JPH06138046A - Foreign matter inspection device - Google Patents

Abstract

PURPOSE:To compensate the output of a photoelectric detector accurately when sensitivity is changed by compensating the level of a photoelectric signal basing on specific constant data which are determined according to detection sensitivity. CONSTITUTION:High and low applied voltages and high and low VCA data are previously stored at an applied voltage storage part 89 and a VCA (voltage- controlled amplifier) data storage part 79, respectively. When a foreign matter is detected, sensitivity switching is instructed with a signal 93 from an input means 92, a sensitivity controlling part 90 specifies 91 which detection sensitivity of the high and low sensitivity data stored in the storage parts 89 and 79 should be selected, and applied voltages 86-88 and VCA data 76a-76c are output to photoelectric detectors 34, 32, and 30 using a photo multiplexer and VCAs 73-75, respectively. The applied voltages 86-88 are changed for roughly switching the amplitude of the detectors 30, 32, and 34 and the VCAs 73-75 are controlled for changing the degree of current/voltage conversion of preamplifiers 70-72 and for finely adjusting the amplitude.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection apparatus, and more particularly to detecting defects such as foreign matter adhered to the surface of a reticle mask (hereinafter referred to as a reticle) used in a semiconductor exposure process or a pellicle mounted on the reticle. It is related to the device.

[0002]

2. Description of the Related Art There are various types of conventional foreign matter inspection apparatuses of this type, and, for example, a scan type foreign matter inspection apparatus has been proposed. Since such a scan type foreign matter inspection apparatus is disclosed in detail in Japanese Patent Publication No. 63-64738, it will be briefly described here. In this apparatus, laser light emitted from a laser light source or the like irradiates an object to be inspected (reticle or the like). The laser beam and the surface to be inspected are relatively scanned over the entire surface to be inspected on the reticle by a scanner such as a galvanometer scanner or a polygon mirror and a stage that can move the reticle. Multiple photoelectric detectors are arranged so that the scanning area can be seen from different directions.Based on the difference in properties between the scattered light from the foreign matter and the diffracted light from the circuit pattern provided on the reticle, only the foreign matter is detected. To detect. That is, the diffracted light from the circuit pattern has a very strong scattering directivity, but the scattered light from the foreign matter has a relatively weak scattering directivity and is scattered isotropically. Therefore, in all of the photoelectric detectors arranged in multiple directions, if a light amount above a certain level is received, it is determined as a foreign substance, and if any one of the photoelectric detectors is below the certain level, it is determined to be a pattern. Then, the foreign matter and the pattern are distinguished and only the foreign matter is detected. Further, since the arrangement of the photoelectric detectors with respect to the scanning region of the laser light by the scanner is different, the solid angle of the received light entering the photoelectric detector is different. Further, the angles formed by the laser beam and the photoelectric detector are also different. Therefore, even though the photoelectric detectors detect the same foreign matter, a difference occurs in the output from the photoelectric detectors. In order to correct this, VCA (Voltage Control Anplif) that changes the amplification of the output from the photoelectric detector
ier) is provided in this foreign matter inspection device.

A light beam parallel to the surface to be inspected is irradiated substantially horizontally to the surface to be inspected, and the object to be inspected is moved in a direction substantially perpendicular to the direction of incidence of the light beam on the surface to be inspected. There is also known an apparatus that inspects a foreign substance by making it possible to irradiate the entire surface and detecting side scattered light from the surface to be inspected with a photoelectric detector (one-dimensional photo array). Also in this apparatus, when scattered light of a predetermined level or more is incident on the one-dimensional photo array, it is determined as a foreign substance. Here, since the intensity distribution of the incident light flux in the incident direction on the surface to be inspected (arrangement direction of the one-dimensional photo array) is not constant, the amplification degree of the photoelectric signal from the one-dimensional photo array or a predetermined level is set as the incident light. Is changed according to the intensity distribution of.

In these inspection apparatuses, in order to detect only the foreign matter, the difference in the scattering characteristic between the scattered light from the foreign matter and the diffracted light from the circuit pattern is utilized. That is, the diffracted light from the circuit pattern has a very strong scattering directivity,
The scattered light from the foreign matter is isotropically scattered. Therefore, by arranging the photoelectric converter in a position that avoids diffracted light,
The diffracted light from the circuit pattern does not enter the photoelectric converter, and the scattered light from the foreign matter enters the photoelectric converter. In addition, by arranging a plurality of photoelectric converters, the diffracted light from the circuit pattern does not enter any one of the photoelectric converters, and the output from the photoelectric converters, for example, is ANDed to obtain the circuit pattern and the foreign matter. Can be distinguished.

