Anomalous Diffusion Of Boron Research Articles

The redistribution modeling of implanted impurity stimulated by vacancies

The mechanism of diffusion, stimulated by the formation of radiation defects, anomalous diffusion of boron into silicon carbide from the vapor phase, is described based on the two-component model of interaction of the impurity with own defects. The model of the anisotropic shift of the implanted impurity, namely, the diffusion concentration equation of the impurity containing the application describing the drift, stimulated by vacancies, is proposed to explain the experimental data. It is shown that the coefficient of vacancy diffusion does not depend either on the direction – on the surface or on it, or on the method of annealing – thermal or photonic.

Formation of Ultra Shallow p+/n Junction in Silicon Using a Combination of Low-Temperature Solid Phase Epitaxy and Non-Melt Double-Pulsed Green Laser Annealing

MOSFETs scaling-down is an effective way to attain high-performance CMOS operating with lower power and leakage current. However, short channel effects have become a serious problem due to the shortening of channel length. One of the promising methods to suppress this problem is by forming a shallow, highly doped and activated source/drain extension region. Fabricating ultra shallow p+/n junction is difficult due to the channeling of boron ions and anomalous boron diffusion during fabrication processes. A combination of Ge pre-amorphization implantation, low-energy boron implantation and two-step annealing, involving low-temperature solid phase epitaxy preannealing followed by non-melt laser annealing was used for forming ultra shallow p+/n junction in silicon. The physical relationship among the regrowth of implanted layer, boron activation and diffusion, and leakage current is investigated. We have succeeded in forming ultra shallow p+/n junction with junction depth of 8 nm and sheet resistance of 920 Ω/□.

Boron diffusion behavior in silicon during shallow p+/n junction formation by non‐melt excimer laser annealing

AbstractBoron diffusion in silicon during the formation of a shallow p+/n junction has been studied. Low‐energy/high‐dose boron was implanted in germanium preamorphized silicon. Preannealing involving rapid thermal annealing for 10 s, followed by annealing involving non‐melt laser annealing for several nanoseconds were then performed to regrow the amorphous layer and to activate dopants. We found that this combination of processes results in anomalous diffusion of boron (despite the annealing being performed within several nanoseconds), which increases the junction depth of annealed samples.

Instability of junctions formed by low energy B implant and low temperature solid phase epitaxy growth

The stability of p+∕n junctions remains a critical issue for device performance. Shallow junctions formed by low temperature solid phase epitaxy growth (LTSPEG) are not stable during additional thermal processes. Anomalous boron diffusion and boron trapping by end-of-range defects are observed during additional furnace annealing. The study shows that, by adding a (MeV) implantation step before LTSPEG, B trapping and B diffusion are significantly reduced during post-LTSPEG annealing. The technique can be used as a method to increase the stability of shallow junctions formed by LTSPEG.

Thermal redistribution of hydrogen and boron in SiO 2 in SiN-capped p-type MOSFET structures

The thermal behavior of boron and hydrogen in a SiN-capped p-type MOSFET was investigated in order to explain SiN-enhanced boron diffusion in SiO 2. Measured hydrogen profiles indicated that hydrogen in the SiN migrated into the gate oxide during annealing under nitrogen. When this structure was annealed under nitrogen, the boron diffusivity in its SiO 2 increased to levels more than two orders of magnitude greater than that reported in SiO 2 annealed under hydrogen without a SiN cap. Nevertheless, the activation energy for boron diffusion in SiO 2 in a SiN-capped sample was the same as that for boron diffusion in SiO 2 annealed under hydrogen. This indicates that SiN-enhanced boron diffusion can be explained by the model proposed for hydrogen-induced boron diffusion: hydrogen termination of defects reduces the activation energy for interstitial-mediated diffusion of boron in SiO 2. Anomalous boron diffusion in SiO 2 in SiN-capped samples is thought to result from the SiN film facilitating the incorporation of a large amount of hydrogen in the SiO 2.

Stability of Ultrashallow Junction Formed by Low-Energy Boron Implant and Spike Annealing

Dopant stabilization after high-temperature thermal spike annealing was investigated. 0.2 keV B implanted silicon wafers were thermally spike-annealed at 1100°C, followed by furnace annealing between 550 and 750°C to study their stabilities. We have observed the anomalous diffusion of boron during the post-spike furnace annealing in nitrogen ambient. It is indicated that p + /n junctions formed by ultralow energy B implant and spike annealing are not stable during subsequent thermal processes. By adding a megaelectronvolt (MeV) implantation after spike annealing, the B profile shows a negligible diffusion during the following furnace annealing at 750°C. The concept of MeV implantation can be used as a method to overcome instability of the shallow junction.

