JP2603078B2 - Defect inspection equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection technique, and more particularly to a technique for inspecting a plate-like object for a defect such as a foreign substance or a scratch (hereinafter referred to as a foreign substance). The present invention relates to a technique effective for inspecting foreign substances on a mask used in a semiconductor device manufacturing process.

[Conventional technology]

With the improvement in the degree of integration of semiconductor devices, circuit patterns have been further miniaturized. Under these circumstances, the generation of defects on the circuit due to foreign matter on the glass mask as the circuit original becomes a major problem. In particular, in a mask (also referred to as a reticle) used in a reduction projection exposure apparatus (stepper), the stepper is used for repetitive exposure.
All chips on the wafer are defective, which is a serious problem.
Therefore, it is important to inspect the quality of the mask before use.

On the other hand, fine particles (for example, 1 μm)
m) It is difficult to completely remove the mask, and in order to determine the quality of the mask, it is necessary to determine the size of foreign matter and the like.

As described above, as a defect inspection apparatus for inspecting foreign matter on a mask, the mask is scanned and irradiated with a laser beam, and by detecting scattered light from the foreign matter, the position of the foreign matter is determined, and the magnitude of the scattered light is determined. In some cases, the size of a foreign substance is determined.

The size of the foreign substance is determined by using sphere beads (polystyrene latex or the like) as a standard sample and comparing the scattered light intensity obtained therefrom with an actually measured value.

Examples of mask inspection technology include “Electronic Materials November 1986 Separate Volume,” Showa
There are P221 to P227 issued on November 20, 61.

[Problems to be solved by the invention]

In such a defect inspection apparatus, the shape of the foreign matter present during the actual semiconductor factory process is various, and the correlation between the foreign matter size determined in terms of standard particles and the actual size of the foreign matter is low. It has been clarified by the present inventor that there is a problem that the inspection accuracy for the size of the image is reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a defect inspection apparatus capable of increasing the inspection accuracy for the size of a foreign substance.

The above and other objects and novel features of the present invention are as follows.
The description of the present specification and the accompanying drawings will be apparent.

[Means for solving the problem]

The outline of a representative invention among the inventions disclosed in the present application will be described as follows.

That is, the object to be inspected is irradiated with a light beam by scanning,
In a defect inspection apparatus that inspects a defect by detecting scattered light, the size of the defect is determined based on the number of times of detection of the scattered light for the same defect obtained by scanning with overlapping light beams. It is composed.

[Action]

By performing the determination of the size of the foreign matter by counting the number of times the foreign matter scattered light is detected, the number of times the foreign matter scattered light is detected is less affected by the direction of light beam irradiation on the foreign matter and the position of the optical sensor. Since a certain correlation is maintained with the size of the foreign matter, the determination of the size of the foreign matter can be performed very accurately.

That is, since the scanning is performed repeatedly, the same foreign matter is irradiated with the light beam a plurality of times, and scattered light is generated for each irradiation. Each time these scattered lights are generated, they are detected by an optical sensor. At this time, the magnitude of the detection signal becomes unstable depending on the irradiation direction of the light beam and the position of the optical sensor, but the number of detections is less affected by the irradiation direction of the light beam and the position of the optical sensor. If the light beam diameter D and its scanning pitch are constant, the number of times the light beam is irradiated on the foreign matter, that is, the number of times the optical sensor detects the light beam, maintains a constant correlation with the size of the foreign matter.

〔Example〕

FIG. 1 is a schematic view showing a mask defect inspection apparatus according to one embodiment of the present invention, and FIGS. 2 and 3 are explanatory views for explaining the operation thereof, FIGS. 6 and 7 are the same diagrams.

In this embodiment, this mask defect inspection apparatus is configured to inspect foreign matter on a mask 1 used in a manufacturing process of a semiconductor device, and an XY table 2 holding the mask 1 as an inspection object is used. Have. The XY table 2 is configured to move the mask 1 in the XY direction, and the controller 3 of the XY table 2 is configured to transmit the amount of the movement as XY coordinates to a display unit described later. A laser oscillator 4 for emitting a laser 5 as a light beam is provided on one side of the XY table 2, and a galvano mirror 6 is provided on the optical axis of the laser oscillator 4 via an optical thread 8 such as a lens. Is arranged to scan the mask 1 in one reciprocating direction and irradiate it.
The controller 7 of the galvanometer mirror 6 is configured to transmit the scanning position of the laser 5 to the display unit as XY coordinates.

