JP5122161B2 - Processing object cutting method - Google Patents

Description

  The present invention relates to a workpiece cutting method for cutting a plate-like workpiece along a planned cutting line.

The following is known as a conventional workpiece cutting method (for example, refer to Patent Document 1). First, a modified region is formed inside the processing object along each of the planned cutting lines set in a grid by irradiating a laser beam with a focusing point inside the plate-shaped processing object To do. Subsequently, the workpiece is cut along the scheduled cutting line extending in a predetermined direction among the planned cutting lines set in a grid shape, and then the cutting is set in the grid shape. The workpiece is cut along the scheduled cutting line extending in the direction intersecting the predetermined direction among the scheduled lines, starting from the modified region.
JP 2006-24676 A

  However, in the above-described conventional method for cutting an object to be processed, in particular, a cutting target line extending in a direction crossing a predetermined direction (that is, an object to be processed that has been cut into a strip shape is cut into chips. For example, there is a case where the workpiece cannot be cut with high precision along the planned cutting line).

  Then, this invention is made | formed in view of such a situation, and cross | intersects a 1st direction in the 1st cutting plan line extended in a 1st direction in a workpiece, and a workpiece. It is an object of the present invention to provide a processing object cutting method capable of accurately cutting a processing object along both of the second scheduled cutting lines extending in the second direction.

  As a result of intensive studies in order to achieve the above object, the inventors of the present invention described above, in the above-described conventional object cutting method, the object to be processed along a cutting scheduled line extending in a direction intersecting with a predetermined direction. It was ascertained that the inability to cut an object with high accuracy was due to the cutting force for cutting the workpiece along the planned cutting line. That is, the cutting force for cutting the workpiece along the planned cutting line extending in the direction intersecting the predetermined direction cuts the workpiece along the planned cutting line extending in the predetermined direction. When the cutting force is greater than the predetermined cutting force, the probability that the workpiece cannot be accurately cut along the scheduled cutting line extending in the direction intersecting the predetermined direction is increased. The present inventors have further studied based on this finding and have completed the present invention. The cutting force is a force applied to cut the workpiece on which the modified region is formed. In other words, a large cutting force means that the load applied to cut the workpiece is larger than a certain force, and the workpiece is cut from the modified region by applying a force larger than a certain force. This means that the modified region is formed in a state that is relatively difficult to break. In addition, a small cutting force means that the load applied to cut the workpiece is smaller than a certain force, and the workpiece is cut starting from the modified region by applying a force smaller than a certain force. This means that the modified region is formed in a state that is relatively easy to break.

That is, in the method for cutting an object to be processed according to the present invention, the first object extending in the first direction in the object to be processed is obtained by irradiating the laser beam with the focusing point inside the plate-like object to be processed. A first modified region serving as a starting point of cutting is formed inside the workpiece along the scheduled cutting line, and the second extended in the second direction intersecting the first direction in the workpiece. A modified region forming step of forming a second modified region serving as a starting point of cutting inside the workpiece along the planned cutting line, and after the modified region forming step, the first modified region A first cutting step that cuts the workpiece along the first scheduled cutting line from the starting point, and after the first cutting step, along the second scheduled cutting line, starting from the second modified region includes a second cutting step of cutting the object, the Te, the object is first In a state of not being cut along the cross-scheduled line and the second line to cut, first required to cut the object along a first line to cut the first modified region as a starting point The cutting force is characterized by being larger than the second cutting force required for cutting the workpiece along the second scheduled cutting line starting from the second modified region.

In this processing object cutting method, in a state where the processing object is not cut along the first scheduled cutting line and the second scheduled cutting line, the first scheduled cutting line starts from the first modified region. The second cutting force required to cut the workpiece along the second scheduled cutting line, starting from the second modified region, is the first cutting force required to cut the workpiece along the line It is bigger than force. Accordingly, first, the workpiece is cut along the first scheduled cutting line with the first modified region as the starting point, and then along the second scheduled cutting line with the second modified region as the starting point. By cutting the object to be processed, the object to be processed can be accurately cut along both the first scheduled cutting line and the second scheduled cutting line.

