Processing methods

Abstract

To reduce a grinding amount of a wafer after a division original point formation.SOLUTION: A processing method for processing a single crystal silicon wafer, in which a device is formed in each region that is formed so as to expose each specific crystal surface contained in a crystal surface {100}, includes a first surface and a second surface, and is segmented with a plurality of division schedule lines provided in a lattice state to the first surface, comprises: a division original point formation step of forming a division original point along each division schedule line; a separation layer formation step of forming a separation layer along the crystal surface of the second surface by moving relatively a focal point and a single crystal silicon wafer along a first direction where an angle of a sharp angle, which is parallel to the crystal surface of the second surface and is formed in a space from a crystal direction <100> is 5° or less; and a separation step of separating the single crystal silicon wafer into a first surface side wafer containing a plurality of devices formed on the first surface side and a second surface side wafer which is positioned at the second surface side and does not contain a device.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a processing method for processing a single crystal silicon wafer having a first surface and a second surface located opposite to the first surface, each of which is formed so as to expose a specific crystal plane included in the crystal plane {100}, and in which devices are formed in each of a plurality of regions partitioned by a plurality of planned dividing lines set in a lattice pattern on the first surface. [Background technology]

[0002] To manufacture semiconductor device chips, a wafer made of, for example, single-crystal silicon is used. Specifically, first, a plurality of division lines are set in a grid pattern on the surface of the wafer, and devices such as ICs (Integrated Circuits) are formed in each of the rectangular regions defined by the division lines.

[0003] Next, cutting or laser processing is performed along each planned dividing line to form dividing starting points on each planned dividing line, and then the back side of the wafer is ground to divide the wafer into multiple device chips (see, for example, Patent Documents 1 and 2).

[0004] However, when grinding the backside, for example, more than half of the wafer's thickness before grinding is removed by grinding, which results in a relatively large amount of wear on the grinding wheel and is uneconomical. In addition, the grinding device becomes dirty with a large amount of grinding debris generated during grinding, which requires frequent cleaning of the grinding device. Frequent cleaning is also a hassle for the operator. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-40520 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-12902 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above problems, and has as its object to reduce the amount of wafer grinding that occurs after forming division start points when dividing a wafer into a plurality of device chips. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a method for processing a single crystal silicon wafer having a first surface and a second surface opposite to the first surface, the first surface being formed so as to expose specific crystal planes included in the crystal plane {100}, and a device formed in each of a plurality of regions partitioned by a plurality of planned dividing lines set in a grid pattern on the first surface, the method comprising the steps of: forming dividing start points for dividing the single crystal silicon wafer along each planned dividing line to a depth corresponding to at least a finished thickness of a device chip; and positioning a focal point of a pulsed laser beam having a wavelength that is transmitted through the single crystal silicon wafer inside the single crystal silicon wafer, and forming a focal point of a pulsed laser beam having a wavelength that is parallel to the crystal plane of the second surface and aligned in a crystal orientation <100> a separation layer forming step of relatively moving the focusing point and the single crystal silicon wafer along a first direction in which an acute angle formed between the focusing point and the single crystal silicon wafer is 5° or less, and forming a separation layer along a crystal plane of the second surface at a depth corresponding to the second surface side from the splitting origin, and after the splitting origin forming step and the separation layer forming step, dividing the single crystal silicon wafer into a first surface side wafer including a plurality of devices formed on the first surface side and a second surface side wafer located on the second surface side and not including any devices, and a separating step of separating the single-crystal silicon wafer into a modified region forming step of forming a modified region by relatively moving the focal point of the laser beam and the single-crystal silicon wafer along the first direction, and an indexing step of relatively indexing and feeding the focal point and the single-crystal silicon wafer in a second direction that is parallel to a crystal plane of the second surface and perpendicular to the first direction, and the separation layer includes the modified region and a crack that propagates from the modified region.In the separation step, an external force is applied to the single crystal silicon wafer to extend the crack in the separation layer, and then the first surface and the second surface are separated from each other to separate the single crystal silicon wafer into the first surface side wafer and the second surface side wafer. A processing method is provided.

