The problem of plasma source ion implantation for a deep, plasma-fille
d, cylindrical hole in a flat plate is considered. The structure of th
e ion-matrix sheath resulting from the application of a zero-rise-time
, negative-voltage pulse to the target is computed. Solutions for the
potential structure in and around the hole are presented. It is found
that the sheath does not conform completely to the hole until the radi
us of the hole is larger than the ion-matrix overlap length. ion traje
ctories across the sheath are found to impact upon the side wails of t
he hole at glancing angles, a situation that is unfavourable to implan
tation.