Huawei EUV lithography is here

On November 15, the State Intellectual Property Office published a new patent by Huawei for "reflective mirror, lithography device and its control method" (CN115343915A)[1], which is related to EUV (extreme ultraviolet) lithography.

As we all know, the Dutch company ASML has monopolized the global high-end chip lithography technology, and the company's state-of-the-art EUV lithography machine has become an indispensable equipment for mass production and industrialization of semiconductors, as well as a guarantee for the continuation of the process in the future. But China so far does not have any EUV lithography machine, Huawei chip dilemma also came from this.

01What has Huawei done?

Let's take a look. What is the gold content of Huawei's new patent?

This patent abstract shows that this application provides a reflector, a lithography device and a control method thereof, which relates to the field of optics and can solve the problem of coherent light not being homogenized due to the formation of a fixed interference pattern; the reflecting surface of the reflector includes a plurality of micro-reflecting surfaces; the plurality of micro-reflecting surfaces includes a first micro-reflecting surface and a second micro-reflecting surface adjacent to the first micro-reflecting surface; the first micro-reflecting surface and the second micro-reflecting surface having a height difference Δh, the height difference Δh lying in the interval (0, kλ]; wherein λ is the wavelength of the extreme ultraviolet light; and k is a positive integer greater than or equal to 1.

Specifically, this patent could solve an important problem for EUV lithography.

As semiconductor processes advance to the 7nm node and below, extreme ultraviolet (EUV) lithography becomes the preferred lithography technology. In EUV lithography, a strong coherent light source is used for lithography, and the coherent light is split into multiple sub-beams with a fixed phase relationship by the illumination system, which will form a fixed interference pattern when projected on the mask plate, resulting in light and dark variations and uneven light intensity. ensure that the lithography process is carried out properly.

The present application provides a reflector, a lithography device and a control method thereof, which can solve the problem that coherent light cannot be homogenized due to the formation of a fixed interferometric pattern.

02Is the Huawei EUV lithography coming?

So, how useful can this patent be in EUV lithography?

According to "Research Progress and Development Trends of Extreme Ultraviolet Lithography Light Sources"[2], the six most critical subsystems of EUV lithography are the EUV light source, illumination system, projection objective, mask stage, dual workpiece stage, and alignment register system.

Let's start with why do we need EUV light? Because it is a simple fact that the shorter the wavelength, the higher the accuracy. In terms of light source development, photolithography has gone through five iterations. From the original high-pressure discharge mercury lamp g-line (436 nm) in the UV band to i-line (365 nm) and then to excimer lasers KrF (248 nm) and ArF (193 nm) in the deep UV band, the current state-of-the-art extreme UV lithography uses 13.5 nm extreme UV light, whose light source wavelength is reduced to 1/30th of that of g-line.

While lithographs with light sources in the 193 nm band and above commonly use refractive optics, EUV lithographs with light sources at 13.5 nm wavelengths use reflective optics, which is determined by the properties of the materials in the extreme ultraviolet band.

EUV lithography places high demands on reflective mirrors, as most materials absorb extreme ultraviolet light and therefore absorb light in the system. For this reason, ASML has developed a completely new optical system which uses ultra-smooth, multi-layer mirrors in a vacuum chamber. Each reflector has over 100 layers of material which have been carefully selected and precisely designed to reflect the maximum amount of EUV light. The mirrors require an extremely demanding flatness, being polished to a smoothness of less than one atomic thickness.

Indeed, reflectors are also critical to the development of the next generation of lithography. ASML is currently developing a next generation EUV platform that increases the numerical aperture from 0.33 NA to 0.55 ("High-NA"). Offering a 70% higher resolution capability than current EUV platforms, the High-NA platform will support processes up to 5 nm.

But this is only one of the many aspects of the EUV lithography machine, in fact the EUV light source is the most central subsystem and the biggest difficulty in achieving stable operation of the EUV lithography machine.

Firstly, reducing the wavelength of light is not easy in itself, as EUV light only exists in outer space. To make EUV lithography possible, ASML has developed a completely new method to generate light for lithography.

In a laser plasma (LPP) light source, droplets of molten tin, approximately 25 microns in diameter, are ejected from the generator at a speed of 70 metres per second. As they fall, the droplets are first hit by a low-intensity laser pulse, which flattens them into a pancake shape. A more powerful laser pulse then evaporates the flattened droplets to create a plasma that emits extreme ultraviolet light. This process is repeated 50,000 times per second in order to produce enough light to make a microchip. This process places high demands on both the laser and the generation of the droplets.

Finally, even if every step of the way is successfully overcome, engineering challenges lie ahead. An EUV lithography machine weighs 180 tonnes, requires 40 containers to transport and takes more than a year to install and commission, and ASML's EUV lithography machine for the 7 nm process has 100,000 components, 90% of which are key equipment from countries around the world. In fact, ASML is only responsible for the design of the whole machine and the integration of each module, the company cannot be separated from the support of more than 5,000 suppliers from the global upstream and downstream industry chain for the materials, equipment, parts and tools used in the production of lithography systems.

According to foreign experts' predictions, there is currently a gap of at least ten years between Chinese lithography technology and ASML. But this is not unusual, because for China to develop high-end lithography is the equivalent of competing with dozens of Western countries. It is not even possible for a major country to achieve technological catch-up overnight, let alone a company like Huawei.

Reference links：

[1]http://epub.cnipa.gov.cn/Dxb/PatentDetail

[2]https://www.opticsjournal.net/Articles/OJe83bd70142deb50a/Abstract