JP2013130501A - Defect detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a defect detection method for reducing influences of heat generated by laser beam on an object to be inspected.SOLUTION: The defect detection method includes: a definition process for defining a plurality of irradiation positions to a side surface smaller in area than a main surface of an object to be inspected and for defining a plurality of reception positions corresponding to the respective plurality of irradiation positions; a reception process for radiating laser beam to the irradiation positions and performing a process for receiving ultrasound at the reception positions corresponding to the irradiation positions at all the plurality of irradiation positions defined in the definition process; and a detection process for detecting defect of the object to be inspected on the basis of the ultrasound received in the reception process. The definition process defines the plurality of irradiation positions and the plurality of reception positions so that a plurality of intersection points are formed by a plurality of straight lines combining the irradiation positions and the reception positions corresponding to the radiation positions when viewed from the main surface side. The detection process detects defect at the respective positions of the plurality of intersection points.

Description

  The present invention relates to a technique for detecting a defect in an inspection object.

  A conventional technique for detecting defects using ultrasonic waves is described in Patent Document 1. In the prior art described in Patent Document 1, first, an ultrasonic wave is emitted by irradiating the main surface 3 of the object to be inspected from the pulse laser light source 2 arranged on the biaxial stage 1 in FIG. generate. Next, the ultrasonic wave propagated from the irradiation point of the laser beam 4 is received by the probe 5. A signal from the probe 5 corresponding to the received ultrasonic wave is detected by the ultrasonic detector 7 via the amplifier 6. Then, the laser beam 4 is irradiated a plurality of times while changing the irradiation position of the laser beam 4 using the biaxial stage 1 so that the entire surface of the main surface 3 is irradiated with the laser beam 4. The computer 8 detects a defect on the main surface 3 based on the ultrasonic wave detected at each irradiation position of the laser beam 4 and specifies the position.

JP 2006-300434 A

  However, in the above-described prior art, the entire surface of the main surface 3 is irradiated with the laser light 4, and thus heat generated by the laser light 4 may adversely affect the main surface 3.

  Accordingly, an object of the present invention is to provide a defect detection method capable of reducing the influence of heat generated by laser light on the main surface as compared with the conventional case.

  In order to achieve the above object, the defect detection method of the present invention defines a plurality of irradiation positions on a side surface having a smaller area than the main surface of an object to be inspected, and a plurality of receptions respectively corresponding to the plurality of irradiation positions. A definition step for defining a position, and a step of irradiating the irradiation position with laser light and receiving an ultrasonic wave at the reception position corresponding to the irradiation position are applied to all of the plurality of irradiation positions defined in the definition step. And a detection step for detecting a defect of the inspection object based on the ultrasonic wave received in the reception step, and the definition step corresponds to the irradiation position and the irradiation position. The plurality of irradiation positions and the plurality of reception positions are defined so that a plurality of intersections are formed when viewed from the main surface side by a plurality of straight lines respectively connecting the reception positions, and the detection step includes The plurality of intersection points And detects a defect at each location.

  As described above, according to the present invention, it is possible to reduce the influence of heat generated by laser light on the main surface as compared with the prior art.

Schematic diagram of the defect detection apparatus in the embodiment The figure which shows the graph of the waveform of the ultrasonic wave acquired when there is no defect in to-be-inspected object in embodiment The figure which shows the graph of the waveform of the ultrasonic wave acquired when the to-be-inspected object has a defect in embodiment BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram for explaining a method of specifying a defect position in an embodiment, (a) a schematic diagram showing a state of determining the presence or absence of a defect on one straight line, and (b) a defect at the position of one intersection of straight lines. The schematic diagram which shows a mode that the presence / absence is determined, (c) The schematic diagram which shows a mode that the presence or absence of the defect in the position of the other intersection of a line is determined Schematic diagram showing the distribution of a plurality of straight lines defined in the embodiment Flowchart showing the operation of the defect detection apparatus in the embodiment Schematic diagram showing another example of the distribution of a plurality of straight lines defined in the embodiment Schematic diagram showing still another example of the distribution of a plurality of straight lines defined in the embodiment Schematic diagram showing still another example of the distribution of a plurality of straight lines defined in the embodiment Schematic diagram of conventional technology

  Hereinafter, embodiments will be described with reference to the drawings.

(Embodiment)
FIG. 1 shows a configuration of a defect detection apparatus 100 according to the embodiment. The defect detection apparatus 100 detects the defect of the inspection object 101 by performing the determination of the presence or absence of the defect of the inspection object 101 and the specification of the position of the defect using the laser beam 102. The inspection object 101 is a flat substrate. In this embodiment, the inspection object 101 is a single crystal silicon wafer having a thickness of 0.2 mm and an outer shape of 125 mm × 125 mm.

  Hereinafter, the configuration of the defect detection apparatus 100 of FIG. 1 will be described.

