Editor-in-Chief Harry Levinson recalls the key role SPIE proceedings played in his early career.

JM3 thanks the reviewers who served the journal in 2023.

Guest editors Ken-Ichiro Mori and Moshe Preil introduce the Special Section on Patterning for Advanced Packaging.

Heterogeneous integration is evolving to acquire finer resolution and larger devices to leverage the advantages provided by more-than-Moore manufacturing and packaging technologies that can help maximize the efficiency and increase the bandwidth of high performance computing systems. 2.xD integration with redistribution layers and large package sizes is one of solutions that can enable complex heterogeneous integration designs for applications, including artificial intelligence, 5G communication, and autonomous driving. For systems requiring large package sizes, panel level packaging (PLP) can offer efficiency and cost advantages over wafer level packaging. PLP, however, poses unique technical challenges, including the requirement to realize uniform fine patterning across the entire rectangular panel. In this paper, we report on our study of resolution and overlay performance using the panel stepper including an introduction of technology innovations supporting 2.xD heterogeneous integration development.

Demand for advanced graphics processing unit, field programmable gate array, and artificial intelligence (AI) chips continues to grow as many systems require more computing power for applications, such as AI processing and deep learning. To produce higher-performance chips, 2.5D silicon interposer technology has been developed and matured as a solution enabling high-speed data transmission between different chips, such as processors and dynamic random access memory. Increased I/O counts are required to enable higher bandwidth communication between semiconductor chips and silicon interposers can help realize higher-performance devices. Microbumps used to interconnect chips and interposers and redistribution layer must be scaled down to achieve high-density connections and next-generation devices also require larger interposers to support heterogeneous integration of multiple dies. We highlight the performance of the FPA-5520iV LF2-option stepper that is designed to provide the optimal stepper performance required for the next generation 2.5D interposers, including submicron resolution, high-accuracy mix-and-match overlay, and large field exposure.

Enabled by multibeam mask writing, curvilinear free-form inverse lithography technology (ILT), and graphics processing unit acceleration, curvilinear masks are quickly becoming the norm in leading edge masks, whether for 193i or for extreme ultra violet (EUV), particularly for contact and via layers. An industry standard for compactly representing curvilinear shapes is being developed for Semiconductor Equipment and Materials International through an industry working group. Bezier and B-spline “Multigon” formats are proposed to augment the piecewise linear polygons that are supported today. Whether these infinite-resolution curvilinear formats are used or piecewise linear polygons are used, there is a question of what constitutes a high enough vertex density to be of some predefined accuracy requirement. With these infinite-resolution curvilinear formats, the vertex density would be lower than with piecewise linear polygons for a particular accuracy requirement. But it is still useful to know what density is theoretically sufficient. We explore the concept of rasterization and the mathematical dual between contours and pixel dose arrays given a particular known resolution limit. We further argue that curvilinear ILT, practically speaking, is all computed in the pixel domain. And all curvilinear masks, with the notable exception of MWCO masks for 193i, are written with multibeam machines using pixel dose arrays. We further argue that all images taken of the resulting masks, whether for inspection, disposition, or for metrology are pictures taken as pixel dose arrays of some resolution with some image processing afterward. Information theory is a branch of computer science that, among other things, gives insight on how much data are sufficient to represent any particular information content. Generally, the field covers the idea of digitizing the analog world to some known limit of resolution. Rasterization is digitalization of images that converts from contours, be it piecewise linear polygons, or some infinite resolution curves, to pixel doses of some pixel size and dose range. Contouring is the converse, going from pixel doses to geometric space. By understanding information theory, how curvilinear mask shapes are computed, and how curvilinear mask shapes are generated on the mask, we compute the theoretical limit of how much data are required to represent 193i and EUV curvilinear masks.

