Laser processing apparatus and laser processing method

Abstract

To efficiently process a wafer while suppressing thermal damage to a wafer.SOLUTION: A laser processing device 1 includes: a support portion 2 that supports a wafer 20 including a plurality of functional elements 22 arranged adjacent to each other via a street 23; an irradiation unit 3 that irradiates the street 23 with laser light; and a control unit 5 that controls the irradiation unit 3 on the basis of information on the street 23 such that irradiation of laser light to first and second regions of the street 23 is carried out at the same time and the power of the laser beam of removing a surface layer in the second region becomes larger than the power of removing the surface layer of the street 23 in the first region. The information on the street 23 includes information indicating that a processing threshold value indicating the difficulty of laser processing in the first region is lower than a processing threshold value in the second region.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laser processing apparatus and a laser processing method.

Background Art

[0002] In a wafer including a plurality of functional elements arranged adjacent to each other via a street, an insulating film (such as a Low-k film) and metal structures (such as metal posts and metal pads) may be formed on the surface layer of the street. In such a case, when a modified region is formed inside the wafer along a line passing through the street and the wafer is diced into chips by extending cracks from the modified region, the quality of the chips may deteriorate, such as film peeling occurring in the portion along the street. Therefore, when dicing a wafer into chips for each functional element, grooving processing may be performed to remove the surface layer of the street by irradiating the street with laser light (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, the structure of the surface layer of the street is usually not uniform and includes regions that are relatively difficult to laser process (have a high processing threshold) and regions with a low processing threshold. For example, when irradiating the street with laser light under conditions that can surely remove metal structures and the like in regions with a high processing threshold, there is a risk of thermal damage occurring in regions with a low processing threshold. Such thermal damage causes deterioration of the chip quality. On the other hand, when irradiating the street with laser light under conditions that can surely suppress thermal damage in regions with a low processing threshold, there is a risk that a part of the metal structure in regions with a high processing threshold remains. In this case, it becomes necessary to irradiate the regions with a high processing threshold with laser light multiple times, etc., and the processing throughput deteriorates.

[0005] Therefore, an object of the present invention is to provide a laser processing apparatus and a laser processing method that can efficiently process a wafer while suppressing the occurrence of thermal damage to the wafer.

Means for Solving the Problems

[0006] A laser processing apparatus according to an aspect of the present invention includes a support unit that supports a wafer including a plurality of functional elements arranged adjacent to each other via a street, an irradiation unit that irradiates the street with laser light, and based on information regarding the street, the irradiation of the laser light to the first region and the second region of the street is simultaneously performed, and a control unit that controls the irradiation unit so that the power for removing the surface layer of the street in the second region is greater than the power for removing the surface layer in the first region. The information regarding the street includes information that the processing threshold indicating the difficulty of laser processing in the first region is lower than the processing threshold in the second region.

[0007] In the laser processing apparatus according to one aspect of the present invention, in the grouping process for removing the surface layer of the street, the irradiation of the laser beam on the first region and the second region is performed simultaneously, and the irradiation unit is controlled so that the power for removing the surface layer in the second region having a higher processing threshold is larger than the power for removing the surface layer in the first region having a lower processing threshold. In this way, when there are regions with different processing thresholds on the street, for example, if the laser beam is irradiated in accordance with the region having a high processing threshold, there is a risk of thermal damage to the region having a low processing threshold. On the other hand, for example, if the laser beam is irradiated in accordance with the region having a low processing threshold, the surface layer of the region having a high processing threshold is not sufficiently removed, so it is necessary to perform the irradiation of the laser beam multiple times, etc., and the throughput of the processing deteriorates. In this regard, in the laser processing apparatus according to one aspect of the present invention, based on the information regarding the processing threshold of each region, for the second region having a relatively high processing threshold, the power for removing the surface layer of the street is made larger than that of the first region, and the irradiation of the laser beam on the first region and the second region is performed simultaneously. In this way, instead of irradiating the laser beam under the same conditions for all regions according to any one of the processing thresholds, the laser beam is irradiated on each region under the conditions for each region and simultaneously so that the higher the processing threshold of the region, the larger the power for removing the surface layer. As a result, laser irradiation with an intensity that does not cause thermal damage to the region having a low processing threshold and laser irradiation with an intensity that does not require repeated processing for the region having a high processing threshold are simultaneously realized. As described above, according to the laser processing apparatus according to one aspect of the present invention, the wafer can be efficiently processed while suppressing the occurrence of thermal damage to the wafer.

[0008] The control unit may increase the power of the laser beam for removing the surface layer in the second region compared to the power of the laser beam for removing the surface layer in the first region by arranging the condensing points of the laser beam such that the number of condensing points of the laser beam per specific range in the second region is larger than the number of condensing points of the laser beam per specific range in the first region. According to such a configuration, it is possible to easily adjust the power of the laser beam for removing the surface layer in each region only by arranging the irradiation positions (condensing points) without adjusting the intensity of the laser beam itself.

[0009] The control unit may increase the power of the laser beam for removing the surface layer in the second region compared to the power of the laser beam for removing the surface layer in the first region by increasing the intensity of the laser beam irradiated to the second region compared to the intensity of the laser beam irradiated to the first region. According to such a configuration, it is possible to easily adjust the power of the laser beam for removing the surface layer in each region only by adjusting the intensity of the laser beam without complicating the arrangement of the condensing points.

[0010] The control unit controls at least one of the support unit and the irradiation unit so that the laser beam moves relatively in the first direction along the street, and the control unit arranges a plurality of condensing points of the laser beam at different positions in the second direction, which is the width direction of the street intersecting the first direction, and which do not overlap each other in the first direction. Although it is desired to arrange the plurality of condensing points densely to some extent, when the plurality of condensing points of the laser beam are arranged linearly in the width direction (second direction) of the street, the intensity distribution of the laser beam in the second direction becomes non-uniform due to the optical interference effect. In this regard, by arranging the plurality of condensing points at positions that do not overlap each other in the first direction (that is, not arranged linearly in the second direction), the influence of the above-described optical interference effect is reduced, and a processing result equivalent to that of a laser beam having a uniform irradiation profile in the second direction can be obtained.

