TWM657713U - Euv microscope - Google Patents

Abstract

An extreme ultraviolet (EUV) microscope utilizing an EUV light source comprises an EUV light source, a monochromator module, a zone-plate, and a detector. A monochromator module receives EUV light from the EUV light source and generates an outgoing focused EUV beam, which is guided to impinge on a mask. The zone-plate includes a central stop, configured to receive the reflected EUV beam and allow a specific diffraction order of the reflected EUV beam to pass through. The detector is configured to receive the specific diffraction order of the reflected EUV beam from the mask and produce its image.

Description

Extreme ultraviolet microscope

This application relates to an extreme ultraviolet (EUV) microscope for use with an extreme ultraviolet (EUV) lithography mask used in the production of electronic chips.

Existing EUV mask imaging devices have been proposed to evaluate the quality of EUV masks. For example, U.S. Patent 6,738,135 describes a novel system for inspecting photolithography masks, which is sometimes referred to as a zone-plate microscope.

It is recognized that zone plate microscopes are highly chromatic and have a wavelength-dependent focal length. This characteristic results in poor resolution if not controlled. Since color effects are dependent on focal length, the shorter the focal length of these devices, the less important color effects become.

In US Patent 6,738,135, a sufficiently short focal length was achieved in order to handle the full typical bandwidth supported by Mo/Si multilayer optics. Although successful, certain drawbacks exist. Namely, the system operating distance of this prior art device is severely limited. Furthermore, the correction of the zone plate center aperture for filtering the zero order flare of the zone plate can be achieved without using it, because at short working distances, the center aperture of such a zone plate would occupy too large a portion of the total optical aperture to be feasible.

EUV microscope equipment for analyzing EUV masks in an efficient manner would constitute a significant advance in the field of electronics.

According to the present application, the above-mentioned problem is solved by using a monochromator module, which further narrows the bandwidth of the generated extreme ultraviolet light beam, thereby allowing a longer working distance.

The EUV mask imaging tool apparatus includes an EUV beam source or EUV emitting source as one of its elements. Such divergence may be produced by laser-generated plasma, discharge-generated plasma, etc. The EUV beam is transmitted to an optional collector that produces a first focused EUV beam. The optional collector is formed by two mirrors with tandem optical power. For example, the collector may include a planar mirror combined with an elliptical or aspherical mirror. In addition, the collector may take the form of a single mirror, such as a spherical, elliptical or aspherical mirror. The beam leaving the collector is used as an intermediate focus of subsequent elements of the apparatus of the present application.

A first intermediate focused extreme ultraviolet (EUV) light from an optional collector is passed to a monochromator module having an entrance and exit slit. This EUV light beam is forwarded to the monochromator module directly or through an intermediate focus produced by the optional collector. The entrance slit of the monochromator module can be eliminated if the intermediate focus size or the actual source size itself is smaller than the required entrance slit size. In some cases, the monochromator module itself may include grazing and/or near-vertical optics and ideally should include scattering elements. In essence, when used without a separate collector, the monochromator module operates as a concentrator and does not form an intermediate focus of the EUV light beam from the EUV light source. The light is then purified using a monochromator module to a λ/Δλ level of 350 or better. Thus, a second focused EUV light beam passes through the monochromator module.

The second focused, purified EUV light beam from the monochromator module is sent to an illumination module, or illuminator. The illumination module focuses the EUV light beam leaving the monochromator module and directs it toward the surface of the mask to be analyzed. Essentially, the illumination module controls the average and angular range of light that illuminates the mask. In some cases, the monochromator module also serves as an illuminator, eliminating the need for a separate illumination module.

The EUV light reflected from the mask passes through a zone plate. The zone plate may optionally include a center shield so that first order light is used without overlap of zero order light. The light passing through the zone plate is sent as an image to a detector such as a charge coupled device (CCD), which typically includes a screen on which the user can observe the EUV reflective properties of the mask. The image can be recorded for subsequent viewing and/or analysis by the user or automated computer software.

