Research On Chemical Mechanical Polishing Of Single-crystal SiC Based On Fenton Reaction

As third-generation semiconductor materials,single crystal silicon carbide(SiC)is characterised by a wide energy band gap,a high breakdown voltage,a high thermal conductivity,a high saturated electron drift velocity and a strong anti-radiation ability.It is a "Core" of solid-state light,source power electronics and microwave RF device.And it has broad application prospects in the semiconductor lighting,a new generation of mobile communications,energy Internet,high-speed rail transportation,new energy vehicles,consumer electronics and other fields.As one of the important applications,the surface of a single crystal SiC for epitaxial substrate requires ultra-smooth,no defects,no surface or sub-surface damage,surface roughness of Ra ? 0.3nm,to meet the needs of epitaxial film growth.However,the high hardness(Mohs hardness of 9.2),hard and brittle,good chemical stability of single crystal SiC,high efficiency ultra-precision planarization of SiC is extremely difficult,and seriously restricts the the application and development of SiC semiconductor devices.In this paper,Fenton's hydroxyl radical(·OH)test and SiC oxidation test were carried out to verify that Fenton reaction could oxidize single crystal SiC.Fenton reaction process can produce a strong oxidizing agent-hydroxyl radical,hydroxyl radical can react with the single crystal SiC to generate the oxide layer.The XPS material properties analysis of the oxide layer shows that the oxide layer is Si O2.The nanoindentation test of the oxide layer shows that the hardness and modulus of the Si O2 layer are much smaller than the original SiC surface.The soft oxide layer can be easily removed by the abrasive grain processing.It is confirmed that the chemical mechanical polishing method based on the Fenton reaction can carry out ultra-smooth planarization of single crystal SiC.From the influence of chemical factors,the concentration of hydroxyl radical produced by Fenton reaction and its effect on SiC chemical mechanical polishing were studied systematically.The effect of the concentration of hydroxyl radical on the oxidation of single crystal were compared.The effect of Fenton reagent(catalyst type,Fe2+ concentration,p H value,H2O2 concentration,etc.)on the production of hydroxyl radicals by Fenton reaction and chemical mechanical polishing.were studied It is found that the higher the hydroxyl radical concentration,the thicker the oxide layer formed on the surface of SiC,the better the effect of SiC chemical mechanical polishing and the higher the polishing efficiency.Under conditions where the p H,Fe2+ concentration,and H2O2 concentration are 3,0.02 wt.% and 5 wt.%,respectively,high-concentration ·OH can be produced in the Fenton reaction.On this basis,a smooth surface of SiC with the roughness Ra 0.187 nm can be obtained after CMP.From the influence of polishing process,the effect of material removal rate and polishing effect on the parameters of abrasive species,abrasive concentration,particle size,polishing pressure and polishing speed were studied by single factor experiment.The choice of colloidal silica abrasive,abrasive concentration of 20%,particle size of 50 nm,polishing pressure of 0.02 Mpa and polishing speed of 60r/min,the effect of processing is the best,and can obtain the smooth surface with roughness Ra?0.3nm.Based on the study of the chemical factors and process parameters of chemical mechanical polishing of SiC based on Fenton reaction,the material removal process of chemical mechanical polishing based on Fenton reaction was analyzed.The effect mechanism of polishing pad properties,wear and contact deformation and its effect on the polishing effect of SiC were studied.The material removal model of single crystal SiC chemical mechanical polishing based on Fenton reaction was established,and the mechanism of chemical mechanical polishing was revealed.The hydroxyl radicals produced by Fenton reaction can react with the single crystal SiC to form soft and easy to remove the Si O2 oxide layer.The oxide layer is removed by the mechanical friction of the abrasive particle.The alternation of chemical and mechanical finally achieves surface material removal of SiC.