  The laser beam 102 emitted from the pulsed laser light source 104 is bent in the traveling direction by the galvanometer mirror 105, and the irradiation position (for example, irradiation position Qxn) of the side surface 101b of the inspection object 101 through the fθ lens 106 and the folding mirror 107. It is focused on. The inspection object 101 is placed on the placement unit 108.

  In this embodiment, in order to efficiently generate ultrasonic waves, an Nd-YAG laser light source having a wavelength of 532 nm as a wavelength having a high light absorption rate by a silicon wafer as the inspection object 101 is used, and a pulse laser light source 104 as an irradiation unit. To adopt. As an example, the laser beam 102 emitted from the pulse laser source 104 has a pulse width of 10 ns and a repetition frequency of 10 kHz.

  On the side surface 101b of the inspection object 101 irradiated with the laser beam 102, thermal expansion occurs instantaneously, and ultrasonic waves are generated as thermally excited ultrasonic waves. The generated ultrasonic wave propagates in the inspection object 101 as a plate wave.

  Here, the effect of irradiating the side surface 101b with the laser beam 102 will be described. The side surface 101b is a surface that connects the surface facing the main surface 101a and the main surface 101a. Further, the area of the side surface 101b is smaller than that of the main surface 101a.

  Since the laser beam 102 is irradiated on the side surface 101b of the inspection object 101 and ultrasonic waves are generated on the side surface 101b, the influence on the main surface 101a due to the laser beam 102 irradiation can be reduced. This is because when the laser beam 102 is irradiated, the main surface 101a may be roughened, oxidized, thermally deformed, or the like, resulting in a deterioration in quality. Incidentally, even if the side surface 101b becomes rough or is subjected to thermal deformation or the like, the influence on the quality is small. This is because the side surface 101b is rarely used in a product. For example, when a semiconductor chip is manufactured from a silicon wafer as the inspection object 101, the semiconductor chip is not cut out from the side surface 101b. Further, when a solar cell is manufactured from a silicon wafer as the inspection object 101, the state of the side surface 101b hardly affects the power generation efficiency.

  In addition, since the influence on the main surface 101a can be reduced, the intensity of the laser beam 102 that cannot be used in the conventional technique (for example, the conventional technique shown in FIG. 10) from the viewpoint of the influence on the surface of the main surface 101a can be obtained. In this embodiment, it may be usable. When the intensity of the laser beam 102 is increased, a larger ultrasonic wave can be generated, and highly sensitive defect detection can be realized.

  Here, the description returns to the configuration of the defect detection apparatus 100 of FIG.

  The reception sensor 103 is a receiver that receives the ultrasonic wave propagated in the propagation direction 109 in the inspection object 101. The reception sensor 103 receives the ultrasonic wave propagated from the irradiation position (for example, irradiation position Qxn) of the laser beam 102 to the reception position (for example, reception position Pxn). The frequency of the ultrasonic wave to be received is 400 kHz or more and 10 MHz or less as an example, and depends on the specification of the reception sensor 103. Here, an aerial ultrasonic sensor having a flat receiving surface 103 a is used as an example of the receiving sensor 103.

  In addition, the reception sensor 103 is disposed above the main surface 101a while being inclined with respect to the normal direction of the main surface 101a (Z-axis direction in FIG. 1). In this case, the reception angle 112 of the reception sensor 103 is set so that the reception sensitivity of the reception sensor 103 is the highest. Specifically, when the reception sensor 103 receives an ultrasonic wave having the same intensity using an inspected object 101 whose defect is not known in advance, the maximum value of the amplitude of the ultrasonic waveform is the largest. The reception angle 112 is set as follows. As an example, the reception angle 112 is 7 degrees. The reception angle 112 is an angle formed between the normal direction w of the reception surface 103a of the reception sensor 103 (the one-dot chain point w in FIG. 1) and the normal direction of the main surface 101a (the Z-axis direction in FIG. 1). Represent.

  The reception sensor 103 outputs a signal corresponding to the received ultrasonic wave, and the output signal is amplified via the preamplifier 110 and collected by the computer 111. In the present embodiment, it is assumed that the reception sensor 103 transmits a signal having a voltage corresponding to the intensity of the received ultrasonic wave to the preamplifier 110.

  The position (for example, irradiation position Qxn) irradiated with the laser beam 102 is moved by the galvanometer mirror 105. Further, by moving the reception sensor 103 by the moving mechanism 113, the position (for example, the reception position Pxn) for receiving the ultrasonic wave is adjusted.

