Silicide Formation in Ti-Si and Co-Si Reactions
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SILICIDE FORMATION in Ti-Si and Co-Si REACTIONS L.A. Clevengert, Q.Z. Hongt, R. Mann*r, J.M.E. Harpert, K. Barmake, C.Cabral, Jr.t, C. Nobilit and G. Ottavianit t IBM T.J. Watson Research Center, PO Box 218, Yorktown Heights, NY 10598 "*IBM Technology Products, Essex Junction, VT 05452 Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015 • Universita Degli Studi Di Modena, Modena Italy
Abstract Titanium silicide and cobalt silicide crystallization and formation reactions are important for the processing of CMOS circuits. We demonstrate that kinetic analysis of these reactions under both high heating rates and isothermal heating conditions allows for the determination of transformation mechanisms. For Ti/Si reactions, we show that the C49 to C54-TiSi 2 transformation can not be bypassed using heating rates up to 3000°C/min. For the crystallization of CoSi2 from amorphous Co-Si thin films without ion irradiation, the crystallization kinetics are characterized by three dimensional growth from quickly consumed nucleation sites. With high dose silicon ion implantation of the as-deposited films, the crystallization mechanism changes to homogeneous nucleation and two dimensional growth.
Introduction Titanium and cobalt disilicide phases have generated interest in the scientific community due to their applications in very large scale (VLSI) and ultra large scale (ULSI) integrated circuits.'-4 Both these silicide phases are widely used in CMOS technologies because of their low resistivities, ability to be used in a self-aligned process, and relatively good thermal stabilities for source, gate and drain contacts. Titanium disilicide is the most heavily used silicide contact in the semiconductor industry. It comes in two forms, high resistivity (60-70 gfl-cm) base-centered orthorhombic C49-TiSi which forms from a reaction between titanium and silicon at approximately 500 to 650°C ana low resistivity (15-18 tfl-cm) face-centered orthorhombic C54-TiSi 2 which occurs at temperatures over 650°C.1- In circuit applications the complete conversion of C49-TiSi 2 into C54-TiSi 2 is critically important in achieving uniformly low resistivity silicide contacts. Lasky et al.4 recently have demonstrated that this transformation is feature size dependent, and their work indicated that the future applicability of titanium silicide contacts in sub-micron devices is limited. CoSi 2 has emerged as an alternative to TiSi 2 It has a similar resistivity to C54-TiSi 2 and its formation is not dependent on feature size.47 In addition, it can be used as a diffusion source for shallow junction formation.8 There is a large amount of literature on kinetics of both TiSi 2 and CoSi 2 formation."9-'7 The9 activation energy for the formation of C49-TiSi 2 has been reported to be 1.8 to 3.1 eV -12 and the activation energy for the C49 to'C54 transformation has been reported to be 3.8 3 4 to 8.0 eV' 9,1 depending on the type of silicon substrate, film structure and analysis technique used. Activation activation energies f
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