A method and system using spectral interference of light from plasma emissions
collected at near grazing incidence to in-situ monitor and control the film thickness
of a non-opaque film. Embodiments of this invention are particularly useful to
all substrate processing chambers equipped to form an in-situ plasma within the
chamber and which are used to deposit or etch non-opaque films. One embodiment
of the method of the present invention forms a plasma within a substrate processing
chamber to deposit a non-opaque film on a wafer substrate within the chamber. During
the plasma deposition process, a plurality of wavelengths of radiation including
those reflected from the top and bottom layer of the film being deposited upon
a wafer surface are collected through an existing viewport, and conveyed to a spectrometer
for measurements via an optical fiber attached near this viewport. These measurements
are analyzed to determine the film's thickness. An alternate embodiment of the
method of the present invention uses an interference filter to confine the spectral
composition of the plasma emissions to an emission at a narrow wavelength interval
and a photodiode to detect the intensity of the emission.