A pair of optical sensors 9 are disposed near the XY table 2 so as to face each other in the scanning direction of the laser 5, and the optical sensors 9 are scattered light 5a of the laser scattered by the foreign matter on the mask 1. Is configured to be able to be effectively detected. A signal processing unit 11 is connected to an output end of the optical sensor 9, the signal processing unit 11 appropriately processes a detection signal from the optical sensor 9, samples a signal having a certain threshold value or more,
It is configured to be sent to the subsequent stage.

The signal processing unit 11 is connected to a maximum peak signal detection unit 12, which extracts a maximum peak signal in a predetermined small area from a peak signal group detected by the optical sensor 9, and extracts the maximum peak signal. And the size signal is transmitted to the first size determination unit 13. The first size determination unit 13 includes a first reference data storage unit.
The storage unit 14 stores, for example, data on the relationship between the scattered light intensity and the bead size as shown in FIG. And the first size determination unit 13 is a first reference data unit.
The data of 14 and the actual magnitude signal from the maximum peak signal detection unit 12 are compared to determine the size of the foreign matter, and the determination result is input to one input terminal of the size determination unit 15. It is designed to input.

Further, a signal counting unit 16 is connected to the signal processing unit 11, and the counting unit 16 counts the number of signals detected by the optical sensor 9 in a predetermined small area and transmits the signal to the second size determination unit 17. It is configured to be. A second reference data storage unit 18 is connected to the second size determination unit 17,
In the storage unit 18, for example, data on the relationship between the count number and the foreign matter size as shown in FIG. 5 is obtained and stored in advance by an experiment or the like. The second size determination unit 17 is configured to compare the data in the second reference data storage unit 18 with the actual count number from the peak signal counting unit 16 to determine the size of the foreign matter. The determination result is input to the other input terminal of the size determination unit 15.

The size determination unit 15 is connected to the display unit 19,
Numeral 19 is configured to display the size of the foreign object together with its position.

 Next, the operation will be described.

The laser 5 emitted from the laser oscillator 4 is scanned by the galvanometer mirror 6 and is irradiated on the mask 1 held on the XY table 2. During this scanning, the mask 1 is sent by the XY table 2 in a direction perpendicular to the scanning direction, so that the laser 5 is relatively entirely scanned in the XY direction.

As shown in FIGS. 2 and 3, the laser 5 irradiated onto the mask 1 has a small beam diameter D as shown in FIGS. The scanning pitch P of the laser 5 (defined by the feed width of the XY table 2 in this embodiment) is set to a size sufficiently smaller than the beam diameter D. The reason why the scanning pitch P is set to be smaller than the beam diameter D is to avoid oversight of foreign matter and to avoid a detection error due to a difference in light amount between the central portion and the peripheral portion of the beam. In FIGS. 2 and 3, the division line orthogonal to the scanning line corresponds to the sampling interval of the signal processing unit 11 for the detection signal.

The laser 5 scanned in this manner is used to scan the foreign matter 20 on the mask 1.
, The scattered light 5a is reflected from the foreign material 20 because the foreign material 20 has an irregular surface. The scattered lights 5a are respectively detected by the optical sensors 9, and the detection signals are sequentially sent to the signal processing unit 11. The reason why the optical sensor 9 is provided as a pair is to control an error due to a difference in the detection position.

The signal processing unit 11 appropriately processes the detection signal. When the detection signal is schematically represented, since the scanning of the laser 5 is performed so as to overlap, as shown in FIG. A plurality of peak signals S appear in a small area corresponding to.
When the peak signal S group is represented by coordinates, it appears as shown in FIG. The signal processed in this way is sent to the maximum peak signal detecting section 12 and the signal counting section 16, respectively.