The edge-based optical proximity correction (OPC) has been serving the industry for more than 20 years with few changes the mask geometry. In the past 10 years, ILT pioneers created the curvilinear mask using alternate algorithms. The two approaches differ so much that the experiences in conventional OPC do not easily translate to the use of ILT, and vice versa. We report a new approach to curvilinear masks that follows the conventional OPC workflow. It creates and manipulates the curvilinear shapes by generalizing the edge-based OPC to vertices. Conventional OPC techniques, including dissection, classification, target point placement, etc., remain as central roles. Full-chip correction results are included to demonstrate the good performance of the curvilinear mask for both contact and line/space patterns. The analysis of critical patterns shows that the curvilinear OPC lifts the mask rule check restriction to the mask shape that limits Manhattan OPC. The turnaround time of creating the curvilinear mask is around two times than that of the Manhattan mask.

As the industry is developing curvilinear mask solutions, some curvilinear postoptical proximity correction (OPC) masks have been reported with file sizes in excess of 10 times the corresponding Manhattan postOPC files, which can greatly impact mask data storage, transfer, and processing. Some file size reduction utilizing spline fittings has been reported in mask postprocessing. However, from an OPC perspective, mask postprocessing is undesirable. In this study, we show that maintaining an adequate density of mask control points (MCPs) is key to achieving the desired on-wafer lithographic performance, regardless of whether the MCPs are connected by spline sections or piecewise-linear segments. Our results suggest that spline-based MULTIGON records (defined by the Curvilinear Working Group convened in 2019) may not offer clear lithographic performance or file size benefits. We will also offer some guidance for controlling piecewise-linear file size without compromising lithographic performance.

Multi-beam mask writers (MBMWs) from IMS Nanofabrication disrupted the mask writing technology in the past decade by offering this technology to the industry with a range of benefits over the preceding variable shaped beam technology. The MBMW-101 enabled write times independent of the pattern complexity, usage of low sensitivity resists at high throughput, and superior resolution and critical dimension uniformity (CDU) capabilities. With these benefits, the technology enabled high volume extreme ultraviolet (EUV) mask manufacturing and the use of inverse lithography technology (ILT) using curvilinear patterns for logic and memory applications to the industry. The MBMW-201 is today’s standard technology for leading edge photo mask patterning and is used in the most advanced mask shops around the globe. Its superior robustness and powerful write modes allow for unprecedented writing efficiency and resolution capability. Now IMS has broadened the spectrum of applications for this technology and released two new products. The MBMW-100 Flex is a versatile mask writer to open multi-beam benefits to mature and intermediate node applications at high throughput and beneficial total cost of ownership, targeting nodes from 32 nm to 10 nm. The MBMW-301 is the third generation leading edge mask writer for ultra-low sensitivity resists with resolution and CDU capabilities meeting EUV high numerical aperture requirements targeting nodes down to 2 nm and beyond. This article will delve into the transformational journey of multi-beam mask writing, from its early beginnings to its current status as the cornerstone of EUV mask production, and provide an overview of the two new models with performance data and lithography results.

With the advent of inverse lithography technology, the landscape of electron beam lithography has undergone a paradigm shift, transitioning from a single variable-shaped beam to a multi-beam writer. Conversely, in the realm of mask process correction (MPC), the majority of techniques continue to depend on the manipulation of figures and edges to adjust shape boundaries. We have developed a MPC system that is integrated within the multi-beam writer. This system leverages the rasterized pixel data for exposure, which is conventionally accessible within the writer itself. We describe how our inline MPC works in the pixel domain instead of geometry domain to improve pattern fidelity of curvilinear shapes without additional turnaround time.

