JPH06123708A - Foreign material inspector - Google Patents

Abstract

PURPOSE:To obtain a device capable of reducing a sensitivity difference caused by a position of a face to be inspected and realizing precise foreign material inspection. CONSTITUTION:A beam 3 is made incident on a pericline film 5 (face to be inspected) in almost parallel and a belt-like illumination area 4 is formed. Sideward scattered light transmitted from the face to be inspected is condensed on an image pick-up device (linear image sensor) 9 with a condenser lens 7. At least one out of the image pick-up device 9, a lens and a reticule stage is moved in the longitudinal direction of the belt-like illumination area 4, so that relation between a condensed position of the scattered light and the relative positions of a plurality of picture elements of the image pick-up device 9 is polarized in the direction of picture element arrangement with a specified quantity (for instance, a half picture element pitch). It is inspected before and after polarization and the size of a foreign material is estimated on the basis of maximum signal intensity.

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 a foreign matter on a pellicle film provided to protect a reticle (also called a photomask) circuit forming surface used in the manufacture of semiconductor elements. The present invention relates to a foreign matter inspection apparatus that is preferably used when inspecting the presence or absence of a foreign matter.

[0002]

2. Description of the Related Art Generally, a semiconductor element such as an IC is manufactured by transferring a circuit pattern formed on a reticle onto a wafer coated with a resist by an exposure device. At this time, if foreign matter such as dust exists on the reticle, the foreign matter is transferred together with the circuit pattern, which causes a reduction in the yield of semiconductor device manufacturing.

Therefore, it is indispensable to inspect the presence or absence of foreign matter on the reticle in the process of manufacturing a semiconductor element, and various foreign matter inspection apparatuses have been proposed conventionally. Further, in order to protect the pattern forming surface of the reticle, a protective film called a pellicle film is often provided on the frame and provided on the pattern forming surface. Even if foreign matter is present on the pellicle film, defects will occur in the transferred circuit pattern. Therefore, it is essential to inspect the foreign matter on the pellicle film as well as on the pattern formation surface.

An example of an apparatus conventionally used for inspecting foreign matter on a pellicle film is, for example, Japanese Patent Laid-Open No. 57-805.
No. 46 is disclosed. Hereinafter, the configuration of the conventional device will be described with reference to FIG. In the figure,
A light beam emitted from a light source 1 such as a semiconductor laser is made into a vertically long parallel beam 3 by a collimator lens 2 and is incident on a pellicle film surface 5 (surface to be inspected) substantially horizontally (for example, an incident angle of about 89). . Thereby, the pellicle film 5
A strip-shaped illumination area 4 is formed on the surface.

The pellicle film 5 is placed on the reticle 6 while being stretched over the pellicle frame. Reticle 6
Is mounted on a reticle stage (not shown),
It is movable in the direction of arrow 10 in the figure (direction orthogonal to the longitudinal direction of the strip-shaped illumination area 4). By moving the reticle stage in the direction of arrow 10, the entire surface of the pellicle film 5 is scanned by the light beam 3.

The side scattered light emitted from the strip-shaped illumination region 4 of the pellicle film 5 is received by the lens 7 which looks at the pellicle film 5 at a small angle from a direction substantially orthogonal to the longitudinal direction of the strip-shaped illumination region 4, and the image pickup element 9 is provided. Focused on top. The image pickup device 9 is composed of a one-dimensional image sensor having a plurality of pixels arranged in the longitudinal direction of the strip-shaped illumination area 4, and the light incident on each pixel is independently photoelectrically converted.

In the apparatus having the above structure, the position where the foreign matter exists can be detected based on the output signal from the image pickup device 9 and the information regarding the position of the reticle stage. Further, since the size of the foreign matter and the intensity of scattered light generally have a correlation, it is possible to estimate the size of the foreign matter from the intensity of the output signal of the image sensor 9.

