An investigation of ion implantation-induced near-surface stresses and their effects in sapphire and glass

Using both cantilever bending and indentation fracture techniques, the generation of near-surface compressive stresses by ion-implantation into sapphire and glass has been monitored and characterized. In all cases, the surface stresses initially increase with ion dose until a critical dose (dependent on material and ion species/ energy) is reached. Beyond this dose, stress relief has been observed and, for sapphire implanted with both Y⁺ and Ti⁺, this has been attributed to the formation and growth of an amorphous layer as monitored by hardness testing. The stress relief has been simply modelled and values estimated for the mechanical strength of the amorphous layer produced. For sapphire, the integrated stress produced over the near-surface volume was found to increase linearly with dose; values of the integrated stress produced by the two different species were similar when considered in terms of energy deposition. Estimates of the contribution to the integrated stress of both the implantation-induced damage and the implanted species profile suggest that the implanted profile makes a minor but significant (20%) contribution. Broadly similar behaviour was observed for soda-lime-silica glass specimens implanted with both C⁺ and N⁺. While the origins of the compressive stress produced are probably similar to those in crystalline materials (i.e. defect production and ion-stuffing), no microstructural explanations for both the observed hardening with increasing dose and stress relief have been forthcoming. However, high-dose implantation of N⁺ into glass leads to blistering and concomitant softening.     

The structural characteristics of radiation damage produced by high energy (2.7 MeV) ion implantation in GaAs

The radiation damage induced by the implantation of 2.7 MeV P⁺ and N⁺ ions with a dose of 6.4 × 10¹⁶ ions cm^–3 into GaAs at room temperature has been studied by transmission electron microscopy. The as-implanted material was found to consist of a buried amorphous layer which was sandwiched between a heavily damaged but crystalline cover layer exhibiting a high density of black dot defects, microtwins and dislocation loops and a less damaged substrate region. Post-implantation annealing of the specimens at 250° C for 6 h resulted in the recrystallization of the amorphous and cover layers by random nucleation of grains producing a polycrystalline region on the single crystal substrate. However, a second stage annealing of these samples at 400° C for 2 h caused an epitaxial regrowth of the implanted layer on the undamaged substrate producing single crystal regions which were heavily twinned on all {111} planes. The results of the present microstructural analyses have been compared with the previous infra-red reflectivity studies on identically implanted GaAs samples to determine the effects of structural changes on the dielectric properties. The two studies are found to be in reasonable agreement. The present results are also compared with those from previous lower energy-lower dose implantations.     

Nanocluster evolution in Ge ion implanted Ta2O5 layers

Ion implantation-induced nanoclusters were synthesized in reactive sputtered Ta₂O₅ films by Ge⁺ implantation and subsequent annealing. The effects of ion fluence and post-implantation thermal treatment on the kinetics of the nanoclustering were investigated. Ge⁺ ions with energy of 40 keV and fluences of 5 × 10¹⁵, 1 × 10¹⁶ and 5 × 10¹⁶ cm^− 2 were implanted in the Ta₂O₅ layers at room temperature. The samples were thermally treated by rapid thermal annealing in vacuum at 700 °C and 1000 °C for 30, 60 and 180 s. Structural studies of all samples were done by Cross-sectional Transmission Electron Microscopy in diffraction and phase contrast mode. Under optimized conditions (high implantation fluence, subsequent annealing) nanoclusters are formed around the projected ion range of the implanted Ge⁺ ions. The structure of the implanted Ta₂O₅ matrix changes from amorphous to orthorhombic when the annealing was performed at 1000 °C. Although the Ta₂O₅ matrix crystallizes, no evidence is obtained for crystallization of the embedded nanoclusters even after annealing at 1000 °C.     

Electron beam annealing of Fe+ implanted Si nanostructures

Silicon nanostructures (nanowhiskers) have been formed at surface densities approximately 10(9) cm-2 by electron beam annealing (EBA) prior to the implantation of 7 keV Fe+ ions to fluences from 1 x 10(13) - 4 x 10(15) Fe+ cm(-2). A second EBA step is then applied to relieve implantation-induced stresses. RBS analysis shows that the implanted Fe remains close to the surface. AFM characterisations of the implanted nanowhiskers before and after the final EBA step are summarised in graphs of height versus surface density. In a striking result it is shown that the nanowhiskers not only survive processing but also grow significantly. For example, at the highest fluence of 4 x 10(15) Fe+ cm(-2), the average height more than doubles: the increases are from 5.0 nm to 6.5 nm under implantation and from 6.5 nm to 11.8 nm under EBA. In addition there is a significant increase in surface density from an initial value of 1.6 x 10(9) cm(-2) to 4.3 x 10(9) cm(-2). These results highlight the feasibility of doping Si surface nanostructures with magnetic ions to fabricate Si devices for spin-dependent enhanced field emission.     

