Photo Resists and Hard Masks
Advances in semi-conductor technology are directly related to the ability of photo-resist developers to create products that can be use to pattern circuits on silicon wafers with feature sizes down to 20nm and below. Photo-resists are typically made of polymers but the limits of polymer based systems are being reached most notably due to the molecular weight of the polymer. The next generation of photo-resists are known as molecular resists—where fullerenes have significant advantages to control feature size and resolution. The advantage is both inherent due to their <1nm size and uniform nature, their ability to be chemically functionalized, chemically bond in 3-dimensions, and high etch resistance due to their high carbon content.
To enable this progression of Moore’s Law, semi-conductor fabrication technology is expected to move to Extreme Ultra-Violet (EUV) lithography by 2016. Leading chip developers, such as Intel and Samsung, have invested several billion dollars in tool-maker ASML to accelerate the development of EUV technology. Likewise, Nano-C has formed an alliance with Irresistable Materials which is now working with development partners to accelerate the growth of fullerene based resists for use in EUV lithography. The fullerene-based EUV resist chemistry work was presented at the 2013 SPIE Advance Lithography Meeting held in San Jose; a clear demonstration of leading edge performance for the key EUV metrics of Resolution, Sensitivity and Line Edge Roughness.
Fullerene-based Spin-on-Carbon (SOC) hard-masks are frequently used to improve the photo-resists’ selectivity to silicon during plasma etching. Furthermore, as chip architectures become increasingly complex the use of hard-masks to improve the aspect ratio of features in silicon is critical. For many emerging multi-layer chip architectures, such as tri-layer etch-stacks , a large height to width ratio is required to maintain small lateral features (see figure below).
Nano-C’s SOC hard-mask is uniquely suited to this task due to the fullerene’s high etch durability in fluorine based ICP plasma etching. This is derived from their high carbon content. In addition, they have high temperature stability that exceeds 450 °C.
Nano-C, Irresistable Materials and their development partners have demonstrated 20nm pattern transfer at aspect ratios of 10:1. Development work continues to achieve sub-20 nm patterns with aspect ratios significantly greater than 20:1. These novel SOCs will lead to reduced energy consumption in chip manufacture (replacing energy intensive CVD), but more importantly will enable high efficiency FinFET/Trigate architectures and thus low power consumption in computing. The chemistry and exceptional performance of the fullerene based spin-on-carbon hard-mask was presented at the 2013 SPIE Advance Lithography Meeting held in San Jose.
Photo-detectors and photo-voltaics
Source: Janssen, et al, MRS Bulletin 1/2005
Pictured here is a schematic of a single layer Organic Solar Cell. The fullerene acts as the n-type semiconductor (electron acceptor). The n-type is used in conjunction with a p-type polymer (electron donor) like polythiophene. They are blended and cast as the active layer to create what is known as a bulk heterojunction. Fullerenes are used on their own or derivitized to increase their solubility and modify their electronic properties. The most commonly used fullerene derivatives in OPV applications are C60 and C70 PCBM, patented compounds, for which Nano-C has an exclusive license. As the preferred n-type material, fullerenes can comprise up to 75% of the active layer by weight. The potential for increasing device efficiency through novel fullerene chemistries continues to expand. For example, alternative derivatives such as C60 ICBA and C60 OQDM have been shown to increase conversion efficiency by over 40% when compared to C60 PCBM in like systems (see E. Voroshazi et al., J. Mater. Chem. 2011, 21, 17345-17352; He, et al., 10/2009, and earlier work by Laird et al (USPTO 8,217,260)).
Device performance continues to increase, and the field continues to attract investment from large and small companies alike. Where cell efficiencies were 5% in 2005, they have since increased to 12% in 2013. The OPV field now includes Eight19, Heliatek, New Energy Technologies, Plextronics, Inc., Solarmer Energy, Inc., and Solar-Press. And in addition, larger companies are investing in this field on their own as well as in joint projects; among them are BASF, Bosch, Merck, Mitsubishi Chemical, and Phillips66. With the high levels of commercial and academic research, we will continue to see gains in efficiency and lifetime. Combined with roll-to-roll fabrication, grid-competitive organic solar power is within reach. The sheer magnitude of OPV’s potential (“an effectively infinite series of polymer solar cells”) was recently demonstrated by F.C. Krebs et al in Denmark (see Energy Technol., 2013. 1, 15-19.)
Organic Photo-detectors (OPD) are light-sensing devices that can be used in applications that range from motion control to medical imaging. Like OPV, they can be thin, light-weight, flexible, printable, and low-cost. Conventional detectors are typically made from silicon-based semi-conductors, and therefore use vacuum deposition processes typically at elevated temperatures. In contrast, OPD’s manufacturing processes are based on low-temperature, atmospheric and solution-based printing on glass or plastic substrates. Developers of OPD include ISORG, NikkoIA SAS and Siemens along with research institutes such as IMEC among others. In addition, companies such as GE and Universal Displays are working to integrate these types of detectors into their devices.
The performance of polymer transistors (Organic Field Effect Transistors (OFETS)) has also been increasing, in part due to a great deal of synergy between OFETS and OPVs. The leading OFETS use the n-type semiconducting properties of fullerenes based on C60, C70 along with C84. Fullerene OFETS fabricated with C84 show greater mobility than C60 or C70 and exhibit greater stability. While more work is needed, the world of polymer electronics is opening up for both fullerenes and single-walled carbon nanotubes.
Antioxidants & Biopharmaceuticals
Fullerenes are powerful antioxidants, reacting readily and at a high rate with free radicals, which are often the cause of cell damage or death. Fullerenes hold great promise in health and personal care applications where prevention of oxidative cell damage or death is desirable, as well as in non-physiological applications where oxidation and radical processes are destructive (food spoilage, plastics deterioration, metal corrosion).
Major pharmaceutical companies are exploring the use of fullerenes in controlling the neurological damage of such diseases as Alzheimer's disease and Lou Gehrig's disease (ALS), which are a result of radical damage. Drugs for atherosclerosis, photodynamic therapy, asthma and anti-viral agents are also in development.
Fullerenes are known to behave like a "radical sponge," as they can sponge-up and neutralize 20 or more free radicals per fullerene molecule. They have shown performance 100 times more effective than current leading antioxidants such as Vitamin E.
Nano-C has also conducted a limited series of screening tests for toxicity with a fullerene derivative formulated for lipid solubility. These preliminary tests for ocular tissue toxicity indicate no adverse effects. The picture to the left shows the high level of solubility in almond oil.
Additives & Other
Fullerenes and fullerenic black are chemically reactive and can be added to polymers and elastomers to create new copolymers with specific physical and mechanical properties. For example, adding small amounts to epoxy composites substantially increases fracture toughness. Much work has been done on the use of fullerenes as polymer additives to modify physical properties and performance characteristics.
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