JP2005316071A - Laser machining device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily correct spherical aberration without causing trouble with a simple constitution. <P>SOLUTION: The laser machining device 1 is equipped with a laser beam source for emitting a laser beam L, a beam collimating means for collimating the flux of the laser beam L emitted from the laser beam source to parallel beams, a condensing optical system 3 condensing the laser beam L in a parallel beams state to the medium, a 1st lens group 4 arranged to move along in the optical axis direction of the parallel beams in the parallel beams between the beam collimating means and the condensing optical system 3 and constituted of one or more lenses, a 2nd lens group 5 arranged in a fixed state in the parallel beams between the 1st lens group 4 and the condensing optical system 3 and constituted of one or more lenses, and a moving means 6 for moving the 1st lens group 4 in accordance with the refractive index of the medium to which the laser beam L is to be condensed and a distance from the surface of the medium to the position to which the laser beam L is to be condensed. In the laser machining device 1, the 2nd lens group 5 is arranged so that its focal position on a back side may exist at least near the position of the entrance pupil of the condensing optical system 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser processing apparatus capable of changing a light source position while keeping a light quantity and a light quantity distribution incident on a pupil plane of an optical system constant. In particular, the present invention relates to an optimum laser processing apparatus capable of condensing light at different depths in a medium or a laser processing apparatus suitable for changing a condensing position.

  Conventionally, there has been a demand for focusing at different depths in the medium, but in this case, spherical aberration is caused. For example, in the biological field, when preparing a microscopic specimen, in most cases, a specimen with a cover glass in which a sample is placed on a slide glass and covered with a cover glass is generally used. Thus, the spherical aberration described above occurs when specimens with different cover glass thicknesses are observed. In addition, some LCD glasses have different thicknesses, and spherical aberration occurs even when observing through a substrate. Further, when the spherical aberration amount is different between different thicknesses (depths), there is a possibility that the light condensing performance is changed (deteriorated).

Therefore, conventionally, various techniques have been employed in order to collect light on the portions having different thicknesses as described above while correcting the spherical aberration and suppressing the change in the light collecting performance.
As one of them, for example, one in which parallel plate glasses having different thicknesses are detachably disposed at the tip of a condensing optical system such as an objective lens is known.
Further, for example, an objective lens with a correction ring for a microscope is known in which various aberrations are satisfactorily corrected over a range of an ultra-wide field of view of about 40 × and NA of 0.93, and performance deterioration due to variations in cover glass thickness is small. For example, see Patent Document 1).
Furthermore, an optical system that corrects spherical aberration by moving a spherical aberration correcting optical system at infinity (No Power Lens) in the optical axis direction is also known (for example, see Patent Document 2).
Furthermore, as shown in FIG. 11, a spherical aberration correction lens 52 is disposed between the objective lens 50 and the light source 51, and the spherical aberration correction lens 52 is moved along the optical axis to correct the spherical aberration. A microscope apparatus is known (see, for example, Patent Document 3).
JP-A-5-119263 (FIG. 1 etc.) JP 2003-175497 A (FIG. 1 etc.) JP 2001-83428 A (FIG. 1 etc.)

By the way, among the spherical aberration corrections described above, those using parallel flat glass have a large performance deterioration due to the inclination of the parallel flat glass. Therefore, high accuracy is required for the frame that holds the parallel flat plate, and the fixing of the parallel flat plate to the frame also requires high accuracy, which is expensive. Moreover, it was necessary to perform replacement manually in a small WD, which was a very time-consuming operation. Furthermore, it was difficult to perform continuous variable.
In addition, the correction ring objective lens described in Patent Document 1 has high accuracy and is expensive and cannot be reduced in cost. Further, it is difficult to automatically adjust the spherical aberration amount according to the light collection position, and it is difficult to cope with automation.
Further, in the optical system described in Patent Document 2, the converging position does not change even when the spherical aberration is corrected because the combined focal length is corrected by a lens having an infinite distance. When attempting to focus on different parts of the medium, the WD always changes, and aberration correction cannot be performed under a constant WD. Further, since a spherical aberration correcting optical system is required in addition to the beam expander, the configuration is complicated, the number of parts is increased, and it is difficult to reduce the cost.

