JP3185878B2 - Optical inspection equipment - Google Patents

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 product such as a substrate having a regularly repeated pattern formed on its surface, for example, a defect of a semiconductor wafer, and more particularly to an optical inspection apparatus utilizing a dark field optical inspection technique. About.

[0002]

2. Description of the Related Art In recent years, high integration of semiconductor devices has been remarkable, and accordingly, it is required that a pattern formed on a surface of a semiconductor wafer used for this semiconductor device is extremely fine. Further, if a defect due to the attachment of a foreign substance or the like occurs on the surface of a semiconductor wafer on which a fine pattern is formed, the semiconductor wafer cannot be used as a highly integrated semiconductor device. Therefore, an optical inspection for a defect on the surface of the semiconductor wafer is performed. .

As an optical inspection method, a method is employed in which a surface to be inspected is irradiated with a light beam, the reflected light is received by a photodetector, and the presence or absence of a defect is inspected based on the result. However, at this time, if the scattered light affected by the defect and the diffracted light from the pattern formed on the surface are mixed, the inspection may be complicated. Therefore, a device is used in which a diffracted light from a pattern is blocked by using a spatial filter, and only normal reflected light from a surface other than the pattern and scattered light affected by a foreign substance or a defect are incident on an optical inspection device. I have.
Usually, the pattern formed on the surface of the semiconductor wafer is often a regular repetitive pattern, and the diffracted light from the pattern has directivity, so that it can be easily cut off by a spatial filter.

[0004]

Problems to be Solved by the Invention
The basic configuration of the optical inspection apparatus disclosed in Japanese Patent Publication No. 4 and Japanese Patent Publication No. Hei 7-503793 is, as schematically shown in FIG. 7, composed of an objective lens 23 directed to an inspection target 30 such as a semiconductor wafer. A Fourier transform optical system 27 provided downstream of the objective lens 23, a spatial filter 22 disposed in the Fourier transform optical system 27, and a magnifying optical system 2.
4, a photodetector 25, and a computer 26 for analyzing the detection result of the photodetector 25. The diffracted light by the pattern 30a to be inspected is blocked by the blocking unit 22a of the spatial filter 22 in the Fourier transform optical system 27. As described above, the conventional optical inspection device requires the magnifying optical system 24 and the Fourier transform optical system 27,
This leads to an increase in the size of the entire inspection apparatus. In addition, an increase in the number of optical components causes a decrease in light quantity, which leads to a prolonged inspection time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a structure capable of satisfactorily blocking diffracted light from a repetitive pattern without using a complicated additional optical system such as a Fourier transform optical system. An object of the present invention is to provide an optical inspection device that can be implemented.

[0006]

An optical inspection apparatus according to the present invention comprises: a light source for irradiating a light beam on an inspection surface of an object to be inspected on which a repetitive pattern is formed; An inspection unit that detects scattered light due to a defect incident via an objective lens when is irradiated, and is disposed between the object to be inspected and the objective lens,
And a spatial filter for blocking diffracted light from the repetitive pattern so as not to enter the said checking means, said space Fi
A magnifying optical system is provided between the filter and the inspection unit.
You.

It is preferable that the inspection section includes a photodetector for receiving the scattered light, and a computer for judging the presence or absence of a defect on the inspection surface based on a detection result of the photodetector.

[0008] The objective lens may be a part of a magnifying optical system provided between the spatial filter and the inspection section.

According to such a configuration, the spatial filter is arranged at a stage before the objective lens (between the object to be inspected and the objective lens), and here, the diffracted light due to the repetitive pattern is blocked. Therefore, there is no need to provide a Fourier transform optical system after the objective lens.

It is preferable that a cross-sectional area of the light beam is equal to or less than 10% of an aperture area of the objective lens. In this case, the area of the opaque region (the part that blocks the diffracted light) of the spatial filter can be kept small, and most of the space filter can be made a transparent region, so that scattered light due to defects can be easily captured and inspection accuracy can be improved.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of this embodiment. This optical inspection apparatus includes a light source 1, a spatial filter 2, an expansion optical system 4 including an objective lens 3, an inspection unit 7 including a photodetector 5 and a computer 6, and a multi-division photodiode 8. Have been. The light source 1 can irradiate a light beam (monochrome light beam) M from an oblique direction to an inspection surface of an inspection target 10 such as a semiconductor wafer placed on a stage 9. As shown schematically in FIG. 2, the inspection surface of the inspection target 10 has a substantially rectangular rectangular pattern 1.
This is a surface on which a regular repeating pattern 10a whose main part is 0b is formed.

