JPH09288064A - Foreign-body detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foreign-body detection apparatus which can detect even a flat foreign body by a method wherein light from a photomask is set to a polarization state so as to be divided into two luminous fluxes, the phase difference between both luminous fluxes is adjusted so as to adjust their amplitude, both luminous fluxes are synthesized in a position in which optical path lengths of both luminous fluxes agree and their intensity distribution is observed. SOLUTION: A luminous flux I1 is made incident on an inspection point Pi at Brewster's angle of a photomask 8. A luminous flux I2 which is reflected and scattered enters a prism 12 via a lens 10 and a filter S, its polarization component is reflected to the direction of a luminous flux LS by a reflecting face 11, and a P-polarized component is transmitted through the direction of a luminous flux LP. The luminous flux LP enters a prism 17 via an optical wedge 15, and it is transmitted through a reflecting face 18 so as to be directed to an analyzer 19. The luminous flux LS is reflected by the reflecting face 18 via an optical-path-length compensation plate 16 so as to be directed to the analyzer 19. The luminous fluxes LS, LP are superposed so as to be changed into a luminous flux 14, and the luminous flux is image- formed on a photoelectric conversion element 20 via a lens L and a mirror M1. The imaged signal of the element 20 is processed by a signal processing part, a foreign body is extracted so as to be communicated to a computer 22, and an inspection result is displayed on a display 24.

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, and more particularly to an apparatus for optically detecting a foreign matter on a photomask on which a circuit pattern of a semiconductor device or the like is drawn.

[0002]

2. Description of the Related Art As a conventional device for detecting foreign matter on a photomask, there is known one disclosed in, for example, Japanese Patent Publication No. 63-64738, and this conventional device detects laser light on the photomask. An irradiation optical system for irradiating and a plurality of detectors for receiving scattered / diffracted light from the photomask are provided. Then, this device detects the foreign matter by utilizing the fact that the directivity of the scattered light from the foreign matter and the directivity of the scattered light from the circuit pattern are different from each other. Specifically, the logical product of the signals from a plurality of detectors is calculated, and when the logical value is "1", it is assumed that foreign matter is attached on the photomask.

[Problems to be Solved by the Invention]

The above-described conventional foreign matter inspection apparatus illuminates the foreign matter and detects only the high-order spatial frequency components of the generated scattered light to detect the foreign matter on the photomask. By the way, when the foreign matter to be detected is flat or has a low step, the scattering intensity of the high-order spatial frequency component becomes small. Therefore, the above-described foreign matter inspection apparatus has a problem that it is difficult to detect a foreign matter having a flat shape or a low step.

The present invention has been made in view of such conventional problems, and an object thereof is to provide a foreign matter inspection apparatus capable of detecting a foreign matter having a flat or low step existing on a photomask. .

[0005]

In order to achieve the above object, according to a first aspect of the present invention, a foreign matter inspection apparatus for optically detecting a foreign matter on a photomask on which a predetermined pattern is drawn is provided. Therefore, the illumination optical system for illuminating the photomask and the first light depending on the polarization state of the light from the photomask
First light beam separating means for separating the second light beam and the second light beam,
Phase difference adjusting means for adjusting a relative phase difference between the second light flux and the second light flux, and an amplitude adjustment for adjusting at least one of the amplitude of the light wave of the first light flux and the amplitude of the light wave of the second light flux. Means and a light flux combining means arranged at a position where the optical path lengths of the first light flux and the second light flux are substantially equal, and the relative phase difference between them is adjusted. And a foreign matter having a means for synthesizing the first light flux and the second light flux whose amplitudes of at least one of the light waves are adjusted, and an observing means for observing the intensity distribution of the light flux synthesized by the light flux synthesizing means. An inspection device is provided. In this case, it is preferable that the foreign matter inspection device has a specular reflection light beam blocking means for blocking the 0th order component of the light from the photomask. Further, it is preferable that the illumination light emitted from the illumination optical system is obliquely incident on the photomask, for example, at the Brewster angle of the transparent substrate material used for the photomask.

