Atomic layer deposition apparatus and method

An atomic layer deposition method, comprising:

• positioning a semiconductor substrate within a deposition chamber;
• feeding a first deposition precursor to the chamber under first vacuum conditions effective to form a first monolayer on the substrate, the first vacuum conditions being maintained at least in part by a first non-roughing vacuum pump connected to the chamber and through which at least some of the first deposition precursor flows, the first non-roughing vacuum pump being operated at a first substantially constant pumping speed while forming the first monolayer;
• and
• after forming the first monolayer, isolating the first non-roughing vacuum pump from the chamber and feeding a purge gas to the chamber under second vacuum conditions maintained at least in part by a second non-roughing vacuum pump connected to the chamber which is different from the first non-roughing vacuum pump and through which at least some of the purge gas flows, the second non-roughing vacuum pump being operated at a second pumping speed which is greater than the first pumping speed.