JP2009265026A - Inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection device, capable of performing an inspection at high speed with high sensitivity. <P>SOLUTION: The inspection device 1 comprises an illumination part 10 for irradiating a surface of a wafer W with illuminating light; a two-dimensional imaging element 33 which detects light from the surface of the wafer W irradiated with the illuminating light; and a CPU 43 which reads optical information detected by the imaging element 33 to inspect the surface of the wafer W based on the optical information and determines a part suitable for inspection in the imaging element 33. The imaging element 33 is a CMOS image sensor capable of partially reading optical information in pixel units, and the CPU 43 reads only the optical information of the part suitable for inspection in the imaging element 33 to perform the inspection. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inspection apparatus for detecting a pattern formed on a surface of a substrate to be tested in a manufacturing process of a semiconductor element, a liquid crystal display element, or the like.

  Conventionally, various apparatuses for inspecting defects such as unevenness and scratches on a substrate surface using reflected light generated from a pattern formed on the surface of a substrate to be tested such as a semiconductor wafer or a liquid crystal glass substrate have been proposed ( For example, see Patent Document 1). In particular, in recent years, with the miniaturization of semiconductor processes, higher accuracy is also required for defect management of the test substrate.

For example, when measuring the pattern width of a test substrate with an SEM (scanning electron microscope), the measurement accuracy is high, but the measurement magnification is high and sampling is performed by sampling several points. It will take. Therefore, the light of a predetermined wavelength emitted from the light source is irradiated onto the surface of the test substrate by epi-illumination through the polarizer and the objective lens, and the reflected light from the test substrate by the illumination is converted into the objective lens and the polarizer. By detecting a Fourier image obtained through an analyzer that satisfies the conditions of crossed Nicols and a field stop with a CCD camera and selecting a place with high sensitivity in the Fourier image, the pattern width can be changed with high sensitivity. An inspection device for detection has been proposed.
JP 2000-155099 A

  However, the method as described above requires a long data transfer time to obtain an image.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an inspection apparatus capable of performing high-speed inspection with high sensitivity.

  In order to achieve such an object, an inspection apparatus according to the present invention includes an illumination unit that irradiates illumination light onto a surface of a test substrate, and an optical for observing the surface of the test substrate irradiated with the illumination light. A system, an image sensor for detecting light on a pupil plane of the optical system or a plane conjugate with the pupil plane, and optical information detected by the image sensor, and reading the surface of the substrate to be tested based on the optical information An inspection unit for inspecting, and a setting unit for obtaining a portion suitable for the inspection in the image sensor. In the image sensor, the optical information can be partially read out in units of pixels. The inspection is performed by reading out the optical information of the part suitable for the inspection in the image sensor.

  In the above invention, the image sensor is preferably a CMOS image sensor.

  Moreover, in the above-mentioned invention, the illumination light is linearly polarized light irradiated on the surface of the test substrate having a repetitive pattern, and the optical system is formed from the surface of the test substrate irradiated with the illumination light. Of the reflected light, it is preferable to receive a polarized light component whose polarization direction is substantially orthogonal to the linearly polarized light.

  Moreover, in the above-mentioned invention, it is preferable that the illuminating unit irradiates the surface of the test substrate with the illumination light by epi-illumination.

  According to the present invention, it is possible to perform inspection at high speed with high sensitivity.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. An inspection apparatus according to the present invention is shown in FIG. As shown in FIG. 1, the inspection apparatus 1 according to the present embodiment mainly includes a wafer stage 5, an objective lens 6, a half mirror 7, an illumination optical system 10, a detection optical system 20, and a control unit 40. Composed.

  On the wafer stage 5, a semiconductor wafer W (hereinafter referred to as a wafer W), which is a substrate to be tested, is placed with the pattern (repetitive pattern) formation surface facing upward. The wafer stage 5 is configured to be movable in three directions of x, y, and z axes orthogonal to each other (note that the vertical direction in FIG. 1 is the z axis direction). Thereby, the wafer stage 5 can support the wafer W so as to be movable in the x-, y-, and z-axis directions. The wafer stage 5 is configured to be rotatable about the z axis.

