Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/02—Details
  • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
  • H01J37/153—Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/02—Details
  • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
  • H01J37/10—Lenses
  • H01J37/145—Combinations of electrostatic and magnetic lenses
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/30—Electron or ion beam tubes for processing objects
  • H01J2237/317—Processing objects on a microscale
  • H01J2237/3175—Lithography

Definitions

• the invention relates to a lens arrangement with a laterally displaceable optical axis for particle beams, in particular for the transmission of regions of an object plane into the image plane by means of electrons, with a combined lens, which consists of a cylindrical lens and a quadrupole lens, which has electrical and / or magnetic fields acted upon
• microscopy methods are used for monitoring, with the aid of which the surface structure is imaged and optically monitored.
• Light-optical and electron-optical methods are customary, the latter methods offering the advantage of a substantially higher resolution due to the much smaller wavelength of the electrons. This means that the distance between points of an object that are close to one another can take on smaller values in the electron-optical method before the two points in the image plane of the imaging arrangement can no longer be separated as individual points.
• low-voltage electron microscopes with rotationally symmetrical immersion objectives are used for the detection and detailed examination of the surface structures mentioned.
• the sample to be examined is illuminated with electrons of low energy within an object field.
• the secondary electrons released during this process are sucked off from the surface of the object by means of an immersion objective and imaged in the image plane with a comparatively high resolution.
• energy filters to limit the imaging to electrons from the low-energy part of the secondary electron spectrum in the range of 1 - 2 eV. In this area the electron yield is high and the energy window can be chosen so narrow that an image with high resolution is possible with a sufficient aperture angle.
• a disadvantage of the known microscopes of the type mentioned is that the image is limited to a very small object field, typically around 100 ⁇ m in diameter, in the immediate vicinity of the optical axis. This leads to objects of larger dimensions, such as the wafer areas with the dimensions of approximately 25 mm ⁇ 25 mm, which are the basis for the production of integrated circuits, being divided into two
• a magnetic dipole field can be superimposed on the quadrupole, which enables the optical axis of the image to be shifted in the direction of the longitudinal extension of the cylindrical lens gap.
• the second device of the type mentioned is DE 196 44 857.4
• the electrostatic cylindrical lens consisting of at least three electrodes, the central electrode of which consists of segments which are electrically insulated from one another in the longitudinal direction of the slot-shaped electrode opening (comb electrode). Because of this structure, the individual segments of the center electrode can be assigned different potentials. In the present device, the potential distribution is selected so that an electrostatic quadrupole is generated, the axis of which can be displaced in the direction of the gap.
• Both of the aforementioned devices are designed as electron-optical individual lenses and are used as probe-forming arrangements in shaped-beam exposure systems. These systems are less suitable for imaging secondary electrons that are triggered in an object plane.
• a system has finally become known from DE 101 36 190.4, in which two non-circular systems of the aforementioned type are used.
• the system enables low-error projection of relatively large areas of a transmission mask located in the object plane onto a wafer located in the image plane.
• the optical axis of the quadrupole and thus the optical axis of the image is shear or magnetic fields shifted over the full width of the wafer area, the projection system maintaining its imaging properties. Accordingly, only a mechanical displacement of the object in one coordinate direction is required in the present system to describe the entire wafer area.
• the system described above is suitable for the projection of masks, but its disadvantage is that it is unsuitable for secondary electron imaging and only allows a comparatively small magnification.
• the use of two lens systems is essential to the system mentioned, the overall system is thus comparatively complex and accordingly expensive to manufacture.
• the object of the invention is to provide a lens arrangement in which the particles emanating from points of an object area, in particular electrons, are mapped into assigned points of the image plane in the physical sense, the object field acquired during the imaging has a comparatively large diameter and can be moved over a comparatively large width of the object without mechanical positioning steps.
• the proposed system enables detection of defects in the surface structure when used for monitoring the wafer production, as well as a detailed examination when defects are detected.
• the combined lens is operated as an immersion lens
• the immersion field in the axial direction consists of at least two successive fields, with - the first field between the object and the first slit diaphragm, the second field between the first and second slit diaphragm or one subsequent aperture pair is present, both fields can be set independently of one another, and the focusing / defocusing effect of the combined lens results from the superimposition of the immersion field, the cylindrical lens field and the quadrupole field.
