Author: MaryRose O'Donnell

The Illinois Plasma Institute (IPI) is proud to announce that graduate student Tag Choi has successfully defended his PhD thesis.

Tag’s dissertation addresses the complexity of chip manufacturing that has increased dramatically alongside the demand for more advanced semiconductor devices. A crucial step in semiconductor manufacturing is deposition, and physical vapor deposition (PVD) is commonly employed to apply metal films. Within PVD techniques, sputtering remains a primary method; however, conventional sputtering struggles to deposit conformal films at modern feature sizes. To address this, High-Power Impulse Magnetron Sputtering (HiPIMS) has emerged as a promising deposition technique. It is a relatively new PVD technique that uses extremely high-power pulses to sputter target materials and create highly ionized plasmas. HiPIMS produces plasmas with higher ion flux and energy and a lower incident angle, resulting in increased film density, higher surface adhesion, better surface smoothness, and improved crystallinity.

This work aims to understand plasmas generated by HiPIMS with positive cathode reversal as a potential PVD technique for semiconductor manufacturing. A plasma sampling mass spectrometer (PSM), a state-of-the-art diagnostic tool that measures time- and mass-resolved ion energy distribution functions (IEDFs), is utilized to evaluate the effects of HiPIMS parameters. Key findings include a reduction in the number of Ar ions with longer main pulse length, the presence of fast ions or ions undergoing a thruster-like effect, and an increase in the number of slow ions as a function of kick pulse length. Spatial and angular ion energy distributions are evaluated to characterize azimuthal ion motion in HiPIMS plasmas using a custom-built magnetron mounted on linear and rotational stages. Angular distributions reveal that Ti ions are mostly accelerated away from the target at angles between 30 and 45 degrees, while Cu ions are uniformly distributed between 0 (normal) and 45 degrees. These results provide deeper knowledge of HiPIMS discharges, offering valuable insights for depositing high-quality films and the development of next-generation PVD tools for semiconductor fabrication.

Congratulations to Tag as he continues his journey after graduation!

Recently, researchers at IPI published a new article that presents a self-consistent hybrid model for simulating SF6/Ar inductively coupled plasma etchers, combining a fast 0D chemistry solver with a 2D electromagnetic/transport solver so that quantities like power-coupling efficiency and plasma density/temperature profiles emerge from the physics rather than being assumed inputs. The model is validated against wafer-plane fluorine measurements from an industrial etcher, and the authors also build a neural-network surrogate that reproduces the converged plasma state nearly 1000x faster, positioning the combined framework as the core of a near-real-time reactor “digital twin” for recipe development.

Read about it here: https://doi.org/10.1088/1361-6463/ae9f67

Congratulations to Tag Choi for being selected as one of five finalists for the 2025 Coburn and Winters (C&W) Student Award, presented by the Plasma Science and Technology Division (PSTD) of the American Vacuum Society (AVS).

As a finalist, Tag will be awarded a cash prize and the opportunity to win the award for an additional cash prize and certificate. After a closed session where he and the other finalists will present their work, the ultimate winner of the award will be announced on Thursday September 25.

Congratulations again to Tag and good luck!

The SMART (Semiconductor Manufacturing and Advanced Research with Twins) USA Institute hosted their inaugural summit on June 26 and 27th in Arlington, Virginia. This summit was an opportunity for leaders within the industry, government, and academia to discuss the future of semiconductor manufacturing in America. Specifically, this summit focused on digital twin research, virtual replicas of physical systems that allow researchers to have real-time monitoring, simulation, and optimization.

IPI’s Associate Director, Professor Dren Qerimi, attended to discuss and learn on behalf of IPI and the University. The University of Illinois at Urbana-Champaign also is now Tier 1 Member of SMART USA, giving the university a voice amongst leaders in the industry and access to resources from other members.

IPI Associate Director Dren Qerimi attended the combined IEEE Pulsed Power & Plasma Scienced Conference and IEEE International Conference on Plasma Science in Berlin, Germany last month. The combined conferences covered topics in plasma science and engineering as well as in pulsed power science and technology.

Professor Qerimi gave a talk titled “University-scale Extreme Ultraviolet Lithography Source” that discussed and explored how cutting-edge EUV technology—an area that is usually reserved for industrial giants—can be reimagined and scaled for academic research environments.

This June, IPI Director David Ruzic established the first named professorship of the NPRE department in honor of his parents, Neil and Carol Ruzic. This professorship will be put towards plasma-related faculty to continue to enhance the department’s mission in plasma engineering.

You can more about the new professorship, its namesakes, and the vision for the future of plasma in NPRE here: New named professorship carries on legacy of Ruzic family | Nuclear, Plasma & Radiological Engineering | Illinois

IPI Associate Director Dren Qerimi traveled to Saudi Arabia in May to attend the “Future of Semiconductors Forum” for two days. This forum was put on by the King Abdullah University of Science and Technology (KAUST). Professor Qerimi had the opportunity to share IPI’s work on the in-house built EUV (Extreme Ultraviolet) source as well as learn from other leaders in the field. This forum offered both great discussions about the next generation of semiconductor technology and offered opportunities to connect with people across the world in the field.

In Professor Qerimi’s own words, he is “Excited about the future we’re building together—across borders and disciplines”.

On Wednesday March 5, 2025, Jeremy Mettler held his final doctor defense in front of more than 30 people! Dr. Mettler’s thesis was titled “On the Development and Application of Etching-Based Fluorine Radical Probes”.

In this PhD thesis, Jeremy investigates the critical role of fluorine chemistry in high aspect ratio silicon etching, a key process in modern semiconductor manufacturing where uniformity, selectivity, and pattern roughness must meet increasingly strict tolerances. Focusing on the discrepancies in fluorine radical reaction rates with silicon, particularly when using SF6, the study introduces an innovative approach to measure fluorine radical densities using spatially resolved radical probes. These probes, featuring thermocouples with reactive tungsten and inert aluminum tips, were tested in the Plasma-Materials Interaction Chamber (PMIC) and a Tokyo Electron (TEL) etcher, demonstrating a linear correlation between probe response and fluorine density in NF3 and SF6 plasmas. Through calibration and kinetic analysis from 100ºC to 700ºC, the probes provided accurate etch rate measurements and revealed spatial fluorine density profiles above the wafer stage, showing that silicon etch rates directly correspond to fluorine radical distribution. Compared to actinometry, which underestimated densities near the wafer center, the probe-based method offered consistent etch probabilities unaffected by fluorine flux variations, providing new insights into silicon etching mechanisms and a valuable tool for studying fluorine radical distributions.

Congratulations to Dr. Jeremy Mettler on his PhD!