Etching Rate and Mechanism of Doped Oxide in Buffered Hydrogen Fluoride Solution

Etching rates of borosilicate, borophosphosilicate, phosphosilicate, and arsenosilicate glass films in various buffered hydrogen fluoride solution (BHF) have been studied. Etching rates were found to depend on the glass composition and dopant concentration as well as the concentration of ammonium fluoride in the BHF. This phenomenon is clearly different from the etching rate of thermal oxide which is hardly affected by the concentration of ammonium fluoride in excess of equimolar to the concentration. The etching rates of the doped films may sometimes be higher than that of a nondoped film but the rate is reduced when certain other dopants are present. This phenomenon is attributable to valence differences between silicon and the dopant elements. If the doped film is electrophilic compared to silicon, the etching rate is higher; if it is nucleophilic, the etching rate is lower. By controlling the type and concentration of the dopant and the concentration of in BHF, it is possible to etch the doped film and thermal oxide at either the same rate or selectivity with respect to one another.