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LOW TEMPEATURE LATERAL CRYSTALLIZATION OF AMORPHOUS SILICON ON GLASS Leila Rezaee*, Aarash Akhavan, Shamsoddin Mohajerzadeh, and Ali Khakifirooz** Thin Film Laboratory , Department of Electrical and Computer Engineering, University of Tehran, Tehran, Iran 14395-515

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[email protected] Currently at Microsystems Technology Laboratories, Massachusetts Institute of Technology Cambridge, MA 02139, U.S.A., [email protected]

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ABSTRACT Low temperature lateral growth of amorphous silicon films has been achieved on thin flexible glasses using ultra-violet assisted metal-induced crystallization technique. 125µm ordinary glass substrate is sputter-coated with 1500Å chromium and a 1000Å SiN layer, respectively. 1000Å Si film was deposited using e-beam evaporation at a temperature of 350°C. Equally spaced dots of nickel pads with 140µm separation were used as seed of crystallization of a-Si layer. Crystallinity of the samples was studied using XRD, SEM and optical microscopy. Some crystallographic etchants were used to develop the crystal orientations for SEM analysis. Based on this study, a lateral growth rate of 2µm/hr is obtained at a temperature of 380oC. Activation energy of 1.4 to 1.5eV is extracted for this UV-assisted MILC process. INTRODUCTION Thin film transistors (TFT) are important constituents of flat panel displays and large area imagers [1,2]. Conventionally these devices are realized using amorphous silicon technology, compatible with glass as the process substrate. These transistors, however, suffer from low carrier mobility and temporal instability [3]. Polysilicon TFT’s are suitable alternatives for such applications. On the other hand, crystallization temperature seems to be a serious obstacle in realizing such devices on glass. Several techniques have been examined to demonstrate the usefulness of glass for realization of polysilicon TFTs among which one can identify solid-phase crystallization (SPC) and excimer laser annealing (ELA)[4,5]. The former technique is energy consuming, which requires rather high temperatures, whereas the latter one needs expensive facility. Metal-Induced Lateral Crystallization is a promising technique in making polysilicon thin film transistors at processing temperatures below 500°C[6]. Temperatures above 450°C do not support the use of ordinary glass and a further reduction in the temperature of annealing is required to facilitate the use of this type of glass as the substrate. We have recently exploited energetic ultra-violet photons to enhance the crystallization at temperatures as low as 400°C using nickel as the seed of crystallization [7]. This considerable reduction in the annealing temperature is realized through exposure of the sample to a UV light source during post-treatment step. The presence of a chromium back reflector layer promotes the crystallinity of the film and its findings have been A22.2.1 Downloaded from https://www.cambridge.org/core. University of California, Santa Cruz, on 23 Dec 2019 at 13:26:06, subject to the Cambridge Core terms of use