DE102018202687A1 - Production method for components of a projection exposure apparatus for semiconductor lithography and projection exposure apparatus - Google Patents

Abstract

The invention relates to an etching method for producing a cavity structure (24) in a component (50, 55) of a projection exposure apparatus (1) with the following method steps:
Definition of the cavity structure (24) to be realized in the component (50, 55)
Defining a plurality of accesses (30) for an etching attack to create the cavity structure (24),
Laser pre-treatment of the areas provided for the cavity structure (24) to prepare the Ätzängriffs
Producing the cavity structure (24) by etching, wherein at least one of the accesses (30) is formed as auxiliary etching access.
Furthermore, the invention relates to a projection exposure apparatus (1) for semiconductor lithography with a plurality of components (50, 55), wherein at least one component (50, 55) has a cavity structure (24) produced by means of selective laser etching and wherein the component (50 , 55) has at least one auxiliary etching access (30) to the cavity structure (24).

Description

The invention relates to a production method of components of a projection exposure apparatus for semiconductor lithography and to a projection exposure apparatus equipped with the corresponding components.

For projection exposure systems, there are extremely high demands on the imaging accuracy and, at the same time, high thermal stress on the components used to image a reticle onto a wafer. These components may, for example, be mirrors or manipulators which are designed as thermally or mechanically actuated optical elements.

For example, in the U.S. Patent US 7,817,249 B2 discloses a projection exposure apparatus for semiconductor lithography, in which aberrations can be corrected by at least one arranged in the projection lens of the projection exposure optical element is heated spatially resolved by the action of directed infrared radiation, whereby a desired temperature and thus refractive index distribution and a certain local deformation over the optical element is achieved across. Due to the thermal inertia of the optical element, however, a rapid adaptation of the desired profile or a quick "neutral switching" of the optical element by re-setting a homogeneous temperature distribution across the optical element by the device disclosed in the document is difficult.

Furthermore, WO 2007/017 089 A1 discloses a manipulator for a projection exposure apparatus for semiconductor lithography, in which a thin liquid layer is located between two optical elements, for example plane-parallel plates, wherein one of the plane-parallel plates can be deformed. The temperature of the liquid is chosen so that the difference of the refractive indices from the liquid to the adjacent plane-parallel plate is as small as possible. Such components pose special technical challenges with respect to small feature sizes.

Especially in EUV and DUV lithography, the demands on the thermal conditioning of optical elements are increasing due to continuously increasing optical specifications. One way to remedy this situation is the direct temperature control, in particular cooling of the optical elements. For this purpose, temperature control or cooling lines must be integrated into the optical elements. Currently, such structures can be realized only with great effort in optical elements.

One method frequently used for this purpose is the so-called selective laser etching SLE (Selective Laser-Induced Etching). Selective laser-induced etching (SLE) is a two-step process in which initially transparent or partially transparent material is locally thermally treated with laser radiation in such a way that the chemical etchability at these sites is increased. For this purpose, a short pulse duration of the laser radiation and a small focus volume in the range of less than ³ microns is required. The focus is moved through the material until a continuous volume is thermally treated in contact with the outer surface of the workpiece. In this case, the contact with the outer surface usually has to be generated by a subsequent mechanical processing.

In the second process step, the material modified by the laser radiation is selectively removed by wet-chemical etching - the structure is virtually developed. A key factor for the structural accuracy is a selectivity in which the etching rate of the modified material is substantially higher in relation to the etching rate of the unmodified material.

For example, in the case of quartz glass, the selectivity is greater than 500: 1, so that fine long channels or other suitable cavities can be produced. Therefore, with the SLE technology, complex 3D cavities can be created in glass or in other materials as the basis for microstructured components.

Particularly advantageous here are the high precision of only 1 μm error tolerance, the full 3D capability and the high process speed through the use of powerful micro-scanners.

When using zero expansion material, which has virtually no change in volume over temperature, the selectivity of the etching rate can be up to 1000: 1. In combination with the increasing mirror diameters due to the increasing numerical aperture of the EUV systems, this leads to disadvantageously very long etching times of several weeks to months in the structures to be produced.

Object of the present invention is to develop a method for the production of components for projection exposure equipment for semiconductor lithography such that the components can be made faster than before and to create a corresponding projection exposure system.