According to the second aspect of the present invention, there is provided a foreign matter inspection device for optically detecting a foreign matter on a photomask on which a predetermined pattern is drawn, the illumination optical system for illuminating the photomask, and the photomask. The light from the mask is split into a first light flux and a second light flux according to the polarization state, the relative phase difference between them is adjusted, and the relative phase difference between them is adjusted. There is provided a foreign matter inspection apparatus including a phase adjusting unit that combines the first light flux and the second light flux, and an observing unit that observes the intensity distribution of the light flux combined by the phase adjusting unit. In this case, it is preferable that the foreign matter inspection device has a specular reflection light beam blocking means for blocking the 0th order component of the light from the photomask. Further, it is preferable that the illumination light emitted from the illumination optical system is obliquely incident on the photomask, for example, at the Brewster angle of the transparent substrate material used for the photomask.

According to a third aspect of the present invention, there is provided a foreign matter inspection device for optically detecting a foreign matter on a photomask on which a predetermined pattern is drawn, the illumination optical system illuminating the photomask, A light beam separating means for separating the light from the photomask into a first light beam and a second light beam according to the polarization state, and an intensity distribution of the first light beam and an intensity of the second light beam separated by the light beam separating means. First to measure each distribution
Also provided is a foreign matter inspection apparatus comprising: a second photoelectric conversion means; and a signal processing means for detecting a foreign matter based on signals from the first and second photoelectric conversion means. In this case, it is preferable that the foreign matter inspection device has a specular reflection light beam blocking means for blocking the 0th order component of the light from the photomask. Further, it is preferable that the illumination light emitted from the illumination optical system is obliquely incident on the photomask, for example, at the Brewster angle of the transparent substrate material used for the photomask.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a photomask is illuminated with obliquely incident illumination light, preferably illumination light incident at an incident angle near the Brewster's angle of a transparent substrate (eg, quartz glass) of the photomask. The reflected / scattered light generated by this illumination light is separated into an S-polarized component and a P-polarized component with respect to the incident surface. Further, by adjusting the polarization characteristic of the illumination light, that is, the incident light, the amplitude of the wavefront of the S-polarized component and the amplitude of the wavefront of the P-polarized component contained in the scattered light generated from the circuit pattern are made to substantially match. Under such incident light conditions, the scattered light generated from the flat foreign matter has many S-polarized components and few P-polarized components. This is because the flat foreign matter is almost an organic substance and a light-transmitting dielectric substance, and its refractive index is almost equal to that of the transparent substrate of the photomask.

Almost 100% of the P-polarized component of incident light passes through the transparent substrate portion of the photomask. However, S
Since several tens of percent of the polarized component is reflected, the reflectance of the underlying substrate of the transparent substrate between the circuit pattern image (amplitude distribution) of the S polarized component and the circuit pattern image (amplitude distribution) of the P polarized component is Differences arise due to differences. In the present invention, the zero-order light blocking filter disposed at the pupil position of the objective lens removes the specular reflection component due to the flat transparent substrate base portion, and the amplitude distribution of the circuit pattern image due to the S polarization component and the P polarization component are used. The circuit pattern image is made similar to the amplitude distribution, the amplitude ratio and phase between them are adjusted, and the circuit pattern image disappears. The optical image remaining under such setting becomes an image of a flat foreign matter.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. Referring to FIG. 1 showing the first embodiment of the present invention, a light beam I0 emitted from a light source 1 which is a laser having a plane of polarization of linearly polarized light passes through a λ / 2 wave plate HW and has an arbitrary direction. It becomes a linearly polarized light beam I1 having a plane of polarization.
By adjusting the direction of the optical axis of the crystal of the λ / 2 wave plate HW1, it is possible to adjust the direction of the polarization plane of the light beam I1. A chrome pattern Cr is formed on the surface SC on which the pattern of the photomask 8 to be inspected is drawn. This surface SC is the surface to be inspected, and the light transmissive foreign matter on this surface is detected.

