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The first wall of an inertial fusion energy reactor may suffer from surface blistering and exfoliation due to helium ion fluxes and extreme temperatures. Tungsten is a candidate for the first wall material. A study of helium retention and surface blistering with regard to helium dose, temperature and tungsten microstructure was conducted to learn how the damaging effects of helium may be diminished. Single crystal and polycrystalline tungsten samples were implanted with 1.3 MeV 3 He in doses ranging from 10 19 /m 2 to 10 22 /m 2 . Implanted samples were analyzed by 3 He(d, p) 4 He nuclear reaction analysis and neutron depth profiling techniques. Surface blistering occurred for doses greater than 10 21 He/m 2 and was analyzed by scanning electron microscopy. Repeated cycles of implantation and flash annealing indicated that helium retention was reduced with decreasing implant dose per cycle. A carbon foil energy degrader, currently in development, will allow a continuous spectrum of helium implantation energy matching the theoretical models of He ion fluxes within the IFE reactor.

The first wall of an inertial fusion energy reactor may suffer from surface blistering and exfoliation due to helium ion irradiation and extreme temperatures. Tungsten is a candidate for the first wall material. A study of helium retention and surface blistering with regard to helium dose, temperature, pulsed implantation, and tungsten microstructure was conducted to better understand what may occur at the first wall of the reactor. Single crystal and polycrystalline tungsten samples were implanted with 1.3 MeV 3He in doses ranging from 1019 m−2 to 1022 m−2. Implanted samples were analyzed by 3He(d,p)4He nuclear reaction analysis and 3He(n,p)T neutron depth profiling techniques. Surface blistering was observed for doses greater than 1021 He/m2. For He fluences of 5 × 1020 He/m2, similar retention levels in both microstructures resulted without blistering. Implantation and flash heating in cycles indicated that helium retention was mitigated with decreasing He dose per cycle.

The helium retention characteristics and helium bubble distribution in tungsten were studied using 3He(d,p)4He nuclear reaction analysis (NRA) and transmission electron microscopy (TEM) on two forms of tungsten: single crystal and polycrystalline, implanted to 1 × 1019 3He/m2 at 850 °C and annealed at 2000 °C. The NRA results revealed that as-implanted single crystal and polycrystalline tungsten exhibited similar helium retention characteristics. Stepwise annealing reduced the helium retention in both single crystal and polycrystalline tungsten when the number of implantation steps and annealing time were increased. The TEM results indicated that microstructure played a large role in helium trapping; the existence of grain boundaries led to significant cavity formation and greater cavity growth. Single crystal tungsten had less trapping sites for helium, allowing long range He diffusion during annealing. The decrease of He retention in polycrystalline tungsten during stepwise annealing was probably due to significant recrystallization, resulting in decrease of grain boundary density.

To understand the helium retention characteristics and helium bubble distribution in tungsten, 3 He(d,p) 4 He nuclear reaction analysis (NRA) and transmission electron microscopy (TEM) have been performed for two forms of tungsten: single crystal and polycrystalline, implanted up to 1x10 19 3 He/m 2 at 850 °C and annealed at 2000°C. The NRA results indicated that as-implanted single crystal and polycrystalline tungsten exhibited similar helium retention characteristics. In addition, a flash anneal at 2000 °C had no effect on the retention of helium. However, when 10 19 He/m 2 was implanted into single crystal tungsten in 1000 cycles of 10 16 He/m 2 each followed by a 2000°C flash anneal, the observed helium yield dropped by 95% compared to 70 % for polycrystalline tungsten. The microstructure of single crystal tungsten implanted with 1x10 19 He/m 2 and annealed at 2000 °C in a single step showed numerous tiny cavities at a depth of ∼1.6 μm, while no visible cavities were observed in the 1000 step annealed single crystal. However, in the case of polycrystalline tungsten, a single step annealing led to significant cavity growth at grain boundaries. The reduced He retention suggests a preference for inertial fusion energy armor of single crystal over polycrystalline tungsten.

Single-crystal GaN films grown on AlN buffer layers previously deposited on 6H-SiC(0001) were studied for radiation damage and its recovery using Rutherford backscattering/channeling, photoluminescence, and cross-sectional TEM. The highest fluence of (1e15 cm{sup -2}) 110 keV Mg and 160 keV Si produced little damage at implantation temperature 550 C. RT damage was higher for same fluences compared to 550 C implantation. The damage was partially annealed by RTA at 1000 C, however, this was not enough to recover the PL signal even for the lowest fluence (1e14 cm{sup -2}). XTEM of as-implanted samples revealed small clusters of defects extended beyond the projected ion range. To recover damage completely, perhaps one needs to go either much higher RTA temperature and/or implant samples in a smaller fluence increment and anneal in between implants to recover the damage.

High‐quality ceramics based heteroepitaxial structures of oxide‐nitride‐semiconductors, i.e., SrTiO3/TiN/Si(100) have been fabricated by in situ pulsed laser deposition. The dependence of substrate temperature and oxygen partial pressure on the crystalline quality of the SrTiO3 films on Si with epitaxial TiN template has been examined. We found that epitaxial growth occurs on TiN/Si(100) above 500 °C, initially at a reduced O2 pressure (10−6 Torr), and followed by a deposition in the range of 5–10×10−4 Torr. X‐ray diffraction (Θ, ω, and Φ scans) and transmission electron microscope (TEM) results revealed an excellent alignment of SrTiO3 and TiN films on Si(100) with a cube‐on‐cube epitaxy. Rutherford backscattering and ion channeling results show a channeling minimum yield (χmin) of ∼13% for the SrTiO3 films. High‐resolution TEM results on the SrTiO3/TiN interface show that the epitaxial SrTiO3 film is separated from the TiN by an uniform 80–90 A crystalline interposing layer presumably of TiNxO1−x (oxy‐n...

