JPS63241342A - Defect inspector - Google Patents

Abstract

PURPOSE:To detect a defect part accurately according to the size thereof, by varying a reference signal in response to spatial layout relationship between a photoelectric detection system and a spot scanning position. CONSTITUTION:A laser beam 1 from a light source 8 is converted into a desired beam diameter and scans with a scanner 2 over a photomask 5. Out of light from a foreign matter attached onto the photomask 5, the scattered light generated on the surface side of the photomask 5 is received with a light receiving element 11 while that generated on the back side thereof with a light receiving element 13. Photoelectric signals of the light receiving elements 11 and 13 are passed through amplifiers 100 and 101 and a signal e1 amplified is introduced into comparators 103 and 104 while a signal e2 is applied into the other input of the comparator 104 through an amplifier 102 with an amplification factor K. A slice voltage Vs from a slice level generator 106 is applied into the other input of the comparator 103. Then, outputs of the comparators 103 and 104 are applied to an AND circuit 105. The slice level generator 106 varies the size of the slice voltage Vs synchronizing a scan signal SC of the scanner 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting foreign matter defects caused by adhesion of minute dust, and more particularly to a defect inspection device for detecting defects such as foreign matter adhering to substrates such as LSI photomasks and reticles.

(2) In the process of manufacturing SI photomasks and wafers, foreign matter may adhere to reticles, masks, etc., and these foreign matter may cause defects in the manufactured masks and wafers. In particular, in the reduction projection type Bakun baking equipment, this defect appears as a common defect in each mask and all chips on the wafer, so it is necessary to strictly inspect it during the manufacturing process. For this reason, it is generally considered to perform a visual inspection for foreign substances, but this method usually requires many hours of inspection, which leads to operator fatigue and a reduction in the inspection rate.

Therefore, in recent years, various devices have been developed that automatically detect foreign particles attached to a mask or reticle by irradiating them with a laser beam or the like. For example, a mask or reticle is irradiated with a laser beam perpendicularly, and the light spot is scanned two-dimensionally. At this time, scattered light from pattern edges on the mask or reticle (edges of light-shielding parts such as chrome) has strong directionality, and scattered light from foreign objects occurs non-directionally. Therefore, an apparatus is known that performs photoelectric detection to discriminate these scattered lights and inspects which part of the mask or reticle the foreign matter is attached to based on the scanning position of the light spot. However, since this device scans the entire surface of the mask or reticle with a light spot, there is a problem in that if the diameter of the light spot is made smaller in order to accurately detect small foreign objects, the inspection time becomes longer.

Furthermore, if the entire surface of the object to be inspected is scanned over a large area with a light spot in order to shorten inspection time, the spatial relationship between the scanning position and the photoelectric detection system will change. Despite being attached to
This results in the inconvenience that one of the two is detected well, but the other is not detected at all.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a defect inspection device that can detect defects such as foreign matter attached to an object to be inspected at high speed, and can always inspect defective portions with stable sensitivity regardless of the scanning position of the light beam. There is a particular thing.

In order to achieve this object, the apparatus of the present invention includes a light beam scanning means (scanner 2) that one-dimensionally scans an object to be inspected with a light beam spot, and a one-dimensional scanning range (L) by this spot from a spatial position. A defective part (foreign object i) is detected within the one-dimensional scanning range.

j, k), and outputs a photoelectric signal according to the intensity of the scattered light.
1; 13; 21; 23; A reference signal (slice voltage V sl ;
VsZ; VsZ; Vi4 i Vs
a slice level generator (160) that generates s), and a comparison circuit (comparators 114; 115; 141; 150) that compares the photoelectric signal with a reference signal and outputs a detection signal when the photoelectric signal is larger than the reference signal. ;151;152
;204;205).

Before explaining the present invention in detail, the state of scattered light generated depending on the adhesion state of foreign matter when a light beam is irradiated onto an object to be inspected will be explained with reference to FIG. 1.2.3. It is assumed here that the light beam is irradiated onto the object to be inspected at oblique incidence. This is to improve the separation of the scattered light from the foreign matter and the scattered light from the light shielding part such as chrome, compared to when the light beam is incident perpendicularly.

Figure 1 shows a pattern-drawn surface of a mask or reticle (hereinafter collectively referred to as a photomask) as an object to be inspected, which is irradiated with laser light as a light beam, and is deposited on the glass plate of the photomask. This figure shows the state of scattering of laser light due to foreign matter attached to the light shielding part and the state of scattering due to foreign matter adhering to the light shielding part. FIG. 2 shows the scattering caused by foreign matter adhering to the glass plate and the scattering caused by the edges of the light shielding part. FIG. 3 shows the state of scattering due to foreign matter adhering to the front and back surfaces of the transparent portion of the glass plate.

In FIG. 1, a laser beam 1 is obliquely incident on a surface S1 (hereinafter, this surface is referred to as pattern surface S1) provided with a light shielding portion 5b provided in close contact with a glass plate 5a of a photomask 5. is regularly reflected by the glass plate 5a or the light shielding part 5b. Note that in the figure, the light beams other than the laser beam 1 represent only scattered light. In Figure 1, the light receiving section (A) consisting of a condensing lens and a photoelectric element is shown to receive the specularly reflected light, but it is actually placed at a position where the specularly reflected laser beam does not enter. do. Moreover, the light receiving part (A) is arranged so as to obliquely look into the irradiated part of the laser beam 1. This is to prevent the reception of scattered light caused by fine irregularities on the pattern surface S of the glass plate 5a or the surface of the light shielding part 5b as much as possible. Further, a surface S2 of the glass plate 5a opposite to the pattern surface S1 (hereinafter referred to as the back surface S2)
A light receiving section (B) including a condensing lens and a photoelectric element is provided on the side. This light receiving part (B) is arranged in a plane symmetrical relationship with the light receiving part (A) with respect to the glass plate 5a (particularly its patterned surface S+), and the irradiated part of the laser beam 1 is diagonally directed from the back surface S2 side. We are anticipating that. In Figure 1, the light receiving part (B)
Although it is shown to receive the laser light that directly passes through the glass plate 5a, in reality, it is provided at a position that does not receive the laser light that directly passes through the glass plate 5a. In other words, the light receiving section (
Both A) and (B) are placed at positions where they receive scattered light non-directionally generated from foreign objects.

Therefore, as shown in the figure, the difference between the scattered light generated by the foreign matter i attached to the transmitting portion of the glass plate 5a and the foreign matter j attached to the light shielding portion 5b will be explained next.

