Junction depth estimation using wet chemical etching for deep junction fabricated by laser doping

In this work, a wet chemical etching technique has been used to estimate the depth of a p-n junction. The wet chemical etchant used is HF/HNO₃/H₂O solution. Subsequent to this process, optical and electron microscope imaging of cross-section was done to estimate the junction depth. This technique has been used for characterizing deep junction (up to 10 μm) formed by laser doping. Sheet resistances were measured after laser doping on 10 mm × 10 mm area with different scan speed from a heavily doped emitter. Sheet resistance reduces as scan speed is reduced. This indicates formation of deeper junction with lower scan speed. Selective emitter was prepared for chemical etching. Chemical etching leads to staining of n-type surface. An etching of 5 min reveals junction depths of different values from 1.8-8.1 μm. The emitter fabricated by thermal diffusion as source for laser doping was measured to be 419 nm thick. SEM study shows clear difference between n and p-type region. Hence, this technique may be very useful when formation of a deep junction is expected or when SIMS study is very difficult.