JP2014106113A - X-ray inspection device and x-ray inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate a volume of a gap part of a measured object by a simple process at high speed.SOLUTION: An X-ray inspection device 100 comprises: an X-ray source 110 that irradiates with an X-ray a copper-filled part serving as a measured object S filled in a through-hole H of a substrate B; an X-ray camera 120 that captures a transmission X-ray image of the measured object S; thickness estimation means 141 for estimating a thickness distribution of the measured object S from the transmission X-ray image and a relation between a preliminarily acquired thickness of a material and a counting number of the transmission X-ray; gap part estimation means 142 for estimating that a part thinner than a predetermined reference value is a part corresponding to a gap part V on the basis of the estimated thickness distribution; gap part shape estimation means 143 for estimating a contour shape of an area corresponding to the gap part; volume calculation part 144 for calculating a volume of the gap part from the contour shape; fill-up ratio calculation means 145; a measured object stage 130 that causes the measured object S to be tilted; and gap part position estimation means 146 for estimating a position of the gap part on the basis of transmission X-ray images before and after tilted.

Description

  The present invention relates to an X-ray inspection apparatus and an X-ray inspection method, and in particular, an X-ray capable of obtaining the thickness of an object to be measured, such as a semiconductor, a printed circuit board, a lithium ion battery, or the volume of voids or cavities. The present invention relates to an inspection apparatus and an X-ray inspection method.

  In a printed circuit board, an IC (Integrated Circuit) circuit, and the like, if there is a void space in the copper filling layer filled in the through hole, stable performance is not exhibited. For this reason, the demand which detects the space | gap formed in the copper filling layer in-line is increasing. When detecting this void, not only the actual volume of the void but also the volume of the void relative to the through-hole volume, that is, the filling rate, the position of the void, and the like are used as criteria for determining the quality of the product. In general, it is said that the volume and position of the gap can be calculated from a CT (Computed Tomography) image of the object to be measured. However, it takes time to obtain a CT image and is not suitable for in-line inspection. Therefore, a method for obtaining the volume, position, and filling rate of the gap at high speed is desired.

  Conventionally, the following techniques have been proposed as a technique for determining the quality of a device under test by obtaining the size of a void in the device under test from the number of X-rays transmitted through the device under test. In Patent Document 1, in a void inspection method for detecting a void contained in a spherical solder bump formed on a substrate or a silicon wafer, following the capture of an X-ray transmission image of the inspection bump, the inspection target A model bump image that is similar to the shape of the bump and that does not have a void or is not determined as a defective product is taken in, and then the difference processing between the two bump images is performed. Obtain either the volume, area, or thickness of the void of the bump to be inspected from the image, and either the volume, area, or thickness of the void of the bump to be inspected, and the volume, area, or thickness of the void of the preset reference value What makes a pass / fail judgment by comparison is described.

Japanese Patent No. 4162386

  However, the method described in Patent Document 1 performs image difference processing to calculate the volume, area, and thickness of only the voids, and does not determine the thickness or filling rate of the non-measurement itself (paragraph). No. 0011 to paragraph No. 0015). Further, the one described in Patent Document 1 needs to capture a model bump image, and takes a long time for processing.

  The present invention has been made in view of the above-described problems, and calculates the thickness of the object to be measured and the accurate volume of the gap at high speed with a simple process, and determines the quality of the product from the filling rate of copper in the through hole. An object is to provide an X-ray inspection apparatus and an X-ray inspection method that can be determined.

