Hot-wall CVD reactor

Figure 4 (a) Cold-wall CVD reactor with parallel vapor flow (b) hot-wall CVD reactor with perpendicular... 

Hot-wall CVD reactors have become increasingly popular due to the ease of obtaining high- quality layers. The stochiometry is usually selected with respect to optimum morphology and doping is varied by changing the partial pressures of the dopants. 

Figure 7. SiH4 molecular trajectories in free molecular flow in a very low pressure (1 Pa) hot-wall CVD reactor for Si epitaxy.

Again, a low-pressure, hot-wall CVD reactor was used for the depositions. Pressures ranged from 300 to 900 mTorr. Phosphorus doping was carried out with trimethylphosphite. For these experiments, some depositions were carried out with oxygen addition. In this case, deposition rates were lowered. Combining trimethylphosphite with oxygen, on the other hand, increased deposition rates. 

Figure 4.39. Schematic of a horizontal hot-walled CVD reactor. Shown is a two-precursor system, where the water sensitive precursor contacts water vapor directly over the heated substrate.

Fig. 7 Schematic drawing of hot-wall CVD reactor used to coat multiple parts.

In a cold-wall CVD only the substrates are heated either inductively or resistively and the wall of the reactor is colder than that of the substrate. Therefore, the deposition mainly occurs on the heated substrate, and negligible deposition on the walls of the reactor. Cold-wall reactors are mainly used for continuous deposition of fibres and depositions where a thermal gradient is required to facilitate CVI. Hot-wall CVD reactors represent one of the major categories of CVD reactors. In such systems, the chamber containing the parts is heated by a furnace from outside. In general, hot-wall reactors have the advantages of being... 

The horizontal hot-wall CVD reactor used in our experiments has been described in detail by Myers et al. [14]. A schematic drawing of the reactor cross-section is shown in Figure 3.2. The growth was conducted... 

When we speak of a cold wall CVD reactor, we refer to a continuous flow system where the wafer is kept at the required high temperature, but all other surfaces bounding on the reacting gases are cold. The objective here is to cause the desired reaction only on the hot wafer and keep all other surfaces free of deposits. In practice this is a goal that can only be partially attained. Although reactions will proceed more slowly on colder surfaces, they will proceed-and films will build up. At the same time the films that form on the colder surfaces may be more porous than the normal film and may spall off more easily. All of which says that in spite of our best efforts, cold walled reactors may have their cold walls an undesirable source of particulates which may end up on the hot substrate. The occurence of such particulates can be minimized by frequent cleaning of the chamber walls to remove deposits. 

There are two general types of CVD reactors, one is the chamber type and the other is the tube type. The tube type reactor is typically a hot wall reactor and has been used in the semiconductor industry for the deposition of simple binary thin films such as SijN. This type of deposition reactor usually has quite large throughput because a few hundred wafers can be loaded and processed. However, the CVD precursors should have large diffusivities in the gas phase and be stable over the homogeneous reactions to produce uniform deposition on a large number of wafers. For tube type reactors, as for all hot wall type reactors, the CVD reaction occurs on the wall of the reactor as well as on the wafers. This increases the consumption of the precursors. Therefore, CVD reactors for BST thin films are the other type, except for a very recent report from Toshiba of Japan. They reported CVD of BST thin films utilizing a tube type reactor which had a rotatory wafer holder to improve the uniformity of deposited films. Details of the CVD reactor have not been reported yet, thus, in this section only the details of chamber type reactors are discussed. 

For example, a hotter and less dense gas above a hot substrate will rise, whereas a cooler and denser gas will sink. Such a situation is often encountered in cold-wall CVD reactors. 

Many of the first papers which discussed the use of (selective) CVD of tungsten for IC applications used conventional hot wall tube CVD reactors [Broadbent et al.44, Pauleau et al.45, Cheung47]. This type of reactor was and still is the workhorse in IC fabs. Excellent films such as TEOS based oxides, thermal silicon-nitride and poly-silicon can be grown in such equipment. Hot wall tube reactors are suitable for these films because such materials stick very well to quartz tubes and are quite transparent to IR radiation of the heating elements. Thus neither particle nor temperature control is a problem. One other major advantage is that high throughputs are typically obtained. 

Li et al. deposited nanosized, partially crystallized SiC powders at temperatures as low as 900 ° C in a hot-wall horizontal quartz tube reactor using liquid carbosUane as a precursor and hydrogen as the carrier gas [90]. Gupta et al. obtained P-SiC nanoparticles (10-30 nm) from a CVD process carried out in a hot-wall tube reactor using hexamethyldisilane as a single source for both silicon and carbon [91]. 

Reactor, hot wall (CVD) A reactor furnace where the CVD gases and the substrates are heated by conduction and radiation from the containing structure (furnace). 