In the microscope apparatus described in Patent Document 3, as shown in FIG. 11, the spherical aberration correction lens 52 can be corrected by moving the spherical aberration correction lens 52 in the optical axis direction. With the movement of 52, the diameter of the light beam incident on the objective lens 50 changes. That is, the spread of the light flux changes. Therefore, as shown in FIG. 12, the amount of light changes, and the brightness on the sample surface changes. Here, when there is an image acquisition means, the brightness of the image is detected, and the power of the light source is changed according to the brightness. Although the brightness can be made constant by controlling the brightness on the image side, there is a problem that the device configuration is complicated.
Further, when there is a light amount distribution in the pupil plane, the light amount distribution may also change. There has been a problem that the light collecting performance changes due to such a change in the light amount distribution. Furthermore, since the spherical aberration correction lens 52 is moved based on the electrical signal from the image acquisition means, it takes time.

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a laser processing apparatus that can easily perform spherical aberration correction without taking time and effort with a simple configuration.

In order to achieve the above object, the present invention provides the following means.
According to a first aspect of the present invention, there is provided a laser light source that emits laser light, parallel light beam means that converts the light beam of the laser light emitted from the laser light source into a parallel light beam, and the laser light in the parallel light beam state in a medium. One or more concentrating optical systems for condensing light, and the parallel light flux between the parallel light flux means and the condensing optical system are arranged to be movable along the optical axis direction of the parallel light flux. A first lens group composed of the above-mentioned lenses, and a single lens unit disposed in a fixed state in the parallel light flux between the first lens group and the condensing optical system. A second lens group; and a moving means for moving the first lens group according to a refractive index of the medium on which the laser beam is to be collected and a distance from the medium surface to a position on which the laser beam is to be collected. In the two lens group, the rear focal position is the entrance of the condensing optical system. To provide a laser machining apparatus is arranged at least near the pupil position.

In the laser processing apparatus according to the present invention, the laser light emitted from the laser light source is converted into a parallel light beam by the parallel light beam means, refracted by the first lens group and the second lens group, respectively, and then applied to the condensing optical system. Incident light is collected in the medium. At this time, the light source position can be moved in the optical axis direction by moving the first lens group in the optical axis direction by the moving means. That is, by moving the first lens group, the light source position seen from the second lens group can be changed, and further, the substantial light source position seen from the condensing optical system can be changed.
By moving the first lens group in accordance with the refractive index of the medium to be condensed and the distance from the medium surface to the position to be condensed, the light source position viewed from the condensing optical system can be changed, and a desired position ( The laser beam can be condensed in a state where the generation amount of spherical aberration is suppressed as much as possible in the depth). Therefore, laser processing can be performed with high accuracy, and for example, a wafer or the like can be cut more accurately.
The second lens group is arranged so that the rear focal position of the second lens group coincides with the entrance pupil position of the condensing optical system, and the first lens group even when the first lens group moves along the optical axis. The collimated light beam incident on the lens always has the same light beam diameter at the entrance pupil position of the condensing optical system, regardless of the position of the first lens group, and is collected without being disturbed by the condensing optical system. That is, it is possible to reduce the light amount change at the condensing position, and the light amount distribution on the entrance pupil plane of the condensing optical system does not change, so that the change in the condensing performance can be suppressed.
Furthermore, since the position of the light source can be changed simply by moving the first lens group, there is no need to move the condensing optical system, the stage, etc. in the direction of the optical axis as in the prior art. Accordingly, the configuration can be simplified, and spherical aberration correction can be easily performed without taking time and effort. Further, since it is not necessary to provide a special optical system unlike a conventional correction ring objective lens or the like, the configuration can be simplified and the cost can be reduced.

  According to a second aspect of the present invention, in the laser processing apparatus according to the first aspect of the present invention, the distance from the lower surface of the condensing optical system to the surface of the medium is maintained at a predetermined distance. There is provided a laser processing apparatus including an observation optical system that includes a focus detection unit or an autofocus mechanism.

  In the laser processing apparatus according to the present invention, the distance from the lower surface of the condensing optical system to the surface of the medium can be maintained at a predetermined distance by the observation optical system. When performing general movement, that is, scanning, the depth from the medium surface can be accurately controlled to a desired depth.

  The invention according to claim 3 is the laser processing apparatus according to claim 1 or 2, wherein a relative distance in the optical axis direction between the condensing optical system and the surface of the medium is constant. I will provide a.

