Electron Beam Annealing Research Articles

Diffusion of Pb in carbon ion-implanted silicon: Discovery of a new crystalline phase after electron beam annealing

A novel phase has been discovered by dual low-energy ion implantation and high vacuum electron beam annealing. (100) p-type Si was implanted with (a) 20 keV 12C + ions to the fluence of 6 × 10 16 cm −2 and (b) 7 keV Pb + ions to the fluence of 4 × 10 15 cm −2. The 12C ion implantation results in an understoichiometric shallow SiC x layer that intersects with the surface. The implanted Pb ions decorate a shallow subsurface region. High vacuum electron beam annealing at 1000 °C for 15 s using a temperature gradient of 5 °C s −1 leads to the formation of large SiC nanocrystals on the surface with RBS measurements showing Pb has diffused into the deeper region affected by the 12C implantation. In this region, a new crystalline phase has been discovered by XRD measurements.

Nanostructuring at the surface of low‐energy lead‐implanted silicon by electron beam annealing

AbstractLow‐energy lead ion implantation and high‐temperature electron beam annealing were used to study the potential of producing Pb nanostructures on Si. Pb+ ions were implanted at high dose into p‐type (100) Si to the depth of 8.0 nm. The implanted samples were annealed under high vacuum conditions with an electron beam at 200–700 °C for 15 s. Rutherford Backscattering Spectrometry (RBS) shows rapid out‐diffusion of Pb atoms above 400 °C. However, some Pb atoms are still present in the near‐surface region after annealing the implanted samples at 700 °C. Lead nanostructures were found on samples annealed above 300 °C. Annealing the samples at 450 °C causes the formation of nanostructures as tall as 4.1 ± 0.1 nm. Many of these are arranged in ‘web‐like’ strings that extend over micrometer distances. Occasionally, much larger nano‐features (as wide as 500 nm in diameter, average height of 1.5 nm) appear in the centre of the strings. Annealing samples well above the melting point of lead results in randomly distributed small nanometer‐sized Si nano‐dots. Copyright © 2008 John Wiley & Sons, Ltd.

Combined AFM-TEM studies of amorphous-crystalline transformation and interface in thin films of Se and Fe2O3

Thin amorphous films of selenium and iron oxide were crystallized by local electron beam annealing. Two types of spherulite-like crystals grown (complicated by ‘transrotational’ lattice ordering) were studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques. The regularities of change in lattice orientations and imperfection along the crystals obtained by TEM are analyzed in parallel with AFM data for the film surface (relief) of the crystal and amorphous surrounding.

Sub-surface retention of Pb atoms in silicon after low-energy ion implantation and electron beam annealing

Low-energy Pb ion implantation into (100) Si and subsequent high-vacuum electron beam annealing was used to study the potential of sub-surface retention of Pb atoms after applying a high temperature annealing process. 7keV Pb+ ions were implanted into p-type (100) Si at room temperature with a fluence of 4×1015ionscm−2. The implantation results in a Pb depth distribution that has a calculated Pb peak concentration of 23.9at.% at a depth of 8.0nm. The Pb implanted Si substrates were annealed with a high-current 20keV electron beam at 200–700°C for 15s. The Pb loss by out-diffusion was measured with RBS. Key results are: (i) minimal Pb loss in samples annealed up to 400°C, (ii) emerging out-diffusion above 400°C, (iii) retention of Pb atoms in the near-surface region in samples annealed up to 700°C. Comparison of the RBS data with the calculated evaporation rate of Pb under similar conditions reveals two distinctive temperature ranges in which the measured Pb loss of the implanted samples disagrees with the calculated Pb loss: (1) Pb atoms diffused out of the samples at a higher rate in the temperature range up to 400°C and (2) the Pb atoms diffused out of the samples at a much slower rate above 450°C. Both phenomena are attributed to the ion implantation process.

