We have studied the structure of hyper-thin (thickness, d less than or equal to 10 nm) SiO2 coatings deposited by plasma-enhanced chemical vapor deposition (PE-CVD) on various polymers (polypropylene, polyimide, polyethyleneterephthalate). Rutherford backscattering spectroscopy (RBS) has shown that the concentration of silicon atoms per unit area is a linear function of the deposition time, t, for t greater than or equal to 0.5 s. Using reactive ion etching (RIE) in O-2 plasma, we observe that the coatings are continuous, not island-like, even for d approximate to 2 nm; this is confirmed by X-ray photoelectron spectroscopy (XPS), at high values of the rake-off angle. In conclusion, PE-CVD film growth on polymers occurs in a layer-by-layer (Frank-van der Merwe), not in a Volmer-Weber (island coalescence) mode.