Abstract
We present an improved CMOS-compatible USRN material prepared using DCS-based chemistry deposited at a low temperature of similar to 300 degrees C. Morphology and composition of these USRN films are characterized using SEM, TEM, EDS and AFM. Surface profilometer is also used to estimate the film stress over an 8-inch wafer. TEM shows that the USRN film is amorphous and AFM measures a low roughness RMS of similar to 0.4 nm over a scan window of 3 mu m x 3 mu m. Optical properties of these USRN films are studied using variable-angle spectroscopic ellipsometry and FTIR spectroscopy. A prism coupler is used to estimate the film propagation loss. Ellipsometry measurement shows refractive index of around 3.09 at 1550 nm wavelength, which is our wavelength of interest. Comparing with USRN films prepared using SiH4-based chemistry, FTIR characterization shows reduced absorbance for films prepared using DCS-based chemistry at wavenumber region where Si-H bonds are located. The absorbance caused by N-H bonds are comparable for USRN films prepared using both DCS-based and SiH4-based chemistries. Si-H bonds and N-H bonds are expected to be the main sources of material absorption near 1550 nm in the USRN material. Characterization results of waveguides fabricated using USRN deposited by this DCS-based chemistry shows propagation loss of similar to 4.9 dB/cm for waveguide width of 1.5 mu m at 1550 nm wavelength. The improved results of DCS-based USRN will help to further cut losses and therefore enhance the performance of CMOS compatible USRN devices in nonlinear signal processing.