Laser processing equipment

Abstract

A laser processing device comprises: a light source for outputting laser light; a spatial light modulator for displaying a modulation pattern for modulating the laser light output from the light source; a focusing lens for focusing the laser light modulated by the spatial light modulator onto an object; and a control unit for controlling the spatial light modulator in a manner that adjusts the modulation pattern in accordance with the traveling direction of the focusing point of the laser light relative to the object.

Description

Technical Field

[0001] The invention relates to a laser processing device. Background Art

[0002] Patent document 1 describes a laser cutting device. The laser cutting device includes: a stage for moving a wafer, a laser head for irradiating the wafer with laser light, and a control unit for controlling each unit. The laser head includes: a laser light source for emitting a processing laser light for forming a modified region inside the wafer, a dichroic mirror and a focusing lens sequentially arranged on the optical path of the processing laser light, and an AF device.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 5743123 Summary of the invention

[0006] Problems to be solved by the invention

[0007] However, in the laser cutting device described above, for example, the shape of the laser light-converging point (hereinafter sometimes referred to as the "light-converging shape") affects the processing results such as the extension amount of the crack self-modified region. In addition, when the light-converging shape is maintained constant, the traveling direction of the laser light-converging point relative to the object such as the wafer (hereinafter sometimes referred to as the "laser traveling direction") affects the processing results. Therefore, in the above-mentioned technical field, it is preferable that the light-converging shape can be adjusted according to the laser traveling direction.

[0008] Therefore, an object of the present invention is to provide a laser processing device capable of adjusting the focusing shape of laser light according to the traveling direction of the focusing point of laser light.

[0009] Technical means of solving problems

[0010] That is, the laser processing device of the present invention comprises: a light source that outputs laser light; a spatial light modulator that displays a modulation pattern for modulating the laser light output from the light source; a focusing lens that focuses the laser light modulated by the spatial light modulator onto an object; and a control unit that controls the spatial light modulator in a manner that adjusts the modulation pattern in accordance with the direction of travel of the focal point of the laser light relative to the object.

[0011] The laser processing device includes a spatial light modulator. Therefore, the control unit can adjust the focusing shape by adjusting the modulation pattern displayed on the spatial light modulator. In particular, in the laser processing device, the control unit adjusts the modulation pattern corresponding to the laser traveling direction and displays it on the spatial light modulator. In this way, according to the laser processing device, the focusing shape can be adjusted according to the laser traveling direction.

[0012] However, the focusing shape can be adjusted by adjusting the modulation pattern displayed on the spatial light modulator as described above. Therefore, in order to obtain the desired processing result, it is preferable to fully ensure the adjustment margin of the modulation pattern. On the other hand, the inventors have found that in the case of processing by moving the laser light focal point in one direction relative to the wafer and in the case of processing by moving the laser light focal point in the opposite direction, if the modulation pattern (i.e., the focusing shape) is adjusted at the same time (while maintaining it constant), the adjustment margin is only a minor problem.

[0013] The inventors of the present invention have conducted further research to solve the above problems and have found that if the modulation pattern is adjusted according to the direction of travel of the laser light-converging point relative to the wafer (the direction of travel of the laser), the adjustment margin of the modulation pattern is expanded. As a result, the desired processing result can be obtained regardless of the direction of travel of the laser. The inventors of the present invention have completed the following invention as a result of further research based on this insight.

[0014] That is, in the laser processing device of the present invention, the control unit may adjust the modulation pattern separately in the first case where the light-converging point moves in the first direction relative to the object and in the second case where the light-converging point moves in the second direction opposite to the first direction relative to the object. In this way, the modulation pattern is adjusted separately in the first direction and the second direction opposite to the first direction of the laser beam, thereby expanding the adjustment limit of the modulation pattern.

[0015] In the laser processing device of the present invention, the control unit may adjust the modulation pattern in the first case so that the shape of the light-converging point becomes an arc convex in the first direction, and in the second case so that the shape of the light-converging point becomes an arc convex in the second direction. In this way, by adjusting the modulation pattern so that the light-converging shape of the laser light becomes an arc convex in the traveling direction, the amount of progress of the cracks from the modified area formed at the light-converging point of the laser light can be increased.

[0016] In the laser processing device of the present invention, the control unit may adjust the modulation pattern in the first case so that the shape of the light-converging point becomes an arc convex in the second direction, and in the second case so that the shape of the light-converging point becomes an arc convex in the first direction. In this way, by adjusting the modulation pattern so that the light-converging shape of the laser light becomes an arc convex in the opposite direction to the traveling direction, the progress of cracks from the modified area formed at the light-converging point of the laser light can be suppressed.

[0017] The laser processing device of the present invention may also include: a display unit for displaying information; and an input unit for accepting input, wherein the display unit displays information for urging input of parameters for adjusting the modulation pattern, the input unit accepts input of the parameters, and the control unit adjusts the modulation pattern according to the parameters accepted by the input unit. In this case, the modulation pattern can be adjusted in accordance with the input of the user.

[0018] In the laser processing device of the present invention, the modulation pattern may include a spherical aberration correction pattern for correcting the spherical aberration of the laser, and the parameter may include an offset along the traveling direction of the center of the spherical aberration correction pattern relative to the center of the pupil plane of the focusing lens. In this way, by setting the offset of the spherical aberration correction pattern as a parameter, the focusing shape of the laser can be adjusted in a manner that controls the extension amount of the crack (for example, it can be adjusted to the above-mentioned arc shape).

[0019] In the laser processing device of the present invention, the modulation pattern may include a coma pattern for imparting positive coma to the laser, and the parameter may include the magnitude of the coma. In this way, even if the magnitude of the coma imparted to the laser is set as a parameter, the focusing shape of the laser can be adjusted in a manner that controls the extension amount of the crack (for example, it can be adjusted to the above-mentioned arc shape), similarly to the case where the offset amount of the spherical aberration correction pattern is used as a parameter.

[0020] Effects of the Invention

[0021] According to the present invention, it is possible to provide a laser processing apparatus capable of adjusting the focusing shape of laser light according to the traveling direction of the focusing point of laser light. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram showing the structure of a laser processing device according to one embodiment.

[0023] Figure 2 This is a top view of a wafer according to one embodiment.

