Wafer processing method, device chip manufacturing method

Abstract

To achieve efficient thinning of a wafer with devices arranged thereon.SOLUTION: A wafer processing method for processing a wafer having a plurality of devices formed on a first surface thereof includes: a protective layer formation step of positioning a first focal point of a first laser beam at a first height position and emitting the first laser beam onto the wafer from a second surface side, thereby forming a protective layer; a separation start point formation step of positioning a second focal point of a second laser beam at a second height position being more distant from the first surface than the first height position and emitting the second laser beam onto the wafer from the second surface side, thereby forming a separation start position made up of a modified layer and a crack; and a separation step of applying external force to the wafer to divide the wafer at the separation start position and separating a separated body including the second surface from the wafer.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a processing method for processing a wafer having a first surface and a second surface opposite to the first surface, wherein a plurality of devices are formed on the first surface, and a method for manufacturing device chips, wherein the wafer is subsequently divided to form individual device chips. [Background technology]

[0002] Semiconductor device chips are generally manufactured using a disc-shaped wafer made of a semiconductor material such as silicon (Si) or silicon carbide (SiC). Multiple devices are arranged on the first surface of this wafer, and the wafer is thinned by grinding from the second surface side. When the wafer is divided into individual devices, individual device chips are obtained. The obtained device chips are then mounted and used in various electronic devices such as mobile phones and personal computers.

[0003] However, when grinding materials with high Mohs hardness, such as silicon carbide, the high wear rate of the grinding wheel used for grinding and the long processing time have been problematic. Therefore, a method was developed to thin a wafer by forming a separation point (delamination layer) consisting of a modified layer and cracks across the entire surface at a certain height within the wafer, and then applying an external force to the wafer to split it into two at this separation point (see Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-28072 [Overview of the project] [Problems that the invention aims to solve]

[0005] The formation of the separation point is performed by scanning the focal point of the laser beam across the entire region where the separation point is intended to be formed, while irradiating the wafer from the second surface side with the laser beam. However, with this method, components of the laser beam that did not contribute to the formation of the separation point could travel further through the wafer and reach the first surface, potentially damaging devices placed on the first surface. Therefore, it was necessary to limit the output of the laser beam or to set the formation height of the separation point far away from the first surface, which prevented the efficient formation of the separation point.

[0006] In view of this, the object of the present invention is to provide a wafer processing method that can efficiently thin a wafer on which a device is disposed on a first surface, and a device chip manufacturing method that can efficiently manufacture device chips by dividing the wafer. [Means for solving the problem]

[0007] According to one aspect of the present invention, a wafer processing method for processing a wafer having a first surface and a second surface opposite to the first surface, wherein a plurality of devices are formed on the first surface, comprising: a protective layer formation step of positioning a first focal point of a first laser beam of a wavelength that penetrates the wafer at a first height position inside the wafer, irradiating the wafer with the first laser beam from the second surface side while relatively moving the first focal point and the wafer along the first surface to form a protective layer at the first height position inside the wafer; and after the protective layer formation step, positioning a second focal point of a second laser beam of a wavelength that penetrates the wafer at the first height position inside the wafer. A wafer processing method is provided, comprising: a separation point formation step, in which the wafer is positioned at a second height position further from the first surface, and the second laser beam is irradiated onto the wafer from the second surface side while the second focusing point and the wafer are relatively moved along the first surface, thereby forming a modified layer at the second height position in the wafer and forming cracks extending from the modified layer to form a separation point composed of the modified layer and the cracks; and a separation step, in which, after the separation point formation step, an external force is applied to the wafer to divide the wafer at the separation point, separating the separated body including the second surface from the wafer so that the second surface does not remain on the wafer.

[0008] Preferably, the first laser beam in the protective layer formation step has less influence on the device than the second laser beam that reaches the first surface without passing through the protective layer.

[0009] Preferably, after performing the separation step, the process further includes a grinding step in which the back surface of the wafer exposed on the opposite side of the first surface is ground to remove the protective layer and flatten the back surface.

[0010] Furthermore, according to another aspect of the present invention, a method for manufacturing a device chip by dividing a wafer having a first surface and a second surface opposite to the first surface, wherein a plurality of devices are formed on the first surface, comprising: a protective layer formation step of positioning a first focal point of a first laser beam of a wavelength that penetrates the wafer at a first height position inside the wafer, irradiating the wafer with the first laser beam from the second surface side while relatively moving the first focal point and the wafer along the first surface to form a protective layer at the first height position inside the wafer; and after the protective layer formation step, positioning a second focal point of a second laser beam of a wavelength that penetrates the wafer at a second height position further from the first surface than the first height position inside the wafer, and moving the second focal point and the wafer along the first surface A method for manufacturing a device chip is provided, comprising: a separation origin formation step of irradiating the wafer with a second laser beam from the second surface side while moving the wafer to form a modified layer at a second height position in the wafer and to form cracks extending from the modified layer to form a separation origin composed of the modified layer and the cracks; a separation step of applying an external force to the wafer after the separation origin formation step to divide the wafer at the separation origin and separate the separated body including the second surface from the wafer so that the second surface does not remain on the wafer; a grinding step of grinding the back surface exposed on the opposite side of the first surface of the wafer after the separation step to remove the protective layer and flatten the back surface; and a division step of dividing the wafer for each device to manufacture a plurality of device chips each equipped with the device.

[0011] Preferably, the first laser beam in the protective layer formation step has less influence on the device than the second laser beam that reaches the first surface without passing through the protective layer. [Effects of the Invention]

[0012] According to one aspect of the present invention, a wafer processing method and a device chip manufacturing method are described below. First, the first focusing point of a first laser beam is positioned at a first height position, and a protective layer is formed with the first laser beam. Subsequently, the second focusing point of a second laser beam is positioned at a second height position, which is further from the first surface than the first height position, and the second laser beam is irradiated onto the second focusing point. This forms a separation point on the wafer.

[0013] In this case, when the second laser beam is irradiated onto the wafer, the second laser beam, which passes through the second focal point and travels toward the first surface of the wafer, reaches the protective layer before the first surface. Then, the second laser beam reaches the first surface in a reduced state due to reflection, absorption, scattering, etc., by the protective layer. Alternatively, the second laser beam does not reach the first surface at all. Therefore, when the second laser beam is irradiated onto the wafer, the device is less likely to be damaged compared to when no protective layer is formed.

[0014] When this protective layer is formed on the wafer, the second laser beam can be focused to a height closer to the first surface than before, allowing the separation starting point to be formed at a height closer to the first surface. In this case, the amount of material removed when the wafer is ground and thinned after the separation step can be reduced, thus reducing the wear on the grinding wheel and extending its lifespan.

[0015] Furthermore, in this case, the separator separated from the wafer can be made thicker. This thick separator can then be used as a new wafer for manufacturing device chips. When manufacturing device wafers from this new wafer, the thick separator can still be retained. In other words, material loss can be reduced, and more device chips can be manufactured.

[0016] Accordingly, according to one aspect of the present invention, a wafer processing method is provided that can efficiently thin a wafer on which a device is disposed on a first surface, and a device chip manufacturing method is provided that can efficiently manufacture device chips by dividing the wafer.

