2015 PST Awardees

The Outstanding Achievement Award

The Photopolymer Science and Technology Award No.151100

Christopher K. Ober, Cornell University

The Photopolymer Science and Technology Award No.151100, the Outstanding Achievement Award 2015, was presented to Christopher Kemper Ober (Cornell University) for his outstanding achievements in photopolymer science and technology, “Development of new advanced photoresist for microelectronics”.


  Christopher K. Ober is the Francis Bard Professor of Materials Engineering, Materials Science and Engineering, Cornell University. He received B. Sc. (1978) degree in chemistry from the University of Waterloo, Canada, M. S. (1980) and Ph. D (1982) degrees in chemistry from the Department of Polymer Science & Engineering, University of Massachusetts, Amherst, joined the Department of Materials Science & Engineering, Cornell University in 1986, and was promoted a full professor in 2001. He has developed new F2 and ArF resists, block copolymers resists, and nanoparticle resists with excellent resolution and extremely high sensitivity. He was the President, IUPAC polymer division (2008-2011), and was named a Fellow of the American Chemical Society in 2009 and a Fellow of the American Association for the Advancement of Science in 2014.

The Best Paper Award 2015

The Photopolymer Science and Technology Award 152100

Dustin W. Janes1, Takejiro Inoue2,3, Bradley D. McCoy1, Ishita Madan1, Paul F. Nealey2, C. Grant Willson1 and Christopher J. Ellison1,

1. The University of Texas, 2. The University of Chicago, 3. Toray Industries

   The Photopolymer Science and Technology Award No. 152100, the Best Paper Award 2015, was
presented to Dustin W. Janes, Takejiro Inoue, Bradley D. McCoy, Ishita Madan, Paul F. Nealey, C. Grant Willson, and Christopher J. Ellison for their outstanding contribution published in Journal of Photopolymer Science and Technology, 27, (2014) 435-440, entitled “Photochemical Reactions for Replicating and Aligning Block Copolymer Thin Film Patterns”.

 

The Best Paper Award 2015

The Photopolymer Science and Technology Award 152200

Shinji Matsui1,5, Hiroshi Hiroshima2,5, Yoshihiko Hirai3,5 and Masaru Nakagawa4,5,

1. University of Hyogo, 2. National Institute of Advanced Industrial Science and Technology (AIST), 3. Osaka Prefecture University, 4. Tohoku University, 5. JST-CREST

   The Photopolymer Science and Technology Award No.152200, the Best Paper Award 2015, was presented to Shinji Matsui, Hiroshi Hiroshima, Yoshihiko Hirai, and Masaru Nakagawa, for their outstanding contribution published in Journal of Photopolymer Science and Technology, 27, (2014) 61-72, entitled “Breakthrough Achievement In Nanoimprint Lithography using PFP Condensable Gas”.

 

Their achievements are described below.

The Outstanding Achievement Award

The Photopolymer Science and Technology Award No.151100

Christopher K. Ober, Cornell University

 

  The Photopolymer Science and Technology Award No.151100, the Outstanding Achievement Award 2015, was presented to Christopher Kemper Ober (Cornell University) for his outstanding achievements in
photopolymer science and technology, “Development of new advanced photoresist for microelectronics”.


  Christopher K. Ober is the Francis Bard Professor of Materials Engineering, Materials Science and Engineering, Cornell University. He received B. Sc. (1978) degree in chemistry from the University of Waterloo, Canada, M. S. (1980) and Ph. D (1982) degrees in chemistry from the Department of Polymer Science & Engineering, University of Massachusetts, Amherst, joined the Department of Materials Science & Engineering, Cornell University in 1986, and was promoted a full professor in 2001. He has developed new F2 and ArF resists, block copolymers resists, and nanoparticle resists with excellent resolution and extremely high sensitivity. He was the President, IUPAC polymer division (2008-2011), and was named a Fellow of the American Chemical Society in 2009 and a Fellow of the American Association for the
Advancement of Science in 2014.


