Effect of film thickness and laser energy density on the microstructure of a-GaAs films after excimer laser crystallization

2007 ◽  
Vol 102 (1) ◽  
pp. 013519 ◽  
Author(s):  
Daniel Pirzada ◽  
Pankaj Trivedi ◽  
David Field ◽  
Gary J. Cheng
Keyword(s):  
Energy Density ◽  
Film Thickness ◽  
Excimer Laser ◽  
Laser Energy ◽  
Laser Energy Density ◽  
Laser Crystallization ◽  
Gaas Films ◽  
Excimer Laser Crystallization

Effect of Film Thickness and Laser Energy Density on the Structural Characteristics of Laser-Annealed Polycrystalline Gallium Arsenide Films

2006 ◽  
Author(s):  
Gary J. Cheng ◽  
Daniel Pirzada ◽  
Pankaj Trivedi ◽  
David Field
Keyword(s):  
Energy Density ◽  
Film Thickness ◽  
Electron Backscatter Diffraction ◽  
Laser Energy ◽  
Structural Characteristics ◽  
Grain Morphology ◽  
Fiber Texture ◽  
Laser Energy Density ◽  
Laser Crystallization ◽  
Sio2 Substrate

Scanning electron microscopy and high-resolution electron backscatter diffraction (EBSD) have been used to study the texture and microstructure evolution during the crystallization of initially amorphous GaAs thin films. A KrF excimer laser, with 30 ns pulse duration was used for crystallization of a-GaAs grown on SiO2 Substrate using molecular beam epitaxy (MBE) technique. The effect of laser energy density and film thickness on grain morphology has been studied. The integrated information on grain size distribution, preferred orientation, and nature of grain boundaries provides useful information to postulate the mechanism of grain-growth and likely role of different contributing parameters in the evolution of final texture under the highly transient processing conditions prevailing during the short laser irradiation. The results show that for thick films the laser crystallization results in a weak <111> fiber texture. While for a thinner films the grains have a strong <001> texture that strengthens with a decrease in film thickness and increase in laser energy density.

The Effect of Film Thickness and Pulse Duration Variation in Excimer Laser Crystallization of Thin Si Films

1996 ◽  
Vol 452 ◽  
Author(s):  
J. P. Leonard ◽  
M. A. Bessette ◽  
V. V. Gupta ◽  
James S. Im
Keyword(s):  
Energy Density ◽  
Film Thickness ◽  
Partial Melting ◽  
Pulse Duration ◽  
Excimer Laser ◽  
Silicon Film ◽  
Silicon Films ◽  
Laser Crystallization ◽  
Crystal Silicon ◽  
Excimer Laser Crystallization

AbstractRecognizing that the processing window in conventional excimer laser crystallization corresponds mainly to the partial melting regime, and that this can be properly simulated using a one-dimensional model, we investigate numerically the melting and solidification of thin silicon films on SiO2. Here a portion of the silicon film is melted and subsequent vertical solidification is initiated from the lower interface bounding the unmelted region. Upper and lower energy density limits for this regime are calculated for crystal silicon films of thickness 10 to 300 nm, and for pulse duration ranging from 10 to 200 ns. These calculations show that increasing pulse duration requires proportionally more incident energy density to partially melt the film, while decreasing film thickness reduces the range of energy densities over which partial melting can occur. The results are explained in terms of characteristic thermal diffusion distances and the enthalpy change associated with melting. In view of the results we discuss optimization of the conventional excimer laser crystallization and the avoidance of complete melting during the process.

Considerations for Large Area Fabrication of Integrated a-Si and Poly-Si TFTs

1994 ◽  
Vol 336 ◽  
Author(s):  
P. Mei ◽  
G. B. Anderson ◽  
J. B. Boyce ◽  
D. K. Fork ◽  
M. Hack ◽  
...  
Keyword(s):  
Grain Size ◽  
Energy Density ◽  
Laser Energy ◽  
Gate Insulator ◽  
Laser Energy Density ◽  
Laser Crystallization ◽  
Large Area ◽  
Low Leakage ◽  
Threshold Voltages ◽  
Excellent Method

ABSTRACTThe combination of a-Si low leakage pixel TFTs with poly-Si TFTs in peripheral circuits provides an excellent method for reducing the number of external connections to large-area imaging arrays and displays. To integrate the fabrication of the peripheral poly-Si TFTs with the a-Si pixel TFTs, we have developed a three-step laser process which enables selective crystallization of PECVD a-Si:H. X-ray diffraction and transmission electron microscopy show that the polycrystalline grains formed with this three-step process are similar to those crystallized by a conventional one step laser crystallization of unhydrogenated amorphous silicon. The grain size increases with increasing laser energy density up to a peak value of a few Microns. The grain size decreases with further increases in laser energy density. The transistor field effect mobility is correlated with the grain size, increasing gradually with laser energy density until reaching its maximum value. Thereafter, the transistors suffer from leakage through the gate insulators. A dual dielectric gate insulator has been developed for these bottom-gate thin film transistors to provide the correct threshold voltages for both a-Si and poly-Si TFTs.

