Etch
and wide lines have different Ni silicide phase
formed because of this Ni effective thickness
effect. Indeed, for a same RTA, but different
initial Ni(Pt) layer thickness, we have different
silicide phase formed. Thicker Ni(Pt) required a
much longer RTA to form the same silicide phase
than the thinner Ni(Pt) layer (Figure 6).
The parasitic oxidation with HCl based
selective etching, therefore, appears
preferentially on small features or near the
sidewalls in general. According to these silicide
formation characterizations, depending on
formation temperature and features size, we control nickel salicide migration. Platimum is not Figure 7 - SEM top
Issue III 2009
believe that the oxidation effect is due to the easily removed with the etchants commonly view of a pattern for
square4
reaction of the Ni rich silicide phase with the used for selective metal removal during the Ti or same silicide process
.com
chlorine and oxidant based chemistries. Co salicide formation process. Standard SPM a, (above left)) silicon
Normalized polysilicon line resistance as a chemistries have proven ineffective in removing oxide formation over
function of RTA temperature and as a function of excess platinum. pattern sides after a
line width for the case of unreacted NiPt While HCl based chemistries are effective in Cl-based selective
stripping with hot SPM solution is shown in 5b. removing excess Pt at 65nm, their selectivity etch. b (above) No
When the hot SPM solution is used to strip decreases at 45 and 32 nm. In addition, these oxide formation after
unreacted Ni(Pt), no abnormal resistance HCl based chemistries tend to cause parasitic hot-SPM based
oasiasemiconductor
increase for low formation anneal temperatures oxidation of the Ni rich phase of silicide after selective etch
.eur
is observed. Figure 7 compares patterned lower temperature formation anneals. A new,
www
structures for Cl based and hot SPM based high temperature SPM based removal process,
selective etch after low temperature formation however, has proven to be effective in selectively
21
anneal. The parasitic oxidation phenomenon is removing unreacted Pt without causing parasitic
not observed with the hot SPM solution. oxidation, thereby, enabling the extended use of
Platinum is increasingly being used in the Ni(Pt) salicide process into future CMOS
advanced devices as an alloy with nickel to help generations.
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