Mechanistic study of borosilicate glass growth by low-pressure chemical vapor deposition from tetraethylorthosilicate and trimethylborate

A reaction mechanism and film morphology as a function of reactor conditions and post growth thermal annealing for borosilicate glass (BSG), (SiO₂)_x(B₂O₃)_1−x, films deposited from tetraethylorthosilicate (TEOS), trimethylborate (TMB), and oxygen (O₂) precursors by low-pressure chemical vapor deposition (LPCVD) was determined. An empirically derived reaction model for BSG film growth is proposed that predicts the growth rate and composition of BSG films up to 70 mole% B₂O₃. The BSG reaction model includes a strongly adsorbed TEOS-derived intermediate that forms SiO₂ and a direct surface reaction of TMB, in O₂, to form B₂O₃. This model is supported by growth rate and mass spectroscopic data. The BSG film morphology, investigated using atomic force microscopy, was found to have a root-mean-square roughness of 0.5 nm, with the precise film morphology being a function of reactor conditions. The BSG film roughness increases with film thickness, temperature, and boron content. Thermal annealing of the films in a water-free environment leads to planarization of the BSG governed by the film composition and anneal temperature.     

Redistribution of phosphorus implanted into silicon doped heavily with boron

The special features of redistribution of phosphorus implanted into silicon wafers with a high concentration of boron (N _B=2.5×10²⁰ cm^?3) were studied. It is shown that, in silicon initially doped heavily with boron, the broadening of concentration profiles of phosphorus as a result of postimplantation annealing for 1 h in the temperature range of 900–1150°C is significantly less than in the case of lightly doped silicon. The results are interpreted in terms of the impurity-impurity interaction with the formation of stationary boron-phosphorus pairs. The binding energy of boron-phosphorus complexes in silicon was estimated at 0.6–0.8 eV.     

Annealing of deep boron centers in silicon carbide

The effect of annealing on the efficiency of high-temperature luminescence of 6H-SiC samples grown under varied conditions and doped with boron was studied. A part of the samples was subjected to neutron or fast-electron irradiation. It is shown that the efficiency of high-temperature luminescence is determined by the concentration of deep boron-related centers, revealed by capacitance spectroscopy as D centers. High-temperature treatment leads to dissociation of the D centers, which are B_Si-V _C complexes, with part of the boron atoms becoming electrically inactive. It is established that deep boron centers are thermally stable up to ≈1500°C. The preservation of these centers at higher temperatures (up to 2600°C) is due to the presence in SiC crystals of clusters acting as sources of nonequilibrium carbon vacancies. Clusters of this kind are contained in crystals grown with an excess of silicon or irradiated with high-energy particles. This circumstance accounts for the strong dependence of both the concentration of D centers and the temperature of their annealing on sample preparation conditions.     

Dependence of dicarbon annealing temperature in <Emphasis Type="Italic">n</Emphasis>-Si on oxygen concentration in the crystal

The role of oxygen in the mechanism of dissociation of the dicarbon complex in n-Si into components is considered. It is assumed that released interstitial carbon atoms C_i migrate through the crystal and react with both substitutional carbon C_s and interstitial oxygen with the resulting formation of complexes C_iC_s and C_iO_i, respectively. The solution of a system of equations describing the formation of interstitial carbon atoms in the course of annealing of dicarbon show that the rate constant for the reaction of annealing of the C_iC_s complex (the G center) depends on the oxygen concentration. This dependence is treated as the dependence of the activation energy for annealing of a C_iC_s complex and, consequently, the dissociation energy of this complex on oxygen concentration. A more accurate value of dissociation energy for the G center was determined as 1.08±0.03 eV.     

The behaviour of boron molecular ion implants into silicon

Implants of boron molecular ions into silicon have been studied using a variety of experimental techniques, but with emphasis on sheet resistance annealing characteristics and transmission electron microscopy. Boron halide compound molecules have been implanted and equivalent dose sequential implants of atomic species used as control conditions. The implants studied were B⁺, BCl₂⁺, BCl⁺, Cl⁺ + B⁺, BF₂⁺, BF⁺ and B⁺ + F⁺ at 25 keV/B atom and B⁺, BBr₂⁺ and Br₂⁺ + B⁺ at 12 keV/B atom.The implantation of molecular ions enables conditions of varying damage to be studied with constant dose, dose rate and energy of the dopant species. In addition to damage effects the halogen atoms produce species effects in the implanted zone. The escape of the halogen atoms has been measured as a function of the annealing temperature.The significant differences which exist between the behaviour of silicon implanted with these various conditions are considered with reference to the damage structures observed by transmission electron microscopy. The boron-fluorine molecular implants are shown to offer some advantages as a means of implanting boron.     

