Spectroscopic investigation of local bonding in zirconium silicate high-k dielectric alloys for advanced microelectronic applications

Local bonding of Zr-, Si-, and O-atoms in plasma-deposited, and post-deposition annealed, (ZrO₂)_x(SiO₂)_1−x alloys was investigated by FTIR, XPS, and AES as a function of x. FTIR was used to investigate changes in film internal structure with (i) composition, and (ii) post-deposition annealing temperature. FTIR and XRD indicate films with 10%, 23%, 50% and 61% ZrO₂ are amorphous as deposited, and thermodynamically stable when annealed at temperatures up to 800°C. However, a chemical phase separation into crystalline ZrO ₂ and amorphous SiO₂ at 900°C was demonstrated in alloys with 50% and 61% ZrO₂. Changes in FTIR absorbance spectra with x are interpreted by aspects of local bonding which then serve as a basis for a bonding model that describes systematic changes in amorphous morphology and bonding coordination with x. Based on this bonding model, donor-acceptor pair bonds (between non-bonding pairs on network O-atoms, or O-atoms in H ₂O, and Zr-ions) are identified in alloys with low ZrO₂ content.; Based on the principle of electronegativity equalization by Sanderson, atomic partial charge was calculated for Zr, Si and O as a function of x. Calculated partial charge linearly decreases in magnitude for Zr and Si, and increases for O, with increasing x. Alloys were characterized by off-line XPS and on-line AES where measured (i) peak-shapes and (ii) chemical shifts with x are interpreted by a modified charge-potential model, which incorporates the results of calculated partial charge, as well as aspects of local bonding. Evidence of donor-acceptor pair bonding in alloys with low ZrO₂ content is identified by XPS. XPS O1s spectra provide additional evidence of a chemical phase separation at 900°C. Combining as deposited XPS O1s and AES OKVV results, an empirical model for the compositional dependence of valence band offset energies with Si is presented; the results of this model predict a non-linear sigmoidal compositional dependence. This sigmoidal character results from the discrete nature of O-atom bonding coordination and systematic changes in coordination with x.