Metrology Feasibility Study in Support of the National Direct-Drive Program

The 100-Gbar Laser Direct Drive program calls for ablator capsules with no defects larger than 0.5 mu m in lateral dimension and fewer than ten defects with lateral dimensions between 0.1 and 0.5 mu m. Compared to laser indirect drive capsules, this represents > 10x reduction of defect length scale and > 500x reduction in defect number density. This presents major challenges to both fabrication and metrology. In this paper, we will discuss the proof-of-principle work conducted at General Atomics to identify metrology techniques suitable for 100-Gbar target characterization. We present a detailed study of dark-field imaging, laser scatterometry, and environmental scanning electron microscopey. We identify dark-field imaging as the best approach for meeting the 100-Gbar metrology needs.