JP3867110B2 - Laser processing method - Google Patents

Description

  The present invention relates to a laser processing method used for cutting an object to be processed such as a semiconductor material substrate, a piezoelectric material substrate or a glass substrate.

  One of laser applications is cutting, and general cutting by laser is as follows. For example, a portion to be cut of a workpiece such as a semiconductor wafer or a glass substrate is irradiated with laser light having a wavelength that is absorbed by the workpiece, and the portion to be cut by the absorption of the laser light is directed from the front surface to the back surface of the workpiece. The workpiece is cut by advancing heating and melting. However, in this method, the periphery of the region to be cut out of the surface of the workpiece is also melted. Therefore, when the object to be processed is a semiconductor wafer, among the semiconductor elements formed on the surface of the semiconductor wafer, there is a possibility that the semiconductor elements located around the region are melted.

As a method for preventing melting of the surface of the workpiece, for example, there is a laser cutting method disclosed in Patent Document 1 and Patent Document 2 below. In the cutting methods disclosed in these documents, a part to be processed is heated by a laser beam, and the object to be processed is cooled to cause a thermal shock at the part to be processed. Cut the object.
JP 2000-219528 A JP 2000-15467 A

  However, in the cutting methods disclosed in these documents, if the thermal shock generated on the workpiece is large, the surface of the workpiece is cracked off the planned cutting line or to the previous portion not irradiated with laser. Unnecessary cracks such as the above may occur. Therefore, these cutting methods cannot perform precision cutting. In particular, when the object to be processed is a semiconductor wafer, a glass substrate on which a liquid crystal display device is formed, or a glass substrate on which an electrode pattern is formed, this unnecessary crack may damage the semiconductor chip, the liquid crystal display device, or the electrode pattern. is there. Moreover, since these cutting methods have a large average input energy, the thermal damage given to the semiconductor chip or the like is also large.

  An object of the present invention is to provide a laser processing method in which unnecessary cracks are not generated on the surface of a workpiece and the surface does not melt.

The laser processing method according to the present invention extends along the planned cutting line of the processing object by irradiating the laser beam with the converging point inside the wafer-shaped processing object, and the extending direction. A modified region in which one end and the other end of the workpiece reach the outer edge of the workpiece is formed inside the workpiece, and the workpiece is cut along a planned cutting line using the modified region as a starting point for cutting. And

  In the laser processing method according to the present invention, the modified region is formed inside the processing object by irradiating the processing object with the laser beam with the focusing point aligned. If there is any starting point at the location where the workpiece is to be cut, the workpiece can be cut with a relatively small force. According to the laser processing method of the present invention, the processing object can be cut by breaking the processing object along the scheduled cutting line starting from the modified region. Therefore, since the workpiece can be cut with a relatively small force, it is possible to cut the workpiece without generating unnecessary cracks off the planned cutting line on the surface of the workpiece.

  In the laser processing method according to the present invention, the modified region is locally formed inside the processing object. Therefore, since the laser beam is hardly absorbed on the surface of the processing object, the surface of the processing object does not melt. In addition, a condensing point is a location which the laser beam condensed. The line to be cut may be a line actually drawn on the surface or inside of the workpiece, or may be a virtual line.

  According to the laser processing method according to the present invention, it is possible to cut the processing object without causing melting or cracks that are out of the planned cutting line on the surface of the processing object. Therefore, the yield and productivity of a product (for example, a display device such as a semiconductor chip, a piezoelectric device chip, and a liquid crystal) manufactured by cutting the workpiece can be improved.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the laser processing method and the laser processing apparatus according to the present embodiment, the modified region is formed by multiphoton absorption. Multiphoton absorption is a phenomenon that occurs when the intensity of laser light is very high. First, multiphoton absorption will be briefly described.

Photon energy hν is smaller than the band gap E _G of absorption of the material becomes transparent. Therefore, a condition under which absorption occurs in the material is hv> E _G. However, even when optically transparent, increasing the intensity of the laser beam very Nhnyu> of _{E G} condition (n = 2, 3, 4, a, ...) absorbed in the material occurs. This phenomenon is called multiphoton absorption. In the case of a pulse wave, the intensity of the laser beam is determined by the peak power density (W / cm ² ) at the condensing point of the laser beam. For example, the multiphoton is obtained under conditions where the peak power density is 1 × 10 ⁸ (W / cm ² ) or more. Absorption occurs. The peak power density is determined by (energy per pulse of laser light at the condensing point) / (laser beam cross-sectional area of laser light × pulse width). In the case of a continuous wave, the intensity of the laser beam is determined by the electric field intensity (W / cm ² ) at the condensing point of the laser beam.

  The principle of laser processing according to this embodiment using such multiphoton absorption will be described with reference to FIGS. FIG. 1 is a plan view of a workpiece 1 during laser processing, FIG. 2 is a cross-sectional view taken along line II-II of the workpiece 1 shown in FIG. 1, and FIG. 3 is a workpiece after laser processing. 4 is a plan view of the workpiece 1, FIG. 4 is a cross-sectional view taken along line IV-IV of the workpiece 1 shown in FIG. 3, and FIG. 5 is taken along line V-V of the workpiece 1 shown in FIG. FIG. 6 is a plan view of the cut workpiece 1.

  As shown in FIGS. 1 and 2, the surface 3 of the workpiece 1 has a planned cutting line 5. The planned cutting line 5 is a virtual line extending linearly. In the laser processing according to the present embodiment, the modified region 7 is formed by irradiating the processing object 1 with the laser beam L by aligning the condensing point P inside the processing object 1 under the condition that multiphoton absorption occurs. In addition, a condensing point is a location where the laser beam L is condensed.

