Investigation of Dopant Effects in CoSi2 and NiSi Fully Silicided Metal Gates

Abstract

CoSi 2 full silicidation ͑FUSI͒ of doped poly-Si metal gates was investigated to further the understanding of the modulation of effective work function from dopants in CoSi 2 and NiSi FUSI gated metal oxide semiconductor devices. By using a TiN-capping layer to manipulate the dopant distribution, dopants have been confirmed to be effective in tuning the work function for both CoSi 2 and NiSi. However, from the drastic reduction of the As tuning effect in CoSi 2 , we understand that the amount of effective work function tuning is not only directly dependent on the interfacial dopant concentration, but the mechanism of dopant tuning the work function is strongly dependent of the bulk material type.Full silicidation ͑FUSI͒ of doped polysilicon gate has recently been proposed with a process compatible with present complementary metal oxide semiconductor ͑CMOS͒ technology to form tunable work function metal gates. NiSi, TiSi, and HfSi FUSI gates have been shown with tunable effective work function from variation of the type and concentration of dopants in poly-Si. As, B, P, and Sb dopants were found to be capable of setting threshold voltages suitable for n-and p-channel metal oxide semiconductor ͑NMOS and PMOS͒ transistors. 1-10 The mechanism of dopant incorporation on tuning the effective work function has not been thoroughly understood; possibilities of this change include metal/dielectric interface dipole formation, or interfacial grain structure change, etc. To enhance our understanding on this issue, CoSi 2 FUSI gates has been formed in comparison to the commonly researched NiSi FUSI gates with identical dopant incorporation processes. Undoped CoSi 2 FUSI gates also exhibits an effective work function near midgap. 2 Due to agglomeration effects and the reaction kinetics of CoSi 2 , some concerns need to be addressed for integration in the gate-last process when fully siliciding small poly-Si gate dimensions. 10 Other reports have suggested that high-temperature processes cause metal diffusion of Co toward the gate dielectric. 11 However, CoSi 2 is an attractive candidate for the FUSI gate due to its low resistivity and excellent thermal stability which is capable of withstanding the high S/D annealing temperature. In this work, a TiN-capping layer has also been added on the gate material to help identify the relationship between the distribution of As and B dopants and the work function. A distinct difference in the effect of dopant on work function tuning in CoSi 2 compared to that in NiSi has been observed. The role of the TiN-capping layer on dopant distribution on As-doped samples is also different from that observed in B-doped samples, and the trend in NiSi FUSI gates. 12 Explanation of the mechanism for dopant tuning effect is still uncertain; however, this observation suggests that dopants still play a factor in the work function change of CoSi 2 , and the differences in effective work function modulation is highly dependent on the bulk silicide material. ExperimentalCapacitors with 2.5 nm thick gate oxid...

Advanced high-κ dielectric stacks with polySi and metal gates: Recent progress and current challenges

“…With respect to silicide materials for FUSI gates, most of the ones explored so far are common silicides that are already in use for source/drain contacts or other microelectronics processes, such as molybdenum silicides [119,120,138], tungsten silicides [122], titanium silicides [136], hafnium silicides [134], platinum silicides [131,133], cobalt silicides [123,141] and nickel silicides [21,121,, germanides, and alloys. Nickel-based silicide materials are emerging as a leading candidate for FUSI gates for several reasons: 1) low resistivity (;15 -25 lX-cm; 2) low volume expansion (less than 20%); and 3) the fact that this material has already been introduced into Si FEOL processing for sub-90-nmtechnology nodes.…”