Phosphorus Implantation Research Articles

Complex Diagnostics of Silicon-on-Insulator Layers after Ion Implantation and Annealing

A technology was developed for activating ion-implanted dopants in silicon-on-insulator layers at a low annealing temperature (600°C) using the pre-amorphization technique of a silicon device layer. In the case of phosphorus implantation, silicon was amorphized directly by dopant ions. In the case of boron implantation for pre-amorphization, the layers were preliminary irradiated with argon or fluorine ions. Complex diagnostics of the implanted layers was carried out using secondary ion mass spectrometry, X-ray diffractometry and small-angle X-ray reflectometry. The combination of methods made it possible to characterize the impurity distribution, the degree of silicon crystallinity, the layer thicknesses, and the interface widths in structures. The results of diagnostics of the structure and composition correlate well with calculations in the SRIM software package and the electrophysical characteristics of the layers after annealing. It was shown that the use of argon for pre-amorphization of silicon interfered with the recrystallization process and did not make it possible to achieve acceptable electrical characteristics of the doped layer. Amorphization with phosphorus and pre-amorphization with fluorine during boron implantation allowed obtaining the required values of the resistance of the doped layers after annealing at a temperature of 600°C. The use of a complex approach made it possible to optimize the modes of amorphization, ion doping, and annealing of silicon-on-insulator structures at low temperatures, necessary for the creation of light-emitting device structures based on silicon-germanium nanoislands.

Temperature effects on elastic constants and related properties of apatites

The application of apatites, a class of naturally occurring calcium phosphate minerals with the most common forms being hydroxyapatite (HAP), fluorapatite (FAP) and chlorapatite (ClAP), range from primary production of phosphorus, to bone and dental implants, to potential usage in carbon sequestration and nuclear waste immobilization including those that involve exposure to high temperatures. Due to their hexagonal structure, apatites have five independent elastic constants: nevertheless, experimental studies commonly report isotropic properties, and limited computational results available in the literature exhibit a large scatter. Moreover, investigation of temperature dependence of apatite elastic properties which would be essential for designing future applications is yet to be addressed in the current state of the art. In this work, we evaluate the single crystal elastic constants of the three apatite structures using stress–strain relationships: first from density functional theory (DFT) using ultrasoft pseudopotential with PBEsol exchange–correlation functional under generalized gradient approximation (GGA) on a single unit cell , and then with molecular dynamics (MD) with a 5×5×5 unit cell using a core–shell based potential model at temperatures varying from 10K to 1500K. In this temperature range, apatites exhibit the highest stiffness along the ‘c’ axis, and their elastic constants noticeably decrease with increasing temperature. At very high temperatures, C33 becomes greater than C11 for both FAP and ClAP. It is noteworthy that our DFT study exhibits better conformity with experimental findings when compared to other DFT studies reported in literature. Additionally, MD studies have demonstrated favorable consistency in predicting elastic constants, potentially as a result of fitting potential parameters to experimental data. We also calculate various effective isotropic elastic properties from our single crystal MD results and study their temperature dependence as a substitute for first principles modeling of large polycrystalline systems. All the apatites have very comparable bulk, shear, and elastic moduli, but FAP has slightly higher values, and interestingly, HAP’s Poisson’s ratio shows no variation with temperature. This study sets the baseline with which any future studies on high-temperature applications of apatites (such as carbonate or radionuclide rich apatites) can be compared.

Investigation of Reducing Interface State Density in 4H-SiC by Increasing Oxidation Rate.

