Laser beam correction method

Abstract

To provide a laser beam correction method capable of performing a correction of a position of a sprit laser and a line laser at high accuracy.SOLUTION: A laser beam correction method contains a step of performing an edge cutting processing for forming a first groove of two rows in parallel each other along a processing feeding direction by collecting a sprit laser to a laser irradiation surface via a laser optical system while relatively moving a laser optical system (14) to a processing feeding direction against a positioning workpiece (W2) containing a material that a laser irradiation mark at least laser irradiation surface can be easily detected, and performing a hollowing processing for forming a second groove by collecting a line laser to the laser irradiation surface via the laser optical system; a step of detecting first and second grooves by a microscope (20); and a step of correcting a light collecting position of the sprit laser and the line laser on the basis of a detection result of the first groove and the second groove.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser beam correcting method, and more particularly to a laser beam correcting method for a laser processing apparatus that irradiates a wafer with laser beam to perform laser processing. [Background technology]

[0002] In the field of semiconductor device manufacturing, wafers (semiconductor wafers) are known in which multiple devices are formed by stacking a low-dielectric-constant insulating film (Low-k film) and a functional film that forms circuits on the surface of a substrate such as silicon. In such wafers, the multiple devices are partitioned into a grid by grid-like streets, and the individual devices are manufactured by dividing the wafer along the planned division lines.

[0003] Low-k films are brittle and prone to peeling, so when dicing using a blade, the low-k film may peel off, damaging the device. To address this brittleness and peelability of low-k films, a method is known in which two first grooves that divide the low-k film are formed on both sides of the planned dividing line by laser ablation, and then a second groove is formed between the two first grooves (for example, Patent Document 1).

[0004] Laser ablation processing uses two types of laser light: a split laser with a split shape to form the first groove, and a line laser with a line shape to form the second groove. In this type of laser ablation processing, if there is one focusing lens, switching between the split laser and line laser shapes may cause a shift in the focusing position on the wafer. On the other hand, if there are two or more focusing lenses, switching shapes is not necessary, but a shift in the relative position of the focusing lenses may cause a shift in the focusing position on the wafer. Since a shift in the focusing position on the wafer deteriorates the processing quality, it is necessary to adjust the focusing positions of these two types of laser light.

[0005] In relation to the above point, Patent Document 1 discloses a method for correcting the positions of a first groove and a second groove by forming a first groove on a planned dividing line in a device region of a wafer and forming a second groove on a planned dividing line in a peripheral surplus region. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-154009 Summary of the Invention [Problem to be solved by the invention]

[0007] In the method described in Patent Document 1, since the excess area on the outer periphery of the wafer is processed, if the split laser and the line laser are misaligned, laser grooves with improper shapes may be formed in some areas. If laser grooves with improper shapes exist, they may cause uneven wear on the blade during blade processing after laser ablation processing.

[0008] Furthermore, depending on the wafer, it may be difficult to detect the position of the laser groove due to the influence of the pattern or debris, etc. With such a wafer, there is a risk that the focusing position of the laser light cannot be correctly corrected.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laser beam correction method that can accurately correct the positions of a split laser and a line laser. [Means for solving the problem]

[0010] In order to solve the above problem, a laser beam correction method according to a first aspect of the present invention includes the steps of: moving a laser optical system relative to a workpiece for alignment, the laser optical system including a material on at least the laser irradiation surface of which laser irradiation marks are easy to detect, in the processing feed direction, while focusing a split laser on the laser irradiation surface via the laser optical system to perform edge cutting processing to form two first grooves that are parallel to each other along the processing feed direction, and focusing a line laser on the laser irradiation surface via the laser optical system to form a second groove; detecting the first groove and the second groove using a microscope; and correcting the focusing positions of the split laser and the line laser based on the detection results of the first groove and the second groove.

[0011] A laser beam correcting method according to a second aspect of the present invention is the method of the first aspect, wherein the work for alignment is a wafer or alignment paper with a polyimide film.

