EP0257038A1 - Method and apparatus for the production of high resolution images - Google Patents

Method and apparatus for the production of high resolution images

Info

Publication number
EP0257038A1
EP0257038A1 EP19860903512 EP86903512A EP0257038A1 EP 0257038 A1 EP0257038 A1 EP 0257038A1 EP 19860903512 EP19860903512 EP 19860903512 EP 86903512 A EP86903512 A EP 86903512A EP 0257038 A1 EP0257038 A1 EP 0257038A1
Authority
EP
European Patent Office
Prior art keywords
production
high quality
hologram
laser
radiation
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19860903512
Other languages
German (de)
French (fr)
Inventor
Gillian Margaret Davis
Ian Norman Ross
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Publication of EP0257038A1 publication Critical patent/EP0257038A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms

Definitions

  • This invention relates to methods and apparatus for the production of high resolution images. It finds particular appli ⁇ cation in photolithographic techniques used for the manufacture of integrated circuits.
  • photolithographic techniques used for the manufacture of integrated circuits.
  • rare gas halide lasers have been used in both contact and imaging printers (K. Jain and R.T. Keith, Applied Optics Z__ 648 (1948).
  • current throughputs are as much limited by step and repeat processes, whilst the resolution is as much limited by the characteristics of the imaging system as by the properties of the radiation used.
  • apparatus for the production of high quality resolution images over large areas comprising a source of radiation, a holographic recording of a radiation mask and means for reconstructing an image of said radiation mask in the vicinity of a predetermined surface in order selectively to illuminate said surface with said radiation.
  • Figure 1 is a diagram showing the production of a holographic recording of a radiation mask
  • Figure 2 is a similar diagram showing the arrangement of the holographic recording in apparatus for the reconstruction of an image of the radiation mask.
  • radiation from a krypton fluoride excimer laser 1 passes by way of a lens LI and mirror Ml to a beam splitter B.
  • An object beam 2 passes by way of a second mirror M2 through an object comprising a mask 3 usable for photolithographic processing of semiconductor devices and onto a holographic recording medium 5 by way of a focussing mirror M4.
  • a reference beam 4 passes by way of a lens L2, a mirror M3 and a further lens L3 to form together with the object beam 2 a holo ⁇ graphic recording on a recording medium 5 in a plane adjacent to the mask.
  • Reconstruction of the holographic image 6 is performed by radiation from an excimer laser 7 which passes by way of a beam expander (L, and L4) and two mirrors M5, M6 to the hologram H which has been processed to reconstruct with high efficiency in reflection.
  • the image of the photolithographic mask is formed by reflection in a concave mirror M4.
  • the hologram is located near the image plane of the mask.
  • the spatial coherence of the recording beams need not be high since both reference and object beams are spatially matched at the hologram plane.
  • This spatial matching of the beams minimises the requirement on the mechanical stability of all optical components before the beam splitter.
  • the hologram is recorded close to the image plane but sufficiently far from it to reduce the effect in reconstruction of defects in the hologram plane.
  • the object beam at the hologram plane is entirely 'specular'; that is to say it has no scattered components and consists only of a flat or spherical wavefront transmitted and diffracted by the mask.
  • the reconstruction from the hologram so produced is not illuminated by random phase components as would be the case for a scattered light hologram and hence does not show image speckle which would prevent the attainment of adequate uniformity and resolution for microcircuit replication. It is important to eliminate all sources of scatter both in recording and recon ⁇ struction as these will give a background speckle pattern in the image plane.
  • the recording geometry was selected for being simple, in ⁇ expensive and achromatic.
  • the mirror is used with a NA 0.24 giving potentially sub-micron resolution at a wavelength of 249 nm.
