Anomalous Grain Growth in Sputtered CoCrMn Thin Films
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Anomalous Grain Growth in Sputtered CoCrMn Thin Films Hajung Song, Soon-Ju Kwon, and Kyung-Ho Shin1 Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Kyungbuk, 790-784, Korea 1 Nano Device Research Center, Future Technology Research Division, Korea Institute of Science and Technology, Seoul, 130-650, Korea ABSTRACT This paper presents anomalous grain growth in sputtered hcp CoCrMn thin films: The grain size is about 250 nm wide and a few micrometers long in the film of only 50 nm thickness. Both selected area diffraction (SAD) and x-ray texture analysis indicate that the perpendicular direction to the substrate is parallel to the zone axis of hcp and hcp. SAD also indicates that short axis of elongated grains is the c-axis of hcp structure, i.e. grains are elongated in the orthogonal direction to the c-axis. In addition, these elongated grains compose a grain bunch, in which grains are parallel to each other. Phi ( φ ) scan at grazing incidence x-ray diffraction (GID) geometry reveals that bunches are, as a whole, randomly oriented. However, neighboring bunches are misoriented about 10-20 degrees with each other, which is consistent with TEM observation. Such an anomalous grain growth of CoCrMn thin film is explained in views of mechanisms of nucleation and surface energy minimization.
INTRODUCTION Secondary grain growth, which results in large grain size structure, is often observed during thin film growth processes and attributed to surface/interface energy minimization [1-3]. At the initial stage of film formation, nuclei form generally with random orientation. This randomly oriented state maintains until the nuclei impinge to each other, i.e. film has no preferred orientaion at impingement stage in normal case. However, further growth is governed by the rule of surface energy minimization [1]. Grains with less surface/interface energy grow faster over the others and determine the final film structure. In this study, we report very interesting anomalous microstructure in sputtered CoCrMn thin films, which is believed to have different origin from the frequently observable secondary grain growth.
EXPERIMENTAL DETAILS ANELVA SPF-312H magnetron sputtering system was used for the deposition of Co63Cr31Mn6 (CoCrMn) thin films. Argon pressure, deposition power, and substrate temperature were 10 mTorr, 100 Watts, and 150 , respectively. Film structure was investigated using various XRD techniques and TEM. In addition to the symmetric and asymmetric XRD studies, grazing incidence x-ray diffraction (GID) was performed to obtain the detailed information of the film microstructure.
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DISCUSSION Figure 1 shows the abnormal microstructure of CoCrMn thin film deposited on the thermally oxidized Si(100) substrate. The grain
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