The influence of crystallographic orientation on the wetting of silicon on quartz single crystals

Abstract

Dynamic hexagonal spreading patterns of small silicon droplets on the basal plane (001) of quartz were observed by video microscopy. A detailed analysis of the hexagonal triple line demonstrates that the patterns show slight chiral distortions that can be attributed to the screw axis of the substrate crystal. This article reveals the detailed influence of crystal symmetry on the anisotropy of reactive wetting. In this context, a first discussion about the interplay of wetting and etching of a crystal is provided.

SiO gas emission and triple line dynamics of small silicon droplets on quartz

“…Using a two-point-calibration on the melting points of the silicon and nickel provides temperature values between 1500 and 1800 K with an estimated accuracy of 75 K. By extrapolation of the measured intensities the absolute temperature is determined. In order to record the droplet's triple line motion, the center position and the average contour radius (see [9]) were online determined by a further Labtech Labview VISION Assistant program for every single picture. In the experiment the silicon crystal is melted, then slowly heated up to the melting point of nickel (T¼1746 K) and kept at this temperature for about one minute.…”

“…These signals are taken as time stamps for synchronization of the time dependent mass spectrum and the recorded video. To exclude an influence of the cavity on the evolution of the hexagonal spreading pattern, further experiments were accomplished on a polished plane substrate that has been explained in detail in reference [9].…”

“…The major importance of triple lines for the geometry and motion of interfaces and the possible occurrence of anisotropic triple lines in sessile drop experiments on crystalline surfaces has been discussed in literature [10] and references herein. An overview of our previous experiments concerning geometric analysis of the triple line is given elsewhere [9]. It demonstrates the importance of the crystallographic orientation and hence the kind of chemical coordination of oxygen at the crystal surface.…”

“…In unidirectional crystallization of silicon for mc-Si solar cells the amount of oxygen impurities plays an essential role as well, as these impurities can reduce the carrier lifetime [8]. In order to obtain a better understanding of the reactive wetting of quartz by silicon we have studied small silicon droplets on single crystals by means of the sessile drop method in vacuum [9]. The observation of these droplets from above revealed periodic spreading patterns with a hexagonally shaped triple line.…”

“…As the dynamics of wetting have not been addressed in Ref. [9], we now want to present new experimental data concerning the dynamics of the reactive wetting process. For a chemical understanding it is important to gain insight into the reaction dynamics and the products of the reaction.…”