APPLICATION OF THEORY:      JUNCTION DEPTH

The calculated values for concentration can offer information about the device structure. For example if dopant atoms diffuse in silicon, to create a pn junction, one would like to know until where they diffuse, thus the junction depth (see picture below). Also, if the junction is abrupt , as desired, or not. Knowing the solutions for concentrations gives the possibility to change the fabrication conditions (temperature, for example) in order to obtain the desired profile.

• Surface concentration is limited by solid solubility
• Depth profile is determined by time and diffusivity (=diffusion constant)

           If for example the bulk material is silicon doped with boron, and phosphorous is added, the junction depth is the distance where phosphorous concentration is equal to the boron concentration. The junction depth depends on the type of diffusion process. For:

• Drive in diffusion:
• Predeposition diffusion: