WO2013174398A1

WO2013174398A1 - Reticle, reticle-chuck, reticle positioning system and optical system

Info

Publication number: WO2013174398A1
Application number: PCT/EP2012/002159
Authority: WO
Inventors: Moritz Becker; Dirk Heinrich Ehm; Stefan-Wolfgang Schmidt; Vera Butscher; Thomas Ihl
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2012-05-22
Filing date: 2012-05-22
Publication date: 2013-11-28

Abstract

A reticle (18) for use in a microlithographic projection exposure apparatus, comprises a reticle body (42) containing a pattern (16) and reticle coupling means (36), by means of which the reticle body (42) can be detachably coupled with a reticle-chuck (30). The reticle coupling means (36) are adapted such that the coupling of the reticle (18) with the reticle-chuck (30) can be effected by magnetic forces. Further, a Reticle-chuck (30) is provided which comprises a support unit (60) and chuck coupling means (38), by means of which a reticle (18) can be detachably coupled with the support unit (60). The chuck coupling means (38) are adapted such that the coupling of the reticle (18) with the support unit (60) can be effected by magnetic forces. Furthermore, a reticle positioning system (28) is described, wherein such a reticle (18) and such a reticle-chuck (30) are coupled to form a chuck-unit (32). Finally, an optical system having an illumination device (12) for illuminating an optical reticle (18) containing a pattern (16) and a projection objective (14) for imaging the reticle pattern (16) is provided with such a reticle positioning system (28).

Description

Reticle, reticle-chuck, reticle

positioning system and optical system

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reticle for use in a microlithographic projection exposure apparatus, comprising: a) a reticle body containing a pattern; b) reticle coupling means, by means of which the reticle

body can be detachably coupled with a reticle-chuck; and to a reticle-chuck for an optical reticle, in particular for positioning an optical reticle in a microlithographic projection exposure apparatus or an inspection apparatus, comprising : a) a support unit; b) chuck coupling means, by means of which a reticle can be detachably coupled with the support unit.

In addition, the invention relates to a reticle positioning system for positioning a reticle, in particular for positioning a reticle in a microlithographic projection exposure apparatus or a reticle inspection apparatus, wherein a reticle and a reticle-chuck are coupled to form a chuck- unit .

Furthermore, the invention relates to an optical system, in particular a microlithographic optical system, comprising: a) an illumination device for illuminating an optical reticle containing a pattern; b) a projection objective for imaging the reticle pattern; c) a reticle positioning system for positioning the optical reticle . 2. Description of Related Art

Microlithography (also referred to as photolithography or simply lithography) is a technology for the fabrication of semiconductor devices. The process of microlithography, in conjunction with the process of etching, is used to pattern features in thin film stacks that have been formed on a substrate, for example a silicon wafer. The wafer is coated with a photoresist which is a material that is sensitive to radiation .

The wafer with the photoresist on top is exposed to projection light in a projection exposure apparatus. The apparatus projects a reticle containing a pattern onto the photoresist so that the latter is only exposed at certain locations which are determined by the reticle pattern.

A projection exposure apparatus typically includes an illumination system for illuminating the reticle, a reticle stage for positioning, i.e. locating and orienting, the reticle, a projection objective and a wafer alignment stage for aligning the wafer coated with the photoresist. The illumination system illuminates a field on the reticle and the projection objective projects the reticle pattern within that field on the wafer with diminished proportions. The shorter the wavelength of the projection light, the smaller structures can be defined on the photoresist by means of the projection exposure apparatus. For that reason nowadays projection light in the spectral region of extreme ultraviolet (EUV) light having an average wave length of 13.5 nra is increasingly used.

Since a single reticle is used for the fabrication of a plurality of semiconductor devices and for illuminating a plurality of wafers, defects on the reticle and on its pattern will fatally effect the overall semiconductor production process. Therefore, a reticle must be produced with the utmost care as well as the precision and the quality of the reticle pattern must be carefully assessed prior to the use of the reticle. For the quality inspection for example, the inspection tool AIMS™ (Aerial Image Metrology System) of Carl Zeiss AG is established.

The pattern of the reticle defines the frontside of the reticle. To transfer a reticle into an EUV projection exposure apparatus or a microlithographic inspection apparatus, it is known in the art, for example, to firstly frontside fix the reticle to a baseplate of a so called EUV Inner Pod (EIP) , with the backside of the reticle remaining uncovered. Secondly, by means of a handling robot the EIP, which now supports the reticle, is moved close to an electrostatic chuck of an EUV projection exposure apparatus or an inspection apparatus with the reticle's backside facing the electrostatic chuck. The using of electrostatic chucks as a reticle handling apparatus is well known in the art as "E-chucking" .

