Active Doping Levels Research Articles

Dopant Activation Depth Profiling for Highly Doped Si:P By Scanning Spreading Resistance Microscopy (SSRM) and Differential Hall Effect Metrology (DHEM)

Heavily n-doped epitaxially grown Si layers are of great importance for source/drain (S/D) application in advanced node nMOS devices. For contact resistivity reduction, the dopant activation level is very important. Various techniques are being used to evaluate dopant activation in Si:P layers. Among these two methods are Scanning Spreading Resistance Microscopy (SSRM) and Differential Hall Effect Metrology (DHEM). SSRM uses an atomic force microscope equipped with a hard conductive probe that is scanned in contact mode on the cross-sectioned sample’s surface and measures spreading resistance. Measured resistance values as a function of depth are converted into resistivity and carrier concentration depth profiles using calibration measurements and conversion relationships. DHEM provides depth profiles of mobility, resistivity and carrier concentration through a semiconductor layer by making successive sheet resistance (Rs) and Hall voltage measurements using Hall effect/Van der Pauw techniques, as the electrically active thickness of the layer is reduced through successive oxidation steps. Controlled oxidation is achieved by electrochemical anodization. Data collected can then be processed to yield the depth profiles. In this contribution we have carried out SSRM and DHEM measurements on Si:P epi layers subjected to different processing conditions including annealing and ohmic contact fabrication. Secondary Ion Mass Spectrometry (SIMS) was used to measure the total (active + inactive) dopant profiles through the films. Effects of these processes on dopant diffusion and activation were studied and the results from DHEM and SSRM were compared.In-situ phosphorus (P) doped Si epi-layers were grown over 300mm diameter boron doped monitor wafers. While one set was kept as the reference, a second set was treated by a spike-annealing process at 1000 °C. In a third set a Ti/TiN contact fabrication process was carried out and the contact was removed before analysis. In the fourth set contact process was applied to the spike annealed wafer before removal of the Ti/TiN layers. Bulk sheet resistance measurements were made using 4-point probe (4PP) for all the samples. SSRM measurements were carried out at IMEC. Cross-shaped Van der Pauw test-patterns were formed on 8mmx8mm areas on the samples and DHEM measurements were performed at ALP. Figure below shows the dopant depth profiles obtained by SIMS and the carrier concentration profiles from DHEM and SSRM techniques for samples D02 (as deposited Si:P) and D03 (spike annealed). One can make some general observations from the data in this figure. The total dopant concentration as measured by SIMS is ~ 1.4E21/cm3. There is only a small difference in the total dopant distribution profiles (SIMS) between the as deposited sample and the spike annealed sample. However, the spike annealed sample shows much higher dopant activation as measured by DHEM. Carrier concentration is ~2.5x higher in sample D03 (~5E20/cm3) compared to sample D02 (~2E20/cm3). Activation levels measured by SSRM, however, are lower for both samples, and the peak carrier concentration value increases only slightly upon spike annealing, going from ~2E20/cm3 in sample D02 to ~2.2E20/cm3 in sample D03. DHEM clearly indicates the sharp interface between the p-type substrate and the n-type epi-layer and its depth calibration agrees well with the expected thicknesses of the epi layers. The tail of the SSRM data is much more graded. Data from other samples will be presented and discussed in the final manuscript. Figure 1

Towards Ultra-Low Specific Contact Resistance on P-Type and N-Type Narrow Bandgap GeSn Semiconductors

