JPH0357945A - Defect inspection instrument - Google Patents

Abstract

PURPOSE:To enable judgment of whether a defect exists on the surface or back of a flat object by performing a photoelectric detection of scattered light individually at each specified wavelength area subjected to spectral analysis to compare sizes of photoelectric signals thus obtained. CONSTITUTION:A reticle with a pellicle is placed on a two-dimensional scanning stage 40 and moves in directions x and y with respect to an irradiation beam. A stage controller 46 controls a motor 48 using positional information from an encoder 42 as feedback input to move the stage 40 two-dimensionally. After amplified with amplifiers 60d-60f, output signal levels of optoelectro transducers 28d-28f are converted into digital values with A/D converters 62d-62f to be stored in a memory 52 through a processor 44. After the end of scanning of the stage 40, the processor 44 reads out an inspection data at each scanning position from the memory 52 to compute a required ratio and moreover, the results are compared in size with a reference ratio to discriminate an attached surface. Then, the results are shown on a displayer 54.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an apparatus for inspecting fine particulate foreign matter adhering to a light-transmitting flat object, such as glass or a thin polymer film such as nitrocellulose. The present invention relates to an inspection device capable of determining foreign matter defects on the front and back surfaces of a flat object.

[Conventional technology]

Conventionally, this type of device has had a structure as shown in FIG. 3 as an example. In FIG. 3, pellicles (polymer thin films) 33 are stretched across a frame 35 at regular intervals on the surface of a reticle (or mask) 34 for manufacturing semiconductor devices. This pellicle 33 is used to prevent foreign matter from directly adhering to the surface of the reticle 34. The thickness of the pellicle 33 is approximately 1 μm, and it transmits 90% or more of exposure illumination light (wavelength 436 ns, 365 nm, etc.). rate. The thickness (standoff) of the frame 35 is approximately a few inches thick, and this is determined in consideration of the depth of focus on the reticle side of the projection optical system of the exposure apparatus.

When projecting and exposing an IC pattern onto a wafer using such a reticle with a pellicle, a foreign object image on the reticle surface may be reduced in size and transferred onto the wafer according to the reduction magnification of the projection optical system, but the pellicle 33 Images of foreign matter of the same size attached to the wafer will be largely defocused on the wafer and will not be resolved. However, the size of the foreign object on the pellicle 33 is too large (several + μm or more).
Then, it appears as a defocused shadow. Therefore, as shown in FIG. 3, it is necessary to also inspect foreign matter attached to the pellicle 33. Illumination light (coherent light, quasi-monochromatic light, etc.) emitted from the light source 31 vertically illuminates the pellicle 33 via the condenser lens 32 .

If a foreign object exists within the irradiation area (spot irradiation area) of the pellicle 33, scattered light with relatively weak directionality is generated from the foreign object.

This scattered light is focused by a condensing lens 35 onto the light receiving surface of a photoelectric converter (photomultiplier, etc.) 36 .

Then, it is determined whether or not it is a foreign object based on the level of the photoelectric signal. At this time, it is necessary to inspect the entire surface of the pellicle 33, so a mechanism is provided to scan the illumination light one-dimensionally (or two-dimensionally) and to move the pellicle 33 one-dimensionally. In addition, as other pellicle inspection equipment,
As disclosed in Japanese Patent No. 52696, a laser beam is irradiated onto the surface to be inspected at a grazing angle to form a band-shaped irradiation area on the surface of the inspection object, and side scattering of the scattered light from the irradiation area is detected. It is also known to detect foreign objects by placing a one-dimensional array sensor in a position that receives light. [Problems to be Solved by the Invention] However, in the conventional technique as shown in FIG.
It was not possible to determine whether it was attached to the back side (hereinafter referred to as the back side) or the light source side (hereinafter referred to as the front side). Furthermore, the method disclosed in Japanese Patent Publication No. 63-52696 can only detect foreign matter only on the front side of a flat object. In addition, as a method for determining whether foreign matter is attached to the front or back surface of the glass base +1i (reticle, mask, etc.), Japanese Patent Laid-Open No. 58
A technique disclosed in Japanese Patent No. 62544 is also known, which uses a photoelectric element that receives scattered light generated in the space on the front side of the substrate and detects scattered light generated in the space on the back side of the substrate. A pair with a photoelectric element is required.

