Toshiba and Canon team up for developing 15nm nanoimprint lithography

Toshiba and Canon team up for developing 15nm nanoimprint technology

Toshiba and Canon, two of the major Japanese companies operating in the semiconductor business, have teamed up to develop nanoimprint technology for NAND applications. As we discussed already in this blog a few days ago Canon is seriously committed to nanoimprint lithography and they have recently bought Molecular Imprints, a company based in Texas, US, to gain traction with the new technology.

Nanoimprint lithography has the potential to revolutionize the lithography market but so far suffered from a series of problems that prevented full adoption for IC patterning: the main one being lack of alignment precision between two consecutive imprints.

If this and other problems (such as defectivity in the master mold and planarity control between the master mold and the substrate) will be overcome, nanoimprint lithography may become a serious alternative to conventional lithography due to the relatively inexpensive cost of imprinting a large number of wafers with a single master mold.

While logic patterning may still be challenging for nanoimprint lithography, NAND patterning has been seen for a while as the first step for full-scale adoption of the technology in mass production.

The strategy adopted by the two companies will require the installation of Canon machines at Toshiba` s plant in Mie prefecture. As for how the Research and development costs will be split between the two companies, a formal detailed announcement will be done later this year.

Currently, Toshiba is competing for the top spot in the NAND market with Samsung electronics of Korea with both contenders trying to reduce the cost of patterning per wafer and increasing the number of transistors packed per area.

The current patterning for NAND is based on 19nm lithography technology, with plans to move to a thinner and more precise 16nm~17nm process this summer.

Toshiba is already using ASML lithography machines and will add Canon imprint machines thanks to this collaboration.

Link (in Japanese):

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Nanoimprint technology – Canon to acquire Molecular Imprints Inc.

Nanoimprint technology

Canon Inc. of Japan has finalized a deal to acquire Austin-based Molecular Imprints Inc., according to press release issued on Feb. 13. Molecular Imprints, one of the market and technology leaders for nanopatterning systems solutions, has agreed to sell its semiconductor nanoimprint lithography equipment business to Canon as part of Canon`s bid to bolster its chipmaking equipment business. The price for the acquisition of Molecular Imprints was not disclosed, but the Nikkei business daily estimated it at more than $98 million.

In 2004, Canon began its own research into nanoimprint technology to enter the market for lithography equipment for leading-edge high-resolution patterning. A business alliance was established with Molecular Imprints in 2009, when Canon carried out joint development with the US company for mass production of semiconductor components using the Jet and Flash Imprint Lithography (J-FIL) technology of Molecular Imprints. This partnership aimed to enable the industry to continue on Moore’s Law bypassing the cost burden and resolution limits of traditional optical and EUV lithography. J-FIL is planned to be adopted for advanced FLASH memory within the next two years.

Canon, a stepper manufacturer, is facing increasing difficulties to compete in the stepper market due to the increasing costs of R&D associated with immersion and EUV technologies. Since the stepper market is becoming increasingly consolidated and in the hands of the market leader ASML, Canon is now looking to diversify its micro and nano-patterning device offer by exploring technologies alternative to the traditional optical patterning

Molecular Imprints was founded by S.V. Sreenivasan and Grant Wilson, both professors at the University of Texas at Austin. It is an industry leader for high-resolution, low-cost-of-ownership nanopatterning systems and solutions. Mark Melliar-Smith, CEO of Molecular Imprints, stated that the business alliance with Canon had yielded great progress in the pursuit of low-cost nanolithography solutions for the semiconductor industry.

Dr. Toshiaki Ikoma, CTO of Canon, notes that the acquisition of Molecular Imprints will strengthen the “Industry and Others” business unit of Canon. The acquisition is part of Phase IV of Canon`s Excellent Global Corporation Plan, where one of the strategies is business development via globalized diversification.

Canon decided to make Molecular Imprints a wholly owned unit after considering the outlook for volume production using the technology in the mid-to-long term future. The terms of the agreement will allow Molecular Imprints to retain the same company name and with most of the personnel. It was also reported that Canon plans to set up an office at the same place where Molecular Imprints is currently established.

