JPH0769272B2 - Foreign matter inspection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an apparatus for inspecting foreign matter such as minute dust, and more particularly to a substrate such as a photomask, a reticle, or a semiconductor wafer used in the manufacturing process of integrated circuits. The present invention relates to a device for inspecting adhered foreign matter.

[Prior Art] In a photolithography process, which is one of manufacturing processes of integrated circuits, a circuit pattern is transferred onto a semiconductor wafer by a reticle, a photomask, or the like (hereinafter referred to as “reticle”). When foreign matter such as dust adheres to the reticle, the foreign matter image is transferred to the semiconductor wafer and appears as a defect in the circuit pattern. As a result, it causes a decrease in manufacturing yield. Therefore, it is necessary to inspect whether or not foreign matter is attached to the surface of the reticle before performing the transfer.

As a method of detecting such foreign matter, there is a method of focusing a laser beam or the like on a reticle for scanning, receiving scattered light emitted from the foreign matter, and detecting the foreign matter by the scattered signal.

In the case of inspecting a foreign matter by the above method, when the reticle is irradiated with light, scattered light is generated not only from the foreign matter but also from the pattern edge of the reticle. Therefore, it is necessary to distinguish these scattered lights. In this case, the scattered light from the pattern edge has a strong directivity, whereas the scattered light from the foreign matter occurs relatively omnidirectionally. Therefore, by arranging a plurality of photoelectric detection means at a predetermined angle and comparing the scattered signals obtained from each photoelectric detection means to determine the directivity of the light, the scattered signal due to the pattern edge and the scattered signal due to the foreign matter are detected. Can be distinguished. By adopting the above means, it becomes possible to detect the foreign matter attached to the reticle.

On the other hand, in recent years, a method of preventing foreign matter from adhering to the reticle by attaching a foreign matter adhesion prevention film (hereinafter referred to as “pellicle”) at a predetermined distance from the surface of the reticle has been performed. In this method, the pellicle is mounted so as to cover the surface of the reticle via a support frame so that foreign matter does not directly adhere to the reticle surface.

As described above, when projection exposure is performed by the exposure apparatus using the pellicle, even if a foreign substance adheres to the surface of the pellicle, the foreign substance image is not focused on the projected object, that is, the semiconductor wafer surface. The foreign matter image is not transferred to the semiconductor wafer.

However, even in this case, if the foreign matter attached to the surface of the pellicle is relatively large, there is a possibility that uneven exposure may occur on the semiconductor wafer surface. Further, even if a pellicle is used, foreign matter may adhere to the reticle.

Therefore, the foreign matter inspection is necessary even when the pellicle is used as described above.

[Problems to be Solved by the Invention] In general, the detection sensitivity of foreign matter depends on the beam diameter of the light beam scanning the surface to be inspected. The smaller the beam diameter, the higher the detection sensitivity, and the smaller foreign matter can be detected. It is possible. However, the smaller the beam diameter, the longer the time required to scan the entire surface to be inspected uniformly.

In the conventional foreign matter inspection apparatus, the reticle surface and the pellicle surface are inspected with the same beam diameter, that is, the same sensitivity. On the other hand, as to the foreign matter on the pellicle, as described above, even if a relatively large foreign matter is attached, it is difficult to be transferred to the semiconductor wafer. In other words, the reticle and the pellicle differ in the size of the foreign matter that can be tolerated, and the pellicle allows even larger foreign matter.

Therefore, when the pellicle surface is inspected by using the conventional foreign matter inspection apparatus as described above, even a foreign matter smaller than necessary is inspected during the inspection, and as a result, the foreign matter inspection is performed more than necessary. There was a problem that it took a long time.

The present invention has been made in view of the above-mentioned conventional problems, and foreign matter inspection capable of performing inspection with optimum detection sensitivity and inspection time regardless of whether inspecting a reticle or a pellicle. The purpose is to provide a device.

