Etching a substrate: processes – Forming or treating optical article
Reexamination Certificate
1999-09-27
2003-06-10
Alanko, Anita (Department: 1765)
Etching a substrate: processes
Forming or treating optical article
C216S026000, C216S052000, C216S088000, C216S097000
Reexamination Certificate
active
06576150
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates, in general, to a process for producing a glass article that can be used to transmit or reflect light, and, in particular, to a process for producing a glass article having at least one planar side wall that is oblique with respect to a main surface of the glass article.
More specifically, the invention relates to a process for producing a glass article having at least one trench which is substantially trapezoidal in cross section, or having at least one slot, or having at least one substantially frustopyramidal pit/through-hole. It further relates to a process for producing an optoelectronic module having a glass article produced in this way.
Until now, trenches that are trapezoidal in cross section have been produced in glass articles by sawing. The degree of roughness and level of surface damage is greatly dependent upon the saw blade used. Frustopyramidal pits or through-holes cannot be produced by a sawing process and significant outlay is required to produce them by boring and grinding.
German published, non-prosecuted Patent Application DE 43 21 582 A1 discloses a process for making a reflecting oblique face on the surface of an article. The article contains an interface that defines a plane and extends as far as the surface of the article. Two materials with different etching rates that can be etched isotropically using a particular etchant meet at the interface. The surface of the article is etched for a particular length of time with the particular etchant while allowing this etchant to act simultaneously on the materials with the different etching rates. Articles fabricated in this way are, in particular, employed in two-way transmission and reception modules, hybrids, multiplex components and other optical circuits in optical telecommunications.
G.A.M.C. SPIERINGS: “Review of wet chemical etching of silicate glasses in hydrofluoric acid based solutions”, Journal of Materials Science, vol. 12, No. 23, December 1993, pages 6261-6273 discloses the use of aqueous HF solutions for isotropically etching silicate glasses. When a mask film is sufficiently adhered to the glass, a semicircular boundary of the etched edge results. The etched edge can be formed with a tapering wall structure by appropriately controlling the photoresist mask material and the fixed etching rate. A similar effect can be obtained when an additional film is used between the glass to be etched and the mask material. The additional film must have a higher etching rate than that of the glass. The ratio between the etching rates of the additional film and the glass determines the inclination of the etched edge.
The INSPEC database, Institute of Electrical Engineers, Stevenage, GB, INSPEC No. 3737969 discloses a wet chemical process for the formation of inclined window edges during the selective etching of SiO/sub 2 films. The dependency of the etching profile on the etchant temperature and on the photoresist thickness has been investigated. The angle of inclination decreases significantly with temperature, but does not depend on the photoresist thickness.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a technologically simpler process for producing a glass article having at least one planar side wall that is oblique with respect to a main surface of the glass article. The object of the process is to produce a glass article with trenches which are substantially trapezoidal in cross section, or slots, or substantially frustopyramidal pits or through-holes in a straightforward way.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for producing a glass article having at least one recess defining at least one planar side wall that is oblique with respect to a main surface of the glass article. The process includes providing a glass article having a main surface and made of a borosilicate glass; providing an etching mask on the main surface of the glass article, the etching mask having at least one etching window; anisotropically wet chemically etching the glass article through the etching window with an etching mixture to obtain a recess with at least one planar side wall forming an angle with the main surface of the article; and determining a magnitude of the angle by varying a parameter selected from the group consisting of an etching temperature, an etching time, and a composition of the etching mixture.
The invention provides a process in which a glass article, which consists essentially of borosilicate glass, is produced. An etching mask, which is provided with at least one etching window, is then applied to a main surface of the glass article. By anisotropic etching through the etching window, a recess is then formed in the glass article with at least one locally planar side wall which is oblique with respect to the main surface, with the etching mask being undercut-etched. “Locally planar” means that at least one subregion of the side wall is a planar surface.
An etching mixture that essentially contains hydrofluoric acid, nitric acid and/or ammonium fluoride is preferably used for etching. Etching depths in excess of 100 &mgr;m can thereby advantageously be produced. By varying the etching parameters and the composition of the etching mixture, the angle formed between the main surface and the planar region of the side boundary, for example a side wall of a trapezoidal trench or slot or a frustopyramidal pit, can be adjusted.
The following etching conditions are, for example, preferably selected:
Etching mixture: 10-50% strength hydrofluoric acid
Etching temperature: 10-60° C.
Etching time: 1-180 minutes (for large etching depths in excess of 100 &mgr;m, even longer)
The etching mask is preferably produced by applying a metal layer to the main surface of the glass article and subsequently structuring the metal layer using photographic techniques. These are process steps known from semiconductor technology for the production of etching masks and will not therefore be explained in further detail at this point.
In accordance with an added feature of the invention, the process includes providing the glass article with an additional main surface that is opposite from the main surface of the glass article; providing a support that is substantially unaffected by the etching mixture; fastening the additional main surface of the glass article to the support; performing the step of providing the etching mask so that the etching mask has a plurality of etching windows; and performing the step of anisotropically wet chemically etching so that the glass article is etched through the plurality of etching windows.
In accordance with an additional feature of the invention, the process includes performing the step of anisotropically wet chemically etching so that the glass article is etched through the plurality of etching windows all the way to the support.
In accordance with a further feature of the invention, the process includes providing the glass article with an additional main surface that is opposite from the main surface; performing the step of providing the etching mask so that the etching mask has a plurality of etching windows; performing the step of anisotropically wet chemically etching so that the glass article is etched through the plurality of etching windows to form a plurality of recesses selected from the group consisting of substantially frustopyramidally shaped pits and trenches with a substantially trapezoidal crosssection; applying the main surface of the glass article to a support; and grinding the additional main surface of the glass article to form a glass product selected from the group consisting of a plurality of glass prisms that are separated from one another and a glass article with a plurality of through-holes having a substantially frustopyramidal shape.
In accordance with a further added feature of the invention, the process includes performing the step of grinding the additional main surface of the glass article to o
Alanko Anita
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Stemer Werner H.
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