Competition for ASML New approach for EUV lithography: More efficient and cheaper than ASML's standard

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Due to the necessary amount of light reflections in the current construction of the machines in EUV lithography, about 1 percent of the EUV energy arrives at the wafer— this is quite cost-intensive. A design from OIST proposes a change in the projection path so that more than ten percent arrives at the wafer.

EUV lithography systems have become almost indispensable in the manufacture of advanced semiconductor chips in order to produce fine structures on silicon wafers such as for AI processors or DRAM memory. The most successful provider of these systems is likely to be the Dutch company ASML, which supplies the world's largest semiconductor manufacturers TSMC, Samsung and Intel with the devices. If ASML were ever to falter and be unable to build any of the sometimes costly machines, then the semiconductor industry could potentially face a problem.

However, this is already the case with regard to EUV lithography. Because the conventional construction of the EUV systems wastes a lot of energy. The EUV light is steered with mirrors that reflect the rays along the optical path in a zigzag pattern through open space. "However, as this method deviates the light from the central axis, important optical characteristics are sacrificed and the overall performance of the system is reduced", explain those responsible at OIST, the Okinawa Institute of Science and Technology. Therefore, Professor Tsumoru Shintake suggests a new structure that would reduce the complexity and cost of EUV lithography.

Gallery

EUV light and the power drop per reflection

In EUV lithography, a CO₂ laser is used to generate extreme ultraviolet (EUV) light which is necessary for creating tiny semiconductor structures. In this process, droplets of liquid tin are formed in a vacuum chamber and are bombarded by a high-powered laser based on carbon dioxide (CO₂). The laser heats the tin and creates a plasma that is 40 times hotter than the sun and emits EUV light with a wavelength of 13.5 nm. Specially coated mirrors collect and focus this EUV light, which is then guided through a mask to project the desired pattern onto a silicon wafer coated with photoresist.

The use of a CO₂ laser has the advantage that it delivers the high power and precise pulses necessary for the efficient generation of the plasma. However, the integration and control of the system is complex and requires precise coordination, leading to high operational and maintenance costs. In addition to a large amount of electrical energy, the CO₂ laser drive also requires a large amount of water for cooling.

So there could be room for improvement. This is where Shintake's proposal, which has already been patented by OIST, comes into play. Shintake suggests reducing the number of mirrors from the EUV source to the wafer to four, as more than 10 percent of the energy expended would be transmitted in this way. "This means that even a small EUV source with a power of some tens of watts can work just as effectively. This can lead to a significant reduction in power consumption," Shintake argues.

Two birds with one stone

The projector, the heart of EUV lithography, transfers the image of the photomask onto the silicon wafer. In Shintake's vision, it consists of only two mirrors, similar to an astronomical telescope. "This configuration is unimaginably simple when you consider that conventional projectors require at least six reflecting mirrors. This was made possible by a careful reconsideration of the theory for correcting aberration in optics. It's a triumph of classical physics over quantum physics," says Professor Shintake. "The performance has been checked with optical simulation software (OpTaliX) and is guaranteed to be sufficient for the production of advanced semiconductors."

Shintake overcame the problem of needing too many mirrors with the invention of the so-called "dual line field", which irradiates a flat mirror photomask from the front with EUV light, without affecting the optical path. He explains, "If you aim two flashlights, one in each hand, diagonally and at the same angle at a mirror in front of you, then the light from one flashlight always hits the other, which is unacceptable in lithography. But if you move your hands outward, without changing the angle of the flashlights, until the center is perfectly illuminated from both sides, the light can be reflected without colliding with the light from the opposing flashlights."

If Shintake's approach can be implemented, as the extensive tests in simulation suggest, then this could significantly reduce the costs of EUV lithography and also the production of advanced semiconductor chips. On the one hand, energy costs are reduced, on the other hand, the system becomes less complex and therefore more reliable. Thanks to the optimized optical path, the system operates with an EUV light source of only 20 W, which leads to a total power consumption of less than 100 kW. Conventional systems often require more than 1MW of power. (sb)

Link: Can we improve the energy efficiency of EUV lithography?

Link: Innovative EUV lithography technology dramatically increases energy efficiency and reduces capital cost of semiconductor manufacturing

This article was first published on our sister portal "ELEKTRONIK PRAXIS" (German Edition), Vogel Communications Group