Microstructural Studies of Co Silicide Layers Formed on SiGe and SiGeC
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ABSTRACT Transmission electron microscopy is used to investigate the structural development as a function of the annealing temperature of Co-silicides prepared on SiGe and SiGeC. The transition temperature from Co(SiGe) into Co(SiGe) 2 is higher for SiGeC than for SiGe.
INTRODUCTION Metal-silicides have been widely used in Si based devices because of their low resistivity, low contact resistance and high thermal stability [1]. Compared to the previously used C54TiSi 2 , CoSi 2 has attracted much interest due to its better properties for ultra large scale integrated circuits (ULSI) fabrication [2]. SiGe/Si alloys have been used for high performance electron device applications, such as heterojunction bipolar transistors, heterojunction field effect transistors, and infrared detectors [3]. However, owing to the lattice-mismatch between Si and Ge ( - 4%), misfit dislocations are formed if the layer thickness exceeds a critical value, which leads to the limitation of device design flexibility. Recently, it was shown that the strain introduced by the Ge atoms can be compensated by the addition of substitutional carbon [4]. Metal reaction with SiGe alloys has been reported for Pt, Pd, Ti and Co [5-12]. Among the various silicides, CoSi 2 is a very attractive material because of its low resistivity and possibility of self-aligned formation at relatively low temperature. This paper presents the investigation of the structural development as a function of the annealing temperature of Co-silicides prepared on SiGe and SiGeC.
EXPERIMENTS The SiGe and SiGeC layers used in this work are grown by rapid thermal chemical vapour deposition on n-type Si(1 00) substrates. The thickness of SiGe and SiGeC is 35nm and 32nm, respectively. The Ge contents as measured by Rutherford backscattering spectrometry (RBS), are 20% for the SiGe layer and 18% for the SiGeC layer. The nominal C content is 0.9%. The wafers are dipped in HF solution before loading in a DC magnetron sputtering system for deposition of a 18nm thick Co layer. Silicidation of Co with SiGe and SiGeC is performed by
359 1997 Materials Research Society Mat. Res. Soc. Symp. Proc. Vol. 448 ©
rapid thermal processing (RTP) in a N 2 ambient at temperatures from 500 to 1000*C. The annealing time is always 30s. The microstructure of these implanted samples is investigated with a JEM 200CX transmission electron microscope operating at 200 kV. Energy-dispersive x-ray spectroscopy (EDX) analysis is performed with a CM200-FEG TEM. Cross-sectional specimens for transmission electron microscopy (TEM) studies are prepared by mechanical thinning and subsequent ion milling. The normal of the TEM thin foil is parallel to the [011] direction of the silicon substrate.
RESULTS The x-ray diffraction (0/20) patterns taken from the as-deposited layers on the SiGe and SiGeC samples [12] show strong (002) texture of the Co films. The cross-sectional high resolution electron microscopy (XHREM) images with the beam direction parallel to the [011] direction of the silicon substrate, such as figu
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