With the introduction of its fifth-generation NXE:3400B scanner, ASML brought EUV to High- Volume Manufacturing for 7 nm node lithography and beyond with full support of pellicle. This paper presents an update on lithographic performance results obtained with the NXE:3400B, characterized by an NA of 0.33, a Pupil Fill Ratio (PFR) of 0.2 and throughput capability of 125 wafers per hour. Advances in source power and system availability have enabled a continued increase of productivity. To maximize the number of yielding dies per day excellent Overlay, Focus, and Critical Dimension (CD) control have been realized, combining intrinsic tool stability with holistic control schemes. We will also show matching performance for both Overlay and Imaging, and further improvements in Focus Process Dependencies for the 5nm node.
Immersion lithography has been developed in a tremendous pace. Starting in late 2001, the technology now has moved
to volume production of advanced flash memories. The immersion exposure system has been the key enabler in this
progress. In this paper we discuss the evolution of the TWINSCAN immersion scanning exposure tools, and present an
overview of its performance on imaging, lens heating control, overlay, focus and defects. It is shown that stable
performance assures 45-nm device volume manufacturing. Extendibility of immersion towards 38-nm and 32-nm is
discussed. For NAND the next device half pitch will be around 38-nm and it is shown that with 1.35 NA and low k1
dipole or CQUAD illumination a final extension with single exposure is possible. For the 32-nm node and beyond
double patterning methods are required till EUV lithography is ready to be used in volume production. To secure tight
CD tolerance the overlay performance of the immersion tools need to be tightened to numbers well below 3-nm. The
paper presents overlay improvements towards the requirements for double patterning.
Water based immersion lithography is now widely recognized a key enabler for continued device shrinks beyond the
limits of classical dry lithography. Since 2004, ASML has shipped multiple TWINSCAN immersion systems to IC
manufacturers, which have facilitated immersion process integration and optimization. In early 2006, ASML
commenced shipment of the first immersion systems for 45nm volume production, featuring an innovative in-line
catadioptric lens with a numerical aperture (NA) of 1.2 and a high transmission polarized illumination system. A
natural extension of this technology, the XT:1900Gi supports the continued drive for device shrinks that the
semiconductor industry demands by offering 40nm half-pitch resolution. This tool features a projection lens based on
the already proven in-line catadioptric lens concept but with an enhanced, industry leading NA of 1.35. In this paper, we
will discuss the immersion technology challenges and solutions, and present performance data for this latest dual wafer
stage TWINSCAN immersion system.
This paper discusses the current performance and the evolution of five generations TWINSCAN immersion scanning
exposure tools. It is shown that production worthy overlay and focus performance can be achieved at high scan speeds.
The more critical part for immersion tools is related to defects, but also here improvements resulted in production
worthy defect levels. In order to keep the defect level stable special measures are needed in the application of wafers.
Especially Edge Bead Removal (EBR) design and wafer bevel cleanliness are important.
The polarization properties of light become more and more important as numerical apertures of the projection lens increase. With unpolarized light the contrast of the image is degraded because of poor interference of the TM component of the light. By applying only TE linear polarized illumination light, the contrast loss can be minimized. The challenge will be to control the polarization variation throughout the imaged field. Besides contrast also the light incoupling in the resist depends on polarization. The different polarization directions (TE and TM) induce virtual dose differences. Immersion lithography reduces this effect due to reduced incident angles at a given lens NA. In the upcoming era beyond 0.9 NA, imaging enhancements by polarized illumination are needed. There are several components in a lithographic scanner which potentially influence polarization properties. Apart from illuminator and projection lens the reticle blank and the patterned mask absorber including 3D effects may impact the final intensity distribution in the resist. Last but not least the ability to measure the polarization state is a prerequisite to actively control polarization within the exposure system. The ability to assess the unpolarized and polarized projection lens performance with the on-scanner interferometer (ILIAS<sup>TM</sup>) allows us to do this. In order to verify the benefits and challenges of polarized illumination systems, we built a prototype illuminator and tested it on both a 0.85 NA ArF system as well as on a 0.93 NA ArF system. Next to the successful qualification of illuminator and projection lens we were able to verify the expected gain in imaging performance with polarized light. In this paper we present results of the experimental work and compare the data with our simulations.
