Low-energy STEM of multilayers and dopant profiles

Area of Science:

• Materials Science
• Physics
• Microscopy

Background:

• Conventional scanning electron microscopes (SEM) typically image surface topography.
• Adapting SEM for transmission imaging offers complementary analytical capabilities.

Purpose of the Study:

• To modify a scanning electron microscope (SEM) for scanning transmission mode (STEM).
• To investigate contrast mechanisms and resolution limits in STEM mode.
• To evaluate different electron detection strategies for STEM imaging.

Main Methods:

• Modification of a LaB6 source SEM for scanning transmission electron microscopy (STEM).
• Implementation of two detection strategies: direct transmitted electron collection and secondary electron collection from transmitted electrons.
• Investigation of semiconductor multilayers and dopant profiles in As-implanted Si specimens.

Main Results:

• Image contrast follows mass-thickness contrast principles.
• Resolution is consistently limited by the electron probe size, irrespective of specimen thickness or beam broadening.
• Detection strategy influences image appearance (bright-field vs. dark-field).
• Contrast analysis requires considering transmitted electron angular distribution and secondary yield dependence on incidence angle.

Conclusions:

• The modified SEM effectively operates in STEM mode for material analysis.
• Understanding contrast and resolution is crucial for interpreting STEM images.
• Detection strategy choice impacts image interpretation and requires careful consideration of electron scattering and yield phenomena.