Detailed investigations of the pre-oxidation phosphorus implantation process are required to increase the oxidation rate in 4H-SiC metal-oxide-semiconductor (MOS) capacitors. This study focuses on the SiO2/SiC interface characteristics of pre-oxidation using phosphorus implantation methods. The inversion channel mobility of a metal-oxide-semiconductor field effect transistor (MOSFET) was decreased via a high interface state density and the coulomb-scattering mechanisms of the carriers. High-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) were used to evaluate the SiO2/SiC interface's morphology. According to the energy-dispersive X-ray spectrometry (EDS) results, it was found that phosphorus implantation reduced the accumulation of carbon at the SiO2/SiC interface. Moreover, phosphorus distributed on the SiO2/SiC interface exhibited a Gaussian profile, and the nitrogen concentration at the SiO2/SiC interface may be correlated with the content of phosphorus. This research presents a new approach for increasing the oxidation rate of SiC and reducing the interface state density.

Time evolution of donor activation at low temperatures with co-implantation of phosphorus and hydrogen in silicon

We report on the study of the donor activation behavior at low temperatures using subamorphizing implantation of phosphorus and hydrogen to develop three-dimensional integrated circuits. We show that the activation efficiency of phosphorus 0° implantation angle is superior to that at 7° due to the broad defect and donor profiles. At 370 °C, the carrier concentration was enhanced by hydrogen co-implantation at a dose of 1015 cm−2. However, the enhancement quickly decayed, and the carrier concentration at 400 °C was lower than that in the sample without hydrogen. The change in the activation behavior suggests that the enhancement in the carrier concentration was due to the defect complexes generated by hydrogen implantation. By eliminating defect complexes, the passivation of phosphorus by hydrogen atoms became evident. At 500 °C, hydrogen caused phosphorus deactivation at the beginning of the annealing process. The carrier concentration then recovered, indicating dehydrogenation during further annealing.

22.8% efficient ion implanted PERC solar cell with a roadmap to achieve 23.5% efficiency: A process and device simulation study

Among all available photovoltaic (PV) technology options, c-Si based passivated emitter rear cell (PERC) has already proved its mettle by delivering more than 22% conversion efficiency at the industrial level. However, designing of PERC solar cell device remains a challenge owing to recombination and absorption losses, which eventually restrict the performance of the device toward achieving an Auger efficiency limit of 29.4%. The primary contributor to these losses is emitter recombination losses that limits the performance of PERC devices. The n+-emitter region in the proposed PERC devices is formed using ion implantation followed by a diffusion process. The impact of process variables such as dose (cm−2), energy (keV), diffusion time (s), and diffusion temperature (oC) on the PERC device performance is not much explored. Therefore, in an attempt to fulfill this research gap, the emitter region performance in terms of ion implantation of phosphorus, influence of local back surface field (BSF) doping concentration (1017 to 1019 cm−3), and back surface recombination velocity (SRV 101–107 cm/s) on PERC device performance followed by the loss analysis is examined in this work. An upright pyramid textured structure with constant height (5 μm) and industrial standard stacked dielectric anti-reflective coating layers, SiNX/SiO2 and Al2O3/SiNX at front and back side respectively is realized using different process statements such as deposit, etch, implantation, and diffusion with the help of a Silvaco TCAD software. Investigations reveal that the PERC device can deliver an efficiency of 22.8% with 150 μm boron-doped crystalline silicon (c-Si) wafer at an optimum phosphorous dose (5 × 1015 cm−2), BSF doping (1019 cm−3), and SRVn (107 cm/s). Short-circuit current density (JSC) of 40.8 mA/cm2, open-circuit voltage (VOC) of 0.686 V, and fill factor (FF) of 81.54% are obtained for the structure under consideration. A roadmap to achieve 23.5% conversion efficiency has also been reported by assuming a carrier selective contact at the backside with a surface recombination velocity of 10 cm/s.

