For decades, the semiconductor industry has been looking to extreme-ultraviolet (EUV) lithography as the next big advance in the manufacture of microchips. But EUV, which uses short-wavelength light to produce super-powerful microchips, has proven quite challenging due to the sophisticated nature of the light source and optics required to make mass production feasible. However, recent advances in EUV technology are proving more promising than ever, and it’s now estimated that production-level EUV machines will be ready by 2015. This news is highly promising for the vacuum industry, since the new EUV machines will feature vacuum chambers to house the delicate lithography process.
Today, nearly all microchips are made using deep-ultraviolet lithography (as compared to extreme-ultraviolet lithography), a photography-like process that focuses light through several lenses to etch circuit patterns onto chips. In cameras, lenses focus light onto film to create photos, but in lithography, light is focused through lenses onto silicon wafers to create the integrated circuit design.
The first step in the process is to direct the light onto a mask, which acts like a stencil of the circuit pattern that will be carved into the wafer. The light is directed onto the mask and then through several optical lenses that shrink the pattern down until it’s small enough to be projected onto the silicon. The silicon is covered by a light-sensitive, liquid-plastic coating, called photoresist, that reacts to the light. This reaction hardens some portions of the wafer and leaves others soft. The silicon is then put through a chemical wash, which leaves only the hardened circuit pattern created by the mask.
The key to creating more powerful chips is to make the circuit patterns as small as possible, so the maximum number of transistors can be placed on the wafer. To get smaller circuit patterns, you need a shorter wavelength light source, so finer features can be etched onto the chips. Currently, deep ultraviolet lithography can get the wavelength of the light down to 193 nanometers, but it can’t get any shorter than that without having the light absorbed by the glass lenses. When the lenses absorb the light, it doesn’t reach the silicon wafer, so no circuit pattern can be created. Because of this, we’ve reached a point where it’s impossible to fit any more transistors onto the chips without using a new light source.
“We’ve reached the limits of what a 193nm wavelength is small enough to etch,” said Hot Hardware’s Joel Hruska.
The next-step light source is EUV, which has a wavelength of 13.5 nanometers. The shorter wavelength provides for higher resolution circuit patterns, which ultimately allows for more transistors to be added, creating a more powerful microprocessor. However, working with the exceptionally short EUV light source complicates the lithography process.
First off, traditional optical lenses cannot be used with EUV because they absorb light. Instead, a series of concave and convex mirrors coated with multiple layers of molybdenum and silicon are used to reflect the light onto the silicon. Even using these special mirrors, only 70 percent of the EUV light is reflected, with the other 30 percent absorbed by the mirrors. In fact, the EUV wavelengths are so short that even air absorbs them, and this is where vacuum equipment comes into play. To ensure that there is no air to absorb the EUV light, the entire process must take place inside a vacuum chamber. This is what makes the development of EUV so exciting for the vacuum industry.
One of the first EUV machines was created by ASML and shipped to Samsung Electronics in 2011. However, this machine, the NXE:3100, was merely for pre-production and could only develop 5 to 10 wafers per hour—far below the amount needed for full-scale production. Since then, ASML has shipped several more NXE:3100s to customers worldwide, who are using the machines to fine-tune the production process. By the first quarter of 2013, these NXE:3100 systems had exposed more than 30,000 wafers.
The main thing holding back mass production EUV is the brightness of the light source. EUV requires a very bright light in order to make mass production of chips fast enough to be financially feasible. However, to get the light bright enough for high-volume production requires a high level of input power. In February, ASML was able to get the power level of the NXE:3100 up to 55 watts, which allows for the exposure of 43 wafers per hour. ASML’s next generation of EUV machine, the NXE:3300, ships later this year. Using its higher-power laser, ASML estimates that the device will be able to demonstrate up to 80 watts of power by the end of 2013. By 2015, ASML predicts it will be able to get the NXE:3300 power level up to 250 watts, which would be production level and capable of producing 125 wafers per hour.
“We confirm our expectation of the ramp of EUV-enabled semiconductor production in 2015, supported by our NXE:3300 scanners,” former ASML CEO Eric Meurice told the hardware review website X-Bit Labs.
The 2015 date is important because that’s when the semiconductor industry is expected to transition to the 10-nanometer manufacturing node. If ASML is able to deliver mass-production EUV at that point, the technology should prove to be a huge boost to the semiconductor field. The semiconductor research firm Imec has tested the new NXE:3300,and the company’s senior vice president for process technology development, An Steegen, told IEEE Spectrum that the 10 nanometer node is best bet for EUV.
“This is the node when EUV has to happen, when it would really make a difference,” Steegen says.
EUV and Vacuum
The recent developments in EUV technology are highly encouraging for the vacuum industry. If EUV machines can be brought up to mass production speeds in the next few years, there’s likely to be a significant increase in the demand for vacuum equipment. Given this, vacuum equipment manufacturers should keep a close eye of the latest developments in EUV technology.