JPH0982739A - Inspecting device of bonding wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the height precisely by detecting the position of the maximum brightness of the image of a luminescent spot on a focal plane and obtaining the height of bonding wire considering this position in a case where the position of the peak brightness changes with surface contour of a bonding wire. SOLUTION: A camera device is mounted on a XYZ stage 5 and takes the picture of images on different focal planes obtained by changing the height in the direction of optical axis. The image signals are processed by an image processing device 6 sequentially and the height of the bonding wire 1 is determined as follows. A detecting line 16 is determined in The direction vertical to the wire from the coordinate of a first and a second bonds 22 and 23 that are input in advance and the difference of the brightness is measured along the detecting line 16. Comparing it with that of other focal planes and the focal plane with maximum variation of the brightness is defined as the focal plane nearest to the height of the wire 1. Therefore, the height of the top position can be measured precisely in the case where the peak position of the brightness changes depending on the surface contour of the bonding wire 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting the shape of a bonding wire on a semiconductor element.

[0002]

2. Description of the Related Art Conventionally, as a device for inspecting the height of a bonding wire, as described in Japanese Patent Application Laid-Open No. 7-63530, a bonding wire on a semiconductor element illuminated by a luminous flux from an illuminating device is used. Bonding wire inspection that calculates the wire height by capturing multiple images of the reflected light from the bonding wire while changing the height of the image pickup device and image-processing the brightness change of the bright spot on the wire top of these image signals. A device has been proposed.

Further, in the same publication, the top position of the bonding wire is scratched or the top position is ground into a flat surface due to friction with the capillary or the wire guide, and the bright spot of the wire top is compared with other wires. If the brightness is too small and dark, or if the brightness is too bright and the brightness signal is saturated, or if the height of the wire is outside the capture range and the height of the wire cannot be calculated when an image is captured by capturing the height at a preset position, The setting conditions related to height measurement such as the amount of illumination light, the reference height of the image pickup device, the image pickup height feed amount, and the number of image pickup screens are automatically set again, and under the reset conditions, images are taken again and bonding is performed. There has been proposed a bonding wire inspection device that calculates the height of a wire.

[0004]

However, in the case where the top position of the bonding wire is scratched or the top position is scraped into a flat surface due to friction with the capillary or the wire guide, the image pickup device at the time of image pickup The position of the bright spot center may vary depending on the height of the. For example, when observing the movement of the bright spots in the image from the lower height to the higher height during image capturing, the center of the bright spot may shift in a certain direction. Therefore, originally, it is necessary to calculate the luminance change amount at the center of the bright spot by image processing, but in the above-described conventional technique, the luminance change amount on the same coordinate axis on the image pickup device surface in the image pickup apparatus is calculated. When the point shift occurs, it is not possible to obtain the luminance change amount of the bright point that should be calculated originally. There is also a problem that this causes deterioration of measurement accuracy. In view of this problem of the conventional technique, an object of the present invention is to increase the height of the bonding wire in the bonding wire inspection device even when the bright spot of the wire top of the image signal obtained by the imaging device is displaced. It is to be able to inspect accurately.

[0005]

In order to achieve this object, according to the present invention, an illuminating means for epi-illuminating a bonding wire on a semiconductor element, an imaging means for imaging the illuminated bonding wire, and an imaging means. , Information processing for obtaining the height of the bonding wire based on the brightness of the bright spot image in the image data of each focal plane of the bonding wire obtained by imaging the focal plane at a plurality of positions in the height direction In the bonding wire inspection device including means, the information processing means detects a position where the brightness in each of the bright spot images is maximum, and in consideration of this position,
It is characterized in that the height of the bonding wire is obtained.

[0006]

According to this, the position where the brightness in the bright spot image on each focal plane is maximum is detected, and the height of the bonding wire is obtained in consideration of this position. The height of the bonding wire can be obtained with high accuracy even when the peak position of the brightness changes in accordance with the above.

[0007]

【Example】

[Embodiment 1] FIG. 1 is a block diagram showing a bonding wire inspection apparatus according to a first embodiment of the present invention. In the figure, 1 is a bonding wire on a semiconductor element, 2
Is an imaging device including an imaging system such as an optical microscope and an imaging system such as a CCD camera, 3 is an illuminating device having a light source for epi-illuminating the bonding wire 1, and 4 is light from the illuminating device 3 to the bonding wire 1. A half mirror for vertical incidence, 5 is an XYZ stage for moving the image pickup device 2 in the horizontal and vertical directions, 6 is an image processing device for processing an image signal from the image pickup device 2, and 7 is a control of the entire system. The central control unit 8 performs the display, the display unit 8 displays the results of the central control unit 7, and the input unit 9 inputs the central control unit 7.

