JP3867105B2 - Semiconductor substrate cutting method - Google Patents

Description

  The present invention relates to a semiconductor substrate cutting method used for cutting a semiconductor substrate in a semiconductor device manufacturing process or the like.

As this type of technology in the past, Patent Literature 1 and Patent Literature 2 describe the following technology. First, an adhesive sheet is attached to the back surface of the semiconductor wafer via a die bond resin layer, and the semiconductor wafer is cut with a blade while the semiconductor wafer is held on the adhesive sheet to obtain a semiconductor chip.
JP 2002-158276 A JP 2000-104040 A

  However, in the technique as described above, when cutting the semiconductor wafer held on the pressure-sensitive adhesive sheet with a blade, it is necessary to perform precise cutting so that the pressure-sensitive adhesive sheet is not cut.

  Therefore, the present invention has been made in view of such circumstances, and a semiconductor substrate can be accurately cut into a semiconductor chip, and in particular, a semiconductor capable of extremely increasing the cutting accuracy of the back surface of the semiconductor substrate. An object is to provide a method for cutting a substrate.

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 functional element formed on a surface thereof, and includes laser light along a planned cutting line inside the semiconductor substrate. Is formed in the semiconductor substrate to form a melt-processed region that is once melted and re-solidified, to form a planned cutting portion in the melt-processed region, and from the melt-processed region to the back surface of the semiconductor substrate. The method includes a step including causing cracks to reach and a step of cutting the semiconductor substrate into a semiconductor chip along a planned cutting portion.

  In this semiconductor substrate cutting method, the semiconductor substrate is irradiated with a laser beam along a planned cutting line to form a melt processing region inside the semiconductor substrate, and the cutting target portion is formed in the melting processing region. Can be formed. In addition, before the semiconductor substrate is cut into semiconductor chips in the next process, a semiconductor that has extremely high cutting accuracy on the back surface of the semiconductor substrate by causing cracks to reach the back surface of the semiconductor substrate from the melt processing region in advance. The substrate can be cut.

In addition, the semiconductor substrate cutting method according to the present invention includes a semiconductor substrate in which a plurality of functional elements arranged in a matrix are formed on a surface, and laser light is irradiated between adjacent functional elements to thereby form a semiconductor. A melt processing region, which is a lattice-like once melted and re-solidified region passing between the functional elements, is formed inside the substrate, and a portion to be cut is formed in the melt processing region. The method includes a step including causing a crack to reach the back surface, and then a step of cutting the semiconductor substrate into semiconductor chips each having a functional element along a portion to be cut.

  In this method of cutting a semiconductor substrate, a laser beam is irradiated between adjacent functional elements inside a semiconductor substrate on which a plurality of functional elements arranged in a matrix are formed. It is possible to form a lattice-shaped melt processing region passing between the functional elements, and to form a planned cutting portion in the melt processing region. In addition, before the semiconductor substrate is cut into semiconductor chips each having functional elements on the front surface in the next step, by causing cracks to reach the back surface of the semiconductor substrate from the melt processing region in advance, A semiconductor substrate with extremely high cutting accuracy can be cut.

  According to the semiconductor substrate cutting method of the present invention, the semiconductor substrate can be cut into semiconductor chips with high accuracy, and in particular, the cutting accuracy of the back surface of the semiconductor substrate can be made extremely high.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a preferred embodiment of a semiconductor substrate cutting method according to the present invention will be described in detail with reference to the drawings.

  In the method for cutting a semiconductor substrate according to the present embodiment, a modified region by multiphoton absorption is formed inside the semiconductor substrate by irradiating a laser beam with a focusing point inside the semiconductor substrate. A planned cutting portion is formed by the region. Therefore, prior to the description of the method for cutting a semiconductor substrate according to the present embodiment, a laser processing method that is performed to form a portion to be cut will be described focusing on multiphoton absorption.

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 the semiconductor substrate 1 during laser processing, FIG. 2 is a cross-sectional view taken along the line II-II of the semiconductor substrate 1 shown in FIG. 1, and FIG. 3 shows the semiconductor substrate 1 after laser processing. 4 is a cross-sectional view taken along line IV-IV of the semiconductor substrate 1 shown in FIG. 3, and FIG. 5 is a cross-sectional view taken along line V-V of the semiconductor substrate 1 shown in FIG. FIG. 6 is a plan view of the cut semiconductor substrate 1.

