Laser processing apparatus and processing method

Abstract

This disclosure provides a laser processing apparatus that allows for easy adjustment of the focusing position of the laser beam. [Solution] A laser processing apparatus according to one aspect of the present disclosure comprises a stage on which a workpiece is placed, a laser unit that emits laser light, a reflecting unit that reflects the laser light emitted from the laser unit toward a workpiece placed on the stage, a first moving means for moving the stage in a first direction parallel to the laser light toward the workpiece placed on the stage, and in a second and third direction which are mutually orthogonal and orthogonal to the first direction, and a second moving means for moving the reflecting unit in the first direction.

Description

Technical Field

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

Background Art

[0002] In recent years, the demand for semiconductors has been increasing in many industries, and it has been required to efficiently manufacture semiconductor wafers. A laser processing method for efficiently manufacturing a wafer for semiconductors by forming a plurality of modified layers in an ingot is known (Japanese Patent Application Laid-Open No. 2020-141009).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the laser processing method described in the above publication, the depth of focus of the laser beam is changed in the axial direction of the ingot, and a plurality of modified layers are formed in order from a deep position to a shallow position. By separating the plurality of modified layers, a plurality of substrate materials can be obtained. In addition, since the focus position of the laser beam is close to the surface of the ingot (the incident surface of the laser beam) in the modified layer formed at the shallow position, it can be formed thinner than the modified layer at the deep position, and it is said that the surface roughness of the separation surface of the substrate material separated by the modified layer at the shallow position can be reduced, and the material loss during polishing can be reduced.

[0005] Since the amount of energy of the laser beam appropriate for forming the modified layer may vary depending on the material and characteristics of the ingot (object to be processed), etc., the position where the laser beam is focused may be intentionally shifted with respect to the center in the axial direction of the formed modified layer. In addition, the position where the modified layer is formed changes depending on the thickness of the obtained substrate material. For this reason, it is desired that the focusing position of the laser beam in the axial direction of the object to be processed can be easily adjusted.

[0006] In light of the circumstances described above, this disclosure aims to provide a laser processing apparatus that allows for easy adjustment of the laser beam focusing position. [Means for solving the problem]

[0007] A laser processing apparatus according to one aspect of the present disclosure, made to solve the above problems, comprises a stage on which a workpiece is placed; a laser unit that emits laser light; a reflecting unit that reflects the laser light emitted from the laser unit toward a workpiece placed on the stage; a first moving means for moving the stage in a first direction parallel to the laser light toward the workpiece placed on the stage, and in a second and third direction which are mutually orthogonal and orthogonal to the first direction; and a second moving means for moving the reflecting unit in the first direction. [Effects of the Invention]

[0008] A laser processing apparatus according to one aspect of this disclosure allows for easy adjustment of the focusing position of the laser beam. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic front perspective view showing a laser processing apparatus according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a schematic side perspective view showing the laser processing apparatus shown in Figure 1. [Figure 3] Figure 3 is a schematic planar perspective view showing the laser processing apparatus shown in Figure 1. [Modes for carrying out the invention]

[0010] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0011] (1) A laser processing apparatus according to one aspect of the present disclosure comprises a stage on which a workpiece is placed, a laser unit that emits laser light, a reflecting unit that reflects the laser light emitted from the laser unit toward a workpiece placed on the stage, a first moving means for moving the stage in a first direction parallel to the laser light toward the workpiece placed on the stage, and in a second and third direction which are mutually orthogonal and orthogonal to the first direction, and a second moving means for moving the reflecting unit in the first direction.

[0012] The laser processing apparatus allows for easy adjustment of the position where the laser beam is focused within the workpiece by moving the reflective portion in the first direction. Therefore, appropriate laser energy can be applied to a predetermined position within the workpiece, and a desired modified layer can be easily formed.

[0013] (2) In (1) above, the reflecting part may have a galvanometer optical system. By having a galvanometer optical system in the reflecting part, the processing of the workpiece can be performed efficiently.

[0014] (3) In (1) or (2) above, in the first direction, the maximum travel distance of the reflective portion by the second moving means may be five times or more the maximum travel distance of the stage by the first moving means. The ability of the reflective portion to move further than the travel distance of the stage improves the ease of processing with the laser light.

[0015] (4) In any of (1) to (3) above, the maximum travel distance of the reflective portion by the second moving means may be 50 mm or more. Having a travel distance of 50 mm or more for the reflective portion makes it easier to apply appropriate laser energy to a desired position within the workpiece.

[0016] (5) In any one of (1) to (4) above, the laser unit may have a spatial light phase modulator that modulates the phase of the laser light. By having the optical phase modulator in the laser unit, the ease of adjusting the position where the laser light is focused can be further improved.

