There must be some link between the world of semiconductors and pastry: why it’s okay to talk about silicon wafers, but no one would have expected a chip microwave biscuits. Yet James Hwang, a lecturer in Cornell University’s Department of Materials Science and Engineering, is the author along with other colleagues of a research project that will revolutionize the way the semiconductors of tomorrow are made. Tomorrow, however, not too far away because the latest chip (actually a System-on-chip) of the iPhone 14, which is called A16 Bionic, was made by the supplier Tsmc with a 4 nanometer production process. According to Hwang, the new technique should allow “leading manufacturers like Tsmc and Samsung to scale down to just 2 nanometers“.
In practice, the development of the sector aims at increasing the microminiaturization since for the same surface it is possible to have more transistors and therefore consequently increase the computing “power”. The problem, however, is that the current production techniques based on the rapid thermal annealer (transl. rapid thermal annealing), as the engineer Gianluca Fabi, postdoctoral researcher at Cornell explains, beyond a certain threshold they do not ensure the desired results and therefore alternatives must be identified. The microwave is a possibility, especially for what is now labeled as next generation semiconductor – in short, the new generation semiconductors.
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Did he really use a domestic microwave?
Professor Hwang, PhD student Chandrasekhar Savant, postdoctoral fellow Mohammed Javad Asadi, and the eight other researchers who signed the research published in Applied Physics Letters really used a common, partially modified microwave to prove their theory. But obviously for industrial production it will be necessary to use machinery capable of operating on a large scale.
The central theme is that the production of the materials that make up the transistors and other elements of the microchips is very reminiscent of cooking in the oven: different ingredients are mixed and then heated. “Biscottare” is a bit like one decrease because in reality unlike tradition – the ancients biscuitcooked twice – here it is cooked several times, depending on the type of chip to be obtained.
“For example, phosphorus is added to silicon and the resulting mixture is annealed, or heated, to correctly position the phosphorus atoms so that they are active for current conduction.“explains Associate Director of Marketing and Communications for the College of Engineering, Syl Kacapyr. So far the procedure is proven, but with the reduction of production processes the silicon needs to be mixed with ever higher concentrations of phosphorus to achieve the desired current level. Fabi, who mainly dealt with the design of the microwave components and is involved in the patent, confirms that with “the scaling of the dimensions is necessary to increase the doping of the material“.
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However, the increase in doping, or the addition of impurities to the silicon, creates a side effect: with traditional cooking techniques there is a risk of reaching a critical threshold that no longer ensures the production of adequate semiconductors.
“We need phosphorus concentrations above its equilibrium solubility in silicon. This goes against nature. The silicon crystal expands, causing immense voltage and making it potentially useless for electronics“, sostiene Hwang.
The solution was intuited some time ago by Tsmc, the world‘s leading manufacturer. He theorized that microwaves could be used to control all phenomena, because as happens even at home with microwave ovens, cooking is often not uniform. And so it was enough to modify the device for greater control of the standing waves that prevented the correct activation of the dopant – the phosphorus-based solution in short. The result is to obtain the desired reaction without risking damaging the silicon crystal.
“In practice, normally inside an oven of this type the microwaves bounce from one side to the other and based on the interference there may be points where the electric field is not uniform. We have intervened on this front by reducing any critical issues“, concludes the young engineer from Ancona.
The landing on the market
The first semiconductors based on this new manufacturing technique are expected to hit the market in 2025, according to Hwang. And the prospect is that even the geometry of the transistors used in microchips will change. Historically they have always been built with a vertical design: like dorsal fins on a surface. But recently we are starting to experiment with a horizontal arrangement, a kind of nanosheet that is supposed to increase the density. The procedure devised at Cornell would be ideal for this design.