JP2925154B2 - Appearance inspection method for masks etc. - Google Patents

Description

The present invention relates to a photomask used for manufacturing a semiconductor, a photomask used for manufacturing a lead frame used for an integrated circuit or a shadow mask used for a color television CRT, etc. Also, the present invention relates to a method for inspecting the appearance of a mask or the like for inspecting the appearance of a product manufactured using a photomask.

(Prior Art) Conventionally, as a method for inspecting a photomask suitable for a semiconductor or a lead frame, a photomask is a multi-faceted pattern in which the same pattern is repeatedly arranged on the same mask. As shown in the figure, the same position between adjacent patterns was imaged by a television camera, and the presence or absence of a defect was inspected based on the identity of the obtained signals.

That is, as shown in FIG. 12, the signals obtained by imaging the patterns (2) and (2a) at the same position of the photomask (1) with the two television cameras (3) and (3a) are compared with the comparison circuit (4). The difference is input to the determination circuit (5) as a difference signal, and a determination is made at the slice level set by the determination circuit to generate a defect presence / absence signal.

In the case of a reticle in which only one pattern is formed on a photomask, the pattern of the reticle (6) is imaged by a camera (3) as shown in FIG. 13 and stored in a magnetic tape or the like. Original circuit (design) data (7) and comparison circuit (8) via data conversion circuit (9)
The appearance inspection for determining the presence / absence of a defect was performed by comparing the above.

(Problems to be Solved by the Invention) However, since a photomask for a shadow mask used for a color television cathode-ray tube mainly has a one-sided pattern, a conventional mask having the same pattern as a conventional adjacent pattern as shown in FIG. Comparison inspection is not possible, and the comparison with the original image data as shown in Fig. 13 shows that the shadow mask has a large size exceeding 40 inches and the number of writing shots is larger than that of a photomask for semiconductors which is around 5 inches. Since the number of shots was several million and the original image data was enormous, it was practically difficult to implement the device. The automatic inspection was not performed by the device, and the operator had to rely on manual visual inspection.

On the other hand, in recent years, market trends have become more sophisticated, and in color televisions, the demand for large-size and high-resolution CRTs has rapidly increased, and the demand for large-size and high-resolution CRTs is increasing every day.

In addition, technologies such as LCDs and plasma displays have been developed as display elements other than cathode ray tubes, and conventional small-sized to large-sized display elements are becoming more widespread.

Under these circumstances, photomasks for shadow masks, LCDs, plasmas, and the like have become larger and more finely patterned, and there has been a demand for an automatic inspection of a high-resolution large-sized one-sided pattern instead of a conventional visual inspection.

(Means for Solving the Problems) In view of the above points, the present invention provides a method for performing a high-speed, high-resolution, appearance inspection for the presence or absence of a defect without comparing a large one-sided pattern with original image data. Things.

That is, the present invention provides an inspection for reading an image of a pattern from two axially symmetric positions of an axially formed pattern, determining a difference between the two read images, and detecting a defect formed on the pattern. In the method, image reading at two axially symmetric positions is performed by two imaging means independently, and is an appearance inspection method for a mask or the like in which the two imaging means are tilted so that the two visual fields contact at least.

Further, the image reading at the two axially symmetric positions is performed independently by two image pickup means, and the image reading element is arranged so as to be shifted from the optical axis of the image pickup lens so that the fields of view of the two image pickup means are at least in contact with each other. This is a method for inspecting the appearance of a mask or the like to be used.

(Operation) The present invention takes advantage of the fact that a pattern of a shadow mask or the like is a pattern formed to be axially symmetric, and takes an image of an axially symmetric position of a shadow mask or the like by using two sets of imaging devices or one set of imaging devices. The presence or absence of a defect is determined from the identity of the obtained signals.

(Example) Hereinafter, a specific example will be described.

Shadow masks are generally in the form of round holes (dots), slots, or blinds called aperture grilles. Both round holes and slot holes are arranged in a zigzag pattern. In each case, the pattern of each dot, slot, and sludge is arranged symmetrically with respect to an axis passing through the center of the shadow mask. FIG. 6 shows an example of the pattern of the slot hole type shadow mask (10). Each slot pattern is arranged symmetrically about the symmetry axis.

