Nanometer-Level Alignment Using Interferometric-Spatial-Phase-Imaging (Ispi) During Silicon Nanowire Growth

We describe a method of detecting nanometer-level gap and tip/tilt alignment between a focusing zone plate mask and a silicon substrate using interferometric-spatial-phase-imaging (ISPI). The zone plate mask is used to generate sub-micrometer focused light spot to induce silicon nanowire growth in a CVD process. ISPI makes use of diffracting fringes from gratings and checkerboards fabricated on the mask to determine the correct gapping distance for the focusing zone plates. The method is capable of detecting alignment inside a gas-flow chamber with variable pressure.