In any of the above methods, the magnitude of the photoelectric signal from the photoelectric detector is compared with a predetermined level in consideration of scattered light or diffracted light which is a noise component, and the magnitude of the photoelectric signal is equal to or higher than the predetermined level. When it is, it is determined to be a foreign substance. By relatively adjusting the predetermined level and the magnitude of the photoelectric signal, the foreign matter detection sensitivity (the foreign matter detection capability of the apparatus according to the foreign matter size to be managed) is adjusted.

Further, in recent years, with the diversification of reticle varieties, the level of foreign matter size to be managed is divided into several levels, and there is an increasing demand for being able to change a plurality of detection sensitivities with one foreign matter inspection apparatus. . To meet this demand, for example, it is proposed in Japanese Patent Laid-Open No. 63-285449 to change the beam diameter of the light beam irradiating the inspection object on the inspection surface.

[0007]

However, the present inventor has found that the following problems occur when the detection sensitivity is changed as described above. For example, consider a case where there are two foreign matter management standards (detection sensitivities) on the inspection object. φ
If the foreign matter of 1 μm or more is attached, it is judged as defective (the minimum detection sensitivity is 1 μm), and if the foreign matter of φ0.5 μm or more is judged as the defective (minimum detection sensitivity is 0.5 μm, There are two detection sensitivities (in some cases).

In order to deal with the above two cases, as absolute calibration of the detection sensitivity of the foreign substance inspection apparatus, φ1 μm polystyrene true spherical beads and φ0.5 are used as the respective detection sensitivity standards.
Absolute sensitivity calibration of the device may be performed with both μm polystyrene true spherical beads. However, when a foreign substance inspection is performed using a plurality of photoelectric detectors, even if the ratio of the scattered signal amounts of the polystyrene true spherical beads of φ1 μm and φ0.5 μm is 10 times in one photoelectric detector, the other photoelectric detectors. Then, it is not always 10 times.

Similarly, even between different devices, φ1μ
It is not always the case that the devices having different ratios of m and the scattered signal amount of the polystyrene true spherical beads of φ0.5 μm are different. Further, since the VCA amplification characteristic according to the scanning position of the light beam changes between φ1 μm and φ0.5 μm, it is not enough to make the beam diameter variable. The reason why such a phenomenon occurs is that the polystyrene true spherical beads of φ1 μm and φ0.5 μm do not have exactly the same scattering characteristics, and the physical phenomenon is called Mie scattering (Mie scattering) phenomenon. It has been clarified in the literature.

Therefore, unlike the prior art, it is not possible to accurately change the sensitivity by simply changing the beam diameter. Further, for the same reason, the sensitivity cannot be accurately changed by simply changing the amplification degree of the signal from the photoelectric detector. The present invention has been made in view of the above problems, and an object thereof is to accurately correct the output of the photoelectric detector even when the sensitivity is changed.

It is another object of the present invention to accurately correct the outputs of the plurality of photoelectric detectors even when the sensitivity is changed.

[0012]

In order to solve the above problems, according to the present invention, an irradiation means (60) for irradiating an object to be inspected (10) with light and a light from an area to be inspected of the object to be inspected are received. Then, the light receiving means (34, 32, 30) for outputting a photoelectric signal according to the intensity of the received light is compared with the magnitude of the photoelectric signal and a predetermined reference value (84) to detect a foreign substance on the inspection object. The foreign matter inspection device for detection has at least two types of detection sensitivities determined by the relative relationship between the magnitude of the photoelectric signal and a predetermined reference value, and a sensitivity setting means (9) for selecting the detection sensitivity.
0) ;; correction means for correcting the magnitude of the photoelectric signal based on predetermined constant data (applied voltage data, VCA data) determined according to the detection sensitivity; and storage means (89, 92) for storing the predetermined constant data. ) And; data reading means for reading constant data corresponding to the set detection sensitivity from the storage unit in synchronization with the sensitivity setting by the sensitivity setting means) 9)
0, 78) and.

