A method for manufacturing a semiconductor structure includes etching trenches in a semiconductor substrate to form a semiconductor fin between the trenches; converting sidewalls of the semiconductor fin into hydrogen-terminated surfaces each having silicon-to-hydrogen (S—H) bonds; after converting the sidewalls of the semiconductor fin into the hydrogen-terminated surfaces, depositing a dielectric material overfilling the trenches; and etching back the dielectric material to fall below a top surface of the semiconductor fin.