  The condensing point P is moved along the planned cutting line 5 by relatively moving the laser light L along the planned cutting line 5 (that is, along the direction of the arrow A). Thereby, as shown in FIGS. 3 to 5, the modified region 7 is formed only inside the workpiece 1 along the planned cutting line 5. The laser processing method according to the present embodiment does not form the modified region 7 by causing the workpiece 1 to generate heat by causing the workpiece 1 to absorb the laser light L. The modified region 7 is formed by transmitting the laser beam L through the workpiece 1 and generating multiphoton absorption inside the workpiece 1. Therefore, since the laser beam L is hardly absorbed by the surface 3 of the workpiece 1, the surface 3 of the workpiece 1 is not melted.

  In the cutting of the workpiece 1, if there is a starting point at the location to be cut, the workpiece 1 is broken from the starting point, so that the workpiece 1 can be cut with a relatively small force as shown in FIG. 6. Therefore, the processing object 1 can be cut without causing unnecessary cracks on the surface 3 of the processing object 1.

  In addition, the following two kinds of cutting | disconnection of the processing target object from the modification | reformation area | region can be considered. One is a case where, after the modified region is formed, an artificial force is applied to the workpiece, so that the workpiece is cracked and the workpiece is cut from the modified region as a starting point. This is, for example, cutting when the thickness of the workpiece is large. When artificial force is applied, for example, bending stress or shear stress is applied to the workpiece along the planned cutting line of the workpiece, or thermal stress is generated by giving a temperature difference to the workpiece. It is to let you. The other is that when the modified region is formed, the modified region starts as a starting point, and naturally breaks in the cross-sectional direction (thickness direction) of the workpiece, resulting in the workpiece being cut. It is. For example, when the thickness of the workpiece is small, even one modified region is possible, and when the workpiece is large, a plurality of modified regions can be formed in the thickness direction. . Even in the case of this natural cracking, it is possible to cleave only the surface on the part where the modified part is formed, without causing cracks to advance to the surface on the part where the modified region is not formed at the location to be cut. Since it is possible, the cleaving can be controlled well. In recent years, since the thickness of semiconductor wafers such as silicon wafers tends to be thin, such a cleaving method with good controllability is very effective.

  As modified regions formed by multiphoton absorption in this embodiment, there are the following (1) to (3).

(1) In the case where the modified region is a crack region including one or a plurality of cracks The laser light is focused on the inside of the object to be processed (for example, a piezoelectric material made of glass or LiTaO ₃ ), Irradiation is performed under conditions where the electric field strength is 1 × 10 ⁸ (W / cm ² ) or more and the pulse width is 1 μs or less. The magnitude of the pulse width is a condition that a crack region can be formed only inside the workpiece without causing extra damage to the workpiece surface while causing multiphoton absorption. As a result, a phenomenon of optical damage due to multiphoton absorption occurs inside the workpiece. This optical damage induces thermal strain inside the workpiece, thereby forming a crack region inside the workpiece. The upper limit value of the electric field strength is, for example, 1 × 10 ¹² (W / cm ² ). The pulse width is preferably 1 ns to 200 ns, for example. The formation of the crack region by multiphoton absorption is described in, for example, “Inside of glass substrate by solid-state laser harmonics” on pages 23-28 of the 45th Laser Thermal Processing Research Papers (December 1998). It is described in “Marking”.

  The inventor obtained the relationship between the electric field strength and the size of the cracks by experiment. The experimental conditions are as follows.

(A) Workpiece: Pyrex (registered trademark) glass (thickness 700 μm)
(B) Laser
Light source: Semiconductor laser pumped Nd: YAG laser
Wavelength: 1064nm
Laser light spot cross-sectional area: 3.14 × 10 ⁻⁸ cm ²
Oscillation form: Q switch pulse
Repeat frequency: 100 kHz
Pulse width: 30ns
Output: Output <1mJ / pulse
Laser light quality: TEM ₀₀
Polarization characteristics: Linearly polarized light (C) Condensing lens
Transmittance with respect to laser beam wavelength: 60% (D) Moving speed of mounting table on which workpiece is mounted: 100 mm / second

Note that the laser light quality TEM ₀₀ means that the light condensing performance is high and the light can be condensed up to the wavelength of the laser light.

FIG. 7 is a graph showing the results of the experiment. The horizontal axis represents the peak power density. Since the laser beam is a pulsed laser beam, the electric field strength is represented by the peak power density. The vertical axis represents the size of a crack portion (crack spot) formed inside the workpiece by one pulse of laser light. Crack spots gather to form a crack region. The size of the crack spot is the size of the portion having the maximum length in the shape of the crack spot. Data indicated by black circles in the graph is for the case where the magnification of the condenser lens (C) is 100 times and the numerical aperture (NA) is 0.80. On the other hand, the data indicated by the white circles in the graph is when the magnification of the condenser lens (C) is 50 times and the numerical aperture (NA) is 0.55. From the peak power density of about 10 ¹¹ (W / cm ² ), it can be seen that a crack spot is generated inside the workpiece, and the crack spot increases as the peak power density increases.

  Next, in the laser processing according to the present embodiment, a mechanism for cutting a workpiece by forming a crack region will be described with reference to FIGS. As shown in FIG. 8, the laser beam L is irradiated to the workpiece 1 by aligning the condensing point P inside the workpiece 1 under the condition that multiphoton absorption occurs, and a crack region is formed along the planned cutting line. 9 is formed. The crack region 9 is a region including one or a plurality of cracks. As shown in FIG. 9, the crack further grows starting from the crack region 9, and the crack reaches the front surface 3 and the back surface 21 of the workpiece 1 as shown in FIG. 10, and the workpiece 1 as shown in FIG. 11. The workpiece 1 is cut by cracking. Cracks that reach the front and back surfaces of the workpiece may grow naturally or may grow when a force is applied to the workpiece.

