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Atomic layer sensitive in-situ plasma etch depth control with reflectance anisotropy spectroscopy (RAS)
Author(s): Christoph Doering; Ann-Kathrin Kleinschmidt; Lars Barzen; Johannes Strassner; Henning Fouckhardt
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Paper Abstract

Reflectance anisotropy spectroscopy (RAS) allows for in-situ monitoring of reactive ion etching (RIE) of monocrystalline III-V semiconductor surfaces. Upon use of RAS the sample to be etched is illuminated with broad-band linearly polarized light under nearly normal incidence. Commonly the spectral range is between 1.5 and 5.5 eV. Typically the spectrally resolved difference in reflectivity for light of two orthogonal linear polarizations of light is measured with respect to time - for example for cubic lattices (like the zinc blende structures of most III-V semiconductors) polarizations along the [110] and the [-110] direction. Local anisotropies on the etch front cause elliptical polarization of the reflected light resulting in the RAS signal. The time and photon energy resolved spectra of RAS include reflectometric as well as interferometric information. Light with wavelengths well above 100 nm (even inside the material) can be successfully used to monitor surface abrasion with a resolution of some tens of nanometers. The layers being thinned out act as optical interferometers resulting in Fabry-Perot oscillations of the RAS-signal. Here we report on RAS measurements assessing the surface deconstruction during dry etching. For low etch rates our experimental data show even better resolution than that of the (slow) Fabry-Perot oscillations. For certain photon energies we detect monolayer-etch-related oscillations in the mean reflectivity, which give the best possible resolution in etch depth monitoring and control, i.e. the atomic scale.

Paper Details

Date Published: 26 June 2017
PDF: 6 pages
Proc. SPIE 10329, Optical Measurement Systems for Industrial Inspection X, 1032911 (26 June 2017); doi: 10.1117/12.2269708
Show Author Affiliations
Christoph Doering, Technische Univ. Kaiserslautern (Germany)
Ann-Kathrin Kleinschmidt, Technische Univ. Kaiserslautern (Germany)
Lars Barzen, Technische Univ. Kaiserslautern (Germany)
Johannes Strassner, Technische Univ. Kaiserslautern (Germany)
Henning Fouckhardt, Technische Univ. Kaiserslautern (Germany)


Published in SPIE Proceedings Vol. 10329:
Optical Measurement Systems for Industrial Inspection X
Peter Lehmann; Wolfgang Osten; Armando Albertazzi Gonçalves, Editor(s)

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