2348 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 57, NO. 9, SEPTEMBER 2010 Location- and Orientation-Controlled (100) and (110) Single-Grain Si TFTs Without Seed Substrate Tao Chen, Ryoichi Ishihara, and Kees Beenakker Abstract—This paper reports on high-performance (100)- and (110)-oriented single-grain thin-film transistors (SG-TFTs) fab- ricated below 600 ◦ C without any seed substrate. Orientation has been controlled by μ-Czochralski process with an excimer laser. The field-effect mobility of the n-channel transistor is 998 cm 2 /V · s for (100) SG-TFTs and 811 cm 2 /V · s for (110) SG-TFTs. The field-effect mobility of the p-channel transistor is 292 cm 2 /V · s for (100) SG-TFTs and 429 cm 2 /V · s for (110) SG-TFTs. Index Terms—Laser crystallization, thin-film transistors. I. I NTRODUCTION T HIN-FILM transistors have numerous advantages over traditional CMOS technology, which uses bulk Si sub- strate. These include large area, low temperature, and substrate flexibility. The μ-Czochralski process [1] has realized single- grain (SG) Si TFTs with an electron mobility of 600 cm 2 /V · s, which is comparable to the silicon-on-insulator (SOI) coun- terpart. However, variation in mobility was as high as 20% due to the random crystallographic orientation of the grains, resulting in effective mass variation [2] between the grains. It is therefore important to control both the surface and the in- plane orientation of the location-controlled grains. One solution is to control the crystallographic orientation by growing a seed on glass or SiO 2 before the μ-Czochralski process. This paper shows that metal-induced lateral crystallization (MILC) can grow both (100) and (110) surface-orientation-controlled poly- Si on SiO 2 by anisotropic tensile stress [3]. The MILC poly- Si has been used as a seed for the μ-Czochralski process, and both (100) [4] and (110) [5] surface-orientation- and location-controlled Si grains have been realized. Furthermore, (110) surface-orientation-controlled SG-TFTs with low Ni con- centration [6] are also reported. The electron mobility was 441 cm 2 /V · s due to the (110) surface orientation control [6], which left room for improvement. This paper reports both surface- and in-plane-orientation-controlled (100) and (110) SG-TFTs without any seeding substrate. The electron and hole mobilities are optimized by the surface and in-plane orientation along the current flow of (001)/[1 10] and (011)/[100], respec- tively. Electron and hole mobilities of 998 and 429 cm 2 /V · s, respectively, which surpass the SOI counterpart, are presented. Manuscript received January 28, 2010; revised June 22, 2010; accepted June 22, 2010. Date of current version August 20, 2010. The review of this brief was arranged by Editor S. Deleonibus. The authors are with Delft Institute of Microsystems and Nanoelectronics (DIMES), Delft University of Technology, Delft 2628 CT, The Netherlands (e-mail: echosteve@hotmail.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TED.2010.2055510 Fig. 1. TEM cross section of in-plane orientation control at the MILC corner. II. EXPERIMENT A. (100) and (110) Seed Layer Grown by MILC The (100) and (110) seeds have been formed by MILC as follows: 15-nm Ni was deposited on 250-nm a-Si in a rectangular SiO 2 window and further annealed at 600 ◦ C for 4 h. Fig. 1(a) schematically shows the MILC growth process: (100) surface-oriented poly-Si grows at a corner due to a higher tensile stress, and (110) surface-oriented poly-Si grows straight from the four flat sides of the rectangle [3]. Fig. 1 shows a cross- sectional transmission electron microscope (TEM) image of the poly-Si near the corner of the Ni pattern. The (001) surface- oriented poly-Si grains with an in-plane orientation of [110] along a direction of 45 ◦ from the corner was seen. It was also found that, near the side of the rectangular Ni region, the (110) surface-oriented poly-Si has an in-plane orientation of [100] along the perpendicular direction to the side [3]. To increase the area of the (100)-oriented poly-Si by MILC, the corner was repeatedly placed on a line with a zigzag Ni pattern [3]. To grow (110)-oriented poly-Si by MILC, a rectangular Ni pattern is applied [3]. B. MILC With Grain Filter Process Fig. 2(a)–(d) shows the cross-sectional structure for the orientation and location control of the grains. A grid of 1.2-μm deep cavities (grain filter) with a diameter of 100 nm was 0018-9383/$26.00 © 2010 IEEE