The masks are designed such that positive resists can be used. AZ5214 can also be used in 'image reversal' mode (that requires a reversal bake and a flood exposure). The optical resist processes are very uncritical because we make all small features with the e-beam.
Negative tone optical resist for single-layer lift-off
Official resist page
This resist comes from DIMES (courtesy C. Martin, AMC). There is a TUDelft recipe for it here. Leiden recipe:
Here is a graph of the time neede to dissolve the exposed parts in maD 533s, as function of exposure time. Dissolving unexposed parts takes 20 sec. UV meter gave 28 MW/cm2.
Here is a graph of the time needed for developing, as function of the maD-532-concentration. Exposure time was 15 sec (this is very uncritical). UV meter gave 29 MW/cm2.