Si Ion Irradiation Research Articles

Photoluminescence from Si ion irradiated SiO 2/Si/SiO 2 films with elevated substrate temperature

Photoluminescence (PL) from the Si ion irradiated SiO 2/Si/SiO 2 layers on Si substrate at room temperature and elevated substrate temperatures has been studied to elucidate the luminescence origins. The irradiation of Si ions into SiO 2/Si/SiO 2 layers instead of SiO 2 films was performed to improve the PL intensity by increasing the number of proper-sized Si nanocrystals. Before annealing at high temperature, a luminescence band around 450 nm is observed. This luminescence band was found to originate from the diamagnetic defect known as B 2 band generated by Si ion irradiation. The intensity of this band increases when ion irradiation is carried out at high substrate temperature. After annealing at high temperature, the PL peaks originating from the B 2 band disappear and a new PL peak appears around 700 nm. This luminescence band is associated with ∼5-nm sized Si nanocrystals. Also it can be found that the PL peak intensity around 700 nm is significantly increased with the high substrate temperature during ion irradiation. Therefore, it is concluded that ion irradiation into SiO 2/Si/SiO 2 layers is more effective than ion implantation into SiO 2 films to obtain an intensive PL peak originating from Si nanocrystals.

Granularity controlled irradiation response of cuprate superconductors

Confining to an energy range where ions can neither create defects through elastic energy loss nor they can create defects through latent track formation, we study the effect of 140 MeV Si-ion irradiation in YBa 2Cu 3O 7− x (YBCO). We show that the evolution of superconducting and normal state properties in such situation is largely governed by the initial defects structure, particularly the grain boundary characteristics of the YBCO system. Both intra- and inter-granular defect structure in films of two batches were made widely different by having Ag as composite and substituent in one and by aging the other prior to irradiation. Evolution of the resistivity vs temperature characteristics in these films with ion fluence reveals the importance of Ag in bringing about both inter- and intra-granular modifications and making the films insensitive to ion irradiation.

From Radiation Induced Leakage Current to Soft Breakdown in Irradiated MOS Devices With Ultrathin Gate Oxide

ABSTRACTMetal Oxide Semiconductor (MOS) capacitors with ultra-thin oxides have been irradiated with ionising particles (8 MeV electrons or Si, Ni, and Ag high energy ions), featuring various Linear Energy Transfer (LET) ranging over 4 orders of magnitude. Different oxide fields (Fbias) were applied during irradiation, ranging between flat-band and 3 MV/cm. We measured the DC Radiation Induced Leakage Current (RILC) at low fields (3-6 MV/cm) after electron or Si ion irradiation. RILC was the highest in devices biased at flat band during irradiation. In devices irradiated with higher LET ions (Ni and Ag) we observed the onset of Soft-Breakdown phenomena. Soft-Breakdown current increases with the oxide field applied during the stress.

Glancing incidence diffuse X-ray scattering studies of implantation damage in Si

Diffuse X-ray scattering (DXS) at glancing incidence is a potentially powerful means for elucidating damage structures in irradiated solids. Fundamental to the analysis of diffuse X-ray scattering data is a knowledge of the atomic displacement field around defects, which for implantation damage in crystals like Si has been difficult to obtain using analytical solutions of elastic continuum theory. We present a method for predicting the diffuse scattering pattern by calculating the displacement field around a defect using fully atomistic simulations and performing discrete sums for the scattering intensity. We apply the method to analyze experimental DXS results of defects produced by 4.5 keV He and 20 keV Ga irradiations of Si at temperatures of 100–300 K. The results show that the self-interstitial in ion-irradiated Si becomes mobile around 150 K, and that amorphization of silicon by light and medium-heavy projectiles occurs homogeneously through the buildup of interstitial clusters, and not within single cascade events.

Self ion irradiated Si probed with enhanced depth resolution positron annihilation spectroscopy

Standard positron annihilation spectroscopy (PAS) measurements of implanted Si are limited in the detail that is obtainable on the distribution of the implantation induced defects. In particular, accessing the defect tail distribution is difficult due to the large numbers of defects in the peak concentration and the inherent decrease in depth resolution with increasing positron energy. Enhanced depth resolution positron annihilation spectroscopy overcomes these problems by combining standard positron measurements with the controlled removal of thin layers of the implanted sample. The technique is described in detail and examples of its capabilities are shown using both simulated and experimental (50 keV 5 × 10 13 cm −2, self-implanted Si) data.

