Automatic monitor for ammonia in clean room air

Ammonia in a lithography process environment causes degradation of lithographic performance in chemically amplified resist systems. An air monitor was developed for analyzing the ammonia in clean-room air by combining a diffusion scrubber sampling system and an ion chromatography for detection. Air samples ranging in concentration from sub mu g/m(3) to 60 mu g/m(3) could be measured at 10-min intervals (minimum) with good reproducibility. A multiple-point monitor was also developed by augmenting the original. The monitor had two diffusion scrubber units each of which consisted of a diffusion scrubber, an air pump, and a valve for changing two sampling ports. When one diffusion unit was measuring the air sample, the other was on standby and conditioned with the next air sample for 25 min. Since the air sample measurement and the conditioning with the next air sample were carried out concurrently, the time lag could be shortened and it took only 1 hour to measure at four different points.