JP2000088525A - Alignment detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform precise alignment of a mask and a work, without using an expensive optical system. SOLUTION: In an alignment detecting method which performs the alignment of a mask alignment mark 1a formed on a mask, and a work alignment mark 4 formed on a work, on the basis of an image obtained by photographing both alignment marks with a camera, the alignment of both alignment marks can be performed precisely on the basis of the photographed images, without being influenced by the distortion of the photographed picture images caused by the aberration of the optical system of the camera, by photographing the mask alignment mark 1a and the work alignment mark 4 in the central region of the visual field of the camera, and performing the alignment of both alignment marks.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for aligning a mask and a work (alignment) when manufacturing a shadow mask for a CRT display, a semiconductor integrated circuit or the like by repeating a photolithography process.

[0002]

2. Description of the Related Art Shadow masks for CRT displays,
When manufacturing a semiconductor integrated circuit or the like, generally, a plurality of masks are prepared, and a photolithography process including exposure, development, etching, and the like is repeated by the number of masks. As described above, when the photolithography process is repeated a plurality of times, the alignment device maintains a predetermined positional relationship between the pattern formed in the previous photolithography process and the pattern to be formed in the current photolithography process. Is being performed.

Conventionally, this type of alignment apparatus is provided with an illumination optical system (including a lens) and a CCD camera facing a glass mask, and transmits light from the illumination optical system to a printed circuit board or the like via a glass master. The reflected light is incident on a CCD camera to capture an image. Based on the captured image, a mask alignment mark formed on a mask and a work alignment formed on the work are formed. It is configured to perform alignment with the mark.

In this case, the positioning of the mask has been performed only by putting the mask alignment mark formed on the mask (glass mask) within the field of view of the CCD camera. That is, as shown in FIG. 5, even if the mask alignment mark 1a is located at a peripheral portion within the field of view E of the CCD camera, the mask alignment mark 1a and the work alignment mark 4 are imaged at the peripheral position. The alignment of the two alignment marks is performed based on the image data, and then the exposure is performed.

[0005]

However, at the peripheral portion in the field of view E of the CCD camera, as shown in FIG. 5, the mask alignment mark 1a and the work alignment mark 4 are caused by the aberration of the optical system (mainly a lens). The image was distorted. For this reason, the mask and the work cannot be accurately aligned, and the relative positional relationship deviates from the original positional relationship, which is a factor of reducing the yield.

In order to solve this problem, it is conceivable to use an optical system with a small aberration. However, even if an optical system with a small aberration is used, it is practically impossible to completely eliminate the aberration. In addition, the optical system becomes expensive.

The present invention has been made under such a background, and an object of the present invention is to enable accurate alignment between a mask and a work without using an expensive optical system.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a method for aligning a mask alignment mark formed on a mask with a work alignment mark formed on a work by using both alignment marks. Is performed based on an image captured by a camera, the mask alignment mark and the work alignment mark are imaged in a central region of a field of view of the camera, and the alignment marks are aligned.

As described above, by taking an image of the mask alignment mark and the work alignment mark in the central region of the field of view of the camera and aligning the two alignment marks, the influence of the distortion of the photographed image due to the aberration of the optical system of the camera. Thus, both alignment marks can be accurately positioned based on the captured image without receiving the image.

At this time, for example, the center point of the field of view of the camera,
Alternatively, after moving the mask so that the center point of the mask alignment mark is located at a predetermined reference position in the center area of the field of view, the movement of the work is controlled with the position of the mask and the camera fixed, and the mask alignment mark and the work alignment are adjusted. Align with the mark.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are schematic structural views of an alignment detecting device according to an embodiment of the present invention. 1 and 2
As shown in the figure, the glass mask 1 has a rectangular transparent portion 1.
a and an opaque portion 1b surrounding the transparent portion 1a. Since the transparent portion 1a substantially functions as a mask alignment mark, the transparent portion 1a is hereinafter referred to as a mask alignment mark 1a.

A metal work (or a glass or plastic work) 3 such as a printed circuit board or a lead frame is arranged below the glass mask 1, and a work alignment mark 4 is formed on the work 3. Is formed. This work alignment mark 4 is not transparent like the mask alignment mark 1a,
Or it is constituted by a convex portion.

Here, as shown in FIG. 2, the glass mask 1 is attached to the mask stage 10 by vacuum suction, and the mask stage 10 is, for example, XYθ.
The glass mask 1 is movably supported by a table. The work 3 is movably supported by a work stage 13 formed of an XY table or the like, and is movable in the XY directions with respect to the glass mask 1.

