The first 0.55NA extreme ultraviolet lithography tools continue to progress towards production without the delays and technology gaps seen with the introduction of 0.33NA EUVL. Carry-over of proven modules and technologies from 0.33NA is providing the expected benefits in predictability and schedule, while the resources concentrated on the innovative anamorphic optics have delivered system-level aberrations and resist imaging performance consistent with the design and planned application of the tools. At the same time, the healthy ecosystem sustained by heavy usage of 0.33NA EUVL in high-volume manufacturing has supported the incremental enhancements in masks, resist, underlayers, etching, inspection, and metrology needed to insert 0.55NA EUVL on the Intel 14A process node. Introduction at this node avoids the need for excessive multi-patterning with 0.33NA EUV and is particularly beneficial when front-side metal pitches are co-optimized with backside power delivery. With the ecosystem for initial introduction in place, we are already working on enhancements such as a 6x12 mask format to extract the full productivity potential from the High NA platform while simplifying design by eliminating the need to consider die-stitching locations in floor plans for large die. Finally, there is growing optimism that numerical apertures significantly beyond 0.55NA are technically feasible, though work continues to make the business case to justify development of “hyperNA” production tools.
Due to their increasingly complex 3D geometries, upcoming gate all around (GAA) devices pose new metrology challenges for which there is not yet any established HVM metrology solution, in particular for various critical timed etch steps [5]. Soft x-ray (SXR) scatterometry using 10-20 nm wavelength light is a promising next-generation metrology technique for 3D profile metrology and overlay (OVL) applications. This wavelength regime offers unique benefits over existing metrology techniques today: (1) Short wavelengths allow for higher resolution measurements than traditional visible wavelengths could offer, enabling measurement of structures at device pitches. (2) Primarily single scattering yields low correlation between parameters and aids physical interpretation of signals. This enables many parameters of interest to be extracted accurately and simultaneously. (3) SXR provides 3D capability, with stack heights up to 400 nm supported and high depth resolution due to the broadband source and sensor. These properties together make SXR suitable for measuring the 3D profiles of advanced devices such as gate all around (GAA) transistors, as well as after develop (ADI) overlay at device pitch. In this paper, we demonstrate SXR for profile metrology of GAA devices. We show sensitivity to average SiGe lateral recess etch depth as well as individual nanosheet critical dimensions, which cannot be reliably accessed by other nondestructive, inline metrology techniques available today. We furthermore demonstrate sensitivity in ADI OVL measurements directly on device-pitch structures in the presence of an underlying patterned nuisance layer.
Strong production demand for 0.33NA EUV Lithography has enabled investments in further tool development, resulting in a steady roadmap of 0.33NA tools with improved imaging, overlay, defectivity and productivity, as well as a robust ecosystem supporting use of these tools in HVM. In parallel, co-investments by end users in development and initial production of 0.55NA tools has kept this technology on track for production in 2025, only six years after 0.33NA tools entered production. Continued innovation in semiconductor device structures and processes is on track to support use of the designed resolution and EPE of the 0.55NA tools to continue scaling.
Review of near and long term extension challenges for EUV lithography at 0.33 and 0.55NA. Focus on mask and infrastructure gaps + opportunities and a review of progress made in critical areas to support EUV extension.
This past year has witnessed a sharp increase in EUV lithography progress spanning production tools, source and infrastructure to better position the technology for HVM readiness. While the exposure source remains the largest contributor to downtime and availability, significant strides in demonstrated source power have bolstered confidence in the viability of EUVL for insertion into HVM production. The ongoing development of an EUV pellicle solution alleviates industry concern about one significant source of line-yield risk. In addition to continued expected improvements in EUV source power and availability, the ability to deliver predictable yield remains an ultimate gate to HVM insertion. Ensuring predictable yield requires significant emphasis on reticles. This includes continued pellicle development to enable the readiness and supply of a robust pellicle solution in advance of 250W source power, as well as improvements in mask blank defectivity and techniques to detect and mitigate reticle blank and pattern defects.
As the design rules and the actual sizes of the patterns being printed continue to shrink well below half the wavelength of light being utilized, the budgets associated with all variations in imaging likewise continue to squeeze to tighter required tolerances. In this environment, the control and adjustment of the imaging has continued to increase in importance. Building upon previous work in the field of lens adjustment and optimization, additional methods have been developed and implemented which enable more specialized adjustment towards the optimization of given priorities associated with a given patterning step. Specifically, it is fast becoming typical to leverage all available degrees of adjustment freedom uniquely for each critical layer identified in a given process. Various optimization goals are discussed, with procedures and results presented for each. Examples of these include: 1) optimization of a single machine towards the best possible ultimate CD uniformity performance while staying within a specified range of allowed residual distortion 2) optimization of ultimate distortion magnitude, while staying within a budgeted level of imaging/CD uniformity performance 3) optimization of specific aberrations while maintaining all others within budgeted levels of allowed magnitude The motivations driving each of these sorts of optimizations will be discussed, as well as limitations that may exist from various sources, including metrology, process variation and it effects, and the imaging tool. The impact such optimization capability can have on the defined CD budget will also be discussed, towards the goal of qualifying and, where possible, quantifying the overall improvement possible through application of these optimization techniques. These sorts of improvements and their documentation can allow for feedback into the device design process, leveraging the reduced level of variation resulting from such optimizations.
Tilt in the optic axis of the illumination system with respect to the projection lens manifests itself as a shift of the illumination source intensity distribution in the pupil plane of that projection lens. The impact of this error category upon various types of patterns and among various imaging configurations is studied through image simulation as well as experiment. Issues addressed will include:-Methods of measuring illuminator tilt -Sensitivity of sample cases to illumination tilt, including pattern placement issues as well as pattern fidelity issues -Aberration influence and coupling with illumination tilt influences -Ramifications of illuminator tilt impacts. Finally, comments will be made regarding this error category as it may impact the increasingly stringent process complexities and reducing linewidth sizes required by the processes being developed for the near future.
We present photoluminescence (PL) from Te-rich ZnSeTei_ alloys and ZnSeTei_/ZnTe superlattices
and discuss the growth of these materials on GaSb epilayers on GaSb substrates. We show that growing ZnTe on
GaSb substrates eliminates several bound exciton peaks which occur in ZnTe grown on GaAs. The ZnSeTei_
epilayers show bright luminescence from centers over 100 meV below the expected band edge. PL from ZnSeTe1_
alloys and superlattices is qualitatively very different from PL from CdZni.Te alloys and CdZniTe/ZnTe
superlattices .
We present photoluminescence spectra from CdZnj_Te /ZnTe and ZnSe,,Tei_ /ZnTe strained
layer superlattices grown by MBE, and analyze the band alignments and strain effects. Our results
are based on fitting the dominant photoluminescence peaks to the superlattice band structure obtamed
by k •theory. We find that the valence band offset of the CdZniTe /ZnTe system is quite
small. On the other hand, the photoluminescence data from the ZnSeTei_ /ZnTe superlattices
suggest that the band alignment is type II, with a large valence band offset. We also investigate
the band gap bowing in the ZnSeTej_ alloys, and determine the individual components of the
bowing in valence and conduction bands. Based on our results for band alignments, we evaluate the
prospects for minority carrier injection in wide bandgap heterostructures based on ZnSe, ZnTe, and
CdTe.
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