Excimer Laser Crystallized Amorphous Silicon Films: Effects of Shot Density and Substrate Temperature

1991 ◽  
Vol 219 ◽  
Author(s):  
R. I. Johnson ◽  
G. B. Anderson ◽  
S. E. Ready ◽  
J. B. Boyce
Keyword(s):  
Energy Density ◽  
Substrate Temperature ◽  
Amorphous Silicon ◽  
Laser Energy ◽  
Silicon Films ◽  
Laser Energy Density ◽  
Laser Crystallization ◽  
Average Grain Size ◽  
Substrate Temperatures

ABSTRACTLaser crystallization of a-Si thin films has been shown to produce materials with enhanced electrical properties and devices that are faster and capable of carrying higher currents. The quality of these polycrystalline films depends on a number of parameters such as laser energy density, shot density, substrate temperature, and the quality of the starting material. We find that the average grain size and transport properties of laser crystallized amorphous silicon films increase substantially with laser energy density, increase only slightly with laser shot density, and are unaffected by substrate temperatures of up to 400°C. The best films are those processed in vacuum but films of fair quality can also be obtained in air and nitrogen atmospheres.

A Novel Two-Pass Excimer Laser Crystallization Process to Obtain Homogeneous Large Grain Polysilicon

1999 ◽  
Vol 558 ◽  
Author(s):  
L. Mariucci ◽  
R. Carluccio ◽  
A. Pecora ◽  
V. Foglietti ◽  
G. Fortunato ◽  
...  
Keyword(s):  
Excimer Laser ◽  
Crystallization Process ◽  
Laser Energy ◽  
Spatial Modulation ◽  
Lateral Growth ◽  
Laser Crystallization ◽  
First Pass ◽  
Wide Energy ◽  
Excimer Laser Crystallization ◽  
Polysilicon Tft

ABSTRACTNew approach to control the lateral growth mechanism through the opportune spatial modulation of the absorbed laser energy and with a two-pass excimer laser crystallization process is presented. In the first pass, spatial modulation of the light intensity has been obtained by irradiating the sample through a patterned mask in contact with the sample. Lateral growth is triggered when the irradiated regions are fully melted and a lateral extension of the grains in excess to 1 μm has been observed for samples irradiated at RT. In order to homogeneously crystallize the sample, the film can be re-irradiated (second pass) without the mask. By using opportune energy densities it can be induced a complete melting of the residual a-Si regions (masked areas during the first pass), while partially melting the polysilicon regions (unmasked areas during the first pass). Different mask geometries have been investigated and for optimized conditions, the sample area can be fully covered with laterally grown grains. The proposed novel technique can be rather attractive for polysilicon TFT fabrication, being characterized by only a two laser-shot process and wide energy density windows.

Excimer Laser Crystallization of Nanocrystalline Silicon Thin Films

2015 ◽  
Vol 1120-1121 ◽  
pp. 361-368
Author(s):  
Li Jie Deng ◽  
Wei He ◽  
Zheng Ping Li
Keyword(s):  
Thin Films ◽  
Energy Density ◽  
Excimer Laser ◽  
Silicon Film ◽  
Threshold Energy ◽  
Nanocrystalline Silicon ◽  
Lateral Growth ◽  
Laser Crystallization ◽  
Silicon Thin Films ◽  
Excimer Laser Crystallization

Nanocrystalline silicon (nc-Si) thin film on glass substrate is subjected to excimer laser crystallized by varying the laser energy density in the range of 50~600 mJ/cm2. The effect of excimer laser crystallization on the structure of silicon film is investigated using Raman spectroscopy, X-ray diffraction, atomic force microscopy and scanning electron microscopy. The results show that polycrystalline silicon thin films can be obtained by excimer laser crystallization of nc-Si films. A laser threshold energy density of 200 mJ/cm2 is estimated from the change of crystalline fraction and surface roughness of the treated films. The growth of grain is observed and the crystallization mechanism is discussed based on the super lateral growth model. The nanocrystalline silicon grains in the films act as seeds for lateral growth to large grains.