[Means for Solving Problems] A foreign matter inspection apparatus according to the present invention includes a beam diameter changing means for changing a beam diameter of a light beam on a surface to be inspected and presence / absence of foreign matter based on each photoelectric signal of a photoelectric detecting means. The above-mentioned problem is solved by providing the determining means for determining the size of the beam and the beam diameter corresponding to different beam diameters.

[Operation] In the present invention, the beam diameter changing means for changing the beam diameter of the light beam on the surface to be inspected and the presence / absence of foreign matter and the size thereof corresponding to the different beam diameters based on each photoelectric signal of the photoelectric detecting means. Since it is possible to inspect by changing the beam diameter on the surface to be inspected according to the object to be inspected by providing the determining means for performing the determination based on It is possible to perform the inspection with the detection sensitivity according to the above, that is, the beam diameter, and the scanning speed according to the beam diameter.

EXAMPLES Examples of the present invention will be described in detail below with reference to the accompanying drawings.

(First Embodiment) FIG. 1 is a perspective view showing the configuration of an embodiment of the present invention.
First, the configuration and operation of this embodiment will be described.

In the figure, 10 is a reticle, which is placed on a stage 12 with only the peripheral portion supported. A pellicle 20 is mounted on the reticle 10 via a support frame 22. Further, the above-mentioned table 12 can be moved in the y direction in the xyz coordinate system in the figure by the motor 14 and the feed screw 16.
The amount of movement of the platform 12 in the y direction is measured by a length measuring device 18 such as a linear encoder. Further, the above-described object table 12 is configured to be movable also in the z direction by an appropriate means (not shown).

Next, the laser beam L is output from an appropriate oscillating means (not shown), adjusted to an arbitrary beam diameter by the expander 1, the condenser lens 26, and other optical elements, and then is radiated onto the reticle 10 or the pellicle 20 to be inspected. Oblique incidence. The incident angle of the laser beam L, that is, the angle formed by the plane of the object to be inspected, is an angle at which the laser beam L does not vignet on the support frame 22, preferably about 10 ° to 80 °.

Next, the operation of scanning the surface to be inspected with the laser beam L will be described.

The laser beam L output as described above is scanned within a predetermined range in the x direction on the surface to be inspected, for example, the reticle 10 by a scanning mirror, for example, a galvanometer scanner mirror 28 (hereinafter, this range will be referred to as "scanning range S ")). At this time, at the same time, the motor 14 is also driven to move the stage 12, thereby moving the reticle 10 in the y direction at a speed slower than the scanning speed of the laser beam L in the x direction.

As described above, by scanning the laser beam L in the x direction and moving the reticle 10 in the y direction,
It is possible to scan the entire surface of the reticle 10 as the inspection object with the laser beam L.

As for the irradiation position of the laser beam L on the reticle 10, the measurement value corresponding to the irradiation position of the laser beam L output from the length measuring device 18 on the reticle 10 in the y direction is measured in the x direction. By detecting the deflection angle of the galvano scanner mirror 28, it is possible to know each of the x and y directions.

Next, the operation of changing the beam diameter of the laser beam L on the surface to be inspected will be described.

An aperture 2 is provided so that it can be appropriately inserted on the optical axis between the expander 1 and the galvano scanner mirror 28. Comparing the case where the aperture 2 is inserted on the optical axis and the case where the aperture 2 is not inserted, the convergent beam numerical aperture after passing through the condenser lens 26 becomes smaller in the former case. As a result, the beam diameter of the laser beam L on the focus, that is, on the surface to be inspected becomes large. The beam diameter is changed by appropriately inserting or removing the aperture 2 on the optical axis as described above.

When the beam diameter is changed and the inspection is performed with a different beam diameter, the conveyance speed of the stage 12 in the y direction can be changed accordingly. Because
Since the scanning width in the y direction, which can be covered by one scanning of the beam L in the x direction, expands as the beam system expands,
This is because the transport speed of the reticle 10 in the y direction can be increased.

As described above, when increasing the beam diameter, the stage
The transport speed of 12 can be set large.

