A Novel ONO Inspection Methodology for DRAM Deep Trench Structure

The oxide-nitride-oxide (ONO) is one of the critical layers in the deep trench (DT) capacitor of the modern DRAM structure. This paper highlights a ONO inspection methodology, which used the silicon wet etching to enhance the ONO leakage point. First, a hole was milled nearby the leakage ONO, which was localized by using focused ion beam (FIB). Then, silicon was removed by an etching solution from the opening. When the poly of DT is etched through the ONO weak point, the leakage site will be enhanced. With the silicon wet etching enhancement, the ONO leakage point is easy to be observed by X-S FIB inspection. The real ONO leakage point is useful information for the root cause finding and the process improvement.