[0008]

However, the conventional foreign matter inspection apparatus as described above has the following problems. That is, in the image pickup device (one-dimensional image sensor) used for detecting the scattered light from the surface to be inspected, in addition to the photosensitive section that photoelectrically converts incident light, a dead zone (charge transfer section, etc.) that does not perform photoelectric conversion. ) Exists, and even if foreign matters of the same size are located in different locations on the surface to be inspected, the condensing position on the image sensor will differ, resulting in a difference in sensitivity depending on the location of the foreign matter. There was a problem. Hereinafter, this point will be specifically described with reference to FIGS.

First, in FIG. 6A, the beam spot 3
No. 2 is condensed in the substantially center of the pixel 31a of the image sensor, and the signal intensity in this case has a peak at a position corresponding to the pixel 31a as shown in FIG. 6B. On the other hand, in FIG. 7A, the beam spot 32 is the pixel 3 of the image sensor.
The light is focused such that the center of the beam spot is located in the dead zone, that is, between 1a and 31b. The signal strength in this case is as shown in FIG.
A peak whose intensity is lower and whose half value width is larger than that in FIG. 6B appears at a position corresponding to the middle of b.

As is clear from comparing FIG. 6 and FIG.
In the conventional foreign matter inspection apparatus, even if the foreign matter is the same, the output signal intensity from the image pickup element varies depending on the position where the foreign matter exists, and it is not possible to perform highly accurate inspection.

The present invention has been made in view of the above point, and an object of the present invention is to provide an apparatus capable of reducing the difference in sensitivity due to the position of existence of foreign matter and realizing highly accurate foreign matter inspection. Is.

[0012]

According to a first aspect of the present invention, there is provided a foreign matter inspection apparatus, which comprises an irradiation optical system for irradiating a surface to be inspected with a light beam substantially horizontally to form a strip-shaped illumination area on the surface to be inspected. A condensing optical system for condensing scattered light emitted from the strip-shaped illumination region of the surface to be inspected, and a plurality of pixels arranged at a predetermined pitch along at least the longitudinal direction of the strip-shaped illumination region, In order to achieve the above object, in a foreign matter inspection device, which comprises an image pickup means for detecting the condensed scattered light, and inspects the presence or absence of a foreign matter on the surface to be inspected based on an output signal from the image pickup means. Further comprising a displacement means for relatively displacing the condensing position of the condensed scattered light and the plurality of pixels along the arrangement direction of the pixels, and the condensing position and the plurality of pixels. Inspecting for the presence of the foreign matter in a state in which the pixel is relatively displaced Than it is.

In the foreign matter inspection apparatus according to the second aspect, the deviation amount by the deviation means is approximately 1/2 of the pitch of the plurality of pixels of the image pickup means.

The deviation means in the foreign matter inspection apparatus according to claim 3 moves at least one of the surface to be inspected, the condensing optical system, and the imaging means by an amount according to the pitch of the plurality of pixels. It has a moving means.

According to a fourth aspect of the foreign matter inspection apparatus, an irradiation optical system for irradiating the surface to be inspected with a light beam substantially horizontally to form a strip-shaped illumination region on the surface to be inspected, and the surface of the surface to be inspected. A condensing optical system that condenses scattered light emitted from a band-shaped illumination area,
An image pickup unit having a plurality of pixels arranged at a predetermined pitch along at least the longitudinal direction of the strip-shaped illumination region, and detecting the condensed scattered light; and an output signal from the image pickup unit. In order to achieve the above-mentioned object, a foreign matter inspection device for inspecting the presence or absence of a foreign matter on the surface to be inspected has a dividing means for dividing the scattered light through the condensing optical system, and the division A plurality of the image pickup means is provided on the emission side of the scattered light thus obtained, and the pixels of the plurality of image pickup means are displaced by a predetermined amount along the pitch direction of the pixels.

[0016]

The operation of the present invention will be described with reference to FIGS. First, when a foreign substance is present at a certain position P on the surface to be inspected, the scattered light from the foreign substance is generated by the pixel 3 as shown in FIG.
It is assumed that the light is focused on the center of 1a. On the other hand, when a foreign substance is present at another position Q on the same surface to be inspected, the scattered light from the foreign substance is focused in the dead zone between the pixels 31a and 31b as shown in FIG. 7A. In this state, as described above, even if the foreign matter existing at the positions P and Q is the same, the detection signal of the foreign matter at the position P becomes stronger than the position Q.

