High-power EUV lithography: spectral purity and imaging performance

With the introduction of the NXE:3400B scanner, ASML has brought EUV to High-Volume Manufacturing (HVM). The high EUV power of >200W being realized with this system satisfies the throughput requirements of HVM, but also requires reconsideration of the imaging aspects of spectral purity, both from the details of the EUV emission spectrum and from the DUV emission. This paper will present simulation and experimental results for the spectral purity of high-power EUV systems, and the imaging impact of this, both for the case of with and without a pellicle. Also, possible controls for spectral purity will be discussed, and a novel method will be described to measure imaging impact of varying CE and DUV. It will be shown that CE optimization towards higher source power leads to reduction in relative DUV content, that the small deltas in EUV source spectrum for higher power do not influence imaging. It will also be shown that resulting variations in DUV do not affect imaging performance significantly, provided that a suitable reticle black border is used. In short, spectral purity performance is not a bottleneck for increasing power of EUV systems to well above 250W.

Extreme ultraviolet lithography (EUVL) is the leading technology for patterning at the 32 nm technology node and be-yond. EUVL light at 13.5 nm is used to print circuits. This light is produced by heating fuel (Xe, Sn) in EUV sources to a very high temperature by using either magnetic compression or laser irradiation. Today EUV source power remains the number one concern for implementation of EUVL in high volume manufacturing. Over the last few years, much pro-gress has been made in EUV source performance and availability. Today, alpha level high power (~10 W) EUV sources have been integrated in alpha level EUVL scanners. Medium and low power EUV sources are used for in-house metrol-ogy and performance studies on EUV mask blanks, EUV masks, photoresists, and optical elements. These compact dis-charge sources with medium power in the range of 10-100 mW/sr/2% bandwidth and low power EUV tubes are being used by various RD today, these low power EUV sources are instrumental in allowing in-house R&D projects. In this paper, the latest status of high power EUV sources, low and medium power metrology sources, and some of their appli-cations are described.

Implementation of extreme ultra violet lithography (EUVL) for printing features of dimensions around 32nm and below has faced multiple challenges that have been overcome mostly through tool and process engineering. Currently, the main concern for implementation of EUVL in high volume manufacturing is related to stochastic defects, such as line bridges or breaks, which may occur randomly and have an impact on device performance.1 Photon shot noise, in addition to the inherent process variability and material non-homogeneities can lead to defects on the final patterned structures. As the pitch and critical dimension (CD) approach 32nm pitch and below, the dependency of stochastics defects increases exponentially. This paper fits within imec’s EUV stochastics and defectivity program, which investigates the key parameters for the generation and mitigation of defects from both a theoretical and practical approach. Initially, a reference process has been established and a methodology has been developed to capture and characterize bridge-type defects after pattern transfer into relevant layers for metrology and applications. Optical inspection and scanning electron microscopy (SEM) review are used to collect information on the number and types of defects present over large patterned areas (in the order of cm2). With a well-defined inspection technique, experiments related to fundamentals as well as materials and processes are continuously run. In the past years, imec has been leading the fundamental work on stochastic defects.2,3 De Bisschop et al. identified the “defect cliff”, or the exponential dependency of defect density as a function of space CD for multiple parameters, such as resist formulation and exposure/imaging conditions. More recently, the focus has changed to the investigation of the “defect floor”, which as the name suggests, is a flat response of defects to CD. The defect floor suggests that defectivity cannot be further improved, making one of the most relevant problems to solve for implementation of EUV in high volume manufacturing (HVM). Our results show a decomposition of the potential contributors to explore the effect of processing conditions related to scanner, track and pattern transfer on final defect density for a chemically amplified resist and attempt a comparison to a metal-oxide resist. Goal is to understand the contributors to the defect floor and identify an effective route to avoid/minimize defect formation.

