JPH0554622B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a visual inspection apparatus for inspecting defects in semiconductor pellets, for example.

[Technical background of the invention and its problems]

Generally, on an integrated circuit production line, a mask pattern is formed on a wafer and then it is diced to separate it into semiconductor pellets, which are then subjected to post-processes such as bonding. This is the most important step in making a decision, and visual inspection for scratches, dirt, etc. is essential. For this reason, in the past, for example, a mask pattern was formed on a wafer and then visually observed using a microscope, or the pattern-formed surface of the wafer was imaged and the patterns of adjacent pellets were compared with each other to determine the presence or absence of defects. is being inspected. However, semiconductor pellets are prone to cracking or chipping at the edges when the wafer is divided by dicing, and when each semiconductor pellet is placed in a tray, the surface of the pellet may be contaminated, crushed, or scratched. Therefore, even if the wafer is determined to be defect-free, it cannot necessarily be said that the semiconductor pellet is a good product.

Therefore, recently, defect inspection has been carried out in the state of semiconductor pellets. However, when attempting to inspect this semiconductor pellet, each pellet is in a divided state, so an inspection method that mutually compares captured images of adjacent patterns used in wafer inspection is required. cannot be applied. For this reason, conventionally, an inspector performs inspection by visual observation using a microscope. However, such inspection by visual observation has low inspection efficiency and inspection accuracy, and thus has not been able to improve productivity.

On the other hand, it is also being considered to image each semiconductor pellet individually and automatically detect defects from the binarized image, but the imaging means conventionally used for wafer inspection uses illumination from perpendicularly above the surface to be inspected. The reflected image was taken vertically upward, and each wiring pattern was inspected one by one. For this reason,
Defects such as cracks and chips that occur at the edges of semiconductor pellets can be detected with high accuracy, but surface defects such as dirt and crushing, which are common in semiconductor pellets, cannot be detected at high speed and at low cost. Ta.

[Purpose of the invention]

The present invention provides a visual inspection device that can detect defects with high efficiency and accuracy without relying on an inspector, and can detect any type of defects with high accuracy and with a simple configuration. The purpose is to provide.

[Summary of the invention]

The present invention provides a first illumination means that performs vertical epi-illumination, and a second illumination means that performs illumination from diagonally above, illuminates the object to be inspected with each of these illumination means, and drives these illuminations. The setting of the binarization level for the captured image signal obtained by imaging the object to be inspected is changed according to the following. Then, edge defects of the object to be inspected are detected from a binary pattern image when illuminated by the first illumination means, and surface defects of the object to be inspected are detected from a binary pattern image when illuminated by the second illumination means. To detect.

[Embodiments of the invention]

FIG. 1 shows the configuration of a visual inspection apparatus according to an embodiment of the present invention, where 1 indicates a base and 2 indicates an XY table. This XY table 2 is operated by step motors 21 and 22.
A semiconductor pellet 3 as an object to be inspected is taken out from a stocker (not shown) by a collector and placed on the table 2a. On the other hand, an imaging device 5 is disposed vertically above the semiconductor pellet 3 while being supported by a support shaft 51. This imaging device 5 has a fixed arm 52 attached to the support shaft 51 so as to be movable up and down, and a microscope 53 for enlarging the surface to be inspected of the semiconductor pellet 3 and an image enlarged by the microscope 53 on the fixed arm 52. An industrial television (ITV) camera 54 for imaging is fixed.

By the way, this imaging device 5 is provided with two different illumination devices 6 and 7. Among these, the first illumination device 6 reflects the output light of the light source 61 with a semi-transparent mirror 62 as shown in FIG. 2a.
The semiconductor pellet 3 placed on the XY table 2 is vertically illuminated. On the other hand, the second illumination device 7 includes a light source 71 and the microscope 53.
The output light from the light source 71 is irradiated from the light projecting part 72 onto the semiconductor pellet 3 from diagonally above as shown in FIG. 2b. The surface to be inspected is illuminated obliquely. The angle of this oblique illumination is optimally 20 degrees to 30 degrees (150 degrees to 160 degrees) with respect to the surface of the semiconductor pellet 3.

Now, the captured image obtained by the ITV camera 54 is first binarized by the binarization circuit 81 according to a predetermined binarization level, and then temporarily stored in the image capture memory 82, and then the control circuit 83 It is beginning to be introduced in This control circuit 83 has a microprocessor as a main control section, and as shown in FIG. Each control function includes a means 35 and a lighting switching means 36. The imaging control means 31 drives the ITV camera 54, sets a binarization level in the binarization circuit 81, and controls writing and reading operations of the image memory 82. The visual field control means 32 is
The XY table 2 via the motor drive circuit 84
By driving the ITV camera 54, the imaging field of view of the semiconductor pellet 3 of the ITV camera 54 is variably controlled.
The position detecting means 33 detects the position of the semiconductor pellet 3 from an image obtained by vertical epi-illumination. Further, the edge defect detection means 34 detects edge defects such as cracks and chips by determining the signal level of the binarized pattern image obtained during the vertical epi-illumination. Also, surface defect detection means 35
By determining the signal level of the binary pattern image obtained under the oblique illumination, surface defects such as dirt, crushing, and surface scratches on the semiconductor pellet 3 are detected. Finally, the lighting switching means 36
is the light source 61 of the first lighting device 6 and the second
By driving the light sources 71 of the illumination device 7 separately, the surface to be inspected of the semiconductor pellet 3 is subjected to vertical epi-illumination and oblique illumination, respectively.

