Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session Y14: Focus Session: Supercritical Carbon Dioxide Processing |
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Sponsoring Units: FIAP Chair: Shubhra Gangopadhyay, U of Missouri Room: LACC 403 B |
Friday, March 25, 2005 11:15AM - 11:51AM |
Y14.00001: Supercritical Fluid Technology for Interconnect Fabrication Invited Speaker: Supercritical fluids (SCFs) offer a unique technology platform for semiconductor devices. The absence of surface tension, favorable transport properties and densities that approach those of liquids provide a means for solution-based processes in an environment that behaves much like a gas. These attributes are ideally suited for executing materials chemistries within the smallest device features. This talk will describe the motivation for SCF-based processes and survey potential applications including the deposition of metals including Cu, Ru, and Co, and the etching of metal oxides. Particular attention will be paid to the rapid and efficient preparation of ordered, mesoporous ultra-low dielectric constant (ULK) organosilicate films by the three dimensional replication of structured organic templates in supercritical carbon dioxide. These ULK films are sufficiently robust to survive CMP. [Preview Abstract] |
Friday, March 25, 2005 11:51AM - 12:27PM |
Y14.00002: Development of Supercritical Processing in BEOL Cleans Invited Speaker: Supercritical CO$_{2}$-based (SC-CO$_{2})$ processing permits rapid mass transport, high penetration capability into pores and narrow features, low reagent concentrations, and an environmentally benign alternative to current back end cleans---key issues in future semiconductor technology nodes. Because of these assets, supercritical processing is a candidate for a number of semiconductor cleans applications such as plasma damage repair, pore sealing, photoresist/BARC removal and metal deposition. Plasma processing of porous low-k films often remove surface layers and hydrophobic functional groups (creating silanol (Si-OH) species), densify near-surface layers, and increase dielectric constants. Further, this damaged region is vulnerable to additional thickness losses during wet etch. Supercritical silylation reactions (e.g., SC-CO$_{2}$ + hexamethyldisilazane (HMDS)) have been shown to react with post-plasma silanols replacing some fraction of the lost hydrophobic groups, thus, repairing the dielectric constant. We have examined the depth of reactant penetration into the low-k and the fraction of silylated silanols as functions of temperature, pressure, pore size, and silylating agent (e.g., HMDS and alkylchlorosilanes). In addition, we have detailed the effect of heat treatments on pre- and post-silylated silanols, and the impact of these heat treatments on film dielectric constants. Recent efforts have shown that supercritical silylation reactions protect plasma-damaged regions from wet etch losses and prevent intrusion of metal species into low-k pores. We have examined damage protection as functions of ashing conditions, silylating agents, and wet etch conditions. Pore sealing has been studied as functions of silylating agent, heat treatment, and penetrant species. [Preview Abstract] |
Friday, March 25, 2005 12:27PM - 12:39PM |
Y14.00003: Supercritical Fluid Research Capabilities and Collaborations at Los Alamos National Laboratory Kirk Hollis, Jerry Barton, Craig Taylor, Laurie Williams, Melvin Carter The supercritical fluids facility (SCRUB) at Los Alamos National Laboratory is a unique research center with a history of successful collaboration with the industrial sector. This presentation will focus on one of these collaborations with DuPont EKC Technology in the continuing development of Supercritical Carbon DiOxide Resist Removal (SCORR). This research has studied co-solvents that effectively remove photoresist from integrated circuit wafers. The technical capabilities of the SCRUB include small-scale equipment, 1-20 ml, up to industrialized pilot scale processes. Initial work focused on the phase behavior of binary mixtures using a small volume (20ml) view cell. A series of SCCO$_{2}$ /co-solvent phase diagrams were investigated over ranges of pressure, temperature and concentration variables. Mixtures of interest were scaled to a 500ml vessel to test removal effectiveness, keeping the conditions (pressure / temperature) within the single phase region during the pulsing process of SCORR. Results from these tests are used to finalize conditions for pilot scale test on 200mm wafers in a 10L vessel. Selected results from all steps will be presented to emphasize the R{\&}D process. [Preview Abstract] |
Friday, March 25, 2005 12:39PM - 12:51PM |
Y14.00004: SCORR - Supercritical Carbon Dioxide Resist Removal Craig Taylor, Jerry Barton, Kirk Hollis, Jim Rubin, Laurie Williams Supercritical Carbon diOxide Resist Removal, SCORR, is an emerging technology that may enable the further miniaturization of photolithography processes in industry. SCORR utilizes the physical properties of supercritical fluids (SCFs) to remove coatings, residues, and particles from the high-aspect-ratio and small minimal dimension structures required in modern integrated circuits. In the SCORR process, it is the diffusion of the SCF into the polymer and the resultant swelling that is utilized to debond materials from the surface. By ``tuning'' with pressure, temperature and modifier the SCF is more readily absorbed into the photoresist. This plasticizes the polymer and lowers its glass transition temperature maximizing polymer swelling. Subsequent pressure ``pulsing'', forces a rapid volume expansion effectively debonding the polymer from the substrate. Small amounts of modifier may be added to act at the polymer/substrate interface to further enhance debonding. To optimize the swelling and pulsing steps, a single supercritical phase needs to be maintained. The minimal interfacial tension of SCFs results in a surface boundary layer flow condition that allows the fluid to then remove extremely small particles and residue layers. [Preview Abstract] |