Comparison of p–n junction formed by BF2 and B implantation in silicon microstrip detector with low and high thermal budget: impact of fluorine on electrical characteristics

The influence of crystal damage on the electrical properties and the doping profile of the implanted p⁺–n junction has been studied at different annealing temperatures using process simulator TMA-SUPREM4. This was done by carrying out two different implantations; one with implantation dose of 10¹⁵ BF₂⁺ ions/cm² at an energy of 80 keV and other with 10¹⁵ B⁺ ions/cm² at 17.93 keV. Substrate orientation 1 1 1 of phosphorus-doped n-type Si wafers of resistivity 4 kΩ cm and tilt 7° was used, and isochronally annealing was performed in N₂ ambient for 180 min in temperature range between 400°C and 1350°C. The diode properties were analysed in terms of junction depth, sheet resistance. It has been found that for low thermal budget annealing, boron diffusion depth is insensitive to the variation in annealing temperature for BF₂⁺-implanted devices, whereas, boron diffusion depth increases continuously for B⁺-implanted devices. In BF₂⁺-implanted devices, fluorine diffusion improves the breakdown voltage of the silicon microstrip detector for annealing temperature upto 900°C.For high thermal budget annealing, it has been shown that the electrical characteristics of BF₂⁺-implanted devices is similar to that obtained in B⁺-implanted devices.     

Effect of ion doping on the dislocation-related photoluminescence in Si+-implanted silicon

The study is concerned with the effect of the additional implantation of Si samples with C⁺, O⁺, B⁺, P⁺, and Ge⁺ impurity ions followed by annealing at 800°C on the behavior of the dislocation photoluminescence line D1, induced in the samples by implantation with Si⁺ ions at a stabilized temperature followed by annealing in an oxidizing Cl-containing atmosphere. It is established that the intensity of the D1 line strongly depends on the type of incorporated atoms and the dose of additional implantation. An increase in the D1 line intensity is observed upon implantation with oxygen and boron; at the same time, in other cases, the D1 luminescence line is found to be quenched. The mechanisms of such behavior, specifically, the role of oxygen and its interaction with implanted impurities are discussed.     

Low-dislocation relaxed SiGe grown on an effective compliant substrate

An effective compliant substrate was successfully fabricated for growth of high quality relaxed SiGe templates. The compliant substrate was fabricated by synthesizing a 20% B₂O₃ concentration borosilicate glass in the silicon on insulator wafers through boron and oxygen implantation followed by high temperature annealing. Substrates with 5%, 10% and 20% B₂O₃ were used for 150 nm Si_0.75Ge_0.25 epitaxy. Double-axis x-ray diffraction measurements determined the relaxation and composition of the Si_1−xGe_x layers. Cross-sectional transmission electron microscopy was used to observe the lattice of the SiGe epilayer and the Si substrate, dislocation density and distribution. Raman spectros-copy was combined with step etching to measure the samples. For 20% BSG sample, the strain in the thin Si layer was calculated from the Raman shift and it matched the results from DAXRD very well. The density of threading dislocation on the surface of 500 nm Si_0.75Ge_0.25 layers was 2×10⁴ cm⁻² for the sample on the 20% borosilicate glass substrate. This method is promising to prepare effective compliant substrate for low-dislocation relaxed SiGe growth.     

Density functional theory calculations for estimation of gettering sites of C,H, intrinsic point defects and related complexes in Si wafers

Very recently, a C₃H₅ cluster ion implantation technique for proximity gettering has been reported with the low energy of around 10¹⁵/cm² dose without recovery heat treatments. The main feature of this technique is that the gettering efficiency is higher than that by C monomer implantation, even though irradiation defects are too small to clarify by TEM observation. In the present work, we evaluate the binding energies of metal atoms with candidate gettering sites of C, H, intrinsic point defects and related complexes in Si wafers induced by C₃H₅ cluster ion implantation or different methods, for example, H implantation etc. by using density functional theory calculations. In addition to C and H atoms, we consider donor P and O atoms contained in an n- CZ-Si wafer for use in a CMOS image sensor. The simplest complexes of substitutional/interstitial C (C_s/C_i), H_i, P_s, O_i, and incorporated intrinsic point defects (vacancy (V) and self-interstitial Si (I)) by C₃H₅ implantation were also considered. We found that C_s–I (= C_i), C_i–C_i, H_i–I, VH_n (n=1–3), and VO complexes are the best candidates for gettering sites. Gettering by C₃H₅ cluster ion implantation is more effective than that by C monomer implantation due to the formation of VH_n (n=1–3) and H_i–I complexes, which provides more effective gettering sites.     

