Diffusion practice problems
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Read the Diffusion example calculations class notes.
Phosphorus is diffused into a silicon wafer using a two-step process. The final profile must meet the following requirements:
- surface concentration: N(0) = 9x1019 cm–3 and
- junction depth: xj = 1 μm.
The wafer has a constant background doping of NB = 3x1016 cm–3.
Design the diffusion (choose values for D1t1 and D2t2) to meet the requirements.What is the dose that would be introduced into the silicon during the deposition step? Also, choose temperatures and times for the drive and depostion steps to give the correct Dt for each. (There are many possible answers for each Dt. The values given below are not unique.)
The surface concentration during the depositon step is determined by the solid-solubility limit.
For this diffusion use Ns = 1x1021 cm–3.