JP5946307B2 - Wafer division method - Google Patents

Description

  The present invention relates to a wafer dividing method in which a device having a metal layer formed on a back surface thereof is divided into individual device chips, each of which is formed in a surface area defined by division lines.

  Semiconductor wafers where devices such as IC and LSI are formed in each area partitioned by a plurality of division lines formed in a grid pattern on the front surface are divided after the back surface is ground and processed to the desired thickness. The semiconductor device chips are divided into individual semiconductor device chips along a planned line, and the divided semiconductor device chips are widely used in various electric devices such as mobile phones and personal computers.

  There are many types of semiconductor wafers, and a metal layer as an electrode is formed on the back surface of the discrete wafer in which a plurality of discrete devices such as IGBTs (insulated gate bipolar transistors) are formed on the surface.

  Also, an epitaxial layer (semiconductor layer) such as gallium nitride (GaN) is formed on the surface of a crystal growth substrate such as a sapphire substrate or SiC substrate, and a plurality of optical devices such as LEDs are formed in a lattice pattern on the epitaxial layer. In the optical device wafer formed by being divided by the planned dividing lines, a metal layer is formed as a reflective film on the back side of the crystal growth substrate in order to improve the luminance of the optical device such as an LED.

  However, if a wafer having a metal layer on the back side is cut with a cutting blade, the machining feed rate will be low, and the cutting blade may become clogged, resulting in defective cutting and eventually damage the wafer. is there.

  Therefore, there is a method of forming a modified layer inside the wafer by irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer, and dividing the wafer into individual device chips using the modified layer as a starting point. (For example, refer to Japanese Patent No. 3408805).

Japanese Patent No. 3408805 JP 2006196664 A1

  However, when a modified layer is formed inside a wafer using a laser beam having a wavelength that is transmissive to the wafer, the metal layer blocks the laser beam, so that the metal layer is disclosed in Patent Document 2. It must be removed by ablation or the like.

  This metal layer can be removed by cutting with a cutting blade. However, if the metal layer is removed too much, the performance as a device will be reduced, but it will be sufficient to form a modified layer inside the wafer. It is necessary to remove the metal layer.

  In particular, in a crystal growth substrate such as a sapphire substrate or a SiC substrate, there is a direction in which it is difficult to break even if a modified layer is formed due to the influence of crystal orientation. Such a substrate for crystal growth also has a problem that it cannot be cleaved into individual devices unless a particularly thick modified layer is formed on a line to be divided in a direction difficult to break.

  The present invention has been made in view of such points, and the object of the present invention is to have a metal layer on the back surface and to prevent cracking even if a modified layer is formed inside due to the influence of crystal orientation. It is an object of the present invention to provide a wafer dividing method capable of reliably dividing a wafer into individual device chips.

According to the present invention, a plurality of first division lines that are formed on the surface and extend in the first direction are perpendicular to the first division line and are less likely to break compared to the first division line. A wafer in which a device is formed and a metal layer is formed on the back surface in each region partitioned by a plurality of second division lines extending in the second direction is divided into the first and second divisions. A wafer dividing method for dividing along a predetermined line, wherein the wafer is held by a chuck table with the metal layer side exposed, and the metal layer in a region corresponding to the first scheduled line of the wafer A first metal layer removing step that removes the wafer, and the wafer is held on the chuck table with the metal layer side exposed, and the metal layer in a region corresponding to the second scheduled division line of the wafer is removed. 2 metals After performing the removing step and the first and second metal layer removing steps, a condensing point of a laser beam having a wavelength having transparency to the wafer is positioned inside the wafer, and the metal layer of the wafer A modified layer forming step of irradiating the region from which the metal layer has been removed along the first and second division lines to form a modified layer inside the wafer; A cleaving step of cleaving the wafer into individual device chips by applying an external force to the wafer after performing the material layer forming step, and in the first and second metal layer removing steps, the second metal The width of the metal layer to be removed in the layer removal step is wider than the width of the metal layer to be removed in the first metal layer removal step, and the modified layer forming step corresponds to the second scheduled division line. region Since the metal layer is widely removed, and the amount of the laser beam transmitted to the inside of the wafer is less blocked by the metal layer, the modification formed inside the wafer along the second division line is performed. There is provided a wafer processing method characterized in that the number of quality layers is larger than that of the modified layer formed inside the wafer along the first division line .

