Condenser lens, laser processing device, and laser processing method

Abstract

A focusing lens, a laser processing device, and a laser processing method are provided that make it possible to change the focusing position of laser light and to easily align each lens of a lens group. [Solution] A condenser lens 11 condenses a first laser beam L1 as laser light input from a light source and emits it toward a medium 2. The condenser lens 11 includes a lens group 13 having a first lens group 16 that changes the first laser beam L1 into a diverging beam state, and a second lens group 17 that condenses and emits the first laser beam L1 that has passed through the first lens group 16. The first lens group 16 has a condensing position adjustment unit 19 consisting of at least one lens that adjusts the condensing position of the first laser beam L1 by moving it in the optical axis direction.

Description

[Technical Field]

[0001] The present invention relates to a condenser lens, a laser processing apparatus, and a laser processing method. [Background technology]

[0002] Conventionally, as disclosed in Patent Document 1, a laser processing apparatus capable of changing the focusing position of laser light irradiated onto a medium is well known. This laser processing apparatus has a first lens group and a second lens group between a collimating beam means for converting a beam of laser light emitted from a laser light source into a collimated beam and a focusing optical system for focusing the collimated laser light into a medium. The first lens group is composed of one or more lenses arranged to be movable along the optical axis direction of the collimated beam. The second lens group is composed of one or more lenses fixedly arranged between the first lens group and the focusing optical system. In this laser processing apparatus, the focusing position relative to the medium is changed by moving the first lens group using a moving means. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4686135 Summary of the Invention [Problem to be solved by the invention]

[0004] In the laser processing device of Patent Document 1, the first lens group, the second lens group, and the focusing optical system are each composed of independent elements. Therefore, although the laser processing device of Patent Document 1 can change the focusing position of the laser light relative to the medium, it is difficult to ensure the alignment of the first lens group, the second lens group, and the focusing optical system.

[0005] An object of the present invention is to provide a focusing lens, a laser processing apparatus, and a laser processing method that make it possible to change the focusing position of laser light while facilitating alignment of each lens in a lens group. [Means for solving the problem]

[0006] The focusing lens that solves the above problem is configured to focus laser light input from a light source and emit it toward a medium, and is equipped with a lens group having a first group that makes the laser light diverge and a second group that focuses and emits the laser light that has passed through the first group, and the first group has a focusing position adjustment unit consisting of at least one lens that adjusts the focusing position of the laser light by moving it in the optical axis direction.

[0007] A laser processing device that solves the above problem includes a laser processing mechanism that focuses a first laser beam input from a first light source using a focusing lens and processes a medium using the first laser beam from the focusing lens, and an autofocus mechanism that, when the medium moves in a direction intersecting the optical axis direction during processing, detects the amount of displacement of the surface of the medium in the optical axis direction based on the reflected light of a second laser beam irradiated onto the medium from a second light source, and adjusts the focus of the focusing lens based on the amount of displacement in the optical axis direction, so that processing is performed at a position that follows the amount of displacement in the optical axis direction.The focusing lens includes lens groups having a first group that causes the first laser beam to be in a diverging state, and a second group that focuses the first laser beam that has passed through the first group and emits it to the medium, and the first group has a focusing position adjustment unit consisting of at least one lens that adjusts the focusing position of the first laser beam by moving it in the optical axis direction using the autofocus mechanism.

[0008] A laser processing method that solves the above problem includes a laser processing step of focusing a first laser beam input from a first light source using a focusing lens and processing a medium with the first laser beam from the focusing lens, and an autofocus step of detecting an amount of displacement of the surface of the medium in the optical axis direction based on reflected light of a second laser beam irradiated onto the medium from a second light source when the medium moves in a direction intersecting the optical axis direction during processing, and adjusting the focus of the focusing lens based on the amount of displacement in the optical axis direction so that processing is performed at a position that follows the amount of displacement in the optical axis direction, wherein the focusing lens is provided with a lens group having a first group that causes the first laser beam to be in a diverging state and a second group that focuses the first laser beam that has passed through the first group and emits it to the medium, and the autofocus step includes a process of adjusting the focusing position of the first laser beam by moving a focusing position adjustment unit consisting of at least one lens of the first group in the optical axis direction.

[0009] According to the present disclosure, among the lenses constituting the lens group of the focusing lens, a predetermined lens in the first group is used as a focusing position adjustment unit that changes the focusing position of the laser light. In this way, the lens of the focusing position adjustment unit, which is provided so as to be movable in the optical axis direction to change the focusing position of the laser light, is integrated with the other lenses in the lens group. This makes it easy to align each lens in the focusing lens. Therefore, it is possible to easily align each lens in the lens group while making the focusing position of the laser light variable. [Effects of the Invention]