Therefore, in the first aspect of the present invention, there is provided the displacing means for relatively displacing the condensing position of the scattered light from the surface to be inspected and the plurality of pixels of the image pickup means along the arrangement direction of the pixels. ,
The foreign substance inspection is performed in a state in which the light collecting position and the plurality of pixels of the image pickup unit are relatively deviated. That is, referring to the examples of FIGS. 6 and 7, the condensing position of the scattered light and the plurality of pixels of the image pickup means are relatively displaced by about ½ of the pixel pitch along the arrangement direction of the pixels. As a result, the scattered light from the foreign matter present at the position P is focused on the dead zone of the image pickup means as shown in FIG. 7A, and the scattered light from the foreign matter present at the position Q is shown in FIG. 6A. The inspection can be performed while the light is focused on the center of the pixel. Therefore, if the foreign matter inspection is performed both before and after the deviation of the light-condensing position and the plurality of pixels of the image pickup means, and the one having the larger signal strength is adopted as the final detection signal, the position P and the position Q are selected. If a foreign substance is the same, both will be detected at the same signal level.

Further, according to the invention of claim 4, the scattered light from the surface to be inspected through the condensing optical system is divided, and an image pickup means is provided on the outgoing side of the divided scattered light. The position of the image pickup device is set so that each pixel is displaced by a predetermined amount along the pixel arrangement direction. Specifically, if the positional relationship between the condensing position of each divided scattered light and the pixel is deviated by about 1/2 pixel pitch between the image pickup means, the inspection can be performed in both states of FIG. 6 and FIG. By adopting the one with the larger signal strength as the detection signal, the problem of the sensitivity difference due to the position can be solved as in the first aspect.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 is a perspective view showing a schematic configuration of a foreign matter inspection apparatus according to a first embodiment of the present invention. In the figure, a light beam emitted from a light source 1 such as a semiconductor laser is made into a vertically long parallel beam 3 by a collimator lens 2 and is incident on a pellicle film 5 (inspection surface) substantially horizontally (for example, an incident angle of about 89). To be done. As a result, the strip-shaped illumination area 4 is formed on the surface of the pellicle film 5.

At this time, it goes without saying that the incident angle of the light beam 3 is not limited to 89. However, when the incident angle becomes small, the light transmitted through the pellicle film 5 increases and the light transmitted through the pellicle film 5 increases. There is an inconvenience that it is reflected by the pattern on the reticle 6 and is received by the image pickup means 9 (described later). Therefore, in order to avoid erroneous detection of the pattern on the reticle 6 and the foreign matter on the pellicle film 5, it is preferable that the light beam 3 be incident in a state of being substantially horizontal.

The pellicle film 5 is placed on the reticle 6 while being stretched on the pellicle frame. Reticle 6
Is mounted on a reticle stage (not shown),
It is movable in the direction of arrow 10 in the figure (direction orthogonal to the longitudinal direction of the strip-shaped illumination area 4). By moving the reticle stage in the direction of arrow 10, the entire surface of the pellicle film 5 is scanned with the light beam. In this embodiment, the reticle 6 is transferred from the transport device (not shown) to the foreign substance inspection device, and the foreign substance inspection is sequentially performed from the back side in the drawing (the reticle stage is sequentially moved in the direction of 10b). When the strip-shaped illumination area 4 reaches the end of the pellicle film 5 on the front side of the drawing, the reticle stage moves in the opposite direction (the direction 10a in the figure) to perform the inspection, and the second inspection ends. Then, the reticle 6 is delivered to the transport device.

