AVS 63rd International Symposium & Exhibition
    Thin Film Monday Sessions
       Session TF+PS+SE-MoA

Paper TF+PS+SE-MoA10
Molybdenum Back Contacts Deposited by High Power Impulse Magnetron Sputtering

Monday, November 7, 2016, 4:40 pm, Room 102B

Session: Plasma-based Deposition Techniques and Film Characterization
Presenter: Arutiun Ehiasarian, Sheffield Hallam University, UK
Authors: D.A. Loch, Sheffield Hallam University, UK
A.P. Ehiasarian, Sheffield Hallam University, UK
Correspondent: Click to Email
Molybdenum thin films used in chalcopyrite solar cells can influence the Na diffusion rates and the texture of the Cu(InGa)Se2 absorber according to the microstructure and morphology. The lowest resistivity films are achieved at low working pressure and are accompanied by high residual stress and poor adhesion due to the resulting high energy of the deposited flux. High Power Impulse Magnetron Sputtering was employed to ionise the sputtered flux, achieve high adatom mobility at low energy and influence the growth of Mo back contacts. Pulse durations in the range 60 to 1000 µs, sputtering voltages between 800 and 1500 V and deposition pressures of 2×10-3 mbar and 4×10-3 mbar resulted in ten-fold variations in the flux ratios of Mo1+/Mo0 Mo2+/Mo1+, Ar2+/Ar1+ and Mo1+/Ar1+ as determined by optical emission spectroscopy and time-resolved plasma-sampling energy-resolved mass spectroscopy. The energy of metal and gas double and single-charged ions reduced with pulse duration and increased with voltage. The microstructure of the films varied from open columnar with faceted tops to fully dense as observed by secondary electron microscopy. The reflectivity of the films improved by 20% compared to industry-standard materials. The lowest resistivity was in the range of 12 µΩ-cm as observed by four-point probe measurements of 570 nm thick films. The correlation between resistivity, microstructure, crystallographic texture, stress and deposition flux characteristics is discussed.