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In this manuscript, a method of generating an ultra-long optical needle (depth-to-width ratio 37.5:1) is proposed and demonstrated by focusing an azimuthally polarized beam. In theory, the action mechanism between the incident beam and the amplitude modulation element, the spiral phase modulation element, the focusing lens were studied based on the Richards and Wolf's theory. The relationship between the intensity distribution of the optical needle and the structure parameter of the element were obtained, thus leading to the complete design model and design standard. In experiment, the annular amplitude modulation element and spiral phase modulation element were fabricated by lithography. The optical needle was obtained based on a custom-designed optical setup in our laboratory. The optical system consists of an annular aperture (3.9-mm inner diameter, 80-μm annular width), a spiral phase plate (topological charge of 1), and an objective lens with numerical aperture of 0.95. Finally, an optical needle with a subwavelength size (0.416λ) and an ultra-long depth of focus (15.6λ) was obtained, showing an excellent agreement with our theoretical model.

The patterning requirements of next generation lithographic processes and the desire to keep manufacturing costs down have pushed the lithographers to explore the advantages of the curvilinear masks. Multiple studies backed by the experimental results have demonstrated the lithographic advantage of the curvilinear (CL) photomasks over the rectilinear (RL) approximations by showing improved MEEF, depth of focus (DoF) and common DoF (CDoF) for variety of patterns on the same mask, ILS and, as a result, process window (PW) of the CL masks over its close RL siblings [1,2]. Manufacturability of the CL masks has been limited due to the architecture of the Variable Shaped Beam (VSB) writers, which made it prohibitive from both mask data preparation (MDP) and mask writing perspective. The availability of Multi Beam Mask Writers (MBMW) has removed these roadblocks and brought introduction of the curvilinear masks much closer to reality. The development of novel approaches for MDP and Mask Proximity Correction (MPC) as it is demonstrated by Bork et al in [3] brought further advances in availability of the CL masks for high volume manufacturing (HVM). Traditionally the Inverse Lithography Technology (ILT) has offered the most potential to achieve significant lithographic advantage over RL masks but has suffered from very long data preparation runtimes which presented an additional hurdle for broad deployment in manufacturing. While various speed up options such as machine learning-based acceleration, and GPU processing [4,5] are being explored, the full chip ILT run time still represents significant challenge in the HVM world. This paper will concentrate on two OPC approaches that allow CL mask generation without run time penalties associated with full chip ILT processing. The first is based on a hybrid methodology that allows for generation of the CL mask shapes by using fast ILT-based algorithms for SRAF generation while the main features are controlled to allow for full chip processing within the reasonable time. The second approach is more appropriate for the memory applications where patterns are highly repetitive. Due to high level of repetition, it is acceptable to use full ILT correction carried over a small area of the chip and to utilize pattern matching (PM) methodologies to propagate both SRAFs and OPC-corrected features from unique to non-unique pattern placements. Such a methodology allows for the full ILT advantages in the highly critical memory array areas.

The use of photomask can maximally realize the power of parallel pattern replication in photolithography. Although there exists linewidth standard in the metrology tools, in practice, there may exists some variation in the linewidth definition from different chip makers. Experience indicates that such variation can be as much as 1~2 nm (1X). Since the mask bias can affect photo process window, the determination of which can be very important to the setup of the lithography process. Of course, the optimum setting can be obtained through wafer exposure. However, ever since the introduction of Model Based Optical Proximity Correction (MBOPC), the linewidth uniformity across different patterns is mostly accomplished by OPC model and correction. Therefore, it is important that the mask dimension be as close to the reality as possible to make OPC model more physical, which have better extendibility to patterns that may lie along the edge of the design rules or even slightly outside the design rules. Ever since the use of 193 nm immersion lithography, the mask dimension may be very close to the size of the wavelength, mask 3D scattering effect becomes very significant, which can reduce imaging contrast, increase Mask Error Factor (MEF), and reduce common Depth of Focus (DoF) for all patterns. The setting of the accurate mask dimension becomes more important, even critical. However, we can also utilize this process window sensitivity to the mask dimension to determine the real mask dimension through comparing wafer exposure data and simulation. This will require very accurate physical modeling. In this paper, we will propose this method.

Direct laser writing commonly uses high numerical objective oil lens and femtosecond lasers to realize high precision micro-nano fabrication. Here we report a simple maskless lithography system utilizing a controllably designed high NA planar diffractive lens based on binary amplitude modulation and a diode laser at 405nm wavelength to realize submicron far-field lithography. The design procedure is based on vectorial Rayleigh-Sommerfeld diffraction integrals and genetic algorithm realized by Matlab programming language. The planar diffractive lens reported here can be designed to produce a tightly focused spot (~300-800nm) with an ultra-long depth of focus(~4μm) at a focal length of 1mm.

Metalenses offer the ground-breaking opportunity to realize highly performing low-weight, flat and ultrathin, optical elements which substantially reduce size and complexity of imaging systems. Today, a major challenge in metalenses design is still the realization of achromatic optical elements ideally focussing a broad wavelength spectrum at a single focal length. Here we present a fast and effective way to design and fabricate extremely thin all-dielectric metalenses, optimally solving achromaticity issues by means of machine learning codes. The enabling technology for fabrication is a recently developed hyper resolute two-photon direct laser writing lithography equipment. The fabricated metalenses, based on a completely flat and ultrathin design, show intriguing optical features. Overall, achromatic behavior, focal length of 1.14 mm, depth of focus of hundreds of microns and thickness of only few nanometers allow considering the design of novel and efficient imaging systems in a completely new perspective.

