In one embodiment in which a technology which is capable of reducing voids that can occur when burying an insulating film into a trench while suppressing process complication, a method MT for processing a wafer W is provided. The wafer W has a groove 62 formed on the main surface 61 of the wafer W. The method MT includes: step S1 of accommodating the wafer W in a processing chamber 4 of a plasma processing apparatus 10; step S2 of starting supplying a first gas into the processing chamber 4; step S3 of starting supplying plasma generation high-frequency power into the processing chamber 4; and step S4 of starting intermittent supplying a second gas into the processing chamber 4 and starting supplying a third gas into the processing chamber 4 together, the first gas is a nitrogen-containing gas, the second gas is a gas that does not contain halogen, and the third gas is a gas that contains halogen.