Direct Formation of C54 Phase on the Basis of C40 TiSi 2 and Its Applications in Deep Sub-Micron Technology
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Direct Formation of C54 Phase on the Basis of C40 TiSi2 and Its Applications in Deep Sub-Micron Technology S. Y. Chen1, Z. X. Shen1, S. Y. Xu1, A. K. See2, L. H. Chan2 and W. S. Li2 1 Department of Physics, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260 2 Chartered Semiconductor Manufacturing Ltd., 60 Woodlands Industrial Park D, Street 2, Singapore 738406 ABSTRACT A simple and novel salicidation process applying pulsed laser annealing as the first annealing step was used to induce TiSi2 formation. Both Raman spectroscopy and transmission electron microscope results confirm the formation of a new phase of Ti disilicide, the pure C40 TiSi2 after laser irradiation. Direct C54 phase growth on the basis of C40 template bypassing the C49 phase is accomplished at the second annealing temperature as low as 600oC. Line width independent formation of the C54 phase was observed on patterned wafers using this salicidation process and “fine line effect” is thus eliminated. INTRODUCTION Titanium disilicide is a very important material and has been widely used in IC industry [1]. Nowadays, rapid thermal annealing (RTA) is applied for TiSi2 formation with the typical ramping rate of 30~100 oC/s. The high resistivity (60~70 µΩ-cm) C49 phase usually forms first at RTA temperature of 550~700oC. During subsequent annealing at 750~850oC, C49 phase transforms to the stable low resistivity (15~20 µΩ-cm) C54 TiSi2 which is the desired phase for IC applications [2]. However, such C49 to C54 phase transition is extremely difficult on narrow poly-silicon lines due to the lack of C54 nucleation sites arising from the large C49 grain size [1]. This “fine line effect” was discovered in early 1990s, and has become the major challenge for Ti salicide technology ever since [3]. The conventional methods including various implantation to reduce C49 grain size [4,5] were helpful but not able to solve the fine line effect completely [6]. Direct formation of C54 TiSi2 bypassing C49 phase is very promising to eliminate the fine line effect. Among the intensive efforts made, 3 approaches are proved to enhance the C54 formation effectively. Mann et al [7], Kittl et al [8] and Mouroux et al [9] have demonstrated in their work that the C54 phase formation temperature can be lowered by 100-150oC by implanting a small dose of Mo ions into Si substrate prior to Ti film deposition [7,8], or by depositing a thin Ta layer of about 1 nm thick, between Ti and substrate Si [9]. Mouroux et. al. proposed that upon annealing, a layer of C40 (Ta, Ti)Si2 ternary phase formed initially at the interface. C40 (Ta, Ti)Si2 and C54 TiSi2 phases have similar (< 3% lattice mismatch) basal hexagonal planes [9] and as a consequence, this interfacial C40 phase acts as a template which allows the direct growth of C54 TiSi2 on top. C49 TiSi2 however, has a very different crystalline structure from C40 phase, making it difficult to nucleate on C40 crystals. Therefore, C40 phase facilicates the growth of C54 TiSi2, and hinders the formation of C49 phase. Des
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