LASER PROCESSING DEVICE

Abstract

Laser processing device (2), comprising: a clamping table (34) that holds a workpiece (10); a laser beam application unit (4) which applies a laser beam to the workpiece (10) held by the clamping table (34) in order to process the workpiece (10); an X-axis feeding mechanism (50) which performs a relative processing feeding of the clamping table (34) and the laser beam application unit (4) in an X-axis direction; a Y-axis feed mechanism (52) that performs a relative processing feed of the clamping table (34) and the laser beam application unit (4) in a Y-axis direction orthogonal to the X-axis direction; and a control unit (100), wherein the laser beam application unit (4) comprises: a laser oscillator (44) that oscillates a laser, a condenser (42) which condenses the laser beam emitted by the laser oscillator (44) onto the workpiece (10) held by the clamping table (34) at a position in a Z-axis direction orthogonal to the X-axis and Y-axis directions, wherein the condenser (42) is a condenser lens (42a) with a chromatic aberration, a beam splitter (70) arranged on a first beam path (S1) connecting the laser oscillator (44) and the condenser (42), a broadband light source (61) arranged on a second beam path (S2) branched off from the beam splitter (70), a spectroscope (62) which is arranged between the broadband light source (61) and the beam splitter (70) and which diverts the laser beam from the second beam path (S2) to a third beam path (S3), a Z-position detection unit (64) arranged on the third beam path (S3) branched off from the spectroscope (62) and which detects a Z-position in the Z-axis direction of the workpiece (10) according to an intensity of light corresponding to a wavelength of return light (L1) which is generated when the light from the broadband light source (61) is condensed by the condenser (42) and reflected by the workpiece (10) held by the clamping table (34), and a condenser movement mechanism (43) that moves the condenser (42) in the Z-axis direction according to the Z-position.

Description

TECHNICAL BACKGROUND Technical field

[0001] The present invention relates to a laser processing device for applying a laser beam to a workpiece held by a clamping table in order to process the workpiece. Description of the related technique

[0002] A wafer formed with several components such as integrated circuits (ICs) and large scale integrations (LSIs) on a front surface, which is divided by several intersecting division lines, is divided into individual component chips by a laser processing device and the component chips thus divided are used for electrical devices such as mobile phones and PCs.

[0003] The laser processing device comprises a clamping table that holds a workpiece, a laser beam application unit that applies a laser beam to the workpiece held by the clamping table in order to process the workpiece, an X-axis feeder mechanism that performs a processing feed of the clamping table and the laser beam application unit in an X-axis direction, a Y-axis feeder mechanism that performs a processing feed of the clamping table and the laser beam application unit in a Y-axis direction, and a control unit, and can process the wafer with high accuracy.

[0004] Additionally, the laser beam application unit comprising the laser processing device includes one of a type in which a laser beam of such a wavelength that it is absorbed in a workpiece is applied to subject an upper surface of the workpiece to ablation processing (see, for example, Japanese Patent Application No. 2004-188475); and one of such a type in which a laser beam of such a wavelength that it is transmitted through the workpiece is applied to the interior of the workpiece to form a modified layer (see, for example, Japanese Patent No. 3408805).

[0005] In particular, due to variability in the thickness or waveform of the wafer, it might be impossible to form the modified layer at a desired internal position within the workpiece when using this method. In light of this, a technology has been proposed for measuring the height of an upper or lower surface of the wafer using a measuring instrument and for positioning a laser beam condensation point at a suitable internal position of the wafer (see Japanese patent application no. 2012-002604).

[0006] DE 10 2018 214 743 A1 relates to a height detection device for detecting the height of a workpiece, such as a semiconductor wafer or similar, which is held on a clamping table, and to a laser processing device which includes such a height detection device. PRESENTATION OF THE INVENTION

[0007] The technology described in Japanese patent application no. 2012-002604 involves applying light with a predefined wavelength range to the workpiece and obtaining a spectral interference waveform from the reflected light. This allows the height of the wafer, which represents the workpiece, to be detected. However, measuring the wafer height using the spectral interference waveform has a problem: the measurement accuracy is low because a spectral interference waveform generated by a layered material on the upper surface of the wafer acts as a disturbance. Additionally, measurement using the spectral interference waveform requires applying light to a comparatively large measurement area, and it is difficult to perform a highly accurate measurement at a precisely defined baseline within a narrow area.

[0008] Accordingly, an objective of the present invention is to provide a laser processing device that is capable of appropriately measuring the height of a workpiece and performing laser processing at a desired position.

[0009] According to one aspect of the present invention, a laser processing device is provided, comprising: a clamping table that holds a workpiece; a laser beam application unit that applies a laser beam to the workpiece held by the clamping table in order to process the workpiece; an X-axis feed mechanism that performs relative processing feeds of the clamping table and the laser beam application unit in an X-axis direction; a Y-axis feed mechanism that performs relative processing feeds of the clamping table and the laser beam application unit in a Y-axis direction orthogonal to the X-axis direction; and a control unit. The laser beam application unit comprises: a laser oscillator that oscillates a laser; a condenser;the laser beam emitted by the laser oscillator is condensed onto the workpiece held by the clamping table at a position in a Z-axis direction orthogonal to the X-axis and Y-axis directions, wherein the condenser is a condenser lens with chromatic aberration, a beam splitter arranged on a first beam path connecting the laser oscillator and the condenser, a broadband light source arranged on a second beam path branching off from the beam splitter, a spectroscope arranged between the broadband light source and the beam splitter and branching off from the second beam path to a third beam path, a Z-position detection unit arranged on the third beam path branching off from the spectroscope and which detects a Z-position in the Z-axis direction of the workpiece according to a wavelength of return light generated,When the light from the broadband source is condensed by the condenser and reflected by the workpiece held by the clamping table, a corresponding intensity of light is detected, and a condenser movement mechanism moves the condenser in the Z-axis direction according to the Z-position.