  Preferably, the wafer is formed such that the interval between the second divisional lines is narrower than the interval between the first divisional lines. Preferably, in the metal layer removing step, a condensing point of a laser beam having a wavelength having an absorptivity with respect to the wafer is positioned on the upper surface of the wafer, and along the first and second division lines from the metal layer side of the wafer. Then, ablation processing is performed by irradiating a laser beam, and the metal layer is partially removed.

  According to the wafer dividing method of the present invention, a thick modified layer is formed on the planned dividing line in a direction that is difficult to break, so that the metal layer is widely removed and a sufficient amount of laser beam is modified inside the wafer. While it is possible to reach the layer formation position, the metal layer removal width is narrowed in the splitting line in the direction that is easy to break, so that the performance degradation as a device can be suppressed as much as possible.

  In addition, when the vertical and horizontal sizes of the devices to be cleaved are different, it is more difficult to cleave the planned division line on the long side than to cleave the planned division line on the short side because it is less subject to bending stress. It is also effective to increase the removal width of the metal layer in order to thicken the modified layer of the planned dividing line on the long side.

1 is a perspective view of a laser processing apparatus suitable for carrying out the wafer dividing method of the present invention. It is a block diagram of a laser beam irradiation unit. It is a perspective view of an optical device wafer. It is a longitudinal cross-sectional view of an optical device wafer. It is a back surface side perspective view of the optical device wafer supported by the annular frame via the dicing tape. It is sectional drawing of the optical device wafer of the state hold | maintained at the chuck table. It is a perspective view which shows a 1st metal layer removal step. It is a perspective view which shows a 2nd metal layer removal step. 9A is a longitudinal sectional view of the optical device wafer after the first metal layer removing step is performed, and FIG. 9B is a longitudinal sectional view of the optical device wafer after the second metal layer removing step is performed. It is sectional drawing which shows a modified layer formation step. It is a perspective view which shows a modified layer formation step. FIG. 12A is a schematic cross-sectional view showing the amount of laser beam irradiated to the first division line where the removal width of the metal layer is narrow, and FIG. 12B is a line 12B-12B in FIG. It is sectional drawing. FIG. 13A is a schematic cross-sectional view showing the amount of laser beam irradiated to the second division line with a wide removal width of the metal layer, and FIG. 13B is a line 13B-13B in FIG. It is sectional drawing. It is a top view of the wafer in which the elongate device was formed. FIG. 15A is a rear perspective view of a wafer that does not have a metal layer in the rear surface area corresponding to the outer peripheral surplus area, and FIG. 15B is a plan view thereof. It is a longitudinal cross-sectional view which shows a cleaving step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a schematic perspective view of a laser processing apparatus 2 suitable for carrying out the wafer dividing method of the present invention.

  The laser processing apparatus 2 includes a first slide block 6 mounted on a stationary base 4 so as to be movable in the X-axis direction. The first slide block 6 is moved along the pair of guide rails 14 in the machining feed direction, that is, the X-axis direction, by the machining feed means 12 including the ball screw 8 and the pulse motor 10.

  A second slide block 16 is mounted on the first slide block 6 so as to be movable in the Y-axis direction. That is, the second slide block 16 is moved in the indexing direction, that is, the Y-axis direction along the pair of guide rails 24 by the indexing feeding means 22 constituted by the ball screw 18 and the pulse motor 20.

  A chuck table 28 is mounted on the second slide block 16 via a cylindrical support member 26, and the chuck table 28 can be moved in the X-axis direction and the Y-axis direction by the processing feed means 12 and the index feed means 22. . The chuck table 28 is provided with a clamp 30 that clamps an annular frame that supports the wafer sucked and held by the chuck table 28.

