Rf vs dc sputter gun copper coating of laser fusion targets

Rf excitation of sputtering sources will be needed for deposition dielectric coatings on laser fusion targets. The current study has shown that for metals the major disadvantages of rf compared to dc excitation are lower attainable deposition rates and, for spherical substrates, rougher surface finishes at comparable deposition rates. The morphologies of rf sputtergun coated copper films on both planar substrates and molecular beam levitated hollow glass microspheres were examined and compared to previous work using the same Sloan and sputtered films (SF) sputterguns with dc power. The SF gun consistently produced smoother coatings than the Sloan gun. The SF gun produced the smoothest rf coatings on levitated microspheres at the highest argon pressure (6 μm) and lowest deposition rate (45 A/s). The data were used to hypothesize that resputtering off these isolated spherical substrates is an important factor for surface morphology