When the reticle approaches the chuck, it is coupled with the chuck due to the force of attraction applied by the chuck. Finally, the EIP is removed and the reticle is held by the chuck, only. This transfer procedure is well known i the art.

The reticle and the chuck thus form a chuck-unit as a part of a reticle positioning system by which the reticle can be positioned in the EUV projection exposure apparatus or the inspection apparatus by moving and aligning the E-chuck.

Defects on the reticle can be based on several causes. For example, in both the production process and the inspection process, the reticle is in danger of being contaminated by particles. It has been found that one major contributor to reticle defect generation by particle contamination is the process chain of reticle handling, E-chucking and gripping of the reticle prior to its use and movement in an EUV projection exposure apparatus or an inspection apparatus.

In particular, when the reticle is coupled with the electro static chuck, the reticle contacts the chuck in a plane manner with a high pressure surface contact. This surface contact however can lead to a particle generation with the result of reticle defects, significantly decreasing the quality of the reticle pattern.

To reduce the risk of defects on the reticle, it is there^¬ fore a challenge to avoid such a particle contamination during the production and the inspection process.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provi de a reticle and a reticle-chuck as well as a reticle positioning system and an optical system as mentioned above which make it possible to establish a strong coupling of th reticle and the reticle-chuck avoiding a high pressure sur- face contact between the reticle and the reticle-chuck.

According to the invention, in view of the reticle and the reticle-chuck this object is achieved in that the reticle coupling means are adapted such that the coupling of the reticle with the reticle-chuck can be effected by magnetic forces and the chuck coupling means are adapted such that the coupling of the reticle with the support unit can be effected by magnetic forces.

The invention is based on the research that the reticle can securely be held in a distance from the reticle-chuck avoiding a direct surface contact between the reticle and the reticle-chuck, reducing the danger of a particle contami- nation of the reticle.

As to the reticle, effective magnetic forces can be established if the reticle coupling means comprise magnets, in particular magnets selected from the Sm-Co-Group or Nd-Fe-B- Group.

The reticle coupling means may comprise a number of magnetic burls rising from the reticle body to prevent the reticle body from contacting the reticle-chuck.

When the burls have a cross-section which includes outer edges, torgue effects on the reticle can be reduced. In particular, the burls are shaped like a tetrahedron, the base thereof being situated on the reticle body.

As to the reticle-chuck, effective magnetic forces can be established if the reticle coupling means comprise magnets units which are configured to work with magnets on the reticle . In one preferred embodiment, the magnet units are electromagnetic units which work with computer-aided controlling means, wherein the electromagnet units and the controlling means are configured to hold the reticle in a state of magnetic levitation allowing the compensation of shear forces and dynamical damping of vibrations.

In case that the chuck coupling means comprise a number of recesses, wherein each recess is adapted to accommodate at least a portion of a complementary burl of the reticle, the reticle body can effectively be prevented from contacting the reticle-chuck.

In one embodiment, the recesses have a cross-section which includes outer edges and are preferably shaped like a tetra hedron .

In view of the reticle positioning system, the object of th invention is achieved in that the positioning system comprises a reticle and a reticle-chuck including a number or all of the limitations as defined above.

Finally, in view of the optical system, the object of the invention is achieved in that such a reticle positioning system is provided. The optical system is preferably a microlithographic projection exposure apparatus or a micro- lithographic reticle inspection apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features and advantages of the present invention ma be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings in which: Figure 1 is a schematic perspective view of a projection exposure apparatus;

Figure 2 is a partial section through the projection

exposure apparatus shown in Figure 1;

Figure 3 is a partial phantom side view of a reticle

positioning system comprising a reticle and a reticle-chuck;

Figure 4A is a side view of the reticle;

Figure 4B is a view on a coupling side of the reticle

providing reticle coupling means;

Figures 5A and 5B are up-scaled views of a part of the

reticle coupling means;

Figure 6A is a side view of the reticle-chuck;

Figure 6B is a view on a coupling side of the reticle-chuck providing chuck coupling means;

Figure 7 is an illustration of a reticle handling process for transferring the reticle to the chuck.

DESCRIPTION OF PREFERRED EMBODIMENTS

As an example of an optical system, Figure 1 shows a perspective and highly simplified view of a microlithogra- phic projection exposure apparatus 10 which comprises an illumination system 12 and a projection objective 14.

The projection objective 14 images pattern 16 of fine features on a reticle 18 onto a light sensitive layer made from a photoresist on a substrate, for example on a silicon wafer 22.

The illumination system 12 generates an EUV-light beam 24 to illuminate the pattern 16 on the reticle 18. In case of the present embodiment, the illumination system 12 generates EUV-light having an average wavelength of 13.5 nm and a spectral half width of about 1 % such that the EUV-light beam 24 mainly defines wavelength between 13.36 nm and 13.64 nm.

