Excellent characteristics of polycrystalline silicon (poly-Si) thin-film transistors (TFTs) with long and narrow grains aligned one-dimension have been experimentally clarified for the first time. The field effect mobility and on-off transition slope of n-channel and p-channel devices were as high as 685 cm 2 V À1 s À1 and 190 mV/decade and 145 cm 2 V À1 s À1 and 104 mV/ decade, respectively. Fluctuations of characteristics were considerably reduced by widening the channel, and uniform characteristics were observed when there were approximately twenty long grains within the channel. These results were obtained when the TFT channel was formed within a region free from grain boundaries formed by head-on collision of laterally growing grains and seeds used to initiate lateral grain growth. Material properties are discussed from the viewpoint of device characteristics.
Characteristics have been investigated for both KrF excimer-laser light and KrF excimer-laser crystallization of Si thin films. The results were applied to design an optical system for growing densely packed and large grains. A high-resolution beam profiler confirmed that the laser light intensity distribution on the sample surface had a nearly ideal triangular form with a maximum-to-minimum intensity ratio of approximately 2, as designed. This distribution could grow 5-mm-long grains with a packing efficiency close to 100% by a single laser light pulse.
Phase-modulated excimer laser annealing ͑ELA͒ is an advanced excimer-laser crystallization method characterized by the intensity modulation of irradiated light by a phase modulator. In this method, a temperature gradient is formed in melted Si and large crystal grains are laterally grown at predetermined positions. In order to form grains with a high packing efficiency, a periodic "V-shaped" form of the light intensity distribution is desired. In the present study, a novel duty phase modulator is developed for projectiontype PMELA. The light intensity distribution on the sample surface can be freely controlled and its design method is simple. We confirmed that a V-shaped light intensity distribution could be achieved by preparing a prototype duty phase modulator. In addition, crystallization was carried out with this duty phase modulator and 5-m-long crystal grains with a high packing efficiency were successfully grown.Excimer laser crystallization ͑ELC͒ is a key technology for polycrystalline Si thin-film transistors ͑poly-Si TFTs͒ designed for system-on-glass devices and has been the subject of numerous studies. Phase-modulated excimer laser annealing ͑PMELA͒, which we have been investigating, is an advanced ELC method featuring the intensity modulation of irradiated light on a-Si using a phase modulator ͑Fig. 1͒. In this method, a temperature gradient is formed in melted Si and large crystal grains grow laterally at predetermined positions. In this way, a TFT channel section can be prepared from a single-crystal grain. TFTs of higher performance can be prepared from these large crystal grains than from conventional poly-Si.In order to form a whole circuit, it is necessary to grow large crystal grains with a high packing efficiency. For this purpose, the distribution of the light intensity is determined based on the following characteristics of lateral growth.1. Lateral growth starts at a certain "lateral growth starting intensity". At a lower light intensity, Si does not melt or it remains in the form of fine grains.2. Lateral growth takes place along the direction of the temperature gradient, namely, the direction of the light intensity gradient. If this gradient is small, the lateral growth will stop halfway.Based on these characteristics, we have identified the optimum distribution to have a periodic "V-shaped" form to grow crystal grains with a high packing efficiency. As shown in Fig. 2, crystal nuclei are generated at the bottom of the V-shape irradiating light intensity distribution. Subsequently, lateral growth can take place along the gradient of the V-shape to peak intensity points. In this way, it is possible to grow large crystal grains with a high packing efficiency. It is important that the light intensity at the bottom of the V-shape is exactly the lateral growth starting intensity. If the intensity at the bottom of the V-shape is too low, large grains cannot be formed in those regions. If the intensity at the bottom of the V-shape is too high, random nucleation, resulting in small grains, takes...
We have developed an advanced sample structure for large-grain growth by excimer-laser crystallization of Si. More than 10μm long grains were grown laterally in a 50nm thick Si layer by phase-modulated excimer-laser annealing. A photosensitive SinormalOx capping layer prepared using a conventional plasma-enhanced chemical vapor deposition apparatus enables this longer lateral growth with lower irradiated intensity of laser light than those with the conventional SinormalO2 capping layer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.