Epitaxial silicon thin films

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. 

Silicon Epitaxy. A critical step ia IC fabricatioa is the epitaxial depositioa of sdicoa oa an iategrated circuit. Epitaxy is defined as a process whereby a thin crystalline film is grown on a crystalline substrate. Silicon epitaxy is used ia bipolar ICs to create a high resistivity layer oa a low resistivity substrate. Most epitaxial depositioas are doae either by chemical vapor depositioa (CVD) or by molecular beam epitaxy (MBE) (see Thin films). CVD is the mainstream process. 

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. 

Compounds in groups IIA-IVB may be prepared in bulk form by direct reaction and grown by gradient freeze or Bridgman techniques. Thin-film direct reaction is capable of making MgaSi in epitaxial form on silicon. ... 

The critical aspect of modern thin film technology is the growth of epitaxial layers. We illustrate the importance of epitaxial growth and strainengineering in producing light emitting films on silicon substrates. 

The CVD method is very versatile and can work at low or atmospheric pressure and at relatively low temperatures. Amorphous, polycrystalline, epitaxial, and uniaxially oriented polycrystalline layers can be deposited with a high degree of purity, control, and economy. CVD is used extensively in the semiconductor industry and has played an important role in past transistor miniaturization by making it possible to deposit very thin films of silicon. CVD also constitutes the principal building technique in surface micromachining (see below). 

The increase of the substrate temperature up to 100 °C results in an appearance of the new surface phase ((2/3) 3x(2/3) 3)-R30° (Fig. lb). This surface phase looks to be a thin epitaxial magnesium silicide film with the misfit 1.9 % with a silicon lattice [5]. According to our EELS data this surface phase is characterized by surface (hux = 9.8 eV) and bulk (hux, = 13.6 eV) plasmons, while for thick magnesium silicide films the surface (hoy = 10.3 eV) and bulk (htav= 14.6 eV) plasmons are typical [8]. The observed difference could be caused by tension of surface phase lattice. At further adsorption the metallic magnesium grows atop the silicide surface phase. 

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