  As shown in FIGS. 1 and 2, there is a desired cutting line 5 on the surface 3 of the semiconductor substrate 1 where the semiconductor substrate 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 used as the planned cutting line 5 on the semiconductor substrate 1). In the laser processing according to the present embodiment, the modified region 7 is formed by irradiating the semiconductor substrate 1 with the laser beam L while aligning the condensing point P inside the semiconductor substrate 1 under the condition that multiphoton absorption occurs. In addition, a condensing point is a location where the laser beam L is condensed.

  The condensing point P is moved along the planned cutting line 5 by relatively moving the laser light L along the planned cutting line 5 (that is, along the direction of the arrow A). Thereby, as shown in FIGS. 3 to 5, the modified region 7 is formed only inside the semiconductor substrate 1 along the planned cutting line 5, and the planned cutting portion 9 is formed by the modified region 7. In the laser processing method according to the present embodiment, the modified region 7 is not formed by causing the semiconductor substrate 1 to generate heat when the semiconductor substrate 1 absorbs the laser light L. The modified region 7 is formed by transmitting the laser beam L through the semiconductor substrate 1 and generating multiphoton absorption inside the semiconductor substrate 1. Therefore, since the laser beam L is hardly absorbed by the surface 3 of the semiconductor substrate 1, the surface 3 of the semiconductor substrate 1 is not melted.

  In the cutting of the semiconductor substrate 1, if there is a starting point at the cutting position, the semiconductor substrate 1 breaks from the starting point, so that the semiconductor substrate 1 can be cut with a relatively small force as shown in FIG. 6. Therefore, the semiconductor substrate 1 can be cut without causing unnecessary cracks in the surface 3 of the semiconductor substrate 1.

  The following two methods can be considered for cutting the semiconductor substrate starting from the planned cutting portion. One is a case where after the formation of the planned cutting portion, an artificial force is applied to the semiconductor substrate, whereby the semiconductor substrate is cracked starting from the planned cutting portion, and the semiconductor substrate is cut. This is cutting when the thickness of the semiconductor substrate is large, for example. The artificial force is applied, for example, by applying bending stress or shear stress to the semiconductor substrate along the planned cutting portion of the semiconductor substrate, or generating thermal stress by applying a temperature difference to the semiconductor substrate. That is. The other one is a case where by forming the planned cutting portion, the semiconductor substrate is naturally cracked from the planned cutting portion toward the cross-sectional direction (thickness direction) of the semiconductor substrate, and as a result, the semiconductor substrate is cut. . For example, when the thickness of the semiconductor substrate is small, this is possible by forming the planned cutting portion by one row of the modified region. When the thickness of the semiconductor substrate is large, a plurality of portions are arranged in the thickness direction. This is made possible by forming the planned cutting portion by the modified region formed in a row. In addition, even when this breaks naturally, in the part to be cut, the part corresponding to the part where the part to be cut is formed without cracking on the surface of the part corresponding to the part where the part to be cut is not formed Since it is possible to cleave only, the cleaving can be controlled well. In recent years, since the thickness of a semiconductor substrate such as a silicon wafer tends to be thin, such a cleaving method with good controllability is very effective.

  Now, as the modified region formed by multiphoton absorption in the present embodiment, there is a melting processing region described below.

A condensing point is set inside the semiconductor substrate, and laser light is irradiated under the condition that the electric field intensity at the condensing point is 1 × 10 ⁸ (W / cm ² ) or more and the pulse width is 1 μs or less. As a result, the inside of the semiconductor substrate is locally heated by multiphoton absorption. By this heating, a melt processing region is formed inside the semiconductor 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 semiconductor 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) Semiconductor 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 semiconductor substrate is mounted: 100 mm / second

  FIG. 7 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. 8 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. 7 is 350 μm, the melt processing region 13 by multiphoton absorption is formed near the center of the silicon wafer, that is, at a portion of 175 μm from the surface. In this case, the transmittance is 90% or more with reference to a silicon wafer having a thickness of 200 μm. Therefore, the laser beam is hardly absorbed inside the silicon wafer 11 and almost all is transmitted. This is not because the laser beam is absorbed inside the silicon wafer 11 and the melt processing region 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.

