Focal depth limitations prevent use of normal lithography tools and processes on three-dimensional structures. A relatively little known form of uniform metal trace patterning over extreme 3-D structured wafers by a multi-step exposure method, called stitching technology, has recently been developed by Hewlett-Packard Company, with equipment support from the Ultratech Stepper Company, the result of which is being reported in this paper. The basic idea is to slice the metal lines to be patterned into topographic layers that can each be exposed in one step. Patches of patterned metal lines can thus be stitch-ed to one another (thus, the term stitching). Exposure of one photo-resist layer by stitching takes several individual exposures at different focus planes. A patent has been applied for this method on behalf of the Hewlett Packard Company. Results of the present investigation demonstrate the superior uniformity of metal trace pattern over 350-um deep trenches produced by multi-step exposure, as compared to the conventional single-step exposure method, typically used on planar semiconductor wafer. The integrated method offers an enabling technology for patterning of extensive topography typically required for a multitude of MEMS structures and designs, novel interconnect structures as well as advanced packaging applications. The method is simple, accurate and relatively low-cost in comparison with other 3-D exposure techniques available and capable of 3-D structure patterning.
A relatively little known form of photoresist coating for special applications of 3D structured wafer patterning by spray technology has been studied, specifically on the OnmiSpray coating technology developed by Electronics Vision Group Austria. Results of the present investigation confirm the superior uniformity of photoresist coating by spray technology on the high topography wafer structure compared to the conventional spin coating method, typically used on planar semiconductor wafer structure. Special attention is paid to the improvement of photoresist coverage on the convex corners of the 3D structure by rounding them off first in a TMAH solution. The integrated method offers an enabling technology for patterning of extensive topography typically required for a multitude of MEMS structures and designs, novel interconnect structures as well as advanced packaging applications. The method is simple, fast and low cost in comparison with other photoresist coating techniques available and capable of 3D structure patterning.