Nitrogen passivation of the interface states near the conduction band edge in 4H-silicon carbide

J. R. Williams, G. Y. Chung, C. C. Tin, K. McDonald, D. Farmer, R. K. Chanana, R. A. Weller, S. T. Pantelides, O. W. Holland, M. K. Das, L. A. Lipkin, Leonard C Feldman

Research output: Chapter in Book/Report/Conference proceedingConference contribution

6 Citations (Scopus)

Abstract

This paper describes the development of a nitrogen-based passivation technique for interface states near the conduction band edge [Dit(Ec]) in 4H-SiC/SiO2. These states have been observed and characterized in several laboratories for n- and p-SiC since their existence was first proposed by Schorner, et al. [1]. The origin of these states remains a point of discussion, but there is now general agreement that these states are largely responsible for the lower channel mobilities that are reported for n-channel, inversion mode 4H-SiC MOSFETs. Over the past year, much attention has been focused on finding methods by which these states can be passivated. The nitrogen passivation process that is described herein is based on post-oxidation, high temperature anneals in nitric oxide. An NO anneal at atmospheric pressure, 1175°C and 200-400sccm for 2hr reduces the interface state density at Ec-E ≅ 0.1 eV in n-4H-SiC by more than one order of magnitude - from > 3×1013 to approximately 2×1012cm-2eV-1. Measurements for passivated MOSFETs yield effective channel mobilities of approximately 30-35cm2/V-s and low field mobilities of around 100cm2/V-s. These mobilities are the highest yet reported for MOSFETs fabricated with thermal oxides on standard 4H-SiC and represent a significant improvement compared to the single digit mobilities commonly reported for 4H inversion mode devices. The reduction in the interface state density is associated with the passivation of carbon cluster states that have energies near the conduction band edge. However, attempts to optimize the the passivation process for both dry and wet thermal oxides do not appear to reduce Dit(Ec) below about 2×1012cm-2eV-1 (compared to approximately 1010cm-2eV-1 for passivate Si/SiO2). This may be an indication that two types of interface states exist in the upper half of the SiC band gap - one type that is amenable to passivation by nitrogen and one that is not. Following NO passivation, the average breakdown field for dry oxides on p-4H-SiC is higher than the average field for wet oxides (7.6MV/cm compared to 7.1MV/cm at room temperature). However, both breakdown fields are lower than the average value of 8.2MV/cm measured for wet oxide layers that were not passivated. The lower breakdown fields can be attributed to donor-like states that appear near the valence band edge during passivation.

Original languageEnglish
Title of host publicationMaterials Research Society Symposium - Proceedings
EditorsA. Argarwal, M. Skowronski, J.A. Cooper, E. Janzen
Volume640
Publication statusPublished - 2001
EventSilicon Carbide- Materials, Processing and Devices - Boston, MA, United States
Duration: Nov 27 2000Nov 29 2000

Other

OtherSilicon Carbide- Materials, Processing and Devices
CountryUnited States
CityBoston, MA
Period11/27/0011/29/00

Fingerprint

Interface states
Conduction bands
Passivation
Silicon carbide
Nitrogen
Oxides
Carbon clusters
Thermooxidation
Nitric oxide
Valence bands
silicon carbide
Atmospheric pressure
Nitric Oxide
Energy gap

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials

Cite this

Williams, J. R., Chung, G. Y., Tin, C. C., McDonald, K., Farmer, D., Chanana, R. K., ... Feldman, L. C. (2001). Nitrogen passivation of the interface states near the conduction band edge in 4H-silicon carbide. In A. Argarwal, M. Skowronski, J. A. Cooper, & E. Janzen (Eds.), Materials Research Society Symposium - Proceedings (Vol. 640)

Nitrogen passivation of the interface states near the conduction band edge in 4H-silicon carbide. / Williams, J. R.; Chung, G. Y.; Tin, C. C.; McDonald, K.; Farmer, D.; Chanana, R. K.; Weller, R. A.; Pantelides, S. T.; Holland, O. W.; Das, M. K.; Lipkin, L. A.; Feldman, Leonard C.

Materials Research Society Symposium - Proceedings. ed. / A. Argarwal; M. Skowronski; J.A. Cooper; E. Janzen. Vol. 640 2001.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Williams, JR, Chung, GY, Tin, CC, McDonald, K, Farmer, D, Chanana, RK, Weller, RA, Pantelides, ST, Holland, OW, Das, MK, Lipkin, LA & Feldman, LC 2001, Nitrogen passivation of the interface states near the conduction band edge in 4H-silicon carbide. in A Argarwal, M Skowronski, JA Cooper & E Janzen (eds), Materials Research Society Symposium - Proceedings. vol. 640, Silicon Carbide- Materials, Processing and Devices, Boston, MA, United States, 11/27/00.
Williams JR, Chung GY, Tin CC, McDonald K, Farmer D, Chanana RK et al. Nitrogen passivation of the interface states near the conduction band edge in 4H-silicon carbide. In Argarwal A, Skowronski M, Cooper JA, Janzen E, editors, Materials Research Society Symposium - Proceedings. Vol. 640. 2001
Williams, J. R. ; Chung, G. Y. ; Tin, C. C. ; McDonald, K. ; Farmer, D. ; Chanana, R. K. ; Weller, R. A. ; Pantelides, S. T. ; Holland, O. W. ; Das, M. K. ; Lipkin, L. A. ; Feldman, Leonard C. / Nitrogen passivation of the interface states near the conduction band edge in 4H-silicon carbide. Materials Research Society Symposium - Proceedings. editor / A. Argarwal ; M. Skowronski ; J.A. Cooper ; E. Janzen. Vol. 640 2001.
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author = "Williams, {J. R.} and Chung, {G. Y.} and Tin, {C. C.} and K. McDonald and D. Farmer and Chanana, {R. K.} and Weller, {R. A.} and Pantelides, {S. T.} and Holland, {O. W.} and Das, {M. K.} and Lipkin, {L. A.} and Feldman, {Leonard C}",
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AU - Williams, J. R.

