JP2011258850A - Void detection method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detection method and a device for a void which exists in a glued wafer when manufacturing the glued wafer.SOLUTION: When two wafers are glued and bonded together to manufacture a glued wafer, a void is detected in the glued wafer based on a transmission shape made by the boundary of a bonding part and a non-bonding part in the gluing process, the presence of a void in the glued wafer is judged by the contrast between the transmission shape in the wafer where no void is actually generated and the transmission shape in the glued wafer, the shape of a glued border is approximated by a quadratic curve to obtain a curvature at the apex of the quadratic curve, the obtained curvature and a curvature in the case where no void predetermined for every position of the glued border is generated are contrasted to obtain an error, and it is judged that there is the void in the glued wafer when the obtained error exceeds a prescribed value.

Description

  The present invention relates to a void detection method and apparatus, and more particularly to a method and apparatus for detecting voids present in a bonded wafer when a bonded wafer is manufactured.

  In recent years, a wafer having an SOI (Silicon on Insulator) structure (hereinafter referred to as an “SOI wafer”) has attracted attention for further improvement in device performance. The SOI wafer has a structure in which a silicon single crystal layer (SOI layer) is formed on a buried oxide film (Buried Oxide, BOX layer), and has a parasitic capacitance much higher than that of a device manufactured on a bulk substrate. It is expected to be a next-generation high-performance VLSI wafer excellent in high-speed operation, low power consumption, high withstand voltage characteristics, radiation resistance, etc. due to its small and simple manufacturing process and easy device miniaturization.

  One method of manufacturing an SOI wafer is a bonding method. In this bonding method, the surfaces of the silicon support substrate and / or the active substrate for manufacturing the device are oxidized, and then bonded to each other and subjected to heat treatment at a high temperature of about 1200 ° C. to bond the oxide films to each other or the oxide film and silicon. This is a method for manufacturing an SOI wafer.

  The bonding method has advantages that the crystal quality of the SOI layer and the breakdown voltage characteristic of the BOX layer are high compared to the SIMOX method of manufacturing an SOI wafer by injecting oxygen ions into the silicon substrate and performing a heat treatment, The uniformity of the film thickness is inferior, and voids (voids) that are non-bonded regions between two wafers may occur. Due to such voids, the bonded wafer is peeled off in the device process and a wafer defect occurs. Therefore, various techniques for preventing the generation of voids have been proposed so far.

  For example, Patent Document 1 proposes a method for manufacturing a bonded wafer that improves the yield rate of bonded wafers by setting the bonding speed of two semiconductor substrates corresponding to the state of the main surface of the semiconductor substrate. is doing.

  Patent Document 2 proposes a bonding apparatus that prevents the generation of voids in the peripheral portion of the bonded substrate by controlling the bonding progress speed within a specified range.

  On the other hand, in Patent Document 3, when two wafers are bonded, the inside of the chamber in which the wafers are bonded is depressurized and bonded by the action force of only the weight of the stacked wafers, thereby generating voids at the bonding interface. We propose a bonded wafer manufacturing apparatus and manufacturing method that can effectively and easily suppress the bonding, and can bond together without unevenness.

JP 7-245250 A JP 2007-194347 A JP 2009-64827 A

  However, in the methods described in Patent Documents 1 to 3, it is still difficult to completely prevent the generation of voids in the bonded wafer. Therefore, an inspection process is required to determine the presence or absence of voids after manufacturing the bonded wafer and to remove defective wafers having voids. Conventionally, the determination of the presence / absence of voids is generally performed by visual inspection by an operator using a void inspection device using infrared light. For example, when the size of the void is small, the determination is erroneous. There is a fear.

  Therefore, an object of the present invention is to provide a method and an apparatus for detecting a void existing in a bonded wafer with high accuracy when manufacturing the bonded wafer.

