After a film layer 6 formed from a die attach film 4 and a UV tape 5 has been provided as a mask on a semiconductor wafer 1, boundary trenches 7 for partitioning semiconductor elements 2 formed on a circuit pattern formation surface 1a are formed in the film layer 6, thereby making a surface 1c of a semiconductor wafer 1 exposed. The exposed surface 1c of the semiconductor wafer 1 in the boundary trenches 7 is etched by means of plasma of a fluorine-based gas, and the semiconductor wafer 1 is sliced into semiconductor chips 1′ along the boundary trenches 7.