The spatial filter 2 is interposed between the inspection surface of the object 10 to be inspected and the objective lens 3 and has a transmitting portion (transparent region) 2a capable of transmitting the monochrome light beam M and a blocking portion for blocking the same. (Opaque area) 2b. Specifically, a blocking part 2b is formed corresponding to the repetitive pattern 10a on the inspection surface of the inspection target 10, and is provided so as to block the diffracted light by the repetitive pattern 10a.

The magnifying optical system 4 includes the objective lens 3 and is movable in the horizontal direction relatively to the stage 9 on which the inspection object 10 is placed. The photodetector 5 detects the light beam transmitted through the transmitting portion 2a of the spatial filter 2 and expanded by the magnifying optical system 4, and transmits the result to the computer 6. The multi-segment photodiode 8 receives the reflected light (zero-order diffracted light) of the monochrome light beam M from the inspection surface, and transmits the result to the computer 6. The computer 6 includes a light detector 5
Is analyzed to determine the presence or absence of a defect on the inspection surface of the inspection target 10, and the detection result of the multi-segment photodiode 8 is analyzed to analyze the magnification optical system 4 and the inspection target 10.
Is controlled with respect to the stage 9 where is placed.

An inspection method using this optical inspection apparatus will be described.

First, an object to be inspected 10 such as a semiconductor wafer
Is placed on the stage 9 such that the inspection surface (the surface on which a regular repeating pattern is formed) faces the spatial filter 2. Then, the light source 1 irradiates a monochrome light beam M which is a parallel light beam to the inspection surface. When the inspection surface of the inspection target 10 is irradiated with monochrome light, the specular reflection light and the pattern 1
Diffracted light due to 0a is generated on the inspection surface, and in some cases, scattered light is generated due to some defect 10c present on the inspection surface.

As shown in FIG.
The ordinary reflected light (0th-order diffracted light) from the portion other than the portion a is reflected at an angle corresponding to the incident angle obliquely incident from the light source 1, and is incident on the multi-segment photodiode 8, and the spatial filter 2 and the objective lens 3. And does not enter the magnifying optical system 4 and the photodetector 5. Therefore,
Light reflected by the portion other than the repetitive pattern 10 a (zero-order diffracted light) is not detected by the light detection unit 5.

On the other hand, when there is any defect 10c on the inspection surface, as shown in FIG. 3, light scattered by the defect 10c is generated from the inspection surface. Since the scattered light is omnidirectional and spreads in various directions, a part of the scattered light is incident on the spatial filter 2 and is transmitted through the transmission part 2 a to be incident on the magnifying optical system 4 from the objective lens 3. The scattered light transmitted through the magnifying optical system 4 is detected by the photodetector 5.

Further, the light source 1 generates a repetitive pattern 10a.
When the monochrome light beam M is irradiated on the upper side, the pattern 1
The light diffracted by Oa spreads in a lattice shape, and a part of the light enters the spatial filter 2. However, as schematically shown in FIG. 4, the blocking portion 2b provided in the spatial filter 2 blocks the diffracted light, so that the diffracted light does not pass in the direction of the objective lens 3 and the magnifying optical system 4 And does not enter the photodetector 5. Specifically, the spatial filter 2 is provided with a blocking portion 2b by applying a light-blocking paint to a position corresponding to a lattice point of diffracted light spreading in a lattice shape.

As a result, what is detected by the photodetector 5 through the magnifying optical system 4 is that any defect 10c
Is only the scattered light due to the defect 10c when exists.
Then, the computer 6 analyzes the data of the photodetector 5 and detects the presence of scattered light.
It can be seen that a defect 10c due to a foreign matter or the like exists on the inspection surface of FIG.

FIGS. 3 and 4 schematically show only a part of the scattered light and the diffracted light for easy understanding in the drawings.

Note that the computer 6 is configured to
By moving the stage 9 on which is placed in the horizontal direction, the inspection area is scanned on the inspection surface of the inspection target 10, and the defect is detected over the entire surface of the inspection target 10. That is, when the stage 9 moves in the horizontal direction, the irradiation area of the monochrome light beam from the light source 1 is scanned, and the range where the light enters the photodetector 5 via the spatial filter 2 and the magnifying optical system 4 moves. In addition, the spatial filter 2, the light source 1,
The magnifying optical system 4 including the objective lens 3, the photodetector 5 of the inspection unit 7, and the multi-segment optical sensor 8 can be integrally moved in the vertical direction in FIG. The distance between the inspection target 10 and the inspection surface changes.

