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Quantum Size Effect in Polysilicon Gates

Published online by Cambridge University Press:  22 February 2011

N. Lifshitz ,
S. Laryi  and
T. T. Sheng
N. Lifshitz
Affiliation:
AT&T Bell Laboratories Murray Hill, New Jersey 07974
S. Laryi
Affiliation:
AT&T Bell Laboratories Murray Hill, New Jersey 07974
T. T. Sheng
Affiliation:
AT&T Bell Laboratories Murray Hill, New Jersey 07974
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Abstract

It has been observed by several authors that metal-oxide-semiconductor devices with polycrystalline Si (polySi) gates behave differently depending on the doping species in polySi: the work-function difference between the silicon substrate and the gate (øps) is higher when the gates are doped with arsenic than when they are doped with phosphorus.

We believe that the different behavior of øps. can be explained by different grain textures at the polySi/SiO2 interface. Our transmission electron microscoey of the films indicates that while P-doped material consists of large (≈3000Å) grains, As-doped polySi preserves its as-deposited columnar structure – even after a high temperature anneal. Moreover, at the interface with the gate oxide an as-deposited microstructure with very small (≈100Å) “embrionic” grains is preserved. On the basis of these observations, we suggest a model for the different behavior of ø ps. The model is based on a quantum-size effect which becomes important for such small grain dimensions at the interface in As-doped polySi. This effect drastically reduces the number of states available in the conduction band at low energies. The resulting shift of the Fermi level provides a qualitative explanation for the observed puzzling difference between the work-functions of Asand P- doped polySi.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 106: Symposium G – Polysilicon Films and Interfaces , 1987 , 45
Copyright
Copyright © Materials Research Society 1988

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References

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