[0013]

In the present invention, a plurality of detection sensitivities can be set, and the constants relating to the detection sensitivities are not fixed values but can be changed. The absolute value calibration (correction of VCA data, accurate sensitivity correction among a plurality of photoelectric detectors, etc.) can be performed, and the reliability of the inspection apparatus can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of a foreign matter inspection apparatus suitable for an embodiment of the present invention. In FIG. 1, the reticle 10 is placed on the stage 12, and the stage 12 can be moved in the Y direction by the drive unit 14. The movement amount of the stage 12 can be measured by a length measuring device 18 including a linear encoder or the like. The reticle 10 is provided with a pellicle 20 via a support frame 22. Light source (eg Ar laser or He
(-Ne laser or the like) 60, a light beam L emitted from a reticle 10 is deflected and scanned in the X direction by a scanner 28 such as an expander 1, a galvano scanner or a polygon mirror, and a scanning lens (for example, fθ lens) 26.
The light beam converges upward to form a scanning line S that is substantially parallel to the X direction. By scanning the light beam in the X direction and moving the reticle 10 in the Y direction by the driving unit 14 at a speed slower than that, it is possible to scan the light beam on the entire surface of the reticle 10.

If there is a defect such as the foreign matter 63 on the surface of the reticle 10, the scattered light 65 is generated from the foreign matter 63 by the light beam L passing through the scanning lens 26. The scattered light 65 is photoelectrically detected by the light receiving lenses 40, 41, 42 and photoelectric detectors 34, 32, 30 such as photomultipliers provided after the respective lenses. Slits 46, 44, 42 are provided on the light incident side of these photoelectric detectors 34, 32, 30 to block light from other than the scanning line S. Optical axis l of light-receiving lens 40, 38, 36
₃ , l ₂ and l ₁ are arranged so as to intersect at the center of the scanning line S.

On the other hand, a circuit pattern 64 for transferring to the wafer is provided on the surface of the reticle 10, and diffracted light 66 is generated from the circuit pattern 64. In order to detect only the foreign matter, it is necessary to detect the scattered light 65 from the foreign matter and the diffracted light 66 from the circuit pattern separately. Therefore, the difference in the scattering characteristics between the scattered light 65 and the diffracted light 66 is used. That is, the diffracted light 66 from the circuit pattern 64 has a very strong scattering directivity, but the scattered light 65 from the foreign matter 63.
Has a relatively weak scattering directivity and scatters almost isotropically. Therefore, if all the photoelectric detectors 34, 32, 30 arranged in multiple directions receive a light amount above a certain level, it is regarded as a foreign substance, and even one of the photoelectric detectors 34, 32, 30 is below a certain level. If it is the amount of light, it is determined to be a pattern, and the foreign matter and the pattern are distinguished, and only the foreign matter is detected.

Further, in this apparatus, the aperture 2 can be inserted and removed between the expander 1 and the scanner 28 by a drive unit (not shown). The aperture 2 is inserted in the optical path of the light beam L when detecting a foreign matter with low sensitivity, and the aperture 2 is detected when detecting a foreign matter with high sensitivity.
Move out of the optical path. The inner diameter of the aperture 2 is smaller than the diameter of the light beam L in the plane perpendicular to the optical axis of the expander 1. By inserting the aperture 2 in the optical path of the light beam L, the beam diameter on the reticle 10 is changed. Making it big.

A block diagram of the detection circuit is shown in FIG.
The photoelectric detectors 34, 32 and 30 output electric signals S1, S2 and S3, respectively, which are substantially proportional to the amount of received light. The signals S1, S2, S3 are amplified by the preamplifiers 70, 71, 72 to become signals S4, S5, S6, and VCA (Vo
ltage Control Anplifier) 73, 74, 75. The VCA is a circuit that can change the amplification factor according to the input voltage 76. The scanner 28 also has a variable deflection angle depending on the input voltage 77. Therefore, the scanner controller 78 controls the scanner 28 and the VCA 7 simultaneously.
The amplification degree of 3, 74, 75 can be controlled.

