DE10132819B4 - Optical component manufacturing method e.g. for light guiding bar, involves abrading coating layer on surface of optical component having base material with optically active three-dimensional shape - Google Patents

Abstract

The method involves abrading the coating layer applied onto the surface of an optical component having a base material with an optically active three-dimensional shape to obtain high fit accuracy. - An INDEPENDENT CLAIM is included for optical component.

Description

The The invention relates to a method for producing optical components, in particular those of a crystalline base material with a increased stability as well the optical elements thus obtained and their use.

optical Components such as lenses and prisms are different for making Optics for a variety of uses known for a long time. They usually consist of one for electromagnetic Radiation continuous Base material which has an optically active spatial form or geometry, the direction of the piercing wave ray at their surfaces Distract at entry and exit. This is usually done that - if possible - the optical active mold mainly in plastics poured directly into a model or optical glass or crystals of a block of material by chiselling, sawing and Grinding is worked out.

The surface however, such optical elements are not completely smooth, but has more or less microscopically large bumps, which is also called microroughness. Now kick a ray of light on such unevenness, he enters another in or Exit angle with the optical element in interaction as a on a completely smooth surface incident light beam. Therefore, this beam or the electromagnetic Shaft according to the changed entry / exit angle in an undesirable Direction distracted. In this way, there is one for each optical component or lens typical scattered light, which is the Performance impaired.

It are already diverse Investigations have been made to the surfaces of such optical components to smooth. After grinding, polishing and etching the micro-roughness optical surfaces not let arbitrarily reduce, is already attempts have been made by vapor deposition of a dielectric material with the same or the approximate to even out the same refractive index. In this case, as described in DD 288 466 A5, the dielectric Layer, for example, by reactive electron beam evaporation applied. In this approach, however, only so a lot of material on the surface vaporized, that the depths or valleys of the microroughness more or less filled up which creates a smoother surface.

In addition, from the DE 198 30 449 A1 a method of manufacturing a mirror is known, in which a body of crystal, in particular a silicon crystal, is molded close to the final shape and then a thin layer of an amorphous material made of quartz glass is deposited. The deposition takes place by means of CVD. Subsequently, the final polish takes place with optionally attaching further reflective layers.

This However, method assumes that the optical surface before the vapor deposition of the dielectric layer already optimally polished is, i. optimal or minimal micro-roughness is generated. To produce such a highly polished minimum micro-roughness However, a variety of processing steps is necessary. Everyone Processing step practices but additional Stress on the molecular scaffold, in particular to the crystal structure of the base material. This Stress leads in addition to already existing crystal or material defects to additional Micro disorders in the Molecular structure of the base material or leads to discharges of voltages in the material, e.g. caused by already existing crystal defects become. This reduces the stability of the base material. has the material has and is particularly crystalline a single crystal, then it can happen that by slight temperature stress or mechanical stresses the crystal is destroyed or jerkily moving along a crystal surface around those in the crystal body reduce existing stresses or stress. By editing, in particular the grinding and polishing of such materials, get by the associated material removal crystal defects to the Surface, so these crystal defects release their tension while releasing energy can discharge what more to the previously described offset or even to cancel or less big material pieces leads. such Effects are especially in soft and high purity crystals particularly pronounced. Especially with high-purity crystals are foreign atoms, most of them inappropriate size small caused glassy areas. These areas act as a putty that a gliding of a lattice is macroscopically impeded. Due to the Transmission requirement and the demand for highest homogeneity and lowest stress birefringence have to Crystals for the optical lithography in ultra high purity UV.

The material defects described above cause a further reduction in the yield in the production of optical components. Considering the already reduced for large - scale technical process yield in the rearing of large, highly homogeneous, oriented single crystals, as required for optical components with large diameter, such as in lenses for microlithography, then an increase of the Committee during processing or Manufacture of such optical components to an additional enormously cost-increasing Verrin the yield of the entire process.

For the quality of such High-performance optics, as well as their components or their optical Elements is not only the minimization of stray light, but also their optically active spatial form or their geometry. It is aimed at the actual Shape of the optical component as close as possible to the theoretical shape adapt. The conventional procedure was that one of the optimal or theoretical lenses or prism shape corresponding Negative model is made, in which the finished lens or prism is inserted. Minimal deviations from the optimal Fit then show up as Newtonian rings. The fewer Newton rings are seen, the better fits a manufactured lens in the negative form, i. the more it has the desired optimal uniform lens curvature or Prism angle up. The quality The lens shape is therefore also referred to as Passegenauigkeit or Passe. More modern measuring methods work without contact with the help of interferometers. The shape of the surface will over one on the examinee reflected wave, with a reference wave for interference high accuracy with suitable computational evaluation methods determined.

It has now been found in crystals that try to prevent from stray light to a low microroughness to polish, no good pass can be reached. On the other hand, trying a good Passing through strong polishing results in increased microroughness the surface and thus to considerable stray light losses.

