Barrel reactors

CVD reactors can have one of several configurations. Each has particular advantages and disadvantages. Reactors that support wafers horizontally have difficulty controlling the deposition uniformity over all the exposed wafers. Reactors having vertical wafer support produce uniform deposition, but are mechanically complex. Barrel reactors are not suited for extended operation at temperatures greater than 1200°C. 

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).

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. 

Figure 1 illustrates conventional CVD reactors. These reactors may be classified according to the wall temperature and the deposition pressure. The horizontal, pancake, and barrel reactors are usually cold-wall reactors where the wall temperatures are considerably cooler than the deposition surfaces. This is accomplished by heating the susceptor by external rf induction coils or quartz radiant heaters. The horizontal multiple-wafer-in-tube (or boat) reactor is a hot-wall reactor in which the wall temperature is the same as that of the deposition surface. Therefore, in this type of reactor, the deposition also occurs on the reactor walls which presents a potential problem since flakes from the wall deposit cause defects in the films grown on the wafers. This is avoided in the cold-wall reactors, but the large temperature gradients in those reactors may induce convection cells with associated problems in maintaining uniform film thickness and composition. 

The two major modelling approaches based on either boundary layer approximations or well developed laminar flow have also been applied to the barrel reactor. Dittman (11) used a Chilton-Colburn analogy for flow over a flat plate to predict Si growth... 

All plasma exposures were carried out in an IPC (International Plasma Corporation) 2005 capacitance-coupled barrel reactor at 13.56MHz. The reactor was equipped with an aluminum etch tunnel and a temperature controlled sample stage. Pressure was monitored with an MKS capacitance manometer RF power was monitored with a Bird R.F. power meter and substrate temperature was measured with a Fluoroptic thermometer utilizing a fiber optic probe which was immune to R.F. noise. 

Fig. 6. IR transmission (a-c) and difference (d.e) spectra of O, plasma etched PBTMSS films hst m Table II. Samples I - RIE -400 V 2 - SME 3 - high-pressure RIE - high-bias RIE, 5 - barrel reactor etched. Curves a are for the initial film b for the film treated as given, n Table I, c after additional RIE at 20 mTorr and -400 V for 10 min. Curves d-b-a, e-c a.

Contrary to the increase in oxidation observed during standard RIE, films subjected to one of the passivation pretreatments (with the exception of the barrel reactor process) showed little further increase in oxide conversion beyond the initial pretreatment conversion. Only the films pretreated by high pressure oxygen plasma in the barrel reactor showed a further increase in oxide conversion on subsequent "standard" RIE (curve 5e). 

The sputtering time required for the atomic composition of the surface layer to reach that of the unetched, i.e., virgin PBTMSS depended on the passivation pretreatment process. The time increased in the order SME > high bias > barrel reactor reflecting the differences in thickness of the oxide layer. These results are also in qualitative agreement with the IR results presented in Figure 6 and Table II. 

Fig. 9. AES atomic concentration depth profile for a PBTMSS film on Au/Si. Film etched for 1 min. in a barrel reactor at 850 mTorr O2.

Contrary to the observations reported by Bagley et al. (7) on the etching of an organosilsesquioxane in a barrel reactor, the PBTMSS etching process does not proceed beyond the surface layer, probably because much higher elasticity of the PBTMSS network causes collapse of the micropores through which the active species diffuse into the film. 

One of the key steps in the chip-making process is the deposition of different semiconductors and metals on the surface of the chip. This step can be achieved by CVD. CVD mechanisms were discussed in Chapter 10 consequently, this section will focus on CVD reactors. A number of CVD reactor types have been used, such as barrel reactors, boat reactors, and horizontal and vertical reactors. A description of these reactors and modeling equations are given by Jensen. 

The volume-loaded barrel reactor shown in Fig. 19c, is not used for applications that require anisotropic etching. A typical example is photoresist stripping. High... 

Figure 4-13. (a) Schematic of horizontal tube (b) schematic of cylindrically symmetric vertical barrel reactor tube (c) schematic of circularly symmetric Planetary Reactor (d) schematic of vertical pedestal reactor (pedestal may be rotated or entire reactor may be inverted) and e) schematic of cluster tool type reactor systems. (Courtesy of EMCORE Corp.). 

The barrel reactor, Figure 4-13c, wraps a horizontal tube into a cylindrical symmetric space. While this allows for multiple wafers to be deposited upon in parallel, it does not eliminate depletion effects, and these systems generally do not have multiple rows of wafers. 

Barrel reactors as shown in Figure 4-13b are somewhat popular in Si technology. For OMVPE they are marketed by a few vendors such as Spire Corporation. Barrel reactor designs have seen little change in recent years, and Spire has recently introduced a closed space RDR system. 

FIGURE 15.3 Schematic diagram of coaxial reactor (a), barrel reactor (b), and grooved barrel reactor (c) built for devulcanization of rubbers. 

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