Here, when the photoelectric detectors 34, 32, 30 receive scattered light through the light receiving lenses 40, 38, 36 (when obtaining optical information), the light receiving lenses 40, 38, 3 are provided.
The amount of information differs depending on where the principal ray of the light beam incident on 6 is directed. For example, the distance from the light receiving lenses 40, 38, 36 to the irradiation position of the light beam L when the light beam L irradiates the vicinity of one end 61 on the scanning line S and when irradiates the vicinity of the other end 62. Will change. For this reason,
The solid angle of the received light that enters the light receiving lens changes, and the amount of light that can be received naturally changes. Further, the angle between the optical axis of the light receiving lens and the light beam L also changes, and even when completely identical scattering objects, for example, polystyrene true spherical beads of the same particle size are lined up on the scanning line S, the photoelectric signal depends on the position in the X direction. S
The output values of 1, S2 and S3 change. The amount of change is corrected, and the amplification degrees of the VCAs 73, 74, and 75 are changed so that the output signals are always constant regardless of the position of the light beam L in the X direction. The change in the amplification degree of the VCA 73, 74, 75 is executed based on the voltage signal 76 output from the scanner controller 78 according to the position in the X direction.

Next, the output signals S7, S8 and S9 from the VCAs 73, 74 and 75 are input to the comparators 80, 81 and 82. The comparators 80, 81, 82 are the reference voltage generator 83.
Reference voltage 84 and VCA 73, 74, 7 output by
The output signals from S5, S7, S8 and S9 are compared. The output signals of the comparators 80, 81 and 82 are the reference voltage 84.
If it is above, the digital "1" is output signal S10, S
11 and S12, and if the reference voltage is 84 or less, a digital "0" is output signal S10, S11, S12.
Output as. Digital output signals S10, S11, S
12 is ANDed by the AND circuit 85, and the signal S1
Digital "1" is output as the output signal S13 only when all of 0, S11, and S12 are digital "1". This is the detection signal of presence of foreign matter.

As described above, the diffracted light 66 from the pattern 64
Has a strong directivity, so that even if the diffracted light 66 is received, at least one of the photoelectric detectors 34, 32, and 30 has a small amount of received light. Therefore, at least one of the comparators 80, 81, 82 outputs a digital "0". Therefore, AND
The output S13 from the circuit 85 becomes a digital "0" and is not erroneously detected as a foreign substance.

Here, if a photomultiplier is used for the photoelectric detectors 34, 32 and 30, the amplification degree is changed by the preamplifiers 70, 71 and 72 in the photomultiplier. Further, the amplification degree is also changed by changing the voltage between the cathode and the anode of the Photomul (hereinafter referred to as applied voltage). When the applied voltage is increased, the amplification degree increases in proportion to the 7th to 8th power of the applied voltage. For this reason, in this embodiment, a photomultiplier is used as the photoelectric detector, and the applied voltage is changed as the amplification degree is changed so that the preamplifiers 70, 71, and 72 perform delicate adjustment of the amplification degree.

The applied voltages 86, 87, 88 applied to the photoelectric detectors 34, 32, 30 are output from the applied voltage storage unit 89. The amplification degree is switched by changing the applied voltage 86, 87, 88. Rough switching of the amplification degree is performed by changing the applied voltage 86, 87, 88, and the VCA 73, 74, 75 is controlled to finely adjust the amplification degree by changing the current / voltage conversion degree of the preamplifiers 70, 71, 72. . Preamplifier 7
Fine adjustment of the amplification degree of 0, 71, 72 may be performed by sending data from the storage unit 79 to the VCA 73, 74, 74, or by providing a storage unit separate from the storage unit 79 and directly preamplifiers 70, 71 ,. The amplification degree 21 may be finely adjusted.

As described above, the VCAs 73, 74 and 75 amplify the outputs S4, S5 and S6 of the preamplifiers 70, 71 and 72 with different amplification degrees depending on the scanning direction (X direction) of the incident beam L. The amplification degree data 76a, 76b, 76c corresponding to the X direction in the VCAs 73, 74, 75 are stored in the VCA data storage unit 79 in the scanner control unit 78.

The low / high sensitivity data stored in the applied voltage storage section 89 and the VCA data storage section 79 is stored in the sensitivity control section 9.
By the signal 91 indicating which detection sensitivity is switched from 0,
Which sensitivity data is used is specified. Signal 9
According to the designation of 1, the predetermined applied voltages 86, 87 and 88 from the applied voltage storage unit 89 and the predetermined VCA data 76a, 76b and 76c from the VCA data storage unit 79 are photoelectric detectors 34, 32 and 30, respectively. And VCA 73, 74, 7
5 is output.