Effects of 10-MeV ion irradiation on Au/Ta studied with scanning tunneling microscopy

Adhesion of a 10-nm Au film on a Ta substrate is enhanced with 10-MeV Si ion irradiation at room temperature. The modifications of surface topography on a Au film are investigated by Scanning Tunneling Microscopy (STM). Surface craters and defects have been observed in this metal/metal system. It is shown that the higher the dose of ion irradiation, the higher the density and the bigger the size of the craters. The craters which are several nanometers in diameter extend from the surface into the interfacial region. A threshold dose at which the Au film can pass the Scotch tape test is determined, and the mechanism of the adhesion enhancement by ion bombardment is discussed.

Defects formed during 1 MeV Si ion-irradiation of GeSi/Si strained-layer heterostructures at elevated temperatures

The strain relief observed in GeSi/Si strained-layer heterostructures irradiated with MeV ions at elevated temperature (253°C) is shown to be consistent with the accumulation of excess vacancies in the alloy layer. Partial recovery of the as-grown strain during subsequent annealing to temperatures <750°C coincides with the appearance of macroscopic voids. Since the tensile strain per vacancy is reduced by clustering this is believed to account for the observed strain recovery. At higher temperatures, >750°C, accelerated strain relaxation is shown to coincide with the growth of large intrinsic dislocation loops from the alloy–substrate interface. After annealing at 900°C, unirradiated alloys contain a low density of orthogonal misfit dislocations. Irradiated samples contain intrinsic irregular loop-like defects extending between the alloy–substrate interface and the surface.

The effect of swift heavy ion irradiation on perpendicular magnetic anisotropy in Fe-Tb multilayers

The effect of swift heavy ion irradiation of Fe-Tb multilayers has been studied using x-ray reflectivity and conversion electron Mössbauer spectroscopy measurements. The energy deposited in the multilayer in the form of electronic excitations results in significant modification of the interfaces. During 80 MeV Si ion irradiation the interfacial roughness is found to increase linearly with irradiation dose. Mössbauer measurements provide evidence of segregation of Fe and Tb atoms in the intermixed region, which may be the cause of the observed increase in the interfacial roughness. The as-deposited multilayer exhibits a large perpendicular magnetic anisotropy, which shows a monotonic decrease with irradiation dose. The observed decrease in perpendicular magnetic anisotropy is a combined effect of the stress relaxation in the bulk of layers and an increase in the interfacial roughness. 150 MeV Ag ion irradiation causes additional intermixing at the interface, accompanied by a large reduction in perpendicular magnetic anisotropy.

Effects of MeV Si ion irradiation on the properties of shallow P + N junctions

The effects of post-ion implantation on the properties of P + N junction formed by BF 2 ion implantation in SiO 2/Si (1 0 0) have been studied in this paper. As for the post-irradiation using MeV Si ions, there is a critical dose for Si ions. When the dose is less than the critical dose, post MeV Si ion irradiation induces reduction of the anomalous diffusion of B atoms. However, when the dose is higher than the critical dose, MeV Si ion irradiation induces further enhancement of the anomalous diffusion of B atoms. As for the electrical properties of the P + N junction, post-ion irradiation using 1.0 MeV 5 × 10 14 Si/cm 2 reduced the density of the leakage currents by three orders of magnitude. The post-Si ion irradiation either by MeV ions or 70 keV ions leads to a reduction of the breakdown voltage of the junction.

Dissipative Structure Formation in Cold-Rolled Fe and Ni during Heavy Ion Irradiation

We report 4-probe resistivity measurements of cold-rolled Ni and Fe during 100 MeV oxygen ion irradiation, at 300 K. The resistivity shows increase and saturation, marked by jumps. Employing 200 MeV silver ion irradiation of Fe and Si(100) and topographically identifying strain at an artificial interface in the latter, we assign the resistivity behavior to atomic rearrangements arising from dissipation of incident ion energy at internal interfaces of Ni and Fe, with positive feedback.

