Low-dose Implantation Research Articles

Two-beam cross-modulation photocarrier radiometry: principles and contrast amplification in semiconductor subsurface imaging

A two-beam photo-carrier radiometry (PCR) technique of semiconductors has been developed. The technique operates on the superposition of superband-gap and subband-gap laser beams which results in the cross-modulation of the backscattered subband-gap laser intensity by the harmonically varying free-carrier-wave density-dependent infrared absorption coefficient. A theory of this two-beam cross-modulation approach and various experimental configurations applied to the imaging of electronic contamination and defects in silicon wafers are presented. Owing to the nonlinear interaction of the two beams, the configuration revealed a new optoelectronic effect, the decrease of the residual subband-gap absorption coefficient due to the decreased carrier capture cross-section brought about by the depletion of occupied band-gap states in the presence of photons produced by radiative recombination. Quantitative values of the optoelectronic constant B associated with the rate of depletion of free-carrier capture cross-section with superband-gap intensity, as well as of IeR, the intensity of radiative recombination emissions, were obtained. These values cannot be measured by conventional PCR or other single-ended optoelectronic techniques. The theory explains the experimental dependence of electronic transport properties on the intensity of the subband-gap beam and accounts for optoelectronic imaging contrast amplification in contaminated or defect semiconductors. The two-beam cross-modulation PCR was further shown to enhance the imaging contrast of a certain electronic contamination type (Fe in p-Si). A dramatic phase contrast enhancement of subsurface defects made by low-dose proton implantation was demonstrated at superband-gap laser intensity levels one order of magnitude lower than possible with single-ended optoelectronic imaging methodologies. This is tentatively attributed to relatively low-injection trap-filling well below optoelectronic trap saturation.

ZnTe precipitates formed in SiO 2 by sequential implantation of Zn + and Te + ions

Ion implantation is a versatile tool for the formation of compound semiconductor nanocrystal precipitates in a host medium with the ultimate goal to form quantum dots for use in device technology. Low dose (1 × 10 16 cm −2) implantations of tellurium and zinc ions have been performed in a 250 nm thick SiO 2 layer thermally grown on 〈1 1 1〉 silicon. Their respective energies (180 and 115 keV) have been chosen to produce 5–10 at.% profiles overlapping at a mean depth of about 100 nm. Subsequent thermal treatments at 700 and 800 °C lead to the formation of nanometric precipitates of the compound semiconductor ZnTe. Their size, crystalline structure and depth distribution have been studied as a function of annealing temperature using transmission electron microscopy (TEM) and Rutherford backscattering spectrometry. For the lowest temperature the TEM images shows a cloudy band of ZnTe, but for the highest temperature, the ZnTe nanocrystals are self organized into two layers parallel to the surface. Their mean diameter ranges between 4 and 30 nm, as a function of annealing temperature.

Influence of the Ge Dose in Ion-implanted SiO2 Layers on the Related Nanocrystal-memory Properties

ABSTRACTThin silicon dioxide (SiO2) on Si layers with embedded germanium nanocrystals (Ge-ncs) were fabricated using 74Ge+-implantation at 15 keV and subsequent annealing. Transmission electron microscopy and Rutherford backscattering spectrometry have been used to study the Ge redistribution in the SiO2 films as a function of implantation dose under specific annealing conditions. At low implantation doses, Germanium is found to segregate at the Si/SiO2 interface leading to poor electrical properties. At higher doses and when the disorder limit of one displacement per atom is reached at the interface, transmission electron microscopy revealed the formation of a Ge-nc layer array located close to the Si/SiO2 interface and an another one inside the SiO2 host material. This near-interface high density (>1012 ncs/cm2) nc-layer is found to act as a floating gate embedded within the silicon dioxide. Capacitance-voltage measurements performed on metal-oxide-semiconductor structures containing such implanted SiO2 layers show significant memory properties (few volts hysteresis) at low programming voltages (<|10V|) due to the presence of Ge-ncs near the Si/SiO2 interface

