Thermal dopant diffusion

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)... 

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... 

The preparational route for these luminescent ceramics follows the known ceramic technologies [12,13]. They are generated by thermally induced diffusion densification of powder aggregates below their melting temperature, which is referred to as sintering. As a consequence of this preparational route the properties of such ceramic scintillators are not only determined by the host lattice and the dopants (like the luminescent activator), but additionally by the processing technique. 

In the oxidation process, a layer of dopant is apphed to the surface of sihcon and patterned sihcon dioxide for subsequent thermal diffusion into the sihcon. The masking property of the Si02 is based on differences in rates of diffusion. Diffusion of dopant into the oxide is much slower than the diffusion into the sihcon. Thus, the dopants reach only the sihcon substrate. Oxide masks are usually 0.5—0.7 p.m thick. 

The thermal oxidation process is an essential feature of planar-device fabrication and plays an important role in the diffusion of dopants in Si. In the thermal oxidation process, Si reacts with either oxygen or water vapor at temperatures between 600 and 1250 °C to form Si02. The oxidation reaction may be represented by the following two reactions ... 

In Section 17.3.2(i) we have indicated a range of uses for polysilicon. For all of these applications there is a need to control layer structure. In addition, careful control of doping levels is also necessary. This can be done with post-deposition doping but this requires a high temperature (typically >900°C) in order to move the dopant atoms from the surface and to drive them into the layer. This high temperature diffusion step can cause thermal damage. One solution is to use in situ doping at the normal temperature of polysilicon deposition i.e., ca. 600°C. 

There is considerable evidence that hydrogen diffusion is the mechanism of thermal equilibration. The evidence is necessarily indirect because the hydrogen apparently does not participate directly in the defect or dopant states, but acts as a catalyst to the motion. For example, the movement of a hydrogen atom from one Si—H bond at site A to a neighboring dangling bond at site B is described by... 

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