Single-Step Lift-off Process with Toluene and Shipley 1813 Type photoresist
Ali Rostami, Saeid Masoumi
"Lift-off" is a simple, easy method for making metallic patterns on a substrate, especially for metals such as platinum and nickel which are difficult to be etched by conventional methods that involve wet chemical or dry reactive ion etching. The mechanism of the toluene single-step lift-off process is defined. The toluene penetrates to some depth into the resist film during the soaking cycle, extracting residual casting solvent and low-molecular-weight resin species. The toluene is subsequently removed by a rinse cycle. The penetrated layer of resist develops at a slower rate than the underlying bulk resist, producing the lift-off structure. Variances in the structure of the photoresist lift-off image are the result of complex interactions among exposure, toluene soaking, development, and post-application baking conditions. Effects produced by these variables can be controlled by monitoring the linewidth, overhang, and height of the lift-off resist structure using a scanning electron microscope (SEM). So, the purpose of this paper is to provide the details of the lift-off process using toluene to create the patterns with the highest accuracy. After each test, cross section of the patterned dry film side wall is observed under a microscope to check if a profile is obtained.