The Mechanism of Excimer Laser-Induced Amorphization of Ultra-Thin Si Films

1993 ◽  
Vol 321 ◽  
Author(s):  
T. Eiumchotchawalit ◽  
James S. Im
Keyword(s):  
Energy Density ◽  
Excimer Laser ◽  
Supercooled Liquid ◽  
Transformation Mechanism ◽  
Quenching Rate ◽  
Tem Analysis ◽  
Si Substrates ◽  
Complete Melting ◽  
Small Crystals ◽  
Si Films

ABSTRACTTo better understand the involved phase transformation Mechanism, we are studying the excimer laser-induced amorphization (ELA) of ultra-thin Si films on oxidized Si substrates. In this paper, we show that the onset of amorphization of hydrogen-free Si films on SiO2 substrates upon increases in the energy density is associated with the onset of complete melting of the film. Once complete melting occurs, further increases in the incident energy density and/or increases in the substrate temperature can lead to incomplete amorphization of the film. Planar view TEM analysis of nearly-amorphized Si films reveals a heterogeneous microstructure, which consists of a mixture of densely dispersed amorphous-like annular regions (∼20 to 40 μm−2), embedded within and typically separated by a region containing finegrained small crystals. Such a cellular microstructure strongly suggests that amorphization occurred not via a homogeneous but via a heterogeneous transformation. In particular, the microstructure paints a scenario in which amorphization proceeded via nucleation of solids, which is then followed by interfacial amorphization. The experimental results unambiguously reveal (1) that the previously proposed criteria of the melt duration and the vertical temperature gradient are irrelevant in determining amorphization of supercooled liquid Si films and (2) that the quenching rate, not surprisingly, is the important parameter.

Grain Boundary Location-Controlled Polt-Si Films for Tft Devices Obtained Via Novel Excimer Laser Process

1994 ◽  
Vol 358 ◽  
Author(s):  
H. J. Kim ◽  
James S. Im
Keyword(s):  
Grain Boundary ◽  
Excimer Laser ◽  
Crystallization Process ◽  
Critical Distance ◽  
Capping Layer ◽  
Complete Melting ◽  
Boundary Location ◽  
Si Films ◽  
Active Channel ◽  
Induced Crystallization

ABSTRACTBased on a previously acquired physical understanding of the excimer-laser-induced crystallization process, we have developed a new crystallization technique that produces controlled microstructures and possesses a wide processing window. A patterned oxide capping layer was used as an antireflective coating to induce complete melting of an Si film under an SiO2 pattern, and partial melting of the Si film in the areas not under the capping layer—allowing controlled super lateral growth to proceed from the incompletely melted portion of the film to the completely melted portion. For the simple stripes used in this investigation, when the width of the completely molten region is less than a critical distance (above which nucleation of solids occurs in the middle of the completely melted regions), the resulting microstructure has large and elongated grains with one precisely located grain boundary running parallel to the stripe In the middle of the oxide capped region.Arrangement of TFT devices on the resulting Grain boundary Location-Controlled (GLC) Si films with one (or zero) grain boundaries located perpendicular to the flow of electrons within the active channel portion of the TFT devices is illustrated. Such devices are expected to possess performance and uniformity characteristics that are superior to currently available poly-Si TFT devices.

Excimer Laser Induced Crystallization of Amorphous Silicon-Germanium Films

1993 ◽  
Vol 321 ◽  
Author(s):  
A. Slaoui ◽  
C. Deng ◽  
S. Talwar ◽  
J. K. Kramer ◽  
B. Prevot ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Excimer Laser ◽  
Silicon Germanium ◽  
Laser Energy ◽  
Electron Gun ◽  
Laser Crystallization ◽  
Time Resolved ◽  
Si Substrates ◽  
Si Films ◽  
Amorphous Silicon Germanium

ABSTRACTApplication of excimer laser crystallization of Amorphous silicon (a-Si) has introduced a new, interesting potential technology for the fabrication of polycrystalline (poly-Si) thin film transistors. We are currently studying polycrystalline Si1−xGex thin films in order to determine whether this material can lead to improved electrical properties or to better processing requirements when compared with polycrystalline Si films. In this work we analyze by RBS, TEM, Raman spectroscopy and surface reflectance, the structure of thin Amorphous Si1−xGex films after irradiation with a XeCl excimer laser. The Amorphous SiGe films were prepared by evaporation of Si and Ge onto oxidized Si substrates using an electron gun in vaccum. The effects of laser energy fluence during irradiation are investigated. The Amorphous to crystalline transition is followed by in-situ measurement of time-resolved reflectivity.

