Materials for monolithic integration of optical functions on CMOS

Abstract

This thesis, under the program called MEMPHIS (Merging Electronics and Micro & Nano Photonics in Integrated Systems - http://www.smartmix-memphis.nl/), focuses on the selection and optimization of materials and low temperature processes to realize waveguides and photodetectors on top of complementary metal-oxide-semiconductor (CMOS). Germanium-silicon (GeSi) was chosen as the material for photodetectors. Thin amorphous GeSi films were crystallized using a pulsed green laser. Preformed lines were employed during the crystallization process to steer the formation of large grains within specified boundaries. This originates from the notion that photodetectors fabricated on films with controlled location and density of grain-boundaries can have fewer recombination centers as well as less device-to-device variability. Further the electrical activation of ion-implanted p- and n-type dopants in as-deposited polycrystalline GeSi films was studied using three different activation methods: furnace, rapid thermal and laser annealing. For reference the crystallization of ion-implanted amorphous GeSi films was also explored. The samples were physically and electrically characterized to assess their applicability in above-CMOS process technologies. On this end silicon oxynitride (SiON) was chosen as the material for waveguides. A detailed analysis of the deposition (at a low fabrication temperature of 150 °C) and properties of SiON films was performed. This was aimed towards realizing films with low optical losses in the visible and near-infrared wavelength range. The influence of the deposition parameters such as SiH4 fraction, deposition pressure and Ar/N2 ratio on the film properties was experimentally investigated using spectroscopic ellipsometry, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. These findings were consistent with the chemical modeling of gas-phase composition of the plasma thereby leading to better understanding of the deposition process. The propagation losses were determined using the prism coupling technique for various IR wavelengths ranging between 1300 nm and 1600 nm. Propagation losses as low as 0.5 ± 0.05 dB/cm at 1300 nm wavelength were measured, a very significant outcome for a low temperature deposited waveguide material.