A novel I-line phase shift mask (PSM) technique for submicron T-Gate formation

Abstract

Submicron T-gate formation using I-line stepper with phase shift mask (PSM) technique [1,2,3] has become very attractive for GaAs MMIC technology due to its low capital investment and high throughput. In this paper a novel submicron (<0.2mum) T-gate technology using phase shift mask technique is reported. The 8% half-tone PSM was selected for the definition of the isolated narrow space. Before lithography, 2500Angstrom SiN film was deposited on the wafer. After I-line PSM exposure and RIE etch of the silicon nitride film, openings with less than 0.25mum wide were formed on the SiN film. To further reduce the dimension of the openings, the wafer was then deposited addition 500Angstrom nitride and etched back using RIE without any mask. Less than 0.2mum openings were formed on the wafer after the dry etch. The wafer was then coated with another layer of photoresist to form lift-off structure. Gate length of 0.185mum was obtained using this technique. This novel process is a high throughput T-gate process compared to conventional E-beam lithography technology for GaAs MMIC production.