Laser cutting device

Abstract

Provided is a laser cutting device capable of improving the cross-sectional quality when cutting a workpiece in a subsequent process. The laser cutting device 10 includes: a laser light source 22 that outputs laser light L to be irradiated toward a wafer W; a condensing section 37 having a condensing lens 38 through which the laser light L passes, and condensing the laser light L output from the laser light source 22; and an aberration correction lens 42 that imparts aberration to the laser light L by changing the relative distance from the condensing lens 38 included in the condensing section 37.

Description

Technical Field

[0001] This invention relates to laser cutting apparatus. Background Technology

[0002] Patent Document 1 discloses a laser processing apparatus that forms laser processing marks on the interior of a wafer along a predetermined cutting line by aligning a focal point with the interior of the wafer and irradiating it with a laser. The laser processing apparatus described in Patent Document 1 corrects aberrations to suppress laser aberrations.

[0003] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2016-107334 However, as described in Patent Document 1, even when suppressing aberrations in the laser irradiating the wafer, long cracks originating from the laser processing marks may form inside the wafer along with the laser processing marks. If long cracks form inside the wafer, the cross-sectional quality during subsequent wafer dicing processes may be reduced. Summary of the Invention

[0004] In view of the above facts, the present invention aims to provide a laser cutting apparatus that can improve the cross-sectional quality when cutting the workpiece in subsequent processes.

[0005] The laser cutting apparatus according to the first method includes: a laser source that outputs the laser to irradiate the workpiece; a focusing section having a plurality of lenses through which the laser passes to focus the laser output from the laser source; and an aberration imparting section that imparts aberrations to the laser by changing the relative distance between the lenses included in the focusing section.

[0006] Invention Effects As explained above, the laser cutting apparatus of the present invention has the excellent effect of improving the cross-sectional quality when cutting the workpiece in subsequent processes. Attached Figure Description

[0007] Figure 1 This is a schematic structural diagram of the laser cutting apparatus according to an embodiment of the present invention.

[0008] Figure 2 This is a conceptual diagram illustrating the formation of laser processing marks inside a wafer, showing the state of laser-suppressed aberrations.

[0009] Figure 3 This is a conceptual diagram illustrating the formation of laser processing marks inside a wafer, showing the state of aberrations imparted by the laser.

[0010] Figure 4This is a conceptual diagram showing multiple laser processing traces, which consist of multiple laser processing traces formed inside the wafer.

[0011] Figure 5 This is a conceptual diagram showing a multi-layer laser-processed layer formed inside a wafer.

[0012] Figure 6 This is a conceptual diagram showing a multi-layer laser-processed layer formed inside a wafer.

[0013] Figure 7 This is a conceptual diagram showing a multi-layer laser-processed layer formed inside a wafer.

[0014] Figure 8 This is a conceptual diagram showing a multi-layer laser-processed layer formed inside a wafer.

[0015] Figure 9 This is a conceptual diagram illustrating the multiple laser processing traces involved in the modified example.

[0016] Figure 10 This is a conceptual diagram illustrating the multiple laser processing traces involved in the modified example.

[0017] Explanation of reference numerals in the attached figures 10: Laser cutting equipment; 22: Laser light source; 28: Spatial light modulator; 37: Concentrating light section; 38: Condensing lens; 42: Lens for aberration correction (aberration imparting part, aberration suppressing part); P2: Aberration suppression to prevent laser processing marks; P3: Aberrations give laser processing marks; P4: Multiple laser processing marks; L1: Laser; W: Wafer (the workpiece being processed). Detailed Implementation

[0018] Below, refer to Figures 1 to 10 This invention describes the implementation of the laser cutting apparatus involved in the present invention.

[0019] The laser cutting apparatus 10 according to this embodiment, as a pre-processing step for cutting the wafer W, is an apparatus that irradiates the wafer (workpiece) W with a laser L, forming laser processing marks inside the wafer W along a predetermined cutting line. Furthermore, in the following description and drawings, the irradiation direction of the laser L is designated as the Z direction, a direction contained in a plane orthogonal to the Z direction is designated as the X direction, and a direction orthogonal to both the Z and X directions is designated as the Y direction. In this embodiment, the Z direction is the vertical direction.

