GB2414858A

GB2414858A - A workpiece or specimen support assembly for a charged particle beam system

Info

Publication number: GB2414858A
Application number: GB0412430A
Authority: GB
Inventors: Tao Zhang
Original assignee: Nanobeam Ltd
Current assignee: Nanobeam Ltd
Priority date: 2004-06-03
Filing date: 2004-06-03
Publication date: 2005-12-07
Also published as: WO2005119363A3; GB0412430D0; TW200603263A; WO2005119363A2

Abstract

A workpiece or specimen support assembly for an ion or electron beam system, e.g. an electron beam lithography system or a scanning electron beam microscope, comprises a chuck 2 and a chuck support 3. The chuck 2 has three feet 6,7,8 and the chuck support 3 has three radial grooved tracks 22,23,24 pointing to a common origin. The feet 6,7,8 may be in the form of spherical segments. The tracks 22,23,24 receive respective feet 6,7,8 and allow relative movement between the chuck 2 and the support 3 should they expand differentially. In an alternative arrangement, there are radial tracks on the chuck 2 which receive posts upstanding from the support 3. The support 3 may be an x-y positioning stage or, as shown, a laser interferometer mirror assembly comprising mirror blocks 14,15.

Description

241 4858 - 1 Assembly for supporting a workpiece or specimen in a charged

particle beam system

Description

The present invention relates to an assembly for supporting a workpiece or specimen in a charged particle beam system.

In an electron beam lithography system, an assembly for supporting a workpiece comprises a chuck and a chuck support usually in the form of a laser interferometer mirror assembly. The assembly is mounted on an x-y positioning stage.

The chuck is typically formed from a ceramic and the mirror assembly is formed from a glass. Because the chuck and mirror assembly are made of different materials, they have different thermal expansion characteristics. When a workpiece is loaded into the system, the chuck and mirror assembly warm up and expand at different rates. Thus, the chuck can move relative to the mirror assembly. This introduces unknown, time-varying offset errors. One solution is to load the workpiece and delay exposure until the chuck and mirror assembly thermally stabilise. However, this practice greatly reduces throughput.

The present invention seeks to provide an assembly for supporting a workpiece or specimen in a charged particle beam system, such as in an electron beam lithography system.

According to a first aspect of the present invention there is provided an assembly for supporting a workpiece or specimen in a charged particle beam system, the assembly comprising a chuck and a chuck support, the chuck having at least three feet and the chuck support having at least three radial tracks pointing to a common origin, the feet and tracks arranged such that when the chuck is placed on the chuck do support, at least three of said tracks each receives a respective foot.

If the chuck expands or contracts relative to the chuck support, each foot can travel radially along a respective track, thus helping to prevent rotation of the chuck - 2 relative to the chuck support. Furthermore, the common origin can be used as a reference point when compensating for thermal expansion.

The chuck may have three feet. The chuck may have at least four feet, but at least s one foot may not provide support when said chuck is placed on said chuck support.

Three feet may be equidistant from one another. This can have the advantage of providing mechanical stability.

The feet may be bonded to the chuck, for example they may be brazed or vacuum brazed to the chuck. The chuck may be formed from a ceramic, such as alumina and the feet may be formed from an alloy or ceramic.

Each foot may be in the form of a spherical segment. Each foot may be in the form of a hemisphere. Each foot may have a spherical radius between 1 and 3 mm. Each foot may have a height between 1 and 5 mm. The feet may be substantially identical.

The chuck support may have three tracks. The chuck support may have at least four tracks, but at least one track may not provide support when said chuck is placed on said chuck support.

The tracks may comprise grooves. The grooves may be 'V' shaped in crosssection.

The grooves may be cut into respective pillars upstanding from a surface of the 2s chuck support or may be cut into a surface of the chuck support. The tracks may be inclined.

The chuck support may be an interferometer mirror assembly.

According to a second aspect of the present invention there is provided an assembly for supporting a workpiece in a charged particle beam system, the assembly comprising a chuck and a chuck support, the chuck having at least three radial tracks pointing to a common origin and the chuck support having at least three . - 3 posts, the posts and tracks arranged such that when the chuck is placed on the chuck support, at least three of the posts is each received by a corresponding track.

According to a third aspect of the present invention there is provided a chuck for supporting a workpiece or specimen in a charged particle beam system, the chuck having at least three, substantially identical feet, each foot having the form of a spherical segment vacuum brazed to the chuck.

According to a fourth aspect of the present invention there is provided a support for a chuck for supporting a workplace or specimen in a charged particle beam system, the chuck support having at least three radial tracks pointing to a common origin.

