A novel gradient composition spreading and nanolayer stacking process for combinatorial thin-film materials library fabrication

A novel magnetron sputtering process is proposed to fabricate a combinatorial thin-film materials library with highly precise composition spreading. In order to produce a gradient composition spreading for a specific target, a moving shutter is used to cover the deposition substrate step by step with a fixed step-length. By rotating the substrate and repeating the step-by-step masked deposition with different targets in turn, a heterogeneous precursor structure is obtained with alternate stacking of different material layers, each of which is in a step-by-step wedge-shaped thickness cross section. By controlling the thickness of each layer at the nanometer scale, a multilayer structure is formed to facilitate the interlayer diffusion between different precursor layers. It may also define the boundaries of individual sample pixels, resulting in improved composition spreading resolutions for the prepared materials library. A combinatorial magnetron sputtering system is designed with reciprocating rectangular targets, a narrow slit between the substrate and the target, and a quartz crystal microbalance feedback to control the deposition uniformity, resulting in a variation better than 3% across a 76 x 76 mm substrate. Three individual deposition chambers are designed in an annular distribution with 90 degrees angle between each other. Moreover, a step-by-step moving shutter and a rotating substrate holder are incorporated. Combinatorial materials libraries with more than 10 000 individual compositions could be obtained using this system. A Ti-Zr-Ni ternary alloy library was fabricated for demonstration in which the sheet resistance spreading diagram of the Ti-Zr-Ni library was studied as a function of the composition.