Crystallization Of Amorphous Silicon Films Research Articles

Ni-Induced Lateral Fast Crystallization of Amorphous Silicon Film by Microwave Annealing

Polycrystalline Si (poly-Si) thin films for application to display devices and solar cell are generally fabricated by crystallizing amorphous Si (a-Si) thin film precursors. In this paper, studies on Ni-induced lateral crystallization of a-Si thin films by microwave annealing at low temperature were reported. The crystallization of a-Si thin films was enhanced by applying microwaves to the films. The poly-Si films were invested by Optical Microscopy, X-ray Diffraction (XRD) , Raman Spectroscopy and Scanning Electron Microscope(SEM). After processing of Ni-induced lateral crystallization by microwave annealing above 500°C, the a-Si has begun to be crystallized with large grains having the main (111) orientation. The rate of crystallization at 550°C is about 0.033μm/min. Compared to Ni-induced lateral crystallization by conventional furnace annealing, Ni-induced lateral crystallization by microwave annealing both lowers the crystallization temperature and reduces the time of crystallization. The crystallization mechanism during microwave annealing was also studied. The technique that combines Ni-induced lateral crystallization with microwave annealing has potential applications in thin-film transistors (TFT’s) and solar cell.

Effects of irradiation conditions on the lateral grain growth during laser crystallization of amorphous silicon films on borosilicate glass substrates

The effects of preheating laser power and pulse laser energy on the size and crystallinity of laterally grown grains by dual-laser crystallization of amorphous silicon (a-Si) films on borosilicate glass substrates were investigated. Plasma-enhanced chemical vapor deposition was adopted for the deposition of the a-Si films in order to reduce the process temperature and thus the diffusion of metal impurities from the glass substrate to the deposited a-Si films. It was found that the preheating laser power is critical in enhancing grain size, whereas the pulse laser energy is closely related to crystal quality. It is demonstrated that by properly adjusting the process conditions, laterally grown grains of 50-μm size could be obtained.

Aluminium-induced crystallization of amorphous silicon films deposited by DC magnetron sputtering on glasses

Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) films were deposited by DC magnetron sputtering technique with argon and hydrogen plasma mixture on Al deposited by thermal evaporation on glass substrates. The a-Si/Al and a-Si:H/Al thin films were annealed at different temperatures ranging from 250 to 550°C during 4h in vacuum-sealed bulb. The effects of annealing temperature on optical, structural and morphological properties of as-grown as well as the vacuum-annealed a-Si/Al and a-Si:H/Al thin films are presented in this contribution. The averaged transmittance of a-Si:H/Al film increases upon increasing the annealing temperature. XRD measurements clearly evidence that crystallization is initiated at 450°C. The number and intensity of diffraction peaks appearing in the diffraction patterns are more important in a-Si:H/Al than that in a-Si/Al layers. Results show that a-Si:H films deposited on Al/glass crystallize above 450°C and present better crystallization than the a-Si layers. The presence of hydrogen induces an improvement of structural properties of poly-Si prepared by aluminium-induced crystallization (AIC).

Fabrication of High-Quality Polycrystalline Silicon Film by Crystallization of Amorphous Silicon Film Using AlCl3 Vapor for Thin Film Transistors

Development of high quality polycrystalline silicon film is in strong demand for active matrix organic light emitting displays. In this study, AlCl3 vapor was applied to enhance the crystallization of amorphous silicon film. The crystallization of amorphous Si showed that round-shaped Si grains were nucleated from amorphous Si film and they impinged each other to form polyhedral-shaped grains. The grain size in the crystallized Si film was very large and the surface roughness was very small. The field-effect hole mobility and subthreshold swing of the p-channel thin film transistor were 94 cm2/V s and 0.4 V/decade, respectively. The high performance of this thin film transistor is attributed to the large grain size, high crystallinity, and smooth surface of the poly-Si film crystallized in AlCl3 vapor.