Extreme ultraviolet (EUV) lithography is crucial to enabling technology scaling in pitch and critical dimension (CD). Currently, one of the key challenges of introducing EUV lithography to high volume manufacturing (HVM) is throughput, which requires high source power and high sensitivity chemically amplified photoresists. Important limiters of high sensitivity chemically amplified resists (CAR) are the effects of photon shot noise and resist blur on the number of photons received and of photoacids generated per feature, especially at the pitches required for 7 nm and 5 nm advanced technology nodes. These stochastic effects are reflected in via structures as hole-to-hole CD variation or local CD uniformity (LCDU). Here, we demonstrate a synergy of film stack deposition, EUV lithography, and plasma etch techniques to improve LCDU, which allows the use of high sensitivity resists required for the introduction of EUV HVM. Thus, to improve LCDU to a level required by 5 nm node and beyond, film stack deposition, EUV lithography, and plasma etch processes were combined and co-optimized to enhance LCDU reduction from synergies. Test wafers were created by depositing a pattern transfer stack on a substrate representative of a 5 nm node target layer. The pattern transfer stack consisted of an atomically smooth adhesion layer and two hardmasks and was deposited using the Lam VECTOR PECVD product family. These layers were designed to mitigate hole roughness, absorb out-of-band radiation, and provide additional outlets for etch to improve LCDU and control hole CD. These wafers were then exposed through an ASML NXE3350B EUV scanner using a variety of advanced positive tone EUV CAR. They were finally etched to the target substrate using Lam Flex dielectric etch and Kiyo conductor etch systems. Metrology methodologies to assess dimensional metrics as well as chip performance and defectivity were investigated to enable repeatable patterning process development. Illumination conditions in EUV lithography were optimized to improve normalized image log slope (NILS), which is expected to reduce shot noise related effects. It can be seen that the EUV imaging contrast improvement can further reduce post-develop LCDU from 4.1 nm to 3.9 nm and from 2.8 nm to 2.6 nm. In parallel, etch processes were developed to further reduce LCDU, to control CD, and to transfer these improvements into the final target substrate. We also demonstrate that increasing post-develop CD through dose adjustment can enhance the LCDU reduction from etch. Similar trends were also observed in different pitches down to 40 nm. The solutions demonstrated here are critical to the introduction of EUV lithography in high volume manufacturing. It can be seen that through a synergistic deposition, lithography, and etch optimization, LCDU at a 40 nm pitch can be improved to 1.6 nm (3-sigma) in a target oxide layer and to 1.4 nm (3-sigma) at the photoresist layer.

In 2019, finally, extreme ultraviolet (EUV) lithography has been applied to high volume manufacturing (HVM) for preparing advanced semiconductor devices. That was very important year for EUV enthusiasts and semiconductor industry. Because it takes for a long time, more than 30 years, to study EUV lithography for realizing HVM. With recent rapid progress on the source power improvement, EUV lithography development including photoresist materials has been achieved HVM requirements. However, the performance of EUV resist materials are still not enough for the expected HVM requirements, even by using the latest qualifying EUV resist materials. One of the critical issues is the stochastic issues, which will be become ‘defectivity’, like a nano-bridge or a nano-pinching. The analyzing summary of the stochastic factors in EUV lithography, and their improvement status are described in this paper. 2 (two) major stochastic issues, which are photon stochastic and chemical stochastic, were observed in the lithography steps. And the improvement status of each stochastic issues including lithographic results are also described.

Extreme-UV lithography (EUVL) is the most promising candidate of next generation technology for hp20nm node device manufacturing and beyond, however there are many critical issues to solve in the light source, tools, mask and photo resist. Regarding the development of a photo resist, it is necessary for high volume manufacturing (HVM) to improve LWR, resolution limit and sensitivity. Additionally, concerning about deterioration of a patterning performance by Out-of-Band (OoB) light existing in the EUV light, and contamination problem of exposure tool due to the photo resist outgassing are the key issues which have to be resolved toward HVM by EUVL. Especially, the outgassing problem can become a significant issue for fine patterning under high dose exposure condition. This paper proposes the novel solution for these critical issues with the application of a top coat material which is named OBPL (Outgassing & out-of-Band Protection Layer) on photo resist. The key characteristics of OBPL material are to have a role in protection against the OoB adverse effect to keep up the photo resist performance, to suppress the outgassing from photo resist as a barrier layer and to enhance the lithographic performance such as photo resist profile and process window. In designing the OBPL material, the optical property needs having not only the high absorbance of DUV (Deep-UV) light in OoB range but also high transmittance for 13.5nm wavelength to prevent the sensitivity loss. Furthermore, it is found that the polymer backbone affects the outgassing barrier capability in previous evaluation. Based on these investigations, a state-of-the-art OBPL achieves quite a positive lithographic result with sufficient OoB absorption and outgassing suppression. Moreover, this material has applicability to all types of photo resist including NTD (Negative-Tone Development) process. This paper describes the result of the feasibility study for OBPL and the lithography performance with EUV full field scanner.