In the maximum peak signal detection unit 12, for example, the maximum peak signal Smax is extracted from the peak signal group in the small area corresponding to the beam diameter D, and the magnitude of the maximum peak signal Smax is determined by the first size determination unit. Sent to 13.
The determination unit 13 compares the magnitude of the signal with the data of the first reference data storage unit 14 to determine the size of the foreign matter 20 that has reflected the maximum peak signal Smax. For example, as shown by an imaginary arrow in FIG. 4, when the actual scattered light intensity transmitted from the maximum peak signal detection unit 12 is 0.5 V, the size of the foreign substance is 6 μm.
m.

Thus, the size of the foreign matter 20 determined by the first size determination unit 13 is input to one input terminal of the size determination unit 15.

On the other hand, the peak signal counting section 16 counts the number of peak signals in a small area corresponding to the beam diameter D, for example, and sends the counted value to the second size determination section 17. The determination unit 17 compares the count value with the data in the second reference data storage unit 18 to determine the size of the foreign matter 20 that has reflected the signal corresponding to the count value. For example, as indicated by an imaginary arrow in FIG. 5, when the actual count value sent from the counting unit 16 is “13”, the foreign matter size is determined to be 6 μm.

Thus, the size of the foreign matter 20 determined by the second size determination unit 17 is input to the other input terminal of the size determination unit 15.

In the size determination unit 15, the size from the first size determination unit 13 and the size from the second size determination unit 17 are compared, and if they match each other, the size is determined to be correct and displayed. It is sent to the unit 19.

If the sizes of the two determination units 13 and 17 do not match, both sizes are stored and the display unit 19
Sent to and displayed. Then, for example, when the direction of the mask 1 is changed and scanning is performed again in a different direction, the size determination unit 15 determines the inspection result stored in the first time and the current time in the second time. The inspection result is compared with the same foreign substance, the correct one is determined based on the coincidence rate or the like, and both sizes in the first and second times are sent to the display unit 19 and displayed.
This display result is used for analysis of the scanning operator and the like.

Incidentally, when the maximum peak signal detection unit 12 extracts the maximum peak signal Smax, it transmits the extraction result to the display unit 19. In the display unit 19, the position of the foreign matter 20 on the mask 1 is obtained based on the generation time of the maximum peak signal Smax, the feed signal from the controller 3 of the XY table 2, and the scanning signal from the controller 7 of the galvanometer mirror 6. And XY
Display by coordinates. Further, the size of the foreign matter 20 determined as described above is displayed in association with the position coordinates of the foreign matter 20.

By the way, as described above, when the determination of the size of the foreign matter is performed using the reference data of the true spherical beads as an intermediate value, an error occurs in the determination of the size of the actual foreign matter. This is because the shape of the actual foreign substance is not a true sphere. In other words, in the case of true spherical beads, the peak of the scattered light is detected with a stable size regardless of the laser irradiation direction and the position of the optical sensor, whereas in the case of actual foreign matter, the laser irradiation is performed. This is because the scattered light peak has a stable magnitude only in a specific direction depending on the direction and the position of the optical sensor. Further, since the material is different from the true spherical beads, the overall signal level is also different. In the case of using such a determination method, as shown in FIG. 6, it has been experimentally determined that the determination size of the apparatus tends to be determined to be smaller than the actual foreign matter size.

However, in the present embodiment, the determination of the size of the foreign matter is performed not only by using the reference data of the true spherical beads as an intermediary, but also by the count value of the beak signal of the foreign matter scattered light. The determination error is greatly suppressed irrespective of the actual irradiation direction of the laser beam to the foreign matter, the position of the optical sensor, and the material.

That is, the number of the peak signals S of the scattered light maintains a constant correlation with the actual size of the foreign matter regardless of the irradiation direction of the laser and the position of the optical sensor. That is, since the laser 5 is scanned repeatedly, the laser 5 is irradiated to the same foreign substance 20 a plurality of times, and the scattered light is
5a is generated respectively. The scattered light 5a is detected by the optical sensor 9 each time it is generated. At this time, the magnitude of the detection signal becomes unstable depending on the irradiation direction of the laser 5 and the position of the optical sensor 9 as described above, but the number of detections is affected by the irradiation direction of the laser 5 and the position of the optical sensor 9. Less. If the beam diameter D (half-width) of the laser 5 and the scanning pitch P thereof are constant, the number of times the laser 5 irradiates the foreign matter 20, that is, the number of times the optical sensor 9 detects, is constant with the size of the foreign matter 20. The correlation will be maintained.

