Effects of Ti-Capping on Formation and Stability of Co Silicide. I. Solid Phase Reaction of Ti to Co/Si System

Abstract

As complementary metal oxide semiconductor (CMOS) devices are scaled down to subhalf-micrometer design rules, the self-aligned silicide (salicide) structure has become an essential technology for high speed logic in very-large-scale integrated (VLSI) circuits. 1 Among all the metal silicides, Ti silicide has been the most widely used because of its low electrical resistivity and wide applicability. However, there are difficulties with using conventional Ti salicide for future subquarter-micrometer dimensions which are related to thermal stability and narrow lines effects. These include (i) a slow rate of phase transition from high resistivity C-49 TiSi 2 to low resistivity C-54 TiSi 2 , resulting in a large increase in sheet resistance, especially for narrow lines (the narrow line effect); 2,3 (ii) relatively low thermal stability caused by agglomeration of the TiSi 2 film; 2 and (iii) suppression of TiSi 2 formation on heavily As-doped n ϩ polycrystalline Si (poly-Si) and n ϩ diffusion regions, resulting from the lower formation energy of TiAs (Ϫ110 kJ/g atom) than TiB (Ϫ84 kJ/g atom) or TiSi 2 (Ϫ74 kJ/g atom) (the dopant effect). 4,5 Even though the narrow line and dopant effects can be overcome by preamorphization implantation with As, 6 Sb, and Ge, 7 the low thermal stability still limits the process window. 8 Thus self-aligned CoSi 2 is an attractive alternative to TiSi 2 , due to both its linewidthindependent sheet resistance and high thermal stability. 9 To prevent oxidation during silicidation, TiN films are most widely used for capping the Co in the Co salicide process. 10,11 The TiN-capped Co salicide process can successfully reduce the gate resistance, even for a gate length of 0.065 m, 12 but produces nonuniform CoSi 2 /Si interfaces or CoSi 2 spiking. 11,13 Roughness at the CoSi 2 /Si interface can impact the ability to make a shallow junction, due to the possibility of increased diode leakage in regions where the silicide has grown deeper into the silicon. Several studies have reported on processes for forming a uniform and epitaxial CoSi 2 film. Solid-state reactions between a bilayer Co/Ti and Si substrate titanium-interlayer mediated epitaxy (TIME), has been suggested as a new method for forming epitaxial CoSi 2 film. 14-18 The Ti interlayer serves as an oxygen scavenger and a diffusion barrier, which limits the Co-Si reaction. Recently, a Co-Ti alloy system was proposed to form flat and heteroepitaxial CoSi 2 films on Si substrates. 19 Ti significantly widened the process window for the formation of epitaxial CoSi 2 layers. On the other hand, Tung et al. 20 demonstrated that the use of a chemical oxide prior to Co deposition [oxide mediated epitaxy (OME)] resulted in the formation of highly uniform epitaxial CoSi 2 films. In addition, an organometallic chemical vapor deposited (OMCVD) carbonic cobalt was reported to produce thick and uniform epitaxial CoSi 2 films on Si(100) substrates after annealing at 800ЊC for 5 min. 21 Unfortunately, the TIME process has serious problems, such as the forma...

Diode Analysis of Advanced Processing Modules for Deep-Submicrometer CMOS Technology Nodes

“…Using a titanium capping layer improves the smoothness of the CoSi 2 /Si interface. 33 A lower uniformity of the CoSi 2 is expected for a thicker silicide. For a targeted junction depth of 100 nm, a remaining junction depth of about 64 and 57 nm is expected for the 10/8 and 12/8 conditions, respectively.…”

Pulsed laser-induced silicidation on TiN-capped Co∕Si bilayers

“…2 Moreover, it has been reported that the TiN capping layer has improved the current driving capability of p-type metal-oxide semiconductor field-effect transistors ͑pMOSFETs͒ compared to Ti capping layer. CoSi 2 has been widely used for sub-0.25 m CMOS technology due to its low resistivity, good thermal stability, and the absence of fine-line effect in narrow lines.…”

Thermal stability study on nanoscale polysilicide resistors

“…[3][4][5][6][7][8][9] Process-related studies have proposed several theoretical models for the thermal stability of the silicided thin poly film. Among all silicides, cobalt silicide ͑CoSi 2 ͒ is the most popular material beyond the 0.25 m node because of its linewidth dependence being less than that of titanium silicide ͑TiSi 2 ͒.…”