JPH0256626B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for detecting foreign matter defects caused by adhesion of minute dust, and more particularly to an apparatus for inspecting foreign matter adhering as defects on substrates such as LSI photomasks and retakes.

In the process of manufacturing LSI photomasks and wafers, foreign matter may adhere to the reticle, mask, etc., and these foreign matter may cause defects in the manufactured masks and wafers. Particularly in a reduction projection type pattern printing apparatus, since this defect appears as a common defect in all chips of each mask wafer, 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
Inspections last for hours, causing worker fatigue.
This results in a reduction in the inspection rate. Therefore, in recent years, various devices have been developed that automatically detect only foreign matter attached to a mask or reticle by irradiating it 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 (edges of light-shielding parts such as chrome) on the mask or reticle 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 the smaller the diameter of the light spot in order to accurately detect small foreign objects, the longer the inspection time will be.

Furthermore, this device can determine whether the foreign matter is attached to the light-shielding part such as chrome or the glass surface (light-transmitting part), and whether the foreign matter is attached to the light-transmitting part. It has not been possible to inspect the state of so-called foreign matter adhesion, such as distinguishing whether it is adhered to the surface of the object to be inspected on which the laser light enters or whether it is adhered to the back surface thereof.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a defect inspection apparatus that can detect foreign matter adhering to an object to be inspected at high speed and can inspect the state of adhesion of foreign matter at high speed.

Before describing embodiments of the present invention, 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 FIGS. 1, 2, and 3. It is assumed here that the light beam irradiates the object to be inspected with 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 that a laser beam as a light beam is irradiated onto the patterned surface of a mask or reticle (hereinafter collectively referred to as a photomask) as an object to be inspected. This figure shows the scattering of laser light and the scattering caused by 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 glass plate 5 of a photomask 5 is shown.
Surface _S1 provided with a light shielding part 5b provided in close contact with a
(Hereinafter, this surface will be referred to as a pattern surface _S1 .) The laser beam 1 that is obliquely incident on the pattern surface S1 is specularly 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 Fig. 1, the light-receiving part A, which consists of a condensing lens and a photoelectric element, is shown to receive the specularly reflected light, but in reality, it is placed at a position where the specularly reflected laser light does not enter. . Moreover, the light receiving part A is arranged so as to obliquely look into the irradiated part of the laser beam 1.
This is the pattern surface _S1 of the glass plate 5a and the light shielding part 5.
This is to avoid receiving as much scattered light as possible due to minute irregularities on the surface of b.

Further, a light receiving section B including a condenser lens and a photoelectric element is provided on the surface _{S 2 (} hereinafter referred to as the back surface S ₂ ) of the glass plate 5a opposite to the pattern surface S 1 . This light-receiving section B is connected to the glass plate 5a (particularly its patterned surface).
It is disposed in a plane-symmetric relationship with the light receiving section A with respect to S ₁ ), and the irradiated portion of the laser beam 1 is obliquely viewed from the back surface S ₂ side. In FIG. 1, the light receiving section B is shown so as to receive the laser light that directly passes through the glass plate 5a, or is actually provided at a position where it does not receive the laser light that directly passes through the glass plate 5a. That is, the light receiving sections A and B are both arranged at positions where they receive scattered light generated non-directionally from a foreign object.

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

The magnitude of the photoelectric signal detected by the light receiving section A is almost the same for both the foreign substances i and j. That is, when foreign objects i, j are irradiated with laser beam 1, foreign objects 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, a part of the scattered light 1b generated by the foreign object i passes through the glass plate 5a and reaches the light receiving section B. Generally, the scattered light 1b is smaller than the scattered light 1a, but due to the adhesion of foreign matter i to the light receiving sections A and B, some kind of photoelectric signal is generated in both the light receiving sections A and B. 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 edge part and receive only the light from the scattering hole, it is difficult to determine whether the scattered light is due to foreign matter or the edge part. It is necessary to determine whether 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.) Since the light shielding part 5b has a layer thickness of about 0.1 μm and is in close contact with the pattern surface _S1 , it directly faces the outside of the glass plate 5a, but the scattered light 1C and the glass The intensity of the scattered light 1d traveling toward the inside of the plate 5a is approximately equal to that of the scattered light 1d. Scattered light 1
d passes through the inside of the glass plate 5a and then 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
Since the scattered light 1e floats higher, the scattered light 1e travels toward the inside of the glass plate _5a from the pattern surface S1.
is weaker than the scattered light 1f traveling toward the foreign object side of the surface _S1 .
This tendency shows that the light receiving areas A and B for the pattern surface _S1
The smaller the elevation angle of the light receiving direction, 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 j only partially contacts the surface _S1 , and most of it protrudes into space. This can also be explained by the fact that scattering occurs in free space, and when the scattered light is incident on the pattern surface _S1 at a grazing angle, the reflectance becomes high, and the proportion of light entering the inside of the pattern surface _S1 is smaller than that of the pattern surface S1. Therefore, pattern surface S ₁
Scattered light on the side of S2 is detected by the light receiving part A, and the scattered light that has passed through the back surface _S2 is also detected by the light receiving part B at the same time, and a judgment is made as to whether the ratio of the amount of light between the two is, for example, twice or more. Accordingly, it can be determined whether the scattering is caused by foreign matter or by the edge portion of the light shielding portion 5b.

