FIB lamella preparation

FIB lamella preparation

The main goal of the lift out process is to extract a small piece of a bulk like sample (typical SEM sample) and attach it to a grid suitable for TEM imaging. The desired sample outcome is a lamella thin enough to be suited for TEM/STEM/EELS/EDX measurements (<100nm is desirable). Throughout this document it is assumed that the operator is an experienced SEM user, always works at eucentric height (the crossover of the ion and electron beam) and has an understanding of the chamber geometry. Furthermore, all settings are material and sample dependent. As a rule of thumb, the harder a material is the more difficult it is to mill with the ion beam. As an example, 20nA is on the low end for milling larger sections of corundum efficiently but 2.8nA is almost too aggressive for gold.

1,2: Protective Pt deposition

Fig 1: Sketch of electron beam Pt deposition.

Fig 2: Sketch of subsequent platinum deposition.

File:Fig3 1.tif File:Fig3 2.tif Fig 3: SE images acquired before and after electron beam deposited platinum. When a suitable region of interest has been located selected by SEM, it is necessary to protect the surface from damage from the ion beam. A typical deposition scheme is illustrated on fig 1. The first layer is deposited using the electron beam to minimize surface damage from the subsequent ion beam deposition, imaging and milling. The deposition is done by exposing the sample to a precursor of metal organic gas and scanning the electron beam over the area where deposition is desired. This causes the gas molecules to decompose and parts of the decomposed products deposit on the surface. The electron beam settings used for the deposition are high tension (HT) of 2-5kV with a high current 5.5nA. The deposition thickness listed in the sketch are approximate numbers and are sample dependent. Remember to insert and heat the Pt GIS prior to choose “Pt ebeam structure” for the Pt deposition with the electron beam and the “Pt dep” for deposition with the ion beam. The reason for even having an ion beam deposition afterwards is that the ion beam leaves a much thicker deposition within a reasonable time which protects against the ion beam in the following steps. There is a clear risk of damaging the surface during both depositions. The HT and current used for the ion beam assisted deposition is 30kV and 0.26nA.

Note: A typical stage tilt of 0o and 52o are used for the elctron beam deposition and ion deposition. Your needs may vary depending on sample geometry/requirements. If you wish to use another deposition such as carbon or tungsten you may need to tilt the sample differently.

(Anton Bay Andersen, March 2020)

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