Journal of Applied physics,Vol.33 : 1962年に発表されたレオロジー関連の論文

A method of fabricating an integrated circuit on a silicon carbide substrate is disclosed that eliminates wire bonding that can otherwise cause undesired inductance. The method includes fabricating a semiconductor device on a first surface of a silicon carbide substrate and with at least one metal contact for the device on the first surface of the substrate. The opposite, second surface of the substrate is then ground and polished until it is substantially transparent. The method then includes masking the polished second surface of the silicon carbide substrate to define a predetermined location for a via that is opposite the device metal contact on the first surface; etching the desired via through the desired masked location until the etch reaches the metal contact on the first surface; and metallizing the via to provide an electrical contact from the second surface of the substrate to the metal contact and to the device on the first surface of the substrate.

Method of forming vias in silicon carbide and resulting devices and circuits

(IEEE Transactions on Electron Devices,36(12):2816-2820)Field-Drifting Resonant Tunneling Through a-Si:H/a-Sil-xCx:H Quantum Wells at Different Locations of the i-Layer of a p-i-n Structure

Silicon carbide (SiC) semiconductor devices for high power applications are now commercially available as discrete devices. Recently Schottky diodes are offered by both USA and Europe based companies. Active switching devices such as bipolar junction transistors (BJTs), field effect transistors (JFETs and MOSFETs) are now available on the commercial market. The interest is rapidly growing for these devices in high power and high temperature applications. The main advantages of wide bandgap semiconductors are their very high critical electric field capability. From a power device perspective the high critical field strength can be used to design switching devices with much lower losses than conventional silicon based devices both for on-state losses and reduced switching losses. This paper reviews the current state of the art in active switching device performance for both SiC and GaN. SiC material quality and epitaxy processes have greatly improved and degradation free 100 mm wafers are readily available. The SiC wafer roadmap looks very favorable as volume production takes off. For GaN materials the main application area is geared towards the lower power rating level up to 1 kV on mostly lateral FET designs. Power module demonstrations are beginning to appear in scientific reports and real applications. A short review is therefore given. Other advantages of SiC is the possibility of high temperature operation (> 300 °C) and in radiation hard environments, which could offer considerable system advantages.

SiC power devices — Present status, applications and future perspective

This paper reviews the present knowledge on silica films (SiO2) on silicon carbide (SiC). First, kinetic of thermal oxidation of SiC is described, and the effects of a great number of parameters (various SiC polytypes, substrate type, substrate orientation...) are discussed. Mainly, thermal oxides grown on SiC are close to stoichiometric silica and the oxidation rate depends on the terminal face of the SiC monocrystal. The next four sections discuss the electrical properties of the oxide, and of the oxide/SiC interface, and especially the effects of materials and technological process on the interface state density and the effective oxide charge (Section 5), and the origin of the interface states are discussed in detail (Section 6). Oxides grown on n-type SiC have electrical properties (in terms of dielectric strength, leakage currents, interface trap, and oxide charges) measured by means of metal-oxide-semiconductor (MOS) structures, similar to oxides grown on silicon. Until recently, p-type SiC MOS structures have had a large equivalent oxide charge and larger interface state densities in spite of many efforts, compared to silicon MOS structures. It seems nevertheless that recent studies have improved the SiO2/SiC interfacial quality. Aluminum, carbon and alkali species are ihs main suspected contaminants. Finally, Section 7 presents the applications of oxide films in SE-based devices: MOS capacitors and MOS field effect transistors (MOSFETs) for microelectronics, MOSFETs for power electronics, and some applications using silica layers as a passivation layer. In spite of a smaller than required carrier mobility in the inversion layer, MOS field effect transistors (MOSFETs) have been demonstrated to operate up to 650 degreesC and integrated circuits based on NMOS and PMOS technologies have been successfully operated up to 300 degreesC. Vertical power MOSFETs are also of importance but their performances are still limited by a specific on-resistance larger than device requirements. The effect of charges present in the oxide on the electrical properties of high voltage diodes is also briefly discussed.

Silica films on silicon carbide: a review of electrical properties and device applications

High-voltage blocking (2.7-kV) implantation-free SiC bipolar junction transistors with low ON-state resistance (12 mOmegaldrcm2) and high common-emitter current gain of 50 have been fabricated. A graded-base doping was implemented to provide a low-resistive ohmic contact to the epitaxial base. This design features a fully depleted base layer close to the breakdown voltage providing an efficient epitaxial JTE without ion implantation. Eliminating all ion implantation steps in this approach is beneficial for avoiding high-temperature dopant activation annealing and for avoiding generation of lifetime-killing defects that reduce the current gain.

