martes, 17 de julio de 2018

reduccion carbotermica del sílice

  1 SiO2 + C reduccion carbotermica del sílice

Silicon carbide (SiC) is a very attractive material for the fabrication of microelectronic and optoelectronic devices due to its wide bandgap, high thermal conductivity, excellent thermal and chemical stability and its resistance to radiation damage and electrical breakdown [1]. SiC has over 170 different polytypes [2]. The most common forms are 4H, 6H, known as the hexagonal (α-SiC) types, and the cubic 3C-SiC type [2-5]. Among the various polytypes, the 3C-SiC variety possesses unique properties, including a high electron mobility up to 1000 cm2/Vs and a consequent high saturation drift velocity. 

1.1        критическая толщина

Es importante la obtención de filmes de SiC de alta calidad y sencillez de obtención, ya que se puede aplicar en Celdas solares, sensores y componentes electrónicos.
Una problemática diferente es la cuestión de la deposición de filmes delgados en sustratos apropiados de silicio, ya que habitualmente el error entre los parámetros de red del sustrato y de los Filmes de SiC supera el 15%, provocando tensiones tendientes a liberarse  mas alla del grueso critico del film como dislocaciones.  
Crystallographic defects give rise to residual stresses in the crystals. The stresses can occur through a variety of mechanisms in SiC crystals.
Se propone el uso de buffer layer de SiO2, térmicamente obtenido en la superficie del Silicio por anneado a 600 oC , lo que permitiría , al mismo tiempo , la reaccion entre Carbono y sílice , mientras que las tensiones residuales en el film serian menores, dado el menor desfase en los parámetros de red del SiO2 y el C.

1.2         2.2 El SiO2 obtenido por anneado de placas de Silicio.

ECS Journal of Solid State Science and Technology, 4 (8) N96-N98 (2015)
Structural Analyses of Thin SiO2 Films Formed by Thermal Oxidation of Atomically Flat Si Surface by Using Synchrotron Radiation X-Ray Characterization
Kohki Nagata, Atsushi Ogura, Ichiro Hirosawa, Tomoyuki Suwa, Akinobu Teramoto, Takeo Hattori, and Tadahiro Ohmid.

Thin SiO2 films were fabricated on the Si (001) substrate.
thermal oxidation was carried out in a pure oxygen atmosphere with three different temperatures. We prepared a SiO2 sample grown with an 800◦ C process for 82 min, with a 900◦ C process for 13 min and with an 1100◦ C process for 30 sec. These thicknesses of SiO2 films were approximately 7 nm.

Figure 3a shows the GIXRD profiles obtained for the SiO2 film formed in the highly pure oxygen atmosphere at 900◦ C. A sharp diffraction peak at 2θ = 17.6◦ was apparently observed with a broad amorphous peak. In addition, a weak diffraction peak at 2θ = 28.0◦ was also observed in single logarithmic plot of intensity which emphasize weak peak (Fig. 3b). The difference in the azimuthal angle between the two peaks was approximately 18◦ , which confirms that the peaks correspond to the (110) and (120) diffractions of the alpha-cristobalite. These results indicate that the thin SiO2 film has a partially crystalline structure with an amorphous component and that the crystalline structure maintained a preferential orientation. The alpha-cristobalite-like structure in bulk region of thick SiO2 film has also been reported in previous research.7 Cristobalite-like structure take over crystalline periodicity of crystalline Si after oxidation process. It was considered that homogeneous oxidation reaction should be essential to maintain the partially crystalline structure.
In addition, in-plane lattice constants estimated from diffraction angles indicated a = b = 5.7 Å. They were larger than those of conventional alpha-cristobalite,25 implying the crystalline-like structure in thin SiO2 film was distorted isotropically. These results indicated that an alpha-cristobalite-like structure was formed by reflecting the crystalline structure of the Si substrate.
La presencia de cristobalita deformada ha sido identificada en otros trabajos.
The atomic arrangement is essentially the same as that of the B-cristobalite structure of the cubic system, except that it is tetragonally deformed: the lattice is elongated along the c axis so as to fit the lateral lattice spacing to that of the Si substrate [7] and to keep the bond distance between the Si and 0 at about 1.6 A.

1993 J. Phys.: Condens. Matter 5 6525
X-ray diffraction evidence for epitaxial microcrystallinity in thermally oxidized Si02 thin films on the Si(OO1) surface.
Isao Takahashi, Takayoshi Shimura and Jimpei Harada
Department of Applied Physics, Nagoya University, Chiiusa-ku, Nagoya 46461, Japan

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