EUV lithography (EUVL) is the candidate for next generation lithography to be introduced by the semiconductor industry to HVM (high volume manufacturing) in 2013. The power of the EUVL light source has to be at least 115W at a wavelength of 13.5nm. A laser produced plasma (LPP) is the main candidate for this light source but a cost effective laser driver is the key requirement for the realization of this concept. We are currently developing a high power and high repetition rate CO 2 laser system to achieve 50 W intermediate focus EUV power with a Tin droplet target. A high conversion efficiency (CE) from laser energy to EUV in-band energy is the most important issue for the concept to be realized. A CE of more than 2 % has been obtained with a Tin target and a CO 2 laser which is also predicted by numerical simulation analysis. The high CE requires a short laser pulse of less than 15 ns. This paper describes the development of a CO 2 laser system that is based on RF-excited, axial flow CO 2 laser amplifiers. The system produces a short pulse length about 15 ns and a nominal average power of several kW at a repetition rate of 100 kHz, An output power of 2.6 kW has been achieved with a pulse length between 15~30 ns at 130 kHz repetition rate at small signal amplification. The phase distortion of the laser beam after amplification is negligible and the beam can be focused to about 150mm diameter in 1/e 2 . The conceptual design of the CO 2 laser system for LPP EUVL light source, and the laser performance are reported. The further increase of the amplification efficiency is discussed to obtain 5 kW average output power.

The following topics are dealt with: low-power electronics; Internet of Things; integrated circuit design; video coding; integrated circuit manufacture; CMOS integrated circuits; field programmable gate arrays; magnetic sensors; calibration; power consumption.

Extreme UltraViolet (EUV) lithography is a new technology for production of integrated circuits. In EUV lithographic machines, optical elements are heated by absorption of exposure energy. Heating induces thermoelastic deformations of optical elements and consequently, it creates wavefront aberrations. These Thermally Induced Wavefront Aberrations (TIWA) can significantly degrade the resolution of EUV lithographic machines. One of the ways to correct TIWA and consequently, to improve the resolution of EUV lithographic machines, is to use the Adaptive Optics (AO) technique and predictive control algorithms. However, the predictive control of TIWA is a challenging problem, mainly because the dynamical behavior of TIWA is described by thermoelastic Partial Differential Equations (PDEs). By discretizing the thermoelastic equations using the finite difference or finite element methods, large-scale state-space models can be obtained. A striking feature of these state-space models is that they have sparse (multi) banded matrices. Consequently, these state-space models can be interpreted as large-scale networks of local subsystems. All this implies that the problem of correcting TIWA can be placed in a much more general context of identifying, estimating and controlling large-scale interconnected (distributed) systems. However, currently used estimation and control algorithms are not computationally feasible for large-scale systems. For this reason, this thesis focuses on the development of computationally efficient identification, estimation and control algorithms for large-scale interconnected systems. In this thesis, we prove that the inverses of (finite-time) Gramians of large-scale interconnected systems, obtained by discretizing PDEs, belong to a class of off-diagonally decaying matrices. Consequently, these inverses can be approximated by sparse (multi) banded matrices with O(N) complexity, where N is the number of local subsystems. To compute the approximate inverses, the Chebyshev approximation method and the Newton iteration are used. On the basis of these theoretical results, we develop novel estimation and identification algorithms for large-scale interconnected systems. The computational and memory complexity of these methods scale with O(N). This is the main advantage over the traditional estimation and identification methods, which complexity is O(N^3). Furthermore, in this thesis we develop and experimentally verify AO control algorithms for predictive correction of TIWA. The experimental results give a good first indication for a possible implementation of the developed predictive control algorithms in EUV lithographic machines. Finally, we develop and experimentally test an iterative learning control algorithm for high performance correction of wavefront aberrations.

While extreme ultraviolet lithography (EUVL) is the leading candidate of the next generation lithography, the challenge of managing blank defects must be overcome before EUVL being put to practical use. Besides the efforts of manufacturing defect free blanks, the use of mitigation technique called “pattern shift” is now considered to be a more feasible solution. Whether we aim for defect free blanks or use pattern shift, however, it is quite important to understand the properties of the defects on EUV masks. Of particular interest is to distinguish phase defects from amplitude defects, and pits from bumps. To address the need to understand defect properties, the Actinic Blank Inspection (ABI) high volume manufacturing (HVM) model has acquired a review function using a 1200x magnification optics capable of accurately measuring the size and shape of defects. In this paper, we will discuss how the ABI HVM model classifies defects into pits and bumps.

