Mask Dependent Etch Rates II: The Effect of Aluminum vs. Photoresist Masking on the Etch Rates of Silicon and Silicon Dioxide in Fluorine Containing Plasmas

Plasma etch rates of silicon and silicon dioxide when masked with photoresist and aluminum are compared. It was observed that the aluminum masked silicon had an enhanced etch rate relative to photoresist masking with a variety of fluorocarbon (, , and ) and nonfluorocarbon ( and ) containing etch gases. It is also shown that the aluminum masked silicon dioxide etch rate is depressed relative to that of photoresist masked but that this effect is limited to the fluorocarbon etch gases. It is shown that the aluminum mask is responsible for affecting the etch rates and not the photoresist mask. Evidence is presented that favors a mechanism by which excess fluorine radicals are catalytically produced at the aluminum mask surface. The relative amount of silicon etch rate enhancement is strongly linked to the oxygen concentration present in the etch gas mixture. This is consistent with a competition between fluorine and oxygen for reaction with and attachment to the aluminum surface. It is postulated that is a catalyst for fluorine production and is not.