  Note that the first and second modified regions that are the starting points of cutting are irradiated with laser light with the focusing point inside the object to be processed, so that multiphoton absorption and other factors are generated inside the object to be processed. It is formed by causing light absorption. Further, the second cutting force for cutting the workpiece along the second scheduled cutting line starting from the second modified region is such that the workpiece is cut along the first scheduled cutting line. This is the cutting force required in a state where it is not.

  In the workpiece cutting method according to the present invention, in the modified region forming step, the first modified region is formed inside the workpiece along the first scheduled cutting line, and then the second cutting scheduled. It is preferable to form the second modified region along the line inside the workpiece. When the first cutting force is greater than the second cutting force, the thickness of the workpiece is generally greater from the first modified region as the starting point than from the second modified region. It is difficult to crack in the vertical direction. Thus, before the second modified region is formed, the first modified region is formed along the first cutting planned line inside the workpiece, thereby forming the first modified region. Then, the extension of the crack in the thickness direction of the workpiece is suppressed, and the degree of warping of the workpiece due to the crack is reduced. Therefore, after the formation of the first modified region, the second modified region can be accurately formed inside the workpiece along the second scheduled cutting line. In addition, when the modified region is formed in the planned cutting line in the direction intersecting the planned cutting line in which the modified region has been formed earlier, the subsequent modified region is the previous modified region at the intersection of the planned cutting line. It becomes discontinuous under the influence of. Therefore, when the first cutting force is larger than the second cutting force, the first modified region is formed inside the object to be processed along the first cutting planned line, and then the second cutting scheduled. By forming the second modified region along the line inside the workpiece, cutting can be performed with high accuracy without causing problems such as meandering and chipping of the cut surface at the intersection and its periphery. it can. This is because if there is a discontinuous part of the modified region in the planned cutting line that requires a large cutting force, the discontinuous part and its surroundings will be forcibly cracked when a large force necessary for cutting is applied. Based on the meandering and chipping of the cut surface.

  In the processing object cutting method according to the present invention, in the modified region forming step, the number of columns of the first modified region formed with respect to one first scheduled cutting line and one second The number of columns of the second modified region formed with respect to the planned cutting line, the laser beam irradiation condition for forming the first modified region, and the second modified region It is preferable that the irradiation condition of the laser beam for forming the is different. Accordingly, the relationship between the magnitude of the first cutting force and the magnitude of the second cutting force can be made appropriate. The laser light irradiation conditions include, for example, pulse energy, repetition frequency, pulse width, formation interval (pitch) of modified regions, and the like.

  In the processing object cutting method according to the present invention, the processing object is more along the first cutting planned line than the second cutting planned line before the modified region forming step. It is preferable that a crack in the thickness direction of the workpiece is difficult to occur. Such a workpiece is suitable for the workpiece cutting method according to the present invention because the first cutting force tends to be larger than the second cutting force.

  In the workpiece cutting method according to the present invention, the workpiece may include a semiconductor substrate, and the first and second modified regions may include a melt processing region.

  According to the present invention, the first cutting scheduled line extending in the first direction in the workpiece and the second cutting schedule extending in the second direction intersecting the first direction in the workpiece. The workpiece can be accurately cut along both lines.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a preferred embodiment of a workpiece cutting method according to the present invention will be described in detail with reference to the drawings. In the present embodiment, a phenomenon called multiphoton absorption is used to form a modified region inside the workpiece. Therefore, first, a laser processing method for forming a modified region by multiphoton absorption will be 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, ···) the intensity of laser light becomes very high. 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 the laser processing method according to this embodiment using such multiphoton absorption will be described with reference to FIGS. As shown in FIG. 1, there is a planned cutting line 5 for cutting the workpiece 1 on the surface 3 of the wafer-like (plate-like) workpiece 1. The planned cutting line 5 is a virtual line extending linearly. In the laser processing method according to the present embodiment, as shown in FIG. 2, the modified region 7 is formed by irradiating the laser beam L with the focusing point P inside the processing object 1 under the condition that multiphoton absorption occurs. Form. In addition, the condensing point P is a location where the laser light L is condensed. Further, the planned cutting line 5 is not limited to a straight line but may be a curved line, or may be a line actually drawn on the workpiece 1 without being limited to a virtual line.

