Next-generation EUV lithography machine, ASML says this

In ASML offices around the world, a formula in the field of optics - the Rayleigh criterion - is posted.

Among them, CD (critical dimension) is the critical dimension, which is used to measure the size of the smallest structure that can be printed by the lithography system; λ is the wavelength of the light source; NA is the numerical aperture, indicating the incident angle of the light; k1 One is related to optical and process optimization related constants.

As shown in the formula, in order to make CD smaller, λ can be reduced or NA can be increased while k1 remains unchanged. This is why the light source of lithography machines has evolved over the past many years from i-line, KrF, ArF, and ArF Immersion with a wavelength of 365nm to EUV with a wavelength of 13.5nm.

As for NA, according to ASML, smaller structures can be printed by using lenses/mirrors with larger NA. In addition to larger lenses, ASML has also increased our ArF by maintaining a thin film of water between the last lens element and the wafer, taking advantage of the breaking index of water to increase the NA (so-called immersion system). System NA. After the wavelength moves towards EUV, ASML is also developing the next generation EUV system - EUV 0.55 NA (high NA). We have increased the numerical aperture from 0.33 to 0.55.

ASML explains that the lithography system is essentially a projection system. For example, in its DUV system, light is projected through the pattern blueprint to be printed (called a "mask" or "reticle"); while in its EUV system, light is reflected through the reticle. By encoding a pattern in the light, the system's optics shrink and focus the pattern onto a photosensitive silicon chip. After the pattern is printed, the system moves the wafer slightly and makes another copy on the wafer.

During the chip manufacturing process, the photolithography machine repeats this process until the wafer is covered with patterns, completing one layer of the wafer chip. To make a complete microchip, this process needs to be repeated layer by layer, stacking patterns to create an integrated circuit (IC). According to ASML analysis, the simplest chip has about 40 layers, while the most complex chip can have more than 150 layers.

“The size of the features to be printed varies from layer to layer, which means different types of lithography systems are used for different layers – our latest generation EUV system is used for the most critical layers with the smallest features, while our ArFi, ArF , KrF and i-line systems are available for less critical layers with larger features," ASML said in the earnings release.

As mentioned above, in order to make smaller CDs on critical layers, ASML is promoting a High-NA lithography machine with a numerical aperture of 0.55. Martin van den Brink said that customers will conduct research and development on it between 2024 and 2025, and Large-scale mass production is expected to take place between 2025 and 2026.

In an interview with Dutch media bits-chips last September, Martin van den Brink said bluntly: "The transition period of lithography technology is bad. Because if you mess up, things will become a mess, especially now that this organization has It’s so big.” He also pointed out that unlike the evolution from DUV to EUV, the risk will be much smaller for High-NA lithography machines, mainly because the infrastructure on the equipment has not changed much.

“The biggest challenge in developing High-NA technology was building the metrology tools for EUV optics. High-NA mirrors are twice the size of the previous generation and need to be flat within 20 picometers. To achieve these goals, a Validation in a vacuum container so big that 'you could fit half a company in it'" says Martin van den Brink.

Martin van den Brink said that when he first started the High NA EUV project in 2017, he thought it would be the last NA for EUV lithography machines, because at that time he believed that High NA came too late and did not have enough shrinkage. Able to recover investment. He also revealed that his partner Zeiss did not want to participate in this project at first.

Although there are many difficulties, High NA EUV lithography machine is about to become a reality. As mentioned in the report, one thing the semiconductor industry also wants to know is whether there is a successor to High-NA.

The report pointed out that Jos Benschop, ASML’s vice president of technology, had revealed at the 2021 SPIE Advanced Lithography Conference that a possible alternative, a new level of wavelength, was not an option. It's all about angle - the efficiency with which EUV mirrors reflect light depends heavily on the angle of incidence. Reducing the wavelength changes the angular range so that the lens must become too large to compensate. While ASML is working on it, Van den Brink said that personally, he doesn't think hyper-NA will prove feasible. "We are working on it, but that doesn't mean it will go into production. For many years, I have suspected that high-NA will be the last NA, and this belief has not changed." Van den Brink said.

According to him, technically, hyper-NA (above 0.7, maybe 0.75) is theoretically possible. But he also asked: How much room is there in the market for larger lenses? Can we sell these systems? He also emphasized at the time that if the cost of Hyper-NA increased as fast as we saw with high-NA, it would be almost unviable economically.

However, in a recent earnings report, Van den Brink said that EUV with an NA higher than 0.7 (called Hyper NA) may become a reality soon after the end of this decade (I could talk about EUV with an NA higher than 0.7 (known as Hyper NA) potentially becoming a reality shortly after the end of this decade); . However, the most appropriate guide to follow is actually: It all comes down to cost. We need to increasingly focus on reducing costs – this means not reducing resources but ensuring that the solutions we bring to market are simpler, more sustainable, more effective, easier to maintain, easier to manufacture and more reliable Scalability.

Van den Brink emphasized that it would be irresponsible for me to jump to the next product without understanding the cost and complexity constraints imposed on these products. This is exactly what ASML is doing with its new optical metrology system that will be available in 2023. The company revisited the project within tight cost parameters and has been able to implement new technology that is many times more cost-effective than before. Likewise, ASML is continuing its efforts to control the cost of current 0.33 NA EUV systems as well as High-NA and Hyper-NA systems to ensure that demand for scaling remains strong.

"Ten years ago, when we developed High-NA, we couldn't imagine that NA above 0.55 even existed. So Hyper-NA was very, very difficult to achieve. What's great is that our business and R&D capabilities can handle all of these things at the same time. We can develop technologies like Hyper-NA while focusing on cost control, simplicity, sustainability, manufacturability and maintainability," Van den Brink said in the financial report.

In other words, Hyper-NA EUV lithography machine may really become a reality.