ASML’s 300mm scanner-systems are built on the TWINSCAN (XT/NXT) platform and yield high productivity levels for dry as well as immersion litho-scanners. NXT:1980Di immersion scanners yield productivity levels as high as 275wph while maintaining the overlay accuracy. The NXT:1980Di can be equipped with a new leveling mode that results in a significant reduction of the time that is spent on measuring the wafer focus height map. In the new leveling mode the focus height map is measured employing the full width of the level sensor and thereby minimizing the number of leveling scans. In this paper we describe the implementation of the LIL-method in the TWINSCAN platform design. Here, we report on the focus / leveling performance for both test as well as customer product wafers, and present a productivity outlook on the performance gain for a selected set of exposure use-cases.
Scanners in High-Volume-Manufacturing conditions will experience a large range of reticles that vary in reticle transmission and reticle diffraction characteristics. Especially under full production loads reticles will heat up due to the exposure light-load and as such experience thermo-mechanical deformations. The resulting reticle pattern distortion can be partially translated in a deteriorated overall system overlay. Due to the geometry of the reticle and exposure fields, these reticle thermal effects are in general barrel-shape distortions that can be well corrected with the available set of lens manipulators. Nevertheless node-over-node the residual overlay errors associated with thermo-mechanical reticle deformation needs further reduction since it contributes to the total onproduct overlay performance. To reduce overlay caused by reticle temperature drift, NXT1980Di includes an active cooling mechanism suppressing the reticle temperature changes during exposure significantly. Even though the reticle temperature excursions are well suppressed, residual intra-wafer overlay drift effect can still be observed. Before exposure of a wafer, reticle deformation is measured during reticle align using in-line alignment / image sensors (TIS or PARIS). This is enabled by adding alignment markers around the circumference of the image field on the reticle. The measured reticle deformations are then fed to the system control network and dynamically corrected for by making use of the available manipulators in the scanner and the projection lens. Wafer-by-wafer reticle distortion measurements are performed to accurately capture the transient dynamics present in reticle heating during normal production lots. A new version of Reticle Heating Feed-forward Control (RHC2) is introduced that uses reticle-heating-induced deformation measurements over time and exposure sequence information to calibrate reticle-deformation-predictionmodels. These models are based on thermo-mechanical models that simulate reticle deformation under various exposure conditions and are applied in-line to the exposures to reduce intra-wafer overlay drift effects.
Adjustment and control of the illumination pupil asymmetry is relevant for wafer alignment and overlay of lithography tools. Pupil asymmetries can cause a tilt in aerial image (Aerial Image Tilt, or AIT). This AIT, combined with a focus offset, leads to a horizontal image shift. Pupil asymmetries can be related to a shift of the entire illumination pupil (geometrical telecentricity) caused by illuminator misalign. Another type of pupil asymmetry is energetic imbalance (quantified by pupil Center of Gravity, COG). The scanner can show pupil variation across the exposure slit. <p> </p>In general the COG at the edge of the slit is often worse than in the center part of the slit. Recently, ASML has released the NXT:1980Di that is equipped with an enhanced illuminator to improve pupil COG variation across the slit. In this paper we explore the performance of this scanner system and show that the AIT variation across the slit is also reduced significantly.
Overlay is one of the key factors which enables optical lithography extension to 1X node DRAM manufacturing. It is natural that accurate wafer alignment is a prerequisite for good device overlay. However, alignment failures or misalignments are commonly observed in a fab. There are many factors which could induce alignment problems. Low alignment signal contrast is one of the main issues. Alignment signal contrast can be degraded by opaque stack materials or by alignment mark degradation due to processes like CMP. This issue can be compounded by mark sub-segmentation from design rules in combination with double or quadruple spacer process. Alignment signal contrast can be improved by applying new material or process optimization, which sometimes lead to the addition of another process-step with higher costs. If we can amplify the signal components containing the position information and reduce other unwanted signal and background contributions then we can improve alignment performance without process change. In this paper we use ASML's new alignment sensor (as was introduced and released on the NXT:1980Di) and sample wafers with special stacks which can induce poor alignment signal to demonstrate alignment and overlay improvement.
