Study On The Mechanism Of Single Crystal 6H-SiC Ultraviolet Photocatalysis Assisted Chemical Mechanical Polishing

As the third-generation semiconductor material with excellent performance,single-crystal silicon carbide has the advantages of chemical stability,wide band gap,high thermal conductivity,high saturation carrier drift speed,high electrical breakdown field,etc.High-performance wafer materials for electronic devices with extreme conditions offer broad application prospects and good development prospects.The epitaxial process requires that the surface of the substrate substrate is an ultra-smooth surface with a roughness of Ra0.3 nm or less and no surface/subsurface damage,so as to achieve the conditions for epitaxial film growth.However,since single-crystal silicon carbide is chemically stable,large in hardness,and strong in brittleness,it is a typical difficult-to-process material,and it is difficult for the traditional process to effectively guarantee its processing efficiency and processing quality.In this paper,UV-assisted chemical mechanical polishing of single-crystal silicon carbide wafers is studied.The photocatalyst produced by ultraviolet light generates highly oxidative hydroxyl radicals（·OH）which can effectively react with silicon carbide wafers to make the surface hard,The low oxide reaction layer is conducive to abrasive removal,which can effectively improve its polishing efficiency and improve surface quality.First,during the experiment of degrading methyl orange,by measuring the light transmittance and redox potential at different process parameters and at different times,the influence rules of different process parameters on the·OH produced by the UV photocatalytic reaction were obtained.Carried out the research on the pretreatment and grinding process of the polishing specimen under different conditions,and obtained the effects of different abrasive particle sizes,different grinding pressures,and different material grinding discs on the grinding surface morphology.Secondly,the effects of different types of photocatalysts and electron capture agents on UV-catalyzed polishing are studied.Three photocatalysts,TiO₂,ZnO and CeO₂,were selected for comparative experiments of photocatalytic reactions.The photocatalytic reaction rate of two photocatalysts,ZnO and CeO₂,at different concentrations was studied in depth.The surface roughness Ra decreases as the material removal rate increases.That is,the more violent the ultraviolet photocatalytic reaction,the faster the rate ofOH production,which causes the thickness of the reaction layer during polishing to increase and the polishing material removal rate to increase.As a comparison,using potassium permanganate and phosphoric acid as electron capture agents for UV-assisted polishing has certain effects.The surface quality after H₂O₂ for UV-assisted polishing is the best.Large and increased,but the surface roughness Ra decreases first and then increases as the material removal rate increases.Thirdly,the catalysis of the two active catalysts SiO₂ and CeO₂,TiO₂ and CeO₂ mixed,the experimental results show that the photocatalytic reaction rate has a certain synergistic effect.Through experiments on different types of polishing pads,it is proved that polyurethane polishing pads can obtain better polishing effect during the processing of diamond abrasives,and the material removal rate and surface quality of polyurethane doped diamond polishing pads are better than polyurethane polishing pads.Finally,the nano scratch test under different loads on the wafer surface proves that the load is linearly related to the scratch depth.Combined with the scratch experiment results,the mechanism of UV-assisted polishing to remove the scratches was studied.It was found that under certain process conditions,the abrasive material rotates in the residual abrasive scratch groove,which will cause the internal materials and surface materials of the scratches to be removed at the same time.There is no obvious change in the depth of scratches,but the width of scratches is obviously increased,which further affects the accuracy of the surface profile and makes it difficult to remove the scratches.It is necessary to combine the original state of the processed surface and optimize the process conditions to remove the scratches.