[0012] A laser beam correction method according to a third aspect of the present invention is such that, in the first or second aspect, when edge cutting and hollowing are performed, one of the split laser and the line laser is scanned in the processing feed direction, and the other of the split laser and the line laser is scanned in a direction oblique to the processing feed direction.

[0013] A laser beam correcting method according to a fourth aspect of the present invention is the first or second aspect, in which the split laser and the line laser are focused on a workpiece to be aligned as a single-pulse laser.

[0014] A laser beam correcting method according to a fifth aspect of the present invention is the method of any one of the first to fourth aspects, wherein an overlap ratio of the split laser and the line laser on the laser irradiation surface is set to zero.

[0015] A laser beam correction method according to a sixth aspect of the present invention is any of the first to fifth aspects, in which at least two alignment marks are formed on the workpiece for alignment along the processing feed direction, and the focusing positions of the split laser and the line laser are corrected based on the detection results of the alignment marks and the first and second grooves.

[0016] A seventh aspect of the present invention relates to a laser beam correction method according to any one of the first to sixth aspects, wherein the workpiece for alignment is held on a sub-table separate from a table for holding the workpiece to be machined. [Effects of the Invention]

[0017] According to the present invention, the positions of the split laser and the line laser can be corrected with high precision. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of a laser processing device according to one embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of a wafer to be processed. [Figure 3] FIG. 3 is an explanatory diagram for explaining laser processing along odd-numbered streets. [Figure 4] FIG. 4 is an explanatory diagram for explaining laser processing along the even-numbered streets. [Figure 5] FIG. 5 is a plan view showing the arrangement of the table and sub-tables. [Figure 6] FIG. 6 is a plan view showing an example in which the workpiece W2 for alignment has been subjected to edge cutting and hollowing. [Figure 7] FIG. 7 is an enlarged view of part VII in FIG. [Figure 8] FIG. 8 is a diagram for explaining the laser beam correcting method according to the first embodiment. [Figure 9] FIG. 9 is a plan view showing an alignment workpiece according to the second embodiment. [Figure 10] FIG. 10 is a diagram for explaining a laser beam correcting method according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser beam correcting method according to an embodiment of the present invention will now be described with reference to the accompanying drawings.

[0020] [Laser processing equipment] Figure 1 is a schematic diagram of a laser processing device according to one embodiment of the present invention. As shown in Figure 1, the laser processing device 1 performs laser processing (ablation groove processing) on ​​a wafer W1 as a pre-process before dividing the wafer W1 into multiple chips C (see Figure 2). Note that the X, Y, and Z directions in the figure are mutually orthogonal, with the X and Y directions being horizontal directions and the Z direction being a vertical direction. Here, the X direction corresponds to the processing feed direction of the present invention.

[0021] Figure 2 is a plan view of a wafer W1 to be processed. As shown in Figure 2, the wafer W1 is a laminated body in which a low-k film and a functional film that forms a circuit are laminated on the surface of a substrate such as silicon. The wafer W1 is divided into multiple areas by multiple streets S (planned division lines) arranged in a grid pattern. Each of these divided areas is provided with a device D that constitutes a chip C.

[0022] The laser processing apparatus 1 performs laser processing on the wafer W1 along each street S, as indicated by the bracketed numbers (1) to (4), ... in the figure, thereby removing low-k films and the like on the substrate.

[0023] At this time, in order to reduce the takt time required for laser processing of the wafer W1, the laser processing apparatus 1 alternately switches the relative movement direction when moving the laser optical system 14 (described later) relative to the wafer W1 in the X direction for each street S.

[0024] For example, when laser processing is performed along odd-numbered streets S indicated by parenthesized numbers (1), (3), ... in the figure, the laser optical system 14 is moved relative to the wafer W1 in one direction in the X direction, that is, the forward direction X1. When laser processing is performed along even-numbered streets S indicated by parenthesized numbers (2), (4), ... in the figure, the laser optical system 14 is moved relative to the wafer W1 in the other direction in the X direction, that is, the backward direction X2 opposite to the forward direction X1.

