SEMATECH, an international semiconductor research consortium, and UW-Madison have been teaming up for over decade to study advancements in technology. This year, SEMATECH graciously donated a Zygo phase-shifting interferometer to UW-Madison’s Computational Mechanics Center.
The phase-shifting interferometer is a device commonly used to measure optical components. With the goal of making computer chips smaller and faster, the Computational Mechanics Center has made a home for the instrument and begun research.
SEMATECH’s senior staff member Chris Van Peski chose to move the interferometer from Austin, Texas to UW-Madison to better serve the industry as a whole. Van Peski was previously using the device for the same type of research, but in light of his recent retirement passed the torch to Roxann Engelstad’s lab.
Jacob Zeuske, a UW-Madison mechanical engineering graduate student, plays a large role in the experimentation with the interferometer. He is one of two people with access to the high-tech machine—the other being Engelstad, the head of the department. Zeuske is using the interferometer to explore extreme ultraviolet lithography (EUVL) technology so that the process can be perfected to produce computer chips that are a fraction of the size, 100 times faster and can hold 1000 times as much memory.
The VeriFire MST interferometer, is the model of the device donated by SEMATECH and is manufactured by Zygo. It uses a wavelength shifting laser and data acquisition techniques to enable simultaneous measurements of both the front and back surface of transparent optics. “Basically what we are doing is measuring gaps between two surfaces,” Zeuske says. Currently, the lab is taking measurements of the flatness of the circular glass plates (known as substrates) for SEMATECH, and the data from these measurements is used as the input to models which simulate EUVL processes.
Essentially, lithography is a method of transferring a pattern from one surface to another. The Computational Mechanics Center is concerned with the mechanical aspects of EUVL; the lab is using the interferometer to measure the glass plates and predict any deformation in the glass substrates that may happen while being patterned.
In the future, when the technology is in use, a circuit pattern will be deposited into a layer of the glass plate and then reflected onto the silicon wafer. While the pattern is being put into the glass, it is possible that some bowing may occur,. This means that in addition to any pre-existing non-flatness, there will be some irregularities in the substrate. “It’s really important that the glass is flat when you do this; if it’s not flat, the pattern you put on it will be distorted,” Zeuske says. When working on nanometer scale, accuracy is very important so it is imperative to know what is going to be reflected. The glass can be flattened by using an electrostatic chuck to create an electrostatic force that pulls the glass into a flatter shape. “You can never achieve perfect flatness, but if we know what we have, we can correct for it,” Zeuske says. The lab is experimenting to see if the non-flatness measured by the interferometry system can be corrected by altering the initial pattern in the substrate.
Prior to the donation of the interferometer, UW-Madison collaborated with SEMATECH on various other projects. In 1997, SEMATECH funded a $2 million research project lead by Engelstad at UW-Madison. At that time, the semiconductor manufacturing process needed to be revamped and the mechanical engineering department simulated four new approaches for the consortium of semi-conductor manufacturers. The EUVL, which is what UW-Madison’s new interferometer uses, was one of the methods modeled in 1997.
With this donation, the Computational Mechanics Center is on the forefront of leading technology in this field. Currently there is a limit on how small computer chips can be made. However, “It is hoped that it [EUVL] will allow the patterning of much smaller features. It holds the potential for achieving nanometer scale features,” says Zeuske, which could lead to many new possibilities.