How the smallest damage at the surface of semiconductor crystals develops into large defects

December 4, 2017 by Monika Landgraf, Karlsruhe Institute of Technology
How the smallest damage at the surface of semiconductor crystals develops into large defects
When processing semiconductor wafers, small surface defects may lead to large defects inside and to steps on large surface areas. Credit: Figure: D. Hänschke/KIT

Using non-destructive imaging methods, a team of scientists at KIT obtains three-dimensional insights into the interior of crystals. They determine important data about line-shaped defects that largely influence the deformation behavior of crystals. These so-called dislocations impede the production of computer chips. As reported in the Physical Review Letters, the scientists combine two X-ray methods with a special type of light microscopy.

Even a few dislocations in silicon wafers can lead to defective computer chips and, hence, to undesired production rejects. "It is therefore important to understand how a minor mechanical surface propagates into the depth of the crystal under typical process impacts, such as heat," says Dr. Daniel Hänschke, physicist of KIT's Institute for Photon Science and Synchrotron Radiation. His team has succeeded in precisely measuring dislocations and studying their interactions with each other and with external impacts. The scientists analyzed how a single surface defect spreads into an armada of hexagonal defect lines, while completely undamaged areas may remain in the center of such a three-dimensional network. "The resulting collective movement can raise or lower large surface areas on the opposite side of the wafer and cause the formation of steps, which may adversely affect the fabrication and function of microstructures," Hänschke points out.

Combined with mathematical model calculations, the results allow to better understand the underlying physical principles. "Models used so far are mainly based on data measured by electron microscopy in very small crystal samples," Dr. Elias Hamann, another member of the team, explains. "Our method can also be applied to study large, flat crystals, such as commercially available wafers," he adds. "This is the only way to determine detailed relationships between the initial, minute original damage and the resulting extensive crystal deformations that may cause major problems far away from the onset of the defect."

The new measurement method combines X-ray techniques at the KARA synchrotron of KIT and the ESRF European synchrotron in Grenoble with so-called CDIC light microscopy. The findings obtained will help improve existing models for the prognosis of defect formation and defect propagation and, hence, provide indications of how the fabrication process of computer chips can be optimized. The number of transistors arranged on a square centimeter of a wafer surface already reaches several billions, with increasing tendency. Even smallest defects on and in the crystal may cause thousands of these small circuits to fail and the corresponding chips to be unusable. Industry is highly interested in further minimizing the defect rate in the future.

How the smallest damage at the surface of semiconductor crystals develops into large defects
When processing semiconductor wafers, small surface defects may lead to large defects inside and to steps on large surface areas. (Silizium = Silicon). Credit: D. Hänschke/KIT

Explore further: Researchers image perfectly smooth side-surfaces of 3-D silicon crystals with a scanning tunneling microscope

More information: D. Hänschke et al. Correlated Three-Dimensional Imaging of Dislocations: Insights into the Onset of Thermal Slip in Semiconductor Wafers, Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.215504

Related Stories

Materials science: Perfecting the defect

May 3, 2012

Strong metals have a tendency to be less ductile — unless the metal happens to be a peculiar form of copper known as nanotwinned copper. The crystal structure of nanotwinned copper exhibits many closely-spaced interruptions ...

Recommended for you

Walking crystals may lead to new field of crystal robotics

February 23, 2018

Researchers have demonstrated that tiny micrometer-sized crystals—just barely visible to the human eye—can "walk" inchworm-style across the slide of a microscope. Other crystals are capable of different modes of locomotion ...

Recurrences in an isolated quantum many-body system

February 23, 2018

It is one of the most astonishing results of physics—when a complex system is left alone, it will return to its initial state with almost perfect precision. Gas particles, for example, chaotically swirling around in a container, ...

Seeing nanoscale details in mammalian cells

February 23, 2018

In 2014, W. E. Moerner, the Harry S. Mosher Professor of Chemistry at Stanford University, won the Nobel Prize in chemistry for co-developing a way of imaging shapes inside cells at very high resolution, called super-resolution ...

Hauling antiprotons around in a van

February 22, 2018

A team of researchers working on the antiProton Unstable Matter Annihilation (PUMA) project near CERN's particle laboratory, according to a report in Nature, plans to capture a billion antiprotons, put them in a shipping ...

Urban heat island effects depend on a city's layout

February 22, 2018

The arrangement of a city's streets and buildings plays a crucial role in the local urban heat island effect, which causes cities to be hotter than their surroundings, researchers have found. The new finding could provide ...

0 comments

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.