Study On Sputtering Behavior And Sputtering Cleaning Of Magnetron Sputtering Target

In ultralarge scale integrated circuits,the use of copper(Cu)instead of aluminum(Al)as an interconnecting material is increasingly used because of copper’s higher conductivity,which not only reduces delay time,but also enables higher current density at lower voltages,minimizing heat generation and power requirements.In addition to the direct effect of sputtering process on the quality and performance of Cu thin films,the target material and its surface characteristics as the main material source of sputtering thin films will also affect the sputtering process and then affect the performance of the thin films.The sputtering stage and the sputtering cleaning stage in the process of sputtering coating are studied in this paper.Aiming at the sputtering cleaning stage,the influence of different working gases on the cleaning efficiency of pure copper surface was explored.Aiming at the sputtering stage,the effects of different grain sizes and different original surfaces on sputtering morphology,target voltage and film morphology were investigated.In addition,the etching mechanism of Cu target was also studied.The main findings are as follows:(1)The mechanism of sputtering etching of pure copper with grain size of 150 μm is studied.By changing the power parameters and the original surface roughness,the variation of the surface morphology of polycrystalline pure copper with etching time under different conditions is investigated.Scanning electron microscope and white light interferometer are used to characterize the grain orientation,surface morphology and surface roughness of polycrystalline pure copper after etching.The results show that the etching of polycrystalline copper is strongly influenced by grain orientation.The surface etching damage of {1 0 0}oriented grains is more serious than that of {1 1 1} and {1 1 0} oriented grains.The difference in etching rate leads to the formation of "step structure" between grains with different orientations.The grain boundary widened obviously with the increase of etching time.Many bumps or holes caused by ion sputtering were observed on the surface of the sample.The number of columnar prominences decreased with the increase of etching time.The evolution of surface roughness of pure copper samples after sputtering showed two stages: rapid increase to gradual stability.(2)In the sputtering cleaning stage,it is found that the removal effect of argon plasma on the surface pollutants of pure copper samples is better than that of nitrogen plasma.In the process of sputtering bombardment cleaning,the weight loss of the sample increases with the increase of sputtering bias,and the weight loss rate presents a periodic change rule.The reflectance test results show that the reflectance of the surface after argon plasma cleaning is about 33%,and that of the surface after nitrogen plasma cleaning is about 20%.Three-dimensional morphology analysis shows that the increase of surface roughness can be attributed to plasma etching on the surface of the sample.In addition,long-term plasma etching results in the redeposition of atoms or atomic groups on the surface of copper samples.(3)In the study of pure copper target at sputtering stage,the influence of copper target with different grain size and different original roughness on target voltage,surface roughness and film morphology are studied.The results show that the sputtering morphology of target surface is closely related to the grain size.The target voltage varies with the surface topography of the target during sputtering.In addition,the higher the original surface roughness of the targets,the higher the surface roughness after sputtering.The surface morphology of the completely sputtered region is independent of the original morphology of the Cu target.After sputtering,the uniformity of Cu target films with rough original surface is poor.