METHOD AND APPARATUS FOR MEASURING DUST IN SEMICONDUCTOR PRODUCTION PROCESS

摘要

PURPOSE:To detect ultrafine particles, by a method wherein floating particles are irradiated with a part of a two-split laser beam to generate a scattered beam thereof while the other part thereof is combined with the scattered beam by a frequency deviation thereof and a beat signal detectable from the composite beam is detected. CONSTITUTION:A part of an emission beam from a laser 11 is transmitted through a beam splitter 12 and passes through a detection cell 3. The scattered beam within the cell 3 passes through lenses 5 and 6 and a slit 7 and then through a beam splitter 17 via a lens 16. On the other hand, light reflected with the splitter 12 is inputted into acoustooptical modulators 13 and 14 and the emission beam with the frequency deviated is reflected with a total reflecting mirror 15 to be incident into a splitter 17. A composite beam obtained from the splitter 17 comes into a silicon avalanche photodiode 18 and an output current thereof is counted by a counter 10 through an amplifier 19 and a waveform digitizer 20. This enables the checking of weak scattered beams due to ultrafine particles thereby allowing the detection of the ultrafine particles.