Appeal No. 2006-0293
Application No. 10/071,809
A. The Rejections on Appeal
The examiner finds that Tsai discloses a method of etching metal silicide using
chlorine and oxygen under the same pressure and power ranges as disclosed and
claimed by appellant, with flow rates of 20-800 sccm of chlorine and 1-50 sccm for
oxygen (Answer, page 3). The examiner recognizes that Tsai does not disclose the
claimed oxygen concentration of greater than or equal to 25% by volume (id.).
However, the examiner finds that Tsai teaches that a high concentration of oxygen is
desirable and etches the metal silicide at a much greater rate (Answer, sentence
bridging pages 3-4). The examiner also finds that Tsai teaches that the power ratio may
be optimized (Answer, page 4). From these findings, the examiner concludes that it
would have been obvious to one of ordinary skill in this art to determine the optimum
parameters through routine experimentation to etch
the metal silicide at a high rate and selectivity with respect to the underlying polysilicon
layer (id.). We disagree.
As correctly argued by appellant (Brief, page 4, footnote 2, and page 9, footnote
6), and apparently overlooked by the examiner (Answer, page 5), the disclosure of Tsai
mistakenly recites that the etching selectivity “increases” with increasing flow rates of
oxygen while in fact the data of Tsai establish that etching selectivity decreases with
higher flow rates of oxygen since the polysilicon etch rate increases with increasing flow
rates of oxygen (compare Tsai, col. 7, ll. 63-66, with Figure 4, and also compare Tsai,
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