  The computer 111 includes a control unit 111a, an acquisition unit 111b, a determination unit 111c, a definition unit 111d, and a specification unit 111e. The controller 111a controls the pulse laser light source 104, the galvano mirror 105, and the moving mechanism 113 in order to perform the series of operations described above. The control unit 111a transmits a timing signal for causing the pulsed laser light source 104 to emit laser light. The timing signal from the control unit 111a is also transmitted to the acquisition unit 111b. The acquisition unit 111 b acquires an ultrasonic waveform corresponding to the ultrasonic signal transmitted from the reception sensor 103 via the preamplifier 110. The acquisition unit 111b acquires the waveform of the ultrasonic wave received by the reception sensor 103 for a certain time from when the timing signal is received. The acquisition unit 111b acquires information on the irradiation position (for example, irradiation position Qxn) of the laser beam 102 and the reception position (for example, reception position Pxn) of the laser beam 102 when acquiring the ultrasonic waveform, Store it in association. The acquisition unit 111b acquires information on the irradiation position and the reception position from the control unit 111a. The determination unit 111c determines the presence or absence of a defect based on the ultrasonic waveform acquired by the acquisition unit 111b. The definition unit 111d and the specifying unit 111e will be described later.

  The determination result of the presence / absence of a defect and the result of specifying the position of the defect are displayed on the display unit 114 according to a command from the determination unit 111c or the specification unit 111e of the computer 111.

  Here, a method for determining the presence or absence of a defect in the inspection object 101 by the defect detection apparatus 100 will be described.

  When the irradiation position Qxn is irradiated with the laser beam 102 and ultrasonic waves are received using the reception sensor 103 at the reception position Pxn, the ultrasonic waves propagated from the irradiation position Qxn to the reception position Pxn can be received. That is, the propagation path of the received ultrasonic wave is a straight line connecting the irradiation position Qxn and the reception position Pxn. In this case, the waveform of the ultrasonic wave acquired when there is no defect in the propagation locus is shown in FIG. FIG. 2 represents a graph obtained by receiving ultrasonic waves for 8 (μs), where 0 (μs) is the time when the laser beam 102 is irradiated to the irradiation position Qxn in FIG. In the graph of FIG. 2, the vertical axis represents amplitude (V) and the horizontal axis represents time (μs). It can be understood from the amplitude of the graph of FIG. 2 that the ultrasonic wave generated at the irradiation position Qxn is received at the reception position Pxn after about 3 (μs).

  Next, FIG. 3 shows an ultrasonic waveform acquired when a defect exists in the propagation locus. The graph of FIG. 3 is acquired in a state where a defect exists between the irradiation position Qxn and the reception position Pxn, unlike the state of FIG. FIG. 3 represents a graph obtained by receiving ultrasonic waves for 8 (μs), where 0 (μs) is the time point when the irradiation position Qxn of FIG. 1 is irradiated with the laser beam 102. In the graph of FIG. 3, the vertical axis indicates amplitude (V), and the horizontal axis indicates time (μs). As in FIG. 2, it can be understood that the ultrasonic wave generated at the irradiation position Qxn is received at the reception position Pxn after about 3 (μs).

  Comparing FIG. 2 and FIG. 3, it can be understood that when a defect is present in the propagation locus, the amplitude of the acquired ultrasonic waveform is smaller than that when there is no defect. This is because the intensity of the received ultrasonic wave is weakened due to the influence of defects present in the propagation locus. From this, it can be seen that the presence or absence of a defect can be determined by using the amplitude of the acquired waveform of the ultrasonic wave.

  In the present embodiment, when the maximum value of the acquired ultrasonic waveform is lower than the threshold value, it is determined that a defect exists in the ultrasonic propagation trajectory. The ultrasonic trajectory is represented by a straight line connecting the irradiation position Qxn and the reception position Pxn. Hereinafter, a straight line connecting the irradiation position and the reception position may be simply referred to as a straight line. An example of the threshold value is 0.1 (V). Note that the presence / absence of a defect may be determined based on a feature amount such as the frequency of the ultrasonic waveform and the amount of change in propagation time instead of the maximum value of the ultrasonic waveform. In this case, ultrasonic feature values received from a reference object having no defect (the same type as the inspection object 101) are stored as reference feature values, and the actually received ultrasonic feature values and reference feature values are stored. To determine the presence or absence of a defect.

  Here, an operation of generating an ultrasonic wave by irradiating the irradiation position Qxn with the laser beam 102 of FIG. 1 and receiving the generated ultrasonic wave at the reception position Pxn is performed by using an ultrasonic wave propagated from the irradiation position Qxn to the reception position Pxn. It is described as receiving operation. Further, when the ultrasonic wave propagated from the irradiation position Qxn to the reception position Pxn is received and it is determined that there is a defect based on the received ultrasonic wave, the defect is on the straight line connecting the irradiation position Qxn and the reception position Pxn. Shall exist. When the ultrasonic wave propagated from the irradiation position Qxn to the reception position Pxn is received and it is determined that there is no defect based on the received ultrasonic wave, the defect is on the straight line connecting the irradiation position Qxn and the reception position Pxn. Shall not exist.

