The application of customized and freeform illumination source shapes is a key enabler for continued shrink using
193 nm water based immersion lithography at the maximum possible NA of 1.35. In this paper we present the
capabilities of the DOE based Aerial XP illuminator and the new programmable FlexRay illuminator. Both of these
advanced illumination systems support the generation of such arbitrarily shaped illumination sources. We explain how
the different parts of the optical column interact in forming the source shape with which the reticle is illuminated.
Practical constraints of the systems do not limit the capabilities to utilize the benefit of freeform source shapes vs. classic
pupil shapes. Despite a different pupil forming mechanism in the two illuminator types, the resulting pupils are
compatible regarding lithographic imaging performance so that processes can be transferred between the two illuminator
types. Measured freeform sources can be characterized by applying a parametric fit model, to extract information for
optimum pupil setup, and by importing the measured source bitmap into an imaging simulator to directly evaluate its
impact on CD and overlay. We compare measured freeform sources from both illuminator types and demonstrate the
good matching between measured FlexRay and DOE based freeform source shapes.
This paper describes the principle and performance of FlexRay, a fully programmable illuminator for high NA
immersion systems. Sources can be generated on demand, by manipulating an array of mirrors instead of the traditional
way of inserting optical elements and changing lens positions. On demand (freeform) source availability allows for
reduction in R&D cycle time and shrink in k1. Unlimited tuning allows for better machine to machine matching.
FlexRay has been integrated in a 1.35NA TWINSCAN exposure system. We will present data of FlexRay using
measured traditional and freeform illumination sources. In addition system performance qualification data on stability,
reproducibility and imaging will be shown. The benefit of FlexRay for SMO enabling shrink is demonstrated using an
SRAM example.
This paper describes the principle and performance of a fully programmable illuminator for a high-NA immersion
system. Sources can be generated on demand, by manipulating an array of mirrors instead of the traditional way of
inserting optical elements and changing lens positions. All mirrors are always used to create the source such that no light
is lost when switching from one source shape to another.
Measured sources generated with this new type of illumination system will be shown and compared to the target sources
generated by source mask optimization software or targets of traditional sources. Comparison between measured and
target source will be done both in parameters of a pupil fit model and by simulated imaging impact. Also the first results
in resist obtained on a XTIV 1950Hi 1.35 NA tool equipped with this illuminator are presented and compared to
measurements on the same system when it was equipped with an Aerial XP illumination system.
In recent years speckle in optical projection microlithography received increasing interest because of its potential contribution to linewidth roughness (LWR). Speckle is a light interference effect that causes the dose delivered to the reticle to be nonuniform, causing a linewidth variation of the patterns imaged in the resist. The contrast of the speckle pattern is shown to be caused by a combination of temporal and spatial coherence effects of the light. The temporal part, determined by the bandwidth of the laser light and the duration of the laser pulse, is found to be the dominant contributor to speckle in today's ArF optical lithography. The spatial distribution of the speckle pattern depends on the intensity distribution of the light in the pupil. Consequently, the spatial frequencies of the LWR induced by speckle depend on the illumination condition, which is confirmed experimentally by exposing wafers with different amounts of speckle contrast. The experiments demonstrate that the amplitude of the LWR induced by speckle is consistent with theory and simulations. Its amplitude is small compared to other sources of LWR, but it is clearly present and should not be ignored when extending ArF optical lithography into future technology nodes.
In recent years the topic of speckle in optical projection microlithography received increasing interest because of its
potential contribution to line width roughness (LWR). Speckle is a light interference effect that causes the dose delivered
to the reticle to be not uniform. This will cause a line width variation of the patterns imaged in the resist. The contrast of
the speckle pattern is shown to be caused by a combination of temporal and spatial coherence effects of the light. The
temporal part, determined by the bandwidth of the laser light and the duration of the laser pulse, is found to be the
dominant contributor to speckle in today's ArF optical lithography. The spatial distribution of the speckle pattern
depends on the intensity distribution of the light in the pupil. Consequently the spatial frequencies of the LWR induced
by speckle will depend on the illumination condition, which is confirmed experimentally by exposing wafers with
different amounts of speckle contrast. The experiments demonstrate that the amplitude of the LWR induced by speckle is
consistent with theory and simulations. Its amplitude is small compared to other sources of LWR, but it is clearly present
and should not be ignored when extending ArF optical lithography into future technology nodes.
