The Resist Wiki article “Positive two-layer lift-off systems” describes the principle of these two-layer systems. During the application of lift-off structures, temperatures above 150 °C occur frequently, for example during sputtering. If the usual photo resists are used as top layer, the lift-off structure melts and thus becomes useless for the process.
Almost all photo resists contain PMA (PGMEA) as a solvent. This solvent is therefore the most common thinner and offered by us as AR 300-12 angeboten. The PMA is often used for the removal of edge beads.
Adhesive agents serve to improve adhesion, e.g. the adhesion promoter AR 300-80, which is applied by spin coating as thin layer of approximately 15 nm immediately before the resist coating. It is also possible to evaporate HMDS on the substrate, in this process, the monomolecular coat on the wafer surface improves adhesion, because it becomes hydrophobic and better attaches to the resist.
Lift-off structures are needed for many technologies. There are one-layer and two-layer processes. For one-layer, only one resist is used. Typical examples are negative resists, see Resist-Wiki “Generation of undercut structures with negative resists”. However, there are also positive resists (AR-P 5300) for the lift-off. There is only a slight difference, though in most cases, which, however, is sufficient for many procedures.
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.
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.
A new strong solvent remover is able to solve resist layers tempered at room temperature. It is remarkable that the remover takes the same effect on novolak based as well as PMMA based resists and thus is suited for versatile applications. It must be pointed out, however, that the flash point of the remover is below 21 °C and therefore needs to be handled with care.
The new special resist SX AR-N 4810/1 is a chemically enhanced photo resist based on PMMA, which can be developed waterfree – crucial in the case of moisture-sensitive substrates – with organic solvents.
Roland and Coopmans intensively studied the fundamentals of the top surface imaging technology which is based on a selective resist silylation process (DESIRE process). A positive photoresist specifically optimised for this purpose with considerably increased content of light-sensitive components (LSCs) is exposed image-wise.