  This completes the description of the method for determining the presence or absence of defects by the defect detection apparatus 100. In this determination method, even if the presence / absence of a defect existing on a straight line connecting the irradiation position Qxn and the reception position Pxn can be determined, the position of the defect on the straight line cannot be specified. This is because the correlation between the position of the defect and the acquired ultrasonic waveform is low. For example, when a defect exists on a straight line connecting the irradiation position Qxn and the reception position Pxn, the waveform of the acquired ultrasonic wave hardly changes regardless of the position on the straight line. Therefore, the defect detection apparatus 100 implements a defect position specifying method described below.

  A method for specifying the position of a defect by the defect detection apparatus 100 will be described with reference to FIGS. 4A to 4C show the irradiation position (Qx1, Qy1, Qy2) of the laser beam 102 on the rectangular inspection object 101 and the ultrasonic reception positions (Px1, Py1, Py2) by the reception sensor 103. FIG. It is shown. Further, it is assumed that a dimple defect 120 exists as a defect in the inspection object 101. The dimple defect 120 indicates a defect due to a dent or a dent.

  As shown in FIG. 4A, the laser beam 102 is irradiated to the irradiation position Qx1 of the side surface 101bxr parallel to the X axis, and ultrasonic waves are received using the reception sensor 103 at the reception position Px1 of the side surface 101bxl opposite to the side surface 101bxr. Suppose that the same waveform as the ultrasonic waveform shown in FIG. 3 is received. In this case, it can be seen that the dimple defect 120 exists on the straight line Lx1 connecting the irradiation position Qx1 and the reception position Px1. However, at this time, the position of the dimple defect 120 on the straight line Lx1 cannot be specified.

  Next, as shown in FIG. 4B, the laser beam 102 is irradiated to the irradiation position Qy1 of the side surface 101byu parallel to the Y axis, and the ultrasonic wave is received at the reception position Py1 of the side surface 101byd on the opposite side of the side surface 101byu. In this case, it is assumed that the same waveform as the waveform of the ultrasonic wave shown in FIG. 2 is received. In this case, it can be seen that the dimple defect 120 does not exist on the straight line Ly1 connecting the irradiation position Qy1 and the reception position Py1. 4A, it can be specified that at least the dimple defect 120 does not exist at the intersection I11 between the straight line Lx1 and the straight line Ly1. In other words, it can be seen that the dimple defect 120 exists at a position other than the intersection point I11 on the straight line Lx1.

  Subsequently, as shown in FIG. 4C, when the laser beam 102 is irradiated to the irradiation position Qy2 of the side surface 101byu and the ultrasonic wave is received at the reception position Py2 of the side surface 101byd, the waveform signal shown in FIG. Is received. In this case, it can be seen that the dimple defect 120 exists on the straight line Ly2 connecting the irradiation position Qy2 and the reception position Py2. Based on the result of FIG. 4A, it can be specified that the dimple defect 120 exists at the intersection I12 between the straight line Lx1 and the straight line Ly2.

  From the above, the method for identifying the position of the defect as shown in FIGS. 4A to 4C is summarized as follows. First, the presence or absence of a defect (dimple defect 120) on each straight line is determined using the straight line Lx1, the straight line Ly1, and the straight line Lx2. Then, the position of the intersection (I12) formed by the straight lines (Lx1 and Ly2) determined to have the defect (dimple defect 120) is specified as the position where the defect (dimple defect 120) exists.

  4 (a) to 4 (c) have been described in a simplified manner, so that only when a defect exists at either the intersection point I11 in FIG. 4 (b) or the intersection point I12 in FIG. 4 (c), The position of the defect cannot be specified. That is, it is only possible to detect defects at the positions of the intersection point I11 and the intersection point I12. Therefore, in this embodiment, the irradiation position where the laser beam 102 is irradiated and the reception position where the ultrasonic wave is received are defined as follows.

  An irradiation position and a reception position defined in this embodiment are shown in FIG. Irradiation positions Qx1 to Qxn (n is a natural number greater than 1) positioned at equal intervals on the side surface 101bxr, irradiation positions Qy1 to Qym (m is a natural number greater than 1) positioned at equal intervals on the side surface 101byu, and the side surface 101bxl Reception positions Px1 to Pxn positioned at intervals and reception positions Py1 to Pym positioned at equal intervals on the side surface 101byd are shown.