  A column 32 is erected on the stationary base 4, and a casing 35 for accommodating the laser beam irradiation unit 34 is attached to the column 32. As shown in FIG. 2, the laser beam irradiation unit 34 includes a laser oscillator 62 that oscillates a YAG laser or a YVO4 laser, a repetition frequency setting unit 64, a pulse width adjustment unit 66, and a power adjustment unit 68. .

  The pulse laser beam adjusted to a predetermined power by the power adjusting means 68 of the laser beam irradiation unit 34 is reflected by the mirror 70 of the condenser 36 attached to the tip of the casing 35 and further collected by the condenser objective lens 72. The light is applied to the optical device wafer 11 held on the chuck table 28.

  At the tip of the casing 35, an image pickup means 38 for detecting a processing region to be laser processed in alignment with the condenser 36 in the X-axis direction is disposed. The imaging means 38 includes an imaging element such as a normal CCD that images the processing region of the optical device wafer 11 with visible light.

  The imaging means 38 further outputs an infrared irradiation means for irradiating the optical device wafer 11 with infrared rays, an optical system for capturing the infrared rays irradiated by the infrared irradiation means, and an electrical signal corresponding to the infrared rays captured by the optical system. Infrared imaging means including an infrared imaging device such as an infrared CCD is included, and the captured image signal is transmitted to a controller (control means) 40.

  The controller 40 includes a central processing unit (CPU) 42 that performs arithmetic processing according to a control program, a read-only memory (ROM) 44 that stores a control program, and a random read / write that stores arithmetic results. An access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52 are provided.

  Reference numeral 56 denotes a processing feed amount detection means comprising a linear scale 54 disposed along the guide rail 14 and a read head (not shown) disposed on the first slide block 6. Is input to the input interface 50 of the controller 40.

  Reference numeral 60 denotes index feed amount detection means comprising a linear scale 58 disposed along the guide rail 24 and a read head (not shown) disposed on the second slide block 16. The detection signal is input to the input interface 50 of the controller 40.

  An image signal picked up by the image pickup means 38 is also input to the input interface 50 of the controller 40. On the other hand, a control signal is output from the output interface 52 of the controller 40 to the pulse motor 10, the pulse motor 20, the laser beam irradiation unit 34, and the like.

  Referring to FIG. 3, there is shown a front side perspective view of an optical device wafer 11 which is a processing target of the dividing method of the present invention. FIG. 4 is a longitudinal sectional view of the optical device wafer 11. The optical device wafer 11 is configured by laminating an epitaxial layer (semiconductor layer) 15 such as gallium nitride (GaN) on a sapphire substrate 13. The optical device wafer 11 has a front surface 11a on which an epitaxial layer 15 is laminated, and a back surface 11b on which a metal layer 21 such as aluminum as a reflective film is formed.

  The sapphire substrate 13 has a thickness of 100 μm, for example, and the epitaxial layer 15 has a thickness of 5 μm, for example. A plurality of first division planned lines 17a extending in the first direction and a plurality of second division planned lines 17b extending in a direction orthogonal to the first direction are formed in the epitaxial layer 15, An optical device 19 such as an LED is formed in each region partitioned by one scheduled division line 17a and second scheduled division line 17b.

  Due to the crystal orientation of the sapphire substrate 13, when a modified layer is formed inside the optical device wafer along the division lines 17 a and 17 b and an external force is applied to the optical device wafer 11 to cleave it into individual device chips, There are directions that are difficult to break.

  Which direction is difficult to break differs for each optical device wafer manufacturer. Even in the same manufacturer, the direction in which cracking is difficult in the same lot is the same, but different lots may be different.

  Therefore, in carrying out the wafer dividing method of the present invention, after forming a modified layer on an optical device wafer of a lot, the optical device wafer is divided using the modified layer as a dividing starting point, and in any direction. It is detected whether the division line is difficult to break, and the division method of the present invention is implemented based on the detection result. Here, it is assumed that the second division line 17b is in a direction in which it is difficult to break.

