Abnormal grain growth of sputtered CuNi(Mn) thin films
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The evolution in both stress and microstructure was investigated on sputtered Cu0.57Ni0.42Mn0.01 thin films of 400 nm thickness during the first temperature cycle up to 550 °C. Samples from stress–temperature measurements up to various maximum temperatures were analyzed by x-ray diffraction, scanning and transmission electron microscopy, and Auger electron spectroscopy. The columnar grains with lateral diameters of about 20 nm in the as-deposited state coarsen to about 400 nm above 300 °C. Probably due to the impurity (Mn) drag effect, the coarsening occurs by abnormal grain growth rather than by normal grain growth, starting near the film–substrate interface. The stress development results from a combination of densification due to grain growth and plastic stress relaxation.
I. INTRODUCTION
CuNi coatings are interesting because of their application as thin-film resistors and thermocouples.1– 4 The film stress is of importance for the long-term stability of such devices. It is particularly noted that stress generation during annealing can cause problems. Stress is generated by any structural change associated with a densification of the film. Two microstructural processes may take place in materials with defects during annealing. These processes are (i) recovery (rearrangement and annihilation of point defects and dislocations), and (ii) grain coarsening (recrystallization, normal grain growth, or abnormal grain growth).5,6 With respect to grain coarsening in thin films, mostly normal grain growth is reported. This has been shown in in situ transmission electron microscopy (TEM) observations on Al7 and Cu8 thin films. Thus far, studies devoted to the correlation between stress development and microstructural evolution have been carried out on face-centered-cubic (fcc) Al or Cu metallization films. It has been difficult to distinguish the stress contributions resulting from grain growth, hillocking, dislocation motion, or diffusional flow.7,9–14 Therefore, investigations on an fcc solidsolution thin film may give additional insight into the correlation between stress and microstructural evolution in fcc metallic films. Very recently, the stress relaxation of Cu0.57Ni0.42Mn0.01 thin films, with microstructure stabilized in a previous thermal cycle, was studied, and grain-boundary-diffusion controlled plastic flow was discussed as a decisive deformation mechanism.15 In this article, stress development during the first thermal cycle of the same films is 1062
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J. Mater. Res., Vol. 15, No. 5, May 2000 Downloaded: 16 Mar 2015
considered. During this cycle, grain coarsening takes place. Two questions are important: (i) the mechanism of grain coarsening and (ii) the contribution of grain coarsening to stress development. The stress was studied during temperature cycling in vacuum (Sec. III. A). By cycling samples to various maximum temperatures and then characterizing the microstructure, the stress and microstructure were correlated. The microstructure was studied by x-ray diffraction (XRD)
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