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, light receiving sections A and B are provided obliquely behind the part of the photomask that is irradiated with the laser beam 1, that is, on the incident side of the laser beam 1, and receive backscattered light from so-called foreign objects. . Here, when the laser beam 1 is incident on the surface of the photomask 5 on which no pattern is formed, that is, the back surface _S2 , the laser beam is scattered by the foreign matter k attached to the back surface _S2 , and a pattern is formed. It shows the difference in scattering due to foreign matter i attached to the side pattern surface _S1 . The laser hole 1 is obliquely incident on the back surface _S2 ,
Some of it is reflected, and some of it is transmitted and reaches the pattern surface _S1 . Scattered light 1g by the foreign object k 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 _S1 , the light transmitted through the inside of the glass plate 5a and appearing as scattered light 1h on the laser beam incident surface from the back surface _S2 is received. Photoelectric conversion is performed by part A. By the way, when comparing the scattered light 1i that does not enter the glass plate 5a from the scattering hole 1h and the pattern surface S ₁ among the scattered light caused by the foreign material i, the scattered light 1h is a reflection loss due to the pattern surface S ₁ and the back surface S ₂ . Therefore, the intensity is weaker than that of the scattered light 1i. The intensity ratio of these two is the light receiving part A, B
The closer the reception direction of the scattered light is to the back surface S ₂ or the pattern surface S ₁ , the larger the scattered light tends to be. This is based on the fact that the greater the angle of incidence of light, the greater the reflectance at the surface. Therefore, by monitoring the outputs of the light receiving sections A and B while changing the incident position of the laser beam 1 on the photomask 5, signals as shown in FIGS. 4a and 4b are obtained, respectively. Here, the vertical axes in FIG. 4 a and b represent amounts proportional to the intensity of scattered light received by the light receiving sections A and B, respectively, and the horizontal axes represent time or the position of the laser spot with respect to the photomask 5. . foreign object k
When the laser beam is scattered by
Comparing PA1 and PB1, PA1 is about 3 to 8 times larger than PB1, and in terms of scattering by foreign matter i,
Waveforms like signal waveforms A2 and B2 are obtained, and when comparing the sizes PA2 and PB2, PB2 is larger than PA2.
It becomes about 3 to 8 times larger. Therefore, when the scattered light exceeds a certain level, and the output ratio of the light receiving part A to the light receiving part B is K times, for example, 2 times or more, the foreign matter is attached to the back surface _{S2 on} the laser beam incident side. It can be determined that

Next, an example of a defect inspection apparatus which is the starting point of the present invention will be explained based on FIGS. 5 and 6. This example is more suitable for inspecting raw glass without a pattern or a mask having a relatively simple pattern than a photomask having a complicated pattern. Further, this example is an example for explaining the above-mentioned principle more specifically, and is not publicly known.

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 stage 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 stage 9 is measured by a length measuring device 7 such as a linear encoder. On the other hand, the laser light from the laser light source 8 is appropriately converted into an arbitrary beam diameter by an optical member such as an expander (not shown) or a condensing lens 3 to increase the light intensity per unit area. This laser beam 1 is a vibrator,
A scanner 2 having a vibrating mirror such as a galvano mirror measures the range L in the x direction on the photomask 5.
Scan inside. At this time, the scanning laser beam 1 is obliquely incident on the surface (xy plane) of the photomask 5 at an incident angle of, for example, 70° to 80°. Therefore,
The irradiated part of the laser beam 1 on the photomask 5 is
In the figure, it becomes an elliptical spot extending approximately in the y direction. Therefore, the laser beam 1 is
The area over which the photomask 5 is scanned is a band-shaped area having a range L in the x direction and a predetermined extent in the y 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 y 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 y direction.

Furthermore, light receiving elements 11 and 13 are provided to detect optical information from foreign matter adhering to the photomask 5, that is, scattered light generated non-directionally.
Among these light receiving elements, the element 11 corresponds to the light receiving section 1, and the photomask 5 is irradiated with the laser beam 1.
is arranged so as to receive scattered light generated from the front side. 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. Further, the scattered light is focused on each light receiving surface of the light receiving elements 11 and 13 by lenses 10 and 12. Then, the scanning range L of the laser material 1 is set so that the optical axis of the lens 10 is oblique to the x-y plane.
is set so that approximately the center of the area is viewed from the front side of the photomask 5. On the other hand, the optical axis of the lens 12 is
It is determined to be plane symmetrical to the optical axis of the lens 10 with respect to the xy plane. Further, the optical axes of the lenses 10 and 12 are set obliquely with respect to the longitudinal direction of the scanning range L, that is, so as to form a small angle with respect to the xz plane.

In FIG. 6, photoelectric signals from light receiving elements 11 and 12 are input to amplifiers 100 and 101, respectively.
The amplified photoelectric signal e ₁ is sent to two comparators 10
3,104 respectively. Further, the amplified photoelectric signal e ₂ is applied to the other input of the comparator 104 via the amplifier 102 with the amplification factor K. Note that when the amounts of light received by the light receiving elements 11 and 13 are equal, the signals e ₁ ,
Both e ₂ have the same size. Furthermore, comparator 1
The other input of 03 is the slice level generator 1.
A slice voltage Vs from 06 is applied. Then, each output of the comparators 103 and 104 is applied to an AND circuit 105. This slice level generator 1
06 is a scanning signal for vibrating the scanner 2
Change the magnitude of slice voltage Vs in synchronization with SC. This is done by scanning the laser beam 1 to detect the light receiving element 1.
1 to the irradiation position of the laser beam 1 changes. That is, this is because the solid angle at which the lens 10 receives the scattered light changes. Therefore, in synchronization with scanning, the slice voltage is adjusted according to the irradiation position of laser beam 1.
Configure Vs to be variable.

In this configuration, the amplification factor K of the amplifier 102
is set in the range of 1.5 to 2.5, for example 2. This is because, among the scattered light generated from foreign matter attached to the incident side of the laser beam 1, the ratio of the size of the scattered light generated on the incident side to the size of the scattered light transmitted through the photomask 5 is shown in FIGS. 3 and 4. As explained 2
This is because it will more than double.

Further, the comparator 103 determines that the signal e ₁ is the slice voltage
Outputs logical value "1" only when it is larger than Vs. Further, the comparator 104 compares the signal e ₁ and Ke ₂ obtained by multiplying the signal e ₂ by K, and outputs a logical value of “1” only when e ₁ >Ke ₂ . Therefore, the AND circuit 105 outputs both the comparators 103 and 104 with a logic value of "1".
A logical value "1" is generated only when .