The CVD process is accomplished using either a hot-wall or a cold-wall reactor (Fig. 13). In the former, the whole chamber is heated and thus a large volume of processing gases is heated as well as the substrate. In the latter, the substrate or substrate fixture is heated, often by inductive heating. This heats the gas locally. 

Thermal CVD requires high temperature, generally from 800 to 2000°C, which can be generated by resistance heating, high-frequency induction, radiant heating, hot plate heating, or any combination of these. Thermal CVD can be divided into two basic systems known as hot-wall reactor and cold-wall reactor (these can be either horizontal or vertical). 

Typical Reactor Design. Table 5.1 lists typical CVD production reactors which include cold-wall and hot-wall reactors operating at low or atmospheric pressures. The decision to use a given system should be made after giving due consideration to all the factors of cost, efficiency, production rate, ease of operation, and quality. 

Several different types of CVD reactors exist. The cold wall design, which used to be the most common type of reactor, is now less frequently used and the hot-wall reactor has filled its place. Some new and interesting concepts exist as well. These are referred to as chimney-type reactors. The main difference between the hot- or old-wall type reactors and the chimney-style reactor is the transport of materials, which will be explained in the following sections. 

A review article on the CVD processes used to form SiC and Si3N4 by one of the pioneers in this area, Erich Fitzer [Fitzer, E., and D. Hegen, Chemical vapor deposition of silicon carbide and silicon nitride—Chemistry s contribution to modem silicon ceramics, Angew. Chem. Int. Ed. Engl, 18, 295 (1979)], describes the reaction kinetics of the gas-phase formation of these two technical ceramics in various reactor arrangements (hot wall, cold... 

The CVD process is accomplished using either a hot-wall or a cold-wall reactor (Fig. 13). In the former, the whole chamber is heated and thus a... 

Nitride Coatings. Carbide tips coated with titanium nitride or titanium carbonitride are usually manufactured by a CVD process using T1CI4, H4, and N2 in a hot-wall reactor. 

As most organometallic precursors, V(NEt2)4 pyrolysis involves a complicated mechanism highly dependent on the experimental conditions. For this reason, the CVD experiments were conducted at reduced pressure (Table 15.4) in order to improve the diffusivity of the species, reduce their interactions in the gas phase and disfavor subsequent reactions. Two CVD units (hot-wall and cold-wall) of the same geometry were used in this study. Since the reactions in the gas phase are likely to be different in these two types of reactors, we could use them to study the influence of the gas phase chemistry on the growth rate. The composition of the deposits was studied as a function of the substrate temperature under He gas and as a function of the nature of the carrier gas when H2 and NH3 were added in various amounts. 

Dimensionless Quantities and Reactor Types. Transport phenomena in CVD reactors can be described in terms of two broad groups (1) hot-wall, low-pressure reactors and (2) cold-wall, reduced- and atmospheric-pressure reactors. 

To demonstrate the main features of the flow in horizontal CVD reactors, the deposition of silicon from silane is used as an example (87). The conditions are as follows an 8-cm-wide reactor with either adiabatic side walls or side walls cooled to the top wall temperature of 300 K, a 1323 K hot susceptor (bottom wall), a total pressure of 101 kPa, and an initial partial pressure of silane in H2 of 101 Pa. The growth rate of silicon is strongly influenced by mass transfer under these conditions. Figure 8 shows fluid-particle trajectories and spatially varied growth rates for three characteristic cases. 

Numerous modeling studies of CVD reactors have been made and are summarized in recent review papers (I, 212). Table 3 in reference 212 lists major examples of CVD models up to mid-1986. Therefore, rather than giving an exhaustive list of previous work, Table V presents a summary of the major modeling approaches and forms the basis for the ensuing discussion, which is most appropriately handled in terms of two groups (1) hot-wall LPCVD systems and (2) cold-wall, near-atmospheric-pressure reactors. In LPCVD reactors, diffusion and surface reaction effects dominate, whereas in cold-wall reactors operated at near-atmospheric pressures, fluid flow and gas-phase reactions are important in predicting performance, as discussed earlier in relation to transport phenomena. 

In this section we will review the various types of CVD reactors scientists and engineers have used for the development of thermal CVD processes. This will be distinct from the commercial reactors used for production which will be covered in a later chapter. A similar review of reactors for development of plasma-enhanced CVD processes will be made at the end of the next chapter. We will cover the so-called cold wall systems for either single or multiple wafers first, followed by a discussion of continuous belt systems. Finally, we will review the hot wall reactor approach. 

Figure 15 Hot-wall, parallel-plate reactor for plasma-enhanced CVD. (Courtesy of Pacific Western Systems, Inc.)...

Chapter 6 is devoted to typical commercially-available CVD reactor systems, including cold-wall and hot-wall systems. Several new commercial reactors are also reviewed. 

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