Therefore, a novel extreme ultraviolet (EUV) mask imaging tool is provided, which is characterized by using an asynchronous extreme ultraviolet light source that delivers partially coherent or incoherent extreme ultraviolet (EUV) light to an integrated monochromator module and a zone plate with a central aperture to mitigate zero-order flare.

Therefore, the object of this application is to provide a novel extreme ultraviolet (EUV) mask imaging tool that is capable of visualizing and evaluating extreme ultraviolet (EUV) lithography masks efficiently and economically.

Another object of the present application is to provide a novel EUV mask imaging tool that allows visualization and evaluation of EUV masks at a lower cost than prior art EUV imaging/inspection tools.

Another object of the present application is to provide a new extreme ultraviolet (EUV) mask imaging tool that includes a novel optical design with a shorter track length and smaller, more easily maintained imaging optics that are lacking in comparable prior art tools.

Another object of this application is to provide a new extreme ultraviolet (EUV) mask imaging tool that eliminates the color effects found in existing zone plate microscopes.

Another object of this application is to provide a novel extreme ultraviolet (EUV) mask imaging tool that uses a zone plate with a central aperture or shield to filter the zone plate zero-order flare.

Another object of this application is to provide a novel extreme ultraviolet (EUV) mask imaging tool for visualizing and evaluating extreme ultraviolet (EUV) lithography masks that is capable of measuring such masks with high accuracy and repeatability.

Another object of this application is to provide a novel extreme ultraviolet (EUV) mask imaging tool that is compatible with conventional mask blank transfer systems and can be operated in standard clean rooms typically used to manufacture semiconductor wafers.

As the description proceeds, the present application has other objects and advantages, especially as to its specific properties and features, which will become apparent.

See the following accompanying drawings, which further describe the application for which patent protection is claimed.

10: Tools and equipment

10A, 10B, 10C, 10D: Device

12: Extreme ultraviolet light source

14,22,32: Extreme ultraviolet light beam

16: Collector

18,36: Plane reflector

20,38: Reflector

23: Concentrator

24: Cylindrical grating

26: Entrance slit

28: Export gap

30: Monochrome module

34: Lighting module

40: Lighting beam

42: Zone plate

43: Center shield

44: Surface

45: Zero-order light

46:Mask

47: First-level light

48: Beam

49: Shadow

50: Detector

FIG1 is a schematic diagram depicting elements of an embodiment of the apparatus of the present application.

FIG2 is an isometric view showing an embodiment of a lighting module of the device of the present application.

FIG3 is a schematic diagram showing the position of the zone plate relative to the mask in the apparatus of the present application.

FIG4 is a schematic diagram showing the operation of the zone plate of the device of the present application.

FIG5 is a block diagram depicting the device of the present application.

Figure 6 is a block diagram showing another embodiment of the device of the present application.

Figure 7 shows another embodiment of the device of the present application.

Figure 8 shows another embodiment of the device of the present application.

Figure 9 shows another embodiment of the device of the present application.

For a better understanding of the present application, reference is made to the following detailed description of the preferred embodiment, which should be referenced to the above-mentioned accompanying drawings.

Various aspects of the present application will derive from the following detailed description, which should be read in conjunction with the accompanying drawings described above.

Referring to FIG. 1 , the reference numerals are used to describe the tool apparatus 10 as a whole. The tool apparatus 10 includes an extreme ultraviolet light source 12 as one of its components, and the extreme ultraviolet light source 12 may be a laser-generated plasma source. However, the extreme ultraviolet light source 12 may also come from a discharge-generated plasma source, etc. The following table shows the optical specifications of the tool apparatus 10:

Referring to FIG. 1 , an EUV light beam 14 from an EUV light source 12 is sent to a collector 16, which may be in the form of one or two or more mirrors with tandem optical power. The collector 16 generates a first focused EUV light beam 22. For example, the collector 16 of the device 10A of FIG. 5 may include a plane mirror 18 in series with the aspherical or elliptical mirror 20 of FIG. 5 . However, in the embodiment device 10B of FIG. 6 , the collector 16 may also include only a single aspherical or elliptical mirror 20.