[0024] Figure 3 yes Figure 2 A cross-sectional view of a portion of a wafer is shown.

[0025] Figure 4 It is shown Figure 1 A schematic diagram showing the structure of a laser irradiation unit.

[0026] Figure 5 It is shown Figure 4 Diagram of the relay lens unit shown.

[0027] Figure 6 yes Figure 4 A partial cross-sectional view of a spatial light modulator is shown.

[0028] Figure 7 This is a schematic diagram for explaining an example of adjustment of the spotlight shape.

[0029] Figure 8 It is a diagram showing an example of a spotlight shape.

[0030] Fig. 9 It is a diagram showing changes in the focused shape when the offset amount of the spherical aberration correction pattern is changed in multiple stages.

[0031] Fig.10 This is a schematic diagram showing the state of laser processing in a state where the spherical aberration correction pattern is offset.

[0032] Fig.11 This is a table showing the relationship between the offset amount of the spherical aberration correction pattern and the processing result.

[0033] Fig.12 This is a cross-sectional photograph showing the relationship between the offset amount of the spherical aberration correction pattern and the processing result.

[0034] Fig.13 It is a diagram showing the relationship between the modulation pattern and the focusing shape.

[0035] Fig.14 This is a diagram showing an input receiving unit in a state where information is displayed.

[0036] Fig.15 This is a diagram showing an input receiving unit in a state where information is displayed.

[0037] Fig.16 This is a schematic plan view showing an example of laser processing.

[0038] Fig.17 A diagram showing a cross section of a semiconductor substrate when an odd number of scans have been performed. DETAILED DESCRIPTION

[0039] Hereinafter, an embodiment will be described in detail with reference to the accompanying drawings. In each figure, the same or equivalent parts are marked with the same symbols and repeated descriptions are omitted. In addition, in each figure, an orthogonal coordinate system defined by an X-axis, a Y-axis, and a Z-axis is sometimes shown.

[0040] Figure 1 Schematic diagram showing the structure of a laser processing device according to one embodiment. Figure 1 As shown, the laser processing apparatus 1 includes a stage 2, a laser irradiation unit 3, a drive unit 9, and a control unit 10. The laser processing apparatus 1 is an apparatus for forming a modified region 12 in the object 11 by irradiating the object 11 with laser light L.

[0041] The stage 2 supports the object 11 by adsorbing, for example, a thin film attached to the object 11. The stage 2 can move in the X direction and the Y direction, and can rotate around an axis parallel to the Z direction. The X direction and the Y direction are the first horizontal direction and the second horizontal direction that intersect (orthogonal) each other, and the Z direction is the vertical direction.

[0042] The laser irradiation unit 3 focuses the laser light L having transmittance to the object 11 and irradiates the object 11. When the laser light L is focused inside the object 11 supported by the stage 2, the laser light L is particularly absorbed in the portion corresponding to the focal point C of the laser light L, and a modified region 12 is formed inside the object 11.

[0043] The modified region 12 is a region whose density, refractive index, mechanical strength, and other physical properties are different from those of the surrounding non-modified region. Examples of the modified region 12 include a melt-processed region, a crack region, an insulation breakdown region, and a refractive index change region. The modified region 12 may be formed such that a crack extends from the modified region 12 toward the incident side of the laser L and the opposite side thereof. Such a modified region 12 and cracks are used, for example, to cut the object 11.

[0044] As an example, if the stage 2 is moved in the X direction and the focal point C is moved relative to the object 11 in the X direction, a plurality of modified points 12s are formed so as to be arranged in one row in the X direction. One modified point 12s is formed by irradiation with one pulse of laser light L. One row of modified regions 12 is a collection of a plurality of modified points 12s arranged in one row. Adjacent modified points 12s may be connected to each other or separated from each other depending on the relative moving speed of the focal point C relative to the object 11 and the repetition frequency of the laser light L.

[0045] The driving unit 9 supports the laser irradiation unit 3. The driving unit 9 moves the laser irradiation unit 3 in the Z direction.

[0046] The control unit 10 controls the operation of the stage 2, the laser irradiation unit 3, and the drive unit 9. The control unit 10 has: a processing unit 101, a storage unit 102, and an input receiving unit (display unit, input unit) 103. The processing unit 101 is configured as a computer device including a processor, a memory, a storage body, and a communication device. In the processing unit 101, the processor executes software (program) read into the memory, etc., controls the reading and writing of data in the memory and the storage body, and the communication of the communication device. The storage unit 102 is, for example, a hard disk, etc., which stores various data. The input receiving unit 103 is an interface unit that displays various information and receives input of various information from the user. In the present embodiment, the input receiving unit 103 constitutes a GUI (Graphical User Interface).

[0047] [Structure of the object]

[0048] Figure 2 This is a top view of a wafer according to one embodiment. Figure 3 yes Figure 2 The object 11 of this embodiment is, as an example, Figure 2 , 3 The wafer 20 shown in FIG. 2 includes: a semiconductor substrate 21, and a functional element layer 22. The semiconductor substrate 21 has a surface 21a and a back surface 21b. As an example, the back surface 21b is a first surface that becomes an incident surface of the laser L, etc., and the surface 21a is a second surface on the opposite side of the first surface. The semiconductor substrate 21 is, for example, a silicon substrate. The functional element layer 22 is formed on the surface 21a of the semiconductor substrate 21. The functional element layer 22 includes a plurality of functional elements 22a arranged two-dimensionally along the surface 21a.

[0049] The functional element 22a is, for example, a light receiving element such as a photodiode, a light emitting element such as a laser diode, a circuit element such as a memory, etc. The functional element 22a may also be three-dimensionally constructed by stacking multiple layers. A notch 21c indicating a crystal orientation is provided in the semiconductor substrate 21, but an orientation plane may be provided instead of the notch 21c.

[0050] The wafer 20 is cut along each of the multiple lines 15 for each functional element 22a. The multiple lines 15 pass between each of the multiple functional elements 22a when viewed from the thickness direction of the wafer 20. More specifically, the line 15 passes through the center (center in the width direction) of the cutting street area 23 when viewed from the thickness direction of the wafer 20. The cutting street area 23 extends in the functional element layer 22 in a manner passing between adjacent functional elements 22a. In the present embodiment, the multiple functional elements 22a are arranged in a matrix along the surface 21a, and the multiple lines 15 are set in a grid shape. Among them, the lines 15 are imaginary lines, but can also be actually drawn lines.