Next, the function and operation of the example shown in FIGS. 5 and 6 will be explained. First, when a foreign object is attached to the surface on the laser beam incidence side, when the laser beam 1 irradiates only that foreign object, the signal e ₁ becomes larger than the slither voltage Vs, and the comparator 103 has a logical value of "1". , and the comparator 103 outputs a logical value of "1".
Also, at this time, e ₁ > Ke ₂ , and the comparator 104
also outputs a logical value of "1". Therefore, the AND circuit 105 generates a logic "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 is specularly reflected by the glass surface of the photomask 5, and part of it irradiates the foreign matter on the back surface. Therefore, among the scattered light from the foreign object, the scattered light that reaches the light receiving element 11 has a smaller value than the scattered light that reaches the light receiving element 13, that is, e ₁ <Ke ₂ , and the comparator 104 has a logical value of "0". Output. Therefore, at this time e ₁ >
Even if Vs is established, AND circuit 105
produces a logical value of "0". Furthermore, when scattered light is generated from the edge portion _of the light shielding part, as shown in _FIG . Outputs the value "0". Therefore, AND circuit 105 generates a logical value of "0".

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

In this way, the AND circuit 105 outputs the logical value "1" as the inspection result only when foreign matter is attached to the front side (laser light incident side) of the photomask 5.

As mentioned above, this example has an extremely simple configuration when only the detection of large foreign objects is required due to weak scattering due to circuit patterns, etc., and it is possible to determine whether the foreign objects are attached to the front side or the back side. 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 the reticle and mask used in the 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 1/10x reduction lens, the smallest size that can be transferred with a foreign object attached to the back side without a pattern to be transferred is the same as the smallest size that can be transferred with a foreign object attached to the side with a circuit pattern. It is approximately 1.5 times longer in length and approximately twice as large in area.
Therefore, it is necessary to detect foreign matter adhering to the back surface with the necessary sensitivity. In order to detect foreign matter on the back side, it is sufficient to use the photomask upside down in the apparatus described in the example of FIGS. 5 and 6. 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 light scattered by a foreign object on the side without a circuit pattern and the size of the foreign object, Since the relationship between the sizes of the objects will be different, an error will occur in determining the size of the foreign object. Moreover, 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, the following example can be considered. This example is a further development of the examples shown in FIGS. 5 and 6 described above, and although it is not publicly known, it will be disclosed as a technology underlying the present invention.

Therefore, the technology that is the basis of the present invention (hereinafter referred to as "basic technology") will be explained based on FIGS. 7 to 9. FIG. 7 shows a perspective view of the basic technology of the defect inspection device, and the differences from the example shown in FIG. 5 are as follows.
Furthermore, 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, Figure 9 shows that
FIG. 2 is a connection diagram of a detection circuit suitable for this basic technology.

In FIG. 7, explanations of components having the same configuration and operation as the example of FIG. 5 will be omitted. In this basic technology, a light receiving system having substantially the same solid angle of light receiving is provided on the incident side of the laser beam 1 of the photomask 5 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, a condenser lens 22 that obliquely view the back side of the photomask 5, and a light-receiving system. It is composed of an element 23. Of course, each optical axis of lenses 20 and 22 is
It faces approximately the center of the scanning range L. moreover,
Each optical axis is determined to coincide with a plane including the longitudinal direction x of the scanning range L (a plane parallel to the xz plane of the xyz coordinate system). Also, at this time, lens 2
The angle between the lens 10 and the optical axis of the lens 10 is determined to be approximately 30 to 45 degrees. The same applies to the angle formed by the optical axes of the lens 22 and the lens 12.

Therefore, here, we take advantage of the fact that the directionality of the light scattered by the foreign object and the light scattered by the circuit pattern is different for the light traveling to the front side of the photomask 5.
Further, foreign matter is inspected by utilizing the difference in the intensity ratio of light traveling to the front side and the back side of the photomask 5 depending on the foreign matter and the circuit pattern.

FIG. 8 a, b, c, d are light receiving elements 21, 11,
The magnitude of the photoelectric signals from 23 and 13 is plotted on the vertical axis, and the time is plotted on the horizontal axis in common in FIGS. 8a to 8d. If the spot of 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 enters the circuit pattern and is scattered, the outputs from the photoelectric elements 21, 11, 23, and 13 in FIG. 7 become A1, B1, C1, and D1 in FIG. 8, respectively.
Each peak value is PA1, PB1, PC1, PD
It becomes 1. In this case, since the scattered light has directivity, the photoelectric output of the light receiving elements 21 and 11 is greater than peak PB1 at PA1, but since the directionality is not perfect, peak PB1 is not zero. The output peak values PC1 and PD1 of the light receiving elements 23 and 13 on the back side of the photomask 5 have values close to PA1 and PB1, respectively. This is as explained in FIG. 2 above. However, if the laser light is scattered by a foreign object, the output from each light receiving element will be A.
2, B2, C2, and D2, and their peak values are PA2, PB2, PC2, and PD2, respectively. The difference between PA2 and PB2 is small because the directionality of the scattered light is small, but there is a difference between PA2 and PC2, and between PB2 and PD.
There is a big difference between 2, with a ratio of 3 to 8 times.
PA2 and PB2 are larger. For example, the smaller peak value PB1 of the scattered signals from the circuit pattern
If the signals shown in FIGS. 8a and 8b are sliced using a smaller level SL as the slicing voltage in an attempt to detect weak scattered light caused by as small a foreign object as possible, the circuit pattern will also be determined as a foreign object. However, by finding 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, the signal in FIG.
, and the signal shown in Figure 8b also exceeds SL, and if this ratio is more than a certain value, for example, 2 times or more, then it is determined that it is a foreign object, then even if a low level SL as described above is used, Only foreign objects can be detected correctly.