The photomask 8 is held by a holding member 94 and can be translated in the xy plane by a driving unit 98. The light beam I1 emitted toward the inspection point Pi is incident on the photomask 8 at an angle of θ1. In this embodiment, θ1 = 33.7 ° is set so that the Brewster angle of quartz glass used as the transparent substrate of the photomask 8 is obtained. Luminous flux I
The optical axis AX is set in the regular reflection direction by the photomask 8 of No. 1, and the lens 10 and the like are arranged along the optical axis AX. The front focal plane of the lens 10 is located on the inspection plane Pi. The rear focal plane is formed at a position approximately 1 times the focal length f of the lens 10, and the 0th-order light blocking filter S is provided at that position. The 0th-order light blocking filter S blocks the specularly reflected light of the light flux I1 from the photomask 8.

The light beam I2 reflected and scattered by the inspection point Pi passes through the lens 10 and the 0th-order light blocking filter S and reaches the prism 12. Reflection surface 11 of prism 12
Is a polarization beam splitter, which reflects the S-polarized component in the direction of the light beam LS and at the same time reflects the P-polarized component in the light beam L.
The light is transmitted in the P direction. The light flux LP passes through the optical wedge 15 arranged on the optical path and reaches the prism 17. The reflecting surface 18 is a polarization beam splitter, which allows the P-polarized light beam LP to pass therethrough, and the light beam LP is directed to the analyzer 19. At the same time, the light flux LS passes through the optical path length compensation plate 16 disposed on the optical path and reaches the prism 17. The light flux LS is reflected inside the prism 17, and since this light flux LS is S-polarized light, it is reflected by the reflecting surface 18 and goes out of the prism 17.

After the reflecting surface 18 of the prism 17, the light beam LP and the light beam LS are superposed on each other to form a light beam I3, and pass through an analyzer 19 to form a light beam I4. This luminous flux I4
Passes through the lens L and is reflected by the mirror M1,
For example, an image is formed on the light receiving surface of the photoelectric conversion element 20 including a one-dimensional charge coupled image pickup element (CCD). Analyzer 19
And the light flux LP and the light flux LS have the same polarization direction, and thus the light flux LP and the light flux LS become coherent, so that the light receiving surface of the photoelectric conversion element 20 has the S of the photomask 8 under test.
An interference image of the polarized image and the P-polarized image is formed.

The image pickup signal SIG output from the photoelectric conversion element 20 is input to the signal processing section 21, and the signal processing section 21.
Uses a well-known signal processing technique to depict a light-transmitting foreign substance. Further, the signal processing unit 21 communicates with the computer 22 to perform predetermined signal processing, and the computer 22 displays the inspection result of the foreign matter on the display 24. The computer 22 also communicates with the interface 23. The operator inputs the inspection content into the interface 23. Examples of the inspection content include information such as detection sensitivity and inspection area (area, position).

When actually inspecting a foreign substance, first, the direction of the analyzer 19 shown in FIG.
It is set so that a polarization component having an angle of 45 ° with respect to the polarization direction of LS is passed. Next, the photomask 8 is moved so that the dense portion of the chrome pattern Cr including a plurality of circuit patterns in the illumination area and the inspection point Pi coincide with each other. At this time, while measuring the intensity of the interference image on the photoelectric conversion element 20, the optical wedge 15 is operated to change the optical path length of the light flux LP. Then, the optical wedge 15 is fixed at a position where the intensity of the interference image in the dense portion of the chrome pattern Cr is minimized.
Next, while rotating the λ / 2 plate HW, the chromium pattern Cr
The intensity of the interference image of the dense portion of is measured, and the λ / 2 plate HW is fixed at the position where the intensity is minimized. By the above-described operation, the phase and amplitude of the S-polarized component and the phase and amplitude of the P-polarized component of the scattered light generated from the dense portion of the chrome pattern Cr can be made almost the same, and the interference of the dense portion of the chrome pattern Cr can be achieved. The image can be substantially erased.

FIG. 2A is an enlarged view showing a dense portion of the chromium pattern Cr on the mask blank MB.
In this example, the chromium patterns Cr are arranged at equal intervals. FIG. 2B shows the wavefronts of the two coherent light waves WS and WP that have passed through the analyzer 19 (FIG. 1), and the vertical axis A represents the amplitude. Since the phase and amplitude of the scattered light WS from the chrome pattern Cr and the phase and amplitude of the scattered light WP are substantially the same, no interference image appears, as shown in FIG. 2 (c). Here, the vertical axis t represents the intensity.

