JP2003017536A - Pattern inspection method and inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pattern inspection method and an inspection apparatus for eliminating reflected light from an irregular circuit pattern edge efficiently with a simple spatial filter, and implementing a high-precision inspection of a semiconductor wafer having an irregular circuit pattern such as logic. SOLUTION: The pattern inspection apparatus comprises a stage 1 for mounting a wafer 9 to be inspected, a floodlight optical system 2, a condenser optical system 3 provided with a spatial filter 13 for shading reflected light, a beam split 4 for splitting light passing through the condenser optical system 3 into two in a predetermined light amount ratio, a laser intensity monitoring optical system 5, an imaging optical system 6 provided with two pieces of one-dimensional CCD cameras 19A and 19B, an image processing unit 7 for processing outputs of the one-dimensional CCD cameras 19A and 19B of the imaging optical system 6 to perform defect discrimination, and a laser power controlling unit 8 for controlling power of respective power source 10A and 10B of the flood light optical system 2 based on outputs of two photoreceptors 16A and 16B of the laser intensity monitoring optical system 5. Reflected light from an irregular circuit pattern edge such as a logic pattern is eliminated with a simple spatial filter, thus making it possible to detect a defect on the circuit pattern with high precision.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting a pattern on a wafer, a mask or the like on which an irregular pattern such as a logic LSI is formed, and more particularly to a pattern inspection using a dark field optical inspection technique. A method and an inspection apparatus.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have been highly integrated, the patterns formed on the surfaces of semiconductor wafers used for semiconductor devices have become extremely fine. When foreign matter adheres to a semiconductor wafer on which a fine pattern is formed, defects such as open and short patterns occur. Therefore, in the semiconductor wafer manufacturing process, optical inspection is performed on the foreign matter and defects caused thereby.
As such an optical inspection method, a light beam is applied to the wafer to be inspected and the reflected light is received by a photodetector, and the presence or absence of foreign matter or defects is inspected based on the result of the received light intensity distribution or the like. There is an optical inspection method. In order to increase the inspection accuracy in this method, it is important to separate the reflected light from the foreign matter or defect from the reflected light from the pattern formed on the surface of the wafer to be inspected.

As a conventional technique for separating such reflected light, an example of an inspected wafer having a repeating pattern of memory cells and the like has been proposed. In this conventional technique, in order to remove the diffracted light due to the repeated pattern of the wafer to be inspected, JP-A-5-118994 and JP-A-7-10 are used.
A Fourier transform filter is used as described in Japanese Patent No. 3907. Its basic configuration is as schematically shown in FIG. 11, and is provided with a light projecting means 51 for irradiating the surface of the wafer 58 to be inspected on the stage 50 with light obliquely from above. Further, the objective lens 5 is provided directly above the wafer 58 to be inspected.
2 and a Fourier transform optical system 54 having a Fourier transform filter (spatial filter) 53 provided in the latter stage of the objective lens 52, a magnifying optical system 55, a photodetector 56, and the detection results of the photodetector 56 are analyzed. And a computer 57 that operates. Then, the wafer 5 to be inspected is projected by the light projecting means 51.
The surface of 8 is irradiated with light, the light reflected by the wafer to be inspected is condensed by the objective lens 52, and the photodetector 56 by the magnifying optical system 55.
The foreign substance is detected by analyzing the light intensity pattern imaged by the photodetector 56 by the computer 57.

At this time, diffracted light is generated in the reflected light by the regular circuit pattern 59 formed on the surface of the wafer to be inspected 58, and this diffracted light is removed by the Fourier transform optical system 54. That is, the diffracted light is blocked by the blocking unit 53a formed in the Fourier transform filter 53 in the Fourier transform optical system 54 to distinguish it from irregular scattered light from foreign matters, defects 60 and the like. As described above, by attenuating the spatial frequency component corresponding to the pattern 59 formed on the surface of the wafer 58 to be inspected in the reflected light detected by the photodetector 56, the defect in the pattern or the foreign matter 60 becomes a pattern. The obtained dark field image is enhanced as compared with, and the detection accuracy of foreign matters and defects is improved.

[0005]

As described above, the Fourier transform filter in the conventional foreign matter or defect detection apparatus is effective for removing diffracted light from a repetitive pattern such as a memory cell. There is a problem that reflected light from an edge of an irregular circuit pattern such as a pattern cannot be removed. As a technique for removing the reflected light from such a circuit pattern edge, for example, Japanese Unexamined Patent Application Publication No. Hei 7 (1994)
There are techniques described in JP-A-270144 and JP-A-7-270326. The former is a technique that utilizes the fact that the amount of light scattered by minute foreign matter is larger than the amount of light scattered by the edges of the circuit pattern, and the latter is a technique that utilizes the fact that the scattered light in the pattern is larger in forward scattering than in backward scattering. However, the reflected light from the edge of the circuit pattern generally has a large intensity variation due to the state of the reflecting surface or a disturbance such as vibration, and also has a large variation in the scattering state. Therefore, it is difficult for any of the techniques described in the above publications to deal with the intensity variation of the reflected light from the circuit pattern edge and the situation variation as described above, and the foreign matter and the defect are detected only under limited conditions. There is a problem that you can not.

An object of the present invention is to reduce speckle noise due to minute irregularities on the wafer to be inspected and intensity fluctuations depending on the reflection characteristics of the pattern to be inspected, and to simplify the reflected light from the irregular circuit pattern edge. Provided is a pattern inspection method and an inspection apparatus which can be efficiently removed by a special spatial filter and can inspect a wafer or a mask having an irregular circuit pattern such as a logic with a high S / N ratio at high speed and at low cost. .

[0007]

According to the pattern inspection method of the present invention, the surface of an object to be inspected having an irregular pattern such as a logic circuit pattern is irradiated with laser beams of different wavelengths at different incident angles, and A step of finely scanning each of the laser beams on the surface of the object to be inspected; a step of shielding the reflected light of the laser beam on the surface of the object to be inspected while receiving scattered light of the laser beam; A step of branching the laser beam condensed by the optical optical system and controlling the laser intensity of the laser beam emitted from the projecting optical system based on the one branched laser beam, and the other branched laser beam Imaging the surface of the object to be inspected based on light, and performing defect determination based on the imaging output. Here, the minute scanning of the laser beam with respect to the inspected object is performed in parallel with one side of the rectangular pattern forming the main part of the irregular pattern. Further, it is preferable that the object to be inspected is moved at a constant speed in a direction orthogonal to the scanning direction of the laser light.

The pattern inspection apparatus of the present invention irradiates the surface of an object having an irregular pattern such as a logic circuit pattern with laser beams of different wavelengths at different incident angles and emits the laser beams. A light projecting optical system for performing minute scanning on the surface of the object to be inspected, and a condensing optical system that shields reflected light of the laser light on the surface of the object to be inspected and receives scattered light of the laser light, Laser beam splitting means for splitting the laser beam focused by the focusing optical system, and laser intensity for controlling the laser intensity of the laser beam emitted from the projecting optical system based on one of the split laser beams. It is characterized by comprising a control means and a defect determination means for capturing an image of the surface of the inspected object based on the other branched laser beam and performing defect determination based on the imaged output.

That is, as a more specific configuration of the present invention, the projection optical system includes two laser light sources which irradiate the wafer to be inspected at different incident angles and have different wavelengths, and the two laser light sources. Scanning optical means located on the optical axis for finely scanning the laser light respectively, the condensing optical system includes an objective lens for receiving scattered light from the surface of the inspection object, and the objective lens. And a spatial filter which is placed in front of the optical filter and shields the reflected light from the pattern edge of the object to be inspected, and the laser beam splitting means splits the laser beam passing through the condensing optical system into two at a predetermined light amount ratio. And a first dichroic mirror that splits one of the two laser beams split by the beam splitter into the wavelength of the laser beam. Two light receiving elements for respectively receiving the two laser beams wavelength-split by the first dichroic mirror, and a laser power control section for controlling the laser power of the two laser light sources based on the outputs of these light receiving elements. And a second dichroic mirror for splitting the other laser beam split into two by the beam splitter into a wavelength of the laser beam, and a wavelength split by the second dichroic mirror. It is characterized in that it is provided with two CCD cameras that respectively receive and image two different laser beams, and an image processing unit that processes the image pickup outputs of these CCD cameras and performs defect determination.

Here, in the present invention, it is preferable to have the following configuration. The scanning optical means in the light projecting optical system is a minute high-speed scanning by AOD or the like, and its scanning cycle is at least one digit shorter than the image capturing cycle of the one-dimensional CCD camera of the imaging optical system. The spatial filter of the condensing optical system is an elongated light-shielding mask installed close to the objective lens, and the objective lens has a long side parallel to the irradiation direction of the laser light. The structure is arranged on the center line. The laser power control unit peak-holds the outputs of the two light-receiving elements of the laser intensity control unit in the scanning cycle of the light-projecting optical system, and projects the peak values so that the peak values become a reference level. It has a function of controlling the two laser powers of the optical optical system respectively in a feedback manner. Further, in the determination processing in the defect determining means, the ratio of the data for each line captured by the one-dimensional CCD camera to the reference data is obtained, and the value is out of the average value beyond the determination level. The configuration is such that a location is extracted as a defect. Further, the determination by the defect determining means is performed by comparison between adjacent chips or comparison with master data.

Further, in the pattern inspection apparatus of the present invention, in addition to the one projection optical system, another projection optical system is provided, and the irradiation directions of these two projection optical systems are orthogonal to each other. Good. In this case, the laser scanning direction and the scanning width of the two projection optical systems are the same. Further, the two projecting optical systems are arranged orthogonally on the center line of the objective lens, and the spatial filter has a cross mark shape. Further, each laser light of the projection optical system has a rotation moving mechanism capable of adjusting the incident angle of the reference laser on the wafer to be inspected.

In the pattern inspection method and inspection apparatus of the present invention, the illumination method is replaced by general fixed laser irradiation, and the laser light is swept at a high speed and minutely within the measurement area, so that the laser light shakes or the stage vibrates. The speckle noise due to random fluctuations in brightness and minute unevenness on the wafer surface is reduced, and a spatial filter is also provided to efficiently cut specular reflection from the pattern edge. Also, two laser beams with different incident angles are used. The directivity of the scattering caused by the shape of the foreign matter is detected by irradiating the laser beam, and the intensity of the laser beam is controlled by the feed bag in real time.
By keeping within the allowable measurement range of the D camera, inspection with a high S / N ratio can be provided.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the pattern inspection apparatus of the present invention. The wafer 9 to be inspected is placed on the stage 1 with the surface thereof facing upward. A projection optical system 2 for irradiating the surface of the wafer 9 to be inspected with laser beams having different incident angles and different wavelengths.
The projection optical system 2 includes the above-mentioned wafer 9 to be inspected.
Sets of laser light sources 10A and 10A for irradiating laser beams of different wavelengths on the surfaces of
B, and a scanning optical means 11A located on the optical axes of the two sets of laser light sources 10A and 10B, and finely scanning the laser light on the surface of the wafer 9 to be inspected within a required angle range sandwiching the optical axis. , 11B.

On the other hand, a condensing optical system 3 is arranged immediately above the wafer 9 to be inspected, and a laser intensity monitor optical system 5 and an imaging optical system for the condensing optical system 3 via a beam splitter 4. 6 are arranged optically coupled. The condensing optical system 3 is placed in front of the objective lens 12 for condensing the light reflected from the surface of the wafer 9 to be inspected, and is placed in front of the objective lens 12 to expose the surface of the wafer 9 to be inspected. And a spatial filter 13 that blocks the reflected light from the edge of the circuit pattern. The beam splitter 4 outputs the laser light that has passed through the condensing optical system 3 at a predetermined light quantity ratio.
Divide into two.

The laser intensity monitor optical system 5 includes a first imaging lens 14 placed on the optical axis with respect to one laser beam reflected by the beam splitter 4, and the first imaging lens. A first dichroic mirror 15 arranged after 14 for splitting laser light according to wavelength;
Two light receiving elements 16A, 16 for respectively receiving the two laser beams wavelength-split by the dichroic mirror 15
B and. The first guicroic mirror 1
Reference numeral 5 corresponds to each wavelength of the two laser light sources 10A and 10B, and separates each laser light of these laser light sources 10A and 10B. The image forming optical system 6 also includes a second image forming lens 17 placed on the optical axis similarly for the other laser beam that has passed through the beam splitter 6, and the second image forming lens 17 A second dichroic mirror 18 which is disposed after the beam splitter and splits the laser beam according to the wavelength, and two one-dimensional CCD cameras 19 which respectively receive the two laser beams wavelength-split by the second dichroic mirror 18.
A and 19B are provided. The second guichroic mirror 18 corresponds to the respective wavelengths of the two laser light sources 10A and 10B and splits the laser light of the laser light sources 10A and 10B.

The image forming optical system 6 is connected to an image processing section 7 which processes the outputs of the two one-dimensional CCD cameras 19A and 19B to discriminate defects. Further, based on the outputs of the two light receiving elements 16A and 16B of the laser intensity monitor optical system 5, the respective laser light sources 10A and 10B of the light projecting optical system 2 are provided.
A laser power control unit 8 for controlling the power of is connected.

FIG. 2 is a detailed view showing a configuration relating to one of the laser light sources 10A and 10B constituting the light projecting optical system 2, which is one of the laser light sources 10A. The same applies to the laser light source 10B. Laser light source 10A
The scanning optical means 1 for deflecting the laser emitted from the laser light source 10A within a range of a minute angle to perform scanning.
1A is provided. The scanning optical means 11A is an AO formed of an acousto-optic element such as lead molybdate.
A D (acousto-optic deflector) 20, a driver 21 for applying a high frequency signal whose frequency changes periodically to the AOD 20A, and a ramp wave signal whose frequency changes at a predetermined period and frequency width to the driver 21. It is composed of a function generator 22 for generating and inputting, and a lens 23 placed at a position separated by a focal length on the optical axis of the AOD 20. The driver 21 changes and controls the frequency of the high-frequency signal applied to the AOD based on the ramp wave signal generated by the function generator 22, so that the emission angle of the laser light transmitted through the AOD 20 is changed and deflected and deflected. The laser light is scanned by the lens 23 as telecentric convergent light on the wafer 9 to be inspected, and the rectangular pattern 25 of the wafer 9 to be inspected is scanned.
A scanning area 24 parallel to one side is formed. Standard AO
The scanning angle of D20 is several degrees, and a minute scanning area of about 100 μm × several mm can be formed by using a lens having an appropriate focal length. The deflection angle of the AOD is determined by the frequency of the ramp wave output from the function generator 22, and the frequency (f
s) is set so as to change at several hundred Hz, which is about two orders of magnitude larger than the image capturing period (about several kHz) of the CCD camera of the imaging optical system, and the laser light is scanned at high speed. Such high-speed scanning produces an optical averaging effect and incoherence of laser light, and random luminance fluctuations caused by laser light blur and stage vibration, and speckle noise due to minute irregularities on the wafer surface are generated. Can be reduced.

On the other hand, FIG. 3 is a view of the spatial filter 13 provided in the condensing optical system 3 as seen from the stage 1 side. The spatial filter 13 has an elongated shape, and the objective lens 1 is arranged such that its long side is parallel to the laser irradiation direction 26.
It is placed close to the center line of 2. The function of the spatial filter 13 will be described with reference to FIG. 4 (a),
FIG. 6B is a diagram schematically showing the reflection characteristic at the circuit pattern edge 29 orthogonal to the laser irradiation direction. The incident laser light 27 irradiated at a certain incident angle (α) on the surface of the wafer 9 to be inspected is reflected by both lateral edges of the circuit pattern 29 intersecting the laser light 27, but the edge portion is slightly fine. It is a slope having a certain curvature when viewed visually, and the incident laser light 27 is reflected most strongly in directions 28a and 28b determined by the incident angle (α) and the inclination of the edge portion. Therefore, the specularly reflected light from the lateral edge has a strong directivity, and when viewed two-dimensionally, a certain limited region 30 parallel to the optical axis of the incident laser light 27 as shown in FIG.
Most of it will be reflected. Therefore, as shown in FIG. 3, on the center line of the objective lens 12 of the condensing optical system 3, in other words, on the vertical plane including the optical axis of the incident laser light 27, the spatial filter 13 is parallel to the laser irradiation direction 26. As a result, by providing an elongated light-shielding mask, the reflected light 23 from the lateral edge can be efficiently shielded. On the other hand, the laser light scattered by the defect in the pattern can be received regardless of the light shielding mask.

In order to make full use of the above characteristics, in the present invention,
A laser beam is scanned in parallel with one side of a rectangular pattern forming a main part of a circuit pattern, and the stage 1 is moved at a constant speed in a direction orthogonal to the scanning direction of the laser to inspect the wafer 9 to be inspected.
By mechanically scanning, the inspection that removes the reflected light from the edge is realized. It is considered that the reflected light 28 from the lateral pattern edge portion can be adjusted so as not to enter the opening portion of the objective lens 12 by increasing the incident angle (α) of the laser. This corresponds to having an inclination in the range of 90 degrees, and a part of the lateral edge reflected light 28 is incident on the opening of the objective lens 12. Therefore, without the spatial filter 13, the reflected light 28 from the normal lateral edge cannot be blocked.

FIG. 5 is a block diagram of the laser power controller 8 shown in FIG. The laser power control unit 8
The trigger generator circuit 32 for generating a trigger signal in synchronization with the output signal 36 of the function generator 22 of the projection optical system 2 and the trigger 35 for the output 35 of the light receiving elements 16A and 16B of the laser intensity monitor optical system 5. A peak hold circuit 31 that samples and holds the peak value in one cycle of the trigger signal in synchronization with the trigger signal of the generation circuit 32, and a differential amplifier circuit 33 that detects the difference between the reference voltage 37 and the output of the peak hold circuit 31. A laser driver 34 for controlling the drive currents of the laser light sources 10A and 10B based on the output signal of the differential amplifier circuit 33.

The laser power control method of the laser power control unit 8 will be specifically described with reference to FIG. 9A and 9B show a trigger cycle (pulse output cycle) 38 of the trigger generation circuit 32, that is, a pulse signal associated with one scanning cycle of the AOD 20 in the projection optical system 2 and a line of a one-dimensional CCD camera. It is a figure showing the relation of scan cycle time 39. Since laser scanning is faster by one digit or more than line scanning by a one-dimensional CCD camera, a one-dimensional CCD camera detects an integrated value of scattered light output in a plurality of laser scannings (one digit or more). . On the other hand, in the peak hold circuit 31, the light receiving elements 16A during one laser scanning in synchronization with the trigger pulse,
The output 35 of 16B is sampled by the number of pixels of the one-dimensional CCD camera, and the maximum value (peak value) is detected. Therefore, during the line scan time of the one-dimensional CCD camera, the laser intensity is adjusted so that the output of the differential amplifier circuit 33, which detects the difference between the detected maximum value and the reference value, becomes zero. The maximum value during one line scan of the camera can be controlled to a certain target value. FIG. 6C is a diagram schematically showing a change in detection intensity during the line scan time of the one-dimensional CCD camera. When there is no power control, the detection intensity increases in proportion to the exposure time, and when the scattered light intensity is high, the detected value reaches the saturation level 40, while when the scattered light intensity is low, sufficient detection is possible for determination. The strength cannot be obtained. On the other hand, if the above-described power control is performed, the maximum value of any line scan can be controlled to a certain reference level 41 regardless of the scattered light intensity.

