JPH09281051A - Inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inspection apparatus for a reticle, by which the defect of the phase difference amount of a shifter in all regions inside a binary reticle is inspected in a short time and a contamination such as a dust particle, a low-step foreign body or the like impeding an exposure operation is inspected simultaneously, and which can be used as an inspection apparatus for a foreign body with reference to a reticle without a shifter. SOLUTION: The inspection apparatus is provided with a first microscope means by which at least one out of a transmission amplitude differential image, a transmission intensity differential image and a reflection intensity differential image can be changed into an image, a first signalization means and a photoelectric transaction means which generate a transmission amplitude differential signal, a transmission intensity differential signal and a reflection intensity differential signal which express the transmission amplitude differential image, the transmission intensity differential image and the reflection intensity differential image so as to be photoelectrically transduced independently, and a signal-intensity adjusting means which can adjust the relative intensity ratio of the transmission amplitude differential signal, the transmission intensity differential signal and the reflection intensity differential signal. The relative intensity ratio is adjusted by the intensity adjusting means, and an error signal is computed on the basis of the signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate defect inspection apparatus.

[0002]

2. Description of the Related Art A conventional binary reticle shifter phase difference amount defect inspection apparatus is, for example, SPEI, Proceedings series V.
olume 2254, "Photomask and X-Ray Mask technology,
As described in p.294-301, it is a device for measuring the phase amount of a phase shifter. The phase shifter part to be inspected in the reticle is placed in the visual field of the optical microscope, and the It is a phase shift amount measuring device for a reticle with a phase shifter, which measures the phase amount of one sampled point.

Therefore, the conventional apparatus of this kind can obtain only the inspection result for each sampled point for each inspection, and is not suitable for inspecting all the defects in the reticle. . Further, there is no idea of simultaneously detecting a phase difference amount defect and a contaminant such as dust or a low step foreign material.

[0004]

In view of such a situation, the present invention inspects defects of the phase difference amount of the shifter in all the areas in the binary reticle in a short time, and additionally interferes with the exposure of foreign matters and the like. An object of the present invention is to provide a reticle defect inspection apparatus that can simultaneously detect contaminants such as dust and low step foreign matter, and can be used as a foreign matter inspection apparatus for a reticle without a shifter.

[0005]

In order to achieve the above object, the present invention provides, for example, a defect inspection apparatus for inspecting a defect of a substrate, which includes a transmission amplitude differential image, a transmission intensity differential image, and a reflection intensity differential image. First capable of imaging at least one of the images
And a microscope means for producing a transmission amplitude differential image, a transmission intensity differential image, and a transmission amplitude differential signal, a transmission intensity differential signal, and a reflection intensity differential signal, which are independently photoelectrically converted and represent a differential signal. After having adjusted the relative intensity by the intensity adjustment means, the photoelectric conversion means and the signal intensity adjustment means capable of adjusting the relative intensity ratio of the transmission amplitude differential signal, the transmission intensity differential signal, and the reflection intensity differential signal. A low step foreign matter detecting means for calculating an error signal based on these signal intensities and mainly detecting a low step foreign matter based on the error signal,
Further, a second microscope means capable of imaging at least one of a transmission dark field image and a reflection dark field image, and a transmission dark field image, a transmission dark field signal representing the reflection dark field image, and a reflection dark field signal, It has two signalizing means, mainly detects the dust foreign matter by using at least one of the transmitted dark field signal and the reflected dark field signal, and made it possible to detect both the foreign matter with the low step and the dust foreign matter.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the features of an inspection apparatus according to an embodiment of the present invention. Many of the conventional foreign matter inspection devices depend on, for example, only the dark field optical system. For this reason, foreign matter such as dust that has a prominent feature in its shape is easily detected, but it is flat without any prominent feature in the shape such as a stain or a semi-transparent organic residue. No foreign material could be detected. Further, such a simple bright-field optical system is not sufficient for detecting foreign matter on a flat surface, and a technique for improving the contrast of a phase object is required.

The low step foreign matter detecting section of the present invention can easily detect the low step foreign matter by using an optical system which does not detect the circuit pattern as shown in FIG. At the same time, it is possible to easily detect dusty foreign substances by using an optical system that does not detect a circuit pattern, by dark field microscope technology and combination technology of transmitted dark field image and episcopic dark field image, which is unique to the present invention. is there.