[0010] Preferably, the second beam path includes an optical fiber, the light from the broadband light source is guided by the optical fiber, the light applied from an end face of the optical fiber is guided through a collimating lens to the beam splitter, which transmits the light, a clearance adjustment mechanism is arranged in the second beam path to adjust a clearance between the end face of the optical fiber and the collimating lens, and a condensing position of the light from the broadband light source condensed by the condenser is set by the clearance adjustment mechanism.

[0011] Preferably, the laser oscillator oscillates a laser with a wavelength such that it is transmitted through the workpiece, and the condenser positions a condensation point within the workpiece to form a modified layer.

[0012] Preferably, the control unit has a coordinate storage section that stores the Z-position detected by the Z-position detection unit in the Z-axis direction of the workpiece in a Z-axis coordinate together with X-axis and Y-axis coordinates, and the control unit controls the condenser movement mechanism based on the coordinates stored in the coordinate storage section to machine the workpiece held by the clamping table.

[0013] Preferably, the control unit controls the condenser movement mechanism depending on the Z-position detected by the Z-position detection unit in the Z-axis direction in order to machine the workpiece held by the clamping table.

[0014] According to the present invention, several condensation points corresponding to wavelengths contained in the light emitted by the broadband light source are applied to the workpiece, and the height is measured according to the intensity of the light at the wavelength at which the condensation point corresponds to the workpiece. Therefore, suitable height measurement is possible when a layered material is present on the upper surface of the wafer, and measurement accuracy is increased without generating interference, as in the case of a spectral interference waveform. Additionally, since the height of a focused position is measured, a precisely defined base can be measured in a narrow area, such as a road.

[0015] The above and other problems, features and advantages of the present invention and its implementation will best become clearer by studying the following description and attached claims, with reference to the attached drawings, which show some preferred embodiments of the invention, and the invention will be best understood thereby. SHORT FIGURE DESCRIPTION Fig. Figure 1 is a general perspective view of a laser processing device according to an embodiment of the present invention; Fig. 2 is a block diagram representing an optical system of the in Fig. 1 represents the laser processing device shown; Fig. 3 is a side view showing one way in which a condensation point can be formed by a [missing information] at a [missing information] in Fig. 1. The condenser lens arranged in the condenser shown is formed at different positions based on a wavelength; Fig. 4 is a schematic diagram to illustrate the principle of a Fig. 2 illustrated free space adjustment mechanism; Fig. 5 is a schematic diagram showing a transfer example of one through another in Fig. 2 shows the detected waveform of the Z-position detection unit; Fig. 6A is a Z-coordinate table stored in a control unit; Fig. 6B is a table stored in a Z-coordinate memory section of the control unit; Fig. 7A is a side view showing one way in which laser processing is performed while the Z-position is detected; and Fig. Figure 7B is a schematic diagram illustrating a transmission example of a waveform detected by the Z-position detection unit when a Fig. Laser processing is carried out as shown in 7A. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS

[0016] A laser processing device according to embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Fig. Figure 1 shows a general perspective view of a laser processing device 2 according to the present embodiment. The laser processing device 2 comprises a laser beam application unit 4 as a processing means, which is arranged on a base 2A and which applies a laser beam to a plate-shaped workpiece, a holding unit 22, which holds the plate-shaped workpiece, an imaging unit 6, which images the workpiece held by the holding unit 22, a feeding mechanism 23, which performs a relative processing feeding of the laser beam application unit 4 and the holding unit 22 and which moves the imaging unit 6 and the holding unit 22 relative to each other, and a frame body 26 with a vertical wall section 261 erected on a lateral side of the feeding mechanism 23 on the base 2A and a horizontal wall section 262 extending in a horizontal direction from an upper end section of the vertical wall section 261.

[0017] An optical system (to be described later) with the laser beam application unit 4 is housed in the horizontal wall section 262 of the frame body 26. A condenser 42, which forms part of the laser beam application unit 4, is arranged on one side of a lower surface of a tip section of the horizontal wall section 262, and the imaging unit 6 is located next to the condenser 42 in an X-axis direction indicated by an arrow X in the figure. A display unit 8 with a touch panel function for displaying the processing conditions of the laser processing device 2 and for the operator to input the processing conditions is arranged on an upper side of the horizontal wall section 262. Note that a plane defined by the X-axis direction and a Y-axis direction is essentially horizontal.

[0018] As in Fig. As shown in Figure 1, the holding unit 22 comprises a rectangular plate 30, movable in the X-axis direction and attached to the base 2A so that it is movable in the X-axis direction; a rectangular plate 31, movable in the Y-axis direction and attached to the plate 30, movable in the X-axis direction and attached in the Y-axis direction; a cylindrical support column 32, attached to an upper surface of the plate 31, movable in the Y-axis direction; and a rectangular cover plate 33, attached to an upper end of the support column 32. A clamping table 34 is arranged on the cover plate 33 and extends through a slot formed above the cover plate 33. The clamping table 34 holds a circular, plate-shaped body and is designed to be rotatable by a rotary drive unit (not shown) housed in the support column 32.A circular suction clamping device 35, made of a porous material with air ventilation holes and extending essentially horizontally, is arranged on an upper surface of the clamping table 34. The suction clamping device 35 is connected to a suction medium (not shown) by a line extending through the support column 32, and four clamps 36 are arranged at intervals around the circumference of the suction clamping device 35. The clamps 36 engage an annular frame when the plate-shaped body held by the frame is attached to the clamping table 34.

