JP7628442B2 - Laser Processing Equipment - Google Patents

Description

The present invention relates to a laser processing device.

Patent document 1 describes a laser processing device. This laser processing device is equipped with a spatial light modulator for modulating laser light emitted from a light source. The spatial light modulator modulates the laser light by displaying a modulation pattern on a liquid crystal layer based on a voltage applied to the liquid crystal layer.

JP 2015-223620 A

In Patent Document 1, the spatial light modulator is constructed by stacking a drive circuit layer, a pixel electrode layer, a reflective film, an alignment film, a liquid crystal layer, an alignment film, a transparent conductive film, and a transparent substrate in this order on a semiconductor substrate. In such a spatial light modulator, when a signal indicating a modulation pattern is input to the drive circuit layer, a voltage corresponding to the signal is applied to each pixel electrode, and an electric field is formed between each pixel electrode and the transparent conductive film. When this electric field is formed, the alignment direction of the liquid crystal molecules in the liquid crystal layer changes for each region corresponding to each pixel electrode (hereinafter sometimes referred to as "pixel"), and the refractive index changes for each region corresponding to each pixel electrode. This state is the state in which the modulation pattern is displayed on the liquid crystal layer.

When a modulation pattern is displayed on the liquid crystal layer, laser light is incident on the liquid crystal layer from the outside through the transparent substrate and transparent conductive film, reflected by the reflective film, and emitted from the liquid crystal layer to the outside through the transparent conductive film and transparent substrate, and the laser light is modulated according to the modulation pattern displayed on the liquid crystal layer. In this way, with a spatial light modulator, it is possible to modulate the laser light by appropriately setting the modulation pattern to be displayed on the liquid crystal layer.

An image signal can be used as a signal for displaying a modulation pattern on the spatial light modulator. In this case, a voltage corresponding to the gradation value of the image signal input to the spatial light modulator is applied to the liquid crystal layer, and a refractive index change corresponding to the voltage value occurs, thereby displaying the modulation pattern. Then, the laser light incident on the spatial light modulator is phase-modulated according to this modulation pattern. Therefore, in this case, the image signal and the modulation pattern, and the gradation value of the image signal and the amount of phase modulation imparted to the laser light by the modulation pattern correspond to each other. In the following, the amount of phase modulation imparted to the laser light by the modulation pattern may be referred to simply as the phase modulation amount of the modulation pattern.

However, the actual phase modulation amount of the modulation pattern may be dulled compared to the ideal state. The inventors have found that this dulling of the phase modulation amount may cause the following problems.

In other words, when a spatial light modulator with a phase modulation capability of up to 2π is to display a modulation pattern including an area with a phase modulation amount greater than 2π, the modulation pattern is reproduced by folding back the area exceeding 2π. In this case, due to the dulling of the phase modulation amount, the modulation state of the laser light may differ between the area of the modulation pattern where folding back occurs (inverted area) and the area where folding back does not occur (normal area). Therefore, if there is a bias in the ratio of inverted areas to normal areas in the modulation pattern, the change in the ratio will be large when the modulation pattern changes, and as a result, the change in the modulation state of the laser light will also be large. Note that, as an example, the modulation state of the laser light is the diffraction efficiency of the laser light when the modulation pattern is a diffraction grating pattern.

On the other hand, the inventor has found that the following problem may occur due to the fact that the folded portion of the phase modulation amount is unevenly present in a part of the modulation pattern. That is, when the folded portion of the phase modulation amount is unevenly present in a part of the modulation pattern, the focusing state of the laser light may vary between the part of the laser light modulated through the part where the folded portion is unevenly present and the part of the laser light modulated without passing through the part where the folded portion is unevenly present. Therefore, it is necessary to suppress the influence of the dulling of the phase modulation amount of the modulation pattern and the uneven distribution of the folded portion of the phase modulation amount in the modulation pattern.

The present invention aims to provide a laser processing device that can suppress the effects of the dulling of the phase modulation amount of the modulation pattern and the uneven distribution of the folding back portion of the phase modulation amount in the modulation pattern.

The laser processing device according to the present invention is a laser processing device for forming a modified region in an object by irradiating the object with laser light, and includes a support section for supporting the object, a light source for emitting laser light, a spatial light modulator for modulating the laser light emitted from the light source according to a modulation pattern and emitting the modulated laser light, a focusing section including a focusing lens for focusing the laser light emitted from the spatial light modulator toward the object, and a control section for inputting an image signal to the spatial light modulator and causing the spatial light modulator to display a modulation pattern according to the image signal, and the control section controls the movement of at least one of the support section and the focusing section to form a modified region in the object. A processing process is performed in which the focal point of the laser light is moved relative to the object along the X direction along the light incidence surface, and the object is irradiated with the laser light. A gradation value corresponding to the phase modulation amount in the modulation pattern is set in each of the areas constituting the image signal. In the processing process, the control unit inputs an image signal including a first signal whose gradation value changes at a constant slope from a minimum value to a maximum value from a region corresponding to one end of the modulation pattern in the first direction to a region corresponding to the other end of the modulation pattern in the first direction to the spatial light modulator, thereby causing the spatial light modulator to display a modulation pattern including a first pattern corresponding to the first signal.

In this laser processing device, the control unit inputs an image signal to the spatial light modulator, thereby causing the spatial light modulator to display a modulation pattern, and performs processing while modulating the laser light according to the modulation pattern. In the image signal, a gradation value corresponding to the phase modulation amount at each position of the modulation pattern is set for each region constituting the image signal. In other words, in the spatial light modulator, the phase modulation amount at each position of the modulation pattern is set to an amount corresponding to the gradation value of each region of the image signal, so that a desired pattern is displayed as a whole. The image signal includes a first signal in which the gradation value changes at a constant gradient from a region corresponding to one end of the modulation pattern to a region corresponding to the other end of the modulation pattern. As a result, the modulation pattern displayed on the spatial light modulator includes a first pattern in which the phase modulation amount changes in one direction at a constant gradient according to the first signal. According to the present inventor, when the modulation pattern includes such a first pattern, the influence of the dulling of the phase modulation amount of the modulation pattern and the uneven distribution of the folding back portion of the phase modulation amount in the modulation pattern are suppressed.

In the laser processing device according to the present invention, in the processing process, the control unit may input an image signal including a second signal corresponding to the second pattern to the spatial light modulator so as to display a modulation pattern including the second pattern for splitting the laser light into multiple processing lights on the spatial light modulator. In this case, the second pattern is superimposed on the modulation pattern. In such a case, the variation between the multiple processing lights is suppressed.

In the laser processing device according to the present invention, the first direction may be a direction that corresponds to a direction that intersects with the branching direction of the laser light. In this case, it is possible to more effectively suppress the variation between the processing lights.

In the laser processing device according to the present invention, in the processing process, the control unit may input an image signal including a third signal corresponding to the third pattern to the spatial light modulator so as to display a modulation pattern including a third pattern for changing the focusing position of the laser light depending on the radial position of the focusing lens on the spatial light modulator. In this case, it is possible to suppress uneven distribution of the folded portion of the phase modulation amount in the third pattern so as to correspond to a specific radial position of the focusing lens, and suppress variation in the focusing state of the laser light.

