Polymer Pen Lithography

Fengwei Huo, Zijian Zheng, Gengfeng Zheng, Louise R. Giam, Hua Zhang, Chad A. Mirkin

 

19 September 2008, Science Vol 321

 

Purpose of Study

 

Lithography tools have problems generating both nano- and microscale features in a single experiment in a parallel, high-throughput, direct manner.  This paper reports a low cost, high-throughput lithography technique capable of creating feature sizes that range from 90 nm to hundreds of microns.  Polymer pen lithography (PPL) combines the feature size control of Dip pen lithography (DPN) with the large area capabilities of contact printing.

 

Method:

 

A master mold is created by conventional photolithography followed by wet etching; this mold contains thousands of pyramidal-shaped holes.  PDMS (polydimethylsiloxane) fills this mold and is attached to a glass substrate creating an array of elastomeric polymer tips.  The substrate and thin PDMS backing behind the tips improves the uniformity of the array over a large area.  The PDMS is dipped in the ink you want to use, and the ink is absorbed into the array; unlike DPN, the PDMS acts as a reservoir allowing a greater amount of polymer to be patterned.  When the array is brought into contact with a substrate, the ink is delivered at the points of contact; the amount of ink deposited is a function of time and force.  Like DPN, the deposited ink varies linearly with time; but due to the elastomeric nature of PDMS, as force is applied, the pyramids deform and become blunt against the substrate.  This increases the rate of deposition and allows for vastly different feature sizes to be produced by a single mask.  This elastic nature of PDMS also makes it easies to bring all the tips into contact with a substrate without changing your deposition of ink; the PDMS compresses before it deforms.

 

Key Findings:

 

(1)  Creation of a lithography technique capable of patterning with a large degree of freedom in the feature sizes created.  This allows for a single mask to be used, both increasing speed and lowering costs.

(2)      The dependence of the transfer rate on force applied perpendicular to the substrate, due to the elastic characteristics of PDMS, allows for precise control over feature sizes over a range that beforehand was unthinkable.

(3)      Demonstration of feature sizes ranging from 90 nm to hundreds of microns, and creation of an integrated gold circuit created by PPL.