This object is achieved by a device or a method having the features of the independent claims. The subclaims relate to advantageous developments and variants of the invention.

• - Festlegung der in der Komponente zu realisierenden Hohlraumstruktur, also im Wesentlichen die Planung der in der Komponente gewünschten Hohlraumgeometrie.
• - Festlegung einer Mehrzahl von Zugängen für einen Ätzangriff zur Schaffung der Hohlraumstruktur. Dabei wird unter einem Zugang ein Bereich verstanden, durch welchen das entsprechend vorbehandelte Material mit der ätzenden Substanz in Kontakt gelangen kann.
• - Laservorbehandlung der für die Hohlraumstruktur vorgesehenen Bereiche zur Vorbereitung des Ätzangriffs. Die vorgesehenen Bereiche sind damit diejenigen Bereiche, in welchen durch den Ätzangriff das Material abgetragen werden soll.
• - Herstellen der Hohlraumstruktur durch Ätzen, wobei erfindungsgemäß mindestens einer der Zugänge als Hilfs-Ätzzugang ausgebildet ist.

An etching method according to the invention for producing a cavity structure in a component of a projection exposure apparatus comprises in particular the following method steps:

• - Determining the to be realized in the component cavity structure, so essentially the planning of the desired cavity geometry in the component.
• - Establishing a plurality of accesses for an etching attack to create the cavity structure. In this case, an access means a region through which the correspondingly pretreated material can come into contact with the corrosive substance.
• Laser pre-treatment of the areas provided for the cavity structure in preparation for the etching attack. The intended areas are thus those areas in which the material is to be removed by the etching attack.
• - Producing the cavity structure by etching, wherein according to the invention at least one of the accesses is formed as an auxiliary Ätzzugang.

An auxiliary etch access is to be understood as an access that serves primarily to accelerate the formation of the cavity structure in the component by the etching attack, namely by the corrosive substance reaching the pretreated material in the component in more places than the etching substance A case would be if an etching attack took place only on the accesses provided anyway for the later functionality of the component. Typically, the auxiliary etch access may be resealed after the complete formation of the desired cavity structure.

Advantageously, at least one of the auxiliary etch approaches can be made by etching; It is of course also possible to use a mechanically abrasive method for this purpose.

The closing of the auxiliary access can be done in particular by gluing or bonding.

In an advantageous variant of the invention, the auxiliary etching access can have a longitudinal axis which is different from a main alignment axis of the cavity structure, that is to say in particular runs obliquely or else perpendicular to it.

The cavity structure may be formed in one embodiment of the invention as a tempering channel for influencing the temperature of the component; This variant is - in addition to other applications - in particular for cases in which it is the component to a mirror body.

Because the closure comprises a temperature sensor or a flow sensor, the cavity created anyway by the auxiliary etching access can be supplied to a further sensible use. In this case, the sensor or its parts can be used as part of the closure; in extreme cases, the closure can be completely formed by a correspondingly adapted in its form sensor, which is glued, for example, in the cavity. In the case of a temperature sensor, the temperature of the mirror material can then be determined by the direct contact of the sensor with the surrounding material.

Furthermore, the invention makes it possible to design the cavity structure in a simple manner such that different temperature-controlled fluid circuits can be realized.

• 1 den prinzipiellen Aufbau einer EUV-Projektionsbelichtungsanlage, in welcher die Erfindung verwirklicht sein kann,
• 2 eine Schnittansicht einer exemplarischen Komponente mit einem Temperierkanal nach dem Stand der Technik,
• 3a eine erste Ausführungsform der Erfindung,
• 3b eine weitere Ausführungsform der Erfindung; und
• 4 eine Schnittansicht einer Komponente in einer weiteren Ausführungsform der Erfindung.

Embodiments and variants of the invention will be explained in more detail with reference to the drawing. Show it

• 1 the basic structure of an EUV projection exposure apparatus in which the invention can be realized,
• 2 3 a sectional view of an exemplary component with a tempering channel according to the prior art,
• 3a a first embodiment of the invention,
• 3b another embodiment of the invention; and
• 4 a sectional view of a component in a further embodiment of the invention.

