From 8a555497a121caff7bc77fffbeb52269e53c8868 Mon Sep 17 00:00:00 2001 From: hackbard Date: Tue, 8 Mar 2011 17:35:35 +0100 Subject: [PATCH] started ibs --- bibdb/bibdb.bib | 30 +++++++++++++++++++++++++++++- posic/thesis/sic.tex | 40 +++++++++++++++++++++++++--------------- 2 files changed, 54 insertions(+), 16 deletions(-) diff --git a/bibdb/bibdb.bib b/bibdb/bibdb.bib index b10d713..cb3ae4a 100644 --- a/bibdb/bibdb.bib +++ b/bibdb/bibdb.bib @@ -2597,7 +2597,9 @@ ENERGY", URL = "http://link.aip.org/link/?APL/62/3336/1", doi = "10.1063/1.109063", - notes = "interfacial energy of cubic sic and si", + notes = "interfacial energy of cubic sic and si, si self + interstitials necessary for precipitation, volume + decrease, high interface energy", } @Article{chaussende08, @@ -3924,3 +3926,29 @@ notes = "h incorporation on si surface, lower surface mobility", } + +@Article{newman85, + author = "Ronald C. Newman", + title = "Carbon in Crystalline Silicon", + journal = "MRS Online Proceedings Library", + volume = "59", + number = "", + pages = "403", + year = "1985", + doi = "10.1557/PROC-59-403", + URL = "http://dx.doi.org/10.1557/PROC-59-403", + eprint = "http://journals.cambridge.org/article_S194642740054367X", +} + +@Article{goesele85, + author = "U. Gösele", + title = "The Role of Carbon and Point Defects in Silicon", + journal = "MRS Online Proceedings Library", + volume = "59", + number = "", + pages = "419", + year = "1985", + doi = "10.1557/PROC-59-419", + URL = "http://dx.doi.org/10.1557/PROC-59-419", + eprint = "http://journals.cambridge.org/article_S1946427400543681", +} diff --git a/posic/thesis/sic.tex b/posic/thesis/sic.tex index 5961c39..8af85c0 100644 --- a/posic/thesis/sic.tex +++ b/posic/thesis/sic.tex @@ -115,8 +115,8 @@ In the following, the principal difficulties involved in the formation of crysta 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. -Excellent reviews of SiC formation have been published by Wesch \cite{wesch96} and Davis~et~al. \cite{davis91}. +The presented methods, thus, focus on vapor transport growth processes such as \ac{CVD} or \ac{MBE} and the sublimation technique. +Excellent reviews of the different SiC growth methods have been published by Wesch \cite{wesch96} and Davis~et~al. \cite{davis91}. \subsection{SiC bulk crystal growth} @@ -154,16 +154,16 @@ Further efforts have to be expended to find relations between the growth paramet \subsection{SiC epitaxial thin film growth} Crystalline SiC layers have been grown by a large number of techniques on the surfaces of different substrates. -Most of the crystal growth processes are based on chemical vapor deposition (CVD), solid-source molecular beam epitaxy (MBE) and gas-source MBE (GSMBE) on Si as well as SiC substrates. -In CVD as well as gas-source MBE, C and Si atoms are supplied by C containing gases like CH$_4$, C$_3$H$_8$, C$_2$H$_2$ or C$_2$H$_4$ and Si containing gases like SiH$_4$, Si$_2$H$_6$, SiH$_2$Cl$_2$, SiHCl$_3$ or SiCl$_4$ respectively. -In the case of solid-source MBE atoms are provided by electron beam evaporation of graphite and solid Si or thermal evaporation of fullerenes. -The following review will exclusively focus on CVD and MBE techniques. +Most of the crystal growth processes are based on \ac{CVD}, solid-source \ac{MBE} (SSMBE) and gas-source \ac{MBE} (GSMBE) on Si as well as SiC substrates. +In \ac{CVD} as well as GSMBE, C and Si atoms are supplied by C containing gases like CH$_4$, C$_3$H$_8$, C$_2$H$_2$ or C$_2$H$_4$ and Si containing gases like SiH$_4$, Si$_2$H$_6$, SiH$_2$Cl$_2$, SiHCl$_3$ or SiCl$_4$ respectively. +In the case of SSMBE atoms are provided by electron beam evaporation of graphite and solid Si or thermal evaporation of fullerenes. +The following review will exclusively focus on \ac{CVD} and \ac{MBE} techniques. The availability and reproducibility of Si substrates of controlled purity made it the first choice for SiC epitaxy. The heteroepitaxial growth of SiC on Si substrates has been stimulated for a long time due to the lack of suitable large substrates that could be adopted for homoepitaxial growth. Furthermore, heteroepitaxy on Si substrates enables the fabrication of the advantageous 3C polytype, which constitutes a metastable phase and, thus, can be grown as a bulk crystal only with small sizes of a few mm. The main difficulties in SiC heteroepitaxy on Si is due to the lattice mismatch of Si and SiC and the difference in the thermal expansion coefficient of \unit[8]{\%}. -Thus, in most of the applied CVD and MBE processes, the SiC layer formation process is split into two steps, the surface carbonization and the growth step, as proposed by Nishino~et~al. \cite{nishino83}. +Thus, in most of the applied \ac{CVD} and \ac{MBE} processes, the SiC layer formation process is split into two steps, the surface carbonization and the growth step, as proposed by Nishino~et~al. \cite{nishino83}. Cleaning of the substrate surface with HCl is