Fundamental understanding of the physics and modeling of boron source/drain extension evolution during CMOS device fabrication

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Date

2003

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Kohli, Puneet

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Abstract

Improvements in the integrated circuit performance over the past three decades have been mainly possible by the downward scaling of device dimensions. Device scaling requires that all lateral and vertical dimensions of the transistor be scaled. In the last decade, in order to continue conventional scaling of the source/drain junctions, the semiconductor industry has relied heavily on decreasing the implant energy, and also on minimizing the thermal budget of the activation anneal. With Transient Enhanced Diffusion less pronounced for low implant energies and sharper anneal temperature profiles, interactions of dopant atoms and point defects with surface films and interfaces are becoming of paramount importance in determining the concentrations of dopants and point defects, and therefore the resulting device structures. A nitride spacer with an underlying deposited TEOS oxide, that behaves as a convenient etch stop layer, is a popular choice for sidewall spacer in modern CMOS process flows. In this work the effect of the silicon nitride spacer process on the B profile in silicon and the related dose loss of B from the Si into the silicon dioxide has been investigated. This is reflected as a dramatic decrease in the junction depth. The influence of the nitride spacer chemistry on B dose loss from the Si has also been investigated. The different nitride chemistries result in different B dose loss. A new model that predicts B junction depths and dose loss during fabrication of ultra-shallow junctions has been developed. A study of the interactions of dopant atoms and silicon point defects with silicon oxide films during annealing for ultra-shallow junction formation has been included. A new method for activation of source/drain junctions by microwave annealing has been proposed.

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