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Ggradient effect of microstructure and texture evolution during annealing of cold rolled high purity tantalum plates

Tantalum (BCC structure) is a refractory metal with a range of excellent physical and chemical properties, such as excellent corrosion resistance, good ductility, etc., making it an ideal material for microelectronics and sputtering targets. In semiconductor integrated circuit industry, the quality of sputtered films is highly required, and the grain size and crystal orientation distribution of sputtered target material have a direct effect on the quality of sputtered films. Different crystal orientations and different grain sizes will lead to different sputtering rates in the process of magnetron sputtering. In order to ensure the quality of the sputtered films, the average grain size of the target material is required to be less than 100μm, and the grain size is equiaxed and the texture is randomly distributed. Rolling and annealing processes are commonly used to refine grain and homogenize texture.

The recrystallization annealing technology is mainly driven by the deformable storage energy to form new grains without distortion through the formation and migration of large Angle grain boundaries in the deformed matrix. This technique is an important means to change and control the internal structure and properties of metals. Many factors affect the recrystallization behavior of metals, such as initial grain size, impurity elements, deformation structure (including strain mode, strain path and strain variable), annealing conditions and crystal orientation, etc. By observing the microstructure of the single crystal under annealing condition, it is found that the recrystallization of the {111} oriented grains is more likely to occur than that of the {100} oriented grains. The {100} oriented grains were still recovered after unidirectional rolling and annealing at 1673K. Low temperature annealing is difficult to activate the recrystallization of the {100} oriented deformation zone, while high temperature isothermal annealing is easy to cause abnormal grain growth.

Compared with the conventional one-way rolling technology, 135° circumferential rolling for tantalum plate texture gradient along the thickness direction is weakening effect to a certain extent, but near surface area remain strong {100} texture, and the center area of the {111} texture, which inevitably cause during the process of high purity tantalum plate in the subsequent annealing microstructure gradient along the thickness direction, and in reaction to the phenomenon is still lack of related research. This work by using X-ray diffraction (XRD) technology of cold-rolled tantalum plates of different thickness area (near surface and center area) focuses on characterizing the recrystallization texture, and by using electron back scattering diffraction technology test results with electron backscattered diffraction (EBSD) along the thickness direction of the microscopic texture characterization, this paper studies the annealing process of tantalum sputtering target material along the thickness direction of the micro structure and macro texture evolution law, the texture of follow-up to explore suitable control technology and organization optimization technology to offer help.

The microstructure evolution of 87% circa-rolled tantalum plate after annealing for 5 min, 10 min, 30 min, 60 min, 90 min and 120 min at 1323K was systematically studied by electron backscattering diffraction (EBSD), X-ray diffraction (XRD) and microhardness techniques. The experimental results show that the recrystallized nucleation occurs first in the deformed microstructure in the central region, and the nucleation process in this region is mainly dominated by the large Angle grain boundary nucleation mechanism, while the subgrain nucleation mechanism plays a major role in the near surface region. Secondly, the recrystallization kinetics of the central region is faster than that of the near-surface region. After the recrystallization, the central {111}< UVW > texture (<111>// Nd (plate normal)) has a higher strength, while the near-surface {100}< UVW > texture (<100>// Nd) has a relatively higher strength. The {111}< UVW > in the central region of the deformed tantalum plate has high texture strength, high storage energy and serious internal grain fragmentation, so recrystallization occurs earlier. In the near surface region {100}< UVW >, the texture strength is high, the degree of internal grain fragmentation is relatively small, and the storage energy is low, which leads to a longer recovery incubation period. As a result, the recrystallized structure and texture have gradient effect along the thickness direction.
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