Electron-beam-induced carbon contamination on silicon: characterization using Raman spectroscopy and atomic force...

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Electron-beam-induced carbon deposition is a common artifact in scanning electron microscopy (SEM).
• Understanding the properties of this carbon film is crucial for accurate SEM analysis and contamination mitigation.
• Previous studies have primarily focused on the formation mechanism rather than the detailed characterization of the deposited film and its substrate interactions.

Purpose of the Study:

• To characterize the nature of electron-beam-induced carbon film deposition on silicon wafers.
• To investigate the influence of the deposited carbon film on the opto-electrical properties of the silicon substrate.
• To compare the observed Raman intensity enhancements with theoretical models of field enhancement.

Main Methods:

• Silicon wafers were exposed to a 15 kV electron beam with a 300 pA probe current.
• Raman spectroscopy was employed to analyze the chemical composition and crystallite size of the deposited film.
• Atomic force microscopy (AFM) was used to determine the film's morphology and cross-sectional profile.
• Raman intensity mapping and finite-difference time-domain (FDTD) modeling were utilized to study spatial variations in signal and local field enhancement.

Main Results:

• The deposited film was identified as amorphous carbon with an estimated crystallite size of 125 Å.
• AFM revealed a raised and textured film profile corresponding to the electron beam's raster pattern.
• Raman intensity mapping showed significant enhancement at the film's edges and corners, exceeding predictions based on thickness alone.
• The observed Raman enhancement correlated with modeled local field enhancement at the coating boundaries.

Conclusions:

• Electron-beam-induced carbon deposition results in amorphous carbon films with distinct morphological and optical properties.
• The deposited carbon film induces localized disturbances in the substrate's opto-electrical properties, particularly at the film's edges.
• This phenomenon is comparable to Raman edge enhancement observed in silicon due to surface structure, highlighting the impact of contamination on nanoscale optical measurements.