Crystallization Of Amorphous Si Films Research Articles

Crystallization of Optically Thick Amorphous Silicon Films by Near-IR Femtosecond Laser Processing

We demonstrated efficient crystallization of amorphous Si films induced by their direct irradiation with near-IR femtosecond laser pulses coming at sub-MHz repetition rate. Comprehensive analysis of morphology and composition of the laser-annealed film by atomic-force microscopy, Fourier-transform IR, Raman and energy dispersive X-ray spectroscopy as well as numerical modeling of optical spectra confirmed efficient crystallization of amorphous Si and high-quality of the obtained films opening pathway for applications in thin-film solar cells, transistors and displays.

Influence of Ni concentration on the crystallization of amorphous Si films and on the development of different Ni-silicide phases

The crystallization mechanism was the subject of the present study which reports on the structure, and the Ni-silicide formation, of Si films containing different concentrations of Ni. The films were prepared by sputtering and were analyzed by compositional and structural characterization techniques. Additional information was obtained by thermal annealing the films up to 800 °C. The experimental results indicated that, in the as-deposited form, the films are amorphous, homogeneous, and with Ni contents in the ∼0–40 at. % range. Moreover, the development of Si and/or Ni-silicide crystalline structures was susceptible to factors like the Ni concentration, the annealing temperature and the annealing process (if cumulative or not, for example).

Raman spectral analysis of Si films solid-phase-crystallized on glass substrates using pulse laser with crystallization-induction layers of yttria-stabilized zirconia

The solid-phase crystallization of amorphous Si films with/without a crystallization-induction (CI) layer of yttria-stabilized zirconia (YSZ) was performed using a Nd:YAG pulse laser. We investigated the crystallinity of the Si films by Raman spectroscopy. It was found that, at the same crystalline fraction, the FWHM of the crystalline silicon (c-Si) peak for Si/YSZ/glass was smaller than that for Si/glass. The result is considered to be due to the CI effect of the YSZ layer. This was confirmed by scanning electron microscopy observation, which showed that the grain size of Si on YSZ layers was more uniform than that on glass substrates. On the other hand, at a lower beam energy, the crystalline quality of the Si films was found to be better although the increase in the crystallization rate with the pulse number N is smaller. On the basis of the above results, the crystallization model of an a-Si film on a YSZ layer is speculated.

Layer Transfer and Simultaneous Crystallization of Amorphous Si Films with Mid-Air Structure Induced by Near-Infrared Semiconductor Diode Laser Irradiation

Layer transfer and simultaneous crystallization of amorphous Si (a-Si) films induced by near-infrared semiconductor-diode-laser (SDL) irradiation have been investigated. The a-Si films supported by columns on a starting substrate (quartz) and a counter substrate (glass and polyethylene terephthalate) were face-to-face contact, and an SDL irradiated the a-Si films. After SDL irradiation, the Si films of 6 × 6 mm2 area were completely transferred and crystallized simultaneously on the counter substrates. In-situ monitoring revealed that the layer transfer took place either in the solid phase or the liquid phase followed by phase transformation in the cooling period.

Solution-Based Metal Induced Crystallization of Amorphous Silicon Films

A viscous Nickel (Ni) solution was applied on amorphous Si films by spin coating and its effect on the crystallization of amorphous Si films was investigated with a two-step annealing process. The experimental results show that with the help of the two-step annealing, the crystallization of the film can take place at 500oC. At the same time, the crystalline fraction gets up to 79.4% after annealing at a high temperature of 520oC and the grain size of the polycrystalline Si films is approximately 200 nm.

Solid-phase crystallization of amorphous Si films on glass and Si wafer

When amorphous silicon films deposited on glass by physical or chemical vapor deposition are annealed, they undergo crystallization by nucleation and growth. The growth rate of Si crystallites is the highest in their 〈111〉 directions along or nearly along the film surface. The directed crystallization is likely to develop the 〈110〉//ND or 〈111〉//ND oriented Si crystallites. As the annealing temperature increases, the equiaxed crystallization increases, which in turn increases the random orientation. When amorphous Si is under a stress of the order of 0.1 GPa at about 540 °C, the tensile stress increases the growth rate of Si grains, whereas the compressive stress decreases the growth rate. However, the crystal growth rate increases with the increasing hydrostatic pressure, when the pressure is of the order of GPa at 530–540 °C. These phenomena have been discussed based on the directed crystallization model advanced before, which has been further elaborated.

Crystallization of amorphous Si film by microwave annealing with SiC susceptors

Crystalline silicon film is extremely important for low-cost, high performance Si-based devices, such as thin film transistors and solar cells. This study employs an elliptical microwave applicator to process the material placing near the field maximum. It is demonstrated that microwave irradiation incorporating with SiC susceptors is able to crystallize amorphous silicon film on glass substrate at a low temperature below 600 °C in a short period of 600 s. The reasons for such a fast processing time and a low annealing temperature are not clear.

