Characterization of High-k Dielectric Materials on Silicon Using Angle Resolved XPS

Importance of the Topic

The ongoing scaling of silicon‐based transistors demands ultrathin gate dielectrics with minimal leakage. Traditional SiO2 layers reach physical limits at sub‐nanometer thicknesses, driving the integration of high‐k materials such as HfO2 and Al2O3. Detailed chemical and structural analysis of these layers is essential for device performance and reliability.

Objectives and Study Overview

This application note demonstrates how X‐ray photoelectron spectroscopy (XPS) and angle‐resolved XPS (ARXPS) can characterize high‐k dielectric stacks on silicon. Key aims include assessing layer thickness, elemental distribution, chemical states, interface composition, and wafer‐scale uniformity.

Methodology and Instrumentation

ARXPS exploits variations in electron emission angle to obtain depth‐sensitive chemical information without material removal. Main approaches:

• Relative depth plots: log ratio of grazing vs normal emission peak areas to map layer ordering
• Multi‐layer thickness calculations: Avantage software computes thicknesses of up to three stacked films
• Line scans and mapping: acquisitions across wafer diameter or in 2D to evaluate uniformity
• Depth profiling: maximum‐entropy reconstruction of concentration profiles from ARXPS data

Instrumentation Used:

• Thermo Scientific Theta Probe and Theta 300 XPS systems
• Avantage data analysis software with multi‐layer thickness calculator

Key Results and Discussion

Relative depth plots on mixed HfO2/Al2O3/SiO2 stacks clearly resolved surface carbon, buried Si, and overlapping metal oxide layers. Using atomic layer deposition (ALD), Al2O3 thickness increased with cycle number while SiO2 remained constant; adventitious carbon varied with Al2O3 presence but not thickness. Line‐scan measurements across 200 mm wafers revealed thickness variations of ~0.7 nm. XPS maps distinguished Hf‐bound O (low binding energy) from Al/Si‐bound O (higher binding energy), exposing non‐uniform growth. Si 2p spectra showed that HfO2 grown by ALD on ≥1 nm SiO2 preserved oxide chemistry, whereas thinner or HF‐etched surfaces promoted hafnium silicate formation. Depth profiles reconstructed from ARXPS data captured the spatial overlap of HfO2, Al2O3, SiO2, and surface carbon. In contrast, sputter profiling induced HfO2 reduction to metallic Hf, illustrating ARXPS’s non‐destructive advantage.

Benefits and Practical Applications

The combined XPS/ARXPS approach enables:

• Non‐destructive, angle‐resolved measurement of ultrathin dielectric thicknesses
• Quantitative assessment of interfacial silicate vs oxide formation
• High‐resolution chemical state mapping to guide process optimization
• Wafer uniformity evaluation for quality control

Future Trends and Potential Applications

Advances may include higher angular resolution, in situ ARXPS during deposition, integration with TEM/ERD for correlative analysis, and machine‐learning‐driven spectral deconvolution. Emerging high‐k compounds and 2D dielectric layers will benefit from these refined surface‐analysis techniques.

Conclusion

XPS and ARXPS provide comprehensive, non‐destructive characterization of high‐k dielectric stacks on silicon, delivering critical insights into thickness, composition, chemical states, and uniformity. These methods support process development and quality assurance in advanced semiconductor manufacturing.

References

• Thermo Fisher Scientific Application Note 31021: Characterization of High‐k Dielectric Materials on Silicon Using Angle Resolved XPS
• Thermo Fisher Scientific Application Note 31014: Principles of ARXPS Analysis