JPH0682381A - Foreign matter inspection device - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention stabilizes submicron-order fine foreign matter adhered to a circuit pattern substrate such as a photomask, especially a reticle having a phase shift film for the purpose of improving transfer resolution. It is to provide the device which detects by doing. [Structure] The scattered light generated by the oblique illumination (2) is NA
An optical system (41) of 0.4 or more is used to collect light from the back surface of the sample, and a rewritable spatial filter (44) provided on the Fourier transform surface blocks the diffracted light from the circuit pattern and divides the optical path into two parts. (49) for giving an adjusted amount of phase difference to the optical path, a detection optical system (4) for forming an image on the detector (51) and causing the interference, and a processing system (5) for processing the detection result. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection apparatus for detecting foreign matter adhering to a circuit pattern of a reticle, a photomask or the like (hereinafter referred to as a reticle), and more particularly, to a simple foreign matter of submicron order And an apparatus for detecting foreign matter on the reticle and mask, which has a phase shift film for the purpose of improving the transfer resolution, etc., which is performed before transferring onto a wafer with various configurations.

[0002]

2. Description of the Related Art In an exposure process of a reticle or the like used for manufacturing an LSI or a printed circuit board, a circuit pattern of the reticle or the like is inspected before printing and transferring on a wafer. Even if micron-order minute foreign matter is present, the foreign matter does not normally transfer the circuit pattern to the wafer, which causes a problem that all the LSI chips are defective. This problem has become more apparent with the recent high integration of LSIs, and the presence of finer foreign matter on the order of submicrons has become unacceptable.

In order to prevent the above transfer failure, the foreign matter inspection before the exposure process is indispensable, and various foreign matter inspection techniques have been conventionally provided for management of the reticle and the like. However, the inspection of the circuit pattern of the reticle and the like is A method of obliquely irradiating with a light source having good directivity such as a laser beam and detecting scattered light generated from a foreign substance is generally used because of its advantage in view of inspection speed and sensitivity. However, in the above inspection method, scattered light is also generated from the edge portion of the circuit pattern such as the reticle, so it is necessary to devise a method for discriminating and detecting only the foreign matter from this scattered light, and the technology for that is disclosed. There is.

Among them, the method of comparing with the model pattern can effectively remove scattered light from the edge portion, and is therefore effective for detecting fine foreign matters in the highly integrated circuit pattern edge in recent years. .

JP-A-58-204345 and JP-A-58-37923 disclose methods of detecting an image defect by a circuit pattern defect inspection apparatus and image processing of software. The disclosed method is a method of determining a defect from a difference in the shape of an image, and is suitable for detecting a defect in a circuit pattern in which the shape is a problem, but a resolution of an imaging optical system smaller than the defect is required, It is not suitable for foreign substance inspection, which is useful only for detecting the presence or absence of the substance.

On the other hand, the method of extracting the foreign matter by utilizing the diffraction and interference phenomenon of light can detect the foreign matter even if the foreign matter is smaller than the resolution of the imaging optical system.

The first is disclosed in Japanese Patent Laid-Open No. 50-77082. The disclosed method utilizes the fact that the circuit pattern of the LSI has repeatability and the foreign matter has no repeatability. A spatial filter that emphasizes the normal part of the circuit pattern is placed on the optical Fourier transform surface of the circuit pattern, and the scattered light image that includes the scattered light from both the circuit pattern and the foreign matter interferes with the scattered light image with the emphasized circuit pattern. Only the scattered light from the foreign matter is detected by erasing by.

The second method is disclosed in JP-A-63-200042 and JP-A-2-24539.
These cause the scattered lights from the same part of two reticles having the same circuit pattern to interfere with each other by shifting the phase by π, and detect only the difference between the scattered lights from both reticles, that is, a defect or a foreign substance. It is a thing.

In addition, Japanese Patent Laid-Open Nos. 60-154634 and 60-154635 disclose devices for inspecting pattern defects on a wafer by optical filtering.

[0010]

As described above, as the size of the foreign matter to be detected becomes smaller, the problem of overlooking the foreign matter that affects the LSI manufacturing has become a problem.

Recently, in order to improve the transfer resolution of a circuit pattern on a reticle formed of a metal thin film such as chromium, a transparent or semi-transparent film called a phase shift film or a phase shifter is provided between the circuit patterns on the reticle. A reticle provided with a circuit pattern made of a film (having a film thickness that is an odd multiple of approximately 1/2 the wavelength of the exposure light source) has been developed. This film is transparent or semi-transparent, but a circuit pattern (thickness of about 0.1 μm) formed of a metal thin film such as chromium.
Since it has a structure that is several times thicker, the scattered light from the edge part of the film is several times to several tens of times larger than the scattered light from the conventional circuit pattern edge part. However, the detection sensitivity of foreign matter is significantly reduced. For this reason, JP-A-60-154634 and JP-A-60-154634
In the method disclosed in Japanese Patent Publication No. 154635, it is difficult to detect a foreign substance by separating it from a circuit pattern, which has been a problem. In addition, JP-A-50-77082
The method disclosed in the publication is mainly for memory LSI.
Since the repeatability of such circuit patterns is used, it cannot be applied to a peripheral part of a circuit having no repeatability even in a memory LSI or a reticle of a logic circuit LSI having fundamentally low repeatability.

