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On-wafer solution brings power devices to market faster

Posted: 29 May 2007 ?? ?Print Version ?Bookmark and Share

Keywords:power IC device? on-wafer characterization? high-current probe? high-voltage probe? IGBT?

Cascade Microtech Tesla power IC device system

In an effort to help power device manufacturers shorten time-to-market and overcome on-wafer probing challenges, Cascade Microtech Inc. announces its Tesla power IC device characterization system.

Addressing the need for engineers and test technicians to safely characterize power IC devices, the Tesla system touts a complete on-wafer solution for overtemperature, low contact resistance measurements of power semiconductors of up to 60A (current in pulsed mode) and 3,000V (coaxial measurement).

Power IC devices, such as power diodes, thyristors, power MOSFETs and IGBTs, are increasingly being used in a wide range of applications in the telecoms, industrial, automotive, military/aerospace and consumer electronics sectors. Moreover, demand for power devices is fueled by several factors, including the environmental concern to lower power consumption. Pressured to deliver new power devices to the market quickly, the industry needs to speed up its development process.

"For years, the power IC device industry has faced the challenge of characterizing and measuring their device parameters at the wafer level," said Cali Sartor, senior product manager of Cascade. She also noted that "power device manufacturers would package devices before measurements or develop an in-house fixture" due to the lack of support for higher voltage and current testing.

Cut time, cost
Sartor pointed out that while packaging provides accurate data, it adds time and cost to the development process. In-house solutions, on the other hand, cause time and safety issues.

"The Tesla system opens the door for on-wafer characterization of power devices," Sartor said. Cascade's new measurement system gets rid of packaging, thus reducing the time and cost associated with it. "One engineer has claimed that what could be completed in one day with an on-wafer probe station can take up to 40 days in package."

Moreover, the system allows test engineers to make measurements for different device types and sizes. Hence, it eliminates the need to develop custom solutions for different devices, saving time and labor.

"This gives power device engineers the ability to improve their productivity as much as forty times," Sartor estimated.

The thinner, the tougher
"The key trend for power devices is thinning wafers," Sartor explained. With average wafers having 100?m thickness and going thinner, on-wafer device characterization is becoming more complex.

Holding down thin wafers on a standard wafer chuck is difficult, Sartor said. Moreover, thin wafers tend to "potato-chip" or curl at the ends, posing a problem for wafer probing with low contact resistance between the wafer and the chuck.

The Tesla chuck can handle thin wafers with the Vacuchannel chuck technology, which provides the right amount of vacuum to protect against wafer breakage and probe damage. It supports a low contact resistance between the wafer and chuck, and 3-, 4-, 6- and 8-inch wafer diameters.

The Tesla characterization system also features two new wafer probes: high-current and high-voltage probes. The high-current probe reduces probe and/or device destruction at high currents, supporting up to 10A of current in continuous mode and up to 60A in pulsed mode. This new probe minimizes contact resistance at the wafer to probe the interface, thus reducing device heating. Moreover, the probe distributes the current over many contact points, which are joined by metal that is used to pull heat from the probe tip.

Meanwhile, the high-voltage probe ensures operator safety and high-performance electrical measurement path. It enables a coaxial measurement of up to 3,000V and triaxial measurements up to 1,100V. Thus, it enables power device engineers to understand more of the characteristics of their device in the off state.

Other features of the on-wafer characterization system replaceable probe tips, handsfree scope, safety interlock and remote system operation.

According to Sartor, the company worked with several customersincluding several fabs in Korea and Japanto define the Tesla system's functionalities. "In the definition phase of a project, it is critical to get input from target customers about the required key measurements and features to define a product that will make them more competitive in the market place," she added.

- Maria Cecilia Carpena
EE Times-Asia

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