  The inventors have investigated the mechanism by which voids are generated when manufacturing a bonded wafer, and the propagation drawn by the boundary between the bonded portion and the non-bonded portion in the bonding process (hereinafter referred to as “bonded boundary”). When the shape and void generation are closely related, and no void occurs, the curvature at the vertex of the quadratic function when the propagation shape is approximated by a quadratic function is determined for each position of the bonding boundary. It was found to exist within a predetermined range. Therefore, as a result of earnestly examining the method of determining the presence or absence of voids when manufacturing a bonded wafer, the propagation shape of the bonding boundary is approximated by a quadratic curve when no void is generated, and the apex of the quadratic curve The curvature at is obtained in advance for each position of the bonding boundary as a curvature condition value, and the actual curvature of the propagation shape of the bonding boundary when bonding two wafers is compared with the curvature condition value. When the actual curvature error with respect to the curvature condition value exceeds a predetermined value, it has been found that it is effective to determine that a void exists in the bonded wafer, and the present invention has been completed.

  That is, the void detection method of the present invention is based on the propagation shape drawn by the boundary between the bonded portion and the non-bonded portion in the bonding process when two wafers are bonded and bonded to produce a bonded wafer. The presence or absence of voids in the wafer after the bonding is determined.

  Further, in the void detection method of the present invention, the presence or absence of voids in the wafer after bonding is based on a comparison between the propagation shape in a wafer that does not actually generate voids and the propagation shape in the wafer after bonding. It is characterized by determining.

  In the void detection method of the present invention, the propagation shape is compared by detecting the boundary from an image of the bonded wafer photographed by photographing means for each position of the boundary, and then determining the propagation shape of the boundary. Performing with the actual curvature at the apex of the quadratic curve obtained by approximating with a quadratic curve, and approximating the propagation shape with a quadratic curve for each position of the boundary for the wafer that does not actually generate voids Then, the curvature at the apex of the quadratic curve is obtained in advance as a curvature condition value, and when an error in the actual curvature with respect to the curvature condition value exceeds a predetermined value, a void exists in the bonded wafer. It is characterized by determining.

  Furthermore, in the void detection method of the present invention, the propagation speed of the boundary is taken into account when determining the presence or absence of the void.

  Further, in the void detection method of the present invention, for the wafer without the occurrence of voids, the propagation speed is obtained in advance as a propagation speed condition value for each boundary position, and the boundary is determined for each boundary position. After determining the actual propagation speed, if an error in the actual propagation speed with respect to the propagation speed condition value exceeds a predetermined value, it is determined that a void exists in the bonded wafer. is there.

  The void detection apparatus of the present invention is a device for detecting voids in a bonded wafer when bonding and bonding two wafers to produce a bonded wafer. An analysis device is provided that detects a void in the bonded wafer based on the propagation shape drawn by the boundary with the non-bonded portion.

  Further, in the void detection device of the present invention, the analysis device stores, as a curvature condition value, the curvature of the boundary propagation shape obtained in advance for each position of the boundary when no void occurs. A storage unit for storing an image of the bonded wafer imaged by an imaging apparatus; a curvature calculating unit for approximating the boundary with a quadratic curve to obtain an actual curvature at the apex of the quadratic curve; and the curvature condition And a determination unit that determines that a void is present at the interface between the two wafers when an error in the actual curvature with respect to the value exceeds a predetermined value.

  In the void detection device of the present invention, the analysis device further includes a propagation velocity calculation unit that obtains an actual propagation velocity of the boundary, and the storage unit is a void that is obtained in advance for each position of the boundary. Is further stored as a propagation velocity condition value when the boundary propagation velocity does not occur, and the determination unit, when an error of the actual propagation velocity with respect to the propagation velocity condition value exceeds a predetermined value, It is determined that a void exists in the bonded wafer.

  ADVANTAGE OF THE INVENTION According to this invention, the presence or absence of the void in a bonded wafer can be detected with high precision during manufacture of a bonded wafer. Moreover, since it is not necessary to inspect for the presence or absence of voids after manufacturing the bonded wafer, the productivity of the bonded wafer can be improved.

