Recently, we have developed a new detector structure, which is known as the resonator- QWIP or R-QWIP. With the new structure, we demonstrated quantum efficiency (QE) as high as 70% in single detectors and 30 - 40% in focal plane arrays (FPAs) with 9 μm cutoff. In this study, we designed a broadband, 10 μm cutoff R-QWIP FPA using a more accurate refractive index. To achieve the theoretical prediction, the substrates of the detectors have to be removed completely to prevent the escape of unabsorbed light out of the detectors. The height of the diffractive elements (DE) and the thickness of the active resonator must also be uniformly produced within 0.05 μm accuracy. To achieve these specifications, two optimized inductively coupled plasma (ICP) etching processes are developed. Using these etching techniques, a number of single detectors were fabricated to verify the analysis before FPA production. In general, test data support the theoretical predictions.