Study On Process Optimization And Properties Of Y₂O₃ Coating Prepared By Atmospheric Plasma Spraying

Dry etching is one of the most important steps in silicon wafer manufacture.Plasma is usually used to process wafer,while active atoms or radicals react with the wafer material,generating volatile substances that are taken away by the vacuum system,so as to achieve the purpose of etching.However,in the production process,fluorine plasma will also erode the inner components of the etched cavity,leading to reduced service life of equipment parts and increased maintenance costs.At the same time,the etched products formed fall off from the inner wall in the form of suspended particles and disperse in the cavity,resulting in wafer contamination and reduced yield.Therefore,the plasma etching resistance of the components in the etching cavity should be improved.It is usually achieved by plasma spraying ceramic coating on its surface.Y₂O₃ is a plasma etching resistant coating widely used in semiconductor industry at present.However,there is a lack of systematic study on the preparation process of coatings and the connection between the preparation process,microstructure and properties of coatings.In this paper,the process parameters of Y₂O₃ etching resistant coating by APS were optimized by orthogonal experimental design.The effect of process parameters on coating properties and phase transition during coating spraying were studied.The etching behavior of the coating in fluorine plasma and the effect of porosity on the etching process were analyzed.The main conclusions are as follows:In the process of preparing Y₂O₃ coating by APS with Ar /H2 as working gas,there is a phase transition from cubic to monoclinic.Spray parameters will affect the extent of phase transformation,and the content of monoclinic Y₂O₃ is about 5%-8%.The 150 mm spray distance provides the maximum impact pressure for the particles,resulting in the highest monoclinic content.The surface morphology of the coating can reflect the melting-impact-spreading of particles to a certain extent.The cross-section morphology of the coating shows that the coating and the substrate bond closely,and the bonding mode is mechanical occlusal.Different extent of pores,cracks and other defects in the coating will affect the properties of the coating.APS parameters have significant influence on the porosity of the coating,and then affect the bonding strength,hardness,etching rate and dielectric strength.Within the design range of experimental parameters,the coating porosity is affected by the process parameters as follows: first decreases and then increases with the increase of main argon,first decreases and then almost unchanged with the increase of hydrogen,first decreases and then increases with the increase of spraying spacing,and gradually decreases with the increase of spraying speed.The following optimal parameters were determined: main argon gas flow 50 NLPM,hydrogen flow 6NLPM,spraying distance150 mm,spraying speed 900mm/s.After spraying with the optimal parameters,the porosity of the sample was found to be the lowest,which is reduced by about 27.9%.The hardness is increased but not obvious.The binding strength increased by 14.3%.The dielectric strength increased by 5.9%.The etching rate decreased by 10.3%.The plasma etching process increases the surface roughness of the sample.On the sample surface,fluoride content is basically stable at a low level,and fluoride element accounts for about 10at%.The loss mechanism of Y₂O₃ ceramic coating under plasma etching can be summarized as local etching and uniform etching.For the defects such as pores and cracks in the coating,the corrosion starts selectively from the edge,and then corrosion traces that reflect the pore shape are formed,and the corrosion speed is relatively fast.For the dense area in the coating,uniform corrosion occurs and the corrosion rate is slower.The same pits are formed,and the corrosion along the grain boundary is more serious.The samples with lower porosity possess better etching resistance due to the smaller exposed surface area in the plasma atmosphere.There is a significant correlation between the porosity and the etching rate of the coating.Reducing the porosity is the key to improve the etching resistance of the Y₂O₃ coating.