DE102021201939A1 - Method for brazing a support structure, support structure and projection exposure system - Google Patents

Abstract

The invention relates to a method for brazing at least one soldering gap (3) between elements (2) of a support structure (1) for optics under vacuum conditions, according to which a nickel-based solder material (4) is used which, in addition to nickel, contains 25% by weight up to 30% by weight chromium, in total 8% by weight to 12% by weight phosphorus and silicon and an impurity content of at most 0.8% by weight, preferably 0.76% by weight.

Description

The invention relates to a method for brazing according to the preamble of claim 1.

The invention also relates to a support structure according to the preamble of claim 11.

The invention also relates to a projection exposure system for semiconductor lithography according to the preamble of claim 23.

In a known manner, an optical system for guiding and shaping light beams, such as a lens or a mirror, is exposed to thermal effects. The absorption of light, in particular light with a small wavelength, leads to an input of thermal energy into the optics. Furthermore, thermal radiation emitted by a light source in addition to the light leads to a further input of thermal energy.

Often the optics for guiding and shaping light beams are arranged on a support structure in such a way that the optics are designed to be electromechanically adjustable in an orientation and a position by means of suitable adjustment devices, in particular actuators. An unavoidable heat development on the part of the adjustment devices leads to further heat input into the optics.

In the case of optics located in a vacuum, a heat dissipation opposite to the heat input is greatly reduced, since heat transfer to a gas surrounding the optics is greatly reduced in the vacuum.

Lithography systems, in particular projection exposure systems, have a large number of optics for guiding and shaping light beams. In particular in the case of microlithographic DUV (Deep Ultra Violet) projection exposure systems and very particularly in the case of microlithographic EUV projection exposure systems in a vacuum, the optics, in particular the lenses or mirrors, are exposed to a large amount of heat input.

In a manner known per se, the support structure for the optics therefore has, inter alia, the task of causing a heat flow that is counter to the heat input and of achieving a cooling effect.

To achieve the cooling effect, in the prior art, it has been found to be advantageous to manufacture the support structure from materials with good thermal conductivity. A design of the support structure and the optics that allow good heat transport, for example by using large cross-sectional areas, has also proven to be advantageous. This applies in particular to a connection area between the optics and the support structure.

In order to achieve an advantageously constant high temperature difference, and thus to achieve a high heat transfer, it is known from the prior art that the support structure itself has cooling devices. The cooling devices are mostly realized by cooling channels that run within the support structure and that take up a coolant. Possible coolants include gases and coolants, especially water.

By regularly exchanging the coolant, a defined heat dissipation away from the support structure can thus be made possible.

In the case of the supporting structure located in the vacuum, tightness of the cooling channels is of particular importance, since a leak in the cooling channels can lead to the coolant escaping from the cooling channels. If coolant escapes into an evacuated area, this can lead to a deterioration in vacuum conditions, in particular to the presence of gases and - in the case of evaporation of the coolant - vapors in an area actually intended as a vacuum.

In the production of the support structure, a cover and a cooling base body are usually connected in the prior art in such a way that they together form the support structure. Here, the cover and the cooling base body each have structures which, after the cover is connected to the cooling base body, form the cooling channels which are arranged in an interior of the support structure.

The connection between the cover and the cooling base body is therefore of particular importance for the tightness of the cooling channels.

In the case of support structures that carry cooling water, in particular support systems that are made, for example, of stainless steel, it has proven advantageous to connect the cover to the cooling base body by means of a soldering or welding process.

According to the prior art, the cover and the basic cooling body each have joining surfaces which form a soldering gap and at which they are connected by means of hard soldering under vacuum.

To braze the cover and the cooling body, a brazing material arranged in a region of the joining surfaces is used together with the Lid and the cooling body heated in such a way that the solder material melts. The molten solder material, a solder melt, then fills the soldering gap and forms a connection with the materials on which the joining surfaces are based and, after solidification, forms a soldered connection.

The quality of the soldered connection is therefore of particular importance for the tightness of the cooling channels. Inadequate wetting behavior of the solder melt, for example, can contribute to reducing the quality of the soldered connection.

The disadvantage of the prior art is that the solder melts that result from the solder materials that are commonly used exhibit inadequate wetting behavior. As a result, the joining surfaces may not be completely covered with molten solder and the soldered connection is incomplete and not homogeneous.

In such soldering applications in the field of brazing in a vacuum, nickel base solders with admixtures of boron and relatively low chromium contents are often used, which have considerable disadvantages in terms of service life due to the water-sensitive and also brittle solder phases.

In particular, structures or support structures which carry cooling water and which are produced by means of a soldering process using conventional nickel-based solders can show signs of corrosion and softening that are detrimental to service life. Other standardized nickel base solders suggest other disadvantages.

Another disadvantage of the prior art is that the solder materials used, after the melt has solidified, can have brittle phases in a central area of the soldering gap or in a central area of the soldered connection, which can lead to a reduction in the tightness.

Accordingly, undesirable so-called brittle phases can develop in larger soldering gaps. Likewise, edge areas with a low level of chromium, or chromium binding, can occur in an adjacent area, provided this consists of the base material stainless steel, which can lead to further destabilization of the overall system.

In particular, from a soldering gap width of 50 µm, continuous, brittle, intermetallic phases can occur, which can break in a glass-like fracture pattern.

Also, design-specific requirements can only be implemented to a limited extent due to the solder material, since very small solder gap widths of, for example, less than 50 μm are advantageous for the solder materials usually used, due to the brittle phases occurring with larger gaps and a loss of strength, which, however, are poorly reliable in terms of manufacturing are realizing. In the case of a soldering gap that is undesirably too wide, an inadequate soldered connection can then occur - due to the insufficient amount of the soldering material provided for filling the gap.

The present invention is based on the object of creating a method for brazing between elements of a support structure which solves the disadvantages of the prior art, in particular has a high level of impermeability and a long service life.

According to the invention, this object is achieved by a method with the features mentioned in claim 1.

