Toward site-specific dopant contrast in scanning electron microscopy.

Area of Science:

• Materials Science
• Nanotechnology
• Semiconductor Physics

Background:

• Scaling semiconductor devices to nanometer dimensions necessitates 3D quantitative analysis of dopant concentrations.
• Scanning electron microscopy (SEM) offers promising dopant contrast imaging, but challenges remain, particularly for buried layers requiring site-specific preparation.
• Focused ion beam (FIB) milling is a key technique for site-specific sample preparation in advanced microscopy.

Purpose of the Study:

• To optimize site-specific sample preparation using FIB for enhanced dopant contrast in SEM.
• To investigate the formation and impact of the electronically dead layer during FIB polishing.
• To assess the detectability of low dopant concentrations and contamination levels.

Main Methods:

• Site-specific sample preparation using focused Ga ion beam (FIB) milling with a decreasing ion energy polishing sequence.
• Scanning electron microscopy (SEM) for imaging dopant contrast.
• Theoretical modeling to understand the electronically dead layer.
• Comparison with cleaved samples for contrast and contamination analysis.

Main Results:

• Achieved dopant contrast values comparable to cleaved samples.
• Demonstrated detection of dopant concentrations as low as 1x10^16 cm-3.
• Identified the electronically dead layer as an amorphized silicon layer formed during FIB polishing.
• Observed significantly suppressed contamination on FIB-treated samples compared to cleaved ones.

Conclusions:

• Optimized FIB preparation significantly enhances SEM dopant contrast for nanometer-scale analysis.
• The developed method allows for quantitative 3D dopant concentration analysis at low levels.
• FIB polishing is a viable technique for preparing samples for high-resolution dopant imaging, overcoming limitations of traditional methods.