A Stress Relief Method to Control Warping of Focused Ion Beam Prepared Membranes for Transmission Electron Microscopy

Abstract

The continued decrease in microelectronic feature dimensions has led to a reliance on the focused ion beam (FIB) for site-specific transmission electron microscopy (TEM) specimen preparation. To maximize the capabilities of the FIB, methods must be developed to consistently produce specimens thin enough to generate TEM lattice images. The limiting factor in producing quality TEM specimens by either the traditional or lift-out method is the final thickness of the specimen.The FIB is used to prepare TEM specimens by removing the bulk material that surrounds a desired feature by sputtering with a focused gallium ion beam. Successively lower beam currents are used to sputter away material until an electron transparent membrane (-0.2 μm) containing the desired feature remains. For a 300 keV TEM, lattice imaging of silicon requires additional membrane thinning to less than 0.05 μm.The loss of rigidity during the thinning process makes the membrane highly prone to deformation due to residual stresses, linear expansion, and ion beam interaction.