Crystallization of Amorphous Silicon and Dopant Activation using Xenon Flash-Lamp Annealing (FLA)
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Crystallization of Amorphous Silicon and Dopant Activation using Xenon Flash-Lamp Annealing (FLA) T. Mudgal1, C. Reepmeyer1, R. G. Manley2, D. Cormier3 and K.D. Hirschman1 1
Electrical & Microelectronic Engineering Department, Rochester Institute of Technology, Rochester, New York, 14623, USA 2
Corning Incorporated, Science and Technology, Corning, New York, 14870, USA
3
Industrial & Systems Engineering Department Rochester Institute of Technology, Rochester, New York, 14623, USA
ABSTRACT Flash-lamp annealing (FLA) has been investigated for the crystallization of a 60 nm amorphous silicon (a-Si) layer deposited by PECVD on display glass. Input factors to the FLA system included lamp intensity and pulse duration. Conditions required for crystallization included use of a 100 nm SiO2 capping layer, and substrate heating resulting in a surface temperature ~ 460 °C. An irradiance threshold of ~ 20 kW/cm 2 was established, with successful crystallization achieved at a radiant exposure of 5 J/cm 2, as verified using variable angle spectroscopic ellipsometry (VASE) and Raman spectroscopy. Nickel-enhanced crystallization (NEC) using FLA was also investigated, with results suggesting an increase in crystalline volume. Different combinations of furnace annealing and FLA were studied for crystallization and activation of samples implanted with boron and phosphorus. Boron activation demonstrated a favorable response to FLA, achieving a resistivity < 0.01 Ω•cm. Phosphorus activation by FLA resulted in a resistivity ~ 0.03 Ω•cm. INTRODUCTION Recent advancements in large-format display devices have pushed hydrogenated amorphous silicon (a-Si:H) to its performance limit. Low-temperature polycrystalline silicon (LTPS) and metal-oxide based thin-film transistors (TFTs) are candidates for replacement of a-Si:H for highperformance applications. Excimer laser annealing (ELA) based LTPS is in manufacturing, however due to its high-cost and increased process complexity it has been commercialized only for small format displays. The applicability of ELA for Gen10 glass is questionable, and the flatpanel display industry is searching for alternative LTPS strategies which are cost-effective and easily scalable to large glass panel production. FLA is a technique which anneals the material using a series of short but intense bursts of broad spectrum light from xenon flash lamps, and can readily be extended to accommodate arbitrarily large substrates. While FLA has been shown to crystallize thin a-Si films on glass [1, 2], the reports on fabricated TFTs have been very limited [3]. This work investigates the ability to crystallize a-Si using FLA, and to activate implanted boron and phosphorus as dopants for TFT fabrication. The influence of adding a small amount of nickel to the silicon layer is also investigated as a means to enhance crystallization using the FLA process [4].
EXPERIMENT A 60 nm a-Si:H layer was deposited on 150 mm diameter Corning EAGLE XG® display glass wafers using PECVD. The deposition was performed using SiH4 and H
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