Enhanced nucleation of polycrystalline diamond has been achieved on Si(100) with an intermediate layer of carbonitride. The carbonitride film was formed by an ion beam assisted deposition method and was characterized by Rutherford backscattering, X-ray photoelectron and laser Raman spectroscopies. The diamond deposition was accomplished using a hot filament chemical vapor deposition technique. Diamond film quality was examined with the help of laser Raman spectroscopy and scanning electron microscopy.

The effects of damages produced by implantation of Te, Er, Hg, and Pb ions into undoped (100) GaSb single crystals and their recovery by Rutherford backscattering (RBS)/channeling were investigated. The implantations with dosages in the range of 1013 to 1015 ions/cm2 were carried out at liquid nitrogen temperature, at energies corresponding to a projected range of 447A in GaSb. Near surface damage equivalent to that of an amorphous layer was observed even at lower doses. The samples were annealed at 600°C for different durations, with the Te implanted sample of the lowest dosage exhibiting the best recovery (Χmin = 11%) compared to others. This value of Χmin nearly corresponds to that of the virgin crystal. Examination of the surface morphology as a function of mass, dosage, and annealing duration revealed that it was strongly influenced by the dosage of the implanted ions.

A technique has been developed whereby a thin layer (∼ 1 μm thick) can be removed, intact, from the surface of a single-crystal diamond. This process involves the creation of a sacrificial layer below the crystal's surface by ion implantation followed by selective etching of this sacrificial layer in order to free the overlying diamond plate. In combination with homoepitaxial growth of diamond films by chemical vapor deposition (CVD), this process presents the possibility of generating multiple single-crystal diamond wafers from one regenerative substrate. Such a method might make diamond a cost effective material for microelectronics applications. We have also combined this lift-off technique with a technique for patterning diamond with an excimer laser microbeam to produce free-standing diamond components with submillimeter dimensions. In this paper we discuss the lift-off technique and give some examples of its application to diamond micromachining.

In this study Cu films of 30 nm and 200 nm thickness have been grown on natural type IIb semiconducting diamond C(001) substrates by electron-beam evaporation at 500 °C in UHV. As evidenced by Rutherford backscattering/channeling techniques and in situ low-energy electron diffraction, the as-deposited layers were shown to be epitaxial, with χCu = 49%. In addition, the technique of atomic force microscopy has demonstrated island morphology, indicative of three-dimensional growth. Moreover, the Cu films displayed excellent adhesion properties with the underlying diamond substrate. Corresponding current-voltage (I–V) measurements conducted at room temperature have shown rectifying characteristics. In addition, a Schottky barrier height of ΦB ≈ 1.1eV has been determined from ultraviolet photoemission spectroscopy.

We have constructed a chemical vapor deposition/etching system consisting of a 2.45 GHz microwave generator (ASTeX S‐1000) and two movable coaxial magnetic coils. A unique rotatable planar Langmuir probe was designed to characterize the plasma. The Langmuir probe measurements showed an anisotropic character of the plasma which was mainly a result of the magnetic field gradient and propagation direction of the microwaves. By placing the coils at certain distances from the microwave window and adjusting the current through the coils, a critical condition was established, known as ‘‘high mode plasma.’’ In this high mode, the plasma ion density was more than four times that in the normal mode. The physical basis of the high mode involved placing the electron cyclotron resonance critical field (875 G) just in front of the microwave window with a positive magnetic field gradient toward the direction of microwave propagation. This condition produced a high absorption of microwave power and also prevented charged...

A transition from Ge segregation to trapping during high‐pressure oxidation of GexSi1−x alloys has been observed. The atomic fraction x of Ge was varied from 0.4% to 26%, and oxidations were performed at 740 °C under 102 atm of dry O2. It was observed that the effect of oxidation on the Ge distribution could be divided into three stages. In the initial stage of the oxidation, Ge was segregated from the growing oxide and accumulated in a Ge‐rich layer at the oxide/alloy interface. For alloys with high Ge content this initial stage was very short. In the second stage of oxidation, after a critical quantity of Ge had accumulated at the interface, there was a transition from segregation to trapping of Ge in the oxide. In the third stage, the critical amount of Ge remained segregated at the interface, and the final oxide layer was Ge free. A kinetic model based on a steady‐state equilibrium between the diffusive flux of Si across the Ge‐rich layer and the rate of Si consumption by the oxidation reaction predic...

