Solid State Phenomena Vols. 108-109

Abstract: The properties of cobalt as a contaminant in p-type silicon are studied by using cobaltimplanted wafers annealed by RTP or by RTP plus a low temperature furnace annealing. It is shown that after RTP most cobalt is under the form of CoB pairs. A quantification of cobalt contamination is provided based upon SPV measurements and optical pair dissociation. However, this quantification fails in furnace-annealed wafers because of the formation of a different level. It is shown that the CoB level is located near the band edges, whereas the level formed upon a low temperature furnace annealing is located near midgap. Besides, when the cobalt concentration is high enough a small fraction of cobalt is in a level different from the CoB pair even in RTP samples. This level can probably be identified with a previously observed midgap level. It is suggested that the same level is formed in RTP plus low temperature furnace annealed samples and in high concentration RTP annealed samples, and that this level may consist in some cobalt agglomerate.

Abstract: We present a comprehensive description of synchrotron-based analytical microprobe techniques used to locally measure the diffusion length and chemical character of metal clusters in multicrystalline silicon (mc-Si) solar cell material. The techniques discussed are (a) X-ray fluorescence microscopy, capable of determining the spatial distribution, elemental nature, size, morphology, and depth of metal-rich particles as small as 30 nm in diameter; (b) X-ray absorption microspectroscopy, capable of determining the chemical states of these metal-rich precipitates, (c) X-ray beam induced current (XBIC), which maps the minority carrier recombination activity, and (d) Spectrally-resolved XBIC, which maps the minority carrier diffusion length. Sensitivity limits, optimal synchrotron characteristics, and experimental flowcharts are discussed. These techniques have elucidated the nature and effects of metal-rich particles in mc-Si and the physical mechanisms limiting metal gettering from mc-Si, and have opened several promising new research directions.

Abstract: In this work the efficiencies of different surface passivation techniques are compared. This paper emphasizes on the passivation provided by SiNx:H layers that is commonly used in photovolaic industry as surface passivation and anti reflection layer. The method used to evaluate the surface recombination velocity is detailed and discussed. It is shown that light phosphorus diffusion at 850°C – 20 min provides good surface passivation of n-type silicon surface and noticeable passivation of p-type, that can be improved by SiNx:H Layer.

Abstract: This work proposes some improvements over the current state-of-the-art of carbon measurement in silicon by means of Fourier Transform Infrared Spectroscopy (FTIR) at low temperature (77 K), as described in the ASTM F1391-93 (2000) standard method.

Abstract: Laser scattering tomography (LST) and band-to-band photoluminescence (PL) are applied for supporting a MEMS process optimization. Process wafers are based on magnetic CZ grown silicon material. LST allows the characterization of number-size distributions of oxygen precipitates in various stages of the process flow. Precipitation is shown to be affected by the design of high-temperature anneal post initial oxidation. PL gives useful information on relative concentration level and radial distribution of recombination centers within process wafers. The initial oxidation leads to significant reduction of recombination centers. The combined LST/PL information enables valuable conclusions towards process optimization.

Abstract: We report on electron holography as a promising candidate for diagnostics in silicon technology and research. Electron holography determines the local phase shift of the electron wave passing through a sample. The phase is proportional to the 2D projected electrostatic potential in the sample and thus reveals p-n junctions and, indirectly, doping. We demonstrate detection of submonolayer boron layers in Si and SiGe, measurement of Ge concentration in SiGe and qualitative 2D oxygen mapping in SiO2/Si structures with 0.5 nm resolution, and comparison of doping in two bipolar transistors with different base implant. Resolution and noise limits are discussed.

Abstract: A probing of the atomic environment of positron in Cz-Si single crystal heat-treated at T=600C and T=450C has been performed by one-dimensional angular correlation of annihilation radiation (ACAR). It has been established that positrons get trapped by the oxygen-related complexes. The penetration of positrons into the core region of surrounding atoms results in emission of the elementally specific high-momentum annihilation radiation. The processes of expelling of positron from ion cores and its penetration into the core region are regulated by the potential barrier (to be considered as the Coulomb’s one as a first approximation). The characteristic electron-positron ion radius and the probabilities of correlated events of the highmomentum annihilation are due to the chemical nature of the ion cores of atoms involved in the composition of the oxygen-related complexes. The interpretation of the results is based on the notion of the positron localization in the field of negative effective charge resulted from comparatively high electron affinity of the oxygen impurity atom. The presence of a free volume (perhaps, a vacancy) as well as the carbon atom in the microstructure of the oxygen-related positron-sensitive thermal defects is briefly discussed.

Abstract: Measurement of carbon concentration in CZ silicon by infrared absorption spectroscopy was examined. Noise level was suppressed down to 10-4 in unit of absorbance. Residual differential absorption between the sample and reference was removed by fitting the phonon absorption spectrum to the background absorption spectrum. The effect of narrowing of absorption spectral range was examined. As a result, it was possible to measure the differential carbon concentration down to about 1×1014/cm3. Measurement of commercial wafer was also established.