DUV lithography has successfully adopted both bright and dark mask tonalities. This gives the freedom to chip manufacturers to choose the optimum combination of mask and resist tonality for their product [1]. In EUV lithography, however, there has been a clear preference for dark field masks, driven by the prevalence of positive tone resist processes, and their relative insensitivity to multilayer defects. Future customer nodes, however, may require negative tone (metal-oxide) resist processes [2][3], resulting in a requirement to use bright field masks. Therefore, a deeper understanding of bright and dark field imaging is needed in order to provide guidance to ASML customers in choosing the optimal approach. In this work we consider the fundamentals of bright and dark field imaging based on the diffraction theory of aerial image formation [4]. We will show that bright field imaging has an intrinsic potential for higher optical NILS (normalized image log-slope), especially for isolated features, but with a lower depth of focus. The theoretical results are compared to rigorous simulations. Experimental bright vs dark-field results is also presented for comparison. Wafer based data has been obtained on an NXE:3400 scanner, whilst aerial image measurements have been obtained using the Aerial Image Measurement System for EUV (AIMS® EUV) at Zeiss. These experimental results confirm the theoretical expectations. The main goal of the paper is to draw attention to bright versus dark field comparison for EUV and to kick off more studies in this direction.

Features in forbidden pitch have limited exposure latitude and depth of focus in lithography exposure. This paper provides an analysis of forbidden pitch in extreme ultraviolet lithography (EUVL) from the perspective of rigorous simulation and source mask optimization (SMO). In the stage of rigorous simulation, S-litho is used to analyze the normalized image log slope (NILS) of test patterns from different critical layer in 5nm node. Then the process windows of these test patterns are simulated and compared by the lithography simulator Proteus WorkBench. From the result analysis, the forbidden pitches of critical layer in 5nm node are summarized. In addition, the strategy of mitigating the negative effect of forbidden pitch is proposed with the help of computational lithography.

Precise measurement of wafer flatness with high sensitivity and high spatial resolution is essential to realize high yields in nano-scale lithography because the depth of focus in this technology is relatively small. We report on a highly precise site flatness measurement system that employs a pair of heterodyne interferometers and achieves sub-nanometer precision for polished 300-mm silicon wafers. The determined overall mean standard deviation for the site flatness front-surface least-squares fit range is 0.21 nm. Furthermore, this system allows us to obtain images of the wafer flatness via scanning with a high spatial resolution of approximately 12 µm. These results suggest that the heterodyne interferometer-based system is a suited candidate for use at the next-generation 16-nm half-pitch technology node.

High-NA extreme ultraviolet lithography (EUVL) is going to deliver the high-volume manufacturing (HVM) patterning for sub-3nm technology node for the semiconductor industry. One of the critical challenges is to develop suitable EUV photoresists at high resolution with high sensitivity and low line-width roughness (LWR) at reduced film thickness needed for high-NA by its reduced depth of focus (~1/NA2). The resist performance is generally limited by the resolution-LWR sensitivity (RLS) tradeoff, and it is critical to find new materials to support the future lithography nodes. EUV interference lithography (EUV-IL) is a powerful and efficient technique to test new materials at high resolution. In this work, we evaluate the performance of about 120 EUV resists, including molecular resist, inorganic resist, chemically-amplified resist (CAR), and chemically-amplified resist with a metal sensitizer (metal-CAR). Among all tested resists, we selected and compared six resists with the best performance in dose-to-size, line-width roughness, and maximal exposure latitude for 16 nm and 14 nm half-pitch (HP) lines/spaces (LS). A molecular resist showed the lowest dose to resolve HP 16 nm (29 mJ/cm2) and 14 nm (31 mJ/cm2), still featuring low LWRunbiased (2.7 nm and 3.1 nm, respectively). We observed that there is steady progress in EUV resist development: the LWR of the resists was improved in comparison with the results of the last two years as we noted that the amount of the resists within given dose and LWR threshold increased from 10 % to 33% for HP 14 nm. For contact holes, CAR gave the lowest LCDU of 2.2 nm for HP 20 nm with the lowest doses (21.1 mJ/cm2). While inorganic resists resolved pillars with highest resolution HP down to 18 nm with LCDU of 2.1 nm.

In modern semiconductor lithography world, doubtlessly, scanners using DUV as light source still be main work horses to push physical limits of semiconductor devices to a new level. Meanwhile, as the semiconductor devices diversified to many different types, for example, logic, DRAM, NAND ash, CMOS Image Sensor (CIS), etc., lithography performances needed are also diversified. For example, CH/VIA layers in the-state-of-the-art logic processes require improved lithography Process Window (PW) due to their shallow Depth of Focus (DOF). On the other hand, engineers working in the field of modern 3D-NAND ash memory and CIS lithography are needed to deal with problems induced by thick resists. Efforts by chip makers, scanner vendors solved the problems in some degree. For example, focus drilling multi-exposure, has improved DOF of some specific layers substantially. But all these approaches have some kinds of issues, such as, throughput losses, etc. As a light source maker, we believe we can make unique contributions to solve the issues. In this report, we are going to show that our advanced Spectral Engineering (SE), a cost-effective way, can provide chip makers with an alternative to cope with the challenges stated above.

Markets continuously demand higher resolution and higher productivity in flat panel display (FPD) exposure systems. Our solution to improve resolution and productivity is the use of broadband wavelength illumination. A larger depth of focus (DOF) is also very important to achieve higher productivity because inadequate DOF can cause product defects. To obtain higher resolution and larger DOF, off axis illumination (OAI) conditions have been widely used. OAIs using a narrowband wavelength illumination are well documented and sufficiently studied. On the other hand, Canon FPD exposure tools use a broadband illumination source to achieve higher resolution and productivity. To obtain sufficient OAI effects in broadband exposure lithography, new technology should be developed with consideration of broadband wavelength because OAI effects are different between broadband and narrowband illumination. In this paper we introduce divided spectrum illumination (DSI), a new design concept proposed to achieve both high resolution and large DOF by optimizing the broadband illumination source wavelength band depending on the illumination angle. Experimental imaging results of line and space patterns with a line width of 1.0-μm and pitch of 2.0-μm showed that the DSI design improved resolution. Results showed that test patterns imaged using traditional narrowband OAI could not be resolved at the top of the resist even at the best focus, however resist profiles using DSI were sharp enough to retain pattern fidelity at the top of resist. DOF with DSI also improved 21 % compared to traditional OAI.

