One object of the present invention is to provide a structure of a transistor including an oxide semiconductor in a channel formation region in which the threshold voltage of electric characteristics of the transistor can be positive, which is a so-called normally-off switching element, and a manufacturing method thereof. A second oxide semiconductor layer which has greater electron affinity and a smaller energy gap than a first oxide semiconductor layer is formed over the first oxide semiconductor layer. Further, a third oxide semiconductor layer is formed to cover side surfaces and a top surface of the second oxide semiconductor layer, that is, the third oxide semiconductor layer covers the second oxide semiconductor layer.

To provide a transistor in which a channel is formed in an oxide semiconductor and which has stable electrical characteristics. To suppress shift in threshold voltage of a transistor in which a channel is formed in an oxide semiconductor. To provide a normally-off switching element having a positive threshold voltage as an n-channel transistor in which a channel is formed in an oxide semiconductor. A base insulating layer is formed over a substrate, an oxide semiconductor layer is formed over the base insulating layer, a first gate insulating layer is formed over the oxide semiconductor layer, a second gate insulating layer is formed over the first gate insulating layer by a sputtering method or an atomic layer deposition method at a substrate temperature of higher than or equal to 100 C., and a gate electrode layer is formed over the second gate insulating layer.

Provided is a field-effect transistor (FET) having small off-state current, which is used in a miniaturized semiconductor integrated circuit. The field-effect transistor includes a thin oxide semiconductor which is formed substantially perpendicular to an insulating surface, a gate insulating film formed to cover the oxide semiconductor, and a gate electrode which is formed to cover the gate insulating film. The gate electrode partly overlaps a source electrode and a drain electrode. The source electrode and the drain electrode are in contact with at least a top surface of the oxide semiconductor. In this structure, three surfaces of the thin oxide semiconductor are covered with the gate electrode, so that electrons injected from the source electrode or the drain electrode can be effectively removed, and most of the space between the source electrode and the drain electrode can be a depletion region; thus, off-state current can be reduced.

According to one embodiment, a semiconductor device includes first to third semiconductor regions and first to third conductors. The second semiconductor region is separated from the first semiconductor region in a first direction. The third semiconductor region is provided between the first and the second semiconductor regions. The third conductor is separated from the third semiconductor region in a second direction intersecting the first direction. The third semiconductor region includes first and second partial regions. The first partial region includes a first metal element, and is amorphous. The second partial region is stacked with the first partial region in the second direction, and is polycrystalline. A first concentration of the first metal element in the first partial region is higher than a second concentration of the first metal element in the second partial region, or the second partial region does not include the first metal element.

Embodiments with present disclosure provides a gate-all-around FET device including extended bottom inner spacers. The extended bottom inner prevents the subsequently formed epitaxial source/drain region from volume loss and induces compressive strain in the channel region to prevent strain loss and channel resistance degradation.

Embodiments with present disclosure provides a gate-all-around FET device including a patterned or lowered bottom dielectric layer. The bottom dielectric layer prevents the subsequently formed epitaxial source/drain region from volume loss and induces compressive strain in the channel region to prevent strain loss and channel resistance degradation.

According to one embodiment, a first transistor includes a first semiconductor region, a second semiconductor region, a third semiconductor region, a first gate insulating film, and a first gate electrode. The first semiconductor region is provided in a first semiconductor layer extending in a second direction substantially perpendicular to the surface of the semiconductor substrate from the first line. The second semiconductor region is provided above the first semiconductor region in the first semiconductor layer. The third semiconductor region is provided above the second semiconductor region in the first semiconductor layer. The first gate insulating film covers a first side face of the first semiconductor layer. The first gate electrode covers the first side face of the first semiconductor layer through the first gate insulating film. The first transistor has an asymmetrical structure with respect to a center face of the second semiconductor region in the second direction.

An object is to provide a semiconductor device having a structure with which parasitic capacitance between wirings can be sufficiently reduced. An oxide insulating layer serving as a channel protective layer is formed over part of an oxide semiconductor layer overlapping with a gate electrode layer. In the same step as formation of the oxide insulating layer, an oxide insulating layer covering a peripheral portion of the oxide semiconductor layer is formed. The oxide insulating layer which covers the peripheral portion of the oxide semiconductor layer is provided to increase the distance between the gate electrode layer and a wiring layer formed above or in the periphery of the gate electrode layer, whereby parasitic capacitance is reduced.

To reduce power consumption and suppress display degradation of a liquid crystal display device. To suppress display degradation due to an external factor such as temperature. A transistor whose channel formation region is formed using an oxide semiconductor layer is used for a transistor provided in each pixel. Note that with the use of a high-purity oxide semiconductor layer, off-state current of the transistor at a room temperature can be 10 aA/m or less and off-state current at 85 C. can be 100 aA/m or less. Consequently, power consumption of a liquid crystal display device can be reduced and display degradation can be suppressed. Further, as described above, off-state current of the transistor at a temperature as high as 85 C. can be 100 aA/m or less. Thus, display degradation of a liquid crystal display device due to an external factor such as temperature can be suppressed.

An approach to providing a barrier in a vertical field effect transistor with low effective mass channel materials wherein the forming of the barrier includes forming a first source/drain contact on a semiconductor substrate and forming a channel with a first channel layer on the first source/drain contact. The approach further includes forming the barrier on the first channel layer, and a second channel layer on the barrier followed by forming a second source/drain contact on the second channel layer.