Effect of Low Temperature ion Irradiation on the Microstructure of Nitride Ceramics

AbstractCross-section transmission electron microscopy was used to investigate the microstructure of polycrystalline silicon nitride (Si3N4) and aluminum nitride (AIN) following 2 MeV Si ion irradiation at 80 and 400 K up to a fluence of 4×1020ions/m2(maximum damage of ∼ 10 displacements per atom, dpa). A buried amorphous band was observed at both temperatures in Si3N4in the region corresponding to the peaks in the implanted ion and displacement damage. From a comparison of Si3N4specimens irradiated at different fluences, it is concluded that the amorphization is primarily controlled by the implanted Si concentration rather than the displacement damage level. Si3N4 amorphization did not occur in regions well-separated from the implanted ions for doses up to at least 3 dpa at 80 K, whereas amorphization occurred in the ion implanted region (calculated Si concentration &gt;0.01 at.%) for damage levels as low as ∼0.6 dpa. The volumetric swelling associated with the amorphization of Si3N4, is &lt;10%. Amorphization was not observed in any of the irradiated AIN specimens. A moderate density of small (∼3 nm) defect clusters were observed in the crystalline damaged regions of both the Si3N4and AIN specimens at both irradiation temperatures. Aligned network dislocations were also observed in the AIN specimen irradiated to high dose at 80 K.

Crystallinity improvement of epitaxial CeO 2 films by high-energy ion irradiation

The high-energy ion assisted crystallinity improvement of epitaxially grown CeO 2 (110) films on Si(100) is investigated using the irradiation of B, C, O, and Si ions with a dose of 1 × 10 15 ions/cm 2 and an energy ranging from 1 to 4 MeV. The crystallinity improvement, which is evaluated by Rutherford backscattering with channeling, is correlated to the ratio of the electronic deposition energy ( De) to the nuclear deposition energy ( Dn). The crystalline quality is improved with inceasing De Dn above 200. The net crystallinity improvement is determined by the dominance between the defect annihilation driven by the inelastic collisions with electrons and the damage production by nuclear collisions. For De Dn < 200 , the damage production exceeds the defect annihilation. In the extreme case of 4 MeV Si ion irradiation with De Dn = 171 , the energy dependence of the ratio of aligned to random yield reveals the defect type change in the irradiated films.

Threshold Irradiation Dose for Amorphization of Silicon Carbide

AbstractThe amorphization of silicon carbide due to ion and electron irradiation is reviewed with emphasis on the temperature dependent critical dose for amorphization. The effect of ion mass and energy on the threshold dose for amorphization is summarized showing only a weak dependence near room temperature. Results are presented for 0.56 MeV silicon ions implanted into single crystal 6H-SiC as a function of temperature and ion dose. From this, the critical dose for amorphization is found as a function of temperature at depths well separated from the implanted ion region. Results are compared with published data generated using electron and xenon irradiating species. High resolution TEM analysis is presented for the Si ion series showing the evolution of elongated amorphous islands oriented such that their major axis is parallel to the free surface. This suggests that surface or strain effects may be influencing the apparent amorphization threshold. Finally, a model for the temperature threshold for amorphization is described using the Si ion irradiation flux and the fitted interstitial migration energy which was found to be ∼0.56 eV. This model successfully explains the difference in the temperature-dependent amorphization behavior of SiC irradiated with 0.56 MeV silicon ions at 1×10-3 dpa/s and with fission neutrons irradiated at 1×10-6 dpa/s irradiated to 1 5 dpa in the temperature range of ∼340 ±10K.

Reduction of secondary defects in 50 keV P +-implanted Si(100) by MeV Si ion irradiation

The reduction of secondary defects in 50 keV P + implanted silicon has been studied by the Rutherford backscattering/channeling technique. It is found that the secondary defects in the P + damaged region was reduced by MeV Si ion irradiation. As for the case of low dose P + ion implantation in Si, the reduction of pre-amorphization defects was less sensitive to the dose of MeV Si ions. However, in the higher dose P + implanted sample, more end of range defects were reduced by a higher dose MeV Si ion irradiation. The gettering effect of extended defects for point defects is discussed.