It is a figure which shows the structure of (a) top view, (b) side view, and (c) analysis apparatus of the bonded wafer manufacturing apparatus in which the test | inspection apparatus of this invention was integrated. It is a schematic diagram of (a) a bonded wafer and (b) a detected bonding boundary. (A) The bonding boundary in the case where a void is generated, and (b) A schematic view showing a state in which the bonding boundary is propagated and a void is generated. (A)-(c) is a schematic diagram which shows a mode that the bonding boundary propagates in the bonding process. It is a figure which shows the structure of the analyzer in the case of considering the propagation speed of a bonding boundary in the case of determination of the presence or absence of a void.

Hereinafter, a void detection method and apparatus according to the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a bonded wafer manufacturing apparatus in which the void detection apparatus of the present invention is incorporated. The manufacturing apparatus 1 includes an active wafer cassette 11a and a support wafer cassette 11b, a wafer transfer unit 12, a wafer aligner 13, an infrared light source 14, a bonding chamber 15, a decompression unit 16, and an imaging unit 17. And an analysis device 18, a display device 19, a control device 20, and a non-defective wafer cassette 21a and a defective wafer cassette 21b. The void detection device 2 includes an imaging unit 17 and an analysis device 18, and the analysis device 18 includes a storage unit 18a, a bonding boundary detection unit 18b, a curvature calculation unit 18c, and a determination unit 18d. . Hereinafter, each component will be described.

  The active-side wafer cassette 11a and the support-side wafer cassette 11b store the active-side wafer A and the support-side wafer B that are used for manufacturing bonded wafers, respectively.

  The wafer transfer means 12 takes out the support-side wafer A and the active-side wafer B stored in the active-side wafer cassette 11a and the support-side wafer cassette 11b, transfers them to the wafer aligner 13, and positions the active-side wafer A that has been positioned. The support-side wafer B is transported from the wafer aligner 13 to the stage 15 b in the bonding chamber 15. Further, the bonded wafer manufactured in the bonding chamber 15 is transferred to the non-defective wafer cassette 21a or the defective wafer cassette 21b based on the detection result of the void in the wafer. As the wafer transfer means 12, a general back surface adsorption type robot transfer apparatus can be used.

  The wafer aligner 13 rotates the active side wafer A and the support side wafer B and positions them at a predetermined reference angle.

  The infrared light source 14 emits infrared light for observing the propagation state of the bonding boundary when the active wafer A and the support wafer B are bonded together. As the infrared light source 14, for example, a semiconductor laser can be used.

The bonding chamber 15 is a chamber for manufacturing the bonded wafer C by bonding the active side wafer A and the support side wafer B therein, and uses, for example, a stainless steel container having a cylindrical shape or a polygonal shape. can do. The bonding chamber 15 is configured such that a wafer can be taken in and out from the side surface thereof, and a stage 15b on which the support side wafer B is placed is provided. The upper lid 15a is preferably made of a transparent material such as quartz so that the progress of the bonding of the two wafers can be confirmed.
The material of the stage 15b is not particularly limited. Further, the shape of the stage 15b is not particularly limited, but is preferably a convex shape or a convex shape close to flat in terms of the effect of reducing voids.

  The decompression means 16 decompresses the inside of the bonding chamber 15 to a predetermined pressure. By reducing the pressure inside the bonding chamber 15, even when the diameter of the wafer exceeds 300 mm, it is possible to quickly remove the air remaining at the bonding interface and suppress the generation of voids. The decompression means 16 can be a decompression pump, for example.

  Here, the pressure in the bonding chamber 15 is set to 0.01 kPa to normal pressure. The reason why the lower limit of the pressure is set to 0.01 kPa is that the throughput is increased and the productivity is lowered, and the bonded wafer may be contaminated by the dust generated from the components in the chamber 15. .

  The imaging means 17 detects the reflected light of the infrared light irradiated to the bonded wafer C by the infrared light source 14 and images the bonding boundary D in the bonded wafer C. The photographing means 17 can be an infrared camera, for example.

  As will be described in detail below, the analysis device 18 analyzes the propagation shape of the bonding boundary D from the image of the bonded wafer C photographed by the photographing means 17, and based on the propagation shape, in the wafer after bonding. Detect voids.