Interfacial electronic structure engineering on molybdenum sulfide for robust dual-pH hydrogen evolution

Molybdenum disulfide, as an electronic highly-adjustable catalysts material, tuning its electronic structure is crucial to enhance its intrinsic hydrogen evolution reaction (HER) activity. Nevertheless, there are yet huge challenges to the understanding and regulation of the surface electronic structure of molybdenum disulfide-based catalysts. Here we address these challenges by tuning its electronic structure of phase modulation synergistic with interfacial chemistry and defects from phosphorus or sulfur implantation, and we then successfully design and synthesize electrocatalysts with the multi-heterojunction interfaces (e.g., 1T0.81-MoS2@Ni2P), demonstrating superior HER activities and good stabilities with a small overpotentials of 38.9 and 95 mV at 10 mA/cm2, a low Tafel slopes of 41 and 42 mV/dec in acidic as well as alkaline surroundings, outperforming commercial Pt/C catalyst and other reported Mo-based catalysts. Theoretical calculation verified that the incorporation of metallic-phase and intrinsic HER-active Ni-based materials into molybdenum disulfide could effectively regulate its electronic structure for making the bandgap narrower. Additionally, X-ray absorption spectroscopy indicate that reduced nickel possesses empty orbitals, which is helpful for additional H binding ability. All these factors can decrease Mo-H bond strength, greatly improving the HER catalytic activity of these materials.

Phosphorus implantation into 4H-SiC at room and elevated temperature

Phosphorus implantation is essential to create localized n-type doped regions in 4H-SiC. The realized profiles may, however, deviate from the desired ones, affecting device properties. In order to characterize typical process parameters and to enable correct prediction of the desired structures, phosphorous implantation into 4H-SiC with a variety of doses and energies is performed at room and elevated temperature. Exemplary post-implantation annealing shows no significant influence on the phosphorus distribution. The as-implanted profiles, analyzed by secondary ion mass spectrometry, show a clear dependence on implantation dose and temperature. High sample temperature at implantation suppresses channeling in case of low and medium doses due to increased lattice vibrations, while crystal damage is restored in case of high doses leading to increased opportunities for channeling, pointing toward different crystal damage and energy loss mechanisms. Finally, the Monte Carlo profiles of the simulation tools stopping and range of ions in matter (SRIM) and Sentaurus Process are critically compared with the experimental profiles.

Comparison of Different Ways of Extra Phosphorus Implantation Which Decrease the Threshold Voltage and On-resistance of UMOS

A method to decrease the threshold voltage and on-resistance is discussed in this paper, which is adding extra phosphorus implantation into silicon. There are two ways to implant extra phosphorus without adding a mask. The first way is to implant extra phosphorus after the field oxide etching, and the second way is to implant extra phosphorus with the source region mask before the N+ implantation. Compare the results of the two ways to find their characteristics and choose the appropriate one.

Stencil-masked phosphorus-implanted silicon for solar cell applications

Stencil-masked phosphorus implantation on silicon wafers is demonstrated for solar cell applications. Line-shaped window patterns with areas of 156 mm × 156 mm and 125 mm × 125 mm are laid out in the silicon stencil mask with diameters of 200 and 300 mm, respectively. According to laser optical microscopy and scanning electron microscopy observation, the phosphorus-implanted line is 100 μm wide with an edge roughness of a few micrometers. Based on the silicon-stencil-masked phosphorus implantation, the fabrication process of alternative phosphorus-implanted and boron-diffused patterns on silicon wafers is proposed. During the post-implantation wet oxidation process, a thick oxide layer is grown on the phosphorus-implanted silicon, acting as a protective layer for the subsequent diffusion of boron. Scanning capacitance microscopy observation reveals the p-type polarity in boron-diffused silicon and the n-type in phosphorus-implanted silicon with homogeneous contrast along the textured surface. Silicon-stencil-masked ion implantation has potential as a selective doping method on silicon wafers for solar cells.

