Method for forming semiconductor structure

A method for forming a semiconductor structure, comprising:

• providing a first substrate, the first substrate including a first surface and second surface opposite to each other, wherein the first substrate includes first ions and the first ions have a first concentration;
• forming a first epitaxial layer on the first surface of the first substrate, wherein the first epitaxial layer includes second ions and the second ions have a second concentration and the second concentration is smaller than the first concentration;
• forming a second epitaxial layer on the first epitaxial layer and a third epitaxial layer located on the second epitaxial layer, wherein:
• the second epitaxial layer includes third ions, the third ions have a third concentration, the third epitaxial layer includes fourth ions, the fourth ions have a fourth concentration, and the fourth concentration is smaller than the third concentration;
• and
• thinning the first substrate from the second surface of the first substrate until a surface of the second epitaxial layer is exposed.