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Journal Articles

Impact of post-nitridation annealing in CO$$_{2}$$ ambient on threshold voltage stability in 4H-SiC metal-oxide-semiconductor field-effect transistors

Hosoi, Takuji*; Osako, Momoe*; Moges, K.*; Ito, Koji*; Kimoto, Tsunenobu*; Sometani, Mitsuru*; Okamoto, Mitsuo*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*

Applied Physics Express, 15(6), p.061003_1 - 061003_5, 2022/06

 Times Cited Count:1 Percentile:37.1(Physics, Applied)

The combination of NO annealing and subsequent post-nitridation annealing (PNA) in CO$$_{2}$$ ambient for SiO$$_{2}$$/SiC structures has been demonstrated to be effective in obtaining both high channel mobility and superior threshold voltage stability in SiC-based metal-oxide-semiconductor field-effect transistors (MOSFETs). N atoms on the SiO$$_{2}$$ side of the SiO$$_{2}$$/SiC interface incorporated by NO annealing, which are plausible cause of charge trapping sites, could be selectively removed by CO$$_{2}$$-PNA at 1300$$^{circ}$$C without oxidizing the SiC. CO$$_{2}$$-PNA was also effective in compensating oxygen vacancies in SiO$$_{2}$$, resulting high immunity against both positive and negative bias-temperature stresses.

Journal Articles

Comprehensive physical and electrical characterizations of NO nitrided SiO$$_{2}$$/4H-SiC(11$$overline{2}$$0) interfaces

Nakanuma, Takato*; Iwakata, Yu*; Watanabe, Arisa*; Hosoi, Takuji*; Kobayashi, Takuma*; Sometani, Mitsuru*; Okamoto, Mitsuo*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*

Japanese Journal of Applied Physics, 61(SC), p.SC1065_1 - SC1065_8, 2022/05

 Times Cited Count:6 Percentile:79.58(Physics, Applied)

Nitridation of SiO$$_{2}$$/4H-SiC(11$$overline{2}$$0) interfaces with post-oxidation annealing in an NO ambient (NO-POA) and its impact on the electrical properties were investigated. Sub-nm-resolution nitrogen depth profiling at the interfaces was conducted by using a scanning X-ray photoelectron spectroscopy microprobe. The results showed that nitrogen atoms were incorporated just at the interface and that interface nitridation proceeded much faster than at SiO$$_{2}$$/SiC(0001) interfaces, resulting in a 2.3 times higher nitrogen concentration. Electrical characterizations of metal-oxide-semiconductor capacitors were conducted through capacitance-voltage ($$C-V$$) measurements in the dark and under illumination with ultraviolet light to evaluate the electrical defects near the conduction and valence band edges and those causing hysteresis and shifting of the $$C-V$$ curves. While all of these defects were passivated with the progress of the interface nitridation, excessive nitridation resulted in degradation of the MOS capacitors. The optimal conditions for NO-POA are discussed on the basis of these experimental findings.

Journal Articles

Impact of nitridation on the reliability of 4H-SiC(11$$bar{2}$$0) MOS devices

Nakanuma, Takato*; Kobayashi, Takuma*; Hosoi, Takuji*; Sometani, Mitsuru*; Okamoto, Mitsuo*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*

Applied Physics Express, 15(4), p.041002_1 - 041002_4, 2022/04

 Times Cited Count:2 Percentile:51.2(Physics, Applied)

The leakage current and flat-band voltage (VFB) instability of NO-nitrided SiC (11$$bar{2}$$0) (a-face) MOS devices were systematically investigated. Although NO nitridation is effective in improving the interface properties, we found that it reduces the onset field of Fowler-Nordheim (F-N) current by about 1 MVcm$$^{-1}$$, leading to pronounced leakage current. Synchrotron X-ray photoelectron spectroscopy revealed that the nitridation reduces the conduction band offset at the SiO$$_{2}$$/SiC interface, corroborating the above finding. Furthermore, systematical positive and negative bias stress tests clearly indicated the VFB instability of nitrided a-face MOS devices against electron and hole injection.

Oral presentation

Reliability issues in Nitrided SiC MOS devices

Kobayashi, Takuma*; Nakanuma, Takato*; Suzuki, Asato*; Sometani, Mitsuru*; Okamoto, Mitsuo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

no journal, , 

We investigated the reliability of nitrided SiC MOS devices in terms of oxide leakage and flatband voltage stability. Although nitrided MOS devices on non-basal planes are known to have superior on-state performances, we found that the nitridation not only leads to pronounced oxide leakage but also hampers the flatband voltage stability in response to electron and hole injection. In the presentation, we will show how the nitridation modifies the MOS interfaces based on the results of synchrotron radiation X-ray photoelectron spectroscopy and discuss the possible cause of reliability degradation.

Oral presentation

Nitridation-induced degradation of SiC (1-100) MOS devices

Kobayashi, Takuma*; Nakanuma, Takato*; Suzuki, Asato*; Sometani, Mitsuru*; Okamoto, Mitsuo*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*

no journal, , 

Together with a standard NO nitridation, a high channel mobility ($$sim$$ 100 cm$$^{2}$$V$$^{-1}$$s$$^{-1}$$) is obtained for SiC MOSFETs fabricated on non-basal planes, such as (1-100) m-face. Since these planes appear on the side wall of trench formed on (0001) Si-face, they can be directly applied to trench MOSFETs which have low on-resistance. Despite their advantages, the characteristics of MOS devices on non-basal planes, including the impact of nitridation, is not well investigated. In this work, we focused on SiC MOS devices on m-face and studied their physical and electrical characteristics in detail.

Oral presentation

Leak current mechanisms in NO-nitrided SiC(1$$bar{1}$$00) MOS devices

Suzuki, Asato*; Nakanuma, Takato*; Kobayashi, Takuma*; Sometani, Mitsuru*; Okamoto, Mitsuo*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*

no journal, , 

Gate leakage mechanism in NO-nitrided SiC(1$$bar{1}$$00) MOS devices was investigated. Experimental current density-oxide field characteristics at 25-200$$^{circ}$$C were reproduced assuming Fowler-Nordheim (FN) and Poole-Frenkel (PF) mechanisms. Although NO nitridation is effective in improving the channel mobility of SiC MOSFETs, the nitridation reduces the conduction band offset at the SiO$$_{2}$$/SiC interface and increases the FN current. Furthermore, it was found that the nitridation cannot remove the defects that cause the PF current.

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