Embodiments described herein relate to materials and processes for patterning and etching features in a semiconductor substrate. In one embodiment, a method of forming a composite amorphous carbon layer for improved stack defectivity on a substrate is provided. The method comprises positioning a substrate in a process chamber, introducing a hydrocarbon source gas into the process chamber, introducing a diluent source gas into the process chamber, introducing a plasma-initiating gas into the process chamber, generating a plasma in the process chamber, forming an amorphous carbon initiation layer on the substrate, wherein the hydrocarbon source gas has a volumetric flow rate to diluent source gas flow rate ratio of 1:12 or less; and forming a bulk amorphous carbon layer on the amorphous carbon initiation layer, wherein a hydrocarbon source gas used to form the bulk amorphous carbon layer has a volumetric flow rate to a diluent source gas flow rate of 1:6 or greater to form the composite amorphous carbon layer.