Suitability of oxide electronic conductors [e.g. ruthenium oxide (RuOx) and indium-tin-oxide (ITO)] as contact metallization for ferroelectric films (e.g. PbZrxTi1−xO3) was investigated using techniques such as Rutherford backscattering spectrometry, x-ray diffraction and electron spectroscopy for chemical analysis. Thin films of RuOx and ITO were deposited on Si substrates by reactive sputtering. Either PbO or PZT (x = 0.53) films were deposited onto the conducting oxides and the specimens were annealed at various temperatures between 400°C and 700°C. Less intermixing was found in Si/RuOx/ PZT films when compared to Si/ITO/PZT under similar processing conditions. The ferroelectric properties of PZT films on RuOx electrodes are compared to those on Pt electrodes. The PZT films show improved fatigue properties on RuOx electrodes.

We have implanted sodium, phosphorus and arsenic into single crystal type IIa diamond as possible n-type dopants. Particular emphasis was applied to the implantation of sodium at different temperatures and doses; combined implantation energies of 55,80 and 120 keV were used to provide a uniformly doped layer over approximately 100 nm depth. The implanted layers exhibited semiconducting behavior with a single exponential activation energy between 0.40 and 0.48 eV, as determined by temperature dependent resistance measurements. A sample implanted to a concentration of 5.10{sup 19} Na{sup +}/cm{sup 3} at 550{degrees}C exhibited a single activation energy of 0.415 eV over a temperature range from 25 to 500{degrees}C. Thermal annealing above 900{degrees}C was found to remove implantation damage as measured by optical absorption and RBS/channeling. However, concomitant increases in the resistance and the activation energy were observed. Implantation of {sup 22}Ne was used to introduce a damage density equivalent to the {sup 23}Na implant, while not introducing an electrically active species. The activation energy and electrical resistance were similar but higher than those produced by implantation with sodium. We conclude that the electrical properties of the Na-implanted samples were at least partly due to electrically active Na, but that residual implantation damagemore » was still important.« less

Epitaxial thin films of Cu 2 O have been deposited on (100) MgO substrates by pulsed excimer laser ablation technique. Chemical polishing of the substrates by etching them in hot phosphoric acid prior to film deposition is found to be a critical step in realizing epitaxy. A KrF excimer laser operating at 248 nm wavelengths was used for ablation. The depositions were carried out at the laser energy density of 2 J/cm 2 and the pulse repetition rate of 5 Hz. The substrate temperature was held at 700°C and the oxygen partial pressure during deposition and cooling was 10 −3 Torr. The epitaxial nature of the deposited films was established via X-ray diffraction (XRD) and Rutherford back-scattering (RBS) channelling measurements. The epitaxial films thus obtained were then subjected to ion bombardment for studies of damage formation. Implantations were carried out using 110 keV Ar + ions over a dose range between 5 x 10 14 and 1.5 x 10 16 ions/cmz. The as-grown and implanted samples were subjected to resistivity versus temperature measurements in view of the importance of the Cu-O system in the context of the phenomenon of high temperature superconductivity.

Stoichiometric films of cupric and cuprous oxide are deposited on Si, MgO, and Y‐ZrO2 substrates by pulsed excimer laser ablation technique. It is found that the equilibrium phase diagram based considerations dictate the phase formation. The films are characterized by small‐angle x‐ray diffraction, infrared, and UV‐visible spectroscopies and Rutherford backscattering spectroscopy. It is shown that epitaxy of Cu2O films can be realized on single crystal MgO (100) substrates and the corresponding film resistivity is of the order of 40–60 Ω cm.

Si2p electron attenuation lengths in SiO2 were measured at 1150 and 1380 eV using SiO2 films prepared by dry oxidation of 〈100〉 Si wafers. SiO2 thicknesses were determined using both ellipsometry and Rutherford backscattering spectrometry/channeling. Thicknesses determined by the two methods were within 3% for all but one sample. Electron attenuation lengths were calculated using three different methods, resulting in values of 3.0 nm for 1150 eV and 3.5 nm for 1380 eV.

Epitaxial growth of Y-ZrO 2 buffer layer followed by that of the high- T c Y 1 Ba 2 Cu 3 O 7−δ on Si (100) substrate has been realized by pulsed excimer laser ( λ =248 nm ) ablation, without chemical removal of the native surface oxide on silicon. The influence of substrate surface preparation conditions and the substrate temperature on the crystallinity and quality of the Y-ZrO 2 buffer layers has been examined. it is observed that cubic Y-ZrO 2 films can be deposited epitaxially on Si (100) without chemical removal of the thin native oxide if the deposition is carried out at 800°C, initially at a reduced oxygen pressure (1 x 10 −6 Torr) followed by a deposition at higher pressure (5 x 10 −4 Torr). The crystalline qualities of the deposited films have been studied by X-ray diffraction, high resolution transmission electron microscopy (HREM) and Rutherford backscattering channeling techniques. The X-ray results reveal the high degree of c -axis orientation normal to the film surface. The χ min in the channeled RBS spectrum has been found to have values of 8% and 13% for Y-ZrO 2 and Y 1 Ba 2 Cu 3 O 7−δ films, respectively. The HREM results on the Y-ZrO 2 / Si interface show that the epitaxial layer of Y-ZrO 2 is separated from the crystalline silicon substrate by a few nanometer bridging layer of amorphous (or microcrystalline) SiO x . Typically, the superconducting films of thickness 5000 A deposited on silicon with a 1500 A epitaxial Y-ZrO 2 buffer layer have T c as high as 88 K and J c of more than 10 5 A/cm 2 at 77 K.