The invention according to claim 1, which solves the above problem, is an X-ray source for irradiating a measurement object formed in a shape defined by a known material with X-rays, and a transmission X-ray count of the measurement object. Transmission X-ray image acquisition means for acquiring a transmission X-ray image based on the distribution of the acquired X-ray image, the acquired transmission X-ray image, and the relationship between the thickness of the material acquired in advance and the transmission X-ray count. A thickness estimating means for estimating the thickness distribution of the object to be measured; and a gap estimating means for determining that a portion thinner than a predetermined reference value is a portion corresponding to the gap portion based on the estimated thickness distribution; A gap shape estimating means for estimating the contour shape of the area corresponding to the estimated gap portion, a volume calculating means for calculating the volume of the gap portion from the contour shape, and a measurement for the volume to be measured By the volume ratio of the measured object That and a packing ratio calculating means for calculating the filling factor, it is X-ray inspection apparatus according to claim.
According to the present invention, from the acquired transmission X-ray image, the thickness distribution of the object to be measured is estimated, the void portion is further estimated, and the void shape is further estimated to obtain the void volume and filling rate. The volume and filling rate of the voids in the device under test can be calculated quickly and accurately.

Similarly, the invention according to claim 2 is the X-ray inspection apparatus according to claim 1, wherein the object to be measured is inclined with respect to the X-ray source, and the object to be measured is inclined by the inclination means. From the tilted X-ray transmission image acquired in a state tilted with respect to the X-ray source and the X-ray transmission image acquired without tilting with respect to the target object and the X-ray source, And a gap portion position estimating means for estimating the position of the gap portion.
According to the present invention, the gap position estimated in a state where the object to be measured is tilted with respect to the X-ray source is compared with the gap position estimated in a state where the measurement object is not tilted, and the thickness of the gap portion in the DUT is measured. The direction position can be estimated.

Similarly, the invention described in claim 3 irradiates an object to be measured formed in a shape defined by a known material with X-rays, and transmits X based on a distribution of transmitted X-ray counts of the object to be measured. A step of acquiring a line image; a step of estimating a thickness distribution of the object to be measured from a relationship between the acquired transmission X-ray image, the thickness of the material acquired in advance and the transmission X-ray count; and A step of estimating from the estimated thickness distribution that a portion thinner than a predetermined reference value is a portion corresponding to the void portion; and a step of estimating a contour shape of the region corresponding to the estimated void portion; A step of calculating the volume of the gap from the contour shape, and a step of obtaining a filling rate that is a ratio of the volume of the measured object to the volume that the object to be measured should have. Is that X-ray inspection method.
According to the present invention, from the acquired transmission X-ray image, the thickness distribution of the object to be measured is estimated, the void portion is further estimated, and the void shape is further estimated to obtain the void volume and filling rate. The volume and filling rate of the voids in the device under test can be calculated quickly and accurately.

Similarly, the invention according to claim 4 is the X-ray inspection method according to claim 3, wherein the transmitted X-ray image is acquired in a state where the object to be measured is tilted with respect to the X-ray source; And a step of estimating a position of a gap in the measurement object from a transmission X-ray image acquired without tilting the measurement object with respect to the X-ray source.
According to the present invention, the position of the void portion in the DUT is compared by comparing the transmitted X-ray image in a state where the object to be measured is tilted with respect to the X-ray source and the transmitted X-ray image in a state where the object is not tilted. Can be estimated.

  According to the X-ray inspection apparatus and the X-ray inspection method according to the present invention, the accurate volume of the void of the object to be measured can be calculated at high speed with a simple process.

It is a block diagram which shows the X-ray inspection apparatus which concerns on embodiment of this invention. It is a flowchart which shows the processing operation of the same X-ray inspection apparatus. The acquired transmission X-ray image etc. are shown, (a) is a transmission X-ray image, (b) is a graph which shows the signal intensity profile of (a), (c) is the transmission X shown by (a). This is an image in which the signal intensity of the line image is emphasized. It is a figure which shows the relationship between an X-ray transmission image and the thickness of copper. FIG. 6 shows the result of converting an X-ray transmission image into the copper thickness of the object to be measured, where (a) is a 3D image, (b) is an image from the Z direction, (c) is an x- An image corresponding to a cross section along the z plane, (d) is an image corresponding to a cross section along the yz plane of (a). It is a figure which shows the relationship between the state of a space | gap, and the profile of X-ray image signal intensity | strength. It is a graph which shows the thickness dimension of the direction of a to-be-measured object to the same X-ray inspection apparatus. It is a figure which shows the method of estimating the shape of a space | gap part from the distribution state of thickness. It is a figure which shows the 1st method of calculating the filling rate of a through hole with the X-ray inspection apparatus which concerns on embodiment. It is a figure which shows the 2nd method of calculating the filling rate of a through hole with the same X-ray inspection apparatus. It is a figure which shows the relationship between the position of the space | gap in a to-be-measured object, and the acquired X-ray transmission image.

