Nature 485, 221–224 (2012)

The difference in chemical composition between a substrate and a deposited thin film creates intrinsic stress, which stores a certain amount of potential energy at the interface. In many cases this could be a source of unwanted cracking and material failure. However, Koo Hyun Nam, Il Park and Seung Hwan Ko have now harnessed this energy to produce controlled patterns in a silicon nitride thin film deposited on a silicon wafer.

The researchers — who are based at Ewha Womans University and KAIST — etched a micrometre-scale notch on the silicon substrate that concentrates local stress at its tip and initiates a crack as the thin film is deposited on top. The crack, which is typically deep enough to encompass both materials, propagates in a direction that depends on the crystal orientation of the substrate and can travel to the end of the silicon wafer. As a result, the Korean team also devised a stopping structure that absorbs the excess energy and allows the position that the crack stops at to be controlled. The cracks, which can either be wavy or straight depending on operating conditions, are about 10 to 100 nm wide.

Because crack propagation is a self-sustained process, the approach could perhaps provide an alternative to existing lithographic techniques for large-area patterning.