Massachusetts Institute of Technology

Jersey Nuclear-avco Isotopes, Inc.

Patrick N Everett

Henry Ignatius Smith

Euclid E Moon

William F Delaney

Mark L Schattenburg

William C Goltsos

Marsden P Griswold

Robert E Knowlden

A method and system of interference lithography (also known as interferometric lithography or holographic lithography) which utilizes phase-locked, scanning beams (so-called scanning beam interference lithography, or SBIL). The invention utilizes a high-precision stage that moves a substrate under overlapped and interfering pairs of coherent beams. The overlapped beams interfere, generating fringes, which form a pattern 'brush' for subsequent writing of periodic and quasi-periodic patterns on the substrate. The phase of the fringes in the overlapped region is phase-locked to the motion of the precision stage. The invention includes methods for forming, overlapping, and phase-locking interfering pairs of beams on a variety of substrates; methods for measuring and controlling the period, phase, and angular orientation of fringes generated by the overlapping beams; and methods for measuring and controlling the effects of stage mechanical and thermal drift and other disturbances during the writing process.

Method and system for interference lithography utilizing phase-locked scanning beams

An apparatus and method of measuring the gap between one substantially planar object, such as a mask, and a second planar object, such as a substrate. The invention achieves a high degree of sensitivity, accuracy, capture range, and reliability, through a novel design of a mark located only on the mask-plate. The light is inclined to the surfaces so associated optical components do not interrupt the exposing beam used in lithography. The same optics are used as for aligning overlay. Each gapping mark on the mask-plate includes one or more two-dimensional gratings, each with period constant in the incident plane, but varying in the transverse plane. When illuminated, two images are formed of each of the two-dimensional gratings, with fringes resulting from interference between paths having traveled different distances through the gap and the mask-plate as a result of successive diffractions and reflections. Phase and geometric measurements from these images yield accurate measurement of the gap between the plates. Direct calibration, referenced to the light-wavelength, is obtained from a diffractive Michelson technique that uses a linear grating also included within the gapping mark.

Optical gap measuring apparatus and method having two-dimensional grating mark with chirp in one direction

Alignment marks on first and second plates include a plurality of periodic gratings. A grating on a first plate has a period or pitch p.sub.1 paired up with a grating on the second plate that has a slightly different period p.sub.2. A grating on the first plate having a period p.sub.3 is paired up with a grating on the second plate having a slightly different period p.sub.4. Illuminating the gratings produces a first interference pattern characterized by a first interference phase where beams diffracted from the first and second gratings overlap and a second interference pattern characterized by a second interference phase where beams diffracted from the third and fourth gratings overlap. The plates are moved until the difference between the first and second interference phases correspond to a predetermined interference phase difference. Further invention uses an interrupted-grating pattern on the second plate with certain advantages. Further advantages are obtained using a checkerboard pattern on the second plate. In addition two inventions are made for measuring gap. One method uses the same marks on the second plate as used in aligning, and the second uses no marks on the second plate, which is an advantage in some cases.

Optical interference alignment and gapping apparatus

Optical alignment apparatus having multiple parallel alignment marks

A technique for aligning features on opposite surfaces of a substrate by generating a fiducial image at an image plane and identifying the location of the image at a viewing device remote therefrom, e.g., a video display screen. The substrate is placed so that one surface thereof, on which a feature is to be placed in alignment with a corresponding feature already present on the other oppositely disposed surface, is at the image plane. The one surface has photoresist material thereon. With the fiducial image turned off, an image of the feature on the other oppositely disposed surface is presented at the viewing device and the substrate is moved in the image plane until the image of the feature at the viewing device is at the previously identified location of the fiducial image. The fiducial image is then regenerated to mark its location in the photoresist material at the one surface of the substrate, such location then being in alignment with the corresponding feature on the other oppositely disposed surface thereof.

Technique for aligning features on opposite surfaces of a substrate

A technique for measuring the distance between the edges of a feature positioned on a substrate wherein the feature is illuminated with light on either side of the edges and the light intensities at either side of each of the edges are detected and are balanced at the detected light intensities regions sufficiently removed from the edges to prevent an adverse diffractive effect thereon so as to produce regions of minimum light intensity at the edges, the positions of which can be determined and the distance between said regions of minimum intensity can be measured.

Measurements using balanced illumination optical microscopy

A device for aligning a flexible mask with a substrate when the substrate is mounted on a vacuum chuck member which includes a surround member surrounding the exposed surface of the substrate. The mask is held on a mask holder and the chuck member and mask holder are movable toward and away from each other. The surround member rests on a flexible element which effectively causes the surround member to float so that when the mask is brought into contact with the substrate, the mask always lies in the same plane as the exposed surface of the substrate and the exposed surface of the surround member and no distortion of the mask occurs.

Device and method for the alignment of masks

A single element interposed in a laser resonator cavity provides for AM mode-locking, Q-switching and dumping in a sequential operation in which a Pockels cell or like polarization rotation device is first energized to prevent build-up of radiation in a laser cavity, is then switched to provide for mode-locking by energization with a periodically varying signal, and is finally energized to dump a single mode-locked pulse. The sequential operation permits the use of a single electro-optic element and a single pair of electrodes. Q-switching, mode-locking and dumping are accomplished utilizing the same physical effect in the crystal, e.g., polarization rotation.

Laser mode locking, Q-switching and dumping system

A single electro-optic device is provided for simultaneously mode-locking and chirping the output of a laser by simultaneously applying to the electrodes of the electro-optic device a periodic signal superimposed on a voltage ramp. The electro-optic device in general utilizes a crystal of the type which changes refractive index in accordance with an applied voltage. As a result, FM mode-locking is achieved through the use of the periodic signal, whereas mode lines are displaced or shifted in frequency during the generation of the laser output by virtue of the changing bias supplied by the voltage ramp.

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Concord, MA, United States of America

Patrick N Everett