• the lens arrangement according to the present invention is based on a combination lens which is known per se and is described in the prior art and consists of an electrostatic cylindrical lens and a magnetic or electrostatic quadrupole lens.
• the optical axis of the quadrupole lens can be moved parallel to itself.
• the means for shifting the optical axis comprise electrostatic or magnetic fields.
• this lens is operated as an immersion lens, in particular as an immersion objective.
• an immersion field on the lens which in the present invention consists of at least two fields adjoining one another in the axial direction.
• the first field lies between the object and the first slit diaphragm, the second field between the first and second slit diaphragms.
• This version enables the strength of both fields to be set independently.
• the focus of the lens arrangement as a whole is influenced by the interaction of the
• Immersion field, the cylindrical lens field and the quadrupole field determined.
• Immersion slit lenses have the disadvantage that the refractive effect of the immersion field can only act in one cut due to the slit-shaped design of the lens. If no countermeasures are taken, this property leads to a very different behavior of the paraxial fundamental orbits in both main sections. The consequence of this is a very strongly astigmatic image in the area of the immersion field, which can only be corrected with great effort using very strong quadrupole lenses.
• a key idea of the invention is to prevent the greatly different optical behavior in both main sections from the outset by means of an adapted potential profile in the area between the object surface and the objective lens. It is preferred to design the immersion lens in such a way that the potential difference between the object surface and the first slit of the lens is comparatively small. An essential prerequisite for this is the splitting of the immersion field into at least two fields adjoining one another in the axial direction.
• the proposed design leads to a moderate astigmatic splitting in both main sections of the lens, so that with the help of the focusing / defocusing effect of the quadrupole lens inherent in the combined lens, stigmatic imaging is possible without the use of further (strong) quadrupole fields.
• the quadrupole lens is oriented so that its
• Focusing takes place in the section in which the cylindrical lens is without focusing, and defocusing in the section in which the cylindrical lens focuses.
• the axis of the cylindrical lens enables the optical axis of the image to be shifted, the maximum shift being in the range of centimeters.
• the area imaged in a region around the optical axis with constant optical quality can therefore be displaced by comparatively large distances over the object.
• Control of a wafer during its manufacture can therefore be traversed with a dimension of the wafer area using purely electron-optical means without a mechanical displacement of the object being necessary.
• the object only has to be mechanically displaceable for scanning the second dimension.
• the use of the immersion lens according to the present invention results in considerable time savings or opens up the possibility of a significantly shorter duration of the controls accompanying the production , The controls to be carried out then no longer limit the throughput of the production system.
• the proposed system enables both flaws in the surface structure to be detected and, in the case of flaws which have been identified, a detailed examination.
• Typical system data when operating in detection mode are a resolution of 50 nm and an imaged object field with an edge length of approximately 100 ⁇ m, while a resolution of 10 nm can be achieved when operating in the mode for detailed examination.
• the thickness is the first
• Slit diaphragm of the combined lens is formed much larger than that of the subsequent slit diaphragms.
• This constructive measure has the effect that only a small penetration of the immersion field between the first and second diaphragm emerges towards the object. Accordingly, this field can be chosen to be large without negative consequences for the size of the astigmatism that occurs. For this very reason, on the other hand, as already stated, the field between the first diaphragm and the object is set to be comparatively small, which is made possible by splitting the immersion field into two independently predeterminable fields.
• Typical values for the potential applied to the first aperture are 1-2 kV, for the potential applied to the subsequent aperture in the order of 10-20 kV.
• the mean potential on the first slit diaphragm also determines the field strength at the location of the object.
• a comparatively low potential on the first aperture therefore advantageously leads to a low loading of the object by the immersion field.
• Typical values for the electric field at the location of the wafer are 500-1000 V / mm.
• the change in the position of the optical axis of the said quadrupole lens is carried out continuously and preferably in the direction of the slit of the slit diaphragms.
• the advantage of this embodiment is that the object can be scanned without gaps in the coordinate direction parallel to the slot, the length of the scanned strip taking on the greatest possible value.
• the object is then carried out in such a way that a strip of the object is scanned by electron-optical means approximately in the length of the aperture slits and in the width of the transmitted object field, after scanning the optical axis of the arrangement is set back to the original edge of the object and on that by the strip width a streak is again scanned in the direction of the diaphragm slots.
• the size of the immersion field and / or the cylindrical lens field and / or the quadrupole field depends on the position of the axis of the
• Quadrupols can be specified differently.