The present invention is also based on the object of creating a support structure which solves the disadvantages of the prior art and which in particular has a high degree of impermeability and a long service life.

According to the invention, this object is achieved by a support structure with the features mentioned in claim 11.

The present invention is also based on the object of creating a projection exposure system which solves the disadvantages of the prior art.

According to the invention, this object is achieved by a projection exposure system having the features mentioned in claim 23.

In the method according to the invention for brazing at least one brazing gap between elements of a support structure for an optical system under vacuum conditions, a nickel-based brazing material is used which, in addition to nickel, has 25% by weight to 30% by weight chromium. Furthermore, the solder material has in total 8th % To 12% by weight of phosphorus and silicon and an impurity content of at most 0.8% by weight, preferably 0.76% by weight.

The solder material used according to the invention shows better wetting behavior in comparison to other solder materials, as a result of which the elements of the support structure can be better connected in comparison to other hard soldering methods.

In the method according to the invention, the elements of the support structure are soldered under vacuum conditions through the use of a solder material whose solder melt exhibits particularly good and pronounced wetting behavior. Here, the solder material, as well as some of the elements, can reach a temperature range of approx. 1090 ° C. In particular, the temperature range should be chosen so that the elements do not show any temperature-related softening phenomena. Due to a good wetting behavior, the solder melt can cover the joining surfaces which are arranged on the elements to be soldered and which form a soldering gap and thus form a non-sensitized diffusion zone on the surface of the elements in the area of the joining surfaces, which is as extensive as possible. Overall, good flow behavior or wetting behavior can result in continuous filling of the soldering gap with a high solder gap width tolerance at the same time.

Furthermore, the inventive use of the soldering material enables the formation of a soldered connection between the elements of the supporting structure of an optical system under vacuum conditions in such a way that no defects occur in an area of the soldered connection located in a central area between the joining surfaces and / or no grain boundary precipitations, as is commonly used Solder materials is observable.

In the solder material used in the method according to the invention, stable dendritic nickel-chromium-phosphide phases and nickel-chromium-silicide phases can advantageously form, which or occur only to a small extent in soldered joints made from a different solder material than the solder material used in the method according to the invention may be missing. The reason for this is the specific composition of the solder material.

In addition, with the solder material used in the method according to the invention, zones in a base material on which the joining surfaces are based, in particular stainless steel, in which the base material shows a change in its phase composition, can occur to a lesser extent. This disadvantageous change in the base material is more pronounced in the case of solder materials other than the solder material used in the method according to the invention. The reason for this is the specific composition of the solder material. It can advantageously be provided in the method according to the invention that the solder material has an impurity content of at most 0.5% by weight.

Advantageously, it can also be provided in the method according to the invention that the solder material in total 9 Contains wt .-% to 11 wt .-% phosphorus and silicon.

In an advantageous development of the method according to the invention, it can be provided that the solder material, apart from the impurity content, has only nickel, chromium, phosphorus and silicon as components.

This can also ensure that the material composition of the solder material contributes to particularly preferred properties of the soldered connection.

In an advantageous development of the method according to the invention, it can be provided that the solder material, apart from the impurity content, does not contain any boron.

Advantageously, it can be provided in the method according to the invention that the solder material, within the scope of the impurities, is a maximum of 0.5% by weight, preferably a maximum of 0.1% by weight, preferably a maximum of 0.05% by weight, particularly preferred max. 0.01% by weight, boron. The percentages relate to the total mass of the solder material.

It is preferable if the solder material has no boron or at least the proportion of boron is low or boron only occurs as an - mostly unavoidable - impurity in the solder material.

While boron is usually added to the solder material to lower the melting temperature and to accelerate diffusion, the inventors have found that it is advantageous to dispense with boron when brazing a soldering gap between elements of a support structure. The resulting higher melting temperatures of the solder material, which require more intense heating of the elements to be soldered, are justified by the advantages of better wetting and the absence of defects. The occurrence of defects can be aggravated by the simultaneous presence of chromium and boron in the solder material, due to the chromium bonding by borides.

The brazing material used therefore brings about improved properties with regard to a composition, a microstructure, a strength, a flow behavior, a corrosion resistance, a solder gap width independence and / or a reduction in the corrosion sensitization of a base material also to the effects of hydrochloric or sulfuric acid.

In addition, the material composition of the solder material ensures that dendritic eutectic intermetallic Form phases in a ductile composite, which lead to ductile deformation behavior and / or high tensile strength even with large soldering gaps.

In an advantageous development of the method according to the invention, it can be provided that the solder material has 29% by weight of chromium.

The use of chromium as a component of the solder material has the advantage that a possible depletion of chromium in materials from which the elements are formed in the area of the joining surfaces is counteracted. If the elements in the area of the joining surfaces are made from a chromium-nickel steel in particular, a depletion of chromium in the area of the joining surfaces must be counteracted in order to obtain corrosion resistance of the chromium-nickel steel. A use of a solder material with a proportion of chromium in the total mass of 29% has been found to be advantageous within the scope of the invention.

In an advantageous development of the method according to the invention, it can be provided that the solder material 6th Has% phosphorus by weight.

The use of phosphorus as a constituent of the solder material can lead to a reduction of an oxide layer possibly covering the elements, which can be advantageous for developing good wetting behavior on the part of the molten solder. Too large a proportion of phosphorus in a total mass of the solder material, on the other hand, can lead to a brittle solder joint. A use of a solder material with a proportion of phosphorus in the total mass of 6% has proven to be advantageous within the scope of the invention.

In an advantageous development of the method according to the invention, it can be provided that the solder material 4th Has wt .-% silicon.

The use of silicon as a component of the solder material can contribute to an advantageous prevention of brittle areas in the soldered connection. Furthermore, the use of silicon as a component of the solder material can lead to an advantageous increase in the flowability of the solder melt. On the other hand, too high a proportion of silicon in the total mass of the solder material can negatively affect the tensile strength of the soldered joint. A use of a solder material with a proportion of silicon in the total mass of 4% has proven to be advantageous within the scope of the invention.

