Compact high-intensity pulsed x-ray source, particularly for lithography

摘要

A photoemissive photocathode, being a metal with a low work function and preferably tantalum-surfaced cesium-antimonide, is illuminated with pulses of 5320 Å laser light, typically 20 psec at a 20 Hz repetition rate, to emit electrons by the photoelectric effect. The emitted electrons are accumulated in a spatial region near the photocathode by a grid electrode. The same laser pulses activate a semiconductor switch, normally an LiTaO.sub.3 crystal doped with 2.24% Cu, to apply a high voltage, typically 100 Kv, between the photocathode and an anode. The accumulated electrons are accelerated, and focused, as an electron beam that strikes the anode, typically in a focal spot of less than 0.5 mm diameter. Time-resolved x-ray pulses, typically K band of 20 picoseconds duration with 4-10 microjoules energy each, are produced. A laser-induced pulsed wide-area table-top-size embodiment of the x-ray source reliably generates a 1-10 mW/cm.sup.2 flux of hard, 0.1- 1 nm, x- rays from picosecond duration laser pulses, and a 20-40 mW/cm. sup.2 flux of x-rays from 20 ns, 193 nm laser pulses at a pulse repetition rate of 300 Hz minimum, 1,000 Hz typical. The x-ray generation is uniform over a large 20 cm.sup.2 anode area. A mask is placed in direct contact with the anode for lithography.