Thin-film processing on a thick-film multilayer

Spin-on and lithography steps in thin-film processing require planar and smooth surfaces. Usually ceramic substrates with as-fired surface roughness of R(a)<0,1 mu m or with polished surfaces for advanced requirements are used. In general a thick-film hybrid shows an inappropriate surface for a further successful thin-film processing. In this work the influence of surface roughness and topography on the properties of thin-film conductors and the fabrication of vias are investigated. Surface smoothing and local planarisation can be achieved by the use of an thick-film overglaze or by coating the surface with polyimide prior to thin-film processing. The improvements in conductor and via yield are measured by adequate test structures with a conductor width of 25mu m. Based on the results a process is given to provide a thick-film multilayer with a sufficient smooth and planar surface suitable for thin-film processes.