Increasing the mean grain size in copper films and features

Abstract

A new grain-growth mode is observed in thick sputtered copper films. This new grain-growth mode, also referred to in this work as super secondary grain growth (SSGG) leads to highly concentric grain growth with grain diameters of many tens of micrometers, and drives the system toward a {100} texture. The appearance, growth dynamics, final grain size, and self-annealing time of this new grain-growth mode strongly depends on the applied bias voltage during deposition of these sputtered films, the film thickness, the post-deposition annealing temperature, and the properties of the copper diffusion barrier layers used in this work. Moreover, a clear rivalry between this new growth mode and the regularly observed secondary grain-growth mode in sputtered copper films was found. The microstructure and texture evolution in these films is explained in terms of surface/interface energy and strain-energy density minimizing driving forces, where the latter seems to be an important driving force for the observed new growth mode. By combining these sputtered copper films with electrochemically deposited (ECD) copper films of different thickness, the SSGG growth mode could also be introduced in ECD copper, but this led to a reduced final SSGG grain size for thicker ECD films. The knowledge about the thin-film level is used to also implement this new growth mode in small copper features by slightly modifying the standard deposition process. It is shown that the SSGG growth mode can be introduced in narrow structures, but optimizations are still necessary to further increase the mean grain size in features.

Annealing effect on the structure characteristics of nano-scale damascene copper lines

“…1i). This effect has already been reported in the literature [8] and may be associated with downward penetration of the growing grains from the overburden layer.…”

“…The grain growth is frequently found to initiate in the overburden layer [3][4][5][6][7], which presumably behaves as a thin film. Within the lines, however, the microstructure is surprisingly stable and grain coarsening here occurs only via penetration of the growing grains from the overburden [4][5][6][7][8]. It is also reported that the downward grain penetration may also be inhibited in the case of the very narrow lines [4][5][6].…”

Structural Response of Nano-scale Damascene Copper Lines to Annealing

“…1(i)]. This effect has already been reported in the literature 15 and may be associated with downward penetration of the growing grains from the overburden layer. …”

“…Within the lines, however, the microstructure is surprisingly stable and grain coarsening there occurs only via penetration of the growing grains from the overburden layer. 11 15 It has also been reported that the downward grain penetration may be inhibited in the case of very narrow lines. 11 13 High thermal stability of the microstructure within the lines is sometimes attributed to the pinning effect of second-phase particles entrapped during the electrodeposited process.…”

Study of the crystal structure, band gap and dispersion evolution in titanium oxide thin films

“…Secondly, the thicker layer with lower void fraction is more compact and with higher density, also resulting in an increase in the refractive index with an increase of film thickness [30]. Finally, the magnitude of the compressive stress in the thin film increases as the film thickness decreases [31] and a similar trend occurs for the refractive index, in other words, the refractive index decreases as the film thickness increases [32]. In our previous report [12] on amorphous TiO 2 thin films, the refractive indices increase monotonically with increasing film thickness, which has been sufficiently explained by surface and density effect.…”