Qubit information processors are increasing in footprint but currently rely on e-beam lithography for patterning the required Josephson junctions (JJs). Advanced optical lithography is an alternative patterning method, and we report on the development of transmon qubits patterned solely with optical lithography. The lithography uses 193 nm wavelength exposure and 300 mm large silicon wafers. Qubits and arrays of evaluation JJs were patterned with process control which resulted in narrow feature distributions: a standard deviation of 0.78% for a 220 nm linewidth pattern realized across over half the width of the wafers. Room temperature evaluation found a 2.8%–3.6% standard deviation in JJ resistance in completed chips. The qubits used aluminum and titanium nitride films on silicon substrates without substantial silicon etching. T1 times of the qubits were extracted at 26–27 μs, indicating a low level of material-based qubit defects. This study shows that large wafer optical lithography on silicon is adequate for high-quality transmon qubits, and shows a promising path for improving many-qubit processors.

The promise of quantum computing for solving problems of interest to society (e.g., drug design, cryptography, etc) can be advanced by the fabrication of high performance qubits that faithfully replicate the designer's intent. 3D integrated superconducting digital electronics are being considered for energy-efficient, low-latency qubit control, and for readout. The development of 'manufacturing-friendly' qubit architectures is essential for building repeatable, well-controlled qubits into quantum computing systems equipped with 3D integrated qubit control and communication. In this paper, the potential advantages and challenges of qubit and superconducting electronics fabrication using advanced 300mm wafer processes will be discussed, with reference to millikelvin characterization results from qubits fabricated using 193nm lithographic techniques on 300mm wafers. Fabrication of high quality interfaces will be discussed, with high resolution TEM and other analyses guiding such process development, serving to illustrate the potential for further increases in qubit performance through the use of 300mm fabrication.

Extreme ultraviolet (EUV) lithography with reflective photomasks continues to be a potential patterning technology for high volume manufacturing at the 7 nm technology node and beyond. EUV photomasks with alternative materials to the commonly used Mo/Si multilayer (ML) reflector and patterned Ta-based absorber (both of which are known to require shadow effect corrections and lead to large through-focus pattern placement errors) are being actively explored. Because the reflective bandwidth of a Ru/Si ML is significantly wider than the reflective bandwidth of a Mo/Si ML and the effective reflectance plane in Ru/Si is closer to the ML surface, Ru/Si ML coatings may be viable alternatives to the Mo/Si ML coatings that are commercially available today because they will lead to smaller mask 3D effects. In this paper, increases in the peak reflectivity and the reflective bandwidth of Ru/Si ML reflectors by using B4C interlayers to improve the Ru-Si interfaces are discussed. The conclusions of this paper are supported with the results of both experimental measurements and rigorous simulations.

In this paper we compare the imaging performance of several options currently under consideration for use in 0.33 and higher numerical aperture (NA) extreme ultraviolet (EUV) mask stacks, Mo/Si ML reflective coatings with 40 bilayers, Ru/Si multilayer (ML) reflective coatings with 20 bilayers, and a new thinner Ni-based absorber layer on each of these mask stacks. The use of a Ru/Si ML coating with its shallower effective reflectance plane and a 2x thinner Ni-based absorber is expected to significantly reduce both shadow bias requirements and mask telecentricity errors. The conclusions of the paper are supported with the results of both experimental measurements and rigorous simulations.

Availability of defect-free reflective mask has been one of the most critical challenges to extreme ultraviolet lithography (EUVL). To mitigate the risk, significant progress has been made on defect detection, pattern shifting, and defect repair. Clearly such mitigation strategies are based on the assumption that defect counts and sizes from incoming mask blanks must be below practical levels depending on mask specifics. The leading industry consensus for early mask product development is that there should be no defects greater than 80 nm in the quality area, 132 mm x 132 mm. In addition less than 10 defects smaller than 80 nm may be mitigable. SEMATECH has been focused on EUV mask blank defect reduction using Veeco Nexus TM IBD platform, the industry standard for mask blank production, and assessing if IBD technology can be evolved to a manufacturing solution. SEMATECH has recently announced a breakthrough reduction of defects in the mask blank deposition process resulting in the production of two defect-free EUV mask blanks at 54 nm inspection sensitivity (SiO2 equivalent). This paper will discuss the dramatic reduction of baseline EUV mask blank defects, review the current deposition process run and compare results with previous process runs. Likely causes of remaining defects will be discussed based on analyses as characterized by their compositions and whether defects are embedded in the multilayer stack or non-embedded.

