No (at least not entirely: some steps are done in a vacuum or very low pressure), in part because it's harder to get a vacuum than clean enough air. Also it would cause a lot of other problems as well as not solving the whole problem: a lot of processing steps involve applying chemicals to the surface of the wafer, washing off those chemicals, or otherwise handling liquids which would boil in a vacuum. Those chemicals (including just plain water), also carry the same risk of introducing 'killer particles', so they are also a big part of the process control needed in a fab (the levels of contaminants in water that is required on modern process nodes is actually lower than can be detected practically with current technology: the last levels of water purification are effectively done blind, with yield as the only feedback mechanism).