Focused ion beam implantation of Ga in Si and Ge: fluence‐dependent retention and surface morphology

Abstract

Focused ion beam implantation of 30-keV Ga+ ions in single-crystalline Si and Ge was investigated by SIMS, using Cs + primary ions for sputtering. Nine different implantation fluences ranging from 1 × 10 13 to 1 × 10 17 Ga + -ions/cm 2 were used, with implanted areas of 40 × 40 µm 2 . The Ga concentration distributions of these implants were determined by SIMS depth profiling. Such 30-keV Ga implantations were also simulated by a dynamic Monte-Carlo code that takes into account the gradual change of the near-surface composition due to the Ga incorporation. In both approaches, an essentially linear increase of the Ga peak concentrations with fluence is found up to ∼1 × 10 16 cm −2 ; for higher fluences, the Ga content approaches a saturation level which is reached at about (1-2) × 10 17 cm −2 . The measured and simulated peak concentrations of the Ga distributions are in good agreement. The most probable ranges obtained from the experiments correspond closely with the respective values from the simulations. The surface morphology caused by Ga + implantation was investigated by atomic force microscopy (AFM). The AFM data indicate that for low fluences (<3 × 10 15 cm −2 ) the surface within the implanted areas is growing outward (i.e. is swelling). For increasingly higher fluences, sputter-induced erosion of the surface becomes dominant and distinct craters are formed for fluences above ∼1 × 10 16 cm −2 . At the boundary of the implanted region a wall-like structure is found to form upon Ga implantation; its height is growing with increasing fluence, reaching a value of ∼15 nm at 1 × 10 17 Ga + -ions/cm 2 . Copyright

Local nanostructuring of gold thin films through dewetting induced by Ga+ irradiation

“…This result, previously observed in Au films irradiated with 100 keV Ar + ions, was attributed to the sputtering of bigger NPs and a subsequent random redeposition of Au atoms forming smaller aggregates [26]. Therefore, a maximum fluence of $2 Â 10 14 Ga/cm 2 can be used to obtain a monomodal distribution of Au NPs with circular shape; this corresponds to a very low concentration of Ga implanted in the substrate, $0.1 at.% [27], thus limiting substrate contamination.…”

Nanostructures on surfaces by ion irradiation

“…In other experiments using FIB systems for irradiation [150][151][152][153][154][155], extended wall-like structures were found to develop at the periphery of the bombarded areas upon Ga implantation. The AFM topography image in Fig.…”

“…The AFM topography image in Fig. 16a shows such wall-like features at the boundary region of an irradiated area for a Ge specimen bombarded by 30 keV Ga + ions with 3 × 10 16 ions/cm 2 [155]. Figure 16b displays a cross-section line profile of that area and illustrates the pertinent features.…”

“…Figure 16b displays a cross-section line profile of that area and illustrates the pertinent features. For Si and Ge specimens, the height of this wall was found to increase with increasing fluence, reaching a value of ~15 nm at 1 × 10 17 Ga + -ions/cm 2 [155].…”

Control of the micrometric scale morphology of silicon nanowires through ion irradiation-induced metal dewetting

“…Six rectangular regions (each one having a surface of 390 Â 290 mm 2 ) were irradiated by a rastering beam with fluences varying between 2.2 Â 10 12 and 7.0 Â 10 15 Ga/cm 2 . Of course, after the ion irradiation Ga atoms are implanted in the substrate: however, even for the highest fluence we expect a concentration peak lower than 5 at%, located 30 nm below the Si surface [19]. During the irradiation the ion beam was defocused to a spot of $ 2 mm in diameter, much larger than pixel size: this ensures a uniform irradiation all over the scanned surface.…”