AFM, SEM and in situ RHEED study of Cu texture evolution on amorphous carbon by oblique angle vapor deposition

The evolution of the crystal orientation of a Cu film grown on an amorphous carbon substrate without intentional heating under $75\pm 6°$ oblique angle vapor deposition was investigated ex-situ by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and in-situ by reflection high-energy electron diffraction (RHEED). At the initial stage of growth ($<\sim 12\mathrm{nm}$ thick) the diffraction patterns showed uniform rings indicating random nucleations of crystals. With more Cu depositions ($>\sim 100\mathrm{nm}$ thick) the diffraction pattern started to break symmetrically from the middle of the (111) and (200) rings representing the absence of (111) and (200) planes parallel to the substrate. However, after this transition stage, at the thickness of $\sim 410\mathrm{nm}$, the intensity distribution of diffraction patterns appeared asymmetric about the middle of the rings, which is interpreted as the appearance of a tilted (111) texture. Finally the diffraction patterns developed into separated short arcs and showed only a $⟨111⟩⟨\overline{1}10⟩$ II-O (two-orientation) texture. By comparing RHEED patterns with the SEM and AFM images of the final film, we argue that the tilted columns having tilted (111) top faces dominate in the later stage of growth. Furthermore, considering the geometry of crystals and shadowing effects, we argue that the vertices of columns having the highest growth velocity normal to the substrate and therefore receiving the maximum flux will dominate the film growth and determine the tilt angle of the texture and the preference of the azimuthal angle orientation.

Figure 1

A schematic of the experimental setup for reflection high-energy electron diffraction and a deposition source. The electron beam is nearly perpendicular to the flux incident plane. The evaporation source is mounted on a semicircle track and the incident beam direction with respect to the substrate can be varied.

Figure 2

The (a) top view and (b) side view of SEM images of the Cu film grown on an amorphous carbon substrate by an oblique angle deposition at $\sim 75°$ with a total deposition time of $16\mathrm{h}$. The scale bars are $100\mathrm{nm}$ in both (a) and (b). The black arrow in (a) indicates the flux incident direction. The circles mark the typical columns with either trapezoidal or deformed hexagonal shapes. The axes of column structures in (b) tilt about 56° away from the substrate normal. The vertical thickness is $\sim 1.1\mu \mathrm{m}$. The circled column shows an obvious increase of the column width during growth.

Figure 3

A $2\times 2\mu {\mathrm{m}}^2$ AFM image of the Cu film grown on an amorphous carbon substrate by an oblique angle deposition at $\sim 75°$ with a total deposition time of $16\mathrm{h}$. The black arrow indicats the Cu flux incident direction. Three points used for determining the corresponding geometry directions are marked each on the top face $A$, the side face $B$ closely parallel to the Cu flux, and the side face $C$ perpendicular to the Cu flux.

Figure 4

The RHEED patterns of the Cu film grown on an amorphous carbon substrate by an oblique angle deposition at $\sim 75°$ for (a) $11\min$ (b) $91\min$, (c) $6\mathrm{h}$, and (d) $16\mathrm{h}$. The (111), (200), (220), and (113) diffraction rings are labeled in (a). The white arrow on the same pattern (a) represents the flux incident direction. $\theta$ is the polar angle measured from the vertical line in the middle. The two short white arrows in pattern (d) point to the splittings in the (220) diffraction arcs. ${\beta }_{\prime }$ is the tilt angle of the texture. All the images were taken with the electron beam direction nearly perpendicular to the flux incidence plane.

Figure 5

The normalized intensity of the (111) rings versus polar angle $\theta$ for the RHEED patterns measured at $11\min$, $91\min$, $6\mathrm{h}$, and $16\mathrm{h}$ Cu depositions on amorphous carbon substrate at an oblique angle $\sim 75°$.

Figure 6

The calculated diffraction patterns for the $⟨111⟩⟨\overline{1}10⟩$ II-O texture. ${\mathrm{G}}_{\Vert }$ and ${\mathrm{G}}_{\mathrm{z}}$ represent the parallel and normal components of the reciprocal lattice vector G, respectively.

Figure 7

(a) A schematic of the growth of one column along the column axis. $\beta$ and ${\beta }^{\prime }$ are the tilt angles of the top face and column axis measured from the substrate normal, respectively. $\alpha$ is the flux incident angle and $\gamma$ is the angle between two faces. $V_f$ is the velocity perpendicular to the top face. The growth velocity $V_{\nu }$ of vertex $A$ is projected to components $V_{\nu p}$ and $V_{\nu n}$ that are parallel and normal to the substrate, respectively. The inset shows a 3-D schematic of a column. (b) A schematic of the growth of the top surface of one column viewed perpendicular to the (111) plane, in which $⟨\overline{1}10⟩$ aligns at $\varphi \sim 30°$ with respect to flux incident plane. The dashed line represents the flux incident plane viewing perpendicular to the (111) plane. The small inner trapezoid bordered by gray lines and the larger outer trapezoid bordered by dark lines are the top faces of the column at the two consequent growth times. Each open circle represents an atom. The $⟨\overline{1}10⟩$ and $⟨11\overline{2}⟩$ directions are perpendicular to the ⟨111⟩ direction.