Influence of thermal spikes on preferred grain orientation in ion-assisted deposition

Abstract

Theoretical models are presented to explain how thermal spike processes can induce the development of preferred orientation of polycrystalline grains during ion-assisted atomic deposition and thin film growth. Two ion energy regimes are investigated. In the first, higher-energy regime, ions penetrate growing grains and generate defects at rates dependent upon the probability of ion channeling in individual grains. The volume free-energy density of different grains is, therefore, different and the thermal spike arising from each ion impact results in preferential growth of grains with the lowest volume free-energy density. In the second, lower-energy regime, ions do not penetrate nor create defects in grains but the ion-induced thermal spikes centered on the surface can enhance surface atomic migration and lead to preferential growth of grains with the lowest surface free-energy density. The results in these two regimes are compared with the predictions of a model for preferred grain orientation evolution in the absence of ion assistance and where minimization of surface free-energy density is the driving process. Ion energy, ion flux density, depositing atom flux density, and system temperature conditions are established where ion-assisted and non-ion-assisted rates of preferred grain orientation become comparable. It is shown that, in general, the tendency toward preferred orientation is not a simple function of the energy per deposited atom.

A structure zone diagram including plasma-based deposition and ion etching

“…the liquid "freezes", large amplitude thermal vibration still facilitate diffusion, especially the migration of interstitials inside grains and adatoms on the surface. The driving force is the gradient of the chemical potential [35], leading to minimization of the volume free energy and surface free energy density, respectively, with contributions of interface and elastic strain energies [15], and often resulting in a film where grains have a preferred orientation.…”

Role of heavy ion co-implantation and thermal spikes on the development of dislocation loops in nanoengineered silicon light emitting diodes

“…1(a)) we observe relatively small (up to $35 nm diameter) dislocation loops distributed around the projected range of previously implanted boron. The loops that developed in the sample implanted to 10 13 Tm cm À2 ( Fig. 1(b)) are still located around the boron projected range but they are considerably larger (some irregularly shaped ones are above 200 nm long) than in the previous case.…”

“…16 The TEM results imply that Tm ion implantation induces two effects in the Si substrate: (1) partial annealing due to thermal spikes, and (2) crystal damage with partial or full amorphization of Si for the two highest Tm doses. Indeed, by comparing the images from samples implanted at 10 12 and 10 13 Tm cm À2 we observe much larger loops for the 10 13 Tm cm À2 sample, although both samples had the same post-implantation annealing. This suggests that ripening of loops occurred during implantation to the higher Tm dose.…”

“…After initial nucleation the loops develop by the Ostwald ripening mechanism, increasing in size and decreasing in density with annealing time, but the total number of Si interstitials trapped in the loops remains constant. 19 The lattice occupancy of the Tm species could not be evaluated at this stage, but the implanted doses in the efficient devices (10 12 and 10 13 Tm cm…”

“…20); 8 there is also evidence of the influence of ion induced thermal spikes in broadening of tracer profiles in silicon 9 and numerous reports on the grain growth in polycrystalline metallic films upon ion irradiation. [10][11][12][13][14] Nevertheless, nucleation and growth of extrinsic crystalline defects (dislocation loops in this case) in a host material under ion induced thermal spikes has not yet been reported. 15 During implantation the targets were held at room temperature, and inclined by 7 off normal to avoid channeling.…”