Induction of Conditioning Gas and Its Optimization in Nonconventional Plasma Machining Process of Fused Silica

摘要

Plasma machining is a noncontact-type material removal process, which utilizes chemical reaction of active radical/ions with substrate for material removal. Hence, surface chemistry plays a vital role in material removal rate. In the present work, a new process methodology for in situ silica substrate surface cleaning as well as conditioning using plasma is presented. It involves removing of contamination layers deposited over time during plasma processing. In this paper, cleaning properties of metastable oxygen were utilized to remove the deposited carbon contamination formed during plasma processing. It makes the substrate free from contamination as well as conditioning of it. In situ monitoring method is developed using emission spectroscopy, and it helped in optimization of the conditioning gas composition. This combination of He and O_2 conditioning gases has effectively removed the contamination layers. The substrate conditioning using optimized conditioning gases prior to plasma processing enhances material removal rate (～200%) of fused silica substrate. This methodology helps in achieving sustained material removal rate during plasma processing without opening plasma chamber for substrate cleaning. As this process does not disturb the plasma processing cycle, hence, this methodology helps in saving a lot of time and cost of plasma machining.