The Evaluation of a Single-Step Lift-off Process Using the Method of Response Surface Analysis

The method of metallization after resist exposure and development as described by Hatzakis et al, has been shown tb be useful in the fabrication of semiconductor metal interconnections [1, 2]. A more recent innovation of this method, the "Single-Step Lift-off Process" [3], has been shown to be less complicated and easier to use than most other lift-off processes. In this process, the top layer of a single resist film is made less soluble than the underlying resist material by soaking in a solvent. This top layer will now develop at some rate less than the remaining resist film thus causing an overhang of resist- suitable for metal liftoff applications. A typical process flow for this process is given in Fig. 1. For this test series, the image size and undercut measurements were done after image develop using scanning electron microscope cross-section pictures. Also, the time required to develop through the exposed resist film was monitored and is labeled as the develop end point. All times referred to in this report will be as a percentage beyond the end-point time.