9. How high is the plasma etch resistance of e-beam resists?
Electron beam resists of the AR 6000 and AR 7000 production line display quite different etch resistance features in dry etch processes such as e.g. argon sputter and CF4. Novolak-based e-beam resists have a high etch stability, while PMMA resists are significantly more susceptible to etching. Prior to the etch process, a postbake at 110 °C for re-stabilization increases the etch stability slightly. The etch stability can be further improved by an addition of aromatic conjugated compounds.
Resist etch rates are highly dependent on the etch conditions. In addition to the equipment used (plasma etcher), the rate is also influenced by the etch gas composition, pressure, temperature, and voltage.
The following etch rates (nm/min) were determined for our e-beam resists at 5 Pa and 240 – 250 V bias:
AR-P 6000 (PMMA) AR-P/N 7000 (Novolak)
Argon sputter: 18 – 22 8 – 9
CF4: 56 – 61 33 – 38
80 CF4 + 16 O2: 89 – 93 151– 169
O2-Plasma: 311– 350 165– 173
Careful etch procedures (low pressure and voltage) lead to a higher resistance of the resist, but the etch process requires more time. Thorough cooling during the etching improves the resistance likewise. If
resists are etched too much (e.g. temperatures too high), the subsequent removal step will cause major problems.