JPS6364738B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting foreign matter that becomes a defect such as minute dust, and particularly to a photomask for LSI,
The present invention relates to an inspection device that detects foreign matter attached to a reticle or a circuit pattern of a wafer as a defect.

In the process of manufacturing LSI photomasks and wafers, foreign matter may adhere to the reticle, wafer, mask, etc., and these foreign matter may cause defects in the manufactured masks and wafers. Particularly in a reduction projection type pattern printing apparatus, this defect appears as a common defect in each mask and in all chips of a wafer, so it is necessary to strictly inspect it during the manufacturing process. For this reason, it is generally considered to carry out 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, as a device that automatically inspects the foreign matter present on the surface of an inspected object having a circuit pattern, a laser beam is incident and scanned on the surface of the inspected object from a perpendicular or almost vertical direction, and the scattered light from the foreign object is detected. Devices that collect and detect light have been proposed. However, this device had the drawback that the inspection time was inevitably increased because the laser beam was focused and scanned sequentially over a small area.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a defect inspection apparatus that can reliably and quickly detect foreign substances present on a patterned object to be inspected.

In order to achieve this object, the present invention is constructed as follows.

A light beam, such as a laser beam, is obliquely incident on the surface of the object to be inspected, and the portion of the surface irradiated by the light beam is scanned (two-dimensionally) over the surface. At least one of the plurality of photoelectric means receives light so as not to receive scattered light generated by the pattern, and all of the plurality of photoelectric means receive light scattered light generated by foreign matter on the surface. A device is arranged to inspect the presence or absence of foreign matter based on the output signal of the light receiving device.

Next, we will explain embodiments of the present invention, but before that, we will explain how the edges of a circuit pattern are scattered when a focused light beam, such as a laser beam, is irradiated onto the edges of a circuit pattern. will be explained using the principle diagram shown in FIG.

In FIG. 1, it is assumed that the surface to be inspected extends on the xy plane of the orthogonal coordinate system xyz. A circuit pattern 2 is provided on the surface to be inspected. It is assumed that the edge 2a of pattern 2 forms an angle ψ with the y-axis. Coordinate system as shown in figure
Laser light 1 is incident on the origin 0 of xyz. Therefore, the origin 0 becomes the point of incidence. This laser beam 1
is the angle θ with respect to the surface to be inspected, that is, the x-y plane
, and the projection onto the x-y plane coincides with the y-axis. At this time, the scattered light of the laser light 1 is distributed and spread in a conical shape with the origin 0 as the apex on the opposite side to the direction of incidence. This cone-shaped scattered light is
It appears to be divided into two by a plane.

Here, when the laser beam 1 is obliquely incident on the edge 2a (incident obliquely with respect to the surface to be inspected),
The way the scattered light spreads is uniquely determined to some extent. As shown in the figure, the transmitted light and specularly reflected light of the laser beam 1 become cone-shaped scattered light such that the generating lines L1 and L2 of the cone, respectively, and the direction l of the edge 2a become the center line of the cone. Therefore, bus line L1
is on the lower side of the xy plane, and the generatrix L2 is set on the upper side. Here, as special cases, the angle ψ is 0° and 90°. First, when ψ=0°, the scattered light spreads in a conical shape with an apex angle of 2θ centered on the y-axis. When ψ=90°, the apex angle is 180°, that is, it spreads in the y-z plane.

In this way, when the edge of a pattern is irradiated with laser light, scattered light having directionality (strong directionality) is generated depending on the angle of incidence with respect to the edge. On the other hand, if a foreign object exists on the surface to be inspected and is irradiated with laser light, scattered light will spread from the foreign object in all directions. If the foreign object is sufficiently small compared to the laser beam spot, the laser power per unit area for the foreign object will not change, so the angle θ relative to the surface to be inspected is made small (for example, less than 90 degrees and an acute angle of 10 degrees or more). It is more efficient to irradiate a wider area of the pattern.

