Morphology of TiSi 2 and ZrSi 2 on Si(100) and (111) surfaces
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The morphologies of ZrSi2 on S i ( l l l ) and TiSi2 on S i ( l l l ) and (100) have been investigated, and the results compared and contrasted. Films were prepared by UHV deposition of Ti or Zr onto clean, reconstructed Si(100) or (111) substrates, and reacted by in situ annealing. The sheet resistivity of the ZrSi2 was measured and found to be 33-42 yu,O-cm. The morphologies were examined by transmission and scanning electron microscopy. In particular, the islanding properties were studied; both the temperature of the onset of islanding and the island characteristics were measured. The surface and interface energies have been determined from the contact angles of the silicide islands, according to a solid-state capillarity model. The system of ZrSi2 on S i ( l l l ) was found to have surface and interface energies lower than those of the system of TiSi2 on Si(100), but higher than those of the system TiSi2 on S i ( l l l ) . ZrSi2 on S i ( l l l ) was found to island at a higher temperature than TiSi2 on either substrate, a result attributed to kinetic effects. Areal coverage of the islands was measured, and the results were consistent with the solid-state capillarity model. For both TiSi2 and ZrSi2, increasing faceted structure was observed with increasing anneal temperature. Preferred faceting planes were found to be of S i ( l l l ) and (100) type for TiSi2 islands and of S i ( l l l ) type for ZrSi2. Faceted islands were apparently epitaxial. As the solid-state capillarity model does not directly apply to islands with a faceted structure, an observation of the percentage of faceted islands produced by different annealing temperatures was used to suggest the processing conditions in which the model is applicable.
I. INTRODUCTION The need for new materials to be used as contacts and interconnections in microelectronic devices has been apparent in the face of ever-decreasing device dimensions. For interconnects, the doped polysilicon lines often used, while having several other favorable properties, have too high a resistance (—500 ,ufl-cm) to be useful for some VLSI applications. Many different metal silicides, among them Ti, Ta, W, Mo, and more recently Zr, with resistivities an order of magnitude less than polysilicon, have been studied as possible interconnect materials.1 To limit reactions with underlying structures, these silicides have been used as shunts over polysilicon. These "polycides" thus capitalize on both the good interface qualities of the polysilicon and the low resistivity of the silicide. The same silicides are often considered for source or drain contacts. In these applications, the metal is deposited directly onto the crystalline substrate and annealed to cause a thin film reaction. Titanium silicide has long been of interest for use in contacts and interconnects on VLSI devices, because it exhibits the lowest resistivity of the common refractory silicides. The material has a major drawback, however, in that it shows a persistent tendency for surface roughening or islanding. Previous studi
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