George G. Barclay

Liquid crystalline and rigid-rod networks

Abstract Starting about a decade ago, researchers began to explore the use of LC networks as a means of coupling mechanical forces to the mesomorphic character of networks. In so doing, the field of LC elastomers was created and the resulting ferroelectric and piezoelectric materials are beginning to revolutionize the field of polymers. More recently, industry has begun to investigate rigid-rod and LC thermosets as a means of introducing the desirable physical properties of LC thermoplastics in thermoset systems. These polymer networks offer such capabilities as tuned coefficients of thermal expansion and increased fracture toughness. Finally, efforts are being made to develop networks which while not necessarily mesomorphic, do have highly oriented structures to produce networks with NLO properties. Long-term orientational stability is one of the features offered by these new materials. This review will examine all three types of networks, with the major focus being on LC thermosets.

Methacrylate resists and antireflective coatings for 193-nm lithography

Methacrylates were the first class of resist to be examined for use in 193nm lithography. They are still useful today, but have a very different molecular structure because of the requirements for development in 0.262N tetramethyl ammonium hydroxide and high etching resistance. A major driving force for their continued use is the availability of a wide variety of methacrylate monomers and the use of free racial polymerization which imparts a wide range of properties to the polymers and makes them very cost effective.

Subnanometer wavelength metrology of lithographically prepraed structures: a comparison of neutron and X-ray scattering.

The challenges facing current dimensional metrologies based on scanning electron microscopy (SEM), atomic force microscopy (AFM), and light scatterometry for technology nodes of 157 nm imaging and beyond may require the development of new metrologies. We provide results of initial tests of a measurement technique based on Small Angle X-ray Scattering (SAXS) capable of rapid measurements of test samples produced using conventional test masks without significant sample preparation. Using a sample photoresist grating, the technique is shown to apply to both organic, including photoresist, and inorganic patterns, including metal and oxide. The sub-Angstrom wavelength provides nanometer level resolution, with significant room for increased resolution. SAXS provides a dramatic improvement over the use of small angle neutron scattering (SANS) in measurement resolution. An additional advantage is the potential of developing a SAXS-based metrology tool on a laboratory scale.

New ESCAP-type resist with enhanced etch resistance and its application to future DRAM and logic devices

This new photoresist system extends the capability of the ESCAP platform previously discussed. (1) This resist material features a modified ESCAP type 4-hydroxystyrene-t-butyl acrylate polymer system which is capable of annealing due to the increased stability of the t-butyl ester blocking group. The resist based on this polymer system exhibits excellent delay stability and enhanced etch resistance versus previous DUV resists, APEX and UV2HS. Improved stabilization of chemically amplified photoresist images can be achieved through reduction of film volume by film densification. When the host polymer provides good thermal stability the soft bake conditions can be above or near the Tg (glass transition) temperature of the polymer. The concept of annealing (film densification) can significantly improve the environmental stability of the photoresist system. Improvements in the photoacid generator, processing conditions and overall formulation coupled with high NA (numerical aperture) exposure systems, affords linear lithography down to 0.15 micrometer for isolated lines with excellent post exposure delay stability. In this paper, we discuss the UV4 and UV5 photoresist systems based on the ESCAP materials platform. The resist based on this polymer system exhibits excellent delay stability and enhanced etch resistance versus APEX-E and UV2HS. Due to lower acrylate content, the Rmax for this system can be tuned for feature-type optimization. We demonstrate sub-0.25 micrometer process window for isolated lines using these resists on a conventional exposure tool with chrome on glass masks. We also discuss current use for various device levels including gate structures for advanced microprocessor designs. Additional data will be provided on advanced DRAM applications for 0.25 micrometer and sub-0.25 micrometer programs.

3-Dimensional Lineshape Metrology Using Small Angle X-ray Scattering

The need for sub‐nanometer precision metrology of dense patterns for future technology nodes challenges current methods based on light scatterometry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). We provide results of initial tests of a measurement technique based on small angle x‐ray scattering (SAXS) capable of rapid measurements of test samples produced using conventional test masks without significant sample preparation. The sub‐Angstrom wavelength provides nanometer level resolution, with the possibility of increased precision after further refinement of the technique. SAXS results are shown for a test photoresist grating at a variety of angles, demonstrating an ability to extract information on 3‐dimensional pattern shape.