FIG. 3A is a diagram showing an example in which the light-transmissive foreign matter D exists on the mask blank MB. FIG.
(B) shows the wavefronts of the two coherent light waves WS and WP that have passed through the analyzer 19 (FIG. 1). Since the light wave WS of the S-polarized component generally has a high reflectance for the foreign matter D, As shown in FIG. 3 (b), the wavefront having a considerable amplitude without the 0th-order light is obtained, while the lightwave WP of the P-polarized component is
Since the reflectance of the foreign matter D is generally very low, the wavefront has a very small amplitude. Therefore, as shown in FIG. 3C, the obtained interference image is an image equivalent to the image by the Schlieren method in which the 0th-order light is absent.

FIG. 4 shows a second embodiment of the present invention. In principle, this second embodiment is also substantially the same as the above-mentioned first embodiment. However, in the first embodiment, the Mach-Zehnder interferometer is configured by the prism 12 and the prism 17, and the optical wedge is provided in one of the two optical paths to give the phase difference, whereas in the second embodiment. In the example, Babine Soleil Compensator B acts in its place.

In FIG. 4, the configuration until the light beam I2 reaches the 0th-order light blocking filter S is the same as that of the first embodiment shown in FIG. The light beam I2 is reflected by the mirror M.
It is reflected by 2 and reaches Babinet Soleil Compensator B. Babinet Soleil Compensator B
Is composed of prisms PR1, PR2 and PR3. The position of the prism PR3 can be adjusted by a screw N, and by operating this screw N to adjust the position of the prism PR3, a P-polarized light component (polarized light parallel to the paper surface) incident on the Babinet-Soleil compensator B is polarized. It is possible to change the phase difference between the S polarization component and the S polarization component (polarization perpendicular to the paper surface).

Therefore, by adjusting the Babinet-Soleil compensator B and the .lamda. / 2 wave plate HW in the same manner as in the first embodiment, the first embodiment is also performed in the second embodiment.
An interference image similar to that in the embodiment can be obtained. In addition, also in the second embodiment, the analyzer 19 is fixed so as to pass the polarization component that makes an angle of 45 ° with the P polarization component and the S polarization component.

FIG. 5 shows a third embodiment of the present invention. In FIG. 5, the configuration until the light flux I2 reaches the 0th-order light blocking filter S is the same as that of the first embodiment shown in FIG. The light flux I2 passes through the 0th-order light blocking filter S and reaches the polarization beam splitter PBS.
The polarization beam splitter PBS converts the S polarization component into a light flux LS.
And the P-polarized component is transmitted in the direction of the light beam LP.

The light beam LP is incident on the light receiving surface of the photoelectric conversion element 20P arranged near the pupil. The amplitude of the image pickup signal output from the photoelectric conversion element 20P is adjusted by the light amount balance adjustment unit 30P, and the image pickup signal whose amplitude is adjusted is input to the inverting input terminal of the comparator 31. On the other hand, the light flux LS is incident on the light-receiving surface of the photoelectric conversion element 20S arranged near the pupil. Photoelectric conversion element 2
The image pickup signal output from 0S is the light amount balance adjustment unit 3
The amplitude is adjusted in 0S, and the image pickup signal whose amplitude is adjusted is input to the non-inverting input terminal of the comparator 31. The signal output from the comparator 31 is input to the signal processing unit 21, and the signal processing unit 21 draws the light transmissive foreign substance by a known signal processing technique. Further, the signal processing unit 21 communicates with the computer 22 to perform predetermined signal processing, and the computer 22 displays the inspection result of the foreign matter on the display 24. The computer 22 also communicates with the interface 23.

FIG. 6 (a) is a view similar to FIG. 2 (a), and shows the dense portion of the chromium pattern Cr on the mask blank MB and the light transmissive foreign matter D in an enlarged manner. FIG.
(B) shows the wavefronts of the two light waves WS and WP before passing through the 0th-order light blocking filter S, and the vertical axis t represents the intensity. In addition, FIG. 6C shows a zero-order light blocking filter S.
Shows the wavefronts of the two light waves WS and WP after passing through, and the vertical axis t represents the intensity.

