Spectroscopic Investigation of Local Bonding in Zirconium Silicate High-k Dielectric Alloys for Advanced Microelectronic Applications

Abstract

Local bonding of Zr-, Si-, and O-atoms in plasma-deposited, and post-deposition annealed, pseudo-binary (ZrO2)x(SiO2)1-x alloys was investigated by Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) as a function of alloy composition, x. Alloys were deposited at 300°C onto Si-substrates by a remote plasma enhanced-metal organic chemical vapor deposition (RPE-MOCVD) process. Film composition was determined off-line by Rutherford Backscattering Spectrometry (RBS) and these results were then used to calibrate on-line AES for determining composition. X-ray diffraction (XRD) was used to establish the crystalline/non-crystalline character of the films as deposited, and following subsequent post-deposition annealing.

FTIR measurements were performed off-line and the results were 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 ZrO2 and amorphous SiO2 (or an amorphous SiO2 rich Zr-silicate alloy) at 900°C was demonstrated in alloys with 50% and 61% ZrO2. FTIR spectroscopy provides evidence of chemical phase separation in the alloy with 23% ZrO2 at 900°C as well, but XRD shows no evidence of ZrO2 crystallization. The observed changes in the FTIR absorbance spectra with alloy composition, and post-deposition annealing temperature, 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 composition. Based on this bonding model, donor-acceptor pair bonds (between non-bonding pairs on network O-atoms, or O-atoms in H2O, and Zr-ions) in SiO2 rich alloys with low ZrO2 content are systematically replaced by ionic Zr?O bonds with increasing x.

Based on the principle of electronegativity equalization by Sanderson, atomic partial charge (which represents the net charge on an atom as a result of chemical bonding) 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. As deposited Zr-silicate alloys were characterized by off-line XPS and on-line AES where measured (i) peak-shapes and (ii) chemical shifts with alloy composition are interpreted by a modified charge-potential model, which incorporates the results of calculated partial charge, as well as aspects of local bonding. Based on XPS Zr3d core-level chemical shifts, evidence of donor-acceptor pair bonding in alloys with low ZrO2 content (x ≤ ∼0.3) is identified by XPS, consistent with the bonding model established by FTIR spectroscopy. Following a 900°C anneal for 60s, XPS O1s spectra provide additional evidence of a chemical phase separation in alloys with 35%, 45% and 60% ZrO2. 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 alloy composition.