The instruction to switch the sensitivity is given based on the signal 93 from the input means 92. Further, the data stored in the applied voltage storage unit 89 and the VCA data storage unit 79 is such that a plurality of true spherical beads of a predetermined reference (φ0.5 μm, φ1 μm) are arranged in the scanning line S direction, and the photoelectric detector 34 according to each reference. , 32, 30 to detect the applied voltage data and VCA data for each reference, the applied voltage data is stored in the applied voltage storage unit 89, and the VCA data is stored in the VCA data storage unit 79. Keep it. When the variation between the devices is small, the applied voltage data and the VCA data are obtained by a predetermined foreign matter inspection device, these data are input by the input means 92, and the applied voltage storage unit 89 and the VCA are input.
It may be stored in the data storage unit 79.

Next, the sensitivity switching process of this embodiment will be described with reference to FIG.
This will be described with reference to FIGS. 4, 5, and 6. Here, the detection sensitivity for switching is set in two stages, high sensitivity is based on φ0.5 μm polystyrene true spherical beads, and low sensitivity is based on φ1 μm polystyrene true spherical beads. The reference means, for example, wherever the 0.5 μm polystyrene true spherical beads are attached on the reticle, the photoelectric detectors 34, 32, 30 are used.
Is to finally equalize the output signals from. Specifically, as shown in FIG. 6, the output S7 after VCA,
S8 and S9 are set to a specified constant voltage in switching between high sensitivity and low sensitivity. Therefore, as shown in FIG. 6, 1 is required for high sensitivity (φ0.5 μm polystyrene true spherical beads) regardless of the position in the X direction.
(V) and 1 (V) even when the sensitivity is low (φ1 μm polystyrene true spherical beads).

FIG. 3 is a diagram showing the output of the preamplifier when the sensitivity is 1 time, FIG. 3A shows the output S4 from the preamplifier 70, and FIG. 3B shows the output S from the preamplifier 71.
3 shows the output S6 from the preamplifier 72.
Indicates. In FIGS. 3A to 3C, the horizontal axis represents the position of the light beam L, and the vertical axis represents the output (voltage value) of the preamplifier.
Is shown.

FIG. 4 is a diagram showing the output of the preamplifier when the applied voltage applied to the photoelectric detector is changed according to the sensitivity. FIG. 4A shows the output S4 from the preamplifier 70 after the applied voltage is corrected. 4 (b) shows the output S5 from the preamplifier 71 after the applied voltage correction, and FIG. 4 (c) shows the output from the preamplifier 72 after the applied voltage correction. Figure 4
4A to 4C, the horizontal axis represents the position of the light beam L, and the vertical axis represents the output (voltage value) of the preamplifier. Here, in FIGS. 3 and 4, the output from each preamplifier is the output of the preamplifier at the time of low sensitivity S4L, S5L, S6L.
, And the output of the preamplifier at high sensitivity is S4H, S5
H and S6H are shown. When the sensitivity is low in Fig. 4, the photoelectric detector 3
Applied voltage data 86L and 87L applied to 4 and 32 are 1 /
It is 10 times, and the applied voltage data applied to the photoelectric detectors 34 and 32 at the time of high sensitivity is 86H and 87H 2 times. In addition, the applied voltage data 8 applied to the photoelectric detector 30 when the sensitivity is low
8L is 1/8 times, and the applied voltage data 88H applied to the photoelectric detector 30 at high sensitivity is 1 time.

FIG. 5 is a diagram showing VCA data when the VCA correction degree is changed according to the sensitivity, and FIG.
Shows VCA data 76a added to VCA 73, and FIG.
5B shows the VCA data 76b added to the VCA 74, and FIG. 5C shows the VCA data 76 added to the VCA 75.
c is shown. In FIGS. 4A to 4C, the horizontal axis represents the position of the light beam L, and the vertical axis represents the correction degree (correction coefficient). Here, in FIG. 5, the VCA data at low sensitivity is 7
VCA at high sensitivity indicated by 6aL, 76bL, 76cL
Data are shown as 76aH, 76bH, 76cH.

FIG. 6 is a diagram showing the output of the VCA after the applied voltage and the VCA data have been corrected. FIG. 6A shows the VCA 73.
6B shows the output from the VCA 74, and FIG. 6C shows the output from the VCA 75. 6A to 6C, the horizontal axis represents the position of the light beam L and the vertical axis represents the VCA output (voltage value). here,
In FIG. 6, the VCA output when the sensitivity is low is S7L, S8L,
Shown by S9L, VCA output at high sensitivity is S7H, S8
H and S9H are shown. As shown in FIG. 6, VCA at low sensitivity
The output and the VCA output at high sensitivity are equal.