For this reason, it may be possible to distinguish between the front and back sides of a pellicle with foreign matter attached using the same principle, but when the pellicle is attached to a reticle, scattered light is blocked by the reticle pattern (chrome layer), and inspection is impossible. Knowing whether the foreign matter attached to the pellicle exists on the front side or the back side is important in the photolithography process.
It has extremely important meaning. If foreign matter adheres to the back side of the pellicle, in the worst case, the foreign matter will separate from the pellicle and re-adhere to the reticle, resulting in defects in shots of exposed wafers using the reticle. Therefore, for such a reticle, it is necessary to remove the pellicle together with the frame, remove foreign matter from the reticle, and replace it with a new pellicle.

Therefore, it is important to know for sure whether or not a new pellicle needs to be replaced before exposing the actual device. The present invention aims to provide a defect inspection device that can detect the presence or absence of foreign matter attached to a thin film such as a pellicle, or a thin glass plate, etc., and can easily and reliably discriminate between the front and back surfaces (adhered surface discrimination). Purpose. [Means for Solving the Problems] In order to achieve the above object, the present invention uses polychromatic light having a predetermined wavelength band or white (broadband) light to illuminate a flat object as a test object. A wavelength-selective optical element (microink mirror, cold mirror, prism, etc.) is installed in the receiving system for the scattered light from defects such as foreign objects, and the scattered light for each specific wavelength range is individually detected. By photoelectrically detecting and comparing the magnitude of these photoelectric signals, we were able to determine whether a defect exists on the front or back surface of a flat object. [Operation] FIG. 1 is a diagram explaining the principle of the present invention, in which the pellicle 11
Pellicle 1 with foreign matter 12 attached to the back side of pellicle 1
The case where polychromatic light (or white light) S1 is irradiated perpendicularly from the surface side of 1 is shown. From the conclusion, when photoelectrically detecting the scattered light from a foreign object through the bericle 1l as shown in Fig. 1, the wavelength distribution of the scattered light toward the photoelectric detector is the polychromatic light S1.
The wavelength distribution is different from that of . On the other hand, when a foreign object is attached to the surface side of the pellicle 11, the scattered light from the foreign object heads toward the photoelectric detector while maintaining almost the same wavelength distribution as the polychromatic light S1. Therefore, by detecting the difference in the wavelength distribution of the scattered light incident on the light receiving system, it is possible to identify the surface on which foreign matter has adhered. The above will be further explained in detail with reference to Figure 1. In the state shown in Fig. 1, among the scattered light generated from the foreign object l2, the scattered light S returns to the surface side at an angle θ1 with respect to the polychromatic light S1.
Let's focus on 2. The scattered light St is further divided into light S, which is emitted from the surface of the pellicle 11 and heads toward the light receiving system, and light S4, which travels toward the back surface by internal reflection. The emission angle θ2 of the light S is the pellicle l1
If the refractive index of is n, then the following equation is obtained. θ! =sin −' (n −sin θ. )−・
------- (1) On the other hand, optical S. The light is refracted and reflected on the back surface of the velicle 11 and is divided into light SS and S6, and the light S reflected on the inside is refracted and reflected on the surface of the velicle 11. Of the light S, the light S that is refracted and emitted from the surface of the pellicle 11 heads toward the light receiving system almost parallel to the light S. Therefore, the exit angle of the light S is also θ2.

Here, the phase difference δ between the lights S and S is expressed by the following equation, where d is the thickness of the pellicle l1.