[0010] The present invention can make it possible to change the focusing position of the laser light and facilitate the alignment of each lens in the lens group. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a configuration diagram of a laser processing device according to an embodiment; [Figure 2] 1(a) and 1(b) are explanatory diagrams showing an outline of the cutting of a medium. [Figure 3]10 is a ray diagram of a laser beam when a focusing position adjusting unit of a focusing lens is in an initial position. FIG. [Figure 4] 10 is a diagram showing the beam of laser light when the focusing position adjustment unit of the focusing lens is at the maximum movement position. FIG. [Figure 5] FIG. 2 is an explanatory diagram showing the boundary between the first lens group and the second lens group of the condenser lens. [Figure 6] 10 is a graph showing the change in spherical aberration with respect to the depth of the focusing position when the medium is silicon. [Figure 7] 10 is a graph showing calculated changes in the spherical aberration coefficient of the medium interface with respect to the depth of the focusing position for various numerical apertures when the medium is silicon. [Figure 8] 10 is a graph showing calculated changes in the spherical aberration coefficient of the medium interface with respect to the numerical aperture for three patterns of focal position depth when the medium is silicon. [Figure 9] 10 is a graph of coefficients obtained by fitting. [Figure 10] 5A and 5B are explanatory diagrams showing the operation of a focus position adjustment unit. [Figure 11] FIG. 10 is a schematic diagram of a collecting lens according to another example. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present disclosure will be described below. (Laser processing device 1) 1, the laser processing device 1 includes a stage 3 on which a medium 2 is placed and transported, and a laser head 4 that irradiates laser light onto the medium 2 placed on the stage 3. The laser head 4 includes a laser processing mechanism 5 that irradiates the medium 2 with laser light to process the medium 2, and an autofocus mechanism 6 that detects displacement of the medium 2 in the optical axis direction of the laser light and adjusts the irradiation position of the laser light from the laser processing mechanism 5.

[0013] The medium 2 is, for example, a workpiece to be physically processed by laser light, such as a wafer that is a material for semiconductor integrated circuits. Examples of wafers include semiconductor substrates, glass substrates, and piezoelectric ceramic substrates. The laser processing device 1 is, for example, a laser dicing device that irradiates the medium 2 with laser light to fracture the medium 2 while changing the focusing position by transporting the medium 2 using a stage 3, thereby dividing the medium 2 into chips.

[0014] The laser processing apparatus 1 is equipped with a control device 8 that controls the operation of the laser processing apparatus 1. The control device 8 is composed of, for example, a processor, a memory, an input / output circuit, etc. The control device 8 controls the laser processing mechanism 5 and the autofocus mechanism 6 based on a processing program stored in the memory, thereby processing the medium 2 placed on the stage 3, i.e., cleaving the medium 2. The control device 8 cleaves the medium 2 according to input conditions input by an operator.

[0015] (Stage 3) As shown in FIG. 1, the stage 3 is configured to be movable in, for example, the X-axis direction, the Y-axis direction, the Z-axis direction, and the θ-direction. The X-axis and Y-axis directions are, for example, located on a horizontal plane and extend in directions perpendicular to each other. The Z-axis direction is, for example, the vertical direction. The θ-direction is, for example, the direction of rotation about the Z-axis direction. The medium 2 is placed on the stage 3 so that, for example, the surface opposite to the device surface is the laser irradiation surface. The laser head 4 irradiates the laser irradiation surface of the medium 2 with laser light to fracture the medium 2.

[0016] (Laser processing mechanism 5) 1, the laser processing mechanism 5 has a first light source 9, a dichroic mirror 10, and a condenser lens 11. The first light source 9 emits a first laser beam L1 for processing the medium 2. The first laser beam L1 has, for example, a pulse width of 1 μs or less and a peak power density of 1×10 at the focal point. 8 (W / cm 2The first light source 9 emits a pulsed first laser beam L1 toward the dichroic mirror 10. The first light source 9 emits a pulsed first laser beam L1 toward the dichroic mirror 10. The first laser beam L1 has the following characteristics:

[0017] The dichroic mirror 10 is disposed on the optical path of the first laser light L1. The dichroic mirror 10 transmits the first laser light L1 and reflects the second laser light L2 emitted from the autofocus mechanism 6. The second laser light L2 is bent by the dichroic mirror 10 so as to share part of the optical path with the first laser light L1, and is then irradiated onto a condenser lens 11.

[0018] The control device 8 irradiates the first laser light L1 from the first light source 9, and causes the first laser light L1, which has passed through the dichroic mirror 10, to be focused inside the medium 2 on the stage 3 by the focusing lens 11. The medium 2 on the stage 3 is processed by the first laser light L1 focused inside (laser processing step). The focusing position of the first laser light L1 inside the medium 2 is adjusted, for example, by slightly moving at least a part of the lens of the focusing lens 11 in the Z-axis direction without changing the distance between the medium 2 and the focusing lens 11.

[0019] (Cutting of medium 2 by first laser beam L1) 2(a), when the focal point of the pulsed first laser light L1 is set inside the medium 2 in the thickness direction, the energy of the first laser light L1 that has passed through the surface of the medium 2 is concentrated at the focal point inside the medium 2. As a result, a modified region P is formed near the focal point inside the medium 2. The modified region P is a starting point for fracturing the medium 2, and is formed locally inside the medium 2.

