JPH0334576B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is directed to detecting foreign objects on the surface of a transparent substrate such as a photomask or reticle, in particular, to avoid 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 light beam, and the transparent substrate 5 is scanned through the fθ lens 3 and through the optical path 4 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 a foreign object is present, the scattered light will spread in all directions, so a detection optical system consisting of a condenser lens 12 and a light receiving element 14 is installed in such a way that the scanning line 8 is faced 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 a 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, the scattered light therefrom 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]

The purpose of the present invention is to solve the problems of the prior art described above.
Eliminates the effects of scattered light caused by foreign objects on the circuit pattern, pellicle frame, and pellicle film on the board, and can always accurately detect foreign objects on the board even if the position of the board surface changes. The present invention provides a foreign object detection device.

[Summary of the invention]

That is, in order to achieve the above object, the present invention includes a laser light source, a polarizing element that converts the laser light from the laser light source into polarized laser light, and a pellicle for the polarized laser light polarized by the polarizing element. an illumination optical system having a first optical axis tilted with respect to the substrate surface to irradiate the substrate surface with a foreign matter adhesion prevention means formed thereon through the pellicle; an illumination device having a scanning optical system that scans in a direction having an intersecting angle of approximately 90 degrees with respect to the axis; and the first optical axis and the substrate surface for detecting reflected light from a foreign substance on the substrate through the pellicle. A detection optical system having a second optical axis tilted with respect to the substrate surface at an intersection angle of approximately 90 degrees at the top, and of the reflected light detected by the detection optical system, there is no foreign matter on the frame, the pellicle, and the like. A detection device comprising a light shielding element that blocks reflected light from a circuit pattern on a substrate, and a photoelectric conversion device that receives reflected light from a foreign object on the substrate obtained by passing through the light shielding element and converts it into a signal. , a substrate vertical position detection means for detecting the vertical position of the surface of the substrate; and a foreign object on the substrate whose position on the substrate surface detected by the substrate vertical position detection means is obtained by passing through the light shielding element. A foreign object detection device is characterized in that it is equipped with a control means for controlling the depth of focus to fall within an allowable depth of focus in order to receive reflected light from the object with an allowable sensitivity.
Further, the present invention provides that the substrate vertical position detection means of the foreign object detection device is provided at a position different from the foreign object detection position where the illumination device and the detection device are installed, and the control means controls the vertical position of the surface of the substrate. The present invention is provided with a moving means for moving to the foreign object detection position in a corrected state, so that the substrate vertical position detecting means can be easily installed.

[Embodiments of the invention]

The present invention will be specifically described below based on embodiments shown in the drawings. FIG. 3 is a diagram showing an embodiment of detecting foreign matter on a substrate such as a photomask or reticle when a transparent pellicle film body for preventing foreign matter from adhering to the substrate according to the present invention is attached to the substrate.
That is, the laser beam emitted from the laser oscillator 1 is converted into a linearly polarized wave (horizontal wave) (for example, S-polarized light) in a specific direction by a polarizing element 15, and is converted into a linearly polarized wave (horizontal wave) (for example, S-polarized light) in a specific direction by a galvanometer mirror 2 connected to a motor 2 that rotates or oscillates. After total reflection, the laser beam is irradiated obliquely onto the substrate 5 through the lens 3, and scanned in a straight line in a direction that intersects with this at a 90 degree angle, so that the laser beam reflected from the foreign object 10 on the substrate surface is also applied in the above scanning direction. Detection is performed by a detection device 19 provided obliquely to the substrate. With such a configuration, high-speed foreign matter inspection can be performed. The detection device 19 consists of an analyzer 17, a condensing lens 12, a slit-shaped light shielding device 18, and a photoelectric conversion element 14. In particular, the slit-shaped light shielding device 18 is shown in FIG. 3B.
As shown in FIG. 2, it is provided to detect only the reflected light from the foreign matter 10 present on the substrate 5 surface, and the reflected light from the upper surface of the frame 6 of the pellicle film body, the pellicle film 1
This is to limit the detection area so that foreign objects on the surface of the substrate 5 are not mistakenly detected as foreign objects on the surface of the substrate 5.

In this method, variations in the thickness of the board mounted on the foreign object inspection device affect the foreign object detection performance.
FIG. 4 is an enlarged view of the slit-shaped light shielding device 18 as viewed from arrow _A11 in FIG. 3A. FIG. 5a shows a state in which the laser beam 4 is focused on the surface of the substrate 5 (the slit-shaped light shielding device is positioned at the center with respect to foreign matter on the center surface of the substrate). Figure 5b,
5c shows the position of foreign matter in the slit-shaped light shielding device 18 when the thickness of the substrate 5 exceeds the reference value (5a in this case) and when it does not, but the position of the substrate surface changes. Therefore, the foreign object 10 is not irradiated with the laser light, making it impossible to detect the foreign object.

What is shown in FIG. 4 is intended to explain the case where the thickness of the substrate 5 changes significantly (due to variations from lot to lot in manufacturing the substrate). The laser beam 4 irradiated onto the substrate 5 has a circular cross section.
FIG. 5A is a diagram showing how a laser beam is irradiated to a foreign object existing on the surface of the substrate 5 and the focus of the substrate 5 is changed, and FIG. 5B is a diagram showing the intensity change of the reflected light from the foreign object 10 as the focus changes. FIG. As the substrate 5 moves upward or downward due to positional changes, the intensity of the laser beam irradiating the foreign object also gradually becomes weaker. Here, if 80% of the intensity of the reflected light from the foreign object 5 is assumed to be an allowable uniform sensitivity, then ΔZ can be the allowable depth of focus of the substrate 21. Therefore, as shown in FIG. 6, the position of the surface of the substrate 5 is measured using a plurality of detectors 20, and the measured average position Za is calculated from the measured value D. If the substrate 5 is changed in the thickness direction so that the deviation +Z from Zo (position in the state of 5a) falls within the allowable depth of focus ΔZ, it is possible to correct variations in board thickness, etc.