In the laser processing device according to the present invention, the control unit may change the gradation value in the first signal at a constant gradient from the minimum value to the maximum value from a region corresponding to one end of the modulation pattern in a second direction intersecting the first direction to a region corresponding to the other end of the modulation pattern in the second direction. In this case, the gradation value of the image signal changes at a constant gradient in two directions intersecting each other. Therefore, it is possible to suppress the influence of the blunting of the phase modulation amount and the uneven distribution of the folding back portion of the phase modulation amount within the plane of the spatial light modulator corresponding to the two directions.

In the laser processing device according to the present invention, the control unit may change the gradation value in the first signal so that it has multiple periods in at least one direction. In this case, it is possible to more reliably suppress the influence of the dulling of the phase modulation amount and the uneven distribution of the folding back portion of the phase modulation amount.

The present invention provides a laser processing device that can suppress the effects of the dulling of the phase modulation amount of the modulation pattern and the uneven distribution of the folding back portion of the phase modulation amount in the modulation pattern.

FIG. 1 is a schematic diagram showing a laser processing device according to the present embodiment. FIG. 2 is a cross-sectional view of a portion of the spatial light modulator shown in FIG. FIG. 3 is a plan view of a wafer, which is the subject of one embodiment. FIG. 4 is a cross-sectional view of a portion of the wafer shown in FIG. FIG. 5 is a cross-sectional view of a wafer for explaining an example of the operation of the laser processing device in the case of three-point branching. FIG. 6 is a schematic diagram showing an example of a modulation pattern. FIG. 7 is a schematic diagram showing an example of a modulation pattern. FIG. 8 is a schematic diagram showing an example of a modulation pattern including a diffraction grating pattern. FIG. 9 is a diagram showing an example of a diffraction grating pattern. FIG. 10 is a diagram showing a state in which a distortion correction pattern is superimposed on a diffraction grating pattern. FIG. 11 is a diagram showing an example of a diffraction grating pattern. FIG. 12 is a diagram showing an example of an averaging pattern. FIG. 13 is a diagram showing an example of a modulation pattern formed by superimposing an averaged pattern on a diffraction grating pattern. FIG. 14 is a diagram showing an example of a modulation pattern formed by superimposing an averaging pattern on a distortion correction pattern. FIG. 15 is a schematic diagram showing the relationship between the condenser lens and the laser light. FIG. 16 is a diagram showing an example of a shaping pattern. FIG. 17 is a cross-sectional photograph showing the processing result when the shaping pattern shown in FIG. 16 is used. FIG. 18 is a diagram showing a modulation pattern formed by superimposing the averaging pattern shown in FIG. 12 on the shaping pattern shown in FIG. FIG. 19 is a cross-sectional photograph showing the processing result when the shaping pattern shown in FIG. 16 and the modulation pattern shown in FIG. 18 are used. FIG. 20 is a diagram showing a modified example of the averaging pattern. FIG. 21 is a diagram for explaining a modified example of the shaping pattern. FIG. 22 is a diagram for explaining a modified example. FIG. 23 is a diagram for explaining a modified example.

Hereinafter, an embodiment will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted.
[Configuration of laser processing device]

Figure 1 is a schematic diagram showing a laser processing device according to this embodiment. As shown in Figure 1, the laser processing device 1 includes a support unit 2, a light source 3, an optical axis adjustment unit 4, a spatial light modulator 5, a focusing unit 6, an optical axis monitor unit 7, a visible imaging unit 8, an infrared imaging unit 9, and a control unit 10. The laser processing device 1 is a device that forms a modified region 12 in an object 11 by irradiating the object 11 with laser light L. In the following description, the three mutually orthogonal directions are referred to as the X direction, the Y direction, and the Z direction, respectively. In this embodiment, 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.

The support unit 2 supports the object 11 so that the surface 11a of the object 11 is perpendicular to the Z direction, for example by adsorbing a film (not shown) attached to the object 11. The support unit 2 is movable along both the X direction and the Y direction, and can rotate around an axis parallel to the Z direction.

The light source 3 emits laser light L, for example, by a pulse oscillation method. The laser light L is transparent to the object 11.

The optical axis adjustment unit 4 adjusts the optical axis of the laser light L emitted from the light source 3. In this embodiment, the optical axis adjustment unit 4 adjusts the optical axis of the laser light L while changing the traveling direction of the laser light L emitted from the light source 3 to be along the Z direction. The optical axis adjustment unit 4 is composed of, for example, multiple reflecting mirrors whose positions and angles can be adjusted.

The spatial light modulator 5 is disposed in the housing H. The spatial light modulator 5 modulates the laser light L emitted from the light source 3. In this embodiment, the laser light L traveling downward from the optical axis adjustment unit 4 along the Z direction enters the housing H, and the laser light L that enters the housing H is reflected horizontally by the mirror M1 so as to form an angle with the Y direction, and the laser light L reflected by the mirror M1 enters the spatial light modulator 5. The spatial light modulator 5 modulates the laser light L thus entered while reflecting it horizontally along the Y direction.

The focusing unit 6 is attached to the bottom wall of the housing H. The focusing unit 6 focuses the laser light L modulated by the spatial light modulator 5 on the object 11 supported by the support unit 2 from the surface 11a side along the Z direction. In this embodiment, the laser light L reflected horizontally along the Y direction by the spatial light modulator 5 is reflected downward along the Z direction by the dichroic mirror M2, and the laser light L reflected by the dichroic mirror M2 enters the focusing unit 6. The focusing unit 6 focuses the laser light L thus incident on the object 11. In this embodiment, the focusing unit 6 is configured by attaching a focusing lens unit 61 to the bottom wall of the housing H via a driving mechanism 62. The driving mechanism 62 moves the focusing lens unit 61 along the Z direction, for example, by the driving force of a piezoelectric element.

In addition, an imaging optical system (not shown) is arranged between the spatial light modulator 5 and the focusing unit 6 inside the housing H. The imaging optical system constitutes a double-telecentric optical system in which the reflecting surface of the spatial light modulator 5 and the entrance pupil plane of the focusing unit 6 (the focusing lens 61a described later) are in an imaging relationship. As a result, the image of the laser light L on the reflecting surface of the spatial light modulator 5 (the image of the laser light L modulated by the spatial light modulator 5) is transferred (imaged) onto the entrance pupil plane of the focusing unit 6.

A pair of distance measurement sensors S1, S2 are attached to the bottom wall of the housing H, positioned on either side of the focusing lens unit 61 in the X direction. Each distance measurement sensor S1, S2 emits distance measurement light (e.g., laser light) to the surface 11a of the object 11, and obtains displacement data of the surface 11a by detecting the distance measurement light reflected by the surface 11a.

The optical axis monitor unit 7 is disposed within the housing H. The optical axis monitor unit 7 detects a portion of the laser light L that has passed through the dichroic mirror M2 (e.g., 0.5 to 5% of the laser light L that has entered the dichroic mirror M2). The detection result by the optical axis monitor unit 7 indicates, for example, the relationship between the optical axis of the laser light L that enters the focusing lens unit 61 and the optical axis of the focusing lens unit 61.

