Solid State Phenomena Vols. 108-109

Abstract: Silicon-based power device performances are largely affected by metal contamination occurring during device manufacturing. Among the usual gettering techniques, recent developments were done on high dose helium implantation. Even though the gettering efficiency of this technique has been demonstrated in device application, the required doses are still extremely high for an industrial application. Recently, it has been shown that the use of H/He co-implantation limits the total requested doses [1]. In this paper, co-implantation of H/He, which has been already used to reduce the dose in the smart-cut® process is explored. The goal of this work is to decrease efficiently the implanted dose maintaining an efficient metallic gettering without degrading the Si surface. The impact of H implantation on He implantation induced defects is carefully studied. The TEM observations have evidenced that hydrogen addition drastically modified the defect band structure and promotes the cavity growth.. Additionally, we demonstrate that an efficient gettering can be obtained.

Abstract: Radiation hardness of silicon detectors based on thin epitaxial layer for the LHC upgrade was studied. No type inversion was observed after irradiation by 24 GeV protons in the fluence range (1.5–10)⋅1015 cm–2 due to overcompensating donor generation. After long-term annealing highly irradiated devices show decrease of effective doping concentration and then undergo type inversion. All mentioned means that thin epitaxial devices might be used for innermost layers of vertex detectors and need moderate cooling during beam off time. Properly chosen scenario might help to restore their working characteristics.

Abstract: Different methods of defect engineering are applied in this study for ion beam synthesis of a buried layer of SiC and SiO2 in Si. The initial state of phase formation is investigated by implantation of relatively low ion fluences. He-induced cavities and Si ion implantation generated excess vacancies are intentionally introduced in the Si substrate in order to act as trapping centers for C and O atoms and to accommodate volume expansion due to SiC and SiO2 phase formation. Especially the simultaneous dual implantation is shown to be an effective method to achieve better results from ion beam synthesis at implantation temperatures above 400oC. For SiC synthesis it is the only successful way to introduce vacancy defects. The “in situ” generation of vacancies during implantation increases the amount of SiC nanoclusters and improves crystal quality of Si in the case of SiO2 synthesis. Also the pre-deposition of He-induced cavities is clearly advantageous for the formation of a narrow SiO2 layer. Moreover, in-diffusion of O by surface oxidation can substitute a certain fraction of the O ion fluence necessary to obtain a buried homogeneous SiO2 layer. The results show that defect engineering for SiC and SiO2 synthesis is working. However, the implementation of a single action is not sufficient to achieve a significant improvement of ion beam synthesis. Only an optimized combination of the different versions of defect engineering can bring about pronounced better results.

Abstract: Surface passivation in silicon wafers is investigated by contactless photoconductance measurements. It is shown that the deposition of a-Si:H layers on top of c-Si wafers leads to passivation of the c-Si surface. Passivation by Si3N4 of the p c-Si surface is at least partially due to the depletion layer at the interface. The separation of excess charge carriers by the depletion field is responsible for a relatively slowly decaying part of the signal not directly related to bulk recombination. An HF dip is not sufficient for an appropriate passivation of p c-Si but immersion in I2/ethanol solution is promising.

Abstract: The type and density of the point defects that are generated in the Si surface layer during thermal oxidation depend on the oxidation condition: temperature, cooling rate, oxidation time, impurity content. The interaction between point defects with extended defects and impurities affect the Si-SiO2 interface properties. The influence of point defects may be diminished and the interface properties improved by an appropriate choice of oxidation conditions.

Abstract: A possibility of magnetic-field-induced modification of structural defects in silicon crystals is studied. It is shown that magnetic field action essentially affects the structuredependent properties of Si (mechanical and electrophysical)

Abstract: Effect of hydrostatic pressure (HP) on out – annealing of defects in self – implanted silicon (Si:Si, Si+ doses 5x1016 cm-2 and 1x1017 cm-2, energies 50 keV and 160 keV), treated for 1 – 10 h at up to 1400 K (HT) under HP ≤ 1.4 GPa, has been investigated by photoluminescence, X-ray and related methods. Applied at 720 – 1270 K enhanced pressure does not affect or affects adversely Si:Si structure while at 1400 K assists in its improvement. HP – dependent transformations in Si:Si at HT are related to effect of HP on diffusion of point defects, such as silicon interstitials and vacancies produced at implantation. Out - annealing of defects in self - implanted silicon is dependent also on spatial position of damaged areas in Si substrate.

Abstract: In the present work, we report on the effects of the implantation temperature on the formation of bubbles and extended defects in Ne+-implanted Si(001) substrates. The implantations were performed at 50 keV to a fluence of 5x1016 cm-2, for distinct implantation temperatures within the 250°C≤Ti≤800°C interval. The samples are investigated using a combination of cross-sectional and plan-view Transmission Electron Microscopy (TEM) observations and Grazing Incidence Small-Angle X-ray Scattering (GISAXS)measurements. In comparison with similar He implants, we demonstrate that the Ne implants can lead to the formation of a much denser bubble system.

Abstract: Theoretical consideration for technologically important phenomena in defect engineering of Czochralski silicon was performed with first principles calculation. (i) Point defect behaviour during crystal growth, (ii) enhanced oxygen precipitation in p/p+ epitaxial wafers, and (iii) Cu gettering by impurities are main topics in this work. Following results are obtained. (i) Interstitial Si I is dominant in p type Si while vacancy V is dominant in n type Si during crystal growth when dopant concentration is higher than about 1x1019atoms/cm3. (ii) In initial stage of oxygen precipitation including a few interstitial oxygen (O) atoms, BOn complex is more stable than On complex. The diffusion barrier of O atom in p+ Si is reduced to about 2.2eV compared with the barrier of about 2.5eV in intrinsic Si. (iii) In substitutional B, Sb, As, P and C atoms, only B atom can be an effective gettering center for Cu.