  The storage unit 18a stores images photographed at predetermined time intervals from the start to the end of the bonding by the photographing unit 17, and the position of the bonding boundary D at the interface between the active side wafer A and the support side wafer B. The curvature for the bonding boundary D obtained in advance for each case where no void is generated is stored as a curvature condition value.

  The bonding boundary detection unit 18b detects a bonding boundary D existing in the bonded wafer C from two temporally continuous images stored in the storage unit 18a.

  The curvature calculation unit 18c approximates the bonding boundary D detected by the bonding boundary detection unit 18b with a quadratic curve, and obtains the curvature at the vertex of the quadratic curve.

  The determination unit 18d compares the curvature obtained by the curvature calculation unit 18c with the curvature condition value stored in the storage unit 18a to obtain an error. As will be described in detail later, the obtained error is 10%. When exceeding, it determines with a void existing in the bonded wafer C. FIG.

  The display device 19 is configured to display an image of the bonded wafer C photographed by the photographing means 17 so that an operator can visually check the progress of wafer bonding.

  The control device 20 controls the stage 15b provided in the bonding chamber 15 so that the bonded wafer C is manufactured by bonding the active wafer A and the support wafer B together.

  The non-defective product wafer cassette 21a and the defective product wafer cassette 21b store wafers determined to be non-defective products and defective products among the bonded wafers C manufactured in the bonding chamber 15, respectively.

  Such a void detection device 2 can detect the presence of voids in the bonded wafer. Further, by using the bonded wafer manufacturing apparatus 1 in which the void detection device 2 is incorporated, a bonded wafer having no void can be manufactured.

Next, the void detection method of the present invention will be described.
In the detection method of the present invention, when two wafers are bonded and bonded to produce a bonded wafer, the bonding is performed based on the propagation shape drawn by the boundary between the bonded portion and the non-bonded portion in the bonding process. It is characterized by detecting voids in later wafers. The presence or absence of voids in the wafer after bonding is determined by comparing the propagation shape in a wafer that does not actually generate voids with the propagation shape in the wafer after bonding, and the shape of the bonding boundary is secondarily determined. Approximate with a curve to obtain the curvature at the apex of the quadratic curve, and compare the obtained curvature with the curvature in the case where no void is obtained in advance for each position of the bonding boundary to obtain an error and obtain When the obtained error exceeds a predetermined value, it is determined that a void exists in the bonded wafer.

  In the present invention, in the bonded wafer manufacturing apparatus 1 shown in FIG. 1, at one point on the end of the main surface of the support side wafer B (active side wafer A) placed on the stage 15 b in the bonding chamber 15. Then, a bonded wafer C is manufactured by overlapping and bonding one end portion of the active side wafer A (support side wafer B).

  At that time, the propagation state of the bonding boundary D is constantly observed from the start to the end of the bonding. Specifically, the main surface of the bonded wafer C is imaged by the imaging means 17 through the outer lid 15a of the bonding chamber 15 at predetermined time intervals (that is, at each bonding boundary position). Then, an image as schematically shown in FIG. 2A is obtained, and a bonding boundary D existing in the bonded wafer C is photographed. The photographed image is displayed on the display device 19 and stored in the storage unit 18a.

  As shown in FIG. 2B, a difference between two temporally continuous images stored in the storage unit 18a, that is, a difference in luminance value of each pixel of the image is obtained, and appropriate image processing is performed. The region where the bonding boundary D has propagated during the photographing time interval can be extracted. When the photographing time interval is sufficiently small, for example 0.05 seconds, the propagation shape of the bonding boundary D can be regarded as a curve.

  As described above, when the void does not occur, the inventors have found that the curvature at the vertex of the quadratic function when the propagation shape of the bonding boundary D is approximated by a quadratic function is It was found that each position is within a predetermined range, and for each position of the bonding boundary D, an error with respect to the average value is approximately 10% or less. On the other hand, when a void occurs, as shown in FIG. 3A, when the shape of the bonding boundary D is greatly distorted and the propagation of the bonding boundary D proceeds, the void as shown in FIG. E occurs. Therefore, for each position of the bonding boundary D, an average value of curvature when no void E occurs is obtained in advance as a curvature condition value and stored in the storage unit 18a.