Above the glass mask 1, an optical system 7 including a lens 5 and a half mirror 6, a CCD camera 8, and two alignment cameras 11 having an illumination device 9 are arranged. Light from the illuminating device 9 is incident on the glass mask 1 via the half mirror 6 and the lens 5, and is incident on the work 3 (work alignment mark 4) via the transparent mask alignment mark 1 a formed on the glass mask 1. Lighting is performed. Then, the reflected light based on the epi-illumination is incident on the CCD camera 8 via the lens 5 and the half mirror 6, whereby the mask alignment mark 1a and the work alignment mark 4 are imaged.

The CCD camera 8 operates based on the image.
An image processing unit (not shown) for calculating a relative shift between the two alignment marks is provided. The two alignment cameras 11 are mounted on the frame 12 so as to be independently movable. The two alignment cameras 11 are provided for the following reason. That is, the mask alignment mark 1a and the work alignment mark 4
Is formed, the glass mask 1 can be formed using only the pair of marks, no matter how the shape of the marks is devised.
It is not possible to prevent a rotational deviation from occurring between the workpiece 3 and the workpiece 3. Therefore, in general, two mask alignment marks 1a and two work alignment marks 4 are formed on the glass mask 1 and the work 3, and these two pairs of marks (the distance between the two pairs of marks is set as large as possible). Two alignment cameras 1 for individual imaging
1 is provided.

The moving mechanism of the two alignment cameras 11, the moving mechanism of the CCD camera 8, and the moving mechanisms of the mask stage 10 and the work stage 13 are connected to a controller 14. Then, based on the relative displacement between the mask alignment mark 1a and the work alignment mark 4 obtained by the image processing unit of the CCD camera 8, the controller 14 controls the mask stage 10 or the work so as to eliminate the relative displacement. By controlling the movement of the stage 13, the glass mask 1 and the work 3 are aligned.

In this case, the image processing section of the CCD camera 8 determines the center points of the marks from the images of the mask alignment mark 1a and the work alignment mark 4, and the controller 14 determines that the center points of the two marks coincide. Then, the movement of the mask stage 10 or the work stage 13 is automatically controlled. Note that the controller 14
It is composed of a computer system or the like having a keyboard, a display device, and the like. The movement of the mask stage 10, the work stage 13, and the alignment camera 11 can be manually controlled by key operation or the like.

Next, an alignment detecting method unique to the present invention will be described.

When the mask alignment mark 1a and the work alignment mark 4 are imaged in the peripheral area of the visual field E of the CCD camera 8 and the glass mask 1 and the work 3 are aligned (see FIG. 5), an optical system is used. The image of the mask alignment mark 1a and the work alignment mark 4 is distorted due to the aberration of the lens 7 (especially the lens 5), and the center point of both marks cannot be accurately obtained. Strictly becomes impossible. Therefore, in the present embodiment, as shown in FIG. 3, the mask alignment mark 1a and the work alignment mark 4 are imaged in the central region of the visual field E of the alignment camera 11 (CCD camera 8).

That is, first, the glass mask 1 is attached to a designated position of the mask stage 10 by vacuum suction. In this case, the mask alignment mark 1a on the glass mask 1 usually enters the visual field E of the CCD camera 8, but if the mask alignment mark 1a does not enter the visual field E of the CCD camera 8, the controller 14 By moving the mask stage 10 by performing key operations while looking at the display screen, the mask alignment mark 1
a falls within the field of view E of the CCD camera 8.

After the mask alignment mark 1a enters the field of view E of the CCD camera 8, the glass mask 1 (that is, the center of the field of view of the CCD camera 8) is automatically processed by the controller 14 so that the glass mask 1 comes to the center of the field of view of the CCD camera 8. The positioning control of the mask stage 10) is performed.

It should be noted that the mask alignment mark 1a is C
When entering the field of view E of the CD camera 8, the mask alignment mark 1a may be located at the periphery of the field of view E of the CCD camera 8, as shown in FIG. In this case, the captured image of the mask alignment mark 1a is distorted, and its center coordinates cannot be accurately determined by the image processing unit. Even if it is intended to control the movement so that the center point of the mark 1a comes, it will be slightly shifted. However, by repeating such a correction process several times, the correction can be performed so that the center point of the mask alignment mark 1a comes to the center point of the field of view E of the CCD camera 8, as shown in FIG.

It should be noted that although it takes some time to correct the position of the mask alignment mark 1a a plurality of times, this correction process is performed as a preparation work for actually exposing the work 3. And does not significantly affect the exposure process. Further, since the position correction of the mask alignment mark 1a is performed so as not to be affected by the aberration of the optical system 7, the position correction of the mask alignment mark 1a is performed within a range not affected by the aberration of the optical system 7. Strictly set the center point to the field of view E of the CCD camera 8.
Need not be aligned with the center point of the
The position correction of the mask alignment mark 1a can be performed only once.