Illumination light emitted from the illuminating device 3 is vertically incident on the bonding wire 1 through the half mirror 4 (epi-illumination). The bonding wire 1 is usually a gold wire or an aluminum wire having a diameter of several tens of μm.
Since it has a loop shape as shown in FIG. 2, when reflected light is illuminated along the optical axis of the image pickup device 2, the reflected light from the horizontal part of the top of the bonding wire is attached to the upper part of the bonding wire 1. The device 2 captures a bright spot image having a higher brightness than the surrounding area. The image signal captured by the image capturing device 2 is arithmetically processed by the image processing device 6.

On the other hand, the image pickup device 2 is attached to the XYZ stage 5, and the image pickup device 2 picks up images of different focal planes by changing the height in the optical axis direction.
The image signals are sequentially processed by the image processing device 6, and the image processing device 6 thereby calculates the loop height of the bonding wire 1. In this way, the image processing device 6 calculates the heights for all the bonding wires 1 while moving the XYZ stage 5 in accordance with the instruction from the central control device 7, and the central control device 7 displays the result as a result. Output to 8.

FIG. 3 shows an example of an image captured using epi-illumination. As shown in the figure, the bonding wire 1
The horizontal part 13 of the top of is captured with high brightness. This part is called a bright spot. FIG. 4 is a diagram showing a height relationship between the bonding wire 1 and the imaging device 2. In the figure, F1 to F5 represent focal planes of the image forming system of the image pickup device 2, and while moving the image pickup device 2 in the vertical direction,
An image at each focal plane of F5 is captured. Find the bright spot 13 of the bonding wire 1 from the captured image, and
The height of the top of the bonding wire 1 is calculated from the change in the luminance on each focal plane.

FIG. 11 is a flowchart of a process for obtaining the loop height (top height) of the bonding wire 1. When this processing is started, first, each of the focal planes F1 to F5
Processing unit 6 converts an image signal obtained by capturing an image at
The image signals for five screens are sequentially stored in the internal storage device (steps S1 to S5). The height intervals of the focal planes for five screens may be unequal intervals, but here they are made equal intervals to simplify the processing. Also, the focal plane F1
The central control unit 7 to F5 are arranged so that the focal plane in the middle, that is, the focal plane F3, is aligned with the top height of the designed bonding wire 1 previously input using the input unit 9.
Is controlled by

Next, F1 to F1 stored in the image processing device 6 are stored.
The bright spot of the bonding wire 1 is found from the image of 5 screens of F5 (step S6). Specifically, as shown in FIG. 5, on all focal planes, a bright spot extraction window 15 is provided at a position on the image pickup screen where bright spots are expected with respect to the image processing apparatus 6, and the bright spot extraction window 15 is provided within the window. Extracts a dark shape with a bright center. In this embodiment, in order to improve the accuracy in the height direction, the image pickup apparatus 2 uses an imaging system having a shallow depth of focus, and therefore bright spots can be found on all images on the focal planes F1 to F5. is not. Therefore, although the order of imaging is not limited, for example, the focal planes F3, F
The bright points are searched for in the order of 4, F2, F5, and F1 from the center to the outer side, and when the bright points are found, this processing ends. Next, processing for correcting the deviation of the bright spot is performed on the focal plane where the bright spot is found (step S7). FIG.
Is a flowchart showing this processing. FIG. 6 (a)
6B is a cross-sectional view of the bonding wire 1 in the case where the wire surface is scraped, and FIG. 6B is each focal plane F1 when the wire image of FIG.
~ F5 images are shown. Here, in order to simplify the description, it is assumed that the bright spots are extracted on the focal planes F2, F3, and F4. The bright spot may be displaced in the wire direction or in the direction perpendicular to the wire. However, since the bright spot is usually displaced in the direction perpendicular to the wire, a correction method in the direction perpendicular to the wire will be described here. .

