be described below with reference to fig8 the capacitive cleaning electrode 80 may tap rf power from a selected winding of the inductive coil antenna 45 thus eliminating the need for a separate rf power source for the capacitive cleaning electrode 80 the rf power applied to the capacitive cleaning electrode 80 is preferably adjusted to achieve the requisite balance between contaminant deposition rate and bombarding rate either by adjusting the rf power level of the separate rf generator 85 in the embodiment of fig1 or by moving the coil tap in the embodiment of fig8 how to reach the balance between deposition and bombarding rates is best understood by reference to fig3 which illustrates the deposition rate ordinate as a function of the bias potential abscissa on the surface in question the negative portion of the ordinate is a region of 34 negative 34 deposition or in other words removal this region is preferably avoided at all costs since what is removed is all material including the underlying material of the surface itself not merely the contaminants thereon fig3 shows that at first as the surface potential is increased from zero the deposition rate increases this is because some minimal kinetic energy is required to achieve a strong bond between the deposited particle and the material on the surface and the kinetic energy increases with the bias potential thereafter above a certain rf bias potential the.