[0020] <Structure of a Laser Cutting Device> like Figure 1 As shown, the laser cutting apparatus 10 includes: a wafer moving part 11 for holding a wafer W; a laser head 20 for irradiating the wafer W with a laser L; and a control part 50 for controlling the wafer moving part 11 and the laser head 20.

[0021] The wafer moving part 11 is disposed on the main body base 16. The wafer moving part 11 has a worktable 12 disposed on the main body base 16 and a stage 13 disposed on the worktable 12.

[0022] The worktable 12 can move the stage 13 along the X, Y, and Z directions. In addition, the worktable 12 can also move the stage 13 in the θ direction (the direction of rotation centered on the central axis extending along the Z direction).

[0023] The stage 13 is mounted on top of the worktable 12. The stage 13 holds the wafer W on it.

[0024] The wafer W is a circular plate-shaped component, held on the stage 13 with its thickness direction aligned with the Z-direction. The upper surface WA of the wafer W faces the laser head 20, and the laser L is irradiated from the upper surface WA side.

[0025] The laser head 20 includes: a laser source 22 that emits a laser L; a spatial light modulator 28 that modulates the phase of the laser L emitted from the laser source 22; a focusing section 37 that focuses the laser L onto the interior of a wafer W; and an aberration correction lens 42 that corrects aberrations of the laser L focused onto the interior of the wafer W. Additionally, the laser head 20 includes a beam expander 24 and a λ / 2 wavelength plate 26 disposed between the laser source 22 and the spatial light modulator 28, and a reducing optical system 36 disposed between the spatial light modulator 28 and the focusing lens 38.

[0026] The laser source 22 outputs a laser L1 that irradiates the wafer W. Specifically, the laser source 22, under the control of the control unit 50, outputs a processing laser L for forming laser processing marks inside the wafer W.

[0027] The beam expander 24 amplifies the laser L output from the laser source 22 to the appropriate beam diameter for use in the spatial light modulator 28.

[0028] The λ / 2 wavelength plate 26 is adjusted to face the laser incident polarization plane toward the spatial light modulator 28.

[0029] The spatial light modulator 28 is a phase modulation type, which modulates the laser L output from the laser source 22. The spatial light modulator 28 takes the laser L output from the laser source 22 as input, presents a defined holographic pattern (modulation pattern) of the phase of the modulated laser L in multiple pixels arranged in two dimensions, and outputs the phase-modulated laser L.

[0030] The spatial light modulator 28 may be, for example, a spatial light modulator (SLM) using reflective liquid crystal on silicon (LCOS). The operation of the spatial light modulator 28 and the holographic pattern presented by the spatial light modulator 28 are controlled by the control unit 50.

[0031] The spatial light modulator 28 described in this embodiment causes the laser L1 to be focused relative to the interior of the wafer W at multiple focusing positions arranged along the thickness direction (i.e., the Z direction) of the wafer W.

[0032] The reduced optical system 36 is an afocal optical system (telecentric optical system on both sides) consisting of a first lens 36a and a second lens 36b, which reduces and projects the laser L modulated by the spatial light modulator 28 onto the focusing part 37.

[0033] The focusing section 37 focuses the laser L1 output from the laser source 22. The focusing section 37 has multiple lenses. The multiple lenses of the focusing section 37 include a focusing lens 38 through which the laser L1 passes and an aberration correction lens (aberration imparting section, aberration suppressing section) 42.

[0034] The condenser lens 38 is an objective lens (infrared objective lens) that focuses the laser L onto the interior of the wafer W. Alternatively, the condenser lens 38 can be a single lens or composed of multiple lenses arranged along the travel direction of the laser L.

[0035] An aberration correction lens 42 is positioned between the second lens 36b and the condenser lens 38 of the reducing optical system 36. The laser L passes through the aberration correction lens 42. The aberration correction lens 42 can be moved by a drive unit (not shown). Specifically, as... Figure 2 Arrow A1 and Figure 3 As shown by arrow A2, the aberration correction lens 42 is designed to be movable along the travel direction of the laser L. By moving, the aberration correction lens 42 can correct the relative distance to the condenser lens 38. The aberration correction lens 42 corrects the aberrations of the laser L1 illuminating the wafer W by correcting the relative distance to the condenser lens 38. Furthermore, the aberration correction lens 42 can be a single lens or composed of multiple lenses arranged along the travel direction of the laser L.

