A two-year study on the feasibility of High-n Immersion Lithography shows very promising results. This
paper reports the findings of the study.
The evaluation shows the tremendous progress made in the development of second-generation
immersion fluid technology. Candidate fluids from several suppliers have been evaluated. All the
commercial fluids evaluated are viable, so there are a number of options. Life tests have been conducted on
bench top fluid-handling systems and the results referenced to full-scale systems. Parameters such as Dose
per Laser Pulse, Pulse Rate, Fluid Flow Rate, and Fluid Absorbency at 193nm, and Oxygen/Air
Contamination Levels were explored. A detailed evaluation of phenomena such as Last Lens Element
(LLE) contamination has been conducted. Lens cleaning has been evaluated.
A comparison of High-n fluid-based technology and water-based immersion technology shows
interesting advantages of High-n fluid in the areas of Defect and Resist Interaction. Droplet Drying tests,
Resist Staining evaluations, and Resist Contrast impact studies have all been run. Defect-generating
mechanisms have been identified and are being eliminated. The lower evaporation rate of the High-n fluids
compared with water shows the advantages of High-n Immersion.
The core issue for the technology, the availability of High-n optical material for use as the final
lens element, is updated. Samples of LuAG material have been received from development partners and
have been evaluated. The latest status of optical materials and the technology timelines are reported.
The potential impact of the availability of the technology is discussed. Synergy with technologies
such as Double Patterning is discussed. The prospects for <22nm (hp) are evaluated.
In this paper we report the status of our feasibility work on high index immersion. The development of high
index fluids (n>1.64) and high index glass materials (n>1.9) is reported. Questions answered are related to
the design of a high NA optics immersion system for fluid containment and fluid handling, and to the
compatibility of the fluid with ArF resist processes.
Optical design and manufacturing challenges are related to the use of high index glass materials
such as crystalline LuAG or ceramic Spinel. Progress on the material development will be reviewed.
Progress on immersion fluids development has been sustained. Second-generation fluids are
available from many suppliers. For the practical use of second-generation fluids in immersion scanners, we
have evaluated and tested fluid recycling concepts in combination with ArF radiation of the fluids. Results
on the stability of the fluid and the fluid glass interface will be reported. Fluid containment with immersion
hood structures under the lens has been evaluated and tested for several scan speeds and various fluids.
Experimental results on scan speed limitations will be presented.
The application part of the feasibility study includes the imaging of 29nm L/S structures on a 2-beam interference printer, fluid/resist interaction testing with pre- and post-soak testing. Immersion defect
testing using a fluid misting setup was also carried out. Results of these application-related experiments
will be presented and discussed.
Immersion Lithography is now the most important technique for extending optical lithography's capabilities and meeting the requirements of the Semiconductor Industry Association (SIA) roadmap. The introduction of water as an immersion fluid will allow optical lithography to progress as far as the 45nm (half pitch) node using ArF scanning systems such as the XT1700i. Developments are under way to explore the use of immersion lithography beyond this performance level and toward the 32nm (half pitch) node. This paper examines the progress that has been made, particularly with the use of 2nd-generation immersion fluids. The requirements of the exposure system are defined. Issues associated with achieving the requirements are reviewed and discussed. Special attention is given to clarifying the optical materials and the issues associated with extending optical designs to hyper-numerical aperture (NA) levels. A number of threshold levels for the numerical apertures are set by the refractive index of the available materials in the lithographic film stack. These are defined. The requirements of high refractive index fluids are detailed. The performance of experimental samples is compared to system requirements. Fluid interaction with photoresists and topcoats are examined. The results of stain tests and soak tests for fluid samples on resist are reported. Data is supplied on resist imaging for 32nm line and space L/S.