  First, based on the ultrasonic wave propagated from the irradiation position Qx1 to the reception position Px1, the presence / absence of a defect on the straight line Lx1 connecting the irradiation position Qx1 and the reception position Px1 is determined. The method for determining the presence or absence of a defect on the straight line Lx1 is the same as that described with reference to FIGS. Subsequently, the presence / absence of a defect on the straight line Lx2 connecting the irradiation position Qx2 and the reception position Px2 is determined. Then, a straight line Lx3 connecting the irradiation position Qx3 and the reception position Px3,... A straight line Lxn connecting the irradiation position Qxn and the reception position Pxn, and the presence / absence of defects located on these straight lines are sequentially determined. Further, a straight line Ly1 connecting the irradiation position Qy1 and the reception position Py1, a straight line Ly2 connecting the irradiation position Qy2 and the reception position Py2,... A straight line Lym connecting the irradiation position Qym and the reception position Pym, and positions on these straight lines The presence / absence of defects to be determined is sequentially determined. Thereafter, a straight line determined to have a defect is extracted from the straight lines Lx1 to Lxn and Ly1 to Lym. Then, the position of the intersection formed on the straight line determined to have a defect is specified as the position where the defect exists. For example, when it is determined that a defect exists only in the straight line Lx1, the straight line Lx2, and the straight line Ly2, the intersection point I12 and the intersection point I22 formed by these straight lines can be specified as positions where the defect exists. Note that intersections other than the intersections I12 and I22 can be specified as positions where no defect exists.

  When the irradiation position and the reception position defined as shown in FIG. 5 are used, the accuracy of specifying the position of the defect depends on the distribution of the intersections I11 to Inm. The distribution of the intersections I11 to Inm is caused by the distribution of the straight lines Lx1 to Lxn and Ly1 to Lym. For this reason, the defect detection apparatus 100 in FIG. 1 defines straight lines Lx1 to Lxn and Ly1 to Lym that are distributions of desired intersections I11 to Inm when viewed from the main surface 101a side. Based on the ultrasonic wave propagated on the defined straight line, the position of the defect is specified from the intersection points I11 to Inm. In order to improve the accuracy, straight lines are arranged so that the distribution of the intersections I11 to Inm when viewed from the main surface 101a side (Z-axis direction) is dense. In this case, the number of straight lines increases and the distance between the straight lines becomes closer. Along with this, the number of irradiation positions and reception positions also increases, the intervals between irradiation positions become closer, and the intervals between reception positions become narrower.

  Moreover, the precision which pinpoints the position of a defect also depends on the thickness of each straight line (straight line Lx1-Lxn, Ly1-Lym). This is because information in the thickness direction of the straight line does not appear in the acquired ultrasonic waveform. For this reason, each straight line is defined to have a desired thickness. The thickness of each straight line is determined according to the spot diameter of the laser beam (laser beam 102 in FIG. 1) irradiated to each irradiation position. The size of the spot diameter is adjusted by the fθ lens 106 in FIG.

  In this embodiment, the distance between the centers of the irradiation positions is 0.1 μm, and the distance between the centers of the reception positions is 0.1 μm. Further, the spot diameter of the laser beam 102 at the irradiation position is 0.1 μm, and the thickness of each straight line is 0.1 μm. In this case, the size of the intersections is 0.1 μm × 0.1 μm, and the intersections are distributed without gaps when viewed from the main surface 101a side. For the sake of explanation, in FIG. 5, the irradiation positions Qx1 to Qxn and Qy1 to Qym are described with a certain interval, but actually, the irradiation positions Qx1 to Qxn and Qy1 to Qym are distributed without any gap. Similarly, the reception positions Px1 to Pxn and Py1 to Pym are actually distributed without any gaps. Similarly, the intersections I11 to Inm are also distributed without gaps.

  Here, the number of times the laser beam 102 is irradiated in order to carry out the method of specifying the position of the defect by the defect detection apparatus 100 of FIG. 1 will be described in comparison with the conventional method of FIG.

  When a defect located at one of the intersections I11 to Inm in FIG. 5 is specified by the conventional method of FIG. 10, it is necessary to irradiate the laser beam by the number of the intersections I11 to Inm. When n is 4 and m is 3, the number of intersections is 12, and the number of times of laser light irradiation in the conventional method is 12.

  On the other hand, in the method for specifying the position of the defect by the defect detection apparatus 100 in FIG. 1, the laser beam 102 is irradiated to the irradiation positions Qx1 to Qx4 and Qy1 to Qy3, and therefore the number of times of irradiation with the laser beam 102 is seven. Although one straight line is obtained by one irradiation of the laser beam 102, the number of intersections can be made larger than the number of straight lines by intersecting this straight line with a plurality of other straight lines. For this reason, in the method of specifying the position of the defect by the defect detection apparatus 100 in FIG. 1, the number of points irradiated with the laser light 102 can be reduced as compared with the conventional method in FIG. When the number of times the laser beam 102 is irradiated is reduced by the defect detection apparatus 100 in FIG. 1, the influence of heat on the main surface 101a by the laser beam 102 can be reduced. Further, since the time required for irradiation with the laser beam 102 can be reduced, the time required for specifying the position of the defect is shortened.

  As described above, in order to reduce the number of times of irradiation with the laser beam 102 as compared with the conventional method of FIG. 10, in the present embodiment, the definition unit 111d of FIG. Define multiple reception locations. At this time, the number of intersections formed by the plurality of straight lines is set to be larger than the number of the plurality of straight lines to be defined.

