The new “savior” of EUV lithography

On June 30, 2022, South Korea's Samsung Electronics officially announced that it would begin mass production of 3nm chips, using the most advanced EUV lithography technology and GAA (Gate-all-around) transistor technology. This also enabled Samsung Electronics to become the world's first mass-produced 3nm chip foundry ahead of China's TSMC.

South Korea's Samsung Electronics officially announced the mass production of 3nm chips.

According to an official statement from Samsung Electronics, compared with traditional 5nm process chips, chips based on its first-generation 3nm GAA process reduce power consumption by 45%, improve performance by 23%, and reduce area by 16%.

Samsung Electronics also claims that the second-generation 3nmGAA manufacturing process is under development. The next-generation process will reduce the power consumption of the chip by 50%, improve the performance by 30%, and reduce the area by 35%.

In the second half of 2023, Samsung Electronics will begin mass production of chips at its P3 line in Pyeongtaek, South Korea. By the end of 2023, Samsung Electronics’ new factory in Tyler, Texas, will be completed. According to the latest process technology roadmap announced by Samsung Foundry at SFF 2023, the company plans to launch the 2nm SF2 process in 2025 and the 1.4nm SF1.4 process in 2027.

However, Samsung Electronics has had a lot of controversies in advanced processes such as 3nm, 4nm, and 5nm. It has experienced delays in product launches and slow improvement in process yields below 10nm, causing its major customers to turn to TSMC. For example, Qualcomm's first-generation mobile platform Snapdragon 8+ switched from Samsung Electronics' 4nm foundry to TSMC's 4nm foundry.

On July 11, 2023, Park Sang-woo, a researcher at Hi Investment & Securities, said in a report: "Samsung Electronics has recently successfully improved the yield rate of the 4nm process." According to the report, Samsung Electronics' 4nm process yield rate exceeded 75% this year, and the 3nm process yield rate exceeded 75%. The process yield exceeds 60%. Starting from the second half of this year, the core chips of smartphones, PCs and other equipment will evolve to 3nm. With TSMC unable to fully absorb 3nm process orders, Samsung Electronics’s yield improvement will undoubtedly increase its chip foundry for companies such as Qualcomm and Nvidia. probability. Especially for comparison, TSMC's 4nm process yield is about 80%, and the 3nm process yield is about 55%.

There is no doubt that South Korea's Samsung Electronics Co. is not inferior to any competitor in terms of technological advancement, but yield rate is the main pain point.

In the past 20 years, EUV light source, EUV mask and EUV photoresist have been the three major technical challenges of EUV lithography. More than 10 years ago, EUV light sources usually ranked first among the three major technical challenges. In recent years, with the continuous progress of EUV light sources, EUV masks began to rank first among the three major technical challenges. One of the most difficult aspects of EUV masking is the EUV film (Pellicle).

EUV film is a high-end consumable in the form of an ultra-thin film that needs to be replaced regularly, preventing it from being on the top layer of the EUV mask while allowing high EUV light transmittance. It is mounted a few millimeters above the photomask surface and protects the EUV mask surface from airborne particles or contaminants during the EUV exposure process. If particles land on the EUV film, they will not be exposed on the wafer because they are out of focus, minimizing exposure defects. However, in the EUV lithography process, EUV light passes through the EUV film twice, once into the EUV mask, and the other time out of the EUV projection optical system, which causes the temperature of the EUV film to increase by 6,001,000 degrees Celsius.

Without (left) and with EUV film

EUV mask diagram

EUV thin films protect extremely expensive 6-inch EUV masks in EUV lithography (a single EUV mask costs over $300,000) from particles that might land on its surface. In particular, this is most important for the production of CPU chips. The reason is that the CPU chip uses a single-die reticle, and any defect in the EUV mask may cause the entire wafer to fail! Using a 25-die photomask results in only a 4% yield reduction across the wafer. In other words, for large-area chips, it is absolutely impossible without the protection of EUV film. For small area chips, protection without EUV film may be feasible.

