Investigation of High Aspect Ratio Amorphous Carbon Etching in NAND Flash Memory

The amorphous carbon layer (ACL), used as the hard mask for the etching of deep hole in NAND flash memory, was etched using O 2 /SO 2 and pulsed dual-frequency inductively coupled plasma. The oxide mask was gradually collapsed and distorted during the ACL etching due to the high bias power, which can cause poor uniformity and even etching stops. In this paper, a method is proposed to remove the mask above the hole and enlarge the mask space CD, which is good for byproduct to diffuse out and reactants to reach the etch front and then good uniformity and bottom critical dimension controllability are obtained.