PROCEEDINGS ARTICLE | February 15, 2012
Proc. SPIE. 8298, Sensors, Cameras, and Systems for Industrial and Scientific Applications XIII
KEYWORDS: Wafer-level optics, Antireflective coatings, Polishing, Silica, Silicon, Sapphire, Transmittance, Back illuminated sensors, Semiconducting wafers, Wafer bonding
There is a growing need in scientific and industrial applications for dual-mode, passive and active 2D and 3D LADAR
imaging methods. To fill this need, solid-state, single photon sensitive silicon avalanche photodiode (APD) detector
arrays offer high sensitivity and the possibility to operate with wide dynamic range in dual linear and Geiger-mode for
passive and active imaging. To support the fabrication of large scale, high quantum efficiency and high resolution
silicon avalanche photodiode arrays and other advanced solid-state optoelectronics, a novel, high transmittance, backilluminated
silicon-on-sapphire substrate has been developed incorporating a single crystal, epitaxially grown aluminum
nitride (AlN) antireflective layer between silicon and R-plane sapphire, that provides refractive index matching to
improve the optical transmittance into silicon from sapphire. A one quarter wavelength magnesium fluoride
antireflective layer deposited on the back-side of the sapphire improves optical transmittance from the ambient into the
sapphire. The magnesium fluoride plane of the Si-(AlN)-sapphire substrate is bonded to a fused silica wafer that
provides mechanical support, allowing the sapphire to be thinned below 25 micrometers to improve back-illuminated
optical transmittance, while suppressing indirect optical crosstalk from APD emitted light undergoing reflections in the
sapphire, to enable high quantum efficiency and high resolution detector arrays.