[0036] like Figure 2As shown, the aberration correction lens 42 is in the state of the uncorrected aberration of laser L1 (refer to...). Figure 2 (a) The position below is moved in a manner close to the condenser lens 38 (refer to arrow A1), thereby suppressing the aberration of laser L1 (refer to...). Figure 2 (b) By suppressing the aberrations of laser L1, the spot shape of laser L1 becomes a shape with shorter lengths in the in-plane directions (X and Y directions) of wafer W. Therefore, the intensity of laser L1 is increased in the in-plane directions. In addition, in this embodiment, the state of uncorrected aberrations of laser L1 refers to the state in which aberrations exist in the thickness portion of wafer W that laser L1 passes through before reaching the focusing point.

[0037] On the other hand, the spot shape of laser L1 also becomes shorter in the thickness direction (Z direction). Therefore, the length of the laser processing mark P2 formed by the aberration-suppressed laser L1 (aberration-suppressed laser processing mark) in the thickness direction (Z direction) of wafer W is shorter than that formed by the uncorrected laser L1. On the other hand, for wafer W, cracks are generated starting from the laser processing mark along with the formation of the laser processing mark. The crack C2 generated by the aberration-suppressed laser L1 is longer than that generated by the uncorrected laser L1.

[0038] like Figure 3 As shown, the aberration correction lens 42 is in the state of the uncorrected aberration of laser L1 (refer to...). Figure 3 (a) The position below is moved away from the condenser lens 38 (refer to arrow A2), thereby imparting aberrations to laser L1 (refer to...). Figure 3 (b) In other words, the aberration of laser L1 is increased. By imparting aberrations to laser L1, the spot shape of laser L1 becomes a shape with a longer length in the in-plane directions (X and Y directions) of wafer W. Therefore, the intensity of laser L1 becomes lower in the in-plane directions.

[0039] However, the spot shape of laser L1 also becomes longer in the thickness direction (Z direction). Therefore, the region with higher intensity from laser L1 is longer in the thickness direction. Consequently, the laser processing mark P3 formed by the aberration-inducing laser L1 (aberration-inducing laser processing mark) is longer in the thickness direction (Z direction) of wafer W compared to the laser processing mark P1 formed by the uncorrected aberration laser L1. On the other hand, the crack C3 generated by the aberration-inducing laser L1 is shorter than the crack C1 generated by the uncorrected aberration laser L1.

[0040] Furthermore, as described above, the spatial light modulator 28 enables the laser L1 to be focused relative to the interior of the wafer W at multiple (in this embodiment, two as an example) focusing positions arranged in the thickness direction (i.e., the Z direction) of the wafer W. Thus, as... Figure 4 As shown, laser L1 can be focused at multiple locations inside wafer W to form multiple laser processing marks (two in this embodiment, for example) arranged along the thickness direction. By connecting multiple laser processing marks, a longer laser processing mark in the thickness direction of wafer W can be formed compared to a single laser processing mark. Figure 4 In this embodiment, laser L1, in a state where aberrations are imparted to laser L1, forms two laser processing marks P3 (hereinafter referred to as "aberration-imparted laser processing marks P3"). By combining the two aberration-imparted laser processing marks P3, a laser processing mark P4 that is longer in the thickness direction of the wafer W is formed (hereinafter referred to as "multiple laser processing marks P4"). In addition, in the multiple laser processing marks P4 involved in this embodiment, the two aberration-imparted laser processing marks P3 arranged in the Z direction partially overlap each other.

[0041] like Figure 1 As shown, the control unit 50 consists of a CPU (Central Processing Unit), memory, input / output circuitry, etc., and controls the operation of each part of the laser cutting apparatus 10. That is, the control unit 50 controls the operation of each part (wafer moving part 11 or laser head 20, etc.) under optimal conditions to form laser processing marks P1, P2, and P3.

[0042] <The function of laser cutting equipment> Next, the operation of the laser cutting apparatus 10 in this embodiment will be explained. Hereinafter, as... Figure 5 As shown, an example of forming a multi-layered (five-layered) laser processing layer PL inside a wafer W using a laser cutting apparatus 10 will be described. The laser processing layer PL is a layer with multiple laser processing marks arranged at predetermined intervals in the X direction. Figure 5 In the example, all the laser-processed layers PL are composed of laser-processed traces P4 formed by combining two laser-processed traces P3 formed by aberration-imparting laser L1.

