JP4085259B2 - X-ray fluoroscope for wafer inspection - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray fluoroscopic apparatus, and more particularly to an X-ray fluoroscopic apparatus that automatically performs a fluoroscopic inspection of a large number of solder bumps and the like formed on a semiconductor wafer.
[0002]
[Prior art]
In the manufacturing process of a semiconductor chip, such as a BGA, generally, a plurality of solder bumps and the like are formed on the surface of a semiconductor wafer corresponding to each chip, and each solder bump is formed at a stage before being cut into chips. The presence or absence of voids in the inside is inspected using an X-ray fluoroscope.
[0003]
With the miniaturization of semiconductor devices, the size of solder bumps has also been miniaturized, and it is required to inspect even the above-mentioned voids having a diameter of about 20 μm. In order to inspect the presence or absence of such fine voids with an X-ray fluoroscope, it is necessary to use an X-ray tube having a focal point of about 1 to 2 μm as an X-ray source, and an X-ray tube having such a focal point. There is only a transmission type which is called an open tube at present. Therefore, conventionally, an open tube has been used as an X-ray source in an X-ray fluoroscope for inspecting the presence or absence of voids in solder bumps formed on a semiconductor wafer as described above (for example, Patent Document 1). reference).
[0004]
[Patent Document 1]
JP2001-296256 (3rd page, FIG. 1)
[0005]
[Problems to be solved by the invention]
By the way, in a conventional X-ray fluoroscopic apparatus for performing a fluoroscopic inspection of a plurality of solder bumps and the like formed on a semiconductor wafer, the semiconductor wafer is automatically loaded and unloaded, but it is necessary to input the wafer type. There has not been put into practical use a system in which the visual field of a line detector is positioned at a position to be subjected to a fluoroscopic inspection, such as the position where individual solder bumps are formed, and automatically sequentially inspected.
[0006]
This is because it is difficult to position the sample table and automatically recognize the arrangement of the solder bumps because the solder bumps on the semiconductor wafer are arranged differently depending on the manufacturer and are very random. An X-ray tube called an open tube is difficult to keep the irradiation X-ray intensity constant over a long period of time, and is required to inspect a large number of solder bumps formed on a semiconductor wafer one by one. This is because, for example, the brightness of the X-ray fluoroscopic image cannot be kept constant during long-time operation.
[0007]
An object of the present invention is to provide a wafer inspection X-ray fluoroscopy device capable of automatically inspecting solder bumps and the like on a semiconductor wafer by overcoming high technical barriers to automatic inspection as described above.
[0008]
[Means for Solving the Problems]
The X-ray fluoroscopic apparatus for wafer inspection according to the present invention includes an X-ray source, an X-ray detector disposed opposite to the X-ray source, and disposed between these X-ray source and X-ray detector for inspection. A sample table mounted with a semiconductor wafer and movable in three axial directions perpendicular to each other including the X-ray optical axis direction, and a fluoroscopic inspection of the wafer on the sample table by image processing using the output of the X-ray detector In the X-ray fluoroscopic apparatus for wafer inspection provided with the image processing means for performing the above-mentioned processing, the transfer means for transferring the wafer onto the sample table, and the X-ray transmission information of the wafer placed on the sample table are stored in advance. Automatic wafer type recognition means for automatically recognizing the wafer type by comparison with a plurality of types of wafer patterns, and a map of a plurality of positions to be inspected on the wafer from the X-ray transmission information after the wafer type recognition The automatic And a table automatic positioning / inspection means for performing a fluoroscopic inspection by automatically moving the sample table in order to obtain X-ray transmission information at each position to be inspected according to the generated map. (Claim 1).
[0009]
Here, in the present invention, every time the table automatic positioning / inspecting means performs positioning and fluoroscopic inspection of the sample table a predetermined number of times, a reference sample arranged in advance on the sample table is attached to the X-ray detector. The sample table is automatically moved to fit within the field of view, and the X-ray transmission information is used to keep the brightness of the X-ray fluoroscopic image constant and to adjust the image processing conditions for inspection. It is preferable to employ a configuration (Claim 2) including brightness / processing condition adjusting means for giving an adjustment command to the source controller and the image processing means.
[0010]
The present invention uses the X-ray transmission information from the X-ray detector to automatically recognize the wafer type and to map the position to be inspected, thereby achieving the intended purpose. In addition to this, as in the invention according to claim 2, by adjusting the brightness during the automatic inspection, a large number of chips can be inspected at a time.