1 shows an example of the basic structure of an EUV projection exposure system 1 for microlithography, in which the invention can find application. An illumination system of the projection exposure apparatus 1 points next to a light source 3 an illumination optics 4 for illuminating an object field 5 in an object plane 6 on. One by the light source 3 generated EUV radiation 14 as optical useful radiation is by means of a light source in the 3 integrated collector aligned so that they are in the area of a Zwischenfokusebene 15 undergoes an intermediate focus before moving to a field facet mirror 2 meets. After the field facet mirror 2 becomes the EUV radiation 14 from a pupil facet mirror 16 reflected. With the aid of the pupil facet mirror 16 and an optical assembly 17 with mirrors 18 . 19 and 20 become field facets of the field facet mirror 2 in the object field 5 displayed.

Illuminated is a in the object field 5 arranged reticle 7 that of a schematically represented Reticlehalter 8th is held. A merely schematically illustrated projection optics 9 serves to represent the object field 5 in a picture field 10 into an image plane 11 , Pictured is a structure on the reticle 7 on a photosensitive layer in the area of the image field 10 in the picture plane 11 arranged wafers 12 , by a wafer holder also shown in detail 13 is held. The light source 3 can emit useful radiation, in particular in a wavelength range between 5 nm and 30 nm.

The invention can also be used in a DUV system not explicitly shown here. A DUV system is in principle like the EUV system described above 1 constructed, in a DUV system mirrors and lenses can be used as optical elements and the light source of a DUV system emits a useful radiation in a wavelength range of 100 nm to 300 nm.

2 shows one as in 1 described mirror 18 a lithographic system according to the prior art. The mirror 18 includes a mirror body 21 with a mirror surface 23 to which a reflective layer not separately designated in the figure is applied. The reflective layer is designed so that it reflects the EUV radiation used in the lithography system as best as possible. The mirror 18 In addition, as a cavity structure includes a close to the mirror surface 23 in the mirror body 21 integrated tempering channel 24 by selective laser etching in the substrate of the mirror body 21 was produced. In this case, the substrate may be made of a ceramic material. The tempering channel 24 may be formed as a very delicate structure due to the aforementioned advantageous manufacturing method, the diameter may be, for example, in the range of 1 micron to 100 microns. In principle, tempering channels of any cross-section and dimensioning in the mirror 18 be introduced. The tempering channel 24 may in particular be filled with a tempering or cooling medium, for example with air, water or another medium, which by means of a pump, not shown by the tempering 24 can be transported.

During operation of the EUV system, depending on the structures located on the reticle and the required distribution of the intensity of the illumination light, the so-called illumination setting, the pupil is illuminated to varying degrees with light, thereby increasing the imaging quality. These lighting settings can lead to an inhomogeneous light distribution on the mirrors, whereby, for example, the mirror 18 is heated unevenly. This in turn results in deformations in the mirror body 21 , The unevenness of the mirror surface due to the deformation of the mirror 23 lead to errors in the image of the structure on the wafer. To avoid deformations on the mirror surface 23 is usually for the mirror body 21 uses a material with a very low coefficient of thermal expansion, such as ULE. In addition, the mirror 18 be irradiated with light of a wavelength which does not correspond to the wavelength of the EUV radiation before the actual exposure. Because of its wavelength, which deviates from the wavelength of the EUV radiation, this light is reflected by the reflecting layer optimized for reflection of EUV radiation to a different degree, in particular far less, but largely absorbed. This may cause the mirror 18 be pre-heated to anticipate the heating by the useful light used for imaging.

So that the heat distribution set before the operation and thus the topography of the mirror surface 23 while operating at its optimum, the mirror becomes 18 through the tempering channel 24 , which is flowed through with a fluid, tempered. So it can be through the irradiation in the mirror 18 introduced heat absorbed by the fluid and transported away. In principle, the fluid can also heat in the mirror 18 be introduced. This heat can vary depending on the distribution of the tempering channels 24 in separate sections locally in the mirror 18 be introduced.

