Integrated circuits having source/drain structure and method of making

A method of making a semiconductor device, the method comprising:

• forming a gate structure over a substrate;
• etching the substrate to define a recess in the substrate;
• depositing a first silicon-containing material structure in the recess, wherein depositing the first silicon-containing material structure comprises:
• depositing a first layer having an uppermost surface below a top surface of the substrate and a bottommost surface in direct contact with the substrate;
• depositing a second layer over the first layer, wherein at least a portion of the second layer is below the top surface of the substrate;
• depositing a third layer over the second layer, wherein an entirety of the third layer is above the top surface of the substrate, a first region of the third layer is thinner than a second region of the third layer, thickness is measured in a direction perpendicular to the top surface of the substrate, and a width, measured perpendicular to the thickness, of the third layer is equal to a width of the first layer.

An integrated circuit comprising:

• a gate structure over a substrate;
• and
• a first silicon-containing material structure in a recess adjacent to the gate structure, wherein the first silicon-containing material structure comprises:
• a first layer having an uppermost surface below a top surface of the substrate and a bottommost surface in direct contact with the substrate;
• a second layer over the first layer, wherein an entirety of the second layer is above the top surface of the substrate, a first region of the second layer closer to the gate structure has a variable thickness, a second region of the second layer farther from the gate structure has a uniform thickness, and thickness is measured in a direction perpendicular to the top surface of the substrate;
• and
• a third layer between the first layer and the second layer, wherein an entirety of the third layer is below the top surface of the substrate.