MICRO: Defect Analysis

Nurit Raccah, Daniel Rogers, Ehud Tzuri, and Arik Shavit, As IC feature sizes continue to shrink well below the wavelength of visible light, there is an increasing need for high-resolution, high-throughput inspection tools to accelerate process development and optimize production. At the 90-nm technology node and beyond, characterizing shrinking yield-critical defects requires the detection of the new defect types that result from the integration of new materials and processes. These requirements lead to a natural trade-off between sensitivity and throughput. The increasing cost of inspection suggests that new inspection approaches are needed. A deep-ultraviolet (DUV) laser-based bright-field inspection technology developed by Applied Materials (Santa Clara, CA) was used to characterize two advanced DRAM process modules. The inspection method enabled engineers to address specific processing issues rapidly. This article focuses on inspection strategies for three DRAM layers. In addition, the article compares current optical inspection tools and correlates tool data results with end-of-line probe results. Automated bright-field wafer inspection tools, which were introduced more than 20 years ago, have traditionally used lamps as illumination sources. While these tools have evolved to become industry standards, they face limitations as chipmakers begin to address the needs of 65-nm processes and below. The achievable illumination levels of lamp-based bright-field inspection tools are inherently limited. Time-delay-integration cameras can compensate in part for the low signal levels of traditional bright-field tools, but they too are limited in the low-light-flux regime. As a result, the instruments' sensitivity for materials that are susceptible to light damage or lack reflectivity can degrade substantially. The DUV-laser-based inspection tool discussed in this article offers simultaneous bright-field and 3-D-channel imaging to perform in-line inspection of advanced processes. With a photomultiplier tube (PMT) detector, the tool operates at high resolution with a throughput of several wafers per hour, making it suitable for production applications.