[0011] The above-described laser processing apparatus further includes an imaging unit that acquires image data of the street, and the control unit may specify the first region and the second region based on the image data. In this way, based on the captured image data, the first region and the second region in the street of the wafer are specified, so that each region of the street can be appropriately specified and laser light irradiation corresponding to the region can be appropriately performed.

[0012] A laser processing method according to an aspect of the present invention includes a first step of preparing a wafer including a plurality of functional elements arranged adjacent to each other via a street, and after the first step, based on information regarding the street, in a first region, the power for removing the surface layer of the street is less than that in a second region. A second step of simultaneously irradiating the first region and the second region of the street with laser light so that the power for removing the surface layer is larger, and the information regarding the street includes information that a processing threshold indicating the difficulty of laser processing in the first region is lower than the processing threshold in the second region. According to such a laser processing method, similarly to the above-described laser processing apparatus, the wafer can be efficiently processed while suppressing the occurrence of thermal damage to the wafer.

[0013] The above-described laser processing method may further include a third step of acquiring image data of the street after the first step and before the second step, and specifying the first region and the second region based on the image data. According to such a laser processing method, each region of the street can be appropriately specified and laser light irradiation corresponding to the region can be appropriately performed.

[0014] The above-described laser processing method may further include a fourth step of forming a modified region inside the wafer along a line passing through the street after the first step. According to such a laser processing method, by causing a crack extending from the modified region to reach the street along the line, the wafer can be diced into chips for each functional element.

Advantages of the Invention

[0015] According to the present invention, it is possible to efficiently process a wafer while suppressing the occurrence of thermal damage to the wafer.

Brief Description of the Drawings

[0016]

Figure 1

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Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted. [Configuration of Laser Processing Apparatus]

[0018] As shown in FIG. 1, the laser processing apparatus 1 includes a support unit 2, an irradiation unit 3, an imaging unit 4, and a control unit 5. The laser processing apparatus 1 is an apparatus that performs grooving processing for removing the surface layer of the street of the wafer 20 by irradiating the laser beam L onto the street of the wafer 20 (details will be described later). In the following description, three mutually orthogonal directions are referred to as the X direction, the Y direction, and the Z direction, respectively. As an example, the X direction is the first horizontal direction, the Y direction is the second horizontal direction perpendicular to the first horizontal direction, and the Z direction is the vertical direction.

[0019] The support unit 2 supports the wafer 20. The support unit 2 holds the wafer 20 by sucking, for example, a film (not shown) attached to the wafer 20 so that the surface of the wafer 20 including the street faces the irradiation unit 3 and the imaging unit 4. As an example, the support unit 2 is movable along each of the X direction and the Y direction, and is rotatable about an axis parallel to the Z direction as a center line.

[0020] The irradiation unit 3 irradiates the laser beam L onto the street of the wafer 20 supported by the support unit 2. The irradiation unit 3 includes a light source 31, a shaping optical system 32, a spatial light modulator 38, an imaging optical system 39, a mirror 33A, a condensing unit 34A, a light source 35, a beam splitter 36, a lens 34B, a mirror 33B, and an imaging element 37.

[0021] The light source 31 emits a laser beam L. The shaping optical system 32 adjusts the laser beam L emitted from the light source 31. As an example, the shaping optical system 32 includes at least one of an attenuator that adjusts the output of the laser beam L and a beam expander that expands the diameter of the laser beam L. The spatial light modulator 38 modulates the phase of the laser beam L. The spatial light modulator 38 modulates the laser beam L according to the modulation pattern displayed on the liquid crystal layer. The modulation pattern is a hologram pattern for applying modulation. The spatial light modulator 38 is, for example, a spatial light modulator (SLM) of a reflective liquid crystal (LCOS: Liquid Crystal on Silicon). The imaging optical system 39 forms an image of the laser beam L modulated by the spatial light modulator 38. The imaging optical system 39 constitutes, for example, a two-sided telecentric optical system in which the modulation plane of the spatial light modulator 38 and the entrance pupil plane of the condenser 34A are in an imaging relationship. The mirror 33A reflects the laser beam L transmitted through the imaging optical system 39 and makes it incident on the condenser 34A. The condenser 34A condenses the laser beam L reflected by the mirror 33A onto the street of the wafer 20 supported by the support 2.

[0022] The light source 35 emits visible light. The beam splitter 36 reflects a part of the visible light emitted from the light source 35 and makes it incident on the lens 34B, and transmits the rest. The visible light incident on the lens 34B passes through the lens 34B, the mirror 33A, and the condenser 34A and irradiates the street of the wafer 20 supported by the support 2. The imaging device 37 detects the visible light reflected by the street of the wafer 20, passes through the condenser 34A, the mirror 33A, the lens 34B, and the beam splitter 36, and is reflected by the mirror 33B. In the laser processing apparatus 1, the control unit 5 moves the condenser 34A along the Z direction so that, for example, the focusing point of the laser beam L is located on the street of the wafer 20 based on the detection result by the imaging device 37.

[0023] The imaging unit 4 acquires image data of the streets of the wafer 20 supported by the support unit 2. The imaging unit 4 includes a beam splitter 42, a lens 43B, a condenser unit 43A, and an imaging element 44. The beam splitter 42 reflects the visible light emitted from the light source 35 and transmitted through the beam splitter 36 and makes it incident on the lens 43B. The visible light incident on the lens 43B passes through the lens 43B and the condenser unit 43A and is irradiated onto the streets of the wafer 20 supported by the support unit 2. The imaging element 44 detects the visible light reflected by the streets of the wafer 20 and transmitted through the condenser unit 43A, the lens 43B, and the beam splitter 42.