The visible imaging unit 8 is disposed within the housing H. The visible imaging unit 8 emits visible light V and obtains an image of the object 11 using the visible light V. In this embodiment, the visible light V emitted from the visible imaging unit 8 is irradiated onto the surface 11a of the object 11 via the dichroic mirror M2 and the light collecting unit 6, and the visible light V reflected by the surface 11a is detected by the visible imaging unit 8 via the light collecting unit 6 and the dichroic mirror M2.

The infrared imaging unit 9 is attached to the side wall of the housing H. The infrared imaging unit 9 emits infrared light and captures an image of the object 11 using the infrared light. In this embodiment, the housing H and the infrared imaging unit 9 can move together in the Z direction.

The control unit 10 controls the operation of each part of the laser processing device 1. The control unit 10 has a processing unit 101, a memory unit 102, and an input reception unit 103. The processing unit 101 is configured as a computer device including a processor, memory, storage, a communication device, etc. In the processing unit 101, the processor executes software (programs) loaded into the memory, etc., and controls the reading and writing of data in the memory and storage, as well as communication by the communication device. The memory unit 102 is, for example, a hard disk, and stores various data. The input reception unit 103 is an interface unit that receives input of various data from an operator. In this embodiment, the input reception unit 103 constitutes a GUI (Graphical User Interface).

In the laser processing device 1 configured as described above, when the laser light L is focused inside the object 11, the laser light L is absorbed in a portion corresponding to the focusing point C of the laser light L, and a modified region 12 is formed inside the object 11. 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 melting process region, a crack region, an insulation breakdown region, and a refractive index change region. The modified region 12 has a characteristic that cracks tend to extend from the modified region 12 to the incident side of the laser light L and the opposite side. Such a characteristic of the modified region 12 is utilized to cut the object 11.

As an example, we will explain the operation of the laser processing device 1 when forming a modified region 12 inside the object 11 along a line 15 for cutting the object 11.

First, the laser processing device 1 rotates the support part 2 about an axis parallel to the Z direction so that the line 15 set on the object 11 is parallel to the X direction. Next, based on an image (e.g., an image of a functional element layer of the object 11) acquired by the infrared imaging unit 9, the laser processing device 1 moves the support part 2 along the X direction and the Y direction so that the focal point C of the laser light L is located on the line 15 when viewed from the Z direction. Hereinafter, this "alignment of the focusing part 6 with respect to the processing start position on the line 15" is referred to as "alignment".

Then, based on the image (e.g., an image of the surface 11a of the object 11) acquired by the visible imaging unit 8, the laser processing device 1 moves the housing H (i.e., the focusing unit 6) along the Z direction so that the focusing point C of the laser light L is located on the surface 11a. Hereinafter, such "alignment of the focusing unit 6 with respect to the surface 11a" is referred to as "height setting." Next, using that position as a reference, the laser processing device 1 moves the housing H (i.e., the focusing unit 6) along the Z direction so that the focusing point C of the laser light L is located at a predetermined depth from the surface 11a.

Then, the laser processing device 1 emits the laser light L from the light source 3 and moves the support part 2 along the X direction so that the focal point C of the laser light L moves relatively along the line 15. Hereinafter, the "relative movement direction of the laser light L with respect to the object 11" will be referred to as the "relative movement direction A of the laser light L". At this time, the laser processing device 1 operates the drive mechanism 62 of the focusing part 6 so that the focal point C of the laser light L is located at a predetermined depth from the surface 11a based on the displacement data of the surface 11a acquired by the distance measuring sensor located in front of the pair of distance measuring sensors S1, S2 in the relative movement direction A of the laser light L.

As a result, a row of modified regions 12 is formed along the line 15 and at a certain depth from the surface 11a of the object 11. When the laser light L is emitted from the light source 3 by the pulse oscillation method, multiple modified spots 12s are formed so as to be lined up in a row along the X direction. One modified spot 12s is formed by irradiation with one pulse of laser light L. One row of modified regions 12 is a collection of multiple modified spots 12s lined up in a row. Adjacent modified spots 12s may be connected to each other or separated from each other depending on the pulse pitch of the laser light L (the value obtained by dividing the relative moving speed of the focal point C with respect to the object 11 by the repetition frequency of the laser light L).
[Configuration of spatial light modulator]

The spatial light modulator 5 of this embodiment is a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator). FIG. 2 is a cross-sectional view of a portion of the spatial light modulator shown in FIG. 1. As shown in FIG. 2, the spatial light modulator 5 is configured by stacking a drive circuit layer 52, a pixel electrode layer 53, a reflective 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.

The semiconductor substrate 51 is, for example, a silicon substrate. The drive 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 by the drive circuit layer 52.

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 facing the reflective film 54, and the alignment film 57 is provided on the surface of the liquid crystal layer 56 opposite the reflective film 54. Each alignment film 55, 57 is formed of, for example, a polymeric material such as polyimide, and the contact surface of each alignment film 55, 57 with the liquid crystal layer 56 is subjected to, for example, a rubbing treatment. The alignment films 55, 57 align the liquid crystal molecules 56a contained in the liquid crystal layer 56 in a fixed direction.

The transparent conductive film 58 is provided on the surface of the transparent substrate 59 on the alignment film 57 side, and faces the pixel electrode layer 53 with the liquid crystal layer 56 and the like sandwiched therebetween. 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 transmit the laser light L.

In the spatial light modulator 5 configured as described above, when an image signal indicating a modulation pattern is input from the control unit 10 to the drive circuit layer 52, a voltage corresponding to the image 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. When this electric field is formed, the arrangement direction of the liquid crystal molecules 216a in the liquid crystal layer 56 changes for each region (pixel 56p) corresponding to each pixel electrode 53a, and the refractive index changes for each region corresponding to each pixel electrode 53a. This state is the state in which the modulation pattern is displayed in the liquid crystal layer 56.

With the modulation pattern displayed on the liquid crystal layer 56, when laser light L enters the liquid crystal layer 56 from the outside through the transparent substrate 59 and the transparent conductive film 58, is reflected by the reflective film 54, and is emitted from the liquid crystal layer 56 to the outside through the transparent conductive film 58 and the transparent substrate 59, the laser light L is modulated according to the modulation pattern displayed on the liquid crystal layer 56. In this way, with the spatial light modulator 5, by appropriately setting the modulation pattern to be displayed on the liquid crystal layer 56, it is possible to modulate the laser light L (for example, modulate the intensity, amplitude, phase, polarization, etc. of the laser light L).
[Configuration of the object]

Figure 3 is a plan view of a wafer, which is an object of one embodiment. Figure 4 is a cross-sectional view of a portion of the wafer shown in Figure 3. The object 11 of this embodiment is a wafer 20, as shown in Figures 3 and 4. The wafer 20 has a first surface 20a and a second surface (laser light incident surface) 20b opposite the first surface 20a. The wafer 20 is constructed by stacking a functional element layer 22 on a semiconductor substrate 21.

The semiconductor substrate 21 is, for example, a silicon substrate. The semiconductor substrate 21 has a first surface 21a and a second surface 21b opposite to the first surface 21a. The second surface 21b is the second surface 20b of the wafer 20. The semiconductor substrate 21 is provided with a notch 21c indicating the crystal orientation. Note that the semiconductor substrate 21 may be provided with an orientation flat instead of the notch 21c.

