We use electron microscopy and x-ray diffraction to study the microstructure of TiN deposited on Al. In contrast to previous work, we show that the TiN has a large (≈1 &mgr;m) grain size arising from its epitaxial orientation on the underlying Al. Within a single grain, the TiN has a heavily voided columnar structure that closely mimics the appearance of fine grains. The within-grain columnar structure arises from the usual shadowing mechanism for sputtered films, and has a weak dependence on the deposition temperature. ©1997 American Institute of Physics.