JPH06186168A - Method and apparatus for inspecting defect - Google Patents

Abstract

PURPOSE:To identify whether a defect on a reticle R is a foreign matter or a damage. CONSTITUTION:A laser beam La passed through a circular opening 1a and a reticle are relatively scanned, and a peak value of levels of photoelectric signals to be obtained from photoelectric detectors 13, 14 is detected as first defect information (first inspection). Then, a laser beam Lb passed through a circular opening 2b of an aperture diameter different from that of the opening 2a and the reticle R are relatively scanned, and a peak value of levels of photoelectric signals to be obtained from photoelectric detectors 13, 14 is detected as second defect information (second inspection). A ratio of the peak values of the signals to be obtained by the first and second inspections is compared with a ratio of beam diameters of the beams La, Lb on the reticle R to decide whether a defect on the reticle R is a foreign matter or a damage.

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 minute defect on a substrate, and more particularly to an apparatus for inspecting a defect state on a substrate such as a photomask, a reticle, a semiconductor wafer used in the manufacturing process of an integrated circuit. It is a thing.

[0002]

2. Description of the Related Art In a lithography process, which is one of manufacturing processes of integrated circuits, a circuit pattern of a mask (reticle) is transferred to a photoresist coated on a substrate such as a semiconductor wafer. At this time, if the reticle has a defect, that is, if foreign matter such as dust is attached to the surface of the reticle or if the surface is scratched, the image of the foreign matter or scratch is transferred to the semiconductor wafer. . As a result, it appears as a defect in the circuit pattern transferred onto the wafer, which causes a reduction in manufacturing yield. Therefore,
It is necessary to inspect the state of defects on the surface of the reticle before transferring.

The scratches on the reticle referred to here are, for example, scratches caused by contact between an obstacle and the surface of the reticle during transportation of the reticle, or by some cause. It may be like a crack on the reticle. Hereinafter, the defects generated on the surface of the reticle itself as described above will be collectively referred to as “scratches”.

A method for inspecting such defects, especially foreign matter attached to the reticle, is disclosed in Japanese Patent Publication No. 63-64738 filed by the same applicant as the present application. This is to detect the position and the size of the foreign matter by conducting a laser beam focusing on the reticle for scanning and photoelectrically detecting the reflected light (scattered light) from the foreign matter.

[0005]

By the way, when a foreign substance adheres to the reticle, the foreign substance can be removed by washing the reticle or blowing clean air (air blow). However, if the reticle is scratched, the scratch cannot be removed. Therefore, whether or not the reticle is a scratch that causes a defect in the circuit pattern transferred to the semiconductor wafer, that is, the reticle is used in the lithography process. It is necessary to judge whether or not it can be used.

However, in the conventional defect inspection apparatus as described above, only the foreign matter is targeted as the defect on the reticle, and for example, even if the reticle is scratched, it is detected as the foreign matter. That is, it was not possible to determine whether the defect on the reticle was a foreign substance attached to the reticle or a scratch on the reticle itself. Therefore, after cleaning the reticle once, perform a defect inspection again,
Alternatively, unless the surface of the reticle was observed with a microscope, it was impossible to determine whether the defect was a foreign substance or a scratch.

The present invention has been made in view of the conventional problems as described above. Whether the defect on the reticle is due to the adhesion of foreign matter, that is, the foreign matter adhered on the reticle and the scratches on the reticle It is an object of the present invention to provide a defect inspection method and apparatus capable of discriminating a defect.

[0008]

In order to make the present invention easier to understand, the present invention will be described with reference to FIGS. 1 and 2 which are one embodiment. In order to solve such problems, the present invention provides
The laser beam L is irradiated onto the surface of the object (reticle) R to be inspected, and the scattered light l ₁ , l ₂ generated from the surface of the reticle R when the reticle R and the laser beam L are relatively scanned is detected by the photoelectric detector 13. , 14 in the defect inspection method for inspecting the defect state on the surface of the reticle R, the light passes through the circular opening 2a, and the first state on the surface of the reticle R is detected.
The first inspection for detecting the first defect information Ia, Ib corresponding to the magnitude of the photoelectric signal obtained from the photoelectric detectors 13, 14 when the reticle R and the laser beam L having the beam diameter of The laser beam L that passes through the process and the circular opening 2b and has the second beam diameter on the surface of the reticle R.
And the reticle R are scanned relative to each other, the photoelectric detector 1
2nd corresponding to the magnitude of the photoelectric signal obtained from 3 and 14
Second inspection step for detecting defect information Ia ′, Ib ′ of
Based on the first and second defect information, a determination step of determining whether or not the defect on the reticle R is a foreign substance attached to the reticle R is included.

