Characterization of Silicon Oxide and Oxynitride Layers

Importance of the Topic

Accurate characterization of ultra-thin silicon oxide and oxynitride layers is critical for semiconductor device performance and reliability. Non-destructive depth profiling and chemical state analysis enable detection of interfacial contamination and precise control of dielectric properties.

Objectives and Overview

This study demonstrates the use of Parallel Angle Resolved XPS (PARXPS) to measure film thickness, uniformity, chemical composition, nitrogen distribution, and dose in silicon oxide and oxynitride films. Comparison with ellipsometry and reproducibility tests validate the technique.

Methodology and Instrumentation

Samples of silicon oxide and silicon oxynitride on silicon were analyzed using PARXPS with Thermo Scientific Theta Probe and Theta 300 instruments. Film thickness was cross-validated by ellipsometry and contamination layers quantified by SIMS. Dynamic repeatability tests involved ten sequential measurements at multiple wafer sites.

Main Results and Discussion

• Accuracy: PARXPS thickness measurements correlate linearly with ellipsometry within ~1%, offset by a ~0.8 nm contamination layer undetected by ellipsometry.
• Precision: Dynamic repeatability yields relative standard deviations of 0.3–0.5% for thickness and 0.46–1.37% for nitrogen dose across multiple sites and wafers.
• Chemical States: Angle-resolved N 1s spectra reveal two nitrogen environments (Na and Nb), with Nb localized at the oxynitride–silicon interface.
• Depth Profiling: Maximum entropy analysis generates non-destructive concentration profiles confirming the distribution of nitrogen species and quantifying layer thickness (~2.6 nm) and doses.
• Sputter Profiling Comparison: Low-energy argon sputtering alters Nb to Na, leading to misinterpretation of depth distribution; PARXPS avoids this artifact.
• Mapping: Wafer maps of thickness (49 to 522 points) show uniformity within 0.79% and nitrogen dose variations of ~2.15% on 300 mm wafers.

Benefits and Practical Applications

PARXPS provides non-destructive, reproducible analysis of ultra-thin dielectric films with simultaneous thickness, chemical state, and depth distribution information. It supports process control in microelectronics manufacturing and quality assurance.

Future Trends and Applications

Integration of PARXPS with in situ monitoring and thinner dielectric materials, coupling with complementary surface analysis techniques, and expansion into other advanced material systems will enhance process optimization and device reliability.

Conclusion

Parallel angle resolved XPS on Thermo Scientific Theta instruments delivers high accuracy, precision, and chemical specificity for silicon oxide and oxynitride films. The method surpasses ellipsometry in distinguishing contamination and chemical states, offering reliable depth profiling without sputter-induced artifacts.

Used Instrumentation

• Thermo Scientific Theta Probe
• Thermo Scientific Theta 300
• Parallel Angle Resolved XPS configuration

References

• Seah MP and White RG. Surface and Interface Analysis, 2002, volume 33, page 960.
• Thermo Fisher Scientific Application Note AN31025.