DE102020203765A1 - Optical assembly; Projection exposure system and method for producing an optical assembly - Google Patents

Abstract

The invention relates to an optical assembly (40) for semiconductor lithography, in particular for a projection exposure system (1), with an optical element (41), a connection element (46) and a connecting element (44, 45) for connecting the optical element (41). with the connection element (46), a material of the optical element (41) and of the connecting element (44, 45, 60.x) having the same coefficient of thermal expansion.
The invention also relates to a method for producing an optical assembly (40) for semiconductor lithography, in particular for a projection exposure system (1), the optical assembly (40) in addition to an optical element for at least one connecting element (44, 45, 60.x) Comprises connection to a connection element (46), with the following process steps:
- Production of the optical element (41).
- Manufacture of the connecting element (44,45,60.x).
- Production of the connection element (46).
- Bonding of the connecting element (44,45,60.x) to the optical element (41) and the connection element.

Description

The invention relates to an optical assembly for a projection exposure system for semiconductor lithography, a projection exposure system and a method for producing such an optical assembly.

Projection exposure systems for semiconductor lithography are subject to extremely high demands on the image quality in order to be able to produce the desired microscopic structures as free of errors as possible. In a lithography process or a microlithography process, an illumination system illuminates a photolithographic mask. The light passing through the mask or the light reflected by the mask is projected by projection optics onto a substrate (for example a wafer) coated with a light-sensitive layer (photoresist) and attached to the image plane of the projection optics, in order to place the structural elements of the mask on the light-sensitive Transfer coating of the substrate. The requirements for the positioning of the image on the wafer and the intensity of the light provided by the lighting system are increased with each new generation, which leads to a higher heat load on the optical elements used in the projection optics and in the lighting system.

Usually, the optical elements, which are designed as mirrors in EUV projection exposure systems, that is to say in systems that are operated with electromagnetic radiation with a wavelength of less than 30 nm, are tempered by direct water cooling. For this purpose, the mirrors comprise recesses in the form of fluid channels through which tempered water flows and thereby lead the heat away from the mirror. The supply lines for the temperature control water are mechanically connected to the mirror, which can lead to deformations of the optically used surface of the mirror. In addition, vibrations can be transmitted from the outside to the mirror. The connection of the supply lines, which are usually sealed by means of seals or adhesives, lead to transient stresses which, in contrast to constant deformations, cannot be maintained structurally. Transient voltages and vibrations can negatively affect the image quality.

The object of the present invention is to provide a device which eliminates the disadvantages of the prior art described above. Another object of the invention is to provide a method for producing such a device.

These objects are achieved by a device and a method with the features of the independent claims. The subclaims relate to advantageous developments and variants of the invention.

An optical assembly according to the invention for semiconductor lithography, in particular for a projection exposure system, comprises an optical element, a connection element and a connection element for connecting the optical element to the connection element. A material of the optical element and the connecting element have the same coefficient of thermal expansion. This has the advantage that no stresses are formed due to differences in the coefficient of thermal expansion of the materials of the connected elements of the assembly and the resulting deformations can be avoided.

In particular, the material can comprise a material with a coefficient of thermal expansion of less than 10ppm / K, preferably less than 100ppb / K, particularly preferably less than 10ppb / K. The materials can usually only achieve such a low coefficient of thermal expansion in a selected temperature range that can be set during the production of the material, for example in a range from 20 to 25 ° Celsius. One example of such a material is Zerodur ^® . This has the advantage that, in the event of a temperature difference in the optical assembly, the connecting element introduces almost no deformations into the optical element of the assembly, which is designed, for example, as a mirror.

In one embodiment of the invention, the connecting element can be designed as a mechanical decoupling element. The decoupling element can decouple mechanical stimuli or disturbances that are introduced into the connection element from the mirror, so that only negligible mechanical stimuli and disturbances reach the optical element.

In a further embodiment of the invention, the connecting element can be designed as a fluid line. The fluid line can be designed in such a way that it cannot transmit any or almost no forces from the connection element to the mirror. For this purpose, the fluid line can comprise, for example, a bend or tapers.

Furthermore, at least one connecting element can be produced monolithically. As a result of the monolithic production of the connecting element, additional connecting points, such as adhesive bonds, can be avoided. the Monolithic production has the further advantage that the functional elements, such as the joints of the decoupling elements, can be produced with a low tolerance. It is also conceivable to manufacture the connecting element in individual parts and then join them together by bonding.