  In the wafer dividing method of the present invention, since the laser beam for forming the modified layer is incident from the back side of the optical device wafer 11, the surface side of the optical device wafer 11 is covered with an adhesive tape as shown in FIG. The dicing tape T is attached to a certain dicing tape T, and the outer periphery of the dicing tape T is attached to the annular frame F. As a result, the optical device wafer 11 supported by the annular frame F via the dicing tape T has a form in which the metal layer 21 formed on the back surface is exposed.

  In the wafer dividing method of the present invention, as shown in FIG. 6, the optical device wafer 11 is sucked and held by the chuck table 28 via the dicing tape T, and the annular frame F is fixed by the clamp 30. In this state, the metal layer 21 formed on the back surface of the optical device wafer 11 is exposed.

  Since the optical device wafer 11 is sucked and held by the chuck table 28 with the metal layer 21 exposed in this way, the first and second scheduled division lines 17a and 17b can be imaged by the imaging unit 38 through the metal layer 21. Can not.

  Therefore, in the present invention, the optical device wafer 11 is imaged from the lower side by the imaging unit 74 as described in Japanese Patent Application Laid-Open No. 2010-82644 or Japanese Patent Application Laid-Open No. 2010-87141. The lines 17a and 17b are detected, and alignment that aligns the condenser 36 with the first and second scheduled division lines 17a and 17b is performed using a well-known technique such as pattern matching.

  After the alignment, as shown in FIG. 7, a laser beam having a wavelength that absorbs light from the condenser 36 to the optical device wafer 11 is irradiated from the back side of the optical device wafer 11, that is, from the metal layer 21 side. Then, a first metal layer removing step for forming a narrow metal layer removing groove 23 by ablation along the first division line 17a is performed.

  In this first metal layer removal step, narrow metal layer removal grooves 23 are formed by ablation along all the first planned division lines 17a extending in the first direction of the optical device wafer 11 while sequentially indexing and feeding. Form.

  Next, the chuck table 28 is rotated 90 degrees, and as shown in FIG. 8, a laser beam having a wavelength that absorbs light from the condenser 36 to the optical device wafer 11 is emitted from the back side of the optical device wafer 11, that is, Irradiation from the metal layer 21 side is performed, and a second metal layer removing step for forming a wide metal layer removing groove 25 along the second division planned line 17b is performed.

  In this second metal layer removing step, a wide metal layer is formed by ablation along all the second scheduled division lines 17b extending in the second direction of the optical device wafer 11 while sequentially indexing and feeding the chuck table 28. A removal groove 25 is formed.

  9A is a longitudinal sectional view of the optical device wafer 11 in which the narrow metal layer removal groove 23 is formed by the first metal layer removal step, and FIG. 9B is the second metal layer removal step. 2A and 2B are longitudinal sectional views of the optical device wafer 11 in a state where a wide metal layer removal groove 25 is formed.

  The processing conditions for the first and second metal layer removal steps are set as follows, for example.

Light source: LD excitation Q switch Nd: YAG laser Wavelength: 355 nm (third harmonic of YAG laser)
Average output: 1.5W
Repetition frequency: 50 kHz
Processing feed rate: 100 mm / s

  Instead of the first and second metal layer removal steps by the ablation process described above, the first and second metal layer removal steps may be performed using two types of cutting blades having different cutting edge widths. . In this case, the first metal layer removing step is performed with a cutting blade having a narrow cutting edge, and the second metal layer removing step is performed with a cutting blade having a wide cutting edge.

  After performing the first and second metal layer removing steps, as shown in FIG. 10, the condensing point of the laser beam having a wavelength transmissive to the optical device wafer 11 is positioned inside the optical device wafer 11, A laser beam 27 is irradiated from the metal layer 21 side of the optical device wafer 11 to the region where the metal layer 21 is removed along the first planned division line 17a or the second planned division line 17b, and the chuck table 28 is moved to an arrow. A modified layer forming step for forming the modified layer 29 inside the optical device wafer 11 is performed by processing and feeding in the X1 direction.

