Reduction of The Phase Transition Temperature of TiSi 2 on Si(111) Using a Ta Interlayer
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ABSTRACT The effect of a thin Ta interlayer on the C49 to C54 phase transition of TiSi 2 on Si(1I1) was examined. The Ta interlayered samples were prepared by depositing Ta and Ti films sequentially on Si( 11) substrates in a UI-IV system. As control samples, 100A Ti films were deposited directly on clean Si( 11) substrates. The deposited substrates were annealed for 10 min, in-situ, at temperatures between 500'C and 750'C using 50'C increments. The TiSi 2, which formed in this UHV process, was analyzed with XRD, AES, SEM, TEM, and four-point probe measurements. The control samples exhibited the C49 to C54 transition at a temperature of 750'C. However, the TiSi 2 samples with 5A and 10A Ta interlayers displayed a significant reduction of the phase transition temperature. The XRD analysis indicated that the C49 to C54 transition temperature of TiSi 2 was lowered by -200 0C. The sheet resistance measurement showed a low resistivity characteristic of C54. The SEM and TEM micrographs showed that the Ta interlayer also suppressed the surface agglomeration of the C54 TiSi 2 film. The AES analysis data indicated that the composition of the titanium silicide showed the expected Ti:Si stoichiometry of 1:2.
INTRODUCTION Among the refractory metal silicides, titanium silicide is one of the most widely used and studied silicides because of its importance in the technology of Si based semiconductor devices. The low resistivity and high thermal stability of TiSi 2 are of significant value in the application of this material to current device structures. However, titanium silicide exhibits a significant surface roughening when it forms C54 TiSi 2 at high temperatures (>650 0C). The TiSi 2 compound exhibits two polymorphic structures: a metastable C49 phase (resistivity: 60-70 pQ-cm, base-centered orthorhombic) and a stable C54 phase (resistivity: 15-20 paL-cm, face-centered orthorhombic) [1, 2]. The metastable, higher resistance C49 phase is observed to form initially in reactions of Ti on Si. To achieve low resistivity phase TiSi 2 . higher temperature anneals (>650'C) are required to transform the C49 phase to the C54 phase [3]. The C49 to C54 transition temperature of TiSi 2 has been reported to depend on the Ti film thickness, linewidth. dopant concentration and Si substrate orientations [4, 5, 6]. The goal of this research is to form a uniform and low resistance film of C54 TiSi 2 [7, 8]. There have been several research reports on methods to reduce the transition temperature of TiSi 2. These include refractory metal implantation and a preamorphization implant of the Si substrate [9, 10, 11]. In these studies, the mechanism responsible for the lowering the transition temperature of TiSi 2 has been explained as an increase in the nucleation density of the C54 phase in the C49 matrix and a reduction in the energy barrier to nucleate the C54 phase. These processes result. to some extent, in a lowering of the transition temperature of TiSi 2. Another approach, which has resulted in a reduction of the phase transformation temper
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