[0008] Preferably, the processing method further includes, after the separating step, a grinding step of grinding a third surface side of the first surface side wafer located opposite the first surface and dividing the first surface side wafer into a plurality of device chips. Preferably, the first-surface wafer and the second-surface wafer separated in the separation step have the same diameter. Preferably, in the splitting start point forming step, the splitting start points are formed by cutting grooves in the single crystal silicon wafer with a cutting blade, or by forming processed grooves in the single crystal silicon wafer by ablation processing. Preferably, in the separation layer forming step, the focal point of the laser beam is positioned inside the single crystal silicon wafer in a state where it is branched into multiple beams. [Effects of the Invention]

[0009] According to one aspect of the present invention processing In the method, a splitting starting point is formed at a depth corresponding to the finished thickness of the device chip in the splitting starting point forming step, and a separation layer is formed at a depth corresponding to the second surface side of the splitting starting point in the separation layer forming step.

[0010] Furthermore, in the separation step, the single crystal silicon wafer is separated, starting from the separation layer, into a first-surface-side wafer including a plurality of devices formed on the first-surface-side and a second-surface-side wafer located on the second-surface-side and not including any devices.

[0011] By grinding the separation layer side of the first surface side wafer, the first surface side wafer can be divided into a plurality of device chips, and therefore the amount of grinding of the single crystal silicon wafer can be reduced compared to the case where the single crystal silicon wafer is divided into a plurality of device chips by grinding the single crystal silicon wafer from the second surface of the single crystal silicon wafer. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. [Figure 2] FIG. 2 is a plan view of a wafer. [Figure 3] FIG. 1 is a flow diagram of a processing method. [Figure 4] FIG. 2 is a perspective view of the laser processing device. [Figure 5] FIG. 2 is a schematic diagram of a laser beam irradiation unit. [Figure 6] FIG. 10 is a perspective view showing a division starting point forming step. [Figure 7] FIG. 10 is a partial cross-sectional side view showing a division start point forming step. [Figure 8] FIG. 10 is a perspective view showing a separation layer forming step. [Figure 9] FIG. 10 is a partial cross-sectional side view showing a separation layer forming step. [Figure 10] 10A and 10B are diagrams illustrating a modified region forming step in the separation layer forming step. [Figure 11] 10 is a cross-sectional view of a portion of a wafer showing a separation layer formed in the first and second modified region formation steps. FIG. [Figure 12] 10A and 10B are diagrams illustrating how an external force is applied to the wafer in the separation step. [Figure 13] FIG. 1 is a cross-sectional view of a portion of a wafer showing a separation layer with connected cracks. [Figure 14] FIG. 14(A) is a partial cross-sectional side view showing the separation step, and FIG. 14(B) is a partial cross-sectional side view showing the front side wafer and the back side wafer after the separation step. [Figure 15] FIG. [Figure 16] FIG. 2 is a perspective view showing a plurality of device chips. [Figure 17] 1 is a graph showing the width of separation layers formed inside a wafer when a laser beam is irradiated onto linear regions each along a different crystal orientation. [Figure 18] FIG. 10 is a partial cross-sectional side view showing how the front surface side is cut. [Figure 19] FIG. 19(A) is a flow diagram of a processing method according to the second embodiment, and FIG. 19(B) is a flow diagram of a processing method according to the third embodiment. [Figure 20] FIG. 10 is a partial cross-sectional side view showing a state in which ablation processing is performed on the surface side. [Figure 21] FIG. 21(A) is a flow diagram of a processing method according to the fourth embodiment, and FIG. 21(B) is a flow diagram of a processing method according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view showing a wafer 11, and Fig. 2 is a plan view showing the wafer 11. Note that the wafer 11 in this specification refers to a single crystal silicon wafer. Fig. 2 also shows the crystal orientation of the wafer 11.

[0014] The wafer 11 has a disk shape and has a substantially circular front surface (first surface) 11a and a back surface (second surface) 11b. The back surface 11b is located on the opposite side to the front surface 11a in the thickness direction of the wafer 11.

[0015] The diameter of the wafer 11 is, for example, about 300 mm (12 inches), and the thickness from the front surface 11a to the back surface 11b is about 775 μm. However, the diameter and thickness of the wafer 11 are not limited to this example.