1 and 2 show an example of the configuration of an apparatus based on the method of the present invention.

Two sets of imaging devices are held so that the visual field moves on the same straight line in a direction orthogonal to the axis of symmetry (Y) of the shadow mask.

In FIGS. 1 and 2, (3) and (3a) are cameras as two imaging devices, (11) and (11a) are holding devices thereof, and (14) and (1).
4a) shows the feed motor of the camera. A shadow mask photomask (a glass dry plate, a chrome mask, or the like) to be inspected is held on a stage (13) that is moved by a feed motor (15) in parallel with the symmetry axis (Y).

Each of the two imaging devices (3) and (3a) has a CCD line sensor, and a pattern image of a glass dry plate on the stage (13) is formed on a light receiving surface of the CCD line sensor by a lens. The video signals of the two CCD line sensors enter the comparison circuit (16), calculate the difference, and are input as a difference signal to the judgment circuit (17). The judgment is made based on the slice level set by the judgment circuit (17). Emits a signal. The inspection operation by this device is as follows. The two imaging devices (3) and (3a) are positioned so as to sandwich the axis of symmetry (Y) so that their fields of view are in contact with each other.

In this state, if the images of the two CCD line sensors are simultaneously taken out from the symmetric axis side to the outside, image signals at symmetric positions can be obtained. In the obtained image signal, the difference component between the two is extracted by a comparison circuit (16). If the difference component corresponds to the defect size to be detected, it exceeds the slice level of the determination circuit and is obtained as a defect detection signal. Is extracted. Since the CCD line sensor has a linear visual field, a band-like range can be inspected by repeatedly taking out and processing image signals from the CCD line sensor while moving the stage in the symmetric axis direction. Furthermore, two sets of imaging devices (3)
(3a) is released from the axis of symmetry by the visual field width, the stage is moved, and the inspection is performed in a strip shape. In this manner, the two sets of imaging devices (3) and (3a) are arranged equidistant from the axis of symmetry (Y), and the entire surface is inspected by repeating the scanning in the form of a band by moving the stage (13).

The two sets of imaging devices are arranged and configured as shown in FIGS. 3A and 3B because the visual fields are arranged on the same straight line and need to move. In the figure, (3) and (3a) are cameras, and (18) and (18a) are light projection light sources.

Generally, when the optical axis (the visual axis) of the imaging device is perpendicular to the object, the two sets of imaging systems cannot see the same position as shown in FIG. However, it is also difficult to have a contacting visual field if the visual field is very small. 4th
In the figure, (19) indicates the visual field axis of the camera, and (a) indicates the untestable area.

By inclining the optical axis (viewing axis) of the imaging system with respect to the object as shown in FIG. 3, it is possible to arrange the imaging system at the same position or a field of view in contact with the object. In this case, the built-in
The arrangement direction of the CCD line sensor element is the direction shown in FIG. 5 (shown for one camera), and the difference in optical path difference due to the inclination is minimized. Further, as shown in FIG. 2, the imaging devices are movably held by independent supports (11) and (11a), respectively, and two imaging devices (3) and (3a) are placed on the object.
Are arranged in such a manner that their optical axes (viewing axes) (19) coincide. The moving direction of the image pickup apparatus is made to coincide with the arrangement direction of the CCD line sensor element, and a belt-shaped image can be input by moving the stage (13).

FIG. 7 shows another embodiment of the arrangement of the two sets of imaging devices. In FIG. 3, the optical axis of the image pickup lens of the image pickup device is arranged to be inclined, whereas in the method of FIG. 7, the optical axis of the lens is set to be the object by two sets of image pickup devices (3) and (3a). It is a light receiving element in order to have the same visual field between two sets of imaging devices, or a visual field in contact with each other, positioned vertically with respect to the object.
CCD line sensors (20) (20a) with two sets of CCDs from the optical axis
This is a tilt-and-shoot method in which the line sensors (20) and (20a) are offset in the direction away from each other and arranged horizontally. Depending on how the offset amount is determined, it is possible to set a partially overlapping field of view from the same field of view and a touching field of view. (3) (3a) in the figure
Is a camera, (20) (20a) is a line sensor, (21) (2
1a) shows a lens, and (b) shows a line sensor field of view.

