JPH0343581B2 - - Google Patents

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 an apparatus for inspecting defects such as foreign matter adhering to a substrate such as an LSI photomask or reticle.

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 each mask and all chips of a 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 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 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 a mask or reticle has strong directionality, while 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, with this device, it is possible to check whether foreign matter has adhered to the light-shielding part such as chrome or not on the glass surface (light-transmitting part).
Also, in the case of foreign matter that has adhered to the light transmitting part, it is possible to distinguish whether it is attached to the laser beam incident side of the object to be inspected or to its back side. It was not possible to inspect the state of adhesion of so-called foreign substances, such as dirt or debris.

Therefore, the present invention aims to detect defects such as foreign particles attached to a transparent substrate (mask or reticle) formed by partially adhering a patterned layer of chromium or the like, by reducing false detection due to the influence of the patterned layer and at high speed. It is also important to be able to inspect foreign matter adhered to either side of the transparent substrate under the same inspection conditions, and to ignore foreign matter defects adhered to the light-shielding pattern layer, The purpose is to inspect only foreign matter defects attached to parts.

In order to achieve this object, the present invention is constructed as follows. That is, irradiation means 2, 3, and 8 irradiate the light beam 1 from one side of a light-transmissive substrate 5a on which a pattern layer 5b with a minute thickness is partially adhered to a flat surface.
and out of the scattered light generated when the light beam irradiates defects i, j, k such as minute foreign matter attached to the surface of the substrate, or a part of the pattern layer 5b, only one of the substrates is first photoelectric detection means 11, 21, 31 that receives scattered light that advances into the space on the surface side;
and second photoelectric detection means 13, 23, and 41 for receiving scattered light traveling into the space on the other side of the substrate, and based on each photoelectric signal from the first photoelectric detection means and the second photoelectric detection means. The defect inspection device detects the presence of the defect by reducing erroneous detection by the pattern layer, wherein the level of the photoelectric signal from the first photoelectric detection means 11, 21, 31 is a predetermined reference level Vs1, Vs
a first comparison means 103, 114, 115, 141 that outputs a first detection signal when the level is 2 or more; , 41, which outputs a second detection signal when the level of the photoelectric signal from
Comparing means 10, 118, 119; when both the first detection signal and the second detection signal are output, outputting a detection signal indicating that the defect is present on one side of the substrate; Computing means 105, 120, and 202 are provided.

Further, in the second invention of the present application, the irradiation means 2, 3, and 8 make the light beam 1 obliquely incident on the surface of the substrate, and maintain the angle of oblique incidence substantially. A light beam scanner 2 performs one-dimensional scanning along a scanning line L intersecting the traveling direction of the light beam; a first state in which the scanning light beam enters the substrate from one surface side; a first switching member for switching to a second state in which light is incident from the other surface side;
The level of the photoelectric signal from one of the photoelectric detection means 13, 23, and 41 is 1 with respect to the level of the photoelectric signal from the other photoelectric detection means.
Comparing means 104, 118, 119 outputting a detection signal when the ratio is greater than or equal to a second switching means 200 for switching the connection between the photoelectric signal of the detection means and the photoelectric signal of the second photoelectric detection means;
In the above state, the defect present on one side of the substrate is detected, and in the second state, the defect present on the other side of the substrate is detected.

Furthermore, in the third invention of the present application, the level of the photoelectric signal from the first photoelectric detection means 11, 21, 31 is a predetermined first reference level Vs,
First comparison means 103, 114, 115, 141 that outputs the first detection signal when Vs1, Vs2 or more
and; when the level of the photoelectric signal from the first photoelectric detection means reaches a ratio greater than 1 to the level of the photoelectric signal from the second photoelectric detection means 13, 23, 41, a second photoelectric signal is detected. the second outputting the detection signal;
Comparing means 104, 118, 119; and a third comparing means 20 that outputs a third detection signal when the level of the photoelectric signal from the second photoelectric detecting means is equal to or higher than the second reference level Vs4, Vs5 close to zero.
4,205; When the conditions are such that the first, second and third detection signals are all output, a detection signal indicating that the defect exists in a light-transmitting part other than the light-shielding pattern layer on the substrate. A calculation means 202 is provided for outputting .