Prospective crystallization of amorphous Si films for new Si TFTs

AbstractProspective crystallization results of amorphous silicon film are reviewed and are discussed. Silicon TFTs are playing an important role for Active‐Matrix Flat Panel Displays (AM‐FPD) based on amorphous or poly‐Si thin‐film transistors (TFTs). Poly‐Si TFTs provide a possibility to develop highly functional system on pane (SoP) applications. In order to get a high performance TFT, large poly‐crystal grains or high cystallinity for the film is required. Two basic crystallization techniques namely solid phase crystallization (SPC) and excimer laser crystallization (ELC) are reviewed and relating issues are described. A grain growth technique has been developed based on the two crystallization techniques, so far. In order to mount a poly‐Si TFT system on a flexible panel such as a plastic, an excimer laser of UV pulse beam has an advantage for the TFT channel as well as for the source and drain contacts as a ultra‐low temperature poly‐Si (U‐LTPS) process. To realize a high performance TFT of uniform and high carrier mobility, location control crystallization had been proposed. Some of the distinctive results for crystal orientation control of (100) and (111) face using the laser crystallization techniques are described. In the future, single‐crystalline Si TFT of a functional 3D structure is expected to realize an advanced SoP for ubiquitous electronics era. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modeling and Experimental Analysis in Excimer‐Laser Crystallization of Amorphous Si Films on a Glass Substrate with Different Buffer Layers

In this work, the excimer‐laser‐induced crystallization of amorphous silicon (a‐Si) films was investigated numerically and experimentally. The basic structure is an a‐Si film on a glass substrate. The control parameters are the laser intensity and the pulse number. The effects of SiO2 and Si3N4 layers located between the Si film and glass substrate were also studied. In the microstructure analysis of the laser‐irradiated area, the critical fluences (full‐melt threshold, FMT) between the partial melting and complete melting regimes can be found by applying scanning electron microscopy. An efficient two‐dimensional numerical model is carried out to predict the critical fluences (FMT) and the transient temperature distribution during the laser processing. From the analysis of temperature responses, the FMT obtained from the simulation results of the proposed model agree fairly well with those from the experimental data reported in the literature and acquired in this research.

Crystallization of amorphous Si films by thermal-plasma-jet-induced ultrarapid thermal annealing and application to thin-film transistor fabrication

Crystallization of amorphous Si films by thermal-plasma-jet-induced ultrarapid thermal annealing and application to thin-film transistor fabrication

Study of low-temperature crystallization of amorphous Si films obtained using ferritin with Ni nanoparticles

A polycrystalline silicon thin film with a high crystallinity was obtained using ferritin with a Ni core (7nm), which enabled us to precisely control the density and position of the nucleus for crystal growth. The core density of ferritin adsorbed on the amorphous silicon surface was controlled in the range from 109cm−2to1011cm−2. Crystal growth was performed at 550°C in N2. Crystallinity or grain size strongly depended on Ni core density. Polycrystalline silicon film with the average grain size of 3μm and a high crystallinity was obtained at a low Ni atom density of 1012cm−2.

Crystallization of amorphous-Si films by pulsed YAG2ω green laser for polycrystalline Si TFT fabrication

— A pulsed YAG2ω green laser with a line-shaped beam was applied in the crystallization process to fabricate polycrystalline-Si TFTs, and this procedure was compared with excimer-laser annealing (ELA). YAG2ω lasers are superior to excimer lasers in that they have fewer items to maintain and a longer working time ratio. The crystallization mechanism for YAG2ω laser annealing (YLA) based on the lateral growth of grain is different from that of ELA. Its fluence margin was obtained from the n-channel mobility measured from fabricated TFTs and was found to be twice as large as that for ELA. We also found that overlapping irradiation does not change the mobility of TFTs. This is because the distribution of grain size is almost the same as in non-overlapping regions. This suggests the possibility of overlapping irradiation in YLA.

Crystallization of amorphous-Si films by flash lamp annealing

The crystallization of amorphous silicon films deposited on glass, using the flash lamp annealing process was realized and studied. The duration of the flash is 20 ms, about two orders of magnitude shorter than the standard rapid thermal annealing process. The a-Si films deposited on Corning glass were irradiated with different energy densities and crystallized exhibiting grains with a mean size up to 6 μm. In order to reduce the strain due to the thermal gradient, the samples were preheated from the backside. The ability of the FLA process to eliminate the ingrain defects in already crystallized poly-Si films at 600 °C is also demonstrated.

Microstructural Evolution of Polycrystalline Si Films during Ni-Silicide-Mediated Lateral Crystallization

Microstructural evolution of polycrystalline Si films during Ni-silicide-mediated lateral crystallization of amorphous Si films has been studied. The growth direction of the crystallized needle-like grains was not parallel to the crystallization direction of the film. The grains were aligned nearly parallel to each other and consequently, a macroscopic quasi grain was formed. The dominant growth directions of the needle-like grains with respect to the crystallization direction were and which were well matched for the growth of {110}-oriented, needle-like grains along the 〈111〉 directions with 70° branching and 110° branching, respectively. The length of the transition region in front of the silicide-mediated lateral crystallization was about 5 μm; thin-film transistors should not be located here because of poor microstructure. © 2004 The Electrochemical Society. All rights reserved.

