THE CVD OF SILICON

This approach was successfully used in modeling the CVD of silicon nitride (Si3N4) films [18, 19, 22, 23]. Alternatively, molecular dynamics (MD) simulations can be used instead of or in combination with the MC approach to simulate kinetic steps of film evolution during the growth process (see, for example, a study of Zr02 deposition on the Si(100) surface [24]). Finally, the results of these simulations (overall reaction constants and film characteristics) can be used in the subsequent reactor modeling and the detailed calculations of film structure and properties, including defects and impurities. 

In the previous section, we discussed the CVD of silicon thin films. For the pressures and temperatures at which those depositions were carried out, the films were polycrystalline. If the depositions had been carried out at higher temperatures, single-crystal (epitaxial) films would have been possible. In this section, we will discuss some of the factors that govern the growth of epi silicon films. 

Uses Sterically hindered reducing agent to install highly hindered di-t-butylsilylene group for protection of 1,2 and 1,3-diols upon thermolysis, as source of silicon for the CVD of silicon carbide... 

Silicon oxynitride (SiO cN),) films exhibit properties that fall somewhere between those of Si02 and those of Si3N4 films and have diverse applications in microelectronics. The oxynitride layers can be obtained if nitrogen oxide (N2O) is involved in the reaction of silane with ammonia [108, 109, 117-119], when silicon nitride is deposited onto an oxidized silicon substrate (silicon dioxide nitrification is incomplete at 800°C [100, 107]), or upon addition of gaseous oxygen during the CVD of silicon nitride [64, 100, 104, 120]. 

The thermal nitration of a H-terminated Si surface and the CVD of silicon nitride were studied in situ by FTIR-IRRAS [160, 161]. The adsorption and thermal decomposition of phosphine (PH3) on a Si surface was also studied by IR absorption depending on the coverage and the exposure to the flux, PH3 adsorbs both nondissociatively and dissociatively, and the IR absorption peaks... 

Generally, epitaxial films have superior properties and, whenever possible, epitaxial growth should be promoted. The epitaxial CVD of silicon and III-V and E-VI compounds is now a major process in the semiconductor industry and is expected to play an increasingly important part in improving the performance of semiconductor and optoelectronic designs (see Chs. 13-15). 

Plasma CVD was first developed in the 1960s for semiconductor applications, notably for the deposition of silicon nitride. The number and variety of applications have expanded greatly ever since and it is now a major process on par with thermal CVD. 

This chapter is a review of the CVD of non-metallic elements and covers boron, silicon, and germanium. Silicon and germanium are borderline elements with metalloid characteristics. Both are important semiconductor materials, particularly silicon, which forms the backbone of the largest business in the world the electronic industry. All three materials are deposited by CVD on an industrial scale and a wide variety of CVD reactions are available. 

Fluorinated Silicon Oxide. The introduction of fluorine in the ratio of 2 to 14 at.% lowers the dielectric constant, which is reported as low as 3.0. This is a major factor in the design of dielctric films. The CVD of these fluorinated compounds is accomplished by plasma-CVD and usually with Sip4 as a fluorine source. Also available are fluorinated compounds, such as fluorotriethoxysilane (FTES), l,2bis(methyldifluorosilyl)ethane, and 2,5disilahexane.P2]... 

The III-V and II-VI compounds refer to combination of elements that have two, three, five, or six valence electrons. They have semiconductor properties and are all produced by CVD either experimentally or in production. The CVD of these materials is reviewed in Ch. 12. Many of their applications are found in optoelectronics where they are used instead of silicon, since they have excellent optical properties (see Ch. 15). Generally silicon is not a satisfactory optical material, since it emits and absorbs radiation mostly in the range of heat instead of light. 

A recent competitor to CVD in the planarization of silicon dioxide is the sol-gel process, where tetraethylorthosilicate is used to form spin-on-glass (SOG) films (see Appendix). This technique produces films with good dielectric properties and resistance to cracking. Gas-phase precipitation, which sometimes is a problem with CVD, is eliminated. 

Use the data of Appendix C to answer the following questions. (Assume that ACp is negligible—but would this affect your answer ) (a) At what temperature does CVD of silicon from SiH4 become thermodynamically feasible (b) Would CVD of solid Si (mp 1410 °C) from SiCU (g) be feasible under any circumstances, assuming that the liberated chlorine could be tolerated ... 

Materials processing, via approaches like chemical vapor deposition (CVD), are important applications of chemically reacting flow. Such processes are used widely, for example, in the production of silicon-based semiconductors, compound semiconductors, optoelectronics, photovoltaics, or other thin-film electronic materials. Quite often materials processing is done in reactors with reactive gases at less than atmospheric pressure. In this case, owing to the fact that reducing pressure increases diffusive transport compared to inertial transport, the flows tend to remain laminar. 

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. 

The reactions that have been used to create epi silicon films commercially involve the H2 reduction of the chlorosilanes. As we learned earlier in Chapter 1 in studying the equilibrium behavior of the H-CI-Si system, we can deposit solid silicon from SiCI4 + H2, SiCI3H, or SiCI2H2. Also, H2 can be added to the latter two, if desired. Obviously, silicon will also deposit from SiH4. The deposition rates of Si as a function of temperature, at atmospheric pressure, from the CVD of the above source gases are shown in Figure 16. 

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