Low energy ion irradiation of H-terminated Si(001): Hydrogen sputtering, beam-induced(2 × 1) reconstruction, and Si epitaxy

Low energy ion irradiation of H-terminated Si(001): Hydrogen sputtering, beam-induced(2 × 1) reconstruction, and Si epitaxy

Low energy ion irradiation of H-terminated Si(001): hydrogen sputtering, beam-induced (2 × 1) reconstruction, and Si epitaxy

Low energy (15–50 eV) noble gas ion irradiation at low temperatures (< 300°C) enables formation of a Si(001)-2 × 1 surface reconstruction that has been hydrogen-terminated by a hydrofluoric acid dip prior to irradiation. Using 15 eV He + irradiation, a (2 × 1) reconstruction can be formed at temperatures as low as 50°C, the lowest temperature ever reported for formation of this reconstruction. The (2 × 1) reconstruction occurs as a result of surface hydrogen removal by sputtering and recoil implantation into the silicon substrate. Molecular dynamics simulations of low energy irradiation of a hydrogen-terminated silicon surface indicate that chemically-enhanced physical sputtering of silicon occurs in addition to physical sputtering of hydrogen. The hydrogen sputtering yield is found to be strongly dependent on surface hydrogen coverage. The results suggest that low energy ion irradiation can be used to tailor the hydrogen coverage, and thus also the chemical reactivity of the silicon surface.

Analysis of irradiated Ag and Si by molecular dynamics and simulated HREM images

In order to clarify the limits of HREM observations of defects due to radiation damage, a simulation method has been designed which combines molecular dynamics and HREM simulation. Disorder due to ion irradiation in Si and Ag is simulated by using a molecular dynamics technique and HREM images are computed by a multislice dynamic procedure. The conditions to achieve a good HREM visibility of such defective structures have been investigated by analyzing the effects of the physical inputs of molecular dynamics as well as the ones of the instrumental parameters of TEM observations. This analysis indicates that the structure of the damaged region is not critical. On the contrary, the fractional disorder is of paramount importance and determines the conditions leading to an appreciable contrast of the disordered region against the crystalline background.

Gettering effects in BF2-implanted Si(100) by ion-beam defect engineering

The gettering effects of ion-beam defect engineering (IBDE) in BF2-implanted silicon have been studied. It has been shown that the IBDE technique may be useful in the improvement of the properties of BF2-implanted silicon. The gettering layer introduced by MeV Si ion irradiation and formed during the process of thermal annealing collects not only impurities but also simple defects. Thus, it effected (1) reductions of secondary defects and F impurity accumulation in the BF2-doped region; (2) reduction of the anomalous diffusion of B atoms; and (3) enhancement of the electrical activation of B atoms.

Effects of High Energy Ion Irradiation on Crystallization of Amorphous Germanium Films Deposited on Calcium Fluoride Substrates

AbstractAmorphous (a-) Ge films were deposited on air-cleaved CaF2 (111) substrates at different deposition temperatures (Td). The films were irradiated with 0.9 MeV Ge or Si ions at low ion current intensity (1c) l00nA/cm2. Their structural changes were studied by Rutherford backscattering spectrometry (RBS) -channeling technique and thin film x-ray diffraction (XRD) measurement. It was found that the films were epitaxially crystallized by Ge and Si ion irradiation although they included randomly oriented grains. Ge ion irradiation was more effective for the crystallization than Si ion irradiation. However, the amount of the randomly oriented grains was slightly higher when using Ge ions. On the other hand, ion irradiation to the films prepared at high Td also exhibited higher incidence of randomly oriented grains.

X-ray Topography of Strain Fields Induced by 100 MeV Ti7+ Ion Irradiated Si(100)

AbstractThe lattice deformation caused by 100 MeV Ti7+ ion irradiation in Si (100) has been studied using X-ray topographic techniques. An important finding is the appearance of a strain field perpendicular to the ion beam direction in the irradiated region well separated from the projected range of implanted ions. This in-plane strain extends in the bulk of the sample and is not merely confined to the surface. The implanted region has been found to experience an out of plane strain which is expected to be tensile in nature.