[0024] The control unit 5 controls the operations of each part of the laser processing apparatus 1. The control unit 5 includes a processing unit 51, a storage unit 52, and an input reception unit 53. The processing unit 51 is a computer device including a processor, a memory, a storage, a communication device, and the like. In the processing unit 51, the processor executes software (program) read into the memory and the like, controls the reading and writing of data in the memory and the storage, and communication by the communication device. The storage unit 52 is, for example, a hard disk or the like and stores various data. The input reception unit 53 is an interface unit that receives input of various data from an operator. As an example, the input reception unit 53 is at least one of a keyboard, a mouse, and a GUI (Graphical User Interface). [Configuration of Wafer]

[0025] As shown in FIGS. 2 and 3, the wafer 20 includes a semiconductor substrate 21 and functional elements 22. The semiconductor substrate 21 has a front surface 21a and a back surface 21b. The semiconductor substrate 21 is, for example, a silicon substrate. A notch 21c indicating the crystal orientation is provided in the semiconductor substrate 21. An orientation flat may be provided in the semiconductor substrate 21 instead of the notch 21c. The functional elements 22 are formed on the front surface 21a of the semiconductor substrate 21. The functional elements 22 include a plurality of functional elements 22a. The plurality of functional elements 22a are two-dimensionally arranged along the front surface 21a of the semiconductor substrate 21. Each functional element 22a is, for example, a light receiving element such as a photodiode, a light emitting element such as a laser diode, or a circuit element such as a memory. Each functional element 22a may be three-dimensionally configured with a plurality of layers stacked.

[0026] A plurality of streets 23 are formed in the wafer 20. The plurality of streets 23 are regions exposed to the outside between adjacent functional elements 22a. That is, the plurality of functional elements 22a are arranged adjacent to each other via the streets 23. As an example, the plurality of streets 23 extend in a lattice pattern so as to pass between adjacent functional elements 22a with respect to the plurality of functional elements 22a arranged in a matrix. As shown in FIG. 4, an insulating film 24 and a plurality of metal structures 25, 26 are formed on the surface layer of the street 23. The insulating film 24 is, for example, a Low-k film. Each of the metal structures 25, 26 is, for example, a metal pad. The metal structure 25 and the metal structure 26 are different from each other in at least one of, for example, thickness, area, and material.

[0027] As shown in FIGS. 2 and 3, the wafer 20 is planned to be cut for each functional element 22a along each of the plurality of lines 15 (that is, diced for each functional element 22a). Each line 15 passes through each street 23 when viewed in the thickness direction of the wafer 20. As an example, each line 15 extends so as to pass through the center of each street 23 when viewed in the thickness direction of the wafer 20. Each line 15 is a virtual line set on the wafer 20 by the laser processing apparatus 1. Each line 15 may be a line actually drawn on the wafer 20. [Operation of Laser Processing Apparatus and Laser Processing Method]

[0028] The laser processing apparatus 1 performs grooving processing to remove the surface layer of each street 23 by irradiating each street 23 with the laser beam L. Specifically, the control unit 5 controls the irradiation unit 3 so that the laser beam L is irradiated onto each street 23 of the wafer 20 supported by the support unit 2, and the control unit 5 controls the support unit 2 so that the laser beam L moves relatively along each street 23. At this time, based on the information regarding the street 23, the control unit 5 makes the power for removing the surface layer of the street 23 in the second region of the street 23 larger than the power for removing the surface layer of the street 23 in the first region of the street 23, and controls the irradiation unit 3 so that the irradiation of the laser beam L to the first region and the second region is performed simultaneously. Here, the "information regarding the street 23" is "information that the processing threshold indicating the difficulty of laser processing in the first region is lower than the processing threshold in the second region". Such a difference in the processing threshold is due to the non-uniform structure of the surface layer of the street 23. That is, the street 23 includes a region (first region) where laser processing is relatively easy and a region (second region) where laser processing is relatively difficult.

[0029] As described above, instead of irradiating the entire area of the street 23 with the laser beam L under the same conditions, the laser beam L is irradiated to each area simultaneously under the conditions for each area so that the higher the processing threshold of each area, the greater the power for removing the surface layer. This enables simultaneous realization of laser irradiation with an intensity that does not cause thermal damage to areas with a low processing threshold and laser irradiation with an intensity that does not require repeated processing for areas with a high processing threshold. As a result, while suppressing the occurrence of thermal damage to the wafer 20, the wafer 20 can be efficiently processed.

[0030] With reference to the flowchart of FIG. 5, a laser processing method using the laser processing apparatus 1 will be described. It is assumed that, as a premise for performing the processing described below, the processing threshold indicating the difficulty of processing has been specified for each area in the street 23. Specifically, it is assumed that, as information regarding the street 23, it has been specified that the processing threshold in the first area is lower than the processing threshold in the second area. Such information regarding the street 23 may be specified, for example, by preparing a test wafer in advance, irradiating the wafer with a laser beam to form a modified area, and specifying the crack state extending from the modified area. The information regarding the street 23 is stored by the storage unit 52 of the control unit 5 of the laser processing apparatus 1.

[0031] As shown in FIG. 5, first, a wafer 20 is prepared (S01 shown in FIG. 5) (first step). Subsequently, in the laser processing apparatus 1, while the wafer 20 is supported by the support unit 2, image data of each street 23 of the wafer 20 is acquired by the imaging unit 4 (S02 shown in FIG. 5). The image data is stored by the storage unit 52 of the control unit 5 of the laser processing apparatus 1. Subsequently, in the laser processing apparatus 1, grooving processing is performed on the wafer 20 (S03 shown in FIG. 5) (second step).

