Laser processing equipment

Abstract

This invention provides a laser processing apparatus capable of accurately correcting the positions of split lasers and line lasers. [Solution] The laser processing apparatus (1) includes a table (T1, T2) that holds a workpiece for alignment, the laser irradiation surface of which is at least a material in which laser irradiation marks can be easily detected; a laser optical system (14) that performs edge cutting by focusing a split laser onto the laser irradiation surface to form two parallel first grooves along the processing feed direction, and performs hollowing by focusing a line laser onto the laser irradiation surface to form a second groove; a relative movement mechanism (22) that moves the laser optical system relative to the table in the processing feed direction; a microscope (20) that detects the first groove and the second groove; and a control device (10) that corrects the focusing positions of the split laser and the line laser based on the detection results of the first groove and the second groove.

Description

Technical Field

[0001] The present invention relates to a laser beam correction method, and particularly to a laser beam correction method in a laser processing apparatus that irradiates a wafer with a laser beam to perform laser processing.

Background Art

[0002] In the field of semiconductor device manufacturing, a wafer (semiconductor wafer) is known in which a plurality of devices are formed by a laminate in which a low dielectric constant insulator film (Low-k film) and a functional film forming a circuit are laminated on the surface of a substrate such as silicon. In such a wafer, a plurality of devices are partitioned in a lattice pattern by lattice-shaped streets, and individual devices are manufactured by dividing the wafer along a planned division line.

[0003] Since the Low-k film is brittle and easily peeled off, in dicing using a blade, the Low-k film may be peeled off and damage the device. To cope with such vulnerability and peelability of the Low-k film, after forming two first grooves for dividing the Low-k film on both sides of the planned division line by laser ablation processing, a method of forming a second groove between the two first grooves is known (for example, Patent Document 1).

[0004] In laser ablation processing, two types of laser beams are used: a split laser beam having a split shape for forming the first groove and a line laser beam having a line shape for forming the second groove. In such laser ablation processing, when there is one condensing lens, there is a possibility that a deviation in the condensing position on the wafer may occur by switching the shapes of the split laser beam and the line laser beam. On the other hand, when there are two or more condensing lenses, shape switching is unnecessary, but a deviation in the condensing position on the wafer may occur due to a deviation in the relative positions of the condensing lenses. Since the processing quality deteriorates when the condensing position deviates on the wafer, it is necessary to adjust the condensing positions of these two types of laser beams.

[0005] In relation to the above, Patent Document 1 discloses a method for correcting the positions of the first groove and the second groove by forming a first groove on the division line within the device region of the wafer and a second groove on the division line within the outer peripheral excess region. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-154009 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In the method described in Patent Document 1, when processing the excess area on the outer edge of the wafer, if the positions of the split laser and the line laser are misaligned, laser grooves with an improper shape may be formed in some areas. The presence of improperly shaped laser grooves may cause uneven wear on the blade during blade processing after laser ablation.

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

[0009] This invention has been made in view of these circumstances, and aims 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] To solve the above problems, a laser beam correction method according to a first aspect of the present invention includes the steps 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 of a workpiece for alignment whose laser irradiation surface includes a material in which laser irradiation marks can be easily detected, while moving the laser optical system relative to the workpiece in the processing feed direction; and performing hollowing processing to form a second groove by focusing a line laser on the laser irradiation surface via the laser optical system; detecting the first and second grooves using a microscope; and correcting the focusing positions of the split laser and the line laser based on the detection results of the first and second grooves.

[0011] In the second aspect of the present invention, the laser beam correction method is such that, in the first aspect, the alignment workpiece is a wafer or alignment paper with a polyimide film.

[0012] A third aspect of the present invention relates to a laser beam correction method in which, in the first or second aspect, when performing edge cutting and hollowing, 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 fourth aspect of the present invention relates to a laser beam correction method in which, in the first or second aspect, a split laser and a line laser are focused onto a workpiece for alignment as single-pulse lasers.

[0014] A fifth aspect of the present invention relates to a laser beam correction method in which, in any of the first to fourth aspects, the overlap ratio of the split laser and the line laser on the laser irradiation surface is set to 0.