[0043] First, by moving the aberration correction lens 42, adjustments are made to make the aberration of the laser L the desired aberration. In this embodiment, in order to form a laser processing mark P4 connected by two aberration-assigned laser processing marks (aberration-assigned laser processing marks) P3, aberration adjustment is performed to assign the aberration.

[0044] Next, after the wafer W, which will be processed, is placed on the stage 13, the wafer W is aligned using an alignment optical system (not shown).

[0045] Next, while the worktable 12 is fed along the horizontal direction (X direction in this embodiment) (that is, while the wafer W is moved relative to the laser L), the laser head 20 irradiates the wafer W with the laser L.

[0046] At this time, the laser L output from the laser source 22 is amplified in diameter by the beam expander 24, reflected by the first mirror 30, and its polarization direction is changed by the λ / 2 waveplate 26 before entering the spatial light modulator 28.

[0047] The laser L incident on the spatial light modulator 28 is modulated according to the prescribed holographic pattern presented by the spatial light modulator 28.

[0048] The laser L emitted from the spatial light modulator 28 is reflected sequentially by the second reflector 31 and the third reflector 32, then passes through the first lens 36a, and is further reflected by the fourth reflector 33 and the fifth reflector 34. It then passes through the second lens 36b and the aberration correction lens 42 before entering the condenser lens 38. Thus, the laser L emitted from the spatial light modulator 28 is reduced in size and projected onto the condenser lens 38 by the reducing optical system 36 composed of the first lens 36a and the second lens 36b. Finally, the laser L entering the condenser lens 38 is focused into the interior of the wafer W.

[0049] Since the focusing point of the laser L incident from the top WA (laser incident surface) of wafer W is set inside the thickness direction of wafer W, the laser L passing through the top WA of wafer W concentrates energy at the focusing point inside wafer W, forming laser processing marks based on multiphoton absorption near the focusing point inside wafer W. Specifically, in this embodiment, since multiple focusing points are formed inside wafer W using spatial light modulator 28, as... Figure 5 The diagram shows multiple laser processing marks (laser processing marks with aberrations) connected together, forming a multi-laser processing mark P4. Furthermore, as described above, since the wafer W is moved relative to the laser L along the X direction, multiple multi-laser processing marks P4 arranged along the X direction are formed. Thus, a laser processing layer PL is formed.

[0050] In this embodiment, as described above, five laser processing layers PL are formed. Therefore, by changing the focusing point of the laser L in the thickness direction of the wafer W and repeatedly moving the wafer W relative to the laser head 20, five laser processing layers PL are formed. Specifically, the first laser processing layer PL1 located at the bottommost side is formed first. When the formation of the first laser processing layer PL1 is completed, the focusing point of the laser L is changed upwards. Next, the second laser processing layer PL2 located above the first laser processing layer PL1 is formed. This operation is repeated to form the third laser processing layer PL3, the fourth laser processing layer PL4, and the fifth laser processing layer PL5. Thus, all five laser processing layers PL are formed. At this time, gaps with unformed multi-laser processing marks P4 and cracks C3 are provided between adjacent laser processing layers PL in the Z direction.

[0051] When the laser processing layer PL is formed in multiple layers along the predetermined cutting line, the worktable 12 is indexed and fed in the Y direction by one pitch, and the next predetermined cutting line is also formed by the laser processing layer PL in the same way.

[0052] When a laser processing mark P is formed along the predetermined cutting lines parallel to all X directions, the stage 12 is rotated 90°. Similarly, a laser processing layer PL is formed along all predetermined cutting lines parallel to the Y direction orthogonal to the previously formed predetermined cutting lines.

[0053] As the laser processing layer PL is formed along all the predetermined cutting lines, the wafer W is cut and divided into individual chips at the predetermined cutting lines. In this way, the laser processing of a wafer W is completed.

[0054] <Functions and Effects> According to this embodiment, the following effects are achieved.