The merger has the advantage of having a new company with the same name, the same key personnel, intellectual IP rights jointly owned with Canon, and multiple system platforms that are designed to support the growing need for nanoscale patterning in consumer electronics and biomedical applications. David Gino, COO of Molecular Imprints, stated that the company is looking forward to provide low-cost nanoscale manufacturing solutions to the hard disk drive, display, biotechnology, and other emerging markets. Gino is set to become the CEO of the new Molecular Imprints once the merger is complete. The deal is expected to be completed by April this year after government and shareholder approvals.

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Variants of nano imprint lithography

Variants of nano imprint lithography

In addition to the above mentioned thermal and UV-nano imprint lithography, there a big number of variety of processes about nanoimprint that have flourished in recent years, such as laser assisted direct imprint, Sub-10 nm NIL, combined thermal and UV nanoimprint, electrical field-assisted NIL, soft UV-NIL, reverse NIL, Jet and Flash imprint lithography process

Reverse imprint lithography process Using the reverse nanoimprint process, instead of having the polymer spin coated on the substrate, we have polymer coated on the mold and then transferred into the substrate due to the different surface energy between the mold and the substrate that allows an easy transfer of polymer from the mold to the substrate.

Using this process, it is possible to create 3d structures relatively easier than with other methods, but the downside is that the mold gets easily dirty and the process can not therefore be used for large scale production.

Applications of the reverse imprint lithography process are: metallic nanowires, optical devices and microchannels.

Roll-to-roll imprint lithography process

In order to overcome one of the major limitations of traditional nano imprint lithography, that is the inability to imprint large areas at low cost, a new technology called roll-to-roll imprint has been developed.

Roll-to-roll imprint is a continuous and simple process that can allow patterning of large areas at a relatively low cost.

The process is relatively simple and involves a roller mold that imprints the flat substrate by rolling over it in a continuous and uniform way: with roll-to-roll imprint lithography features down to 50nm and lower have been demonstrated for large areas.

Nanoimprint on large areas

Large area imprint lithography can be done in other ways other than roll-to-roll imprint and step-and-repeat imprint.

In detail, preparing a large area mold that completely covers the substrate to be imprinted in a one-shot imprint is something not easy but somehow possible in some cases. In order to be able to perform a uniform imprint over the whole wafer surface and to overcome issues of flatness and uniformity several techniques have been pioneered, such as the Air Cushion Press that is used to ensure the pressure and pattern uniformities.

The technique is interesting but still far from commercial utilization due to the issues above: so far results have been achieved for patterns down to 200nm and with wafers up to 200mm

Laser-assisted direct nanoimprint

This technique is used to perform the nanoimprint directly on the surface without the use of a polymer film to transfer the patter from the mold to the substrate.

A laser melts the surface of the substrate so that the mold can directly pattern the substrate.

Usually the mold is made by hard and resistant metals such as nickel and the substrate needs to be made of a material which can be melt quite easily.

The advantage of the technique is that does not require a step of etching of the substrate and that flatness requirements become less stringent due to the fact that the surface of the substrate is melt.

The speed of the process is also a plus and patterns down to 10nm have been produced with this technique

One of the main drawbacks of the technique is that the process is hardly appropriate for full production due to the dirt that inevitably gets stuck into the mold after several imprints

Thermal and UV-NIL combined nanoimprint

This technique has been pioneered by Obducat and allows to combine UV-nanoimprint patterning with the use of heat to achieve better results

Substrate conformal imprint lithography

Substrate conformal imprint lithography bridges the gap between large area lithography using a soft stamp and small area lithography using a small stamp with high resolution: the technique aims at achieving the advantages of both techniques (large area and high resolution) minimizing the drawbacks of the soft stamp, which is the inability to reach high resolutions due to problems of thermal expansion.

Using this technique, patterns down to 50nm have been achieved on substrate that did not meet stringent planarity requirements.

