Finding the True Measure of Nanoscale 'Roughness'

Jun 16, 2005
Finding the True Measure of Nanoscale 'Roughness'

Straight edges, good. Wavy edges, bad. This simple description holds true whether you are painting the living room or manufacturing nanoscale circuit features.
In a technical paper* published in June, researchers at the National Institute of Standards and Technology (NIST) and SEMATECH describe an improved method for determining nanoscale "linewidth roughness," an important quality control factor in semiconductor fabrication. Their research shows that current industry measurement methods may be exaggerating roughness of the smoothest circuit features by 40 percent or more above true values.

Image: A colorized scanning electron microscope image shows the "waviness" or roughness of edges on reference lines made of silicon that are about 100 nanometers wide. Credit: B. Bunday, SEMATECH/K. Talbott, NIST

As circuit features shrink in size to below 50 nanometers, wavy or rough edges within semiconductor transistors may cause circuit current losses or may prevent the devices from reliably turning on and off with the same amount of voltage.

"With this type of measurement," says NIST's John Villarrubia, "besides the real roughness there is also a false roughness caused by measurement noise. Our method includes a correction to remove bias or systematic error from the measurement."

Random noise, by definition, causes the measured value to be sometimes higher, sometimes lower than the true value, and can be minimized by simply averaging an adequate number of measurements. Systematic error, however, is consistently above or consistently below the true value due to some quirk of the measurement method.

The noise in nanoscale scanning electron microscope (SEM) images consistently adds extra roughness, says Villarrubia. The NIST/SEMATECH method involves taking two or more images at exactly the same location on a circuit feature, comparing the values, and subtracting the false roughness caused by measurement noise. SEM manufacturers should be able to incorporate the new method into their proprietary software for automated linewidth roughness measurements.

* J.S. Villarrubia and B.D. Bunday, Unbiased Estimation of Linewidth Roughness, Proceedings of SPIE 5752 (2005) pp. 480-488.

Source: NIST

Explore further: Solving molybdenum disulfide's 'thin' problem

add to favorites email to friend print save as pdf

Related Stories

Researchers study fluctuations in solar radiation

Mar 18, 2015

The Sun is the Earth's principal source of energy and climate driver. Yet sometimes it sends more light to the Earth than other times. Astronomers working with Natalie Krivova at the Max Planck Institute ...

Helicopter drones on Mars

Mar 18, 2015

NASA's Jet Propulsion Laboratory recently announced that it is developing a small drone helicopter to scout the way for future Mars rovers. Why would Mars rovers need such a robotic guide? The answer is that ...

Humble neutron is valuable tool in geology

Mar 16, 2015

With the ability to analyse the properties of the Earth's internal components to the atomic scale in conditions only found kilometres below our feet, recent studies have allowed geoscientists to study our ...

Hubble Source Catalog: One-stop shopping for astronomers

Mar 14, 2015

Astronomers at the Space Telescope Science Institute and the Johns Hopkins University, both in Baltimore, Maryland, have created a new master catalog of astronomical objects called the Hubble Source Catalog. ...

Recommended for you

Solving molybdenum disulfide's 'thin' problem

Mar 27, 2015

The promising new material molybdenum disulfide (MoS2) has an inherent issue that's steeped in irony. The material's greatest asset—its monolayer thickness—is also its biggest challenge.

Designer's toolkit for dynamic DNA nanomachines

Mar 26, 2015

The latest DNA nanodevices created at the Technische Universitaet Muenchen (TUM)—including a robot with movable arms, a book that opens and closes, a switchable gear, and an actuator—may be intriguing ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.