Atomic imprint crystallization: Externally-templated crystallization of amorphous silicon

Abstract

In this paper, we demonstrate the crystallization of an amorphous Si layer via atomic imprint crystallization (AIC), where an amorphous Si layer is crystallized by solid phase epitaxy (SPE) from an externally impressed single-crystal Si template that is then peeled off via delamination following crystallization. Microstructural analysis using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) studies of the delaminated (crystallized) films reveals that the top surface of the amorphous Si layer is crystallized by SPE with regions (up to ∼5 mm diameter) composed of epitaxial domains (lateral size of few μm), all of which bear the same crystalline orientation as that of the template crystal. Unlike conventional SPE, the crystallization is not uniform across the entire region: the grains contain crystal defects such as dislocations, stacking faults, and twins; and while the crystallization is initiated at the top surface of the film, the thickness of the single-crystalline area is limited to ∼40 nm from the top surface. Clearly, the AIC approach leads to SPE (aligned with the template's crystalline orientation) over areas as large as few mms, but the crystallization is defective and incomplete through the film. We attribute this to be a consequence of the tensile stress field created at the amorphous/crystalline frontline by the volume change of amorphous Si during the crystallization. Our results establish the feasibility of imprint crystallization, and points to the direction of a new process that may enable the creation of single crystal pockets in integrated device stacks in a scalable fashion without the need for an underlying single crystal substrate. However, our results also indicate that the crystallization is of a poor quality and indicates the need for further optimization of the crystallization method.