Self-assembled germanium nanostructures formed using electron-beam annealing

Abstract Germanium nanostructures have been fabricated on silicon substrates using ion-beam sputtering growth followed by an ex-situ annealing step. The substrates are not heated during growth, resulting in a post-growth deposited layer ∼225 nm thick with a surface which has no evidence of nanostructure formation. Following annealing at temperatures of 400–700 °C dramatic nanostructuring is observed at the surface. For temperatures below 600 °C atomic force microscopy analysis reveals dense arrays of nanostructures with heights typically around 5–30 nm. Increased feature size and surface roughening is observed for samples annealed above 600 °C, with a broadened size distribution centred at 450 nm. This is assigned to intermixing at the Si/Ge interface, which reduces the stress in the layer, allowing larger features to form.

Optimised process for fabricating functional silicon nanowhisker arrays

Silicon nanostructures, called silicon nanowhiskers, are grown by electron beam annealing of wafer silicon. It is desirable to be able to control sizes and locations of arrays of silicon nanowhiskers for field emission applications. Nitrogen, oxygen and silicon ions were implanted at 15–24keV with fluences ranging from 1012 to 1015ionscm−2 to investigate the possibility of suppressing the silicon nanowhisker growth in specified regions and to search for the minimum level of implanted ions necessary to suppress silicon nanowhisker growth. Particularly interesting results were obtained for the nitrogen ion implantation series where total suppression is achieved by implanting 5×1014N+cm−2. However, implanting 1×1014N+cm−2 results in an increase in nanowhisker density of a factor of three coupled with a decrease in nanowhisker height by a factor of two. Silicon was also found to suppress silicon nanowhisker growth successfully; however oxygen implantations resulted in a decrease of nanowhisker growth with increasing fluence but suppression of nanowhisker growth at 1×1015O+cm−2 was not achieved. Selected results are presented showing the possibility of controlling the silicon nanowhisker growth area by low-energy nitrogen and silicon ion implantation.

Enhanced optical and electrical transitions of LaMg 2Ni alloy film upon hydrogen loading/unloading

An LaMg 2 Ni alloy film was prepared by electron beam evaporation plus annealing. Upon hydrogen loading/unloading, the film shows the reversible conversion from a metallic, reflecting state to a semiconducting, color-neutral transparent one. The contrast ratio of the resistivity between two states is over four orders of magnitude. The lower reflection in the dehydrogenated film is attributed to the rough surface originated from the previous hydrogenation.

How it really happened: The history of p-type doping of gallium nitride

The first single crystal thin film layers of gallium nitride (GaN) were grown in 1969, but it was not until 1989 that conducting p-type films of GaN were finally achieved. Many unsuccessful attempts to produce p-type GaN by annealing techniques including thermal and electron beam annealing were attempted in those intervening twenty years. We discuss here the reason for the early failures, and how the problems were overcome.

Field emission from gadolinium silicide prepared by ion implantation with electron beam annealing

A silicon-based field emission cathode, the rare earth silicide GdSi2 was prepared by implanting Gd ions into silicon using a metal vapor vacuum arc ion source and subsequently annealed by electron beam. For as-implanted samples, turn-on field was about 21V∕μm at a current density of 1μA∕cm2 and a field emission current density of 1mA∕cm2 was reached at an applied field of 34V∕μm. After annealing, the turn-on field could be as low as 9V∕μm and the current density of 1mA∕cm2 can be reached at an applied field of 14V∕μm. X-ray diffraction with x-ray photoelectron spectroscopy analyses and atomic force microscopy were used to characterize microstructure changes of the samples. The results showed that these excellent field emission characteristics were attributed to the GdSi2 compounds formed in the samples. The field emission mechanism was discussed in terms of Fowler-Nordheim (FN) theory. It was found that FN plots could be divided into two segments obviously, and this was perhaps because of the thermal effect in the process of field emission.

