A new approach to continuous crystal sheet growth

Abstract

A new approach to the production of crystal ribbon from bulk silicon is presented. The method takes advantage of the changes in the physical properties of silicon as it passes through the solid-liquid phase change. A silicon ribbon is used as the seed and a small melt zone is produced within the seed by the introduction of electrical currents gradients. A stable, nearly planar growth interface is developed which makes a small angle with the plane of the ribbon. Replenishment of the melt may be introduced in the liquid phase. During the growth process the heat of fusion is removed from the solid-liquid interface in a direction perpendicular to the pulling direction. The analysis of the heat flow indicates that a stable melt zone with the desirable configuration may be formed and that it may be maintained with low RF power. The small angle that the solid-liquid interface makes with the pulling direction permits a high pulling speed with a slow growth rate. A very small temperature gradient can be maintained along the ribbon length well beyond the solid-liquid interface. This low gradient coupled with the slow controlled growth rate and the stable growth interface is expected to eliminate unwanted dendritic growth and permit wide ribbons at high pull rates to be grown.