As shown in FIG. 1, a multi-segmented photodiode 8 receives the reflected light (zero-order diffracted light) of the monochrome light beam M from the inspection surface, and the computer 6 controls the inside of the magnifying optical system 4 based on the difference output. Focus adjustment is automatically performed by adjusting the position of a lens group including the objective lens 3 (not shown except for the objective lens 3).

[Example 1] A specific example of the above-described embodiment will now be described.

In the first embodiment, the object to be inspected is a semiconductor wafer 1 on which memory chips of 16 mega DRAMs are arranged.
The magnifying optical system 4 is an optical system including the objective lens 3 having a long working distance of 16.5 mm and a large aperture of 24 mm, and the light source 1 has a diameter of 0.6.
The spatial filter 2 is a laser oscillator that emits a millimeter HeNe laser beam (monochrome light beam M). The spatial filter 2 is provided with an opaque region 2 b so as to block only light diffracted from the repetitive pattern 10 a of the semiconductor wafer 10. The area 2a is transparent.

In this embodiment, the surface of the semiconductor wafer 10 is irradiated with a HeNe laser from the light source 1, and the light diffracted by the pattern 10 a and the light scattered by the defect 10 c are made incident on the spatial filter 2. Note that ordinary reflected light (0th-order diffracted light) from a portion other than the pattern is reflected by the multi-division photodiode 8
, And does not enter the spatial filter 2. Diffracted light by the pattern 10a that has entered the spatial filter 2 is blocked by the opaque region 2b. Only the light scattered by the defect 10c passes through the transparent area 2a of the spatial filter 2,
It is taken into the magnifying optical system 4 from the objective lens 3. This scattered light is expanded by the expansion optical system 4, captured by the light detector 5, and detected by the computer 6.
Thus, when light is detected by the photodetector 5, the defect 10c that causes scattered light is regarded as existing on the surface of the semiconductor wafer 10, and the computer 6 determines that the semiconductor wafer 10 is a defective product having the defect 10c. It is determined that there is.

The computer 6 moves the stage 9 on which the semiconductor wafer 10 is placed in the horizontal direction with respect to the magnifying optical system 4 and scans the irradiation area of the monochrome light beam M, while scanning the surface of the semiconductor wafer 10 as described above. Defect detection is performed over the entire surface. In particular, the monochrome ray M
Scanning is preferably performed in parallel or perpendicular to one side of the rectangular pattern 10b forming the main part of the repetitive pattern 10a shown in FIG.

In this embodiment, an 8-inch semiconductor wafer 1
The defect detection of the entire surface of No. 0 could be performed at high speed in a short time of 3 minutes. Further, in this embodiment, a defect having a diameter of about 0.25 μm could be detected with a detection rate of about 95%. The multi-segment photodiode 8 receives the reflected light (0th-order diffracted light) of the monochrome light beam from the inspection surface, and the computer 6 automatically adjusts the focus of the magnifying optical system 4 based on the difference output.

As the light source 1, a photodiode, a photomultiplier, a CCD array, a TDI sensor, a CMOS image sensor, or the like can be used.

Next, a method of manufacturing the spatial filter 2 of the present embodiment will be described with reference to FIG. The spatial filter 2 of the present embodiment is formed by printing an opaque area on a transparent sheet.

A semi-transparent screen 12 having a light diffusing function is arranged at the same position where the spatial filter 2 is arranged when the semiconductor wafer 10 is inspected, and the semiconductor wafer to be inspected is placed on the screen 12. The repetitive pattern 10a formed on 10 (non-defective non-defective product) is projected. The projected view of the diffracted light from the repetitive pattern 10a is taken into the CCD image sensor 15 via the magnifying optical system 14 including the objective lens 13 having a magnification of 1 which is lower than the objective lens used for inspection. After adjusting the contrast, magnification, and the like of the diffraction pattern of the diffracted light obtained in this way by image processing of the computer 16, the area where the lattice points of the diffracted light spread in a lattice pattern are projected becomes opaque, and the other parts are opaque. The spatial filter 2 is formed by performing printing on a transparent sheet using a printing machine by setting the filter to be transparent. In the drawings, the diffracted light from the repetitive pattern 10a and the diffracted light are
The scattered light scattered by 2 is schematically shown by one line, but actually spreads in various directions.

