Doping of silicon with selenium by diffusion from the gas phase

Selenium-doped silicon single crystals are studied for the case of an impurity introduced by diffusion from the gas phase. Doping is performed in sealed quartz ampules at a temperature of 1240°C over the course of 240 h. The dependence of the concentration of the introduced deep donor centers of various types on the diffusant vapor pressure p _Se is examined. It is found that samples with a concentration of atomic Se centers exceeding 10¹⁵ cm^?3 can be obtained at comparatively low p _Se (0.02–0.06 atm). In this case, the content of diatomic Se₂ complexes is lower by an order of magnitude and more. The results obtained may be of interest for those who study nonlinear optical phenomena involving deep donor centers in silicon.     

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.     

Concentration-dependent diffusion of boron and phosphorus in silicon

A calculation is made of the tail of the impurity concentration profile resulting from concentration-dependent diffusion from a constant surface concentration into a semi-infinite medium. The calculation predicts that if the concentration dependence at low impurity concentrations is negligible, the low concentration portion of the doping profile should still take the familiar form,C = C'_{s} erfc (x/2 D_{i^{frac{1}{2}}}t^{frac{1}{2}}). Diis the commonly known diffusion coefficient at low impurity concentrations, whileC'_{s}is the "apparent" surface concentration.C'_{s}depends on the actual surface concentration and also depends on how the diffusion coefficient varies with impurity concentration at high concentrations. It is a constant for a given diffusion system but could be orders of magnitude higher than the actual surface concentration. Empirical data have been obtained for boron and phosphorus diffusions in silicon and found to be in good agreement with this prediction.     

Simulation of near-surface proton-stimulated diffusion of boron in silicon

A quantitative model for near-surface redistribution of doping impurity in silicon in the course of proton-stimulated diffusion is developed for the first time. According to the model, the near-surface peak of the impurity concentration is caused by migration of neutral impurity—self-interstitial pairs to the surface with subsequent decomposition of these pairs and accumulation of the impurity at the silicon surface within a thin layer (referred to as δ-doped layer). The depletion and enhancement regions that are found deeper than the near-surface concentration peak are caused by expulsion of ionized impurity by an electric field from the near-surface region of the field penetration. The field appears due to the charge formed in the natural-oxide film at the silicon surface as a result of irradiation with protons. The diffusion-kinetic equations for the impurity, self-interstitials, vacancies, and impurity—self-interstitial pairs were solved numerically simultaneously with the Poisson equation. It is shown that the results of calculations are in quantitative agreement with experimental data on the proton-stimulated diffusion of boron impurity in the near-surface region of silicon.     

Effect of oxidation on orientation-dependent boron diffusion in silicon

The orientation dependence of boron diffusion in silicon has been investigated, with emphasis on the effect of surface oxidation. It is demonstrated that the presence of an oxide is not sufficient to cause enhanced diffusion in (100) silicon, but the oxide must be growing. Also, the segregation effect has been shown to be the dominant means of transport of boron atoms to the growing oxide, but the segregation coefficient does not appear to be strongly orientation dependent. The difference in surface lattice densities for the different orientations is unlikely to be directly responsible for the observed anisotropy, but the resulting difference in bond densities may be in part responsible, as suggested by the temperature variation of the effect.     

Two-step rapid thermal diffusion of boron into silicon using a boron nitride solid diffusion source

A two-step rapid thermal diffusion process of boron into silicon using a boron nitride solid diffusion source is described. During the first step, HBO² glass is transferred onto the silicon wafer from the diffusion source by keeping the temperature of the silicon wafer at 750° C while the diffusion source is at about 900° C. Boron is, then, diffused into the silicon wafer from HBO² glass at 1000° C or 1100° C in N₂ during the second step. Extremely shallow junctions with junction depths of about 20 nanometers and sheet resistances of about 350 ohms/sq can be achieved with this method as well as relatively deep junctions with junction depths of about 175 nanometers and sheet re-sistances of about 55 ohms/sq. When the diffusion is performed at 1100° C, both the junction depth and electrically active boron concentration at the surface increase as the ambient gas is changed from N₂ to O₂ while the sheet resistance decreases. A boron rich layer which has high resistivity is not formed at the surface when the diffusion is performed at 1100° C in O₂ ambient. This work was supported by Ministry of Science and Technology, Korea     

Simulation of the concentration dependence of boron diffusion in silicon

Boron diffusion in silicon with a high surface concentration was simulated on the basis of the dual pair mechanism. The calculations were compared with experimental data and the calculations using the SUPREM-3 code. It was shown that the model proposed allows us to describe the concentration profiles and the concentration dependence of the boron diffusivity in a wide temperature range: 800–1100°C.     

