| When the dimensions of the silicon transistor go below 70 nm, it is generally believed that current optical lithography will not meet the resolution requirements. Electron-beam lithography (EBL) provides a potential alternative solution at these dimensions. However, present EBL systems can't provide acceptable throughput. To obtain high throughput as well as high resolution, multiple electron-beam systems will be required.; Thin-film gated photocathodes provide a promising technology for such multiple-beam, high throughput EBL systems. These devices use a thin-film photoemitting material on a transparent substrate which is illuminated by a continuous wavelength (CW) ultraviolet laser with wavelength of 257 nm from the backside of the substrate. The photoemitted electron-beams are modulated electrically by a thin-film gate constructed above the photocathodes. This novel structure removes the complex optical system that is necessary for other photocathode approaches. The simplicity of defining and scaling the electron-beam size, the potential high brightness, and the compatibility with conventional silicon processing make gated photocathode arrays an attractive approach for multiple-beam electron-beam lithography.; This thesis carried out a detailed study of thin-film gated photocathodes. Energy distribution curves (EDC) and angular distribution curves (ADC) of photoemission from gold thin films were first studied theoretically and experimentally to understand and model the emission characteristics from thin-film photoemitters. A theoretical model for gated photocathodes based on these EDC and ADC results was developed to address the operational principles and to calculate currents as a function of gate voltage for a variety of conditions. Different device fabrication schemes were examined, and once a successful scheme was demonstrated ten different gated photocathodes with different geometry configurations were fabricated for detailed experimental characterization. The excellent agreement between theoretical and experimental results verifies the theoretical model that was developed for gated photocathodes. Extrapolation of the experimental results suggests that arrays of such devices can efficiently modulate emitted currents without interference between them with the application of only a few volts to the gates. From this study, it can be concluded that arrays of thin-film gated photocathodes offer an attractive option for use in multiple-beam electron-beam lithography. |