[0020] As shown in FIG. 2(b), while the medium 2 is being transported in the X-axis direction along a planned cutting line (dicing line), a pulsed first laser beam L1 is intermittently irradiated onto the medium 2, thereby successively forming modified regions P in the horizontal direction inside the medium 2. When multiple modified regions P are formed inside the medium 2, the balance of intermolecular forces in the medium 2 is disrupted. As a result, the medium 2 is naturally cut starting from the modified region P, or is cut by applying a slight external force.

[0021] In the case of a thick medium 2, the modified region P may be formed in not only one layer in the vertical direction but also multiple layers in the vertical direction. Furthermore, the modified region P is not limited to being formed intermittently, but may also be formed continuously. The method of forming the modified region P intermittently makes the medium 2 less likely to crack than the method of forming the modified region P continuously. Therefore, the method of forming the modified region P intermittently and the method of forming the modified region P continuously may be selected and executed as appropriate depending on the thickness of the medium 2, safety during transportation, and other circumstances.

[0022] (Condenser lens 11) As shown in Figures 3 and 4, the condenser lens 11 includes a lens group 13 configured by arranging a plurality of lenses in the optical axis direction. The lens group 13 is configured, for example, by combining a plurality of convex lenses and concave lenses. The lens group 13 is housed inside a hollow housing 14. The housing 14 is formed, for example, in a cylindrical shape, and houses the lens group 13 in an internal housing chamber 15. In this way, the lenses of the lens group 13 are arranged together in the housing chamber 15 of one housing 14.

[0023] The lens group 13 has a first group (hereinafter referred to as the first lens group 16) that makes the laser light diverge, and a second group (hereinafter referred to as the second lens group 17) that collects and emits the laser light that has passed through the first lens group 16. The first lens group 16 is, for example, a collection of lenses that are located far from the focusing point of the laser light among the lenses that make up the lens group 13. The second lens group 17 is a collection of lenses that are located close to the focusing point of the laser light among the lenses that make up the lens group 13. Hereinafter, the first lens group 16 may be referred to as the rear group because it is far from the focusing point, and the second lens group 17 may be referred to as the front group because it is closer to the focusing point.

[0024] (Light collection position adjustment unit 19) 3 and 4, the focusing lens 11 has a focusing position adjustment unit 19 consisting of at least one lens that adjusts the focusing position of the first laser light L1 by moving it in the optical axis direction. In the laser processing apparatus 1, the focusing position of the first laser light L1 with respect to the medium 2 changes as needed. For this reason, in the laser processing apparatus 1, the focusing position adjustment unit 19 is provided in the focusing lens 11, thereby making the focusing position of the first laser light L1 variable.

[0025] The focusing position adjustment unit 19 is a lens among the lenses of the first lens group 16 that is configured to be movable in the optical axis direction, and in this example, is the lens that is closest to the incident side of the first laser light L1. The focusing position of the focusing lens 11 with respect to the medium 2 changes depending on the position of the focusing position adjustment unit 19 in the optical axis direction.

[0026] 3, when the focusing position adjustment unit 19 is located at an initial position closest to the incident side of the first laser beam L1, the focusing position of the focusing lens 11 is set to the surface of the medium 2. Also, as shown in Fig. 4, when the focusing position adjustment unit 19 is located at a maximum movement position farthest from the incident side of the first laser beam L1, the focusing position of the focusing lens 11 is set to the deepest part of the medium 2. Note that it is preferable that the movement of the focusing position adjustment unit 19 in the optical axis direction be guided by a guide shape such as a rail groove formed on the inner surface of the accommodation chamber 15 of the housing 14.

[0027] As shown in FIG. 1 , the focusing position adjustment unit 19 is disposed at or near the entrance pupil position of the focusing lens 11. The entrance pupil position is used, for example, as a reference position for setting the numerical aperture NA of the effective lens or for confirming the accurate state of the wavefront of light. In the focusing lens 11 designed according to the medium 2 as will be described later, by moving the focusing position adjustment unit 19 disposed at or near the entrance pupil position of the focusing lens 11, the focusing position of the focusing lens 11 can be adjusted so that a change in the spherical aberration of the focusing lens 11 caused by a change in the optical path within the focusing lens 11 and a change in the spherical aberration at the interface of the medium 2 caused by a change in the focusing position relative to the medium 2 cancel each other out. In other words, by moving the focusing position adjustment unit 19, the focusing position and spherical aberration of the focusing lens 11 relative to the medium 2 can be adjusted.

[0028] 1, the laser processing apparatus 1 includes a first actuator 20 that serves as a drive source for the focusing position adjustment unit 19. For example, an electric actuator is used as the first actuator 20. The control device 8 adjusts the position of the focusing position adjustment unit 19 via driving the first actuator 20, thereby switching the focusing position of the focusing lens 11 with respect to the medium 2.

[0029] (Boundary between the first lens group 16 and the second lens group 17) 5, a solid line indicates a ray diagram of the first laser beam L1 when the focusing position adjustment unit 19 is at the initial position, and a dashed line indicates a ray diagram of the first laser beam L1 when the focusing position adjustment unit 19 is at the maximum movement position. In this example, the boundary between the first lens group 16 and the second lens group 17 is the point where the height of the outermost ray in the lens radial direction changes (point M in this example).