  • the imaging mirror may be used at 1:1 magnification to keep down the holographic exposure, and minimise the mirror imaging aberrations.
  • the technique might be modified usefully for higher magnification to reduce the resolution requirement of the hologram and to reduce the intensity on the hologram in the reconstructing stage. The latter may be essential if the hologram is to be used for photoablation lithography with short pulse excimer lasers as this requires high single pulse energies.
  • d width of hologram
  • ⁇ angle between object and reference beam.
  • the maximum requirement on coherence length ( ⁇ «"* 90 ) would be 5 cm corresponding to a laser bandwith of less than 0.2 cm . It is straightforward to achieve this linewidth with excimer lasers.
  • Repositioning of the hologram after processing can be achieved simply and to adequare accuracy by interferometry.
  • the hologram is replaced in the original recording arrangement thus giving rise to two 'object' beams, the original beam from the object and a beam reconstructed by the hologram from the original reference beam.
  • the 'object' beams give a two beam interference pattern which shows the departure of the hologram from its correct position.
  • the excimer laser used in this embodiment was a commercial pulsed KrF laser operating at a wavelength 249 nm and line narrowed to S30.3 cm and had a beam divergence less than 100 j ⁇ rad.
  • the holograms were recorded using a single laser pulse of duration 20 ms
  • Reference to object beam intensity ratio is not critical and had a value of 4:1.
  • the developed hologram was coated with aluminium by evaporation and replaced for reconstruction.
  • the reconstructed image was obtained by reversing the optical process, as already indicated, and recorded on a photoresist-coated plate placed in the exact position of the original mask.
  • the photoresist was given an
  • a necessary part of the process of microcircuit replication requires accurate referencing of the wafer to achieve good image fidelity and precise relative positioning of sequential circuit layers.
  • the holographic technique does not require accurate repositioning of the hologram so long as the wafer can be accurately positioned in the image plane.
  • Fiducial marks on microcircuit masks and common to all masks will be reconstructed by the holographic process and may be used for referencing as in current commercial machines.
  • a further holographic design feature is proposed which may be used to assist the image referencing.
  • a secondary hologram of all or just special features of the mask is recorded at the same time as the main mask hologram on the same resist surface without disturbing the geometry.
  • This - 6 - secondary hologram may be either superimposed onto the main hologram or alongside it as required, and it may be recorded at a longer wavelength, perhaps in the visible, to optimise the convenience and speed of the referencing process.
  • the narrowest linewidth observed ('1 um' line) was about 1.5 pi, comparing well with the diffraction limited linewidth, for a 0.24NA system at 633 nm, of approximately 1.5 ⁇ m (1/e intensity points).
  • a hologram of an area of mask of diameter 35 mm showed that, as expected, the resolution can be maintained over large object fields and in regions where the mirror imaging has large aberrations.
  • KrF holography a resolution of 1 um can be achieved.
  • Use of a shorter wavelength improves resolution but not to an extent expected by reduction in wavelengths. This limit on resolution as the limit can be explained as being imposed by the grain size of the photographic emulsion together with the limited resolution of our UV microscope.
  • Speckle noise resulting from scatter in the photographic emulsion is seen to be considerably worse at the shorter wave ⁇ length and this also affects the observed resolution to some extent.
  • the reconstructing efficiency was greatly improved by depositing a layer of aluminium onto the hologram by thermal evaporation.
  • the reconstructed image fidelity was not affected by increasing the linewidth of the reconstructing beam from 0.1 cm to 50 cm , and was only slightly affected (resolution ***2 ⁇ m) by reducing the transverse coherence from single transverse mode to 5-10 x diffraction limit.

