Modeling and laboratory scale proof of concept of the horizontal ribbon growth process: Application to silicon wafer manufacturing
In this work we focus on the development of the Horizontal Ribbon Growth technique to produce highly pure silicon wafers for use in solar cells. We divide this preliminary work in two parts: a small scale experiment and the development of mathematical models to describe the crystallization phenomena. We begin by constructing a laboratory scale experiment to demonstrate the HRG concept using water as the working fluid. We made use of the fact that ice floats on water just like silicon would float on top of its melt. Therefore it is possible to conveniently test and analyze the operability of this technique. We find that the initial seeding process needs to be carefully controlled in order to extract a uniform wafer. Appropriate surface cooling and wall heating are necessary to guarantee the continuous formation of an ice film. We then develop simple mathematical models to predict the crystallization rate and thermal profiles of the system. We state that the driving force for crystallization is convective cooling and the film grows in one direction (downwards). Finally we propose how to validate the model using experimental data and how to extend the work to grow silicon ribbons.
Improvements in the Horizontal Ribbon Growth technique for single crystal silicon
Abstract An improved Horizontal Ribbon Growth (HRG) technique for growing single crystal ribbons of silicon is described. Starting with the essential concept of the Bleil process, namely the “growth wedge”, improvements were achieved in the process by introducing gas cooling and developing techniques for obtaining a “large wedge factor” (or wedge length to ribbon ratio). These refinements have led to demonstrations of high growth rates (maximum of 415 mm/min for single crystal and 850 mm/min for polycrystal ribbons). Various other improvements in the practice of HRG, such as a specially designed crucible, pulling in an inclined direction, and generation of desired melt flow patterns, are also described. They have led to a more stabilized growth operation from the start of seeding through steady-state growth.
Web Growth of Semiconductors
A novel process for growth of diamond‐lattice semiconductors is described, and a model is proposed for the growth mechanism. For germanium the process yields extended thin flat sheets, typically 1 cm wide and 0.1 mm thick, of good crystalline quality and relatively flat {111} surfaces. The sheet, or web, freezes from a liquid film drawn up by surface tension between two coplanar dendrites which originate from a single seed and are grown from the melt simultaneously with the sheet. Resistivity throughout the sheet is quite uniform. Etching of germanium webs shows them to be essentially dislocation‐free and does not reveal any microsegregation of impurities. Silicon and indium antimonide have also been grown in this manner.The proposed model postulates that although the dendrites at either side of the web grow beneath the melt surface in usual dendritic fashion, the faces of the web itself normally have no extension below the melt surface. The exterior contact angle between the solid and liquid surfaces is ...