The control circuit 83 also has a function of changing the setting of the binarization level of the binarization circuit 81 according to the light source of the first lighting device 6 or the light source 71 of the second lighting device 7 driven by the lighting switching means 36. have.

Next, the operation of the apparatus configured as described above will be explained according to the control procedure of the control circuit 8. FIGS. 4a and 4b are flowcharts showing the control procedure.

When the semiconductor pellet 3 is set at a predetermined position on the XY table 2 and an inspection start switch (not shown) is operated in this state, the control circuit 83 first controls the light source 61 of the first illumination device 6 in step 4a. A drive signal is emitted, which causes the semiconductor pellet 3 to
Perform vertical epi-illumination. In this state, in step 4b, a drive signal is output to the ITV camera 54 to start the imaging operation, and the obtained image signal is binarized by the binarization circuit 81 and then stored in the image memory 82. . At this time, the control circuit 83 sets a relatively high binarization level to the binarization circuit 81 in order to detect the bonding pad for detecting the position of the semiconductor pellet 3. This binarization level is set to an intermediate value between the image signal level of the bonding pad portion (approximately 0.8V) and the image signal level of the portion excluding the bonding pad (approximately 0.4V). FIG. 5a shows an example of the resulting binary pattern image, in which only the bonding pad portion 3b is detected as being at the "H" level. When the binary pattern image for position detection is obtained, the control circuit 83 then detects the bonding pad 3b from the binary pattern image by pattern recognition in step 4c, and detects the semiconductor pellet 3 from that position. Detect the position of. Then, in step 4d, the XY table 2 is driven via the motor drive circuit 84 to adjust the position of the semiconductor pellet 3, thereby setting the initial position of the imaging field of view.

After completing the positioning of the imaging position, the control circuit 83 first drives the ITV camera 54 in step 4e to take an image of the surface to be inspected of the semiconductor pellet 3, and converts the obtained image signal into a binary image signal. After being binarized by the conversion circuit 81, the image memory 8
2. By the way, at this time, the control circuit 8
3 is a signal to the binarization circuit 81 for detecting a portion excluding the bonding pad portion, at a binary conversion level lower than the detection level of the bonding pad, for example, an image of the portion excluding the bonding pad portion. Set to an intermediate value between the signal level (0.4V) and the stocker 4 image signal level (0.2V). Therefore, as a result of this binarization, the image memory 82 stores two images in which the portion 3a excluding the bonding pad portion is at the "H" level and the XY table surface 2a is at the "L" level, as shown in FIGS. 5b and 5c, for example. A value pattern image is stored. In addition, Fig. 5b shows the binarized pattern image when there are no edge defects such as cracks or chips, and Fig.
shows an example of a binarized pattern image when the same defect exists. Then, in step 4f, the control circuit 83 determines the signal level at the end of the portion 3a excluding the bonding pad portion in the binarized pattern image to detect an end defect, and then in step 4g, detects an end defect. Determine the presence or absence of defects. still,
This determination means is performed, for example, by detecting the presence or absence of a signal corresponding to a defect from a signal obtained by digitizing the output of the ITV camera 54 for each scanning line. If it is determined that there is no defect, the XY table 2 is driven to remove the semiconductor pellet 3 in step 4i.
The ITV camera 54 is moved in the imaging field of view,
Thereafter, the process returns to step 4e and the defect detection operation described above is repeated. Then, the inspection for edge defects is repeatedly performed on the entire circumference of the edge of the semiconductor pellet 3, and when it is determined in step 4h that the inspection for edge defects for one pellet has been completed, the process moves to step 4j as shown in FIG. 4b. . On the other hand, during the inspection for these end defects, if it is determined in step 4g that there is an end defect, the control circuit 83 ends the inspection of the semiconductor pellet at that point and proceeds to step 4s in FIG. 4b. At this point, a command to remove the semiconductor pellet is output, and the next semiconductor pellet is inspected.