Further, in the defect inspection apparatus of the present invention,
Corresponding to the magnitude of photoelectric signals output from the photoelectric detectors 13 and 14 when the reticle R and the laser beam L are relatively scanned, and the shading plate 2 that makes the beam diameter of the laser beam L on the reticle R variable. The storage member 31 that stores the defect information Ia and Ib described above and the storage member 31 when the reticle R and the laser beam L are relatively scanned under the first beam diameter set by the light shield plate 2. Output from the photoelectric detectors (13, 14) when the reticle R and the laser beam L are relatively scanned under the first defect information and the second beam diameter different from the first beam diameter. Second defect information Ia ′, Ib ′ corresponding to the magnitude of the photoelectric signal
The determination member 32 that determines whether or not the defect on the reticle R is a foreign substance attached to the reticle R based on
And decided to prepare.

[0010]

According to the present invention, when the beam diameter (irradiation area of the light beam) of the light beam irradiated on the surface of the object to be inspected is changed, the intensity change of the scattered light generated from the foreign matter on the surface,
Paying attention to the difference (difference) between the change in the intensity of scattered light caused by the scratch and the difference in the intensity change before and after the change of the beam diameter, the foreign matter and the scratch are distinguished. This will be described below with reference to FIG.

FIG. 5A shows a state in which a light beam 200 having a predetermined beam diameter (irradiation area is 1 mm ² ) is scanned in the direction of the arrow on the surface to be inspected on which the dust A is attached, and from the foreign matter A. It is a figure showing the photoelectric signal 201 obtained when the scattered light is photoelectrically detected. FIG. 5B shows the light beam 2 shown in FIG.
A light beam 203 having a beam diameter larger than 00 (irradiation area is 4 mm ² ) scans the surface to be inspected with the same foreign matter A as in FIG. It is a figure showing the photoelectric signal 204 obtained when the scattered light from is photoelectrically detected. Where the light beams 200 and 2
Assuming that 03 is the same light quantity, the irradiation light quantity (luminance) K ₁ per unit area of the light beam 200 and the light beam 203
Of the luminance of K ₂ is K ₂ / K ₁ = 1/4 (hereinafter, K 2
The value of ₂ / K ₁ is called the reference value). Therefore, the peak value Pa of the photoelectric signal 201 and the peak value P of the photoelectric signal 204
It is clear that the relationship with b is Pb / Pa = 1/4, which is the same as the reference value.

Similarly, FIG. 5C shows a state in which the surface to be inspected with the scratch B is scanned by the same light beam 200 as in FIG. 5A in the direction of the arrow and the scattered light from the scratch B. It is a figure showing the photoelectric signal 202 obtained when photoelectrically detecting. Further, FIG. 5D shows a state in which the same light beam 203 as in FIG. 5B is scanned in the direction of the arrow on the surface to be inspected having the same scratch B as in FIG. 5C and the scratch B. It is a figure showing the photoelectric signal 207 obtained when the scattered light from is photoelectrically detected. As can be seen from the figure, the length of the flaw B irradiated by the light beam is almost doubled by doubling the beam diameter. That is, the flaw detected by the light beam 200 and the flaw detected by the light beam 203 have different sizes. Therefore, the peak value Pd of the photoelectric detection signal 207 and the photoelectric signal 2
The relationship with the peak value Pc of 02 is Pd / Pc> 1/4.

As described above, according to the present invention, the first surface on the surface to be inspected is
Defect information (Pa, Pa obtained by the defect inspection of the inspection object using the light beam (light beam 200) having the beam diameter of
Pc) and the second defect information (Pb, Pd) obtained by the defect inspection of the inspected object using the light beam (light beam 203) having the second beam diameter different from the first beam diameter. (Pb / Pa, Pd / Pc) and the ratio of the first beam diameter to the second beam diameter (light beam 200 and light beam 203).
In the case of (1) and (2), a reference value corresponding to 1/2), that is, the luminance ratio (1/2) ^{2 of the} light beam 200 and the light beam 203 is compared, and the defect is a foreign substance adhered to the inspection surface. It is possible to determine whether or not it is a scratch on the surface to be inspected. Note that the scratch B in FIG. 5 is one linear continuous scratch, but it may be a discontinuous scratch with a series of small scratches, a curved scratch, or a combination of these scratches. However, it is possible to distinguish from a foreign substance by the same action as described above.

