Novel electron beam lithography technique for submicron T-gate fabrication

Submicron T gates have been fabricated using the high resolution electron beam lithography technique. The footprint of the T gate has been written in high molecular weight poly-methyl methacrylate (PMMA), whereas the top of the T gate is defined in AZ PF 514. A 400 nm thick layer of PMMA was first exposed and developed followed by the spinning of AZ PF 514. A wide line defining the top of the T gate was written in this resist which after development gave a T-shaped cross section. As both the bottom and the top of the T gate are dealt with independently, therefore, the technique provides a high degree of control and flexibility in the fabrication process. Moreover, the possibility of shorting of the top of the T gate with the Ohmic metallization is virtually impossible. Consequently, the-process is a very good candidate for low-noise GaAs metal-semiconductor field-effect transistors (MESFETs) fabrication in which a narrow drain-to-source gap is required. GaAs MESFETs with T-shaped gates have been fabricated and characterized by de measurements. (C) 1997 American Vacuum Society.