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Etch Control by Use of Infrared Reflectivity Measurement

IP.com Disclosure Number: IPCOM000121922D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Ray, M: AUTHOR

Abstract

When an array of holes or trenches is etched into a surface, long wavelength (infrared) light reflected from the region being etched varies as predicted by "Effective Medium Theory" described in "Optical Response of Microscopically Rough surfaces" by D. E. Aspnes, Phys . Rev . B41(1990). Thus, depth of etched trenches is monitored by measuring intensity of reflected light of wavelength four to twenty- five times greater than the width of trenches or islands being formed by etching. Incident light may be polarized to enhance reflected light intensity change as a function of trench depth.

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Etch Control by Use of Infrared Reflectivity Measurement

      When an array of holes or trenches is etched into a
surface, long wavelength (infrared) light reflected from the region
being etched varies as predicted by "Effective Medium Theory"
described in "Optical Response of Microscopically Rough surfaces" by
D. E. Aspnes, Phys .  Rev .  B41(1990). Thus, depth of etched
trenches is monitored by measuring intensity of reflected light of
wavelength four to twenty- five times greater than the width of
trenches or islands being formed by etching.  Incident light may be
polarized to enhance reflected light intensity change as a function
of trench depth.

      Referring to the figure, a monitor region is formed by an array
of islands of photoresist 2 over material 4, a material which is very
resistant to etching during subsequent etching of substrate 6.  Next,
material 4 is removed between islands of photoresist 2. Then,
trenches are etched in substrate 6.

      This monitor region is illuminated by a beam of infrared light
incident at a near normal angle to the surface being etched.
Reflected light intensity varies with depth of etching in the same
manner as would be expected if the trenched region was replaced by a
uniform thickness of a layer having an appropriate index of
refraction - an "effective medium" - which is reduced in thickness by
the etching process.

      Etched trench depth is measured by electron microscopy and
related to change in meas...