After years of delay, EUV lithography machine is finally ready

At the 2017Q4 earnings conference held recently, TSMC revealed that the production capacity of its extreme ultraviolet lithography (EUV lithography) machines has made great progress. Its power supply has been increased to 160W to assist in 7nm and 5nm manufacturing, and the 250-watt EUV has also been installed.

ASML, the only supplier of EUV lithography machines, also stated at the 2017 Semicon West Semiconductor Equipment Exhibition that the 250-watt EUV light source is ready. The company's 2017 financial report also emphasized that its EUV lithography machine meets the performance specification of 125WPH (125 wafers per hour). That means that the EUV lithography machine originally planned to be launched in 2004 is finally ready after a delay of thirteen years.

Over the past few decades, the semiconductor industry has achieved rapid development under the guidance of Moore's Law. In order to meet the requirement of Moore's Law that "the number of transistors integrated in a chip of the same area doubles every 18 months", wafer fabs have been promoting the update of process technology. However, with the evolution of nodes, the industry generally believes that traditional lithography will encounter obstacles at 65nm or 45nm, so they are looking for new solutions, and EUV is their main choice.

EUV refers to light with a wavelength of 13.5nm. Compared with the 193nm light source used in mainstream lithography machines, the new EUV light source can carve smaller channels on silicon wafers, thereby integrating more transistors on the chip, thereby improving chip performance and continuing Moore's Law. However, in the process of promoting EUV lithography machines, various problems were encountered, and the commercialization of EUV lithography machines was delayed again and again. The industry's R&D investment in EUV is conservatively estimated to exceed 20 billion US dollars. The power of the light source is the main reason why EUV lithography machines have not been commercialized.

During the operation of EUV lithography, a power source is needed to convert plasma into light with a wavelength of 13.5nm, which is then reflected by the mirror several times before being projected onto the wafer. However, the previous power source cannot provide enough power for EUV to meet economic feasibility. This requires understanding the requirements for EUV lithography:

Simply put, the goal of introducing EUV lithography is to simplify the original double-layer patterning of traditional lithography into a single layer of EUV, thereby reducing the number of mask layers and reducing production complexity. In order to achieve the production efficiency of 250 to 270WPH of existing traditional lithography machines, EUV lithography machines require at least 125WPH efficiency to achieve COO (cost of ownership) and OEE (overall equipment efficiency), which requires a 250-watt light source. But until 2012, ASML, the only supplier of EUV lithography machines, only achieved a 25-watt light source.

In order to accelerate the development of light sources, they spent $2.5 billion to acquire Cymer, the world's leading excimer laser source provider, in 2012. According to Zhihuiya, a global leading patent search platform, Cymer is a company that focuses on laser, X-ray and deep ultraviolet light sources. The acquisition of Cymer allowed ASML to directly obtain the lithography light source technology that is crucial to its development from the source. This in turn accelerated the development of EUV lithography machines.

According to reports, Cymer uses a method called "laser plasma", which uses an amplifier derived from metal cutting technology to generate a powerful carbon dioxide laser in a vacuum chamber, which irradiates a beam of ultra-pure tin droplets that are emitted 50,000 times per second through the chamber. When the laser pulse hits the tin droplets, the droplets are heated into plasma and produce EUV rays. Then, a mirror collector reflects the light generated by the process into the lithography machine.

Based on this method, ASML and Cymer continued to improve and reached a power of 200 watts in 2016. By the second half of 2017, they finally achieved a 250-watt light source and an efficiency of 125WPH, which means that the commercialization of EUV lithography machines is just around the corner.

With the development of HPC and smartphones, the requirements for chip performance are getting higher and higher, and the demand for advanced processes by design manufacturers is also rising. At TSMC's Q4 earnings conference, TSMC said that it already has 50 7nm customers, which is the best proof. Facing this market, as mentioned at the beginning of the article, wafer foundries need to turn their attention to EUV lithography machines for help. Samsung Foundry, which just became independent from Samsung Group in May 2017, is the most radical one among them.