  The illumination optical system 10 includes a light source 11 (for example, a white LED or a halogen lamp), a condenser lens 12, an illuminance uniformizing unit 13, an aperture stop 14 in order of arrangement from the left side to the right side in FIG. A field stop 15, a collimator lens 16, and a detachable polarizer 17 (polarization filter) are included.

  Here, the light emitted from the light source 11 of the illumination optical system 10 is guided to the aperture stop 14 and the field stop 15 via the condenser lens 12 and the illuminance equalizing unit 13. The illuminance uniformizing unit 13 scatters illumination light and uniformizes the light quantity distribution. An interference filter can also be included. The aperture stop 14 and the field stop 15 are configured such that the size and position of the opening can be changed with respect to the optical axis of the illumination optical system 10. Therefore, in the illumination optical system 10, by operating the aperture stop 14 and the field stop 15, the size and position of the illumination area can be changed and the aperture angle of the illumination can be adjusted. The light that has passed through the aperture stop 14 and the field stop 15 is collimated by the collimator lens 16, passes through the polarizer 17, and enters the half mirror 7.

  The half mirror 7 reflects light from the illumination optical system 10 downward and guides it to the objective lens 6. Thereby, the wafer W is incidentally illuminated by the light from the illumination optical system 10 that has passed through the objective lens 6. On the other hand, the light incident on the wafer W can be reflected by the wafer W, return to the objective lens 6 again, pass through the half mirror 7, and enter the detection optical system 20.

  The detection optical system 20 includes a detachable analyzer 21 (polarization filter), a lens 22, a half prism 23, a belt run lens 24, a field stop 25, in order of arrangement from the lower side to the upper side in FIG. And a two-dimensional image sensor 33. The analyzer 21 is arranged so as to be in a crossed Nicols state (a state in which the polarization directions are orthogonal) with respect to the polarizer 17 of the illumination optical system 10. Since the polarizer 17 of the illumination optical system 10 and the analyzer 21 of the detection optical system 20 satisfy the condition of crossed Nicols, the amount of light received by the detection optical system 20 is zero unless the polarization main axis rotates in the pattern of the wafer W. Close to.

  The half prism 23 branches the incident light beam in two directions. One light beam passing through the half prism 23 forms an image of the surface of the wafer W on the field stop 25 via the belt run lens 24 and projects the image of the pupil plane of the objective lens 6 onto the two-dimensional image sensor 33. Therefore, the luminance distribution on the pupil plane of the objective lens 6 is reproduced on the imaging surface of the two-dimensional image sensor 33, and an image (Fourier image) of the wafer W Fourier-transformed by the two-dimensional image sensor 33 can be captured. It is. The Bertrand lens is generally a converging lens that connects the image of the rear focal plane of the objective lens to the focal plane of the eyepiece, but an optical system such as a microscope is generally telecentric on the image side. Since the rear focal plane of the objective lens is the pupil plane, in this embodiment, the lens 24 that forms an image of the pupil plane of the objective lens 6 on the imaging plane of the two-dimensional imaging device 33 is referred to as a belt run lens 24. .

  The field stop 25 can change the aperture shape in a plane perpendicular to the optical axis of the detection optical system 20. Therefore, the two-dimensional image sensor 33 can detect information in an arbitrary region of the wafer W by operating the field stop 25. The other light beam passing through the half prism 23 is guided to a second two-dimensional image sensor 50 for capturing an image of a normal wafer W that has not been Fourier-transformed.

  Here, the reason why the Fourier image (that is, the image of the pupil plane of the objective lens 6) is imaged in the defect inspection of the present embodiment is as follows. If an image obtained by directly imaging the pattern of the wafer W is used in the defect inspection, the pattern defect cannot be optically detected when the pattern pitch is less than the resolution of the inspection apparatus. On the other hand, in the Fourier image, if there is a defect in the pattern of the wafer W, the symmetry of the reflected light is lost, and the luminance, color, etc. of portions orthogonal to the optical axis of the Fourier image change due to structural birefringence. Therefore, even when the pattern pitch is less than the resolution of the inspection apparatus, it is possible to detect a defect in the pattern by detecting the change in the Fourier image.