  When the bonded wafer C is actually manufactured by bonding the active side wafer A and the support side wafer B in a state where the curvature condition value in the case where the void E does not occur is prepared in advance, the following A determination process is performed to determine whether or not there is a void E in the bonded wafer C. That is, first, the main surface of the bonded wafer C is photographed by the photographing means 17 at a predetermined time interval, and the photographed image is stored in the storage unit 18a.

  Next, the pasting boundary detection unit 18b reads two temporally continuous images stored in the storage unit 18a, obtains a difference between the two images, and extracts the pasting boundary D. Subsequently, the curvature calculation unit 18c approximates the bonding boundary D with a quadratic curve and calculates the curvature at the apex of the quadratic curve. Finally, the determination unit 18d compares the actual curvature and the curvature condition value stored in the storage unit 18a. If the error of the actual curvature with respect to the curvature condition value exceeds 10%, the void E is It is determined that it exists.

  In this way, when manufacturing a bonded wafer, the void which exists in this bonded wafer can be detected with high precision.

  Note that the curvature with respect to the bonding boundary D described above varies depending on the bonding conditions such as the wafer size, surface state, reduced pressure level, bonding start position, and the like. Therefore, a curvature condition value is prepared in advance for each bonding condition. In the case of detecting the void E, the curvature condition value for the actual bonding condition is used.

  As described above, the bonding boundary D is approximated by a quadratic curve, and the curvature at the vertex of the quadratic curve is used as a determination condition for the presence of voids in the bonded wafer, thereby accurately determining the presence or absence of void E. Although there is a possibility that the void E cannot be detected as a change in the propagation shape in the vicinity of the outermost peripheral portion of the bonded wafer, the propagation of the bonding boundary D is detected in addition to the detection of the change in the propagation shape of the bonding boundary D. By taking the speed into account, the determination accuracy of the presence or absence of void E can be further improved. That is, when the bonding boundary D propagates as shown in FIGS. 4A to 4C, the propagation speed of the bonding boundary D when the void E does not occur is examined. As in the case of the curvature. For each position of the bonding boundary D, it has been found that the error with respect to the average value is approximately 10% or less.

  Therefore, as shown in FIG. 5, the analysis device 18 is configured to further include a propagation speed calculation unit 18 e that calculates the propagation speed of the bonding boundary D, and the bonded wafer C is applied to the bonded wafer C as in the case of the curvature. The average value of the propagation speed when no void E occurs is obtained in advance for each position of the bonding boundary D as a propagation speed condition value, and stored in the storage unit 18a. Then, when manufacturing the bonded wafer C by bonding and bonding two wafers, the actual propagation speed of the bonding boundary D is obtained at each position of the bonding boundary D, and the actual propagation speed and When the error of the actual propagation speed with respect to the propagation speed condition value exceeds 10% compared with the previously determined propagation speed condition value read from the storage unit 18a, it is determined that the void E exists in the bonded wafer C. To do.

  Thus, when the determination unit 18d determines whether or not there is a void in the bonded wafer, the propagation shape of the bonding boundary is approximated by a quadratic curve and added to the curvature at the vertex of the quadratic curve. By taking into account the propagation speed of the bonding boundary, it is possible to reliably detect voids present in the bonded wafer.

