Method of manufacturing semiconductor structure

A method of manufacturing a semiconductor structure, comprising:

• providing a substrate, wherein the substrate comprises multiple array regions and a non-array region, the non-array region surrounds the array regions and comprises a core region and a periphery region, the core region is located on a periphery of the array regions and also arranged between the array regions, the periphery region is located on a periphery of the core region, and the core region comprises a first transistor region and a second transistor region, the peripheral region comprises a third transistor region and a fourth transistor region;
• forming a mask layer on the substrate;
• removing the mask layer on the non-array region;
• forming a first oxide layer on the non-array region;
• removing the first oxide layer on the first transistor region, to expose a top surface of the first transistor region;
• forming an epitaxial layer on the exposed top surface of the first transistor region;
• removing the first oxide layer only on the second transistor region and keeping the first oxide layer on the third transistor region and the fourth transistor region;
• and
• forming a second oxide layer on the second transistor region and the epitaxial layer and also on a remaining first oxide layer on the third transistor region and the fourth transistor region;
• wherein a thickness of the first oxide layer is greater than a thickness of the second oxide layer.