Nanoelectrode lithography

This technique combines the use of an electrode with nanoimprint

The mold has to be conductive and the patterning process is combined with an electrochemical reaction that allows the oxide pattern to get transferred directly into the substrate surface

While still called as “nanoimprint”, the technique is quite different from traditional nanoimprint where the pattern is mechanically transferred to the surface while the process here happens by electrochemical reaction

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The two main categories of nanoimprinting

The two main categories of nanoimprinting

While there are many different flavours of nanoimprinting processes, two main ones are:

      • Thermal nanoimprinting (also called as hot embossing)
      • UV-nanoimprinting

Thermal nanoimprint technology

Thermal nanoimprint technology has been the first kind of nanoimprinting process ever used and the original one adopted by Prof. Chuo back in 1996.

The thermal nanoimprint process is very easy to understand and straightforward: a layer of thermoplastic polymer is deposited on the surface of the substrate by spin coating or alternative method; then the substrate is placed inside the imprint machine along with the mold and the mold is pressed against the substrate at a set pressure.

The substrate received a precise amount of heat from the machine and the temperature of the polymer rises over the glass-transition temperature and becoming soft.

The mold is kept pressed against the substrate for an amount of time, after that the substrate is cooled down and the mold is released

After the pattern is transferred to the mold polymer layer, it is then transferred to the beneath silicon substrate surface by etching process

UV-nanoimprint technology

UV-nanoimprint technology process is different from thermal nanoimprint in two aspects: it does not use heat to soften the polymer layer but UV light and requires a UV-transparent mold.

With UV-nanoimprint technology, the polymer used on the substrate surface is a UV-curable photopolymer and not a thermoplastic one as in the case of thermal nanoimprint; this allows the process to be effective at considerably lower pressures and helps to avoid the issue of thermal expansion

As discussed, the main advantage of thermal nanoimprint over UV-nanoimprint is that molds of any material can be used while, in case of UV-nanoimprint technology, only UV-transparent materials can be used

However, since UV-nanoimprint uses mainly UV light to deform the polymer, considerably lower pressure levels on the substrate are needed to be able to transfer the pattern to the polymer

Moreover, the advantage of not needing much heat to deform the polymer brings other advantages such as much lower special deformation of the pattern due to applied heat and therefore a better alignment accuracy and the ability to imprint larger areas.

As for UV-nanoimprint, there are two sub-categories: hard-mold UV-nanoimprint and soft-mold UV-nanoimprint: as the name implies, hard-mold UV-nanoimprint is a process that uses a quartz or other rigid mold, while soft-mold nanoimprinting uses a soft mold usually made in polymer.

Hard-mold UV-nanoimprint technology has two main shortcomings if compared to soft-mold UV-nanoimprint: the mold is rigid and therefore there are sometimes issues while releasing the mold from the substrate; moreover, there are other issues when trying to imprint large areas due to the inherent issues of flatness of the mold and the substrate.

Lack of perfect flatness in either the mold or the substrate can lead to defectivity in the pattern or, in worst cases, to a breakage or the substrate to the mold.

Using a soft mold, however, leads to some shortcomings too: while issues of flatness between the mold and the surface are greatly resolved while using a soft mold and releasing is far easier, problems like thermal expansion and non-uniformities are worsened due to the elasticity of the mold itself

Deformation of the pattern due to even small quantities of heat can become a significant problem at lower resolutions and this may lead to additional issues when the surface to be patterned is large and therefore the thermal expansion rate of the mold polymer varies across the substrate surface

A variant of the UV-nanoimprint process is the so-called Step and Flash ® process.
Using this process, initlally developed at the University of Texas, the polymer is deposited on the substrate not by spin coating or by any other machine, but by a pattern generator which is embedded in the imprint machine. After the polymer has been deposited, a soft mold is gently pressed over the substrate surface and the pattern exposed to a UV-lamp.
After the soft mold is detached, the patterned polymer is etched and the unnecessary features are removed.

Other further categorizations of the process are: single step or multiple step and single layer and multiple layer nanoimprint

Single step nanoimprinting involves the patterning as a one-time process while multiple step process (also called step-and repeat nanoimprint) involves multiple step patterning of usually large areas of substrate with smaller area molds.

Single layer nanoimprinting is the traditional process where one single layer of pattern is transferred into the substrate surface, multiple layer nanoimprinting instead requires thhe patterning of multiple layers of patterning over the same area.

