POLYSILICON GATE ETCHING IN HIGH-DENSITY PLASMAS .2. X-RAY PHOTOELECTRON-SPECTROSCOPY INVESTIGATION OF SILICON TRENCHES ETCHED USING A CHLORINE-BASED CHEMISTRY

We have used x-ray photoelectron spectroscopy (XPS) to study the chemi cal constituents present on the surfaces after etching of poly-Si feat ures masked with photoresist. Poly-Si etch rates were determined using in sial HeNe laser ellipsometry. The wafers were etched in a low pres sure, high density plasma, helicon source using a chlorine/helium gas mixture. The XPS analysis chamber is connected to the reactor chamber via an ultrahigh vacuum chamber allowing quasi in situ analysis of the etched samples. Electrostatic charging of insulating surfaces and geo metric shadowing of photoelectrons by adjacent photoresist lines have been used to differentiate photoemission signals from the tops, sidewa lls, and bottoms of the features. Blanket and photoresist masked poly- Si samples were etched without biasing the substrate. The poly-Si etch rate decreased as a function of etching time and finally stopped due to the deposition of an oxide film. When biasing the sample, etching o ccurred and anisotropic etching profiles could be obtained. A thin oxi de film was found on the sidewalls of the photoresist and poly-Si afte r etching. The thickness of the oxide film increased with etching time . No silicon was found on top of the photoresist. The silicon oxide fi lm deposited on the surfaces resulted from the sputtering of the quart z tube located in the plasma generation region. Substantial amounts of chlorine were found on the tops, sidewalls and bottoms of the feature s. The chlorine concentrations on the sidewalls of the features etched at high bias power were comparable to those found on the horizontal s urfaces when a low bias power was applied. The chlorine concentrations on the tops and bottoms of the features increased with increasing bia s power. A low coverage of oxygen was found on all surfaces. The oxyge n concentration on the sidewalls of the features also increased with e tching time. Less oxygen was found on the bottom of the poly-Si trench es. Small amounts of carbon were detected on the bottoms of the featur es. A substantial coverage of carbon was present on the poly-Si sidewa lls and was about half that found on the tops and sidewalls of the pho toresist. These results indicate that the etching of the photoresist a nd the erosion of the quartz tube may enhance anisotropic etching. (C) 1996 American Vacuum Society.