  Then, 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, in the direction of arrow A in FIG. 1). Thereby, as shown in FIGS. 3 to 5, the modified region 7 is formed inside the workpiece 1 along the planned cutting line 5, and this modified region 7 becomes the cutting start region 8. Here, the cutting starting point region 8 means a region that becomes a starting point of cutting (cracking) when the workpiece 1 is cut. The cutting starting point region 8 may be formed by continuously forming the modified region 7 or may be formed by intermittently forming the modified region 7.

  In the laser processing method according to the present embodiment, the surface 3 of the workpiece 1 is hardly absorbed by the surface 3 of the workpiece 1, so that the surface 3 of the workpiece 1 is not melted.

  If the cutting start region 8 is formed inside the processing target 1, cracks are likely to occur from the cutting start region 8, so that the processing target 1 is cut with a relatively small force as shown in FIG. 6. be able to. Therefore, the processing object 1 can be cut with high accuracy without causing unnecessary cracks on the surface 3 of the processing object 1.

  The following two types of cutting of the workpiece 1 starting from the cutting start region 8 are conceivable. First, after the cutting start region 8 is formed, when the artificial force is applied to the processing target 1, the processing target 1 is broken starting from the cutting start region 8 and the processing target 1 is cut. It is. This is, for example, cutting when the workpiece 1 is thick. The artificial force is applied by, for example, applying bending stress or shear stress to the workpiece 1 along the cutting start region 8 of the workpiece 1 or giving a temperature difference to the workpiece 1. It is to generate thermal stress. The other one forms the cutting start region 8 so that it is naturally cracked from the cutting start region 8 in the cross-sectional direction (thickness direction) of the processing target 1, and as a result, the processing target 1 is formed. This is the case when it is disconnected. This is possible, for example, when the thickness of the workpiece 1 is small, and the cutting start region 8 is formed by one row of the modified region 7, and when the thickness of the workpiece 1 is large. This is made possible by forming the cutting start region 8 by the modified region 7 formed in a plurality of rows in the thickness direction. Even in the case of natural cracking, cracks do not run on the surface 3 of the portion corresponding to the portion where the cutting start region 8 is not formed in the portion to be cut, and the portion where the cutting start region 8 is formed. Since only the corresponding part can be cleaved, the cleaving can be controlled well. In recent years, since the thickness of the workpiece 1 such as a silicon wafer tends to be thin, such a cleaving method with good controllability is very effective.

  In the laser processing method according to the present embodiment, there are cases (1) to (3) below as the modified region.

(1) In the case where the modified region is a crack region including one or a plurality of cracks, the focusing point is set inside the object to be processed (for example, a piezoelectric material made of glass or LiTaO ₃ ), and the electric field strength at the focusing point is Irradiation with laser light is performed under conditions of 1 × 10 ⁸ (W / cm ² ) or more and a pulse width of 1 μs or less. The magnitude of this pulse width is a condition that allows a crack region to be formed only inside the workpiece without causing extra damage to the surface of the workpiece 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, the mechanism of cutting the workpiece by forming the crack region will be described with reference to FIGS. As shown in FIG. 8, under the condition that multiphoton absorption occurs, the converging point P is aligned with the inside of the workpiece 1 and the laser beam L is irradiated to form a crack region 9 along the planned cutting line. The crack region 9 is a region including one or more cracks. The crack region 9 thus formed becomes a cutting start region. As shown in FIG. 9, the crack further grows from the crack region 9 (that is, from the cutting start region), and the crack is formed on the front surface 3 and the back surface 21 of the workpiece 1 as shown in FIG. 10. As shown in FIG. 11, the workpiece 1 is broken and the workpiece 1 is cut. A crack that reaches the front surface 3 and the back surface 21 of the workpiece 1 may grow naturally, or may grow when a force is applied to the workpiece 1.

