Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
  • G21K1/06—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diffraction, refraction or reflection, e.g. monochromators

Definitions

• the present invention relates to an X-ray optic and more particularly it relates to an optical arrangement which can focus electro-magnetic radiation in the range of frequencies commonly referred to as X-ray.
• Focussed X-rays are or have the potential to be used in a wide range of applications such as X-ray lithography for the manufacture of micro-chips and for micro-machining, in spatially resolved X-ray fluorescence analysis, sub-cellular probing, X-ray microscopy and in scientific instrument manufacture. In these applications an intense X-ray source is required and the ability to focus X-rays can increase the useable source intensity.
• zone plates are capable of forming high-resolution images they, and multilayer mirrors, suffer from several drawbacks such as low efficiencies, the need for monochromatic illumination and small zone plate apertures.
• Grazing incidence reflective optics are widely used in several applications but have not been used in high resolution imaging systems because of aberrations.
• polycapillary optics have large apertures, large bandpass and high transmission efficiency they are difficult to design and manufacture as several constraints have to be overcome, these include the limitation that the channel width, cross sectional shape and curvature are such that there are only a few reflections down each channel (ideally two) as, with more than two reflections, correspondence between object and image conjugate points may be lost, so it is necessary to vary channel width, shape and curvature along the length of the channels.
• the open area of the channels at the optic entrance should be a large percentage of the total area (>80%), however a large open area makes the optic very fragile and variation in reflectivities, absorption and scattering due to surface roughness are disadvantages.
• an optical array which comprises a plate, the surface of which is formed of a plurality of X-ray transparent zones separated by X-ray opaque bands, the X-ray opaque bands being of a thickness such that, when a beam of X-rays from a source is projected onto the plate, at least some of the X-rays are reflected off the outermost walls of the said bands and there being a control means able to shape the plate to form a curved surface so as to be able to focus X-rays passing through the plate.
• an optical array comprising a plurality of X-ray opaque bands separated by X-ray transparent zones, the X-ray opaque bands being dimensioned such that, when a beam of X-rays from a source is projected onto the array, at least some of the X-rays are reflected off walls of the said bands, the array being deformable to dynamically vary the angle of reflection of said X-rays.
• thickness of the X-ray opaque bands is meant the distance measured from the base of the bands to its top i.e. the height above the adjacent X-ray transparent zone.
• the zones are preferably in the form of rings and that the structure comprises a plurality of X-ray transparent channels separated by X-ray opaque walls.
• the rings on the plate can be in the form of concentric circles or they can be elliptical, oval etc.
• the walls preferably have a height such that there is at least one reflection in each channel and, in a thin flat plate, a small variation of angle of incidence of the X- ray on the outer wall of the channels can be used for one to one imaging, but channel diameters must be small to reduce losses due to unreflected X-rays, however if the channel diameters are too small some X-rays may undergo double reflections from both wall of the channels and be lost. If the plate is thicker aberrations can be induced as the incidence angle varies along the channel, but fewer X-rays pass right through.
• the dimensions of the plate will depend on the application.
• the width of the channels preferably increases radially outwards to allow for the increasing incidence angle and preferably the width of the channels is larger than the width of the X-ray opaque sections between the channels.
• the width of the channels will depend on the application.
• the plate can be formed by directly etching a substrate formed of an X-ray opaque material so that the X-ray transparent channels are formed through the plate, or by depositing rings of X-ray opaque material onto a substrate in the form of a plate or membrane to build up the structure of the invention.
• a lost mould process can be used.
• a structure of the size and shape of the optical array is fabricated in a material which can be removed e.g. by melting, and a mould is formed from this structure and the material removed. This mould is then used to form the optical array of the invention.
• Materials which can be used to form the array include metals such as nickel and these can be supported on a substrate if required.
• the channel walls must be smooth to prevent loss of reflectivity. Typical roughness must be less than a fraction of a wavelength, which can be achieved for X-rays with electroplated nickel.
