Appeal 2005-2100
Application 09/826,038
with the processing requirements determined in the second step (Specification, p. 2, ll.
20-29).
We first note that on page 1 of Appellant’s specification, Appellant admits that it
has been known to measure the thickness of a film before and after etching steps of the
film in an effort to stabilize processing (Specification, p. 1, ll. 10-29). The
measurement is used to feed back a measurement result to etching requirements.
Appellant’s specification describes several embodiments as examples of the use
of the feedforward technique. Embodiment 1 is described in detail on pages 7-9 of the
Specification, and illustrated in Figs 2A and Fig. 2B. An example is described of a
typical semiconductor process that involves controlling the step difference between the
surface of an isolation oxide film to be embedded in a trench and the surface of a
silicon substrate, during the course of manufacture of an element isolation structure
through use of a trench structure.
As depicted in Fig. 2A, the silicon substrate 31 is subjected to dry etching, using
silicon nitride film 32 as a mask, to form a trench structure. Thereafter, the oxide film
35 is removed by CMP (chemical-and-mechanical polishing), followed by several
steps of etching. It is stated that during the course of CMP, errors are likely to occur,
making it difficult to accurately form a step difference (Specification, p. 7, ll. 28-33,
p.8, ll. 1-19).
As shown in Fig. 2B, according to Appellant’s first embodiment, after the above-
described CMP processing, the thickness of the oxide film 33 is measured. The
resultant measurement value is reflected in the requirements for etching the oxide film
33, by means of the feedforward technique. The oxide film 33 is etched according to
the optimal requirement (Specification, page 8, ll. 20-33 and p. 9, ll. 1-10). In this
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