New technique simplifies flat-panel display fabrication


Brad Petersen, ECE Illinois

Kanti Jain
Kanti Jain

ECE Kanti Jain and postdoctoral researcher Junghun Chae have devised a new technique for patterning indium tin oxide films, a component of flat panel displays, which simplifies the current manufacturing process and could potentially save money. The technique uses laser-driven photoablation and lift-off instead of the multistep, traditional microlithography process.

"In the conventional fabrication method of microelectronic devices and flat panel displays, many processes are required to make a pattern including deposition of material, photoresist coating and baking, exposure, developing, etching, and photoresist stripping," Jain explained. "Using our innovative process, the developing and etching processes are not required anymore."

The use of photoablation in patterning is not new. However, Jain and Chae believe they can eliminate common problems that have limited its use in patterning inorganic materials, including rough edges and high fluence requirements, by using a lift off technique.

This image shows the pattern left after photoablation.
This image shows the pattern left after photoablation.

In the new fabrication technique, a layer of photoresist is first cured and then, using photoablation, patterned. The process of photoablation uses a laser to remove in one step unwanted material by photofragmentation of long-chain polymeric molecules. Next, a layer of indium tin oxide is applied. Finally, the remaining photoresist is stripped away, essentially lifting off with it any unwanted indium tin oxide and leaving behind the desired pattern of indium tin oxide. Jain and Chae have demonstrated clean patterning using a small enough fluence, or concentration of laser radiation, for photoablation so as to avoid harming any structures below the indium tin oxide layer and also to enable high processing throughput.

According to Jain, the technique could be used in manufacturing any microelectronic device from flat-panel displays to nanoscale semiconductor devices. The greatest benefit may be realized with process steps that are expensive and used in devices produced in high volumes. "It is well known that the microlithography process is the most expensive processing step in the whole fabrication cycle," he said. "Therefore, innovation in the most expensive step is the best and most effective approach to reduce the production cost." The benefits of the new technique also involve lowered cost from reduced chemical usage and chemical waste management. Plus, with fewer steps involved, overall production time can be decreased.

Jain and his colleagues described their new method in a paper published in the June 25 issue of Applied Physics Letters. Collaborators in the research also include scientists from Anvik Corporation of Hawthorne, NY, a manufacturer of microlithography and photoablation systems.

The team is in the process of securing a patent for the technique. Jain said plans to collaborate with other researchers in perfecting and commercializing the new technique are already in place.