The spatial filter 2 thus formed
Can reduce the area of the opaque region 2b to 10% or less of the area of the transparent region 2a. Therefore, when an optical inspection of the semiconductor wafer 10 is performed using the spatial filter 2,
The possibility that most of the scattered light from the defect of the semiconductor wafer 10 passes through the transparent area 2a and enters the magnifying optical system 4 and is captured by the photodetector 5, and the scattered light is blocked by the spatial filter 2 and not detected. Extremely low. Then, since the diffracted light due to the repetitive pattern 10a is blocked and only the scattered light due to the defect is incident on the photodetector 5, the diffracted light and the scattered light are not confused at the time of detection, and the noise is small (signal-to-noise ratio). Accurate) easy to perform accurate recognition. Therefore, as described above, a defect having a diameter of about 0.25 μm can be detected with a detection rate of about 95%.

To supplement this point, in this embodiment, a thin HeNe laser beam having a diameter of 0.6 mm, which is 1/10 or less of that of the objective lens 3 having an opening surface having a large diameter of 24 mm, is used. Is effective for improving the inspection accuracy. In the configuration of the present embodiment, the spatial filter is arranged in front of the objective lens 3 (between the object 10 to be inspected and the objective lens 3) unlike the related art.
If the diameter of the monochromatic light beam M to be irradiated is large, the diffracted light from the repetitive pattern 10a of the inspection object 10 becomes large, so that the opaque region (light shielding portion) of the spatial filter also
It must be formed as large as the diameter of the monochrome light beam. In some cases, before the diffracted light from the repetitive pattern 10a enters the objective lens 3, the diffracted light from the adjacent rectangular pattern 10b may spread and partially overlap. Conventionally, the objective lens 3
There is no idea to block this diffracted light by providing a spatial filter in front of. Further, if a spatial filter is provided in front of the objective lens 3, the opaque area occupies most of the spatial filter and becomes dark.
It becomes difficult to sufficiently capture the scattered light from the defect to be inspected. Conventionally, as shown in FIG. 7, a Fourier transform optical system 27 is provided after the objective lens 23 in addition to the magnifying optical system 24, and the spatial filter 22 is provided in the Fourier transform optical system 27, so that a repetitive pattern is obtained. It tries to block the diffracted light.

On the other hand, in the present embodiment, since the thin monochrome light beam M (HeNe laser beam) of 1/10 or less of the objective lens 3 is used, the repetitive pattern 10
Since the diffracted light from a can be cut off by the spatial filter 2 in a relatively small state, the area of the opaque region 2b of the spatial filter 2 is 1
It was able to be less than a percent. Therefore, a large part of the spatial filter 2 is occupied by the transparent region 2a, is bright, and can sufficiently capture scattered light from a defect of the inspection object 10. Then, since the diffracted light due to the pattern is blocked at a stage before the objective lens 3, the scattered light due to the defect can be detected without providing a Fourier transform optical system. Note that the transmission part 2a of the spatial filter 2 may be a gap.

[Embodiment 2] In this embodiment, a light source 11 for irradiating two HeNe lasers as monochrome light beams M is used.
And irradiating it orthogonally to the semiconductor wafer 10,
The scattered light from a defect on the semiconductor wafer 10 is taken into the magnifying optical system 4 from the objective lens 3 via the spatial filter 2. Then, the light detector 5 and the computer 6 detect scattered light from the defect.

According to the present embodiment, the defect detection on the entire surface of the 8-inch semiconductor wafer 10 can be performed at high speed in a short time of 2 minutes and 30 seconds by using two HeNe lasers. In this example, a defect having a diameter of about 0.25 μm could be detected with a detection rate of about 98%. As described above, by using two HeNe lasers, the inspection can be performed at higher speed and with higher accuracy. Other configurations are the same as those of the first embodiment.

[0037]

According to the optical inspection apparatus of the present invention, it is possible to reduce the size of a diffracted light from a repetitive pattern without using a complicated additional optical system such as a Fourier transform optical system as in the prior art. With a low-cost configuration, a defect to be inspected can be quickly and accurately detected.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical inspection device of the present invention.

