The fast heavy ion beam enhanced adhesion of thin Cu film on Si substrate was studied for a wide range of Cl ion beam doses and for beam energies of 2.0

3.0 and 4.0 MeV. It is found that there are two types of enhanced adhesion. The surfaces of Si substrates were observed by means of a scanning electron microscope (SEM) after low dose ion bombardment. The micrographs show that no microcracks exist on the surfaces. This result seems to disagree with the explanation of low dose enhanced adhesion caused by the crazes on the substrate surface.