Method for forming alignment keys of semiconductor structure and semiconductor structure having alignment keys

A semiconductor structure having alignment keys, comprising:

• a substrate, wherein at least one low voltage region, at least one medium voltage region, at least one high voltage region and at least one alignment mark region are defined on the substrate, and the at least one high voltage region is adjacent to the at least one alignment mark region;
• a first trench, formed in the at least one medium voltage region of the substrate;
• a second trench, formed in the at least one alignment mark region of the substrate and extending to a junction of the at least one alignment mark region and the at least one high voltage region, wherein the second trench has a sidewall, the first trench has a first depth, the second trench has a second depth, and the second depth is greater than the first depth;
• a recessed surface, formed in the at least one high voltage region of the substrate adjacent to the junction, wherein the recessed surface is connected to the sidewall, and an angle is formed between the recessed surface and the sidewall;
• at least one deep doped well, formed in the at least one medium voltage region and the at least one low voltage region;
• and
• at least one high-voltage doped well, formed in the at least one high voltage region and the at least one alignment mark region, wherein a doping type of the deep doped well is different from a doping type of the high voltage doped well.