[0051] [Structure of laser irradiation unit]

[0052] Figure 4 It is shown Figure 1 A schematic diagram showing the structure of a laser irradiation unit. Figure 5 It is shown Figure 4 Diagram of the relay lens unit shown. Figure 6 yes Figure 4The laser irradiation unit 3 includes: a light source 31, a spatial light modulator 5, a focusing lens 33, and a 4f lens unit 34. The light source 31 outputs the laser light L by, for example, a pulse oscillation method. The laser irradiation unit 3 may also be configured without the light source 31, and the laser light L may be introduced from the outside of the laser irradiation unit 3.

[0053] The spatial light modulator 5 modulates the laser light L output from the light source 31. The condenser lens 33 condenses the laser light L modulated by the spatial light modulator 5 toward the object 11 (semiconductor substrate 21). The 4f lens unit 34 has a pair of lenses 34A and 34B arranged on the optical path of the laser light L from the spatial light modulator 5 toward the condenser lens 33. The pair of lenses 34A and 34B constitute a bilateral telecentric optical system in which the modulation surface 5a of the spatial light modulator 5 and the incident pupil surface (pupil surface) 33a of the condenser lens 33 are in an imaging relationship. As a result, the image of the laser light L on the modulation surface 5a of the spatial light modulator 5 (the image of the laser light L modulated in the spatial light modulator 5) is transferred (imaged) on the incident pupil surface 33a of the condenser lens 33. Among them, Fs in the figure represents a Fourier plane.

[0054] The spatial light modulator 5 is a spatial light modulator (SLM) of a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) and is formed by laminating a driving circuit layer 52, a pixel electrode layer 53, a reflection film 54, an alignment film 55, a liquid crystal layer 56, an alignment film 57, a transparent conductive film 58, and a transparent substrate 59 in this order on a semiconductor substrate 51.

[0055] The semiconductor substrate 51 is, for example, a silicon substrate. The driving circuit layer 52 forms an active matrix circuit on the semiconductor substrate 51. The pixel electrode layer 53 includes a plurality of pixel electrodes 53a arranged in a matrix along the surface of the semiconductor substrate 51. Each pixel electrode 53a is formed of, for example, a metal material such as aluminum. A voltage is applied to each pixel electrode 53a through the driving circuit layer 52.

[0056] The reflective film 54 is, for example, a dielectric multilayer film. The alignment film 55 is provided on the surface of the liquid crystal layer 56 on the side of the reflective film 54, and the alignment film 57 is provided on the surface of the liquid crystal layer 56 on the side opposite to the reflective film 54. Each alignment film 55, 57 is formed of a polymer material such as polyimide, and a rubbing treatment is applied to the contact surface of each alignment film 55, 57 with the liquid crystal layer 56. The alignment films 55, 57 align the liquid crystal molecules 56a contained in the liquid crystal layer 56 in a certain direction.

[0057] The transparent conductive film 58 is provided on the surface of the transparent substrate 59 on the side of the alignment film 57, and is opposite to the pixel electrode layer 53 via the liquid crystal layer 56 and the like. The transparent substrate 59 is, for example, a glass substrate. The transparent conductive film 58 is formed of, for example, a light-transmitting and conductive material such as ITO. The transparent substrate 59 and the transparent conductive film 58 allow the laser light L to pass through.

[0058] In the spatial light modulator 5 configured as described above, if a signal representing a modulation pattern is input from the control unit 10 to the drive circuit layer 52, a voltage corresponding to the signal is applied to each pixel electrode 53a, and an electric field is formed between each pixel electrode 53a and the transparent conductive film 58. If the electric field is formed, the arrangement direction of the liquid crystal molecules 216a in the liquid crystal layer 56 changes according to each region corresponding to each pixel electrode 53a, and the refractive index changes according to each region corresponding to each pixel electrode 53a. This state is a state in which the modulation pattern is displayed on the liquid crystal layer 56. The modulation pattern is used to modulate the laser light L.

[0059] That is, when the liquid crystal layer 56 displays a modulation pattern, the laser light L is incident on the liquid crystal layer 56 from the outside through the transparent substrate 59 and the transparent conductive film 58, and is reflected by the reflective film 54. When the laser light L is emitted from the liquid crystal layer 56 through the transparent conductive film 58 and the transparent substrate 59 to the outside, the laser light L is modulated according to the modulation pattern displayed on the liquid crystal layer 56. In this way, according to the spatial light modulator 5, the modulation of the laser light L (for example, the modulation of the intensity, amplitude, phase, polarization, etc. of the laser light L) can be performed by appropriately setting the modulation pattern displayed on the liquid crystal layer 56. Figure 5 The modulation surface 5 a shown is, for example, a liquid crystal layer 56 .

[0060] In the present embodiment, the laser irradiation unit 3 irradiates the wafer 20 with the laser light L from the back surface 21b side of the semiconductor substrate 21 along each of the plurality of lines 15, thereby forming two rows of modified regions 12a and 12b inside the semiconductor substrate 21 along each of the plurality of lines 15. The modified region (first modified region) 12a is the modified region closest to the surface 21a of the two rows of modified regions 12a and 12b. The modified region (second modified region) 12b is the modified region closest to the modified region 12a of the two rows of modified regions 12a and 12b, and is also the modified region closest to the back surface 21b.

[0061] The two rows of modified regions 12a and 12b are adjacent to each other in the thickness direction (Z direction) of the wafer 20. The two rows of modified regions 12a and 12b are formed by relatively moving the two focal points C1 and C2 along the line 15 with respect to the semiconductor substrate 21. The laser light L is modulated by the spatial light modulator 5 in such a manner that the focal point C2 is located at the rear side in the traveling direction and at the incident side of the laser light L with respect to the focal point C1.

[0062] As an example, the laser irradiation unit 3 can irradiate the wafer 20 with laser light L from the back side 21b of the semiconductor substrate 21 along each of the plurality of lines 15, under the condition that the cracks 14 extending over the two rows of modified regions 12a and 12b reach the surface 21a of the semiconductor substrate 21. As an example, for a single crystal silicon substrate, i.e., a semiconductor substrate 21 having a thickness of 775 μm, two focal points C1 and C2 are respectively aligned at positions 54 μm and 128 μm from the surface 21a, and the wafer 20 is irradiated with laser light L from the back side 21b of the semiconductor substrate 21 along each of the plurality of lines 15.