[0019] The feeding mechanism 23 has an X-axis feeding mechanism 50 and a Y-axis feeding mechanism 52. The X-axis feeding mechanism 50 converts a rotary motion of a motor 50a into a linear motion via a ball screw 50b, transmits the linear motion to the plate 30, which is movable in the X-axis direction, and moves the plate 30, which is movable in the X-axis direction, back and forth along guide rails 27 at the base 2A in the X-axis direction. The Y-axis feed mechanism 52 converts a rotary motion of a motor 52a into a linear motion via a ball screw spindle 52b, transmits the linear motion to the plate 31 movable in the Y-axis direction and moves the plate 31 movable in the Y-axis direction back and forth along the guide rails 37 on the plate 30 movable in the X-axis direction.

[0020] The laser processing device 2 according to the present embodiment has an X-axis direction feed rate detection means 28 for detecting the feed rate (X-coordinate position) in the X-axis direction of the clamping table 34. The X-axis direction feed rate detection means 28 has a linear scale 28a arranged along the guide rail 27 and a read head (omitted in the illustration) which is arranged on the side of the lower surface of the X-axis movable plate 30 and which moves along the linear scale 28a together with the X-axis movable plate 30. In the present embodiment, the read head of the X-axis direction feed rate detection means 28 sends a pulsed signal with one pulse per 1 µm to a control unit 100.

[0021] Furthermore, the laser processing device 2 has a Y-axis direction feed rate detection means 38 for detecting the Y-axis feed rate (Y-coordinate position) in the Y-axis direction of the plate 31, which is movable in the Y-axis direction. The Y-axis direction feed rate detection means 38 has a linear scale 38a arranged along the guide rail 37 on the plate 30, which is movable in the X-axis direction, and extending in the Y-axis direction, and a read head (not shown in the illustration) which is arranged on the side of the lower surface of the plate 31, which is movable in the Y-axis direction, and which moves along the linear scale 38a together with the plate 31, which is movable in the Y-axis direction. Similar to the X-axis direction feed rate detection device 28, the Y-axis direction feed rate detection device 38 sends a pulsed signal of one pulse per 1 µm to the control unit 100.The control unit 100 detects the Y-coordinate position of the clamping table 34 by counting the pulsed signal input to it. While the X- and Y-coordinate positions of the clamping table 34 of the holding unit 22 are accurately detected by the X-axis direction input quantity detection means 28 and the Y-axis direction input quantity detection means 38, the clamping table 34 can be moved relative to the imaging unit 6 and the laser beam application unit 4 and positioned at a desired position.

[0022] The imaging unit 6 images the plate-shaped body held by the clamping table 34 forming the holding unit 22 and is used for alignment in order to align the condenser 42 of the laser beam application unit 4 with a processing area of ​​the plate-shaped body.

[0023] The laser processing device 2 includes the control unit 100. The control unit 100 includes a computer and has a central processing unit (CPU) for performing arithmetic operations according to a control program, a random access memory (ROM) for storing the control program and the like, a working memory (RAM) capable of reading and writing to temporarily store detection values, calculation results, and the like, an input interface, and an output interface (details omitted from the illustration). Note that while the control unit 100 is in Fig. 1 is shown outside the laser processing device 2 for easier explanation, but in practice it is housed inside the laser processing device 2.

[0024] The workpiece 2 to be processed by the laser processing device 2 with a laser is, for example, a semiconductor wafer 10, as shown in Fig. Figure 1 shows that the wafer 1 has several structural elements formed on one of its surfaces, while it is subdivided by several roads 12 and is held to an annular frame F by an adhesive strip T. With reference to Fig. Section 2 below describes the optical system containing the laser beam application unit 4. Note that for the sake of simplicity, the dimensional relationships of the components shown in Section 2 are simplified. Fig. The two depicted configurations are appropriately adapted and differ from the actual dimensional relationships.

[0025] As in Fig. As shown in Figure 2, the laser beam application unit 4 comprises a laser oscillator 44, which oscillates a laser; a condenser 42, which condenses a laser beam LB emitted by the laser oscillator 44 onto a wafer 10 held by the clamping table 34 of the holding unit 22; a beam splitter 70 arranged in a first beam path S1, which connects the laser oscillator 44 and the condenser 42; a broadband light source 61 arranged in a second beam path S2 branching off from the beam splitter 70; a spectroscope 62, which is arranged between the broadband light source 61 and the beam splitter 70 and which branches off from the second beam path S2 to a third beam path S3; and a Z-position detection unit 64, which is arranged in the third beam path S3 branching off from the spectroscope 62 and which detects a Z-position in the Z-axis direction. which is the surface position of wafer 10, detected according to the intensity of light corresponding to the wavelength of the feedback light L1,This is generated when light L0 from the broadband light source 61 is condensed by the condenser 42 and reflected from the wafer 10 held by the holding unit 22, and a condenser movement mechanism 43 is provided that moves the condenser 42 in the Z-axis direction shown by R1 or R2 in the figure according to the Z-position (Z-coordinate) detected by the Z-position detection unit 64. The condenser movement mechanism 43 includes, for example, a piezoelectric element, a voice coil motor, or the like, and is precisely controlled based on a command signal generated by the control unit 100.

[0026] The laser oscillator 44 emits the laser beam LB, for example, such that it is transmitted through the wafer 10 at a wavelength of 1340 nm. The beam splitter 70, arranged in the first beam path S1, has, for example, a dichroic mirror. The beam splitter 70 is arranged such that it reflects light with a wavelength of 1300 to 1400 nm, including the wavelength of the laser beam LB emitted by the laser oscillator 44, and transmits light with other wavelengths. The laser beam LB reflected by the beam splitter 70 is directed to the condenser 42, and the condensation point is positioned by a condenser lens 42a at a predetermined inner position of the wafer 10 to form a modified layer.

[0027] The second beam path S2 mentioned above consists primarily of an optical fiber FB. The broadband light source 61 is located at one end of the second beam path S2, and the broadband light L0 emitted by the broadband light source 61 could be white light containing a balanced range of wavelengths, for example, from 150 to 850 nm. The light source 61 could be, for example, a halogen light source, a light source with a superluminescent diode (SLD), a light source with a light-emitting diode (LED), a supercontinuum light source, etc. The wavelength range of the light L0 emitted by the broadband light source 61 is not limited to the range mentioned above and could be a narrower or a wider range.

