Method for recording processing conditions and laser processing device

Abstract

A method for capturing processing conditions for laser processing to form a weakened area in a functional element layer is provided by irradiating an object with laser light from the side of a first surface, wherein the object comprises a substrate with a first surface and a second surface opposite the first surface, and the functional element layer is provided on the second surface of the substrate, the method comprising: a first step of performing a first processing operation a plurality of times as laser processing at different positions in the first surface, while changing a convergence position of the laser light in a Z-direction that intersects the first surface within a region that includes an interface between the substrate and the functional element layer.

Description

Processing condition acquisition method and laser processing device

[0001] The present disclosure relates to a processing condition acquisition method and a laser processing apparatus.

[0002] Patent Document 1 describes a method for forming a weakened region along a line to be cut in a metal film formed on the back side of a workpiece by irradiating the surface of the workpiece with laser light, with the laser light incident on the surface of the workpiece. At this time, the focal point of the laser light is positioned outside the silicon wafer of the workpiece.

[0003] Patent No. 5322418

[0004] According to the method described in Patent Document 1, a weakened region having a predetermined depth is formed in a metal film along the line to be cut, which makes it possible to accurately cut an object along the line to be cut with a relatively small external force. In particular, in recent years, low-k films have been adopted as insulating films in order to accommodate the miniaturization of device wiring, and multiple films, metal wiring, and metal films are sometimes stacked in the cutting region due to an increase in the number of layered patterns associated with three-dimensionalization, making it more effective to form a weakened region as described above. Accordingly, a method for acquiring suitable processing conditions for forming a weakened region is desired.

[0005] Therefore, an object of the present disclosure is to provide a processing condition acquisition method and a laser processing device that are capable of acquiring processing conditions suitable for forming a weakened region.

[0006] The processing condition acquisition method according to the present disclosure is a processing condition acquisition method for acquiring laser processing conditions for forming a weakened region in the functional element layer by irradiating laser light from the first surface side of an object having a substrate including a first surface and a second surface opposite the first surface, and a functional element layer provided on the second surface of the substrate, and includes: a first step of performing a first processing as laser processing multiple times at different positions within the first surface while changing the focusing position of the laser light in a Z direction intersecting the first surface within a range including the interface between the substrate and the functional element layer; a second step of acquiring an interface image by imaging the interface between the substrate and the functional element layer from the first surface side using transmitted light that passes through the substrate at each of the positions within the first surface where the multiple first processing has been performed; and a third step of acquiring, as one of the laser processing conditions, the range of the focusing position in the Z direction of the first processing at which an interface image including damage from the laser light was acquired among the multiple interface images acquired in the second step.

[0007] In this method, laser processing conditions for forming a weakened region in the functional element layer on the second surface side of the object are acquired by irradiating a laser beam from the first surface side of the substrate of the object. To this end, multiple laser processing operations are performed while varying the focusing position of the laser beam in the Z direction within a range including the interface between the substrate and the functional element layer. Furthermore, at each of the multiple laser processing operations, an image of the interface between the substrate and the functional element layer is captured to obtain an interface image. Depending on the focusing position, this interface image may or may not show an image of damage caused by the laser beam. When the focusing position of the laser beam is within a range where an image of damage appears in the interface image, a weakened region that enables high-quality cutting of the object tends to be formed favorably. Therefore, in this method, the range of focusing positions of the laser processing, within which an interface image including an image of damage caused by the laser beam is acquired, is acquired as one of the laser processing conditions. In this way, this method makes it possible to acquire favorable processing conditions (the range of focusing positions) for forming a weakened region.

[0008] In the processing condition acquisition method according to the present disclosure, the range of positions in the Z direction in which the focusing position is changed in the first step may include a first range located closer to the first surface than the interface and a second range located on the opposite side of the interface from the first surface and wider than the first range. Here, the range of focusing positions in which the weakened region is preferably formed is more likely to be obtained closer to the functional device layer than to the interface between the substrate and the functional device layer. Therefore, by widening the range in which the focusing position is changed closer to the functional device layer than to the interface, it is possible to more quickly and reliably acquire this range.

[0009] The processing condition acquisition method according to the present disclosure may include, after the first, second, and third steps, a fourth step of cutting the object and capturing an image of the surface of the functional device layer of the cut object, wherein the first step may involve irradiating the laser light along the X direction along the first surface, and the fourth step may involve cutting the object along the X direction. In this way, by actually cutting the object and capturing an image of the surface of the functional device layer, it is possible to determine a more suitable focusing position by evaluating the cutting quality.

[0010] The processing condition acquisition method according to the present disclosure may include a fifth step of performing second processing as laser processing multiple times at different positions on the first surface while changing the number of bursts of laser light that is pulsed light, a sixth step of acquiring first-surface images by imaging the first surface at each of the positions on the first surface where the second processing multiple times has been performed, and a seventh step of acquiring, as another condition for laser processing, the number of bursts of the second processing for which a first-surface image showing no damage to the first surface has been acquired among the multiple first-surface images acquired in the sixth step. In this case, it is possible to acquire suitable processing conditions (number of bursts) that enable the formation of a weakened region without damaging the first surface, which is the incident surface of the laser light.

