Rutherford backscattering study of crystal orientation dependent annealing effects in high-dose antimony implanted silicon

High dose implantations (10¹⁶ ions/cm²) of antimony in silicon result in concentrations far above the solid solubility of antimony in silicon. Rutherford backscattering was used to study the behaviour of damage and antimony concentration profiles for 〈100〉 and 〈111〉 substrates. The measurements were performed for various annealing treatments, implantation temperatures and implantation energies. A crystal orientation dependent outdiffusion of antimony towards the surface, a highly supersaturated phase of substitutional antimony at 600°C and a strong reverse annealing effect at higher temperatures were found.     

Boron implantations in silicon: A comparison of charge carrier and boron concentration profiles

The concentration profiles of boron implanted in silicon were measured using secondary ion mass spectrometry. The accompanying charge carrier profiles were determined by Hall-effect sheet-resistivity measurements combined with layer removal by anodic oxidation and etching. From a mutual comparison of these profiles an electrically inactive boron fraction was found to exist in the region of maximum boron concentration. This fraction can be correlated with boron precipitates. In high dose implantations the precipitates still exist after annealing at 1000°C. In the tail of the profile a small electrically inactive boron fraction was observed. This fraction was correlated with fast diffusing non-substitutional boron. Near the surface a charge carrier peak was found that can be correlated with the damage caused by implantation. The interpretation of the observed electrical effects was facilitated by investigations on boron concentration profiles of layers implanted with different doses and annealed in accordance with different time-temperature schedules.     

The electrical behaviour of abrupt ion implanted and diffused P+N junctions

Abstract

Results are reported of measurements of the properties of diodes formed by ion implantation, and for comparison boron diffused P⁺N diodes of similar area close by on the same chip. The four group III acceptor impurities were implanted separately to a dose of 5 × 10¹⁵ ions/cm² at room temperature into similar samples of suitably masked silicon. Boron ions were also implanted at liquid nitrogen temperature and 450°C. Annealing was limited to a maximum temperatare of 550 °C.

Measurements have been made of sheet resistance, forward and reverse I-V characteristics (from 10^?9 amps/cm²), reverse breakdown voltage, noise, minority carrier storage time and junction series resistance.

The bulk properties of boron implanted diodes were found to be reproducible. The introduction of recombination centres by implantation is the major factor influencing variation in these properties between one implantation condition and another. Changes in surface oxide conditions probably affect reverse leakage currents and breakdown voltages.

The properties of boron implanted diodes are considered suitable for applications such as the MOSFET, and are superior to those of the AI, Ga and In implanted diodes.     

磷离子注入速率对4H-SiC(0001)晶格恢复与电阻率降低的影响

高剂量的磷离子注入4H-SiC(0001)晶面，注入速率从1.0×1012到4.0×1012 P+ cm-2s-1变化，而注入剂量固定为2.0×1015 P+ cm-2。室温注入，1500oC的高温下退火。利用光荧光和拉曼谱分析注入产生的晶格损伤以及退火后的残余缺陷。通过霍耳测试来分析注入层的电学性质。基于上述测试结果，发现通过减小磷离子的注入速率，极大地减少了注入层的损伤及缺陷。考虑到室温注入以及相对较低的退火温度(1500 oC)，在注入速率为1.0×1012 P+ cm-2s-1及施主浓度下为4.4×1019 cm-3的条件下，获得了非常低的方块电阻106 Ω/sq。     

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.     

Nd: YAG laser annealing of gallium-implanted silicon

A Q-switched Nd: YAG laser with a pulse duration of 20 ns was used to investigate effects of laser annealing in gallium implanted silicon. Rutherford backscattering and Hall-effect measurements were performed to evaluate the annealed layer. Differential Hall-effect measurements were carried out to obtain carrier concentration profiles after annealing. It was found that a maximum sheet carrier concentration of 8×10¹⁵ cm⁻² can be obtained for a gallium implantation of 10¹⁶ cm⁻² by laser annealing with an energy density of more than 1.0 J cm⁻². Although the peak carrier concentration was found to be 8.0×10²⁰ cm⁻³, the annealed layer showed polycrystalline structures even after annealing with an energy density up to 4J cm⁻². The annealing took place in the solid phase in this energy density range.     

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.     

Location of self-interstitial atoms in boron-implanted silicon by means of rutherford backscattering of channelled ions

Abstract

For locating self-interstitial atoms in silicon by means of Rutherford backscattering of channelled ions, boron has been implanted at room temperature and at the temperature of liquid nitrogen. The employed implantation doses were 2. 10¹⁴ cm^?2 and 7. 10¹³ cm^?2, respectively. The experiments have been performed at 300 K and at 120 K to reduce ionization-stimulated annealing. The beam of 1.4 MeV He⁺-ions was highly collimated.

