Laser processing apparatus and method for measuring transient lens effects

Abstract

To provide a laser processing apparatus that can suppress fluctuations in the focal position of a laser beam due to transient lensing effects caused by nonlinear optical effects. [Solution] The laser processing apparatus comprises a light source that emits a laser beam, an output adjustment unit that adjusts the output of the laser beam emitted from the light source, a light guide unit that guides the laser beam whose output has been adjusted by the output adjustment unit to the workpiece, and a control unit. The light guide unit comprises a beam angle adjustment unit that adjusts the beam angle of the laser beam, and a focusing optical system that focuses the laser beam whose beam angle has been adjusted by the beam angle adjustment unit toward the workpiece. The control unit changes the beam angle of the laser beam, which is adjusted by the beam angle adjustment unit, according to the output of the laser beam adjusted by the output adjustment unit.

Description

[Technical Field]

[0001] The present invention relates to a laser processing apparatus and a method for measuring transient lens effects. [Background technology]

[0002] Ultraviolet light has the advantage of being able to be focused to a smaller beam diameter than visible light and infrared light, possesses high energy, and has a high absorption rate in various materials. To take advantage of these characteristics, ultraviolet lasers (hereinafter also called "UV lasers") have been used in laser processing equipment and lithography exposure equipment in recent years. In such equipment that irradiates with UV lasers, the UV laser is passed through transmissive optical elements such as lenses, beam splitters, prisms, and protective windows to control the beam diameter and position of the UV laser relative to the target object.

[0003] In devices that irradiate with UV lasers, the size of the irradiation spot and the position of the focal point may change unintentionally during UV laser irradiation. Specifically, when the laser beam has a Gaussian intensity distribution, the temperature at the center of the lens becomes higher than that at the periphery, causing the refractive index at the center of the lens to decrease compared to the periphery, and altering the function of the lens. This is known as the "thermal lensing effect" or "thermal aberration." Even when the lens is formed from a material that absorbs little ultraviolet light, it is difficult to completely prevent the occurrence of the thermal lensing effect. Therefore, technologies to suppress the adverse effects of the thermal lensing effect have been proposed (for example, Patent Documents 1 and 2).

[0004] Patent Document 1 describes a silica glass component for ultraviolet optics that reduces thermal aberration caused by irradiation with a UV laser. Patent Document 1 explains that in order to reduce thermal aberration, attention should be paid to the amount of absorption of the UV laser rather than the transmittance of the UV laser, and proposes a method for measuring the amount of UV laser absorption in a silica glass component. In this method, the change in refractive index in the silica glass component when a UV laser is transmitted is measured as a wavefront fluctuation using a high-precision wavefront sensor, and the amount of UV laser absorption in the silica glass component is calculated from the measured wavefront fluctuation.

[0005] Patent Document 2 describes a laser processing apparatus having a first optical component that is susceptible to the thermal lensing effect and a wavefront compensating optical component configured to correct wavefront aberration caused by the thermal lensing effect. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2010-155736 [Patent Document 2] Special Publication No. 2022-518898 [Overview of the project] [Problems that the invention aims to solve]

[0007] When a thermal lensing effect occurs, the refractive index at the center of the lens decreases compared to the periphery. This change in refractive index weakens the function of the convex lens. Therefore, when a thermal lensing effect occurs, the focal length of the lens increases, and the point of focus shifts away from the lens. In other words, the working distance increases. It is also possible that the irradiated area of ​​a transmissive optical element may bulge due to thermal expansion, and in rare cases, it may become close to the shape of a convex lens. However, because the refractive index is also lower in this area due to the lower density, there is no convex lens effect in this area.

[0008] On the other hand, the inventors have found that in devices that irradiate with high-brightness UV lasers, the focal point may shift in the direction of approaching the lens. As described above, when a thermal lensing effect occurs, the focal point shifts in the direction of moving away from the lens, so this phenomenon is considered to be a transient lensing effect caused by a nonlinear optical effect, which is different from the thermal lensing effect (described later). This transient lensing effect caused by a nonlinear optical effect also degrades the function of the device. From the viewpoint of suppressing such adverse effects, firstly, a method for measuring the transient lensing effect caused by a nonlinear optical effect is needed. Secondly, a laser processing device that can utilize these measurement results to suppress fluctuations in the focal position of the laser beam due to the transient lensing effect caused by a nonlinear optical effect is also needed.

[0009] The object of the present invention is to provide a laser processing apparatus that can suppress fluctuations in the focal position of a laser beam due to transient lens effects caused by nonlinear optical effects. Another object of the present invention is to provide a method for measuring transient lens effects caused by nonlinear optical effects, which can be used when adjusting the above-mentioned laser processing apparatus. [Means for solving the problem]

[0010] The first aspect of this invention relates to the following laser processing apparatus.