Ion Beam Deposition (IBD) has been the primary technique used to deposit EUV mask blanks since 1995 when it was discovered it could produce multilayers with few defects. Since that time the IBD technique has been extensively studied and improved and is finally approaching usable defectivities. But in the intervening years, the defectivity of magnetron sputtering has been greatly improved. This paper evaluates the suitability of a modern magnetron tool to produce EUV mask blanks and the ability to support HVM production. In particular we show that the reflectivity and uniformity of these tools are superior to current generation IBD tools, and that the magnetron tools can produce EUV films with defect densities comparable to recent best IBD tool performance. Magnetron tools also offer many advantages in manufacturability and tool throughput; however, challenges remain, including transitioning the magnetron tools from the wafer to mask formats. While work continues on quantifying the capability of magnetron sputtering to meet the mask blank demands of the industry, for the most part the remaining challenges do not require any fundamental improvements to existing technology. Based on the recent results and the data presented in this paper there is a clear indication that magnetron deposition should be considered for the future of EUV mask blank production.

High numerical aperture (high-NA) extreme ultraviolet (EUV) is one option to enable a higher resolution than EUV can achieve with single patterning. An industry effort to achieve consensus on the key parameters of high-NA EUV is described. At high-NA, three-dimensional (3D) mask effects cause a loss of contrast in the image that is recovered by increasing the scanner de-magnification. This leads to a tradeoff between wafer field and mask size that has considerable impact on mask cost and scanner cost of ownership.

For full commercialization, extreme ultraviolet lithography (EUVL) technology requires the availability of EUV mask blanks that are free of defects. This remains one of the main impediments to the implementation of EUV at the 22 nm node and beyond. Consensus is building that a few small defects can be mitigated during mask patterning, but defects over 100 nm (SiO2 equivalent) in size are considered potential "killer" defects or defects large enough that the mask blank would not be usable. The current defect performance of the ion beam sputter deposition (IBD) tool will be discussed and the progress achieved to date in the reduction of large size defects will be summarized, including a description of the main sources of defects and their composition.This paper will discuss the main sources of >100 nm defects in the IBD tool and a path forward for eliminating similar to 70% of the large defects found during multilayer deposition (i.e., stainless steel and aluminum oxide particles).

EUV lithography is needed by the semiconductor industry for both its resolution and for the process simplification it provides compared to multiple patterning. However it needs many innovations to make it a success and is an expensive technology to develop. Major areas of concern are source power, defect free mask availability, defect freedom during use and resist performance. Long term it will also need improved mask and material technology for higher NA EUV imaging. SEMATECH is working on mask technology, defects and resist technology for EUV imaging and has developed new mask inspection technology, novel approaches to EUV resist, lower defectivity mask blanks and improved cleaning methods. SEMATECH's work enables the semiconductor industry to share the cost of developing EUV technology and accelerates the progress of EUV.