  As shown in FIG. 5, the irradiation positions Qx1 to Qxn are on the side surface 101bxr, the irradiation positions Qy1 to Qym are on the side surface 101byu, the reception positions Px1 to Pxn are on the side surface 101bxl, and the reception positions Py1 to Pym are on 101byd, respectively. When defined, the number of intersections formed is n × m. The number of times the laser beam 102 is irradiated is n + m, and the number of defined straight lines is also n + m. Therefore, if n and m are set so as to satisfy Expression (1), the number of times of irradiation with the laser light 102 can be reduced as compared with the conventional method of FIG.

  Next, the operation of the defect detection apparatus 100 of FIG. 1 will be described according to the flowchart of FIG.

  In step S1, a plurality of straight lines are defined on the main surface 101a by the definition unit 111d in FIG. Linear data for definition is stored in advance in the definition unit 111d in accordance with the shape of the main surface 101a. In this case, the definition unit 111d transmits the defined straight line information to the control unit 111a. In order to suppress the number of times of irradiation with the laser beam 102, the plurality of straight lines are arranged on the main surface 101a so that the number of intersections formed by the plurality of straight lines is larger than the number of the plurality of defined straight lines. Defined in The straight line includes information on the irradiation position and the reception position, and defining the straight line is synonymous with defining the irradiation position and the reception position corresponding to the irradiation position.

  In step S2, the position for irradiating the laser beam 102 to the end of one straight line (referred to as a straight line of interest) among the plurality of straight lines defined on the main surface 101a in step S1 is aligned. Further, the position of the reception sensor 103 is adjusted in order to receive the ultrasonic wave at the other end of the straight line of interest. The operation of aligning the position for irradiating the laser beam 102 is performed by controlling the galvano mirror 105 and the moving mechanism 113 by the control unit 111a that has received straight line information from the definition unit 111d.

  In step S3, the laser beam 102 is irradiated to the irradiation position that is one end of the target straight line whose position is matched in step S2. At this time, the laser beam 102 is emitted from the pulse laser light source 104 that has received the timing signal from the controller 111a. The control unit 111a also transmits a timing signal to the acquisition unit 111b. Furthermore, the control unit 111a also transmits information on the target straight line whose position is matched in step S2 to the acquisition unit 111b.

  In step S4, an ultrasonic wave is received at the receiving position which is the other end of the target straight line irradiated with the laser beam 102 in step S3. The acquisition unit 111b receives a timing signal from the control unit 111a, starts acquiring an ultrasonic signal from the reception sensor 103, and acquires an ultrasonic waveform at an acquisition time that is a fixed time. As the acquisition time, an arbitrary value is set by the user based on the shape of the main surface 101a and the acoustic impedance, and stored in advance in the acquisition unit 111b. In this embodiment, 1 millisecond is set as an example of the acquisition time. The operation of “irradiating a laser beam to an irradiation position that is one end of a straight line (line of interest) and acquiring an ultrasonic waveform at a reception position that is the other end” May be described as an "receive" operation. The acquisition unit 111b associates the acquired waveform of the ultrasonic wave with the information on the attention line received from the control unit 111a, and sends the information to the determination unit 111c as information on the ultrasonic wave propagated on the attention line. Furthermore, the acquisition unit 111b transmits a completion signal to the control unit 111a when the reception of the ultrasonic wave is completed on the straight line of interest (when the acquisition time has elapsed).

  In step S5, it is determined whether or not there is a defect on the target straight line from which the ultrasonic wave is received. The determination unit 111c receives information on the ultrasonic wave that has propagated on the target straight line from the acquisition unit 111b, and determines the presence / absence of a defect on the target straight line based on the information. At this time, the determination unit 111c determines the presence / absence of a defect on the target line by comparing the threshold value stored in advance with the feature amount in the information of the ultrasonic wave propagated on the target line. As a result of the determination, if it is determined that there is a defect on the target straight line, information on the target straight line is transmitted from the determination unit 111c to the specifying unit 111e and stored in the specifying unit 111e. When it is determined that there is no defect on the target straight line, the information on the target straight line is not transmitted to the specifying unit 111e.

  In step S6, it is determined whether ultrasonic waves have been received from all of the plurality of straight lines defined in step S1. If there is a straight line that does not receive ultrasonic waves, the process returns to step S2, and alignment is performed for the straight line that does not receive ultrasonic waves (No in step S6). If ultrasonic waves have been received for all of the plurality of defined straight lines, the process proceeds to step S7 (Yes in step S6). In addition, this step S6 is performed by the control part 111a.

  In step S7, the presence or absence of a defect in the inspection object 101 is determined. After step S6, when there is no information stored in the specifying unit 111e, the specifying unit 111e determines that the inspection object 101 has no defect. This is because there is no straight line determined to be defective by the determination unit 111c. If it is determined that the inspection object 101 is not defective, the process proceeds to step S8 (No in step S7). If there is straight line information stored in the specifying unit 111e, it is determined that the inspection object 101 has a defect, and the process proceeds to step S9 (Yes in step S7).

