In-Hyuk Song

A new high-performance poly-Si TFT by simple excimer laser annealing on selectively floating a-Si layer

A new poly-Si TFT with a single grain-boundary has been fabricated by a simple ELA method which employs a selectively floating a-Si active layer. A thermally insulating air-gap between the floating a-Si and substrate successfully induces the lateral grain growth. Large lateral grains exceeding 4 /spl mu/m have been grown by a single laser irradiation with wide ELA process window. The proposed poly-Si TFT exhibits high mobility of 331 cm/sup 2//V sec due to the high-quality grains.

A poly-Si TFT fabricated by excimer laser recrystallization on floating active structure

This letter reports a. new excimer laser annealing (ELA) method to produce large polycrystalline silicon (poly-Si) lateral grains exceeding 4 /spl mu/m. A selectively floating amorphous silicon (a-Si) flint with a 50 nm-thick air-gap was irradiated by a single-pulse XeCl excimer laser and uniform lateral grains were grown due to the lateral thermal gradient caused by the low thermal conductivity of the air. A poly-Si thin-film transistor (TFT) with two high-quality 4.6 /spl mu/m-long lateral grains was fabricated by employing the proposed ELA and high field-effect mobility of 331 cm/sup 2//Vsec was obtained due to. the high-quality grain structure.

A high-performance multichannel dual-gate poly-Si TFT fabricated by excimer laser irradiation on a floating a-Si thin film

A new excimer laser annealing (ELA) process that uses a floating amorphous-Silicon (a-Si) thin film with a multichannel structure is proposed for high-performance poly-Si thin-film transistors (TFTs). The proposed ELA method produces two-dimensional (2-D) grain growth, which can result in a high-quality grain structure. The dual-gate structure was employed to eliminate the grain boundaries perpendicular to the current flow in the channel. A multichannel structure was adapted in order to arrange the grain boundary to be parallel to the current flow. The proposed poly-Si TFT exhibits high-performance electrical characteristics, which are a high mobility of 504 cm/sup 2//Vsec and a low subthreshold slope of 0.337 V/dec.

Enhanced formation of luminescent nanocrystal Si embedded in Si/SiO2 superlattice by excimer laser irradiation

The effect of excimer laser annealing on the formation of luminescent nanocrystal Si (nc-Si) embedded in Si/SiO2 superlattice is investigated. An amorphous Si/SiO2 superlattice consisting of 20 periods of 2 nm thin Si layers and 5 nm thin SiO2 layers was deposited on Si using electron cyclotron resonance plasma-enhanced chemical vapor deposition. Excimer laser annealing alone did not result in any nc-Si luminescence even at an energy density sufficient to melt the Si layers. However, if the nc-Si is preformed by a thermal anneal, subsequent excimer laser annealing will result in a threefold increase of the nc-Si luminescence intensity. The temperature dependence of the nc-Si luminescence spectrum, lifetime, and intensity indicates that excimer laser annealing activates luminescent nc-Si by removing defects and amorphous regions in thermally crystallized Si layers without significant changes in the size or shape of nc-Si.

Poly-Si thin film transistors fabricated by combining excimer laser annealing and metal induced lateral crystallization

Two μm long polycrystalline silicon (poly-Si) grains were obtained by irradiating a XeCl excimer laser beam on metal induced laterally crystallized (MILC) poly-Si films due to gradual melting temperature decrease of the MILC poly-Si near the nickel-rich metal induced crystallized (MIC) poly-Si. Poly-Si thin film transistors (TFTs) fabricated by employing the large poly-Si grains, exhibited considerably improved field effect carrier mobility and ON/OFF current ratio compared with conventional MILC and/or excimer laser annealed (ELA) poly-Si TFTs due to reduction of defect density in the poly-Si channel. Our experimental results showed that the combination of ELA and MILC might be beneficial for practical device application.

A new multi-channel dual-gate poly-Si TFT employing excimer laser annealing recrystallization on pre-patterned a-Si thin film

We have proposed a new excimer laser annealing method which employs a floating a-Si thin film structure and the effect of pre-patterning. The proposed ELA produces two-dimensional grain growth so that a high quality grain structure can be obtained. We have also fabricated poly-Si TFTs by adapting the proposed ELA method. The dual-gate structure is used for the elimination of grain boundaries in the channel. The proposed poly-Si TFT exhibits high performance electrical characteristics, e.g. a high mobility of 504 cm/sup 2//V sec and low subthreshold slope of 0.337 V/dec.