Further, the methods disclosed in JP-A-63-200042 and JP-A-2-24539 require two reticles having the same circuit pattern. In many cases, only one reticle, which is an original plate of an LSI, is manufactured, and it is not practical to manufacture an extra reticle that requires an expensive manufacturing apparatus and a large amount of time only for inspection.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a transparent or semitransparent substrate having a circuit pattern, in particular, a reticle having a circuit pattern made of a phase shift film for improving transfer resolution. An object of the present invention is to provide a foreign matter inspection apparatus capable of stably detecting fine foreign matter of sub-micron order adhered on a circuit pattern such as with stable separation from the circuit pattern with a simple optical configuration.

[0014]

In order to achieve the above object, the foreign matter inspecting apparatus according to the present invention has a foreign matter adhering to a transparent or semitransparent substrate sample having a circuit pattern, such as a photomask or a reticle. At least in a foreign matter inspection apparatus that detects the substrate sample by using an illumination system that irradiates the substrate sample and an imaging optical system that forms an image of an illuminated inspection region on a detector. , Y, and Z, and an inspection stage including a stage unit and a control drive system for the stage unit, and a circuit for irradiating spots on the circuit pattern for the purpose of improving S / N of a signal by obliquely coherent light. A light illumination system, a means for amplitude-dividing a light flux of a detection image into two light fluxes in an imaging optical system for imaging an illuminated inspection area on a detector, and a phase difference between the two light fluxes which is not 0 or π. Means to give , A means for interfering the two light fluxes given a phase difference on a detector, a signal outputted by an output value of a binarizing circuit for setting an output of the detector with a threshold value, and the X, Y, The foreign matter data from the control signal of the Z stage is arithmetically displayed on the foreign matter display device.

[0015]

When the two coherent illumination light images are caused to interfere with each other and only the non-coincidence portions of the respective detection images, that is, the defect and the foreign matter are detected, the reference of the Twyman Green interference system is made as in JP-A-63-200042. Generally, a reticle, a mask, or the like is arranged at the position of the light generation mirror and the position of the sample to be inspected, the scattered light is condensed by the lens, and the light is interfered on the half mirror. However, this configuration requires two reticles and masks as described above, and the device scale is large and complicated.

On the other hand, when the object to be detected is limited to a height (thickness) different from the circuit pattern on the inspection sample such as a foreign substance, the configuration of the sharing interference system can be applied.

In a focusing optical system that illuminates a substrate sample such as a reticle and forms an image of the illuminated inspection area on a detector, the luminous flux of the detected image is amplitude-divided into two luminous fluxes, and an image formed by the two luminous fluxes is formed. When they are matched and interfere with each other on the detector, the two light beams interfere with each other at an angle on the detector.

It has been confirmed by experiments by the present inventors that there is a phase difference amount in which only the detected image from the circuit pattern is erased when a certain phase difference amount is given to the two light beams to cause interference. By this, in the optical path after splitting the luminous flux,
By providing a means for giving a phase difference amount corresponding to the height of the foreign matter to be detected to the two light fluxes and the circuit pattern, only the scattered light from the foreign matter is detected by the detector without being affected by the scattered light from the circuit pattern. It becomes possible to detect. Further, the foreign matter detection signal can be obtained by binarizing the output of the detector with a predetermined threshold value.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of one embodiment of the present invention will be described below with reference to FIG. In the figure, reference numeral 1 is an inspection stage unit, and the inspection stage unit 1 includes a Z stage 9 which is fixed to an upper surface of a reticle 6 having a pellicle 7 by a fixing means 8 and is movable in the Z direction, and a reticle through the Z stage 9. 6, an X stage 10 that moves the reticle 6 in the X direction, a Y stage 11 that similarly moves the reticle in the Y direction, a stage drive system 12 that drives each of the Z stage 9, the X stage 10, and the Y stage 11, and a reticle 6 And a focus position detecting control system 13 for detecting the position in the Z direction, and each stage is controlled so that focusing can always be performed with required accuracy during the inspection of the reticle 6.

The X stage 10 and the Y stage 11 are scanned as shown in FIG. 2, and the scanning speed thereof can be set arbitrarily.
Set a constant acceleration time of 2 seconds, a constant velocity motion of 4.0 seconds, and a constant deceleration time of 0.2 seconds, and a stop time of about 0.2 seconds is 1 /
It is formed so that the maximum speed is about 25 mm / sec and the amplitude is 105 mm in two cycles, and the Y stage 11 is synchronized with the uniform acceleration time and uniform deceleration time of the X stage 10 to step the reticle 6 by 0.5 mm. If it is configured to move in the Y direction likewise, if 200 times are transferred during one inspection time, it is possible to transfer 100 mm in about 960 seconds, and scan a 100 mm square area in about 960 seconds. You will be able to do it. In addition, the control system 1 for detecting the focal position
Reference numeral 3 may be one using an air micrometer, one detecting a position by a laser interferometry method, or one having a configuration of projecting a fringe pattern and detecting the contrast thereof. The coordinates X, Y, Z are the directions shown in the figure.