Excimer Laser Annealed Poly-Si TFT Technologies

1995 ◽  
Vol 377 ◽  
Author(s):  
Fujio Okumura ◽  
Kenji Sera ◽  
Hiroshi Tanabe ◽  
Katsuhisa Yuda ◽  
Hiroshi Okumura
Keyword(s):  
Energy Density ◽  
Leakage Current ◽  
Excimer Laser ◽  
Laser Annealing ◽  
Laser Energy ◽  
Gate Insulator ◽  
Excimer Laser Annealing ◽  
Threshold Voltage Shift ◽  
Si Films ◽  
Current Reduction

ABSTRACTThis paper describes the excimer laser annealed (ELA) poly-Si TFT technologies in terms of excimer laser annealing of Si films, the leakage current, and the TFT stability. A laser energy density and a shot dependencies of TFT characteristics was analyzed by TEM, SEM, and Raman. The mobility increases with increasing not only the energy density but also the shot density. The mobility increase with the energy density is due to the grain size enlargement. On the other hand, the mobility increase up to 10 to 20 shots is due to a decrease of defects, including small grains, grain boundaries and defects inside grains. The contribution of grain-growth is small. The ELA TFT has a micro-offset structure to reduce the leakage current. Moreover, we have proposed a dynamic leakage current reduction structure. The combination of these technologies provides a sufficiently small leakage current for AMLCDs. The stability of the gate insulator was analyzed. The TFT shows negative threshold voltage shift under gate bias stress. This is due to water penetration and the subsequent field activated chemical reaction in the gate insulator. The dissociation of Si-OH bonds with hydrogen-bonded water was a fundamental contributor. The shift was suppressed sufficiently by hydrogen passivation. Obtained ELA TFTs;s have mobilities of over 100 cm2/Vsec, threshold voltages of less than 3 V, effective leakage currents of less than 10−13 A, and are stable more than 10 years.

Modeling Analysis of Excimer Laser Crystallization of a-Si Films with Nanosecond Temperature Response

2006 ◽  
Vol 505-507 ◽  
pp. 283-288 ◽  
Author(s):  
Chien Hung Chang ◽  
Long Sun Chao
Keyword(s):  
Melting Point ◽  
Partial Melting ◽  
Latent Heat ◽  
Excimer Laser ◽  
Maximum Temperature ◽  
Complete Melting ◽  
Melting Regime ◽  
Surface Reflectivity ◽  
Si Films ◽  
Temperature Responses

In the fabrication of a poly-Si film, an a-Si thin layer on glass substrate is melted by the irradiation of an excimer laser with the duration of nanosecond scale, and then is cooled down to form the poly-Si one. For analyzing the fabricating process, an efficient two-dimensional numerical model has been developed in this work, based on the finite difference method and the specific heat/enthalpy method used to handle the release of latent heat. The model can simulate the heat transfer, melt and solidification behavors of a-Si films subjected to the laser irradiation. Numerical analysis was performed by solving the heat flow equation which incorporates the material properties of temperature dependence, the surface reflectivity of silicon film, the variation of the incident power density with time and heat lose by the radiation and convection from the film surfaces into the surroundings. From the analysis of temperature responses for different laser intensities, the thresholds corresponding to the surface and full melting of the Si film can be found. The temperature responses are essentially different in the partial-melting and the complete-melting regimes. The Ft (surface melting threshold) and Fc (full-melt threshold) obtained from the simulation results of the proposed model in this study agree fairly well with those from the experimental data reported in the literature. In the partial-melting regime, the maximum temperature is close to the melting point of amorphous Si, since it is the point where solid a-Si is transformed into liquid state and the high latent heat can absorb extra energy to keep the temperature at the melting point. The fluence larger than Fc is the complete-melting regime, the maximum temperature increases with fluence. It is also found that the variation of the surface reflectivity gives a good way to observe the phase change and the melting duration. When the a-Si melts, the reflectivity rapidly goes up to a steady value which is consistent with the reflectivity of liquid silicon, and stays there until the melt silicon begins to solidify. As the irradiation energy of laser increases, the melting duration in the silicon layer is prolonged.

