In Situ Stress Measurements of Co-Based Multilayer Films
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YOUNG-SUK KIM AND SUNG-CHUL SHIN Department of Physics, Korea Advanced Institute of Science and Technology, Yusung-Gu, Taejon 305-701, Korea
ABSTRACT We have constructed an apparatus for in situ measurement of stress of the film prepared by sputtering using an optical non-contact displacement detector. A change of the gap distance between the detector and the substrate, caused by stress of a deposited film, was detected by a corresponding change of the reflectivity. The sensitivity of the displacement detector was 5.9 1iV/A and thus, it was turned out to be good enough to detect stress caused by deposition of a monoatomic layer. The apparatus was applied to in situ stress measurements of Co/X(X=Pd or Pt) multilayer thin films prepared on the glass substrates by dc magnetron sputtering. At the very beginning of the deposition, both Co and X sublayers have subjected to their own intrinsic stresses. However, when the film was thicker than about 100 A, constant tensile stress in the Co sublayer and compressive stress in the X sublayer were observed, which is believed to be related to a lattice mismatch between the matching planes of Co and X.
INTRODUCTION Stress in a film is known as a prime limitation to the growth of very thick films and an important factor that influences many physical properties of thin films. For instance, stress on the magnetic thin film affects magnetic anisotropy via inverse magnetostriction mechanism. In particular, the stress induced-anisotropy is often referred to one of the origins of perpendicular magnetic anisotropy in Co-based multilayer films[ I]. Various methods have been suggested for stress measurements[2], among which the cantilever beam technique pioneered by Klockholm[3] is widely used. In this method, one side of the substrate is fixed by a substrate holder and the other side of the substrate is free to move. Stress of a film is determined by detecting the deflection of a thin substrate as the film is deposited on it. The cantilever capacitance methd [4] has been popularly adopted for in situ measurement of deflection. However, this method cannot be applied to a sputtering system, since the capacitance is largely influenced by plasma existed during sputtering process. Therefore, we have adopted an optical method, where a change of the reflectivity with deflection of a substrate was monitored. In this paper, we describe an in situ stress-measurement apparatus using an optical displacement detector and report in situ stress measurements of Co/X (X=Pd, Pt) multilayer films prepared by dc magnetron sputtering.
285 Mat. Res. Soc. Symp. Proc. Vol. 382 ©1995 Materials Research Society
EXPERIMENT Description of an apparatus In Fig. 1, we depict a schematic diagram of an optical displacement-detection apparatus for in situ measurement of stress of a film. A displacement sensing probe, detecting a deflection of the substrate was composed of 38 multimode optical fibers of 50-ýtm core diameter and it was located behind the free end of the substrate. 38 optical fibers glued using a liqui
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