The side scattered light emitted from the strip-shaped illumination area 4 of the pellicle film 5 is received by the condenser lens 7 which looks at the pellicle film 5 at a small angle from a direction substantially orthogonal to the longitudinal direction of the strip-shaped illumination area 4, and an image is picked up. It is focused on the element 9. The image pickup device 9 is composed of a one-dimensional image sensor having a plurality of pixels arranged in the longitudinal direction of the strip-shaped illumination area, and the light incident on each pixel is independently photoelectrically converted.

Further, in this embodiment, the image pickup device 9 has a moving means 16 (15, 14 will be described later) for moving the image pickup device 9 by a predetermined amount in the pixel arrangement direction (direction of arrow 13 in the drawing). Is provided. The length of the pixels of the image sensor 9 in the vertical direction (direction orthogonal to the pixel arrangement direction) is not particularly limited, but the surface to be inspected (pellicle film 5).
When there is unevenness, the light-condensing position of scattered light fluctuates in the vertical direction of the pixel. Therefore, it is desirable to set the length to match the fluctuation amount.

Next, a foreign matter inspection method using the above-mentioned foreign matter inspection apparatus will be described. First, the first inspection described above is performed while the reticle stage is moved in the direction of arrow b. At this time, information regarding the presence / absence of foreign matter, the existing position, and the size obtained from the output signal of the image sensor 9 is stored in a memory (not shown).

After the first inspection, the moving means 1
6, the image sensor 9 is moved in the direction of arrow 13 by an amount corresponding to about 1/2 pixel pitch. That is, the positional relationship between the condensing position of scattered light and the pixels of the image sensor 9 is deviated by about ½ pixel pitch in the pixel arrangement direction.

Subsequently, in this state, the second inspection is performed while the reticle stage is moved in the direction of arrow a (the direction opposite to the first inspection). As for the second inspection, information about presence / absence of foreign matter, existing position, and size is stored in a memory (not shown) as in the first inspection. At this time, with respect to the position of the foreign matter, a position in which the movement amount (1/2 pixel pitch) of the image sensor 9 is corrected is obtained.

After the completion of the second inspection, the first detection result and the second detection result are compared, and the larger one of the two is adopted as the signal strength (information regarding the size of the foreign matter). By doing so, even if scattered light is detected in the state as shown in FIG. 7 in the first inspection, the image sensor 9
In the second inspection in which is shifted by 1/2 pixel pitch, scattered light will be detected in the state of FIG. 6, and the size of the foreign matter can be accurately estimated regardless of the position where the foreign matter exists.

In the above embodiment, the image pickup device 9 is moved by the moving means 16, but the moving means 14 moves the reticle stage in the direction of arrow 11 as shown in FIG. Is also good. Also,
By tilting the condenser lens 7 with respect to the optical axis by the moving means 15 (arrow 12), the positional relationship between the condensing position of scattered light and the pixels of the image sensor 9 can be deviated.
That is, at least one of the image pickup device 9, the condenser lens 7, and the pellicle film 5 (test surface) may be moved relatively.

Further, in the above embodiment, the foreign matter inspection is performed twice, and at the first time and the second time, the condensing position of the scattered light and the image pickup element 9 are taken.
The relative positional relationship of the image pickup element 9 (or the lens 7 and the reticle stage) is changed by using an electrostrictive element or the like.
May be vibrated at a high speed with an amplitude corresponding to a 1/2 pixel pitch. If the vibration speed at this time is sufficiently higher than the moving speed of the reticle stage in the direction of arrow 10, the maximum strength within the amplitude is taken to perform the foreign matter inspection without the sensitivity difference depending on the position in one inspection. You can

Next, FIG. 2 is a plan view showing the structure of a foreign matter inspection apparatus according to the second embodiment of the present invention. The apparatus of the present embodiment has the same configuration as the irradiation optical system (light source 1, collimator lens 2), condenser lens 7, reticle stage, and the like of the apparatus of FIG. In this embodiment, the scattered light that has passed through the condenser lens 7 is the beam splitter 1.
Divided by 7. Then, the scattered light transmitted through the beam splitter 17 is imaged by the image sensor (one-dimensional image sensor) 9a.
The scattered light reflected by the beam splitter 17 is collected on the image pickup device (one-dimensional image sensor) 9b. The image pickup devices 9a and 9b are deviated by a predetermined amount in the pixel array direction.

