JPS63268245A - Inspecting method for foreign matter and equipment therefor - Google Patents

Abstract

PURPOSE:To enable detecting only harmful foreign matter discriminating from a pattern, by detecting selectively the luminous flux only which passes through the aperture of an objective outside the aperture of incident side of the contraction projection lens of an exposure equipment, after scattering and diffraction due to foreign matter and defects. CONSTITUTION:The number of apertures (abbreviated as N.A. hereinafter) of the incident side (object side) of a demagnification projection lens is designed as a value to obtain a sufficient resolution for the image formation of a pattern on a reticle. Inspection region on the reticle 6 is limited, and the reticle 6 is scanned by a sample stand part 1, so that the examination for all inspection region is enabled. Therefor, an objective 41 is applied whose N.A. is larger than that of the contraction projection lens usually used. In order to detect foreign matter as well as damaging ones, a light shielding plate 44 is not always necessary to be matched with the N.A. of the incident side of the contraction projection lens employed in an exposure equipment, and it is sufficient enough to be matched with the degree of spatial coherence of a transmitting illumination part 2 and a direct illumination part 3. That is, only the 0th-order diffraction light of illumination from the transmitting illumination part 2 and the direct illumination part 3 may be shielded.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for transferring patterns on a reticle and a mask onto a wafer in a reticle and mask exposure process used to manufacture LSIs, printed circuit boards, etc. The present invention relates to a method and apparatus for detecting foreign objects and defects on the reticle and mask, which are performed before the reticle and mask are inspected, and is particularly suitable for inspecting foreign objects and defects on the reticle and mask in a short time with easy operation. This invention relates to a method and device for inspecting foreign substances.

[Conventional technology]

The exposure process used in LSI manufacturing involves printing and transferring a chrome pattern on a thick plate called a reticle 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, in recent years, as LSIs have become highly integrated and wiring patterns have become finer, smaller foreign particles have become a problem. In addition, there were eight problems with foreign matter in the flat thin film, including resist residue during reticle manufacturing, chromium or chromium oxide etching residue for pattern formation, and impurities dissolved in the reticle cleaning solution that aggregated during cleaning and drying. However, the number is on the rise.

Conventionally, the above-mentioned foreign matter and defect inspection apparatuses include means for obliquely irradiating and scanning a substrate with a laser beam, and a means for scanning the substrate with an irradiation point and a focal point of the laser beam, as described in, for example, Japanese Patent Laid-Open No. 59-65428. A first lens is provided above the substrate so that the surfaces thereof almost coincide with each other and collects the scattered light of the laser beam, and a first lens is provided on the Fourier transform surface of the lens to collect the scattered light from the substrate pattern. A light shielding plate that blocks light; a second lens that performs inverse Fourier transform on scattered light from a foreign object obtained through the light shielding plate; 1. The lens consists of a slit that is provided at the imaging point of the second lens and blocks scattered light from other than the laser beam irradiation point on the substrate, and a light receiver that receives the scattered light from the foreign object that has passed through the slit. 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 capture 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 Japanese Patent Application Laid-open No. 58-139278, data detected using an irradiation and detection optical system similar to that of an exposure device is compared with standard reticle data or designed data. Defect detection methods have been proposed.

[Problem that the invention seeks to solve]

Among the above-mentioned conventional techniques, Japanese Patent Application Laid-Open No. 59-65428 discloses that the light reflected from the foreign object is separated from the light reflected from the pattern by a light-shielding plate, and only the light reflected from the foreign object is detected by a slit. It has the feature that the detection mechanism is simple because foreign matter is detected by a binary method. Since foreign objects are detected using indirect lighting, only the reflected light from the chrome pattern at a specific angle is blocked, so all glue U h
Foreign objects cannot be distinguished from the pattern.

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. The number of foreign objects that pose a problem (especially when the pattern is fine) increases. This also means that the number of foreign objects that cause the same degree of harm but do not cause actual harm increases.1 The number of false alarms increases, and There is a problem that the work of checking, analyzing, and removing the data increases, which significantly reduces work efficiency.

Next, among the above-mentioned conventional techniques, Japanese Patent Application Laid-Open No. 58-139728
In this issue, since it has the same optical system as the exposure device,
Although it has the feature that the configuration of the optical system is simpler than the above-mentioned conventional technology, on the other hand, the image signal processing system that compares data is more complicated than the above-mentioned conventional technology, and inspection requires a lot of time. There is.