Full-chip curvilinear inverse lithography technology (ILT) requires mask writers to write full reticle curvilinear mask patterns in a reasonable write time. We jointly study and present the benefits of a full-chip, curvilinear, stitchless ILT with mask-wafer co-optimization (MWCO) for variable-shaped beam (VSB) mask writers and validate its benefits on mask and wafer at Micron Technology. The full-chip ILT technology employed, first demonstrated in a paper presented at the 2019 SPIE Photomask Technology Conference, produces curvilinear ILT mask patterns without stitching errors, and with process windows enlarged by over 100% compared to the OPC process of record, while the mask was written by multibeam mask writer. At the 2020 SPIE Advanced Lithography Conference, a method was introduced in which MWCO is performed during ILT optimization. This approach enables curvilinear ILT for 193i masks to be written on VSB mask writers within a practical, 12-h time frame, while also producing the largest process windows. We first review MWCO technology, then curvilinear ILT mask patterns written by VSB mask writer, and then show the corresponding 193i process wafer prints. Evaluations of mask write times and mask quality in terms of critical dimension uniformity and process windows are also presented.

Masking with polystyrene (PS) nanospheres, also known as colloidal lithography, is suitable for many technological applications. In this study, an evaporation-driven self-assembly process was applied and the surface coverage behavior of the nanospheres was monitored in terms of the surface coverage rate of the PS nanospheres and the change in the amount of hexagonal closed packed structures as a function of the suspension ratio, the drying temperature, and the tilt angle. Using this method, a well-ordered and homogeneous PS monolayer with a surface coverage rate of 82% (or relative surface coverage rate of 98%) was achieved on a 1×1 cm2 substrate surface.

Lithography hotspot (LHS) detection is crucial for achieving manufacturability design in integrated circuits (ICs) and ensuring the final yield of ICs chips. Recognizing the challenges posed by conventional deep learning-based methods for lithographic hotspot detection in meeting the demands of advanced IC manufacturing accuracy, this study introduces an LHS detection approach. This approach leverages multi-scale feature fusion to identify defects in lithographic layout hotspots accurately. This method incorporates the convolutional block attention module into the backbone network to enhance the focus of the model on the layout area. Additionally, a feature pyramid is employed to merge deep and shallow features from the layout pattern, significantly enhancing the capability of hotspot detection network to extract both image and semantic features. Concurrently, by utilizing a dense block that directly interconnects various layers, the network gains the capacity to capture the correlation between low-level and high-level features, thereby enhancing the perceptual capabilities of the model. Experimental results demonstrate the superiority of the algorithm across accuracy, false alarm, F1 score, and overall detection simulation time compared to alternative lithographic hotspot detection algorithms.

Critical dimension control is essential in the semiconductor industry and becomes more challenging as photolithography limits keep getting pushed to reach technological nodes smaller than 10 nm. To ensure the quality and control of the processes, it becomes necessary to explore new metrology techniques. In this sense, critical dimension small-angle x-ray scattering (CDSAXS) has been identified as a potential candidate for determining the average shape of a line grating with a sub-nanometric precision. We benchmark the CDSAXS results obtained at the synchrotron to the optical critical dimension, critical dimension scanning electron microscopy, and transmission electron microscopy measurements collected from industrial metrology tools either at the manufacturing line or in the characterization laboratory. Emphasis is placed on the impact of the use of independent model for each technique and the benefits of unifying it in a unique model. We also discuss the differences between all of these multi-scale and multi-physics techniques, question our capacity to compare them, and eventually correlate the results obtained on several samples.

Indium nitrate hydrate films are evaluated as potential extreme ultraviolet (EUV) resists. To study the feasibility of these indium nitrate-based sol–gel precursor films as an EUV resist, the uniformity and stability of these films are examined as a function of metal composition, precursor concentration, chemical sources, precursor dissolution time, solvent drying time, post-application bake conditions, and relative humidity during the deposition. A 0.1 M indium nitrate hydrate solution forms a 20-nm thick resist, which is ideal for EUV lithography. We find two types of defects: macroscale defects that are visible under an optical microscope and nanoscale defects that can only be detected using an atomic force microscope. Both types of defects are affected by humidity during spin coating, dissolution time, and water content in the solvent. Hence, they are likely due to undissolved or re-crystallized indium nitrate hydrate crystals. The spin-coated indium nitrate hydrate films show great stability with no changes in defect density for up to 3 weeks. Using a 92-eV electron beam as a proxy for the EUV source, exposed regions of the film become insoluble upon exposure, acting as a negative-tone resist. Results of operando Fourier-transform infrared spectroscopy and residual gas analysis during the exposure show that the solubility switch is accompanied by the decomposition of nitrate species and the release of water. These results demonstrate the potential of indium nitrate hydrate films as an effective inorganic EUV resist.