[0017] (6) The processing method according to one aspect of the present embodiment is a method of processing a workpiece using the laser processing apparatus according to any one of (1) to (5) above, including a step of placing the workpiece on the stage, a step of moving the reflection unit, and a step of irradiating the workpiece with the laser light emitted from the laser unit.

[0018] Since the processing method processes the workpiece using the laser processing apparatus according to any one of (1) to (5) above, a desired modified layer can be easily formed inside the workpiece.

[0019] [Details of the Embodiment for Carrying out the Invention] Hereinafter, embodiments of the present disclosure will be described in detail while appropriately referring to the drawings. The drawings are diagrams schematically showing the embodiments, and the shape, size, scale, arrangement, etc. of each component (member) may be different from the actual ones.

[0020] <Laser Processing Apparatus> As shown in FIGS. 1 to 3, the laser processing apparatus 1 mainly includes a stage 10 on which a workpiece T is placed, a laser unit 20 that emits laser light L (illustrated by a dashed line), and a reflection unit 30 that reflects the laser light L emitted from the laser unit 20 toward the workpiece T placed on the stage 10. The stage 10, the laser unit 20, and the reflection unit 30 are arranged inside a casing C. The laser processing apparatus 1 forms a modified layer M inside the workpiece T.

[0021] The modified layer M is formed by the continuous connection of the parts where the composition of the processing object T is modified, which can be caused by any factor that causes the composition change here refers to the focusing of the laser beam L. The processing object T is melted, broken (minute fractures), etc. by the focusing of the laser beam L, resulting in partial modification. The laser beam L is focused at a predetermined position (depth) from the surface of the processing object T (the surface where the laser beam L is incident), and irradiated substantially parallel to the surface, thereby generating a plurality of modified parts. The modified layer M is formed by the continuous progression and connection of these modified parts. The processing object T is separated by this modified layer M, and a wafer or the like can be obtained by polishing the separation surface of the separated processing object T (substrate material).

[0022] 〔Processing Object〕 The processing object T is not particularly limited as long as its interior can be processed by a laser beam. Examples include wafers and ingots for semiconductors. The material of the processing object T is not particularly limited, and examples include SiC (silicon carbide) and GaN (gallium nitride). The shape of the processing object T in plan view is not particularly limited, and for example, it may be substantially circular. The diameter of the substantially circular processing object T is not particularly limited, and it may be 4 inches, 6 inches, 8 inches, or 10 inches.

[0023] 〔Stage〕 The stage 10 is configured to be movable in a first direction (Z direction) parallel to the laser beam L directed towards the placed processing object T, and in a second direction (X direction) and a third direction (Y direction) that are perpendicular to each other and perpendicular to the first direction. That is, the laser processing apparatus 1 includes first moving means (not shown) for moving the stage 10 in the X, Y, and Z directions. The stage 10 moves in the Z direction to adjust the position where the laser beam L is focused, and moves in the X-Y direction when forming the modified layer M. The first moving means is not particularly limited, and for example, it may have a known ball screw, electric motor, etc.

[0024] The amount of movement (movable distance) of the stage 10 by the first moving means described above is not particularly limited, and may be, for example, 300 mm to 500 mm in the X and Y directions, and 80 mm to 150 mm in the Z direction. The movement speed of the stage 10 in the X and Y directions is not particularly limited, and may be, for example, 80 mm / s to 700 mm / s. The upper limit of the minimum movement distance (resolution) of the stage 10 in the Z direction is not particularly limited, and may be 5 μm, 2 μm, or 1 μm. The lower limit of the minimum movement distance described above is not particularly limited, and may be, for example, 0.1 μm. By setting the minimum movement distance within the above range, the focusing position of the laser beam L can be adjusted with high precision.

[0025] [Laser section] The laser unit 20 includes a light source (laser oscillator) that emits short-pulse laser light, an amplifier, an excitation laser that excites the amplifier, and a laser unit 21 that emits laser light L, and a plurality of reflectors 22. The laser unit 21 should be capable of arbitrarily adjusting the wavelength, pulse width, repetition frequency, and output of the emitted laser light L. The laser unit 21 should emit a femtosecond pulse laser.

