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Thickness Evaluation for 2nm SiO2 Films, a Comparison of Ellipsometric, Capacitance-Voltage and HRTEM Measurements



James R. Ehrstein, Curt A. Richter, Deane Chandler-Horowitz, Eric M. Vogel, Donnie R. Ricks, Chadwin Young, Steve Spencer, Shweta Shah, Dennis Maher, Brendan C. Foran, Alain C. Diebold, Pui-Yee Hung


We have completed a comparison of SiO2 film thicknesses obtained with the three dominant measurement techniques used in the IC industry . This work is directed at evaluating metrology capability that might support NIST- traceable Reference Materials for very thin dielectric films. The low temperature thermal oxide wafers, with a nominal thickness of 2nm,. included blanket SiO2 wafers, and wafers with arrays of fabricated capacitors with four different areas. Because of known accretion of surface contamination, the single-wavelength ellipsometry measurements were made immediately after a thermal desorption cycle. These measurements were analyzed using both a single-layer optical model and an interface-layer model that has been used previously for NIST Oxide Thickness Standard Reference Materials. The effects of gate/field oxide overlap-capacitance were eliminated by extrapolating the available data sets to values of capacitance per unit area. Oxide thickness was determined using three computer codes developed to account for quantum-mechanical effects in the substrate and for depletion in the polysilicon. Additional capacitors, away from the center were analzyed by C-V and also used for TEM analysis. A range of thicknesses was found with each of the methods, but with some overlap of values. HRTEM and STEM values showed less consistency between wafers than the CV data for the capacitors used and were seen to be more influenced by local variations such as interface non-uniformities. The TEM-based thicknesses were slightly larger than the largest values obtained from C-V measurements, which, in turn, varied by just over 0.3 nm depending on the QM correction algorithm used. Ellipsometry-based thickness fell within the range defined by C-V and TEM-based values, but had a clear dependence on optical model and substrate optical index used. Sources of variation and estimates of uncertainty for the analyses are presented. Implications for of these results for Reference Materials are discussed.
Proceedings Title
Characterization and Metrology for ULSI Technology: 2003
Conference Dates
March 24-28, 2003
Conference Location
Austin, TX, USA
Conference Title
2003 International Conference on Characterization and Metrology for ULSI Technology


gate dielectrics, reference materials, silicon dioxide, thin film metrology


Ehrstein, J. , Richter, C. , Chandler-Horowitz, D. , Vogel, E. , Ricks, D. , Young, C. , Spencer, S. , Shah, S. , Maher, D. , Foran, B. , Diebold, A. and Hung, P. (2003), Thickness Evaluation for 2nm SiO2 Films, a Comparison of Ellipsometric, Capacitance-Voltage and HRTEM Measurements, Characterization and Metrology for ULSI Technology: 2003, Austin, TX, USA, [online], (Accessed June 8, 2023)
Created September 29, 2003, Updated October 12, 2021