The phenomena associated with dopant redistribution in TiSi 2 , CoSi 2 , NiSi, Pd 2 Si, and PtSi, as would be used in a silicide-As-diffusion-source process, were examined. Segregation of dopant (B) into a surface layer, evaporation of dopant, and slow, grain-boundary diffusion, were found to occur in annealed, implanted silicides. For CoSi 2 , 1.6×10 14 boron atoms/cm, were found to segregate to the silicide surface, independent of the initial implant dose, possibly as B 2 O 3

In order to characterize the deep damage produced by high-energy 0.5–2.0 MeV implants of As and P into p-type (100)Si, we have employed a laser induced photothermal reflectance measurement technique and the standard RBS/channeling technique using 2 MeV He + beams. The implantation dose was varied from 1 × 10 12 to 1 × 10 14 ions/cm 2 . The correlation between the thermal wave signal intensity and the displaced atom density, as determined by RBS/channeling, is presented. The variation of the thermal wave intensity for different implant angles in silicon wafers at room temperature was also studied. The measurements have demonstrated that this technique can be used to monitor the dose of high-energy ion implantations into Si.

With the objective of obtaining shallow junctions, we have made a comparative study of the distribution profiles of phosphorus ions implanted into Si(100) at 5 to 200 keV, along different crystalline directions, viz. the [001] axis, the (310) plane with 7° tilt away from [001], and a random equivalent direction, defined by 5.2° tilt, and 7° rotation from the (100) plane. The P implants were also performed in amorphous Si, and through a thin SiO2 layer at the same energies for comparison. The P depth profiles in Si were measured by SIMS with 14.5 keV Cs ions. The damage profiles in Si(100) crystals were studied by RBS/channeling of 2 MeV He ions. The role of the implants along the selected orientations is discussed in light of the resulting depth of the tails of the implanted dopants distribution.

Growth of SiGe alloys on GaAs substrates at temperatures as low as 590 °C is described. The growth has been accomplished using the pyrolysis of disilane (Si2H6) and germane (GeH4) at such temperatures. The layers were characterized electrically and show n‐type conduction with carrier concentrations of ∼1×1018 cm−3. The high quality of the SiGe layers is evident in the Rutherford‐backscattering/channeling results on SiGe/GaAs structures. A χmin of 5.6% has been obtained for a Si0.05Ge0.95 layer on GaAs. χmin increases with increasing silicon content in the SiGe layers. The SiGe alloy layers were also studied by x‐ray diffraction, and the composition was determined assuming coherent, tetragonally distorted growth of SiGe on GaAs. The distortion calculations, based on theoretical elastic constants, were confirmed using Auger electron spectroscopy to determine alloy composition.

Elastic recoil coincidence spectroscopy (ERCS) is a scattering-recoil coincidence technique with a high sensitivity for profiling light elements ranging from H up to O in thin film samples. In this technique He+ ions with energies of at least 2 MeV are incident on a thin target, typically 2 μm thick, and the energies of both forward scattered He ions and elastically recoiled light atoms are detected in coincidence using detectors subtending large solid angles. From each pair of energies the depth where scattering has taken place as well as the mass of recoiled atoms can be derived. ERCS is preferably applied to profile light elements in a heavier matrix and in cases where a low beam current (< 1 nA) or a low total ion dose is required to reduce damage, e.g. to study polymer samples, or for microbeam analysis. A gain in counting rates of 2–3 orders of magnitude compared to conventional elastic recoil detection analysis (ERDA) and a depth resolution of 20 nm can be achieved. In a first experiment, we applied ERCS to profile simultaneously C and O in thin polycarbonate foils and in a second experiment we have analyzed O and B in thin B-diffused Si crystals. In this paper we discuss the basic principles of ERCS and describe in detail the derivation of concentration-versus-depth profiles from coincidence spectra measured for polycarbonate and Si samples.

The coincidence spectrometry technique developed by Chu and Wu [1,2] was applied to find the depth profile of 25 keV 6 Li ions implanted into an Al foil, using the 6 Li(n, α) 3 H reaction. The energies of the emitted α and 3 H particles were measured in coincidence by two particle detectors mounted on opposite sides of the Al foil. The Li concentration-depth profile was derived by mapping the 4 He 3 coincidence counts in energy space. Because of the increase in solid angle subtended by the detectors, an improvement of two orders of magnitude in counting statistics could be achieved with no loss of depth resolution. Some suggestions for further improvement are also discussed.

We have developed elastic recoil coincidence spectroscopy (ERCS), a technique with high sensitivity to profile light elements, ranging from H up to O, in thin polymer foils or in thin samples containing heavier elements. In this technique, MeV He+ ions are incident on a thin target, typically 2 μm thick, and the energies of both the forward-scattered He ions and the elastically recoiled light atoms are detected in coincidence. Concentration-versus-depth profiles can be derived from the measured number of coincidence events for a depth range of up to l μm and for all recoiled light elements. This is done by relating each pair of energies of scattered and recoiled atoms to a depth where scattering has occurred and to the mass of the recoiled elements. To analyze the coincidence spectra and to derive concentration-versus-depth profiles, computer programs have been developed. To demonstrate the capabilities of ERCS we have chosen polycarbonate films (48 at.% C, 9 at.% O) and have derived the expected uniform concentration-depth profiles from the coincidence spectra for a depth range of 1 μm. In a second experiments, ERCS was applied to profile B and O in a thin boron-diffused Si window.

