In-Situ, Time Resolved, Kinetics of Reactions in Co-Ge thin Films
- PDF / 285,485 Bytes
- 5 Pages / 420.48 x 639 pts Page_size
- 3 Downloads / 173 Views
IN-SITU, TIME RESOLVED, KINETICS OF REACTIONS IN Co-Ge THIN FILMS R.M. Walser, Byung-Hak Lee, Alaka Valanju, Winston Win and M.F. Becker Dept. of Electrical and Computer Engineering; The University of Texas, Austin, TX 78712 ABSTRACT We report the first kinetic study of metal-semiconductor interface reactions using insitu, time resolved, laser interferometry. Diffusion couples with Co/Ge thicknesses of 1500 A/1500 A were sputter deposited on silicon wafers, and vacuum-annealed at temperatures between 300°C-400*C. Under these conditions polycrystalline CoGe was expected to form [1]. Real time laser (HeNe 6328 A) interferograms for each anneal were recorded in-situ. These data were supplemented by information from AES and X-ray. For temperatures below 400*C the diffusion controlled formation of CoGe was observed. The composition was confirmed by Auger depth profiling that showed uniform Co and Ge concentrations when the reaction went to completion. The well defined interferences fringes were formed by the dissolution of amorphous Ge. The activation energy = 1.6 eV for the formation of CoGe were determined with precision from the temperature dependence of the time required to anneal the fixed X/4 distance between adjacent minima and maxima of the interferogram. We discuss the evidence for formation of an intermediate Co-rich compound following the initial diffusion of Co into Ge. The results of these experiments indicate that optical interferometry will be a valuable adjunct to other techniques used to study metalsemiconductor interface reactions. INTRODUCTION In-situ, time resolved, laser interferometry has been extensively used for studying the kinetics of silicon solid phase epitaxy [2J. It offers a continuous, in-situ, non destructive method of studying the growth of the crystalline interface. A depth resolution of 10 A can be obtained in the near surface region. In this work we used laser interferometry to measure the reaction kinetics of compound formation at the interface of a metal-semiconductor (Co-Ge) diffusion couple. In this novel technique, a highly accurate deternination of the reaction order and kinetic parameters is made by continuously measuring the time dependent changes in the in-situ, isothermal optical surface reflection. EXPERIMENTAL The substrates were single crystal 20 mil thick p-type silicon. The 6328 A line of a HeNe laser (2 mm 2 beam) was used for interferometry. A polycrystalline thin film of Co was initially deposited on the substrate followed by the deposition of an amorphous Ge layer. The layers were each 1500 A thick and sequentially sputtered from elemental targets in an RF diode sputtering system without breaking vacuum. Tile background pressure was 10-7 Torr and the sputter gas (Ar) pressure was 10 mTorr. The deposition rates for Co and Ge were 150 A/min and 187.5 A/nain respectively. A detailed description of the in-situ laser interferometry measurement and apparatus can be found in [3]. The incident laser beam was split in two beams, one of which was used as a reference beam. The
Data Loading...