(2) When the reforming region is a melt processing region The focusing point is set inside the object to be processed (for example, a semiconductor material such as silicon) and the electric field strength at the focusing point is 1 × 10 ⁸ (W / cm ^2). ) Irradiation with laser light is performed under the above conditions with a pulse width of 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 melt treatment region is a region once solidified after melting, a region in a molten state, or a region re-solidified from a molten state, and can also be referred to as a phase-changed region or a region in which the crystal structure has 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. 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 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
N. A. : 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. The size in the thickness direction of the melt processing region 13 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 thickness t of the silicon substrate 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 the Nd: YAG laser of 1064 nm, 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 13 by multiphoton absorption is formed near the center of the silicon wafer 11, 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 13 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 melt processing region 13 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.

  Note that a silicon wafer is cracked as a result of generating cracks in the cross-sectional direction starting from the cutting start region formed by the melt processing region and reaching the front and back surfaces of the silicon wafer. The The cracks that reach the front and back surfaces of the silicon wafer may grow naturally or may grow by applying force to the silicon wafer. And when a crack naturally grows from the cutting start region to the front and back surfaces of the silicon wafer, the case where the crack grows from a state where the melt treatment region forming the cutting starting region is melted, and the cutting starting region There are both cases where cracks grow when the solidified region is melted from the molten state. However, in either case, the melt processing region is formed only inside the silicon wafer, and the melt processing region is formed only inside the cut surface after cutting as shown in FIG. In this way, when the cutting start region is formed by the melt processing region inside the workpiece, unnecessary cracking off the cutting start region line is unlikely to occur during cleaving, so that cleaving control is facilitated. Incidentally, the formation of the melted region is not only caused by multiphoton absorption, but may also be caused by other absorption effects.

(3) When the modified region is a refractive index changing region The focusing point is set inside the object to be processed (for example, glass), and the electric field intensity at the focusing point is 1 × 10 ⁸ (W / cm ² ) or more. Laser light is irradiated under the condition that the pulse width is 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, the case of (1) to (3) has been described as the modified region, but if the cutting starting region is formed as follows in consideration of the crystal structure of the wafer-like workpiece or its cleavage property, Using the cutting start region as a starting point, it becomes possible to cut the workpiece with a smaller force and with high accuracy.

That is, in the case of a substrate made of a single crystal semiconductor having a diamond structure such as silicon, the cutting start region is formed in a direction along the {111} plane (first cleavage plane) or the {110} plane (second cleavage plane). Is preferred. In the case of a substrate made of a zinc-blende-type III-V compound semiconductor such as GaAs, the cutting start region is formed in the direction along the (011) plane or the (0-1-1) plane. preferable. Furthermore, in the case of a substrate having a hexagonal crystal structure such as sapphire (Al ₂ O ₃ ), the (0001) plane (C plane) is the main plane and the (1-100) plane or the (−1100) plane is used. It is preferable to form the cutting starting point region in the above direction.

  Note that the orientation flat is formed on the substrate along the direction in which the above-described cutting start region is to be formed (for example, the direction along the (111) plane in the single crystal silicon substrate) or the direction perpendicular to the direction in which the cutting start region is to be formed. By using the orientation flat as a reference, it is possible to easily and accurately form the cutting start area along the direction in which the cutting start area is to be formed on the substrate.

  Next, a preferred embodiment of the workpiece cutting method according to the present invention will be described.

