The general aim of electron beam lithography is to achieve a maximum resolution, and therefore mostly very thin layers are used (50 – 500 nm). In a few cases however also very small structures with high aspect ratio are of interest. Examples for possible applications are electroforming processes or the generation of a nano-library for the storage of smallest substance samples. For this purpose, 4 μm-thick layers of the e-beam resist SX AR-N 7700.38 were exposed, tempered and developed (AR 300-47).
The acceleration voltage was 20 kV, the current 50 pA. Structural width values were strongly dose-dependent. In the case of an overexposure, the proximity effect (which is particularly pronounced at an acceleration voltage of 20 kV) becomes clearly visible as evident from the broadening of structures (Fig. 2). I an optimal dose is applied, 500-nm bars can be generated with a film thickness of 4 μm (aspect ratio 8). The aspect ratio is expected to improve further at higher acceleration voltages.
Fig. 1 Bars: 500 nm, height: 4 μ m, 30 μ C/cm², 20 kV
Fig. 2 Bars: 1 μ m, height: 4 μ m, 50 μ C/cm², 20 kV