Silicon growth process

Naturally, aU the defects noted above for silicon may also be imaged in other crystalHne materials. However, they are often of lower importance, whereas the larger-scale defects that have been ehminated from the silicon growth process can assume prime importance. 

An example of an analysis done on polysilicon and single-crystal Czochralski silicon (CZ) is shown in Table 1. As can be seen, polysilicon, which was used to grow the crystal, is dirtier than the CZ silicon. This is expected, since segregation coefficients limit the incorporation of each element into the crystal boule during the crystal growth process. All values shown in the table are from bulk analysis. Table 2 shows NAA data obtained in an experiment where surface analysis was accom-... 

Epitaxy is a term that denotes the growth of a thin crystalline film on a crystalline substrate. When the epitaxial film is of the same material as the substrate (for instance silicon on silicon), the process is known as homoepitaxy. When film and substrate are of different... 

The process of substituting elements for the silicon is called doping, while the elements are referred to as dopants. The amount of dopant that is required in practical devices is very small, ranging from about 100 dopant atoms per million silicon atoms downward to 1 per billion. Dopants are usualty added to the silicon after the crystal growth process, when an integrated circuit is being formed on the surface of the wafer. 

In the early days of silicon device manufacturing the need for surfaces with a low defect density led to the development of CP solutions. Defect etchants were developed at the same time in order to study the crystal quality for different crystal growth processes. The improvement of the growth methods and the introduction of chemo-mechanical polishing methods led to defect-free single crystals with optically flat surfaces of superior electronic properties. This reduced the interest in CP and defect delineation. 

The substrate for this CVD process is a thin silicon rod, called a slim rod, which serves as a nucleation site for the depositing silicon. After deposition, the EGS, or polysilicon, is processed in the Czochralski (CZ) growth process. 

Figure 7.44 Silicon growth rate as a function of SiCLt concentration. Reprinted, by permission, from S. Wolf, and R. N. Tauber, Silicon Processing for the VLSI Era, Vol. 1, p. 127. Copyright 1986 by Lattice Press.

Epitaxial Layers. Epitaxial deposition produces a single crystal layer on a substrate for device fabrication or a layer for multilevel conductive interconnects which may be of much higher quality than the substrate. The epitaxial layer may have a different dopant concentration as a result of introducing the dopant during the epitaxial growth process or may have a different composition than the substrate as in silicon on sapphire. Methods used for epitaxial growth include chemical vapor deposition (CVD), vapor phase epitaxy (VPE), liquid phase epitaxy (LPE), molecular beam epitaxy (MBE) and solid phase epitaxy (SPE). 

This approach was successfully used in modeling the CVD of silicon nitride (Si3N4) films [18, 19, 22, 23]. Alternatively, molecular dynamics (MD) simulations can be used instead of or in combination with the MC approach to simulate kinetic steps of film evolution during the growth process (see, for example, a study of Zr02 deposition on the Si(100) surface [24]). Finally, the results of these simulations (overall reaction constants and film characteristics) can be used in the subsequent reactor modeling and the detailed calculations of film structure and properties, including defects and impurities. 

Schematic diagrams illustrating the growth process of the Co2Si layer in the Co-Si and Co-CoSi couples are presented in Figs 4.7 and 4.8, separately for the two hypothetical extreme cases in which only one component is diffusing. If diffusion of cobalt is dominant, as in Fig. 4.7, then the growth of the Co2Si layer in the Co-Si couple is due to a partial chemical reaction between the diffusing cobalt atoms and the surface silicon atoms...

Fig. 4.8. Schematic diagram to illustrate the growth process of the Co2Si layer in the Co-Si and Co-CoSi diffusion couples in the hypothetical case where only silicon is the diffusing species.

Without a doubt, a complete picture of the dynamics of dissociative chemisorption and the relevant parameters which govern these mechanisms would be incredibly useful in studying and improving industrially relevant catalysis and surface reaction processes. For example, the dissociation of methane on a supported metal catalyst surface is the rate limiting step in the steam reforming of natural gas, an initial step in the production of many different industrial chemicals [1]. Precursor-mediated dissociation has been shown to play a dominant role in epitaxial silicon growth from disilane, a process employed to produce transistors and various microelectronic devices [2]. An examination of the Boltzmann distribution of kinetic energies for a gas at typical industrial catalytic reactor conditions (T 1000 K)... 

The mechanism of formation of zeolites is very complex, stemming from the diversity of chemical reactions, including various polymerization and depolymerization equilibria, nucleation and crystal growth processes. The physical and chemical nature of the reactants, which typically involve a source of aluminum and silicon along with hydroxides and salts determine the formation of zeolites. Physical effects such as aging, stirring, and temperature also play an important role. These effects lead to the complexity of zeolite formation, but are also responsible for the large number of frameworks that can be synthesized and the rich chemistry associated with this area. Cl. 21... 

A different application of chemical equilibrium leads to an explanation of how the incorporation of defects and dopants depends on the growth conditions (Winer and Street 1989). Section S.l describes the unexpected rf power and gas concentration dependence of the dopant distribution coefficient, particularly for arsenic doping. A schematic diagram of the growth process is shown in Fig. 6.19, in which three-fold and four-fold silicon and dopants are deposited from the gas phase. The deposition reactions proposed for arsenic doping are... 

Pore formation in silicon can be considered a growth process in which the growing phase (the pores) propagates into a receding phase (bulk silicon). This approach allows the analysis of pore propagation by techniques used to model a wide range of processes, such as physical deposition, aggregation, evaporation/condensation, and solidification [139-141]. 

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