Significant improvement of device performance was observed for the excimer laser annealed ͑ELA͒ poly-Si thin film transistors ͑TFTs͒ by the incorporation of fluorine atoms using the ion implantation technique. This is presumably due to the relaxation of mechanical stress at the poly-Si/buffer-oxide interface and the passivation of trap-states in the poly-Si channel region and at the gate-oxide/poly-Si interface. We achieved high performance ELA poly-Si TFTs with a very low off-current of ϳ0.26 pA/m and a very high On/Off current ratio of about 10 8 . Moreover, the fluorine ion implantation also greatly improved the reliability of the ELA poly-Si TFTs with respect to the hot-carrier stress, presumably due to the formation of strong Si-F bonds.Excimer laser annealing ͑ELA͒ is a promising scheme for the crystallization of amorphous silicon in the fabrication of lowtemperature processed ͑LTP͒ poly-Si thin film transistors ͑TFTs͒ because the laser process can result in high-quality polysilicon films with very few in-grain defects. 1,2 However, a grain size of less than 100 nm as a result of extremely high solidification velocity inherent to the ELA process has been a troublesome problem. 2,3 Thus, the ELA polysilicon films usually contain a high density of grain boundaries, leading to lowered carrier mobility and degraded performance of the TFTs. Many techniques have been employed to reduce the detrimental effects of grain boundaries by either enlarging the grain size 4,5 or passivating the grain boundaries. 6,7 In addition, there is also a serious problem of mechanical tensile stress associated with the ELA process because of the large mismatch of thermal expansion coefficient between the molten polysilicon film and the buffer oxide layer of glass substrates. It is well known that the mechanical stress at the interface usually induces a large number of interface defect-states and thus deteriorates the electrical characteristics of the metal oxide semiconductor ͑MOS͒ devices. 8,9 Nevertheless, only a few studies have been reported regarding the effects of this mechanical stress on the performance of the ELA poly-Si TFTs. 5,10,11 In recent years, the incorporation of fluorine into gate-dielectrics of MOS devices by various processes has been used to induce the local strain relaxation and thus reduce the interface state density of MOS field-effect transistors ͑MOSFETs͒. 8,9 It was also reported that the defect states of the solid phase crystallized ͑SPC͒ LTP poly-Si TFTs can be passivated by fluorine ion implantation; 12 however, the SPC poly-Si TFTs have not experienced a large thermal expansion mismatch at the poly-Si/buffer-oxide interface because of the lack of laser irradiation process. Moreover, it was found that diffused fluorine spices from the SiO x F y dielectric can reduce the defect state density in the active channels of TFTs. 13,14 In this work, fluorine ions were implanted into the active regions before excimer laser irradiation for the fabrication of the high-performance ELA poly-Si TFTs. The implantatio...

This work investigates the correlation between electrical characteristics and gate-oxide/polysilicon interface morphology for excimer-laser-annealed ͑ELA͒ poly-Si thin-film transistors ͑TFTs͒. The main feature of ELA poly-Si films is protrusion at grain boundaries that makes the film surface appear very rough. The surface roughness increases with increasing laser energy density and causes degradation of off-current and reliability for the ELA poly-Si TFTs. This degradation of the off-current is attributed to the lower channel resistance due to the increase in crystallinity of the poly-Si layer and the enhancement of localized electric field arising from the protrusions at the grain boundaries. In addition, the increase of localized electric field also degrades device reliability. Passivation of gate oxide/poly-Si channel by NH 3 -plasma treatment was found to be favorable in improving the performance and reliability of the ELA poly-Si TFTs.Low-temperature processed ͑LTP͒ polycrystalline silicon thinfilm transistors ͑poly-Si TFTs͒ are attracting much attention for use in active matrix liquid crystal displays ͑AMLCDs͒ because of their higher field-effect mobility and driving current compared to amorphous silicon TFTs currently used for large-area electronics. 1 Thus, integration of the AMLCD and its peripheral driver circuits on a single glass substrate is of great advantage for the LTP poly-Si TFTs. In order to fabricate LTP poly-Si TFTs on a glass substrate, all of the fabrication processes must be carried out at low temperatures of no more than 600°C.It is well known that excimer laser annealing ͑ELA͒ is a very promising scheme for the crystallization of amorphous silicon because the laser process heats thin silicon films to the melting point on several tens of nanoseconds that allows the films to melt and recrystallize without significantly heating the glass substrate. Moreover, it has been reported that ELA resulted in high-quality polysilicon films with very few intragrain defects, leading to significant improvement in the electrical characteristics of poly-Si TFTs. 2-5 However, during the phase transformation from liquid to solid in the laser crystallization, many protrusions are formed at the oxide/ polysilicon interface, causing a very rough surface of polysilicon. 6 The enhanced electric field arising from the asperities at the rough surface led to adverse effects on the electrical characteristics and also created reliability problems in the ELA poly-Si TFTs. 7,8 The surface roughness inherent to the ELA process has been a troublesome problem. In recent years, many investigations have been reported regarding the formation mechanism of protrusions and the reduction scheme of the surface roughness, 5,6,9-11 whereas little study has been made with respect to the correlation between device behavior and interface morphology for the ELA poly-Si TFTs. 12 In this study, correlation between electrical characteristics and oxide/ polysilicon interface morphology of the ELA poly-Si TFTs is investigated, in particular...