In this case, the two imaging devices (3) and (3a) are provided on the same support (22) as shown in FIG.
(22a) enables the form of moving.

FIG. 9 shows another embodiment of FIG. 3, in which an imaging device is provided as shown in FIG. 4, and an undetected area (a) corresponding to the mounting pitch (c) between the two imaging devices is formed by an electric method. It is explanatory drawing of the method which makes an inspection possible.

As described above, in the arrangement of the imaging device shown in FIG. 4, the two imaging devices can be brought close to each other only by the solid width of the device, and can be arranged between the symmetric positions at a position sufficiently distant from the axis of symmetry. Cannot extract the image at the symmetric position.

On the other hand, in FIG. 9, two imaging devices (3) are arranged on the same straight line in the direction orthogonal to the symmetry axis as in the above-described embodiments.
Instead of arranging the visual field of (3a), the visual fields of the two imaging devices (3) and (3a) are arranged in the same direction as the axis of symmetry (Y). When the stage is sent to the A side in the state of FIG. 9 and the signal is taken out from the CCD line sensor, the signal at the same position of the photomask on the stage is taken out from the B side image pickup device. After the stage is moved between the two imaging devices. In order to take this out at the same time, a signal delay circuit (23) corresponding to the mounting pitch (c) of the two imaging devices is provided in front of the comparison circuit (24) in the A-side imaging device. With such a configuration, the fields of view of the two imaging devices are arranged in contact with the symmetry axis or at the same distance as shown in FIG. 9 and the stage is moved, and if a signal is taken out from the CCD line sensor, the two symmetry positions are obtained. Two images can be taken out at the same time, and a comparative inspection of a symmetric position becomes possible even near the axis of symmetry.

The delay circuit (23) is inserted in the camera (3) on the A side.
A method in which a delay circuit is used on the side that switches the side and reads the image in advance may be used.

 FIG. 10 shows another embodiment of FIG.

In the above-described embodiments, the method of extracting the same position signal between the symmetry axes at the same time by using two imaging devices has been described, but FIG. 10 shows the imaging device as a set and an axially symmetric comparison test. Is shown.

The field of view of the CCD line sensor camera of the imaging device is arranged in the same direction as the symmetry axis (Y), and scans the photomask on the stage in the direction orthogonal to the symmetry axis (Y). The data read by scanning is recorded in the image memory. When the entire area is scanned or the entire width is scanned in a band and recorded in the memory, data at the same position with respect to the symmetry axis (y) set in the memory is sequentially taken out and compared. Thus, axial symmetry and comparative inspection are performed. In addition, since the axial symmetry and the comparison inspection are performed by one set of imaging devices, the devices are simplified.

In the method described above, the imaging device uses a CCD line sensor, but it is also possible to use an element of a type other than the CCD, and to use an area sensor other than the line sensor to make the stage intermittent instead of continuous feed. The system may be used.

As described above, according to the present invention, a defect inspection can be performed at high speed and with high resolution without comparing a large one-sided pattern with original image data. It is also possible to inspect a multi-faceted pattern arranged axially symmetrically.

In the case of the axial symmetry inspection, the readout method of the CCD line sensor etc. is to read and compare with the mirror image from the symmetry axis, but if it is read out from the same direction with two imaging devices, it is not arranged axially symmetric Inspection of a multi-faceted pattern is also possible.

In the above-described embodiment, as a method for comparing image data, a difference operation is performed on an analog image signal obtained from a CCD line sensor or the like of two imaging devices by a calculator to obtain a difference signal, and this difference signal is set. Although the comparison is shown as an analog comparison in which a defect is detected based on whether or not the reference value exceeds the reference value, a method in which these are converted into digital signals for comparison and collation may be used. In addition to the method of judging from the above, a method of judging a defect from the size of the difference portion as shown as an example in FIG. 11 may be used.

