Modified microwave oven cooks up next-gen semiconductors
By Syl Kacapyr
A household microwave oven modified by a Cornell Engineering professor is helping to cook up the next generation of cellphones, computers and other electronics after the invention was shown to overcome a major challenge faced by the semiconductor industry.
The prototype was built by James Hwang, a research professor in the Department of Materials Science and Engineering, and aims to advance research that he and co-authors detailed in a paper published Aug. 3 in Applied Physics Letters.
Producing the materials that make up transistors and other microchip components is similar to baking, in that material ingredients must be mixed together and then heated, among other steps, in order to produce a desired electrical current. For instance, phosphorus is added to silicon and then the mixture is annealed, or heated, to position the phosphorus atoms into the correct place so that they are active in current conduction.
But as microchips continue to shrink, the silicon must be doped, or mixed, with higher concentrations of phosphorus to produce the desired current. Semiconductor manufacturers are now approaching a critical limit in which heating the highly doped materials using traditional methods no longer produces consistently functional semiconductors.
“We need concentrations of phosphorus that are higher than its equilibrium solubility in silicon. That goes against nature,” Hwang said. “The silicon crystal expands, causing immense strain and making it potentially useless for electronics.”
Hwang’s modified microwave oven overcomes this challenge by using microwaves to activate the excess dopants. Just like with household microwave ovens that sometimes heat food unevenly, previous microwave annealers produced “standing waves” that prevented consistent dopant activation, but Hwang’s prototype selectively controls where the standing waves occur. Such precision allows for the proper activation of the dopants without excessive heating or damage of the silicon crystal.
The annealing technique was first achieved with laboratory equipment and reported by a group that included Hwang and collaborators from the Taiwan Semiconductor Manufacturing Company (TSMC) and DSG Technologies, among others. Hwang said his prototype will advance the research, which could be used to produce semiconductor materials and electronics appearing around the year 2025.
Hwang has filed two patents for the prototype microwave annealer with postdoctoral researcher Gianluca Fabi and doctoral student Chandrasekhar Savant.
“A few manufacturers are currently producing semiconductor devices that are 3 nanometers,” Hwang said. “This microwave approach can potentially enable leading manufacturers such as TSMC and Samsung to scale down to just 2 nanometers.”
The breakthrough could change the geometry of transistors used in microchips. For more than 20 years, transistors have been made to stand up like dorsal fins so that more can be packed on each microchip, but manufacturers have recently begun to experiment with a new architecture in which nanosheets are stacked vertically that can further increase the density and control of transistors. The excessively doped materials enabled by microwave annealing would be key to the new architecture.
The research was supported by the Ministry of Science and Technology of Taiwan, and the prototype is being supported by an Ignite: Cornell Research Lab to Market grant from Cornell’s Center for Technology Licensing.
Syl Kacapyr is associate director of marketing and communications for the College of Engineering.
Editor’s note: James Hwang’s prototype was not used for the research published in Applied Physics Letters on Aug 3. An original version of this story incorrectly described the role of Hwang’s device in the research.