Infrared sensors play a critical role in detection, guidance, and targeting in today's military systems and warfighter
equipment, ranging from man-portable to space-borne. Although significant progress is being made in the development
of IR imagers, another important component of IR sensors has not evolved significantly-the optics. Current IR lenses
are primarily made of expensive single-crystal germanium with tedious mechanical fabrication operations that include
grinding, polishing, and edging. There is an industry wide need for lower cost and higher performance IR lenses.
Agiltron has developed a technology to directly mold IR lenses to net-shape without additional finishing operations.
This manufacturing technology produces optics with many-fold reductions in cost, size, weight, and fabrication time.
The ability to reproducibly manufacture aspheric optics with complex net-shapes reduces the number of lenses
traditionally required for imaging systems, providing aberration correction as well as system weight and size reductions.
Additionally, anti-reflective surfaces can be molded into the glass, eliminating the need for expensive AR coatings. This
technology utilizes a new chalcogenide glass material that reduces temperature induced index of refraction changes to
near zero, and has a thermal expansion coefficient similar to aluminum. The result is a new generation of low cost, high
performance and thermally robust IR lens systems.
As the demand for mid wavelength infrared (MWIR) focal plane arrays (FPAs) continues to increase, the quality of InSb
surfaces becomes more stringent. State-of-the art InSb contains <20 etch pits/cm2 (EPD), and provides a surface suitable
for rapid oxide desorption and high quality MBE growth. In order to satisfy resolution and sensitivity requirements for
advanced MWIR FPA imaging systems ( 1 to 5.4 μm region @77°K), the surface and sub-surface of the material must
be of excellent quality. CMP has proven to be a qualified finishing process for InSb surfaces in the fabrication of
IRFPAs. However, a time consuming surface etch is universally required in the IRFPA manufacturing process. Gas
cluster ion beam processing (GCIB) has been shown to significantly enhance the surface oxide desorption of both GaSb
and InSb substrates for MBE growth and provides an alternate surface finish for IRFPA manufacturing. The use of GCIB
may preclude the need for surface etching, thus reducing IRFPA processing time and chemical cleanup. This study
examines the comparison of CMP and GCIB finishes on InSb surfaces and the effect on final IRFPA device pass rates.
NF3/O2 dual energy GCIB surface processing was used in this study. Atomic force microscopy (AFM), cross-section
transmission electron microscopy (XTEM), and rocking curve x-ray diffraction (XRD) examine the surface and subsurface InSb integrity. A comparison of pass-rates for completed IRFPAs with the CMP and GCIB surface shows the pass-rate to be the same, opening the possibility for etch step elimination.
The surfaces of single-crystal wafers of sapphire and silicon carbide with microelectronic-grade high polish were exposed to a gas-cluster ion beam (GCIB) and significant reductions in roughness were observed. Atomic-force microscopy revealed that the typical initial surfaces consisted of a fine but small random roughness together with relatively large and sharp asperities. The latter were removed efficiently and GCIB smoothing process improvements are reported. The SiC wafers also have a high density of shallow scratch marks and these too were removed, with the average roughness Ra falling below 4 angstrom after the best process. Analysis of the SiC by Rutherford backscattering spectroscopy in channeling mode revealed that when the GCIB process was adjusted so that asperities and scratch marks were removed, there was no increase in near- and at-surface damage. In particular, no lattice damage was observed of the sort typically caused by ion implantation prior to annealing. Significantly, it was found that oxygen gas cluster ion beams provided superior results with SiC as compared with argon GCIB. Surface smoothing mechanisms are proposed to explain these results.
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