(2) When the modified region is a melt processing region The laser beam is focused on the inside of the object to be processed (for example, a semiconductor material such as silicon), and the electric field strength at the focused point is 1 × 10 ⁸ (W / Cm ² ) or more and the pulse width is 1 μs or less. As a result, the inside of the workpiece is locally heated by multiphoton absorption. By this heating, a melt processing region is formed inside the workpiece. The melting treatment region means at least one of a region once solidified after melting, a region in a molten state, and a region in a state of being resolidified from melting. It can also be said that the melt-processed region is a phase-changed region or a region where the crystal structure is changed. The melt treatment region can also be said to be a region in which one structure is changed to another structure in a single crystal structure, an amorphous structure, or a polycrystalline structure. In other words, for example, a region changed from a single crystal structure to an amorphous structure, a region changed from a single crystal structure to a polycrystalline structure, or a region changed from a single crystal structure to a structure including an amorphous structure and a polycrystalline structure. To do. When the object to be processed has a silicon single crystal structure, the melt processing region has, for example, an amorphous silicon structure. In addition, as an upper limit of an electric field strength, it is 1 * 10 < ¹² > (W / cm < ² >), for example. The pulse width is preferably 1 ns to 200 ns, for example.

  The inventor has confirmed through experiments that a melt-processed region is formed inside a silicon wafer. The experimental conditions are as follows.

(A) Workpiece: silicon wafer (thickness 350 μm, outer diameter 4 inches)
(B) Laser
Light source: Semiconductor laser pumped Nd: YAG laser
Wavelength: 1064nm
Laser light spot cross-sectional area: 3.14 × 10 ⁻⁸ cm ²
Oscillation form: Q switch pulse
Repeat frequency: 100 kHz
Pulse width: 30ns
Output: 20μJ / pulse
Laser light quality: TEM ₀₀
Polarization characteristics: Linearly polarized light (C) Condensing lens
Magnification: 50 times
NA: 0.55
Transmittance with respect to laser beam wavelength: 60% (D) Moving speed of mounting table on which workpiece is mounted: 100 mm / second

  FIG. 12 is a view showing a photograph of a cross section of a part of a silicon wafer cut by laser processing under the above conditions. A melt processing region 13 is formed inside the silicon wafer 11. In addition, the size in the thickness direction of the melt processing region formed under the above conditions is about 100 μm.

  The fact that the melt processing region 13 is formed by multiphoton absorption will be described. FIG. 13 is a graph showing the relationship between the wavelength of the laser beam and the transmittance inside the silicon substrate. However, the reflection components on the front side and the back side of the silicon substrate are removed to show the transmittance only inside. The above relationship was shown for each of the silicon substrate thicknesses t of 50 μm, 100 μm, 200 μm, 500 μm, and 1000 μm.

  For example, when the thickness of the silicon substrate is 500 μm or less at the wavelength of 1064 nm of the Nd: YAG laser, it can be seen that the laser light is transmitted by 80% or more inside the silicon substrate. Since the thickness of the silicon wafer 11 shown in FIG. 12 is 350 μm, the melt processing region by multiphoton absorption is formed near the center of the silicon wafer, that is, at a portion of 175 μm from the surface. In this case, the transmittance is 90% or more with reference to a silicon wafer having a thickness of 200 μm. Therefore, the laser beam is hardly absorbed inside the silicon wafer 11 and almost all is transmitted. This is not because the laser beam is absorbed inside the silicon wafer 11 and the melt processing region is formed inside the silicon wafer 11 (that is, the melt processing region is formed by normal heating with laser light). It means that the processing region is formed by multiphoton absorption. The formation of the melt-processed region by multiphoton absorption is described in, for example, “Evaluation of processing characteristics of silicon by picosecond pulse laser” on pages 72 to 73 of the 66th Annual Meeting of the Japan Welding Society (April 2000). Are listed.

  In addition, a silicon wafer is cut | disconnected as a result by generating a crack toward a cross-sectional direction starting from the melt processing region and reaching the front and back surfaces of the silicon wafer. The cracks that reach the front and back surfaces of the silicon wafer may grow naturally or may grow by applying force to the workpiece. In addition, the crack grows naturally from the melt processing area to the front and back surfaces of the silicon wafer when the crack grows from the area once solidified after being melted, or when the crack grows from the melted area. And at least one of the cases where cracks grow from a region in a state of being resolidified from melting. In either case, the cut surface after cutting is formed with a melt treatment region only inside as shown in FIG. In the case where the melt processing region is formed inside the object to be processed, since the unnecessary cracks that are off the planned cutting line are not easily generated at the time of cleaving, cleaving control is facilitated.

(3) When the modified region is a refractive index changing region The laser beam is focused on the inside of the object to be processed (for example, glass), and the electric field intensity at the focused point is 1 × 10 ⁸ (W / cm ² ). Irradiation is performed under the above conditions with a pulse width of 1 ns or less. When the pulse width is made extremely short and multiphoton absorption occurs inside the workpiece, the energy due to the multiphoton absorption is not converted into thermal energy, and the ion valence change and crystallization occur inside the workpiece. Alternatively, a permanent structural change such as polarization orientation is induced to form a refractive index change region. The upper limit value of the electric field strength is, for example, 1 × 10 ¹² (W / cm ² ). For example, the pulse width is preferably 1 ns or less, and more preferably 1 ps or less. The formation of the refractive index changing region by multiphoton absorption is described in, for example, “The Femtosecond Laser Irradiation to the Inside of Glass” on pages 105 to 111 of the 42nd Laser Thermal Processing Research Institute Proceedings (November 1997). Photo-induced structure formation ”.

  As described above, according to the present embodiment, the modified region is formed by multiphoton absorption. Then, in the present embodiment, the processing object is modified by irradiating the processing object with the laser beam so that the linearly polarized direction of the linearly polarized laser light is aligned with the cutting line of the processing object. An area is formed. Thereby, when the laser beam is a pulsed laser beam, the dimension in the direction along the planned cutting line can be relatively increased in the modified spot formed by one-shot shot (that is, one-pulse laser irradiation). it can. This inventor confirmed this by experiment. The experimental conditions are as follows.