2 is a first illumination system, 3 is a second illumination system,
Both are independent and consist of the same components. Reference numerals 21 and 31 denote laser light sources. The wavelengths λ of the laser light source 21 are different from each other, for example, 514.5 nm and the wavelength λ of the laser light source 31 is, for example, 532 nm, but the wavelengths may be the same. Reference numerals 22 and 32 are condenser lenses, which condense the luminous fluxes emitted from the laser light sources 21 and 31, respectively, and irradiate them onto the circuit pattern of the reticle 6.

In this case, the incident angle i of the two with respect to the circuit pattern is set to be larger than about 30 ° in order to avoid the objective lens 41 of the detection optical system 4 described later, and when the object is the reticle 6 on which the pellicle 7 is mounted. Should be less than approximately 80 ° to avoid the pellicle 7, so approximately 30 ° <i <80 °.

A detailed configuration example of the first illumination system 2 and the second illumination system 3 will be described with reference to FIG. Figure 3 is the first
Is a diagram showing a configuration example of the illumination system 2 (in this case, the second illumination system 3 side is omitted because it has the same configuration). In the figure, the same symbols as those in FIG. 1 indicate the same components. 21 is a laser light source. 223 is a concave lens, 224 is a cylindrical lens, 225 is a collimator lens, 226 is a condenser lens, and the condenser lens 22 is formed by reference numerals 223 to 226. The laser light source 21 is arranged so as to have linearly polarized light having an electric field vector in the X ′ direction (this state is called S-polarized light). For example, the S-polarized light has an incident angle i of about 6
At 0 °, the reflectance on the glass substrate is about 5 times higher than in the case of P-polarized light (for example, Hiro Kubota, Applied Optics (Iwanami Zensho), page 144). Is possible. Then, in order to increase the illuminance of the first illumination system 2 and the second illumination system 3, the numerical aperture (NA) of the focusing system is set to about 0.1 and the laser beam is set to about 1
Although the aperture is narrowed down to 0 μm, the depth of focus is shortened to about 30 μm by this aperture, and the inspection visual field 15 shown in FIG.
It becomes impossible to focus on the entire area S (500 μm). However, in this embodiment, as a countermeasure against this, the cylindrical lens 224 is tilted around the X ′ axis shown in FIG. 2 (FIG. 2 shows the tilted state).
Even if the incident angle i is 60 °, it is possible to focus on the entire area S of the inspection visual field 15, and the signal processing system 5 described later is used.
When a one-dimensional solid-state imaging device is used for the detectors 51, 551 of the above, the inspection area of the inspection visual field 15 is detected by the detectors 51, 551.
Even if it becomes linear, it becomes possible to illuminate the linear inspection region with high illuminance and uniform distribution. Further, when the cylindrical lens 224 is tilted not only around the X ′ axis shown in FIG. 2 but also around the Y ′ axis, for example, even when the incident angle i is 60 ° and the light is emitted from any direction, the entire inspection visual field 15 is obtained. It is possible to perform linear illumination with high illuminance and uniform distribution on S. In FIG. 1, reference numeral 4 denotes a detection optical system, which includes an objective lens 41 facing the reticle 6, a half mirror 47 that divides the optical path into two, mirrors 48 and 448 that change the directions of the optical paths, and a half that combines the optical paths. A mirror 447, a phase difference amount generating means 49 for giving a phase difference amount to two optical paths, viewing zone lenses (hereinafter referred to as field lenses) 43 and 443 provided near the image forming position of the objective lens 41, and an inspection visual field of the reticle 6. 15 is composed of a band-shaped light-shielding portion provided at the position of Fourier transform with respect to 15 and spatial filters 44 and 444 having a transmitting portion on the outside thereof, and imaging lenses 45 and 445. The inspection visual field 15 on the reticle 6 will be described later. Detector 5 of signal processing system 5
It is configured to form an image at 1.

Since the phase difference amount generating means 49 gives a phase difference amount to one of the divided optical paths, it may be a glass plate having a thickness adjusted or a transparent thin film formed on a glass substrate. The phase difference amount generating means 49 is more adaptable to the sample to be inspected when the phase difference amount can be arbitrarily adjusted, and is a wedge prism provided with a mechanical moving mechanism or a liquid crystal capable of electrically controlling the phase difference amount. Devices and electro-optic crystals are preferred.

The field lenses 43 and 443 move the focus position 46 above the objective lens 41 to the spatial filters 44 and 44.
An image is formed on 444.

The field lenses 43 and 443, the spatial filters 44 and 444, and the image forming lenses 45 and 44 described above.
5 is only divided by the half mirror 47, and is in an optically equivalent position except for the phase difference amount given by the phase difference unit 49.

Reference numeral 5 is a signal processing system. The signal processing system 5 binarizes the detector 51 and the output of the detector 51.
It comprises a digitizing circuit 52, a microcomputer 54, and a display means 55.

