JP4146863B2 - Semiconductor substrate cutting method - Google Patents

Description

  The present invention relates to a method for cutting a semiconductor substrate by laser processing.

In recent years, various layers such as those obtained by crystal growth of a semiconductor operation layer such as GaN on an Al ₂ O ₃ substrate for semiconductor devices, and those obtained by bonding another glass substrate on a glass substrate for liquid crystal display devices, etc. There is a demand for a technique for cutting a workpiece having a structure with high accuracy.
Conventionally, a blade dicing method or a diamond scribe method is generally used to cut a workpiece having such a laminated structure.

  The blade dicing method is a method of cutting and cutting a workpiece with a diamond blade or the like. On the other hand, with the diamond scribe method, a diamond point tool is used to provide a scribe line on the surface of the object to be processed, and a knife edge is pressed against the back surface of the object to be processed along the scribe line to divide and cut the object to be processed. Is the method.

However, in the blade dicing method, for example, when the object to be processed is for the above-described liquid crystal display device, a gap is provided between the glass substrate and another glass substrate. There is a risk that shavings and lubricating cleaning water may get in. Also, in the diamond scribe method, when the object to be processed has a high hardness substrate such as an Al ₂ O ₃ substrate, or when the object to be processed is a glass substrate bonded together. In addition, scribe lines must be provided not only on the front surface but also on the back surface of the workpiece, and there is a risk that cutting defects may occur due to misalignment of the scribe lines provided on the front and back surfaces. Even a semiconductor substrate having a laminated portion on the surface is difficult to cut well.

  This invention is made | formed in view of such a situation, solves the above problems, and provides the cutting method of the semiconductor substrate by the laser processing which can cut | disconnect a semiconductor substrate with high precision. Objective.

In order to achieve the above object, a method for cutting a semiconductor substrate according to the present invention is a method for cutting a semiconductor substrate having a laminated portion formed on a front surface, and expands a laser beam with a back surface of the semiconductor substrate as a laser beam incident surface. By irradiating without passing through the tape , a melt-processed region that is once melted and re-solidified is formed inside the semiconductor substrate, and this melt-processed region forms a cutting start region along the planned cutting line of the semiconductor substrate. And a step of cutting the semiconductor substrate into a plurality of portions starting from the cutting start region.

  According to the present invention, the semiconductor substrate can be irradiated with laser light from the back side of the semiconductor substrate to form a melt processing region along a desired cutting line to be cut inside the semiconductor. If the semiconductor substrate is cut into a plurality of portions using this melting processing region as a cutting starting region, the unnecessary cracks that are out of the cutting starting region are unlikely to occur during cutting.

The method for cutting a semiconductor substrate according to the present invention is a method for cutting a semiconductor substrate having a laminated portion formed on the front surface, and the back surface of the semiconductor substrate is used as a laser light incident surface, and laser light is irradiated without passing through an expanding tape. As a result, a melt-processed region that is once melted and re-solidified inside the semiconductor substrate is formed in the thickness direction of the semiconductor substrate, and the semiconductor substrate is scheduled to be cut by this melt-processed region. And a step of forming a cutting starting region that is biased toward the surface side in the thickness direction of the semiconductor substrate, and a step of cutting the semiconductor substrate into a plurality of portions starting from the cutting starting region.

  According to the present invention, the semiconductor substrate is irradiated with laser light from the back surface side of the semiconductor substrate to form a melt treatment region along the desired cutting line to be cut inside the semiconductor so as to be biased toward the front surface side. Can do. Then, when the semiconductor substrate is cut into a plurality of portions using the melting processing region as a cutting start region, unnecessary cracks that are out of the cutting starting region are unlikely to occur during cutting. In particular, since the melt processing region is biased toward the surface side of the substrate, the surface side can be cut more accurately.

  In the present invention, the cutting start region can include the center in the thickness direction of the semiconductor substrate.

  Further, in the present invention, in the step of forming the cutting start region, when imaging a surface including the planned cutting line, the formation of the cutting start region can be controlled by the imaging data.

