Research and Optimization of Composition and Processing Parameters of Tantalum Crystal Wafer CMP Polishing Slurry
Tantalum wafer chemical mechanical polishing(CMP)is a key process in semiconductor manufacturing.The work aims to achieve a highly planar and smooth surface texture on the tantalum wafer.The effectiveness of CMP was determined by the combined effects of chemical corrosion and mechanical abrasion.In this study,electrochemical experiments were conducted to determine the optimal combination and ratio of glycine and persulfate,with hydrogen peroxide as oxidants.The experiments utilized the Wuhan correst CS310M electrochemical workstation,with a mercury-oxidized mercury electrode as the reference,a platinum electrode as the auxiliary,and a tantalum electrode(with an exposed area of 1 cm2)as the working electrode.The optimal combination was found to be a mixture of glycine and hydrogen peroxide,with mass fractions of 0.3 wt.％and 3 wt.％,respectively,resulting in a corrosion rate of 0.005 62 mm/a.Subsequently,to establish the optimal range of process parameters for subsequent response surface experiments,single-factor CMP experiments were conducted using the electrochemically determined polishing solution.The process parameters tested were polishing pressure,polishing disc rotation speed,and polishing fluid flow rate,with values ranging from 6.5 to 9.5 kg,30 to 90 r/min,and 45 to 105 mL/min,respectively.The experiments were performed on a 1-inch diameter,1 000 μm thick tantalum wafer that underwent preliminary grinding using the UNIPOL-1200S automatic polishing machine,with a GL-86 type velvet polishing pad.The optimal ranges for the polishing pressure,polishing disc rotation speed,and polishing fluid flow rate were determined to be 7 to 9 kg,50 to 70 r/min,and 65 to 85 mL/min,respectively.Additionally,response surface experiments were designed based on the ranges determined by the single-factor experiments.CMP experiments were carried out according to the response surface experimental design,and the results were input into Design-Expert 13 software to establish a mathematical predictive model and plot response surface graphs.The model was validated to be effective and reasonable.Analysis of the response surface graphs revealed that the degree of influence on the polishing effect,from highest to lowest,was polishing pressure,polishing disc rotation speed,and polishing fluid flow rate.Therefore,the emphasis should be placed on adjusting the polishing pressure in the polishing experiments.The interaction between polishing pressure and polishing disc rotation speed significantly influenced the polishing effect,while the interaction between polishing pressure and polishing fluid flow rate,as well as the interaction between polishing disc rotation speed and polishing fluid flow rate,were not significant.Based on the mathematical model,the optimal process parameter combination was predicted,with a polishing pressure of 8.1 kg,a polishing disc rotation speed of 70 r/min,and a polishing fluid flow rate of 79 mL/min.Under these conditions,the achieved material removal rate and surface roughness were 29.445 nm/min and 0.152 nm,respectively.The study ultimately determines that glycine can slow down the corrosion rate,while oxidants can accelerate the corrosion rate of tantalum.Mixed electrochemical experiments show that glycine can also mitigate the promoting effect of oxidants on the corrosion of tantalum.Therefore,glycine can be used in conjunction with oxidants to control the corrosion of tantalum.The use of response surface analysis can determine the optimal process parameter scheme,yielding favorable polishing effects,thereby reducing experimental costs and improving experimental efficiency.
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