Optimized FIB silicon samples suitable for lattice parameters measurements by convergent beam electron diffraction

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Physics

Background:

• Focused ion beam (FIB) milling is a common technique for preparing samples for electron microscopy.
• Convergent beam electron diffraction (CBED) is a powerful method for measuring local strain in crystalline materials.
• Potential artefacts from FIB milling can affect the accuracy of strain measurements.

Purpose of the Study:

• To evaluate the impact of FIB milling artefacts on strain measurements using CBED.
• To determine the suitability of FIB preparation for accurate strain analysis in microelectronic devices.
• To quantify the thickness of the amorphous layer produced by FIB milling and its effect on strain.

Main Methods:

• Utilized CBED and electron energy loss spectroscopy (EELS) to determine sample geometry (amorphous and crystalline layer thickness).
• Measured the thickness of the FIB-amorphized sidewall layer.
• Compared strain measurements from FIB-prepared samples with those prepared by cleavage and tripod methods.

Main Results:

• Optimized FIB preparation reduced the amorphous layer thickness to approximately 7 nm per side.
• The damaged layer introduced by FIB milling did not cause measurable strain in pure silicon.
• FIB preparation, when optimized, allows for strain measurements with a sensitivity of ~2.5 x 10(-4), close to theoretical limits.
• The damaged layer significantly degraded the quality of CBED patterns.

Conclusions:

• Optimized FIB milling is a viable technique for preparing samples for accurate strain measurements in microelectronic devices.
• Minimizing the amorphous layer thickness is crucial for reliable strain analysis.
• While FIB preparation can introduce artefacts that reduce pattern quality, it does not introduce significant strain in silicon.