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Photoreactive Topcoat to Reduce Thin Film Interference in Photoresist

IP.com Disclosure Number: IPCOM000121245D
Original Publication Date: 1991-Aug-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Bruce, J: AUTHOR [+2]

Abstract

By varying the optical path length in a photoresist film stack during a photolithographic exposure, light absorption interference effects are minimized.

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This is the abbreviated version, containing approximately 55% of the total text.

Photoreactive Topcoat to Reduce Thin Film Interference in Photoresist

      By varying the optical path length in a photoresist film
stack during a photolithographic exposure, light absorption
interference effects are minimized.

      Thin film interference effects on monochromatic steppers
influence the absorbed dose in a photoresist film. Small changes in
resist thickness can change the fraction of light absorbed in the
resist, resulting in significant line width changes. Resist thickness
changes can occur either due to nonuniformity induced by applying
tooling or non-conformal coating of resist over topography. By
coating the photoresist with another thin film which undergoes a
change in refractive index upon exposure to light, interference
effects during lithographic exposure are minimized.

      A topcoat may be applied by spin coating after photoresist
apply and bake. The topcoat ideally has the following properties:
      1. Low absorption at the exposing wavelength.
      2. Change in index of refraction or thickness upon irradiation
to either the exposing wavelength or another wavelength.
      3. No interaction with the photoresist.
      4. Easily removed.

      As the resist film is exposed, the topcoat is also exposed
(either at the same wavelength, or by an off-axis light source at a
different wavelength). The effect of changing the refractive index in
the topcoat is to shift the location of absorption maximum in the
resi...