  According to the method for cutting a semiconductor substrate according to the present invention, even when there are various laminated portions on the front surface side of the semiconductor substrate, a laser beam is irradiated from the back surface side of the semiconductor substrate, so that the melt processing region is formed inside the semiconductor substrate. And a cutting start region along a desired cutting line to be cut can be formed. Then, it is possible to cut the substrate with a relatively small force with high accuracy, starting from the cutting start region. Therefore, according to this semiconductor substrate cutting method, the semiconductor substrate can be cut with high accuracy.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the cutting method by laser processing according to the present embodiment, a modified region by multiphoton absorption is formed inside a workpiece. This laser processing method, particularly multiphoton absorption, will be described first.

If the photon energy hν is smaller than the absorption band gap E _G of the material, the material becomes optically 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 the condition that 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 desired scheduled cutting line 5 on which the workpiece 1 is to be cut. The planned cutting line 5 is a virtual line extending in a straight line (the actual cutting line 5 may be drawn on the workpiece 1 to form the planned cutting line 5). 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 surface 3 of the workpiece 1 is preferably flat and smooth in order to prevent the laser light L from being scattered on the surface 3.

  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). As a result, as shown in FIGS. 3 to 5, the modified region 7 is formed only inside the workpiece 1 along the planned cutting line 5, and the cutting start region 8 is formed by the modified region 7. . 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.

  The cutting of the substrate starting from the cutting start region is completed by applying an artificial force to the substrate after forming the cutting start region. That is, by applying a tensile stress in a direction crossing the cutting start region of the substrate, the substrate is cracked from the cutting start region and the substrate is cut.

In the present embodiment, the modified regions formed by multiphoton absorption include the following (1) to (3).
(1) When the modified region is a crack region including one or a plurality of cracks, the focusing point is set inside the substrate (for example, a piezoelectric material made of sapphire, glass, or LiTaO ₃ ), and the electric field intensity at the focusing point. Is 1 × 10 ⁸ (W / cm ² ) or more and the pulse width is 1 μs or less. The magnitude of this pulse width is a condition under which a crack region can be formed only inside the substrate without causing extra damage to the surface of the substrate while causing multiphoton absorption. As a result, a phenomenon of optical damage due to multiphoton absorption occurs inside the substrate. This optical damage induces thermal strain inside the substrate, thereby forming a crack region inside the substrate. 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 obtained the relationship between the electric field strength and the size of the cracks by experiment. The experimental conditions are as follows.
(A) Substrate: Pyrex (registered trademark) glass (thickness 700 μm)
(B) Laser light source: semiconductor laser excitation Nd: YAG laser wavelength: 1064 nm
Laser beam spot cross-sectional area: 3.14 × 10 ⁻⁸ cm ²
Oscillation form: Q switch pulse repetition frequency: 100 kHz
Pulse width: 30ns
Output: Output <1 mJ / pulse laser light quality: TEM ₀₀
Polarization characteristics: Linearly polarized light (C) Condensation lens Transmittance with respect to laser beam wavelength: 60% (D) Moving speed of mounting table on which substrate is mounted: 100 mm / sec Note that the laser beam quality is TEM ₀₀ . It means that the light can be condensed up to the wavelength of the laser beam with high light condensing property.

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 indicates the size of a crack portion (crack spot) formed inside the substrate 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. It can be seen that crack spots are generated inside the substrate from the peak power density of about 10 ¹¹ (W / cm ² ), and the crack spots increase as the peak power density increases.

  Next, in the laser processing according to the present embodiment, a mechanism for cutting the substrate 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 more cracks. A cutting start region is formed by the crack region 9. As shown in FIG. 9, when an artificial force (for example, tensile stress) is applied to the workpiece 1, the crack further grows from the crack region 9 (that is, from the cutting start region), As shown in FIG. 10, the crack reaches the front surface 3 and the back surface 21 of the workpiece 1, and the workpiece 1 is broken as the workpiece 1 is broken as shown in FIG. 11.

(2) When the modified region is a melted region, the focusing point is aligned with the inside of the substrate (for example, a semiconductor material such as silicon), and the electric field strength at the focusing point is 1 × 10 ⁸ (W / cm ² ) or more. In addition, the laser beam is irradiated under the condition that the pulse width is 1 μs or less. As a result, the inside of the substrate is locally heated by multiphoton absorption. By this heating, a melt processing region is formed inside the substrate. 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 substrate 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) Substrate: Silicon wafer (thickness 350 μm, outer diameter 4 inches)
(B) Laser light source: semiconductor laser excitation Nd: YAG laser wavelength: 1064 nm
Laser beam spot cross-sectional area: 3.14 × 10 ⁻⁸ cm ²
Oscillation form: Q switch pulse repetition frequency: 100 kHz
Pulse width: 30ns
Output: 20 μJ / pulse laser light Quality: TEM ₀₀
Polarization characteristics: Linearly polarized light (C) Condensing lens magnification: 50 × N. A. : 0.55
Transmittance with respect to laser beam wavelength: 60% (D) Moving speed of mounting table on which substrate 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, when the melting region 13 by multiphoton absorption is formed near the center of the silicon wafer 11, the silicon wafer 11 is formed at a portion of 175 μm from the surface of the silicon wafer 11. 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.

