Manufacturability considerations for fully depleted SOI

Performance advantages of SOI technology have been widely published. However, a critical step in the maturation of any technology is progressing from demonstrating best case performance advantages to demonstrating repeatable performance. For a technology to be production qualified, target values must be met for critical parameters, with lot parametric variations within the required tolerances. We examine fully depleted SOI from this point of view. As a result of the very thin Si films used in fully-depleted SOI, sensitivities are found for process steps such as oxidation, salicide formation, and photolithography that are not found in bulk silicon or partially-depleted SOI. Since one of most important SOI substrate parameters is the thickness of the Si film (tsi), we focus here on how key electrical parameters are affected by tsi, for both mean and standard deviation. We find that not only is the tsi variation across a single wafer important, but that it must be controlled lot to lot. This impacts SOI wafer suppliers, as well as VLSI production flows in which sacrificial oxidations are done.<
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