Biomedical Engineering Reference
In-Depth Information
Figure 4.27
The mask patterns used for the lithography process. While the bottom left pattern is
the one that was used for the bottom part (supports), the other three patterns were used to fabricate
top parts with 1, 3, and 4 hanging beams, respectively
Soft Baking
Immediately after the samples were spin coated, they were placed on a hotplate using a
vacuum line to ensure hard contact, after which the temperature was set to 115
◦
Cand
the samples baked for 1 minute.
Exposure
To transfer the mask pattern to the photo resist, a conventional mask aligner (Karl Suss
MA6) was used. The exposure time was selected to be 5 s, while a 270 W mercury lamp
(in soft contact mode) was used.
Developing
For the developing step, the samples were agitated in a solution of photo resist developer
(MF-319 from Shipley) for about 1 minute at room temperature. After developing, samples
were inspected under a microscope to detect any probable defects. A picture of some of
the samples after this developing step is shown in Figure 4.28.
Hard Baking
In order to reinforce the photoresist for subsequent etching processes, a hard baking step
was required, in which samples were heated in an oven for 30 minutes at a temperature
of 105
◦
C.