RBS,infrared and diffraction compared analysis of SiC synthesis in C implanted silicon

Monocrystalline (111) and (100) silicon substrates were implanted with singly charged carbon ions, and synthesis of silicon carbide through thermal processes was considered. Implantation energies from 10 to 40 keV were used with fluences ranging between 5×10¹⁶ and 5×10¹⁷ ions cm^?2. Analysis of the material obtained was performed using Rutherford backscattering, infrared spectra and electron diffraction. Correlations between corresponding data reported here give evidence of the respective influence of implantation energy, fluence, substrate orientation and annealing temperature.     

Flash-lamp annealing of semiconductor materials—Applications and process models

Flash-lamp annealing (FLA) on a millisecond time scale has been shown to be a promising tool in the preparation of high-quality semiconducting materials. The process imposes time varying through-thickness temperature profiles on the substrates being processed, and consequently thermal stresses. A combined thermal and optical model has been developed to predict the substrate temperature distribution and this model has been linked to a structural model to compute stresses and deflections. The paper shows how these models can be used to explore process conditions in flash lamp annealing, with particular regard to the annealing of ion implants in silicon and the crystallization of amorphous silicon layers on glass substrates.     

Amorphization, recrystallization and end of range defects in germanium

The controlled doping of germanium by ion implantation is a process which requires basic research before optimization. For this reason, we have experimentally studied by transmission electron microscopy both the kinetics of amorphization and of recrystallization of Ge during ion implantation (Ge, P and B) and further annealing. As in Si, the crystalline to amorphous phase transition occurs through the linear accumulation of damage with the dose until a certain threshold is reached above which the material turns amorphous. We show that the Critical Damage Energy Density (CDED) model can be used in germanium to predict the existence, position and extension of amorphous layers resulting from the implantation of ions for almost all mass/energy/dose combinations reported here and in the literature. During annealing, these amorphous layers recrystallize by solid-phase epitaxy following an Arrhenius-type law which we have determined. We observe that this regrowth results in the formation of extended defects of interstitial type. During annealing these defects evolve in size and density following an Ostwald ripening mechanism which becomes non-conservative (defects “evaporate”) as the temperature is increased to 600 °C. These results have important implications for the modeling of diffusion of implanted dopant in Ge. Transient diffusion may also exist in Ge, driven by an interstitial component usually not evidenced under equilibrium conditions.     

Superconductivity and Mössbauer effect of Nb3Sn produced by Sn implantation

We have implanted Sn, Ge, and Si into Nb films. The resulting Nb-Sn compounds and their annealing behavior have been analyzed by the Mössbauer effect and compared to samples obtained by diffusion of Sn into Nb foils. Mössbauer spectra show that Nb₃Sn is obtained just by implantation, but with a T _cof only 5 K. The 925°C annealing temperature necessary to form the A15 structure with long-range order of Nb chains and T _cvalues up to 17.8 K is at least 100 °C higher in implanted samples than in samples prepared by diffusion of Sn into Nb. This is explained in terms of implantation-induced lattice defects. The metastable A15 phases of Nb₃Ge and Nb₃Si could not be formed by Ge or Si implantation, regardless of target or annealing temperature. It is suggested that the high-energy ions only form phases stable at high temperatures and with low T _cvalues.On leave from North Dakota State University, Fargo, North Dakota.     

Rutherford backscattering/channeling study of the implanted MeV Au+ in silicon

1.0 MeV Au⁺ ions were implanted into a Si single crystal and an amorphous silicon film at room temperature. For the case of the Si single crystal, ion implantation was performed at angles of 7, 45 and 60°, respectively. The amorphous silicon film was deposited on SiO₂ substrate with a thickness of ∼500 nm. The longitudinal and lateral distributions of implanted Au ions in silicon were measured by Rutherford backscattering spectrometry. The lateral spread was estimated from the tilt angle implantation. The results show that the experimental mean projected range is larger than the calculated value by ∼20%, and the experimental range straggling and lateral spread deviate significantly from the TRIM prediction. The damage in the Si single crystal induced by MeV Au⁺ under different fluences was studied by Rutherford backscattering/channeling. Also, the thermal behaviour of the implanted Au⁺ in silicon was investigated.     

Raman study of ion-implanted hydrogenated amorphous silicon

The effect of silicon and hydrogen ion implantations on the structural properties of hydrogenated amorphous silicon films was studied by means of Raman spectroscopy, with the aim of revealing the influence of hydrogen atoms inserted into the silicon matrix on its short-range order. To separate the implantation-induced increase in the structural disorder from the effect of the implanted hydrogen, the implantation doses of silicon and hydrogen ions were selected to create closely similar numbers of host-atom displacements. The results obtained suggest that the presence of hydrogen in amorphous silicon reduces the structural disorder related to variations in the silicon bond length, but affect the bond-angle deviations to a lesser extent.     