The scattered light generated in this way is collected by a condensing lens,
It can be detected electrically by a photoelectric detector. However, as mentioned above, since the pattern is generally a geometric planar shape, the scattered light from the edges of the pattern has directionality, so in order to detect the scattered light from foreign objects, it is necessary to A plurality of photoelectric detectors may be arranged so as to look at the laser beam irradiation area from different directions. Next, an embodiment of the present invention will be described with reference to FIG. 2.

FIG. 2 is a perspective view showing the configuration of an apparatus according to an embodiment of the present invention. The object to be inspected 10 is assumed to be a reticle, mask, or wafer including a circuit pattern. The surface of the object to be inspected 10 is assumed to be on the xy plane of the coordinate system xyz in the figure. The laser beam 1 may be transmitted through an expander (not shown), as appropriate.
The beam is converted into an arbitrary beam diameter by an optical member serving as a condensing optical system for irradiation, such as the condenser lens 11, and then narrowed down to a spot light to increase the light intensity per unit area. The laser beam 1 scans the object to be inspected 10 in the x direction by a scanner 12 (vibrator, galvano mirror, etc.) serving as a beam scanning means. At this time, the scanning laser beam 1 is applied obliquely to the surface of the object 10 to be inspected (for example, at an angle of incidence of 70° to
80°). Therefore, the approximately one-dimensional irradiation portion 1 of the laser beam 1 on the inspected object 10
In the figure, the spots 3 to 15 have an elliptical shape extending approximately in the y direction. Further, the scanning position of the laser beam 1 scanned by the scanner 12 is detected by photoelectric elements 22 and 23. On the other hand, the object to be inspected 10 is placed on a mounting table 49 and can be moved in a direction 24 substantially perpendicular to the scanning direction of the laser beam 1 by a movement 50 of a motor or the like, and the irradiation section is scanned in the y direction. . This mounting table 49 is provided with a suitable movement measuring means, for example, a linear encoder 51, and based on the measured value, the irradiation position of the laser beam 1 on the object to be inspected 10 in the y direction can be measured. It is.

The photoelectric elements 19, 20, and 21 are irradiated with laser light 1 from different spatial directions.
It is arranged so as to receive the scattered light from 15. Scattered light is focused on each light receiving surface of the photoelectric elements 19, 20, 21 by condensing lenses 16, 17, 18. Further, the optical axes of the respective condensing lenses 16, 17, and 18 are arranged obliquely with respect to the surface of the object to be inspected 10, that is, the xy plane. This is because, assuming that the angle of the optical axis with respect to the x-y plane is the light receiving angle, this light receiving angle is made small so as to be less susceptible to the influence of diffused reflection of the pattern surface itself of the object 10 to be inspected. Note that in this embodiment, the photoelectric elements 19, 20,
21 is arranged approximately at the same distance from the center 14 of the scanning direction of the laser beam 1. Furthermore, as is clear from FIG. 2, when viewed within the x-y plane, each of the three condenser lenses 16, 17, 18 looks at the approximately one-dimensional irradiation portions 13 to 15 from different angular directions. In addition, the object to be inspected 10 of the laser beam 1
It is placed in a position that avoids the direction of specular reflection on the surface.

Next, the operation of detecting a foreign object present on the object to be inspected 10 using this apparatus will be explained. While scanning the laser beam 1 with the scanner 12, the object 1 to be inspected is
0 in the y direction on the x-y plane. During this operation, when the laser beam 1 irradiates the edge of the pattern, the scattered light is accompanied by strong directivity as described above.
Therefore, among the photoelectric elements 19, 20, and 21 that can detect scattered light from different directions, only a specific photoelectric element receives the scattered light from the edge. Therefore,
The arrangement of each photoelectric element is determined so as not to simultaneously receive scattered light from the edges of the pattern. Further, when the laser beam 1 irradiates a foreign object during scanning, light scattered by the foreign object occurs in all directions, that is, almost non-directionally. Therefore, in this case, all of the photoelectric elements 19, 20, and 21 receive the scattered light from the foreign object. Furthermore, if a foreign object exists near the edge of the pattern, the scattered light from the edge is received by a specific photoelectric element, and the scattered light from the foreign object is received by all the photoelectric elements. On this occasion,
The photoelectric output signal of each photoelectric element takes a different value depending on the angle of incidence of the laser beam 1 on the edge (or on the surface), the size of the foreign object, and the like.

