Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/0004—Microscopes specially adapted for specific applications
  • G02B21/002—Scanning microscopes
  • G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
  • G02B21/0052—Optical details of the image generation
  • G02B21/006—Optical details of the image generation focusing arrangements; selection of the plane to be imaged
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/0004—Microscopes specially adapted for specific applications
  • G02B21/002—Scanning microscopes
  • G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/0004—Microscopes specially adapted for specific applications
  • G02B21/002—Scanning microscopes
  • G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
  • G02B21/0036—Scanning details, e.g. scanning stages
  • G02B21/0044—Scanning details, e.g. scanning stages moving apertures, e.g. Nipkow disks, rotating lens arrays
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/0004—Microscopes specially adapted for specific applications
  • G02B21/002—Scanning microscopes
  • G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
  • G02B21/0052—Optical details of the image generation
  • G02B21/0064—Optical details of the image generation multi-spectral or wavelength-selective arrangements, e.g. wavelength fan-out, chromatic profiling
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/0004—Microscopes specially adapted for specific applications
  • G02B21/002—Scanning microscopes
  • G02B21/0024—Confocal scanning microscopes (CSOMs) or confocal "macroscopes"; Accessories which are not restricted to use with CSOMs, e.g. sample holders
  • G02B21/008—Details of detection or image processing, including general computer control
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B2210/00—Aspects not specifically covered by any group under G01B, e.g. of wheel alignment, caliper-like sensors
  • G01B2210/50—Using chromatic effects to achieve wavelength-dependent depth resolution