[0028] The light L0 generated by the broadband light source 61 travels directly forward through the spectroscope 62, and the light L0 applied by an end face 63 of the optical fiber FB is guided by a collimating lens 65 arranged on the second beam path L2. A clearance adjustment mechanism 80, which supports the area surrounding the end face 63 of the optical fiber FB and adjusts the clearance between the end face 63 and the collimating lens 65, is arranged on the second beam path S2. The clearance adjustment mechanism 80 comprises a holding device 82 for an optical fiber, which supports the area surrounding the end face 63 of the optical fiber FB, a pulse motor 84, and a ball screw 86, which transmits the rotation of the pulse motor 84 to the holding device 82 for the optical fiber and converts the rotation into a linear motion.With the pulse motor 84, which can be rotated normally or backwards, the position of the end surface 63 of the optical fiber FB can be moved forwards or backwards in the direction indicated by an arrow R3 or R4.

[0029] The light L0 applied from the end face 63 of the optical fiber FB and guided to the collimation lens 65 is transmitted through the beam splitter 70 to be directed to the first beam path S1 and is guided into the condenser lens 42a arranged on the condenser 42. In the present embodiment, the condenser lens 42a is a condenser lens with chromatic aberration, and the L0 transmitted through the condenser lens 42a forms a condensation point at positions different based on wavelengths over a predetermined range (approximately 30 µm) on the optical axis of the condenser lens 42a, including the front surface of the wafer 10 held on the clamping table 34. In particular, as shown in Fig. Figure 3 shows that, in the case where a condensation point P0 of the light contained in the light L0 with a wavelength of 500 nm is located on the front surface 10a of the wafer 10, the condensation point of the light with a wavelength shorter than 500 nm forms on the upper side relative to the position where the condensation point P0 of the light with a wavelength of 500 nm is formed; for example, a condensation point P1 of the light with a wavelength of 200 nm is formed 15 µm above the position of the condensation point P0. Additionally, the condensation point of the light with a wavelength longer than 500 nm is formed on the lower side relative to the position where the condensation point P0 is formed; for example, a condensation point P2 of the light with a wavelength of 800 nm is formed 15 µm below the position of the condensation point P0.In other words, the condensation point of the light L0 generated by the broadband light source 61 is formed by the action of the condenser lens 42a in the range of approximately -15 to +15 µm with respect to the position of the upper surface of the wafer 10.

[0030] The principle of the aforementioned free-space adjustment mechanism 80 is explained with reference to Fig. 4 will be described. Note that Fig. Figure 4 is a schematic representation to explain the effect of the free-space adjustment mechanism 80, in which components such as the beam splitter 70, the condenser 42, and the optical fiber holder 82 are omitted. A focal point position at which the light L0 applied by the end face 63 of the optical fiber FB is collimated by the collimating lens 65 to become parallel light is designated as a reference position B. In the case where the end face 63 of the optical fiber FB is located at the reference position B, the light passing through the collimating lens 65 and the condenser lens 42a forms a condensation point at a position designated PB in the figure.

[0031] In the case where the end face 63 of the optical fiber FB is moved relative to the reference position B in the direction indicated by arrow R3, the light L0 travels from the end face 63 as shown by a dashed line, and the position of a condensation point Pa formed by the condenser lens 42a is moved upwards relative to the condensation point PB formed when the end face 63 is at the reference position B. Conversely, if the end face 63 of the optical fiber FB is moved relative to the reference position B in the direction indicated by arrow R4, the light L0 travels from the end face 63 as shown by a solid line, and the position of a condensation point Pb formed by the condenser lens 42a is moved downwards relative to the aforementioned condensation point PB.The condensation point position of the light L0 can be set to any position independently of the condensation point position of the laser beam LB, which is applied as it passes through the first optical beam path S1 set by such an action of the free-space adjustment mechanism 80. Note that, since the condenser lens 42a is a condenser lens with chromatic aberration as described above, when the end face 63 of the optical fiber FB is moved vertically by the free-space adjustment mechanism 80, the entire portion of the predetermined area over which the condensation point is formed based on a wavelength of the light contained in the light L0 is moved vertically.

[0032] As in Fig. As shown in Figure 3, if the predefined area over which the condensation point of the light L0 is formed is positioned near the front surface 10a of the wafer 10, the light with a predefined wavelength that formed the condensation point is reflected at the front surface 10a of the wafer 10 to generate feedback light L1. The feedback light L1 is not broadband light, but is light that mainly contains the predefined wavelength that formed the condensation point described above, which was positioned at the front surface 10a of the wafer 10.

[0033] As from Fig. As can be seen in Figure 2, the return light L1 reflected from the front surface 10a of the wafer 10 reaches the spectroscope 62 by traveling back through the beam path along which the light L0 applied by the broadband light source 61 travels, that is, through the beam splitter 70, the collimating lens 65, and the optical fiber FB. As shown in the figure, it is then diverted by the spectroscope 62 into the third beam path S3, which is distinct from the second beam path S2 and in which the broadband light source 61 is located, in order to be directed to the Z-position detection unit 64. The spectroscope 62 is designed to divert the light traveling through the optical fiber FB, and, for example, a known optical circulator could be used as the spectroscope 62.

[0034] The Z-position detection unit 64, for example, comprises a diffraction grating 64a, which splits and scatters the input return light L1 on a wavelength basis, and a line sensor 64b, which receives the light L2 split by the diffraction grating 64a and detects the optical intensity on a wavelength basis according to the position at which the light is received. The line sensor 64b is a sensor in which several light-receiving elements, such as charge-coupled devices (CCDs), are arranged in a row in a predetermined direction and detects an optical intensity through each light-receiving element. A signal detected by the line sensor 64b is transmitted to the control unit 100, and the wavelength and optical intensity of the return light L1 are detected based on the signal detected by the Z-position detection unit 64.