Effectiveness of charged vacancies in diffusion of implanted boron in silicon

A method is proposed to obtain the temperature dependence of the index of effectiveness of charged vacancies relative to neutral ones in boron diffusion in silicon from an implanted source. The temperature dependence compares favourably with some theoretical results and enables the inclusion of third order-effects in processing simulation programs.     

Model of doped-oxide-source diffusion in silicon

A new theory of the doped oxide diffusion technique in silicon has been developed. Compared to the existing theories, it uses fore physically realistic boundary conditions. The theory was satisfactorily evaluated with radio phosphorus diffusion into (111) silicon. Between 1100 and 1275°C the transfer of phosphorus into silicon was found to be controlled by a surface barrier process and not by segregation between the oxide and silicon. The kinetics of the interfacial conductance process has been shown to involve chemically transformed elemental dopant and a probable vacancy-related defect. Phosphorus concentration profiles, controlled by its diffusivity in the mixed oxide, were processed to produce surface-induced intrinsic diffusivities. In contrast to the single defect-controlled diffusion processes known in most materials, it is seen that in silicon, under non-oxidizing conditions, the nature of the defect responsible for diffusion of dopants depends on the process employed. Technologically important quantities of surface concentration, junction depth and profile shape by the doped oxide process can bow be predicted accurately for the first time.     

Indirect boron diffusion in amorphous silicon modeled by kinetic Monte Carlo

In this paper, we present an atomistic kinetic Monte Carlo (KMC) model for boron diffusion in amorphous silicon (a-Si). Boron diffusion is assumed to be indirect, mediated by dangling bonds (DBs) present in a-Si. The model shows a transient character due to a-Si relaxation modeled by DB annihilation. In addition, B produces clusters at higher concentrations, leading to an immobile B part. The model, when calibrated, has been successfully applied to experiments of thermal anneals of amorphized B marker layers and B implantation into preamorphized Si. In addition, we studied the contribution of B diffusion in a-Si in ultrashallow junction (USJ) formation of advanced technologies. We have also used the model to demonstrate how the contribution to diffusion of B in a-Si in current and future technologies can be higher than in c-Si.     

高浓度硼深扩散自停止腐蚀层硅片工艺研究

为制备用于硅溶片工艺的高浓度硼深扩散自停止腐蚀层硅片,对扩散掺杂工艺进行了研究。结合预淀积和再分布两种条件下扩散的特点,采用两步法工艺制备了高浓度硼深扩散硅片,研究了影响杂质浓度和扩散深度的再分布与预淀积时间比。扩散所得硅片的测试结果与理论计算相当吻合,当再分布与预淀积时间比为1.5倍时,扩散结深为21.7μm,自停止腐蚀层为14μm。     

Boron-rich layer properties formed by boron spin on dopant diffusion in n-type silicon

Starting with N-type base, a p-type emitter is formed using boron spin on dopant (BSoD) which results in formation of boron rich layer (BRL) on top of the emitter and can be used in selective emitter and FF improvements in solar cells. In this work, the morphologies of BRL for varying thicknesses, depending on the diffusion conditions, have been studied to know their impact on emitter formation. The characterizations show that BRL properties are dependent on its thickness and its boron concentration. BRL has amorphous phase with peak boron concentration over 10²¹ atoms/cm³, thickness less than 100 nm, refractive indices of 1.4–1.6 and contact resistance 1.0–6.0 mΩ-cm². The bond properties of the constituent elements of BRL vary depending on the thickness.     

