Browsing by Subject "Photobase generator"
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Item Catalysis and materials development for photolithography(2014-08) Mesch, Ryan Alan; Willson, C. Grant, 1939-; Keatinge-Clay, Adrian; Ellison, Christopher; Rose, Michael; Stevenson, KeithIn recent years the microelectronics industry as found itself at an impasse. The tradition pathway towards smaller transistors at lower costs has hit a roadblock with the failure of 157 nm lithography and the continued delays in 13.5 nm extreme ultra violet light sources. While photolithography has been able to keep pace with Moore’s law over the past four decades, alternative patterning technologies are now required to keep up with market demand. The first section of this dissertation discusses the new resolution enhancement technique develop in the Willson lab termed pitchdivision. Through the incorporation of specifically tailored photobase generators (PBGs) into commercially available resists, the resolution of current 193 tools may be doubled. Special two-stage PBGs were designed and synthesized to increase the image fidelity of pitchdivision patterns. The next project deals with the design, synthesis, and evaluation of resists that find amplification through unzipping polymers. An aromatizing polyester polymer that acts as dissolution inhibitor in novolac and is inherently sensitive to 13.5 nm exposure is discussed. Initial results show excellent sensitivity and promise towards a new class of EUV resists.Item Design and development of base-catalyzed materials for microelectronics applications(2016-08) Dick, Andrew R.; Willson, C. Grant, 1939-; Ellison, Christopher J.; Freeman, Benny; Mack, Chris; Ho, Paul SMost lithographic processes in the microelectronics industry rely on the use of processes catalyzed by photochemically generated acids. The generation of organic bases photochemically is much less common, but allows for design of new resolution enhancement techniques and packaging materials. The microelectronics industry has been able to continue its path toward smaller transistors for several decades, but recently 157 nm and EUV lithography processes have faced delays. Alternative strategies such as double patterning are now required to keep the pace of scaling and they greatly increase manufacturing costs. This dissertation discusses a resolution enhancement technique termed pitchdivision designed to extend 193 nm lithography. This process depends on addition of a photobase generator (PBG) to commercial photoresists that enables printing of both positive and negative features, effectively doubling resolution. Using PBGs that require two separate photochemical events to generate base allows for improved image quality over standard PBGs. The use of PBGs in photosensitive polyimide packaging materials is also detailed. In packaging of integrated circuits, there is a need for an insulating material having low dielectric constant that provides support for the wires connecting the silicon chip to the circuit board. Aromatic polyimides meet many of the integration requirements, and can be patterned using PBGs in a base-catalyzed process. However, the UV absorbance of such materials is too high for thick films. The fluorinated polyimide pyromellitic dianhydride-co-2,2’-bis(trifluoromethyl)benzidine (PMDA-TFMB) was therefore auditioned for this use. PMDA-TFMB was printed using 365 nm lithography using near-UV PBGs and achieved resolution as small as 2.5 μm. This material was found to have a dielectric constant around 3.0, and a coefficient of thermal expansion of 6 ppm/K. Further work on the system sought to improve both material properties and lithographic patterning. The use of alternative monomers was explored. New PBGs capable of producing stronger amidine bases were also synthesized and used to cure PMDA-TFMB. Finally, the discovery of new catalysts for low temperature curing of polyimides is described. These materials include organic and inorganic salts that allow for the complete curing of polyimides below 200°C. The material properties of films cured with these catalysts are described.Item Design and development of material-based resolution enhancement techniques for optical lithography(2011-08) Gu, Xinyu; Willson, C. G. (C. Grant), 1939-The relentless commercial drive for smaller, faster, and cheaper semi-conductor devices has pushed the existing patterning technologies to their limits. Photolithography, one of the crucial processes that determine the feature size in a microchip, is currently facing this challenge. The immaturity of next generation lithography (NGL) technology, particularly EUV, forces the semiconductor industry to explore new processing technologies that can extend the use of the existing lithographic method (i.e. ArF lithography) to enable production beyond the 32 nm node. Two new resolution enhancement techniques, double exposure lithography (DEL) and pitch division lithography (PDL), were proposed that could extend the resolution capability of the current lithography tools. This thesis describes the material and process development for these two techniques. DEL technique requires two exposure passes in a single