  Hereinafter, an X-ray inspection apparatus and an X-ray inspection method according to embodiments for carrying out the present invention will be described. FIG. 1 is a block diagram showing an X-ray inspection apparatus according to an embodiment of the present invention. The X-ray inspection apparatus 100 according to the embodiment obtains the volume and position of a void portion V (Void) of a copper filling portion filled by plating in the through hole H of the substrate B as the object to be measured S. The copper filling portion as the object to be measured S is formed by filling the through hole H with uniform copper, and has a predetermined shape, that is, a cylindrical shape having an upper surface and an upper surface. Further, the X-ray inspection apparatus 100 detects the position of the gap V in the measurement object S, for example, the upper part, the center part, and the lower part. In FIG. 1, the copper filling portion, which is the substrate B, the through hole H, and the object to be measured S, is greatly described with respect to the X-ray inspection apparatus 100.

  As shown in FIG. 1, the X-ray inspection apparatus 100 acquires an X-ray source 110 that irradiates the measurement object S with X-rays and a transmission X-ray image based on the distribution of the transmission X-ray count number of the measurement object S. And an X-ray camera 120 that is a transmission X-ray image acquisition means, and a DUT stage 130 on which the DUT S is arranged. The X-ray camera 120 is connected to a processing unit 140 that detects the volume and position of the gap V based on the acquired transmission X-ray image. Further, the processing unit 140 performs a driving process for the X-ray source 110, the X-ray camera 120, and the measurement object stage 130.

  The X-ray source 110 irradiates X-rays along the z axis in FIG. The X-ray camera 120 acquires a transmission X-ray image on the xy plane corresponding to the transmission X-ray count number that penetrates the measurement object S along the z direction from the lower surface toward the upper surface. In the portion where there is no void V, the thickness dimension of the copper filling layer is large and the transmission X-ray count is reduced, and as a result, the signal intensity of the transmission X-ray image is weakened. On the other hand, in the portion where the void portion V exists, the size of the copper filling layer is small and the amount of transmitted X-rays is increased. As a result, the signal intensity of the transmitted X-ray image is increased.

  The processing unit 140 determines the thickness distribution of the measurement object S from the relationship between the transmission X-ray image acquired by the X-ray camera 120, the thickness of the same material as the copper filling layer acquired in advance and the transmission X-ray count. A thickness estimation means 141 for estimating the gap, a gap estimation means 142 for estimating that a portion thinner than a predetermined reference value based on the estimated thickness distribution is a portion corresponding to the gap, and the estimated gap Void shape estimation means 143 for estimating the contour shape of the portion, volume calculation means 144 for calculating the volume of the void portion from the contour shape, and filling rate calculation for calculating the filling rate of the copper laminated portion with respect to the volume of the through hole H Means 145, gap position estimating means 146, and drive control means 147 for controlling the driving of the X-ray source 110, the X-ray camera 120 and the DUT stage 130.

  The processing unit 140 includes a computer having auxiliary storage means such as a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and a hard disk drive (HDD). The functions of the thickness estimation means 141, the gap estimation means 142, the gap shape estimation means 143, the volume calculation means 144, the gap position estimation means 146, and the drive control means 147 are executed by executing a processing program stored in the HDD or the like. Is realized.

  The X-ray source 110 is connected to an input unit 150 composed of a keyboard, a mouse, a touch panel, etc., and an image display unit 160 composed of a liquid crystal display. An operator's instruction is input from the input unit 150, and various images such as a transmitted X-ray image and an image being processed are displayed on the image display unit 160.