λ Therefore, the condition that the phase difference δ is exactly 360'', that is, δ
The wavelength λm at which = 2mπ (where m is an arbitrary integer) is as follows. 2 ° n 0 d 0 COS θ1 λm (3) Also, from equation (1), the angle θ1 is, so by substituting this into equation (3), the specific wavelength λm Hato becomes. Therefore, when the angle between the optical axis of the scattered light receiving system and the normal to the pellicle 11 is set to θ2, the light S incident on the scattered light receiving system
．． ,S? The spectral characteristics of have a peak at wavelength λm, and are attenuated in wavelength ranges on both sides of the peak.

In the present invention, by examining the spectral characteristics of the scattered light from the foreign matter adhering to the pellicle, the surface to which the foreign matter has adhered is determined. As is clear from the above principle, if the angle (90° - θ2) between the optical axis of the scattered light receiving system and the pellicle surface is adjusted appropriately,
It can be seen that even under the same illumination conditions, the specific wavelength λm that is the peak in the spectral characteristics of the scattered light changes.

Similarly, by tilting the irradiation optical axis of the polychromatic light SI from perpendicular to the pellicle, the specific wavelength λm changes, but as the inclination of the irradiation optical axis increases, foreign matter on the pellicle surface is irradiated. There is a difference between the beam intensity and the beam intensity that irradiates the foreign matter on the back surface of the pellicle, and furthermore, the spectral characteristics of the irradiation beam that penetrates the back surface may change. Therefore, it is desirable that the irradiation axis of the polychromatic light (white light) S1 be close to perpendicular to the surface to be inspected.

To give an example here, the thickness d of the pellicle is 1 μm.
, when the refractive index n is 1.5 and the scattered light acceptance angle θ2 is 80°, the specific wavelength λm that becomes the peak from the above equation (4) is λm″.2.26/m (where m is an integer). If it is assumed that the peak wavelength λm appears in the visible range, then λ4ξ565n is equal to m=4.

The peak wavelength next to this peak wavelength in the visible range is m-
3, when m=5, respectively λ3ξ753 r+a+
, λ5! =i452nw+. In addition, when detecting scattered light, make sure that the light receiving system is not sensitive to wavelengths longer than the adjacent peak wavelength λ3 and shorter than λ5, or change the wavelength band of the illumination light between wavelengths λ3 and λ5. It is better to limit it to [Embodiment] FIG. 2 shows the configuration of an inspection apparatus according to a first embodiment of the present invention. The light source 21 is a white light source such as a tungsten lamp or a halogen lamp. In this embodiment, a wide-band light source with continuous spectral characteristics is used. Assume that illumination light of wavelength is used. The illumination light (white light) from the light B21 enters the condenser lens 22 via the beam splitter 26.

The optical axis of the condensing lens 22 is set perpendicular to the surface of the vericle 23 stretched over the reticle 24, and the illumination light is directed to the vericle 23.
The light is focused within a local area (for example, 1 Peng angle) on 3. At this time, it is preferable to provide an illumination field stop (aperture) at a position conjugate with the pellicle 23 in the illumination optical system, so that the illumination local area on the pellicle 23 is shaped into a clean rectangle, a minute slit, or a circle.

On the other hand, the scattered light receiving system includes a condenser lens 25 having an optical axis inclined at an angle θ with respect to the normal line of the vericle 23, and looks into the illumination area of the vericle 23. Here, the angle θ is
As explained earlier, the specific wavelength λm that is the peak on the spectral characteristics of the scattered light is determined so that it can be sufficiently identified.
In practice, the angle is set in the range of 45 to 85 degrees.

Now, a part of the scattered light from the foreign object passes through the lens 25 and is split into light in two wavelength ranges by the microchroic mirror 27c, and the light in the wavelength range reflected by the microchroic mirror 27c is transmitted to the photoelectric converter. The light is received at 28d. The light in the wavelength range that passes through the guichroic mirror 27c is further divided into light in two wavelength ranges by the guichroic mirror 27d. The light in the wavelength range reflected by the guichroic mirror 27d is received by the photoelectric converter 28e, and is then reflected by the guichroic mirror 27d.
The light in the wavelength range that passes through 7d is received by the photoelectric converter 28f.