lithographic cycle. The first exposure is performed with a mask that has a relaxed pitch, and the mask is then shifted by half pitch and re-used for the second exposure. The resolution of the resulting pattern on the wafer is doubled with respect to the features on the mask. This technique can be enabled with a type of material that functions as optical threshold layer (OTL). The key requirements for materials to be useful for OTL are a photoinduced isothermal phase transition and permeance modulation with reverse capabilities. A number of materials were designed and tested based on long alkyl side chain crystalline polymers that bear azobenzene pendant groups on the main chain. The target copolymers were synthesized and fully characterized. A proof-of-concept for the OTL design was successfully demonstrated with a series of customized analytical techniques. PDL technique doubles the line density of a grating mask with only a single exposure and is fully compatible with current lithography tools. Thus, this technique is capable of extending the resolution limit of the current ArF lithography without increasing the cost-of-ownership. Pitch division with a single exposure is accomplished by a dual-tone photoresist. This thesis presents a novel method to enable a dual-tone behavior by addition of a photobase generator (PBG) into a conventional resist formulation. The PBG was optimized to function as an exposure-dependent base quencher, which mainly neutralizes the acid generated in high dose regions but has only a minor influence in low dose regions. The resulting acid concentration profile is a parabola-like function of exposure dose, and only the medium exposure dose produces a sufficient amount of acid to switch the resist solubility. This acid response is exploited to produce pitch division patterns by creating a set of negative-tone lines in the overexposed regions in addition to the conventional positive-tone lines. A number of PBGs were synthesized and characterized, and their decomposition rate constants were studied using various techniques. Simulations were carried out to assess the feasibility of pitch division lithography. It was concluded that pitch division lithography is advantageous when the process aggressiveness factor k₁ is below 0.27. Finally, lithography evaluations of these dual-tone resists demonstrated a proof-of-concept for pitch division lithography with 45 nm pitch divided line and space patterns for a k₁ of 0.13.Item Photocrosslinkable nonlinear optical polymers and directly-patternable polyimide dielectrics(2014-08) Bell, William Kenneth, III; Willson, C. Grant, 1939-; Ellison, Christopher; Anslyn, Eric; Ho, Paul; Keatinge-Clay, Adrian; Rose, MichaelThe development of high-efficiency nonlinear optical (NLO) polymers has opened up many opportunities in the field of electro-optics. However, current NLO polymers do not meet stability requirements for semiconductor integration. In an effort to improve this, we examined the effects of crosslinking following electric field poling. A series of photocrosslinkable polymers bearing side chain chromophores was synthesized, poled and evaluated on the basis of the thermal stability of Second Harmonic Generation. Photoinitiation allowed for control of the onset of curing. Crosslinking was monitored by FTIR and optimal conversion was achieved by applying a slow temperature ramp during exposure. The ultimate stability of the poled polymers was directly related to the number of crosslinking substituents attached to the chromophore pendant group. With two reactive groups per chromophore significant SHG was retained at temperatures beyond the polymer Tg. In integrated circuit packaging there is a need for directly-patternable polymers of low dielectric constant. Bridging the gap between the high-value silicon chip and circuit board is a substrate comprising alternating layers of metal conductor and polymer dielectric. PMDA-ODA, an aromatic polyimide, meets many of the requirements for integration and can be patterned using a photobase generator (PBG). Due to absorbance by the PMDA-ODA precursor, this PBG must have activity at visible wavelengths. Several oxime urethanes were synthesized and evaluated as candidate long wavelength PBG. These compounds exhibit clean photochemistry and high visible light sensitivity. Unfortunately, carbamate thermal stability is insufficient for patterning PMDA-ODA. For improved material properties, PMDA-TFMB, a fluorinated polyimide, was also evaluated. Importantly, the polymer precursor is sufficiently transparent to employ thermally-stable near-UV photobases. With photobase, 2.5 micron features were resolved in PMDA-TFMB. An ancillary benefit of this methodology is reduced cure temperature (~200 °C), a traditional drawback of polyimides. This material demonstrates a dielectric constant near 3 and a thermal expansion coefficient (CTE) of approximately 6 ppm/°C in-plane. Through-plane thermal expansion is somewhat problematic, with a CTE of approximately 160 ppm/°C, and will likely require a nanoparticle composite strategy. However, this combination of material and lithographic properties make PMDA-TFMB a promising candidate for this application.