[0032] Specifically, the control unit 5 controls the irradiation unit 3 so that the laser beam L is irradiated onto each street 23 of the wafer 20 supported by the support unit 2, and controls the support unit 2 so that the laser beam L moves relatively along each street 23. At this time, based on the image data of each street 23 acquired from the imaging unit 4 and the information on the street 23 acquired in advance, the control unit 5 makes the power for removing the surface layer of the street 23 in the second region of the street 23 larger than the power for removing the surface layer of the street 23 in the first region of the street 23, and controls the irradiation unit 3 so that the laser beam L is irradiated onto the first region and the second region simultaneously (details will be described later).

[0033] In the laser processing apparatus 1, based on the image data of each street 23 acquired from the imaging unit 4, the control unit 5 specifies in advance the position information of the first region and the second region in each street 23 (third step) (the position information is stored by the storage unit 52 of the control unit 5 of the laser processing apparatus 1), makes the power for removing the surface layer of the street 23 in the second region larger than the power for removing the surface layer of the street 23 in the first region, and controls the irradiation unit 3 so that the laser beam L is irradiated onto the first region and the second region simultaneously.

[0034] Subsequently, as shown in FIG. 6, in a laser processing apparatus (not shown), by irradiating the wafer 20 with the laser beam L0 along each line 15, a modified region 11 is formed inside the wafer 20 along each line 15 (S04 shown in FIG. 5) (fourth step). The modified region 11 is a region where the density, refractive index, mechanical strength, and other physical properties are different from those of the surrounding unmodified region. Examples of the modified region 11 include a melted region, a crack region, an insulation breakdown region, a refractive index change region, and the like. The modified region 11 has the property that cracks tend to extend from the modified region 11 to the incident side and the opposite side of the laser beam L0.

[0035] Subsequently, as shown in FIG. 7, in an expand device (not shown), the expand film 12 is expanded, so that cracks extend in the thickness direction of the wafer 20 from the modified region 11 formed inside the semiconductor substrate 21 along each line 15, and the mass-production wafer 20 is diced into chips for each functional element 22a (S05 shown in FIG. 5).

[0036] Next, the process of the control unit 5 will be described in more detail. Based on the information regarding the street 23 (information that the processing threshold of the first region is lower than that of the second region), the control unit 5 simultaneously irradiates the first region and the second region of the street 23 with laser light, and controls the irradiation unit 3 so that the power for removing the surface layer of the street 23 in the second region is greater than the power for removing the surface layer of the street 23 in the first region.

[0037] The control unit 5 increases the power for removing the surface layer of the street 23 in the second region compared to the power for removing the surface layer of the street 23 in the first region, for example, by arranging the condensing points of the laser light so that the number of condensing points of the laser light per specific range in the second region is larger than the number of condensing points of the laser light per specific range in the first region. The control unit 5 controls the arrangement of the condensing points of the laser light, for example, by adjusting the modulation pattern (hologram pattern) displayed on the liquid crystal layer of the spatial light modulator 38.

[0038] FIGS. 8 and 9 are diagrams for explaining the laser irradiation mode when controlling the arrangement of the condensing points of the laser light described above. In FIGS. 8 and 9, (a) is a diagram showing the first region 23x and the second region 23y in the street 23 of the wafer 20, (b) is a diagram showing the irradiation positions (condensing points) of the laser light, and (c) is a diagram showing the number of irradiation times (number of condensing points) for each region. Note that the "extending direction" (first direction) of the street 23 described below is the left-right direction in FIG. 8 and the like, and the "width direction" (second direction) of the street 23 is the up-down direction in FIG. 8 and the like.

[0039] In the example shown in FIG. 8, as shown in FIG. 8(a), both end portions in the width direction of the street 23 are the first regions 23x formed of a material with a low processing threshold, and the central portion in the width direction of the street 23 is the second region 23y formed of a material with a high processing threshold. Note that "the processing threshold is low" for the first region 23x indicates that the processing threshold is lower compared to the second region 23y, and "the processing threshold is high" for the second region 23y indicates that the processing threshold is higher compared to the first region 23x. For such a street 23, for example, laser light is irradiated at the irradiation position (focus point) as shown in FIG. 8(b). In the example shown in FIG. 8(b), at both end portions in the width direction of the street 23 corresponding to the first region 23x, there is only one irradiation position (focus point) in the extending direction of the street 23. Also, at the central portion in the width direction of the street 23 corresponding to the second region 23y, there are three irradiation positions (focus points) along the extending direction of the street 23 per a specific range. The specific range here is a predetermined range in the width direction, and in the example shown in FIG. 8, it is the range in the width direction of the first region 23x. That is, in the example shown in FIG. 8, in the second region 23y, when viewed in terms of the range (size) in the width direction of the first region 23x, there are three irradiation positions (focus points) along the extending direction of the street 23 per each range. As shown in FIG. 8(c), when laser light is irradiated at the focus points shown in FIG. 8(b) and the wafer 20 is moved in the extending direction of the street 23 with respect to the laser light, along the extending direction of the street 23, for the first region 23x, the number of focus points of the laser light per a specific range is one (one-time irradiation), and for the second region 23y, the number of focus points of the laser light per a specific range is three (three-time irradiation), and the laser light irradiation is repeatedly performed.