[0063] At this time, the wavelength of the laser L is 1099nm, the pulse width is 700ns, and the repetition frequency is 120kHz. In addition, the output of the laser L in the focal point C1 is 2.7W, the output of the laser L in the focal point C2 is 2.7W, and the relative moving speed of the two focal points C1 and C2 relative to the semiconductor substrate 21 is 800mm / second.

[0064] The formation of the two rows of modified regions 12a, 12b and the cracks 14 is performed as follows. That is, in a subsequent process, the back surface 21b of the semiconductor substrate 21 is ground to thin the semiconductor substrate 21, and the cracks 14 are exposed on the back surface 21b, and the wafer 20 is cut into a plurality of semiconductor devices along each of the plurality of lines 15.

[0065] [Adjustment of spotlight shape]

[0066] As described above, in the laser processing device 1, the laser light L output from the light source 31 is incident on the spatial light modulator 5. The modulation pattern is displayed on the spatial light modulator 5. Therefore, the laser light L incident on the spatial light modulator 5 is modulated by the modulation pattern, and then incident on the focusing lens 33 via the 4f lens unit 34, and focused on the object 11. Therefore, the shape of the focal point of the laser light L (hereinafter sometimes referred to as "focusing shape") can be adjusted by adjusting the modulation pattern displayed on the spatial light modulator 5. An example of adjustment of the focusing shape is described below.

[0067] Figure 7 This is a schematic diagram for explaining an example of adjusting the spotlight shape. Figure 7 In the example shown, the modulation pattern is offset. More specifically, various patterns such as a deformation correction pattern for correcting the deformation of the wavefront, a grid pattern for branching the laser light, a slit pattern, an astigmatism pattern, a coma pattern, and a spherical aberration correction pattern are displayed on the spatial light modulator 5 (a pattern after overlapping these patterns is displayed). Among them, by offsetting the spherical aberration correction pattern Ps, the focusing shape can be adjusted.

[0068] exist Figure 7In the example of FIG. 5 , the center Pc of the spherical aberration correction pattern Ps is offset by an offset amount Ox1 toward the negative side in the X direction relative to the center Lc (beam spot) of the laser light L in the modulation surface 5a. As described above, the modulation surface 5a is transferred to the entrance pupil surface 33a of the condenser lens 33 by the 4f lens unit 34. Therefore, the offset in the modulation surface 5a is offset toward the positive side in the X direction in the entrance pupil surface 33a. That is, in the entrance pupil surface 33a, the center Pc of the spherical aberration correction pattern Ps is offset by an offset amount Ox2 toward the positive side in the X direction from the center Lc of the laser light L and the center of the entrance pupil surface 33a (here, coincident with the center Lc).

[0069] On the other hand, if the center Pc of the spherical aberration correction pattern Ps is offset toward the positive side in the X direction relative to the center Lc of the laser light L in the modulation plane 5a, the center Pc of the spherical aberration correction pattern Ps is offset toward the negative side in the X direction from the center Lc of the laser light L and the center of the entrance pupil plane 33a. In this way, by offsetting the spherical aberration correction pattern Ps, the shape of the light-converging point C1 (and the light-converging point C2) of the laser light L is deformed compared to when there is no offset.

[0070] Figure 8 This is a diagram showing an example of a focused light shape (intensity distribution). Figure 8 The figures show the light-collecting shapes in the cross section including the X direction and the Z direction. Figure 8 (a) shows the focusing shape when the spherical aberration correction pattern Ps is biased toward the negative side of the X direction on the entrance pupil plane 33a (that is, the positive side of the X direction on the modulation surface 5a), Figure 8 (c) shows a focusing shape when the spherical aberration correction pattern Ps is offset toward the positive side of the X direction (that is, the negative side of the X direction in the modulation surface 5a) on the entrance pupil plane 33a. Figure 8 (b) is the focusing shape when there is no bias.

[0071] like Figure 8 As shown in FIG. 1 , by biasing the spherical aberration correction pattern Ps in the X direction, the focusing shape becomes asymmetric with respect to the optical axis center Ax. Figure 8 As shown in (a), if the spherical aberration correction pattern Ps is biased toward the negative side in the X direction with respect to the entrance pupil plane 33a, the intensity distribution becomes biased toward the positive side in the X direction relative to the optical axis center Ax (arc-shaped intensity distribution convex toward the negative side in the X direction). Figure 8 As shown in (c), with the entrance pupil plane 33a as a reference, if the spherical aberration correction pattern Ps is biased toward the positive side in the X direction, an intensity distribution is obtained that is biased toward the negative side in the X direction relative to the optical axis center Ax (an arc-shaped intensity distribution that is convex toward the positive side in the X direction).

[0072] Fig. 9 It is a diagram showing changes in the focused shape when the offset amount of the spherical aberration correction pattern is changed in multiple stages. Fig. 9 The "offset [pixel] SLM plane" in represents the offset amount on the modulation surface 5a, and negative (-) represents the negative side in the X direction. As described above, here, the sign of the offset amount of the spherical aberration correction pattern Ps on the modulation surface 5a is opposite to the sign of the offset amount of the spherical aberration correction pattern Ps on the incident pupil surface 33a.

[0073] In addition, "BE (μm)" is the correction amount of the spherical aberration correction pattern Ps, "Z [μm]" is the focusing position of the laser light L in the Z direction, and "CP [μm]" is the focusing correction amount. Fig. 9 As shown in FIG. 1 , by changing the offset amount (of the center Pc) of the spherical aberration correction pattern Ps in stages, the focusing shape can be changed in stages. Fig. 9 The "(third-order) coma aberration" in ref. 2 represents the magnitude of the third-order coma aberration corresponding to each focusing shape.

