Chemical Etching Method Helps Transistors Stand Tall
July 28, 2016 | University of IllinoisEstimated reading time: 3 minutes

Smaller and faster has been the trend for electronic devices since the inception of the computer chip, but flat transistors have gotten about as small as physically possible. For researchers pushing for even faster speeds and higher performance, the only way to go is up.
University of Illinois researchers have developed a way to etch very tall, narrow finFETs, a type of transistor that forms a tall semiconductor “fin” for the current to travel over. The etching technique addresses many problems in trying to create 3-D devices, typically done now by stacking layers or carving out structures from a thicker semiconductor wafer.
“We are exploring the electronic device roadmap beyond silicon,” said Xiuling Li, a U. of I. professor of electrical and computer engineering and the leader of the study. “With this technology, we are pushing the limit of the vertical space, so we can put more transistors on a chip and get faster speeds. We are making the structures very tall and smooth, with aspect ratios that are impossible for other existing methods to reach, and using a material with better performance than silicon.”
Typically, finFETs are made by bombarding a semiconductor wafer with beams of high-energy ions. This technique has a number of challenges, Li said. For one, the sides of the fins are sloped instead of straight up and down, making them look more like tiny mountain ranges than fins. This shape means that only the tops of the fins can perform reliably. But an even bigger problem for high-performance applications is how the ion beam damages the surface of the semiconductor, which can lead to current leakage.
The Illinois technique, called metal-assisted chemical etching or MacEtch, is a liquid-based method, which is simpler and lower-cost than using ion beams, Li said. A metal template is applied to the surface, then a chemical bath etches away the areas around the template, leaving the sides of the fins vertical and smooth.
“We use a MacEtch technique that gives a much higher aspect ratio, and the sidewalls are nearly 90 degrees, so we can use the whole volume as the conducting channel,” said graduate student Yi Song, the first author of the paper. “One very tall fin channel can achieve the same conduction as several short fin channels, so we save a lot of area by improving the aspect ratio.”
The smoothness of the sides is important, since the semiconductor fins must be overlaid with insulators and metals that touch the tiny wires that interconnect the transistors on a chip. To have consistently high performance, the interface between the semiconductor and the insulator needs to be smooth and even, Song said.
Right now, the researchers use the compound semiconductor indium phosphide with gold as the metal template. However, they are working to develop a MacEtch method that does not use gold, which is incompatible with silicon.
“Compound semiconductors are the future beyond silicon, but silicon is still the industry standard. So it is important to make it compatible with silicon and existing manufacturing processes,” Li said.
The researchers said the MacEtch technique could apply to many types of devices or applications that use 3-D semiconductor structures, such as computing memory, batteries, solar cells and LEDs.
The National Science Foundation, the International Institute for Carbon-Neutral Energy Research (I2CNER) and Lam Research supported this work. The co-authors of this work include U. of I. postdoctoral researcher Parsian Mohensi (now a professor at the Rochester Institute of Technology) and graduate student Seung Hyun Kim; Jae Cheol Shin, a professor at Yeungnam University in South Korea; Tatumi Ishihara, a professor at I2CNER in Japan; and Ilesanmi Adesida, a U. of I. professor of electrical and computer engineering. Li also is affiliated with the Micro and Nanotechnology Laboratory at the U. of I.
Suggested Items
Indium Corporation Expert to Present on Automotive and Industrial Solder Bonding Solutions at Global Electronics Association Workshop
06/26/2025 | IndiumIndium Corporation Principal Engineer, Advanced Materials, Andy Mackie, Ph.D., MSc, will deliver a technical presentation on innovative solder bonding solutions for automotive and industrial applications at the Global Electronics A
Indium Elevates Two Leaders Advancing PCB Assembly Innovation
06/10/2025 | Indium CorporationWith its commitment to innovation and growth through employee development, Indium Corporation is pleased to announce the promotions of Wisdom Qu to Senior Product Manager for PCB Assembly Products and Kevin Brennan to Senior Product Development Specialist.
Indium Joins Virginia Tech Center for Power Electronics Systems Industry Consortium
06/03/2025 | Indium CorporationIndium Corporation®, a leading materials refiner, smelter, manufacturer, and supplier to the global electronics, semiconductor, thin-film, and thermal management markets, has joined Virginia Tech’s Center for Power Electronics Systems (CPES), an industry consortium that supports power electronics initiatives to reduce energy use while growing capability.
Indium Promotes O’Leary to Director of Global Accounts
05/27/2025 | Indium CorporationIndium Corporation, a leading materials refiner, smelter, manufacturer, and supplier to electronics, semiconductor, thin-film, and thermal management industries, announces the promotion of Brian O’Leary to Director of Global Accounts.
Indium to Feature Materials Solutions for Semiconductor Packaging and Assembly at ECTC
05/22/2025 | Indium CorporationIndium Corporation®, an industry leader in innovative materials solutions for semiconductor packaging and assembly, will feature its lineup of high-reliability products at the Electronics Component and Technology Conference (ECTC), taking place May 27-30 in Dallas, Texas.