A further variant for the structure of three-layer systems uses 950k PMMA as bottom resist, AR-P 617 as middle layer and CSAR 62 as top resist. There is no mixing during the coating, thus ensuring a defined layer buildup. AR-P 617 can be coated on all PMMA’s (50k – 950k) without any problems, besides, the coating with AR-P 6200 (CSAR 62) is successful as well since anisole does not dissolve AR-P 617.
T-gate structures are often required for the fabrication of electronic components (MEMS, HEMTs). Corresponding nanostructures can be realized via e-beam lithography in multi-layer processes. Generally, resist layers with different sensitivities like e.g. PMMAs with varying molecular weight distributions are coated on top of each other, irradiated with electrons and then developed in one step.
By comparison with PMMA resists, CSAR 62 is characterized by a higher sensitivity and a significantly better plasma etch resistance. The main components of the resist are poly(α-methylstyrene-co-chloromethacrylic acid methyl ester), an acid generator and the safer solvent anisole. The higher sensitivity results from the addition of halogen atoms to the polymer chain.
CSAR 62 is routinely used to produce innovative quantum devices at the TU Delft (Mr. Toivo Hensgens, TU-Delft, the Netherlands). For the structures shown below, a 72 nm layer of CSAR 62 was exposed to 100 kV and then developed with amyl acetate.
To evaluate the suitability of various developers for CSAR 62, Dr. Lothar Hahn (Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology) kindly provided various substrates which had previously been exposed to 100 kV e-beam irradiation (dose variations).
In addition to the use in e-beam lithography, the highly sensitive e-beam resist CSAR 62 can also be structured by exposure to UV radiation since the resist strongly absorbs UV radiation in the wavelength range of 190 – 240 nm.
Mr. Y. Nori from Lancaster University (Department of Physics, UK) could very successful generate structures for the production of photonic crystals with CSAR 62.
Even the highly sensitive e-beam resist CSAR 62 can be used as mask for an etching process with HF (BOE, 10:1).
These nanostructures may e.g. serve as optical antennas for the detection of single molecules. To avoid the undesirable charges on the quartz substrate, Electra 92 was used successfully.
The sensitivity of CSAR 62 is strongly influenced by the choice of the developer. In comparison to the standard developer AR 600-546, the sensitivity can be increased almost tenfold if AR 600-548 is used instead.