Site‐specific 35‐minute TEM ‐lamella preparation by FIB ‐ SEM

Abstract

Sample preparation by DualBeam (FIB‐SEM) allows site specific TEM lamella to be prepared and is the number one use case for such instruments worldwide. This technique is quite complicated and the variety of different materials and site specific orientation can complicate the process such that a great deal of knowledge and experience is usually required to achieve top results. Improvements in the robustness of various hardware components combined with technology advances are enabling automation of best known methodologies for lamella preparation such that novice users can obtain consistent results. This results in a shorter time to prepare a lamella and a more consistent quality result. Automation for different materials presents challenges due to differences in milling rates, hardness, structural differences and intended orientation. With semiconductor materials the similarity of materials makes it possible for fully automated process development due to the consistency of sample types, though often the end‐pointing on today's small structures can be quite demanding. In such cases the final thinning is often still done manually. For materials science, FEI has chosen to segment three phases of the preparation process. The distinct three routines allow the most flexibility for different sample types: chunk milling, lift‐out and thinning to electron transparency. Any of these steps can be run manually if desired or required for a particular application. Chunk milling is the process of defining the area of interest, laying protective layers of the correct thickness, and making fiducials to be used throughout the process for ion beam placement. Bulk milling is done at relatively high currents to make the process fast and then an undercut and cleanup produces a lift‐out ready thick lamella. Lift‐out has been semi‐automated with the user identifying the tip of the lift‐out probe and the sample or grid edge and the software making the required moves. Attaching and releasing the sample/probe/grid is controlled by user placed patterns for milling or deposition when requested by the guided workflow. The EasyLift manipulator with rotation and high stability is essential. Scripts exist for the rotating EasyLift EX manipulator that allow 90 dedgree or 180 degree lamella attachment to further improve TEM lamella quality. Once attached to the grid, the final script for thinning can be used. Currently final polishing scripts can be tweaked for hard or soft materials and finishing can be specified to the desired lamella thickness with 5kV surface cleaning. On the newer Helios systems the 0.5kV image looks as good as the 2kV from previous FIB sources and thus the lower currents can very effectively be used for automated final polishing. The presentation will demonstrate an interactive guided TEM Sample preparation process on the Helios DualBeam. This method shortens the TEM lamella preparation process for expert users and enables novice users to obtain routine, high quality results. The method proposed can be used on almost any material to prepare lamellas from soft and hard materials and examples are shown in Figure 1. Guided TEM Sample preparation is available on the newest FEI DualBeams and can help meet TEM lamella preparation challenges in materials science.