(A) Workpiece: Pyrex (registered trademark) glass wafer (thickness 700 μm, outer diameter 4 inches)
(B) Laser
Light source: Semiconductor laser pumped Nd: YAG laser
Wavelength: 1064nm
Laser light spot cross-sectional area: 3.14 × 10 ⁻⁸ cm ²
Oscillation form: Q switch pulse
Repeat frequency: 100 kHz
Pulse width: 30ns
Output: Output <1mJ / pulse
Laser light quality: TEM ₀₀
Polarization characteristics: Linearly polarized light (C) Condensing lens
Magnification: 50 times
NA: 0.55
Transmittance with respect to laser beam wavelength: 60% (D) Moving speed of mounting table on which workpiece is mounted: 100 mm / second

  In each of Samples 1 and 2 which are processing objects, a pulse laser beam was shot by one pulse with a focusing point inside the processing object, and a crack region due to multiphoton absorption was formed inside the processing object. Sample 1 was irradiated with linearly polarized pulsed laser light, and sample 2 was irradiated with circularly polarized pulsed laser light.

  FIG. 14 is a view showing a photograph of the plane of the sample 1, and FIG. 15 is a view showing a photograph of the plane of the sample 2. These planes are the incident surface 209 of the pulse laser beam. The symbol LP schematically shows linearly polarized light, and the symbol CP schematically shows circularly polarized light. FIG. 16 is a diagram schematically showing a cross section taken along line XVI-XVI of sample 1 shown in FIG. FIG. 17 is a view schematically showing a cross section taken along line XVII-XVII of sample 2 shown in FIG. A crack spot 90 is formed inside a glass wafer 211 that is a workpiece.

  As shown in FIG. 16, when the pulse laser beam is linearly polarized, the size of the crack spot 90 formed by one pulse shot is relatively large in the direction along the direction of linearly polarized light. This indicates that the formation of the crack spot 90 is promoted in this direction. On the other hand, as shown in FIG. 17, when the pulse laser beam is circularly polarized, the size of the crack spot 90 formed by one pulse shot does not increase in a specific direction. The size of the crack spot 90 in the direction in which the length is maximum is larger in the sample 1 than in the sample 2.

  From this experimental result, it will be explained that the crack region along the cutting line can be efficiently formed. 18 and 19 are plan views of crack regions formed along the planned cutting line of the workpiece. By forming a large number of crack spots 90 formed by one pulse shot along the planned cutting line 5, a crack region 9 along the planned cutting line 5 is formed. FIG. 18 shows a crack region 9 formed by irradiating the pulsed laser light so that the direction of linear polarization of the pulsed laser light is along the planned cutting line 5. The crack spot 90 has a relatively large dimension in this direction by promoting the formation along the direction of the planned cutting line 5. Therefore, the crack region 9 along the planned cutting line 5 can be formed with a small number of shots. On the other hand, FIG. 19 shows a crack region 9 formed by irradiating the pulse laser beam with the direction of linear polarization of the pulse laser beam orthogonal to the line 5 to be cut. Since the dimension of the crack spot 90 in the direction of the planned cutting line 5 is relatively small, the number of shots for forming the crack region 9 is larger than in the case of FIG. Therefore, the crack region forming method according to this embodiment shown in FIG. 18 can form the crack region more efficiently than the method shown in FIG.

  Further, in the method shown in FIG. 19, since the pulse laser beam is irradiated with the direction of the linear polarization of the pulse laser beam orthogonal to the planned cutting line 5, the crack spot 90 formed at the time of the shot is Formation is promoted in the width direction. Therefore, if the extension of the crack spot 90 in the width direction of the planned cutting line 5 becomes too large, the workpiece cannot be precisely cut along the planned cutting line 5. On the other hand, in the method according to the present embodiment shown in FIG. 18, the crack spot 90 formed at the time of the shot does not extend so much in a direction other than the direction along the planned cutting line 5. Cutting is possible.

  In addition, although it demonstrated in the case of linearly polarized light about making the dimension of a predetermined direction relatively large among the dimensions of a modification area | region, the same can be said of elliptically polarized light. That is, as shown in FIG. 20, the formation of the crack spot 90 is promoted in the major axis b direction of the ellipse representing the elliptically polarized light EP of the laser beam, and the crack spot 90 having a relatively large dimension along this direction can be formed. . Therefore, when the crack region is formed so that the long axis of the ellipse representing the elliptical polarization of the laser beam having the ellipticity other than 1 is along the planned cutting line of the workpiece, the same effect as in the case of the linear polarization is obtained. Occurs. The ellipticity is half the length of the short axis a / half the length of the long axis b. As the ellipticity decreases, the size of the crack spot 90 along the major axis b direction increases. Linearly polarized light is elliptically polarized light having an ellipticity of zero. When the ellipticity is 1, it becomes circularly polarized light, and the dimension of the crack region in the predetermined direction cannot be relatively increased. Therefore, in this embodiment, the case of ellipticity 1 is not included.

  Although the description has been made in the case of the crack region that the dimension in the predetermined direction among the dimensions of the modified region is relatively large, the same can be said for the melting treatment region and the refractive index change region. Further, the pulse laser beam has been described, but the same can be said for the continuous wave laser beam.

  Next, a specific example of this embodiment will be described.

[First example]
A laser processing apparatus according to the first example of the present embodiment will be described. FIG. 21 is a schematic configuration diagram of the laser processing apparatus 200. The laser processing apparatus 200 emits a laser light source 101 that generates laser light L, a laser light source control unit 102 that controls the laser light source 101 in order to adjust the output and pulse width of the laser light L, and the laser light source 101. An ellipticity adjusting unit 201 that adjusts the ellipticity of the polarization of the laser light L, and a 90 ° rotation adjusting unit 203 that adjusts the polarization of the laser light L emitted from the ellipticity adjusting unit 201 by approximately 90 °. Prepare.

