Jw. Lee et al., Degradation of TA(2)O(5) gate dielectric by TiCl4-based chemically vapor deposited TiN film in W/TiN/Ta2O5/Si system, JPN J A P 1, 40(4B), 2001, pp. 2810-2813
Tantalum pentoxide was adopted as a gate dielectric for obtaining gate oxid
e with less than 3.0 nm SiO2 equivalent thickness and low leakage current.
Physical vapor deposited (PVD) TiN or TiCl4-based chemical-vapor-deposited
(CVD) TiN was used as the barrier material between the W electrode and Ta2O
5 layer. The thermal stability and electrical property of each barrier were
evaluated at an elevated temperature of 900 degreesC. In the as-deposited
condition and after annealing at 800 degreesC, PVD and CVD TiN show similar
electrical proper-ties. However, after annealing at 900 degreesC, CVD TiN
barriers show much lower breakdown fields and higher leak-age current compa
red with PVD TiN, indicating that CVD TiN has worse barrier performance tha
n PVD TiN. Microvoids are formed in the Ta2O5 layer along the PVD TiN/Ta2O5
interface after annealing at 900 degreesC. It is found that Ta diffuses in
to the TiN layer leaving microvoids behind. Ta2O5 is more severely damaged
in the CVD TiN system after annealing. The high content of residual Cl in C
VD TiN was found to reduce Ta2O5 and generate free Ta and O. Free Ta and O
atoms that are generated from the reduction of Ta2O5 diffuse into the TiN l
ayer and hence produce macrovoids and disconnected areas in the Ta2O5 layer
. The transmission electron microscopy (TEM) images and secondary ion mass
spectrometry (SIMS) depth profiles are in good agreement with the electrica
l properties of W/TiN/Ta2O5/Si gate devices.