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Fabrication Techniques For Highly Uniform, Large-Crystal Polycrystalline Silicon Thin Films

From: http://www.ibridgenetwork.org Time:2014.07.24

Polycrystalline silicon thin films are used in a wide array of electronic applications such as integrated circuits, displays, and solar cells. Such films are typically manufactured by heating amorphous silicon films with a pulsed excimer laser to induce crystallization by annealing. This technology comprises several improvements to the excimer laser annealing (ELA) process for production of high-quality polycrystalline silicon thin films including: (a) use of an advanced excimer laser annealing (AELA) system to control the shape and melt profile of melted film regions by appropriate adjustment of the laser beam profile; (b) sequential firing of the laser to extend the region of film melted; (c) irradiation during or immediately after solidification of crystals; (d) irradiation of a film region by sequences of laser pulses to increase pulse duration range with low energy loss.

(Picture from http://www.bing.com)

Increased control over laser parameters combined with the use of multiple laser tubes enables formation of large crystal grains with highly uniform boundaries.

The boundaries between crystal grains reduce charge carrier (electron) transport mobility and thereby increase the film's electrical resistance. Increasing the size of the grains produced during annealing can improve the efficiency and performance of displays and photovoltaic cells constructed from large-grain polycrystalline films. This technology permits the growth of larger crystals than possible with current ELA methods and boosts the uniformity of the boundaries between crystal grains. Increasing control over the shape of melted film regions and the extent to which different portions of an irradiated region melt enables formation of crystals with more directed grain boundaries and hence improved charge carrier mobility. Irradiation with sequential pulses further increases film uniformity by promoting lateral growth of large crystal grains by extension of the regions melted by the laser. Furthermore, irradiation during or immediately after crystal solidification improves control over the thickness of the grown film. Lastly, boosting the energy density of the laser pulses used to melt the film beyond that of a single laser enables larger grains to form with fewer pulses than possible with a single laser.


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