Detection of electronic defects in semiconductor thin-films during plasma processing

半導体プラズマプロセス中の薄膜材料の欠陥検出

In semiconductor device fabrication, a variety of thin-film materials are deposited and etched away by means of plasma processing technology. The device performance is often limited by electronic defects, which are generated in the film during plasma processing. So, it is necessary to reduce these defects by precisely controlling the plasma processing, based on the knowledge of the defect generation and annihilation kinetics. In this study, we have developed an unique technique for detecting the electronic defects by measuring the photocurrent(*) in the film under illumination of light at two different wavelengths. Using this in-situ and real-time technique, the defect generation and annihilation are successively monitored during plasma processing. The defect monitoring is useful for the development of advanced plasma processing, that is required for state-of-the-art semiconductor devices. Although the developed technique is demonstrated under the plasma deposition process of amorphous silicon films for solar cell applications, it can be applied to other semiconductor plasma processing, including etching and surface treatments. * Photocurrent is the electronic current in the semiconductor materials, excited by illumination of light. The illumination of light generates free electron-hole pairs in semiconductors.

半導体デバイスの作製には，様々な薄膜材料の成膜（デポジション）と加工（エッチング）がプラズマプロセス技術を用いて繰り返し行われる。デバイスの性能は，プロセス中に生じる薄膜材料の欠陥（electronic defects）によって制限されるが，これまでその欠陥をプロセス中に検出する技術がなく，欠陥の発生と修復のメカニズムは十分に理解されていなかった。そこで、本研究では，薄膜材料に二種類の異なる波長の光を照射し光電流（＊）を計測することで，欠陥をその場でリアルタイムに検出する技術を開発した。本技術を用いることで，プロセス中に欠陥をモニタリングすることが可能になり，また，欠陥のモニタリングを通して，デバイスの高品質化や歩留まり向上を効果的に進めることが可能になる。本稿では，太陽電池向けアモルファスシリコンの成膜プロセスを対象に本技術を紹介するが，エッチングや表面処理等の他の半導体プラズマプロセスにも適用可能である。

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