Deuteron microprobe analysis of carbon in the transition region between SiC and Si nanostructures grown on Si

Carbon ion implantation and high vacuum electron beam annealing have been applied to produce 200–300 nm large SiC nanocrystals on silicon. Simultaneously, Si nanostructures, called silicon nanowhiskers, grow in the unimplanted region of the (1 0 0) Si substrate during the annealing treatment. The lateral transition region between the SiC nanocrystals and Si nanostructures has been investigated using optical microscopy, deuteron microscopy and atomic force microscopy. Carbon distributions were measured via the 13C(d, p 0) 14C nuclear reaction with a focused scanning deuteron beam with an energy of 1.05 MeV. It has been found that the carbon distribution is directly linked to the growth of the SiC nanostructures. At the boundary between the implanted and un-implanted region, the amount of carbon decreases over 50 μm which causes an abrupt depletion of SiC nanocrystals at this transition region. Specific results outline the important role of nuclear microscopy in nanotechnology process development.

Simultaneous formation of SiC and Si nanostructures on silicon by local ion implantation and electron beam annealing

The authors demonstrate the fabrication of SiC nanocrystals on silicon by carbon ion implantation into silicon followed by electron beam annealing at 1000°C. A continuous asymmetric, pyramidal ridge around 20nm in height is observed at the boundary between the implanted and unimplanted regions. Adjacent to the ridge within the implanted region appears a trough which is continuous around the perimeter of the implanted/unimplanted boundary. The surface of the unimplanted region consists of pyramidal structures with an average height of 5–10nm which cover the entire surface.

A nuclear reaction analysis and optical microscopy study on controlled growth of large SiC nanocrystals on Si formed by low-energy ion implantation and electron beam annealing

Ion implantation of 20keV 12C+ ions into (100), p-type silicon with ion fluence of 8×1016at.cm−2 followed by an electron beam annealing under high vacuum conditions has been performed to investigate the formation of crystalline nano-scale SiC features on the silicon surface. Depending on the implantation and annealing conditions, the SiC nanocrystal numbers and average spacing can be controlled by adjusting the implantation and annealing conditions. Typically 300–1000 SiC nanocrystals are produced per 1000μm2 spaced 0.7–1.2±0.1μm. Nuclear reaction analysis measurements using the deuterium induced 12C(d,p)13C reaction show that carbon is present in the implanted and annealed samples and varies only to a small degree by the annealing time. However, by not using a liquid nitrogen trap surrounding the targets during implantation, the carbon contamination on the surface reduces the number of SiC nanocrystals and increases their average distance. Specific results are discussed.

Pulsed electron beam annealing: A tool for post-implantation damage control in SiC

The possibility of reversing ion implantation damage in SiC using pulsed electron beam annealing is investigated. Using Raman spectroscopy, photo luminescence and infrared reflectance it is shown that good recovery can be obtained for an electron-energy fluence of 1.1 Jcm -2 .

Formation of large SiC nanocrystals on Si(100) by 12C implantation and electron beam annealing

Abstract Scanning electron microscopy and nuclear reaction analysis have been used to study annealing effects of 10 keV 12 C implanted and electron beam annealed silicon (1 0 0) substrates that cause the formation of large SiC nanocrystals named nanoboulders on silicon. Wafer silicon was implanted with varying fluences from 0.38 to 1.14 × 10 17 atoms cm −2 and subsequently annealed at 1000 °C for 15 s. The deuterium induced 12 C(d, p) 13 C reaction was used to measure the 12 C dose quantitatively. It was found that the implanted carbon remained in the specimen after annealing. This result, coupled with geometrical analyses of the resulting nanostructures suggest that following nucleation, the SiC nanocrystals grow as a result of C and Si diffusion across the substrate surface, that became oxide free during annealing under vacuum conditions.

Field emission properties of self-assembled silicon nanostructures formed by electron beam annealing

Arrays of silicon nanostructures on n- and p-type silicon (1 0 0) substrates were fabricated using electron beam annealing of untreated silicon at 1100 °C. Following annealing for 15 s, the nanostructures exhibit an average height of 8 ± 1 nm and a surface density of 11 μm −2 , independent of the substrate conduction type. Following annealing for 600 s the individual nanostructures coalesce and the surface appears roughened with an rms roughness of 30 nm. The field emission properties of these nanostructure arrays have been assessed and electron emission through Fowler–Nordheim tunnelling was confirmed. The difference in threshold field for electron emission from the nanostructured and roughened substrates is related to the geometrical differences between the substrate surfaces. At large electric fields, space charge limited conduction dominates the field emission characteristics of the nanostructured surface.