  Silicon wafers are cracked in the cross-sectional direction starting from the planned cutting portion formed in the melt processing region, and the cracks reach the front and back surfaces of the silicon wafer, resulting in cutting. Is done. 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. In addition, when a crack naturally grows from the planned cutting part to the front and back surfaces of the silicon wafer, the crack grows from a state where the melt treatment region forming the planned cutting part is melted, and the planned cutting part. There are both cases where cracks grow when the solidified region is melted from the molten state. However, in both cases, 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 planned cutting portion is formed in the semiconductor substrate in the melt processing region, unnecessary cracks that are off the planned cutting portion line are less likely to occur at the time of cleaving, so that cleaving control is facilitated.

  Next, a laser processing apparatus used in the laser processing method described above will be described with reference to FIG. FIG. 9 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 semiconductor substrate 1 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, and the mounting table 107 are set to X A Y-axis stage 111 for moving in the Y-axis direction orthogonal to the axial 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.

  Since the Z-axis direction is a direction orthogonal to the surface 3 of the semiconductor substrate 1, it is the direction of the focal depth of the laser light L incident on the semiconductor substrate 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 semiconductor substrate 1. Further, the converging point P is moved in the X (Y) axis direction by moving the semiconductor substrate 1 in the X (Y) axis direction by the X (Y) axis stage 109 (111).

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, Nd: YLF laser, and titanium sapphire laser. When forming the melt processing region, it is preferable to use an Nd: YAG laser, an Nd: YVO ₄ laser, or an Nd: YLF laser. In this embodiment, pulsed laser light is used for processing the semiconductor substrate 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 semiconductor substrate 1 mounted on the mounting table 107 with visible light, and the same optical axis as the dichroic mirror 103 and the condensing lens 105. And a visible light beam splitter 119 disposed above. 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 passes through the planned cutting line 5 of the semiconductor substrate 1. Illuminate the containing surface 3.

  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 based on the imaging data. The stage control unit 115 controls the movement of the Z-axis stage 113 based on the focus data so that the visible light is focused on the surface 3. Therefore, the imaging data processing unit 125 functions as an autofocus unit. The imaging data processing unit 125 calculates image data such as an enlarged image of the surface 3 based on the imaging data. This image data is sent to the overall control unit 127, where various processes are performed by the overall control unit, and sent to the monitor 129. Thereby, an enlarged image or the like is displayed on the monitor 129.

  Data from the stage controller 115, image data from the imaging data processor 125, and the like are input to the overall controller 127. Based on these data, the laser light source controller 102, the observation light source 117, and the stage controller By controlling 115, the entire laser processing apparatus 100 is controlled. Therefore, the overall control unit 127 functions as a computer unit.

  A procedure for forming the planned cutting portion by the laser processing apparatus 100 configured as described above will be described with reference to FIGS. FIG. 10 is a flowchart for explaining the procedure for forming the planned cutting portion by the laser processing apparatus 100.

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

  The semiconductor substrate 1 is mounted on the mounting table 107 of the laser processing apparatus 100. Then, visible light is generated from the observation light source 117 to illuminate the semiconductor substrate 1 (S105). The imaging device 121 images the surface 3 of the semiconductor substrate 1 including the illuminated planned cutting line 5. The planned cutting line 5 is a desired virtual line for cutting the semiconductor substrate 1. 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 (S107).

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

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

  Subsequently, the laser light L is generated from the laser light source 101, and the laser light L is applied to the cutting line 5 on the surface 3 of the semiconductor substrate 1. Since the condensing point P of the laser beam L is located inside the semiconductor substrate 1, the melting processing region is formed only inside the semiconductor substrate 1. Then, the X-axis stage 109 and the Y-axis stage 111 are moved along the planned cutting line 5, and the planned cutting portion along the planned cutting line 5 is formed in the melt processing region formed along the planned cutting line 5. It is formed inside the substrate 1 (S113).

  Thus, the formation of the planned cutting portion by the laser processing apparatus 100 is completed, and the planned cutting portion is formed inside the semiconductor substrate 1. When the planned cutting portion is formed inside the semiconductor substrate 1, it is possible to generate a crack in the thickness direction of the semiconductor substrate 1 starting from the planned cutting portion with a relatively small force.

