Metal-induced Lateral Crystallization poly-Si Research Articles

Effect of Ultrathin Silicon Oxide Film for Enhanced Performance and Reliability of Metal-Induced Laterally Crystallized Thin-Film Transistors Using Silicon Nitride as a Gate Dielectric

In this work, we successfully fabricated high performance and excellent reliability of metal-induced laterally crystallized (MILC) polycrystalline-silicon thin-film transistors (poly-Si TFTs) with various surface treatments. The MILC poly-Si TFTs using silicon nitride as a gate dielectric shows high grain-boundary and interface trap-density with the MILC poly-Si film. Therefore, several surface treatment techniques, including oxidizing silicon surface with HNO3, H2SO4, and HCl, as well as N2O plasma treatment, were investigated. Comparing the characteristics of the proposed MILC poly-Si TFTs, the N2O plasma treated was the most effective, showing superior electrical performance and reliability to the other surface treatment methods. The role of the N2O plasma is to insert nitrogen into the poly-Si surface, which causes a relaxation and passivation of the trap states by producing Si≡N strong bonds, while the surface treatments using acids simply oxidize Si atoms.

High-Performance Poly-Si Thin-Film Transistor With High-<inline-formula> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> ZrTiO<sub>4</sub> Gate Dielectric

High-performance poly-Si thin-film transistors (poly-Si TFTs) with metal-induced laterally crystallized (MILC) poly-Si channel and high-k ZrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> (ZTO) gate dielectric are shown for the first time. The MILC poly-Si and ZTO dielectric showed smooth interface (~1.8 nm) with a low interfacial layer and 4.1 nm of effective-oxide thickness. The electrical performance of MILC poly-Si TFT with ZTO exhibited low threshold voltage of -0.5 V, steep subthreshold slope of 0.25 V/decade, high I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> of 1.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> , and high field-effect mobility of 250 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs. These characteristics correspond to the best performance of the poly-Si TFTs with high-k gate dielectric reported so far. Moreover, the driving current and field-effect mobility of poly-Si TFT with ZTO gate dielectric were ten times higher than that of poly-Si TFT with deposited-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectric.

Retrograde-Mask Processed Polysilicon TFT for High Performance, Planar Structure, and Stable Operation

We fabricated polysilicon thin-film transistors (TFTs) using a retrograde-mask process (RMP) showing high electrical performance, planar geometry, and stable driving characteristics. The electrical performance of RMP polysilicon TFT was compared with conventional metal-induced laterally crystallized (MILC) polysilicon TFTs. The fabrication process changed the masking steps of the conventional pattern, but did not require an additional mask. It was found that the conventional MILC poly-Si TFT typically showed a hump current, and had a serious reliability problem due to the NiSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> contamination at the corner edges and geometry effect. One the other hand, an RMP poly-Si TFT improved the hump and the TFT's reliability due to the absent of NiSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> at the edges and the large effective channel length and width.

Thermal Stress Effects on the Electrical Properties of p-Channel Polycrystalline-Silicon Thin-Film Transistors Fabricated via Metal-Induced Lateral Crystallization

We developed a method to compact the glass sheets of a flat-panel displays that use metal-induced laterally crystallized (MILC) polycrystalline-silicon (poly-Si) thin-film transistors (TFTs), and the effects of thermal stress on the fabricated devices were compared against those of a bare-glass device. The glass substrate was exposed to a temperature of 650 °C for 40 h in order to suppress the glass shrinkage to 0.01 ppm, which suitable for a MILC poly-Si TFT process. The compressive strain that originates from glass shrinkage generally increases the size of the micro-cracks and the vacancies, and as a result, most of the electrical parameters of a bare glass device (such as the on-current, off-current, field-effect mobility, subthreshold slope, and threshold voltage) had a higher level of degradation than those of the device with the compacted glass. The increase in the on-current and the field-effect hole mobility under the compressive strain for poly-Si TFTs showed a similar behavior to that of single-crystalline-silicon (c-Si) TFTs under compressive strain. However, the increase in the off-current was the converse of that of strained c-Si TFT.

Leakage Current Suppression on Metal-Induced Laterally Crystallized Polycrystalline Silicon Thin-Film Transistors by Asymmetrically Deposited Nickel

The electrical performance of low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) fabricated by metal-induced lateral crystallization (MILC) is greatly affected by metal catalyst contaminations, such as Ni and Ni silicide trapped in the channel, since they concentrate in front of laterally grown crystallites. In the present work, the effect of the MILC/MILC boundary (MMB) on MILC polycrystalline silicon (poly-Si) TFTs is investigated by the comparison of MILC poly-Si TFTs with MMB at the center of the channel, and equivalent TFTs with MMB at a position ejected from the channel. The MMB location was controlled by the Ni catalyst position. Both a low off-state leakage current and a free from short channel effect (kink effect) were observed in high electric-field conditions. Furthermore, the field-effect mobility and drain current noise were drastically improved by ejecting the MILC boundary in the source direction.

