Plasma amplified photoelectron process endpoint detection apparatus

Abstract

A plasma processing apparatus and process endpoint detection method including a plasma chamber for processing an item that has a first portion of a first material and a second portion of a second material, with the first and second materials having different work functions, and a structure for generating a plasma in the plasma chamber, with the plasma generating structure including at least a pair of RF-power electrodes with one of them being excited by an RF excitation frequency. The apparatus further includes a structure for generating and ejecting electrons from the second material only when the second material is exposed to the plasma, and a structure for increasing the energies of these generated electrons and accelerating these electrons into the etching plasma with sufficient energy to generate secondary electrons in the plasma. The apparatus further includes a structure for receiving a plasma discharge voltage signal, a structure for filtering the discharge electrical voltage signal to remove the RF excitation frequency and any DC components therein, and a structure for amplifying the natural frequencies of excitation and decay of the plasma discharge voltage perturbation signal, to thereby detect the processing endpoint. In a preferred embodiment, the electron energy increasing and accelerating structure includes a structure for generating an electrode voltage sheath, and a structure for generating the electrons within this voltage sheath to thereby accelerate the electrons into the plasma. The electron generating structure includes a structure for directing a beam of photons in a selected energy range onto the item to be processed, which energy range is not sufficient to eject photoelectrons from the first material, but is high enough to generate photoelectrons from areas of exposed second material.