As an example, the boundary wavelength of Gikroic Mirror 27c is 5.
00n- cold mirror (reflects the short wavelength side and transmits the long wavelength side), and if the guichroic mirror 27d is a cold mirror with a boundary wavelength of 600 nm, then the magnitude of the output signal of the photoelectric converter 27d is Vd. is the wavelength of 500n of the scattered light from the foreign object (pellicle irradiation area).
It corresponds to the total amount of light distributed in a shorter wavelength range. Further, the magnitude Ve of the output signal of the photoelectric converter 28e corresponds to the total amount of light distributed in the wavelength range of 500 nm to 600 r+n+, and the magnitude Vf of the output signal of the photoelectric converter 28f corresponds to 600 rv+ It depends on the total amount of light distributed in a longer wavelength range.

Therefore, two dichroic mirrors 27C127d
functions as a spectroscopic means that divides the wavelength distribution of scattered light into three wavelength ranges.

By the way, in Fig. 2, there is a beam splinter 2 in the illumination optical path.
6 is arranged to guide a part of the illumination light toward a reference system, which will be explained in detail later.

Now, FIG. 4 shows an example of a processing circuit for evaluating each output signal of the photoelectric converters 28d, 28e, and 28f. In this embodiment, in order to simplify the explanation, the reticle 24 with a velicle is placed on a two-dimensional scanning stage 4o, and the x. , y direction. Further, the movement of the scanning stage 40 is measured by a coordinate position measuring device (such as an encoder) 42 with a resolution finer than the size of the local illumination area.

In FIG. 4, a processor 44 outputs a movement command to a stage controller 46. The stage controller 46 uses the position information from the encoder 42 as feedback input to control the motor 48 to move the stage 40 to the second position.
Move dimensionally. The position information of the encoder 42 is input to a manipulating coordinate generation circuit 50 that converts the position of the foreign object so that it can be displayed on an Lm-square or 5-square map.

The output signal level of each photoelectric converter 28d, 28e, 28f is amplified by amplifiers 60d, 60e, 60f, and then analog-to-digital converter (A/D) 62d, 62e, 6
2f into a digital value, and the processor 44
The data is stored in the memory 52 via.

The display 54 displays the inspection results using a color cathode ray tube, and displays the entire surface of the pellicle 23 in a grid map of 1 square or 5 mo + square, and if the detected foreign object is on the surface side, a grid map of 3 squares corresponding to the location of the foreign object is displayed. Or 5!
For example, fill the corner area in green, and the back side in red. In addition, the size of detected foreign objects is classified into three ranks, such as A rank, B rank,
Characters of C rank are also displayed at the same time. The rank display may be expressed by the grade ffl (g degrees) when filled in green or red, or may be expressed by slightly changing the tone. Now, in the actual inspection, the stage 40 is moved one-dimensionally in the X direction, then stepped in the Y direction by the size of the local illumination area, and then moved again in the X direction, which is repeated in sequence. Information regarding the mutual standard ratio of the magnitude of each photoelectric signal is stored in the memory 52 in advance. This standard ratio is, for example, the ratio of the photoelectric signals Vd, Ve,
It is determined to be approximately equal to Vd/Ve or Vf/Ve. In this embodiment, settings are made such that the peak wavelength λm on the spectral characteristics appears in the wavelength range that the photoelectric converter 28e receives. Therefore, the ratio Vd/Ve (or Vf/Ve) when the foreign object is on the front side is almost equal to the standard ratio, and the ratio Vd/Ve (or Vf/Ve) when the foreign object is on the back side is almost equal to the standard ratio.
f/Ve) will be significantly different from the standard ratio (eg, a large value).