[0074] As described above, by adjusting the offset amount of the spherical aberration correction pattern Ps to adjust the focusing shape, it is possible to control processing results such as the extension amount of the crack 14. Fig.10 This is a schematic diagram showing the state of laser processing in a state where the spherical aberration correction pattern is offset. Fig.10 (a) shows a first case (hereinafter sometimes referred to as "forward processing") in which the focal point C1 of the laser light L (the same also applies to the focal point C2 not shown) is moved in the positive X direction, that is, the first direction D1, relative to the semiconductor substrate 21 (wafer 20) to perform processing. Here, the focal point C1 is moved relatively in the first direction D1 by moving the stage 2 and the semiconductor substrate 21 in the second direction, which is the opposite direction (negative X direction) to the first direction D1.

[0075] Fig.10 (b) shows a second case (hereinafter sometimes referred to as "return processing") in which the focal point C1 of the laser L moves in the negative X direction, that is, the second direction D2, relative to the semiconductor substrate 21. Here, by moving the stage 2 and the semiconductor substrate 21 in the first direction D1, the focal point C1 moves in the second direction D2 relatively. Fig.10 , the diagram shows a case where the shape of the focal point C1 is adjusted individually in the first case and the second case so as to become an arc shape convex toward the traveling direction of the focal point C1. Fig.10The example is an example of individual adjustment in which the first case becomes an arc convex in the first direction D1 and the second case becomes an arc convex in the second direction D2. On the other hand, in the first and second cases, if the focusing shape is maintained constant while processing, the following problems will occur. Here, adjusting the focusing shape (or maintaining it constant) means adjusting the offset of the spherical aberration correction pattern Ps (or maintaining it constant).

[0076] Fig.11 (a) represents the processing result (the extension amount of the crack) when processing is performed while maintaining the focusing shape to be constant in the first case (forward processing) and the second case (return processing). Here, the offset amount (X-offset (pixel)) of the spherical aberration correction pattern Ps is constant in the forward processing and the return processing and changes from +6.5 to -6.5 in 2-pixel increments. Processing result A represents a state in which the crack 14 reaches the surface 21a of the semiconductor substrate 21, which is an example of a preferred processing result. Processing result B represents a state in which the crack 14 reaches the surface 21a of the semiconductor substrate 21, but black stripes (areas where the crack is not connected) occur between the modified area 12a and the modified area 12b. Processing result C represents a state in which the crack 14 does not reach the surface 21a of the semiconductor substrate 21.

[0077] like Fig.11 As shown in (a), when the offset amount (light-concentrating shape) is set constant in the forward processing and the return processing, the offset amount for obtaining the processing result A in both the forward processing and the return processing is only the "reference" (when the offset amount is 0). In other words, when the offset amount (light-concentrating shape) is set constant in the forward processing and the return processing, even if the offset amount is adjusted to control other processing results, there is no limit to the adjustment (at least it becomes less than ±2.5).

[0078] In contrast, Fig.11 (b) and Fig.12 ( Fig.12 The cross-sectional photograph shows Fig.10 The following is the processing result when the offset amount (focusing shape) is adjusted separately in forward processing and return processing. Fig.11 (b) and Fig.12 As shown, in this case, in the forward machining, the machining result A is obtained within the range of the offset amount of -4.5 from the reference, and in the return machining, the machining result A is obtained within the range of the offset amount of +4.5 from the reference. Therefore, for example, when the offset amount is to be adjusted in order to control other machining results, the adjustment boundary of the offset amount of 4.5 is obtained for each of the forward machining and the return machining.

[0079] In the above example, the offset amount of the spherical aberration correction pattern Ps is adjusted to adjust the focused shape, but the focused shape may be adjusted by using other methods of the spatial light modulator 5 .

[0080] Fig.13 (a) shows the focusing shape obtained when the spherical aberration correction pattern Ps is biased as described above. Fig.13 The "coma" in (b) indicates the light focusing shape obtained when the offset of the spherical aberration correction pattern Ps is set to 0 and the coma pattern is displayed on the spatial light modulator 5 to give the laser light L a positive coma aberration. Fig.13 As shown in (b), even by giving positive coma to the laser light L, the same focusing shape as when the spherical aberration correction pattern Ps is offset is obtained. This is considered to be because offsetting the spherical aberration correction pattern Ps and giving coma to the laser light L have the same meaning.

[0081] Among them, positive coma refers to the coma that is assigned a positive coefficient in the Zernike polynomial, which is mainly affected by the third-order term of the polynomial, but also includes the influence of higher-order terms (such as fifth-order terms). In addition, it is equivalent to the case where the spherical aberration correction pattern Ps is biased with an offset of -5 relative to the modulation surface 5a as a reference, and the coma (third order) is set to Lv7. In addition, the offset amount of the spherical aberration correction pattern Ps is proportional to the size of the coma and increases as a quadratic function. In addition, the correction amount (BE [μm]) of the spherical aberration correction pattern Ps is proportional to the size of the coma and increases as a quadratic function.

[0082] In addition, if Fig.13 As shown in the "Airy Beam" of (b), even if the modulation pattern is used to set the laser L as an Airy beam, the same focusing shape as when the spherical aberration correction pattern Ps is offset is obtained. According to this modulation pattern, coma aberration and astigmatism (3rd order) are overlapped and given to the laser L. In any of the above cases, the adjustment boundary of the modulation pattern is expanded by adjusting the modulation pattern individually in the forward processing and the return processing.

[0083] [Embodiments of Laser Processing Device]

[0084] Based on the above findings, the laser processing apparatus 1 of the present embodiment can adjust the focusing shape of the laser light L in accordance with the traveling direction of the focusing point C1 of the laser light L. Therefore, in the laser processing apparatus 1, the control unit 10, through the control of the input accepting unit 103, adjusts the modulation pattern in accordance with the traveling direction of the focusing point C1 (focusing point C2) of the laser light L relative to the semiconductor substrate 21 (wafer 20), and displays information for urging the user to input the parameters of the modulation pattern on the input accepting unit 103.

[0085] Fig.14 (a) is an example of information K1 displayed in the input receiving unit 103. In the information K1, the offset (LBA offset) of the spherical aberration correction pattern Ps (center Pc) processed in the forward path and the offset (center Pc) of the spherical aberration correction pattern Ps processed in the return path are displayed as parameters of the modulation pattern.