The variation in activity of recombination centers in silicon <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> structures under the conditions of acoustic loading

Using the method of differential coefficients of current-voltage characteristics, deep levels in the Cz-Si p-n structures are studied under the ultrasonic loading conditions (longitudinal waves of a frequency of 4–26 MHz and intensity as high as 0.6 W/cm²). The levels with thermal activation energy of 0.44, 0.40, 0.37, 0.48, and 0.46 eV are revealed. It is assumed that these levels are associated with the E center, bistable B_SO_2i complex, and interstitial atoms captured by dislocation loops, respectively. It is established that ultrasound induces an increase in the contribution to the recombination processes of shallower levels and a decrease in activation energy of defects. The possibility of acoustoinduced reversible reconstruction of the configuration of the B_SO_2i complex is analyzed.     

Effect of annealing in argon on the properties of thermally deposited gallium-oxide films

The effect of the annealing temperature on the I–V, C–I, and G–V characteristics and transparency of gallium-oxide films is investigated. The films are fabricated by the thermal evaporation of Ga₂O₃ powder on n-GaAs wafers. It is shown that the films which are amorphous after deposition crystallize upon annealing at temperatures T _an ≥ 800°C. The electrical characteristics and photoresponse of the V/Ni-GaAs-GaAs-Ga _x O _y -V/Ni samples to visible radiation depend on the structure and phase composition of the films.     

Optical and electrical properties of thin wafers fabricated from nanocrystalline silicon powder

The infrared transmittance spectra and dark conductivity of wafers fabricated from nanocrystalline silicon powder (nc-Si) have been studied. The initial nc-Si powder is first synthesized by laser-induced silane dissociation, with the temperature of the surrounding buffer gas varied from 20 to 250°C, and then compacted at pressures from 10⁸ to 10⁹ Pa. It is found that compaction of the nc-Si powder results in formation of Si-H, Si-CH_x, and O_y-Si-H_x structures (x, y=1–3). The formed structures break down under annealing, with the Si-H and Si-CH_x complexes disintegrating at the lowest annealing temperature (t = 160°C). The dark conductivityof the nc-Si wafers is shown to increase along with the buffer gas temperature at which the starting powder was prepared. Two temperature regions are found in which the dark conductivity behaves in radically different ways. At wafer temperatures T ≥ 270 K, conductivity is mediated by free carriers, whereas, at lower temperatures, electron transport is governed by hopping conduction over localized states in the band gap.     

A study of recombination centers in irradiated <Emphasis Type="Italic">p</Emphasis>-Si crystals

p-Si samples irradiated with 8-Mev electrons are studied. It is suggested that the multicomponent V₃+O or V₂+O₂ complexes are not recombination centers on the basis of an analysis of the dependences of the minority-carrier lifetime τ, the resistivity ρ, the concentration p, and the Hall mobility μ_H on the temperature of isochronous annealing T_ann. Deep donors with energy levels at ΔE_i=E_v+0.40 eV and the V₃+O₃ and the V₃+O₂ complexes affect the values of μ_H and τ. The curves of isochronous annealing are used to determine the annealing-activation energies E_ann for defects such as K centers, interstitial carbon atoms C_i, the V+B and V₂+O₂ complexes, divacancies V₂, and defects with a level at ΔE_i=E_v+0.20 eV. These energies were found to be equal to E_ann=0.9, 0.25, 1.6, 2, 1.54, and 2.33 eV, respectively.     

Detection of hydrogen impurity in silicon radiation detectors

The behavior of silicon particle detectors irradiated with 2.5-MeV electrons during subsequent annealing is studied. Annealing at 100–250°C was found to result in the formation of two types of traps with the levels E _c ?0.32 eV and E_v+0.29 eV. Increasing the annealing temperature to 300°C makes both traps disappear. On the basis of data obtained, it was concluded that these traps are related to hydrogen-containing complexes. The presence of hydrogen in a crystal results in a decrease in the annealing temperature for vacancy-oxygen (VO) complexes and complexes consisting of carbon and oxygen interstitials (C_iO_i). The reason for this phenomenon is the passivation of these complexes by hydrogen, which results in the formation of electrically active VOH centers {with the level E _c ?0.32 eV} in an intermediate stage of this process. It is assumed that hydrogen penetrates the structures under investigation in one of the stages of their fabrication.     

Hopping ε2 conductivity of boron-doped a-Si:H films annealed in hydrogen at high temperature

It is shown that the high-temperature annealing in hydrogen flow results in substantial modification of the temperature dependence of the conductivity of boron-doped and undoped a-Si:H films. For doped films subjected to annealing, the ε₂ conductivity related to hopping between localized states near the valence-band edge appears in the intermediate temperature range, along with the contributions of the band conductivity and the variable-range hopping conductivity. The ε₂ conductivity becomes possible due to an increase in the concentration of electrically active boron atoms and to the appreciable shift of the Fermi level after high-temperature annealing of doped films in hydrogen atmosphere. The experimentally measured parameters of the ε₂ conductivity make it possible to determine the width of the energy region, in which the density of localized states near the valence band falls off nonexponentially.     