Peculiarities of silicon carbide crystal growth under the diffusion mechanism of vapour transfer

In the present work the gas dynamics in the growth zone of SiC crystals is investigated. It is shown that the propagation of SiC vapour from the growth cavity walls towards the lids is effected by diffusion. On this basis the calculation of the concentration distribution of SiC vapour (n), the equilibrium vapour concentration (n_s) and the supersaturation (α = [(n – n_s)/n_s] × 100%) in the crystal growth zone at different radial and axial gradients is carried out by solving the Laplace equation in cylindrical co-ordinates for a stationary case corresponding to the conditions of crystal growth. The results obtained are compared with the available experimental data, which gives the possibility of explaining some of the observed peculiarities during SiC crystal growth from the vapour phase by the sublimation method.     

Electrically active centers formed in silicon during the high-temperature diffusion of boron and aluminum

The parameters of electrically active centers formed during the high-temperature diffusion of boron and aluminum into silicon in various media are studied by the Hall method and capacitance spectroscopy. It is found that the variation in the resistivity of the n base of the structures with p-n junctions fabricated in the study is controlled by the formation of three donor levels Q1, E4, and Q3 with the energies E _c - 0.31, E _c - 0.27, and E _c - 0.16 eV. Diffusion in a chlorine-containing atmosphere introduces only a single level E4, but its concentration is 2.5 times lower, compared with diffusion in air. The values of the ionization energy of the Q3 level, measured under equilibrium (Hall effect) and nonequilibrium (capacitance spectroscopy) conditions, almost coincide. The deepest level E1 with an energy of E _c - 0.54 eV, formed upon diffusion in both media, has no effect on the resistivity in the n base of the structures.     

Semi-insulating silicon carbide layers obtained by diffusion of vanadium into porous 4H-SiC

Semiconductors - Semi-insulating silicon carbide layers have been obtained by diffusion of vanadium into porous 4H-SiC. The diffusion was performed from a film deposited by cosputtering of silicon...     

液相烧结碳化硅陶瓷腐蚀行为的显微观察

研究了AlN-R2O3（稀土氧化物）液相烧结碳化硅陶瓷在HF、HCl、NaOH、KOH、K3Fe（CN）6等单独或混合液中的腐蚀行为。检测了试样腐蚀前后的失重,用扫描电镜观察了试样腐蚀前后的显微形貌。结果表明,室温或煮沸条件下试样在HF、HCl、NaOH、KOH强酸、强碱中主要表现为晶隙液相腐蚀,晶隙间的玻璃相被腐蚀掉后留下形似岛屿的SiC晶粒,晶粒紧密相接的晶界未受侵蚀。试样在酸中比在碱中的腐蚀程度重。室温下腐蚀进程缓慢,煮沸后腐蚀迅速;在K3Fe（CN）6液中基本不受腐蚀;而在K3Fe（CN）6与KOH的混合水溶液中主要以晶界腐蚀为主,该混合液能很好地将晶体边缘轮廓腐蚀出来。在强酸中试样失重先快后慢;在强碱中试样不失重或失重轻微。     

Atomic level modeling of boron diffusion through silicon oxide before and after plasma nitridation

Ab initio quantum chemical calculations on model systems containing one siloxane bond have been employed to get insight into the mechanisms of boron diffusion in silicon oxide and suppression of boron penetration into gate oxide by plasma-induced nitridation. Calculated energies of insertion of various dopants into siloxane bond show a certain correlation with experimental diffusion activation energies through silicon oxide. Plasma-induced nitridation leads to incorporation of nitrogen atoms into siloxane bond. Energy gain for B insertion into a nitridized siloxane bond dramatically increases compared to its insertion into a regular siloxane bond: from ≈3 eV to more than 10 eV. This might be a plausible explanation of the B diffusion retardation after plasma nitridation. Semi-empirical quantum chemical methods showed a qualitative agreement with ab initio ones for insertion energies and have been applied to larger model systems. Model calculation of the neutral N atom interaction with a siloxane bond containing the hydroxyl group suggested a possible explanation for an absence of nitridation of oxide fluxes composed only of low energy neutral N atoms.