Imprint Lithography using Nanocrystalline CVD Diamond Molds

Abstract

Micro-/nanoimprint lithography is a high-throughput, high-resolution, and low-cost mass production fabrication process often used for creating microfluidic devices and optical components. In the imprint lithography process, a surface pattern of a stamp is replicated into a material by mechanical contact and three dimensional material displacements. These stamps are exposed to high pressures and temperatures and need to be able to withstand these circumstances in order to be durable. Diamond is potentially the ideal surface material for an imprint lithography stamp, since it has a high hardness, a high thermal conductivity coefficient, a low thermal expansion coefficient, it is chemically inert and highly wear resistant.
Up until now, only molds made completely out of diamond have been used for imprint lithography. These molds were fabricated using single crystal or polished Chemical Vapor Deposited (CVD) diamond, which were then micro-structured by focused ion beam, reactive ion etching or e-beam lithography. Unfortunately, the availability of large area, single crystal diamond is very limited, and therefore extremely costly. On the other hand, diamond synthesis by chemical vapor deposition provides the possibility to deposit polycrystalline diamond films on areas up to tens of cm2. However, it is a rather slow process where typical growth rates are about 1 μm/hour, and thus production of full diamond stamps is time consuming and expensive.
In this thesis, two new methods for the fabrication of CVD diamond imprint lithography molds have been developed. In the first method, a layer of 0.5 μm CVD diamond is deposited on micro-structured silicon. The second method makes use of porous silicon templates through which diamond can be grown, resulting in micro-structured diamond molds. Since polishing micro-structured diamond layers is not possible, the molds were coated with an anti-adhesion layer in order to facilitate release of the mold after imprinting. Both methods proved to be suited for imprinting into a cyclic olefin copolymer developed by TOPAS (grade 6013). With the first method, imprint dimensions of 1 μm with a depth of 350 nm were realized, and imprint dimensions of 2.5 μm with a depth of 2 μm were realized with the second fabrication method. These new approaches greatly reduce complexity of the fabrication process for durable stamps, and thereby the costs involved in creating imprint lithography stamps.