Diffusion studies of Be-implanted GaAs by SIMS and electrical profiling

Secondary ion mass spectrometry (SIMS) has been used with differential resistivity and Hall effect measurements to study the 900°C diffusion of implanted Be in GaAs. Some outdiffusion of Be into the Si₃N₄ encapsulant occurs for surface Be concentrations above 1 × 10¹⁸cm^?3. However, excellent agreement between the electrical and atomic profiles indicates that 85–100% of the Be remaining after annealing is electrically active. The concentration-dependent diffusion observed for implanted Be in GaAs was not significantly altered in experiments using hot substrate implants, two-step anneals, or annealing with Ga and As overpressure.     

Doping and radiation damage profiles of P+ ions implanted in silicon along the [110] axis

Several doses of 200 KeV phosphorus ions have been implanted under channeling conditions along the [110] direction in silicon.

Range distribution has been determined for the three implant doses 10¹³, 10¹⁴, 10¹⁵ P⁺/cm² both with the electrical measurements and the neutron activation techniques.

The radiation damage distribution has been determined both with 290 KeV proton back-scattering analysis and with transmission electron microscopy (TEM) observations.

Good agreement has been found between electrical and neutron activation profiles in the samples where 100% of the implanted dose had been electrically activated by means of annealing.

Carrier concentration profiles, from samples implanted with 10¹⁵ P⁺/cm², determined after two different annealing temperatures (500°C and 700°C) have bcen compared with the radiation damage distribution and a correlation between damage and phosphorus electrical activation process seems to be possible.

Maximum damage peak, as determined by back-scattering analysis, shifts from ～0.4 μ depth in the lower dose(5 × 10¹⁴ P⁺/cm²), to ～0.22 pm depth in the higher implanted dose (4 × 10¹⁵ P⁺/cm²). Damage distribution of phosphorus ions random implanted in the same experimental conditions shows 3 peak at ～0.2 μn depth.

In accordance with the back-scattering analysis, T.E.M. observations on 10¹⁵P⁺/cm² implanted samples show the presence of amorphous regions at depth between 0.25 and 0.5 μm from the surface. In the most damaged layer ～0.3μm in depth, a surface density of ～10¹²/cm² amorphous regions 25-50 A diameter was observed.     

3D molecular imaging SIMS

Thin monolayer and bilayer films of spin cast poly(methyl methacrylate) (PMMA), poly(2-hydroxyethyl methacrylate) (PHEMA), poly(lactic) acid (PLA) and PLA doped with several pharmaceuticals have been analyzed by dynamic SIMS using SF₅⁺ polyatomic primary ion bombardment. Each of these systems exhibited minimal primary beam-induced degradation under cluster ion bombardment allowing molecular depth profiles to be obtained through the film. By combing secondary ion imaging with depth profiling, three-dimensional molecular image depth profiles have been obtained from these systems. In another approach, bevel cross-sections are cut in the samples with the SF₅⁺ primary ion beam to produce a laterally magnified cross-section of the sample that does not contain the beam-induced damage that would be induced by conventional focussed ion beam (FIB) cross-sectioning. The bevel surface can then be examined using cluster SIMS imaging or other appropriate microanalysis technique.     

Influence of annealing on the concentration profiles of boron implantations in silicon

The influence of annealing on the concentration profiles of boron implanted into silicon with does of 10¹⁴ ions/cm² up to 10¹⁶ ions/cm² and an energy of 70 keV was studied. The concentration profiles were measured with Secondary Ion Mass Spectrometry (SIMS). The broadening of the concentration profiles during annealing can be described as a superposition of effects resulting from a relatively immobile and a mobile boron fraction. The properties of the immobile boron fraction were studied by measuring the influence of a boron implantation on the distribution of a homogeneous boron background dope. From these experiments it was concluded that the immobile boron fraction consists of boron precipitates. The properties of the mobile fraction were studied from concentration profiles that were obtained after annealing during different periods at the same temperature. It was found that during the initial stage of the annealing process a fast broadening of the profile occurs; this was assumed to be due to an interstitial type boron diffusion. After prolonged annealing the much slower substitutional type diffusion prevails, due to trapping of the interstitial boron atoms by vacancies. The reliability of the SIMS method, as applied to profile measurements, was checked for the high boron doses used in this investigation. Excessive boron precipitates, obtained after annealing of a high dose, such as 10¹⁶ ions/cm² at about 1000°C, appear to give some increase of the ion yield.     

