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Quevedo-Lopez, Manuel Angel, Materials properties of hafnium and zirconium silicates:
metal interdiffusion and dopant penetration studies. Doctor of Philosophy (Materials
Science), August 2002, 278 pages, 10 tables, 142 figures, references.
Hafnium and Zirconium based gate dielectrics are considered potential candidates
to replace SiO2 or SiON as the gate dielectric in CMOS processing. Furthermore, the
addition of nitrogen into this pseudo-binary alloy has been shown to improve their
thermal stability, electrical properties, and reduce dopant penetration.
Because CMOS processing requires high temperature anneals (up to 1050 °C), it
is important to understand the diffusion properties of any metal associated with the gate
dielectric in silicon at these temperatures. In addition, dopant penetration from the doped
polysilicon gate into the Si channel at these temperatures must also be studied. Impurity
outdiffusion (Hf, Zr) from the dielectric, or dopant (B, As, P) penetration through the
dielectric into the channel region would likely result in deleterious effects upon the
carrier mobility.
In this dissertation extensive thermal stability studies of alternate gate dielectric
candidates ZrSixOy and HfSixOy are presented. Dopant penetration studies from dopedpolysilicon through HfSixOy and HfSixOyNz are also presented. Rutherford backscattering
spectroscopy (RBS), heavy ion RBS (HI-RBS), x-ray photoelectron spectroscopy (XPS),
high resolution transmission electron microscopy (HR-TEM), and time of flight and
dynamic secondary ion mass spectroscopy (ToF-SIMS, D-SIMS) methods were used to
characterize these materials. The dopant diffusivity is calculated by modeling of the
dopant profiles in the Si substrate.
In this disseration is reported that Hf silicate films are more stable than Zr silicate
films, from the metal interdiffusion point of view. On the other hand, dopant (B, As, and
P) penetration is observed for HfSixOy films. However, the addition of nitrogen to the Hf
– Si – O systems improves the dopant penetration properties of the resulting HfSixOyNz
films.