Transistor structure and manufacturing method thereof

The invention provides a transistor structure and a preparation method thereof. The transistor structure comprises a substrate, a gate structure, a plurality of first pocket doped regions, a plurality of second pocket doped regions, a plurality of source/drain extension regions and a plurality of source/drain regions. The gate structure is located on the substrate. A plurality of first pocket doped regions are located in the substrate beside the gate structure. The doping of the first pocket doped region includes a Group IVA element. A plurality of second pocket doped regions are located in the substrate beside the gate structure. The depth of the second pocket doped region is greater than the depth of the first pocket doped region. The plurality of source/drain extension regions are located in the plurality of first pocket doped regions. A plurality of source/drain regions are located in the substrate beside the gate structure. The source/drain extension region is located between the source/drain region and