[0025] Fig. 3 is an explanatory diagram for explaining laser processing along odd-numbered streets S. Fig. 4 is an explanatory diagram for explaining laser processing along even-numbered streets S.

[0026] 3 and 4, in this embodiment, edge cutting and hollowing are performed simultaneously (in parallel) as laser processing. The edge cutting is laser processing performed using two first laser beams (split lasers) L1, and forms two parallel edge cutting grooves G1 (two first grooves; ablation grooves) along the street S.

[0027] The hollowing process is a laser process for forming a hollow groove G2 (second groove; ablation groove) between the two edge cutting grooves G1 formed in the edge cutting process. In this embodiment, the hollowing process is performed using a second laser beam (line laser) L2 having a larger diameter than the two first laser beams L1.

[0028] In the laser processing device 1, in either case where the laser optical system 14 is moved relative to the wafer W1 in the forward direction X1 or in the backward direction X2, the edge cutting process is performed prior to the hollowing process.

[0029] As shown in FIG. 1, the laser processing device 1 includes a control device 10, a first laser light source 12A, a second laser light source 12B, a laser optical system 14, a microscope 20, and a relative movement mechanism 22.

[0030] As shown in Figure 1, two tables (table T1 and sub-table T2) are installed on the stage. A wafer (product workpiece) W1 to be processed is loaded and held on table T1. Meanwhile, a workpiece W2 for alignment is loaded and held on sub-table T2.

[0031] In this embodiment, laser processing is performed on a workpiece W2 for alignment held on a sub-table T2 using a first laser beam L1 and a second laser beam L2, and deviation of the processing position is corrected.

[0032] Here, it is preferable that the alignment workpiece W2 contains a material whose laser irradiation surface (surface) is at least easy to detect laser irradiation marks (grooves). As the alignment workpiece W2, for example, a wafer with a polyimide film (e.g., a silicon wafer) or alignment paper (e.g., burn paper or laser thermal paper) can be used. Furthermore, as the alignment workpiece W2, a workpiece with a highly reflective surface to be irradiated with the laser, for example, a workpiece with a mirror-finished surface, can also be used.

[0033] Under the control of the control device 10, the stage ST is moved in the X and Y directions by a relative movement mechanism 22 and rotated around the Z axis.

[0034] The first laser light source 12A emits laser light LA, which is a pulsed laser light having conditions (wavelength, pulse width, repetition frequency, etc.) suitable for edge cutting processing, to the laser optical system 14. The second laser light source 12B emits laser light LB, which is a pulsed laser light having conditions (wavelength, pulse width, repetition frequency, etc.) suitable for center cutting processing, to the laser optical system 14.

[0035] The laser optical system 14 forms two first laser beams L1 for edge cutting processing based on the laser beam LA from the first laser light source 12A. Furthermore, the laser optical system 14 forms one second laser beam L2 for center cutting processing based on the laser beam LB from the second laser light source 12B. The laser optical system 14 then emits (irradiates) the two first laser beams L1 from the first condenser lens 16 toward the street S. Furthermore, under the control of the control device 10, the laser optical system 14 selectively emits (irradiates) the second laser beam L2 from the second condenser lens 18A or 18B toward the street S.

[0036] Furthermore, the laser optical system 14 is moved in the Y and Z directions by a relative movement mechanism 22 under the control of the control device 10.

[0037] The microscope 20 is fixed to the laser optical system 14 and moves integrally with the laser optical system 14. The microscope 20 photographs an alignment reference (not shown) formed on the wafer W1 before the edge cutting and hollowing processes. The microscope 20 also photographs the two edge cutting grooves G1 and hollowing groove G2 formed along the street S by the edge cutting and hollowing processes. The photographed image (image data) taken by the microscope 20 is output to the control device 10, and the control device 10 displays it on a monitor (not shown).