Electron Energy Analysis of Germanium and Silica Layers on Silicon Substrates

1975 ◽  
Vol 33 ◽  
pp. 96-97
Author(s):  
R. W. Ditchfield ◽  
A. G. Cullis
Keyword(s):  
Epitaxial Growth ◽  
Electron Energy ◽  
Silicon Substrates ◽  
Secondary Phases ◽  
Si Substrates ◽  
Transmission Electron ◽  
Layer Structures ◽  
Si Films ◽  
Electron Energy Loss ◽  
Growth Centres

An energy analyzing transmission electron microscope of the Möllenstedt type was used to measure the electron energy loss spectra given by various layer structures to a spatial resolution of 100Å. The technique is an important, method of microanalysis and has been used to identify secondary phases in alloys and impurity particles incorporated into epitaxial Si films.Layers Formed by the Epitaxial Growth of Ge on Si Substrates Following studies of the epitaxial growth of Ge on (111) Si substrates by vacuum evaporation, it was important to investigate the possible mixing of these two elements in the grown layers. These layers consisted of separate growth centres which were often triangular and oriented in the same sense, as shown in Fig. 1.

Formation of Large, Orientation-Controlled, Nearly Single Crystalline Si Thin Films on SiO2 Using Contact Printing of Rolled and Annealed Nickel Tapes

2003 ◽  
Vol 762 ◽  
Author(s):  
Hwang Huh ◽  
Jung H. Shin
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
High Resolution ◽  
Amorphous Silicon ◽  
Tem Analysis ◽  
Contact Printing ◽  
Single Crystalline ◽  
High Resolution Tem ◽  
Lateral Crystallization ◽  
Si Films

AbstractAmorphous silicon (a-Si) films prepared on oxidized silicon wafer were crystallized to a highly textured form using contact printing of rolled and annealed nickel tapes. Crystallization was achieved by first annealing the a-Si film in contact with patterned Ni tape at 600°C for 20 min in a flowing forming gas (90 % N2, 10 % H2) environment, then removing the Ni tape and further annealing the a-Si film in vacuum for2hrsat600°C. An array of crystalline regions with diameters of up to 20 μm could be formed. Electron microscopy indicates that the regions are essentially single-crystalline except for the presence of twins and/or type A-B formations, and that all regions have the same orientation in all 3 directions even when separated by more than hundreds of microns. High resolution TEM analysis shows that formation of such orientation-controlled, nearly single crystalline regions is due to formation of nearly single crystalline NiSi2 under the point of contact, which then acts as the template for silicide-induced lateral crystallization. Furthermore, the orientation relationship between Si grains and Ni tape is observed to be Si (110) || Ni (001)

Rapid Epitaxial Growth of Si and SiGe Mono-Crystalline Films on Silicon-on-Glass Substrates by Reactive CVD Using SiH4, GeH4, and F2

2012 ◽  
Vol 1426 ◽  
pp. 331-337
Author(s):  
Hiroshi Noge ◽  
Akira Okada ◽  
Ta-Ko Chuang ◽  
J. Greg Couillard ◽  
Michio Kondo
Keyword(s):  
Epitaxial Growth ◽  
Heating Temperature ◽  
Exothermic Reaction ◽  
Epitaxial Films ◽  
Si Substrates ◽  
Glass Substrates ◽  
Good Crystallinity ◽  
Crystalline Films ◽  
Si Films ◽  
First Time