We have systematically investigated the effect of oxygen partial pressure (PO2) on the crystalline quality of SrTiO3 films grown on MgO (001) substrates using pulsed laser deposition and established optimized conditions for the growth of high-quality epitaxial films. The crystalline quality is found to improve significantly in the O2 pressure range of 0.5–1 mTorr, compared to the films deposited at higher pressures of 10–100 mTorr. The x-ray diffraction rocking curves for the films grown at PO2 of 1 mTorr and 100 mTorr yielded full width at half-maximum (FWHM) of 0.7° and 1.4°, respectively. The in-plane x-ray φ scans showed epitaxial cube-on-cube alignment of the films. Channeling yields χmin were found to be

GaN films were implanted with 150 keV Ar+ at temperatures up to 1100 ��C to a dose of 3��1015 cm-2. Concentration profiles of Ar were measured by secondary ion mass spectroscopy and depth distributions of ion-induced damage were estimated from Rutherford backscattering/channeling spectra. No redistribution of Ar atoms was detected up to 700 ��C. At 1000 ��C a deep penetrating diffusion tail and a shift of the Ar peak to the surface were observed. At temperatures higher than 800 ��C shift of the damage peak to the surface was also observed. We attributed the shift of the Ar peak and the damage peaks to evaporation of thin layer of GaN during high-temperature implantation and estimated its temperature dependence.

Crystalline damage created by ion-implantation of dopant impurities in ZnO (0001) substrates was characterized as a function of atomic mass of implanted species using triple-axis (2θ-ω/ω) x-ray diffraction and Rutherford backscattering (RBS). The former revealed the presence of implantation-induced strain through the broadening of the isometric and asymmetric 2θ-ω reflections. However, RBS indicated that the damage introduced during implantation of these ions was insufficient to transform the crystalline lattice into a completely amorphous state. Additional XRD characterization as a function of annealing temperature of the implanted materials showed a reduction in the broadening of the isometric reflections, indicating that structural recovery of implanted ZnO crystals can be achieved.

A systematic investigation of damage accumulation in GaN films induced by Ar+ as a function of implantation temperature and dose rate has been conducted. Depth distribution of disorder was measured by Rutherford Backscattering/Channeling spectrometry. Two disordered regions were identified in the damage depth distribution: a surface peak and a bulk damage peak. These regions exhibited different behavior as a function of implantation temperature. The displaced atomic density in the bulk damage peak displayed a “reverse annealing” behavior in temperature range from 500 °C to 700 °C, which we attributed to formation of characteristic secondary defects. The influence of implantation temperature and dose rate on the radiation damage accumulation is discussed.

In this work, we present a detailed investigation of disorder accumulation in gallium nitride (GaN) implanted with Ar+ ions as a function of implantation temperature and ion dose. Implantations were carried out with energy 150 keV in a dose range between 3 t 1014 and 3 t 1016 cm-2 at a variety of substrate temperatures from room temperature to 1000dC. Depth distributions of the disorder were measured by Rutherford Backscattering spectrometry In the channeling mode and Ar depth profiles were obtained by Secondary Ion Mass spectrometry. Two disordered regions were identified in the damage depth distribution: a surface peak and a bulk damage peak. Both damage peaks exhibited a well-defined transition dose above which the damage level increased dramatically. With increasing implantation temperature up to 1000dC, the amount of damage in the surface peak decreased for the whole dose range studied. The amount of disorder in the bulk damage peak was less sensitive to the increase of implantation temperature and in addition displayed a ""reverse annealing"" behavior, which was attributed to the formation of characteristic secondary defects.

A systematic investigation of the damage accumulation in GaN films induced by 150keV Ar ions as a function of implantation temperature and dose rate has been conducted. The depth distribution of the disorder in the Ga sublattice has been measured by RBS/channeling spectrometry with a glancing angle detector geometry to provide enhanced depth resolution. Two disordered regions were identified in the damage depth distribution: a near-surface peak and a bulk damage peak. These regions exhibit different behavior as a function of implantation temperature. The height of the near-surface peak, as expected, decreased with implantation temperature approaching the magnitude of the unimplanted sample. The displaced atomic density in the bulk damage peak also followed this tendency and decreased in the temperature range from room temperature to 500°C. The implantation at higher temperatures resulted in an increase in the amount of damage, reaching a maximum at about 700°C and displayed a characteristic “reverse annealing” behavior. Further increase of the implantation temperature to 1000oC reduced the disorder. The influence of the dose rate and implantation temperature on the radiation damage accumulation is discussed.

We describe a new method for removing thin, large area sheets of diamond from bulk or homoepitaxial diamond crystals. This method consists of an ion implantation step, followed by a selective etching procedure. High energy (4–5 MeV) implantation of carbon or oxygen ions creates a well‐defined layer of damaged diamond that is buried at a controlled depth below the surface. For C implantations, this layer is graphitized by annealing in vacuum, and then etched in either an acid solution, or by heating at 550–600 °C in oxygen. This process successfully lifts off the diamond plate above the graphite layer. For O implantations of a suitable dose (3×1017 cm−2 or greater), the liftoff is achieved by annealing in vacuum or flowing oxygen. In this case, the O required for etching of the graphitic layer is also supplied internally by the implantation. This liftoff method, combined with well‐established homoepitaxial growth processes, has considerable potential for the fabrication of large area single crystalline dia...