  Next, a semiconductor substrate cutting method according to the present embodiment will be described. Here, a silicon wafer 11 which is a semiconductor wafer is used as the semiconductor substrate.

  First, as shown in FIG. 11A, an adhesive sheet 20 is attached to the back surface 17 so as to cover the back surface 17 of the silicon wafer 11. The pressure-sensitive adhesive sheet 20 has a base 21 having a thickness of about 100 μm, and a UV curable resin layer 22 having a thickness of about several μm is provided on the base 21. Further, a die bond resin layer 23 that functions as an adhesive for die bonding is provided on the UV curable resin layer 22. A plurality of functional elements are formed in a matrix on the surface 3 of the silicon wafer 11. Here, the functional element means 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.

  Subsequently, as shown in FIG. 11B, the silicon wafer 11 is irradiated with laser light from the surface 3 side with the focusing point inside the silicon wafer 11 using, for example, the laser processing apparatus 100 described above. A melt processing region 13 which is a reforming region is formed inside, and the planned cutting portion 9 is formed by the melt processing region 13. In the formation of the planned cutting portion 9, the laser light is irradiated so as to run between the plurality of functional elements arranged in a matrix on the surface 3 of the silicon wafer 11. It is formed in a lattice shape so as to run directly below.

  After the formation of the scheduled cutting portion 9, as shown in FIG. 12A, the adhesive sheet 20 is expanded by the sheet expanding means 30 so as to pull the periphery of the adhesive sheet 20 outward. Due to the expansion of the adhesive sheet 20, a crack is generated in the thickness direction starting from the planned cutting portion 9, and this crack reaches the front surface 3 and the back surface 17 of the silicon wafer 11. Thereby, the silicon wafer 11 is accurately cut for each functional element, and the semiconductor chip 25 having one functional element is obtained.

  At this time, the opposing cut surfaces 25a and 25a of the adjacent semiconductor chips 25 and 25 are in close contact with each other and are separated as the adhesive sheet 20 is expanded. Simultaneously with the cutting, the die bond resin layer 23 that is in close contact with the back surface 17 of the silicon wafer 11 is also cut along the planned cutting portion 9.

  Note that the sheet expanding means 30 may be provided on the stage on which the silicon wafer 11 is placed when the scheduled cutting portion 9 is formed, or may not be provided on the stage. When not provided on the stage, the silicon wafer 11 placed on the stage is conveyed by the conveying means onto the other stage provided with the sheet expanding means 30 after the formation of the scheduled cutting portion 9.

  After the expansion of the pressure-sensitive adhesive sheet 20, as shown in FIG. 12B, the UV-curable resin layer 22 is cured by irradiating the pressure-sensitive adhesive sheet 20 with ultraviolet rays from the back surface side. Thereby, the adhesive force between the UV curable resin layer 22 and the die bond resin layer 23 is reduced. In addition, you may perform this ultraviolet irradiation before the expansion start of the adhesive sheet 20. FIG.

  Subsequently, as shown in FIG. 13A, the semiconductor chips 25 are sequentially picked up using a suction collet or the like as pick-up means. At this time, the die bond resin layer 23 is cut into the same outer shape as the semiconductor chip 25, and the adhesion between the die bond resin layer 23 and the UV curable resin layer 22 is reduced. The die-bond resin layer 23 cut on the back surface is picked up in a close contact state. Then, as shown in FIG. 13B, the semiconductor chip 25 is placed on the die pad of the lead frame 27 through the die bond resin layer 23 in close contact with the back surface thereof, and filler bonding is performed by heating.

  As described above, in the method for cutting the silicon wafer 11, the silicon wafer 11 is cut into the silicon wafer 11 along the desired cutting line to be cut by the melt processing region 13 formed by multiphoton absorption. A planned portion 9 is formed. Therefore, when the adhesive sheet 20 attached to the silicon wafer 11 is expanded, the silicon wafer 11 is accurately cut along the scheduled cutting portion 9, and the semiconductor chip 25 is obtained. At this time, the opposing cut surfaces 25a and 25a of the adjacent semiconductor chips 25 and 25 are in close contact with each other at an initial stage and are separated as the adhesive sheet 20 is expanded, so that they are in close contact with the back surface 17 of the silicon wafer 11. The die bond resin layer 23 that has been cut is also cut along the planned cutting portion 9. Therefore, compared with the case where the silicon wafer 11 and the die bond resin layer 23 are cut by the blade without cutting the base material 21, the silicon wafer 11 and the die bond resin layer 23 are cut along the planned cutting portion 9 much more efficiently. It becomes possible to cut.