[0011] [1] A laser processing apparatus comprising: a light source that emits a laser beam; an output adjustment unit that adjusts the output of the laser beam emitted from the light source; a light guide unit that guides the laser beam whose output has been adjusted by the output adjustment unit to a workpiece; and a control unit, wherein the light guide unit comprises a beam angle adjustment unit that adjusts the beam angle of the laser beam; and a focusing optical system that focuses the laser beam whose beam angle has been adjusted by the beam angle adjustment unit toward the workpiece; and the control unit changes the beam angle of the laser beam, which is adjusted by the beam angle adjustment unit, according to the output of the laser beam adjusted by the output adjustment unit. [2] The laser processing apparatus according to [1], wherein the control unit increases the divergence angle of the laser beam adjusted by the divergence angle adjustment unit as the output of the laser beam adjusted by the output adjustment unit increases. [3] The laser processing apparatus according to [1] or [2], wherein the control unit changes the divergence angle of the laser beam, which is adjusted by the divergence angle adjustment unit, in order to suppress fluctuations in the focal position of the laser beam due to transient lens effects caused by nonlinear optical effects.

[0012] The second aspect of the present invention relates to the following method for measuring transient lens effects.

[0013] [4] A method for measuring transient lens effects caused by nonlinear optical effects in a laser processing apparatus, comprising the step of measuring the divergence angle of a laser beam that has passed through a transmissive optical element included in the laser processing apparatus. [5] The method for measuring the transient lens effect described in [4], wherein in the step of measuring the divergence angle of the laser beam, the output of the laser beam that passes through the transmissive optical element is changed while measuring the divergence angle of the laser beam.

[0014] The third aspect of the present invention relates to the following method for measuring transient lens effects.

[0015] [6] A method for measuring the change in focal position due to transient lens effect caused by nonlinear optical effects in a laser processing apparatus, comprising the steps of guiding a laser beam that has passed through a transmissive optical element included in the laser processing apparatus to an aperture or slit, and measuring the output of the laser beam that has passed through the aperture or slit. [7] The method for measuring the transient lens effect according to [6], further comprising the step of comparing the output of the laser beam before it passes through the transmissive optical element with the output of the laser beam after it has passed through the aperture or the slit. [8] When the output of the laser beam passing through the aperture or the slit exceeds a predetermined value, further including the step of determining that the fluctuation of the focal position is caused by the transient lens effect, the method for measuring the transient lens effect according to [6] or [7].

Advantages of the Invention

[0016] According to the present invention, even when irradiating with a UV laser, a laser processing apparatus capable of suppressing fluctuations in the focal position of a laser beam due to a transient lens effect caused by a non-linear optical effect can be provided. Further, according to the present invention, a method for measuring the transient lens effect can also be provided.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a laser processing apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a graph showing the relationship between the input fluence of a laser beam and the change amount of the working distance in a convex lens where a transient lens effect caused by a non-linear optical effect occurs. [Figure 3] FIG. 3 is a graph showing the relationship between the input fluence of a laser beam and the change amount of the divergence angle of the beam after passing through the lens in four types of convex lenses. [Figure 4] FIG. 4 is a graph showing the relationship between the change amount of the divergence angle and the spot diameter in a convex lens where a transient lens effect caused by a non-linear optical effect occurs. [Figure 5] FIG. 5 is a schematic diagram showing the configuration of a transient lens effect measuring apparatus according to an embodiment of the present invention. [Figure 6] FIG. 6 is a schematic diagram showing the configuration of a transient lens effect measuring apparatus according to a modified example of the present invention. [Figure 7] FIG. 7 is a schematic diagram showing the configuration of a laser processing apparatus according to an embodiment capable of implementing the method for measuring the second transient lens effect. [Figure 8]Figures 8A and 8B are schematic diagrams illustrating the second method for measuring transient lens effects. [Figure 9] Figure 9 is a graph showing the relationship between the output of the laser beam and the proportion of the laser beam that passed through the aperture for two types of convex lenses. [Modes for carrying out the invention]

[0018] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to this embodiment.

[0019] 1. Laser processing equipment First, we will describe a laser processing device that can suppress fluctuations in the focal position of the laser beam due to transient lensing effects caused by nonlinear optical effects, even when irradiating with a high-brightness UV laser.

[0020] Figure 1 is a schematic diagram showing the configuration of a laser processing apparatus 100 according to one embodiment of the present invention. As shown in Figure 1, the laser processing apparatus 100 has a light source 110, an output adjustment unit 120, a light guide unit 130, and a control unit 140. In this embodiment, the light guide unit 130 has a beam diameter adjustment unit 131, a beam divergence angle adjustment unit 132, and a focusing optical system 133.

[0021] The laser processing apparatus 100 according to this embodiment processes the workpiece 300 by irradiating it with a laser beam 210 emitted from a light source 110. The workpiece 300 is not particularly limited as long as it is laser-processable. Examples of workpieces 300 include semiconductors such as silicon, metals such as copper, alloys such as Invar, glass, ceramics, resins, laminated composite materials thereof, and printed circuit boards.

[0022] As described above, the laser processing apparatus 100 according to this embodiment processes the workpiece 300 by irradiating it with a laser beam 210 emitted from a light source 110. At this time, the control unit 140 changes the divergence angle of the laser beam 210, which is adjusted by the divergence angle adjustment unit 132, according to the output of the laser beam 210 adjusted by the output adjustment unit 120. This suppresses fluctuations in the focal position of the laser beam 210 due to transient lens effects caused by nonlinear optical effects.