[0014]

1 is a perspective view showing a schematic structure of a defect inspection apparatus according to a first embodiment of the present invention. A description will be given below with reference to FIG. In FIG. 1, the reticle R is a mounting table 6
It is placed on top of it with only its periphery supported.
The mounting table 6 is controlled by the motor 7 and the feed screw 8 in XY
It is movable in the Y direction in the Z coordinate system. The amount of movement of the mounting table 6 in the Y direction is measured by the length measuring device (for example, linear encoder) 9. Also, the mounting table 6
Is configured to be movable also in the Z direction by a driving means (not shown).

The laser beam L emitted from the light source LS is an expander 1 composed of lenses 1a and 1b.
2 circular apertures 2
The beam diameter of a predetermined size is adjusted by the light shielding plate 2 provided with a and 2b. The light shielding plate 2 can appropriately position the circular openings 2a and 2b in the optical path of the laser beam L by the motor 3. The laser beam L that has passed through the circular aperture (aperture 2a in FIG. 1) is reflected by a scanning mirror (for example, a galvano mirror or a polygon mirror) 4, is condensed in a spot shape by a condenser lens 5, and is formed on the surface of the reticle R (pattern surface). , Or a glass surface). The laser beam L projected on the reticle R is scanned within a predetermined range in the X direction on the reticle R by the galvanometer mirror 4 and the motor 10 (hereinafter,
This range is referred to as a scanning range XS). Further, a main control system (not shown) (32 in FIG. 2, which will be described later) scans the reticle R with the laser beam L by the galvanometer mirror 4 one-dimensionally, and drives the reticle R on the mounting table 6 with the motor 7 and the feed screw 8. To move in the Y direction. By making the moving speed of the reticle R in the Y direction slower than the moving speed of the laser beam L in the X direction, the laser beam L can be scanned over the entire surface of the reticle R.

Here, with respect to the X coordinate of the scanning position (coordinate point) of the laser beam L on the reticle R, the rotary encoder 1 for detecting the deflection angle of the galvanometer mirror 4.
It can be detected based on the measurement value output by 0A (the measurement value corresponding to the irradiation position of the laser beam L on the reticle R in the X direction). Regarding the Y coordinate, since the incident angle of the laser beam L on the reticle R is constant, the measurement value output by the linear encoder 9 (measurement corresponding to the irradiation position of the laser beam L on the reticle R in the Y direction). Value).

Photoelectric detectors 13 and 14 for detecting scattered light from the reticle R are arranged above the reticle R (Z direction side in FIG. 1). Photoelectric detector 1
Reference numerals 3 and 14 are arranged at positions where the specularly reflected light of the laser beam L from the reticle R and the diffracted light from the circuit pattern are avoided. Condensing lenses 11 and 12 that condense scattered light
Is provided. The optical axes of the condenser lenses 11 and 12 are arranged so as to be oblique with respect to the surface (XY plane) of the reticle R (the incident angle is within a range of 10 ° to 80 °, respectively). Further, they are also arranged so as to be oblique (the azimuth angle is within a range of 15 ° to 80 °) with respect to the beam scanning direction (X-axis direction). Further, the extension lines of the respective optical axes intersect at the scanning center Q of the laser beam L, and the photoelectric detectors 13 and 14 are arranged at positions substantially equidistant from the scanning center Q.

FIG. 2 is a block diagram showing an example of a signal processing circuit for processing photoelectric signals output from the photoelectric detectors 13 and 14 of this embodiment. The configuration will be described below. The output sides of the photoelectric detectors 13 and 14 are amplifiers 21 and 22.
It is connected to one input side of each of the comparators 23 and 24 and the memory 31 via. The other input side of each of the comparators 23 and 24 is connected to the reference voltage generator 30, and the reference voltage generator 30 inputs a predetermined reference voltage to each comparator. The output sides of the comparators 23 and 24 are connected to the input side of a theoretical sum circuit (OR circuit) 25. When the OR circuit 25 receives a signal from at least one of the comparators 23 and 24, the defective signal S is stored in the memory 31.
And to the coordinate calculation unit 35.

Upon receiving the defect signal S from the OR circuit 25, the coordinate calculator 35 measures the position where the defect exists, that is, the coordinate value on the reticle R, based on the output signals from the linear encoder 9 and the rotary encoder 10A. To do. Then, this position information is output to the memory 31 and the drive control system (controller) 34. When the memory 31 receives the defect signal S, the level (voltage value) of the output signals from the amplifiers 21 and 22 corresponds to the position information (coordinate value) on the coordinate system XY output from the coordinate calculator 35. Attach and memorize. The main control system 32 reads out necessary data from the memory 31, determines the type of defect (foreign matter, scratch) and ranks the sizes by a predetermined arithmetic processing, and then displays the arithmetic result on a display unit (CRT). Etc.) to 33. The controller 34 controls the driving of the motors 3, 7, 10 based on the signals from the linear encoder 9 and the rotary encoder 10A and the drive command from the main control system 32.