  In addition, since the opposing cut surfaces 25a, 25a of the adjacent semiconductor chips 25, 25 are in close contact with each other, the cut semiconductor chips 25 and the cut die bond resin layers 23 are almost the same. The outer shape is the same, and the die bond resin is prevented from protruding from the cut surface 25 a of each semiconductor chip 25.

  The above-described cutting method of the silicon wafer 11 was a case in which the cracks starting from the planned cutting portion 9 did not occur in the silicon wafer 11 until the adhesive sheet 20 was expanded as shown in FIG. However, as shown in FIG. 14 (b), before expanding the adhesive sheet 20, a crack 15 starting from the scheduled cutting portion 9 is generated, and this crack 15 is formed on the front surface 3 and the back surface 17 of the silicon wafer 11. May be reached. As a method of generating the crack 15, for example, a stress applying means such as a knife edge is pressed against the back surface 17 of the silicon wafer 11 along the planned cutting portion 9, so that the silicon wafer 11 is bent along the planned cutting portion 9. There are a method for generating stress and shear stress, and a method for generating thermal stress on the silicon wafer 11 along the planned cutting portion 9 by giving a temperature difference to the silicon wafer 11.

  As described above, after forming the planned cutting portion 9, if stress is generated on the silicon wafer 11 along the planned cutting portion 9 and the silicon wafer 11 is cut along the planned cutting portion 9, the cutting is performed with extremely high accuracy. A semiconductor chip 25 can be obtained. Even in this case, when the adhesive sheet 20 attached to the silicon wafer 11 is expanded, the opposing cut surfaces 25a and 25a of the adjacent semiconductor chips 25 and 25 are in close contact with each other, so that the adhesive sheet 20 Since they are separated with the expansion, the die bond resin layer 23 that is in close contact with the back surface 17 of the silicon wafer 11 is cut along the cut surface 25a. Therefore, even by this cutting method, the silicon wafer 11 and the die bond resin layer 23 can be formed much more efficiently than when the silicon wafer 11 and the die bond resin layer 23 are cut by the blade without cutting the base material 21. It becomes possible to cut along the planned cutting portion 9.

  When the thickness of the silicon wafer 11 is reduced, even if no stress is generated along the planned cutting portion 9, as shown in FIG. 11 may reach the front surface 3 and the back surface 17.

  Further, as shown in FIG. 15A, if the planned cutting portion 9 is formed by the melt processing region 13 in the vicinity of the surface 3 inside the silicon wafer 11, and the crack 15 reaches the surface 3, cutting is performed. The cutting accuracy of the surface (that is, the functional element forming surface) of the obtained semiconductor chip 25 can be made extremely high. On the other hand, as shown in FIG. 15B, the adhesive sheet 20 can be obtained by forming the planned cutting portion 9 by the melt treatment region 13 in the vicinity of the back surface 17 inside the silicon wafer 11 and allowing the crack 15 to reach the back surface 17. The die bond resin layer 23 can be cut with high accuracy by the expansion.

  Next, an experimental result in the case of using “LE-5000 (trade name)” of Lintec Corporation as the adhesive sheet 20 will be described. 16 and 17 are schematic views showing a series of states when the adhesive sheet 20 is expanded after the planned cutting portion 9 is formed in the silicon wafer 11 by the melt processing region 13, and FIG. Is the state immediately after the expansion of the adhesive sheet 20, FIG. 16B is the state during expansion of the adhesive sheet 20, FIG. 17A is the state after the expansion of the adhesive sheet 20, and FIG. 17B is the semiconductor chip. This is the state at the time of 25 pickup.

