SiNx-submicrometer coatings - Optimization of the film properties

The influence of the deposition conditions on the properties of SiNx-coatin gs was investigated. The characterized SiNx-coatings were deposited by the help of reactive magnetron sputtering. Gas pressure and film thickness were varied. Scanning electron microscopic views of the cross sections show a c olumnar structure varying with the deposition parameters. The different str uctures are comparable to the known structure zone models. There is a trans ition from dense structures to open columnar structures with increasing gas pressure. The Microstructure of coatings also changes with increasing film thickness. Especially deposition conditions promoting shadowing effects le ad to a large growth of the column diameter with increasing thickness. The intrinsic stresses and the ultramicrohardness of the coatings change wi th changing gas pressure, too. Dense structures have high intrinsic stresse s and a high hardness while coarse columnar structures have low intrinsic s tresses and a low hardness. The influence of the deposition parameters on w ear behaviour and adhesion of the SiNx-coatings was investigated by cavitat ion tests. Dense coatings with high intrinsic stresses show adhesion failur es, and coatings with lower stresses and coarse columnar structures fail be cause of their lower intrinsic stability. Thus, there is an optimum gas pre ssure, at which the best properties are reached. It can be shown that with decreasing film thickness adhesion increases.