Patent Application
20080038456
1. Field of the Invention
The present invention is related to a method and system for forming a clear aperture on an optical element held in an optical system.
2. Background Art
Many optical systems include optical elements (e.g., lenses) that are held in specific locations and orientations in a light path. Care must be taken to minimize any force on the lens causing twisting or bending of the lens, and distortion of the optical characteristics of the lens. This is because distortion can cause a light beam passing through the lens to be misdirected. Typically, the lens is supported through the use of gluing or adhering a support device to its circumferential edge, which can substantially reduce or eliminate any distortion. However, stray or scattered light inside the lens can deteriorate the glue, which in some cases causes the lens to separate from the support device, hereby allowing the lens to shift position and misdirect the light.
For example, in lithography systems lenses can be held in this arrangement. Lithography is a process used to create features on the surface of a substrate. Such substrates can include those used in the manufacture of flat panel displays (e.g., liquid crystal displays), circuit boards, various integrated circuits, and the like. Frequently used substrates for such applications are a semiconductor wafer or a glass substrate. While this description is written in terms of a semiconductor wafer for illustrative purposes, one skilled in the art would recognize that this description also applies to other types of substrates known to those skilled in the art.
During lithography, a wafer, which is disposed on a wafer stage, is exposed to an image (e.g., a pattern) formed by an illumination system outputting an illumination beam that interacts with a pattern generating device (e.g., a reticle, mask, a spatial light modulator (e.g., a digital mirror device, a grating light valve, a liquid crystal display device, or the like), a contrasting device, etc.), or array thereof. The image is projected onto the surface of the wafer by exposure optics located within a lithography apparatus. Either or both of the illumination system and the exposure optics may include one or more lenses supported as described above.
In optical systems, such as lithography systems, that use smaller and smaller wavelengths of light (e.g., extreme ultra violet, etc.), even a small distortion or misalignment of the lens can cause errors in the features, which can make a patterned feature inoperable. Thus, a lens needs to be held in a stationary position throughout the process.
In order to protect the glue or adhesive holding the support device to the lens, typically a protection layer is applied to a circumferential portion of the lens. The protection layer is used to absorb light and/or protect the glue or adhering material from damage due to interaction with scattered or stray light inside the lens. A central portion or “clear aperture” of the lens must be protected or “masked”.
Therefore, what is needed is a mask for the clear aperture that can: define a sharp border for the clear aperture with specified tolerance, be spatially positioned to a specified tolerance, be free of pinholes or other defects which would allow the glue protection to obscure the clear aperture, be easily removable so as to leave no damage or distortion or contamination on the surface of the clear aperture, and be applied in such a way as to minimize handling of the optic and thereby minimize opportunity to damage the lens. Further, the mask can be applicable to a range of optics and clear apertures of widely varying shapes and sizes with minimal re-tooling. Further, the mask can be amenable to aqueous/mechanical cleaning and can have outgas levels low enough so as not to interfere with subsequent vapor deposition steps.
Aspects of the present invention provide a system and method that can be used to cover a portion (e.g., a clear aperture) of an optical element (e.g., a lens) during coating of another portion (e.g., a circumferential portion) of the optical element. This can be done to protect the clear aperture during coating of an adhesive protection layer proximate a circumferential edge of the lens without damaging or altering the clear aperture through the removal of the covering.
In an embodiment of the present invention a method is provided that includes at least the following steps. An optical element is held so that a first portion of the optical element is covered and a second portion of the optical element is exposed. A first coating is provided on the second portion of the optical element. The optical element is released from being held. A second coating is provided on the optical element. The first and second coatings are removed from the second portion of the optical element, such that the clear aperture is not damaged or optically altered.
Further embodiments, features, and advantages of the present inventions, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers may indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number may identify the drawing in which the reference number first appears.
Overview
While specific configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. A person skilled in the pertinent art will recognize that other configurations and arrangements can be used without departing from the spirit and scope of the present invention. It will be apparent to a person skilled in the pertinent art that this invention can also be employed in a variety of other applications.
An embodiment of the present invention provides a method including at least the following steps. A first mask is clamped to an optic, such that a clear aperture of the optic is exposed, but a surface of the optic to which a glue protection will be applied is covered. A second mask, (e.g., lacquer) can be applied to the clear aperture (the aperture now defined by the clamped on first mask). The lacquer is allowed to cure, the first mask is removed, the optic is cleaned by aqueous/mechanical processes, and the glue protection layer is applied to an entire face of the optic (e.g., using vapor deposition)n. The glue protection layer can be insoluble in both aqueous and organic solvents. Lastly, the lacquer is removed with an organic solvent, such as, but not limited to, acetone.