   Prof. Ober has engaged in development of many photoresists including F2, ArF, and EUV resists, and contributed to the progress of photopolymer science and technology as described below.
1. He has investigated photoresists that are processed in non-polar “orthogonal” solvents such as supercritical CO2 and hydrofluoroethers. Such resists undergo little pattern collapse because of the low surface energies of the developer.
2. Ober has pioneered the use of block copolymers (bcp) in photoresists, first investigating bcps for surface modifiers and etch-resistant additives for conventional photoresists as early as 1994. Subsequent studies have focused on the directed self-assembly (DSA) of new photoresist bcps in which one of the blocks is a highly sensitive crosslinkable unit and the other is easily removed. Ober’s goals include creating more lithographically sensitive bcps with a more easily removed sacrificial block, better long-range control, and creation of multiple ordered phases in a single block copolymer. Ober has developed unique block copolymer based on hydroxy styrene and -methylstyrene. In this work he has shown that solvent vapor annealing provides the ability to create longrange order. Using graphoepitaxy he has further established that microphase alignment can be introduced over long range. By combining with negative tone patterning and selected annealing solvents Ober and his group have shown that more than one pattern (lines and dots) can be created in a single layer bcp resist. Solvent annealing has also been used in a new system, the PMMA-blockpoly(hydroxyethyl methacrylate) bcp. Using mixed
solvents, Ober has shown that many microstructures are possible (sphere, cylinder, lamella and gyroid) from a single block copolymer and these structures can be easily trapped in the solid state. More recently his focus has been on block copolymers containing trifluoroethyl methacrylate blocks because of their great sensitivity.
3. Ober and his group have studied molecular glasses (MG) as possible replacements for polymer based photoresists. Their small size, amorphous (glassy) character, high Tg and good etch resistance make them very interesting for highresolution patterning. Ober and his group have created a number of chemically amplified MG materials based on calixarenes and novolac-like MGs. In addition, through collaborations with Japanese researchers he has explored MGs made from hexaphenyl benzene and noria. Using EUV patterning he has shown that high resolution (sub-30 nm) patterns with good LER values can be produced. Ober working with NIST researchers has also shown that the intrinsic LER of molecular glasses is better than a polymer photoresist, but that the development speed is extremely high. More recently he has explored molecular glass photoresists for pattering organic semiconductors
using the concept of orthogonal processing.
4. In recent work, Ober and his group have shown that metal oxide nanoparticles, 2 to 3 nm in size, can act as superb EUV photoresists and have excellent resolution and extremely high sensitivity (~3-5 mJ/cm2). These materials originally developed as additives to increase RI and etch resistance of conventional photoresists, these nanoparticles, made from zirconium or hafnium oxide, can be patterned as both negative and positive tone materials and do not involve chemical amplification. These nanoparticle resists are among the most sensitive materials tested to date under EUV conditions.

Currently Ober is working on understanding the fundamental photopatterning mechanism of these photoresists. Interestingly, the more transparent material is more sensitive and capable of the highest resolution (~20 nm) in contrast to current thinking on EUV resist design. 

 

 

The Best Paper Award 2015

The Photopolymer Science and Technology Award 152100

Dustin W. Janes1, Takejiro Inoue2,3, Bradley D. McCoy1, Ishita Madan1, Paul F. Nealey2, C. Grant Willson1 and Christopher J. Ellison1,

1. The University of Texas, 2. The University of Chicago, 3. Toray Industries

 

   The Photopolymer Science and Technology Award No. 152100, the Best Paper Award 2015, was
presented to Dustin W. Janes, Takejiro Inoue, Bradley D. McCoy, Ishita Madan, Paul F. Nealey, C. Grant Willson, and Christopher J. Ellison for their outstanding contribution published in Journal of Photopolymer Science and Technology, 27, (2014) 435-440, entitled “Photochemical Reactions for Replicating and Aligning Block Copolymer Thin Film Patterns”.

 

   Immersion 193-nm lithography is currently widely used at a commercial level. To extend its resolution further to finer patterns, several lithography candidates have been investigated. One leading candidate to replace 193-nm lithography for future nodes is extreme ultraviolet EUV lithography. However, insertion of EUV lithography into high volume manufacturing is delayed as it is still far from the current 193-nm lithography throughput due to difficulty in development of a sufficient 13.5-nm power source. DSA (directed self-assembly) has gained great attention as one of the next generation patterning technologies since it is simple and compatible with conventional lithography processes.
   DSA utilizes phase separated domains of block copolymers induced by molecular self-assembly as an etch mask. These domains show a range of shapes, including hexagonal close packed cylinders and lamellar stacks that resemble features such as hole and line and space structures present in today’s devices. The cylinder structures can be used for contact hole shrink processes due to the difficulty in direct patterning of small contact holes with acceptable CD (critical dimension) uniformity. However, chemical and/or physical guiding patterns are required for DSA of block copolymers into device oriented structures.

