From: hackbard Date: Tue, 23 Nov 2010 16:16:55 +0000 (+0100) Subject: started fabrication chapter X-Git-Url: https://hackdaworld.org/gitweb/?a=commitdiff_plain;h=58d21ebff9e5d2deed6a8958c5db9a416329a2fb;p=lectures%2Flatex.git started fabrication chapter --- diff --git a/posic/thesis/sic.tex b/posic/thesis/sic.tex index e9b44e4..c729f24 100644 --- a/posic/thesis/sic.tex +++ b/posic/thesis/sic.tex @@ -96,16 +96,42 @@ Thus the cubic phase is most effective for highly efficient high-performance ele \caption{3C-SiC unit cell. Yellow and grey spheres correpsond to Si and C atoms respectively. Covalent bonds are illustrated by blue lines.} \label{fig:sic:unit_cell} \end{figure} -The 3C-SiC unit cell is shown in Fig.~\ref{fig:sic:unit_cell}. +Its unit cell is shown in Fig.~\ref{fig:sic:unit_cell}. 3C-SiC grows in zincblende structure, i.e. it is composed of two fcc lattices, which are displaced by one quarter of the volume diagonal as in Si. However, in 3C-SiC, one of the fcc lattices is occupied by Si atoms while the other one is occupied by C atoms. -Its lattice constant of \unit[0.436]{nm} compared to \unit[0.543]{nm} from that of Si results in a lattice mismatch of almost \unit[20]{\%}, i.e. four lattice constants of Si match five SiC lattice constants. -Thus, the Si density of SiC is only slightly lower, i.e. \unit[97]{\%}, than that of Si. +Its lattice constant of \unit[0.436]{nm} compared to \unit[0.543]{nm} from that of Si results in a lattice mismatch of almost \unit[20]{\%}, i.e. four lattice constants of Si approximately match five SiC lattice constants. +Thus, the Si density of SiC is only slightly lower, i.e. \unit[97]{\%} of plain Si. \section{Fabrication of silicon carbide} -SiC usually manmade. -The unique properties driving its applications in the same time harden the fabrication of SiC ... +Although the constituents of SiC are abundant and the compound is chemically and thermally stable, large deposits of SiC have never been found. +Due to the rarity, SiC is typically man-made. +The development of several methods was necessary to synthetically produce SiC crystals matching the needs of a respective application. +The fact that natural SiC is almost only observed as individual presolar SiC stardust grains near craters of primitive meteorite impacts, already indicates the complexity involved in the synthesis process. + +The attractive properties and wide range of applications, however, have triggered extensive efforts to grow this material as a bulk crystal and as an epitaxial surface thin film. +In the following, the principal difficulties involved in the formation of crystalline SiC and the most recent achievements will be summarized. + +Though possible, melt growth processes \cite{nelson69} are complicated due to the small C solubility in Si at temperatures below \unit[2000]{$^{\circ}$C} and its small change with temperature \cite{scace59}. +High process temperatures are necessary and the evaporation of Si must be suppressed by a high-pressure inert atmosphere. +Crystals grown by this method are not adequate for practical applications with respect to their size as well as quality and purity. +The presented methods, thus, focus on vapor transport growth processes such as chemical vapor deposition (CVD) or molecular beam epitaxy (MBE) and the sublimation technique. + +\subsection{SiC bulk crystal growth} + +The industrial Acheson process \cite{acheson} is utilized to produce SiC on a large scale by thermal reaction of silicon dioxide (silica sand) and carbon. +Due to the insufficient and uncontrollable purity, material produced by this method, originally termed carborundum by Acheson, can hardly be used for device applications. +However, it is often used as an abrasive material and as seed crystals for subsequent vapor phase growth and sublimation processes. + +van Arkel (CVD) + +Lely (sublimation) + +modified Lely or modified sublimation + +though significant advances have been achieved a bunch of defects ... + +\subsection{SiC epitaxial thin film growth} \section{Ion beam synthesis of cubic silicon carbide}