[0086] That is, here, the control unit 10, through the control of the input receiving unit 103, when observed from the direction (here, the Z direction) intersecting the incident surface of the laser L of the semiconductor substrate 21 (here, the back side 21b), individually adjusts the modulation pattern in a first case (forward processing) in which the focal point C1 moves in a first direction (for example, the positive X direction) relative to the semiconductor substrate 21, and in a second case (return processing) in which the focal point C1 moves in a second direction (for example, the negative X direction) opposite to the first direction relative to the semiconductor substrate 21, so that information for urging the user to input the offset amount (parameter) of the spherical aberration correction pattern Ps is displayed on the input receiving unit 103.

[0087] Here, as an example, an example is shown in which an offset of -2.5 is input in the forward processing and +2.5 is input in the return processing. In contrast, the input receiving unit 103 receives the input of the offset of the spherical aberration correction pattern Ps by the user. Next, the control unit 10 adjusts the modulation pattern according to the offset received by the input receiving unit 103 and displays it on the spatial light modulator 5.

[0088] Fig.14 (b) shows the instruction value from the control unit 10 to the spatial light modulator 5 , that is, the address of the center Pc of the spherical aberration correction pattern Ps displayed on the spatial light modulator 5 on the modulation plane 5 a . Fig.14 The values ​​shown in (b) are not displayed in the input receiving unit 103. As described above, only the offset of the spherical aberration correction pattern Ps is input to the input receiving unit 103. In contrast, the control unit 10 outputs a specific address for realizing the input offset to the spatial light modulator 5.

[0089] As an example, when the addresses of the X direction and the Y direction of the center of the entrance pupil plane 33a of the condenser lens 33 are (X: -15.5, Y: -23.5), the control unit 10 specifies the address of the center Pc of the spherical aberration correction pattern Ps on the modulation plane 5a as (X: -18.0, Y: -23.5) in the forward processing, and specifies the address of the center Pc of the spherical aberration correction pattern Ps on the modulation plane 5a as (X: -13.0, Y: -23.5) in the return processing. This is because in the above example, the offset amount of the spherical aberration correction pattern Ps is -2.5 in the forward processing and +2.5 in the return processing.

[0090] In this way, the modulation pattern displayed on the spatial light modulator 5 includes the spherical aberration correction pattern Ps, and the parameters of the modulation pattern include the offset amount of the spherical aberration correction pattern Ps.

[0091] on the other hand, Fig.15 (a) is an example of other information K2 displayed on the input receiving unit 103. In addition, Fig.15 (b) shows the instruction value of the control unit 10 to the spatial light modulator 5, that is, the size of the coma aberration of the coma aberration pattern displayed on the spatial light modulator 5. Fig.15 As shown in (a) of FIG. 1 , here, information prompting the input of the magnitude of coma aberration is displayed on the input receiving unit 103 instead of the offset amount of the spherical aberration correction pattern Ps.

[0092] Here, as information for prompting the user to input the size of the coma aberration, the input receiving unit 103 may display a "coma pattern" so that the user can easily recognize that the coma pattern is adjusted. Fig.15 The actual values ​​(here +0.037 and -0.037) of the coma pattern displayed on the spatial light modulator 5 shown in (b) are inputted, and the values ​​(here +37 and -2.5) corresponding to the actual values ​​and easily recognized by the user are inputted. Fig.15 The values ​​shown in (b) are not the values ​​displayed on the input accepting unit 103 .

[0093] On the other hand, even when the control unit 10 adjusts the coma pattern displayed on the spatial light modulator 5, it may be displayed as a "round trip suppression pattern" instead of a "coma pattern" as described above in the input receiving unit 103, or may be displayed as a "crack inclination X" (or other displays). That is, any display that is easy for the user to recognize when controlling the processing result can be performed.

[0094] As described above, the modulation pattern displayed on the spatial light modulator 5 includes a coma aberration pattern, and the magnitude of the coma aberration is included as a parameter of the modulation pattern.

[0095] As described above, the laser processing device 1 performs actual laser processing in a state where the modulation pattern is displayed on the spatial light modulator 5 according to the parameters accepted by the input accepting unit 103. In the laser processing device 1, for example, Fig.16 As shown, various laser processing can be performed. Fig.16 In the example shown in (a), the focal point C1 (focal point C2) of the laser L is moved around the outer edge of the semiconductor substrate 21 (wafer 20), thereby forming modified regions 12a, 12b and cracks 14 along the outer edge of the semiconductor substrate 21.

[0096] Thus, the annular region along the outer edge of the semiconductor substrate 21 can be cut from the semiconductor substrate 21 (trim processing is possible) with the modified regions 12a, 12b and the crack 14 as the starting point. At this time, for example, the stage 2 and the wafer 20 are rotated around an axis parallel to the Z direction, so that the focal point C1 of the laser L can be rotated. At this time, the traveling direction of the focal point C1 of the laser L (laser traveling direction) becomes only the first direction D1, for example, which is the positive X direction, relative to the semiconductor substrate 21.

[0097] Therefore, at this time, the laser processing device 1 performs the following operations. The input receiving unit 103 displays information for urging input of the parameters of the modulation pattern in such a manner that the modulation pattern is adjusted according to the first direction D1, which is the traveling direction of the focal point C1 of the laser light L with respect to the semiconductor substrate 21. In addition, the input receiving unit 103 receives the input of the parameters, and the control unit 10 adjusts the modulation pattern based on the parameters received by the input receiving unit 103 and displays it on the spatial light modulator 5.

[0098] On the other hand, Fig.16 In the examples shown in (b) and (c), by moving the focal point C1 of the laser L relative to the semiconductor substrate 21 along each of the lines 15 (by scanning), the modified regions 12a, 12b and the cracks 14 are formed along each of the lines 15. Thus, the semiconductor substrate 21 can be cut (cuttable) along each of the lines 15 with the modified regions 12a, 12b and the cracks 14 as starting points.

[0099] In these cases, there are cases where the position of the focal point C1 of the laser light L in the Z direction is changed for one line 15 and scanning is performed an odd number of times, and cases where scanning is performed an even number of times. In the case of performing an odd number of scans, as shown in FIG. Fig.16As shown in (b), the laser travel direction is different in at least one line 15 scanned and in other lines 15 adjacent to the one line. That is, at this time, the laser travel direction is the positive X direction, i.e., the first direction D1 (forward processing) and the laser travel direction is the negative X direction, i.e., the second direction D2 (return processing) are exchanged at least for each line 15 (when the odd number is 3 or more, the exchange is performed even within one line).