Brief Description of the Drawings

[0017] [Figure 1] It is a perspective view schematically showing a wafer. [Figure 2] It is a perspective view schematically showing a laser processing apparatus. [Figure 3] It is a block diagram schematically showing the configuration of a laser beam irradiation unit. [Figure 4] It is a cross-sectional view schematically showing a wafer in a protective layer formation step. [Figure 5] It is a cross-sectional view schematically showing a wafer in a separation starting point formation step. [Figure 6] Each of FIGS. 6(A) and 6(B) is a cross-sectional view schematically showing a wafer in a separation step. [Figure 7] It is a perspective view schematically showing a wafer in a grinding step. [Figure 8] It is a cross-sectional view schematically showing a wafer being ground. [Figure 9] It is a perspective view schematically showing a wafer being divided. [Figure 10] It is a flowchart showing the flow of each step of a wafer processing method and a device chip manufacturing method.

Modes for Carrying Out the Invention

[0018] Referring to the accompanying drawings, embodiments of the present invention will be described. FIG. 1 is a perspective view schematically showing a wafer 11 processed by a wafer processing method and a device chip manufacturing method according to this embodiment. Cross-sectional views schematically showing the wafer 11 are included in FIGS. 4 and the like. The wafer 11 is formed from a semiconductor material such as silicon (Si) or silicon carbide (SiC). However, the material of the wafer 11 is not limited to this.

[0019] The wafer 11 is disc-shaped and has a substantially circular first surface (front) 11a and a second surface (back) 11b. The second surface 11b is located on the opposite side of the wafer 11 from the first surface 11a in the thickness direction of the wafer 11. The diameter of the wafer 11 is, for example, about 300 mm (12 inches), and the thickness from the first surface 11a to the second surface 11b is about 500 μm. However, the diameter and thickness of the wafer 11 are not limited to this example.

[0020] Notches 13 indicating the crystal orientation of the wafer 11 are formed on the outer periphery of the wafer 11. The notches 13 indicate a specific crystal orientation contained in the wafer 11. As shown in Figure 1, multiple division lines (streets) 15 are set in a grid pattern on the first surface 11a.

[0021] A device 17, such as an IC (Integrated Circuit), is formed in each of the multiple regions demarcated by the multiple division lines 15. As described later, by thinning the wafer 11 and dividing it along the division lines 15, device chips each containing a device 17 can be manufactured.

[0022] Figure 2 is a schematic perspective view of the laser processing apparatus 2 used for laser processing of wafer 11. Note that the X-axis direction (second direction) and Y-axis direction (first direction) shown in Figure 2 are mutually orthogonal directions on the horizontal plane, and the Z-axis direction is a direction (vertical direction) that is orthogonal to the X-axis direction and the Y-axis direction, respectively.

[0023] The laser processing apparatus 2 has a base 4 that supports each component. An X-axis and Y-axis movement mechanism 6 is provided on the upper surface of the base 4. The X-axis and Y-axis movement mechanism 6 has a pair of Y-axis guide rails 8 that are fixed to the upper surface of the base 4 and arranged along the Y-axis direction.

[0024] A Y-axis movable plate 10 is attached to the upper side of a pair of Y-axis guide rails 8 in a manner that allows it to slide along the pair of Y-axis guide rails 8. A ball screw is provided on the lower side of the Y-axis movable plate 10.

[0025] The ball screw has a nut portion (not shown) fixed to the lower surface of the Y-axis moving plate 10. The screw shaft 12 is rotatably connected to the nut portion using a ball (not shown). The screw shaft 12 is positioned along the Y-axis direction between a pair of Y-axis guide rails 8.

[0026] A motor 14 for rotating the screw shaft 12 is connected to one end of the screw shaft 12. When the motor 14 is operated, the Y-axis moving plate 10 moves along the Y-axis direction. The pair of Y-axis guide rails 8, the Y-axis moving plate 10, the screw shaft 12, the nut, the motor 14, etc. constitute the Y-axis moving mechanism.

[0027] A pair of X-axis guide rails 16 are fixed to the upper surface of the Y-axis moving plate 10. The pair of X-axis guide rails 16 are arranged along the X-axis direction. An X-axis moving plate 18 is attached to the upper side of the pair of X-axis guide rails 16 in a manner that allows it to slide along the pair of X-axis guide rails 16.

[0028] A ball screw is provided on the underside of the X-axis moving plate 18. The ball screw has a nut portion (not shown) fixed to the underside of the X-axis moving plate 18. The screw shaft 20 is rotatably connected to the nut portion using a ball (not shown).

[0029] The screw shaft 20 is positioned along the X-axis direction between a pair of X-axis guide rails 16. A motor 22 for rotating the screw shaft 20 is connected to one end of the screw shaft 20. When the motor 22 is operated, the X-axis moving plate 18 moves along the X-axis direction.

[0030] A pair of X-axis guide rails 16, an X-axis moving plate 18, a screw shaft 20, a nut, a motor 22, etc. constitute the X-axis moving mechanism. A cylindrical table base 24 is provided on the upper side of the X-axis moving plate 18. The table base 24 has a rotational drive source (not shown), such as a motor.

[0031] A disc-shaped chuck table 26 is positioned at the top of the table base 24. The rotational drive source can rotate the chuck table 26 within a predetermined angular range using a straight line passing through the center of its holding surface 26a and parallel to the Z-axis direction as the axis of rotation. The chuck table 26 has a disc-shaped frame made of non-porous metal.

[0032] A disc-shaped recess (not shown) is formed in the center of the frame. A disc-shaped porous plate made of ceramics is fixed in this recess. A predetermined flow path (not shown) is formed in the frame. Negative pressure is transmitted from a suction source (not shown), such as an ejector, to the upper surface of the porous plate via the predetermined flow path.

[0033] The annular upper surface of the frame and the circular upper surface of the porous plate are substantially flush, and function as a substantially flat holding surface 26a for suction holding the wafer 11. While the wafer 11 is held by suction on the holding surface 26a, it can be moved along either the X-axis or Y-axis direction by the X-axis and Y-axis movement mechanism 6.

[0034] Multiple clamp units 26b (four in this embodiment) are provided on the outer circumference of the chuck table 26 at approximately equal intervals along the circumferential direction of the chuck table 26. Each clamp unit 26b grips the frame of the frame unit, which will be described later.

[0035] A support structure 30 is provided on a predetermined area of ​​the base 4 located behind the X-axis and Y-axis movement mechanism 6. A Z-axis movement mechanism 32 is provided on one side of the support structure 30 that is aligned with the Y-Z plane. The Z-axis movement mechanism 32 has a pair of Z-axis guide rails 34.

[0036] A pair of Z-axis guide rails 34 are fixed to one side of the support structure 30 and are arranged along the Z-axis direction. A Z-axis movable plate 36 is attached to the pair of Z-axis guide rails 34 in a manner that allows it to slide along the pair of Z-axis guide rails 34.

[0037] A ball screw (not shown) is provided on the back side of the Z-axis moving plate 36. The ball screw has a nut portion (not shown) fixed to the back side of the Z-axis moving plate 36. A screw shaft (not shown) is rotatably connected to the nut portion using a ball.

[0038] The screw shaft is positioned between a pair of Z-axis guide rails 34 along the Z-axis direction. A motor 38 for rotating the screw shaft is connected to the upper end of the screw shaft. When the motor 38 is operated, the Z-axis moving plate 36 moves along the Z-axis direction.

