Polysilicon epitaxial

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 ... 

The short penetration depth of UV/blue photons is the reason that frontside CCD detectors have very poor QE at the blue end of the spectrum. The frontside of a CCD is the side upon which the polysilicon wires that control charge collection and transfer are deposited. These wires are 0.25 to 0.5 /xm thick and will absorb all UV/blue photons before these photons reach the photosensitive volume of the CCD. For good UV/blue sensitivity, a silicon detector must allow the direct penetration of photons into the photosensitive volume. This is achieved by turning the CCD over and thinning the backside until the photosensitive region (the epitaxial layer) is exposed to incoming radiation. 

Here, it is easy to see the various layers and steps necessary to form the IC. We have already emphasized the formation of the n- and p-wells 8uid the individual proeess steps needed for their formation. Note that an epitaxial layer is used in the above model. There are isolation barriers present which we have already discussed. However, once the polysilicon gate transistors are formed, then metal Interconnects must then be placed in proper position with proper electrical isolation. This is the function of the dielectric layers put into place as succeeding layers on the IC dice. Once this is done, then the wafer is tested. 

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. 

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. 

Polysilicon production Epitaxial deposition Fiber optics... 

In metallurgy, according to Ramachandran et al., hydrogen is used in the reduction stage in the production of nickel in a process known as the Sheritt Gordon Process. In electronics, hydrogen is used in the epitaxial growth of polysilicon by wafer and circuit manufacturers. 

Another type of integrated micromachined structure different from the anchored polysilicon surface films occurs by adding the micromachined structure to the wafer after the IC is created by plating or film deposition. Texas Instruments DLP technology with aluminum metal is the most well known example [3]. However, these types of structures are not used in large-scale automotive production. Another class of micromachined devices is made from silicon-on-insulator (SOI) components and could easily be described as surface micromachined, since they have mechanical structures on the surface. These devices use the buried oxide of the bonded wafer as the sacrificial layer [6]. A similar structure created by epitaxial deposition of silicon over oxide produces a polysilicon structure [7]. Figure... 

Epitaxial growth of polysilicon Manufacture of vacuum tubes, light bulbs Heat bonding of materials ( brazing )... 

Chemical Vapor Deposition. Chemical vapor deposition (CVD) is a process where by the heat-induced decomposition of gases form different semiconductor layers such as silicon dioxide, silicon nitride, polysilicon, and gallium arsenide on the surface of the wafer. When the layer formed is a continuation of the crystalline structure of the substrate, the process used is epitaxial growth. Other, non-epitaxial forms of CVD involve the deposition of layers that are a different structure than the substrate. Table 5 outlines typical chemistries associated with CVD. 

Epi-seal encapsulation developed by Kenny et al. at Stanford University consists of a 20 50-p,m thick epitaxially grown polysilicon encapsulation layer covered by 4 ttm passivation oxide. Aluminum partially covers the encapsulation to form electrical interconnects [109], Investigation on the hermeticity and diffixsion behaviors of epi-seal wafer-scale polysilicon thin-film encapsulation revealed that hermeticity of the encapsulation is gas species specific hydrogen and helium easily travel in and out of the encapsulation, but nitrogen and argon do not [110],... 

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