FIG. 1 shows a differential interference image for detecting a low step foreign matter,
It is shown that the intensity differential image is used, and the reflection dark field image and the transmission dark field image are used to detect dusty foreign matter. Further, as a functional feature of the inspection device of the present invention, dusty foreign matter,
It is to be able to easily and automatically sort by examining a detection system that detects a semitransparent foreign substance. Also, if automatic classification is not required, it is easy to display the comprehensive result.

FIG. 2 is a schematic view of an optical system suitable for the inspection apparatus according to the embodiment of the present invention. The light beam emitted from the laser is deflected by the scanning means, separated by the Nomarski prism by a minute angle, and by the objective lens, it becomes two light beams separated by a minute distance and narrowed down into two minute light spots. Since the two beam spots are separated by a very small distance, they can be regarded as one spot in fact.

The minute light spot optically scans the surface to be inspected on the reticle by the deflecting action of the scanning means. The reticle is placed on a stage that can move at a constant speed, and is conveyed by the stage in the direction perpendicular to the optical scanning direction, and the minute light spot raster-scans the entire surface to be inspected. The scattered light component, the direct reflected light, and the direct transmitted light generated from the minute light spot are photoelectrically converted by the detector as described below.

In the differential amplitude image detection system for both transmission and reflection, two differential interference image detectors for independently photoelectrically converting the rays separated by the polarization beam splitter are installed. These two detectors output a differential interference image 1 and a differential interference image 2 of transmission and reflection. Similarly, the intensity differential detection system for both transmission and reflection is provided with two bright-field image detectors that independently photoelectrically convert the rays separated by the polarization beam splitter. These two detectors output a bright field image 1 and a bright field image 2 which are transmitted and reflected.

Although the transmission and reflection dark-field image detector is shown as a single detector, when applying the well-known spatial frequency filtering technique, a plurality of light receiving elements are arranged vertically symmetrically with the reticle in between. . Bright field, dark field scattered light components, direct reflected light, and direct transmitted light are incident on these detectors, and are photoelectrically converted.

Next, the signal processing circuit will be described with reference to FIG. The transmission differential interference interference images 1 and 2 are two wavefront interference images divided by the Nomarski prism by a predetermined distance, and the two wavefronts have different phase differences when they interfere with each other. In particular, the differential amplifier A1 outputs a transmission amplitude differential signal when an interference image with a phase difference of 180 ° + α ° and 180 ° −α ° for one arbitrary α with a phase difference of 180 ° as a boundary is input. When the reflected differential interference contrast images 1 and 2 have exactly the same conditions,
The differential amplifier A2 outputs a reflected amplitude differential signal.

The transmitted bright-field images 1 and 2 are bright-field images with one wavefront separated by a predetermined distance by a Nomarski prism, and these are a transmission intensity differential signal by a differential amplifier A3. The reflected bright-field images 1 and 2 are also reflected intensity differential signals by the differential amplifier A4. Above 4
The image of the defect-free circuit pattern of the two differential signals is removed by the defect-free circuit pattern removal circuit 1, and mainly has information of a low step foreign material. It becomes a low step foreign matter signal.

The reflected dark-field image and the transmitted dark-field image are input to the defect-free circuit pattern removal circuit 2 as electric signals representing them, which mainly serve as a dust particle signal having information of dust particles. The low step foreign matter signal and the dust foreign matter signal are binarized by a window comparator in the dust foreign matter / low step foreign matter sorting circuit and converted into a detection signal with the foreign matter. When the foreign matter is present, the low step foreign matter signal and the dust foreign matter signal are detected. Information on the signal strength and the existing position is stored in the inspection result storage for dust and foreign matters and the low step foreign matter inspection result storage in the inspection result storage.
After the inspection is completed, these data are read and displayed in the inspection result display device, whichever is the most suitable one of the dust foreign material inspection result display device, the low step foreign material inspection result display device or the total result display device. To be done. Further, it is easy for the operator to select the display method.