Therefore, as shown in FIG. 7, by providing a plurality of detectors 20 on the surface (or the bottom surface) of the substrate 5 to measure the position of the substrate, it is possible to correct the position of the substrate due to variations in board thickness, etc. can.

That is, in the present invention, as shown in FIGS. 7 and 8, the surface position of the substrate 5 mounted on the stage 21 is measured by a plurality of detectors 20a to 20d provided on the surface of the substrate 5. The correction mechanism 22 is constituted by a driving means such as a motor, an air servo, etc., and is provided in the moving mechanism 23 so that the surface of the surface is at a constant reference position.
The foreign matter inspection is performed after correcting the position of the board, such as the board thickness, in advance before the inspection. That is, since it is difficult to catch the reflected light of the obliquely irradiated laser spot 4 and install the substrate 5 in a predetermined position, the above-mentioned configuration was adopted.
FIG. 9 is a diagram showing a block diagram of an embodiment of the present invention. The signals from the detectors 20a to 20b are sent to the adder 24.
The servo circuit 26 issues a command to the motor drive circuit 27 based on this signal, and operates the correction mechanism 22 by the rotation of the motor 28. The structure is such that the thickness of the substrate 5, etc. is corrected.

FIG. 10 is a diagram showing the overall configuration of an embodiment of a foreign object detection device equipped with a plate thickness correction mechanism of the present invention. The substrate 5 mounted on the stage 21 is the detector 20
a, 20d, the correction mechanism 22 causes the surface to match a certain reference position, and the moving mechanism 23 sends the foreign object below the foreign object detection unit 30 to detect the foreign object.

〔Effect of the invention〕

As explained above, according to the present invention, when the advantages of obliquely polarized laser beam scanning illumination and obliquely shielded light detection are utilized, even if the surface position of the substrate changes slightly due to uneven thickness, etc., foreign particles can be detected. This has a subtle effect on the detection sensitivity of the foreign matter, so by satisfying both of these requirements, it is possible to eliminate scattered light from foreign objects without being affected by the frame of the pellicle film on the substrate surface or the circuit pattern formed on the substrate. This has the effect of being able to effectively and accurately detect minute foreign matter with a size of about 1 to 2 μm.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional foreign object detection device.
FIG. 2 is a diagram showing the irradiation state of the laser spot viewed from the direction of arrow A in FIG. Figure 5 is a diagram showing variations in the intensity of reflected light from foreign objects due to variations in the surface position of the substrate, Figure 6 is a diagram showing measurement of the substrate surface position by a detector, and Figure 7 is a diagram showing the measurement of the substrate surface position. FIG. 8 is a diagram showing an embodiment of the substrate position detection section according to the present invention, FIG. 9 is a diagram showing a block diagram, and FIG. 10 is a diagram showing a foreign object according to the present invention. FIG. 1 is a diagram illustrating an overall schematic configuration of an embodiment of a detection device. 5... Substrate, 20... Detector, 21... Stage, 22... Correction mechanism, 23... Movement mechanism, 24
... Adder, 25 ... Averaging circuit, 26 ... Servo circuit, 27 ... Motor drive circuit, 28 ... Motor.

Claims (1)

[Scope of Claims] 1. A laser light source, a polarizing element that converts the laser light from the laser light source into polarized laser light, and a method for preventing foreign matter from adhering to the polarized laser light polarized by the polarizing element by forming a pellicle on the frame. An illumination optical system having a first optical axis inclined with respect to the substrate surface so as to irradiate the substrate surface on which the means is mounted through the pellicle, and the polarized laser beam at an intersecting angle with respect to the first optical axis. an illumination device having a scanning optical system that scans in a direction in which the angle is approximately 90 degrees;
A detection optical system having a second optical axis inclined with respect to the substrate surface at an intersection angle of approximately 90 degrees with the optical axis of the substrate surface, and of the reflected light detected by the detection optical system, the frame , a light shielding element that blocks light reflected from a foreign object on the pellicle and a circuit pattern on a substrate, and a photoelectric conversion device that receives reflected light from the foreign object on the substrate that passes through the light shielding element and converts it into a signal. a detection device having: a substrate vertical position detection means for detecting the vertical position of the surface of the substrate;
The position of the surface of the substrate detected by the substrate vertical position detection means falls within a permissible depth of focus in order to receive the reflected light from the foreign matter on the substrate obtained by passing through the light shielding element with permissible sensitivity. What is claimed is: 1. A foreign object detection device comprising: control means for controlling. 2. The substrate vertical position detection means is provided at a position different from the foreign object detection position where the illumination device and the detection device are installed, and the substrate surface vertical position is corrected by the control means when the foreign object detection position is corrected. 2. The foreign object detection device according to claim 1, further comprising a moving means for moving the foreign object to the foreign object detection device. 3. The foreign object detection device according to claim 1, wherein the light shielding element is composed of an analyzer and a slit.