Reaction products in synchrotron radiation induced dry etching of Ga and Cu

Light induced dry etching using synchrotron radiation (SR) in the VUV range and chlorine as etching gas has been applied to metals (Cu) and semiconductors (GaAs). High quality replica of a mask are etched by irradiation with filtered radiation and the reaction products are analyzed by depth dependent Auger spectroscopy (ADP). For Cu, etching leads to thick CuClx product layers which originate from light induced reactions at the interface between chemisorbed chlorine and the product layer combined with a diffusion of Cu from the substrate to this interface which is attributed to an electrostatic potential perpendicular to the films (Cabrera–Mott mechanism). The anisotropy of etching is preserved despite a transport of Cu through a product layer of about 16 μm. The reaction products swell in volume by nearly a factor of two due to the Cl intake. For GaAs etched with Cl2 the product layer itself consists exclusively of Ga. The thickness of the product layer is restricted to about 1 μm, different to the Cu/Cl2 system. The reaction proceeds again at the interface between chemisorbed chlorine and product layer and is limited by the transport of As. This transport of As (alone or together with Ga) follows a Cabrera–Mott mechanism. During etching As reacts completely with the Cl and forms AsClx. All AsClx molecules are volatile and desorb while Ga sticks.