PA-CVD

In most cases, CVD reactions are activated thermally, but in some cases, notably in exothermic chemical transport reactions, the substrate temperature is held below that of the feed material to obtain deposition. Other means of activation are available (7), eg, deposition at lower substrate temperatures is obtained by electric-discharge plasma activation. In some cases, unique materials are produced by plasma-assisted CVD (PACVD), such as amorphous silicon from silane where 10—35 mol % hydrogen remains bonded in the solid deposit. Except for the problem of large amounts of energy consumption in its formation, this material is of interest for thin-film solar cells. Passivating films of Si02 or Si02—deposited by PA CVD are of interest in the semiconductor industry (see SEMICONDUCTORS). 

FIGURE 10. SEM of Pt fractal channels prepared by PA-CVD on Sn02 . Reproduced from Reference 76 by permission of IEEE... 

Formation of platinum fractal-like structures is possible by PA-CVD (19% Ar, 80% O2, 1% SnMe4) on tin oxide thin films using Pt(acac)2 as starting material . The platinum aggregates show a dendritic structure of fractional dimension D ca 1.1-1.6 (Figure 10). The occurrence of such aggregates has been correlated to the concentration of the platinum precursor and to the radio-frequency power applied to the substrate electrode. Fabrication of microsensors integrated on silicon wafers with the help of photoresistors is possible . 

Numerous deposition methods, such as ionized metal plasma deposition, physical vapor deposition, ALD, CVD, PA-CVD, PE-CVD, electroplating and electroless plating have been used to deposit copper films on different substrates. For CVD and ALD, several copper(I) and copper(II) enolates were developed which may be of interest as suitable precursors. The use of these complexes enabled the development of new technologies that are demanded to fulfill the requirements of the microelectronic industry. 

A close collaboration between designers and surface engineers is required in the future. Schaeffler delivers around 75 million high-quality PVD- and (PA)CVD-coated components every year that enable outstanding applications, preserve resources and meet increasing customer requirements. 

Pa (10 10 ° Torr)) condition such that the volatile species travels at a relatively high velocity to the substrate wafer. The growth rate is 0.01-0.3 ///min which starts to be competitive with CVD deposition rates. 

G. Lucovsky, D. E. Ibbotson, and D. W. Hess, eds.. Characterisation of Plasma-PInhanced CVD Processes Materials Kesearch Society Symposium Proceedings, Vol. 165, Materials Research Society, Pittsburgh, Pa., 1990. 

The gases used in the CVD reactor may be either commercially available gases in tanks, such as Ar, N2, WF, SiH, B2H, H2, and NH Hquids such as chlorides and carbonyls or soflds such as Mo carbonyl, which has a vapor pressure of 10 Pa (75 mtorr) at 20°C and decomposes at >150° C. Vapor may also come from reactive-bed sources where a flowing haUde, such as chlorine, reacts with a hot-bed material, such as chromium or tantalum, to give a gaseous species. 

Gordon,R. G., Recent Advances in the CVD of Metal Nitrides and Oxides, Proc. of the Conf on MOCVD of Electronic Ceramics, Material Research Soc., Pittsburgh, PA (1994)... 

Geriatric Considerations - Summary Increased risk of side effects in patients with CVD and hepatic dysfunction. Theophylline has a narrow therapeutic index and is associated with numerous drug interactions. Target serum concentrations are 5-20 mg/L, with adverse effects increasing between 15-20 mg/L. Hepatic metabolism and renal excretion declines with age and the half-life of theophylline increases by 3 to 9 hours in older adults. Smoking induces theophylline metabolism therefore, if a pa-tienf sfops smoking, empiric dosage reduction may be indicated and follow serum concenfrafions closely. 

Fig. 2.23 Computational solution to a CVD reactor, stagnation-flow problem. The white arrows illustrate the streamlines, and the color (grayscale) illustrates the temperature field. Flow enters both through a porous showerhead assembly and through an annular channel adjacent to the outer wall. The exhaust exits downward through the annular channel. The process is running at a reduced pressure of 10,000 Pa (approximately one-tenth of atmospheric pressure). The fluid properties are those for air.

Consider the design of a channel-flow CVD reactor as illustrated in Fig. 5.23. The flow is presumed to be isothermal at a temperature T = 1000 K and the nominal process pressure is p = 1 x 103 Pa. At nominal operting conditions, the flow enters the sloping section with a mean velocity of V = 10 m/s. The active reactant (species A) is carried as a trace component in helium. There is a 300 mm section of the lower wall (including the... 

A PVD-type reactor can be one in which molecules reach the surface directly in a molecular beam from some source or sources in which raw materials are vaporized. At the pressures commonly used (<10 6 Pa), the vaporized material encounters few intermolecular collisions while traveling to the substrate. Historically, higher pressure processes, such as sputtering and close-spaced vapor transport, have been classified as PVD (I). These processes also use physical means to generate the gas-phase species. However, the transport phenomena that need to be modeled for such higher pressure processes are more similar to CVD than PVD because of the diffusive-convective nature of transfer from the gas phase to the substrate. 

Low-Pressure CVD Processes. Low-pressure CVD (LPCVD) (—101 Pa) is the main tool for the production of polycrystalline Si dielectric and passivation films used in Si IC (integrated-circuit) manufacture (1, 20, 21). The main advantage of LPCVD is the large number of wafers that can be coated simultaneously without detrimental effects to film uniformity. This capability is a result of the large diffusion coefficient at low pressures, which... 

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

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. 

Figure 14. Examples of concentration-driven recirculations in an isothermal (550 K) vertical CVD reactor for the growth of a Hg-containing compound at 101 kPa showing streamlines (left side) and isoconcentration curves (right side). The inlet Hg partial pressures were (a) 10.1 kPa and (b) 10.1 Pa (Reproduced with permission from reference 205. Copyright 1988 Elsevier.)...

The silicon carbide-based ceramic layer is obtained by CVD activated by a microwave plasma (2.45 GHz) on the tantalum previously cleaned by an argon plasma (56 min, 133 Pa, 250 W) at a temperature identical to the deposition temperature (T = 570°C), lower than the substrate annealing temperature. After readjustment of the total pressure and microwave power by introduction of a precursor (TMS) in the argon flow, the SiC coating is produced under selected conditions (66 Pa, TMS/Ar = 0.2/5.5 l.h-, T = 570°C, 350 W) derived from a previous parametric study. Coatings obtained then presented low dry friction coefficients. The mechanical properties, which are essential in order to be able to appreciate the mechanical stability, were acquired by several methods ... 

R.J. Holdsworth, PA. Martin, D. Raisbeck, and M.E. Pemble, In Situ, Monitoring of Atmospheric Pressure Tin Oxide CVD Using Near-Infrared Diode Laser... 

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. 

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