Therefore, when the pellicle 20 having a large tolerance for the diameter of the adhered foreign matter is to be inspected, the beam diameter can be enlarged and the inspection can be performed. Therefore, by increasing the transport speed of the stage 12, The time required to scan the entire surface of the pellicle 20 with the laser beam L is shortened as compared with the case where the reticle 10 has a normal beam diameter as an inspection target.

Next, the configuration of the laser light detection system will be described.

Above the stage 12, photoelectric detectors 30, 32, 34 for detecting scattered light from foreign matter attached on the surface to be inspected are arranged. On the light incident side of these photoelectric detectors 30, 32, 34,
Lenses 36, 38, 40 for condensing scattered light from a foreign substance are provided via rectangular slits 42, 44, 46, respectively. These slits 42, 44, 46 are arranged at positions substantially conjugate with the scanning range S on the surface to be inspected, in close contact with or close to the photoelectric detectors 30, 32, 34 together with the image of the scanning range S. .

The slits are provided to prevent stray light from entering each photoelectric detector. That is, when the laser beam L is scanned on the surface to be inspected, for example, the reticle 10, when the laser beam L approaches the support frame 22, the reflected light generated on the back surface or front surface of the reticle 10 is further reflected by the support frame 22. The reflected light is a photoelectric detector
Stray light to 30, 32, and 34 may cause uneven exposure. Therefore, it is necessary to prevent such stray light from entering each photoelectric detector.As such a preventive measure, each rectangular slit is provided on the light incident side of each photoelectric detector, and such stray light is applied to each photoelectric detector. This is to prevent it from entering.

The photoelectric detectors and the slits may not be in close contact or close to each other as described above, but the photoelectric detectors and the slits may be separated from each other via, for example, a relay optical system.

Next, the optical axes l1, l2, l3 of the lenses 36, 38, 40 and the photoelectric detector 3
Specific arrangement directions of 0, 32, and 34 will be described with reference to FIGS. 2 and 3.

FIG. 2 is a plan view for explaining the configuration on the xy plane of this embodiment. First, the direction of arrangement on the XY plane will be described with reference to this drawing.

In the figure, first, in the photoelectric detector 30, the optical axis 11 of the lens 36 is arranged at an appropriate position on the extension of the laser beam L in the scanning direction. On the other hand, in the photoelectric detectors 32 and 34, the optical axes l2 and l3 of the lenses 38 and 40 intersect at the scanning center Q of the laser beam L, and the azimuth angles ψa and ψb of the respective optical axes with respect to the scanning direction are 15 ° to 80 °, respectively. It is arranged to be in the range of °.

Next, the arrangement in the plane including the z axis will be described with reference to FIG. FIG. 3 is a side view showing the configuration of this embodiment in the z-axis direction.

First, the photoelectric detectors 30, 32, 34 are all arranged above the surface to be inspected, that is, on the irradiation surface side. Then, in the plane including the z-axis, the extension lines of the optical axes l1, l2, and l3 of the lenses 36, 38, and 40 all intersect at the scanning center Q of the laser beam L and the angle of each optical axis with respect to the scanning plane. All of θ1, θ2, and θ3 are in the range of 10 ° to 80 ° and are arranged at positions that are substantially equidistant from the scanning center Q.

Depending on the light receiving optical system, it is possible to more effectively receive the scattered light on the scanning range S if it is arranged so that the extension lines of the optical axes l1, l2, and l3 intersect at a position slightly deviated from the scanning center Q. There are cases.

Next, a specific operation of forming a spot having a predetermined beam diameter on each surface to be inspected will be described.

First, the stage 12 is moved in the z direction by an appropriate means (not shown) so that the minimum spot size position of the laser beam L is located on the surface of each inspected object.

Next, when the reticle 10 is to be inspected, set the aperture 2 to the expander 1 and the galvano scanner mirror.
When the pellicle 20 is to be inspected and is located at a position other than the optical axis between the aperture 28 and the optical axis 28, the aperture 2 is positioned on the optical axis.