[0055] In this embodiment, an aberration correction lens 42 is provided, which is configured to move along the Z-direction. By moving the aberration correction lens 42 in the Z-direction, the relative distance between the lenses included in the focusing section 37 (in this embodiment, for example, the aberration correction lens 42 and the focusing lens 38) can be changed, thereby imparting aberrations to the laser L. Therefore, since the focusing section of the laser L can be lengthened in the thickness direction (thickness direction of the wafer W, Z-direction), a longer laser processing mark P3 in the thickness direction of the wafer W can be formed inside the wafer W. Therefore, when the laser processing layer PL is formed within a predetermined range in the thickness direction of the wafer W, the number of laser processing layers PL can be reduced compared to the case where the laser processing layer PL is formed by a shorter laser processing mark P1 or laser processing mark P2 in the thickness direction of the wafer W. Therefore, the efficiency of laser cutting processing using the laser cutting apparatus 10 can be improved.

[0056] Furthermore, when laser processing marks are formed inside wafer W, cracks occur along with them. When multiple laser processing layers PL are formed inside wafer W, if cracks in adjacent laser processing layers PL in the vertical direction connect with each other, laser processing marks cannot be formed regularly and uniformly inside wafer W, potentially resulting in non-uniform laser processing marks. If non-uniform laser processing marks are formed inside wafer W, the cross-sectional quality when cutting wafer W in subsequent processes may deteriorate. Additionally, the location or direction of cracks that accompany the formation of laser processing marks is difficult to predict and control. Therefore, in the case of long cracks, the likelihood of cracks connecting with each other increases.

[0057] On the other hand, in this embodiment, an aberration is imparted to the laser L, forming a relatively long laser processing mark P3 in the thickness direction of the wafer W inside the wafer W. The longer laser processing mark P3 results in shorter cracks C3 generated during its formation. Therefore, in this embodiment, cracks that are difficult to predict in location or direction of extension and are difficult to control can be shortened, thus making it less likely for cracks to connect with each other. Therefore, a uniform laser processing mark can be formed inside the wafer W. Therefore, the cross-sectional quality when cutting the wafer W in subsequent processes can be improved. Therefore, the quality of the chip manufactured from the wafer W can be improved.

[0058] Furthermore, by imparting aberrations to the laser L to form a longer laser processing mark P3 in the thickness direction of the wafer W, the straightness of the cross-section during subsequent wafer W cutting can be improved. Additionally, adverse effects from cleavage or crystal orientation of the wafer W can be suppressed. Furthermore, dust generated during subsequent wafer W cutting can be suppressed. Due to these factors, the quality of the chip manufactured from the wafer W can be improved.

[0059] Furthermore, in this embodiment, the spatial light modulator 28 focuses the laser L relative to the interior of the wafer W at multiple focusing positions arranged along the thickness direction of the wafer W. Therefore, in a single processing step, a multi-laser processing mark P4 with a relatively long thickness direction can be formed inside the wafer W. Thus, the number of laser processing layers PL can be further reduced. Therefore, the efficiency of laser cutting using the laser cutting apparatus 10 can be further improved.

[0060] [Variation Example] In the above embodiments, such as Figure 5 The example shown illustrates a multi-layer laser-processed layer PL entirely composed of multiple laser processing marks P4, but the invention is not limited thereto. For example, as... Figures 6 to 8As shown, both aberration-inducing laser traces P4 and aberration-suppressing laser traces P2 (hereinafter referred to as "aberration-suppressing laser traces P2") can be formed on the wafer W.

[0061] In the case of combining multiple laser processing marks P4 and aberration-suppressing laser processing marks P2, such as Figure 6 As shown, all laser processing traces contained in the lowest first laser processing layer PL1 and the highest fifth laser processing layer PL5 in the laser processing layer PL formed on wafer W can be set as aberration suppression laser processing traces P2, and all laser processing traces contained in the second laser processing layer PL2 to the fourth laser processing layer PL4 formed in between (in other words, on the inner side of wafer W in the thickness direction) can be set as multi-laser processing traces P4.

[0062] In addition, such as Figure 7 As shown, in the laser processing layer PL formed on wafer W, all laser processing traces contained in the top fifth laser processing layer PL5 can be set as aberration-suppressing laser processing traces P2, and all laser processing traces contained in other laser processing layers PL can be set as multi-laser processing traces P4.