Stability studies of ultrashallow junction formed by low energy boron implant and spike annealing

The stability of junctions formed by spike anneal remains a crucial issue for the device performance. In this study, 0.2 keV B implanted silicon was thermally spike annealed at 1100 °C. Samples were then furnace annealed under temperatures between 550 and 750 °C to study their stabilities. We have observed the anomalous diffusion of boron during the post-spike furnace annealing in nitrogen ambient. The anomalous behavior shows two features in the near-surface region and in the tail region. B diffusion in the tail region was transient, e.g., with an enhancement of 103×equilibrium at 700 °C for the first 60 s. In the near-surface region, a large number of B atoms move toward the native oxide/Si interface with a diffusion rate also transient and similar to that observed in the tail region. It is indicated that interstitials are generated due to spike annealing and will cause instability of the junction during the following thermal processes.

Fluorine implantation effect on boron diffusion in Si

Boron diffusion was studied in the BF2+ implanted Si by secondary ion mass spectroscopy. Anomalous boron diffusion was observed in the excess Si region of the amorphized layer at low temperatures below 300 °C. This was explained by a diffusion model where boron was assumed to diffuse by way of an intermediate species BI formed of interstitial Si(SiI) and substitutional boron. It is also found that fluorine plays a significant role in enhancing boron diffusion even at an annealing temperature as low as 300 °C, although the enhanced boron diffusion was reported only to occur at annealing temperatures above 600 °C. Fluorine may hinder SiI from growing into large clusters which need a high temperature annealing to dissociate into freely migrating species. Exponential diffusion profile of fluorine could be explained by a model of SiI–F complex formation. This complex consumes SiI resulting from small Si clusters which could dissociate at low annealing temperatures. This result also supports that boron diffusion at high annealing temperatures may be suppressed by co-implantation of fluorine.

Point Defect-Based Modeling of Transient Diffusion of Boron Implanted in Silicon Along Random and Channeling Directions

ABSTRACTA point defect-based model, which has been developed to describe diffusion and electrical activation of boron in crystalline silicon during post-implantation annealing, is used to simulate the anomalous diffusion of boron implanted into silicon along the random and [100] channeling directions. The model predictions are compared to data measured by Chu et al.

Control of anomalous boron diffusion in the base of Si/SiGe/Si heterojunction bipolar transistors using PtSi

In Si/SiGe/Si heterojunction bipolar transistor structures, very shallow arsenic implant on the emitter has been found to cause anomalous boron diffusion in the base. This phenomenon imposes stringent constraints on the device fabrication processes. We discovered that by using platinum silicide, which also served as a self-aligned low resistance contact material to the emitter and base, the anomalous diffusion in the base was significantly reduced. In this letter, we report the experiment results, and propose possible explanations.

The process limitation for forming Ti silicided shallow junction by BF2+ implantation into thin polycrystalline Si films and subsequent Ti silicidation

Excellent shallow p+n junctions have been formed by implanting BF2+ ions into thin polycrystalline Si films and subsequent annealing; these junctions which show a leakage of 1 nA/cm2 and a junction depth of about 0.05 μm. An anomalous boron diffusion occurs when subsequent silicidation is carried out. Silicidation using 300-Å Ti just slightly affected the junction profile. However, the junction is considerably deepened for 600-Å Ti silicidation, yielding a resulting depth of about 0.11 μm. The large boron redistribution is attributed to the point defects induced by silicidation. Hence, proper silicide thickness should be chosen to retain the junction profile as well as to reduce the parasitic source/drain resistance.

Characterisation of heterojunction bipolar transistors incorporating Si/Si 1−xGe x epitaxial double layers with n + emitter implants

Transistors fabricated with systematic variations in Ge fraction, base doping and junction spacer width show near-ideal electrical characteristics. Emitter implantation generates anomalous boron diffusion in the base.

Suppression of anomalous diffusion of ion-implanted boron in silicon by laser processing

Anomalous diffusion of ion-implanted boron in silicon has been suppressed by using the laser annealing (LA) technique. For the rapid thermal annealing process, the high-dosage boron implant significantly enhanced the anomalous diffusion of boron in Si largely due to increased density of interstitial clusters. The mechanism that electrically active dopants contribute to diffusion is confirmed. The dopant activation is primarily determined from the heating process rather than the holding time interval. Hence, the optimum annealing regime, attaining high-performance shallow p+-n junctions, is to increase the dopant activation efficiency during the temperature-ramping process as well as to shorten the holding interval. Having an ultrahigh heating rate, the LA technique serves as an excellent annealing scheme to significantly suppress the anomalous diffusion and considerably promote the dopant activation.

