Parametric optimisation of plasma polishing process using response surface methodology

ABSTRACT

The plasma polishing process is one of the non-conventional techniques used to remove material at the atomic level from the substrate. During the polishing of the fused silica substrate, the process parameters, namely radio-frequency (RF) power, pressure ratio (SF₆/O₂), and total pressure of the plasma chamber, are investigated and optimised for material removal rate (MRR) and % change in surface roughness (% ΔR_a) using response surface methodology. The optimum values obtained for MRR and % ΔR_a are 0.012 mm³/min and 3.59, at RF power of 60 W, pressure ratio of 3, and total pressure of 14.3 mbar. The experimental results reveal that surface roughness slightly increases from 0.344 to 0.356 μm after plasma processing at optimised process conditions. Moreover, the plasma-processed fused silica substrate is characterised using field emission scanning electron microscopy and energy dispersive X-ray spectroscopy, which depict the presence of silicon, oxygen, and fluorine on the processed substrate.

KEYWORDS:

• Plasma polishing
• fused silica
• surface roughness
• optimisation
• subsurface defects
• modelling
• material removal rate
• FESEM

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

We thank the Science and Engineering Research Board, New Delhi, India, for its financial support of project No. E.C.R./2018/002801 titled ‘Design and development of a novel plasma processing set up for uniform nanopolishing of prism and any freeform surfaces of fused silica’.