Effects of Arsenic Doping on Chemical Vapor Deposition of Titanium Silicide

Abstract

Titanium silicide (TiSi 2 ) has long been used in complementary metal oxide silicon (CMOS) integrated circuits because of its low resistivity and compatibility with standard processes. 1 With the scaling of device dimensions into the deep submicron regime, two problems related to the conventional self-aligned silicide (SALICIDE) process have emerged. The first problem is the so-called narrow-line effect which describes the difficulty in conversion of TiSi 2 from the high resistivity C49 phase into the low resistivity C54 phase on narrow polysilicon lines. 2 Several new growth methods have been suggested to solve this problem, including the use of titanium alloys 3 and molybdenum implants. 4 The second problem is the silicon substrate consumption during silicide formation, which makes the SALICIDE process incompatible with ultrashallow junctions. Metal oxide semiconductor field effects transistor (MOSFETs) with elevated source/ drain structures have been proposed to address this problem. 5,6 Selective chemical vapor deposition (CVD) of TiSi 2 has been proposed as an alternative process to form contacts to ultrashallow junctions without silicon consumption. It has also been suggested that C49-C54 conversion occurs more readily for this process although this area still lacks an in-depth investigation. The CVD process was first introduced by Tedrow et al. 7 in 1985, and it has attracted considerable interest from researchers in U.S., Japan, and France. [8][9][10][11][12][13][14][15][16] Silicides are formed on heavily doped source/drain regions and polycrystalline silicon gates. For the conventional SALICIDE process, the effects of dopants on the formation and characteristics of silicides have been extensively studied. For TiSi 2 , several general remarks can be made: (i) TiSi 2 growth rate depends on dopant type and concentration. The growth rate is highest on undoped and borondoped substrates, lower on heavily phosphorous-doped substrates, and lowest on heavily arsenic-doped substrates 17,18 ; (ii) Ti reacts with boron and arsenic to form stable compounds such as TiAs and TiB 2 , which makes TiSi 2 unsuitable as a dopant out-diffusion source to form junctions [18][19][20] ; (iii) TiSi 2 films formed on arsenic-doped substrates are thermally less stable. 21 Most studies on CVD TiSi 2 have concentrated mainly on understanding the first principles of the process on undoped or moderately doped substrates, or on heavily doped silicon with an undoped silicon epitaxial interlayer. 22,23 Only a few studies exist concerning TiSi 2 deposition on heavily doped substrates. [24][25][26][27] It appears, however, that arsenic does effect deposition and consumption. 25 In a recent report, 28 this group presented experimental results on TiSi 2 deposition on heavily boron-doped substrates. It was conclud-ed that implanted boron does not have a strong influence on the deposition process. Shallow p ϩ -n junctions (X j ϭ 1000 Å) with 800 Å thick TiSi 2 contacts were successfully fabricated. It was also shown by a preliminary experiment...

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

“…These results were consistent with the previous observations which indicate that higher deposition temperatures reduce consumption and that consumption mostly occurs during the initial stages of deposition. 10 Figure 4 also shows that the dependencies of the actual arsenic loss on temperature and time follow the same trends as those due to consumption, which suggests that the additional mechanisms must also be closely related to consumption. The injection of vacancies into the substrate during consumption is believed to be the reason for the enhanced arsenic diffusion, which is discussed in detail later in this paper.…”

“…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.…”

A study of nickel and cobalt silicides formed in the Ni/Co/Si(1 0 0) system by thermal annealing

“…TiSi 2 was the first used silicide [7]. However, its electrical resistance increased abruptly with the line width for narrow lines (below 0.25 mm) [8,9]. For CoSi 2 , it was found that this silicide consumed a relatively large amount of silicon resulting in a thick silicide layer [10].…”

Microstructure evolution of the Ir-inserted Ni silicides with additional annealing

“…However, TiSi 2 is unsuitable for the nano-scale CMOS process because of its dependence on line width and its high temperature agglomeration [7,8]. CoSi 2 also has problems such as high temperature agglomeration, volume expansion, and the need for an excessive cleaning process to remove the native oxide [9].…”