Simulation Analysis Of Sputter Ion Pump Cathode Plate’s Sputtering Process

Sputter ion pump,also known as Penning pump,is a clean vacuum pump widely used in ultra-high vacuum systems.The electrons in the space of the anode of the sputter ion pump collide with gas molecules under the action of electromagnetic field to generate Penning discharge.The positive ion bombards the cathode to sputter titanium atoms,and deposits a film on the anode tube to adsorb the gas,thereby achieving the purpose of gas removal.There are no moving parts in the pump cavity,and it has the advantages of simple structure,no noise,no vibration,no oil pollution,no need for refrigerant,simple and reliable use.Sputter ion pumps have been continuously developed and used in ultra-high vacuum fields such as high-energy particle accelerators,space simulation,electronics industry,and heavy ion medical machines.With the demand for ultra-high vacuum environment in China’s high-tech scientific instruments and equipment,national major projects,the demand for high-performance ion pumps is also increasing.In this paper,the theory of field emission,particle collision,charged particle motion,Penning discharge and other processes of sputter ion pump pumping unit is introduced.SRIM2013 is used as calculation software.The simulation analysis of sputtering process of sputter ion pump cathode plate based on Monte Carlo method.The sputtering process was simulated to study the distribution of gas ions and recoil target atoms in the cathode plate under different incident conditions,as well as the energy loss during the collision process,the variation of sputtering yield and splashing atomic state.By simulating the sputtering process of cathode plates with different incident conditions,the range and radial depth of nitrogen ions in the cathode plate increase with the increase of incident ion energy.As the angle of incidence increases,the ion range decreases and the radial depth increases.The recoil target atoms have the same pattern as the incident ions in the cathode plate.Cathode plate materials and gas ion species have an effect on the distribution of ions and recoil target atoms in the cathode plate and energy loss.Next,the law of the spattered atoms under different conditions is simulated and analyzed.The sputtering yield increases with the increase of the incident ion energy.When the incident angle is 70°～80°,the sputtering yield reaches the highest;Under the same incident conditions,the sputtering yield of Ar ions is larger than that of N ions;the sputtering yield of the Ta cathode plate is larger than that of the Ti cathode plate.The statistical analysis of the information of the spattered atoms is carried out.The angles of the spattered atoms are mostly distributed around 50°～70°.As the incident ion angle andt energy increasing,the angular distribution of the spattered atoms is shifted to the small angle region.The energy of the spattered atoms is mainly concentrated in the range of tens of electron volts,and most of the energy loss is in the cascade collision.Based on the results of the simulation analysis,an improved structure of the sputter ion pump unit was proposed.The pumping speed expression of the pumping unit is derived and compared with the experimental test to improve the pumping theory.It provides a theoretical basis for the design optimization of domestic sputter ion pumps.