[0011] A laser processing apparatus according to the present disclosure is a laser processing apparatus that acquires laser processing conditions for forming a weakened region in the functional element layer by irradiating a target object having a substrate including a first surface and a second surface opposite to the first surface, and a functional element layer provided on the second surface of the substrate, with laser light from the first surface side, and includes a support unit that supports the target object, a laser irradiation unit that irradiates the target object supported by the support unit with laser light from the first surface side, an imaging unit that images the target object supported by the support unit from the first surface side using transmitted light that passes through the substrate, and a control unit that controls the laser irradiation unit and the imaging unit, a first process for performing a first processing as laser processing multiple times at different positions within the first surface by controlling the laser irradiation unit while changing the focusing position of the laser light in the Z direction intersecting the first surface within a range including the interface between the substrate and the functional element layer; a second process for controlling the imaging unit to capture an image of the interface between the substrate and the functional element layer from the first surface side using transmitted light at each of the positions within the first surface where the first processing was performed multiple times, and a third process for recording each of the multiple interface images captured in the second process in association with the corresponding focusing position of the first processing.

[0012] This device acquires laser processing conditions for forming a weakened region in the functional element layer on the second surface side of the object by irradiating a laser beam from the first surface side of the substrate of the object. To achieve this, multiple laser processing operations are performed while varying the focusing position of the laser beam in the Z direction within a range including the interface between the substrate and the functional element layer. Furthermore, an interface image is acquired by capturing an image of the interface between the substrate and the functional element layer at each of the multiple laser processing operations. As described above, depending on the focusing position, this interface image may or may not show an image of damage caused by the laser beam. Furthermore, when the focusing position of the laser beam is within a range where an image of damage appears in the interface image, a weakened region that enables high-quality cutting of the object tends to be formed. Therefore, this device records each of the multiple interface images in association with the corresponding focusing position of the laser processing. By referencing this record, it is possible to acquire, as one of the laser processing conditions, the range of focusing positions of the laser processing from which an interface image including an image of damage caused by the laser beam was acquired. In this way, this device makes it possible to obtain suitable processing conditions (range of light collection position) when forming a weakened region.

[0013] The laser processing apparatus according to the present disclosure may include a display unit that displays the images captured by the imaging unit, and the control unit may execute a fourth process that controls the display unit to display each of the interface images recorded in the third process on the display unit. In this case, based on the interface image displayed on the display unit, it is possible to easily grasp the range of the laser processing focus position from which an interface image including an image of damage caused by the laser beam was acquired among the multiple interface images.

[0014] According to the present disclosure, it is possible to provide a processing condition acquisition method and a laser processing device that are capable of acquiring processing conditions suitable for forming a weakened region.

[0015] FIG. 1 is a schematic diagram showing the general configuration of a laser processing apparatus according to this embodiment. FIG. 2 is a schematic cross-sectional view for explaining laser processing performed by the laser processing apparatus shown in FIG. 1. FIG. 3 is a flowchart showing an example of a processing condition acquisition method performed by the laser processing apparatus shown in FIG. 1. FIG. 4 is a schematic cross-sectional view showing one step of the processing condition acquisition method shown in FIG. 3. FIG. 5 is a graph for explaining changes in the number of bursts. FIG. 6 is a diagram showing a plurality of first surface images. FIG. 7 is a schematic cross-sectional view showing one step of the processing condition acquisition method shown in FIG. 3. FIG. 9 is a diagram showing a plurality of interface images. FIG. 10 is a schematic diagram showing the general configuration of a head unit according to a modified example.

[0016] An embodiment will be described below with reference to the drawings. In the description of each drawing, the same or corresponding elements are given the same reference numerals, and redundant description may be omitted. In addition, each drawing may illustrate an orthogonal coordinate system defined by an X-axis, a Y-axis, and a Z-axis. The Z-direction of the coordinate system is, for example, the vertical direction. Furthermore, the X-direction and the Y-direction are, for example, two horizontal directions that intersect (are perpendicular to) each other.

[0017] FIG. 1 is a schematic diagram showing the overall configuration of a laser processing apparatus according to this embodiment. As shown in FIG. 1, the laser processing apparatus 1 includes a table (support unit) 10, a head unit 20, a control unit 30, an input unit 31, a display unit 33, and a recording unit 35. The table 10 is, for example, a transparent table that is transmissive to at least visible light and near-infrared light, and supports an object 5. The object 5 includes a first surface 5a and a second surface 5b opposite the first surface 5a. The object 5 is supported on the table 10 via tape 6 provided on the second surface 5b. The tape 6 is held by a frame unit 7 and is, for example, a transparent tape that is transmissive to at least visible light and near-infrared light.

[0018] The table 10 may be provided with a first movement mechanism (not shown) for moving the table 10 in at least one of the X direction, Y direction, and Z direction. As a result, the control unit 30 controls the first movement mechanism, so that the table 10 can be driven in at least one of the X direction, Y direction, and Z direction.

[0019] The object 5 includes a substrate 51 and a functional device layer 52. The substrate 51 includes a first surface 5a and a second surface 51b opposite the first surface 5a. The functional device layer 52 is provided on the second surface 51b. Here, the second surface 5b of the object 5 is the surface of the functional device layer 52 opposite the substrate 51. The substrate 51 is, for example, a semiconductor substrate including silicon or the like. The functional device layer 52 is a layer including a plurality of functional devices (semiconductor devices) arranged in the X direction and the Y direction. In the functional device layer 52, a plurality of functional devices may be stacked along the Z direction. Furthermore, the functional device layer 52 may include metal wiring, a metal film, or an insulating film such as a low-k film.

