Ion-Beam Induced Suicide Formation: Markers and Moving Species
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L. S. HUNG AND J. W. MAYER Department of Materials Science and Engineering, Ithaca, NY 14853
Cornell University,
ABSTRACT The moving species in near-noble metal silicide formation was investiWith thermal gated using embedded markers and Rutherford backscattering. annealing of Ni-siuicides, Ni is the dominant diffusing species while in This ion-induced reactions both Ni and Si diffuse across the silicide. difference in behavior is not a result of the formation of amorphous Si We propose that during ion irradiation nor is it caused by release of Si. the diffusion of Si is associated with the formation of defects in the silicide layer generated within the collision cascade. I.
INTRODUCTION
The formation of silicide layers by thermal annealing of a metal film deposited on single crystal Si follows a well-established [1,2] pattern: with near-noble and associated metals (Ni, Pd, Pt and Co) on Si, the dimetal silicide, M2Si, is formed at temperatures of 200 to 300°C and with refractory metals (such as Cr, Mo, and W) the disilicide, MSi 2 , is formed at higher temperatures, 450 to 600°C. This difference in behavior is attributed to the ability to break the covalent bond in Si. Temperatures of around 500°C are required in disilicide formation where the Si diffuses across the The lower temperature encountered in Nisilicide to react with the metal. silicide formation, for example, is attributed [3] to the diffusion of Ni across the silicide and alteration of the Si bonding configuration at the Si/silicide interface. The identity of the moving species during silicide formation is determined by the use of markers in conjunction with Rutherford backscattering (RBS). As illustrated in Figure 1, the aisplacement of the marker relative to the growth of the silicide can be used to find the amount of Si or metal transported past the marker. The displacement of the marker and the amount of silicide formed can be measured by RBS. There are three considerations [4] in the choice of markers: i) the marker should be chemically inert with respect to its surrounding, ii) the marker should not modify the phase formation or the moving species and iii) the displacement of the marker should This last requirement can be met by emdepend on the transport of atoms. bedding the marker in the silicide (Fig. I) and the other requirements by appropriate choice of the marker species. Ion irradiation (or ion beam mixing), as well as thermal annealing, leads to silicide formation [see for example references 5-7]. There are strong correlations in the results of thermal anid ion-induced silicide formation: the same phases are formed initially [8], the amount of mixing scales with thermal rates [9], and segregation of impurities at interfaces (netal/silicide and Si/siuicide) occurs [10] in both cases. There is one major difference that has been reported [4,11]: during the growth of near-noble silicides by ion irradiations, Si plays a major role as a diffusing species. The focus of this paper is on the possible causes of this behavior. We use Ni-silicide
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