Comparison of Strain Characteristics and Contact Resistances of Heavily Phosphorus‐Doped Si Formed by Phosphorus Implantation and In Situ Phosphorus‐Doped Si Epitaxial Growth

As transistor sizes reduce, the effect of contact resistivity on power consumption increases. To reduce contact resistivity, heavily phosphorus‐doped Si grown via in situ phosphorus‐doped (ISPD) Si epitaxial growth is studied actively. Laser spike annealing to the heavily phosphorus implanted (IMP) layers is demonstrated to replace ISPD Si epitaxial growth process and phosphorus profiles and strain characteristics are evaluated. Regardless of the doping method, the phosphorus concentrations of both samples and their tensile strains are equivalent. After laser annealing, the metal‐silicidation is conducted to measure contact resistivity. The Ni‐silicide formed on IMP sample has 3D clusters inducing greater morphological degradation than ISPD samples. The contact resistivity of IMP sample measured using the circular transmission line model (CTLM) (1.2–8.3 × 10−8 Ω cm2) is similar to that of the ISPD sample (1.1–5.5 × 10−8 Ω cm2) after Ni‐silicidation of the ISPD layer. This study performs strain engineering by achieving low contact resistance at lower cost while applying strain using the IMP process rather than the epitaxial process.

Electrical, charge transients and photo response study of as-deposited and phosphorus implanted Cd1-xZnxTe devices for PV applications

High quality polycrystalline Cd1-xZnxTe (CZT) thin films with compositions (x = 0, 0.25, 0.5, 0.75, 1) were deposited on glass substrates by thermal evaporation technique followed by phosphorus implantation schedules at 800 keV and 1200 keV, carried out on the same samples. Detailed electrical properties of as deposited and implanted CZT films were investigated as a function of Zn content, such as, current-voltage (I–V), Charge based Deep Level Transient Spectroscopy (Q-DLTS), trap level energies (ET), Transient of Photo Voltage (TPV) and kinetics of photo current with variable light intensity ranges performed to study and evaluate the potential of this scheme for potential usage in the development of solar cells. It was observed that phosphorus implant increases the electrical conductivity, consequently, provides sufficiently higher carrier concentration for Photo Voltaic (PV) applications. The resistivity, carrier dynamics, charge transients, deep/trap assisted levels and intensity (visible light) controlled photo-responses, of CZT films are found to be tailored by selecting suitable Zn content and specific energy of phosphorus dopant, which may have ramifications for process development in CZT-based PV technology.

Особенности массопереноса при ионной имплантации

Исследованы продукты реакции, полученные при ионной имплантации азота, кислорода и фосфора в вольфрамовую мишень. Выяснены условия создания новых соединений при высокодозной имплантации, приводящей к процессам быстрого массопереноса ионов в материал мишени. Установлено, что ионная имплантация азота в вольфрам приводит к возникновению фазы внедрения W2N с ГЦК-структурой; имплантация кислорода — к образованию фазы с плотноупакованной ГЦК-структурой, близкой по структуре и параметрам к W20; фосфора — к образованию фосфида вольфрама W2P с орторомбической структурой после дополнительного отжига при температурах, превышающих 800-900 0С. Сделана оценка локального давления потока ионов на поверхность мишени, которое приводит к локальному искривлению кристаллической решетки, благодаря чему возможен быстрый массоперенос имплантированных ионов в материале мишени.
 Образование фаз внедрения при ионной имплантации является результатом локализации сдвиговой деформации в условиях ускоренного массопереноса. В условиях высокодозной ионной имплантации формируются высоконеравновесные пересыщенные твердые растворы, а также высокодефектные структурно-неравновесные состояния с высокой кривизной кристаллической решетки.

Dissociation and Formation Kinetics of Iron–Boron Pairs in Silicon after Phosphorus Implantation Gettering

Herein, the results of a systematic study on the kinetics of dissociation and formation of iron–boron (FeB) pairs in boron‐doped Czochralski silicon after phosphorus implantation gettering of iron at different temperatures are reported. The aim herein is threefold: 1) investigation of the dissociation kinetics of the FeB pairs by standardized illumination as a function of iron concentration after the gettering process; 2) study of the kinetics of their association; and 3) extraction of the characteristic parameters of these two phenomena for gettered samples, in particular the effective time constants of dissociation and association as well as the constant of material, which describes the dissociation rate well in the absence of other recombination channels.