[0026] The laser unit 20 may have a spatial light phase modulator 23 that modulates the phase of the laser beam L. By having a spatial light phase modulator 23, the irradiation pattern of the laser beam L can be changed, thereby improving the ease of processing (modifying) the workpiece T according to its characteristics. The optical path of the laser beam L may include a first optical path P1 that guides the laser beam L to the reflecting unit 30 without passing it through the spatial light phase modulator 23, and a second optical path P2 that guides the laser beam L to the reflecting unit 30 after passing it through the spatial light phase modulator. The laser unit 20 may have an optical path switching means that can arbitrarily select between the first optical path P1 and the second optical path P2. The optical path switching means of this embodiment includes a first switching reflector 24 and a second switching reflector 25. The first switching reflector 24 and the second switching reflector 25 are configured to swing between a reflection position that reflects the laser beam L and a passing position that allows the laser beam L to pass through without reflection. By controlling the first switching reflector 24 to swing to the reflection position, the second switching reflector 25 is swung to the passing position, and vice versa, the first optical path P1 and the second optical path P2 can be selected.

[0027] The laser unit 20 has an output reflector 26 that reflects the laser beam L so that it is emitted in the Z direction (see Figure 2). The reflector unit 30 has an input reflector 31 that guides the laser beam L reflected by the output reflector 26 into its interior.

[0028] [Reflector] The reflecting unit 30 reflects the laser beam L guided by the incident reflecting mirror 31 toward the workpiece T placed on the stage 10. That is, in addition to the incident reflecting mirror 31, the reflecting unit 30 has one or more internal reflecting mirrors (not shown). The reflecting unit 30 also has a lens (not shown) for focusing the laser beam L that has been reflected toward the workpiece T at a desired position. The laser beam L is focused at the focal point of this lens. Specifically, the cross-sectional diameter of the laser beam L is minimized at the focal point. The reflecting unit 30 may have multiple of the above lenses. Alternatively, the reflecting unit 30 may have lens holding means configured to allow the above lenses to be attached and detached and replaced with any selected lens.

[0029] The reflective section 30 is configured to be movable in the Z direction. That is, the laser processing apparatus 1 includes a second moving means (not shown) for moving the reflective section 30 in the Z direction. The second moving means is not particularly limited and may include, for example, a known electric motor and a ball screw.

[0030] The position where the modified layer M is formed (distance in the Z direction from the surface of the workpiece T) is determined by the thickness of the resulting substrate material. The amount of polishing required to form the substrate material into a wafer changes depending on the surface roughness of the separation surface separated by the formed modified layer M, so the position is determined including this amount of polishing. Because the reflective section 30 can move in the Z direction, the laser processing apparatus 1 can easily adjust the position where the laser beam L is focused even when the above position changes, and can form the modified layer M at the desired position on the workpiece T.

[0031] In the workpiece T, modification may occur not only at the focal point of the laser beam L, but also at a position close to the focal point. Specifically, modification may occur when the laser beam L has sufficient energy before the focal point (upstream of the focal point in the direction of laser beam L propagation). In such cases, the focal point of the laser beam L may be shifted relative to the surface where the modified layer M is to be formed (the separation surface when separated) to form the modified layer M. That is, the focal point may be set to a position deeper than the center in the thickness direction (Z direction) of the modified layer M to be formed. Furthermore, the intensity of the laser beam L in cross-section has a Gaussian distribution, and the rise of the peak is large at the focal point, which can make it difficult to reduce the surface roughness of the separation surface separated by the formed modified layer M. Since the reflective section 30 of the laser processing apparatus 1 can move in the Z direction, the focusing position of the laser beam L can be easily adjusted with respect to the surface on which the modified layer M is to be formed, thereby enabling the formation of the modified layer M at the desired position and allowing easy control of the surface roughness of the separated surface when separated by the formed modified layer M.

[0032] In the Z direction, it is preferable that the maximum travel distance of the reflective section 30 by the second moving means be 5 times or more than the maximum travel distance of the stage 10 by the first moving means. The lower limit of the maximum travel distance of the reflective section 30 relative to the maximum travel distance of the stage 10 by the first moving means may be 8 times or 10 times. The upper limit of the maximum travel distance of the reflective section 30 relative to the maximum travel distance of the stage 10 by the first moving means is not particularly limited and may be, for example, 20 times.

[0033] The maximum travel distance of the reflective section 30 should preferably be 50 mm or more. The lower limit of the maximum travel distance of the reflective section 30 may be 80 mm or 100 mm. The upper limit of the maximum travel distance of the reflective section 30 is not particularly limited and may be, for example, 200 mm. Because the reflective section 30 can move within the above range, the laser processing device 1 can process workpieces T with greatly different thicknesses (length in the Z direction) (for example, workpieces with a thickness of 50 mm or more and workpieces with a thickness of 1 mm or less).

[0034] The upper limit of the minimum travel distance (resolution) of the reflective portion 30 in the Z direction may be 10 nm or 5 nm. The lower limit of the minimum travel distance is not particularly limited and may be, for example, 1 nm. By setting the minimum travel distance within the above range, the focusing position of the laser beam L can be adjusted with high precision.

