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The plasma etching of wafers is interferometrically monitored, using, in lieu of a laser beam, light emitted from the excited plasma as a source of monochromatic light.
English (United States)
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Indirect Optical Endpoint Monitoring
The plasma etching of wafers is interferometrically monitored, using, in lieu
of a laser beam, light emitted from the excited plasma as a source of
By selecting one or several dominant lines in the optical spectrum and
measuring their intensity variations, the etch process and layer thickness are
monitored with high resolution. Indirect Optical Endpoint Monitoring (IOEP) may
be used in conventional etch chambers which do not allow geometrically
accommodating impinging and reflected laser beams.
The figure shows the set-up used for IOEP. Wafers 2 with clear measuring
areas 3 along their edges are arranged in an etch chamber 1 where the excited
plasma of a glow discharge 11 emits light with an isotropically spatial distribution.
Light emanating from space angle 8 is selected by an optical system after having
been reflected at the thin layer to be etched in clear area 3. The light is focussed
and transmitted by a lens 10, positioned outside etch chamber 1, to an optical
cable 7 and from there to a monochromator 5 or a filter connected to a detector,
such as a photomultiplier 6, which measures intensity variations as a function of
film caused by thin-film interference at clear area 3.
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