[0100] On the other hand, in the case of an even number of scans, Fig.16 As shown in (c), the laser travel direction is the same over a plurality of lines 15, and the first situation and the second situation are exchanged within one line 15. In any case, the first situation and the second situation are mixed, so the laser processing device 1 performs the following operation.

[0101] That is, the input accepting unit 103 displays information for urging the input of parameters by individually adjusting the modulation pattern in the first case where the focal point C1 moves in the first direction D1 relative to the semiconductor substrate 21 and in the second case where the focal point C1 moves in the second direction D2 opposite to the first direction D1 relative to the semiconductor substrate 21 when viewed from the direction (Z direction) intersecting the incident surface of the laser light L of the semiconductor substrate 21 (here, the back surface 21b). In addition, the input accepting unit 103 accepts the input of the parameter. Next, the control unit 10 individually adjusts the modulation pattern in the first case and the second case based on the parameter accepted by the input accepting unit 103 and displays it on the spatial light modulator 5.

[0102] In other words, the control unit 10 controls the spatial light modulator 5 in such a manner as to adjust the modulation pattern in accordance with the direction of travel of the focal point C1 of the laser light L relative to the semiconductor substrate 21. More specifically, the control unit 10 adjusts the modulation pattern separately in a first case where the focal point C1 travels in a first direction D1 relative to the semiconductor substrate 21 and in a second case where the focal point C1 travels in a second direction D2 opposite to the first direction D1 relative to the semiconductor substrate 21. As described above, the control unit 10 can adjust the modulation pattern using the offset amount of the spherical aberration correction pattern Ps and / or the size of the coma aberration as parameters. At this time, the shape of the focal point C1 is controlled to be convex in the first direction D1 or the second direction.

[0103] Therefore, the control unit 10 may adjust the modulation pattern in the first case so that the shape of the focal point C1 becomes an arc convex toward the first direction D1, and in the second case so that the shape of the focal point C1 becomes an arc convex toward the second direction D2. Alternatively, the control unit 10 may adjust the modulation pattern in the first case so that the shape of the focal point C1 becomes an arc convex toward the second direction D2, and in the second case so that the shape of the focal point C1 becomes an arc convex toward the first direction D1.

[0104] Fig.17 2 is a diagram showing a cross section of a semiconductor substrate when an odd number of scans have been performed. Here, the focal point of the laser L is set to only the focal point C1 (set to 1 focus), and 5 scans are performed from the surface 21a side (5-scan processing). In one of the multiple lines 15, the 1st, 3rd, and 5th scans are equivalent to the first case (forward processing) in which the laser travel direction is the first direction D1, and the modified region 12a, the modified region 12c, and the modified region 12e are formed respectively. Similarly, the 2nd and 4th scans are equivalent to the second case (return processing) in which the laser travel direction is the second direction D2, and the modified region 12b and the modified region 12d are formed.

[0105] On the other hand, in the other lines 15 adjacent to the above-mentioned one line 15 among the plurality of lines 15, the first, third, and fifth scans correspond to the second case (return processing) in which the laser travel direction is the second direction D2, and the modified region 12a, the modified region 12c, and the modified region 12e are formed respectively. Similarly, the second and fourth scans correspond to the first case (forward processing) in which the laser travel direction is the first direction D1, and the modified region 12b and the modified region 12d are formed.

[0106] The wavelength of the laser light L at this time was set to 1099 nm, the pulse width was set to 400 nsec, and the repetition frequency was set to 100 kHz. In addition, the output of the laser light L at the focal point C1 was set to 1.5 W in the first to fourth scans and to 1.3 W in the fifth scan. In addition, the relative moving speed of the focal point C1 with respect to the semiconductor substrate 21 was set to 490 mm / sec.

[0107] Here, as adjustment of the modulation pattern parameters, the offset amount of the spherical aberration correction pattern Ps and the magnitude of the coma aberration are adjusted. The respective parameters are as follows.

[0108] First time: In the forward processing, the offset amount was -3.5 and the coma aberration was Lv3. In the return processing, the offset amount was +3.5 and the coma aberration was Lv-3.

[0109] Second time: In the forward processing, the offset amount was -4.5 and the coma aberration was Lv3. In the return processing, the offset amount was +4.5 and the coma aberration was Lv-3.

[0110] Third time: In the forward processing, the offset amount was -25 and the coma aberration was Lv3. In the return processing, the offset amount was +25 and the coma aberration was Lv-3.

[0111] Fourth time: In the forward processing, the offset amount was -25 and the coma aberration was Lv3. In the return processing, the offset amount was +25 and the coma aberration was Lv-3.

[0112] Fifth time: In the forward processing, the offset amount was -25, and the coma aberration was Lv3. In the return processing, the offset amount was +25, and the coma aberration was Lv-3.

[0113] Thereby, a processing result is obtained in which the cracks 14 extending from the modified region 12a reach the surface 21a.

[0114] As described above, the laser processing device 1 includes the spatial light modulator 5. Therefore, the control unit 10 can adjust the focusing shape by adjusting the modulation pattern displayed on the spatial light modulator 5. In particular, in the laser processing device 1, the control unit 10 adjusts the modulation pattern according to the laser traveling direction and displays it on the spatial light modulator 5. In this way, according to the laser processing device 1, the focusing shape can be adjusted according to the laser traveling direction.

[0115] Furthermore, in the laser processing device 1, the control unit 10 adjusts the modulation pattern individually in the first case where the focal point C1 moves in the first direction D1 relative to the semiconductor substrate 21 and in the second case where the focal point C1 moves in the second direction D2 opposite to the first direction D1 relative to the semiconductor substrate 21. In this way, the modulation pattern is adjusted individually in the first direction and the second direction opposite to the laser moving direction, thereby expanding the adjustment margin of the modulation pattern.

[0116] Furthermore, in the laser processing device 1, the control unit 10 may adjust the modulation pattern in the first case so that the shape of the light-converging point C1 becomes an arc shape convex in the first direction D1, and in the second case so that the shape of the light-converging point C1 becomes an arc shape convex in the second direction D2. In this way, by adjusting the modulation pattern so that the light-converging shape of the laser light L becomes an arc shape convex in the traveling direction, the amount of progress of the cracks from the modified area formed at the light-converging point C1 of the laser light L can be increased.