  In addition, when an artificial force such as tensile stress is applied to a silicon wafer, a crack is generated in the cross-sectional direction starting from a cutting start region formed in the melt processing region, and the crack is generated in the silicon wafer. As a result, it is cut by reaching the front and back surfaces. Further, 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. When the cutting start region is formed in the substrate with the melt processing region, unnecessary cracks that are out of the cutting start region line are less likely to occur during cutting, and cutting control is facilitated.

(3) When the modified region is a refractive index changing region, the focusing point is set inside the substrate (for example, glass), the electric field intensity at the focusing point is 1 × 10 ⁸ (W / cm ² ) or more, and the pulse width Is irradiated with laser light under the condition of 1 ns or less. When the pulse width is made extremely short and multiphoton absorption occurs inside the substrate, the energy due to the multiphoton absorption is not converted into thermal energy, and the ionic valence change, crystallization, polarization orientation, etc. are inside the substrate. A permanent structural change is induced to form a refractive index changing 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.

  As described above, the cases of (1) to (3) have been described as the modified regions formed by multiphoton absorption. However, the cutting starting region is formed as follows in consideration of the crystal structure of the substrate and its cleavage property. For example, the substrate can be cut with a smaller force and with higher accuracy from the cutting start region.

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 group compound semiconductor such as GaAs, it is preferable to form the cutting start region in the direction along the (110) plane. Furthermore, in the case of a substrate having a hexagonal crystal structure such as sapphire (Al ₂ O ₃ ), the (1120) plane (A plane) or (1100) plane ( It is preferable to form the cutting start region in a direction along the (M plane).

  Note that, for example, when a disc-shaped wafer is cut as a substrate, the above-described cutting start region should be formed (for example, the direction along the (111) plane in the single crystal silicon substrate) or the cutting start region should be formed. If the orientation flat is formed on the wafer along the direction orthogonal to the direction, the cutting start region along the direction in which the cutting start region should be formed can be easily and accurately formed on the wafer by using the orientation flat as a reference. It becomes possible.

  Next, a laser processing apparatus used in the laser processing method described above will be described with reference to FIG. FIG. 14 is a schematic configuration diagram of the laser processing apparatus 100.

  The laser processing apparatus 100 includes a laser light source 101 that generates laser light L, a laser light source control unit 102 that controls the laser light source 101 to adjust the output and pulse width of the laser light L, and the reflection function of the laser light L. And a dichroic mirror 103 arranged to change the direction of the optical axis of the laser light L by 90 °, a condensing lens 105 for condensing the laser light L reflected by the dichroic mirror 103, and a condensing lens A mounting table 107 on which the workpiece 1 to be irradiated with the laser beam L condensed by the lens 105 is mounted; an X-axis stage 109 for moving the mounting table 107 in the X-axis direction; A Y-axis stage 111 for moving in the Y-axis direction orthogonal to the X-axis direction, and a Z-axis stage 1 for moving the mounting table 107 in the Z-axis direction orthogonal to the X-axis and Y-axis directions 3, and a stage controller 115 for controlling the movement of these three stages 109, 111 and 113.

  The converging point P is moved in the X (Y) axis direction by moving the workpiece 1 in the X (Y) axis direction by the X (Y) axis stage 109 (111). Since the Z-axis direction is a direction orthogonal 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. Thereby, for example, when a laminated structure is provided on the workpiece 1, the condensing point P can be adjusted to a desired position inside the workpiece 1.

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 Nd: YVO ₄ laser and Nd: YL.
There are F laser and titanium sapphire laser. In this embodiment, 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 laser processing apparatus 100 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 beam splitter 119 for visible light 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 100 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 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 100 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 100, 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 of the workpiece 1 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 of the workpiece 1. 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 100 is controlled. Therefore, the overall control unit 127 functions as a computer unit.