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 foreign matter that causes actual damage from a chrome pattern existing at any angle. It is in.

[Means for solving problems]

The above purpose is to provide a foreign matter inspection method for inspecting foreign matter adhering to the surface of a sample when the sample is exposed to light. This is achieved by blocking diffracted light other than light scattered by foreign matter from the sample with a light shielding plate placed on the Fourier transform surface of the imaging optical system that forms an image on the instrument and processes the detection signal. A foreign matter inspection device for inspecting foreign matter adhering to the surface of a sample when exposed to light by an exposure device, the means for placing the sample and the degree of spatial coherence for transmitting illumination of the sample being adjustable. an imaging optical system that images the sample on a detector and processes a detection signal; and 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 other diffracted light.

[Effect]

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 N and A) 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 minute foreign matter is present, the light beam scattered and diffracted by the foreign matter passes through the entrance side N, A, and outside 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-mentioned literature, by placing a disk-shaped spatial filter on the Fourier transform surface of the imaging optical system,
Spatial frequency determined by the diameter of this disk-shaped spatial filter For example, if the inside of a lens is covered with a circle with radius d', only a pattern with a specific spatial frequency determined by the size of radius d' It is stated that it cannot be resolved. Therefore, this description can also be applied to a technique that detects only a foreign object by utilizing the difference in the number of spatial cycles 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 block the same area as the incident side N and A of the reduction projection lens, that is, the diffracted light, out of the light beam incident on the lens used in the exposure apparatus, using a light shielding plate, thereby preventing foreign matter from entering the lens. It captures only scattered light.

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〕

Hereinafter, FIGS. 1 to 4, which are one embodiment of the present invention, will be described.

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, and an epi-illumination section.

The "sample stage part" includes two stages 9 that fix the reticle 6 having the pellicle 7 by a fixing means 8 and scan it in two directions, and an X stage 10 that scans the reticle 6 in the X direction via these two stages 9. , which scans the particle 6 in the Y direction via the X stage 10 and the second stage 9.
A stage 11, 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 two directions, and a command from the focus position detection system 13. It has a processing system 14 that drives the stage drive system 12, and is configured to be able to focus the reticle 6 on the inspection center with the minimum necessary accuracy.

The X stage 10 has a constant acceleration time of about 0.1 seconds and a constant acceleration time of about 0.1 seconds.
, is formed to perform periodic motion with a maximum speed of about 1 mm/sec and an amplitude of 200 mm in a % period of uniform motion of 1 second and constant deceleration time of 0.1 seconds.

The Y stage 11 is formed to move the reticle 6 in the Y direction in steps of 0.15 +++ m in synchronization with the uniform acceleration time and uniform deceleration time of the X stage 10, and is If it is transferred 670 times, it is possible to transfer 100mm in about 130 seconds, so 100m
An area of m square can be scanned in about 130 seconds.

Although this embodiment uses X and Y stages 10 and 11, the present invention is not limited to this; for example, it is also possible to use an Xθ stage that scans in the rotational direction and the X direction. Furthermore, the scanning speed described above is merely an example, and it goes without saying that it may be set arbitrarily as necessary.

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 name of the transmitted illumination unit is to select the G-line (wavelength 436 tnrrt) or i-line (wavelength 365211 m) used in the exposure device (not shown) from the light beam emitted from the mercury lamp 21 to the color separation filter B. When the condensing lens B focuses the light onto the diffuser plate U, the light diffused by the diffuser plate U is emitted from a limited area by the circular diaphragm 5, and the collimator lens The reticle 6 is irradiated with the light by entering the reticle.

The diaphragm 5 is installed at approximately the focal point position of the collimator lens section, and is formed so that the image is formed at a focal point position 46 shown by a chain line above the collimator lens % and the objective lens 41 of the detection section. There is.

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 It is necessary to make the angle θ the same. Here sinθ
is referred to as the "degree of spatial coherence."

Furthermore, in the illumination of the exposure device, since it is necessary to uniformly illuminate the entire range on the reticle 1, an integrator (hereinafter referred to as an indicator), which is a collection of rod-shaped lenses in place of the diffuser plate array, is used. It uses optical elements. The function of this indexer is basically the same as that of the diffuser plate array, and the inspection range to which the present invention is applied is the reticle 6.
Since the power is from several hundred microns to 1.2 mW, the above-mentioned array of diffusers 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 5 installed behind the diffuser plate array, the exposure apparatus using the reticle 1 The aperture of the aperture 5 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, the position of the aperture 14 is not necessarily installed at the focal position of the collimator lens.

