FLOW-RATE RULE FOR HIGH-ASPECT-RATIO SIO2 HOLE ETCHING

Residence time effects on high aspect ratio SiO2 hole etching with a 9 0% Ar addition to C4F8 have been studied using a planar type neutral l oop discharge. An adopted wide-type antenna instead of the original na rrow one enabled us to improve uniformity of ion currents, electron de nsities, and plasma generation over a wide range of pressure. Thus, th e residence time (tau) dependence of radical and ion densities, and et ched features were investigated for various pressures (P). It was foun d that the conditions which achieved high aspect ratio features follow ed a straight line passing an origin in the tau-P diagram. This demons trated that the high aspect ratio feature etching was determined unequ ivocally by the adequate flow rate, because the gradient of the line r esulted in the reciprocal of the flow rate. On the other hand, at shor t tau, a large amount of radicals generated due to suppressed recombin ation produced the excess polymer deposition, causing the ''etch stop. '' At longer tau, ions and radical densities decreased due to recombin ation and thus dominated Ar+ ion sputtered the mask resist, forming th e tapered feature. (C) 1998 American Vacuum Society.