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

Abstract

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.