Research On Plasma-Assisted Cluster Magnetorheological Finishing Of Single Crystal SiC Wafer

Single crystal SiC,a representative materials of third-generation semiconductors,is widely applied as a substrate for high-performance electronic apparatus.Its surface is required to be atomically smooth and free of sub-surface damage.However,single crystal SiC has high hardness,high brittleness,and chemical inertness,making it a hard and brittle material that is difficult to process.This paper proposes a plasma-assisted cluster magnetorheological finishing(MRF)method.First,plasma treatment is used to reduce the hardness of the Siface of single crystal SiC.And then magnetorheological polishing is used to quickly remove surface materials and reduce surface roughness to achieve high-efficiency and ultra-smooth planarization of single crystal SiC.First,the feasibility and effectiveness of plasma-assisted cluster MRF of single crystal SiC was analyzed.The plasma oxidation test was carried out on the Sisurface of single crystal SiC.Through scanning electron microscope and EDS energy spectrum analysis,it was found that the surface roughness of single crystal SiC after plasma oxidation treatment increased,the content of C element decreased,and the content of O element increased,which proved that an oxide layer was formed on the surface of SiC after plasma treatment.The surface hardness of SiC after treatment was tested by nanoindentation experiment.It was found that the surface hardness of SiC after plasma treatment was 7.5 GPa,which was less than 20%of the original surface.The single crystal SiC after the oxidation treatment was subjected to the cluster MRF test,and a lower surface roughness and a flattened surface can be obtained.Secondly,a systematic process study was carried out on plasma-assisted cluster MRF.The effects of oxidation mode,scanning step,radio frequency power,oxygen flow rate,and scanning period on the uniformity and thickness of SiC surface oxide layer were studied by single factor experiments.When using scanning oxidation method,0.5 mm scanning step,800W RF power,50sccm oxygen flow,and 5 scanning cycles,the SiC oxidation effect is the best,and a uniform oxide layer of more than 100 nm can be obtained.The effects of abrasive type,abrasive particle size and abrasive concentration on cluster MRF were studied by single factor experiment.After polishing with CeO₂ abrasive with a particle size of 3?m and an abrasive concentration of 3 wt.%for 20 minutes,the surface oxide layer was completely removed and the polishing effect was the best,with the lowest surface roughness.And finally,plasma oxidation cluster MRF with optimized process parameters was used to obtain a super smooth surface with a surface roughness of Ra 0.49 nm.Finally,the polishing mechanism of plasma oxidation cluster magnetorheological polishing was studied.Through XPS energy spectrum analysis,it was found that obvious Si-O₂ characteristic peak appeared on the surface after plasma treatment,which proved that the composition of the oxide layer generated on the SiC surface by plasma oxidation was SiO₂.It was found that the width and depth of the wear scars of the plasma-treated samples are much greater than those of the non-plasma-treated samples by friction and wear tests,which proves that the oxidized SiC surface has better mechanical processing performance and is easier to remove materials.Based on the actual machining experiments,a single crystal SiC surface creation model of plasma-assisted cluster MRF was established to reveal its material removal mechanism.