ADDITIVE NITROGEN EFFECTS ON OXYGEN PLASMA DOWNSTREAM ASHING

Using an improved actinometry method, additive nitrogen effects on oxygen plasma downstream ashing have been studied. The ion current of the Langmuir probe and emission intensity change in OI(7774) and OI(8446) as a function of nitrogen mixing ratio showed that emission caused by dissociative excitation of oxygen molecules did not significantly influence the actinometry in our experiment. Thus, the actinometry measured accurate relative concentrations of atomic oxygen in the plasma by selecting XeI(4671) or XeI(4624) for the actinometer to OI(7774) and OI(8446) or by using ArI(7503) or ArI(7067) for the actinometer to OI(6258) and OI(4368). The change in the ashing rate and the relative concentration of atomic oxygen as a function of the nitrogen mixing ratio corresponded well, and both values at 10% nitrogen mixing were twice those with no nitrogen mixing. The activation energy was unchanged regardless of additive nitrogen. Therefore the role of nitrogen as the additive impurity gas is only to increase oxygen in the plasma. © 1990 IOP Publishing Ltd.