  Next, a process for detecting the volume and position of the void portion V of the measurement object S by the X-ray inspection apparatus 100 will be described. FIG. 2 is a flowchart showing the processing operation of the X-ray inspection apparatus. First, the measurement object S is placed on the measurement object stage 130. At this time, the object to be measured S is not inclined with respect to the X-ray irradiation direction z of the X-ray source 110 with the object stage 130 as the initial position. That is, in this state, the center of the measurement object S is arranged along the z axis.

  Then, under the control of the drive control means 147, the X-ray source 110 irradiates the measurement object S with X-rays and acquires a transmission X-ray image with the X-ray camera 120 (step S1). At this time, the X-rays pass through the object to be measured S from the lower surface toward the upper surface. Therefore, the density of the transmitted X-ray image obtained is determined in accordance with the count of transmitted X-rays at each part of the xy plane corresponding to the measurement object S.

  FIG. 3 shows the acquired transmission X-ray image, etc. (a) is a transmission X-ray image, (b) is a graph showing the signal intensity profile of (a), and (c) is shown by (a). This is an image in which the signal intensity of the transmitted X-ray image is emphasized. In this example, the central portion 210 of the object S to be measured is dark (FIG. 3A), and it can be seen that the count number of the central portion 210 is increased in the signal intensity profile. Further, when the signal intensity of the transmission X-ray image in FIG. 3A is emphasized, the central portion 210 becomes clear.

  Next, the thickness estimation means 141 converts the transmission X-ray count obtained from the transmission X-ray image into a copper thickness value at each position on the xy plane (step S2), and the object to be measured The thickness distribution of S is estimated (step S3). The conversion from the transmission X-ray count number to the thickness of the object S to be measured is first made into a transmission ratio obtained by dividing the count of each point of the X-ray transmission image of the object S to be measured, which is a copper-filled layer, by the total transmission value. Substituting this transmission ratio into the conversion function to copper fill layer thickness. This conversion function is obtained in advance by measuring a copper filling layer as a reference. Thereby, the distribution of the copper thickness (z direction) in the xy plane can be acquired.

  The conversion function to copper filling layer thickness is demonstrated. FIG. 4 is a diagram showing the relationship between the X-ray transmission image and the copper thickness. As shown in FIG. 4A, the intensities I1 to In of transmitted X-rays by X rays having an irradiation intensity I0 are obtained using a number of copper plates having thicknesses T0 to Tn as samples. Then, as shown in FIG. 4B, the relationship with the X-ray transmittance (Ii / I0) at the thickness Ti is calculated from the X-ray transmittance from T = f (Ii / I0) (FIG. 4B). Define the conversion function for copper thickness.

  FIG. 5 shows the result of converting the X-ray transmission image into the thickness dimension of the copper material of the object to be measured, where (a) shows a three-dimensional thickness distribution and (b) shows the xy plane. The figure which showed thickness distribution in the above, (c) is a figure equivalent to the cross section along the xz plane of (a), (d) is equivalent to the cross section along the yz plane of (a). It is a figure to do. In this example, it can be seen that there is a region having a small thickness dimension corresponding to the gap V in the vicinity of the central portion in the xy plane.

  Note that the actual shape of the void V cannot be determined because it is obtained from the X-ray transmission image and determined by the profile. FIG. 6 is a diagram showing the relationship between the state of the air gap and the profile of the X-ray image signal intensity. For example, when the void portion V has an elliptical cross-sectional shape as shown in FIG. 6A, the transmitted X-ray intensity is the dimension in the height direction of the void portion V as shown in FIG. It is determined by h1, h2, h3,. For this reason, the intensity of the transmitted X-ray of the void V having an elliptical cross section passes through the void (the right diagram in FIG. 6B) where the void V has heights h1, h2, h3,. This is the same as that shown in FIG. 6C. For this reason, the shape of the space V is not specified from the transmission signal profile for X-rays.

  Next, the gap estimation unit 142 estimates the position of the gap estimation unit 142 on the xy plane (step S4). FIG. 7 is a graph showing the thickness dimension of the object to be measured. In the space | gap part estimation means 142, when the breadth dimension X of the space | gap part V and the depth dimension Y are larger than the predetermined threshold value predetermined, it estimates that it is a location where the space | gap part V exists.