[0039] A support 40 is fixed to the surface side of the Z-axis moving plate 36. The support 40 supports a part of the laser beam irradiation unit 42. Figure 3 is a schematic block diagram showing the configuration of the laser beam irradiation unit 42. In Figure 3, some of the components of the laser beam irradiation unit 42 are shown as functional blocks.

[0040] The laser beam irradiation unit 42 has a laser oscillator 44 fixed to the base 4. The laser oscillator 44 has, for example, Nd:YVO4 or Nd:YAG as the laser medium and emits a pulsed laser beam L having a wavelength (e.g., 1342 nm, 1064 nm) that penetrates the wafer 11. A It fires.

[0041] Laser beam L A The output is then adjusted by an attenuator 46 before proceeding to a branching unit 48. The branching unit 48 in this embodiment is composed of a spatial light modulator and / or a diffractive optical element (DOE) including a liquid crystal phase control element called an LCOS-SLM (Liquid Crystal on Silicon - Spatial Light Modulator).

[0042] The branching unit 48 is the laser beam L A It has the function of branching the laser beam L emitted from the irradiation head 52. For example, the branching unit 48 has the function of branching the laser beam L emitted from the irradiation head 52. AThe laser beam L forms a plurality of condensing points arranged at substantially equal intervals along the Y-axis direction. A is branched.

[0043] In FIG. 3, an example is shown in which the laser beam L is branched by the branching unit 48 so as to form five condensing points P1 to P5. A However, the laser beam L may be branched so as to form a predetermined number of condensing points of two or more (more preferably two or more and 16 or less). A may be branched.

[0044] The branching unit 48 also has a function of simply transmitting the laser beam L without branching it. By controlling the operation of the branching unit 48, the presence or absence of branching of the laser beam L A can be selected. A

[0045] Incidentally, the branching unit 48 may have a diffraction grating instead of the LCOS-SLM. Since the diffraction grating branches the laser beam L so as to form a predetermined number of condensing points, when the laser beam L A is not branched, the diffraction grating may be removed from the optical path of the laser beam L A . Alternatively, the laser beam irradiation unit 42 may not include the branching unit 48. A

[0046] The laser beam L emitted from the laser oscillator 44 A is reflected by the mirror 50 and guided to the irradiation head 52. The irradiation head 52 houses a condensing lens (not shown) for condensing the laser beam L A and the like.

[0047] The irradiation head 52 is arranged to face the holding surface 26a during laser processing, and the laser beam L A is emitted to the holding surface 26a. The irradiation head 52 is provided at the front end of a cylindrical housing 54 whose long hand portion is arranged along the Y-axis direction (see FIG. 2).

[0048] The housing 54 is fixed to a portion of its rear end by a support 40. Furthermore, the imaging unit 56 is fixed to the side of the housing 54 located near the irradiation head 52 in a manner that allows it to face the holding surface 26a.

[0049] The imaging unit 56 is, for example, a visible light camera unit having an objective lens, a light source such as an LED (Light Emitting Diode), and an image sensor such as a CCD (Charge-Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor.

[0050] In the case of a visible light camera unit, for example, a photodiode made of Si (silicon) is used as the image sensor. The imaging unit 56 may also be an infrared camera unit having a light source such as an LED and an image sensor.

[0051] In the case of an infrared camera unit, for example, a photodiode made of InGaAs (indium gallium arsenide) is used as the image sensor. Using an infrared camera unit, even if the first surface 11a is held by attraction at the holding surface 26a, the first surface 11a can be imaged by passing through the wafer 11 from the second surface 11b side.

[0052] The irradiation head 52, housing 54, imaging unit 56, etc., can be moved integrally along the Z-axis direction by the Z-axis movement mechanism 32. A cover (not shown) is provided on the base 4 to cover the above-mentioned components.

[0053] A touch panel 58 is provided on the front of this cover. The touch panel 58 functions as an input device such as a capacitive touch sensor and a display device such as a liquid crystal display. The operator can set processing conditions for the laser processing device 2 via the touch panel 58 and also view the image of the wafer 11 obtained by the imaging unit 56.

[0054] The laser processing apparatus 2 is used to form separation points on the wafer 11. When forming separation points on the wafer 11, first, the wafer 11 is placed on the chuck table 26 with the second surface (back surface) 11b facing upwards, and the wafer 11 is held in place by suction using the chuck table 26.

[0055] Then, the laser beam irradiation unit 42 positions a focal point at a predetermined height inside the wafer 11, and the laser beam is focused from the second surface 11b side of the wafer 11 to form a modified layer and cracks extending from the modified layer. The modified layer and cracks function as separation points (delamination layers). Then, by applying an external force to the wafer 11 and separating it vertically at the separation points, the wafer 11 can be thinned efficiently.

[0056] However, of the laser beam irradiated onto the wafer 11 from the laser beam irradiation unit 42, the component that does not contribute to the formation of a separation point and is not absorbed by the wafer 11 (leakage light) continues to travel through the wafer 11 and reaches the first surface 11a. Since the device 17 is formed on the first surface 11a, the device 17 may be damaged by this component of the laser beam (leakage light).

[0057] Therefore, conventionally, it was necessary to limit the output of the laser beam used to form the separation point in order to prevent damage to the device 17. Forming a high-quality separation point with a low-intensity laser beam required a long time for laser processing, making it difficult to form the separation point efficiently.

[0058] Furthermore, conventionally, in order to prevent damage to the device 17, it was necessary to move the focal point of the laser beam at a predetermined distance or more from the first surface 11a. In this case, after separating the wafer 11 at the separation point and removing the separation body including the second surface 11b, a large portion of the wafer 11 is removed during the grinding process performed to finish the wafer 11 to a predetermined thickness. As a result, the grinding wheel used for grinding wears out quickly, requiring frequent replacement of the grinding wheel, which is uneconomical.

[0059] Therefore, in the wafer processing method and device chip manufacturing method according to this embodiment, a protective layer is formed on the wafer 11 before forming the separation point, so that the wafer 11 on which the device 17 is disposed on the first surface 11a can be efficiently thinned. In this case, the laser beam irradiated onto the wafer 11 when forming the separation point hits the protective layer, and the laser beam is reflected, attenuated, scattered, etc. by the protective layer.

[0060] Therefore, the device 17 becomes less susceptible to damage, and the laser beam can be irradiated onto the wafer 11 under stronger irradiation conditions. In addition, the separation point can be formed closer to the first surface 11a. In this case, the amount of material removed from the wafer 11 is reduced, and the wear of the grinding wheel is reduced, thus extending the life of the grinding wheel. Furthermore, the time required for grinding is also reduced, allowing for more efficient processing of the wafer 11 and more efficient manufacturing of device chips.

[0061] The following describes in detail each step of the wafer processing method and device chip manufacturing method according to this embodiment. In the wafer processing method and device chip manufacturing method according to this embodiment, some of the steps described below may be omitted, and steps other than those described below may be further performed.

[0062] Here, the wafer processing method according to this embodiment is included in the device chip manufacturing method. Therefore, the steps constituting the device chip manufacturing method will be described below. Figure 10 is a flowchart showing the flow of each step in the device chip manufacturing method according to this embodiment.