P implantation doping of Ge: Diffusion, activation, and recrystallization

We have studied doping profiles, activation levels, and defect annealing of P introduced in Ge by ion implantation at different doses and energy, and annealed under various conditions by rapid thermal annealing. Common to all implant energies, ion-implanted P in Ge exhibits a “box profile” at high implant doses, when a sufficiently high thermal budget is applied—similarly to the concentration-dependent diffusion of P introduced in Ge from a high-concentration solid source. Upon proper annealing conditions, the active P concentration is limited to (5–6)×1019at.∕cm3, implying a 50% activation level of the total retained atoms for high-dose implants and 100% for the low-dose implants. A low thermal budget is sufficient to fully regrow the amorphous layer formed by high-dose P implantations, without evidence of residual defects in the regrown germanium layer and at the end of range of the P implant.

Electronic Properties and Thermal Stability of Defects Induced by MeV Electron/Ion Irradiations in Unstrained Germanium and SiGe Alloys

Deep states produced during γ irradiation of germanium have been compared with the defects produced by 1 and 3MeV silicon ion implantation. The deep states have been studied using DLTS and Laplace DLTS techniques. Isochronal annealing has been used to investigate the defect evolution and stability over the range 100 to 500°C. It is found that while irradiation damage can be removed with a very low thermal budget, the implantation damage is more complex and much more difficult to remove. By comparing low (1010cm-2) and high (1012cm-2) implantation doses it appears that both the complexity and stability of defects increases with increasing dose. Similar experiments have been performed on Ge rich Si1-xGex (x=0.992). The focus of this work has been on vacancy related defects. It is believed that the diffusion of both acceptors and donors is vacancy mediated in Ge and so vacancy clusters rather than interstitial clusters are expected to be the technologically significant defect in enhanced diffusion. The significance in terms of junction leakage and generation currents are discussed in the paper in the context of the observed defect reactions.

Defect Removal, Dopant Diffusion and Activation Issues in Ion-Implanted Shallow Junctions Fabricated in Crystalline Germanium Substrates

The formation of shallow junctions in germanium substrates, compatible with deep submicron CMOS processing is discussed with respect to dopant diffusion and activation and damage removal. Examples will be discussed for B and Ga and for P and As, as typical p- and n-type dopants, respectively. While 1 to 60 s Rapid Thermal Annealing at temperatures in the range 400-650oC have been utilized, in most cases, no residual extended defects have been observed by RBS and TEM. It is shown that 100% activation of B can be achieved in combination with a Ge pre-amorphisation implant. Full activation of a P-implant can also be obtained for low-dose implantations, corresponding with immobile profiles. On the other hand, for a dose above the threshold for amorphisation, a concentration-enhanced diffusion of P occurs, while a lower percentage of activation is observed. At the same time, dose loss by P out-diffusion occurs, which can be limited by employing a SiO2 cap layer.

Curiethérapie du cancer prostatique : haut débit ou bas débit de dose ?

Low-dose brachytherapy for prostate cancer was actually proposed in the first years of the XXth century. Its modern version (iodin 125 or palladium 103 permanent implants) now benefits from some 15 years of experience in a few pioneer centers, with very satisfactory results in term of efficacy/toxicity ratio. More recently, a high-dose rate (HDR) prostate brachytherapy technique has been introduced. Initially utilized essentially as a "boost" irradiation combined with external radiotherapy, it is now being proposed by some authors as a monotherapy for selected localized prostate cancers. Although sophisticated radiobiological models have been proposed to compare those two dose-rates, they are not considered to be valid and reliable enough to compare such different irradiation schemes (A low-dose rate irradiation lasting several months vs a few high-dose fractions given in a few days). When it comes to the implantation techniques, it seems that most of the technical problems which arose for both schemes have been solved, and that the experience of a given team is now much more important than the technique itself. Clinical results cannot be reliably compared so far, the follow-up of the patients treated by HDR brachytherapy being usually shorter, and the patients treated with HDR usually presenting with more advanced lesions. Radioprotection features are very different, with no accident reported for low-dose rate implants. For HDR no irradiation is given at all to the staff and family during a normal application, but one has to face the threat of manipulating high activity sources, with a few accidents or incidents reported in the literature. Financial studies show that for more than 20-30 patients treated in a year, HDR is more economical, although a decrease in the cost of the seeds could change the picture. In conclusion, for low-risk localized prostate cancer, it does not appear reasonable to give up using a low-dose rate technique, which proved to be both efficient and poorly toxic. This actually corresponds to the recent GEC-ESTRO recommendations. For the other patients, a dose escalation is appealing: this could be performed using brachytherapy (LDR or HDR), with or without hormonotherapy. Several trials are ongoing or will be activated very soon to try and answer.