To obtain the configuration of implantation-induced self-interstitial atoms symmetry considerations have been performed.

The location experiments presented indicate the existence of isolated self-interstitial atoms in silicon. Under the conditions of these experiments the interstitial atoms assume a (110) split configuration of orthorhombic symmetry.     

Electrical activation of boron-implanted silicon during rapid thermal annealing

The electrical activation of boron implanted in crystalline and preamorphized silicon has been investigated during rapid thermal annealing performed with halogen lamps. Samples implanted with B⁺ fluences ranging between 5×10¹⁴ and 1×10¹⁶cm⁻² and treated at temperatures between 900°C and 1100°C have been examined. When boron is implanted in crystalline Si, activation proceeds slowly atT<1000°C and cannot be completed in times typical of rapid thermal annealing (a few tens of seconds). The analysis of carrier profiles indicates that the time constant for activation is strongly affected by local damage and dopant concentration. If the total boron concentration exceeds equilibrium solubility, precipitation occurs concomitant to activation, even if the substitutional boron fraction is still lower than equilibrium solubility. ForT≧1000°C complete activation is obtained in times of about 10 s. In the case of preamorphized Si the activation occurs very quickly, during the recrystallization of the amorphous layer, for all the examined temperatures.     

Defect removal after low temperature annealing of boron implantations by emitter etch‐back for silicon solar cells

Ion implantation offers new possibilities for silicon solar cell production, e.g. single side doping that can be structured in‐situ with shadow masks. While phosphorus implantations can easily be annealed at low temperature, the annealing of boron implantations is challenging. In this study, we use low energy implantations of boron (1 keV and 5 keV) with a projected range of 5.6 nm and 21.2 nm that form defects causing charge carrier recombination after a low temperature anneal (950 °C, 30 min). An ozone‐based wet chemical etching step is applied to remove this near surface damage. With increasing chemical etch‐back the electrical quality (i.e. emitter saturation current density, J_0e) improves continuously. The calculated limit for J_0e was reached with an abrasion of 35 nm for 1 keV and 85 nm for 5 keV implantations, showing that the relevant defects causing charge carrier recombination are located very close to the surface, corresponding to the as‐implanted profile depth. This emitter etch‐back allows for the fabrication of defect free boron doping profiles with good sheet resistance uniformity (standard deviation <2%). With the resulting characteristics (sheet resistance <100 Ω/sq, surface doping concentration >5 × 10¹⁹ cm^–3, J_0e < 30 fA/cm²), these boron profiles are well suited for silicon solar cells. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Nitrogen centers in GaP produced by hot implantation

Backscattering yields of 1.5 MeV?He⁺ ions and low temperature photoluminescence (PL) spectra were measured in GaP crystals implanted with 200 keV?N⁺ ions as functions of ion-dose, temperature during implantation and annealing temperature after implantation. Backscattering results indicate that hot implantation at 500°C greatly reduces radiation damage. The PL intensities of NN lines become maximum in the sample implanted with N⁺ ions of 3 × 10¹⁴cm^?2 at 500°C, and annealed at 1000°C for 1 hr with aluminum glass. The PL intensity is comparable to that of the nitrogen-doped sample during liquid phase epitaxy which is widely accepted as the best method of introducing nitrogen into GaP crystals. In the case of 500°C—hot implantation, the radiation damage produced during implantation is annealed out at 700 ~ 800°C and the implanted nitrogen substitutes for the phosphorous sites after annealing at 900 ~ 1000°C. Some kinds of defects or strains remain around the NN centers even in implanted samples with a maximum PL efficiency. These defects or strains don't seem to reduce the PL efficiency. In the case of room temperature implantation, PL efficiency decreases to one-hundredth or one-thousandth due to the formation of the non-crystalline state compared with hot implantation.     