In particular, the connecting element can be connected to the optical element by bonding. The connecting elements can be made of the same material as a base body of the mirror. The connection by bonding can lead to a non-transient connection between the connecting element and the mirror, which connection comprises the same rigidity and mechanical strength as the mirror and the connecting element itself. By bonding, the two parts can behave as if they were made from one piece.

Furthermore, a material of the connection element can have the same coefficient of thermal expansion as the optical element and the connection element. The connection element can be designed, for example, as a connection plate which can comprise two parts arranged in layers. The part directed towards the mirror can be made of the same material as the mirror base body, so that the connection elements can also be connected to the connection plate by bonding. The second part can comprise metal, for example, in order to simplify the connection to a support frame and other add-on parts.

In addition, the connection element can comprise an interface to a fluid supply. The fluid supply can be designed as an inflow which opens into a distributor formed in the connection element. One or more fluid lines can be connected to the distributor on the side facing the mirror and thereby supply several fluid channels in the mirror base body with a fluid. In the case of a plurality of fluid lines, a plurality of inflows with fluids at different temperatures can alternatively be connected to the fluid channels through the connection element.

Furthermore, the connection element can comprise a coordinated mass damper. The formation of a two-mass oscillator with the optical element, connecting element and connection element can lead to vibrations that can be minimized with one or more coordinated mass dampers.

A projection exposure system according to the invention can comprise an optical assembly according to one of the embodiments described above.

• - Herstellung des optischen Elementes.
• - Herstellung des Verbindungselementes.
• - Herstellung des Anschlusselementes.
• - Bonden des Verbindungselementes mit dem optischen Element und des Anschlusselementes.

A method according to the invention for producing an optical assembly for semiconductor lithography, in particular for a projection exposure system, wherein the optical assembly comprises, in addition to an optical element, at least one connection element for connection to a connection element, comprises the following method steps:

• - Production of the optical element.
• - Manufacture of the connecting element.
• - Production of the connection element.
• - Bonding of the connecting element with the optical element and the connection element.

This has the advantage that errors in the production of the often complex geometries of the connecting elements have no effect on the yield in the production of the optical assembly.

In this case, the connecting element and the optical element, which can be designed as a mirror, and the connection element, which can be designed as a connection plate, for example, can be bonded directly. It is known from semiconductor production that glass wafers can be permanently connected to one another by direct bonding. The method is based on the formation of covalent oxygen bonds between the various glass surfaces. The process is best described by the equation X-Si-OH + HO-Si-X → X-Si-O-Si-X + H2O ↑, where X stands for the glass matrix of the two joining partners. The water content in direct bonding is very low, so that bonding can also be carried out in a vacuum environment. For the process, both surfaces are brought to a flatness of at least 20 nm and a roughness of 0.5 nm RMS by magneto-rheological and chemical polishing. Then both surfaces are activated. The actual joining process usually takes place in clean room conditions under normal air pressure, which means that the process can be flexibly adapted to different geometries of components and dimensions.

Furthermore, the connecting element can be bonded silicatically to the optical element and the connection element. The principle is the same as described above, with the water content in bonding being significantly higher than in direct bonding. Both processes can be carried out at temperatures in the range of 20 ° Celsius to 250 ° Celsius, so that the temperature can be far from the softening temperature of the material for the base body of the mirror.

Of course, it is also advantageous for the method described if a material of the optical element and the connecting element - in particular in a temperature range which corresponds to the usual operating temperatures in projection exposure systems - have the same coefficient of thermal expansion. Overall, the above-described elements can advantageously be connected to one another with the method described above.

• 1 den prinzipiellen Aufbau einer EUV-Projektionsbelichtungsanlage, in welcher die Erfindung verwirklicht sein kann,
• 2 den prinzipiellen Aufbau einer DUV-Projektionsbelichtungsanlage, in welcher die Erfindung verwirklicht sein kann,
• 3 eine erste Ausführungsform einer erfindungsgemäßen Baugruppe,
• 4a,b Schnittansichten der ersten Ausführungsform der Baugruppe,
• 5a,b Detailansichten von Verbindungselementen,
• 6 eine weitere Ausführungsform der erfindungsgemäßen Baugruppe, und
• 7 ein Flussdiagramm zu einem erfindungsgemäßem Herstellverfahren.