Positron beam studies of argon-irradiated polycrystal α-Zr

Doppler broadening spectroscopy was performed using a variable-energy positron beam to investigate the effect of defects induced by 150-keV Ar-ion-irradiated α-Zr bulk material. S parameter in the damaged layer of the as-irradiated sample induced by ion irradiation increased with the increasing implantation dose. Isochronal annealing between 350 and 800°C in vacuum studies was carried out to investigate the thermal stability of defects in the oxide surface and damaged layer for low-dose (1×1014cm2) and high-dose (1×1016cm2) irradiated samples. The results of S-W plot measured at different annealing temperatures showed that the positron-trapping center had changed. The Ar-decorated voids or vacancies, which formed in high-dose implantation samples by Ar ions combining with open-volume defects, are stable and do not recover until at high annealing temperatures. Comparing the annealing behavior of the high-dose and low-dose implantation samples show that the recovery process of open-volume defects such as vacancies and voids will be delayed by the excess Ar concentration.

Optical properties of stoichiometric LiNbO3 waveguides formed by low-dose oxygen ion implantation

The planar waveguides in z-cut stoichiometric LiNbO3 crystal have been fabricated by 3.0 MeV oxygen ion implantation with the dose of 6×1014ions∕cm2 at room temperature. The modes of the waveguides were measured by the prism-coupling method with the wavelength 633 and 1539 nm, respectively. The refractive index profiles of the waveguides were reconstructed using reflectivity calculation method. The Rutherford backscattering/channeling technique was used to investigate the damage produced by the ion implantation, the minimum yield of the spectra was 4.52%. The propagation loss of waveguide was 0.61 dB/cm obtained by fiber probe technique. It was found that positive changes of extraordinary refractive indices happened in the guiding regions, and such change increased after the annealing treatment at 260 °C for 60 min.

Effects of the technology of implanting nitrogen into buried oxide layer on the characteristics of partially depleted SOI nMOSFET

The effects, caused by the process of the implantation of nitrogen in the buried oxide layer of SIMOX wafer, on the characteristics of partially depleted silicon_on_insulator nMOSFET have been studied. The experimental results show that the channel electron mobilities of the devices fabricated on the SIMON (separation by implanted oxygen and nitrogen) wafers are lower than those of the devices made on the SIMOX (separation by implanted oxygen) wafers. The devices corresponding to the lowest implantation dose have the lowest mobility within the range of the implantation dose given in this paper. The value of the channel electron mobility rises slightly and tends to a limit when the implantation dose becomes greater. This is explained in terms of the rough Si/SiO2 interface due to the process of implantation of nitrogen. The increasing negative shifts of the thre shold voltages for the devices fabricated on the SIMON wafers are also observed with the increase of implanting dose of nitrogen. However, for the devices fabri cated on the SIMON wafers with the lowest dose of implanted nitrogen in this pap er, their threshold voltages are slightly larger on the average than those prepa red on the SIMOX wafers. The shifts are considered to be due to the increment of the fixed oxide charge in SiO2 layer and the change of the density of the int erface-trapped charge with the value and distribution included. In particular, t he devices fabricated on the SIMON wafers show a weakened kink effect, compared to the ones made on the SIMOX wafers.

