Silica glasses doped with rare earth ions are well known for their use as fiber optics lasers and amplifiers. The performance of fiber optics devices greatly depends on the spatial distribution of doped ions in the glass. One of the most powerful instruments to probe local arrangements and the spatial distribution of paramagnetic ions in solids is pulse EPR technique. In this work we present preliminary results of the electron spin echo study of erbium-doped SiO2 glass co-doped with F, N. The samples were synthesized by means of plasma chemical deposition. Experiments were carried out using a home-built ESE spectrometer operating at a frequency of 9.4 GHz at the temperature range between 1.6 K and 4.2 K. The echo-detected spectra were recorded using a two-pulse echo sequence 2p/3-t-2p/3-echo. The time delay t was kept fixed while sweeping the magnetic field. The phase relaxation times are measured with a two-pulse echo sequence and the spin-lattice relaxation times are measured with a saturation pulse followed by two-pulse echo sequence. We studied 3 different types of Er3+ -doped SiO2 glasses: co-doped with F, co-doped with N and co-doped with F, N. In all samples we have found at least 4 types of paramagnetic centers. In echo-detected spectra at the magnetic field corresponding g ~ 2, we observed broad and narrow lines. We suppose these two lines are due to defects in glass structure. At the temperatures 1.6-2K we observed a broad line that is quite differ from the lines at g ~ 2. We attribute it to single Er3+ ions. The lines near zero magnetic fields we attribute to pairs and clusters of Er3+ ions. The electron spin echo envelope modulation due to F and N nuclei was observed in studied samples. Our study leads us to conclusion that SiO2 glass co-doped only with F contains less number of clusters than ones co-doped with N or co-doped with N and F.