Grain boundary character distribution of nanocrystalline Cu thin films using stereological analysis of transmission electron microscope orientation maps.

Stereological analysis has been coupled with transmission electron microscope (TEM) orientation mapping to investigate the grain boundary character distribution in nanocrystalline copper thin films. The use of the nanosized (<5 nm) beam in the TEM for collecting spot diffraction patterns renders an order of magnitude improvement in spatial resolution compared to the analysis of electron backscatter diffraction patterns in the scanning electron microscope. Electron beam precession is used to reduce dynamical effects and increase the reliability of orientation solutions. The misorientation distribution function shows a strong misorientation texture with a peak at 60°/[111], corresponding to the Σ3 misorientation. The grain boundary plane distribution shows {111} as the most frequently occurring plane, indicating a significant population of coherent twin boundaries. This study demonstrates the use of nanoscale orientation mapping in the TEM to quantify the five-parameter grain boundary distribution in nanocrystalline materials.

Effect of downscaling nano-copper interconnects on the microstructure revealed by high resolution TEM-orientation-mapping.

In this work, a recently developed electron diffraction technique called diffraction scanning transmission electron microscopy (D-STEM) is coupled with precession electron microscopy to obtain quantitative local texture information in damascene copper interconnects (1.8 µm-70 nm in width) with a spatial resolution of less than 5 nm. Misorientation and trace analysis is performed to investigate the grain boundary distribution in these lines. The results reveal strong variations in texture and grain boundary distribution of the copper lines upon downscaling. Lines of width 1.8 µm exhibit a strong <111> normal texture and comprise large micron-size grains. Upon downscaling to 180 nm, a {111}<110> bi-axial texture has been observed. In contrast, narrower lines of widths 120 and 70 nm reveal sidewall growth of {111} grains and a dominant <110> normal texture. The microstructure in these lines comprises clusters of small grains separated by high angle boundaries in the vicinity of large grains. The fraction of coherent twin boundaries also reduces with decreasing line width.