Effect Of Substrate Bias On Sputtering Behavior And Ions Property Of Magnetron Sputtering Discharge

Magnetron sputtering is widely used in the thin films deposition.The substrate bias is one of the important methods to control the structure and property of the films.Many investigations have shown that the crystallization and microstructure,the mechanical,optical,electrical and tribological properties,the chemical composition as well as the deposition rate of films can be improved or controlled by applying the substrate bias.These improvements were usually thought to relate to the increase of ions bombarding the substrate under the action of substrate bias.As a bias is applied to the substrate,due to the difference in electron and ion mobilities in the plasma,negative self-bias voltage on the substrate is induced.Under the action of negative bias,ions are accelerated toward the substrate with moderate energies.When these ions arrive or impact the substrate,they will transfer their kinetic energy to the adatoms and improve the surface diffusivity of them.Therefore,by this plasma-surface interaction,the growth and properties of films can be improved.Because many works were mainly paid attentions to the correlation between the substrate bias and the structure and property of films,and lacking of the detail investigation on ions behavior,it is generally thought that the role of substrate bias is to enhance the ionic bombardment.However,some works thought that the ion bombardment determined by the ion energy distribution(IED)because the ion energy is influenced by the collisions in the substrate sheath.In additional,the simulation and experimental measurement also supported that the RF substrate bias had more effect on the IED at the substrate.So,the detail investigations on ions behavior with substrate bias are needed.In this thesis,the effect of radio-frequency(13.56 MHz and 27.12 MHz)substrate bias on sputtering behavior and ions property of Ag target magnetron discharge were investigated.The sputtering behavior was investigated by the electric characteristics of magnetron target and bias discharges using voltage-current(I-V)probe technique.The ion velocity distribution function(IVDF),the maximum ion energy and ion flux density were measured at the substrate by a retarding field energy analyzer.The mechanism on the effect of substrate bias on IVDF was discussed.It was found that the substrate bias led to the decrease of sputtering power,voltage and current with the amplitude<7.5%.The substrate bias also led to the broadening of IVDFs and the increase of ion flux density,made the energy divergent of ions impacting the substrate.This effect was further enhanced by increasing bias power and reducing discharge pressure.The 13.56 MHz substrate bias led to the increase of ion flux density,the broadening of IVDFs,and the divergence of ion energy onto the substrate.The 27.12 MHz substrate bias led to the further increase of ion flux density,but the narrowing of IVDFs,and the centralization of ion energy.This effect was further enhanced by reducing discharge pressure.By voltage-current probe measurement on the electric characteristics of bias discharge,the change of IVDFs with substrate bias was found to mainly relate to the increase of bias voltage.According to above results,it can be found that for the magnetron sputtering,the RF substrate bias plays an important role in controlling ions energy distribution and ion flux density.The increase of ions bombarding on the grown films should be related to the ions energy density onto the substrate,depended on both the ions energy distribution and the ions flux density.