An analytical study of etch and etch-stop reactions for GaAs on AlGaAs in CCl2F2 plasma

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Abstract
We have studied selective reactive ion etching of GaAs on AlGaAs in CCl2F2 plasma in situ by optical emission spectroscopy and mass spectrometry and have analyzed etched surfaces, before and after air exposure, by x‐ray photoelectron spectroscopy. Data from etching GaAs samples indicate that volatile arsenic fluorides, chlorides and fluorochlorides, and gallium chlorides are the products formed, leaving a stoichiometric GaAs surface with adsorbed F and Cl for the particular plasma conditions we used. Data from samples etched to AlGaAs, where the etching process stops, demonstrate that the stopping is due to formation of nonvolatile AlF3 and GaClxFy, leaving a surface nearly depleted of arsenic. This etch‐stop ‘‘layer’’ is between 4 and 10 monolayers in thickness. After air exposure this surface consists of gallium and aluminum oxides and a small percentage of arsenic oxide with about the same quantities of Ga, Al, and As as on the surface before exposure to air. This differs from a wet‐etched (in dilute ammonium hydroxide and hydrogen peroxide), air‐exposed AlGaAs surface for which the composition is rich in arsenic oxide.

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