High performance low temperature polycrystalline Si thin-film transistors fabricated by silicide seed-induced lateral crystallization

A novel and simple crystallization method for high performance polycrystalline silicon (poly-Si) thin-film transistors (TFTs) using Ni silicide seed-induced lateral crystallization (SILC) was proposed in this study, and it includes no additional deposition and/or etching processes that are not found in the fabrication of conventional metal-induced lateral crystallization (MILC) TFTs. The poly-Si thin films crystallized by SILC were characterized by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Micro-Raman spectroscopy. The electrical properties were obtained from ID-VG transfer curves and the interface trap density was determined by Levinson plot analysis. The results show that SILC poly-Si films have lower Ni contamination, better crystallinity, and higher crystalline fraction than MILC poly-Si films. The p-channel SILC poly-Si TFTs exhibited a mobility of 66 cm2/V·s, a minimum leakage current of 3.4 × 10−11 A at VD = −5 V, a subthreshold slope of 0.85 V/dec, and a maximum on/off ratio of 5.0 × 106, all of which resulted in a high-performance device which surpassed conventional MILC poly-Si TFTs.

Gettering of Ni silicide to minimize the leakage current in metal-induced crystallized polycrystalline silicon thin-film transistors

Metal-induced lateral crystallization (MILC) technology has been regarded as the only alternative for low temperature polycrystalline silicon (poly-Si) since it became apparent that laser technology still had intrinsic problems for industrial use. The only problem with MILC poly-Si thin-film transistors (TFTs) is a relatively large leakage current, which has been reported to be due to Ni silicides trapped at the grain boundaries of the poly-Si thin film on the way to lateral crystallization. In this work, the trapped Ni silicides have been removed by catalytic phase transformation. This process has ameliorated not only the problem of leakage current but it has also improved other electrical properties, such as field effect mobility and subthreshold slope by gettering of the Ni silicide.

Effect of CF4 Plasma on Properties and Reliability of Metal-Induced Lateral Crystallization Silicon Transistors

In this study, a plasma etching treatment was applied to metal-induced lateral crystallization (MILC) polycrystalline silicon thin film transistors (poly-Si TFTs). It was found that the electrical properties and reliability of the MILC poly-Si TFTs were improved by the treatment. The minimum off-state currents were also reduced. This is because this etching method involves not only passivating the trap states but also etching away the Ni-related defects on the top surface of MILC poly-Si.

Improved Electrical Performance of MILC Poly-Si TFTs Using $\hbox{CF}_{4}$ Plasma by Etching Surface of Channel

In this letter, a new manufacturing method for metal-induced lateral crystallization (MILC) polycrystalline silicon thin-film transistors (poly-Si TFTs) using CF4 plasma was proposed. It was found that CF4 plasma effectively minimizes the trap-state density by etching away the top surface of MILC and passivating the trap states, leading to superior electrical characteristics such as high field-effect mobility, low threshold voltage, low subthreshold slope, low leakage current, and high ON-/ OFF-current ratio. CF4-plasma MILC TFTs also possess high immunity against the hot-carrier stress and thereby exhibit better reliability than that of conventional MILC TFTs. Moreover, the manufacturing processes are simple (without any additional thermal annealing step) and compatible with MILC TFT processes.

Etching Treatment of MILC Poly-Si TFTs Using CF4 Plasma to Improve Electrical Performance

In this study, CF4-plasma was employed to improve the electrical performance of metal-induced lateral crystallization (MILC) polycrystalline silicon thin film transistors (poly-Si TFTs). It was found that CF4-plasma minimize effectively the trap-state density during etching surface of channel, leading to superior electrical characteristics such as high field-effect mobility, low threshold voltage, low subthreshold slope, low leakage current, and high on/off current ratio.

Improved Electrical Characteristics and Reliability of MILC Poly-Si TFTs Using Fluorine-Ion Implantation

In this letter, fluorine-ion (F+) implantation was employed to improve the electrical performance of metal-induced lateral-crystallization (MILC) polycrystalline-silicon thin-film transistors (poly-Si TFTs). It was found that fluorine ions minimize effectively the trap-state density, leading to superior electrical characteristics such as high field-effect mobility, low threshold voltage, low subthreshold slope, and high on/off-current ratio. F+-implanted MILC TFTs also possess high immunity against the hot-carrier stress and, thereby, exhibit better reliability than that of typical MILC TFTs. Moreover, the manufacturing processes are simple (without any additional thermal-annealing step), and compatible with typical MILC poly-Si TFT fabrication processes.

Effect of Pd Addition on Ni-Induced Lateral Crystallization and Poly-Si TFTs

The effect of Pd addition to a Ni layer on the metal-induced lateral crystallization (MILC) and the performance of poly-Si thin-film transisters (TFTs) were studied. By adding 5 atom % Pd, the growth rate of Ni-ILC was faster two times than that of pure Ni-ILC without the degradation of TFTs. The minimum leakage current of TFTs was reduced from 7.5 X 10 - 1 0 to 3.6 X 10 - 1 0 A at V d - 10 V. But further addition of Pd worsened the properties of TFTs. These results were in accord with the microstructural variation of MILC poly-Si as the concentration of Pd.

