A thickness model for the [formula omitted] stack in the titanium salicide process module

Abstract

A reliable TiSi 2 TiN stack thickness model is an essential component for modeling the titanium salicide process, and such a model is not well-developed in current process simulators and in the literature. To determine this model, a design of experiments was set up to examine five process variables, namely, as-deposited Ti thickness, reaction temperature, reaction time, As + implanted dose, and the reaction ambient pressure. Weight and sheet resistance measurements were used to evaluate the thickness and efficiency of reaction (%Ti converted to suicide). A good first-order linear model was obtained, with a residual standard deviation (variation of model from data) of ~30 Å. The model establishes quantitatively, that the TiSi 2 thickness is proportional to the as-deposited Ti thickness and reaction temperature, inversely proportional to the implanted As + dose, and weakly proportional to the reaction time. Since TiN and TiSi 2 are competing reactions, TiN exhibits inverse functional relationships with the variables, as compared with TiSi 2. The efficiency of the reaction also has been quantified by the model. The ambient pressure has been found to have no impact on either the TiSi 2 TiN stack thickness, or the reaction efficiency. The model has been validated by cross-sectional transmission electron microscopy, which agrees with the model prediction within experimental error.