  In step S8, a non-defective product display is displayed on the display unit 114. The display unit 114 performs display according to a command from the specifying unit 111e.

  In step S9, the defect position specifying method is performed using the straight line information stored in the specifying unit 111e. Here, the position of the defect is specified by the specifying unit 111e in accordance with the position of the intersection formed by the straight line determined to have a defect.

  In step S10, information on the position of the defect identified in step S9 is displayed on the display unit 114.

  As described above, the defect detection apparatus 100 of FIG. 1 operates. As described above, by using the defect detection apparatus 100 of FIG. 1, the number of times of irradiation with the laser beam 102 can be reduced, and accumulation of thermal damage to the main surface 101a due to irradiation of the laser beam 102 can be reduced. Can do.

  Note that step S5 in FIG. 6 may be performed after step S6. In this case, first, after receiving ultrasonic waves from all of the plurality of straight lines, the presence / absence of a defect in each straight line is determined.

  Here, the operation of the defect detection apparatus 100 will be summarized.

  First, in the defining step, in step S1 in FIG. 6, a plurality of irradiation positions are defined on the side surface 101b having a smaller area than the main surface 101a of the inspection object 101, and a plurality of irradiation positions respectively corresponding to the plurality of irradiation positions. A definition process for defining the reception position is performed. In this definition process, a plurality of irradiation positions and a plurality of intersections are formed by a plurality of straight lines connecting the irradiation positions and the reception positions corresponding to the irradiation positions so that a plurality of intersections are formed as viewed from the main surface 101a side. Define the receiving position.

  Next, in steps S2 to S4 and S6, the process of irradiating the irradiation position with the laser beam 102 and receiving the ultrasonic wave at the reception position corresponding to the irradiation position is performed in all of the plurality of irradiation positions defined in the definition process. A receiving step is performed.

  Then, the detection process which detects the defect of the to-be-inspected object 101 based on the ultrasonic wave received by the receiving process is implemented by step S5 and step S9. In this detection step, a defect at each position of the plurality of intersections is detected.

  As described above, the influence on the main surface 101a due to the heat generated by the laser beam 102 can be reduced.

  Furthermore, in step S1, it is desirable to define a plurality of irradiation positions and a plurality of reception positions so that the number of intersections is larger than the number of the plurality of straight lines in the defining step. Thereby, in the defect detection method by the defect detection apparatus 100 of FIG. 1, the number of points irradiated with the laser light 102 can be reduced as compared with the conventional method of FIG.

  Here, another example of a plurality of straight lines defined by the definition unit 111d in FIG. 1 will be described.

  In FIG. 5, since the irradiation positions Qx1 to Qxn are defined on the side surface 101bxr and the irradiation positions Qy1 to Qym are defined on the side surface 101bxl, it is necessary to move the irradiation position in two axial directions (X-axis direction and Y-axis direction). Configuration may be complicated. Therefore, as shown in FIG. 7, a plurality of straight lines are defined so that the irradiation positions Qx1 to Qxn are located only on the side surface 101bxr. Thereby, the movement of the irradiation position is limited to only one axis direction (X-axis direction). Similarly, reception positions Px1 to Pxm are defined on the side surface 101bxl. In this case, by using straight lines with different angles, even if the irradiation positions Qx1 to Qxn are positioned only on the side surface 101bxr, the number of intersections can be increased more than the number of straight lines. Furthermore, in the case of FIG. 7, it is also possible to define a straight line so that a plurality of irradiation positions correspond to one reception position. As a result, the number of operations for moving the reception position can be reduced, and the time required to complete the defect location method may be shortened.

  Further, when specifying the position of the defect, the position of the defect may be specified by creating a gray image with a straight line determined to have a defect. For example, when the main surface 101a of FIG. 5 is set to 0 gradation (black) and a straight line determined to have a defect is distributed to the main surface 101a as 1 gradation (gray), it is determined that there is a defect. The gradation of the intersection formed by the straight lines is two gradations (white), and the position of the defect can be specified based on such a gradation difference. Further, as shown in FIG. 7, when three straight lines form an intersection, it is possible to more clearly identify the position of the defect by creating a grayscale image with an increased number of gradations. it can.

  Here, another example of the irradiation position and the reception position when the number of intersections is larger than the number of straight lines will be described with reference to FIG.