Fast-Pulse Excimer-Laser-Induced Processes in a-Si:H

1989 ◽  
Vol 164 ◽  
Author(s):  
K. Winer ◽  
R.Z. Bachrach ◽  
R.I. Johnson ◽  
S.E. Ready ◽  
G.B. Anderson ◽  
...  
Keyword(s):  
Energy Density ◽  
Excimer Laser ◽  
Impurity Concentration ◽  
Laser Annealing ◽  
Laser Energy ◽  
Laser Energy Density ◽  
Excimer Laser Annealing ◽  
Near Surface ◽  
Pulse Excimer Laser ◽  
Fast Pulse

AbstractThe effects of fast-pulse excimer laser annealing of a-Si:H were investigated by measurements of electronic transport properties and impurity concentration depth profiles as a function of incident laser energy density. The dc dark conductivity of laser-annealed, highly-doped a-Si:H increases by a factor of ∼350 above a sharp laser energy density threshold whose magnitude increases with decreasing impurity concentration and which correlates with the onset of hydrogen evolution from and crystallization of the near-surface layer. The similarities between the preparation and properties of laser-crystallized a-Si:H and pc-Si:H are discussed.

Excimer Laser Induced Crystallization of Amorphous Silicon Near Threshold

1989 ◽  
Vol 157 ◽  
Author(s):  
R.Z. Bachrach ◽  
K. Winer ◽  
J.B. Boyce ◽  
F.A. Ponce ◽  
S.E. Ready ◽  
...  
Keyword(s):  
Energy Density ◽  
Laser Beam ◽  
Amorphous Silicon ◽  
Excimer Laser ◽  
Laser Energy ◽  
Laser Energy Density ◽  
Square Root ◽  
Threshold Behavior ◽  
Sharp Threshold ◽  
Induced Crystallization

ABSTRACTUsing a suitably homogenized excimer laser beam, we have shown that the threshold for crystallization of amorphous silicon is well defined and exhibits a square root dependence on the laser energy density above threshold. This sharp threshold behavior can be exploited in a number of ways.

Considerations for Large Area Fabrication Of Integrated a-Si and Poly-Si TFTs

1994 ◽  
Vol 345 ◽  
Author(s):  
P. Mei ◽  
G. B. Anderson ◽  
J. B. Boyce ◽  
D. K. Fork ◽  
M. Hack ◽  
...  
Keyword(s):  
Grain Size ◽  
Energy Density ◽  
Laser Energy ◽  
Gate Insulator ◽  
Laser Energy Density ◽  
Laser Crystallization ◽  
Large Area ◽  
Low Leakage ◽  
Threshold Voltages ◽  
Excellent Method

AbstractThe combination of a-Si low leakage pixel TFTs with poly-Si TFTs in peripheral circuits provides an excellent method for reducing the number of external connections to large-area imaging arrays and displays. To integrate the fabrication of the peripheral poly-Si TFTs with the a-Si pixel TFTs, we have developed a threestep laser process which enables selective crystallization of PECVD a-Si:H. X-ray diffraction and transmission electron microscopy show that the polycrystalline grains formed with this three-step process are similar to those crystallized by a conventional one step laser crystallization of unhydrogenated amorphous silicon. The grain size increases with increasing laser energy density up to a peak value of a few microns. The grain size decreases with further increases in laser energy density. The transistor field effect mobility is correlated with the grain size, increasing gradually with laser energy density until reaching its maximum value. Thereafter, the transistors suffer from leakage through the gate insulators. A dual dielectric gate insulator has been developed for these bottom-gate thin film transistors to provide the correct threshold voltages for both a-Si and poly-Si TFTs.

Effect of Excimer Laser Annealing on Optical Properties of GaN Films Deposited by R.F. Magnetron Sputtering

2001 ◽  
Vol 693 ◽  
Author(s):  
Man Young Sung ◽  
Woong-Je Sung ◽  
Yong-Il Lee ◽  
Chun-Il Park ◽  
Woo-Boem Choi ◽  
...  
Keyword(s):  
Thin Films ◽  
Energy Density ◽  
Magnetron Sputtering ◽  
Buffer Layer ◽  
Excimer Laser ◽  
Laser Annealing ◽  
Laser Energy ◽  
Laser Energy Density ◽  
Excimer Laser Annealing ◽  
Zno Buffer Layer

Abstract:GaN thin films on sapphire were grown by RF magnetron sputtering with ZnO buffer layer. The tremendous mismatch between the lattices of GaN and sapphire can be partly overcome by the use of thin buffer layer of ZnO. The dependence of GaN film quality on ZnO buffer layer was investigated by X-ray diffraction(XRD). The properties of the sputtered GaN are strongly dependent on ZnO buffer layer thickness. The optimum thickness of ZnO buffer layer is around 30nm. Using XRD analysis, we have found the optimal substrate temperature which can grow high quality GaN thin film. In addition, the effect of excimer laser annealing(ELA) on structural and electrical properties of GaN thin films was investigated. The surface roughness and images according to the laser energy density were investigated by atomic force microscopy(AFM) and it was confirmed that the crystallization was improved by increasing laser energy density.

Sign in / Sign up

Export Citation Format

Share Document