In an advantageous development of the method according to the invention, it can be provided that the brazing is carried out under high vacuum conditions.

Carrying out a brazing process under vacuum conditions has the advantage that a reaction of the solder melt formed from the solder material with gases from an atmosphere surrounding the solder material is at least largely prevented, since the space surrounding the solder melt has been evacuated by gases. In comparison to the implementation under vacuum conditions, implementation under high vacuum conditions has the advantage that the probability of an undesired reaction of the solder melt with any remaining gas molecules that may be present is reduced even further.

Carrying out the brazing process under a protective gas atmosphere can also be advantageous, the atmosphere surrounding the molten solder containing at least approximately exclusively noble gases or sufficiently inert gases, i.e. inert gases which show almost no reaction with the molten solder. No vacuum or high vacuum then has to be generated for this purpose, provided that a sufficiently large volume flow of noble gas or inert gas can be established which can displace more reactive gases from the atmosphere surrounding the molten solder.

Robust support structures, in particular robust support structures or cooling structures that carry a cooling medium, can therefore be implemented by adapting the method according to the invention in terms of process technology.

In an advantageous development of the method according to the invention, at least one solder deposit opening into the soldering gap is formed in at least one of the elements such that the soldering deposit has at least one bevel in a transition area to the soldering gap.

The solder material is arranged in solder deposits before the elements and the solder material are heated. If the solder melt forms in the course of the heating process, it can emerge from the solder depot into the soldering gap. This can advantageously be simplified by avoiding flow resistances in a transition area between the solder deposit and the soldering gap. If, in particular, the solder deposit in the transition area to the soldering gap has as few acute angled or right-angled edges as possible, but at least one bevel, then the molten solder flowing out into the soldering gap is facilitated, for example by capillary forces.

Acute-angled or right-angled edges can prevent the molten solder from flowing out, for example by acting as a nucleation nucleus for a The formation of a solid phase and / or the formation of a large contact angle between the molten solder and a surface of the elements in a region of the edge due to the surface tension of the molten solder. Forming the transition area as a bevel can help avoid these disruptions.

Furthermore, due to the advantageous good flow and wetting behavior of the solder melt, which is caused by the solder material, the solder deposit can be arranged at points further away from a cooling channel and / or fewer solder deposits are required per unit area of the joining surfaces, since the solder melt covers longer distances can. The solder deposit must then be designed and calculated with a correspondingly larger capacity.

In an advantageous development of the method according to the invention it can be provided that at least one solder stop is formed in at least one of the elements in order to prevent the solder material introduced into the soldering gap from flowing further, the at least one solder stop as a solder collecting reservoir opening into the soldering gap and / or is designed as a nose, projection and / or step protruding into the soldering gap.

The already described use of the solder material, the solder melt of which exhibits good wetting behavior, can lead to extensive expansion of the solder material in the soldering gap. It can therefore be advantageous to restrict the spread of the solder material in the soldering gap at defined locations.

This can be achieved by geometric elements functioning as solder stoppers in order to be able to dispense with chemical solder stoppers due to the associated undesired side effects.

For this purpose, the elements can have solder collecting reservoirs as solder stoppers, for example, which are designed in such a way that the solder melt, which flows into the soldering gap in the soldering gap, flows into the latter and thus does not spread further in the soldering gap. It is advantageous here if a capacity of the solder collecting reservoir is designed to be matched to an expected volume of the solder melt flowing into the solder collecting reservoir.

Likewise, as solder stops, the elements can, for example, have structures that protrude into the soldering gap and that represent flow resistances for the solder melt. Such lugs, projections and / or steps protruding into the soldering gap can counteract the spread of the solder melt in the soldering gap in that the solder melt is prevented by capillary forces from exiting a local narrowing of the soldering gap caused by protrusions, protrusions and / or steps protruding into the soldering gap . The solder melt can therefore not leave the constriction in the direction of a not yet wetted area. Furthermore, such solder stops can limit the spread of the solder melt due to the formation of a large contact angle between the solder melt and a surface of the elements in the region of the edge due to the surface tension of the solder melt. In this case too, positioning of the solder stops in the soldering gap that is appropriate to the volume of the solder melt to be expected is advantageous.

Solder stops that are designed as steps and / or edges, but do not protrude into the soldering gap, but expand it and / or exert a capillary force on the solder melt located in the soldering gap, as well as combinations of the above-mentioned solder stop designs can also be advantageous.

Solder stops that limit the spread of the solder melt through a specific surface modification on the joining surfaces within the soldering gap can also be advantageous. Possible effects of the surface modifications can be a lotus effect or a chemical reaction, which can lead to the formation of solid phases or phases with slower flow behavior.

In an advantageous development of the method according to the invention, it can be provided that a spacer is formed on at least one of the elements between which the soldering gap is formed in such a way that the elements can be positioned in a defined manner relative to one another, so that the soldering gap between the elements has a defined geometric shape Expression, preferably of constant width, is formed.

As a result of the use of a solder material with good wetting behavior provided in the method according to the invention, the soldering gap can be made very narrow or also very wide, since the solder melt can spread sufficiently well even in a very narrow soldering gap and the soldered connection is formed sufficiently homogeneously in a wide gap will. If the soldering gap is very narrow, however, only a very small absolute positioning error can be tolerated. For example, if the soldering gap with a width of 500 µm is aimed for in known methods, an absolute positioning error of 50 µm can be tolerated under certain circumstances. If the soldering gap with a width of 50 μm is aimed for in the method according to the invention, an absolute positioning error of 50 μm can no longer be tolerated.

This is remedied by the formation of spacers on at least one of the elements, which position the elements relative to one another and thus keep them at a defined distance from one another. This leads to a defined geometry of the soldering gap between the elements.

An advantageous support structure for an optical system is given by the features of claim 11.