[0023] (Transient lensing effect caused by nonlinear optical effects) As mentioned above, in transient lensing effects caused by nonlinear optical effects, unlike thermal lensing effects, the focal point shifts in the direction closer to the lens. This is because when the above transient lensing effect occurs, the beam divergence angle after passing through the lens becomes smaller than the expected value. When the above transient lensing effect occurs, the size of the focal spot on the workpiece 300 increases, resulting in a decrease in the laser intensity I (W / cm²) per unit area. 2 The size may become too small, making it impossible to achieve the desired processing.

[0024] Figure 2 is a graph showing the relationship between the input fluence of a pulsed laser beam and the change in working distance in a convex lens where transient lensing effects due to nonlinear optical effects occur. The horizontal axis represents the input fluence (W / cm²) of the pulsed laser beam. 2 The graph shows the input fluence at 47.75 W / cm², with the vertical axis representing the input fluence of 47.75 W / cm². 2 This graph shows the change in working distance (mm) relative to the working distance at the given time. From this graph, it can be seen that as the output of the laser beam increases, the working distance decreases due to the transient lensing effect described above, meaning that the focal point shifts closer to the lens.

[0025] Figure 3 is a graph showing the relationship between the input fluence of a pulsed laser beam and the change in beam divergence angle after passing through the lens for four types of convex lenses. The horizontal axis represents the input fluence (W / cm²) of the pulsed laser beam. 2The graph shows the input fluence at 1.84 W / cm², with the vertical axis representing the input fluence of 1.84 W / cm². 2 This graph shows the change in the divergence angle (mrad) relative to the divergence angle at a given value. The graph also shows an approximate straight line. From this graph, it can be seen that for some lenses (lens 1 and lens 2), the divergence angle decreases as the laser beam output increases due to the transient lensing effect described above. It can also be seen that the degree of the transient lensing effect differs depending on the lens. In this graph, it can be seen that the transient lensing effect occurs in two types of lenses (lens 1 and lens 2), but it appears that the transient lensing effect does not occur in the remaining two types of lenses (lens 3 and lens 4).

[0026] Figure 4 is a graph showing the relationship between the change in divergence angle and the spot diameter in a convex lens where transient lens effects due to nonlinear optical effects occur. The horizontal axis shows the change in divergence angle (μrad) relative to the divergence angle when the spot diameter at the reference plane is minimum (125 μm), and the vertical axis shows the spot diameter at the reference plane (μm). This graph also shows an approximation curve. The dashed line indicates the tolerance limit when the allowable range of the change in spot diameter is set to +10%. From this graph, it can be seen that when the allowable range of the change in spot diameter is set to +10%, the change in divergence angle is allowed to be up to ±20 μrad.

[0027] The mechanism of transient lensing effects caused by nonlinear optical effects is presumed to be as follows, but is not limited to this.

[0028] The focal length of a lens is uniquely determined by the refractive index of the material constituting the lens, the shape of the lens, and the size of the lens. During laser processing, it is substantially impossible for the shape and size of the lens to change. Therefore, the above transient lens effect is considered to be caused by a change in the refractive index of the lens. The refractive index n of a substance is a function of the wavelength of light. Since the wavelength of the laser beam is fixed in laser processing, the refractive index n is usually treated as a constant. However, when a high-intensity laser beam passes through a lens, the refractive index may change due to the nonlinear optical effect. That is, the refractive index n becomes a function of the laser intensity I p and is expressed by the following formula (1). [Equation] Here, n0 is the linear refractive index (so-called ordinary refractive index), and n2 is the nonlinear refractive index. When the laser beam is a pulsed laser beam, I p is the peak laser output per unit area (W / cm 2 ). Let the optical energy per pulse be E (J), the pulse width be Δt (s), and the area of the irradiation spot be s (cm 2 ), then I p is expressed by the following formula (2). [Equation] When the pulse width and repetition frequency of the pulsed laser beam, and the lens used are the same, when comparing the transient lens effect caused by the nonlinear optical effect while changing the output of the pulsed laser beam, the average output I may be used for comparison instead of the peak laser output I per unit area (I p can be replaced with I for comparison discussion).

[0029] ​​When irradiating with normal light, the nonlinear refractive index n² is small, so the nonlinear term n²I can be ignored (i.e., n ~ n0). However, when irradiating with a high-brightness laser beam, the laser intensity I is large, so the nonlinear term n²I cannot be ignored, and n becomes larger than n0. Furthermore, if the laser beam has a Gaussian intensity distribution, the laser intensity I is greatest at the center of the beam and decreases as you move away from the center of the beam. Therefore, the refractive index n is greatest at the center of the beam (usually coinciding with the center of the lens) and decreases as you move away from the center of the beam. In other words, due to the nonlinear effect, the laser beam generates such a refractive index distribution in the lens as it passes through it. This refractive index distribution acts as a convex lens, shifting the focal point of the laser beam towards the lens.

