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Abstract

Based on the recently developed MCs2 + secondary ion mass spectrometry methodology, the GeSi interdiffusion has been investigated, using Ge(:B) solid sources, for Ge concentrations between 0 and 100 at. %. A strong dependence of the interdiffusion with the Ge content of SiGe alloys, formed during annealing, has been shown. The BoltzmannMatano method was used to extract the interdiffusivity values for all the temperatures studied (750, 800, 850, and 900 °C) in the full range of SiGe compositions. Two regimes of interdiffusion have been identified, both exhibiting an exponential increase in the interdiffusion coefficient as a function of the Ge concentration. The high Ge content regime (>65 at. %) is in good agreement with the values known in the "extreme" cases of Ge diffusion in Si (0 at. %), Ge self-diffusion, and Si diffusion in Ge (100 at. %), while in the low Ge content regime (<50 at. %), the presence and evolution of misfit dislocation can explain the important values of interdiffusivity found in this work. The observed results are perfectly reproduced by a simple empirical model in which the effect of the Ge concentration and the presence of misfit dislocations are taken into account. Based on the evolution of B delta layers (in Si) and Ge depth profiles during NH3 annealing, we showed that the GeSi interdiffusion is predominately assisted by a vacancy mechanism with a slightly interstitial contribution in the full range of Ge concentrations. We have estimated the interstitial fraction coefficient, fGeSiI, to ~ 0.17 at 900 °C. Finally, the effect of in situ B doping is studied, which is found to induce a retardation of the GeSi interdiffusion.

Abstract

Current fabrication processes of MOS source/drain ultra-shallow junctions (dopant implantation in a preamorphised substrate, followed by ultra-rapid anneals at high temperature) generate defects which can degrade their electrical properties. The understanding of the physical phenomena responsible for this degradation is essential for the optimization of the fabrication processes. Among these phenomena, the impact of Boron Interstitial Clusters (BICs) on the carrier mobility has not yet been clearly understood. In this work, we present an empirical method for the self-consistent interpretation of SIMS and Hall effect measurements of boron doped ultra-shallow junctions that allows to estimate the activation level of the doped layers (maximum active dopant concentration, active dose fraction) and, for the case of partially activated structures, to assess whether or not the carrier mobility is affected by the electrically inactive BICs. Both epitaxial and implanted structures were studied. We found that, depending on the fabrication conditions, the maximum active dopant concentrations extracted from the studied samples may differ from the boron solid solubility at the process temperature. In addition, for the partially electrically active structures, a degradation of the drift mobility due to the presence of BICs is shown, which is experimentally confirmed by low temperature Hall effect measurements, indicating the existence of an additional Coulomb-type scattering mechanism.

Mots-Clés / Keywords

Ultra shallow junctions; Hole mobility; Hall effect; Boron interstitial clusters; SIMS;

Abstract

The formation and evolution of F-induced nanobubbles in Si was investigated. Si samples were preamorphized, implanted with F, and partially regrown by solid phase epitaxy (SPE). It is shown that nanobubbles are formed already in the amorphous side of partially regrown samples and are then incorporated in crystalline Si during SPE. The bubbles are interpreted as the result of the diffusion and coalescence of F atoms and dangling bonds already in the amorphous matrix. During high temperature annealing after SPE, F outdiffuses; correspondingly, the bubbles partially dissolve and transform from spherical- to cylinder-shaped bubbles.

Abstract

The pile-up of arsenic at the Si/SiO2 interface after As implantation and annealing was investigated by high resolution Z-contrast imaging, electron energy-loss spectroscopy (EELS), grazing incidence x-ray fluorescence spectroscopy (GI-XRF), secondary ion mass spectrometry, x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, as well as Hall mobility and four-point probe resistivity measurements. After properly taking into account their respective artifacts, the results of all methods are compatible with each other, with EELS and GI-XRF combined with etching providing similar spatial resolution on the nanometer scale for the dopant profile. The sheet concentration of the piled-up As at the interface was found to be ~1×1015 cm2 for an implanted dose of 1×1016 cm2 with a maximum concentration of ~10 at. %. The strain observed in the Z-contrast images also suggests a significant concentration of local distortions within 3 nm from the interface, which, however, do not seem to involve intrinsic point defects.

Abstract

The segregation and pile-up of arsenic atoms at the Si/SiO2 interface in steady state was investigated in detail by a combination of gracing incidence x-ray fluorescence spectroscopy (GI-XRF) measurements, electrical measurements, etching on the nanometer scale, and measurements of the step heights by interferometry. Using GI-XRF measurements and removal of the highly doped segregation layer by a sensitive etching process it was possible to distinguish clearly between the piled-up atoms and the arsenic atoms in the bulk over a large range of implantation doses, from 3×1012 to 1×1016 cm2. The samples were annealed at different temperatures from 900 °C to 1200 °C for time periods long enough to make sure that the segregation reflects an equilibrium state. With additional step height measurements at line-space structures, the thickness of the layer with the piled-up arsenic and the shape of the segregation profile was determined. Electrical measurements indicated that the segregated arsenic atoms are deep donors with an electrical activity that increases eventually to full electrical activation for high sheet concentrations of the segregated atoms. The measured data can be modeled as a steady state of neutral arsenic atoms in the segregation layer with positively charged substitutional arsenic atoms and free electrons. For the highest concentration, a saturation of the sheet concentration of segregated arsenic atoms was observed that correlates with the increase in electrical activation. For the use in process simulation programs, a three-phase segregation model was adapted and calibrated.

