Dependence of Stress on Background Pressure in Sputtered Mo/Si Multilayer Films
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ABSTRACT 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 x 10-5 to 6.0 x 10-8 torr. For multilayers of the same period but with thicker Mo layers, the dependence on background pressure is even stronger. X-ray (X = 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.
INTRODUCTION The stress in a multilayer (ML) film is determined by the stresses in the individual layers that comprise the multilayer, and by any interfacial stresses that may be present. The deposition stresses in the individual layers, i.e., the stresses resulting from non-equilibrium growth conditions, are highly dependent on the details of the deposition conditions. Thus, the stress in a ML film, as in a single-layer film, is process dependent, in general. In the case of sputtered films, the stress depends on such parameters as working gas pressure, substrate bias, and substrate temperature. For example, it is by now well-known that the stress in single-layer films prepared by magnetron sputtering can be adjusted from tensile to compressive simply by decreasing the pressure of the working gas [1], and the same effect was reported recently for ML films [2]. In order to control precisely the stress in ML films, we must, therefore, first characterize any dependencies of ML stress on deposition conditions. In this paper we report the results of an investigation of the stress dependence on background pressure in ML films composed of molybdenum and silicon layers prepared by magnetron sputtering. The stress in Mo/Si MLs has been reported previously [3]; however, to our knowledge, the dependence of stress on background pressure in these, or in any other ML structures, has not. We present here only a brief summary of this research; a more complete description will be published elsewhere. 137
Mat. Res. Soc. Symp. Proc. Vol. 356 01995 Materials Research Society
EXPERIMENT ML films were deposited by DC magnetron sputtering, using argon (99.998% purity) as the working gas, maintained at a pressure of 1.5 mTorr (0.2 Pa) with a closed-loop-fe
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