Roles of Extended Defect Evolution on the Anomalous Diffusion of Boron in Si during Rapid Thermal Annealing

The role of extended defect evolution on the anomalous diffusion of boron during rapid thermal annealing (RTA) was studied by investigating the diffusion behavior of boron implanted into various Si substrates using secondary ion mass spectroscopy and transmission electron microscopy, i.e., predamaged wafers with low dose Si implantation, preamorphized wafers with high dose Si implantation, and single‐crystal wafers without any previous implantation. Low‐dose Si preimplantation reduced the channeled tail significantly in subsequent boron implantation and resulted in a larger anomalous diffusion of boron and faster annealing of extended defect during RTA compared to crystalline Si samples. Diffusion of boron implanted into preamorphized Si was found to be anomalous in nature and its magnitude was dependent upon the RTA temperature. The temperature dependence was found to be due to the difference in the density of dislocation loops formed during RTA at the original amorphous/crystalline (a/c) interface. These loops determined the effectiveness of the trapping Si interstitials diffusing from the crystalline side of the original a/c interface to the epitaxially regrown region. Anomalous diffusion of boron in the crystalline Si samples was found to be a strong function of implant dose. Diffusion displacement increased and anomalous diffusion effect lasted longer with increasing implant dose. Diffusion enhancement for longer periods of time in samples with higher implant doses was related to the formation and annealing of extended defects. At very high doses , where the peak boron concentration was above the solid solubility, excess diffusion in the high boron concentration region was observed. The excess diffusion was explained in terms of segregation of boron into interstitial dislocation loops in the early stage of RTA and the subsequent annealing of these dislocation loops after the initial large anomalous tail diffusion.

Boron Diffusion in Silicon‐on‐Insulator Structures Formed by Oxygen Implantation

was implanted at low and high doses into 1986 and 1988 SIMOX substrates and annealed at different temperatures for different periods of time. Transmission electron microscopy combined with secondary ion mass spectrometry and spreading resistance were used for the analysis of the microstructural defects after implantation and annealing, and the determination of boron redistribution, and the associated resistivity profile, respectively. A pile‐up phenomenon close to the upper interface of the silicon film and an anomalous boron diffusion were observed for low‐dose implant. The cause of these phenomena is attributed to the silicon film quality as can be concluded from a comparison between the 1986 and 1988 samples. The McNabb and Foster model for diffusion plus trapping associated with a phenomenological model for anomalous boron diffusivity was solved in order to take into account these effects. The boron redistribution for high‐dose implant presents the same features in the SIMOX structure as in bulk silicon. The role which the implant defects play during boron diffusion was highlighted and discussed.

Extended defect evolution in boron-implanted Si during rapid thermal annealing and its effects on the anomalous boron diffusion

Effects of extended defect evolution on the anomalous diffusion of ion-implanted boron during rapid thermal annealing (RTA) have been studied using transmission electron microscopy and secondary-ion mass spectroscopy. It has been found that for low-dose boron implants (<1×1014 cm−2), no extended defects can be observed after RTA at 1000 °C, and the anomalous diffusion saturates within less than 10 s. However, extended defects are developed for high-dose boron implants (>5×1014 cm−2), and the anomalous diffusion persists for a much longer time and is dose dependent. Extended defect evolution has been characterized and correlated with the observed anomalous boron diffusion behaviors.

Implantation damage and anomalous diffusion of implanted boron in silicon

The anomalous diffusion of implanted boron in silicon damaged by self-implantation has been investigated by cross-section transmission electron microscopy and secondary-ion mass spectroscopy. During rapid thermal annealing, bulges in the boron profile are observed at the edges of the defected band and the profile broadening is accompanied by the shrinking of the band. The decay time became unobvious due to the emission of point defects from the edges of the defected band. It is suggested that the anomalous diffusion of boron is related to the point defects produced by implantation and emitted from the defected band.

Transient diffusion of boron implanted in SI along random and channeling directions

We have studied anomalous diffusion of boron implanted into silicon along the [100] channeling direction versus random directions for 5, 10, and 40 keV, 2 × 10 14 cm 2 boron implantations. Three different annealing conditions, 800 °C for l h, 900 °C for 30 min, and 1000 °C for 10 s, were studied. Anomalous diffusion was observed for all implants annealed at all conditions. The amount of enhanced diffusion is 10–50% higher in the implants along the channeling direction than along the random directions. We attribute the mechanism of the diffusion enhancement to the annealing of ion implantation damage. The difference of diffusion enhancement between channeled implants and random implants are due to the difference in damage profile of the two different implants. Electrical activity of boron is observed for random and for channeled implantations, and the shape of the Hall profile agrees with that of SIMS.

Anomalous diffusion of boron implanted into silicon along the [100] direction

We have observed transient enhanced diffusion of boron implanted into silicon along the [100] channeling direction and compared it with that of boron implanted in a ‘‘random’’ direction. It is found that the anomalous boron displacement for the channeled implants is significantly greater than for the random counterparts. An empirical explanation for the greater displacement of the channeled implants is proposed that is related to the spatial distribution of the implanted boron and the lattice damage generated by the implantation process.

Discussion of “Anomalous Boron Diffusion in Silicon from Planar Boron Nitride Sources” [J. Stach and A. Turley (pp. 722–724, Vol. 121, No. 5)

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