The ZEP 520(direct writing) and ZEP 7000 (mask fabrication) are characterised by goodproperties. Both resists are considerably more sensitive than PMMA resists (ZEP520 by a factor of 3), and ZEP 7000 is in addition approximately twice assensitive as ZEP 520. The plasma etch resistance is comparable with that ofnovolac photoresists, and a very high resolution of 10 nm can be achieved at afilm thickness of less than 100 nm. Different developers are available toeither obtain a high sensitivity or a high resolution.
All customers who cherished the good qualities of the popular ZEP 520 can now lookforward to an equivalent e-beam resist with clear price advantage. Afterintensive development work, Allresist was able to reach and partly even exceedthe application benefits of the ZEP520, e.g. with respect to the easy fabrication of lift-off structures.
Theexcellent results obtained with the CSAR 62 were presented on the HARMNST 2013in Berlin. The poster whichwas published within the context of this congress outlines a few of theoutstanding resist properties in detail.
Ina simple, stable process, an excellent resolution of 10 nm at a film thickness of 180 nm was realised with CSAR 62 (=SX AR-P 6200/2) . Usingdeveloper X AR 600-54/8, a very highsensitivity of 10 µC/cm² (30 kV) was achieved. Our CSAR 62 thus also offers agood alternative for the highly sensitive mask-ZEP 7000.
A particularly advantageous feature is theeasy fabrication of lift-off structures. The plasma etch resistance of CSAR62 and ZEP 520 is comparably high and 2x better than the plasma etch resistance of PMMA resists.CSAR 62 is available as of May 2013.
CSAR 62 – Operatingprinciple
In comparisonwith PMMA resists, the CSAR 62 is characterised by a higher sensitivity andsubstantially improved plasma etch resistance. Main components of the resistare poly(α-methylstyrene-co-methyl chloroacrylate), an acid generator and thesafer solvent anisole. The higher sensitivity results from an introduction ofhalogen atoms into the polymer chain. Generally, chlorine is used for thispurpose (as also for the CSAR 62 – methyl chloroacrylate ),but bromine or iodine are also possible. The chlorine atom supports breaking ofthe polymer chain during irradiation with electrons. In addition, a halogen-containingacid generator enhances this effect. The introduction of further reactivehalogens accelerates the attack on the polymer chain even more. As a result,less energy (a lower dose) is required to break the high-molecular polymer intosmaller fragments. These fragments quickly dissolve in the developer, while theunexposed, still high-molecular resist areas are not attacked by the developer.
Supporting thefraction of the chain by addition of a temperature-stable acid generator gavethis resist its name – C hemical S emi A mplified R esist. Sincethe acid generator is activated during the process of electron irradiation,layers require no tempering after exposure.
The improvedplasma etch resistance results from the introduction of aromatic substituentssuch as e.g. phenyl, naphthyl or anthracyl groups into the polymer. The CSARfurthermore contains α-methylstyrene to provide etch stability. Due to their π -electrons,aromates are considerably more stable in the presence of different plasmas ascompared to aliphatic polymers like PMMA and thus reach the same level ofstability like photoresists. Photoresists are mainly composed of novolacs(cresole mixtures condensed with formaldehyde) with possess, due to thecresoles, a high content of aromates and are therefore more stable during plasmaetching processes.