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.
In many cases, substrates meant to be structured may not be heated above 50 – 70 °C. These can be glass partitions which distort at higher temperatures and thus might lose their size accuracy. However, some organic polymers which are to be coated are temperature sensitive. Moreover, thermosensitive structures may already exist on the substrates.
In some applications, the substrate on which the negative resist is to be applied cannot be heated. This may be the case for sensitive glass and especially for very big substrates.
Air bubbles often occur when resist bottles are e.g. shaken or moved around before coating, or if a resist is diluted. They may also appear if the coating step is performed immediately after opening of the resist bottle, particularly if the resist temperature is not allowed to adjust to room conditions.
The simplest but nevertheless highly effective removers are sodium hydroxide (NaOH) and potassium hydroxide (KOH) solutions. Already a 4 % KOH solution will remove basically all novolac-based photo- and e-beam resists within a few seconds.
There are two main groups of developers: solvent-based and aqueous-alkaline developers. The solvent-based ones are intended mainly for PMMA e-beam resists, for CSAR 62 and also for special polymer based products. In this process, solvents such as methylisobutylketone (MIBK), IPA (partly with water) for PMMA, amyl acetate, MIBK, DEK, DEM, xylol for CSAR 62 and ethylbenzene as well as hexane are used for the protective coating.