Here, when the amplification degree of the output from the preamplifier 70 is fixed, the preamplifier outputs S4, S5, S shown in FIG.
As shown in FIG. 6, X direction dependency is obtained in each case where two polystyrene true spherical beads of φ0.5 μm and φ1 μm are used. And in this case φ0.5μm and φ1μm
The two polystyrene true spherical beads of No. 2 differ in the absolute detection signal amount and also in the shape of the change curve in the X direction. Therefore, the applied voltage storage unit 89 and the VCA data storage unit 79 respectively store the high and low applied voltages and the high and low VCA data respectively.

In this way, in order to store the data for each of the low sensitivity and the high sensitivity, and to store the two data for the low sensitivity and the high sensitivity for each of the number (3) of photoelectric detectors. , Total 6 applied voltage data, VCA
Store each data individually. These data follow the instruction of the switching control unit 90, and when the instruction of low sensitivity is given, the signals 86L, 87L, 88L are sent to the photoelectric detector 3.
4, 32 and 30 are sent from the applied voltage storage unit 89, and when there is a high sensitivity instruction, data 86H, 87H and 88H are sent to the photoelectric detectors 34, 32 and 30. As shown in FIG. 3, the preamplifier outputs S4, S5, and S6 at this time have different output characteristics between low sensitivity and high sensitivity. Further, in the VCA 73, 74, 75, data 76a, 76b, 76c whose amplification degree (magnification) changes according to the X direction.
Optimal data depending on whether the designated sensitivity is low sensitivity or high sensitivity is multiplied to each output S4, S5, S6. The VCA data storage unit 79 stores the VCA data 76a and 7 shown in FIG.
If 6b and 76c (low / high) are stored and there is a low sensitivity instruction from the switch controller 90, VCA
Outputs data 76aL, 76bL, 76cL S4, S
When there is a high sensitivity instruction by multiplying S5, S6, VCA data 76aH, 76bH, 76cH are output S4, S5, S6.
Get on. Therefore, if there is a high sensitivity indication, if φ
When a reticle having 0.5 μm polystyrene true spherical beads attached is inspected by the apparatus according to the present invention, an output signal of 1 (V) is always output S regardless of the position on the reticle in the X direction.
7, obtained from S8 and S9. Also, when there is a low sensitivity instruction, if a reticle with φ1 μm polystyrene true spherical beads attached is inspected, an output signal of 1 (V) is similarly obtained from the outputs S7, S8, and S9.

Not only switching between high and low sensitivity, but also 2
If more than one sensitivity reference is provided, the applied voltage storage unit 89,
The data stored in the VCA data storage unit 79 may be stored according to the number of sensitivity switchings. In addition, the scanner control unit 78 calls the VCA data from the VCA data storage unit 79 each time the scanner 28 is driven.

In the embodiment of the present invention, the foreign matter inspection on the reticle surface has been mainly described, but not only in the foreign matter inspection on the pellicle surface, but also in the case of detecting the circuit pattern defect of the reticle or the mask. Applicable. Pattern defects such as a reticle are also detected with a plurality of sensitivities such as low and high. When performing high-sensitivity detection,
In the pattern defect inspection apparatus, a method of increasing the magnification of the objective lens can be considered. At this time, when detecting a defect that is small in proportion to the numerical aperture of the objective lens, the amount of light may be reduced, or the brightness may change in the field of view and the periphery of the field of view may become dark, so that sufficient foreign matter detection may not be possible. In such a case, in order to make the absolute value of the detection sensitivity and the uniformity within the visual field uniform when the objective is changed with respect to the reference pattern (for example, a pinhole defect intentionally created), an objective lens is used. The present invention is also used when performing correction according to the pixels of an image pickup device such as a CCD provided at a position conjugate with the surface to be inspected.

The photoelectric converter is not limited to the photomultiplier. In general, photoelectric detectors are roughly classified into fixed elements such as SPDs (silicon photodiodes) and photoelectric tubes such as photomultipliers. In the case of SPD, the amplification degree can be changed by changing the current-voltage conversion rate of the preamplifier provided in the latter stage of SPD. Of course, the scope of the present invention also includes using the SPD to change the current-voltage conversion rate of the preamplifier to change the amplification degree.

