Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70375—Multiphoton lithography or multiphoton photopolymerization; Imaging systems comprising means for converting one type of radiation into another type of radiation
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/0005—Production of optical devices or components in so far as characterised by the lithographic processes or materials used therefor
  • G03F7/001—Phase modulating patterns, e.g. refractive index patterns
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/20—Exposure; Apparatus therefor
  • G03F7/2051—Exposure without an original mask, e.g. using a programmed deflection of a point source, by scanning, by drawing with a light beam, using an addressed light or corpuscular source
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70408—Interferometric lithography; Holographic lithography; Self-imaging lithography, e.g. utilizing the Talbot effect

Definitions

• the present application describes a technique of using quantum-entangled particles, e.g. photons, for lithography for etching features on a computer chip that are smaller than the wavelength of light used in the etching process, by some fraction related to the number of entangled particles.
• quantum-entangled particles e.g. photons
• the "superposition principle” is illustrated by a famous hypothetical experiement, called the cat paradox, a cat in a box with a vial of poison.
• the vial containing the poison could equally likely be opened or not opened. If the box/cat/poison is decoupled from its environment, then the cat achieves a state where it is simultaneously dead and not dead. However, any attempt to observe the cat, causes the system to default to dead or alive.
• Lithography is a process of etching features on a substrate. Photolithography uses light to etch these features. Each spot can be etched, or not etched, to form a desired feature. In general, it is desirable to make the features as small as possible.
• a lithographic pattern is etched on a photosensitive material using a combination of phase shifters, substrate rotators, and a Mach-Zehnder or other optical interferometer.
• the minimum sized feature that can be produced in this fashion is on the order of one-quarter of the optical wavelength [Brueck 98] .
• the only way to improve on this resolution classically is to decrease the physical wavelength of the light used in the etching process.
• Optical sources and imaging elements are not readily available at very short wavelengths, such as hard UN or soft x ray.
• the present system uses a plurality of entangled particles, e.g., photons, in a lithographic system to change the lithographic effect of the photons.
• the multiple entangled photons can etch features whose size is similar to that which could only be achieved by using light having a wavelength that is a small fraction of the actual light wavelength that is used.
• two entangled photons can be used a form an interference pattern that is double the frequency, or half the size, of the actual optical frequency that is used.
• This operation goes against the established teaching and understanding in the art that the wavelength of the illuminating light forms a limit on the size of features that can be etched. Usually, these features could not be made smaller than one-quarter or one-half of the wavelength of the light used to carry out the etching.
• the present system enables forming features that are smaller than one-quarter of the wavelength of the light that is used, by some multiple related to the number of entangled particles that are used.
• the present system for quantum lithography uses an interferometer that forms an interference pattern whose fringe spacing depends on both the number of entangled photons entering the device as well as their wavelength. Multiple entangled photons are used within the interferometer. These n entangled photons experience a phase shift that is greater, by a factor of n, than the normal phase shift that would be experienced by a single photon of the same wavelength in the same device. The changed phase shift forms a changed interference pattern in the output to achieve a changed frequency of interference fringes. By so doing, finer features can be etched.
• n-fold improvement in linear resolution is obtained by using n entangled particles, e.g. photons.
• a two dimensional lithographic operation effectively squares the improvement to density (n 2 ) .
• the entangled quantum lithography system makes it possible to etch features, for example, that are 1 to 10 nanometers apart, using radiation that has a wavelength , of 100 nanometers or more .
• the present system reduces the etched feature size without requiring more energetic particles.
• FIG. 1 shows a basic block diagram of the present system
• FIG. 2 shows a photon down converter
• FIG. 3 shows a diagram of the result with corrected photons
• FIG. 4 shows a detailed view of the interferometer.
• the present system replaces the classic "analog" optics of a lithographic system that has new "digital" optics that use a number of quantum-entangled particles, e.g. photons, electrons or the like. This will obtain the increased resolution, and reduction of feature size without shortening the physical wavelength.
• This system uses quantum entanglement effects to produce the same result as that previously obtained by using a shorter wavelength.
• Analog optics operates according to the so-called Rayleigh diffraction limit which imposes a restriction on minimum feature size that can be etched by a photon or other particle. This minimum feature size cannot be smaller than a wavelength.
• the minimum size lines are on the order of ⁇ /2 or ⁇ /4, where ⁇ is the optical wavelength used for the exposure. This limit on line sizes generally holds whenever classical optics and lenses are used for lithographic etching.
• Quantum entangled photons are used in this application for reducing the size of the features.
• the minimum size feature is on the order of one-quarter the optical wavelength.
• the interference pattern has the form I (l+cos2knx) , resulting in an effective resolution of the interference pattern that scales linearly with n.
• the size of the feature is a function of the number of entangled photons n.
• a single photon can be downconverted into two photons of lower wavelength.