The magnitude of the photoelectric signal detected by the light receiving part (A) is
The foreign substances i and j are almost the same. That is, when foreign objects t and J are irradiated with laser beam 1, foreign object i.

This is because if the magnitudes of j are equal, the intensity of the non-directionally generated scattered light 1a will also be equal. However, some of the scattered light 1b generated by the foreign object i is scattered through the glass plate 5a.
The light passes through and reaches the light receiving section (B). Generally, scattered light 1b
is smaller than the scattered light 1a, but the light receiving part (A),
In (B), some kind of photoelectric signal is generated due to the adhesion of foreign matter i. Of course, the scattered light from the foreign matter j adhering to the light shielding part 5b does not reach the light receiving part (B).

Therefore, by examining the photoelectric signals of the light receiving parts (A) and (B), it is possible to determine whether the foreign matter has adhered to the transparent part of the glass plate 5a or the light shielding part 5b.

By the way, at the edge portion of the light shielding portion 5b, reflected light with strong directivity and scattered light with non-directionality are generated. Therefore,
Even if the light-receiving parts (A) and (B) are arranged so as to avoid the highly directional reflected light from the edges and receive only the scattered light, it is difficult to determine whether the scattered light is due to foreign matter or not. It is necessary to determine whether it is a thing or not. The principle of this will be explained based on FIG. Also in FIG. 2, the light receiving section for receiving scattered light is arranged in the same way as in FIG.

The obliquely incident laser beam 1 is specularly reflected by the pattern surface S1 of the photomask 5, but is scattered by the foreign matter i or the edge portion of the light shielding portion 5b as a circuit pattern. (Specular reflection light, etc. are omitted.) ti, the base portion 5b has a layer thickness of 0.
Since it is in close contact with the pattern surface S1 with a thickness of about 1 μm, the scattered light IC directly directed to the outside of the glass plate 5a and the glass plate 5
The intensity of the scattered light 1d traveling toward the inside of the light a is almost equal to that of the scattered light 1d. After passing through the inside of the glass plate 5a, the scattered light 1d exits from the back surface S2. On the other hand, the size of the foreign object is several μm or more, and the light scattered by the foreign object i is
Because it floats higher, the scattered light 1e that travels toward the pattern surface S toward the inside of the glass plate 5a is weaker than the scattered light 1f that travels toward the foreign object side of the surface S. This tendency is the light receiving part (^) for the pattern surface S1.

The smaller the elevation angle of the light receiving direction in (B), the stronger the difference in magnitude between the two photoelectric signals becomes.

This phenomenon is caused by the fact that the scattered light behaves as a surface wave with respect to the light shielding part 5b that is in close contact with the surface S1, but the foreign object i comes into contact with the surface S only in a part of it, and most of it protrudes into space, so it is free to move. This can also be explained by the fact that when the scattered light is scattered in space and is incident on the pattern surface S at a close angle, the reflectance becomes high and the proportion of light entering the inside of the pattern surface S1 is smaller. Therefore, the scattered light is transmitted to the light receiving part (A) on the side of the pattern surface S.
At the same time, the scattered light that has passed through the back surface S2 is also detected by the light receiving part (B), and it is determined whether the scattering is caused by a foreign object or not by the light shielding part 5b, by determining whether the ratio of the amount of light between the two is, for example, twice or more. It is possible to determine whether it is caused by an edge portion.

Next, the principle of discriminating foreign matter adhering to the front and back sides of the glass plate 5a will be explained with reference to FIG.

In this figure, the light receiving parts (A) and (B) are provided diagonally backward from the part on the photomask that is irradiated with the laser beam 1, that is, on the incident side of the laser beam 1. Receives scattered light.

Here, when the laser beam 1 is incident on the surface of the photomask 5 on which the pattern is not formed, that is, the back surface S2, the scattering of the laser beam by the foreign matter k attached to the back surface S2 and the side on which the pattern is formed are explained. It shows the difference in scattering due to foreign matter i attached to the pattern surface SI. laser beam l
is obliquely incident on the back surface St, part of it is reflected, and part of it is transmitted, and reaches the pattern surface S. Scattered light 1 by foreign object k
g is photoelectrically converted by the light receiving section (A). Also, among the scattered light caused by the foreign matter i attached to the transparent part of the pattern surface S, the scattered light 1h that passes through the inside of the glass plate 5a and appears on the laser beam incident surface from the back surface S2 is reflected in the light receiving section. (A) is photoelectrically converted. By the way, when comparing the scattered light 1h and the scattered light 11 that does not enter the inside of the glass plate 5a from the pattern surface Sl among the scattered light caused by the foreign material i, the scattered light 1h has a reflection loss caused by the pattern surface S and the back surface S2. Therefore, the intensity is weaker than that of the scattered light 11.

The intensity ratio between the two tends to increase as the direction in which the scattered light is received by the light receiving sections (A) and (B) approaches the back surface S2 or the pattern surface S1. This is based on the fact that the larger the angle of incidence of light, the more the reflectance on the surface increases.
While changing the incident position on the light receiving part (A), (
When the output of B) is monitored, signals as shown in FIGS. 4(a) and 4(b) are obtained. Therefore, Figure 4 (al
The vertical axis in (b) represents the amount proportional to the intensity of the scattered light received by the light receiving sections (A) and (B), respectively, and the horizontal axis represents the time or the position of the laser spot with respect to the photomask 5. . In the case of scattering of laser light by a foreign object k, the signal waveform AI in FIG.

Bl, and comparing the signal magnitudes FAI and PH1, FAI is about 3 to 8 times larger than PBI, and in the case of scattering by foreign object i, the signal waveform A2. A waveform like B2 is obtained, and when comparing the sizes PA2 and PH1,
PH1 is about 3 to 8 times larger than PA2. Therefore,
When the scattered light exceeds a certain level, if the output ratio of the light receiving part (A) to that of the light receiving part (B) is twice, for example, twice or more, foreign matter is attached to the back surface st on the laser beam incident side. It can be determined that

Next, embodiments of the present invention will be described based on the drawings.

FIG. 5 is a perspective view showing a first embodiment of the defect inspection apparatus, and FIG. 6 is a circuit diagram showing an example of a detection circuit suitable for the configuration of FIG. 5.

This embodiment is more suitable for inspecting plain glass without a pattern or a mask having a relatively simple pattern than a photomask having a complicated pattern.