[0020] The head unit 20 includes a first focusing unit 21, a first camera 23, a second camera 25, and a housing 26. The first focusing unit 21, the first camera 23, and the second camera 25 are housed within the housing 26. The first focusing unit 21 includes a lens, and focuses the processing laser light L1, which is emitted from a light source outside the housing 26 and introduced into the housing 26, onto the object 5 via mirrors M1 and M2. Therefore, the head unit 20 is a laser irradiation unit that irradiates the object 5 supported on the table 10 with the laser light L1 from the first surface 5a side. The laser light L1 is transparent to the substrate 51 of the object 5. As an example, the wavelength of the laser light L1 is approximately 1064 nm, and the pulse width is approximately 9 ps.

[0021] The first light collecting unit 21 collects the first observation light L2, which is emitted from a light source outside the housing 26 and introduced into the housing 26, via the mirror M2 and is directed toward the object 5. The first camera 23 captures an image of the object 5 by receiving the reflected light of the first observation light L2 irradiated onto the object 5 and reflecting it via the mirrors M2, M1, and M3b. The first observation light L2 is, for example, visible light. In this case, the first camera 23 is sensitive to visible light and near-infrared light. As a result, the head unit 20 functions as a first imaging unit that captures an image of the object 5 supported on the table 10 from the first surface 5a side using the first observation light L2 (acquires an image of the first surface 5a).

[0022] Furthermore, the first light collecting unit 21 collects transmitted light L3, which is emitted from a light source outside the housing 26 and introduced into the housing 26, via mirrors M3a, M3b, M1, and M2, toward the object 5. The second camera 25 captures an image of the transmitted light L3, which is reflected from the object 5 via mirrors M2, M1, M3b, and M3a. The transmitted light L3 is, for example, near-infrared light, and is transparent to the substrate 51 of the object 5. In this case, the second camera 25 is sensitive to near-infrared light. The second camera 25 may be, for example, an InGaAs camera. In this way, the head unit 20 also functions as a second imaging unit (imaging unit) that captures an image of the object 5 supported on the table 10 from the first surface 5a side using the transmitted light L3 that passes through the substrate 51. The head unit 20 is configured so that the laser light L1, the first observation light L2, and the transmitted light L3 are irradiated onto the object 5 coaxially.

[0023] In the above example, the laser processing apparatus 1 has light sources for the laser light L1, the first observation light L2, and the transmitted light L3 external to the head unit 20. However, at least one of the light sources may be internal to the head unit 20. The head unit 20 may be provided with a second movement mechanism (not shown) for moving the head unit 20 in at least one of the X, Y, and Z directions. The control unit 30 controls the second movement mechanism to drive the head unit 20 in at least one of the X, Y, and Z directions. The movement directions of the table 10 and the head unit 20 may be set, at least in combination, so that the object 5 can be moved relative to the irradiation positions of the laser light L1, the first observation light L2, and the transmitted light L3 in any of the X, Y, and Z directions.

[0024] The laser processing apparatus 1 includes a second focusing unit 27 and a third camera 29. The second focusing unit 27 and the third camera 29 are disposed on the opposite side of the head unit 20 across the table 10. The second focusing unit 27 includes a lens and focuses second observation light L4 emitted from a predetermined light source onto the object 5 via a mirror M4. The third camera 29 captures an image of the object 5 by receiving the reflected light of the second observation light L4 irradiated onto the object 5 via the mirror M4. The second observation light L4 is, for example, visible light. In this case, the third camera 29 is sensitive to visible light and near-infrared light. The second focusing unit 27 and the third camera 29 function as a third imaging unit that captures an image of the object 5 supported on the table 10 from the second surface 5b (the surface of the functional element layer 52) side using the second observation light L4 (acquiring an image of the second surface 5b, which is the surface of the functional element layer 52).

[0025] The control unit 30 is configured as a computer device including a processor, memory, storage, communication devices, etc. In the control unit 30, the processor executes software (programs) loaded into the memory, etc., and controls the reading and writing of data from and to the memory and storage, as well as communication via the communication devices. The control unit 30 controls the operation of each part of the laser processing apparatus 1. The specific operation of the control unit 30 will be described later.

[0026] The input unit 31 accepts input from a user and outputs the input to the control unit 30. The display unit 33 displays various information such as information accepted as input by the input unit 31, information output from the control unit 30, or information recorded in the recording unit 35. The input unit 31 and the display unit 33 may be integrated into a GUI (Graphical User Interface). The recording unit 35 records various information.

[0027] With the laser processing apparatus 1 described above, laser processing can be performed to form a weakened region J in the functional element layer 52 by irradiating the object 5 with laser light L1. FIG. 2 is a schematic cross-sectional view illustrating laser processing performed by the laser processing apparatus shown in FIG. 1. As shown in FIG. 2, with the laser processing apparatus 1, the object 5 is supported on the table 10 so that the first surface 5a faces the head unit 20, and the laser light L1 is irradiated from the first surface 5a. At this time, the focal point P (focusing position) of the laser light L1 is positioned near the interface B between the substrate 51 and the functional element layer 52 in the Z direction (inside the functional element layer 52 in the illustrated example).