Next, the features of the power control according to the present invention will be described in detail with reference to the output image of the one-dimensional CCD camera. FIG. 7 is a schematic diagram for explaining the effect of power control in a portion where the scattering intensity from the original pattern is large. FIG. 10A shows a state where saturation occurs when there is no power control. Even if there is a defect in the saturated portion, it cannot be detected because the difference from the non-defective product cannot be detected. The figure (b) has shown the case where power control is performed to the same location as the figure (a). One-dimensional CCD
Reference level 4 with the maximum value in the detection area of the camera
Since it is controlled to be 1, the entire intensity distribution can be accurately grasped. If the defect 42 exists in this detection area, the defect location has the maximum intensity, and the detected value shows the intensity distribution as shown in FIG.

A determination method of the image processing unit based on the signal obtained by this power control will be described. As described above, the data frame for each line captured by the one-dimensional CCD camera is converted so that the maximum value becomes the reference level. Therefore, if data for each line is similarly obtained for the reference product and the inspected product by the CCD camera and then the ratio between the corresponding pixels for these data is obtained, the normal portion becomes a certain value. , Different values can be obtained only in the defective part. Explaining with reference to FIG. 7, normal portions a0 and b
The ratio of the detected intensities of 0 and a1, b1 is I
Although it is 1 / I0, which is smaller than 1, the ratio between the defective portions c0 and c1 is larger than 1. Therefore, it is possible to determine the defective portion by taking a ratio between the measured product and the non-defective product and examining the deviation from the average value. In addition, in the projection optical system 2, 2
By irradiating two laser beams, it is possible to detect defect locations that are difficult to appear with one laser beam. Furthermore, two laser beams are used to detect the defect detection intensity and the difference in position, thereby improving the defect detection accuracy. It is possible to improve, and the criterion for comparison in the present invention is either the adjacent chip or the master data.

As described above, the conventional inspection apparatus uses the Fourier transform filter effective only for the repetitive pattern of the memory cell or the like, whereas the external space for efficiently shielding the edge reflected light of the rectangular pattern. Equipped with a filter, the inspection of irregular circuit patterns has a high S / N ratio.
It becomes possible to carry out in ratio. In addition, by scanning the laser light at high speed within the measurement area, random brightness fluctuations due to laser light blurring, stage vibration, etc. and speckle noise due to minute irregularities on the wafer surface are reduced, and the S / N ratio is reduced. It is possible to further improve. Furthermore, by irradiating two laser beams with different incident angles, the directivity of scattering due to the shape of the defect is detected, and by controlling the intensity of the laser beam in a real-time feed bag, the defect size and By suppressing the intensity fluctuation due to the surface condition of the pattern within the allowable measurement range of the CCD camera, it becomes possible to further improve the S / N ratio.

On the other hand, FIG. 8 is a schematic diagram for explaining the effect of power control in a portion where the scattering intensity from the original pattern is small. FIGS. 9A and 9B show the state of foreign matter detection when power control is not performed. FIG. 9A is a normal sample, and FIG.
Each represents a detected image of a sample having 2. If the size of the defect is small and the change in its intensity is small, it is difficult to detect the difference from the non-defective product, and since the difference from the background noise level is small, it becomes more difficult to discriminate the foreign matter. FIGS. 7C and 7D show the case where power control is performed at the same location. Since the overall intensity level can be increased, the detection intensity of the defect 42 is increased and detection becomes easier. It is considered that when the laser power is increased, the background noise also increases in proportion to it, but the effect does not appear unless the scattered light enters the objective lens, and as a result, the S / N ratio is improved. Is planned.

In the present invention, it is also possible to adopt a configuration in which lasers of two wavelengths are made incident by changing their respective incident angles. That is, in the case of the above-described embodiment, the rotation moving mechanism may be attached to the two laser light sources, and the tilt angle of each laser light source can be changed and adjusted by the rotation moving mechanism.
The scattered light from the defect has a great change in the directivity of reflection depending on the shape and surface condition. Therefore, in order to reliably capture the scattered light from a small defect, it is necessary to use a condensing lens having a large solid angle (high NA) or to provide a plurality of detectors in various directions. Furthermore, if the directivity of scattering can be evaluated based on the measurement data at multiple locations,
It is possible to more accurately identify and classify defects. By irradiating two laser beams having different wavelengths at different incident angles in this way, the same effect as installing two detectors in different directions can be obtained. By performing a directivity analysis such as obtaining a ratio or a difference, it is possible to improve defect discrimination accuracy and classification accuracy.