In FIG. 5, a photomask 5 as an object to be inspected is placed on a stage 9 with only its peripheral portion supported. The mounting table 9 can be moved one-dimensionally as indicated by an arrow 4 in the figure using a motor 6, a feed screw, and the like.

Here, the pattern surface of the photomask 5 is defined as the xy plane of the xyz coordinate system as shown in the figure. The amount of movement of the mounting table 9 is measured by a length measuring device 7 such as a linear encoder. On the other hand, the laser light 1 from the laser light source 8 is
The beam is converted to an arbitrary beam diameter by optical members such as an expander (not shown) and a condensing lens 3, thereby increasing the light intensity per unit area. This laser beam 1 is a pipe lake,
A scanner 2 having a vibrating mirror such as a galvanometer scans the area on the photomask 5 in the X direction.

At this time, the scanning laser beam 1 is applied to the surface of the photomask 5 (
For example, the light is incident obliquely at an incident angle of 70° to 80' with respect to the x-y plane. Therefore, the photomask 5 of the laser beam 1
The irradiated portion at the top is a thin circular spot extending approximately in the X direction in the figure. Therefore, the area where the photomask 5 is scanned by the laser beam 1 by the scanner 2 becomes a band-shaped area with a predetermined spread in the X direction.

In order for the laser beam 1 to actually scan the entire surface of the photomask 5, the aforementioned motor 6 is also driven at the same time, and the photomask 5 is moved in the X direction at a speed lower than the scanning speed of the laser beam 1. At this time, the length measuring device 7 outputs a measurement value related to the irradiation position of the laser beam 1 on the photomask 5 in the X direction.

In addition, optical information from foreign matter adhering to the photomask 5,
That is, light receiving elements 11 and 13 are provided to detect scattered light that occurs non-directionally.

Among these light receiving elements, the element 11 corresponds to the light receiving section (A) and is arranged to receive scattered light generated from the front side of the photomask 5 irradiated with the laser beam 1. On the other hand, the light-receiving element 13 corresponds to the light-receiving section (B) and is arranged to receive scattered light generated from the back side. Furthermore, the scattered light is focused on each light receiving surface of the light receiving elements 11 and 13 by lenses 10 and 12. And the optical axis of the lens 10 is x-
It is set so that approximately the center of the scanning range of the laser beam 1 is viewed from the front side of the photomask 5 so as to be oblique to the y plane. On the other hand, the optical axis of the lens 12 is determined to be symmetrical with the optical axis of the lens 10 with respect to the xy plane. The optical axes of the lenses 10° and 12 are arranged obliquely with respect to the longitudinal direction of the scanning range, that is, x
- It is defined so as to form a small angle with the z plane.

In FIG. 6, each photoelectric signal of the light receiving elements 11 and 13 is
are input to amplifiers 100 and 101, respectively.

The amplified photoelectric signal e is sent to two comparators 103.
104. Also, the amplified photoelectric signal e2
is applied to the other input of comparator 104 via amplifier 102 for the amplification factor. Note that when the amounts of light received by the light receiving elements 11 and 13 are equal, the signal e1. ．． e! both have the same size. Furthermore, the slice voltage v2 from the slice level generator 106 is applied to the other input of the comparator 103.

And each output of the comparators 103 and 104 is connected to the AND circuit 10.
5. This slice level generator 106 changes the magnitude of the slice voltage v2 in synchronization with the scanning signal SC for vibrating the scanner 2. This is laser beam 1
This is because the distance from the light receiving element 11 to the irradiation position of the laser beam 1 changes due to the scanning, that is, the solid angle of the scattered light reception of the lens 10 changes. Therefore, in synchronization with scanning, the slice voltage V,
Configure it to be variable.

In this configuration, the amplification factor of the amplifier 102 is 1.5.
~2.5, for example 2.

This means that among the scattered light generated from foreign matter adhering to the incident side of the laser beam 1, the ratio of the magnitude of the scattered light generated on the incident side to the magnitude of the scattered light transmitted through the photomask 5 is as shown in FIG.
This is because, as explained in FIG. 4, the number is more than doubled.

Further, the comparator 103 outputs a logical value "1" only when the signal e is larger than the slice voltage V. Also, the comparator 104 outputs the signal e, and the signal e is doubled to Ke! and outputs a logical value "1" only when e, > Ke. Therefore, AND circuit 105 connects comparator 103.
Only when the outputs of 104 are both logic value "1", the logic value r
Generate lJ.

Next, the function and operation of this embodiment will be explained. First, when a foreign object is attached to the surface on the incident side of the laser beam 1, when the laser beam 1 irradiates only that foreign object, the signal e becomes larger than the slice voltage v3, and the comparator 103 outputs a logical value rl.
Output J. Further, at this time, e, > Ke, and the comparator 104 also outputs a logical value of "1". Therefore, the AND circuit 105 generates a logical value of "1".

Next, if foreign matter is attached to the back surface, since the laser beam 1 is obliquely incident on the photomask 5, most of it will be specularly reflected by the glass surface of the photomask 5, and a portion will illuminate the foreign matter on the back surface. do. Therefore, among the scattered light from the foreign matter, the light receiving element 1
The scattered light reaching 1 has a smaller value than the scattered light reaching the light receiving element 13, that is, eI<Ke! becomes, comparator 10
4 outputs a logical value rOJ. Therefore, at this time el
Even if >%It holds true, the AND circuit 105
generates an embedded "0". Furthermore, when scattered light is generated from the edge of the light-shielding part, the amounts of light received by the light-receiving elements 11 and 13 are approximately equal, as shown in FIG.
e, and the comparator 104 outputs the logical value rOJ.

Therefore, AND circuit 105 generates a logic value of "0".

Note that the magnitude of the slice voltage V is related to the ability to detect foreign objects, and the smaller the slice voltage V is, the smaller the foreign object can be detected.

In this way, only when foreign matter is attached to the front side (laser light incident side) of the photomask 5, the AND circuit 105 outputs the logical value rlJ as the inspection result.

As described above, this embodiment has a very simple configuration when scattering by circuit patterns etc. is weak and only the detection of large foreign objects is required. It has the feature of being able to discriminate and test at high speed.

What has been described above is a case in which a laser beam is incident from the side on which a circuit pattern is formed, and foreign matter adhering to the incident surface is detected. By the way, in a reticle or mask used in a reduction projection exposure apparatus, not only foreign matter attached to the circuit pattern side but also foreign matter attached to the back surface without a pattern is transferred. When using a 1710x reduction lens, the minimum size that can be transferred with a foreign object attached to the back side without the pattern to be transferred is the same as the minimum size that can be transferred with a foreign object attached to the side with the circuit pattern.
It is about 1.5 times longer in length and about twice as large in area.