Lateral Crystallization Velocity in Explosive Crystallization of Amorphous Silicon Films Induced by Flash Lamp Annealing

Lateral Crystallization Velocity in Explosive Crystallization of Amorphous Silicon Films Induced by Flash Lamp Annealing

High-Quality Polycrystalline Silicon Film Crystallized from Amorphous Silicon Film using NiCl2 Vapor

The development of high-quality polycrystalline silicon film is of interest for active-matrix organic light-emitting displays. Here, NiCl2 vapor was applied for the first time to enhance the crystallization of amorphous silicon film. The crystallization of amorphous Si showed that round-shaped Si grains grow and become impinged to form polyhedral-shaped grains with diameters of 10 to 25 μm. It was found that the growth of large grains was possible via the merging of fine needle grains with the same directional growth. The crystallized film showed a high degree of crystallinity and a very smooth surface with a roughness of 0.53 nm. The field-effect hole mobility and subthreshold swing of the p-channel thin-film transistor fabricated using the poly-Si film were 113 cm2/ and 0.4 V/decade, respectively. The high performance of the thin-film transistor is attributed to the large grain size, the high crystallinity, the low Ni contamination and the smooth surface of the poly-Si film crystallized in NiCl2 vapor.

Arc-instability generated during the Joule heating induced crystallization of amorphous silicon films

Joule heating induced crystallization (JIC) was accomplished by applying an electric field to a conductive layer located beneath the amorphous silicon film. This study found that an intense arc is generated at the interface between the silicon and the electrode. The artificial modification of a JIC-sample structure led us to the finding that arc generation is caused by the dielectric breakdown of a SiO 2 layer that is sandwiched between the transformed polycrystalline silicon and a conductive layer at high temperatures during Joule heating.

Thermite Reaction Between CuO Nanowires and Al for the Crystallization of a-Si

Nanoenergetic materials were synthesized and the thermite reaction between the CuO nanowires and the deposited nano-Al by Joule heating was studied. CuO nanowires were grown by thermal annealing on a glass substrate. To produce nanoenergetic materials, nano-Al was deposited on the top surface of CuO nanowires. The temperature of the first exothermic reaction peak occurred at approximately <TEX>$600^{\circ}C$</TEX>. The released heat energy calculated from the first exothermic reaction peak in differential scanning calorimetry, was approximately 1,178 J/g. The combustion of the nanoenergetic materials resulted in a bright flash of light with an adiabatic frame temperature potentially greater than <TEX>$2,000^{\circ}C$</TEX>. This thermite reaction might be utilized to achieve a highly reliable selective area crystallization of amorphous silicon films.

Aluminum-induced crystallization of amorphous silicon films deposited by hot wire chemical vapor deposition on glass substrates

Aluminum-induced crystallization of amorphous silicon films is discussed. Amorphous Si films were deposited by hot wire chemical vapor deposition onto Al coated glass substrates at 430 °C. Complete crystallization of a-Si films was achieved during a-Si deposition by controlling Al and Si layer thicknesses. The grain structure of the poly-Si films formed on glass substrate was evaluated by optical and electron microscopy. Continuous poly-Si films were obtained using Al layers with a thickness of 500 nm or less. The average grain size was found to be 10–15 μm, corresponding to a grain size/thickness ratio greater than 20.

Laser crystallization of amorphous silicon films investigated by Raman spectroscopy and atomic force microscopy

The intrinsic and phosphorous (P)-doped hydrogenated amorphous silicon thin films were crystallized by laser annealing. The structural properties during crystallization process can be investigated. Observed redshifts of the Si Raman transverse optical phonon peak indicate tensile stress present in the films and become intense with the effect of doping, which can be relieved in P-doped films by introducing buffer layer structures. Based on experimental results, the established correlation between the stress and crystalline fraction ( X C) suggests that the relatively high stress can limit the increase in X C and the highest crystalline fraction is obtained by a considerable stress release. At high laser energy density of 1250 mJ/cm 2, the poorer crystalline quality and disordered structure of the film originating from the irradiation damage and defects lead to the low electron mobility.

