A method of forming an amorphous carbon layer on a substrate in a substrate processing chamber, includes introducing a hydrocarbon source into the processing chamber, introducing argon, alone or in combination with helium, hydrogen, nitrogen, and combinations thereof, into the processing chamber, wherein the argon has a volumetric flow rate to hydrocarbon source volumetric flow rate ratio of about 10:1 to about 20:1, generating a plasma in the processing chamber at a substantially lower pressure of about 2 Torr to 10 Torr, and forming a conformal amorphous carbon layer on the substrate.