Hot-Wall

Fischer J E, Werwa E and Fleiney P A 1993 Pseudo epitaxial Cgq films prepared by a hot wall method Appi. Rhys. A 56 193-6... 

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. 

For example, vaporization may occur as a result of heat absorbed, by radiation and convection, at the surface of a pool of hquid or as a result of heat absorbed by natural convect ion from a hot wall beneath the disengaging surface, in which case the vaporization takes place when the superheated liquid reaches the pool surface. Vaporization also occurs from falling films (the reverse or condensation) or from the flashing of hquids superheated by forced convec tion under pressure. 

When the steam was shut off and, 15 minutes later, the agitator was switched off, heat transferred from the hot wall above the liquid level to the top part of the liquid, which became hot enough for a runaway reaction to start. This resulted in a release of TCDD (dioxin), which killed a number of nearby animals, caused dermatitis (chloracne) in about 250 people, damaged vegetation near the site, and required the evacuation of about 600 people (Kletz 1994). 

For hot wall vessels, the increased strength may be such that the use of chromium and molybdenum alloy steels will be cheaper. Also, these steels may be required to prevent hydrogen attack and to reduce oxidation and sulfidation. 

This is too hot an installation for V-belt drives. However, they may be used if ventilation is good and perhaps an insulated hot wall is interposed between the sheaves and fan housing. Allowance must be made for belt losses from manufacturers tables and also any other mechanical losses of the driver. If a motor is used, the shaft output should be 5 hp to cover losses and allow for nonoverload. The 0.2 overload at peak conditions does not justify a 7.5 hp motor because expected operations will be at 3.0, and a 5 hp motor can usually be overloaded 10% without difficulty. 

Carbon steel, cold wall as opposed to hot wall. ... 

The temperature distribution has a characteristic maximum within the liquid domain, which is located in the vicinity of the evaporation front. Such a maximum results from two opposite factors (1) heat transfer from the hot wall to the liquid, and (2) heat removal due to the liquid evaporation at the evaporation front. The pressure drops monotonically in both domains and there is a pressure jump at the evaporation front due to the surface tension and phase change effect on the liquid-vapor interface. 

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). 

Hot-Wall Reactors. A hot-wall reactor is essentially an isothermal furnace, which is often heated by resistance elements. The parts to be coated are loaded in the reactor, the temperature is raised to the desired level, and the reaction gases are introduced. Figure 5.6 shows such a furnace which is used for the coating of cutting tools with TiC, TiN, and Ti(CN). These materials can be deposited alternatively under precisely controlled conditions. Such reactors are often large and the coating of hundreds of parts in one operation is possible (see Ch. 18). 

Hot wall reactors have the advantage of close temperature control. A disadvantage is that deposition occurs everywhere, on the part as well as on the walls of the reactor, which require periodic cleaning or the use of a disposable liner. 

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. 

Danielson, D., Yau, L., and David, K., Dry Scrub to Improve Hot Wall Nitride Equipment Reliability, Semiconductor International, pp. 170-173 (Sept. 1989)... 

Patterson, D. E., et al., Thermochemical Vapor Deposition of Diamond in a Carbon-Halogen-Oxygen and/or Sulfur Atmospheric Hot-Wall Reactor, in Applications of Diamond Films and Related Materials, (Y. Tzeng, et al., eds.), Elsevier Science Publishers, pp. 569-576 (1991)... 

From an examination of Equation 8.1, it can be seen that several things can be done to improve the heat-transfer rate. Quite often the simplest approach is to increase the temperature differential, by using higher-pressure steam or a hot oil supply. In some cases this may have adverse effects, for example a very hot wall temperature may lead to fouling, or, worse, initiate unwanted reactions. This is likely to be more pronounced in cases where mass transfer is poor. In some instances this practice may... 

Chemical Vapor Deposition- Deposition of silicon oxide films is accomplished by CVD equipment. Either plasma CVD or ozone oxidation is used. Blanket tungsten films are also deposited by CVD equipment to create contact and via plugs. Polysilicon and silicon nitride films are deposited in hot-wall furnaces. TiN diffusion barrier films are deposited by either sputtering or CVD, the latter giving superior step coverage. 

Hot reactor walls are sometimes used as a means to increase the density of the films that are deposited on the walls. This reduces the amount of adsorbed contaminants on the walls, and leads to lower outgassing rates. A hot wall is particularly of interest for single-chamber systems without a load-lock chamber. Material quality is similar to the quality obtained with a cold reactor wall [145],... 

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

ZnS, CdS, (ZnxCd x)S Hot-wall reactor,under active secondary vacuum Glass and III-V substrates, growth at 400 °C. ZnS poor-quality films. CdS and (ZnxCdi x)S good-quality films. CdS epitaxially growth on (lOO)-oriented GaAs and InP substrates 180... 

ZnSe, CdSe Hot-wall reactor Deposited elemental selenium 181... 

N3)2Ga N(CH2CH2NEt2)2 ] low volatility Horizontal hot-wall LP-CVD Growth temperature 750-950 °C, preferred orientation of crystallites perpendicular to c-plane of sapphire substrate, no additional N source 287... 

N3)2Ga (CH2)3NMe2 ] nonpyrophoric, nonexplosive [(N3)In (CH2)3NMe2 2] Horizontal hot-wall LP-CYD Horizontal hot-wall Epitaxial film growth, no additional N source Amorphous and 143... 

N3)AlMe2(H2NBut)] nonpyrophoric Horizontal hot-wall LP-CVD Amorphous and epitaxial film growth at 900 °C, no additional N source 143... 

Figure 6.11. Schematic of two of the reactors used (a) atmospheric pressure horizontal hot-wall reactor (Reactor A) and (b) vertical cold-wall reactor (Reactor B).

Three different reactors were used to deposit CuInS2 films via AACVD. Reactor A, shown schematically in Fig. 6.11a, was primarily used in the parametric studies described below. This is a horizontal, atmospheric pressure, hot-wall reactor with a plate-type 2.5-MHz ultrasonic nebulizer from Sonaer Ultrasonics. The precursor (1.5-3.5g) was dissolved into distilled toluene (50-400 ml) and fed into the nebulizer using a syringe pump. The nebulizer... 

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