Influence of the Substrate Temperature on the Texture of MgO Films Grown by Ion Beam Assisted Deposition
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Influence of the Substrate Temperature on the Texture of MgO Films Grown by Ion Beam Assisted Deposition Liliana Stan, Paul N. Arendt, Raymond F. DePaula, Igor Usov, James R. Groves Superconductivity Technology Center, Los Alamos National Laboratory Los Alamos, NM 87545 ABSTRACT The variation in the substrate temperature during ion beam assisted deposition (IBAD), which employs the use of energetic ions to bombard a growing film, has been shown to influence the quality of crystalline texture in MgO films. Determining the acceptable deviation from the optimum ion to molecule ratio for different substrate temperatures establishes the optimum MgO deposition conditions. For each fixed deposition temperature, a set of samples was produced by varying the ion assist beam current from sample to sample while keeping the deposition rate constant. In this way, the ion to molecule ratio was modified and the range of achieving well textured films was determined. The investigation of the MgO texture dependence on the substrate temperature reveals that the best in-plane alignment is obtained at ~25 °C. At this temperature, MgO films with in-plane orientation distribution as low as 3.7° full width at half maximum (FWHM) have been attained. MgO films deposited at temperatures higher than 100 °C have broad in-plane alignment. Although, the deposition at the lowest temperature (-150 °C) did not improve the in-plane texture, the acceptable deviation from the optimum ion to molecule ratio for achieving biaxially textured films was the largest. As a trend, the acceptable ion to molecule deviation decreases with increasing substrate temperature. This is especially important for continuous IBAD MgO depositions where less restrictive conditions are desired. INTRODUCTION MgO thin films grown using IBAD proved to be a suitable biaxially textured template for YBCO coated conductors [1-3]. Much work has been already done for optimizing the deposition parameters that influence the biaxial texture of MgO films [4-7]. It has been shown that the substrate temperature plays an important role in the quality of the crystalline texture of the MgO films. MgO texture improves by decreasing the deposition temperature from 300 to 25 °C [8]. Radiation damage accumulation experiments in MgO crystals with different orientations suggested that the MgO crystallographic texture should be better at even lower deposition temperatures [9]. In vacuum systems, only conductive (via the substrate holder) and radiative thermal exchanges are possible. Thus, if good thermal contact between the substrate and its holder does not occur, a significant change in temperature results in the IBAD process due to the energetic ion bombardment of the growing film. This is even more likely to happen during the continuous deposition of MgO. Therefore, the investigation of the texture dependence on substrate temperature is necessary to determine the optimum temperature for the MgO growth. Also by determining the acceptable deviation from the optimum ion to molecule ratio for di
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