Semiconductor technology has developed considerably during the past several decades. The exponential growth in microelectronic processing power has been achieved by a constant scaling down of integrated cir, cuits. Smaller fea ture sizes result in increased functional density, faster speed, and lower costs. One key ingredient of the LSI technology is the development of the lithog raphy and microfabrication. The current minimum feature size is already as small as 0.2 /tm, beyond the limit imposed by the wavelength of visible light and rapidly approaching fundamental limits. The next generation...