Self-Lubrication of Chlorine-Implanted Titanium Nitride Coating

Chlorine implantation into TiN coatings decreases the wear loss and the friction coefficient. Even by low-dose chlorine implantation, the wear volume is decreased by three orders of magnitude or more, and the friction coefficient becomes <0.1. This self-lubrication mechanism is related to the presence and mobility of implanted chlorine atoms inside the columnar TiN microstructure. According to observations of chlorine-implanted TiN coatings using high-resolution transmission electron microscopy, the chlorine atoms are present in the damaged region, where TiN is composed of nanosized grains. From these data, a self-lubrication mechanism is proposed with chlorine catalyzing the oxidation of titanium and leading to the formation of some tribological reaction product.

Formation of waveguides by implantation of 3.0MeV Ni2+

3.0 MeV Ni2+ in the beam doses from 1×1013to9×1014ions∕cm2 are implanted into LiNbO3 single crystals at room temperature. After 300°C annealing for 30min in air ambient, dark mode measurement is done by the prism-coupling technique. Waveguides from both raised extraordinary index layer and barrier-confined are formed by low and high beam dose implantation, respectively. In the samples implanted by mediate beam doses, a phenomenon of “missing mode” is observed. The experimental results are analyzed and compared with the simulated results from a theoretical model, which is based on the assumption that the change of index induced by implantation is mainly governed by degradation of polarization and reduction of material density. With a fiber probe, the waveguide loss from single transverse magnetic mode is measured, which is about 3dB∕cm.

Comparative study of SOI/Si hybrid substrates fabricated using high-dose and low-dose oxygen implantation

Hybrid substrates comprising both silicon-on-insulator (SOI) and bulk Si regions have been fabricated using the technique of patterned separation by implantation of oxygen (SIMOX) with high-dose (1.5 × 1018 cm−2) and low-dose ((1.5–3.5) × 1017 cm−2) oxygen ions, respectively. Cross-sectional transmission electron microscopy (XTEM) was employed to examine the microstructures of the resulting materials. Experimental results indicate that the SOI/Si hybrid substrate fabricated using high-dose SIMOX is of inferior quality with very large surface height step and heavily damaged transitions between the SOI and bulk regions. However, the quality of the SOI/Si hybrid substrate is enhanced dramatically by reducing the implant dose. The defect density in transitions is reduced considerably. Moreover, the expected surface height difference does not exist and the surface is exceptionally flat. The possible mechanisms responsible for the improvements in quality are discussed.

8.5-&amp;lt;tex&amp;gt;$hbox mOmega cdot hbox cm^2$&amp;lt;/tex&amp;gt;600-V Double-Epitaxial MOSFETs in 4H–SiC

The most important issue in realizing a 4H-SiC vertical MOSFET is to improve the poor channel mobility at the MOS interface, which is related to high on-resistance. This letter focuses on a novel 4H-SiC vertical MOSFET device structure where a low acceptor concentration epitaxial layer is used as a channel. We call this structure a double-epitaxial MOSFET (DEMOSFET). In the structure, the p-well is composed of two p-type epitaxial layers, while an n-type region between the p-wells is formed by low-dose n-type ion implantation. A buried channel is formed at the surface of the upper p/sup $/epitaxial layer. A fabricated DEMOSFET showed an on-resistance of 8.5 m/spl Omega//spl middot/cm/sup 2/ at a gate voltage of 15 V and a blocking voltage of 600 V. This on-resistance is the lowest so far reported for a vertical MOSFET with a blocking voltage of 600 V.

Formation of two-dimensional photonic-crystal structures in silicon for near-infrared region using fine focused ion beams

One of the two variants of producing two-dimensional photonic crystals in silicon is the formation of ordered macropore structures in a silicon substrate. The characteristic pore dimensions (the diameter and the wall thickness between pores) determine the wavelength range in which such a pore structure exhibits the properties of a photonic crystal. For the near-infrared region, these dimensions approach 1 µm or fall in a submicron region. An ordered structure of macropores with such dimensions is formed in this work using fine focused ion beams to provide the stimulating effect of implanted ions on pore nucleation in given sites on the silicon substrate surface. Pores are shown to nucleate at sites subjected to ion irradiation even at a low implantation dose (2×1013 ion/cm2). A model describing the orienting effect of ion irradiation on pore nucleation is proposed.