Now, when the end defect inspection described above is completed and the process moves to step 4j, the control circuit 83 then stops the operation of the first lighting device 6 that has been in the driving state until then, and switches the second lighting device in its place. A drive signal is output to the light source 71 of No. 7 to start oblique illumination by the second illumination device 7. In other words, the form of illumination for the semiconductor pellet 3 is switched. In this state, first, in step 4k, the semiconductor pellet 3 detected in step 4c during the vertical epi-illumination is detected.
The initial position of the imaging field of view is set according to the position of 81
After the image is binarized according to a predetermined binarization level, it is stored in the image memory 82. At this time, the binarization level is set to an intermediate value between the image signal level of the portion 3a excluding the bonding pad portion and the image signal level of the surface defect, so if there is no surface defect, as shown in FIG. As shown in FIG. 6a, the entire area becomes "L" level, while if there is a surface defect, the defective portion 3c appears as "H" level as shown in FIG. 6b, for example. This is because by performing oblique illumination, the illumination light is totally reflected in the part 3a excluding the normal bonding pad part and is not introduced into the ITV camera 54, whereas in the surface defect part 3c, the illumination light is reflected diagonally from above. Illumination light is diffusely reflected
This is because it is guided by the ITV camera 54.

Then, the control circuit 83 detects surface defects such as stains and crushing on the surface of the semiconductor pellet 3 from the thus obtained binary pattern image by counting the number of "H" level pixels in step 4m. Thereafter, in step 4n, the presence or absence of surface defects is determined. If it is determined that there are no defects, the surface defect inspection operation is repeated every time the position of the imaging field of view is moved by the XY table 2 in step 4p in the same way as when detecting the edge defects, and the entire area of one pellet is inspected. When it is determined in step 4o that the process has been completed, the process moves to step 4r to output a signal indicating that there are no defects, that is, a non-defective product signal, and then, if there is a next semiconductor pellet 3, this semiconductor pellet 3 is inspected. Transition. On the other hand, if it is determined in step 4n that there is a defect during the inspection operation for each surface defect, step 4s is performed at that point.
Then, an exclusion command is output, and the next semiconductor pellet 3 is inspected.

In this way, with this embodiment, it is possible to automatically inspect each semiconductor pellet 3 for defects, and by performing vertical epi-illumination and oblique illumination, each of these illuminations can detect edge defects such as cracks and chips, and dirt. By detecting surface defects such as cracks and cracks separately, all defects can be detected easily, quickly, and accurately without performing complicated image processing. Therefore, the configuration can be simplified and productivity can be improved.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, vertical epi-illumination is first performed to detect edge defects, and then diagonal illumination is switched to detect surface defects, but this order may be reversed. . However, in this case, it is necessary to once perform vertical epi-illumination to detect the position of the semiconductor pellet 3 before performing oblique illumination. Further, in the above embodiments, the case where semiconductor pellets are inspected for defects has been described, but the present invention can be similarly applied to any product in which end defects and surface defects occur. In addition, the configuration, control procedure, control content, defect detection means, imaging means, visual field control means, etc. of each illumination device can be modified in various ways without departing from the gist of the present invention.

〔Effect of the invention〕

As described in detail above, according to the present invention, vertical epi-illumination and oblique illumination are switched to detect edge defects such as cracks and chips on the inspected object and surface defects such as dirt and crushing, respectively. It is possible to provide an external appearance inspection device that can detect various defects with different image signal levels when imaging the image with high accuracy, reliably, and with a simple configuration.

[Brief explanation of the drawing]

The figures are for explaining a visual inspection apparatus according to an embodiment of the present invention. Fig. 1 shows the overall configuration of the apparatus, and Fig. 2 a and b show vertical epi-illumination and oblique illumination, respectively. 3 is a block diagram showing the functions of the control circuit, FIGS. 4a and 4b are flowcharts showing the control procedure of the control circuit, and FIGS. 6
Figures a and b are schematic diagrams showing binarized pattern images for use in explaining the operation. 1... Base, 2... XY table, 3... Semiconductor pellet, 3a... Portion excluding bonding pad portion, 3b... Bonding pad portion, 3c... Surface defect portion, 5... Imaging device, 5
3...Microscope, 54...ITV camera, 6...First illumination device, 7...Second illumination device, 81...
Binarization circuit, 82... image memory, 83... control circuit, 84... motor drive circuit.

Claims (1)

[Claims] 1. A first device that performs vertical epi-illumination on an object to be inspected.
a second illumination means for illuminating the object to be inspected from diagonally above; and an imaging device for capturing an image of the inspected surface of the object to be inspected, which is separately illuminated by these illumination means, vertically above the object to be inspected. a binarization circuit that has a variable setting binarization level and binarizes a captured image signal obtained by the imaging device; and a captured image device that has been binarized by the binarization circuit. an image memory that stores a binarized pattern image; an illumination switching means that separately drives either the first illumination means or the second illumination means; and the illumination switching means that is driven by the illumination switching means. binarization changing means for changing the setting of the binarization level of the binarization circuit according to the first illumination means or the second illumination means; and storage in the image memory during illumination by the first illumination means. means for detecting an edge defect of the object to be inspected from a binary pattern image that is displayed; An appearance inspection device comprising: a means for detecting defects; and a means for detecting defects. 2. The appearance inspection apparatus according to claim 1, wherein the object to be inspected is a semiconductor pellet.