[0030] Thus, the refractive index distribution resulting from the transient lensing effect caused by nonlinear optical effects is the opposite of the refractive index distribution resulting from the thermal lensing effect. For this reason, in the thermal lensing effect, the focal point shifts away from the lens, but in the transient lensing effect caused by nonlinear optical effects, the focal point shifts towards the lens. The laser processing apparatus 100 according to this embodiment suppresses fluctuations in the focal position of the laser beam 210 due to the transient lensing effect caused by this nonlinear optical effect.

[0031] (Configuration of laser processing equipment) As described above, the laser processing apparatus 100 includes a light source 110, an output adjustment unit 120, a light guide unit 130, and a control unit 140 (see Figure 1). The light guide unit 130 includes a beam diameter adjustment unit 131, a beam divergence angle adjustment unit 132, and a focusing optical system 133. The individual components of the laser processing apparatus 100 will be described below.

[0032] The light source 110 emits a laser beam 210. The type of laser beam 210 is not particularly limited and can be appropriately selected depending on the application. Examples of laser beams 210 include continuous wave (CW) laser beams and pulsed laser beams. In this embodiment, the light source 110 emits a pulsed laser beam.

[0033] The wavelength of the laser beam 210 is not particularly limited as long as it can perform the desired processing on the workpiece 300. The type of light source 110 can also be appropriately selected according to the wavelength of the laser beam 210 used. When the wavelength of the laser beam 210 is short, transient lensing effects due to nonlinear optical effects are likely to occur. Therefore, the laser processing apparatus 100 according to this embodiment is particularly effective in laser processing using low-wavelength laser beams such as ultraviolet lasers (UV lasers). In this specification, an ultraviolet laser refers to a laser with a wavelength of 100 to 400 nm. Examples of UV laser wavelengths include 355nm (third harmonic of Nd:YAG laser), 266nm (fourth harmonic of Nd:YAG laser), 351nm (xenon fluorine excimer laser), 308nm (xenon chlorine excimer laser), 248nm (krypton fluorine excimer laser), 193nm (argon fluorine excimer laser), 343nm (fiber laser), and 250-400nm (harmonics of titanium sapphire laser).

[0034] When the laser beam 210 is a pulsed laser beam, the pulse width of the laser beam 210 is not particularly limited as long as the desired processing can be performed on the workpiece 300. When the pulse width of the laser beam 210 is short, transient lensing effects due to nonlinear optical effects are likely to occur. Therefore, the laser processing apparatus 100 according to this embodiment is particularly effective in laser processing using pulsed laser beams with short pulse widths, such as nanosecond pulsed lasers, picosecond pulsed lasers, and femtosecond pulsed lasers. For example, the pulse width of the laser beam 210 is 20 nanoseconds or less, preferably less than 1 picosecond, and more preferably in the range of 50 to 500 femtoseconds.

[0035] The output adjustment unit 120 adjusts the output of the laser beam 210 emitted from the light source 110. The configuration of the output adjustment unit 120 is not particularly limited as long as it can perform the above functions. Examples of the output adjustment unit 120 include a power controller, an attenuator, and a modulator.

[0036] The output of the laser beam 210 is not particularly limited as long as it can perform the desired processing on the workpiece 300. When the output of the laser beam 210 is high, transient lensing effects due to nonlinear optical effects are likely to occur. Therefore, the laser processing apparatus 100 according to this embodiment is particularly effective in laser processing using high-output laser beams such as ultraviolet lasers (UV lasers). Here, when the laser beam 210 is a CW laser beam, the output of the laser beam 210 means the average output (W), and when the laser beam 210 is a pulsed laser beam, the output of the laser beam 210 means the pulse energy (J). From the viewpoint of transient lensing effects due to nonlinear optical effects, the output per unit area of ​​each transmissive optical element is important. That is, when the laser beam 210 is a CW laser beam, the power density (W / cm²) is important. 2 ) is important, and if laser beam 210 is a pulsed laser beam, then fluence (J / cm) 2 ) and peak power per unit area (I p W / cm 2 ) is important.

[0037] The light guide unit 130 guides the laser beam 210, whose output has been adjusted by the output adjustment unit 120, to the workpiece 300. As described above, in this embodiment, the light guide unit 130 has a beam diameter adjustment unit 131, a beam divergence angle adjustment unit 132, and a focusing optical system 133.

[0038] The beam diameter adjustment unit 131 adjusts the diameter of the laser beam 210 whose output has been adjusted by the output adjustment unit 120. The configuration of the beam diameter adjustment unit 131 is not particularly limited as long as it can achieve the above function. In the example shown in Figure 1, the beam diameter adjustment unit 131 is a combination of a plano-concave lens and a plano-convex lens. The beam diameter adjustment unit 131 may be configured to arbitrarily adjust the diameter of the laser beam 210 based on instructions from the control unit 140. In this case, the diameter of the laser beam 210 may be changed by moving at least one of the plano-concave lens and the plano-convex lens in the optical axis direction. Alternatively, a variable focus lens, a transmission diffractive optical element, a transmission phase modulation element (e.g., LCOS-SLM), a deformable mirror, a reflective diffractive optical element, or a reflective phase modulation element (e.g., LCOS-SLM) may be used as the beam diameter adjustment unit 131.