<Superscript>10</Superscript>B<Superscript>+</Superscript>-ion implantation into photoresist

100-keV ¹⁰B⁺ ions were implanted into photoresist in different directions at a fluence of 1×10¹⁴ cm^-2, and their depth distribution was determined by means of the neutron depth profiling technique. In no case were the projectile ions found to come to rest according to their predicted implantation profiles. Instead, they are always found to undergo considerable long-range migration. During the irradiation process this motion appears to be enhanced by the radiation damage, and during the subsequent annealing steps one deals with thermal diffusion. The implant redistribution is always found to be governed strongly by the self-created damage, insofar as both electronic and nuclear defects in the polymer act as trapping centers. The implant redistribution shows a pronounced directional dependence, essentially as a consequence of the spatial distribution of the electronic energy loss. The changes of the nuclear defect distribution during thermal annealing are studied by a specially developed tomographic method in three dimensions. PACS 61.72.Ww; 61.80.Jh; 61.41.+e; 66.30.-h; 66.30.Jt     

Structural state of III nitride layers implanted with erbium ions

The defect structure of AlGaN/GaN superlattices and GaN layers grown through vapor-phase epitaxy from organometallic compounds is investigated using x-ray diffraction analysis before and after implantation with erbium ions at an energy of 1 MeV and a dose of 3 × 10¹⁵ cm^?2, as well as after annealing. For a superlattice with a total thickness larger than the implantation depth, the satellites of the superlattice region strained under the action of ions disappear in the x-ray diffraction pattern after annealing at temperatures higher than 900°C. This suggests that the radiation-induced defects responsible for the positive deformation in the layer are annealed at these temperatures. However, annealing even at a temperature of 1050°C does not lead to complete recovery of the initial state and the positive deformation in the remaining regions is caused by residual defects. An analysis of the x-ray diffraction patterns demonstrates that, in samples with thin superlattices located at the depth corresponding to maximum radiation damage, the periodic structure that disappears after implantation at a dose of 3 × 10¹⁵ cm^?2 is not recovered even after annealing at a temperature of 1050°C. This inference is confirmed by the results of examinations with an electron microscope.     

The study of damage and optical properties in LiNbO3 implanted by MeV Er and He ions

Abstract

Two LiNbO₃ (X and Y cut) crystals from different companies were implanted by 3.0 MeV Er ions to a dose of 7.5 × 10¹⁴ ions/cm² and 3.5 × 10¹⁴ ions/cm² with different beam current densities, respectively. After annealing at 1060°C in air for 2 hours, one LiNbO₃ sample was implanted by 1.5 MeV He ions to a dose of 1.5 × 10¹⁶ ions/cm². The Rutherford backscattering/channeling and prism coupling method have been used to study the damage and optical properties in implanted LiNbO₃. The results show: (1) the damage in LiNbO₃ created by 3.0 MeV Er ions depends strongly on the beam current density; (2) after annealing at 1060°C in air for 2 hours, a good Er doped LiNbO₃ crystal was obtained; (3) there is waveguide formation possible in this Er-doped annealed LiNbO₃ after 1.5 MeV He ion implantation. It is suggested that annealing is needed to remove the damage created by MeV Er ions before the MeV He ion implantation takes place, to realize the waveguide laser for Er doped LiNbO₃.     

Annealing behaviour of high-dose-implanted nitrogen in InP

Concentration profiles of nitrogen in vacuum-annealed p- and n-type single-crystal (1 0 0) InP implanted with 1 × 10¹⁶ 30 keV¹⁵N⁺ ions cm^–2 have been studied by Secondary Ion Mass Spectrometry (SIMS) and Nuclear Resonance Broadening (NRB) techniques. Damage induced by the nitrogen implantation was studied by Rutherford Backscattering Spectrometry (RBS) and channeling. Annealing the samples led to loss and redistribution of nitrogen in the temperature range from 575 to 675 °C. At temperatures from 575 to 600 °C, rapid migration of nitrogen towards the sample surface was observed. The n-type InP material had a very dominant tendency for surface nitrogen build-up, whereas the p-type material had a markedly smaller surface peak in the nitrogen distribution. The surface peak in n-type material is due to sulphur acting partly as a diffusion barrier. SIMS analyses showed sulphur build-up on the surface in the course of annealing. At temperatures from 600 to 675 °C, the nitrogen profiles of n- and p-type InP were similar. A small loss of nitrogen was observed at 625–675 °C. Two different recovery stages were observed at 575–600°C and at 625–650 °C. The corresponding activation energies for nitrogen loss are 2.9 and 3.0 eV, respectively.     