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, rather than vertically entering the light beam.

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 by irradiating a laser beam as a light beam to detect foreign particles attached to the glass plate of the photomask. This figure shows the scattering of laser light caused by the laser beam and the scattering caused by foreign matter adhering to the light shielding part. Second
The figure shows scattering caused by foreign matter adhering to the glass plate,
This figure shows the state of scattering due to the edge portion of the light shielding portion. 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 obliquely incident on the pattern surface S1 is specularly reflected by the glass plate 5a or the light shielding plate 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 section A consisting 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 beam 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 to prevent the reception of scattered light caused by fine irregularities on the pattern surface _S1 of the glass plate 5a and the surface of the light shielding part 5b as much as possible. Furthermore, a surface S ₂ (hereinafter referred _to as
Set the back side to S ₂ . ) side is provided with a light receiving section B including a condensing lens and a photoelectric element. This light receiving part B is
For the glass plate 5a (especially its patterned surface S ₁ ),
It is arranged in a plane symmetrical relationship with the light receiving part A, and the back side
The area irradiated by laser beam 1 is viewed diagonally from the _S2 side. In FIG. 1, the light receiving section B is shown to receive the laser light that directly passes through the glass plate 5a, but in reality, it is 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 section A,
Both B are arranged at positions where they receive scattered light generated non-directionally from foreign objects.

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 scattered light 1a generated non-directionally will be equal. However, some 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 the 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 scattered light, it is difficult to determine whether the scattered light is caused by foreign matter or by 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.) Light shielding part 5
Since the layer b has a thickness of about 0.1 μm and is in close contact with the pattern surface _S1 , the intensity of the scattered light 1c that goes directly to the outside of the glass plate 5a and the scattered light 1d that goes to the inside of the glass plate 5a. are almost equal. 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 becomes stronger as the angle of elevation of the light receiving direction of the light receiving sections A and B with respect to the pattern surface _S1 is made smaller, as the difference in the magnitude of the photoelectric signals between the two becomes stronger. This phenomenon is caused by the fact that the scattered light behaves as a surface wave against the light shielding part _5b that is in close contact with the surface S1, but the foreign object i contacts the surface _S1 only in part, 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, the scattered light on the side of the putter surface _S1 is detected by the light receiving part A, and the scattered light passing through the back surface _S2 is also detected by the light receiving part B at the same time, and the ratio of the amounts of both lights is doubled, for example. By determining whether the scattering is caused by foreign matter or not, it can be determined whether the scattering is caused by the edge portion of the light shielding portion 5b. That is, it is possible to distinguish between minute substances that are in close contact with the glass plate, such as the edges of the light-shielding portion 5b, and minute substances that are protruding and adhered to the glass plate, such as foreign objects.