Immersion scanners remain the critical lithography workhorses in semiconductor device manufacturing. When progressing towards the 7nm device node for logic and D18 device node for DRAM production, pattern-placement and layer-to-layer overlay requirements keep progressively scaling down and consequently require system improvements in immersion scanners. The on-product-overlay requirements are approaching levels of only a few nanometers, imposing stringent requirements on the scanner tool design in terms of reproducibility, accuracy and stability.<p> </p> In this paper we report on the performance of the NXT:1980Di immersion scanner. The NXT:1980Di builds upon the NXT:1970Ci, that is widely used for 16nm, 14nm and 10nm high-volume manufacturing. We will discuss the NXT:1980Di system- and sub-system/module enhancements that drive the scanner overlay, focus and productivity performance. Overlay, imaging, focus, productivity and defectivity data will be presented for multiple tools. <p> </p>To further reduce the on-product overlay system performance, alignment sensor contrast improvements as well as active reticle temperature conditioning are implemented on the NXT:1980Di. Reticle temperature conditioning will reduce reticle heating overlay and the higher contrast alignment sensor will improve alignment robustness for processed alignment targets. <p> </p>Due to an increased usage of multiple patterning techniques, an increased number of immersion exposures is required. NXT:1980Di scanner design modifications raised productivity levels from 250wph to 275wph. This productivity enhancement provides lower cost of ownership (CoO) for customers using immersion technology.
Progressing towards the 10nm and 7nm imaging node, pattern-placement and layer-to-layer overlay requirements keep on scaling down and drives system improvements in immersion (ArFi) and dry (ArF/KrF) scanners. A series of module enhancements in the NXT platform have been introduced; among others, the scanner is equipped with exposure stages with better dynamics and thermal control. Grid accuracy improvements with respect to calibration, setup, stability, and layout dependency tighten MMO performance and enable mix and match scanner operation. The same platform improvements also benefit focus control. Improvements in detectability and reproducibility of low contrast alignment marks enhance the alignment solution window for 10nm logic processes and beyond. The system’s architecture allows dynamic use of high-order scanner optimization based on advanced actuators of projection lens and scanning stages. This enables a holistic optimization approach for the scanner, the mask, and the patterning process. Productivity scanner design modifications esp. stage speeds and optimization in metrology schemes provide lower layer costs for customers using immersion lithography as well as conventional dry technology. Imaging, overlay, focus, and productivity data is presented, that demonstrates 10nm and 7nm node litho-capability for both (immersion & dry) platforms.
In this paper we report on the performance enhancements on the NXT immersion scanner platform to support the immersion lithography roadmap. We particular discuss scanner modules that enable future overlay and focus requirements. Among others we describe the improvements in grid calibrations and grid matching; thermal control of reticle heating with dynamic systems adjustments; aberration tuning and FlexWave-lens heating control as well as aberration- and overlay-metrology on wafer-2-wafer timescales. Finally we address reduction of leveling process dependencies, stage servo dynamics and wafer table flatness to enhance on-product focus and leveling performance. We present and discuss module- and system-data of the above mentioned scanner improvements.
Immersion lithography is being extended to the 20-nm and 14-nm node and the lithography performance requirements need to be tightened further to enable this shrink. In this paper we present an integral method to enable high-order fieldto- field corrections for both imaging and overlay, and we show that this method improves the performance with 20% - 50%. The lithography architecture we build for these higher order corrections connects the dynamic scanner actuators with the angle resolved scatterometer via a separate application server. Improvements of CD uniformity are based on enabling the use of freeform intra-field dose actuator and field-to-field control of focus. The feedback control loop uses CD and focus targets placed on the production mask. For the overlay metrology we use small in-die diffraction based overlay targets. Improvements of overlay are based on using the high order intra-field correction actuators on a field-tofield basis. We use this to reduce the machine matching error, extending the heating control and extending the correction capability for process induced errors.