FIG. 7 shows the measured size by the scattered light counting method with respect to the actual foreign matter size, and it is understood that the accuracy is extremely high.

 According to the above embodiment, the following effects can be obtained.

(1) By determining the size of the foreign matter by counting the peak signal of the foreign matter scattered light, the number of peak signals of the foreign matter scattered light is not affected by the irradiation direction of the light beam to the foreign matter and the position of the optical sensor. In order to maintain a constant correlation with the actual size of the foreign matter, the size of the foreign matter can be determined extremely accurately regardless of the irradiation direction of the light beam to the foreign matter and the position of the optical sensor.

(2) By setting the diameter of the light beam to be larger than that of the foreign matter and by setting the scanning pitch to be small, the number of times of detecting foreign matter scattered light can be increased. Can be enhanced.

(3) It is possible to complement each other by using a method of determining the size of a foreign substance based on the count of foreign substance scattered light and a method of determining the size of a foreign substance based on the intensity of the foreign substance scattered light.
The accuracy of the determination can be further increased.

Although the invention made by the inventor has been specifically described based on the embodiment, the present invention is not limited to the embodiment, and it is needless to say that various modifications can be made without departing from the gist of the invention. Nor.

For example, the size determination method based on the counting of the foreign matter scattered light and the size determination method based on the intensity of the foreign matter scattered light are not limited to being used in combination, and only the size determination method based on the counting of the foreign matter scattered light is used. It may be configured as follows.

The light beam is not limited to using a laser, and the scanning method is not limited to using a structure in which a galvanomirror and an XY table are used in combination.

In the above description, the case where the invention made by the present inventor is mainly applied to the mask defect inspection technology which is the field of application as the background has been described. However, the present invention is not limited to this. Can also be applied. In particular, the present invention has an excellent effect when applied to a technique for inspecting minute defects in a plate-like object.

〔The invention's effect〕

The effect obtained by the representative one of the inventions disclosed in the present application will be briefly described as follows.

By performing the determination of the size of the foreign matter by counting the peak signal of the foreign matter scattered light, the number of peak signals of the foreign matter scattered light is not affected by the irradiation direction of the light beam to the foreign matter and the position of the optical sensor. In order to maintain a constant correlation with the size of the foreign matter, the size of the foreign matter can be determined extremely accurately regardless of the irradiation direction of the light beam to the foreign matter and the position of the optical sensor.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a mask defect inspection apparatus according to one embodiment of the present invention, FIG. 2 and FIG. 3 are explanatory diagrams for explaining the operation thereof, FIG. 4, FIG. 6 and 7 are the same diagrams. 1 ... mask (inspection object), 2 ... XY table, 3 ...
Controller, 4 laser oscillator, 5 laser (light beam), 5a scattered light, 6 galvanomirror, 7
... controller, 8 ... optical thread, 9 ... optical sensor, 11 ...
... Signal processing section, 12 ... Maximum peak signal detection section, 13 ... First size determination section, 14 ... First reference data storage section, 15 ...
Size determination section, 16 peak signal counting section, 17 second size determination section, 18 second reference data storage section, 19 display section, 20 foreign matter, D beam diameter, P ... scanning pitch.

Claims (3)

(57) [Claims] An object to be inspected is scanned and irradiated with a light beam,
A defect inspection apparatus for inspecting a defect by detecting scattered light, wherein the light beam is scanned at a pitch smaller than an outer diameter maintained constant, and the light beam is irradiated by being overlapped by this scanning. A defect inspection apparatus, wherein the number of times of detection of scattered light from a region corresponding to a cross-sectional area of the light beam in an inspection object is counted, and the size of the defect is determined based on the counted number of detections. 2. The size of the defect is determined by comparing the number of times of detection of the scattered light with data obtained from the relationship between the number of times of detection and the size of the defect. 2. The defect inspection apparatus according to claim 1. 3. The method according to claim 1, wherein the intensity of the scattered light is measured and the size of the defect determined based on the intensity is compared with the size of the defect determined based on the number of times the scattered light is detected. The defect inspection device according to claim 1 or 2.