The support structure according to the invention for an optical system has at least two elements, between which at least one soldering gap is formed. It is provided that a solder material is introduced into the soldering gap, which connects the elements to one another. It is also provided that the solder material is based on nickel and the solder material has, in addition to nickel, 25% by weight to 30% by weight chromium, in total 8% by weight to 12% by weight phosphorus and silicon. It is also provided that the solder material has an impurity content of at most 0.8% by weight, preferably 0.76% by weight.

In the case of the support structure according to the invention, it can advantageously be provided that the solder material has an impurity content of at most 0.5% by weight.

In the case of the support structure according to the invention, it can also advantageously be provided that the solder material contains a total of 9% by weight to 11% by weight phosphorus and silicon.

In an advantageous development of the support structure according to the invention, it can be provided that the solder material has 29% by weight of chromium and / or the solder material has 6% by weight of phosphorus and / or the solder material has 4% silicon and / or the solder material, apart from the impurity content, does not contain boron.

Advantageously, in the case of the support structure according to the invention, it can be provided that the solder material within the scope of the impurities is a maximum of 0.5% by weight, preferably a maximum of 0.1% by weight, preferably a maximum of 0.05% by weight, particularly preferred max. 0.01% by weight, boron. The percentages relate to the total mass of the solder material

This composition is sold, for example, under the name Brazelet Ni613 by the company Höganäs AB, Höganäs, Sweden. The inventors have recognized that this soldering material for brazing a soldering gap between elements of a support structure for an optical system exhibits advantageous properties under vacuum conditions. In particular, the properties of a soldered connection formed from the solder material described within the soldering gap have proven to be particularly advantageous for the support structure.

The properties of the soldered connection appear particularly advantageous when the soldered connection comes into contact with a coolant. If the soldered connection shows defects, for example, the coolant may, under certain circumstances, pass through the soldered connection. The extremely rare occurrence of defects in the soldered joint using a nickel-based solder material which, in addition to nickel, contains 29% by weight chromium and 6% by weight phosphorus and 4% silicon and which, apart from the impurity content, preferably contains no boron , therefore improves, among other things, the sealing effect of the soldered connection against coolants.

If the solder material of the soldered connection comes into contact with liquid or gaseous substances, for example coolants, in addition to the lowest possible number of defects, the highest possible corrosion resistance of the soldered connection or the solder material is advantageous. If a chemical reaction resulted in corrosion of the soldered joint, this could on the one hand change the composition of the coolant and corroded particles could pass through the coolant to other areas of a cooling circuit, on the other hand, corrosion-related defects in the soldered joint could in turn reduce the leakage the soldered connection are impaired. The described composition of the solder material leads to soldered connections which show an advantageous high corrosion resistance.

In an advantageous development of the support structure according to the invention, at least one solder deposit opening into the soldering gap is formed in at least one of the elements such that the soldering deposit has at least one bevel and / or a radius in the transition area to the soldering gap.

It is also conceivable for the solder deposit to be designed as a dovetail.

In an advantageous development of the support structure according to the invention, it can be provided that the bevel is at an angle of 5 ° to 85 °, preferably 15 ° to 75 °, more preferably 30 ° to 60 °, in particular 35 ° to 55 °, with respect to the course of the soldering gap , runs inclined.

For a configuration of the bevel described above, particularly suitable angular ranges have resulted within the scope of the invention, under which the bevel of the solder deposit can meet the course of the soldering gap. Here, an optimization of a capillary action is against an optimization of a Weighing up the volume of a solder meniscus resulting from wetting.

If the bevel is designed to run very flat in relation to the soldering gap, a high capillary force arises, but the solder deposit has a small volume. In addition, bevels running flat in relation to the soldering gap are geometrically difficult to implement. If the bevel is designed to run very steeply in relation to the soldering gap, a large solder meniscus and a low capillary force are created, but the solder deposit has a large volume.

Instead of forming an inherently planar bevel, rounding off the transition from the solder deposit to the soldering gap is also conceivable. The solder deposit would therefore have a radius instead of a bevel. In particular, a combination of the various mentioned geometric designs of the transition area is also conceivable.

In an advantageous development of the support structure according to the invention, it can be provided that at least one of the elements has at least one solder stop in order to prevent the solder material that can be introduced into the soldering gap from flowing further along the soldering gap.

In an advantageous development of the support structure according to the invention, it can be provided that the at least one solder stop is formed in an area in which the soldering gap opens into a cooling channel of the support structure.

The arrangement of a solder stop in a transition area between the soldering gap and a cooling channel is particularly advantageous in the case of a coolant-cooled support structure which has at least one cooling channel. If the cooling channel borders on a soldering gap, it must be ensured that the soldered connection or the solder melt does not protrude or penetrate into the cooling channel and impede any circulation of the coolant in the cooling channel. A solder material with the components according to the invention exhibits very good flowability of the solder melt. It can therefore be advantageous to take measures to prevent the solder melt from escaping from the soldering gap in the direction of the cooling channel. This is preferably done by the described arrangement of the solder stop at a transition area between the soldering gap and the cooling channel.

A solder stop located too far from the cooling channel can cause the formation of an area of the soldering gap that is not filled with solder material and thus, on the one hand, a reduction in the joining surfaces and the strength of the soldered connection, and, on the other hand, the creation of a cavity in a cooling system that prevents the flow of the Can hinder coolant and in which deposits can form.

According to the invention, it can also be provided that solder stops are formed along the soldering gap, not an area in which the soldering gap opens into a cooling channel of the support structure. These can have an advantageous effect in order to prevent uncontrolled spreading of the solder melt there. Under certain circumstances, this can be advantageous in order to prevent uneven filling of the soldering gap, for example due to the force of gravity or other forces. It would be conceivable that, without suitably placed solder stops, the solder melt from all solder deposits collects at a deepest point that can be reached by the solder melt and penetrates into the solder deposits present there or from there into cooling channels.

In an advantageous development of the support structure according to the invention, it can be provided that the at least one solder stop is designed as a solder collecting reservoir which opens into the soldering gap.

