SU8

SU8Edit

1.   Deposit

primer on metallic substrate: primer (special for gold)

spin xx” @ xxrpm (rise time xx”)
spin xx” @ xxrpm (rise time xx”)     ~xx nm layer

The primer layer must be dried (on hot plate xx’ @ ~xx°C) and wafer must be cooled down prior to resist spin.

resist: SU8 2005

dispense 3 mL for 3 inches wafer

Dispense at constant rate in the center of the wafer, and do not empty the container to avoid bubbles. The resist is viscous so any bubble is trapped, and causes irregularity in the layer.

spin 1000 rpm 3” (rise time 10”) to spread the resist over the wafer
spin 30” for a uniform coat (rise time ~2”)

*Depends on development time. Values are given for the procedure explained below for a 3" wafer.

2.  Post spin bake="Soft Bake"  (solvent evaporation)

Hot plate 1’
Temperature range: 65°C

Hot plate 2’
Temperature range: 95°C

If not long enough, the wafer will stick to the mask during exposure.

Wafer must be cooled down before exposure

3.  Exposure

25 mJ/cm2/µm
(taking into account "after-spin thickness")

4.  Development

developper: SU8 Developer

First determination of timing on unexposed wafer: observe the disparition of a white film

parameters 27/09/2007:
-exposed wafer, spinned 3000rpm, soft bake, exposure 125mJ/cm2 (MJB3), development 1’30.

Rinse: Isopropanol
to stop development, at Tamb ~1’-2’ with agitation

5.  Dry:

Nitrogen

6.  Cure:

Vacuum oven
40’ @ 185°C

7.  Descum:

Eliminate SU8 residues

RIE
O₂: 10 cc
P = 5 µbar 

8.  Recycle

9.  Supplementary info

-No constraint on ion milling
-There is a general problem of adhesion of metals on plastics, which is solved by milling the plastic surface right before evaporating the metal. However, this step was replaced in the fabrication of meander filters by a RIE step.