The processor 44 responds to a sampling command output from the map coordinate control circuit 50 each time the stage 42 moves by one position, for example, and controls the A/Ds 62d, 62e,
Each output value of 62f is stored in Me-E-+J52.

After the stage 40 scans, the processor 44 reads out the inspection data (Vd, Ve, Vf) for each scanning position W (sampling position W) from the memory 52, and calculates the ratio V d /V.
e (or V f /V e ), and further compares the magnitude relationship between the result and a standard ratio to determine the adhesion surface, and displays the result on the display 54. The processor 52 also ranks the different proboscis sipes based on the magnitude of the photoelectric signal level and displays the results. In this embodiment, the light received by the photoelectric converter 28e is reinforced with a phase difference of 2 mπ as explained in FIG. 1, so the light intensity level does not necessarily correspond to the size of the foreign object.

Therefore, in order to determine the size of the foreign object, it is preferable to evaluate the signal levels (Ve, Vf) from the other photoelectric converters 28d and 28f.

Next, a second embodiment of the present invention will be explained with reference to FIG. In the second embodiment, the illumination light (white light) itself is separated with the same characteristics as the spectroscopic means in the scattered light receiving system to create a reference signal for each wavelength range, and standardization is performed using this reference signal. It is. In FIG. 2, the illumination light branched by the beam splinter 26 is split into two wavelength ranges by a dichroic ink mirror 27a, and the light transmitted through this is further split into two wavelength ranges by a dichroic ink mirror 27b. .

The wavelength selection characteristics of the dichroic mirror 27a are the same as those of the dichroic mirror 27c, and the wavelength selection characteristics of the dichroic mirror 27b are the same as those of the dichroic mirror 27d.
is the same as Therefore, the photoelectric converter 28a has, for example, 5
Receives the total amount of light of wavelengths on the shorter wavelength side than 00n-,
The photoelectric converter 28b receives the total amount of light in the intermediate wavelength range of 500 nm to 600 nm, and the photoelectric converter 28c receives the total amount of light in the wavelength range longer than 600 nm.

FIG. 5 shows an example of the structure of the processing circuit in the second embodiment, in which standardization is performed using a divider.

Although division is performed in an analog manner here, division may also be performed using a processor program.

The signal Va output from the photoelectric converter 28a and amplified by the amplifier and the signal Vd output from the photoelectric converter 28d and amplified by the amplifier are input to the divider 70A, and the divider 70A calculates SA=Va. /Vd value is output.

Similarly, the signal vb from the photoelectric converter 28b and the photoelectric converter 2
The signal Ve from 8e is divided into S B by the divider 70B.
= Vb/Ve is calculated, and the signal Vc from the photoelectric converter 28c and the signal vf from the photoelectric converter 28f are divided by the divider 70G into SC=Vc/V.
The calculation of f is performed.

Similar to FIG. 4, processor 44 inputs output values SA, SB, SC via an analog-to-digital converter and stores them in memory 52.

In the first embodiment, changes in signal levels between different wavelength ranges were compared using standard values, but here, the adhesion surface can be determined by simply evaluating the magnitude relationship between the standardized output values SASSB and SC. I can do it.

