Browse Prior Art Database

Method for Optical Interference Measurement and Control of Etching

IP.com Disclosure Number: IPCOM000107793D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 105K

Publishing Venue

IBM

Related People

Kerbaugh, ML: AUTHOR [+4]

Abstract

By means of a geometry comprised of a number of small islands of an etch-stop material having a refractive index different than the index of refraction of an overlying transparent material to be etched, the point of complete removal of the overlying material and planarization is detected by monochromatic light interference monitoring. The same or similar geometry, without a requirement for index of refraction differences, is used to measure and control depth of etching into material between islands of etch stop by a different optical interference mechanism. Sensitivity of etch-depth measurement below the planarization point can be enhanced by using short wavelength illumination which might not penetrate the material being etched, thus not usable in overlayer etch monitoring and control.

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Method for Optical Interference Measurement and Control of Etching

       By means of a geometry comprised of a number of small
islands of an etch-stop material having a refractive index different
than the index of refraction of an overlying transparent material to
be etched, the point of complete removal of the overlying material
and planarization is detected by monochromatic light interference
monitoring. The same or similar geometry, without a requirement for
index of refraction differences, is used to measure and control depth
of etching into material between islands of etch stop by a different
optical interference mechanism. Sensitivity of etch-depth measurement
below the planarization point can be enhanced by using short
wavelength illumination which might not penetrate the material being
etched, thus not usable in overlayer etch monitoring and control.

      Referring to Fig. 1, islands of etch stop 12, e.g., silicon
nitride, are defined on substrate 10, e.g., a silicon wafer, and then
the entire surface is coated with a material, e.g., polycrystalline
silicon.  Incident monochromatic light L1 (and parallel arrows) is
partially reflected from the surface of material 14 and partially
refracted and reflected from the top surface of the islands of
material 12 to result in observed light LO (and parallel arrows)
returning to a detector (not shown).

      This well-known interference measurement method, with
interference occurring within the translucent material being etched,
is standard practice in measuring material removed in reactive ion
etching.  This mechanism continues during etch removal of material 14
from top surface location t0 until the top surface of material 12 is
exposed at t1, as shown in Fig. 2.  Thickness of material 14 removed
is proportional to the index of refraction of material 14 and number
of minima or maxima in the relative intensity RI vs. time plot until
the t1 level is reached.  Though there is a continued interference
phenomenon observed as material 14 is removed from regions of
substrate 10 not protected by etch stop 12, it is arising from a
different mechanism.  There is a new maximum (constructive
interference) without first continuing to a minimum (destructive
interference).  This discon...