Extreme UV chip defects may force a new approach to processor design

Chips built with extreme ultraviolet (EUV) light are plagued with random defects with no obvious solution, according to research presented at a chipmakers’ conference reported in EETimes. The EUV hardware seems to work acceptably for 7nm or larger processes, but below this scale, small defects are cropping up that ruin the chip and prove hard to detect.

Photolithography is the process used to etch the patterns that make up chips into a silicon wafer. The wafer is coated with a material that is light-sensitive photoresist. This wafer will be confronted with light that is bright’s shone through a mask. Areas hidden by the mask shall retain their photoresist layer; those exposed right to the UV will totally lose it. The wafer will be etched plasma that is using acid. Parts of the wafer that are still covered in photoresist are protected during the etching, retaining their silicon oxide; those whose photoresist has been removed are etched away.

Smaller wavelengths of light finer that is enable in the mask and therefore finer information within the etching. Processors today, constructed on a 14nm procedure, currently utilize features being far smaller compared to the wavelength of regular UV light; they use methods like multi-patterning (by which numerous masks and exposure that is light are used) to reach ever smaller sizes. These steps that are additional production some time mistake prices, thus the attention in smaller wavelengths. With EUV, smaller chip features could possibly be produced without requiring techniques that are such

The chip-building industry has been talking about using EUV photolithography—light with a wavelength of 13.5nm, compared to the 193nm ultraviolet in use today—since the late 1990s. In theory, EUV should make it easier to build processors with smaller features—narrower wires, tinier transistors—but getting EUV to work has proven problematic. EUV is strongly absorbed by air and by the materials used to make lenses; it can still be redirected and focused, by using mirrors as opposed to contacts. Efficient generation of high-intensity EUV has additionally been hard. Commercial applications require at the very least 250W light sources, with Intel claiming it requires up to 1kW.

GlobalFoundries, Samsung, and TSMC have actually all outlined intends to make use of 250W EUV sources for 7nm production. This will be at known level that researchers are seeing problems. These problems include both areas where not material that is enough etched away, causing shorts between cables within the chip, and areas in which excessively is etched away, causing gaps and rips in items that should really be constant.

GlobalFoundries VP of analysis George Gomba described defect that is similar with EUV and said that the EUV hardware—the NXE-3400 from ASML—wasn’t yet up to the standard the company needs. He also said that better systems for inspecting the EUV masks are needed. Research is also needed to improve the photoresists, to understand their behavior when exposed to EUV and reduce the true wide range of defects.

If these issues can not be ironed away, they could force a approach that is different chip design. Chips that combine memory with processing elements and chips based on neural networks are more resilient to defects that are manufacturing while the specific bad elements are disabled while nevertheless salvaging the chip all together. IBM’s real North neuron-simulating processor has a grid of 4096 elements, each combining some memory with a few compute energy, and a week ago scientists posted through them) that they had built “memtransistors.” These combine transistors with memristors (devices that change their resistance depending on their “memory” of how much electric charge has passed. These hybrids computation that is integrate memory at an extremely low degree.

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