ELECTRON-BEAM ULTRAVIOLET HYBRID EXPOSURE COMBINED WITH NOVEL BILAYERRESIST SYSTEM FOR A 0.15-MU-M T-SHAPED GATE FABRICATION PROCESS/

Electron-beam/ultraviolet (UV) exposure technology to produce undercut T-shaped resist cavities with bottom openings as small as 0.15 mu m i s demonstrated with a novel bilayer resist system for AlInAs/InGaAs hi gh electron mobility transistors operated at the millimeter-wave band. We employed an image reversal resist (AZ5206E) for the top layer and a polydimethyl glutarimide (PMGI) for the bottom layer. The top layer is delineated by UV exposure and the bottom layer is delineated by ele ctron-beam direct writing. These resist layers are developed layer by layer in different content aqueous tetramethyl ammonium hydroxide solu tion. Resist profiles are extremely well controlled because exposure a nd development of both layers are completely independent. A reliable o verhang structure for metal liftoff, with a 0.15 mu m footprint, was o btained. Gate length variation of less than +/- 10% on a 3-in.-diam In P substrate was successfully accomplished. In addition, an interesting phenomenon was noted. The combination of these two resists leads to a n electron-beam sensitivity decrease of PMGI. This phenomenon is close ly related to the change of molecular weight distribution in PMGI. The novel bilayer resist system also allows the further improvement of re solution. This would provide a practical means for electron-beam litho graphy in the nanometer region. (C) 1996 American Vacuum Society.