Pattern transfer on a vertical cavity sidewall using SU8

In this paper, a process to realize metal lines on the sidewall of high aspect ratio cavities is developed. As an alternative to conventional photoresist, SU8 is used to define patterns on vertical sidewalls of deep cavities while maintaining compatibility with conventional IC processes. When transferring a pattern onto a 3D structure, especially the coating process, cavity filling and step coverage become important issues and require specific attention. A highly uniform SU8 coating is obtained and 20 ?m wide aluminium lines across 60 ?m deep cavities are realized. Problems related to overexposure and to aluminium etching are presented as well. The resistance of the aluminium structures on top, bottom and sidewall of the cavities is measured and discussed.