The processor 44 compares the output values SA, SB, and SC, and when SA;SB#SC, it determines that the foreign object is on the surface side of the pellicle (light receiving system side), and SA>SB<SC. It is determined that it is on the back side. This is because the signal levels Vd and Vf of the scattered light from the foreign object on the back side are smaller than those in the case of the foreign object on the front side, and the signal Ve is relatively larger. Incidentally, such a judgment circuit can also be constructed discretely using analog comparators, logic ICs, etc. FIG. 6 shows the configuration of a defect inspection apparatus according to a third embodiment of the present invention, and the illumination optical system is provided with a cylindrical (or toric) lens 80 whose generatrix direction is perpendicular to the y direction. The optical axis AXo of the cylindrical lens 80 is perpendicular to the surface of the bevel 23, and the cylindrical lens 80
The white illumination light focused by becomes slit-shaped illumination light SL extending in the X direction on the bezel 23. The reticle 24 with a pellicle is moved by a one-dimensional slider (not shown), etc.
move at a constant speed in a direction. The slit-shaped illumination light SL has a length approximately equal to the width of the bezel 23 in the X direction, and the entire surface can be inspected by scanning the reticle 24 in the Y direction only. On the other hand, the scattered light receiving system includes a mirror M1 imaging optical system 82 arranged along the optical axis AXr,
1 relay system 86, guikroic mirror 27d, and 3
One-dimensional imaging devices (COD etc.) 84d, 84e, 84
It is admonished by f. ξ ra M is the optical axis AX of the imaging optical system 82
r to the surface of the pellicle 23 at a predetermined angle (5' to 20
The imaging optical system 82 is configured to bend the slit-shaped illumination light S reflected by the mirror M.
An image of the irradiation region L is formed on the one-dimensional image sensor 84d. At this time, the scattered light from the irradiation area is formed on the one-dimensional imaging device 84 by the guichroic mirror 27c as a foreign object night vision image based on a short wavelength of, for example, 500 nm or less. The image created by the imaging optical system 82 is transmitted to the relay system 8
6 to approximately the same magnification, and two wavelength ranges (500 nn+ to 6
00 nm and 600 nm or more), and then re-imaged on one-dimensional imaging devices 84e and 84f, respectively.

Therefore, a night vision image of a foreign object is formed on the one-dimensional image sensor 84e by intermediate wavelength components (500 nm to 600 nm) within the slint-like irradiation area, and a foreign object night vision image is formed on the one-dimensional image sensor 84f using a medium wavelength component (500 nm to 600 nm) within the irradiation area. A night vision image of a foreign object is produced by wavelength control (600 nm or more). Here, the one-dimensional image sensor 84d
, 84e, 84f have a plurality of pixels along the longitudinal direction (X direction) of the irradiation area of the slit-shaped illumination light SL, so the measurement resolution of the foreign object position in the longitudinal direction of the irradiation area is the same as that of the one-dimensional imaging devices 84d, 84e, It is determined by the number of pixels of 84f. For example, if the length of the slit-shaped illumination light SL (width of the pellicle 23 in the Even if the image of the frame is created, it is 0.2 pixels above the pellicle.
A resolution of m+* (200 μm) can be obtained. Further, the reference system is constructed by branching a part of the illumination light with a beam sub-switcher 26 as shown in FIG.
, 27b into three wavelength ranges, and the amount of light in each wavelength range is received by photoelectric elements 84a, 84b, and 84c. As for the processing circuit, standardization is performed using a divider as in FIG. 5.

FIG. 7 illustrates the waveform of one line of image signals from the one-dimensional image sensors 84d, 84e, and 84f. Synchronization works so that there is a constant relationship between the readout cycle for one line and the moving speed of the reticle 24 in the y direction.
Here, an image signal for one line is obtained each time the reticle 24 moves by the width of the slit-shaped illumination light SL in the y direction.

FIGS. 7(A), (B), and (C) show image signals of the one-dimensional image sensors 84d, 84e, and 84f, respectively, the vertical axis represents pixel signal levels Vd, Ve, and Vr, and the horizontal axis represents pixel signal levels. represents a number. The signal levels d, Ve, and Vf are compared in magnitude after being standardized based on the output signal levels of the photoelectric elements 84a, 84b, and 84c, respectively. In FIG. 7, it is assumed that signal levels above a certain value are obtained at pixel positions P, , Pt, and P3.

