The metallization of diamond by ion beam assisted deposition (IBAD) and subsequent sputter deposition was investigated. IBAD was adopted to prepare three metallization schemes for diamond substrates, i.e., Ti/Ni, Ti/Cr and T/W. A AuSn solder layer was deposited onto these systems using a sputtering technique. Metallization samples were subsequently furnace annealed. Characterization of the multi-layered films was performed using Rutherford backscattering spectrometry. The results showed that the diamond/Ti/Ni/AuSn and diamond/Ti/W/AuSn systems exhibit poorer thermal stability owing to Sn from AuSn solder reacting with the barrier metal during annealing. However, the diamond/Ti/Cr/AuSn structure appeared to be stable during annealing.