Process of TEM sample preparation

Pre-thinning

Since a focused Ga ion beam with a maximum diameter at the sub-micrometer level is used in the FIB technique, the sputtering speed is not so high as in other ion milling techniques [1, 2]. To reduce the FIB milling time, pre-thinning of the sample using a polisher or cutter is required. There is no definite sample target thickness to be achieved by pre-thinning, but a typical thickness used for FIB milling is in the range of 50 to 100 μm in most cases. Preparing thinner samples promises shorter FIB milling times but we should be careful not to cause any structural and chemical changes in the sample at this stage [3]. Note that the thinner samples may become more stressed during the pre-thinning process than the thicker ones. There are various techniques and tools to be used for the pre-thinning process. A micro-cleaving system is widely used for pre-thinning of the devices with single crystal Si or GaAs substrates. The system allows cleaving of the sample including the circuit of interest quite easily and precisely and the cleaved sample may be directly FIB milled or first sliced to 10 to 20 μm using a fine blade prior to the FIB milling. In the case of polycrystalline materials such as metals, ceramics, and their composites, mechanical-polishing or dicing can be done. Relatively soft materials such as polymers, rubbers, and papers can be sliced with a razor blade.