Next, an optical system suitable for dust detection will be described.
As shown in FIG. 4, the dark field detection system is arranged at a position where the direct transmitted light and the direct reflected light of the illumination light do not enter. As shown in FIG. 4, since the bright-field transmission amplitude image can be regarded as the addition result of the DC component and the image in the opposite phase of the bright-field reflection amplitude image, the bright-field transmission amplitude image and the bright-field reflection amplitude image field AC component 0 Scattered light components (diffraction images) other than the next light have similar shapes, and in the dark field optical system symmetrically arranged in the vertical direction as shown in FIG. 2, the intensity ratio of the scattered light of the circuit pattern is constant in the vertical direction. Therefore, either monitor these intensity ratios or make gain adjustments up and down so that the intensity ratio becomes 1, and then create a signal representing the signal intensity difference,
By monitoring this, it is possible to detect the occurrence of scattered light caused by a foreign substance, in which the signal intensity ratios of the upper and lower sides generated from other than the circuit pattern are different from the circuit pattern.

FIG. 5 shows the calculation result regarding the detection of foreign matter by this method. From this, the signal intensity ratio between the foreign object and the circuit pattern is significantly different between the transmitted image and the reflected image, and the foreign object can be detected by monitoring the intensity ratio, and the intensity ratio of the circuit pattern signal can be reflected and transmitted by adjusting the gain of the electrical system. If it is set to 1: 1, the difference becomes zero (pattern difference image), and an image in which only foreign matter remains (foreign matter difference image) is obtained. FIG.
Shows an example of low step foreign matter detection by a transmission / reflection interference image.

FIG. 6 shows two coherent optical images due to transmitted rays laterally displaced by the Nomarski prism. When there is a phase difference of an odd multiple of π between these wavefronts, the interference image shown in FIG. 6 is obtained and only the edges are brightened. FIG. 6 shows two coherent optical images due to reflected rays laterally displaced by the Nomarski prism. When there is a phase difference of an odd multiple of π between these wavefronts, the interference image of FIG. 6 becomes similar to that of FIG. 6, and only the edges are brightened. The intensity values of these interference images are generally different. This is because the transmission image depends on the transmittance of the mask substrate and the reflection image depends on the transmittance of the circuit pattern. If the relative intensity of these images is adjusted to 1: 1 and then an error signal indicating a difference is created, the error signal becomes zero in any circuit design unless there is a defect such as a foreign substance. This is because the reflection interference image and the transmission interference image are similar and the intensity ratio is always a constant value. By monitoring the change in the error signal, it is possible to detect a foreign substance and an abnormality in the phase amount of the phase shifter. It goes without saying that the change in the intensity ratio between the reflection interference image and the transmission interference image may be directly monitored. FIG. 7 shows an example of low step foreign matter detection based on a bright field image and an interference image.

FIG. 7 shows two bright-field reflection images (intensity images) laterally displaced by the Nomarski prism, which are photoelectrically converted separately. The difference in intensity of these intensity images is shown in FIG. The reflected intensity differential image has the polarity reversed at the rising and falling edges. Fig. 7 shows lateral shift due to the Nomarski prism, and the phase difference between the two wavefronts is π.
It is an interference image at an odd multiple of / 2.

FIG. 7 shows π for the case where the light is laterally displaced by the Nomarski prism and the phase difference between the two wavefronts is
It is an interference image when the difference is an odd multiple of. The interference images with and are separately photoelectrically converted, and the differential image of the reflection amplitude of the difference in these intensities is obtained. This is an image like that, and is an image almost similar to that in FIG. 7. The intensity values of these differential images are generally different. This is because the differential reflection intensity image depends on the reflectance of the mask substrate, and the amplitude differential image depends on the reflectance of the circuit pattern and the pattern thickness. By adjusting the relative intensity of these images to 1: 1 and then generating an error signal indicating the difference, the error signal becomes almost zero in any circuit design unless there is a defect such as a foreign substance. (Strictly speaking, the second-order differential component remains.) This is because the reflection interference image and the transmission interference image are substantially similar to each other, so that the intensity ratio is always a substantially constant value. By monitoring the change in the error signal, it is possible to detect a foreign substance and an abnormality in the phase amount of the phase shifter. It goes without saying that the change in the intensity ratio between the reflection interference image and the transmission interference image may be directly monitored.

