Laser Holograms Could Revolutionize 3D Chip Manufacturing

Semiconductors CPU Computer Chip Illustration — Researchers at UMass Amherst developed a novel method for aligning 3D semiconductor chips using laser light and concentric metalenses, projecting holograms that reveal even atomic-scale misalignments. This breakthrough could reduce chip manufacturing costs, enable advanced 3D electronics, and lead to compact, affordable sensors.

The approach uses lasers and holograms to detect misalignments as small as 0.017 nanometers.

Researchers at the University of Massachusetts Amherst have developed a new method for aligning 3D semiconductor chips by shining a laser through concentric metalenses patterned onto the chips, creating a hologram. Their work, published in <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="

Nature Communications

<em>Nature Communications</em> is an open-access, peer-reviewed journal that publishes high-quality research from all areas of the natural sciences, including physics, chemistry, Earth sciences, and biology. The journal is part of the Nature Publishing Group and was launched in 2010. "Nature Communications" aims to facilitate the rapid dissemination of important research findings and to foster multidisciplinary collaboration and communication among scientists.

” data-gt-translate-attributes=”[{"attribute":"data-cmtooltip", "format":"html"}]” tabindex=”0″ role=”link”>Nature Communications, could significantly reduce the cost of manufacturing 2D chips, support the development of 3D photonic and electronic chips, and open the door to affordable, compact sensor technologies.

Semiconductor chips power electronic devices by enabling them to process, store, and transmit information. These functions rely on precise patterns of components embedded in the chip. However, the traditional 2D chip design has reached the limits of its technological potential, and 3D integration is now seen as the most promising path forward.

Simulated and Measured Results of Different Sizes of Lateral Misalignment — Simulated and measured results of different sizes of lateral misalignment, from 150 nm to 1 micrometer (or 1,000 nm). Credit: Amir Arbabi

To build a 3D chip, several 2D chips are stacked together. Their layers must be aligned with extreme precision, down to tens of nanometers. This alignment must occur across all three dimensions: front to back, side to side, and the vertical distance between layers (known as the x, y, and z axes).

Limitations of traditional alignment

“The traditional approach for aligning two layers is to look with a microscope for marks (typically corners or crosshairs) on the two layers and to try to overlap them,” explains Amir Arbabi, associate professor of electrical and computer engineering at UMass Amherst and senior author on the paper.

Holographic Feedback Reveals Chip Alignment Precision — [Left] Semiconductor layers are stacked using concentric metalenses as alignment marks. [Right] Light shines through these marks to project a hologram. The alignment or misalignment of the lenses dictates the hologram’s appearance. Credit: Amir Arbabi

Existing microscope-based alignment methods are ill-suited for making these 3D chips.

“The microscope cannot simultaneously see both crosshairs in focus because the gap between the layers is hundreds of microns, and the motion to refocus between la yers introduces opportunities for the chips to shift and further misalign.” says Maryam Ghahremani, doctoral candidate and lead author on the paper. Also “the smallest features you can resolve are set by the diffraction limit, which is around 200 nanometers,” she adds.

Simulated and Measured Results of Different Sizes of Misalignment in the Gap Between Two Layers — Simulated and measured results of different sizes of misalignment in the gap between two layers, from 1 micrometer (or 1,000 nm) to 3 µm. Credit: Amir Arbabi

Breakthrough in nanometer-scale detection

The new alignment method created by Arbabi and his team has no moving parts and can see misalignments between two distant layers at a much smaller scale. The researchers were hoping to reach 100-nm precision. Instead, their method finds errors up to 0.017 nm along side-to-side measures (x and y axes) and 0.134 nm when assessing the distance between the two chips (z-axis).

“Consider you have two objects. By looking at the light that goes through them, we can see if one moved by the size of an <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="

atom

An atom is the smallest component of an element. It is made up of protons and neutrons within the nucleus, and electrons circling the nucleus.

” data-gt-translate-attributes=”[{"attribute":"data-cmtooltip", "format":"html"}]” tabindex=”0″ role=”link”>atom with respect to the other one,” Arbabi says, far exceeding their expectations. The naked eye can spot errors as small as a few nanometers, and computers can read even smaller ones.

Visualizing Nanometer Scale Misalignment With Holographic Intensity Patterns — Computers can read misalignments undetectable by the naked eye, as illustrated by this 10-nm lateral misalignment. Credit: Amir Arbabi

To achieve this, they embedded alignment marks made from concentric metalenses on the semiconductor chip. When light from a laser shines through these marks on both chips, it projects two interfering holograms. “This interference image shows if the chips are aligned or not, as well as the direction and the amount of their misalignment,” says Ghahremani.

“[Chip alignment] is a big, costly challenge for some of the companies that work in manufacturing semiconductor tools,” Arbabi says. “Our approach addresses one of the challenges of making them.” Lower costs also increase access to this technology for smaller startup companies looking to innovate with <span class="glossaryLink" aria-describedby="tt" data-cmtooltip="

semiconductors

Semiconductors are materials with electrical conductivity that falls between conductors and insulators, making them essential for modern electronics. They are typically crystalline solids, the most common of which is silicon, used extensively in the production of electronic components such as transistors and diodes. Semiconductors are unique because their conductivity can be altered and controlled through doping—adding impurities to the material to change its electrical properties. This property allows them to serve as the foundation for integrated circuits and microchips, powering everything from computers and smartphones to advanced medical devices and renewable energy technologies. The behavior of semiconductors is also crucial in the development of various electronic, photonic, and quantum devices.

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Arbabi also points out that this method can be used to make displacement sensors that can be used for measuring displacements and other quantities. “Many physical quantities that you want to detect can be translated to displacements, and the only thing you need is a simple laser and a camera,” he says. For instance, “if you want a pressure sensor, you could measure the movement of a membrane.” Anything that involves movement —vibration, heat, acceleration — can in theory be tracked by this method.

Reference: “3D alignment of distant patterns with deep-subwavelength precision using metasurfaces” by Maryam Ghahremani, Andrew McClung, Babak Mirzapourbeinekalaye and Amir Arbabi, 14 October 2024, Nature Communications.
DOI: 10.1038/s41467-024-53219-z

Funding: U.S. National Science Foundation