FIG. 9 is a block diagram of a detection circuit as the basic technology of the present invention, in which the light receiving element 2 shown in FIG.
1, 11, 23, 13 are amplifiers 110, 1, respectively.
11, 112, and 113. These four amplifiers 110 to 113 are composed of light receiving elements 21, 11, 2.
The output signals e ₁ , e ₂ , e ₃ , and e ₄ are also made to be equal if the amounts of light incident on the lenses 3 and 13 are equal. The comparator 114 outputs the output signal e ₁ and the eighth
It compares the slice voltage Vs ₁ as the level SL shown in FIG. a, and outputs a logic value "1" when e ₁ >Vs ₁ . The comparator 115 compares the output signal e ₂ with the slice voltage Vs ₂ as the level SL shown in FIG. 8b, and outputs a logic value "1" when e ₂ >Vs ₂ .
In addition, in order to distinguish between the scattered light generated on the front side and the back side of the photomask 5 due to foreign objects and edges, the output signals e ₃ and e ₄ are respectively sent to the amplifier 1 with the amplification factor K.
16,117. This amplification degree K is the 6th
Similar to the example in the figure, it is set to one value in the range of 1.5 to 2.5, for example 2. The comparator 118 compares the output signal e ₁ and the output signal Ke ₃ of the amplifier 116, and outputs a logic value "1" only when e ₁ >Ke ₃ . The comparator 119 compares the output signal e ₂ and the output signal Ke ₄ of the amplifier 117, and outputs a logical value "1" when e ₂ >Ke ₄ . And comparator 11
The respective outputs of 4, 115, 118, and 119 are input to an AND circuit 120, and when the AND is established, a logic value "1" representing the presence of foreign matter is generated as an inspection result. Furthermore, the slice voltages Vs ₁ and Vs ₂ are output from the slice level generator 121, and the slice voltages Vs 1 and Vs 2 are
Similar to the example in the figure, its magnitude changes in response to the scanning signal SC. However, the slice voltage Vs ₁ , Vs ₂
The individual sizes and degrees of change vary slightly. This will be explained with reference to FIGS. 10a and 10b. FIG. 10a is a perspective view of FIG. 7 viewed from above the photomask 5. FIG.

Here, in the scanning range L of the laser beam 1 on the photomask 5, the central portion thereof is assumed to be a position C ₁ and both end portions thereof are assumed to be positions C ₂ and C ₃ , respectively. As described above, the distances from the light receiving elements 21 and 11 to the position _C1 are both equal. Therefore, the same foreign object is located at positions C ₁ , C ₂ ,
It is described below as being attached to _C3 .

If a foreign object is attached to position _C1 , the reception solid angles of the light-receiving elements 21 and 11 will be approximately equal to the scattered light generated by the foreign object, so the above-mentioned signal
The sizes of e ₁ and e ₂ are also almost equal. Therefore, when the spot of the laser beam 1 is at the position _C1 , the slice voltages _Vs1 and _Vs2 are set to be equal in magnitude.

Further, if a foreign object is attached to position C ₂ , the amount of light received by the light receiving element 11 will be greater than the amount of light received by the light receiving element 21 . Therefore, the signal e ₂ is larger than the signal e ₁ , so the slice voltage is Vs ₂ > Vs ₁
It is necessary to specify. However, since position C ₂ is far away from each light receiving element 21, 11,
There is not that much difference between the signals e ₁ and e ₂ . Therefore,
The slice voltages Vs ₁ and Vs ₂ are approximately equal in magnitude,
It satisfies Vs ₂ > Vs ₁ and is set to be smaller than the slice voltage at position C ₁ . On the other hand, the foreign object
If it adheres to C ₃ , the signal e ₁ will have an extremely large value because the position C ₃ is the closest to the light receiving element 21 . In addition, since the light receiving solid angle of the light receiving element 11 looking at the position _C3 changes greatly with respect to the positions _C1 and _C2 , the signal _e2 has a smaller value than that at the positions _C1 and _C2 . . Therefore, the slice voltages satisfy Vs ₁ >Vs ₂ with a fairly large difference, and are each set to be larger than the slice voltage at position C ₁ .

FIG. 10b shows how each slice voltage changes with respect to the positions C ₁ to C ₃ described above. Figure 10b
The vertical axis represents the magnitude of the slice voltage, and the horizontal axis represents the position of the scanning range L.

As mentioned above, the magnitudes of the slice voltages Vs ₁ and Vs ₂ are both equal at the position C ₁ and at the position C ₂
, Vs ₂ > Vs ₁ and at position C ₃ Vs ₁ > Vs ₂
It changes continuously so that This change is not necessarily linear, but often curved, like the change in slice voltage _Vs1 . In order to obtain this curved change, a conversion circuit having logarithmic characteristics, a polygonal line approximation circuit, or the like may be used for the slice level generator 121, for example.

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 signals e ₁ and e ₂ are e ₂ >
e becomes ₁ . 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, respectively, and the output signal
e ₃ and e ₄ become e ₃ ≒ e ₁ and e ₄ ≒ e ₂ .

Therefore, e ₁ <Ke ₃ and e ₂ <Ke ₄ , and both comparators 118 and 119 output a logical value of "0".
Therefore, the AND circuit 120 generates a logic value of "0" for the scattered light from the edge portion.

Furthermore, when scattered light is generated from foreign matter attached to the pattern surface of the photomask, the output signals e ₁ and e ₂ are both larger than the slice voltages Vs ₁ and Vs ₂ , and the output signals e ₃ and e ₄ are respectively larger than the slice voltages Vs 1 and Vs 2. It becomes 1/3 to 1/8 times as large as the output signals e ₁ and e ₂ . And the output signal
e ₃ and e ₄ are multiplied by K, but since K is set between 1.5 and 2.5, e ₁ >Ke ₃ and e ₂ >Ke ₄ . Therefore, the comparison circuits 114, 115, 118, and 119 all output a logic value "1", and the AND circuit 120 outputs a logic value "1".

When scattered light is generated from foreign matter attached to the back surface of the photomask, the amount of light received by the light receiving elements 23 and 13 becomes larger than the amount of light received by the light receiving elements 21 and 11, as shown in FIG. For this reason, e ₁ <
Ke ₃ , e ₃ <Ke ₄ , and the outputs of the comparators 118 and 119 both have a logical value of “0”. 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 basic technology of the present invention, two pairs of light receiving elements 11 and 13 and a pair of light receiving elements 21 and 23 are used to selectively and strongly receive scattered light generated at the edge portions of a pattern. Since the pair is provided, it is possible to accurately detect attached foreign matter even on a photomask having a complicated pattern while avoiding the influence of scattering caused by the pattern.