[0063] In the device chip manufacturing method according to this embodiment, a protective layer formation step S10 is performed to form a protective layer on the wafer 11 before performing the separation origin formation step S20 to form separation origins on the wafer 11. The protective layer formation step S10 and the separation origin formation step S20 are performed, for example, by the laser processing apparatus 2 described above. The cross-sectional view shown in Figure 4 schematically illustrates the process of performing the protective layer formation step S10.

[0064] To begin the protective layer formation step S10, first, the wafer 11 is placed on the chuck table 26. Then, after placing the wafer 11 on the chuck table 26, the wafer 11 is held in place by suction using the chuck table 26.

[0065] Here, when placing the wafer 11 on the chuck table 26, the first surface 11a on which the device 17 is formed on the wafer 11 is oriented toward the holding surface 26a of the chuck table 26, and the second surface 11b of the wafer 11 is exposed upwards. This is because the laser beam cannot be irradiated onto the wafer 11 from the first surface 11a side in order to avoid the laser beam directly hitting the device 17 formed on the first surface 11a.

[0066] Furthermore, protective tape or the like may be pre-attached to the first surface 11a of the wafer 11 to protect the device 17. This protective tape may also be arranged on the wafer 11 with a diameter larger than the wafer 11, and the outer periphery of the protective tape may be attached to the ring frame. In this case, the ring frame is fixed by the clamp unit 26b of the chuck table 26. Note that in each cross-sectional view, the device 17 formed on the first surface 11a and the protective tape or the like attached to the first surface 11a are omitted.

[0067] In the protective layer formation step S10, the laser beam irradiation unit 42 and the chuck table 26 are raised and lowered relative to each other along the Z-axis. This adjusts the height of the first focal point 52b, which is the focal point of the first laser beam 52a irradiated onto the wafer 11 from the laser beam irradiation unit 42 in the protective layer formation step S10. The first focal point 52b of the first laser beam 52a is then positioned at a first height position H1 inside the wafer 11. This first height position H1 will be described in detail later.

[0068] Next, the irradiation head 52 of the laser beam irradiation unit 42 and the chuck table 26 are moved relative to each other along a horizontal plane including the X-axis and Y-axis directions, thereby moving the first focal point 52b and the wafer 11 relative to each other along the first surface 11a. That is, the processing feed is started. Then, while moving the first focal point 52b and the wafer 11 relative to each other, the laser beam irradiation unit 42 is operated to irradiate the wafer 11 with a first laser beam 52a of a wavelength that penetrates the wafer 11 from the second surface 11b side.

[0069] When a first laser beam 52a with a wavelength that penetrates the wafer 11 is focused at a first focal point 52b inside the wafer 11, a portion of the first laser beam 52a is absorbed by the wafer 11, and the wafer 11 is modified near the first focal point 52b, forming a protective layer 64. This protective layer (modified layer) 64 has the function of protecting the device 17 formed on the first surface 11a side from the second laser beam that is irradiated onto the wafer 11 in the separation point formation step S20 described next.

[0070] The irradiation conditions for the first laser beam 52a irradiated onto the wafer 11 in the protective layer formation step S10 will be described later, along with the irradiation conditions for the second laser beam irradiated onto the wafer 11 in the separation point formation step S20, which will be described next.

[0071] In the device chip manufacturing method according to this embodiment, after the protective layer formation step S10, a separation point formation step S20 is performed to form separation points consisting of a modified layer and cracks on the wafer 11. The cross-sectional view shown in Figure 5 schematically illustrates the process of performing the separation point formation step S20. When the separation point formation step S20 is performed in the laser processing apparatus 2 following the protective layer formation step S10, the wafer 11 is continued to be held by suction using the chuck table 26.

[0072] In the separation point formation step S20, the laser beam irradiation unit 42 and the chuck table 26 are raised and lowered relative to each other along the Z-axis. This adjusts the height of the second focal point 52d, which is the focal point of the second laser beam 52c irradiated onto the wafer 11 from the laser beam irradiation unit 42 in the separation point formation step S20. In this adjustment, the second focal point 52d of the second laser beam 52c is positioned at a second height position H2 that is higher than the first height position H1 inside the wafer 11.

[0073] Next, the irradiation head 52 of the laser beam irradiation unit 42 and the chuck table 26 are moved relative to each other along the horizontal plane, thereby moving the second focusing point 52d and the wafer 11 relative to each other along the first surface 11a. That is, the processing feed is started. Then, while moving the second focusing point 52d and the wafer 11 relative to each other, the laser beam irradiation unit 42 is operated to irradiate the wafer 11 with a second laser beam 52c of a wavelength that penetrates the wafer 11 from the second surface 11b side.

[0074] When a second laser beam 52c with a wavelength that penetrates the wafer 11 is focused at a second focal point 52d inside the wafer 11, a portion of the second laser beam 52c is absorbed by the wafer 11, and the wafer 11 is modified near the second focal point 52d, forming a modified layer 66. Furthermore, cracks 68 extending from the modified layer 66 are simultaneously formed. This modified layer 66 and cracks 68 constitute a separation starting point 70.

[0075] Here, the irradiation conditions for the second laser beam 52c may be set so that the wafer 11 is processed with a stronger intensity than the first laser beam 52a. However, the intensity of the first laser beam 52a and the intensity of the second laser beam 52c are not limited to this. Also, the wavelengths of the first laser beam 52a and the second laser beam 52c may be the same, and both may be emitted from the irradiation head 52 of a single laser beam irradiation unit 42. In this case, differences are made in the irradiation conditions of the two in items other than wavelength.

[0076] In the device chip manufacturing method according to this embodiment, after the separation starting point formation step S20, an external force is applied to the wafer 11 to divide the wafer 11 at the separation starting point 70, and a separation step S30 is performed to separate the separated body including the second surface 11b from the wafer 11.

[0077] Figures 6(A) and 6(B) each include a schematic cross-sectional view of the wafer 11 during the separation step S30. This separation step S30 is performed, for example, in the separation apparatus 71 shown in Figures 6(A) and 6(B). This separation apparatus 71 has a holding table 73 that holds the wafer 11 on which the separation starting point (exfoliation layer) 70 is formed.

[0078] The holding table 73 has a circular top surface (holding surface), and a porous plate (not shown) is exposed on this holding surface 73a. Furthermore, this porous plate is in communication with a suction source (not shown), such as a vacuum pump, via a flow path or the like provided inside the holding table 73. When this suction source operates, a negative pressure is generated in the space near the holding surface 73a of the holding table 73.

[0079] Furthermore, a separation unit 72 is provided above the holding table 73. This separation unit 72 has a cylindrical support member 74. A ball screw type lifting mechanism (not shown), for example, is connected to the upper part of this support member 74. The separation unit 72 moves up and down by operating this lifting mechanism. The lower end of the support member 74 is fixed to the center of the upper part of a disc-shaped base 76. The separation unit 72 is equipped with a suction mechanism (not shown) that applies negative pressure to the lower surface of the base 76 and can function as a suction pad.

[0080] In the separation device 71, for example, the separation step S30 is carried out in the following procedure. Specifically, first, the wafer 11 on which the separation starting point 70 is formed is placed on the holding surface 73a of the holding table 73 so that the second surface 11b is exposed upwards. At this time, the first surface 11a faces the holding surface 73a. Next, the suction source connected to the holding table 73 is activated, and the wafer 11 is held in place by suction on the holding table 73.

