<title>Low-temperature activation method of poly-Si films using rapid thermal annealing</title>

Abstract

Abstract Doped polysilicon (poly-Si) films with a low resistivity have been successfully obtained at a low temperature usingnovel processing technology, which was combined with the rapid thernial annealing (RTA) and ion-doping methods. P-doped poly-Si films with a sheet resistance of 3k Q/EJ were achieved with a process temperature 220°C lower than thatof the conventional process which combined the RTA and ion implantation methods. The uniformity of sheetresistancefor P-doped poly-Si films prepared by the novel process was better than that for the excimer laser annealing (ELA). Thethreshold voltage (Vth), subthreshold swing (S) and field effect mobility (WE)forn-channel thin film transistors (TFTs)with a lightly doped drain (LDD) structure using the novel process were 2.OV, O.3V/dec., and 70cm2/V•s, respectively. 1. Introduction Recently, polysilicon (poly-Si) thin film transistors (TFTs) using a low-temperature process (<600°C) have beenaggressively developed in order to achieve low-cost and high-performance Liquid-Crystal-Displays (LCDs) withintegrated driver circuits1. In the process of developing the poly-Si TFTs, the method for activating the dopants hasbeen important for obtaining high-performance poly-Si TFTs. The dopants have been mainly activated by the excirnerlaser annealing (ELA) method27. However, this method results in lower throughput and lower uniformity than that ofthe rapid thenrial annealing (RTA) method. On the other hand, the RTA method required a higher process temperaturethan that for the ELA method, and could not be used to activate dopants in poly-Si films prepared on glass substrates.In this paper, we report on a novel low-temperature process combined with the RTA and ion-doping methods.P—doped poly-Si films with a lower sheet resistance, which are suitable for poly-Si TFT LCDs, were obtained on glasssubstrates using the process. The field effect mobility (1FE) was as high as 70cm2/V•s. The off current was below1012A under Vgs 0 to -25V with an LDD structure prepared by this novel process. This process will be very useful forobtaining poly-Si TFTs with unifonn performance on a glass substrate.