Method of soldering optical materials to metallic frames and framed units

The invention relates to a method according to the preamble of Claim 1 and an assembly according to the preamble of Claim 8.

From DE 38 27 318 A soldering of quartz glass is, inter alia, with a nickel-iron alloy having an intermediate ring from Aluminum, coated with tin or zinc and gold or silver known. The parts are soldered in the oven at about 600 ° C. The is focus of this patent application to the tightness of the Connection directed.

JP 1/215 745 A (Derwent WPI abstract) describes the furnace brazing of quartz glass with metal with a solder made of indium, tin, Silicon carbide and carbon at temperatures above 100 ° C and under pressure. Coatings are not provided. Stresses are relieved by the solder layer.

According to JP 58/120 578 A (Derwent WPI Abstract) is quartz, Borosilicate glass or other materials, preferably by Baking a paste with a film of precious metal coated. A piece of metal is titanium or zirconium and then coated with silver or silver-copper solder. Both parts are assembled and in a vacuum or heated under protective gas. The braze used conditionally case high temperatures. The parts are preferably formed complex and porous or foamy. Optical elements are not addressed.

Wanted is a technique that allows the optical elements Versions can be soldered. This requires low complied with process temperatures below about 200 ° C to below 150 ° C. are to thin optical layers, but also the Lens material per se, such as optical glass, quartz glass, Calcium fluoride or other fluorides protect. at the same time are thermal and other stresses including Compressive stresses during the brazing process as before and then to keep minimal because they of the resistance Material and the optical function represents a significant hazard represent. At the same time has a sufficient strength of Connection with a tensile shear strength in excess of about 10 N / mm² be achieved.

This object is achieved by a method according to claim 1 and an assembly of claim 8. Advantageous Embodiments are subject of the dependent claims 2 to 7 and 9 to 15th

Soldering with a common temperature control of all partners maintains thermal stresses minimal, which by low melting solder is supported.

The first coatings of both parts ensure good Strength, allow the respective antioxidant layers easy handling while avoiding fluxes that before all optical surfaces of lenses and the like considerable risks would represent.

be explained in detail, the invention is exemplified with reference to the Drawings, their<dl tsize="8" compact="compact"><dt>figure 1</dt><dd>Lens and replaced with layers in the invention Oven shows all schematically.</dd></dl>

The part 1 of transparent material is shown For a lens, especially a high-precision UV lens Quartz glass or calcium fluoride, the part of a Projection exposure system for microlithography. Regarding disorders such as changes in shape or Stress-induced birefringence of individual lenses, such a system extremely sensitive. Particularly, the material is calcium fluoride its crystal structure also against temperature differences the workpiece fragile. High-quality anti-reflective coatings on the lens (not shown here) can not likewise thermally strained to avoid changes.

The version 2 is adapted to these needs. The lens 1 is in a thin film coating system with an adhesive layer 11, a solderable diffusion barrier layer 12 and a first oxidation resistant layer 13 is provided. These Coating takes place in a vacuum coating system with a mask which the optically used surfaces of the lens 1 reliably covers. Sputtering has proved particularly proven suitable thin-film technology, since at low Temperatures well adhering layers are produced.

Serving as the holding part 2 is in advance with Lot 22 provided. To low-melting solder to a metal part 2 of being able to connect steel, however, is a Wetting auxiliary layer first applied to the metal part of the second

The following coated thereon solder layer 22 is preferably coated with an oxidation protective layer 23rd Thus, the coated part 2 can without affecting the Lots are handled and are heated.

Since the solder layer 22 has a thickness of approximately 100 microns, are Thin-film techniques such as sputtering for their preparation impractical. All three layers 21 to 23 are therefore preferably galvanically applied. The same Coating technology for all three layers has the great Advantage of being in immediate succession without major occur handling effort and without storage time in the oxidation would, can be performed.

The coated lens 1 and the coated version 2 are successive positions - to be required adjustment and Holding devices used - and placed in an oven third Its interior 4 is preferably N₂ or other Inert gas flooded. Means (electric) heating elements 31 is the furnace 3 is heated until the melting temperature of the solder 22 is achieved. This then forms with the two Oxidation protective layers 23 and 13 and mainly with the Diffusion barrier layer 12 alloys and wetted surface the transparent part 1 (the lens) in the connecting area.

For an example, Table 1 gives the preferred Layer materials and thicknesses.<tables><table><tgroup cols="4"><tbody><row><entry namest="1" nameend="2" align="center" /><entry namest="3" align="center">material</entry><entry namest="4" align="center">Thickness [microns]</entry></row><row><entry align="left">1</entry><entry align="left">lens</entry><entry align="left">Ca F₂</entry></row><row><entry align="left">11</entry><entry align="left">adhesive layer</entry><entry align="left">Cr</entry><entry align="center">0.5</entry></row><row><entry align="left">12</entry><entry align="left">Diffusion barrier layer</entry><entry align="left">Ni</entry><entry align="center">5</entry></row><row><entry align="left">13</entry><entry align="left">1. oxidation protection layer</entry><entry align="left">Au</entry><entry align="center">0.1</entry></row><row><entry align="left">23</entry><entry align="left">2. oxidation protection layer</entry><entry align="left">Au</entry><entry align="center">0.1</entry></row><row><entry align="left">22</entry><entry align="left">solder</entry><entry align="left">SnPb</entry><entry align="center">100</entry></row><row><entry align="left">21</entry><entry align="left">Wetting auxiliary layer</entry><entry align="left">Ni</entry><entry align="center">5</entry></row><row><entry align="left">2</entry><entry align="left">version</entry><entry align="left">stainless steel</entry></row></tbody></tgroup></table></tables>

The melting temperature is in the 183 ° C. The heating takes place in 15 minutes, cooling to room temperature in 30 min. The tensile shear strength of the compound reached 15 MPa.

For quartz glass as the transparent part are the same Layers as appropriate to calcium fluoride, as well as for Pure aluminum and titanium as amended materials. brass or Copper as amended materials do not require Wetting auxiliary layer 21st

Quartz glass instead of calcium fluoride that can also handle larger thermal stresses, so that hereby the heating without an oven, for example, inductively, by a hot plate, a can usw.erfolgen infrared radiator.

As Lote other alloys with low come Melting point in question, eg 52In48Sn with 118 ° C and 80In15Pb5Ag with 149 ° C melt temperature.

As anti-oxidation coating 13, 23 all come to the Lot 22 or known to the diffusion barrier layer 12 Passivation in question.

The layer thicknesses may of course be varied. Especially the thickness of the solder layer 22, the tolerance of the mating surfaces adapted to the transparent member 1 and the metal 2 will.