[0016] The wafer 11 is formed so that a specific crystal plane included in the crystal plane {100} is exposed on each of the front surface 11a and the back surface 11b. For example, as shown in Figure 2, the crystal plane (100) is exposed on the back surface 11b, and the crystal plane (100) is also exposed on the front surface 11a.

[0017] That is, the normals (crystal axes perpendicular to each surface) of the back surface 11b and the front surface 11a are aligned along the crystal orientation

[0100] . Note that due to processing errors during the manufacture of the wafer 11, each of the back surface 11b and the front surface 11a may be slightly tilted from a specific crystal plane included in the crystal plane {100}.

[0018] Specifically, each of the back surface 11b and the front surface 11a may be a surface that forms an acute angle of 1° or less with the crystal plane (100). In other words, the crystal axis perpendicular to the back surface 11b and the front surface 11a may be along a direction that forms an acute angle of 1° or less with the crystal orientation

[0100] .

[0019] In this specification, the expression "the front surface 11a and the back surface 11b are formed so as to expose a specific crystal plane included in the crystal plane {100}" means that the front surface 11a and the back surface 11b are not only specific crystal planes included in the crystal plane {100} but also planes that are slightly inclined from the specific crystal plane.

[0020] "Slightly tilted from a specific crystal plane" means, for example, that the acute angle formed between the front surface 11a and the back surface 11b and the crystal plane (100) is 1° or less. Meanwhile, a notch 13 indicating the crystal orientation of the wafer 11 is formed on the outer periphery of the wafer 11.

[0021] The direction from the notch 13 to the center A of the back surface 11b (or the center of the front surface 11a) is <110> In this embodiment, as shown in FIG. 2, the direction from the notch 13 to the center A is the crystal orientation

[0011] .

[0022] 1, a plurality of planned division lines (streets) 15 are set in a grid pattern on the surface 11a. A device 17 such as an IC (Integrated Circuit) is formed in each of a plurality of regions partitioned by the plurality of planned division lines 15.

[0023] Next, a method for processing the wafer 11 (that is, a method for manufacturing the device chips 35) for dividing the wafer 11 into a plurality of device chips 35 by processing the wafer 11 along each of the planned dividing lines 15 will be described.

[0024] 3 is a flow diagram of the processing method according to the first embodiment. The processing method is outlined as follows: first, the wafer 11 is held on a chuck table 26 (see FIG. 4), which will be described later (holding step S10). Then, a laser processing device 2 (see FIG. 4) is used to form division start points 23 (see FIG. 7) on the front surface 11a of the wafer 11 (division start point forming step S20).

[0025] Next, a separation layer 25 (see FIGS. 9 to 12) is formed inside the wafer 11 using the laser processing device 2 (separation layer forming step S30). Thereafter, the wafer 11 is separated, starting from the separation layer 25, into a front surface side wafer (first surface side wafer) 31 having the devices 17 and a back surface side wafer (second surface side wafer) 33 having no devices 17 (see FIGS. 14(A) and 14(B)) (separation step S40).

[0026] Next, the separation surface (third surface) 31a side of the front surface side wafer (first surface side wafer) 31 having the device 17, which is located opposite to the front surface 11a, is ground (see Figure 15), thereby dividing the front surface side wafer 31 into multiple device chips 35 (grinding step S50) (see Figure 16).

[0027] Fig. 4 is a perspective view of the laser processing device 2. Note that the X-axis direction (left-right direction), Y-axis direction (front-back direction), and Z-axis direction (up-down direction, vertical direction) shown in Fig. 4 are perpendicular to one another.

[0028] The laser processing device 2 has a base 4 that supports each of the components. An X-axis / Y-axis movement mechanism 6 is provided on the upper surface of the base 4. The X-axis / Y-axis movement mechanism 6 is fixed to the upper surface of the base 4 and has a pair of Y-axis guide rails 8 that are arranged along the Y-axis direction.

[0029] A Y-axis moving plate 10 is attached to the upper surfaces of the 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 surface of the Y-axis moving plate 10.

[0030] The ball screw has a nut portion (not shown) fixed to the underside of the Y-axis moving plate 10. A screw shaft 12 is rotatably connected to the nut portion using balls (not shown). The screw shaft 12 is disposed between a pair of Y-axis guide rails 8 along the Y-axis direction.

[0031] 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 a Y-axis moving mechanism.

[0032] 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 surface 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.