Mainstream high-end lithography is currently focusing on 32 nm node and 22 nm node where 1.35 NA immersion
technology is well established for the most critical layers. Double-patterning and spacer-patterning techniques have been
developed and are being widely used to print the most critical layers.
Further down the lithography roadmap we see 1x nm nodes coming where EUV lithography will take over critical
layers from immersion. In order to enable a smooth industry-wide transition towards EUV, 1.35 NA immersion
technology will continue to play a critical role in manufacturing front end layers in the coming years. Using immersion
technology beyond the 22 nm node, we expect an increase in the use of double and even quadruple patterning
technology for the critical layers. This demands tighter control of especially overlay and focus performance on the 1.35
NA immersion tools. Also fully flexible illumination and wave front control will be needed to optimize the contrast for
these low k1 applications.
In this paper we present the state-of-the-art system performance of today's 1.35 NA ArF immersion tool production
workhorse, the TWINSCAN NXT:1950i. Furthermore we show the required scanner improvements on imaging, overlay
and cost of ownership to enable device shrink below the 20 nm node in 2013 using immersion technology.
The semiconductor industry has adopted water-based immersion technology as the mainstream high-end litho enabler
for 5x-nm and 4x-nm devices. Exposure systems with a maximum lens NA of 1.35 have been used in volume
production since 2007, and today achieve production levels of more than 3400 exposed wafers per day. Meanwhile
production of memory devices is moving to 3x-nm and to enable 38-nm printing with single exposure, a 2nd generation
1.35-NA immersion system (XT:1950Hi) is being used. Further optical extensions towards 32-nm and below are
supported by a 3rd generation immersion tool (NXT:1950i).
This paper reviews the maturity of immersion technology by analyzing productivity, robust control of imaging, overlay
and defectivity performance using the mainstream ArF immersion production systems. We will present the latest results
and improvements on robust CD control of mainstream 4x-nm memory applications. Overlay performance, including
on-product overlay control is discussed. Immersion defect performance is optimized for several resist processes and
further reduced to ensure high yield chip production even when exposing more than 15 immersion layers.
Immersion lithography started to become the main workhorse for volume production of 45-nm devices, and while
waiting for EUV lithography, immersion will continue to be the main technology for further shrinks. In a first step
single exposure can be stretched towards the 0.25 k1 limit, after which various double patterning methods are lining up
to print 32-nm and even 22-nm devices. The immersion exposure system plays a key role here, and continuous
improvement steps are required to support tighter CD and overlay budgets. Additionally cost of ownership (COO) needs
to be reduced and one important way to achieve this is to increase the wafer productivity. In this paper we discuss the
design and performance of a new improved immersion exposure system XT:1950i. This system will extend immersion
towards 38-nm half pitch resolution using a 1.35 NA lens and extreme off axis illumination (e.g. dipole). The system
improvements result in better CDU, more accurate overlay towards 4-nm and higher wafer productivity towards 148-
wph. Last but not least a next step in immersion technology is implemented. A novel immersion hood is introduced
giving more robust low and stable defects performance.
Laser cutting has been investigated for a number of aluminum-synthetic laminates, newly developed materials for the aeronautic and automotive industry. The materials consist of alternating aluminum and synthetic layers. It is shown that these materials can be cut at rates comparable to those of homogeneous aluminum alloys. The cuts show little dross attachment. Also some damage on the synthetic layers has to be accepted. These results initiated a modeling exercise, which resulted in a numerical simulation code. The applied cutting model is based on describing the material in several horizontal layers, each with its own specific thermophysical and optical properties. The separate layers are coupled by known mass, energy and force balanced equations.