That is, in FIG. 11, the analog signals obtained from the imaging devices (3) and (3a) are first binarized by a binarization circuit (25), converted into digital signals, and converted into two binarized images. The difference between the signals is determined by a comparison circuit (exclusive OR), that is, an exclusive OR circuit (26), and the difference signal is counted by a counting circuit (27) in synchronization with a CCD reading clock in the camera, and is continuously calculated. When the difference signal becomes equal to or larger than the preset count value, a defect determination signal is output from the Q terminal.

Although FIG. 11 shows an example using hard-wired logic, realization is possible with circuits other than those shown in FIG.

(Effect of the Invention) An inspection method for reading a pattern image from two axially symmetric positions of an axially symmetric pattern, determining a difference between the two read images, and detecting a defect formed on the pattern. According to the first aspect of the present invention, two axially symmetric image readings are independently performed by two imaging units, and the two imaging units are tilted so that the two visual fields contact at least. By using it, it is possible to perform high-speed and high-image defect inspection without comparing a large one-sided pattern with the original image data, and also possible to inspect an axially symmetrically arranged multi-sided pattern,
By tilting the visual axis of the imaging system with respect to the object,
The same position of the object can be seen, and even if the field of view is smaller than the dimensions of the imaging system, the object can be seen in the field of contact that is in contact. Is possible.

According to the second aspect, the image reading at the two axially symmetric positions is independently performed by the two image pickup means, and the image reading element is moved by the light of the image pickup lens so that the fields of view of the two image pickup means are at least in contact with each other. Depending on how to take the offset amount when used while being shifted from the axis, it is possible to set a partially overlapped view and a touched view from the same view. Therefore, a form in which the two sets of imaging devices are provided on the same support and moved are possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for imaging an axially symmetric position of a shadow mask according to the present invention and judging the presence or absence of a defect based on the obtained identity. FIG. 2 is a diagram showing two sets of image capturing devices according to the present invention. FIG. 3 (a) and FIG. 3 (b) are diagrams for judging the presence / absence of a defect by using an object held so that the visual field moves on the same straight line in a direction orthogonal to the symmetry axis of FIG. FIG. 4 is an explanatory view of a cross section and a side surface in which a visual axis is inclined with respect to an object to be determined and the presence or absence of a defect is determined for determining presence or absence of a defect. FIG. 5, FIG. 5 is an explanatory view showing the relative movement of the object to be symmetrical and the imaging system in the case of FIG. 3, FIG. 6 is an explanatory view of a shadow mask, FIG. B) The front and the front according to another embodiment of the present invention in which two sets of image pickup devices are arranged. FIG. 8 is an explanatory view in which two sets of image pickup devices are provided on the same support, and FIGS. 9 (a) and 9 (b) show mounting pitches of two image pickup devices according to the present invention. 10 (a) and 10 (b) are explanatory diagrams of a case where the imaging device according to the present invention is provided as a set, and FIG. 11 is a diagram illustrating the present invention. FIG. 12 and FIG. 13 are explanatory diagrams showing two different conventional defect detection methods. (1) Photomask (3) (3a) Camera (4) (8) (16) (24) Comparison circuit (5) (17) Judgment circuit (13) Stage (14) (15) (22a) Motor (18) Light source (20) Line sensor (21) Lens (23) Signal delay circuit (25) Binarization circuit (26) ) …… Exclusive OR circuit (exclusive OR) (27) …… Count circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-218806 (JP, A) JP-A-62-274249 (JP, A) JP-A-61-126454 (JP, A) JP-A-61-126454 28809 (JP, A) JP-A-52-23986 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 11/00-11/30 102 G01N 21/84-21/91

Claims (2)

(57) [Claims] An inspection method for reading an image of a pattern from two axially symmetric positions of an axially symmetric pattern, determining a difference between the two read images, and detecting a defect formed on the pattern. Wherein the image reading at two axially symmetric positions is performed independently by two image pickup means, and the two image pickup means are used at an angle so that the two fields of view are at least in contact with each other. Method. 2. An inspection method for reading an image of a pattern from two axially symmetric positions of an axially symmetric pattern, determining a difference between the two read images, and detecting a defect formed on the pattern. In, image reading at two axially symmetric positions is performed independently by two imaging means, and the image reading elements are arranged shifted from the optical axis of the imaging lens so that the fields of view of the two imaging means are at least touching. An appearance inspection method for a mask or the like characterized by using.