Metrology of SIMOX buried oxide and nitride/STI CMP

Abstract

The increase in demand for faster and more powerful microprocessors in recent years has been the driving force to introduce new materials and processes into semiconductor fabrication facilities. As each fabrication facility tries to maximize its yield, it is mandatory that there exist metrology techniques to characterize both materials and processes. This mandate is the motivation behind this thesis. In this thesis, the metrology of two different systems used in VLSI technology are investigated. The first system is the material, Separation by IMplanted OXygen (SIMOX) buried oxide. SIMOX technology has been studied extensively as a viable alternative to bulk silicon technology in radiation-hard and low-power applications. However, there is still a lack of knowledge on the nature of the defects present in the SIMOX buried oxide and their impact on basic BOX electrical characteristics, such as BOX high-field conduction. In this thesis, greater understanding about the excess-silicon related defects in the buried oxide has been obtained concerning their nature, origin, and impact on the conduction characteristics. Further understanding about the silicon islands in the buried oxide has also been obtained concerning their formation and impact on the high-field conduction characteristics. Finally, a metrological application of the BOX high-field conduction model is demonstrated. The second system is the process, Nitride/Shallow Trench Isolation (STI) Chemical Mechanical Polishing (CMP). CMP processes have been heralded as a way to planarize films and structures on wafers to a degree which has not been possible before. However, recent studies have shown that the uniformity of CMP processes depends on the layout-pattern density. To address this issue, an oxide CMP model has been developed to show the relationship between layout-pattern density and the polish rate. However, there is an uncertainty as to how this single-material system model can be extended to other material systems and dual-materials systems. In this thesis, the metrology and modeling techniques for oxide CMP are extended to nitride CMP in order to understand the pattern-density and materials dependence for this particular CMP process. In addition, the planarization and uniformity of the two-material system for STI structures is investigated. A model explaining the relationship between a particular STI layout-pattern density and the resulting planarization is developed.