[0030] (Autofocus mechanism 6) As shown in FIG. 1 , the autofocus mechanism 6 includes a second light source 22, a condenser lens 23, a knife edge 24, a mirror member 25, a focus lens group 26, a half mirror 27, an imaging lens 28, and a detector 29. The focus lens group 26 includes a fixed lens 30 whose position is fixed and a movable lens 31 that is movable toward and away from the fixed lens 30. When the medium 2 moves in a direction intersecting the optical axis direction during processing, the autofocus mechanism 6 of this example detects the amount of displacement in the optical axis direction on the surface of the medium 2 based on the second laser light L2 irradiated onto the medium 2 from the second light source 22. The autofocus mechanism 6 adjusts the focus of the condenser lens 11 based on the amount of displacement in the optical axis direction, thereby allowing processing to be performed at a position that tracks the amount of displacement in the optical axis direction.

[0031] As described above, the surface of the medium 2 may have irregularities, and therefore, in order to perform stable cutting, it is necessary to adjust the focusing position of the first laser beam L1 in accordance with the irregular shape of the surface of the medium 2. Therefore, in this example, the autofocus mechanism 6 irradiates the medium 2 with a laser beam separate from the laser beam used for processing, detects the surface shape of the medium 2 from changes in the amount of light, and drives the focusing position adjuster 19 based on the detection results to optimize the focusing position of the first laser beam L1 (autofocus process).

[0032] For example, an LD (Laser Diode) light source or an SLD (Super Luminescent Diode) light source is used as the second light source 22. The second laser light L2 emitted from the second light source 22 has a wavelength different from that of the first laser light L1 and is light that can be reflected on the surface of the medium 2.

[0033] The second laser light L2 emitted from the second light source 22 passes through the condenser lens 23, and then is partially blocked by the knife edge 24. The light that proceeds without being blocked by the knife edge 24 passes through the mirror member 25 and the focus lens group 26, and is then reflected by the half mirror 27 and also by the dichroic mirror 10. The second laser light L2 reflected by the dichroic mirror 10 proceeds along the shared optical path together with the first laser light L1, is collected by the condenser lens 11, and is irradiated onto the medium 2.

[0034] The second laser light L2 irradiated onto the medium 2 is reflected by the surface of the medium 2. The second laser light L2 reflected from the medium 2 returns to the condenser lens 11 and travels along the shared optical path, is reflected in order by the dichroic mirror 10 and the half mirror 27, passes through the focus lens group 26, and is then reflected by the mirror member 25. The light reflected by the mirror member 25 is condensed by the imaging lens 28 and irradiated onto the detector 29.

[0035] Detector 29 receives the light from imaging lens 28 on its light-receiving surface and forms a condensed image on the light-receiving surface. Detector 29 is, for example, a two-segment photodiode having a light-receiving element (photoelectric conversion element) divided into two. In this case, detector 29 divides and receives the condensed image of the reflected light of second laser beam L2 and outputs detection signals according to the respective light intensities to control device 8.

[0036] The control device 8 detects the amount of displacement of the surface of the medium 2 in the Z-axis direction from a reference position based on the detection signal input from the detector 29. The amount of displacement is, for example, the defocus distance between the surface of the medium 2 and the focal point of the second laser light L2. The control device 8 controls the first actuator 20 based on the amount of displacement of the surface of the medium 2 in the Z-axis direction from the reference position, thereby moving the focusing position adjustment unit 19 of the focusing lens 11 and adjusting the focusing position of the first laser light L1. This makes it possible to adjust the focusing position of the first laser light L1 so as to follow the unevenness of the surface of the medium 2.

[0037] However, when the focusing position of the first laser beam L1 of the focusing lens 11, i.e., the processing depth of the modified region P, is changed, the focal position of the second laser beam L2 also changes in accordance with the change in the focusing position of the first laser beam L1. Therefore, the control device 8 adjusts the focal position of the second laser beam L2 by moving the movable lens 31 along the optical path direction based on the detection signal of the detector 29. This optimizes the focal position of the second laser beam L2 even when the processing depth of the modified region P is changed.

[0038] (Focus position adjustment unit 33) 3, the second lens group 17 has a focus position adjustment unit 33 consisting of at least one lens that adjusts the focusing position by following the minute movement of the medium 2 so that the spherical aberration of the lens group 13 does not change. Meanwhile, in the laser processing apparatus 1, the medium 2 moves at high speed in the horizontal direction (for example, the X-axis direction in FIG. 3) during processing. At this time, the medium 2 generates minute vibrations (shakes) in the optical axis direction (vertical direction: the Z-axis direction in FIG. 3). Therefore, since the minute vibrations of the medium 2 in the optical axis direction affect the focusing position of the first laser light L1, the laser processing apparatus 1 is provided with a focus position adjustment unit 33 to take measures against these minute vibrations.

[0039] The focus position adjustment unit 33 is configured to move several lenses in the second lens group 17 at the tips closest to the medium 2 in the optical axis direction. The movement of the focus position adjustment unit 33 in the optical axis direction is preferably performed by, for example, minute vibrations along the optical axis direction. The focus position adjustment unit 33 is a lens portion in the second lens group 17 that minutely drives the lenses by moving back and forth by minute amounts in the optical axis direction.

[0040] In this example, the second lens group 17 has, for example, a region (region E shown in FIG. 3) where the marginal ray angle of the light beam is "zero" or has a slight positive (or slightly negative) gradient. The focus position adjustment unit 33 in this example is configured by allowing (several) lenses located further distal than region E to move slightly back and forth in the optical axis direction. By making the lenses located further distal than the region where the marginal ray angle is "zero" or has a slight positive (or slightly negative) gradient movable, spherical aberration does not worsen even if a configuration is adopted in which some lenses in the second lens group 17 are slightly vibrated.

[0041] 1, the laser processing apparatus 1 includes a second actuator 34 that serves as a drive source for the focus position adjustment unit 33. For example, an electric actuator is used as the second actuator 34. The control device 8 drives the second actuator 34 to generate minute movements in the focus position adjustment unit 33, thereby adjusting for minute vibrations of the medium 2 in the optical axis direction during processing.

[0042] (Spherical aberration characteristics between lens group 13 and the medium interface) As shown by the dashed-dotted line ray diagram in Figure 5, when the first laser light L1 is focused inside the medium 2, the ray height at the first lens group 16 decreases, and conversely, the ray height at the second lens group 17 increases. Therefore, while the spherical aberration at the first lens group 16 decreases, the spherical aberration at the second lens group 17 increases. The absolute value of the spherical aberration is larger at the second lens group 17 than at the first lens group 16. Therefore, the spherical aberration of the focusing lens 11 increases overall.

[0043] Fig. 6 is a graph showing the change in spherical aberration with respect to the depth d of the focusing position when the medium 2 is silicon. Fig. 6 also shows the change in the Seidel coefficient as the change in spherical aberration. In Fig. 6, the change in spherical aberration of the first lens group 16 is indicated by a dashed-dotted line, the change in spherical aberration of the second lens group 17 by a solid line, the change in spherical aberration at the medium interface (medium surface) by a dashed line, and the sum of all these changes in spherical aberration is indicated by a two-dot chain line.

[0044] As shown in Figure 6, the change in spherical aberration of the second lens group 17 takes the waveform of a linear function with a positive sign, while the change in spherical aberration at the medium interface takes the waveform of a linear function with a negative sign. As can be seen, the change in spherical aberration of the second lens group 17 and the change in spherical aberration at the medium interface change in opposite directions. Therefore, if the spherical aberration coefficient S1 of the focusing lens 11 is designed so that the change in spherical aberration of the focusing lens 11 is offset by the change in spherical aberration at the medium interface, no special spherical aberration correction process is required. Therefore, in the present disclosure, this characteristic is utilized to minimize the change in spherical aberration.

[0045] (spherical aberration coefficient S1 of lens group 13) Figure 7 is a graph showing the calculated change in the spherical aberration coefficient S1 of the medium interface versus the depth d of the focusing position for various numerical apertures NA when the medium 2 is silicon. The spherical aberration coefficient S1 of the medium interface is a linear function of the depth d of the focusing position, regardless of the numerical aperture NA. Therefore, the formula S1(NA, d) for calculating the spherical aberration coefficient S1 of the medium interface is estimated to be the following formula (1) when expressed as a function of "f(NA)", which is a function of the numerical aperture NA, and the depth "d" of the focusing position. Note that "k" in formula (1) is a coefficient. S1(NA,d)=k×d×f(NA) …(1) Figure 8 is a graph showing the calculated change in the spherical aberration coefficient S1 of the medium interface versus the numerical aperture NA for three patterns of focal position depth d (0 [mm], 0.4 [mm], 0.8 [mm]) when the medium 2 is silicon. It can be seen that the spherical aberration coefficient S1 of the medium interface is a fourth-order function of the numerical aperture NA. Therefore, the formula S1(NA, d) for calculating the spherical aberration coefficient S1 of the medium interface is estimated to be the following formula (2) when expressed as a function of the numerical aperture NA, "f(NA)", and the focal position depth "d". S1(NA,d) = k × d × NA 4 …(2) Therefore, the spherical aberration coefficient S1 of the lens group 13 is set to a value that satisfies the following equation (3). S1=k×d×NA 4 …(3) When the medium 2 is silicon (refractive index n=3.54), it has been confirmed that the optimum value of the coefficient k is approximately "-0.26" through actual calculations using the above-mentioned equations (1) and (2). Therefore, the spherical aberration coefficient S1 of the lens group 13 must satisfy the following equation (4) if it is an optimum value, and otherwise must be within the range of the following equation (5). |S1|=0.26×d×NA 4 …(4) |S1|=k×d×NA 4 (Note: 0.13 <k<0.52) …(5) Here, for example, if medium 2 is water (refractive index n = 1.33), and the depth d of the same focusing position is the same for silicon and water, then the adjustment range for water, which has a lower refractive index n than silicon, will be greater in terms of converted optical path length. For this reason, the change in optical path within lens group 13 will be greater for water than for silicon, resulting in a greater change in spherical aberration within lens group 13. On the other hand, the absolute value of the spherical aberration occurring at the medium interface will be smaller for water, which has a smaller refractive index n. Thus, when medium 2 is water, the change in spherical aberration within lens group 13 will be greater, while the change in spherical aberration at the medium interface will be smaller.