[0038] The relative movement mechanism 22 includes an XYZ actuator and a motor, and moves the stage ST in the XY directions and rotates it about a rotation axis, and moves the laser optical system 14 in the Z direction under the control of the control device 10. This allows the relative movement mechanism 22 to move the laser optical system 14 relative to the stage ST and the wafer W1. Note that the method of relative movement is not particularly limited as long as it is possible to move the laser optical system 14 relative to the stage ST (wafer W1) in each direction (including rotation).

[0039] By driving the relative movement mechanism 22, it is possible to align the laser optical system 14 with respect to the processing start position, which is one end of the street S to be processed, and to relatively move the laser optical system 14 in the X direction (the forward direction side X1 or the backward direction side X2) along the street S. In addition, by driving the relative movement mechanism 22 to rotate the stage ST by 90°, it is possible to make each street S along the Y direction of the wafer W1 parallel to the X direction, which is the processing feed direction.

[0040] The control device 10 is configured, for example, by a personal computer, and includes various processors (for example, a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit)), a memory, and a storage device. The various functions of the control device 10 may be realized by one processor, or may be realized by multiple processors of the same or different types. The control device 10 comprehensively controls the operations of the first laser light source 12A, the second laser light source 12B, the laser optical system 14, the microscope 20, the relative movement mechanism 22, etc.

[0041] Fig. 5 is a plan view showing the arrangement of the table T1 and the sub-table T2. As shown in Fig. 5, in this embodiment, the sub-table T2 for holding the alignment workpiece W2 is provided near the table T1 for holding the wafer W1 to be processed. Note that the symbol F shown in Fig. 5 denotes a frame for holding the wafer W1.

[0042] 5, sub-table T2 is provided on stage ST and is movable together with table T1, but the present invention is not limited to this. Sub-table T2 may not be provided on stage ST, but may be movable independently of table T1.

[0043] FIG. 6 is a plan view showing an example in which the edge cutting and hollowing processes have been performed on the workpiece W2 for alignment, and FIG. 7 is an enlarged view of part VII in FIG.

[0044] When performing position correction, first, the surface of the workpiece W2 for alignment is subjected to edge cutting and hollowing to form two edge cutting grooves G1 and hollowing grooves G2 along the X direction.

[0045] Next, the microscope 20 photographs the two edge cutting grooves G1 and the center cut groove G2, and the control device 10 detects the Y-direction positions (Split Y position and Line Y position) of the two edge cutting grooves G1 and the center cut groove G2.

[0046] Next, the control device 10 adjusts the laser optical system 14 based on the detection results of the Split Y position and the Line Y position. That is, the irradiation positions of the first laser light (split laser) L1 and the second laser light (line laser) L2 are adjusted so that the center cut groove G2 (Line Y position) is contained within the two edge cut grooves G1 (Split Y position) and partially overlaps with the two edge cut grooves G1. As shown in FIG. 7, when the Y coordinates of the edges of the two edge cut grooves G1 are Ys1, Ys2, Ys3, and Ys4 and the Y coordinates of the edges of the center cut groove G2 are Yl1 and Yl2, the irradiation positions of the first laser light (split laser) L1 and the second laser light (line laser) L2 are adjusted so that Ys1 > Yl1 > Ys2 and Ys3 > Yl2 > Ys4.

[0047] In correcting the position of the laser beam, in addition to adjusting the irradiation positions of the first laser beam L1 and the second laser beam L2, the beam diameter or intensity of the second laser beam L2 may be adjusted to adjust the width of the hollow groove G2.

[0048] According to this embodiment, it is possible to prevent the wafer W1 to be processed from being processed in a state in which the focusing position of the first laser light (split laser) L1 and the focusing position of the second laser light (line laser) L2 are misaligned.

[0049] In addition, in this embodiment, a workpiece W2 for alignment can be selected that allows easy detection of the grooves formed by the first laser light (split laser) L1 and the grooves formed by the second laser light (line laser) L2, so that the focus position misalignment can be reliably detected.