1 , the first focused EUV light beam 22 from the collector 16 is transmitted to a monochromator module 30. The monochromator module 30 includes an entrance slit 26 and an exit slit 28 on either side. As such, the monochromator module 30 thus performs a focusing function for re-imaging the EUV light from the entrance slit 26 to the exit slit 28. In essence, the monochromator module 30 is used to clean up the received light to a level of λ/Δλ of 350 or better. The monochromator module 30 may take the form of any suitable device known in the art and, when used with the collector 16, may be obtained from Extreme Ultraviolet (EUV) Technologies, Inc. of Martinez, California as part number B151667. For example, the monochromator module 30 may externalize the monochromator module 30 having the concentrator 23 and the cylindrical grating 24 that causes the UV light to exit the exit slit 28. The second focused EUV light beam 32 passes through the exit slit 28.

The second extreme ultraviolet light beam 32 leaving the exit slit 28 travels to the illumination module 34 (illuminator) of FIG. 1 . In one form of the embodiment device 10A, the illumination module 34 may include a combination of the plane reflector 36 and the elliptical or aspherical reflector 38 in FIG. 7 . In the embodiment device 10C of FIGS. 2 and 8 , the illumination module 34 may also be formed by a single elliptical or aspherical reflector 38. The illumination module 34 is used both to focus the light leaving the monochromator module 30 and to limit the angular range of illumination. The illumination module 34 produces an illumination beam 40 having a width of about 10 μm on the mask 46 .

The functions of the monochromator module 30, the illumination module 34, and the collector 16 can be combined into a single entity, such as the monochromator module 30 in the embodiment 10D of FIG. 9. In this embodiment, the extreme ultraviolet light beam 32 from the monochromator module 30 is directly transmitted to the mask 46, so that the monochromator module 30 can produce an image without using the collector 16 or the illumination module 34.

Referring again to FIGS. 1 , 3 and 4 , the re-illumination beam 40 leaving the illumination module 34 passes through a zone plate 42, wherein the illumination beam 40 having the aforementioned 10 μm width is carried on the surface 44 of the mask 46, see also FIGS. 7 to 9 . FIG. 3 depicts the position of the zone plate 42 relative to the mask 46 and the mask 46 surface 44. The zone plate 42 is shown in its functional lens shape in FIG. 4 . The beam 48 reflected from the mask 46 and passing through the zone plate 42 is sent to the detector 50, which may be an imaging sensor, which may be a charge coupled device (CCD) camera cooled in a vacuum, as will be discussed in more detail below. Referring again to FIG. 4 , the zone plate 42 preferably includes a center shutter 43 to prevent overlap of the zero-order light 45 and the diffracted first-order light 47 of the zone plate 42. The center shutter 43 creates a shadow 49 between the zone plate 42 and the charge coupled device (CCD). It should be noted that the diffracted first-order light 47 of the zone plate 42 is a useful target imaging area of the beam 48 reflected from the mask 46.

Thus, when the detector 50 is a charge coupled device (CCD), the charge coupled device (CCD) is used as a detector to reveal any defects on the surface 44 of the mask 46. Such defects may appear as any anomalies on the screen associated with the charge coupled device (CCD). The charge coupled device (CCD) may take the form of a vacuum internally cooled CCD manufactured by Great Eyes of Berlin, Germany. Such a charge coupled device (CCD) has a pixel pitch range of 13μm×13μm.

Although the present application has been described in considerable detail in the aforementioned implementation scheme of the present application for the purpose of complete disclosure of the present application, it is obvious to those skilled in the art that many changes may be made to these details without departing from the spirit and principles of the present application.