  As shown in FIG. 8, the irradiation positions Qx1 to Qx4 are defined on the side surface 101bxr, and the reception positions Px1 to Px4 corresponding to these irradiation positions are defined on the side surface 101bxl. In this case, it can be understood that the plurality of straight lines connecting the reception positions corresponding to the irradiation positions form six intersections when viewed from the main surface 101a. Thus, by increasing the number of intersections formed rather than the number of straight lines, the number of times of irradiation with the laser light 102 can be reduced, and the influence of the heat of the laser light on the main surface can be reduced. In this case, the number of times of irradiation with the laser beam 102 is 4, and the number of intersections is 6. When it is desired to detect a defect only in the region 121, the time required for detecting the defect can be shortened by defining the irradiation position and the reception position as shown in FIG. If the number of straight lines is four or more as shown in FIG. 8, it is possible to increase the number of intersections rather than the number of straight lines, and the number of times of irradiation with the laser light 102 is reduced as compared with the conventional method of FIG. it can.

  Further, another example of the irradiation position and the reception position when the number of intersections is larger than the number of straight lines will be described with reference to FIG.

  As shown in FIG. 9, the irradiation positions Qx1 to Qx3 are defined on the side surface 101bxr, and the reception positions Px1 to Px3 corresponding to these irradiation positions are defined on the side surface 101bxl. Further, the irradiation positions Qy1 and Qy2 are defined on the side surface 101byu, and the reception positions Py1 and Py2 corresponding to these irradiation positions are defined on the side surface 101byd. In this case, it can be understood that the plurality of straight lines connecting the reception positions corresponding to the irradiation positions form six intersections when viewed from the main surface 101a. This is the minimum combination of n and m that satisfies Equation (1). Thus, by increasing the number of intersections formed rather than the number of straight lines, the number of times of irradiation with the laser light 102 can be reduced, and the influence of the heat of the laser light on the main surface can be reduced.

  Note that the side surface 101b may be irradiated with the laser light 102 without using the folding mirror 107.

  If the inspection object 101 is a thin plate having a thickness of about 1 mm or less, a defect in the inspection object 101 can be detected even when the irradiation position distributed in a row on the side surface 101b is irradiated with the laser beam 102. When the thickness of the inspection object 101 exceeds 1 mm, it is desirable to arrange the irradiation positions in two rows on the side surface 101b.

  Further, the position for receiving the ultrasonic waves is not limited to the side surface 101b. The receiving sensor 103 that receives ultrasonic waves does not affect the main surface 101a like the laser light 102, and therefore may receive ultrasonic waves at any position on the main surface 101a. That is, the installation position of the reception sensor 103 may be changed according to the defect area whose position is to be specified. For example, in FIG. 1, when it is desired to specify the position of only the defect around the side surface 101b, the reception position Pxn may be disposed near the irradiation position Qxn, and the reception sensor 103 may be disposed above the reception position Pxn.

  In addition, the position where the laser beam 102 is irradiated and the position where the ultrasonic wave is received may be changed by moving the placement unit 108 using the moving mechanism 113. That is, the moving mechanism 113 and the galvanometer mirror 105 are used as a moving unit that changes the irradiation position of the laser beam 102 by the pulse laser light source 104 that is an irradiation unit and the reception position of the ultrasonic wave by the reception sensor 103 that is a receiver. Use it. Note that the control of the moving mechanism 113 and the galvanometer mirror 105 is performed by the control unit 111a. Further, the placement unit 108 may have a function as a moving mechanism. As the moving mechanism 113, an automatic stage, an actuator, or the like is used.

  Further, the type of the pulse laser light source 104 may be any laser light source such as a gas laser, a solid-state laser, or a semiconductor laser. What is necessary is just to employ | adopt the optimal thing according to the kind of to-be-inspected object 101. FIG.

  The defect detection method of the present invention can also be applied to silicon wafers used in semiconductors and solar cells, or applications that detect defects such as cracks and dimples in metals and glasses.

DESCRIPTION OF SYMBOLS 100 Defect detection apparatus 101 Inspection object 101a Main surface 101b, 101bxr, 101bxl, 101byu, 101byd Side surface 102 Laser light 103 Reception sensor 104 Pulse laser light source 111 Computer

Claims (2)

Defining a plurality of irradiation positions on a side surface having a smaller area than the main surface of the object to be inspected, and defining a plurality of reception positions respectively corresponding to the plurality of irradiation positions;
A receiving step of irradiating the irradiation position with laser light and performing a step of receiving ultrasonic waves at the reception position corresponding to the irradiation position with respect to all of the plurality of irradiation positions defined in the definition step;
Detecting a defect of the inspection object based on the ultrasonic wave received in the reception step, and
In the defining step, the plurality of irradiation positions are formed such that a plurality of intersections are formed when viewed from the main surface side by a plurality of straight lines respectively connecting the irradiation positions and the reception positions corresponding to the irradiation positions. And the plurality of receiving positions,
The detection step is a defect detection method for detecting a defect at each position of the plurality of intersections. The defining step defines the plurality of irradiation positions and the plurality of reception positions so that the number of the plurality of intersections is larger than the number of the plurality of straight lines.
The defect detection method according to claim 1.

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