Solidification is a common process used in the manufacture of bulk metals, and is fundamentally a phase transformation from liquid to solid that has been studied for many years. In the case of rapid solidification, which is characterized by rapid heat loss and a high interface velocity, non-equilibrium conditions prevail and are not yet understood very well [1-3]. In this research, we present experimental results of RLS (rapid lateral solidification) under the newly geometric heat flow and growth direction.
A pulsed excimer laser is applied as an energy source to melt copper thin films. This leads to rapid resolidification upon cooling, and unique solidification microstructures [4-8]. Using this technique, we are able to successfully prepare RLS microstructures that are reproduceable and controllable through the laser process parameters. Much of the work presented here is an investigation of the rapid solidification process indirectly by examination of the post-solidified microstructure using electron microscopy. We have quantitatively studied several aspects of the microstructure, and address critical questions associated with the current theories. This includes identification of four-zone microstructure and quantification of mechanisms governing defect generation and texture formation.
Copper films with thickness of 100 nm, 200 nm, 500 nm and 1000 nm have been melted by single pulse of 248 nm laser, and the induced RLS areas are consisted with partial two-dimensional ribbon grains with low defect density and strong texture.
The length and width of the RLS grains will increase with the thickness of the thin films. The 200 nm thick copper thin films are characterized to reach the maximized length of 22 um with about 1.2 um width, while the 1000 nm thick ones reach 40 um in length with about 1.6 um width. Furthermore, the resolidified grains will form very strong textures during RLS, and the textures increase with the thickness too. The 200 nm thick copper thin films are characterized of strong <100> texture in the growth direction, while the 1000 nm thick ones have <100> textures in the three geometric directions. The defect density is not found to have relationship with the thickness. However, in all of the copper thin films with different thickness, the defect density is characterized to be high only at the beginning RLS and at the end of RLS. The mainly parts of PLS areas are found to be perfect with very low defect density.
This unique microstructure of RLS thin films is expected to be better in electronic properties than deposited thin films [9-10], and is potentially applied in electronic nano-device in near future.
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