Structural Response of Nano-scale Damascene Copper Lines to Annealing

Abstract

The high-resolution electron backscatter diffraction (EBSD) technique was applied to study microstructure and texture changes in the overburden layer as well as in upper and bottom parts of nano-scale damascene copper lines during annealing in a temperature range of 200-500°C. The microstructure in overburden layer was found to coarsen significantly at 200°C. At higher temperatures, however, it was established that the overburden layer and both parts of the lines were surprisingly stable. It was also shown that the microstructure in all studied regions was stabilized after achieving the same level of total grain-boundary area per unit volume. This observation has been interpreted as indirect evidence that grain growth behavior in the lines was governed by the pinning effect of second-phase particles entrapped during the electrodeposition process.

Microstructural characteristics of electrodeposited damascene copper lines

“…his texture is oten observed in deposited copper ilms and commonly attributed to minimization of surface energy [22,23]. It was also noteworthy that this texture component notably strengthened with annealing temperature [11]. he material of the overburden layer also contained a minor fraction of <100>//ND iber texture, which was typically associated with annealing twins in the <111> grains.…”

“…Both components were as expected in this region. However, the observed pronounced strengthening of the out-of-plane texture with temperature [11] presumably indicated growth of the bottom grains. If so, the vertical grain growth in the lines involved not only downward penetration of the overburden grains but also upward propagation of the bottom grains.…”

“…Microstructure in the upper part of the lines seems to be relatively coarse grained (~150-200 nm). One of the possible explanations for this efect is downward penetration of the growing grains from the overburden layer [10,11]. As follows from variation of the STEM contrast as well as from the presence of thin extinction contours, the material is characterized by large internal stresses.…”

“…Annealing at 200 o C led to signiicant microstructural changes in the overburden layer in very narrow copper wires [11] (ig.3). he microstructure substantially coarsened achieving a typical grain size of ~2 mm, the grains became essentially equiaxed and typically contained annealing twins (an example is indicated by the arrow in ig.3a).…”

“…Despite signiicant industrial importance and considerable academic interest, microstructural observations in the nano-scale wires are still limited to a few examples [3][4][5][6][7][8][9]. It is important to emphasize that the analysis of nano-scale copper wires in most cases has been done on samples ater annealing, including suiciently detailed investigation [10,11], but, to the best of the authors' knowledge, there is no data about microstructure of nanoscale damascene copper lines before annealing, immediately ater electrodeposition; in other words, data in present work are likely to be regarded as a novelty. his work presents an analysis of microstructure and texture in as-deposited copper wires as well as ater annealing in an attempt to establish a better understanding of the grain-growth behaviour in these materials.…”