Tetsuo Hatakeyama

High performance strained-Si p-MOSFETs on SiGe-on-insulator substrates fabricated by SIMOX technology

We have proposed a new MOSFET structure, strained-Si/Si/sub 0.9/Ge/sub 0.1/-on-Insulator (SSGOI) MOSFETs applicable to the sub-100 nm generation. This SSGOI structure was successfully fabricated by the combination of SIMOX technology and the Si re-growth technique. The strained-Si in SSGOI was found to have good crystal quality and very flat interfaces. SSGOI p-MOSFETs exhibited good FET characteristics. It was demonstrated, for the first time, that the hole mobility of the SSGOI p-MOSFETs is higher that of the universal mobility of conventional Si p-MOSFETs.

Dependence of acceptor levels and hole mobility on acceptor density and temperature in Al-doped p-type 4H-SiC epilayers

The temperature-dependent hole concentration p(T) and hole mobility μp(T) are obtained in p-type 4H-SiC epilayers with several Al-doping densities. From p(T), the densities and energy levels of acceptors are determined by the graphical peak analysis method (free carrier concentration spectroscopy: FCCS) without any assumptions regarding the acceptor species. In the heavily Al-doped case, the excited states of acceptors affect p(T) because the Fermi level is located between the valence band maximum and the acceptor level (i.e., the ground state level of the acceptor), indicating that a distribution function for acceptors, which includes the influence of excited states of acceptors, should be required. Here, FCCS can determine acceptor densities and acceptor levels using any distribution function (e.g., the Fermi-Dirac distributing function or the distribution function including the influence of excited states). Two types of acceptor species are detected in the lightly Al-doped epilayers, while only one typ...

Impact ionization coefficients of 4H silicon carbide

Anisotropy of the impact ionization coefficients of 4H silicon carbide is investigated by means of the avalanche breakdown behavior of p+n diodes on (0001) and (112¯0) 4H silicon carbide epitaxial wafers. The impact ionization coefficients are extracted from the avalanche breakdown voltages and the multiplication of a reverse leakage current, due to impact ionization of these p+n diodes. The breakdown voltage of a p+n diode on a (112¯0) wafer is 60% of that on a (0001) wafer, and the extracted impact ionization coefficients of 4H silicon carbide show large anisotropy. We have shown that the anisotropy of the impact ionization coefficients is related to the anisotropy of carrier heating and drift velocity, which are due to the highly anisotropic electronic structure of 4H silicon carbide.

Parameters required to simulate electric characteristics of SiC devices for n-type 4H-SiC

In order to obtain some of the parameters required to simulate the electric characteristics of silicon carbide (SiC) power electronic devices in a wide temperature range from startup temperatures (⩽30°C) to steady-operation temperatures (⩾200°C), we discuss the dependence of the two donor levels on the total donor density (ND) as well as the dependence of the electron mobility on the total impurity density (Nimp) and operating temperature (T) in the n-type 4H–SiC. The temperature-dependent electron concentration n(T) and electron mobility μn(T) in the n-type 4H–SiC epilayers with several nitrogen-doping densities are obtained from the Hall-effect measurements. By the graphical peak analysis method (free carrier concentration spectroscopy: FCCS) without any assumptions regarding the donor species, the two types of donor species are detected from n(T). Moreover, the energy level and density of each donor species are determined by the FCCS. Using these results, we obtain the parameters with which the depende...

Measurement of Hall Mobility in 4H-SiC for Improvement of the Accuracy of the Mobility Model in Device Simulation

In order to construct a reliable parameter set for the physic al modeling of 4H-SiC, we are collecting and examining the physical parameters. The results of mobility measurement are presented and compared with the built-in model in the device simulator. The doping depe n nce of the electron mobility is in agreement with the built-in model, whereas that of the hole mobility is different from the built-in model in the higher doping region. Further, the anisotropy of the electron and hole mobility is investigated. The anisotropy of the electron mobility ) 0001 ( / ) 00 1 1 ( > < μ > < μ is about 0.83 and is in agreement with the built-in model. The anisotropy of the hole mobility is observed and it is estimated to be 1.15. To our knowledge, this is the first report of the anisotropy of the hole mobility in 4H-SiC. Introduction Silicon carbide devices have outstanding features, namely higher speed and lower loss than silicon devices. Among the many polytypes of SiC, 4H-SiC has attracted gre at att ntion as a candidate material for the next generation of power semiconductor devices, due t o the excellent physical properties such as the electric breakdown field and mobility. In order to r alize SiC devices that make the best use of the excellent physical properties, device simulati on technology of SiC is indispensable. However, the comprehensive and reliable parameter set for the physic al modeling of 4H-SiC for device simulators has not been reported. As a first step in the construction of a reliabl e par meter set for the physical modeling of 4H-SiC, we are collecting and examini ng the physical parameters systematically by fabricating test chips that consist of the el ments for physical property measurements. This paper is the first report on our ongoing research . The final goal of our research is the release of the comprehensive parameter set. In this paper, we present results of mobility measurement and compare them with the previous results. Experimental Figure 1 shows the top view of a test chip of the first lot. A prec ise patterning of contact, electrode and mesa by the mask process guarantees the precision of the physical property measurements. A test chip consists of elements (Hall bars and the square and clover shaped four terminal pattern) for mobility measurements and pin diodes for the impact ionization coefficient mea surements. Hall bars are tilted to the crystallographic axis every fifteenth degree in order to de ect the anisotropy of the mobility. Test chips were fabricated on 4H-SiC epitaxial wafers. For the measurements of the electron mobility, Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 443-446 doi:10.4028/www.scientific.net/MSF.433-436.443

