A method for making a perpendicular magnetic recording write head that has a write pole, a trapezoidal-shaped trailing shield notch, and a gap between the write pole and notch uses a reactive ion beam etching (RIBE) process in CHF3 that removes filler material at the side edges of the write pole and thus widens the opening at the side edges. The gap is formed of a nonmagnetic mask film, such as alumina, a nonmagnetic metal protective film and a nonmagnetic gap layer. The nonmagnetic metal film is substantially less reactive to CHF3 than the filler material and protects the underlying mask film and write pole during the widening of the opening. The gap layer and trailing shield notch are deposited into a widened opening above the write pole, so the sides of the notch diverge to cause the generally trapezoidal shape.