required prior to carbonization. During carbonization the Si surface is chemically converted into a SiC film with a thickness of a few nm by exposing it to a flux of C atoms and concurrent heating up to temperatures about \unit[1400]{$^{\circ}$C}. In a next step, the epitaxial deposition of SiC is realized by an additional supply of Si atoms at similar temperatures. @@ -172,12 +172,12 @@ Next to surface morphology defects such as pits and islands, the main defects in APB defects, which constitute the primary residual defects in thick layers, are formed near surface terraces that differ in a single-atom-height step resulting in domains of SiC separated by a boundary, which consists of either Si-Si or C-C bonds due to missing or disturbed sublattice information \cite{desjardins96,kitabatake97}. However, the number of such defects can be reduced by off-axis growth on a Si \hkl(0 0 1) substrate miscut towards \hkl[1 1 0] by \unit[2]{$^{\circ}$}-\unit[4]{$^{\circ}$} \cite{shibahara86,powell87_2}. This results in the thermodynamically favored growth of a single phase due to the uni-directional contraction of Si-C-Si bond chains perpendicular to the terrace steps edges during carbonization and the fast growth parallel to the terrace edges during growth under Si rich conditions \cite{kitabatake97}. -By MBE, lower process temperatures than these typically employed in CVD have been realized \cite{hatayama95,henke95,fuyuki97,takaoka98}, which is essential for limiting thermal stresses and to avoid resulting substrate bending, a key issue in obtaining large area 3C-SiC surfaces. +By \ac{MBE}, lower process temperatures than these typically employed in \ac{CVD} have been realized \cite{hatayama95,henke95,fuyuki97,takaoka98}, which is essential for limiting thermal stresses and to avoid resulting substrate bending, a key issue in obtaining large area 3C-SiC surfaces. In summary, the almost universal use of Si has allowed significant progress in the understanding of heteroepitaxial growth of SiC on Si. However, mismatches in the thermal expansion coefficient and the lattice parameter cause a considerably high concentration of various defects, which is responsible for structural and electrical qualities that are not yet statisfactory. The alternative attempt to grow SiC on SiC substrates has shown to drastically reduce the concentration of defects in deposited layers. -By CVD, both, the 3C \cite{kong88,powell90} as well as the 6H \cite{kong88_2,powell90_2} polytype could be successfully grown. +By \ac{CVD}, both, the 3C \cite{kong88,powell90} as well as the 6H \cite{kong88_2,powell90_2} polytype could be successfully grown. In order to obtain the homoepitaxially grown 6H polytype, off-axis 6H-SiC wafers are required as a substrate \cite{kimoto93}. %In the so called step-controlled epitaxy, lateral growth proceeds from atomic steps without the necessity of preceding nucleation events. Investigations indicate that in the so-called step-controlled epitaxy, crystal growth proceeds through the adsorbtion of Si species at atomic steps and their carbonization by hydrocarbon molecules. @@ -190,7 +190,7 @@ Additionally, 6H-SiC was observed on clean substrates even for a tilt angle as l Thus, 3C nucleation is assumed as a result of migrating Si and C cointaining molecules interacting with surface disturbances by a yet unknown mechanism, in contrast to a model \cite{ueda90}, in which the competing 6H versus 3C growth depends on the density of surface steps. Combining the fact of a well defined 3C lateral growth direction, i.e. the tilt direction, and an intentionally induced dislocation enables the controlled growth of a 3C-SiC film mostly free of DPBs \cite{powell91}. -Lower growth temperatures, a clean growth ambient, in situ control of the growth process, layer-by-layer deposition and the possibility to achieve dopant profiles within atomic dimensions due to the reduced diffusion at low growth temperatures reveal MBE as a promising technique to produce SiC epitaxial layers. +Lower growth temperatures, a clean growth ambient, in situ control of the growth process, layer-by-layer deposition and the possibility to achieve dopant profiles within atomic dimensions due to the reduced diffusion at low growth temperatures reveal \ac{MBE} as a promising technique to produce SiC epitaxial layers. Using alternating supply of the gas beams Si$_2$H$_6$ and C$_2$H$_2$ in GSMBE, 3C-SiC epilayers were obtained on 6H-SiC substrates at temperatures between \unit[850]{$^{\circ}$C} and \unit[1000]{$^{\circ}$C} \cite{yoshinobu92}. On \hkl(000-1) substrates twinned \hkl(-1-1-1) oriented 3C-SiC domains are observed, which suggest a nucleation driven rather than step-flow growth mechanism. On \hkl(0-11-4) substrates, however, single crystalline \hkl(001) oriented 3C-SiC grows with the c axes of substrate and film being equal. @@ -204,20 +204,30 @@ To realize single monolayer growth precise control of the gas supply