JPH0334577B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is aimed at detecting foreign objects on the surface of a transparent substrate such as a photomask or reticle, in particular, without being affected by obstacles on the back surface of the substrate or near the detection surface. The present invention relates to a foreign object detection device.

[Prior art]

To detect microscopic foreign objects on transparent substrates such as photomasks and reticles for semiconductor manufacturing, a method is to irradiate the substrate obliquely with a laser and detect the scattered light from the foreign object with a photomultiplier tube or other light-receiving element. is being attempted.

FIG. 1 shows an example of this. Laser light 4 emitted from laser oscillator 1 passes through galvano mirror 2
The light beam is deflected by the f-theta laser 3 and passes through the optical path 4, and the transparent substrate 5 is scanned so that the spot 10 moves along the scanning line 8. If there are no foreign objects, the laser beam will be reflected and travel straight. On the other hand, if there is a foreign object, the scattered light will spread in all directions, so a detection optical system consisting of a condensing lens 12 and a light receiving element 14 is installed in such a way that the scanning line 8 faces from the direction in which it extends. It detects light 9. By moving the transparent substrate 5 at a constant speed in the X direction, in conjunction with the scanning of the laser beam 4 in the Y direction,
Full-scale detection is now possible.

In addition, recently, in order to prevent foreign matter from adhering to the transparent substrate 5, a pellicle film having a structure in which a thin film 7 made of nitrocellulose is attached to a metal frame 6 has been used. To avoid vignetting of the laser beam, set the illumination angle ω and detection angle θ to 3 to 40.
I've started to take it more seriously.

FIGS. 2 a to 2 d show locations where abnormal scattered light is generated that can be detected in this apparatus, as viewed from direction A in FIG. 1.

First, when the laser beam 4 is irradiated at point D on the detection surface at an angle ω, the refracted light reaches the back surface E of the substrate because the substrate 5 is transparent. Pattern 15 (second
If a foreign object 16 (FIG. 2b) is present, scattered light from the foreign object 16 can be detected.

In addition, when there is a pellicle film, if there is a large foreign object 16 at the point F where the laser beam 4 crosses the pellicle thin film 7 above the substrate 5 (FIG. 2c), or if the laser beam 4 is reflected on the surface of the substrate 5. When the scattered light hits the edge of the metal frame 6 of the pellicle membrane at point G (FIG. 2d), the scattered light generated can be detected.

Therefore, the methods tried above have the problem that obstacles such as the back surface or the pellicle film cause false detection.

[Purpose of the invention]

In view of the problems of the prior art described above, an object of the present invention is to reliably remove the influence of scattered light caused by foreign matter, etc. on the circuit pattern, pellicle frame, and pellicle film on the substrate, and to accurately remove foreign matter on the substrate. An object of the present invention is to provide a foreign object detection device capable of detecting foreign objects.

[Summary of the invention]

That is, in order to achieve the above object, the present invention uses a laser light source and a laser light emitted from the laser light source to be irradiated in a spot shape through the pellicle onto the surface of a substrate on which a foreign matter adhesion prevention means formed with a pellicle of a frame is attached. The illumination optical system preferably has a first optical axis tilted with respect to a direction perpendicular to the substrate surface, and the laser beam is arranged at a substantially intersecting angle with respect to the first optical axis.
an illumination device having a scanning optical system that scans in a direction of 90 degrees, and an intersection angle of approximately 90 degrees between the first optical axis and the substrate surface in order to detect light reflected from a foreign object on the substrate through the pellicle. and a detection and focusing optical system having a second optical axis inclined with respect to a direction perpendicular to the substrate surface, and of the reflected light detected by the detection and focusing optical system, foreign matter on the frame, the pellicle, and the substrate are detected. a slit that blocks reflected light from the upper circuit pattern and is installed at a conjugate position of the scanning line of the laser spot irradiated onto the substrate at an angle with respect to a plane perpendicular to the second optical axis; and a photoelectric conversion device that receives reflected light from the foreign substance on the substrate obtained by passing through the slit and converts it into a signal.

[Embodiments of the invention]

The present invention will be specifically described below based on embodiments shown in the drawings. FIG. 3 shows an embodiment of the foreign object detection device of the present invention. That is, in the present invention, the slit 13 is installed between the condenser lens 12 and the light receiving element 14 shown in FIG. 1, and the scattered light obtained from sources other than the substrate is blocked, so that only the foreign matter present on the substrate can be detected. This is how it was done. The details are as follows. That is, when the location where the abnormally scattered light occurs shown in FIG. 2 is viewed from the top surface of the substrate, it becomes as shown in FIG. 4. In this way, the laser beam 4 has D, E,
Scattered light may be generated at each point F and G.
When a part of this scattered light is focused by the condensing lens 12, spots D', E', F', and G' are formed on the imaging plane 18. Therefore, if the slit 13 is provided to block only the abnormally scattered light of E', F', and G',
Only the scattered light from the point D to be inspected is transmitted to the light receiving element 1.
4 is reached. Here, the optical axis of the condensing lens 12 is within a plane that includes the extension of the scanning line 8 of the laser beam 4.

On the other hand, FIG. 5 shows a view of FIG. 3 viewed from direction C. The optical axis 19 of the condensing lens 12 is inclined at an angle of θ with respect to the scanning line 8 of the laser beam. The scattered lights emitted from points I, O, and J on the scanning line 8 are imaged by the condenser lens 12 as points I', O', and J' on the image plane 18. Therefore, the light shielding plate 13 is formed into a slit shape. This makes it possible to detect only foreign matter present on the transparent substrate 5. That is, scattered light generated only from point D on the transparent substrate 5 can be detected.