Abstract

Un appareil de production d'images de grande surface à haute résolution d'un masque holographique comprend un laser excimer (7) et un étaleur de faisceau (L1, L4, M6, M5) pour diriger un faisceau sur un hologramme de réflexion (H) situé à proximité du plan de l'image du masque. L'image du masque est formée par réflexion dans un miroir concave (M4).An apparatus for producing high resolution large area images of a holographic mask includes an excimer laser (7) and a beam spreader (L1, L4, M6, M5) for directing a beam onto a reflection hologram (H ) located near the mask image plane. The image of the mask is formed by reflection in a concave mirror (M4).

Description

- 1 -
METHOD AND APPARATUS FOR THE PRODUCTION OF HIGH RESOLUTION IMAGES This invention relates to methods and apparatus for the production of high resolution images. It finds particular appli¬ cation in photolithographic techniques used for the manufacture of integrated circuits. In an endeavour to increase the handling speed of photolitho¬ graphic apparatus used in the manufacture of integrated circuits, and also to increase their resolution thereby achieving higher component packing densities, rare gas halide lasers have been used in both contact and imaging printers (K. Jain and R.T. Keith, Applied Optics Z__ 648 (1948). However, current throughputs are as much limited by step and repeat processes, whilst the resolution is as much limited by the characteristics of the imaging system as by the properties of the radiation used.
We have shown that both these limitations can be removed by using a holographic process which does not necessarily require high quality optics for high resolution and because of this there is no fundamental limitation on field size. In consequence the full resolution benefit of short wavelength excimer lasers can be realized and large areas, for example, the entire wafer area can be exposed at once, obviating the need for current time-wasting step and repeat techniques. Holography has potentially a number of other advantages. The correct image referencing is simpler since it is referenced into the same position as the original object (or mask) and the original mask position is not critical. Point defects or scratches accruing on the hologram are not important if the hologram is recorded in an out of focus plane of the object. The geometry is very flexible and can generally be adjusted to suit requirements or convenience. The numerical aperture of the holographic imaging system can easily be made very large giving a potential resolution equal to the wavelength (0.19 um for the ArF laser). - 2 -
According to the present invention there is provided apparatus for the production of high quality resolution images over large areas, comprising a source of radiation, a holographic recording of a radiation mask and means for reconstructing an image of said radiation mask in the vicinity of a predetermined surface in order selectively to illuminate said surface with said radiation.
The particular methods and apparatus proposed are in consider¬ able part directed to alleviating the tolerances on source and geometry which would probably rule out holography as a .feasible technique for microcircuit replication.
An embodiment of the invention will now be particularly described with reference to the accompanying drawings in whic :-
Figure 1 is a diagram showing the production of a holographic recording of a radiation mask; and Figure 2 is a similar diagram showing the arrangement of the holographic recording in apparatus for the reconstruction of an image of the radiation mask.
Referring now to Figure 1 of the drawings, radiation from a krypton fluoride excimer laser 1 passes by way of a lens LI and mirror Ml to a beam splitter B. An object beam 2 passes by way of a second mirror M2 through an object comprising a mask 3 usable for photolithographic processing of semiconductor devices and onto a holographic recording medium 5 by way of a focussing mirror M4. A reference beam 4 passes by way of a lens L2, a mirror M3 and a further lens L3 to form together with the object beam 2 a holo¬ graphic recording on a recording medium 5 in a plane adjacent to the mask.
Reconstruction of the holographic image 6 is performed by radiation from an excimer laser 7 which passes by way of a beam expander (L, and L4) and two mirrors M5, M6 to the hologram H which has been processed to reconstruct with high efficiency in reflection. The image of the photolithographic mask is formed by reflection in a concave mirror M4. The hologram is located near the image plane of the mask. With this arrangement the coherence requirements in recording and reconstruction, geometrical requirements on the reconstructing beam, and the requirements on optical quality of the hologram medium and substrate are reduced and become simple to satisfy. Further, using the extra optics (L„, L_ and P.) shown in the recording reference beam (Figure 1) the spatial coherence of the recording beams need not be high since both reference and object beams are spatially matched at the hologram plane. This spatial matching of the beams minimises the requirement on the mechanical stability of all optical components before the beam splitter. The hologram is recorded close to the image plane but sufficiently far from it to reduce the effect in reconstruction of defects in the hologram plane. The object beam at the hologram plane is entirely 'specular'; that is to say it has no scattered components and consists only of a flat or spherical wavefront transmitted and diffracted by the mask. The reconstruction from the hologram so produced is not illuminated by random phase components as would be the case for a scattered light hologram and hence does not show image speckle which would prevent the attainment of adequate uniformity and resolution for microcircuit replication. It is important to eliminate all sources of scatter both in recording and recon¬ struction as these will give a background speckle pattern in the image plane.
The recording geometry was selected for being simple, in¬ expensive and achromatic. The mirror is used with a NA 0.24 giving potentially sub-micron resolution at a wavelength of 249 nm. The imaging mirror may be used at 1:1 magnification to keep down the holographic exposure, and minimise the mirror imaging aberrations. The technique might be modified usefully for higher magnification to reduce the resolution requirement of the hologram and to reduce the intensity on the hologram in the reconstructing stage. The latter may be essential if the hologram is to be used for photoablation lithography with short pulse excimer lasers as this requires high single pulse energies.
