Increased doping depth of Al in wet-chemical laser doping of 4H-SiC by expanding laser pulse

Laser doping of silicon with the help of precursors is well established in photovoltaics. Upon illumination with the constant or pulsed laser beam, the silicon melts and doping atoms from the doping precursor diffuse into the melted silicon. With the proper laser parameters, after resolidification, the silicon is doped without any lattice defects. Depending on laser energy and on the kind of precursor, the precursor either melts or evaporates during the laser process. For high enough laser energies, even parts of the silicon’s surface evaporate. Here, we present a unified model and simulation program, which considers all these cases. We exemplify our model with experiments and simulations of laser doping from a boron oxide precursor layer. In contrast to previous models, we are able to predict not only the width and depth of the patterns on the deformed silicon surface but also the doping profiles over a wide range of laser energies. In addition, we also show that the diffusion of the boron atoms in the molten Si is boosted by a thermally induced convection in the silicon melt: the Gaussian intensity distribution of the laser beam increases the temperature-gradient-induced surface tension gradient, causing the molten Si to circulate by Marangoni convection. Laser pulse energy densities above H > 2.8 J/cm2 lead not only to evaporation of the precursor, but also to a partial evaporation of the molten silicon. Without considering the evaporation of Si, it is not possible to correctly predict the doping profiles for high laser energies. About 50% of the evaporated materials recondense and resolidify on the wafer surface. The recondensed material from each laser pulse forms a dopant source for the subsequent laser pulses.

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Increasing Laser-Doping Depth of Al in 4H-SiC by Using Expanded-Pulse Excimer Laser

Materials Science Forum ◽

10.4028/www.scientific.net/msf.963.412 ◽

2019 ◽

Vol 963 ◽

pp. 412-415

Author(s):

Akihiro Ikeda ◽

Takahi Shimokawa ◽

Hiroshi Ikenoue ◽

Tanemasa Asano

Keyword(s):

Laser Pulse ◽

Excimer Laser ◽

Pulse Width ◽

Optical Pulse ◽

Laser Intensity ◽

Al Doping ◽

Laser Doping ◽

Pulse Excimer Laser ◽

Peak Intensity

Al doping into 4H-SiC performed by irradiating pulse-width-expanded excimer laser to an Al film deposited on the 4H-SiC surface is investigated. An optical pulse stretcher was constructed to produce the laser pulse whose peak intensity was reduced as half as that of the original pulse and pulse width was expanded from 55 ns to 100 ns. The irradiation of the expanded pulses is found to reduce the ablation of the materials from the surface and enable irradiation of multiple shots. As the result, doping depth of Al is significantly increased. The multiple shots of the expanded pulses is also fund to decrease the sensitivity to spatial non-uniformity of laser intensity and increase the uniformity of doped region.

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Structures of chemically stabilized ceramics

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100150459 ◽

1993 ◽

Vol 51 ◽

pp. 924-925

Author(s):

Pratibha L. Gai ◽

M. A. Saltzberg ◽

L.G. Hanna ◽

S.C. Winchester

Keyword(s):

High Temperature ◽

Calcium Nitrate ◽

Nitrate Hexahydrate ◽

Chemical Route ◽

Cubic Form ◽

Tetragonal Form ◽

Wet Chemical ◽

Wet Chemical Route ◽

Final Composition ◽

Aluminium Nitrate Nonahydrate

Silica based ceramics are some of the most fundamental in crystal chemistry. The cristobalite form of silica has two modifications, α (low temperature, tetragonal form) and β (high temperature, cubic form). This paper describes our structural studies of unusual chemically stabilized cristobalite (CSC) material, a room temperature silica-based ceramic containing small amounts of dopants, prepared by a wet chemical route. It displays many of the structural charatcteristics of the high temperature β-cristobalite (∼270°C), but does not undergo phase inversion to α-cristobalite upon cooling. The Structure of α-cristobalite is well established, but that of β is not yet fully understood.Compositions with varying Ca/Al ratio and substitutions in cristobalite were prepared in the series, CaO:Al2O3:SiO2 : 3-x: x : 40, with x= 0-3. For CSC, a clear sol was prepared from Du Pont colloidal silica, Ludox AS-40®, aluminium nitrate nonahydrate, and calcium nitrate hexahydrate in proportions to form a final composition 1:2:40 composition.

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