The detector 51 is formed of, for example, a charge transfer type one-dimensional solid-state image pickup device, and detects a signal from a circuit pattern on the reticle 6 while scanning the X stage 10. In this case, the reticle 6 is used. The presence of the foreign matter above increases the input signal level and the light intensity, so that the output of the detector 51 is also increased. It should be noted that if a one-dimensional solid-state image sensor is used for the detector 51 as described above, there is an advantage that the detection field of view can be widened while maintaining the resolution, but the invention is not limited to this, or a two-dimensional one can be used. A single element can also be used.

The binarization circuit 52 is preset with a threshold value for binarization, and an output value equal to or higher than the reflected light intensity corresponding to a foreign substance of a desired size output from the detector 51 is input. In this case, it is formed so as to output the logic level "1".

The shading correction circuit 113 and the 4-pixel addition processing circuit 114 will be described later.

The block processing circuit 112 is a binarization circuit 5.
This circuit takes in the signal from 2 and prevents double counting of the two signals, which will be described later.

Further, the microcomputer 54 determines that "there is a foreign substance" when the block processing circuit 112 outputs the logic level "1", and detects the position information of the X stage 10 and the Y stage 11 and the detector which is not a single element. In the case of 51, the foreign substance position information calculated from the pixel position in the element and the detection output value of the detector 51 are stored as foreign substance data, and the result is output to the display means 55.

The operation of the inspection device will be described below.
In the figure, the same symbols as those in FIG. 1 indicate the same components.

First, an example of an overlooked foreign matter in the prior art is shown in FIG.
Shown in. These foreign substances are the foreign substances whose dimensions should be detected.

In the foreign matter inspection device on the reticle showing the problems in the conventional device in FIG. 10, there is a system in which the scattered light from the circuit pattern formed on the reticle is removed and only the scattered light from the foreign matter is detected. , Becomes an important point of technology.

Therefore, a method of analyzing the polarization state of scattered light, a method of comparing the outputs of a plurality of detectors, etc. have been developed and put into practical use. However, in order to avoid the influence of scattered light generated from the circuit pattern in any of them, an optical system having a small aperture of NA 0.1 is arranged obliquely so as to avoid scattered light from the circuit pattern. In such a configuration, there is a problem that an irregularly shaped foreign substance is easily missed for the reason described later.

The NA used here is determined by the aperture diameter of the lens and the distance to the target object. Numerical value expressing the characteristics of the lens. Specifically, using θ in the figure on the right, NA =
It is a numerical value obtained by Sinθ.

Another problem is the pattern removal technique which has been used as an auxiliary in various inspection techniques in response to the miniaturization of circuit patterns. Many of these adopt a method of automatically lowering the detection sensitivity of the foreign matter detector when a circuit pattern is found during inspection. In such a method, there is a problem that foreign substances near the pattern edge are missed while reducing erroneous detection of the circuit pattern.

Now, the solution measures for these two problems will be described below. Pictures 1004 and 1005 in FIG. 12 are observations of scattered light generated when a foreign substance is irradiated with a laser from above. What should be noted in this photograph is that the scattered light (e) from the foreign matter is directionally distributed. Therefore, in the conventional low NA detector 1001, unless the detector is installed at an appropriate position, the scattered light (e) generated from the foreign matter is not necessarily incident on the low NA optical system in a good condition, and it may be overlooked. Occurs. Moreover, since the distribution of the scattered light varies depending on the size and shape of the foreign matter, it is virtually impossible to properly arrange the optical system having a low NA for all the foreign matter.

FIG. 11 shows a result of experimentally measuring this.
Shown in. The scattered light distribution when a foreign substance is illuminated with a laser beam having an incident angle of 60 ° is changed while the detection angle is changed by the detection optical systems 1001 and 1002 having a low NA (NA≈0.1). Measured and shown. This figure shows point A1
At 001, the detection level exceeds the detection threshold, whereas at point B1002, the detection threshold is not exceeded and detection cannot be performed. Since the scattered light distribution of the real foreign matter is not constant, it is shown that the detection performance is not stable in the low numerical aperture detection methods such as A and B. Therefore, in the present invention, a configuration is adopted in which scattered light from foreign matter having various scattering distributions is effectively condensed by a high NA detection optical system 41 having a large aperture, specifically, an NA of 0.4 to 0.6. is doing.

With this configuration, a high NA detection optical system can be realized for the first time, and when NA is selected to be 0.5, the aperture area can be about 20 times that of the low NA detection optical system.

Next, a method of removing scattered light from the circuit pattern by the high NA detection optical system will be described.

FIG. 5 is a plan view for explaining the angle pattern of the circuit pattern, FIG. 6 is a view showing the distribution of scattered light on the Fourier transform plane, and FIG. 7A is a view showing the corner portion of the circuit pattern. 7 (B) is a detailed view of the "A" portion in FIG. 7 (A).