The laser light source 101 is an Nd: YAG laser that generates pulsed laser light. Other lasers that can be used for the laser light source 101 include an Nd: YVO ₄ laser, an Nd: YLF laser, and a titanium sapphire laser. In the case of forming a crack region or a melt treatment region, it is preferable to use an Nd: YAG laser, an Nd: YVO ₄ laser, or an Nd: YLF laser. When forming the refractive index changing region, it is preferable to use a titanium sapphire laser.

  The ellipticity adjusting unit 201 includes a quarter-wave plate 207 as shown in FIG. The quarter-wave plate 207 can adjust the ellipticity of elliptically polarized light by changing the azimuth angle θ. That is, when incident light of, for example, linearly polarized light LP enters the quarter wavelength plate 207, the transmitted light becomes elliptically polarized light EP having a predetermined ellipticity. An azimuth angle is an angle formed by the major axis of the ellipse and the X axis. As described above, in the present embodiment, a number other than 1 is applied as the ellipticity. By the ellipticity adjusting unit 201, the polarization of the laser light L can be elliptically polarized EP having a desired ellipticity. The ellipticity is adjusted in consideration of the thickness, material, etc. of the workpiece 1.

  When irradiating the workpiece 1 with the laser beam L of the linearly polarized light LP, the laser light L emitted from the laser light source 101 is the linearly polarized light LP, so that the laser light L remains the linearly polarized light LP and passes through the quarter wavelength plate. As described above, the ellipticity adjusting unit 201 adjusts the azimuth angle θ of the quarter-wave plate 207. Further, since the linearly polarized laser beam L is emitted from the laser light source 101, the ellipticity adjusting unit 201 is not necessary when only the linearly polarized laser beam is used for laser irradiation of the workpiece 1.

The 90 ° rotation adjusting unit 203 includes a half-wave plate 205 as shown in FIG. The half-wave plate 205 is a wave plate that produces polarized light orthogonal to linearly polarized incident light. That is, for example, when incident light of linearly polarized light LP _{1 having} an azimuth angle of 45 ° is incident on the half-wave plate 205, the transmitted light becomes linearly polarized light LP ₂ rotated by 90 ° with respect to the incident light LP ₁ . The 90 ° rotation adjusting unit 203 operates to arrange the half-wave plate 205 on the optical axis of the laser light L when rotating the polarization of the laser light L emitted from the ellipticity adjusting unit 201 by 90 °. . When the 90 ° rotation adjusting unit 203 does not rotate the polarization of the laser light L emitted from the ellipticity adjusting unit 201, the 90 ° rotation adjusting unit 203 moves the half-wave plate 205 outside the optical path of the laser light L (that is, the laser light L is 1). / The place where it does not pass through the two-wave plate 205).

  The laser processing apparatus 200 further includes a dichroic mirror arranged so that the laser light L whose polarization is not rotated or adjusted by 90 ° by the 90 ° rotation adjusting unit 203 is incident and the direction of the optical axis of the laser light L is changed by 90 °. 103, a condensing lens 105 for condensing the laser light L reflected by the dichroic mirror 103, and a workpiece 1 irradiated with the laser light L condensed by the condensing lens 105 are placed. A mounting table 107, an X-axis stage 109 for moving the mounting table 107 in the X-axis direction, a Y-axis stage 111 for moving the mounting table 107 in the Y-axis direction orthogonal to the X-axis direction, and the mounting table 107 The Z-axis stage 113 for moving the X-axis in the Z-axis direction orthogonal to the X-axis and Y-axis directions, and the XY plane of the mounting table 107 are rotated about the thickness direction of the workpiece 1 as an axis. It includes a θ-axis stage 213 in order, and a stage controller 115 for controlling the movement of these four stages 109,111,113,213 and.

  Since the Z-axis direction is a direction perpendicular to the surface 3 of the workpiece 1, the Z-axis direction is the direction of the focal depth of the laser light L incident on the workpiece 1. Therefore, by moving the Z-axis stage 113 in the Z-axis direction, the condensing point P of the laser light L can be adjusted inside the workpiece 1. Further, the movement of the condensing point P in the X (Y) axis direction is performed by moving the workpiece 1 in the X (Y) axis direction by the X (Y) axis stage 109 (111). The X (Y) axis stage 109 (111) is an example of a moving unit.

  In the first example, pulsed laser light is used for processing the workpiece 1, but continuous wave laser light may be used as long as multiphoton absorption can be caused. The condensing lens 105 is an example of a condensing unit. The Z-axis stage 113 is an example of means for aligning the laser beam condensing point with the inside of the workpiece. By moving the condensing lens 105 in the Z-axis direction, the condensing point of the laser light can be adjusted to the inside of the object to be processed.

  The laser processing apparatus 200 further includes an observation light source 117 that generates visible light to illuminate the workpiece 1 placed on the mounting table 107 with visible light, and the same light as the dichroic mirror 103 and the condensing lens 105. A visible light beam splitter 119 disposed on the axis. A dichroic mirror 103 is disposed between the beam splitter 119 and the condensing lens 105. The beam splitter 119 has a function of reflecting about half of visible light and transmitting the other half, and is arranged so as to change the direction of the optical axis of visible light by 90 °. About half of the visible light generated from the observation light source 117 is reflected by the beam splitter 119, and the reflected visible light passes through the dichroic mirror 103 and the condensing lens 105, and the line 5 to be cut of the workpiece 1 or the like. Illuminate the surface 3 containing

  The laser processing apparatus 200 further includes an imaging element 121 and an imaging lens 123 disposed on the same optical axis as the beam splitter 119, the dichroic mirror 103, and the condensing lens 105. An example of the image sensor 121 is a charge-coupled device (CCD) camera. The reflected light of the visible light that illuminates the surface 3 including the planned cutting line 5 passes through the condensing lens 105, the dichroic mirror 103, and the beam splitter 119, is imaged by the imaging lens 123, and is imaged by the imaging device 121. And becomes imaging data.

