If an electron beam with high energy is channeled onto a resist layer (5- 100 keV), forward scattering ( 90° in direction of arrival). The deflection causes the electron beam to widen, thus reducing resolution.
The minimum necessary exposure time for a certain area, at a given exposure dose, can be calculated by the following correlation: Area * dose = Duration of exposure * beam current.
A further mask-based technology is SCALPEL (Scattering with Angular Limitation Projection Electron-beam Lithography). Due to the interposed mask, certain parts of the electron beam are shadowed. The scattering layer strongly deflects incident electrons. A great advantage of this procedure as compared to electron absorption is less loading and less heating of the mask.
Raster scan principle is a procedure in which the electron beam is led line by line over the exposure area, comparable to the beam guidance in an electron microscope. The structures are exposed by switching the electron beam on and off while continuously moving the substrate (XY regulation).
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.
PPA layers can also be structured by laser ablation. Substrates coated with AR-P 8100 were structured with pulsed laser light at different wavelengths at the IOM Leipzig (Dr. Klaus Zimmer). In this process, architectures with very little edge roughness could be generated. In the absorption range of PPA, at 248nm, complete ablation was achieved without damaging the silicon substrate.
The resists Atlas 46 S = AR-N 4600-10 and Atlas 46 R = AR-N 4650-10 are photoresists with negative effect and high layer thickness with extremely stable resist structures. In addition, AR-N 4650-10 is removable easily and thus very well suited for photolithographic and electro-plating applications. The characteristics of AR-N 4600-10 are comparable to those of SU-8.
For a surprisingly high number of applications, it is important to disable the transparency of the substrates completely, while still having the option to generate structures.
The resists most widely used by far are the positive photo resists, followed by negative photo resists. However, there are other special resists as well.
Image reversal resists are positive resists with an additional amine. Depending on the manufacturing process, positive or negative images can be generated.
Spray coating is often used for the coating of complex topologies. There are various manufacturers of spray coating equipment, probably the best known are EV Group and Süss Microtec. Both producers use different strategies and devices for spraying, and therefore ready-to-use spray resists must be adjusted for the particular equipment.