Next, the circular opening 2 provided in the light shielding plate 2
When a and 2b are inserted in the optical path of the laser beam L,
The characteristics of the laser beams La and Lb with which the reticle R is irradiated will be described. In the present embodiment, the diameter ratio of the circular openings 2a and 2b provided in the light shielding plate 2 is 2: 1. Generally, in a laser beam having the same frequency, the beam diameter of the laser beam incident on the condenser lens and the numerical aperture NA of the converged beam after passing through the condenser lens are in inverse proportion to each other. Therefore, the radius of the beam La radiated on the reticle R after passing through the circular opening 2a is equal to the circular opening 2b.
Becomes 1/2 of the radius of the beam Lb which passes through and irradiates the reticle R. That is, the area of the beam La on the reticle R is ¼ of the area of the beam Lb on the reticle R. Since the illuminance distribution of the laser beam L is a Gaussian distribution, the ratio of the light amounts of the beams La and Lb with which the reticle R is irradiated is not 4: 1 which is the same as the area ratio, and P: 1.
(P <4 positive real number). In this embodiment, P = 3 in order to simplify the calculation. From the above relationship, the ratio of the brightness (the amount of light per unit area) of the beam La and the beam Lb on the reticle R is (1/4) / (3 /
1) = 1/12. Hereinafter, the value of the luminance ratio (1/12) in this embodiment will be referred to as a reference value.

Next, a defect inspection by the laser beam La passing through the circular opening 2a (first inspection) and a defect inspection by the laser beam Lb passing through the circular opening 2b (second inspection).
A method of determining whether the detected defect is a foreign substance or a scratch by using will be described with reference to FIGS. 1 and 2. Each photoelectric signal output from the photoelectric detectors 13 and 14 by the first inspection is compared with the reference voltage from the reference voltage generator 30 by the comparators 23 and 24. Then, when the level (voltage value) of each input photoelectric signal is larger than the reference voltage, the comparators 23 and 24 detect that there is a defect on the surface of the reticle and detect the signal (for example, “1”).
Level) is output to the OR circuit 25. The OR circuit 25 outputs the defect signal S to the memory 31 when a signal is input from at least one of the comparators 23 and 24. The defect signal S is a signal for informing that there is a defect on the reticle R. Therefore, when the memory 31 receives the defect signal S, it outputs the peak values (first defect information) Ia and Ib of the output signals from the amplifiers 21 and 22 to the position information (coordinate value) output from the coordinate calculation unit 35. ) And store it.

Now, when the first inspection is completed, the controller 34 rotates the motor 3 to arrange the circular opening 2b in the optical path of the laser beam L. The beam Lb that has passed through the circular opening 2b irradiates the reticle R with an irradiation area that is four times as large as that of the beam La and a luminance of 1/12. Here, since the position on the reticle R where the defect exists is known by the first inspection, the controller 34 in the second inspection causes the laser beam Lb to scan only the partial area including the defect.
The motor 7 and the motor 10 are controlled. For example, the mounting table 6 is positioned so that the Y coordinate on the reticle R irradiated by the laser beam Lb and the Y coordinate on the reticle R where the defect is located are aligned, and the laser beam Lb is moved by the galvanomirror 4 in the X direction ( The scanning range XS) is scanned only once.
By repeating this operation, all the defects on the reticle R can be scanned with the laser beam Lb. By controlling the motor 7 and the motor 10 in this way, the time spent for the second inspection can be significantly reduced. Further, when the defect signal S is input to the memory 31 as in the first inspection, the peak values (second defect information) Ia ′ and Ib ′ of the output signals from the amplifiers 21 and 22 are output from the coordinate calculation unit 35. It is stored in association with the output position information.

When the first inspection and the second inspection are completed, the main control system 32 reads out all the defect information Ia, Ib, Ia ', Ib' stored in the memory 31, and the first photoelectric detector detects each defect information. Ratio Ia of 1st defect information and 2nd defect information
^, / Ia, Ib ^, / Ib are calculated. Then, in the main control system 32, at least one of the ratios of the first defect information and the second defect information is a reference value (laser beam La,
If the value is larger than 1/12 which is the luminance ratio of Lb), the detected defect is judged as a scratch, and both are almost 1/12.
If it is, it is determined as a foreign substance. This judgment method is
The explanation is omitted here because it is based on the reason as described in the above-mentioned action section.