[0050] In the laser beam correcting method according to this embodiment, it is possible to apply the following Examples 1 to 3 in combination.

[0051] [Example 1] FIG. 8 is a diagram for explaining the laser beam correcting method according to the first embodiment.

[0052] In the first embodiment, when machining the workpiece W2 for alignment, the second condenser lens 18A or 18B is moved in the Y direction to scan the second laser light (line laser) L2 in the Y direction, thereby performing oblique cutting.

[0053] Next, the two edge cutting grooves G1 and the center cut groove G2 are photographed using the microscope 20, and the positions of the two edge cutting grooves G1 and the center cut groove G2 are detected. Then, the Y-direction position Yo of the second condenser lens 18A or 18B at the point Po where the equidistant line (center line) Ycs between the two edge cutting grooves G1 intersects with the center line Ycl of the center cut groove G2 is determined.

[0054] When processing the wafer W1, by aligning the Y direction positions of the second focusing lenses 18A and 18B with Po, it is possible to prevent the processing of the wafer W1 to be processed in a state where the focusing positions of the first laser light (split laser) L1 and the second laser light (line laser) L2 are misaligned.

[0055] In addition, when performing oblique cutting, the edge cutting process and the hollowing process do not need to be performed in parallel. For example, after the first laser light (split laser) L1 is formed along the X direction, oblique cutting may be performed while moving the second condenser lens 18A or 18B or the illumination optical system 14.

[0056] Conversely to the above example, the hollow groove G2 may be formed along the X direction, and the two edge grooves G1 may be formed by cutting obliquely.

[0057] [Example 2] FIG. 9 is a plan view showing an alignment workpiece according to the second embodiment.

[0058] An alignment mark M1 is formed on the workpiece W2a for alignment according to Example 2. In the example shown in Fig. 9, the alignment mark M1 is cross-shaped and at least one pair (two marks) of marks are formed.

[0059] When correcting the laser irradiation position, the relative movement mechanism 22 aligns the arrangement direction of the pair of alignment marks M1 with the processing feed direction (X direction) and performs edge cutting and hollowing to form two edge cutting grooves G1 and hollowing grooves G2. Then, the amount of deviation δ in the Y direction between the line segment connecting the pair of alignment marks M1 and the center lines of the two edge cutting grooves G1 and hollowing grooves G2 along the X direction is calculated, and the irradiation positions of the first laser light (split laser) L1 and the second laser light (line laser) L2 are corrected based on the amount of deviation δ in the Y direction.

[0060] If the alignment workpiece W2a is a wafer with a polyimide film, the alignment mark M1 can be formed, for example, by removing a portion of the polyimide film. If the alignment workpiece W2a is alignment paper, the alignment mark M1 can be formed, for example, by printing.

[0061] According to Example 2, by using an alignment workpiece W2a with an alignment mark, it is possible to measure and correct the deviation between the target processing position and the actual processing position in addition to the relative positions of the first laser light (split laser) L1 and the second laser light (line laser) L2.

[0062] [Example 3] FIG. 10 is a diagram for explaining a laser beam correcting method according to the third embodiment.

[0063] In Example 3, when machining the workpiece W2 for alignment, single-pulse lasers are irradiated as the first laser beam (split laser) L1 and the second laser beam (line laser) L2, or machining is performed with the overlap ratio of the first laser beam L1 and the second laser beam L2 set to 0. This makes it possible to inspect in advance the two-dimensional machining shape of one pulse of each laser beam, as shown in Fig. 10.

[0064] FIG. 10 shows an example in which the overlap ratio of the irradiation positions of the first laser beam L1 and the second laser beam L2 is set to 0, and single pulses of the first laser beam L1 and the second laser beam L2 are irradiated.

[0065] In FIG. 10, symbols Sp1 and Sp2 indicate an example in which a single-pulse laser is irradiated as the first laser light L1, and symbols L1 and L2 indicate an example in which a single-pulse laser is irradiated as the second laser light L2.