• the background for this configuration lies in the fact that the image errors of the arrangement increase with increasing deflection of the imaging optical axis from the geometric center of the arrangement and therefore the optical resolution is lower the further the axis of the quadrupole from the center of the slot to
• Edge of the slot is shifted.
• the occurrence of the image defects can, however, be effectively countered by a change in the excitation of the lens arrangement which is associated with the shift.
• a strategy that is dependent on the shift is therefore the Image correction necessary, which is ensured by the proposed design of the fields.
• the invention provides for the aforementioned cylindrical lens to be formed by an electrostatic lens and the said quadrupole lens optionally to be formed by an electrostatic or magnetic lens.
• the quadrupole field can be generated from a rectangular opening in a material of high magnetic permeability, at the edges of which current-carrying conductors run parallel to the optical axis of the cylindrical lens.
• the current flow in the conductors is parallel on opposite edges of the opening and opposite on the perpendicular edges.
• a simple technical solution for this arrangement provides for the conductors to be formed by a coil which is wound on a yoke and which is arranged in the interior of a slot-shaped opening, the conductors being oriented parallel to the optical axis.
• the displacement of the optical axis can advantageously be achieved by superimposing a magnetic dipole.
• a dipole field parallel to the longitudinal axis of the slit in the slit diaphragms of the cylindrical lens causes the optical axis of the quadrupole to shift in this same direction.
• the easiest way to make the dipole is to use two spaced yokes made of a magnetically conductive material, each of which is wrapped with a coil.
• the generation of the dipole field by electrical currents enables a continuous displacement of the dipole by appropriately specifying the excitation current.
• the combined lens has at least three slit diaphragms, of which at least one in the longitudinal direction of the slit consists of segments which are electrically insulated from one another (comb diaphragm), and the segments can be subjected to different electrical potentials are.
• comb diaphragm By means of suitable potentials on the individual segments of the slit diaphragm, multipole fields can be generated, as well as fields that migrate in time over the comb diaphragm.
• suitable potentials on the individual segments of the slit diaphragm multipole fields can be generated, as well as fields that migrate in time over the comb diaphragm.
• a feature of the invention is the application of potential to the segments which lead to the formation of a quadrupole field.
• the magnetic or electrostatic quadrupole lens of the two design variants, together with the cylindrical lens, have the imaging properties of a round lens in a first approximation if the quadrupole field is oriented so that the focusing takes place in the section in which the cylindrical lens is without focusing, and the defocusing in that Cut in which the cylindrical lens focuses. Due to a suitable specification of the fields, stigmatic images can therefore be achieved with the present lens arrangement.
• the potentials on the individual segments are time-dependent, and they therefore move successively from one segment to the next.
• the quadrupole field and the optical axis connected to its axis are shifted
• the present lens arrangement is used in semiconductor lithography to control the surface structure in the production of wafers.
• the use of the lens arrangement according to the invention in this area has been sufficiently explained by the embodiment of the invention reproduced in the preceding part.
• the present invention also includes the use of the proposed lens arrangement as a cathode lens, which can be used in multi-beam systems or multi-shaped beam systems.
• Embodiments and Details of the invention in this area of application are given in the following section.
• At least one slit diaphragm is designed as a comb diaphragm and the segments are acted upon by potentials by means of which a plurality of electrostatic quadrupole lenses lying side by side in the direction of the slit can be generated.
• the orientation of the individual quadrupole fields is oriented such that the
• Focusing takes place in the section in which the cylindrical lens is without focusing, and defocusing in the section in which the cylindrical lens focuses.
• the individual quadrupoles in cooperation with the present immersion field and the cylindrical lens field each form stigmatically imaging elements.
• a plurality of object areas lying separately from one another in an object plane are therefore simultaneously imaged in corresponding areas in the image plane.
• the object plane of the lens arrangement according to the invention is formed by the surface of a cathode, from which electrons can be released at defined points by photoeffect.
• Each of the defined positions is assigned a quadrupole of the slit lens.
• the electrons emanating from a defined point are sucked out through the fields of the lens arrangement that are effective on the surface of the cathode and focused using the cylindrical lens and the respective quadrupole lens.
• the focusing leads to a cross-over in the cross-over plane, whereby as many images of the electron sources are generated as there are defined areas for triggering photoelectrons.