In FIG. 4A, 70 is a fixing means 8.
The foreign matter on the reticle 6 fixed on the Z stage 9 by 81 is a linear portion of the circuit pattern 80, and 82 is a corner portion of the circuit pattern 80. When the coherent light is obliquely irradiated on the reticle 6 by the illumination system and the generated scattered light is condensed by the objective lens 41, the circuit pattern 80 on the reticle 6 and the reticle 6 surface of the illumination system 2 or 3 shown in FIG. The angle θ defined by the positional relationship with the projected image 60 on top is 0.
The scattered light of the angle pattern (hereinafter referred to as the 0 ° pattern) at the angle of ∘ is shown in FIG. 6 on the Fourier transform surface of the objective lens 41.
It appears in a band shape as shown in (a). Here, the kind of the angle θ of the circuit pattern 80 is limited to the angle pattern of 0 °, 45 °, 90 °, and the scattered light (b) from the patterns of 45 ° and 90 ° as shown in FIG. , (C) do not enter the pupil of the objective lens 41 and therefore do not affect the detection. On the other hand, the scattered light from the foreign matter 70 has no directivity and thus spreads over the entire Fourier transform surface as shown in FIG. 6 (e). Therefore, the spatial filter 4 having the band-shaped light-shielding portion on the Fourier transform surface and the light-transmitting portion on the outside thereof.
By disposing 4, 444 to block scattered light (a) from the 0 ° pattern shown in FIG. 4 (A), the foreign matter 70 can be discriminated from the circuit pattern 80 and detected.

However, the circuit pattern corner portion (see FIG.
It shows in (D). The scattered light from) cannot be sufficiently blocked by a linear spatial filter. For this reason 1
When detection is performed with a detection pixel of 0 × 20 μm (see FIG.
It shows in (B). ), Scattered light from a plurality of pattern corners enters the pixel, and only the foreign matter cannot be detected.

Therefore, in the present invention, as shown in FIG. 8, a field lens lens 45 for re-imaging is arranged at a position after passing through the spatial filter, and the pixel of the detector is 2 × 2 μ on the sample.
The resolution has been increased to m □ (shown in Fig. 4C), the influence from the circuit pattern has been eliminated as much as possible, and foreign matter of 0.5 µm can be detected. In addition, here, the pixel of the detector is 2 × 2 μm
I set it as □, but the reason is as follows,
The size does not necessarily have to be 2 × 2 μm □.

The pixel size in this case may be smaller than the pattern size L on the reticle. Therefore, 0.8
A reticle used when exposing a μm process LSI with a stepper having a reduction rate of 1/5 is about 0.8 × 5 = 4μ.
m, 0.5 μm Process LSI: 0.5 × 5 =
It suffices to detect with a pixel smaller than 2.5 μm. Also,
Actually, the value may be further increased or decreased as long as the influence from the pattern corner can be sufficiently reduced.

Specifically, the minimum pattern size on the reticle to be inspected is desirable. If the size is about the minimum pattern size, less than two corners are included in one pixel of the detector. More specifically, in a 64 MDRAM reticle having a minimum size of about 1.5 μm, a pixel size of about 1 to 2 μm is desirable.

In recent years, it has been studied to use a pattern (shifter pattern) formed of a phase shifter film together with a conventional circuit pattern formed of a metal thin film for the purpose of improving transfer resolution. This film is transparent, though the film thickness is adjusted to a constant value.
Since the structure has a thickness several times as thick as the chrome portion (about 0.1 μm in thickness), the scattered light from the edge portion is larger than the scattered light from the edge portion of the chrome portion. Become. For this reason, in addition to the solid discrimination method so far, new ideas are needed.

A reticle with a phase shift film is generally
After forming the chrome part (up to this point, it is the same process as the reticle without the shifter film), the shifter film material is applied or sputtered on the entire surface, and the pattern of the shifter film (shifter pattern) is formed by the etching process. Is. Therefore, if foreign matter is present on the chromium portion before film formation, the film formation may be adversely affected, and defects such as bubbles and chips may be generated in the shifter film. Therefore, in addition to the foreign matter inspection after the shifter pattern formation described above, the foreign matter inspection of the entire surface including the chrome portion before and after the film formation (in the method of the present invention, defects such as bubbles and chips are the same as foreign matter). Can be detected). However, in this case, the shifter pattern is not formed yet, and scattered light from the shifter pattern is not generated, so that the conventional technique can be used. Therefore, the foreign matter detection after forming the phase shift film will be described.

FIG. 13 shows the result of a detection experiment conducted by the inventors of the present invention on an experimental apparatus having the configuration of the present invention. The vertical axis in the figure represents the amount of scattered light detected, the measurement point indicated by ◯ 511 is the scattered light from a 0.5 μm foreign matter, and the measurement point indicated by Δ512 is the scattered light from the phase shifter film. Represent The horizontal axis in the figure indicates the amount of phase difference given to the divided two optical paths, φ ₀ is the case where the amount of phase difference is zero, and φ min is the interference result on the detector due to the scattered light from the circuit pattern. The state where the phase difference is adjusted to the minimum is shown, and φmax is the state where the phase difference is adjusted to maximize the interference result on the detector due to the scattered light from the circuit pattern. From the figure, by adjusting the amount of phase difference to φmin, the scattered light from the phase shift film decreases, the scattered light from the foreign material becomes larger, and the foreign material can be detected only by binarizing the detection output. It turns out that

Next, another embodiment of the optical system 4 of the present invention will be described.

