Dopant profiling based on scanning electron and helium ion microscopy

Area of Science:

• Materials Science
• Semiconductor Physics
• Microscopy Techniques

Background:

• Mapping donor distributions is crucial for semiconductor device characterization.
• Scanning Electron Microscopy (SEM) often requires specialized energy-filtering for effective doping contrast.
• Secondary Electron (SE) signal analysis is key in SEM for visualizing doping profiles.

Purpose of the Study:

• To compare the effectiveness of doping contrast generation in SEM and Scanning Helium Ion Microscope (SHIM).
• To evaluate the sensitivity and capabilities of SHIM for donor profiling.
• To correlate experimental doping contrast profiles with theoretical potential energy distributions.

Main Methods:

• Comparative analysis of doping contrast in SEM and SHIM.
• Utilizing secondary electron (SE) signals for imaging.
• Employing energy-filtering techniques in SEM.
• Measuring doping contrast profiles of thin p-layers.
• Calculating potential energy distributions.

Main Results:

• SHIM achieves strong doping contrast without energy filtering, unlike SEM.
• SHIM demonstrates higher sensitivity to donor density changes (≥10^16-10^17 donors/cm³).
• SHIM's sensitivity limit for acceptors is >2x10^17 acceptors/cm³.
• Experimental doping contrast profiles correlate well with calculated potential energy distributions.
• SHIM's shorter SE escape depth (1.8nm) in silicon is advantageous over SEM (7nm).

Conclusions:

• SHIM is a more effective technique for donor profiling than SEM.
• The shorter secondary electron escape depth in SHIM enhances sensitivity for subsurface analysis.
• Low-energy SE signals with short escape depths are optimal for precise donor profiling.