Residual Lattice Damage Research Articles

Tailoring spin defects in diamond by lattice charging

Atomic-size spin defects in solids are unique quantum systems. Most applications require nanometre positioning accuracy, which is typically achieved by low-energy ion implantation. A drawback of this technique is the significant residual lattice damage, which degrades the performance of spins in quantum applications. Here we show that the charge state of implantation-induced defects drastically influences the formation of lattice defects during thermal annealing. Charging of vacancies at, for example, nitrogen implantation sites suppresses the formation of vacancy complexes, resulting in tenfold-improved spin coherence times and twofold-improved formation yield of nitrogen-vacancy centres in diamond. This is achieved by confining implantation defects into the space-charge layer of free carriers generated by a boron-doped diamond structure. By combining these results with numerical calculations, we arrive at a quantitative understanding of the formation and dynamics of the implanted spin defects. These results could improve engineering of quantum devices using solid-state systems.

Comprehensive Characterization of Dual Implanted Silicon after Electrical Activation Annealing

Formation of low resistivity junctions is essential for fabricating high performance devices with advanced device modes. Significant effort has been expended, industry wide, to develop low resistivity junctions, over the years. However, the understanding of implant activation and implant damage recovery process is not sufficient. Development of noncontact implant residual damage monitoring techniques would be beneficial in process development for advanced node devices. In this study, we have investigated the effect of annealing temperature and time on the sheet resistance (Rs) of dual (P+ 1.0MeV, 4.0 x 1013 cm-2 + B+ 10keV, 3.0 x 1014cm-2) implanted p--Si(100) wafers using a single wafer furnace-based (hot wall) rapid thermal annealing (RTA) system over a wide range of annealing conditions (350-800oC, 60-150s). Room temperature photoluminescence (RTPL) spectra were measured from all wafers under two different excitation wavelengths (650 and 785 nm) for additional clues on electrical properties of pn junctions, which cannot be obtained from the Rs measurements. Multiwavelength (457.9, 488.0 and 514.5 nm) Raman characterization was done on all wafers for additional insights on the degree of residual lattice damage, after RTA, under different conditions. After all on wafer measurements were completed, secondary ion mass spectroscopy (SIMS) dopant (P and B) depth profiling was done to assess dopant diffusion during the annealing process.Rs values showed strong and systematic change with RTA temperature and time, as expected. RTPL spectra also showed large variations in intensity and wavelength distribution corresponding to the RTA temperature and time. Multiwavelength Raman characterization results showed gradual increase of intensity with the RTA temperature. Three regions of different Raman shift values, corresponding to the Si lattice stress and possibly the degree of residual implant damage, were also noted. SIMS P and B depth profiles did not show significant changes. Correlation among characterization results from various techniques and RTA conditions will be presented.

Density Changes in Plutonium Observed from Accelerated Aging using Pu-238 Enrichment

Plutonium, because of its radioactive nature, ages from the “inside out” by means of self-irradiation damage and thus produces Frankel-type defects (vacancies and self-interstitial atoms) and defect clusters. The self-irradiation damage in Plutonium-239 occurs mainly by α-particle decay, where most of the damage comes from the U-235 recoil nucleus. The defects resulting from the residual lattice damage and helium in-growth could result in microstructural and physical property changes. Because these self-irradiation effects would normally require decades to measure, with a fraction (7.5 wt%) of Pu-238 is added to the reference plutonium alloy thus accelerating the aging process by approximately 18 times the normal rate. By monitoring the properties of the Pu-238 spiked alloy over a period of about 3.5 years, the properties of plutonium in storage can be projected for periods up to about 60 years. This paper presents density and volume changes observed from the immersion density and dilatometry measurements equivalent to aging the reference plutonium alloys to nine years.

Characterization of Ni-implanted GaN and SiC

High concentrations (>10 21 cm −3) of Ni were introduced into GaN and SiC by ion implantation at 350 °C. On subsequent annealing at 700 °C, there was more residual lattice damage in GaN compared to SiC. Both materials showed ferromagnetism with transition temperatures below 50 K. No secondary phases could be detected by transmission electron microscopy (TEM) or selected area diffraction in either GaN or SiC. The direct implantation process appears useful for studying ion/substrate combinations for potential spintronic applications.

