(100) Silicon Etch‐Rate Dependence on Boron Concentration in Ethylenediamine‐Pyrocatechol‐Water Solutions

The (100) silicon etch‐rate dependence on boron concentration in ethylenediamine‐pyrocatechol‐water (EPW) solutions at 110°C has been measured by successive etching of boron‐diffused silicon. The etch rate begins to decrease near 1019cm−3and decreases approximately as the fourth power of doping over three orders of magnitude in etch rate. The etch‐rate ratio between heavily and lightly doped silicon appears insensitive to pyrazine concentration from 0.01 to 6.0g/liter E, oxygen exposure of the etch solution, and light. The etch‐rate decrease is sensitive to hole concentration and not to atomic concentration of boron or stress. The etch‐rate dependence may be explained by assuming that the hydrogen‐evolution cathodic half‐reaction of the oxidation‐reduction reaction is the rate‐determining step. The reason for the etch‐rate decrease as the hole concentration increases is given in terms of increased Auger recombination of large numbers of electrons chemically produced at the silicon surface during etching. Excellent agreement with experiment is obtained. Similarities of this etch system and the phenomenon of silicon staining are discussed in terms of oxidation‐reduction reactions. Application to control of thickness and uniformity of boron‐doped silicon membranes is discussed.