Characterization of damage behavior induced by low-temperature BGe molecular ion implantation in silicon

The present study utilized Raman scattering spectroscopy (RSS) to characterize damage behavior induced by implanting 77 keV BGe molecular ions into Si<100> wafers at low substrate temperatures under various ion fluences. The low substrate temperatures under investigation included liquid nitrogen temperature (LT) and room temperature (RT). Rapid thermal annealing (RTA) at 1050 °C for 25 s in nitrogen ambient was adopted in order to perform the post-annealing treatments. The as-implanted results revealed that the longitudinal optical (LO) phonon Raman peak (indicating the crystalline silicon phase) exhibited a decrease in peak intensity, peak position, and peak area but an increase in full-width at half-maximum (FWHM) of the peak as ion fluence increased or substrate temperature decreased. However, the transverse optical (TO) phonon Raman peak (indicating the amorphous silicon phase) decreased in peak position and FWHM of the peak but increased in peak intensity and peak area when ion fluence increased or substrate temperature decreased. The amount of implantation-induced damage in the LT specimens is greater than it is in the RT ones. However, the as-annealed results revealed that the amount of residual damage in the LT specimens is slightly smaller than it is in the RT ones and the difference widens as ion fluence increases.     

CuCl+注入α-Al2O3晶体退火后表面亚微米颗粒的形成情况研究

CuC l+离子注入不同晶向的α-A l2O3晶体中,对在还原气氛下退火后的试样进行SEM表面观察。结果发现,不同注入条件和不同温度退火的不同晶向α-A l2O3晶体表面均形成弥散的亚微米颗粒。说明CuC l+离子注入α-A l2O3晶体产生的缺陷损伤在退火过程中,单个分散的带电色心缺陷与CuC l+离子形成的缺陷缔合体在恢复过程中发生了CuC l原子的偏聚,随着退火时间的增加,偏聚程度提高而形成颗粒,并逐渐长大形成亚微米颗粒。颗粒的大小和分布随注入条件以及退火温度不同而不同。     

Friction and wear of ion-implanted metals—A review

A review is given of the current status of friction and wear testing with ion-implanted metals, mostly centred on ferrous materials. The changes in coefficients of friction measured under low speed conditions are ascribed to the modification of oxidation properties and to decohesion below the implanted layer due to implantation-induced damage. Wear tests carried out under pin-on-disc and crossed-cylinder geometries show that high doses (above 10¹⁷ cm^-2) of nitrogen and other ions reduce the mild wear rate on steels by a factor of at least 10. The beneficial effects of ion implantation continue beyond the original range of the implanted ions. This is consistent with a mechanism by which dislocations acting as traps for nitrogen and carbon provide wear resistance. Continued effectiveness against wear may arise from thermal or stress-induced migration of implanted atom-defect complexes below the contact region. High dose nitrogen implantation also leads to nitride formation and so hardness increases can be accounted for directly. For inhomogeneous materials such as cemented tungsten carbide it is more difficult to account for the improvements in wear properties. Nitrogen and carbon implantation is thought to reduce the plastic flow of cobalt and hence to decrease the wear rate of the composite carbide.     

Effects of ion implantation on the hardness and friction behaviour of soda-lime silica glass

Ion implantation-induced changes in the near-surface mechanical properties of soda-lime silica glass have been investigated by indentation and scratch testing and have been found to be more complicated than changes in the corresponding properties of crystalline ceramic materials. Argon, nitrogen, carbon and potassium ions were used with energies in the range 45–300 keV. Hardness and scratch friction tests were performed under ambient laboratory conditions. At low doses, a decrease in hardness and an increase in both friction and surface stress are observed which are attributed to the electronic damage produced by ion implantation. At higher doses, the hardness increases again and a maximum is produced similar to the behaviour observed for crystalline materials. Similarly there is found to be a second stress and friction peak at this dose. This behaviour is shown to be due to the build-up of displacement damage produced by ion implantation and is thus very similar to the radiation hardening (and eventual amorphization) behaviour of ion-implanted crystalline ceramics. For glass, amorphization probably corresponds to some change in the existing amorphous state which, in turn, is responsible for the reduction in hardness, stress and friction at the highest doses.     

Controlling the growth of ZnO quantum dots embedded in silica by Zn/F sequential ion implantation and subsequent annealing

We report the formation of embedded ZnO quantum dots (QDs) by Zn and F ion sequential implantation and subsequent annealing. Optical absorption and photoluminescence spectrum measurements, transmission electron microscopy bright field images and selected area electron diffraction patterns indicate that ZnO QDs were formed after annealing in air or vacuum at temperatures higher than 500?°C. Atomic force microscopy images show a comparatively flat surface of the annealed samples, which indicates that only very few Zn atoms are evaporated to the surfaces. The formation of ZnO QDs during the thermal annealing can be attributed to the direct oxidization of Zn nanoparticles by the oxygen molecules in the substrate produced during the implantation of F ions. The quality of ZnO QDs increases with the increase of annealing temperature.     

