Gate oxide improvement: statistics and methodology

Optimizing the gate oxide quality of logic processes is a difficult and important task: due to the missing redundancy, a large variety of hard to analyze products (small burn in statistics), and increasing product requirements (large gate oxide area, high electric field). This contribution describes statistical considerations and a methodology applied to monitor and improve the gate oxide quality of logic processes. A variety of test structures, which are sensitive to the influence of different process blocks, are used to identify possible gate oxide quality hazards. This work clearly indicates the necessity to examine a variety of test structures with large GOX areas, to separate the influence of different processing steps and substrate materials. A continuous GOX-monitoring and improvement is an important tool to ensure increased oxide reliability and to fulfill the continuously increasing product requirements