What is Extreme Ultraviolet Lithography?


May 20, 2022

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Silicon manufacturing involves multiple processes. First, builders must grow the wafer from a silicon crystal through the Float Zone or Czochralski method. The growth process also includes doping, which introduces substances to the wafer to enhance its conductivity.  

Finally, makers have to assemble the integrated circuit and create the finished product. However, before they can do that, the wafer will need to go through the lithographic process. This procedure is vital in guaranteeing the performance of the resulting chip in its intended application.

Silicon manufacturing Wafers in steel holder box on table

Why is Lithography Essential to Semiconductor Manufacturing?

Every chip and motherboard has embedded integrated circuits arranged in a specific manner. Assemblers at the manufacturing facility will need to have a circuit board to ensure the correct placement of each component.  

This guide will have to be printed onto the surface of the wafer, and that is where lithography or photolithography helps. The process embeds the geometric shapes on the wafer to aid manufacturers in building the electronic device. Also, the type of lithography used directly influences how many transistors workers can fit into a single silicon wafer.

How the Process Works

The first step in lithography is to prepare the mask. The mask will have the draft of the circuit pattern that will then be transferred to the silicon wafer. An emitter passes light through optical lenses that resize the design to fit into the mask.  

The next step is to project or transfer the circuit pattern to the wafer itself. Manufacturers will first coat the silicon wafer with a liquid plastic called a photoresist. They will need 1 mL to 1.5 mL of the solution. They will also require a pressure clamp, which will secure the wafer. The semiconductor is attached to the clamp and spun at high RPMs. At the same time, the photoresist solution is poured onto its surface.

Once the wafer is evenly coated with the photoresist, the makers will expose the mask and semiconductor to ultraviolet light. The photoresist is sensitive to UV radiation and will harden around the pattern. The light will hit only the mask, and any areas with photoresist not covered will remain in liquid form to be removed later.

Lithography and Light Wavelength

The wavelength of light used in lithography is crucial. Shorter wavelengths are known for their higher frequencies and more robust energy levels. In the context of lithography, light rays with short wavelengths make more powerful processors possible by engraving more transistors into the wafer.  

Hence, silicon manufacturing companies use progressively shorter wavelengths, exemplifying Moore’s Law in the context of light emissions. Every new generation of microprocessors makes giant leaps in performance compared to the products that preceded them in the market.  

Checking microchips on silicon wafer manufacturing

What Is Moore’s Law?

In 1965, Gordon Moore said that he expected microprocessors to become more powerful every two years by doubling the number of transistors in the motherboard, processor and peripherals. Gordon later established Intel Corporation, one of the leading semiconductor companies until today. Intel’s technology would be heavily influenced by Moore’s observations.  

Moore’s Law is apparent in the design of Intel’s processors throughout the decades. The Pentium 4 single-core processors, which dominated the market from 2000 to 2008, had 42 million transistors. It was a leap compared to its predecessor, the Pentium 3, with only 28 million transistors in its chipset.  

However, the Pentium processors pale compared to the latest Core i7, 12700k, with billions of transistors. Intel even announced in 2021 that its Ponte Vecchio artificial intelligence chip will have 100 billion transistors.

Some experts in the semiconductor industry say that implementing Moore’s Law in the next generation of computer processors will be challenging. The current technology for photolithography, Deep Ultraviolet Lithography (DUVL), uses a 193-nanometer wavelength for its light rays.  

Silicon manufacturing companies will have to find ways to surpass 100 billion transistors, given the limits of DUVL. That’s where Extreme Ultraviolet Lithography (EUVL) could be ideal.

History of EUVL

EUVL’s research and development has been around since the 1970s. The tech traces its roots to R&D for X-ray lithography, which scientists later concluded to be too expensive. The study ceased in 1980, but engineers continued to play with X-ray lithography until they discovered EUVL, which they initially called the “soft X-ray.”

The technology would only enter the spotlight after Intel and Samsung announced in 2018 their adoption of EUV for their latest chips. Both companies said that their next chips will be made using EUV at a wavelength of 7 nanometers. EUV eventually encountered several hurdles that delayed the mass production of the lithographic machines.

However, things appear to be looking up. ASML announced last year that they are completing the final component that will make the next-generation EUV machine functional by this year. Afterwards, the company expects Intel to build the hardware’s first batch of chips and release them in 2023.  

Pros and Cons of Using EUVL

EUVL’s most significant advantage over DUVL is its shorter wavelength. The 193-nanometer wavelength is roughly ten times longer than the 13.5-nanometer length of EUV lithograph machines. The extremely short wavelength makes it possible to produce integrated circuits 10 times denser and 10 times more efficient than chips made using DUVL.

Personal computers and laptops are not the only electronic devices to harness the benefits of EUVL chips. Smartphones, smartwatches and tablets can take full advantage of these advances. These gadgets use processors and ICs denser than those used by PCs given their size. Mobile device makers can cram even more transistors with EUVL without changing the dimensions of their products.

EUVL’s most apparent drawback is in its maintenance and upkeep. Lithographic machines are enormous. Its components are connected by about 40 kilometers of cables crammed into a bus-sized case. For now, 13.5 nanometers is the standard wavelength, while engineers study ways to shrink it further to 7 nanometers and below. This research will require immense funding, and results remain uncertain.

silicon manufacturing Wafer on white background with clipping path

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