We have developed a new scheme of process control combining a CD metrology system and an exposure tool. A new
model based on Neural Networks has been created in KLA-Tencor's "KT Analyzer" which calculates the dose and
focus errors simultaneously from CD parameters, such as mid CD and height information, measured by a scatterometry
(OCD) measurement tool. The accuracy of this new model was confirmed by experiment. Nikon's "CDU master" then
calculated the control parameters for dose and focus per each field from the dose and focus error data of a reference
wafer provided by KT Analyzer. Using the corrected parameters for dose and focus from CDU master, we exposed
wafers on an NSR-S610C (ArF immersion scanner), and measured the CDU on a KLA SCD100 (OCD tool). As a result,
we confirmed that CDU in the entire wafer can be improved more than 60% (from 3.36nm (3σ) to 1.28nm (3σ)).
Extreme Ultra Violet Lithography (EUVL) has been widely regarded as the lithography technology to succeed
optical lithography. It is now considered as one of the most promising technologies below hp45nm node [1], following
ArF immersion lithography considering trend of achievable process K1 factors. In this paper we would like to present
our significant progress on the development of EUV exposure tool. There are several key important areas which should
be developed to realize EUVL to be feasible, such as reflective mask, resist, and tool itself. The reflective mask features
such characteristics as pellicle-less, ultra-smooth blank flatness and defect free. The resist should be of high sensitivity
and small line edge roughness (LER) as well as fine resolution. EUV exposure tool itself consists of major modules
such as EUV light source, projection optics, vacuum body, vacuum stages, and so on. Nikon has developed new
polishing technologies such as ion-beam figuring and elastic emission machining, and new ultra high-precision
interferometers for aspheric surface metrology. Our multi-layer coating technology has been also improved. High
reflective Mo/Si multi layer coating has been successfully achieved and irradiation tests using synchrotron radiation
have been conducted. Successful achievement of those developments enables us to produce full-field projection optics
for EUVL process development tool called EUV1. The proto-type development of full-field projection optics has been
successfully completed and its technical achievement has reflected into production optics. Preparation of complete set
of production and metrology tools necessary for projection optics production was completed and all tools are now in
full operation.
Nikon has already developed dual pod reticle carrier for EUV1 tool. In parallel Nikon has been developing the
same concept carrier for HVM in cooperation with Canon and Entegris.
Regarding to EUV1 tool development, all modules of EUV1 such as full-field projection optics module,
illumination optics module, vacuum body module, vacuum compatible reticle/wafer stage modules, reticle/wafer loader
modules, EUV light source module have been completed. Nikon has already started EUV1 module installation process
and the module level function and basic performance have been being checked. Nikon will complete module integration
to achieve the first exposure result. Some development results will be shown which lead to confidence for realization of
EUVL. Nikon also would like to announce that development of 1st generation production EUVL tool named EUV2 has
been studied.
Extreme Ultra Violet Lithography (EUVL) has been widely regarded as the lithography technology to succeed optical lithography. It is now considered as one of the most promising technologies below hp45nm node [1], following ArF immersion lithography considering trend of achievable process K1 factors shown in Fig. 1. In this paper we would like to present significant progress on the development of EUV exposure tool. There are several key important areas which should be developed to realize EUVL to be feasible such as reflective mask, resist, and tool itself. The reflective mask features such characteristics as pellicle-less, ultra-smooth blank flatness and defect free. The resist should be of high sensitivity and small line edge roughness (LER) as well as fine resolution. EUV exposure tool itself consists of major modules such as EUV light source, projection optics, vacuum body, vacuum stages, and so on. As far as EUVL optics development is concerned, through the development of high-NA small-field EUV exposure system (HiNA) in conjunction with EUVA (Extreme Ultraviolet Lithography System Development Association) projects, we have developed new polishing technologies such as ion-beam figuring and elastic emission machining, and new ultra high-precision interferometers for aspheric surface metrology. Wave front sensor system has been also developed partly in EUVA project. A new wave front sensor system which can be used for evaluating the projection optics with EUV light has already been installed in New SUBARU synchrotron facility in University of Hyogo. Our multi-layer coating technology has been also improved. High reflective Mo/Si multi layer coating has been successfully achieved and irradiation tests using synchrotron radiation have been conducted [8]. Successful achievement of those developments enables us to produce full-field projection optics for EUVL process development tool called EUV1. Proto-type development of full-field projection optics has been successfully completed and evaluated to be of enough performance. Preparation of complete set of production and metrology tools necessary for projection optics production was completed and all tools are now in full operation.
