High-speed and precise laser interferometry developed for plasma electron-density diagnostics

レーザー干渉計によるプラズマ電子密度計測の高速・高精度化

Laser interferometry is an optical method typically utilized to measure refractive index and distance. It is also known that the interferometry can detect electron density in plasmas by detecting the refractive-index variation induced by electron generation. Measurement technologies of the electron density are necessary for development of plasma material processes including those used in semiconductor device fabrication, since electron collision reactions such as ionization, excitation, and dissociation are keys to control plasma-assisted deposition and etching processes. The author has studied the laser interferometry to achieve more precise electron-density measurements by developing new interferometry arrangements. Detection speed of the refractive-index variation and elimination of gas-number density effects on the total measured signal are the main topics of this study.

レーザー干渉計は物質の屈折率や2点間の距離を精密に測定する光学的手法であり，プラズマ発生に伴う屈折率変動を捉えることで電子密度診断が可能であることが知られている。半導体製造に関わる薄膜堆積，エッチングプロセスに用いられる低圧熱非平衡プラズマ中の化学反応機構では，電子衝突による電離・励起・分子解離反応が重要な位置を占め，電子密度の計測技術はプラズマプロセス技術の発展に欠かせない。筆者は，従来のレーザー干渉計の装置構成を発展させ，屈折率計測の高速化やガス密度変動の影響除去などを実証し，より正確な電子密度測定を目指した研究を進めている。

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