AU - Chung, G. Y.

AU - Tin, C. C.

AU - McDonald, K.

AU - Farmer, D.

AU - Chanana, R. K.

AU - Weller, R. A.

AU - Pantelides, S. T.

AU - Holland, O. W.

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N2 - This paper describes the development of a nitrogen-based passivation technique for interface states near the conduction band edge [Dit(Ec]) in 4H-SiC/SiO2. These states have been observed and characterized in several laboratories for n- and p-SiC since their existence was first proposed by Schorner, et al. [1]. The origin of these states remains a point of discussion, but there is now general agreement that these states are largely responsible for the lower channel mobilities that are reported for n-channel, inversion mode 4H-SiC MOSFETs. Over the past year, much attention has been focused on finding methods by which these states can be passivated. The nitrogen passivation process that is described herein is based on post-oxidation, high temperature anneals in nitric oxide. An NO anneal at atmospheric pressure, 1175°C and 200-400sccm for 2hr reduces the interface state density at Ec-E ≅ 0.1 eV in n-4H-SiC by more than one order of magnitude - from > 3×1013 to approximately 2×1012cm-2eV-1. Measurements for passivated MOSFETs yield effective channel mobilities of approximately 30-35cm2/V-s and low field mobilities of around 100cm2/V-s. These mobilities are the highest yet reported for MOSFETs fabricated with thermal oxides on standard 4H-SiC and represent a significant improvement compared to the single digit mobilities commonly reported for 4H inversion mode devices. The reduction in the interface state density is associated with the passivation of carbon cluster states that have energies near the conduction band edge. However, attempts to optimize the the passivation process for both dry and wet thermal oxides do not appear to reduce Dit(Ec) below about 2×1012cm-2eV-1 (compared to approximately 1010cm-2eV-1 for passivate Si/SiO2). This may be an indication that two types of interface states exist in the upper half of the SiC band gap - one type that is amenable to passivation by nitrogen and one that is not. Following NO passivation, the average breakdown field for dry oxides on p-4H-SiC is higher than the average field for wet oxides (7.6MV/cm compared to 7.1MV/cm at room temperature). However, both breakdown fields are lower than the average value of 8.2MV/cm measured for wet oxide layers that were not passivated. The lower breakdown fields can be attributed to donor-like states that appear near the valence band edge during passivation.

AB - This paper describes the development of a nitrogen-based passivation technique for interface states near the conduction band edge [Dit(Ec]) in 4H-SiC/SiO2. These states have been observed and characterized in several laboratories for n- and p-SiC since their existence was first proposed by Schorner, et al. [1]. The origin of these states remains a point of discussion, but there is now general agreement that these states are largely responsible for the lower channel mobilities that are reported for n-channel, inversion mode 4H-SiC MOSFETs. Over the past year, much attention has been focused on finding methods by which these states can be passivated. The nitrogen passivation process that is described herein is based on post-oxidation, high temperature anneals in nitric oxide. An NO anneal at atmospheric pressure, 1175°C and 200-400sccm for 2hr reduces the interface state density at Ec-E ≅ 0.1 eV in n-4H-SiC by more than one order of magnitude - from > 3×1013 to approximately 2×1012cm-2eV-1. Measurements for passivated MOSFETs yield effective channel mobilities of approximately 30-35cm2/V-s and low field mobilities of around 100cm2/V-s. These mobilities are the highest yet reported for MOSFETs fabricated with thermal oxides on standard 4H-SiC and represent a significant improvement compared to the single digit mobilities commonly reported for 4H inversion mode devices. The reduction in the interface state density is associated with the passivation of carbon cluster states that have energies near the conduction band edge. However, attempts to optimize the the passivation process for both dry and wet thermal oxides do not appear to reduce Dit(Ec) below about 2×1012cm-2eV-1 (compared to approximately 1010cm-2eV-1 for passivate Si/SiO2). This may be an indication that two types of interface states exist in the upper half of the SiC band gap - one type that is amenable to passivation by nitrogen and one that is not. Following NO passivation, the average breakdown field for dry oxides on p-4H-SiC is higher than the average field for wet oxides (7.6MV/cm compared to 7.1MV/cm at room temperature). However, both breakdown fields are lower than the average value of 8.2MV/cm measured for wet oxide layers that were not passivated. The lower breakdown fields can be attributed to donor-like states that appear near the valence band edge during passivation.

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