Next, the main control system 32 determines the size of the detected defect. Regarding the size of the defect, the correspondence relationship between the size of the detected photoelectric signal peak value (defect information) and the size of the actual defect (foreign matter or scratch) is statistically obtained in advance, and the relationship and the actual photoelectric Detectors 23, 24
Can be obtained by comparing with the output signal from Here, in this embodiment, since there are two photoelectric detectors and the defect inspection is performed twice, there are four pieces of defect information obtained from one defect on the reticle R. In this way, when there is a plurality of defect information for one defect, the main control system 3
In No. 3, the defect information having the minimum signal level is selected, and then the defect size is divided into ranks (for example, A, B, C, etc.) by using the information, and the defect position information is displayed together with the display unit 33. Output. The display unit 33 displays the surface of the reticle R divided at appropriate intervals (so-called map) on the screen, and the rank (A) output from the main control system 32 at the map position corresponding to the detected defect position. , B, C) are displayed. At this time, if the defect is a foreign substance, it is displayed in black characters, and if it is a flaw, it is displayed in white characters by inverting the displayed characters in black and white.

By the defect inspection as described above, it becomes possible to accurately determine whether the defect on the surface of the reticle R is a foreign substance or a scratch, and the reticle R is appropriately treated depending on the type of the defect. Can be given. Next, a modified example of the method for determining the size of a defect from the first defect information and the second defect information in this embodiment will be described with reference to FIG.

After the first inspection in the above-described first embodiment is completed, the main control system 32 reads the first data from the memory 31.
The size of the defect is determined from the defect information Ia and Ib. However, at this point in time, it is not known whether the detected defect is a foreign substance or a scratch. As for the determination of the size, the memory 31
The defect information read out from the one having the minimum signal level is selected, and the defect size is ranked and output to the display unit 33. Then, the display unit 33 displays the input rank (for example, A, B, C, etc.) in black characters on the map. Further, the main control system 32 uses the first defect information Ia,
A correction value (reference value 1/12 described above) is given to Ib. The corrected defect information Ia / 12 and Ib / 12 are used as a comparison reference (slice level) of the second defect information obtained by the second defect inspection described later.

Next, the second inspection in the first embodiment described above is performed, and when this second inspection is completed, the main control system 32 reads the second defect information Ia ', Ib' stored in the memory 31. Here, according to the second inspection, the photoelectric detectors 13, 14 are
It is not necessary to store the photoelectric signal (second defect information) obtained from the memory 31 in the memory 31, and the circuit configuration may be such that it is directly output to the main control system 32 by using a switch such as a switch.

Now, the main control system 32 uses the second defect information I
a ', Ib' and the slice level Ia / found in the first inspection
12 and Ib / 12, respectively, and the second defect information I
If at least one of a'and Ib 'has a value larger than the slice level, it is determined that the defect on the reticle is a scratch. On the map of the display unit 33 by the first inspection, all detected defects are displayed as foreign matter at the map position corresponding to the position on the reticle R, and their sizes are ranked and displayed. Therefore, the main control system 32 ranks (A, B,
C) and defect position information are output to the display unit 33. Then, the display unit 33 reverses the black and white display of the defects determined as scratches among the defects classified and displayed on the map in the first inspection, and further redisplays the rank of the size of the scratches if necessary. .

With the above signal processing method, the presence or absence of a defect on the reticle can be promptly displayed in the first inspection, and the second inspection can determine whether the defect is a foreign substance or a scratch. be able to. FIG. 3 is a block diagram showing an example of a signal processing circuit for each photoelectric signal obtained by each photoelectric detector when four photoelectric detectors are provided in this embodiment. The signal processing circuit shown in FIG. 3 will be described below. Further, members having the same functions as those of the signal processing circuit shown in FIG. 2 are designated by the same reference numerals.

As shown in FIG. 1, the photoelectric detectors 13 and 14 are provided in the positive direction of the Y-axis with respect to the reticle R (space on the laser beam incident side). Further, the photoelectric detectors 53 and 54 are respectively provided in the negative direction of the Y axis with respect to the reticle R, and the incident angle with respect to the reticle R and the azimuth angle with respect to the X axis direction are the same as those in the first embodiment. The photoelectric detectors 13, 14, 53, 54 are arranged so as to surround the reticle R when viewed from the Z-axis direction.

