# Low-Temperature and Low-Pressure Silicon Nitride Deposition by ECR-PECVD for Optical Waveguides  
[PERSON]  
1 Department of Engineering Physics and Centre for Emerging Device Technologies, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada; [EMAIL_ADDRESS] (J.W.M. );  
[EMAIL_ADDRESS] (C.S. ); [EMAIL_ADDRESS] (PM.J; [EMAIL_ADDRESS] (J.D.B.B) 1223-1241-1  
and are more suited to post-fabrication processing. Low-loss silicon nitride waveguides have been fabricated using PECVD [16]. One main disadvantage of PECVD techniques is the relatively high concentration of incorporated hydrogen in the samples, resulting in low-density structures and producing low-refractive index films. These highly hydrogenated films also exhibit more significant optical losses in the C-band due to Si-H and N-H bonds [2]. It is possible to remove the hydrogen from the films either through annealing or utilizing precursor gases that do not contain hydrogen, such as switching from NH\({}_{3}\) to N\({}_{2}\)[17]. Other varieties of CVD techniques can help mitigate the high concentrations of hydrogen. These include inductively coupled plasma (ICP-PECVD) [18; 19], high-density plasma (HDP-CVD) [13] and electron cyclotron resonance (ECR-PECVD) [20; 21; 22; 23; 24]. These techniques allow for high power densities, resulting in greater dissociation of the precursor gases and lower hydrogen incorporation into the films. Low pressures of 1-2 mTorr are realized in ECR-PECVD by using a strong magnet to confine and stabilize the plasma during deposition, whereas inductively coupled plasma (ICP) techniques typically operate at pressures \(>\)10 mTorr [13]. Interestingly, in the case of ICP-PECVD and ECR-PECVD, the reaction chamber is separate from the plasma chamber, allowing for high-quality films to be produced at low temperatures and pressures without the risk of surface damage from high energy bombardment. Limiting surface damage is of particular interest in waveguide fabrication as scattering at the material interface is a significant source of optical loss. Optical waveguide fabrication through ECR-PECVD has been explored [16; 25; 26] in various systems, demonstrating it as a viable candidate for the fabrication of visible and NIR waveguides. Variation in film stoichiometry by changing the nitrogen/silane (N\({}_{2}\)/SiH\({}_{4}\)) gas ratio during ECR-PECVD fabrication has been investigated, with optical losses of \(<\)1.0 and 1.5 dB/cm at 1310 and 1550 nm for N-rich and nearly stoichiometric films, respectively [2]. However, films in [2] were deposited at 350 \({}^{\circ}\)C and a minimum chamber pressure of 650 mTorr, which is two orders of magnitude higher than the deposition pressures shown here. By measuring optical loss at visible and NIR telecom wavelengths, and characterizing film stoichiometry as well as unwanted contaminants such as oxygen, we demonstrate a non-stoichiometric film capable of suitable device performance, fabricated at relatively low deposition pressures and temperatures compared to the existing literature. We report on hydrogenated silicon nitride films deposited using a low-temperature and low-pressure ECR-PECVD system. The stoichiometry of the films and the impacts of annealing on the hydrogen content are studied through Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA), respectively. Low-pressure recipes ranging from 1.1 to 2.4 mTorr with deposition temperatures of 140 \({}^{\circ}\)C show pre-annealing optical losses in the visible to NIR range suitable for integrated optical devices. We demonstrate that the associated optical losses of hydrogenated non-stoichiometric PECVD silicon nitride (SiO\({}_{\text{x}}\)N\({}_{\text{y}}\):H\({}_{\text{z}}\)), as reported in the literature [13], are reasonable for specific applications requiring low-temperature deposition conditions and access to thicker films up to 650 nm.