    Prof. Willson, Prof. Nealey, Prof. Ellison and their groups think that duplication steps based on transfer printing processes could address this problem by lessening the frequency at which relatively slow and/or expensive top-down techniques are employed. Replicas of original block copolymer patterns can be fabricated by transferring polymer to unpatterned substrates while they are in close, conformal contact. The transfer techniques involve the light exposure which activates covalent bonds between the replica substrate and block copolymer surface patterns.
    Liquid conformal layer materials containing photopolymerizable acrylates in contact with PS-PMMA DSA patterns are crosslinked by UV light, producing a network with pendant benzophenone and residual acrylate groups. Benzophenone is excited by UV exposure and can abstract hydrogen from both PS and PMMA blocks, creating free radicals at the abstraction site and benzophenone. Propagation of the free-radicals present in PS-PMMA to residual acrylate groups forms covalent bonds between the top surface of the PS-PMMA film and the conformal layer.
    Separation of the sample stack recovers the original guiding pattern as well as a new chemically patterned substrate replicated from the original pattern. The liquid, photopolymerizable conformal layer is employed so that the patterns are replicated continuously over large areas(>>1cm2). Using a single lithographically directed chemical pattern, 10 replicas were generated, each possessing 28 nm periodicity, perpendicularly oriented microdomains, and long-range epitaxial alignment.
    It should be noted that they have demonstrated the DSA pattern transfer with light exposure, where the transferred pattern size is far smaller than the wavelength of the exposure light. While they show the presence of some defects, the process has not cleanroom, which would likely reduce these defects. In essence, this technique is considered to be a nanopattern transfer method using contact printing and light-induced surface grafting technology. Since these photochemical printing methods have transferred nanopatterns 10 times successively, this study suggests that many high density patterns can be fabricated from lower density original patterns by combining this transfer techniques with
conventional DSA techniques.
    As described above, Prof. Willson, Prof. Nealey, Prof. Ellison and their groups have conducted fundamental and valuable research on the development of DSA technology that is important for future establishment in large scale integration.

 

 

The Best Paper Award 2015

The Photopolymer Science and Technology Award 152200

Shinji Matsui1,5, Hiroshi Hiroshima2,5, Yoshihiko Hirai3,5 and Masaru Nakagawa4,5,

1. University of Hyogo, 2. National Institute of Advanced Industrial Science and Technology (AIST), 3. Osaka Prefecture University, 4. Tohoku University, 5. JST-CREST

 

   The Photopolymer Science and Technology Award No.152200, the Best Paper Award 2015, was presented to Shinji Matsui, Hiroshi Hiroshima, Yoshihiko Hirai, and Masaru Nakagawa, for their outstanding contribution published in Journal of Photopolymer Science and Technology, 27, (2014) 61-72, entitled “Breakthrough Achievement In Nanoimprint Lithography using PFP Condensable Gas”.

 

   Nanoimprint lithography is an important fine-pattern fabrication technology that transfers nanoscale fine structures on a mold to polymer materials easily. Ultraviolet (UV) curing nanoimprinting allows the fabrication of the finest patterns under room temperature and low pressure with high throughput.
    Recently, electron beam lithography has achieved a fabrication resolution of several nanometers; however, its throughput is not suitable for mass production. In contrast, conventional printing technology has the advantage of good throughput but poorer fineness in pattern fabrication.
    Nanoimprint lithography solves both the resolution and throughput issues of conventional methods by taking the advantages of conventional technologies and presents the possibility of fine pattern fabrication with a feature size less than 22 nm.
    However, there remain several limitations to applying nanoimprint technology. For instance, there are urgent needs to eliminate defects due to bubble trapping, to make the thickness of the residual layer uniform and to improve the demolding process in industrial use.

    The present article proposes an advanced method of solving the above issues and verifies the performance of the method as follows.
1) Bubble defects and their elimination

In UV nanoimprint lithography, a UV transplant quartz mold is pressed onto a UV curable resist. In this step, air is trapped in the mold cavity and causes so-called bubble defects. To solve this problem, the authors proposed the use of condensable gas. The important feature of the gas is its condensation at a pressure slightly higher than atmospheric pressure. The gas 1,1,1,3,3-pentafluoropropane (PFP) is the most promising candidate since it is non-flammable, safe to use, and inexpensive, and has zero ozone depletion potential.
    Experiments show that bubble trapping is effectively eliminated under a low-pressure pressing condition without pollution agents and demonstrate the transfer of a fine pattern with a feature size of 45 nm.
2) Uniform thickness of the residual layer

A residual layer is formed after pattern transfer. There is a strong demand for thickness uniformity of the residual layer in lithographic applications. However, due to pattern density, the residual layer thickness is not always uniform. To solve this problem, the authors proposed the volute uniform mold of the pattern cavity and demonstrated its performance in UV nanoimprint lithography.
3) Smooth demolding

To prevent adhesion between the UV curable polymer and the mold, the mold surface is coated with an anti-sticking layer. However, long-term durability of the layer is hardly guaranteed for safe demolding without defects. The authors newly propose fluorosurfactants as an inner release agent for UV resists to help ensure a smooth release. Additionally, the effects of PFP gas, which assists demolding, are discussed according to the results of experimental investigations. The results suggest over 2000 demolding cycles can be performed without fatal defects or damage. Using synthetic UV resin, the 22-nm convex resist lines had a best value of LER(3σ) = 1.2 nm and the best value of LWR(3σ) = 1.8 nm, and over 20,000 repeated imprints were achieved with a single mold. Furthermore, a fluorescent UV-curable resin is proposed for the in-situ observation of imprinted patterns after demolding, allowing the quantitative evaluation of performance.
    The present article also reviews UV nanoimprint lithography and makes suggestions for next-generation UV nanoimprint technology aiming toward 22-nm lithography.