Quasi-direct current plasma immersion ion implantation

Quasi-dc (direct current) plasma immersion ion implantation (PIII) is demon strated in the long-pulse mode. To prevent plasma extinction as a result of the sheath reaching the vacuum chamber wall in long-pulse experiments, a g rounded grid is used to partition the chamber into two halves. The pulse wi dth can be readily increased to 500 mus that is more than 10 times longer t han that in typical low-pressure PIII experiments for monoenergetic implant ation (ion mean free path > sheath thickness). The electron saturation curr ent measured by the Langmuir probe indicates that the grounded grid indeed stops the propagation of the plasma sheath. After the plasma sheath reaches the grounded grid, the pulse current drops to a smaller value indicative o f the quasi-dc PIII mode. The plasma recovery time is found to be 800 mus t hereby limiting the maximum pulsing frequency to below 1 kHz, and the prefe rred pulse duration window is between 100 and 500 mus. The secondary ion ma ss spectrometry profiles show that low energy ions are reduced using long p ulses. This operation mode thus offers the unique advantage of a smaller lo w-energy ion component, that is, more monoenergetic ion distribution, and l ess surface damage compared to conventional short-pulse PIII. When compared to dc-PIII, this mode retains the discharge characteristics and works well for insulators. (C) 2001 American Institute of Physics.