Semiconductor devices: Under mounting stress

Nov 07, 2012
The ability to monitor stress on silicon wafers may give rise to even smaller circuits. Credit: iStockphoto/Thinkstock

The recently developed ability to measure physical changes in silicon when processed into microelectronic devices could improve fabrication techniques for even smaller circuits.

Thinner semiconductor wafers to house are needed so that more can be packed into ever-smaller electrical products. Thinning, however, makes the wafers brittle and prone to warping or breaking. A technique for measuring the stress in those chips during production is now available, thanks to developmental work led by Xiaowu Zhang at the A*STAR Institute of Microelectronics, Singapore. The resulting information could enable miniature but robust .

The conversion from bare wafer to useful device can be an arduous one for a sheet of silicon, particularly when it is only a few millimeters thick. can involve bombarding the wafer with a beam of ions, dipping it in corrosive acids to etch , exposing it to plasmas for cleaning, or coating it in layers of hot metal to create electrical contacts. Then, the wafer must be fixed into a package.

Zhang and his co-workers designed and built stress sensors directly onto a silicon wafer to monitor the strain that such packaging exerts. They took advantage of the piezoresistive effect in silicon—when a force is applied to a silicon wafer, it pushes atoms closer together. In turn, the change in atom distribution alters the way an electrical current passes through the material, which can be measured as a change in resistance. Each stress sensor consisted of 16 resistors (see image). Since the piezoresistive properties of silicon are well known, Zhang and his co-workers could simply convert the changes in resistance to a corresponding change in stress.

By equally distributing 17 such sensors on the sample surface, the researchers monitored the stress in a silicon wafer during a number of common packaging processes. These included coating the wafer in a thin film and attaching a small bump of solder. They also embedded the sensors into a plastic test board, which they dropped repeatedly. Zhang and co-workers also developed a data acquisition system that could monitor the stresses during this impact test.

"Semiconductors are a multibillion-dollar industry," explains Zhang. "This stress data should enable the design of novel packaging technologies and reduce the chance of device damage during processing and during daily use and accidents, such as dropping the device."

Evaluating the stresses on a device wafer during other processes, including a technique known as 'through-silicon via', in which electrical connections are passed all the way through the wafer, will be the next step in the team's research, says Zhang.

Explore further: Renesas announces SRAM using leading-edge 16 nm FinFET for automotive information systems

More information: Zhang, X., Rajoo, R., Selvanayagam, C. S., Kumar, A., Rao, V. S. et al. Application of piezoresistive stress sensor in wafer bumping and drop impact test of embedded ultrathin device. IEEE Transactions on Components, Packaging and Manufacturing Technology 2, 935–943 (2012). ieeexplore.ieee.org/xpl/articl… _Number%3A6205691%29

add to favorites email to friend print save as pdf

Related Stories

Microtechnology: An alignment assignment

Jan 21, 2011

Microelectromechanical systems (MEMS), which consist of tiny moving parts driven by electrical signals, have found ready applications in optical communication systems. They are attractive in part because they ...

New Infrared Tool Measures Silicon Wafer Thickness

Jul 13, 2005

In the last few years, semiconductor circuit features have shrunk to sub-100 nanometer dimensions, while the size of the thin silicon wafers that these circuits are constructed on has grown from 200 millimeters ...

Next generation devices get boost from graphene research

Jan 22, 2010

(PhysOrg.com) -- Researchers in the Electro-Optics Center (EOC) Materials Division at Penn State have produced 100 mm diameter graphene wafers, a key milestone in the development of graphene for next generation ...

Recommended for you

Cyclist's helmet, Volvo car to communicate for safety

5 hours ago

Volvo calls it "a wearable life-saving wearable cycling tech concept." The car maker is referring to a connected car and helmet prototype that enables two-way communication between Volvo drivers and cyclists ...

California puzzles over safety of driverless cars

5 hours ago

California's Department of Motor Vehicles will miss a year-end deadline to adopt new rules for cars of the future because regulators first have to figure out how they'll know whether "driverless" vehicles ...

Britain's UKIP issues online rules after gaffes

6 hours ago

UK Independence Party (UKIP), the British anti-European Union party, has ordered a crackdown on the use of social media by supporters and members following a series of controversies.

Sony saga blends foreign intrigue, star wattage

6 hours ago

The hackers who hit Sony Pictures Entertainment days before Thanksgiving crippled the network, stole gigabytes of data and spilled into public view unreleased films and reams of private and sometimes embarrassing ...

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.