Intel's efforts to build a practical quantum computer are focused on developing a scalable spin-qubit platform leveraging industrial high-volume semiconductor manufacturing expertise and 300 mm fabrication infrastructure. Here, we provide an overview of the design, fabrication, and demonstration of a new customized quantum test chip, which contains 12-quantum-dot spin-qubit linear arrays, code named Tunnel Falls. These devices are fabricated using immersion and extreme ultraviolet lithography (EUV), along with other standard high-volume manufacturing (HVM) processes as well as production-level process control. We present key device features and fabrication details as well as qubit characterization results confirming device functionality. These results corroborate our fabrication methods and are a crucial step toward scaling of extensible 2D qubit array schemes.

Current visible and ultraviolet light imprinting methods for manufacturing computer chips have reached their maximum limitations and the extreme ultraviolet (EUV) region has been selected as a possible successor. While extreme ultraviolet lithography (EUVL) offers a solution to advancing Moore's Law, several problems persist pursuant to large-scale industrial and high volume manufacturing. Laser produced plasmas (LPP) from tin targets have been demonstrated to emit EUV radiation (13.5 nm light) with an industrially acceptable conversion efficiency, although debris accumulation on the collector optics is still an issue.1

Exposing extreme ultraviolet lithography at Intel

Deep-learning-based SEM image denoiser Dorin Cerbu1, Sandip Halder1, Philippe Leray1 1IMEC, Kapeldreef 75, B-3001 Leuven, Belgium We report the development of a new method to denoise SEM images with the help of artificial neural networks. Upon using a preprocessing and training scheme tailored for SEM images of structures, most often encountered in semiconductor manufacturing, we can efficiently denoise images affected with varying degrees of noise severity and origin. In the figure below, we show an example of how we can use this filter efficiently to treat noisy images and improve the image quality. This can help in acquisition of more stable and better metrology data. Fig1(a) original image (b) Image which has been denoised using deep-learning based algorithms This development is of utmost importance for the case of post-litho processing step where resist nanostructures when SEM inspected are usually impacted by the electron beam and shrink, hence skewing critical dimension measurements. This is especially true as we push towards sub N-10 nm nodes. Application of our deep-learning processing scheme allows efficient noise reduction on SEM inspection images and helps us discern minor details previously shadowed by noise. This is extremely important as we move towards using EUV in high volume manufacturing. Small details can be crucial to understand the root-cause of stochastic and process defects. In previous work, we have already shown different approaches to understand stochastic defects [1-2]. The goal of this work is to enhance the image quality as much as possible to gain further fundamental understanding on nano-defects. [1] S. Halder et. al., ‘Using machine learning techniques to understand EUV stochastics, SPIE Photomask Technology + Extreme Ultraviolet Lithography, 2018 [2] K. Sah et.al., ‘EUV stochastic defect monitoring with advanced Broadband optical wafer inspection and e-Beam review systems’, SPIE Photomask Technology + Extreme Ultraviolet Lithography, 2018

A search for novel materials for making multilayers of high reflectivity has been driven by the vigorous demand towards miniaturizing photonics. A typical consumer of high performance multilayers (MLs) is the extreme ultraviolet lithography (EUVL) based on the 13.5 nm laser produced plasma (LPP) source. To sustain “Moore’s law” and print fine features below 10 nm on integrated circuits (IC), source of radiation for the EUVL has to shift towards even shorter wavelengths where 6.x nm wavelength seems to be immediate successor. However, the 6.x nm EUV lithography needs MLs of reflectivity performance above 70 % to support high volume manufacturing (HVM). It is clear that more work is required particularly on the development of MLs with high reflectance, stable to thermal heat and sufficient lifetime. In this work new MLs of B4C/CeO2 are deposited, analyzed and characterized for the first time. Combinations of X-ray reflectometry (XRR) and EUV reflectance measurements near resonance edge of boron are analyzed to derive structural and optical parameters of MLs. ML coatings of B4C/CeO2 MLs have shown similar reflectance performance with the leading candidate MLs around 6.x nm wavelength. Analysis shows that interlayer diffusion is a major reason for low reflectivity performance. Cross-sectional scanning electron microscopy (SEM) images of the MLs have proved formation of interlayer diffusion.