In addition to the projection optical system 2 (referred to as 2A) shown in FIG. 1, FIG. 9 further enables detection of various defects.
It is the figure which showed another Example which provided the other set of projection optical system 2B in the direction orthogonal to the above projection optical system 2A. The figure shows the configuration of the inspection apparatus shown in FIG. 1 as seen from above, and another set of projection optical systems 2B is added to the position on the front side of the inspection stage 1. The structure of the projection optical system 2B is the same as that of the projection optical system 2A, and the scanning width of the laser light is also the same. Further, in this case, as shown in FIG. 10, in order to cut the specular reflection light from the circuit pattern edge orthogonal to the incident directions 26A and 26B of the projection optical systems 2A and 2B, respectively, as shown in FIG. Instead of the one-direction light-shielding mask 13 shown, a light-shielding mask 27 having a cross mark shape is arranged close to the objective lens 12. In this way, by installing the two projection optical systems 2A and 2B so as to be orthogonal to each other, in addition to the change of the reflection directivity by the operation of the incident angle, the change of the reflection directivity by the operation of the incident surface is brought about. The defect detection accuracy and the classification accuracy can be improved.

[0028]

As described above, the pattern inspection apparatus of the present invention includes an external spatial filter that efficiently shields the edge reflected light of a rectangular pattern, and a laser micro-scanning optical system for reducing speckle noise. , A plurality of laser incident optical system for detecting the scattering directivity of the defect, and a dynamic laser power control means for the fluctuation of the detection intensity due to the size and shape of the defect, and using this pattern inspection device On the other hand, by minutely scanning the laser light, blocking the reflected light at the pattern edge by the spatial filter, and executing the pattern inspection method of the present invention for inspecting the pattern defect while controlling the laser power, logic etc. There is an effect that a defect on an irregular circuit pattern can be detected with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a semiconductor wafer inspection apparatus of the present invention.

FIG. 2 is a configuration diagram of a projection optical system.

FIG. 3 is a schematic diagram of a spatial filter.

FIG. 4 is a diagram schematically showing reflection characteristics at a circuit pattern edge orthogonal to the laser irradiation direction.

FIG. 5 is a diagram showing a configuration of a laser power control unit.

FIG. 6 shows the pulse output cycle of the trigger generation circuit and one-dimensional CC
It is a figure showing the relation of the line scan cycle of a D camera.

FIG. 7 is a schematic diagram for explaining the effect of power control in a portion where the scattering intensity from the original pattern is large.

FIG. 8 is a schematic diagram for explaining the effect of power control in a portion where the scattering intensity from the original pattern is small.

FIG. 9 is a schematic view showing another embodiment of the present invention.

FIG. 10 is a diagram showing an outline of a mask in an embodiment including two projection optical systems.

FIG. 11 is a schematic diagram of an optical inspection device using a conventional Fourier transform filter.

[Explanation of symbols]

1 stage 2 Projection optical system 3 Focusing optical system 4 beam splitter 5 Laser intensity monitor optical system 6 Imaging optical system 7 Image processing unit 8 Laser power controller 9 Inspected wafer 10A, 10B laser light source 11A, 11B scanning optical means 12 Objective lens 13 Spatial filter 14 First imaging lens 15 First dichroic mirror 16A, 16B light receiving element 17 Second imaging lens 18 Second dichroic mirror 19A, 19B One-dimensional CCD camera 20 AOD (acousto-optic deflector) 21 driver 22 Function Generator 31 Peak hold circuit 32 Trigger generation circuit 33 Differential amplifier circuit 34 Laser driver

Claims (10)