[0033] 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. A screw shaft 20 is rotatably connected to the nut portion using balls (not shown).

[0034] The screw shaft 20 is disposed 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.

[0035] The pair of X-axis guide rails 16, the X-axis moving plate 18, the screw shaft 20, the nut portion, the motor 22, etc. constitute the X-axis moving mechanism. A cylindrical table base 24 is provided on the upper surface side of the X-axis moving plate 18. The table base 24 has a rotation drive source (not shown) such as a motor.

[0036] A disk-shaped chuck table 26 is disposed on top of the table base 24. The rotary drive source can rotate the chuck table 26 within a predetermined angular range around a rotation axis that passes through the center of the holding surface 26a of the chuck table 26 and is parallel to the Z-axis direction. The chuck table 26 has a disk-shaped frame made of non-porous metal.

[0037] A circular recess (not shown) is formed in the center of the frame. A circular porous plate made of ceramic is fixed in this recess. There are 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.

[0038] The annular upper surface of the frame and the circular upper surface of the porous plate are substantially flush with each other and function as a substantially flat holding surface 26a for suction-holding the wafer 11. While being suction-held by the holding surface 26a, the wafer 11 can be moved along either the X-axis or the Y-axis by the X-axis / Y-axis moving mechanism 6.

[0039] A plurality of clamp units 26b (four in this embodiment) are provided at approximately equal intervals around the periphery of the chuck table 26. Each clamp unit 26b clamps a frame 19b (see FIG. 16) of the wafer unit 21, which will be described later.

[0040] A support structure 30 is provided on a predetermined area of ​​the base 4 located behind the X-axis / Y-axis movement mechanism 6. A Z-axis movement mechanism 32 is provided on one side of the support structure 30 along the YZ plane. The Z-axis movement mechanism 32 has a pair of Z-axis guide rails 34.

[0041] The 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 moving 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.

[0042] 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 balls.

[0043] The screw shaft is disposed along the Z-axis direction between a pair of Z-axis guide rails 34. 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.

[0044] A support 40 is fixed to the front surface side of the Z-axis moving plate 36. The support 40 supports a part of the laser beam irradiation unit 42. Fig. 5 is a schematic diagram of the laser beam irradiation unit 42. In Fig. 5, some of the components of the laser beam irradiation unit 42 are shown in functional blocks.

[0045] 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 the like as a laser medium, and emits a pulsed laser beam L having a wavelength (for example, 1342 nm) that is transmitted through the wafer 11 (i.e., single crystal silicon). A is emitted.

[0046] Laser beam L A The output of the optical fiber is adjusted by an attenuator 46 and then advances to a branching unit 48. The branching unit 48 of this embodiment includes an LCOS-SLM (Liquid Crystal on Silicon - Spatial Light Modulator).

[0047] The branching unit 48 branches the laser beam L A For example, the branching unit 48 branches the laser beam L emitted from the irradiation head 52. A The laser beam L is focused so that it forms multiple focal points arranged at approximately equal intervals along the Y-axis. A Branch out.

[0048] In FIG. 5, the laser beam L is split into five focusing points P1 to P5 by the splitting unit 48. A In this example, the laser beam L is split into two or more (more preferably, two or more and sixteen or less) focal points. Amay be branched.

[0049] The branching unit 48 branches the laser beam L A By controlling the operation of the branching unit 48, the laser beam L A You can choose whether or not to branch.

[0050] The splitter unit 48 may have a diffraction grating instead of the LCOS-SLM. The diffraction grating splits the laser beam L so as to form a predetermined number of focal points. A Since the laser beam L A When the laser beam is not split, A All you have to do is remove the diffraction grating from the optical path.

[0051] The laser beam L passing through the branching unit 48 A The laser beam L is reflected by a mirror 50 and guided to an irradiation head 52. A The laser beam is reflected by the reflector 11. The reflector 11 houses a condenser lens (not shown) that condenses the reflected light.

[0052] The irradiation head 52 is disposed so as 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 longitudinal portion is arranged along the Y-axis direction (see FIG. 4).

[0053] A portion of the rear end of the housing 54 is fixed by the support 40. Furthermore, an 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.

[0054] 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 imaging element such as a CCD (Charge-Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor.

