Chemical topography of anisotropic etching of polycrystalline Si masked with photoresist

The chemical constituents present on the surface of small poly-Si features that were etched in a chlorine plasma were determined. Poly-Si films on SiO2-covered Si(100) substrates were masked with photoresist stripes and then etched downstream from a helical resonator, high-density plasma source. rf biasing of the sample provided low-energy ion bombardment to enhance anisotropic etching. These conditions match those in high-density plasma sources that are currently being developed elsewhere for commercial use. After etching, samples were transferred under ultrahigh vacuum to an analysis chamber equipped with an x-ray photoelectron spectrometer. Shadowing of photoelectrons by adjacent etched stripes was used to determine the chemical constituents on the tops, sides, and bottoms of etched features. Monolayer coverages of Cl and SiO2 were found on the sides of the photoresist mask, while the top of the mask was covered with a monolayer of Cl, and no Si was detected. The Si on the side of the mask was deposited as a result of the slight etching of the glass tubing in the plasma source region. The etched poly-Si trench bottoms are also covered with Cl, at levels comparable to those found in unmasked regions that were subjected to equal amounts of ion bombardment. However, a relatively small amount of Cl covers the sides of the etched poly-Si features. A low coverage of O was also found on all exposed poly-Si surfaces, and is also due to etching of the glass tubing. The O coverage was small compared to Cl on horizontal poly-Si surfaces, but comparable to Cl on the side of the poly-Si features. Very little C was detected on etched poly-Si sidewall surfaces, indicating that erosion of the photoresist plays no role in passivating etched sidewalls.