JPH0816651B2 - Double-sided foreign matter detection method and device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided foreign matter detecting method for discriminatingly detecting minute foreign matter attached to each of the front surface and the back surface of a transparent substrate having a circuit pattern formed on the front surface thereof. It relates to the device. 2. Description of the Related Art A conventional foreign matter inspection apparatus is constructed as shown in FIG. That is, the foreign matter 2 existing on the wafer 1 is irradiated with the S-polarized laser light 5 and 6 emitted from the S-polarized laser oscillators 3 and 4 obliquely from above in two directions, and the foreign matter 2 emits the S + P polarized laser light 7 from the foreign matter 2. Is reflected. After this S + P-polarized laser light 7 is condensed by the objective lens 8, only the S-polarized laser light is blocked by the S-polarization cut filter 9, and only the P-polarized laser light 10 is passed through the field-selecting diaphragm 11 to the photoelectric conversion element 12. To detect. Only S-polarized laser light is reflected from the circuit pattern difference. Therefore, the presence of foreign matter can be known from the output of the photoelectric conversion element 12. This conventional foreign matter inspection apparatus is intended to detect foreign matter existing on a wafer. Further, as a conventional technique, Japanese Patent Laid-Open No. 57-12 is used.
No. 8834 is known. However, the prior art described above does not turn over and the surface of the transparent substrate on which the circuit pattern is formed, which is the same as the state of actual projection exposure, faces downward. No consideration was given to the problem of trying to detect minute foreign matter attached to each of the front surface and the back surface separately. In order to solve the above-mentioned problems of the prior art, the object of the present invention is to provide a transparent substrate having a circuit pattern on its surface with the surface on which the circuit pattern is formed facing downward, which is the same as the actual state of projection exposure. By making it possible to inspect minute foreign substances adhered to both the front surface and the back surface separately, it is possible to reliably inspect the minute foreign substances, eliminate defective exposure due to the minute foreign substances adhered to the transparent substrate, and contribute to a large improvement in semiconductor production yield. The present invention provides a double-sided foreign matter detecting method and apparatus therefor. In order to achieve the above object, the present invention provides linearly polarized laser illumination light to each of the front and back surfaces of a transparent substrate (reticle) having a circuit pattern formed on the front surface. The front surface illumination condensing optical system and the back surface illumination condensing optical system are slanted by 67.5 ± 15 degrees from the vertical direction of the transparent substrate surface to perform linear scanning to perform condensing spot illumination and the transparent substrate to the straight line. Scanning in a direction substantially perpendicular to the horizontal scanning direction, the scattered light from each of the front surface and the back surface is tilted by 67.5 ± 15 degrees from the direction perpendicular to the transparent substrate surface, and substantially from the linear scanning direction. The circuit pattern is collected by the front-side detection light-collecting optical system and the back-side detection light-collecting optical system, and the light-shielding means provided in each of the front-side detection light-collecting optical system and the back-side detection light-collecting optical system. Scattering from the edges of And each of the light condensed through each light shielding means is received by each of the front surface photoelectric conversion means and the back surface photoelectric conversion means, and the signal detected from the front surface photoelectric conversion means and the back surface photoelectric conversion means. According to the double-sided foreign matter detection method, the foreign matter adhered on the front surface of the transparent substrate on which the circuit pattern is formed and the foreign matter adhered on the rear surface of the transparent substrate are distinguished and detected based on a signal detected from is there. Further, according to the present invention, a linearly polarized laser illumination light is tilted 67.5 ± 15 degrees from the direction perpendicular to the transparent substrate surface on each of the front surface and the back surface of a transparent substrate (reticle) having a circuit pattern formed on the surface to form a focused spot. A front surface illumination condensing optical system and a back surface illumination condensing optical system, and scanning means for scanning the transparent substrate in a direction substantially perpendicular to the linear scanning direction,