By designing the solder stop as a solder collecting reservoir, a volume of the solder material can be designed to be at least slightly larger than the capacity of the soldering gap, which can lead to reliable coverage and reliable wetting of the joining surfaces. This in turn can lead to a reliable formation of a complete soldered connection.

In an advantageous development of the support structure according to the invention, it can furthermore be provided that the at least one solder stop is designed as a nose, projection and / or step that protrudes into the soldering gap.

A capillary effect of a solder stop geometry thus also acts in the soldering gap. This also promotes a filled soldering gap.

In an advantageous development of the support structure according to the invention, it can furthermore be provided that at least one of the elements has at least one spacer which is arranged between the elements in such a way that the soldering gap between the elements is formed with a defined geometric shape, preferably constant width.

In the case of the support structure according to the invention, it can advantageously be provided that the elements are designed in such a way that they are inserted into one another in a groove and the groove has a rounded base.

One advantage of such a rounded configuration of the soldering gap between the elements representing the tongue and groove is that the soldering gap is widened on a base side of the groove and a capillary force that may occur there is counteracted. This is particularly advantageous when the volume of the solder material is to be designed to be as small as possible. In this context, particular reference is made to plugs soldered into grooves.

In the case of the support structure according to the invention, it can advantageously be provided that the at least one spacer is arranged in such a way that it does not protrude into the soldering gap.

Arranging the at least one spacer in such a way that it does not protrude into the soldering gap has the advantage that the solder melt created from the solder material is not hindered from spreading in the soldering gap and can therefore fill the soldering gap evenly.

On the other hand, it can advantageously also be provided in the case of the support structure according to the invention that the at least one spacer is arranged in such a way that it protrudes into the soldering gap.

Arranging the at least one spacer in such a way that it protrudes into the soldering gap has the advantage that a constant soldering gap width can be ensured over the entire height of the soldering gap.

It can also be provided that some of the spacers protrude into the soldering gap, while another part of the spacers does not protrude into the soldering gap.

Robust support structures, in particular robust support structures that carry coolant, can therefore be implemented by means of design-specific adaptations.

In an advantageous development of the support structure according to the invention, it can be provided that the two elements, between which the at least one soldering gap is formed, are made of stainless steel and / or copper.

A design of the elements forming the soldering gap from copper or stainless steel has the advantage that a soldered connection made of the soldering material in the support structure according to the invention that is placed on these materials is particularly durable and both materials have high corrosion resistance to a large number of potentially corrosive substances.

It can be provided that both elements are made of stainless steel. However, both elements can also be made of copper. It can also be advantageous for one element to be made of copper and the other to be made of stainless steel.

If both elements are made of stainless steel, the properties of the soldered connection are particularly advantageous. In particular, the formation of advantageously stable dendritic nickel-chromium-phosphide phases and nickel-chromium-silicide phases, which can only occur to a small extent or be absent in soldered connections made of a different solder material than the solder material used in the support structure according to the invention. The reason for this is the specific composition of the solder material.

In addition, with the solder material used in the method according to the invention, zones in a base material on which the joining surfaces are based, in particular stainless steel, in which the base material shows a change in its phase composition, can occur to a lesser extent. This disadvantageous change in the base material is more pronounced in the case of solder materials other than the solder material used in the support structure according to the invention. The reason for this is the specific composition of the solder material.

In an advantageous development of the support structure according to the invention, it can be provided that the support structure is designed as a coolant-carrying, in particular cooling-water-carrying, support structure for cooling the optics.

If the supporting structure carries coolant, preferably cooling water, preferably in an interior of the supporting structure, this allows large amounts of heat to be transported away efficiently by means of the cooling water. A possible control of the temperature and the amount of cooling water flowing through the supporting structure per unit of time allows the temperature of the supporting structure to be controlled in a desired, narrow temperature corridor. Water is suitable for this because of its relatively large specific heat capacity and, when using ultrapure water, the possibility of residue-free evaporation in the event that it escapes from the supporting structure into a vacuum. An advantage of the support structure according to the invention, the solder material of which is both corrosion-resistant and has a sealing effect with respect to water, is particularly evident when using water.

In an advantageous development of the support structure according to the invention, it can be provided that one element is designed as a cover and one element is designed as a cooling body.

Such a design of the elements can, for example, form a cooling channel in that the cover is soldered to the cooling base body, provided that the cover and / or the cooling base body are suitable for this purpose, for example by having recesses and / or grooves and / or grooves forming the cooling channel Have recesses. In particular, the cover and the cooling base body can be designed in such a way that they have surfaces which are suitable for forming a soldering gap which enables a gap-free soldered connection between the cover and the cooling base body.

However, it is also conceivable that the two elements are designed in such a way that they are connected at a point other than the soldering gap. Such a connection can be formed by a one-piece design of the two elements or by connection techniques such as brazing and / or welding and / or screws.

Features that have been described in connection with the method according to the invention can also be advantageously implemented for the support structure according to the invention - and vice versa. Furthermore, advantages that have already been mentioned in connection with the method according to the invention can also be understood in relation to the support structure according to the invention - and vice versa.

The method according to the invention and the support structure according to the invention make it possible, due to the improved flowability of the solder melt, to implement smaller and simpler cover geometries.

At this point it should be mentioned that the geometric configurations of both the solder stops and the solder deposits also represent independent inventions, detached from the solder material used in the method according to the invention and in the support structure according to the invention. In particular, the described spatial and physical features of the elements to be connected can also develop an advantageous effect with other solder materials.

The support structure can in particular be a support structure for optics or an optical element of a lithography system, in particular a projection exposure system for semiconductor lithography, in particular an EUV projection exposure system. The optical element for which the support structure is set up can be both an optical element of projection optics and an optical element of the lighting system, including an optical element of the radiation source, in particular also the collector.

The invention relates to a projection exposure system for semiconductor lithography with an illumination system with a radiation source and optics which have at least one support structure for an optical element, at least one of the support structures being at least partially processed and / or at least using a method according to one of claims 1 to 10 is partially designed according to one of claims 11 to 22.