At position P1, the three signal levels Vd, Ve, and Vf are all large, and after normalization, V a / V d, V
b/VeSVc/Vf becomes approximately equal, and it is determined that the foreign object at position P1 is on the surface side. Also, at position P2, although the signal levels Vd, Ve, and Vf are all small, the normalized ratios Va/Vd, Vb/Ve, and Vc/V
f are almost equal, and it is determined that the foreign object at position P2 is also on the front side. Also, depending on the signal level, the foreign object at position itP is better than the foreign object at position P! It can be seen that it is larger than the foreign object. On the other hand, at position P, the signal level Ve is considerably larger than the signal levels Vd and Vf. Therefore, the ratios Va/Vd, Vb/Ve, V at position P after normalization are
Comparing the magnitude of c / V f, V b / V
Only e has two different values, indicating that a foreign object at position P exists on the back side.

When the slit-shaped illumination light SL is irradiated to the vellicle all at once as in this embodiment and an image of the irradiation area is captured, the illumination light SL
It is desirable that the illuminance distribution in the longitudinal direction be uniform. However, if uniformity cannot be obtained, data on the illuminance distribution may be obtained in advance and the signal level may be corrected for each pixel of the image signal (or for each plurality of pixels in a certain section). Then, normalization is performed using the corrected signal level, and the magnitude relationship between the normalized ratios can be evaluated.

Regarding the signal level correction method, please refer to the Japanese Patent Publication No. 635269.
It is also disclosed in Publication No. 6.

Although each embodiment of the present invention has been described above, several other variations are possible. Therefore, these modified examples will be described below.

First, as the illumination light, light from a mercury discharge lamp including a plurality of bright line spectra, or light coaxially synthesized from a plurality of light emitting diodes (or semiconductor lasers) having different center wavelengths, etc. can be used. Furthermore, if the illumination light is turned into a spot and scanned over the pellicle one-dimensionally using a polygon mirror galvanometer, etc., the angle of incidence of the illumination light (beam) on the pellicle will change depending on the one-dimensional scanning position. Sometimes. Normally, in this type of method, the scattered light receiving system (imaging lens, etc.) is fixed so that the entire one-dimensional scanning trajectory is viewed from a specific spatial direction, so the incident angle changes depending on the scanning position of the spot beam. Therefore, the reception level (sensitivity) of scattered light changes. Therefore, it is necessary to provide a circuit that changes the signal level of the photoelectric element in the light receiving system, or the slice level for determining the presence or absence of foreign objects, depending on the scanning position of the spot beam. Incidentally, in each of the embodiments, the scattered light receiving system was placed in the space on the illumination light incident side relative to the pellicle, but if the pellicle is stretched over a frame and can be inspected by itself, the light receiving system It can also be placed in the space opposite to the side. Even in this case, it is desirable to set the optical axis of the light receiving system at a small angle (approximately 5 to 45 degrees) with respect to the pellicle surface to reduce the amount of scattered light received from the pellicle itself. Furthermore, by arranging multiple scattered light receiving systems so that they look at the illumination light irradiation area from different directions, and comparing the detection results obtained with each receiving system, the accuracy of detecting foreign objects and the ability to identify the size are increased. You can also. In this case, there is an advantage that even if the attached foreign object has a relatively large scattering directionality, it can be detected reliably. Furthermore, the guichroic mirror used as a wavelength selection element used in the scattered light receiving system may be replaced by other color filters or prisms (dispersive elements). When using a prism, the spectral distribution of the incident scattered light can be photoelectrically detected using a one-dimensional array sensor, and the difference between the spectral distribution from the foreign object on the front side and the spectral distribution from the foreign object on the back side can be determined. However, in spectroscopy using a prism, the intensity of scattered light from foreign objects is low, so it may be difficult to ensure a good S/N ratio during photoelectric detection.