Definitions

• the illuminating light is split longitudinally spectrally and focused on an object, with each focus point corresponding to a certain wavelength.
• the light reflected from the object reaches a dispersive element via a beam splitter and is focused by this onto a photodiode array.
• the strongest signal is determined by reading the photodiode array and related to the object surface.
• US Pat. No. 4,965,441 describes a scanning, ie point-by-point confocal arrangement with increased depth resolution, dispersive elements being arranged in the evaluation beam path for wavelength separation.
• WO 92/01965 describes an arrangement for simultaneous image generation with a moving pinhole in the illumination beam path, the objective having a high chromatic aberration and the arrangement being intended to be used as a profile sensor.
• WO 95/00871 also describes an arrangement with a moving pinhole and a focusing element with axial chromatism, wherein in
• a system for generating a color height image is also implemented, for example, with the CSM additive for the applicant's axiotron microscope.
• the height profile is inspected by visual evaluation of the color image.
• a special application is wafer inspection, i.e. the detection of defects on wafers (e.g. particles on top, irregularities in the structure). Defects become visible as areas with different colors. In this way, height differences ⁇ 0.1 ⁇ m can be differentiated in color.
• the accessible height range, the color spread, depends on the lens used and is, for example, 4 ⁇ m for a 50x lens.
• the detection of a defect size of 0.1 ⁇ m is considered necessary.
• the minimum detectable defect size is determined by the resolution, the inspection speed by the computer capacity.
• Considerable electronic computational effort has to be made to process the information at the appropriate speed. If, for example, a wafer with a diameter of 300 mm is scanned with a 0.3 ⁇ m grid, a total of 10 12 pixels must be processed with digital image processing.
• the object of the invention is to enable a rapid yet highly accurate detection of wafer defects.
• the method of integral spectral decomposition and analysis of the color image information shown has the advantage that defects whose height expansion is less than 0.1 ⁇ m can be detected.
• optical preprocessing by means of spectral decomposition also enables faster processing of the present height profile, since the height profile of the entire image field is compressed in the spectrum.
• An arrangement according to the invention can also be used to implement a highly precise autofocus, which will be discussed in more detail below.
• Fig. 1 The measuring and evaluation principle according to the invention
• Fig. 2 Different height profiles and corresponding color - height spectra.
• Fig. 3 The shift of a spectral line due to a height difference
• Spectrometer entry slit Fig. 5 A first version with cross-section converter Fig. 6: A second version with cross-section converter Fig. 7: A version with a color camera for image evaluation Fig. 8: A version with several lasers of different wavelengths Fig. 9: Spectra for different height profiles Focusing on two levels with laser wavelengths 11 and 12 Table 1: Color spreads for different lenses 1 with a light source 1, which can be a white light source, but can also consist of several lasers of different wavelengths or multi-line lasers, collector lens 2
• the hole pattern 5 is preferably a rotating one
• the grid arrangement is moved appropriately for scanning the image and generates a parallel confocal image.
• a targeted longitudinal color error is introduced into the beam path in such a way that after the beam has passed through the color corrected one
• Height information is optically coded by a corresponding color representation.
• a dispersive element 9 which can be, for example, a prism or holographic grating on a diode row or
• CCD - line 10 shown, which is connected to an evaluation and processing unit 14.
• the color-coded height profiles are thus broken down into an equivalent color spectrum. This is shown in Fig. 2 a - d.
• the spectral positions of the maxima correspond to the corresponding contour lines, while the number of
• the object is located on an xy shift table, not shown, and is scanned either in a continuous movement or in a step-and-go procedure.
• Height information about the location on object 0 is given.
• the height setting in the z direction is controlled by an autofocus system or by a special height control algorithm described below.
• 2 a - d shows a height profile H and a defect point F to be detected as well as the spectrum S AD corresponding to the profile and measured on the receiver 10 and the difference spectra S AB.A-C, AD formed during the evaluation.
• Two adjacent spectra are recorded and subtracted from one another, as shown schematically in FIG. 2.
• a routine for example peak search routine, as is usually used in optical spectroscopy, the maxima in the difference spectrum are determined which are above a predetermined noise level. If such maxima are present, there is a defect in the area examined.
• the position and the corresponding spectra or the reference spectrum are saved.
• the spectra are evaluated in more detail later in a classification unit, since the position and half-width range contain further information about the type of defects that are used for a defect classification. 2.
• the comparison of spectra is carried out as described under 1., but an ideal stored spectrum is used as the comparison spectrum.
• this height control is necessary, since a difference in height leads to a shift of the spectra to one another.
• this height control can be carried out with a conventional autofocus system or with the height control algorithm described below, which uses the spectral height information.
• spectral deviation ⁇ from a wavelength ⁇ o which corresponds to a height deviation ⁇ z, is shown schematically.
• the height of the object to be examined relative to the imaging optics is determined by a suitable z setting, e.g. B. z-table chosen so that a certain spectral line corresponds to a certain height level of the object.
• This line ⁇ 0 target maximum
• ⁇ 0 target maximum
• the Z table position is readjusted using an adjusting element, preferably a piezo adjusting element. If the deviation is less than this previously defined value, the entire spectrum is shifted accordingly by electronic means and then one of the defect detection algorithms described above is carried out.
• the above-mentioned method for height control is suitable - advantageously as an autofocus method for a confocal microscope.
