This interface can be used to evaluate vertical diffusion and junction formation of a typical pn junction for a variety of dopants. The base substrate is crystalline <100> silicon of either p-type or n-type with a known resistivity. The dopant can be either boron, arsenic or phosphorus. The diffusion profile resulting from pre-deposition and drive-in can be calculated and plotted.
During the pre-deposition step a known dose of impurity is introduced into silicon. Based on the temperature and time of this process, the junction depth and surface concentration can be calculated. This is usually a shallow junction and follows a constant source diffusion profile. The resulting junction depth, surface concentration and sheet resistance can be calculated.
The dose introduced during pre-deposition step is diffused deeper into silicon during the drive-in step till it reaches the desired depth and resistivity. For a given temperature and time of drive-in, the resulting junction depth, sheet resistance and surface concentration can be found out.
The plotter will show separate profiles for the pre-deposition and drive-in steps. The depth at which these profiles meet the background concentration of the wafer is the junction depth. Using the crosshair tool this location can be read out from the graph. The concentration at any depth can also be found out from the graph.