Multiple challenges, including the availability of a reliable high power source, defect free mask, and proper resist material, have forced extreme ultraviolet (EUV) lithography to be considered for sub-10 nm half-pitch nodes. Therefore, techniques such as phase shift masks (PSMs) or high numerical aperture (NA) lithography might be considered. Such techniques require thin EUV absorber materials to be optimized to reduce EUV mask shadowing effects. Despite the challenges in dry etching of Ni and finding proper chemistries with a high etch selectivity to suitable capping materials, we decided to examine the chemical stability of Ni for existing mask cleaning chemistries. Ni, after Ag, has the highest absorption in EUV light at lambda=13.5 nm, which makes it a proper candidate-in pure form or in mixing with other elements-for thin absorber film. Depending on the composition of the final material, proper integration schemes will be developed.We studied Ni stability in commonly used mask cleaning processes based on ammonium hydroxide/hydrogen peroxide (APM) and water mixtures. Ni films deposited with an ion beam deposition technique with a thickness of 35 nm are sufficient to totally absorb EUV light at lambda=13.5 nm. Multiple cleanings of these Ni films resulted in Ni oxidation-confirmed by time-of-flight secondary ion mass spectroscopy (TOF-SIMS) analysis as NiO with thickness about 1.5 nm. Furthermore, Ni oxidation processes are self-limiting and oxide layer thickness did not increase with a further cleaning. A three minute exposure to sulfuric acid/hydrogen peroxide mixture (SPM) can remove NiO and Ni totally. To protect Ni film from etching by SPM chemistry a 3 nm Si capping was used on top of Ni film. However, Si capping was removed by APM chemistry and could not protect Ni film against SPM chemistry. TiO2 may be a very good capping layer for EUV optics but it is not suitable for EUV mask blanks and will be removed by APM chemistries.

Nontelecentric illumination in extreme ultraviolet (EUV) lithography leads to pattern shifts through focus called telecentricity errors. As the industry moves toward finer pitch structures and higher numerical apertures (NA) to improve resolution, the effects of telecentricity errors become more significant. These telecentricity errors are dependent on pattern pitch, pattern type, lens aberrations, mask stack, to name a few. In this paper, a novel technique to measure telecentricity errors using EUV mask images from an actinic mask inspection tool, called the SEMATECH High NA Actinic Reticle Review Project (SHARP) is presented. SHARP is SEMATECH's second generation actinic mask imaging tool developed by Lawrence Berkeley National Laboratory. The SHARP can image masks at different numerical aperture settings, even beyond the currently available scanner NA of 0.33 (high-NA EUV) and also has a set of programmable illuminator choices. A tuned multilayer EUV mask blank was fabricated with test structures optimized for imaging on SHARP. The test structures were designed to cover a variety of critical dimensions and pitches. The mask design was fabricated on a tuned multilayer blank optimized for NA > 0.4. The mask was fabricated at Advanced Mask Technology Center and imaged on the SHARP. SHARP images were analyzed in software customized for edge position extraction of features. Pattern shifts through focus were calculated for a variety of pitches under different NA and illumination settings. The results show a monotonic increase in pattern shifts as NA increases. Also, at a given NA, the pattern shift is dependent on pattern pitch. The paper provides a detailed discussion on the experiment setup, analysis of the results and applicability of these results to high volume manufacturing of semiconductor devices using production EUV scanners.

Particle formation is a major problem in extreme ultraviolet masks, and one source of these particles has been identified to be the targets used to produce the mask surfaces. In particular, the silicon (Si) and ruthenium (Ru) target appear to produce more particles, especially silicon. The evidence of this is seen as a rough region on the edges of the silicon target. The features in the region were found to be triangular mesas pointing in the direction of the incident beam. The aim of this research is to prevent the mesa formation features on the target and thus reduce particle formation on the target. Both Si and Ru targets were sputtered using different ion beam conditions to understand the mesa formation mechanisms on the target and explore the ion beam conditions that can mitigate mesas. A simple 2D Monte-Carlo computer model (Illinois surface analysis model) was used to understand the formation of mesas with different incident angles of ion beam (0°, 35°, 54°, 75°) that agrees with the shapes of mesas seen in the experiments. Additionally, srim was used to calculate sputtering yields to better understand the different mechanisms between Si and Ru. It is concluded from both experiment and calculation results that an effective way to stop mesas formation is to have a sample oscillating between 0° and the desired angle during sputtering.