  Further, the relationship between the incident angle of the illumination light on the wafer W and the imaging position in the pupil plane will be described with reference to FIG. As shown by the broken line in FIG. 2, when the incident angle of the illumination light to the wafer W is 0 °, the imaging position on the pupil is the pupil center. On the other hand, as shown by the solid line in FIG. 2, when the incident angle is 64 ° (corresponding to NA = 0.9), the imaging position on the pupil is the outer edge of the pupil. That is, the incident angle of the illumination light on the wafer W corresponds to the radial position in the pupil on the pupil. Further, the light that forms an image at a position within the same radius from the optical axis in the pupil is light that is incident on the wafer W at the same angle.

  The two-dimensional image pickup device 33 is a CMOS image sensor having a Bayer array color filter array, picks up the above-described Fourier image, and can freely set a readout area in units of pixels. ) Only at high speed. Note that a circuit that enables such partial reading is provided in the two-dimensional image sensor 33 (on-chip).

  The control unit 40 includes a recording unit 41 that records Fourier image data, an input interface 42, a CPU 43 that executes various arithmetic processes, a monitor 44, and an operation unit 45. Perform overall control. The recording unit 41, the input interface 42, the monitor 44, and the operation unit 45 are electrically connected to the CPU 43, respectively. The CPU 43 analyzes the Fourier image by executing the program, obtains a region having high sensitivity to the change of the pattern in the Fourier image picked up by the two-dimensional image pickup device 33, or the wafer W in the Fourier image. Read only areas that are sensitive to pattern changes. The input interface 42 has a connector for connecting a recording medium (not shown) and a connection terminal for connecting to an external computer (not shown), and reads data from the recording medium or the computer. Do.

  A method for inspecting the wafer W using the inspection apparatus 1 configured as described above will be described with reference to the flowcharts shown in FIGS. First, a method for determining a region having high sensitivity to a pattern change in a Fourier image captured by the two-dimensional image sensor 33 will be described using the flowchart shown in FIG. In the determination method of the highly sensitive region, first, in step S101, the polarizer 17 of the illumination optical system 10 and the analyzer 21 of the detection optical system 20 are inserted on the optical axis. In the next step S102, the light source 11 of the illumination optical system 10 is turned on.

  In the next step S <b> 103, the wafer W on which the repeated pattern is formed is placed on the wafer stage 5, and the pattern to be measured (one shot) on the wafer W is moved below the objective lens 6 by the wafer stage 5. At this time, a wafer W on which a plurality of patterns having the same shape with different exposure conditions (dose and focus) are used is used. The wafer W is aligned (positioned) on the wafer stage 5, and an arbitrary position can be observed by controlling the position of the wafer stage 5.

  Then, the illumination light emitted from the light source 11 passes through the aperture stop 14 and the field stop 15 via the condenser lens 12 and the illuminance uniformizing unit 13, and is converted into parallel light by the collimator lens 16 and then the polarizer 17. After being reflected by the half mirror 7, the wafer W is irradiated through the objective lens 6. Then, the reflected light from the wafer W passes through the objective lens 6 and the half mirror 7 and enters the detection optical system 20, and the light incident on the detection optical system 20 includes the analyzer 21, the lens 22, the half prism 23, A Fourier image is projected on the imaging surface of the two-dimensional imaging device 33 through the Bertrand lens 24 and the field stop 25.

  Therefore, in the next step S104, a Fourier image is captured by the two-dimensional image sensor 33, and the captured Fourier image is recorded in the recording unit 41.

  In the next step S105, the CPU 43 determines whether or not all necessary patterns on the wafer W have been imaged. If the determination is yes, the process proceeds to step S106, and if the determination is no, the process returns to step S103, and a pattern (another shot) that has not yet been imaged is moved below the objective lens 6 to perform image capture in step S104. . As a result, the recording unit 41 records color data of a plurality of Fourier images having different exposure conditions for the same shape pattern.

In step S106, the CPU 43 generates luminance data (average value) of R (red), G (green), and B (blue) for each position of the Fourier image for each Fourier image. First, as shown in FIG. 5, the luminance data is obtained by dividing a Fourier image (for example, the Fourier image FI ₁ of the first frame) into a plurality of square lattice-like divided regions P at equal intervals in the vertical and horizontal directions. For each divided region P, an average of RGB luminance values is obtained for each color. This process is performed for each Fourier image. Thus, the Fourier image FI ₁ ～FI _n from the first frame to the n th frame, for each divided area P of each Fourier image, R, G, generates each luminance data indicating the gradation of each color component of B Will be.

