Reaction products of organosilane compounds or polydiphenylsilazane compounds and a novolac resin having phenolic groups can be used as O.sub.2 RIE barrier materials in semiconductor etching processes. These materials have low O.sub.2 etch rates and can be spun on to form crack-free thick layers. Particular RIE barrier materials contemplated have the general formula: ##STR1## wherein A is a methyl or phenyl group.