GeSn alloys are group IV semiconductors that have attracted remarkable interest owing to their ability of strain and bandgap engineering by controlling the Sn content, their compatibility with the Si CMOS platform and their tunable and direct band gap. These material properties make GeSn a promising candidate for many electronic and optoelectronic applications including among others tunnel field effect transistors, infrared (IR) photodectors, and IR emitters. However, in order to produce high quality GeSn devices to enable these applications, it is of paramount importance to develop ohmic metal contacts with very low specific contact resistivity on both n-type and p-type doped GeSn layers used in these devices. This could be achieved by realizing high doping levels and attaining low intrinsic barrier heights between the metal and the contacted GeSn layer.The growth of metastable GeSn semiconductors is typically performed at temperatures well below 400 ºC to avoid Sn segregation and phase separation, which would compromise the opto-electronic properties of the material. [1] Therefore, major care is required when developing post-growth processes that are commonly required for device fabrication. For instance, ohmic contact formation using the conventional process of rapid thermal annealing of nickel contacts cannot be made and the GeSn cannot be cured after dopant implantation because of the very limited thermal budget. We investigated both the epitaxial growth of highly doped layers, as well as the passivation of undoped GeSn samples in order to circumvent these limitations and achieve the desired barrier heights for both p-type and n-type GeSn while varying the Sn content.First, epitaxially grown GeSn layers with p- and n-type doping are demonstrated. For GeSn doping, the CVD growth of in-situ doped GeSn layers is done using B2H6 for p-type, and AsH3 for n-type. We show high active doping levels in the orders of 1019 and 1020 cm-3 for both p-GeSn and n-GeSn, respectively. These results were obtained from the capacitance voltage measurements (CV) using metal oxide semiconductor (MOS) back-to-back devices. In addition, secondary ion mass spectroscopy (SIMS) and atom probe tomography (APT) data support the high and uniform doping levels.Secondly, since the strong Fermi level pinning (FLP) of Ge is a major problem in the development of n-type contacts due to the loss of metal work function modulation of the barrier height [2], it is expected that the GeSn materials system with low Sn levels exhibits the same behavior, thereby degrading the properties of direct metal/n-GeSn contacts. Therefore, we develop processes aiming to release the Fermi level pinning at metal/GeSn interface, thus restoring the metal work function control of the barrier height. Samples used in this study are CVD grown intrinsic GeSn relaxed samples with increasing Sn concentrations up to 11 at. %. These samples are unintentionally p-type with defect doping levels in the order of 1017 cm-3 as obtained by CV measurements on MOS devices. Our process starts by chemical passivation of these samples, then the deposition and patterning of four metals with different work functions close to the band gap is realized to obtain transfer length method (TLM) structures used for current-voltage (IV) measurements. We then extract the contact properties of these devices and estimate the change of the barrier height induced by the chemical passivation due to the depinning of the FL. This demonstrates the potential use of our process in the fabrication of future metal/n-GeSn contacts. Acknowledgements O.M. acknowledges support from NSERC Canada (Discovery, SPG, and CRD Grants), Canada Research Chairs, Canada Foundation for Innovation, Mitacs, PRIMA Québec, and Defence Canada (Innovation for Defence Excellence and Security, IDEaS).

Encoding Highly Nonequilibrium Boron Concentrations and Abrupt Morphology in p-Type/n-Type Silicon Nanowire Superlattices.

Although silicon (Si) nanowires (NWs) grown by a vapor-liquid-solid (VLS) mechanism have been demonstrated for a range of photonic, electronic, and solar-energy applications, continued progress with these NW-based technologies requires increasingly precise compositional and morphological control of the growth process. However, VLS growth typically encounters problems such as nonselective deposition on sidewalls, inadvertent kinking, unintentional or inhomogeneous doping, and catalyst-induced compositional gradients. Here, we overcome several of these difficulties and report the synthesis of uniform, linear, and degenerately doped Si NW superlattices with abrupt transitions between p-type, intrinsic, and n-type segments. The synthesis of these structures is enabled by in situ chlorination of the NW surface with hydrochloric acid (HCl) at temperatures ranging from 500 to 700 °C, yielding uniform NWs with minimal nonselective growth. Surprisingly, we find the boron (B) doping level in p-type segments to be at least 1 order of magnitude above the solid solubility limit, an effect that we attribute to a high incorporation of B in the liquid catalyst and kinetic trapping of B during crystallization at the liquid-solid interface to yield a highly nonequilibrium concentration. For growth at 510 °C, four-point-probe measurements yield active doping levels of at least 4.5 × 1019 cm-3, which is comparable to the phosphorus (P) doping level of n-type segments. Because the B and P dopants are in sufficiently high concentrations for the Si to be degenerately doped, both segments inhibit the etching of Si in aqueous potassium hydroxide (KOH) solution. Moreover, we find that the dopant transitions are abrupt, facilitating nanoscale morphological control in both B- and P-doped segments through selective KOH etching of the NW with a spatial resolution of ∼10 nm. The results presented herein enable the growth of complex, degenerately doped p-n junction nanostructures that can be explored for a variety of advanced applications, such as Esaki diodes, multijunction solar cells, and tunneling field-effect transistors.

