Study On Polishing Chemistry During Chemical Mechanical Polishing Of Sic Single Crystals

Silicon carbide (SiC), one of new semiconductor materials, is widely used forLEDs, high power devices and space mirrors. Regarding chemical mechanical polishing(CMP) treatment of SiC substrates, the removal mechanism is still poorly understood.Taking SiC polished single crystals (0001) plane as the model systems, wesystematically study the effects of media, polishing slurry and solution on the CMPtreatments using the AFM microscale scratching method, aiming to clarify the involvedpolishing chemistry. The results will have important implications for practical CMPtreatments of SiC substrates.The strong oxidation power of KMnO4for SiC crystals is revealed and a possibleoxidation reaction is proposed after comparing the effects of various media on the localscratching behavior, studied using AFM and XPS techniques. High removal rate isobserved for scratching in KMnO4solution than in water and air using both AFM sharptips and silica microspheres as model abrasive particles. The observed step-terracestructures with alternating terrace width is explained within the concept framework ofsurface energy difference of two atomic layers and overall surface energy minimizationwhen the surface is worn in oxidative solutions such as KMnO4.The local removal rate change in KMnO4solutions under varied load, duration,solution concentration and pH conditions are studied using AFM microscale scratchingmethod. It is found that the interplay of surface and solution chemistry and wearing ofAFM tips is responsible for the observed changes of removal rate, i.e., the lowestremoval rate for the2h scratching test, jump in the removal rate for concentrationshigher than5×10-3mol/L, decreasing removal rate for more basic solutions due toreduced oxidation power.Pt microspheres, prepared using a spark discharging method, are used as typicalsoft metallic abrasives to further explore the polishing chemistry involved in polishingof SiC crystals. AFM microscale scratching tests, using the attached Pt microspheres asthe single abrasive particle, confirmed again the important role of surface oxidation inpromoting materials removal. The challenges of revealing correct mechanism formetallic Pt as practical abrasives are discussed when comparing with literature results.