Gamma Irradiation Effects on 4H-SiC MOS Capacitors and MOSFETs

2006 ◽  
Vol 527-529 ◽  
pp. 1063-1066 ◽  
Author(s):  
Ayayi Claude Ahyi ◽  
S.R. Wang ◽  
John R. Williams
Keyword(s):  
Field Effect ◽  
Gamma Dose ◽  
Interface Traps ◽  
Valence Band Edge ◽  
Field Effect Mobility ◽  
Irradiation Effects ◽  
Mos Capacitors ◽  
Channel Mobility ◽  
Radiation Induced ◽  
Radiation Tolerant

The effects of gamma radiation on field effect mobility and threshold voltage have been studied for lateral n-channel 4H-SiC MOSFETs passivated with nitric oxide. MOS capacitors (n and p) and n-channel lateral MOSFETs were irradiated unbiased (floating contacts) for a total gamma dose of 6.8Mrad (Si). The MOS capacitors were used to study the radiation-induced interface traps and fixed oxide charge that affect the performance of the MOSFETs. Radiationinduced interface traps were observed near the SiC valence band edge and just above mid-gap, and field effect channel mobility was reduced by 18-20% following irradiation. Even so, 4HMOSFETs appear to be more radiation tolerant than Si devices.

High Channel Mobility 4H-SiC MOSFETs

2006 ◽  
Vol 527-529 ◽  
pp. 961-966 ◽  
Author(s):  
Einar Ö. Sveinbjörnsson ◽  
G. Gudjónsson ◽  
Fredrik Allerstam ◽  
H.Ö. Ólafsson ◽  
Per Åke Nilsson ◽  
...  
Keyword(s):  
Field Effect ◽  
Phonon Scattering ◽  
Conduction Band Edge ◽  
Clear Correlation ◽  
Stable Operation ◽  
Interface Traps ◽  
Field Effect Mobility ◽  
Threshold Voltage Shift ◽  
Mos Capacitors ◽  
Positive Threshold

We report investigations of MOS and MOSFET devices using a gate oxide grown in the presence of sintered alumina. In contrast to conventionally grown dry or wet oxides these oxides contain orders of magnitude lower density of near-interface traps at the SiO2/SiC interface. The reduction of interface traps is correlated with enhanced oxidation rate. The absence of near-interface traps makes possible fabrication of Si face 4H-SiC MOSFETs with peak field effect mobility of about 150 cm2/Vs. A clear correlation is observed between the field effect mobility in n-channel MOSFETs and the density of interface states near the SiC conduction band edge in n-type MOS capacitors. Stable operation of such normally-off 4H-SiC MOSFET transistors is observed from room temperature up to 150°C with positive threshold voltage shift less than 1 V. A small decrease in current with temperature up to 150°C is related to a decrease in the field effect mobility due to phonon scattering. However, the gate oxides contain sodium, which originates from the sintered alumina, resulting in severe device instabilities during negative gate bias stressing.

Borosilicate Glass (BSG) as Gate Dielectric for 4H-SiC MOSFETs

2018 ◽  
Vol 924 ◽  
pp. 502-505 ◽  
Author(s):  
Yong Ju Zheng ◽  
Tamara Isaacs-Smith ◽  
Ayayi Claude Ahyi ◽  
S. Dhar
Keyword(s):  
Borosilicate Glass ◽  
Field Effect ◽  
Gate Dielectric ◽  
Trap Density ◽  
Interface Trap Density ◽  
Interface Trap ◽  
Interface Traps ◽  
Field Effect Mobility ◽  
Channel Mobility

In this work, we investigate the effect of borosilicate glass (BSG) as gate dielectric on dielectric/4H-SiC interface traps and channel mobility in 4H-SiC MOSFETs. The interface trap characterization by C−ψs analysis and I-V characterization show lower fast interface trap density (Dit) as well as significant improvement of channel field-effect mobility on devices with BSG than that on devices with standard NO anneal. In addition, the results indicate interface trap density decreases with increasing B concentration at the interface of BSG/4H-SiC, which in turn, results in higher channel mobility.