  In the laser processing apparatus according to the present invention, the relative distance in the optical axis direction between the condensing optical system and the surface of the medium, that is, the WD is set to be constant, so that the autofocus mechanism can be simplified. Can be configured at low cost.

According to the laser processing apparatus of the present invention, the first lens group is moved in accordance with the refractive index of the medium to be collected and the distance from the medium surface to the position to be collected, so that the light enters the second lens group. The position of the laser beam can be changed, that is, the position of the light source viewed from the condensing optical system can be changed, so that the laser beam is condensed at a desired position (depth) while suppressing the generation amount of spherical aberration as much as possible. be able to. Therefore, laser processing can be performed with high accuracy.
In addition, the second lens group whose rear focal position coincides with the entrance pupil position of the condensing optical system does not change the diameter of the light beam incident on the entrance pupil of the condensing optical system. The light quantity distribution inside can be made constant, and the change in the light collecting performance can be suppressed.
Furthermore, since the position of the light source can be changed simply by moving the first lens group, the configuration can be simplified, and the spherical aberration can be easily corrected without taking time and effort.

Hereinafter, a first embodiment of a laser processing apparatus according to the present invention will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, the laser processing apparatus 1 of the present embodiment includes a laser light source (not shown) that emits laser light L, a lens (not shown) that converts the light beam of the laser light L emitted from the laser light source into a parallel light beam, and the like. The parallel light beam means, the condensing optical system 3 having the objective lens 2 for condensing the laser light L in the parallel light beam state in the medium, and the parallel light beam between the parallel light beam means and the objective lens 2 The first lens (first lens group) 4 is movably arranged along the optical axis direction of the first lens 4 and is fixed in a parallel light beam between the first lens 4 and the objective lens 2. The second lens (second lens group) 5 and the first lens according to the refractive index of the wafer (medium) A where the laser light L is to be collected and the distance from the surface of the wafer A to the position where the laser light is to be collected. 4 is connected to the converging optical system 3 and the moving means 6 for moving 4 It is, and an observation optical system 7 to maintain a distance from the lower surface of the objective lens 2 to the surface of the wafer A to a predetermined distance.
The wafer A is placed on a stage (not shown) that can move in the XY directions.

The first lens 4 is a biconcave lens and is fixed to a lens frame (not shown). The moving means 6 is connected to the lens frame, and moves the first lens 4 via the lens frame. Further, the moving means 6 is connected to a control unit (not shown) and operates in response to a signal from the control unit.
The control unit includes an input unit that can input predetermined information, and a calculation unit that calculates the movement amount of the first lens 4 based on each input information (input data) input by the input unit. Accordingly, the moving means 6 is moved by a predetermined amount according to the calculation result. In addition to the control unit of the moving unit 6, the control unit also controls the laser light source so that the light beam is emitted after the movement of the first lens 4 is completed.

  The second lens 5 is a convex lens, the plane side is directed to the first lens 4 side, that is, the convex surface side is directed to the objective lens 2 side, and the rear focal position is the entrance pupil position of the objective lens 2. It is arranged at a position at least near.

The observation optical system 7 includes a light source 10 that emits linearly polarized semiconductor laser light L ′, a first lens 11 that makes the semiconductor laser light L ′ irradiated from the light source 10 parallel light, and the first lens 11. A polarizing beam splitter 12 disposed adjacent to the second beam 13, a second lens 13 for converging and diverging the semiconductor laser light L ′ transmitted through the polarizing beam splitter 12, and a semiconductor laser light L ′ diverged by the second lens 13. A third lens 14 for collimated light, a quarter-wave plate 15 for converting the polarization of the semiconductor laser light L ′ transmitted through the third lens 14 into circularly polarized light, and a semiconductor laser transmitted through the quarter-wave plate 15 The light L ′ is reflected so that the direction of the optical axis is changed by 90 degrees and incident on the objective lens 2. The return light from the objective lens 2 is reflected by the polarizing beam splitter 12. And a photodiode 19 disposed on the rear side of the fourth lens 18 and cylindrical lens 17 to be incident the body laser beam L 'on the cylindrical lens 17.
The dichroic mirror 16 is set so as to reflect the semiconductor laser light L ′ and transmit light of other wavelengths, for example, the laser light L emitted from the laser light source.

