Abstract: A device includes a bottom transistor, a top transistor, and an epitaxial isolation structure. The bottom transistor includes a first channel layer, first source/drain epitaxial structures, and a first gate structure. The first source/drain epitaxial structures are on opposite sides of the first channel layer. The first gate structure is around the first channel layer. The top transistor is over the bottom transistor and includes a second channel layer, second source/drain epitaxial structures, and a second gate structure. The second source/drain epitaxial structures are on opposite sides of the second channel layer. The second gate structure is around the second channel layer. The epitaxial isolation structure is between and in contact with one of the first source/drain epitaxial structures and one of the second source/drain epitaxial structures, such that the one of the first source/drain epitaxial structures is electrically isolated from the one of the second source/drain epitaxial structures.

Abstract: A device comprises a first semiconductor layer, a dielectric layer, a second semiconductor layer, and a gate structure. The first semiconductor layer is over a substrate. The first semiconductor layer comprises a first channel region and first source/drain regions on opposite sides of the first channel region. The dielectric layer is over the first semiconductor layer. The second semiconductor layer is over the dielectric layer. The second semiconductor layer comprises a second channel region and second source/drain regions on opposite sides of the second channel region. The gate structure comprises a first portion extending in the dielectric layer, a second portion wrapping around the first channel region of the first semiconductor layer, and a third portion wrapping around the second channel region of the second semiconductor layer.

Abstract: A method includes forming an epitaxial stack over a semiconductor substrate, wherein the epitaxial stack comprises a plurality of sacrificial layers and a plurality of channel layers alternately arranged over the semiconductor substrate, and each of the sacrificial layers is a multi-layer film comprising a bottom epitaxial layer, a middle epitaxial layer over the bottom epitaxial layer, and a top epitaxial layer over the middle epitaxial layer, wherein the middle epitaxial layer has a lower germanium concentration than the bottom and top epitaxial layers; laterally recessing the sacrificial layers to form sidewall recesses alternating with the channel layers; forming inner spacers in the sidewall recesses; forming source/drain epitaxial structures on opposite sides of the channel layers.

Abstract: A device comprises source/drain regions over a substrate and spaced apart along a first direction, a first gate structure between the source/drain regions, and a first channel structure surrounded by the first gate structure. The first channel structure comprises alternately stacking first semiconductor layers and second semiconductor layers. When viewed in a cross section taken along a second direction perpendicular to the first direction, central axes of the second semiconductor layers are laterally offset from central axes of the first semiconductor layers.

Abstract: A device includes a bottom transistor, a top transistor, and an epitaxial isolation structure. The bottom transistor includes a first channel layer, first source/drain epitaxial structures, and a first gate structure. The first source/drain epitaxial structures are on opposite sides of the first channel layer. The first gate structure is around the first channel layer. The top transistor is over the bottom transistor and includes a second channel layer, second source/drain epitaxial structures, and a second gate structure. The second source/drain epitaxial structures are on opposite sides of the second channel layer. The second gate structure is around the second channel layer. The epitaxial isolation structure is between and in contact with one of the first source/drain epitaxial structures and one of the second source/drain epitaxial structures, such that the one of the first source/drain epitaxial structures is electrically isolated from the one of the second source/drain epitaxial structures.

Abstract: A method includes forming a semiconductor structure on a substrate; performing a first etching process on the semiconductor structure to form a fin structure upwardly extending above the substrate; performing a second etching process to trim the fin structure to have a reverse-trapezoidal cross-sectional profile; forming source/drain regions on opposite regions of the fin structure; forming a gate structure between the source/drain regions.

Abstract: A device comprise a first semiconductor channel layer over a substrate, a second semiconductor channel layer over the first semiconductor channel layer, and source/drain epitaxial structures on opposite sides of the first semiconductor channel layer and opposite sides of the second semiconductor channel layer. A compressive strain in the second semiconductor channel layer is greater than a compressive strain in the first semiconductor channel layer. The source/drain epitaxial structures each comprise a first region interfacing the first semiconductor channel layer and a second region interfacing the second semiconductor channel layer, and the first region has a composition different from a composition of the second region.