[0039] The divergence angle adjustment unit 132 adjusts the divergence angle of the laser beam 210 based on instructions from the control unit 140. The configuration of the divergence angle adjustment unit 132 is not particularly limited as long as it can achieve the above function. In the example shown in Figure 1, the divergence angle adjustment unit 132 is a combination of two convex lenses and an automatic stage that moves one of the convex lenses in the optical axis direction.

[0040] The focusing optical system 133 focuses the laser beam 210, whose divergence angle has been adjusted by the divergence angle adjustment unit 132, toward the workpiece 300. The configuration of the focusing optical system 133 is not particularly limited as long as it can achieve the above functions. The focusing optical system 133 may be composed of a combination of multiple transmissive optical elements, a combination of multiple reflective optical elements, or a combination of transmissive and reflective optical elements. The focusing optical system 133 may also have a function to scan the laser beam 210 on the workpiece 300. For example, the focusing optical system 133 may include a galvanometer scanner. In this embodiment, the focusing optical system 133 is composed of a combination of multiple reflective optical elements including a galvanometer scanner, and does not include any transmissive optical elements.

[0041] The overall configuration of the light guide unit 130 is not particularly limited as long as it can achieve the above functions. In the example shown in Figure 1, the light guide unit 130 has two mirrors 134 in addition to the beam diameter adjustment unit 131, the divergence angle adjustment unit 132, and the focusing optical system 133.

[0042] The control unit 140 is connected to the light source 110, the output adjustment unit 120, the divergence angle adjustment unit 132, and the focusing optical system 133, and receives information from them and controls their operation. For example, the control unit 140 changes the divergence angle of the laser beam 210, which is adjusted by the divergence angle adjustment unit 132, according to the output of the laser beam 210 adjusted by the output adjustment unit 120. At this time, the control unit 140 changes the divergence angle of the laser beam 210, which is adjusted by the divergence angle adjustment unit 132, in order to suppress fluctuations in the focal position of the laser beam 210 due to transient lens effects caused by nonlinear optical effects. Specifically, the control unit 140 has information about the relationship between the output of the laser beam 210 and the optimal divergence angle of the laser beam 210 that should be adjusted by the divergence angle adjustment unit 132. The control unit 140 then increases the divergence angle of the laser beam 210, which is adjusted by the output adjustment unit 120, as the output of the laser beam 210 increases, thereby suppressing fluctuations in the focal position. The control unit 140 is, for example, a computer that runs software.

[0043] As described above, the control unit 140 has information about the relationship between the output of the laser beam 210 and the optimal divergence angle of the laser beam 210 to be adjusted by the divergence angle adjustment unit 132. This information can be generated, for example, based on information obtained by the first transient lens effect measurement method described later.

[0044] (Operation of the laser processing machine) Next, the operation of the laser processing device 100 will be described.

[0045] When performing laser processing using the laser processing device 100, the laser beam 210 emitted from the light source 110 is adjusted by the output adjustment unit 120, which is controlled by the control unit 140, according to the type of workpiece 300 and the processing content. The laser beam 210 with adjusted output has its beam diameter adjusted by the beam diameter adjustment unit 131, its divergence angle adjusted by the divergence angle adjustment unit 132, and then focused and irradiated onto the workpiece 300 by the focusing optical system 133. If necessary, the laser beam 210 is scanned over the workpiece 300 by the focusing optical system 133. By irradiating the workpiece 300 with the laser beam 210 in this way, processing such as cutting, drilling, and scribing can be performed on the workpiece 300.

[0046] The light guide section 130, including the focusing optical system 133, is selected and incorporated in the appropriate position based on the set values ​​(design values) of each optical element. Therefore, under normal circumstances, the laser beam 210 should form a focal point at the position set by the control unit 140. However, when using a high-brightness laser beam 210, a transient lens effect due to a nonlinear optical effect may occur in the transmissive optical element through which the laser beam passes. As a result, the focal point of the laser beam 210 that has passed through the light guide section 130, which includes the transmissive optical element where the transient lens effect occurred, may shift towards the lens side rather than to the intended position.

[0047] In the laser processing apparatus 100 according to this embodiment, the control unit 140 stores the extent to which transient lensing occurs (how much the divergence angle changes) in each transmissive optical element included in the light guide unit 130, or in the light guide unit 130 as a whole, in relation to the output of the laser beam 120. The control unit 140 then changes the divergence angle of the laser beam 210 using the divergence angle adjustment unit 132 to counteract this transient lensing effect. Therefore, in the laser processing apparatus 100 according to this embodiment, fluctuations in the focal point due to transient lensing caused by nonlinear optical effects can be suppressed, and laser processing can be performed appropriately.

[0048] (effect) As described above, the laser processing apparatus 100 according to this embodiment can suppress fluctuations in the focal position due to transient lens effects caused by nonlinear optical effects, thereby enabling appropriate laser processing.