The tempering channel 24 has been produced in the example shown by selective laser etching. In this method, in a first step by means of laser irradiation, the mirror material also within the mirror body 21 be specifically changed in its properties. The material changed in this way is then dissolved out in an etching bath. The dissolution ratio of unaltered material to altered material is usually in a range of 1: 500 to 1: 1000, so the altered material is dissolved 500 to 1000 times faster by the etching bath than the unaltered material, thereby mainly removing the altered material of the structures and the unchanged material remains. The increasing numerical aperture (NA) of modern objectives in projection exposure systems and the resulting increase in mirror diameter increase the duration of the etching process during production the temperature control channels considerably. For example, a must like in 2 exemplified mirror 18 with a radius of 250 mm, around a tempering channel whose diameter can be, for example, in the range of 1 .mu.m to 100 .mu.m, and which extends below the mirror surface over the entire diameter of the mirror 18 extends, lie in the etching bath for up to 3 months until the material changed by the laser irradiation is completely removed. This is a significant disadvantage of the production of the tempering channel used in the prior art 24 , In addition, the in 2 schematically illustrated arrangement of the tempering 24 also disadvantageous in that the by the fluid 25 in the tempering channel 24 dissipated heat the mirror body 21 tempered as a whole and therefore not suitable for different areas of the mirror 18 to regulate different temperatures.

3a shows as a first embodiment of the invention as a component a mirror 50 with integrated tempering channel 24 as a cavity structure. The mirror shown 50 shows on its mirror surface 23 opposite side accesses 30 , These accesses 30 reach until just before that level in the mirror body 21 in which the actual tempering channel 24 runs. The plane in which the tempering channel 24 runs, is also Temperierkanalebene below 26 called; it can be in a range of for example 7 - 10mm below the mirror surface 23 lie. The accesses 30 in 3a are perpendicular to the mirror surface 23 arranged, but can also be at any other angle to the mirror surface 23 or the tempering channel 24 run. The accesses 30 are dimensioned such that the production can be carried out by conventional means such as drilling and is not necessarily dependent on the selective laser etching as a manufacturing process.

In the end faces 32 of the entrances 30 is also breakthroughs using the method described above by changing the mirror material and then etching 33 to the actual tempering channel 24 made, in turn, advantageously perpendicular, but also at any other angle to the tempering 24 can run. The breakthroughs 33 create further attack surfaces for the etching liquid, so that a simultaneous, parallel etching in different areas of the mirror material is possible and thus the for the production of the entire tempering 24 required total etching time significantly shortened. The accesses 30 thus serve as auxiliary Ätzzugänge; they are in the example shown following the production of the tempering 24 through closures 34 closed again. The closures 34 For example, they can be glued or bonded and are advantageously made of the same material as the mirror body 21 manufactured.

The closures 34 the breakthroughs 33 In addition, temperature sensors which are not shown separately in the figure may contain, for example, the temperature of the mirror body 21 and / or of the fluid contained in the tempering 51. There are also sensors for a flow measurement of the fluid conceivable.

3b shows a second embodiment of the invention. As in 3a are on the mirror back accesses 30 created as auxiliary Ätzzugänge, which has access to the tempering 24 from the back of the mirror 50 allow. Compared to the in 3a the embodiment shown, the actual tempering extends 24 no longer over the entire diameter, but only between the breakthroughs 33 , each one the front of an access 30 with the in the Temperierkanalebene 26 located tempering 24 connect. This embodiment has the same advantages over the prior art in terms of the duration of production by means of selective laser etching as in 3a shown embodiment.

The two breakthroughs 33 can for the tempering channel 24 be used as an inlet or outlet, so that a fluid through the inlet of the temperature control 24 fed and discharged through the outlet again. The accesses 30 may also be designed to be part of the inlet or outlet, respectively.

4 shows a variant of the invention, in which over the diameter of the mirror 55 example, three tempering channels 24 each with an inlet and outlet associated with the respective temperature control channel, as in 3b represented, are arranged. By connecting the three individual temperature control channels 24 associated fluid circuits, for each of which the temperature and / or the flow of the fluid can be controlled separately, a desired temperature profile in the mirror body 21 be set.

At the mirror body 21 and with it from the mirror surface 23 In this way, heat can be dissipated in certain areas, that is, cooled, and heat is supplied to other areas, that is to say heated, by the inhomogeneous irradiation of the mirror surface 23 resulting temperature differences of the mirror surface 23 to minimize or the mirror surface 23 in all areas to a constant temperature. Likewise, the mirror can deliberately be deformed deliberately to the deformation of other optical Elements, in particular mirrors, in the system to compensate; In this case, the mirror would be used in the manner of a manipulator.

An embodiment of several tempering channels on different tempering channel planes can be advantageous for mirrors which, for example, have different mirror thicknesses perpendicular to the mirror surface.

