Effect of Pre-cooling Treatment on the Formation of C54 Phase Titanium Silicide
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Effect of Pre-cooling Treatment on the Formation of C54 Phase Titanium Silicide Lin Zhang and Yong Keun Lee School of Materials Engineering, Nanyang Technological University, Singapore 639798 ABSTRACT In this paper, the effect of pre-cooling treatment on the low resistivity C54 phase titanium silicide film growth was investigated. Our experimental results and micro-structural analysis show that, by introducing such cooling treatment into the titanium silicide process to precede the conventional rapid thermal annealing, the low resistivity C54 phase formation can be enhanced. Defects at the Si/Ti interface caused by the thermal mismatch between titanium and silicon layers during the cooling treatment were found to contribute to the increase of the C49 nucleus sites. This help to supply more C49 grain boundaries and triple junction sites at which the C54 phase could nucleate. This discovery has the potential to reduce the complexity and cost associated with forming low resistivity titanium silicide on sub-micron structures for future ULSI application.
INTRODUCTION The formation of TiSi2 has been intensively studied due to its technological importance in microelectronics industry. As one of the most widely used contact materials, TiSi2 has many advantages including low resistivity, high thermal stability, and maturity of the self-aligned silicide process [1]. It is generally accepted that TiSi2 is a polymorphic material and may exist as two phases: one is the base-centered orthorhombic C49 phase with a high resistivity of 60-90µΩcm, and the other is the face-centered orthorhombic C54 phase with a low resistivity of 12-20µΩcm. In the Ti/Si reaction, with the increasing of annealing temperature, nucleation and growth of the metastable C49 phase has always been observed to precede the nucleation of the C54 phase. As the low-resistivity stable C54 phase is desired for a contact material, transformation from C49 to C54 phase is a necessary path for TiSi2 formation. A certain thermal budget should be satisfied in this step for a complete C54 phase formation, while too high process temperature is not desired since it may cause dopant rediffusion and contact overgrowth on the sidewall oxide spacer. With the scaling of Ti salicide to deep-sub-micro features, however, the C54 phase formation becomes more difficult due to the scarcity of C54 forming nuclei and its formation temperature may rise to 700-850°C depending on the device features [2,3]. In order to keep using TiSi2 in further generations of ultra-large scale integrated (ULSI) circuits, many efforts have been made to reduce the resistivity of TiSi2 as well as the C54 phase formation temperature. Some important breakthroughs include applying pre-amorphization implantation (PAI) treatment [1,4], and inducing refractory metal ion implantation to the Si substrate or refractory metal interposed layer between Ti and Si [5-8]. These alternative methods have the effect of shrinking the C49 grain size, and thus increasing the triple junction sites contained in the C49 grain boun
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