In the following, exemplary embodiments and variants of the invention are explained in more detail with reference to the drawing. Show it

• 1 the basic structure of an EUV projection exposure system in which the invention can be implemented,
• 2 the basic structure of a DUV projection exposure system in which the invention can be implemented,
• 3 a first embodiment of an assembly according to the invention,
• 4a, b Sectional views of the first embodiment of the assembly,
• 5a, b Detailed views of fasteners,
• 6th a further embodiment of the assembly according to the invention, and
• 7th a flowchart for a manufacturing method according to 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. A lighting system of the projection exposure machine 1 points next to a light source 3 an illumination optics 4th for illuminating an object field 5 in one object level 6th on. One by the light source 3 generated EUV radiation 14th as useful optical radiation is by means of an in the light source 3 Integrated collector aligned in such a way that it is in the area of an intermediate focus plane 15th passes through an intermediate focus before moving onto a field facet mirror 2 meets. According to the field facet mirror 2 becomes the EUV radiation 14th from a pupil facet mirror 16 reflected. With the help of the pupil facet mirror 16 and an optical module 17th with mirrors 18th , 19th and 20th become field facets of the field facet mirror 2 in the object field 5 pictured.

A is illuminated in the object field 5 arranged reticle 7th , that of a reticle holder shown schematically 8th is held. A projection optics shown only schematically 9 serves to map the object field 5 in an image field 10 in an image plane 11 . A structure is imaged on the reticle 7th onto a light-sensitive layer in the area of the image field 10 in the image plane 11 arranged wafers 12th , that of a wafer holder also shown in detail 13th is held. The light source 3 can emit useful radiation in particular in a wavelength range between 1 nm and 120 nm.

In 2 is an exemplary projection exposure system 21 shown, in which the invention can also be used. The projection exposure system 21 is used to expose structures on a substrate coated with photosensitive materials, which generally consists predominantly of silicon and is used as a wafer 22nd is referred to, for the production of semiconductor components, such as computer chips.

The projection exposure system 21 essentially comprises a lighting device 23 , a reticle holder 24 for receiving and exact positioning of a mask provided with a structure, a so-called reticle 25th , through which the later structures on the wafer 22nd be determined, a wafer holder 26th for holding, moving and exact positioning of this wafer 22nd and an imaging device, namely a projection lens 27 , with several optical elements 28 and mirrors 30th that over sockets 29 in a lens housing 30th of the projection lens 27 are held.

The basic functional principle provides that the reticle 25th introduced structures on the wafer 22nd be mapped; the mapping is usually made smaller.

The lighting device 23 provides one for imaging the reticle 25th on the wafer 22nd required projection beam 31 in the form of electromagnetic radiation, this being in particular in a wavelength range between 100 nm and 300 nm. A laser, a plasma source or the like can be used as the source for this radiation. The radiation is in the lighting device 23 Shaped via optical elements in such a way that the projection beam 31 when hitting the reticle 25th has the desired properties in terms of diameter, polarization, shape of the wavefront and the like. About the projection beam 31 becomes an image of the reticle 25th generated and from the projection lens 27 correspondingly reduced on the wafer 22nd transferred, as already explained above. The reticle 25th and the wafer 22nd are moved synchronously, so that areas of the reticle are practically continuous during a so-called scanning process 25th on corresponding areas of the wafer 22nd can be mapped. The projection lens 27 has a large number of individual refractive, diffractive and / or reflective optical elements 28 such as lenses, mirrors, prisms, end plates and the like, these being optical elements 28 can be actuated, for example, by one or more of the actuator arrangements described here.

3 Figure 3 shows a first embodiment of the invention in which an optical assembly 40 is shown. The assembly 40 includes one as a mirror 41 formed optical element, connecting elements 44 , 45 and one as a connection plate 46 formed connection element. The mirror 41 comprises a base body 42 , which is made of a material with a coefficient of thermal expansion that generates almost no deformation due to a change in temperature in a predetermined temperature range of 20 to 25 ° Celsius. The mirror 41 is with a coating 43 to reflect on the in 1 and 2 projection exposure systems shown 1 , 21 used light 14th , 31 for mapping the structure of the reticle 7th , 25th on the wafer 12th , 22nd coated. At that of the coating 43 facing away from the underside of the base body 42 are those as feathers 44 and pipes 45 formed connecting elements arranged. The pipes 45 each have an arc that increases the rigidity of the tubes 45 in the main direction of action of the springs 44 reduced, thereby reducing the influence of the rigidity of the pipes 45 on the overall stiffness of the fasteners 44 , 45 is reduced. The other ends of the fasteners 44 , 45 are with the connection plate 46 tied together. The fasteners 44 , 45 and a first part 47 the connection plate 46 with which the fasteners 44 , 45 are made of the same material as the mirror body 42 and therefore have the same coefficient of thermal expansion as this one. The fasteners 44 , 45 are with the main body 42 and the first part 47 the connection plate 46 connected by a bonding process, such as direct or silicate bonding. The connection plate 46 includes in addition to the first part directed towards the rear of the mirror 47 a second part 48 which one on the one from the mirror 41 facing away from the first part 47 is arranged and is connected to this by an adhesive; soldering or another type of connection is also conceivable here. The second part 48 is made of a metal and includes the interface with an inflow 49 and a drain 50 a fluid supply, not shown. On the underside of the second part facing away from the mirror 48 is next to the inflow 49 and the drain 50 also a coordinated mass damper 51 arranged through which the vibrations between the mirror 41 and the connection plate 46 be reduced.