  As shown in FIG. 16A, immediately after the expansion of the adhesive sheet 20 is started, the silicon wafer 11 is cut along the planned cutting portion 9, and the opposing cut surfaces 25a and 25a of the adjacent semiconductor chips 25 are in close contact with each other. Is in a state. At this time, the die bond resin layer 23 has not been cut yet. And as shown in FIG.16 (b), with the expansion of the adhesive sheet 20, the die-bonding resin layer 23 is cut | disconnected along the scheduled cutting part 9 so that it may be shredded.

  When the expansion of the pressure-sensitive adhesive sheet 20 is thus completed, the die bond resin layer 23 is also cut for each individual semiconductor chip 25 as shown in FIG. At this time, a portion 23b of the die bond resin layer 23 remained thin on the base material 21 of the adhesive sheet 20 between the semiconductor chips 25 and 25 spaced apart from each other. Further, the cut surface 23 a of the die bond resin layer 23 cut together with the semiconductor chip 25 was slightly concave with respect to the cut surface 25 a of the semiconductor chip 25. This reliably prevents the die bond resin from protruding from the cut surface 25a of each semiconductor chip 25. Then, as shown in FIG. 17B, the semiconductor chip 25 could be picked up with the cut die bond resin layer 23 using an adsorption collet or the like.

  When the die bond resin layer 23 is made of a non-stretchable material or the like, as shown in FIG. 18, the die bond resin is formed on the base material 21 of the adhesive sheet 20 between the semiconductor chips 25 and 25 spaced apart from each other. Layer 23 does not remain. Thereby, the cut surface 25a of the semiconductor chip 25 and the cut surface 23a of the die bond resin layer 23 adhered to the back surface thereof can be substantially matched.

  Further, as shown in FIG. 19A, an adhesive sheet 20 having a base material 21 and a UV curable resin layer 22 is attached to the back surface 17 of the silicon wafer 11 via the UV curable resin layer 22, After forming the planned cutting portion 9 by the melt processing region 13, as shown in FIG. 19B, the periphery of the adhesive sheet 20 is expanded outward to cut the silicon wafer 11 into the semiconductor chips 25. Also good. Also in this case, it becomes possible to cut the silicon wafer 11 along the scheduled cutting portion 9 with higher accuracy than in the case where the silicon wafer 11 is cut with a blade while leaving the adhesive sheet 20.

  And also in the cutting method of the silicon wafer 11 using the adhesive sheet 20 having the base material 21 and the UV curable resin layer 22, as described with reference to FIG. 19, until the adhesive sheet 20 is expanded. Is not only the case where cracks starting from the planned cutting part 9 do not occur in the silicon wafer 11, but before expanding the adhesive sheet 20 as shown in FIG. 20 (FIG. 20B), the planned cutting part 9 The crack 15 starting from may be allowed to reach the front surface 3 and the back surface 17 of the silicon wafer 11 (FIG. 20A). Moreover, as shown in FIG. 21, before expanding the adhesive sheet 20 (FIG. 21B), the crack 15 starting from the planned cutting portion 9 may reach the surface 3 of the silicon wafer 11 ( 21 (a)) or FIG. 22, before the adhesive sheet 20 is expanded (FIG. 22 (b)), the crack 15 starting from the planned cutting portion 9 reaches the back surface 17 of the silicon wafer 11. You may make it (FIG.22 (a)).