In the apparatus having such a configuration, if the image pickup devices 9a and 9b are displaced by, for example, 1/2 pixel pitch, one of the image pickup devices 9a detects scattered light in the state shown in FIG. While the other image pickup device 9b detects scattered light in the state of FIG. 7, the other image pickup devices 9a and 9b
It is possible to reduce the difference in sensitivity depending on the position of the foreign matter by adopting one of the output signals of b having the larger signal strength.

Next, FIG. 3 is a perspective view showing the structure of a foreign matter inspection apparatus according to a third embodiment of the present invention, and FIG. 4 is a plan view of the apparatus of FIG. The device of the present embodiment is basically the same as the device of FIG. 1, and differs from the device of the first embodiment in that a parallel plane plate 8 is provided as a displacement means. In the figure,
A plane parallel plate 8 is obliquely provided between the condenser lens 7 and the image sensor 9, and is rotatable around the optical axis of the condenser lens 7. That is, as shown in FIG. 4, by rotating the plane-parallel plate 8, the optical path of the scattered light from the condenser lens 7 can be changed from 21 to 22 in the figure, and the scattered light collecting position can be changed. Can be displaced in the pixel array direction of the image sensor 9.

Therefore, after performing the first inspection while feeding the reticle stage as in the first embodiment, the parallel plane plate 8 is rotated by a predetermined amount to move the reticle stage in the opposite direction, and then the second time. If the inspection is performed and one of the output signals from the image pickup device 9 having a larger signal strength is adopted, the difference in sensitivity due to the position on the surface to be inspected can be reduced. Alternatively, an electrostrictive element or the like may be attached to the plane parallel plate 8 to vibrate at high speed, and the size of the foreign matter may be determined based on the maximum strength within the amplitude. in this case,
It is possible to perform a foreign matter inspection without a difference in sensitivity depending on the position with a single inspection.

However, in the apparatus shown in FIGS.
Since the deviation amount of the scattered light on the image pickup element 9 at the focusing position is a function of the angle, when the chief ray passing through the focusing lens 7 is inclined, it is gathered as it goes to the periphery except on the axis. There arises a problem that the deviation amount of the light position becomes large, and it becomes difficult to control the deviation amount. Further, the variation in the vertical direction (direction orthogonal to the longitudinal direction of the band-shaped illumination region) of the pixels of the image pickup device 9 at the scattered light condensing position also becomes large. For this reason, in the apparatus shown in FIGS. 3 and 4, it is desirable that the condenser lens 7 is an image-side telecentric system and the dimension of the pixel in the vertical direction is sufficiently long.

When the condenser lens 7 is not an image side telecentric optical system, for example, as shown in FIG.
Instead of the plane parallel plate 8 shown in FIGS. 3 and 4, a lens-shaped concentric lens 8a that is concentric with the diaphragm (exit pupil) of the condenser lens 7 may be provided. The concentric lens 8a is provided so as to be swingable in the direction of the arrow in the figure with a point C in the figure as the center. Then, the image sensor 9
When moving the condensing position of the upper scattered light, the concentric lens 8a is tilted in the direction of the arrow in the figure.

In the above embodiment, the relative deviation amount between the condensing position of scattered light and the pixel is explained as 1/2 pixel, but the deviation amount is limited to 1/2 pixel. not,
For example, a quarter pixel pitch may be used. Further, in the above-described embodiment, the one-dimensional image sensor is used as the image pickup element, but in some cases, the two-dimensional image sensor is used to relatively disperse the condensing position of scattered light and the pixel in two orthogonal directions. It may be arranged to inspect it. Also, regarding the output signal processing of the image sensor 9, it is not always necessary to obtain the maximum intensity, and, for example, 1
It is also possible to obtain the average of the detection signals of the second and second inspections and estimate the size of the foreign matter based on this value. Further, in the above description, the inspection on the pellicle film has been described as an example, but the apparatus of the present invention can be applied to the foreign matter inspection of the reticle itself and other inspections of the surface to be inspected.

