Thin films with high surface roughness: thickness and dielectric function analysis using spectroscopic ellipsometry.

Area of Science:

• Materials Science
• Optics
• Surface Science

Background:

• Spectroscopic ellipsometry is a powerful technique for thin film characterization.
• High surface roughness in thin films complicates optical property determination.
• Existing models often struggle with films exceeding 10 nm peak-to-valley roughness.

Purpose of the Study:

• To develop a reliable optical surface roughness model for thin films with significant roughness.
• To enable accurate dielectric function determination using spectroscopic ellipsometry.
• To simplify complex optical models by reducing unknown parameters.

Main Methods:

• Developed a roughness layer (RL) model based on atomic force microscopy (AFM) histogram analysis.
• Utilized counting statistics for theoretical generalization to non-conducting materials.
• Integrated root mean square (RMS) values from AFM directly into the optical model.

Main Results:

• The proposed model reliably determines dielectric functions for thin films with >10 nm peak-to-valley roughness.
• Demonstrated the model's applicability to organic thin films, exemplified by N,N'-dimethoxyethyl-3,4,9,10-perylene-tetracarboxylic-diimide (DiMethoxyethyl-PTCDI).
• The model successfully characterized a highly rough DiMethoxyethyl-PTCDI film, previously considered non-homogeneous.

Conclusions:

• The novel optical surface roughness model enhances thin film analysis via spectroscopic ellipsometry.
• The model's direct AFM RMS input simplifies parameter reduction in complex optical evaluations.
• This approach is broadly applicable to non-conducting materials with high surface roughness.