  The polarization beam splitter 12 transmits, for example, P component linearly polarized light, which is a vibration component parallel to the incident surface, of linearly polarized light, and reflects S component light, which is a vibration component perpendicular to the incident surface. It has a function to make it. The control unit feedback-controls the stage based on a detection signal such as a focusing error signal received by the photodiode 19 to move the stage in the vertical direction (optical axis direction). That is, autofocus is performed. Thus, the semiconductor laser light L ′ is adjusted so that the surface of the wafer A is always in focus.

A case will be described in which laser processing is performed by condensing the laser light L at a position having a different depth from the surface of the wafer A by the laser processing apparatus 1 configured as described above.
First, as shown in FIG. 2, the refractive index of the wafer A, the distance from the surface of the wafer A to the position to be condensed, for example, 50 μm, the NA of the objective lens 2, the objective lens 2 and the wafer A are input to the control unit. The distance from the surface, that is, the WD value and the wavefront data measured in advance of the objective lens 2 are input (S1). The calculation unit calculates the amount of movement of the first lens 4 based on the input data (S2). After completion of the calculation, the control unit controls the moving means 6 to move in the optical axis direction based on the calculation result, and moves the position of the first lens 4 to a predetermined position (S3).

After the movement of the first lens 4 is finished, the control unit sends a signal to the laser light source to emit the laser light L (S4). The emitted laser light L is converted into a parallel light beam by the parallel light beam means and is incident on the first lens 4. Then, the laser light L is refracted by the first lens 4 to be in a divergent light state and is incident on the second lens 5. That is, the position of the divergence point of the laser beam L in the optical axis direction is changed by moving the first lens 4. The diverged laser beam L is refracted again by the second lens 5, then enters the objective lens 2 and is condensed from the surface of the wafer A to a desired depth (50 μm).
At this time, as described above, the position of the first lens 4 is moved in the optical axis direction in accordance with the desired depth to adjust the position of the divergence, so that the generation amount of spherical aberration can be suppressed as much as possible. The laser beam L can be efficiently condensed at a desired position.

  In addition, when the laser beam L is condensed at a position different from the above-described condensing point, that is, at a different depth, data including a new distance from the surface of the wafer A is input to the input unit as described above. input. Based on the calculation result by the calculation unit, the control unit operates the moving unit 6 to move the first lens 4 to a new position along the optical axis direction. As a result, the laser light L is refracted at a position different from the position described above to enter a divergent light state and is incident on the second lens 5. At this time, since the laser light L is incident on the first lens 4 in a parallel light flux state, even when the first lens 4 moves along the optical axis, the light beam incident on the first lens 4. If the distance (s) from the axis is constant, the angle (q) of the light beam after passing through the first lens 4 does not change (is parallel). The rays whose angles do not change (parallel) are collected (be sure to pass) at one point on the rear focal plane of the second lens 5. The rear focal position of the second lens 5 and the entrance pupil position of the condensing optical system 3 are arranged so as to coincide with each other, and the parallel light beam incident on the first lens 4 is the position of the first lens 4. Regardless, the light beam diameter is always the same at the entrance pupil position of the condensing optical system 3, and the condensing optical system 3 condenses the light. Since the diameter of the light beam incident on the condensing optical system 3 does not change, it is possible to suppress the change in the light amount at the condensing position and the change in the light amount distribution in the pupil plane as in the prior art.

  Here, when the laser beam L is condensed in the wafer A, the energy is concentrated at one point (condensing point) to cause a crack. In particular, since it is possible to focus the laser beam L in a state where the spherical aberration is suppressed as much as possible at a position where the depth is different, it is possible to accurately generate a crack at a desired position. Then, with the laser beam L condensed at a predetermined depth, the stage is scanned in the horizontal direction and laser processing is performed, thereby connecting adjacent cracks to each other so that the wafer A has an arbitrary size, for example, Can be cut into chips.

In particular, in the present embodiment, since the observation optical system 7 is provided, the scanning can be performed in a state where the distance between the objective lens 2 and the surface of the wafer A is constant when scanning.
That is, when scanning is performed, the linearly polarized semiconductor laser light L ′ is emitted from the light source 10. The irradiated semiconductor laser light L ′ becomes parallel light by the first lens 11 and then enters the polarization beam splitter 12. Then, after becoming P-component linearly polarized light that is a vibration component parallel to the incident surface, the light is converged by the second lens 13 and then diverges. Then, the diverged light becomes parallel light again by the third lens 14 and enters the quarter-wave plate 15. At this time, the parallel light has a light flux width corresponding to the objective lens 2. The semiconductor laser light L ′ that has passed through the quarter-wave plate 15 and becomes circularly polarized light is reflected by the dichroic mirror 16 and enters the objective lens 2. The light incident on the objective lens 2 is illuminated on the surface of the wafer A.