In the next step S107, paying attention to the same divided area as shown in FIG. 6, the CPU 43 converts the gradation difference data indicating the gradation difference between the Fourier images FI _{1 to} FI _n in the same divided area into R, G , B for each color component. Specifically, _assuming that an arbitrary divided region on the Fourier image FI is P _m , first, for each Fourier image FI _{1 to} FI _n , luminance data of each color component in the divided region P _m (obtained in step S106). Each). Then, the difference among the gradation values of luminance data corresponding to the divided area P _m, R, G, and maximum and minimum values extracts the maximum and minimum values of each color component, extracted in B Calculate the value. And these processes are performed about all the division areas. Thus, for all the divided areas of the Fourier image, gradation difference data indicating a gradation difference between the Fourier image in the divided area P _m (the difference value between the maximum value and the minimum value of the gradation) is, R, G , B are generated for each color component.

  In step S108, the CPU 43 determines the maximum and minimum gradation values among the divided areas of the Fourier image based on the gradation difference data (difference value between the maximum and minimum gradation values) obtained in step S107. A color and a divided region having a maximum difference value from the value are obtained, the divided region is determined as a region having high sensitivity, and this is determined as a detection condition. 7 to 9 are diagrams showing the distribution state of the gradation difference in each divided region of the Fourier image for each color component. In the examples of FIGS. 7 to 9, the upper left area of the gradation difference B shown in FIG. 9 is the maximum sensitivity area. In this way, in order to detect a change in the line width and profile of the pattern with high sensitivity, it is determined which color of R, G, and B should be used and which divided region should be used in the Fourier image. Can do.

  As described above, it is possible to detect an unknown pattern change from an image captured by the two-dimensional image sensor 33. However, when a CCD image sensor is used for the two-dimensional image sensor 33, all pixels must be read for reading data, so that the reading time becomes long and throughput does not increase.

  A method for detecting a change in pattern at high speed with high sensitivity will be described with reference to the flowchart shown in FIG. In this pattern detection method, first, in step S201, the polarizer 17 of the illumination optical system 10 and the analyzer 21 of the detection optical system 20 are inserted on the optical axis. Next, in step S202, the CPU 43 sets a reading area (pixel) of the two-dimensional image sensor 33 so as to read only the region of the maximum sensitivity obtained in steps S101 to S108.

  In the next step S203, the light source 11 of the illumination optical system 10 is turned on. Next, in step S <b> 204, the wafer W to be inspected is placed on the wafer stage 5, and the pattern to be inspected (for one shot) on the wafer W is moved below the objective lens 6 by the wafer stage 5.

  Then, the illumination light emitted from the light source 11 passes through the aperture stop 14 and the field stop 15 via the condenser lens 12 and the illuminance uniformizing unit 13, and is converted into parallel light by the collimator lens 16 and then the polarizer 17. After being reflected by the half mirror 7, the wafer W is irradiated through the objective lens 6. Then, the reflected light from the wafer W passes through the objective lens 6 and the half mirror 7 and enters the detection optical system 20, and the light incident on the detection optical system 20 includes the analyzer 21, the lens 22, the half prism 23, A Fourier image is projected on the imaging surface of the two-dimensional imaging device 33 through the Bertrand lens 24 and the field stop 25.

  Then, in the next step S205, the CPU 43 determines only pixel data of a region that is highly sensitive to the pattern change of the wafer W in the Fourier image from the readout area (pixel) of the two-dimensional image sensor 33 set in step S202. , And the brightness (light quantity) of the reflected light is measured from the read pixel data (from the brightness change) to detect a change in the pattern on the wafer W (that is, a defect in the pattern). For example, when the image size of the two-dimensional image sensor 33 is 800 × 600 pixels and the size of the reading area is 10 × 10 pixels, the ratio of the pixels to be read is 0.02%, so that reading can be performed very quickly.

  As described above, according to the inspection apparatus 1 of the present embodiment, the CPU 43 reads only pixel data (optical information) in a reading area with high sensitivity to the pattern change of the wafer W in the two-dimensional imaging element 33. Since the data transfer time can be shortened by minimizing the number of pixels from which data is read, the pattern formed on the surface of the wafer W can be inspected at high speed with high sensitivity. At this time, it is preferable to use a CMOS image sensor as the two-dimensional imaging device 33. In this way, in the CMOS image sensor, such partial reading can be easily performed, so that it is relatively easy. The above effects can be obtained.