[0049] As mentioned above, even with similar transmissive optical elements, there are differences in the degree to which the transient lensing effect occurs (see Figure 3). Therefore, the control unit 140 cannot simply change the divergence angle of the laser beam 210 according to the output of the laser beam 210 adjusted by the output adjustment unit 120, but rather needs to change the divergence angle of the laser beam 210 by considering how much the transient lensing effect occurs in each transmissive optical element included in the light guide unit 130, or in the light guide unit 130 as a whole. In the laser processing apparatus 100 according to this embodiment, for example, the degree of the transient lensing effect in each transmissive optical element included in the light guide unit 130, or the transient lensing effect in the light guide unit 130 as a whole, measured by the first transient lensing effect measurement method described later, is grasped, and the divergence angle of the laser beam 210 is adjusted by the divergence angle adjustment unit 132. Therefore, in the laser processing apparatus 100 according to this embodiment, laser processing can be performed appropriately under optimal conditions for each apparatus.

[0050] Each component in the laser processing apparatus 100 becomes operational when powered on, but the output of the laser beam 210 changes over time for various reasons. In particular, the output of the light source 110 (laser oscillator) is prone to change from the time the power is turned on until the power supply and temperature stabilize. Furthermore, the output of the light source 110 may also change between different days due to the effects of aging of the light source 110 and changes in the surrounding environment. In the laser processing apparatus 100 according to this embodiment, the amount of adjustment of the divergence angle by the divergence angle adjustment unit 132 is not fixed, but changes according to the output of the laser beam 210. Therefore, the laser processing apparatus 100 according to this embodiment can always perform laser processing appropriately under optimal conditions.

[0051] 2. Method for measuring the first transient lens effect Next, a first measurement method for measuring transient lens effects caused by nonlinear optical effects in the laser processing apparatus described above will be explained. In the first transient lens effect measurement method described here, the transient lens effect is measured by measuring the divergence angle of the laser beam that has passed through a transmissive optical element.

[0052] (Transient lens effect measuring device) Figure 5 is a schematic diagram showing the configuration of a transient lens effect measuring device 400 according to one embodiment of the present invention for carrying out the first transient lens effect measurement method. As shown in Figure 5, the transient lens effect measuring device 400 includes a light source 110, an output adjustment unit 120, an object mounting unit 410, a divergence angle measuring unit 420, and a control unit 430.

[0053] The transient lens effect measuring device 400 according to this embodiment measures the transient lens effect caused by the nonlinear optical effect in the transmissive optical element by measuring the divergence angle of the laser beam 210 that has passed through the transmissive optical element to be measured, which is installed in the object mounting section 410.

[0054] The following describes each component of the transient lens effect measuring device 400.

[0055] The light source 110 and output adjustment unit 120 are the same as those in the laser processing apparatus 100. Also, the two mirrors 134 shown in Figure 5 are the same as those in the laser processing apparatus 100.

[0056] The object mounting section 410 is used to mount the transmissive optical element to be measured. The transmissive optical element to be measured is not particularly limited and may be one or multiple elements. Examples of transmissive optical elements to be measured include lenses, protective windows, beam splitters, and prisms. Figure 5 shows a combination of a convex lens and a concave lens, but the transmissive optical element to be measured may be a single flat protective window. Alternatively, the transmissive optical element to be measured may be the entire light guide section of the laser processing apparatus. For example, in the laser processing apparatus 100 shown in Figure 1, the transient lens effect in the entire light guide section 130 of the laser processing apparatus 100 may be measured by installing the divergence angle measuring section 420 instead of the workpiece 300.

[0057] The divergence angle measuring unit 420 measures the divergence angle of the laser beam 210 based on instructions from the control unit 430. The configuration of the divergence angle measuring unit 420 is not particularly limited as long as it can perform the above functions. The divergence angle measuring unit 420 may be, for example, a beam profiler or M 2 It's a meter.

[0058] The control unit 430 is connected to the light source 110, the output adjustment unit 120, and the beam angle measuring unit 420, and receives information from them and controls their operation. For example, the control unit 430 changes the output of the laser beam 210 using the output adjustment unit 120, while causing the beam angle measuring unit 420 to measure the beam angle of the laser beam 210. The control unit 430 is, for example, a computer that runs software.

[0059] (Method for measuring transient lens effects) Next, as the first method for measuring transient lens effects, the operation of the transient lens effect measuring device 400 will be described.

[0060] The transmissive optical element to be measured is placed in the object placement unit 410. In this state, the control unit 430 controls the light source 110 and the output adjustment unit 120 to irradiate the transmissive optical element to be measured with a laser beam 210 of a predetermined output. At the same time, the control unit 430 measures the divergence angle of the laser beam that has passed through the transmissive optical element to be measured using the divergence angle measuring unit 420. The control unit 430 may also determine whether the measured divergence angle matches the design value, or to what extent it deviates.

[0061] The control unit 430 may control the light source 110, the output adjustment unit 120, and the divergence angle measuring unit 420 to measure the divergence angle of the laser beam 210 that has passed through the transmissive optical element to be measured, while changing the output of the laser beam 210 that irradiates the transmissive optical element to be measured. In this way, information can be obtained about the relationship between the output of the laser beam 210 and the amount of change in the divergence angle (the degree of transient lensing effect caused by nonlinear optical effects) in the transmissive optical element to be measured.