High-Mobility SiC MOSFETs with Alkaline Earth Interface Passivation

2016 ◽  
Vol 858 ◽  
pp. 671-676 ◽  
Author(s):  
Daniel J. Lichtenwalner ◽  
Vipindas Pala ◽  
Brett A. Hull ◽  
Scott Allen ◽  
John W. Palmour
Keyword(s):  
Nitric Oxide ◽  
Field Effect ◽  
Alkaline Earth ◽  
Phonon Scattering ◽  
Breakdown Strength ◽  
Field Effect Transistors ◽  
Oxide Semiconductor ◽  
Field Effect Mobility ◽  
Channel Mobility ◽  
Alkaline Earth Elements

Alkaline earth elements Sr and Ba provide SiO2/SiC interface conditions suitable for obtaining high channel mobility metal-oxide-semiconductor field-effect-transistors (MOSFETs) on the Si-face (0001) of 4H-SiC, without the standard nitric oxide (NO) anneal. The alkaline earth elements Sr and Ba located at/near the SiO2/SiC interface result in field-effect mobility (μFE) values as high as 65 and 110 cm2/V.s, respectively, on 5×1015 cm-3 Al-doped p-type SiC. As the SiC doping increases, peak mobility decreases as expected, but the peak mobility remains higher for Ba interface layer (Ba IL) devices compared to NO annealed devices. The Ba IL MOSFET field-effect mobility decreases as the temperature is increased to 150 °C, as expected when mobility is phonon-scattering-limited, not interface-trap-limited. This is in agreement with measurements of the interface state density (DIT) using the high-low C-V technique, indicating that the Ba IL results in lower DIT than that of samples with nitric oxide passivation. Vertical power MOSFET (DMOSFET) devices (1200V, 15A) fabricated with the Ba IL have a 15% lower on-resistance compared to devices with NO passivation. The DMOSFET devices with a Ba IL maintain a stable threshold voltage under NBTI stress conditions of-15V gate bias stress, at 150 °C for 100hrs, indicating no mobile ions. Secondary-ion mass-spectrometry (SIMS) analysis confirms that the Sr and Ba remain predominantly at the SiO2/SiC interface, even after high temperature oxide annealing, consistent with the observed high channel mobility after these anneals. The alkaline earth elements result in enhanced SiC oxidation rate, and the resulting gate oxide breakdown strength is slightly reduced compared to NO annealed thermal oxides on SiC.

Comparison of channel mobility and oxide properties of MOSFET devices on Si-face (0001) and A-face (11-20) 4H-SiC

2014 ◽  
Vol 1693 ◽  
Author(s):  
Daniel J. Lichtenwalner ◽  
Lin Cheng ◽  
Scott Allen ◽  
John W. Palmour ◽  
Aivars Lelis ◽  
...  
Keyword(s):  
Valence Band ◽  
Barrier Height ◽  
Field Effect ◽  
Phonon Scattering ◽  
Electron Tunneling ◽  
Negative Temperature ◽  
Field Effect Mobility ◽  
Channel Mobility ◽  
P Type ◽  
And Control

ABSTRACTIn this report we present results comparing lateral MOSFET properties of devices fabricated on Si-face (0001) and A-face (11-20) 4H-SiC, with nitric oxide passivation anneals. We observe a field-effect mobility of 33 cm2/V.s on p-type 5×1015 doped Si-face. These devices have a peak field-effect mobility which increases with temperature, indicative of a channel mobility limited by coulomb scattering. On 1×1016 p-type A-face SiC, the peak channel mobility is observed to be 80 cm2/V.s, with a negative temperature dependence, indicating that phonon-scattering effects dominate, with a much lower density of shallow acceptor traps. This > 2x higher channel mobility would result in a substantial decrease in on-resistance, hence lower power losses, for 4H-SiC power MOSFETs with voltage ratings below 2 kV. However, MOS C-V and gate leakage measurements indicate very different oxide and interface quality on each SiC face. For example, the Fowler-Nordheim (FN) conduction-band (CB) barrier height for electron tunneling at the SiO2/SiC interface is 2.8 eV on Si-face SiC, while it is 2.5 eV or less on A-face SiC. For the valence-band side, the effective FN barrier height at the valence-band (VB) side of only 1.6 eV on A-face SiC, while the VB barrier height is about 3.1 eV on Si-face SiC. Moreover, C-V of the MOS gate on A-face indicates the presence of a high-density of deep hole traps. It is apparent that oxides on alternative crystal faces, very promising in terms of channel mobility, require further study for complete understanding and control of the interface properties.

