Abstract: Provided is a method for improving the inhibiting characteristics in the upper portion of the gap. In one embodiment of the disclosure, a first inhibitor and a second inhibitor are supplied, therefore more inhibiting radicals may be generated and remove more reaction activation sites from the upper portion of the gap and improve the inhibiting characteristics in the upper portion compared to in the lower portion. The substrate processing method of the disclosure may facilitate further filling the gap with negative slope and complex structure.