UV Laser Annealing Effect on Mechanical Properties of Boron Doped Amorphous Carbon Films As Hardmasks

Abstract

The hard forms of amorphous carbon (a-C, diamond like carbon) include hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon have raised interest as coating materials. Recently, boron doped amorphous carbon films have been studied as hardmask materials. The hardmasks are utilized to fabricate advanced semiconductor devices, including dynamic random access memory (DRAM) and vertical NAND flash memory. As decreasing of feature sizes on DRAM and NAND, the hardmask materials need to exhibit a high etch selectivity with low internal stress and good mechanical strength. In this work, we have prepared boron doped amorphous carbon film deposited with the fixed B2H6 flow rate as a function of the process temperature using plasma enhanced chemical vapor deposition (PECVD). Boron has been widely known efficient dopant for passivating the oxidation of various carbon materials. We investigated the physical and optical properties of film with the refractive index, hardness and chemical bonding configuration. Especially, the effect of ultraviolet (UV) laser annealing on the hardness was studied using nano-indentation. UV annealing caused a change of chemical bonding configuration, i.e., sp2/sp3 bonding ratio and C-H bonds, through analysis of the Fourier transform-infrared (FT-IR) and RAMAN spectrum. UV annealed boron doped amorphous carbon thin films exhibited an enhanced hardness, which leads to high etch selectivity. Our results could provide a route to high etch selective hardmask materials development.