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UNIFORM, HIGH PERFORMANCE POLY-SI TFTs FABRICATED BY LASERCRYSTALLIZATION OF PECVD-GROWN a-SI:H D. TOET,*,a T.W. SIGMON,a T. TAKEHARA,b C.C. TSAI,b,† W.R. HARSHBARGER.b Lawrence Livermore National Laboratory, 7000 East Ave., L-271, Livermore CA 94550. b AKT, 3101 Scott Blvd., M/S 9155, Santa Clara, CA 95054. *e-mail: [email protected] † now at: Quanta Display, 188 Wen Hwa 2nd Rd., Kuei Shan Hsiang, Tao Yuan Shien, Taiwan. a

ABSTRACT Polycrystalline silicon thin film transistors (TFTs) were fabricated using laser crystallization of thin amorphous Si films grown by plasma-enhanced chemical vapor deposition. The films were exposed to a scanned XeCl excimer laser beam at 350 mJ/cm2. At this fluence the Si film completely melted and crystallized in the form of uniformly distributed grains with an average size of 39 nm. One of the films was then subjected to a low fluence laser scan (250 mJ/cm2), which resulted in the melting of the top part of the film and lead to an increase in grain size. The TFTs fabricated without the partial melt method had good electrical properties and uniformities. The partial melt method lead to substantial improvements in most device characteristics, while the uniformity remained good. INTRODUCTION The on-panel integration of addressing and switching circuitry in active matrix liquid crystal displays (AMLCDs) will lead to a drastic reduction in production costs, as well as to improved ruggedness and performance [1]. Driver circuits, however, require a much higher performance than can be provided by amorphous silicon (a-Si), the material traditionally used for the fabrication of pixel switches. As a result, the past decade has seen extensive research into the development of low-temperature polycrystalline silicon (poly-Si) processes, which allow the manufacturing of high-mobility thin film transistors (TFTs). Poly-Si TFTs also provide sufficient currents to drive organic light-emitting diodes, enabling further improvements in display performance and ruggedness, as well as a reduction in the power consumption. Short pulsed excimer laser-induced crystallization (ELC) of a-Si [2] is emerging as the leading technique for the fabrication of poly-Si TFTs [3]. This is mainly due to the fact that ELC is compatible with inexpensive low-temperature substrates such as plastic and glass. ELC involves ultrafast melting and resolidification of the near-surface region of the sample and consequently, minimal heating of the substrate [2,4]. Moreover, ELC yields poly-Si films consisting of defectfree grains that can reach sizes of several microns. In contrast, solid phase crystallization (SPC) [5], the most common alternative to ELC, requires temperatures above 600 oC, precluding the use of low-temperature substrates. Furthermore, SPC results in poly-Si films with a high density of intra-grain defects. In this report, we present the characteristics of TFTs made by ELC of hydrogenated amorphous silicon (a-Si:H) thin films grown on glass substrates by plasma-enhanced chemical vapor deposition (PECVD). This technique,