[Claims] 1. A surface of an object to be inspected, which has an irregular pattern such as a logic circuit pattern, is irradiated with laser light having different wavelengths at different incident angles, and the laser light is minute on the surface of the object to be inspected. A step of scanning,
A step of receiving scattered light of the laser light while blocking the reflected light of the laser light on the surface of the object to be inspected, and branching the laser light focused by the focusing optical system A step of controlling the laser intensity of the laser light emitted from the projection optical system based on one laser light, and an image of the surface of the inspected object based on the other branched laser light, and an image output. And a step of performing defect determination based on the pattern inspection method. 2. The pattern inspection according to claim 1, wherein the minute scanning of the laser beam with respect to the inspected object is performed in parallel with one side of a rectangular pattern forming a main part of the irregular pattern. Method. 3. The pattern inspection method according to claim 1, wherein the inspection object is moved at a constant speed in a direction orthogonal to the scanning direction of the laser light. 4. A surface of an object to be inspected having an irregular pattern such as a logic circuit pattern is irradiated with laser light of different wavelengths at different incident angles, and the laser light is minute on the surface of the object to be inspected. A light projecting optical system for scanning, a condensing optical system that shields the reflected light of the laser light on the surface of the object to be inspected and receives scattered light of the laser light, and a condensing optical system. Laser beam splitting unit for splitting the split laser beam, laser intensity control unit for controlling the laser intensity of the laser beam emitted from the projection optical system based on one split laser beam, and the other split And a defect discriminating means for discriminating a defect on the basis of the image pickup output. 5. The projection optical system includes two laser light sources which irradiate the wafer to be inspected at different incident angles and have different wavelengths, and the laser light located on the optical axes of the two laser light sources. Scanning optical means for finely scanning the surface of the wafer to be inspected, the condensing optical system includes an objective lens for receiving scattered light from the surface of the object to be inspected, and a front portion of the objective lens. And a spatial filter that blocks the reflected light from the pattern edge of the object to be inspected, and the laser beam splitting unit splits the laser beam that has passed through the focusing optical system into two at a predetermined light amount ratio. A first dichroic mirror for splitting one of the two laser beams split by the beam splitter into a wavelength of the laser beam; Two light receiving elements for respectively receiving the two laser beams wavelength-dispersed by the dichroic mirror, and a laser power control section for controlling the laser power of the two laser light sources based on the outputs of these light receiving elements. , The defect discriminating means uses the beam splitter 2
A second dichroic mirror for splitting the other laser beam split into two into the wavelength of the laser beam, and two laser beams for wavelength-splitting by the second dichroic mirror are respectively received and imaged. The pattern inspection apparatus according to claim 4, further comprising: a CCD camera; and an image processing unit that processes an image pickup output of the CCD camera to determine a defect. 6. The scanning optical means in the projection optical system is a minute high-speed scanning by an acousto-optic deflector (hereinafter referred to as AOD) or the like, and the scanning cycle is an image of a one-dimensional CCD camera of the imaging optical system. The pattern inspection device according to claim 5, wherein the pattern inspection device is at least one digit shorter than the acquisition period. 7. The spatial filter of the condensing optical system is an elongated light-shielding mask installed close to the objective lens, and the long side thereof is parallel to the irradiation direction of the laser light. The pattern inspection apparatus according to claim 5 or 6, wherein the pattern inspection apparatus is arranged on a center line of the objective lens. 8. A projection optical system is provided in addition to the projection optical system, and the irradiation directions of these two projection optical systems are orthogonal to each other. The pattern inspection apparatus according to any one of claims. 9. The two projection optical systems are arranged at positions orthogonal to each other on the center line of the objective lens, and the shape of the spatial filter is a cross mark so as to be parallel to the laser irradiation direction of each projection optical system. The pattern inspection apparatus according to claim 8, which has a shape of. 10. The laser light source of each of the projection optical systems includes a rotary movement mechanism capable of changing and adjusting an incident angle around a reference point on the surface of the object to be inspected. 9. The pattern inspection apparatus according to any one of 1 to 9.