Effect Of Target Current On Deposited Particles Escape-target Method And Film Growth Behavior Under Oscillating Pulse Electric Field

The great potential of high power impulse magnetron sputtering(HiPIMS)in the preparation of functional films on the surface of mechanical devices is due to the dense structure and excellent adhesion of the films which prepared with high ionization rate,however,the low deposition rate limits its industrialization.Aiming at the technical deficiency of low deposition rate of HiPIMS,according to the fact that the electron work function of the target surface grain boundaries and defects is significantly lower than that inside the grain,and it is expected that a large amount of electrons to escape in the low work function area.The Joule heat increases the thermal electron activity to form a mutual enhancement effect between Joule heat and electron thermal emission.This increases the number of plating particles and electrons between the cathode and anode,creating conditions for simultaneously increasing the ionization rate and deposition rate of the plating particles.Based on the above research ideas,the following research work was carried out:In this paper,the critical temperature Te of electron thermal emission was used as the boundary,and three metal targets with different melting points(TAl<Te,TCu?Te,TTi>Te)were selected.Explore the relationship between the escape-target method of the plating particles and the target current,and the mechanism of the effect of the target current on the microstructure,mechanical properties and corrosion resistance of the film was analyzed.The confocal laser was used to characterize the micro-morphology of the target surface,the XRD and SEM were used to analyze the crystal structure and micro-morphology of the thin film,and the nano-indenter,Rockwell indentation,four-probe resistance and electrochemical workstation were used to analyze the film mechanics and physical properties.The results showed that with the cathode target current increases,the Al target voltage continues to increase,and there is no thermal electron emission in the defect areas such as grain boundaries.However,with the increase of current,the voltage increase of Cu target and Ti target slowed down obviously,When the peak currents of the above two target materials reach 8 A and 11A respectively,part of the current begins to consist of hot electrons emitted at the grain boundaries.When the discharge is in the abnormal glow discharge area where the current is proportional to the voltage,diffusely distributed craters with irregular edges appear on the target surfaces of the three pure metals.At this time,the plating particles missed the target by cascading collision,the cross-sectional micro-morphology of the deposited film is a columnar morphology with many pores,and the deposition rate,adhesion,corrosion resistance and conductivity are relatively poor,but the hardness and the modulus of elasticity are highest,except Cu film.When the peak current is in the area where the current increment is constant and the voltage increment is zero,there are gullies and circular craters distributed on the target surface.The circular crater mainly appears on the surface of the target with low melting point(Al).At this time,the plating particles are mainly escape the target by thermal emission.A large number of thermal emission particles cause the film begin to become dense.The density of Al film and Cu film has been significantly improved.The crystallization degree,adhesion,deposition rate,corrosion resistance and conductivity of the three thin films have significantly improve.The hardness of Cu film reached the highest value of 2.61GPa at 13 A,while the hardness of Al film and Ti film both decreased.It shows that when the target current reaches a certain value,the increase in Ar+bombardment intensity causes a local area of intense thermal electron emission and the thermal emission mechanism of Joule heating effect.The high ionization,high energy and high density characteristics of the plating particles are realized,and a thin film with dense structure and excellent performance can be prepared.The high-frequency pulsed electric field environment can realize the transition of gas discharge from the abnormal glow discharge to the micro-arc discharge.The high-frequency oscillation characteristics of the electric field can increase the amount of Ar+that bombards the target surface.The on-off characteristics of the pulse can maintain the temperature of the target surface stable,which can not only achieve a high film deposition rate and particle ionization rate,but also avoid large-area fusion caused by heat accumulation on the target surface and damage the film quality.