As the semiconductor industry looks into the near future to extend manufacturing beyond 100nm, a new optical lithography system was developed by ASML. To achieve the aggressive industry roadmap and enable high volume manufacturing of sub 100nm resolutions at low k1 requires a number of challenges to be overcome. This paper reviews the design, system performance and measurements of a High NA, Dual stage 193nm TWINSCAN system planned for high volume manufacturing for 80nm applications. The overall system capability to effectively measure and control to a high precision the various attributes upon process control necessary for adequate CD control, in the low k1 regime will be shown. This paper will discuss the needed imaging control and the requirement for an extremely stable and matured platform. The system's dynamic, focus, leveling and dose delivery performance will be shown. Additionally, the automated control features of the optical system will be shown that enable the use of the various resolution enhancement techniques (RET) currently under development. The ability to optimize imaging performance with the control and flexibility in the pupil formation optics will be discussed. Finally, experimental results of an in-situ measurement technique with automated feedback control to optimize projection lens aberrations, which has a direct impact to imaging fidelity, will be shown. In summary, the lithographic system functionality and performance needed to achieve 80nm volume manufacturing will be presented.
Isolated to dense linewidth offsets, also known as proximity bias, can consume a significant portion of the CD budget. As a result, it has received great attention over the recent years. It is demonstrated that proximity bias shows a cyclic swing behavior on reflective substrates with respect to resist thickness variations. The amplitude of proximity bias swing was found to be influenced by coherence, substrate reflectivity, feature dimension and pitch. Proximity bias swing is caused by differences in optical path lengths of light passing through the resist film. Due to different diffraction angles for different pitches, the incoupling positions for different pitches vary. The offset in CD swing incoupling positions for different pitches results in proximity bias swing. At low coherence however, an averaging effect on diffraction angles from different pitches takes place due to the wide range of angles of light passing through the mask. In addition, the impact of exposure margin variations on resolution and proximity bias was demonstrated. Low exposure margins offer high resolution. As a consequence, high proximity bias is observed. Furthermore, different line to space ratios were studied to identify the transition point between dense and isolated features with respect to proximity bias swing. At high coherence ((sigma) equals 0.35) it was observed that for 0.25 micrometers features with pitches smaller than 0.65 micrometers , proximity bias swing is larger than the +/- 0.5% CD budget, which makes it impossible to do effective application of proximity bias correction schemes. At low coherence, only limited proximity bias swing was found. Through variation of bake conditions it was demonstrated that these process variations had no measurable effect on proximity bias swing. Optical settings, in combination with substrate reflectivity, are the main contributors to (eliminate) proximity bias swing.
In this paper, (sub) 0.18 micrometers KrF DUV processes are optimized for logic Front-End-Of-Line (FEOL) CMOS applications. A commercial DUV resist is used without resolution enhancement techniques such as phase-shift masks and off-axis illumination. The full patterning process is considered, i.e., in the final optimized process account is taken of the etch process. Statistical data shows that a stable process was obtained. However, due to minimal process windows at gate level after poly-etch, 0.18 micrometers FEOL cannot be realized in production with KrF DUV.
To meet the high productivity standards, set by current top- end stepper systems, the use of excimer laser sources and high scanning speeds are essential. This paper reports on a new Step & Scan system capable of exposing 26 X 33 mm fields, using a 248 nm DUV-lens with a variable Numerical Aperture of 0.40 to 0.63. The system is equipped with an advanced AERIAL<SUP>TM</SUP> illuminator which allows the user to choose coherence and illumination modes on a job-by-job basis. The double telecentric lens is equipped with lens manipulators to allow on-site aberration control. Results are presented on dynamic image distortion, field flatness and dynamic imaging performance. Performance of the overlay accuracy and dose accuracy at high scanning speeds proves that Step & Scan technology is now developed to a level suitable for use in high volume sub 0.25 micrometers manufacturing.
This paper shows, that as resolution is pushed into regions below 0.6 (lambda) /NA, understanding the effects of wavefront aberrations is crucial to producing stepper systems that can meet end-user requirements. We show how aberrations can affect the choice of optimum NA and partial coherence for a given reticle object when considering critical dimension uniformity and depth of focus. The ability to measure the complete wavefront and extract meaningful full-field aberration data is shown using an advanced through-the-lens interferometer that operates at the wavelength and bandwidth of the lithographic radiation. The impact of aberrations an image quality criteria is shown through a sensitivity analysis using an imaging approximation model that represents various image criteria as a weighted sum of aberration coefficients. The validity and use of such a model is shown by correlation to full- field experimental measurements.
This paper shows the suitabilily of i-line photolithography for production at 0.30 tm. The process performance is
demonstrated through the use of off-axis illumination, high NA projection lens, and a state of the art photoresist system.
The minimum required depth of focus for a suitable 0.30 tm process is derived as 0.95 tm over at least a 10% process
window. This will result in a 0.60 m common corridor over a square 22 mm imaging feId.
In addition to the dense and isolated lines, a preliminary investigation of contact hole performance using chrome and
phase shift masks was completed.