Reduction in minority carrier storage effect by fluorine ion implantation damage

Damage is produced in p-n diodes by fluorine ion implantation to reduce minority carrier storage effect. The switching time, reverse leakage current, andI-Vcharacteristics were investigated for annealing temperature between 450°C and 650°C. The accelation energy is 130 keV and doses are 10¹³-10¹⁵/cm². Annealing causes restoration in switching time, but leakage current increases with annealing temperature rise for doses more than 1 × 10¹⁴/cm². The best diodes indicate 1.5-order reduction in switching time and 10 nA in reverse leakage current. These properties, caused by implantation damage, are retained after long-cycle annealing at 450°C and are expected to be stable under practical use. These diodes can be obtained by annealing at 450°C and they furnish satisfactory diode performance.     

Very shallow boron junctions in Si by implantation and SOD diffusion obtained by RTP

Because of their very large integration capabilities and continuous scaling, the CMOS devices are the basic element in the current-integrated circuits. Their scaling up to sub-micrometric scale presents advantages like diminution of power consumption, faster devices and a larger level of integration. But the physics limitations begin to be important at these dimensions, anomalous effects like hot electrons, leakage currents and punch through, among others, appear. These effects can be reduced if, at the source/drain region, shallow junctions are obtained with junction depth (x_j) less than 200 nm. To achieve this goal, new junction fabrication methods, which include pre-amorphization [S.D. Kim, C.M. Park, J.C.S. Woo, Formation and control of box-shaped ultra-shallow junction using laser annealing and pre-amorphization implantation, Solid State Electron. 49 (2005) 131–135] are required. Other alternative techniques that do not require ion implantation [T. Uchino, P. Ashburn, Y. Kiyota, T. Shiba, A CMOS-compatible rapid vapor-phase doping process for CMOS scaling, IEEE Trans. Electron Devices 51(1) (2004) 14–19.], in order to prevent surface crystal damage and as a consequence the inhibition of boron interstitial clusters and {3 1 1} defects [R.T. Crosby, K.S. Jones, M.E. Law, L. Radic, Dislocation loops in silicon–germanium alloys: the source of interstitials, Appl. Phys. Lett. 87 (192111) (2005) 1–3.], which are the trigger of the “transient enhanced diffusion” (TED) process are used. In this essay, it is shown that rapid thermal process, allow the fabrication of very shallow junctions with a x_j less than 300 nm by using with high energies and high doses of boron/BF₂ ions implantation. By this way the slow dissolution of the dislocation loops, present at the end of range (EOR) of the implanted boron, allow this process. These obtained junctions are compared with those prepared by using the spin on doping (SOD) technique. The diffusion profiles obtained by both processes and their electrical properties are measured and compared for their application as S–D regions in a current CMOS process.     

Tungsten masking against boron implantation

Electron-beam evaporated and ion-beam sputtered films have been successfully used as masks against high-dosage boron implantation. Evaporated films were found to be somewhat more effective, probably because of their higher density. The predicted value for the required mask thickness was in satisfactory agreement with the experimentally determined value.     

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     

Precipitation of boron in silicon on high-dose implantation

Precipitation of boron implanted in silicon with a dose of 1 × 10¹⁶ cm⁻² is studied in relation to the concentration of substitutional boron $ C_{B_0 } $ C_{B_0 } introduced before implantation and before subsequent annealing at 900°C. It is shown that $ C_{B_0 } $ C_{B_0 } = 2.5 × 10²⁰ cm⁻³ is the critical concentration, at which the formation of precipitates is independent of the concentration of point defects introduced by implantation (far from or close to the mean projected range R _p ) and constitutes the prevailing channel of deactivation of boron. At lower concentrations $ C_{B_0 } $ C_{B_0 } close to the equilibrium concentration, precipitation is observed only far from R _p , in the regions of reduced concentrations of point defects. At the same time, in the region of R _p with a high concentration of point defects, most boron atoms are drawn into clustering with intrinsic interstitial atoms with the formation of dislocation loops and, thus, become electrically inactive as well.     

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.     

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.     

Formation of a quasi-periodic boron distribution in silicon, initiated by ion implantation

The temperature range in which oscillating impurity distributions are formed in heavily boron-doped silicon irradiated with boron ions B⁺ is found. It is hypothesized that the effect is associated with boron clustering processes which proceed more efficiently in the region of the maximum of the implanted impurity distribution and at the boundaries of the ion irradiation region. Fiz. Tekh. Poluprovodn. 31, 338–341 (March 1997)     

Formation of shallow photodiodes by implantation of boron into mercury cadmium telluride

Hall-effect measurements on p-type MCT implanted with 1 × 1014 B+/cm2 at 150 keV show that an abrupt junction is formed at a depth of 0.6 ± 0.12 ?m after annealing at 230° for 7 min with a ZnS cap. Prior to the anneal the carrier profile was graded and extended to a depth of 5.0 ± 1.0 ?m. Photodiodes have been formed by a dual implant of 5 × 1014 B+/cm2 at 100 keV and 50 keV, and after annealing a five-fold improvement in Ro A has been measured to give a value of 1.2 ?cm2.     

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.     

High-tilt-angle boron implantation into polycrystalline Si gates

We ion-implanted B into 400-nm-thick polycrystalline Si and evaluated the profiles. The ion-implanted profiles were almost the same for tilt angles of 0/spl deg/ and 7/spl deg/. The channeling tail was more significant than the profile in crystalline Si with a tilt of 0/spl deg/. The channeling phenomenon was significantly suppressed by high-tilt angles because ions cross grain boundaries. We succeeded in expressing these prominent profiles through using an analytical model.     

The effect of boron,oxygen, and fluorine in ion implanted GaAs

Effects of boron, fluorine, and oxygen in GaAs have been investigated by electrical characterization using current-voltage, capacitance-voltage and deep level transient spectroscopy techniques. Ion implantation at 100 keV energy was conducted with doses of 10¹¹ and 10¹²/cm². Carrier compensation was observed in each implanted sample. The compensation effect strongly depended on ion implantation condition and ion species. More free carriers were compensated for higher dose and heavier species; however, severe surface damage would also be induced that degrade electrical performance. Rapid thermal annealing treatment showed the heavier ion implanted samples to be more thermally stable. Defect levels for each implanted species were compared and identified. A native shallow defect E4 was easily removed by ion implantation. In higher dose and heavier ion implantation, both electron and hole traps were induced. However, in some cases, heavier ion implantation also removed native defects. Acceptor-type surface states were created by implantation that degrade material electrical characteristics and also reduce the effect of compensation. The damage induced traps were mostly point-defects or point-defect/impurity complexes as evidenced by sensitivity to heat treatment.     

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.     

Monte Carlo simulation of boron implantation into single-crystalsilicon

An improved Monte Carlo simulation model has been developed for boron implantation into single-crystal silicon. This model is based on the Marlowe Monte Carlo code and contains significant improvements for the modeling of ion implantation, including a newly developed local electron concentration-dependent electronic stopping model and a newly developed cumulative damage model. These improvements allow the model to reliably predict boron implant profiles not only as a function of energy, but also as a function of other important implant parameters such as tilt angle, rotation angle, and dose. In addition, profiles of implant generated point defects (silicon interstitials and vacancies) can be calculated     

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.     

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.     

Transistors with boron bases predeposited by ion implantation and annealed in various oxygen ambients

Ion implanted bases result in better uniformity and wafer to wafer reproducibility for base resistors and transistor gain compared to diffused bases. However, when implanted boron is used as a replacement for a chemically predeposited base on