Search
Menu
Cognex Corp. - Smart Sensor 3-24 GIF LB

Newly Created Molecules Drive Lithography Technique

Facebook X LinkedIn Email
ATLANTA, March 30, 2007 -- New two-photon absorbing molecules that are sensitive to light at short wavelengths are helping to produce 3-D polymer line structures as small as 65 nm wide. The 3-D multiphoton lithography technique could compete with existing processes for making nanoscale electronic, photonic and microfluidic devices.Perry&Chen.jpg
A Georgia Institute of Technology research team led by Joe Perry (left, with researcher Vincent Chen) has produced 3-D polymer line structures as small as 65 nm wide using new two-photon absorbing molecules. (Georgia Tech Photo: Gary Meek)
Fabricating such small features (a nanometer is one-billionth of a meter) normally requires expensive electron beam or extreme ultraviolet lithography equipment. However 3-D multiphoton lithography simplifies the process and reduces the cost, researchers said, by using two-photon absorbing molecules.

"Being able to obtain line widths down to 65 nanometers, which is substantially below prior published work of 100 nanometers, opens up new applications for multiphoton lithography," said Joseph Perry, a professor in the Georgia Institute of Technology School of Chemistry and Biochemistry and the Center for Organic Photonics and Electronics.

The technique scans a laser beam across a substrate coated with a polymer resin containing a unique dye to create a desired hardened polymer structure. The laser writing process takes advantage of the fact that the chemical reaction of cross-linking occurs only where molecules have absorbed two photons of light. Since the rate of two-photon absorption drops off rapidly with distance from the laser's focal point, only molecules at the focal point receive enough light to absorb two photons.

Seth Marder and Stephen Barlow, also researchers in the School of Chemistry and Biochemistry and the Center for Organic Photonics and Electronics, synthesized the unique molecule called DAPB, 4,4'-bis(di-n-butylamino)biphenyl, to initiate the chemical reaction leading to the hardening of the polymers when exposed to laser light.

"We needed a dye with good two-photon absorption at a wavelength of 520 nanometers, so we tried DAPB," said Perry. "DAPB proved to be very effective in this kind of lithography."

The molecule developed by Marder and Barlow is about 10 times more efficient at absorbing light by two-photon absorption than commercial ultraviolet photoactive materials. That efficiency allowed Perry and graduate students Wojciech Haske and Vincent Chen, research scientist Joel Hales and postdoctoral associate Wenting Dong to create 3-D patterns with nanoscale lines at light intensities low enough to avoid damaging the polymers.PhotonicCrystals.jpg
Scanning electron microscope images of woodpile-type photonic crystal structures fabricated with 520-nm excitation at (a) higher power and at (b) lower power using DABP. Magnified images of the structures are shown below their respective overview images. (Image: Wojciech, H. et al.)
For the experiments, a film of the polymer resin containing DAPB was formed. When the film was exposed to the focused laser, DAPB was excited and triggered cross-linking, leaving the insoluble scanned structure on the surface of a substrate when placed in a developer solution.

Meadowlark Optics - Building system MR 7/23

Since Perry controls where the titanium:sapphire pulsed laser scans with a computer program, the polymers can be cross-linked in any pattern including 3-D stacks of straight lines that are connected and sturdy. The laser beam is turned on to expose lines of polymer and off when no line should be drawn.

Conventional lithography involves creating a specific pattern on a mask for each new layer and exposing each layer to light and developing it. With this new technique, 3-D layered nanostructures can be created simply by having a computer program scan a different pattern for each layer. Mask templates become unnecessary and the coating, exposing and developing processes only have to be conducted once.

"We can create essentially any pattern we want. For this work, some of the patterns look like walls or lines suspended across walls and some are like a tall stack of crisscrossed lines," said Perry.

"We can write very small lines and create stacked-up grids of lines called photonic crystals," Perry said. "This work shows that we can fabricate functional photonic microdevices with tailored transmission capabilities."

It takes only 10 minutes to create a 20 µm by 20 µm structure with 30 layers, Perry said. He envisions using this technology to create compact microspectrometers on a chip for use in telecommunications and sensors. It may also be used as a compact way to separate the multiple wavelengths traveling through a fiber-optic cable.

This type of simple, table-top technology may also be useful to fabricate customized types of circuits with many layers, which would be extremely expensive with standard methods because each layer would require a special mask.

"With the combination of the right molecule and short wavelength light, we've demonstrated that we can obtain nanoscale features. We're at 65 nanometers now and we're still trying to go smaller," Perry said.

The fabrication method and dye were described in the March 19 issue of Optics Express. The research was supported by the Office of Naval Research APEX Consortium and the National Science Foundation, through the Science and Technology Center for Materials and Devices for Information Technology Research. Perry and Marder co-founded a company in 2003 called Focal Point Microsystems that is working to commercialize the technology.

For more information, visit: www.gatech.edu

Published: March 2007
Glossary
electron beam
A stream of electrons emitted by a single source that move in the same direction and at the same speed.
lithography
Lithography is a key process used in microfabrication and semiconductor manufacturing to create intricate patterns on the surface of substrates, typically silicon wafers. It involves the transfer of a desired pattern onto a photosensitive material called a resist, which is coated onto the substrate. The resist is then selectively exposed to light or other radiation using a mask or reticle that contains the pattern of interest. The lithography process can be broadly categorized into several...
nano
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
photonic crystals
Photonic crystals are artificial structures or materials designed to manipulate and control the flow of light in a manner analogous to how semiconductors control the flow of electrons. Photonic crystals are often engineered to have periodic variations in their refractive index, leading to bandgaps that prevent certain wavelengths of light from propagating through the material. These bandgaps are similar in principle to electronic bandgaps in semiconductors. Here are some key points about...
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
polymer
Polymers are large molecules composed of repeating structural units called monomers. These monomers are chemically bonded together to form long chains or networks, creating a macromolecular structure. The process of linking monomers together is known as polymerization. Polymers can be classified into several categories based on their structure, properties, and mode of synthesis. Some common types of polymers include: Synthetic polymers: These are human-made polymers produced through...
sensor
1. A generic term for detector. 2. A complete optical/mechanical/electronic system that contains some form of radiation detector.
ultraviolet
That invisible region of the spectrum just beyond the violet end of the visible region. Wavelengths range from 1 to 400 nm.
3-D3-D multiphoton lithographyBasic ScienceBiophotonicsCommunicationsDAPBelectron beamfiber opticsindustriallithographymicrofluidicMicroscopymicrospectrometermoleculesnanonanostructureNews & Featuresphotonicphotonic crystalsphotonicspolymerpulsed laserssensorSensors & Detectorsspectroscopytelecommunicationstwo-photontwo-photon absorptionultravioletLasers

We use cookies to improve user experience and analyze our website traffic as stated in our Privacy Policy. By using this website, you agree to the use of cookies unless you have disabled them.