For quality patterning of microstructures, it is essential that all process parameters are optimized to ensure well-developed 3D profile of the resist. Advances in direct laser lithography have provided maskless and rapid prototyping methods of manufacturing microstructures. Among all other process parameters, the quality of the patterned structure is critically affected by the depth of focus adjustments of the laser spot. In this study, a simulation approach is adopted and the LAB Module of GenISys lithography simulation software is implemented to determine the optimum depth of focus for negative photoresist material. Modeling and studying straight-line structure at different focusing depths at constant exposure dosages is carried out in this work. At the constant dosage of 45 mJ/cm2, the 15 µm depth of focus yields the best quality for the 3D resist profile.

Direct laser writing (DLW) is a versatile and reliable lithography method widely used in many micro and nano fabrication areas. However, the resolution of DLW is limited by the optical diffraction limit. Many methods have been proposed to improve the lithography resolution, but with either high cost or increasing the complexity of the system. Here, we propose a high numerical aperture binary-amplitude-type zone plate lens that can achieve a sub-wavelength focal spot with a large depth of focus and long working distance. The critical dimension of such a lens is set at micrometer scale for ease of fabrication. By integrating the as-designed planar lens into a DLW system, we experimentally demonstrate less than 300 nm lithography resolution with exposure depth larger than 500 nm. Our results show the possibility of writing sub-micrometer scale structures with the integration of a planar lens into the DLW system, which enables miniaturization and compactness of lithography instruments for many applications.

EUV lithography has enabled shrinking feature sizes up until iN7 using the current Ta-based mask absorber. As we explore next generation nodes, iN5 and beyond, the mask three dimensional (M3D) effects will have a significant impact at wafer level due to the mask architecture, and the oblique illumination angles [1-2]. In order to mitigate these effects, we explore the optical performance of two alternative mask absorber candidates; a High-k absorber and an attenuated phase shifting mask absorber (AttPSM) and compare them to the current Ta-based mask absorber. We evaluate and compare the mask absorbers for memory and logic layers by lithographic source-mask optimization (SMO) using Mentor’s pxSMO tool with ASML’s NXE3400B settings. For memory, contact-holes are simulated using dark-field mask whereas the pillars case is simulated with bright field mask to evaluate bright field as a mask option for EUV with alternative mask absorbers. For logic case, we test these absorbers on iN5 self-aligned block (SAB) layer [3]. The self-aligned block layer is also simulated by adding sub-resolution assist features (SRAFs) to predict the insertion point of SRAFs for logic designs and see if new mask absorber material can reduce the need of SRAF insertion. SMO for memory case shows higher common depth of focus (cDOF) and lower edge placement error (EPE) for High-k absorber over the conventional TaBN mask absorber, whereas significant gain in normalized image log slope (NILS) is observed for the AttPSM absorber. The logic case also has better performance in terms of common depth of focus (cDOF), NILS, EPE mask error enhancement factor (MEEF) and process variation band (PV-band). Adding SRAF’s to iN5 SAB improves the PV-band and image shift through focus for all three cases.

EUV technology with its state-of-the-art tool generation equipped with a Numerical Aperture (NA) of 0.33 and providing 13 nm resolution is on the brink of entering high volume manufacturing. Extending the roadmap down to a resolution of 8 nm requires a high-NA successor tool. ASML and ZEISS are jointly developing an EUV scanner system with an NA of 0.55 to enable the continuation of Moore’s law throughout the next decade. In this paper we motivate the top-level requirements of this high-NA tool, deduce implications on system design and present how they are solved in the tool. In particular, we address implications of the high-NA leading to large mirror sizes, introduction of a central obscuration and an anamorphic lens design resulting in the transition from full to half field. A consequence of the high-NA is a reduced depth of focus which is dealt with by an improved focus control of the system. The aberration level of the high-NA tool will be significantly reduced w.r.t. the NA 0.33 tool generation. This is achieved by extreme aspheres accompanied by an advanced mirror manufacturing process with corrections down to atomic scale. To enable mirror manufacturing to this precision the limits of mirror metrology are pushed out by transferring the whole measurement process into vacuum. Finally, we will give an update on the current status of the high-NA tool development and the build-up of the necessary infrastructure.

More than Moore strategies have been a hot topic for more than a decade, and Redistributed line (RDL) layers in next generation interposers will require sub-micron patterning. A key lithography challenge for fine-RDL in interposer applications is providing a sufficient Depth of Focus (DoF) to accurately resolve sub-micron features. To meet this demand, Canon's FPA-5520iV steppers can now provide new projection optics offering Numerical Aperture (NA) 0.24 imaging and 52 x34 mm exposure field. FPA-5520iV steppers with NA 0.24 provide excellent 0.8 µm resolution performance throughout all imaging fields.

With the introduction of EUV lithography into early manufacturing, the lithography community still struggles with some imaging issues, like the magnitude of usable depth of focus, and reduced contrast which can impact stochastic effects such as defectivity and line edge roughness. In recent years EMF mask effects and their impact on best focus shift in EUV lithography were investigated, and alternative absorber stacks were proposed in order to improve control of focus and contrast. Recently, interest in phase shifting masks has resurfaced, and there are proposals for alternative absorber stacks that depend on feature type to be patterned. In this paper, we investigate the phenomenon that for a dipole the separate images of the two monopoles do not overlap with each other. This means that the contrast for the dipole is measurably lower than that of the individual monopoles. We discuss the impact of this effect on contrast and usable depth of focus, propose a method to measure this image split effect, and investigate which absorber materials can reduce it. One approach to suppressing the image split has been the choice of a material that is index matched to vacuum, which therefore shows a negligible image split behavior. While this image split is indeed largely suppressed for absorbers with n ≈ 1, those materials have markedly low intrinsic image contrast, making them unsuitable as absorbers. Instead, we have converged on absorbers that create either a significant phase shift or feature very strong absorption, with recent proposals coming close to a π phase shift for attPSM. We hypothesize that the close index match to vacuum is detrimental to imaging because a larger part of the light is absorbed which would otherwise have contributed to imaging.