[0040] In the example shown in FIG. 9, as shown in FIG. 9(a), both end portions in the width direction of the street 23 are the second regions 23y formed of a material with a high processing threshold, and the central portion in the width direction of the street 23 is the first region 23x formed of a material with a low processing threshold. For such a street 23, laser light is irradiated at an irradiation position (focus point) as shown in FIG. 9(b), for example. In the example shown in FIG. 9(b), at both end portions in the width direction of the street 23 corresponding to the second region 23y, there are four irradiation positions (focus points) along the extending direction of the street 23. Also, at the central portion in the width direction of the street 23 corresponding to the first region 23x, there is only one irradiation position (focus point) along the extending direction of the street 23 per a specific range. The specific range here is a predetermined range in the width direction, and in the example shown in FIG. 9, it is the range in the width direction of the second region 23y. That is, in the example shown in FIG. 9, in the first region 23x, when viewed in terms of the range (size) in the width direction of the second region 23y, there is only one irradiation position (focus point) along the extending direction of the street 23 per each range. As shown in FIG. 9(c), when laser light is irradiated at the focus points shown in FIG. 9(b) and the wafer 20 is moved in the extending direction of the street 23 with respect to the laser light, along the extending direction of the street 23, for the first region 23x, the number of focus points of the laser light per a specific range is one (one-time irradiation), and for the second region 23y, the number of focus points of the laser light per a specific range is four (four-time irradiation), and the laser light irradiation is repeatedly performed.

[0041] FIG. 10 and FIG. 11 are diagrams for explaining an irradiation position design example in the case of controlling the arrangement of the laser light focusing points. In FIGS. 10 and 11, (a) is a design example of the laser irradiation arrangement, (b) is a pattern of the laser focusing positions, and (c) is a modulation pattern (hologram pattern) displayed on the spatial light modulator 38. FIG. 10 shows an example in which both end portions in the width direction of the street 23 are the second region 23y and there are five focusing points per specific range, and the central portion in the width direction of the street 23 is the first region 23x and there are two focusing points per specific range. FIG. 11 shows an example in which both end portions in the width direction of the street 23 are the first region 23x and there is one focusing point per specific range, and the central portion in the width direction of the street 23 is the second region 23y and there are three focusing points per specific range.

[0042] In the example shown in FIG. 10, for example, the laser irradiation arrangement is as shown in FIG. 10(a). As shown in FIG. 10(a), for example, the distance between both end portions of the focusing points in the first direction is 76.8 μm, and the distance between both end portions of the focusing points in the second direction is 57.6 μm. Then, as the hologram pattern for realizing the pattern of the laser focusing positions shown in FIG. 10(b), the hologram pattern shown in FIG. 10(c) is generated. In the example shown in FIG. 11, for example, the laser irradiation arrangement is as shown in FIG. 11(a). As shown in FIG. 11(a), for example, the distance between both end portions of the focusing points in the first direction is 96 μm, and the distance between both end portions of the focusing points in the second direction is 57.6 μm. Then, as the hologram pattern for realizing the pattern of the laser focusing positions shown in FIG. 11(b), the hologram pattern shown in FIG. 11(c) is generated.

[0043] Further, for example, the control unit 5 may increase the power of the laser light for removing the surface layer of the street 23 in the second region by increasing the intensity of the laser light irradiated to the second region as compared with the intensity of the laser light irradiated to the first region. The control unit 5 controls the intensity of the laser light, for example, by adjusting the modulation pattern (hologram pattern) displayed on the liquid crystal layer of the spatial light modulator 38.

[0044] FIGS. 12 and 13 are diagrams for explaining the laser irradiation mode when controlling the intensity of the laser light described above. In FIGS. 12 and 13, (a) is a diagram showing a first region 23x and a second region 23y in the street 23 of the wafer 20, and (b) is a diagram showing the irradiation intensity of the laser light.

[0045] In the example shown in FIG. 12, as shown in FIG. 12(a), both end portions on the width direction sides of the street 23 are the first regions 23x made of a material with a low processing threshold, and the central portion in the width direction of the street 23 is the second region 23y made of a material with a high processing threshold. For such a street 23, for example, as shown in FIG. 12(b), when the intensity of the laser light irradiated to the second region 23y is set to 1.0, the laser light is irradiated so that the intensity of the laser light irradiated to the first region 23x becomes 0.3.

[0046] In the example shown in FIG. 13, as shown in FIG. 13(a), both end portions on the width direction sides of the street 23 are the second regions 23y made of a material with a high processing threshold, and the central portion in the width direction of the street 23 is the first region 23x made of a material with a low processing threshold. For such a street 23, for example, as shown in FIG. 13(b), when the intensity of the laser light irradiated to the second region 23y is set to 1.0, the laser light is irradiated so that the intensity of the laser light irradiated to the first region 23x becomes 0.3.

[0047] FIG. 14 and FIG. 15 are diagrams for explaining an example of irradiation position design when controlling the intensity of laser light. In FIGS. 14 and 15, (a) is an example of the design of laser irradiation arrangement, (b) is a pattern of laser focusing positions, and (c) is a modulation pattern (hologram pattern) displayed on the spatial light modulator 38. FIG. 14 shows an example in which both end portions in the width direction of the street 23 are the first region 23x and the relative intensity of the laser light is set to 0.3, and the central portion in the width direction of the street 23 is the second region 23y and the relative intensity of the laser light is set to 1.0. FIG. 15 shows an example in which both end portions in the width direction of the street 23 are the second region 23y and the relative intensity of the laser light is set to 1.0, and the central portion in the width direction of the street 23 is the first region 23x and the relative intensity of the laser light is set to 0.3.

[0048] In the example shown in FIG. 14, for example, the laser irradiation arrangement is as shown in FIG. 14(a). As shown in FIG. 14(a), for example, the distance between both end portions of the focusing point in the first direction is set to 57.6 μm, and the distance between both end portions of the focusing point in the second direction is set to 57.6 μm. Then, as a hologram pattern for realizing the pattern of the laser focusing position shown in FIG. 14(b), the hologram pattern shown in FIG. 14(c) is generated. In the example shown in FIG. 15, for example, the laser irradiation arrangement is as shown in FIG. 15(a). As shown in FIG. 15(a), for example, the distance between both end portions of the focusing point in the first direction is set to 57.6 μm, and the distance between both end portions of the focusing point in the second direction is set to 57.6 μm. Then, as a hologram pattern for realizing the pattern of the laser focusing position shown in FIG. 15(b), the hologram pattern shown in FIG. 15(c) is generated.

