Monitoring of reactive species or etch by-products provides endpoint signal.

Endpoint relies on etch stop layer.

Scanned monochromator allows full spectrum analysis.

Trace achieved when etching SiOx layers down to a Si substrate.

It shows a typical trace obtained when etching SiOx layers down to a Si substrate. The large picture shows the full emission spectra of the plasma. The blue and red marker lines correspond to the emission peaks of CO, which is an SiOx etch by-product, at 483 nm and 520 nm.
The small graph in the top right hand corner shows the fall in the intensity of these CO etch by-product emission peaks, as the last SiOx is removed. By monitoring the time derivative of this CO emission intensity it is possible to obtain a very reliable endpoint trigger.

single beam laser interferometry

SiO2 via hole ething

laser interferometry for the Bosch process