Pattern transfer in x-ray mask absorbers is often accomplished by reactively etching in chlorine containing plasmas. In this article, we show that the etch rate of one such absorber, TaSi, is a strong function of substrate temperature. We also show that the etch rate Versus temperature behavior of TaSi is a result of the Ta in the film. Hence, other Ta based absorbers (Ta, Ta4B, TaGe, etc.) may also exhibit a similar behavior. We use finite element modeling to demonstrate that under cei-tain conditions, significant temperature variations can exist on a National Institute Standards and Technology (NIST) x-ray mask which in turn can;lead to etch rate variations. We also present experimental verification of these modeling results. Finally, through modeling, we discuss the effect of this etch rate variation on the pattern placement accuracy of NIST x-ray masks.