[0028] That is, the laser light L1 passes through the substrate 51 and is focused at the focusing position, where it is used to process the object 5. In this state, the table 10 and / or the head unit 20 are driven along the X direction, whereby the focusing point P of the laser light L1 is moved along the X direction relative to the object 5. As a result, the laser light L1 is irradiated onto the object 5 along a line A along the X direction. As a result, a weakened region J is formed in the functional element layer 52 along the line A.

[0029] The weakened region J is a region where the functional device layer 52 has been weakened. Weakened regions include embrittlement. Weakening of the functional device layer 52 refers to thermal damage such as melting and evaporation due to absorption of the laser light L1, changes in chemical bonds due to laser irradiation, and non-thermal processing such as cutting or ablation in at least a portion of the functional device layer 52 (e.g., a portion of the functional device layer 52 and at least one of the layers constituting the functional device layer 52). Weakening of the functional device layer 52 refers to a state in which the functional device layer 52 is more susceptible to cutting or breaking than an untreated region (an unweakened region) when subjected to bending stress, tensile stress, or other stress. The weakened region (embrittlement region) J can also be considered a region where traces of laser irradiation have been created, and is more susceptible to cutting or breaking than an untreated region. The weakened region J may be formed continuously in a line shape in at least a portion of the functional device layer 52, or may be formed intermittently according to the pulse pitch of the laser irradiation.

[0030] That is, when the weakened region J is formed by irradiating the laser beam as a pulsed beam, by arranging a plurality of weakened spots, each of which is formed by irradiating one pulse of laser beam, adjacent weakened spots may be continuously connected, intermittently connected, or separated and independent from each other. Furthermore, the weakened spots may be exposed on the surface (second surface 5 b) of the functional element layer 52, and the exposed weakened spots may be continuously connected, intermittently connected, or separated and independent from each other.

[0031] The lines A are set along the X direction so as to pass through street regions between the functional elements included in the functional element layer 52 (in practice, a plurality of lines A may be set in a grid pattern along the X and Y directions). The lines A are planned cutting lines for cutting the object 5 for each functional element. Therefore, by forming the weakened regions J in the functional element layer 52 (street regions) along the lines A as described above, it becomes possible to cut the object 5 along the lines A with high precision using a relatively small external force.

[0032] In recent years, in order to cope with the trend toward finer wiring in devices, low-k films have been adopted as insulating films, and the number of layered patterns has increased with the trend toward three-dimensionality, resulting in the formation of multiple layers of films, metal wiring, and metal films, making it more effective to form the weakened region J as described above. Accordingly, a method for acquiring suitable processing conditions for forming the weakened region J is desired. Therefore, the laser processing apparatus 1 acquires suitable processing conditions for laser processing to form the weakened region J. The acquisition of these processing conditions will be described below.

[0033] 3 is a flowchart showing an example of a processing condition acquisition method performed by the laser processing apparatus shown in FIG. As shown in FIG. 3, first, the energy of the laser light L1 emitted from the first focusing unit 21 (objective lens) is set (step S1). As shown in FIG. 4, the laser light L1 emitted from the first focusing unit 21 is attenuated by reflection from the first surface 5a, which is the incident surface of the target 5 for the laser light L1, and absorption by the substrate 51 before reaching the interface B between the substrate 51 and the functional device layer 52. Therefore, the energy E of the laser light L1 emitted from the first focusing unit 21 is calculated using the formula "e = E × (1 - reflectance) × transmittance" relative to the energy e of the laser light L1 at the interface B required to form a weakened region J in the functional device layer 52.

[0034] The "reflectance" indicates the reflectance of the first surface 5a of the laser beam L1, and is, for example, 31.9%. The transmittance is the transmittance of the laser beam L1 through the substrate 51 and is calculated based on the relationship between the absorption coefficient α of the substrate 51 and the thickness t of the substrate 51: "Amount of transmitted light = Amount of incident light × exp(-αt)." For example, the transmittance is 41.0%. Therefore, when the energy e is 45 μJ, the above calculation formula becomes 45 μJ = E × (1 - 0.319) × (0.41), and the energy E is calculated to be approximately 160 μJ. In step S1, the energy E of the laser beam L emitted from the first focusing unit 21 can be set at the light source by inputting the calculated value via the input unit 31. However, in step S1, the control unit 30 may automatically calculate and set the energy E based on various conditions, such as the thickness and structure of the target object 5 or the type of laser processing.

[0035] Next, as shown in FIG. 3, other parameters are set (step S2). Here, the pulse pitch and number of passes of the laser light L1 are set. The number of passes refers to the number of times (number of scans) that the laser light L1 is irradiated onto one line A while changing the focusing position in the Z direction (or while maintaining the focusing position in the Z direction). Here, as an example, the pulse pitch can be set to approximately 0.5 μm, and the number of passes can be set to 1 pass. In step S2, the light source can be set by accepting input of the parameters via the input unit 31. However, in step S2, the control unit 30 can also automatically select and set the parameters based on various conditions, such as the thickness and structure of the target object 5 or the mode of laser processing.