Substitutional Carbon Loss in Si:C Stressor Layers Probed by Deep-Level Transient Spectroscopy

Further scaling of CMOS transistors goes hand in hand with continued straining of the channel, in order to boost the device performance. However, in a bulk FinFET architecture several of the standard techniques lose their effectiveness, so that stress engineering becomes more and more difficult [1]. It has been shown that for n-channel bulk FinFETs, Si:C source/drain stressors are very effective [1], explaining recent research interest [2]-[4]. Si:C hetero-epitaxial layers with about 1% C and highly P-doped can be deposited by a selective Chemical Vapor Deposition (CVD) epitaxial growth based on a cyclic deposition and etching process [5]. One important issue, however, is to maintain throughout further processing as high as possible substitutional carbon in the stressors in combination with an as high as possible active P concentration, to reduce the contact resistance [3],[6]. It has been observed that application of a post-deposition laser anneal (LA) increases the dopant activation level [7] but at the same time results in lower layer stress [6], suggesting the loss of substitutional carbon. In this paper, a Deep-Level Transient Spectroscopy (DLTS) analysis is performed to address this issue. Undoped Si:C layers have been deposited on p-type CZ silicon substrates by a cyclic CVD process as described previously [7]. Al Schottky barriers with different diameters have been thermally evaporated. Typical current-voltage (I-V) and 1 MHz capacitance-voltage (C-V) curves are represented in Fig. 1. Fourier-transform (FT) DLTS has been performed from 75 K to room temperature using different bias pulses from VR to VP, as indicated schematically in Fig. 2, showing the depth probed by the measurements. The analysis was performed on as-grown layers and after an 850 oC Rapid Thermal Annealing in N2 for 5 min. As shown in Fig. 3, a hole trap around 180 K is clearly observed in the -0.5 V-->0 V spectrum after RTA, which is absent (or much smaller) in the as-grown sample. Closer to the surface, some hole trap appears as well in the as-grown layer (Fig. 4). Focusing on the RTA sample in Fig. 5, it is clearly shown that in the silicon substrate, a hole trap with activation energy of 0.4 eV is present, which, according to the comparison in Fig. 6 most likely corresponds with the CiOi level. It indicates that during RTA, interstitial carbon (Ci) is formed, next diffuses in the silicon substrate where it becomes trapped by interstitial oxygen (Oi). Similar Cidiffusion has been reported before even during laser annealing [8]. Closer to the epi layer, a broad band of hole trap states is present in Fig. 5, which could correspond with some active carbon cluster type of defects.

Interpretation of the degradation of silicon HIT solar cells due to inadequate front contact TCO work function

The degradation of the open circuit voltage (VOC) and of the I–V characteristics of p+/n amorphous silicon/crystalline silicon heterojunction solar cells (a-Si:H(p+/i)/c-Si(n) HIT cells) due to the use of transparent conducting oxide (TCO) with small work function at the front contact is investigated. The influence of the TCO work function on the band diagrams, carrier profiles and I–V characteristics in the dark and under illumination is studied by means of AFORS-HET device simulations supported by circuit modeling. It is found that when the TCO work function is not high enough to ensure a good ohmic contact with p-type heavily doped a-Si:H(p+) the VOC degradation is due to the rectifying Schottky barrier at the TCO/a-Si:H(p+) interface. On the other hand, if in addition to the small TCO work function the p-type active doping level in a-Si:H(p+) is reduced, the hole concentration in the p+ inversion layer emitter at the hetero-interface significantly drops leading to a strong enhancement of the emitter dark current and to serious VOC degradation. Moreover, if carrier recombination at the hetero-interface is significant, the weak inversion layer emitter may collapse at a relatively low cell voltage leading to total cell failure.

Organo-arsenic molecular layers on silicon for high-density doping.

This article describes for the first time the controlled monolayer doping (MLD) of bulk and nanostructured crystalline silicon with As at concentrations approaching 2 × 10(20) atoms cm(-3). Characterization of doped structures after the MLD process confirmed that they remained defect- and damage-free, with no indication of increased roughness or a change in morphology. Electrical characterization of the doped substrates and nanowire test structures allowed determination of resistivity, sheet resistance, and active doping levels. Extremely high As-doped Si substrates and nanowire devices could be obtained and controlled using specific capping and annealing steps. Significantly, the As-doped nanowires exhibited resistances several orders of magnitude lower than the predoped materials.

