# Low-Temperature and Low-Pressure Silicon Nitride Deposition by ECR-PECVD for Optical Waveguides
## 3 Characterization and Results
### Stoichiometry  
As shown in Table 1, a second round of depositions was performed to produce thinner films, on carbon substrates for RBS measurements, as well as 2 \(\times\) 2 cm\({}^{2}\) Si pieces for annealing and ERDA measurements. The SiO\({}_{\text{x}}\)N\({}_{\text{y}}\):H\({}_{\text{z}}\) films deposited on carbon substrates were used to measure RBS data while allowing for a separation of recoil energies between the film and substrate, while the films deposited on Si pieces were used to quantify the amount of hydrogen incorporation via ERDA. Data were collected using a Tandetron accelerator with He\({}^{4+}\) ions at a 1.8 MeV 4\({}^{\circ}\) incident for RBS, and a 2.9 MeV incident at a grazing angle of 75\({}^{\circ}\) for ERDA. The data obtained for each film are shown in Figure 5. The uncertainty is reflected in the data point size for RBS, while the ERDA data are fit with higher sample-dependent uncertainty due to a higher sensitivity with changing fit parameters. The deposition recipes studied produce films of varying N/Si composition ratios, which demonstrate oxygen and argon contents of 10-20 and \(<\) 1%, respectively. We observe the expected trend of decreasing Si content as the N\({}_{\text{2}}\)/Ar flow increases, and conversely, the film composition becomes closer to a stoichiometric N/Si ratio of 1.333, as indicated in Figure 5a. However, this trend is no longer observed with further increasing N\({}_{\text{2}}\)/Ar:SiH\({}_{\text{4}}\)/Ar flow rate ratios, as shown in [2]. We observe less nitrogen content in Film 5, at 20 sccm of N\({}_{\text{2}}\)/Ar flow, during deposition. This is also coupled with an increase in oxygen content in the film. The films contain 10 to 20% oxygen, as shown in Figure 5a, which would indicate the deposition of silicon-oxynitride films. However, the relatively high oxygen content does not correlate with the expected refractive index in such films, which typically have indices ranging from 1.48 to 1.68 using PECVD [34; 35]. Future work aims to understand the distribution and bonding nature of O\({}_{\text{2}}\) in this system using Fourier  
Figure 4: (a) AFM amplitude plot for Film 2 annealed, (b) Film 3 unannealed and (c) Film 3 annealed. Figure 5: (a) Film composition determined from RBS excluding hydrogen with N/Si ratio indicated. (b) Hydrogen incorporation determined from ERDA before annealing. The incorporated hydrogen after annealing was measured to be below 0.1 at.% for all films. Connecting lines are to help guide the eye. transform infrared spectroscopy (FTIR). The contamination is expected to be due to water vapour present in the vacuum chamber due to sample transfer, and possible N\({}_{2}\)/Ar contamination with ambient O\({}_{2}\) from the gas transit lines before the MFC. The oxygen content is also anticipated to be a cause of the decreased N content as more Si-O bonds start to be favoured during deposition, rather than Si-N bond formation [36]. The abundance of oxygen in our film matrix can be explained by the presence of oxygen radicals in the plasma. At low N\({}_{2}\)/Ar flow rates, there are low quantities of N radicals leading to Si-H or Si-Si bonds becoming favourable, resulting in the production of a silicon-rich film [37; 38]. This effect is observed in Figure 5a, with a flow rate of 10 sccm of N\({}_{2}\)/Ar producing a silicon-rich SiO\({}_{x}\)N\({}_{y}\):H\({}_{x}\) film. ERD measurements show typical hydrogen incorporation of roughly 20% across the deposited films for ECR-PECVD deposition [13]. The lowest-loss film (Film 3) is also the film showing the lowest hydrogen incorporation of 17.2 \(\pm\) 0.5 at.%. After annealing, all films show below 0.1 at.% hydrogen incorporation. Future work will focus on minimizing hydrogen in the chamber by decreasing the SiH\({}_{4}\)/Ar flow, and possibly including argon flow to keep operating pressures at \(\sim\)1-2 mTorr while also decreasing the N\({}_{2}\)/Ar flow. This may also be beneficial in reducing the O\({}_{2}\) content in the film or potentially providing insight into its sources.