Rapid lateral solidification of pure Cu and Au thin films encapsulated in SiO2

Abstract

Excimer laser melting and lateral resolidification is demonstrated in 200nm thick Cu and Au elemental metal thin films encapsulated between SiO2 layers. Projection irradiation is used to selectively and completely melt lines 3to30μm wide in the metal film—with rapid lateral solidification originating from the unmelted sidewalls of the molten region—resulting in large columnar grains, extending transversely to the middle of the line. Transmission electron microscopy reveals twinning structures and other defects typical of rapid solidification. Encapsulation and control of the fluence are found to be crucial parameters necessary to prevent film dewetting while molten.

Electron microscopy of geometrically confined copper thin films after rapid lateral solidification

“…We have recently used single-pulse excimer laser-induced rapid lateral solidification (RLS) to produce large, very high aspect ratio grains in thin Cu films that are geometrically confined between amorphous silicon oxide capping-and under-layers on Si [3]. Rapid solidification processing of metals and alloys can produce a wide variety of nonequilibrium phases and microstructural configurations that are of interest for technologically useful thin films [2].…”

Four-zone solidification microstructure formed by laser melting of copper thin films

“…This resulted in localized melting of the copper film in a narrow line of adjustable width [13] as shown in Fig. 1.…”

“…With the application of excimer laser-induced rapid lateral solidification (RLS) to thin copper films, we have previously demonstrated that large single-crystalline grains can be located at specifically selected sites on a wafer substrate [13]. It involves rapidly and completely melting a localized spot in the metal film on nanosecond timescale, followed by lateral resolidification into the molten pool.…”

“…It involves rapidly and completely melting a localized spot in the metal film on nanosecond timescale, followed by lateral resolidification into the molten pool. Process conditions and film configurations for obtaining RLS microstructures have been given in detail elsewhere [13]. This thin film laser melting technique represents a departure from traditional solid-phase recrystallization of thin films, and offers the ability to attain novel ultra-large-grain microstructures at precise locations under well-controlled solidification conditions.…”

“…Under the conditions of complete melting within the line region, solidification occurs laterally from the outer edges toward the center of the line[13]. The vectors marked 'GD' indicates the lateral growth direction, corresponding to the average direction of motion of the solidification fronts.…”