Access resistance reduction in Ge nanowires and substrates based on non-destructive gas-source dopant in-diffusion

To maintain semiconductor device scaling, in recent years industry has been forced to move from planar to non-planar device architectures. This alone has created the need to develop a radically new, non-destructive method for doping. Doping alters the electrical properties of a semiconductor, related to the access resistance. Low access resistance is necessary for high performance technology and reduced power consumption. In this work the authors reduced access resistance in top–down patterned Ge nanowires and Ge substrates by a non-destructive dopant in-diffusion process. Furthermore, an innovative electrical characterisation methodology is developed for nanowire and fin-based test structures to extract important parameters that are related to access resistance such as nanowire resistivity, sheet resistance, and active doping levels. Phosphine or arsine was flowed in a Metalorganic Vapour Phase Epitaxy reactor over heated Ge samples in the range of 650–700 °C. Dopants were incorporated and activated in this single step. No Ge growth accompanied this process. Active doping levels were determined by electrochemical capacitance–voltage free carrier profiling to be in the range of 1019 cm−3. The nanowires were patterned in an array of widths from 20–1000 nm. Cross-sectional Transmission Electron Microscopy of the doped nanowires showed minimal crystal damage. Electrical characterisation of the Ge nanowires was performed to contrast doping activation in thin-body structures with that in bulk substrates. Despite the high As dose incorporation on unpatterned samples, the nanowire analysis determined that the P-based process was the better choice for scaled features.

On the possible role of the interfacial inversion layer in the improvement of the performance of hydrogenated amorphous silicon/crystalline silicon heterojunction solar cells [HIT

The energy band diagram of the hetero-interface between p-type hydrogenated amorphous silicon (a-Si:H(p+)) and n-type crystalline silicon (c-Si(n)) obtained using AFORS-HET one dimensional device simulations reveals that a p+ inversion layer is induced at the hetero-interface, in the c-Si side, with or without the presence of a buffer intrinsic a-Si:H(i) spacer. Such an inversion layer controls the performance of the a-Si:H(p+)/a-Si:H(i)/c-Si(n) HIT cell, because it pushes the p/n junction 20nm in the c-Si and acts as the cell effective emitter. The formation of the inversion layer is controlled by the valence band offset and by the positioning of the Fermi energy in the energy band-gap. The latter is influenced by the active doping level in the doped a-Si:H(p+) and by the dangling bond defect density in the a-Si:H bulk and at the a-Si:H/c-Si interface. By inserting an intrinsic a-Si:H spacer, the defect density at the interface is strongly reduced, which not only decreases the interface recombination, but also ensures the proper formation of the inversion layer. The study also suggests that significantly reduced band-gap narrowing in the inversion layer emitter contributes to the higher open circuit voltage achieved in the HIT cell compared to c-Si cell with excellent front surface passivation.

Deactivation of phosphorus in silicon due to implanted nitrogen

AbstractDeactivation of phosphorus due to nitrogen incorporation was quantitatively investigated. Coimplantation was performed to produce nitrogen profiles overlapping phosphorus profiles in preamorphized silicon. Nitrogen was found to retard phosphorus activation after recrystallization of the amorphous layer. When phosphorus activation was completed, a gap of dopant activation level was observed between samples implanted with and without nitrogen. The gap of the activation level increased linearly with the doses of nitrogen and phosphorus. This implies formation of inactive complexes by pairing of phosphorus and nitrogen atoms. However, the gap disappeared when the peak profile of nitrogen shifted toward the surface during additional annealing at 750 °C for long times. This indicates that the complexes were not stable and therefore dissolved with nitrogen diffusion. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Simultaneous Activation and Crystallization by Low-Temperature Microwave Annealing for Improved Quality of Amorphous Silicon Thin-Film Transistors

In this study, activation and crystallization in short channel amorphous Si TFTs were demonstrated using a novel microwave annealing (MWA) technique. Both low-temperature MWA and rapid thermal annealing (RTA) were compared to study the dopant activation level. We successfully activated the source/drain region, improved the electronic mobility and suppressed the short-channel effects using low temperature MWA. This can reduce the annealing temperature and processing time below that of solid phase crystallization (SPC). This technique is promising for realizing a high utility rate of AM-LCDs with low cost. © 2012 The Electrochemical Society. [DOI: 10.1149/2.003201ssl] All rights reserved.

