BSI: Advanced DD and AR Coatings
By: Alacron, Inc.
Alacron, Inc., makers of high performance machine vision technology for more than 25 years, now has a back side imaging camera (BSI). Among the many markets and applications that will find Alacron’s new technology useful is the semiconductor industry, where Alacron’s BSI offers better, faster and more financially efficient wafer inspection. Additional markets include medical, aeronautics, military, and other manufacturing industries, wherever spectral extremes such as deep ultraviolet (DUV) and high energy tolerance is needed.
Back side imaging is performed by applying the light to the side opposite the electronic of the sensor. Typically the sensor is thinned so the drift path of the generated photoelectrons is as short as possible.
Alacron’s BSI camera offers the following advantages:
Delta doping is a process by which a large surface potential is created to direct photoelectrons generated at the surface toward the photo diodes of an imaging array. The penetration depth of (UV) photons into silicon is several nanometers. Photoelectrons generated by (UV) photons recombine without propagating to the photo diodes in the absence of passivation because they are trapped near the surface. In addition the photo diodes experience a lateral capture effects in BSI applications, effectively increasing the fill factor to 100% in such applications.
Antireflective (AR) coatings are applied to the sensor to reduce the loss of photons due to reflection of the bare silicon surface. Over fifty percent of the photons usually are lost to reflection in the absence of AR coatings. AR coatings can be designed for specific wave lengths. For example, an AR coating for 263 nm can improve transmission to above 90 percent, and above 80 percent for 193 nm.
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