Scattering light scattered from each of the front surface and the back surface is inclined by 67.5 ± 15 degrees from the vertical direction of the transparent substrate surface, is condensed from substantially the linear scanning direction, and is reflected from the edge of the circuit pattern. The front-side detection light collection optical system and the back-side detection light collection optical system having a light-shielding means for shielding light, and the front-side detection light collection optical system and the back-side detection light collection optical system through the respective light-shielding means. A photoelectric conversion means for the front surface and a photoelectric conversion means for the back surface, which receive each of the emitted light, and based on a signal detected from the photoelectric conversion means for the front surface and a signal detected from the photoelectric conversion means for the back surface, A double-sided foreign matter detection device, characterized in that it is configured to detect a foreign matter attached on a front surface of a transparent substrate on which a circuit pattern is formed and a foreign matter attached on a rear surface of the transparent substrate, separately. In an exposure apparatus such as a reduction projection type automatic mask aligner, when a circuit pattern formed on a reticle, a photomask or the like is transferred by step-and-repeat onto a semiconductor wafer, the reticle pattern, the photomask or the like is transferred. If there is a foreign substance on the wafer, the image (shadow) of the foreign substance is transferred onto the wafer together with the circuit pattern, and all the single exposure portions (chips) on the finished wafer become defective. Therefore, in a reticle, photomask, etc., without turning over (without changing the foreign matter adhesion state), the state in which the circuit pattern formed that is the same as the state in which actual projection exposure is performed is facing down, and the foreign matter attached on both sides It is necessary to distinguish and inspect. It is conceivable that the foreign matter existing on the circuit pattern surface affects the exposure even if it is a minute foreign matter, and the foreign matter removing condition is changed depending on whether the foreign matter exists on the circuit pattern surface or on the back surface. Further, foreign matters existing on the circuit pattern may also move, and when the foreign matter moves, it may interfere with the exposure, and it is necessary to detect the foreign matters existing on the circuit pattern. Therefore, according to the above-described structure of the present invention, in the reticle, the photomask, or the like, the surface on which the circuit pattern is formed, which is the same as the actual projection exposure state, is turned down without turning over (without changing the foreign matter adhesion state). In this state, it is possible to inspect the foreign matters attached to both sides with high reliability, eliminate defective exposure due to minute foreign matters attached to the transparent substrate, and contribute to a large improvement in semiconductor production yield. The present invention will be specifically described below based on the embodiments shown in the drawings. FIG. 2 is a diagram showing an embodiment of an apparatus for detecting foreign matter on a substrate when the pellicle body according to the present invention is mounted on a substrate such as a photomask or a reticle. That is, the laser light 30 emitted from the laser oscillator 27 becomes a linearly polarized wave (horizontal wave) in a specific direction by the polarization element 29, and is totally reflected by the galvano mirror 28 connected to the rotating or oscillating motor 34, and the lens 31 is reflected. After that, it reaches the mirror 32. After that, the mirrors 35a, 36a or 35b, 36
tilt angle α = 7. from the oblique direction on the surface of the substrate 21 via b.
It is incident at 5 ° to 37.5 °. The galvanometer mirror 28 oscillates at a constant rotational speed, and the lens 31 moves to the galvanometer mirror 2.
This is an f.theta. Lens (illumination condensing optical system) capable of linearly scanning the laser spot 80 on the surface of the substrate 21 in proportion to the rotation angle of 8. Laser light 30 is used to detect the reflected light 25 from the foreign matter 24 existing on the surface of the substrate 21 shown in FIG.
The analyzers 41a, 4 such as an S-polarization shut filter are arranged at a right angle (90 ° ± 10 °) to a and 30b and obliquely above the horizontal plane of the substrate 21 with an inclination angle β = 7.5 ° to 37.5 °.