Following heat treatments of Pt encapsulated Ni80Cr20 thin films on silicon substrates at temperatures ranging from 300 to 500 °C, it has been discovered that Cr atoms segregate at the original NiCr/Si interface to form an amorphous layer, while Ni atoms diffuse into the Si to form Ni silicide. The Cr‐rich amorphous layer acts as a ‘‘semipermeable membrane’’ which selectively passes Ni to form a very uniform NiSi layer.

Thin films of AlxGa1−xN (0.05 ≤ x ≤ 0.96) having smooth surfaces were deposited directly on both vicinal and on-axis 6H-SiC(0001) substrates. Cross-sectional TEM of Al0.13Ga0.87N revealed stacking faults near the SiC/Nitride alloy interface and numerous threading dislocations. EDX, AES and RBS were used to determine the compositions, which were paired with their respective CL near band-edge emission energies. A negative bowing parameter was determined. The CL emission energies were similar to the bandgap energies obtained by SE. FE-AES of the initial growth of Al0.2Ga0.8N revealed an aluminum rich layer near the interface. N-type (silicon) doping was achieved for AlxGa1−xN for 0.12 ≤ x ≤ 0.42. Al0.2Ga0.8N/GaN superlattices were fabricated with coherent interfaces. Additionally, HEMT structures using an AlN/GaN/AlN buffer structure were fabricated.

Applications of electric and/or magnetic filters to Rutherford backscattering (RBS) and elastic recoil detection analysis (ERDA) were studied with the aim of improving their performance such as detection limit and depth resolution. A novel RBS technique combined with a charged particle energy filter (CPEF) has been proposed for the detection of contaminants on Si wafers. The CPEF is an electric deflector of charged particles. In this technique, it is placed between a sample and a detector and plays the role of filtering undesirable backscattered signals originated in silicon atoms in the sample from contaminant signals. Experimental results have shown that the CPEF can suppress the silicon signals selectively and appreciably. Another study has been done for ERDA technique using a charge particle energy filter (CPMF) for the analysis of hydrogen depth profile on the surface of a sample. The CPMF is a magnetic deflector of charged particle. It works to remove high energy backscattered particles. As a result, the thickness of the foil in front of a detector can be thinner. The results of calculation have shown that the thickness can be reduced by around 40%.

Monocrystalline AlxGa1−xN(0001) (0.05 ≤ x ≤ 0.70) thin films, void of oriented domain structures and associated low-angle grain boundaries, have been grown at high temperatures via OMVPE directly on vicinal and on-axis α(6H)-SiC(0001) wafers using TEG, TEA and ammonia in a cold-wall, vertical, pancake-style reactor. The surface morphologies were smooth and die densities and distributions of dislocations were comparable to that observed in GaN(0001) films grown on high temperature A1N buffer layers. Double-crystal XRC measurements showed a FWHM value as low as 186 arc sec for the (0002) reflection. Spectra obtained via CL showed strong near band-edge emissions with FWHM values as low as 31 meV. The compositions of the AlxGa1−xN films were determined using EDX, AES and RBS and compared to the values of the bandgap as measured by spectral ellipsometry and CL emissions. A negative bowing parameter was found. Controlled n-type, Si-doping of AlxGa1−xN for x ≤ 0.4 has been achieved with net carrier concentrations ranging from ≈ 2 × 1017 cm−3 to 2 × 1019 cm−3. Acceptor doping with Mg for x < 0.13 was also successful.

As the typical feature size of silicon integrated circuits, such as in VLSI technology, has become smaller, the surface cleanliness of silicon wafers has become more important. Hence, detection of trace impurities introduced during the processing steps is essential. A novel technique, consisting of a “Charged Particle Energy Filter (CPEF)” used in the path of the scattered helium ions in the conventional Rutherford Backscattering geometry, is proposed and its merits and limitations are discussed. In this technique, an electric field is applied across a pair of plates placed before the detector so that backscattered particles of only a selected energy range go through slits to strike the detector. This can be used to filter out particles from the lighter substrate atoms and thus reduce pulse pileup in the region of the impurity signal. The feasibility of this scheme was studied with silicon wafers implanted with 1×1014 and 1×1013 14pe/cm2 at energy of 35 keV, and a 0.5 MeV He+ analysis beam. It was found that the backscattered ion signals from the Si atoms can be reduced by more than three orders of magnitude. This suggests the detection limit for contaminants can be improved by at least two orders of magnitude compared to the conventional Rutherford Backscattering technique. This technique can be incorporated in 200–300 kV ion implanters for monitoring of surface contaminants in samples prior to implantation.