EMD Performance Materials provides a broad material portfolio for photolithography, Chemical Shrink and EUV Rinse materials are two categories of aqueous materials enabling advanced patterning. Chemical Shrink materials generate an additional layer on the surface of photoresist pattern through chemical/physical interactions, resulting in finer trench or hole structures. The technique helps IC manufacturers improve process margin and reduce cost of ownership by relaxing the requirements for lithography. EMD has been engaged in development of the technology for over two decades, and introduced materials for multiple generations of lithography. The first generation Chemical Shrink material, AZ® R200 was commercialized for i-line and KrF applications around 2000. From then on, several commercial platforms were released targeting for ArF, ArF-immersion, and ArF NTD (Negative Tone Development) photoresists. Shrink amount depends on the material platforms and photoresists, it can be controlled from several nm to 100 nm with the process conditions, mainly shrink bake temperature. Well-controlled through-pitch proximity is one of the key advantages of the technique as well. Chemical shrink process is a straightforward and well-established in-track process. Not only smaller pattern sizes are achieved, effective DOF (Depth of Focus) is improved, but also surface smoothing of photoresist is expected. Rinse materials are a unique offering from EMD to alleviate capillary force hence mitigate pattern collapse in very fine photoresist pattern through reducing surface tension with novel surfactants. Based on the knowledge and know-hows learned during the development of rinse materials for ArF and ArF immersion lithography processes in the past decades, new material platforms have been developed to extend the technique to meet the ever more critical requirements in EUV lithography. AZ® Extreme 10 was commercialized as the world first rinse material dedicated for EUV lithography, designed for L/S (Line and Space) pattern of 22nm hp patterning. To further improve the compatibility with the latest EUV photoresists for finer pattern, 18nm hp and beyond, AZ® SPC-708 is newly commercialized in 2018. It is expected that AZ® SPC-708 helps reduce photoresist residues during development process in addition to its function of collapse mitigation. EMD Performance Materials is committed to providing novel solutions to confront the increasing technical challenges in advanced patterning.

Printing of sub-100nm half-pitch periodic structures is demonstrated using Displacement Talbot Lithography (DTL) and a deep ultra-violet light source. DTL is a recently developed mask-based photolithography for forming high-resolution periodic structures over large areas using a relatively simple and low-cost system. A phase shift mask consisting of a 40×40mm2 transmission grating with a half-pitch of 150nm is fabricated by electron-beam lithography followed by reactive ion etching. The geometry of the phase grating is optimized by numerical simulation. Using this mask, dense line/space patterns and two-dimensional arrays of pillars, both with a half-pitch of 75nm, are printed onto silicon wafers. This new technique is suitable for uniform and high-throughput patterning of large-areas for such applications as moths-eye anti-reflective nanostructures, distributed feedback lasers, zeroth-order gratings, wire-grid polarizers and engineered substrates for LEDs. Display Omitted A Displacement Talbot lithographic system at 266nm exposure wavelength is realized.75nm printing resolution and large depth of focus are achieved.Uniform printing of large-area 150nm-period line/space gratings is demonstrated.The application of the technique to wire-grid polarizers is proposed.

In this paper, we report on a type of SU-8 microstructure with vertical sidewalls used for polydimethydiloxane (PDMS) microchannels. Multi-layer lithography using focal plane changing approach is proposed to expose the SU-8 photoresist based on a digital micromirror device (DMD) maskless lithography system. We used a light-emitting diode source with a wavelength of 405 nm. The thickness of the SU-8 is divided into multi-layers according to the depth of focus. Each layer corresponds to a depth of focus, and then, a virtual mask is designed for the layer. Finally, each layer is exposed to changes in the focal plane. The results indicate that the actual profile of the SU-8 mold shows good agreement with the design profile without any T-profiles. Additionally, there is better linewidth in the proposed method compared with multi-exposure by a single fixed focal plane. The PDMS microchannels result also demonstrate the stability of the SU-8 mold.

The current industry standard tantalum-based mask absorber (60 nm TaBN) gives strong 3D electromagnetic field (EMF) effects at wafer level, such as shadowing and pitch-dependent best focus shifts. A thinner mask absorber with higher EUV extinction coefficient or a phase shifting mask can mitigate 3D EMF effects [1]. The alternative mask absorber materials would enable further downscaling to foundry 5nm node using state-of-the-art EUV scanners (with 0.33 numerical aperture “NA”) and facilitate future high NA imaging using single exposure. Here we evaluate insertion options on the patterning roadmap for alternative EUV mask absorbers, including high-k absorbers and attenuated phase shifting masks (attPSM) [1-2]. All studies are using relevant designs from foundry N5 logic node. Two alternative mask candidates are compared with the standard TaBN mask. We bring theoretical proof of concept that alternative mask absorber materials generate significant imaging gain in terms of established success criteria. On a set of predefined types of clips (with variations of 1D/2D, horizontal/vertical, dense/isolated patterns), we seek for higher depth of focus (DoF), higher image log slope (ILS), high illumination efficiency (ideally it would be equal to 1), lower pattern shift through focus (i.e., lower tele-centricity errors), lower mask error enhancement factor (MEEF). Source mask optimization (SMO) on N5 logic clip shows a more balanced source and larger common process window for high-k absorber over Ta-based absorber. Using the optical proximity correction (OPC) engine with high-k mask absorber, shows significant gain on overlapping process window (PW), process variation (PV) band, and less line end shortening. Applying advanced Resolution Enhancement Techniques (RET), sub-resolution assist features (SRAFs) on N5 designs demonstrated an improved process in terms of common depth of focus (cDoF), and image shift through focus. It was also observed that the process not using SRAFs with the high-k absorber had superior process window and image shift compared to the Ta-based case with SRAFs. Therefore, adoption of such high-k absorbers could potentially postpone the need for SRAFs.

With the adoption of extreme ultraviolet (EUV) lithography in high volume manufacturing (HVM) to enable the sub-7nm scaling roadmap, defect characterization brings new challenges and learnings. Traditional approaches to process window discovery (PWD) methodology developed2,3,4 using broadband plasma optical inspection also hold in the realm of EUV lithography. Although there is substantial depth of focus for regular patterns, focus continues to be an important modulation parameter for logic patterns. Dose is an important modulation parameter especially due to stochastic defects.1 Further, overlay is another important parameter when it comes to hybrid integration schemes such as self-aligned quadruple patterning (SAQP) and EUV block patterning, for example, in BEOL layers. In this paper, we will discuss PWD results on a foundry N5 equivalent M2 layer, studying both SAQP and block integration with direct EUV patterning. We also demonstrate the impact of EUV stochastics to the overall process window and develop useful analysis methodologies.