1b, condenser lenses (detection condenser optical system) 40a, 40b,
Slit-shaped light-shielding devices (field-of-view limiting means) 39a, 39b,
Detection devices 37a and 37b, which are composed of photoelectric conversion elements (photoelectric conversion means) 38a and 38b, are installed at symmetrical positions about the center of the reticle in the direction of the substrate 21y. Analyzer 41a,
Reference numeral 41b is for extracting a linearly polarized wave of the reflected light 25 from the foreign matter 24 in a specific direction. The extracted light passing through the analyzer is condensed by the condenser lenses 40a and 40b into the slit-shaped light shielding device 3
The photoelectric conversion elements 38a and 38b are reached via 9a and 39b. Photoelectric conversion element 3 such as a photomultiplier tube having high sensitivity
8a and 38b generate electric signals proportional to the received light intensity. The pair of illumination devices 35a, 36a and 35b, 36b and the detection devices 37a, 37b are provided in FIG. 2 for the following reason. FIGS. 5 and 6 are views showing the irradiation direction of the laser light 30 and the detection direction of the reflected light 25 of the foreign matter 24. As a means for preventing the laser beams 30a and 30b and the reflected beam 25 of the foreign matter 24 from being blocked by the frame 22 of the pellicle, the substrate 21 is divided in half as shown in FIG. 5, and the laser beam 30a is always provided from the opposite side of the inspection area. , 30b, and at the same time, the reflected light 25 of the foreign matter 24 is also detected from the side opposite to the area where the foreign matter 24 exists. That is, if the inspection area of the substrate 21 is divided into four areas as shown in FIG. 6, the laser beam 30a is irradiated when inspecting the areas A and C, and the laser beam 30b is irradiated when inspecting the areas B and D. To irradiate. In this case, switching between the laser beams 30a and 30b is performed by rotating the mirror 32 (FIG. 2) by 90 degrees with the motor 33. Detection device 37
a indicates that the laser spot 80 is A or B on the surface of the substrate 21.
, And the detector 37b is activated when the laser spot 80 is in the area C to D on the surface of the substrate 21. That is, in synchronization with the rotation angle of the galvano mirror 28, the detection signal of the photoelectric conversion element 38a or 38b such as a photomultiplier tube is turned on / off by an electric circuit. Further, since the detection sensitivity of the reflected light 25 from the foreign matter changes depending on whether the foreign matter 24 is present near the center of the substrate 21 or when the foreign matter 24 is present at the end, the present apparatus has an electrical function for foreign matter detection. The threshold value (slice level) is changed in synchronization with the position of the laser spot 80 on the surface of the substrate 21. FIG. 7 shows an outline of the detection circuit. The analog signal of the photoelectric conversion element 38a or 38b is a voltage amplifier 42.
It is input to the multiplexer 43 via a and 42b. The multiplexer 43 forms the gate signal 51 shown in FIG. 8B in synchronism with the drive signal 50 shown in FIG. 8A, which is proportional to the rotation angle output from the galvano-mirror drive device 44, and the photoelectric conversion element 38a, Alternatively, only the signal of 38b is passed. The analog signal 52 shown in FIG. 8D is generated by the threshold value circuit (comparator) 47 in the threshold value generation circuit 46 that varies the voltage in synchronization with the electric signal output from the galvano-mirror drive circuit 44. The signal 54 shown in FIG. 8E is obtained by comparison with the variable threshold signal 53 shown. In this case, when the detection signal 52 exceeds the threshold value 53, the peak value of the detection signal 52 is calculated by the A / D converter 49 as the y coordinate electric signal 50 obtained from the galvanometer mirror driving device 44 and the x coordinate of the table driving device 45. Since the (x, y) coordinate position on the substrate 21 determined based on the x-coordinate electric signal obtained from the detection sensor is stored in the storage device 48, the (x, y) existence position of the foreign matter can be grasped. It is possible to observe the size and shape of a foreign substance after detecting the foreign substance with a microscope or the like. Although the above description is based on the upper surface foreign matter detection device 85 of the substrate 21, when detecting the foreign matter on the lower surface of the substrate 21, the lower surface foreign matter detection device of the substrate 21 is shown in FIG. It is possible to install one set of 90 on the lower surface of the substrate 21. In this case, the configuration of the device and the configuration of the electric circuit may be exactly the same. In the reticle for the 1/10 reduction projection type mask aligner, foreign matter on the upper surface of the reticle is 10 to 20 μm or more,
Since it is necessary to detect foreign matter of 2 to 5 μm or more on the lower surface pattern surface, it is necessary to set the thresholds of the upper surface / lower surface foreign matter detection devices 85 and 90 to the above foreign matter detection level. In the above description, the reticle foreign matter inspection is used as a single unit. However, by mounting the apparatus on the mask aligner, it is possible to inspect the foreign matter attached to the mask aligner after the reticle is mounted. As described above, according to the present invention, the frame 22 (thickness 2) of the 107 mm square pellicle mounted on the substrate surface is used.
mm, height 4 mm, or 6.3 mm) in order to avoid the influence of the frame of the pellicle, as shown in FIG. 10, a position (α = 22.5 ° ± 15) where irradiation can be performed on the substrate surface.
