We have used small angle neutron scattering and synchrotron x-ray photoelectron spectroscopy to determine microstructure variations in HfO2 and Hf silicate, (HfO2)x (SiO2)1-x, x ~ 0.7, gate dielectric thin films deposited on Si (100) substrates. 3 nm thick films exposed to a post deposition anneal (PDA) of NH3/700ºC/60s exhibit a significant amount of N in the bulk film, quantified by nuclear reaction analysis, and corroborated by intense Hf-N peak in binding energy spectra. We report on the effectiveness of N to suppress the diffusivity and retard crystallization kinetics. Therefore, by comparing NH3 PDA with N2 PDA at 700ºC/60s, the influence of incorporated N has been decoupled from that of the thermal cycle alone. Ultra-thin nanophased materials have extremely high surface to volume ratio and the specific surface area dependence of crystallization has been addressed by characterizing 2 nm and 4 nm thick films exposed to each anneal processes. X-ray diffraction spectra indicate N exchanges for O in the crystal cell structure where Hf-N bonds will contribute local strain in tetragonal and monoclinic HfO2 [1]. The Hf-N bonds may also coexist in some volume fraction as an amorphous HfxOyNz composition. Additionally, Hf silicate samples with duplicate anneal processing has been spectroscopically analyzed and we report on the mechanistic pathways associated with phase separation and subsequent crystallization of end member oxide, HfO2, corresponding to the influence of N in the bulk films. Samples exposed to a rapid thermal anneal (RTA) process of N2/1000ºC/10s (full polycrystalline) have been analyzed for comparison [2-3].

References

1 D. I. Bazhanov, et al. J. Appl. Phys. 97 (2005).

2 P. S. Lysaght, et al. J. of Non-Crys. Solids, 303, pp 54-63, (2002).

3 S. Stemmer, Y. Li, B. Foran, P. S. Lysaght, S. K. Streiffer, P. Fuoss, Appl. Phys, Lett. 83, pp 3141-3143, (2003).

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