We have measured the stress in Mo/Si multilayer films deposited by magnetron sputtering, using the wafer-curvature technique, and find a strong dependence on background pressure. For multilayers containing 40 bilayers of ˜4.3 nm Si layers and ˜2.6 nm Mo layers, the stress increases from approximately −280 MPa (compressive) to −450 MPa as the background pressure in the deposition chamber (i.e., measured just prior to deposition) decreases from 1.0 } 10−5 to 6.0 } 10−8 torr. For multilayers of the same period but with thicker Mo layers, the dependence on background pressure is even stronger. X-ray (λ = 0.154 nm) diffraction measurements reveal a slight increase in interfacial roughness for films deposited at high background pressure. Atomic concentrations of incorporated oxygen and carbon, measured with Auger electron spectroscopy, were found to be less than ˜0.5 at.% for all samples. However, the average hydrogen concentration, as determined from forward-recoil-scattering measurements, was found to vary from ˜0.3 at.% to ˜1.6 at.%, increasing with both background pressure and Mo layer thickness. We discuss possible mechanisms for the observed dependence of film stress on background pressure, including gas incorporation and the affect of residual gas atoms on adatom mobility.