Nikon has studied reticle protection method and developed Dual Pod Concept in cooperation with Canon. Nikon also has developed its own reticle cover to be implemented in EUV1 tool.
Nikon has completed almost all module fabrication such as full-field projection optics module, illumination optics module, vacuum body module, vacuum compatible reticle/wafer stage modules, reticle/wafer loader modules, and EUV light source module. Nikon has already got into module integration production process to meet EUV1 development schedule. Nikon announced to start EUV1 tool installation in 1st half of 2007 and has been proceeding it on schedule. Nikon also would like to announce that development of 1st generation production EUVL tool dubbed EUV2 is now considered and that system concept design is under way.
Extreme Ultra Violet Lithography (EUVL) is considered as the most promising technology below hp45nm node, following ArF immersion lithography. In this paper we would like to present significant progress on the development of EUV exposure tool with recent encouraging data of mirror polishing accuracy and evaluation results of Nikon reticle protection concept. EUV exposure tool consists of major important modules such as EUV light source, projection optics, and so on. As far as EUVL optics development is concerned, through the development of high-NA small-field EUV exposure system (HiNA), our mirror polishing and metrology technologies of aspheric mirror surface and multi-layer coating technology have been remarkably improved and enable us to fabricate high-precision aspheric mirrors which meet the specification for EUV pre-production tools called EUV1. In the EUVA (Extreme Ultraviolet Lithography System Development Association) project, we have developed new polishing technologies such as ion-beam figuring and new high-precision interferometers for aspheric surface metrology. Wave front sensor systems have been also developed partly in EUVA project. Installation of a new wave front sensor system which can be used for evaluating the full-field projection optics with EUV light has already been started in New SUBARU synchrotron facility in University of Hyogo. EUV1 tool system design and its detailed design of all modules such as full-field projection optics module, illumination optics module, vacuum body module, vacuum compatible reticle/wafer stage modules, reticle/wafer loader modules have been completed. The results of development and prototyping of major modules such as vacuum stage modules and vacuum body module have been reflected in the actual tool design. Nikon has been also heavily involved in the infrastructure development such as mask handling development. In order to meet industry demands, Nikon has been already getting into EUV1 module fabrication phase. Nikon announces that EUV1 tool is scheduled to be delivered in 1st half of 2007.
Electron Projection Lithography (EPL) is considered one of promising technologies below 45nm node, especially for contact/via holes and gate layers. EPL has some nice features such as very high resolution to be applied for two device nodes, large process margin associated with large depth of focus and an expected lower CoO. Nikon has been developing an EPL tool, so-called EB Stepper. NSR-EB1A is the first EB Stepper that was designed as R&D tool for 65nm technology node and that was already delivered for Selete (Semiconductor Leading Edge Technologies, Inc.) at Tsukuba in Japan. Nikon has developed two NSR-EB1A tools so far, one system for Selete as a 300mm wafer system and the other for Nikon's development and evaluation as a 200mm wafer system. Both tools have already started to show full performance data and good stability characteristics. The latest EB1A tool performance shows very good results in such data as the resolution of 50nm 2:1 L/S and 60nm 1:1 dense contact holes patterns, stitching accuracy of around 18nm, and overlay accuracy of around 20nm(X+3sigma).
As we move technology further and further down the geometry scale we are coming upon imaging situations where our use of existing optical lithography is being questioned due to the lack of process margin in manufacturing lines. This is especially apparent in the imaging of contacts where memory devices, that generally have the densest arrays of these features, may no longer be able to print the desired features. To overcome this it is necessary to either modify the design, a very expensive and time consuming process, or find an imaging process capable of printing the desired features. Electron Projection Lithography (EPL) provides an option to print very small features with a large process margin.
In this paper we detail the performance of both memory and logic based designs in an EPL process. We detail the manufacture and results of stencil mask manufacture. Data is also presented showing the imaging results (DOF, exposure latitude, pattern transfer) of features down to 50nm imaged on Nikon’s EB1A tool.
The development of Electron Projection Lithography (EPL) has proceeded for more than 10 years since its first description. EPL is regarded as a practical technology for 65 nm technology node and below. Nikon has been developing an EPL tool, named as the EB stepper. NSR-EB1A is the first EPL tool that has full functions for practical R&D use such as dynamic exposure by combination of electron beam deflection and stage scanning, wafer alignment, and so on. Some features of the EB stepper, which uses a 100 kV electron beam, are high resolution, and a large process margin associated with large depth of focus (DOF). Large DOF is a major feature of electron beam lithography.
