JPH0582933B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is directed to a reticle and mask exposure process used to manufacture LSIs or printed circuit boards, in which patterns on the reticle and mask are transferred onto a wafer. This invention relates to a foreign matter inspection method and apparatus for detecting foreign matter and defects on the reticle and mask before transfer, particularly for inspecting foreign matter and defects on the reticle and mask in a short time with easy operation. The present invention relates to a suitable foreign substance inspection method and device. [Prior Art] In the exposure process used in LSI manufacturing, a chrome pattern on a thick plate called a reticle is printed and transferred onto a semiconductor wafer. In this process, if foreign matter or defects are present on the reticle, the pattern will not be accurately transferred to the semiconductor wafer, resulting in all LSI chips being defective. Therefore, inspection for foreign matter and defects before exposure is essential for reticle management. In addition, as LSIs have become highly integrated and wiring patterns have become finer, smaller foreign particles have become a problem. In addition, foreign matter on the flat thin film, such as resist residue from reticle manufacturing, etching of chromium or chromium oxide for pattern formation, and impurities dissolved in the reticle cleaning solution that aggregated during cleaning and drying, can become a problem.
The number is on the rise. Conventionally, the above-mentioned foreign object and defect inspection apparatuses have been used, for example, as described in Japanese Patent Laid-Open No. 59-65428,
means for irradiating and scanning the substrate with laser light from an oblique direction; and a first means for condensing the scattered light of the laser light, which is provided above the substrate so that the irradiation point of the laser light and the focal plane approximately coincide with each other. a lens, a light-shielding plate provided on the Fourier transform surface of the first lens to block regularly scattered light from the substrate pattern, and a second lens for inverse Fourier-transforming the scattered light from foreign objects obtained through the light-shielding plate. , consisting of a slit that is provided at the imaging point of the second lens and blocks scattered light from sources other than the laser beam irradiation point on the substrate, and a light receiver that receives scattered light from foreign objects that have passed through the slit. is proposed. This proposal focuses on the fact that patterns generally consist of the same direction or a combination of two or three directions within the field of view, and uses a spatial filter installed on the Fourier transform surface to filter out the diffracted light from the patterns in these directions. By removing the foreign matter, only the light reflected from the foreign object is emphasized and detected. In addition, conventionally, for example, as described in JP-A-58-139278, data detected using the same irradiation and detection optical system as an exposure device is compared with standard reticle data or designed data. Defect detection methods have been proposed. [Problems to be Solved by the Invention] Among the above-mentioned conventional techniques, Japanese Patent Application Laid-Open No. 59-65428 uses a light shielding plate to separate the light reflected from a foreign object from the light reflected from a pattern, and a slit to separate the light reflected from a foreign object from the light reflected from a pattern. The detection mechanism is simple because it detects only the reflected light from the foreign object and the foreign object is detected using a binarization method, but on the other hand, it is difficult to detect the foreign object by using a laser beam illumination from an oblique direction. Since foreign objects are detected using indirect illumination, which is different from the original exposure equipment, only the reflected light from chrome patterns at a specific angle is blocked, making it impossible to distinguish foreign objects from all chrome patterns. Can not. Furthermore, when detecting by indirect means as described above, foreign objects that do not cause actual damage (hereinafter referred to as false alarms) may also be detected. In particular, as patterns become finer and the number of foreign objects that become a problem increases, the number of foreign objects that cause the same degree of harm but do not cause actual damage also increases, which increases the number of false alarms and increases the number of foreign objects that cause foreign object checks. , analysis, and removal work increases, resulting in a significant decrease in work efficiency. Next, among the above-mentioned conventional techniques, JP-A No. 58-139728
In this patent, the optical system has the same optical system as the exposure device, so the configuration of the optical system is simpler than that of the prior art described above. However, on the other hand, the image signal processing system for comparing data is There are problems that are more complex than the technology and require a lot of time to inspect. An object of the present invention is to provide a method and apparatus for detecting foreign matter that solves each of the problems of the prior art and makes it possible to separate and detect only foreign matter that causes actual damage from a chrome pattern that is present at an arbitrary angle. It is in. [Means for Solving the Problems] The above object is to improve the degree of spatial coherence of the means for transmitting illumination to the sample in a foreign matter inspection method for inspecting foreign matter adhering to the surface of the test sample during exposure of the sample. A light-shielding plate placed on the Fourier transform surface of the imaging optical system, which focuses the sample almost uniformly on the detector and processes the detection signal, blocks diffracted light other than light scattered by foreign matter from the sample. In a foreign matter inspection device that