivity, electron concentration and electron mobility is measured. Detailed evaluation. In a sample etched by 200 nm by RIE using oxygen, it was confirmed that the phosphorus-doped thin film formed by CVD growth has improved electron mobility and electrical conductivity. Compared with the case where a substrate without RIE was used, the mobility increased by 1.6 times and the electrical conductivity increased by 2.5 to 6 times. Similar results were obtained by RIE with hydrogen and mixed gas (oxygen + CF 4 ).
以上の結果を総合すると、表１に記載した３種類の反応ガスの種類、処理時間、処理深度の違いによっては、基板の表面荒さ自体は、原子間力電子顕微鏡（ＡＦＭ）による観察
（図示外）によっても基本的な違いは観測されなかった。しかし、その上に成長したダイヤモンド薄膜には、欠陥の有無等に違い現れ、ＲＩＥ処理したものがＲＩＥ処理しないものに比し、品質向上に格段の違いがあることが認められた。
To summarize the above results, the surface roughness of the substrate itself can be observed with an atomic force electron microscope (AFM) (not shown) depending on the types of reaction gases described in Table 1, the processing time, and the processing depth. ), No fundamental difference was observed. However, the diamond thin film grown thereon appeared different depending on the presence or absence of defects, and it was recognized that the RIE-treated one had a marked improvement in quality compared to the one not subjected to RIE.
これらのことから、反応性イオンエッチング（ＲＩＥ）処理は見かけの表面荒さには影響しないが、ダイヤモンド薄膜に欠陥を生じさせる要因となる、例えば、基板の傷を除去する効果があり、これによって、従来の機械研磨した場合では奏し得なかった欠陥抑制効果が発現され、ＣＶＤ法によるダイヤモンド合成、特に、ｎ型特性に優れたダイヤモンド薄膜を合成するにおいては、再現性よく安定して得ることができる、という特有且つ格別の作用効果を奏しうるものと考えられる。 From these facts, reactive ion etching (RIE) treatment does not affect the apparent surface roughness, but has the effect of removing scratches on the substrate, for example, which cause defects in the diamond thin film, Defect suppression effect that could not be achieved by conventional mechanical polishing is expressed, and can be stably obtained with high reproducibility when synthesizing diamond by CVD method, particularly when synthesizing a diamond thin film having excellent n-type characteristics. It is thought that it is possible to produce a unique and special effect.
以上の各種工程、試験による実施例ではリンを添加したｎ型ダイヤモンドを得ることに力点をおき、これまで困難であったｎ型ダイヤモンドを容易に合成しうることを具体的に示したが、本発明は、ｎ型に限定されることはない。すなわち、ＣＶＤ法により欠陥のないダイヤモンドを合成しようとするにおいて有効に作用し、寄与するものであることは勿論である。 In the above examples of various processes and tests, emphasis was put on obtaining n-type diamond to which phosphorus was added, and it was specifically shown that it was possible to easily synthesize n-type diamond, which was difficult until now. The invention is not limited to n-type. That is, of course, it acts effectively and contributes in trying to synthesize diamond having no defects by the CVD method.
以上に説明したように、本発明によって、欠陥のないダイヤモンド、典型的にはこれまで困難であったｎ型ダイヤモンド薄膜を簡単に得ることができるようになった。その意義は極めて大である。すなわち、本発明は、ダイヤモンドの有効性、利用価値を高めたというだけではなく、今後、宇宙空間のような厳しい環境下での使用に耐えられるハイパワー、高速デバイス設計が求められ場合、低欠陥のｎ型半導体特性を有するダイヤモンド薄膜を提供することが可能となったことで、前述したニーズにも応えられ、ニーズを実現することが一気に可能となること、現実化しうることを意味し、その意義はきわめて大きい。今後は、Ｓｉ半導体に代わる、あるいは補填する、一層効果的なデバイス設計が可能となり、広く利用され、産業の発展に寄与するものと確信する。 As described above, the present invention makes it possible to easily obtain a defect-free diamond, typically an n-type diamond thin film that has been difficult until now. The significance is extremely great. In other words, the present invention not only increases the effectiveness and utility value of diamond, but also requires low-defects when high-power, high-speed device design that can withstand use in harsh environments such as outer space is required in the future. By providing a diamond thin film having n-type semiconductor characteristics, it is possible to meet the above-mentioned needs and to realize the needs all at once, which means that it can be realized. Significance is enormous. In the future, it will be possible to design more effective devices that can replace or supplement Si semiconductors, and will be widely used and contribute to industrial development.
Claims (5)
The method for synthesizing a diamond thin film according to any one of claims 1 to 4, wherein a diamond substrate surface that is etched to produce a diamond thin film is a {111} plane.
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| JPH1081587A (en) * | 1996-09-03 | 1998-03-31 | Natl Inst For Res In Inorg Mater | Synthesis of phosphorus-doped diamond |
| JP2003277183A (en) * | 2002-03-22 | 2003-10-02 | Sumitomo Electric Ind Ltd | Method for producing diamond single crystal, diamond single crystal substrate, and method for producing the same |
| WO2003106743A1 (en) * | 2002-06-01 | 2003-12-24 | 住友電気工業株式会社 | N-type semiconductor diamond producing method and semiconductor diamond |
| JP2005263592A (en) * | 2004-03-22 | 2005-09-29 | Sumitomo Electric Ind Ltd | Diamond single crystal substrate |
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| JPH1081587A (en) * | 1996-09-03 | 1998-03-31 | Natl Inst For Res In Inorg Mater | Synthesis of phosphorus-doped diamond |
| JP2003277183A (en) * | 2002-03-22 | 2003-10-02 | Sumitomo Electric Ind Ltd | Method for producing diamond single crystal, diamond single crystal substrate, and method for producing the same |
| WO2003106743A1 (en) * | 2002-06-01 | 2003-12-24 | 住友電気工業株式会社 | N-type semiconductor diamond producing method and semiconductor diamond |
| JP2005263592A (en) * | 2004-03-22 | 2005-09-29 | Sumitomo Electric Ind Ltd | Diamond single crystal substrate |
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