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, the laser beam 1 is directed to the surface of the photomask 5 on which no pattern is formed, that is, the back surface S ₂
It shows the difference between the scattering of laser light by a foreign object k attached to the back surface S ₂ and the scattering by a foreign object i attached to the pattern surface S ₁ on the side where the pattern is formed. The laser beam 1 is obliquely incident on the back surface _S2 , part of which is reflected, and part of which is transmitted, reaching the patterned surface _S1 . Scattered light 1g by the foreign object k is photoelectrically converted by the light receiving section A. Also, pattern surface S ₁
Among the scattered light caused by the foreign matter i attached to the transparent part of the glass plate 5a, 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 photoelectronized by the light receiving part A. converted. By the way, when comparing the scattered light 1h of the scattered light caused by the foreign substance i with the scattered light 1i that does not enter the inside of the glass plate 5a from the pattern surface _S1 , the scattered light 1h is
Since it suffers reflection loss from S ₁ and the back surface S ₂ , its intensity is weaker than that of the scattered light 1i. The intensity ratio between the two tends to increase as the light receiving direction of the scattered light of the light receiving sections A and B is made to be close to the back surface _S2 or the pattern surface _S1 . This is based on the fact that the greater the angle of incidence of light, the greater the reflectance at the surface. Therefore, while changing the incident position of the laser beam 1 on the photomask 5,
By monitoring the output of , signals such as those shown in FIG. 4 a and b are obtained. Therefore, the vertical axes in FIGS. 4A and 4B 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. When the laser beam is scattered by the foreign object k, the signal waveforms A1 and B1 in FIG.
is about 3 to 8 times larger than PB1, and the scattering by the foreign object i yields signal waveforms A2 and B2, and when comparing the sizes PA2 and PB2,
PB2 is about 3 to 8 times larger than PA2. Therefore, when the scattered light exceeds a certain size, the light receiving part A
If the output ratio with respect to the light receiving part B is K times, for example, twice or more, it can be determined that foreign matter is attached to the back surface _S2 on the laser beam incident side.

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 foreign matter inspection device, 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 beam 1 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 range L in the x direction on the photomask 5 is scanned by a scanner 2 having a vibrating mirror such as a galvanometer mirror. 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 70° to 80°, for example. Therefore, the irradiated portion of the photomask 5 with the laser beam 1 becomes a circular spot extending approximately in the y direction in the figure. 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.
Of these light receiving elements, the element 11 corresponds to the light receiving section A, 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. The scanning range L of the laser beam 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 symmetrical with the optical axis of the lens 10 with respect to the xy plane. In addition, lenses 10 and 12
The respective optical axes of are determined to be oblique to the longitudinal direction of the scanning range L, that is, to form a small angle with respect to the xz plane.

In FIG. 6, photoelectric signals from light receiving elements 11 and 13 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. The outputs of the comparators 103 and 104 are connected to the AND circuit 1.
05. This slice level generator 10
6 is a scanning signal for vibrating the scanner 2
Change the magnitude of the slice voltage Vs in synchronization with SC. This is because the scanning of the laser beam 1 changes the distance from the light receiving element 11 to the irradiation position of the laser beam 1, that is, 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, AND circuit 105
generates a logic value "1" only when the outputs of comparators 103 and 104 are both logic values "1".

Next, the function and operation of this embodiment will be explained. First, if a foreign object is attached to the surface on the incident side of the laser beam 1, and the laser beam 1 irradiates only that foreign object,
The signal e ₁ will be greater than the slice voltage Vs,
Comparator 103 outputs a logical value of "1". Also,
At this time, e ₁ >Ke ₂ and the comparator 104 also outputs the logical value "1". Therefore, the AND circuit 105
produces 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 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 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 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. , the length is approximately 1.5 times larger and the area ratio is approximately twice as large. 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 apparatus described in the first embodiment with the photomask 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 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 particles 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, 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 foreign matter 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, the same configuration as the first embodiment,
Explanation of those having functions 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, 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, the optical axes of the lenses 20 and 22 face approximately the center of the scanning range L. Furthermore, 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). In addition, at this time, the angle formed by the optical axes of the lens 20 and the lens 10 is 30~
It is set around 45 degrees. lens 22 and lens 1
The same applies to the angle formed by the second optical axis.

Therefore, in this embodiment, in addition to utilizing the fact that the directivity of scattered light due to foreign objects and circuit patterns is different for light traveling toward the front side of photomask 5, the directionality of scattered light due to foreign objects and circuit patterns is different, and furthermore, the directionality of scattered light due to foreign objects and circuit patterns is different from that of light traveling to the front side and back side of photomask 5. Differences in light intensity ratios are also used to inspect for foreign substances.

FIG. 5 is a perspective view of this embodiment, showing the object 5 to be tested.
Also shown are a movable table 9 on which a movable table 9 is set, a motor 6 for driving the movement of the movable table 9, and an encoder 7 for detecting the position in the direction of the arrow 4.