[0015] In the sixth aspect of the present invention, the laser beam correction method is characterized in that, in any of the first to fifth aspects, at least two alignment marks are formed on the alignment workpiece 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] In the laser beam correction method according to the seventh aspect of the present invention, in any of the first to sixth aspects, the alignment workpiece is held on a sub-table separate from the table for holding the workpiece to be processed.

Advantages of the Invention

[0017] According to the present invention, the positions of the split laser and the line laser can be accurately corrected.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 1 is a schematic diagram of a laser processing apparatus according to an 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 even-numbered streets. [Figure 5] FIG. 5 is a plan view showing the arrangement of the table and the sub-table. [Figure 6] FIG. 6 is a plan view showing an example in which the alignment workpiece W2 is subjected to trimming and punching. [Figure 7] FIG. 7 is an enlarged view of part VII of FIG. 6. [Figure 8] FIG. 8 is a diagram for explaining the laser beam correction method according to Example 1. [Figure 9] FIG. 9 is a plan view showing the alignment workpiece according to Example 2. [Figure 10] FIG. 10 is a diagram for explaining the laser beam correction method according to Example 3.

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments of the laser beam correction method according to the present invention will be described with reference to the attached drawings.

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

[0021] Figure 2 is a plan view of the wafer W1 to be processed. As shown in Figure 2, the wafer W1 is a laminate formed by stacking a low-k film and a functional film that forms circuits on the surface of a substrate such as silicon. The wafer W1 is divided into multiple regions by multiple streets S (planned division lines) arranged in a grid. Devices D that constitute a chip C are provided in each of these divided regions.

[0022] As shown by the parenthetical numbers (1) to (4) in the figure, the laser processing apparatus 1 removes the low-k film and the like on the substrate by performing laser processing on the wafer W1 along each street S.

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

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

[0025] Figure 3 is an explanatory diagram illustrating laser processing along odd-numbered streets S. Figure 4 is an explanatory diagram illustrating laser processing along even-numbered streets S.

[0026] As shown in Figures 3 and 4, in this embodiment, edge cutting and hollowing are performed simultaneously (in parallel) as laser processing. Edge cutting is a laser processing method that uses 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 that forms a hollowing groove G2 (second groove, ablation groove) between the two edge cutting grooves G1 formed by the edge cutting process. In this embodiment, this hollowing process is performed using a second laser beam (line laser) L2 which has a larger diameter than the two first laser beams L1.

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

[0029] As shown in Figure 1, the laser processing apparatus 1 comprises 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 set up on the stage. The wafer (product workpiece) W1 to be processed is loaded and held on table T1. Meanwhile, the alignment workpiece W2 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 subtable T2 using a first laser beam L1 and a second laser beam L2 to correct any misalignment of the processing position.

[0032] Here, it is preferable that the alignment workpiece W2 contains a material in which at least the laser irradiation surface (surface) is easily detectable as a laser irradiation mark (groove). 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-sensitive paper) can be used. Alternatively, as the alignment workpiece W2, a workpiece with a high reflectivity on the surface irradiated by the laser, for example, a workpiece with a mirror-finished surface, may be used.

[0033] The stage ST moves along the X and Y directions and rotates around the Z axis by the relative movement mechanism 22 under the control of the control device 10.

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

[0035] The laser optical system 14 forms two first laser beams L1 for edge cutting based on the laser beam LA from the first laser light source 12A. The laser optical system 14 also forms one second laser beam L2 for hollowing 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 focusing 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 focusing lens 18A or 18B toward the street S.

[0036] Furthermore, the laser optical system 14 is moved in the Y and Z directions by the 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. Before edge cutting and hollowing, the microscope 20 photographs the alignment reference (not shown) formed on the wafer W1. The microscope 20 also photographs the two edge cutting grooves G1 and hollowing grooves G2 formed along the street S by the edge cutting and hollowing processes. The images (image data) captured by the microscope 20 are output to the control device 10 and displayed on a monitor (not shown) by the control device 10.

