Study On The Chemical Mechanical Polishing Liquid And Its Process Of A-plane Sapphire Wafer

As a-plane?1120?sapphire has high hardness?Mohs hardness of 9?,high melting point?2040°C?,good light transmission,excellent electrical insulation and stable chemical properties,it has been an important optical material and widely used in military,aviation Aerospace,infrared windows and other optical components.Since the surface quality of the sapphire wafer has an important influence on the performance of the optical element,extreme demands are placed on the surface quality of the sapphire wafer.Chemical Mechanical Polishing?CMP?,as an ultra-precision processing technique for achieving global planarization,can obtain an ultra-smooth non-damaged wafer surface,which has been widely used in the surface finishing of wafers.Therefore,in order to obtain A-directional sapphire wafers with higher material removal rate?MRR?and better surface quality,ultra-precision machining of A-directional sapphire wafers using CMP was conducted in this paper.The composition of the polishing liquid and the polishing process parameters for A-directional sapphire were studied.The effects of wafer polishing were analyzed,and the material removal mechanism during CMP polishing was analyzed.The specific research content and main conclusions are as follows:?1?First of all,a-Al₂O₃,SiO₂,and CeO₂ were used as the abrasive grains in the polishing slurry to investigate the effect of a-Al₂O₃,SiO₂,and CeO₂ abrasive grains on the polishing efficiency of a-plane sapphire wafers.The experimental results show that the use of silica polishing solution can obtain better polishing effect.Secondly,by changing the p H value of the polishing slurry,the effect of pH value on the polishing performance of the wafer is discussed.The results show that the use of the silica polishing solution with pH8 can achieve a higher polishing efficiency.Then,the concentration of silica abrasive particles in the polishing slurry is changed to investigate the effect of abrasive concentration on the MRR of the wafer.The test results show that the MRR of the wafer increases with the increase of the abrasive concentration,and when the concentration of abrasive particles is from 10 wt%to 12 wt%,the tendency of the MRR becomes flat.Finally,cationic,anionic,zwitterionic and non-ionic surfactants are added to the 10 wt%silica polishing solution to investigate the CMP effect of a-plane sapphires.The effect of the test results show that the polishing effect was better at pH9,p H12,pH12,and pH12,respectively.In addition,in a strong alkali environment,the surfactants all contribute to improving the material removal rate and surface quality of the wafer.?2?During investigating the parameters of the polishing process,orthogonal experiments were used to analyze the effect of the polishing slurry flow rate,the rotating speed of the polishing plate,and the polishing pressure on the CMP polishing a-plane sapphire wafer.The experimental results show that the polishing pressure has the greatest effect on the material removal rate,followed by the rotation speed of the polishing plate,and the polishing slurry flow rate has little effect on the material removal rate.?3?For the polishing effect,particle size measurement,Zeta potential test,and Scanning Electron Microscope?SEM?observation are used to investigate the interaction between polishing solution and a-plane sapphire wafers.The test results show that when the pH value is less than 8,according to the double-layer DLVO theoretical analysis,the electrostatic repulsion between abrasive particles is smaller than the electrostatic attraction due to Brownian motion,resulting in agglomeration of abrasive particles.By adding cationic,zwitterionic,and nonionic surface activity,the surfactant cannot improve the dispersion stability of the abrasive particles at pH 6,but the anionic surfactant can improve the situation.And through the SEM observation,due to electrostatic attraction,the abrasive particles will be adsorbed on the surface of the wafer at pH 6 to affect the polishing effect.As the pH value increases,making the absolute value of the Zeta potential increases,the electrostatic repulsion between the abrasive particles in the polishing slurry increases and the dispersion stability of the polishing slurry increases.Meanwhile,the electrostatic force of the SiO₂ abrasive particles and the wafer surface increases when the pH value increases.With the increase of repulsion,the abrasive particles are rarely adsorbed on the surface of the wafer,and even at pH 12,the SiO₂ abrasive particles are not observed on the surface of the wafer.?4?Finally,through the friction and wear test,the effects of different abrasive particle concentrations,different pH values,and different surfactants on the tribological behavior of a-plane sapphire wafers during CMP are investigated.The experimental results show that an appropriate increase in abrasive concentration and surfactant concentration can reduce the friction coefficient between the polishing pad and the wafer.In an alkaline environment,as the pH value increases,the number of Al-O-Si bonds between the wafer and the surface increases,and the friction coefficient between the polishing pad and the wafer increases.In the same kind of polishing slurry,increasing the polishing pressure can increase the friction between the polishing pad and the wafer,but it does not change the friction coefficient between the two.