Therefore, it is necessary to detect foreign matter attached to the back surface with the necessary sensitivity. In order to detect foreign matter on the back side, the photomask may be used with the apparatus described in the first embodiment turned upside down. However, even with this method, the following problem occurs with a photomask having a complicated pattern. In other words, when trying to determine the size of a foreign object based on the relationship between the detected intensity of the scattered light caused by the foreign object on the side of the circuit pattern surface and the size of the foreign object, Since the relationship between the sizes of the particles will be different, an error will occur in determining the size of the foreign object. Not only that, but the detection of foreign matter itself becomes difficult due to the influence of scattered light from the edges of the light-shielding portions of the pattern.

Therefore, a second embodiment of the present invention will be described based on FIGS. 7 to 9. FIG. 7 shows a perspective view of a second embodiment of the defect inspection device, which differs from the first embodiment in that another set of light receiving sections is provided. FIG. 8 is a diagram showing the photoelectric output of each light receiving element due to scattered light from a foreign object. Furthermore, FIG. 9 is a connection diagram of a detection circuit suitable for this second embodiment.

In FIG. 7, descriptions of components having the same configurations and functions as those of the first embodiment will be omitted. In this second embodiment, a light receiving system having a substantially equal light receiving solid angle is provided on the side of the photomask 5 on which the laser beam 1 is incident and on the opposite side thereof. As shown in FIG. 7, this light-receiving system includes a condenser lens 20 and a light-receiving element 21 that obliquely view the front side (laser light incident side) of the photomask 5, and a condenser lens 22 that obliquely view the back side of the photomask 5. and a light receiving element 23. Of course, the optical axes of the lenses 20 and 22 are directed approximately toward the center of the scanning range. Furthermore, each optical axis is a plane including the longitudinal direction X of the scanning range (x of the xyz coordinate system).
- plane parallel to the z plane).

Further, at this time, the angle formed by the optical axes of the lens 20 and the lens IO is set to be around 30 to 45 degrees. The same applies to the angle formed by the optical axes of the lens 22 and the lens 12.

Therefore, in this embodiment, in addition to utilizing the fact that the directivity of scattered light due to the foreign matter and the circuit pattern is different for the light traveling to the front side of the photomask 5, the light traveling to the front side and the back side of the photomask 5 due to the foreign matter and the circuit pattern is further utilized. The difference in the intensity ratio of the two is also used to inspect for foreign substances.

FIG. 7 is a perspective view of this embodiment, and also shows a moving table on which the object to be inspected 5 is installed, a motor for driving the movement of the moving table, and an encoder for detecting the position of the moving table.

In FIGS. 8(a), (b), tc>, and (d), the vertical axis represents the magnitude of the photoelectric signals from the light receiving elements 21.11 and 23.13, and the horizontal axis represents the magnitude of the photoelectric signals from FIGS. 8(a) to 8(d). (d) Commonly shown over time. If the laser beam 1 is scanned at a constant speed on the photomask 5, the horizontal axis also corresponds to the spot position. When the laser beam is incident on the circuit pattern and is scattered, the photoelectric elements 21.11.
The outputs from 23.13 are AI, Bl, and Bl, respectively, in Figure 8.
C1, DI, and each peak value is PAL
, PBI, Pct.

It becomes PDI. In this case, since the scattered light has directivity, the photoelectric output of the light receiving elements 21 and 11 is
PAI is larger than that, but since it is not completely directional, the peak FBI is not zero. Output peak value, PCI, PDI of the light receiving element 23.13 on the back side of the photomask 5
have values close to FAI and FBI, respectively. This is as explained in FIG. 2 above. However,
When the laser beam is scattered by a foreign object, the output from each light receiving element is A2. B2. C2 and D2, and their respective peak values are PA2. PB2. PO2°PD2. There is a small difference between PA2 and PB2 due to the small directivity of the scattered light, but there is a difference between PA2 and PO2 and between PB2 and PD2.
There is a large difference between PA2. P
B2 is larger. For example, a level SL smaller than the smaller peak value FBI of the scattered signals from the circuit pattern.
If we try to slice the signals in Figures 8(al and 8(b)) using the slicing voltage to detect the weak scattered light caused by as small a foreign object as possible, the circuit pattern will also be judged as a foreign object. The ratio of the outputs of the light receiving element 21 and the light receiving element 23 in Fig. 7 and the ratio of the outputs of the light receiving element 11 and the light receiving element 13 in Fig. 7 are determined, and the signal in Fig. 8 (a) exceeds SL and the signal in Fig. 8 (b) If a foreign object is determined only when the signal exceeds SL and this ratio is more than a certain value, for example, twice or more, then the low level S as described above can be detected.
Even if L is used, only foreign objects can be detected correctly.

FIG. 9 is a block diagram of signal processing in this embodiment, and the light receiving elements 21, 11, 23, and 13 shown in FIG.
input to amplifiers 110.111.112.113. These four amplifiers 110 to 113 are connected to light receiving elements 21.11.
．． 23.If the amounts of light incident on 13 are equal, then the output signal e,.

eZ + 83 + 13a are also made equal.

The comparator 114 compares the output signal e with the slice voltage Vsl as the level SL shown in FIG. 8(a), and outputs a logical value of "1" when eI>vII.

The comparator 115 compares the output signal e2 with the slice voltage V as the level SL shown in FIG.
> v, □, the logical value rlJ is output. In addition, in order to determine the difference in scattered light generated on the front side and the back side of the photomask 5 due to foreign matter and edge portions, output signals e and C are used.
4 are respectively input to amplifiers 116 and 117 for amplification.

This amplification degree is 1.5 to 2.5 as in the first embodiment.
, for example, 2.

The comparator 118 compares the output signal e1 and the output signal Ke of the amplifier 116, and outputs a logical value "1" only when e, > Ke3. The comparator 119 compares the output signal e2 and the output signal Ke of the amplifier 117, and calculates 6 z
> Outputs logical value "1" only when Ke 4. Then, each output of the comparators 114, 115, 118, and 119 is input to the AND circuit 120, and when the AND is established,
The logical value “1” indicates that a foreign object is present as a result of the inspection.
” occurs. Further, the slice voltages V□, ν are output from the slice level generator 121, and their magnitude changes in response to the scanning signal SC, as in the first embodiment.

