Precursor vaporized precursors

In PECVD, the plasma generation region may be in the deposition chamber or precede the deposition chamber in the gas flow system. The latter configuration is called remote plasma-enhanced CVD (RPECVD). In either case, the purpose of the plasma is to give activation and partial reaction/reduction of the chemical precursor vapors so that the substrate temperature can be lowered and still obtain deposit of the same quaUty. 

Processing variables that affect the properties of the thermal CVD material include the precursor vapors being used, substrate temperature, precursor vapor temperature gradient above substrate, gas flow pattern and velocity, gas composition and pressure, vapor saturation above substrate, diffusion rate through the boundary layer, substrate material, and impurities in the gases. Eor PECVD, plasma uniformity, plasma properties such as ion and electron temperature and densities, and concurrent energetic particle bombardment during deposition are also important. 

Precursor Vapor pressure (torr) Comments and temperature References... 

Sb precursor Vapor pressure (torr) Minimum achievable growth temperature (alloy grown ) (°C) Comment References... 

A schematic illustration of the gas-to-particle conversion route is shown in Figure 7.37. Precursor vapors react at high temperatures to form molecules of intermediate... 

Frequently, bursts of new particles are detected within the boundary layer over land or sea. Such phenomena have been investigated using simultaneous measurements of ultrafme aerosols and their precursor vapors—namely HjSO,—which strongly constrain the mechanisms of particle formation. Observations obtained at a clean continental site at Idaho Hill, Colorado on September 21, 1993 have been analyzed with the APM [30]. Since the variations in H2S04 vapor were carefully characterized in this instance, its production rate was constrained in the simulations to match the observed... 

Figure 4.S7. SEM images of an electroluminescent phosphor particle, ZnS (used in backhght displays for cell phones, watches, etc.), before (a) and after (b) the deposition of an aluminum oxide thin film. This film is a transparent coating that prevents the phosphor particle from undergoing humidity-accelerated decay. A technique known asfluidized-bed CVD was used, where a carrier gas both delivered the precursors to a vertically aligned CVD chamber, and dispersed the powdery sample in order to expose all surface regions to the precursor vapors.

Uses Inexpensive Precursors Soluble precursors are used instead of expensive, high vapor pressure organometallics. 

VDP of polyimides is usually performed in vacuum (pressures <10 Pa). Just as in any CVD process, the deposition parameters greatly influence the properties of the polyimide thin films. The effect of a few notable ones viz., substrate temperature and the relative fluxes of the precursor vapors is the focus of the next section. 

As the VDP of polyimides involves two precursors, diamine and dianhydride, the relative amounts of fluxes of the precursor vapors need to be controlled carefully to obtain high quality polyimide thin films. The effects of both excess dianhydride as well as the diamine components have been studied and reported in literature, It was observed that, excess dianhydride (PMDA) undergoes desorption when cured after deposition leading to poor thermal stability. 

In chemical vapor deposition (CVD) reactive vapor precursors react to produce solid materials in the gas phase or at the solid-gas interface on the substrate surface at appropriate temperatures. Typical precursors used in the CVD process are metal hydrides, metal chlorides, and metal organic compounds. In the case that the precursor species are metal organic compounds, the process is called metal-organic chemical vapor deposition (MOCVD). The precursor molecules are introduced into a reactor sometimes with a carrier gas and decompose by means of heat, irradiation of UV light, or electrical plasma formed in the gas. Thermal CVD is the most commonly used method. This technique has an advantage that refractory materials can be vapour-deposited at relatively low temperatures,... 

Fu et al. [131] prepared MCM-41 aluminosilicates using the two-step approach described earlier [68]. They first prepared well defined aluminosilicate polyanions AljjSig., (0H)j02( j5 (0 < X < 4) oligomers to be used as precursors. These precursors were then precipitated with CjgTMABr and treated with water vapor at 110 °C for 3 days. This method not only affords MCM-41 aluminosilicates with variable Si/Al ratios down to the lowest possible ratio of 1/1, but it offers additional flexibility in the design of new materials by using suitable building blocks. 

For the initial formation of a solid phase on a substrate surface from vapor precursors through heterogeneous nucleation, as is schematically illustrated in Figure 20.2, the critical nucleus size, r, and the corresponding energy barrier, AG, are given by the following equations ... 

Aerosol-assisted CVD introduces rapid evaporation of the precursor and short delivery time of vapor precursor to the reaction zone. The small diffusion distance between the reactant and intermediates leads to higher deposition rates at relatively low temperatures. Single precursors are more inclined to be used in AACVD therefore, due to good molecular mixing of precursors, the stoichiometry in the synthesis of multicomponent materials can be well controlled. In addition, AACVD can be preformed in an open atmosphere to produce thin or thick oxide films, hence its cost is low compared to sophisticated vacuum systems. CVD methods have also been modified and developed to deposit solid phase from gaseous precursors on highly porous substrates or inside porous media. The two most used deposition methods are known as electrochemical vapor deposition (EVD) and chemical vapor infiltration (CVI). 

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