1.) Are there exact data available for the high etch resistance of ma-P 1200 resists?
The resists of the ma-P 1200 series exhibit a good etch resistance. E.g. ma-P 1200 gives very good results in dry etching (as with CF4 or high density SF6/O2 plasma).
The etch rates of the resists strongly depend on the etching conditions. The etching equipment has an influence, the amount of open wafer surface to be etched, the etch gas composition and all other parameters such as pressure, temperature or voltage.
ma-P 1200 resists show a good thermal stability. That enables the thermal stabilisation of the resists for the subsequent plasma etching. E.g. a hardbake is recommendable at 120°C in an oven (with a temperature ramp to minimize the pattern rounding). For that also a stronger prebake is necessary. In case of a 7.5µm thick film of ma-P 1275 that would be a prebake at 110°C for 5 - 10 min on a hotplate.
We cannot deliver any more detailed data. This is nearly impossible since etching conditions can differ very much from lab to lab.
2.) How can I avoid bubbles in the resist film?
Several reasons for the formation of bubbles in the resist are possible.
Big bubbles could arise if the resist was shaken too much, or if the resist has undergone a bigger temperature change. They should disappear when the resist can "relax" a while (i.e. when the bottle is kept under constant climatic conditions in the cleanroom for some time). This applies mainly for resists of a higher viscosity.
Bubbles occurring during the prebake of thick resist films are caused by the solvent evaporation. It is important to maintain a certain relaxation time between spin-coating and prebake to avoid this. Only high viscosity resists show this tendency.
Smaller bubbles in the exposed area could have several reasons. Adjusting the respective process condition prevents the bubble formation:
- The resist film isn´t dry enough, i.e. it wasn´t sufficiently softbaked (= prebaked).
- The exposure dose was much too high. This is connected with a distinctly decreased developing time compared to the one at standard processing conditions.
- c) Too much primer was used (HMDS on Si and SiO2).
- d) The cleanroom conditions were out of the tolerances. Especially a too high humidity can cause bubble formation.
3.) Is ma-P 1200 resistant to strong acids?
In general ma-P 1200 positive photoresists withstand strong acids very well. Tests have shown that 2.5 µm thick ma-P 1225 and 7.5 µm thick ma-P 1275, both processed under standard conditions, resist concentrated HCl at 45…50 °C for at least 10 minutes without any problems. No erosion of the resist film is observed.
Concentrated HF is challenging for all photoresists (cf. QUESTION 4).
Also strongly oxidising acids can cause some problems. The resist stability depends on the temperature and composition of the etchant in such cases.
4.) Can I use ma-P 1200 resists as etch mask for HF glass etching?
HF etching is a very demanding. HF doesn´t attack the resist. But it can diffuse under the photoresist and lift it from below causing bad adhesion of the resist on the substrate. This is why a film thickness as high as possible should be chosen, and the resist should be hardened (stronger prebake + hardbake). Nevertheless it depends strongly on the HF concentration and the etch time to what extend the photoresist sustains the etching.
In the literature it is mentioned that ma-P 1200 is suitable for etching with buffered HF [*].
[*] A. Pozzato, S. Dal Zilio, G. Fois, D. Vendramin, G. Mistura, M. Belotti, Y. Chen, M. Natali, Microelectronic Eng. 83 (2006), 884-888, doi:10.1016/j.mee.2006.01.012
5.) Can I use positive photoresists for lift-off processes?
For lift-off processes a bi-layer resist system can be applied. E.g. LOR (a not photosensitive polymer provided by MicroChem Corp. for various film thicknesses) can be used as bottom layer. In a second step a positive resist e.g. from the ma-P 1200 series is applied as top layer. During the aqueous-alkaline development of the exposed areas of the positive resist film also the LOR film underneath is dissolved. The undercut profile in the bottom layer is adjusted by varying the development time and the prebake conditions for the LOR layer.
For some applications you can do the lift-off with a single-layer resist which does not give an undercut profile. E.g. the use of ma-P 1200 resist without an additional bottom layer would be sufficient - preferably with a somewhat higher film thickness to give sidewalls that can be reached by the stripper. The quality of the edges of the deposited metal layer is slightly worse than in a bi-layer process in this case.
6.) Is there a developer that doesn´t corrode Al and Al containing substrates, respectively?
We recommend to apply “Developer Concentrate” by DOW Electronic Materials for developing resists of the ma-P 1200 series on Al and Al containing substrates. You can purchase the developer from our company. The developer is based on metasilicate which practically doesn´t corrode Al.
Examples of ma-P 1200 applications in the literature:
 W. Schrott, M. Svoboda, Z. Slouka, D. Šnita, Metal electrodes in plastic microfluidic systems, Microelectronic Engineering, 86 (2009), 1340-1342;
ma-P 1275 is used as mould for electroplating Au and Cu structures to be used in plastic microfluidic systems.
 P.W. Leech, G.K. Reeves, A.S. Holland, Reactive ion etching of TiN, TiAlN, CrN and TiCN Films in CF4/O2 and CHF3/O2 Plasmas, Mater. Res. Soc. Symp. Proc. 890 (2006), 0890-Y08-13.1-6;doi: 10.1557/PROC-0890-Y08-13
ma-P 1205 is used as etch mask for plasma etching in the manufacture of stamps for imprint lithography.
 G. Kaltsas, A. Petropoulos, K. Tsougeni, D. N. Pagonis, T. Speliotis, E. Gogolides, A. G. Nassiopoulou, A novel microfabrication technology on organic substrates - Application to a thermal flow sensor, Journal of Physics: Conference Series 92 (2007) 012046; doi:10.1088/1742-6596/92/1/012046
ma-P 1275 is used in a lift-off process with Pt deposition in the manufacture of a thermal flow sensor.
 J.-C. Galas, D. Bartolo, V. Studer, Active connectors for microfluidic drops on demand, New J. Phys. 11 (2009) 075027;
After reflow ma-P 1275HV is used as mask for moulding PDMS in the fabrication of active microfluidic connectors.