Influence of plasma parameters on properties of ITO films produced by reactive pulsed dual magnetron deposition

Middle frequency dual reactive magnetron sputter deposition was used in order to prepare the Indium tin oxide (ITO) films with an optimum of resistance and transmittance. The films were deposited on Si covered with 500 nm SiO2 and soda lime glass substrates. The plasma ions and neutrals flow parameters have been studied during the deposition process by the Langmuir probe, HIDEN analyzer, and optical emission spectroscopy. Complex characterization of the ITO films have been carried out in order to relate their properties with pulsed magnetron operation parameters. The optical constants and the thickness of these films were determined by means of spectroscopic ellipsometry (SE) operating within the wavelength range l=300-1700 nm. The optical transmittance was measured for l=350-2000 nm. Four probe technique was used to determine the film specific resistance. The dependence of the ITO film properties on the O2/Ar partial pressure relation was obtained similarly to known researches. The influence of the pulse duration and base pressure level on the film characteristics was detected. The decrease of the magnetron pulse on-time to the values of about 50 micro seconds, leads to strong increase of the films resistance at their high transmittance. The AFM data for these samples demonstrated five-times increase of the film grain sizes compared to those obtained at the on-time values 100 micro seconds. The observed decrease of optical transmittance in the near IR spectral range corresponds to the decrease of the film resistance. High optical transmittance at low resistance is found only at certain relation between the free electron plasma and relaxation frequency. The grading of optical constants was revealed by SE while the other techniques did not show depth grading of the film properties. Annealing of the ITO films in air atmosphere reduces the film resistance.