[0049] Further, the control unit 5 controls the support unit 2 so that the laser light relatively moves in the first direction (the extending direction of the street 23) along the street 23, and at different positions in the second direction (the width direction of the street 23) that do not overlap each other in the first direction, a plurality of focusing points of the laser light may be arranged.

[0050] FIG. 16 is a diagram for explaining the interference effect of light. In FIG. 16, the black circles indicate the designed focusing points of the laser light irradiated simultaneously, and the graph beside the black circles shows an example of the actually observed light intensity distribution. When performing the grooving process on the street 23, uniform processing is required in the width direction (the second direction) of the street 23. However, as shown in FIG. 16, when a plurality of laser lights are linearly formed simultaneously in the width direction (the second direction) of the street 23, due to the light interference effect in which the plurality of laser lights interfere with each other, the intensity distribution is different from that in the case of single irradiation, and the intensity distribution becomes non-uniform.

[0051] FIG. 17 is a diagram for explaining the laser irradiation mode when the focusing points of a plurality of laser lights are displaced and arranged on the plane. In FIG. 17, the black circles indicate the focusing points of the laser light, the horizontal direction indicates the extending direction (the first direction) of the street 23, and the vertical direction indicates the width direction (the second direction) of the street 23. As a method for avoiding the non-uniformity of the light intensity distribution due to the above-described light interference effect, as shown in FIG. 17(a), it is conceivable to arrange the focusing points of the plurality of laser lights at different positions in the second direction and non-overlapping positions in the first direction. In this way, by displacing and arranging the focusing points of the plurality of laser lights on the plane, the influence of the above-described light interference effect is not received. Further, as shown in FIG. 17(a), when the laser light relatively moves in the first direction along the street 23, the processing marks are the same as those in the case where the focusing points are not displaced and arranged on the plane (the focusing points are arranged side by side in the second direction), so that it is possible to obtain a processing result equivalent to a uniform irradiation (top hat) profile. Incidentally, as shown in FIG. 17(b), by arranging the focusing points of the plurality of laser lights at non-overlapping positions in the first direction and overlapping positions (partially overlapping positions) in the second direction, the focusing points (processing points) can be arranged at a high density, and without being affected by the interference effect, the interval between the processing points in the second direction that can be substantially obtained can be arbitrarily narrowed.

[0052] Further, the control unit 5 may dynamically change the arrangement of the laser beam focusing points (laser irradiation pattern) according to the wafer structure during the grouping process. The control unit 5 identifies the wafer structure based on the image data of each street 23 acquired from the imaging unit 4 during the grooving process, and controls the irradiation unit 3 so as to obtain an arrangement of laser beam focusing points corresponding to the identified wafer structure.

[0053] In the example shown in FIG. 18, as the structures of the streets 23 of the wafer 20, structures W1, W2, W3, and W4 are shown. In structure W1, both end portions in the width direction of the street 23 are the first regions 23x formed of a material with a low processing threshold, and the central portion in the width direction of the street 23 is the second region 23y formed of a material with a high processing threshold. In structure W2, both end portions in the width direction of the street 23 are the second regions 23y, and the central portion in the width direction of the street 23 is the first region 23x. In structure W3, the same processing threshold (for example, the first region 23x) is applied to the entire region. In structure W4, both end portions in the width direction and the central portion in the width direction of the street 23 are the first regions 23x, and the position sandwiched between the first regions 23x is the second region 23y.

[0054] In this case, during the grooving process, when the control unit 5 determines that it is the structure W1 based on the image data of the street 23 acquired from the imaging unit 4, it refers to the storage unit 52 (memory) and performs laser irradiation with the laser irradiation pattern C1. In the laser irradiation pattern C1, only one irradiation position (focus point) is provided in the extending direction of the street 23 at both ends in the width direction of the street 23, and three irradiation positions (focus points) are provided along the extending direction of the street 23 per specific range in the central portion in the width direction of the street 23. During the grooving process, when the control unit 5 determines that it is the structure W2 based on the image data of the street 23 acquired from the imaging unit 4, it refers to the storage unit 52 (memory) and performs laser irradiation with the laser irradiation pattern C2. In the laser irradiation pattern C2, four irradiation positions (focus points) are provided along the extending direction of the street 23 at both ends in the width direction of the street 23, and only one irradiation position (focus point) is provided along the extending direction of the street 23 per specific range in the central portion in the width direction of the street 23. During the grooving process, when the control unit 5 determines that it is the structure W3 based on the image data of the street 23 acquired from the imaging unit 4, it refers to the storage unit 52 (memory) and performs laser irradiation with the laser irradiation pattern C3. In the laser irradiation pattern C3, a plurality of focus points of the laser light are arranged at different positions in the second direction (width direction of the street 23) and positions that do not overlap with each other in the first direction. During the grooving process, when the control unit 5 determines that it is the structure W4 based on the image data of the street 23 acquired from the imaging unit 4, it refers to the storage unit 52 (memory) and performs laser irradiation with the laser irradiation pattern C4. In the laser irradiation pattern C4, the intensity of the laser light irradiated to the second region 23y is made higher than the intensity of the laser light irradiated to the first region 23x.

[0055] FIG. 19 is a flowchart of a laser processing method in the case where the arrangement of laser beam focusing points (laser irradiation pattern) is dynamically changed according to the wafer structure during grooving processing. As shown in FIG. 19, in this laser processing method, first, the processing start position of the street 23 of the wafer 20 is set to the pre-observation position (step S101). The pre-observation position is the position irradiated with visible light related to imaging by the imaging unit 4.

