Predeposition boron

Boron. For the predeposition of boron, the most prevalent species in the gas phase in the furnace is B203. Once B203 is deposited on the silicon surface, the oxide reacts with the silicon to bring about doping, as shown in equation 4. 

Figure 1 is a plot of boron concentration versus ps that illustrates Henry s law. When the solid solubility of boron in silicon is reached, Henry s law no longer applies. Thus, most predeposition steps are operated at a sufficiently high partial pressure in the dopant gas phase to achieve solid solubility of the dopant in the silicon. This requirement provides a natural control for reproducible diffusion results. 

A jxanction in silicon is made by doping it with boron. This is done by first depositing a layer of boron on tire chip (predeposition), followed by what is termed drive-in diffusion. If the deposition step requires 5 min, at what distance from the surface is the concentration of boron raised by 3 x 10 afoms/cm during this interval The density of pure boron is 5.1 x 10 atoms/cm, ifs diffusivity 5.8 x Ifb pm /h. 

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