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The spatially resolved surface chemical composition or ‘‘chemical topography’’ of submicron features [polycrystalline silicon (poly-Si) masked with photoresist (PR) lines] etched in high density, low pressure helical resonator Cl2/O2 plasmas has been quantitatively determined using angle resolved x-ray photoelectron spectroscopy (XPS). The chemical topography of plasma etched microelectronic materials is important in understanding how impinging ions and neutrals interact with surfaces to influence etched profiles. The spatial origin of XPS signals was determined from a combination of geometric shadowing of photoelectrons by adjacent features, electrostatic charging of insulating surfaces, XPS signal calibration versus take-off angle, x-ray attenuation, and geometric modeling. Equal line and space width (0.75–2.0 μm) features, unmasked poly-Si, and unpatterned PR surfaces were examined following plasma etching and vacuum sample transfer. For pure Cl2 plasmas, Cl surface concentration was found to be similar for horizontal and vertical surfaces of the poly-Si and PR. Only a small amount of Si was found on the PR sidewall, and similarly, little C or O was observed on the side of the poly-Si features, indicating that sidewall passivation is not occurring. O coverage on all surfaces increased with O2 addition to the plasma. For Cl2/5% O2 plasmas, a small amount of O was found on the poly-Si trench bottom, and more (but still submonolayer) on the poly-Si sidewall. Also, more Cl, O, and Si were found on the PR sidewall with 5% O2. For Cl2/10% O2 plasmas, rough surfaces were observed by scanning electron microscopy (SEM). On poly-Si trench bottoms, O coverage is comparable to Cl at roughly a monolayer. On poly-Si sidewalls, O and Cl coverages are again comparable, but the O coverage is about double that found on the trench bottoms. The most dramatic effect by far at 10% added O2 is the formation of a thick SiOx Cly layer (where x≊y≊1) on the side of the PR, detected by both XPS and SEM. The quantitative analysis method developed in this study is readily applicable to other etching gases and materials.

Quantitative chemical topography of polycrystalline Si anisotropically etched in Cl2/O2 high density plasmas J. Vac. Sci. Technol. B 13, 214 (1995); 10.1116/1.588355Fabrication of xray masks using anisotropic etching of (110) Si and shadowing techniques

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Articles you may be interested inOn the mechanism of laser-induced desorption-ionization of organic compounds from etched silicon and carbon surfaces Competitive halogenation of silicon surfaces in HBr/Cl2 plasmas studied with xray photoelectron spectroscopy and in situ, realtime, pulsed laserinduced thermal desorption A laserinduced fluorescence study of OH desorption from Pt(111) during oxidation of hydrogen in O2 and decomposition of waterWe have used laser-induced thermal desorption, combined with laser-induced fluorescence of SiCI(g) to study, in real time, the Si-chloride (SiClx(ads» layer that is present on the surface during Si etching in a high-plasma density, low pressure Cl 2 helical resonator plasma. The SiClx(ads) layer that builds up during etching contains about twice as much CI as the saturated layer that forms when Si is exposed to Cl 2 gas. By varying the laser repetition rate we determined that the surface is chlorinated with an apparent first-order time constant of -6 ms at 1.0 mTorr, and 20 ms at 0.3 mTorr. Therefore in the plasma at pressures above -0.5 mTorr, the SiClx(ads) layer reaches saturated coverage on a time scale that is short compared to the time required to etch one monolayer (40 ms). From the weak dependence of the SiClx(ads) layer coverage on discharge power (0.2-1 W fcm 3 ), substrate bias voltage (from 0 to -50 V dc), and pressure (0.5-10 mTorr) , we conclude that ion flux, and not neutral etchant flux (i.e., CI and C1 2 ) , limits the etch rate, even in a low pressure, high-charge-density plasma. The chemically enhanced CIt sputtering yield is 0.38 at an ion energy of 50 eV and 0.60 at 125 eV. Because of the relatively low neutral-to-ion flux ratios (-2:1 at the lowest pressures) compared to reactive ion etching conditions, a substantial portion of the chlorine needed to form volatile products can be provided by the impinging ions. The SiClx(ads) layer does not change appreciably «10% decrease in CI coverage) after the plasma is extinguished and the gas is pumped away. Consequently, post-etching surface analysis measurements on samples that are transferred under ultrahigh vacuum to an analysis chamber provide information on the surface as it was during etching. The SiClx(ads) coverage and etch rate decreases with increasing addition of O 2 to C1 2 , due to the competition for adsorption sites by O.