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TEM Sample Preparation

There are three FIB-based methods to prepare TEM samples：pre-thin, lift-out and omni-probe.

pre-thin

The figure shows a typical process for the pre-thin method which thins down samples to 5-10 um by mechanical polish and then to 0.1 um by FIB lithography.

This method can be employed to create large (~50 um) and uniform TEM samples without deformation. However, it is more complicated and time-consuming compared to other methods.

Lift-out

This figure shows a typical process for the lift-out method, which uses FIB to locally thin down samples. The thin area is separated from the sample by “U-cut” which employs FIB to bombard the area edge. Finally, the thin specimen is shifted to a Cu-grid with carbon films by a glass probe with static electrical attraction.

This is the most efficient sample preparation method with a typical working time of less than one hour and is thus widely used. However, it holds a drawback of being hard to rework or process specimens after shifting to Cu-grids. Therefore, the quality of the treated sample is highly dependent on the preparation ability of engineers.

Omni-probe

This figure shows a typical process for the omni-probe method, which uses FIB to locally thin down samples to 1 to 2 um. A probe is connected to the thin area by FIB-deposition of Pt. The probe is used to shift the thinned specimen to a proper position and angle for precisely modifying the specimen morphology by FIB bombardment. The modifying process can be performed several times until the morphology is proper for TEM inspection.

Although this process needs a longer working time of 1.5 to 2 hours, its reworking power is proper for error-unacceptable sample preparation.

(a)-(f) Processes of sample preparation

(a)-(b) sticking sample to probe

(d) shift sample to the holder

(e) disconnecting sample and probe

(f) put holder with the sample to TEM

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