Amorphous silicon carbide and its application in silicon micromachining

A new passivation material for application in microsystem technologies is presented for the first time. Silicon carbide is known to have good chemical resistance and mechanical properties. The deposition of layers reported here was performed in a parallel-plate plasma reactor with hexamethyldisilane (HMDS). The HMDS was supplied by a liquid bubbler line and argon was used as carrier gas to provide a sufficiently high flow of gas. The principal deposition parameters investigated are temperature and r.f. power. These parameters have the most direct influence on the layer properties compared to other possible parameters such as total flow, r.f. frequency or total pressure. Besides the primary results for deposition rate, homogeneity and step coverage, further important properties for the application are stress in the layers and etch resistance. These properties were investigated in relation to the chemical composition of the amorphous silicon carbide. The amount and kind of stress (compressive or tensile) influence the adhesion of the layers to different materials and also the application as membranes. Tempering of the carbide at 450 and 1000 °C was also part of our investigation even though the latter temperature is not compatible with aluminium.