# Low-Temperature and Low-Pressure Silicon Nitride Deposition by ECR-PECVD for Optical Waveguides
## 4 Conclusion  
We deposited SiO\({}_{x}\)N\({}_{y}\):H\({}_{x}\) films on various substrates using ECR-PECVD with a fixed SiH\({}_{4}\)/Ar precursor and varied N\({}_{2}\)/Ar flow at 140 \({}^{\circ}\)C from 1.60 to 2.45 mTorr. To characterize the films, we used VASE and prism coupling to measure the refractive index and thickness, as well as the optical loss, respectively, before and after annealing. Refractive indices ranging from 1.81 to 2.07 were measured before annealing with optical losses as low as 1.3, 0.3 and 1.5 \(\pm\) 0.1 dB/cm at 638, 980 and 1550 nm, respectively, for films varying in thickness from 300 to 650 nm. Annealing for 1 h at 1000 \({}^{\circ}\)C in N\({}_{2}\) resulted in decreased thicknesses and increased refractive indices, pointing towards film densification, and hydrogen removal. Post-annealing loss measurements show a decrease of 0.8 \(\pm\) 0.1 dB/cm from 1.52 to 1.57 \(\upmu\)m. We quantified surface roughness with AFM, showing an RMS roughness of 1.0 \(\pm\) 0.1 nm for unannealed and annealed films of varying optical losses. Annealing was shown to decrease the peak-peak roughness amplitude by 1.65 \(\pm\) 0.40 nm. We verified hydrogen removal using ERDA and observed it to decrease from 17.2 to 22.6 to 0.1 at.% after annealing. RBS was used to investigate the atomic composition of the films and showed films of varying N/Si stoichiometry with high oxygen content ranging from 10.6% to 19.3%. Despite the films being non-stoichiometric SiO\({}_{x}\)N\({}_{y}\):H\({}_{x}\) and having medium hydrogen incorporation, low optical losses were still achieved from the visible to L telecommunication band using low deposition pressures and temperatures. This opens the possibility of applying such films in integrated photonic devices, particularly for post-processing fabrication of such devices on samples already containing temperature- or pressure-sensitive organic or metal layers. Future work aims to reduce the hydrogen incorporation in the films by reducing the SiH\({}_{4}\)/Ar gas flow rate during deposition, to reduce and gain further insight into oxygen sources and bonding mechanisms in the films via FTIR and to characterize the stress in deposited SiO\({}_{x}\)N\({}_{y}\):H\({}_{x}\) films.  
**Author Contributions:** Conceptualization, J.D.B.B., P.M. and D.B.B.; Methodology, D.B.B., J.W.M. and C.S.; Software, D.B.B. and C.S.; Validation, D.B.B., J.D.B.B. and P.M.; Formal Analysis, D.B.B., J.W.M. and C.S.; Investigation, D.B.B., J.W.M. and C.S.; Resources, J.D.B.B., and P.M.; Data Curation, D.B.B., and J.W.M.; Writing--Draft Preparation, D.B.B.; Writing--Review & Editing, D.B.B., J.W.M., J.D.B.B. and P.M.; Visualization, D.B.B. and J.D.B.B.; Supervision, J.D.B.B.; Project Administration, J.D.B.B. and P.M.; Funding Acquisition, J.D.B.B. and P.M. All authors have read and agreed to the published version of the manuscript.  
**Funding:** Natural Sciences and Engineering Research Council of Canada (NSERC) (STPGP 494306, RGPIN-2017-06423); Canadian Foundation for Innovation (CFI) (CFI Project # 35548).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data available in a publicly accessible repository.  
**Acknowledgments:** We thank [PERSON] and [PERSON] of the Centre for Emerging Device Technologies (CEDT) at McMaster University for their assistance with fabrication, and [PERSON] and [PERSON] from Western University at the Tandetron facilities for assistance with RBS and EDRA.  
**Conflicts of Interest:** The authors declare no conflict of interest.