In this paper, we provide an overview of various technologies for scaling tin laser-produced-plasma (LPP) extremeultraviolet (EUV) source performance to enable high volume manufacturing (HVM). We will show improvements to source architecture that facilitated the increase of EUV power from 100W to 250W, and the technical challenges for power scaling of key source parameters and subsystems. The performance of critical subsystems such as the Droplet Generator and Collector protection will be shown, with emphasis on stability and lifetime. Finally, we will describe current research activities and provide a perspective for LPP EUV sources towards 500W.
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.
The use of customized illumination modes is part of the pursuit to stretch the applicability of immersion ArF lithography.
Indeed, a specific illumination source shape that is optimized for a particular design leads to enhanced imaging results.
Recently, freeform illumination has become available through pixelated DOEs or through FlexRayTM, ASML's
programmable illuminator system, allowing for virtually unconstrained intensity distribution within the source pupil.
In this paper, the benefit of freeform over traditional illumination is evaluated, by applying source mask co-optimization
(SMO) for an aggressive use case, and wafer-based verification. For a 22 nm node SRAM of 0.099 μm² and 0.078 μm2
bit cell area, the patterning of the full contact and metal layer into a hard mask is demonstrated with the application of
SMO and freeform illumination. In this work, both pixelated DOEs and FlexRay are applied. Additionally, the match
between the latter two is confirmed on wafer, in terms of CD and process window.
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.
The practical limit of NA using water as immersion liquid has been reached. As a consequence, the k1 in production for
the coming technology nodes will decrease rapidly, even below k1=0.25.This means that new imaging solutions are
required. Double patterning and spacer techniques in combination with design for manufacturing are developed to
support the 22nm node. However, from an imaging point of view the main challenge is to extend and improve single
exposures at k1 of 0.26 to 0.31. In this paper we will present ingredients to support single exposure (as a part of a double
patterning solution).
The following ingredients to extend single exposure are presented in this paper: 1) Extreme Dipole illumination (pole
width = 20° and ring width = 0.08σ) to demonstrate tight CD control of 1.5nm across the wafer for a flash gate layer with
a half pitch of 38nm. 2) The benefits of complex freeform illumination pupils for process window, pattern fidelity and
MEEF using a DRAM active area pattern, and 3) the advantage of TE polarization for rotated structures while
maintaining intensity in preferred polarization state.
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.
We present a complete method for the characterization and modeling of flare based on the measurement of the modulation transfer function (MTF) of scanners. A point-spread function (PSFscat) representing only the scattered light or flare in the tool is inferred by comparing the measured MTF with a calculated MTF for aberration-free imaging. This PSFscat is then used to predict the effect of flare for different layouts. In particular, local variations in pattern density are shown to couple with mid- and short-range flare and lead to significant CD non-uniformity across the field. Finally, we examine double exposure techniques that are sensitive to flare because of the total light reaching the wafer, from the two masking steps.
The objective of the Reticle Error Correction (REC) is to determine the exposure tool fingerprint in the Across Chip Linewidth Variation (ACLV). Extensive reticle and wafer measurements indicate hidden reticle issues contributing to ACLV. Some of these obscure reticle issues originate from the way the mask is produced, e.g. due to mask processing and mask writer equipment. Mask processing is traditionally focused upon as the largest cause for ACLV, but on high quality masks, mask writer properties can appear. In order to take these additional properties into account, an extended REC model is required using information from the "nearest neighbors". If not all the required reticle properties are measured and used, either by choice or by tool inability, then a reticle fingerprint also (partially) dominates the exposure tool fingerprint. The quality of the reticle measurements determines how well the exposure tool fingerprint can be revealed. REC is used to separate reticle and exposure tool contributions from ACLV. The methods that are used, and the results that are obtained, serve as a guide in showing where improvements can be made in mask making, mask metrology and exposure tools.
To extend KrF lithography below the 180nm SIA design rule node in manufacturing, an advanced DUV step and scan system utilizing a lens with an NA up to 0.7 will be required to provide sufficient process latitude. Towards the SIA's 150nm design rule node, manufacturing challenges for 248nm lithography include contact hole printing, iso-dense bias control and adequate across the field CD uniformity. All will benefit from higher NA lenses. In the paper, result obtained on a PAS 5500/700B DUV Step and Scan system are presented. The system design is based on the PAS 5500/500 with a new 0.7NA Starlith lens, AERIAL II illuminator and ATHENA advanced alignment system. Imaging of dense and isolated lines at 180nm, 150nm and below as well as 180nm and 160nm contact holes is shown. In addition to imaging performance, image plane deviation, system distortion fingerprints, single-machine overlay and multiple-machine matching results are shown. Using the ATHENA alignment system, alignment reproducibility as well as overlay result on CMP wafers will be shown. It is concluded that this exposure tool is capable of delivering imaging and overlay performance required for mass production at the 150nm design rule node, with potential for R and D applications beyond.
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