[0035] The control unit 100 of the present embodiment comprises a Z-coordinate table 110, which is used when the Z-position is detected by the Z-position detection unit 64, and a coordinate storage section 120 in which the detected Z-position (Z-coordinate) in the Z-axis direction of the front surface 10a of the wafer 10 is stored in correlation with an X-axis coordinate and a Y-axis coordinate, which are detected by the X-axis direction feed rate detection means 28 and the Y-axis direction feed rate detection means 38. The control unit 100 generates a function of controlling the condenser movement mechanism 43 to move the condensation point position of the condenser 42 depending on the Z-position stored in the coordinate storage section 120 and of applying laser processing to the wafer 10 held by the holding unit 22.

[0036] The laser processing device 2 of the present embodiment essentially has the configuration as described above, and the method of laser processing to be applied to the wafer 10 as a workpiece using the laser processing device 2 will be described below.

[0037] At the time of performing laser processing by the in Fig. In the laser processing device 2 shown above, the wafer 10, which is carried on the ring-shaped frame F by the adhesive strip T, is prepared, placed on the clamping table 34 and held under suction by actuating the suction device not shown.

[0038] Next, the feed mechanism 23 is actuated to position the clamping table 34 directly below the imaging unit 6. The surface of the wafer 10 is imaged, and an imaging process such as a pattern comparison is performed to detect the position of the path 12 on the wafer 10, onto which the laser beam LB is to be applied (alignment). After the alignment has been performed, the clamping table 34 is moved further, and an end section of the path 12, where laser processing on the wafer 10 is to be initiated, is positioned directly below the condenser 42.

[0039] When the processing start position on the wafer 10 is positioned directly below the condenser 42, the condenser movement mechanism 43 is actuated based on a control signal from the control unit 100, and the condensation point P0 of the light L0 condensed by the condenser lens 42a of the condenser 42, formed by the light with a wavelength of 500 nm, is formed at a height above the front surface 10a of the wafer 10 based on shape information (see Fig. 3) In this case, in the free-space adjustment mechanism 80, the end face 63 of the optical fiber FB is positioned at the reference position where the light L0 applied by the end face 63 of the optical fiber FB is collimated by the collimating lens 65 to be parallel light, and the end face 63 is positioned on a shape base of the wafer 10 precisely at a position according to a thickness. Note that the X-coordinate and the Y-coordinate of the processing start position are specified by the X-axis direction feed rate detection means 28 and the Y-axis direction feed rate detection means 38 and are, for example, (X1, Y1).

[0040] However, there may be slight variability in the thickness of wafer 10 depending on its position, or wafer 10 may have a wave-like shape. Therefore, in practice, as described above, even if the condensation point P0 of the light condensed by condenser 42 is positioned at a specific position on a shape basis according to the thickness of wafer 10, it might not necessarily be located on the front surface 10a of wafer 10.

[0041] In the present embodiment, the broadband light source 61 is actuated and the condenser movement mechanism 43 is actuated to apply light L0, which is white light. As described above, the light L0 applied by the broadband light source 61 is guided through the second beam path S2, the beam splitter 70, and the first beam path S1 to the condenser lens 42a and forms a condensation point near the front surface 10a of the wafer 10. Since the condenser lens 42a is a condenser lens with chromatic aberration, the light L0 forms condensation points at different positions over a predetermined width on the optical axis of the condenser lens 42a according to the length of all wavelengths constituting the light L0 over a predetermined area, including the front surface 10a of the wafer 10 held by the clamping table 34. In view of this, as in Fig. Figure 3 shows the condenser movement mechanism 43 to position the condensation point P0 exactly at the position where the front surface 10a of the wafer 10 is located, adjusted so that the light with the wavelength (500 nm) that formed the condensation point at the position designated by P0 is most strongly reflected.

[0042] The return light L1 reflected at the position designated P0 is guided through the first beam path S1 and the second beam path S2 to the spectroscope 62, and the light L1 branched off to the third beam path S3 and guided to the Z-position detection unit 64 passes through the diffraction grating 64a of the Z-position detection unit 64, is thereby converted into scattered light L2 according to the length of a wavelength, and is applied to the light sensor 64b. Here, in the case where the scattered light L2 is directed to the Z-position detection unit 64, since the scattered light L2 is not broadband light but is light obtained by strong reflection of the light with a wavelength (500 nm) that has formed the condensation point at the position designated P0 in the figure, the optical intensity signal of the scattered light L2 applied to the line sensor 64b is transmitted to the control unit 100 in order to generate a Fig. 5 to form the waveform shown in (a) (represented by a solid line).

[0043] If a peak is formed at a position corresponding to a wavelength of 500 nm by the scattered light L2, as mentioned above, the following applies: Fig. The Z-coordinate table 110 shown in Figure 6A, which was previously stored in the control unit 100, is used. The Z-coordinate table 110 is a table in which wavelengths at which peaks of a waveform detected by the line sensor 64b appear are recorded, and the corresponding Z-coordinates are recorded. In the case where the wavelength at which a peak of a waveform formed by the feedback light L1 reflected at (X1, Y1) is 500 nm, it is detected, with reference to the Z-coordinate table 110, that the Z-coordinate (Z) 11 ) “0.0 µm”. If the value of Z 11In this way, each value is detected at (X1, Y1, Z). 11 ) of the prepared in control unit 100 in Fig. 6B shows coordinate storage section 120 stored.