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 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, respectively, in FIG. Peak values are PA1, PB1, PC1, PD1
becomes. 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 of the light receiving elements 23 and 13 on the back side of the photomask 5, PC1 and PD1 are PA1 and PB1, respectively.
It has a value close to . This is as explained in FIG. 2 above. However, when the laser beam is scattered by a foreign object, the outputs from each light receiving element are A2, B2, C2, and D2, and the 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 the difference between PA2 and PC2 and PB
There is a large difference between 2 and PD2, with PA2 and PB2 being larger at a ratio of 3 to 8 times. For example, the smaller peak value of the scattered signals from the circuit pattern
If an attempt is made to slice the signals shown in FIGS. 8a and 8b using a level SL smaller than PB1 as the slicing voltage 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, the light receiving element 2 in FIG.
1 and the output of the light receiving element 23, and the ratio of the output of the light receiving element 11
Find the ratio of the output of the light receiving element 13 and the output of the light receiving element 13, and if the signal in FIG. 8a exceeds SL and the signal in FIG.
If it is determined that it is a foreign object only when there is more than double the amount, it is possible to correctly detect only the foreign object even if the low level SL as described above is used.

FIG. 9 is a block diagram of the signal processing of this embodiment, and shows the light receiving elements 21, 11, 2 shown in FIG.
3 and 13 are amplifiers 110, 111, and 11, respectively.
Enter 2,113. These four amplifiers 110
~113 is the output signal if the amounts of light incident on the light receiving elements 21, 11, 23, and 13 are equal.
e ₁ , e ₂ , e ₃ , and e ₄ are also made equal.

The comparator 114 compares the output signal e ₁ with the slice voltage Vs ₁ as the level SL shown in FIG. 8a, 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 11 with the amplification factor K.
Enter 6,117. The amplification degree K is set to one value in the range of 1.5 to 2.5, for example 2, as in the first embodiment.

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 comparators 114, 115, 118, 1
Each output of 19 is 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. In addition, the slice voltages Vs ₁ and Vs ₂ are generated by the slice level generator 1.
21, and its 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 ₁ and Vs ₂ are slightly different. 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 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 the position C ₁ , 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 above-mentioned signals e ₁ ,
The size of e ₂ is also almost equal. Therefore, when the spot of laser beam 1 is at position C ₁ , the slice voltage
Vs ₁ and Vs ₂ are set to be equal in size.

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,
The magnitudes of the signals e ₁ and e ₂ are not much different. Therefore, Vs ₂ > Vs ₁ with not much difference in slice voltage
satisfies and is set smaller than the slice voltage at position _C1 .

On the other hand, if a foreign object attaches to position C ₃ , position C ₃
is the location closest to the light receiving element 21, so
The signal e ₁ has an extremely large value. In addition, the light receiving element 11 has a solid angle _of light reception looking into the position C ₃ ,
Since the signal e ₂ changes greatly with respect to C ₂ , the position
The value is smaller than that at C ₁ and C ₂ . Therefore, the slice voltage has a fairly large difference, Vs ₁ > Vs ₂
, and are each set to be larger than the slice voltage at position _C1 .

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
becomes e ₂ > e ₁ . Furthermore, as shown in FIG. 2, the amount of light received by the light receiving elements 23 and 13 is approximately equal to the amount of light received by the paired light receiving elements 21 and 11, respectively, and the output signals e ₃ and e ₄ are e ₃ ≒e ₁ , e ₄ ≒e ₂ .
Therefore, e ₁ < Ke ₃ , e ₂ < Ke ₄ , and comparator 1
18 and 119 both output logical value "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 second embodiment, the pair of light receiving elements 11 and 13 and the light receiving element 2 are configured to selectively and strongly receive scattered light generated at the edge portions of the pattern.
Since the two pairs, ie, the pair No. 1 and No. 23, are provided, even when using 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, the configuration of the detection circuit in the second embodiment is changed.
This will be explained using figures. The basic configuration is the same as the detection circuit described in the second embodiment. 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 the light receiving element paired therewith (one of the elements 23 and 13). This shows the result of determining whether it is a foreign object or 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 perfectly 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 e ₃ and e ₂ and e 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 fourth embodiment of the present invention, FIG.
This will be explained based on FIG. This embodiment further includes another light receiving element 31 in addition to the second embodiment,
This further reduces 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
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 _l2 is the scanning range L.
The optical axes l ₁ and l ₃ are set at a small angle, for example, around 30°, with respect to the scanning range L.