• the plate can be made include silicon, silicon carbide and the plate can be formed from a single silicon wafer of the type made commercially by Virginia semiconductors Inc. Such a silicon wafer can be patterned to form the structure of the invention e.g. by iso tropic plasma etching, lithography etc.
• the plate is curved and the greater the degree of curvature the shorter the focal length of the array.
• the curvature can be spherical, parabolic, etc. and the degree of curvature can be varied depending on the wavelength of the X-rays, the distance of the X-ray source from the plate and the purpose of the focussed beam of X-rays etc.
• the degree of curvature and hence magnification achievable will be limited by the elasticity and stability of the material of the plate under bending stresses.
• the ability to vary the curvature enables an X-ray zoom lens to be obtained
• the plate can be curved by any suitable method either before or after forming the structure of the invention.
• a method of forming the curvature of the plate is to deposit a prestressed layer on the silicon wafer after it has been patterned to give a biomorph stress induced curvature.
• radial ribs of silicon are coated with a metal film which, when cooled will be in compressive stress.
• the degree of curvature and hence the focal length of the structure can be changed by varying the temperature at specific points by localised heating e.g. using miniature heaters.
• Another method of curving the plate is to apply a differential pressure across the plate so that the plate is curved.
• the structure of the invention is formed on a silicon wafer by lithography the plate mounted in a sealed chamber with helium, which is X-ray transmissive, on one or both sides of the plate, by varying the differential pressure the degree of curvature can be varied.
• An alternative method of curving the plate is to coat the plate with a piezoelectric material so that variation in an electric current applied to the piezoelectric material will vary the curvature of the plate.
• the ability to vary the curvature, whichever method is used, enables an X-ray zoom lens to be formed and X-rays can be focussed to provide a concentrated beam of X-rays with a controlled degree of concentration.
• This enables the MO As of the present invention to give enhanced performance in existing or potential applications such as X-ray lithography, spatially resolved X-ray fluorescence analysis, sub-cellular probing, X-ray microscopy and in scientific instrument manufacture, imaging X-ray microscopy, spatially resolved fluorescence microscopy, photemission microscopy and astronomy.
• the present invention is not wavelength specific and can be used with hard X-rays and soft X-rays of a range of wavelengths, including the range of wavelengths commonly referred to as Extreme Ultraviolet (EUN).
• EUN Extreme Ultraviolet
• Fig. 1 is a schematic side view of a flat MOA
• Fig. 2 is a schematic side view of a curved MOA
• Fig. 3 is a front view of fig. 2
• Fig. 4 is a front view showing the use of a biomorph
• Fig. 5 is a schematic view of the use of pressure to bend the MOA
• a plate (1) formed from a silicon wafer has gaps (3) etched on its surface by isotropic plasma etching so as to form a series of concentric X-ray opaque bands of silicon (2) and X-ray transparent gaps (4).
• the gaps (3) are wider than the bands (2) to give an open web structure. In practice there will be many more bands than are illustrated.
• the plate can be fabricated by depositing bands (2) onto a substrate (1).
• the plate (5) is curved as shown so that the X-rays from source A are focussed at (B) so that there is concentration of the X-rays.
• radial ribs (6) are formed of a metal such as nickel so that, as the metal cools, there is a biomorph induced stress which curves the plate (7) to form the shape shown in fig.2.
• the curvature can be electrically controlled by varying the current applied to the coating.
• the plate can be curved by localised heating.
• a plate (8) is placed in a sealed pressure chamber (9) so that the two sections (9a) and (9b) are separated by the plate (8).
• the chamber is sealed by pressure sealing caps (10) and (11) and the sections (9a) and (9b) contain helium.
• the plate (8) is curved as shown.
• One of the sections (9a) or (9b) can be exposed to atmospheric pressure.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Analysing Materials By The Use Of Radiation (AREA)

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• 2000
  • 2000-11-24 JP JP2001540790A patent/JP2003515728A/ja active Pending
  • 2000-11-24 EP EP00977734A patent/EP1243002A1/de not_active Withdrawn
  • 2000-11-24 CA CA002392378A patent/CA2392378A1/en not_active Abandoned
  • 2000-11-24 CN CN00816088A patent/CN1391697A/zh active Pending
  • 2000-11-24 WO PCT/GB2000/004494 patent/WO2001039210A1/en not_active Application Discontinuation
  • 2000-11-24 AU AU15369/01A patent/AU1536901A/en not_active Abandoned
• 2003
  • 2003-07-14 HK HK03105083.4A patent/HK1052793A1/zh unknown

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