In the previous paper, we reported data of dynamic resolution and subfield stitching accuracy as preliminary performances that were obtained by NSR-EB1A. Recently the development of EPL reticle is significantly progressed. Today, high quality 200 mm diameter EPL reticle is available from plural mask suppliers. Using 200mm EPL reticle, we achieved subfield stitching accuracy about 20nm (3s). And we also evaluated total performance such as CD uniformity, overlay accuracy. This paper reports the latest performance of NSR-EB1A.
Electron Projection Lithography (EPL) has a high potential for applicability beyond the ITRS 65 nm node, especially for contacts and gate layers. The concept of synchronization control of the Nikon EB stepper is explained. The reticle stage and the wafer stage are servo controlled to target positions individually. The residual stage position errors are compensated by the electron beam deflection control. The electron beam deflection is feed forward controlled using predicted stage position data from a subsystem called “Filter/Predictor”. The performance of the stage position prediction of the Filter/Predictor is described. This paper also reports the performance of the first EB stepper tool, the NSR-EB1A, during its preliminary adjustment phase. Dynamic scanning and stitching exposure, which requires synchronization of both the beam deflection motion and the stage scanning motion, was realized. Dynamic resolution of 100 nm and dynamic subfield stitching accuracy of 25 nm (3sigma) were obtained, and further improvement is expected.
For position measurements of the EPL reticle, a new concept reticle holder is proposed. This holder clamps the same surface during measurement as during exposure in Nikon's EPL tool, the EB Stepper. Thus the holder reproduces the deformation caused by clamping in a metrology tool with that in the EB Stepper. Investigation by simulation is described. Furthermore, an experimental holder based on this concept was manufactured, and the deformation of a 200 mm EPL reticle was measured. The experimental results and simulation results show an advantage of this method.
In Electron Projection Lithography (EPL) that is desigend for 65nm production tool, proximity effect correction (PEC) is an important issue for an accurate feature size control. Reticle resizing meethod is adopted for its correction. High controllability (ΔCD within ±10%) of critical dimension (CD) is required after proximity effect correction. For estimating the CD controllability, we have evaluated its dependency on exposure dose and beam blur in resizing method for the first time in EPL using Nikon's EPL experimental column (acceleration voltage=100kV, magnification=1/4, sub field size=250×250μm). Evaluating patterns were the target size of 100nm isolated line and twin lines. Beam blur was controlled by changing focus and was measured by Aerial Image Sensor (AIS). Groups of different biased patterns were located at different distances from large pattern on the wafer respectively. As a result, CD variation by proximity effect was 35-40 nm for 100nm-isolated. Under our recommended condition that resizing range in puls side was equal to that in minus side (±20%), blur latitude and dose latitude satisfied our CD uniformity budget and mask enhanced error factor (MEF) was around 1, then reticle fabrication CD controllability from budget requirement was satisfied. Therefore it was shown that proposed proximity effect correction method achieved high CD controllability.
The imaging concept of electron projection lithography (EPL) with a silicon stencil reticle is explained. A silicon membrane thickness of 1-2 micrometers is suitable for the reticle. A scattering contrast of greater than 99 percent is expected. Nikon is developing EPL tool as EB stepper. Sub- field size is 0.25 mm square and deflection length is 5mm on wafer. The wafer is exposed with a sub-field by sub-field bias by the deflection control of the electron beam. The basic system configuration of EB stepper is introduced. Examples of error budgets of CD variations and Overlay/Stitching accuracy for 65nm technology node are shown. The latest data of electron optics and vacuum compatible stages for EB stepper are introduced. 70nm patterns are resolved in the entire sub-field. The status of infrastructure of technology related to EPL reticle and data post processing software are explained.
KEYWORDS: Signal detection, Image sensors, Calibration, Silicon, Sensors, Electron beams, Electron beam lithography, Signal to noise ratio, Optical testing, Projection lithography
A direct means of measuring the image blur of electron beam projection lithography (EPL) tools is described. We developed an aerial image sensor using a Si membrane knife-edge and a transmitted electron detection technique. The aerial image sensor is designed to increase signal amplitude and signal contrast in order to yield a large signal to noise ratio even under a low beam current density condition. The image blur can be quantified accurate to a few nanometers because the measurement error due to the sensor is extremely small. The aerial image sensor was installed in Nikon's electron beam projection experimental column and was evaluated. The measured image blur, defined as the distance between the 12% and 88% points of the beam edge profile, under the optimum condition was 13 nm, and the measurement repeatability was 3 nm (3 sigma). The application of this technique to a system calibration is demonstrated. Focus and astigmatism were measured and the optimum settings of focus coils and stigmators were determined with excellent repeatability. The potential for this technique to provide an automated self-calibration system on EPL tools is clearly shown.