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. This light receiving amount element 31
The output of is processed by the 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. The comparator 141 receives a slice voltage corresponding to the spot position of the laser beam in response to the scanning signal SC from the slice level generator 121.
Vs ₃ input. This comparator 141 is connected to the amplifier 1
When the output signal e ₅ of 40 exceeds the slice voltage Vs ₃ , it outputs a logic value "1", otherwise it outputs a logic value "0". Other circuit elements in FIG. 13 are the same as in the third embodiment. This fourth example is
Compared to the third embodiment, since the light receiving system (light receiving element 31, lens 30) is provided in one redundant direction, the probability that light scattered by the circuit pattern will be mistakenly detected as a foreign object is extremely small. It has characteristics.

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 fifth embodiment. The difference from the fourth 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. Preamplifier 110, 111, 140
The output signals e ₁ , e ₂ , e ₅ are the slice voltages Vs ₁ , output from the slice level generator 160 by the comparators 150 , 151 , 152, respectively.
Compared with Vs ₂ and Vs ₃ . At this time, the slice voltages input to the comparators 150, 151, and 152 are higher than the slice voltages input to the comparators 114, 115, and 141, and no matter how strongly the light scattering due to the circuit pattern occurs, the output signal e ₁ ,
It is set higher than the minimum values of e ₂ and e ₅ . Therefore, comparators 150, 151, 1
52 and AND circuit 153, AND circuit 1
53 generates a logical value of "1" only when very strong scattered light is generated from a foreign object. AND circuit 15
The output of 3 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 becomes close to the power supply voltage, causing the output of the amplifiers 112 and 113 for the light receiving elements 23 and 13 on the back side of the object to be measured to increase. The comparators 118 and 119, which compare K times the magnitude of the output from the amplifiers 110 and 111, do not operate correctly and the light is scattered from a foreign object, but both comparators 118 and 119 detect the circuit pattern. If the device operates as if it were detecting scattered light from a foreign object, foreign matter cannot be detected in other embodiments, but it can be detected in this embodiment. In addition to the comparators 114, 115, and 141 that perform comparisons with low slice voltages as described above, there is a comparator 15 that performs comparisons with high slice voltages.
0, 151, 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 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 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 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 sixth embodiment of the present invention will be described based on FIG. 15. In addition to the fifth 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 center 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 from the edge portion of the pattern is the scattered light 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 can 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 foreign matter, and when the foreign matter is also detected by the light receiving elements 13, 23, and 41 on the back side, it can be determined that the foreign matter has adhered to the transparent portion of the photomask 5. 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 the foreign object is detected on the front side and the back side of the photomask 5.

Further, when using the detection circuits in the fourth and fifth 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, on the back side.
41 photoelectric signals and output signals e ₁ ~
Configured to generate e ₅ . of course,
It is better to perform this switching after the photoelectric signal of each light receiving element has been amplified once. This switching is done by signal 2
This is done by 01. 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 purpose, the laser beam 1 may be guided by an appropriate optical path switching member in the same way as the front side is irradiated onto the back side of the photomask 5 in FIG. 14.

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 that foreign substances attached to both sides can be detected extremely quickly and accurately. Become.

