Materials Science in Semiconductor Processing 7 (2004) 419–422 Low-temperature non-metal-induced crystallization of germanium for fabrication of thin-film transistors Bahman Hekmatshoar, Arash Khajooeizadeh, Shams Mohajerzadeh à , Davood Shahrjerdi, Ebrahim Asl-Soleimani Thin Film laboratory, ECE Department, University of Tehran, Tehran, Iran Available online 19 October 2004 Abstract Device-quality poly-Ge layers were grown at temperatures as low as 200 1C by successive hydrogenation and annealing steps, with no need to any metal incorporation. Hydrogenation is performed in a PECVD apparatus with 150 W RF hydrogen plasma and annealing is carried out in the same system in N 2 ambient. As a result, grains of the order of 100 nm are formed in the Ge layer. It has been observed that hydrogenation at high temperatures may be destructive to the Ge layer. Successive hydrogenation and annealing at respective temperatures of 150 and 200 1C would result in a device-quality poly crystalline Ge layer which has been employed for fabrication of depletion-mode thin-film transistors. These TFTs show a field-effect mobility of 80 cm 2 /Vs for holes and an ON/OFF ratio of more than 10 3 , indicating the feasibility of this technique for applications in large-area electronics. r 2004 Elsevier Ltd. All rights reserved. Keywords: Hydrogenation; Low-temperature processing; Non-metal-induced crystallization; Poly-Ge TFTs 1. Introduction Polycrystalline semiconductor materials are superior to amorphous layers in many aspects with respect to applications in large-area electronics. Carrier mobility is the most prominent parameter determining the electrical behavior of semiconductor devices, which may be drastically improved by crystallization. However, the potential complexity and cost of the crystallization step imposed by high-temperature annealing requirements may deduct from the feasibility of the process as well as compatibility with low-temperature flexible substrates aimed for reel-to-reel processing or flexible display applications. Therefore, special attention has been paid to low-temperature crystallization techniques. Variety of approaches have been proposed for lowering the crystallization temperature of semiconduc- tors, including the metal-induced crystallization (MIC) [1], metal-induced lateral crystallization (MILC) [2] and Excimer laser annealing (ELA) [3]; however, the reduced crystallization temperatures are still too high for many flexible substrates. In general, germanium is more promising than silicon for low-temperature processing due to its inherently lower crystallization temperature and higher carrier mobility. In the previous works, Al- [4–6] and Cu-induced [7,8] crystallization of Ge have been studied. Though of achieving reasonably low crystallization temperatures, Al incorporation degrades the semiconductor properties due to metal contamina- tion; on the other hand, Cu-MIC of Ge needs temperatures as high as 400 1C. We have recently ARTICLE IN PRESS 1369-8001/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.mssp.2004.09.019 à Corresponding author. Tel./fax: +98 21 8011235. E-mail address: smohajer@vlsi.uwaterloo.ca (S. Mohajerzadeh).