The use of admittance methods in determining the properties of deposited polysilicon
The use of admittance methods in determining the properties of deposited polysilicon
The use of small signal admittance methods in determining the properties of deposited polysilicon using a metal-oxide-polysilicon-silicon (MOPS) structure is described. The admittance response of a MOPS structure is related to specific current paths in the polysilicon and using this a method of extracting carrier mobilities and capture cross sections of grain boundary traps is found.
The starting point of the analysis is the extraction of a trap state density from the quasi-static capacitance-voltage curve. From the trap density Poisson's equation is solved and component values of an equivalent circuit that directly map the small signal current flow are calculated. The equivalent circuit is then solved using a transmission line matrix method.
For the first time a complete description of the processes that affect the admittance of a MOPS device is given. The analysis shows that the conductance loss due to carrier flow in the conduction and valence bands must be taken into account in order to extract trap properties. It is shown how the variation in conductance with bias at high frequency cannot be reconciled with the trap state density extracted from the quasi-static capacitance. The discrepancy is ascribed to the presence of interface states and because of this the presence of band tails cannot be asserted.
The limits on the extraction process are shown to depend on knowing accurate values for the oxide capacitance, flatband voltage and polysilicon fermi level. By fitting conductance-frequency curves for MOPS capacitors made on n and p-type substrates limits can be placed on the values polysilicon carrier mobilities, trap concentration and trap capture cross section for traps within a few kT of the polysilicon fermi level.
University of Southampton
1997
Carter, Julian Charles
(1997)
The use of admittance methods in determining the properties of deposited polysilicon.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The use of small signal admittance methods in determining the properties of deposited polysilicon using a metal-oxide-polysilicon-silicon (MOPS) structure is described. The admittance response of a MOPS structure is related to specific current paths in the polysilicon and using this a method of extracting carrier mobilities and capture cross sections of grain boundary traps is found.
The starting point of the analysis is the extraction of a trap state density from the quasi-static capacitance-voltage curve. From the trap density Poisson's equation is solved and component values of an equivalent circuit that directly map the small signal current flow are calculated. The equivalent circuit is then solved using a transmission line matrix method.
For the first time a complete description of the processes that affect the admittance of a MOPS device is given. The analysis shows that the conductance loss due to carrier flow in the conduction and valence bands must be taken into account in order to extract trap properties. It is shown how the variation in conductance with bias at high frequency cannot be reconciled with the trap state density extracted from the quasi-static capacitance. The discrepancy is ascribed to the presence of interface states and because of this the presence of band tails cannot be asserted.
The limits on the extraction process are shown to depend on knowing accurate values for the oxide capacitance, flatband voltage and polysilicon fermi level. By fitting conductance-frequency curves for MOPS capacitors made on n and p-type substrates limits can be placed on the values polysilicon carrier mobilities, trap concentration and trap capture cross section for traps within a few kT of the polysilicon fermi level.
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Published date: 1997
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Local EPrints ID: 460284
URI: http://eprints.soton.ac.uk/id/eprint/460284
PURE UUID: 72d9cb80-6d34-4dfc-a5c4-c556033aab4c
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Date deposited: 04 Jul 2022 18:17
Last modified: 04 Jul 2022 18:17
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Author:
Julian Charles Carter
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