Surface Chemistry of GaAs(100) after Treatment with Aqueous H 3 PO 4 Solution
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SURFACE CHEMISTRY OF GaAs(100) AFTER TREATMENT WITH AQUEOUS H 3PO 4 SOLUTION V. A. BURROWS AND V. S. G. KONDAPURAM Arizona State University, Dept. of Chemical, Bio, and Materials Engineering and Center for Solid State Electronics Research, Tempe, AZ 85287-6006 ABSTRACT The interaction of semiconductor surfaces with aqueous acid solutions is important in chemical cleaning and etching. Wet chemical treatments are advantageous because they cause little damage to the surface and do not usually require high temperatures. The surface chemistry of GaAs after treatment with phosphoric acid was studied using multiple internal reflection infrared spectroscopy. The treatment left behind a thin film containing several types of PxOy bonds. The chemical nature of the film was observed to change with time as new species would form on the surface. INTRODUCTION Although gas-phase methods are replacing liquid based processes for cleaning and etching of semiconductors, liquid based methods still enjoy extensive use in stripping and cleaning operations. Ideally, any surface chemical process would remove only undesired material, and leave behind a surface chemically and morphologically compatible with subsequent processing steps and which has the desired electronic properties. Though some nearly ideal liquid-based processes exist for cleaning of silicon, processes for GaAs are much less well-developed. In addition, most liquid based methods have been developed with little knowledge of the underlying chemistry. As a result, the success of such processing is unpredictable, and dependent upon apparently obscure details of the process recipe. For example, treatment of GaAs with buffered hydrofluoric acid has been shown [1] to leave behind a residue of ammonium fluorides which reacts with the surface to form ammonium hexafluorometallates if the treatment is not followed by an immediate thorough water rinse. Surface infrared spectroscopy is a low energy photonic technique which has been implemented in numerous studies, primarily for investigating adsorption and reaction at metal surfaces but has been finding increased use as a probe for semiconductor surface chemistry. In this study GaAs(100) was treated with 50% H 3 PO 4 solution and a time dependent surface infrared study was performed. EXPERIMENTAL DETAILS Surface infrared spectroscopy in the multiple internal reflection mode was used to investigate the surface chemistry of GaAs after treatment with
Mat. Res. Soc. Symp. Proc. Vol. 282. 01993 Materials Research Society
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aqueous phosphoric acid solution. The semi-insulating (100)- oriented GaAs sample was polished on both faces and cut to 4 cm x 2 cm x 0.5 mm. The 2 cm edges were beveled to 45" in the form of a parallelogram prism. Modulated infrared light supplied by a Nicolet 60SX FTIR spectrometer was focused onto one beveled edge. It entered into the sample, reflected multiple times from the sample faces, exited from the other beveled edge, and was focused onto a liquid nitrogen-cooled HgCdTe detector. Each spectrum was signal av
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