However, a further problem with such a detection circuit is that when the scattered light due to the pattern is extremely strong, it becomes impossible to compare the intensities of the scattered light from the front and back sides of the object to be inspected.

Therefore, an embodiment according to the present invention for solving this problem will be described below.

As a first embodiment of the present invention, a modified configuration of the detection circuit shown in FIG. 9 will be described with reference to FIG. 11. The basic configuration is the same as the detection circuit explained in FIG. However, in this embodiment, attention is paid to the light receiving element with the smaller output among the light receiving elements 21 and 11 arranged on the laser beam incidence side, and the light receiving element arranged on the back surface side is The device is configured to determine whether the ratio of outputs between the two elements is K times or more.

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. The respective output signals e ₁ and e ₂ of the amplifiers 110 and 111 are input to a comparator 130, and the magnitude of the output signals e ₁ and e ₂ is detected. This comparator 130 is, for example, e ₁ >
When e ₂ , a logical value "1" is output, and when e ₁ < e ₂ , a logical value "0" is output. The output of the comparator 130 as it is and the output from the inverter 131
The inverted ones are AND gates 133 and 1, respectively.
32. Further, output signals from comparators 118 and 119 are connected to the other inputs of AND gates 132 and 133, respectively.
Each output signal of the AND gates 132 and 133 is inputted via an OR gate 134 to an AND circuit 120 that generates a test result.

In such a configuration, for example, the light receiving element 21
When the amount of light received by the light receiving element 11 is larger than the amount of light received by the light receiving element 11 (due to scattering from the edge portions of the pattern, etc.), the output signals e ₁ and e ₂ become e ₁ >e ₂ . Therefore, the comparator 130 outputs the logical value "1", and the AND gate 1
32 is closed and AND gate 133 is opened. Therefore, at this time, if the comparators 118 and 119 both output the logical value "1", then the comparator 11
Only the output of 9 is applied to the OR gate 134 via the AND gate 133.

In this way, the output of the OR gate 134 is determined by the ratio of the photoelectric signal between the light receiving element receiving a smaller amount of light among the light receiving elements 21 and 11 and its paired light receiving element (one of the elements 23 and 13). This shows the result of determining whether the foreign object is an edge.

As described above, as in this embodiment, the output signals e ₁ and e ₂
Selecting the smaller one means selecting the light receiving direction where the influence of scattering from the circuit pattern is small, so that the highly directional scattered light from the fine circuit pattern enters the light receiving system in only one direction, and the signal processing , especially the output signal of the amplifier, causing saturation of the
This not only prevents the inability to compare the intensities of the light receiving systems on the front and back sides of the object to be inspected, but also prevents errors in the geometrical arrangement of the condensing lenses of the light receiving system that look at the front and back sides of the photomask. If the images are not completely symmetrical, there is also the advantage of reducing false detection of foreign objects.

Note that in the above embodiment, the comparators 118, 1
19 determines e ₁ -Ke ₃ and e ₂ -Ke ₄ for the photoelectric signals shown in FIGS. 4a and 4b, and determines the output depending on whether the results are positive or negative. however,
Even if a circuit is provided that calculates the ratio between e ₁ and Ke ₃ and e ₂ and Ke ₄ using a divider or the like and determines whether the result is greater than or equal to K, the same result as in the above embodiment can be obtained. able to perform a function.

Next, regarding the second embodiment of the present invention, FIG.
This will be explained based on FIG. 13. In this embodiment, one more light receiving element 31 is provided in addition to the first 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 light receiving element 31 are
0. The lens 10 is arranged so that the surface of the photomask 5 on the laser beam incident side, that is, the pattern surface, can be viewed from the direction opposite to the optical axis of the lens 10.

Here, the relationship between the optical axes of the lenses 10, 20, and 30 will be described. Furthermore, these three lenses 10,
It is assumed that 20 and 30 have the same optical characteristics, and that the characteristics of the three light receiving elements 11, 21, and 31 are also the same.
Also, let the optical axes be l ₁ , l ₂ , and l ₃ , respectively. Optical axis l ₁ , l ₂ ,
l ₃ are both relative to the pattern surface of photomask 5,
It is set at a small angle, for example around 10 to 30 degrees. Further, the distances from the center of the scanning range L of the laser beam 1 to each of the light receiving elements 11, 21, and 31 are set equal.

In the figure, when the photomask 5 is viewed from above, the optical axis l ₂ coincides with the longitudinal direction (scanning direction) of the scanning range L, and the optical axes l ₁ and l ₃ are small with respect to the scanning range L. The angle is set at around 30°, for example.

By determining the optical axes l ₁ , l ₂ , and l ₃ in this way, the scattered light generated at the edge of the pattern is
Of the three light receiving elements 11, 21, 31, almost no light is received by one light receiving element. Furthermore, as a general tendency, when the scattered light from the edge portion of the pattern is strongly received by both 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 of the light receiving elements 11, 21, and 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. Comparator 1
In response to the scanning signal SC from the slice level generator 121, a slice voltage Vs ₃ corresponding to the spot position of the laser beam is inputted to 41. This comparator 14
1, the output signal e ₅ of the amplifier 140 is the slice voltage
When Vs exceeds ₃ , a logic value "1" is output, otherwise a logic value "0" is output. Other circuit elements in FIG. 13 are the same as in the first embodiment. Compared to the first embodiment, this second 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 and 21 and the light receiving element 31 look into the center of the scanning range L from opposite directions, the slice voltages Vs ₁ and Vs ₂ are
The trend of change in slice voltage Vs ₃ is made to be opposite. That is, the slice voltage Vs ₃ is obtained by reversing the slope of the slice voltage Vs ₂ in FIG. 10b described above.