An embodiment of the present invention will now be described with reference to the accompanying drawings in which: Figure I is an exploded view of a support and laser interferometer mirror assembly in accordance with an aspect of the present invention; Figure 2 is a side view of a part of the chuck shown in Figure 1; Figure 3 is a plan view of a chuck shown in Figure 1; Figure 4 is a plan view of the chuck support shown in Figure 1; Figure 5 is a side view of the a part of the chuck support shown in Figure 1; and Figure 6 is a side view of a part of the chuck and a part of the chuck support when the chuck is placed on the chuck support as illustrated in Figure 1.

Referring to Figure 1, an assembly 1 for supporting a workpiece or specimen in a charged particle beam system includes a chuck 2 and a chuck support 3 in the form of a laser interferometer mirror assembly. The assembly 1 is mounted on an x-y positioning stage (not shown), which has been omitted from the drawing for clarity.

In this example, the assembly 1 is used to support a workpiece, such as semiconductor wafer (not shown), in an electron beam lithography system (not shown). However, the assembly 1 may be used to support a workpiece in other charged particle beam systems, such as an ion beam system. The assembly 1 can also be used to support a specimen to be inspected in a microscope, such as a scanning electron beam microscope.

The chuck 2 is in the form of a flat disk having a first flat face 4, i.e. a top surface, s for receiving a workpiece (not shown) and a second flat face 5, i.e. an underside surface. The chuck 2 is substantially circular and has a diameter of about 200 mm and a thickness of about 3 to 6 mm. In this example, the chuck has a thickness of 5 mm. The chuck 2 has three feet or pads 6, 7, 8, attached to its second flat surface 5.

The chuck 2 is formed from alumina, although other ceramics and some nonmagnetic alloys or metals, such as titanium (Ti), may be used.

Referring also to Figure 2, each foot 6, 7, 8 is in the form of a spherical segment fused or bonded to the second flat surface 5 of the chuck 2.

By "spherical segment" we mean a solid defined by the intersection of a plane with a sphere. In this example, the larger of two solids defined by the intersection of a plane with a sphere is used. However, a hemisphere can be used. A frustum, such as a frusto-sphere, i.e. a solid defined by the intersection of two parallel planes with a sphere, or a non-spherical shape, such as a cone or frusto-cone, may also be used.

The feet 6, 7, 8 are formed from tungsten carbide (\Y1C) and are brazed to the chuck 2 in a vacuum at a temperature below the melting point of the materials forming the feet 6, 7, 8 and the chuck 2. Other alloys, a metal or a ceramic may be used. The alloy, metal or ceramic may have substantially the same coefficient of thermal expansion as the ceramic forming the chuck 2. Those skilled in the art will appreciate that a suitable material, as well as a process for brazing the feet to the chuck, may be found by routine experiment. The feet 6, 7, 8 may be bonded to the chuck 2 using other methods, such as by fusing or gluing.

The feet 6, 7, 8 have a spherical radius, r, of 2 mm with a tolerance of less than 10 m. However, the spherical radius, r, may be between 1 mm and 3 mm. The tolerance may be less than 10 1lm. The feet 6, 7, 8 have a thickness, I, of 2.8 mm, although the thickness, I, may be between 1 mm and 5 mm. The feet 6, 7, 8 are not set into recesses or holes in the chuck 2, although they may be set into recesses or holes.

Referring to Figure 3, the feet 6, 7, 8 define a circle 9 having a centre 10 which may s or may not be concentric with the geometric centre 11 of the chuck 2. The feet 6, 7, 8 are not arranged equidistantly from one another, although they may be.

The chuck 2 may be provided with further feet (not shown), although the further feet may not provide support. For example, more than one set of feet may be provided to enable the chuck 2 to be placed on different chuck supports.

Referring to Figure 4, the interferometer mirror assembly 3 comprises a base 12 with an upper surface 13 and first and second mirror blocks 14, 15. The first and second mirror blocks 14, 15 are mounted on the upper surface 13 using respective pairs of supports 16, 17, 18, 19 using glue. The mirror blocks 14, 15 have respective outwardly-facing side surfaces 20, 21 which provide orthogonal mirrors for positioning the mirror assembly 3 using laser interferometry. The mirror assembly 3 may comprise an integral base and mirror blocks, machined from a single block.

On the upper surface 13, the interferometer mirror assembly 3 includes three radial tracks 22, 23, 24, which point to a common origin 25. The tracks 22, 23, 24 are in the form of grooves which are 'V'-shaped in transverse cross section formed on top of rectangular pillars 26, 27, 28 upstanding from the upper surface 13. The grooves 23, 24, 25 have perpendicular sides and a flat bottom, although other 'V'- groove arrangements can be used. The pillars 26, 27, 28 have a height of 10 mm and a tolerance of less than 10 m. However, the pillars 26, 27, 28 may be taller or shorter. The tolerance may be less than 1,um.

Referring to Figure 5, the pillars 26, 27, 28 each have a depending post 29, 30, 31 which slot into respective cylindrical holes 32, 33, 34 in the base 12 and fixed using glue. However, the pillars 26, 27, 28 may be integrally formed with the base 12. - 6

Alternatively, the pillars 26, 27, 28 may be omitted and the grooves 22, 23, 24 cut into the surface 13 of the base 12.

