Study On The Key Technology Of Radical Plasma Processing Of SiC Components

Silicon carbide(SiC)has become a common material for space mirrors due to its many excellent properties.At present,the main processing flow of SiC mirror manufacturing is:milling forming fine grinding→plating modified layer→ultra precision machining.The plating modified layer mainly uses PVD method to prepare silicon(Si)modified layer,while ultra precision machining involves CNC tool polishing,magnetorheological polishing,ion beam polishing and gasbag polishing.In order to solve the mismatch problem between silicon modified layer and SiC material,this paper focuses on the preparation technology of silicon modified layer,and explores the introduction of radical microwave plasma(RPS)processing technology into the process of SiC.Firstly,two kinds of RF magnetron sputtering methods were compared to prepare SiC modified layer.Then,the etching characteristics of RPS were studied.Finally,the etching effects of RPS on SiC components and films were compared,which provided a reference for the subsequent RPS processing.The results are as follows:Process exploration of SiC modified layer prepared by magnetron sputtering:SiC thin films were prepared by direct sputtering based on SiC target and reactive sputtering of silicon target and methane,and the characteristics of SiC thin films prepared by the two processes were explored;It is found that the deposition rate increases from 11.3 nm/min to 36.5 nm/min in the range of 20%to 70%of methane,and Rq value changes little in the range of 20%to 60%of methane,but tends to increase in the range of 70%.In methane reactive sputtering process,the ratio of silicon to carbon can be adjusted,but it is not easy to control;Based on the SiC target technology,the surface roughness Rq changes little with the increase of deposition time,that is,the thickness of the film,and the Si/C ratio is close to 1:1.The films prepared by both methods are 8H-SiC.At the same target power,the deposition rate of silicon target is faster than that of silicon carbide target.The etching characteristics of the remote Radical Plasma Source(RPS)equipment:the Langmuir probe was used to characterize the radical plasma produced by RPS source,and the ion/electron density was less than the lower detection limit of the Langmuir probe(1012 m-3);The etching rate uniformity of RPS equipment is 3.4%in the horizontal range of Φ300mm;Different etching angles(sharp angle between the surface normal of substrate and the axis of RPS source),the RPS etching is anisotropic.0° to 75°,the etching rate increased from 47.8nm·min-1 to 74.2 nm·min-1;75° To 90°,the etching rate is reduced to 25.7nm·min-1;The mass flow rate of CF4 is from 500sccm to 3000sccm,and the etching rate increases from 59.7nm·min-1 to 4889.8 nm·min-1,4000sccm,the etching rate decreases to 3116.9 nm·min-1;And with the increase of CF4 mass flow,there are more and more etching residues on the surface.The results of XPS analysis showed that there were four elements,namely oxygen,silicon,carbon and fluorine.Radical plasma etching silicon carbide:after many experiments with different process parameters,RPS could not etch S-SiC,and could not remove the damage layer;With the increase of CF4:O2 gas flow rate,the RPS etching rates of both annealed and non annealed SiC films increase;The etching rate of non annealed SiC film is higher than that of annealed SiC film;Under the same RPS etching parameters,the average etching depth of 6H-SiC film is 492.4nm,which is higher than that of 8H-SiC film 441.0nm;In the experiment,with the increase of CF4 mass flow,there are more and more etching residues on the surface.XPS analysis results show that there are mainly oxygen,silicon,carbon and fluorine in the surface residues.There is a great difference between RPS etching S-SiC and SiC films.