In order to make good quality economical diamond electronic devices, it is essential to grow films and to dope these films to obtain n- and p- type conductivity. This review talk discuss first doping by ion implantation plus annealing of the implantation damage, and second flow to make large area single crystal diamonds. C implantation damage below an estimated Frenkel defect concentration of 7% could be recovered almost completely by annealing at 950C. For a defect concentration between 7 and 10%, a stable damage form of diamond (``green diamond``) was formed by annealing. At still higher damage levels, the diamond graphitized. To introduce p-type doping, we have co-implanted B and C into natural diamond at 77K, followed by annealing up to 1100C. The resulting semiconducting material has electrical properties similar to those of natural B-doped diamond. To create n-type diamond, we have implanted Na{sup +}, P+ and As{sup +} ions and have observed semiconducting behavior. This has been compared with carbon or noble element implantation, in an attempt to isolate the effect of radiation damage. Recently, in order to obtain large area signal crystals, we have developed a novel technique for removing thin layers of diamond from bulk or homoepitaxialmore » films. This method consists of ion implantation, followed by selective etching. High energy (4--5 MeV) implantation of carbon or oxygen ions creates a well-defined layer of damaged diamond buried at a controlled depth. This layer is graphitized and selectivity etched either by heating at 550C in an oxygen ambient or by electrolysis. This process successfully lifts off the diamond plate above the graphite layer. The lift-off method, combined with well-established homoepitaxial growth processes, has potential for fabrication of large area single-crystal diamond sheets.« less

Ion implantation technique is being investigated as an alternate technique for doping GaSb. Hence an understanding of the production and removal of the damage is essential. In this paper, we report on the damages produced by implantation of Te, Er, Hg and Pb ions into undoped (100) GaSb single crystals and their recovery by Rutherford backscattering (RBS)/channeling. The implantations of 1013 to 1013 ions/cm2 in GaSb were done at liquid nitrogen temperature at energies corresponding to the same projected range of 447Å. A comparison of the damage produced by the different ions and their recovery was made by RBS/channeling along axis of GaSb. Near surface damage equivalent to that of an amorphous layer was observed even at lower doses. Upon annealing at 600°C for 30 sec., the Te implanted samples showed best recovery compared to others (Xmin = 11%), the value of Xmin being better than those normally observed in unimplanted Te-doped substrates.

Results are reported from an investigation of the properties of boron nitride thin films. The BN films were deposited by the method of plasma enhanced chemical vapor deposition (PECVD) from mixtures of ammonia and diborane. The deposition variables were RF power, pressure, ammonia partial pressure, diborane partial pressure, diluent type (nitrogen or argon), and temperature. The films were characterized for their stoichiometry, hydrogen content, stress, refractive index, and especially for their dielectric properties. It was observed that the main parameters affecting the dielectric constant were the ratio of ammonia to diborane flow, and the deposition temperature. The dielectric constant decreased with increasing ammonia to diborane ratio, while it increased with decreasing deposition temperature. The lowest dielectric constant value achieved was 4.0 ·, 0.1. Nitrogen dilution allowed the deposition of boron nitride films with the lowest dielectric constant value at ammonia to diborane ratios smaller than those required under argon dilution, which suggests some incorporation of nitrogen into the boron nitride matrix from the diluent.

Heteroepitaxial Ge layers were grown on vicinal Si(100) by molecular beam epitaxy (MBE) at substrate temperatures of 500°C and 900°C. The layers grown at 500°C were topographically smooth with planar interfaces and a typically high threading dislocation density at the surface (> 108cm−2). Layers grown at 900°C (nucleation at 500°C) showed smooth topography, an interface highly facetted on (111) planes and a dense network of dislocations that is well confined to the interfacial region. Etch pit density measurements indicated that defect densities at the surface were as low as 1 × 105cm−2. Biaxial tensile strains of 1.2 × l0−3 and 2.5 × l0−3 were measured by Raman spectroscopy for the 500°C and 900°C layers, respectively. RBS/channeling spectra supported crosssection TEM results indicating interfacial defect confinement in the layers grown at 900°C. A model describing thermal radiation absorption suggests that interfacial Ge melting occurred during the high temperature growths.

In the present study we report the first results pertaining to the heteroepitaxial growth of Ti films on 6Hs-SiC (0001). The Ti epitaxial films of typically 400s-1000 A thickness have been deposited at room temperature in ultras-high vacuum (< 10−9 torr) using both thermal and electron beam evaporation sources. Ins-vacuo techniques of low energy electron diffraction (LEED) and xs-ray photoelectron spectroscopy (XPS) have been used to monitor the surface structure and interface chemistry during growth. An unreconstructed (1×1) ordered LEED pattern corresponding to that of the SiC (0001) surface was observed for all Ti coverages. Epitaxial growth of Ti has been confirmed from crosss-sectional TEM diffraction patterns and images, which indicate the presence of threading dislocations to relieve a 4% lattice mismatch strain. Rutherford backscattering (RBS) with channeling of 2 MeV He+ ions gave X = 0.71 for Ti deposited at room temperature. Currents-voltage measurement for both uns-annealed and annealed Ti contacts displayed rectifying characteristics with low leakage currents (≈ 6 nA at −10V) and low ideality factors (1.02−1.08).

Investigation has continued into the use of SixGe1−x multilayer structures (MLS) as a buffer layer between a Si substrate and a GaAs epitaxial layer in order to accommodate the 4.1% lattice mismatch. SixGe1−x 4-layer and 5-layer structures terminating in pure Ge have been grown using molecular beam epitaxy. Subsequent GaAs heteroepitaxy has allowed evaluation of these various GaAs/SixGe1−xMLS/Si (100) structures. Antiphase domain boundaries have been eliminated using vicinal Si (100) substrates tilted 6° off-axis toward [011], and the etch pit density in GaAs grown on a 5-layer SixGe1−x MLS on vicinal Si (lOO) was measured to be 106 cm−2.