10: Tools and equipment

12: Extreme ultraviolet light source

14,22,32: Extreme ultraviolet light beam

16: Collector

23: Concentrator

24: Cylindrical grating

26: Entrance slit

28: Export gap

30: Monochrome module

34: Lighting module

40: Lighting beam

42: Zone plate

44: Surface

46:Mask

48: Beam

50: Detector

Claims (17)

An extreme ultraviolet microscope, comprising: an extreme ultraviolet light source; a monochromator module, the monochromator module receiving extreme ultraviolet light from the extreme ultraviolet light source and generating an outgoing focused extreme ultraviolet light beam, the outgoing focused extreme ultraviolet light beam being guided to be carried on a mask for reflecting from the mask as a reflected extreme ultraviolet light beam; a zone plate, the zone plate including a central shield, the zone plate receiving the reflected extreme ultraviolet light beam and allowing a certain order of the reflected extreme ultraviolet light beam to pass; and a detector for receiving the certain order of the reflected extreme ultraviolet light beam from the mask and generating an image thereof. The extreme ultraviolet light microscope as described in claim 1 additionally comprises a collector for receiving extreme ultraviolet light from the extreme ultraviolet light source, the collector provides a focused extreme ultraviolet light beam, and the extreme ultraviolet light received by the monochromator module comprises the focused extreme ultraviolet light beam from the collector. An extreme ultraviolet light microscope as described in claim 1, which additionally comprises an illumination module, which intercepts and re-images the outgoing focused extreme ultraviolet light beam directed toward the mask from the monochromator module, and generates a re-imaged extreme ultraviolet light beam to the mask for reflection therefrom. An extreme ultraviolet microscope as described in claim 2, wherein the collector comprises two mirrors connected in series. An extreme ultraviolet microscope as described in claim 4, wherein the collector comprises a plane reflector and an elliptical reflector connected in series. An extreme ultraviolet microscope as described in claim 2, wherein the collector comprises an elliptical reflector. An extreme ultraviolet microscope as described in claim 2, wherein the collector comprises an aspherical reflector. An extreme ultraviolet microscope as described in claim 3, wherein the illumination module comprises two reflective mirrors connected in series. An extreme ultraviolet microscope as described in claim 3, wherein the illumination module comprises a plane reflector connected in series with an elliptical reflector. An extreme ultraviolet microscope as described in claim 3, wherein the illumination module includes an aspherical reflector. An extreme ultraviolet microscope as described in claim 3, wherein the illumination module comprises an elliptical reflector. An extreme ultraviolet microscope as described in claim 1, wherein the extreme ultraviolet light source comprises extreme ultraviolet light generated by generating a laser-generated plasma. An extreme ultraviolet light microscope as described in claim 1, wherein the extreme ultraviolet light source is generated by generating a discharge-generated plasma. The extreme ultraviolet light microscope as described in claim 12 additionally comprises a collector for receiving extreme ultraviolet light from the extreme ultraviolet light source, the collector provides a focused extreme ultraviolet light beam, and the extreme ultraviolet light received by the monochromator module comprises the focused extreme ultraviolet light beam from the collector. The extreme ultraviolet microscope as described in claim 13 additionally comprises a collector for receiving extreme ultraviolet light from the extreme ultraviolet light source, the collector provides a certain focused extreme ultraviolet light beam, and the extreme ultraviolet light received by the monochromator module comprises the certain focused extreme ultraviolet light beam from the collector. An extreme ultraviolet light microscope as described in claim 12, which additionally includes an illumination module that intercepts and re-images the outgoing focused extreme ultraviolet light beam directed toward the mask from the monochromator module and generates a re-imaged extreme ultraviolet light beam to the mask for reflection therefrom. An extreme ultraviolet light microscope as described in claim 13, which additionally includes an illumination module that intercepts and re-images the outgoing focused extreme ultraviolet light beam directed toward the mask from the monochromator module and generates a re-imaged extreme ultraviolet light beam to the mask for reflection therefrom.