Subtractive Pattern Transfer

Reactive ion etching (RIE) has been used for subtractive pattern transfer into silicon substrates, where the resist acts as an etch mask. Etching is particularly challenging with ultra-thin photoresist, since the gases used to etch the silicon also etch the resist. Using cryogenic temperatures suppresses the resist etching and a successful dry etching process has been developed as detailed in Fig. 17.8. A short SF6 plasma etch was carried out at 173 K to transfer the resist pattern 120 nm deep into the silicon substrate. An anisotropic etch profile was achieved with an etch rate of 10 nm/s under the following conditions: SF6 gas flow rate of 100 sccm, power density of 0.45 W/cm2, etch pressure of 55 mTorr, and dc bias of -153 V.

Spin diluted S1805, 60 nm

Spin diluted S1805, 60 nm

Fig. 17.8. Schematic diagram illustrating processing steps for subtractive pattern transfer using RIE. The pattern is defined first with the 60 nm thin resist and subjected to SF6 plasma etching at 173°K

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