IEICE TRANS. ELECTRON., VOL.E89–C, NO.10 OCTOBER 2006 1377 INVITED PAPER Special Section on Electronic Displays A Novel Selected Area Laser Assisted (SALA) System for Crystallization and Doping Processes in Low-Temperature Poly-Si Thin-Film Transistors Ryoichi ISHIHARA †a) , Arie GLAZER †† , Yoel RAAB †† , Peter RUSIAN †† , Mannie DORFAN †† , Benzi LAVI †† , Ilya LEIZERSON †† , Albert KISHINEVSKY †† , Yvonne VAN ANDEL †† , Xin CAO †† , Wim METSELAAR †† , Kees BEENAKKER †† , Sara STOLYAROVA ††† , and Yael NEMIROVSKY ††† , Nonmembers SUMMARY CMOS poly-Si thin-film transistors (TFTs) were fabri- cated through crystallization and GILD processes by a novel selected area laser assisted (SALA) system. The system enables a local area irradiation of small beams of a pulsed solid-state laser of frequency tripled Nd:YAG. The novel TFT process eliminated 3 doping mask steps of the conventional process. On-off current ratios for both types of poly-Si TFTs were im- proved by SALA. The field effect mobility of n- and p-channel TFTs is 84 cm 2 /Vs and 75 cm 2 /Vs, respectively. key words: polycrystalline-Si, thin-film transistors, gas immersed laser doping, solid-state laser 1. Introduction Excimer-laser crystallization has been used for manufactur- ing low-temperature poly-Si TFTs for active-matrix liquid- crystal displays (AMLCDs). However the poly-Si TFTs have typically a relatively high non-uniformity in the tran- sistor characteristics [1], which makes an obstacle for the application to large organic light emitting diode (OLED) panels. This is predominantly due to power instability of the laser and light intensity variation on the substrate. Recently a solid-state laser crystallization system [2] has been studied extensively for replacement of the excimer-laser, however low-output laser power limits the throughput of the crystal- lization process. Furthermore, CMOS process in the poly-Si TFTs demands additional masking processes due to the ne- cessity of the selective doping, resulting in a low yield and high production cost. Gas immersed laser doping (GILD) process [3] was proposed to avoid the additional masking steps, however a local selective exposure of the light is re- quired. In this paper, we introduce a novel selected area laser assisted (SALA) system, which allows the local irradiation of small and multi solid-state laser beams with a great po- Manuscript received February 20, 2006. Manuscript revised May 10, 2006. † The author is with the Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Tech- nology, Feldmannweg 17, P. O. Box 5053, 2600 GB Delft, The Netherlands. †† The authors are with Orbotech Corporation, Yavne, Israel. ††† The authors are with the Department of Electrical Engineer- ing, Technion-Israel Institute of Technology, Haifa, Israel. a) E-mail: r.ishihara@tudelft.nl DOI: 10.1093/ietele/e89–c.10.1377 sition accuracy. Compared to the conventional solid-state laser annealing system, the new system allows an effective use of the relatively low-power solid-state laser resulting in a stable and high throughput laser irradiation over a large glass substrate. Furthermore, if the SALA system is ap- plied to GILD, a reduction of the mask number in the CMOS poly-Si TFTs process will be realized owing to the local ir- radiation of small laser beams. The system was used for both crystallization and GILD processes in the poly-Si TFT fabrication. The microstructure of crystallized poly-Si film, doping profile and electrical characteristics of the poly-Si TFTs were investigated. 2. Selected Area Laser Assisted (SALA) System The feasibility of a Selected Area Laser Assisted (SALA) system was evaluated by Orbotech in Israel and shown in Fig. 1. It uses a multi-beam solid-state laser system with a precise area selection. A pulsed solid-state laser of fre- quency tripled Nd:YAG (λ = 354 nm, t = 100 ns) passes through a beam splitter and is divided into 100–200 small beams. The sub-beams are individually steered and modu- lated. On the average most of the sub-beams are modulated and steered to required selected positions on the substrate (on-state) or dumped away (off-state) depending on the ar- ray layout. While the laser head illuminates sites along the X direction, the substrate can move in the Y direction, thus the whole area of the substrate can be covered. Here the laser can skip unnecessary area, e.g., outside the TFT is- lands area, making the usage of laser more efficient. The se- lected laser beams are finally focused by quartz lenses and Fig. 1 SALA system. Copyright c  2006 The Institute of Electronics, Information and Communication Engineers