In an embodiment, a structure includes: a semiconductor substrate; a gate spacer over the semiconductor substrate, the gate spacer having an upper portion and a lower portion, a first width of the upper portion decreasing continually in a first direction extending away from a top surface of the semiconductor substrate, a second width of the lower portion being constant along the first direction; a gate stack extending along a first sidewall of the gate spacer and the top surface of the semiconductor substrate; and an epitaxial source/drain region adjacent a second sidewall of the gate spacer.

A transistor structure and a manufacturing method thereof are provided. In the transistor structure, the substrate has an active area (AA); the gate including a body portion, a first extension portion and a second extension portion is disposed on the substrate in the AA; the first and second extension portions are connected to the body portion extending in a first direction; the first extension portion is located at the first side of the AA and partially overlaps the AA; the second extension portion is located at the second side of the AA and partially overlaps the AA; the material of the first and second extension portions is different from that of the body portion; the first and the second doped regions are disposed in the substrate at two sides of the gate in a second direction; the gate dielectric layer is disposed between the gate and the substrate.

A semiconductor device includes a gate structure on a substrate, in which the gate structure includes a main branch extending along a first direction on the substrate and a sub-branch extending along a second direction adjacent to the main branch. The semiconductor device also includes a first doped region overlapping the main branch and the sub-branch according to a top view and a second doped region overlapping the first doped region. The invention includes a plurality of contact plugs, the first doped region does not overlap with the contact plugs, and wherein the plurality of contact plugs comprises a first contact plug and a second contact plug disposed at different sides of the main branch.

In an embodiment, a device includes: a gate structure over a substrate; a gate spacer adjacent the gate structure; a source/drain region adjacent the gate spacer; a first inter-layer dielectric (ILD) on the source/drain region, the first ILD having a first concentration of an impurity; and a second ILD on the first ILD, the second ILD having a second concentration of the impurity, the second concentration being less than the first concentration, top surfaces of the second ILD, the gate spacer, and the gate structure being coplanar; and a source/drain contact extending through the second ILD and the first ILD, the source/drain contact coupled to the source/drain region.

A method may include forming a dummy dielectric layer over a substrate, and forming a dummy gate over the dummy dielectric layer. The method may also include forming a first spacer adjacent the dummy gate, and removing the dummy gate to form a cavity, where the cavity is defined at least in part by the first spacer. The method may also include performing a plasma treatment on portions of the first spacer, where the plasma treatment causes a material composition of the portions of the first spacer to change from a first material composition to a second material composition. The method may also include etching the portions of the first spacer having the second material composition to remove the portions of the first spacer having the second material composition, and filling the cavity with conductive materials to form a gate structure.

A method may include forming a dummy dielectric layer over a substrate, and forming a dummy gate over the dummy dielectric layer. The method may also include forming a first spacer adjacent the dummy gate, and removing the dummy gate to form a cavity, where the cavity is defined at least in part by the first spacer. The method may also include performing a plasma treatment on portions of the first spacer, where the plasma treatment causes a material composition of the portions of the first spacer to change from a first material composition to a second material composition. The method may also include etching the portions of the first spacer having the second material composition to remove the portions of the first spacer having the second material composition, and filling the cavity with conductive materials to form a gate structure.

A semiconductor device includes a substrate; two source/drain (S/D) regions over the substrate; a gate stack over the substrate and between the two S/D regions; a spacer layer covering sidewalls of the gate stack; an S/D contact metal over one of the two S/D regions; a first dielectric layer covering sidewalls of the S/D contact metal; and an inter-layer dielectric (ILD) layer covering the first dielectric layer, the spacer layer, and the gate stack, thereby defining a gap. A material of a first sidewall of the gap is different from materials of a top surface and a bottom surface of the gap, and a material of a second sidewall of the gap is different from the materials of the top surface and the bottom surface of the gap.

A semiconductor device includes a substrate, a gate stack over the substrate and a gate spacer on a sidewall of the gate stack. The gate spacer includes an outer spacer and an inner spacer between the gate stack and the outer spacer. The outer spacer and the inner spacer have same k-value reduction impurities, and a concentration of the k-value reduction impurities in the inner spacer is greater than a concentration of the k-value reduction impurities in the outer spacer.

In an embodiment, a device includes: a gate structure over a substrate; a gate spacer adjacent the gate structure; a source/drain region adjacent the gate spacer; a first inter-layer dielectric (ILD) on the source/drain region, the first ILD having a first concentration of an impurity; and a second ILD on the first ILD, the second ILD having a second concentration of the impurity, the second concentration being less than the first concentration, top surfaces of the second ILD, the gate spacer, and the gate structure being coplanar; and a source/drain contact extending through the second ILD and the first ILD, the source/drain contact coupled to the source/drain region.

A method for fabricating a semiconductor device is provided. The method includes forming a fin structure extending along a first lateral direction; forming a dummy gate structure that is over a portion of the fin structure and extends along a second direction perpendicular to the first lateral direction; growing source/drain structures that are respectively coupled to ends of the portion of the fin structure; removing the dummy gate structure to form a gate trench; lining inner sidewalls of the gate trench with a gate spacer; and forming an active gate structure in the gate trench.