Semiconductor device and manufacturing method thereof

A semiconductor device, comprising:

• a plurality of fin structures extending in a first direction disposed over a substrate;
• a gate structure extending in a second direction crossing the first direction disposed over a first portion of the fin structures;
• first epitaxial layers disposed over second portions of each of the fin structures of the plurality of fin structures,
• wherein the second portions are located on opposing sides of the gate structure, and an uppermost surface of the second portions is at a level below uppermost surfaces of the first portions as viewed in cross section;
• second epitaxial layers disposed over the first epitaxial layers,
• wherein the first and second epitaxial layers are U-shaped as viewed in cross section;
• third epitaxial layers disposed over the second epitaxial layers and filling the U-shape of the first and second epitaxial layers,
• wherein the third epitaxial layers extend into the second epitaxial layers to a depth from an uppermost surface of the second epitaxial layers greater than half a depth of the second epitaxial layers as viewed in cross section, wherein the depth of the second epitaxial layer is measured from the uppermost surface of the second epitaxial layer to a lowermost surface of the second epitaxial layer,
• wherein a concentration of dopant in the third epitaxial layers is greater than a concentration of the dopant in the second epitaxial layers, and the concentration of the dopant in the second epitaxial layers is greater than a concentration of the dopant in the first epitaxial layers;
• and
• fourth epitaxial layers having a concentration of a dopant less than the concentration of the dopant in the third epitaxial layers disposed over the third epitaxial layers,
• wherein the dopant in the fourth epitaxial layers is same as or different than the dopant in the third epitaxial layers.

A semiconductor device, comprising:

• a plurality of fin structures extending in a first direction over a substrate;
• epitaxial source/drain structures disposed over the plurality of fin structures,
• wherein the epitaxial source/drain structures include a first layer having a first concentration of a dopant, a second layer having a second concentration of the dopant, the second layer is disposed over the first layer, a third layer having a third concentration of the dopant, and the third layer is disposed over the second layer,
• wherein the third concentration of the dopant is greater than the second concentration of the dopant, and the second concentration of the dopant is greater than the first concentration of the dopant,
• wherein each of the epitaxial source/drain structures is a merged source/drain structure, wherein at least the third layers of adjacent epitaxial source/drain structures are merged, and
• wherein a height in a third direction substantially perpendicular to the first and second directions from a level of upper surfaces of adjacent fin structures of the plurality of fin structures to an uppermost point of a lower surface of the merged adjacent epitaxial source/drain structures is greater than a thickness of the merged source/drain structure in the third direction from the uppermost point of the lower surface of the merged adjacent epitaxial source/drain structures to a top surface of the merged adjacent epitaxial source/drain structures;
• and
• cap layers having a fourth concentration of the dopant disposed over the epitaxial source/drain structures,
• wherein the fourth concentration of the dopant is less than the third concentration of the dopant.