This paper summarizes findings on the iN7 platform (foundry N5 equivalent) for single exposure EUV (SE EUV) of M1 and M2 BEOL layers. Logic structures within these layers have been measured after litho and after etch, and variability was characterized both with conventional CD-SEM measurements as well as Hitachi contouring method. After analyzing the patterning of these layers, the impact of variability on potential interconnect reliability was studied by using MonteCarlo and process emulation simulations to determine if current litho/etch performance would meet success criteria for the given platform design rules.
EUV sources emit a broad band DUV Out-of-Band (OOB) light, in particular, in the wavelength range 100-400 nm. This can cause additional exposure of EUV resists made that are based on a ArF/KrF resist platform. This DUV light is partially suppressed while travelling through the optical path but a non-negligible part of it reaches wafer level and impacts imaging.
This is important for imaging at the edges of an image field when fields are printed very close to each other on the wafer (so-called butted fields, with zero field to field spacing). DUV light is reflected from the reticle black border (BB) into a neighboring exposure field on the wafer. This results in a CD change at the edges and in the corners of the fields and therefore has an impact on CD uniformity. Experimental CDU results are shown for 16 nm dense lines (DL) and 20 nm isolated spaces (IS) (N7 logic design features) in the fields exposed at 0 mm and 0.5mm distance on the wafer. Areas close to the edge of the image field are important for customer applications as they often contain qualification and monitoring structures; in addition, limited imaging capabilities in this area may result in loss of usable wafer space.
In order to understand and control OOB DUV light, it must be measured in the scanner. DUV measurements are performed in resist using a special OOB reticle coated with Aluminum (Al) having low EUV reflectance and high DUV reflectance. A model for DUV light impact on the imaging is proposed and verified. For this, DUV reflectance data is collected in the wavelengths range 100-400 nm for Al and BB and the ratio of reflectances of these materials is determined for assumed scanner and resist OOB spectra. Also direct BB OOB test is performed on the wafer and compared to Al OOB results. The sensitivity of 16 nm DL and 20 nm IS to OOB light is experimentally determined by means of double exposure test: a wafer with exposed imaging structures undergoes a second flood exposure from a DUV reflective material (Al or BB).
Finally, several OOB mitigation strategies are discussed, in particular, suppression of DUV light in the scanner (~3x improvement), recent successes of DUV suppression for 16 nm imaging resist (~1.8x improvement) and DUV reflectance mitigation in the reticle black border (~3.8x). An overview of OOB test results for multiple NXE systems will be shown including systems with new NXE:3350 optics with improved OOB suppression.
In this paper we introduce new source-mask co-optimization (SMO) capabilities for EUV with specific support of the details of imaging with NXE:33×0 scanners. New algorithms have been developed that fully exploit the adjustability of the light distribution inside the NXE:33×0 flexible illuminator, FlexPupil. The fast NXE M3D+ model accurately predicts the reflective 3D mask effects and enables novel pupil symmetries and mask defocus optimization. This mitigates the H-V bias, Bossung tilt, and pattern shift caused by shadowing and non-telecentricity, and reduces the sensitivity to flare. New pupil optimization flows will be shown. The optimized pupils are fully compliant with NXE:33×0 scanner specifications. We will demonstrate enhanced imaging performance of this NXE specific SMO on 7 nm node logic cut masks and show benefits up to 20% improved CD uniformity, and a reduction in the maximum pattern shifts.
With the introduction of the NXE:3100 NA=0.25 exposure system a big step has been made to get EUV
lithography ready for High Volume Manufacturing. Over the last year, 6 exposure systems have been
shipped to various customers around the world, active in Logic, DRAM, MPU and Flash memory, covering
all major segments in the semi-conductor industry. The integration and qualification of these systems have
provided a great learning, identifying the benefits of EUV over ArF immersion and the critical parameters
of the exposure tool and how to operate it.
In this paper we will focus specifically on the imaging performance of the NXE:3100 EUV scanner.
Having been operational for more than a year a wide range of features were evaluated for lithographic
performance across the field and across wafer. CD results of 32nm contact holes, 27nm isolated and dense
lines, 27nm two-bar, 22nm dense L/S with Dipole, as well as several device features will be discussed and
benchmarked against the current ArF immersion performance. A budget verification will be presented
showing CD and contrast budgets for a selection of lithographic features. The contribution of the resist
process and the mask will be discussed as well.
The litho performance optimization will be highlighted with the 27nm twobar and isolated lines features
that are sensitive to the illuminator pupil shape and projection lens aberrations.
We will estimate the amount of resist induced contrast loss for 27 and 22nm L/S based on measurements of
Exposure Latitude and the contributors from the exposure system.
We will further present on the impact of variations in the mask blank and patterned mask on imaging, with
several new contributors to take into account compared to traditional transmission masks.
Finally, the combined results will be projected to the NXE:3300 NA=0.33 exposure system to give an
outlook for its imaging performance capabilities.
In this paper we perform a fundamental study on the impact of mask absorber in ArF immersions
lithography: the mask 3D effects. From simulations and analysis of diffraction coefficients we could
identify a range of relevant features and imaging and placement phenomena. For these features,
experimental results were obtained to pinpoint the mask 3D effects. We will demonstrate how to
model and understand the mask 3D effects and give solutions to counteract the mask 3D effects.
In this paper we describe the basic principle of FlexWave, a new high resolution
wavefront manipulator, and discuss experimental data on imaging, focus and overlay.
For this we integrated the FlexWave module in a 1.35 NA immersion scanner. With
FlexWave we can perform both static and dynamic wavefront corrections. Wavefront
control with FlexWave minimizes lens aberrations under high productivity usage of the
scanner, hence maintaining overlay and focus performance, but moreover, the high
resolution wavefront tuning can be used to compensate for litho related effects.
Especially now mask 3D effects are becoming a major error component, additional
tuning is required. Optimized wavefront can be achieved with computational lithography,
by either co-optimizing source, mask, and Wavefront Target prior to tape-out, or by
tuning Wavefront Targets for specific masks and scanners after the reticle is made.