inspects foreign matter that adheres to the surface of a sample when the sample is exposed to light by an exposure device, the device includes a means for placing the sample, and a means for placing the sample on the surface of the sample by transmitting illumination. a transmitted illumination means formed to be able to adjust the degree of spatial coherence; an imaging optical system that images the sample on a detector and processes a detection signal; This is achieved by providing a light shielding plate that blocks diffracted light other than light scattered by foreign matter from the sample. [Function] The present invention focuses on the fact that the light beam contributing to image formation is diffracted and scattered by foreign objects and defects, which causes transfer failures. Generally, the numerical aperture (hereinafter referred to as NA) on the entrance side (object side) of a reduction projection lens is designed to a value that provides sufficient resolution to image a pattern on a reticle. Therefore, the light beam that contributes to the image formation of the pattern passes through the aperture on the entrance side of the reduction projection lens, but the light beam that passes outside this aperture does not contribute to the image formation of the pattern. If a minute foreign object is present, the light beam scattered and diffracted by the foreign object passes outside the incident side NA of the reduction projection lens and becomes an obstacle to pattern imaging. This point can be further understood from, for example, the description in ``Response Function of Optical System with Spatial Filter'' in ``Wave Optics'' by Hiroshi Kubota, pages 387 to 389. That is, in the above literature,
By placing a disc-shaped spatial filter on the Fourier transform surface of the imaging optical system, the spatial frequency determined by the diameter of this disc-shaped spatial filter can be obtained. For example, if the inside of the lens is covered with a circle with radius d' , it is stated that only patterns having a specific spatial frequency determined by the size of this radius d' are not resolved. Therefore, this description can also be applied to a technique that detects only foreign objects by utilizing the difference in spatial frequency between the pattern and the foreign object, or in other words, the difference in size between the pattern and the foreign object. The present invention utilizes the above-mentioned principle to use an illumination system equivalent to the illumination system used in an exposure apparatus and an objective lens having an NA larger than the NA of the reduction projection lens.
The same area as the incident side NA of the reduction projection lens, that is, the diffracted light, is blocked by a light shielding plate, thereby allowing only the scattered light from foreign objects to be taken in. Therefore, in the present invention, it is possible to select and detect only the light beam that is scattered and diffracted by foreign objects and defects and passes through the aperture of the objective lens outside the aperture on the entrance side of the reduction projection lens of the exposure device. Therefore, it is possible to detect only foreign substances that cause actual damage by distinguishing them from patterns. [Example] Below, Figs. 1 to 4, which are an example of the present invention, are shown.
The diagram will be explained. As shown in FIG. 1, the foreign matter inspection apparatus according to the present invention includes a sample stage section 1 , a transmitted illumination section 2 , an epi-illumination section 3, a detection section 4, and a detection processing section 5. The sample stage section 1 includes a Z stage 9 that fixes a reticle 6 having a pellicle 7 by a fixing means 8 and scans it in the Z direction, and an X stage 10 that scans the reticle 6 in the X direction via this Z stage 9.
A Y stage 1 scans the reticle 6 in the Y direction via the X stage 10 and the Z stage 9.
1, a stage drive system 12 that drives each of the stages 9, 10, and 11; a focus position detection system 13 that detects the position of the reticle 6 in the Z direction; The reticle 6 has a processing system 14 that drives the system 12, and is configured to be able to focus the reticle 6 with the minimum necessary accuracy at all times during inspection. The X stage 10 has a uniform acceleration time of about 0.1 seconds, a uniform motion of 0.1 seconds, and a uniform deceleration time of 0.1 seconds.
It is designed to move in two cycles at a maximum speed of about 1 mm/sec and an amplitude of 200 mm. The Y stage 11 is formed to move the reticle 6 in the Y direction in steps of 0.15 mm in synchronization with the uniform acceleration time and uniform deceleration time of the X stage 10, and transfers the reticle 6 in the Y direction in steps of 0.15 mm during one inspection period. Since it is possible to move 100 mm in about 130 seconds by transferring the probe once, it is possible to scan an area of 100 mm square in about 130 seconds. Note that in this embodiment, the X/Y stages 10 and 11
However, it is not limited to this, for example, XΘ that scans the rotation direction and the
It goes without saying that a stage may be used, and the scanning speed may be set as desired, as the above is just an example. Further, the focal position detection system 13 may be one that uses an air micrometer, one that detects the position by laser interferometry, or one that projects a striped pattern and detects its contrast. The transmitted illumination unit 2 uses a color separation filter 22 to select the g-line (wavelength 436 mm) or i-line (wavelength 365 mm) used in an exposure device (not shown) from the light beam emitted from the mercury lamp 21, and selects the g-line (wavelength 436 mm) or i-line (wavelength 365 mm) from the light beam emitted from the mercury lamp 21, 2
3, when the light is focused on the diffuser plate 24, the light diffused by the diffuser plate 24 is emitted from a portion limited by the circular aperture 25, enters the collimator lens 26, and irradiates the reticle 6. has been done. Note that the aperture 25 is the collimator lens 26.