[0036] Next, a defocus value is calculated when the focal position of the laser light L in the Z direction is at interface B (step S3). In step S3, as shown in FIG. 5A, the defocus value DB is the relative movement amount of the first focusing unit 21 (head unit 20) for changing the focal position of the laser light L from a state in which the focal position (focus point P) of the laser light L is aligned with the first surface 5a to interface B, and is calculated based on the thickness T5 of the substrate 51 and a coefficient based on the refractive index of the substrate 51, etc. The coefficient is the ratio of the movement amount of the focal point P inside the substrate 51 to the movement amount of the focal point P outside the substrate 51, and is approximately 4.11 in the case of the silicon substrate 51 and this experimental system. The thickness T5 of the substrate 51 is, for example, approximately 730 μm. As a result, the defocus value DB is calculated to be, for example, approximately 178 μm by dividing the thickness T5 by the coefficient. In step S3, the setting can be performed by inputting the value calculated in this way via the input unit 31. However, also in step S3, the control unit 30 may automatically calculate and set the defocus value DB based on various conditions such as the thickness and structure of the object 5 or the mode of laser processing.

[0037] Next, the number of bursts of the laser light L1 is set (step S4: steps 5, 6, and 7). More specifically, the laser light L1 is pulsed light as shown in FIG. 6, and the number of bursts constituting each pulse (burst number) can be set. FIG. 6(a) shows a case where the burst number is 1 (i.e., no burst), and FIG. 6(b) shows a case where the burst number is 4 (i.e., four bursts). The pulse pitch is the same value set in step S2 (e.g., 0.5 μm), and the period T (frequency interval) is about 5 μs, but the burst interval TP is, for example, 25 ns in the case of four bursts. Note that the numerical values ​​shown are examples where the repetition frequency is 200 kHz.

[0038] The light intensity in the case of four bursts is reduced to about one-fourth of the light intensity in the case of one burst. Therefore, when the number of bursts is changed, the presence or absence of damage to the first surface 5a, which is the incident surface of the laser light L1, changes. For this reason, in this step S4, the number of bursts is set so as not to cause damage to the first surface 5a.

[0039] To achieve this, in step S4, the control unit 30 first controls the first movement mechanism and / or the second movement mechanism and the laser irradiation unit to set the focusing position of the laser light L1 in the Z direction to a predetermined position, and then irradiates the target object 5 with the laser light L1 multiple times at different positions on the first surface 5a while changing the number of bursts of the laser light L, thereby performing laser processing (second processing) (step S5). At this time, the focusing position of the laser light L1 in the Z direction can be set to the position of the interface B, for example, by using the defocus value DB set in step S3. Furthermore, the specific numerical value of the number of bursts for each second processing can be set, for example, to a value input via the input unit 31.

[0040] Furthermore, in each second processing, the laser beam L1 can be irradiated along one line A for one burst number. That is, in this step S4, after the laser beam L1 is irradiated along one line A with one burst number, the focusing position of the laser beam L1 can be moved in the Y direction to be positioned on another line A, and the laser beam L1 can be irradiated along the other line A with a different burst number. In this case, different positions on the first surface 5a mean different positions in the Y direction.

[0041] Subsequently, in step S4, the control unit 30 controls the first moving mechanism and / or the second moving mechanism and the first imaging unit to capture images of the first surface 5a at each position on the first surface 5a where the second processing has been performed multiple times, thereby obtaining first surface images (step S6). Here, for example, after capturing an image of the first surface 5a for one line A using the first observation light L2 and the first camera 23, the head unit 20 is moved relatively to another line A, and an image of the first surface 5a for the other line A is captured using the first observation light L2 and the first camera 23, thereby obtaining multiple first surface images.

[0042] 7 is a diagram showing multiple first-surface images. As shown in FIG. 7, in the case of a 4-burst laser beam L1 where the number of bursts is four, a 6-burst laser beam L1 where the number of bursts is six, and a 10-burst laser beam L1 where the number of bursts is ten, damage D occurs on the first surface 5a, and the first-surface images F1 to F3 include an image M of the damage D extending along the X direction. In contrast, in the case of a 14-burst laser beam L1 where the number of bursts is fourteen, no damage D occurs on the first surface n5a, and the first-surface image F4 does not include an image M of the damage D. Note that a reticle image R is shown in each of the first-surface images F1 to F4 in FIG.

[0043] Thus, in step S4, the control unit 30 can associate the acquired multiple first-side images with the burst numbers corresponding to the first-side images and display them side by side on the display unit 33. At the same time, in step S4, the control unit 30 acquires, as a laser processing condition, the burst number of the second processing corresponding to the first-side image 5a that is not damaged (the smallest number among the acquired multiple first-side images, which is 14 in this example) (step S7). Here, the control unit 30 may automatically acquire the burst number of the second processing corresponding to the first-side image that does not contain the damage image M by image processing of the first-side image, or may acquire the burst number by inputting the burst number that is determined to be not damaged on the first side 5a based on the multiple first-side images displayed on the display unit 33.

[0044] Then, in step S4, the number of bursts to be used in actual processing is set based on the acquired number of bursts (e.g., 14). Here, the acquired number of bursts itself may be set, or a number of bursts obtained by adding a predetermined margin to the acquired number of bursts (e.g., 16) may be set.

