Effect of auxiliary magnetic field on the conformal coverage of the microtrenches in high power impulse magnetron sputtering

Abstract

Abstract In PVD technology, it has been demonstrated that the conformal coverage on the microtrench can be improved by substrate biasing, but to a limited extent. Inspired by this, applying an auxiliary magnetic field in HiPIMS was proposed to reinforce the effect of substrate bias on conformal coverage capability. Zr films were deposited on the two microtrenches (aspect ratio of 4.75:1 and 1:1) by the HiPIMS with the auxiliary magnetic field and the conventional HiPIMS, operated at different substrate bias. The coverage ratio and film morphology of Zr films on the two microtrenches were systematically investigated by SEM. It showed that the introduction of the auxiliary magnetic field achieved an improved conformal coverage on two differently sized microtrenches, exhibiting a denser morphology, higher coverage ratio and higher uniformity. Moreover, the composition of the plasma impinging into the microtrenches and the electric field of substrate bias surrounding the microtrenches were analyzed by OES and finite element method. The plasma behavior and the deposition mechanism on the microtrenches were discussed. It revealed that the auxiliary magnetic field greatly increases the collision events, plasma density and thus the proportion of low energy ions in front of the substrate. These altered plasma characteristics make three contributions to the coverage of the microtrenches: (i) enhanced plasma density provided more film-forming species for microtrenches (ii) and appropriately increased the degree of resputtering on the bottom of the microtrenches under the substrate bias, and (iii) a higher proportion of low energy ions reinforced the deflection of the substrate bias on the motion path of incident plasma. They fundamentally enhance the effectiveness of substrate bias on plasma behavior control and weaken the shadowing effect. The results demonstrated that HiPIMS operating with auxiliary magnetic field and substrate bias is a reliable solution to improve the coverage ratio and dense morphology of the microtrenches.