[0011]
That is, the plurality of kinds of semiconductor wafers that might be subjected to inspection, by storing in advance respective patterns, the X-ray transmission information of a wafer placed on the sample table, the type of the wafer Can be recognized. If the type of wafer can be recognized, the mutual positional relationship of the solder bumps to be inspected can be understood, and by mapping the positions of several solder bumps from the X-ray transmission information, all the solder bumps can be mapped. Become. According to the map created in this way, the specimen table is sequentially positioned so that the individual solder bumps and the like are within the field of view of the X-ray detector, thereby efficiently performing the fluoroscopic inspection of the individual solder bumps and the like. be able to.
[0012]
Then, as in the invention according to claim 2, each time the fluoroscopic inspection is performed for the set number of times during the fluoroscopic inspection of individual solder bumps, the reference sample prepared in advance is the field of view of the X-ray detector. The X-ray source controller and the image processing means are automatically adjusted so that the X-ray transmission information is obtained by positioning the sample table so as to enter the X-ray image, and the brightness and image processing conditions of the X-ray fluoroscopic image are kept constant. For example, an X-ray fluoroscopic image can be maintained at a constant luminance for a long time even when an open tube is used, and a large number of solder bumps and the like can be automatically inspected by a series of operations.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic diagram showing a main mechanical configuration and a block diagram showing an electrical configuration.
[0014]
The X-ray tube 1 is arranged so that the irradiation X-ray optical axis L faces upward in the vertical (z-axis) direction. The X-ray tube 1 faces the X-ray tube 1 and above it, for example, an image intensifier and a CCD. An X-ray camera 2 is arranged. A sample table 3 for mounting the semiconductor wafer W to be inspected is disposed between the X-ray tube 1 and the X-ray camera 2.
[0015]
The sample table 3 is supported so as to be movable in three axial directions that are orthogonal to each other including the z-axis direction that is the optical axis direction of the X-ray, and includes an x-axis moving mechanism 3x, a y-axis moving mechanism 3y, and a z-axis moving mechanism 3z. Are independently moved in the x-, y-, and z-axis directions.
[0016]
The sample table 3 is accommodated in a protective box (not shown) having a door that can be opened and closed, and the semiconductor wafer W to be inspected is carried to the X-ray fluoroscopic position on the sample table 3 outside the door. Alternatively, a transfer robot 4 for unloading from the position is arranged, and the opening / closing of the transfer robot 4 and the door is driven and controlled by a drive signal from the transfer controller 5.
[0017]
Further, as shown in a schematic plan view in FIG. 2, the sample table 3 has a low density for mounting a sample made of, for example, carbon for mounting a semiconductor wafer W on a substantially central portion of a structural material 3a such as metal. A plate material 3b is disposed, and a reference sample mounting low density plate material 3c made of carbon or the like for mounting a reference chip R is disposed adjacent to the sample mounting low density plate material 3b. ing.
[0018]
The X-ray tube 1 is of an open type and includes an objective magnetic lens 1b for focusing the electron beam on the target 1a. The magnetic lens 1b is supplied from the X-ray controller 6. The focus position can be changed in the x- and y-axis directions by operating according to the drive signal and changing the drive signal. For example, the focus position of the electron beam on the target 1a is changed by thermal deformation of the filament that generates electrons. If it has changed, it can be adjusted so that it can be restored by changing this drive signal. Further, a tube current and a tube voltage for the X-ray tube 1 are supplied from the X-ray controller 6.
[0019]
The output from the X-ray camera 2 is taken into the image processing device 7. In this image processing apparatus 7, as shown below, for image processing for identifying the type of the semiconductor wafer W, image processing for mapping, and automatic inspection of solder bumps formed on the semiconductor wafer W Image processing can be performed.
[0020]
The X-ray controller 6 and the image processing device 7 described above are placed under the control of the control device 8, and operate according to commands from the control device 8. The image processing device 7 and the control device 8 are actually one system mainly composed of a computer and its peripheral devices, and are constructed by installing programs corresponding to the computer. .
[0021]
Next, the operation at the time of automatic operation of the solder bump on the semiconductor wafer W according to the above embodiment will be described. FIG. 3 is a flowchart showing an overall procedure of a series of automatic operation operations, FIG. 4 is a flowchart showing a detailed procedure of wafer type automatic recognition processing, FIG. 5 is a flowchart showing a detailed procedure of position automatic correction processing, and FIG. These are the flowcharts which show the detailed procedure of a bump | vamp automatic inspection process.