Suppression of donor-vacancy clusters in germanium by concurrent annealing and irradiation

Diffusion of phosphorous and arsenic in germanium under in situ proton irradiation has been performed and analyzed with secondary ion mass spectrometry. Dopant profiles corresponding to proton-exposed regions exhibit a higher penetration depth and more pronounced box shape than profiles of nonexposed regions. Continuum theoretical simulations reveal that diffusion under irradiation is much less affected by inactive donor-vacancy clusters than diffusion under annealing only. The suppression of donor-vacancy clusters is caused by interstitials in supersaturation and vacancy concentrations close to thermal equilibrium. Concurrent annealing and irradiation have the potential to attain high active doping levels in Ge.

Activation of Implanted n-Type Dopants in Ge Over the Active Concentration of 1×10[sup 20] cm[sup −3] Using Coimplantation of Sb and P

One of the greatest challenges in fabricating a Ge-channel n-MOSFET is achieving a high n-type dopant activation within the source and drain regions. Conventional approaches to increase the electrically active doping level have been proven to be unsatisfactory, and typically the highest activation of n-type dopants is 4 × 10 19 cm -3 using phosphorus. This article describes a method to enhance the activation level of n-type dopants in Ge. Coimplantation of phosphorus and antimony leads to dopant activation over 1 X 10 20 cm -3 at 500°C. The enhancement of n-type dopant activation is attributed to reducing the implantation damage upon annealing due to increase in solid solubility of the dopants.

On the diffusion and activation of ion-implanted n-type dopants in germanium

Some unresolved issues with respect to diffusion and activation of n-type ion-implanted dopants in germanium and of particular interest for shallow junction formation are pointed out and critically discussed. In particular, the absence of extrinsic diffusion during rapid thermal annealing at electron concentrations in the range of a few times 1019 cm−3 and the occurrence of a saturation dopant activation level of the order of 5×1019 cm−3 have been investigated more closely. It is shown that the former can be understood by considering a diffusivity enhancement factor (n/ni)2, with n the free electron concentration and ni the intrinsic carrier concentration, respectively. The saturation of the dopant activation, on the other hand, is determined by the density of states in a degenerately doped semiconductor. Based on these insights, some guidelines for controlling the excess n-type dopant diffusion and activation in germanium can be derived.

Use of p- and n-type vapor phase doping and sub-melt laser anneal for extension junctions in sub-32 nm CMOS technology

We evaluated the combination of vapor phase doping and sub-melt laser anneal as a novel doping strategy for the fabrication of source and drain extension junctions in sub-32 nm CMOS technology, aiming at both planar and non-planar device applications. High quality ultra shallow junctions with abrupt profiles in Si substrates were demonstrated on 300 mm Si substrates. The excellent results obtained for the sheet resistance and the junction depth with boron allowed us to fulfill the requirements for the 32 nm as well as for the 22 nm technology nodes in the PMOS case by choosing appropriate laser anneal conditions. For instance, using 3 laser scans at 1300 °C, we measured an active dopant concentration of about 2.1 × 10 20 cm − 3 and a junction depth of 12 nm. With arsenic for NMOS, ultra shallow junctions were achieved as well. However, as also seen for other junction fabrication schemes, low dopant activation level and active dose (in the range of 1–4 × 10 13 cm − 2) were observed although dopant concentration versus depth profiles indicate that the dopant atoms were properly driven into the substrate during the anneal step. The electrical deactivation of a large part of the in-diffused dopants was responsible for the high sheet resistance values.

Growth System, Structure, and Doping of Aluminum-Seeded Epitaxial Silicon Nanowires

We have examined the formation of silicon nanowires grown by self-assembly from Si substrates with thin aluminum films. Postgrowth and in situ investigations using various Al deposition and annealing conditions suggest that nanowire growth takes place with a supercooled liquid droplet (i.e., the vapor-liquid-solid system), even though the growth temperatures are below the bulk Al/Si eutectic temperature. Wire morphology as a function of processing conditions is also described. It is shown that when Al environmental exposure is prevented before wire growth a wide process window for wire formation can be achieved. Under optimum growth conditions, it is possible to produce excellent crystal quality nanowires with rapid growth rates, high surface densities, low diameter dispersion, and controlled tapering. Photoelectron spectroscopy measurements indicate that the use of Al leads to active doping levels that depend on the growth temperature in as-grown nanowires and increase when annealed. We suggest that these structural and electronic properties will be relevant to photovoltaic and other applications, where the more common use of Au is believed to be detrimental to performance.

