An isotropic deposition method for trench narrowing of thin film magnetic write head features to be created by reactive ion etching. According to the method, a photolithographically defined photoresist trench is formed over a hardmask and underlying polymer layer as part of tri-layer resist process. Instead of performing the usual hardmask and polymer etching steps using the photoresist mask pattern, a spacer layer is deposited isotropically or directionally at an angle to cover the vertical side walls of the trench. The spacer layer is etchable by the hardmask etch process but resistant to the polymer etch process. When the hardmask etch process is performed, the spacer layer material applied to the trench side walls remains intact, thereby defining a narrowed trench that is extended by the subsequent base layer etch process.