The influence of HBr discharge ambience on SiO2 etching is investigated. A batch type parallel-plate reactive ion etching (RIE) dry etcher was used. The discharge ambience was changed by changing the numbers of poly-Si and SiO2 wafers in the same chamber. It is found that as the number of poly-Si wafers increased, the poly-Si etch rate slightly decreased due to a loading effect and SiO2 etching rate drastically increased. The selectivity of poly-Si / SiO2 decreased with increasing the ratio of the loaded poly-Si number in the same chamber. When A12O3 wafers instead of poly-Si wafers were loaded with SiO2 substrates, SiO2 etching rate enhancement did not occur. Therefore, increase of SiO2 etch rate could not be explained using a loading effect. From the results of mass analysis during etching in Si contained HBr plasma, etching products SiBrx (x=1,2,3) peaks were observed. Namely, when the Si etching products were supplied to SiO2 surface, SiO2 etch rate increased. In order to suppress the enhancement of SiO2 etch rate, the etch temperature must be reduced.