How was the 7nm chip in the Huawei Mate 60 Pro produced in China?

Dataderivedbybenchmarkingplatformsandthird-partyteardownreportsindicatethattheKirin9000Sisa7nmchipsinceitisclearlylabeledas“manufacturedinChina.”However,thespecializedEUV(ExtremeUltraviolet)lithographymachinesneededforproducing7nmchipshasbeensubjecttoexportcontrolstoChinasince2019,andChinesechipfoundrieshaveaccessonlytoDUV(DeepUltraviolet)lithographymachineswithwavelengthsof193nanometers.

The 7nm Kirin 9000S chip could be made possible in two ways. One is a breakthrough in domestic EUV lithography machines, and the other is chip manufacturers using DUV to indirectly produce 7nm chips. However, the latter is much more likely than the former.

Using DUV lithography machines with a wavelength of 193nm can cover process nodes of 28nm and above. Using DUV to manufacture 7nm chips might seem impossible because the shortest wavelength of light from a commercial DUV lithography machine is 193nm, which is 28 times larger than 7nm. However, the industry has indeed managed to manufacture 7nm chips with DUV lithography machines.

The gap was bridged thanks to the iteration from DUV dry lithography to DUV immersion lithography. Although the wavelength of DUV lithography machine's light source is only 193nm, light experiences refraction when passing through water, effectively shortening the wavelength. The refractive index of 193nm ultraviolet light in water is approximately 1.44, resulting in a wavelength of around 134nm. Building upon this principle, immersion lithography was proposed by Burn J. LIN in 1987 by introducing a layer of ultra-pure water between the wafer surface and the lens of the lithography machine. The water causes the ultraviolet light to refract, effectively reducing the wavelength to 134nm.

To increase NA, larger lenses are needed. Using multiple exposure techniques, TSMC started producing 7nm chips (N7) using DUV in June 2016, and Samsung began mass production of 7nm chips (7LPP) in 2018. Only then did using DUV to produce 7nm chips become a reality.

However, using DUV to manufacture 7nm chips requires the coordination of various technologies, including Phase Shift Masks (PSM), Off-Axis Illumination, Optical Proximity Correction (OPC), Source-Mask Optimization (SMO), and lithography. These technologies gave rise to a new subfield called Computational Lithography. The enormous data required for computational lithography led NVIDIA's GPUs to become essential tools, with the cuLitho, a software acceleration library, claiming to speed up computational lithography by 40 times.

In conclusion, the industry has gone to great lengths to make DUV capable of manufacturing 7nm chips. If the industry were to continue using DUV for 5nm chip production, fourfold exposure would not be sufficient. It would require 6-8 times of exposure, more mask plates, longer lithography times, and higher material costs, making it unbearable. Therefore, it is better that when 5nm chips were ready, EUV lithography machines are also prepared, thus liberating the industry from the burdensome multiple exposures. As a result, the 7nm chips represent the last generation of processes manufactured using DUV in the industry's current landscape.