Abstract
Laser crystallization of a-Si film on insulating substrate is a promising technology to fabricate three-dimensional integrations (3D ICs), flat panel displays (FPDs), or flexible electronics, because the crystallization can be performed on room temperature substrate to avoid damage to the underlying devices or supporting plane. Orientation-controlled grain-boundary-free films are required to improve the uniformity in electrical characteristics of field-effect-transistors (FETs)fabricated in those films. This paper describes the recently found simple method to obtain {100}-oriented grain-boundary-free Si thin-films stably, by using a single scan of continuous-wave (CW)-laser lateral crystallization of a-Si with a highly top-flat line beam with 532 nm wavelength at room temperature in air. It was difficult to control crystal orientations in the grain-boundary-free film crystallized by the artificial modulation of solid-liquid interface, and any other trial to obtain preferential surface orientation with multiple irradiations resulted in grain boundaries. The self-organized growth of the {100}-oriented grain-boundary-free films were realized by satisfying the following conditions: (1) highly uniform top-flat line beam, (2) SiO2 cap, (3) low laser power density in the vicinity of the lateral growth threshold, and (4) single scan crystallization. Higher scan velocity makes the process window wide for the {100}-oriented grain-boundary-free film. This crystallization is very simple, because it is performed by a single unseeded scan with a line beam at room temperature substrate in air.
Highlights
Directions and obtained grain boundary patterns of (a) in the Si3 films crystallized by the conventional with the elliptical line beam for the non-patterned
The observation of the grain boundaries after the delineation by Secco etching of the crystallized film reveals that the grain boundaries can be eliminated from a defined area in the CW-laser crystallization, if isotherms are modulated by beam shaping [26,27,28,29], stripe cap patterning [30,31], Si island patterning [32,33,34], or substrate patterning [35]
We have found that a simple line beam can realize the symmetrical {100} normal direction (ND), scan direction (SD), and transverse direction (TD) crystal
Summary
Demand for monolithic three-dimensional integrations (3D ICs) [1,2], flat panel displays (FPDs) on flexible substrates, or flexible electronics have been increased recently. Figure shows a comparison of crystal growthCLC directions and obtained grain boundary patterns of (a) in the Si3 films crystallized by the conventional with the elliptical line beam for the non-patterned and CLC; note that the magnifications of images are different from each other. The observation of the grain boundaries after the delineation by Secco etching of the crystallized film reveals that the grain boundaries can be eliminated from a defined area in the CW-laser crystallization, if isotherms are modulated by beam shaping [26,27,28,29], stripe cap patterning [30,31], Si island patterning [32,33,34], or substrate patterning [35] The idea of these methods is to make the temperature of the controlled crystal growth region less than that of the peripheral regions, to suppress the disturbance to the growth region from the random nucleation at the peripheral.
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