FIG. 14 is a block diagram showing a detection circuit according to a third embodiment. The difference from the second embodiment is that three comparators 150, 151,
152, an AND circuit 153, an OR circuit 154, and a slice level generator 160 that generates two types of voltages as slice voltages Vs ₁ , Vs ₂ , and Vs ₃ , respectively. The two voltages of each slice voltage maintain a predetermined difference from each other and change according to the scanning signal SC.

Output signals of preamplifiers 110, 111, 140
e ₁ , e ₂ , and e ₃ are comparators 150 and 1, respectively.
Slice level generator 160 by 51, 152
It is compared with the slice voltages Vs ₁ , Vs ₂ , and Vs ₃ output from the. At this time, comparators 150, 15
The slice voltage input to 1,152 is the comparator 11
4, 115, and 141, and set it to be higher than the minimum value of the output signals e ₁ , e ₂ , and e ₃ no matter how strongly the light scattering due to the circuit pattern occurs. has been done. Therefore, the comparators 150, 151, 152 and the AND circuit 153 generate a logical value of "1" only when extremely strong scattered light is generated from 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 third embodiment 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 becomes close to the power supply voltage, causing the photodetector elements 23, 13 on the back side of the object to be detected.
The comparators 118 and 119 that compare the magnitude of the outputs from the amplifiers 112 and 113 with the magnitudes of the outputs from the amplifiers 110 and 111 do not operate correctly, and even though the light is scattered from a foreign object, , comparator 11
8 and 119 both operate as if they were detecting scattered light from the circuit pattern, foreign matter cannot be detected in other embodiments, but can be detected in this embodiment. As mentioned above, the comparators 114, 115, 141 perform the comparison with the low slice voltage.
In addition, comparators 150, 151, and 152 are provided for comparison with a high slice voltage, and foreign matter that causes strong scattered light is detected by these comparators.

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 false detections 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 third 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, the structure can have the intended function of the third embodiment.

In addition, in FIGS. 11, 13, and 14, a comparator 130, AND gates 132, 133, and an OR circuit 134 are used, but as shown in FIG. You can connect it as shown below.

Next, a fourth embodiment of the present invention will be described based on FIG. 15. In addition to the third embodiment, this embodiment also includes one more light receiving element 41 and a condensing lens 40.
It has been established. The optical axis of this lens 40 is set 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 middle part of the scanning range L is viewed from the back surface of the photomask 5.

In this embodiment, the photoelectric signals of the light receiving elements 11, 21, and 31 that receive scattered light from the laser beam incidence side are compared with respective slice voltages and processed to obtain an AND, as in the previous embodiment. be done. This determines whether the scattered light is from the edge portion of the pattern or from a foreign object. On the other hand, the photoelectric signals of the light receiving elements 13 and 23 for processing the scattered light from the back surface of the photomask 5 may be processed by the detection circuit as in the above-mentioned embodiment, but may be processed by a simpler detection circuit. It will be processed.

For example, the photoelectric signals of the light receiving elements 13, 23, 41 are processed by a circuit configured similarly to the detection circuit of the light receiving elements 11, 21, 31. In this way, the light receiving element 1 on the laser beam incident side
1, 21, and 31 detect a foreign substance, and when the foreign substance is also detected by the light receiving elements 13, 23, and 41 on the back side, it can be determined that the foreign substance has adhered to the transparent portion of the photomask 5. In this case, the peak value of the photoelectric signal of each photodetector when a foreign object is detected is
By considering the front side and the back side of the photomask 5, there is an advantage that the size of the foreign object can be determined extremely accurately.

Further, when using the detection circuits in the second and third embodiments as they are, it is preferable to provide a switching circuit 200 as shown in FIG. 16. This switching circuit 200
are light receiving elements 11, 21, 31 on the laser beam incident side
Each photoelectric signal and the light receiving elements 13, 23, 4 on the back side
1 to each photoelectric signal and output signals e ₁ to _{e 5.}
is configured to occur. Of course, it is better to perform this switching after the photoelectric signals of each light receiving element have been amplified once. This switching is done by signal 20
1. With this configuration, when inspecting the back side of the photomask 5, for example, the operation of turning the photomask 5 upside down and placing it is unnecessary. For this reason, the laser beam 1 may be guided to the back surface of the photomask 5 in FIG. 14 by an appropriate optical path switching member in the same way as the front side is irradiated.

Therefore, if the signal 201 is changed in response to switching of the optical path switching member, there is no need to turn over the photomask 5, so foreign substances attached to both sides can be detected very quickly and accurately. .

Next, a fifth embodiment will be described. In the fifth embodiment, it is assumed that the arrangement of each light receiving element is the same as that in FIG. 7 used to explain the basic technology of the invention. As previously explained with reference to FIG.
Scattered light from the foreign substance j attached to the light shielding part 5b is detected by the light receiving part A and is detected by the light receiving part B. Otherwise, it will not be detected. This is the seventh
The photoelectric signals of each light-receiving element shown in the figure will be explained with reference to FIG. 17. Figures 17a, b, c, and d show the magnitude of the photoelectric signals from the light-receiving elements 21, 11, 23, and 13 on the vertical axis, respectively, and time on the horizontal axis. also corresponds to the laser spot position. Here, 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. 17a and 17b. On the other hand, the light receiving element 23,1
3 are photoelectric signals C3 and C3, respectively, as shown in FIG. 17c and d.
Approximately zero is output as D3. Further, when the laser beam is scattered by a foreign substance i as shown in FIG. 1, the light receiving elements 21, 11, 2 as shown in FIG.
3 and 13 are photoelectric signals A4, B4, C4, and D4, respectively.
occurs. That is, as shown in FIGS. 17c and 17d, the photoelectric signals C4 and D4 of the light receiving elements 23 and 13 are not zero, but some output is obtained. Furthermore, P.A.
4, PB4, PC4, PD4 are photoelectric signals A4, B4,
These are the respective peak values of C4 and D4. Therefore, the small slice voltages Vs ₄ and Vs ₅ are set to peak values PC4 and Vs 5, respectively.
If it is set to the middle of PD4, in the case of foreign object i, the photoelectric signals of the light receiving elements 23 and 13 are both at the slice voltage.
However, in the case of foreign object j, the slice voltage does not exceed Vs ₄ and _{Vs 5 ,} and foreign objects i _and j can be distinguished. Therefore, next, a fifth embodiment will be specifically described.

