This study investigates electron trapping in a SiO2 layer during the electron beam (e-beam) deposition of 50–277 nm thick CaF2 films on a Si/SiO2 substrate. The trapping phenomenon was studied using the photoelectron emission (PE) technique. The Si/SiO2 substrates were fabricated by thermally growing an amorphous 1 µm thick SiO2 layer on a Si wafer. Following the e-beam deposition of CaF2 films, the PE current from the Si/SiO2/CaF2 structures was measured. PE was excited by UV photons with an energy range of 4–6 eV. The results showed that the registered photoelectrons were emitted both from the films and the substrate. Analysis of the recorded PE spectra revealed distinct PE maxima that were associated not with CaF2 films but with electrons trapped in defect centres within the SiO2 layer. These defect centres likely existed in the as-fabricated SiO2 layer and could trap electrons during the e-beam deposition process of the CaF2 films. The same PE maxima were observed in the PE spectra of a bare Si/SiO2 substrate when irradiated with weak electrons of energies up to 1.5 keV emitted by a thermionic cathode. The dependence of PE intensity on electron irradiation dose and film thickness was also investigated. It was found that the integrated intensity of PE emission was directly proportional to the electron irradiation dose for both Si/SiO2 substrates and CaF2 films. However, for a 277 nm thick CaF2 film, a sharp decrease in the integrated intensity was observed. This decrease was attributed to the metallization of the CaF2 film as a result of electron irradiation. The formation of calcium clusters within the film was influenced by the electric field arising during electron irradiation, leading to the observed changes in the PE intensity and spectrum shape. Additional experiments confirmed the metallization process, where electron irradiation of different thickness CaF2 films resulted in varying PE intensity changes. The relaxation time of the PE intensity was measured, suggesting low conductivity in the 277 nm thick film due to tunnelling transitions between calcium clusters.