Development of Localized Plasma Etching System for Failure Analyses in Semiconductor Devices: (3)
Etching-Monitoring Using Quadrupole Mass Spectrometry

Abstract

  Quadrupole mass spectrometry (QMS) has been applied to monitor the etching processes in a localized plasma etching system. An inward plasma was employed for etching in which the etching gas was discharged in the narrow gap between the etched sample and the entrance of an evacuating capillary tube. As the etching products are immediately evacuated through the capillary, a QMS system equipped at the capillary exit is able to analyze the products without any loss in concentration via diffusion into the chamber. Two kinds of samples, thermally grown SiO₂ on Si and spin-coated polyimide film on Si, were etched, and the chemical species in the evacuated etching gas were analyzed with QMS, which enables monitoring of the composition of the surface being etched. Samples of thermal SiO₂ were etched with CF₄ plasma. The peak height of the SiF₃⁺ signal during the SiO₂ etching was lower than that observed during etching of the silicon substrate, leading to endpoint detection. The endpoint detection of the polyimide film etching was conducted using two etching gases: pure O₂ and pure CF₄. When O₂ was used, the endpoint was detected by the decrease of the mass peak attributed to CO. When CF₄ was employed, the plasma was able to etch both the polyimide film and Si substrate. Then the endpoint was detected by the increase of the mass peak of SiF₃⁺ produced by the etching of the Si substrate.