[0081] Next, the lifting mechanism of the separation unit 72 is activated to lower the separation unit 72 from above the holding table 73, bringing the lower surface of the base 76 into contact with the second surface 11b of the wafer 11. Figure 6(A) schematically shows the state in which the lower surface of the base 76 is in contact with the second surface 11b of the wafer 11.

[0082] In separation step S30, an external force is applied to the wafer 11 before, during, or simultaneously with the contact between the base 76 and the wafer 11. When an external force is applied to the wafer 11, cracks 68 contained in the separation starting point 70 extend, causing the wafer 11 to separate at the separation starting point 70 into a first surface 11a side and a second surface 11b side. When the wafer 11 is separated at the separation starting point 70, a separated body 21 including the second surface 11b is formed, leaving the thinned wafer 19 on the first surface 11a side.

[0083] By applying negative pressure (suction force) to the separator 21 from the base 76 of the separation unit 72, the separator 21 is held in place by suction at the base 76, and the lifting mechanism of the separation unit 72 is activated to raise the separation unit 72, thereby removing the separator 21 from the thinned wafer 19. Alternatively, the base 76 of the separation unit 72 is brought into contact with the wafer 11 before separation, negative pressure is applied from the base 76, and then the separation unit 72 is raised. In this case, an external force is applied to lift the wafer 11, causing the wafer 11 to separate from the separation starting point 70, and the separator 21 is lifted, leaving the thinned wafer 19 behind. Figure 6(B) is a schematic cross-sectional view showing the wafers 11, 19 and the separator 21 when the separator 21 is removed.

[0084] Here, we will describe the external forces applied to the wafer 11 in separation step S30. For example, ultrasonic vibrations may be applied to the wafer 11 as an external force. In this case, for example, an ultrasonic transducer composed of a piezoelectric element or the like may be incorporated into the separation unit 72 of the separation device 71, and ultrasonic vibrations may be applied to the wafer 11 as an external force through the base 76. Alternatively, the external force may be applied to the wafer 11 by the base 76 rising while holding the wafer 11 by attraction. In this case, an external force is applied to the wafer 11 that attempts to lift it.

[0085] Furthermore, the external force applied to the wafer 11 and the method of applying the external force are not limited to these. For example, an external force may be applied to the wafer 11 by inserting a claw-shaped or wedge-shaped insertion member (not shown) into the wafer 11 from the side, and the wafer 11 may be separated by the external force applied by the insertion member.

[0086] In this case, the tip of the insertion member is positioned at the second height position H2 of the wafer 11 (see Figure 5, etc.), and the insertion member is inserted into the wafer 11 from the side. As a result, the crack 68 at the separation point 70 progresses from the outer circumference of the wafer 11, and the wafer 11 separates vertically across the entire surface of the separation point 70. In this case, it is convenient if the insertion member is positioned on the outer circumference of the base 76 of the separation unit 72.

[0087] Note that the separation step S30 does not necessarily have to be performed using a dedicated separation device 71 as shown in Figures 6(A) and 6(B). For example, the laser processing apparatus 2 may be equipped with a separation unit 72, and the separation step S30 may be performed on the chuck table 26 of the laser processing apparatus 2 immediately following the separation starting point formation step S20. In this case, the chuck table 26 functions as the holding table 73 of the separation device 71.

[0088] By forming a separation point 70 on the wafer 11, applying an external force to separate the wafer 11, and removing the separation body 21 including the second surface 11b, a thinned wafer 19 can be easily obtained. At this time, the second surface 11b is not left on the thinned wafer 19. Here, the surface newly exposed on the opposite side of the first surface 11a is called the back surface 11c. By thinning the wafer 11 in this way to obtain a thinned wafer 19, the amount of wafer 19 removed during grinding, which is performed when thinning the wafer 19 to the final finished thickness in the grinding step S40 described next, becomes extremely small.

[0089] In the device chip manufacturing method according to this embodiment, after the separation step S30, a grinding step S40 is performed to grind the back surface 11c exposed on the opposite side of the first surface 11a of the thinned wafer 11 (wafer 19). In the grinding step S40, the thinned wafer 11 (wafer 19) is ground from the back surface 11c side to flatten the back surface 11c and thin the wafer 11 to the final finished thickness. At this time, the protective layer 64 that was formed on the wafer 11 in the protective layer formation step S10 and remains on the wafer 19 after thinning is removed.

[0090] Figure 7 is a schematic perspective view showing the grinding step S40, and Figure 8 is a schematic cross-sectional view showing the grinding step S40. Figures 7 and 8 schematically show some of the components of the grinding apparatus 78 in which the grinding step S40 is performed. Here, the grinding apparatus 78 for grinding the thinned wafer 11 (wafer 19) will be described.

[0091] The grinding device 78 has a disc-shaped chuck table 80. The chuck table 80 has a disc-shaped frame made of non-porous ceramics. A disc-shaped recess (not shown) is formed in the center of the frame.

[0092] A disc-shaped porous plate made of ceramics is fixed in this recess. A predetermined channel (not shown) is formed in the frame. Negative pressure is transmitted from a suction source (not shown), such as an ejector, to the upper surface of the porous plate via the predetermined channel.

[0093] The upper surface of the porous plate is conical in shape, with the central part slightly protruding compared to the outer edge. The circular upper surface of the porous plate and the annular upper surface of the frame are almost flush, and function as a substantially flat holding surface 80a for suction holding the wafer 11.

[0094] A ring-shaped and flat table base (not shown) is provided at the bottom of the chuck table 80 to rotatably support the chuck table 80. Furthermore, a tilt adjustment mechanism (not shown) is provided at the bottom of the table base to adjust the tilt of the chuck table 80.

[0095] Furthermore, a spindle constituting the rotating shaft 80b is connected to the lower part of the chuck table 80. A rotational drive source (not shown), such as a motor, is connected to the spindle via pulleys, belts, etc. When the rotational drive source is operated, the chuck table 80 rotates around the rotating shaft 80b.

[0096] A grinding unit 82 is positioned above the chuck table 80. The grinding unit 82 has a cylindrical spindle housing (not shown) whose longitudinal portion is arranged substantially parallel to the vertical direction.

[0097] A ball screw type machining feed mechanism (not shown) is connected to the spindle housing, which moves the grinding unit 82 along a predetermined direction (for example, the vertical direction). A portion of a cylindrical spindle 84 is also rotatably housed in the spindle housing.

[0098] A rotational drive source, such as a motor, is provided at the upper end of the spindle 84. A disc-shaped mount 86 is fixed to the lower end of the spindle 84. An annular grinding wheel 88 is mounted on the lower surface of the mount 86.

[0099] The grinding wheel 88 has a base 90 made of aluminum alloy. The upper surface of the base 90 is positioned in contact with the mount 86. On the lower surface of the base 90, a plurality of grinding wheels 92 are arranged at approximately equal intervals along the circumferential direction of the base 90.

[0100] Each grinding wheel 92 comprises, for example, a binder such as metal, ceramics, or resin, and abrasive grains such as diamond or cBN (cubic boron nitride). Abrasive grains with a relatively large average particle size are used in coarse grinding wheels, while abrasive grains with a relatively small average particle size are used in finish grinding wheels.