Friday, March 25, 2005 12:51PM - 1:03PM |
Y14.00005: Supercritical CO2 for Resist Development: Towards an All-Dry Lithography Process Nelson Felix, Yu (Jessie) Mao, Karen Gleason, Christopher Ober The increased use of organic solvents, halogenated solvents, and water in manufacturing and processing of ICs has led to a need of environmentally responsible and energy efficient processes. Alternatives to the previously mentioned solvents have been researched and one possibility is supercritical carbon dioxide (scCO$_{2})$. It has been well established that by adding a small volume of polar solvents (also called co-solvents) to an scCO$_{2}$ mixture, the solubility of a polar solute in scCO$_{2}$ can dramatically increase. This fact makes scCO$_{2}$ technology extremely attractive as an alternative solvent for lithography. Various resist platforms were tested to demonstrate their ability to be developed in CO$_{2}$. These include copolymers of functionalized methacrylates or phenolics with perfluorooctyl methacrylates, homopolymers of functionalized methacrylates, and novel small molecule resists. Films were either deposited via spin-coating or hot filament chemical vapor deposition (Gleason Group, MIT). Depending on the resist system, features on the order of 100 nm were obtained after development in scCO$_{2}$. [Preview Abstract] |
Friday, March 25, 2005 1:03PM - 1:15PM |
Y14.00006: Effect of Ionic Conductivity of Elevated Pressure TMAHCO3 /MeOH/CO2 Mixtures on Cleaning Efficiency Galit Levitin, Dennis W. Hess Carbon-dioxide (CO$_{2\_}$based elevated pressure cleaning mixtures are being considered as environmentally benign alternatives for photoresist and plasma etch residue removal in integrated circuit and microelectronic device manufacture. Despite many attractive features, CO$_{2}$ is non- polar and has little solvating power for photoresist or inorganic materials. Therefore, addition of polar modifiers is necessary. Addition of tetramethylammonium bicarbonate (TMAHCO$_{3})$ in methanol to CO$_{2}$ at elevated pressure and temperature (3000 psi, and 70\r{ }C) efficiently removes photoresist and post plasma etch residues. Our previous studies of the phase behavior of various cleaning mixtures have demonstrated that the cleaning phase state significantly affects cleaning effectiveness. In this work, measurements of ionic conductivity of elevated pressure cleaning solutions was studied to gain insight into the chemical-physical properties of TMAHCO$_ {3}$ /methanol/CO$_{2}$ mixtures, and the resulting effect on residue removal efficiency. Ionic conductivity of cleaning mixture gives information on both the behavior of ions in the mixture and the solvation properties of the fluid medium. This work discusses the characterization of the TMAHCO$_{3}$ /methanol-modified fluids by measuring the ionic conductivity as a function of concentration and mole fraction of CO$_{2}$ at various temperatures and pressures. The ionic conductivity displays a strong dependence on the dielectric properties of the fluid medium. [Preview Abstract] |
Friday, March 25, 2005 1:15PM - 1:27PM |
Y14.00007: Atomic Layer Deposition of High-k Dielectrics Using Supercritical CO$_2$ Rajesh Shende, Jorge Lubguban, Maslina Othman, Shubhra Gangopadhyay Atomic layer deposition (ALD) of high-$\kappa $dielectric was performed in supercritical CO$_{2}$ (SCCO$_{2})$, using a two-step reaction sequence.~~ In step one, tetraethoxy silane (TEOS) precursor was injected in SCCO$_{2}$ at 80-100\r{ }C and 50 MPa pressure to obtain a chemisorbed surface monolayer, which was then oxidized into SiO$_{2 }$using peroxide entrained in SCCO$_{2}$. ALD process was controlled by estimating precursor solubility and its mass transport with respect to the density of SCCO$_{2, }$and~correlating these parameters with precursor injection volume. In the ALD process, 7 pulses of precursor were used anticipating deposition of one atomic layer in each of~the pulses. The thickness of the SiO$_{2}$ atomic layers deposited using SCCO$_{2}$ was measured by variable angle spectroscopic ellipsometry (VASE), and the $C-V$ measurements were also performed. The result obtained using VASE indicates that there were 7 monolayers of SiO$_{2}$ with total thickness of 35 \textit{{\AA}}, and the dielectric constant of the deposited layers was 4.0$\pm $0.1. Our initial findings clearly demonstrate that SCCO$_{2}$ is capable of atomic layer deposition of high quality dielectric films at very low process temperatures preventing interface reaction.~~~More research is in progress to achieve ALD of HfO$_{2}$ and TiO$_{2}$ in SCCO$_{2}$. [Preview Abstract] |
Friday, March 25, 2005 1:27PM - 1:39PM |
Y14.00008: Supercritical CO2/Co-solvents Extraction of Porogen and Surfactant to Obtain Jorge Lubguban, Arnold Lubguban, Maslina Othman, Rajesh Shende, Shubhra Gangopadhyay A method of pore generation by supercritical CO$_{2}$ (SCCO$_{2})$/co-solvents extraction for the preparation of nanoporous organosilicate thin films for ultralow dielectric constant materials is investigated. A nanohybrid film was prepared from poly (propylene glycol) (PPG) and poly(methylsilsesquioxane) (PMSSQ) whereby the PPG porogen are entrapped within the crosslinked PMSSQ matrix. Another set of thin films was produced by liquid crystal templating whereby non-ionic (polyoxyethylene 10 stearyl ether) (Brij76) and ionic (cetyltrimethylammonium bromide) (CTAB) surfactant were used as sacrificial templates in a tetraethoxy silane (TEOS) and methyltrimethoxy silane (MTMS) based matrix. These two types of films were treated with SCCO$_{2}$/co-solvents to remove porogen and surfactant templates. As a comparison, porous structures generated by thermal decomposition were also evaluated. It is found that SCCO$_{2} $/co-solvents treatment produced closely comparable results with thermal decomposition. The results were evident from Fourier Transform Infrared (FT- IR) spectroscopy and optical constants data obtained from variable angle spectroscopic ellipsometry (VASE). [Preview Abstract] |
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