Rapid Selective Annealing of Cu thin films on Si Using Microwaves

A key requirement for future integrated circuit fabrication is lower processing temperatures at all stages of fabrication. Typical rapid thermal annealing processes, utilizing infrared radiation, heat the film as well as the substrate and create the potential for device reliability problems. Microwave annealing may enable a novel solution to the problem of selective annealing of metallic or other conductive thin films, which is possible in the limit where the metal film thickness is less than the skin depth of the material at microwave frequencies. This technique is advantageous because the relatively low absorption of silicon deters substrate heating and the metallic thin film shields the rest of wafer. We have investigated the quality factor, Q, and temperature of silicon as a function of its doping concentration and power input into the microwave cavity. As a particular application of microwave selective annealing, we have microwave annealed sub-micron Cu thin films sputtered on patterned SiO₂/Si substrates and demonstrated an improvement in trench filling for use in interconnect metallization applications