Rudolph broadens wafer inspection

Rajiv Roy Rudolph Technologies

In the wake of these decisions, I asked Rajiv Roy, Rudolph's marketing manager for final manufacturing and test, to assess the hot issues in wafer inspection today and how the company's latest acquisition fits into that picture.

“We have always positioned ourselves as a process-oriented company,” commented Roy. “We utilize what we call 'a camera with measurement,' generally looking for 'macro-defects'—defects of 1 micron or more in size, several orders of magnitude larger than the circuit's smallest features. In 2006, we merged with August Technologies, a maker of two-dimensional wafer-inspection equipment. The RVSI product line broadens our expertise in that area by giving us three-dimensional capability, an important enhancement with today's ever-smaller wafer features.”

“People have always appreciated RVSI's technology but questioned their financial stability. For customers, our acquisition alleviates those reservations,” he explained. “In addition, RVSI Inspection's 3-D capability addresses a very specific new and fast-growing requirement by the wafer-fabrication industry. For years, people have been striving to increase device circuit density by making features smaller. Today, we routinely see 90-nm geometries, soon to be 45 nm, then 32. At the same time, the cost of that shrinkage has skyrocketed.”

Roy continued: “A less-expensive alternative would stack chips vertically in a single package. Such an architecture, though, requires the use of bump-type interconnects and through-silicon vias, inherently three-dimensional features, on the wafer. Wire-bond interconnects can't meet the new devices' speed specifications. You have to verify bump integrity on each individual die before bonding them together to ensure that the fabrication process leaves no contaminants. Contaminants can cause minor explosions or other reliability problems when heated, and if you do not detect a contaminant prior to the bonding step, it will never show up when you inspect the stacked die. We are concentrating our efforts in that area.”

But applying inspection techniques to ensure wafer quality extends beyond the wafer-inspection step itself. As circuit logic has become increasingly complex and companies want to test more than one device at a time, the probe cards used in probe-based wafer tests have become much more expensive.

Rudolph also employs inspection methods to ensure integrity of those cards. Needles must conform to precise placement and height specifications and must make proper contact with wafer sites. To maintain test accuracy and reduce damage to wafer surfaces, cards must undergo comprehensive analysis throughout their useful lives. Rudolph is now able to verify this part of the process through its acquisition of Applied Precision, makers of equipment that subjects the probe cards to a verification that Roy refers to as “inspection with data.”

“Because of the demand for high-temperature wafer testing,” explained Roy, “the probe quality has to be tightly controlled. You need more tools. Applied gave us a couple of hundred such tools worldwide in one step.”

He concluded, “By combining Rudolph's expertise with the parts of the total picture contributed by these other companies, we can now provide the full solution from one place. To serve the automobile industry, for example, where consumption of semiconductors has exploded in recent years and the companies exhibit a well-known zero tolerance for failures, adding RVSI's powerful three-dimensional wafer scanner enhances our ability to offer a comprehensive, cost-effective three-dimensional solution.”