By the way, as explained in the principle of the present invention, the scattered light from the foreign matter on the back side of the pellicle peaks at a specific wavelength λm, and the wavelength ranges on both sides of that peak (between λm and λm+1, and between λm and λm-1) ), the intensity is significantly attenuated. Therefore, first illumination light with a bandwidth of about 100n centered on a specific wavelength λm and a bandwidth of about 100n separated from the center wavelength λm of this illumination light by more than several +nw on the long wavelength side or on the short wavelength side. The second illumination light and the second illumination light may be generated from a different light source or the same light source, and may be irradiated onto the same area on the pellicle. In this case, the light receiving system is provided with a gicroic mirror that separates the wavelength range of the first illumination light and the wavelength range of the second illumination light, and the magnitude relationship between the signal levels from the two photoelectric detection means is evaluated. Therefore, when the specific wavelength λm is about 565 nm, when using a white light source such as a halogen lamp, the pellicle is irradiated with only the wavelength range of 500 rv to 700 nm filtered out of the light from the halogen lamp. 1
The light receiving system is made to have a sensitivity distribution from 500n1 to 60Qna+, and the second light receiving system is made to have a sensitivity distribution from 600n1 to 700ns.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to not only detect the presence or absence of defects such as foreign matter attached to a thin transparent object such as a pellicle, but also to
It can also be determined whether the defect is on the front or back side of the transparent object.
It is possible to prevent defects from occurring during the lithography process.

Furthermore, if this inspection device is used in conjunction with an automatic pellicle pasting device, it is possible to check for foreign matter on the back of the pellicle while the pellicle is temporarily attached to a mask or reticle, and if there is no foreign matter on the back, the final pasting can be carried out. If there is a problem, it is possible to safely automate a series of tasks such as removing the temporary pellicle and replacing it with another pellicle.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention, FIG. 2 is a diagram showing the configuration of a device according to the first embodiment of the present invention, FIG. 3 is a diagram showing the configuration of a conventional device, and FIG. The figure is a block diagram showing the configuration of the signal processing system in the first embodiment, FIG. 5 is a block diagram showing the configuration of the signal processing system in the inspection device according to the second embodiment, and FIG. 6 is the block diagram showing the configuration of the signal processing system in the inspection device according to the second embodiment. A tilted view showing the configuration of the inspection device. FIG. 7 is a graph diagram explaining the state of photoelectric detection in the third embodiment. [Explanation of symbols of main parts] 21... Light source, 22, 25... Condensing lens, 23... Pellicle, 24... Reticle, 26.・・・・・・Beam splinter 27a, 27b, 27c, 27d ・・・・Guicroic coffee 2 8 a, 2 8 b, 2 8 c, 2 8
d, 2 8 e, 28f...Photoelectric converter

Claims (2)

[Claims] (1) In an apparatus that illuminates a light-transmitting flat object to inspect defects such as foreign matter existing on the front and back surfaces of the flat object, polychromatic light having an intensity distribution over a predetermined wavelength band is illuminated on the flat object. irradiation means for irradiating toward one of the surfaces; a plurality of photoelectric detectors that receive scattered light generated by the defect by irradiation with the polychromatic light, dividing it into a specific wavelength range using a wavelength selection element; and determining means for determining whether the defect exists on the front or back surface of the flat object based on a comparison of the magnitudes of signals output from each of the photoelectric detectors. Inspection equipment. (2) In an apparatus that illuminates a light-transmitting flat object to inspect defects such as foreign matter existing on the front and back surfaces of the flat object, polychromatic light having an intensity distribution over a predetermined wavelength band is illuminated on the flat object. an irradiation means for irradiating toward either one of the surfaces; a first spectroscopy means for dispersing the polychromatic light from the irradiation means; and a first dispersion means for separately dispersing the amount of light for each specific wavelength range separated by the first spectroscopy means. a first photoelectric detection means for detecting; a second spectroscopy means for spectrally dispersing the scattered light generated by the defect due to the irradiation with the polychromatic light with substantially the same characteristics as the first spectroscopy means; a second photoelectric detection means for individually detecting the amount of light for each specific wavelength range; determining a ratio of signal magnitudes from each of the first photoelectric detection means and the second photoelectric detection means for each of the specific wavelength ranges; , based on the magnitude relationship of the ratio between different specific wavelength ranges,
A defect inspection device characterized by comprising: determining means for determining whether the defect is present on either the front or back surface of the flat object.