As the EUV lithography is extending beyond 7nm technology, design to mask strategy becomes more complex. New challenges including advanced OPC and ILT in mask optimization, curvilinear masks, shrinking Mask Rule Checking (MRC), Sub-Resolution Assist Features (SRAF) generation and formation, and other complex mask geometries drive the needs to study this synergy from different stages of the flow from Optical Proximity Correction (OPC), Mask Process Correction (MPC), fracturing, to mask writing and inspection. In this study, different OPC and SRAF mask formations including curvilinear masks, controlled Manhattanized approximations of curvilinear masks, and conventional masks are generated. We illustrate whether curvilinear masks have any demonstrable lithographic benefits. A quantitative comparison of how the Manhattanization impacts mask formation. The image quality metrics such as Image Log Slope (ILS), Process Viability (PV) Band, and Depth of Focus (DOF) from various OPC mask flavors including different MRC settings and different mask forms are compared and discussed. The mask manufacturability study is conducted to identify any major challenges and approaches to minimize, including assessing the value and need for native curvilinear write tool support on a MultiBeam Mask Writer (MBMW) or a single beam Vector Shaped Beam (VSB) mask writer.

Lithography requirements for Advanced Packaging & MEMS are very different compared to mainstream semiconductor industries’ needs. Even if the market entry barrier is much lower in the “More than Moore” market, customer adoptions needs are higher in the packaging area with respect to resolution, overlay, sidewall angle, and depth of focus (DOF), wafer handling for wafer bow and backside alignment. Key technical trends, requirements and challenges regarding the lithography technologies will be addressed in this paper. In addition, more insights on the current and emerging lithography methods for More than Moore devices will be included, as well as market forecast, competitive landscape of the major equipment suppliers addressing these fields.

In this study, direct laser writing (DLW) lithography is employed to fabricate a large-scale and high-numerical-aperture super-oscillatory lens (SOL), which is capable of achieving a sub-Abbe–Rayleigh diffraction limit focus in the optical far-field region by delicate interference. Large-diameter (600 μm), amplitude-modulated and phase-type SOLs with the smallest annular ring width of 1 μm are fabricated, and they have high quality. The dependence of DLW printing on the fabrication parameters including substrate materials, laser power, and scanning speed is well investigated. A standard procedure to manufacture high-quality binary amplitude SOLs is presented, which avoids direct printing patterns on metal films and reduces the surface roughness dramatically. Random displacements between squares constituting SOLs are discussed, and their influence on the focusing performance is studied by both numerical simulations and experiments. The optical performances of the SOLs fabricated by the DLW method are experimentally characterized, and a needle-like focus with a spot size of 0.42λ and a depth of focus of ∼6 μm are confirmed at a working distance of 100 μm for λ = 633 nm, thus giving an effective numerical aperture as high as 1.19 in air. As a complementary sub-micrometer fabrication method between traditional lithography and nanofabrication method, DLW is proved to be a promising approach to manufacture SOLs, presenting advantages of relatively high speed, low equipment volume, less complexity and sub-micrometer lateral resolution. Such SOLs can be very useful in high resolution bio-imaging on rough surfaces and in the related research fields. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Published version

Inverse lithography is increasingly being used as a viable OPC solution to maximize process window (PW), improve CD uniformity (CDU) and minimize the mask error factor (MEF), especially for memory devices. The device yield is typically limited by the process window of a few critical layers, and the Via layer is identified as one of the process window limiters for advanced 3D-NAND devices. To maximize the on-chip yield, ASML has developed advanced image based Mask-3D (M3D) inverse technology that can optimize freeform mask shapes and enhance design printability throughout the mask optimization flow. Mask rule checks (MRC) and side-lobe printing are optimized simultaneously to deliver the maximum process window. The advanced image based M3D inverse lithography technology (ILT) is used to perform full chip mask correction on the Via layer of a 3D-NAND device. 3D NAND devices contain highly repetitive cell and page buffer patterns. To ensure the full chip device performance, the consistency of the mask correction is important. Our strategy is to use the computationally intensive mask optimization solution from the new advanced image based M3D inverse technology to generate a freeform mask which gives the best lithography performance. We then use Tachyon’s Pattern Recognition and Optimization (PRO) engine to propagate the freeform mask solution of the repetitive patterns to the full chip. The periphery of the chip is optimized using conventional OPC methods. The simulation results from the advanced image based M3D inverse technology are compared against the baseline flow, which uses a standard inverse solution. The simulation results from both the flows are further validated on wafer. Significant improvement in overlapping process window (OPW) and CD uniformity is observed using the new advanced inverse technology. The simulation data shows a 32% improvement in depth of focus (DOF), a 5% improvement in the image log slope (ILS) and a 25% reduction in best focus shift (BFS) range. The improvement has also been verified at the wafer-level.

Developing a new lithographic process routinely involves usage of lithographic toolsets and much engineering time to perform data analysis. Process transfers between fabs occur quite often. One of the key assumptions made is that lithographic settings are equivalent from one fab to another and that the transfer is fluid. In some cases, that is far from the truth. Differences in tools can change the proximity effect seen in low k1 imaging processes. If you use model based optical proximity correction (MBOPC), then a model built in one fab will not work under the same conditions at another fab. This results in many wafers being patterned to try and match a baseline response. Even if matching is achieved, there is no guarantee that optimal lithographic responses are met. In this paper, we discuss the approach used to transfer and develop new lithographic processes and define MBOPC builds for the new lithographic process in Fab B which was transferred from a similar lithographic process in Fab A. By using PROLITHTM simulations to match OPC models for each level, minimal downtime in wafer processing was observed. Source Mask Optimization (SMO) was also used to optimize lithographic processes using novel inverse lithography techniques (ILT) to simultaneously optimize mask bias, depth of focus (DOF), exposure latitude (EL) and mask error enhancement factor (MEEF) for critical designs for each level.