Irradiation device (27, 29) is installed at the right angle (9)
Diagonally above the substrate (β = 22.5 ° ± 15)
The detection device 37 is provided at (°) to detect foreign matter on the substrate 21. However, in the present invention, the irradiation light 30 is applied to the substrate 2
As shown in FIG. 4, the reflected light 26a from the upper surface of the frame 22 of the pellicle film body, the reflected light 26b from the reticle pattern surface 21a, and the pellicle film 23 as shown in FIG.
The reflected light 26c from the upper foreign matter 58 is erroneously detected as a foreign matter on the surface of the substrate 21. Here, since the foreign matter 58 existing on the pellicle film 23 is separated from the substrate 21, the foreign matter 58 is out of focus during projection exposure and does not cause exposure failure. Therefore, the present invention has dealt with erroneous detection by adding the pinhole-shaped light shielding device 57 shown in FIG. 10 and the slit-shaped light shielding device 39 shown in FIG. 11 to the detection device. When detecting a foreign substance on the surface of the substrate using the detection device to which the pinhole-shaped shading device 57 shown in FIG. 10 is added, the substrate 21 is moved in one direction while being moved or rotated in the x and y directions (not shown). 2) Put it on
It needs to be manipulated dimensionally. In addition, the substrate 2 is formed by using the detection device to which the slit-shaped shading device 39 shown in FIG. 11 is added.
When detecting the foreign matter 24 on the surface No. 1, the illumination light is scanned in one direction (y direction) by a scanning procedure (including the galvano mirror 28 and the f.theta. Lens 31 etc.) to scan the substrate 21 with x.
It is possible to detect foreign matter on the entire surface of the substrate by mounting it on a direction table (not shown) and moving it in a direction (x direction) orthogonal to the scanning of the illumination light. 10 and 11 described above
By adopting the pinhole / slit shading device shown in FIG. 2 in the present invention, the pellicle frame 22 as shown in FIG.
Foreign matter on the substrate surface can be detected with high sensitivity without being affected by reflected light such as. Further, by polarizing the illumination light (for example, S-polarized light) and adding an analyzer (for example, S-polarized shut filter) 41 to the detection device, the foreign matter and the gap portion of the circuit pattern are separated from each other as compared with the prior art. It is possible to further improve the sensitivity of the minute foreign matter by utilizing the difference in the polarization angle characteristics of the scattered reflected light between them. Further, in the above embodiment, the smaller the tilt angles α and β, the more effectively the change in the polarization angle can be detected, so the detection sensitivity is improved. However, due to the influence of the frame of the pellicle and the like, both α and β have an angle of 22.5. ± 15 degrees is optimal. Further detection device 3
The uniformity of the detection sensitivity can be improved by directing the optical axes of 7a and 37b (centers of the slits) to points a and b in FIG. 6 (lines x ₁ x ₂ when moving the reticle). As described above, according to the present invention,
In a reticle, photomask, etc., without turning over (without changing the foreign matter adhesion state), with the surface on which the circuit pattern is formed that is the same as the state of actual projection exposure facing down, separate the foreign matter adhered to both sides. In addition, it is possible to perform inspection with high reliability, and it is possible to eliminate defective exposure due to minute foreign matter adhering to the transparent substrate and to contribute to a large yield improvement in semiconductor production.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining a conventional technique. FIG. 2 is a configuration diagram showing an embodiment of the present invention. FIG. 3 is a diagram showing a basic configuration of the present invention. FIG. 4 is a diagram showing an influence of a pellicle frame. FIG. 5 is a diagram showing a relationship between illumination light and an inspection area and a relationship between a foreign matter detection direction and an inspection area. FIG. 6 is a diagram showing a relationship between inspection areas on a substrate. FIG. 7 is a diagram showing an electric circuit of the present invention. 8 is a diagram showing a signal waveform obtained by the circuit shown in FIG. FIG. 9 is a diagram showing a configuration of an apparatus for inspecting foreign matter on upper and lower surfaces of a substrate. 10A is a diagram showing a case where the detection device shown in FIG. 3 is equipped with a pinhole light-shielding device, and FIG. 10B is shown in FIG.
