Room-Temperature Recrystallization in Thick Bias-Sputtered Copper Deposits

Abstract

Deposits of copper up to 1 mm thick were formed at room temperature in a triode sputtering apparatus using a krypton discharge under various conditions of sputtering rate, gas purity, and substrate bias. Room-temperature recrystallization and grain growth displaying no twins were observed within 9 h after removal from the sputtering apparatus. This resulted in a dominant orientation of {100} planes parallel to the substrate-deposit interface. Recrystallization rate increased as a function of increasing deposition rate, gas purity, and substrate bias. It was hypothesized that high intrinsic stress levels in the deposit provided both vacancies and the driving force for their diffusion to grain boundaries. Grain boundaries composed of {100} planes then adsorbed vacancies and moved by a combination of climb and glide. This movement was made possible by the elimination of barrier impurities, primarily oxygen, with the negative bias applied to the substrate during sputtering.

Increasing the mean grain size in copper films and features

“…Contrary to popular belief, the self-annealing phenomenon for Cu is not a unique consequence of the electroplating process. Although there is early work by Patten et al [101] describing microstructural evolution during the storage of sputtered deposited Cu films, room-temperature, self-annealing has not been widely observed in physical vapour deposited copper [102]. Recently, Rossnagel et al [103] and Bernat et al [104] showed that the resistivity in sputtered deposited copper films (with thickness below 100nm) descreases during storage after deposition.…”

Recrystallization Textures of Metals and Alloys

“…Patten et al [24] formed deposits of Cu up to 1mm in thickness at room temperature in a triode sputtering apparatus using a krypton discharge under various conditions of sputtering rate, gas purity, and substrate bias. The 3.81 cm diameter target was made from commercial grade OFHC forged Cu-bar stock containing approximately 100 ppm oxygen by weight with only traces of other elements.…”

Residual stress analysis in thick uranium films

“…Current research on sputtered films deposited with a bias voltage is based mostly on thin films (<300 nm) with FCC and BCC structures. Patten et al study the effects of a small substrate bias (À70 V) on the microstructure of thick Cu and Cr films (up to 1.0 mm) [19,20], however there is no measure of residual stresses. For thin films, there are a few samples of the effects of bias on the residual stresses.…”

“…Literature on thick films (25 lm) is very sparse with few exceptions [8,19]. Current research on sputtered films deposited with a bias voltage is based mostly on thin films (<300 nm) with FCC and BCC structures.…”