The functional element layer 22 is provided on the first surface 21a of the semiconductor substrate 21. The functional element layer 22 includes a plurality of functional elements 22a arranged in a matrix along the first 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, a circuit element such as a memory, etc. Each functional element 22a may be configured three-dimensionally by stacking a plurality of layers.

The wafer 20 is cut into each functional element 22a along each of the multiple lines 15. The multiple lines 15 extend in a lattice pattern along the second surface 21b of the wafer 20 so as to pass between each of the multiple functional elements 22a (more specifically, through the center of the street region 23 extending to pass between adjacent functional elements 22a) 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 device 1. Note that each line 15 may be a line actually drawn on the wafer 20.
[Example of operation of laser processing device]

Figure 5 is a cross-sectional view of a wafer to explain an example of the operation of a laser processing device in the case of three-point branching. As shown in Figure 5, in the laser processing device 1, the wafer 20 is supported by the support part 2 so that the second surface 20b of the wafer 20 is perpendicular to the Z direction. Then, the control part 10 controls the spatial light modulator 5, and a predetermined modulation pattern (e.g., a modulation pattern including a diffraction pattern) is displayed on the liquid crystal layer 56 of the spatial light modulator 5. In this state, the laser light L is emitted from the light source 3, and the laser light L is focused on the wafer 20 from the second surface 20b side by the focusing part 6. In other words, the laser light L is modulated by the spatial light modulator 5, and the modulated laser light L is focused on the wafer 20 from the second surface 20b side by the focusing part 6.

As a result, the laser light L is branched (diffracted) into multiple processing lights L1, L2, and L3 including zero-order light, and multiple focal points C1, C2, and C3 of the multiple processing lights L1, L2, and L3 are positioned at different positions in the Z direction and the X direction. In this embodiment, the processing light L2 is the zero-order light. The focal point C1 of the processing light L1 is located forward of the focal point C2 of the processing light L2, which is the zero-order light, in the relative movement direction A of the laser light L, and the focal point C3 of the processing light L3 is located rearward of the focal point C2 of the processing light L2, which is the zero-order light, in the relative movement direction A of the laser light L. As an example, the processing light L1 is +1-order light, and the processing light L3 is -1-order light.

In this embodiment, the laser light L is modulated by the spatial light modulator 5 so that the multiple focal points C1, C2, and C3 have a positional relationship in which the focal point C2 is located closer to the first surface 20a of the wafer 20 in the Z direction as it approaches the front in the relative movement direction A of the laser light L. In other words, the laser light L is modulated by the spatial light modulator 5 so that the focal point C2 is located closer to the first surface 20a of the wafer 20 in the Z direction than the focal point C3, and the focal point C1 is located closer to the first surface 20a of the wafer 20 in the Z direction than the focal point C2. Furthermore, in this embodiment, the laser light L is modulated by the spatial light modulator 5 so that the processing light L1 that is branched to the frontmost side in the relative movement direction A of the laser light L among the multiple processing lights L1, L2, and L3 has the largest output (energy, intensity). In addition, even if there is a processing light among the multiple processing lights L1, L2, and L3 that has an output equal to the output of processing light L1, if the output of the other processing lights is less than the output of processing light L1, processing light L1 is included in the case where it has the largest output.

In a state where the laser light L is branched into a plurality of processing lights L1, L2, and L3 including a zero-order light, the support part 2 is controlled by the control part 10 so that the X direction coincides with the extending direction of the line 15 and the plurality of focusing points C1, C2, and C3 move relatively along the line 15. As a result, three rows of modified regions 12 are formed along one line 15. The distances from the second surface 20b of the wafer 20 to the respective modified regions 12 are different from each other, and the depth at which each modified region 12 is formed corresponds to the depth at which each focusing point C1, C2, and C3 is aligned. The above is an example of the operation of the laser processing device 1, and an example of the processing process performed by the control part 10. In the above example, an example in which the laser light L is branched into three processing lights L1, L2, and L3 has been described, but the processing process is not limited to this, and the laser light L may be branched into two or four or more processing lights, or the laser light L may be used without being branched.
[Issues surrounding spatial light modulators and knowledge related to solutions]

Next, the first problem when using the spatial light modulator 5 as described above and the inventor's findings regarding a method for solving the first problem will be described. FIG. 6 is a diagram showing an example of a modulation pattern displayed on a spatial light modulator. FIG. 6(a) shows an ideal modulation pattern Pi, and FIG. 6(b) shows an actual modulation pattern Pr. As shown in FIG. 6, for example, between adjacent pixels 56p at pixel pitch D, dulling may occur in the actual modulation pattern Pr with respect to the phase modulation amount of the ideal modulation pattern Pi. The inventor has found that this dulling in the phase modulation amount may cause the following problems.

That is, as shown in FIG. 7, when attempting to display a modulation pattern Pl including an area with a phase modulation amount greater than 2π (for example, 2π to 6π) for a spatial light modulator 5 with a phase modulation ability of an upper limit of 2π (see FIG. 7(a)), the modulation pattern Pl is reproduced by folding back the area exceeding 2π (see FIG. 7(b)). In this case, due to the slowing of the phase modulation amount, the modulation state of the laser light L may differ between the area of the modulation pattern Pl where folding has occurred (inverted area) and the area where folding has not occurred (normal area). This point will be explained in more detail.

First, an image signal can be used as a signal for displaying a modulation pattern on the spatial light modulator 5. In this case, a voltage corresponding to the gradation value of the image signal input to the spatial light modulator 5 is applied to the liquid crystal layer 56, and a refractive index change corresponding to the voltage value occurs, thereby displaying the modulation pattern. Then, phase modulation corresponding to this modulation pattern is performed on the laser light incident on the spatial light modulator 5. Therefore, in this case, the image signal and the modulation pattern, and the gradation value of the image signal and the amount of phase modulation applied to the laser light L by the modulation pattern correspond to each other. For this reason, hereinafter, the gradation value and the amount of phase modulation may be described as having the same meaning.

Here, the modulation pattern includes a diffraction grating pattern for splitting the laser light L into three processing lights L1, L2, and L3. FIG. 8 is a schematic diagram showing an example of a modulation pattern including a diffraction grating pattern. In both examples of FIG. 8, the spatial light modulator 5 has a phase modulation capability of 2π, and the phase modulation amount (phase difference) is set to 0 [rad] when the gradation value is 0, and 2π [rad] when the gradation value is 256.

In the example shown in FIG. 8(a), only the diffraction grating pattern Pg with a gradation value T1 of 82 is shown. In this case, in the diffraction grating pattern Pg, the gradation value T1 does not exceed 256, i.e., the phase modulation amount does not exceed 2π, so no inversion region occurs.

In the example shown in FIG. 8B, a modulation pattern Pc1 is shown in which an offset pattern Pb1 with a constant offset value Q1 of 100 is superimposed on a diffraction grating pattern Pg with a gradation value T1 of 82. In this case, the total gradation value T2 (gradation value T1 + offset value Q1) in the modulation pattern Pc1 is 182, which does not exceed 256, i.e., the phase modulation amount does not exceed 2π, so no inversion region occurs. Note that the offset pattern is intended to show a schematic example of a case in which a certain modulation pattern (e.g., a diffraction grating pattern) is superimposed on another modulation pattern (e.g., a distortion correction pattern or an aberration correction pattern of the spatial light modulator 5).

