Glancing-angle ion bombardment for modification and monitoring of semiconductor surfaces

Abstract

Using glancing-angle ion bombardment for surface modification rather than conventional near-normalincidence ions has the advantages of reducing damage and implantation projected ranges, reducing channeling, reducing sputtering, and preferentially removing surface asperities leading to flat surfaces. The effects of bombardment conditions on the surface morphology and perfection of GaAs (001), InP (001), and Si (001) surfaces are reported. Air-exposed surfaces were cleaned and smoothened to near atomic flatness without damage under optimal conditions. Sputtering yield, measured using film thicknesses and changes in reflection high-energy electron diffraction oscillations, decreased with decreasing incidence angle. The low sputtering yield and minimal damage make a glancing-angle geometry ideal for real-time characterization by ion scattering spectroscopy. Surface composition measurements on single monolayers of InAs on GaAs showed that the glancing-angle Ar beam did not measurably change the In coverage over relatively long times. A new ion beam monitoring technique was also developed that utilizes the advantages of glancing-angle ions. Specular scattering of 3 keV He ions was observed for incidence angles of 2-6 ~ from GaAs (001). Oscillation in the specularly scattered ion current during GaAs growth were observed with periods corresponding to monolayer growth times. The oscillations allow a simple quantitative interpretation based on scattering by adatoms and step edges.

Glancing-Angle Ion Enhanced Surface Diffusion on GaAs(001) during Molecular Beam Epitaxy

“…Chason et al [17] have shown that near-normal incidence ions modify RHEED oscillations by creating surface vacancies that can annihilate with deposited adatoms. However, the vacancy creation is associated with sputtering, and sputter yields are very low for small f as discussed above [6,7]. Thus, the ion-induced change in Fig.…”

“…However, these studies suggest unique possibilities for film growth. In particular, glancing-incidence ions are mostly reflected rather than penetrating at flat defect-free portions of a surface, resulting in minimal ion damage, gas entrapment, or sputtering [6,7]. On the other hand, the ions can transfer considerable momentum to surface defects.…”

“…Studies of glancing-incidence angle ions, defined as angles f ഠ 1 ± 10 ± relative to the surface plane, have been confined to modifications of static surfaces rather than growth surfaces [6]. However, these studies suggest unique possibilities for film growth.…”

“…Third, x-ray diffraction measurements and simulations showed no change in the period of InGaAs͞GaAs superlattices due to 3 keV, f 3 ± Ar ions. The low sputtering yield is due to the low probability of penetration for the glancing incidence ions [6,7].…”

Computer simulation of layer‐by‐layer sputtering at grazing low‐energy ion‐surface interactions

“…The sputtering process has been the subject of both scientific investigations for a long time and recent rapid developing micro‐ and nanotechnologies. Processes such as plasma etching and sputter deposition that involve ion bombardment at relatively low (~ 100 eV) ion energies are widely used in semiconductor processing . However, using glancing‐angle ion bombardment for surface modification rather than conventional near‐normal incidence allows expanding the energy range up to ~10 keV and has the advantages of reducing damage (such as crater formation) leading to extremely smooth surfaces .…”