  The laser processing apparatus 200 further includes an imaging data processing unit 125 to which imaging data output from the imaging element 121 is input, an overall control unit 127 that controls the entire laser processing apparatus 200, and a monitor 129. The imaging data processing unit 125 calculates focus data for focusing the visible light generated by the observation light source 117 on the surface 3 based on the imaging data. The stage control unit 115 controls the movement of the Z-axis stage 113 based on the focus data so that the visible light is focused on the surface 3. Therefore, the imaging data processing unit 125 functions as an autofocus unit. The imaging data processing unit 125 calculates image data such as an enlarged image of the surface 3 based on the imaging data. This image data is sent to the overall control unit 127, where various processes are performed by the overall control unit, and sent to the monitor 129. Thereby, an enlarged image or the like is displayed on the monitor 129.

  Data from the stage controller 115, image data from the imaging data processor 125, and the like are input to the overall controller 127. Based on these data, the laser light source controller 102, the observation light source 117, and the stage controller By controlling 115, the entire laser processing apparatus 200 is controlled. Therefore, the overall control unit 127 functions as a computer unit.

  Next, the laser processing method according to the first example of the present embodiment will be described with reference to FIGS. FIG. 24 is a flowchart for explaining this laser processing method. The workpiece 1 is a silicon wafer.

  First, the light absorption characteristics of the workpiece 1 are measured with a spectrophotometer or the like (not shown). Based on the measurement result, the laser light source 101 that generates the laser light L having a wavelength transparent to the workpiece 1 or a wavelength with little absorption is selected (S101). Next, the thickness of the workpiece 1 is measured. Based on the measurement result of the thickness and the refractive index of the workpiece 1, the amount of movement of the workpiece 1 in the Z-axis direction is determined (S103). This is because the focusing point P of the laser beam L positioned on the surface 3 of the workpiece 1 in order to position the focusing point P of the laser beam L inside the workpiece 1, This is the amount of movement in the Z-axis direction. This movement amount is input to the overall control unit 127.

  The workpiece 1 is mounted on the mounting table 107 of the laser processing apparatus 200. Then, visible light is generated from the observation light source 117 to illuminate the workpiece 1 (S105). The imaging device 121 images the surface 3 of the workpiece 1 including the illuminated cutting line 5. This imaging data is sent to the imaging data processing unit 125. Based on this imaging data, the imaging data processing unit 125 calculates focus data such that the visible light focus of the observation light source 117 is located on the surface 3 (S107).

  This focus data is sent to the stage controller 115. The stage controller 115 moves the Z-axis stage 113 in the Z-axis direction based on the focus data (S109). Thereby, the focal point of the visible light of the observation light source 117 is located on the surface 3. The imaging data processing unit 125 calculates enlarged image data of the surface 3 of the workpiece 1 including the planned cutting line 5 based on the imaging data. This enlarged image data is sent to the monitor 129 via the overall control unit 127, whereby an enlarged image near the planned cutting line 5 is displayed on the monitor 129.

  The movement amount data determined in advance in step S <b> 103 is input to the overall control unit 127, and this movement amount data is sent to the stage control unit 115. The stage control unit 115 moves the workpiece 1 in the Z-axis direction by the Z-axis stage 113 to a position where the condensing point P of the laser light L is inside the workpiece 1 based on the movement amount data ( S111).

  Next, the ellipticity adjusting unit 201 adjusts the ellipticity of the laser beam L of linearly polarized light LP emitted from the laser light source 101 (S113). By changing the azimuth angle θ of the quarter-wave plate in the ellipticity adjusting unit 201, the laser light L having the elliptically polarized light EP having a desired ellipticity can be obtained.

  First, since the workpiece 1 is processed along the Y-axis direction, the major axis of the ellipse representing the elliptically polarized light EP of the laser light L coincides with the direction of the planned cutting line 5 extending in the Y-axis direction of the workpiece 1. (S115). This is achieved by rotating the θ axis stage 213. Therefore, the θ-axis stage 213 functions as a long-axis adjusting unit or a linearly polarized light adjusting unit.

  Since the workpiece 1 is processed along the Y-axis direction, the 90 ° rotation adjusting unit 203 performs adjustment so as not to rotate the polarization of the laser light L (S117). That is, the operation of arranging the half-wave plate outside the optical path of the laser beam L is performed.

  Laser light L is generated from the laser light source 101, and the laser light L is irradiated to the planned cutting line 5 extending in the Y-axis direction of the surface 3 of the workpiece 1. FIG. 25 is a plan view of the workpiece 1. The workpiece 1 is irradiated with the laser beam L such that the major axis representing the ellipse of the elliptically polarized light EP of the laser beam L is along the rightmost cutting scheduled line 5 of the workpiece 1. Since the condensing point P of the laser beam L is located inside the workpiece 1, the melting region is formed only inside the workpiece 1. The Y-axis stage 111 is moved along the planned cutting line 5, and the melting processing region is formed inside the workpiece 1 along the planned cutting line 5.

  Then, the X-axis stage 109 is moved to irradiate the adjacent cutting scheduled line 5 with the laser beam L, and in the same manner as described above, the melt processing region is placed inside the workpiece 1 along the adjacent cutting planned line 5. Form. By repeating this, a melt processing region is formed inside the workpiece 1 along each scheduled cutting line 5 in order from the right (S119). In addition, when irradiating the processing target object 1 with the laser beam L of linearly polarized light LP, it becomes as shown in FIG. That is, the laser beam L is irradiated to the processing object 1 so that the direction of the linearly polarized light LP of the laser beam L is along the planned cutting line 5 of the processing object 1.

  Next, the 90 ° rotation adjusting unit 203 performs an operation of placing the half-wave plate 205 (FIG. 23) on the optical axis of the laser light L. Thereby, adjustment is performed to rotate the polarization of the laser beam L emitted from the ellipticity adjusting unit 201 by 90 ° (S121).