, and is formed so that the image is formed at a focal position 46 shown by a chain line above the collimator lens 26 and the objective lens 41 of the detection unit 4 . Furthermore, in order to achieve the above object of the present invention,
It is necessary not only to make the wavelength of the illumination light the same as that of the illumination light used in the exposure apparatus, but also to make the angle Θ of the light beam incident on one point 15 on the reticle b the same. Here, sinΘ is the "spatial coherence degree"
It is defined as Furthermore, since the illumination of the exposure device needs to uniformly illuminate the entire range on the reticle 1,
In place of the diffuser plate 24, an optical element called an integrator (hereinafter referred to as an indexer), which is a collection of rod-shaped lenses, is used. The function of this indexer is basically the same as that of the diffuser plate 24, and the inspection range to which the present invention is applied is the reticle 6.
Since the thickness ranges from several hundred microns to 1.2 mm, the diffusion plate 24 is sufficient. Furthermore, since the incident angle Θ of the light beam incident on the reticle 6 is determined by the size of the indexer, that is, the diameter of the aperture 25 installed behind the diffuser plate 24, the exposure apparatus using the reticle 1 The aperture of the diaphragm 25 is set to have the same degree of spatial coherence as the illumination used. Furthermore, in the exposure apparatus, since the position of the indexer is not necessarily installed at the focal position of the collimator lens 26, the position of the aperture 14 does not necessarily need to be installed at the focal position of the collimator lens 26. However, in order to make the incident angle Θ of the light beam constant at any position within the irradiation range of the light on the reticle 6, it is preferable that the aperture 25 be installed at the focal position of the collimator lens 26. This has the effect that the illumination conditions for the light beam within the measurement range can be made the same and the conditions for detecting foreign objects can be made the same. The epi-illumination section 3 passes the light emitted from the mercury lamp 31, passes through the color separation filter 32, the condensing lens 33, the diffuser plate 34, and the diaphragm 35, and passes the light through the relay lens 36 to the half mirror of the detection section 4 . 42
and an objective lens 41 so that the reticle 6 is irradiated with the light. Note that the objective lens 41 is connected to the transmitted illumination section 2.
It has the same function as the collimator lens 26. Further, the relay lens 36 is installed at a focal point 46 above the objective lens 41 to create an apparent aperture. Specifically, a real image of the aperture 35 is formed at the focal point position 46. Furthermore, in the epi-illumination section 3 as well, the wavelength of the irradiation light and the reticle 6 are determined similarly to the transmission illumination section 2 .
The aperture of the diaphragm 35 is determined so that the angle Θ ₂ of the light beam incident on any one point 15 above is the same as that of the illumination light used in the exposure device. Further, since the epi-illumination section 3 is installed to detect foreign matter on the chrome pattern on the reticle 6, it is unnecessary if there is no need to detect foreign matter on the chrome pattern. Furthermore, if the epi-illumination section 3 is used simultaneously with the transmitted-illumination section 2 , there is a problem that the signal from the edge of the pattern becomes large, so if this becomes a problem, it is necessary to use them separately. The wavelength of the irradiation light does not necessarily have to be g-line and i-line, and may be other broadband light including g-line and i-line. The reason for this is that the foreign matter and the pattern have different diffraction conditions for light of all wavelengths, so even if the light is in the optical band, the foreign matter can be detected separately from the pattern. The detection unit 4 has an objective lens 41, a half mirror 42, a field lens 43, a light shielding plate 44, and an image forming unit 45, and has an inspection point 15 on the reticle 6.
is formed so as to be imaged onto the inspection device 51 by the objective lens 41 and the imaging lens 45.
