Mechanism of Etch Stop in High Aspect-Ratio Contact Hole Etching

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Abstract
The mechanism of etch stop in contact hole etching has been studied. It was found that in high aspect ratio holes, even though the incident ions lose charge due to collision with the sidewall, they are able to bombard the bottom of the hole maintaining their high energy. It was also confirmed that the redeposition of sputtered species from the fluorocarbon polymer on the hole sidewall induces the etch stop at the bottom of the high-aspect hole. Furthermore, it was observed that etch stop occurs at higher aspect ratios for the same hole diameter in oxide films with higher boron and phosphorous dopant concentrations. This is explained by the effective removal of etch-inhibiting carbon species due to the release of more oxygen at a higher etch rate in highly doped oxide film. In conclusion, the etch stop in a high-aspect-ratio hole is determined by the balance between the effects of high-energy-species bombardment and etch inhibition of carbon species.