  Next, the light reflected on the surface of the wafer A is collected by the objective lens 2 and then enters the quarter-wave plate 15 reflected by the dichroic mirror 16, and the S component which is a vibration component perpendicular to the incident surface. Becomes polarized light. This light passes through the third lens 14 and the second lens 13, then enters the polarization beam splitter 12, and is reflected toward the fourth lens 18. Then, after being converged by the fourth lens 18, it passes through the cylindrical lens 17 and forms an image on the photodiode 19. The formed detection signal such as a focusing error signal is sent to the control unit (S5). The control unit performs calculation based on the sent detection signal (S6), and moves the stage in the vertical direction (optical axis direction) so that the focus of the semiconductor laser light L ′ matches the surface of the wafer A (S7). ). That is, autofocus is automatically performed and control is performed so that the distance between the condensing optical system 3 and the surface of the wafer A is always constant.

  Thus, scanning can be performed while the distance between the objective lens 2 and the surface of the wafer A is always kept constant. Therefore, even if the stage is slightly curved or there is some error in the movement of the stage, the laser beam L can be accurately condensed to a desired depth. Therefore, scanning can be performed while controlling the condensing position more accurately from the surface of the wafer A, and laser processing can be performed with higher accuracy.

  When changing the position where the laser beam L is condensed when performing the above-described scanning, scanning is performed after the autofocus offset amount calculation (S8) is performed in advance. For example, when scanning is performed with the laser beam L condensed at a depth of 100 μm from the surface and then scanning is performed with the laser beam L condensed at a depth of 50 μm, the WD value needs to be set to an optimum value. There is. As the WD value changes, it is necessary to offset the autofocus by a predetermined amount. In other words, the WD value can be corrected by calculating the autofocus offset amount. After performing this correction, scanning at different depths is performed.

Next, a second embodiment of the laser processing apparatus of the present invention will be described with reference to FIG. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
The difference between the second embodiment and the first embodiment is that, in the first embodiment, the relative distance in the optical axis direction between the objective lens 2 and the surface of the wafer A, that is, the WD was not constant. On the other hand, in the second embodiment, the WD is constant.
That is, after the positions of the stage and the objective lens 2 in the optical axis direction are set in advance, settings are made so that both positions are always maintained at the same position. Therefore, as shown in FIG. 3, it is not necessary to calculate the offset amount again after the autofocus offset amount is initially set, so that the time required for the offset can be shortened and the throughput can be improved.

Next, a third embodiment of the laser processing apparatus of the present invention will be described with reference to FIG. In the third embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
The difference between the third embodiment and the first embodiment is that, in the first embodiment, the first lens 4 is a biconcave lens, whereas the laser processing apparatus of the third embodiment is the first lens. Reference numeral 4 denotes a convex lens, and the plane side faces the second lens 5 side.
In the case of the present embodiment, similarly to the first embodiment, the light beam incident in the parallel light beam state is always refracted in the same state and is incident on the second lens 5 regardless of the position of the first lens 4. The laser processing apparatus of this embodiment has the same operational effects as the laser processing apparatus of the first embodiment.

Next, a fourth embodiment of the laser processing apparatus of the present invention will be described with reference to FIG. In the fourth embodiment, the same components as those in the third embodiment are denoted by the same reference numerals, and the description thereof is omitted.
The difference between the fourth embodiment and the third embodiment is that, in the third embodiment, the second lens group is composed of one convex lens, that is, the second lens 5, whereas the fourth embodiment is different from the fourth embodiment. The second lens group 20 of the embodiment is configured by two lenses 21 and 22.
That is, the second lens group 20 of the present embodiment includes a biconcave lens 21 disposed on the convex lens 4 side as the first lens group and a biconvex lens disposed adjacent to the biconcave lens 21 as shown in FIG. 22. The rear focal position of the entire second lens group 20 is positioned in the vicinity of the entrance pupil position of the objective lens 2.