Therefore, after suitably amplifying the photoelectric output signals of each photoelectric element 19, 20, and 21 with an amplifier, the output signal and a predetermined reference signal are compared with a comparator.
It is detected whether or not scattered light is generated from the irradiation part of the laser beam 1 in the direction of the photoelectric element. This will be explained with reference to FIG.

The photoelectric signals of the photoelectric elements 19, 20, 21 are amplified by amplifiers 30, 31, 32, respectively. The difference between each output signal of the amplifiers 30, 31, and 32 and the reference signal 33 is taken by differential amplifiers 34, 35, and 36, respectively.

The logic circuit 37 performs a predetermined logical operation, for example, a logical product (AND) operation, from each differential output (binarized digital signal or analog signal proportional to the difference). Therefore, as described above, when all the photoelectric elements output sufficient photoelectric signals, the logic circuit 37 outputs a predetermined detection signal. That is, a detection signal is output only when a foreign object on the object to be inspected 10 is irradiated with the laser beam 1.

This detection signal, the measurement value by the movement amount measuring means 51, and the laser beam 1 by the photoelectric elements 22 and 23
The position of the foreign object on the object to be inspected 10 is determined based on the scanning position value.

Note that the photoelectric signals of the photoelectric elements 22 and 23 become the largest when the scanned laser beam 1 crosses each element. Therefore, for example, when the photoelectric signal of the element 22 reaches a maximum by the counting means 43, the start signal 42 is generated to start counting a predetermined reference pulse, and when the photoelectric signal of the element 23 reaches a maximum, A stop signal 44 is generated to stop the counting. Then, the number of pulses counted during this period is calculated by a suitable calculation means to determine the position of the spot of the laser beam 1 on the object to be inspected 10 (the position in the x direction on the x-y plane). Further, each photoelectric signal of the three photoelectric elements 19, 20, 21 may be
Each one comes in different sizes. For example, in FIG. 2, if a foreign object exists near the irradiation section 13,
The photoelectric signal of the photoelectric element 19 is the largest, followed by the photoelectric signal of the photoelectric element 20, and the photoelectric signal of the photoelectric element 21 is the smallest. Therefore, when determining the position of a foreign object based on each photoelectric signal, the magnitude of each signal is corrected depending on the position of the foreign object.

For this purpose, amplification converters 38, 39, 40 are provided after each amplifier 30, 31, 32. The converters 38, 39, and 40 incorporate, for example, a plurality of resistors and switches, and the resistance value changes by switching the switches. The controller 41 controls the converters 38, 39,
A time-series sequential signal 45 is output to 40. This sequential signal 45 is, for example, a signal that generates one pulse when one scanning period of the laser beam 1 is equally divided. converter 3
8, 39, and 40 simultaneously change the resistance value in a time-series manner by inputting the sequential signal 45. As a result, the amplification converters 38, 39, 40
The degree of amplification changes. In addition, at this time, the converters 38, 3
The resistance value change of 9, 40 is determined according to the arrangement of the photoelectric elements 19, 20, 21 with respect to the scanning position of the irradiation part of the laser beam 1, and as a result, the change in the resistance value of the three amplifiers 3
The changes in the amplification degree with respect to time of 0, 31, and 32 are not the same.

In this way, the signal from the foreign object that has been subjected to the predetermined correction provides a signal that statistically depends only on the size, regardless of the position of the foreign object. That is, the corrected signal values (transducers 38, 39,
40 output signal, etc.), it may be compared with data regarding the size of the foreign object that has been statistically determined in advance.

As mentioned above, the three photoelectric elements 19, 20, 2
It is also possible to determine the approximate size of the foreign object from each photoelectric signal of 1 at the same time as detecting the foreign object.

Furthermore, in order to simultaneously inspect the back surface of the plate-shaped object 10 to be inspected, a beam splitter or the like may be used to split the laser beam 1 and make it obliquely incident on the back surface.
At this time, in order to detect scattered light from foreign matter on the back surface, a plurality of photoelectric elements are further arranged in the same way as those on the front surface.