The inner diameter of the aperture 2 is appropriately determined so as to have a predetermined beam diameter.

Next, a means for judging the presence or absence and the size of a foreign matter based on the outputs of the photoelectric detectors 30, 32, 34 will be described with reference to FIG.

FIG. 4 is a circuit diagram showing an example of signal processing means for processing a photoelectric signal from the photoelectric detector.

First, the configuration will be described.

In the figure, the output sides of the photoelectric detectors 30, 32, 34 are connected via respective amplifiers 70, 72, 74 to amplification degree converters 76, 78, 80 such as voltage controlled amplifiers (VCA).

Further, these amplification degree converters 76, 78, 80 are connected to the controller 82, and the amplification degree of the amplification degree converters 76, 78, 80 can be individually changed by the controller 82.

Next, the output side of the amplification degree converters 76, 78, 80 is a comparator.
It is connected to one input side of each of 84,86,88.
On the other hand, the other input side of these comparators 84, 86, 88 is connected to a reference voltage generator 90, and a predetermined reference voltage is input to each comparator by this reference voltage generator 90. .

The output sides of the comparators 84, 86, 88 are connected to the input side of the AND circuit 92, and the value of the logical product of the AND circuit 92 is output as a foreign matter detection signal.

Next, the processing operation of the signal processing circuit for detecting a foreign substance as described above will be described.

First, since each detection signal detected by the photoelectric detectors 30, 32, 34 changes depending on the distance between each photoelectric detector and the position to be inspected, the amplification degree converters 76, 78, 80 respectively detect each detection signal. Make a correction.

That is, the output photoelectric signals of the photoelectric detectors 30, 32, 34 have different signal values depending on the position on the reticle 10, even when the shape or size of the foreign matter is the same. Specifically, even for a foreign substance on the same beam scanning line, the photoelectric signal due to the foreign substance closer to the photoelectric detector is larger than the photoelectric signal due to the foreign substance distant from the photoelectric detector.

Therefore, if it is left as it is, it is inconvenient to determine the presence or absence of a foreign matter based on each photoelectric signal, and the size of the foreign matter cannot be determined based on the magnitude of the signal value. Therefore,
It is necessary to correct the photoelectric signal value corresponding to the inspection position and remove the variation due to the inspection position. Therefore, the amplifiers 70, 72,
Amplification degree converters 76, 78, 80 are provided on the output side of 74, respectively, and the setting of the amplification degree is changed by the controller 82 to correct the fluctuation of the photoelectric signal value depending on the position of the foreign matter.

The operation of changing the amplification degree by the controller 82 is performed in the following sequence.

First, the scanning of the laser beam L in the x direction is started and the amplification operation of the controller 82 is started. During scanning of the laser beam L, the controller 82 continuously changes the amplification degrees of the amplification degree converters 76, 78, 80 in accordance with the distance from the beam position on the surface to be inspected. Then, when the scanning of the laser beam L in the x direction is completed, the amplification operation of the controller 82 is also completed. This series of operations is repeated every time the laser beam L is scanned in the x direction.

The amplification degree of the amplification degree converters 76, 78, 80 and its change amount are determined in advance by the arrangement of the photoelectric detectors 30, 32, 34, that is, the distance from the surface to be inspected.

By correcting the amplification degree for each photoelectric signal as described above, it is possible to eliminate the factor of fluctuation of the signal value due to the position of the beam.

Next, each detection signal whose variation due to the inspection position is corrected is
It is binarized by the comparators 84, 86, 88.

As mentioned above, the scattered light from foreign matter is omnidirectional,
The photoelectric signals output from the photoelectric detectors 30, 32, 34 due to the scattered light from the foreign matter are all large signals. On the other hand, since the scattered light due to the pattern edge has directivity, at least one signal among the output photoelectric signals in the photoelectric detectors 30, 32, 34 becomes small.

