About Us > Faculty & Staff > Faculty > Robert Brainard
Professor of Nanoscience
Dr. Robert Brainard Discusses Nanoscience at CNSE
Watch Professor Brainard's "Inside CNSE" video interview on the use of extreme ultraviolet (EUV) photoresists in making computer chips
- Ph.D. (Organic Chemistry), Massachusetts Institute of Technology, 1985
- B.S. (Chemistry), University of California, Berkeley, 1979
- Extreme ultraviolet (EUV, 13.4 nm) photoresist exposure mechanisms
- High quantum efficiency EUV photoresists
- Non-outgassing acetal blocking groups and polymers
- 193nm blocking groups and polymers
- New photoacid generator (PAG) chemistry
- 193i shrink technology
- Acid amplifiers
Dr. Brainard's research is concerned with the design, synthesis and characterization of new molecules and polymers for their use in nanotechnology. His projects are equally divided between those involving the synthesis of new compounds and those involving characterizing the functionality of these new materials in chemical systems relevant to nanotechnology.
Much of this research is focused on applications important to the electronics industry: Photoresists, Photoacid Generators, Shrink Technology, Acid Amplifiers. Since the 1970s, this fast-paced industry has been able to double the speed of computers every eighteen months. These technological advances are only made possible by the equally rapid pace of invention and discovery in these important chemical systems.
EUV Exposure Mechanisms. In order to make EUV technology economically viable, EUV resists will need to make dramatic improvements in sensitivity, LER and resolution. In his 2004 SPIE paper, Dr. Brainard and coworkers defined the quantum efficiency of photoresists as the ratio between the number of acid molecules generated during exposure and the number of photons absorbed. The authors investigated the quantum efficiency of EUV-2D to better understand the mathematical relationships between the numbers of photons, numbers of acid molecules and LER. The resulting quantum efficiency for EUV-2D is 2.08. While this quantum efficiency is impressive, higher quantum efficiency may be required for resists reaching the target sensitivity, LER and resolution goals. A simple comparison between the energy of a single EUV photon with the energy required to activate each PAG molecule indicates that there is enough energy in an EUV photon to activate 20-30 PAGs. Dr. Brainard's group is pursuing mechanistic and material studies directed at increasing quantum efficiency of EUV resists. This may be the best way to create EUV resists capable of meeting sensitivity and LER resist goals.
Non-Outgassing Acetal Blocking Group Chemistry. One of the most important components of any photoresist is the chemical reaction that differentiates the developer solubility properties of the exposed region of the resist from the unexposed regions of the resist. This chemistry is particularly interesting in the case of chemically amplified positive and negative resists. Both Extreme Ultraviolet (EUV) Lithography and Immersion 193nm Lithography (193i) are vying for the 32nm node on the electronics industry's roadmap. The success of these technologies will, in a large part, depend upon the availability of photoresists to deliver performance in four critical areas:
- Sensitivity (Photospeed)
- Post Exposure Delay (PED)
- Outgassing/Immersion Fluid Contamination
Most EUV resists are "high-temperature" resists and are baked after exposure (Post-Exposure Bake or PEB) at 100-130 ºC, but "low-temperature" resists also exist and can use PEB temperatures as low as 25 ºC. Currently, the photoresist with the best EUV resolution and lithographic performance is IBM's low-temperature KRS resist. The inventors of KRS have argued that the diffusion of photogenerated acid in high-temperature resists blur the aerial image of the light during exposure and thereby severely limit resolution. Further, they argue, the low temperature reactivity of the KRS resists allow for less acid diffusion and better resolution. However, despite the excellent resolution properties of the low-temperature KRS resists, they have a drawback known as outgassing. When the chemical transformation occurs during exposure, small molecules are produced during exposure that can be released and can contaminate the very sensitive optics of the multimillion dollar stepper. Dr. Brainard's group is interested in developing a high-resolution, low-temperature photoresist that will not outgas. Similarly, we are interested in developing a low-temperature 193i polymer that will not eliminate molecules that will contaminate immersion fluids.