On the other hand, in the example shown in FIG. 8(c), a modulation pattern Pc2 is shown that is configured by superimposing an offset pattern Pb2 with a constant offset value Q2 of 200 on a diffraction grating pattern Pg with a gradation value T1 of 82. In this case, the total gradation value (gradation value T1 + offset value Q2) in the modulation pattern Pc2 is 282, and an excess T3 that exceeds 256 (i.e., a portion where the phase modulation amount exceeds 2π) is generated. This excess T3 is calculated as "offset value Q2 + gradation value T1 - 256". For this reason, in this modulation pattern Pc2, folding back of the phase modulation amount occurs, resulting in an inversion region.

The gradation value T4 of the modulation pattern Pc2 in the inversion region is calculated by subtracting the excess T3 from the offset value Q2. That is, the gradation value T4 of the modulation pattern Pc2 is calculated as "offset value Q2 - (offset value Q2 + gradation value T1 - 256)". According to this, the gradation value T4 here is 174. Note that hereinafter, the gradation value T1 may be referred to as the gradation value of the normal region, and the gradation value T4 may be referred to as the gradation value of the inversion region.

When the laser light L is split into three processed lights L1, L2, and L3, and there is no blunting of the phase modulation amount, when the gradation value T1 in the normal rotation area of the diffraction grating pattern Pg is 82 (when the phase modulation amount is 0.64π), the diffraction efficiency of the processed lights L1 and L3, which are ±1st order light, and the diffraction efficiency of the processed light L2, which is 0th order light, match, and the output balance of the processed lights L1, L2, and L3 is achieved. In a similar case, when the gradation value T4 in the inversion area is 174 (when the phase modulation amount is 1.36π), the diffraction efficiency of the processed lights L1, L2, and L3 also match, and the output balance is achieved.

On the other hand, in the actual case where there is a blunting of the phase modulation amount, when the gradation value T1 in the normal rotation area is 89 (when the phase modulation amount is 0.70π), the diffraction efficiency of the processed light L1 and L3, which are ±1st order light, and the diffraction efficiency of the processed light L2, which is the 0th order light, match, and the output balance of the processed light L1, L2, and L3 is achieved. When the gradation value T1 in the normal rotation area is 89, the gradation value T4 of the inverted area corresponding to this gradation value T1 is 167 (see the above calculation formula). And when the gradation value T4 in the inverted area is 167 (when the phase modulation amount is 1.30π), the output balance of the three processed lights L1, L2, and L3 is greatly disrupted, and the 0th order light becomes relatively weak. In other words, when there is a blunting of the phase modulation amount, the diffraction efficiency varies between the normal rotation area and the inverted area.

Here, in the case of modulation pattern Pc3 (see FIG. 10) which is constructed by superimposing distortion correction pattern Pd which acts at least partially as offset patterns Pb1, Pb2 (adding offset values Q1, Q2 to diffraction grating pattern Pg) on diffraction grating pattern Pg shown in FIG. 9, normal region R1 and inverted region R2 are mixed. Even if there is variation in diffraction efficiency between normal region R1 and inverted region R2 as described above, in cases where diffraction grating pattern Pg is used alone or the gradation value is constant throughout the modulation pattern, the gradation value can be recalculated based on actual measurement and correction can be performed.

However, as shown in FIG. 10, in practice, multiple modulation patterns are combined or various modulation patterns are switched between, making such correction difficult. When the laser light L is split into two processing lights at an equal ratio, the gradation value T1 in the normal rotation region R1 and the gradation value T4 in the inverted region R2 are both 128, and no problem occurs. However, when the laser light L is split into two processing lights at different ratios, a similar problem occurs.

In particular, in the modulation pattern Pc1 (see FIG. 11(b)) to which a relatively small offset value is applied to the diffraction grating pattern Pg shown in FIG. 11(a), the ratio of the normal region R1 to the inverted region R2 is 1:0 (the entire region is normal region R1), whereas in the modulation pattern Pc2 (see FIG. 11(c)) to which a relatively large offset value is applied, the ratio of the normal region R1 to the inverted region R2 is 0:1 (the entire region is inverted region R2), resulting in large variations in diffraction efficiency depending on the patterns and regions superimposed on the diffraction grating pattern Pg. Note that the horizontal axis of each graph in FIG. 11 indicates the number (number) of pixels 56p of the liquid crystal layer 56 as the position of the modulation pattern. In other words, 256 on the horizontal axis indicates the position of the modulation pattern corresponding to the 256th pixel 56p from one end of the liquid crystal layer 56.

From this perspective, if the bias in the ratio between the normal region R1 and the inverted region R2 is suppressed, the variation in the diffraction efficiency according to the type of modulation pattern to be synthesized and the variation in the diffraction efficiency according to each region of the modulation pattern are suppressed, and the effect of the dulling of the phase modulation amount is mitigated. Therefore, here, an averaging pattern is used to average the ratio between the normal region R1 and the inverted region R2.

Figure 12 is a diagram showing an example of an averaging pattern. As shown in Figure 12, the averaging pattern Ps is a modulation pattern in which the gradation value changes at a constant slope from the minimum value (0) to the maximum value (256) (the phase modulation amount changes from 0 to 2π) from one end of the averaging pattern Ps to the other end.

Figure 13 shows an example of a modulation pattern formed by superimposing an averaged pattern on a diffraction grating pattern. (a) of Figure 13 shows a modulation pattern Pc4 formed by superimposing an averaged pattern Ps on a diffraction grating pattern Pg, (b) of Figure 13 shows a modulation pattern Pc5 formed by superimposing an offset pattern Pb1 and an averaged pattern Ps on a diffraction grating pattern Pg, and (c) of Figure 13 shows a modulation pattern Pc6 formed by superimposing an offset pattern Pb2 and an averaged pattern Ps on a diffraction grating pattern Pg.

In the modulation pattern Pc4, the ratio of the normal region R1 to the inverted region R2 is 0.67 to 0.33, in the modulation pattern Pc5, the ratio of the normal region R1 to the inverted region R2 is 0.67 to 0.33, and in the modulation pattern Pc6, the ratio of the normal region R1 to the inverted region R2 is 0.73 to 0.27. In either case, the ratio of the normal region R1 to the inverted region R2 is averaged compared to when the averaging pattern Ps is not used. As a result, the bias in the ratio of the normal region R1 to the inverted region R2 is suppressed, and the variation in the diffraction efficiency according to the type of modulation pattern to be synthesized and the variation in the diffraction efficiency according to each region of the modulation pattern are suppressed, and the effect of the dulling of the phase modulation amount is mitigated.

Here, it is possible to adjust the degree of averaging by changing the gradient (foldback period) of the gradation values in the averaging pattern Ps. The example in FIG. 12 is an example in which the gradient is 0.5 and the period is 1, so that the gradation values increase from 0 to 256 as the position of the averaging pattern Ps changes from 0 to 512. On the other hand, if the period is 2, the gradient of the gradation values in the averaging pattern Ps doubles, so that the gradation values increase from 0 to 256 as the position of the averaging pattern Ps changes from 0 to 256, and then increase again to 0 to 256 as the position of the averaging pattern Ps changes from 257 to 512.