• the advantages of confocal microscopy are known to be that a defined object plane, the focal plane, is worked out in the image. The confocal principle suppresses the optical image from another level. Therefore, only the focus plane is visible in the image.
• a certain wafer level can be focused using the confocal principle. All other layers appear dark in this image. In applications in which only a certain level is to be examined, the confocal method is therefore advantageous. This simplifies digital image processing for defect detection.
• confocal microscopy for the analysis of special levels, for example a wafer, requires a highly accurate autofocus system that focuses precisely on the level of interest.
• Usual autofocus methods (such as the triangulation method) only measure the altitude of a certain object point. Depending on the structure at hand, this does not necessarily focus on the level of interest. Averaging processes over several object points also focus only on any plane.
• the present invention permits the recording of a height histogram, ie the height distribution over a specific object area, by means of the spectral analysis. An evaluation of this distribution according to the height control algorithm given above then enables focusing on a specific plane, which corresponds, for example, to the wavelength ⁇ 0 in FIG. 3.
• a microscope objective 7 with a tube lens (not shown) generates an intermediate image Z, which lies in the plane of the pinhole arrangement 5.
• This intermediate image is imaged, for example, on the camera output KA of the microscope with the aid of imaging optics 9.
• a diode array spectrometer which consists of a grating 12, here a holographic grating, a diode row 13 and an evaluation unit 14, consisting here of memory, display unit and comparator.
• the object is scanned by a step-and-go mode with an xy- table, not shown.
• Known interferometric displacement measuring systems are provided for detecting the table position, for example, the control and detection of the table position in the x, y and Z direction being coupled to the spectral evaluation by a connection to the evaluation unit 14. In this embodiment, therefore, only a part of the intermediate image field is transferred to the spectrometer.
• the evaluation or defect detection takes place in the evaluation unit by means of a comparison with a stored ideal height professional (die-to-database comparison) or with one or more previous height profiles (die-to-die comparison) in accordance with the defect detection algorithm shown above with the height control algorithm shown.
• part of the intermediate image field imaged on the camera output KA is mapped with a disordered glass fiber bundle 15, which serves as a cross-sectional converter, in a diode array spectrometer consisting of a grating 13, a diode array 13 and an evaluation unit 14, by the fibers are arranged in the intermediate image plane as a light entrance bundle and in front of the entrance slit 11.
• a larger area of the intermediate image field can be spectrally analyzed at the same time.
• an anamorphic (cylinder-optical) cross-sectional converter 16 is used to image the intermediate image in the spectrometer slit 11 in a further advantageous embodiment according to FIG. 6, ie the imaging scales in the slit direction and perpendicular to the slit direction are different.
• This embodiment has the advantage that the entire intermediate image field or a larger part of it can be spectrally analyzed.
• the evaluation and defect detection as well as the raster movement and z control - are carried out as already described.
• a camera K which is mounted on the camera output KA of the microscope, is used for the spectral analysis of the entire intermediate image.
• the analysis is carried out pixel by pixel by comparing the gray values, when using a color camera by pixel-by-pixel color comparison.
• the gray values or colors are counted pixel by pixel and displayed spectrally according to color or gray value in a histogram.
• the spectral color information can also be obtained by using two black and white cameras in combination with different filters, as described in WO 95/00871 and SCANNING, Vol. 14, 1992, pp. 145-153.
• the height control is carried out by an autofocus system, preferably by the autofocus method shown above, and the defect detection by the defect detection algorithm shown.
• FIG. 8 shows a further embodiment, the white light source being replaced by illumination with 3 differently colored lasers L1-L3.
• the white light source being replaced by illumination with 3 differently colored lasers L1-L3.
• different image planes can now be highlighted.
• the resulting spectrum consists only of the lines of the laser wavelengths ⁇ i, ⁇ 2 and ⁇ 3 used .
• the integral number of events of the respective lines is proportional to the area share of the corresponding focus level. If there are defects in this plane, the number of photons detected decreases accordingly, as shown schematically in FIG. 9 for two wavelengths.
• Defects therefore only manifest themselves in the integral number of detected events, but not, as in the embodiments with a white light source, also in different wavelengths.
• the cross-sectional converters shown in the described embodiments are used as cross-sectional converters 14.
• the anamorphic figure 16 is shown.
• the specified defect detection algorithm is simplified. After subtracting the spectra only in the range of laser wavelengths used events are counted above a noise threshold. The number of these events is then proportional to the area share of the defect on the corresponding contour line.
• Table 1 shows the typical color spreads for different lenses.

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• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Computer Vision & Pattern Recognition (AREA)
• General Engineering & Computer Science (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Microscoopes, Condenser (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
• Length Measuring Devices By Optical Means (AREA)

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• 1997
  • 1997-03-29 DE DE19713362A patent/DE19713362A1/de not_active Ceased
• 1998
  • 1998-03-03 US US09/194,299 patent/US6674572B1/en not_active Expired - Fee Related
  • 1998-03-03 JP JP10541092A patent/JP2000512401A/ja not_active Ceased
  • 1998-03-03 EP EP98912431A patent/EP0904558A2/de not_active Ceased
  • 1998-03-03 WO PCT/EP1998/001177 patent/WO1998044375A2/de not_active Application Discontinuation

Non-Patent Citations (1)

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