• the polarization, energy and position of the resulting two photons are correlated because of conservation principles. In this particular case, the position correlation provides scaling properties. The ability to produce these entangled photons is well understood.
• the present system uses particle beams which are quantum in nature to carry out this operation. These beams are composed of streams of single photons, each of which is an individual quantum particle that is decoupled from the system around it. The correlated particles are made to behave in a way that is non-locally correlated. In accordance with quantum mechanical theory, the position, direction of motion, and frequency of each photon depends on the other photon (s) .
• the number state has no classical analog, as the coherent state does.
• Figure 1 shows a block diagram of the overall quantum lithographic etching system.
• a single photon 101 of specified frequency is output from laser 99. This photon is sent to a downconverter 100.
• a downconverter of this type receives a high-frequency photon into a nonlinear optical crystal such as of a material as KTP.
• a nonlinear interaction in the crystal generates a pair of daughter photons. If the original photon has frequency ⁇ and vector wave number k , then the daughter photons have the very same quantities, ⁇ , ⁇ 2 , k l f k 2 .
• the particles obey the laws of conservation of energy and momentum in the form,
• FIG. 2 The schematic for the down-conversion process is shown in Fig. 2.
• Incoming high frequency photons from the left are down-converted in a nonlinear crystal and produce two daughter photons that are correlated in both momentum and frequency.
• the vector wave number conservation condition, Eq. (lb) is degenerate in azimuthal angle about the initial photon propagation axis, generating a typically circular pattern of photons .
• FIG. 3 A typical spectral pattern is shown in Fig. 3. Choosing two points equidistant apart, as illustrated by the crosses in the figure 3, identifies by angular separation a particular down converted pair.
• the correlated photon particles are coupled through a coupler system 110 to beam splitter 122.
• This is the input beam splitter which can be for Mach Zehnder interferometer with beam splitters 122, mirrors 126, 128, and a phase shifter 130.
• the Interferometer produces parallel lines as its output. It has been demonstrated in Brueck, 98, " Interferometric lithograph - from Periodic Arrays to Arbitrary Patterns", Microelectron Eng 42: 145- 148 Mar 1998, that etching a series of parallel lines can be generalized in the lithographic domain into forming any desired feature.
• the correlations between the photons are quantum in nature, and the angular relation allows selection of a particular photon moving in a particular path, generating
• FIG. 4 A more detailed schematic of the Mach-Zehnder interferometer (MZI) is shown in Fig. 4.
• First and second correlated input photons 1 and 2 are input to both ports A and B.
• I Io (l+cos2kx) where, k-2 / ⁇ is the optical wave number, and x is the path difference between the first path 400 and the second path 402.
• the correlated photons enter the two ports entangled N at a time.
• the N-photon interference pattern in that case oscillates N times as fast as before. Since the fringe intensity is proportional to the exposure rate, the minimal etchable feature size ⁇ x determined by the Rayleigh Cri terion is given by the intensity minimum-to-maximum condition
• both photons either take the upper path together, or they both take the lower path together. Quantum mechanically, this is written as,
• a 2 represents a bi-photon in the upper or lower branch mode
• the first state vector corresponds to one of the correlated photons, and the second to the other.
• the bi -photon state is entangled in number and position. There are only two possibilities: they both take the high road 400 or they both take the low road 402. Since it is impossible to distinguish, even in principle, which of these possibilities occurred—quantum mechanics demands that the probability amplitudes associated with these two paths be added to create an interference pattern.
• each photon in the correlated pair contributes one factor of kx for a total of 2kx phase shift.
• the number entanglement of the down- converted photon pair causes the photons to "talk" to each other in a nonlocal way. There is nothing at all like this in classical theory, where there are no photons—only “analog" electromagnetic waves. In a sense, the correlated photon pair behaves like a single entity, which is why it is referred to as a di -photon.
• This digital quantum mechanical object accumulates phase in the interferometer in a very nonstandard fashion.
• this object accumulates phase twice as fast as a single photon or a pair of un- entangled photons would. Since the phase shift is proportional to the path difference divided by the wavelength, and the wavelength is fixed, this means that the same path
• FIG. 1 shows a two- input port interferometer 120 whose output gives the desired photon interference pattern. This is used to write an arbitrary pattern 140 on a photographically sensitive material resist 145.
• the present invention replaces the classical electromagnetic fields with the appropriate quantum photon creation and annihilation operators corresponding to the various ports .
• the classical optical beam is replaced by a quantum stream of n entangled photons.
• a simple optical beam splitter can take an unentangled number direct - product state and convert it into a nonseparable entangled number-state output, of the form of Eq. (4), needed for this device.
• the laser used herein is a titanium sapphire laser, producing an output wave on the order of 100 to 200 nanometers.
• the optically nonlinear crystal is a KDP crystal doped with LiI0 3 .
• interferometer Any kind of interferometer could be used. While the present specification describes a Mach Zehnder Interferometer, any other kind can be used with these teachings.

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• General Physics & Mathematics (AREA)
• Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

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• 2000
  • 2000-05-19 WO PCT/US2000/013931 patent/WO2000075730A1/en active Application Filing
  • 2000-05-19 AU AU73288/00A patent/AU7328800A/en not_active Abandoned
  • 2000-05-19 EP EP00961318A patent/EP1203265A4/de not_active Withdrawn

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