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17 May 2010 PIN photodiodes with significantly improved responsivities implemented in a 0.35µm CMOS/BiCMOS technology
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Abstract
We report on monolithically integrated PIN photodiodes whose responsivity values could be significantly enhanced over the whole spectral range by the implementation of a Bottom Antireflective Coating (BARC) process module into austriamicrosystems 0.35μm CMOS as well as high-speed SiGe BiCMOS technologies. The resulting photodiodes achieve excellent responsivities together with low capacitances and high bandwidths. We processed finger-photodiodes with interdigitated n+ cathodes, which are especially sensitive at low wavelengths, and photodiodes with full area n+ cathodes on very lightly p-doped start material. We present a method of depositing an antireflective layer directly upon the Si surface of the photodiode by changing the standard process flow as little as possible. With just one additional mask alignment and a well controlled etch procedure we manage to remove the thick intermetal oxide and passivation nitride stack over the photodiodes completely without damaging the Si surface. The following deposition of a CVD Silicon Nitride BARC layer not only minimizes the reflected fraction of the optical power but also acts as passivation layer for the photodiodes. Another benefit of BARC processing is the fact that in-wafer and wafer-to-wafer quantum efficiency variations can be dramatically reduced. In our experiments we deposited BARC layers of different thicknesses that were optimised for violet, red and infrared light. Responsivity measurements resulted in values as high as R=0.27A/W at λ=410nm, R=0.53A/W at λ=670nm and R=0.5A/W at λ=840nm.
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I. Jonak-Auer, A. Marchlewski, S. Jessenig, A. Polzer, W. Gaberl, A. Schmiderer, E. Wachmann, and H. Zimmermann "PIN photodiodes with significantly improved responsivities implemented in a 0.35µm CMOS/BiCMOS technology", Proc. SPIE 7719, Silicon Photonics and Photonic Integrated Circuits II, 77190U (17 May 2010); https://doi.org/10.1117/12.853703
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