Effects of N2O Anneal on Channel Mobility of 4H-SiC MOSFET and Gate Oxide Reliability

2005 ◽  
Vol 483-485 ◽  
pp. 697-700 ◽  
Author(s):  
Keiko Fujihira ◽  
Yoichiro Tarui ◽  
Kenichi Ohtsuka ◽  
Masayuki Imaizumi ◽  
Tetsuya Takami
Keyword(s):  
Field Effect ◽  
Gate Oxide ◽  
Field Effect Mobility ◽  
Channel Mobility ◽  
Oxide Reliability ◽  
Anneal Temperature

The effect of N2O anneal on channel mobility of inversion-type 4H-SiC n-channel MOSFET has been systematically investigated. It is found that the mobility increases with increasing anneal temperature from 900 to 1150°C. The highest field effect mobility of 30 cm2/Vs is achieved by 1150°C anneal for 3 h, which is about 20 times higher than that for non-annealed MOSFET. In order to investigate the oxide reliability, TDDB measurement has been performed on SiO2 grown on n-type 4H-SiC. The oxide lifetime is found to be drastically improved by N2O anneal.

Shallow Traps at P-Doped SiO2/4H-SiC(0001) Interface

2011 ◽  
Vol 679-680 ◽  
pp. 338-341 ◽  
Author(s):  
Dai Okamoto ◽  
Hiroshi Yano ◽  
Shinya Kotake ◽  
Tomoaki Hatayama ◽  
Takashi Fuyuki
Keyword(s):  
Photoelectron Spectroscopy ◽  
Field Effect ◽  
Field Effect Transistors ◽  
Metal Oxide Semiconductor ◽  
Oxide Semiconductor ◽  
Interface Traps ◽  
Channel Mobility ◽  
X Ray ◽  
Capacitance Voltage ◽  
Shallow Traps

We report on electrical and physical investigations aimed to clarify the mechanisms behind the high channel mobility of 4H-SiC metal–oxide–semiconductor field-effect transistors processed with POCl3 annealing. By low-temperature capacitance–voltage analysis, we found that the shallow interface traps are effectively removed by P incorporation. Using x-ray photoelectron spectroscopy, we found that the three-fold coordinated P atoms exist at the oxide/4H-SiC interface. The overall results suggest that P atoms directly remove the Si–Si bonds and thus eliminate the near-interface traps.

Effect of NH3 Post-Oxidation Annealing on Flatness of SiO2/SiC Interface

2013 ◽  
Vol 740-742 ◽  
pp. 723-726 ◽  
Author(s):  
Narumasa Soejima ◽  
Taishi Kimura ◽  
Tsuyoshi Ishikawa ◽  
Takahide Sugiyama
Keyword(s):  
Nitrous Oxide ◽  
Field Effect ◽  
Inversion Layer ◽  
Trap Density ◽  
Interface Trap Density ◽  
Interface Trap ◽  
Field Effect Mobility ◽  
Interfacial Roughness ◽  
Cross Sectional ◽  
Mos Capacitors

We investigated the effects of the post-oxidation annealing (POA) atmosphere on the electrical properties and interfacial roughness of SiO2 deposited on a 4H-SiC (0001) face and SiC. POA in ammonia (NH3) gave MOS capacitors with a lower interface trap density and n-channel MOSFETs with higher field-effect mobility than POA in nitrous oxide (N2O) or nitrogen (N2). In contrast, POA in N2O gave a lower interface trap density than POA in N2, but it gave the lowest field-effect mobility of all the samples. Cross-sectional TEM observations revealed that N2O POA gave a higher interfacial roughness than NH3 POA. We thus considered that N2O POA degraded the inversion-layer mobility due to increased roughness scattering.