The invention is particularly suitable for use with a microlithographic DUV (Deep Ultra Violet) projection exposure system and very particularly for use with a microlithographic EUV projection exposure system. A possible use of the invention also relates to immersion lithography.

Features that have been described in connection with the support structure according to the invention and the method according to the invention can of course also be advantageously implemented for the projection exposure system according to the invention for semiconductor lithography - and vice versa. Furthermore, advantages that have already been mentioned in connection with the support structure according to the invention and the method according to the invention can also be understood in relation to the projection exposure system for semiconductor lithography - and vice versa.

In addition, it should be pointed out that terms such as “comprising”, “having” or “with” do not exclude any other features or steps. Furthermore, terms such as “a” or “that” which refer to a single number of steps or features do not exclude a plurality of features or steps - and vice versa.

Exemplary embodiments of the invention are described in more detail below with reference to the drawing.

The figures each show preferred exemplary embodiments in which individual features of the present invention are shown in combination with one another. Features of an exemplary embodiment can also be implemented separately from the other features of the same exemplary embodiment and can accordingly be easily combined with features of other exemplary embodiments by a person skilled in the art to form further useful combinations and subcombinations.

In the figures, functionally identical elements are provided with the same reference symbols.

• 1 eine EUV-Projektionsbelichtungsanlage;
• 2 eine DUV-Projektionsbelichtungsanlage;
• 3 eine immersionslithographische Projektionsbelichtungsanlage;
• 4 eine prinzipmäßige Darstellung eines Ausschnitts einer erfindungsgemäßen Tragstruktur;
• 5a-c prinzipmäßige Darstellungen verschiedener Lotdepots;
• 6 eine prinzipmäßige Darstellung eines Ausschnitts einer Tragstruktur; und
• 7a-f prinzipmäßige Darstellungen des Bereichs VII der 6 mit verschiedenen Lotstopps.

They show schematically:

• 1 an EUV projection exposure system;
• 2 a DUV projection exposure system;
• 3 an immersion lithographic projection exposure system;
• 4th a schematic representation of a section of a support structure according to the invention;
• 5a-c principle representations of various solder depots;
• 6th a schematic representation of a section of a support structure; and
• 7a-f principle representations of the area VII of the 6th with different plumb stops.

1 shows an example of the basic structure of an EUV projection exposure system 400 for semiconductor lithography to which the invention can be applied. A lighting system 401 the projection exposure system 400 has next to a radiation source 402 a look 403 for illuminating an object field 404 in one object level 405 on. A is illuminated in the object field 404 arranged reticle 406 , that of a reticle holder shown schematically 407 is held. A projection optics shown only schematically 408 serves to map the object field 404 in an image field 409 in one image plane 410 . A structure is imaged on the reticle 406 onto a light-sensitive layer in the area of the image field 409 in the image plane 410 arranged wafers 411 , that of a wafer holder also shown in detail 412 is held.

The radiation source 402 can EUV radiation 413 , in particular in the range between 5 nanometers and 30 nanometers, in particular 13.5 nanometers, emit. For controlling the path of the EUV radiation 413 optically differently designed and mechanically adjustable optical elements are used, which are mounted on a support structure according to the invention, which is shown in more detail below 1 can be arranged (in 1 not shown). The optical elements of the in 1 illustrated EUV projection exposure system 400 designed as adjustable mirrors in suitable embodiments mentioned below only by way of example.

The one with the radiation source 402 generated EUV radiation 413 is by means of an in the radiation source 402 integrated collector so that the EUV radiation 413 in the area of an intermediate focus plane 414 passes through an intermediate focus before the EUV radiation 413 on a field facet mirror 415 meets. According to the field facet mirror 415 becomes the EUV radiation 413 from a pupil facet mirror 416 reflected. With the help of the pupil facet mirror 416 and an optical assembly 417 with mirrors 418 , 419 , 420 become field facets of the field facet mirror 415 in the object field 404 pictured.

In 2 is an exemplary DUV projection exposure system 100 shown. The projection exposure system 100 has a lighting system 103 , a reticle day 104 said device for receiving and exact positioning of a reticle 105 , through which the later structures on a wafer 102 be determined, a wafer holder 106 for holding, moving and exact positioning of the wafer 102 and an imaging device, namely a projection lens 107 , with several optical elements 108 that over sockets 109 in a lens housing 140 of the projection lens 107 are kept on.

The optical elements 108 can be used as individual refractive, diffractive and / or reflective optical elements 108 such as B. lenses, mirrors, prisms, end plates and the like can be formed.

The basic functional principle of the projection exposure system 100 that provides that in the reticle 105 introduced structures on the wafer 102 can be mapped.

The lighting system 103 provides one for imaging the reticle 105 on the wafer 102 required projection beam 111 in the form of electromagnetic radiation. A laser, a plasma source or the like can be used as the source for this radiation. The radiation is in the lighting system 103 Shaped via optical elements so that the projection beam 111 when hitting the reticle 105 has the desired properties in terms of diameter, polarization, shape of the wavefront and the like.

By means of the projection beam 111 becomes an image of the reticle 105 generated and from the projection lens 107 correspondingly reduced on the wafer 102 transfer. The reticle 105 and the wafer 102 are moved synchronously, so that areas of the reticle are practically continuous during a so-called scanning process 105 on corresponding areas of the wafer 102 can be mapped.

In 3 is a third projection exposure system 200 in training as an immersion lithographic DUV projection exposure system, for example shown. On the further background of such a projection exposure system 200 is for example on the WO 2005/069055 A2 referenced, the content of which is incorporated into the present description by reference; The exact functionality is therefore not discussed in detail at this point.

Can be seen, comparable to the DUV projection exposure system 100 according to 2 , a reticle day 104 through which the later structures on the wafer 102 that is on the wafer holder 106 or wafer table is arranged to be determined. The projection exposure system 200 the 3 also has several optical elements for this purpose, in particular lenses 108 and mirror 201 , on.