  Next, a laser beam L is generated from the laser light source 101, and the laser beam L is applied to the planned cutting line 5 extending in the X-axis direction of the surface 3 of the workpiece 1. FIG. 27 is a plan view of the workpiece 1. The laser beam L is applied to the workpiece 1 such that the major axis of the ellipse representing the elliptically polarized light EP of the laser beam L is along the planned cutting line 5 extending in the X-axis direction at the bottom of the workpiece 1. Irradiated. Since the condensing point P of the laser beam L is located inside the workpiece 1, the melting region is formed only inside the workpiece 1. The X-axis stage 109 is moved along the scheduled cutting line 5, and the melting processing region is formed inside the workpiece 1 along the planned cutting line 5.

  Then, the Y-axis stage 111 is moved so that the laser beam L irradiates the cutting line 5 immediately above, and in the same manner as described above, the melt processing region is aligned with the cutting line 5. Form inside. By repeating this, a melt processing region is formed inside the workpiece 1 along each scheduled cutting line in order from the bottom (S123). In addition, when irradiating the workpiece 1 with the laser beam L of the linearly polarized light LP, it is as shown in FIG.

  Then, the workpiece 1 is cut by bending the workpiece 1 along the planned cutting line 5 (S125). Thereby, the workpiece 1 is divided into silicon chips.

  The effect of the first example will be described. According to this, the pulsed laser light L is irradiated on the planned cutting line 5 under the conditions that cause multiphoton absorption and the focusing point P is aligned inside the workpiece 1. Then, by moving the X-axis stage 109 and the Y-axis stage 111, the condensing point P is moved along the scheduled cutting line 5. As a result, a modified region (for example, a crack region, a melt processing region, a refractive index change region) is formed inside the workpiece 1 along the planned cutting line 5. If there is any starting point at the location where the workpiece is to be cut, the workpiece can be cut with a relatively small force. Therefore, the workpiece 1 can be cut with a relatively small force by dividing the workpiece 1 along the scheduled cutting line 5 starting from the modified region. Thereby, the processing target object 1 can be cut | disconnected without generating the unnecessary crack which remove | deviated from the cutting planned line 5 on the surface 3 of the processing target object 1. FIG.

  Further, according to the first example, the cutting laser beam L is irradiated to the cutting line 5 under the condition that causes the multi-photon absorption in the processing target 1 and the focusing point P is set inside the processing target 1. ing. Therefore, the pulse laser beam L passes through the workpiece 1 and the pulse laser beam L is hardly absorbed by the surface 3 of the workpiece 1, so that the surface 3 is damaged by melting due to the formation of the modified region. There is no.

  As described above, according to the first example, it is possible to cut the workpiece 1 without causing unnecessary cracks or melting off the planned cutting line 5 on the surface 3 of the workpiece 1. Therefore, when the workpiece 1 is, for example, a semiconductor wafer, the semiconductor chip can be cut out from the semiconductor wafer without causing unnecessary cracking or melting of the semiconductor chip off the line to be cut. The same applies to a workpiece on which an electrode pattern is formed on the surface, and a workpiece on which an electronic device is formed on the surface, such as a glass substrate on which a display device such as a piezoelectric element wafer or liquid crystal is formed. Therefore, according to the first example, the yield of a product (for example, a display device such as a semiconductor chip, a piezoelectric device chip, or a liquid crystal) manufactured by cutting the workpiece can be improved.

  In addition, according to the first example, the cutting planned line 5 on the surface 3 of the workpiece 1 is not melted. (This is the interval.) Thereby, the number of products produced from one piece of processing object 1 increases, and productivity of a product can be improved.

  Further, according to the first example, since laser light is used for cutting the workpiece 1, more complicated processing than dicing using a diamond cutter becomes possible. For example, even if the planned cutting line 5 has a complicated shape as shown in FIG. 29, the cutting process can be performed according to the first example.

  Further, according to the first example, as shown in FIGS. 25 and 27, the long axis direction of the ellipse representing the elliptically polarized light EP of the pulsed laser light L is along the planned cutting line 5 on the workpiece 1. Thus, the pulse laser beam L is irradiated. For this reason, since the dimension of the crack spot in the direction of the planned cutting line 5 is relatively large, a crack region along the planned cutting line 5 can be formed with a small number of shots. Thus, in the first example, the crack region can be formed efficiently, so that the processing speed of the processing object 1 can be improved. Further, since the crack spot formed at the time of the shot does not extend so much in the direction other than the direction along the planned cutting line 5, the workpiece 1 can be precisely cut along the planned cutting line 5. These effects are the same in the examples described later.

[Second example]
Next, a second example of this embodiment will be described focusing on differences from the first example. FIG. 30 is a schematic configuration diagram of the laser processing apparatus 300. Of the constituent elements of the laser processing apparatus 300, the same constituent elements as those of the laser processing apparatus 200 according to the first example shown in FIG.

  The laser processing apparatus 300 is not provided with the 90 ° rotation adjusting unit 203 of the first example. The θ-axis stage 213 can rotate the XY plane of the mounting table 107 around the thickness direction of the workpiece 1 as an axis. As a result, adjustment is performed to relatively rotate the polarization of the laser light L emitted from the ellipticity adjusting unit 203 by 90 °.

  A laser processing method according to the second example of the present embodiment will be described. Also in the second example, the operations from step S101 to step S115 of the laser processing method according to the first example shown in FIG. 24 are performed. Since the 90 ° rotation adjusting unit 203 is not provided in the second example, the operation in the next step S117 is not performed.

  After step S115, the operation of step S119 is performed. By the operation so far, the workpiece 1 is processed as shown in FIG. 25 in the second example as in the first example. Thereafter, the stage control unit 115 performs control to rotate the θ-axis stage 213 by 90 °. Due to the rotation of the θ-axis stage 213, the workpiece 1 is rotated 90 ° in the XY plane. Thereby, as shown in FIG. 31, the major axis of the elliptically polarized light EP can be aligned along the planned cutting line that intersects the planned cutting line 5 in which the modified region forming step has already been completed.