[0056] Subsequently, the time difference Δt = l / vs between the pre-observation optical path and the processing optical path is calculated (step S102). Here, l is the separation distance between the pre-observation optical path and the processing optical path, and vs is the moving speed of the wafer 20. The pre-observation optical path is the optical path of visible light related to imaging by the imaging unit 4, and the processing optical path is the optical path related to laser irradiation by the irradiation unit 3. By deriving the time difference Δt, it is possible to specify at what timing the laser irradiation pattern should be changed according to the imaging result after imaging.

[0057] Subsequently, the movement of the support unit 2 (stage) on which the wafer 20 is placed is started (step S103). Subsequently, an imaging element 44 of the imaging unit 4 images a structure image (material structure image) of the street 23 of the wafer 20 (step S104), and it is determined whether or not the end structure of the street 23 of the wafer 20 is detected (step S105). If it is detected, the laser irradiation is stopped (step S108), and the process ends.

[0058] On the other hand, if the end structure is not detected, a laser irradiation pattern corresponding to the structure of the street 23 is specified, and after the above-described Δt, the irradiation pattern (hologram) corresponding to the specified structure is displayed on the spatial light modulator 38 (step S106). Then, the laser irradiation is started (step S107), and the process of step S104 is performed again.

[0059] Note that the control unit 5 may control the power density (laser irradiation intensity) by shifting the focus position of the focusing points in some regions, for example, and adjust the power for removing the surface layer in each region of the street 23.

[0060] An example of each parameter in the laser processing described in the embodiment is as follows. Wavelength: 515 nm, Pulse width: 600 fs, Repetition frequency: 20 kHz, Pulse energy: 2.5 μJ, Resolution of computer hologram: 1.6 μm / pixel, Objective lens: NA0.26, 10x. [Operation and effect]

[0061] The laser processing apparatus 1 according to the present embodiment includes a support portion 2 that supports a wafer 20 including a plurality of functional elements 22 arranged adjacent to each other via a street 23, an irradiation portion 3 that irradiates the street 23 with laser light, and a control portion 5 that controls the irradiation portion 3 based on information regarding the street 23 such that irradiation of the street 23 with laser light in a first region and a second region is simultaneously performed, and the power for removing the surface layer of the street 23 in the second region is greater than the power for removing the surface layer in the first region. The information regarding the street 23 includes information that the processing threshold indicating the difficulty of laser processing in the first region is lower than the processing threshold in the second region.

[0062] In the laser processing apparatus 1 according to the present embodiment, in the grouping process for removing the surface layer of the street 23, the irradiation of the laser beam to the first region and the second region is simultaneously performed, and the irradiation unit 3 is controlled so that the power for removing the surface layer in the second region having a higher processing threshold is larger than the power for removing the surface layer in the first region having a lower processing threshold. In this way, when there are regions with different processing thresholds in the street 23, for example, if the laser beam is irradiated according to the region with a high processing threshold, there is a risk of thermal damage in the region with a low processing threshold. On the other hand, for example, if the laser beam is irradiated according to the region with a low processing threshold, the surface layer of the region with a high processing threshold will not be sufficiently removed, so it is necessary to perform the irradiation of the laser beam multiple times, etc., and the processing throughput will deteriorate. In this regard, in the laser processing apparatus 1 according to the present embodiment, based on the information regarding the processing thresholds of each region, for the second region with a relatively high processing threshold, the power for removing the surface layer of the street 23 is made larger than that of the first region, and the irradiation of the laser beam to the first region and the second region is simultaneously performed. In this way, instead of irradiating the laser beam under the same conditions for all regions according to any one of the processing thresholds, the laser beam is irradiated to each region under the conditions for each region and simultaneously so that the power for removing the surface layer becomes larger for the region with a higher processing threshold according to the processing threshold of each region. As a result, laser irradiation with an intensity that does not cause thermal damage to the region with a low processing threshold and laser irradiation with an intensity that does not require repeated processing for the region with a high processing threshold are simultaneously realized. As described above, according to the laser processing apparatus 1 according to the present embodiment, the wafer 20 can be efficiently processed while suppressing the occurrence of thermal damage to the wafer 20.

[0063] The control unit 5 may increase the power of the laser beam for removing the surface layer in the second region compared to the power of the laser beam for removing the surface layer in the first region by arranging the condensing points of the laser beam such that the number of condensing points of the laser beam per specific range in the second region is larger than the number of condensing points of the laser beam per specific range in the first region. According to such a configuration, without adjusting the intensity of the laser beam itself, it is possible to easily adjust the power of the laser beam for removing the surface layer in each region only by arranging the irradiation positions (condensing points).

[0064] The control unit 5 may increase the power of the laser beam for removing the surface layer in the second region compared to the power of the laser beam for removing the surface layer in the first region by increasing the intensity of the laser beam irradiated to the second region compared to the intensity of the laser beam irradiated to the first region. According to such a configuration, without complicating the arrangement of the condensing points, it is possible to easily adjust the power of the laser beam for removing the surface layer in each region only by adjusting the intensity of the laser beam.

[0065] The control unit 5 controls at least one of the support unit 2 and the irradiation unit 3 so that the laser beam relatively moves in the first direction along the street 23, and the control unit 5 arranges a plurality of condensing points of the laser beam at different positions in the second direction, which is the width direction of the street 23 intersecting the first direction, and which do not overlap each other in the first direction. Although it is desired to arrange the plurality of condensing points densely to some extent, when the plurality of condensing points of the laser beam are arranged linearly in the width direction (second direction) of the street 23, the intensity distribution of the laser beam in the second direction becomes non-uniform due to the interference effect of light. In this regard, by arranging the plurality of condensing points at non-overlapping positions in the first direction (that is, not arranged linearly in the second direction), the influence of the above-described interference effect of light is reduced, and a processing result equivalent to that of a laser beam having a uniform irradiation profile in the second direction can be obtained.