[0022]
First, the semiconductor wafer W to be inspected is carried onto the sample table 3 by the transfer robot 4, and then automatic wafer type recognition processing is performed. In the wafer type automatic recognition processing, as shown in FIG. 4, the X-ray detection is performed so that the sample table 3 is moved and X-ray fluoroscopic images are obtained sequentially from the end of the semiconductor wafer W mounted on the sample table 3. The field of view of the device 2 is scanned to create an X-ray fluoroscopic image of the entire semiconductor wafer W. Next, paying attention to the second chip from the wafer edge, an image of the entire chip is created. The reason for paying attention to the second chip from the end of the wafer is that there is a high probability that a solder bump is missing in the outermost chip, and an accurate pattern may not be obtained.
[0023]
A plurality of types of semiconductor wafer patterns are stored in the image processing apparatus 7 in advance, and the type of the semiconductor wafer W is determined from the patterns and X-ray fluoroscopic images.
[0024]
Next, automatic position correction processing is performed. In this position correction processing, as shown in FIG. 5, when the type of the semiconductor wafer W has not been determined, the semiconductor wafer W is not set, and the fluoroscopic image is displayed. Parameters for determining the wafer type, such as the chip pitch of the wafer W, are automatically measured, and the parameters are stored as a new type of wafer.
[0025]
When the index of the wafer type is finished, 8 points at the end of the wafer W are automatically detected and the controller 8 is instructed by itself. Adopting these 8 teachings has the following advantages.
[0026]
That is, in order to precisely align the solder bumps on the wafer, an accuracy of about 10 μm is required. The accuracy of 10 μm is a common accuracy for a general xyz table, but the table for an X-ray fluoroscopic apparatus has a low density (such as a low mechanical strength) and a weak plate such as the above-mentioned X-ray irradiation inspection range. Since it has to be composed of a single sheet, rigidity as in a general table cannot be obtained, and it is necessary to perform position correction on the assumption that neither the x-axis nor the y-axis can slide on a straight line. If the x-axis and y-axis are orthogonal and can slide on a straight line in the direction of each axis, teaching of other parameters is necessary, but 4 teaching points are necessary for automatic mapping of the wafer. The point is enough. However, as described above, with the low-rigidity table, sufficient position information cannot be obtained with this, and the inventors' research has revealed that the following 8-point teaching program is effective.
[0027]
In the 8-point teaching program, eight points at each corner of the wafer W are determined as shown in FIG. In FIG. 7, (x1, y1) to (x8, y8) indicate xy coordinates. Actually, there are chips arranged vertically and horizontally, and there is a chip interval. However, for the sake of simplicity, it is assumed that solder bumps are arranged at equal intervals, and there are n rows of bumps arranged vertically and m rows of bumps arranged horizontally. If there is,
[0028]
The point (x3, y3) and the point (x5, y5) and each point obtained by dividing m between these points, that is, x coordinates, x3, x3 + (x5-x3) / m, x3 + 2 (x5-x3) / m ... Are obtained, and the point (x4, y4) and the point (x6, y6) and each point obtained by equally dividing the point into m, that is, x4, x4 + (x6-x4) / m in the x coordinate, x4 + 2 (x6−x4) / m... is obtained, and a straight line connecting points facing each other in the y-axis direction among these points is drawn. Similarly, the points (x1, y1) and (x7, y7) and the points obtained by dividing n between these points, that is, y coordinates, are y1, y1 + (y7−y1) / n, y1 + 2 (y7− .., y1) / n..., and the points (x2, y2) and (x8, y8) and the points obtained by dividing them into n, that is, y2, y2 + (y8-y2) / n in the y coordinate , Y2 + 2 (y8−y2) / n..., And draws a straight line connecting points facing each other in the x-axis direction among these points. As a result, a grid that intersects at the position of each solder bump arranged in a matrix is formed, and the coordinates of the intersection of these lines are calculated and used as mapping data.
[0029]
After completing the above mapping, the bump automatic inspection process is executed. In this bump automatic inspection processing, as shown in FIG. 6, the sample table 3 is positioned in the x and y axis directions according to the mapping data, and the presence or absence of voids is determined by image processing of the X-ray fluoroscopic image of each solder bump. inspect. Each time the number of solder bump inspections reaches a preset number, the sample table 3 is automatically moved so that the reference chip R is within the field of view of the X-ray camera 2, and the brightness of the X-ray fluoroscopic image is obtained. In the case where there is a change, the tube voltage and the tube current with respect to the X-ray tube 1 are adjusted to maintain the brightness of the X-ray fluoroscopic image at the initial brightness. At the same time, the magnetic lens 1b of the X-ray tube 1 is adjusted to adjust the focal position of the electron beam with respect to the target 1a. Then, the image processing environment parameter and each threshold value are adjusted.