Effects of Ni implantation into bulk and epitaxial GaP on structural and magnetic characteristics

Structural and magnetic characteristics of Ni-implanted GaP were measured for doses in the range 3–5×10 16 cm −2. After subsequent annealing at 700 °C, transmission electron microscopy (TEM) showed residual lattice damage which was more significant in highly carbon-doped epi layers as compared to bulk GaP substrates. The magnetization measurements showed two different contributions, one present at ≤75 K and the other below ∼225 K. No secondary phase formation was detected in either type of GaP.

Raman scattering studies on low-energy nitrogen-implanted semi-insulating GaAs

Liquid-encapsulated Czochralski (LEC) grown undoped semi-insulating (SI) gallium arsenide (GaAs) single crystals have been implanted with 120 keV nitrogen ion (N +) of fluences 1×10 14, 1×10 15 and 1×10 16 cm −2 . Raman scattering studies of the as-grown and implanted samples have been carried out at room temperature and analyzed. It is observed that the A 1(LO) phonon mode frequency decreases with increase of fluence, whereas the full width at half maximum (FWHM) increases and the area under the peak decreases. All these effects are due to the lattice disorder induced by the implantation. The implanted samples have been annealed at 673 K. They show a partial recovery of the A 1(LO) phonon mode frequency and the FWHM which tend towards the unimplanted values due to partial annealing of the implantation-induced lattice damage. The post-implantation annealed samples show an increase of the area under the peak due to the enhanced Raman scattering caused by the surface roughness which was caused by the implantation. This increase in area was less at high fluences because of the residual lattice damage induced by the implantation, which caused the decrease of the area.

Variable-dose (1017–1020 cm−3) phosphorus ion implantation into 4H–SiC

Multiple-energy box profile elevated-temperature (700 °C) phosphorus ion implantations were performed into 4H–SiC in the doping range of 1×1017–1×1020 cm−3. The implanted material was annealed at 1500, 1600, or 1650 °C with an AIN encapsulant to prevent degradation of the SiC surface. Within this temperature range the sheet resistance does not change significantly for a given dose. The percentage of electrical activation of the P donors initially decreased with increasing implant dose for P-implant concentration up to 3×1019 cm−3 and then increased again at higher doses. For 1×1020 cm−3 P implant, a carrier concentration of 4×1019 cm−3 was measured at room temperature. In the 1017 cm−3 P doping concentration range substitutional activation greater than 85% was measured. Despite performing the implants at 700 °C, a significant amount of as-implanted damage was observed in the Rutherford backscattering (RBS) spectrum, even for 1018 cm−3 range P implantations. The RBS yield after annealing is near the virgin level for P concentrations up to 1×1019 cm−3, but above this concentration the RBS yield is above the virgin level, indicating a significant amount of residual lattice damage in the crystal.

Material and n–p junction characteristics of As- and Sb-implanted SiC

Abstract Single and multiple energy As and Sb implantations were performed into p-type 6H–SiC epitaxial layers at room temperature (RT) and 800°C. Secondary ion mass spectrometry measurements showed severe implant loss for annealing temperatures >1500°C. Rutherford backscattering spectroscopy/channeling (RBS/C) measurements indicated a high degree of residual lattice damage for RT implantations even after 1600°C annealing while less damage was detected in 800°C implanted samples. Electrical activations (ratios of sheet carrier concentrations to implant doses) of 11 and 20% were measured for 800°C As and Sb implantations annealed at 1500°C, respectively. The Schottky capacitance–voltage profiling measurements indicated substitutional concentrations in the low 1018 cm−3 range for both As and Sb. Based on the experimental data, carrier ionization energies of 130 and 88 meV were estimated for As and Sb donors, respectively. Vertical n–p junction diodes were made by using multiple energy As and Sb implanted epitaxial layers. Elevated temperature As implanted diodes exhibited a room temperature reverse leakage current of ≈8×10−8 A/cm2 with no passivation at −100 V bias and a forward series resistance of 460 Ω.