Correlation between Field Effect Mobility and Accumulation Conductance at 4H-SiC MOS Interface with Barium

2018 ◽  
Vol 924 ◽  
pp. 477-481
Author(s):  
Kosuke Muraoka ◽  
Seiji Ishikawa ◽  
Hiroshi Sezaki ◽  
Tomonori Maeda ◽  
Shinichiro Kuroki
Keyword(s):  
Linear Correlation ◽  
Field Effect ◽  
Interface State ◽  
State Density ◽  
Interface State Density ◽  
Field Effect Mobility ◽  
Mos Capacitors

A correlation between field effect mobility and an accumulation conductance has been investigated at 4H-SiC MOS interface with barium. 4H-SiC n-channel MOSFETs and n-type MOS capacitors were fabricated with a barium-introduced SiO2and a conventional dry SiO2. The field effect mobility was enhanced by introducing the barium-introduced SiO2. It is found that there is a linear correlation between the mobility and the accumulation conductance. The MOS interface of the barium-introduced SiO2had a lower interface state density of 2×1011cm-2eV-1than that of the conventional dry SiO2.

Investigation of Degradation of Inversion Channel Mobility of SiC MOSFET due to the Increase of Channel Doping

2005 ◽  
Vol 483-485 ◽  
pp. 829-832 ◽  
Author(s):  
Tetsuo Hatakeyama ◽  
Takatoshi Watanabe ◽  
Junji Senzaki ◽  
Makoto Kato ◽  
Kenji Fukuda ◽  
...  
Keyword(s):  
Hall Mobility ◽  
Carrier Density ◽  
Field Effect ◽  
Doping Concentration ◽  
Free Carrier ◽  
Hall Voltage ◽  
Field Effect Mobility ◽  
Channel Mobility ◽  
Free Carrier Density ◽  
Inversion Channel

This paper reports on the degradation of inversion channel mobility of SiC MOSFET caused by the increase of channel doping. SiC MOSFETs were fabricated on three wafers, the doping concentrations of the epitaxial layer of which were 16 10 2× cm-3 (sample A), 17 10 2× cm-3 (sample B) and 17 10 4× cm-3 (sample C). The field effect mobility sharply decreases as the doping concentration increases. Hall mobility measurements have been done to investigate the degradation of the mobility due to doping. The measurement of sample A shows that, as a consequence of the decrease of the free carrier density due to MOS interface traps, the Hall mobility is as much as a factor of ten higher than the field effect mobility. In contrast, in regard to the measurement of sample B and sample C, we encountered unstable Hall voltage and could not obtain reproducible results. This implies that such high-density traps are generated that a channel disappears in the higher-doping samples.

Effect of Graphite Cap for Implant Activation on Inversion Channel Mobility in 4H-SiC MOSFETs

2009 ◽  
Vol 615-617 ◽  
pp. 773-776 ◽  
Author(s):  
Harsh Naik ◽  
K. Tang ◽  
T. Paul Chow
Keyword(s):  
Low Temperature ◽  
Carrier Concentration ◽  
Threshold Voltage ◽  
Hall Mobility ◽  
Field Effect ◽  
Gate Oxide ◽  
Subthreshold Slope ◽  
Field Effect Mobility ◽  
Channel Mobility ◽  
Inversion Channel

The effects of using a graphite capping layer during implant activation anneal on the performance of 4H-SiC MOSFETs has been evaluated. Two sets of samples, one with the graphite cap and another without, with a gate oxide process consisting of a low-temperature deposited oxide followed by NO anneal at 1175°C for 2hrs were used for characterization. Various device parameters, particularly threshold voltage, subthreshold slope, field-effect mobility, inversion sheet carrier concentration and Hall mobility have been extracted for the two processes.

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