Along with device shrinkage, higher accuracy will continuously be required from photo-lithography tools in order to enhance on-product yield. In order to achieve higher yield, the advanced photo-lithography tools must be equipped with sophisticated tuning knobs on the tool and with software that is flexible enough to be applied per layer. This means photo-lithography tools must be capable of handling many types of sub-recipes and parameters simultaneously.
To enable managing such a large amount of data easily and to setup lithography tools smoothly, we have developed a total lithography system called Litho Turnkey Solution based on a new software application platform, which we call Plug and Play Manager (PPM). PPM has its own graphical user interface, which enables total management of various data. Here various data means recipes, sub-recipes, tuning-parameters, measurement results, and so on. Through PPM, parameter making by intelligent applications such as CDU/Overlay tuning tools can easily be implemented. In addition, PPM is also linked to metrology tools and the customer’s host computer, which enables data flow automation. Based on measurement data received from the metrology tools, PPM calculates correction parameters and sends them to the scanners automatically. This scheme can make calibration feedback loops possible. It should be noted that the abovementioned functions are running on the same platform through a user-friendly interface. This leads to smart scanner management and usability improvement.
In this paper, we will demonstrate the latest development status of Nikon’s total lithography solution based on PPM; describe details of each application; and provide supporting data for the accuracy and usability of the system. Keywords: exposure
This paper investigates the possibility of 193 nm immersion lithography extensions to sub-10 nm technology nodes using
the patterning scheme of unidirectional (1D) grating lines and cuttings. Technological feasibility down to 5 nm nodes is
examined with experimental data of self-aligned multiple patterning method (SAxP) and Litho-Etch (LE) cuttings. For
the cutting by LE repetition, relationship between node definition and the repetition number n (LE^n) is discussed. Cost
is evaluated for SADP, SAQP and SAOP to generate unidirectional grating formation, and the following LE^n cutting
process. Finally, schemes of gridded cutting and trim are introduced, and found to be advantageous to keep the scaling
merit of transistor cost at 7 and 5 nm technology nodes.
Current technology nodes, as well as subsequent generations necessitate ongoing improvements to the mix-and-match overlay (MMO) capabilities of lithography scanners. This work will introduce newly developed scanner solutions to address this requirement, and performance data from the latest generation immersion scanner, the NSR-S622D, will be introduced. Enhanced MMO accuracy is imperative for the 22 nm half-pitch and future technology nodes. In order for the matched overlay accuracy to approach single machine overlay (SMO) capabilities, MMO errors must be reduced further. The dominant MMO error sources can be divided into three main areas: SMO, lens distortion matching and wafer grid matching. Nikon continues to decrease these matching error contributors over time, and the latest generation NSRS622D immersion scanner provides a number of innovative solutions to satisfy the most demanding overlay matching requirements ; as a result MMO performance within 3nm is achieved on S622D. Moreover, overlay master system is developed for further product overlay accuracy and stability improvement.
To achieve the 2 nm overlay accuracy required for double patterning, we have introduced the NSR-S620D immersion
scanner that employs an encoder metrology system. The key challenges for an encoder metrology system include its
stability as well as the methods of calibration. The S620D has a hybrid metrology system consisting of encoders and
interferometers, in XY and Z. The advantage of a hybrid metrology system is that we can continuously monitor the
position of the stage using both encoders and interferometers for optimal positioning control, without any additional
metrology requirements or throughput loss. To support this technology, the S620D has various encoder calibration
functions that make and maintain the ideal grid, and control focus. In this paper we will introduce some of the encoder
calibration functions based on the interferometer. We also provide the latest performance of the tool, with an emphasis
on overlay and focus control, validating that the NSR-S620D delivers the necessary levels of accuracy and stability for
the production phase of double patterning.
Double patterning requires extremely high accuracy in overlay and high uniformity in CD control. For the 32 nm half
pitch, the CDU budget requires less than 2 nm overlay and less than 2 nm CD uniformity for the exposure tool. To meet
these requirements, Nikon has developed the NSR-S620D. It includes a new encoder metrology system for precise stage
position measurement. The encoder system provides better repeatability by using a short range optical path. For CD
uniformity control, various factors such as focus control, stage control, and dose control affect the results. Focus
uniformity is evaluated using the phase shift focus monitoring method. The function of "CDU Master" provides dose and
focus correction across the exposure slit, along the scan direction, and across the wafer. Stage synchronization variability
will also influence CD control. In this paper, we will show the actual results and analysis of the overall performance of
S620D, including the exposed result of pitch splitting double patterning. S620D has sufficient performance for the 32 nm
half pitch double patterning generation and shows potential for double patterning at the 22 nm half pitch node.
The problem of the alignment tree for double patterning (DP) is presented. When the 2nd DP exposure is aligned to the
underlying zero layer, the space CD uniformity is shown to be well outside the budget for the 32 nm HP node. Aligning
the 2nd DP layer to the zero layer gives better overlay results, but aligning the 2nd DP pattern to the 1st DP pattern gives
results well within the overlay requirements for the 32 nm HP. Aligning the 2nd DP layer to the 1st DP layer is
recommended to give the best CD uniformity and overlay results. Experimental results show, qualitatively, the CD
uniformity is significantly worse when the 2nd pattern is aligned to the zero layer, but the overlay for both alignment trees
could be corrected to roughly the same levels. The raw overlay data shows a significantly different signature for the two
alignment trees, possibly caused by alignment mark signal differences between the marks on the zero and 1st layers, or
distortion of the zero layer after the first etch. The requirements for a DP exposure tool were reviewed and can be
summarized as improved dose control, improved overlay performance, and significantly higher throughput.