Excimer Laser Annealing Effect on Nickel-Induced Crystallized Polycrystalline Silicon Film

The effects of XeCl excimer laser annealing on a nickel-induced crystallized polycrystalline silicon (poly-Si) film are described A XeCl excimer laser was irradiated on a metal induced laterally crystallized (MILC) poly-Si film which incorporated 2 μm wide metal induced crystallized (MIC) poly-Si line patterns. On the irradiation of the laser beams with various laser energy densities from 270 to 490 mJ/cm 2 , different melt and recrystallization phenomena were observed in the MILC poly-Si and in the MIC poly-Si region because the MIC poly-Si film had much higher Ni content than the MILC poly-Si film. To investigate the effect of the Ni content in the poly-Si film during the laser annealing, transmission electron microscopy and secondary ion mass spectrometry were used. Our experimental results show that the melting temperature of the poly-Si film decreases as the Ni content increases. With the optimum laser irradiation energy density of 370 mJ/cm 2 , 2 μm long poly-Si grains grew in the MILC poly-Si film due to the gradual decrease of the melting temperature of the MILC poly-Si near the Ni-rich MIC poly-Si.

A new poly-Si TFT structure with air cavities at the gate-oxide edges

We propose a new poly-Si TFT structure employing air cavities at the edges of gate oxide in order to reduce the threshold voltage shift after electrical stress and to decrease the large leakage current. Due to the low dielectric constant of air, the air cavity behaves as a thick insulator reducing the vertical electric field near the drain, so that poly-Si region under air cavity acts as an offset. The new poly-Si TFT structure has been successfully fabricated by employing wet etching of the gate oxide followed by atmospheric pressure chemical vapor deposition (APCVD) oxide deposition. Our experimental results show that the leakage current is considerably reduced without decrease of the on-current and the device stability such as threshold voltage shift under high-gate bias is also improved.We propose a new poly-Si TFT structure employing air cavities at the edges of gate oxide in order to reduce the threshold voltage shift after electrical stress and to decrease the large leakage current. Due to the low dielectric constant of air, the air cavity behaves as a thick insulator reducing the vertical electric field near the drain, so that poly-Si region under air cavity acts as an offset. The new poly-Si TFT structure has been successfully fabricated by employing wet etching of the gate oxide followed by atmospheric pressure chemical vapor deposition (APCVD) oxide deposition. Our experimental results show that the leakage current is considerably reduced without decrease of the on-current and the device stability such as threshold voltage shift under high-gate bias is also improved.

A poly-Si TFT integrated gate-data line-crossover structure employing an air-gap for large-size AMLCD panel

We have fabricated a novel poly-Si TFT integrated at the gate-data line-crossover structure without sacrificing the electrical characteristics. The aperture ratio of the panel was increased considerably because the TFT was located under the opaque metal line. In particular, we employed a low dielectric air-gap between the gate line and data lines, which reduced capacitance between the gate and data lines, enabling the signal delay of the data line to be significantly decreased. The fabricated TFT was successfully operated, and the proposed structure found to reduce the delay time by a factor of nine compared with conventionally constructed panel without air-bridges.We have fabricated a novel poly-Si TFT integrated at the gate-data line-crossover structure without sacrificing the electrical characteristics. The aperture ratio of the panel was increased considerably because the TFT was located under the opaque metal line. In particular, we employed a low dielectric air-gap between the gate line and data lines, which reduced capacitance between the gate and data lines, enabling the signal delay of the data line to be significantly decreased. The fabricated TFT was successfully operated, and the proposed structure found to reduce the delay time by a factor of nine compared with conventionally constructed panel without air-bridges.

Effects of selective Si ion implantation on excimer laser annealing of dehydrogenated a-Si film

Abstract The effects of selective Si + ion implantation on excimer laser annealing (ELA) of PECVD a-Si thin film were investigated. The selective Si + ion implantation was employed to amorphize a-Si film locally and the lateral grain growth was successfully induced. In the selectively implanted region, the threshold excimer laser energy for a-Si melting was 85 mJ/cm 2 while that of the implanted region was 105 mJ/cm 2 , which may be attributed to the fact that high-energy implantation with high density may amorphize a-Si film effectively and may weaken atomic bonding energy in the implanted a-Si film. Periodically arranged lateral grains were successfully formed near the implanted region and grain size was up to 1 μm .