[0055] In the case of a visible light camera unit, for example, a photodiode made of Si (silicon) is used as the imaging element. Note that the imaging unit 56 may be an infrared camera unit having a light source such as an LED and an imaging element.

[0056] In the case of an infrared camera unit, for example, a photodiode made of InGaAs (indium gallium arsenide) is used as the imaging element. By using the infrared camera unit, even when the front surface 11a side is suction-held by the holding surface 26a, it is possible to capture an image of the planned dividing line 15 on the front surface 11a through the wafer 11 from the back surface 11b side.

[0057] The irradiation head 52, the housing 54, the imaging unit 56, etc. can be moved integrally along the Z-axis direction by the Z-axis movement mechanism 32. A cover (not shown) that covers the above-mentioned components is provided on the base 4.

[0058] A touch panel 58 is provided on the front surface of this cover. The touch panel 58 functions as an input device such as a capacitance type touch sensor and as a display device such as a liquid crystal display. Via the touch panel 58, an operator can set processing conditions for the laser processing device 2 and can also view images of the wafer 11 obtained by the imaging unit 56.

[0059] Next, a method for processing the wafer 11 will be described along the steps shown in Fig. 3. First, prior to the holding step S10, a wafer unit 21 is formed in which the wafer 11 is supported by an annular frame 19b via a protective tape 19a having a diameter larger than that of the wafer 11 (see Fig. 7).

[0060] More specifically, the front surface 11a of the wafer 11 is attached to the center of the protective tape 19a, and one side of a metal, annular frame 19b having an opening with a larger diameter than the wafer 11 is attached to the outer periphery of the protective tape 19a, thereby forming the wafer unit 21.

[0061] In this embodiment, the wafer 11 is processed in the form of this wafer unit 21, but the steps from the holding step S10 to the grinding step S50 may also be performed without using the frame 19b, with a protective tape 19a of approximately the same diameter as the wafer 11 attached to the surface 11a side.

[0062] In the holding step S10, the front surface 11a is suction-held by the holding surface 26a, and the frame 19b is clamped by each clamp unit 26b. At this time, the back surface 11b is exposed upward. Next, the wafer 11 is laser-processed to form modified regions 23a that function as division start points 23 along each of the planned division lines 15 (division start point forming step S20).

[0063] The modified region 23a is a region where the crystallinity of the wafer 11 is disturbed due to multiphoton absorption, and is irradiated with the laser beam L A The mechanical strength is reduced compared to the unirradiated area.

[0064] When the modified region 23a is formed, a crack 23b extending from the modified region 23a to the front surface 11a side and the back surface 11b side is concomitantly formed. A The division starting point 23 formed using the above indicates a modified region 23a.

[0065] In the division start point forming step S20, first, the deviation between one planned division line 15 and the X-axis direction is detected using the imaging unit 56. Then, the chuck table 26 is rotated around a predetermined rotation axis so that one planned division line 15 and the X-axis direction become approximately parallel.

[0066] And the laser beam L AWithout branching, the laser beam L A One of the focal points is positioned between the back surface 11b and a depth 11d from the back surface 11b corresponding to the finished thickness 11c of the device chip 35. For example, when the finished thickness 11c is 50 μm, the focal point is set at a position 70 μm from the front surface 11a.

[0067] Thereafter, the chuck table 26 is moved in the X-axis direction to form a modified region 23a from one end to the other end of one of the planned dividing lines 15 at least at the depth 11d.

[0068] Fig. 6 is a perspective view showing the division starting point forming step S20, and Fig. 7 is a partial cross-sectional side view showing the division starting point forming step S20. However, for ease of explanation, the distance between adjacent modified regions 23a is exaggerated in Fig. 7.

[0069] For convenience, the protective tape 19a and the frame 19b are omitted in Fig. 6, and the frame 19b is omitted in Fig. 7. The laser processing conditions are set, for example, as follows.

[0070] Laser beam wavelength: 1342nm Average output: 0.5W to 1W (predetermined value) Pulse repetition frequency: specified value between 60kHz and 90kHz Processing feed rate: specified value between 600mm / s and 800mm / s Number of passes: A predetermined number between 1 and 3

[0071] The number of passes is the number of times the laser beam L passes from one end of one planned dividing line 15 to the other end. A of Wafer 11 to When the number of passes is two or more, a modified region 23a is further formed at a depth position different from the depth 11d.