Modeling and Experiments of Dopant Diffusion and Defects for Laser annealed Junctions and advanced USJ

ABSTRACTLaser annealed junctions and advanced ultra shallow junctions are studied in both atomistic modeling and experiments. SIMS and sheet resistance measurement for spike-RTA + Laser annealing show that additional laser annealing after spike-RTA (“+Laser”) improve the dopant activation level without increasing in junction depth. “+Laser” effect become effective in the combination of low spike-RTA temperature and high laser temperature. This effect is significant for As doped layer. Spike-RTA based junction has a limitation in viewpoint of Rs-Xj trade-off. Laser-only annealing is promising candidate to overcome this limitation. Boron diffusion with laser-only annealing is investigated. As atomistic kinetic Monte Carlo modeling show that BnImcomplexes and End-of-Range (EOR) defects are formed during sub-millisecond annealing time range. Impact of F co-implant on Boron diffusion and EOR defect evolution during sub-millisecond annealing are also investigated.

Chemical and electrical dopants profile evolution during solid phase epitaxial regrowth

Solid phase epitaxial regrowth (SPER) is a promising method for junction formation of sub-65 nm complementary metal–oxide–semiconductor technology nodes. This is mainly due to a high dopant activation level, easy control over electrical junction depth, excellent abruptness, and limited boron diffusion. In the present research we investigate in detail the activation process and the chemical profile change after SPER junction activation with respect to the regrowth temperature. We also obtain the electrically active profiles. We find that the process window for SPER between T=620 °C and T=740 °C offers the best activation level and has a dopant profile similar to the as-implanted. While increasing the regrowth temperature, we observe the gradual increase of the transient enhanced diffusion effect and formation of B trapping centers in the end-of-range (EOR) region. At temperatures as high as T=800 °C and T=850 °C the dopant activation beyond the original a-Si layer is observed and the high metastable B activation in the junction drops dramatically. All these changes can be associated with release of Si interstitials from the EOR region due to dissolution of 〈311〉 defects.

Observation of enhanced transport in carbon-doped InGaAsN after in situ anneal and its impact on performance of NpN InGaP/InGaAsN heterojunction bipolar transistors

The incorporation of a low band gap carbon-doped InGaAsN material into a standard GaAs heterojunction bipolar transistor (HBT) has great potential to achieve higher operating efficiency at lower bias conditions. In order to improve the performance of the initial as-grown InGaAsN-based HBTs (with 1% N and 3% In for an energy band gap EG of 1.2 eV), the effects of different thermal treatments on material quality and their impact on dc and rf characteristics on small-area devices are examined in this letter. A degradation of the base transport is observed after a postgrowth anneal associated with lower current gain β and degraded microwave properties. An in situ anneal approach under inert ambient conducted following the emitter growth, increases the active doping level (with a base sheet resistance RSH three times lower than the as-grown structure and demonstrates suitable high frequency performance for a device with such a large amount of nitrogen in the base.

Magnetotransport of delta-doped In0.57Ga0.43As on InP(001) grown between 390 and 575° C by molecular beam epitaxy

Silicon (Si) delta- (δ-) doped In0.53Ga0.47As layers were grown by molecular beam epitaxy on InP(001) substrates between 390 °C and 575 °C. Subbands formed at the δ layer were examined with Hall and Shubnikov-de Haas effect measurements in conjunction with self-consistent Poisson-Schrödinger modeling. Below a growth temperature of 525 °C we find good agreement with modeling, but above 525 °C a decrease in active doping level suggests possible surface aggregation, or reaction with impurities in the growth chamber. Significant surface segregation spread of the Si is only found for growth above 450 °C. There is some evidence that DX-like centers may be present, since their incorporation improves slightly the quality of the fits to subband occupancies. Samples grown at 390 °C show strong persistent photoconductivity at low temperatures, attributed to defect states in the InGaAs.

Modeling of the Kinetics of Dopant Precipitation in Silicon

In heavily doped silicon, dopant aggregation leads to a reduction in the electrically active concentration. For thermal cycles typical of very large scale integrated circuit fabrication, the kinetics of this precipitation process can play a critical role in determining the active doping levels and thus device electrical characteristics. In this work, we develop a general kinetic precipitation model which explicitly considers the time evolution of the precipitate size density, and is thus able to account for a broad range of behavior. We compare our model to previously published experimental data for arsenic and phosphorus activation/deactivation in silicon over a wide temperature range (300 to 800°C), and find that it can account accurately for the experimental observations, including reverse annealing following a temperature step.