The present disclosure provides a method of fabricating a semiconductor device. The method includes forming a patternable layer over a substrate. The method includes forming a first layer over the patternable layer. The method includes forming a second layer over the first layer. The second layer is substantially thinner than the first layer. The method includes patterning the second layer with a photoresist material through a first etching process to form a patterned second layer. The method includes patterning the first layer with the patterned second layer through a second etching process to form a patterned first layer. The first and second layers have substantially different etching rates during the second etching process. The method includes patterning the patternable layer with the patterned first layer through a third etching process.