[0072] In the division starting point forming step S20, the laser beam L is focused at different positions in the depth direction of the wafer 11. ALaser processing can be performed with the laser beam L branched, and the laser beam L is aligned along the Y-axis. A The laser processing may be performed in a branched state.

[0073] A laser beam L is directed from one end of one planned dividing line 15 to the other end. A After irradiation, the chuck table 26 is indexed and fed in the Y-axis direction by a predetermined distance (index). Thereafter, a modified region 23a is formed from one end to the other end of another planned dividing line 15 adjacent to the processed planned dividing line 15 in the Y-axis direction.

[0074] In this way, after the modified regions 23a are formed along all the planned dividing lines 15 along one direction, the chuck table 26 is rotated by 90°, and the modified regions 23a are formed along all the planned dividing lines 15 along the other direction perpendicular to the one direction.

[0075] In this manner, dividing starting points 23 (ie, modified regions 23a) for dividing the wafer 11 are formed along each of the dividing lines 15 at least between the depth 11d and the rear surface 11b.

[0076] After the splitting starting point formation step S20, the laser processing device 2 is subsequently used to form a separation layer 25 along the crystal plane (100) of the front surface 11a and the back surface 11b at a predetermined depth corresponding to the back surface 11b side of the splitting starting point 23 (separation layer formation step S30).

[0077] Fig. 8 is a perspective view showing the separation layer forming step S30, and Fig. 9 is a partial cross-sectional side view showing the separation layer forming step S30. For convenience, protective tape 19a and frame 19b are omitted from Fig. 8, and frame 19b is omitted from Fig. 9.

[0078] 9, dots are added to the depth ranges where the modified regions 23a and the cracks 23b are formed in the thickness direction of the wafer 11. In the separation layer forming step S30, first, the imaging unit 56 is used to image the depth from the notch 13 to the backFace 11 b The direction (crystal orientation

[0011] in this embodiment) going to the center A of the crystal is detected.

[0079] Next, as shown in Figure 8, back Face 11 b The chuck table 26 is rotated around a predetermined rotation axis so that the acute angle formed by the direction (crystal orientation

[0011] ) advancing to the center A of the crystal and the X-axis direction is 45°.

[0080] This allows the wafer 11 to be parallel to the crystal plane (100) and aligned with the crystal orientation <100> The orientation of the wafer 11 is adjusted so that one of the crystal orientations,

[0010] , is parallel to the X-axis direction.

[0081] And the laser beam L A The light-converging points P1 to P5 are positioned at a predetermined depth inside the wafer 11 on the back surface 11b side of the dividing starting point 23. The light-converging points P1 to P5 are set, for example, at predetermined positions from a position at half the thickness of the wafer 11 to a position at a predetermined thickness, starting from the back surface 11b (when the total thickness is 775 μm, predetermined positions from 387.5 μm to 600 μm from the back surface 11b).

[0082] In this embodiment, the focusing points P1 to P5 are positioned closer to the rear surface 11b than the splitting starting point 23 (modified region 23a), so that the laser beam L A This can prevent the particles from being scattered.

[0083] Thereafter, in the vicinity of one end of the wafer 11 in the Y-axis direction, the focal points P1 to P5 and the wafer 11 are moved relatively from one end to the other end of the outer periphery of the wafer 11 along the X-axis direction, so that the laser beam L is focused along the crystal orientation

[0010] (first direction). A (See line 25c1 in FIG. 8.) The laser processing conditions are set, for example, as follows.

[0084] Laser beam wavelength: 1342nm Average power at one focal point: 0.5W Pulse repetition frequency: 60kHz Processing feed rate: 360mm / s Number of passes: A predetermined number between 1 and 3

[0085] 10, modified regions 25a are formed along the movement directions of the respective focusing points P1 to P5 (modified region forming step S32). That is, multiple modified regions 25a are formed at approximately the same depth position in the Z-axis direction, aligned along the Y-axis direction, and extending along the X-axis direction.

[0086] Fig. 10 is a diagram showing the modified region forming step S32 in the separation layer forming step S30. Note that Fig. 10 shows the width B and thickness C of the separation layer 25 formed in one modified region forming step S32.