As shown in FIG. 3, photoelectric detectors 13 and 14, amplifiers 21 and 22, and a comparator 2 surrounded by broken lines.
A circuit Ca composed of 3, 24 and an OR circuit 25 (a circuit having the same configuration as part of the block diagram shown in FIG. 2)
And the photoelectric detectors 53 and 54 and the amplifier 5 surrounded by broken lines
5, 56, comparators 57 and 58, and OR circuit 59
The circuit Cb is composed of exactly the same structure. Therefore, the description of the circuits Ca and Cb is omitted here.

The output signal Sa from the circuit Ca and the output signal Sb from the circuit Cb are input to the AND circuit 26. This AND circuit outputs the defect signal S to the memory 31 only when both the output signals Sa and Sb are input, that is, when the level becomes "1". Upon receiving the defect signal S, the memory 31 stores the levels of the output signals from the amplifiers 21, 22, 55, 56 in association with the positions on the coordinate system XY.
Since the subsequent signal processing method is exactly the same as the signal processing method of the first embodiment described above, description thereof will be omitted here.

Here, this apparatus is a target of the defect inspection.
Several types of reticles with various circuit patterns must be inspected. There is also a reticle that has a circuit pattern in a diagonal direction with respect to the XY coordinate system on the reticle.
If one of the photoelectric detectors 13 and 14 in the first embodiment (FIGS. 1 and 2) receives the diffracted light from such a circuit pattern, it is detected as a defect. Therefore, with a signal processing circuit as shown in FIG. 3, for example, one photoelectric detector (for example, the photoelectric detector 13) is used.
Even when the diffracted light from the circuit pattern has been received, only the output signal Sa is input to the AND circuit 26, and the output signal Sb from the circuit Cb is not input.
Therefore, the defect signal S is not output from the AND circuit 26. In this way, erroneous detection due to the reticle circuit pattern can be prevented, and more accurate defect detection can be expected.

In the present embodiment, the defect inspection by the beam passing through the circular opening 2a is the first inspection, the circular opening 2
Although the defect inspection by the beam passing through b is the second inspection, conversely, the defect inspection by the beam passing through the circular opening 2b may be the first inspection, and the defect inspection by the beam passing through the circular opening 2a may be the second inspection. . FIG. 4 is a perspective view showing a schematic configuration of a defect inspection apparatus according to the second embodiment of the present invention. 4, members having the same functions as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

A description will be given below with reference to FIG. Light source L
A and LB are the laser beam L in the first embodiment, respectively.
Laser beams L having the same light amount but different wavelengths₁,
L₂(For example, Ar with a wavelength of 488 nm⁺Laser and wavelength
Emits a 633 nm He-Ne laser). laser
Beam L ₁, L₂Are circular openings 2a and 2b, respectively.
After passing through the shading plates 20A and 20B, the dichroic
It is coaxially combined by the ic mirror 18. This
The Beam L₁, L₂Is similar to the first embodiment shown in FIG.
Then, the reticle R is mounted by the galvanometer mirror 4 and the mounting table 6.
Scan the entire surface of the. And is it a defect on reticle R?
Scattered light l₁, L₂Is a dichroic mirror 17
Incident on. The dichroic mirror 17 is a short wavelength laser.
The Beam L₁Generated from the surface of reticle R
Scattered light l₁Laser beam L of long wavelength₂Irradiation of
Scattered light l generated from the surface of the reticle R by₂Through
It Therefore, scattered light l₁Is the light through the condenser lens 15A
Incident on the detector 16A and scattered light l₂Is the condenser lens 15
It is incident on the photoelectric detector 16B via B. Dichroic
Scattered light that passes through the mirror 17₂Photoelectric detection
The device 16B corresponds to the above-described first embodiment (photoelectric detectors 13, 1).
They are arranged under the same conditions as 4).

FIG. 5 is a block diagram showing a processing circuit for photoelectric signals obtained from the photoelectric detectors 16A and 16B in the second embodiment shown in FIG. The configuration will be described below. In FIG. 5, photoelectric detectors 16A, 1 surrounded by broken lines
6B, amplifiers 41 and 42, comparators 43 and 44, O
The circuit Cd including the R circuit 45 is the circuit Ca shown in FIG.
And Cb, which have exactly the same configuration, and therefore, the description thereof is omitted here. One input side of the comparators 43 and 44 is connected to the reference voltage generator 40, and the reference voltage generator 40 inputs a predetermined reference voltage to each comparator. Further, the OR circuit 45 outputs the defect signal S to the determination unit 46 and the coordinate calculation unit 49.