The illumination system 12 illuminates a stationary field 26 on the bottom of the reticle 18 which may have the shape of a ring segment as illustrated. The projection objective 14 images a diminished image of the reticle pattern 16 within the illuminated field 26 onto the wafer 22.

The projection objective 14 is configured for a scan operation and the reticle 18 as well as the wafer 22 is moved in opposite directions during the projection process as indicated in Figures 1 and 2 by arrows PI and P2 at a speed that depends on the magnification of the projection objective 14.

The position, i.e. the location and the orientation, of the reticle 18 can be adjusted by means of a reticle positioning system 28 that comprises the reticle 18 and a reticle-chuck 30, simply referred to as chuck 30 hereinafter. The reticle 18 and the chuck 30 are operatively coupled to a movable chuck-unit 32 by means of a coupling device 34 which

comprises reticle coupling means 36 provided on the reticle 18 and chuck coupling means 38 provided on the chuck 30. The chuck unit 32 can be moved and oriented by driving means 40 which are schematically indicated in Figure 2, only.

The reticle 18 exhibits a reticle body 42 having a frontside 44 containing the pattern 18 and a backside 46 which is arranged opposing a coupling side 48 of the chuck 30 when the reticle 18 and the chuck 30 are operatively coupled. As can be seen in figure 3, the reticle 18 and the chuck 30 are operatively coupled such that a space 50 remains between the opposing surfaces 44, 46 of the reticle 18 and the chuck 30, respectively, avoiding a particle contamination of the reticle 18 caused by a direct contact of the reticle 18 and the chuck 30.

For that, the reticle coupling means 36 comprise a number of magnetic pins or burls 52 which rise from the backside 46 of the reticle body 42 (see figures 4 and 5) . In case of the present embodiment, four burls 52 are arranged on the reticle's backside 46 at the four edges of the reticle body 42. In general terms, at least three burls 52 are provided, but the number of burls 52 can be more than four.

The burls 52 extend in a direction perpendicular to the principal plane of the reticle body 42. In case of the present embodiment, the burls 52 are formed like a tetrahedron that is truncated at one top 54, only, the base thereof being situated on the reticle body 42. Thus, the burl 52 tapers in the direction away from the reticle 18. The truncated top 54 of the burl 52 is formed by a permanent magnet 56 which may be a magnet of the Sm-Co-Group or the Nd-Fe-B-Group, for instance.

As can be seen in figures 6A and 6B, the chuck coupling means 38 comprise four recesses 58 in a support unit 60 of the chuck 30 which is supposed to fix the reticle 18 (see figure 6) . The recesses 58 are complementary to the burls 52 of the reticle 18 in view of geometry and position. Thus, each recess 58 extends coaxial to a respective burl 52 and has a triangular cross-section. All of the recesses 58 taper in the direction towards the interior of the chuck 30, but are formed such that the burls 52 are not capable of being completely accommodated within an associated recess 58.

Therefore, even if the burls 52 of the reticle 18 are inserted into the recesses 58 of the chuck 30 as deep as possible, the space 50 between the reticle body 18 and the chuck 30 is always established. In general terms, each recess 58 is adapted to accommodate at least a portion of a particular complementary burl 52 of the reticle 18.

The chuck coupling means 38 additionally comprise four counter-magnet units 62. In the simplest case, a single counter-magnet unit 62 is a permanent magnet which is located within the interior of the support unit 60 adjacent to the ground of an associated recess 58 therein such that the polarity thereof is complementary to the polarity of the reticle magnets 56.

The counter-magnet units 62 substantially work as a magnetic gripper and, in the optimum configuration, are designed to hold the reticle 18 in a state of magnetic levitation allowing the compensation of shear forces and dynamical damping of vibrations. For this, the counter-magnet units 62 are preferably electromagnetic units which work with

appropriate computer-aided controlling means 64 which are shown in figure 2 in dashed lines, only.

The dimensions and the magnetic moment of the burls 52 may be varied and adapted to the counter-magnet units 62 as long as gravity and torques acting on the reticle can be

compensated by means of the counter-magnet units 62.

However, in general terms, the reticle coupling means 38, i.e. the burls 52 and the reticle magnets 56, and the chuck coupling means 38, i.e. the recesses 58 and the counter- magnet units 62, are adapted such that the coupling of the reticle 18 to the chuck 30 and the support unit 60 thereof, respectively, is effected by magnetic forces, when the burls 52 of the reticle 18 are inserted into the recesses 58 in the support unit 60 of the chuck 30. The reticle 18 is detachably coupled with the chuck 30 and the support unit 60 thereof, respectively.