  Further, as described above, it is preferable to detect the luminance (Fourier image) of the pupil plane in the detection optical system 20 (objective lens 6) using the two-dimensional imaging device 33. In this way, Even when the pitch of the pattern is less than the resolution of the inspection apparatus, it is possible to detect a defect in the pattern by detecting a change in the pattern in the Fourier image.

  At this time, it is preferable that the detection optical system 20 receives a polarization component whose polarization direction is substantially orthogonal to the illumination light that is linearly polarized light out of the light from the wafer W. In this way, a so-called crossed Nicol state is obtained. Thus, a highly sensitive inspection using structural birefringence becomes possible. The polarization directions of the polarizer 17 and the analyzer 21 are not limited to 90 ° (in a crossed Nicol state), but may be finely adjusted according to the rotation of elliptically polarized light due to structural birefringence generated in the pattern to be inspected. Good.

  At this time, it is preferable to illuminate the surface of the wafer W by epi-illumination. In this way, the size of the apparatus can be reduced.

  In the above-described embodiment, the inspection apparatus 1 that performs the defect inspection of the wafer W has been described as an example. However, the test substrate is not limited to the wafer W, and may be a liquid crystal glass substrate, for example.

  In the above-described embodiment, a region having high sensitivity to a change in pattern is determined based on the gradation difference data (difference value between the maximum value and the minimum value of the gradation). It is not something that can be done. Therefore, a modified example of the method for determining a highly sensitive region will be described using the flowchart shown in FIG. As in the case of the above-described embodiment, this method uses a wafer W on which a plurality of patterns having the same shape with different exposure conditions (dose and focus) are formed, and a Fourier image of each pattern and a line for each pattern. Based on the width data, a region having high sensitivity to the pattern change is determined. The line width data corresponding to the above pattern is obtained by using a line width measuring instrument such as a scatterometer or a scanning electron microscope (SEM), and these line width data groups are input in advance. It is assumed that the data is input from the interface 42 and recorded in the recording unit 41.

  First, similarly to the above-described embodiment, in step S151, the polarizer 17 of the illumination optical system 10 and the analyzer 21 of the detection optical system 20 are inserted on the optical axis. In the next step S152, the light source 11 of the illumination optical system 10 is turned on.

  In the next step S153, a wafer W on which a plurality of patterns having the same shape with different exposure conditions (dose and focus) are formed is placed on the wafer stage 5, and a pattern (one shot) to be measured on the wafer W is measured. The wafer stage 5 is moved below the objective lens 6. In the next step S154, a Fourier image is captured by the two-dimensional image sensor 33, and the captured Fourier image is recorded in the recording unit 41.

  In the next step S155, the CPU 43 determines whether or not imaging has been completed for all patterns on the wafer W. If the determination is yes, the process proceeds to step S156. If the determination is no, the process returns to step S153, and a pattern (another shot) that has not been imaged yet is moved below the objective lens 6 to perform the image capture in step S154. .

  In step S156, as in the above-described embodiment, the CPU 43, for each Fourier image, brightness data (average value) of R (red), G (green), and B (blue) for each divided region of the Fourier image. Are generated respectively.

In the next step S157, attention is paid to the same divided area, and the CPU 43 calculates an approximate expression indicating the change rate between the gradation value and the line width of the pattern in the same divided area of each of the Fourier images FI _{1 to} FI _n as R , G, and B for each color component. Specifically, _assuming that an arbitrary divided region on the Fourier image FI is P _m , first, the line width data of the pattern corresponding to each of the Fourier images FI _{1 to} FI _n is read from the recording unit 41. At this time, for each of the Fourier images FI _{1 to} FI _n , the luminance data of each color component in the divided region P _m (obtained in step S156) is extracted. Next, for each of the Fourier images FI _{1 to} FI _n , a correspondence relationship between the line width of the pattern and the gradation value of the luminance data in the divided area P _m is obtained.