New PAG Chemistry. Photoacid Generators (PAGs) are at the heart of every chemically amplified resist. While the electronics industry has been well served by three basic types of PAG classes (Onium, Imide, and Diazo), there are other types of PAG classes that could be developed based on a simple set of assumptions. Dr. Brainard's group will investigate the design, synthesis and evaluation of new types of PAG molecules.
193 nm Shrink Technology. One of the biggest challenges to optical lithography is imaging dense arrays of contact holes. As the diameter of these holes diminish, the focus latitude and process window decreases. One solution is to image the contact holes at larger sizes (to get acceptable process windows), then shrink the contact holes with subsequent chemical treatment. Although chemical processes for shrinking contact holes is known, they suffer from disadvantages such as thickness loss, decrease in throughput and pitch sensitivity. Dr. Brainard's group will explore new chemical approaches to solve this critical problem.
Acid Amplification. Photogenerated Acid is an extremely important component to all high resolution resists used to manufacture state of the art electronic devices. A class of compound, known as acid amplifiers, have been shown to autocatalyically generate acid. In theory, chemicals of this sort could bring many benefits to photoresists. However, in practice, the acid amplifiers that have been developed, are either unstable or generate only weak acids. Dr. Brainard's group is interested in developing stable acid amplifiers that generate strong acids.
Thomas Köhler, Robert L. Brainard, Patrick P. Naulleau, David Van Steenwinckel, Jeroen H. Lammers, Kenneth A. Goldberg, Joseph F. Mackevich, and Peter Trefonas Performance of EUV Photoresists on the ALS Micro Exposure Tool, Proceedings of SPIE 2005, 5753, pp 754-764.
Koehler, Thomas; Brainard, Robert L.; Naulleau, Patrick P.; Lammers, Jeroen H.; Steenwinckel, David Van; Goldberg, Kenneth A.;Mackevich, Joseph F.; Trefonas, Peter; Performance of EUV Photoresists on the ALS Micro Exposure Tool, 3rd International EUVL Symposium 2004.
Chandhok, Manish; Cao, Heidi; Wang, Yueh; Gullikson, Eric M.; Brainard, Robert L.; Robertson, Stewart A. Techniques for directly measuring the absorbance of photoresists at EUV wavelengths. Proceedings of SPIE (2004), 5374, 861-868.
Brainard, Robert L.; Trefonas, Peter; Lammers, Jeroen H.; Cutler, Charlotte A.; Mackevich, Joseph F.; Trefonas, Alexander; Robertson, Stewart A. Shot noise, LER, and quantum efficiency of EUV photoresists. Proceedings of SPIE (2004), 5374 (Pt. 1), 74-85.
Brainard, Robert L.; Cobb, Jonathan; Cutler, Charlotte A. Current status of EUV photoresists. Journal of Photopolymer Science and Technology (2003), 16(3), 401-410.
Cutler, Charlotte A.; Mackevich, Joseph F.; Li, Jieming; O'Connell, Donna J.; Cardinale, Gregory F.; Brainard, Robert L. Effect of polymer molecular weight on AFM polymer aggregate size and LER of EUV resists. Proceedings of SPIE (2003), 5037, 406-417.
Cobb, Jonathan L.; Brainard, Robert L.; O'Connell, Donna J.; Dentinger, Paul M. EUV lithography: patterning to the end of the road. Materials Research Society Symposium Proceedings (2002), 705, 91-100.
Brainard, Robert L.; Barclay, George G.; Anderson, Erik H.; Ocola, Leonidas E. Resists for next generation lithography. Microelectronic Engineering (2002), 61-62 707-715.
Brainard, Robert L.; Guevremont, Jeffrey M.; Reeves, Scott D.; Zhou, Xin; Nguyen, Thinh B.; Mackevich, Joseph F.; Taylor, Gary N.; Anderson, Erik H. Multiple anion nonvolatile acetal (MANA) resists. Journal of Photopolymer Science and Technology (2001), 14(4), 531-542.
