Design and simulation of permissible tolerance during fabrication of infrared-induced transmission filters

The design and simulated performance characteristics of narrow band-induced transmission infrared filters in the wavelength range of 2000 to 4500 nm are presented, These dielectric-spacer-metal-spacer-dielectric (D-S-M-S-D) filter structures are composed of Si as high index dielectric (D) and Al₂O₃ as low index dielectric (D) or spacer (S) and Al as the metal (M). Typically, a total of 10, 12, or 13 layers are required with an aluminum layer in the middle of the filter stack. The bandwidth of these filters is in the range of 20 to 25 nm. Rejection of these filters in the long wavelength range is very good. The effect of thickness errors on the performance of filters has been analyzed. Based on the numerical simulation of an actual fabrication process, the permissible tolerance for process monitoring is investigated. Numerical simulations show that a high production yield may be obtained if the reflectance errors are kept within ±0.1% during process monitoring in the manufacture of these filters.