Diffusion dopants

When the structure of a metal changes, it is because there is a driving force for the change. When iron goes from b.c.c. to f.c.c. as it is heated, or when a boron dopant diffuses into a silicon semiconductor, or when a powdered superalloy sinters together, it is because each process is pushed along by a driving force. 

A report on doping of polyacetylene by metal halides 462-463) shows that the interplanar spacing increases with the size of the anion and clustering is inferred to occur at low dopant levels as the dopant reflection appears at about 3 mol% while much of the material is still undoped. It is not totally clear whether similar effects might be the result of a combination of slow dopant diffusion and a diffusion coefficient which is dependent on dopant concentration this is discussed in more detail below. 

In view of the uncertainties regarding the native point defect in Si, it is necessary in discussions of self-diffusion and dopant diffusion to take account of both types of defects. 

Point Defect Models of Diffusion in Silicon. Under conditions of thermal equilibrium, a Si crystal contains a certain equilibrium concentration of vacancies, C v°, and a certain equilibrium concentration of Si self-interstitials, Cz°. For diffusion models based on the vacancy, Cv° Cf and the coefficients of dopant diffusion and self-diffusion can be described by equation 27 (15)... 

For diffusion models based on self-interstitials, C° Cv°. Dopant diffusion and self-diffusion are assumed to occur via an interstitialcy mechanism (32). Mobile complexes consisting of self-interstitials in various charge states and impurities are assumed to exist. 

Excess Point Defects and Low-Thermal-Budget Annealing. Submicrometer VLSI (very-large-scale integration) technologies require low thermal budgets (the product of dopant diffusivity and diffusion time) to limit the diffusional motion of dopants. Two options exist to reduce the thermal... 

Additive processes ion implantation, 361 metal layer deposition, 361 resist requirement, 361 vapor dopant diffusion, 361 Additives for F scavenging, 415 Advanced very-large-scale integrated-circuit package, 490, 492 Aluminum... 

Kim, J., McMurray, J.S., Williams, C.C. and Slinkman, J. (1998) Two-step Dopant Diffusion Study Performed in Two Dimensions by Scanning Capacitance... 

Frequently, dopants diffuse and the enhanced properties they impart to the silver halides are transitory. Much is known about how divalent cations... 

Figure 2.12 Crucible for dopant diffusion into porous SiC...

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