Abstract: A device comprises a plurality of nanosheets, source/drain stressors, and a gate structure wrapping around the nanosheets. The nanosheets extend in a first direction above a semiconductor substrate and are arranged in a second direction substantially perpendicular to the first direction. The source/drain stressors are on either side of the nanosheets. Each of the source/drain stressors comprises a first epitaxial layer and a second epitaxial layer over the first epitaxial layer. The first and second epitaxial layers are made of a Group IV element and a Group V element. An atomic ratio of the Group V element to the Group IV element in the second epitaxial layer is greater than an atomic ratio of the Group V element to the Group IV element in the first epitaxial layer.

Abstract: A device includes a bottom transistor, a top transistor, and an epitaxial isolation structure. The bottom transistor includes a first channel layer, first source/drain epitaxial structures, and a first gate structure. The first source/drain epitaxial structures are on opposite sides of the first channel layer. The first gate structure is around the first channel layer. The top transistor is over the bottom transistor and includes a second channel layer, second source/drain epitaxial structures, and a second gate structure. The second source/drain epitaxial structures are on opposite sides of the second channel layer. The second gate structure is around the second channel layer. The epitaxial isolation structure is between and in contact with one of the first source/drain epitaxial structures and one of the second source/drain epitaxial structures, such that the one of the first source/drain epitaxial structures is electrically isolated from the one of the second source/drain epitaxial structures.

Abstract: A device comprises a gate structure, n-type source/drain features, p-type source/drain features, an NFET channel, and a PFET channel. The gate structure is over a substrate. The n-type source/drain features are on opposite first and second sides of the gate structure, respectively. The p-type source/drain features are on opposite third and fourth sides of the gate structure, respectively. The NFET channel extends within the gate structure and connects the n-type source/drain features. The PFET channel extends within the gate structure and connects the p-type source/drain features. The NFET channel and the PFET channel are vertically spaced apart by the gate structure.

Abstract: A device comprises source/drain regions over a substrate and spaced apart along a first direction, a first gate structure between the source/drain regions, and a first channel structure surrounded by the first gate structure. The first channel structure comprises alternately stacking first semiconductor layers and second semiconductor layers. When viewed in a cross section taken along a second direction perpendicular to the first direction, central axes of the second semiconductor layers are laterally offset from central axes of the first semiconductor layers.

Abstract: A device comprises a plurality of nanosheets, source/drain stressors, and a gate structure wrapping around the nanosheets. The nanosheets extend in a first direction above a semiconductor substrate and are arranged in a second direction substantially perpendicular to the first direction. The source/drain stressors are on either side of the nanosheets. Each of the source/drain stressors comprises a first epitaxial layer and a second epitaxial layer over the first epitaxial layer. The first and second epitaxial layers are made of a Group IV element and a Group V element. An atomic ratio of the Group V element to the Group IV element in the second epitaxial layer is greater than an atomic ratio of the Group V element to the Group IV element in the first epitaxial layer.

Abstract: The present disclosure generally relates to a gate-all-around (GAA) transistor. The GAA transistor may include regrown source/drain layers in source/drain stressors. Atomic ratio differences among the regrown source/drain layers are tuned to reduce strain mismatch among the semiconductor nanosheets. Alternatively, the GAA transistor may include strained channels formed using a layer stack of alternating semiconductor layers having different lattice constants.

Abstract: A method includes forming a fin structure having a stack of alternating first semiconductor layers and second semiconductor layers over a substrate; forming a dummy gate structure across the fin structure; etching portions of the fin structure to expose portions of the substrate; forming source/drain stressors over the exposed portions of the substrate; after forming the source/drain stressors, removing the dummy gate structure; after removing the dummy gate structure, removing the first semiconductor layers such that the second semiconductor layers are suspended between the source/drain stressors; and forming a gate structure to surround each of the suspended second semiconductor layers. The source/drain stressors each comprise a first source/drain layer and a second source/drain layer over the first source/drain layer. An atomic concentration of a Group IV element or a Group V element in the second source/drain layer is greater than that in the first source/drain layer.