In contrast to photolithography, the solution of e-beam lithography is practically unlimited by wavelength. Electrons of an energy of 25keV have a wave length of < 0,01 nm. The maximum resolution thus is crucially determined by the beam diameter.
A part of the high-energy electrons which impact on the substrate is stopped and cannot be conducted at all or only very slowly toward ground, especially in the case of insulating substrates such as quartz. The substrate and respectively the resist charges itself negatively and the electron beam is deflected uncontrollably from the desired position during exposure.
Report on the two layer system, respectively lift-off: AR P-617 (250nm) with PPA (30nm), development followed by vapor coating of Al (40nm).
An alternative version of the structure of two layer systems emanates from only one resist: AR-P 617 (PMMAcoMA 33). At increasing temperature, AR-P 617.08 becomes linearly more sensitive.
PMMA resists work positively under standard conditions. The long polymer chains are broken into small fragments by the irradiation process. PMMA 950k with a molar mass of 950 000 g/mol is primarily reduced to a molar mass of about 5000 g/mol. These short-chain polymers are readily soluble in the developer, which is not the case for the polymer with the initial high molar mass.
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.