[0062] (modified version) Figure 6 is a schematic diagram showing the configuration of a transient lens effect measuring device 400 according to a modified version of the present invention for carrying out the first transient lens effect measurement method. As shown in Figure 6, the transient lens effect measuring device 400 has a light source 110, an output adjustment unit 120, an object mounting unit 410, a divergence angle measuring unit 420, and a control unit 430, as well as a beam sampler 440 and an output measuring unit 450. This transient lens effect measuring device 400 can also measure the output of the laser beam 210 that has passed through the transmissive optical element to be measured.

[0063] (effect) As described above, the first transient lens effect measurement method makes it possible to measure transient lens effects in a laser processing apparatus that are caused by nonlinear optical effects. The first transient lens effect measurement method can measure the transient lens effect for each transmissive optical element included in the light guide section 130, or it can measure the transient lens effect for the entire light guide section 130. For example, the first transient lens effect measurement method can be used to acquire information that forms the basis for the control of the divergence angle adjustment section 132 by the control unit 140 before the delivery of the laser processing apparatus 100 according to the above embodiment.

[0064] 3. Second method for measuring transient lens effects Next, a second measurement method for measuring transient lens effects caused by nonlinear optical effects in the laser processing apparatus described above will be explained. In the second transient lens effect measurement method described here, the transient lens effect is measured by measuring the output of the laser beam transmitted through the aperture or slit.

[0065] (Laser processing equipment) Figure 7 is a schematic diagram showing the configuration of a laser processing apparatus 500 according to one embodiment of the present invention, which can carry out a second method for measuring transient lens effects. As shown in Figure 7, the laser processing apparatus 500 has, in addition to the configuration of the laser processing apparatus 100 shown in Figure 1, a beam sampler 510, an aperture (or slit) 520, and an output measuring unit 530.

[0066] The laser processing apparatus 500 according to this embodiment guides a portion of the laser beam 210, which has passed through a transmissive optical element included in the light guide unit 130, to an aperture 520, and measures the output of the laser beam 210 that has passed through the aperture 520 to measure the transient lens effect caused by the nonlinear optical effect in the transmissive optical element. In this embodiment, the laser processing apparatus 500 consists of a plurality of reflective optical elements, including a galvanometer scanner, and does not include a transmissive optical element.

[0067] Below, we will only describe the components of the laser processing apparatus 500 that are not included in the laser processing apparatus 100 shown in Figure 1.

[0068] The beam sampler 510 reflects a portion of the laser beam 210 that has passed through the transmissive optical element of the light guide unit 130 toward the aperture 520.

[0069] The aperture 520 has a through-hole that partially allows the laser beam 210 to pass through. The shape of the through-hole of the aperture 520 is not particularly limited and may be circular or not. For example, the aperture 520 may be a so-called slit having a rectangular through-hole.

[0070] The output measurement unit 530 measures the output of the laser beam 210. The configuration of the output measurement unit 530 is not particularly limited as long as it can perform the above functions. The output measurement unit 530 is, for example, a power meter.

[0071] The control unit 140 is connected to the light source 110, the output adjustment unit 120, the divergence angle adjustment unit 132, and the focusing optical system 133, as well as the output measurement unit 530, and receives information from these units and controls their operation. For example, the control unit 140 changes the output of the laser beam 210 using the output adjustment unit 120, while causing the output measurement unit 530 to measure the output of the laser beam 210. The control unit 140 is, for example, a computer that runs software.

[0072] (Method for measuring transient lens effects) Figures 8A and 8B are schematic diagrams illustrating a second method for measuring transient lensing effects. As shown in Figure 8A, the aperture 520 is positioned to block a portion of the laser beam 210 that reaches the output measurement unit 530. In this state, increasing the output of the laser beam 210 may cause transient lensing effects due to nonlinear optical effects in the transmissive optical elements included in the light guide unit 130. When the transient lensing effect occurs, as shown in Figure 8B, the focal point shifts towards the lens, increasing the proportion of the laser beam 210 that reaches the output measurement unit 530. Therefore, by detecting the laser beam 210 that has passed through the aperture 520, it is possible to determine the extent of the transient lensing effect.

[0073] Figure 9 is a graph showing the relationship between the output of the laser beam and the proportion of the laser beam that passed through the aperture for two types of convex lenses. From this graph, it can be seen that with one lens (lens 1), as the output of the laser beam 210 increases, the proportion of the laser beam 210 that passed through the aperture 520 increases, indicating that a transient lens effect due to nonlinear optical effects occurred. On the other hand, with the other lens (lens 2), even when the output of the laser beam 210 is increased, the proportion of the laser beam 210 that passed through the aperture 520 does not change, indicating that no transient lens effect due to nonlinear optical effects occurred.

[0074] As a specific example of a second method for measuring transient lens effects, the operation of the laser processing apparatus 500 shown in Figure 7 will be described.

