W. Richard Bowen and Nidal Hilal 4

200 7. MICRO/NANOENgINEERINg ANd AFM FOR CELLULAR SENSINg
(A)
(B)
Photolithography
(a)
(b)
(c)
(d)
Mask
Etching Lift-off
(e) (g)
(f)
(h)
Photoresist
Substrate
(a) (b) (c)
(f) (e) (d)
Metal
FIgurE 7.2 Schematic diagram of methods used in micropatterning. (A) Photolithography
and (B) microcontact printing. In photolithography a mask with opaque and transparent
features is brought into contact with a substrate coated with a photosensitive polymer (photoresist)
(a and b). UV light is shone through the mask, exposing the polymer beneath the
transparent regions of the mask (c). The mask is removed and the resist developed, removing
either the exposed or unexposed regions of the resist depending on the resist type (d).
The resist layer can be used as a protective mask during a process to etch the unprotected
regions of the substrate (e)–(f). Alternatively, metal can be evaporated onto the sample,
remaining on the regions of exposed substrate after the resist has been dissolved in a ‘lift-off’
process (g)–(h). In microcontact printing, a topographically patterned stamp is ‘inked’ by
contacting it with a sample coated with the desired chemical species (a)–(c). When the inked
stamp is brought into contact with a clean substrate, the species are deposited on the surface
in patterned regions dictated by the topography of the stamp (d)–(f).