  Next, a laser processing method according to this embodiment using the laser processing apparatus 100 described above will be described. FIG. 15 is a perspective view showing a wafer 1a that is an object to be processed in the laser processing method according to the present embodiment. FIG. 16 is a plan view of the wafer 1a shown in FIG. FIG. 17 is an enlarged view showing a VI-VI section and a VII-VII section of the wafer 1a shown in FIG.

  Referring to FIGS. 15 to 17, the wafer 1 a is flat and has a substantially disk shape. Referring to FIG. 16, a plurality of scheduled cutting lines 5 are set on the surface 3 of the wafer 1a so as to intersect vertically and horizontally. The planned cutting line 5 is a virtual line assumed for cutting the wafer 1a into a plurality of chip portions. This scheduled cutting line 5 may be assumed along the cleavage plane of the wafer 1a, for example.

  The wafer 1 a has an orientation flat (hereinafter referred to as “OF”) 19. In the present embodiment, the OF 19 is formed with the direction parallel to one direction of the planned cutting lines 5 intersecting vertically and horizontally as the longitudinal direction. The OF 19 is provided for the purpose of easily discriminating the cutting direction when the wafer 1a is cut along the scheduled cutting line 5.

Referring to FIG. 17, the wafer 1 a includes a substrate 15 made of semiconductor (Si) and a stacked portion 4 stacked on the surface 6 of the substrate 15. The stacked portion 4 includes interlayer insulating films 17a and 17b made of an insulating material (SiO ₂ ), and a first wiring layer 19a and a second wiring layer 19b made of metal (W). The interlayer insulating layer 17 a is laminated on the surface 6 of the substrate 15, and a first wiring layer 19 a is laminated on the element forming region set on the surface 6 by being divided from each other. The first wiring layer 19a and the substrate 15 are electrically connected to each other by a plug 20a provided so as to penetrate the interlayer insulating layer 17a. The interlayer insulating layer 17b is stacked on the interlayer insulating layer 17a and the first wiring layer 19a, and the second wiring layer 19b is stacked on the interlayer insulating layer 17b in a region corresponding to the first wiring layer 19a. Has been. The second wiring layer 19b and the first wiring layer 19a are electrically connected to each other by a plug 20b provided so as to penetrate the interlayer insulating layer 17b.

  In the region on the interlayer insulating layer 17b and in the gap between the second wiring layers 19b, a planned cutting line 5 is assumed. That is, when the wafer 1 a is viewed from the front surface 3 side, the interlayer insulating layers 17 a and 17 b in the stacked portion 4 overlap with the planned cutting line 5. In the planned cutting line 5, the surface of the interlayer insulating layer 17b (that is, the surface 3 of the wafer 1a) is flat and smooth.

  18 and 19 are flowcharts for explaining the laser processing method according to the present embodiment. 20 to 22 are cross-sectional views of the wafer 1a for explaining the laser processing method.

  Referring to FIG. 18, first, an expandable tape 23, which is an extensible film, is attached to the back surface 21, which is one surface of the wafer 1a (S1, FIG. 20). The expand tape 23 is made of, for example, a material that expands by heating, and is used to separate the wafer 1a into chips in a later process. The expanding tape 23 may be extended by applying a force in the extending direction, for example, in addition to the expanding tape 23 by heating.

  Subsequently, a cutting starting point region 8 is formed along the planned cutting line 5 inside the substrate 15 of the wafer 1a (S3, FIGS. 21A and 21B). Here, FIG. 21B is a cross-sectional view showing a VIII-VIII cross section of the wafer 1a shown in FIG. That is, by irradiating the condensing point P inside the substrate 15 with the laser beam L using the region corresponding to the cutting line 5 on the surface 3 which is the other surface of the wafer 1 a as the laser beam incident surface, The melt processing region 13 is formed as a reforming region. This melting treatment area 13 becomes a cutting start area 8 when the wafer 1a is cut.

  Here, FIG. 19 is a flowchart showing a method of forming the cutting start region 8 on the wafer 1a using the laser processing apparatus 100 shown in FIG. In the present embodiment, the wafer 1 a is arranged on the mounting table 107 of the laser processing apparatus 100 so that the surface 3 faces the condensing lens 105. That is, the laser beam L is incident from the surface 3 of the wafer 1a.

