It depends on all the cladding layers you are using for your waveguides. Normally thermal SiO2 is the bottom cladding for Si or Si3N4 waveguides and then the most important property of the PECVD top cladding is the refractive index. In particular you want the PECVD SiO2 to have the same refractive index as thermal SiO2. This can be easily achieved with either silane based ammonia free, silane and ammonia or TEOS PECVD processes. The stress is mainly dependent on the lf bias. Some PECVD tools provide separate hf and lf biases that then allow the strain to be tuned but you also then have to be careful that very low strain ends up with more nitride in the layer and a higher refractive index that could produce slab modes. For examples of PECVD processes that work well see Article 1.4 million Q factor Si3N4 micro-ring resonator at 780 nm wa...
Some of the properties I have discussed in my paper for ONO MIM capacitor..