[0044] Next, the X-axis feed mechanism 50 is actuated to feed the clamping table 34 by a predetermined distance in the X-axis direction, thereby positioning the next Z-position measurement point (X2, Y1) directly below the condenser 42. In this case, the feedback light L1 reflected at (X2, Y1) is directed to the Z-position detection unit 64, and the scattered light L2 is directed to the line sensor 64b. If the waveform formed by the line sensor 64b in this case exhibits a Fig. 5. The waveform shown in (b) (represented by a dotted line) indicates that the condensation point formed by a wavelength of 700 nm is positioned on the front surface 10a of wafer 10 and, using the waveform shown in (b), is located on the front surface 10a of wafer 10. Fig. 6A shown in the Z-coordinate table 110 detects that the Z-coordinate value (Z 21 ) at (X2, Y1) is "-10.0 µm". If the value of Z 21 In this way, each value is detected at (X2, Y1, Z). 21 ) of the coordinate storage section 120 of the control unit 100.

[0045] Furthermore, the X-axis feed mechanism 50 is actuated to feed the clamping table 34 in the X-axis direction by a predetermined distance, and the next Z-position measuring point (X3, Y1) is positioned at the condenser 42. In this case, the feedback light L1 reflected at (X3, Y1) is directed to the Z-position detection unit 64, and the scattered light L2 is directed to the line sensor 64b. In the case where the waveform formed by the line sensor 64b in this case is a Fig. 5. The waveform shown in (c) (represented by a dotted line) indicates that the condensation point formed by a wavelength of 300 nm is positioned on the front surface 10a of the wafer and, using the waveform shown in (c), that the condensation point is located on the front surface 10a of the wafer. Fig. 6A shown in the Z-coordinate table 110 detects that the Z-coordinate value (Z 31 ) at (X3, Y1) is "+10.0 µm". If the value of Z 31In this way, each coordinate value is detected at (X3, Y1, Z). 31 ) of the coordinate storage section 120 of the control unit 100.

[0046] In the manner described above, while the clamping table 34 is advanced in the X-axis direction by the specified distance, the Z-position is detected and stored in the coordinate storage section 120 in the state in which it is correlated with the X-coordinate and the Y-coordinate. After the Z-position has been detected and stored along the entire range of a road 12, the Y-axis feed mechanism 52 is actuated to position the adjacent road 12 at a position directly below the condenser 42. Then, similarly to the above, the Z-position corresponding to the X-coordinate and the Y-coordinate is detected, and each value is stored as described above. Fig. Figure 6B is stored in coordinate storage section 120. Such a measurement is performed over the entire area of ​​wafer 10, allowing the Z-coordinate or thickness to be detected over the entire area of ​​the front surface 10a of wafer 10. Note that, since variability in the thickness of wafer 10 generally does not occur suddenly, the specified distance for Z-position detection can, for example, be the width between adjacent roads 12, and a value obtained by performing an interpretation calculation or the like can be used for a Z-position between adjacent roads 12.

[0047] With the aforementioned design, it is ensured that even if there is variability in thickness or a wavy surface on wafer 10, or if a layered material is present on the front surface 10a of wafer 10, the height of the front surface 10a of wafer 10 can be measured appropriately, and measurement accuracy is increased without being affected by disturbances, such as those that occur when using a spectral interference waveform. Furthermore, since the height position is measured by the feedback light L1 at the position where the condensation point is formed, advantageous measurement is possible even when measuring the height in a narrow range, such as when measuring the height position of road 12.

[0048] After the Z-positions are stored across the entire area of ​​the front surface 10a of the wafer 10 in the state correlated with the X- and Y-coordinates as described above, a laser beam LB is applied to the wafer 10 by the laser beam application unit 4 to perform laser processing. In this case, the condenser movement mechanism 43 is actuated based on the Z-position temporarily stored in the coordinate storage section 120, thereby moving the condenser 42 forward or backward in the Z-axis direction.In particular, in the present embodiment, the laser processing device 2 actuates the X-axis feed mechanism 50 and the Y-axis feed mechanism 52 to move the clamping table 34, positions the condensation point of the laser beam LB with a wavelength (1340 nm) such that it is transmitted through the wafer 10, at a position at a predetermined depth (for example 50 µm) from the front surface 10a of the wafer 10 and forms a modified layer.In this case, while the X-coordinate and Y-coordinate of the laser beam application position LB are detected by the X-axis direction input detection means 28 and the Y-axis direction input detection means 38, the height of the front surface 10a of the wafer 10, which is to serve as a reference point for the formation of the modified layer, is set to the Z-position stored in the coordinate storage section 120 in the state correlated with the X-coordinate and the Y-coordinate. Consequently, the condensation point of the laser beam LB can be suitably positioned at the specified depth (50 µm) from the front surface 10a of the wafer 10 across the entire area of ​​the wafer 10.

[0049] The present invention is not limited to the embodiment described above, and various modifications are provided. In the embodiment described above, an example is given in which, prior to laser processing of the wafer 10, the Z-position (Z-coordinate) at each measuring point on the front surface 10a of the wafer 10 is temporarily detected, the Z-positions are stored in the coordinate storage section 120 of the control unit 100 in a state correlated with the X-coordinates and the Y-coordinates, and laser processing is carried out while the condenser movement mechanism 43 is actuated based on the Z-position stored in the coordinate storage section 120. However, the procedure for laser processing carried out based on the present invention is not limited to this. With reference to Fig. 7A as well Fig. Section 7B below describes other embodiments of laser processing operations performed using the laser processing device described above.

[0050] As in Fig. As shown in Figure 2, the beam splitter 70 is arranged in the optical system comprising the laser processing device 2, and the beam splitter 70 transmits the light L0, which consists of wavelengths other than 1300 to 1400 nm, while reflecting the laser beam LB with a wavelength of 1340 nm. Here, even when the laser beam LB is applied to the wafer 10 to form a modified layer within the wafer 10, light with wavelengths other than the reflected light of the laser beam LB is not emitted from the front surface of the wafer 10. Therefore, even if broadband light L0 is simultaneously applied by the broadband light source 61 while the laser beam LB is applied to perform laser processing, it is possible to detect the height of the wafer 10.Using this, the control unit 100 can control the condenser movement mechanism 43 depending on the position detected by the Z-position detection unit 64 in the Z-axis direction and can process the wafer 10 held by the clamping table 34 of the holding unit 22. The procedure is described in more detail below.