[0075] The control unit 140 controls the light source 110 and the output adjustment unit 120 to emit a laser beam 210 with a predetermined output. At the same time, the control unit 140 guides the laser beam 210 that has passed through the transmissive optical element included in the laser processing apparatus 500 to the aperture 520, and has the output measurement unit 530 measure the output of the laser beam 210 that has passed through the aperture 520. The control unit 140 compares the output of the laser beam 210 before it passed through the transmissive optical element with the output of the laser beam 210 that has passed through the aperture 520 (for example, it calculates the proportion of the laser beam 210 that has passed through the aperture 520). The control unit 140 may then determine that a change in the focal position due to the transient lensing effect has occurred if the output of the laser beam 210 that has passed through the aperture 520 (or the proportion of the laser beam 210 that has passed through the aperture 520) exceeds a predetermined value.

[0076] The control unit 140 may control the light source 110, the output adjustment unit 120, and the output measurement unit 530 to measure the output of the laser beam 210 after it has passed through the aperture 520 while changing the output of the laser beam 210. In this way, information can be obtained about the relationship between the output of the laser beam 210 in the transmissive optical element being measured and the output of the laser beam 210 after it has passed through the aperture 520 (the degree of transient lensing effect due to nonlinear optical effects).

[0077] (effect) As described above, the second transient lens effect measurement method makes it possible to measure transient lens effects caused by nonlinear optical effects in a laser processing apparatus. The second transient lens effect measurement method can also be used in a laser processing apparatus 500 to measure transient lens effects across the entire light guide section 130 by incorporating the aperture 520 and the output measurement unit 530. For example, the second transient lens effect measurement method can be used after delivery of the laser processing apparatus 500 to calibrate the information that forms the basis for the control of the divergence angle adjustment unit 132 by the control unit 140, or to confirm changes over time in the transmissive optical elements.

[0078] 4. Others In the explanations so far, we have described a laser processing apparatus for cutting or otherwise processing an object, and a method for measuring the transient lens effect in said laser processing apparatus, but the present invention is not limited to these. For example, the present invention can also be applied to exposure apparatus for lithography. [Industrial applicability]

[0079] The laser processing apparatus and transient lens effect measurement method according to the present invention are useful, for example, in the manufacture of semiconductor devices. [Explanation of symbols]

[0080] 100, 500 laser processing equipment 110 Light source 120 Output adjustment section 130 Light guide section 131 Beam diameter adjustment section 132. Spread angle adjustment section 133 Focusing Optical System 134 Mirror 210 Laser Beams 300 objects to be processed 400 Transient Lens Effect Measurement Device 410 Object installation section 420 Angle of spread measurement section 430 Control Unit 440, 510 Sampler 450, 530 Output measurement section 520 Aperture (Slit)

Claims

1. A light source that emits a laser beam, An output adjustment unit that adjusts the output of the laser beam emitted from the light source, A light guide unit that guides the laser beam, whose output has been adjusted by the output adjustment unit, to the workpiece, Control unit and It has, The light guide section is A beam divergence angle adjustment unit for adjusting the divergence angle of the laser beam, A focusing optical system that focuses the laser beam, whose divergence angle has been adjusted by the divergence angle adjustment unit, toward the workpiece, It has, The control unit changes the beam divergence angle of the laser beam, which is adjusted by the beam divergence angle adjustment unit, according to the output of the laser beam adjusted by the output adjustment unit. Laser processing equipment.

2. The laser processing apparatus according to claim 1, wherein the control unit increases the divergence angle of the laser beam adjusted by the divergence angle adjustment unit as the output of the laser beam adjusted by the output adjustment unit increases.

3. The laser processing apparatus according to claim 1 or 2, wherein the control unit changes the divergence angle of the laser beam, which is adjusted by the divergence angle adjustment unit, in order to suppress fluctuations in the focal position of the laser beam due to transient lens effects caused by nonlinear optical effects.

4. A method for measuring transient lens effects caused by nonlinear optical effects in a laser processing apparatus, A method for measuring transient lens effects, comprising the step of measuring the divergence angle of a laser beam that has passed through a transmissive optical element included in the laser processing apparatus.

5. The method for measuring the transient lens effect according to claim 4, wherein in the step of measuring the divergence angle of the laser beam, the output of the laser beam that passes through the transmissive optical element is changed while measuring the divergence angle of the laser beam.

6. A method for measuring the variation in focal position due to transient lens effects caused by nonlinear optical effects in a laser processing apparatus, A method for measuring transient lens effects, comprising the steps of guiding a laser beam that has passed through a transmissive optical element included in the laser processing apparatus to an aperture or slit, and measuring the output of the laser beam that has passed through the aperture or slit.

7. The method for measuring a transient lens effect according to claim 6, further comprising the step of comparing the output of the laser beam before it passes through the transmissive optical element with the output of the laser beam after it has passed through the aperture or the slit.

8. A method for measuring a transient lens effect according to claim 6 or 7, further comprising the step of determining that a change in the focal position due to the transient lens effect is occurring when the output of the laser beam that has passed through the aperture or the slit exceeds a predetermined value.

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