Predict the depth of the Si–P thin film after 1.5 h, if the target concentration is 5% of the surface
Consider Phosphorous (P) doping of a silicon (Si) wafer shown in Figure 1 for the fabrication of
solid-state microelectronic devices. Consider a simplified case where the P-atom, concentration is
constant at the interface. As the diffusion coefficient of P atoms in crystalline silicon is very low, and
only a thin film of Si–P is desired, P atoms do not penetrate very far into the Si. Therefore, the P
atoms cannot ‘‘see’’ through the entire thickness of the wafer, and the Si solid serves as a semi-
infinite sink for the diffusion process.
Consider the P doping of crystalline Si at 1100 °C, a temperature high enough to promote
Phosphorous diffusion. The surface concentration of Phosphorous (cAs) in the Si is 2.5 * 1020 atoms
P/cm3
solid Si, which is relatively dilute, as pure solid Si is 5 * 1022 atoms Si/cm3
solid. Furthermore,
the P-rich coating is considered as an infinite source relative to the amount of P atoms transferred, so
that cAs is constant.
Predict the depth of the Si–P thin film after 1.5 h, if the target concentration is 5% of the surface
value. Also plot the phosphorous concentration profile against the depth of silicon wafer (use graph
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