Examples of the present invention will be described below.
(Invention Example 1)
300 bonded wafers C are manufactured using the bonded wafer manufacturing apparatus 1 in which the void detection device 2 of the present invention shown in FIG. 1 is incorporated, and the presence or absence of the void E in the bonded wafer C is determined. . At that time, only the curvature at the vertex when the propagation shape of the bonding boundary D was approximated by a quadratic curve was considered. The specific procedure is as follows.
A single crystal silicon wafer having a diameter of 200 mm is prepared as the active side wafer A and the support side wafer B, and an oxide film is formed only on the surface of the active side wafer A. First, the active wafer A was taken out from the active wafer cassette 11a, aligned through the wafer aligner 13, and then placed on the stage 15b in the bonding chamber 15 that can be decompressed. Next, after positioning the support side wafer B via the wafer aligner 13, the support side wafer B was placed on the active side wafer A placed on the stage 15 b in the bonding chamber 15. At this point, the propagation of bonding has not yet started.
Subsequently, the pressure in the bonding chamber 15 is reduced to 0.1 kPa, and weighting is applied from the end region of the wafer to start propagation of the bonding boundary D and start acquiring an image of the propagation shape of the bonding boundary D. . Images were saved every 05 seconds.
Thereafter, after the bonding process was completed, the stored propagation shape image of the bonding boundary D was analyzed, and the presence or absence of the void E in the bonded wafer C was determined. In that case, it determined based only on the curvature in the vertex at the time of approximating the bonding boundary D with a quadratic curve.
Finally, after the inside of the bonding chamber 15 is returned to normal pressure, the bonded wafer C that has been subjected to the bonding process is determined to be non-defective and defective based on the determination result, and the bonded wafer determined to be non-defective. C was stored in the non-defective wafer cassette 21a, and the bonded wafer C determined to be defective was stored in the defective wafer cassette 21b. This process was repeated continuously for 300 sheets, and the presence or absence of void E was determined.
As a result of the above determination, two sheets were determined to be defective products having voids, and the remaining 298 sheets were determined to be non-defective products having no voids. Next, two wafers determined to be defective products were visually inspected using infrared light for each of the two wafers using a conventional void inspection apparatus. Was confirmed to exist. Similarly, visual inspection was performed on 298 wafers that were determined to be non-defective products, and it was confirmed that all were non-defective products. Further, out of the two wafers in which the void E was observed, a very small size of the void E of about 0.5 mm was observed in one wafer. This indicates that the void detection device 2 of the present invention can reliably detect even a minute void as a change in propagation shape.

(Invention Example 2)
As in the case of Invention Example 1, 300 bonded wafers C are manufactured using the bonded wafer manufacturing apparatus 1 in which the void detection device 2 of the present invention shown in FIG. The presence or absence of void E in the inside was determined. At that time, in addition to the curvature at the apex when the propagation shape of the bonding boundary D was approximated by a quadratic curve, the determination was made in consideration of the propagation speed of the bonding boundary D.
As a result, one sheet was determined to be a defective product having void E, and the remaining 299 sheets were determined to be non-defective products having no void E. Next, when one wafer determined to be defective is subjected to visual inspection using a conventional void inspection apparatus, that is, an infrared ray for each wafer, the outermost peripheral portion of the wafer (the outermost periphery) It was confirmed that void E was present in a region within 5 mm from the end). Similarly, when the above-mentioned non-defective product was determined and visual inspection was performed on 299 wafers, it was confirmed that all were non-defective products. This indicates that the void detection device 2 that takes into account the propagation speed of the present invention can reliably detect even a minute void generated at the outermost peripheral portion of the wafer.

(Comparative example)
Similarly to Invention Example 1, 300 bonded wafers C were manufactured using the bonded wafer manufacturing apparatus 1 in which the void detection device 2 of the present invention shown in FIG. The presence or absence of void E was determined, and the manufactured bonded wafer C was recovered. At that time, the manufacture of the bonded wafer C and the determination of the presence or absence of the void E were performed in the same manner as in Invention Example 1. As a result, it was determined that 3 sheets were defective and 297 were non-defective.
Next, after confirming the identification numbers given to the back surfaces of the three wafers determined to be defective, the wafers are randomly loaded into 297 determined to be good and 300 bonded wafers C are bonded. It was.
Subsequently, the 300 bonded wafers C were subjected to a void inspection visually by a conventional operator. At that time, the result determined by the apparatus was not notified to the operator who performed the visual inspection. As a result, it was determined that 2 sheets were defective and 298 sheets were non-defective.
As a result of collating the identification numbers of the two wafers determined as defective by the visual inspection with the identification numbers of the wafers determined as defective by the void inspection apparatus 2 of the present invention, it is confirmed that they match. It was done. However, one of the three defective wafers determined by the void inspection apparatus 2 was determined to be a non-defective product by visual inspection. Therefore, when the visual inspection is performed again on the wafer which is determined to be a non-defective product by the visual inspection and determined to be a defective product by the void inspection apparatus 2, it is found that a small void E having a size of 0.5 mm exists. It was. Thus, it can be seen that the presence of voids may be missed in the visual inspection.