EUVL requires a high yield of low-defect density reflective mask blanks, one of the top two critical technology gaps for the commercialization of this technology. One of the major sources of mask blank defects is the top of the substrate due to substrate quality, cleaning residue, and handling-or storage-induced defects. SEMATECH's current inspection tool, the Lasertec 7360, can detect defects down to 37 nm on quartz substrates in dense scan mode. Defects below 40 nm on these substrate are difficult to detect, which challenges the quantification and characterization, and hence the determination of defect sources. SEMATECH developed a thin film decoration technique to quantify sub-40 nm defects and analyze composition to pinpoint defect sources. The technique involves oblique angle deposition in an ion beam deposition system, which decorates the particle. The decoration of particles is optimized by depositing enough thin film so that defects can be detected by the Lasertec7360 and yet keeping the film thin enough to employ several metrology techniques to efficiently analyze defect composition. The challenges involved with the metrology of such embedded defects and the impact of oblique angle deposition will be discussed. A theoretical model of defect decoration that can successfully simulate the thin film deposition on top of the defects will be provided. The effect of angle, deposition rate, and deposition time to quantify the decoration effect will also be presented.

The authors investigated the influence of surface roughness of stainless-steel shields in an ion beam sputtering chamber on the particle defect density of deposited 50 pairs of Mo/Si bilayer films ([Mo/Si]50) used in extreme ultraviolet mask blanks. Shields with varying arithmetic average surface roughness (Ra range approximately 3 to 20 μm) were mounted close to the sputtering targets and the substrate, and along the vacuum chamber interior wall. Silicon-rich particles (Si and Si/Mo) with diameters in the range of several tens of nanometers or more were quantified within a 142 mm× 142 mm area of the prepared blank film using a mask blank inspection tool. Si-rich particle defect density was found to be proportional to the inverse square of the shield surface roughness, suggesting that Si-rich particles arise from the shield surface. The shields with roughness exceeding 8 μm effectively suppressed the accumulation of Si-rich particle defects on the mask blank film.

The ability of optical lithography to steadily produce images at increasingly smaller dimension while maintaining pattern fidelity of devices with greater complexity has enabled the success of Moore's Law. Although 193 nm immersion and double patterning techniques have proven successful in extending optical lithography, the strategies proposed for further extension are too costly to support device manufacturing. As a result, greater focus has been shifted to resolving the challenges hindering extreme ultraviolet lithography (EUVL) adoption as the mainstream lithography solution. While similar to conventional optical lithography, there are unique challenges to EUVL, one of which is the change from transmission masks to the reflective masks required for EUVL. The use of reflective reticles greatly increases complexity of EUV reticle structure when compared to the binary masks used with optical lithography. Maximizing the reflectance an EUV mask requires the use of a multilayer Bragg reflector deposited on a finely polished substrate with a thin absorber film on top used to define the device pattern. Although similar in form to the substrates used in optical lithography, the tolerances on figure, surface finish, and defects are significantly more stringent for EUV substrates. Control of aberrations and maintaining pattern fidelity places tight constraints on the flatness and roughness of the EUV substrate; imperfections and particles can result in printable defects. The Bragg reflector of the EUV mask consists of 40 to 50 Si/Mo bi-layers deposited using an ion beam deposition tool. This film stack must be deposited to meet the reflectivity and uniformity requirements of the exposure tool and must be completely free of defects. The absorber film is typically a tantalum-based nitride layer selected for its ability to absorb EUV radiation and maintain thermal stability. The thickness and morphology of this film must be tightly controlled to enable use as the patterning film for the device. In addition to the increase in complexity of the mask, introduction of EUVL requires infrastructure development of new substrate, mask blank, and finished reticle inspection tools and techniques for handling and storage of a mask without a pellicle. This paper will highlight recent advances in the ability to produce pilot line quality EUV mask blanks to meet the near-term requirements and review the existing technology gaps which must be closed to extend the current capability to meet HVM needs. A special focus will be put on substrate and mask blank defect densities; other process and infrastructure challenges will also be discussed.