Ion-implantation in bulk semi-insulating 4H–SiC

Multiple energy N (at 500 °C) and Al (at 800 °C) ion implantations were performed into bulk semi-insulating 4H–SiC at various doses to obtain uniform implant concentrations in the range 1×1018–1×1020 cm−3 to a depth of 1.0 μm. Implant anneals were performed at 1400, 1500, and 1600 °C for 15 min. For both N and Al implants, the carrier concentration measured at room temperature for implant concentrations ⩽1019 cm−3 is limited by carrier ionization energies, whereas for the 1020 cm−3 implant, the carrier concentration is also limited by factors such as the solubility limit of the implanted nitrogen and residual implant damage. Lattice quality of the as-implanted and annealed material was evaluated by Rutherford backscattering spectroscopy measurements. Residual lattice damage was observed in the implanted material even after high temperature annealing. Atomic force microscopy revealed increasing deterioration in surface morphology (due to the evaporation of Si containing species) with increasing annealing temperature. The surface damage is in the form of long furrows running in one direction across the wafer to a depth of ∼25 nm from the surface for samples annealed at 1600 °C for 15 min. We measured room temperature sheet resistivities of ∼70 and 1.2×104 Ω/sq., respectively, for 2×1019 cm−3 N (1500 °C annealing) and 1×1020 cm−3 Al (1600 °C annealing) implanted samples.

Method of dry-etching evaluation using quantum dots

New dry-etch processes, such as low-power reactive-ion etching (RIE) and electron cyclotron resonance, offer very low levels of residual lattice damage. These levels are below the resolution limits of traditional characterisation methods like Raman, photoluminescence, Schottky diode, etc. We show that the single-electron charging of a quantum dot fabricated using dry etching offers a very sensitive method of damage detection. For SiCl4SiF4 RIE of GaAs we find a defect density of around 1015 cm−3, which is at the level of the background impurity concentration in the as-grown material.

Structural and Optical Properties of Rare-Earth Doped Lithium Niobate Waveguides Formed by Mev Helium Implantation

AbstractResults of investigations of optical waveguides formed by high energy helium implantation into lithium niobate codoped with 5 mol% MgO and 1 mol% Tm3+ or 1 mol% Er3+ are reported. A comparative study of structural and luminescence properties between implanted and untreated samples has been performed by means of Rutherford backscattering (RBS) combined with channeling and photoluminescence methods, respectively in order to investigate residual lattice damage and the incorporation of the optical active rare earths. For the case of Tm a full substitutional incorporation on the lithium site and a high crystal quality in both bulk and implanted waveguide material has been found. For Er doped lithium niobate the channeling results show a fraction of Er randomly incorporated or forming precipitates and a deterioration of the waveguide's lattice. The optical investigations show in both cases only a slight broadening of the emission lines of the rare earths in the waveguides compared to the bulk material.

Annealing in a mercury bath of In+ and B+ implanted Cd0.23Hg0.77Te studied by resonant Raman scattering and Hall effect measurements

Resonant Raman scattering by longitudinal optical phonons has been used to study the effect of annealing in a hot Hg bath on 113In+ and 11B+ implanted Cd0.23Hg0.77Te. Up to the highest doses of 1×1013 cm−2 for In and 1×1014 cm−2 for B, respectively, Raman spectroscopy indicates a full recovery of the crystalline perfection for annealing temperatures around 320 °C and annealing times ≥10 min. This recovery is accompanied by an electrical activation of the implants. Control experiments have been carried out to prove that the electrical activity is not due to residual lattice damage and that the immersion in the Hg bath by itself has no effect on the Raman spectrum.

