Browse Prior Art Database

Laser Ablation Endpoint Detector

IP.com Disclosure Number: IPCOM000108340D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 83K

Publishing Venue

IBM

Related People

Baltz, JG: AUTHOR [+4]

Abstract

Disclosed is a device for detecting the endpoint of a laser ablation polymer etching process; in particular, the case of etching polymers over another material with a markedly higher ablation threshold is addressed. It is an observation that the intensity of the luminescent plume, that accompanies the etching action, is substantially diminishing once the polymer is removed and the laser radiation is incident on the underlying higher ablation threshold material. Thus by monitoring the intensity of the visible light component of the luminescent plume, the endpoint of the etching process can be discerned.

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Laser Ablation Endpoint Detector

       Disclosed is a device for detecting the endpoint of a
laser ablation polymer etching process; in particular, the case of
etching polymers over another material with a markedly higher
ablation threshold is addressed.  It is an observation that the
intensity of the luminescent plume, that accompanies the etching
action, is substantially diminishing once the polymer is removed and
the laser radiation is incident on the underlying higher ablation
threshold material.  Thus by monitoring the intensity of the visible
light component of the luminescent plume, the endpoint of the etching
process can be discerned.

      A device with this capability is useful in the etching of
polymer layers that exhibit gross variations in thickness over the
area of a substrate.  The need for a preprogrammed overetch capable
of adequately processing the thicker regions at the expense of
throughput at the thinner regions is eliminated.

      The endpoint detector is depicted in the figure.  In this
embodiment of the device, a photodiode used in the photovoltaic mode
is employed as a radiation transducer. The potential developed at
photodiode cathode is inverted with unity gain by a 741 operational
amplifier.  The output of this stage shows a voltage proportional to
the intensity of the light collected.  The value of the gain (-1
here) is not critical.

      The second stage of the circuit uses a CMP-05 comparator chip
and produces a negative pulse when the potential at the inverting
input exceeds a preset reference level.  The reference level is
chosen as the result of experiment.  Positive feedback...