DESCRIPTION OF SYMBOLS 1 Bonded wafer manufacturing apparatus 2 Void detection apparatus 11a Active side wafer cassette 11b Support side wafer cassette 12 Wafer conveyance means 13 Wafer aligner 14 Infrared light source 15 Bonding chamber 15a Outer lid 15b Stage 16 Decompression means 17 Imaging means 18 Analysis apparatus 18a Storage unit 18b Bonding boundary detection unit 18c Curvature calculation unit 18d Determination unit 18e Propagation speed calculation unit 19 Display device 20 Control device 21a Non-defective wafer cassette 21b Defective wafer cassette A Active side wafer B Support side wafer C Bonded wafer D Bonding Boundary E Void

Claims (8)

In producing a bonded wafer by bonding and bonding two wafers,
A void detection method comprising: determining the presence or absence of a void in a wafer after bonding based on a propagation shape drawn by a boundary between a bonded portion and a non-bonded portion in the bonding process.   The presence / absence of voids in the wafer after bonding is determined by comparing the propagation shape in a wafer that does not actually generate voids with the propagation shape in the wafer after bonding. The detection method according to. The contrast of the propagation shape is obtained by detecting the boundary from an image of the bonded wafer photographed by photographing means for each position of the boundary and then approximating the propagation shape of the boundary with a quadratic curve. With the actual curvature at the vertex of the quadratic curve,
For the wafer that does not actually generate voids, approximate the propagation shape with a quadratic curve for each position of the boundary, and obtain in advance the curvature at the vertex of the quadratic curve as a curvature condition value,
3. The detection method according to claim 2, wherein when the error of the actual curvature with respect to the curvature condition value exceeds a predetermined value, it is determined that a void exists in the bonded wafer.   The detection method according to claim 1, wherein a propagation speed of the boundary is taken into account when determining the presence or absence of the void. For the wafer without the occurrence of voids, for each position of the boundary, the propagation speed is determined in advance as a propagation speed condition value,
After obtaining the actual propagation speed of the boundary for each position of the boundary, if the error of the actual propagation speed with respect to the propagation speed condition value exceeds a predetermined value, there is a void in the bonded wafer The detection method according to claim 4, wherein the determination is performed. In an apparatus for detecting voids in a bonded wafer when bonding and bonding two wafers to produce a bonded wafer,
An apparatus for detecting a void, comprising: an analysis device that detects a void in a wafer after bonding based on a propagation shape drawn by a boundary between a bonding portion and a non-bonding portion in the bonding process. The analysis device includes:
Stored in advance as a curvature condition value, the curvature of the boundary propagation shape obtained when the void does not occur, which is obtained in advance for each position of the boundary, and stores the image of the bonded wafer imaged by the imaging device And
A curvature calculator that approximates the boundary with a quadratic curve to obtain an actual curvature at the apex of the quadratic curve;
When an error in the actual curvature with respect to the curvature condition value exceeds a predetermined value, a determination unit that determines that a void exists at the interface between the two wafers;
The detection apparatus according to claim 6, further comprising: The analysis device further includes a propagation velocity calculation unit for obtaining an actual propagation velocity of the boundary,
The storage unit further stores, as a propagation velocity condition value, a propagation velocity of the boundary obtained in advance for each position of the boundary when no void occurs.
The determination unit according to claim 7, wherein when the error of the actual propagation speed with respect to the propagation speed condition value exceeds a predetermined value, it is determined that a void exists in the bonded wafer. Detection device.

Images