[0045] In the next step, a set range of the focusing position of the laser beam L1 in the Z direction is acquired (step S5). More specifically, in step S5, as shown in Fig. 8, the control unit 30 controls the first moving mechanism and / or the second moving mechanism and the laser irradiation unit to change the focusing position (focus point P) of the laser beam L1 in the Z direction within a range including the interface B, thereby performing laser processing (first processing) multiple times at different positions on the first surface 5a (first step, first process).

[0046] Here, for example, after irradiating the laser beam L1 along one line A at one focusing position, the focusing position of the laser beam L1 is moved in the Y direction to be positioned on another line A, and the laser beam L1 can be irradiated at another focusing position along the other line A. In this case, different positions within the first surface 5a mean different positions in the Y direction.

[0047] Furthermore, changing the focusing position within a range including the interface B means changing the defocus value around the defocus value DB, since the defocus value DB where the focusing position is the interface B as described above has been acquired. As an example, the defocus value DB is 178 μm, and the first processing can be performed while changing the defocus value from 174 μm to 202 μm at a pitch of 2 μm. Specific numerical values ​​of these defocus values, such as the start value, end value, and pitch, can be acquired by, for example, accepting input via the input unit 31.

[0048] Subsequently, in step S5, the control unit 30 controls the first moving mechanism and / or the second moving mechanism and the second imaging unit to capture an image of the interface B from the first surface 5a side using the transmitted light L3 that passes through the substrate 51 at each position on the first surface 5a where the first processing has been performed multiple times, thereby obtaining an interface image (second step, second processing). Here, for example, after capturing an image of the interface B for one line A using the transmitted light L3 and the second camera 25, the head unit 20 is moved relatively to another line A, and an image of the interface B for the other line A is captured using the transmitted light L3 and the second camera 25. In this way, multiple interface images can be obtained.

[0049] FIG. 9 is a diagram illustrating a plurality of interface images. FIG. 9 illustrates a selection of interface images D1 to D6 from the plurality of interface images acquired as described above. The defocus values ​​corresponding to the interface images D1 to D6 increase sequentially from interface image D1 to interface image D6. As an example, interface image D1 corresponds to a defocus value of 178 μm, interface image D2 corresponds to a defocus value of 182 μm, interface image D3 corresponds to a defocus value of 186 μm, interface image D4 corresponds to a defocus value of 190 μm, interface image D5 corresponds to a defocus value of 194 μm, and interface image D6 corresponds to a defocus value of 198 μm. Here, of interface images D1 to D6, interface images D2 to D5 contain images N of damage caused by laser light L1.

[0050] Thus, depending on the focusing position (defocus value) of the laser light L1, an image N of damage caused by the laser light L1 may or may not appear in the interface image. When the focusing position of the laser light L1 is within a range in which the image N of damage appears in the interface image, a weakened region J that enables high-quality cutting of the object 5 tends to be suitably formed. Here, as an example, it is considered that a defocus value at which a weakened region J is suitably formed exists within the defocus value range of 182 μm to 194 μm, which corresponds to interface images D2 to D5.

[0051] Based on this knowledge, in step S5, the control unit 30 subsequently acquires, as one of the laser processing conditions, the range of focal positions in the Z direction of the first processing, from which interface images D2 to D6 containing the damage image N of the laser beam L1 were acquired (third step). As an example, a defocus value range (i.e., a focal position range) of 182 μm to 194 μm corresponding to interface images D2 to D5 may be acquired. The control unit 30 may also automatically determine whether the damage image N is included in a certain interface image by image processing of the interface images.

[0052] Alternatively, the control unit 30 may record each of the acquired interface images in the recording unit 35 in association with the corresponding focusing position of the first processing (third process), and may also control the display unit 33 to display each of the interface images recorded in the recording unit 35 on the display unit 33 (fourth process). This may prompt the user to determine whether or not a damage image N is included in a certain interface image based on the interface image displayed on the display unit 33.

[0053] Incidentally, the range of the light-condensing position where weakened region J is suitably formed in functional device layer 52 is more likely to be obtained on the functional device layer 52 side than on interface B between substrate 51 and functional device layer 52. In the above example, the defocus value DB where the light-condensing position becomes interface B is 178 μm, but by changing the defocus value in the range of 174 μm to 202 μm, interface images D2 to D6 including damage image N at 182 μm to 194 μm are obtained.

[0054] In this way, the range of Z-direction positions (defocus values) for changing the focusing position in step S5 can include a first range (e.g., a defocus value range of 174 μm to 178 μm) located closer to the first surface 5a than the interface B, and a second range (e.g., a defocus value range of 178 μm to 202 μm) located closer to the second surface 5b than the interface B and wider than the first range.

[0055] In the next step, a more suitable value for the focusing position is determined from the range of focusing positions obtained in step S5 (step S6). To achieve this, in step S6, the object 5, which has been subjected to the first processing at the multiple focusing positions in step S5 to form weakened regions J, is first cut along each of the weakened regions J (step S4). The weakened regions J are formed along each of multiple lines A extending along the X direction. Therefore, in this step, the object 5 is cut along each of multiple lines A extending along the X direction.