  14 and 19, first, the light absorption characteristics of the substrate 15 and the interlayer insulating layers 17a and 17b are measured by a spectrophotometer or the like (not shown). Based on this measurement result, the laser light source 101 that generates the laser light L having a wavelength that is transparent or less absorbed with respect to the substrate 15 and the interlayer insulating layers 17a and 17b is selected (S101).

  Subsequently, the amount of movement of the wafer 1a in the Z-axis direction is determined in consideration of the thickness, material, refractive index, and the like of the substrate 15 and the interlayer insulating layers 17a and 17b (S103). This is based on the condensing point P of the laser beam L located on the surface 3 of the wafer 1a in order to align the condensing point P of the laser beam L with a desired position inside a predetermined distance from the surface 3 of the wafer 1a. This is the amount of movement of the wafer 1a in the Z-axis direction. This movement amount is input to the overall control unit 127.

  The wafer 1a is placed on the mounting table 107 of the laser processing apparatus 100 so that the surface 3 of the wafer 1a faces the condensing lens 105 side. Then, visible light is generated from the observation light source 117 to illuminate the surface 3 of the wafer 1a (S105). The surface 3 of the illuminated wafer 1 a is imaged by the image sensor 121. Imaging data captured by the imaging element 121 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 of the wafer 1a (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 focus of the visible light of the observation light source 117 is located on the surface 3 of the wafer 1a. The imaging data processing unit 125 calculates enlarged image data of the surface 3 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. Based on the movement amount data, the stage control unit 115 moves the wafer 1a in the Z-axis direction by the Z-axis stage 113 so that the position of the condensing point P of the laser light L is a predetermined distance inside from the surface 3 of the wafer 1a. Move (S111).

  Subsequently, the laser light L is generated from the laser light source 101, and the surface 3 of the wafer 1a is irradiated with the laser light L. Since the condensing point P of the laser beam L is located inside the substrate 15, the melting region 13 is formed only inside the substrate 15. Then, the X-axis stage 109 and the Y-axis stage 111 are moved along the planned cutting line 5 to form a plurality of melting processing regions 13, or the melting processing region 13 is formed continuously along the planned cutting line 5. As a result, the cutting start region 8 along the planned cutting line 5 is formed inside the substrate 15 (S113).

  In this step S113, as shown in FIG. 21B, the cutting start region 8 is located on the back surface 21 side of the center of the cutting start region 8 in the thickness direction of the substrate 15 with respect to the center 16 of the substrate 15 in that direction. It forms so that it may be located in. In other words, the cutting start region 8 is formed so as to be biased toward the back surface 21 side from the center of the substrate 15. At this time, the cutting starting point region 8 is formed so that the cutting starting point region 8 includes the center 16 of the substrate 15. As an example of dimensions of the cutting start region 8, when the thickness of the substrate 15 is 100 μm, the center of the cutting start region 8 is preferably about 40 μm from the back surface 21 and the width of the cutting start region 8 is about 40 μm, for example.

  Referring to FIG. 18 again, after the cutting start region 8 is formed in the substrate 15 of the wafer 1a, the wafer 1a is cut into a plurality of chip-like portions 24 along the cutting start region 8 (S5, FIG. 22). That is, the expanding tape 23 is stretched to apply a tensile stress to the cutting start region 8, and the wafer 1 a is cut into a plurality of chip-like portions 24 starting from the cutting start region 8. And the space | interval 26 is opened between several chip-shaped parts 24 by extending the expanded tape 23 as it is. At this time, at the same time as the substrate 15 is cut, the interlayer insulating layers 17a and 17b overlapping the planned cutting line 5 are also cut at the same time.

  As described above, in the laser processing method according to the present embodiment, the wafer 1a is to be cut with the modified region 7 formed by the phenomenon of multiphoton absorption inside the substrate 15 of the wafer 1a. A cutting starting point region 8 along the planned cutting line 5 can be formed. Then, by expanding the expanded tape 23 mounted on the back surface 21 of the wafer 1a, a tensile stress can be suitably applied to the cutting start region 8 formed inside the substrate 15. As a result, the substrate 15 can be divided and cut with high accuracy with a relatively small force starting from the cutting start region 8, so that, for example, even when the wafer 1a has the laminated portion 4 on the substrate 15, this laminated portion. 4 can be cut together with the substrate 15 with high accuracy. Therefore, according to this laser processing method, the wafer 1a can be cut with high accuracy.

