Amorphous carbon process optimization to increase hard mask and lithographic capabilities by its step coverage improvement

The capabilities of hard mask (HM) and lithographic are strongly depended on the step coverage (S/C) of HM. Using C2H2 base amorphous carbon (a-C) as HM gets better sidewall S/C than using C3H6 one due to superior sticking coefficient (higher C/H ratio). As to performance of against PR rework, overlay mark without damage is displayed by adopting C2H2 base a-C even five times PR rework. In our case, bad sidewall S/C of a-C film induces the device pattern damage of micro control unit (MCU). After optimizing the process of C2H2 base a-C based on DOE trend of process parameter, sidewall S/C marvelously increases from 49% to 91%. Therefore, the amount of device pattern damage of MCU is obviously reduced.