  As shown in FIGS. 14 and 15, the workpiece 1 includes a GaAs wafer (semiconductor substrate) 12 and a functional element layer 16 including a plurality of functional elements 15 and formed on the main surface of the GaAs wafer 12. ing. The GaAs wafer 12 has a zinc-blende structure, with the main surface being a (100) plane, a plane parallel to the orientation flat 6 is a (011) plane or a (0-1-1) plane, and a plane perpendicular to the orientation flat 6 is It is a (0-1 1) plane or a (0 1-1) plane. The functional element 15 is, for example, a semiconductor operation layer formed by crystal growth, a light receiving element such as a photodiode, a light emitting element such as a laser diode, or a circuit element formed as a circuit, and the orientation flat 6 of the GaAs wafer 12. Are formed in a matrix form in a direction parallel to and perpendicular to.

The workpiece 1 configured as described above is cut for each functional element 15 as follows. First, as shown in FIG. 16, the expanded tape 23 is attached to the back surface 21 of the workpiece 1. Subsequently, the workpiece 1 is fixed on a mounting table (not shown) of the laser processing apparatus with the functional element layer 16 facing upward. And as shown in FIG. 14, the cutting planned line (1st cutting planned line) extended in the direction (1st direction) perpendicular | vertical to the orientation flat 6 so that it may pass between the adjacent functional elements 15 and 15. FIG. 5 _1, and orientation line to cut (the second line to cut) extending in a direction parallel (second direction) flat 6 5 set _2.

Subsequently, as shown in FIG. 17A, the surface 3 of the workpiece 1 is used as the laser beam incident surface, and the laser beam L is irradiated inside the GaAs wafer 12 with the focusing point P being irradiated, so that the mounting table is moved. by relatively moving the converging point P along each line to cut 5 ₁ extending in a direction perpendicular to the orientation flat 6. Multiple times for the focal point line to cut 5 ₁ relative one movement of P along the respective cutting lines 5 ₁ (e.g., 5 times) carried out, but the position to align the focal point P by changing the distance from the surface 3 each time, from the rear face 21 side in this order, one molten processed region (first modified region) of the plurality of rows with respect to the line to cut 5 ₁ 13 ₁ GaAs wafer 12 One row is formed inside each.

After forming the molten processed region 13 _1, as shown in FIG. 17 (b), the surface 3 of the object 1 in the interior of the GaAs wafer 12 as the laser light entrance surface with its focusing point P of laser light L irradiated, by the movement of the mounting table, relatively moving the converging point P along each line to cut 5 ₂ extending in a direction parallel to the orientation flat 6. The relative movement of the converging point P along each line to cut 5 _2, with respect to one line to cut 5 ₂ while changing each time the distance from the surface 3 of the position to align the focal point P multiple Te (e.g., 5 times) it is carried out, from the rear face 21 side in this order, one molten processed region (second modified regions) of the plurality of rows with respect to the line to cut _{5 2} 13 ₂ GaAs wafer 12 One row is formed inside each.

Note that the molten processed region ₁₃ 1, 13 _2, there is a case where cracks are mixed. Further, the number of columns of the melt processing regions 13 ₁ and 13 ₂ formed inside the GaAs wafer 12 with respect to _one cutting scheduled line 5 ₁ and 5 ₂ varies depending on the thickness of the GaAs wafer 12 and the like. However, the present invention is not limited to a plurality of columns and may be a single column.

Subsequently, the expanded tape 23 is expanded as shown in FIG. Then, the direction in this state, with respect to the rear face 21 of the object 1, by pressing a knife edge 41 through the expandable tape 23, the direction parallel to the orientation flat 6 (i.e., the line to cut 5 ₂ extends ). Thus, acts bending stress in the object 1, molten processed regions 13 ₁ as a starting point, the orientation the object 1 is strip along each line to cut 5 ₁ extending in a direction perpendicular to the flat 6 Disconnected. At this time, since the expanded tape 23 is in an expanded state, the workpieces 1 cut into strips are separated from each other, as shown in FIGS.

