It is advantageous for the fabrication of three-dimensional structures if the gradation (contrast) is low. A resist with very high contrast will always generate perpendicular resist flanks. Smallest changes of the dose induce a rapid shift from undeveloped to the completely developed state. If the gradation is low, the dose difference between the undeveloped and the completely developed state is accordingly high.
Layers and structures of e-beam polymers possess different temperature resistance properties. PMMA layers are generally the most stable.
Applying an acceleration voltage of 100 kV has the advantage that the proximity effect due to electron backscattering can be avoided.
Very even and smooth 300nm ridges could be achieved with AR- 7520.17new and a coating thickness of 400nm.
We now succeeded in finding a remarkable solution for high-layer e-beam structuring. The negative resist CAR 44 (AR-N 4400-10) was coated to yield a layer with a height of 9.5 μm, dried, and irradiated.
A new application field for Atlas 46 is electron beam lithography, as experiments with a thin Atlas resist layer patterned by e-beam lithography demonstrated. At a layer thickness of 450 nm, 200 nm lines were written into this layer. The sensitivity was 70 μC/cm² at an acceleration voltage of 100 kV.
For an optimum handling of EUV lithography using the RWTH system, a sensitivity range of 30-40 mJ/cm² is desired. A Medusa 82 sample supplemented with 2.5 % photoacid generator (PAG) already reached this target range. These investigations will be continued within the scope of a research project.
The addition of photoacid generators (PAGs) can significantly increase the sensitivity of Medusa 82 (see Resist Wiki “Medusa with photoacid generator”). Another option is to add a PEB after e-beam exposure. Even if substrates were previously stored for several days, the sensitivity significantly increases depending on the temperature and the duration of the PEB.
One disadvantage of HSQ and Medusa 82 is the comparably low sensitivity, which can however be increased by an addition of photoacid generators.
In the final stage of the Eurostar PPA-Litho project which was aimed to develop the resist Phoenix, we achieved to generate far more stable PPA polymers by optimizing the synthesis procedure. Pure polyphthalaldehydes which were subjected to a “stress test” for 14 days at 37 °C showed no decomposition. These resists can thus be shipped without cooling; this however only applies to pure PPA polymers.