Subsurface Processing of Electronic Materials Assisted by Atomic Displacements

In the early years of doping of semiconductors by ion implantation, atomic displacements and residual lattice damage were considered undesirable byproducts of an otherwise controllable doping process. Steps were taken to minimize disorder during implantation and/or to remove it as completely as possible during a subsequent annealing process. In many cases, such as boron- or phosphorus-implanted silicon, annealing temperatures exceeding 900°C were necessary to achieve the desirable electrical properties. Indeed, removal of implantation damage remains a crucial issue, particularly as device dimensions shrink and the need has arisen for substantially lower processing temperatures. The advent of high-energy (MeV) implantation in specific processing steps and the increasing use of more complex (often multilayer) compound semiconductors has added further to the need to understand and control ion damage and its annealing in semiconductors.Over the past decade, there has been a growing realization that implantation induced atomic displacements and defects can have significant advantages in processing. For example, it was realized early that ion damage, and resultant defect fluxes to and from lattice disruptions, can “getter” and trap undesirable impurities that would otherwise interfere with device operation. More recently, it has been possible to use ion beams to tailor damage structures and form amorphous-crystalline superlattices, to remove pre-existing damage and induce crystallization of amorphous layers at very low temperatures, to form ultrapure amorphous silicon for studying thermodynamic properties of this phase, or to mix films with semiconductors and form stable compounds such as silicides. Indeed, ion damage has been used to electrically isolate devices, to form optical waveguides and cavities, and to improve the junction properties of deeply doped layers. These issues are briefly reviewed in this article.

Residual damage after annealing of Be and O implanted GaAs/AlGaAs hetero bipolar transistors

Beryllium (2.5·1014/cm2 at 40 keV and 7.5·1014/cm2 at 90 keV) and oxygen (1013/cm2 at 380 keV) were implanted into a GaAs/AlGaAs-HBT (hetero bipolar transistor) to facilitate the formation of an ohmic contact with the p-type base using planar technology. The layer sequence and doping levels of the HBT are listed in table 1. Annealing was performed using optical RTA (rapid thermal anneal) equipment, at 860 °C, for 3 s. Technological data as well as SIMS, electrical, and photoluminescence measurements are published in detail elsewhere. This paper focuses on the residual lattice damage in the annealed HBT. TEM investigations were performed at 200 keV beam voltage using cross-sectional specimens.Fig.l shows a dark-field micrograph taken with a {200} reflection. The different layers are numbered (cf. table 1) and can be distinguished by differences in overall contrast. The residual damage consists of Frank type (b=a/3<111>) and perfect(b=a/2<110>) dislocation loops. The perfect loops are prismatic. Most of them lie in the <110> plane perpendicular to the Burgers vector b. All loops are of interstitial type. Defects are only found in the top three layers of the HBT which corresponds to the depth of the Be implantation. The defect distribution is inhomogeneous (Fig.1): While there are rather large loops (up to 200 nm) together with small ones in the GaAs layers of cap and base, only small loops (up to 30 nm) can be observed in the AlGaAs emitter layer.

Plasma etching of III–V semiconductors in CH4/H2/Ar electron cyclotron resonance discharges

We have investigated the etch rates, residual lattice damage, surface morphologies, and chemistries of InP, InGaAs, AlInAs, and GaAs plasma etched in electron cyclotron resonance (ECR) CH4/H2/Ar discharges. The etch rates of InP and InGaAs increase linearly with additional rf biasing of the substrate, and are approximately a factor of 2 faster than for GaAs. Under our conditions the etch rate of Al0.52Ga0.48As is very low (∼25 Å min−1) even for the addition of 100 V rf bias. In all of these materials the residual damage layer remaining after dry etching is very shallow (∼20 Å) as evidenced from Schottky barrier height and photoluminescence measurements combined with wet chemical etching. InP shows significant P depletion with the addition of rf biasing during the ECR etching while GaAs retains a near-stoichiometric surface. Hydrogen passivation of shallow donors in n-type GaAs occurs to a depth of ∼3000 Å during exposure to the CH4/H2/Ar discharge for long periods (60 min). The surface morphologies in the In-based materials become roughened for etching with the addition of rf biasing while GaAs displays smooth, residue-free surfaces under these conditions.

