Gas pressure effects on thickness uniformity and circumvented deposition during sputter deposition process

In sputter deposition processes, the thickness distribution of the film is affected by experimental conditions such as gas pressure, target-substrate (T-S) distance and target elements. To study these effects, we have designed a sample holder with three quartz crystal microbalance (QCM) thickness monitors on its surface and measured the distribution of the depositing flux around the sample holder, including the circumvented deposition onto the back face. As for the gas pressure dependence for a T-S distance of about 50 mm, the relative deposition flux on the back face was found to be at its maximum at pressures of 1-2 Pa. Above this pressure, the uniformity of the flux on the front face became gradually worse. The observed characteristics could be reproduced by a Monte-Carlo simulation of the particle transport process. The reduction of the circumvented deposition and the uniformity degradation at high gas pressures were ascribed to the start of thermalization of sputtered particles and the shrinkage of its spatial profile toward the target.