The Effects of Titanium Silicide Formation on Dopant Redistribution

Abstract

This paper reports on boron and arsenic redistribution during the TiSi2 self-aligned silicide process as applied to shallow (<0.2 ~tm) junctions. Dopant loss was seen to occur through evaporation from the silicide surface, segregation into the Ti-rich outer layer which is subsequently removed, and diffusion into the silicide layer. Depending on the silicide and junction annealing temperatures, up to 99% of the implanted dopant dose can be lost via these three mechanisms. Dopant loss is particularly acute when the silicide is formed concurrently with recrystallization/annealing of the junction implant, before the dopant diffuses into the silicon. Germanium preamorphization, to eliminate channeling of the ion implanted dopants, further aggravates the loss of boron but has a slightly beneficial effect with arsenic. Oxide capping of the silicide before annealing reduces dopant evaporation and increases the dopant concentration at the silicide contact, but at the expense of increased junction depth. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 155.69.4.4 Downloaded on 2015-06-04 to IP

Titanium-based ohmic contacts in advanced CMOS technology

“…Whether or not Ti silicidation at low temperature leads to different P redistribution at the TiSi x /n + -Si interface is inspected by secondary ion mass spectroscopy (SIMS), as displayed in figure 11. It is revealed that a portion of P atoms diffuse into the ultrathin TiSi x , and no accumulation of P at the TiSi x /n + -Si interface is evident for both the reference and the sample with Ge PAI, due to higher diffusivity of P in TiSi x than that in Si [68][69][70]. It is worth noting that with Ge PAI, the out-diffusion of P atoms is aggravated since a strong intermixing between Ti and Si is revealed.…”

Ultra Shallow Junction Formation Using Diffusion from Silicides: II . Diffusion in Silicides and Evaporation

“…The redistribution of dopant within the silicide presents two more fundamental issues; the extensive loss of dopant via evaporation, which can often amount to 90% of the implanted dose (10), and the diffusion of dopant within the silicide. Dopant diffusion in silicides can be divided into two groups; those with very slow bulk diffusion, where only grain boundary diffusion plays a role, and those where the bulk diffusion is rapid enough so that dopant can distribute more or less homogeneously throughout the grains in the films.…”

“…9, demonstrating the effect of slow As diffusion through the silicide. If diffusion through the silicide becomes rate limiting, the evaporation rate should be determined by the diffusional flux which can be written as F = D-- [10] CoSi2, which is far more than the amount evaporated. Thus, it is believed that the diffusion of boron in CoSi2 is not the rate limiting step of the dopant loss process.…”

“…Dopant redistribution in silicide-silicon bilayers has been studied for a variety of silicides and dopants, and summarized in several review papers (4)(5)(6). However, not as many reports exist on quantitative measurement of dopant evaporation (7), for example As in TiSiz (8,9), B and As in TiSi2 (10), and As in TaSi2 (11). One approach used to reduce dopant evaporation from silicides is the use of a capping oxide, as has been applied for TiSi2 (12,13) and for CoSi2 (13)(14)(15)(16).…”

“…One approach used to reduce dopant evaporation from silicides is the use of a capping oxide, as has been applied for TiSi2 (12,13) and for CoSi2 (13)(14)(15)(16). Nevertheless, at least one earlier study (10) found that the amount of dopant lost into a capping layer above silicon was as great as the amount of evaporation that occurred without a cap; in that case, a cap did not increase the total dopant left in the silicon. This paper studies the dopant evaporation in five different silicides, Ti, Co, Ni, Pd, and Pt silicides, used in a SADS process with emphasis on CoSi2.…”