In 4a is a section through the in 3 illustrated optical assembly 40 shown. The cutting plane is selected in such a way that the path of a fluid from the inflow 49 via the one in the connection plate 46 trained distributor 56 and a pipe 45 into one in the main body 42 of the mirror 41 trained fluid channel 58 is made clear. After the fluid enters the fluid channel 58 has flowed through it, it is via a pipe 45 , one also in the connection plate 46 trained collector 57 and the drain 50 discharged again and fed to a device, not shown, for conditioning the fluid. In the 4a are also the connection points created by the bonding 52 , 53 , 54 , 55 between mirror body 42 and pipe 45 or spring 44 and the connection plate 46 and the pipe 45 or the spring 44 shown. The interfaces correspond in terms of mechanical stability and thermal loading capacity to that of the solid material, so that the optical assembly 40 behaves mechanically and thermally as if made from one part. On the underside of the connection plate 46 is a cone 59 formed on which the tuned mass oscillator 51 is arranged.

4b shows a section through the connection plate 46 , with the cutting plane at the level of the connection of the manifold 56 and the collector 57 with the pipes 45 lies. On the left of the 4b is the distributor 56 shown, which on the one hand with the inflow 49 (shown in dashed lines because it is arranged in a lower level) and on the other hand with the pipes 45 which the in 4a illustrated fluid channels 58 with the distributor 56 connect, connected. On the right side of the 4b is the collector 57 shown, also with the pipes 45 and the drain 50 (shown in dashed lines because it is arranged in a lower level) and is connected by the fluid channels 58 The flowed fluid collects and drains 50 supplies the device for conditioning.

the 5a and 5b show detailed views of decoupling elements 60.x, which in place of the in the 3 and 4a illustrated springs 44 the mirror 41 from the connection plate 46 can decouple.

This in 5a shown decoupling element 60.1 comprises a connection element 61 , which each have a joint 64.1 with two leaf springs 63.1 connected is. The leaf springs 63.1 are arranged tilted at an angle to each other and at their other end also via a joint 64.1 with an intermediate element 65.1 tied together. On the opposite side of the Intermediate element 65.1 are again 2 leaf springs 63.2 arranged by 90 ° to the leaf springs 63.1 are rotated and have a joint 64.1 with the intermediate element 65.1 are connected. Again through a joint 64.1 are the leaf springs 63.2 at its other end with a connection element 62 for connection to the mirror body 42 tied together. The connection element 61 includes a connection surface 67 for connection to the in 3 connection plate shown 46 and the connection element 62 includes a connection surface 68 for connection to the mirror body 42 .

This in 5b shown decoupling element 60.2 includes like that in the 5a shown decoupling element 60.1 a connection element 61 with the interface 67 , an intermediate element 65.2 and a connector 62 with the interface 68 . The Elements 61 , 62 , 65.2 are each with a joint 64.2 connected, with the joints 64.2 are also arranged rotated 90 ° to each other. Both decoupling elements 60.1 , 60.2 can through the design of the joints 64.1 , 64.2 and in the case of decoupling element 60.1 the leaf springs 63.1 , 63.2 and their angle to each other to a certain rigidity and thus decoupling effect between the connection plate 46 and mirror 41 be interpreted.

6th shows another embodiment of the tubes 45 in the optical assembly 40 with mirror 41 and connection plate 46 . The pipes 45 are to the connecting surfaces 52 , 54 arranged tilted, so that the overall height of the optical assembly 40 compared to the in 3 illustrated optical assembly 40 is reduced. For decoupling are in the pipes 45 Tapers 66.1 , 66.2 formed which increases the rigidity of the pipe 45 in the area of the tapers 66.1 , 66.2 and thus to a decoupling between the connection plate 46 and mirror body 42 to lead. The decoupling elements 60.x are only shown as simple bars.

7th shows one possible method for manufacturing an optical assembly 40 for semiconductor lithography, in particular for a projection exposure system 1 , the optical assembly 40 next to an optical element 41 at least one connecting element 44 , 45 , 60.x for connection to a connection element.

In a first process step 71 becomes the optical element 41 manufactured.