The grooves 22, 23, 24 are parallel, i.e. horizontal, with the surface 13 of the mirror s assembly 3. However, the grooves 22, 23, 24 may be inclined or ramped, for example becoming lower with an increase in radius. The grooves 22, 23, 24 each have a length of 10 mm, a width of 3 mm and a tolerance of better than 20 m.

The tolerance may be better than 10,um. Other tracks shapes, such as cylindrical troughs, may be used. The interferometer mirror assembly 3 is formed from Zerodur (RTM), although it may be formed from another glass having a low coefficient of expansion characteristics.

Referring to Figures 1 and 6, the feet 6, 7, 8 and the grooves 22, 23, 24 are arranged such that the feet 6, 7, 8 sit in respective grooves 22, 23, 24 when the chuck 2 is placed on the mirror assembly 3.

If the chuck 2 expands or contracts relative to the interferometer mirror assembly 3, the feet 6, 7, 8 slide or travel radially in their respective grooves 22, 23, 24 and the chuck 2 does not rotate relative to the interferometer mirror assembly 3.

Furthermore, the common origin 25 provides a reference point which can be used to measure and/or to determine compensation for movement arising from thermal expansion.

It will be appreciated that many modifications may be made to the embodiment 2s hereinbefore described. For example, feet may be provided on the mirror assembly and the tracks may be provided on the chuck. The chuck support need not be a mirror assembly and may be, for example, an x-y positioning stage. 4 l - 7

Claims

Claims 1. An assembly for supporting a workpiece or specimen in a charged

particle beam system, the assembly comprising a chuck and a chuck support, said chuck s having at least three feet and said chuck support having at least three radial tracks pointing to a common origin, said feet and tracks arranged such that when said chuck is placed on said chuck support, at least three of said tracks each receive a respective foot.
2. An assembly according to claim 1, wherein said chuck has three feet.
3. An assembly according to claim 1, wherein said chuck has at least four feet.
4. An assembly according to claim 3, wherein at least one foot does not provide support when said chuck is placed on said chuck support.
5. An assembly according to any preceding claim, wherein three feet are equidistant from one another.
6. An assembly according to any preceding claim, wherein said feet are bonded to said chuck.
7. An assembly according to any preceding claim, wherein said feet are brazed to said chuck.
8. An assembly according to any preceding claim, wherein said feet are vacuum brazed to said chuck.
9. An assembly according to any preceding claim, wherein said chuck is formed from a ceramic.
10. An assembly according to any preceding claim, wherein said chuck is formed from alumina. - 8
11. An assembly according to any preceding claim, wherein said feet are formed from an alloy.
12. An assembly according to any preceding claim, wherein said feet are formed from a ceramic.
13. An assembly according to any preceding claim, wherein each foot is in the form of a spherical segment.
14. An assembly according to claim 10, wherein each foot is in the form of a hemisphere.
15. An assembly according to any preceding claim, wherein each foot has a spherical radius less than 2 mm.
16. An assembly according to any preceding claim, wherein each foot has a height less than 3 mm.
17. An assembly according to any preceding claim, wherein said feet are substantially identical.
18. An assembly according to any one of claims 1 to 17, wherein said chuck support has three radial tracks pointing to a common origin.
19. An assembly according to any one of claims 1 to 17, wherein said chuck support has at least four radial tracks pointing to a common origin.
20. An assembly according to claim 19, wherein at least one foot does not provide support when said chuck is placed on said chuck support.
21. An assembly according to any preceding claim, wherein said tracks comprise grooves. - 9 -
22. An assembly according to claim 21, wherein said grooves are 'V' shaped in cross-section.

s
23. An assembly according to claim 21 or 22, wherein said grooves are cut into respective pillars upstanding from a surface of the chuck support.
24. An assembly according to claim 21 or 22, wherein said grooves are cut into a surface of said chuck support.
25. An assembly according to any preceding claim, wherein said tracks are inclined.
26. An assembly according to any preceding claim, wherein said chuck support is a interferometry mirror assembly.
27. An assembly substantially as hereinbefore described with reference to Figures 1 to 6 of the accompanying drawings.
28. An assembly for supporting a workpiece or specimen in a charged particle beam system, the assembly comprising a chuck and a chuck support, said chuck having at least three radial tracks pointing to a common origin and said chuck support having at least three posts, said posts and tracks arranged such that when said chuck is placed on said chuck support, at least three of said posts is each received by a respective track.
29. A chuck for supporting a workpiece or specimen in a charged particle beam system, said chuck having at least three substantially identical feet, each foot having the form of a spherical segment and being bonded to the chuck.
30. A support for a chuck for supporting a workpiece or specimen in a charged particle beam system, said chuck support having at least three radial tracks pointing to a common orlgm.