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 using 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. Scattered light from the foreign object j attached on the top is detected only by the light receiving part A, and is detected by the light receiving part B.
It is not detected depending on the This will be explained with reference to FIG. 17 as a photoelectric signal of each light receiving element in FIG. 7. Figure 17 a, b, c, and d are the light receiving elements 2, respectively.
The magnitude of the photoelectric signals from 1, 11, 23, and 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. Here, when the laser beam is scattered by a foreign object j as shown in FIG.
1 and 11 are photoelectric signals A as shown in Fig. 17a and b, respectively.
3, generates B3. On the other hand, the light receiving elements 23, 13
are the photoelectric signals C3 and D, respectively, as shown in Fig. 17c and d.
As 3, approximately zero is output. Furthermore, when the laser beam is scattered by a foreign object i as shown in Fig. 1,
As shown in FIG. 17, the light receiving elements 21, 11, 23,
13 generate photoelectric signals A4, B4, C4, and D4, respectively. 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, PA4,
PB4, PC4, PD4 are photoelectric signals A4, B4, C
4 and D4. Therefore, the small slice voltages Vs4 and Vs5 are set to the respective peak values PC4 and PD4.
If it is set in the middle of
The photoelectric signals of 3 and 13 both have a slice voltage of Vs4,
exceeds Vs5, but in the case of foreign object j, the slice voltage
Foreign matter i and j can be distinguished without exceeding Vs4 and Vs5. Therefore, next, a seventh 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 in the second embodiment shown in FIG. The difference is that comparators 204 and 205 are provided, and their outputs are input to an AND circuit 202 in parallel. The comparator 204 is the amplifier 11
The output e ₂ of 2 is compared with the slice power Vs4 output from the slice level generator 203, and if e ₃ > Vs4, a logic value "1" is output, otherwise a logic value "0" is output. 205 compares the output _e4 of the amplifier 113 with the slice voltage Vs5;
If e ₄ >Vs5, a logical value “1” is output, otherwise a logical value “0” is output. Here the slice voltage
The magnitudes of Vs4 and Vs5 are determined as explained in FIG. 16 above, and the magnitudes change depending on the spot position. The way of change is from 1st to 6th.
This is as explained in each embodiment. In such a configuration, when the laser beam hits a foreign object attached to the glass plate (light transmitting part), the comparators 204 and 205 output a logical value of "1", and the other comparators 114, 115, 118, 119
also outputs the logical value "1", so the AND circuit 20
The output of 2 has a logical value of "1", indicating that a foreign object has been detected. However, when the laser beam is incident on a foreign substance attached to the light shielding part, the comparator 204,
The output of the AND circuit 205 becomes a logical value "0", and the output of the AND circuit 202 becomes a 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-blocking portion, which does not affect the printing of the mask pattern, can be ignored.

In this way, compared to the case where foreign matter is detected without distinguishing whether it is a light-transmitting part or a light-shielding part, this embodiment detects foreign matter only in the light-shielding part, and the degree of cleaning of the photomask is affected by the printing of the pattern. Even though the mask is durable, it reduces the need to clean it again if it is contaminated or to replace it with another mask with the same pattern.
For this reason, in manufacturing semiconductor devices, time and
It has economically advantageous characteristics.

In this seventh 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 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 discriminating and detecting foreign matter attached to the light-transmitting part and the light-blocking part. Function is the first and third
It goes without saying that the same addition can be made in each of the embodiments .about.6.

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, multiple light-receiving elements are provided that look into the surface on the laser beam incidence side.
The number of light receiving elements looking into the back surface may be one.

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 received scattered light 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 to correspond to the laser spot scanning position, that is, the scanning signal SC By changing it in synchronization with 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 Vs1 and Vs2 in FIGS. 9 and 11 are set to a common constant voltage. Then, the gain of the amplifiers 110 and 111 is set to 1
It is variable depending on the spot position. As an example, the relationship between the gains of the amplifiers 110 and 111 may be determined as shown in FIG. This diagram is
Corresponding to FIG. 10b described above, at position C ₁ , the gain G ₁ of amplifier 110 and
1 and the gain G ₂ are both made 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.