It is a top view of a semiconductor substrate under laser processing by a laser processing method concerning this embodiment. It is sectional drawing along the II-II line of the semiconductor substrate shown in FIG. It is a top view of the semiconductor substrate after the laser processing by the laser processing method concerning this embodiment. FIG. 4 is a cross-sectional view of the semiconductor substrate shown in FIG. 3 taken along line IV-IV. FIG. 5 is a cross-sectional view taken along line VV of the semiconductor substrate shown in FIG. 3. It is a top view of the semiconductor substrate cut | disconnected by 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 flowchart for demonstrating the formation procedure of the cutting scheduled part by the laser processing apparatus which concerns on this embodiment. It is a schematic diagram for demonstrating the cutting method of the silicon wafer which concerns on this embodiment, (a) is the state by which the adhesive sheet was affixed on the silicon wafer, (b) is the cutting | disconnection by the fusion | melting process area | region inside a silicon wafer This is a state in which a planned portion is formed. It is a schematic diagram for demonstrating the cutting method of the silicon wafer which concerns on this embodiment, (a) is the state by which the adhesive sheet was expanded, (b) is the state by which the adhesive sheet was irradiated with the ultraviolet-ray. It is a schematic diagram for demonstrating the cutting method of the silicon wafer which concerns on this embodiment, (a) is the state in which the semiconductor chip was picked up with the cut | disconnected die-bond resin layer, (b) is a semiconductor chip having a die-bond resin layer It is in a state where it is joined to the lead frame. It is a schematic diagram which shows the relationship between the silicon wafer in the cutting method of the silicon wafer which concerns on this embodiment, and a cutting plan part, (a) is the state in which the crack which started from the cutting plan part has not generate | occur | produced, (b) This is a state in which cracks starting from the planned cutting portion have reached the front and back surfaces of the silicon wafer. It is a schematic diagram which shows the relationship between the silicon wafer and the scheduled cutting part in the silicon wafer cutting method according to the present embodiment, and (a) shows a state where a crack starting from the planned cutting part reaches the surface of the silicon wafer. (B) is a state in which the crack starting from the planned cutting portion reaches the back surface of the silicon wafer. It is a schematic diagram for demonstrating one Example of the cutting method of the silicon wafer which concerns on this embodiment, (a) is the state immediately after the expansion start of an adhesive sheet, (b) is the state in the expansion of an adhesive sheet. . It is a schematic diagram for demonstrating one Example of the cutting method of the silicon wafer which concerns on this embodiment, (a) is the state after completion | finish of expansion of an adhesive sheet, (b) is the state at the time of the pick-up of a semiconductor chip. . It is a schematic diagram for demonstrating the other Example of the cutting method of the silicon wafer which concerns on this embodiment. It is a figure for demonstrating the case where the crack which started from the cutting plan part does not generate | occur | produce in the further another Example of the cutting method of the silicon wafer which concerns on this embodiment, (a) is a cutting plan part by a fusion | melting process area | region. The state after being formed, (b) is a state in which the adhesive sheet is expanded. It is a figure for demonstrating the case where the crack which started from the cutting scheduled part reaches | attains the surface and back surface of a silicon wafer in the further another Example of the cutting method of the silicon wafer which concerns on this embodiment, (a) A state after the planned cutting portion is formed by the melt treatment region, (b) is a state in which the adhesive sheet is expanded. It is a figure for demonstrating the case where the crack which started the cutting | disconnection plan part in the other Example of the cutting method of the silicon wafer which concerns on this embodiment arrives at the surface of a silicon wafer, (a) is a fusion | melting process area | region. (B) is a state after the adhesive sheet has been expanded. It is a figure for demonstrating the case where the crack which started the cutting | disconnection plan part in the further another Example of the cutting method of the silicon wafer which concerns on this embodiment arrives at the back surface of a silicon wafer, (a) is a fusion | melting process area | region. (B) is a state after the adhesive sheet has been expanded.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 3 ... Surface, 5 ... Planned cutting line, 7 ... Modified area | region, 9 ... Planned cutting part, 11 ... Silicon wafer, 13 ... Melting process area, 15 ... Crack, 17 ... Back surface, 20 ... Adhesive sheet , 21 ... base material, 23 ... die bond resin layer, 25 ... semiconductor chip, L ... laser beam, P ... condensing point.

Claims (2)

A method for cutting a semiconductor substrate having a functional element formed on a surface thereof, wherein the semiconductor substrate is irradiated with laser light along a planned cutting line, and is once solidified after being melted inside the semiconductor substrate . Forming a melt-processed region that is a region, forming a portion to be cut with the melt-processed region, and causing a crack to reach the back surface of the semiconductor substrate from the melt-processed region; and
And then cutting the semiconductor substrate into a semiconductor chip along the planned cutting portion. A lattice that passes between the functional elements inside the semiconductor substrate by irradiating laser light between the adjacent functional elements inside the semiconductor substrate on which a plurality of functional elements arranged in a matrix are formed. Forming a melt-processed region that is a region once melted and re-solidified , forming a planned cutting portion in the melt-processed region, and causing a crack to reach the back surface of the semiconductor substrate from the melt-processed region. Including a process;
And then cutting the semiconductor substrate into the semiconductor chips each having the functional element along the planned cutting portion.

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