Enhancement of adhesion by megaelectronvolt ion bombardment

Abstract

It has been demonstrated that the adhesion of a wide variety of film-substrate combinations can be dramatically improved by megaelectronvolt ion bombardment. Although the results are similar in most cases, it is becoming clear that several mechanisms may be involved in the process. For example, in the 35Cl 4+ ion bombardment (6–21 MeV) of gold films on vitreous SiO 2 substrates, there are two distinct dose regimes where enhanced adhesion occurs. One is centered at 10 13 35Cl 4+ ions cm −2, coincident with the formation of bombardment-induced surface cracks in the SiO 2. The other occurs above an ion-energy-dependent threshold (about 10 14 35Cl 4+ ions cm −2). We have also observed that the adhesion enhancement for gold on GaAs depends strongly on the type and level of doping. For example, both silicon- and tellurium-doped n-type GaAs have a sharp threshold in enhanced adhesion near 10 14 35Cl 4+ ions cm −2 for 18 MeV 35Cl + ion irradiation. However, although chromium-compensation-doped p-type GaAs reaches the same final adhesion levels, there is a smooth increase versus dose starting below 10 12 35Cl 4+ ions cm −2. Several possible mechanisms will be discussed and compared with the data.