Revitalization of Single Layer Lift-off For Finer Resolution and Challenging Topography

Randy Redd, David Maurer, L. Scott Klingbeil
Motorola Semiconductor Product Sector

The necessity for metal lift-off processes in the compound semiconductor industry is very acute because of the need to pattern non-reactive metals such as gold. As the gallium arsenide industry matures from the niche markets of the past to competing with the mainstream semiconductor industry, reducing manufacturing costs becomes increasingly important to ensure continued growth. Moreover, newer technologies have pushed the typical requirements for lift-off into a realm difficult to achieve with many existing methods. Presented, is the development work of a single layer and single exposure lift-off silicon nitride dry etch process prior to metal evaporation. Daily process control has been demonstrated with a variation of ± 0.032µ on 1.2µ nominal features. This lift-off technique relies upon a single layer of photo resist with no added costs for additional dielectric deposition and etch processes or applications of photosensitive polyamide layers. In addition to being relatively low cost, the improved performance has enabled development of new technologies with fine line requirements and challenging topographies.