A high resolution double layer photoresist structure for lift-off technology

A novel process of preparing a double layer positive photoresist structure for lift-off technique is described. The key step in the process is a treatment of first resist surface in a CF4plasma to form a thin buffer layer which is UV transparent and insoluble in resist solvents and alkaline aqueous developers. AZ-2400 and AZ-1300 series positive photoresists are selected to process the "overhang" resist profile suitable for lift-off application. Al line 1 µm high and 1 µm wide can be lifted cleanly. A structure of 1 µm by 1 µm grating was processed to demonstrate the resolution capability and undercut control of the new double layer resist process. Fabrication of a 1 µm gate GaAs MESFET is described to demonstrate the application.