Multi-technique composition, coverage and band gap analysis of ALD-grown ultra thin films

Importance of the Topic

The development of ultra-thin high-k dielectric films such as HfO2 is critical for advanced semiconductor applications due to their impact on device performance and scaling. Reliable multi-technique analysis enables comprehensive characterization of composition, thickness, coverage, and electronic properties, ensuring quality control and accelerating material optimization.

Objectives and Study Overview

This study employs a combination of X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS) and reflected electron energy loss spectroscopy (REELS) integrated in the Thermo Scientific Nexsa XPS System to monitor the growth and properties of atomic layer deposited (ALD) HfO2 films on SiO2/Si substrates across multiple ALD cycles. The primary goals are to quantify hafnium deposition, assess surface coverage, and determine the band gap of the resulting films.

Methodology

• ALD deposition of HfO2 films on SiO2/Si substrates over 0–100 cycles.
• Acquisition of XPS survey spectra after each ALD cycle to track Hf and Si signals.
• Calculation of film thickness via Beer–Lambert attenuation using Avantage Data System, based on XPS intensity ratios and known material densities.
• Surface coverage assessment through ISS by analyzing energy loss of He+ ions scattered from the top monolayer.
• Band gap measurement via REELS by identifying the onset of inelastic electron scattering in energy loss spectra.

Used Instrumentation

• Thermo Scientific Nexsa XPS System with capabilities for XPS, ISS, REELS, UPS, Raman and AES.
• Avantage Data System software for automated data processing, thickness and band gap calculations.
• Dual source flood gun for charge compensation and REELS excitation.

Main Results and Discussion

• XPS data revealed a steady increase in HfO2 composition and calculated film thickness ranging from 0 to ~10 nm as ALD cycles progressed.
• ISS measurements indicated that Si signal disappears between 20 and 50 ALD cycles, marking full surface coverage by HfO2.
• REELS analysis provided rapid band gap determination, with clear onset of inelastic scattering corresponding to the expected dielectric gap of HfO2.

Benefits and Practical Applications

• Integrated multi-technique approach offers a comprehensive quality control solution for thin-film production.
• Precise thickness and coverage measurements ensure uniformity and reliability of high-k dielectric layers.
• Rapid band gap determination supports material screening for semiconductor, photovoltaic and LED applications.

Future Trends and Potential Applications

Advances in multi-modal surface analysis will continue to enhance the characterization of increasingly complex thin films and nanostructured materials. Combining in situ and operando measurements with high spatial resolution techniques will drive innovation in semiconductor device fabrication, energy materials, and surface coatings. Integration with machine learning algorithms for automated data interpretation may further accelerate materials discovery and process optimization.

Conclusion

The Nexsa XPS System demonstrates the power of integrating XPS, ISS, and REELS within a single automated platform to deliver detailed insights into composition, thickness, coverage and electronic properties of ALD-grown HfO2 films. This streamlined workflow supports rigorous quality control and paves the way for optimized design of next-generation dielectric materials.