Alex K. Raub

Integration of block copolymer directed assembly with 193 immersion lithography

An integration scheme of block copolymer directed assembly with 193 nm immersion lithography is presented. It is experimentally shown that a thin silicon nitride film can be used as an antireflective coating (ARC). With such an ARC, directed assembly of a block copolymer (BCP) to triple the feature density of a chemical pattern was demonstrated. A high quality of assembly was obtained over a large area, and pattern transfer feasibility was illustrated. The integration of feature density multiplication via directed assembly of a BCP with 193 nm immersion lithography provided a pattern quality that was comparable with existing double patterning techniques, suggesting that the process could be a promising candidate for extending the use of current 193 immersion lithography tools to higher pattern densities.

Lithographically Defined Porous Carbon Electrodes

The special nature of the C C bond can lead to various polymorphic forms of carbon such as graphite, glassy-carbon, fullerenes (such as buckyballs), carbon nanotubes, and diamond. Electrodes made from carbon exhibit many useful properties including wide potential windows, low background capacitance, resistance to fouling, and catalytic activity for manyanalytes compared to solidmetal electrodes. In addition to the intrinsic material properties of carbon, functionalized films can be produced through chemical modification using a wide range of chemistries. Because of this flexibility and utility, fabrication of both macroand microporous carbon films, with their commensurate increase in surface area, continues to receive significant research interest. Some of the specific applications for porous carbon materials include fuel cells, electrochemical double layer capacitors, high surface area catalytic supports, water purification, and gas separation. Recently, it has been found that pyrolyzed photoresist films (PPFs) have the same unique properties of carbon electrodes with an advantage that they canbe lithographically defined. The goal of this work was to create lithographically defined porous pyrolyzedcarbonelectrodesandcharacterize thedepositionand electrochemical properties of metal nanoparticles on these electrodes. We report a robust fabrication method capable of producing large area ( 100s cm) submicrometer porous carbon films. In our approach, interferometric lithography (IL) is used topattern thickphotoresist films into 3Dperiodic lattices. These structures are then converted to carbon via pyrolysis under flowing forming gas. During pyrolysis, the non-carbon species in the resist polymer backbone are removed, while the bulk of the carbon remains. The patterned structures undergo significant shrinkage, but remarkably maintain their morphology and adhesion to the substrate. The degree of carbonization is a function of the pyrolysis temperature, which has a profound

Deep-UV immersion interferometric lithography

Liquid immersion lithography (LIL) can extend the resolution of optical lithography well beyond today’s capabilities. The half-pitch limit is given by the well-known formula P=λ/(4/NA), where λ is the optical wavelength and NA=nsin(θ) is the numerical aperture of the exposure device with n the refractive index of the exposure medium. Through the use of exposure media such as purified water (n of 1.44 at 193 nm), it is possible to reduce minimum pitches by a factor of as much as 44% - a full technology node. Beyond this simple observation, there is a good deal of work necessary to fully understand the impact of LIL on a lithography processes. This paper will address issues con-cerning resist chemistry and the impact of water immersion on the imaging capabilities of different resist formulations. All resists were evaluated by imaging dense line-space structures at a 65-nm half-pitch both in air and with water im-mersion. Studies of dense 65-nm lines made by immersion imaging in HPLC grade water with controlled variations in resist components were performed. Significant differences were observed and will be discussed.

Imaging capabilities of resist in deep ultraviolet liquid immersion interferometric lithography

Liquid immersion lithography (LIL) extends the resolution of optical lithography to meet industry demands into the next decade. Through the use of exposure media such as purified water (n of 1.44 at 193nm), it is possible to reduce minimum pitches compared with traditional air/vacuum exposures media by a factor of as much as 44%—a full technology node. Beyond this simple observation, there is a good deal of work necessary to fully understand the impact of LIL immersion lithography on a lithography processes. This article addresses the impact of water immersion on the imaging capabilities of different resist formulations. All resists were evaluated by imaging dense line-space structures at a 65-nm half-pitch both in air and with water immersion. Studies of dense 65-nm lines made by immersion imaging in HPLC grade water with controlled variations in resist components were performed. Significant differences were observed and will be discussed.

Fabrication of 22nm half-pitch silicon lines by single-exposure self-aligned spatial-frequency doubling

The relentless progression of semiconductor technology to smaller feature sizes will likely soon outstrip the theoretical linear system limits of today’s optical lithography tools (a half-pitch of λ∕4n or 34nm with a 193nm wavelength source and water immersion). We demonstrate a self-aligned process involving only a single lithographic exposure followed by spatial-frequency doubling that results a half-scaling of the original pattern and have achieved a 22nm half-pitch pattern with 193nm water immersion. A lithographic pitch of 89nm was realized with a 193nm ArF-excimer laser source and de-ionized-water immersion interferometric lithography. A self-aligned spatial-frequency doubling technique, taking advantage of the well-known anisotropic etching of silicon by KOH, was used to affect the frequency doubling. A protective layer (metal) was deposited parallel to the (110) direction of a (100) silicon wafer and the sample was immersed in an appropriate KOH solution, resulting in a series of 44.5nm opening wi...