Harry Levinson, director of HJL Lithography, said: "Trying to do EUV lithography without EUV film is painful. It requires more inspection and still has the potential for yield loss."

EUV mask

Joost Bekaert, researcher at IMEC, the "brain" of Euromicroelectronics, said: "Few materials have a high EUV transmittance of more than 90% and at the same time can withstand more than 600W of EUV light radiation. In addition, the film needs to be strong to prevent On a large area (approximately 110mm x 140mm) EUV mask". Specifically, EUV films must meet the following strict standards:

1. The thickness is only a few tens of nm (usually 20-30nm), and the large-size film corresponds to an area of ​​110 mm × 140 mm.

2. In order not to affect the process yield, the transmittance must exceed at least 90%, and the non-uniformity (3σ) ≤ 0.4%;

3. Withstand EUV radiation with power density up to 5W/cm² (corresponding EUV power is 400 W);

4. Strong mechanical properties, the maximum acceleration is 100 m/s² ( corresponding to the moving speed of the film on the EUV lithography machine mask stage), and the Young's modulus exceeds 1 TPa;

5. The maximum environmental pressure change tolerance is 3.5 mbar/s;

6. Reflectivity <0.005%, "zero defects". It can withstand extremely harsh operating environments: 1000°C high temperature, multiple deflation and pumping processes, and the film does not show any cracks or breaks.
   

Photolithography technicians have experienced a long and tortuous process in the research and development of EUV films. The main reason is that most materials have strong absorption in the EUV band. People have explored a variety of materials such as polysilicon, silicon nitride, carbon nanotubes and graphene, and have debated many times whether EUV lithography must use EUV films.

The earliest developer of EUV films was ASML. After hard work, ASML successfully developed a polysilicon EUV film with an area of ​​106 mm × 139 mm in 2014, but its thickness was 70nm and its EUV transmittance was as high as 86%. In 2019, the thickness of polysilicon EUV film reached 50nm, and the EUV transmittance reached a maximum of 88%.

Polycrystalline silicon EUV film developed by ASML

In 2019, ASML launched the first commercial EUV film and licensed the technology to Japan's Mitsui Chemicals, which began mass sales in the second quarter of 2021. At this point, the debate over whether EUV lithography must use EUV films is over.

Commercial polysilicon EUV film

IMEC has also been conducting research on EUV films. Different from ASML's technical route, IMEC uses carbon nanotubes, with an EUV transmittance as high as 97.7%! Production efficiency can be increased by approximately 25%.

Carbon Nanotube EUV Film

A Finnish company, Canatu, is commercializing carbon nanotube EUV films. Canatu Company originated from the Nanomaterials Research Laboratory of Aalto University in Finland. Since 2010, Canatu has been studying carbon nanotube EUV films and improving manufacturing processes. More than 150 patents have been obtained, covering 25 categories. Canatu established its first production line to produce carbon nanotubes in 2015 and cooperated with IMEC to develop EUV films based on carbon nanotubes.

Next, the graphene EUV film appears.

The 2010 Nobel Prize in Physics was awarded to Andre Geim and Konstantin Novoselov, scientists at the University of Manchester in the United Kingdom, for their work on graphene materials. Research excellence. The award was given "for ground breaking experiments regarding the two-dimensional material grapheme".

2010 Nobel Prize in Physics

According to the Nobel official website, Andre Geim was born in Sotegyi, Russia, in 1958 to a family of German descent. He lived with his maternal grandparents for the first seven years of his life. Only later did Geim discover that his grandfather and father, both physicists, had spent several years in labor camps. After receiving his PhD in physics from the Russian Academy of Sciences in Chernogolovka, Geim worked at several European universities including Nijmegen in the Netherlands. Game has been at the University of Manchester, UK, since 2001.

