In a large variety of lift-off applications, the resist layer is exposed to high thermal loads. In particular during sputtering processes without additional cooling, temperatures of more than 150 °C may occur. Positive-tone resists based on novolacs begin to melt at these temperatures and render thus a subsequent lift-off process impossible.
Allresist developed for this reason a series of temperature-stable negative photoresists. One of the first samples, the SX AR-N 4340/10, was assessed in the CTR Research Center for Intelligent Sensors with respect to its resistance to higher temperatures.
Process procedure: In a first step, the non-light-sensitive bottom resist AR-P 5460 is applied and tempered at 150 °C. Subsequently, the new negative-tone photoresist SX AR-N 4340/10 is spun onto the bottom resist and dried at 85 °C. After UV-exposure and development with AR 300-44, the desired undercut is obtained. The resist structure was then again tempered at 200 °C.
The undercut was fully preserved in this process (see image 1). This resist is consequently predestined for high-temperature applications. Further investigations with respect to even higher temperature loads are currently in progress. These highly interesting results prompted us to those our new development of a thermally stable negative resist as resist of the month
[Bild] „Twolayer_Temperature“ https://www.allresist.de/wMedia/img/gross/Zweilagen_Temperatur.jpg
Image 1 Lift-off structure of the SX AR-N 4340/10 – AR-P 5460 system tempered at 200 °C.