  In the laser processing method according to the present embodiment, the cutting start region 8 is formed so that the center of the cutting start region 8 is located on the back surface 21 side of the center 16 of the substrate 15 in the thickness direction of the substrate 15. ing. As a result, the cutting start region 8 is biased toward the back surface 21 side of the wafer 1 a, so that the tensile stress caused by expanding the expanded tape 23 attached to the back surface 21 can be more suitably applied to the cutting start region 8. it can. Therefore, the substrate 15 can be cut more accurately with a smaller force. At this time, the cutting starting point region 8 is formed so that the cutting starting point region 8 includes the center 16 of the substrate 15. Thereby, the front surface 3 side of the wafer 1a can be cut more accurately.

  Further, in the laser processing method according to the present embodiment, the wafer 1 a has the stacked portion 4 on the surface 6 of the substrate 15 that overlaps the line 5 to be cut when viewed from the surface 3 side. In this laser processing method, since the substrate 15 can be divided and cut with high accuracy with a relatively small force from the cutting start region 8 formed in the substrate 15, the wafer 1 a is cut on the substrate 15. Even in the case of having the laminated portion 4 overlapping with 5, the laminated portion 4 can be divided and cut together with the substrate 15 with high accuracy.

  In the laser processing method according to the present embodiment, the portion of the laminated portion 4 that overlaps the scheduled cutting line 5 is made of an insulating material. Thereby, since a conductive piece or the like is not generated when the wafer 1a is cut, it is possible to prevent a poor electrical connection due to the conductive piece adhering to any one of the plurality of chip-like portions 24. .

  23A to 23C are cross-sectional views for explaining the first to third modifications of the laser processing method according to the present embodiment. In these modified examples, the thickness of the substrate 15 is as thick as 200 μm (in the above-described embodiment, 100 μm). First, referring to FIG. 23A, in the first modified example, the center of the cutting start region 8 is positioned on the back surface 21 side of the center 16 of the substrate 15 in the thickness direction of the substrate 15. In addition, the cutting starting point region 8 is formed so as not to include the center 16 of the substrate 15. The cutting start region 8 has the same dimensions from the back surface 21 as the cutting start region in the above-described embodiment. Thus, even if the substrate 15 is thick and the cutting start region 8 does not include the center 16 of the substrate 15, a tensile stress can be suitably applied to the cutting start region 8 by stretching the expanded tape 23. It is possible to accurately cut the wafer 1a with a smaller force. However, in consideration of the cutting accuracy on the surface 3 side of the wafer 1a, the cutting starting region 8 is formed so that the cutting starting region 8 includes the center 16 of the substrate 15 as in the embodiment shown in FIG. It is more preferable to do this.

  Further, referring to FIG. 23B, in the second modification, a plurality of cutting starting point regions are formed in the thickness direction of the substrate 15. One cutting start region 8a is formed at the same position as the cutting start region 8 in the first modification. The other cutting start region 8b is formed so that the center of the cutting start region 8b is located near the center 16 of the substrate 15 and the cutting start region 8b includes the center 16 of the substrate 15. As an example of the dimension of the other cutting starting point region 8b in this example, the center position is preferably about 100 μm from the back surface 21 (that is, the center position of the substrate 15) and the width is about 40 μm, for example.

  Referring to FIG. 23 (c), in the third modification, one cutting start region 8a is formed at the same position as the cutting start region 8 in the first modification. Further, the other cutting start region 8 b is arranged such that the center of the cutting start region 8 b is located on the surface 3 side of the center 16 of the substrate 15, and the cutting start region 8 b does not include the center 16 of the substrate 15. Forming. As an example of the dimension of the other cutting starting point region 8b in this example, the center position may be set to about 160 μm from the back surface 21 and the width thereof may be set to about 40 μm, for example.

  In the second modification and the third modification described above, in addition to the cutting start region 8a that is biased toward the back surface 21 of the substrate 15, the cutting starting point located between the cutting starting region 8a and the surface 6 of the substrate 15 is used. Region 8b is formed. Thus, the wafer 1a can be cut with a smaller force, and the front surface 3 side of the wafer 1a can be cut with higher accuracy. In general, the wafer 1a can be cut with a smaller force if the center of at least one cutting start region is located on the back surface 21 side of the center 16 of the substrate 15. Further, the cutting starting region including the center 16 of the substrate 15 and the cutting starting region biased toward the back surface 21 may be the same region as shown in FIG. 21B, or in FIG. 23B. Different regions may be used as shown.

