Nanoimprint Lithography (NIL) remains a versatile technology for replicating optically functional patterns. However, height and roughness conservation over large areas during replication, remains a challenge. In order to identify UV-NIL process capabilities, this study propose to validate the replication of multi-height pillars present on the resist master manufactured by grayscale lithography. Multiple measurement were performed on all pillars before and after replication using profilometry and Atomic Force Microscopy (AFM) to evaluate height and roughness of all patterns. This achievement represents a novel approach to understanding and identifying the capabilities of the UV-NIL process.
3D patterns and miniaturization have emerged as key paths for novel applications in microelectronics, optics, photonics and more. However, the current manufacturing techniques for high-resolution 3D patterning are complex, slow, and expensive. Here, we combine grayscale electron-beam lithography (g-EBL) and nanoimprint lithography (NIL) to overcome these challenges. Indeed, g-EBL allows the fabrication of complex structures with high resolution, while NIL can replicate complex patterns down to the nanometer scale with reduced time and cost. In a first step, the master is fabricated by grayscale electron beam lithography to obtain high resolution. This "resist master" is employed to prevent possible pattern deformation caused by etching and stripping steps. In a second step, this master is replicated by NIL to increase the throughput. In addition, different characterizations are performed after each step in order to evaluate the process. The morphology, dimensions and material properties are studied.
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.
Nanoimprint Lithography (NIL) is a lithography technique suitable for mass production because it can replicate complex patterns down to the nanometer scale with reduced time and cost. The master is one of the key elements of NIL. It determines the resolution of the replicated patterns and plays a role in defectivity. Therefore, it must be characterized to control the replication as properly as possible. Here, we target to create a resist master to achieve 3D structures. This master is made by grayscale electron beam lithography to obtain submicron resolution. In this study, full characterization of structures are presented to validate resist master quality.
Since its beginning in the 90’s NanoImprint Lithography (NIL) has been continuously improved to target the different industry requirements. Using an intermediate soft stamp media was one of the main improvements and has now become a standard technology. Based on that technology, EVG introduces a full wafer imprinting solution, whereas the size of the stamp corresponds to the size of the wafer to imprint. Results obtained at CEA-Leti using this solution, with respect to uniformity, sub-50nm resolution, repeatability, and high aspect ratio patterns, are today state of the art and allow NIL to be considered as an HVM technology. Nevertheless, further development is carried out on different aspects such as overlay (OVL) which is the scope of this work.
Different contributors of OVL as translation, rotation but also distortion are dissociated and analyzed. Alignment repeatability is studied. Additionally, imprint to imprint OVL correction terms are applied. A dedicated methodology has been established and allows to obtain global OVL signature. According to the above, main process contributors are highlighted and studied in the paper to separate influence of each of them. Finally, different ways to improve overlay are discussed and some of them - which could be linked to hardware, process or both - are evaluated. Overall, the OVL status obtained and first improvements bring NIL technology closer to the alignment requirements of the industry.
First, Grayscale I-Line lithography process developed in CEA-Leti allows to manufacture a variety of 3D patterns based on the well-known photolithography technology. Grayscale photolithography is an innovative and alternative approach to create 3D patterns such as microlenses for example. Exposure of a low contrast resist at different doses results in different thicknesses in the resist film. The variation of the intrinsic dose is obtained by using a binary mask that has different chromium densities, thus modulating the exposure intensity on the resist surface1. Secondly, the NanoImprint Lithography (NIL) is a technology capable of reproducing a wide morphological range. NIL is increasingly requested for the reproduction of 3D patterns. Initially, standard NIL process uses a hard master usually composed of Si or SiO2. The proposed work validates the quality of the replication by the NanoImprint process of a "resist master" created by grayscale lithography. This approach facilitates the manufacturing process of a master by avoiding the etching step and offering a cost-effective solution. The measurement of several types of 3D patterns are performed before and after replication during this study. CD preservation is evaluated for 32 types of microlenses simultaneously replicated. Finally, the combination of the Grayscale and NanoImprint technologies allows to considerably increasing the printing possibilities. By freeing the difficulties of multiple patterns morphology conservation during the etching, the replication of a resist master permits other potential applications, particularly in the optical field.