For reference and object beam with matched path length at the centre of the hologram, the coherence length requirement in record¬ ing is ** d sinθ where d = width of hologram and θ = angle between object and reference beam. For a 4 inch wafer and hologram the maximum requirement on coherence length (θ «"* 90 ) would be 5 cm corresponding to a laser bandwith of less than 0.2 cm . It is straightforward to achieve this linewidth with excimer lasers.
Holograms were recorded in Shipley photoresist type AZ2415. Recent developments have shown this material to be well fitted to recording high resolution, efficient, scatter free holograms at excimer laser wavelengths. Other materials are possible but photoresist, being a 'surface relief hologram, can also be reflection coated for high efficiency and replicated onto more robust material.
Repositioning of the hologram after processing can be achieved simply and to adequare accuracy by interferometry. -The hologram is replaced in the original recording arrangement thus giving rise to two 'object' beams, the original beam from the object and a beam reconstructed by the hologram from the original reference beam. The 'object' beams give a two beam interference pattern which shows the departure of the hologram from its correct position.
The excimer laser used in this embodiment was a commercial pulsed KrF laser operating at a wavelength 249 nm and line narrowed to S30.3 cm and had a beam divergence less than 100 jαrad. The holograms were recorded using a single laser pulse of duration 20 ms
2 and with an exposure of ""^mJ/crn on the photoresist. Reference to object beam intensity ratio is not critical and had a value of 4:1.
The developed hologram was coated with aluminium by evaporation and replaced for reconstruction. The reconstructed image was obtained by reversing the optical process, as already indicated, and recorded on a photoresist-coated plate placed in the exact position of the original mask. The photoresist was given an
2 exposure (approximately 50mJ/,cm ) to enable development which totally removed the resist in exposed areas as would be required in microcircuit replication.
Resolution -tests of a line and dot pattern chart with elements down to 1 μn in dimension showed errors in edge positions and linewidths to be well under 1 μ . and close to the diffraction limit of this particular embodiment. Exposure levels indicate that even with a modest holographic reconstruction efficiency of say 20% total laser energy to expose a complete 10 cm x 10 cm wafer would be approximately 50J. with current commercial models a complete wafer exposure time of 1 S is feasible. A broadband laser can be used in reconstruction since coherence is only required across the area of hologram contri¬ buting to each point in the reconstructed image. Since the hologram is recorded close to an image plane this area is small, perhaps only of millimetre size. A test of this feature of the design showed a degradation of resolution to 2 μm while using the total bandwith (50 cm ) of the KrF excimer laser.
A necessary part of the process of microcircuit replication requires accurate referencing of the wafer to achieve good image fidelity and precise relative positioning of sequential circuit layers. The holographic technique does not require accurate repositioning of the hologram so long as the wafer can be accurately positioned in the image plane. Fiducial marks on microcircuit masks and common to all masks will be reconstructed by the holographic process and may be used for referencing as in current commercial machines. However a further holographic design feature is proposed which may be used to assist the image referencing. A secondary hologram of all or just special features of the mask is recorded at the same time as the main mask hologram on the same resist surface without disturbing the geometry. This - 6 - secondary hologram may be either superimposed onto the main hologram or alongside it as required, and it may be recorded at a longer wavelength, perhaps in the visible, to optimise the convenience and speed of the referencing process. The narrowest linewidth observed ('1 um' line) was about 1.5 pi, comparing well with the diffraction limited linewidth, for a 0.24NA system at 633 nm, of approximately 1.5 μm (1/e intensity points). A hologram of an area of mask of diameter 35 mm showed that, as expected, the resolution can be maintained over large object fields and in regions where the mirror imaging has large aberrations. For KrF holography a resolution of 1 um can be achieved. Use of a shorter wavelength improves resolution but not to an extent expected by reduction in wavelengths. This limit on resolution as the limit can be explained as being imposed by the grain size of the photographic emulsion together with the limited resolution of our UV microscope.
. Speckle noise resulting from scatter in the photographic emulsion is seen to be considerably worse at the shorter wave¬ length and this also affects the observed resolution to some extent.
The reconstructing efficiency was greatly improved by depositing a layer of aluminium onto the hologram by thermal evaporation.
The reconstructed image fidelity was not affected by increasing the linewidth of the reconstructing beam from 0.1 cm to 50 cm , and was only slightly affected (resolution ***2 μm) by reducing the transverse coherence from single transverse mode to 5-10 x diffraction limit. These are particular advantages of the near focal plane geometry used and enable simple and powerful lasers to be used in reconstruction if desired.
We achieved 1 um resolution in the holographic reconstruction of a resolution mask using a wavelength of 249nm from a pulsed KrF excimer laser. The main limitation in the process used resulted from background speckle (not image speckle) due to grain scatter - 7 - in the photographic emulsion and this limited both the resolution and the signal to noise ratio. With the use of photoresist as the recording medium this limitation can be eliminated and a resolution below 0.5 m can be achieved. A further improvement is expected 5 if an ArF laser operating at a wavelength of 193 nm is used and
- in this case it may be possible to record the hologram by photo- ablation and hence eliminate the development process. Further modifications may also be made, e.g. (i) high efficiencies with good fidelity can be achieved by ] Q aluminising the hologram and operating in reflection.
(ii) large area masks can be recorded without loss in fidelity. (iii) geometries such as the one used enable the use of compara¬ tively unsophisticated lasers and allow reasonable tolerances in the optical quality of the hologram surface 15 and in the reconstruction geometry.