  FIG. 24A is a cross-sectional view for explaining a fourth modification of the laser processing method according to the present embodiment. FIG. 24B is a cross-sectional view showing the IV-IV cross section of the wafer 1a shown in FIG. The difference between this modified example and the above-described embodiment is that a crack 18 reaching the back surface 21 from the melting processing region 13 (cutting start region 8) is generated in the substrate 15. The crack 18 may be generated continuously along the cutting start region 8 as shown in FIG. 24B, or may be generated intermittently along the cutting start region 8. As a result, the crack 18 spreads toward the front surface 3 of the wafer 1a due to the tensile stress resulting from the expansion of the expanded tape 23 attached to the back surface 21, so that the substrate can be cut more accurately with a smaller force.

  FIG. 25A is a cross-sectional view for explaining a fifth modification of the laser processing method according to the present embodiment. FIG. 25B is a cross-sectional view showing an XX cross section of the wafer 1b shown in FIG. In this modified example, a case where a wafer having a stacked portion different from the above-described embodiment is cut will be described. Unlike the wafer 1a described above, the wafer 1b used here includes a substrate 55 made of an n-type semiconductor. The wafer 1b includes, as the stacked portion 44, an n-type cladding layer 57a stacked on the substrate 55, an active layer 57b stacked on the n-type cladding layer 57a, and a p-type stacked on the active layer 57b. A clad layer 57c and a cap layer 57d laminated on the p-type clad layer 57c are provided. A plurality of divided anode electrodes 59a are provided on the cap layer 57d, and a cathode electrode 59b corresponding to the anode electrode 59a is provided on the back surface 61 of the substrate 55, respectively.

  The laser beam L is incident on the wafer 1b from the planned cutting line 5 between the anode electrodes 59a with the inside of the substrate 55 as the focal point P. Then, the cutting start region 8 by the melt processing region 13 is formed inside the substrate 15. At this time, the cutting start region 8 is formed so that the center position of the cutting start region 8 in the thickness direction of the substrate 55 is closer to the back surface 61 side than the center 46 of the substrate 15. Then, by expanding the expanded tape 23 attached to the back surface 61, the wafer 1b is cut to cut out a plurality of semiconductor laser elements.

  This laser processing method can be applied to wafers having various laminated structures, such as the laminated portion 44 in this example, in addition to the laminated portion 4 in the above-described embodiment.

  FIG. 26 is a flowchart showing a sixth modification of the laser processing method according to the present embodiment. FIG. 27 is a cross-sectional view of the wafer 1a for explaining the present modification. In this modification, a case where the laser beam L is incident from the back surface 21 of the wafer 1a will be described.

  Referring to FIG. 26, first, the cutting start region 8 is formed along the planned cutting line 5 inside the substrate 15 of the wafer 1a (S11, FIG. 27). That is, by irradiating the condensing point P inside the substrate 15 with the laser beam L using the region corresponding to the planned cutting line 5 on the back surface 21 of the wafer 1a as a modified region inside the substrate 15 A melt processing region 13 is formed. This melting treatment area 13 becomes a cutting start area 8 when the wafer 1a is cut.

  Subsequently, an expandable tape 23, which is an extensible film, is mounted on the back surface 21 of the wafer 1a (S13), and the wafer 1a is cut into a plurality of chip-like portions 24 along the cutting start region 8 (S15). Since these steps are the same as those in the above-described embodiment, detailed description thereof is omitted.

  As shown in the present modification, in the laser processing method according to the present embodiment, it is possible to form the cutting start region using the back surface 21 of the wafer 1a as the laser light incident surface. Moreover, the timing which mounts the expanded tape 23 may be after forming a cutting | disconnection starting point area | region like this modification.

  As mentioned above, although embodiment of this invention was described in detail, it cannot be overemphasized that this invention is not limited to the said embodiment.