Hot electron studies of lattice damage created in silicon by implantation of 2.8 MeV protons

Abstract

In this paper we report the results of a study of the annealing properties of the ionized defect density associated with the damage created in the silicon lattice by implantation of 2.8 MeV protons at room temperature. In particular, the annealing of damage created by implanting to a level of 4.43 × 10¹² protons/cm² is reported. The resulting isochronal annealing curve covered the temperature range from 70°C to 460°C. Two major annealing stages are discussed, one a broad stage between 70°C to 200°C and the other an abrupt annealing stage between 440°C to 460°C. Between the temperature range 200°C to 440°C the number of ionized defects remained relatively constant. Above 460°C no detectable effects of the proton implantation remained.     

Positron annihilation studies of defects in 3CSiC hot-implanted with nitrogen and aluminum ions

2 ⁺ and Al⁺ at temperatures from room temperature (RT) to 1200 °C at doses of 10¹³ and 10¹⁵/cm². It is found from Doppler broadening spectra of annihilation gamma-rays obtained by varying the incident positron energy that hot-implantation gives rise to clustering of vacancies, whereas it suppresses amorphization and diminishes the thickness of damaged layers. The average size of such clusters increases with increasing implantation dose and temperature. Vacancy clustering by hot-implantation can be interpreted by the combination of vacancies during implantation. Vacancy type defects in the low-dose (10¹³/cm²) implanted samples are found to be removed by annealing at 1400 °C, whereas large vacancy clusters still remain after 1400 °C annealing in the high-dose (1 0¹⁵/cm²) implanted samples. It is also derived from the depth profile of positron diffusion length that positron scattering centers are produced after annealing at 1400 °C in all implanted samples. Received: 7 March 1997/Accepted: 6 May 1997     

Properties of ion implanted silicon,sulfur, and carbon in gallium arsenide

Work is described in which chromium-doped semi-insulating gallium arsenide has been successfully doped n-type with ion implanted silicon and sulfur, and p-type with ion implanted carbon. A dilute chemical etch has been employed in conjunction with differential Hall effect measurements to obtain accurate profiles of carrier concentration and mobility vs. depth in conductive implanted layers. This method has so far been applied to silicon-and sulfur-implanted layers in both Cr-doped semi-insulating GaAs and high purity vapor grown GaAs. In the case of sulfur implants, a strong diffusion enhancement has been observed during the annealing, presumably due to fast-diffusing, implantation-produced damage. Peak doping levels so far obtained are about 8 × 10¹⁷ electrons/cm³ for silicon implants and 2 × 10¹⁷ electrons/cm³ for sulfur implants. Mobility recovery has been observed to be complete except in regions near the surface which are heavily damaged by the implantation.     

Behavior of antimony above solid solubility in silicon produced by implantation and laser annealing

Abstract

Antimony implantation into <111> silicon was carried out at RT with a dose of 4.5 × 10¹⁵ cm^?2, energy 75 keV. For the annealing of the sample pulses of a Q-switched ruby laser were used with energy density of ～ 1.5 Joule/cm² and duration of 15–20 nsec. Hall effect measurement was applied to determine the electrical activity of the layers. Lattice location and the depth profile of Sb was studied by RBS and channeling technique. Measurements show that after laser annealing Sb occupies mostly substitutional sites in Si with 84% electrical activity. It has been shown that after laser annealing the concentration of Sb in lattice sites is almost an order of magnitude higher than the limit of solid solubility. Isochron and isothermal annealing of these samples up to 1150°C was carried out to study the kinetics of reverse annealing of antimony.     

Characterization of ion implanted n+ layers on tetrahedrically textured silicon surfaces

Ion implantation of 2 × 10^{15 31}P⁺/cm² at 10 keV and furnace annealing at 750° C, 1/2 h, have been used to obtain n⁺ -p junctions on (100) silicon samples having tetrahedrically textured surfaces. This texture was obtained by an anisotropic etching in a hot hydra-zine-water mixture. Morphological properties of the surface (dimension, homogeneity and characteristic of the tetrahedrons) have been analyzed and electrical properties of the implanted layers (sheet resistivity, carrier concentration profile) have been measured. The electrical characteristics of the textured samples are similar to those obtained using samples with flat polished surface; the tetrahe-dral structures are not damaged by the implantation process and they keep their antireflecting properties unaltered.     