  The laser processing apparatus of the present embodiment can achieve the same effects as the laser processing apparatus of the third embodiment, and can further increase the distance (distance) between the second lens group 20 and the objective lens 2. It is possible to arrange other observation systems and the like between them, and the degree of freedom in design can be improved.

Next, a fifth embodiment of the laser processing apparatus of the present invention will be described with reference to FIG. In the fifth embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
The difference between the fifth embodiment and the first embodiment is that, in the first embodiment, the first lens group is composed of a single biconcave lens, that is, the first lens 4. The first lens group 25 of the fifth embodiment is configured by two lenses 26 and 27.
That is, as shown in FIG. 6, the first lens group 25 of this embodiment includes a convex lens 26 arranged with the convex portion facing the laser light source and the parallel beam means side, and both arranged adjacent to the convex lens 26. A concave lens 27 is used. Further, the second lens group of the present embodiment is composed of a single biconvex lens 28.
In the case of the present embodiment, similarly to the first embodiment, regardless of the position of the first lens group 25, the light beam incident in the parallel light beam state is always refracted in the same state and enters the second lens 28. . The laser beam apparatus according to this embodiment has the same effects as the laser processing apparatus according to the first embodiment.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, the first lens group and the second lens group may be configured by a single lens as in the first embodiment, or one or more lenses as in the third and fourth embodiments. You may comprise by the lens of. Each lens is not limited to its type, for example, a convex lens, a concave lens, or a biconvex lens, and may be designed in any combination.

In particular, in each embodiment, the moving means 6 may be set so as to move the first lens group so as to satisfy the following expression.
1 / | f | <0.01
Note that | f | is the combined focal length of the first lens group and the second lens group. By doing this, it is possible to have an afocal part.

In each of the above embodiments, the second lens group may be set so as to satisfy the following formula.
f2> 0
Note that f2 is the focal length of the second lens group.
The entrance pupil position of the condensing optical system is often in the condensing optical system, but the entrance pupil position of the condensing optical system 3 is within the optical system by setting the second lens group to a positive power (convex lens). Even if it exists, the rear focal position of the second lens group can be matched with the entrance pupil position of the condensing optical system 3.

In each of the above embodiments, the first lens group and the second lens group may be set so as to satisfy the following expression.
f1 <0
1 ≦ | f2 / f1 | ≦ 5
Note that f1 is a focal length of the first lens group, and f2 is a focal length of the second lens group.
By making the first lens group negative power (concave lens) and the second lens group positive power (convex lens), the configuration can be made compact. Further, since 1 ≦ f2 / f1, the first lens group can be configured easily. Therefore, not only can it be made inexpensive, but also performance degradation can be suppressed. Since | f2 / f1 | ≦ 5, the optical system can be configured compactly.

Further, as described above, the setting of the first lens group and the second lens group is not limited to f1 <0, 1 ≦ | f2 / f1 | ≦ 5. For example, in each of the above embodiments, the following expression is satisfied. You may set as follows.
f1> 0
0.5 ≦ | f1 / f2 | ≦ 2
By doing so, the focal lengths of both lens groups can be made positive, and relaying can be performed near the same magnification with a simple configuration.

In each of the above embodiments, the moving unit is automatically controlled by the control unit. However, based on the calculation result by the control unit, the moving unit is operated to move the position of the first lens group. It doesn't matter.
Further, spherical aberration correction may be performed using the optical system of the present invention in an aberration correction optical system as shown in FIG. That is, the aberration correction optical system 40 is an optical system that condenses a light beam from a light source (not shown), and a plurality of lenses 41, 42, and 43 that satisfy the following formula are exclusively inserted and removed in the optical path. .
2 (d ² + l × fl × d) NA = f × a
Here, d is the distance from the entrance pupil position of the condensing optical system 3 including the objective lens 2 to the plurality of lenses 41, 42, 43, and l is the light source from the entrance pupil position of the condensing optical system 3. Is the focal position of the plurality of lenses 41, 42, 43, NA is the NA of the light source (NA viewed from the condensing lens), and a is the light collecting point. This is the entrance pupil diameter of the optical system 3. The luminous flux is in a divergent light state, and the plurality of lenses 41, 42, 43 are convex lenses.
In the aberration correction optical system 40 configured in this way, in the case of a divergent light source, even if an attempt is made to observe (condensate) a portion having a different depth in the wafer A, the light amount is constant and the light amount distribution in the pupil plane. Observation (condensation) can be performed with a constant amount of spherical aberration suppressed. Further, unlike the conventional case, there is no need to combine an expensive objective lens such as a correction ring objective lens, or to exchange glasses having different thicknesses.

