Low kinetic energy particle bombardment of a growing film surface has been employed to grow high‐quality copper thin films on silicon and with ideal metal/substrate interface characteristics. It is shown that the energy of Ar ions concurrently bombarding a growing film surface determines the crystal structure of the film. Under relatively low‐energy ion bombardment conditions, (100)‐ or (111)‐oriented Cu films are grown epitaxially on (100) Si or (111) Si surfaces, respectively. On the other hand, completely (111)‐oriented films are obtained either on (100) Si, (111) Si, or surfaces when large ion bombardment energies are employed. It has been found that (111)‐oriented films thus created on are metastable and easily transform by thermal annealing into completely (100)‐oriented films with large grains of about 100 μm. This unique transformation phenomenon has been successfully applied to the formation of almost single‐crystal (100)‐oriented Cu islands on . In situ substrate surface cleaning by extremely low energy Ar ion bombardment has enabled the formation of ideal metal/silicon contacts without any postmetallization alloying heat cycles. Excellent adhesion of Cu thin films on has also been demonstrated by the employment of the in situ substrate surface cleaning.