[0051] In the case of performing laser processing to form a modified layer within the wafer 10 according to the present embodiment, the condenser movement mechanism 43 is first actuated to establish a condensation point position PS of the laser beam LB at a predetermined depth position from the front surface 10a of the wafer 10, for example at a depth position of 50 µm from the front surface 10a, as shown in Fig. Figure 7A shows how to position the condenser lens 42a. Furthermore, by actuating the clearance adjustment mechanism 80, a center position P0 of a predetermined region on the optical axis, where the condensation point is formed by the light L0 applied by the broadband light source 61, is set to be 50 µm above the condensation point position PS of the laser beam LB. The center of the region where the condensation point is formed by the light L0 is a condensation point formed by light with a wavelength of 500 nm. Note that if the position at which the modified layer is to be formed is not the depth position of 50 µm from the front surface 10a of the wafer 10, the clearance adjustment mechanism 80 is actuated according to the depth position to set the center position P0 of the predetermined region on the optical axis of the condenser lens 42a, where the condensation point of the light L0 is to be formed.

[0052] After the position of the condensation point P0 is set by actuating the clearance adjustment mechanism 80, the X-axis feed mechanism 50 and the Y-axis feed mechanism 52 are actuated to move the clamping table 34. This positions the wafer 10 directly under the imaging unit 6. The surface of the wafer 10 is imaged, and an imaging operation, such as a pattern comparison, is performed to align the processing position (path 12) on the wafer 10 with the laser beam application position of the laser beam delivered by the condenser 42 of the laser beam application unit 4. Once the alignment is complete, the clamping table 34 moves further to position an end section of the path, where laser processing on the wafer 10 is to begin, directly under the condenser 42.

[0053] After the laser processing start position is set directly below the condenser 42, the broadband light source 61 is activated to apply light L0, which is white light. The light L0 applied by the broadband light source 61 is guided through the second beam path S2, the beam splitter 70, and the first beam path S1 to the condenser lens 42a, forming a condensation point near the front surface 10a of the wafer 10. Since the condenser lens 42a is a condenser lens with chromatic aberration, the light L0 forms condensation points at different positions over a predetermined width on the optical axis of the condenser lens 42a, corresponding to the length of each wavelength of the light L0 within a predetermined area that includes the front surface 10a of the wafer 10 held by the clamping table 34.

[0054] The laser processing of the present embodiment is configured such that the X-axis feed mechanism 50 and the Y-axis feed mechanism 52 are actuated to move the clamping table 34, and a condensation point of the laser beam LB with a wavelength (1340 nm) such that it is transmitted through the wafer 10 is positioned at a depth of 50 µm from the upper surface 10a of the wafer 10 in order to form the modified layer. In this case, while the X-coordinate and the Y-coordinate of the application position of the laser beam LB are detected by the X-axis direction feed rate detection means 28 and the Y-axis direction feed rate detection means 38, the condensation point PS is positioned at a location where the modified layer is to be formed. Here, as in Fig. Figure 7A shows that, in the case where the condensation point P0 is positioned at the location of the front surface 10a of the wafer 10, the light with the wavelength (500 nm) forming the condensation point at the position designated by P0 is most strongly reflected to form the return light L1. The return light travels back through the first beam path S1, the beam splitter 70, and the second beam path S2, is then spectrally scattered by the spectroscope 62, and is directed to the Z-position detection unit 64, which, as in Figure 7A, is used for detection. Fig. 7B shows, for example, a waveform (see (A) in the figure) which forms a peak value at the position of a wavelength of 500 nm through the feedback light L1.

[0055] The position at which the condensation point P0 is formed by a wavelength of 500 nm, and the position at which the condensation point PS of the laser beam LB is formed, are set by the free-space adjustment mechanism 80 described above to be spaced 50 µm apart. Therefore, when the laser beam LB is applied in the aforementioned state, where the condensation point P0 is positioned on the front surface 10a of the wafer 10, it is possible to form the modified layer at the desired position, i.e., at a depth of 50 µm from the front surface 10a of the wafer 10.

[0056] If the laser processing is caused to progress along path 12, the height of the front surface 10a could change due to variability in thickness, waveform, or the like within the wafer 10. For example, if the height of the front surface 10a is changed to a lower side, the peak of the waveform detected by the Z-position detection unit 64 will move to a side with a longer wavelength, as shown in Fig. 7B is represented by a dotted line (B). If the peak position of the waveform is changed to the position with a wavelength of 600 nm, this means that the height of the front surface 10a of the wafer 10 deviates by -5.0 µm (by 5.0 µm towards the bottom), as shown by reference to the Z-coordinate table 110 in Fig. As can be seen in Figure 6A. If the laser processing continues in this state, the condensation point PS of the laser beam LB forming the modified layer will therefore form at a position 45 µm from the front surface 10a of the wafer 10, so that the modified layer is not formed at the desired position. Here, upon detecting that the peak position of the waveform detected by the Z-position detection unit 64 has changed to a position with a wavelength of 600 nm, the control unit 100 actuates the condenser movement mechanism 43 to lower the position of the condenser 42 by 5 µm. Consequently, the position at which the light L0 and the laser beam LB are condensed by the condenser 42 is lowered by a total of 5 µm, and the peak position of the waveform detected by the Z-position detection unit 64 is shifted from the position designated by (B) to the position designated by (A), as shown in Fig. 7B is represented by an arrow. In other words, the condensation point PS of the laser beam LB is controlled depending on the Z-position of the front surface 10a of the wafer 10 detected by the Z-position detection unit 64, thereby continuously forming the modified layer at a depth position of 50 µm from the front surface 10a of the wafer 10.

