Deposition zone temperature

The run-to-run deposition zone temperature (350-425 °C) was the first parameter varied. Temperature variation affected film stoichiometry [Fig. 6.25(a)] and crystalline orientation [Fig. 6.25(b)], while not significantly affecting the deposition rate [Fig. 6.25(c)], From Fig. 6.25(a), we can see that the films were closest to stoichiometry when deposited at 395 °C. Cu-to-In ratios ranged from... 

Variation of the deposition zone temperature affected the film stoichiometry and crystalline structure while not significantly affecting the deposition rate. A deposition zone temperature was optimized at 395 °C to produce (112)-oriented films without any detectable secondary phases. The susceptor location within the furnace did not affect the stoichiometry of deposited films, but it did alter morphology. Moving the susceptor toward the evaporation zone... 

Hydrothermal system at discharge zone is composed of five reservoirs such as ore deposit/zone IV boundary, zone III/II boundary, zone II/I boundary, zone I/fresh country rocks boundary and temperature of each reservoir is 250°C, 220°C, 150°C, 100°C, and 25 °C, respectively. 

The growth rate is quite sensitive to the axial temperature profile. An axial temperature profile that increases along the reactor because it improves the deposition uniformity is commonly used in industry. The temperature of each successive zone in the furnace (defined by the furnace elements in Figure E14.5a) can be adjusted by voltage applied to variac heaters. The zone temperatures are assumed constant within each zone, T-,j = 1,..., ntv where ntz is the number of temperature zones to be used,... 

Figure 7.10 illustrates a the dimensions of proposed reactor, which directs reactive gases over a ring of wafers. A cooling assembly can maintain the surface temperature of the deposit zone at 7 = 400°C, while the remainder of the lower wall and the upper walls are maintained at a higher temperature of Tw = 800°C. A principal design consideration... 

Assume that the system is being used to deposit cadmium onto the wafers. The inlet gas is primarily He, which carries a 1% trace of monatomic Cd vapor. The inlet mixture temperature is at the nominal wall temperature of T — 800°C. The cadmium vapor reacts to form a film on the lower-temperature deposition zone with a sticking coefficient of Y =0.8. All other sections of the reactor walls are presumed to be chemically inert. The process is intended to run at a nominal reduced pressure of p = 0.05 bar. 

Direct deposition of the contacts and gate insulator on to the crystal [95, 96], In this technique the gate dielectric is the polymer parylene, which forms conformal coatings with good dielectric and mechanical properties. The polymer is deposited in a three-zone reactor, in which the deposition zone can be kept at room temperature. 

Fig. 23. Thermochromatography of 106Ru in 02 gas (20 ml/min) in an empty quartz column. The solid line represents the temperature profile in the column. Two different Ru zones were observed after completion of the experiment (for details see text). Some of the Ru was not volatilized at the starting position. The dashed lines indicates the modeled deposition zone of a species transported by mobile adsorption with -Af/a0(RuO4)=54 kJ/mol. Figure reproduced from [92].

Preparation of Mixtures of -Xylylenes and Separation into Polymer on the Basis of Tc. The distillation and pyrolysis steps were conducted as described above for di-p-xylylene and substituted di-p-xylylenes. The pyrolysis gases were led immediately into a deposition zone which consisted of a 24-inch section of 1-inch i.d. glass tubing. The initial 15-inch section of this tubing (Zone A) was heated to 90°—100°C. The final 9-inch section of the tubing (Zone B) was maintained at room temperature. The end of the deposition zone was connected via rubber tubing through the dry ice trap to the pump. 

Chemical vapor deposition is a very complex process. There are numerous factors such as type, shape, and size of reactor, gas flow rate and arrangement that can affect the properties of the coating. Therefore, it is necessary to review briefly the process itself which includes reactor, reaction zones, temperature, pressure, precursors, and gas flow dynamics before discussing the thermodynamics and kinetics of the CVD. 

For the purposes of this discussion, deposition temperature is defined as the gas temperature close to the substrate. Due to the exhaust flow in the deposition hoods and the natural rising of hot air, the deposition temperature profile is skewed above the flame s longitudinal axis. The actual temperature of the substrate in the deposition zone depends upon the substrate material — size, absorption and emissivity characteristics — as well as the dwell time of the flame on one area of the substrate and whether or not any cooling is being applied to the substrate. 

It has been found that a higher deposition temperature causes a wider deposition zone. The above deposition process has been analyzed through a theoretical model that reveals the importance of the vapor and gas diffusivities, bulk phase reactant concentrations and the pore size of the support [Lin and Burggraaf, 1992]. Practically speaking, in order for the pores of the support to be plugged, their pore diameters should not be too large, preferably significantly smaller than 1 pm. 

Fig. 1.20 Thermochromatographic separation of the expected homologues of SHE in metallic state [83], The temperatures at the deposition zones maxima are indicated.

Figure 5.33 shows the microstructure characteristics of C/C composites fabricated by the TG-CVI process. The rough laminar pyrocarbon (RL) is located near the heating source at position 1 in Figure 5.32b and the corresponding microstructure is shown in Figure 5.33a. A mixture of smooth laminar and isotropic structure pyrocarbon (SL+ISO) at position 2 is formed and its microstructure is shown in Figure 5.33b. At and near the depositing zone, the pyrocarbon has a smooth laminar structure (SL), and the related microstructures are shown in Figure 5.33c and d. The structure characteristic of the pyrocarbon is dependent on the deposition temperature, the concentration and nature of the precursor as well as those of intermediates. During the TG-CVI process the width of the depositing zone (8) depends on the deposition temperature (Td), the...

For a given thermal gradient higher deposition temperatures result in a wider depositing zone. In this case the pores are very easily trapped within the composites because of the complex architecture of the preforms and a bottleneck effect for the bottle-shaped pores this produces poor infiltration for these pores. A relatively low deposition temperature and steep thermal gradient give rise to high density and uniform densification. 

The methane temperature before entering the deposition zone is assumed to be too low to activate ary chemical reactions. It is heated to the reaction temperature immediately once it enters the deposition zone. 

Table VII. Deposit Mass and Relative Build-Up Rates for the Three Pennsylvania Steam Coals at Three Furnace Temperatures (Deposition Zone Gas Temperature,...

Several conditions are necessary to achieve this process. Firstly, the reactants must be volatile and stable so that they can be transported to and from the deposition zone. Secondly, the solid product should have low vapor pressure under the deposition condition. The film properties (such as the film thickness and purity) depend strongly on the process parameters such as the reactor geometry, gas flow rate, gas composition, substrate temperature, and pressure. The CVD performed under low pressure, is especially referred to as the low pressure CVD (LP-CVD). 

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