In FIG. 1, after splitting by the half mirror 47, the light is split by the half mirror 447 through the field lens, the spatial filter and the re-imaging lens, but the optical path is split only by the phase difference amount generating means 49. By doing so, a configuration without using two sets of lenses and filters is possible. Figure 1
4 shows its configuration. In FIG. 15, the optical path is formed by the mirror 48 so that the optical paths of the two divided optical paths are almost equal. This is because if the optical path lengths of the two optical paths are significantly different,
This is because the imaging magnification on the detector 51 may differ greatly, which may adversely affect the interference result. Further, the phase difference amount correction plate 449 in the figure substantially corrects the change in the optical path length due to the provision of the phase difference amount generating means 49. This allows
It is prevented that the difference in optical path length between the two optical paths exceeds the spatial coherent length of the light source and no longer interferes. Of course, it is not necessary if the spatial coherence length of the light source is sufficient.

In FIG. 16, two mirrors 48 are added to FIG. 15 so that the objective lens 41 and the detector 51 are coaxially positioned. This allows the mirror 4
If 8 is moved to the outside of the optical path, the structure can be easily switched to a normal optical system. In FIG. 17, interference is realized on the detector 51 only by adjusting the angles of the two mirrors 48 without using the half mirror 447. Half mirror 44
It is possible to prevent a decrease in S / N due to the use of No. 7. Figure 1
8 is a modification of FIG. 17 based on the same concept as in FIG.

In FIG. 19, the angles of the mirror 48 and the half mirror 47 are finely adjusted so that the mirror 448 can be adjusted.
Is a configuration that does not require.

FIG. 20 shows an example of realization of the phase difference amount generating means, which is indicated by a dotted line in the figure after splitting into two optical paths by a half mirror 47 (a half prism is used in the figure, but the effect is the same). One of the optical paths shown is folded back by two mirrors 492, and the phase difference amount can be adjusted by moving the two mirrors left and right in the drawing by a moving mechanism 493. FIG. 21 shows a configuration in which the amount of phase difference can be adjusted by mechanically moving the wedge prisms 491 and 492, a mirror 4448 for roughly adjusting the optical path length is provided, and the change in optical path length due to the wedge prisms 491 and 492 is corrected. Therefore, a correction plate 449 made of a glass substrate is provided.

Next, a method for stabilizing the detection by the above-described configuration will be described.

This is especially true for array-type detectors
If the detection / judgment of foreign matter is performed in pixel units, the following inconveniences occur.

As an example of the case where the foreign matter is detected / determined with the pixel size of the detector of 2 × 2 μm □, the foreign matter is detected across a plurality of (2 to 4) pixels as shown in FIG. Under the conditions described above, the scattered light from the foreign matter is dispersed into a plurality of pixels, and as a result, the detection output of one pixel is 1
/ 2 to 1/4 (actually, about 1/3 due to the influence of crosstalk between detector pixels), and the detection rate of foreign matter is reduced. Further, the positional relationship between the pixels of the detector and the minute foreign matter is very delicate due to its size, and changes with each inspection. In this case, even if the same sample is used, the results differ from test to test, and the reproducibility of detection decreases.

Therefore, this time, as shown in FIG. 23, the detection pixels are reduced to 1 × 1 μm □, and the detection outputs of four adjacent 1 × 1 μm □ pixels of each pixel are electrically added.
Simulate the detection output by × 2μm □ pixel. This value is obtained by overlapping by 1 μm (a, b, c,
d), the maximum value (a in the figure) is used as a representative output of 2 × 2 μm □ pixels to detect the foreign matter. As a result, the fluctuation of the detection output from the same foreign matter is ± 10% in actual results.
The reproducibility of 80% or more can be secured for all foreign matters.

FIG. 24 shows a block diagram of a specific example of the 4-pixel addition processing circuit. This is a one-dimensional image sensor in which 512 pixels when reduced to 1 μm are arranged. An output 2503 from an odd-numbered pixel and an output 2502 of an even-numbered pixel of the one-dimensional image sensor are separately output. This is an example of a (general) one-dimensional image sensor. 256-stage shift register 2501, 1-stage shift register 2505, and 1 pixel (1 μm reduced by adders 2505 to 2508).
4 pixels (2 × 2 pixels) shifted in 4 directions by m) are added, and the average value of each average value is obtained by the dividers 2509 to 2512. Then, the maximum value determination circuit 2513 obtains the maximum value in the four directions, and the detected value 2514 from the foreign matter is obtained.
Output as.

In this method, only foreign matter is made bright and apparent by optical processing and detection is performed. Therefore, when the detected signal is larger than the set threshold value, it is determined that there is foreign matter (binarization). Therefore, foreign matter can be detected. However, the detection signal has variations in sensitivity characteristics (about ± 15%) for each pixel of the one-dimensional image sensor, and sensitivity unevenness (shading) due to the illuminance distribution of the illumination light source. As a result, as shown in FIG. 25, pixels that detect even the same foreign matter
The magnitude of the detection signal varies depending on (the position in the Y direction), and it is impossible to stably detect the foreign matter by binarizing with the threshold value.