Water-based immersion lithography using ArF illumination is able to provide optical solutions as far as the 45-nm node, but is not able to achieve the 38- or 32-nm nodes as currently defined. Achieving these lithographic nodes will require new, higher refractive index fluids to replace the water used in first-generation immersion systems. We have developed a number of such second-generation high-index fluids for immersion lithography at 193 nm. These highly transparent fluids have 193-nm indices up to 1.664. To understand the behavior and performance of different fluid classes, we use spectral index measurements to characterize the index dispersion, coupled with Urbach absorption edge analysis and Lorentz Oscillator modeling. Interference imaging printers have long been available, and they now have a new use: a rapid, cost-effective way to develop immersion lithography, particularly at extremely high resolutions. Although interference printers will never replace classical lens-based lithography systems for semiconductor device production, they do offer a way to develop resist and fluid technology at a relatively low cost. Their simple image-forming format offers easy access to the basic physics of advanced imaging. Issues such as polarization of the image-forming light rays, fluid/resist interaction during exposure, topcoat film performance, and resist line edge roughness (LER) at extremely high resolutions, can all be readily studied. 32-nm 1:1 line/space (L/S) imaging is demonstrated using two of the second-generation fluids. These resolutions are well beyond current lens-based system capabilities. Results on the performance of various resists and topcoats are also reported for 32-nm L/S features.
The 38nm and 32nm lithography nodes are the next major targets for optical lithography on the Semiconductor Industry Roadmap. The recently developed water-based immersion lithography using ArF illumination will be able to provide an optical solution for lithography at the 45nm node, but it will not be able to achieve the 38nm or the 32nm nodes as currently defined. To achieve these next lithographic nodes will require new, very high refractive index fluids to replace the water used in current immersion systems. This paper describes tests and experiments using an interference immersion lithography test jig to develop key technology for the 32nm node. Interference imaging printers have been available for years, and with the advent of Immersion Lithography, they have a new use. Interference immersion image printing offers users a rapid, cost-effective way to develop immersion lithography, particularly at extremely high resolutions. Although it can never replace classical lens-based lithography systems for semiconductor device production, it does offer a way to develop resist and fluid technology at a relatively low cost. Its simple image-forming format offers easy access to the basic physics of advanced imaging. Issues such as: Polarization of the image forming light rays; Fluid/resist interaction during exposure; Topcoat film performance; and the Line Edge Roughness (LER) of resists at extremely high resolutions can all be readily studied. Experiments are described and results are provided for work on: 32nm imaging tests; high refractive index fluid testing using 193nm wavelength at resolutions well beyond current lens-based system capabilities; and polarization configuration testing on 45nm, 38nm, and 32nm L/S features. Results on the performance of resists and topcoats are reported for 32nm L/S features.
157 nm has been explored as a lithographic technology for several years on small field imaging tools with encouraging results. Significant progress has occurred in tool platform design, resist performance, and optical material quality. However, a major test of a new lithography comes when full field, scanned images can be produced as this becomes a crucial test of system performance and uniformity. We report on early results from a 22 mm x 26 mm (slot x scan) field Micrascan VII 157 nm lithography scanner obtained using a binary reticle. In addition, a full field alternating phase shift reticle was fabricated on modified fused silica1 and used to extend the imaging capability. Resolution and uniformity data from both reticles will be presented. The lithographic performance will also be compared to simulations using predicted performance from the scanner.
This study takes an integrated approach utilizing a combination of high NA 193 nm lithography, a sidewall chrome alternating aperture (SCAA) phase shift mask, optical proximity correction (OPC) and customized illumination in an attempt to demonstrate the feasibility of using 193 nm lithography to support the 65 nm node. A SCAA mask was designed and built with line/space patterns ranging in pitch from 300 nm down to 140 nm. A range of mask biases were applied to the zero and pi spaces in order to examine to response of the lithography to a combination of the SCAA approach and asymmetric biasing. In combination to the asymmetric biasing, overlay bracketing was applied in order to measure the chrome overlay tolerances of the mask. Simulations suggested that an unconventionally small sigma of 0.15 would be the optimum coherence for a high 193 nm optical system. A custom 0.15 sigma partial coherence illuminator was, therefore, built and installed in the experimental ASML Micrascan V 0.75 NA 193 nm scanner. Wafers were exposed using 190 nm of 193 nm resist and an organic BARC. The 70 nm 1:1 line/space patterns resolved with a depth of focus of about 0.2 μm. The 75 nm 1:1 line/space patterns showed a 0.3-0.4 μm depth of focus. Both of these process windows were limited by pattern collapse. Addressing the pattern collapse may improve the depth of focus. Comparing mask measurements to wafer measurements show that little or no asymmetric biasing in necessary to balance the pitch. Moreover, the measured pitch was stable over a focus range of at least 0.4 microns demonstrating that any phase imbalance present was not significantly affecting the observed lithography.
