Provided are a substrate film and a method of manufacturing the substrate film. The substrate film may have excellent thermal resistance and dimensional stability, has excellent stress relaxation to prevent damage of a wafer caused by remaining stress, inhibits damage to or flying-off of the wafer caused by application of a non-uniform pressure during the processing of the wafer, and has excellent cuttability. Accordingly, the substrate film of the present invention can be effectively used as a processing sheet in a process of processing various kinds of wafers including dicing, back-grinding or picking-up.