  Further, the shape of the region corresponding to the space V is estimated by the space shape estimation means 143. FIG. 8 is a diagram showing a method for estimating the shape of the gap from the thickness distribution state. The gap shape estimation means 143 determines the reference surface 220 and the contour surface 230 of the area whose thickness is reduced by the gap V in the area estimated as the gap V in the acquired thickness distribution image. Thus, the shape of the gap V is estimated.

  The reference surface 220 and the contour surface 230 can be obtained by processing the thickness distribution graph shown in FIG. 8 by a method such as a least square method. The reference plane 220 can be accurately estimated from the volume of the gap by measuring in advance with an existing surface shape measuring instrument such as a confocal microscope or an interference microscope.

  Then, the region surrounded by the obtained reference surface 220 and contour surface 230 is integrated by a known method to obtain the volume of the gap V (step S6). In this process, even when the shape of the gap V is different, it may be calculated as the same volume.

Next, the filling rate calculation means 145 calculates the filling rate of copper in the through hole H (step S7). When the diameter of the through hole d, the height was is h, the volume of the through hole becomes V0 = πhd ^2/4. The measured volume V1 of the copper filling portion is V1 = (V0−v), where v is the volume of the gap V. Therefore, the filling rate is obtained as V1 / V0.

  In the X-ray inspection apparatus 100 according to the embodiment, the filling rate is calculated by the following method for simple calculation. First, the first method will be described. FIG. 9 is a diagram illustrating a first method for calculating the through-hole filling rate in the X-ray inspection apparatus according to the embodiment. Let V1 be the volume of the packed bed, which is the object to be measured S, obtained from the X-ray transmission image. The diameter of the large opening (for example, the lower surface) is approximated by a circle, and this diameter is d1. V1 is obtained by converting the X-ray transmission image into a copper thickness and integrating the copper thickness data in the circular region represented by d1 with the copper thickness data linked to the XY coordinates. Next, the volume of the through hole H is approximately determined as V0 from the diameter d1 and the height H1 of the opening on the lower surface of the through hole. And the filling rate V0 / V1 is calculated | required from this Vo and V1. From this filling rate, the quality of the entire through hole can be evaluated. A design value may be used for V0.

  Next, the second method will be described. In this method, the filling rate in a range of a predetermined diameter db selected from the measured object S is obtained. FIG. 10 is a view showing a second method for calculating the filling rate of the through hole by the X-ray inspection apparatus. The diameter of the small side (for example, the upper surface) of the opening of the height distribution of the measurement object S obtained from the X-ray transmission image is circularly approximated, and this diameter is defined as d2. Furthermore, this diameter d2 is multiplied by a predetermined ratio b, and the diameter of the cylindrical portion for measuring the filling rate is defined as db. Thereby, the volume Vb0 of the cylinder to be measured is obtained from the opening db and the height H1. The volume Vb is obtained by converting the X-ray transmission image into a copper thickness and integrating the copper thickness data in the circular region represented by db with the copper thickness data linked to the XY coordinates. The filling rate Vb / Vb0 is determined from the volume Vb0 of the target cylinder and the measured volume Vb. From this filling rate, a minute abnormality in the through hole, such as a void, can be evaluated. The ratio b can be freely selected according to the purpose.

  Further, in the present embodiment, the position of the gap V is estimated. Therefore, the device under test stage 130 is driven under the control of the drive control means 147, and the device under test S is tilted by a predetermined angle with respect to the X-ray radiation direction (step S8). Note that the X-ray source 110 and the X-ray camera 120 can be tilted with respect to the measured object S instead of tilting the measured object S.

