With the introduction of the NXE:3100 NA=0.25 exposure system a big step has been made to get EUV
lithography ready for High Volume Manufacturing. Over the last year, 6 exposure systems have been
shipped to various customers around the world, active in Logic, DRAM, MPU and Flash memory, covering
all major segments in the semi-conductor industry. The integration and qualification of these systems have
provided a great learning, identifying the benefits of EUV over ArF immersion and the critical parameters
of the exposure tool and how to operate it.
In this paper we will focus specifically on the imaging performance of the NXE:3100 EUV scanner.
Having been operational for more than a year a wide range of features were evaluated for lithographic
performance across the field and across wafer. CD results of 32nm contact holes, 27nm isolated and dense
lines, 27nm two-bar, 22nm dense L/S with Dipole, as well as several device features will be discussed and
benchmarked against the current ArF immersion performance. A budget verification will be presented
showing CD and contrast budgets for a selection of lithographic features. The contribution of the resist
process and the mask will be discussed as well.
The litho performance optimization will be highlighted with the 27nm twobar and isolated lines features
that are sensitive to the illuminator pupil shape and projection lens aberrations.
We will estimate the amount of resist induced contrast loss for 27 and 22nm L/S based on measurements of
Exposure Latitude and the contributors from the exposure system.
We will further present on the impact of variations in the mask blank and patterned mask on imaging, with
several new contributors to take into account compared to traditional transmission masks.
Finally, the combined results will be projected to the NXE:3300 NA=0.33 exposure system to give an
outlook for its imaging performance capabilities.
Extreme ultraviolet lithography (EUVL) sources emit a broad spectrum of wavelengths ranging from EUV to DUV and
beyond. If the deep ultraviolet (DUV) reaches the wafer it will affect imaging performance by exposing the photoresist.
Hence it is critical to determine the amount of DUV out of band (OoB) present in a EUVL tool, as well as its effect on
the printed features on the wafer.
In this study we investigate the effect of DUV OoB in EUVL. A model is developed in order to be able to quantify the
DUV/EUV ratio at wafer level and all the required input parameters are estimated in the range from 140 to 400nm, as
well as for the EUV at 13.5nm. The transmission of the optical system was estimated based on the optical design and
reflectivity measurements of the mirrors. The mask reflectivity for multilayer (ML) and absorber was measured at
wavelengths down to 140 nm and for EUV. The sensitivity to EUV and DUV for a variety of resist platforms was
measured at 13.5 nm, 157 nm, 193 nm, 248 nm and 365 nm. The source spectra were also measured. By using these
inputs, it was possible to estimate the DUV/EUV ratio for two different ASML tool configurations, the EUV Alpha
Demo Tool and the NXE:3100. Both NXE:3100 with LPP (laser produced plasma) source and Alpha Demo Tool with
DPP (discharge produced plasma) source show less than 1% DUV/EUV ratio in resist.
The modeling predictions were compared to experimental results. A methodology is introduced to measure the
DUV/EUV ratio at wafer level in situ. With this aim, an aluminum coated mask was fabricated and its reflectivity was
qualified in both EUV and DUV wavelength range. By comparing the dose to clear exposures of a reflective blank and
of the aluminum mask, it is possible to quantify the DUV/EUV ratio. The experimental results are in order of magnitude
agreement with modeling predictions. The proposed experimental approach can be used to benchmark the DUV
sensitivity of different resist platforms and may be used to monitor DUV OoB.
To extend the application of current optical lithographic tools to next generation production technology, it is necessary to reduce the k1 factor in Rayleigh's resolution equation. Double dipole lithography (DDL) is one of the candidates for a low-k1 imaging technique and it is a viable solution for 65- and 45-nm technology nodes. Because DDL takes has the advantage of extreme off-axis illumination of the dipole, the printing capability of small features as well as their through-pitch common process window can be enhanced. However, as a dipole illuminator gains the benefits of high contrast only for structures perpendicular to the dipole orientation, the original mask layout must be converted into horizontal and vertical components and printed in a double exposure. Throughput will be sacrificed due to the multiple exposures. Nevertheless, DDL mask manufacture is relatively simple compared to the production of the more complicated phase shift mask (PSM) and chromeless phase lithography (CPL). As regards an overlay issued from the separate image composition, several papers have shown the minor effect on pattern fidelity using the current ArF scanner. To split the design layout according to the pattern orientation, the double exposure scheme needs an automatic layout conversion algorithm. To integrate the H V conversion with model- and/or rule-based optical proximity corrections (OPCs), several approaches for pattern decomposition associated with OPC treatment have been suggested. In this paper we will go over the development of model- and rule-based OPC treatment and will focus on current technology for accurate model-based OPC development with empirical model calibration. Using the technique the lithographic performances such as pattern fidelity, process window as well as overlay error sensitivity will be demonstrated. We focus on a 65-nm technology node with k1 near 0.31. Based on the success of tool development and verification, the DDL with full-chip OPC-treated decomposition will become a mature low-k1 imaging solution.
Double Dipole Lithography (DDL) has been demonstrated to be capable of imaging complex 2D patterns for full-chip application. Due to inherently high aerial image contrast, we have found that there is strong potential for this technology to meet manufacturing line width roughness (LWR) and critical dimension uniformity (CDU) requirements for the 65nm node using ArF binary chrome masks or 6% attenuated phase shift mask (AttPSM). For patterning at k1 less than 0.35, DDL is a Resolution Enhancement Technology (RET) that offers an acceptable process window without resorting to costly hard phase shift masks. To use DDL for printing actual IC device patterns, the original design data must be converted into “vertical (V)” and “horizontal (H)” masks for the respective X and Y dipole exposures. An improved model-based DDL mask data processing steps has been demonstrated that it is possible to convert complex logic and memory data to X-Y dipole exposure compatible layout. Due to the double exposure, stray light must be well controlled to ensure uniform printing across the entire chip. One solution to minimize stray light is to apply large patches of chrome in open field areas to reduce the background transmission during exposure. Unfortunately, this is not feasible for most poly gate masks using a positive resist process. In this work, we report an improved model based DDL layout conversion methodology for full-chip application. A new generation of DDL technology reticle set was developed to verify the performance. Background light shielding is a critical part of the DDL. We report an innovative shielding scheme to minimize the negative impact of stray light for the critical features during double exposures.
Double Dipole Lithography (DDL) is one of the candidates for extending optical lithography into the k1=0.30 regime. In 2001 the first experimental 2D elbow structures were reported. In 2002 a rule based decomposition and a model assisted decomposition method were presented. In 2003 a new, model based decomposition step has been presented. Now we present the results of applying this model based decomposition by discussing the first experimental results on a 0.75 NA ArF scanner printing 70 nm lines at various pitches (160 nm and larger, i.e. k1=0.31 and up). We provide an assessment of the current state of maturity of the DDL technology for the low-k1 regime (0.3..0.4). This is based upon CD uniformity, 2D pattern fidelity and through pitch process latitude behavior.
Double Dipole Lithography (DDL) has been demonstrated to be capable of patterning complex 2D patterns. Due to inherently high aerial imaging contrast, especially for dense features, we have found that it has a very good potential to meet manufacturing requirements for the 65nm node using ArF binary chrome masks. For patterning in the k1<0.35 regime without resorting to hard phase-shift masks (PSMs), DDL is one unique Resolution Enhancement Technique (RET) which can achieve an acceptable process window. To utilize DDL for printing actual IC devices, the original design data must be decomposed into “vertical (V)” and “horizontal (H)” masks for the respective X- and Y-dipole exposures. An improved two-pass, model-based, DDL mask data processing methodology has been established. It is capable of simultaneously converting complex logic and memory mask patterns into DDL compatible mask layout. To maximize the overlapped process window area, we have previously shown that the pattern-shielding algorithm must be intelligently applied together with both Scattering Bars (SBs) and model-based OPC (MOPC). Due to double exposures, stray light must be well-controlled to ensure uniform printing across the entire chip. One solution to minimize stray light is to apply large patches of solid chrome in open areas to reduce the background transmission during exposure. Unfortunately, this is not feasible for a typical clear-field poly gate masks to be patterned by a positive resist process. In this work, we report a production-worthy DDL mask pattern decomposition scheme for full-chip application. A new generation of DDL technology reticle set has been developed to verify the printing performance. Shielding is a critical part of the DDL. An innovative shielding scheme has been developed to protect the critical features and minimize the impact of stray light during double exposure.
For cost-effective Integrated Circuit (IC) manufacturing, it is highly desirable to use Binary-Chrome Masks (BIMs) instead of Phase Shifting Masks (PSMs). For the 70nm technology node, it is of particularly appealing if Argon Fluoride (ArF) BIMs can still be used. In this paper, we demonstrate that double dipole ArF exposure together with BIMs is capable of achieving acceptable overlapped process window for printing 70nm Critical Dimension (CD) features. The main challenge of using such a technique for IC manufacturing is how to properly decompose the original mask patterns into two separate orientation masks (vertical and horizontal). To compensate for the possible two-dimensional (2D) pattern distortion due to the strong proximity effect, a novel set of
Currently, the 130 nm SIA node is being implemented at leading edge semiconductor manufacturing facilities. Previously, this node appeared to be the insertion point for 193 nm lithography. However, it is evident that for the majority of applications 248 nm will be the wavelength of choice. This once again raises the question how far DUV lithography (248 nm) will take us. To investigate this, overlay, imaging and productivity related issues have to be considered. Although these items become more and more linked at low k1-factors (e.g. overlay and imaging), this paper will focus on some of the imaging related topics.
Even with increasing numerical apertures and decreasing wavelength sin optical lithography, the practical k1 factor used in IC fabrication will continue to decrease ever closer to the theoretical 0.25 limit. This paper presents result of a feasibility study on 0.11 micrometers imaging with dipole illumination on a 0.70 NA KrF tool using a binary mask. The obvious advantage of dipole illumination techniques is the strong enhancement of exposure latitude (EL) and depth of focus (DOF) for specific dense structures. However, there are also many drawbacks for other feature types and geometries. These must be either avoided or overcome. To deal with these drawbacks int eh best way, detailed knowledge of the unwanted effects is needed. This article deals with two categories of trade-offs that must be considered when applying dipole illumination.
As critical dimensions continue to shrink in line with the SIA roadmap, the ratio of printed feature size and accepted wavelengths for optical lithography is driving inexorably towards the theoretical limitation of 0.25 for the Raleigh equation constant, k1. With the drive to lower k1 values fundamental limitations start to impact optical lithography. One example is the inability to simultaneously print features at different duty cycles with acceptable process windows. In the k1 regime down to 0.5, dense and isolated features could be printed in one with acceptable process windows. Today advanced lithography is operating at k1 values of 0.42-0.37 using KrF excimer laser light sources at a wavelength ((lambda) ) of 248nm. High lens Numerical Aperture (NA) is required to obtain sufficient aerial image contrast for dense lines, but results in reduced depth of focus which scales proportional to (lambda) /NA2. Using off-axis illumination techniques such as annular illumination can compensate the reduction in depth of focus for dense lines. For isolated lines high NA has only limited impact on the aerial image contrast due to the difference in the diffraction pattern and only serves to reduce the limited depth of focus which, unlike dense lines, does not benefit from the application of off-axis illumination. Use of increasingly strong imaging enhancement techniques will be required at lower k1 values resulting in further trade-offs to be addressed in pattern dependency. For example, quadrupole and di-pole off-axis illumination provides stronger enhancement to the available process window than annular illumination but only for features with specific orientations. In this paper an overview of the different imaging enhancement techniques will be given and examples of the trade-offs between enhancement and techniques, constraints on orientations and duty cycles will have to be applied in the device design. Alternatively, individual device layers will have to be separated by feature type, duty cycle and orientation to allow optimum enhancement techniques to be applied for each feature using multiple exposures. These approaches will be required if optical lithography at k1 values around 0.3 is to be realized. In the paper we will compare the use of two very strong enhancement techniques, dipole illumination and alternating (Levinson type) Phase Shift Mask with respect to process latitude, complexity and aberration sensitivity. To complete the review of low k1 the economic viability of optical lithography utilizing these strong enhancement techniques will be analyzed in terms of Cost of Ownership.