Today, designing high-performance optical filters or photonic circuits is still challenging. The efforts made by academics and industrials to filter light and/or confine it within waveguides continue through many applications. As examples, it can be mentioned optical communications between microelectronic chips, or miniaturized optical components (spectrometer, biosensors) for lab on chip application.
Due to its low optical losses within visible and near IR wavelength, by its optical index comprised between the ones of semiconductors and SiO2 , but also for its compatibility with CMOS technologies, SiN (silicon nitride) is known as a key material in integrated photonics or as a passivating and anti-reflective layer in the field of photovoltaics. However, when a low-temperature CVD process is used to deposit SiN, mechanical stresses in the layer can be tuned and it can induce significant local modifications of its optical properties. This is also the case for the layers underlying the SiN. This photo-elastic effect observed and demonstrated in different material systems, could be considered as a detrimental effect since the residual stresses in the layers of the photonic devices or circuits can affect the propagation properties of the guiding structures. However, recently in the framework of a first collaboration between McMaster University in Canada and FOTON Institute in France, some advances have been achieved to control and understand this mechanical stress inside SiN layers. Now, these preliminary studies pave the way to tune finely the SiN optical properties to optimize such layers for future passive optical devices.
Institut FOTON (Université Rennes, INSA-Rennes, CNRS, France) and Engineering Physics Department, McMaster University (Hamilton, Ontario, Canada)
Pr. Peter MASCHER (McMaster University), Christophe LEVALLOIS and Pr. Jean-Pierre LANDESMAN (Rennes)
