Patterned negative electron affinity photocathodes for maskless electron beam lithography

This work focuses on two issues crucial to achieving high throughput with a negative electron affinity semiconductor photocathode source. Monte Carlo simulations indicate that for a 50 kV system, as much as 8 mu A of current may be delivered to the wafer to achieve a raw throughput of 20 8 in. wafers per hour with 0.1 mu m minimum feature size (assuming a resist sensitivity of 10 mu C/cm(2)). In order to achieve the throughput potential of this approach, suboptical emission areas are required; this suggests the use of cathode patterning. Two patterning alternatives have been investigated experimentally, and both approaches have been used to generate arrays of more than 100 electron beams with source sizes as small as 150 nm. However, each type of patterned cathode presents unique challenges to fabrication and performance in a practical multibeam system. Different source configurations (number of beams, beam current, beam spacing, etc.) create a system-level tradeoff between resolution and throughput. Results from patterned cathode experiments and system modeling are presented. (C) 1998 American Vacuum Society. [S0734-211X(98)15806-7].