HSQ / FOX16 resists

This is a negative resist and the highest resolution ebeam resist available. Our machine has regularly demonstrated < 10nm resolution with this resist. Chemically, once exposed to the ebeam, it is similar to SiO2 which makes it a very interesting etch mask for Si etching. It also has very low line edge roughness (LER) which is one of the most important problems to resolve in future < 20nm CD devices. Ultimate resolution is unknown. Isolated features < 8nm are achievable. 22nm period gratings have been demonstrated (11nm lines 11nm spaces).

HSQ is the chemical abbreviation which actually stands for hydrogen silsesquioxane. Commercially this is made by Dow Corning and is called XR-1541-002, XR-1541-006 and FOX16.

HSQ can be very difficult to use. It needs to be stored in a refrigerator at 4 degrees C. It is very sensitive to the surface condition of your sample and so correct surface preparation can make the difference between your features sticking to the surface well, or just washing away in developer. We have found that performing an oxygen plasma clean or using piranha bath prior followed by the oxygen plasma clean or at least dehydration bake can be useful in helping to prepare a good surface.

Polarity

Negative

Doses

Dose can be quite high. Large features typically have doses around 700µC/cm2, for very high resolution features 7000µC/cm2 or higher. Dose is heavily dependent on the concentration of developer used. CD26 requires lower doses, TMAH25% is very aggressive and only highly dosed and crosslinked resists survives the developer. 

Resolution

Few nanometers.

Chemical capabilities

For Si HSQ has very good dry etch selectivity. This resist can be striped with SiO2 wet etchant in a BHF bath (contaminated BHF bath on the Plade oxide in zone 2).

Quick process

Before processing choose 1 beaker from the HSQ shelf in the dry cabinet and rinse it with a small amount of developer (MF CD26).

Step Description Program/Parameters
1 pre-processing – adhesion 5min oxygen plasma at high power, or Piranha bath followed by oxygen plasma/5min dehydration bake
2 substrate cooling 1min
3 HSQ coating see spin curves below
4 resist exposure on the ebeam doses between 700 and 10000µC/cm2
5 resist development 30sec-2min in MF_CD_26 or TMAH25% on the water/base wetbench
6 substrate rinsing and drying rinse with DI water in the water/base wet bench until the resistivity is >12Mohms. If you have delicate structures then rinse with IPA after water (the wafer surface must stay wet during all this rinsing process!). Dry with nitrogen


When you have finish empty beaker into the water waste, rinse the beakers with water and put them into the HSQ recycling tray (which is on the base wet bench).

Spin curves