The The invention thus has for its object the yield of such production processes of optical components and at the same time the stability to increase such components, as well as the micro-roughness and thus the emergence of stray light and at the same time form a good pass.

According to the invention this Task by the method of claim 1, the optical element of Claim 10 and the use according to claim 11 solved. there is an optical component in a known per se in each case desired optically modeled active mold, then applied a topcoat and through Removal of the cover layer reaches the fitting accuracy. It will the optically active form usually by pruning a blank, i. by removing or targeted Removal of material received.

It Surprisingly, it has turned out that by the procedure according to the invention the number of processing steps of the component, in particular the grinding and polishing, from about 20 to just a few, about 5, steps can be reduced, which is the exercise of mechanical stress and / or heat stress considerably reduced on the lenses.

Besides, has It has been shown that the application of a cover layer, the stability of the optical component elevated, because it's like a belt spontaneous changes counteracts in the base material of the component.

Of more, it has surprisingly demonstrated that it is possible in this way both micro-roughness and thus to reduce the stray light losses as well as simultaneously to achieve a high accuracy of fit.

The The present invention therefore relates to a process for the preparation of optical components in which on the surface of a Cover layer is applied and then the fit accuracy the desired Room shape is set by removing the cover layer.

With the method according to the invention can in principle any surface of each optical component are processed. As examples can Here, optical lenses, in particular crystal lenses, are called.

In a preferred embodiment, these optical lenses consist of highly crystalline materials, in particular single crystals. Preferred crystal materials are, for example, NaF, KF, CaF ₂ , BaF ₂ , LiF and MgF ₂ .

In the method according to the invention, a dielectric material is preferably used for the cover layer. Suitable materials for this purpose are, for example, MgF ₂ , Al ₂ O ₃ , SiO ₂ or LaF ₃ .

The refractive indices of the materials of the cover layer and the optical base material may be the same or different. However, it is preferred that they are only slightly different. Deviations of up to 30% still provide advantages, in particular deviations of up to 10%, preferably up to 5%, have proved particularly suitable. With such small differences in the refractive power is still an excellent compensation of optical surface defects possible. If, for example, a lens material has a particularly low refractive index, it is preferable for the cover layer to be applied to use a material which is not highly refractive. As a rule, it can be stated that the refractive index of the starting material of the covering layer is higher, in particular slightly higher than that of the material of the optical component. Since vapor-deposited layers always have a slightly lower refractive index than dense starting materials (eg quartz glass to SiO ₂ layer), the refractive index difference can thus be reduced.

It It has been found that the cover layer is preferably in one Thickness of at least 0.2 μm, especially in the range of 0.3 to 5 microns should be applied. In the end, it depends but the possible Thickness of the top layer of the vapor deposition material and the vapor deposition process from. The more compact the material can be applied, the thicker The topcoat can be executed become. It may not be too thick depending on the material, otherwise unacceptable mechanical stresses occur.

The Cover layer can be applied by various methods. Such methods are known to the person skilled in the art. The greatest compactness reaches the material of the cover layer with ion beam deposition. The one for it The conditions used in each case depend on the material of the cover layer and the optical component.

In front the application of the cover layer, the optical component is usually careful cleaned to remove water, grease and the like from the surface. Subsequently then becomes the surface preferably subjected to a shaping treatment, for example by polishing, in particular by pitch polishing.

It has been found that the optical component conveniently tempered before application of the topcoat and after pre-processing becomes. This will cause voltages caused by crystal buildup errors be and by sawing and grinding the surface have arisen, dismantled. By removing material by one To produce lens shape becomes the original balanced stress state permanently disturbed in the crystal form. Through small influences, like Pressure or temperature, the crystal starts to slip around you to set a new balanced state of tension. It is preferred at temperatures in the range of 70 ° C to 150 ° C annealed. A temperature from 115-125 ° C is special Cheap for the Stress reduction in the crystal after rough preprocessing, one Temperature around 70 ° C after fine pre-processing.

The Figures are for explanation the method according to the invention. Show it:

1 the surface of an optical device comprising the auxiliary layer coated according to the invention;

2 a manufactured by the process according to the invention component which has been processed after application of the auxiliary layer; and

3 a preferred embodiment of the method according to the invention, in which after processing, an anti-reflection layer was further applied.

In 1 is schematically a surface of an optical component 1 shown on top of a cover layer 2 has been applied by the method according to the invention. The surface of the component 1 shows a certain micro-roughness, which is due to the small elevations. The applied topcoat 2 adapts to the surface of the component 1 and also shows surveys.

2 shows a treated by the process according to the invention cover layer 2 pointing to the surface of the optical component 1 has been applied. After a short polishing period, the elevations have disappeared and the machined surface of the cover layer 3 is free from stray light losses.

3 shows a preferred embodiment of the method according to the invention. On the machined surface of the topcoat 3 was an antireflection coating by conventional methods 4 applied. In this way, a smaller refractive index difference is brought about. This conveniently leads to a reduction in reflex.