The intensity of the wavefronts of the two light waves WS and WP after passing through the 0th-order light blocking filter S, as shown in FIG. 6C, excludes the portion corresponding to the light-transmissive foreign matter D. Will be almost the same. Therefore, the light quantity balance adjustment unit 30
After adjusting the intensities of the two light waves WS and WP with S and 30P, the difference between them is taken out with the comparator 31, and further, the signal processing unit 21 performs the signal processing by providing the threshold value ± TH. As shown in FIG. 6D, only the image DS of the light transmissive foreign matter D is obtained. In the third embodiment, the photoelectric conversion elements 20S and 20P are arranged near the pupil position, but instead, they may be arranged on the image plane conjugate with the inspection area. Further, although the subtracter is used as the comparator 31, a divider may be used.

[0025]

As described above, according to the present invention, it is possible to almost eliminate the image of the circuit pattern and detect only the foreign matter having a flat or low step.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a first embodiment of a foreign matter inspection device according to the present invention.

FIG. 2 is a diagram illustrating an image of a circuit pattern.

FIG. 3 is a diagram illustrating an image of a flat foreign matter.

FIG. 4 is a schematic diagram showing a configuration of a second embodiment of the foreign matter inspection apparatus according to the present invention.

FIG. 5 is a schematic view showing the configuration of a third embodiment of the foreign matter inspection device according to the present invention.

FIG. 6 is a diagram illustrating an image of a circuit pattern and a flat foreign matter.

[Explanation of symbols]

 8 Photomask 12 Prism 15 Optical wedge 16 Optical path length compensator 17 Prism 19 Analyzer 20 Photoelectric conversion element 31 Comparator 94 Holding member AX Optical axis B Babinet-Soleil compensator HW λ / 2 Wave plate N screw PBS Polarizing beam splitter Pi Inspection point S 0th-order light blocking filter

Claims (6)

[Claims] 1. A foreign matter inspection apparatus for optically detecting a foreign matter on a photomask on which a predetermined pattern is drawn, comprising: an illumination optical system for illuminating the photomask; and polarization of light from the photomask. A light beam separating means for separating a first light beam and a second light beam according to a state, and a phase difference adjusting means for adjusting a relative phase difference between the first light beam and the second light beam. An amplitude adjusting means for adjusting at least one of an amplitude of a light wave of the first light flux and an amplitude of a light wave of the second light flux, and an optical path length of the first light flux and an optical path length of the second light flux. The first and second light flux synthesizing means arranged at substantially equal positions, wherein a relative phase difference between them is adjusted and at least one of amplitudes of light waves thereof is adjusted.
The foreign matter inspection apparatus, comprising: a light beam combining unit and a second light beam combining unit for observing an intensity distribution of the light beam combined by the light beam combining unit. 2. A foreign matter inspection apparatus for optically detecting a foreign matter on a photomask on which a predetermined pattern is drawn, comprising an illumination optical system for illuminating the photomask, and polarizing light from the photomask. The first light flux is divided into a first light flux and a second light flux according to a state, a relative phase difference between them is adjusted, and a relative phase difference between them is adjusted. A foreign matter inspection device, comprising: a phase adjusting unit that combines the second light flux and an observing unit that observes an intensity distribution of the light flux combined by the phase adjusting unit. 3. A foreign matter inspection apparatus for optically detecting a foreign matter on a photomask on which a predetermined pattern is drawn, comprising an illumination optical system for illuminating the photomask, and polarizing light from the photomask. A light beam splitting unit that splits the light beam into a first light beam and a second light beam according to the state, and an intensity distribution of the first light beam and an intensity distribution of the second light beam that are split by the light beam splitting unit are measured. A foreign matter inspection apparatus, comprising: first and second photoelectric conversion means that perform the above; and signal processing means that detects the foreign matter based on signals from the first and second photoelectric conversion means. 4. The foreign matter inspection apparatus according to claim 1, further comprising a specular reflection light beam blocking unit that blocks a 0th-order component of light from the photomask. 5. The foreign matter inspection apparatus according to claim 1, wherein the illumination light emitted from the illumination optical system obliquely enters the photomask. 6. The foreign matter inspection apparatus according to claim 5, wherein the illumination light emitted from the illumination optical system is incident on the photomask at a Brewster angle of a transparent substrate material used for the photomask.