[0046] For these reasons, it would seem that it would be difficult to achieve aberration correction that cancels out the spherical aberration of the lens group 13 and the spherical aberration at the medium interface when the refractive index n of the medium 2 is small. However, because this aberration correction is a design item determined by calculation, it is theoretically possible to set the spherical aberration coefficient S1 of the lens group 13 so that it cancels out the spherical aberration at the medium interface, even when the refractive index n of the medium 2 is small.

[0047] (Optimization of coefficient k) The coefficient k expressed in equations (1) to (3) and (5) is a value determined by calculation and takes various values ​​depending on the refractive index n of medium 2. For example, when medium 2 is silicon, it has been confirmed that the refractive index n is 3.54 and the coefficient k is approximately -0.26. Furthermore, when medium 2 is water, it has been confirmed that the refractive index n is 1.33 and the coefficient k is approximately -0.31. Therefore, assuming that the coefficient k is a function of the refractive index n, we will consider the formula k(n) for determining the coefficient k.

[0048] Here, a number of points (e.g., 13 points) are selected for the refractive index n of the medium 2 within a predetermined range (e.g., 1.33 to 3.54), and the value of the coefficient k is calculated for each point. This creates a table of refractive index n and the corresponding coefficient k. This table is interpreted as a table of function values ​​of coefficient k versus refractive index n, and coefficient k is fitted as a function of refractive index n to find the coefficient k as a function of refractive index n.

[0049] Figure 9 is a graph of the coefficient k determined by fitting. The graph in Figure 9 shows the change in coefficient k corresponding to the refractive index n at the medium interface. In the fitting, "1 / n" was used as the independent variable. Therefore, the graph in Figure 9 shows the change in coefficient k corresponding to the independent variable 1 / n. From the graph in Figure 9, the formula k(n) for calculating the coefficient k in the formula for calculating the spherical aberration coefficient S1 generated at the medium interface is expressed as the following formula (6).

[0050]

number

[0051]

number

[0052]

number

[0053]

number

[0054]

number

[0055] 5, in the focusing lens 11, the first actuator 20 is driven in accordance with the uneven shape of the interface of the medium 2 detected by the autofocus mechanism 6, and the focusing position adjustment unit 19 is moved in the optical axis direction of the first laser beam L1. As a result, the depth d of the focusing position of the first laser beam L1 is adjusted to a position corresponding to the uneven shape of the medium 2. Therefore, even if unevenness occurs on the surface of the medium 2, a modified region P is formed in an appropriate position corresponding to the uneven shape.

[0056] Furthermore, in this example, the spherical aberration coefficient S1 of the lens group 13 is set so as to be able to cancel out the spherical aberration coefficient S1 of the interface of the medium 2. This makes it possible to reduce the variation in spherical aberration without providing a special mechanism or structure to the laser processing device 1 or the condenser lens 11. This makes it possible to reduce the change in spherical aberration without complicating the configuration of the laser processing device 1 or the condenser lens 11.

[0057] The ratio of the focal length of the first lens group 16 to the focal length of the lens group 13 (first group focal length / lens group focal length) is preferably in the range of 0.2 to 0.6, for example. If this value is too small, the amount of movement required for the focusing position adjustment unit 19 becomes too large, leading to an increase in the size of the device and a complex structure. On the other hand, if this value is too small, the fluctuation in spherical aberration of the lens group 13 becomes too large, making it difficult to cancel out the change in spherical aberration at the medium interface. Therefore, it is preferable that the focal length ratio be set within the above-mentioned range.

[0058] 10, in the condenser lens 11, in order to deal with minute vibrations of the medium 2 in the optical axis direction during processing, the second actuator 34 is driven to slightly vibrate the focus position adjustment unit 33. As a result, even if the medium 2 vibrates in the optical axis direction (horizontal direction) when it is transported horizontally at high speed during processing, the focus position adjustment unit 33, which is a part of the condenser lens 11, is slightly vibrated to follow this vibration. This makes it possible to minimize changes in spherical aberration caused by vibrations of the medium 2 in the optical axis direction.

[0059] In this example, the marginal ray angle of the light beam in the gap (area E shown in FIG. 10) for slightly vibrating the focus position adjustment unit 33 in the second lens group 17 is preferably within the range of ±0.15 rad, for example. Outside this range, the change in the light beam height inside the second lens group 17 becomes large, so that the change in the spherical aberration coefficient S1 even with a slight movement becomes large, making it difficult to maintain a constant spherical aberration coefficient S1 for the entire device. Therefore, the marginal ray angle is preferably set within the above-mentioned range.