[0056] A method of cutting the object 5 may be a method (laser dicing) in which laser light is irradiated onto the object 5 along each of the lines A to form modified areas and cracks extending from the modified areas inside the object 5, and cutting is performed starting from the modified areas and cracks.

[0057] Then, in step S6, the surface (second surface 5b) of the functional element layer 52 of the cut object 5 is imaged (step S4). This allows for the determination of a more suitable focusing position by evaluating the cutting quality corresponding to the first processing at each focusing position based on the obtained images. Note that when imaging the second surface 5b, the third imaging unit consisting of the second focusing unit 27 and the third camera 29 may be used, or a separate imaging device may be used. As a result, suitable processing conditions for forming the weakened region J are acquired.

[0058] As described above, in the processing condition acquisition method according to this embodiment, laser processing conditions for forming a weakened region J in the functional device layer 52 on the second surface 51b of the substrate 51 are acquired by irradiating the substrate 51 with laser light L1 from the first surface 5a. To achieve this, multiple laser processing operations (first processing) are performed while varying the focusing position of the laser light L1 in the Z direction within a range including the interface B between the substrate 51 and the functional device layer 52. Furthermore, at each of the multiple laser processing operations, an interface image is acquired by capturing an image of the interface B between the substrate 51 and the functional device layer 52. The range of the focusing position of the laser light L1, within which an interface image including an image N of damage caused by the laser light L1 is acquired, is then acquired as one of the laser processing conditions. In this way, this method makes it possible to acquire processing conditions suitable for forming the weakened region J (the range of focusing positions, i.e., the range of defocus values ​​in the above example).

[0059] Furthermore, in the processing condition acquisition method according to this embodiment, the range of positions in the Z direction over which the focusing position is changed in step S5 includes a first range located closer to the first surface 5a than the interface B, and a second range that is wider than the first range and located on the opposite side of the first surface 5a (the second surface 5b side) than the interface B. In this way, by widening the range over which the focusing position is changed closer to the functional device layer 52 than the interface B, it is possible to acquire the range more quickly and reliably.

[0060] Furthermore, in the processing condition acquisition method according to this embodiment, in step S6, the object 5 is cut and an image of the surface of the functional device layer 52 of the cut object 5 is captured. In step S5, the laser light L1 is irradiated along the X direction (line A) along the first surface 5a, and in step S6, the object 5 is cut along the X direction. In this way, by actually cutting the object 5 and capturing an image of the surface of the functional device layer 52, it is possible to determine a more suitable focusing position by evaluating the cutting quality.

[0061] In the processing condition acquisition method according to this embodiment, in step S4, the second processing is performed multiple times as laser processing at different positions on the first surface 5a while varying the burst number of the pulsed laser light L1. Also in step S4, the first surface 5a is imaged at each position (line A) on the first surface 5a where the multiple second processing operations were performed to acquire first surface images. The burst number of the second processing at which a first surface image showing no damage to the first surface 5a was acquired among the multiple acquired first surface images is then acquired as another laser processing condition. Therefore, it is possible to acquire suitable processing conditions (burst number) that allow the weakened region J to be formed without damaging the first surface 5a, which is the incident surface of the laser light L1.

[0062] In this embodiment, the laser processing apparatus 1 irradiates the first surface 5a of the substrate 51 of the object 5 with laser light L1 to obtain laser processing conditions for forming a weakened region J in the functional element layer 52 on the second surface 51b of the substrate 51. To achieve this, the first processing, which is laser processing, is performed multiple times while changing the focusing position of the laser light L1 in the Z direction within a range including the interface B between the substrate 51 and the functional element layer 52. Furthermore, at each of the positions (lines A) where the first processing was performed multiple times, the interface B between the substrate 51 and the functional element layer 52 is imaged to obtain an interface image. The laser processing apparatus 1 then records each of the interface images in association with the corresponding focusing positions in the recording unit 35. By referencing the record, the range of focusing positions at which an interface image including an image N of damage caused by the laser light L1 was obtained can be obtained as one of the laser processing conditions. In this way, the laser processing apparatus 1 can obtain processing conditions (the range of focusing positions) suitable for forming the weakened region J.

[0063] Furthermore, the laser processing apparatus 1 according to this embodiment includes a display unit 33 that displays the image captured by the second imaging unit (second camera 25), and the control unit 30 may control the display unit 33 to display each of the interface images recorded in the recording unit 35 on the display unit 33. In this case, based on the interface image displayed on the display unit 33, it becomes possible to easily grasp the range of the focusing position at which the interface image including the image N of damage caused by the laser light L among the multiple interface images was acquired.

[0064] The above embodiment has been described as one aspect of the present disclosure. Therefore, the present disclosure is not limited to the above aspect and can be modified as desired.

[0065] Fig. 10 is a schematic diagram showing the overall configuration of a head unit according to a modified example. The head unit 20A shown in Fig. 10 differs from the head unit 20 in that the optical axes of the laser light L1 and the first observation light L2 and the transmitted light L3 are separate from each other. Therefore, the head unit 20A includes a first focusing unit 21 that focuses the laser light L1 and the first observation light L2 toward the object 5, and a third focusing unit 22 that focuses the transmitted light L3 toward the object 5. Whether the laser light L1, the first observation light L2, and the transmitted light L3 are coaxial or separate can be freely selected.

