Patterning by controlled cracking

Abstract

Crack formation drives material failure and is often regarded as a process to be avoided(1-3). However, closer examination of cracking phenomena has revealed exquisitely intricate patterns such as spirals(4), oscillating(5,6,7) and branched(7) fracture paths and fractal geometries(8). Here we demonstrate the controlled initiation, propagation and termination of a variety of channelled crack patterns in a film/substrate system(9-11) comprising a silicon nitride thin film deposited on a silicon substrate using low-pressure chemical vapour deposition. Micro-notches etched into the silicon substrate concentrated stress for crack initiation, which occurred spontaneously during deposition of the silicon nitride layer. We reproducibly created three distinct crack morphologies-straight, oscillatory and orderly bifurcated (stitchlike)-through careful selection of processing conditions and parameters. We induced direction changes by changing the system parameters, and we terminated propagation at preformed multi-step crack stops. We believe that our patterning technique presents new opportunities in nanofabrication and offers a starting point for atomic-scale pattern formation(12), which would be difficult even with current state-of-the-art nanofabrication methodologies.