In the aberration correction optical system 40 shown in FIG. 7 described above, a plurality of lenses 41, 42, and 43 that are convex lenses are arranged in the divergent light beam. However, as shown in FIG. , 42, 43 may be arranged. In this case, a plurality of lenses 41, 42, 43
Can be a concave lens.
Furthermore, as shown in FIG. 9, a plurality of lenses 41, 42, and 43 that are concave lenses may be arranged in the parallel light flux.
Furthermore, as shown in FIG. 10, a plurality of lenses 41, 42, and 43 may be arranged after the parallel light beam is once converted into convergent light by the convex lens 45.

In each of the above embodiments, the laser beam is condensed in the wafer. However, the laser beam is not limited to the wafer and may be condensed in the medium. Further, the distance to be condensed is set to 50 μm, 75 μm, and 100 μm from the surface of the wafer, but is not limited to these distances and may be arbitrarily set. In addition, the stage is moved to change the relative distance between the objective lens and the wafer surface in the optical axis direction. However, the present invention is not limited to this. For example, the objective lens is moved using a piezo element or the like. Thus, the relative distance may be changed.
In addition, the observation optical system described in the first embodiment is an example. If the distance from the lower surface of the objective lens to the surface of the wafer can be maintained at a predetermined distance, the optical system such as a lens is combined. It doesn't matter.

Further, the present invention includes the following.
[Additional Item 1]
A laser light source for emitting laser light;
Parallel light flux means for making the light flux of the laser light emitted from the laser light source a parallel light flux;
A condensing optical system for condensing the laser beam in the parallel light beam state in a medium;
A first lens group composed of one or more lenses arranged in the parallel light beam between the parallel light beam means and the condensing optical system so as to be movable along the optical axis direction of the parallel light beam. When,
A second lens group configured by one or more lenses arranged in a fixed state in the parallel light flux between the first lens group and the condensing optical system;
A moving means for moving the first lens group according to the refractive index of the medium on which the laser beam is to be collected and the distance from the surface of the medium to the position on which the laser beam is to be collected;
The laser processing apparatus according to claim 2, wherein the second lens group has a rear focal position disposed at least in the vicinity of an entrance pupil position of the condensing optical system.
[Appendix 2]
The laser processing apparatus according to claim 1,
An observation optical system provided in connection with the condensing optical system, and maintaining a distance from the lower surface of the condensing optical system to the surface of the medium at a predetermined distance;
A laser processing apparatus, wherein the observation optical system includes a focus detection means or an autofocus mechanism.
[Additional Item 3]
In the laser processing apparatus according to claim 1 or 2,
The laser processing apparatus, wherein a relative distance between the condensing optical system and the surface of the medium in the optical axis direction is constant.
[Additional Item 4]
In the laser processing apparatus according to any one of additional items 1 to 3,
The laser processing apparatus, wherein the moving means moves the first lens group to a position satisfying the following formula.
1 / | f | <0.01
| F |; In-focus distance between the first lens group and the second lens group [Appendix 5]
In the laser processing apparatus according to any one of additional items 1 to 4,
The laser processing apparatus, wherein the second lens group satisfies the following formula.
f2> 0
f2: Focal length of the second lens group [Appendix 6]
In the laser processing apparatus according to any one of appendices 1 to 5,
The laser processing apparatus, wherein the first lens group and the second lens group satisfy the following expression.
f1 <0
1 ≦ | f1 / f2 | ≦ 5
f1; focal length of the first lens group f2; focal length of the second lens group [Appendix 7]
In the laser processing apparatus according to any one of appendices 1 to 5,
The laser processing apparatus, wherein the first lens group and the second lens group satisfy the following expression.
f1> 0
0.5 ≦ | f1 / f2 | ≦ 2
f1; focal length of the first lens group f2; focal length of the second lens group [Appendix 8]
A laser light source for emitting laser light;
A condensing optical system for condensing the laser light in a medium,
Depending on the refractive index of the medium on which the laser beam is to be collected and the distance from the surface of the medium to the position on which the laser beam is to be collected, a plurality of lenses that satisfy the following formula are exclusively included in the convergent or divergent light beam of the focusing optical system. A laser processing apparatus having a laser focusing optical system, wherein the laser processing optical system is detachably arranged.
2 (d ² + l × fl × d) NA = f × a
d: Distance from the entrance pupil position of the condensing optical system to the plurality of lenses l: Distance from the entrance pupil position of the condensing optical system to the light source position f: Focal position of the plurality of lenses NA: NA of the light source (condensing lens NA seen from)
a: Entrance pupil diameter of condensing optical system [Appendix 9]
A laser light source that emits a laser beam parallel to the optical axis;
An optical system for condensing the laser beam in a medium,
According to the refractive index of the medium to which the laser beam is to be collected and the distance from the surface of the medium to the position to be collected, a plurality of lenses satisfying the following formula are arranged in the laser beam so as to be detachable exclusively. A laser processing apparatus having a featured laser focusing optical system.
b (f−d) / f = a
b: Diameter of a parallel light flux from the light source d: Distance from the entrance pupil position of the condensing optical system to the plurality of lenses f: Focal position of the plurality of lenses a: Entrance pupil diameter of the condensing optical system