The method according to the invention or the support structure according to the invention 1 is not on support structures for optical elements of projection exposure systems 100 , 200 , 400 limited, in particular not to support structures for optical elements of projection exposure systems 100 , 200 , 400 with the structure described. However, the invention is particularly suitable for support structures for optical elements of projection exposure systems, in particular EUV projection exposure systems.

The support structure according to the invention 1 or the method according to the invention for brazing is suitable in principle for all support structures that are used in projection exposure systems 100 , 200 , 400 can be used to receive or grasp in each case its optical element, in particular a lens or a mirror. This can in particular be both a support structure for an optical element of projection optics and an optical element of the lighting system, including an optical element of the radiation source, in particular also the collector.

Although the description of the invention takes place in the exemplary embodiments using support structures for optical elements of projection exposure systems, the disclosure is to be understood in such a way that the method according to the invention or the support structure according to the invention can be used for any elements, in particular for any optical elements.

The following figures represent the invention only by way of example and in a highly schematic manner.

4th shows a basic representation of the support structure according to the invention 1 . The supporting structure 1 here has at least two elements 2 on, between which a soldering gap 3 is formed, wherein in the soldering gap 3 a solder material 4th is introduced which the elements 2 connects with each other. In the present embodiment, the material is solder 4th according to the invention such that the solder material 4th based on nickel and the solder material 4th in addition to nickel, 25 wt% to 30 wt% chromium, in total 8th % To 12% by weight of phosphorus and silicon and an impurity content of at most 0.8% by weight, preferably 0.76% by weight.

In the present embodiment, the material is solder 4th preferably made such that the solder material 4th preferably 29% by weight chromium and preferably 6% by weight phosphorus and preferably 4% silicon and the solder material 4th preferably has no boron apart from the impurity content.

In the in 4th shown embodiment of the support structure 1 is at one of the elements 2 one in the soldering gap 3 opening solder deposit 5 designed such that the solder deposit 5 in the transition area 6th to the soldering gap 3 a bevel 7th having. Alternatively, a radius can also be provided.

Furthermore, one of the elements 2 a plumb stop 8th on to that in the soldering gap 3 insertable solder material 4th in a continued flow along the soldering gap 3 to prevent. Plumb stops 8th can also be used on both elements 2 be trained.

The plumb stop 8th is preferably formed in an area in which the soldering gap 3 in a cooling channel 9 the supporting structure 1 flows out.

The plumb stop 8th is in the in 4th illustrated embodiment as a solder collecting reservoir 10 formed, which in the soldering gap 3 flows out. Alternatively, the plumb stop 8th can also be designed as a nose, protrusion and / or step that enters the soldering gap 3 protrudes. It is also possible that the elements 2 have several differently designed plumb stops.

Furthermore, the support structure 1 as a coolant carrying structure 1 designed to cool optics, in particular an optical element, in particular a mirror or a lens. For cooling, the in 4th illustrated embodiment cooling water 11 through the cooling duct 9 .

Furthermore, it can be provided (not shown) that at least one of the elements 2 has a spacer which is so between the elements 2 is arranged that the soldering gap 3 between the elements 2 is formed with a defined geometric expression, preferably constant width.

It can be provided that the spacer is arranged in such a way that it does not enter the soldering gap 3 protrudes and / or that this into the soldering gap 3 protrudes.

Furthermore, in the present embodiment, the two are elements 2 , between which the at least one soldering gap 3 is formed, formed from stainless steel.

In the exemplary embodiment is one element 2 as a cover and an element 2 designed as a cooling body.

In the present embodiment, the elements 2 brazed under high vacuum conditions.

5a shows a basic representation of a solder deposit 5 , with the bevel 7th compared to the course of the soldering gap 3 runs inclined at an angle of 45 °, preferably by 30 °.

5b shows a basic representation of a solder deposit 5 , with the bevel 7th compared to the course of the soldering gap 3 is inclined at an angle of less than 45 °.

5c shows a basic representation of a solder deposit 5 , with the bevel 7th compared to the course of the soldering gap 3 is inclined at an angle of more than 45 °.

In the present exemplary embodiments, the bevel is 7th of the solder depot 5 compared to the course of the soldering gap 3 inclined at an angle of 5 ° to 85 °, preferably 15 ° to 75 °, more preferably 30 ° to 60 °, in particular 35 ° to 55 °.

6th shows a basic representation of a section of a support structure according to the invention 1 with an area VII in which the soldering gap 3 in a cooling channel 9 the supporting structure 1 flows out.

the 7a until 7f show principle representations of the area VII of the 6th in which the soldering gap 3 in the cooling duct 9 the supporting structure 1 flows out.

7a shows a basic representation of a solder stop 8th , the plumb stop 8th in the present embodiment is designed as a nose.

7b shows a basic representation of a solder stop 8th , the plumb stop 8th is designed as a step in the present embodiment.

7c shows a basic representation of a solder stop 8th , the plumb stop 8th in the present embodiment is designed as a funnel. This is achieved in that a solder stop and the solder stops are formed in both elements 8th then when the items 2 are composed, together form a funnel.

7d shows a basic representation of a solder stop 8th , the plumb stop 8th in the present embodiment is designed as a step on both sides.

For this purpose, it can again preferably be provided that both elements 2 train part of the level.

7e shows a basic representation of a solder stop 8th , the plumb stop 8th in the present embodiment is designed as a step with a projection. The step with the projection is designed in such a way that the soldering gap 3 before reaching the cooling channel 9 has its normal width again, ie the projection borders the widening of the release gap to the cooling channel resulting from the step 9 away.

7f shows a basic representation of a solder stop 8th , the plumb stop 8th in the present embodiment is designed as a step on both sides with a protrusion on both sides. the 7f shows a variant of the 7e , it is provided that both elements 2 are processed in such a way that they jointly form the step on both sides.