It is the A ₁₀ arrow enlarged view. 11A is a diagram showing a case where a slit light-shielding device is provided in the detection device, and FIG. 11B is an enlarged view of the A ₁₁ arrow in FIG. 11A. 12A and 12B are views showing the features of the present invention. [Explanation of reference numerals] 21 ... Substrate, 22 ... Pellicle film frame, 2
3 ... Pellicle film 24 ... Foreign matter, 27 ... Laser oscillator, 2
9 ... Polarizing element 31 ... f.theta. Lens, 38, 38a, 38b ... Photoelectric conversion element 39, 39a, 39b ... Slit-shaped light shielding device 40, 40a, 44b ... Condensing lens, 41, 41a,
Reference numeral 41b ... Detecting devices 42a, 42b ... Voltage amplifiers, 43 ... Multiplexer 44 ... Galvano mirror driving device, 45 ... Table driving device 48 ... Storage device, 50, 51 ... Foreign matter detecting device 57 ... Pinhole-shaped light shielding device

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mitsuyoshi Koizumi             Stock, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Production Engineering Research Laboratory, Hitachi, Ltd.              (56) References JP-A-56-86340 (JP, A)               JP-A-57-128834 (JP, A)               JP-A-56-115945 (JP, A)

Claims (1)

[Claims] 1. Linearly polarized laser illuminating light is applied to each of the front surface and the back surface of the transparent substrate having a circuit pattern formed on the front surface by a surface illumination condensing optical system and a back surface illumination condensing optical system from a direction perpendicular to the transparent substrate surface by 67.5 ±. The transparent substrate is scanned in a straight line with a tilt of 15 degrees to irradiate a focused spot, the transparent substrate is scanned in a direction substantially perpendicular to the linear scanning direction, and scattered light from each of the front surface and the back surface is transparent. 6 from the direction perpendicular to the board surface
Inclination by 7.5 ± 15 degrees, and the light is condensed by each of the front-side detection condensing optical system and the back-side detection condensing optical system substantially from the linear scanning direction, and the front-side detection condensing optical system and the back-side condensing optical system The scattered light reflected from the edge of the circuit pattern is shielded by the light shielding means composed of the analyzer and the field limiting means provided in each of the detection / focusing optical systems, and each of the light condensed through each light shielding means is received by each of the photoelectric conversion means and back photoelectric conversion unit for surface, the formation of the circuit pattern based on the signal detected from the signal and the back photoelectric conversion unit detected from the photoelectric conversion means for surface transparent A double-sided foreign matter detection method, wherein foreign matter attached on the front surface of the substrate and foreign matter attached on the rear surface of the transparent substrate are detected separately. 2. On each of the front surface and the back surface of the transparent substrate having a circuit pattern formed on the surface, linearly polarized laser illumination light is tilted 67.5 ± 15 degrees from the direction perpendicular to the transparent substrate surface and linearly scanned to illuminate a focused spot. Front-side illumination condensing optical system and back-side illumination condensing optical system, scanning means for scanning the transparent substrate in a direction substantially perpendicular to the linear scanning direction, and scattered light from each of the front and back sides. From an analyzer and a field-of-view limiting means that inclines 67.5 ± 15 degrees from the direction perpendicular to the transparent substrate surface, and that collects light from substantially the linear scanning direction and blocks scattered light reflected from the edge of the circuit pattern. The front-side detection light collecting optical system and the back-side detection light collecting optical system having the configured light-shielding means, and the front-side detection light collecting optical system and the back-side detection light collecting optical system through the respective light-shielding means. Received each of the light A front surface photoelectric conversion means that emits light and a back surface photoelectric conversion means, and the circuit pattern is formed on the basis of a signal detected from the front surface photoelectric conversion means and a back surface photoelectric conversion means. A double-sided foreign matter detection device, characterized in that it is configured to detect a foreign matter adhered on the front surface of the substrate and a foreign matter adhered on the rear surface of the transparent substrate in distinction.