However, the individual magnitudes and degrees of change of the slice voltages vs+lv, □ are slightly different. This will be explained using FIG. 10(a) (bl).
FIG. 0(a) is a perspective view of FIG. 7 when viewed from above the photomask 5. FIG.

Here, in the scanning range of the laser beam 1 on the photomask 5, the central part is at a position C1, and both ends are at a position C, respectively.
,C,. As described above, the distances from the light receiving elements 21 and 11 to the position are equal. Therefore, the following description assumes that the same foreign matter is attached to positions C, C, and C3. If a foreign object is attached to the position CI, the solid angles at which the light receiving elements 21 and 11 receive the scattered light generated by the foreign object are approximately equal, so that the signal 13 +
The magnitudes of +ex also become approximately equal. Therefore, when the spot of laser beam l is at position C2, slice voltage V
□.

vs! are set to be of equal size.

Furthermore, if a foreign object is attached to position C2, the light receiving element 21
The amount of light received by the light receiving element 11 is greater than the amount of light received by the light receiving element 11. Therefore, since the signal e2 is larger than the signal e, the slice voltage needs to be set so that Vst>vl+. However, since the positions Ct are both far away from each light receiving element 21.11, the magnitudes of the signals el + ez do not differ much. Therefore, the slice voltage satisfies V,2>V□ with not much difference in magnitude, and is set smaller than the slice voltage at position C8.

On the other hand, when a foreign object adheres to position C3, since position C1 is the closest to the light receiving element 21, the signal e becomes an extremely large value. Further, the light receiving element 11 has a position Wcs
The solid angle of light reception looking into the field is fc+.

Since the signal e2 changes greatly with respect to Ct, the signal e2 is at the position CI
The value is smaller than the ratio at +C2. Therefore, the slice voltage satisfies V□>V, □ with a fairly large difference, and is set to be larger than the slice voltage at position CI.

As mentioned above, the changes in each slice voltage for WC1 to C1 are shown in FIG. 10 (bl). In FIG. 10 (b),
The vertical axis represents the magnitude of the slice voltage, and the horizontal axis represents the position within the scanning range.

As described above, the magnitudes of the slice voltages V□+Vs□ are both equal at the position CI, and are continuously changed so that Vsl>ViZ at the position C2, Vsz>Vl1%, and the position C, ni. Change. This change is not necessarily linear, but often curved like the change in slice voltage V□.

To obtain this curved change, the slice level generator 1
For example, a conversion circuit having logarithmic characteristics, a polygonal line approximation circuit, or the like may be used for 21.

Next, the operation of the circuit shown in FIG. 9 will be explained.

In contrast to the scattered light generated from the edge portions of the pattern, this scattered light has strong directivity, and for example, assume that the amount of light received by the light receiving element 11 is greater than the amount of light received by the light receiving element 21. Therefore, the output signal e and e become greater than e. Furthermore, as shown in FIG. 2, the amount of light received by the light receiving elements 23.13 is approximately equal to the amount of light received by the paired light receiving elements 21.11, and the output signals e and e4 are 〇＋tea
:ex.

Therefore, e, <Ke, and a, <Ke, and the comparators 118 and 119 both output a logic value of "0". Therefore, the AND circuit 120 generates a logical value of "0" for the scattered light from the edge portion.

Furthermore, when scattered light is generated from foreign matter adhering to the pattern surface of the photomask, the output signals el+ ex are both larger than the slice voltage V□+ ViZ, and the output signals e3+ 84 are each larger than the output signal el+ et. te1
It becomes 73 to 178 times larger. Then, the output signal e2
* et is doubled, but since K is set at 1.5 to 2.5, et > Kex + ex >
KE3m. For this reason, the comparison circuits 114, 115.
118 and 119 both output a logic value "1", and the AND circuit 120 outputs a logic value "1".

When scattered light is generated from foreign matter adhering to the back surface of the photomask, as shown in FIG. 3, the amount of light received by the light receiving element 23.13 is greater than the amount of light received by the light receiving element 21.11. Therefore, e4 <Ke= , e, <
Ke, and the outputs of the comparators 118 and 119 both have a logical value rOJ. Therefore, the AND circuit 120 outputs a logical value of "0" with respect to the foreign matter attached to the back surface.

As described above, according to the second embodiment, the pair of light receiving elements 11.13 and the pair of light receiving elements 21.23 are used to selectively and strongly receive the scattered light generated at the edge portions of the pattern. Since a pair is provided, even on a photomask having a complicated pattern, it is possible to avoid the influence of scattering due to the pattern and accurately detect only the attached foreign matter.

Next, as a third embodiment of the present invention, a configuration in which the configuration of the detection circuit in the second embodiment is changed will be described with reference to FIG. The basic configuration is the same as the detection circuit described in the second embodiment. However, in this embodiment, among the light receiving elements 21.11 arranged on the laser beam incidence side, attention is paid to the light receiving element with the smaller output, and the light receiving element is paired with the light receiving element 21.
It is configured to determine whether the output is more than twice as high as that of the light receiving element disposed on the back side.

In FIG. 11, the same functions and operations as in FIG. 9 are given the same reference numerals. Therefore, a configuration different from that in FIG. 9 will be explained. Each output signal el+ et of the amplifiers 110 and 111 is input to a comparator 130 to detect the magnitude of the output signal el+ ex. For example, when e, > e2, this comparator 130 has a logical value of "1".
When eI<ez, a logic value "0" is output.

The output of the comparator 130 as it is and the output inverted by the inverter 131 are each output by an AND gate 1.
33.132. In addition, comparators 1 and 1 are connected to the other inputs of AND gates 132 and 133, respectively.
The output signal from 18.119 is connected.

Each output signal of the AND gates 132 and 133 is passed through an OR gate 134 to an AND circuit 1 that generates a test result.
Enter into 20.

In such a configuration, for example, if the amount of light received by the light receiving element 21 is larger than the amount of light received by the light receiving element 11 (due to scattering from the edge portion of the pattern, etc.), the output signal el+ et will be e,
>e. Therefore, the comparator 130 outputs a logical value "1", the AND gate 132 is closed, and the AND gate 133 is opened. Therefore, at this time the comparator 118
．． For example, if both 119 output the logical value "1",
Only the output of comparator 119 is applied to OR gate 134 via AND gate 133. In this way, the output of the OR gate 134 is transmitted to the light receiving element that receives a smaller amount of light among the light receiving elements 21 and 11, and to the light receiving element paired therewith (element 2).
It shows the result of determining whether it is a foreign object or an edge portion based on the ratio of the photoelectric signal to either one of 3.13).