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Virtual interview about nanoimprinting lithography and its current applications

Nanoimprinting lithography replica

Q: Let` s start to discuss about the current situation of nanoimprint technology and how do you see it as of now. There were a lot of expectations behind nanoimprint a few years ago, do you think nanoimprinting lithography has delivered as promised or not?

A: Until a few years ago, nanoimprinting lithography was one of the candidates of the so-called next-generation lithography that should have replaced conventional optical lithography for the production of ICs in large scale. In this sense, I believe that nanoimprint, along with other technologies as multi-beam and direct self-assembly, can not be seen today as a replacement of conventional stepper lithography. However, I do not think that nanoimprint technology has proven to be a failure, I see many areas of applications outside the conventional IC processing market and I believe that most of the potential of nanoimprinting lithography has yet to be tapped

Q: You have said that nanoimprint, along with other technologies, have not delivered as someone hoped as a potential replacement of optical lithography. Can you explain to us the reasons why this did not happen?

A: There are various reasons why nanoimprinting lithography and other technologies are having a hard time in replacing conventional (stepper) optical lithography, despite the enormous cost of the soon-to-come iteration of stepper machines (namely, EUV steppers). The main reason is that stepper lithography has so many advantages compared with other technologies that it has proven difficult for other candidate technologies to match them. For example: in the case of nanoimprint, alignment and defect control have been the two critical areas where nanoimprint could not match optical lithography. Simply put, a nanoimprinting lithography machine can do not deliver the same level of alignment accuracy that a stepper does. Another problem is defectivity: it is extremely difficult to keep the master mold clean after a large number of imprints and this inevitably translates into defects and impurities being transferred to the imprinted wafers. Therefore, stepper lithography is superior to nanomprinting lithography in such regards

Q: Since there has been a lot of discussions about the skyrocketing costs of stepper lithography for volume IC and DRAM production, do you think new technologies can provide different solutions?

A: Unfortunately, despite the high costs, I do not see viable alternatives other than stepper lithography for ICs and DRAM production,. There are a few companies out there that are promoting nanoimprinting lithography for IC production but I really do not see this change happening in the next few years, unless some really huge technological breakthrough comes forward. It is true that for stepper technology costs are going up with the future adoption of EUV machines but I do not see any alternative to both immersion lithography and EUV. Maybe direct self-assembly will be useful as a complementary technology but still the main lithography process will be stepper based

Q: Being this the case, what do you think about the future of nanoimprint. Will you see nanoimprinting lithography as a niche market application in the future or there is some hope that nanoimprint will become the technology of choice in some bigger markets?

A: As I was saying before, I believe the future for nanoimprinting lithography is bright. The reason being that many markets that today are regarded as niche or even are yet to be tapped and will grow extensively in the future. Nanoimprinting lithography has a lot of advantages in terms of cost and easiness of process when you do not need high alignment capabilities and you have some tolerance in terms of defects: LED patterning, patterning of substrates for cell culture, production of anti-reflecting films are just some of the markets where nanoimprint can be applied easily. I believe that the existing markets I have just listed and other markets will grow exponentially in the next few years

Q: LED patterning and other potential applications have been discussed for quite a while but still we do not see nanoimprinting lithography widely used. Is there a reason for this?

A: One of the reasons has historically been that most of nanoimprint research has focused on replacing stepper technology for volume IC and DRAM production, a technological application nanoimprint is not really fit for. This misconception has led the industry to ignore other potential applications where nanoimprint could have been the technology of choice as such markets were still too small. On the opposite, I believe that the role of nanoimprint will be exactly that of making such niche market grow and create new exciting applications. Let` s take for example roll-to-rollnanoimprint. It is now possible to pattern literally square meters of polymer with a nanopattern at a cost that is orders of magnitude lower than other technologies. Same goes for LED patterning, nanoimprint can be successfully used to pattern sapphire substrates at a cost unmatched by conventional lithography. I believe such are the markets where we should focus on.

Q: You are talking about roll-to-roll nanoimprint. What is the status of this particular technology?

