In nanoimprint template fabrication, the profile of the template features plays a significant role in the profile, release properties, and CD of the imprinted features. We present a study of profile evolution of nanopatterned Si etching for the fabrication of Si nanoimprint templates using a thin Cr hard mask and an HBr inductively coupled plasma (ICP). In this work, we show the effects of chamber pressure, line spacing, mask selectivity, and mask shape on the bowing, notching, microtrenching, and etching rate of nanopatterned silicon for pressures in the range of 2-10 mTorr for line sizes between 20 and 100 nm (1:1 line to space ratio). We observed that, for features with sizes below 50 nm, increasing pressure leads to positively sloped sidewalls and microtrenching. At lower pressures, lower etching rates are observed-together with poorer selectivity and mask faceting. Furthermore, we see a tendency for aspect ratio dependent etching (ARDE) or reactive ion etching (RIE) lag at low pressures. Unlike RIE reactors, dc bias in our ICP etcher decreases with decreasing pressure and constant electrode and ICP power. This suggests that neutral shadowing is the mechanism responsible for ARDE. Under constant power and temperature conditions, due to counterbalancing pressure effects between 2 and 10 mTorr, we obtain optimum imprint profiles at an intermediate pressure of 5 mTorr. (c) 2005 American. Vacuum Society.