Volume 20 - 2011
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Plasma Processes

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By Adrienne Nettles

When you type on a laptop or talk on a cell phone, you probably don't give much thought to the electronic signals you've set in motion. They travel on a microscopic, multi-layered superhighway of sorts, moving along interconnectors to the millions of transistors on today's semiconductor chips.

Jeffry A. Kelber

Jeffry A. Kelber is director of the new Semiconductor Research Corp.-supported Center for Electronic Materials Processing and Integration at UNT. The center is at the forefront of research ensuring semiconductor chips continue to increase in performance while decreasing in size.

Photo by: Angilee Wilkerson

The new Center for Electronic Materials Processing and Integration at the University of North Texas is at the forefront of research ensuring those chips continue to increase in performance while decreasing in size for use in all the everyday electronic devices on which we rely. In a world that requires semiconductor chips to be ever-smaller, faster and cheaper, research in this area has become critical in global economics, says Jeffry A. Kelber, Regents Professor of chemistry and director of the center.

CEMPI brings together the cutting-edge work of Kelber and 11 other experts from UNT, the University of Maryland, the University of California at Berkeley, Rensselaer Polytechnic Institute in New York, Pennsylvania State University, Columbia University, the University of Texas at Arlington, the University of Michigan and Arizona State University.

Launched in April, the center was formed to allow researchers to focus on the fundamental understanding of advanced plasma processes and insulators used in the manufacturing of state-of-the-art semiconductor chips. Plasma processing is used throughout every stage of chip manufacturing, including depositing, etching and cleaning materials.

UNT — with a new clean room on the way and a rare combination of high-powered electron microscopes and other analytical tools — was a natural choice for CEMPI's home site.

"The university has a rich history of research in the processing of semiconductor surfaces and interfaces," Kelber says. "And with our unique research capabilities, we are an ideal lead location for this work."

Shrinking Chips

Center for Electronic Materials Processing and Integration

The new Center for Electronic Materials Processing and Integration at the University of North Texas is directed by Jeffry A. Kelber, Regents Professor of chemistry, and supported by the Semiconductor Research Corp. The center, which is focused on the fundamental understanding of advanced plasma processes and insulators used in manufacturing state-of-the-art semiconductor chips, brings together the cutting-edge work of experts from nine universities.

  • University of North Texas: Jeffry A. Kelber and Oliver Chyan, Department of Chemistry; Jincheng Du and Srinivasan Srivilliputhur, Department of Materials Science and Engineering
  • Arizona State University: Robert Nemanich, Department of Physics
  • Columbia University: Tony Heinz, Departments of Physics and Electrical Engineering; Robert Laibowitz, Department of Electrical Engineering
  • Pennsylvania State University: Deborah Levin, Department of Aerospace Engineering
  • Rensselaer Polytechnic Institute: Joel Plawsky, Department of Chemical and Biological Engineering
  • University of California, Berkeley: David Graves, Department of Chemical Engineering
  • University of Maryland, College Park: Gottlieb Oehrlein, Department of Materials Science and Engineering, Institute for Research in Electronics and Applied Physics
  • University of Michigan: Mark Kushner, Department of Electrical Engineering and Computer Science
  • University of Texas, Arlington: Choong-Un Kim, Department of Materials Science and Engineering

Kelber says the evolution of semiconductor chips is best understood through Moore's Law, which states that the number of transistors on a chip will double every two years as chips get smaller and smaller.

"This is what has allowed us to deliver incredible computer power at very cheap prices over the years," he says. "If you look back, four years ago the cost of a computer was $2,000, but today you can get the same computer with the same power for less than $1,000. The world has come to depend on Moore's Law. It's an economic imperative and demands new materials for adaptation and for affordability in computers and mobile communication."

CEMPI is jointly funded by UNT and the Semiconductor Research Corp., whose member companies have a strong interest in the continuation of Moore's Law. SRC is a consortium of chip makers — including IBM, Texas Instruments and Intel — and chip equipment makers such as Novellus and Applied Materials. They pool funds to support university-based research in electronic materials, electronic device design and fabrication.

Plasma Processing

CEMPI researchers are concentrating on the back-end process of manufacturing semiconductor chips, Kelber says. This involves understanding plasma processing in the etching patterns of dielectrics, which are the insulating materials found on chips, and in the stripping off of polymers.

The etching patterns in dielectrics are used to make circuits on semiconductor chips, but current plasma processes cause chemical and structural damage to the materials, which degrades the function of the chip, Kelber says.

In his work for the center, Kelber uses an experimental ultra-high vacuum system to study interactions of plasma radiation with organosilicate glass and other dielectric materials. The system allows controlled exposures to plasma, ultraviolet radiation and free radicals. He then studies changes in the chemical composition of the surface of the materials using X-ray photoelectron spectroscopy, and he uses bulk analytical techniques — Fourier Transform Infrared and atomic force microscopy — to characterize changes in the materials' structure or surface topography.

"We're seeking to understand the interaction on an atomic level and use that understanding to predict the damage and design methods to control and limit the damage," Kelber says. "The instruments allow us to look at the chemical composition of the surface and changes in the physical structure of the surface."

Collaborative Research

Kelber's work has been supported by the SRC since 1991, and CEMPI provides him with the opportunity to collaborate with other scientists in this area. His research group, which includes seven graduate students, is working closely with the research group of David Graves, professor of chemical and biomolecular engineering at the University of California at Berkeley to understand how damages from plasma processes occur.

Graves says the problem is that the plasma will itself create changes in the porous low dielectric constant thin films his group is studying, raising the dielectric constant and thereby making these new materials less effective.

"My expertise is in plasmas and Dr. Kelber's expertise is surfaces. This problem involves how plasmas alter surfaces, so this is a perfect collaboration. We each complement the other," says Graves, who adds that an equally important component of the center is the collaboration it fosters with industrial partners.

"Our industry colleagues keep us focused on relevant problems, and the academic environment allows industry to have access to the latest techniques and scientific understanding," he says. "It also gives industry access to top graduate students."

State-of-the-Art Facilities

CEMPI researchers at UNT will soon have one of the most advanced materials analysis laboratories at any university to use in their work.

A new $6 million Nanofabrication Analysis and Research Facility will integrate the existing Center for Advanced Research and Technology with a new clean room at Discovery Park, the university's nearly 290-acre research park.

This will aid the scientists in synthesizing and processing samples of new materials and then testing and examining them at the molecular and atomic levels using CART's 27 state-of-the-art instruments and microscopes. Construction began on the center in November.

"The nanofabrication facility will allow us to turn transistors from microelectronics into nanoelectronics," Kelber says. "The clean room will allow us to make device-like structures, such as transistors, interconnectors and dielectrics, and test how various processes affect their function."

The evolution of surface sciences is definitely toward addressing more complex environments, Kelber says.

"The plasma processes used to make chips and the damages they cause are hard to ignore as chips get smaller," he says.

CEMPI's researchers and graduate students converged at Discovery Park in November for the center's first annual review, taking the opportunity to share ideas.

The formation of the center shows how important improving the processing and insulation in semiconductor chips is to the industry, Kelber says.

"As semiconductor devices continue to shrink in size and grow in complexity, the control of these surfaces and interfaces over atomic dimensions becomes crucial to further advances," he says. "Better plasma processing will be a major tool in achieving that goal."

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