Further, the detection unit 4 includes a viewing zone lens (hereinafter referred to as a field lens) 43 near the image forming position of the objective lens 41. This field lens 4
3 forms an image of the upper focal point 46 of the objective lens 41 on the circular light shielding plate 44 . That is, the diaphragm 25 of the transmitted illumination unit 2 passes through the collimator lens 26 and the objective lens 41, is reflected on the reticle 6, and is reflected again into the objective lens 4.
1, passes through the field lens 46, and forms an image on the light shielding plate 44. At this time, the position of the light shielding plate 44 is the position of the Fourier transform of the position of the reticle 6 with respect to the position of the light source, that is, the position of the aperture 25. Generally, the NA of the reduction projection lens of the exposure apparatus on the reticle 6 side is 10% to 40% higher than the degree of spatial coherence of the illumination system of the exposure apparatus (equivalent to the degree of spatial coherence of the transmitted illumination section 2 ).
It is set to a large value of around 10%, and in most cases it is around 10%. Further, since it is necessary for the objective lens 41 to pass the light beam passing outside the entrance side aperture of the reduction projection lens into the aperture, its NA is made larger than the NA of the reduction projection lens. In order to cut off the luminous flux that enters the
The light shielding plate 44 is provided. Therefore, in order to achieve the object of the present invention, it is desirable to calculate the diameter dm of the light shielding plate 44 using the following equation (1). That is, it is desirable that dm=d _S・α・NA/sinΘ _S・(1+δ) (1). Here, d _S is the diameter of the aperture 25, α is the magnification of the imaging system of the aperture 25 and the light shielding plate 44, and NA is the value on the reticle 6 side of the reduction projection lens. sinΘ _S is the degree of spatial coherence of the exposure device. As already mentioned, in this case, if Θ= _ΘS , the foreign object detection conditions can be made the same. Furthermore, it has been confirmed through experiments that δ may be a margin of several percent. Note that if all the inspection areas on the reticle 6 are inspected at the same time, the shape of the objective lens 41 becomes large, making it practically difficult to manufacture. Therefore, the present invention limits the inspection area on the reticle 6 and scans the reticle 6 with the sample stage 1 so that the entire inspection area can be inspected. An objective lens 41 with a large NA can be used. In addition, in order to detect not only foreign substances that cause actual damage but also foreign substances, the light shielding plate 44 does not necessarily need to match the NA of the incident side of the reduction projection lens used in the exposure apparatus, and the It is sufficient to match the degree of spatial coherence of the epi-illumination unit 3 .
That is, the transmitted illumination section 2 and the transmitted illumination section 3
It is sufficient to block the 0th order diffracted light of the illumination light from the above, and it may be larger than this. Specifically, in equation (1) above, NA/sin θ=1, and δ may be set to any value larger than several percent. Furthermore, the degree of spatial coherence of the illumination light does not necessarily have to match the degree of coherence of the exposure apparatus, and the degree of spatial coherence of the illumination light does not necessarily have to be adjusted to the degree of coherence of the exposure apparatus. 25, 35 and the size of the light shielding plate 44 may be determined. Moreover, when the epi-illumination section 3 is not installed,
The half mirror 42, field lens 43, and imaging lens 45 are also omitted, and the light shielding plate 44 is placed at the focal point 46, and the detector 51 is placed at the field lens 43.
It is possible to obtain the effects of the present invention even if the devices are installed in the positions where the devices were previously installed. In this case, an optical system with an extremely simple configuration can be obtained. The signal processing section 5 includes a detector 51, a binarization processing circuit 52, a microcomputer 53, and a CRT.
54. The detector 51 is formed of, for example, a charge transfer type one-dimensional solid-state image sensor, and is mounted on the X stage 10.
The detector 51 detects the signal while scanning. That is, if a foreign object is present on the reticle 6, the level and light intensity will increase, so the output of the detector 51 is designed to increase. Note that the detector 51 is not limited to the one-dimensional solid-state imaging device as described above, but may also be a two-dimensional one or a single element one. The binarization processing circuit 52 is configured to determine the presence or absence of foreign matter by setting a binarization threshold in advance. The microcomputer 53 pre-evaluates an evaluation function, that is, a function of the foreign material causing actual damage, since whether or not a foreign material causes actual damage such as poor transfer is a function of the intensity of the scattered light due to the foreign material and the size of the foreign material. The evaluation function is used to determine the presence or absence of a foreign substance that may cause actual damage, and the result is output to the CRT 54. Since the foreign matter inspection apparatus according to the present invention is constructed as described above, the inspection method will next be explained with reference to FIGS. 2 to 4. As shown in FIG. 2, a pattern 17, two foreign objects 18a and 18b, and a defect 1 are formed on a glass substrate 16.