  In this state, a transmission X-ray image is acquired by the X-ray camera 120 (step S9), and compared with a transmission X-ray image acquired in a state where the measurement object stage 130 is not tilted (acquired in step S1). And the position of the space | gap part V is estimated based on the change of the position estimated as the space | gap part V (step S10). FIG. 11 is a diagram showing the relationship between the position of the air gap in the object to be measured and the acquired X-ray transmission image. In this example, the upper part of the device under test S is tilted to the right in the figure. When the object to be measured S is tilted from the state in which the object to be measured S is not tilted (FIG. 11A), a projection image corresponding to the gap portion V is obtained according to the vertical position of the gap portion V in the measured object S. You can see that it moves.

  That is, when the gap V is near the bottom surface, the projected image of V is shifted to the left from the center as shown in FIG. 11B in the transmission X-ray image. Further, when the gap V is in the center, in the transmission X-ray image, the projected image of V is at the center as shown in FIG. Further, when the gap V is in the vicinity of the upper surface, in the transmitted X-ray image, the projected image of V moves to the right from the center as shown in FIG. In the present embodiment, the position of the gap V is detected using this phenomenon.

  In this example, the approximate position of the gap V can only be obtained, but the inclination angle of the object S, the dimension of the object S, and the moving dimension of the projected image of the gap V can be numerically analyzed. For example, it is possible to accurately calculate the position of the gap portion V in the measurement object S in the z direction.

  As described above, according to the X-ray inspection apparatus 100 according to the embodiment, the accurate volume, filling rate, and position of the void of the object to be measured can be calculated at high speed by a simple process.

DESCRIPTION OF SYMBOLS 100: X-ray inspection apparatus 110: X-ray source 120: X-ray camera 130: DUT stage 140: Processing part 141: Thickness estimation means 142: Gap part estimation means 143: Gap part shape estimation means 144: Volume calculation means 145: Filling rate calculation means 146: gap position estimation means 147: drive control part 150: input means 160: image display means 210: central part 220: reference surface 230: contour surface B: substrate H: through hole S: measured object

Claims (4)

An X-ray source for irradiating an object to be measured formed in a shape defined by a known material with X-rays;
A transmission X-ray image acquisition means for acquiring a transmission X-ray image based on a distribution of transmission X-ray counts of the object to be measured;
A thickness estimating means for estimating a thickness distribution of the object to be measured from the acquired transmitted X-ray image and the relationship between the thickness of the material acquired in advance and the count of transmitted X-rays;
Based on the estimated thickness distribution, a gap estimation means that a place thinner than a predetermined reference value is a place corresponding to the gap,
A void shape estimating means for estimating a contour shape of a region corresponding to the estimated void portion;
Volume calculating means for calculating the volume of the gap from the contour shape;
A filling rate calculation means for obtaining a filling rate which is a ratio of the volume of the measured object to be measured to the volume to be measured;
An X-ray inspection apparatus comprising: Tilting means for tilting the object to be measured with respect to the X-ray source;
Transmission X-ray image acquired in a state where the measurement object is inclined with respect to the X-ray source by the tilting means, and transmission X-ray acquired in a state where the measurement object is not inclined with respect to the X-ray source. The X-ray inspection apparatus according to claim 1, further comprising: a gap position estimation unit that estimates a position of the gap in the object to be measured from an image. Irradiating an object to be measured formed in a shape defined by a known material with X-rays;
Obtaining a transmission X-ray image based on a distribution of transmission X-ray counts of the object to be measured;
Estimating the thickness distribution of the object to be measured from the acquired transmission X-ray image and the relationship between the thickness of the material acquired in advance and the transmission X-ray count;
From the estimated thickness distribution, estimating that a portion thinner than a predetermined reference value is a portion corresponding to the gap,
Estimating a contour shape of an area corresponding to the estimated gap portion;
Calculating the volume of the gap from the contour shape;
Determining a filling factor, which is a ratio of the volume of the measured object to the volume that the object should have;
An X-ray inspection method comprising: Acquiring a transmission X-ray image acquired in a state where the object to be measured is inclined with respect to the X-ray;
Estimating a position of the gap in the measurement object from a transmission X-ray image acquired in a state where the measurement object is not inclined with respect to the X-ray;
The X-ray inspection method according to claim 3, further comprising: