Preparation And Properties Of Suspension Plasma Sprayed Y₂O₃ Coating

Plasma etching resistant coating is a material used to protect key components in the fields of semiconductor devices and displays.It can effectively resist the erosion and corrosion of high-density plasma and avoid particle contamination and wafer defects.Research and development of an extremely etching-resistant material is a challenging task for the semiconductor integration industry and plasma etching technology.Y₂O₃ has excellent chemical stability and heat resistance,and been currently considered as the most widely used plasma etching-resistant coating material.Dense Y₂O₃ coating is one of the solutions to improve plasma etching resistance.Compared with the traditional air plasma spraying（APS）using large particle agglomerated powder feed,suspension plasma spraying（SPS）can use suspension feed prepared by powder with particle size less than 10μm to prepare Y₂O₃ coating.The prepared Y₂O₃coating has the characteristics of high density,uniform structure,high hardness,strong resistance to plasma etching and smooth surface after plasma etching.In this paper,the factors affecting the dispersion performance of Y₂O₃ suspension were studied.PAANH₄ was selected as the dispersant.Considering the five factors of solid phase content,dispersant concentration,ball milling time,p H value of suspension and solvent type,16 suspensions were prepared by orthogonal design.The dispersion stability of nano-Y₂O₃ suspension was characterized by surface tension,viscosity,sedimentation,particle size distribution and Zeta potential.Through the intuitive analysis and variance analysis of the data of the comprehensive experimental results and the calculation of the range,the significance order of each factor affecting the stability of the suspension was finally obtained:solvent type>PAANH₄ concentration>p H>ball milling time>solid content.The optimal parameters for obtaining a stable suspension are:Y₂O₃ powder solid content 20 wt.%,0.5 wt.%ammonium polyacrylate,ball milling time 2 h,p H=8 and solvent 100%water suspension system.The SPS parameters of the plasma etching resistant Y₂O₃ coating were optimized by adjusting the spraying process.The effects of spray distance,liquid feeding rate and longitudinal step of spray gun on the mechanical properties,phase transformation,microstructure and dielectric strength of the Y₂O₃ coating were investigated.The optimal SPS parameters for the Y₂O₃ coating were obtained:total gas flow 180 slpm,gas ratio Ar:N₂:H₂=60:30:10,current 180 A,atomization gas flow 15 L/min,liquid flow rate 35m L/min,spray gun traverse speed 700 mm/s,spray gun longitudinal step 1 mm/step,spraying distance 80 mm,substrate preheating temperature 200°C.The Y₂O₃ coating prepared under the optimized SPS parameters has a single-pass deposition thickness of8.82±0.19μm/pass,a microhardness of 3.78±0.36 GPa,a porosity of 2.35±0.24%,a bonding strength of 36±3.6 MPa,as well as a dielectric strength of 29.74±2.01 k V/mm.The etching behavior of the Y₂O₃ coating in fluorine plasma environment（CF₄/O₂/Ar）at different times（30,60,120 min）and the effect of the coating porosity on the etching rate of the coating were analyzed.After the Y₂O₃ coating was etched for 120 min,the etching signs were very obvious.Compared with the prepared coating,the etching depth of the coating gradually increased and the surface roughness increased significantly.The lowest etching rate of Y₂O₃ coating was 11.48±5.21 nm/min.There was a significant correlation between porosity and etching rate.The coating with lower porosity showed better plasma etching resistance.Reducing porosity was the key to improve the etching resistance of Y₂O₃ coating.