Critical Dimension (CD) 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 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 to determine the average shape of a line grating with a sub-nanometric precision. In this paper we benchmark the CDSAXS results to Optical Critical Dimension (OCD), Critical Dimension Scanning Electron Microscopy (CDSEM) and Transmission Electron Microscopy (TEM) measurements previously collected from industrial metrology tools at manufacturing line and in characterization laboratory. Emphasis is placed on the model used for CDSAXS and how to improve it. We discuss the differences between all these multi-scale and multi-physics techniques, and question our capacity to compare them.
In the domain of advanced patterning, and especially at lithography steps achieve very small sizes becomes more and more crucial. This induces measurement challenges and thus requiring the development of new, precise and robust metrology techniques. To overcome the limited constraints of different techniques, one of the most promising approaches is hybrid metrology. It consists in gathering several metrology techniques to measure all the geometrical parameters which are processed them by an algorithm (mainly machine learning algorithm). This work stands out by using for deep learning a multi-branch neural network to increase the precision of predicts. With a particular attention made to the dataset generation and specific settings for each branch, we developed the potential of this approach which increase the precision of predicts.
Densification and reduction of lithographic features sizes keeping low defectivity is one of the biggest challenges in the patterning area. In order to extend 193 immersion capabilities and meet advanced applications needs, multi exposure image mode is a promising option for non-high volume manufacturing. It allows from a unique pattern with a fixed critical dimension (CD) and pitch, to obtain more dense patterns in a large surface without any process loop of standard flow, a huge benefit compared to litho-etch-litho-etch (LELE) approach. The study carried out explores this method with a specific design of pillars array printed using Negative Tone Development (NTD). The multi-image option relies on exposing multiple times the same initial pattern with a low image-to-image overlay. Based on intrinsic scanner performances, imageto-image placement error should be less than two nm. In this paper, many functionalities are explored to customize patterns from a single and unique mask design. One stake is to transfer (into silicon) a 2 mm * 2 mm pillar array design with a pitch divided by two, covering a wide surface on a 300 mm wafer and answering overlay and stitching requirements. Final results give well defined pillars which intra-wafer CD uniformity (3σ) satisfies application process requests. By using a flexible multi-image mode, mask constraints (cost and quality) can be relaxed, i.e. with a larger pitch structure on the reticle than the targeted one, final feature can be achieved. This development can be extended to hybrid lithography such as NanoImprint Lithography (NIL) or specific applications such as optics.
NanoImprint Lithography (NIL) is not a novel technology anymore1 but huge progress has been achieved for its industrial introduction since its first reporting. One of the main evolutions concerns the use soft stamp media2 ,which is now a standard technology. EVG introduced this technology with a full wafer imprint solution (the size of the stamp corresponds to the size of the wafer to print)3 and results obtained since five years are at the state of the art. Repeatability, uniformity, sub-50nm resolution and high aspect ratio patterns are addressed at the same time4–6 . Nevertheless, some challenges still remain, as e.g overlay7 and in particular the distortion phenomenona 8 , which contribute to the remaining overlay next to global translation and rotation. This study is focused on distortion effect which appears during NIL process using flexible backplanes and its minimization by using different materials. A polymer backplane is compared with a glass backplane which are used as carrier to the soft stamp material. A dedicated methodology to precisely measure this distortion is implemented to remove global alignment signature. Distortion signature is firstly evaluated with a standard soft stamp material and process of reference already established. Distortion fingerprint mapping is obtained for each wafer. Thanks to this mapping, a monitoring distortion plot is extracted, in order to follow the evolution of the distortion depending on wafers (wafer-to-wafer) and lots (lot-tolot). This study highlights that the use of a glass backplane developed by EVG clearly allows to improve the distortion in terms of magnitude but also of stability.
Hybrid metrology is a promising approach to access to the critical dimensions of line gratings with precisions. The objective of this work is about using artificial intelligence (AI), mainly artificial neural network (ANN) to improve metrology at nanoscale characterization by hybridization of several techniques. Namely, optical critical dimension (OCD) or scatterometry, CD–Scanning electron microscopy (CDSEM), CD–Atomic force microscopy (CDAFM) and CD–Small angle x-rays scattering (CDSAXS). With virtual data of tabular–type generated by modelling, the ANN is able to predict the geometrical parameters compared to true measured values with high accuracies and detect irregularities in input data.