Samsung said that they are the first manufacturer in the industry to announce that they will use EUV lithography machines for 7nm chip production. According to Samsung, they will provide related services in the second half of 2018; as for TSMC, according to relevant people in the supply chain, TSMC will start 7nm production at the end of the second quarter, but the first generation of 7nm will use traditional lithography. TSMC said that EUV will not be introduced until 7nm plus in 2019; GlobalFoundries also plans to launch 7nm process in 2018, but like TSMC, it will still use traditional lithography at this time. They plan to introduce EUV in 2019. As for IDM giant Intel, they are secretive about the progress of their advanced processes and EUV, but according to public information, they have purchased more EUV lithography machines than any other company.

EUV lithography machines are undoubtedly the trend of the future.

Gary Patton, CTO of GlobalFoundries, said that if EUV lithography machines were not used at 5nm, the number of lithography steps would exceed 100, which would be crazy. Therefore, EUV lithography machines are undoubtedly the most important production tools for future 5nm and 3nm chips, and the competition for EUV lithography machines will become extremely fierce in the future, because this is the key to determine the future competition of these manufacturers in the advanced process market.

Media reports said that TSMC ordered five EUV lithography machines at the beginning of 2017. South Korean media BusinessKorea also said in October that Samsung intended to purchase 10 EUV lithography machines. There are no reports on the specific number of lithography machines purchased by GlobalFoundries and Intel. But from the perspective of S and T, they are stockpiling a lot of goods. However, ASML's production capacity for EUV lithography machines is not large, which may intensify the competition.

According to ASML's annual report, they shipped only four EUV lithography machines in 2016, and delivered 10 EUV systems in 2017. According to media reports, ASML's EUV lithography machine production can reach 24 units in 2018, but these orders have been snapped up. However, by 2019, ASML will increase its production capacity to 40 units, which will greatly ease the supply pressure of EUV lithography machines.

After basically overcoming the problem of 250W light source, ASML gave a basic explanation to its wafer fab customers, but for the EUV lithography system, there are still some problems that need to be solved.

The first is the issue of the mask;

According to reports, the masks used in EUV are completely different from those used in 193nm immersion lithography. They are composed of nanolayers made of dozens of different materials. According to data surveys, mask manufacturers have produced 1,041 EUV masks in the past 12 months, and the mask yield is currently only 64.3%. However, the number of mainstream masks exposed during the same period reached 462,792, with an average yield of 94.8%. Therefore, how to improve the mask yield and cost issues have become their primary considerations.

Secondly, the EUV film problem cannot be ignored;

Although EUV equipment is now in an ultra-clean environment, dust is inevitably generated during the manufacturing process. If a little dust falls on the mask, it will cause great losses. The film of the mainstream mask is transparent and can withstand the test, but the current EUV film is opaque, so ultra-thin films are needed to make transparent EUV films that can withstand the impact of the EUV lithography machine's vibration and related interference on the mask.

Another important issue is that there is currently no good way to detect defects in photomasks;

Ideally, you can use EUV light to scan the spots that need to be repaired. But this technology, called actinic patterned-mask inspection, is still under research, so all chip manufacturers can only use stopgap measures for mask inspection: some manufacturers use those tools for 193nm lithography. But when it comes to 7nm, using the 193nm method is like looking for fish in a tree. Because although the method is the same, you will always miss something. Chipmakers also use a technology called "print check" to check wafers, but this method is very time-consuming and costly, and it is not acceptable.

For ASML, there is still a light source problem that needs to be solved in the future.

The current 250W light source can be used at 7nm or even 5nm without any problems, but at 3nm, the power requirement for the light source will reach 500W. At 1nm, the power requirement for the light source will even reach 1KW. This will not be an easy problem either.

Let me hope some smart engineers help us figure these out.

By Li Shoupeng, Semiconductor Industry Observer

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