Double patterning has been proposed as a method to extend DUV lithography to 32nm and below. Here, a
new form of double, or higher, multiple exposure technique is proposed. This new form of lithography
uses a combination of Quantum State Control (QuSC) chemistry, Amplitude Modulation Optical
Lithography (AMOL), and multiple micro-stepped exposures, without development between exposures.
Further it is proposed to use this form of lithography (called QuSC-litho), to pattern a perfect grating grid,
and to trim this grid with an earlier generation lithography tool. QuSC lithography uses short optical pulses
to modulate a photochemical pathway while an intermediate is still in a defined vibrational excited state.
This is a variation of Stimulated Emission Depletion Microscopy (STED) developed for fluorescence
microscopy. With this approach immersion tools that produce 90 nm pitch and 45 nm features should be
able to pattern levels with 22 nm features with a 1:1 line-space ratio. This approach is much less sensitive
to misalignment than present double patterning approaches. Key to successful deployment of QuSC
lithography is defining a resist photochemistry consistent with the QuSC process. There are several
approaches to Photo Acid Generator (PAG) - matrix interaction that may be consistent with this approach.
A diffraction-grating based demultiplexer is made to have low polarization dependence and high diffraction efficiency properties. The device is made is made of a Si grism working in reflection and having optimised grove profile easily manufactured by standard crystallographic etch of Si surface.
A collimated radiation field is desired in order to use x-ray lithography to replicate ULSI chips with sub-0.25 micrometers features. Additional field specifications include uniformity of x-ray intensity (+/- 1%), penumbral blur (5 mrad), field size greater than 25 mm X 25 mm, and high x-ray transmission efficiency. Introduction of a multi-polycapillary x-ray wave guide collimator between a laser plasma x-ray source and silicon wafer can produce such a field. We describe progress toward the design and fabrication of such a collimator. We have measured the soft x-ray transmission efficiency and divergence of straight and bent glass polycapillaries composed of capillaries in the 17 - 25 micrometers diameter range, using a laser produced plasma x-ray spectrum peaked at 14 angstroms. Transmission results conform well to theoretical predictions. Experimental results have been used to develop a preliminary design for a polycapillary collimeter structure that can be used with Hampshire Instruments' x-ray lithography stepper systems. The projected x-ray field characteristics, and throughput are discussed.
The comment that typical clean room 'soft' defects (i.e., airborne, carbon-based
particles) are transparent to x-rays is stated as a fundamental attribute of x-ray
lithography. However, data showing lithographic conditions which result in a reduction
in defect density have not yet been widely published. This paper reports an
analysis of defect printability for soft x-ray lithography at wavelengths of 0.6 to
2.2nm and denotes exposure and resist development conditions under which representative
soft and 'hard' reticle defects did not print. Resolution reticles with features
down to 0.5pm were produced using Hampshire's baseline process which consists
of electroplated gold absorber on a silicon support membrane. Latex spheres ranging
in diameter from 0.36 to l.Opm were applied by VLSI Standards, Inc. to simulate soft
defects. The large exposure latitude for x-ray lithography allows using an overexposure
to reduce the impact of lower contrast defects without appreciable CD change.
The printability of soft defects and defect-induced wall angle perturbations in
resist patterns were also investigated through simulations using a modified version
of SAMPLE and the results agreed with the observations. Identification of what constitutes
a printable reticle defect for x-ray lithography is not as straightforward
as that for optical lithography.