Brainard, Robert L.; Henderson, Craig; Cobb, Jonathan; Rao, Veena; Mackevich, Joseph F.; Okoroanyanwu, Uzodinma; Gunn, Scott; Chambers, Janet; Connolly, Susan. Comparison of the lithographic properties of positive resists upon exposure to deep- and extreme-ultraviolet radiation. Journal of Vacuum Science & Technology, B: (1999), 17(6), 3384-3389.
Szmanda, Charles R.; Brainard, Robert L.; Mackevich, Joseph F.; Awaji, Akira; Tanaka, Tsutomu; Yamada, Yutaka; Bohland, John; Tedesco, Serge; Dal'Zotto, Bernard; Bruenger, Wilhelm; Torkler, Michael; Fallmann, Wolfgang; Loeschner, Hans; Kaesmaier, Rainer; Nealey, Paul M.; Pawloski, Adam R. Measuring acid generation efficiency in chemically amplified resists with all three beams. Journal of Vacuum Science & Technology, B: (1999), 17(6), 3356-3361.
Rao, Veena; Cobb, Jonathan L.; Henderson, Craig C.; Okoroanyanwu, Uzodinma; Bozman, Dan R.; Mangat, Pawitter J. S.; Brainard, Robert L.; Mackevich, Joseph. Ultrathin photoresists for EUV lithography. Proceedings of SPIE (1999), 3676, 615-626.
Brainard, Robert L.; Madix, Robert J. Enhanced stability of t-butanol reaction intermediates on oxygen covered copper(110): cleavage of unactivated carbon-hydrogen bonds on metal surfaces. Surface Science (1989), 214(3), 396-406.
Brainard, Robert L.; Peterson, Cynthia G.; Madix, Robert J. Surface-mediated isomerization and oxidation of allyl alcohol on copper(110). Journal of the American Chemical Society (1989), 111(13), 4553-61.
Brainard, Robert L.; Madix, Robert J. Oxidation of tert-butyl alcohol to isobutylene oxide on a silver(110) surface: the role of unactivated carbon-hydrogen bonds in product selectivity. Journal of the American Chemical Society (1989), 111(11), 3826-35.
Brainard, Robert L.; Nutt, W. Rodger; Lee, T. Randall; Whitesides, George M. Intermolecular activation of carbon-deuterium bonds in benzene-d6 by trans-neopentyl(trifluoromethanesulfonato)bis-(trimethylphosphine)
platinum(II). Organometallics (1988), 7(11), 2379-86.
Brainard, Robert L.; Madix, Robert J. Oxidation of tert-butyl alcohol to isobutylene oxide: rate-limiting carbon-hydrogen activation by a Ag(110) surface. JACS (1987), 109(26), 8082-3.
Brainard, Robert L.; Miller, Timothy M.; Whitesides, George M. Mechanisms of thermal decomposition of trans-chloroneopentylbis(tricyclopentylphosphine)-platinum(II). Organometallics (1986), 5(7), 1481-90.
Brainard, Robert L.; Whitesides, George M. The mechanism of thermal decomposition of trans-chloroethylbis(triethylphosphine)platinum(II). Organometallics (1985), 4(9), 1550-7.
Whitesides, George M.; Reamey, Robert H.; Brainard, Robert L.; Izumi, Alan N.; McCarthy, Thomas J. Organometallic reactions of platinum involving metallic hydrides. Annals of the New York Academy of Sciences (1983), 415, 56-66.
Brainard, Robert L. Novel polymers and photoresist compositions comprising same. United States Patent 6,492,087, 2002.
Szmanda; Charles R. Taylor; Gary N.; Brainard; Robert L.; DoCanto; Manuel; Photoresist Compositions; United States Patent 5,876,899; 1999.
Taylor, Gary N.; Brainard, Robert L.; Yamada, Shintaro. Novel polymers and photoresist compositions for short wavelength imaging. PCT Int. Appl. (2002), 31 pp.
Brainard, Robert L.; Szmanda, Charles R. Chemically amplified photoresist composition for imaging with high-energy radiation, manufacture of relief image using it, and product having the relief image. Jpn. Kokai Tokkyo Koho (2002), 42 pp.