Provided is a manufacturing method for manufacturing a SiC substrate having a flattened surface, including etching the surface of the SiC substrate by irradiating the surface of the SiC substrate with atomic hydrogen while the SiC substrate having an off angle is heated. In the etching, the SiC substrate may be heated within a range of 800° C. or higher and 1200° C. or lower.

The invention relates to a method for producing a semiconductor structure, characterised in that the method comprises a step (201) of depositing a crystalline passivation layer continuously covering the entire surface of a layer based on group III nitrides, said crystalline passivation layer, which is deposited from a precursor containing silicon atoms and a flow of nitrogen atoms, consisting of silicon atoms bound to the surface of the layer based on group III nitrides and arranged in a periodical arrangement such that a diffraction image of said crystalline passivation layer obtained by grazing-incidence diffraction of electrons in the direction [1-100] comprises: two fractional order diffraction lines (0, −⅓) and (0, −⅔) between the central line (0, 0) and the integer order line (0, −1), and two fractional order diffraction lines (0, ⅓) and (0, ⅔) between the central line (0, 0) and the integer order line (0, 1).

After a sputtering gas is supplied to a deposition chamber, plasma including an ion of the sputtering gas is generated in the vicinity of a target. The ion of the sputtering gas is accelerated and collides with the target, so that flat-plate particles and atoms of the target are separated from the target. The flat-plate particles are deposited with a gap therebetween so that the flat plane faces a substrate. The atom and the aggregate of the atoms separated from the target enter the gap between the deposited flat-plate particles and grow in the plane direction of the substrate to fill the gap. A film is formed over the substrate. After the deposition, heat treatment is performed at high temperature in an oxygen atmosphere, which forms an oxide with a few oxygen vacancies and high crystallinity.

A transistor includes a multilayer film in which an oxide semiconductor film and an oxide film are stacked, a gate electrode, and a gate insulating film. The multilayer film overlaps with the gate electrode with the gate insulating film interposed therebetween. The multilayer film has a shape having a first angle between a bottom surface of the oxide semiconductor film and a side surface of the oxide semiconductor film and a second angle between a bottom surface of the oxide film and a side surface of the oxide film. The first angle is acute and smaller than the second angle. Further, a semiconductor device including such a transistor is manufactured.

An embodiment is a semiconductor device which includes a first oxide semiconductor layer over a substrate having an insulating surface and including a crystalline region formed by growth from a surface of the first oxide semiconductor layer toward an inside; a second oxide semiconductor layer over the first oxide semiconductor layer; a source electrode layer and a drain electrode layer which are in contact with the second oxide semiconductor layer; a gate insulating layer covering the second oxide semiconductor layer, the source electrode layer, and the drain electrode layer; and a gate electrode layer over the gate insulating layer and in a region overlapping with the second oxide semiconductor layer. The second oxide semiconductor layer is a layer including a crystal formed by growth from the crystalline region.

A silicon carbide semiconductor device has a silicon carbide substrate and an insulating film. The silicon carbide substrate includes a termination region having a peripheral edge, and an element region surrounded by the termination region. The insulating film is provided on the termination region. The termination region includes a first impurity region having a first conductivity type, and a field stop region having the first conductivity type, being in contact with the first impurity region and having a higher impurity concentration than the first impurity region. The field stop region is at least partially exposed at the peripheral edge.

An oxide semiconductor layer which is intrinsic or substantially intrinsic and includes a crystalline region in a surface portion of the oxide semiconductor layer is used for the transistors. An intrinsic or substantially intrinsic semiconductor from which an impurity which is to be an electron donor (donor) is removed from an oxide semiconductor and which has a larger energy gap than a silicon semiconductor is used. Electrical characteristics of the transistors can be controlled by controlling the potential of a pair of conductive films which are provided on opposite sides from each other with respect to the oxide semiconductor layer, each with an insulating film arranged therebetween, so that the position of a channel formed in the oxide semiconductor layer is determined.

In a semiconductor device including a transistor including an oxide semiconductor film and a protective film over the transistor, an oxide insulating film containing oxygen in excess of the stoichiometric composition is formed as the protective film under the following conditions: a substrate placed in a treatment chamber evacuated to a vacuum level is held at a temperature higher than or equal to 180° C. and lower than or equal to 260° C.; a source gas is introduced into the treatment chamber so that the pressure in the treatment chamber is set to be higher than or equal to 100 Pa and lower than or equal to 250 Pa; and a high-frequency power higher than or equal to 0.17 W/cm.sup.2 and lower than or equal to 0.5 W/cm.sup.2 is supplied to an electrode provided in the treatment chamber.

A novel memory device is provided. The memory device includes a plurality of memory cells, and one memory cell includes a first transistor and a second transistor. One of a source and a drain of the first transistor is electrically connected to a gate of the second transistor through a node SN. Data written through the first transistor is retained at the node SN. When an OS transistor is used as the first transistor, formation of a storage capacitor is not needed. A region with a low dielectric constant is provided outside the memory cell, whereby noise from the outside is reduced and stable operation is achieved.

The source region, drain region, buried insulating film, gate insulating film, and gate electrode of the semiconductor device are formed in a main surface of a semiconductor substrate. The buried insulating film is buried in a first trench formed between the source and drain regions. The first trench has a first side surface and a first bottom surface. The first side surface faces the source region in a first direction extending from one of the source and drain regions to the other. The first bottom surface is connected to the first side surface and is along the main surface of the semiconductor substrate. A crystal plane of a first surface of the semiconductor substrate, which is the first side surface of the first trench, is (111) plane. A crystal plane of a second surface of the semiconductor substrate, which is the bottom surface of the first trench, is (100) plane.