The Controlled Etching of Silicon in Catalyzed Ethylenediamine-Pyrocatechol-Water Solutions

Abstract

The etching of single crystal silicon in ethylenediamine-pyrocatecholwater solutions (EPW) has been examined as a function of gross and trace contaminant concentrations, etching bath design, bath silicon content, and oxygen exposure in the temperature interval from 50°-119°C. It has been found that trace quantities of 1,4- and 1,2-diazine catalyze the etch rate on (100) surfaces dramatically while affecting (111) etch rate to a lesser extent. This results in a (100)/(111) anisotropy ratio increase from 13.5, in the absence of pyrazine, to about 19 in the 5g pyrazine/liter ethylenediamine range at 115°C. Coincident with this effect, there is a decrease in the apparent activation energy of etching from 10.8 to 8.4 kcal/mole, making the solution less temperature sensitive. In addition, surface morphology improves with addition of the catalyst. EPW solutions are subject to residue formation in many composition-temperature intervals, and conditions necessary to avoid this undesirable side effect have been defined. Oxygen contamination of EPW solutions also increases silicon etch rate significantly, and this effect appears to be due to the formation of 1,4-benzoquinone which also functions as a catalyst. It has been found, however, that EPW solutions containing 1,4-diazine (pyrazine) are relatively oxygen stable and residue free and can be employed as controlled etchants for single and polycrystalline silicon over the temperature range from 50°-119°C. Two specific quaternary concentrations have been defined for use where (i) high etch rate processes are required, “F” etch, and (ii) where slower removal rates and/or lower etching temperatures are desired, “S” etch. © 1979, The Electrochemical Society, Inc. All rights reserved.