Ion implantation
Why is BF2⁺ sometimes implanted instead of boron alone to form shallow p-type layers?
- ABecause BF2⁺ acts as an n-type dopant
- BBecause BF2⁺ makes the equipment cheaper
- CBecause the molecular ion is heavy, so boron goes in shallower at the same acceleration energy
Show answer and explanation
Answer: C. Because the molecular ion is heavy, so boron goes in shallower at the same acceleration energy
Boron is light and tends to go deep even at low energy. When implanted as BF2⁺, the whole molecule is heavy, so the energy shared by the boron atom is small and it goes in shallower. Because very-low-energy beams are hard to handle, this method has been used.