Abstract: Reduced-pressure (“vacuum”) chambers, and microlithographic exposure systems including one or more of such chambers, are disclosed. The vacuum chamber exhibits reduced deformation of a bulkhead of the chamber during evacuation of the chamber or occurrence of a change in pressure differential across the bulkhead. A “pan” (serving as a secondary wall) is situated at a gap distance from the bulkhead. A secondary reduced-pressure chamber is formed in the gap between the pan and the bulkhead. The secondary reduced-pressure chamber is isolated from atmospheric pressure outside the chamber and from the subatmospheric pressure inside the chamber. The differential between atmospheric pressure and the pressure inside the secondary reduced-pressure chamber is exerted on the pan, but the pressure differential has substantially no effect on the bulkhead, thereby reducing deformation of the bulkhead.