Effects of ion implantation and annealing on mechanical properties of ceramic using nanoindentor techniques

Nanoindentor techniques have been used to obtain the values of hardness and elastic modulus of α-Al2O3 polycrystalline implanted with metallic species at room temperature with 170 keV, doses ranging from 2×1016 to 2×1017 ions cm-2. After implantation, annealing was performed in the temperature range 600–1400°C. An attempt has been made to correlate the mechanical property modifications with physico-chemical analysis. Elastic and plastic properties of the implanted layers, of about 100 nm thickness, have been characterized by microprobe investigation. This has indicated that certain fluences and thermal annealing temperatures are favourable for the improvement of mechanical properties. This revised version was published online in November 2006 with corrections to the Cover Date.     

Redistribution of indium implanted in silicon due to thermal treatment and swift heavy ion irradiation

Silicon layers of 150 nm thickness supersaturated with indium up to ≈5 at% were prepared by multiple energy ion implantation. A redistribution of the implanted impurities caused by post-implantation annealing and following irradiation with swift Bi ions has been observed by means of Rutherford backscattering spectrometry in channelling configuration (RBS/C). It is demonstrated by TEM that the thermal decomposition of the supersaturated Si〈In〉 solution is accompanied by polycrystalline recrystallisation of amorphous silicon, precipitation of the second phase (In) both within the implanted layer and on the surface, as well as by impurity redistribution. The main features of the structure transformation under the influence of the Bi ion irradiation are discussed.     

Cathodoluminescence of rare earth implanted Ga2O3 and GeO2 nanostructures

Rare earth (RE) doped gallium oxide and germanium oxide micro- and nanostructures, mostly nanowires, have been obtained and their morphological and optical properties have been characterized. Undoped oxide micro- and nanostructures were grown by a thermal evaporation method and were subsequently doped with gadolinium or europium ions by ion implantation. No significant changes in the morphologies of the nanostructures were observed after ion implantation and thermal annealing. The luminescence emission properties have been studied with cathodoluminescence (CL) in a scanning electron microscope (SEM). Both β-Ga(2)O(3) and GeO(2) structures implanted with Eu show the characteristic red luminescence peak centered at around 610 nm, due to the (5)D(0)-(7)F(2) Eu(3+) intraionic transition. Sharpening of the luminescence peaks after thermal annealing is observed in Eu implanted β-Ga(2)O(3), which is assigned to the lattice recovery. Gd(3+) as-implanted samples do not show rare earth related luminescence. After annealing, optical activation of Gd(3+) is obtained in both matrices and a sharp ultraviolet peak centered at around 315 nm, associated with the Gd(3+) (6)P(7/2)-(8)S(7/2) intraionic transition, is observed. The influence of the Gd ion implantation and the annealing temperature on the gallium oxide broad intrinsic defect band has been analyzed.     

Formation of Ge nanocrystals in Al2O3 matrix

Ge nanocrystals were formed in Al2O3 matrix by implantation of Ge ions into sapphire (alpha-Al2O3) substrates and subsequent annealing. Diagnostic techniques, Raman spectroscopy, XRD, TEM, EDS, and SAED were employed to monitor and study formation of Ge nanocrystals and their evolution during heat treatments. TEM and EDS analysis revealed the diffusion of Ge ions into the substrate during annealing process. While Ge nanocrystals with mean sizes of 15 nm were observed in the heavily implanted region small nanocrystals with mean sizes of 4 nm were identified underneath this region. Some grains of transition aluminas were formed in the implanted region which was amorphized during the implantation. Extensive stress between the transition aluminas and sapphire matrices and its effects on the matrix were detected. The effect of stress on the Raman and XRD spectra of Ge nanocrystals was discussed.     

Some preliminary studies of the structure of ion bombarded thin films

The paper describes preliminary electron microscopic and diffraction studies of ion implanted and recoil atom implanted thin films. It is shown that oxygen implanted aluminum films form complex cermets consisting of polycrystalline aluminium islands in an amorphous dielectric matrix.The dielectric consists of compounds made up of both substrate and film elements and the implanted oxygen. It has also been shown that oxygen implanted titanium thin films form cermet structures of crystalline TiO in an amorphous dielectric probably containing TiO₂ and compounds of the silica substrate. The structure of silicon oxide films recoil implanted with silver from an argon bombarded silver over layer has been studied. It is shown that the recoil implanted material forms discrete clusters within the substrate and that argon entering the silicon oxide forms bubbles. A recoil implantation coefficient of 1.1 silver atoms per incident argon ion has been measured.