Crystallization of amorphous Si films by pulsed laser annealing and their structural characteristics

Nanocrystalline silicon (nc-Si) films were prepared by pulsed laser annealed crystallization of amorphous silicon (α-Si) films on SiO2-coated quartz or glass substrates. The effect of laser energy density on structural characteristics of nc-Si films was investigated. The Ni-induced crystallization of the α-Si films was also discussed. The surface morphology and microstructure of these films were characterized by scanning electron microscopy, high-resolution electron microscopy, atomic force microscopy and Raman scattering spectroscopy. The results show that not only can the α-Si films be crystallized by the laser annealing technique, but also the size of Si nanocrystallites can be controlled by varying the laser energy density. Their average size is about 4–6 nm. We present a surface tension and interface strain model used for describing the laser annealed crystallization of the α-Si films. The doping of Ni atoms may effectively reduce the threshold value of laser energy density to crystallize the α-Si films, and the flocculent-like Si nanostructures could be formed by Ni-induced crystallization of the α-Si films.

Alternating magnetic field crystallization of amorphous Si films

We investigate the solid phase crystallization of amorphous Si films on glass substrates under alternating magnetic field induction. The kinetics of crystallization are found to be greatly enhanced by alternating magnetic field. While complete crystallization takes heat treatment of more than 14 hours at 570 °C, it can be reduced by applying the megnetic field to 20 minutes. It is assumed that the enhancement of crystallization is associated with an electromotive force voltage generated by alternating magnetic field. This electric field applied in the amorphous Si may possibly be the reason for acceleration of the atomic mobility of crystallization through the modification of atomic potentials

Crystallization of Amorphous Silicon Thin Films Using a Viscous Nickel Solution

A viscous Ni solution was applied on amorphous Si films and its effect on the crystallization of amorphous Si films was investigated. A viscous Ni solution was prepared by dissolving in 1 N HCl and mixing it with propylene glycol. and Ni was uniformly deposited by spin coating and drying the viscous metal solution, and it enhanced the crystallization at lower temperature overcoming the nonuniform coating of diluted acid metal solution. The a-Si films deposited by low pressure chemical vapor deposition with were fully crystallized in 10 h at 500°C by furnace annealing and in 8 h at 480°C by microwave annealing. The enhanced crystallization was due to the mediation by The surface roughness of the crystallized Si films using the Ni solution was smoother than that of the crystallized Si films with Ni metal layer. © 2001 The Electrochemical Society. All rights reserved.

Surface melt dynamics and super lateral growth regime in long pulse duration excimer laser crystallization of amorphous Si films

In this work, the excimer laser induced crystallization of a-Si films on SiO 2 was investigated, using a long pulse duration (200 ns) XeCl source. The microstructural analysis of the laser irradiated area, for incident energy densities comprised between the surface and full melting thresholds of the a-Si layer, respectively, was performed by scanning electron microscopy. A numerical simulation of the surface melt dynamics was also presented and compared to the experimental observations.

Crystallization of amorphous Si films for thin film solar cells

Amorphous Si films prepared by plasma-enhanced chemical vapor deposition (PECVD) have been fully crystallized by pulsed Nd-YAG laser excitation at wavelengths of 1064 and 532 nm. Crystallite quality was observed by Raman spectroscopy showing a line width of ∼5 cm −1 at 520 cm −1. Transmission electron microscopy (TEM) micrographs show crystallite sizes of several hundred nm and crystalline reflection peaks in X-ray diffraction (XRD) are observed. The quality and size of the crystallites prepared at a wavelength of 1064 nm improved with increasing laser energy density and are most sensitive to the energy density near the threshold energy for crystallization. The optimum laser energy densities are sensitive to the film thickness due to interference effects. A comparison of crystallization at wavelengths of 1064 and 532 nm shows no difference in the crystallite quality, but at 532 nm smoother surfaces are obtained. The laser energies for crystallization at 1064 nm are higher but not as much as expected by comparison of the absorption coefficients at 1064 and 532 nm.

The effect of surface nucleation on the evolution of crystalline microstructure during solid phase crystallization of amorphous Si films on SiO2

The effect of surface nucleation on the evolution of crystalline microstructure during the solid phase crystallization (SPC) of an amorphous Si (a-Si) film, deposited by low pressure chemical vapor deposition (LPCVD) on SiO2, has been investigated. The surface nucleation phenomenon was observed by suppressing the interface (a-Si/SiO2) nucleation by the incorporation of oxygen atoms during the initial deposition period of a-Si. It was found that the surface-nucleated polycrystalline Si (poly-Si) had equiaxial grains with the size of about 3–5 μm, while interface-nucleated one had elliptical grains with the size of about 0.3–1 μm.