- Volume 26 Issue 10
The overhang structure of photoresist in optical lithography was studied for the metallization of GaAs-related devices throughout lift-off method. Optical contact aligner with a dose of 8.5 m J/cm\ulcornerand with a wavelength of 300mm was used for ultraviolet exposure of single layer of S1400-27 photoresist. The overhang thickness shows a linear relationship with the soaking time in monochlorobenzene, which its magnitude becomes high at elevated softbake temperature. Such process conditions as a low softbake temperature, a long monochlorohbenzene soaking time and a little exposed energy make the development rate of photoresist lower. The optimum process conditions to obtain a target line-width, which include an appropriate overhang structure such as complete separation between the sidewall of photoresist pattern and the deposited metal edge, are determined as the softbake temperature of 64-74\ulcornerC, the monochlorobenzene soaking time of 10-15min, the ultraviolet exposure time of 70-100sec and the development time of 50-80sec.