成果報告書詳細
管理番号20100000002201
タイトル*平成20年度中間年報 エネルギー使用合理化技術戦略的開発/エネルギー有効利用基盤技術先導研究開発/大口径NTDーSi半導体の均一照射技術に関する研究
公開日2010/11/10
報告書年度2008 - 2008
委託先名独立行政法人日本原子力研究開発機構
プロジェクト番号P03033
部署名省エネルギー技術開発部
和文要約和文要約等以下本編抜粋:1. 研究開発の内容及び成果等
 原子炉における半導体製造方法は中性子核変換ドーピング(Neutron Transmutation Doping:NTD)法と呼ばれており、この方法は天然のシリコン中の30Si(天然存在比:3.05%)に中性子を照射することによって、30Siをリン(31P)に核変換し、シリコン中にリンを均一に添加(ドープ)するものである。高耐圧の絶縁ゲートバイポーラトランジスタ(IGBT:Insulated Gate Bipolar Transistor)では、抵抗率の均一性が重要であり、NTD-Siが使用されている。製造コスト低減のためにウェーハサイズの大口径化を進めると、高い均一性を有するNTD-Siでも次第に面内抵抗率の均一性の低下を引き起こす。したがって、我々は高耐圧IGBTに対応するため、12インチ径ウェーハの面内抵抗率の非均一性を改善する中性子照射技術の確立を目指す。本研究では、まず、中性子輸送計算モンテカルロ計算コードを用いて12インチ径のNTD-Siの径方向中性子束分布を改善する照射条件を解析的に見出し、この条件を実現するための照射実験装置を開発し、中出力研究用原子炉JRR-4(東海村、3.5MW)で12 インチ径シリコンの照射実験を行う。これによって、照射装置の設計手法の妥当性を確証する。次に、この設計手法を用いて、国内の高出力研究用原子炉JRR-3(東海村、20MW)への12インチ径の照射装置の導入を検討し、JRR-3の改造計画を取りまとめる。さらに、本格的なNTD-Si需要を支えるために産業用シリコン照射炉の炉心設計及びその事業性について検討する。以下、平成20年度の活動で得られた研究成果を報告する。
英文要約Title: Study of Uniform Irradiation Technique for Large-Diameter NTD-Si (FY2007-FY2009) FY2008 Annual Report
A Neutron Transmutation Doped Silicon (NTD-Si) semiconductor promotes cost reduction effect of an Insulated Gate Bipolar Transistor (IGBT). The market of IGBT will be more and more expanded to high hybrid cars, electric cars and fuel battery cars that can save the energy, because the IGBT require the high-grade substrate silicon doped by neutron. Hence, it is important to improve neutron uniform irradiation technology for the large size silicon up to 12 inches diameter. In this development program, an irradiation experimental equipment is designed by surveying analytically irradiation conditions to improve the neutron flux distribution in the radial direction for 12 inches NTD-Si with using a neutron transportation calculation code, and irradiation experiments will be carried out in JRR-4 by 2010. Thus the validity of the design technique of the irradiation equipment will be confirmed by the experiments. The fabrication of the equipment was finished in March 2009, and then the equipment will be installed in JRR-4 reactor pool by July 2009. In the experiments, a 12 inches silicon ingot of 60cm in height is irradiated in a graphite reflector. The ingot is rotated during irradiation in order to maintain the condition of uniformly distributed thermal neutron flux. The most suitable uniform irradiation condition for the equipment was obtained with MCNP-5 code. The condition was achieved by a pass-through method that the silicon ingot covered by the thermal neutron filter was moved up and down with whirling motion. The condition was satisfied when silicon was covered by a thermal neutron filter which was made of 2mm thick aluminum alloy with natural boron of 2.0wt%. The neutron absorption reaction ratio of the circumference to the center was within 1.097. This technique must be applied to a research reactor such as JRR-3 of higher neutron flux because the power of JRR-4 is low. Two irradiation facilities for 12 inches NTD-Si in the JRR-3 heavy water tank were designed with most suitable uniform irradiation condition, the amount of production as 50 ohm·cm is estimated at 50 tons/year. In consideration of the reconstruction of JRR-3 that the tank changes to new tank which has two large irradiation pipes, the reactor reactivity for heavy water, the thermal-hydraulic characteristics for core and under plenum were investigated analytically. The results satisfied minimum DNBR and reactivity limitation in official safety estimation. An exclusive reactor for NTD-Si production was designed for three geometry cores that construct 6 x 6 fuel elements, 20 fuel elements around 4 x 4 aluminum block and 3 x 12 fuel elements. The exclusive reactor of 3 x 12 elements is good economical, the net operating profit for 50ohm·cm wafer is estimated that it is 330 million yen/year. This result was reported to the silicon irradiation exclusive reactor project evaluation commission, then the business model including production of medical radio-isotope was discussed.
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