EUVL requires high-yield, low defect density reflective mask blanks, a requirement which is considered one of the top two critical technology gaps for commercialization of the technology. At the SEMATECH Mask Blank Development Center (MBDC), research on defect reduction and yield improvement for EUV mask blanks is being pursued using the Veeco Nexus deposition tool. The defect performance of this tool is one of the factors limiting the availability of defect-free EUVL mask blanks. SEMATECH identified the key components in the ion beam deposition system that are currently impeding the reduction of defect density and the yield of EUV mask blanks. SEMATECH improved the defect performance of the champion blank with 12 defects above 45 nm which is a 36% improvement from the data reported last year for the champion blank (19 defects above 45 nm). The yield analysis on high quality mask blanks from ion beam deposition system is also presented. Substrate quality is currently the biggest source of mask blank defects, while high yield also requires complete elimination of large size defects from deposition. A roadmap to meet the required defectivity specification for EUV mask blanks is presented.

One of the major technical hurdles to be overcome before EUV lithography can enter high volume manufacturing is the amount of defects in EUV mask blanks, many of which occur during the EUV reflector deposition process. The technology currently used to deposit this reflector is ion beam sputter deposition. Understanding the properties of the ion beam and the nature of the plasma in the deposition chamber is therefore critical to understanding defect production mechanisms and subsequently eliminating them.In this work, we have studied how the source parameters influence ion beam divergence, its footprint on the target, and the amount of beam that misses the target and hits the shielding. By optimizing the source parameters, we can modulate certain target-and shield-specific defect types. We have compared our data with models of source performance and found general agreement, enabling the theory to be fine-tuned based on the results of the measurements. Models are being developed to better describe actual source performance. We have also investigated the plasma conditions the ion beam creates in the tool, which is crucial to understanding the transport of defects from their source to the mask. A well characterized ion beam and plasma will lead to process and tool changes that will ultimately reduce defect levels in EUV mask blanks.

Mitigation of pit-type defects proves to be a major hurdle facing the production of a defect-free mask blank for EUV lithography. Recent efforts have been directed toward substrate smoothing methods during deposition. The angle of incidence of the substrate is known to have a significant effect on the growth of defects during deposition. It has been shown that shadowing effects for bump-type defects are reduced when depositing Mo/Si films at near-normal incidence, resulting in a Gaussian growth profile in which the height and volume of the defect are minimized. Conversely, operating at off-normal incidence reduces shadowing of pit-type defects. When altering the angle of incidence of the substrate, the target angle must be changed to maintain uniformity. The resulting mask blank must also meet surface roughness specifications post-deposition while maintaining a low defect density. In this study, various substrate angle and target angle combinations were investigated within the Veeco Nexus Low Defect Density tool at SEMATECH to find optimum in situ pit smoothing conditions using ion beam deposition on both quartz and low thermal expansion material (LTEM) substrates. The possible substrate-target angle combinations are limited by the design of the current deposition tool; therefore, a phase space has been mapped out to determine uniform and non-uniform regions. Other deposition parameters including operating pressure and working gas composition were also explored. After deposition, EUV reflectrometry measurements were taken to evaluate uniformity in the wavelength; surface roughness, change in pit depth, change in full width at half maximum, and pit smoothing power were determined using atomic force microscopy (AFM); transmission electron microscopy (TEM) was used to study the effect of film disruption through the multilayer; and the printability of smoothed pits will be measure actinically using SEMATECH's AIT tool.Preliminary results show that positive values for substrate angles in the uniform region tend to give a high surface roughness after multilayer deposition; however, the combinations with negative substrate angles show promising results. Substrate angles with lower values resulted in better smoothing than the higher substrate angles. AFM results confirmed that pit smoothing power at lower substrate angles is greater than under the standard deposition conditions employed by the tool. Lower chamber pressure was proven to increase the smoothing power of pit-type defects during deposition. Preliminary TEM cross-section data confirmed the smoothing results obtained by AFM analysis. The use of Ne and Xe as working gases is also under review. Extensive AFM analysis, TEM cross-sections, and printability data will be presented.