In a second process step 72 becomes the fastener 44 , 45 , 60.x produced.

In a third process step 73 becomes the connection element 46 manufactured.

In a fourth process step 74 becomes the fastener 44 , 45 , 60.x with the optical element 41 and the connection element 46 joined by bonding.

It goes without saying that not all steps of the method described above have to be carried out in the specified order. In particular the steps 1 until 3 can be done in parallel or in a different order.

List of reference symbols

1

Projection exposure system

2

Field facet mirror

3rd

Light source

4th

Lighting optics

5

Object field

6th

Object level

7th

Reticle

8th

Reticle holder

9

Projection optics

10

Field of view

11

Image plane

12th

Wafer

13th

Wafer holder

14th

EUV radiation

15th

Interfield focus plane

16

Pupil facet mirror

17th

module

18th

mirrors

19th

mirrors

20th

mirrors

21

Projection exposure system

22nd

Wafer

23

Lighting optics

24

Reticle holder

25th

Reticle

26th

Wafer holder

27

Projection lens

28

optical element

29

Frames

30th

Lens housing

31

Projection beam

40

optical assembly

41

mirrors

42

Base body

43

Coating

44

feather

45

pipe

46

Connection element, connection plate

47

first bondable part

48

second part

49

inflow

50

Drain

51

coordinated mass oscillator

52

Mirror / pipe connection surface

53

Connection surface mirror / decoupling element

54

Connection surface connection element / pipe

55

Connection surface connection element / decoupling element

56

Distributor

57

Collector

58

Fluid channel

59

Cones

60.1, 60.2

Decoupling element

61

Connection element Connection plate

62

Connection element mirror

63.1, 63.2

Leaf spring

64.1, 64.2

joint

65.1, 65.2

Intermediate element

66.1, 66.2

rejuvenation

67

Connection surface for connection plate

68

Connection surface for mirrors

71

Process step 1

72

Step 2

73

Step 3

74

Process step 4th

Claims (15)

Optical assembly (40) for semiconductor lithography, in particular for a projection exposure system (1), with an optical element (41), a connection element (46) and a connection element (44, 45) for connecting the optical element (41) to the connection element ( 46), characterized in that a material of the optical element (41) and of the connecting element (44,45,60.x) have the same coefficient of thermal expansion. Optical assembly (40) according to Claim 1 , characterized in that the material comprises a material with a coefficient of thermal expansion of less than 10ppm / K, preferably less than 100ppb / K, particularly preferably less than 10ppb / K. Optical assembly (40) according to one of the Claims 1 or 2 , characterized in that the connecting element (44,45,60.x) is designed as a mechanical decoupling element (44,60.x). Optical assembly (40) according to one of the Claims 1 or 2 , characterized in that the connecting element (44,45,60.x) is designed as a fluid line (45). Optical assembly (40) according to one of the preceding claims, characterized in that at least one connecting element (44, 45, 60.x) is produced monolithically. Optical assembly (40) according to one of the preceding claims, characterized in that the connecting element (44, 45, 60.x) is connected to the optical element (41) by bonding. Optical assembly (40) according to one of the preceding claims, characterized in that a material of the connection element (46) has the same coefficient of thermal expansion as the optical element (41) and the connecting element (44, 45, 60.x). Optical assembly (40) according to one of the preceding claims, characterized in that the connection element (46) comprises an interface (49, 50) to a fluid supply. Optical assembly (40) according to Claim 8 , characterized in that the connecting element (44, 45, 60.x) connects the interface (49, 50) to a fluid channel (58) present in the optical element (41). Optical assembly (40) according to one of the preceding claims, characterized in that the connection element (46) comprises a coordinated mass damper (51). Projection exposure system (1) with an optical assembly according to one of the Claims 1 until 10 . A method for producing an optical assembly (40) for semiconductor lithography, in particular for a projection exposure system (1), the optical assembly (40) in addition to an optical element at least one connecting element (44, 45, 60.x) for connection to a connection element ( 46), with the following procedural steps: - Production of the optical element (41), - Production of the connecting element (44,45,60.x), - Production of the connection element (46), - Bonding of the connecting element (44,45,60.x) to the optical element (41) and the connection element. Procedure according to Claim 11 , characterized in that the connecting element (44,45,60.x), the optical element (41) and the connection element (46) are bonded directly. Procedure according to Claim 12 , characterized in that the connecting element (44, 45, 60.x), the optical element (41) and the connection element (46) are bonded using silicate. Method according to one of the preceding Claims 12 - 14th , characterized in that a material of the optical element (41) and the connecting element (44,45,60.x) have the same coefficient of thermal expansion.

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