THE DEPENDENCE OF SILICON ETCHING ON AN APPLIED DC POTENTIAL IN CF4 + O2 PLASMAS

A copper rod which is biased by a dc potential, V//S, is placed in CF//4 plus O//2 plasmas. The etch rate of a (100) silicon wafer placed on the rod is measured as a function of V//S at various O//2 contents. At the 45% O//2 content, there are plenty of F and O atoms, and a relatively high value of V//S is necessary to enhance the etch rate. At the 10% O//2 content, the density of O atoms decreases remarkably, and the etch rate is enhanced with a low value of V//S. This difference can be interpreted by reference to the O atom adsorption on a silicon surface. The silicon etching of F atoms is enhanced effectively by incident ions with low energy, but incident ions with relatively high energy are necessary to remove adsorbed O atoms. At oxygen-free content with a silicon load on the anode, the numbers of F and O atoms are small, and the enhancement of the etch rate by incident ions is not large, even when V//S increases.