[0030]
When the inspection of all the solder bumps is completed according to the mapping data, the semiconductor wafer W is unloaded from the sample table 3 as shown in FIG. 3, and a series of automatic inspection operations is completed.
[0031]
Of particular note in the above embodiments are the eight teaching points at each corner of the semiconductor wafer W despite the use of the sample table 3 using a low-density material such as carbon. By mapping, the sample table 3 can be moved with a positioning accuracy of about 10 μm so that a large number of fine solder bumps can be accurately accommodated in the field of view of the X-ray camera 2. Further, since the reference chip R is periodically imaged to automatically maintain the brightness of the X-ray fluoroscopic image and the focus of the X-ray tube 1, it is excellent in increasing the enlargement magnification, but for a long time. Even when the open X-ray tube 1 that is not suitable for continuous operation is used, the brightness of the X-ray fluoroscopic image is maintained at the initial brightness of the examination.
[0032]
【The invention's effect】
As described above, according to the present invention, the type of the wafer is recognized from the X-ray transmission information of the semiconductor wafer carried on the sample table, and the map of the position to be inspected such as the solder bump on the wafer is automatically set. The X-ray transmission information of each solder bump and the like is obtained by automatically moving the sample table according to the map, and each solder bump can be automatically and efficiently inspected by image processing.
Further, as in the invention according to claim 2, the X-ray transmission information of the reference sample is periodically obtained, and the brightness of the X-ray fluoroscopic image, the focus of the X-ray source, and the image processing conditions are automatically adjusted. By doing so, it becomes possible to perform a stable fluoroscopic inspection over a long period of time.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic diagram showing a main mechanical configuration and a block diagram showing an electrical configuration.
FIG. 2 is a schematic plan view of a sample table according to an embodiment of the present invention.
FIG. 3 is a flowchart showing an overall procedure of a series of automatic driving operations according to the embodiment of the present invention.
4 is a flowchart showing a detailed procedure of wafer type automatic recognition processing in FIG. 3;
5 is a flowchart showing a detailed procedure of position automatic correction processing in FIG. 3;
6 is a flowchart showing a detailed procedure of bump automatic inspection processing in FIG. 3;
FIG. 7 is an explanatory diagram of an 8-point teaching program used in position automatic correction processing according to the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 X-ray tube 1b Magnetic lens 2 X-ray camera 3 Sample table 3b Low-density board | plate material 3c for sample mounting Low-density board | plate material 3x for reference sample loading x-axis drive mechanism 3y y-axis drive mechanism 3z z-axis drive mechanism 4 Transfer robot 5 Transfer Controller 6 X-ray controller 7 Image processing device 8 Control device W Semiconductor wafer

Claims (2)

An X-ray source, an X-ray detector arranged opposite to the X-ray source, and a semiconductor wafer to be inspected mounted between these X-ray source and X-ray detector and mounted in the direction of the X-ray optical axis Including a sample table movable in three axial directions orthogonal to each other and an image processing means for performing a fluoroscopic inspection of the wafer on the sample table by image processing using the output of the X-ray detector. In fluoroscopic equipment,
By comparing the transfer means for transferring the wafer onto the sample table, the X-ray transmission information of the wafer placed on the sample table, and a plurality of types of wafer patterns stored in advance , the wafer type is automatically determined. Automatically recognizing the wafer type, mapping means for automatically creating a map of a plurality of positions to be inspected on the wafer from the X-ray transmission information after the wafer type recognition, and inspection according to the created map An X-ray fluoroscopic apparatus for wafer inspection, comprising table automatic positioning / inspection means for performing fluoroscopic inspection by automatically moving the sample table to obtain X-ray transmission information at each position to be obtained. The table automatic positioning / inspection means sets the sample table in order to place the reference sample arranged in advance on the sample table within the field of view of the X-ray detector every time the sample table is positioned and fluoroscopically examined a predetermined number of times. The X-ray source controller and image processing means automatically move and keep the brightness of the X-ray fluoroscopic image constant using the X-ray transmission information and adjust the image processing conditions for the inspection. 2. The X-ray fluoroscopic apparatus for wafer inspection according to claim 1, further comprising brightness / processing condition adjusting means for giving an adjustment command to the wafer.

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