The NanoImprint Lithography (NIL) technology by using a soft stamp is today ready for high volume manufacturing (HVM) with the global solution proposed by EVG1. This UV-based imprint, using a transparent stamp is now a standard technology and the most common option for the full wafer imprint, meaning the size of the stamp correspond to the size of the wafer to print. Previous work has shown promising results with strong repeatability and uniformity in terms of critical dimension (CD)2. In 2017, larges features, bigger than 500 nm period, and shallow aspect ratio were qualified3. Latter in 20194, lithography and etching through a Si/SiO2 stack were demonstrated for 25 wafers imprinted in a single run:
- Depending on several diameters contact (from 100 to 50 nm) and densities (from 1:3 to 1:15).
- For line and space arrays with a density of 1:4 and variable spaces widths (from 100 to 50 nm).
In this paper we demonstrate that the limit of the patterns dimension can be pushed to sub-50 nm features thanks to EVG SmartNIL technology, the optimized EVGNIL-UV/AS2 soft stamp material with matching resist as well as the improvement of pattern transfer by dry etching. Based on CDSEM metrology, and SEM cross-sections, high fidelity and reproducibility were demonstrated, with 25 replications in a single run using the same soft stamp. Transfer compatibility of the imprint material was validated until 45 nm line, with 1:4 density. Furthermore, the process window of this NIL technology and its compatibility with applications as photonics and 3D patterning are discussed. The specific developments achieved around stripping of the substrates and the perspectives for low defectivity process are pointed out.
This paper introduces line roughness characterization non-straight patterns made of block copolymers (fingerprint patterns). Line Width Roughness have been determined using Power Spectral Density based on a special edge detection developed at CEA-LETI to extract edges contours. We investigated several process parameters impact on LWR such as the degree of polymerization of different BCPs and the impact of UV irradiation on the roughness of the PS block.
For the most advanced nodes, line roughness reaches the same order of magnitude as the CD. It results in a huge impact on power consumptions and leads to some device failures. Hence, the control of this morphological aspect needs an adapted metrology. CD-SEM is considered as an adapted technique for roughness extraction. It is based on the PSD extraction that allows to obtain roughness information in frequency domain. CD-SAXS has been mentioned as one of the highest potential techniques for microelectronics by ITRS with an expected resolution better than one angstrom. The study presented in this article is based on programmed roughness simulations and first experimental measurements. It demonstrates that a complete PSD can also be extracted from a CD-SAXS analysis and that extended information of roughness can be so deduced. Comparison of SEM and SAXS proves the capability of SAXS technique for the PSD extraction of line roughness. Next challenges to improve this extraction are mentioned.
Currently, Line Edge Roughness (LER) and Line Width Roughness (LWR) control presents a huge challenge for the lithography step in microelectronic industries. For advanced nodes, this morphological aspect reaches the same order of magnitude than the Critical Dimension, which leads to an increased power consumption by transistors and devices. Hence, the control of roughness needs an adapted metrology. This study proposes to manufacture roughness standard samples and their validation. These samples can be used as standards to evaluate the capabilities of several tools. The preliminary part of this study has been carried out with periodical roughness sample to demonstrate the metrology approach. Further, programming of roughness based on Power Spectral Density (PSD) with Auto-Correlation Function (ACF) model is used to achieve roughness close to the real roughness case. A description of how design programmed roughness has been made and its exposition in the real conditions are detailed in this study. Moreover, a specific methodology of control has been developed, the results obtained have been compared with design inputs and mostly validated by experimental processes. This work represents the first step of manufacturing roughness standard samples based on PSD model design.
At modern manufacturing geometries, roughness control presents a huge challenge for the lithography step. For advanced nodes, this morphological aspect reaches the same order of magnitude as the critical dimension (CD). Hence, the control of roughness needs an adapted metrology. Specific samples with designed roughness have been manufactured using e-beam lithography. These samples have been characterized with three different methodologies: CD-scanning electron microscopy, optical critical dimension, and small angle x-ray scattering. The main goal is to compare the capability of each of these techniques in terms of reliability, type of information obtained, time to obtain the measurements, and level of maturity for the industry. The next step will be to develop a hybrid metrology approach for roughness determination with these techniques.
Nowadays, roughness control presents a huge challenge for the lithography step. For advanced nodes, this morphological aspect reaches the same order of magnitude than the Critical Dimension. Hence, the control of roughness needs an adapted metrology. In this study, specific samples with designed roughness have been manufactured using e-beam lithography. These samples have been characterized with three different methodologies: CD-SEM, OCD and SAXS. The main goal of the project is to compare the capability of each of these techniques in terms of reliability, type of information obtained, time to obtain the measurements and level of maturity for the industry.
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