Features

Linear Stage Brings Speed and Precision to Semiconductor Inspection

With some of the most demanding quality control regimens of any industry, semiconductor manufacturers use a variety of sophisticated metrology instruments to inspect wafers at each production step. All of these instruments have something in common: They simply will not function without precision motion stages.

alt“Choosing the right stage for moving wafers around during inspection procedures is vital to achieving the required quality control levels,” explained Brian Bobrzynski, a mechatronics engineer with Semilab, a maker of semiconductor inspection systems.

“At Semilab, we use different types of stages depending on the application. In applications involving contact measurement, we typically favor stages driven by piezomotors to eliminate vibration. In non-contact applications, such as wafer mapping and scanning, speed and precision are more important than vibration reduction.” Semilab selected the LowBoy linear stage for its noncontact systems.

Designed and manufactured by Bell-Everman Inc. (Goleta, CA), the LowBoy linear stage is driven by a cog-free linear servomotor rated for up to 280 N of continuous force. The compact stage is ideal for semiconductor metrology applications that require a reliable and precise linear positioning device in a streamlined package.

“Our engineers had been using the SemiTest platform as our standard and tried to build a 300-mm junction photovoltage (JPV) tool based on it,” said Gyorgy Fule, head engineer at Semilab headquarters in Budapest, Hungary. “However, for measurements like JPV or μ-PCD, the original stage wasn’t fast enough. One of our engineers discovered Bell-Everman and their stages as an alternative. We’ve been using them ever since in several of our platforms.”

LowBoy stages are now used on Semilab’s WT-3000 double FOUP platform, WT-2500 multifunction wafer mapping tool, and QC-2500e near surface doping mapper. The WT-3000 and WT-2500 are standalone measurement platforms that perform many different semiconductor material measurements, such as dielectric characterization and epitaxial layer monitoring. The QC- 2500e measures qualities such as doping concentration and recombination lifetime for epitaxial wafers. In each of these non-contact platforms, positioning speed and precision are critical to achieving the increased throughput required by today’s semiconductor fabs.

alt“The high torque and acceleration provided by the LowBoy means that the stage begins moving almost immediately at full speed. It doesn’t need anywhere near the time to ramp up to full speed as a stepper motor and leadscrew combination, for example,” said Bobrzynski. “The faster the positioning stage moves, the faster the inspection process can take place, which ultimately means greater chip production per shift.”

LowBoys are capable of speeds to 4 m/s with a bidirectional repeatability of ±1 encoder count. Beyond speed and precision, LowBoys also feature a lowprofile design. Even when stacked in a dual-axis configuration, the total height is just 169 mm.

“The low-profile design is helpful because it keeps the overall machine size down. If the stage itself is too tall, there’s not as much room for the metrology equipment,” said Bobrzynski.

This article was contributed by Bell- Everman, Goleta, CA. For more information, visit http://info.hotims.com/45602-320.