This paper describes the system performance for Micrascan VII and reports on some of the photo-resist testing results. The challenges of tool design range from the optical form to new resists. The Micrascan VII architecture has the traditional look of the prior Micrascan family of tools. The evolution of design for operation at 157 nm wavelength has been implemented and is presented. The use of calcium fluoride exclusively in the projection optics design presented many challenges. Performance of the projection optics is shown as well as lithographic results. Initial lithographic results indicate that pattern features well below 100 nm can be printed even with first generation 157 nm resists. 60 nm resist lines with 0.3 μm depth of focus are reported.
This paper studies the resolution limits of optical lithography using phase-shift mask technology. Alternating phase-shift masks are studied in the context of the 70nm lithographic node. The performance of alternating phase-shift masks is measured at the limits of its resolution. Printing issues that result from phase errors on the reticle are observed. These phase errors result in a loss of depth of focus and ultimate resolution. A lithography-system-based solution to the mask phase errors is proposed. A small obscuration aperture that matches the partial coherence of the illumination is placed in the pupil plane of optics to block the zero-order light leakage that results from the phase error. This paper reports the performance and effects of using this obscuration aperture.
Phase-shift masks are an important factor in the extension of optical lithography to the 50nmmode. A critical factor in their implementation is the "Dual reticle exposure technique." This technique uses two reticles: one is typically the high-resolution phase-shift reticle, and the other, a clearing or trimming reticle to remove unwanted phase edge patterns. This paper examines the result ofimplementing this technique on a very-high numerical aperture 193 nm-catadioptric-exposure system. Examples are given for the application of the "Dual Reticle Technique" including applications in which two phase-shift reticles are used to print advanced memory cells. Chromeless phase-shift masks are also shown. Issues with the implementation ofthe technique are examined. These include exposure delay effects, pattern registration, and the impact of the technique on exposure system throughput. Exposure system design developments are reported that will improve exposure system throughput with the dual reticle exposure technique. These include: Double Reticle Stages; and a new concept of exposing the two reticles simultaneously. It is noted that this dual simultaneous exposure system, when combined with a dual wafer stage system, has the potential for exposing 300mm wafers at rates up tp 150 wafers/hour in dual reticle exposure mode.
The evolution of microlithography to 0.25 micrometers and below has driven the need for performance enhancements in several critical areas. Among these are imaging, illumination, and overlay. This paper briefly reviews MicrascanTM III system concepts. The main body of the paper presents system level performance and discusses the key subsystems which enable 0.25 micron imaging and 55 nm overlay. Autocal, MicrascanTM III's image, reticle and wafer position reference subsystem is discussed with respect to functionality and performance with a pulsed illumination source. MicrascanTM III illuminator performance, including automated off axis illumination module are presented. Performance of the magnetically levitated Monostage and its interaction with overlay and imaging is discussed. System performance with respect to resolution, image quality and overlay on product levels is presented and analyzed.
Fully automated, multi-mode CD-SEM metrology, utilizing both backscattered electron (BSE) and secondary electron (SE) detection, has been benchmarked to 180 nm critical dimensions using patterns generated by deep-UV lithography. Comparison of pure BSE with conventional SE SEM data used in a study of across-chip linewidth variation (ACLV) revealed that heterogeneous system matching depends on feature orientation as well as an offset between BSE and SE intensity profiles. The corresponding AFM data show that the BSE measurements are more accurate and less sensitive to feature orientation and sample charging. Using the multi-mode system, we found that SE profiles had a higher signal-to-noise ratio while the BSE profiles gave a better representation of the actual line shape. Static and dynamic measurement precision below 2 nm has been achieved with BSE on etched polysilicon. Move-acquire- measure (MAM) times at this precision were under 10 seconds per site. Models for orientation-independent measurement, generic wafer throughput, and overall equipment effectiveness were used to address the issues of system matching, tool productivity, and factory integration, respectively.
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