A reticle (low reflectivity) with brush residue (a nylon brush residue in the cleaning process, which is a typical low step translucent foreign material found on a reticle) as shown in FIG. It is a reflected brightfield image of a circuit pattern made of a chrome film and having a minimum line width of 2 μm. FIGS. 9, 10 and 11 show foreign object images in which the error signal, that is, the image of the pattern, which is displayed on the inspection result display section by the inspection apparatus of the present invention as the sample, is removed at the same position. FIG. 9 shows FIGS.
5 is a foreign matter image by the dust foreign matter detection method described in 5. FIG. 10 is an image of a foreign substance by the low step foreign substance detection method described with reference to FIG.

FIG. 11 shows a foreign substance image obtained by the low step foreign substance detecting method described with reference to FIG. It can be easily imagined that these foreign substance images can be binarized by the signal intensity and the foreign substances can be detected without being affected by the pattern. In such a case, it can be imagined that there are many foreign substances that can be detected only by a specific inspection method.

In the present invention, these different foreign matter images can be displayed on the inspection result display section. Further, it is possible to automatically classify the foreign matter as a dusty one having a projecting portion or a flat low-step foreign matter based on these inspection results.
Further, by summing up these detection results, it is possible to detect a larger amount of foreign matter than in the case of inspecting alone. Further, in a specific reticle, for example, a reticle with a phase shifter of the Levenson type, the gain of the error signal of the inspection method using the amplitude differential image of the transmission suitable for this inspection is selectively increased, and the pattern is not completely erased in the shifter portion. It is also easy to reduce the gain of the error signal of the inspection method, and it is possible to detect foreign matter with the highest sensitivity for any reticle type.

[0024]

As described above, according to the present invention, a conventional reticle having a circuit pattern using a chrome light-shielding film,
Simultaneously inspecting for halftone reticles with a circuit pattern drawn only by the phase shifter made of a light-transmissive thin film, for abnormal phase shift in the phase shifter and for the presence of foreign matter on the light-transmissive phase object. It is possible to provide an inspection device capable of performing the above.

According to the present invention, since foreign substances are detected simultaneously by a plurality of different inspection methods, it is possible to prevent the detection omission of foreign substances. Further, since the inspection can be performed at the same time by the inspection method suitable for detecting dust foreign matter and the inspection method for detecting low step foreign matter, the detected foreign matter can be automatically classified as dusty or low step foreign matter. In the present invention, the foreign matter images obtained by these different inspection methods can be displayed separately or in an overlapping manner on the inspection result display portion, and the foreign matter can be satisfactorily observed. .

Further, in a specific reticle, for example, a reticle with a phase shifter of the Levenson type, the gain of the error signal of the inspection system using the amplitude differential image of the transmission suitable for this inspection is selectively increased so that the pattern is completely in the shifter portion. It is easy to reduce the gain of the error signal of the inspection method that is not erased, and it is possible to detect foreign matter with the highest sensitivity for any reticle type.

[Brief description of drawings]

FIG. 1 is a feature of the inspection apparatus of the present invention

FIG. 2 is a configuration diagram of an optical system according to an embodiment of the present invention.

FIG. 3 is a configuration diagram of a dust detection optical system according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of the principle of dust detection in the embodiment of the present invention.

FIG. 5 is an explanatory diagram of a simulation result of dust detection according to the embodiment of the present invention.

FIG. 6 is an explanatory view of the principle of detecting a foreign matter with a low step by a transmission / reflection interference image in the embodiment of the present invention.

FIG. 7 is an explanatory diagram of the principle of low step foreign matter detection by an intensity differential image and an amplitude differential image in the embodiment of the present invention.

FIG. 8 is a bright-field image of a reticle with brush residue.

FIG. 9 is a brush residue detection result by the dust detection method of the present invention.

FIG. 10 is an intensity differential image in the embodiment of the present invention,
Brush dust detection result by low step foreign matter detection method by differential amplitude image

FIG. 11 is a result of brush dregs detection by a low step foreign matter detection method based on transmission / reflection interference images in the embodiment of the present invention.

FIG. 12 is a conceptual configuration diagram of a signal processing system in the embodiment of the present invention.

Claims (5)

[Claims] 1. A defect inspecting apparatus for inspecting a defect of a substrate, comprising first microscope means capable of imaging at least one of a transmission amplitude differential image, a transmission intensity differential image and a reflection intensity differential image, A transmission amplitude differential image, the transmission intensity differential image, an independently photoelectrically converted transmission amplitude differential signal representing the reflection intensity differential image, a transmission intensity differential signal, and a reflection intensity differential signal are generated.
A first signal converting unit, a photoelectric converting unit, and a signal strength adjusting unit capable of adjusting a relative intensity ratio of the transmission amplitude differential signal, the transmission intensity differential signal, and the reflection intensity differential signal, the intensity adjusting unit After adjusting the relative intensity by, the error signal is calculated based on these signal intensities, and the foreign matter with a low step is mainly detected based on the error signal. Second microscope means capable of imaging at least one of the reflected dark field images, and second signal conversion means for generating the transmitted dark field image, the transmitted dark field signal representing the reflected dark field image, and the reflected dark field signal. An inspection apparatus characterized in that it mainly detects a dust foreign matter by using at least one of the transmitted darkfield signal and the reflected darkfield signal, and can detect both a foreign matter with a low step and a dust foreign matter. 2. A defect inspecting apparatus for inspecting a defect of a substrate, comprising: first microscope means capable of imaging at least one of a reflection amplitude differential image, a reflection intensity differential image and a transmission intensity differential image; A first signal conversion unit photoelectric conversion unit that generates a reflection amplitude differential signal, a reflection intensity differential signal, and a transmission intensity differential signal that have been independently photoelectrically converted to represent a reflection amplitude differential image, a reflection intensity differential image, and a transmission intensity differential image; , The reflection amplitude differential signal, the reflection intensity differential signal, having a signal intensity adjusting means capable of adjusting the relative intensity ratio of the transmission intensity differential signal, after adjusting the relative intensity by the intensity adjusting means, An error signal is calculated based on these signal intensities, and a foreign substance with a low step is mainly detected based on the error signal. At least one of A second microscope means capable of imaging, and a second signalization means for generating the transmitted dark field image, the transmitted dark field signal representing the reflected dark field image, and the reflected dark field signal, wherein the transmitted dark field An inspection apparatus characterized by mainly detecting dust foreign matter by using at least one of a signal and a reflected dark field signal, and capable of detecting both low-step foreign matter and dust foreign matter. 3. A defect inspection apparatus for inspecting a defect of a substrate, which is capable of imaging at least one of a reflection amplitude differential image, a reflection intensity differential image, a transmission amplitude differential image, and a transmission intensity differential image. Independently photoelectrically converted reflection amplitude differential signal, reflection intensity differential signal, transmission intensity differential signal, transmission intensity differential signal that represents the microscope means and reflection amplitude differential image, reflection intensity differential image, transmission amplitude differential image, transmission intensity differential image And a signal intensity adjustment capable of adjusting a relative intensity ratio of the reflection amplitude differential signal, the reflection intensity differential signal, the transmission amplitude differential signal, and the transmission intensity differential signal. Means for adjusting relative intensity by the intensity adjusting means, calculating an error signal based on these signal intensities, and detecting a foreign matter mainly having a low step based on the error signal. Foreign material Output means, further second microscope means capable of imaging at least one of the transmission dark field image and the reflection dark field image, the transmission dark field image, the transmission dark field signal representing the reflection dark field image, and the reflection dark field A second signal converting means for generating a signal is provided, and dust foreign matter is mainly detected by using at least one of the transmitted dark field signal and the reflected dark field signal, and both the low step foreign matter and the dust foreign matter are detected. Inspection device characterized by being detectable 4. When an image is formed by observing a detected foreign substance by the foreign substance inspection, the same optical system as that used for the foreign substance inspection is used to remove the pattern image and to generate an error signal that allows only the foreign substance to be observed. 3. A display device capable of displaying an image of a proportional luminance signal.
Or the inspection device described in 3. 5. The inspection device according to claim 1, 2 or 3, wherein the use states of a plurality of inspection methods are automatically changed depending on the inspection target.