[0060] (Other types of medium 2) The medium 2 is not limited to silicon (Si) and may be, for example, water. When the medium 2 is water, the spherical aberration coefficient S1 of the lens group 13 must satisfy the following equation (10) if it is an optimal value, based on the same concept as when the medium 2 is silicon, and otherwise must be within the range of the following equation (11). |S1|=0.31×d×NA 4 …(10) |S1|=k×d×NA 4 (Note: 0.16 <k<0.6) …(11) Furthermore, the medium 2 is not limited to silicon (Si) or water, but may be any material that can be used as a semiconductor wafer, such as silicon carbide (SiC), sapphire (Al22), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), and indium phosphide (InP).

[0061] Silicon carbide has a refractive index n of 2.587 and an optimum k coefficient of 0.329. Sapphire has a refractive index n of 1.7557 and an optimum k coefficient of 0.385. Gallium nitride has a refractive index n of 2.3366 and an optimum k coefficient of 0.35. Gallium phosphide has a refractive index n of 3.179 and an optimum k coefficient of 0.283. Gallium arsenide has a refractive index n of 3.666 and an optimum k coefficient of 0.253. Indium phosphide has a refractive index n of 3.456 and an optimum k coefficient of 0.265.

[0062] (Effects of the embodiment) According to the configuration of the above embodiment, the following effects can be obtained. (1) The condensing lens 11 condenses the first laser light L1 as a laser light input from the first light source 9 as a light source, and emits it toward the medium 2. The condensing lens 11 includes a lens group 13 having a first lens group 16 that changes the first laser light L1 into a diverging light state, and a second lens group 17 that condenses and emits the first laser light L1 that has passed through the first lens group 16. The first lens group 16 has a condensing position adjustment unit 19 consisting of at least one lens that adjusts the condensing position of the first laser light L1 by moving it in the optical axis direction.

[0063] According to this configuration, among the lenses constituting the lens group 13 of the condensing lens 11, a predetermined lens of the first lens group 16 is used as a condensing position adjuster 19 that changes the condensing position of the first laser light L1. In this way, the lens of the condensing position adjuster 19, which is provided so as to be movable in the optical axis direction in order to change the condensing position of the first laser light L1, is integrated with the other lenses of the lens group 13. This makes it easy to align the lenses of the condensing lens 11. Therefore, it is possible to easily align the lenses of the lens group 13 while making the condensing position of the first laser light L1 variable.

[0064] (2) The spherical aberration of the lens group 13 and the spherical aberration at the interface of the medium 2 have a characteristic in which the sign changes from positive to negative inversely with a change in the focusing position. The spherical aberration coefficient S1 of the lens group 13 is set to a value that cancels out the spherical aberration at the interface of the medium 2. According to this configuration, by optimizing the spherical aberration coefficient S1 of the lens group 13, it is possible to minimize the change in spherical aberration that occurs in the focusing lens 11 when the focusing position of the first laser beam L1 is changed. Therefore, there is no need to provide a separate mechanism (for example, a correction collar) or structure for minimizing the change in spherical aberration in the focusing lens 11, which contributes to simplifying the configuration of the focusing lens 11.

[0065] (3) The spherical aberration coefficient S1 of the lens group 13 is set to a value that satisfies the above-mentioned formula (3) using the coefficient k, the depth d of the light-condensing position, and the numerical aperture NA of the lens group 13. According to this configuration, the spherical aberration coefficient S1 of the lens group 13 can be set to a suitable value that cancels out the spherical aberration of the lens group 13 and the spherical aberration at the medium interface.

[0066] (4) The coefficient k is set to a value that satisfies the above-mentioned formula (10), where n is the refractive index of the medium 2. According to this configuration, an equation for calculating the coefficient k is set, so that the necessary coefficient k can be easily determined, and therefore the spherical aberration coefficient S1 required for the lens group 13 can also be easily determined.

[0067] (5) When the medium 2 is silicon, the coefficient k is set to a value that satisfies 0.13 < k < 0.52. According to this configuration, the optimal coefficient k when the medium 2 is silicon can be set.

[0068] (6) When the medium 2 is water, the coefficient k is set to a value that satisfies 0.16 < k < 0.6. According to this configuration, the optimal coefficient k when the medium 2 is water can be set. (7) The second lens group 17 has a focus position adjustment unit 33 composed of at least one lens that adjusts the condensing position following the fine drive of the medium 2 so that the spherical aberration of the lens group 13 does not change. According to this configuration, since the focus position adjustment unit 33 of the second lens group 17 is moved in a direction intersecting the conveyance direction of the medium 2, even if the medium 2 is finely driven in a direction intersecting the conveyance direction during processing of the medium 2, it is possible to adjust the condensing position of the lens group 13 so as to follow it. Therefore, it contributes to an improvement in the processing accuracy of the medium 2.

[0069] (8) The spherical aberration coefficient S1 of the lens group 13 is set to a value that satisfies the above-mentioned formula (9). According to this configuration, it can be easily understood within what range of values the spherical aberration coefficient S1 of the lens group 13 should be set.

[0070] (Other embodiments) Note that this embodiment can be implemented with the following modifications. This embodiment and the following modification examples can be implemented in combination with each other within a technically non - conflicting range.