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 diaphragm 5 be installed at the focal position of the collimator lens section. 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 j includes a color separation filter 32 emitted from a mercury lamp 31, a condensing lens 33, and a diffuser plate rear aperture #) 3.
5 passes through a relay lens 36 and is irradiated onto the reticle 6 via the half mirror 42 of the detection section 4 and the objective lens 41.

Note that the objective lens 41 has the same function as the collimator lens of the transmitted illumination section l.

Further, the relay lens field is installed to create an apparent aperture at a focal point 46 above the objective lens 41. Specifically, a real image of the aperture shear is formed at the focal point position 46.

Furthermore, in the epi-illumination unit 3, the transmitted-illumination unit 2
Similarly, the aperture of the aperture shear is determined so that the wavelength of the irradiation light and the angle θ of the light beam incident on any one point 15 on the reticle 6 are the same as those of the illumination light used in the exposure device. ing.

Further, since the epi-illumination unit y 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 l is used at the same time as the transmitted-illumination section, 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 GLM and i-line, but may be other broadband light including gIs and iIs. The reason is that foreign objects and patterns
This is because the diffraction situation is different for light of all wavelengths, so foreign matter can be detected while distinguishing it from patterns even with broadband light.

The detection unit 4 includes an objective lens 41, a half mirror 42, a field lens 43, a light-shielding plate material, and an image formation 45,
The 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 43 forms an image of the upper focal point 46 of the objective lens 41 on the circular light-shielding plate material.

That is, the aperture δ of the transmitted illumination unit 2 passes through the collimator lens and the objective lens 41, is reflected on the reticle 6, passes through the objective lens 41 again, passes through the field lens 46, and is directed to the light shielding plate. An image is formed on the seal.

At this time, the position of the light-shielding plate material is a 7-Lie transformation position of the position of the reticle 6 with respect to the position of the light source, that is, the position of the aperture section.

Here, in general, N and A of the reduction projection lens of the exposure device on the reticle 6 side are 10% higher than the degree of spatial coherence of the illumination system of the exposure device (equivalent to the degree of spatial coherence of the transmitted illumination section 2). It is set large at around 40%,
Most of them are around 10%.

Further, since the objective lens 41 needs to allow the light beam passing outside the entrance side aperture of the reduction projection lens to pass through the aperture, its N, A is replaced by the N, A, of the reduction projection lens.
The light-shielding plate material is provided to cut off the light beams incident on the reduction projection lens N and A.

Therefore, in order to achieve the object of the present invention, it is desirable that the diameter di of the light shielding plate material be calculated using the following equation (1). That is, N, A.

dm=d8−α 5111θB ” (1+6) ・−
-(1) is desirable. Here, ds is the diameter of the aperture δ, α
is the magnification of the imaging system of the diaphragm 5 and the light-shielding plate material, N, A is the value of the reduction projection lens on the reticle 6 side, sin θ8 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 can 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, in the present invention, the inspection area on the reticle 6 is limited and the reticle 6 is scanned multiple times on the sample stage 1 so that all the inspection areas can be inspected. than N, A
, a large objective lens 41 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 material does not necessarily have to be aligned with N and A on the incident side of the reduction projection lens used in the exposure apparatus, g and the degree of spatial coherence of the epi-illumination section A. It is only necessary to block the second-order diffracted light of the half-light FiA, and it may be larger than this.

Specifically, ``°=1'' in the above formula (1) may be set, and δ may be set to an arbitrary value of 5Lllθ which is larger than several percent.

Furthermore, the degree of spatial coherence of the previous ml illumination light does not necessarily have to match the degree of coherence of the exposure apparatus, but must be within the range that satisfies -A (1) above so that the 6o-th order diffracted light can be blocked by the light shielding plate material. In the previous paragraph 5,
The size of the light shielding plate 44 may be determined together with a friend.
- If the epi-illumination unit 1 is not installed, the half mirror 42, field lens 43 and imaging lens 45 are also omitted, and the light shielding plate is placed at the focal position 46 and the detector 51 is placed at the finild lens 43. It is possible to obtain the effects of the present invention even if the optical system is installed in the same position as previously installed.In this case, it is possible to obtain an optical system with an extremely simple configuration. .

