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

Periodic spreading motions of small silicon melt droplets on quartz (SiO2) have been observed by a video microscope and mass signals of the emitted molecules were thereby recorded simultaneously. The triple line of the droplet expands slowly and retracts spontaneously. The intensity of a mass signal at 44 amu is clearly correlated to these changes of the triple line circumference and seems to stem from SiO molecules that are emitted as reaction products from the vicinity of the triple line. The velocity of the triple line has been studied as a function of temperature. Results can be described by an Arrhenius-like behavior with an activation energy of 111±14 kJ mol−1. For a detailed analysis of the experimental results a model for the oxygen transport through the interfaces and its diffusion through the droplet is presented. It can be used to predict etch profiles on the substrate in the vicinity of the triple line by using well known thermophysical data of silicon and quartz. These theoretical profiles are in good agreement with the experimental profiles that have been measured ex-situ by atomic force microscopy and provide a value for the diffusion constant of D=3.3×10−4 cm2 s−1 for oxygen in liquid silicon which fits well with the values used in crystal growth simulations.

► Reaction dynamics of silicon melts wetting quartz single crystals.
► Dissolution and transport of oxygen from quartz to gas phase through Si-melt.
► Modeling of triple line motion caused by reactive wetting.