Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2001-09-19
2004-01-06
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C378S084000
Reexamination Certificate
active
06674577
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an optical element that comprises a substrate, an interlayer and at least one functional layer and is suitable for recovery of the substrate. The invention further relates to a method for recovering a substrate of an optical element comprising a substrate, an interlayer and at least one functional layer.
BACKGROUND OF THE INVENTION
When optical elements are produced, not only flat substrates but also spherical or aspherical substrates may be used. In these cases, the costs of the substrate may exceed the coating costs by a multiple. It is therefore useful in development work if a substrate can be used repeatedly. In production, too, it may be advantageous if coatings that do not meet the specifications can be removed again and the substrate reused. The important thing is that the original form of the substrate is not changed and that the roughness of the substrate surface is not increased. Flawed optical elements can, for instance, have inadequate reflectivity or cause image distortion.
The optical elements can have one or more functional layers, which in turn comprise one or several layers. An example to be cited is a mirror for soft x-rays, which is provided with a coating of molybdenum and silicon films on a silicon substrate to reflect the soft x-rays, whereupon a single-layer protective coating is applied.
The requirements for the substrates, including recovered substrates, are discussed in D. P. Gains, et al, SPIE Vol. 1547 (1991) 228-238. This paper also introduces two methods for repairing optical elements. On the one hand, the flawed layers may be covered with additional correct layers. On the other hand, an interlayer between substrate and functional layer may be etched away and the coating thereby removed. Both of these methods have drawbacks. In the first method, flaws in the surface characteristics and the form of the optical element may be propagated through the individual layers. In addition, cracks may form through stresses and cause the coating to be partially detached. The second method has the drawback that removal takes a long time if the surfaces are relatively large.
A good interlayer must be homogenous and have a surface roughness that is as low as possible. In addition, it must be capable of being etched by substances that do not attack the substrate. For this reason, the aforementioned paper proposes aluminum as the interlayer on a silicon-based substrate. This aluminum interlayer is etched by a solution of hydrochloric acid and copper sulfate. However, optical elements with an aluminum interlayer have lower reflectivity than optical elements without this interlayer.
As mentioned above, the removal of functional layers of an optical element by etching away an interlayer is very time-consuming. For in order to be able to etch away the interlayer, the solution must first penetrate through the functional layer(s). Depending on the substance used, the at least one functional layer can also completely prevent the etching of the interlayer.
Another option to remove the coating from a substrate is dry etching. Such methods are described, for instance in WO 97/31132 and European Application EP 0 422 381 A2. In optical elements, however, it has thus far not been possible to optimize the dry etching process in such a way that the functional layers are removed while the substrate is left intact.
Chemical removal has also been attempted on objects other than optical elements.
German Patent DE 31 10 931 describes a method for removing a flawed copper sulfide coating applied to a cadmium sulfide layer, particularly in a process for producing solar cells. The substrate carrying the two layers is immersed into an aqueous cyanide-ion-containing solution until the flawed copper sulfide coating is completely dissolved, forming copper tetracyanide ions. The cadmium sulfide layer is not dissolved.
German Application DE 37 37 483 A1 describes a method for reusing glass substrates for optically readable compact storage masters. The disk-shaped glass substrates are coated with a layer of photoresist, which is partially exposed and developed. They are subsequently provided with an electrically conductive metal coating and a galvanically applied reinforcement. The latter two metal layers are then removed and serve to produce, either directly or after additional duplicating steps, the optically readable disk-shaped information carriers. This method provides that after removal of the photoresist layer, any residues of the electrically conductive metal coating and the galvanically applied reinforcement adhering to the glass plate be removed by rinsing with an acid and water mixture that attacks the metals.
A similar approach is used in German Patent DE 43 18 178 C2, which deals with a process for chemically removing a coating applied to the surface of a substrate made of glass, glass ceramic or ceramic. The decorated glass is brought into contact with hydrochloric acid and/or sodium hydroxide solution or with sulfuric acid and potassium hydroxide.
U.S. Pat. No. 5,265,143 describes an optical element comprising a substrate, an interlayer and a multilayer coating in which the interlayer dissolves 1000 times faster than the substrate material in an etchant solution at a temperature of 130° C. This interlayer consists particularly of germanium. The multilayer coating is typically made of molybdenum and silicon. The etchant solution used is an aqueous solution of 0.88 mol potassium hexacyanoferrate and 1 mol potassium hydroxide. At room temperature, only the molybdenum dissolved; if the solution is heated to above 60° C., the silicon is dissolved as well. However, re-coated recycled substrates partly showed reflectivities that were only 80% of the reflectivity of the original optical elements. This was attributed to increased surface roughness. To counteract this, a barrier layer of a chemically inert material, e.g. ruthenium, was applied between the interlayer and the substrate. For the production of iridium on glass ceramic mirrors it is suggested to use chromium as the interlayer. However, this should be done only in conjunction with a barrier layer since the surface roughness will otherwise excessively increase.
SUMMARY OF THE INVENTION
Against this background, it is the object of the invention to find an optical element, the substrate of which can be reused while retaining an optimal surface quality, as well as a method for recovering the substrate.
This object is attained by an optical element comprising a substrate, an interlayer and at least one functional layer, which is suitable for recovering the substrate and is characterized by an interlayer consisting of at least one layer of chromium and one layer of scandium.
DETAILED DESCRIPTION OF THE INVENTION
This object is further attained by a method for recovering a substrate of an optical element comprising a substrate, a chromium- and scandium-based interlayer and at least one functional layer, wherein the optical element is immersed in a 15%-30% aqueous hydrochloric acid solution.
If an optical element with an interlayer consisting of at least one layer of chromium and one layer of scandium is immersed into a 15%-30% hydrochloric acid bath, the interlayer dissolves with strong gas formation. The parts of the interlayer and particularly the at least one functional layer which are not dissolved by the hydrochloric acid are split off, as it were, by the gas development. This causes both the interlayer and the at least one functional layer to be virtually completely removed from the substrate. This is all the more surprising since chromium is known to passivate when it comes into contact with hydrochloric acid, so that it does not dissolve in hydrochloric acid.
The first layer on the substrate can be either chromium or scandium. The last layer before the functional coating can likewise be either scandium or chromium.
The advantage of the method according to the invention is that the substrate, which is made of silicon, glass or quartz, is not attacked and therefore retains both its
Carl-Zeiss-Stiftung
Dang Hung Xuan
Hudak, Shunk & Farine Co. LPA
Martinez Joseph P
LandOfFree
Optical element and method for recovering the substrate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical element and method for recovering the substrate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical element and method for recovering the substrate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3242786