The Shinsha processing section 5 includes a detector 51 and a binarization processing circuit 5.
2, a microcomputer &, and a CRT54. The detection 851 is formed by, for example, a charge transfer type one-dimensional solid-state image pickup device, and the detector 51 detects a signal while the X stage 10 is scanned. 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 1. 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.

The binarization processing circuit 52 is configured to determine the presence or absence of foreign matter by setting a threshold value for binarization in advance. The microcomputer 53 has a fault evaluation function.In other words, whether a foreign object causes actual damage such as transfer failure depends on the intensity of the scattered light caused by the foreign object and the size of the foreign object. Therefore, the function of foreign substances that cause actual damage is evaluated in advance, and the presence or absence of the four mantles of cicadas that are harmful to the environment is determined based on this evaluation function, and the result is output to CB'l' 54 mentioned above. It is formed like this.

1. Violence Inspection Apparatus According to the Present Invention Since the device is constructed as described above, the interrogation method will be explained next (see FIGS. 2 to 94). , 6 As shown in FIG.
7, two spring objects 18a and 18b, and a defect 19 are present.Since one of the small foreign objects 18a is minute, it scatters or diffracts light more than the edges 17& of the pattern 17. . That is, the light shielding plate 44
The light beam 56 is scattered outside the range θ that is shielded by light.
is larger than the edge 17 of the pattern 17 & the light flux group.

　　　　　　.

Also, the other large foreign object 18b is due to the fact that the defect 19 of the pattern 17 has a high spatial frequency around it.
7. ．． 58 is meta 5-17. Edge 17' a of a
・The luminous flux becomes larger than 55.
, the output of the detector 51 is as shown in FIG. ,．
58 generates output peaks 59, 60, 61, 62.

On the other hand, when the threshold value is set as shown in FIG. 3 in the 12-value processing circuit 52, the three output vehicles 0, 61, and 62 stand out as outputs above this threshold value. As a result, only the two foreign objects 18a and 18b and the defect 19 on the pattern 17 can be detected.

At this time, the coordinates of the X1Y stages 10 and 11 and the levels of the output vehicles 0 and 61 are stored in a memory managed by the microcomputer criminal, and the stored contents are processed and output to the CRT 54.

〔Effect of the invention〕

According to the present invention, it is possible to selectively detect light that is scattered and diffracted by foreign objects and defects and no longer enters the reduction projection lens of the exposure device by using illumination that is optically equivalent to the illumination of the exposure device. Therefore, it is possible to detect only the foreign substances that cause actual damage, distinguishing them from the particles.

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 possible to use an objective lens with larger N and A than the normally used reduction projection lens. can.

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 pull diagram of a foreign matter inspection device which is an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the scattering and diffraction states of foreign substances and pattern defects on a sample, and Fig. 3 is shown in Fig. 2. FIG. 4 is a diagram of the output curve from the detector due to foreign matter on the sample and pattern defects, and is a diagram obtained by converting the output signal shown in FIG. 3 into a binary value.

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 the means for transmitting illumination of the sample is determined by adjusting the degree of spatial coherence of the means used for transmitting illumination of the sample. A reduction projection used during the exposure with a light shielding plate disposed on the Fourier transform plane of the detection means which is focused to approximately the same degree of spatial coherence as the illumination 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 the aperture of a lens. 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 method for inspecting foreign substances according to claim 1 or 2, characterized in that: 4. In a foreign substance inspection device that inspects foreign substances adhering to the surface of a sample when exposing the sample, a means for placing the sample in a scannable manner and a degree of spatial coherence for transmitting illumination of the sample can be adjusted. a transmitted illumination means formed;
a detection means for forming an image of the sample on a detector and processing a detection signal; and a light shielding device disposed on the Fourier transform surface of the detection means for blocking a light flux passing through the aperture of a reduction projection lens used during the exposure. A foreign matter inspection device characterized by being provided with a plate. 5. The foreign object inspection apparatus according to claim 4, wherein the detection means is configured to binarize the detection signal from the detector. 6. The detection means has an aperture larger than the aperture of the reduction projection lens, and the detection means has an aperture larger than the aperture of the reduction projection lens, and among the light scattered by the foreign matter,
6. The foreign matter inspection apparatus according to claim 5, further comprising an objective lens that allows a light beam that does not enter the aperture of the reduction projection lens to pass through the aperture.