Formation of periodic grain boundary in an Si thin film crystallized by a linearly polarized Nd:YAG pulse laser with an
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A9.32.1
Formation of periodic grain boundary in an Si thin film crystallized by a linearly polarized Nd:YAG pulse laser with an ultra sonic oscillator Hirokazu Kaki, Takehiko Ootani and Susumu Horita JAIST (Japan Advanced Institute of Science and Technology), 1-1 Asahidai, Tatsunokuchi, Ishikawa 923-1292, Japan ABSTRACT In order to obtain a large silicon (Si) grain and to control the location of its boundary in a Si film melting-crystallized by a pulse laser, we have proposed to use periodic thermal distribution spontaneously induced by irradiation of a linearly polarized laser beam. We estimated the suitable amorphous Si (a-Si) thickness taking account of multiple reflection theoretically and confirmed it experimentally. Also, we proposed a novel technique to reduce the irradiation pulse number to control the grain boundary location stably in the crystallized Si film, in which the elastic wave was generated on the surface of a-Si film prior to melting-crystallization by using an ultra sonic oscillator. Owing to this technique, we can control the grain boundary location periodically with only 1 pulse irradiation in the crystallized Si film.
INTRODUCTION Low temperature polycrystalline Si (poly-Si) thin film transistors (TFTs) are widely used for various applications such as driver circuits of active matrix liquid crystal displays (AM-LCDs) and active matrix organic light emitting diode displays (AM-OLED). Moreover, system on panel (SOP) displays in which the system circuits of the controller and memory are integrated with the driver circuits on a glass substrate will be the most suitable application for poly-Si TFTs in the near future [1]. The pulse laser annealing (PLA) method is effective to produce a poly-Si film consisted of larger grain with the high carrier mobility on a glass substrate [2-5]. In order to control the location of the Si grain boundary which reduces the mobility, we proposed a PLA method with a linearly polarized laser beam. By this method, periodic temperature distribution on the surface of the irradiated Si film is generated spontaneously and the grain boundary location in the crystallized Si film is controlled without additional processes and components [6-8]. This temperature distribution is caused by a periodic beam intensity profile modified due to interference between the incident beam and its diffracted beam on the irradiated surface. This periodic spacing Λ is formulated by Rayleigh’s diffraction conditions as Λ≈
λ
n0 (1 ± sin θ i )
(1)
A9.32.2
for a p-polarized beam, where λ is the incident laser wavelength, θi is the angle from the normal incidence and n0 is the refractive index of the incident medium above the surface [9]. However, using this method, some irradiation pulses are needed to control the grain boundary location stably [8]. Reducing the pulse number is desired from a viewpoint of the mass-production. Guosheng et al. calculated the periodic beam intensity on a surface with small sinusoidal corrugation of a bulk specimen [10]. Their calculation result indicates that