Mots-Clés / Keywords

Arsenic; Silicon; Surface segregation; TXRF; GI-XRF;

Abstract

We have studied the Ge-Si interdiffusion from structures in which not, vert, similar300 nm-thick pure Ge(:B) layers were grown on Si 200 mm substrates by CVD at 450 °C. As-grown samples were capped with SiO2 and then annealed in the 750-900 °C range for various times. Using the secondary ion mass spectrometry (SIMS) MCs2+ methodology, we measures precisely the Ge diffused profiles. Boltzmann-Matano analysis was used to extract the interdiffusion coefficients. Si-Ge interdiffusion is found to be strongly dependent on the Ge concentration. Also, an effect of dislocations near the Ge/Si original interface is suggested by our results. A physical model including the various observed effects is proposed, that gives a very good agreement with experiments. Finally, we show that the effect of the in situ B doping of the pure Ge layer is to reduce the interdiffusion.

Mots-Clés / Keywords

Interdiffusion; Germanium; Silicon; CVD; SIMS; MCs2+; Boltzmann-Matano; Defects; Modeling;

Abstract

The detailed knowledge of the effects of the buried interface on defect evolution in silicon-on-insulator wafers is mandatory to accurately control dopant diffusion and activation. To be able to study this phenomenon, quantitative data on end-of-range defect evolution must be obtained taking into account the several possible effects of the buried interface. In this work we report some transmission electron microscopy data acquired to study the effect of the Si top layer/buried oxide interface acting as an interstitial sink in silicon-on-insulator wafers. It is shown that this effect can explain the obtained data and that our results are compatible with a non-conservative Ostwald ripening mechanism describing defect evolution in silicon-on-insulator structures.

Mots-Clés / Keywords

Silicon-On-Insulator (SOI); End-of-range defects; Germanium implant; Transmission electron microscopy;

Abstract

In this work, the evolution of boron trapping at End-of-Range (EOR) defects was investigated by secondary ion mass spectrometry (SIMS) and transmission electron microscope (TEM). Si wafers with a constant boron concentration of 2 × 1018 cm-3 were implanted with 30 keV germanium and with a dose of 1015 cm-2 and then annealed at 700, 800, or 900 °C in an N2 ambient for various times. The experimental results suggest that the evolution of boron-trapping peak is driven by the evolution of {3 1 1} defects and that the dislocation loops contribution to the trapping mechanism is less pronounced. An analytic model for the concurrent boron trapping at {3 1 1} defects and dislocation loops was developed by taking into account the geometry of the EOR defects. The trapped species is represented by neutral BI pairs which can be captured either by {3 1 1} defects or by dislocation loops. The model accurately reproduces the complex evolution of the trapping peak as a function of both the annealing time and temperature. These results confirm that the evolution of the boron-trapping peak is closely related to the evolution of the {3 1 1} defects, therefore suggesting that boron trapping is associated to the capture and release of boron atoms at the {3 1 1} defects formed in the EOR region.

Mots-Clés / Keywords

Boron; Germanium implant; End-of-range defects; SIMS; Transmission electron microscopy;

Abstract

Millisecond annealing as an equipment technology provides temperature profiles which favour dopant activation but nearly eliminate dopant diffusion to form extremely shallow, highly electrically activated junctions. For the 45-nm technology node and beyond, precisely controlled gate under-diffusion is required for optimum device performance. Therefore, on boron and arsenic beamline-implanted wafers, various annealing schemes were investigated for the formation of ultra-shallow and custom-shaped junctions. The main scheme consisted of flash annealing with peak temperatures ranging from 1250 to 1300 °C, combined with spike rapid thermal annealing with peak temperatures in the range from 900 to 1000 °C to achieve a desired junction depth. As alternative, to reduce the sheet resistance of pMOS and nMOS source-drain extensions, combinations of two or three flash anneals in succession were tested. Finally, the standard flash anneal condition of a 750 °C intermediate temperature followed by the flash anneal was changed to a high intermediate temperature of 950 °C followed by the flash anneal up to 1300 °C. The results of all these annealing schemes were analysed by four-point probe measurement. Selected samples were analysed by Hall-effect measurements for peak activation, and by secondary ion mass spectrometry for profile shape as well as diffusion effects. Transmission electron microscopy was used to study residual defects. Selected boron and arsenic dopant profiles were also compared to predictive simulation results which address the diffusion and activation at extrinsic concentrations.