After the workpiece 1 is cut into strips, as shown in FIG. 19 (a), the expanded tape 23 is expanded and the knife 21 is passed through the expanded tape 23 against the back surface 21 of the workpiece 1. by pressing an edge 41, perpendicular to the orientation flat 6 (i.e., lines to cut 5 ₁ extending direction) is moved to. Thus, acts bending stress in the object 1, molten as the processing region 13 ₂ starting point, orientation object 1 is chip-like along each line to cut 5 ₂ extending in a direction parallel to the flat 6 Thus, a large number of semiconductor chips 25 having one functional element 15 are obtained. At this time, since the expanded tape 23 is in an expanded state, the semiconductor chips 25 are separated from each other as shown in FIGS. 19B and 22.

In the above-described workpiece cutting method, the object 1 is, before forming the molten processed region 13 _1, 13 _2, more along the line to cut 5 ₂ extending in a direction parallel to the orientation flat 6, orientation towards along the line to cut 5 ₁ extending in a direction perpendicular to the flat 6, cracks in the thickness direction of the object 1 has become what hardly occurs. It is because of the influence based on the nature of the crystal.

Therefore, the starting point in the workpiece cutting method described above, the first cutting force for cutting the object 1 along the line to cut 5 ₁ molten processed region 13 ₁ as starting point, the molten processed region 13 ₂ second cutting force larger than (cutting force required in a state where the object 1 is not cut along the line to cut 5 ₁₎ for along the line to cut 5 ₂ cutting the object 1 as become. Therefore, first, the molten processed region 13 ₁ along the line to cut 5 ₁ starting to cut the object 1, after which the object along the line to cut 5 ₂ molten processed region 13 ₂ starting by cutting the 1, the object 1 can accurately be cut along each line to cut 5 _1, 5 _2.

In the workpiece cutting method described above, the molten processed region 13 ₁ along the line to cut 5 ₁ after formation within the object 1, molten processed along the line to cut 5 _second region 13 ₂ Is formed inside the workpiece 1. Here, from starting from the molten processed region 13 ₂ found the following starting from the molten processed region 13 _1, cracks in the thickness direction of the object 1 hardly occurs. Thus, prior to forming the molten processed region 13 _2, by the molten processed region 13 ₁ along the line to cut 5 ₁ is formed within the object 1, the formation time of the molten processed region 13 _1, The extension of the crack in the thickness direction of the workpiece 1 is suppressed, and the degree of warpage of the workpiece 1 due to the crack is reduced. Therefore, it is possible after forming the molten processed region 13 _1, accurately to form the molten processed region 13 ₂ within the object 1 along the line to cut 5 _2.

  The present invention is not limited to the embodiment described above.

For example, in the embodiment, one and the number of columns of the molten processed region 13 ₁ is formed for the line to cut 5 _1, one line to cut 5 ₂ molten processed region 13 ₂ formed against Although the number of columns in is the same, they may be different. In the above embodiment, the irradiation conditions of the laser beam for forming the molten processed region 13 _1, although the irradiation conditions of the laser beam for forming the molten processed region 13 ₂ are the same, different them It may be allowed. These, the molten processed region 13 ₁ the first and the magnitude of the cutting force for cutting the object 1 along the line to cut 5 ₁ starting from the line to cut 5 ₂ starting from the molten processed region 13 ₂ The relationship with the magnitude of the second cutting force for cutting the workpiece 1 along the line can be made appropriate.

  FIG. 20 is a graph showing the cutting force of a GaAs wafer having a thickness of 300 μm. Specifically, the melt treatment region was formed under various conditions along the planned cutting line, and the load applied at the time of fracture was measured by a three-point bending test. As a result, when three rows of melt treatment regions are formed with a pulse energy of 10 μJ, when three rows of melt treatment regions are formed with a pulse energy of 13 μJ, when five rows of melt treatment regions are formed with a pulse energy of 10 μJ, melting is performed with a pulse energy of 13 μJ. The load (that is, cutting force) increased in the order in which five rows of treatment areas were formed.