Materials for single-etch double patterning process: surface curing agent and thermal cure resist

Two different pattern curing techniques were developed to stabilize first lithographic images for the single-etch double patterning process. The first method uses a surface curing agent (SCA) that is coated on top of the patterned surface to form a protective coating layer during the curing bake process. It was found that the surface curing process with SCA offers minimum CD changes before and after the double patterning process. Virtually no CD change was observed with the first lithographic images at various curing bake temperatures ranging from 120 ~160°C indicating the curing reaction is limited on the patterned surface. The second method uses a thermal cure resist (TCR) that is a special 193nm photoresist with a crosslinkable functional group to form an insoluble network upon heating at higher temperature. A single-step curing process of the first lithographic images was achieved using TCR by baking the patterned images at 180°C for 60sec. A cross-line contact hole double patterning method was used to evaluate these two different curing techniques and both SCA and TCR successfully demonstrated their capability to print 45nm contact holes with excellent CD uniformity in immersion lithography (1.35NA) with a 45nm half pitch mask. It was also confirmed that both SCA and TCR can be extended to the top-coat free immersion double patterning process using an embedded barrier layer technique.

Advances in vortex via fabrication

Vortex masks composed of rectangles with nominal phases of 0°, 90°, 180° and 270° have been shown to print sub-100nm vias and via arrays when projected into negative resist using 248nm light. Arrays with pitches down to 210nm and CDs as small as 64nm have been reported. While promising, 248nm vortex via images showed some anomalies: The developed contacts were somewhat elliptical, with four different repeating via shapes. The common depth of focus for these four classes of via was limited by their different behaviors through focus. Phase edges in isolated vortex pair structures tended to print, also limiting the useful DOF. These issues can be ameliorated by employing 193nm illumination and a new negative-tone resist. Smaller NAs and higher coherence extend the common depth of focus and larger NAs can be used to print even more tightly spaced patterns. Advanced optical proximity correction techniques can also be applied to reduce the via ellipticity and placement error, and a more optimal choice of geometrical phase depth reduces pattern variability. Further developments and incremental improvements in vortex via design and processing may make it the method of choice for via patterning at the 45nm node.

Mechanistic understanding of post-etch roughness in 193-nm photoresists

Surface roughness of 193 nm resists after a dry etch process is one of the critical issues in the implementation of 193 nm lithography to sub- 100 nm technology nodes. Compared to commercial 248 nm resists, 193 nm photoresists exhibit significant roughness especially under the etch conditions for dielectrics, such as silicon dioxide and silicon nitride. While AFM analysis of DUV resists exhibit the mean roughness (Ra) of ~1 nm after blanket oxide etch, Ra’s of 193 nm resists were found to be in the range of 4 to 7 nm depending on the chemical structure of the resist backbone. In an effort to develop 193 nm resists with improved post-etch roughness (PER), we carried out exhaustive screening of the available 193 nm resist platforms using bulk oxide etch followed by AFM analysis of the resist surface. Benchmarking results indicated that cyclic olefin copolymers, prepared by vinyl addition copolymerization of norbornene derivatives, exhibit significantly better PER than (meth)acrylic copolymers, cyclic olefin/maleic anhydride (COMA) copolymers, or COMA/(meth)acrylic copolymers (COMA hybrid). In this paper, are addressed various factors that influence PER of 193 nm resists and presented solutions to overcome etch inferiority with 193 nm resists for the real device fabrication.

Non-topcoat resist design for immersion process at 32-nm node

At the 32nm node, the most important issue for mass production in immersion lithography is defectivity control. Many methods have been studied to reduce post-exposure immersion defects. Although a topcoat process demonstrates good immersion defect prevention, a topcoat-less resist process is an attractive candidate for immersion lithography due to cost reduction from a simplified process. In this paper we took the innovative approach of chemically designing an internal self-assembling barrier material that creates a thin embedded layer which functions as a topcoat. Data will be presented on this novel self assembly concept, illustrating the control of leaching, contact angle and immersion defects. Several optimized process flows with non-topcoat resists were also studied to decrease the amount of immersion defects. This study was used to verify the capability of a topcoat-less immersion process to achieve the low-defectivity levels required for 32nm node production.

Etch resistance : comparison and development of etch rate models

Etch resistance and post etch roughness of ArF photoresists still remain some of the critical issues during process integration for sub-100nm technology nodes. Compared to phenyl-containing KrF polymers, methacrylate polymers commonly used for ArF lithography show weak bulk etch resistance in addition to a highly damaged surface after standard etch processes. Counter to the photoresist, the etch rates of BARC are required to be very fast to prevent degradation of the photoresist before the image has been transferred to the substrate. There are a number of etch models in the literature which attempt to describe the correlation between polymer structure and blanket etch rates. Ohnishi Parameter and Ring Parameter are the most common etch models correlating atomic and structural trends in the resist polymer and etch rates. These etch models have been tested in two ways: systematically changing the composition of a terpolymer and using polymers with different functional groups. By comparing the etch rates of this large series of polymer structures it was found that these etch models were not sufficient in describing the relationship between the atomic or structural trends in polymer with etch rates. New etch models that describe the structure property relationship and etch rate trends have been developed. These new models show a better correlation with the observed experimental results. Finally, new polymers have been developed, for both ArF and BARC applications. These materials show a significant improvement in term of etch properties.