Arsenic Redistribution during Rapid Thermal Chemical Vapor Deposition of TiSi[sub 2] on Si

Abstract

This paper studies the redistribution behavior of implanted arsenic during selective rapid thermal chemical vapor deposition of titanium disilicide (TiSi 2 ). The arsenic implant doses ranged from 3 ϫ 10 14 cm Ϫ2 to 5 ϫ 10 15 cm Ϫ2 . The TiSi 2 films were deposited either directly on arsenic-implanted silicon substrates or on epitaxial silicon buffer layers selectively deposited with varying thicknesses before TiSi 2 depositions. SiH 4 and TiCl 4 were used as precursors for TiSi 2 depositions and Si 2 H 6 and Cl 2 for selective silicon epitaxial growth. Experimental data revealed that the majority of the implanted arsenic was lost from the silicon substrate into the deposited TiSi 2 films when epitaxial silicon buffer layers were not employed. With the inclusion of the buffer layer, the arsenic loss could be reduced significantly. The loss of arsenic observed could not be explained by considering substrate consumption alone. In both cases, arsenic exhibited strongly enhanced out-diffusion from the silicon substrate into the TiSi 2 film. The injection of vacancies during the TiSi 2 depositions has been proposed as the reason for this enhanced out-diffusion. Monte Carlo simulations have been performed to verify the proposed model. Titanium disilicide (TiSi 2 ) is widely used to form low resistivity contacts to silicon devices. 1 Self-aligned silicide ͑SALICIDE͒ technology is used to form TiSi 2 on source/drain junctions and polysilicon gate electrodes of complementary metal-oxide-silicon ͑CMOS͒ devices. 2 As device dimensions shrink into the deep submicrometer regime, reducing the silicon substrate consumption and achieving the low resistivity C54 phase of TiSi 2 is becoming much more difficult. 3 Selective chemical vapor deposition ͑CVD͒ of TiSi 2 offers an alternative process solution with the potential to alleviate these problems. By introducing titanium and silicon from gaseous sources, TiSi 2 can be formed without substrate consumption. 4,5 Preliminary results have shown that formation of TiSi 2 on fine polysilicon lines can also be improved by CVD. 6 Because TiSi 2 is formed simultaneously on source/drain and polysilicon gate electrodes doped with different impurities, it is important to study the interactions between silicide formation and dopant redistribution in silicon. Extensive research has been carried out on this topic. 7-9 It was found that dopants in Si reduce the silicide growth rate, with arsenic having the strongest impact. Furthermore, during conventional TiSi 2 formation, dopants easily diffuse into the growing silicide without a ''snow plow'' effect. A recent study from this laboratory explored selective CVD of TiSi 2 on heavily arsenicdoped substrates. 10 It was found that arsenic introduces a barrier to TiSi 2 nucleation and results in enhanced substrate consumption. It was also shown that arsenic displays a strong tendency to diffuse into TiSi 2 during deposition. Arsenic loss into TiSi 2 during CVD processing was also observed by Southwell et al. 11 They attributed the effect to the injec...