Before the discovery of graphene, Andre Geim won the "Ig Nobel Prize" in 2000 for his "Flying Frog" project. The basic principle is to overcome gravity through magnetic levitation technology and levitate a frog on the Mid-air. On the day of the award, Andre Geim received the award on the spot. This experiment has also been rated as one of the top ten most popular results of the "Ig Nobel Prize" in the past 18 years. Now, this principle has also been included in the physics textbooks of some foreign universities.

In 1974, Konstantin Novoselov was born in Nezhnetagil, Russia. After studying in Moscow, he pursued his PhD under the supervision of his supervisor Andre Geim, first at Radboud University in Nijmegen, the Netherlands, and then at the University of Manchester in the UK.

Two-dimensional material graphene

According to the Nobel website, carbon exists in several different natural forms. A material made of carbon atoms arranged in a hexagonal lattice and only one atom thick has long been considered a purely theoretical structure. In 2004, Konstantin Novoselov and Andre Geim managed to create this material, graphene, and map its properties: very thin but still very strong, with good thermal and electrical conductivity, Almost completely transparent but very dense. Graphene creates new possibilities in materials technology and electronics.

Published in Science magazine in October 2004

Graphene Materials Paper

Graphene is a new material in which carbon atoms connected by sp² hybridization are closely packed into a single-layer two-dimensional honeycomb lattice structure. This is currently the thinnest material in the world, with a thickness of 0.335nm. The method for preparing graphene by Konstantin Novoselov and Andrei Geim is very simple. They use the mechanical exfoliation method. The academic definition is to apply mechanical force (friction, tension, etc.) to graphene through graphite crystals. Or the method of separating graphene nanosheets from graphite crystals. Simply put, thin sheets are taped off from graphite so that the sheets still contain many layers of graphene. But after gluing it on ten to twenty times, the sheets became thinner and thinner, eventually producing some single layers of graphene.

So far, many laboratory studies of graphene still use mechanical exfoliation methods. Obviously, this method has very low controllability, is difficult to achieve large-scale synthesis, and cannot be industrialized for mass production. As a result, some people joked that it was the "dynamite prize for tearing off tape."

Graphene has many amazing and superior properties. Specifically:

1) High mechanical strength, not easily destroyed, 300 times stronger than steel;

2) It has good tensile properties. It can be stretched to 20% of its own length, exceeding 1TPa. Because of its hexagonal structure, it will deform when stretched but will not be destroyed;

3) As a non-metallic material, it is better than the currently most conductive metal silver, reaching a conductivity of 10 ⁶ S/m

4) The material with the best thermal conductivity in nature is silver. The thermal conductivity of graphene is 5000W/(m·k), which is 10 times stronger than silver. Interface thermal resistance<1 mm²K/W

5) High electron mobility 10000cm²/vs, even 20000cm²/vs.

6) Ultra-thin, large specific surface area, can also transmit light and bend.

There are countless good reputations about graphene. For example, some people call it "the material that changed the 21st century", "the king of materials", etc.

Graphene-based super fast-charging battery

TSMC attaches great importance to EUV mask technology. On the one hand, the company has invented an "EUV mask dry cleaning technology." Unlike traditional wet cleaning processes that use ultrapure water and chemicals, this dry cleaning technology can quickly remove contaminants and significantly reduce contaminants until they pinpoint the source of the contamination through sub-nanometer analysis technology. On the other hand, TSMC has been using its own developed EUV film on its mass production lines since 2019. In 2021, its EUV film production capacity increased 20 times compared with 2019.

Dr. Kevin Zhang, senior vice president of business development at TSMC, declared: “We have obviously invested in this area internally, and I think it is a very unique technology for us. We are able to leverage it to achieve our EUV mass production. If you look at the way we've run at 7 nm, 6 nm and now 5 nm, all using EUV, we've obviously made tremendous progress, so it's definitely something we think we've done well with our unique technology advantages. Good field.”