  And similarly to step S119, by irradiating the processing object 1 with the laser beam L, a melt processing area is formed inside the processing object 1 along each scheduled cutting line 5 in order from the right. Finally, the workpiece 1 is cut in the same manner as in step S125, and the workpiece 1 is divided into silicon chips.

  In the embodiment described above, the modified region formation by multiphoton absorption has been described. However, the present invention does not form a modified region due to multiphoton absorption, and a condensing point is formed inside the workpiece so that the major axis direction of the ellipse representing elliptically polarized light is along the planned cutting line of the workpiece. In addition, the processing object may be cut by irradiating the processing object with laser light. This also makes it possible to efficiently cut the workpiece along the planned cutting line.

It is a top view of the processing target object during laser processing by the laser processing method concerning this embodiment. It is sectional drawing along the II-II line of the workpiece shown in FIG. It is a top view of the processing target after laser processing by the laser processing method concerning this embodiment. It is sectional drawing along the IV-IV line of the workpiece shown in FIG. It is sectional drawing along the VV line of the workpiece shown in FIG. It is a top view of the processing object cut by the laser processing method concerning this embodiment. It is a graph which shows the relationship between the electric field strength and the magnitude | size of a crack in the laser processing method which concerns on this embodiment. It is sectional drawing of the process target object in the 1st process of the laser processing method which concerns on this embodiment. It is sectional drawing of the process target object in the 2nd process of the laser processing method which concerns on this embodiment. It is sectional drawing of the process target object in the 3rd process of the laser processing method which concerns on this embodiment. It is sectional drawing of the process target object in the 4th process of the laser processing method which concerns on this embodiment. It is a figure showing the photograph of the section in the part of silicon wafer cut by the laser processing method concerning this embodiment. It is a graph which shows the relationship between the wavelength of the laser beam and the transmittance | permeability inside a silicon substrate in the laser processing method which concerns on this embodiment. It is a figure showing the photograph of the plane of the sample in which the crack field was formed in the inside by irradiating the pulse laser beam of linear polarization. It is a figure showing the photograph of the plane of the sample in which the crack field was formed in the inside by irradiating with circularly polarized pulsed laser light. It is sectional drawing along the XVI-XVI line of the sample shown in FIG. It is sectional drawing along the XVII-XVII line of the sample shown in FIG. It is a top view of the part along the cutting scheduled line of the processed object in which the crack field was formed by the laser processing method concerning this embodiment. It is a top view of the part along the cutting plan line of the processed object in which the crack field was formed by the laser processing method used as a comparison. It is a figure which shows the laser beam which carried out the elliptical polarization based on this embodiment, and the crack area | region formed by it. It is a schematic block diagram of the laser processing apparatus which concerns on the 1st example of this embodiment. It is a perspective view of the quarter wavelength plate contained in the ellipticity adjustment part concerning the 1st example of this embodiment. It is a perspective view of the half-wave plate contained in the 90 degree rotation adjustment part which concerns on the 1st example of this embodiment. It is a flowchart for demonstrating the laser processing method which concerns on the 1st example of this embodiment. It is a top view of the silicon wafer irradiated with the laser beam which has elliptically polarized light by the laser processing method which concerns on the 1st example of this embodiment. It is a top view of the silicon wafer irradiated with the laser beam which has a linearly polarized light by the laser processing method which concerns on the 1st example of this embodiment. FIG. 26 is a plan view of a silicon wafer in which laser light having elliptically polarized light is irradiated onto the silicon wafer shown in FIG. 25 by the laser processing method according to the first example of this embodiment. FIG. 27 is a plan view of a silicon wafer in which a laser beam having linearly polarized light is irradiated onto the silicon wafer shown in FIG. 26 by the laser processing method according to the first example of the present embodiment. It is a top view of the processed object for demonstrating the pattern which can be cut | disconnected by the laser processing method which concerns on the 1st example of this embodiment. It is a schematic block diagram of the laser processing apparatus which concerns on the 2nd example of this embodiment. FIG. 26 is a plan view of a silicon wafer obtained by irradiating the silicon wafer shown in FIG. 25 with laser light having elliptically polarized light by the laser processing method according to the second example of the present embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Processing object, 5 ... Planned cutting line, 7 ... Modified area | region, L ... Laser beam, P ... Condensing point.

Claims (9)

By irradiating a laser beam with a condensing point inside the wafer-like workpiece, the workpiece extends along the planned cutting line, and one end and the other end in the extending direction are the workpiece. A laser that forms a modified region that reaches the outer edge of an object inside the object to be processed, and cuts the object to be processed along the planned cutting line with the modified region as a starting point for cutting. Processing method.   The modified region extends in a second direction substantially orthogonal to the first direction in the processing object and a plurality of first scheduled cutting lines extending in the first direction in the processing object. The laser processing method according to claim 1, wherein the laser machining method is formed along each of a plurality of second scheduled cutting lines.   3. The laser processing method according to claim 1, wherein the modified region is a melt processing region.   The laser processing method according to claim 1, wherein the modified region is a crack region.   The laser processing method according to claim 1, wherein the modified region is a refractive index changing region.   The laser processing method according to claim 1, wherein the object to be processed is a semiconductor material substrate.   The laser processing method according to claim 1, wherein the object to be processed is a glass substrate.   3. The laser processing method according to claim 1, wherein the object to be processed is a piezoelectric material substrate. The modified region has changed from a single crystal structure to an amorphous structure, from a single crystal structure to a polycrystalline structure, or from a single crystal structure to a structure including an amorphous structure and a polycrystalline structure. The laser processing method according to claim 6, wherein the laser processing method is a melt processing region.

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