Horizontal reactors

Fig. 22. Schematics of chemical vapor deposition epitaxial reactors (a) horizontal reactor, (b) vertical pedestal reactor, (c) multisubstrate rotating disk reactor, (d) barrel reactor, (e) pancake reactor, and multiple wafer-in-tube reactor (38).

Figure 1 Illustrates two general MOCVD reactor configurations, the horizontal reactor and the axlsymmetrlc vertical reactor. The reactant gas (ASH3, Ga(CH3)3 and Al( 013)3) enters cold and heats up as It fiows toward the substrate where a solid film of AlGaAs Is being deposited. The chemical transformations Involved In the deposition process may occur both In the gas phase and on the surface of the growing film.

Figure 1. Two typical MOCVD reactor configurations (a) horizontal reactor (b) vertical reactor.

Boundary layer similarity solution treatments have been used extensively to develop analytical models for CVD processes (2fl.). These have been useful In correlating experimental observations (e.g. fi.). However, because of the oversimplified fiow description they cannot be used to extrapolate to new process conditions or for reactor design. Moreover, they cannot predict transverse variations In film thickness which may occur even In the absence of secondary fiows because of the presence of side walls. Two-dimensional fully parabolized transport equations have been used to predict velocity, concentration and temperature profiles along the length of horizontal reactors for SI CVD (17,30- 32). Although these models are detailed, they can neither capture the effect of buoyancy driven secondary fiows or transverse thickness variations caused by the side walls. Thus, large scale simulation of 3D models are needed to obtain a realistic picture of horizontal reactor performance. 

ZnS MOVPE cold-wall horizontal reactor Epitaxially cubic phase grown on (lll)Si growth at 400 °C. Without carrier gas, hexagonal a-ZnS of poor morphology and crystallinity 182... 

Horizontal mills, 16 65 Horizontal reactor, 22 154, 155 Horizontal retort process, for zinc, 26 577 Horizontal rotary tilting-pan filters,... 

The design of the prepolycondensation reactors depends on the plant capacity. For higher plant capacities, a stirred-tank reactor is connected in series with a horizontal reactor. In Figure 2.39, a horizontal prepolycondensation reactor is shown, operating with rotating perforated discs to increase the specific surface area. 

High purity ethylene gas plus recycle ethylene are fed to a compression chamber, compressed and then fed along with catalyst previously dissolved in a suitable solvent into, parallel horizontal reactors, as many- as eight in parallel. Each reactor consists of a water-filled shell containing a single pipe, coiled to give maximum contact with the water. Reaction conditions are 350-425 F and 2000-3000 psi. 

A continuous bulk polymerization process with three reaction zones in series has been developed. The degree of polymerization increases from the first reactor to the third reactor. Examples of suitable reactors include continuous stirred tank reactors, stirred tower reactors, axially segregated horizontal reactors, and pipe reactors with static mixers. The continuous stirred tank reactor type is advantageous, because it allows for precise independent control of the residence time in a given reactor by adjusting the level in a given reactor. Thus, the residence time of the polymer mixtures can be independently adjusted and optimized in each of the reactors in series (8). 

H. Moffat and K.F. Jensen. Three-Dimensional Flow Effects in Silicon CVD in Horizontal Reactors. J. Electrochem. Soc., 135(2) 459-471,1988. 

Photosensitization is used for large-area photochemically stimulated CVD, because the generation of a sufficient photon flux over a large area to drive the chemistry directly is difficult. Usually, Hg excited by an external Hg lamp is used as a sensitizer. The energy in the excited Hg is then transferred to other gas-phase species that decompose and react to form a thin film. The process is used in horizontal reactors for the deposition of SiOj and SiN Hs from SiH4, NzO, and NH3 (40-42) and to assist the deposition of CdHgTe, in which Hg is a natural gas-phase constituent (43). 

Horizontal Reactors. Horizontal reactor flow may involve both transverse and longitudinal rolls, as well as time-periodic flows. Insights into these phenomena may be gained from previous analysis of idealized, analogous systems, as well as from recent experiments and computations. Analytical studies of flow between two plates of infinite size differentially heated from below (180) and horizontal channel flow (181) indicate that the development of transverse and longitudinal rolls depends on the relative and absolute magnitudes of the dimensionless Rayleigh and Reynolds numbers, Ra and Re, as well as the aspect ratio. 

Previous computations (189) show that the critical value of Rat for non-Boussinesq conditions is approximately the same as that for a Boussinesq fluid in a box heated from below, at least when H2 is the carrier gas. Thus, results from the stability analysis of the classical Rayleigh-Benard problem of a two-dimensional fluid layer heated from below (see reference 190 for a review) may be used to indicate the type of behavior to be expected in a horizontal reactor with insulated side walls. As anticipated from this analysis, an increase in the reactor height from 2 to 4 cm raises the value of Rat to 4768, which is beyond the stability limit, Rat critical = 2056, for a box of aspect ratio 2 (188). The trajectories show the development of buoyancy-driven axial rolls that are symmetric about the midplane and rotating inward. For larger values of Rat (>6000), transitions to three-dimensional or time-de-... 

Figure 10. Comparison of measured (broken lines) and predicted (solid lines) temperatures in a horizontal reactor for two inlet flow velocities of H2 (a) 2 slm (standard liters per minute) and (b) 8 slm (193).

Horizontal reactor at atmospheric and reduced pressure conditions... 

Simple Analytical Models. To derive simple analytical models for horizontal reactors, two flow simplifications have been used boundary layer similarity models and film theory (see Table 3 in reference 212). In these treatments, a constant concentration shape is assumed from the start of the deposition zone or from an axial position after the initial concentration profile development zone. Thereafter, the shape stays constant, with only the absolute magnitude of the concentration changing with axial position. 

Modeling of Miscellaneous CVD Reactors. In addition to the classical CVD reactor configurations discussed in the preceding sections, a wide variety of CVD reactor configurations have been used, including barrel and pancake-type reactors for epitaxy and vertical cross-flow LPCVD reactors. Barrel reactors have often been modeled as horizontal reactors, because the flow geometry of one barrel side is similar to that of a horizontal reactor (Table 3 in reference 212). However, the similarity disappears if buoyancy effects and barrel rotation are included in the analysis. 

Highly exothermal reactions can be applied by external heat exchange (1,39). If a CSTR-type reactor is not desired, the horizontal reactor with interstage cooling is an attractive alternative. 

In 1916 an experimental plant was erected by Bergius near Mannheim however, little progress was made until 1921. In this plant coal paste was hydrogenated in horizontal reactors. In these reactors heated nitrogen at reaction pressure was circulated between a liner and the pressure-retaining wall to supply heat and to prevent reaction hydrogen from corroding the steel of the pressure vessels. The products obtained in this plant... 

The horizontal reactor of the rotating drum type (Fig.8) does not have certain drawbacks characteristic of the vertical reactor. Particularly, rotating drums provide for a more thorough mixing of gaseous chlorine derivative with contact mass, because they increase the time of contact between the phases (10 times in comparison with the fluidised layer) consequently, the degree of chlorine derivative also grows. In the production of phenyl-chlorosilanes they create favourable conditions to increase the yield of di-phenyldichlorosilane. 

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