Tire electron behavior in the downstream of an electron cyclotron, resonance (ECR) plasma used for chemical vapor deposition has been explored from tire thickness fluctuation in the films prepared with a grid. The thickness fluctuation corresponds well to the distribution of the electron flux on the growing surface computed taking into account a correlation between the Larmor radii of electrons and a grid pattern. It is sbown that electrons produced in the ECR plasma move along the magnetic field lines in the Larmor gyration and play a key role in the dissociation of a source gas not only in the gas phase but also on fire growing surface to form films. The investigation of the thickness fluctuation enables Ics to estimate the electron temperature and the mean free path of electrons in the downstream.