Correlation of stress and texture evolution during self- and thermal annealing of electroplated Cu films

Abstract

Electroplated Cu films with different plating conditions and thicknesses are characterized to study the stress and texture evolution involved in the transition of the microstructure during self-annealing. Grain growth during the process induces stress in the film in the tensile direction. Degradation of the (111) texture and enhancement of the (200) texture are observed in the films during the microstructural transition. The rate of self-annealing increases dramatically as the plating current density increases. Self-annealing is significantly retarded in thinner films and in films plated with pulse reverse current. A strong correlation between stress and texture development is demonstrated for all electroplated Cu films under self- and thermal annealing conditions. This correlation is explained by the surface/interface energy and strain energy in anisotropic metal films. Due to the mechanical anisotropy of Cu, the orientation with the lowest total energy changes from (111) to (200) as the dominant energy that determines the film texture changes from surface/interface related to strain related. The texture remains unchanged until the biaxial stress in the film exceeds a critical value. Above the level of critical stress, the (111) texture starts to degrade and the (200) starts to become enhanced, which reduces the strain energy in the film. Different amounts of stress develop in Cu films during thermal annealing depending on the barrier layers; the stress is largest with TaSiN, medium with Ta and smallest with TaN. This suggests that film stress and texture are also affected by the Cu/barrier interface bond strength.

Characterization of copper layers grown by electrochemical mechanical deposition technique

“…These measurements demonstrate that the pad action during film growth influenced orientation of the growing grains, yielding more (200) texture compared to films grown under ECD conditions without any pad interfering with grain growth. As seen from Table 1b, after the annealing step, the peak intensity ratios of the ECD films diminished by a factor of 9, as observed by other investigators [19] who studied ECD copper layers, whereas the peak intensity ratios for the ECMD films remained about the same. This implies that there is more homogeneous distribution of (200) crystallites that nucleated and grew by secondary recrystallization in the ECD films than in the ECMD films.…”

Effect of organic additives on structure, resistivity, and room-temperature recrystallization of electrodeposited copper

“…It is known that for Cu, the elastic strain energy density is the lowest for the (2 0 0) texture and the highest for the (1 1 1) texture [17], while we already mentioned above that the (1 1 1) texture is the most favorable from the point of view of the surface energy minimization. These two facts are the key to understanding the complex recrystallization behavior in our Cu films and could explain both the enhancement of the (1 1 1) texture and the significant enhancement of the (2 0 0) texture.…”

“…It is known that stress can play an important role in this material and recrystallization can occur over a time period from several hours to several years after the electrodeposition at room temperature or much faster as a result of annealing. This results in potential problems for the above-mentioned applications due to associated changes in stress, resistivity, and mechanical properties that in turn can correlate with seed and buffer layer materials [6,[10][11][12][13][14][15][16][17]. It is also well known that electromigration depends on texture and grain size in Cu films [18].…”

Effect of multistep annealing on mechanical and surface properties of electroplated Cu thin films

“…Its kinetics depends on various deposition and post-deposition parameters, such as electrolyte composition, current density, film thickness, seed layer composition, substrate morphology, annealing temperature, etc. [7][8][9][10][11][12][13][14][15] This phenomenon, which leads to a dramatic drop of the resistivity over time, is associated with the evolution of the microstructure at room temperature. The self-annealing for EP Cu films has become a constraint for reliability and reproducibility of Cu interconnect process because changes of grain size and hardness have influence on electromigration and the chemical mechanical polishing (CMP) process.…”