Ageing of laser crystallized and unhydrogenated polysilicon thin film transistors

Rahala, A.; Mohammed-Brahima, T.; Toutah, H.; Tala-Ighil, Boubekeur; Helen, Youri; Prat, Christophe; Raoult, F.

doi:10.1016/s0026-2714(99)00112-2

Cited by 3 publications

(1 citation statement)

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“…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][10][11] whereas little study has been made with respect to the correlation between device behavior and interface morphology for the ELA poly-Si TFTs.…”

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Correlation Between Electrical Characteristics and Oxide/Polysilicon Interface Morphology for Excimer-Laser-Annealed Poly-Si TFTs

Fan¹,

Chen²

2002

J. Electrochem. Soc.

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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...

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