Oxygen and hydrogen accumulation at buried implantation-damage layers in hydrogen- and helium-implanted Czochralski silicon

Oxygen and hydrogen accumulations at buried implantation-damage layers were studied after post-implant-ation annealing of hydrogen- and helium-implanted Czochralski (Cz) silicon. Hydrogen implantation was carried out at energies E=180 keV and doses D=2.7×10¹⁶ cm^-2, and helium implantation at E=300 keV and D=10¹⁶ cm^-2. For comparison hydrogen implantation was also done into float-zone (Fz) silicon wafers. Post-implantation annealing at 1000 °C was done either in H₂ or N₂ atmosphere. Hydrogen and oxygen concentration profiles were measured by secondary ion mass spectroscopy (SIMS). It is shown that the ambient during annealing plays a significant role for the gettering of oxygen at buried implantation-damage layers in Cz Si. For both hydrogen and helium implantations, the buried defect layers act as rather effective getter centers for oxygen and hydrogen at appropriate conditions. The more efficient gettering of oxygen during post-implantation annealing in a hydrogen ambient can be attributed to a hydrogen-enhanced diffusion of oxygen towards the buried implantation-damage layers, where a fast oxygen accumulation occurs. Oxygen concentrations well above 10¹⁹ cm^-3 can be obtained. From the comparison of measurements on hydrogen-implanted Cz Si and Fz Si one can conclude that at the buried defect layers hydrogen is most probably trapped by voids and/or may be stable as immobile molecular hydrogen species. Therefore hydrogen accumulated at the defect layers, and is preserved even after high-temperature annealing at 1000 °C. Received: 3 July 2000 / Accepted: 11 July 2000 / Published online: 22 November 2000     

Defects formation in the dual B+ and N+ ions implanted silicon

Silicon wafers were implanted with 40 keV B⁺ ions (to doses of 1.2×10¹⁴ or 1.2×10¹⁵ cm^–2) and 50 or 100 keV N⁺ ions (to doses from 1.2×10¹⁴ to 1.2×10¹⁵ cm^–2). After implantations, the samples were furnace annealed at temperatures from 100 to 450 °C. The depth profiles of the radiation damages before and after annealing were obtained from random and channeled RBS spectra using standard procedures. Two damaged regions with different annealing behaviour were found for the silicon implanted with boron ions. Present investigations show that surface disordered layer conserves at the annealing temperatures up to 450 °C. The influence of preliminary boron implantation on the concentration of radiation defects created in subsequent nitrogen implantation was studied. It was shown that the annealing behaviour of the dual implanted silicon layers depends on the nitrogen implantation dose.The authors would like to thank the members of the INP accelerator staff for the help during the experiments. The work of two authors (V.H. and J.K.) was partially supported by the Internal Grant Agency of Academy of Science of Czech Republic under grant No. 14805.     

MeV Al+ and Al2+ ions implantation in Si(100): surface roughness and defects in the bulk

This paper deals with the implantation of high-energy (1.0–3.0 MeV) atomic and molecular Al⁺ ions in Si(100) to a fluence of 5×10¹⁴ Al atoms/cm² at room temperature. The molecular effect, i.e. the increase of the displacement yield compared with the sum of the atomic yields, and the damage formation as well as defect behaviour after annealing have been investigated. A detailed experimental study has been made of the evolution of extended secondary defects which form during thermal anneals of Al⁺ or Al₂ ⁺ irradiated silicon. The samples have been examined using combined Rutherford backscattering and channeling experiments together with transmission electron microscopy observations. The surface structure of the implanted wafers has been measured by atomic force microscopy. The results for the implantation-induced roughness at the Si surface, resulting from Al⁺ or Al₂ ⁺ irradiation at the same energy/atom, total atomic fluence, flux rate, and irradiation temperature, are presented and discussed. Received: 19 August 1999 / Accepted: 20 October 1999 / Published online: 23 February 2000     

2.0-MeV Er+ implanted in silicon: depth distribution, damage profile and annealing behaviour