As described above, selecting the smaller of the output signals e and 82 as in this embodiment means selecting the light receiving direction where the influence of scattering of the circuit pattern is small. Prevents strong scattered light from entering the light receiving system in only one direction, causing saturation of the signal processing system, especially the output signal of the amplifier, and making it impossible to compare the intensities of the light receiving systems on the front and back sides of the object to be inspected. In addition, it also has the advantage of reducing false detection of foreign objects when there is an error in the geometrical arrangement of the condensing lens of the light receiving system that looks at the front and back sides of the photomask, and the light converging directions on the front and back sides are not completely symmetrical. arise.

In addition, in the above embodiment, the comparators 118 and 119 are
For the photoelectric signals shown in Fig. 4(a) and (b), (3
1Ke31 eg Ke4 is determined, and the output is determined depending on whether the result is positive or negative. However, even if a circuit is provided that calculates the ratio between e and Ke and et and Keg using a divider or the like and determines whether the result is 1 or more, the same function as in the above embodiment can be achieved. can be fulfilled.

Next, a fourth embodiment of the present invention will be described based on FIGS. 12 and 13. In this embodiment, one more light receiving element 31 is provided in addition to the second embodiment to further reduce the influence of scattered light from the pattern.

In FIG. 12, the difference from the configuration in FIG. 7 is that the condenser lens 30 and the light receiving element 31 are placed on the laser beam incident side of the photomask 5 from the direction opposite to the optical axis of the lens 10. It is arranged so that the surface, that is, the pattern surface is visible.

Here, the relationship between the optical axes of lenses 10, 20, and 30 will be described. It is assumed that these three lenses 10°20.30 have the same optical characteristics, and that the characteristics of the three light receiving elements IL21.31 also have the same characteristics.

Also, each optical axis is set to 1. ,l,,l,. optical axis a,
, Il, , A, and I are all set at a small angle, for example, around 10 to 30 degrees, with respect to the pattern surface of the photomask 5. Further, the distances from the center of the scanning range of the laser beam 1 to each of the light receiving elements 11, 21, and 31 are set equally. In the figure, when the photomask 5 is viewed from above, the optical axis 12 coincides with the longitudinal direction (scanning direction) of the scanning range, and the optical axes 1t, 1. is set at a small angle relative to the scanning range, for example around 30° to 45°.

In this way, each optical axis βl+ 2+ 7! : By determining l, the scattered light generated at the edge of the pattern is
Among the three light receiving elements 11, 21, and 31, almost no light is received by one light receiving element.

Moreover, as a -a tendency, when both the scattered light from the edge portion of the pattern is strongly received by the light receiving elements 11 and 21, the amount of light received by the light receiving element 31 becomes extremely small.

Further, since scattered light is generated non-directionally from foreign objects, the amount of light received by each light receiving element 11, 21, 31 is approximately the same. The output of this light receiving element 31 is processed by a detection circuit shown in FIG.

It is basically the same as the detection circuit shown in FIG. The output of the light receiving element 31 is input to a comparator 141 via an amplifier 140. A slice voltage Ll corresponding to the spot position of the laser beam is inputted to the comparator 141 from the slice level generator 121 in response to the scanning signal SC. This comparator 141 is
When the output signal e5 of the amplifier 140 exceeds the slice voltage Vi3, the logic value is "1", otherwise the logic value is "0".
Output. Other circuit elements in FIG. 13 are the same as in the third embodiment. Compared to the third embodiment, this fourth embodiment has a light receiving system (light receiving element 31, lens 30) in one redundant direction, so light scattered by the circuit pattern may be mistakenly detected as a foreign object. It has the characteristic that the probability that it will happen is extremely small.

Note that since the light receiving elements 11.21 and 31 look at the center of the scanning range from opposite directions, the tendency of change in slice voltage Vs3 is opposite to slice voltage Vsl + Vt2. do it like this. That is,
The slice voltage V is obtained by reversing the slope of the slice voltage v5□ in FIG. 10 (bl) described above.

FIG. 14 is a block diagram showing a detection circuit according to the fifth embodiment. The difference from the fourth embodiment is that three comparators 150, 151, and 152, and an AND circuit 1
53, OR circuit 154, and slice voltage VSI+S□
The difference is that a slice level generator 160 that generates two types of voltages as +Vt3 is added. The two voltages of each slice voltage maintain a predetermined difference from each other, and the scanning signal S
It changes depending on C. Preamplifier 110.111.14
The output signals ell e2+ eg of 0 are the slice voltages v81°v5□ output from the slice level generator 160 by the comparators 150, 151, and 152, respectively.
+ Compared with Vt3. At this time, the comparator 150
．． The slice voltage input to 151 and 152 is the comparator 11.
The output signal e+ is higher than the slice voltage input to 4.115.141, no matter how strong the scattering of light by the circuit pattern occurs.

At least one slice voltage is set to be higher than the minimum value of e2+e5. Therefore, the comparators 150, 151, and 152 and the AND circuit 153 generate a logical value of "1" only when extremely strong scattered light is generated by a foreign object. The output of the AND circuit 153 is input to the OR circuit 154 together with the output of the AND circuit 120. Therefore, the OR circuit 154 outputs a logical value of "1" when a foreign object is detected as an inspection result, regardless of the size of the foreign object. The present invention has the following features compared to each of the embodiments described above. Due to scattering by foreign objects, a large photoelectric signal enters the signal processing system, and the output of each amplifier approaches the power supply voltage (as a result, the output of the amplifier 112.113 for the photodetector 23.13 on the back side of the test object A comparator 1 that compares the magnitude of the output from the amplifiers 110 and 111
In other embodiments, if comparators 118 and 119 operate as if they detected scattered light from both valve circuit patterns, even though 18.119 does not operate correctly and the scattered light is from a foreign object. Although foreign objects cannot be detected, they can be detected in this embodiment. In addition to the comparators 114.115.141 that perform comparisons with low slice voltages as described above, there are comparators 150.1 that perform comparisons with high slice voltages.
This is because the comparators 51 and 152 are provided, and foreign matter that causes strong scattered light is detected by this comparator.

As in this example, using a low slicing voltage to detect a foreign object contributes to increasing the foreign object detection ability, i.e., detecting smaller foreign objects, while using a high slicing voltage contributes to This contributes to preventing malfunctions due to amplifier saturation, etc. Therefore, there is an advantage that weak scattered light from smaller foreign objects can be detected, and only foreign objects can be accurately detected even in the case of strong scattered light. This means that the foreign object detection range has been expanded.