With the processing according to the invention the topcoat, for example by polishing, becomes the performance of the optical component significantly improved. Due to the small refractive index differences between the cover layer and the optical component becomes a significant Improvement of the stray light losses ensured. If, for example a refractive index n = 1.40 for the optical component applies and the cover layer to be applied a Refractive index n = 1.45, the improvement is at least eight times. By examination of the component in the passage can be the effective long-pass error push back further, such as with ion beam ablation or robot polishing.

There transported optical components even at different temperatures and processed, it is preferred for the top layer materials too Use, whose coefficient of expansion is not too much of that of the base material differs. For this reason, the application should be at not to high temperatures. Preferably should be the coefficients of expansion do not differ by more than 20.

The Reduction of the processing steps in the method according to the invention also causes extra Loads of lens material that occur with each step, be reduced. For example, takes place during Ionenstrahlabtrag a strong thermal load of the crystal, so that the Crystals along the crystal surfaces partially complete move. By applying the cover layer, however, have the surface atoms only limited possibilities their place to the outside to switch.

The Invention also relates to the method according to the invention obtained optical components or optical elements. The inventively obtained white optical elements in a preferred embodiment between the surface the base material and the cover layer a known per se anti-reflection layer on. The production and the application of such anti-reflection coatings are known in the art. According to the invention it is also possible the Anti-reflection coating after complete fabrication, i. to working on the topcoat and after obtaining the desired Fitting accuracy and micro roughness an anti-reflection coating on the surface thus obtained apply. In a most preferred embodiment has the optical according to the invention Element between base material and top layer as well as above the topcoat each have an anti-reflective coating.

The processed according to the invention optical components have high performance, so that in the high performance optics, e.g. as lithography lenses, are usable.

The The invention thus also relates to the use of the method according to the invention available optical components for the production of lenses, prisms, light guide rods, optical Windows and optical components for DUV photolithography, for the production of steppers, laser devices, in particular excimer lasers, Wafers, computer chips, as well as integrated circuits and electronic Devices, containing such circuits and chips.

The following embodiment should the inventive method further explain.

EXAMPLE

A crystalline lens of CaF ₂ material obtained from a homogeneous single crystal by sawing and grinding is polished to micro-roughness. It is then carefully cleaned to remove dirt and water from the surface. A further purification step is carried out in a conditioning plant by glow discharge at room temperature over a period of about 30 minutes. As a result, the temperature of the component increases slightly. Subsequently, a cover layer of SiO ₂ in a thickness of 0.5 μ is evaporated. After steaming, the topcoat is processed by polishing anhydrous with diamond polish. Since the surface now no longer has a direction-dependent hardness in the crystal structure, the otherwise common with CaF ₂ trinicity remains much smaller. Subsequent processes, such as ion beam ablation or robotic polishing, allow further targeted rapid convergence of the Passeverbesserung, since here too on an almost glassy surface is removed.

Claims (12)

Method for producing optical components ( 1 ) of a crystalline base material which is permeable to electromagnetic radiation, with increased stability and an optically active spatial form defined by its surfaces of high accuracy of fit by shaping the base material into a blank having the desired spatial form, in which a cover layer ( 2 . 3 ) is applied from a dielectric material to the surface of the thus formed blank, wherein the material of the cover layer ( 2 . 3 ) has an up to 30% higher refractive index than the crystalline base material and wherein the fit accuracy by removing the cover layer ( 2 . 3 ) is achieved. A method according to claim 1, characterized in that as a base material CaF ₂ , BaF ₂ , LiF, NaF and / or KF is used. Method according to one of the preceding claims, characterized in that as cover layer ( 2 . 3 ) MgF ₂ , Al ₂ O ₃ , SiO ₂ pure or mixed and / or a diamond-shaped carbon compound is used. Method according to one of the preceding claims, characterized in that before applying the cover layer ( 2 . 3 ) anneals the preformed blank. Method according to one of the preceding claims, characterized characterized in that the preformed blank again for Restoration of the room shape reworked. Method according to one of the preceding claims, characterized in that the processing of the cover layer ( 2 . 3 ) one by mechanical order, Ionenstrahlabtrag and / or carried out by laser ablation. Method according to one of the preceding claims, characterized in that before and / or after application of the topcoat ( 2 . 3 ) an antireflective coating ( 4 ) is applied. Method according to one of the preceding claims, characterized in that the cover layer ( 2 . 3 ) has a thickness of at least 0.5 microns. Method according to one of the preceding claims 1 to 7, characterized in that the cover layer ( 2 . 3 ) has a thickness of at least 0.2 microns. Optical element obtainable by a method according to one of the preceding claims. Use of an optical element according to claim 10 for the production of lenses, prisms, Lichtleitstäben, optical Windows and optical components for DUV photolithography, steppers, lasers, wafers, Computer chips, and integrated circuits and electronic Devices, containing such circuits and chips. Use of an optical element according to claim 11, wherein the laser is an excimer laser.