List of reference symbols

1

Support structure

2

element

3rd

Solder gap

4th

Solder material

5

Solder depot

6th

Transition area

7th

chamfer

8th

Plumb stop

9

Cooling duct

10

Solder collecting reservoir

11

cooling water

100

Projection exposure system

102

Wafer

103

Lighting system

104

Reticle days

105

Reticle

106

Wafer holder

107

Projection lens

108

Optical element

109

Version

111

Projection beam

140

Lens housing

200

Projection exposure system

201

mirrors

400

Projection exposure system

401

Lighting system

402

Radiation source

403

optics

404

Object field

405

Object level

406

Reticle

407

Reticle holder

408

Projection optics

409

Field of view

410

Image plane

411

Wafer

412

Wafer holder

413

EUV radiation

414

Intermediate focus plane

415

Field facet mirror

416

Pupil facet mirror

417

Optical assembly

418

mirrors

419

mirrors

420

mirrors

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2005/069055 A2 [0134]

Claims (23)

Method for brazing at least one brazing gap (3) between elements (2) of a support structure (1) for optics under vacuum conditions, characterized in that a nickel-based brazing material (4) is used which, in addition to nickel, contains 25% by weight to 30% by weight chromium, in total 8% by weight to 12% by weight phosphorus and silicon as well as a maximum impurity content of 0.8% by weight, preferably 0.76% by weight. Procedure according to Claim 1 , characterized in that the solder material (4), apart from the impurity content, has only nickel, chromium, phosphorus and silicon as components. Procedure according to Claim 1 or 2 , characterized in that the solder material (4), apart from the impurity content, does not contain any boron. Procedure according to Claim 1 , 2 , or 3, characterized in that the solder material (4) has 29% by weight of chromium. Method according to one of the Claims 1 until 4th , characterized in that the solder material (4) has 6 wt .-% phosphorus. Method according to one of the Claims 1 until 5 , characterized in that the solder material (4) has 4 wt .-% silicon. Method according to one of the Claims 1 until 6th , characterized in that the brazing is carried out under high vacuum conditions. Method according to one of the Claims 1 until 7th , characterized in that in at least one of the elements (2) at least one solder deposit (5) opening into the soldering gap (3) is formed in such a way that the soldering deposit (5) in a transition region (6) to the soldering gap (3) has at least one Has a chamfer (7) and / or a radius. Method according to one of the Claims 1 until 8th , characterized in that at least one solder stop (8) is formed in at least one of the elements (2) in order to prevent the solder material (4) introduced into the soldering gap (3) from flowing further, the at least one solder stop (8) as The solder collecting reservoir (10) opening into the soldering gap (3) and / or is designed as a nose, projection and / or step protruding into the soldering gap (3). Method according to one of the Claims 1 until 9 , characterized in that a spacer is formed on at least one of the elements (2) between which the soldering gap (3) is formed such that the elements (2) can be positioned in a defined manner relative to one another, so that the soldering gap (3) between the Elements (2) with a defined geometric expression, preferably constant width, is formed. Supporting structure (1) for an optical system with at least two elements (2) between which at least one soldering gap (3) is formed, wherein a solder material (4) is introduced into the solder gap (3) connecting the elements (2) together, characterized characterized in that the solder material (4) is based on nickel and the solder material (4) in addition to nickel 25 wt .-% to 30 wt .-% chromium, in total 8 wt .-% to 12 wt .-% phosphorus and silicon as well as an impurity content of a maximum of 0.8% by weight, preferably 0.76% by weight. Support structure (1) according to Claim 11 , characterized in that the brazing material (4) has 29% by weight of chromium and / or the brazing material (4) has 6% by weight of phosphorus and / or the brazing material (4) has 4% silicon and / or the brazing material ( 4), apart from the impurity content, does not contain any boron. Support structure according to Claim 11 or 12th , characterized in that in at least one of the elements (2) at least one solder deposit (5) opening into the soldering gap (3) is designed in such a way that the solder deposit (5) in the transition area (6) to the soldering gap (3) has at least one Has a chamfer (7) and / or a radius. Support structure (1) according to one of the Claims 11 until 13th , characterized in that the bevel (7) with respect to the course of the soldering gap (3) at an angle of 5 ° to 85 °, preferably 15 ° to 75 °, more preferably 30 ° to 60 °, in particular 35 ° to 55 °, runs inclined. Support structure (1) according to one of the Claims 11 until 14th , characterized in that at least one of the elements (2) has at least one solder stop (8) to prevent the solder material (4) which can be introduced into the soldering gap (3) from flowing further along the soldering gap (3). Support structure (1) according to Claim 15 , characterized in that the at least one solder stop (8) is formed in an area in which the soldering gap (3) opens into a cooling channel (9) of the support structure (1). Support structure (1) according to Claim 15 or 16 , characterized in that the at least one solder stop (8) is designed as a solder collecting reservoir (10) which opens into the soldering gap (3). Support structure (1) according to one of the Claims 15 , 16 or 17th , characterized in that the at least one solder stop (8) is designed as a nose, projection and / or step which protrudes into the soldering gap (3). Support structure (1) according to one of the Claims 11 until 18th , characterized in that at least one of the elements (2) has at least one spacer which is arranged between the elements (2) in such a way that the soldering gap (3) between the elements (2) has a defined geometric shape, preferably a constant width, is trained. Support structure (1) according to one of the Claims 11 until 19th , characterized in that the two elements (2), between which the at least one soldering gap (3) is formed, are made of stainless steel and / or copper. Support structure (1) according to one of the Claims 11 until 20th , characterized in that the support structure (1) is designed as a coolant-carrying, in particular cooling-water-carrying, support structure (1) for cooling the optics. Support structure (1) one of the Claims 11 until 21 , characterized in that one element (2) is designed as a cover and one element (2) is designed as a cooling body. Projection exposure system (100, 200, 400) for semiconductor lithography with an illumination system (103, 401) with a radiation source (402) and optics (107, 403, 408) which have at least one support structure (1) for an optical element (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201), at least one of the support structures (1) at least partially according to one of the Claims 11 until 22nd formed and / or at least partially with a method according to one of the Claims 1 until 10 is processed.

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