Study On Friction Chemical Mechanical Lapping Of SiC Single Crystal Substrate With Fixed Abrasives

Silicon carbide(Si C),as the third generation of semiconductor materials,is widely used in semiconductor lighting,integrated circuits,new energy vehicles and other fields due to its characteristics such as wide bandgap width,high critical breakdown electric field,high thermal conductivity,high carrier saturation migration rate,low relative dielectric constant,high temperature resistance and radiation resistance.At the same time,silicon carbide single crystal can be used as substrate material for growing gallium nitride and graphene by epitaxial technology.As for the substrate substrate,it is required to have super-smooth and non-damaging high-precision surface quality,but single crystal silicon carbide has high hardness,high brittleness and excellent chemical stability at room temperature,which brings difficulties to the high-efficient ultra-precision machining of silicon carbide.At present,the common processing methods are chemical mechanical lapping and polishing of free abrasives,but this method has low processing efficiency,free abrasives can not be reused,high test cost,and waste liquid treatment is easy to cause environmental pollution.In order to solve this problem,consolidated abrasive lapping technology has attracted extensive attention from scholars due to its advantages such as high processing efficiency,strong process controllability,low processing cost and green environmental protection.In this paper,the effect of bonded abrasive tribological mechanical grinding on the removal rate and surface roughness of silicon carbide monocrystalline wafers was studied,and the tribological reaction process and material removal mechanism were explored.The main research contents are as follows:(1)Study on the abrasive paste for free abrasive tribochemistry mechanical lapping Si C substrateThe influence of oxidizer type,content and diamond particle size on the removal rate and surface roughness of silicon carbide single wafer was studied by single factor test.The results showed that Na OH had the best effect when it was used as oxidant,and the maximum material removal rate reached1768nm/min for the Si surface with 10% Na OH,and 1403nm/min for the C surface with 5%Na OH.However,the surface roughness value after lapping with grinding paste is larger,ranging from 400 nm to 500 nm.The larger the diamond abrasive particle size,the greater the material removal rate,the larger the surface roughness.The white light interferometer observed that the surface corrosion pits,the deepest scratches reached 14.4 ?m,the maximum uplift of the material was 7.686 ?m,the lower the surface quality.The smaller the particle size is,the opposite is true.High efficiency and high precision are difficult to achieve at the same time.The results of the main factors in the abrasive paste were compared.It is found that the interaction between oxidizer and abrasive particles is the main one and the mechanical action is the auxiliary one.It provides a reference for the further development of consolidated abrasive lapping disc.(2)Study on lapping disc for Si C substrate with bonded abrasive friction chemical mechanical lappingAccording to the study of free abrasive tribochemical-mechanical lapping,the composition of consolidated abrasive lapping disc is proposed,and its composition is selected and optimized.A series of consolidated abrasive tribochemical-mechanical abrasive discs have been trial-produced.Then orthogonal test method was used to optimize the process parameters(abrasive particle size,lapping time,lapping speed,lapping pressure)of consolidated abrasive lapping Si C single chip.The results show that the abrasive particle size has a significant effect on the removal rate and surface roughness.When the abrasive particle size is 28 ?m,the grinding speed is 80 r/min,the grinding pressure is 3 psi,and the grinding time is 50 min,the material removal rate is the highest,which is 281 nm/min.There are many scratches on the surface and the depth is 3.3?m.At the abrasive particle size of 3.5 ?m,grinding speed of 60r/min,grinding pressure of 3psi,grinding time of 50 min,the surface roughness is lowest,namely 16nm;the scratch is shallow,namely1.1 ?m;material uplift is only 0.99 ?m.The surface quality is good and the accuracy is high,but the material removal rate is only 18nm/min.It is difficult to achieve both high efficiency and high precision of consolidated abrasive lapping.(3)Comparison of lapping results between consolidated abrasive disc and free abrasive pasteAfter consolidation and free abrasive lapping contrast,the results show that the surface roughness of the workpiece after lapping with abrasive paste is high,about 5 times that of the lapping with consolidated abrasive,and the surface accuracy of the workpiece after lapping with free abrasive is low.The removal rate of free abrasive materials is high,but the preparation of abrasive paste and subsequent processing are time-consuming and laborious.In the same time,the consolidated abrasive can be ground for many times,which indirectly improves the material removal rate.But grinding paste can not be reused,test material consumption is serious,high cost,and improper processing of grinding paste will bring greater pollution to the environment,while grinding disc grinding operation is simple,high utilization of grinding particles,green environmental protection.Generally speaking,the abrasive disc is better than the abrasive paste.(4)Study on the mechanism of friction chemical mechanical lapping of Si C substrate with fixed abrasiveAfter consolidated abrasive tribochemical-mechanical lapping test,the results of SEM observation and energy spectrum analysis show that the solid phase reaction between the additive and the workpiece does occur under the action of tribochemistry.By XRD and jade6 analysis,the reaction products were Si O2-like silica compounds,but the amount of production was small.Component processing method is used to decompose the material removal rate.The effects of chemical,mechanical and their interactions are illustrated by experiments.The results show that the interaction between mechanics and chemistry plays a dominant role in material removal rate,followed by mechanics.Chemical action does not directly remove materials,but generates oxidation products which are easy to be removed by chemical reaction,and then is removed by abrasive machinery.