Xe and Mo ion implantation on austenitic stainless steel: structural modification

Xe ions and Mo ions with 49-keV energy were implanted into an austenite stainless steel at doses between 1×10 15 and 35×10 15 ions cm −2 . Grazing incidence X-ray diffraction was used to analyze the surface structure of implanted sample. Xe implantation went through differentiation of two types of austenite crystallites and formation of constrained ferrite. For low implantation doses, Mo first inserted into austenite cells inducing austenite lattice expansion. Then, as the Mo dose increased, this expansion was combined with the differentiation of two types of austenite crystallites. Above 6×10 15 ions cm −2 a new bcc structure appeared: a ferrite with Mo was formed. High dose implantation leads to partial amorphisation.

Xe and Mo ion implantation on austenitic stainless steel: structural modification

Xe ions and Mo ions with 49-keV energy were implanted into an austenite stainless steel at doses between 1×10 15 and 35×10 15 ions cm −2. Grazing incidence X-ray diffraction was used to analyze the surface structure of implanted sample. Xe implantation went through differentiation of two types of austenite crystallites and formation of constrained ferrite. For low implantation doses, Mo first inserted into austenite cells inducing austenite lattice expansion. Then, as the Mo dose increased, this expansion was combined with the differentiation of two types of austenite crystallites. Above 6×10 15 ions cm −2 a new bcc structure appeared: a ferrite with Mo was formed. High dose implantation leads to partial amorphisation.

Lattice location and optical activation of rare earth implanted GaN

This paper reviews the current knowledge on rare earths (REs) implanted into GaN with a special focus on their lattice location and on the optical activation by means of thermal annealing. While emission channeling experiments have given information on the lattice location of rare earths following low-dose (≈10 13 cm −2) implantation, both in the as-implanted state and after annealing up to 900 °C, the lattice location of higher-dose implants (10 14–10 15 cm −2) and their defect annealing behaviour were studied using the Rutherford backscattering/channeling (RBS/C) method. The available channeling and luminescence results suggest that the optical activation of implanted REs in GaN is related to their incorporation in substitutional Ga sites combined with the effective removal of the implantation damage.

Lattice site and stability of implanted Ag in ZnO

In this work we report on the lattice location of implanted Ag in ZnO single crystals, evaluated by means of the emission channeling technique. Following 60keV low-dose (2×1013cm−2) ion implantation, the β− emission patterns from 111Ag were monitored with a position-sensitive detector as a function of annealing temperature up to 800°C in vacuum. Our experiments revealed that in the as-implanted state around 30% of the Ag atoms are substitutional at the Zn site with root mean square displacements around 0.17–0.28Å. Though this fraction did not change with increasing annealing temperature, upon annealing at 600°C the root mean square displacement of Ag from the Zn site increased considerably, followed by partial outdiffusion during 800°C annealing.

Effect of calcium ion implantation and of immersion in Hank's solution on shape memory properties of Ti-Ni alloy

Ca ion implantation into equi-atomic Ti-Ni alloy and immersion test of the implanted alloy in Hank's solution were carried out to clarify the effect of surface properties on the shape memory phenomena. By the surface analysis using AES, Ca ion concentrated layer was observed at the outermost surface of the implanted materials, lowever, the thickness of that layer was very thin with the implantation dose of this study ( 3x10 20 ions/m 2 ). At the alloy surface, the oxide layer which includes Ti and/or Ni was also observed superposing with the Ca concentration layer. Shape memory properties after Ca ion implantation did not indicate apparent change in comparison with that of the non-implanted materials. However, the properties after the immersion of several months in the Hank's solution changed in some degree. The penetration of hydrogen into the alloy during the immersion test is considered to cause this change in the shape memory properties. Ca ion implantation seemed to suppress the penetration of hydrogen. From the viewpoint to maintain the shape memory properties in high performance level, a low ion implantation dose is favorable. However, when the suppressing of hydrogen penetration and/or Ni dissolution from the alloy are expected, higher dose of Ca ion implantation than in the present study will be preferred.