Fabrication of 2700-V 12- $\hbox{m}\Omega \cdot \hbox{cm}^{2}$ Non Ion-Implanted 4H- SiC BJTs With Common-Emitter Current Gain of 50

A variety of different plasma chemistries, including SF6, Cl2, ICl, and IBr, have been examined for dry etching of 6H-SiC in high ion density plasma tools (inductively coupled plasma and electron cyclotron resonance). Rates up to 4500A-min−1 were obtained for SF6 plasmas, while much lower rates (≤800A·min−1) were achieved with Cl2, ICl, and IBr. The F2-based chemistries have poor selectivity for SiC over photoresist masks (typically 0.4–0.5), but Ni masks are more robust, and allow etch depths ≥10 µm in the SiC. A micromachining process (sequential etch/deposition steps) designed for Si produces relatively low etch rates (<2,000A-min−1) for SiC.

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Plasma chemistries for high density plasma etching of SiC

In this paper, implantation-free 4H-SiC bipolar junction transistors (BJTs) with a high breakdown voltage of 2800 V have been fabricated by utilizing a controlled two-step etched junction-termination extension in the epitaxial base layer. The small-area device shows a maximum direct-current (dc) gain of 55 at JC = 0.33 A (JC = 825 A/cm2) and VCESAT = 1.05 V at Ic = 0.107 A that corresponds to a low specific ON-state resistance of 4 mΩ · cm2. The large-area device has a maximum dc gain of 52 at JC = 9.36 A (JC = 289 A/cm2) and VCESAT = 1-14 V at Ic = 5 A that corresponds to a specific ON-state resistance of 6.8 mΩ · cm2. In addition, these devices demonstrate a negative temperature coefficient of the current gain (β = 26 at 200 °C) and a positive temperature coefficient of the specific ON-state resistance (RON = 10.2 mΩ · cm2 at 200 °C). The small-area BJT shows no bipolar degradation and a low-current-gain degradation after a 150-h stress of the base-emitter diode with a current level of 0.2 A (JE = 500 A/cm2). Furthermore, the large-area BJT shows a VCE fall time of 18 ns during turn-on and a VCE rise time of 10 ns during turn-off for 400-V switching characteristics.

High-Voltage (2.8 kV) Implantation-Free 4H-SiC BJTs With Long-Term Stability of the Current Gain

We report on the investigation of epitaxial TiC ohmic contacts to Al ion implanted 4H–SiC. TiC ohmic contacts were formed by coevaporation of Ti and C60 at low temperature (<500 °C). A sacrificial silicon nitride (Si3N4) layer was deposited on the silicon carbide substrate prior to Al implantation in order to reach a high Al dopant concentration at the surface while maintaining a low dose. The combination of epitaxially grown TiC and the silicon nitride layer resulted in a promising scheme to make low resistivity ohmic contacts. The lowest contact resistivity (ρC) and sheet resistance (Rs) of the implanted layer at 25 °C were as low as 2×10−5 Ω cm2 and 0.6 kΩ/□, respectively.

Electrical characterization of TiC ohmic contacts to aluminum ion implanted 4H–silicon carbide

This paper describes successful fabrication of 4H-SiC bipolar junction transistors (BJTs) with a regrown extrinsic base layer and an etched junction termination extension (JTE). Large-area 4H-SiC BJTs measuring 1.8 times 1.8 mm (with an active area of 3.24 ) showed a common emitter current gain of 42, specific on-resistance of 9 , and open-base breakdown voltage of 1.75 kV at room temperature. The key to successful fabrication of high-current-gain SiC BJTs with a regrown extrinsic base is efficient removal of the regrown layer from the surface of the emitter-base junction. The BJT with regrown layer has the advantage of lower base contact resistivity and current gain that is less sensitive to the distance between the emitter edge and the base contact, compared to a BJT with ion-implanted base. Fabrication of BJTs without ion implantation means less lifetime-reducing defects, and in addition, the surface morphology is improved since high-temperature annealing becomes unnecessary. BJTs with flat-surface junction termination that combine etched regrown layers show about 250 V higher breakdown voltage than BJTs with only etched flat-surface JTE.

M. Ostling

Papers

Fabrication of 2700-V 12- $\hbox{m}\Omega \cdot \hbox{cm}^{2}$ Non Ion-Implanted 4H- SiC BJTs With Common-Emitter Current Gain of 50

Plasma chemistries for high density plasma etching of SiC

High-Voltage (2.8 kV) Implantation-Free 4H-SiC BJTs With Long-Term Stability of the Current Gain

Electrical characterization of TiC ohmic contacts to aluminum ion implanted 4H–silicon carbide

High-Current-Gain SiC BJTs With Regrown Extrinsic Base and Etched JTE