FIG. 18 is a block diagram of signal processing in this embodiment. In FIG. 18, light receiving elements 21, 11,
23, 13, amplifiers 110 to 113, comparators 114, 115, 118, 119 and amplifier 1
16 and 117 have the same function as the circuit shown in FIG. The difference is that the comparators 204, 2
05 is provided, and its output is sent to the AND circuit 2.
02 in parallel. The comparator 204 compares the output e ₃ of the amplifier 112 with the slice voltage Vs ₄ output from the slice level generator 203, and if e ₃ >Vs ₄ , the logic value is "1".
, otherwise it outputs a logical value ``0'', while the comparator 205 compares the output e <sub>4</sub> of the amplifier 113 with the slice voltage Vs <sub>5</sub> and outputs a logical value ``1'' if e ₄ > Vs ₅ ; If not, a logical value of "0" is output. Here, the magnitudes of the slice voltages Vs ₄ and Vs ₅ are determined as explained in FIG. 16 above, and the magnitudes vary depending on the spot position. The manner of the change is as explained in the basic technology of the present invention. In such a configuration, when the laser beam hits a foreign substance attached to the glass plate (light transmitting part), the comparators 204 and 205 output a logical value "1", and the other comparators 114 and 11
5, 118, and 119 also output a logic value of "1", so the output of the AND circuit 202 becomes a logic value of "1", indicating that a foreign object has been detected. However, when the laser beam enters a foreign substance attached to the light shielding part, the outputs of the comparators 204 and 205 have a logical value of "0".
Therefore, the output of the AND circuit 202 is the logical value "0"
becomes. 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-blocking 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 transparent part or the light-blocking part, this embodiment detects the foreign matter only in the light-blocking part and the degree of cleaning of the mask is affected by the printing of the pattern. Even though the photomask is durable, it reduces the need to clean it again if it is contaminated or to replace it with another photomask with the same pattern. Therefore, there are advantages in terms of time and economy in manufacturing semiconductor devices.

In this fifth embodiment, the comparator 20
Although the outputs of comparators 204 and 205 are both 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. Also, the comparator 204
It is also conceivable to calculate the OR of each output of and 205 and input the result to the AND circuit 202.

As mentioned above, this fifth embodiment has been described as adding a new function to the configuration shown in FIG. It goes without saying that the same addition can be made in the first to fourth embodiments as well.

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 a light shielding part, 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 back side does not necessarily need to be arranged symmetrically.

In addition, in the detection circuits of the above embodiments, the slice voltage is changed according to the position of the spot scan of the laser beam, but the solid angle of reception of the scattered light of each light receiving element is changed with respect to the position of the spot scan of the laser beam. If the change in is small, the slice level is constant and does not need to be changed. Furthermore, even if the solid angle of the scattered light reception changes due to laser spot scanning, it is not necessarily necessary to change the slice voltage, and the gain of the photoelectric signal transmission system can be adjusted in accordance with the laser spot scanning position, that is, synchronized with the scanning signal SC. By changing the slice voltage, the slice voltage can be fixed at a constant value.

When controlling the gain of the transmission system in this way, for example, the slice voltages Vs ₁ and Vs ₂ in FIGS. 9 and 11 are set to a common constant voltage. and,
The gains of amplifiers 110 and 111 are made variable according to the spot position of laser beam 1. As an example, the relationship between the gains of the amplifiers 110 and 111 may be determined as shown in FIG. This figure corresponds to the above _- mentioned _FIG .
and the gain G ₂ are both equal. The gain at this time is normalized to 1.

For example, at position C ₂ , the gain G 1 is approximately twice the gain at position C ₁ , and the gain G ₁ is approximately twice the gain at position C 1.
G ₂ is set to 1.2 to 1.5 times, and the gain G ₁ at position C ₃ is 0.2 to 0.4 times the gain at position C ₁ .
The gain _G2 is preferably set to 0.7 to 0.9 times.

Furthermore, in each of the above implementations, the ratio of the outputs of a pair of light receiving elements provided corresponding to the front and back sides of the object to be inspected was compared with a certain value K. and the sum of the outputs of the light-receiving elements 13 and 23 located on the back side, respectively, and determine whether the ratio of the two sums is greater than K to determine whether it is a foreign object or not. It is possible to determine whether or not 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 the signal from a single photoelectric element. Also good.

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

As described above, according to the present invention, scattered light from a pattern and scattered light from a foreign object are discriminated based on the photoelectric signals of each light receiving element as the first photoelectric detector group looking into the surface on the laser beam incidence side. At this time, the photodetector that generates the smallest photoelectric signal is detected among two or more photodetectors as a second photodetector group that looks at the back side of the object to be inspected, such as a photomask, and the photoelectric signal of that photodetector is detected. , foreign matter can be detected extremely accurately depending on the adhesion state, even if the scattered light from the pattern is strong.

In addition, especially when inspecting photomasks and reticle for IC manufacturing, multiple light receiving elements are placed in different directions and a light beam is used. Since the spot is scanned, the influence of the circuit pattern can be prevented and only foreign objects can be detected at high speed. 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. Therefore, by detecting even smaller foreign objects than necessary, it is possible to prevent the time loss of recleaning a reticle or mask that can be used for exposure because it is determined to be contaminated.

Furthermore, in the present invention, the first photoelectric detection means 11; 21 is arranged so as to look into the surface on the incident side of the light beam of the object to be inspected, and the second photoelectric detection means 11; 21 is arranged so as to look into the back surface opposite to the incident side. Means 13; 23 are provided for comparing the magnitude of the photoelectric signal from the first photoelectric detection means between a high slice voltage (second reference level) and a low slice voltage (first reference level), respectively. Comparators 114, 115; 15
0; 151 is provided, and comparators 118; 119 are provided to compare the magnitude of the photoelectric signals from each of the first and second photoelectric detection means, so that the detection is significantly reduced, and at the same time, the detection of foreign objects is The range can be expanded.