Regarding the case where pattern 17 exists, one of the small foreign particles 18a is minute, so pattern 17
The edge 17a scatters or diffracts light more than the edge 17a. That is, the light beam 56 scattered outside the range Θ blocked by the light shielding plate 44 is pattern 1.
The number of the edges 17a of 7 is larger than the luminous flux 55 of the edge 17a. Furthermore, since the spatial frequency around the other large foreign object 18b or the defect 19 of the pattern 17 is high, the light beams 57 and 58 scattered outside the range Θ blocked by the light shielding plate 44 are larger than the light beams 55 of the edge 17a of the pattern 17a. There will also be more. Therefore, the output of the detector 51 generates output peaks 59, 60, 61, 62 due to the respective light beams 55, 56, 57, 58 as shown in FIG. On the other hand, if the threshold value 63 is set in the binarization processing circuit 52 as shown in FIG.
As the above output, the three output peaks 60, 6
1 and 62 protrude, so that only the two foreign objects 18a and 18b and the defect 19 of the pattern 17 can be detected. At this time, the coordinates of the X and Y stages 10 and 11 and the levels of the output peaks 60 and 61 are stored in the memory managed by the microcomputer 53, and the stored contents are processed and
Output to CRT54. [Effects of the Invention] According to the present invention, illumination that is optically equivalent to the illumination of an exposure device is used to eliminate scattering and scattering caused by foreign objects and defects.
Since it is possible to selectively detect the light that is diffracted and no longer enters the reduction projection lens of the exposure device, it is possible to distinguish only foreign substances that cause actual damage from the pattern and detect them. In addition, since the inspection area on the reticle is limited and the entire inspection area can be inspected by scanning the reticle, it is better than the normally used reduction projection lens.
An objective lens with a large NA can be used. Furthermore, the configuration of the illumination system can be simplified, and since a binarization processing circuit is used, the configuration of the detection system can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a foreign matter inspection device that is an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the scattering and diffraction states of foreign matter and pattern defects on a sample, and FIG.
The figure is a diagram of the output curve from the detector due to foreign matter and pattern defects on the sample shown in FIG. 2, and FIG. 4 is a diagram in which the output signal shown in FIG. 3 is binarized. DESCRIPTION OF SYMBOLS 1 ...Sample table part, 2 ...Transmitted illumination part, 3 ...Epi-illumination part, 4 ...Detection part, 5 ...Detection processing part, 6
...Reticle, 7 ...Verifle.

Claims (1)

[Scope of Claims] 1. In a foreign matter inspection method for inspecting foreign matter adhering to the surface of a sample during exposure of the sample, the degree of spatial coherence of means for transmitting illumination of the sample is determined by the degree of spatial coherence of the means for transmitting illumination used during the exposure. a reduction projection lens used during the exposure with a light-shielding plate disposed on the Fourier transform plane of the detection means, which is apertured to approximately the same degree of spatial coherence as the means, and which images the sample on the detector and processes the detection signal; A foreign object inspection method characterized by blocking the speed of light passing through an aperture. 2. The foreign substance inspection method according to claim 1, wherein the detection means binarizes the detection signal. 3. The detection means has an objective lens having an aperture larger than the aperture of the reduction projection lens, and allows a light beam that does not enter the aperture of the reduction projection lens to pass among the light scattered by the foreign object. A foreign matter inspection method according to claim 1 or 2. 4. A foreign matter inspection device for inspecting foreign matter adhering to the surface of a sample when exposing the sample to light, including a means for placing the sample in a scannable manner and a spatial coherence degree for transmitting illumination of the sample so as to be adjustable. a transmission illumination means for imaging the sample on a detector and processing a detection signal; and a detection means for imaging the sample on a detector and processing a detection signal; What is claimed is: 1. A foreign object inspection device comprising: a light-shielding slope that blocks a light flux passing through the foreign matter inspection device. 5. The foreign object inspection device according to claim 4, wherein the detection means is configured to binarize the detection signal from the detector. 6. The detection means is provided with an objective lens having an aperture larger than the aperture of the reduction projection lens, and allowing a light beam that does not enter the aperture of the reduction projection lens to pass through the aperture, out of the light scattered by the foreign object. A foreign matter inspection device according to claim 5, characterized in that: