Various embodiments provide shallow trenches and fabrication methods. In an exemplary method, a semiconductor substrate can be provided. A mask layer can be provided on the semiconductor substrate. An etch-cleaning process can be performed. The etch-cleaning process can include etching the semiconductor substrate to form a shallow trench by one or more etching steps using the mask layer as an etch mask. The etch-cleaning process can further include performing a plasma cleaning process after each of the one or more etching steps. The plasma cleaning process can use a plasma that is electronegative.