[0066] As shown in FIG. 10, in examples Sp1 and L1, the processed shapes of the processed marks by one laser pulse are substantially point-symmetric with respect to each center (center of gravity).

[0067] In contrast, in examples Sp2 and L2, the machining shapes of the machining marks left by one laser pulse are asymmetric with respect to their respective centers (centers of gravity). When the machining shape of the machining marks left by one laser pulse is distorted as in examples Sp2 and L2, if machining feed is performed in the X direction, the depths and widths of the two edge-cut grooves G1 and the core-cut grooves G2 may become uneven. For this reason, the irradiation positions, beam diameters or intensities, orientations of the first condenser lens 16, and orientations of the second condenser lenses 18A and 18B of the first laser beam L1 and the second laser beam L2 are adjusted so that the machining shapes of the machining marks left by one laser pulse are approximately point-symmetric with respect to their respective centers (centers of gravity).

[0068] According to the third embodiment, the split laser and line laser can be corrected more effectively by adjusting the machining shape of the single pulse.

[0069] In addition, in the third embodiment, for example, a white light interference microscope may be used to measure the three-dimensional shape of the processing mark left by one laser pulse, so that inspection including the processing depth, three-dimensional shape, etc. can be performed in advance.

[0070] [Variations] In the above embodiment, a sub-table T2 is provided to hold the alignment workpiece W2, but the sub-table T2 can be omitted. That is, instead of the wafer W1 to be processed, the alignment workpiece W2 is loaded onto the table T1, and laser processing is performed on the alignment workpiece W2 using the first laser beam L1 and the second laser beam L2, and deviation of the processing position is corrected. Thereafter, the wafer W1 to be processed is loaded onto the table T1 and laser processing is performed.

[0071] According to this modification, the sub-table T2 can be omitted when correcting the positional deviation of the first laser beam L1 and the second laser beam L2. [Explanation of symbols]

[0072] REFERENCE SIGNS LIST 1...laser processing device, 10...controller, 12A...first laser light source, 12B...second laser light source, 14...laser optical system, 16...first condenser lens, 18A, 18B...second condenser lens, 20...microscope, 22...relative movement mechanism, T1...table, T2...sub-table

Claims

1. a step of performing edge cutting processing to form two parallel first grooves along the processing feed direction by focusing a split laser on the laser irradiation surface via the laser optical system while moving the laser optical system relatively in the processing feed direction for a workpiece to be aligned, the workpiece including a material on at least which laser irradiation surface is easy to detect laser irradiation marks; and performing hollowing processing to form second grooves by focusing a line laser on the laser irradiation surface via the laser optical system. detecting the first groove and the second groove with a microscope; correcting the focusing positions of the split laser and the line laser based on the detection results of the first groove and the second groove; A laser beam correction method comprising:

2. 2. The laser beam correcting method according to claim 1, wherein the work for alignment is a wafer with a polyimide film or alignment paper.

3. 3. The laser beam correction method according to claim 1, wherein when performing the edge cutting process and the hollowing process, one of the split laser and the line laser is scanned in the processing feed direction, and the other of the split laser and the line laser is scanned in a direction oblique to the processing feed direction.

4. 3. The laser beam correcting method according to claim 1, wherein the split laser and the line laser are focused on the workpiece as a single pulse laser.

5. The laser beam correcting method according to claim 1 , wherein an overlap ratio of the split laser and the line laser on the laser irradiation surface is set to zero.

6. At least two alignment marks are formed on the workpiece for alignment along the processing feed direction, 6. The laser beam correcting method according to claim 1, further comprising correcting focusing positions of the split laser and the line laser based on the detection results of the alignment mark, the first groove, and the second groove.

7. 7. The laser beam correcting method according to claim 1, wherein the workpiece for alignment is held on a sub-table separate from a table for holding a workpiece to be machined.

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