In addition, in the example, three photoelectric elements were arranged, but
If the directivity of the scattered light due to the edges of the pattern is taken into consideration, it is sufficient to simply arrange two photoelectric elements.

As described above, according to the present invention, when inspecting defects on an object to be inspected, a spot irradiated onto a pattern surface can be detected using a simple optical system without reducing the laser power density per unit area for the defect. Since the size can be increased, the number of scans is reduced and inspection time is shortened. Furthermore, there is an advantage that defects can be visually observed by appropriately arranging observation means (for example, an optical microscope) above the laser beam irradiation part.

In addition, the plurality of pairs of light-receiving condensing optical systems and photoelectric detection means that receive scattered light from pattern edges and foreign objects are used to detect scattered light generated from pattern edges with strong directivity during spot light scanning. The spot light is placed so that the irradiated area is viewed from different spatial directions, so that the spots are not affected by the scattered light from the edges of the pattern.
S/N ratio of photoelectric signal (depends on the ratio of scattered light from foreign objects on the surface and scattered light from other places)
will improve.

[Brief explanation of drawings]

Figure 1 is a principle diagram showing the state of scattered light that occurs when the edge of a pattern is irradiated with a light beam.
FIG. 2 is a perspective view showing a foreign matter inspection apparatus according to an embodiment of the present invention, and FIG. 3 is a block diagram showing a signal processing system in the foreign matter inspection apparatus according to an embodiment of the present invention. Explanation of symbols of main parts, 1...Light beam, 2...
...Pattern, 10...Object to be inspected, 12...Scanner, 19, 20, 21...Light receiving device, 37...
Logic circuit, 38, 39, 40...amplification converter.

Claims (1)

[Scope of Claims] 1. The surface of the object to be inspected is scanned with a light beam and the scattered light generated from the object is photoelectrically detected. In an apparatus for inspecting defects in a device, the light beam is focused on the object to be inspected to form a focused spot light, and the angle between the light beam and the surface of the object to be inspected is other than 0°.
a condensing optical system for irradiation that irradiates at an acute angle of less than 90 degrees; and a beam scanning means that scans the spot light of the light beam almost one-dimensionally on the object to be inspected while maintaining the irradiation state of the light beam. ; a plurality of light-receiving condensing optical systems that arrange the irradiated portion by substantially one-dimensional scanning of the spot light at positions viewed from a plurality of mutually different spatial directions, and condense the scattered light generated from the irradiated portion; a plurality of photoelectric detection means for receiving the scattered light collected by each of the plurality of light-receiving focusing optical systems; and detecting the defect based on the magnitude of each photoelectric signal of the plurality of photoelectric detection means. a detection circuit, wherein the spatial direction is determined so that each of the plurality of light receiving condensing optical systems does not simultaneously receive scattered light from the pattern. 2. Each optical axis of the plurality of light-receiving focusing optical systems is set obliquely to the surface of the object to be inspected, and when viewed in a plane parallel to the surface of the object to be inspected, the plurality of light-receiving focusing optical systems 2. The apparatus according to claim 1, wherein the light optical system is disposed at a spatial position where a substantially one-dimensional irradiated portion of the spot light is viewed from different angular directions. 3. The apparatus according to claim 1 or 2, wherein each of the plurality of photoelectric detection means is arranged at approximately the same distance from the center of the approximately one-dimensional irradiation area by the spot light. 4. The beam scanning means has means for outputting a signal corresponding to the approximately one-dimensional scanning position of the spot light, and based on the signal and each photoelectric signal from the plurality of photoelectric detection means, The apparatus according to claim 1, characterized in that the position of the defect is specified within the irradiated part. 5. The detection circuit includes a correction circuit that individually corrects the magnitude of each photoelectric signal from the plurality of photoelectric detection means according to the scanning position, based on the signal corresponding to the substantially one-dimensional scanning position of the spot light; 5. The apparatus according to claim 4, further comprising an arithmetic circuit that discriminates between scattered light from a pattern and scattered light from a defect based on each corrected photoelectric signal.