An approach of solving the inverse lithography problem as a nonlinear, constrained minimization problem over a domain of mask pixels was suggested in the paper by Yu. Granik "Fast pixel-based mask optimization for inverse lithography'' in 2006. This idea was advanced to account for pinching and bridging print contour constraints in the paper "Controlling Bridging and Pinching with Pixel-based Mask for Inverse Lithograph'' by S. Kobelkov and others in 2015. The present paper extends this approach further for solving the enclosure print image constraints, getting maximum common depth of focus, and obtaining uniform PV-bands. Namely, we suggest several objective functions that express penalty for constraint violations. Their minimization with gradient descent methods is considered. A number of applications have been tested with ILTbased pxOPC tool for DUV metal, contacts, and EUV metal layouts; results are discussed showing benefits of each approach.

The next generation beyond 7nm node potentially requires the implementation of Sub-Resolution Assist Features (SRAF) with EUV lithography. This paper aims at providing a clear SRAF strategy for the next generation beyond 7nm node designs through a series of experiments. Various factors are considered, including: stochastic effects, 3D mask effects, through-slit effects, aberrations, and pixelated SMO sources. EUV has 13.5nm as its wavelength, which is much smaller than the wavelength used in ArF lithography, and this gives very different imaging challenges compared to the ArF case. Due to the small wavelength and numerical aperture (NA) of the current EUV tools, depth of focus is not as significant of a concern as in DUV. Instead, EUV lithography is severely challenged by stochastic effects, which are directly linked to the slope of the intensity curve. DUV SRAF has been shown to be a powerful tool for improving NILS/ILS, as well as DOF, and here we explore how that translates into EUV imaging. In this paper, we consider Process Variability (PV) Bands with a variety of process conditions including focus/dose/mask bias changes and also the NILS/ILS as our objective functions, to determine what the best SRAF solution is for a set of test patterns. We have full investigations on both symmetric SRAF and asymmetric SRAF. SRAF can potentially mitigate image shift through focus, i.e. non-telecentricity, caused by EUV 3D shadowing effect. This shadowing effect is pattern dependent and contributes to the overlay variation. As we approach the next generation beyond 7nm node, this image shift can be more significant relative to the overlay budget, hence we further investigate the impact of SRAF placement to the image shift. Moreover, the Center of Focus shift due to the large 3D mask absorber thickness can be potentially mitigated by SRAF implementation. The common process window is significantly impacted by both the center of focus shift and the individual depth of focus. We study the change by adding SRAF using both a symmetric source (standard source) and an asymmetric source (SMO source). Once SRAF is inserted for the test patterns, the common process window is plotted to compare the solutions with and without SRAF. Finally, we understand the importance of using full flare map and full through slit model (including aberration variation through slit) in the main feature correction, but in this paper, we will further evaluate the need of using full models in SRAF insertion. This is a necessary step to determine the strategy of SRAF implementation for the next generation beyond 7nm node.

In the last year, the continuous efforts on the development of extreme ultraviolet (EUV) lithography has allowed to push the lithographic performance of the EUV photoresists on the ASML NXE:3300 full field exposure tool. Today imec N7 node (equivalent to foundry N5) is the first scaling node at which industry will likely insert EUV into production which will bring a reduction in processing steps therefore reducing total cost of ownership [1], increasing yield and reducing time to ramp. However, the high-volume-manufacturing (HVM) requirement to have a cost-effective low exposure dose photoresist ( To be effective during the lithographic EUV material screening phase for such tight pitches, it is necessary to implement complementary metrology analyses that can provide precise information on the resist roughness and a quick feedback on the quantification of nano-failures (nano-bridges, broken lines, merging or missing contacts) induced by a stochastic EUV patterning regime, the random nature of the light-matter interaction and consequent chemical reactions. Beside the traditional approach to characterize a resist with metrics as exposure latitude (EL%), depth of focus (DoF) and line-edge-roughness (LER) based on CDSEM measurements, we have used the power spectra density (PSD) [4] to get an unbiased value of the resist line roughness (LWR and LER) by using Fractilia metroLERTM commercial software. Further, we have used Stochalis imec software [5] to quantify patterning nano failures providing an early stage assessment on the patterning fidelity of the examined resists. We present the resist characterization results for 32nm dense line-space pattern on different substrates and for 36nm dense and orthogonal contact hole pitch pattern for different photoresists. Two positive tone chemically amplified (CA) resists have been identified at the exposure dose of 45mJ/cm2 and 33mJ/cm2 for logic (pitch 32nm dense line/space) and memory (pitch 36nm dense contact holes) use cases, respectively.

Using shorter wavelength for exposure light is one way to achieve high resolution while keeping sufficient depth of focus. We show exposure results for high resolution to confirm the effect of deep UV exposure light. With deep UV light, 1.2-µm line and space pattern and 1.8-µm contact hole pattern are resolved while keeping sufficient depth of focus.

We report a focus shaping technique for nano patterning and optical trapping of nano particles using generalized cylindrical vector beams. Cylindrical polarized light when tightly focused with high NA lens axicon generates highly confined longitudinally polarized focal spot with large depth of focus (DOF) which founds applications in nano patterning and optical trapping of high refractive index particles. We also found by properly tuning the azimuthal component of the cylindrical vector beam, the proposed high NA lens axicon can generate a sub wavelength flat top beam which is highly useful for nano lithographic applications.

We report a multiple patterning approach utilizing digital-micromirror-device (DMD)-based grayscale lithography, providing a solution to improve fabrication accuracy for entire target three-dimensional structure. Because DMD-based lithography system consists a projection lens system, better resolution can be obtained around focal position comparing to the outer region of depth of focus. Thus, for thick-film resist microstructuring, exposing with multiple focal positions with separate grayscale masks leads to improvement of fabrication accuracy. In order to find the best combination of the multiple focal positions and their grayscale masks, the computational optimization is combined to the multiple patterning approach. Through a several experiments, effectiveness of the proposed approach was successfully demonstrated., Eurosensors 2015

We report on the fabrication and analysis of a diffractive lens with binary structure that allows the control of focal length and depth of focus. Beam propagation measurements show that focal length and depth of focus depend upon the structural parameters of prototype lenses.

