The Impact of Annealing Ambient on the Performance of Excimer‐Laser‐Annealed Polysilicon Thin‐Film Transistors

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Abstract
In this work we have investigated the material properties and electrical performance of polycrystalline silicon films formed by an excimer‐laser‐anneal (ELA) process in different annealing environments. Particularly, we investigated the ELA process in air, nitrogen, argon, and helium and compared it with the standard ELA process in vacuum. Polysilicon thin‐film transistors were fabricated using polysilicon material formed by ELA in different environments. We found that while the performance attributes of polysilicon films annealed in vacuum or inert ambient were quite similar, the performance of polysilicon annealed in air was drastically inferior to all. This result was attributed to the increased oxygen incorporation in the film in the case of the ELA process in air. Oxygen increased the density of both deep states and tail states in the polysilicon bandgap. One mechanism, proposed to account for the deterioration in performance, was the oxygen‐induced formation of structural deficiencies in grain boundaries and bulk grain regions and its relation to generation of deep‐state and tail‐state defects. © 1999 The Electrochemical Society. All rights reserved.

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