  Referring to FIG. 11, a perspective view showing the modified layer forming step is shown. In this figure, a laser beam is irradiated along the second division planned line 17b through the wide metal layer removing groove 25, and the light is irradiated. The state in which the modified layer is formed inside the device wafer 11 is shown.

  As shown in FIG. 12A, when the laser beam 27 is irradiated to the narrow metal layer removing groove 23, the outer peripheral side of the laser beam 27 in the width direction of the first division planned line 17a is formed with the metal layer 21. Since the light cannot be transmitted, the light amount of the laser beam condensed inside the optical device wafer 11 becomes small. As a result, a relatively thin modified layer 29a is formed on the optical device wafer 11 as shown in FIG. Formed inside.

  On the other hand, as shown in FIG. 13A, when the laser beam 27 is irradiated to the wide metal layer removal groove 25, the outer peripheral side of the laser beam 27 in the width direction of the second division planned line 17b is the metal layer. Since the amount of light that is hardly blocked or blocked by 21 is small compared to the case shown in FIG. 12A, a large amount of light is condensed inside the optical device wafer 11. As a result, a relatively wide modified layer 29b is formed inside the optical device wafer 11 as shown in FIG.

  The processing conditions of the modified layer forming step are set as follows, for example.

Light source: LD excitation Q switch Nd: YAG laser Wavelength: 1064 nm
Average output: 0.3W
Repetition frequency: 100 kHz
Processing feed rate: 400 mm / s

  After performing the modified layer forming step, a cleaving step of cleaving the optical device wafer 11 into individual optical device chips by applying an external force to the optical device wafer 11 is performed. In this cleaving step, for example, as shown in FIG. 16, the annular frame F is placed on the placement surface of the cylinder 80, and the annular frame F is clamped by the clamp 82. A bar-shaped dividing jig 84 is disposed in the cylinder 80.

  The dividing jig 84 has an upper stage holding surface 86a and a lower stage holding surface 86b, and a vacuum suction path 88 that opens to the lower stage holding surface 86b is formed. The detailed structure of the dividing jig 84 is disclosed in Japanese Patent No. 4361506.

  In order to perform the cleaving step by the dividing jig 84, the upper holding surface 86a and the lower holding surface 86b of the dividing jig 84 are lowered while the vacuum suction path 88 of the dividing jig 84 is vacuumed as indicated by an arrow 90. The dividing jig 84 is moved in the direction of arrow A by contacting the dicing tape T from the side. That is, the dividing jig 84 is moved in a direction orthogonal to the first planned division line 17a or the second planned division line 17b to be divided.

  As a result, when the modified layer 29a or 29b serving as the division starting point moves directly above the inner edge of the upper holding surface 86a of the dividing jig 84, the portion to be divided 17a or 17b having the modified layer 29a or 29b is formed. Bending stress is generated in a concentrated manner, and the optical device wafer 11 is cleaved along the first or second scheduled dividing line 17a, 17b by this bending stress.

  When the division along all the first planned division lines 17a extending in the first direction is completed, the dividing jig 84 is rotated 90 degrees or the cylinder 80 is rotated 90 degrees, so that the first direction Similarly, the second scheduled division line 17b extending in the direction perpendicular to the line is cleaved. As a result, the optical device wafer 11 is divided into individual optical device chips 19.

  In the wafer dividing method of the present embodiment, since the thick modified layer 29b is formed along the second scheduled dividing line 17b extending in a direction difficult to break, the second scheduled dividing line extending in a direction difficult to break. The cleaving along 17b can be easily performed, and it is possible to prevent the occurrence of remaining cracks in the direction in which cracking is difficult.

  Referring to FIG. 14, a plan view of a wafer 11A having a long sized device 19A is shown. In the wafer 11A having such a long sized device 19A, the interval (pitch) between the second divisional lines 17b is formed narrower than the interval (pitch) between the first divisional lines 17a, The direction along the second scheduled division line 17b is not easily cleaved.

