Manufacturing Bits: Feb. 21

AFM-on-a-chip; robot metrology; measuring lasers.


An atomic force microscope (AFM) is a metrology tool that can measure and characterize structures in three dimensions. It uses a tiny probe to enable measurements in chip structures, but the instrument itself is often a large and bulky system.

In response, the University of Texas at Dallas has devised an AFM-on-a-chip technology. The AFM is roughly the size of a dime. Based on MEMS technology, the AFM is about 1 square centimeter in size.

The technology could reduce the cost and complexity of AFM. The AFM from researchers is attached to a small PCB. The PCB consists of circuitry, sensors and other components. It incorporates integrated “xy” electrostatic actuators and electrothermal sensors, according to researchers. It also consists of a piezoelectric layer. This is designed for out-of-plane actuation and integrated deflection sensing of a microcantilever, according to researchers.

Tiny AFM (Source: The University of Texas at Dallas)

Tiny AFM (Source: The University of Texas at Dallas)

The MEMS-based AFM operates in a tapping mode. The cantilever and tip oscillate up and down perpendicular to the sample. All told, the technology can obtain topographic images with a range of up to 8μm × 8μm in a closed loop.

“A standard atomic force microscope is a large, bulky instrument, with multiple control loops, electronics and amplifiers,” said Reza Moheimani, a professor of mechanical engineering at UT Dallas. “We have managed to miniaturize all of the electromechanical components down onto a single small chip.

“An educational version (of an AFM) can cost about $30,000 or $40,000, and a laboratory-level AFM can run $500,000 or more,” Moheimani said on the university’s Web site. “Our MEMS approach to AFM design has the potential to significantly reduce the complexity and cost of the instrument. One of the attractive aspects about MEMS is that you can mass produce them, building hundreds or thousands of them in one shot, so the price of each chip would only be a few dollars. As a result, you might be able to offer the whole miniature AFM system for a few thousand dollars.”

Robot metrology
The National Institute of Standards and Technology (NIST) has developed a next-generation reference reflectometer.

The technology, dubbed ROSI or Robotic Optical Scatter Instrument, measures the intensity and spectrum of light reflected of a sample in any direction. Using a robotic arm, ROSI enables in-plane and out-of-plane measurements. It measures the reflectance and scattering of materials in the ultraviolet to the short-wave infrared wavelength range. That equates to 250nm to 2400nm.

ROSI is designed to replace NIST’s current reference reflectometer, dubbed the Spectral Tri-function Automated Reference Reflectometer (STARR). STARR is not capable of out-of-plane measurements.

With ROSI, a sample is placed in the end of a robotic arm. The 6-axis robotic arm can move a sample into almost any angle with respect to a beam. Then, a separate laser-based light source hits the sample. The 1cm spot size can be tuned to a specific desired color, intensity, and polarization. Finally, a receiver detects the amount of light scattered from the sample.

The ROSI system (Credit: Sean Kelley/NIST)

The ROSI system (Credit: Sean Kelley/NIST)

The system can make three types of measurements. The first is basic mirror samples. The second is bidirectional reflectance distribution function (BRDF) measurements. The third is hemispherical measurements. “We began work to develop this system years ago,” said Heather Patrick, project leader at NIST’s Physical Measurement Laboratory, on the agency’s Web site. “By the middle of 2017 we expect to make the first set of functions available to customers. About a year later, all of the system’s features will be fully operational.”

Measuring lasers
Separately, NIST and Scientech have co-developed a method to gauge the power of high-kilowatt lasers.

Multi-kilowatt laser beams are used to cut through steel and melt bricks into glass. Lasers are used in various applications, such as automotive, industrial and others. In addition, kilowatt lasers are used to drive the power source for extreme ultraviolet (EUV) lithography.

In all cases, the industry needs a tool to tell them how much power the laser is producing. In response, NIST and Scientech have devised a system, which can measure the pressure of the laser light. The technology is capable of measuring laser powers as high as 500 kilowatts.

“Before now, high-power laser measurements relied on sensors that are inherently big and slow,” said John Lehman, leader of PML’s Sources and Detectors Group at NIST. “Furthermore, the calibration of such instrumentation has been expensive and rare.”

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