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(U. S. 6,498,685, issued Dec. 24, 2002) ABSTRACT OF THE DISCLOSURE A maskless, extreme
ultraviolet
(EUV) lithography system uses microlens arrays to focus EUV radiation
(at
an operating wavelength of 11.3 nm) onto diffraction-limited (58-nm
FWHM)
focused spots on a wafer printing surface. The focus spots are
intensity-modulated
by means of microshutter modulators and are raster-scanned across a
wafer
surface to create a digitally synthesized exposure image. The
system
uses a two-stage microlens configuration to achieve both a high fill
factor
and acceptable transmission efficiency. EUV illumination is
supplied
by a 6 kHz xenon plasma source, and the illumination optics comprise an
aspheric
condenser mirror, a spherical collimating mirror, and two sets of flat,
terraced
fold mirrors that partition the illumination into separate illumination
fields
covering individual microlens arrays. (The system has no
projection
optics, because the image modulator elements are integrated with the
microlens
arrays.) The printing throughput is estimated to be 62 (300-mm)
wafers
per hour (assuming a resist exposure threshold of 20 mJ/cm2),
and print resolution is estimated at 70 nanometers for mixed positive-
and
negative-tone patterns (at k1 = 0.6).
MASKLESS,
MICROLENS EUV LITHOGRAPHY SYSTEM WITH GRAZING-INCIDENCE ILLUMINATION
OPTICS
ABSTRACT OF THE DISCLOSURE An EUV lithography system
achieves high-resolution printing without the use of photomasks,
projection optics, multilayer mirrors, or an extremely high-power EUV
source. The system comprises a xenon laser-produced-plasma (LPP)
illumination source (requiring 93W hemispherical EUV emission in the
wavelength range 10-12 nm), all-ruthenium optics (grazing-incidence
mirrors and microlenses) and spatial light modulators comprising
MEMS-actuated microshutters. Two 300-mm wafers are simultaneously
exposed with a single 10 kHz LPP source to achieve a throughput of 6
wafers per hour, per LPP source. The illumination is focused by
the microlens arrays onto diffraction-limited (42-nm FWHM) spots on the
wafer plane, and the spots are intensity-modulated by the microshutters
as they are raster-scanned across the wafer surface to create a
digitally synthesized exposure image. The optical path between
the source and the microlenses traverses seven grazing-incidence
mirrors (two collimator elements and five fold mirrors), which have
high reflection efficiency and essentially unlimited wavelength
bandpass.
FOCUS AND
ALIGNMENT SENSORS AND METHODS FOR USE WITH SCANNING MICROLENS-ARRAY
PRINTER
ABSTRACT
OF THE DISCLOSURE A scanning microlens-array
printer comprises an optical focus/alignment subsystem in which the
optical sensor elements are integrated within a microlens printhead
unit. The unit also incorporates an integrated spatial light
modulator; thus the printhead incorporates all the critical
optomechanical components necessary for high-resolution, maskless,
lithographic printing. Alignment is detected by an
interferometric process in which a reference diffraction grating on a
printing surface coherently combines two optical beams to generate an
interference signal that is sensitive to the grating’s lateral
position. Focus sensing is effected by using the reference
grating to divide a normally-incident convergent beam into two
obliquely-directed reflected beams, and detecting the focus-induced
translational shift in the reflected beams’ focal points.
Author: last update: July 26, 2004 |
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