14 is a diagram showing an example of a modulation pattern formed by superimposing an averaging pattern on a distortion correction pattern. FIG. 14(a) shows a case where an averaging pattern Ps is not used, FIG. 14(b) shows a case where an averaging pattern Ps with a period of 1 is used, FIG. 14(c) shows a case where an averaging pattern Ps with a period of 2 is used, FIG. 14(d) shows a case where an averaging pattern Ps with a period of 4 is used, and FIG. 14(e) shows a case where an averaging pattern Ps with a period of 8 is used. As shown in FIG. 14, the larger the period of the averaging pattern Ps (the larger the gradient of the gradation value), the more the phase modulation amount is folded back, and the bias in the ratio between the normal region R1 and the inverted region R2 is dispersed and averaged. The averaging pattern Ps is, as an example, a shift pattern that has the function of shifting the focal point C of the laser light L.

Next, the second problem when using the spatial light modulator 5 and the inventor's knowledge related to a method for solving the second problem will be described. FIG. 15 is a schematic diagram showing the relationship between the focusing lens and the laser light. As shown in FIG. 15, the focusing lens unit 61 of the focusing section 6 includes a focusing lens 61a for focusing the laser light L toward the wafer 20. In the laser processing device 1, the spatial light modulator 5 modulates the laser light L, thereby changing the focusing position of the laser light L according to the NA region (the position in the radial direction Kd of the focusing lens 61a) into which the laser light L is incident on the focusing lens 61a, and the focusing point C of the laser light L can be shaped into an elongated shape.

Here, by modulating the laser light L using the shaping pattern Pf shown in FIG. 16, the focal point C of the laser light L is shaped to be elongated in the Z direction by changing the focal position of the laser light L in the Z direction so that the focal position of the laser light L becomes deeper in the Z direction (farther away from the condenser lens 61a) as the incident position of the laser light L in the condenser lens 61a moves away from the center in the radial direction Kd. In this shaping pattern Pf, the folded portion B of the phase modulation amount is formed concentrically with respect to the region where the laser light L is incident in the shaping pattern Pf (the region corresponding to the entrance pupil surface of the condenser lens 61a). In other words, in such a shaping pattern Pf, the folded portion B of the phase modulation amount is unevenly distributed in a part of the shaping pattern Pf.

For this reason, there may be variation in the focusing state of the laser light L between the portion of the laser light L that is modulated through the portion of the shaping pattern Pf where the turning portion B is unevenly distributed and the portion that is modulated without passing through the portion where the turning portion B is unevenly distributed. As a result, when another modulation pattern is superimposed on the shaping pattern Pf and an offset is applied to the amount of phase modulation of the shaping pattern Pf, the processing result may change depending on the magnitude of the offset value.

Figure 17(a) is an example showing the processing result when the offset value is 64, and Figure 17(b) is an example showing the processing result when the offset value is 96. As shown in Figure 17, the processing result changes depending on the magnitude of the offset value. This is thought to be because the laser light L modulated in the part where the folded portion B in the shaping pattern Pf is unevenly distributed becomes unintentionally focused.

In contrast, Fig. 18 is a diagram showing a modulation pattern formed by superimposing the averaging pattern shown in Fig. 12 on the shaping pattern shown in Fig. 16. As shown in Fig. 18, in the modulation pattern Pe formed by superimposing the averaging pattern Ps on the shaping pattern Pf, the folding portion B of the phase modulation amount is dispersed throughout the entire region in the modulation pattern Pe where the laser light L is incident, and the positions where the folding portion B is formed are averaged, compared to the shaping pattern Pf.

Figure 19 is a cross-sectional photograph showing the processing results when using the shaping pattern shown in Figure 16 and the modulation pattern shown in Figure 18. (a) of Figure 19 shows the processing result when an offset value of 64 is applied to the shaping pattern Pf, and (b) of Figure 19 shows the processing result when an offset value of 96 is applied to the shaping pattern Pf. (c) of Figure 19 shows the processing result when an offset value of 64 is applied to the modulation pattern Pe, and (d) of Figure 19 shows the processing result when an offset value of 96 is applied to the modulation pattern Pe.

As shown in (a) and (b) of FIG. 19, when the averaging pattern Ps is not superimposed on the shaping pattern Pf, the processing result also changes when the offset value changes. In contrast, as shown in (c) and (d) of FIG. 19, when the averaging pattern Ps is superimposed on the shaping pattern Pf, the change in the processing result with respect to the change in the offset value is small. In this way, by using the averaging pattern Ps, it is possible to suppress the uneven distribution of the turn-around portion B of the phase modulation amount in the modulation pattern, and as a result, the variation in the processing result is suppressed. In the laser processing device 1 according to this embodiment, the following laser processing can be performed by utilizing the above knowledge.
[One example of laser processing according to this embodiment]

First, as described above, the laser processing device 1 according to this embodiment includes a support section 2 for supporting an object 11 (here, a wafer 20), a light source 3 for emitting laser light L, a spatial light modulator 5 for modulating the laser light L emitted from the light source 3 according to a modulation pattern and emitting the modulated laser light L, a focusing section 6 including a focusing lens 61a for focusing the laser light L emitted from the spatial light modulator 5 toward the wafer 20, and a control section 10 for controlling each section of the laser processing device 1. The control section 10 inputs an image signal to the spatial light modulator 5, thereby causing the spatial light modulator 5 to display a modulation pattern according to the image signal.

In such a laser processing device 1, during laser processing, first, the wafer 20 is supported by the support part 2 so that the second surface 20b of the wafer 20 is perpendicular to the Z direction. Next, the control part 10 inputs an image signal to the spatial light modulator 5 to display a predetermined modulation pattern on the liquid crystal layer 56 of the spatial light modulator 5. In this state, the control part 10 controls the light source 3 to emit laser light L from the light source 3, and the laser light L is focused by the focusing lens 61a from the second surface 20b side toward the wafer 20. In other words, the laser light L is modulated by the spatial light modulator 5, and the modulated laser light L is focused by the focusing lens 61a on the wafer 20 from the second surface 20b side. As a result, a focusing point C of the laser light L is formed inside the wafer 20.

At the same time, the control unit 10 controls the movement of the support unit 2 so that the focal point C of the laser light L moves relative to the wafer 20 along a line 15 along the X direction. As a result, the laser light L is irradiated onto the wafer 20 while the focal point C of the laser light L moves relative to the wafer 20 along the X direction (the processing process is executed).

When processing by branching the laser light L is desired, the control unit 10 can input an image signal including a second signal corresponding to the diffraction grating pattern Pg to the spatial light modulator 5 so that a modulation pattern including a diffraction grating pattern Pg (second pattern) for branching the laser light L into multiple processing lights L1, L2, and L3 is displayed on the spatial light modulator 5 in this processing process. The branching direction of the laser light L at this time is, for example, the X direction, which is the processing progress direction. Note that an image signal corresponding to a certain modulation pattern is an image signal in which a gradation value corresponding to the phase modulation amount at each pixel 56p is set in each area of the image signal corresponding to each pixel 56p of the liquid crystal layer 56 of the spatial light modulator 5.

On the other hand, if it is desired to process the focal point C of the laser light L into a long shape, the control unit 10 can input an image signal including a third signal corresponding to the shaping pattern Pf to the spatial light modulator 5 so as to display a modulation pattern including a shaping pattern Pf (third pattern) on the spatial light modulator 5 for changing the focal position of the laser light L depending on the position in the radial direction Kd of the focusing lens 61a during the processing.

