Morphology and microstructure of epitaxial Cu(001) films grown by primary ion deposition on Si and Ge substrates

Abstract

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.

Growth of epitaxial Cu on MgO(001) by magnetron sputter deposition

“…However, a further increase in T s to 200 and 300°C does not lead to narrower ω-rocking curves but a dramatic broadening, with a FWHM of 5.5°. The broadening is attributed to a tilting of 001-oriented Cu to relieve misfit strain, as determined from pole figure analyses, similar to a reported tilt of Cu grains on Ge(001) [6]. Cu has a 14.19% smaller lattice constant than MgO.…”

“…Most work on the epitaxial growth of Cu has been done on H-terminated Si(001) and Si(111) surfaces [4][5][6][7][8][9][10], where the Cu layer grows with (001) Cu ||(001) Si and [100] Cu ||[110] Si on the Si(001) surface and with (111) Cu ||(111) Si on Si(111). However, for both systems, there are two possible orientations for the Cu nucleation, so that the resulting layer is highly twinned.…”

“…Reported epitaxial Cu/MgO(001) growth temperatures T s range from room temperature [10,14] to 185°C [15], 50-300°C [16], 300-350°C [17], 370°C [18], and 580°C [13]. However, it is unclear what temperature yields the highest quality Cu layer since most studies determine the crystalline structure only by XRD ω−2θ scans and reflection high energy electron diffraction-techniques which are relatively insensitive to [6,10,13,16].…”

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

“…88 In these studies the degree of ͕111͖oriented texture increased continuously with increasing ion energy up to 120 eV and r up to 0.68 for an ion energy of 34 eV. Subsequent studies of the self-ion-assisted deposition of Cu on Si and Ge substrates, 89 however, showed an increased tendency for the development of preferred ͕001͖ orientational texture when growth occurred on either ͓100͔or ͓110͔-oriented substrates. Despite lattice mismatch in such cases there will be, of course, a tendency toward heteroepitaxial growth.…”

Control of Ti1−xSixN nanostructure via tunable metal-ion momentum transfer during HIPIMS/DCMS co-deposition

“…1 High-flux, low-energy ion bombardment has been shown to increase nucleation rates 2,3,4 and film density, 4 give rise to renucleation which inhibits the formation of open columnar microstructures associated with high surface roughness, 5,6 reduce defect density, 7 and control preferred orientation. 1,8,9,10 However, the balance is delicate and at higher ion energies, a steep price is extracted in the form of residual ion-induced compressive stress resulting from both recoil implantation of surface atoms and trapping of rare-gas ions in the lattice.…”