[0057] Additionally, if the laser processing is carried out, when the peak of the waveform detected by the Z-position detection unit 64 is as shown in Fig. 7B, represented by a dotted line (C), would be moved to the side of the shorter wavelength and the peak position of the waveform would be changed to the position with a wavelength of 400 nm, meaning that the height of the front surface 10a of wafer 10 deviates by +5.0 µm, as with reference to the Z-coordinate table 110 in Fig. 6A is evident. If the laser processing continues in this state, the condensation point PS of the laser beam LB forming the modified layer is therefore formed at a depth position of 55 µm from the front surface 10a of the wafer 10. Here, upon detecting that the peak position of the waveform detected by the Z-position detection unit 64 has changed to a position with a wavelength of 400 nm, the control unit 100 actuates the condenser movement mechanism 43 to raise the position of the condenser 42 by 5 µm. Consequently, the position at which the light L0 and the laser beam LB are condensed by the condenser 42 is raised by a total of 5 µm, and the peak position of the waveform detected by the Z-position detection unit 64 is moved from the position shown in Figure 6A. Fig.7B is returned from the position designated by (C) to the position designated by (A). In other words, the condensation point PS of the laser beam LB is controlled depending on the Z-position of the front surface 10a of the wafer 10 detected by the Z-position detection unit 64, thereby continuously forming the modified layer at a depth of 50 µm from the front surface 10a of the wafer 10.

[0058] By detecting the Z-position of the front surface 10a of the wafer 10 and actuating the condenser movement mechanism 43 to control it so that the peak of the waveform detected by the Z-position detection unit 64 is maintained normal to the position indicated by a solid line (A), the position of the condensation point PS, at which the modified layer is to be formed, can be suitably positioned at a depth of 50 µm from the front surface 10a and the modified layer can be formed at the desired position.

[0059] Note that, while the above embodiment describes an example in which the present invention is applied to the laser processing device for forming the modified layer within the wafer 10, the present invention is not limited thereto and is also applicable to a laser processing device that positions the condensation point of a laser beam with a wavelength such that it is absorbed in the wafer 10 at the front surface 10a of the wafer 10 in order to apply an ablation treatment to the wafer 10. In this case, it is preferred that, by applying the present invention, the Z-position of the front surface 10a of the wafer 10 is temporarily detected and stored in the Z-coordinate memory section 120 of the control unit 100, and laser processing is performed based on the Z-position stored in the Z-coordinate memory section 120.

Claims

[1] Laser processing device (2) comprising: a clamping table (34) that holds a workpiece (10); a laser beam application unit (4) which applies a laser beam to the workpiece (10) held by the clamping table (34) in order to process the workpiece (10); an X-axis feeding mechanism (50) which performs a relative processing feeding of the clamping table (34) and the laser beam application unit (4) in an X-axis direction; a Y-axis feed mechanism (52) that performs a relative processing feed of the clamping table (34) and the laser beam application unit (4) in a Y-axis direction orthogonal to the X-axis direction; and a control unit (100), wherein the laser beam application unit (4) comprises: a laser oscillator (44) that oscillates a laser, a condenser (42) which condenses the laser beam emitted by the laser oscillator (44) onto the workpiece (10) held by the clamping table (34) at a position in a Z-axis direction orthogonal to the X-axis and Y-axis directions, wherein the condenser (42) is a condenser lens (42a) with a chromatic aberration, a beam splitter (70) arranged on a first beam path (S1) connecting the laser oscillator (44) and the condenser (42), a broadband light source (61) arranged on a second beam path (S2) branched off from the beam splitter (70), a spectroscope (62) which is arranged between the broadband light source (61) and the beam splitter (70) and which diverts the laser beam from the second beam path (S2) to a third beam path (S3), a Z-position detection unit (64) arranged on the third beam path (S3) branched off from the spectroscope (62) and which detects a Z-position in the Z-axis direction of the workpiece (10) according to an intensity of light corresponding to a wavelength of return light (L1) which is generated when the light from the broadband light source (61) is condensed by the condenser (42) and reflected by the workpiece (10) held by the clamping table (34), and a condenser movement mechanism (43) that moves the condenser (42) in the Z-axis direction according to the Z-position. [2] Laser processing device (2) according to claim 1, wherein the second beam path (S2) has an optical fiber (FB), the light from the broadband light source (71) is guided by the optical fiber (FB), the light applied by an end face (63) of the optical fiber (FB) is guided through a collimating lens to the beam splitter (70) which transmits the light, a clearance adjustment mechanism (80) for adjusting a clearance between the end face (63) of the optical fiber (FB) and the collimating lens is arranged in the second beam path (S2), and a condensation position of the light from the broadband light source (71) condensed by the condenser (42) is set by the clearance adjustment mechanism (80). [3] Laser processing device (2) according to claim 1 or 2, wherein the laser oscillator (44) oscillates a laser with such a wavelength that it is transmitted through the workpiece (10), and the condenser (42) positions a condensation point inside the workpiece (10) to form a modified layer. [4] Laser processing device (2) according to one of the preceding claims, wherein the control unit (100) has a coordinate storage section which stores the Z position detected by the Z position detection unit (64) in the Z-axis direction of the workpiece (10) in a Z-axis coordinate together with X-axis and Y-axis coordinates, and the control unit (100) controls the condenser movement mechanism (43) based on the coordinates stored in the coordinate storage section to machine the workpiece (10) held by the clamping table (34). [5] Laser processing device (2) according to one of the preceding claims, wherein the control unit (100) controls the condenser movement mechanism (43) depending on the Z position detected by the Z position detection unit (64) in the Z-axis direction to process the workpiece (10) held by the clamping table (34).

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