Three-dimensional dose uniformity of plasma immersion ion implantation shown with the example of macro-trenches

Plasma Immersion Ion Implantation (PIII) is presently at the border of indu strial application, both in the semiconductor and in the metallurgical fiel d. Among its advantages, the dose uniformity, even if treating three-dimens ional objects, is often quoted. In order to study the homogeneity of PIII, macro-trenches (with dimensions of tens of mm) with different aspect ratios have been treated in an argon plasma. The trenches have been lined with Ta foil coated with a Ta2O5 film. The distinct interference colour of Ta2O5 i s strongly dependent on its layer thickness. Therefore, it is easy to deter mine the remaining layer thickness after implantation, when parts of the Ta 2O5 layer have been removed due to sputtering during Ar ion bombardment. Th e results show that a lateral gradient at the remaining oxide layer thickne ss on the outer sides of the trench is observed while the inner walls of th e trench are hardly affected. In contrast to this, in the bottom of the tre nch a considerable part of the oxide has been lost by sputtering. This show s that there is a considerable treatment inhomogeneity, when complex shaped objects such as trenches are treated with PIII. This is explained with the expansion of the plasma sheath during the high voltage pulses and with the resulting ion trajectories. (C) 1999 Elsevier Science S.A. All rights rese rved.