  Therefore, along the first scheduled cutting line extending in the first direction in the workpiece, five rows of the melt treatment regions are formed with the pulse energy of 13 μJ, and the second crossing the first direction in the workpiece. When three rows of melt processing regions are formed with a pulse energy of 10 μJ along the second scheduled cutting line extending in the direction of the direction, or in the first scheduled cutting line extending in the first direction on the workpiece 5 melt processing regions are formed at a pulse energy of 10 μJ, and the workpiece is melted at a pulse energy of 10 μJ along a second scheduled cutting line extending in a second direction intersecting the first direction in the workpiece. When the processing regions are formed in three rows, it is preferable to first cut the workpiece along the first scheduled cutting line and then cut the workpiece along the second scheduled cutting line. .

  In addition, before the modified region is formed, the second extending along the first cutting planned line extending in the first direction extends in the second direction intersecting the first direction. Specific examples of the plate-like workpiece that is less likely to be cracked in the thickness direction along the planned cutting line include the following. In the case of GaAs, when the main surface is the (100) plane, the first modified region is formed on the (01-1) plane (or (0-11) plane), and the second modified region is ( 0-1-1) plane (or (011) plane). In the case of sapphire, when the principal surface (surface orientation) is the (0001) plane, the first modified region is formed on the (11-20) plane, and the second modified region is (1-100). ) Form on the surface.

In the above embodiment, the knife edge 41 is pressed against the back surface 21 of the workpiece 1 via the expanded tape 23 and moved in a direction parallel to and perpendicular to the orientation flat 6. by the action of bending stress at the object 1, it has been cut along the object 1 line to cut 5 _1, 5 _2, with respect to the rear face 21 of the object 1 through the expandable tape 23, the cut by applying the circuit breaker along the line 5 _1, 5 _2, it may be cut along the object 1 the line to cut 5 _1, 5 _2.

Moreover, in the said embodiment, although the surface 3 of the workpiece 1 was made into the laser beam incident surface, it is good also considering the back surface 21 of the workpiece 1 as a laser beam incident surface. When the back surface 21 of the workpiece 1 is a laser light incident surface, the workpiece 1 is cut into a plurality of semiconductor chips 25 as follows as an example. That is, a protective tape is affixed to the surface of the functional element layer 16, and the protective tape holding the workpiece 1 is fixed to the mounting table of the laser processing apparatus in a state where the functional element layer 16 is protected by the protective tape. Then, the processing inside the object 1 by the combined focal point P is irradiated with laser light L, along each line to cut 5 _1, 5 ₂ rear face 21 of the object 1 as a laser light entrance surface Melt processing regions 13 ₁ and 13 ₂ are formed inside the workpiece 1. Subsequently, the protective tape fixed to the mounting table is separated from the workpiece 1. And after affixing the expanded tape 23 on the back surface 21 of the workpiece 1 and peeling off the protective tape from the surface of the functional element layer 16, the expanded processing region 13 ₁ , 13 ₂ is expanded. Is cut along the planned cutting lines 5 ₁ and 5 ₂ .

  Moreover, in the said embodiment, although the fusion | melting process area | region was formed inside the semiconductor material of a process target object, a crack area | region, a refractive index change area | region, etc. inside a process target object which consists of glass, a piezoelectric material, etc. Other modified regions may be formed.