Double patterning (DP) has now become a fixture on the development roadmaps of many device manufacturers for half pitches of 32 nm and beyond. Depending on the device feature, different types of DP and double exposure (DE) are being considered. This paper focuses on the requirements of the most complex forms of DP, pitch-splitting (where line density is doubled through two exposures) and spacer processes (where a deposition process is used to achieve the final pattern). Budgets for critical dimension uniformity and overlay are presented along with tool and process requirements to achieve these budgets. Experimental results showing 45-nm lines and spaces using dry ArF lithography with a k1 factor of 0.20 are presented to highlight some of the challenges. Finally, alternatives to DP are presented.
Critical processing factors in the lithography process include overlaying the pattern properly to previous layers and
properly exposing the pattern to achieve the desired line width. Proper overlay can only be attained in the lithography
process while the desired line width accuracy is achieved by both lithography and etch processes. Since CD is
substantially influenced by etch processing, therefore, it is possible to say that overlay is one of the most important
processing elements in the lithography process. To achieve the desired overlay accuracy, it is desirable to expose critical
layers with the same exposure tool that exposed the previous or target layer. This need to dedicate a particular exposure
tool, however, complicates the lot dispatching schedule and, even worse, decreases exposure tool utilization. In order to
allow any exposure tool available to print the arriving lot, M&M (Mix and Match) overlay control becomes necessary.
By reducing overlay errors in M&M control, lot dispatching scheduling will become more flexible and exposure tool
utilization will improve.
Since each exposure tool has a unique registration signature, high order errors appear when overlaying multiple layers
exposed with different tools. Even with the same exposure tool, if a different illumination is used, a similar error will be
seen. A correction scheme to make the signature differences has to be implemented, however manually characterizing
each tool's signature per illumination condition is extremely tedious, and is subject human errors. The challenge is to
design a system to perform the corrections automatically.
In the previous paper(1), we have outlined concepts of the system scheme. The system has subsequently been developed
and tested using exposure tools. In this paper test results are shown using automated distortion correction. By analyzing
the results, suggestions for further improvements and further developments are shown.
Nikon's production immersion scanners, including the NSR-S609B and the NSR-S610C, have now been in the field for
over 2 years. With these tools, 55 nm NAND Flash processes became the first immersion production chips in the world,
and 45 nm NAND Flash process development and early production has begun. Several logic processes have also been
developed on these tools. This paper discusses the technical features of Nikon's immersion tools, and their results in
production.
Double patterning (DP) has now become a fixture on the development roadmaps of many device manufacturers for half
pitches of 32 nm and beyond. Depending on the device feature, different types of DP and double exposure (DE) are
being considered. This paper focuses on the requirements of the most complex forms of DP, pitch splitting, where line
density is doubled through two exposures, and sidewall processes, where a deposition process is used to achieve the final
pattern. Budgets for CD uniformity and overlay are presented along with tool and process requirements to achieve these
budgets. Experimental results showing 45 nm lines and spaces using dry ArF lithography with a k1 factor of 0.20 are
presented to highlight some of the challenges. Finally, alternatives to double patterning are presented.
As Moore's Law drives CD smaller and smaller, overlay budget is shrinking rapidly. Furthermore, the cost of advanced
lithography tools prohibits usage of latest and greatest scanners on non-critical layers, resulting in different layers being
exposed with different tools; a practice commonly known as 'mix and match.' Since each tool has its unique signature,
mix and match becomes the source of high order overlay errors. Scanner alignment performance can be degraded by a
factor of 2 in mix and match, compared to single tool overlay operation. In a production environment where scanners
from different vendors are mixed, errors will be even more significant. Mix and match may also be applied to a single
scanner when multiple illumination modes are used to expose critical levels. This is because different illuminations will
have different impact to scanner aberration fingerprint. The semiconductor technology roadmap has reached a point
where such errors are no longer negligible.
Mix and match overlay errors consist of scanner stage grid component, scanner field distortion component, and process
induced wafer distortion. Scanner components are somewhat systematic, so they can be characterized on non product
wafers using a dedicated reticle. Since these components are known to drift over time it becomes necessary to monitor
them periodically, per scanner, per illumination.
In this paper, we outline a methodology for automating characterization of mix and match errors, and a control system
for real-time correction.
Overlay accuracy is a key issue in the semiconductor manufacturing process. To achieve overlay requirements, we developed compensation functions, i.e. Enhanced Global Alignment (EGA), Super Distortion Matching (SDM), and Grid Compensation for Matching (GCM). These functions are capable to reduce all the components except local linear components caused by a wafer global deformation. In this paper we introduce a novel correction framework which includes new compensation function called Shot Correction by Grid Parameter; thereby enabling further enhancements to overlay. Using this novel framework, we show both simulation and experimental data demonstrating improved overlay accuracy.
Nikon has developed cutting-edge lithography tools, and its product lineup encompasses all exposure wavelengths. They are: the NSR-S307E ArF scanner for the 90nm node; the NSR-S207D KrF scanner for the 110nm node; the NSR-SF130 i-line stepper for the middle layer and the new concept NSR-SF200 KrF stepper, which offers unparalleled productivity and cost performance. In addition, a powerful support system is provided, the Lithography Equipment Engineering System, which will allow its customers to use all of these exposure tools simultaneously and derive the maximum benefit of the mix-and-match strategy. The use of this system will increase the uptime and enable their combined performance to exceed that of a stand-alone tool.Latest actual performance data from each of the tools and the result of the optimization performed using application software will be reported.
A KrF step and scan exposure system using a projection lens has been developed. The exposure field is 25mm by 33mm which is large enough to fit two 256Mbit DRAM chips. The maximum numerical aperture is 0.6 and the maximum coherence factor of the illumination system is 0.75 for the maximum numerical aperture. Original design concepts for scanning technologies are introduced. Actual data of the system indicate the sufficient performance for 250nm design rule device production.
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