Chemical vapor deposition processing steps

Chemical vapor deposition processes are complex. Chemical thermodynamics, mass transfer, reaction kinetics and crystal growth all play important roles. Equilibrium thermodynamic analysis is the first step in understanding any CVD process. Thermodynamic calculations are useful in predicting limiting deposition rates and condensed phases in the systems which can deposit under the limiting equilibrium state. These calculations are made for CVD of titanium - - and tantalum diborides, but in dynamic CVD systems equilibrium is rarely achieved and kinetic factors often govern the deposition rate behavior. 

We shall consider three primar> examples as a means of illustrating the main concepts in this chapter. The first example is one of the reactions responsible for smog formation in the atmosphere. It consists of a single, reaction, among three species. The second example is the water gas shift reaction, and it illustrates the case of multiple reactions it consists of three reactions among six chemical species. The third example illustrates the complexity of common industrial reactions of interest, consisting of 20 reactions among 14 species. These reactions have been proposed to describe a silicon chemical vapor deposition process, which is an important step in the production of microelectronic materials. 

Li X, Magnuson CW, Venugopal A, An J, Suk JW, Han B, et al. Graphene films with large domain size by a two-step chemical vapor deposition process. Nano Lett... 

Figure 28.8 Schematic diagram of chemical vapor deposition process and all steps involved in this method [30].

Run-to-run control is particularly useful to compensate for processes where the controlled variable drifts over time. For example, in a chemical vapor deposition process or in a batch chemical reactor, the reactor walls may become fouled due to byproduct deposition. This slow drift in the reactor chamber condition requires occasional changes to the batch recipe in order to ensure that the controlled variables remain on-target. Eventually, the reactor chamber must be cleaned to remove the wall deposits, effectively causing a step... 

An advanced process, completely eliminating all solution processing steps, was proposed by Lock et edP and Gleason and Lock. A true oxidative chemical vapor deposition process (oCVD) was established by depositing an iron(III)-chlo-ride layer on a substrate by sublimating the FeClg in a special reaction chamber. 

These processes are very rapid and allow the preparation of inorganic supports in one step. This technique allows large-scale manufacturing of supports such as titania, fumed silica, and aluminas. Sometimes the properties of the material differ from the conventional preparation routes and make this approach unique. Multicomponent systems can be also prepared, either by multimetallic solutions or by using a two-nozzle system fed with monometallic solutions [22]. The as-prepared powder can be directly deposited onto substrates, and the process is termed combustion chemical vapor deposition [23]. 

Chemical vapor deposition (CVD) is a process whereby a thin solid film is synthesized from the gaseous phase by a chemical reaction. It is this reactive process that distinguishes CVD from physical deposition processes, such as evaporation, sputtering, and sublimation.8 This process is well known and is used to generate inorganic thin films of high purity and quality as well as form polyimides by a step-polymerization process.9-11 Vapor deposition polymerization (VDP) is the method in which the chemical reaction in question is the polymerization of a reactive species generated in the gas phase by thermal (or radiative) activation. 

Silicon Epitaxy. A critical step in IC fabrication is the epitaxial deposition of silicon on an integrated circuit. Epitaxy is defined as a process whereby a thin crystalline film is grown on a crystalline substrate. Silicon epitaxy is used in bipolar ICs to create a high resistivity layer on a low resistivity substrate. Most epitaxial depositions are done either by chemical vapor deposition (CVD) or by molecular beam epitaxy (MBE) (see Thin FILMS). CVD is the mainstream process. 

Fig. 7.20. Comparison of PL spectra at 2 K of a 2.2 /um thick ZnO film on a-plane sapphire and of a ZnO bulk single crystal grown by seeded chemical vapor deposition (Eagle Picher), both (0001) oriented. The PLD film was deposited by a 4-step PLD process [51] and shows a PL spectrum very similar to that of the single crystal. The energies of the assigned luminescence peaks are given in [eV]. The spectral resolution of the PL setup is 1 meV at 3.35 eV [63]...

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