Research On The Mechanism Of Plasma Polishing

Plasma polishing is a low-cost, non-waste and non-pollution super smooth surface processing method. It has many advantages which the classical processing methods don't have and so it has been widely used in many fields such as semiconductor industry and optical element manufacturing. Plasma polishing has been the key technology in microelectronics, optoelectronics and micro-optical element manufacturing.Based on the low pressure RF-generated capacitively coupled plasma apparatus, several experiments were implemented under variant technological parameters to study the polishing effect and removal rate. The effects of RF power and gas flow rate on polishing effect were analyzed. The characteristics of the plasma were diagnosed using Langmuir probe and optical emission spectroscopy. The relationships among plasma characteristics, removal rate and surface roughness were defined. The machining mechanism of optical surface using plasma was preliminary revealed.The results of this research are given as follows. The surface roughness and removal rate of the silica glass increased with the increment of the RF power using argon plasma. The bombardment and sputtering effects appeared if the RF power was too high. The existing of Ar provided an active atmosphere for the generation of SF6 plasma. The SF6 plasma was functional as the carrier of chemical reactive radicals which were the key elements of the polishing process. The addition of O2 to SF6/Ar plasma influenced the polishing effect. When the flow rate of SF6 and O2 were both 30sccm, the surface roughness reached its minimum of 1.OOnm. When the flow rate of SF6 was 40sccm and O2 is 20sccm, the removal rate reached its maximum of 3.6nm/min.According to the results of Langmuir probe diagnosis, the electron temperature of argon plasma increased with the increment of RF power and ranged from 2.41eV to 5.03eV; the electron density of argon plasma increased with the increment of RF power and ranged from 1.2844×1016m-3to 7.7893×1016m-3. The electron temperature of Ar/SF6/O2 plasma differed with variant SF6 and O2 flow rate and ranged from 1.08eV to 2.52eV. The electron density of Ar/SF6/02 plasma was lower than Ar plasma and ranged from 0.2665 X 1016m"3 to 0.6965 X 1016m-3. According to the results of OES, the plasma temperature was 1989-2132K when the RF power was 40-120W. The electron density calculated using OES deviated slightly from the Langmuir probe diagnosis but the trend was coherent.