[0117] Furthermore, in the laser processing device 1, the control unit 10 may adjust the modulation pattern in the first case so that the shape of the light-converging point C1 becomes an arc shape convex in the second direction D2, and in the second case so that the shape of the light-converging point C1 becomes an arc shape convex in the first direction D1. In this way, by adjusting the modulation pattern so that the light-converging shape of the laser light L becomes an arc shape convex in the opposite direction to the traveling direction, the progress of cracks from the modified area formed at the light-converging point C1 of the laser light L can be suppressed.

[0118] In addition, the laser processing device 1 includes an input receiving unit 103 that displays information and receives input. The input receiving unit 103 displays information for urging input of parameters for adjusting the modulation pattern, and receives input of the parameters. Then, the control unit 10 adjusts the modulation pattern according to the parameters received by the input receiving unit 103. Therefore, the modulation pattern can be adjusted according to the input of the user.

[0119] Furthermore, in the laser processing device 1, the modulation pattern includes a spherical aberration correction pattern Ps for correcting the spherical aberration of the laser light L. Next, the parameter includes an offset amount along the first direction D1 of the center Pc of the spherical aberration correction pattern Ps with respect to the center of the entrance pupil plane 33a of the condenser lens 33. In this way, by setting the offset amount of the spherical aberration correction pattern Ps as a parameter, the focusing shape of the laser light L can be adjusted in a manner that controls the extension amount of the crack 14.

[0120] In the laser processing device 1, the modulation pattern includes a coma pattern for imparting positive coma to the laser light L. Next, the parameter includes the magnitude of the coma. In this way, even if the magnitude of the coma imparted to the laser light L is set as a parameter, the focusing shape of the laser light L can be adjusted by controlling the extension amount of the crack 14, similarly to when the offset amount of the spherical aberration correction pattern Ps is used as a parameter.

[0121] The above embodiment is only one aspect of the present invention. Therefore, the present invention can be modified and is not limited to the above-mentioned laser processing device 1.

[0122] For example, in the above-mentioned embodiment, the case where the crack 14 reaches the surface 21a (the surface on the opposite side of the incident surface) of the semiconductor substrate 21 is listed as an example of a preferred processing result among the processing results. This is an example in which it is preferred that the extension amount of the crack 14 is large (the crack 14 is actively extended). At this time, as described above, the parameters of the modulation pattern are adjusted in such a way that the focusing shape becomes an arc convex in the direction of laser travel. On the other hand, there is also a case in which it is preferred that the extension amount of the crack 14 is small (the crack 14 is not actively extended). At this time, it is sufficient to adjust the parameters of the modulation pattern in such a way that the focusing shape becomes an arc convex in the direction opposite to the direction of laser travel.

[0123] In addition, in the above-mentioned embodiment, an example is described in which the control unit 10 adjusts the modulation pattern displayed on the spatial light modulator 5 by accepting the input of parameters from the user. However, the input of parameters from the user is not essential, and the control unit 10 may store the parameters of the modulation pattern corresponding to the traveling direction of the focal point C1 of the laser light L in advance and adjust the modulation pattern according to the parameters.

[0124] In addition, the input acceptance unit 103 may also be configured to display information for urging the input (and accepting input) of the degree of arc shape of the focal point C1 (focal point C2) of the laser L, or the selection of the convex direction, instead of displaying (and accepting input) information for urging the input of the offset amount of the spherical aberration correction pattern Ps and / or the size of the coma aberration (or in addition to it).

[0125] Industrial Applicability

[0126] Provided is a laser processing device capable of adjusting the focusing shape of laser light according to the traveling direction of a focusing point of laser light.

[0127] Explanation of symbols

[0128] 1 ... laser processing device, 5 ... spatial light modulator, 10 ... control unit, 31 ... light source, 33 ... condenser lens, 33a ... entrance pupil plane (pupil plane), 103 ... input receiving unit (display unit, input unit), Ps ... spherical aberration correction pattern.

Claims

1. A laser processing device, wherein: have: A light source for outputting laser light; a spatial light modulator displaying a modulation pattern for modulating the laser light output from the light source; A focusing lens for focusing the laser light modulated by the spatial light modulator onto an object; and a control unit controlling the spatial light modulator so as to adjust the modulation pattern according to the advancing direction of the focal point of the laser light relative to the object, The control unit adjusts the modulation pattern so that the focal point becomes an arc shape convex toward the traveling direction or an arc shape convex toward a direction opposite to the traveling direction.

2. The laser processing device according to claim 1, wherein: The control unit adjusts the modulation pattern separately in a first case where the focal point moves toward a first direction with respect to the object and in a second case where the focal point moves toward a second direction opposite to the first direction with respect to the object.

3. The laser processing device according to claim 2, wherein: The control unit adjusts the modulation pattern in the first case so that the shape of the focal point becomes an arc convex toward the first direction, and in the second case so that the shape of the focal point becomes an arc convex toward the second direction.

4. The laser processing device according to claim 2, wherein: The control unit adjusts the modulation pattern in the first case so that the shape of the focal point becomes an arc convex toward the second direction, and in the second case, adjusts the modulation pattern so that the shape of the focal point becomes an arc convex toward the first direction.

5. The laser processing device according to any one of claims 1 to 4, wherein: have: A display unit for displaying information; and An input unit for receiving input, The display unit displays information for prompting input of parameters for adjusting the modulation pattern, The input unit receives input of the parameter. The control unit adjusts the modulation pattern according to the parameter received by the input unit.

6. The laser processing device according to claim 5, wherein: The modulation pattern includes a spherical aberration correction pattern for correcting the spherical aberration of the laser light. The parameter includes an offset amount of the center of the spherical aberration correction pattern relative to the center of a pupil plane of the condenser lens along the traveling direction.

7. The laser processing device according to claim 5, wherein: The modulation pattern includes a coma pattern for imparting positive coma aberration to the laser light. The parameters include the magnitude of the coma aberration.

8. The laser processing device according to claim 6, wherein: The modulation pattern includes a coma pattern for imparting positive coma aberration to the laser light. The parameters include the magnitude of the coma aberration.

Images