Rejection of P+ contamination in P++ implants on the Eaton 8250

Implants with P⁺⁺ have some risk of contamination with P⁺ at approximately half the desired energy. The dimer P₂⁺ breaks up after extraction resulting in P⁺ ions that have the same magnetic rigidity as P⁺⁺ ions. Medium current implanters used for P⁺⁺ often include a reflective energy filter (REF) after the mass analysis magnet to reject P⁺ ions. As the beam passes through an electrode biased at over half the extraction potential, the P⁺ ions do not have enough energy to pass through and are rejected. The beam transport of the Eaten 8250 includes electrostatic lenses and scanning which are inherently selective against the P⁺ ion because it has half of the electrostatic rigidity (E/Q) of the P⁺⁺ ion. This paper describes the beam transport mechanisms that lead to this effect and shows that P⁺ contamination of P⁺⁺ implants is below the level of detection with SIMS without the use of an REF