For controlling the temperature at the mirror surface 23 and in the mirror body 21 In addition to the measurement of the temperature of the tempering fluid and sensors in the mirror body are advantageous, which are not shown separately in the figures.

For all embodiments shown the 3a . 3b and 4 With a suitable arrangement of the tempering channels, access openings and openings, a combination of drilling or another mechanically abrasive method and selective etching can be used in order to further reduce the production times.

5 describes a method by which the device according to the invention of the 3 - 4 can be made for controlling the temperature of mirrors.

The process steps shown in the figure are preceded by the optical design of the components of the projection exposure apparatus and the structural design of the component without tempering channels.

In a first method step, the cavity structure to be realized in the component is defined.

In the second method step, the accesses, ie also the auxiliary etch accesses, are defined.

In a third process step, the required laser pretreatment is performed.

In a fourth method step, the desired cavity structure is removed from the mirror body by selective laser etching.

In a fifth method step, the auxiliary Ätzzugänge be closed by closures again.

LIST OF REFERENCE NUMBERS

1

Projection exposure system

2

Field facet mirror

3

light source

4

illumination optics

5

object field

6

object level

7

reticle

8th

Reticlehalter

9

projection optics

10

field

11

image plane

12

wafer

13

wafer holder

14

EUV radiation

15

Between the focal plane

16

Pupil facet mirror

17

module

18

mirror

19

mirror

20

mirror

21

mirror body

23

mirror surface

24

tempering

25

fluid

26

Temperierkanalebene

30

Access

33

breakthrough

34

shutter

50

mirror

55

mirror

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• US 7817249 B2 [0003]

Claims (17)

An etching method for producing a cavity structure (24) in a component (50, 55) of a projection exposure apparatus (1) comprising the following method steps: - fixing the cavity structure (24) to be realized in the component (50, 55) - defining a plurality of accesses (30 ) for an etching attack to create the cavity structure (24), - pre-laser treatment of the areas provided for the cavity structure (24) to prepare the Ätzängriffs - producing the cavity structure (24) by etching, characterized in that at least one of the accesses (30) as an auxiliary -Atezzugang is formed. Method according to Claim 1 , characterized in that at least one of the auxiliary etching accesses (30) is produced by etching. Method according to Claim 1 , characterized in that at least one of the auxiliary etching accesses (30) is produced by a mechanically abrasive process. Method according to one of the preceding claims, characterized in that in addition a closing of the opening (33) of at least one auxiliary Ätzzuganges (30) after production of the cavity structure (24). Method according to Claim 4 Characterized in that the sealing is effected via an integral method. Method according to Claim 5 , characterized in that the closing takes place by gluing or bonding. Method according to one of the preceding claims, characterized in that it is in the component (50,55) to a mirror body (21). A projection exposure apparatus (1) for semiconductor lithography comprising a plurality of components (50, 55), wherein at least one component (50, 55) comprises a cavity structure (24) produced by selective laser etching, characterized in that the component (50, 55) is at least an auxiliary etching access (30) to the cavity structure (24). Projection exposure system (1) according to Claim 8 characterized in that a longitudinal axis of the auxiliary etching access (30) is different from a main alignment axis of the cavity structure (24). Projection exposure system (1) according to Claim 8 or 9 characterized in that a longitudinal axis of the auxiliary etching access (30) is perpendicular to a main alignment axis of the cavity structure (24). Projection exposure apparatus (1) according to one of Claims 8 - 10 , Characterized in that the cavity structure (24) is designed as a tempering channel (24) for influencing the temperature of the component (50, 55). Projection exposure apparatus (1) according to one of Claims 8 - 11 , characterized in that the opening (33) of the auxiliary etching access (30) by means of a closure (34) is closed. Projection exposure system (1) according to Claim 12 Characterized in that the closure (34) with the component (50,55) is integrally connected. Projection exposure system (1) according to Claim 13 Is characterized in that the closure (34) with the component (50,55) bonded or bonded. Projection exposure system according to Claim 12 , characterized in that the closure (34) comprises a temperature sensor or flow sensor. Projection exposure system according to one of Claims 8 - 15 , characterized in that the component (50, 55) is a mirror with a mirror body (21). Projection exposure system according to one of Claims 8 - 16 , characterized in that the cavity structure (24) is adapted to realize different temperature fluid circuits.

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