Experimental Study On Chemical Mechanical Polishing Process Optimization Of SIC Wafer

Single crystal 4H-SiC is suitable for the preparation of high-voltage and high-frequency power devices,which can reduce the energy consumption of downstream products and reduce the terminal volume.It is commonly used in emerging fields such as optical microelectronics,new energy vehicles,satellite communications,5G base stations,etc.Due to its high brittleness and rigidity,it is easy to appear damage and crack in processing.The Chemical Mechanical Polishing(CMP)technique is the only effective means to achieve global flatness of polishing.At present,the polishing efficiency of SIC wafers is much lower than that of silicon wafers,and the polishing mechanism has not been unified.Researchers mostly set polishing parameters by semi-empirical means,and the process control technology is not mature enough.In this paper,the effects of process parameters,polishing fluid and polishing pad on the removal efficiency and surface roughness of 4H-SiC polishing were systematically analyzed through theoretical analysis and experimental research,and the optimization scheme of high efficiency and low damage machining of sic wafers was obtained,which provided technical support for meeting the ultra-precision machining of the third generation semiconductor materials.Firstly,the removal mechanism and model of CMP material were analyzed to determine the key factors affecting the polishing effect of SIC wafers.The kinematic model was established to analyze the relative velocities and trajectories under different speed ratios,and the optimal speed ratios with uniform velocity distribution and trajectories were obtained.The three-dimensional contact model of wafer polishing pad was established by using Ansys software,and the influences of polishing pressure,friction coefficient,polishing pad material characteristics and other factors on the surface contact stress distribution and distribution uniformity of 4H-SiC wafer were analyzed.Orthogonal experiment was used to carry out polishing process experiment,and the influence law of pressure,rotational speed,flow rate of polishing fluid,grinding particle size and other factors on material removal rate and surface roughness was studied.The significant sequence of factors was determined.The multi-objective optimization matrix analysis model was used to optimize polishing process parameters.The removal rates of Si plane and C plane are 225.00nm/h and 240.74nm/h,and the removal efficiency of Si plane and C plane is increased by 9.1% and 14.8% compared with the orthogonal experiment combination.At the same time,the surface quality of the two crystal surfaces is also improved after polishing.Single factor experiment was used to study the effect of different polishing fluid,abrasive type and polishing pad material characteristics on material removal rate and surface roughness.The results show that the dispersion stability of the polishing liquid has a certain influence on the polishing effect in the CMP process.The material removal effect of diamond abrasives is greater than that of silica abrasives,but the surface quality after polishing is poor.The material removal rate of polyurethane polishing pad is higher than that of frosted leather and synthetic leather,but the surface quality after polishing is slightly lower than that of frosted leather and synthetic leather.By carrying out the combined polishing experiments of different abrasive particles,the polishing characteristics of silica and diamond abrasive particles were obtained.According to the characteristics,the optimization scheme was developed,and the combined polishing process model was constructed to obtain the best polishing effect of silica and diamond abrasive particles combined polishing.Then,SEM and EDS tests were carried out to analyze the material removal mechanism under different polishing methods.On this basis,a high precision and high efficiency combined polishing method for silicon carbide wafers is developed.Under the condition of a certain polishing precision,the processing efficiency of this method is increased by 16.3%,which verifies the feasibility of the combined polishing method,and provides a new technical idea for the high efficiency and ultra-precision machining of the third generation semiconductor wafers.