Strained silicon structure

A strained silicon structure comprising:

• a substrate having a top surface, wherein the substrate is defined into a low density region and a high density region;
• a first transistor disposed on the top surface and within the low density region;
• and
• a second transistor disposed on the top surface and within the high density region, wherein a cross-sectional profile of a first source/drain region of the first transistor is different from a cross-sectional profile of a second source/drain region of the second transistor;
• a first epitaxial layer disposed within the first source/drain region;
• and
• a second epitaxial layer disposed within the second source/drain region, wherein the first epitaxial layer and the second epitaxial have a same composition.

A strained silicon structure comprising:

• a substrate;
• at least two first transistors disposed on the substrate, and each of the first transistors having a first gate structure;
• and
• at least two second transistors disposed on the substrate, and each of the second transistors having a second gate structure, wherein a first shortest distance between the first gate structures is larger than a second shortest distance between the second gate structures, and a cross-sectional profile of a first source/drain region of each of the first transistors is different from a cross-sectional profile of a second source/drain region of each of the second transistors.