Explosive crystallization of amorphous silicon films by flash lamp annealing

Explosive crystallization (EC) takes place during flash lamp annealing in micrometer-thick amorphous Si (a-Si) films deposited on glass substrates. The EC starts from the edges of the a-Si films due to additional heating from flash lamp light. This is followed by lateral crystallization with a velocity on the order of m/s, leaving behind periodic microstructures in which regions containing several hundreds of nm-ordered grains and regions consisting of only 10-nm-sized fine grains alternatively appear. The formation of the dense grains can be understood as explosive solid-phase nucleation, whereas the several hundreds of nanometer-sized grains, stretched in the lateral direction, are probably formed through explosive liquid-phase epitaxy. This phenomenon will be applied to the high-throughput formation of thick poly-Si films for solar cells.

Nickel Induced Lateral Crystallization of Amorphous Silicon Film by Electroless Planting

A novel deposition way of nickel film for crystallization amorphous silicon film is introduced. Electroless nickel planting is a convenient and inexpensive way to deposit nickel without using the electric field or any large facility. A 200 nm nickel film is deposited on the glass substrates and then a 300nm a-Si film is deposited on the nickel film with a horizontal electric field assisted to enhance amorphous silicon crystallization. The bi-layer film is annealed at 500°C for several hours in the nitrogen atmosphere. The crystallized Si thin films were characterized by Raman spectroscopy, Field emission scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The Raman demonstrates that the a-Si has been crystallized. Furthermore the FE-SEM shows the lateral crystalline morphology, the length of grain is up to 5µm and the EDS reveals the nickel distribution in the MILC and MIC area.

Hydrogenation assisted nickel-induced lateral nano-crystallization of amorphous silicon on flexible plastic substrates at low temperatures

We report ultra low temperature lateral crystallization of amorphous silicon films on flexible plastic substrates suitable for the realization of thin-film transistors. A sequential hydrogenation and annealing is necessary to crystallize silicon films aided with an external mechanical stress at a temperature of 170 °C. Ni is used as the seed for the crystallization using a metal induced crystallization method. For the formation of polycrystalline-silicon thin-film transistors, a lateral crystallization is tried where the seed is placed on the source and drain regions and crystallization progresses from the seed regions towards the central parts of the channel of the thin-film transistor. Scanning electron and transmission electron microscopies were used to investigate the morphology and crystallinity of the layers. The fabricated lateral transistors show an on/off ratio of 2000 and an effective mobility of about 25 cm 2/V s.

Spatially localized current-induced crystallization of amorphous silicon films

Field-enhanced metal-induced solid phase crystallization (FE-MISPC) at room temperature is employed to create microscopic crystalline regions at predefined positions in hydrogen-rich amorphous silicon (a-Si:H) films. Electric field is applied locally using a sharp conductive tip in atomic force microscope (AFM) and nickel electrode below the a-Si:H film. The process is driven by a constant current of −50pA to −500pA while controlling the amount of transferred energy (1–300nJ) as a function of time. Passing current leads to a formation of nanoscale pits in the a-Si:H films. Depending on the energy amount and rate the pits exhibit lower or orders of magnitude higher conductivity as detected by current-sensing AFM. High conductivity is attributed to a local crystallization of the films. This is confirmed by micro-Raman spectroscopy.

Seeding Solid Phase Crystallization of Amorphous Silicon Films with Embedded Nanocrystals

ABSTRACTSilicon nanocrystals with diameters up to 30 nm are used as nucleation seeds for fast solid phase crystallization of amorphous silicon films. Purely amorphous films required an incubation time of up to 12 hours at 600°C prior to the onset of nucleation, while films with nanocrystals embedded between layers of amorphous silicon grew immediately upon annealing in a quartz tube furnace. Structural characterization was performed by heated-stage transmission electron microscopy and Raman spectroscopy.