Then, based on the correspondence between the gradation value of a line width and the divided region P _m of the pattern, approximating that indicates the rate of change of the line width of the gradation values and patterns in the divided area P _m by the least square method Find the formula. Here, the line width of the pattern corresponding to each of the Fourier images FI _{1 to} FI _n is set to y, the gradation value of B (or R or G) in the divided region P _m is set to x, the inclination is set to a, and y When the intercept is b, the approximate expression is expressed by the following expression (1).

  y = ax + b (1)

  The absolute value of the coefficient a corresponds to the reciprocal of the gradation change with respect to the change in the line width of the pattern (that is, the reciprocal of the detection sensitivity with respect to the pattern change). That is, when the absolute value of the coefficient a is small, the gradation change of the Fourier image is large even if the difference in line width is the same, so that the detection sensitivity to the change of the pattern is higher. These processes are performed for each of the R, G, and B color components for all the divided regions.

Next, in step S158, the CPU 43 obtains a correlation error between the approximate expression obtained in step S157 and the line width of the pattern for each of R, G, and B color components in each divided region on the Fourier image. Specifically, deviation data between the line width of the pattern corresponding to each of the Fourier images FI _{1 to} FI _n and the line width of the pattern calculated using the approximate expression are used as R, G, and B color components. The standard deviation is calculated for each color component of each divided region from the calculated deviation data, and the value is used as the correlation error.

  In step S159, based on the coefficient a obtained in step S157 and the correlation error obtained in step S158, the CPU 43 has a small absolute value of the coefficient a in the Fourier image divided region and a sufficient correlation error. A small divided area is obtained, the divided area is determined as a highly sensitive area, and this is determined as a detection condition. Specifically, for example, each divided region is scored according to the small absolute value of the coefficient a and the small correlation error, and a highly sensitive divided region is selected based on the scoring result. decide. Even in this case, in order to detect a change in the line width or profile of the pattern with high sensitivity, it is necessary to determine which color of R, G, and B should be used and which divided region should be used in the Fourier image. Can do.

It is a schematic diagram of the inspection device concerning the present invention. It is explanatory drawing which shows the relationship between the incident angle of the illumination light to a wafer, and the imaging position in a pupil. It is a flowchart which shows the determination method of an area | region with high sensitivity with respect to the change of a pattern. It is a flowchart which shows the method of detecting the change of a pattern at high speed with high sensitivity. It is a figure which shows an example of the state which divided the Fourier image into the area | region. It is a schematic diagram which shows the extraction state of luminance data. It is a figure which shows the distribution state of the gradation difference of R in a Fourier image. It is a figure which shows the distribution state of the gradation difference of G in a Fourier image. It is a figure which shows the distribution state of the gradation difference of B in a Fourier image. It is a flowchart which shows the modification of the determination method of an area | region with high sensitivity.

Explanation of symbols

W wafer (test substrate)
DESCRIPTION OF SYMBOLS 1 Inspection apparatus 6 Objective lens 10 Illumination optical system (illumination part) 17 Polarizer 20 Detection optical system (optical system) 21 Analyzer 33 Two-dimensional image sensor (CMOS image sensor)
40 control unit 43 CPU (inspection unit and setting unit)

Claims (4)

An illumination unit for illuminating illumination light on the surface of the test substrate;
An optical system for observing the surface of the test substrate irradiated with the illumination light;
An image sensor for detecting light in a pupil plane of the optical system or a plane conjugate with the pupil plane;
Reading the optical information detected by the image sensor, and an inspection unit for inspecting the surface of the test substrate based on the optical information;
A setting unit for obtaining a portion suitable for the inspection in the image sensor,
In the image sensor, the optical information can be partially read out in units of pixels,
The inspection apparatus reads out the optical information of a part suitable for the inspection in the image sensor and performs the inspection.   The inspection apparatus according to claim 1, wherein the image sensor is a CMOS image sensor. The illumination light is linearly polarized light applied to the surface of the test substrate having a repetitive pattern;
3. The optical system according to claim 1, wherein the optical system receives a polarization component whose polarization direction is substantially orthogonal to the linearly polarized light in the reflected light from the surface of the test substrate irradiated with the illumination light. The inspection device described.   The said illuminating part irradiates the said illumination light on the surface of the said to-be-tested board by epi-illumination, The inspection apparatus as described in any one of Claim 1 to 3 characterized by the above-mentioned.