[0101] As the spindle 84 rotates, an annular grinding surface is formed by the trajectories of the lower surfaces of the multiple grinding wheels 92. The grinding surface is a plane perpendicular to the longitudinal direction of the spindle 84. Figure 8 shows the grinding step S40. Note that protective tape and the like are omitted in Figure 8.

[0102] In grinding step S40, first, the first surface 11a of the wafer 19 (thinned wafer 11) is held by the holding surface 80a of the chuck table 80 via protective tape. Next, the table base is tilted so that a portion of the holding surface 80a of the chuck table 80 is approximately parallel to the grinding surface of the grinding wheel 88.

[0103] In this state, the chuck table 80 is rotated around the rotating shaft 80b at a predetermined rotational speed (for example, 200 rpm), and the grinding wheel 88 is rotated around the rotating shaft 84a at a predetermined rotational speed (for example, 3000 rpm).

[0104] Furthermore, while supplying a grinding fluid such as pure water from a grinding fluid supply nozzle (not shown) to the contact area between the grinding surface and the back surface 11c of the wafer 19, the grinding unit 82 is moved downward (i.e., processed) at a predetermined processing feed rate (for example, 1.0 μm / s). The grinding surface of the grinding wheel 92 comes into contact with the back surface 11c, and the back surface 11c is ground. The processing feed is continued until the wafer 19 reaches a predetermined finish thickness.

[0105] The grinding step S40 may be carried out in two stages: rough grinding and finish grinding. That is, the back surface 11c side is roughly ground with one grinding unit 82 (i.e., a rough grinding unit) which has a rough grinding wheel 92, and then the back surface 11c side is finish ground with another grinding unit 82 (i.e., a finish grinding unit) which has a finish grinding wheel 92.

[0106] Furthermore, after finish grinding, the back surface 11c may be polished using a polishing unit (not shown). The polishing unit comprises a spindle 84 and a polishing pad attached to one end of the spindle 84. By performing polishing in addition to rough grinding and finish grinding, the flexural strength of the final manufactured device chip can be improved compared to when no polishing is performed.

[0107] In particular, the finished thickness T of the wafer 19 at the completion of grinding step S40. E This is smaller than the distance between the first height position H1 where the protective layer 64 is formed and the first surface 11a. Conversely, the distance between the first height position H1 and the first surface 11a is smaller than the finished thickness T. E It is set to exceed the finished thickness T in grinding step S40. E Before reaching this point, the protective layer 64 formed on the wafer 19 is removed by grinding.

[0108] If the protective layer 64 remains on the wafer 19 after the grinding step S40, the protective layer 64 will also remain on the device chip formed by dividing the wafer 19. If the device chip containing the altered protective layer 64 is subjected to any impact, cracks will extend from the protective layer 64, making the device chip susceptible to destruction. On the other hand, if the protective layer 64 is removed in the grinding step S40, the protective layer 64 will not remain on the final manufactured device chip, thus increasing the strength of the device chip.

[0109] In this embodiment, since the wafer 19 is thinned by the separation of the separator 21, the amount of material removed from wafers 19 and 11 can be reduced compared to the case where wafer 11, in which the separator 21 is not separated, is ground from the second surface 11b. Therefore, the amount of material removed from the grinding wheel 92 can be significantly reduced.

[0110] After the grinding step S40, a metal film, resin film, or the like may be formed on the first surface 11a or the back surface 11c of the thinned wafer 19. Then, when the wafer 19 is finally divided along the planned division line 15 (see Figure 1), individual device chips are formed.

[0111] In the device chip manufacturing method according to this embodiment, after the grinding step S40, a division step S50 is performed in which the wafer 19 is divided for each device 17 in order to manufacture a plurality of device chips, each equipped with a device 17.

[0112] The wafer 19 may be divided, for example, by cutting the wafer 19 with a cutting blade in a cutting device equipped with an annular cutting blade. Alternatively, the wafer 19 may be laser processed in the laser processing device 2 shown in Figure 2. The division step S50 will be described below using the case where it is performed with a cutting device equipped with a cutting blade as an example, but the method of manufacturing the device chip according to this embodiment is not limited thereto.

[0113] Figure 9 is a schematic perspective view showing a wafer 19 being cut and divided by a cutting device 94. As shown in Figure 9, it is preferable that a dicing tape 23 be attached to the back surface 11c of the wafer 19 before it is fed into the cutting device 94, and that a ring frame 25 be attached to the outer circumference of the dicing tape 23.

[0114] In other words, it is preferable that the wafer 19 is integrated with the dicing tape 23 and the ring frame 25 in advance, and that a frame unit 27 including the wafer 19, the dicing tape 23, and the ring frame 25 is formed. In this case, the thinned wafer 19 is easy to handle, and the manufactured device chip is also easy to handle because it is supported by the dicing tape 23.

[0115] Furthermore, if protective tape or the like is attached to the first surface 11a side of the wafer 19 to protect the device 17, it is preferable to remove the protective tape after the frame unit 27 has been formed but before the frame unit 27 is loaded into the cutting machine 94. If dicing tape 23 is attached to the wafer 19, it becomes relatively easy to remove the protective tape from the thinned wafer 19.

[0116] First, the cutting device 94 will be described. The cutting device 94 is equipped with a chuck table (not shown) configured similarly to the chuck table 26 of the laser processing device 2. The upper surface of the chuck table of the cutting device 94 is a holding surface that holds the wafer 19 by suction via the dicing tape 23.

[0117] This holding surface is connected to a suction source (not shown), such as an ejector, via a suction passage (not shown) provided inside the chuck table. Multiple clamps (not shown) are provided around the chuck table to grip the ring frame 25 that supports the wafers 11 and 19 from all sides.

[0118] In the cutting apparatus 94, the chuck table is connected to a rotational drive source (not shown), such as a motor, and rotates around a rotation axis that is roughly parallel to the vertical direction. The chuck table is also fed by a moving mechanism (machining feed unit).

[0119] The cutting device 94 includes a cutting unit 96 above the chuck table. The cutting unit 96 is equipped with an annular cutting blade 100, which cuts the wafer 19. The cutting unit 96 includes a spindle housing 98 that rotatably houses the base end of a spindle (not shown) which forms a rotation axis parallel to the holding surface of the chuck table.

[0120] The spindle housing 98 houses a rotational drive source, such as a motor, which rotates the spindle. When this rotational drive source is activated, the spindle rotates. An annular cutting blade 100 is fixed to the tip of the spindle. Rotating the spindle allows the cutting blade 100 to rotate as well. The cutting blade 100 comprises a grinding wheel portion containing a binder formed in an annular shape from a metal or resin material, and abrasive grains made of diamond or the like, dispersed and fixed within the binder.

[0121] Furthermore, the cutting unit 96 is equipped with a pair of cutting fluid supply nozzles 102 that extend along both sides of the cutting blade 100. While the wafer 19 is being cut by the cutting blade 100, cutting fluid such as pure water is supplied to the cutting blade 100 from the cutting fluid supply nozzles 102. The processing debris and processing heat generated when the wafer 19 is being cut by the cutting blade 100 are removed by the cutting fluid.

