euv maskless lithography j. vac. sci. technol. b 30, 051606 (2012); 9/25/20121k. johnson...

K. Johnson [email protected] 1

EUV Maskless Lithography

J. Vac. Sci. Technol. B 30, 051606 (2012); http://dx.doi.org/10.1116/1.4752112

9/25/2012

K. Johnson [email protected] 2

EUV Maskless Lithography

Concept:• -Scanned-spot array (e.g., 4000-by-4000 array over

10 mm square image field, 2.5 μm spacing)• Spots can be either individually modulated (with an

SLM) or source-modulated (for printing periodic patterns).

9/25/2012

Performance capability (based on JVST-B paper):• ~20 nm print resolution (13.5-nm wavelength, 0.3 NA, EUV source ~40 μm

diameter with 1 steradian collection per image field)• ~30 (300-mm) wafers per hour, with 500 kHz EUV source (“… Using a 10 μm nozzle tin

droplets as small as 17 μm in diameter at a 550 kHz repetition rate have been demonstrated. …” Brandt et al., Ref. 25)

Advantages:• Maskless• Eliminates coherent proximity effects• Comparatively simple optics (e.g., only 2 projection mirrors)• Comparatively moderate EUV power requirement

K. Johnson [email protected] 39/25/2012

Projection Optics

• Two-mirror, flat-image Schwarzschild system• 10-mm square image field• 10-X reduction• 0.3 NA (obscuration: 0.12-NA)

M1

M2

objectsurface

object spot array

detail view 1

Schematic:

Effect of central obscuration on focused image spot:

unobscured

obscured

(Side lobe has relatively minimal effect because image spots do not overlap.)

side lobe


objectsurface

L0

L1

EUV illumination

microchannelarray

virtualobject spot

L2

aperture

intermediatefocus

Schematic(detail view 1)

detail view 2

Spot-Generation Optics

• Phase-Fresnel microlens arrays (L1 & L2) in achromatic configuration (L0 beam shaper optional)

• Transmittance (including lenses, substrates, fill factor losses) about 20%; no spectral narrowing.

• Can accommodate SLM shutters at intermediate foci.

mm

Microlens Fresnel zone structure at edge of object field


Microlens Structure

• Stepped Fresnel profile: 8 bilayers of Mo (20 nm) / Ru (2 nm etch stop) on thin Si substrate

• Minimum Fresnel zone width: 0.9 μm• Deposition tolerances: about 26X less stringent than EUV reflection optics• Axial lens positioning tolerance (focus): about 100X less stringent than

EUV reflection optics• Patterning/alignment tolerances: about 10 nm (comparable to EUV

photomasks)

Microlens profile (detail view 2)


Aberration Compensation

• Microlens design completely eliminates geometric aberration (including image distortion and image field curvature).

• Microlens doublet configuration substantially eliminates chromatic aberration.

Image of object point (at field edge), no aberration correction:

With aberration correction (at 3 wavelengths: 13.4, 13.5, 13.6 nm):

nm nm


EUV Source and Collection Optics

• Power requirement: modest due to comparatively low throughput (e.g., 30 wph) and few near-normal-incidence mirrors.

• Source size requirement: The scan spots are demagnified images of the source; should be within the diffraction limit. (1 steradian collected from a 40-μm source could be partitioned, e.g., into a 4000-by-4000 array of spots with 1-steradian convergence cones and 10-nm geometric spot size).

• Rep rate requirement: Printing throughput is proportional to the rep rate and number of spots (e.g., with a 500 kHz rep rate, 16 million spots, and 10-nm grid step, the scan rate would be 8 cm2/sec).

• Source power sharing: The source size (area) can be N times larger, and the rep rate N times smaller, if N print units are supplied from a single source. (Throughput per source will be the same as N=1.)

• The microlens design can correct moderate imperfections in the collection optics :

– Non-ideal beam shape.– Nonuniform source magnification across microlens array.– Nonuniform radiant intensity across microlens array.


EUV Maskless Lithography Development Tasks• Develop system design outline based on realistic, practical source

characteristics:– Source size? (limits print resolution)– Rep rate? (limits printing throughput)– Power? (comparatively moderate power requirement)

• Develop detailed, full-system optical design; simulate lithography performance.

• Evaluate microlens/microchannel fabrication methods.• Evaluate SLM feasibility.• Economic modeling.• Proof-of-concept prototype (e.g., using the CXRO’s MET tool)• Productization options:

– Source-modulated (alternative to interference lithography, GRATE for HVM)– Full image modulation with SLM (alternative to maskless e-beam, e.g., REBL,

MAPPER)– BEUV (Maskless capability and simplified projection optics could facilitate accelerated

development of 6.x-nm lithography.)

euv maskless lithography j. vac. sci. technol. b 30, 051606 (2012); 9/25/20121k. johnson...

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