First and second buffer regions and an n.sup.−-type drift region are sequentially formed by epitaxial growth on an n.sup.+-type starting substrate. An impurity concentration of the first buffer region is higher than that of the n.sup.−-type drift region and lower than that of the n.sup.+-type starting substrate. An impurity concentration of the second buffer region is higher than that of the first buffer region and continuously increases by a first impurity concentration gradient from a first gradient changing point toward the n.sup.−-type drift region to a second gradient changing point toward the first buffer region; continuously decreases by a second impurity concentration gradient from the first gradient changing point to a first interface; and continuously decreases by a third impurity concentration gradient from the second gradient changing point to a second interface. The second impurity concentration gradient is lower than the third impurity concentration gradient.

A first semiconductor component having a first semiconductor chip and a first heat sink and a second semiconductor component having a second semiconductor chip and a second heat sink are disposed in a cooler. The first semiconductor chip is smaller in size than the second semiconductor chip. A first heat conduction surface between the first semiconductor chip and the first heat sink is smaller in an area than a second heat conduction surface between the second semiconductor chip and the second heat sink. A first region of the cooler where the first semiconductor component is disposed has higher cooling performance than a second region of the cooler where the second semiconductor component is disposed.

An integrated circuit includes a MOSFET device and a monolithic diode device, wherein the monolithic diode device is electrically connected in parallel with a body diode of the MOSFET device. The monolithic diode device is configured so that a forward voltage drop Vf.sub.D2 of the monolithic diode device is less than a forward voltage drop Vf.sub.D1 of the body diode of the MOSFET device. The forward voltage drop Vf.sub.D2 is process tunable by controlling a gate oxide thickness, a channel length and body doping concentration level. The tunability of the forward voltage drop Vf.sub.D2 advantageously permits design of the integrated circuit to suit a wide range of applications according to requirements of switching speed and efficiency.

A semiconductor device includes a semiconductor layer made of SiC. A transistor element having an impurity region is formed in a front surface portion of the semiconductor layer. A first contact wiring is formed on a back surface portion of the semiconductor layer, and defines one electrode electrically connected to the transistor element. The first contact wiring has a first wiring layer forming an ohmic contact with the semiconductor layer without a silicide contact and a second wiring layer formed on the first wiring layer and having a resistivity lower than that of the first wiring layer.

A method for forming a drift region of a superjunction transistor and a superjunction transistor device are disclosed. The method includes forming first regions of a first doping type and second regions of a second type in a semiconductor body such that the first and second regions are arranged alternatingly in the body. The first and second regions are formed by: forming trenches in at least one semiconductor layer; implanting first type dopant atoms and second type dopant atoms into opposing sidewalls of the trenches; filling the trenches with a semiconductor material; and diffusing the dopant atoms in a thermal process so that the first type dopant atoms form the first regions and the second type dopant atoms form the second regions. Each trench has a first width, the trenches are separated by mesa regions each having a second width, and the first width is greater than the second width.

A semiconductor device includes a semiconductor substrate having first and second main surfaces, a first region formed in a surface layer of the first main surface, a drift layer disposed adjacent to the first region, a charge accumulation region having a higher concentration than the drift region, and a trench gate including a trench penetrating the first region and the charge accumulation region, and a gate electrode formed in the trench. The trench gate includes a main trench having a gate electrode to which a gate voltage is applied, and a dummy trench having a gate electrode to which a voltage different from the main trench is applied. The main trench and the dummy trench sandwiches the charge accumulation region, and a contact area S1 between the dummy trench and the charge accumulation region is larger than a contact area S2 between the main trench and the charge accumulation region.

A semiconductor device includes a semiconductor layer of a first conductivity type having a first main surface at one side and a second main surface at another side, a trench gate structure including a gate trench formed in the first main surface of the semiconductor layer, and a gate electrode embedded in the gate trench via a gate insulating layer, a trench source structure including a source trench formed deeper than the gate trench and across an interval from the gate trench in the first main surface of the semiconductor layer, a source electrode embedded in the source trench, and a deep well region of a second conductivity type formed in a region of the semiconductor layer along the source trench, a ratio of a depth of the trench source structure with respect to a depth of the trench gate structure being not less than 1.5 and not more than 4.0, a body region of the second conductivity type formed in a region of a surface layer portion of the first main surface of the semiconductor layer between the gate trench and the source trench, a source region of the first conductivity type formed in a surface layer portion of the body region, and a drain electrode connected to the second main surface of the semiconductor layer.

An SiC semiconductor device includes an SiC semiconductor layer having a first main surface and a second main surface, a gate electrode embedded in a trench with a gate insulating layer, a source region of a first conductivity type formed in a side of the trench in a surface layer portion of the first main surface, a body region of a second conductivity type formed in a region at the second main surface side with respect to the source region in the surface layer portion of the first main surface, a drift region of the first conductivity type formed in a region at the second main surface side in the SiC semiconductor layer, and a contact region of the second conductivity type having an impurity concentration of not more than 1.0×10.sup.20 cm.sup.−3 and formed in the surface layer portion of the first main surface.

An embodiment of a semiconductor device includes a plurality of transistor sections separated from each other and a plurality of diode sections separated from each other. Each transistor section includes an emitter electrode and a collector electrode. Each diode section includes an anode electrode and a cathode electrode. Each transistor section is electrically coupled to a common gate pad. A ratio between an active transistor part and an active diode part of the semiconductor device is adjustable by activating a first number of the transistor sections by selectively contacting the emitter electrodes and the collector electrodes of the first number of transistor sections, and by activating a second number of the diode sections by selectively contacting the anode electrodes and the cathode electrodes of the second number of diode sections.

An SiC semiconductor device includes an SiC semiconductor layer including an SiC monocrystal and having a first main surface as a device surface, a second main surface at a side opposite to the first main surface, and a side surface connecting the first main surface and the second main surface, a main surface insulating layer including an insulating material, covering the first main surface of the SiC semiconductor layer, and having an insulating side surface continuous to the side surface of the SiC semiconductor layer, and a boundary modified layer including a first region that is modified to be of a property differing from the SiC monocrystal and a second region that is modified to be of a property differing from the insulating material, and being formed across the side surface of the SiC semiconductor layer and the insulating side surface of the main surface insulating layer.