Claims

1. Apparatus for the production of high quality resolution images over large areas, characterised in that it comprises a source of radiation, a holographic recording of a radiation mask and means for recons ructing an image of said radiation mask in the vicinity of a predetermined surface in order selectively to illuminate said surface with said radiation.
2. Apparatus for the production of high quality resolution images over large areas as claimed in Claim 1 characterised in that the source of radiation is a broad band laser-.
3. Apparatus for the production of high quality resolution images as claimed in Claim 2 characterised in that the laser is an inert gas-halogen excimer laser.
4. Apparatus for the production of high quality resolution images as claimed in Claim 3 characterised in that the laser is a krypton-fluorine excimer laser.
5. Apparatus for the production of high quality resolution images as claimed in Claim 3 characterised in that the laser is an argon-fluorine laser.
6. Apparatus for the production of high quality resolution images as claimed in any one of the preceding claims characterised in that said holographic radiation mask comprises a hologram recorded close to the image plane, but spaced therefrom in order to reduce the effect of optical reconstruction of defects.
7. Apparatus for the production of high quality images as claimed in Claim 6 characterised in that said hologram is recorded in photo resist.
8. Apparatus for the production of high quality images as claimed in Claim 7 characterised in that it further includes a reflective layer deposited on said hologram.
9. Apparatus for the production of high quality images as claimed in Claim 8 characterised in that said reflective layer is of aluminium.
10. Apparatus for the production of high quality images as claimed in any one of the preceding claims characterised in that said holographic recording incorporates a secondary hologram for alignment purposes.
67M
EP19860903512 1985-06-06 1986-06-06 Method and apparatus for the production of high resolution images Withdrawn EP0257038A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB858514261A GB8514261D0 (en) 1985-06-06 1985-06-06 Production of high resolution images
GB8514261 1985-06-06

Publications (1)

Publication Number Publication Date
EP0257038A1 true EP0257038A1 (en) 1988-03-02

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP19860903512 Withdrawn EP0257038A1 (en) 1985-06-06 1986-06-06 Method and apparatus for the production of high resolution images

Country Status (4)

Country Link
EP (1) EP0257038A1 (en)
JP (1) JPS63500063A (en)
GB (2) GB8514261D0 (en)
WO (1) WO1986007474A1 (en)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8810483D0 (en) * 1988-05-04 1988-06-08 British Aerospace Imaging system
JP3177961B2 (en) 1998-04-14 2001-06-18 日本電気株式会社 Pattern forming method and apparatus by atomic beam holography
WO2001013181A1 (en) * 1999-06-11 2001-02-22 Holtronic Technologies Plc Method and apparatus for recording a hologram from a mask pattern by the use of total internal reflection holography and hologram manufactured by the method

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1547450A1 (en) * 1967-01-17 1969-12-04 Siemens Ag Process for the simultaneous multiple projection of a pattern onto a light-sensitive layer
US3535012A (en) * 1967-10-20 1970-10-20 Nasa Recording and reconstructing focused image holograms
AT323808B (en) * 1969-12-19 1975-07-25 Siemens Ag METHOD FOR MANUFACTURING SEMI-CONDUCTOR COMPONENTS WITH HOLOGRAPHIC PROJECTION OF THE ETCHING PATTERNS AND ARRANGEMENT FOR THEM
JPS537347A (en) * 1976-07-09 1978-01-23 Agency Of Ind Science & Technol Hologram recorder

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8607474A1 *

Also Published As

Publication number Publication date
GB2176628A (en) 1986-12-31
GB8514261D0 (en) 1985-07-10
JPS63500063A (en) 1988-01-07
GB8613806D0 (en) 1986-07-09
WO1986007474A1 (en) 1986-12-18
GB2176628B (en) 1989-07-05

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