In either case, in the processing, the control unit 10 inputs an image signal including a first signal whose gradation value changes at a constant gradient from a minimum value to a maximum value from a region corresponding to one end of the modulation pattern in the first direction to a region corresponding to the other end of the modulation pattern in the first direction to the spatial light modulator, thereby displaying a modulation pattern including an averaged pattern Ps (first pattern) corresponding to the first signal on the spatial light modulator 5. Therefore, at this time, the modulation pattern displayed on the spatial light modulator 5 is a modulation pattern configured by superimposing at least the diffraction grating pattern Pg and/or the shaping pattern Pf and the averaged pattern Ps. Similarly, at this time, in the image signal input to the spatial light modulator 5, a gradation value is set in which at least the gradation value of the second signal and/or the third signal and the gradation value of the first signal are superimposed.

In particular, when the control unit 10 branches the laser light L into multiple processing lights L1, L2, and L3 in the processing process, the first direction, which is the direction in which the gradation value of the averaged pattern Ps changes, can be a direction corresponding to a direction intersecting the branching direction of the laser light L (or a direction corresponding to a direction parallel to the branching direction). In other words, when the branching direction of the laser light L is the X direction, the first direction can be a direction corresponding to the Y direction intersecting the X direction (or a direction corresponding to the X direction).

In addition, the control unit 10 may change the gradation value in the first signal at a constant gradient from the minimum value to the maximum value from a region corresponding to one end of the averaged pattern Ps in a second direction intersecting the first direction to a region corresponding to the other end of the averaged pattern Ps in the second direction. When the first direction is a direction corresponding to the Y direction as described above, the second direction is, for example, a direction corresponding to the X direction. In this case, the averaged pattern Ps in which the phase modulation amount changes at a constant gradient in at least two directions can be displayed on the spatial light modulator 5. Note that the gradient of the gradation value in the first direction and the gradient of the gradation value in the second direction may be the same or different. For example, when the number of pixels 56p of the liquid crystal layer 56 of the spatial light modulator 5 is different in two directions, when the phase modulation amount is changed at a constant gradient (at the same period) from the minimum value to the maximum value from one end to the other end in each direction, the gradient of the gradation value in the first direction and the gradient of the gradation value in the second direction will be different in the image signal.

Furthermore, in the processing, the control unit 10 can generate and input an image signal so that another modulation pattern, such as a distortion correction pattern or an aberration correction pattern of the spatial light modulator 5, is superimposed. In this case, in the spatial light modulator 5, an offset corresponding to these other modulation patterns is applied to the diffraction grating pattern Pg and the shaping pattern Pf, and further, an averaging pattern Ps is superimposed.

In addition, in the processing, when the averaged pattern Ps, which is a shift pattern, is superimposed on the modulation pattern displayed on the spatial light modulator 5, the focal point C of the laser light L may be shifted from the line 15 within the wafer 20. Therefore, in this case, the control unit 10 can control the optical axis adjustment unit 4 so that the focal point C of the laser light L is positioned on the line 15. At this time, the control unit 10 can refer to the image acquired by the visible imaging unit 8 (for example, an image of the second surface 20b of the wafer 20).

As described above, in the laser processing device 1, the control unit 10 inputs an image signal to the spatial light modulator 5, thereby causing the spatial light modulator 5 to display a modulation pattern, and performs processing while modulating the laser light L according to the modulation pattern. In the image signal, a gradation value corresponding to the phase modulation amount at each position of the modulation pattern is set for each region constituting the image signal. In other words, in the spatial light modulator 5, the phase modulation amount at each position of the modulation pattern is set to an amount corresponding to the gradation value of each region of the image signal, so that the desired modulation pattern is displayed as a whole. The image signal includes a first signal whose gradation value changes at a constant gradient from a region corresponding to one end of the modulation pattern to a region corresponding to the other end of the modulation pattern. As a result, the modulation pattern displayed on the spatial light modulator 5 includes an averaged pattern Ps (first pattern) in which the phase modulation amount changes in one direction at a constant gradient according to this first signal. As described above, when the modulation pattern includes such an averaged pattern Ps, the influence of the dulling of the phase modulation amount of the modulation pattern and the uneven distribution of the folding back portion B of the phase modulation amount in the modulation pattern are suppressed.

In addition, in the laser processing device 1, in the processing process, the control unit 10 may input an image signal including a second signal corresponding to the diffraction grating pattern Pg to the spatial light modulator 5 so as to display a modulation pattern including a diffraction grating pattern Pg (second pattern) for branching the laser light L into multiple processing lights on the spatial light modulator 5. In this case, the diffraction grating pattern Pg is superimposed on the modulation pattern. In such a case, the variation between the multiple processing lights L1, L2, and L3 is suppressed.

In addition, in the laser processing device 1, the first direction may be a direction corresponding to a direction intersecting the branching direction of the laser light L. In this case, it is possible to more effectively suppress the variation between the processing lights L1, L2, and L3.

In addition, in the laser processing device 1, in the processing process, the control unit 10 may input an image signal including a third signal corresponding to the shaping pattern Pf to the spatial light modulator 5 so as to display a modulation pattern including a shaping pattern Pf (third pattern) for changing the focusing position of the laser light L depending on the position in the radial direction Kd of the focusing lens 61a on the spatial light modulator 5. In this case, it is possible to suppress the uneven distribution of the folded portion B of the phase modulation amount in the shaping pattern Pf so as to correspond to a specific position in the radial direction Kd of the focusing lens 61a, and suppress the variation in the focusing state of the laser light L.

In addition, in the laser processing device 1, the control unit 10 may change the gradation value in the first signal from a region corresponding to one end of the modulation pattern in a second direction intersecting the first direction to a region corresponding to the other end of the modulation pattern in the second direction, from the minimum value to the maximum value, at a constant gradient. In this case, the gradation value of the image signal changes at a constant gradient in two directions that intersect with each other. Therefore, it is possible to suppress the effect of the blunting of the phase modulation amount and the uneven distribution of the folding back portion of the phase modulation amount within the plane of the spatial light modulator 5 corresponding to the two directions.

Furthermore, in the laser processing device 1, the control unit 10 may change the gradation value in the first signal so that it has multiple periods in at least one direction. In this case, it is possible to more reliably suppress the influence of the dulling of the phase modulation amount and the uneven distribution of the folding back portion of the phase modulation amount.

The above embodiment describes one aspect of the present invention. Therefore, the present invention can be modified without being limited to the above-mentioned aspect.

For example, in the above embodiment, an example was given in FIG. 12 in which the gradient of the gradation value is 0.5 and the period is 1. However, the averaging pattern Ps is not limited to this. FIG. 20 is a diagram showing a modified example of the averaging pattern. The averaging pattern Ps according to the modified example in FIG. 20(a) is an example in which the gradient of the gradation value increases from 0 to 256 while the position of the averaging pattern Ps changes from 0 to 1024 is 0.25, and the period is 1. The averaging pattern Ps according to the modified example in FIG. 20(b) is an example in which the gradient of the gradation value increases from 0 to 256 while the position of the averaging pattern Ps changes from 0 to 256, and the gradient of the gradation value increases again from 0 to 256 while the position of the averaging pattern Ps changes from 257 to 512, with a gradient of 1 and a period of 2. In this example, one folding part is generated. Similarly, in FIG. 20(c), an example in which the gradient is 2 and the period is 4 is shown. In this way, the slope and period of the averaged pattern Ps can be set arbitrarily. Also, the direction in which the period exists is not limited to one direction, and may be two directions.