[0035] The reflective section 30 may have a galvanometer optical system (not shown). The galvanometer optical system has two reflecting mirrors (a first reflecting mirror and a second reflecting mirror) that oscillate to reflect the laser light L at arbitrary angles in the X and Y directions, and two drive units (a first drive means and a second drive means) that drive the oscillation of these two reflecting mirrors. The first reflecting mirror is oscillated by the first drive means to reflect the laser light L at arbitrary angles in the X direction, and the second reflecting mirror is oscillated by the second drive means to reflect the laser light L at arbitrary angles in the Y direction. Because the reflective section 30 has the galvanometer optical system, the laser light L can be moved to any position in the X and Y directions, and the modified layer M can be efficiently formed. Furthermore, since the laser processing apparatus 1 has a stage 10 that can move in the X and Y directions, the modified layer M can be formed beyond the range that the galvanometer optical system can irradiate with laser light L.

[0036] [Processing method] The processing method involves processing a workpiece T with the laser processing apparatus 1. The processing method comprises the steps of: placing the workpiece T on the stage 10; moving the reflector 30; and irradiating the workpiece T with laser light L emitted from the laser unit 20. The irradiation step may include a step of modulating the phase of the laser light L.

[0037] When modulating the phase of the laser beam L, the laser beam L is guided to the second optical path by setting the first switching reflector 24 in the optical path switching means 24 to the passing position and the second switching reflector to the reflection position in the optical path switching means 24, and the phase is modulated by the spatial phase modulator 23. The above phase modulation should be determined according to the material, characteristics, etc., of the workpiece T.

[0038] (Placement process) In the process described above, it is preferable to fix the workpiece T placed on the stage 10. That is, the stage 10 should have fixing means (not shown) for fixing the workpiece T.

[0039] (The process of moving) In the above moving process, the reflector 30 is moved in the Z direction according to the focusing position of the laser beam L so that the modified layer M is formed at the desired position. The stage 10 may also be moved in the Z direction at the same time as the reflector 30 is moved.

[0040] (Irradiation process) In the irradiation process described above, the workpiece T is irradiated with laser light L to form a modified layer M. The modified layer M may be formed by moving the stage 10 in the XY direction, by the galvanometer optical system of the reflecting section 30, or by a combination of these methods.

[0041] After forming a modified layer M by this processing method, a wafer can be obtained by performing the steps of separating the workpiece T with the modified layer M and polishing the separated surface of the workpiece T. In other words, this processing method can be part of a wafer manufacturing method.

[0042] [Other embodiments] The above embodiments do not limit the configuration of the present invention. Accordingly, the above embodiments allow for the omission, substitution, or addition of components of each part of the above embodiments based on the description herein and common technical knowledge, and all such omissions, substitutions, or additions should be interpreted as falling within the scope of the present invention.

[0043] The laser processing apparatus may not have a first moving means. That is, the stage may be immobile in part or all of the X, Y, and Z directions. [Industrial applicability]

[0044] A laser processing apparatus according to one aspect of this disclosure can be suitably used for the efficient manufacture of wafers. [Explanation of symbols]

[0045] 1. Laser processing device 10 stages 20 Laser section 21 Laser Units 22 Reflector 23. Spatial Phase Modulator 24. First switching reflector 25. Second switching reflector 26 Output reflector 30 Reflector 31 Reflector for incidence C Casing L Laser light M Modified layer P1 1st optical path P2 2nd optical path T Workpiece

Claims

1. A stage on which the workpiece to be processed is placed, A laser unit that emits laser light, A reflecting unit that reflects the laser beam emitted from the above-mentioned laser unit toward the workpiece placed on the above-mentioned stage, A first moving means for moving the stage in a first direction parallel to the laser beam directed toward the workpiece placed on the stage, and in a second and third direction which are mutually orthogonal and also orthogonal to the first direction, A second moving means for moving the reflective part in the first direction described above, A laser processing device equipped with the following features.

2. The laser processing apparatus according to claim 1, wherein the reflective portion has a galvanometer optical system.

3. The laser processing apparatus according to claim 1, wherein, in the first direction described above, the maximum travel distance of the reflective portion by the second moving means is five times or more than the maximum travel distance of the stage by the first moving means.

4. The laser processing apparatus according to claim 1, wherein the maximum movement distance of the reflective portion by the second moving means is 50 mm or more.

5. The laser processing apparatus according to any one of claims 1 to 4, wherein the laser unit has a spatial light phase modulator that modulates the phase of the laser light.

6. A method for processing an object using a laser processing apparatus according to any one of claims 1 to 4, The process involves placing the workpiece on the above stage, The process of moving the reflective part, The process involves irradiating the workpiece with laser light emitted from the laser unit. A processing method comprising the following:

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