The detection circuit according to the fifth embodiment has been described above using an example in which the number of light receiving elements is three on the laser beam incident side of the object to be inspected and two on the opposite side. It goes without saying that if there is one or more light-receiving elements on each side, it can be configured to have the intended function of the fifth embodiment.

In addition, in Figure 11.13.14, comparator 1
30 and AND gate 132, 133 and OR circuit 13
4 is used, but comparators 118 and 11 are used as shown in FIG.
9 may be connected so as to be directly applied to the AND circuit 120.

Next, a sixth embodiment of the present invention will be described based on FIG. 15. In this embodiment, in addition to the fifth embodiment, another light receiving element 41 and a condensing lens 40 are provided.

The optical axis of this lens 40 is determined to be plane symmetrical to the optical axis of the lens 30 with respect to the patterned surface of the photomask 5. Of course, the optical axis of the lens 40 is determined so that the center of the scanning range is viewed from the back surface of the photomask 5. In this embodiment, each photoelectric signal of the light receiving element 11, 21, 31 that receives the scattered light from the laser beam incidence side is compared with each slice voltage as in the previous embodiment.
Processed as if searching for AND. This determines whether the scattered light is from the edge of the pattern or from a foreign object. On the other hand, the photoelectric signals of the light receiving elements 13, 23, and 41 for processing the scattered light from the back surface of the photomask 5 are as follows.
Although it may be processed by the detection circuit as in the above-mentioned embodiment,
Can be handled by simpler detection circuits.

For example, the photoelectric signal of the light receiving element 13.23.41 is processed by a circuit configured similarly to the detection circuit of the light receiving element 11.21.31. In this way, if the light receiving element 11.21.31 on the laser beam incidence side detects a foreign object and the light receiving element 13.23.41 on the back side also detects the foreign object, the foreign object will be removed from the photomask 5. It can be determined that it is attached to the transparent part. In this case, there is an advantage that the size of the foreign object can be determined extremely accurately by considering the peak value of the photoelectric signal of each light-receiving element when detecting the foreign object on the front side and the back side of the photomask 5.

Next, a seventh embodiment will be described. In the seventh embodiment, the arrangement of each light receiving element is assumed to be the same as that in FIG. 7 used to explain the second embodiment.

As previously explained with reference to FIG. 1, the scattered light from the foreign matter i attached to the transparent part of the glass plate 5a of the photomask is detected by the light receiving part (A) and the light receiving part (B), but when the light is blocked, Scattered light from the foreign matter j adhering to the portion 5b is transmitted to the light receiving portion (A
), and is not detected by the light receiving section (B). This will be explained with reference to FIG. 16 as a photoelectric signal of each light receiving element in FIG. 7. Figure 16(a)(b)
) (c) (d) are the light receiving elements 21, 11, 23 .
The magnitude of the photoelectric signal from 13 is plotted on the vertical axis, and time is plotted on the horizontal axis, and the horizontal axis also corresponds to the laser spot position. When the laser beam is scattered by a foreign object j as shown in FIG. 1, the light receiving elements 21 and 11 generate photoelectric signals A3 and B3 as shown in FIGS. 16(a) and 16(b), respectively. On the other hand, the photodetector 23.13 receives photoelectric signals C3 and D, respectively, as shown in FIG. 16(C) (dl).
As 3, approximately zero is output. Furthermore, when the laser beam is scattered by a foreign substance i as shown in FIG.
4, B4, C4, D4 are generated. That is, Fig. 16 (C
) As shown in (d), each photoelectric signal C4, D4 of the light receiving element 23.13 is not zero, but some output is obtained. In addition, PA4, PH1, PO2, PD4 are photoelectric signals A4
, B4, C4, and D4. Therefore, each small slice voltage Vs4 + VsS is set to the peak value PC
4. If set to the middle of PD4, in the case of foreign object i, the photoelectric signals of the light receiving element 23.13 will both have the slice voltage v and 4°Vs.
exceeds S, but in the case of foreign object j, the slice voltage v14+
II's! Foreign matter i and j can be distinguished without exceeding S.

Therefore, next, a seventh embodiment will be specifically described.

FIG. 17 is a block diagram of signal processing in this embodiment. In FIG. 17, light receiving elements 21.11.23.13, amplifiers 1101 to 113, comparators 114.115.
118, 119 and amplifiers 116, 117 are shown in FIG.
It has the same function as the circuit in the second embodiment. The difference is that comparators 204 and 205 are provided, and their outputs are input to the AND circuit 202 in parallel. The comparator 204 compares the output e3 of the amplifier 112 with the slice voltage vs4 output from the slice level generator 203, and outputs a logic value "1" if e,>Vs4, and a logic value "0" otherwise. , on the other hand, the comparator 205 compares the output e4 of the amplifier 113 with the slice voltage VsS, and outputs a logic value "1" if 64:>VsS, and otherwise outputs a logic value "0". Here, the magnitude of the slice voltage Vs41 VsS is determined as explained in FIG. 16 above, and the magnitude changes depending on the spot position. The manner of the change is as explained in each of the first to sixth embodiments. In such a configuration, if the laser beam hits a foreign object attached to the glass plate (light transmitting part), the comparator 20
4.205 outputs the logical value "1", and the other comparators 114.115.118.119 also output the logical value "1", so the output of the AND circuit 202 becomes the logical value "1" and a foreign object has been detected. Show that. However, when the laser beam enters a foreign object attached to the light shielding part, the comparator 2
The output of 04.205 becomes the logical value rOJ, and the output of the AND circuit 202 becomes the logical value "0". Therefore, the presence of foreign matter can be detected only when the foreign matter is attached only to the light-transmitting portion, and foreign matter attached to the light-shielding portion, which does not affect the printing of the mask pattern, can be ignored.

In this way, compared to the case where the foreign matter is detected without distinguishing whether the foreign matter is attached to the light-transmitting part or the light-blocking part, in this embodiment, since the foreign matter is attached only to the light-shielding part, the degree of cleaning of the photomask is lower than that of the pattern printing. Even though the photomask can withstand high temperatures, the need to clean it again or replace it with another photomask with the same pattern is reduced.

Therefore, there are advantages in terms of time and economy in manufacturing semiconductor devices.

