Appeal 2007-2494
Application 10/161,134
A. Appellants' specification
[1] According to Appellants' specification, integrated circuitry is
commonly fabricated using photolithography (Specification at 1:10-
11).
[2] In photolithography, a substrate surface is coated with an imagable
material, e.g., a photoresist (Specification at 1:11-13).
[3] A pattern is projected onto the photoresist by focusing light onto
defined portions of the photoresist (Specification at 1:13-15).
[4] The photoresist undergoes a reaction when exposed to the light which
makes the exposed photoresist more ("positive photoresist") or less
("negative photoresist") susceptible to removal by etching
(Specification at 1:15-2:3).
[5] The underlying substrate surface remaining after etching is said to
have "approximately the same pattern" as that projected onto the
photoresist initially (Specification at 2:3-5).
[6] Transferring a pattern from a photoresist layer to an underlying silicon
nitride substrate layer, especially with light having a wavelength of
248 nanometers or less, is said to be problematic because "the pattern
formed in silicon nitride is frequently not the same as the pattern
which was intended to be formed in the photoresist" (Specification at
2:6-14).
[7] According to the specification, the further the photoresist layer is from
the light source, the less efficiently the selected portions of the
photoresist are removed, resulting in formation of foot portions 30 at
locations where the remaining photoresist or "pattern" 26 contacts the
upper surface 23 of the silicon nitride layer 22 (Specification at 7:1-7).
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