In the present study epitaxial Ni(001) films have been grown on natural C(001) substrates (type la and Ha) and homoepitaxial C(001) films. Two deposition techniques including electron-beam evaporation of Ni in a molecular beam epitaxy (MBE) system and evaporation of Ni from a resistively heated tungsten filament have been employed. As evidenced by scanning electron microscopy (SEM), the Ni films deposited by electron-beam evaporation were found to replicate the very fine, unidirectional scratches present on the as polished C(001) substrates. Indeed, the coverage and uniformity of the deposited films would imply a two-dimensional (2-D) growth mode. In comparison, the thermal evaporation of Ni on C(001) substrates results in a highly textured and faceted surface morphology indicative of three-dimensional (3–D) nucleation and growth. Moreover, Rutherford backscattering/channeling measurements have demonstrated that the Ni(001) films deposited by electron-beam evaporation are of superior crystalline quality. Differences in the observed microstructure and apparent growth modes of the epitaxial Ni(001) films have been attributed to the presence of oxygen incorporation in those layers deposited by thermal evaporation.

Thin film ferroelectric structures are being investigated for use as storage capacitors for Non-volatile Random-Access Memories. To integrate ferroelectrics with standard silicon semiconductor processing, a great deal of effort must be spent identifying compatible materials. These materials must be able to withstand both ferroelectric and silicon processing steps involving different temperatures and environments.In this paper we have used Rutherford backscattering spectrometry (RBS) to study the diffusion of ferroelectric Pb(Zr.5Ti.5)O3 elements into thin films of TiOx, TiNx, ZrNx and ZrOx deposited onto thermally grown SiO2. The sample matrix was annealed at various temperatures in argon ambient and analyzed using 2 MeV He+. Diffusion profiles (concentration vs. depth profiles) of the ferroelectric constituents were determined for the different barrier films. Results indicated that ZrN is the most promising barrier layer so far, having shown the least interdiffusion at 700°C.

We have used Rutherford backscattering spectroscopy (RBS) to study the kinetics of NiSi growth during low temperature annealing of a Ni(Cr) layer on Si. During the silicide growth, a Cr-rich amorphous layer was formed between the silicide and the Ni(Cr) layers. This amorphous layer produces a slow and uniform silicide growth rate; the NiSi thickness was 60 nm after a 2h anneal at 475°C. After prolonged annealing, the amorphous layer recrystallized, causing very rapid silicide growth. When a thin (0.5 nm) layer of Pt was deposited between the Si and Ni(Cr) layers, the amorphous layer was thinner, the silicide growth rate was correspondingly greater and the rapid growth stage occurred earlier. The RBS data agreed qualitatively with transmission electron microscopy results for the growth of both the amorphous layer and the silicide.

Capacitors made up of thin films of Ta2O5/TiN on polysilicon have been studied for application to 256 Mbytes dynamic random access memories. In this study, the thermal stability of poly‐Si/Ta2O5 films with TiN electrode film deposited by (i) chemical vapor deposition (CVD) with TiCl4 and NH3, (ii) sputtering, and (iii) metalorganic CVD (MOCVD) was compared. These samples were annealed under vacuum at 700, 800, and 900 °C for 30 min. The as‐deposited and the annealed samples were analyzed by Rutherford backscattering with 2 MeV He+ ions. The CVD TiN films, which contained a small amount of Cl, provided pathways for the underlying Ta2O5 to out‐diffuse during annealing at all temperatures between 700 and 900 °C. The sputtered films were resistant to the diffusion of Ta2O5 up to 800 °C, but relented at 900 °C, with measurable outdiffusion of Ta. There was no noticeable interaction of the Ta2O5 with the TiN layers, deposited by the MOCVD process, at temperatures up to 900 °C. However, the MOCVD TiN films were ...

The first results pertaining to the fabrication of an optically transparent SiC contact on naturally occurring semiconducting diamond C(001) substrates are reported. The SiC layer is formed by electron-beam evaporation of an Si film followed by a two-step high-temperature annealing process. By employing Al dots as a metal mask, mesa heterostructure diodes comprising Al/SiC/C(001) were fabricated by etching in an electron cyclotron resonance oxygen plasma. Rectifying I–V characteristics were obtained from the mesa heterostructures.

Initial results pertaining to the growth and characterization of TiSi2 films deposited on natural single crystal insulating and semiconducting diamond C(001) substrates are reported. The TiSi2 films were formed by the co-deposition of Si and Ti in ultra-high vacuum by electron-beam evaporation. From an analysis of the Raman scattering spectra, both the orthorhombic metastable C49 and stable C54 crystallographic phases of TiSi2 have been identified. As evidenced by scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) the TiSi2 films exhibit a faceted surface morphology indicative of polycrystalline growth. Moreover, the TiSi2 films exhibit excellent adhesion properties with the underlying diamond substrate. Corresponding current-voltage (I-V) measurements conducted at room temperature have demonstrated rectifying characteristics for the TiSi2 films deposited on natural p-type semiconducting diamond substrates. Consistent with the small turn-on voltage of ∼0.2 V, the corresponding I-V measurements recorded at 400°C exhibit ohmic-like behavior. However, upon subsequent annealing of the TiSi2 contacts at 1100°C, stable rectifying I-V characteristics were observed in the 25-400°C temperature range.