In the present invention, as shown in FIG. 26, the shading correction data (b) obtained by previously measuring (a) the shading including the above with the standard sample 111 of FIG. 1 and calculating the reciprocal of this measurement data. ) Is obtained, the amplifier gain of the detector detection signal is changed for each pixel, and the influence of shading is eliminated to detect the foreign matter (c). The standard sample 111 is placed on the inspection stage in FIG. 1 or installed in the vicinity of the inspection stage, but it is also possible to place it on the sample table instead of the reticle only during shading measurement.

The standard sample 111 may be a sample having a surface of fine irregularities and having a uniform scattering characteristic. For example, a glass substrate having a fine processing mark formed by polishing or a thin film having fine irregularities such as a film formed by sputtering aluminum on the substrate is used. However, it is practically difficult to uniformly process the minute irregularities on the standard sample 111 with respect to the pixel 1 × 1 μm □. Therefore, the correction data is obtained from the average value obtained by repeating the shading measurement many times (for example, 1000 times).

Since the scattered light from the minute irregularities has unevenness of strength and weakness, the simple average value (for example, data obtained by repeating 1000 times divided by 1000) is too small, and the calculated value becomes small. Accuracy may decrease.

Under such a condition, the divided value may be set to a fraction of the number of repetitions (for example, 200 after 1000 repetitions).

As shown in FIG. 26, by comparing the shading (a) before correction and the shading (b) before correction, it can be seen that the shading, which was about 50% before correction, is corrected to 5% or less.

If the above-mentioned correction data is remeasured / updated for each inspection, the optical fluctuation component can be removed even if the illumination / detection system and the like are temporally unstable.

FIG. 27 shows a block diagram of a concrete example of the shading correction circuit. A / D the detected value of the one-dimensional image sensor
3212 converted value (here, 256 gradations, 8 bits)
To the subtraction circuit 3209 for subtracting the value of the dark current portion of the one-dimensional image sensor by the data from the memory 3206 controlled by the synchronization circuit 3205 for each pixel, and the shading correction magnification for each pixel by the synchronization circuit 3205. A value 3 obtained by A / D conversion (here, 256 gradations, 8 bits) of the detection value of the multiplication circuit 3210 that multiplies by the data from the memory 3207 to be controlled and the one-dimensional image sensor.
The intermediate bit output circuit 3211 is configured to return the multiplication result, which has double the number of bits of 212 (here, 16 bits) to the original number of bits (here, 8 bits). As can be seen from the figure, this example is an example in which correction is performed by a digital circuit, but similar results can be obtained even if correction is performed in analog before A / D conversion.

When the foreign matter determination is performed in pixel units of 2 × 2 μm square, for example, when there is a foreign matter having a size of 2 μm or more, the number of pixels for which the foreign matter is detected is different from the actual number of foreign matter. Become. If there is one foreign particle of 10 μm, it will be detected with the number of pixels of (10 μm / 2 μm) ² = 25, and if it is attempted to observe the detected foreign object, all 25 detection results will be detected. It is necessary to check it, which causes inconvenience.

Conventionally, this inconvenience is caused by the grouping processing function of checking the connection relation between pixels in which foreign substances are detected by software and judging that "one foreign substance is detected" when the pixels are adjacent to each other. Was avoiding. However, this method requires software-like processing, so that when a large number of detection signals are involved, it takes a long time (for example, about 10 minutes for 1000 detection signals) to cause a new inconvenience.

Therefore, in the present invention, the entire inspection area is divided into blocks of a visual field range (for example, 32 × 32 μm □) that can be observed at one time, and all detection signals in the same block are determined as the same foreign matter (block processing. ). As a result, even a large foreign matter can be observed and confirmed within a visual field range at one time regardless of its shape.

The block process is a simple grouping process in terms of function, but has a feature that it can be easily implemented as hardware. In the present invention, the processing is performed in real time by implementing the block processing in hardware, and the throughput of the apparatus including the inspection time can be significantly improved (in the case of 1000 detection signals, 2/3 or less of the conventional method). FIG. 28 shows a block diagram of a specific example of the block processing circuit.

In the case of the example of FIG. 28, not only the determination of the same foreign matter but also the number of detection signals which are the basis of the determination can be classified and counted by preset large / medium / small threshold values. It is also possible to know the maximum value of the detection signal in the block. From these data, it is devised so that it is possible to estimate the approximate size of a foreign substance and the situation in which a plurality of foreign substances are contained in the same block. Further, a circuit for outputting an inspection stop signal when the number of signals for detecting foreign matter reaches a preset number is also incorporated.

FIG. 29 shows an example of the relationship between the shading correction circuit, the 4-pixel addition processing circuit, and the block processing circuit.

[0076]

Since the present invention is configured as described above, a sub-micron layer adhered on a circuit pattern substrate such as a photomask, particularly a reticle having a phase shift film for the purpose of improving transfer resolution and the like. There is a remarkable effect that a fine foreign matter of the order can be easily and stably separated from the circuit pattern and detected mainly with a simple optical configuration.

[Brief description of drawings]

FIG. 1 is an overall schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an inspection situation of a reticle according to the present invention.

FIG. 3 is a diagram showing a configuration example of the irradiation system in FIG. 1 (in this case, the symmetrical side is omitted because it has the same configuration).

FIG. 4 is a diagram showing an inspection situation of a reticle according to the present invention.

FIG. 5 is a plan view illustrating an angle pattern of a circuit pattern according to the present invention.

FIG. 6 is a diagram showing a distribution state of scattered light and diffracted light on a Fourier transform surface according to the present invention.

FIG. 7A is a diagram showing a corner portion of a circuit pattern,
(B) is a detailed view of the "A" portion of (A).

FIG. 8 is a cross-sectional view showing a configuration of an imaging optical system.

FIG. 9 is a diagram showing an example of a foreign substance overlooked in the prior art.

FIG. 10 is a diagram for explaining a problem of the conventional technique.

FIG. 11 is a diagram for explaining a cause of a problem in the conventional technique.

FIG. 12 is a diagram in which scattered light from a foreign matter is detected by using the high NA optical system according to the present invention.

13 is a diagram showing a result of a detection experiment according to the configuration of the present invention shown in FIG.

FIG. 14 is a diagram showing an example of a detection optical system.

FIG. 15 is a diagram showing an example of a detection optical system.

FIG. 16 is a diagram showing an example of a detection optical system.

FIG. 17 is a diagram showing an example of a detection optical system.

FIG. 18 is a diagram showing an example of a detection optical system.

FIG. 19 is a diagram showing an example of a detection optical system.

FIG. 20 is a diagram showing an example of a detection optical system.

FIG. 21 is a diagram showing an example of a detection optical system.

FIG. 22 is a diagram when a foreign substance is detected by 2 × 2 μm pixels without performing the 4-pixel addition processing.

FIG. 23 is a diagram in which a foreign substance is detected in 1 × 1 μm pixels by a 4-pixel addition process.

FIG. 24 is a block diagram of an example of a 4-pixel addition processing circuit.

FIG. 25 is a diagram showing the influence of shading on foreign matter detection.

26A and 26B show the principle of shading, where FIG. 26A is a diagram showing a result of shading measurement (before correction), FIG. 26B is a diagram showing a result of calculating shading correction data, and FIG. 26C is a result of shading measurement (after correction). ) Is a figure.

FIG. 27 is a block diagram of an example of a shading correction circuit.

FIG. 28 is a block diagram of an example of a block processing circuit.

FIG. 29 is a diagram showing an example of a relationship between a shading correction circuit, a 4-pixel addition processing circuit, and a block processing circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Inspection stage part, 2 ... 1st illumination system, 3 ... 2nd illumination system, 4 ... Detection optical system, 5 ... Signal processing system, 6 ... Reticle, 9 ... Z stage, 10 ... X stage, 11 ... Y stage, 21, 31 ... Laser light source, 44, 444 ... Spatial filter, 51 ... Detector, 52 ... Binarization circuit, 70 ... Foreign matter, 80 ... Circuit pattern, 111 ... Standard sample, 112 ...
Block processing circuit, 113 ... Shading correction circuit,
114 ... 4-pixel addition processing circuit, 223 ... Concave lens, 22
4 ... Cylindrical lens, 225 ... Collimator lens, 226 ... Condensing lens, 47, 447 ... Half mirror, 49 ... Phase difference amount generating means.

Claims (5)

[Claims] 1. A foreign matter inspection apparatus for detecting foreign matter adhered on a transparent or semi-transparent substrate sample having a circuit pattern such as a photomask or reticle, wherein the substrate sample is placed in each of the X, Y, and Z directions. An inspection stage unit including a freely movable stage and its drive control system, an illumination system that obliquely irradiates the surface of the substrate sample on which the circuit pattern is formed, and the substrate sample by irradiation of the illumination system. Detection optics that collects scattered light generated on the screen, blocks the scattered light from the straight line portion of the circuit pattern by a spatial filter provided on the Fourier transform surface of the detection optical system, and forms an image on the detector. A system for detecting foreign matter, comprising: a system and a signal processing system for binarizing an output of the detector by a binarizing circuit with a threshold value set therein, and computing and displaying foreign matter data on the substrate sample. , Amplitude division of the optical path into two in the optical path of the detection optical system, and means for giving the amount of phase difference to each, and after giving the amount of phase difference, the optical paths are synthesized again, and the two optical paths interfere with each other on the detector. A foreign matter inspection device having a configuration. 2. The foreign matter inspection apparatus according to claim 1, wherein in the apparatus, the means for giving the amount of phase difference is constituted by an optical element such as a prism. 3. The foreign matter inspection apparatus according to claim 1, wherein the means for giving a phase difference amount in the apparatus is constituted by a liquid crystal element and a driving power source for the liquid crystal element. 4. The foreign matter inspection apparatus according to claim 1, wherein the means for giving a phase difference amount in the apparatus is composed of an electro-optic crystal and a driving power source thereof. 5. The foreign matter inspection apparatus according to claim 1, wherein the means for giving a phase difference amount in the apparatus is constituted by an optical element such as a prism and a positioning adjustment mechanism thereof.