[0066] 1 is an example in which a transparent table 10 that is transmissive to the second observation light L4, such as visible light and near-infrared light, can be used. However, the laser processing apparatus 1 does not necessarily require the use of a transparent table 10. If the object 5 is supported by an opaque table (e.g., a normal porous table), the third imaging unit, which is composed of the second focusing unit 27 and the third camera 29, can be positioned on the same side of the table as the head unit 20. In this case, when the functional element layer 52 of the object 5 is imaged by the third imaging unit, the object 5 can be re-supported so that the functional element layer 52 faces the third imaging unit.

[0067] Furthermore, in the above example, in each of step S4 of acquiring the number of bursts as a processing condition and step S5 of acquiring the range of the focusing position, an example has been described in which processing is performed along one line A for one number of bursts and one focusing position, but processing may be performed for two or more numbers of bursts and two or more focusing positions at different positions on one line A. This is because processing a length of about 15 mm is considered sufficient to determine the presence or absence of damage images M and N when evaluating a suitable number of bursts and focusing position.

[0068] After the laser processing in which the laser light L1 is incident on the object 5 from the first surface 5a side to form the weakened region J on the functional element layer 52 side as described above, a third processing in which a modified region and a crack extending from the modified region are formed in the substrate 51 by irradiating the laser light, and a fourth processing in which the substrate 51 is ground from the first surface 5a side to thin it to a desired thickness may be further performed. In the third processing, while the laser light is incident on the object 5 from the first surface 5a side, the focusing position of the laser light is relatively moved along the line A, so that a modified region can be formed inside the substrate 51 at the focusing position and a crack extending from the modified region in the Z direction can be formed.

[0069] A processing condition acquisition method and a laser processing device are provided that are capable of acquiring processing conditions suitable for forming a weakened region.

[0070] 1...laser processing device, 5...object, 5a...first surface, 10...table (support part), 20...head part (laser irradiation part, imaging part), 30...control part, 33...display part, 35...recording part, 51...substrate, 51b...second surface, 52...functional element layer, L1...laser light, L3...transmitted light, J...weakened area.

Claims

1. A processing condition acquisition method for acquiring laser processing conditions for forming a weakened region in a functional element layer by irradiating a target object having a substrate including a first surface and a second surface opposite to the first surface with laser light from the first surface side, the processing condition acquisition method comprising: a first step of performing a first processing as the laser processing multiple times at different positions within the first surface while changing the focusing position of the laser light in a Z direction intersecting the first surface within a range including the interface between the substrate and the functional element layer; a second step of acquiring an interface image by capturing an image of the interface between the substrate and the functional element layer from the first surface side using light transmitted through the substrate at each of the positions within the first surface where the first processing has been performed multiple times; and a third step of acquiring, as one of the laser processing conditions, the range of the focusing position in the Z direction of the first processing at which an interface image including damage caused by the laser light was acquired among the multiple interface images acquired in the second step.

2. A processing condition acquisition method as described in claim 1, wherein the range of Z-direction positions in which the focusing position is changed in the first step includes a first range located on the first surface side of the interface, and a second range located on the opposite side of the interface from the first surface and wider than the first range.

3. The processing condition acquisition method according to claim 1 or 2, further comprising a fourth step of cutting the object and imaging the surface of the functional element layer of the cut object after the first step, the second step, and the third step, wherein in the first step, the laser light is irradiated along the X direction along the first surface, and in the fourth step, the object is cut along the X direction.

4. A processing condition acquisition method according to any one of claims 1 to 3, comprising: a fifth step of performing second processing as the laser processing a plurality of times at different positions on the first surface while changing the number of bursts of the laser light which is pulsed light; a sixth step of capturing images of the first surface at each of the positions on the first surface where the second processing has been performed a plurality of times to obtain first surface images; and a seventh step of acquiring, as another condition for the laser processing, the number of bursts of the second processing at which a first surface image showing no damage to the first surface has been obtained among the plurality of first surface images acquired in the sixth step.

5. A laser processing device that acquires laser processing conditions for forming a weakened region in a functional element layer by irradiating a target object having a substrate including a first surface and a second surface opposite to the first surface with laser light from the first surface side, the laser processing device comprising: a support unit that supports the target object; a laser irradiation unit that irradiates the target object supported by the support unit with the laser light from the first surface side; an imaging unit that images the target object supported by the support unit from the first surface side using transmitted light that passes through the substrate; and a control unit that controls the laser irradiation unit and the imaging unit, wherein the control unit controls the laser irradiation unit to perform a first process as the laser processing multiple times at different positions within the first surface while changing the focusing position of the laser light in a Z direction that intersects with the first surface within a range that includes the interface between the substrate and the functional element layer; a second process for capturing an image of an interface between the substrate and the functional element layer from the first surface side using the transmitted light at each position within the first surface where the first processing has been performed multiple times by controlling the imaging unit, and acquiring an interface image; and a third process for recording each of the multiple interface images acquired in the second process in association with each of the corresponding light focusing positions in the first processing.

6. The laser processing device according to claim 5, further comprising a display unit that displays the images captured by the imaging unit, and wherein the control unit controls the display unit to execute a fourth process that causes each of the interface images recorded in the third process to be displayed on the display unit.

Images