Due to the triangular cross section of both the burls 52 and the recesses 58, a position stabilization of the reticle 18 coupled to the chuck 30 is provided. In general terms, the cross section of the burls 52 and the associated recesses 58 include outer edges to prevent a torque effect. The cross section of the burls 52 and the recesses 58 can also differ from a triangle hand may be rectangular or generally

polyangular .

On account of the space 50 between the reticle body 42 and the support unit 60 of the chuck 30, a surface contact to the reticle body 42 during individual reticle handling steps is avoided which in turn decreases the danger of reticle defect generation by particle contamination.

To give an example of the principle of reticle handling according to the present invention, figure 7 schematically illustrates the transfer of the reticle 18 into the

projection exposure apparatus 10, which however is not shown in figure 7.

In step A, the reticle 18 is fixed to a baseplate 66 of an EUV Inner Pod 68 (EIP) , with the backside 46 of the reticle 18 remaining uncovered. By means of a handling robot, which is not specifically shown, the EIP 68 is moved in the proximity of the chuck 30 with the reticle's backside 46 including the burls 52 facing the chuck. The EIP 68 is located and oriented such that the burls 52 of the reticle 18 are positioned coaxially to the recesses 58 of the chuck 30 (see step B) .

The EIP 68 is moved towards the chuck 30 and the burls 52 get into the recesses 58 to establish the magnetic coupling of the reticle 18 and the chuck 30 (see step C) , wherein the space 50 remains between the support unit 60 of the chuck 30 and the backside 46 of the reticle 18.

Thereupon, the EIP 68 is removed (step D) and the reticle 18 remains coupled to the chuck 30 (step E) which now can be further handled as known in the art.

Claims

Reticle for use in a microlithographic projection exposure apparatus, comprising: a) a reticle body (42) containing a pattern (16); b) reticle coupling means (36), by means of which the reticle body (42) can be detachably coupled with a reticle-chuck (30) , characterised in that c) the reticle coupling means (36) are adapted such that the coupling of the reticle (18) with the reticle- chuck (30) can be effected by magnetic forces.

The reticle of claim 1, characterised in that the reticle coupling means (36) comprise magnets (56) , in particular magnets selected from the Sm-Co-Group or Nd- Fe-B-Group .

The reticle of claim 1 or 2, characterised in that the reticle coupling means (36) comprise a number of

magnetic burls (52) rising from the reticle body (42) .

The reticle of one of claims 1 to 3, characterised in that the burls (52) have a cross-section which includes outer edges.

The reticle of claim 4, characterised in that the burls (52) are shaped like a tetrahedron, the base thereof being situated on the reticle body (42) .

Reticle-chuck for an optical reticle, in particular for positioning an optical reticle in a microlithographic projection exposure apparatus or an inspection

apparatus, comprising: a) a support unit (60); b) chuck coupling means (38), by means of which a

reticle (18) can be detachably coupled with the support unit (60), characterised in that c) the chuck coupling means (38) are adapted such that the coupling of the reticle (18) with the support unit (60) can be effected by magnetic forces.

The reticle-chuck of claim 6, characterised in that the reticle coupling means (38) comprise magnets units (62) which are configured to work with magnets (56) on the reticle (18) .

The reticle-chuck of claim 7, characterised in that the magnet units (62) are electromagnetic units which work with computer-aided controlling means (64), wherein the electromagnet units and the controlling means (64) are configured to hold the reticle (18) in a state of magnetic levitation allowing the compensation of shear forces and dynamical damping of vibrations.

The reticle-chuck of one of claims 6 to 8, characterised in that the chuck coupling means (38) comprise a number of recesses (58), wherein each recess (58) is adapted to accommodate at least a portion of a complementary burl (52) of the reticle (18) .

10. The reticle-chuck of claim 9, characterised in that the recesses (58) have a cross-section which includes outer edges .

11. The reticle-chuck of claim 10, characterised in that the recesses (58) are shaped like a tetrahedron.

12. Reticle positioning system for positioning a reticle, in particular for positioning a reticle in a microlitho- graphic projection exposure apparatus or a reticle inspection apparatus, wherein a reticle (18) and a reticle-chuck (30) are coupled to form a chuck-unit (32), characterised by a reticle (18) according to one of claims 1 to 5 and a reticle-chuck (30) according to one of claims 6 to 11.

13. Optical system, in particular a microlithographic

optical system, comprising: a) an illumination device (12) for illuminating an

optical reticle (18) containing a pattern (16); b) a projection objective (14) for imaging the reticle pattern (16) ; c) a reticle positioning system (28) for positioning the optical reticle (18), characterised in that d) the reticle positioning system (28) is a reticle

positioning system (28) according to claim 12.