Electrical activation of phosphorus-donors introduced in 6H-SiC by hot-implantation

Phosphorus ion (P⁺) implantations into 6H-SiC at room temperature (RT), 800 °C, and 1200 °C with mean concentrations of 1᎒¹⁸-5᎒¹⁹ /cm³ were performed to investigate the effects of hot-implantation on the electrical activation of P atoms. Improvement of the electrical activation of P atoms due to hot-implantation is found to depend on their implantation concentration, which can be divided into three regions. In the implantation with P in a low-concentration region (for example, 1᎒¹⁸ /cm³), no significant difference in the carrier concentrations among the samples implanted at RT and elevated temperatures is observed after annealing above 񫰸 °C. In a medium-concentration region, the carrier concentration increases with implantation temperature. When P ions were implanted in a high-concentration region (for example, 5᎒¹⁹ /cm³), the hot-implanted samples exhibit higher carrier concentration as compared with RT-implanted samples. Regarding hot-implantation, the carrier concentration in 800 °C-implanted samples is higher than that in the 1200 °C-implanted samples. This results can be interpreted as a degree of damage introduced by each implantation.     

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.     

Electrical properties of Cd,Zn and S ion-implanted layers in GaAs

The electrical properties of cadmium, zinc, and sulfur ion-implanted layers in gallium arsenide have been measured by the van der Pauw-Hall technique. Ion implantation was performed with the substrates held at room temperature. The dependence of sheet resistivity, surface carrier concentration, and mobility on ion dose and on post-implantation anneal temperature was determined. In the case of 60 keV Cd⁺ ions implanted into n-type substrates, a measurable p-type layer resulted when samples were annealed for 10 minutes at a temperature in the range 600—900°C. After annealing at 300—900°C for 10 minutes, 100 per cent electrical activity of the Cd ions resulted for ion doses ≤ 10¹⁴/cm².

The properties of p-type layers produced by implantation of 85 keV Zn⁺ ions were similar to those of the 60 keV cadmium-implanted layers, in that no measurable p-type behavior was observed in samples annealed below a relatively high temperature. However, in samples implanted with 20 keV Zn⁺ ions a p-type layer was observed after annealing for 10 minutes at temperatures as low as 300°C.

Implantation of sulfur ions into p-type GaAs substrates at room temperature resulted in the formation of a high resistivity n-type layer, evcn before any annealing was performed. Annealing at temperatures up to 200°C or above 600°C lowered the resistivity of the layer, while annealing in the range 300—500°C eliminated the n-type layer.     

Amorphisation of GaN during processing with rare earth ion beams

GaN epilayers grown by metal organic chemical vapor deposition (MOCVD) were implanted with Tm and Eu ions with different energies and fluences and at different temperatures in order to optimize the implantation conditions. The recovery of the implantation damage was studied using both rapid thermal annealing and furnace annealing with nitrogen overpressure of 4×10⁵ Pa. Rutherford backscattering spectrometry in the channeling mode (RBS/C) was used to monitor the evolution of damage introduction and recovery in the Ga-sublattice and transmission electron microscopy (TEM) was carried out for further structural analysis. The RBS/C spectra as well as TEM images show two different damage regions, one at the surface arising from an amorphous surface layer and another one deeper in the crystal coinciding with the end of range of the implanted ions. For implantation with 150 keV at room temperature, even for fluences as low as 3×10¹⁴ at/cm², a thin amorphous surface layer, which becomes thicker with increasing implantation fluence, was observed by TEM. High temperature annealing of these highly damaged layers often results in loss of the amorphous layer and accumulation of the implanted species at the surface rather than a regrowth of the crystal. It was possible to prevent the formation of an amorphous layer by implanting at 500 C. In those samples a large part of the lattice damage was removed during annealing at 1000 C and the recovery of the lattice is similar for both applied annealing methods.     

Low temperature channeling measurements of ion implantation lattice disorder in single crystal silicon

Lattice disorder for 200-keV Sb implantations into silicon has been studied by channeling effect analysis using 400 keV proton backscattering. Implantation and analysis were performed at low temperatures in the same system without warmup. In the temperature region between 85°K and room temperature the disorder production per incident ion at low doses is implantation temperature dependent. Approximately 18,000 silicon scattering centers per incident 200-keV Sb ion are observed for 90°K implantations, and this value is nearly a factor of three greater than at room temperature. Isochronal anneal curves of low fluence, low temperature implantations show, significant annealing below room temperature. The observed disorder production per incident ion decreases with increasing implantation temperature at temperatures 50 to 100°K lower than annealing occurs following 85 or 90°K implants. Strong similarities of the implantation temperature dependence and anneal behavior of the disorder exist for Sb and B implantations into silicon and suggest that much of the lattice disorder produced by ion implantation can be understood in terms of the basic properties of the silicon target material.     