[0087] In the modified region forming step S32, cracks 25b extend from each of the modified regions 25a along a predetermined crystal plane, resulting in the formation of a separation layer 25 inside the wafer 11, the separation layer 25 including the modified regions 25a and cracks 25b extending from each of the modified regions 25a.

[0088] Here, the formation of cracks 25b in single crystal silicon will be described. Single crystal silicon generally cleaves most easily along the crystal plane {111}, and second most easily along the crystal plane {110}.

[0089] Therefore, the crystal orientation of the wafer 11 <110> When the modified region 25a is formed along the {111} crystal plane, many cracks 25b are generated from the modified region 25a and extend along the {111} crystal plane.

[0090] For example, if a modified region 25a is formed along the direction from the notch 13 toward the center A (crystal orientation

[0011] ), many cracks 25b will occur extending from this modified region 25a along the crystal plane {111}.

[0091] On the other hand, crystal orientation <100> When multiple modified regions 25a are formed in a linear region along the line so that, in a planar view, they are lined up in a direction perpendicular to the direction in which this linear region extends, many cracks 25b are generated from each of the multiple modified regions 25a, extending along crystal planes among the crystal planes {N10} (N is a natural number equal to or less than 10, excluding 0) that are parallel to the direction in which the linear modified regions 25a extend.

[0092] For example, as described above, when multiple modified regions 25a are formed in a linear region along the crystal orientation

[0010] (X-axis direction) so that they are aligned in a direction (Y-axis direction) perpendicular to the direction in which this linear region extends in a planar view, there will be an increase in cracks 25b extending from each of the multiple modified regions 25a along crystal planes {N10} (N is a natural number equal to or less than 10, excluding 0) that are parallel to the crystal orientation

[0010] .

[0093] Specifically, when a plurality of modified regions 25a are formed in this way, cracks 25b tend to propagate in the crystal planes shown in the following formulas 1 and 2.

number

[0094]

number

[0095] The acute angle between the crystal plane (100) and the crystal plane {N10} parallel to the crystal orientation

[0010] is greater than 0° and less than 45°. In contrast, the acute angle between the crystal plane (100) and the crystal plane {111} is approximately 54.7°.

[0096] Therefore, the laser beam L along the crystal orientation

[0010] A In the former case, the laser beam L is irradiated along the crystal orientation

[0011] . A In this case, the separation layer 25 tends to be wider and thinner than when the latter case is irradiated.

[0097] Therefore, the ratio (B / C) of width B to thickness C in the separation layer 25 (including the modified region 25a and the crack 25b) shown in FIG. 10 is greater in the former case than in the latter case.

[0098] The laser beam L is incident on the wafer 11 along the crystal orientation

[0010] (first direction) from one end to the other end of the outer periphery of the wafer 11. A After irradiation, the focal points P1 to P5 and the wafer 11 are indexed and fed relative to each other (indexing and feeding step S34).

[0099] In the indexing feed step S34, the chuck table 26 is indexed and fed by a predetermined feed amount along the crystal orientation

[0001] (second direction, Y-axis direction) which is parallel to the crystal plane (100) and perpendicular to the crystal orientation

[0010] (first direction, X-axis direction).

[0100] The feed amount is, for example, equal to or greater than the width B of the separation layer 25. When the width B of the separation layer 25 is a predetermined length of 250 μm or more and 280 μm or less, the feed amount is set to a predetermined value of 520 μm or more and 530 μm or less, for example.

[0101] Next, the modified region forming step S32 is performed again (see line 25c2 in FIG. 8). FIG. 11 is a cross-sectional view of a portion of the wafer 11 showing the separation layer 25 formed in the first and second modified region forming step S32.

[0102] In the second modified region formation step S32, a separation layer 25 (separation layer 25-2) is formed that is approximately parallel to the separation layer 25 (separation layer 25-1) formed in the first modified region formation step S32, is at approximately the same depth as the separation layer 25-1, and is separated from the separation layer 25-1 in the Y-axis direction.

[0103] In this manner, the modified region forming step S32 and the indexing step S34 are repeated to form a plurality of separation layers 25-1, 25-2, etc., each extending from one end to the other in the X-axis direction, from one end to the other in the Y-axis direction, thereby forming the separation layer 25 over substantially the entire surface of the wafer 11 at a predetermined depth.

