LITHOGRAPHY BEYOND LIGHT - MICROCONTACT PRINTING WITH MONOLAYER RESISTS

We describe high-resolution lithography based on transfer of a pattern from an elastomeric ''stamp'' to a solid substrate by conformal conta ct: a nanoscale interaction between substrate and stamp on macroscopic scales that allows transport of material from stamp to substrate. The stamp is first formed by curing poly(dimethyl siloxane) (PDMS) on a m aster with the negative of the desired surface, resulting in an elasto meric solid with a pattern of reliefs, typically a few microns deep, o n its surface. The stamp provides an ''ink'' that forms a self-assembl ed monolayer (SAM) on a solid surface by a covalent, chemical reaction . Because SAMs act as highly localized and efficient barriers to some wet etches, microcontact printing forms part of a convenient lithograp hic system not subject to diffraction or depth of focus limitations wh ile still providing simultaneous transfer of patterned features. Our s tudy helps to define the strengths and limitations of microcontact pri nting with SAMs, a process that is necessary to assess its worth to te chnology. We used lithography based on scanning tunneling microscopy ( STM) to demonstrate that disruption of SAMs on gold allowed the format ion of etched features as small as 20 nm using a CN-/O-2 etch. This re sult implied that etching occurred where damage of a few molecules in the ordered SAM allowed passage of cyanide, whereas adjacent molecules in the SAM remained unperturbed at this scale. Features as small as 3 0 nm etched in gold over areas greater than 1 cm(2) resulted from micr ocontact printing with replicas of electron-beam-formed masters, with the transfer of these printed SAMs requiring only approximate to 1 s. STM studies of these transferred SAMs revealed an achievable order ind istinguishable from that found for SAMs prepared from solution. Facile alignment of printing steps at submicron scales may result from new d esigns of stamps that exploit their limited deformability and lock-and -key-type approaches to mate stamp and substrate.