Direct e-beam lithography of PDMS

In this paper, the viability of directly exposing thin films of liquid poly(dimethylsiloxane) (PDMS) to electron beam (e-beam) irradiation using e-beam lithographic methods for the purpose of creating permanent micro-scale components has been investigated. By exposing 1.1 μm thickness PDMS films to doses in the range 10–50,000 μC/cm2, it was discovered that the structure of the resultant film exhibits four distinct phases, depending upon the exposure dose. These phases were manifested in both the resultant Young’s modulus and thickness of the developed film. It was found that there is a critical dose whereupon the resultant film undergoes solidification and adheres to the counter surface sufficiently to survive the development process. It has been shown that the Young’s modulus of the solid film can be varied over seven orders of magnitude, from that of a viscoelastic material through a rubbery regime to that of a glassy one, by increasing the e-beam dose. At higher doses, excessive backscattering was observed, as well as film swelling, resulting in poor spatial resolution.

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► We have shown that there are four distinct regimes in the e-beam exposure of PDMS.
► The phase, elastic modulus and resultant thickness are highly dependent on dose.
► In the solid region, the elastic modulus is tuneable by three orders of magnitude.