In the above embodiment, FIG. 16 illustrates a shaping pattern Pf for shaping the focal point C of the laser light L into an elongated shape in the Z direction. However, the shaping pattern Pf is not limited to this, and can be modified as desired to shape the focal point C as shown in each diagram of FIG. 21.

Here, when the laser light L is split into multiple processing lights as described above for processing, the above-mentioned measure (first measure) against the variation in the output balance between each processing light is effective. On the other hand, when splitting processing in this way, a measure (second measure) against the effect that the non-modulated light of the laser light L that was not modulated by the spatial light modulator 5 has on the focusing state for the zero-order light (e.g., processing light L2) of each processing light generated by splitting becomes effective.

The averaging pattern Ps has the function of shifting the focal point C of the laser light L. In processing, when the wafer 20 is positioned so that the street region 23 of the wafer 20 is aligned along the X direction, and the focal point C of the laser light L is relatively moved in the X direction within the street region 23, both the first and second measures described above can be addressed by making the averaging pattern Ps such that the focal point C is shifted in the Y direction.

However, as a first measure, the averaging pattern Ps may be shifted by a relatively small amount, such as about 2 μm, at the focal point C in the Y direction, whereas as a second measure, it is more effective to shift the averaging pattern Ps by a relatively large amount, such as about 5 μm or more, at the focal point C in the Y direction. And the second measure is only necessary when using zero-order light, from the viewpoint of suppressing interference between zero-order light and non-modulated light.

Therefore, the required shift amount in the Y direction may differ in the first case where no branching is performed, the second case where branching is performed but the zero-order light is not used, and the third case where branching is performed while using the zero-order light. More specifically, in the first case, there is no need to shift the focal point C in the Y direction to accommodate at least the first and second measures, and in the second case, since the second measure is not required, the shift amount in the Y direction can be suppressed to about 2 μm for the first measure, and in the third case, it is desirable to further consider the second measure and set the shift amount in the Y direction to about 5 μm or more. Therefore, the laser processing device 1 is configured to be able to accommodate such first to third cases.

In other words, in the laser processing device 1, the optical axis is adjusted to a default state in which an averaged pattern Ps with a shift amount in the Y direction of 5 μm is used, and the reference position is a state in which all focal points of the laser light L are shifted in the Y direction by 5 μm. This makes it possible to deal with the first and second measures that are necessary in all of the first to third cases.

However, in such a case, the following new problem may arise. That is, when the width of the street region 23 in the Y direction is narrow, as shown in FIG. 22, if the focal points C1, C2, and C3 of the multiple processing lights L1, L2, and L3 of the laser light L are shifted in the Y direction by a shift amount Ds of about 6 μm, the focal point C0 of the unmodulated light will be positioned on the functional element 22a (active area) facing the street region 23, and there is a risk of light leakage becoming a problem.

As a countermeasure against such a new problem, the laser processing device 1 can be made to deal with the first countermeasure by first adjusting the optical axis to a state in which an averaged pattern Ps with a Y-direction shift amount of 2 μm is used as the default. This makes it possible to suitably deal with the first case in which branching processing is not performed and the second case in which the zeroth-order light is not used. On the other hand, in the laser processing device 1, in the third case in which branching processing using the zeroth-order light is performed, the gradation value is set so that a shift amount in the X direction of about 5 μm is generated in addition to the default averaged pattern Ps that generates a Y-direction shift amount of about 2 μm, so that the focusing points C1, C2, and C3 can be shifted in both the X direction and the Y direction as shown in FIG. 23. In this case, the total shift amount Ds in the X direction and the Y direction can be sufficiently increased while suppressing the shift amount in the Y direction, making it possible to deal with the second problem.

In addition, in a laser processing device, the shift direction of the focal point C in the X direction can be switched by, for example, inverting the sign of the gradient of the gradation value of the averaged pattern Ps depending on whether the moving direction of the focal point C (processing direction) is the positive X direction or the negative X direction. As an example, when the processing direction is the positive X direction, the shift direction of the focal point C can also be the positive X direction, and when the processing direction is the negative X direction, the shift direction of the focal point C can also be the negative X direction.

Furthermore, in the above embodiment, the averaging pattern Ps has been described as having the function of shifting the focal point C of the laser light L along the X direction or the Y direction, but the averaging pattern Ps may also have the function of shifting the focal point C of the laser light L along the Z direction.

1...laser processing device, 2...support unit, 5...spatial light modulator, 6...focusing unit, 10...control unit, 61a...focusing lens.

Claims (6)

A laser processing apparatus for forming a modified region in an object by irradiating the object with laser light, comprising:
A support portion for supporting the object;
a light source for emitting the laser light;
a spatial light modulator for modulating the laser light emitted from the light source in accordance with a modulation pattern and emitting the modulated laser light;
a focusing unit including a focusing lens for focusing the laser light emitted from the spatial light modulator toward the target;
a control unit that inputs an image signal to the spatial light modulator to cause the spatial light modulator to display the modulation pattern corresponding to the image signal;
Equipped with
the control unit controls movement of at least one of the support unit and the focusing unit to move a focusing point of the laser light relative to the object along an X direction along a laser light incident surface of the object, while executing a processing process of irradiating the object with the laser light;
A gradation value corresponding to a phase modulation amount in the modulation pattern is set in each of the regions constituting the image signal,
In the processing, the control unit inputs, to the spatial light modulator, the image signal including a first signal whose gradation value changes at a constant gradient from a minimum value to a maximum value from the region corresponding to one end of the modulation pattern in the first direction toward the region corresponding to the other end of the modulation pattern in the first direction, thereby causing the spatial light modulator to display the modulation pattern including a first pattern corresponding to the first signal.
Laser processing equipment. In the processing, the control unit inputs the image signal including a second signal corresponding to the second pattern to the spatial light modulator so as to display the modulation pattern including a second pattern for splitting the laser light into a plurality of processing lights on the spatial light modulator.
2. The laser processing apparatus according to claim 1. The first direction is a direction corresponding to a direction intersecting a branching direction of the laser light.
The laser processing apparatus according to claim 2. In the processing, the control unit inputs the image signal including a third signal corresponding to the third pattern to the spatial light modulator so as to display the modulation pattern including a third pattern for changing a focusing position of the laser light depending on a position in a radial direction of the focusing lens on the spatial light modulator.
The laser processing device according to any one of claims 1 to 3. the control unit changes the gradation value of the first signal at a constant gradient from a minimum value to a maximum value from the region corresponding to one end of the modulation pattern in a second direction intersecting the first direction to the region corresponding to the other end of the modulation pattern in the second direction.
The laser processing device according to any one of claims 1 to 4. the control unit changes the gradation value in the first signal so as to have a plurality of periods in at least one direction;
The laser processing device according to any one of claims 1 to 5.

Images