Exploring conductivity in ex-situ doped Si thin films as thickness approaches 5 nm

Silicon (Si) has been scaled below 10 nm in multigate and silicon-on-insulator (SOI) device technologies, but clearly Si thickness cannot be reduced indefinitely, as we will run out of atoms eventually. As thickness approaches 5 nm, surfaces and interfaces will significantly impact the electrical behavior of Si, and surface physics cannot be discounted. Below that, bulk material properties will be altered considerably in the few-monolayer limit. One of the most basic defining properties of a semiconductor is its conductivity. To improve conductivity, while inducing a channel by appropriate biasing, it is necessary to define an accurate impurity doping strategy to reduce parasitic resistance. In this paper, we investigated the changing electrical conductivity of SOI films as a function of the Si thickness, in the range of 3–66 nm. SOI films were ex situ doped using three different approaches: liquid/vapor phase monolayer doping of phosphorus using allyldiphenylphosphine, gas-phase doping of arsenic using arsine (AsH3), and room-temperature beam-line ion implantation of phosphorus. The circular transfer length method and micro-four-point probe measurements were used to determine the resistivity of the Si films, mitigating the contribution from contact resistance. The resistivity of the Si films was observed to increase with decreasing Si film thickness below 20 nm, with a dramatic increase observed for a Si thickness at 4.5 nm. This may drastically impact the number of parallel conduction paths (i.e., nanowires) required in gate-all-around devices. Density functional theory modeling indicates that the surface of the Si film with a thickness of 4.5 nm is energetically more favorable for the dopant atom compared to the core of the film.

Investigation of Parasitic Resistance Components in the Case of Microwave Irradiation in Poly-Si Annealing

We fabricated transmission-line method (TLM)-type devices for analysis of the interface uniformity between an aluminum electrode and n-type silicon by using phosphorus implantation. For the dopant activation, we adopted novel microwave irradiation (MWI) as an alternative to rapid thermal annealing (RTA). Also, we investigated the contact resistance (RC), sheet resistance (RS), transfer length (LT) and specific contact resistance (ρC) that affected the thin-film transistor’s (TFT’s) performance through the TLM, and we compared parameters for various annealing methods. MWI showed a RC (2.175 Ω) which is similar to that for RTA (1.825 Ω). Also, MWI resulted in improved LT and ρC (4.426 μm, 0.48×10−4 Ω·cm2, respectively) characteristics compared to RTA (8.238 μm, 0.752 × 10 −4 Ω·cm2, respectively). Consequently, MWI, which has a lower thermal budget showed improved uniformity compared to RTA, and the total processing time was lower. Thus, we expect the MWI method to be an excellent choice for high-performance poly-Si TFT applications and to have various advantages.

Effects of phosphorus implantation time on the optical, structural, and elemental properties of ZnO thin films and its correlation with the 3.31-eV peak

To study the effects of implantation on ZnO thin films grown on Si substrates, we have subjected it to phosphorous ion implantation for 10, 40, and 70 s through plasma immersion ion implantation and rapid thermal annealing. Low-temperature photoluminescence spectra of the as-implanted samples exhibited a reduction in the donor-bound exciton peak at 3.36 eV with implantation time. The photoluminescence spectrum of the 70 s implanted 1000°C-annealed sample confirmed acceptor-type doping. X-ray diffraction measurements showed a reduction in the c-axis length along the <002> direction with implantation time, evidencing phosphorous-ion incorporation in the implanted films, which was further confirmed by the blue shifting of the E2 high peak in the Raman spectra. XPS measurements affirmed the presence of the P 2p peak, a signature of PO bond, and confirmed the substitution of Zn atoms by P atoms and the subsequent formation of the Pzn-2Vzn complex essential for acceptor-type conductivity.

