Manufacturing Bits: March 24

Mouse brains to multi-beam
At the recent SPIE Advanced Lithography conference, Sematech provided an update on its multi-beam, e-beam inspection program.

The goal is to develop a next-generation inspection tool, which could be faster than traditional e-beam inspection and could one day displace brightfield inspection. “Optical inspection is having trouble detecting particles that are smaller than 20nm,” said Benjamin Bunday, senior technical staff member at Sematech. “Of course, e-beam inspection can overcome that. But, of course, it’s very slow.”

In its R&D program, Sematech has recently partnered with Zeiss. Zeiss itself has devised a 61-beam e-beam inspection tool, which was primarily developed for the life sciences arena. Originally, the Zeiss tool was used to inspect organs. “(Zeiss) has a tool that originally was looked at for (use in inspecting) mouse brains,” Bunday said.

Sematech hopes to scale the Zeiss tool to more than 61 beams. The R&D organization also hopes to tailor that tool from Zeiss for the semiconductor industry, which would match or surpass traditional e-beam inspection in terms of throughput.

The multi-beam tool is still in the early stages of development, but it is a promising technology. “It is an alpha tool,” he said. “You can scan 61 little beams in a hexagonal formation, all in parallel. We can scan a millimeter square field of view in about 10 minutes.”

It’s unclear when the tool technology will hit the market. Over time, Sematech will license the technology to a third party. In addition, Hermes, Maglen and MultiBeam are separately developing multi-beam e-beam inspection tools. The first tools from vendors could appear in late 2015 or early 2016.

Multi-scan probe
Scanning probe microscopy (SPM) is a technique that forms images of surfaces using a single physical probe. The technology enables high resolutions, but it has struggled to compete with other inspection systems due to throughput issues.

One research group, TNO, has developed an SPN technology that can measure many sites in parallel. It makes use of multiple miniaturized scanning probe microscopy (MSPM) heads.

TNO’s MSPM system has more than 1,000 times the throughput, as compared to a single SPM unit. It is capable of more than 10 wafers per hour. It provides defect inspection on patterned wafers at sub-10nm resolutions. It also enables defect review capabilities on bare wafers and blank masks at 1nm lateral resolutions.

The system consists of 50 tiny parallel SPM scan heads. It also has a mechatronics positioning system, an automatic probe exchange unit, a high-performance wafer stage and calibration capabilities.

Illustration of parallel SPM, which images several locations on a wafer. (Source: TNO)

It can be used to provide various measurements, such as surface roughness, channel height, width and defects inspections and others. Applications include semiconductors, solar, data storage, bio-medical, pharma and food science.

X-ray record
The National Institute of Standards and Technology (NIST) has developed a new way to reduce the uncertainty in X-ray wavelength measurements.

Researchers have made use of a system called an electronic nulling autocollimator. With this system, X-ray angles can be measured with an uncertainty of 0.06 arcseconds. This is more than three times better than an uncalibrated encoder system, according to NIST.

A laser from the NIST-designed autocollimator (Source: NIST)

Generally, X-ray measurements depend on its ability to measure angles. X-ray wavelengths are measured by passing the beam through special crystals. Then, a system measures the angle that the exiting rays make with the original beam.

By using a redesigned electronic nulling autocollimator, NIST has found a way to reduce the measurement error. The approach uses laser beams bouncing off a mirrored polygon. The polygon is rotated on the same shaft that would carry the crystal.

“While many fields need good X-ray reference data, many of the measurements that presently fill standard reference databases are not great—most data were taken in the 1970s and are often imprecise,” said NIST’s Larry Hudson, on the agency’s Web site.

The new method from NIST may have set an unofficial world’s record in X-ray measurements. “If a giant windshield wiper stretched from Washington D.C. to New York City (364 kilometers) and were to sweep out the angle of one of these errors, its tip would move less than the width of a DVD,” he added.