A: Roll-to-roll nanoimprint is a technology that has been plagued by a number of issues in the past, such as keeping the film flow at a constant rate and at a constant thickness. Keeping thickness variation control has especially been a challenge for wide films. However, I see such hurdles being overcome so I think roll-to-roll will be definitely be used in many applications that require to have polymer surfaces patterned at a low cost and in high quantities, such as in the anti-reflection film market for example.

Q: Thank you for your time

A: Thank you.

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Introduction to nano imprint lithography

nanoimprint lithography

Nano imprint (or nanoimprint) lithography, abbreviated as NIL, is a relatively old patterning technology which has gained traction in the last few years.

Nano imprint technology was introduced back in 1996 by Prof. Chou as an alternative fabrication method to traditional optical lithography.

Due to increasing costs with traditional optical lithography, the industry has been looking in the past few years for alternative technologies that may help fabricating micro and nano-patterns at a lower cost and high throughput: nano imprint lithography promises to deliver to users the ability to pattern at micro and nano-order without all the burden in terms of costs typically associated with optical technology.

The principle behind NIL is straightforward and simple: instead of using an optical mask to draw patterns on a substrate, the pattern is imprinted directly using a stamp which physical creates the pattern on the substrate by deforming the resist placed over the substrate and subsequently etching the part of substrate which need to be removed to create the pattern

Advantages of the technique are

  • Since NIL relies on deforming the polymer deposited on the substrate by physical means and not by optical exposure + etching, there are no issues about diffraction limits of the incoming light or beam scattering
  • NIL is a potentially very fast technique, the pattern needs to be imprinted using an imprint machine and this process can be repeated relatively fast and seamlessly for a number of times
  • Nano imprint lithography is a much cheaper alternative to optical lithography as it does not involve complex stepper machines but a much simpler imprint machine. The cost of the imprint machine itself is only a small fraction of the cost of a top-of-the-notch stepper
  • With nano imprint lithography, resolutions under 10 nm have been consistently achieved. No other patterning technology can reach this level of resolution at such low costs.
  • Master molds, used to imprint on substrates, can be manufactured with E-beam lithography and then used multiple times to imprint on substrates (up to thousands of times)
  • Possible to pattern large areas, patterning of 4″, 6″ and even 8″ wafers has been demonstrated, using roll-to-roll imprint, even larger areas can be imprinted on film
  • For the above reasons, NIL has been added by the International Technology Roadmap for Semiconductors (ITRS) for the 32 and 22 nm nodes.

Various users, as Toshiba, for example, have however shown the reliability of the technology for patterns lower than 22 mm

For historical reasons, many people associate NIL with hot embossing (or thermal nano imprint) due to the fact that the first iteration of the technology was about imprinting on a substrate heating it at relatively high temperature therefore softening the resist polymer and allowing it to deform according to the pattern drawn on the mold.

More recently, a new technology called UV-nano imprint has also gained strength: instead if using heat to deform the substrate, UV light is used.

The UV-curable polymer is deposited over the substrate and the deformation occurs by exposing it to UV-light

Apart from the two main processes (thermal nano imprint and UV-nano imprint), several other alternatives have been developed in the last few years: laser-assisted nano-imprint, roll-to-roll imprint process, reverse imprint lithography and others

Main applications of nano imprint lithography are: HDD platter patterning, sapphire substrate patterning for LED applications, biological devices such as cell-culture plates, optical elements patterning

However, due to the different technology involved, nano imprint has also several disadvantages and point of attention compared to traditional optical technology.

Disadvantages of the technique are

  • Alignment between the mold and the substrate is a critical aspect of the process. With nano imprint technology it is much more difficult to reach the required alignment between mold and substrate due to the inherent nature of the process
  • Defectivity on the mold is also a serious issue. Due to the direct contact between the mold and the substrate, even the small defect on the mold gets replicated into the substrate
  • Mold release from the substrate may be problematic, mold release may cause new defects on the mold and therefore there is the need of replacement of the mold every 100, 500 or 1000 imprints (depending on various process conditions)
  • Due to the fact that pattern transmission between mold and substrate is direct and not reduced as in stepper lithography, the masks used during nano imprint need to be more accurate than conventional optical lithography masks.

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