Reactive ion etching end-point determination by plasma impedance monitoring

Impedance monitoring of a rf glow discharge is successfully used to determine the end point of reactive ion etching. The feasibility of using this technique is demonstrated on diode, triode, and magnetic multipole enhanced triode reactors applied to etching polycrystalline silicon on SiO2 on Si and Si3N4 on Si in an SF6 plasma, and to stripping photoresist on Al on Si in an O2 plasma. The end point of etching is determined by monitoring changes in the induced dc bias, the rf voltage, the rf current, or the phase relationship between them on either of the powered electrodes (in the cases of the triode configurations). This method is easily applicable as in in-process end-point detector and eliminates the need of optical access to either the plasma or the substrate.