In addition, 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 is
The comparison was made with a certain value K, but for example, the sum of the outputs of the light receiving elements 11 and 21 located on the front side and the sum of the outputs of the light receiving elements 13 and 23 located on the back side are calculated respectively, and the sum of the two is calculated. By determining whether or not the ratio of K is greater than K, it is possible to identify whether a foreign object is a foreign object or a circuit pattern, or to determine whether a foreign object is 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.

Furthermore, 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.

As described above, according to the present invention, scattered light is photoelectrically detected on the front side and back side of the object to be inspected, and defect inspection is performed based on the difference in the photoelectric signals. It is possible to selectively and accurately detect whether a defect occurs on the front or back side of an object to be inspected.

Furthermore, according to the example, when inspecting photomasks and reticle for IC manufacturing, multiple light receiving elements are arranged in different directions and the light beam is made obliquely incident, thereby preventing the influence of the circuit pattern and ensuring that the predetermined conditions are met. Only defects can be detected at high speed.
Furthermore, the size of the defect can be detected from the correlation between the intensity of the scattered light and the size of the defect, and only defects of a size that truly cause harm can be detected. Therefore, by detecting even smaller defects 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.

The present invention can be used not only to detect foreign matter attached to a reticle mask, but also to detect defects on an object such as a pattern adhered to a transparent object.
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]

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;
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.
FIG. 0b is a diagram showing changes in slice voltage, FIG. 11 is a diagram showing the first embodiment of the present invention, and FIG. 12 is a diagram showing changes in slice voltage.
A diagram showing a second embodiment of the present invention, FIG. 13 is a diagram showing a detection circuit of a second embodiment of the present invention, FIG.
FIG. 15 shows a detection circuit according to a third embodiment of the invention, FIG. 15 shows a fourth embodiment of the invention, FIG. 16 shows a switching circuit, and FIG.
FIG. 18 is a diagram showing the photoelectric signal of the light receiving element, FIG. 18 is a diagram showing signal processing according to the present invention, and FIG. 19 is a diagram showing the gain of the amplifier. [Explanation of symbols of main parts], 5...Object to be inspected,
11, 21...first photoelectric means, 13, 23...second photoelectric means, 130, 131, 118, 119,
132, 133, 134, 120...detection device.

Claims (1)