• the proposed arrangement can therefore advantageously be used as an electron-optical lighting device with a plurality of spaced use lighting areas. Such arrangements are used in multi-beam systems or multi-shaped beam systems.
• Control of the surface structure of wafers are used, as well as those that are used as a cathode lens.
• an embodiment of the combined lens is preferably designed with more, preferably two further, slit diaphragms as comb diaphragms, and further, preferably two further, unsegmented slit diaphragms are provided.
• the comb diaphragms enable the generation of further, preferably parallel-displaceable, quadrupole fields and / or multipole fields of a higher order. These additional fields are advantageously used to correct image errors that originate in the position of the object field that deviates from the central axis.
• the specification of three comb diaphragms enables fields to be generated which, regardless of the position of the object area to be imaged, lead to an astigmatic and distortion-free imaging.
• the diaphragms serve to limit the penetration of the quadrupole fields.
• an unsegmented diaphragm which is arranged in front of the first segmented slit diaphragm when looking in the direction of the beam path. This diaphragm advantageously limits the range of the quadrupole on the first slit diaphragm towards the object; its potential is expediently chosen to be equal to the average potential of the first comb diaphragm.
• an axial, non-displaceable quadrupole lens is provided as an alternative to a comb screen in the combined lens outside the combined lens.
• Figure 1 Sketch of an immersion objective lens with comb diaphragms
• Figure 2 Sketch of a cathode lens with comb screens
• FIG. 1 shows the essential components of an objective 1 that can be operated as an immersion lens.
• the lens consists of a combined lens, which has both the properties of a cylindrical lens and that of a quadrupole lens.
• the function of the cylindrical lens is present arrangement by a plurality of slit diaphragms 2 - 4, the slits of which are oriented perpendicular to the plane of the drawing and which can be acted upon with different potentials.
• the function of the quadrupole lens is achieved by the present diaphragm arrangement by designing at least one slit diaphragm 2-4 as a comb diaphragm, the segmentation being carried out in the longitudinal direction of the slit, ie perpendicular to the plane of the drawing.
• the relevant diaphragms are constructed from segments which are insulated from one another and to which potentials can be applied which lead to the formation of quadrupole fields.
• the potentials on the individual segments are specified in such a way that the quadrupole fields and thus their axes, which in turn define the optical axis of the image, can be displaced in the direction of the longitudinal direction of the slot.
• all three slit diaphragms 2 - 4 are designed as comb diaphragms, so that quadrupole fields can in principle be generated on each of the diaphragms.
• the system thus has enough degrees of freedom to be able to set an undigested, stigmatic image regardless of the position of the imaging optical axis
• a further diaphragm 8 is arranged between the object plane 6 and the first slit diaphragm 2 and, unlike the other slit diaphragms, is not segmented.
• This diaphragm primarily serves to limit the range of the quadrupole field generated on the first slit diaphragm to object 6.
• the potential of this aperture 8 is expediently chosen to be equal to the average potential of the first comb aperture 2.
• the beam path through the objective 1 is illustrated using the fundamental trajectories.
• the fundamental trajectories are indicated by the reference numerals 9, 10 and 11, 12, the axial trajectories being identified by 9 and 10 and the field trajectories in the x- and y-section by 11 and 12, respectively.
• FIG. 2 shows a lens arrangement that is also used as a cathode lens 1 in a likewise greatly simplified representation.
• the cathode 2 just formed lies in the object plane 3 of the lens 1, which has slit diaphragms 4-6 parallel to the surface of the cathode, at least one of which is designed as a comb diaphragm.
• the longitudinal direction of the slots and their segmentation runs parallel to the plane of the drawing in the present figure.
• the segments of the comb diaphragm (s) are subjected to potentials which lead to several, in the present case four, quadrupoles lying next to one another.
• these local quadrupoles each form stigmatically imaging elements 7-10, which separate the object areas 11-

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• 2001
  • 2001-12-14 DE DE10161680A patent/DE10161680A1/de not_active Withdrawn
• 2002
  • 2002-11-26 EP EP02804845A patent/EP1454334A2/de not_active Ceased
  • 2002-11-26 JP JP2003553594A patent/JP4170224B2/ja not_active Expired - Fee Related
  • 2002-11-26 WO PCT/DE2002/004327 patent/WO2003052790A2/de active Application Filing
  • 2002-11-26 US US10/499,165 patent/US6995378B2/en not_active Expired - Fee Related
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