When the judging section 46 receives the defect signal S, it inputs the output signals from the amplifiers 41 and 42, and outputs the judgment result of judging the kind of defect (foreign matter, scratch) to the main control system 47 by a predetermined arithmetic processing. To do. At the same time, the determination unit 46 selects one of the peak values of the signal levels obtained from the amplifiers 41 and 42 (here, the output signal from the amplifier 41) and outputs it to the main control system 47. Further, when the coordinate calculation unit 49 receives the defect signal S, the output signals from the linear encoder 9 and the rotary encoder 10A in FIG. 4 are input, and the position of the reticle R on the coordinate system XY (coordinate value ) Is measured and the measurement result is output to the main control system 47. The main control system 47 ranks the sizes of the defects based on the above-mentioned peak value, and then determines the defect type output from the determination unit 46 and the measurement result output from the coordinate calculation unit 49. , To the display unit 48.

Now, a method of determining whether the detected defect is a foreign substance or a scratch by the defect inspection in this embodiment will be described with reference to FIGS. 4 and 5. Since the laser beams L ₁ and L ₂ have different beam diameters on the reticle R, the moving speed of the reticle R in the Y direction is adjusted to that of the laser beam L _{1 having} a smaller diameter. Photoelectric signals obtained from the photoelectric detectors 16A and 16B when the laser beams L ₁ and L ₂ and the reticle R are relatively scanned are detected by the detection signals (“1”) via the amplifiers 41 and 42 and the comparators 43 and 44. Level) and the OR circuit 45
Is output to. Here, the signal processing operations of the amplifiers 41 and 42, the comparators 43 and 44, the reference voltage generator 40, and the OR circuit 45 are the same as those in the above-described first embodiment, and therefore description thereof will be omitted.

When the judging section 46 receives the defect signal S from the OR circuit 45, it inputs the output signals from the amplifiers 41 and 42. Then, the ratio Ic '/ Ic of the peak values Ic and Ic' of the level (voltage value) of each signal is calculated, and the calculated value and the reference value H in the present apparatus shown in FIG.
Value corresponding to 12). The determination unit 46 is Ic '
When / Ic = H, the detected defect is determined as a foreign matter, and I
When c ′ / Ic> H, the detected defect is determined as a scratch.
Here, as shown in FIG. 4, the circular openings 2a, 2b of the present apparatus are shown.
Is the same size as each circular opening shown in FIG.
Since the reflectance and the transmittance of the laser beams L ₁ and L ₂ (l ₁ and l ₂ ) at the dichroic mirrors 17 and 18 are different, a correction value is given to the reference value H based on the influence thereof. It is slightly different from 12.

Further, the judging section 46 determines a predetermined laser beam (in this embodiment, the wavelength of A is 488 nm) in this apparatus.
The peak value (Ic) of the level of the output signal obtained from the L ⁺ laser L ₂ , l ₂ ) is selected and output to the main control system 47. This value is used to determine the size of the detected defect in the main control system 47 described later. Coordinate calculation unit 49
When receiving the defect signal S from the OR circuit 45, inputs the output signals from the linear encoder 9 and the rotary encoder 10A and measures the position where the defect exists, that is, the coordinate value on the reticle R based on each signal. Then, this defect information is output to the main control system 47.

The main control system 47 classifies the defect size into ranks (A, B, C) based on the peak value Ic of the signal level output from the judging section 46. The rank signal and the defect type (foreign matter or scratch) signal output from the determination unit 46 are output to the display unit 48 in association with the position information (coordinate values) output from the coordinate calculation unit 49. It Then, the display unit 48 displays the defect type and size rank at the map position corresponding to the position on the reticle R where the defect exists. Since this display unit 48 is the same as the display unit 33 of the first embodiment described above, the description thereof is omitted here.

With the above configuration, when two beams having different beam diameters are irradiated onto the reticle R, it is possible to simultaneously detect the respective scattered lights resulting from the defects on the reticle R. Ratio of photoelectric signals under the system (ratio Ia '/ Ia, Ib' / Ib in the first embodiment)
Equivalent to) can be obtained in a short time. Therefore, when determining the type of the detected defect on the reticle R, it is not necessary to store the level of the detection signal as in the first embodiment, and the memory 31 in FIG. 2 can be omitted. further,
In the first embodiment, the type of defect on the reticle can be determined by performing the inspection twice in time series, but in the present embodiment, the type of defect on the reticle can be determined by one inspection. It is possible to improve the throughput.

Further, in the first and second embodiments of the present invention, the beam diameter changing means of the laser beam for irradiating the reticle R is the shading plates 2 and 20A shown in FIGS.
It is not limited to 20B. For example, in FIG. 1, it is possible to change the focal position of the beam on the reticle R, that is, the beam diameter, by changing the distance between the lenses 1a and 1b of the expander 1. Also, the lenses 1a, 1
It is also possible to change the focal position (beam diameter) of the beam by moving the mounting table 6 directly in the Z direction without changing the interval of b.