Deposition of nanocrystalline silicon films at room temperature

Bond rearrangements, facilitated by H insertion into strained Si–Si bonds have been shown to result in H-induced crystallization of amorphous silicon films. Whether such H-induced rearrangements can lead to synthesis of nanocrystalline films at room temperature has remained an open question. In this article, the authors demonstrate the deposition of thin films containing nanocrystals of silicon using inductively coupled SiH4/H2 plasma at room temperature. Real time in situ spectroscopic ellipsometry and ex situ transmission electron microscopy revealed that the silicon nanocrystals nucleate below the surface, and grow beneath an amorphous silicon crust. This observation validates the hydrogen-induced crystallization model. Analysis of the crystal size distribution shows that the distribution depends on the growth duration rather than the substrate temperature. Observation of crystals as large as 100–150 nm at room temperature indicates that silicon nanocrystals not only nucleate but also grow substantially in the bulk even at room temperature.

Excimer Laser Crystallization of Amorphous Silicon Film with Artificially Designed Spatial Intensity Beam Profile

A method of forming polycrystalline silicon film with large grains at a controlled location using a single irradiation of an excimer laser beam is proposed. The excimer laser beam is modified to have a specific spatial intensity profile, periodic spatial variation of intensity maxima and minima , by means of a specially designed mask composed of transparent and opaque patterns. It is noted that the evolution of polycrystalline silicon microstructure is critically dependent on the melt depth of amorphous silicon at , which we categorized as “partial melting,” “near-complete melting,” and “complete melting” regimes. While the lateral grain growth of polycrystalline silicon increases in proportion to the fluence gradient as the energy density is increased, surprisingly we find that it decreases in the complete melting regime due to the “secondary nucleation” occurring at . By judicious selection of optimum intensity modulation and the spacing between and , we have obtained the maximum lateral grain size of at controlled position.

Millisecond crystallization of amorphous silicon films by Joule-heating induced crystallization using a conductive layer

This study revolved around the introduction of a crystallization technology for amorphous silicon film using Joule-heating. As part of this study, an electric field was applied to a conductive layer to induce Joule-heating in order to generate the intense heat needed to carry out the crystallization of amorphous silicon. Polycrystalline silicon was produced via Joule-heating through a solid state transformation under typical processing conditions. Uniformly distributed fine grains were obtained due to enormously high heating rate of this process. Crystallization was accomplished throughout the sample within the range of milliseconds of the heating, thus demonstrating the possibility of a crystallization route for amorphous silicon films at room temperature.

Self-Assembly of Si Nanoparticles Produced by Aluminum-Induced Crystallization of Amorphous Silicon Film

Aluminum-induced crystallization of amorphous silicon (a-Si) was used to rapidly grow aluminum-doped silicon nanowires (SiNWs) that are parallel to the substrate surfaces on which they are grown. The study reveals that both aluminum thickness and native silicon oxide between Al and a-Si play critical roles in the formation of the nanostmctures. The research results suggest that the rapid in-plane growth of these SiNWs can be attributed to self-assembly of nanosilicon islands, which is different from traditional SiNWs growth mechanisms such as vapor-liquid-solid.

Excimer Laser Crystallization of Amorphous Silicon Film with Artificially Designed Spatial Intensity Profile Beam

A new method to form polycrystalline silicon film with large grains at the controlled location by using a single irradiation of excimer laser beam is proposed for polycrystalline silicon thin film transistor. The excimer laser beam is modified to have a spatial intensity profile - periodic spatial variation of intensity maxima (I_Max) and minima (I_Min) - by the specially designed mask composed of the opaque and the transparent patterns where the opaque pattern size is less than the optical resolution of projection lens. Based on the melt depth of amorphous silicon at the location of I_Min, one can obtain three different regimes, namely, the partial melting, the near-complete melting, and the complete melting. Polycrystalline silicon grains grow vertically and laterally from the seeds at the location of I_Min to the complete molten region of I_Max. The evolution of polycrystalline silicon microstructure is investigated and elucidated in each regime.