In this seventh embodiment, comparator 204.20
Although both outputs of comparators 204 and 205 are input to the AND circuit 202, only the output of either the comparator 204 or 205 may be input to the AND circuit 202. In this case, the structure is simple, but it also has the disadvantage that it is prone to malfunction if noise enters the photoelectric signal. It is also conceivable to obtain the OR of each output of the comparators 204 and 205 and input the result to the AND circuit 202.

As mentioned above, the seventh embodiment has been described as adding a new function to the second embodiment of detecting foreign matter attached only to the light transmitting part, but this function is similar to the first embodiment. It goes without saying that the same addition can be made in each of the third to sixth embodiments.

In each of the embodiments described above, the light-receiving element that receives the scattered light generated on the laser beam incidence side and the light-receiving element that receives the scattered light generated on the back side are arranged symmetrically with respect to the surface of the object to be inspected. ing.

This is because a photomask is used as the object to be inspected.For example, even if a pattern is drawn on a transparent substrate with light-shielding parts, when inspecting an object to be inspected that does not have edges, the front side of the substrate The pair of light-receiving elements looking into the rear side and the rear side do not necessarily need to be arranged symmetrically in a plane. Further, a plurality of light receiving elements looking into the surface on the laser beam incidence side may be provided, and a single light receiving element looking into the back surface may be provided.

Further, in each of the above embodiments, the ratio of the outputs of the pair of light receiving elements provided corresponding to the front and back sides of the object to be inspected was compared to a certain value, but for example, the ratio of the output of the light receiving element 11 located on the front side 21
The sum of the outputs of the light-receiving elements 13 and 23 located on the back side are calculated respectively, and by determining whether the ratio of the two sums is greater than K, it is possible to determine whether it is a foreign object or a circuit pattern. It is possible to identify whether there is a foreign object or whether it is a foreign object attached to the laser beam incident side.

Further, since there is a correlation between the size of the foreign object and the magnitude of the scattering signal, it is also possible to know the size of the foreign object from the peak value of the photoelectric signal or the like when the foreign object is detected. In this case, the signal for which the peak value is determined may be the sum of the outputs of multiple light-receiving elements on the laser beam irradiation side, or it may be a signal from a single photoelectric element. Also good.

Further, by determining the moving position of the object to be inspected and the position of the laser spot scan when the foreign object is detected, it is also possible to know the location of the foreign object on the object to be inspected.

As described above, according to the present invention, when scanning a relatively wide area at high speed with a spot of a light beam, the reference is Since the signal (slice level) is changed, defects such as foreign objects can be detected accurately and at high speed according to their size. Furthermore, the size of the foreign object can be detected from the correlation between the intensity of the scattered light and the size of the foreign object, and only foreign objects that are truly harmful can be detected.

For this reason, by detecting even smaller foreign objects than necessary, reticles and masks that can be used for exposure,
It is possible to prevent the time loss of re-cleaning because it is determined to be contaminated.

The present invention can be used not only to detect foreign matter attached to a city mask, but also to detect foreign matter on an object such as a pattern adhered to a transparent object. Therefore, the present invention can be used to manufacture precision patterns that are free from adhesion of foreign matter such as dust. It is also very useful for time inspection.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the scattering of laser light by foreign matter on the surface of the photomask on which the pattern is drawn, and Figure 2 is a diagram showing the scattering by foreign matter adhering to the glass plate and the scattering by the edge of the light shielding part. , FIG. 3 is a diagram showing the state of scattering due to foreign matter adhering to the front and back surfaces of the transparent part of the glass plate, FIG. 4 is a diagram showing scattered light received by the light receiving part shown in FIG. 3, and FIG. FIG. 6 is a diagram showing a defect inspection device according to a seventh embodiment of the present invention, FIG. 7 is a diagram showing a defect inspection device according to a second embodiment, and FIG. 8 is a diagram showing each light received by scattered light from a foreign object. Figure 9 is a diagram showing the photoelectric output of the element; Figure 9 is a diagram showing the detection circuit according to the second embodiment;
Figure (a) is a top view of the photomask, Figure 10 (b) 8
11 is a diagram showing a detection circuit according to a third embodiment of the present invention; FIG. 12 is a diagram showing a defect inspection apparatus according to a fourth embodiment of the present invention; FIG. 13 is a diagram showing a detection circuit according to a fourth embodiment of the invention, FIG. 14 is a diagram showing a detection circuit according to a fifth embodiment of the invention, and FIG. 15 is a diagram showing a detection circuit according to a sixth embodiment of the invention. 16 is a diagram showing a photoelectric signal of a light receiving element in a seventh embodiment of the present invention; FIG. 17 is a diagram showing a signal processing according to a seventh embodiment of the present invention. It is a diagram showing a circuit. [Explanation of symbols of main parts] l... - laser beam, 2... scanner 5 - inspected object 11.13.21.23.31.41... light receiving element 10
．． 12.20.22.30.40...Condensing lens 106.12L160.203...Slice voltage generator 103.114.115.141.150,151.1
52.204.205 - Comparator Applicant 2 Nippon Kogaku Kogyo Co., Ltd. r-;

Claims (1)

[Scope of Claims] 1. A light beam scanning means that irradiates a light beam from one side of a light-transmissive planar object to be inspected and scans a spot of the light beam one-dimensionally; a photoelectric detection means that views a scanning range from a predetermined spatial position, receives scattered light generated at a defective part within the one-dimensional scanning range, and outputs a photoelectric signal according to the intensity of the scattered light; the light beam; a slice level generator that generates a reference signal whose magnitude changes in time series in response to changes in the geometrical arrangement between the scanning position of the spot and the position of the photoelectric detection means; A defect inspection device comprising: a comparison circuit that compares the magnitude relationship with a reference signal and outputs a detection signal indicating the existence of the defective portion when the photoelectric signal is larger than the reference signal. 2. The photoelectric detection means includes a condensing optical system that views almost the entire one-dimensional scanning range, and a light receiving element that receives the scattered light that is condensed within a solid reception angle of the condensing optical system. 2. The apparatus according to claim 1, wherein the optical axis of the condensing optical system is tilted from the normal to the surface of the object to be inspected. 3. The photoelectric detection means includes a plurality of condensing optical systems that view almost the entire one-dimensional scanning range from a plurality of different spatial positions, and detects scattered light condensed by each of the plurality of condensing optical systems. a plurality of light-receiving elements that receive light, the comparison circuit has a plurality of comparison circuits that input photoelectric signals from each of the plurality of light-receiving elements, and the slice level generator detects time-series size changes. 2. The apparatus according to claim 1, wherein a plurality of reference signals having different values are respectively input to said plurality of comparison circuits.