As critical dimensions shrink, line-edge roughness (LER) and linewidth roughness become of increasing concern. Traditionally, LER is viewed as a resist-limited effect; however, as critical dimensions shrink and LER requirements become proportionally more stringent, system-level effects begin to play an important role. Recent advanced extreme-ultraviolet resist testing results have demonstrated lower bounds on achievable LER at the level of approximately 2–3nm. Here, the authors use modeling to demonstrate that a significant portion of this low bound may, in fact, be do to system-level effects and, in particular, the mask. Of concern are both LER on the mask as well as roughness of the multilayer reflector. Modeling also shows roughness (flare) in the projection optics not to be of concern.

/pdf/system-level-line-edge-roughness-limits-in-extreme-2u2mebkq6w.pdf

System-level line-edge roughness limits in extreme ultraviolet lithography

In an effort to continue the rapid pace of extreme ultraviolet (EUV) learning, the focus of developmental EUV lithography has shifted from low numerical aperture (NA) tools such as the 0.1NA engineering test stand to higher NA tools such as the 0.3NA micro-exposure tool (MET). To support this generation of lithographic optics, a static printing station has been developed at the Advanced Light Source. This synchrotron-based printing system relies on a scanning illuminator to provide real-time coherence (pupil-fill) control. Here, we describe a MET printing station and present early printing results obtained with the Sematech Set-2 MET optic. The resolution limit of baseline EUV resist is presented as well as 30nm equal-line-space printing in an experimental resist.

Extreme ultraviolet microexposures at the Advanced Light Source using the 0.3 numerical aperture micro-exposure tool optic

The recent development of high numerical aperture (NA) EUV optics such as the 03-NA Micro Exposure Tool (MET) optic has given rise to a new class of ultra-high resolution microexposure stations Once such printing station has been developed and implemented at Lawrence Berkeley National Laboratory's Advanced Light Source This flexible printing station utilizes a programmable coherence illuminator providing real-time pupil-fill control for advanced EUV resist and mask development The Berkeley exposure system programmable illuminator enables several unique capabilities Using dipole illumination out to {sigma}=1, the Berkeley tool supports equal-line-space printing down to 12 nm, well beyond the capabilities of similar tools Using small-sigma illumination combined with the central obscuration of the MET optic enables the system to print feature sizes that are twice as small as those coded on the mask In this configuration, the effective 10x-demagnification for equal lines and spaces reduces the mask fabrication burden for ultra-high-resolution printing The illuminator facilitates coherence studies such as the impact of coherence on line-edge roughness (LER) and flare Finally the illuminator enables novel print-based aberration monitoring techniques as described elsewhere in these proceedings Here we describe the capabilities of the new MET printing station and present system characterization results Moreover, we present the latest printing results obtained in experimental resists Limited by the availability of high-resolution photoresists, equal line-space printing down to 25 nm has been demonstrated as well as isolated line printing down to 29 nm with an LER of approaching 3 nm

https://digital.library.unt.edu/ark:/67531/metadc885229/m2/1/high_res_d/901242.pdf

EUV microexposures at the ALS using the 0.3-NA MET projectionoptics

We present a general algorithm for combining measurements taken under various illumination and imaging conditions to quantitatively extract the amplitude and phase of an object wave. The algorithm uses the weak object transfer function, which incorporates arbitrary pupil functions and partially coherent illumination. The approach is extended beyond the weak object regime using an iterative algorithm. We demonstrate the method on measurements of Extreme Ultraviolet Lithography (EUV) multilayer mask defects taken in an EUV zone plate microscope with both a standard zone plate lens and a zone plate implementing Zernike phase contrast.

https://escholarship.org/content/qt90j7x68r/qt90j7x68r.pdf

Quantitative phase retrieval with arbitrary pupil and illumination

Achieving line-edge/width roughness (LER/LWR) specifications remains as one of the most significant challenges facing the commercialization of extreme ultraviolet (EUV) lithography. LER is typically viewed as a resist problem; however, recent simulation results have shown that the mask can also be a significant contributor. Problems arise from both mask absorber LER as well as mask multilayer roughness leading to random phase variations in the reflected beam and consequently speckle. Here we describe these effects in detail and explore how they will impact EUV mask requirements for the 22-nm half-pitch node and beyond. Process window analysis yields mask multilayer roughness specifications on the order of 50 pm.

/pdf/implications-of-image-plane-line-edge-roughness-requirements-dtav32fxzp.pdf

Implications of image plane line-edge roughness requirements on extreme ultraviolet mask specifications

The success of recent static printing experiments at Lawrence Berkeley National Laboratory’s Advanced Light Source (ALS) using the EUV LLC Engineering Test Stand (ETS) Set-2 optic has demonstrated the utility of synchrotron-based EUV exposure stations. Although not viable light sources for commercial lithography, synchrotrons provide clean, convenient, and extremely flexible sources for developmental microfield lithography. The great flexibility of synchrotron-based illumination arises from the fact that such sources facilitate active coherence reduction, thus enabling the coherence function, or pupil fill, to be actively sculpted in real time.
As the commercialization of EUV progresses, the focus of developmental EUV lithography is shifting from low numerical aperture (NA) tools such as the 0.1-NA ETS to higher-NA tools such as the 0.3-NA Micro Exposure Tool (MET). To support printing with MET optics at the ALS, a new printing station has been developed, relying on a scanning illuminator to provide programmable coherence (pupil-fill) control. The illuminator is designed to operate up to a coherence factor (s) of 1 and support the full 200′600 design printed field of view. In addition to a new illuminator design, new focus sensing and dose-control systems have also been implemented. Here we describe the MET printing capabilities in detail and present preliminary printing results with the Sematech Set-2 MET optic.

Status of EUV micro-exposure capabilities at the ALS using the 0.3-NA MET optic

The SEMATECH High-NA Actinic Reticle review Project (SHARP) is a synchrotron-based, EUV-wavelength microscope, dedicated to photomask imaging, now being commissioned at Lawrence Berkeley National Laboratory. In terms of throughput, resolution, coherence control, stability and ease of use, SHARP represents a significant advance over its predecessor, the SEMATECH Berkeley Actinic Inspection Tool (AIT), which was decommissioned in September 2012. SHARP utilizes several advanced technologies to achieve its design goals: including the first Fouriersynthesis illuminator on a zoneplate microscope, EUV MEMS mirrors, and high-efficiency freestanding zoneplate lenses
with numerical aperture values up to 0.625 (4×). In its first week of operation, SHARP demonstrated approximately 150 times higher light throughput than AIT and a spatial resolution down to 55-nm half-pitch with 0.42 4×NA (i.e. the smallest feature size on our test mask.) This paper describes the current status of the tool commissioning and the performance metrics available at this early stage.

/pdf/commissioning-an-euv-mask-microscope-for-lithography-2xeccfhyj6.pdf

Hanjing Huang

Papers

Status of EUV micro-exposure capabilities at the ALS using the 0.3-NA MET optic

Commissioning an EUV mask microscope for lithography generations reaching 8 nm