Influence of boron clustering on the emitter quality of implanted silicon solar cells: an atom probe tomography study

The use of ion implantation doping instead of the standard gaseous diffusion is a promising way to simplify the fabrication process of silicon solar cells. However, difficulties to form high‐quality boron (B) implanted emitters are encountered when implantation doses suitable for the emitter formation are used. This is due to a more or less complete activation of Boron after thermal annealing. To have a better insight into the actual state of the B distributions, we analyze three different B emitters prepared on textured Si wafers: (1) a BCl₃ diffused emitter and two B implanted emitters (fixed dose) annealed at (2) 950°C and at (3) 1050°C (less than an hour). Our investigations are in particular based on atom probe tomography, a technique able to explore 3D atomic distribution inside a material at nanometer scale. Atom probe tomography is employed here to characterize B atomic distribution inside textured Si solar cell emitters and to quantify clustering of B atoms. Here, we show that implanted emitters annealed at 950 °C present maximum clusters due to poor solubility at lower temperature and also highest emitter saturation current density (J_0e = 1000 fA/cm²). Increasing the annealing temperature results in greatly improved J_0e (131 fA/cm²) due to higher solubility and a consequently lower number of clusters. BCl₃ diffused emitters do not contain any B clusters and presented the best emitter quality. From our results, we conclude that clustering of B atoms is the main reason behind higher J_0e in the implanted boron emitters and hence degraded emitter quality. Copyright © 2015 John Wiley & Sons, Ltd.     

The effect of hydrogen on boron diffusion in SiO2

The diffusivity of boron in silicon dioxide may be increased by the introduction of hydrogen into the annealing atmosphere. In this paper we report on the diffusion characteristics of boron ion-implanted into thermally grown SiO₂. A sensitive technique was used in which the boron atoms redistributed into the substrate are characterized by electrical methods. The diffusivity of boron in thermal SiO₂ was measured over the temperature range of 950-1150°C with hydrogen partial pressure from 0 to 0.2 atm. It was found that the diffusion coefficient of boron in oxide at 1150° C increases as the square root of the hydrogen partial pressure. At fixed pressure the temperature dependence of the diffusion coefficient obeys a single-activation-energy exponential rule. At 0.1 atm partial pressure of H₂ the activation energy is 3.0 eV and the preexponential factor is 6 x 10⁵ [cm²/sec.].     

Interstitial carbon formation in irradiated copper-doped silicon

The influence of a copper impurity on the spectrum of defects induced in p-Si crystals containing a low oxygen concentration by irradiation with electrons with an energy of 5 MeV at room temperature is studied by deep-level transient spectroscopy. It is found that interstitial carbon atoms (C _i ) which are the dominant defects in irradiated samples free of copper are unobservable immediately after irradiation, if the concentration of mobile interstitial copper atoms (Cu _i ) is higher than the concentration of radiation defects. This phenomenon is attributed to the formation of {Cu _i , C _i } complexes, which do not introduce levels into the lower half of the band gap. It is shown that these complexes dissociate upon annealing at temperatures of 300–340 K and, thus, bring about the appearance of interstitial carbon.

     

Isochronal annealing study of hydrogen interaction with implantation-induced point defects in p-type silicon

Isochronal annealing with zero and reverse bias applied to Schottky diodes was used to monitor the evolution of hydrogen interaction with point defects observed in hydrogen-implanted p-type silicon, i.e., divacancy (VV), carbon–oxygen interstitial pair (C_iO_i) and two levels at E_v+0.28 and E_v+0.50 eV. The VV and C_iO_i are passivated by hydrogen liberated from hydrogen-containing defects during annealing in the temperature range 90–150°C and reappear upon annealing above 180°C under reverse bias due to hydrogen liberation and its field drift. Two levels at E_v+0.50 and E_v+0.28 eV are ascribed to irradiation-induced and hydrogen-related defects, respectively.     

Long-range effects of ion irradiation, chemical etching, and mechanical grinding on relaxation of a solid solution of iron in gallium phosphide

Electron spin resonance was used to study directly the influence of external factors on a system of defects in gallium phosphide crystals doped nonuniformly with iron. The Fe _s ³⁺ (Ga) ions replacing Ga atoms (the A centers) and Fe _i ⁰ interstitial atoms (the B centers) are considered as indicators and participants in rearrangement of the crystal’s defect system. Long-range effects of ion irradiation with argon, chemical etching, or mechanical grinding on the A and B centers are observed. The long-range effect is explained by plastic deformation of the GaP:Fe crystal and by interaction of dislocations with A and B centers when the crystal is modified by ion irradiation or by removal of a layer that is saturated with Fe _s ³⁺ (Ga) centers and gives rise to stresses from one of the sample surfaces. In the case of ion irradiation, the role of elastic waves that are generated in the stopping zone of argon ions and that interact with B centers and dislocations is apparently important.