Electrical characteristics of MILC poly-Si TFTs with long Ni-offset structure

We have observed that B/sub 2/H/sub 6/-doped amorphous silicon (a-Si) showed a faster growth rate of metal-induced lateral crystallization (MILC) than that of undoped a-Si. From the analysis of the microstructure, it was thought that boron atoms could help modify the growth behavior from that of a branched crystal network to unidirectional crystal growth with few branches and that growth rate could to be enhanced. By using this good crystalline structure at the boundary region between the source/drain and channel, we have successfully fabricated p-type poly-Si thin-film transistors with good electrical properties with a MILC process.

Metal-induced lateral crystallization of a-Si thin films by Ni-Co alloys and the electrical properties of poly-Si TFTs

We have introduced a new process in metal-induced lateral crystallization (MILC). By adding Co to the Ni-MILC process, the electrical characteristics of MILC poly-Si TFTs were considerably improved. In particular, a considerable decrease of TFT leakage current were achieved in both n-type and p-type devices.

Thickness Dependence of Microstructure of Laterally Crystallized Poly-Si Thin Films and Electrical Characteristics of Low-Temperature Poly-Si TFTs

The effects of thickness of a-Si thin films on the resulting microstructure of metal-induced laterally crystallized (MILC) poly-Si and electrical characteristics of MILC low temperature poly-Si (LTPS) thin film transistors (TFTs) were investigated. The TEM images revealed a double-layer structure in the 1000-Å MILC poly-Si thin film. However, for the 400-Å MILC poly-Si thin film, there were single-layer grains within the thin film layer. The reason has been ascribed to the geometry restriction in the crystallization procedure. The average mobility of fabricated MILC LTPS TFTs with active layer thickness of 400 Å showed a little higher than that with 1000 Å active layer. Moreover, the MILC LTPS TFTs with active layer thickness of 400 Å exhibited better electrical uniformity than those with 1000 Å active layer either in threshold voltage or field-effect mobility. The reason should also be attributed to the different crystalline structures within the two thin-film layers. © 2003 The Electrochemical Society. All rights reserved.

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.

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 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 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. © 2001 The Electrochemical Society. [DOI: 10.1149/1.1398279] All rights reserved.

Metal-induced laterally crystallized polycrystalline silicon for integrated sensor applications

A novel metal-induced lateral crystallization (MILC) technique, involving a low temperature crystallization step followed by a high temperature recrystallization step, has been applied to the formation of polycrystalline silicon (poly-Si) with enhanced material characteristics. A range of devices, including piezo-resistors, thermistors, resistors and thin-film transistors, has been fabricated both on MILC and regular low-pressure chemical vapor deposited (LPCVD) poly-Si. Compared to the latter, MILC poly-Si leads to much improved device performance. The piezo-resistive gauge factor of MILC poly-Si is at least double that of LPCVD poly-Si, with a maximum value of 60 measured, higher mobility, steeper subthreshold slope, lower threshold voltage, and higher on-off current ratio have been obtained for thin-film transistors realized on MILC poly-Si that those realized on LPCVD poly-Si. A variety of sensing and electronic devices based on MILC poly-Si can be simultaneously realized, thus making MILC an enabling technology for integrated silicon sensor applications.

Excimer Laser Annealing Effect on MILC Polycrystalline Silicon Film

AbstractXeCl excimer laser was irradiated on metal induced laterally crystallized (MILC) polycrystalline silicon (poly-Si) film in order to eliminate the intra-grain defects of MILC poly-Si film which incorporated 2 μm wide metal induced crystallized (MIC) poly-Si line pattern. On the irradiation of the laser beams, different melt and recrystallization phenomena were observed in the MILC and the MIC poly-Si region due to the Ni content difference in each film. The transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) measurements indicated that the melting temperature of the poly-Si film decreased as the Ni content increased. With the laser irradiation energy density of 370 mJ/cm2, 2 μm long defect-free poly-Si grain was successfully grown in the MILC poly-Si due to the melting temperature variation at the MILC-MIC poly-Si boundary.

Characterization of an individual grain boundary in metal-induced laterally crystallized polycrystalline silicon thin-film devices

A distinct grain boundary (GB) is formed when two crystallization fronts collide in metal-induced laterally crystallized (MILC) polycrystalline silicon (poly-Si) thin films. This has been used to study carrier transport across a single dominant GB. The average number of traps per unit area is found to be about 1.6/spl times/ 10/sup 12//cm/sup 2/ in this GB, significantly higher than that associated with the regular GBs in the bulk of MILC poly-Si. Though this single GB occupies a negligible fraction of the total device volume, it has been found to significantly affect both the resistance of MILC resistors and the leakage current of MILC thin-film transistors.