By the way, the slit 13 is the optical axis 1 of the condenser lens.
If it is provided on the surface 20 at a right angle to the optical axis 9, a point off the optical axis will be defocused, and as shown in FIG. 6, the effect on blocking the light scattered by foreign objects will be lost. here,
13a is a slit plate, 24 is an opening 2 of the slit
2 is the imaging trajectory of the scanning line to be detected, 23 is the condensing trajectory of the scattered light from the back surface, and E ₁ to _{E 3} are the sizes of the spots of abnormal scattered light, and the overlap with the detected scattered light is It turns out that there are so many that it is impossible to discriminate.

However, the slit 13b is
If it is tilted along the line 8, it will look like the one shown in Fig. 7, and it will be possible to distinguish between the two.

At this time, the inclination of the image plane is given by the following equation, where m is the magnification of the condensing lens 12 on the optical axis 19.

tan=1/mtanθ Therefore, when m is large, the value of becomes small and the slope of the slit becomes large, making detection difficult. For example, when θ is 15°, if m is set to about 0.27, then becomes about 45°, which makes it possible to set the angle at which it is easy to form a slit. As described above, the magnification of the condensing lens needs to be 1 or less, although it depends on the angle of θ.

By the way, since the size of the spot of the laser beam irradiated onto the transparent substrate is constant, I,
The sizes of the spot images at I', O', and J' formed by O and J vary because their respective magnifications are different. Furthermore, since the locus of the anomalous scattered light changes for the same reason, 23 and 22 are no longer parallel in FIGS. 6 and 7.

Focusing on this property, it can be seen that in order to secure the discrimination ratio and increase the tolerance for spot fluctuation in the X direction, the shape of the slit 13c can be modified as shown in Fig. 8. . At this time, the width of the slit 13c needs to be larger than the size of the image including the aberration caused by the condensing lens of the laser spot.

The slit is provided between the condenser lens 12 and the light receiving element 14, as shown in 13b in FIG. 3, but in reality, as shown in FIG.
It is preferable to further provide a field lens 25 for condensing light between the light receiving element 14 and the light receiving element 14. This is because since the slit is inclined, it is impossible to bring the light receiving element close enough to the slit, and it is impossible to collect the scattered light on the light receiving surface 26 of the light receiving element without a field lens.

The detection optical system is basically configured as shown in Figure 9, with a polarizing plate and ND filter inserted in the middle of the optical path.
Some aim to improve detection sensitivity.

In assembling the slit 13, it is necessary to accurately align the locus of the scanning line of the laser beam formed by the condensing lens with the position of the slit. Therefore, in the detection optical system, it is necessary to provide a fine adjustment mechanism only at the slit. In FIG. 9, for example, fine adjustment in at least the x and y directions is essential, and if necessary, a rotational fine adjustment mechanism in the x direction and the y direction is provided.

〔Effect of the invention〕

As explained above, according to the present invention, when inspecting minute foreign matter on a transparent substrate, scattered light from the circuit pattern on the back side of the substrate, foreign matter on the pellicle film, pellicle frame, etc. can be completely ignored. It can significantly reduce the rate of false detection of foreign objects, shorten the time for visual confirmation after automatic inspection, and reduce the number of unnecessary cleanings, reducing production costs and improving productivity. Contribute.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a conventional foreign object detection device, FIG. 2 is a side view from the direction A in FIG. 4 is a top view showing a method of shielding abnormally scattered light according to the present invention, FIG. 5 is a side view from the direction C of FIG. 3 showing the principle of slits, and FIGS. 7 and 8 are the shapes of the slits seen from the direction B in FIG. 3, and FIG. 9 is a side view from the direction C in FIG. 3 showing the actual detection optical system. 4... Laser light, 5... Transparent substrate, 8... Scanning line, 12... Condensing lens, 13, 13a, 13
b, 13c...slit, 14...light receiving element, 2
4...Slit aperture, 25...Field lens.

Claims (1)

[Scope of Claims] 1. A laser light source and a laser light emitted from the laser light source are irradiated onto the substrate surface in a spot-like manner through the pellicle onto the substrate surface, which is equipped with a foreign matter adhesion prevention means having a pellicle formed in a frame. an illumination optical system having a first optical axis tilted with respect to the perpendicular direction; and a scanning optical system that scans the laser beam in a direction having an intersecting angle of approximately 90 degrees with respect to the first optical axis. The illumination device is tilted with respect to the vertical direction of the substrate surface at an intersection angle of approximately 90 degrees between the first optical axis and the substrate surface in order to detect reflected light from a foreign substance on the substrate through the pellicle. Of the reflected light detected by the detection focusing optical system having a second optical axis and the detection focusing optical system, the reflected light from the foreign matter on the frame, the pellicle, and the circuit pattern on the substrate is blocked, and A slit is installed at a conjugate position of the scanning line of the laser spot irradiated onto the substrate and is inclined with respect to a plane perpendicular to the second optical axis. A foreign object detection device comprising: a detection device having a photoelectric conversion device that receives reflected light from a foreign object and converts it into a signal. 2. The foreign object detection device according to claim 1, wherein the width of the slit is changed in accordance with the magnification of the detection and focusing optical system that changes depending on the position on the scanning line.