Coherent in Semiconductor Manufacturing: EUV Lithography

The global semiconductor industry is on a trajectory for explosive growth, projected to become a staggering $1 trillion market by 2030 (up from over $500 billion in 2023). This expansion is largely fueled by the continuing miniaturization and increasing power of microprocessors. Every generation of these smaller, more powerful chips enables entirely new technologies and also reduces costs in existing applications. This creates a “virtuous cycle” where improvements in chip technology lead to new products and services, which in turn drive further demand for even more advanced semiconductors.

There are a few key industries driving much of this demand today. One is the automotive industry, where the vehicle is becoming a smart phone on wheels and integrating substantial amounts of computing power. Another area powering growth is high performance computing. This is primarily to meet the expanding need for artificial intelligence (AI) and cloud computing. Along with these markets comes the wireless infrastructure with the proliferation of 5G networks.

Finally, microprocessors play a huge role in industrial markets such as factory automation and logistics. Even though this is a relatively low growth market compared to the consumer related ones, it is a very stable and sustainable one for semiconductors.

Coherent has been providing lasers, optics, and materials that are essential for semiconductor fabrication and device packaging for decades. In some instances, our technology has been a key enabler in microelectronics manufacturing.

And our involvement in this market is likely to increase even further. Because as circuit dimensions shrink to support the trends just mentioned, the tools required to fabricate, assemble, and inspect them must get ever more precise and sophisticated. This provides even greater opportunities for Coherent since our technology often supports increased manufacturing precision and improved throughput.

In this blog, we’ll look specifically at how Coherent products support advancements in the most foundational step of semiconductor fabrication – microlithography.

Extreme Ultraviolet (EUV) Lithography

Lithography, a core process in semiconductor manufacturing, involves projecting circuit patterns from masks onto photosensitive layers on a silicon wafer to create the actual device (e.g. transistor) structures. Traditional semiconductor lithography accomplishes this with excimer lasers operating at 248 nm or 193 nm. These lasers have taken the industry to the “10 nm node” (node is a term related to chip generations often including smaller feature sizes). But to transition to smaller nodes, which may incorporate even smaller features, basic physics dictates that shorter wavelengths of light are required. 

Extreme Ultraviolet Lithography (EUV) represents a pivotal advancement in this realm. EUV lithography uses light at a wavelength of approximately 13.5 nm. This has enabled chip makers to reach the 7 nm, 5 nm, 3 nm, and 2 nm nodes. 

To generate this EUV light, a high-power, infrared CO₂ laser illuminates a stream of tiny, molten tin droplets. The laser vaporizes the tin and forms a plasma (a gas in which electrons are stripped from their atoms). This plasma emits the EUV light. 

Everything about producing and delivering light at this wavelength is complex and challenging, requiring an incredible level of precision, as well as reliable operation under extreme conditions. The latter is key, because downtime in a semiconductor fabrication plant can cost hundreds of thousands, or even millions of dollars, per hour. 

Coherent supplies numerous optics for EUV lithography tools, including diamond windows, laser modulators, and ZnSe laser optics.

Optics for EUV Lithography

The CO₂ laser and beam delivery system in an EUV lithography tool incorporate numerous optical components, such as lenses and mirrors. Of course, Coherent (formerly II-VI) has been the market leader in infrared optics since the 1970s. It’s the technology the company was founded on, and there is no one who understands it better than us. That’s why we are the largest supplier of CO₂ laser optics for EUV CO₂ laser systems.

Another important optic in EUV systems are diamond windows. These are needed to environmentally seal various modules within the laser system while allowing the very high-power CO₂ laser light to pass through unattenuated.

While ZnSe is commonly used for windows at this wavelength and in the EUV system, diamond is preferred in the most extremely demanding locations for several reasons. A primary one is its low thermal lensing at very high power levels. Thermal lensing causes beam distortion, aberrations, and changes in focus position, all of which would compromise system performance.

In addition, diamond has the highest thermal conductivity amongst all known materials, a low coefficient of thermal expansion (CTE), and an extraordinarily high hardness. This means diamond can handle the high power of the laser beam with minimal distortion or deterioration. And it can withstand and efficiently dissipate any heating caused by absorption of laser light.

Coherent is a leading supplier for these large-area polycrystalline diamond windows because we are a vertically integrated manufacturer. We grow the diamond using chemical vapor deposition (CVD) in our reactors, which are based on our own proprietary designs and process technology. This gives us the ability to control crystal growth in a way that yields precisely the characteristics needed for EUV lithography system windows.

Structural Components for EUV Lithography

Our expertise also encompasses the manufacture of components for EUV lithography systems made from specialized ceramic materials, such as reaction bonded silicon carbide (RB-SiC).

RB-SiC exhibits excellent mechanical and thermal stability, making it ideal for a wide range of semiconductor capital equipment applications including inspection, metrology, and lithography. The stability of the structure supporting the EUV optical system is critical and only possible with such RB-SiC ceramics. RB-SiC has a large potential for structural components.

Coherent produces RB-SiC using both traditional ceramics manufacturing processes and newly developed additive manufacturing techniques. With these methods, large and complex shapes can be produced to near-net geometries requiring little precision finishing.

Coherent: Your Partner for Innovation and Success

We have just explored how Coherent products deliver the mix of innovative technology and high performance required by semiconductor tool builders. But other companies make high-performance products, too. Often, our customers choose Coherent for reasons beyond just this.

One of these factors is cost-of-ownership. In the semiconductor business, operating costs associated with a product are frequently more important to the user than its original purchase price. There are a couple of reasons for this.

The first is downtime, which was mentioned previously. Even a brief period of unplanned downtime in a semiconductor production line can be very expensive. Therefore, reliability and uptime are essential because they save the user money and help ensure that they can meet their own production schedules.

The second reason is operational consistency and stability. Semiconductor fabrication has numerous steps. Any variation in equipment operation during one of these steps can change the characteristics of the circuitry being produced in ways that may not be immediately noticed. This means that a manufacturer can be producing bad parts for some time before the problem is discovered. This translates into scrap parts or rework, both of which can be costly and time-consuming.

As a result, tool builders prioritize vendors who demonstrate deep expertise in their own technologies and show a long history of success. They want to partner with companies whose products meet specifications, are delivered on time, and perform consistently – day in and day out – in the demanding semiconductor fabrication environment. Coherent stands out in these respects with a proven track record of exceeding expectations for decades.

As the pace of technological change accelerates, another factor also emerges. Semiconductor tool makers seek suppliers who have substantial internal resources and operational scale, and who can commit to making significant investments in technology. These are needed to keep pace with the ongoing cycles of innovation required to make equipment for fabricating these ever-smaller circuits.

Coherent customers are assured that we maintain a long-term commitment to responsive service.

They also want to know that the vendor is likely to remain in business for decades and will be there to provide service and maintain a supply of spare parts. And, speaking of service, they want it provided immediately – wherever and whenever it is required. The size and stability of Coherent, together with our extensive global service infrastructure, gives our customers the confidence that we will deliver on all these points, today and in the future.  

Learn more about Coherent products and services for the semiconductor industry.

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