Characteristics of Dopant Activation by Sequential Lateral Solidification (SLS)
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Characteristics of Dopant Activation by Sequential Lateral Solidification (SLS) Yong-Hae Kim, Choong-Yong Sohn, Choong-Heui Chung, Young-Wook Ko, and Jin Ho Lee Basic Research Lab., Electronics and Telecommunications Research Institute 161 Gajeong-Dong, Yuseong-Gu, Daejeon, 305-350 Korea ABSTRACT The characteristics of dopant activation by sequential lateral solidification in poly-Si films is investigated using sheet resistance measurement and Raman measurement. Sheet resistance of n+ and p+ doped poly-Si films decreases exponentially as the laser energy increases. The minimum sheet resistance of n+ doped poly-Si films is 150 Ω/□ which is near to that of rapid thermal annealing (RTA) while the minimum sheet resistance of p+ doped poly-Si films is 180 Ω/□ which is less than a half to that of RTA. The sheet resistance of n+ and p+ doped poly-Si increases as the laser energy increases when the laser energy is above 573 mJ/cm2 at which the nucleation occurs. Raman signal of n+ doped poly-Si films shows single peak at 515 cm-1 with all laser energy and has maximum intensity at 566 mJ/cm2 laser energy. Raman signal of p+ doped poly-Si films shows single peak below 413 mJ/cm2 laser energy and double peak above 444 mJ/cm2 laser energy where the fully melting of p+ doped poly-Si film occurs. INTRODUCTION As amorphous (a-Si) thin film transistors (TFTs) have limited carrier mobility, it is difficult to reliably manufacture the addressing and switching circuit for the display. The interest in low temperature poly-Si (LTPS) TFT stems from its much higher mobility than α-Si TFT (up to 200 times greater), which enables it to be used for the full integration of both the drive circuits and the pixel TFTs in a monolithic CMOS technology [1,2]. These studies contain not only the crystallization of a-Si thin film but also the dopant activation of poly-Si film. Sequential lateral solidification (SLS) of the α-Si precursor film is the preferred procedure for the formation of high quality poly-Si film [3,4]. SLS process is the manipulation of the intrinsically unstable super lateral growth phenomenon in a manner that permits flexible design of the resulting material microstructure. Low sheet resistance of doped poly-Si film at source/drain regions and contacts are necessary for high-performance LTPS TFTs. Comparing with conventional furnace annealing, laser annealing can efficiently activate the doping atoms in poly-Si film at room temperature. Several studies have been reported about the dopant activation by laser annealing. Those of them include spin-on-dopant poly-Si film which is annealed by KrF excimer laser, gas immersion laser doping with laser energy, dopant activation of poly-Si film capped with silicon oxide [5-10]. The characteristics of laser activation process is analyzed by sheet resistance, raman spectroscopy and secondary ion mass spectroscopy [1115]. In the present work, the characteristics of dopant activation by SLS in poly-Si films is investigated using sheet resistance measurement and Raman measurement and c
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