to form the However, accurate layer-by-layer growth is achieved under certain conditions, which facilitate the spontaneous desorption of an additional layer of one atom species by supply of the other species \cite{hara93}. Homoepitaxial growth of the 6H polytype has been realized on off-oriented substrates utilizing simultaneous supply of the source gases \cite{tanaka94}. Depending on the gas flow ratio either 3C island formation or step flow growth of the 6H polytype occurs, which is explained by a model including aspects of enhanced surface mobilities of adatoms on a $(3\times 3)$ reconstructed surface. -Due to the strong adsorption of atomic hydrogen \cite{allendorf91} decomposited of the gas phase reactants at low temperatures, however, there seems to be no benefit of GSMBE compared to CVD. +Due to the strong adsorption of atomic hydrogen \cite{allendorf91} decomposited of the gas phase reactants at low temperatures, however, there seems to be no benefit of GSMBE compared to \ac{CVD}. Next to lattice imperfections, incorporated hydrogen effects the surface mobility of the adsorbed species \cite{eaglesham93} setting a minimum limit for the growth temperature, which would preferably be further decreased in order to obtain sharp doping profiles. Thus, growth rates must be adjusted to be lower than the desorption rate of hydrogen, which leads to very low deposition rates at low temperatures. -Solid source MBE (SSMBE), supplying the atomic species to be deposited by evaporation of a solid, presumably constitutes the preffered method in order to avoid the problems mentioned above. +SSMBE, by supplying the atomic species to be deposited by evaporation of a solid, presumably constitutes the preffered method in order to avoid the problems mentioned above. Although, in the first experiments, temperatures still above \unit[1100]{$^{\circ}$C} were necessary to epitaxially grow 3C-SiC films on 6H-SiC substrates \cite{kaneda87}, subsequent attempts succeeded in growing mixtures of twinned 3C-SiC and 6H-SiC films on off-axis \hkl(0001) 6H-SiC wafers at temperatures between \unit[800]{$^{\circ}$C} and \unit[1000]{$^{\circ}$C} \cite{fissel95,fissel95_apl}. In the latter approach, as in GSMBE, excess Si atoms, which are controlled by the Si/C flux ratio, result in the formation of a Si adlayer and the formation of a non-stoichiometric, reconstructed surface superstructure, which influences the mobility of adatoms and, thus, has a decisive influence on the growth mode, polytype and crystallinity \cite{fissel95,fissel96,righi03}. Therefore, carefully controlling the Si/C ratio could be exploited to obtain definite heterostructures of different SiC polytypes providing the possibility for band gap engineering in SiC materials. -To summarize, much progress has been made in SiC thin film growth during the last few years. -However, the frequent occurence of defects such as dislocations, twins and double positioning boundaries limit the structural and electrical characteristics of large SiC films. -Solving these issues remains a challenging problem necessary to drive SiC for potential applications in high-performance electronic device production \cite{wesch96}. +To summarize, much progress has been achieved in SiC thin film growth during the last few years. +However, the frequent occurence of defects such as dislocations, twins and double positioning boundaries limit the structural and electrical quality of large SiC films. +Solving this issue remains a challenging problem necessary to drive SiC for potential applications in high-performance electronic device production \cite{wesch96}. \subsection{Ion beam synthesis of cubic silicon carbide} +Although tremendous progress has been achieved in the above-mentioned growth methods during the last decades, available wafer dimensions and crystal qualities are not yet statisfactory. +Thus, alternative approaches to fabricate SiC have been explored. +In the following ... + +High-dose carbon implantation into \ac{c-Si} with subsequent or in situ annealing was found to result in SiC microcrystallites in Si \cite{borders71}. +\ac{RBS} and \ac{IR} spectroscopy investigations indicate a \unit{10}[at.\%] C concentration peak and the occurence of disordered C-Si bonds after implantation at room temperature followed by crystallization into SiC precipitates upon annealing demonstrated by a shift in the \ac{IR} absorption band and the disappearance of the C profile peak in \ac{RBS}. + +Utilized and enhanced, 30 years devel ... (-32) +By understanding some basci processes (32-36), \ac{IBS} nowadays has become a promising method to form thin SiC layers of high quality exclusively of the 3C polytype embedded in and epitactically aligned to the Si host featuring a sharp interface \cite{lindner99,lindner01,lindner02}. + \section{Substoichiometric concentrations of carbon in crystalline silicon} \section{Assumed cubic silicon carbide conversion mechanisms} -- 2.20.1