Reactions in Metal-Metalloid Multilayers
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REACTIONS IN METAL-METALLOID MULTILAYERS Robert Sinclair and Toyohiko J.Konno Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305
ABSTRACT We have studied the reactions at metal-metalloid interfaces using high resolution transmission electron microscopy, including in situ observation, and differential scanning calorimetry. There is contrasting behavior depending on the affinity for interaction or segregation. For reactive systems, compound formation ultimately results, but this can be preceded by solidstate amorphization. For non-reactive systems, crystallization of the metalloid is often achieved with nucleation and growth mediated by the metal phase. 1. INTRODUCTION Two types of behavior for the reactions which occur at metal-metalloid interfaces have been studied. These can be categorized according to whether the elements produce compounds upon heating (Reactive Systems) or whether they are mutually unreactive (NonReactive Systems). For the former, it is found that solid-state amorphization often precedes formation of the equilibrium compounds, whereas for the latter crystallization of an amorphous (e.g., metalloid) constituent can be promoted. Our work involves cross-section transmission electron microscopy (TEM), including high-resolution and in-situ annealing experiments, Xray diffraction and differential scanning calorimetry (DSC) and we have focused on transition metal/group IV element, metal/metalloid combinations, with some extension to compound semiconductors. 2. EXPERIMENTAL The interfaces of interest were prepared either by deposition of the metal onto a single crystal metalloid (e.g., Si) substrate using standard microelectronics fabrication techniques or in the form of tri- or multi-layers by sputtering. The latter were achieved by dc/rf magnetron sputtering onto the following substrates: (100) Si wafers, cleaved NaCl crystals, and slide glasses coated with photo-resist. These substrates were placed on a rotating table in the chamber which has been described previously. [1] The power of the guns and the speed of the rotation were adjusted to obtain the desired modulation wavelength and composition. The base pressures were in the 10-7 torr range. We studied heat evolution of the sample upon annealing using either a DuPont 9900 DSC, a DuPont 910 or a Perkin-Elmer DSC-7 system. The free standing films were obtained after the NaCI substrate was dissolved in water or after the photo-resist on the slide glasses was dissolved with acetone. The weight of these free standing film was then measured by a microbalance and heating was carried out under an inert atmosphere. Cross-section samples of as-deposited and annealed films were made by a standard procedure. [21 We used a Philips 430ST microscope operated at 300kV (resolution, 0.2nm or better) for the TEM study. In-situ heating experiments were carried out using a Philips single tilt heating holder with the reaction directly recorded by a Gatan image pick-up system. 3. RESULTS AND DISCUSSION 3.1 REACTIVE SYSTEMS Often se
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