[0122] In the splitting step S50, the wafer 19 is loaded into the cutting device 94 and held in place by a chuck table. The chuck table is then rotated to align the orientation of the wafer 19 along the planned splitting line 15 with the processing feed direction of the cutting device 94. The chuck table is also moved along the holding surface to position the cutting blade 100 above the planned splitting line 15. Subsequently, a rotational drive source such as a motor, to which the cutting blade 100 is attached, is activated to start the rotation of the cutting blade 100.

[0123] Next, the cutting blade 100 is lowered to a predetermined height, and the machining feed unit is activated to feed the chuck table, bringing the grinding wheel portion of the rotating cutting blade 100 into contact with the wafer 19, at which point the wafer 19 is cut. As the wafer 19 is cut along the planned division line 15, a division groove 29 is formed in the wafer 19.

[0124] Once the division grooves 29 are formed along all the division lines 15 of the wafer 19, the division of the wafer 19 is completed, and individual device chips, each containing a device 17, are manufactured. Each device chip is then supported by the dicing tape 23.

[0125] Subsequently, when the dicing tape 23 is expanded radially outward within the opening of the ring frame 25, the spacing between device chips widens, making it easier to pick up the device chips from the dicing tape 23. The device chips are then obtained by picking them up from the dicing tape 23. As described above, according to the device chip manufacturing method of this embodiment, individual device chips, each equipped with a device 17, are manufactured.

[0126] Here, we will describe in detail the height position of the first focusing point 52b where the first laser beam 52a is focused (first height position H1) and the height position of the second focusing point 52d where the second laser beam 52c is focused (second height position H2).

[0127] The second height position H2 of the second focal point 52d where the second laser beam 52c is focused is set to be further from the first surface 11a of the wafer 11 than the first height position H1 of the first focal point 52b where the first laser beam 52a is focused. From another perspective, in the device chip manufacturing method according to this embodiment, the first height position H1 is set between the second height position H2 and the first surface 11a.

[0128] In this case, during the separation point formation step S20, when the second laser beam 52c is focused at the second focal point 52d, the components that did not contribute to the formation of the separation point 70 travel through the second focal point 52d and hit the protective layer 64. The second laser beam 52c then reaches the first surface 11a of the wafer 11 in a state where its intensity has been reduced due to reflection, absorption, scattering, etc., by the protective layer 64. Alternatively, the second laser beam 52c does not reach the first surface 11a. Therefore, compared to a case where the second laser beam 52c does not pass through the protective layer 64 and its intensity is not reduced, the device 17 is less likely to be damaged.

[0129] Conventionally, there were restrictions on the irradiation conditions of the second laser beam 52c to prevent damage to the device 17 when the second laser beam 52c passes through the second focal point 52d and reaches the first surface 11a. In addition, the second focal point 52d of the second laser beam 52c had to be located at a predetermined distance or more from the first surface 11a.

[0130] In contrast, if the protective layer 64 is formed in advance at a position closer to the first surface 11a than the second focusing point 52d, it is possible to irradiate the wafer 11 with the second laser beam 52c under irradiation conditions that would conventionally cause damage to the device 17. Therefore, it may be possible to irradiate the wafer 11 with the second laser beam 52c under irradiation conditions that result in higher quality separation points 70.

[0131] Furthermore, when the protective layer 64 is formed, the second laser beam 52c can be focused to a height position closer to the first surface 11a than in the conventional method, so the separation starting point 70 can be formed at a height position closer to the first surface 11a. In this case, the amount of material removed from the wafer 11 in the grinding step S40 performed after the separation step S30 can be reduced, thus reducing the wear of the grinding wheel 92 and extending the life of the grinding wheel 88.

[0132] If the separation starting point 70 can be formed closer to the first surface 11a, the separator 21 separated from the wafer 11 in separation step S30 can be made thicker. This thicker separator 21 can then be used as a new wafer 11 for manufacturing additional device chips. When manufacturing device wafers from this new wafer 11, a thicker separator can still be retained. In other words, material loss can be reduced, and more device chips can be manufactured.

[0133] Next, the irradiation conditions for the laser beam will be explained. In the protective layer formation step S10 and the separation point formation step S20, various setting items included in the irradiation conditions are set to appropriate values, and the laser beams 52a and 52c are irradiated onto the wafer 11. These irradiation conditions include, for example, elements such as the wavelength of the laser beams 52a and 52c, the repetition frequency, the average power, the processing feed rate, the processing feed trajectory, and the height position of the focal points 52b and 52d.

[0134] In the protective layer formation step S10, the irradiation conditions of the first laser beam 52a are set so that a protective layer 64 that performs a predetermined function is formed inside the wafer 11. That is, the first laser beam 52a that contributes to the formation of the protective layer 64 is irradiated onto the wafer 11 under predetermined irradiation conditions so that the intensity of the second laser beam 52c passing through the formed protective layer 64 is sufficiently reduced.

[0135] However, the first laser beam 52a only needs to be able to form a modified layer of a predetermined quality on the wafer 11 that will become the protective layer 64. Unlike the second laser beam 52c, the first laser beam 52a does not need to be able to form cracks on the wafer 11 that extend from the protective layer 64. However, cracks may be formed on the wafer 11 by the first laser beam 52a.

[0136] In particular, the first focusing point 52b is closer to the first surface 11a than the second focusing point 52d, and the wafer 11 does not have a further protective layer to shield the first laser beam 52a when it is irradiated onto the wafer 11. Therefore, the irradiation conditions for the first laser beam 52a are set so that when a portion of the first laser beam 52a that passes through the first focusing point 52b without being absorbed by the wafer 11 reaches the first surface 11a, it does not cause damage to the device 17.

[0137] Furthermore, the irradiation conditions of the first laser beam 52a may be explained in particular by comparing them with the irradiation conditions of the second laser beam 52c that irradiates the wafer 11 in the separation point formation step S20.

[0138] In comparison with the second laser beam 52c, the irradiation conditions for the first laser beam 52a are set such that its intensity is lower than that of the second laser beam 52c. That is, in the protective layer formation step S10, the first laser beam 52a has less influence on the device 17 than the second laser beam 52c. However, the irradiation conditions for the first laser beam 52a and the second laser beam 52c are not limited to these.

[0139] The effect of the second laser beam on device 17 being compared here refers to the effect on device 17 when the second laser beam reaches the first surface 11a without passing through the protective layer 64.

[0140] In the protective layer formation step S10, it is not necessary to form the protective layer 64 over the entire surface of the wafer 11 on a surface parallel to the first surface 11a. The formation position of the protective layer 64 should be determined to correspond to the region irradiated by the second laser beam 52c (the trajectory of the second focal point 52d). That is, in the direction parallel to the first surface 11a, the trajectory of the first focal point 52b in the protective layer formation step S10 and the trajectory of the second focal point 52d in the separation point formation step S20 may coincide.

[0141] Furthermore, the irradiation conditions for the second laser beam 52c are preferably set so that a separation point 70 including the modified layer 66 and cracks 68 is formed at a second height position H2 on the wafer 11 with a predetermined quality. In the device chip manufacturing method according to this embodiment, some of the second laser beam 52c that has passed through the second focal point 52d is reflected, attenuated, etc. by contact with the protective layer 64. Therefore, the second laser beam 52c can be irradiated onto the wafer 11 under irradiation conditions with higher intensity compared to the conventional method.