The present invention can be used not only to detect foreign matter attached to a reticle mask, but also to detect foreign matter on objects such as transparent objects with patterns adhered to them.
It is also very useful for inspection during the manufacture of precision patterns where adhesion of foreign matter such as dust is avoided.

[Brief explanation of drawings]

FIG. 1 is a diagram showing scattering of laser light due to foreign matter on a surface of a photomask on which a pattern is drawn.
Figure 2 is a diagram showing scattering due to foreign matter adhering to the glass plate and scattering due to the edge of the light shielding part;
The figure shows the state of scattering due to foreign matter adhering to the front and back surfaces of the transparent part of the glass plate, Figure 4 shows the scattered light received by the light receiving part shown in Figure 3, Figures 5 and 6 7 is a diagram showing an example of a defect inspection device that is the starting point of the present invention, FIG. 7 is a diagram showing a defect inspection device, FIG. Figure 9 is a diagram showing the detection circuit, Figure 10a is a top view of the photomask, and Figure 10a is a top view of the photomask.
Figure 0b is a diagram showing changes in slice voltage, 11th
The figure shows a first embodiment of the invention, FIG. 12 shows a second embodiment of the invention, and FIG. 13 shows a detection circuit of a second embodiment of the invention. ,
FIG. 14 is a diagram showing a detection circuit according to a third embodiment of the present invention, FIG. 15 is a diagram showing a fourth embodiment of the present invention, FIG. 16 is a diagram showing a switching circuit, and FIG. is a diagram showing a photoelectric signal of a light receiving element, FIG. 18 is a diagram showing signal processing according to the present invention, and FIG.
It is a figure showing the gain of an amplifier. [Explanation of symbols of main parts], inspected object...5,
1st photoelectric element group...11, 21, 2nd photoelectric element group...13, 23, detection circuit...130, 13
1. Detection device...118, 119, 132, 13
3,134,120.

Claims (1)

[Scope of Claims] 1. Based on optical information generated from the inspected object when a light beam is irradiated onto a light-transmissive planar inspected object and the spot of the light beam is scanned in a predetermined direction, In an apparatus for inspecting defects such as attached foreign matter, the scanning range of the light beam is anticipated from a plurality of spatial positions on one side of the object to be inspected, and the scattered light generated from the scanning range is received and the scattered light is detected. at least two first photoelectric detectors that output first signals according to the intensity of the scanning range; at least two second photoelectric detectors that receive scattered light generated from the range and output a second signal corresponding to the intensity of the scattered light; Compare the sizes and choose the smaller first
a detection circuit that detects a specific first photoelectric detector that outputs a signal; and a specific second photoelectric detector that is arranged in a predetermined relationship with the specific first photodetector detected by the detection circuit; and a first signal from the specific first photoelectric detector to output a signal representing the defect. 2 The comparison circuit compares the two first signals e ₁ ; e ₂
and two comparators 118; 119 for comparing the respective magnitudes of the two second signals _e3 ; _e4 , and two gate circuits 132; 133 connected to each output of the two comparators, Either one of the two gate circuits is connected to the detection circuit 130,
13. The device according to claim 1, wherein the device opens in response to a detection result of 131. 3. Claim 1, wherein the specific first photoelectric detector and the specific second photoelectric detector are arranged substantially symmetrically with respect to the surface to be inspected of the object to be inspected. , or the device according to item 2. 4. Each of the first photoelectric detector and the second photoelectric detector includes a condenser lens that condenses scattered light generated from within the scanning range of the spot of the light beam, and the optical axis of the condenser lens is located within the scanning range of the spot. Passing through approximately the center of the range,
4. The apparatus according to claim 3, wherein the apparatus is set to be inclined with respect to the normal line of the surface to be inspected. 5. At least one pair of the specific first photoelectric detector and the specific second photoelectric detector is arranged so as to look into the scanning range from substantially the same direction as the direction of the scanning locus of the light beam. The device according to claim 4, characterized in that: 6 A light beam is irradiated onto a flat, light-transmissive object to be inspected, and when the spot of the light beam is scanned in a predetermined direction, defects such as attached foreign matter are detected based on the optical information generated from the object to be inspected. In an apparatus for inspecting, a first photoelectric detection means predicts a scanning range of the light beam from a spatial position on one surface side of the object to be inspected, receives optical information generated from the scanning range, and outputs a first signal. and; estimating the scanning range of the light beam from a spatial position on the side of the other surface opposite to one surface of the object to be inspected;
a second photoelectric detection means for receiving optical information generated from the scanning range and outputting a second signal; comparing the magnitudes of the first signal and the second signal;
a first comparator that outputs a first detection signal when a predetermined magnitude relationship is satisfied; a first comparator that compares the magnitude of the first signal with a predetermined first reference level; a second comparator that outputs a second detection signal in the above cases; and comparing the magnitude of the first signal with a second reference level set higher than the first reference level;
a third comparator that outputs a third detection signal when the level is equal to or higher than the second reference level; A defect inspection device comprising: a logical operator that outputs a signal indicating that the defect has been detected when at least one of the first detection signal and the third detection signal is input. 7. The device according to claim 6 further includes a circuit 160 for generating two slice voltages, the first reference level and the second reference level, and the circuit substantially adjusts the difference between the two slice voltages. An apparatus characterized in that the slice level is changed according to the scanning position of the light beam while being kept constant. 8. The first reference level is set to be smaller than the magnitude of the first signal obtained in response to a small defect to be detected, and the second reference level is set to be smaller than the magnitude of the first signal obtained in response to a small defect to be detected. When both the first signal and the second signal become so large that accurate comparison operation of the magnitude relationship of the first comparator 114; 115; 141 becomes impossible, the first signal is set to exceed the second reference level. 8. The device according to claim 6 or 7, characterized in that: