Plasma-assisted etch process with endpoint detection

Process for fabrication of an article comprising at least one operation during which the article undergoing fabrication comprises a layer of first material to be etched in at least one preselected region, the layer of first material being overlying a second material to be retained, the first material being etched primarily by a chemical reaction with at least one reactive species produced by a plasma within a plasma reactor, the plasma resulting from imposition of an electrical field across a vapor medium between electrodes, the etching being monitored by means including detection of electromagnetic radiation emitted by an excited species formed as a consequence of a chemical interaction between a species and article material in the preselected region, the means comprising optical path means for illuminating a detector with such radiation, and detector output means, characterized in that

• (a) the optical path means sense substantially only radiation emitted from within a restricted first volume of space adjacent the preselected region, with a contrast of at least 50%, the volume having lateral dimensions less than about 10 mm, and
• (b) the processing conditions are chosen to result in confinement of the excited species formed as a consequence of the chemical interaction to a second volume of space close to the preselected region, with at least a part of the first volume being within the second volume.