Si crystals were implanted with 2.0- MeV Er⁺ at the doses of 5×10¹² ions/cm², 1×10¹⁴ ions/cm², 5×10¹⁴ions/cm², 1×10¹⁵ ions/cm² and 2.5×10¹⁵ ions/cm². Conventional furnace thermal annealing was carried out in the temperature range from 600 °C to 1150 °C. The depth distribution of Er, associated damage profiles and annealing behavioar were investigated using the Rutherford backscattering spectrometry and channelling (RBS/C) technique. A proper convolution program was used to extract the distribution of Er from the experimental RBS spectrum. The obtained distribution parameters, projected range R_p, projected range straggling ΔR_p and skewness SK were compared with those of TRIM96 calculation.The experimental R_p and SK values agree well with the simulated values, while the experimental ΔR_p is larger than TRIM 96 simulated value by a factor of 18%. The damage profile of silicon crystal induced by 2.0-MeV Er⁺ at a dose of 1×10¹⁴ ions/cm² was extracted using the multiple-scattering dechannelling model based on Feldman’s method, which is in a good agreement with the TRIM96 calculation. For the samples with dose of 5×10¹⁴ ions/cm² and more, an abnormal annealing behavioar was found and a qualitative explaination has been given. Received: 11 October 1999 / Accepted: 28 March 2000 / Published online: 5 July 2000     

Simulation of interface broadening of sputter profiled isotopic silicon layers

Abstract

The experimental SIMS profiles of Si³⁰/Si²⁸ multilayers depth profiled using 2–10 KeV Ne⁺, Ar⁺ and Xe⁺ (K. Wittmaack and D. B. Poker, Nucl. Instr. Meth. B47 (1990) 224) have been simulated using a diffusion approximation to ion mixing. Both the leading and trailing edges of peaks in the depth profiles could be fitted for all ion energies by mixing efficiencies of 25, 40 and 65 Å⁵ eV^?1 respectively. These values are larger than the estimates of 5, 11 and 15 Å⁵ eV^?1 from ballistic mixing. The additional contributions to the mixing, 20, 29 and 50 Å eV^?1, scale with cascade energy density, suggesting that stimulated motion in thermal spikes is important. A simple spike model in which cascade defects are trapped at fixed sinks agrees with the experimental mixing efficiencies.     

Interpretation of TOF–SIMS depth profiles from ultrashallow high-k dielectric stacks assisted by hybrid collisional computer simulation

The TRIDYN collisional computer simulation has been modified to account for emission of ionic species and molecules during sputter depth profiling, by introducing a power law dependence of the ion yield as a function of the oxygen surface concentration and by modelling the sputtering of monoxide molecules. The results are compared to experimental data obtained with dual beam TOF–SIMS depth profiling of ZrO₂/SiO₂/Si high-k dielectric stacks with thicknesses of the SiO₂ interlayer of 0.5, 1, and 1.5 nm. Reasonable agreement between the experiment and the computer simulation is obtained for most of the experimental features, demonstrating the effects of ion-induced atomic relocation, i.e., atomic mixing and recoil implantation, and preferential sputtering. The depth scale of the obtained profiles is significantly distorted by recoil implantation and the depth-dependent ionization factor. A pronounced double-peak structure in the experimental profiles related to Zr is not explained by the computer simulation, and is attributed to ion-induced bond breaking and diffusion, followed by a decoration of the interfaces by either mobile Zr or O. PACS 68.49; 79.20; 81.65; 82.80     

Nitrogen implantation in GaAs1−xPx (x=0.4; 0.65)

Nitrogen ions were implanted in GaAs_1−xP_x (x=0.4; 0.65) at room temperature at various doses from 5×10¹² cm⁻² to 5×10¹⁵ cm⁻² and annealed at temperatures from 600°C up to 950°C using a sputtered SiO₂ encapsulation to investigate the possibility of creating isoelectronic traps by ion implantation. Photoluminescence and channeling measurements were performed to characterize implanted layers. The effects of damage induced by optically inactive neon ion implantation on photoluminescence spectrum were also investigated. By channeling measurements it was found that damage induced by nitrogen implantation is removed by annealing at 800°C. A nitrogen induced emission intensity comparable to the intensity of band gap emission for unimplanted material was observed for implanted GaAs_0.6P_0.4 after annealing at 850°C, while an enhancement of the emission intensity by a factor of 180 as compared with an unimplanted material was observed for implanted GaAs_0.35P_0.65 after annealing at 950°C. An anomalous diffusion of nitrogen atoms was found for implanted GaAs_0.6P_0.4 after annealing at and above 900°C.