Novel I-line phase shift mask technique for submicron T-shaped gate formation

A novel submicron (<0.2 μm) T-shaped gate technology using a phase shift mask (PSM) technique is developed. The 8% half-tone PSM was selected for the definition of the isolated narrow space. Before lithography, a 2000 Å SiN film was deposited on the wafer. After i-line PSM exposure and reactive ion etching (RIE) of the silicon nitride film, openings less than 0.2 μm wide were formed on the SiN film. To further reduce the dimensions of the openings, an additional 566 Å nitride was then deposited on the wafer and etched back using RIE without any mask. An opening of 0.167 μm was formed on the wafer after the dry etching process. The wafer was then coated with another layer of photoresist to form a lift-off structure. The T-shaped gate with a length of 0.167 μm was obtained using this technique. The novel T-shaped gate technology is a high-throughput process for both silicon and compound semiconductor devices.