ABSTRACTWe have succeeded in the rapid epitaxial growth of Si, Ge, and SiGe films on Si substrates below 670 ºC by reactive CVD utilizing the spontaneous exothermic reaction between SiH4, GeH4, and F2. Mono-crystalline SiGe epitaxial films with Ge composition ranging from 0.1 to 1.0 have been successfully grown by reactive CVD for the first time.This technique has also been successfully applied to the growth of these films on silicon-on-glass substrates by a 20 - 50 ºC increase of the heating temperature. Over 10 μm thick epitaxial films at 3 nm/s growth rate are obtained. The etch pit density of the 5.2 μm-thick Si0.5Ge0.5 film is as low as 5 x 106 cm-2 on top. Mobilities of the undoped SiGe and Si films are 180 to 550 cm2/Vs, confirming the good crystallinity of the epitaxial films.

Epitaxial Growth Following Crystal Nucleation in Laser-Quenched Si Films on SiO2

2015 ◽  
Vol 1770 ◽  
pp. 67-72
Author(s):  
Vernon K. Wong ◽  
A. M. Chitu ◽  
A. B. Limanov ◽  
James S. Im
Keyword(s):  
Epitaxial Growth ◽  
Growth Model ◽  
Crystal Nucleation ◽  
Key Factors ◽  
Complete Melting ◽  
Melting Regime ◽  
Direct Growth ◽  
Crystal Core ◽  
Excimer Laser Irradiation ◽  
Si Films

ABSTRACTWe have investigated the solidified microstructure of nucleation-generated grains obtained via complete melting of Si films on SiO2 at high nucleation temperatures. This was achieved using a high-temperature-capable hot stage in conjunction with excimer laser irradiation. As predicted by the direct-growth model that considers (1) the evolution in the temperature of the solidifying interface and (2) the subsequent modes of growth (consisting of amorphous, defective, and epitaxial) as key factors, we were able to observe the appearance of “normal” grains that possess a single-crystal core area. These grains, which are in contrast to previously reported flower-shaped grains that fully make up the microstructure of the solidified films obtained via irradiation at lower preheating temperatures (and amongst which these “normal” grains emerge), indicate that epitaxial growth of nucleated crystals must have taken place within the grains. We discuss the implications of our findings regarding (1) the validity of the direct-growth model, (2) the nature of the heterogeneous nucleation mechanism, and (3) the alternative explanations and assumptions that have been previously employed in order to explain the microstructure of Si films obtained via nucleation and growth within the complete melting regime.

Role of grain boundaries in the epitaxial realignment of undoped and As-doped polycrystalline silicon films

1993 ◽  
Vol 8 (10) ◽  
pp. 2608-2612 ◽  
Author(s):  
C. Spinella ◽  
F. Benyaïch ◽  
A. Cacciato ◽  
E. Rimini ◽  
G. Fallico ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Grain Structure ◽  
Native Oxide ◽  
Thermally Induced ◽  
Si Substrates ◽  
As Doping ◽  
Fine Grain ◽  
Si Films ◽  
Polycrystalline Silicon Films ◽  
Reduced Density

The early stages of the thermally induced epitaxial realignment of undoped and As-doped polycrystalline Si films deposited onto crystalline Si substrates were monitored by transmission electron microscopy. Under the effect of the heat treatment, the native oxide film at the poly-Si/c-Si interface begins to agglomerate into spherical beads. The grain boundary terminations at the interface are the preferred sites for the triggering of the realignment transformation which starts by the formation of epitaxial protuberances at these sites. This feature, in conjunction with the microstructure of the films during the first instants of the heat treatment, explains the occurrence of two different realignment modes. In undoped films the epitaxial protuberances, due to the fine grain structure, are closely distributed and grow together forming a rough interface moving toward the film's surface. For As-doped films, the larger grain size leaves a reduced density of realignment sites. Due to As doping some of these sites grow fast and form epitaxial columns that further grow laterally at the expense of the surrounding polycrystalline grains.

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