Lens Holding Systems
Support device 102 can be a resilient device (e.g., a spring, a stiff spring, or the like). A portion 112 of support device 102 is coupled (using coupling coating 302, as described below with respect to
Coating 300 can be used to substantially reduce or eliminate stray or scattered light inside optical element 100 from interacting with coupling coating 302 and deteriorating it. Thus, coating 300 can be seen as a protective layer to protect coupling coating 302. Coating 300 can be an absorbing coating chosen based on a wavelength of light being used in optical system 104 or 204. Various coatings for this purpose will be apparent to one of ordinary skill in the art upon reading this description. All such coatings now known or discovered in the future are contemplated within the scope of the present invention. Coating 300 can be applied using various techniques, for example, vapor deposition or chemical vapor deposition.
Optical Element with Central Portion Covered
Coating 400 can be, but is not limited to, an organic compound, an inorganic compound, an organic composition, and inorganic composition, a polymeric composition, a lacquer, a mixture, an aqueous coating, an aqueous polymeric coating, an acrylic polymer, a polymer film, a polymethyl methacrylate, a paint, an enamel, polymer, or acrylic polymer diluted in a solvent, etc., and mixtures or combinations thereof.
In an embodiment when a solvent is used, the solvent can be an aqueous or non-aqueous solvent, such as acetone, ethyl acetate, ether, chloroform, benzene, toluene, ethanol, methanol, cyclohexane, hydrocarbon-based solvent, ketone-based solvent, ether-based solvent, acetate-based solvent, amide-based solvent, .gamma.-butyrolactone, alcohol-based solvent, silicon-based solvent, anisole, mesitylene, xylene, methyl isobutyl ketone, 1-methyl-2-pyrrolidinone, tetrahydrofuran, isopropyl ether, ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, dimethylacetamide, dimethylformamide, .gamma.-butyolactone, isopropyl alcohol, butyl alcohol, octyl alcohol, silicon solvents, etc., and mixtures or combinations thereof.
These lists of coatings and solvents are not meant to be exhaustive. It is to be appreciated other coatings and/or solvents apparent to one of ordinary skill in the art upon reading this description are also contemplated within the scope of the present invention.
In one embodiment, coating 400 is relatively easy to cast, dries hard and clean (e.g., does not evaporate), is not water soluble, and is relatively easy to completely remove using a non-damaging removing material (e.g., acetone).
Coating 400 can be formed on optical element 100 using various techniques, such as, but not limited to, applying, depositing, spraying, air brushing, and painting. It is to be appreciated that other techniques can also be used, as would be apparent to one of ordinary skill in the art upon reading this description.
Method for Covering Central Portion of Optical Element
In step 502, optical element 100 is held so that first portion 108 of optical element 100 is covered and second portion 110 of optical element 100 is exposed. Optical element 100 can be held with a masking device, or the like, which only covers first portion 108. This preliminary mask can be made of material that is machinable to high precision, is inert to water and typical organic solvents (e.g., acetone, isopropanol, or the like), and is softer than the material from which the optic is made, such that it will not scratch the optic. For example, Delrin can be a preferred material used for this mask. It is to be appreciated that other materials that meet these general guidelines can also be used, and are contemplated within the scope of the present invention.
In step 504, first coating 400 is provided on second portion 110 of optical element 110. Again, as described above, this lacquer can be design to adhere well to the optic, be robust enough to withstand aqueous/mechanical cleaning, be free of pinholes and other defects, be low in outgas once cured so as not to interfere with subsequent vapor deposition of the glue protection layer, and be readily removed by an organic solvent leaving no residue. For example, in a preferred embodiment Maybelline® Cherry Pop! Nail Enamel diluted in ethyl acetate in ratios from 1:2 to 2:1 is applied with an airbrush. It is to be appreciated that numerous other materials and/or compositions can also be used for this lacquer, as are described above, which are apparent to one of ordinary skill in the art upon reading this description as are the methods of application.
In step 506, optical element 100 is released from being held. In step 508, second coating 300 is provided on optical element 100. In step 510, first and second coatings 400 and 300 are removed from second portion 110 of optical element 100. Removal can be accomplished using a removing material, such as acetone or the like, which can substantially completely remove coating 400 without damaging optical element 100.
It is to be appreciated that other, possibly optional, steps can also occur during method 500. For example, processing of optical element 100 can occur, which can include cleaning (e.g., with water having a cleaning material therein), rinsing (e.g., with deionized water), and/or drying of optical element 100. Processing of optical element 100 can occur before step 502, before step 508, and/or after step 510.
In one embodiment, coating 400 can include a coloring material, a dye, or the like. This can help ensure that a visual inspection can be performed to determine whether a thickness of coating 400 is thick enough so that no pin holes are formed in coating 400. Substantial reduction or elimination of pin holes can be desired so that coating 400 is a continuous layer. For example, when coating 400 is a continuous layer, substantially none of coating 302 interacts with lens 100 during step 508.
Once method 500 is completed, support device 102 or 202 can be coupled to first portion 108 of optical element 100 via coupling coating 302.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
This application is a continuation of U.S. patent application Ser. No. 10/756,352, entitled “Method Of Covering Clear Aperture Of Optic During Deposition Of Glue Protection Layer,” and filed on Jan. 14, 2004, the entirety of which is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10756352 | Jan 2004 | US |
| Child | 11826197 | Jul 2007 | US |