After the center point of the mask alignment mark 1a is aligned with the center point of the field of view of the CCD camera 8 in this manner, the alignment of the center point of the mask alignment mark 1a with the center point of the work alignment mark 4 is performed. It is performed automatically under the control of the controller 14. This alignment is performed by controlling the movement of the work stage 13 with the glass mask 1 and the CCD camera 8 fixed.

At this time, for example, as shown in FIG. 4, when the work alignment mark 4 has a cross shape, the center point of the work alignment mark 4 is obtained as follows.

That is, from the image data on the predetermined broken line shown in FIG. 4, the X coordinates of the points A and B at the edge positions on both sides of the vertical bar of the work alignment mark 4 are determined, and the midpoint E is marked. Let it be the X coordinate of the center. Similarly, from the image data on the predetermined broken line, the work alignment mark 4
The Y coordinate of the point C and the D point of the edge position on both sides of the horizontal bar is determined, and the midpoint F is set as the Y coordinate of the mark center. Normally, it is sufficient to set the center points E and F as the center points of the work alignment mark 4. However, when the inclination of the work alignment mark 4 with respect to the mask alignment mark 1 a cannot be ignored, the middle point is similarly indicated by a broken line. Points G and H are determined, and the intersection of EG and DH is set as the center of the work alignment mark 4.

With the above control, the mask alignment mark 1a at the position facing one of the two alignment cameras 11 (CCD camera 8) CCD camera 8
When the alignment between the work alignment mark 4 and the mask alignment mark 1a is completed, the alignment between the mask alignment mark 1a and the work alignment mark 4 at the position facing the other CCD camera 8 is performed in the same manner.

In this case, however, the center point of the other mask alignment mark 1a is set to the visual field E of the CCD camera 8.
When the movement of the mask stage 10 is controlled so as to match the center point of the workpiece, a positional shift occurs between the center point of one of the mask alignment marks 1a and the work alignment mark 4 for which the alignment processing has already been completed. The center position of the other mask alignment mark 1a is adjusted by controlling the movement of the CCD camera 8.
To the center point of the visual field E.

As described above, since the mask alignment mark 1a and the work alignment mark 4 are imaged at the center position of the field of view E of the CCD camera 8, the alignment of the two alignment marks is performed. The alignment between the glass mask 1 and the work 3 can be accurately performed without using a system, and the yield can be improved.

The present invention is not limited to the above embodiment. For example, the mask alignment mark may be aligned not with the center position of the field of view of the alignment camera but with a predetermined reference position in the center area within the field of view. Then, an image of the mask alignment mark and the work alignment mark may be taken at the reference position, and the alignment of the two alignment marks may be performed.

Further, depending on the shape of the mask alignment mark or the work alignment mark, etc., after moving the work alignment mark to the central region of the field of view of the alignment camera, the work stage is controlled to move while the work and the camera are fixed. Alternatively, the alignment between the mask alignment mark and the work alignment mark may be performed.

Further, the image processing section for obtaining the relative displacement between the two alignment marks can be provided not in the CCD camera body but in the controller.

[0034]

As described above, according to the present invention,
In an alignment detection method for performing alignment between a mask alignment mark formed on a mask and a work alignment mark formed on a workpiece based on images of both alignment marks captured by a camera, a center area of a field of view of the camera is provided. Since the mask alignment mark and the work alignment mark are imaged and the two alignment marks are aligned, it is possible to accurately perform the alignment between the mask and the work without using an expensive optical system. Become.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a part of an alignment detection device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram illustrating an entire alignment detection device according to an embodiment of the present invention.

FIG. 3 is a diagram showing an image when a mask alignment mark and a work alignment mark are imaged in a central region of a field of view of an alignment camera.

FIG. 4 is an explanatory diagram for explaining a method of obtaining a center point of a cross-shaped work alignment mark.

FIG. 5 is an explanatory diagram for explaining a conventional problem.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass mask 1a Mask alignment mark 3 Work 4 Work alignment mark 5 Lens 6 Half mirror 7 Optical system 8 CCD camera 9 Illumination device 10 Mask stage 11 Alignment camera 12 Frame 13 Work stage 14 Controller E Camera field of view

Continuation of the front page F term (reference) 2F065 AA12 AA17 AA20 BB02 BB27 CC01 CC20 CC25 EE00 FF04 FF42 HH13 JJ03 JJ05 JJ09 JJ26 NN20 PP01 PP11 PP12 PP13 QQ31 TT02 2H097 KA03 KA12 KA13 KA20 H10 05C 01020C

Claims (1)

[Claims] 1. An alignment detecting method for aligning a mask alignment mark formed on a mask with a work alignment mark formed on a workpiece based on images of both alignment marks captured by the camera. An image of the mask alignment mark and the work alignment mark in a central region of the field of view, and alignment of the two alignment marks is performed.