Ž . Thin Solid Films 383 2001 151153 Hydrogenation in laser annealed polysilicon thin-film transistors Ž . TFTs F.V. Farmakis a,  , D.M. Tsamados a , J. Brini a , G. Kamarinos a , C.A. Dimitriadis b , M. Miyasaka c a LPCS, ENSERG, 23 rue des Martyrs, BP 257, 38016 Grenoble Cedex 1, France b Department of Physics, Uni  ersity of Thessaloniki, 54006 Thessaloniki, Greece c Seiko Epson Corporation, Base Technology Research Center, Owa 3-3-5, Suwa, Nagano 392, Japan Abstract Ž . Hydrogenation effects in excimer laser annealed polysilicon thin-film transistors TFTs were studied. Hydrogen plasma formed from hydrogen diluted with Ar or He was used in order to passivate defects at the polysiliconsilicon oxide interface, as well as in the polysilicon material. It was found that, after hydrogenation, no more than a 10% increase in the carrier mobility is attained, accompanied by a threshold-voltage decrease, due to passivation of deep states at the polysiliconsilicon oxide interface and at the grain boundaries. However, the most important feature of hydrogenated devices is the improvement in the dispersion of their Ž . transfer characteristics. In addition, hot-carrier stress experiments showed that optimization of the type of dilution gas Ar or He and the relative concentration of hydrogen can be carried out in order to improve the device reliability.  2001 Elsevier Science B.V. All rights reserved. Keywords: Polycrystalline; Thin-film transistor; Plasma hydrogenation 1. Introduction Ž Polycrystalline silicon thin-film transistors polysili- . con TFTs are widely investigated, mainly due to their application in active-matrix liquid crystal displays Ž . AMLCDs . The performance of polysilicon TFTs de- pends strongly on defects in the polysilicon and at the  polysilicongate oxide interface 1 . Recently, laser- annealing techniques were applied to improve the polysilicon TFT performance through grain-size en- largement and reduction of the grain boundary and  in-grain defect density 2 . A traditional technique to reduce defects in TFTs is hydrogenation. Various hy- drogenation techniques are currently applied, such as   plasma hydrogenation 3 , hydrogen implantation 4  Corresponding author. Tel.: 33-476856046; fax: 33-476856070. Ž . E-mail address: farmakis@enserg.fr F.V. Farmakis .  and SiN :H encapsulation 5 . An important issue of x the hydrogenation process is its duration, resulting in improvement of the turn-on voltage, carrier mobility and sub-threshold swing, and in the dispersion of the static device characteristics. In this work, we used plasma hydrogenation, with the hydrogen plasma formed by a low % hydrogen diluted with a rare gas, namely helium or argon. The aim of this work was to investigate the effect of various hydro- gen concentrations, diluted with helium or argon, on the device performance, the dispersion of the device parameters and the device reliability. 2. Experimental The studied polysilicon TFTs were fabricated on glass substrates by a low-temperature process described  Ž . elsewhere 2 . Amorphous silicon -Si films 51.8 nm thick were deposited by low-pressure chemical vapor 0040-609001$ - see front matter  2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 4 0 - 6 0 9 0 00 01588-1