[0037]

As described above, in the foreign matter inspection apparatus according to the present invention, the presence / absence of foreign matter is detected in a state in which the condensing position of scattered light from the surface to be inspected and the plurality of pixels of the image pickup means are relatively deviated. Since it is configured to inspect, the difference in sensitivity due to the position on the surface to be inspected can be reduced, and highly accurate foreign matter inspection can be performed.

[Brief description of drawings]

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

FIG. 2 is a plan view showing a schematic configuration of a foreign matter inspection device according to a second embodiment of the present invention.

FIG. 3 is a perspective view showing a schematic configuration of a foreign matter inspection device according to a third embodiment of the present invention.

4 is a plan view of the foreign matter inspection device of FIG.

FIG. 5 is a plan view showing a modification of the third embodiment of the present invention.

6A is a schematic diagram showing how scattered light from a surface to be inspected is condensed at the center of a pixel, and FIG. 6B is a graph showing a signal intensity distribution in the case of FIG. 6A. is there.

FIG. 7A is a schematic diagram showing how scattered light from a surface to be inspected is condensed in a dead zone between pixels,
(B) is a graph showing a signal intensity distribution in the case of (a).

FIG. 8 is a schematic configuration diagram showing a conventional foreign matter inspection device.

[Explanation of symbols]

1 ... Light source, 2 ... Collimator lens, 3 ... Light beam, 4 ...
Strip-shaped illumination region, 5 ... Pellicle film (surface to be inspected), 6 ... Reticle, 7 ... Condensing lens, 8 ... Parallel plane plate, 9, 9a, 9b
... image pickup device, 14, 15, 16 ... moving means, 17 ... beam splitter, 31a, 31b, 31c ... pixel, 32
… Beam spot.

Claims (4)

[Claims] 1. An irradiation optical system which irradiates a light beam to a surface to be inspected substantially horizontally to form a belt-like illumination area on the surface to be inspected, and scattering emitted from the belt-like illumination area on the surface to be inspected. A condensing optical system that condenses light, and an imaging unit that has a plurality of pixels arranged at a predetermined pitch along at least the longitudinal direction of the strip-shaped illumination region, and that detects the condensed scattered light. In a foreign matter inspection device for inspecting the presence or absence of a foreign matter on the surface to be inspected based on an output signal from the imaging means, the condensing position of the condensed scattered light and the plurality of pixels are A displacement unit that relatively displaces along the pixel arrangement direction, and inspects the presence or absence of the foreign matter in a state where the condensing position and the plurality of pixels are relatively displaced. Characteristic foreign matter inspection device. 2. The foreign matter inspection apparatus according to claim 1, wherein the deviation amount by the deviation unit is approximately ½ of the pitch of the plurality of pixels of the imaging unit. 3. The displacing means includes a moving means for moving at least one of the surface to be inspected, the condensing optical system, and the imaging means by an amount corresponding to a pitch of the plurality of pixels. The foreign matter inspection device according to claim 1. 4. An irradiation optical system for irradiating a light beam to a surface to be inspected substantially horizontally to form a belt-like illumination area on the surface to be inspected, and scattering emitted from the belt-like illumination area on the surface to be inspected. A condensing optical system that condenses light, and an imaging unit that has a plurality of pixels arranged at a predetermined pitch along at least the longitudinal direction of the strip-shaped illumination region, and that detects the condensed scattered light. In a foreign matter inspection apparatus for inspecting the presence or absence of a foreign matter on the surface to be inspected based on an output signal from the image pickup means, the foreign matter inspection apparatus has a dividing means for dividing the scattered light through the condensing optical system, A plurality of image pickup means is provided on the emission side of the divided scattered light, and the pixels of the plurality of image pickup means are each deviated by a predetermined amount along the pitch direction of the pixels. The foreign matter inspection device according to claim 1.