Dr. Maria Marced, President of TSMC EU, declared: "One thing, because I am in Amsterdam, we are relatively close to ASML - we have special training from them. I can tell you that having this production in-house really allows us to extend Optical mask life. Normally in EUV lithography, the masks get dirty, so in the shorter term, this really helps us improve EUV lithography and mask production efficiency.”

Samsung Electronics is obviously aware of the importance of EUV films in improving EUV lithography yields, and has been actively developing and evaluating EUV films made of carbon nanotubes and graphene, aiming to develop graphene that meets 92% EUV transmittance. thin films to narrow the market share gap with foundry rival TSMC. At the Samsung Foundry Forum held in October 2021, it was stated: "We have developed a film with an EUV transmittance of 82% and plan to increase the transmittance to 88% by the end of the year." Samsung Electronics is developing large-scale production facilities for graphene EUV films in-house.

An analyst said: "Samsung Electronics promotes the development of EUV films and aims to quickly catch up with the number one foundry company TSMC." Although Samsung Electronics has improved its thin-film technology, it has not yet introduced the material into its dynamic random access memory (DRAM) production lines, arguing that it is too early to apply the material to mass production lines.

In addition to developing its own EUV films, Samsung Electronics is advancing cooperation with major domestic material companies S&S TECH and FST (FINE SEMITECH). Samsung Electronics has invested in S&S TECH and FST to ensure the development of graphene EUV films with an EUV transmittance of 90%.

Korea Graphene Plaza Co., Ltd. is a pioneer in commercializing graphene EUV films. The company was incubated in the laboratory of Seoul National University chemistry professor Kwon Yong-deok and founded in 2012. The company has claimed to have developed graphene EUV films required for EUV lithography of chips at 5nm and below, and is preparing for an initial public offering. Kwon Yong-deok said: "Previously, films were made of silicon. But we used graphene. Graphene films will increase yields for semiconductor companies using ASML EUV lithography equipment."

The company's large-area graphene EUV film is synthesized using a dedicated chemical vapor deposition (CVD) method at high temperatures using carbon dioxide and a catalyst substrate such as copper. The Technion-Israel Institute of Technology purchased three sets of the company’s graphene synthesis and production equipment.

Kwon Yong-deok said: "Simply put, our CVD technology adheres polymer compounds to copper-synthesized graphene, then uses an etchant to remove the copper, and finally separates the graphene from the molecular compounds."

Manufacturing process of graphene EUV film

The price of an EUV film is about $75,000 (the unit price of a protected EUV mask is about $35.75 million). If you do it manually during operation, errors may occur. To this end, FST has developed the "world's first" EUV film mounting/demounting equipment (EUV Pellicle mounter & Demounter) to automatically mount and remove EUV films on EUV masks. FST has also developed an EUV film inspection system using laser and image processing technology to check whether there are foreign objects on the EUV film and its frame. It can also automatically analyze and view foreign objects, identifying their location and characteristics.

Choi Sung-won, Research Director of FST Corporation, said: "With the development of this equipment series, we have laid the foundation to become an EUV total solution company. This series is the first in the world and the first in Korea; their value is recognized by our customers It makes sense to accept it.”

EUV film installation/removal equipment

Kim Bingguo, a former employee of Samsung Electronics, established the startup company EUV Solution in January 2018. The company has developed an equipment EPTR to detect the transmittance of EUV films. EPTR utilizes EUV wavelengths to measure the transmittance and reflectance of direct EUV films at ultra-high speed. EPTR has been installed in a customer company and officially put into use. Lee Dong-geun, Vice President of EUV Solution, said: "EUV film transmittance directly affects project yield, so the process of accurately measuring transmittance becomes increasingly important. Customers who adopt EPTR can develop and measure EUV films more smoothly . When the product leaves the warehouse, you can directly indicate the specification information.

EUV mask with graphene EUV film.

There is no doubt that Korean manufacturers occupy a very advantageous position in the commercial research of graphene EUV films.

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