Research On Ultra-smooth Plane Finishing Method Based On Magnetorheological Foam

In recent years,the semiconductor integrated circuit industry has developed rapidly,and its ever-increasing performance requirements and market demand have made the ultra-smooth surface processing of semiconductor wafers face increasing challenges.For example,chemical mechanical polishing is difficult to process new semiconductor materials with high chemical stability;magnetorheological polishing(MRF)has problems such as low material removal rate,poor polishing liquid stability,and high processing costs.These problems make the processing of semiconductor wafers urgently need more efficient and high-quality ultra-smooth planar polishing technology.In this context,this article proposed a Magnetorheological Foam Plane Finishing(MRFPF)method for the first time.And around the aspacts of increasing the polishing pressure and improving the polishing pressure and the polishing liquid particle distribution uniformity which in turn enhancing the processing performance,this article carries out systematic researches to demonstrate the scientific principles of MRFPF in improving the polishing efficiency and quality.In view of the current problems in ultra-smooth surfaces polishing of semiconductor wafers,a new method,named as magnetorheological foam plane finishing,is proposed to improve the processing efficiency and quality of ultra-smooth surface of compound semiconductor wafers and to reduce the processing difficulty and cost.Based on the high processing efficiency requirements of planar workpieces and the characteristics of magnetorheological foam,a processing system of the MRFPF method was constructed.The processing principle and material removal process were clarified from the macro and micro levels respectively.Based on this,the main influencing factors processing characteristics and main advantages of MRFPF are explicit.From the mesoscopic level,the simulation calculation and analysis of the polishing liquid particle behavior in the MRFPF processing process are carried out,and the mechanism of the magnetorheological foam on the polishing liquid particle distribution behavior is clarified.Based on the force acting on the particles in MRFPF,a molecular dynamics model that considering the effect of porous media is established.The behavior of the polishing liquid particles under different processing parameters is caculated and analyzed.According to the result,the influence law of different processing parameters on the particle distribution behavior along the radial direction of the polishing disc and the optimization parameters that are helpful to improve the uniformity of its distribution is obtained.Finally,the advantages of MRFPF in improving the uniformity of the polishing liquid particles radial distribution and the liquid surface distribution are verified.The polishing fluid flow process in the MRFPF process is studied from the macro level.Based on the fluid dynamics,fluid-solid coupling and magnetic field theory,the fluid-solid coupling effect in the composite polishing medium of MRFPF process is analyzed,and the governing equation of the polishing fluid that flowing in the porous medium is established.Based on this,the pressure distribution model of MRFPF is established.In addition,the pressure distribution on the workpiece surface is calculated by the finite difference and relaxation iteration methods,which verifies the advantages of the MRFPF method over the MRF method in improving the polishing pressure and its distribution uniformity from the theoretical level.Based on the established MRFPF pressure distribution model,the MRFPF processing efficiency and quality prediction model considering different processing conditions are further established.Firstly,the polishing pressure and polishing speed of each point on the workpiece surface under different processing conditions with the processing time are analyzed.And,based on the Preston equation,the material removal rate model under different processing conditions is established.Secondly,the process of multi-abrasive material removal is analyzed based on the single abrasive particle scratching process,and in turn the surface roughness evolution model under different working conditions is established.Finally,the surface topography data after processing was calculated based on the material removal amount under different processing conditions,and the the surface flatness evolution model is established.Taking compound semiconductor wafers as the processing object,comprehensive experimental studies of MRFPF and MRF processing under different working conditions are carried out.First,according to the processing principles and characteristics of MRFPF,an experiment-oriented realization method of magnetorheological foam is explored.Secondly,the effectiveness of the MRFPF pressure distribution model and its advantages in improving polishing pressure and its distribution uniformity compared to MRF are verified by polishing pressure analysis experiments.Finally,polishing experiments under different working conditions are carried out.According to the processing result,the effectiveness of the MRFPF processing efficiency and quality prediction model and its excellent performance in the ultra-smooth surface processing of compound semiconductor wafers are verified.