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 or ion-optical arrangement
  • H01J37/153—Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators

Definitions

• the invention relates to methods for eliminating first, second and third order axial image errors when correcting the third order opening error in electron-optical systems with hexapoles.
• correction of the third-order opening error occurs, among other things, adjustment errors which impair the resolution, which are primarily the first, second and third-order axial image errors, the elimination of which is necessary to achieve the optimum resolution.
• the axial image errors that occur as adjustment errors when correcting the third-order opening error are as follows:
• the previous methods are characterized in that the adjustment errors are eliminated successively with each imaging element of the electron-optical system and progressively in the direction of the beam spread.
• the invention has set itself the task of creating adjustment methods by means of which the first, second and third order axial image defects can be eliminated.
• Correction methods are explained below as a solution, which give a teaching of the manner in which individual axial image errors of the second and third order can be corrected; on the other hand, an adjustment method for eliminating all axial image errors of the first as well as the second and the third order is specified with a corrective for eliminating the spherical aberration of the third order.
• the sizes 7 ⁇ , and ⁇ denote the complex conjugate sizes. The correction of the individual image errors in connection with the description of the adjustment method is explained in more detail below.
• the first step as a prerequisite for eliminating the adjustment errors is determining the size of the respective error coefficients.
• a decisive difference compared to the method known from the prior art is that the image errors behind the overall system, which generally consists of several lenses, are measured precisely in the image plane, so that the errors are only recorded in their entirety and in mutual superimposition become.
• images are taken with beam paths tilted against the optical axis, the individual images being compared to one another
• the number of images is so large that the system of equations at least is determined.
• the evaluation is carried out in such a way that a diffractogram is produced, either in an analogous manner by diffraction or by a Fourier transformation in a mathematical way.
• the image errors C- j , A- can be determined from the diffraction images by a known method. We refer to the contribution by F. Zemlin et al., Ultramicroscopy 3 (1978) 49.
• the other four complex adjustment errors and the real opening error can be determined using a system of equations derived from the eikonal (see Zemlin loc. Cit.) . In the case of the five image errors mentioned above, a system of equations consisting of nine real equations must be derived and solved. In this way, the error coefficients to be eliminated are determined.
• Influencing and eliminating defocusing and first order twofold axial astigmatism are trivial; they are done by changing the focus (in the case of C-,) and by superimposing a quadrupole field (in the case of A.,).
• the second-order errors that is to say the axial coma B 2 and the threefold axial astigmatism A 2 are to be corrected next, since only then is it possible to determine the third-order image errors with sufficient accuracy and consequently also to correct them .
• the removal can be done by a so-called coma stigmator.
• a quadrupole field of the same strength is superimposed on a pair of hexapoles in the corrective system, the product of the sign of the hexapole field and that of the associated quadrupole field being antisymmetric, that is to say opposite to one another. This condition ensures that no 1st order astigmatism is produced.
• the strength and the orientation of these quadrupole fields is determined by the measured coma.
• Another possibility of generating the quadrupole fields can be by moving the optical axis parallel to the axis of the hexapole.
• the correction is done by an additional hexapole field, its strength and direction also is determined by the determined error coefficient.
• the realization takes place by generating such a hexapole field.
• Another way of generating fields is to virtually rotate the corrective hexapoles against each other, which also creates a three-digit field.
• the implementation is carried out by arranging a magnetic round lens between the two hexapoles or using the existing ones. The advantage of this method is that it saves the otherwise necessary way of using a twelve-pole lens to generate a hexapole field of any size and orientation.
• the values of the third order image errors namely the 4-fold axial astigmatism A 3 and the 2-fold star error S 3 , can be determined in the manner described above.
• the correction of these axial image errors follows a common general principle proposed by the invention for the first time.
• the same off-axis image error of a higher order is used to correct the axial image error and by shifting or tilting the optical errors
• equality of the image error means the same behavior, that is to say the same dependence on the complex aperture angle C and its complex conjugate OC.
• the power of the image coordinate corresponds to the difference between the order of the correction used off-axis error and the order of the axial image error to be corrected.
• the off-axis error with linear dependency on '/ ' will be used.
• an axial component one would have, for example, ⁇ 6 n , where the associated off-axis component - assuming the linearity - then reads ⁇ C n>' •
• the 3rd order axial star error there is a (X-, so that the off-axis and in ⁇ linear 4th-order star errors OO 3 /
• the off-axis a-3rd order astigmatism is used.
• the off-axis error can be influenced, so that mutual compensation d. H. the axial error component is eliminated with the aid of the off-axis image error associated in the sense explained above.
• Figure 2 The correction principle of the triple axial astigmatism of the second order A 2
• Figure 3 The correction of the axial astigmatism and the star error of the third order.
• the optical axis shown in dashed lines runs horizontally.
• the hexapoles 1 and 2 limit the system formed by the two round lenses 3 and 4 to the outside.
• a quadrupole field is superimposed in the two hexapoles 1 and 2, which is opposed to one another.
• an anti-symmetry results, by means of which the generation of a first-order astigmatism is avoided.
• the strength and direction of the quadrupole fields must be set to the value of the measured coma.
• such a field can be produced in an elegant manner by displacing the optical axis parallel to the axis of the hexapole, as a result of which a quadrupole field is additionally generated depending on the displacement path.
• Figure 2 deals in principle with the correction of the triple axial astigmatism of the second order.
• a hexapole field is generated according to the strength and direction of the error value to be corrected.
• a magnetic circular lens system 3 4, by means of which the imaging beam path is rotated by Larmor and thus generates a virtual rotation of the two hexapoles 1, 2 relative to one another.
• a hexapole field 3 that can be adjusted in size can also be generated.
• FIG. 3 also shows two hexapoles, with two round lenses 3, 4 arranged therein, between which an intermediate image 5 is generated.
• the same off-axis, higher-order image errors can be brought into effect and used for compensation by an offset in the plane of the intermediate image.
• the next-order off-axis error will be used with a linear nT or for this.
• the fourth-order off-axis star error CT is therefore used and, in the case of third order four-fold axial astigmatism, the fourth order fourth-order off-axis astigmatism.
• the corrections of individual axial image errors shown in the figures are used, among other things, in adjustment methods for eliminating first, second and third order axial image errors when correcting the third order opening error in electronic systems.

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• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Electron Beam Exposure (AREA)
• Lenses (AREA)
• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)

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• 1997
  • 1997-09-08 DE DE19739290A patent/DE19739290A1/de not_active Ceased
• 1998
  • 1998-08-29 WO PCT/DE1998/002596 patent/WO1999013490A1/de not_active Ceased
  • 1998-08-29 US US09/508,239 patent/US6646267B1/en not_active Expired - Lifetime
  • 1998-08-29 JP JP2000511180A patent/JP2001516139A/ja active Pending
  • 1998-08-29 EP EP98951265A patent/EP1012866B1/de not_active Expired - Lifetime
  • 1998-08-29 DE DE59814013T patent/DE59814013D1/de not_active Expired - Lifetime
• 2007
  • 2007-07-11 JP JP2007182485A patent/JP2007266008A/ja active Pending

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