Self Annealing Ion Implantation in thin Silicon Films

AbstractThe self annealing phenomenon was studied utilizing 1 cm diameter, 1 μm thick, <100> oriented silicon films. Previous results established the viability of the self annealing process for medium energy argon beams incident on similar targets [1]. In the current work, doubly aligned backscatter spectra were obtained to improve the sensitivity of the residual lattice damage measurements. In addition, some implantations were performed at elevated temperatures to independently determine the effect of the flux and the sample temperature on the self annealing process. The results showed strong correlations between the implantation flux, sample temperature and the residual lattice damage. Two distinct temperature regions were observed above and below 330 °C with corresponding activation energies of 1.5 eV and 0.1 eV.

Plasma Etching of InP and Related Materials in Electron Cyclotron Resonance CH4/H2/Ar Discharges

We have investigated the etch rates, residual lattice damage, surface morphologies and chemistries of InP, InGaAs, AlInAs and GaAs plasma etched in electron cyclotron resonance (ECR) CH4/H2/Ar discharges. The etch rates of InP and InGaAs increase linearly with additional RF biasing of the substrate, and are approximately a factor of two faster than for GaAs. Under our conditions the etch rate of Al0.52Ga0.48As is very low (≈25γ · min−1) even for the addition of 100 V RF bias. In all of these materials the residual damage layer remaining after dry etching is very shallow (≈20γ) as evidenced from Schottky barrier height and photoluminescence measurements combined with wet chemical etching. InP shows significant P depletion with the addition of RF biasing during the ECR etching while GaAs retains a near-stoichiometric surface. Hydrogen passivation of shallow donors in n-type GaAs occurs to a depth of ≈3000γ during exposure to the CH4/H2/Ar discharge for long periods (60 mins). The surface morphologies of the In-based materials become roughened for etching with the addition of RF biasing while GaAs displays smooth, residue-free surfaces under these conditions.

New ion implantation system with advanced process capabilities

A new ion implantation system has been developed with several significant IC wafer processing improvements resulting from innovations in beam optics, target system, wafer handling, and control electronics design. This paper will concentrate on the process results that have been established thus far with this new system. Implanted wafers are subjected to temperatures of less than approximately 40°C even with beams of 30 mA at 120 keV. This significantly reduces residual lattice damage due to partial annealing, and also significantly reduces photoresist blistering and flow. Wafers are completely flat and planar during implant, providing a constant implant angle and reduced uniformity and depth profile variations due to channeling, as well as providing more uniform wafer temperature. Low ion beam density and a high speed wafer scanning system provides reduced charging of electrically floating semiconductor structures. Data will be presented on implant uniformity, wafer temperature and charging.

Residual lattice damage in As‐implanted and annealed Si

Residual damage in Si was examined by TEM after shallow As+ implantations (40–150 keV) and annealing in the temperature range of 800°–1000 °C. After annealing at 800 °C the damage consists of many small interstitial‐type prismatic dislocation loops. The structures obtained after annealing at higher temperatures are different for implantations into Si covered with a thin (100–200 Å) layer of SiO2 and for implantations of large prismatic dislocation loops and half‐loops intercepted by the Si surface, whereas implantation through oxide results in a layer of irregularly shaped dislocation loops which is not connected to the surface. The development of these structures is discussed as arising from the healing of ion‐bombardment damage and the diffusion of As into deeper regions of Si and from an influence of recoiled O atoms for implantations through SiO2 layers.

Epr of substitutional group V implants in sillcon

Abstract Group V impurities implanted at 400 keV into silicon have been detected in substitutional lattice positions by EPR. Three samples of VFZ, p-type 1200–1500 ohm-cm silicon from the same ingot were implanted with As75, Sb121, and Sb123, respectively. The EPR spectrum of each implanted substitutional impurity was observed after annealing the lattice damage. Only the isotope implanted in each sample was seen. Since only those donors which are electrically active can be observed, this technique measures the electrically active fraction of the implanted species. Upon annealing to 970°C, most of the antimony was active whereas only about 1/5 of the arsenic was observed. Comparisons with backscattering results indicate that between 350 and 600°C, ∼95 per cent of the implanted antimony is substitutional but ∼0 per cent is electrically active. The increase in electrical activity at 600°C is due to the rise of the Fermi level to the donor level as the residual lattice damage anneals. The paramagnetic damage ...