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 processed object cut | disconnected by the laser processing method which concerns on this embodiment. It is a graph which shows the relationship between the peak power density and the magnitude | size of a crack spot 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 internal transmittance | permeability of a silicon substrate in the laser processing method which concerns on this embodiment. It is a top view of the processing target used as the object of the processing target cutting method concerning this embodiment. It is a fragmentary longitudinal cross-sectional view of the workpiece shown in FIG. It is a fragmentary longitudinal cross-sectional view of the workpiece for demonstrating the workpiece cutting method which concerns on this embodiment, and is the state which affixed the expanded tape on the workpiece. It is a fragmentary longitudinal cross-sectional view of the workpiece for demonstrating the workpiece cutting method which concerns on this embodiment, (a) is to a workpiece along the cutting scheduled line extended in the direction perpendicular | vertical to an orientation flat. A state in which the laser beam is irradiated, (b) is a state in which the workpiece is irradiated with the laser beam along a planned cutting line extending in a direction parallel to the orientation flat. It is a fragmentary longitudinal cross-sectional view of the workpiece for demonstrating the workpiece cutting method which concerns on this embodiment, (a) is to a workpiece along the cutting scheduled line extended in the direction perpendicular | vertical to an orientation flat. A state where the knife edge is pressed through the expanded tape, (b) is a state where the workpiece is cut into a strip shape. It is a fragmentary longitudinal cross-sectional view of the workpiece for demonstrating the workpiece cutting method which concerns on this embodiment, (a) is a workpiece along the cutting plan line extended in the direction parallel to orientation flat. A state where the knife edge is pressed through the expanded tape, (b) is a state where the workpiece is cut into chips. It is a graph which shows the cutting force of a 300-micrometer-thick GaAs wafer. It is a top view in the state where the processing object shown in Drawing 14 was cut in the shape of a strip. It is a top view in the state where the processing object shown in Drawing 14 was cut in the shape of a chip.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Processing object, 5 ₁ ... Scheduled cutting line (1st scheduled cutting line), 5 ₂ ... Scheduled cutting line (2nd scheduled cutting line), 12 ... GaAs wafer (semiconductor substrate), 13 ₁ ... Melting process Region (first modified region), 13 ₂ ... Melting region (second modified region), L... Laser light, P.

Claims (6)

By irradiating a laser beam with a condensing point inside the plate-like workpiece, a cutting start point along the first scheduled cutting line extending in the first direction in the workpiece is obtained. Forming a first modified region to be formed inside the workpiece, and along a second scheduled cutting line extending in a second direction intersecting the first direction in the workpiece. A modified region forming step of forming a second modified region serving as a starting point of cutting inside the workpiece;
After the modified region forming step, a first cutting step of cutting the workpiece along the first scheduled cutting line with the first modified region as a starting point;
After the first cutting step, a second cutting step of cutting the workpiece along the second scheduled cutting line starting from the second modified region,
In a state where the workpiece is not cut along the first scheduled cutting line and the second scheduled cutting line, the first modified region is used as a starting point along the first scheduled cutting line. The first cutting force required to cut the workpiece is a second cutting force required to cut the workpiece along the second scheduled cutting line from the second modified region. A method for cutting an object to be processed, characterized by being larger than the cutting force.   In the modified region forming step, after the first modified region is formed inside the workpiece along the first scheduled cutting line, the second modified region is formed along the second scheduled cutting line. The method for cutting an object to be processed according to claim 1, wherein the modified region is formed inside the object to be processed.   In the modified region forming step, the number of columns of the first modified region formed for one of the first scheduled cutting lines and the number of columns of the second scheduled cutting are formed. The method of cutting a workpiece according to claim 1 or 2, wherein the number of columns of the second modified region to be made is different.   In the modified region forming step, the irradiation condition of the laser beam for forming the first modified region is different from the irradiation condition of the laser beam for forming the second modified region. The workpiece cutting method according to claim 1, wherein the workpiece is cut.   Prior to the modified region forming step, the workpiece is more along the first cutting line than in the second cutting line, in the thickness direction of the processing object. The method for cutting an object to be processed according to any one of claims 1 to 4, wherein cracks are hardly generated.   The processing object cutting method according to claim 1, wherein the processing object includes a semiconductor substrate, and the first and second modified regions include a melt processing region.

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