9. How high is the plasma etch resistance of e-beam resists?

Electron beam resists of the AR 6000 and AR 7000 series display quite different etch resistance features in dry etch processes such as e.g. argon sputter and CF₄. Novolac-based e-beam resists have a high etch stability, while PMMA resists are significantly more susceptible to etchings. CSAR 62 has a similarly high etch stability like novolac-based e-beam resists. Prior to the etch process, a postbake at 110 °C for re-stabilization increases the etch stability slightly. Resist etch rates are highly dependent on the respective conditions. In addition to the device used (plasma etcher), the rate is also influenced by 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:

Resist:                                                AR-P 600(0)                               AR-P/N 7000

Argon sputter:                                  10 – 22 nm/min                        8 – 9 nm/min

CF₄:                                                     51 – 61 nm/min                      33 – 41 nm/min

80 CF₄ + 16 O₂:                              116 – 169 nm/min                     89 – 90 nm/min

O₂-Plasma:                                      173 – 350 nm/min                    168 – 170 nm/min

Cautious plasma etch procedures (low pressure and voltage) lead to a higher resistance of the resist, but the etch process itself requires more time. Thorough cooling during the etching improves the resistance likewise. If resists are etched too rigidly (e.g. temperatures too high), the subsequent removal step may cause major problems.