[0038] The relative movement mechanism 22 includes XYZ actuators and a motor, and under the control of the control device 10, it moves the stage ST in the XY direction and rotates it about its rotation axis, and moves the laser optical system 14 in the Z direction. As a result, the relative movement mechanism 22 can move the laser optical system 14 relative to the stage ST and the wafer W1. The method of relative movement is not particularly limited as long as the laser optical system 14 can be moved relative to the stage ST (wafer W1) in each direction (including rotation).

[0039] By driving the relative movement mechanism 22, the laser optical system 14 can be aligned with the processing start position, which is one end of the street S to be processed, and the relative movement of the laser optical system 14 along the street S in the X direction (forward direction X1 or return direction X2). Furthermore, by driving the relative movement mechanism 22 and rotating the stage ST by 90°, each street S along the Y direction of the wafer W1 can be made parallel to the X direction, which is the processing feed direction.

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

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

[0042] In the example shown in Figure 5, the subtable T2 is mounted on the stage ST and is movable together with the table T1, but the present invention is not limited to this. The subtable T2 may not be mounted on the stage ST and may be movable independently of the table T1.

[0043] Figure 6 is a plan view showing an example of edge cutting and hollowing processing performed on a workpiece W2 for alignment, and Figure 7 is an enlarged view of section VII in Figure 6.

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

[0045] Next, the microscope 20 is used to photograph the two edge-cutting grooves G1 and the hollow 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 hollow 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 beam (split laser) L1 and the second laser beam (line laser) L2 are adjusted so that the hollow groove G2 (Line Y position) is contained within the two edge cutting grooves G1 (Split Y position) and partially overlaps with the two edge cutting grooves G1. As shown in Figure 7, if the Y coordinates of the edges of the two edge cutting grooves G1 are Ys1, Ys2, Ys3, and Ys4, and the Y coordinates of the edges of the hollow groove G2 are Yl1 and Yl2, the irradiation positions of the first laser beam (split laser) L1 and the second laser beam (line laser) L2 are adjusted so that Ys1>Yl1>Ys2 and Ys3>Yl2>Ys4.

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

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

[0049] Furthermore, in this embodiment, a workpiece W2 for alignment can be selected in which grooves formed by the first laser beam (split laser) L1 and grooves formed by the second laser beam (line laser) L2 can be easily detected, thereby ensuring reliable detection of focusing position misalignment.

[0050] Furthermore, the laser beam correction method according to this embodiment can be applied in combination with the following Examples 1 to 3.

[0051] [Example 1] Figure 8 is a diagram illustrating the laser beam correction method according to Example 1.

[0052] In Example 1, when processing the alignment workpiece W2, the second focusing lens 18A or 18B is moved in the Y direction to scan the second laser beam (line laser) L2 in the Y direction and perform oblique cutting.

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

[0054] When processing wafer W1, by aligning the Y-direction positions of the second focusing lenses 18A and 18B with Po, it is possible to prevent processing the wafer W1 with a misalignment between the focusing position of the first laser beam (split laser) L1 and the focusing position of the second laser beam (line laser) L2.

[0055] Furthermore, when performing oblique cutting, it is not necessary to perform edge cutting and hollowing in parallel. For example, after forming the first laser beam (split laser) L1 along the X direction, oblique cutting may be performed while moving the second focusing lens 18A or 18B or the illumination optical system 14.

[0056] Alternatively, contrary to the above example, the hollow groove G2 may be formed along the X direction, and the two edge-cutting grooves G1 may be formed by diagonal cuts.

[0057] [Example 2] Figure 9 is a plan view showing the alignment workpiece according to Example 2.

[0058] In Example 2, a workpiece W2a with alignment marks M1 formed on it is used for alignment. In the example shown in Figure 9, the alignment marks M1 are cross-shaped and at least one pair (two) are formed.

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

[0060] Furthermore, 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 a workpiece W2a with alignment marks, it is possible to measure and correct the amount of deviation between the target machining position and the actual machining position, in addition to the relative position of the first laser beam (split laser) L1 and the second laser beam (line laser) L2.

[0062] [Example 3] Figure 10 is a diagram illustrating the laser beam correction method according to Example 3.

[0063] In Example 3, when processing the alignment workpiece W2, either a single-pulse laser is irradiated as the first laser beam (split laser) L1 and the second laser beam (line laser) L2, or processing is performed with the overlap ratio of the first laser beam L1 and the second laser beam L2 set to 0. As a result, as shown in Figure 10, the two-dimensional processing shape of one pulse of each laser beam can be inspected in advance.