When the correction processing of the bright spot shift is started, first,
The first bond 2 pre-input to the central controller 6
The orthogonal direction of the wire is calculated from the coordinates of 2 and the second bond 23 (see FIG. 2). Then, the wire edge detection line 16 (FIG. 3) is provided in the direction perpendicular to the wire on all the focal planes where the bright spots are found. The brightness change amount is calculated along the edge detection line 16 and the peak position of the change amount is taken as the wire edge. At this time, if the focus of the image pickup device 2 is aligned with the height of the wire 1, the edge portion of the wire has a clear difference in brightness and darkness, and the edge portion of the wire is different from other focal planes that are out of focus. The amount of change in luminance becomes large. For example, when the focal plane F3 has a larger brightness change amount at the wire edge portion than the other focal planes, the focal plane F3 can be said to be the focal plane closest to the height of the wire 1.

In this way, if it is possible to specify that the focal plane F3 is the focal plane closest to the height of the wire 1 in step S71, as shown in FIG. The point 13 is binarized (step S72), and the center of gravity 17 of the bright point 13 is calculated (step S72).
75). Then, in the multi-valued image of the focal plane F3 stored in the storage device inside the image processing device 6, the luminance detection line 18 passing through the center of gravity 17 and orthogonal to the wire direction is provided (step S76).

If, in step S71, the difference in brightness between the edge portions of the wire is not clear on all focal planes in which the bright spots are found, and the difference in the amount of change in luminance between the wire edge portions on each focal plane is not recognized. If the focal plane closest to the height of the wire 1 cannot be specified for the reason, the focal planes F2, F
3, the bright points 13 extracted in F4 are binarized to obtain a logical sum (steps S73 and S74). Then, as shown in FIG. 8, the barycenter 17 of the bright points 19 obtained by the logical sum is calculated (step S75), and the luminance detection line 18 perpendicular to the wire direction passing through the barycenter 17 is provided (step S7).
6).

The brightness detection line 18 is used to find the center of the bright spot on each of the focal planes F2, F3, F4 from which the bright spot has been extracted (steps S77 to S79). FIG.
It shows the change in brightness of each of the focal planes F2, F3, and F4 when the brightness of the bright spot 13 is detected along the brightness detection line 18. Since the brightness of the center of the bright spot is the highest, the brightness of the center of the bright spot on each focal plane is the maximum value I2, I3, I
It becomes 4. The bright spot center coordinates 21 have maximum values I2, I3, I
Coordinates on the brightness detection line 18 corresponding to X4, X3,
It is calculated as X4 (step S77). In addition, in order to obtain height information, 3 × is applied to the bright points on each focal plane as shown in FIG.
A processing window 20 of 5 pixels is provided (step S78). The brightness change of each pixel from the focal planes F2 to F4 is obtained in the next process (step S8 in FIG. 11).

In the present embodiment, as shown in FIG. 6, the bright spots are deviated on each focal plane. Therefore, in order to obtain an accurate luminance change of each pixel from the focal planes F2 to F4,
The processing window 20 must be set according to the shifted bright spot. Therefore, the image processing device 6 automatically tracks and captures the bright spot center coordinates 21 in the process of FIG. 7, and sets the window so that the center of the processing window 20 overlaps the bright spot center coordinates 21. An accurate luminance change of each pixel can be obtained in step S8.

Next, the following three tests are performed on the brightness change of each pixel, and the pixel showing the optimum brightness change is extracted as the optimum pixel (step S9). Test 1. Extract bright pixels. Test 2. Pixels having a large brightness change between the focal planes are extracted. Test 3. When the bright spots are extracted on all the focal planes of F1 to F5, the pixels in which the peak of the brightness change exists in F2 to F4 are extracted.

For example, a quadratic curve interpolation is performed on the change in luminance between the focal planes of the pixels common to the focal planes that pass these three tests, and the height of the peak position is calculated as the wire height (step S10). ). Then, it is determined whether or not the height measurement of all the bonding wires has been completed (step S11), and if not completed, the process returns to step S1, and if completed, the wire loop height measurement process is completed. .

[Embodiment 2] In the first embodiment, the height information is obtained by setting the focal plane processing window 20 in which the bright spot center 21 is obtained, but here, the processing window 20 is used.
A method of obtaining height information without using will be described. Also,
In this embodiment, the focal planes F2, F
It is assumed that the bright spots are extracted in F3 and F3.

The position coordinates at the maximum brightness obtained in the brightness detection line 18 obtained in the first embodiment, that is, the bright spot center coordinates 21 are x, and the maximum brightness is i. Therefore, x ₂ and i _{2 at} the focal plane F ₂ and x ₃ and i _{3 at} the focal plane F ₃ , respectively.
At i ₃ , and the focal plane F4, x ₄ and i ₄ are obtained. Then, the maximum brightness value with respect to the brightness center coordinate of each focal plane can be expressed as shown in FIG. 13 by approximating it with a quadratic curve, for example. Further, since the heights of the focal planes F2, F3, and F4 are known in the central control unit 7, if the focal planes are converted into height information and the bright spot center coordinates for each focal plane are approximated by, for example, a quadratic curve or the like, FIG. Can be expressed as

Since the brightness becomes maximum when the top position of the bonding wire 1 is focused on the image pickup device 2, the coordinate X _max corresponding to the maximum value i _max in FIG.
Is the center coordinate of the bright spot on the wire top. Therefore,
As the height of the focal plane corresponding to the bright spot center coordinate x _max , the height H at the top position of the bonding wire 1 can be obtained from FIG.

[Embodiment 3] In the first and second embodiments described above, the shift of the bright spots in the direction perpendicular to the wire is described. However, the brightness detection line is provided in the wire direction so as to pass through the bright spot centroid. In this way, it is possible to deal with the bright spot shift in the wire direction. Further, it goes without saying that if the brightness change line is provided in both the direction perpendicular to the wire and the wire direction so as to pass through the center of gravity of the bright spot, it is possible to cope with the shift of the bright spot in all directions.

[0024]

As described above, according to the present invention, the top position of the bonding wire is scratched, or the top position is scraped in a plane due to friction with the capillary or the wire guide. By tracking and correcting the center position of the bright spot on each focal plane of the bright spot imaging surface,
The height of the top position of the bonding wire can be measured with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing a bonding wire inspection apparatus according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a bonding wire.

3 is a plan view showing an image picked up by the image pickup apparatus shown in FIG. 1 and an edge detection line.

4 is a diagram showing the relationship between the height of the wire and the height of the imaging device in the device of FIG.

5 is a diagram showing a window when a bright spot of a wire in the apparatus of FIG. 1 is extracted by an image pickup apparatus.

FIG. 6 is a cross-sectional view when the surface of the wire is scraped,
FIG. 6 is a diagram showing a shift of a bright spot on a wire.

7 is a diagram showing a luminance detection line when the focal plane closest to the wire height in the apparatus of FIG. 1 can be identified.

8 is a diagram showing a luminance detection line when the focal plane closest to the wire height in the apparatus of FIG. 1 cannot be specified.

FIG. 9 is a diagram showing a change in luminance on each focal plane in the apparatus of FIG.

FIG. 10 is a diagram showing a window for processing a bright spot in the apparatus of FIG.

11 is a flowchart showing a processing method in the apparatus of FIG.

FIG. 12 is a flowchart showing a procedure for correcting the positional deviation of a bright spot in FIG.

FIG. 13 is a diagram showing a state in which the luminance with respect to the central coordinates of the bright spots of each focal plane in the apparatus of FIG. 1 is approximated by a quadratic curve.

14 is a diagram showing a state in which the relationship between the height of the focal plane and the coordinates of the bright spot in the apparatus of FIG. 1 is approximated by a quadratic curve.

[Explanation of Codes] 1: Bonding wire, 2: Imaging device, 3: Illumination device, 4: Half mirror, 5: XYZ stage, 6: Image processing device, 7: Central control device, 8: Display device, 9: Input Device: 10: Pad, 11: Semiconductor chip, 12: Inner lead, 13: Bright spot, 14: Focal plane of imaging device, 1
5: Bright spot extraction window, 16: Edge detection line, 1
7: Bright point centroid, 18: Luminance detection line, 19: Logically ORed bright point, 20: Processing window, 21: Bright point center,
22: first bond, 23: second bond.

Claims (1)

[Claims] 1. An illuminating device for epi-illuminating a bonding wire on a semiconductor element, an imaging device for imaging the illuminated bonding wire, and an imaging device for locating a focal plane at a plurality of height-direction positions. Information processing means for obtaining the height of the bonding wire based on the brightness of the bright spot image in the image data of each focal plane of the bonding wire obtained by imaging the bonding wire inspection device. The means for detecting the position of maximum brightness in each of the bright spot images, and taking this position into consideration, obtains the height of the bonding wire.