High-purity silicon for semiconductors

Although Ge was the first semiconductor to be used commercially, it is Si that now leads the world market. Germanium has been replaced, not only by Si, but by a range of recently developed semiconducting materials. All silicon semiconductors are manufactured by CVD. In Box 

A more recently developed CVD process starts with SiH4 (equation 27.10), which is first prepared from SiHCls by scheme 27.11. 

2SiHCl3 SiHjClz -b SiC 2SiH2Cl2 SiHsCl -b SiHClj 2SiH3Cl SiH4 -b SiHzClz 

The high-grade siUcon produced by CVD is virtually free of B or P impurities, and this is essential despite the fact that doping with B or P is routine. Careful tuning of the properties of n- or p-type semiconductors (see Section 5.9) depends on the controlled addition of B, Al, P or As during their manufacture. 

2SiHCl3 SiH2Cl2 + SiCU 2SiH2Cl2 SiHjCl + SiHClj 2SiH3Cl SiH4 + SiH2Cl2 

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The second example of balancing equations is illustrated for trimethylchloro-sUane, a flammable liquid used to produce high-purity silicon for semiconductor applications. Transportation accidents have resulted in spillage of this chemical and fires that produce carbon dioxide and a fog of silicon dioxide and hydrogen chloride dissolved in water droplets. The unbalanced equation for this reaction is... 

In one case, the separate solvent represents and contains the entrained impurities, while in the other case the molten material acts as the solvent to contain the entrained impurities. The method was developed to provide high-purity germanium for semiconductor research following the invention of the semiconductor junction transistor in 1947. It has since been developed into different variations, most notably the floating zone method used for the production of high-purity silicon single crystals. 

The silicon required by the electronics industry for semiconductor devices has to have levels of key impurities, such as phosphorus and boron, of less than 1 atom in 10 ° Si. Silicon is first converted to the highly volatile trichlorosilane, SiHCls, which is then distilled and decomposed on rods of high purity silicon at 1300 K to give high purity... 

In the early 1950 s it was used to provide high purity silicon and germanium for semiconductor applications. Since then it has been... 

Quartz exhibits a very low coefficient of thermal expansion (0.5 pm/m.K) and an elevated Mohs hardness of seven. Large and pure single crystals of quartz of gem quality called lascas are used due to their high purity in the preparation of elemental silicon for semiconductors (see Section 5.8.1). 

Polished high-purity N-type semiconductor-grade silicon wafers were used for cell growth (Silicon Quest International, Santa Clara, CA, USA). For cell growth, the silicon wafers were cut into small pieces of random shapes of... 

Purification. For those applications that require high purity such as semiconductor components and some nuclear graphites, the material is heat-treated in a halogen atmosphere. This treatment can remove impurities such as aluminum, boron, calcium, iron, silicon, vanadium and titanium to less than 0.5 ppm.f °l The halogen reacts with the metal to form a volatile halide which diffuses out of the graphite. The duration of the treatment increases with increcising cross section of the graphite part. 

Arsenic from the decomposition of high purity arsine gas may be used to produce epitaxial layers of III—V compounds, such as Tn As, GaAs, AlAs, etc, and as an n-ty e dopant in the production of germanium and silicon semiconductor devices. A group of low melting glasses based on the use of high purity arsenic (24—27) were developed for semiconductor and infrared appHcations. 

Silicon in the elemental state has important electronic applications as a semiconductor that were developed only during the last decade. The discovery of these uses was possible only after methods were developed for preparing silicon of extremely high purity. Reduction of Si02 with... 

The deposition temperature range is 250-600°C and the pressure is up to 20 T orr. T o minimize carbon inclusion, the carbonyl is highly diluted with hydrogen (ratio of 1/100) and high purity deposits can be obtained. PI Reaction (6) has a low temperature reaction and isbeing considered for deposition on silicon and III-V semiconductors. 

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