Meeting a specific CD uniformity roadmap becomes more and more difficult as different budget components affecting CD uniformity fail to meet their requirements. For example, reticle manufacturing is at the edge of its potential, and hotplates impact CD uniformity by design. Also, etch processes must be balanced between optimal settings for varying structures. While work continues to enhance the performance of individual budget components, applying local exposure dose compensation with a scanner can provide a near-term solution for improving CD uniformity. Within the wafer processing chain, only the scanner has the unique capability to influence the final quality across-field and field-to-field in a controlled manner, making it the most effective tool for compensation. This paper describes the subsystems required for dose compensation and presents a solution that allows full integration into an automated fabrication environment. Examples will show that both the reticle contribution as well as the process-induced across-wafer fingerprint, including etch, can be improved by up to 50 percent. This improvement is demonstrated both on test structures and on memory device layers.
Current roadmaps show that the semiconductor industry continues to drive the usable Rayleigh resolution towards the fundamental limit (for 50% duty cycle lines) at k1=0.25. This is being accomplished through use of various resolution enhancement technologies (RETs), extremely low aberration optics with stable platforms, and resists processes that have ever-increasing dissolution contrast and smaller diffusion lengths. This talk will give an overview of the latest optical mechanisms that can be used to improve the imaging system for low k1 resolutions. We show 3 non-photoresist techniques to measure the optical parameters of a scanner: 1) a new fast phase measurement interferometer to measure aberrations is presented with an accuracy and repeatability of <3mλ, 2) we introduce a method to measure the illumination profile of the exposing source, and 3) a measurement system to monitor scattered light is presented with correlation to other techniques using a salted pellicle experiment to create controlled scattered light. The optimization of illumination and exposure dose is presented. We show the mechanism for customizing illumination based on specific mask layers. We show how this is done and compare process windows to other more conventional modes such as annular illumination or QUASAR. The optimum design is then implemented into hardware that can give extremely high optical efficiency. We also show how system level control mechanisms can be used to field-to-field and across-field exposure to compensate for lithography errors. Examples of these errors can include reticle CD deviations, wavefront aberrations, and across-field illumination uniformity errors. CD maps, facilitated by SEM and ELM, can give the prescribed changes necessary. We present a system that interfaces to new hardware to compensate these effects by active scanner corrections.
As resolution shrinks, also the demands for litho CD Uniformity are becoming tighter. In replicating the mask pattern into photoresist, a sequence of modules within the patterning cluster (coat, expose, develop, etch) is responsible for CD non-uniformity. So far, the strategy has been to make the contribution of each of these modules as small as possible. The CD Uniformity can be improved in a more efficient way by compensating the various error sources with adapted dose profiles on the scanner. An inventory is made of the requirements for this compensation mechanism. In more detail a description is given how the scanner can apply these dose corrections. With experiments, the feasibility of the concept is proven. Improvements in CD Uniformity over 5nm are demonstrated, both on test structures as well as on real device layers.
A novel analysis methodology, for the breakdown and ranking of the different sources of line width variation, is presented. The method is applied both on the level of an individual wafer, and on multiple wafers in a batch. It enables evaluation of the exposure tool performance in relation to other contributors to line width variation. Separation of the contribution of the exposure tool component from other sources of line width errors, requires sufficiently dense and accurate sampling of the CD variation across a wafer, because of the statistical confidence needed in the budget breakdown analysis. These requirements are met by taking advantage of the excellent performance of Electrical Line Width Measurements in terms of repeatability and data acquisition speed. The exposure tool is found to be only responsible for a limited part of the total CD uniformity across the batch. The largest contributors are reticle and processing components at individual wafer level and the CD offset between the wafers at batch level. The resist process component is larger than expected due to a dominating swirl shaped artifact caus4ed by non optimal track performance. A refined analysis of the full wafer CD uniformity was focused on the systematic contributions from the H-V difference and scan direction. Both of these components appear to be only a small part of the intra die budget.
The thickness non-uniformity and refractive index in- homogeneity of silicon oxynitride thin films, grown by low pressure chemical vapor deposition, have been optimized. The present work was especially motivated by the application of these thin films as well defined waveguides in phase-matched second harmonic generating devices, which are well known for their extremely high requirements to uniformity and homogeneity. However, other demanding integrated optical components like gratings, sensor systems, telecommunication devices, etc., also strongly benefit from highly uniform waveguides.
KEYWORDS: Near field scanning optical microscopy, Microscopes, Near field optics, Atomic force microscopy, Reflection, Optical microscopes, Scanning probe microscopy, Compact discs, Semiconductor lasers, Image resolution
Images obtained with a scanning near field optical microscope (SNOM) operating in reflection are presented. We have obtained the first results with a SiN tip as optical probe. The instrument is simultaneously operated as a scanning force microscope (SFM). Moreover, the instrument incorporates an inverted light microscope (LM) for preselection of a scan area. The SiN probe is operated in the contact regime causing a highly improved lateral resolution in the optical image compared to an alternative set-up using a fiber probe, which is also presented. The combined microscope is operated either in open loop or as a force regulated SNOM. Near field optical images can be directly compared with the topography displayed in the simultaneously recorded SFM image.
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