  Therefore, the wafer dividing method of the present invention can be similarly applied to the wafer 11A having the long device 19A whose direction of difficulty in cracking is independent of the crystal orientation. In this case, a thick modified layer is formed along the second planned division line 17b having a narrow pitch, and a relatively thin modified layer is formed along the first planned division line 17a. Thereafter, by performing a cleaving step using the dividing jig 84 as shown in FIG. 16, the wafer 11A can be cleaved into individual device chips 19A without leaving any cracks.

  As shown in FIG. 15, the wafer dividing method of the present invention is such that the metal layer 21 is formed only on the back surface of the wafer 11 corresponding to the device region 31 in which the plurality of devices 19 are formed, and the outer periphery surrounding the device region 31. The same can be applied to the optical device wafer 11 in which the metal layer 21 is not formed on the back surface of the optical device wafer 11 corresponding to the surplus region 33.

  Since the modified layer formed on the outer peripheral portion of the optical device wafer 11 is more effective as a starting point for splitting, the splitting method of the present invention is more effective if the optical device wafer 11 in which the metal layer 21 is not in the outer peripheral surplus region is used. Is.

  In the above-described embodiment, the example in which the dividing method of the present invention is applied to the optical device wafer 11 has been described. However, the workpiece is not limited to the optical device wafer 11, and there is a direction in which it is difficult to break. The dividing method of the present invention can be similarly applied to a wafer.

DESCRIPTION OF SYMBOLS 11 Optical device wafer 13 Sapphire substrate 15 Epitaxial layer 17a 1st dividing line 17b 2nd dividing line 19 Optical device 21 Metal layer 23 Narrow metal layer removal groove 25 Wide metal layer removal groove 28 Chuck table 29 , 29a, 29b Modified layer 34 Laser beam irradiation unit 36 Concentrator 84 Split jig

Claims (3)

A plurality of first division lines that are formed on the surface and extend in the first direction, and a second direction that is orthogonal to the first division line and that is less likely to break compared to the first division line. A wafer in which a device is formed and a metal layer is formed on the back surface is formed along each of the first and second scheduled division lines in each region partitioned by the plurality of second scheduled division lines. A method of dividing a wafer to be divided,
A first metal layer removing step in which the wafer is held on a chuck table with the metal layer side exposed, and the metal layer in a region corresponding to the first division line of the wafer is removed;
A second metal layer removing step of exposing the wafer to the metal layer side and holding the wafer with a chuck table, and removing the metal layer in a region corresponding to the second division line of the wafer;
After performing the first and second metal layer removing steps, a condensing point of a laser beam having a wavelength transmissive to the wafer is positioned inside the wafer, and the first metal layer is removed from the metal layer side of the wafer. A modified layer forming step of irradiating the region from which the metal layer has been removed along the first and second division lines to form a modified layer inside the wafer; and
A cleaving step of cleaving the wafer into individual device chips by applying an external force to the wafer after performing the modified layer forming step;
In the first and second metal layer removal steps, the width of the metal layer removed in the second metal layer removal step is wider than the width of the metal layer removed in the first metal layer removal step.
In the modified layer forming step, the metal layer in a region corresponding to the second scheduled division line is widely removed, and the amount of the laser beam transmitted to the inside of the wafer is less blocked by the metal layer. The modified layer formed inside the wafer along the second division line is more than the modified layer formed inside the wafer along the first division line. A characteristic wafer processing method.   2. The wafer dividing method according to claim 1, wherein the wafer is formed such that an interval between the second divisional lines is narrower than an interval between the first divisional lines.   In the first and second metal layer removing steps, a condensing point of a laser beam having a wavelength that is absorptive with respect to the wafer is positioned on the upper surface of the wafer, and the first and second metal layer removal steps are performed from the metal layer side of the wafer. The wafer dividing method according to claim 1, wherein the metal layer of the wafer is removed by performing ablation processing by irradiating a laser beam along a second division line.

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