Further, for example, in the device configuration of FIG.
When it is possible to detect m polystyrene true spherical beads, it is extremely easy to reduce the detection sensitivity so that φ1 μm polystyrene true spherical beads serve as a reference. However, conversely, just because φ1 μm polystyrene true spherical beads can be detected, it is not easy to increase the detection sensitivity such that φ0.5 μm polystyrene true spherical beads can be detected with the same configuration. This is because when the surface to be inspected is a reticle, it is unavoidable that diffracted light is generated from the circuit pattern on the reticle. That is, as already described in the section of the prior art, even though the foreign matter and the pattern are distinguished from each other by the difference in the scattering characteristic, the diffracted light of the pattern does not mean that one of the plurality of photoelectric detectors has a light amount of zero and is small. However, since the light is received, the input of the AND circuit 37 becomes all digital "1" if the reference voltage 60 (value to be detected) contrary to FIG. This is because there is a problem that it is erroneously determined to be true. To solve the above-mentioned problems, for example, the technique disclosed in JP-A-63-285449 can be used. JP-A-63-285449
In the above, the incident beam diameter can be changed between the reticle surface and the pellicle surface of the reticle with a pellicle.
The detection sensitivity can be changed by changing the incident beam diameter on one inspection surface (reticle surface or pellicle surface).
That is, as the beam diameter of the incident beam on the surface to be inspected is smaller, the amount of light per unit area on the surface, that is, the brightness is larger, so that smaller foreign matter can be detected.

Since the foreign matter inspection apparatus is originally assumed to be capable of detecting a small foreign matter, it has been described in the above embodiment that the amplification degree after the photoelectric detector is switched. Alternatively, the beam diameter changing method may be used.

[0039]

As described above, according to the present invention, even if the detection sensitivity is switched, the output of the photoelectric detector can be accurately corrected and the sensitivity uniformity in the surface to be inspected can be maintained. Improves reliability. In addition, the reference absolute signal amount and the in-plane uniformity of the inspected surface can be maintained for each sensitivity.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a foreign matter inspection device according to an embodiment of the present invention.

2 is a block diagram showing signal processing of the apparatus of FIG. 1. FIG.

FIG. 3 is a diagram showing preamplifier output for each sensitivity when the applied voltage data is 1 time.

FIG. 4 is a diagram showing preamplifier output after correction of applied voltage for each sensitivity.

FIG. 5 is a diagram showing VCA data by sensitivity.

FIG. 6 is a diagram showing corrected VCA output for each sensitivity.

[Explanation of reference numerals] 34, 32, 30 ... Photoelectric converters 70, 71, 72 ... Preamplifiers 73, 74, 75 ... VCA 80, 81, 82 ... Comparator 85 ... AND circuit 78 ... Scanner controller 79 ... VCA data storage Unit 89 ... Applied voltage storage unit 90 ... Switching controller 92 ... Input means

Claims (6)

[Claims] 1. An irradiation unit for irradiating an object to be inspected with light, a light receiving unit for receiving light from an inspected region of the object to be inspected, and outputting a photoelectric signal according to the intensity of the received light, and the photoelectric device. In a foreign matter inspection device for detecting a foreign matter on the object to be inspected by comparing a signal magnitude and a predetermined reference value, at least a detection sensitivity determined by a relative relationship between the magnitude of the photoelectric signal and the predetermined reference value. Sensitivity setting means having two types and selecting the detection sensitivity; correction means for correcting the magnitude of the photoelectric signal based on predetermined constant data determined according to the detection sensitivity; and storing the predetermined constant data And a data reading unit that reads out the constant data corresponding to the set detection sensitivity from the storage unit in synchronization with the sensitivity setting by the sensitivity setting unit. Inspection equipment. 2. The constant data is data for correcting the magnitude of the photoelectric signal so that the magnitude of the photoelectric signal is constant irrespective of the position where the foreign matter is attached in the inspection area. The foreign matter inspection device according to claim 1, wherein 3. The light receiving means comprises a plurality of light receiving means,
The foreign matter inspection apparatus according to claim 1, wherein the constant data is data for adjusting the magnitudes of photoelectric signals to be equal in each detection sensitivity. 4. The foreign matter inspection apparatus according to claim 1, wherein the sensitivity setting means makes the magnitude of the photoelectric signal variable. 5. The foreign matter inspection apparatus according to claim 1, wherein the sensitivity setting means makes the reference value variable. 6. The irradiation means has a condensing means for condensing the light incident on the inspection object, and the sensitivity setting means makes the spot size of the condensed light variable. The foreign matter inspection device according to claim 1.