Study on self-aligned contact oxide etching using $C5F8∕O2∕Ar$ and $C5F8∕O2∕Ar∕CH2F2$ plasma

A self-aligned contact (SAC) technology is developed for the application of electrical contacts between the local interconnection and the silicon diffusion regions (or plug pad) from a $0.18μm$ device. Commercial memory devices have capping (or spacers) nitride $(Si3N4)$ for protection of Word Line (or Bit Line) and a thin nitride film layer for the SAC etch to stop on. The main problems with SAC etch processes in ULSI devices of sub-$0.1-μm$-design rule are low selectivity to nitride and etching-stop due to high aspect ratio of the contact hole. The key for a successful SAC etch process is control of polymer generation. In this study, the SAC oxide etch will be characterized by $C5F8∕O2∕Ar$ and $C5F8∕O2∕Ar∕CH2F2$ plasmas. As the ratio of $O2$ increases in the $C5F8∕Ar∕O2$ mixture, the amount of polymer decreases and the ability of contact etching increases. The effect of the $CH2F2$ addition to SAC oxide etching in $C5F8∕Ar∕O2$ is the selectivity of oxide to nitride, especially to that of nitride contact bottom for SAC etch stopping, increases. The selectivity of oxide to nitride increases with increasing plasma source power or with decreasing bias power. SAC patterned wafers were characterized using top-down critical dimension scanning electron microscopy (CD-SEM) and transmission electron microscopy (TEM). To analyze the effect of the addition of $CH2F2$ gas to $C5F8∕O2∕Ar$ plasmas, we investigated the chemical species in the gas phase with optical emission spectroscopy (OES). The components and thickness of the fluorocarbon polymer on the contact surface, bottom and sidewall were investigated with transmission electron microscopy, and x-ray photoelectron spectroscopy.