Sindy Würzner

The relationship between microstructure and dislocation density distribution in multicrystalline silicon

The investigation of the grain structure is important to understand the origin of dislocations during crystal growth of multicrystalline silicon. This paper studies the dislocation density distribution for different grain orientations that occur during crystal growth. Single grains are analyzed in detail, including their microstructure. The grain orientations are determined by means of the electron backscatter diffraction technique. The obtained information reveals grain orientations, which allow a higher number of active slip planes during crystal growth process. The number of active slip planes during solidification seems to influence the dislocation density in the final crystal.

Investigations on the Behaviour of Carbon during Inductive Melting of Multicrystalline Silicon

The influence of the CO concentration in the gas phase on the distribution of carbon in Bridgman-grown, multicrystalline silicon is studied. The growth experiments were conducted in a high-vacuum induction furnace either under a CO enriched atmosphere or under CO free conditions. Furthermore, thermodynamic calculations in the system silicon/oxygen/carbon were done. In crystal growth under a CO enriched atmosphere a SiC-containing layer is formed on the top surface of the melt in agreement with the calculated phase diagram. In this case, the level of substitutional carbon in the cystal was found to be almost constant, whereas the axial carbon concentration in crystals grown under CO free conditions increases monotonously according to Scheils law.

Analysis of the topography and the sub-surface damage of Cz- and mc-silicon wafers sawn with diamond wire

The goal of this work was to investigate the influence of different sawing coolants concerning topography parameters and fracture strength of diamond wire sawn Cz- and mc-Si wafers. Therefore, silicon bricks were sawn using glycol- and water-based coolants. Fracture strength was determined by four bending bar fracture test setup. Additionally, crack depth analyses on beveled samples depending on the crystal orientation of the investigated grains have been done by means of XRD measurements. We found a strong indication of a crystal orientation dependency of the crack depth. Furthermore, we have made single scratch tests with a novel scratch test technique, which offers the possibility to use test parameters comparable to real sawing conditions. The scratch tests have been done on Cz-Si. We investigated the cracks using OCM and SEM images as well as Raman spectroscopy of cross section preparations through the single scratches.

Novel combination of orientation measurements and transmission microscopy for experimental determination of grain boundary miller indices in silicon and other semiconductors

The determination of grain boundary planes in multicrystalline material has only been restricted to transmission electron microscope investigations ( Jang et al., 1992 ; Elgat et al., 1985 ) or to metallograpical investigations of the grain boundary ( Randle et al., 1993 ). The first method is expensive, and both are complex and time consuming in grain boundary preparation. This paper proposes the determination of grain boundary planes in semiconductor wafer by a combined application of Electron Back Scatter Diffraction and Infrared Transmission Microscopy. In particular, the new method is demonstrated with directional solidificated multicrystalline silicon.

Comparative Spatially Resolved Characterization of a Czochralski-Grown Silicon Crystal by Different Laser-Based Imaging Techniques

The axial distribution of electrical and optical properties of a 4 inch Czochralski-grown silicon single crystal were analyzed by different methods that can be applied in the scanning mode. These methods were tested with respect to the suitability to reveal growth striations. The residual stress was visualized by SIRIS (Scanning Infrared Stress Inspection System) and SIREX (Scanning Infrared Stress Explorer), the electrical resistivity by LPS (Lateral Photovoltage Scanning) and SRP (Spreading Resistance Profiling), and the lifetime of the minority charge carriers by MDP (Microwave Detected Photoconductivity) mapping. The concentration of interstitial oxygen (Oi) across the growth striations was determined by FTIR (Fourier Transform Infrared) spectroscopy. We demonstrate for the first time on the micrometer scale that the Oi scan is very well-correlated with the profile of Δσ (difference of the in-plane principal stress components). The stress field is tensile oriented in growth direction, i. e. perpendicularly to the growth striations. The stress-concentration coefficient has been estimated to be in the order of 10-13 Pa cm-3 what does agree well with previous XRD results.