A method for depositing, under vacuum, an amorphous layer primarily containing fluorine and carbon onto a substrate (9), characterized in that it comprises a step for depositing this layer with an ion gun (1) for ejecting ions in the form of a beam of accelerated ions that is created from at least one compound containing fluorine and carbon in a gaseous form or saturated vapor supplied to the ion canon. A method of this type makes it possible, in particular, to improve the adherence of an outer layer having a low index of refraction to the underlying layer of an anti-reflective stack. A device suited for carrying out the method is also described.