Appeal No. 2001-2244
Application No. 09/625,144
Specifically, Bosch states “[w]hile elaborate theories have been developed to explain the
plasma etching process, in practice most such processes have been developed largely by
experimentation involving trial and error because of the relatively poor predictability of
results otherwise. Moreover, because of the number of variables involved and because most
etching processes depend critically not only on the particular materials to be etched but also
on the desired selectivity and anisotropy, such experimentation can be time consuming and
success often depends on chance.” (Col. 1, l. 63 to col. 2, l. 5).
Ding discloses a process for etching substrates, and in particular, for etching
dielectric layers, such as silicon dioxide, on semiconductor substrates at high etch rates.
The process gas comprises (i) fluorohydrocarbon gas capable of forming fluorine-containing
etchant species for etching the dielectric layer, (ii) NH3 -generating gas and (iii) carbon-
oxygen gas. (Col. 2, ll. 32-43). According to Ding, the etching process provides
unexpectedly high dielectric etch rates up to about 900 nm/minute in combination with
excellent etching selectivity ratios. (Col. 2, ll. 52-54). The preferred etchant gas
composition comprises (i) fluorohydrocarbon gas selected from the group consisting of
CH3F, CHF3, C2HF5, C2H2F2, and C2H4F2; and (ii) fluorocarbon gas selected from the group
consisting of CF4, C2F6, C3F8, C4F8 and C4F10. The NH3 -generating gas can comprise NH3,
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