For electron beam projection lithography system, it is one of the most important issues to stitch desired patterns accurately. We have found a way to stitch the patterns with high accurate critical dimension by a pattern edge deformation that moderates a stitching error by as much as 2.5 times compared with no-deformed edge.
The latest development status of EB Stepper is reported. The experimental data include the latest resist image data exposed by 100keV electron beam, mask error factors and dosage margins at several backscattered electron levels, transmission data of continuous membrane reticles, and recommended structures for alignment marks, etc. The basic studies related to system design are also explained, those are the strategy for the management of reticle deformation and the stitching accuracy in overlaid layers, etc. Through these data, the resolution capability down to 50nm technology node is clearly shown and alignment/stitching capability is also described. The requirement to a continuous membrane reticle is indicated from experimental data.
KEYWORDS: Image sensors, Signal detection, Calibration, Sensors, Signal to noise ratio, Silicon, Monochromatic aberrations, Electron beams, Projection lithography, Electron beam lithography
A direct means of measuring an image blur of electron beam projection lithography (EPL) tools is described. An aerial image sensor used for the image blur measurement was fabricated and evaluated. The signal to noise ratio (SNR) was very high and the signal contrast was 97%. The measured image blur, defined as the distance between 12% and 88% of the beam edge profile, under the optimum condition was 13 nm and the measurement repeatability was 3 nm (e sigma). The measurement error due to the sensor was extremely small, and a quantitative measurement of the image blur can be realized using this technique. The application of this technique to a system calibration is demonstrated. Focus and astigmatism were measured and the optimum settings of focus coils and stigmators were determined with an excellent repeatability. The potential for this technique to provide an automated self-calibration system on the EPL tools is clearly shown.
The imaging concept of electron projection lithography (EPL) with silicon stencil reticle is explained. A silicon membrane thickness of 1 - 4 micrometer is suitable for the reticle. A scattering contrast of greater than 99% is expected. Nikon EB stepper's dynamic writing strategy of discrete exposure on a sub-field by sub-field basis with deflection control of the electron beam is explained. The basic system configuration of EB stepper is introduced. Examples of error budget for CD variation and Overlay/Stitching are shown. Nikon's policy for countermeasures for critical issues such as proximity effect correction, sub-field/complementary stitching and wafer heating influence are explained. For extensibility down to 70 nm and below, both exposure tool and reticle should be improved.
An electron projection lithography (EPL) system which projects reticle patterns onto a wafer will be applied to sub 100 nm lithography. Requirements for line width accuracy are very strict as feature sizes are less than 100 nm. For electron beam lithography, proximity effect corrections have always been an important issue for accurate feature width control. In this paper characteristics of several correction methods are examined, and appropriate correction methods for 100 kV EPL are introduced. Employing the shape correction method burdens the reticle pattern preparation system much more than other methods. Therefore a calculation method suitable for 100 kV EPL where the backscatter radius is very wide ((beta) b approximately equals 30 micrometer) and the forward scatter radius is narrow ((beta) f approximately equals 7 nm) has been developed. The calculation of deposition energy by the backscattered electron beam is carried out with a coarse grid but wide range. The calculation of the combined effect of the electron scattering blurs from the features is carried out only within a narrow range. The correction calculation is carried out using both of these results. Using this method, accurate and fast calculations can be achieved. Employing the GHOST correction method increases total exposure cost. The practical GHOST correction methods may also be improved. An additional correction method named shape correction with GHOST is also shown.
Nikon is developing an Electron Beam (EB) stepper as one of the next-generation lithography systems for feature sizes of less than 100 nm. As a reticle for the EB stepper using a high power EB (acceleration voltage: 100 kV, current on reticle: 100 (mu) A), a scattering stencil reticle with a grid-grillage structure has been investigated, EB projection experimental column which operates a high power EB was constructed. Some experimental data of scattered electron characteristics using the EB projection experimental column are given as follows: (1) Scattering contrast of 99.9% can be obtained using 100 kV electron beam (membrane thickness; 2 micrometer, aperture half angle onto reticle; 2 mrad). (2) Changes of resist pattern width of 1:1 and 1:2 lines and spaces are around 40% and around 20% respectively due to the proximity effects by backscattered electrons form the silicon substrate. (3) Contrast of EB mark detection for the system calibration, the reticle alignment, and the wafer registration is obtained. Comparing with the values that be obtained by theoretical calculation, some of experimental data gave good agreement.
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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