Comparing the Through-Thickness Gradient of the Deformed and Recrystallized Microstructure in Tantalum with Unidirectional and Clock Rolling

Abstract

Controlling the microstructure homogeneity is crucial in achieving high quality tantalum (Ta) sputtering targets used in integrated circuit fabrication. Unluckily, traditional rolling easily generates a microstructure gradient along the thickness direction in Ta sheets. The deformation and recrystallization behavior of unidirectional and clock rolled Ta with an 87% strain were therefore systematically compared to investigate whether the change of strain-pass can effectively ameliorate the microstructure gradient along the thickness. Electron backscatter diffraction was used to analyze the misorientation characteristics of the deformed grains. A strong microstructure gradient exists in the unidirectional rolled (UR) sheets. Many microshear bands and well-defined microbands occurred in {111} deformed grains in the UR sheets, especially in the center region, while the grain fragmentation with {111} and {100} orientation in the clock rolled (CR) sheets was more homogenous along the thickness. The kernel average misorientation (KAM) and grain reference orientation deviation-hyper (GROD-Hyper) further confirmed these differences. X-ray line profile analysis (XLPA) indicated that the stored energy distribution was more inhomogeneous in the UR sheets. Schmid factor analysis suggested that the strain path changes due to clock rolling promoted the activation of multiple slip systems in {111} oriented grains. Upon static annealing, homogeneous nucleation combined with a slower grain growth rate resulted in finer and more uniform grain size for the CR sheet. In contrast, a strong recrystallization microstructure-gradient along the thickness formed in the UR sheets, which is attributed to the fact that the higher stored energy and more preferential nucleation sites led to faster recrystallization in the center region, as compared with the surface region. Thus, clock rolling can effectively improve the homogeneity of the through-thickness recrystallization microstructure of Ta sheets.

Texture and Microstructure Evolution of Ultra-High Purity Cu-0.1Al Alloy under Different Rolling Methods

“…It is worth noting that the low-angle grain boundaries within the deformed matrix in the 54% CR sample are lower, as compared with the 54% UR sample. Clearly, under the two rolling conditions, compared with the sample obtained by unidirectional rolling, the deformation microstructure of the sample processed by cross rolling is more uniform, and the layer spacing of the deformation band is smaller, which is not easy to cause local stress concentration [7,17,18]. With the increase of strain, grain fragmentation is more severe, especially for the UR sample.…”

“…Crystals 2021, 11, x FOR PEER REVIEW 8 of 12 easy to cause local stress concentration [7,17,18]. With the increase of strain, grain fragmentation is more severe, especially for the UR sample.…”

“…Cu thin film, used as the basic component, can greatly affect the performances of integrated circuits, which also indicates the possible directions to optimize the properties of devices by improving the quality of the Cu film. Among numerous factors changing the quality of the thin film, the sputtering target with features of high purity, grain refinement, random orientations, and large scale should be considered primarily due to the following reasons: (i) Only Cu and Cu alloy targets with purities of 6 N or above can well ensure the uniformity of sputtering film and the fine wiring quality [5]; (ii) the finer the grain is, the faster the sputtering rate is, while the more homogeneous grain size has more uniform deposition rate and sputtering film [6,7]; (iii) for face-centered cubic (FCC) metals, the sputtering rate is S (111) > S (100) > S (110) [8,9], while the atomic line density is L (110) > L (100) > L (111) , indicating that the random crystallographic orientations of the sputtering target can improve the uniformity Crystals 2021, 11, 1113 2 of 12 of film [7,10,11]. Clearly, the uniform and fine grain size combined with random orientations in the target can improve the quality of the sputtering film.…”

“…Their results demonstrated that the texture types formed in 90 • cross rolling and unidirectional rolling were quite different, i.e., strong ND rotating β fiber texture was formed in cross rolling samples, and the recrystallization texture was closely related to the deformation strain. Recently, our works in body-centered cubic (BCC) tantalum [7,[16][17][18] showed that 135 • cross rolling and asymmetric cross rolling [19,20] can effectively improve the texture and microstructure uniformity, as compared with the unidirectional rolling. In this paper, ultra-high purity Cu-Al alloys were deformed to different reductions by unidirectional and cross rolling, and the microstructure and texture evolution of Cu-Al alloys during unidirectional/cross rolling and the subsequent annealing were comparatively studied.…”

Multi-Stage Cold Forging Process for Manufacturing a High-Strength One-Body Input Shaft

“…The microstructure evolution was observed by an EBSD, an Oxford symmetry with JEOL (JSM-7900F) (JEOL Ltd, Tokyo, Japan) [ 25 , 26 ]. The specimens were hot-mounted, mechanically polished by SiC paper, and mirror-finished using diamond suspensions (up to 0.25 μm) and colloidal silica.…”