Research On Solid State Connection Between High Purity Copper And Copper Alloy

High-purity copper targets are mainly used as cathode materials for sputter coating in the semiconductor industry.The deposited thin film wires have a number of merits such as low resistivity,good electrical,thermal conductivity,and good reliability in a large temperature range.Therefore,the industry generally begin to use high-purity copper wiring to replace the previous aluminum wiring in the ?90 nm linewidth process node.The good and stable performance of target welding will directly affect the conductivity during the sputtering process of the target,and the thermal conductivity determines the quality and stability of the film that was deposited by the high-purity copper target.Therefore,it is great significance and practical value to study a large-area diffusion welding technology of high purity copper target and copper base alloy for semiconductor integrated chip magnetron sputtering.In this paper,the defect situation and properties of joints were investigated by using optical microscope,scanning electron microscopy and energy dispersive spectrometer.The effects of different welding process parameters and surface texturing on the microstructure and performance of joints were investigated.The results show that when the welding surface was not textured,even if the welding temperature was greater than the recrystallization temperature of the material,the tensile strength of the joint could not meet the requirements of high-purity sputtered copper target.However,the surface roughening treatment could effectively pierce the surface oxide layer,which acquired a close contact between two fresh bonding faces to form a certain mechanical occlusion strength.In addition,it could increase the contact area of the interface between the two materials,which contributed to the diffusion behavior between atoms.Under certain pressure conditions,the depth of mutual intercalation between two materials depended on the influence of ambient temperature.The higher the temperature,the better the plasticity of the material,and the deeper the embedding.The treated surfaces of 0.22×0.06 mm,0.22×0.11 mm and 0.22×0.16 mm could be effectively embedded in the high-purity copper target body to form a tight bond at 320 ?.At the 260 ? welding temperature,Since the plasticity was decreased,only surface texturing of 0.22×0.11 mm and 0.22×0.06 mm could be completely embedded in the high purity copper target body to form a tight bond.The surface texturing of 0.22×0.16 mm could not be completely embedded at a lower temperature to form a tight joint,and the formed pores might affect the joint performance.The performance of joints that used surface texturing of 0.22×0.11 mm reached 91 MPa.Before the diffusion bonding of the samples,fine and uniform grains were distributed inside the high-purity copper target,but there was still a small amount of incomplete recrystallized grains.The density of small grains was higher.Meanwhile,there was difference between the internal energy of the grains.When the temperature was lower than 260 ?,the performance of the grains was relatively stable.With the temperature increasing to 290 ?-320 ?,the grains with higher internal energy began to change.The grain boundaries gradually became clearer and the grain size began to grow up to 24-28 ?m.When the temperature continued to increase to 350 ?-380 ?,the grain size reached approximately 50 ?m.The crystal grains gained sufficiently driving energy and grew up,so that the grains were in an equilibrium state.The grain boundaries also became stabile,indicating that the recrystallization of the crystal grains was almost completed at this temperature,and the microstructure was in a state of balance.The performance parameters such as bonding rate and tensile strength would obviously improve with the increase of bonding temperature.The results of energy spectrum analysis showed that the diffusion behaviors of element were not obvious at 200 ?.However,it was observed that the Cr element was appeared in the backing plate alloy at 260 ? and 320 ?,which indicated that the strong atomic diffusion between the backing plate and the target occurred at higher temperature.The theoretically higher welding temperature and longer welding time would be beneficial for welding performance.However,due to the particularity of the target products,when the temperature was higher than 260 ?,the grains of the high-purity copper sputtering target itself would start to change,which was not conducive to the performance stability of the target products.When the holding time was more than 5 h,the effect of holding time on the joint performance was not particularly noticeable.Through the study on the process parameters such as texturing treatment,temperature and holding time of the target joints,and considering the cost and performance stability of the products in large-scale production in actually industrial production,it was determined that the optimal diffusion bonding process parameters are: bonding temperature = 260 ?,bonding pressure = 105 MPa,surface texturing type = 0.22 × 0.11 mm,holding time = 5 h.The optimal diffusion bonding process obtained from the experiments was applied to the production of industrial scale 12-inch high-purity copper targets.The bonding rate,strength and grain uniformity of the joints were good,and the deposited film were integrated without any defect.The process requirements of the semiconductor 90-28 nm can be applied to industrial scale production.