Beyond EUV insertion to high-volume manufacturing, the extendibility of the technology is dependent on the cost scaling advantages of high-NA or multi-patterning EUV lithography. Several concerns have been raised regarding the cost and lithographic feasibility of high-NA, including resist performance, productivity, depth of focus, mask infrastructure and field utilization/stitching capability. The intrinsic requirement of half-field exposures for high-NA lithography drives a necessary investigation on reduced field utilization verses stitching performance of the separate half fields. Furthermore, the additional mask for full fields dies will drive additional cost, complexity and overall overhead as compared to EUV NA 0.33 double patterning or other self-aligned technique. Here, the implication to EUV throughput capacity is analyzed within the context of the 7/5/3 nm technology nodes, specifically considering field utilization and scanner productivity as a function of source power and resist dose.

In this study, we propose a set of single-spot experiment to construct a comprehensive model of electron-beam lithography to describe the relation among the incident electrons, resist, and the development conditions such as durations and temperatures. Through the experiments, small feature can be achieved by performing a short-time development due to the high acceleration voltage and large depth of focus of electron-beam system. The singular point in the beginning of the development is also observed in our model and supported by the experimental data. In addition, we verify the characteristic region of each incident spot induced by the point spread function of the electron-beam system. We further fabricate the single line with narrow groove width by utilizing the results from single-spot experiment at low developing temperatures. The line is formed by arranging a series of incident points with a distance close to the characteristic radius. This method can eliminate the proximity effect effectively and thus the groove width is scaled down to 8 nm. By adopting the successful experience in the single line formation, dense array with narrow linewidth is also demonstrated under well suppression of the proximity effect. The minimum groove width of 9 nm with 30 nm pitch is achieved with 5 s development time at -10 °C. Finally, the exceptional capability of pattern transfer is presented due to the high aspect ratio of the resist.

Due to large topographic gaps between the chips and mold substrate, the next generation of high density FO-WLP will require fine RDL plating resists that can achieve as low as 2um line/spaces(L/S) with a wider common depth of focus (DOF) margin. In order to meet these requirements, we developed a novel chemically amplified positive tone resist. In this study, we focused on photo acid generators (PAGs) which are one of the major components of chemically amplified resists. We found that controlling the acidity of the generated acid from PAGs after exposure was a key approach to get good profiles on Cu sputtered substrates and wider DOF margins.

As device shrink, there are many difficulties with process integration and device yield. Lithography process control is expected to be a major challenge due to tighter overlay and focus control requirement. The understanding and control of stresses accumulated during device fabrication has becoming more critical at advanced technology nodes. Within-wafer stress variations cause local wafer distortions which in turn present challenges for managing overlay and depth of focus during lithography. A novel technique for measuring distortion is Coherent Gradient Sensing (CGS) interferometry, which is capable of generating a high-density distortion data set of the full wafer within a time frame suitable for a high volume manufacturing (HVM) environment. In this paper, we describe the adoption of CGS (Coherent Gradient Sensing) interferometry into high volume foundry manufacturing to overcome these challenges. Leveraging this high density 3D metrology, we characterized its In-plane distortion as well as its topography capabilities applied to the full flow of an advanced foundry manufacturing. Case studies are presented that summarize the use of CGS data to reveal correlations between in-plane distortion and overlay variation as well as between topography and device yield.

Extreme ultraviolet (EUV) lithography with 13.5 nm wavelength is the main option for sub-10nm patterning in the semiconductor industry. We report improvements in resist performance towards EUV high volume manufacturing. A local CD uniformity (LCDU) model is introduced and validated with experimental contact hole (CH) data. Resist performance is analyzed in terms of ultimate printing resolution (R), line width roughness (LWR), sensitivity (S), exposure latitude (EL) and depth of focus (DOF). Resist performance of dense lines at 13 nm half-pitch and beyond is shown by chemical amplified resist (CAR) and non-CAR (Inpria YA Series) on NXE scanner. Resolution down to 10nm half pitch (hp) is shown by Inpria YA Series resist exposed on interference lithography at the Paul Sherrer Institute. Contact holes contrast and consequent LCDU improvement is achieved on a NXE:3400 scanner by decreasing the pupil fill ratio. State-of-the-art imaging meets 5nm node requirements for CHs. A dynamic gas lock (DGL) membrane is introduced between projection optics box (POB) and wafer stage. The DGL membrane will suppress the negative impact of resist outgassing on the projection optics by 100%, enabling a wider range of resist materials to be used. The validated LCDU model indicates that the imaging requirements of the 3nm node can be met with single exposure using a high-NA EUV scanner. The current status, trends, and potential roadblocks for EUV resists are discussed. Our results mark the progress and the improvement points in EUV resist materials to support EUV ecosystem.

Display Omitted Analytical expressions of the Talbot effect for self-imaging from low-order diffraction rays were derived.The depth of focus based on Rayleigh's criterion was analytically a quarter of the Talbot distance.In a hexagonal array of a fine pitch, the Talbot distance derived from 2nd-order approximation was not accurate. The Talbot distance of hexagonal array was derived from the accurate analytical expression. The Talbot effect is a self-imaging phenomenon enabling lens-less imaging. The interval of the focus position is called the Talbot distance. To maintain pattern fidelity, the accurate focus position of the self-imaging needs to be known. The depth of focus based on Rayleigh's criterion is analytically a quarter of the Talbot distance. In a hexagonal array of a fine pitch, the Talbot distance derived from 2nd-order approximation is inaccurate. The analytically accurate expression of the Talbot distance for hexagonal arrays is shown in imaging of low-order diffraction rays.

Maskless laser direct writing lithography has been applied in the fabrication of optical elements and electric-optical devices. With the development of technology, the feature size of the elements and devices is required to reduce down to nanoscale. Increasing the numerical aperture of converging lens and shortening the laser wavelength are good methods to obtain the small spot and reduce the feature size to nanoscale, while this will cause the reduction of the depth of focus. The reduction of depth of focus will lead to some difficulties in the focusing and tracking servo controlling during the high speed laser direct writing lithography. In this work, the combination of the diffractive optical elements and the nonlinear absorption inorganic resist thin films cannot only extend the depth of focus, but also reduce the feature size of the lithographic marks down to nanoscale. By using the five-zone annular phase-only binary pupil filter as the diffractive optical elements and AgInSbTe as the nonlinear absorption inorganic resist thin film, the depth of focus cannot only extend to 7.39 times that of the focused spot, but also reduce the lithographic feature size down to 54.6 nm. The ill-effect of sidelobe on the lithography is also eliminated by the nonlinear reverse saturable absorption and the phase change threshold lithographic characteristics.