FIG. 2 is a plan view schematically showing an object to be inspected.

FIG. 3 is a schematic diagram showing a scattered light detection state by the optical inspection device of the present invention.

FIG. 4 is a schematic view showing a state in which diffracted light is blocked by the optical inspection device of the present invention.

FIG. 5 is a schematic view showing a part of a method for manufacturing a spatial filter of the optical inspection apparatus of the present invention.

FIG. 6 is a schematic view showing another embodiment of the optical inspection apparatus of the present invention.

FIG. 7 is a schematic diagram showing a conventional optical inspection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Spatial filter 2a Transparent area (transmission part) 2b Opaque area (blocking part) 3 Objective lens 4 Magnification optical mechanism 5 Photodetector 6 Computer 7 Inspection part 8 Multi-division photodiode 9 Stage 10 Semiconductor wafer (Object to be inspected) 10a Repetitive pattern 10b Rectangular pattern 10c Defect 11 Light source 12 Screen 13 Objective lens 14 Magnifying optical system 15 CCD image sensor 16 Computer M Monochrome light beam

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 21/84-21/958 G01B 11/00-11/30

Claims (17)

(57) [Claims] 1. A light source for irradiating a light beam on an inspection surface of a test object on which a repetitive pattern is formed, and a light beam incident on a defect existing on the inspection surface through an objective lens. Yes an inspection unit for detecting the light scattered by defects, the is disposed between the inspection object the objective lens, a spatial filter for blocking diffracted light from the repetitive pattern so as not to enter the said inspection means A magnifying optical system is provided between the spatial filter and the inspection unit.
Vignetting in which optical inspection apparatus. 2. The inspection apparatus according to claim 1, wherein the inspection unit includes a photodetector that receives the scattered light, and a computer that determines presence or absence of a defect on the inspection surface based on a detection result of the photodetector. An optical inspection device as described. Wherein the objective lens is an optical inspection apparatus according to claim 1 or 2 forming part of the expanding optical system is provided between the spatial filter and the inspection unit. 4. The optical inspection apparatus according to claim 1, wherein the light beam is a monochrome light beam. 5. The light beam according to claim 1, wherein the light beam is a parallel light beam.
The optical inspection device according to any one of claims 1 to 4. 6. The optical inspection apparatus according to claim 1, wherein the light beam is applied obliquely to the inspection surface. 7. The optical inspection apparatus according to claim 1, wherein a cross-sectional area of the light beam is equal to or less than 10% of an opening area of the objective lens. 8. The method according to claim 1, wherein the light beam is a laser beam.
The optical inspection device according to any one of claims 1 to 7. 9. The optical inspection apparatus according to claim 1, wherein two light beams are irradiated on the inspection surface. 10. The optical inspection apparatus according to claim 1, wherein the light beam is scanned parallel or perpendicular to one side of a rectangular pattern forming a main part of the repetitive pattern. 11. The photodetector according to claim 1, wherein the photodetector is a photodiode, a photomultiplier tube, a CCD array, a TDI sensor, or a CMOS image sensor having a built-in image processing function circuit. An optical inspection device according to item 1. 12. The spatial filter is formed by performing image processing on a projection obtained by irradiating the inspection object with the light beam and projecting diffracted light by the repetitive pattern onto a screen. 12. The optical detection device according to any one of items 11 to 11. 13. The objective lens according to claim 1, wherein the objective lens is arranged so that an optical axis thereof is perpendicular to the inspection surface.
The optical inspection device according to any one of claims 1 to 4. 14. A multi-segment optical sensor for receiving light reflected by the inspection surface of the light beam, wherein the inspection unit transmits the scattered light to the inspection unit based on a differential output of the multi-segment optical sensor. The optical inspection apparatus according to claim 1, wherein focus adjustment of irradiation is performed. 15. An optical system including the spatial filter, the light source, the objective lens, and a photodetector of the inspection unit are integrally movable so as to change a distance from the inspection surface. An optical inspection apparatus according to any one of claims 1 to 13. 16. An optical system including the spatial filter, the light source, the objective lens, the photodetector of the inspection unit, and the multi-segment optical sensor, wherein a distance between the inspection surface and the multi-split optical sensor changes. 15. The optical inspection apparatus according to claim 14, wherein the optical inspection apparatus can be integrally moved. 17. The optical inspection apparatus according to claim 1, wherein a portion of the spatial filter that transmits the reflected light is a gap.