Photolithography is a technique used in microfabrication that relies on photosensitive resists to create things such as microcircuits and microprocessors. The technique has been the fabrication standard for nearly 50 years, however, the process has been approaching material limits and state of the art technology has become extremely expensive. As our structures get smaller they require smaller and smaller wavelengths of light to etch circuitry.
While photolithography has been extremely useful in developing our microfabrication technology, it does have limitations. Initially, the process was refined for use in the developing silicon industry, but current technology has approached the fundamental limits of the material. Current photolithography techniques are only applicable to a narrow range of materials mostly deviations of silicon.
In the quest to enable more and more functionalities in microprocessors, researchers have been searching for alternatives to photolithography in microfabrication. Nanomaterials serve as an excellent candidate and have several unique properties that cannot be reliably exploited in larger materials.
Left: A pattern developed by the researchers (about the size of a grain of rice). Right: The lead sulfide particles that make it up (each eight nanometers across). Image courtesy of Dmitri Talapin and Yuanyuan Wang via the University of Chicago
Manufacturing components using these materials has been very challenging, as we lack proper techniques and encounter issues relating to compatibility.
Recently, a research group consisting of members from the University of Chicago and the Argonne National Laboratory created a new process, dubbed DOLFIN, which can be used to manufacture with precision on par with our current state of the art technologies.
The DOLFIN Advantage
There's normally a multitude of steps required to create single layers in nanoscale patterning. There are also normally several sequential layers that need to be patterned. The team circumvented this by eliminating the need for a photoresist.
The process they designed aimed to avoid the use of photoresists by using of ligands that respond to light to induce changes in nanocrystals while in a solvent.
First, the team prepared the pattern materials using the geometrics of specific nanocrystals and attaching them to photoreactive ligands. A standard lithography mask constructed with a form of glass—known as a “mask” in this process—is illuminated and used as a stencil to direct ultra violet light onto the substrate.
Patterns created on inorganic materials. Image courtesy of Dmitri Talapin and Yuanyuan Wang via UChicago Creative
This eliminates the need for a photoresist by utilizing the properties of the photoactive ligand-doused nanocrystals to change structure in the absence of light.
The process has proven to be quite useful and efficient in the creation of multiple layers. Surprisingly, the process has been proven to be compatible with multiple different substrates such as glass, silicon, and varying polymers. The process was capable of outperforming standard photopolymers techniques in the creation of multilayered 3D patterns by cutting the process from 43 steps to 19 while using comparable amounts of UV exposure. The result was a cheaper and more efficient process than traditional photolithography techniques.
Yuanyuan Wang, the paper's lead researcher, with an example mask. Image courtesy of the University of Chicago
“It can be used with a wide range of materials, including semiconductors, metals, oxides or magnetic materials—all commonly used in electronics manufacturing,” said Yuanyuan Wang, lead author and researcher at the University of Chicago.
While the process has proven useful in their current design parameters, it has yet to be scaled up into something such as the mass production of billions of transistors.
The original research article can be found in the Journal of Science.