A Novel Approach to Inspect Abnormalities on the Deep Trench Capacitors in DRAM

Abstract

A novel method has been developed using Focused Ion Beam (FIB) system to create the likely three‐dimensional (3D) image of a deep trench (DT) capacitor in a DRAM cell for process evaluation and failure analysis. The abnormalities in the structures of DT capacitors, especially “DT striation” and “DT‐DT short”, result in the functional failures or retention problems detected in the electrical test, which are very common failures in a DT capacitor DRAM cell. The common method to examine failed DTs is to use FIB milling with its slice‐and‐view capability for both planar and cross‐sectional observations. However, the areas containing the defects in the specific DTs are probably milled away during FIB milling, so that the failure causes could not be found. The new method uses XeF2 etching gas to reveal the likely 3D appearance of the desired DTs, instead of the traditional FIB slice‐and‐view method. The abnormalities on the structures of the specific DTs can then be inspected using Scanning Electron Microscopy (SEM). The innovation of this technique not only provides more information on the desired DTs, but also provides a quick way to identify the possible causes for the failures. In summary, this method will provide an effective way to improve the success rate and turnaround time for the inspection of failed DTs.