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.
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.
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
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.
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.
Proximity effects in optical lithography are under investigation for quite some time. Most of these studies focus on the understanding of the origin of the CD-through- pitch variations and are performed for a single point in the exposure field. Knowing the optical proximity effect, corrections on the reticle can be made to compensate for it (Optical proximity correction, OPC). However, because of the data complexity, corrections for a certain duty cycle are applied independent of location in the exposure field. In order to make CD biasing on the reticle cost effective, the proximity effect variations across the exposure field need to be small. The cycle of measuring the proximity effects, applying corrections to the reticle layout and measuring again on the wafer is very time-consuming. Therefore there is a big gain if proximity corrections, as determined on one individual system, can be applied to other exposure tools without extensive testing and modification of OPC. This implies that proximity effects need to be constant through the slit of an individual tool and constant from one tool to another. In this paper we will study the across slit of the lens and tool-to-tool variation of the optical proximity effect.
This work analyzes the contributions to CD variation by building 3 predictive models that describe linewidth variation. The first model uses an exposure and focus budget analysis to create distributions that are used as input into a Monte Carlo analysis, where the output is a distribution of linewidth. The second model explores the effects of systematic intra-field effects by assuming that lens properties such as aberration will only cause global changes to the CD function, i.e. the function only shifts in focus and exposure. In combination with measurements such as focal pane, illumination uniformity and flare, a description of AFLV is constructed that reveals CD maps of the image field as a function of system focus and exposure. The third model combines the previous two techniques by incorporating random and systematic errors to create an across-wafer linewidth variation simulation. An example is shown using a scanner system and 0.18 micrometers structures. Systematic contributors to AFLV such as aberrations and reticle errors are included, as well as addition of random distributions of tilt eros and full wafer processing errors.