[0066] The laser processing apparatus 1 further includes an imaging unit 4 that acquires image data of the street 23, and the control unit 5 may specify the first region and the second region based on the image data. In this way, based on the captured image data, the first region and the second region in the street 23 of the wafer 20 are specified, so that each region of the street 23 can be appropriately specified and laser light irradiation according to the region can be appropriately performed.

[0067] The laser processing method according to this embodiment includes a first step of preparing a wafer 20 including a plurality of functional elements 22 arranged adjacent to each other via a street 23, and after the first step, based on information regarding the street 23, the surface layer of the street 23 in the second region is removed A second step of simultaneously irradiating the first region and the second region of the street 23 with laser light so that the power for removing the surface layer in the second region is greater than the power for removing the surface layer in the first region, and the information regarding the street 23 includes information that the processing threshold indicating the difficulty of laser processing in the first region is lower than the processing threshold in the second region. According to such a laser processing method, the wafer 20 can be efficiently processed while suppressing the occurrence of thermal damage to the wafer 20.

[0068] The above-described laser processing method may further include a third step of acquiring image data of the street 23 after the first step and before the second step, and specifying the first region and the second region based on the image data. According to such a laser processing method, each region of the street 23 can be appropriately specified and laser light irradiation according to the region can be appropriately performed.

[0069] The above-described laser processing method may further include a fourth step of forming a modified region inside the wafer 20 along a line 15 passing through the street 23 after the first step. According to such a laser processing method, the wafer 20 can be diced into chips for each functional element by causing a crack extending from the modified region to reach the street 23 along the line 15.

Explanation of Reference Numerals

[0070] 1... Laser processing apparatus, 2... Support unit, 3... Irradiation unit, 4... Imaging unit, 5... Control unit, 11... Modification region, 20... Wafer, 22... Functional element, 23... Street, 23x... First region, 23y... Second region.

Claims

1. A support unit that supports a wafer including a plurality of functional elements arranged adjacent to each other via a street; An irradiation unit that irradiates the street with laser light; A control unit that controls the irradiation unit based on information regarding the street such that irradiation of the first region and the second region of the street with laser light is performed simultaneously, and the power for removing the surface layer of the street in the second region is greater than the power for removing the surface layer in the first region; The information regarding the street includes information indicating that a processing threshold value indicating the difficulty of laser processing in the first region is lower than the processing threshold value in the second region; The control unit arranges the condensing points of the laser light such that the number of condensing points of the laser light per a specific range in the second region is greater than the number of condensing points of the laser light per the specific range in the first region, thereby increasing the power for removing the surface layer in the second region as compared to the power for removing the surface layer in the first region, a laser processing apparatus.

2. The control unit increases the intensity of the laser light irradiated to the second region as compared to the intensity of the laser light irradiated to the first region, thereby increasing the power for removing the surface layer in the second region as compared to the power for removing the surface layer in the first region, the laser processing apparatus according to Claim 1.

3. The control unit controls at least one of the support unit and the irradiation unit such that the laser light relatively moves in a first direction along the street; The control unit arranges a plurality of condensing points of the laser light at different positions in a second direction, which is the width direction of the street intersecting the first direction, and which do not overlap each other in the first direction, the laser processing apparatus according to Claim 1 or 2.

4. A support unit that supports a wafer including a plurality of functional elements arranged adjacent to each other via a street; An irradiation unit that irradiates the street with laser light; A control unit that controls the irradiation unit based on information regarding the street such that irradiation of the first region and the second region of the street with laser light is performed simultaneously, and the power for removing the surface layer of the street in the second region is greater than the power for removing the surface layer in the first region; The information regarding the street includes information that the processing threshold indicating the difficulty of laser processing in the first region is lower than the processing threshold in the second region. The control unit controls at least one of the support unit and the irradiation unit so that the laser beam moves relatively in a first direction along the street. The control unit arranges a plurality of condensing points of the laser beam at different positions in a second direction which is the width direction of the street intersecting the first direction and which do not overlap each other in the first direction. A laser processing apparatus.

5. The laser processing apparatus further includes an imaging unit that acquires image data of the street. The control unit identifies the first region and the second region based on the image data. The laser processing apparatus according to any one of claims 1 to 4.

6. A first step of preparing a wafer including a plurality of functional elements arranged adjacent to each other via a street; After the first step, based on the information regarding the street, the first region and the second region of the street are simultaneously irradiated with a laser beam so that the power for removing the surface layer of the street in the second region is greater than the power for removing the surface layer in the first region. A second step, and The information regarding the street includes information that the processing threshold indicating the difficulty of laser processing in the first region is lower than the processing threshold in the second region. In the second step, by arranging the condensing points of the laser beam so that the number of condensing points of the laser beam per specific range in the second region is larger than the number of condensing points of the laser beam per specific range in the first region, the laser beam is removed from the surface layer in the second region. A laser processing method for increasing the power for removing the surface layer in the second region compared to the power for removing the surface layer in the first region.

7. A first step of preparing a wafer including a plurality of functional elements arranged adjacent to each other via a street; After the first step, based on the information regarding the street, the first region and the second region of the street are simultaneously irradiated with a laser beam so that the power for removing the surface layer of the street in the second region is greater than the power for removing the surface layer in the first region. A second step, and The information regarding the street includes information that the processing threshold indicating the difficulty of laser processing in the first region is lower than the processing threshold in the second region. In the second step, at least one of a support part that supports the wafer and an irradiation part that irradiates laser light is controlled so that the laser light relatively moves in a first direction along the street. A laser processing method, in the second step, a plurality of condensing points of laser light are arranged at different positions in a second direction which is the width direction of the street intersecting the first direction and which do not overlap each other in the first direction.

8. The laser processing method according to claim 6 or 7, further comprising a third step of acquiring image data of the street after the first step and before the second step, and specifying the first region and the second region based on the image data.

9. The laser processing method according to any one of claims 6 to 8, further comprising a fourth step of forming a modified region inside the wafer along a line passing through the street after the first step.

Images