193nm dual layer organic BARCs for high NA immersion lithography

Extending the resolution capability of 193nm lithography through the implementation of immersion has created new challenges for ArF B.A.R.C.s. The biggest of which will be controlling reflectivity over a wider range of incident angles of the incoming imaging rays. An optimum B.A.R.C. thickness will depend on the angle of incidence of the light in the B.A.R.C. and will increase as the angle increases. At high angles different polarization have different optimum thicknesses. These confounding effects will make it increasingly difficult to control reflectivity over a range of angles through interference effects within a single homogenous B.A.R.C. Unlike single layer B.A.R.C.s, multilayer B.A.R.C.s are capable of suppressing reflectivity through a wide range of incident angles. In fact, remarkable improvements in antireflective properties can be achieved with respect to CD control and through angle performance with the simplest form of a multilayer B.A.R.C., a dual layer. Here we discuss the attributes of an all organic dual layer B.A.R.C. through simulations and preliminary experiments. One attribute of an organic over inorganic B.A.R.C. in high-NA lithography is its ability to planarize topography. ArF scanners designed to meet the needs of the 45nm node will have a very small depth-of-focus (DOF) which will require planar surfaces.

Study of barrier coats for application in immersion 193-nm lithography

We will describe our barrier coat approach for use in immersion 193 nm lithography. These barrier coats may act as either simple barriers providing protection against loss of resist components into water or in the case of one type of these formulations which have a refractive index at 193 nm which is the geometric mean between that of the resist and water provide, also top antireflective properties. Either type of barrier coat can be applied with a simple spinning process compatible with PGMEA based resin employing standard solvents such as alcohols and be removed during the usual resist development process with aqueous 0.26 N TMAH. We will discuss both imaging results with these materials on acrylate type 193 nm resists and also show some fundamental studies we have done to understand the function of the barrier coat and the role of differing spinning solvents and resins. We will show LS (55 nm) and Contact Hole (80 nm) resolved with a 193 nm resist exposed with the interferometric tool at the University of New Mexico (213 nm) with and without the use of a barrier coat.

Large area three-dimensional photonic crystals with embedded waveguides

Three-dimensional photonic crystals are attractive for very compact waveguide devices. A novel interferometric lithography technique for fabricating three-dimensional photonic crystals is presented, which allows for independent dimensional control of each axis of the crystal. Previous interferometric approaches using 3, 4, 5, or more beams have inherent constraints between the lattice constants and the exposure wavelength. With this new technique, it is possible to control each individual crystal lattice constant largely independent of the exposure wavelength, vastly increasing the available parameter space. Both mathematical models and experimentally realized three-dimensional photonic crystals, over 2 cm2 in size and up to 12 μm, are presented. Photonic crystals with integrated waveguides are of particular significance. A new approach to fabricating waveguides embedded in a three-dimensional photonic crystal is also presented. This approach uses multiple-exposure wavelengths, with one longer wavelength propagating throughout the photoresist for the photonic crystal fabrication and another shorter highly absorptive wavelength for the waveguide fabrication. This new approach to waveguide fabrication leads itself to scalable manufacturing using standard semiconductor lithography equipment.Three-dimensional photonic crystals are attractive for very compact waveguide devices. A novel interferometric lithography technique for fabricating three-dimensional photonic crystals is presented, which allows for independent dimensional control of each axis of the crystal. Previous interferometric approaches using 3, 4, 5, or more beams have inherent constraints between the lattice constants and the exposure wavelength. With this new technique, it is possible to control each individual crystal lattice constant largely independent of the exposure wavelength, vastly increasing the available parameter space. Both mathematical models and experimentally realized three-dimensional photonic crystals, over 2 cm2 in size and up to 12 μm, are presented. Photonic crystals with integrated waveguides are of particular significance. A new approach to fabricating waveguides embedded in a three-dimensional photonic crystal is also presented. This approach uses multiple-exposure wavelengths, with one longer wavelength ...

Integration of Block-Copolymer with Nano-Imprint Lithography: Pushing the Boundaries of Emerging Nano-Patterning Technology.

The extreme nanoscale features prescribed by the International Technology Roadmap for Semiconductors (ITRS, e.g., 11nm half-pitch for dense patterns and 4.5nm critical dimensions by 2022) require infrastructure-heavy extreme ultraviolet (EUV) and/or

Simulation of dense contact hole (κ 1 =0.35) arrays with 193 nm immersion lithography

The resolution limits of optical lithography are usually described by the well-known Raleigh criterion, CD = κ1 (λ/NA). One of the biggest challenges in optical lithography is to reliably print contact holes patterns with κ1 ~ 0.35 using a hyper NA system (NA > 1) especially for relatively small (m × n) arrays. Polarization effects cause deviations from a simple (λ/NA) scaling large NA values. For an isolated hole, n = 1 and for large arrays, n ⪆ 15, the spectral content is mainly contained in the lowest diffracted orders that are captured within the NA of the imaging lens. The most difficult situation is for small arrays (m, n ≈ 2, 3, 4) where the spectral features are broader more of the important image information is contained in the higher diffraction orders. The patterning of contact holes also suffers from tight dose tolerances and high mask error enhancement factors (MEEF) as both the feature and array sizes decrease. A detailed PROLITHTM vector simulation study is reported for three different approaches to printing, isolated contact holes and small to large contact hole arrays with a κ1 of 0.35 and NAs of 1.05 and 1.3: 1) imaging interferometric lithography (IIL, with a single mask and multiple exposures incorporating pupil plane filters), 2) two-exposure dipole illumination, and 3) alternating phase shift masks (alt-PSM). Only the IIL scheme is capable of printing smaller (m, n ≤ 10) at this low κ1 factor. Single exposure alt-PSM does not allow for the necessary polarization control. Periodic assist features provide improved resolution, depth of focus and MEEF, at the expense of a more complex mask and additional nonprinting area surrounding the contact holes.