EBL Bi-layer resist scheme for CdTe/Si submicron structures for lift-off processing

The fabrication of CdTe multi-pixel imaging detectors with the pixels of submicron size and photonic structures requires the use of high resolution lithography technique such as electron beam lithography (EBL). The main drawback of CdTe submicron structures made by the combination of EBL and conventional lift-off processes is the large roughness at the edges of CdTe structure, due of the use of a single polymethylmethacrylate (PMMA). To solve this problem, we used a bi-layer resist scheme of two polymers with different lithography characteristics. The bottom layer was a copolymer which has both minor molecular weight and higher sensibility than the upper PMMA layer. Different exposure doses were experimented, and the length and shape of the undercutting of copolymer layer under PMMA were characterized in the optimum range from 250 to 500@mC/cm^2. These results were applied to the fabrication of submicron CdTe structures by EBL, and subsequent CdTe vapor phase epitaxy (VPE) and lift-off step processing.