Furthermore, in the first and second embodiments of the present invention, two sets of laser beams having different beam diameters are switched (or simultaneously) to irradiate the reticle R, and the beam diameter (irradiation area) is small. The laser beam has a large light intensity,
In addition, a laser beam having a large beam diameter (irradiation area) has a small amount of light. For this reason, a large difference occurs in the brightness (light amount per unit area) of each beam, and the detection accuracy of the defect on the reticle R (the accuracy of determining whether it is a foreign matter or a scratch) is improved. However, in order to determine the type of defect (foreign matter, scratch), it is only necessary to change the irradiation areas of the two sets of laser beams that irradiate the reticle R, that is, the beam diameters,
The light amount may be the same for each beam, or the laser beam having a smaller beam diameter may be smaller.

[0045]

As described above, according to the present invention, it can be determined whether or not the defect on the surface of the object to be inspected is adhesion of foreign matter such as dust. Therefore, if the defect is a foreign substance, it can be removed by cleaning, and if the defect is a flaw, appropriate treatment can be applied to the inspected object depending on its size.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of a defect inspection apparatus according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a signal processing circuit according to a first embodiment of the present invention.

FIG. 3 is a circuit diagram showing a modification of the signal processing circuit according to the first embodiment of the present invention.

FIG. 4 is a perspective view showing a schematic configuration of a defect inspection apparatus according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a signal processing circuit according to a second embodiment of the present invention.

6A and 6B are diagrams showing scanning of the surface of an object to be inspected with light beams having different beam diameters, and photoelectric signals of scattered light generated from foreign matter and scratches on the surface.

[Explanation of symbols]

 1 Beam Expander 2 Light Shield 2a, 2b Circular Aperture 3, 7, 10 Motor 4 Galvanometer Mirror 9 Linear Encoder 13, 14 Photoelectric Detector 31 Memory 32 Main Control System 34 Controller L Laser Beam R Reticle

Claims (5)

[Claims] 1. A light beam is applied to the surface of an object to be inspected, and scattered light generated from the surface when the object to be inspected and the light beam are relatively scanned is received by a photoelectric detector. In the defect inspection method for inspecting a defect state on the surface of the inspection object, when the light beam having a first beam diameter and the inspection object are relatively scanned on the surface of the inspection object, A first inspection step of detecting first defect information corresponding to a magnitude of a photoelectric signal obtained from a photoelectric detector; the light beam having a second beam diameter different from the first beam diameter; A second corresponding to the magnitude of the photoelectric signal obtained from the photoelectric detector when the object is relatively scanned
Second inspection step of detecting defect information of No. 1, and it is determined based on the first and second defect information whether or not the defect on the surface of the object to be inspected is a foreign substance attached to the surface. A defect inspection method comprising a determination step. 2. The determining step comprises: a ratio between the first defect information and the second defect information; and a reference value corresponding to a ratio between the first beam diameter and the second beam diameter. The defect inspection method according to claim 1, wherein 3. The determination step includes a correction value corresponding to a ratio of the first beam diameter and the second beam diameter to at least one of the first defect information and the second defect information. The defect inspection method according to claim 1, wherein the first defect information and the second defect information are compared after being given. 4. The second inspection step determines a predetermined partial area corresponding to the position of the defect based on the position information of the defect on the surface of the inspection object detected in the first inspection step. The defect inspection method according to claim 1, further comprising scanning with the light beam. 5. An irradiation means for irradiating a surface of an object to be inspected with a light beam, a scanning means for relatively scanning the object to be inspected and the light beam, and scattered light generated from a defect on the surface. In a defect inspection apparatus comprising a photoelectric detection means for receiving light, a beam diameter changing means for varying the beam diameter of the light beam on the surface of the inspection object, and relative scanning between the inspection object and the light beam. When I did
A storage unit that stores defect information corresponding to the size of the photoelectric signal output from the photoelectric detection unit; and the object to be inspected and the light under the first beam diameter set by the beam diameter changing unit. First defect information stored in the storage unit when the beam is relatively scanned,
It corresponds to the magnitude of the photoelectric signal output from the photoelectric detection means when the object to be inspected and the light beam are relatively scanned under a second beam diameter different from the first beam diameter. A defect inspection apparatus comprising: a determination unit that determines whether or not the defect on the surface of the object to be inspected is a foreign substance attached to the surface based on the second defect information.