A low-energy, high-brightness, broad beam Cu ion source is used to study the effects of self-ion energy E i on the deposition of epitaxial Cu films in ultrahigh vacuum. Atomically flat Ge͑001͒ and Si͑001͒ substrates are verified by in situ scanning tunneling microscopy ͑STM͒ prior to deposition of 300 nm Cu films with E i ranging from 20 to 100 eV. Film microstructure, texture, and morphology are characterized using x-ray diffraction -rocking curves, pole figure analyses, and STM. Primary ion deposition produces significant improvements in both the surface morphology and mosaic spread of the films: At E i Ͼ37 eV the surface roughness decreases by nearly a factor of 2 relative to evaporated Cu films, and at E i Ӎ35 eV the mosaic spread of Cu films grown on Si substrates is only Ӎ2°, nearly a factor of 2 smaller than that of evaporated Cu. During deposition with E i Ӎ25 eV on Ge substrates, the film coherently relaxes the 10% misfit strain by formation of a tilt boundary which is fourfold symmetric toward ͗111͘. The films have essentially bulk resistivity with ϭ1.9Ϯ0.1 ⍀ cm at room temperature but the residual resistance at 10 K, 0 , shows a broad maximum as a function of E i , e.g., at E i Ӎ30 eV, 0 ϭ0.5 ⍀ cm.
A high degree of 111 preferred orientation with minimal mosaic spread has been shown by many researchers to be essential for electromigration resistance in Al-based interconnects. We have found that 111 texture can be greatly enhanced through the use of low-energy self-ion irradiation during deposition. In these experiments, 300-nm-thick Al layers were grown on SiO2 at 65 °C from highly ionized beams provided by an ultrahigh-vacuum primary-ion deposition (PID) source. Al+ ion energies EAl+ and ion/neutral ratios JAl+/JAl were independently varied from 10 to 120 eV and from 0% to 68%, respectively. All PID Al films exhibited very strong 111 preferred orientations, which increased with increasing EAl+ and/or JAl+/JAl, and azimuthally symmetric x-ray diffraction pole figures with no measurable tilt. The full width at half-maximum intensity Δω of 111 ω-rocking curves decreased continuously from 9.6° with EAl+=10 eV and JAl+/JAl=68% to 2.2° with JAl+/JAl=120 eV compared to 10.6° for films deposited by thermal evaporation. This was accompanied by a continuous decrease in the average grain size from 370 nm for thermal deposition to 90 nm with EAl+=120 eV. The PID Al films exhibited a columnar microstructure with weak competitive column growth. Changing the beam energy after the formation of a continuous layer had only a minor effect on film texture, indicating that the degree of ion-irradiation-induced preferred orientation is controlled during nucleation and/or coalescence while local pseudomorphic forces dominate thereafter. ω-rocking curves from a bilayer film consisting of a 20-nm-thick Al buffer layer grown by PID followed by a 280-nm-thick thermally evaporated Al overlayer were essentially identical to those obtained from 300-nm-thick single-layer PID Al films.
InAs quantum dots were grown on GaAs substrates at various coverages and capped after varying the time of growth interruption. The evolution of this system was examined by correlating photoluminescence and transmission electron microscopy measurements. Results show for the first time the growth interruption to be a critical factor in generating defect-free quantum dot ensembles at coverages well above established metalorganic chemical vapor deposition coverage window for defect-free, Stranski-Krastanow self-organized growth. In addition, our results also support the absence of a stable, dislocation free 3D state and that the chemical potential eventually drives the system towards dislocated quantum dot clusters.
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