Resists are needed to advance extreme ultraviolet (EUV) lithography. In EUV resists, due to the high energy of the incident photons, most of the chemistry arises from the emitted primary and secondary electrons and not the EUV photons themselves. Because the electrons are playing a leading role in EUV patterning, initiating chemical transformations, it is important to characterize their generation, transport, and energy distribution. In this work, we present several experimental techniques to probe model polymer materials to investigate the impact of specific chemical groups on critical resist properties: EUV absorption, electron emission, electron attenuation length (EAL), and energy distribution of emitted electrons. Total electron yield provides information on the conversion of absorbed EUV photons to electrons, and photoelectron spectroscopy provides information on energy distribution of generated electrons. The EAL reveals the distance that the electrons can travel in a resist film, which is related to the electron blur. Correlations between the obtained experimental values are discussed. We explore how different elements or functional groups change the yield, EAL, and energy distribution of emitted electrons, aiming to understand how to control the electron cascade.

This article describes the formation of a 19 nm line critical dimension (CD) using a mask shift double exposure (MSDE) method to extend beyond the resolution limit of the current 38 nm line space pattern line CD in ArF immersion photolithography. There is no change in pitch (76 nm), but experiments are being conducted to reduce extreme line CD using optical trim. In the general photolithography process, patterning is performed by transferring the pattern of a mask to the photoresist (PR) of a wafer through a single exposure. MSDE is a method of patterning by exposing energy to the PR of the wafer twice consecutively without unloading the wafer and mask. It was confirmed that the first and second exposure energies are linearly summed, showing that the combination of the first and second exposure patterns allows for more sophisticated patterning than one exposure. When the two exposure patterns are parallel lines in the MSDE approach, a 19 nm line CD is realized by precisely controlling the line CD according to the exposure interval between the two lines. It is possible to form a line CD smaller than that in the case of a single exposure overdose. In addition, when the two exposure patterns are orthogonal lines in MSDE, a 29 nm pillar pattern can be realized, which is beyond the limit of resolution of ArF immersion lithography. If MSDE is applied to semiconductor process technology, the performance of litho-etch-litho-etch and self-aligned double patterning, which are double patterning technologies, can be improved, and the number of process steps can be reduced. It is also demonstrated that MSDE can be implemented in immersion.

A problem with high aspect ratio x-ray gratings, fabricated by the deep x-ray LIGA process, is the collapse of the metallic structure when the resist is removed. A unique method that consists of positioning perpendicular metal bridges on top of the grating (roof bridges) is described and tested as a solution. First, a theoretical study is carried out on the transmission loss of such grids as a function of the thickness, their spacing, their materials (gold or nickel), and the x-ray energy. Different processes with their own advantages and disadvantages are possible and described. To further satisfy the requirement of curved gratings, two processes are tested in detail: structuring the x-ray grating with a laser and planarization followed by restructuring a second resist layer. In both cases, a second electroplating step is performed. Finally, a grating with a 12 cm bending radius and stabilization is fabricated. To assess the quality of the grids, two complementary methods are used: scanning electron microscopy and angular x-ray transmission. The latter one is an innovatively developed measurement process specially dedicated to x-ray gratings. The results for the fabrication processes are discussed and rated. The stability provided by the roof bridges works as intended, although the overall quality of the grating is slightly reduced.