[0063] In addition, such as Figure 8 As shown, in the laser processing layer PL formed on wafer W, all the laser processing traces contained in the bottom first laser processing layer PL1 can be set as aberration-suppressing laser processing traces P2, and all the laser processing traces contained in the other laser processing layers PL can be set as multi-laser processing traces P4.

[0064] Thus, by forming an aberration-suppressing laser processing mark P2 that easily generates long cracks in the laser processing layer PL (at least one of the first laser processing layer PL1 and the fifth laser processing layer PL5) closest to the surface of wafer W, the crack C2 easily reaches the surface of wafer W. By allowing the crack to reach the surface of wafer W, wafer W can be easily cleaved in subsequent processes.

[0065] On the other hand, by forming multiple laser processing marks P4 with short cracks in adjacent laser processing layers PL containing aberration suppression laser processing marks P2, it is possible to prevent the cracks from connecting with each other. Therefore, uniform laser processing marks can be formed inside the wafer W. Therefore, the cross-sectional quality when cutting the wafer W in subsequent processes can be improved. Therefore, the quality of the chip manufactured from the wafer W can be improved.

[0066] The laser cutting apparatus described above is an example of the embodiments, but the present invention can be appropriately modified without departing from its spirit.

[0067] For example, in the above embodiment, an example of correcting the aberrations of laser L using only the aberration correction lens 42 was described, but the present invention is not limited thereto. For example, the aberration correction lens 42 and the spatial light modulator 28 may also be combined to correct the aberrations of laser L. In this way, the aberrations can be corrected more accurately than if any single device were used to correct the aberrations of laser L.

[0068] Alternatively, for example, three types of laser processing marks can be formed on wafer W: aberration suppression laser processing mark P2, aberration imparting laser processing mark P3, and multiple laser processing marks P4. In the case of forming multiple laser processing marks, for example, laser processing marks formed on a single laser processing layer PL can be unified into one type of laser processing mark, and the laser processing marks formed for each laser processing layer PL can be modified.

[0069] Furthermore, in the above embodiments, as an example of combining multiple laser processing marks, an example in which the aberrations imparted to the laser processing marks P3 partially overlap each other (specifically, Figure 4 The multiple laser processing marks shown in P4 are illustrated, but the invention is not limited thereto. For example, as... Figure 9 As shown, multiple laser processing marks are laser processing marks P3 separated from each other in the Z direction due to aberrations, but they can also be multiple laser processing marks P4A connected to each other due to cracks C3 caused by aberrations accompanying laser processing marks P3. Additionally, as... Figure 10 As shown, multiple laser processing marks can also be multiple laser processing marks P4B in which aberration-induced laser processing marks P3 are separated from each other in the Z direction, and the cracks C3 that accompany the aberration-induced laser processing marks P3 are also separated from each other in the Z direction. In addition, in this case, the cracks C3 are close to each other.

Claims

1. A laser cutting device, comprising: A laser light source that outputs laser light to illuminate the workpiece. A focusing section having multiple lenses through which the laser light passes, thereby focusing the laser light output from the laser source; and The aberration-imposing section imparts aberrations to the laser by changing the relative distance between the lenses included in the focusing section.

2. The laser cutting apparatus according to claim 1, wherein, The laser cutting device includes a spatial light modulator, which modulates the laser light output from the laser source. The spatial light modulator causes the laser to be focused relative to the interior of the workpiece at multiple focusing positions arranged along the thickness direction of the workpiece.

3. The laser cutting apparatus according to claim 1, wherein, The laser cutting device includes an aberration suppression unit that suppresses aberrations in the laser. Multiple laser processing marks are formed inside the workpiece. The multiple laser processing marks include aberration-inducing laser processing marks formed by the laser that imparts aberrations through the aberration-inducing part and aberration-suppressing laser processing marks formed by the laser that suppresses aberrations through the aberration-suppressing part, which are arranged along the thickness direction of the workpiece.

4. The laser cutting apparatus according to claim 3, wherein, The plurality of laser processing marks include the aberration-suppressed laser processing mark closest to the surface of the workpiece and the aberration-imparted laser processing mark further inside the workpiece than the aberration-suppressed laser processing mark.

5. The laser cutting apparatus according to any one of claims 1 to 4, wherein, The laser cutting device includes a spatial light modulator, which modulates the laser light output from the laser source. Aberrations are imparted to the laser by combining the aberration-imparting unit and the spatial light modulator.

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