It is a lineblock diagram showing a 1st embodiment of a laser processing device concerning the present invention. It is an example of the flowchart in the case of condensing a laser beam to the desired depth in a wafer with the laser processing apparatus shown in FIG. It is a flowchart explaining 2nd Embodiment of the laser processing apparatus which concerns on this invention, Comprising: It is an example of the flowchart in the case of condensing a laser beam to the desired depth in a wafer with WD constant. It is a block diagram which shows 3rd Embodiment of the laser processing apparatus which concerns on this invention. It is a block diagram which shows 4th Embodiment of the laser processing apparatus which concerns on this invention. It is a block diagram which shows 5th Embodiment of the laser processing apparatus which concerns on this invention. It is a figure which shows the laser processing apparatus which has arrange | positioned the several convex lens so that attachment or detachment is possible in a divergent light beam. It is a figure which shows the laser processing apparatus which has arrange | positioned the several convex lens so that attachment or detachment is possible in a convergent light beam. It is a figure which shows the laser processing apparatus which has arrange | positioned the several concave lens so that insertion or removal is possible in a parallel light beam. It is a figure which shows the laser processing apparatus which converted the parallel light beam into the convergent light with the convex lens, and arranged the several concave lens in the convergent light so that insertion or removal is possible. It is a figure explaining the correction | amendment of the conventional spherical aberration, Comprising: It is a figure which shows an example of the optical system which can move a spherical aberration correction lens to an optical axis direction. It is the figure which showed the state from which the light quantity in an entrance pupil position changes with the optical system shown in FIG.

Explanation of symbols

L Laser light A Wafer (medium)
DESCRIPTION OF SYMBOLS 1 Laser processing apparatus 3 Condensing optical system 4 1st lens (1st lens group)
5 Second lens (second lens group)
6 Moving means 7 Observation optical system 20 Second lens group 25 First lens group

Claims (3)

A laser light source for emitting laser light;
Parallel light flux means for making the light flux of the laser light emitted from the laser light source a parallel light flux;
A condensing optical system for condensing the laser beam in the parallel light beam state in a medium;
A first lens group composed of one or more lenses arranged in the parallel light beam between the parallel light beam means and the condensing optical system so as to be movable along the optical axis direction of the parallel light beam. When,
A second lens group configured by one or more lenses arranged in a fixed state in the parallel light flux between the first lens group and the condensing optical system;
A moving means for moving the first lens group according to the refractive index of the medium on which the laser beam is to be collected and the distance from the medium surface to the position on which the laser beam is to be collected;
The laser processing apparatus according to claim 2, wherein the second lens group has a rear focal position disposed at least in the vicinity of an entrance pupil position of the condensing optical system. The laser processing apparatus according to claim 1,
An observation optical system provided in connection with the condensing optical system, and maintaining a distance from the lower surface of the condensing optical system to the surface of the medium at a predetermined distance;
A laser processing apparatus, wherein the observation optical system includes a focus detection means or an autofocus mechanism. In the laser processing apparatus according to claim 1 or 2,
The laser processing apparatus, wherein a relative distance between the condensing optical system and the surface of the medium in the optical axis direction is constant.

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