In-line supermapping of storage capacitor for advanced stack DRAM reliability

Model-based infrared reflectometry (MBIR) is a novel nondestructive technology which has been introduced for fast-response in-line monitoring of deep-trench dynamic random access memory (DRAM). However, for mainstream stack DRAM, MBIR application is hard to implement due to underlayer metal reflection noise. Furthermore, the production control of the stack DRAM storage capacitor is always the major concern of yield loss and reliability problems. Traditionally, the production monitoring of the storage capacitor has been performed by an x-sectional scanning electron microscope in a PFA laboratory or electron beam inspection (EBI). Unfortunately, it is quite time consuming and has a high cost. In this paper, we report a successful MBIR measurement at scribing line scatter spot with void fraction analysis methodology on 50-nm stack DRAM. We demonstrate excellent correlation of the electrical storage capacitance with a special donut shape, the EBI of underetched storage contact, and the neighboring storage capacitor shortage. The repeatability of the MBIR test is good with average sigma values of 0.56% for the top void fraction and 1.73% for the bottom void fraction, which indicate that MBIR can become a powerful metrological tool for improving product yield and reliability.