Guard ring assisted RESURF: a new termination structure providing stable and high breakdown voltage for SiC power devices

A new junction termination structure named guard ring assisted reduced surface field (GRA-RESURF) is proposed. The structure maintains a stable and high breakdown voltage without being influenced by the deviation of impurity dose in the RESURF layer or by parasitic charge. The GRA-RESURF structure was adopted on 600 V range 4H-SiC Schottky barrier diodes, and achieved high breakdown voltages with a good production yield.

Physical Modeling and Scaling Properties of 4H-SiC Power Devices

4H silicon carbide (4H-SiC) has great potential for use as a material for power devices owing to its superior electrical properties. The distinctive feature of 4H-SiC is the high avalanche breakdown field and its anisotropy. In order to realize 4H-SiC power devices that make the best use of the excellent physical properties, device simulation, considering anisotropic physical properties is indispensable. This paper reports on the modeling of anisotropic impact ionization coefficients for device simulation, and the effect of anisotropic impact ionization coefficients on the avalanche breakdown of 4H-SiC power devices. We show that the avalanche breakdown voltage is degraded due to the anisotropy of impact ionization coefficients, which is caused by the lateral field at the termination structure. In addition, we precisely evaluate the effect of the high avalanche breakdown field of 4H-SiC on the performance of power devices. Scaling theory is applied for the design of power devices. A new figure of merit (HFOM) is derived as an invariant of scale transformation, which is a function of avalanche breakdown field and regarded as a measure of the performance of the power device.

Temperature-dependent analysis of conduction mechanism of leakage current in thermally grown oxide on 4H-SiC

The conduction mechanism of the leakage current of a thermally grown oxide on 4H silicon carbide (4H-SiC) was investigated. The dominant carriers of the leakage current were found to be electrons by the carrier-separation current-voltage method. The current-voltage and capacitance-voltage characteristics, which were measured over a wide temperature range, revealed that the leakage current in SiO2/4H-SiC on the Si-face can be explained as the sum of the Fowler-Nordheim (FN) tunneling and Poole-Frenkel (PF) emission leakage currents. A rigorous FN analysis provided the true barrier height for the SiO2/4H-SiC interface. On the basis of Arrhenius plots of the PF current separated from the total leakage current, the existence of carbon-related defects and/or oxygen vacancy defects was suggested in thermally grown SiO2 films on the Si-face of 4H-SiC.

Annealing induced extended defects in as-grown and ion-implanted 4H-SiC epitaxial layers

The formation of extended defects in the 4H–SiC epilayer induced by the implantation/annealing process was investigated using synchrotron reflection x-ray topography, KOH etching analysis, and transmission electron microscopy. High temperature annealing was performed for the 4H–SiC epilayer with or without the implantation of nitrogen or aluminum ions. Other than the formation of platelet extrinsic Frank-type faults in the implanted region as reported previously, we find the formation modes of extended defects in following three categories: (i) dislocation formation near the epilayer/substrate interface, (ii) dislocation formation near the implanted region, and (iii) the formation of Shockley-type defects near the surface. The defect morphology and process dependence of each type are also discussed.

Reliability of 4H-SiC(000-1) MOS Gate Oxide Using N2O Nitridation

The oxide reliability of metal-oxide-semiconductor (MOS) capacitors on 4H-SiC(000-1) carbon face was investigated. The gate oxide was fabricated by using N2O nitridation. The effective conduction band offset (Ec) of MOS structure fabricated by N2O nitridation was increased to 2.2 eV compared with Ec = 1.7 eV for pyrogenic oxidation sample of. Furthermore, significant improvements in the oxide reliability were observed by time-dependent dielectric breakdown (TDDB) measurement. It is suggested that the N2O nitridation as a method of gate oxide fabrication satisfies oxide reliability on 4H-SiC(000-1) carbon face MOSFETs.