Patterned growth of self-assembled silicon nanostructures by ion implantation and electron beam annealing

This paper discusses the suppression of self-assembled silicon nanostructure growth through high fluence ion implantation. The nanofabrication procedure involves annealing of untreated Si(100) substrates at 1100°C for 15s using a raster scanned 20keV electron beam. Nanostructuring occurs as a result of kinetic amplification of the surface disorder induced by thermal decomposition of the native oxide. Radiation induced disorder of the Si substrate prior to annealing by ion-implantation modifies the potential energy surface and thus the growth of self-assembled nanostructures. Highly disordered Si(100) surfaces produced by high fluence implantation with nitrogen and silicon ions are shown to completely suppress nanostructure growth. Exploiting this phenomenon we have demonstrated selective area nanostructure growth in microscale regions.

Atmospheric pressure operation of a field emission diode based on self-assembled silicon nanostructures

We report on the field emission from self-assembled silicon nanostructures fabricated on n-type silicon (100) substrates using electron beam annealing. Arrays of nanostructures with an average height of 8nm were formed by substrate annealing at 1100°C for 15s. Simple field emission diode structures were fabricated using these nanostructured silicon substrates as cathodes separated from an aluminium anode by a 1μm thick layer of photoresist. The dielectric leakage current was less than 0.4nA which was found to be a negligible component of the field emitted current flowing through the diode. Following conditioning, the Si nanostructure field emission characteristics become stable and reproducible with Fowler–Nordheim tunneling occurring for fields as low as 3.2Vμm−1. At higher fields, current saturation effects are observed with current-field characteristics typical of space charge limited conduction. The low voltage operation of this device results in suppression of ionizing electron–molecule collisions and the diode has thus been shown to work well at atmospheric pressure.

Surface Preparation of 6H-SiC Substrates by Electron Beam Annealing

An effect of electron beam annealing (EBA) on both surface morphology and characteristics of test Ti/n-6H-SiC contacts was investigated. It was found that the mean roughness of the n-6H-SiC surface decreased from 3.43 nm to 1.35 nm and the surface sheet resistance increased from 3.1 to 4.0 Ω/sq after EBA. The Ti/n-6H-SiC contacts formed on substrates after EBA exhibited ohmic properties, while the same contacts formed on the un-annealed samples were Schottky contacts with the barrier height of 0.63 eV and ideality factor of 1.92.

Effect of crystal orientation on self-assembled silicon nanostructures formed by electron-beam annealing

This paper discusses the growth of silicon nanostructures on silicon (100), (110), and (111) substrates by electron-beam annealing. The nanofabrication procedure involves annealing of the untreated Si substrates at 1100°C for 15s using a raster scanned 20-keV electron beam. Nanostructuring occurs as a result of kinetic amplification of the surface disorder induced by thermal decomposition of the native oxide. Pyramidal and truncated pyramidal nanocrystals were observed on Si(100) surfaces. The nanostructures are randomly distributed over the entire surface and square based, reflecting the twofold symmetry of the substrate surface. Similar square-based pyramidal structures with four equivalent facets are observed following the nanostructuring of Si(110). With Si(111), nanostructure growth occurs preferentially along step edges formed on the vicinal surfaces. Significant differences in the shapes of nanostructures formed on step edges and terraces are related to the different growth mechanisms on the unreconstructed and 7×7 reconstructed domains, respectively.

Effects of predoping and implantation conditions on diffusion of silicon in gallium arsenide subjected to electron-beam annealing

Measurements of capacitance-voltage characteristics and Rutherford backscattering were used to study the parameters of silicon diffusion from preliminarily formed n-type layers into semi-insulating GaAs under electron-beam annealing and conventional heat treatment. The layers were doped with either sulfur or silicon. The degree of 28Si electrical activation and 28Si diffusion coefficient are found to depend on the dopant used to form the n-type layer and on the implantation conditions (continuous or pulsed-repetitive, with a pulse width of 1.3×10−2 s and duty factor of 100).