Therefore, each photoelectric signal is compared with the reference voltage output from the reference voltage generator 90, and binarization is performed by outputting only when it is larger than the reference voltage.

Next, the AND circuit 92 outputs the value of the logical product of the outputs binarized by the comparators 84, 86, 88. In this case, the output of the AND circuit 92 becomes the “H” level of the logical value and is output as the detection signal SD only when output from all of the comparators 84, 86, 88.

Therefore, if the detection signal SD is "H", it is judged as a scattering signal from the foreign matter, and the presence of the foreign matter is detected. When the detection signal SD is "L", it is determined that there is no scattered signal or the scattered signal from the pattern edge, and it is determined that no foreign matter exists.

As described above, the presence or absence of foreign matter can be determined from the detection signal SD.

On the other hand, when the foreign matter is detected, the size of the foreign matter is determined by using the output signals SA, SB, SC of the amplification degree converters 76, 78, 80 corrected as described above. That is, the correspondence between the size of the foreign matter and the smallest signal level among the output signals SA, SB, SC of the amplification converters 76, 78, 80 is statistically obtained in advance, and such data and the actual output signal are obtained. By comparing with, the approximate size of the foreign matter can be obtained.

When the aperture 2 is used to increase the beam diameter, the numerical aperture becomes smaller and the light quantity of the laser beam L decreases, so the controller 82 controls the amplification degree converter 7
Adjustment is performed by uniformly changing the amplification degree of 6,78,80 or by changing the reference voltage of the reference voltage generator 90. As a result, even if the beam diameter changes, the detection sensitivity (for example, size determination) of the foreign matter is kept optimal according to the beam diameter.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a perspective view showing the optical components of the second embodiment of the present invention.

In this embodiment, two expanders having different magnifications are used as means for changing the laser beam diameter on the surface to be inspected.
5a and 5b and switching mirrors 3 and 4 for switching the laser beam L to the optical path La or Lb. The constituent parts other than the constituent parts, such as the beam scanning system and the light receiving system, are all the same as in the first embodiment.

Next, the operation of this embodiment will be described.

The laser beam L output from an appropriate oscillating means (not shown) travels along the optical path La when the switching mirrors 3 and 4 are not inserted in the optical path, is expanded by the expander 5a, and is then expanded. Inspection surface (for example, on reticle 10)
To form a spot having a predetermined beam diameter. Thus, the foreign matter inspection is performed.

Next, when performing a foreign matter inspection on the second surface to be inspected (for example, on the pellicle 20), the stage 12 is moved in the z direction by an appropriate means (not shown), and the two switching mirrors 3 and 4 are simultaneously laser-scanned. It is inserted in the optical path of the beam L. As a result, the laser beam L travels along the optical path Lb, is expanded by the second expander 5b having a different magnification from the expander 5a, and then has a size different from the beam diameter formed on the reticle 10 on the pellicle 20. Spots are formed, and the foreign matter inspection is performed by this.

In the above-described configuration, instead of using the expanders 5a and 5b having different operations and switching magnifications of the switching mirrors 3 and 4, for example, an expander having a variable magnification including a zoom system may be used.

The scattered light signal from the foreign matter detected by the photoelectric detectors 30, 32, 34 is processed by the same signal processing circuit as in the first embodiment, that is, the circuit shown in FIG.

In the second embodiment described above, since the beam system on the surface to be inspected can be changed without losing the light quantity of the laser beam L, it is not necessary to adjust the photoelectric signal due to the change in the light quantity, and the first embodiment is also possible. In this case, the laser light can be used more effectively.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, means for shifting the focus of the laser beam applied to the surface to be inspected and consequently changing the beam diameter is used.

In the figure, the structure of each part is the same as that of the first embodiment except that the aperture 2 shown in FIG. 1 is omitted between the expander constituted by the lenses 1a and 1b and the galvano scanner mirror 28. Is the same as.

