Epitaxial silicon films

As noted earlier in Chapter 3, epitaxial silicon films deposited by CVD can be affected by autodoping. If diffusion of the doping species is excessive, the film is not a useful one. Therefore, quite a lot of effort has been spent to accurately measure the distribution of dopant through the film thickness. 

P Zorabedian, F Adar. Measurement of local stress in laser-recrystallized lateral epitaxial silicon films over silicon dioxide using Raman scattering. Appl Phys Lett 43 177-179, 1983. 

Silicon Epitaxy. Silicon epitaxial films have superior properties. The applications are, however, limited by the high temperature of deposition, which is generally above 1000°C. These reactions use chlorinated compounds of silicon (tetrachloride, trichlorosilane, or dichlorosilane) as precursors as follows ... 

The CVD reactions used to produce epitaxial silicon are described in Ch. 8. Originally, atmospheric-pressure CVD was used, but it is gradually being replaced by low-pressure CVD in spite of higher equipment cost and complexity. Low-pressure CVD appears to yield a better film with less autodoping and pattern shift. 

Polysilicon is a contraction of polycrystalline silicon, (in contrast with the single-crystal epitaxial silicon). Like epitaxial silicon, polysilicon is also used extensively in the fabrication of IC s and is deposited by CVD.f l it is doped in the same manner as epitaxial silicon. Some applications of poly silicon films are ... 

Epitaxial thin films, 24 742 Epitaxy, 22 152, 185. See also Epitaxial growth Heteroepitaxy in FET fabrication, 22 163-164 in HBT fabrication, 22 166, 167 in RTD fabrication, 22 170 silicon purification via, 22 496 197 vitreous silica in, 22 442 Epitaxy crystallization, ion-beam-induced, 14 447-448... 

When classifying chemical products, Seider et al. [3] identify three categories (1) basic chemicals (commodity and specialty chemicals, bio-materials, and polymeric materials) (2) industrial chemicals (films, fibers, paper,. ..) and (3) configured consumer products (dialysis devices, post-it notes, transparencies, drug delivery patches,. ..). In the manufacture of epitaxial silicon wafers, a thin film of crystalline silicon is often deposited on a polished crystalline silicon... 

Epitaxial thin films of silicon, to be deposited on crystalline silicon wafers, require no materials development. Other semi-conductor materials are possible, but silicon continues to be most cost-effective, principally due to the relatively... 

For industrial products, the remaining four steps are elucidated in Fig. 10.4-1. After the Concept Development step (see Fig. 10.3-2), preliminary product design occurs in the Feasibility step of the Stage-Gate process - which is not applicable for epitaxial thin films of silicon, as prototype thin films are normally not needed. 

Using a 260/wafer sales price for epitaxial silicon wafers and the United States MACRS tax-basis depreciation schedule, the investor s rate of return (IRR) is 18.3%. In addition, the return on investment (ROI) is 25.3%. These measures increase significantly with small changes in sales price for example, at 273/wafer, the IRR is 29.9%. Note that the economic analysis is somewhat shielded from variations in the price of epitaxial wafers because it is strongly linked to the price of the incoming polished wafers. In other words, the key metric of interest is the value added to the wafer by the epitaxial film deposition. 

In the present chapter, we will turn our attention to films deposited by thermal CVD that are either dielectrics or semiconductors. There are, as one would expect, many films that can be deposited by this technique. In addition, there are many gaseous reactants that one can use to create each film, the choice depending on the film characteristics desired. Rather then attempt to catalogue all of the possible films and reactants, we will choose instead to focus on silicon dioxide, silicon nitride, polysilicon, and epitaxial silicon as the films of interest. At the same time, we will only look at those reactant gases that have been used for integrated circuit manufacture. An excellent survey of the film types that can be deposited by CVD and the many reactants that have been used to obtain them has been given by Kern.1... 

When we consider silicon films, on the other hand, the nature of the solid deposit is crucial to the behavior of the film. Depending on deposition conditions, we can deposit amorphous, polycrystalline, or single crystal films. As was noted in Chapter 1, the morphology of polycrystalline films can be complex. In the present section, we will review some aspects of polysilicon (poly) thin films deposited by CVD. The final section of this chapter will be devoted to epitaxial silicon thin films. 

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. 

The next three chapters review the deposition of thermally-induced dielectric films (Chapter 3) and metallic conducting films (Chapter 4), as well as plasma-enhanced films of either type (Chapter 5). The many chemical systems employed to create these films are considered, and the nature of the resulting films is presented. Films studied are silicon dioxide, silicon nitride, polysilicon, epitaxial silicon, the refractory metal silicides, tungsten and aluminum. 

For silicon, the process can be used to grow films with thicknesses of 1 jtimto >100 nm. Some processes require high substrate temperature, whereas others do not require significant heating of the substrate. For photovoltaic applications, epitaxial silicon is usually grown using liquid-phase epitaxy (LPE) [1-3] and vapor-phase epitaxy (VPE) [4-6], which is a modification of chemical vapor deposition (CVD). 

S. Jin, H. Bender, L. Stalmans, R. Bilyalov, J. Poortmans, R. Loo, M. Caymax, Transmission electron microscopy investigation of the crystallographic quality of silicon films grown epitaxially on porous silicon,/. Cryst. Growth, 212, 119-127 (2000). 

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