[0142] The first height position H1, which is the height of the first focusing point 52b, and the second height position H2, which is the height of the second focusing point 52d, will be explained in more detail. Wafer 11 is a silicon wafer, the thickness T of wafer 11 (distance from the first surface 11a to the second surface 11b) is 500 μm, and the finished thickness T of wafers 11 and 19 after grinding step S40 is... E Let's explain using the example where the size is 30 μm.

[0143] In this case, the first height position H1, which is the height of the first focal point 52b where the first laser beam 52a is focused, is preferably set above the first surface 11a within a range of 40 μm to 80 μm. That is, the first height position H1 is preferably set at a position 10 μm to 50 μm away from the first surface 11a from the planned height position of the back surface 11c of the wafers 11 and 19 after grinding. The first height position H1 is preferably determined within this range by referring to the amount of grinding performed in grinding step S40.

[0144] In this case, it is preferable that the second height position H2, which is the height of the second focal point 52d where the second laser beam 52c is focused, is set above the first surface 11a in the range of 90 μm to 130 μm. That is, the second height position H2 is preferably set at a distance of about 50 μm from the first surface 11a than the first height position H1. Furthermore, the second height position H2 is preferably set at a height position closer to the first surface 11a so that the separated body 21 separated at the separation starting point 70 can be formed to be thicker.

[0145] In the wafer processing method and device chip manufacturing method according to this embodiment, the range of selection for the irradiation conditions of the second laser beam 52c is wider than in the conventional method, and it is possible to select irradiation conditions that are more suitable. In addition, the separation starting point 70 can be formed at a height position closer to the first surface 11a, and the separation body 21 can be formed to be thicker, making it easier to reuse the separation body 21 as a device wafer.

[0146] Therefore, in the wafer processing method and device chip manufacturing method according to this embodiment, the wafer 11 on which the device 17 is disposed on the first surface 11a can be efficiently thinned, and the wafer 11 can be divided to efficiently manufacture device chips.

[0147] In the above embodiment, the first laser beam 52a and the second laser beam 52c were described as irradiating the wafer 11 with a silicon wafer as an example, but the wafer 11 is not limited to a silicon wafer. For example, the wafer 11 may be a SiC wafer or a wafer made of other materials.

[0148] Even when wafer 11 is not a silicon wafer, the irradiation conditions for the first laser beam 52a should be determined so that a protective layer 64 can be formed on wafer 11. Then, the irradiation conditions for the second laser beam 52c should be determined so that a separation point 70 can be formed on wafer 11.

[0149] Furthermore, the structures and methods of the embodiments described above can be modified as appropriate without departing from the scope of the present invention. [Explanation of Symbols]

[0150] 11 wafer 11a First face 11b Second face 11c back side 13 Notches 15 planned division lines 17 devices 19 wafer 21 Separate body 23 Dicing Tape 25 Ring Frames 27 Frame Unit 29 Dividing groove 2. Laser processing equipment 4 base 6 X-axis Y-axis movement mechanism 8 Y-axis guide rails 10 Y-axis moving plate 12 Screw shaft 14 motors 16 X-axis guide rail 18 X-axis moving plate 20 Screw shaft 22 motors 24 Table base 26 Chuck Table 26a Holding surface 26b Clamp Unit 30 Support structure 32 Z-axis movement mechanism 34 Z-axis guide rail 36 Z-axis moving plate 38 Motors 40 Supports 42 Laser beam irradiation unit 44 Laser oscillators 46 Attenuator 48 Branch Unit 50 Mirror 52 Irradiation heads 52a First laser beam 52b First focusing point 52c Second laser beam 52d Second focusing point 54 Housing 56 Imaging Unit 58 Touch panel 64 Protective layer 66 Modified layer 68 Crack 70 Separation starting point 71 Separation device 72 Separation Units 73 Holding Table 73a Holding surface 74 Support Member 76 base 78 Grinding equipment 80 Chuck Table 80a holding surface 80b Rotation axis 82 Grinding Unit 84 spindles 84a Rotation axis 86 Mount 88 Grinding Wheel 90 base 92 Grinding Wheel 94 Cutting equipment 96 Cutting Unit 98 Spindle Housing 100 cutting blades 102 Cutting fluid supply nozzle

Claims

1. A wafer processing method for processing a wafer having a first surface and a second surface opposite to the first surface, wherein a plurality of devices are formed on the first surface, A protective layer formation step involves positioning a first focal point of a first laser beam of a wavelength that penetrates the wafer at a first height position inside the wafer, irradiating the wafer with the first laser beam from the second surface side while relatively moving the first focal point and the wafer along the first surface, thereby forming a protective layer at the first height position inside the wafer. A separation origin formation step is performed after the protective layer formation step, in which a second focal point of a second laser beam of a wavelength that penetrates the wafer is positioned at a second height position further from the first surface than the first height position inside the wafer, and the second laser beam is irradiated onto the wafer from the second surface side while the second focal point and the wafer are moved relative to each other along the first surface, thereby forming a modified layer at the second height position in the wafer and forming cracks extending from the modified layer to form a separation origin composed of the modified layer and the cracks, A wafer processing method characterized by comprising: after the separation starting point formation step, applying an external force to the wafer to divide the wafer at the separation starting point, separating the separated body including the second surface from the wafer, and leaving the second surface on the wafer.

2. The wafer processing method according to claim 1, characterized in that the first laser beam in the protective layer formation step has less influence on the device than the second laser beam that reaches the first surface without passing through the protective layer.

3. A method for processing a wafer according to claim 1 or 2, further comprising a grinding step of grinding the back surface of the wafer that is exposed on the opposite side of the first surface after performing the separation step, to remove the protective layer and flatten the back surface.

4. A method for manufacturing a device chip, comprising dividing a wafer having a first surface and a second surface opposite to the first surface, wherein a plurality of devices are formed on the first surface, A protective layer formation step involves positioning a first focal point of a first laser beam of a wavelength that penetrates the wafer at a first height position inside the wafer, irradiating the wafer with the first laser beam from the second surface side while relatively moving the first focal point and the wafer along the first surface, thereby forming a protective layer at the first height position inside the wafer. A separation origin formation step is performed after the protective layer formation step, in which a second focal point of a second laser beam of a wavelength that penetrates the wafer is positioned at a second height position further from the first surface than the first height position inside the wafer, and the second laser beam is irradiated onto the wafer from the second surface side while the second focal point and the wafer are moved relative to each other along the first surface, thereby forming a modified layer at the second height position in the wafer and forming cracks extending from the modified layer to form a separation origin composed of the modified layer and the cracks, A separation step is performed after the separation starting point formation step, in which an external force is applied to the wafer to divide the wafer at the separation starting point, and the separated body including the second surface is separated from the wafer so that the second surface does not remain on the wafer. Following the separation step, a grinding step is performed to grind the back surface of the wafer that is exposed on the opposite side of the first surface, to remove the protective layer and flatten the back surface, A method for manufacturing a device chip, comprising: a division step of manufacturing a plurality of device chips, each equipped with a device, by dividing the wafer for each device.

5. The method for manufacturing a device chip according to claim 4, characterized in that the first laser beam in the protective layer formation step has less influence on the device than the second laser beam that reaches the first surface without passing through the protective layer.

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