[0064] Figure 10 shows an example where 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-pulse first laser beam L1 and second laser beam L2 are irradiated.

[0065] In Figure 10, the symbols Sp1 and Sp2 indicate an example where a single-pulse laser is irradiated as the first laser beam L1, and the symbols L1 and L2 indicate an example where a single-pulse laser is irradiated as the second laser beam L2.

[0066] As shown in Figure 10, in Example Sp1 and Example L1, the processed shape of the processing marks from one laser pulse is approximately point-symmetric with respect to their respective centers (centroids).

[0067] In contrast, in examples Sp2 and L2, the processed shape of the processing marks from one laser pulse is asymmetrical with respect to their respective centers (centroids). When the processing feed is performed in the X direction when the processed shape of the processing marks from one laser pulse is distorted, as in examples Sp2 and L2, the depth and width of the two edge cutting grooves G1 and hollow grooves G2 may become uneven. For this reason, the irradiation position, beam diameter or intensity of the first laser beam L1 and the second laser beam L2, the orientation of the first focusing lens 16, and the orientations of the second focusing lenses 18A and 18B are adjusted so that the processed shape of the processing marks from one laser pulse is approximately point-symmetrical with respect to their respective centers (centroids).

[0068] According to Example 3, by adjusting the processing shape of the single pulse, the correction of the split laser and line laser can be performed more effectively.

[0069] Furthermore, in Example 3, for example, a white light interference microscope may be used to measure the three-dimensional shape of the processing marks from one laser pulse, allowing for prior inspection including processing depth and three-dimensional shape.

[0070] [Differentiation] In the above embodiment, a subtable T2 is provided to hold the alignment workpiece W2, but the subtable 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 to correct the misalignment of the processing position. After that, the wafer W1 to be processed is loaded onto the table T1 and laser processing is performed.

[0071] In the modified version, the subtable T2 can be omitted when correcting the positional misalignment of the first laser beam L1 and the second laser beam L2. [Explanation of Symbols]

[0072] 1…Laser processing device, 10…Control device, 12A…First laser light source, 12B…Second laser light source, 14…Laser optical system, 16…First focusing lens, 18A, 18B…Second focusing lens, 20…Microscope, 22…Relative movement mechanism, T1…Table, T2…Subtable

Claims

1. A table for holding alignment workpieces, which includes a material in which at least the laser irradiation surface is easily detectable as a laser irradiation mark, A laser optical system that performs edge cutting by focusing a split laser onto the laser irradiation surface to form two parallel first grooves along the processing feed direction, and performs hollowing by focusing a line laser onto the laser irradiation surface to form a second groove, A relative movement mechanism for moving the laser optical system relative to the table in the processing feed direction, A microscope for detecting the first groove and the second groove, A control device that corrects the focusing positions of the split laser and the line laser based on the detection results of the first groove and the second groove, Laser processing equipment including [specific components].

2. The laser processing apparatus according to claim 1, wherein the alignment workpiece is a wafer or alignment paper with a polyimide film.

3. The laser processing apparatus according to claim 1 or 2, wherein the relative movement mechanism scans one of the split laser and the line laser in the processing feed direction and scans the other of the split laser and the line laser in a direction oblique to the processing feed direction when performing the edge cutting and hollowing processes.

4. The laser processing apparatus according to claim 1 or 2, wherein the laser optical system focuses the split laser and the line laser as single-pulse lasers onto the alignment workpiece.

5. The laser processing apparatus according to any one of claims 1 to 4, wherein the laser optical system makes the overlap ratio of the split laser and the line laser on the laser irradiation surface zero.

6. The aforementioned alignment workpiece has at least two alignment marks formed along the machining feed direction. The laser processing apparatus according to any one of claims 1 to 5, wherein the control device corrects the focusing positions of the split laser and the line laser based on the detection results of the alignment mark and the first groove and the second groove.

7. The laser processing apparatus according to any one of claims 1 to 6, wherein the alignment workpiece is held on a subtable separate from the table for holding the workpiece to be processed.

Images