We present a method that employs the metal-assisted chemical etching technique and a subsequent NH3 plasma treatment for obtaining silica nanoparticles (SNPs) uniformly distributed on an amorphous silicon-rich silicon nitride (SRN) film. These particles ranging from 50 to 300 nm are formed directly from the SRN films, and their density is related to the flow rate of the precursor gas (SiCl4). We determined that the SNPs are a SiOx compound (x > 1) with amorphous structure. Furthermore, the chemical composition of the bulk of the remaining SRN film after the etching in a HF/H2O2-based solution and plasma treatment maintain the properties of a pristine one if the initial thickness of the film is large enough (>= 1 mu m). This method enables the formation of silica nanoparticles directly on a silicon-rich silicon nitride film that could have potential optoelectronic applications, implicit in the optical measurements.