Radiation imagery chemistry: process – composition – or product th – Holographic process – composition – or product
Reexamination Certificate
1999-03-02
2001-12-11
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Holographic process, composition, or product
C430S002000, C430S022000, C430S030000, C359S012000, C359S009000, C356S400000, C356S401000
Reexamination Certificate
active
06329104
ABSTRACT:
FIELD OF THE INVENTION
Lithography methods sometimes require that multiple layers be overlaid onto each other. In order for the information of a first layer to be correctly positioned with respect to information on a second or subsequent layer, registration or “alignment” techniques are required.
A unique and patented (U.S. Pat. No. 4,857,425), holographic micro lithography system presents many problems for old alignment techniques. The current invention is a new method of alignment that is compatible with holographic micro lithography systems.
BACKGROUND
Some printed matter such as newsprint or product labels can be printed in a single layer. An example, newsprint, is usually printed in one layer of a single ink (black). In more advanced systems, some information must be printed on top, overlaid, onto a previously printed layer. Color photographs are printed in four layers, each with a different color ink. Each layer must be accurately overlaid in position onto the previous layer for the image to appear correct. Each layer has reference marks outside the area of information, (i.e. photo). The reference marks can be crosshairs, bullseyes, etc. The marks on the printing mask are aligned to some reference on the printing machine. The next layer, with identically located marks can be aligned to the same reference on the machine and information of the two layers will be correctly registered, or aligned. For a system like color photograph printing, alignment of crosshairs by an unaided eye is sufficient for proper registration. The accuracy required depends on how the information printed will be used. For color photographs, it is intended to be viewed by an unaided human eye at a comfortable reading distance. It is a simple test to find that the registration accuracy is not very precise in such lithographic systems. Anyone who has used a magnifying glass to view such printed photos will recall seeing the colored dots that comprise the photo simply near each other but not aligned in an orderly array.
Lithographic systems for other applications sometimes demand far greater accuracy. An example is electronic circuit boards. The signal traces or electronic transmission paths can be very small. A device that uses multilayer paths will require that the paths of the second level be printed onto the paths of the first level such that the paths are positioned accurately with respect to each other. The width of the transmission path usually dictates the accuracy that the layers must be placed. For electronic applications it is common that the overlay accuracy be one fifth of the signal path width. Very advanced systems that are used to print microelectronics circuits require extremely small tolerances. A modern microelectronics circuit could have electronic paths as narrow as five microns, therefore requiring an overlay of one micron.
Currently holographic lithography systems use blind positioning methods for alignment. Wafer handling machinery can replace a wafer to a position with an accuracy that is a fraction of a millimeter without measurement and feedback means. Blind positioning can only be used for systems that can tolerate very coarse alignment.
SUMMARY OF THE INVENTION
The invention is an apparatus for and method of aligning a hologram with respect to a wafer to be printed. An object of the present invention is to provide an alignment method and alignment apparatus for a holographic lithography system that provides registration accuracies compatible with micron and sub-micron micro lithography. According to the first aspect, a method of position alignment of a hologram with respect to a substrate to be printed which comprises the steps: a) making alignment marks on the substrate to be printed, and making alignment marks on the hologram, either on the hologram substrate or in the hologram recording material layer; b) imaging the alignment marks through an optical path; c) comparing the alignment marks on the hologram with alignment marks on the substrate to be printed; d) adjusting the position of either the substrate to be printed or the hologram is provided.
According to a second aspect of the invention, a method of position alignment of a hologram with respect to a substrate to be printed which comprises the steps: a) making alignment marks on the substrate to be printed, and making alignment marks on the hologram, either on the hologram substrate or in the hologram recording material layer; b) prealigning the hologram with respect to the substrate to be printed; c) illuminating the alignment marks; d) detecting a reflected optical beam passed though an optical path, the path of which is through a prism; e) processing image information from the detected beam using a computer; f) generating an error signal dependent upon to the displacement of the marks with respect to each other; g) moving the wafer with respect to the hologram in accordance with the generated error signal; h) optionally repeating steps c) and d), and also e to g) if the alignment is not sufficient; and i) initiating the lithography process; is provided.
The alignment takes place between a hologram that contains the information of the image to be printed in the lithograph; and a substrate that is to be printed on.
According to a third aspect of the invention, a method of aligning a TIR hologram with respect to a substrate to be printed from the TIR hologram, the TIR hologram having a complex high frequency modulation of refractive index formed by holographically recording a pattern into a holographic recording layer, the method comprising the steps: (a) providing alignment marks on the substrate to be printed; (b) providing alignment marks in the holographic recording layer by including alignment marks in a mask and illuminating the alignment marks in the mask so that the light transmitted by the alignment marks in the mask is non-holographically recorded in the holographic recording layer; (c) illuminating the alignment marks in the holographic recording layer and on the substrate to be printed and imaging the light reflected from the alignment marks through an optical system onto a detector; (d) comparing the positions of the alignment marks in the holographic recording layer with the positions of the alignment marks on the substrate to be printed; and (e) adjusting the relative position of either the substrate to be printed or the TIR hologram in response to the comparison of positions.
According to a fourth aspect of the invention, a method of aligning a second-level pattern recorded in a TIR hologram with respect to a first-level pattern printed on a substrate, comprising: (a) providing a mask bearing the second-level pattern and alignment marks; (b) non-holographically recording the alignment marks in the mask into the holographic recording layer by illuminating the alignment marks in the mask; (c) recording a TIR hologram of the second-level pattern by illuminating the second-level pattern in the mask with an object beam and illuminating the holographic recording layer with a reference pattern; (d) providing a substrate bearing reference alignment marks and the first-level pattern; (e) illuminating the alignment marks in the holographic recording layer and the reference alignment marks on the substrate with an illumination beam and imaging the light reflected from the marks through an optical system onto a detector; (f) comparing the positions of the alignment marks in the holographic recording layer with the positions of the reference alignment marks on the substrate; and (g) adjusting the relative position of either the substrate or the TIR hologram in response to the comparison of positions.
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Clube Francis Stace Murray
Omar Basil Arthur
Angebranndt Martin
Harter Secrest & Emery LLP
Holtronic Technologies Ltd.
Salai Esq. Stephen B.
Shaw Esq. Brian B.
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