[Scope of Claims] 1. Irradiation means for irradiating a light beam from one side of a light-transmissive substrate having a flat surface with a patterned layer of minute thickness partially in close contact with the substrate; A first photoelectric detection unit that receives scattered light that propagates into a space on one side of the substrate among defects such as minute foreign matter attached to the surface or scattered light generated when a part of the patterned layer is irradiated. and a second photoelectric detection means for receiving scattered light traveling into the space on the other side of the substrate,
In a defect inspection device that detects the presence of the defect by reducing false detection by the pattern layer based on each photoelectric signal from the first photoelectric detection means and the second photoelectric detection means, the first photoelectric detection means a first comparison means for outputting a first detection signal when the level of the photoelectric signal from the first photoelectric detection means is equal to or higher than a predetermined reference level; a second comparison means for outputting a second detection signal when the level of the photoelectric signal reaches a ratio greater than 1; the first detection signal and the second detection signal are both output; and a calculation means for outputting a detection signal indicating that the defect exists on one side of the substrate. 2. The first photoelectric detection means includes a plurality of first light receiving elements that obliquely view the light beam irradiation range on one surface of the substrate from different spatial directions; at least one second light-receiving element that obliquely looks into the light beam irradiation range on the other surface; the first comparison means is configured to detect when the level of each photoelectric signal from the plurality of first light-receiving elements is equal to or higher than the reference level; a plurality of first comparators for detecting that the level of at least one photoelectric signal among the respective photoelectric signals from the plurality of first light receiving elements is equal to or greater than that from the second light receiving element; at least one second comparator for detecting that the level of the photoelectric signal has become a ratio greater than 1; Claim 1, further comprising: a logical operator that outputs a detection signal indicating that the defect is present on one side of the substrate when both of the two comparators output a detection signal. The device according to item 1. 3. A plurality of the second light-receiving elements are arranged symmetrically with each of the plurality of first light-receiving elements with respect to the surface of the substrate; The calculation means includes a plurality of second comparators that compare the photoelectric signals with each other with the second light receiving element; and the calculating means compares the levels of the photoelectric signals output from each of the plurality of first light receiving elements. a selection circuit that outputs a selection signal representing the first light receiving element whose level is lower than that of the first light receiving element selected from among the plurality of second comparators in response to the selection signal; Claim 2, further comprising: a prohibition circuit that prohibits outputs other than the second comparator that compares photoelectric signals between the light receiving element and a second light receiving element arranged symmetrically. Equipment described in Section. 4. The second comparison means compares whether the photoelectric signal level from the first photoelectric detection means is 1.5 times or more than the photoelectric signal level from the second photoelectric detection means, and determines whether the photoelectric signal level from the first photoelectric detection means is 1.5 times or more. The device according to any one of claims 1 to 3, wherein the second detection signal is output when: . 5. An irradiation means for irradiating a light beam from one side of a light-transmissive substrate having a flat surface with a pattern layer of a minute thickness partially in close contact with the substrate; a first photoelectric detection means for receiving scattered light that is generated when a defect such as a foreign object or a part of the patterned layer is irradiated and that travels into a space on one side of the substrate; and a second photoelectric detection means for receiving scattered light traveling into the space on the other surface side,
In a defect inspection apparatus that detects the presence of the defect by reducing erroneous detection by the pattern layer based on each photoelectric signal from the first photoelectric detection means and the second photoelectric detection means, A light beam scanner that makes a light beam obliquely incident on the surface of the substrate and scans one-dimensionally along a scanning line intersecting the traveling direction of the light beam while substantially maintaining the angle of oblique incidence. and a first switching member that switches between a first state in which the scanning light beam enters the substrate from one surface side and a second state in which the scanning beam enters the substrate from the other surface side; The level of the photoelectric signal from one of the first photoelectric detection means and the second photoelectric detection means is at least a ratio greater than 1 to the level of the photoelectric signal from the other photoelectric detection means. a comparison means for outputting a detection signal when the first state and the second state are switched; a photoelectric signal of the first photoelectric detection means and the second photoelectric detection means for the comparison means; and a second switching means for switching the connection with the photoelectric signal of the first photoelectric signal based on the detection signal of the comparison means.
A defect characterized in that when in the state, the defect existing on one side of the substrate is detected, and when in the second state, the defect existing on the other side of the substrate is detected. Inspection equipment. 6. Irradiation means for irradiating a light beam from one side of a light-transmissive substrate having a light-shielding pattern layer with a substantially minute thickness partially adhered to a flat surface; a first photoelectric detection means for receiving scattered light that propagates into a space on one surface side of the substrate among the scattered light generated when a part of the light-shielding pattern layer is irradiated with a defect such as a foreign substance; and a second photoelectric detection means for receiving scattered light traveling into the space on the other side of the substrate,
In a defect inspection device that detects a defect existing in a light transmitting portion other than the light-shielding pattern layer among the defects based on each photoelectric signal from the first photoelectric detection means and the second photoelectric detection means, a first comparing means for outputting a first detection signal when the level of the photoelectric signal from the first photoelectric detection means is equal to or higher than a predetermined first reference level; a second comparison means for outputting a second detection signal when the level of the photoelectric signal from the second photoelectric detection means reaches a ratio greater than 1; a third comparison means that outputs a third detection signal when the level is equal to or higher than a second reference level close to zero; and when the condition is such that the first, second, and third detection signals are all output, the defect 1. A defect inspection device, comprising: arithmetic means for outputting a detection signal indicating that a light-transmitting portion of the substrate other than the light-shielding pattern layer is present on the substrate.