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 electric field strength 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 transmittance | permeability inside a silicon substrate in the laser processing method which concerns on this embodiment. It is a schematic block diagram of the laser processing apparatus which concerns on this embodiment. It is a perspective view which shows the wafer used in the laser processing method which concerns on this embodiment. FIG. 16 is a plan view of the wafer shown in FIG. 15. FIG. 17 is an enlarged view showing a VI-VI cross section and a VII-VII cross section of the wafer shown in FIG. 16. It is a flowchart for demonstrating the laser processing method which concerns on this embodiment. It is a flowchart which shows the method of forming a cutting | disconnection start area | region on a wafer using the laser processing apparatus shown by FIG. It is sectional drawing of the wafer for demonstrating the laser processing method. (A) It is sectional drawing of the wafer for demonstrating the laser processing method. (B) It is sectional drawing which shows the VIII-VIII cross section of the wafer shown by Fig.21 (a). It is sectional drawing of the wafer for demonstrating the laser processing method. (A) It is sectional drawing for demonstrating the 1st modification of the laser processing method by this embodiment. (B) It is sectional drawing for demonstrating the 2nd modification of the laser processing method by this embodiment. (C) It is sectional drawing for demonstrating the 3rd modification of the laser processing method by this embodiment. (A) It is sectional drawing for demonstrating the 4th modification of the laser processing method by this embodiment. (B) It is sectional drawing which shows the IV-IV cross section of the wafer shown by Fig.24 (a). (A) It is sectional drawing for demonstrating the 5th modification of the laser processing method by this embodiment. (B) It is sectional drawing which shows the XX cross section of the wafer shown by Fig.25 (a). It is a flowchart which shows the 6th modification of the laser processing method by this embodiment. It is sectional drawing of the wafer for demonstrating the 6th modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Processing object, 1a, 1b ... Wafer, 3 ... Surface, 4 ... Lamination | stacking part, 5 ... Planned cutting line, 6 ... Surface, 7 ... Modified area | region, 8, 8a, 8b ... Cutting origin area | region, 9 ... Crack 11, silicon wafer, 13 melting processing region, 15 substrate, 16 center, 17 a, 17 b interlayer insulating layer, 18 crack, 19 a, 19 b wiring layer, 20 a, 20 b plug, 21 back surface, DESCRIPTION OF SYMBOLS 23 ... Expanding tape, 24 ... Chip-shaped part, 26 ... Space | interval, 100 ... Laser processing apparatus, 101 ... Laser light source, 102 ... Laser light source control part, 103 ... Dichroic mirror, 105 ... Condensing lens, 107 ... Mounting stand, DESCRIPTION OF SYMBOLS 109 ... X-axis stage, 111 ... Y-axis stage, 113 ... Z-axis stage, 115 ... Stage control part, 117 ... Observation light source, 119 ... Beam splitter, 121 ... Image sensor, 23 ... imaging lens 125 ... imaging data processing unit, 127 ... overall control unit, 129 ... monitor, L ... laser light, P ... converging point.

Claims (4)

A method for cutting a semiconductor substrate having a laminated portion formed on a front surface, wherein the semiconductor substrate is once melted by irradiating a laser beam without using an expanding tape with the back surface of the semiconductor substrate as a laser beam incident surface. Forming a melt treatment region that is a post-resolidified region, forming a cutting start region along a planned cutting line of the semiconductor substrate by the melt processing region, and forming the semiconductor substrate from the cutting start region A method for cutting a semiconductor substrate, comprising a step of cutting into a plurality of portions. A method for cutting a semiconductor substrate having a laminated portion formed on a front surface, wherein the back surface of the semiconductor substrate is used as a laser light incident surface, and laser light is irradiated without going through an expanding tape , whereby the thickness of the semiconductor substrate is reduced. In the semiconductor substrate, a melt-processed region that is a region once melted and re-solidified is formed inside the semiconductor substrate, and the thickness of the semiconductor substrate along the planned cutting line of the semiconductor substrate is formed by the melt-processed region. A method for cutting a semiconductor substrate, comprising: a step of forming a cutting start region biased toward the surface side in a direction; and a step of cutting the semiconductor substrate into a plurality of portions starting from the cutting start region.   The semiconductor substrate cutting method according to claim 1, wherein the cutting start region includes a center in a thickness direction of the semiconductor substrate. The method for cutting a semiconductor substrate according to claim 1, wherein in the step of forming the cutting start region, imaging a surface including the planned cutting line is performed.

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