Improved Mg Dopant Activation in p-GaN and Enhanced Electroluminescence in InGaN/GaN LEDs by Plasma Immersion Ion Implantation of Phosphorus

Improved Mg Dopant Activation in p-GaN and Enhanced Electroluminescence in InGaN/GaN LEDs by Plasma Immersion Ion Implantation of Phosphorus

Activation of dopant in silicon by ion implantation under heating sample at 200 °C

Activation and carrier generation are reported in the case of phosphorus implantation with a dose of 2.0 × 1015 cm−2 at 70 keV to crystalline silicon substrates under heating ranging from 200 to 500 °C. The analysis of the optical reflectivity spectra of implanted surfaces revealed that the effective amorphized thickness was low of 2.9 nm in the case of 200 °C-phosphorus implantation, while it was large of 140 nm for implantation at room temperature. The carrier density par unit area increased from 6.9 × 1013 to 4.8 × 1014 cm−2 and the photo-induced minority carrier effective lifetime increased from 2.2 × 10−6 to 1.6 × 10−4 s as the implantation temperature increased from 200 to 500 °C. Defect reduction with 1.3 MPa H2O vapor heating at 250 °C for 3 h increased the carrier density par unit area of the 200 °C-phosphorus-implanted sample to 2.7 × 1014 cm−2. The rectified characteristics were obtained by current–voltage measurement in the case of phosphorus implantation to p-type silicon substrate. Photovoltaic effect was also observed. These results show that the ion implantation under low temperature heating has a capability of p–n junction formation.

Point and extended defect interaction in low – high energy phosphorus implantation sequences

The objective of this paper is to study the phenomenology of the extended defects generated by phosphorus (P) implantations in silicon with a special attention to the interaction with a previous implantation of the same specie already recovered by a furnace annealing. For this purpose we decided to analyze two P implantations: the first is shallower with a projected range of 110 nm and a dose high enough to amorphize the silicon, the second one is implanted after the furnace annealing of the first implantation and has a projected range of 1.4μm. For the deeper implantation different doses (from 1×1013 to 1×1014cm-2) and two different schemes of annealing have been tested. More in depth there is a third P implantation with a projected range of 2.3μm and a dose in the order of some 1013cm-2. Selective etching of silicon, transmission electron microscopy (TEM) and micro-photoluminescence, combined with secondary ion mass spectroscopy (SIMS) were used for the analysis of the implantation defects and for the determination of P distribution, respectively. Analyzing the two implantations separately we note that the shallower and amorphizing implantation left the dislocation loops aligned at the projected range, as expected; instead the couple of the deeper implantations shows the presence of threading dislocations which generate in the implanted zone (between 1 and 3μm) and which increase for many μm reaching the surface and also the deepest zone of the wafer (6.5μm). The situation changes if the implantations are done in the same sample, first the shallow implantation followed by the double implantations in depth. The dislocations are more numerous, but shorter. The interesting fact is that the growth of the defects is inhibited mostly towards the surface, while the zone affected by the defectiveness in depth remains more or less the same.

Scanning Spreading Resistance Microscopy for Doping Profile in Saddle-Fin Devices

Scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) are used to investigate the doping profile of saddle-fin (S-fin) devices in a 30-nm dynamic-random-access-memory (DRAM) technology. Due to the limited resolution of SCM, SCM cannot provide a clear doping profile of an S-fin array device. In the meantime, SSRM and focused ion beam milling during sample preparation provide an opportunity to obtain a 2-D and scanning line doping profile. The common-source region between two adjacent buried word lines is treated with an additional phosphorus (P) implantation with energy and dosage modification to have a doping profile modification in the array devices of DRAM product. With condition of the medium energy and high dosage in this additional P implantation, the row hammer effect of 30-nm DRAM could be minimized by the localized shielding effect from the electric field by a depletion effect. The junction profile of the additional P implantation is about 10 nm deeper than that of the control sample, as verified by SSRM and technology computer-aided design simulation. The experimental results of the doping profile can be used to support a mechanism of improvement of row hammer. The SSRM methodology proposed in this study could be used to optimize the doping profiles in DRAMs for future scaling technology.