Tungsten patterning by reactive ion etching has been studied in batch and single‐wafer reactors using photoresist as the etch mask and a chemistry comprised of CHF3/O2with CF2Cl2. Tungsten etch rate and patterned profile were found to depend upon energetic ion levels and reactor loading, as well as on the basic reactor control parameters of power, pressure, and gas composition. Process conditions suitable for fine‐line anisotropic profile formation through a single layer of resist were demonstrated for the low‐pressure batch reactor. At the higher pressure and power density typical of the single‐wafer reactor, multistep processing was required to balance the competing reactions of etch and deposition of ‘‘polymer’’ in order to maintain process control.