[0071] · As shown in FIG. 11, the condensing position adjustment unit 19 is not limited to a single lens and may be composed of a plurality of lenses. Also, the number of lenses of the focus position adjustment unit 33 is not limited to three and may be a number other than three, such as four for example. Thus, the lens configuration of the condensing lens 11 may be appropriately changed to other configurations as needed.

[0072] · The condensing position adjustment unit 19 may be composed of any lens of the first lens group 16. The focus position adjustment unit 33 may be composed of any of the lenses in the second lens group 17.

[0073] The spherical aberration coefficient S1 of the condenser lens 11 may be set for any of the lenses in the lens group 13. The lenses of the lens group 13 do not necessarily have to be housed in the housing 14, but may be assembled into a single unit.

[0074] The condenser lens 11 is not limited to a processing lens, but may be an objective lens. The control device 8 may be configured by [1] one or more processors operating according to a computer program (software), or [2] a combination of such a processor and one or more dedicated hardware circuits, such as an application-specific integrated circuit (ASIC), that execute at least some of the various processes. The processor includes a CPU and memory, such as RAM and ROM, that stores program code or instructions configured to cause the CPU to execute the processes. The memory (computer-readable medium) includes any available medium that can be accessed by a general-purpose or dedicated computer. Alternatively, instead of a computer including the processor, a processing circuit configured by one or more dedicated hardware circuits that execute all of the various processes may be used.

[0075] While the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to those embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure. [Explanation of symbols]

[0076] 1...laser processing device, 2...medium, 5...laser processing mechanism, 6...autofocus mechanism, 9...light source (first light source), 11...condensing lens, 13...lens group, 16...first lens group as first group, 17...second lens group as second group, 19...focusing position adjustment unit, 22...second light source, 33...focus position adjustment unit, L1...laser light (first laser light), L2...second laser light, S1...spherical aberration coefficient, d...depth of focusing position, k...coefficient, NA...numerical aperture, n...refractive index.

Claims

1. A condenser lens that condenses laser light input from a light source and emits the light toward a medium, a lens group including a first group that causes the laser light to be in a diverging state, and a second group that condenses and emits the laser light that has passed through the first group; The first group is a focusing lens having a focusing position adjusting portion made up of at least one lens that adjusts the focusing position of the laser light by moving in the optical axis direction.

2. the spherical aberration of the lens group and the spherical aberration of the interface of the medium have a characteristic that their signs change from positive to negative inversely with respect to a change in the focusing position, 2. The focusing lens according to claim 1, wherein the spherical aberration coefficient of said lens group is set to a value that cancels the spherical aberration at the interface of said medium.

3. 2. The focusing lens according to claim 1, wherein S1, which is a spherical aberration coefficient of the lens group, is set to a value that satisfies the following formula, where k is a coefficient, d is a depth of the focusing position, and NA is a numerical aperture of the lens group. [Equation 1]

4. 4. The focusing lens according to claim 3, wherein the coefficient k is set to a value that satisfies the following formula, where n is the refractive index of the medium. [Equation 2]

5. 4. The focusing lens according to claim 3, wherein the coefficient k is set to a value that satisfies 0.13<k<0.52 when the medium is silicon.

6. 4. The focusing lens according to claim 3, wherein the coefficient k is set to a value that satisfies 0.16<k<0.6 when the medium is water.

7. 2. The focusing lens according to claim 1, wherein the second group has a focus position adjustment unit made up of at least one lens that adjusts the focusing position by following minute driving of the medium so that spherical aberration of the lens group does not change.

8. a laser processing mechanism that focuses a first laser beam input from a first light source using a focusing lens and processes a medium using the first laser beam from the focusing lens; an autofocus mechanism that, when the medium moves in a direction intersecting the optical axis direction during processing, detects a displacement amount of the surface of the medium in the optical axis direction based on reflected light of a second laser light irradiated onto the medium from a second light source, and adjusts the focus of the condenser lens based on the displacement amount of the optical axis, thereby performing processing at a position that follows the displacement amount of the optical axis, The condenser lens is a lens group including a first group that causes the first laser light to be in a diverging state, and a second group that collects the first laser light that has passed through the first group and emits the collected light to the medium; The laser processing device, wherein the first group has a focusing position adjustment unit consisting of at least one lens that adjusts the focusing position of the first laser light by moving it in the optical axis direction using the autofocus mechanism.

9. a laser processing step of condensing a first laser beam input from a first light source using a condenser lens and processing a medium using the first laser beam from the condenser lens; an autofocusing step of detecting an amount of displacement of the surface of the medium in the direction of the optical axis based on reflected light of a second laser beam irradiated onto the medium from a second light source when the medium moves in a direction intersecting the optical axis direction during processing, and adjusting the focus of the condenser lens based on the amount of displacement in the optical axis direction, so that processing is performed at a position that follows the amount of displacement in the optical axis direction, The condenser lens is a lens group including a first group that causes the first laser light to be in a diverging state, and a second group that collects the first laser light that has passed through the first group and emits the collected light to the medium; The laser processing method, wherein the autofocusing step includes a process of adjusting the focusing position of the first laser light by moving a focusing position adjustment unit consisting of at least one lens of the first group in the optical axis direction.

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