Vacancy trapping and helium decoration in Sb ion-implanted tungsten studied by Mössbauer spectroscopy

Mössbauer effect measurements have been performed using sources of¹¹⁹Sb implanted in W without and with post-implanted helium. Each of the sources was subjected to an isochronal annealing sequence in order to study vacancy trapping, helium decoration and recovery of damage. Four sites have been identified for Sb implanted in tungsten; one of these corresponds with substitutional Sb atoms, two others are assigned to Sb atoms associated with vacancies, while the last one can be either vacancy or impurity associated. The development of site occupation as a function of annealing temperature is in accordance with the one-interstitial model. Injection of 2·10¹⁶ He/cm² leads to nucleation of helium bubbles. Helium atoms that are released from these bubbles at about 1300 K are retrapped by Sb atoms to form new bubbles.     

Magnetic hyperfine interaction after77Br implantation into iron

Radioactive⁷⁷Br ions were implanted at 60 keV and 270 keV into polycrystalline iron foils. The magnetic hyperfine interaction of the daughter nucleus⁷⁷Se in the 250 keV isomeric level was investigated using the perturbed angular correlation technique and fast BaF₂ detectors. The Larmor frequency at room temperature was determined as ω_L=1272(2) MHz, leading to a substitutional hyperfine field ofB _hf(SeFe)=62(6) T. The substitutional fraction rises from 21% at room temperature to about 100% at 790 K annealing temperature. No other well-defined magnetic or electric hyperfine component attributable to impurity-defect complexes was identified. The diffusion of Br atoms in the surface region during the annealing process was studied via Rutherford backscattering with 1.0 MeV α-particles.     

Amorphous GaP produced by ion implantation

Two types of non-crystalline states (“disordered” and “amorphous”) of GaP were produced by using ion implantation and post annealing. A structural-phase-transition-like annealing behaviour from the “disordered” state to the “amorphous” state was observed.The ion dose dependence and the annealing behaviour of the atomic structure of GaP implanted with 200 keV ? N⁺ ions were studied by using electron diffraction, backscattering and volume change measurements. The electronic structure was also investigated by measuring optical absorption and electrical conductivity.The implanted layer gradually loses the crystalline order with the increase of the nitrogen dose.The optical absorption coefficient α and electric conductivity σ of GaP crystals implanted with 200 keV?N⁺ ions of 1 × 10¹⁶ cm^?2 were expressed as αhν = C(hν ? E₀)ⁿ and log $\text{σ = A ? BT}{}^{\mathrm{<mtext>-</mtext><mtext>1</mtext><mtext>4</mtext>}}$, respectively. Moreover, the volume of the implanted layer increased about three percent and the electron diffraction pattern was diffused halo whose intensity monotonically decreases along the radial direction. These results indicate that the as-implanted layer has neither a long range order nor a short range order (“disordered state”).In the sample implanted at 1 × 10¹⁶ cm^?2, a structural phase-transition-like annealing stage was observed at around 400°C. That is, the optical absorption coefficient α abruptly fell off from 6 × 10⁴ to 7 × 10³ cm^?1 and the volume of the implanted layer decreased about 2% within an increase of less than 10 degrees in the anneal temperature. Moreover, the short range order of the lattice structure appeared in the electron diffraction pattern. According to the backscattering experiment, the heavily implanted GaP was still in the non-crystalline state even after annealing.These facts lead us to believe that heavily implanted GaP, followed by annealing at around 400°C, is in the “amorphous” state, although as-implanted Gap is not in the “amorphous” state but in the “disordered” state.     

Hall effect and Raman analysis of residual damage and free electron concentration in Si-implanted GaAs: a quest for better doping efficiency

To tackle the problem of insufficient electrical activation of Si⁺ dopant in GaAs, we have studied a series of heavily Si-implanted and thermally annealed GaAs samples (two different doses, each implanted at three different temperatures and with two implantation rates). A comparative analysis of electrical and optical measurements was done on the same set of samples and correlated with implantation parameters. By temperature dependent Hall-effect measurements carrier density and carrier mobility were determined over the 20-300 K range. The mobility data were analyzed taking into account different scattering mechanisms.The implantation-induced initial damage was determined by Rutherford backscattering, whereas the amount of residual damage present in the samples after thermal annealing was estimated by Raman spectroscopy. Additionally, scattering by LO phonon-plasmon coupled modes was used to study the properties of the free electron gas in the implanted layer, including its depth distribution. Free carrier concentrations deduced from the analysis of the plasmon modes agree with the Hall-effect results. Multi-energy implantation in combination with higher implant temperature is suggested as a way to increase doping efficiency by reducing high local concentrations and lessen the probability of compensating defects formation.