An Electron Microscope Investigation of the Effect of Phosphorous Doping on the Plasma Etching of Polycrystalline Silicon

Abstract

The effects of excess phosphorous on plasma etching of polycrystalline silicon were studied by SEM and TEM. The phosphorous levels were altered by the time duration of POCI~ deposition, by the presence or absence of a phosphosilicate glass layer during high temperature treatments, and by using either an N2 or O~ drive-in anneal thereby causing the snow plow effect of oxidation to locally increase the phosphorous levels. Wherever the phosphorous levels were highest (at the poly-Si free surface or at grain boundaries), the extent of plasma etching was greatest. This etching effect was found to cause poly-Si line edge roughening.* Electrochemical Society Active Member.

Evidence for Free Carrier Dependence of Polysilicon Etch Rate in a Fluorine‐Based Plasma

“…Grain size of polysilicon does not seem to play any significant role, while amorphous silicon shows a higher etch rate. This effect could perhaps explain the results obtained by Irene et al (2), since, in the grain boundary region, which could be modeled as amorphous, etch rate could proceed faster than in the bulk of the grains, giving rise to the observed effects.…”

“…It is well known that polysilicon films that have been heavily doped with phosphorus or arsenic etch faster than undoped ones in halogen plasma (1)(2)(3)(4)(5). There is also evidence that boron doping reduces etch rate, even if the effect is less marked (6).…”

“…Save for the suggestion advanced by Irene et al (2) on the basis of SEM inspection that etch rate is enhanced by dopant segregation at grain boundary, the generally accepted interpretation is that etch rate is controlled by the availability of free electrons in the polysilicon. They play an important role in the chemical adsorption of halogen atoms on the silicon surface, which is the first step of the etching process.…”

Forensic science

“…The reactions of Cu and Fe on silicon dioxide upon heating under vacuum have been studied by XPS (392). The effects of excess phosphorus on plasma etching of polycrystalline silicon were studied by SEM and TEM; where the phosphorus levels were highest, mainly at the polysilicon-free surface and at grain boundaries, the extent of plasma etching was greatest (428). EELS studies of the interface of Si( 100) MOSFETS have been conducted (404).…”