Manufacturing Bits: Nov. 9

Open-source EUV resist metrology; DYI molecular microscopes.


Open-source EUV resist metrology
Paul Scherrer Institute (PSI) has developed an open-source software technology for scanning electron microscopy (SEM) applications. The technology is targeted for EUV resist metrology.

The technology, called SMILE (SEM-Measured Image Lines Estimator), is an open source software technology, which characterizes line and space patterns in a SEM. SMILE is used to measure critical dimensions (CDs), linewidth roughness (LWR) and unbiased LWR.

Resists are critical in extreme ultraviolet (EUV) lithography. Resists, which are light sensitive materials, help form patterns on the wafer.

A CD-SEM is a common metrology tool in the fab. In one application, a CD-SEM is used to define the performance of a resist material. This tool takes images of line patterns and contact hole arrays.

“This approach is commonly used to investigate the quality of a resist platform in terms of roughness, dose sensitivity, and resolution under different exposure and development conditions. A carefully controlled data acquisition procedure and a correct quantitative analysis of the SEM images of the printed wafers are necessary to determine meaningful and comparable results,” said Iacopo Mochi, a scientist at PSI in a recent paper. Others contributed to the work.

Using a standard CD-SEM, there are several commercial software packages available to perform the image analysis tasks for EUV resist metrology. Both the CD-SEM and software are essential for EUV resist metrology

PSI’s SMILE is also geared for EUV metrology. It is a free and open-source software technology for line and space analysis. “The software has been developed for the analysis of SEM images of photoresists and periodic nanostructures. It can perform basic CD measurements, LWR estimation, PSD analysis, bias removal, and defect detection in SEM images. The software features different edge detection algorithms and LWR evaluation protocols that can be customized and extended to address user-specific needs,” Mochi said.

The software is available as a MATLAB code and is under development for open platforms such as Python or Octave, according to PSI.

DYI molecular microscopes
The University of Sheffield has developed an advanced, open-source microscope capable of single-molecule measurements.

Researchers have developed a platform based on single-molecule Förster Resonance Energy Transfer (smFRET) technology, which is capable of resolving distances within and between biomolecules.

At the same time, they developed the smfBox, a cost-effective open-source smFRET platform. Researchers have developed a kit, which provides the instructions, parts list and open-source acquisition software to develop a smFRET platform for the scientific community.

The University of Sheffield has used the smfBox to investigate biological processes, such as DNA damage detection. This in turn would help researchers gain insights into better therapies for diseases, including cancer.

Typically, a smFRET platform is mainly used in specialized labs. It is too expensive to buy outside of a lab. However, the University of Sheffield spent roughly £40,000 to build its open-source system. Generally, this system runs for around £400,000.

“Here we present the smfBox18, a cost-effective confocal-based platform capable of measuring the FRET efficiency between dye pairs on freely diffusing single molecules, using variable alternating laser excitation for verification of correct dye stoichiometry and the determination of accurate FRET correction factors,” said Ben Ambrose, a researcher at the University of Sheffield, in Nature Communications, a technology journal. Others contributed to the work.

“The smfBox is constructed from readily-available optics and optomechanical components, replacing an expensive microscope body with machined anodized-aluminium, which forms a light-tight box housing the excitation dichroic, objective, lenses, and pinhole,” Ambrose said.

Tim Craggs, the lead academic on the project from the University of Sheffield, added: “We wanted to democratize single-use molecule measurements to make this method available for many labs, not just a few labs throughout the world. This work takes what was a very expensive, specialist piece of kit, and gives every lab the blueprint and software to build it for themselves, at a fraction of the cost. Many medical diagnostics are moving towards increased sensitivity, and there is nothing more sensitive than detecting single molecules. In fact, many new COVID tests currently under development work at this level. This instrument is a good starting point for further development towards new medical diagnostics.”

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