Novel Phase Modulator for ELA-Based Lateral Growth of Si

Abstract

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...

Pseudo-Single-Nucleus Lateral Crystallization of Si Thin Films

“…The light intensity profile on the sample surface takes an isolated conelike dip form since dots are as small as the radius of the Airy disk, which is defined by the optical aperture of projection optics. 6) Since it was assumed, in Fig. 1, that as the diameters of dots are decreased gradually from the left to the right, light intensities, I B , at the bottom of the each conelike dip profile are enlarged gradually from the left to the right.…”

P‐194L: Late‐News Poster: High‐Frequency Performance of Sub‐Micrometer Channel‐Length Si TFTs Fabricated on Large Grain Poly‐Si Films

“…Co-planar-type poly-Si TFTs with channel lengths ranging from 0.5 to 2 μm were fabricated on 100 nm-thick poly-Si films with large grains grown by the phase-modulated excimer laser annealing (PMELA) method [1]. One-dimensionally elongated grains were grown by utilizing a duty-type phase-modulator, [2] which created an one-dimensionally periodic light intensity distribution on the film surface. TFTs have a multi-finger gate pattern with a finger length of 20 μm as indicated in Fig.…”

Thin-Film Transistor and Ultra-Large Scale Integrated Circuit: Competition or Collaboration

“…42) Novel laser crystallization techniques, such as the metal-induced, lateral crystal growth, phase-modulated, or selective re-radiation method, have been used to prepare poly-Si thin films. [43][44][45][46] Laser processes have been used in producing poly-Si TFTs on large-area glass substrates. For advanced ULSIC fabrication, laser has been used in preparing submicron structures, such as filling the small vias with the deposited Al or Cu film, shallow junction doping, activation of implanted dopants, and formation of a thin gate oxide layer.…”