The sputter performance of an industrial-scale planar Mo-target over its lifetime: Target erosion and film properties

Abstract

Magnetron sputter deposited Mo-based thin films are widely used as diffusion barriers and metallization layers for signal and data bus lines of flat panel displays or back electrodes of thin film solar cells. These films are deposited at large-scale from rectangular planar sputter targets, with the necessity of constant film thickness and properties over target usage. Within this work, a new 600 × 125 mm2 planar Mo-target was sputtered at a constant power of 3.5 kW until the erosion track reached 80% of the maximum useable target thickness. Every other 50 kWh, films were deposited onto a 9 × 5 matrix of (100) Si in different deposition modes (i.e. static and oscillation of the substrate carrier). By investigating the individual sample sets, the sputter behavior at different stages of target usage could be assessed. The sputter behavior changes with the progressing evolution of an erosion groove and affects thickness, stress and electrical resistivity of the films. In the beginning and end of target usage, films with low electrical resistivity and high tensile stresses are grown, whereas a medium target erosion leads to films with increased resistivity and lower tensile stresses. This time variance is attributed to two competing effects changing with proceeding target erosion, which affect the growth conditions of the films: (i) the increase of the reflection angle of Ar neutrals due to the evolution of an erosion groove, lowering the energy input into the growing film, and (ii) a rising number of Ar+ ions due to an increase of target current, directly affecting the overall number of reflected Ar neutrals, increasing the energy input into the growing film.