Extreme UV lithography (EUVL) has gained considerable attention for several decades as a potential technology for the semiconductor industry and it is now close to being adopted in high-volume manufacturing. At Paul Scherrer Institute (PSI), we have focused our attention on EUV resist performance issues by testing available high-performance EUV resists in the framework of a joint collaboration with ASML. For this purpose, we use the grating-based EUV-IL setup installed at the Swiss Light Source (SLS) at PSI, in which a coherent beam with 13.5 nm wavelength is used to produce a periodic aerial image with virtually 100% contrast and large depth of focus. Interference lithography is a relatively simple technique and it does not require many optical components, therefore the unintended flare is minimized and the aerial image is well-defined sinusoidal pattern. For the collaborative work between PSI and ASML, exposures are being performed on the EUV-IL exposure tool at PSI. For better quantitative comparison to the NXE scanner results, it is targeted to determine the actual NILS of the EUV-IL exposure tool at PSI. Ultimately, any resist-related metrology must be aligned and compared with the performance of EUV scanners. Moreover, EUV-IL is a powerful method for evaluating the resist performance and a resist which performs well with EUV-IL, shows, in general, also good performance with NXE scanners. However, a quantitative prediction of the performance based on EUV-IL measurements has not been possible due to the differences in aerial image formation. In this work, we aim to study the performance of EUV resists with different aerial images. For this purpose, after the real interference pattern exposure, we overlay a flat field exposure to emulate different levels of contrast. Finally, the results are compared with data obtained from EUV scanner. This study will enable not only match the data obtained from EUV- IL at PSI with the performance of NXE scanners, but also a better understanding of resist fundamentals by studying the effects of the aerial image on resist performance by changing the aerial image contrast in a controlled manner using EUV-IL.

In this paper we will describe the development of a new 12% high transmission phase shift mask technology for use with the 10 nm logic node. The primary motivation for this work was to improve the lithographic process window for 10 nm node via hole patterning by reducing the MEEF and improving the depth of focus (DOF). First, the simulated MEEF and DOF data will be compared between the 6% and high T PSM masks with the transmission of high T mask blank varying from 12% to 20%. This resulted in selection of a 12% transmission phase shift mask. As part of this work a new 12% attenuated phase shift mask blank was developed. A detailed description and results of the key performance metrics of the new mask blank including radiation durability, dry etch properties, film thickness, defect repair, and defect inspection will be shared. In addition, typical mask critical dimension uniformity and mask minimum feature size performance for 10 nm logic node via level mask patterns will be shown. Furthermore, the results of work to optimize the chrome hard mask film properties to meet the final mask minimum feature size requirements will be shared. Lastly, the key results of detailed lithographic performance comparisons of the process of record 6% and new 12% phase shift masks on wafer will be described. The 12% High T blank shows significantly better MEEF and larger DOF than those of 6% PSM mask blank, which is consistent with our simulation data.

As a technology ramps up to volume manufacturing, it becomes imperative that variability in yield is reduced. One of the leading contributors to this variation is coming from the wafer edge where uniformity in film thickness significantly rolls-off. In order to widen the process margin at the edge, most advance technologies will remove the edge bead removal in lithography steps to extend the area that remains within the depth of focus. However, without the edge bead removal some photochemical residue was observed at the wafer edge and bevel. A partition inspection on the wafer bevel showed that the photoresist stack at the bevel area is not completely removed. With the process of record rinse at the lithography step, a thicker layer of patterning material is left at the bevel which downstream bevel clean processes cannot remove. By optimizing the bevel rinse, removal of the remaining organic films was improved. The film cut from the patterning layers are receded away from the bevel by tuning the wafer rotation speed during rinse and optimizing the rinse duration. With the optimized rinse it was shown that defect count at the bevel as well as the center to edge yield ratio is improved.

In this paper, we show that optimized Sub-Resolution Assist Features (SRAF) placement rules nearly tripled the depth of focus of the lithography process window for the layer of interest. No SRAF printing was found in wafer SEM images. The detail of how the optimization of Rule Based SRAF (RBSRAF) was carried out is demonstrated step by step. At GLOBALFOUNDRIES, we developed a Best Known Method (BKM) for optimizing RBSRAF. This BKM uses pixelated OPC, SRAF placement rules analysis and simplification, SRAF placement parameters optimization, and SRAF Printing Avoidance. The BKM was applied to the layer of interest, and was proved to be very successful by the Fab wafer CDSEM data. The success of the RBSRAF optimization BKM will have big impact in the semiconductor manufacturing for the next generation technology nodes of 10 nm and 7 nm.

In this paper, we discuss the lithographic qualification of high transmission (High T) mask for Via and contact hole applications in 10nm node and beyond. First, the simulated MEEF and depth of focus (DoF) data are compared between the 6% and High T attnPSM masks with the transmission of High T mask blank varying from 12% to 20%. The 12% High T blank shows significantly better MEEF and larger DoF than those of 6% attnPSM mask blank, which are consistent with our wafer data. However, the simulations show no obvious advantage in MEEF and DoF when the blank transmittance is larger than 12%. From our wafer data, it has been seen that the common process window from High T mask is 40nm bigger than that from the 6% attnPSM mask. In the elongated bar structure with smaller aspect ratio, 1.26, the 12% High T mask shows significantly less develop CD pull back in the major direction. Compared to the High T mask, the optimized new illumination condition for 6% attnPSM shows limited improvement in MEEF and the DoF through pitch. In addition, by using the High T mask blank, we have also investigated the SRAF printing, side lobe printing and the resist profile through cross sections, and no patterning risk has been found for manufacturing. As part of this work new 12% High T mask blank materials and processes were developed, and a brief overview of key mask technology development results have been shared. Overall, it is concluded that the High T mask, 12% transmission, provides the most robust and extendable lithographic solution for 10nm node and beyond.