James Macdougall

Commissioning an EUV mask microscope for lithography generations reaching 8 nm

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.

Actinic mask imaging: recent results and future directions from the SHARP EUV microscope

The SEMATECH High Numerical Aperture Actinic Reticle Review Project (SHARP) is a synchrotron-based extreme ultraviolet (EUV) microscope dedicated to photomask research. SHARP has been operational and serving users since June, 2013, and in eight months, SHARP has recorded over 71,000 high-resolution images. Exposure times are 5 to 8 seconds, and 8 or more through-focus series can be collected per hour at positions spanning the entire mask surface. SHARP’s lossless coherence-control illuminator and variable numerical aperture (NA) enable researchers to emulate the imaging properties of both current and future EUV lithography tools. SHARP’s performance continues to improve over time due to tool learning and upgraded capabilities, described here. Within a centered, 3-μm square image region, we demonstrate an illumination power stability above 99%, and an average uniformity of 98.4%. Demonstrations of through-focus imaging with various illumination coherence settings highlight the capabilities of SHARP.

At-wavelength optical metrology development at the ALS

Nano-focusing and brightness preservation for ever brighter synchrotron radiation and free electron laser beamlines require surface slope tolerances of x-ray optics on the order of 100 nrad. While the accuracy of fabrication and ex situ metrology of x-ray mirrors has improved over time, beamline in situ performance of the optics is often limited by application specific factors such as x-ray beam heat loading, temperature drift, alignment, vibration, etc. In the present work, we discuss the recent results from the Advanced Light Source developing high accuracy, in situ, at-wavelength wavefront measurement techniques to surpass 100-nrad accuracy surface slope measurements with reflecting x-ray optics. The techniques will ultimately allow closed-loop feedback systems to be implemented for x-ray nano-focusing. In addition, we present a dedicated metrology beamline endstation, applicable to a wide range of in situ metrology and test experiments. The design and performance of a bendable Kirkpatrick-Baez (KB) mirror with active temperature stabilization will also be presented. The mirror is currently used to study, refine, and optimize in situ mirror alignment, bending and metrology methods essential for nano-focusing application.

An experimental apparatus for diffraction-limited soft x-ray nano-focusing

Realizing the experimental potential of high-brightness, next generation synchrotron and free-electron laser light sources requires the development of reflecting x-ray optics capable of wavefront preservation and high-resolution nano-focusing. At the Advanced Light Source (ALS) beamline 5.3.1, we are developing broadly applicable, high-accuracy, in situ, at-wavelength wavefront measurement techniques to surpass 100-nrad slope measurement accuracy for diffraction-limited Kirkpatrick-Baez (KB) mirrors. The at-wavelength methodology we are developing relies on a series of wavefront-sensing tests with increasing accuracy and sensitivity, including scanning-slit Hartmann tests, grating-based lateral shearing interferometry, and quantitative knife-edge testing. We describe the original experimental techniques and alignment methodology that have enabled us to optimally set a bendable KB mirror to achieve a focused, FWHM spot size of 150 nm, with 1 nm (1.24 keV) photons at 3.7 mrad numerical aperture. The predictions of wavefront measurement are confirmed by the knife-edge testing. The side-profiled elliptically bent mirror used in these one-dimensional focusing experiments was originally designed for a much different glancing angle and conjugate distances. Visible-light long-trace profilometry was used to pre-align the mirror before installation at the beamline. This work demonstrates that high-accuracy, at-wavelength wavefront-slope feedback can be used to optimize the pitch, roll, and mirror-bending forces in situ, using procedures that are deterministic and repeatable.

Soft x-ray spectroscopy of high pressure liquid

We describe a new experimental technique that allows for soft x-ray spectroscopy studies (∼100-1000 eV) of high pressure liquid (∼100 bars). We achieve this through a liquid cell with a 100 nm-thick Si3N4 membrane window, which is sandwiched by two identical O-rings for vacuum sealing. The thin Si3N4 membrane allows soft x-rays to penetrate, while separating the high-pressure liquid under investigation from the vacuum required for soft x-ray transmission and detection. The burst pressure of the Si3N4 membrane increases with decreasing size and more specifically is inversely proportional to the side length of the square window. It also increases proportionally with the membrane thickness. Pressures > 60 bars could be achieved for 100 nm-thick square Si3N4 windows that are smaller than 65 μm. However, above a certain pressure, the failure of the Si wafer becomes the limiting factor. The failure pressure of the Si wafer is sensitive to the wafer thickness. Moreover, the deformation of the Si3N4 membrane is quantified using vertical scanning interferometry. As an example of the performance of the high-pressure liquid cell optimized for total-fluorescence detected soft x-ray absorption spectroscopy (sXAS), the sXAS spectra at the Ca L edge (∼350 eV) of a CaCl2 aqueous solution are collected under different pressures up to 41 bars.

The SEMATECH high-NA actinic reticle review project (SHARP) EUV mask-imaging microscope

The SEMATECH High Numerical Aperture Actinic Reticle Review Project (SHARP) is a newly commissioned, synchrotron-based extreme ultraviolet (EUV) microscope dedicated to photomask research. SHARP offers several major advances including objective lenses with 4xNA values from 0.25 to 0.625, flexible, lossless coherence control through a Fourier-synthesis illuminator, a rotating azimuthal plane of incidence up to ±25°, illumination central ray angles from 6 to 10°, and a continuously tunable, EUV illumination wavelength. SHARP is now being used to study programmed and native mask defects, defect repairs, mask architecture, optical proximity correction, and the influence of mask substrate roughness on imaging. SHARP has the ability to emulate a variety of current and future lithography tool numerical apertures, and illumination properties. Here, we present various performance studies and examples where SHARP’s unique capabilities are used in EUV mask research.