Next, the operation of this embodiment will be described. When inspecting for foreign matter on the surface of the pellicle 20, one lens of the expander (for example, the lens 1 is used without changing the position of the stage 12 in the z direction).
By moving a) on the optical axis and changing the focal position of the laser beam L, the beam diameter on the pellicle 20 is changed.

At this time, the reticle 10 and the pellicle 20 naturally support the support frame 22.
The inspection position shifts corresponding to the height of the. Therefore, in this case, it is necessary to determine the widths of the slits 42, 44 and 46 so that the scattered light is not blocked by the slits 42, 44 and 46.

In addition, the lenses 1a and 1b of the expander are not moved at all, that is, the focal position of the laser beam L is not changed,
The stage 12 may be moved in the z direction so that the pellicle 20 has a predetermined beam diameter.

Also in this embodiment, the scattered light signal from the foreign matter detected by the photoelectric detectors 30, 32, 34 is processed by the same signal processing circuit as in the first embodiment, that is, the circuit shown in FIG.

[Effects of the Invention] As described above, the present invention determines the presence or absence of foreign matter and its size based on each photoelectric signal of the beam diameter changing means for changing the beam diameter of the light beam on the surface to be inspected. By providing a foreign matter detection circuit that detects the beam diameter in accordance with the beam diameter, it is possible to perform inspection by changing the beam diameter on the surface to be inspected according to the object to be inspected. Since the inspection can be performed with the detection sensitivity corresponding to the tolerance, that is, the beam diameter, and the inspection time can be performed according to the detection sensitivity, the inspection can be performed in the minimum inspection time according to the inspection target. effective.

[Brief description of drawings]

FIG. 1 is a perspective view showing an optical component portion of a first embodiment of the present invention, FIG. 2 is a plan view of a main portion of the first embodiment, and FIG. 3 is a side view of a main portion of the first embodiment. FIG. 4 is a circuit diagram showing an example of signal processing means for photoelectric signals, FIG. 5 is a perspective view showing an optical configuration of a second embodiment of the present invention, and FIG. 6 is a third embodiment of the present invention. It is a perspective view which shows an optical structure. [Explanation of symbols of main parts] 1,5a, 5b ... Expander, 1a, 1b ... Lens, 2 ... Aperture, 3,4 ... Switching mirror, 10 ... Reticle, 20 ... Pellicle, 22 ... Support frame, 30, 32, 34 ... Photoelectric detector, 42,44,46
… Slit, L… laser beam

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kinya Kato 1-6-3 Nishioi, Shinagawa-ku, Tokyo Inside Oi Manufacturing Co., Ltd. of Japan Optical Industry Co., Ltd. (56) Reference JP-A-62-220842 (JP, A) Kai 60-214209 (JP, A) Actual public Sho 62-5646 (JP, Y2)

Claims (2)

[Claims] 1. An irradiation unit for irradiating a surface to be inspected with light, a scanning unit for scanning the light beam emitted from the irradiation unit on the surface to be inspected, and a foreign substance attached to the surface to be inspected. A particle diameter changing means for varying the beam diameter of the light beam on the surface to be inspected, the foreign matter inspecting device comprising a plurality of photoelectric detecting means for receiving scattered light from a plurality of positions at different positions; A foreign matter inspecting apparatus, comprising: a determining unit that determines the presence or absence of a foreign matter and the size thereof based on each photoelectric signal corresponding to different beam diameters. 2. The determining means includes a variable amplifying means for variably amplifying each photoelectric signal of the photoelectric detecting means; a control means for controlling an amplification degree of the variable amplifying means; and a reference voltage generating for generating a reference voltage. And a comparator for binarizing the photoelectric signal amplified by the amplification degree changing means based on the reference voltage output from the reference voltage generator; and a logical product calculating means for outputting a logical product of a plurality of photoelectric signals. The photoelectric signal is corrected by changing the amplification degree of the variable amplifying means or the reference voltage of the reference voltage generating means in response to a change in the light amount due to a change in beam diameter. The foreign matter inspection apparatus according to claim 1, which is characterized in that.