[0104] After forming a separation layer 25 from one end to the other end in the Y-axis direction, the wafer 11 is separated starting from the separation layer 25 into a front side wafer 31 including multiple devices 17 and a back side wafer 33 located on the back side 11b side and not including any devices 17 (separation step S40).

[0105] In the separation step S40, a separation device 60 is used (see FIG. 12). The separation device 60 has a disk-shaped chuck table 62. An annular groove (not shown) of a predetermined depth is formed on the upper surface of the chuck table 62, and an opening is formed on the bottom surface of this groove.

[0106] The opening located at the bottom of the groove is connected to a suction source (not shown) such as a vacuum pump via a specified flow path, so when the suction source is operated, negative pressure is transmitted to the upper surface of the chuck table 62 via the opening and the groove.

[0107] Therefore, the upper surface of the chuck table 62 functions as a holding surface 62a that suction-holds the wafer 11 via the protective tape 19a. A rotation drive source (not shown), such as a motor, is provided below the chuck table 62 to rotate the chuck table 62 around a rotation axis 62b that passes through the center of the holding surface 62a and is substantially parallel to the vertical direction.

[0108] A wedge portion 64 is provided near the chuck table 62. The wedge portion 64 has a relatively sharp end portion 64a. The end portion 64a is arranged so as to face radially inward of the holding surface 62a. Note that instead of the wedge portion 64, a sharp pointed object such as a needle or pin may be used.

[0109] 14(A), a suction unit 66 is provided above the holding surface 62a. The suction unit 66 has a cylindrical housing 68. A ball screw type lifting mechanism (not shown) is connected to the top of the housing 68. By operating this lifting mechanism, the suction unit 66 moves up and down.

[0110] A disk-shaped suction unit 70 having a diameter larger than that of the wafer 11 is fixed to the lower end of the housing 68. A plurality of circular suction ports (not shown) are formed on the lower surface of the suction unit 70. Each suction port is connected to a suction source (not shown) such as a vacuum pump via a flow path formed inside the suction unit 70.

[0111] When the suction source is operated, a negative pressure is transmitted to the suction port, and the lower surface of the suction unit 70 functions as a holding surface 70a that suction-holds the wafer 11. Next, the separation step S40 will be described with reference to FIGS. 12 to 14(B).

[0112] First, the wafer unit 21 is placed on the holding surface 62a so that the back surface 11b is exposed upward. Next, the front surface 11a side is suction-held by the holding surface 62a via the protective tape 19a. Then, one end 64a of the wedge portion 64 is positioned at a height corresponding to the separation layer 25.

[0113] However, the height position of the one end 64a only needs to be near the separation layer 25, and does not necessarily have to be exactly the same height position as the separation layer 25. The orientation of the wedge portion 64 is adjusted so that an external force is applied to the side surface of the wafer 11 in a direction approximately perpendicular to the side surface.

[0114] Then, while rotating the chuck table 62 and the wedge portion 64 relative to each other in the circumferential direction of the chuck table 62, the operator presses one end 64a of the wedge portion 64 into the outer peripheral side surface of the wafer 11, thereby applying an external force to the wafer 11.

[0115] 12 is a diagram showing how an external force is applied to the wafer 11 in the separation step S40. For convenience, the protective tape 19a and the frame 19b are omitted from FIG.

[0116] When an external force is applied, the cracks 25b in the separation layer 25 extend and connect to each other (see FIG. 13). FIG. 13 is a cross-sectional view of a portion of the wafer 11 showing the separation layer 25 in a state where the cracks 25b are connected to each other.

[0117] Next, the suction unit 66 is lowered to bring the holding surface 70a into contact with the back surface 11b. After the back surface 11b is held by suction with the holding surface 70a, the suction unit 66 is raised (see FIG. 14(A)). The wafer 11 is separated into the front surface side wafer 31 and the back surface side wafer 33 starting from the separation layer 25 (separation step S40) (see FIG. 14(B)).

[0118] Fig. 14(A) is a partial cross-sectional side view showing the separation step S40, and Fig. 14(B) is a partial cross-sectional side view showing the front side wafer 31 and the back side wafer 33 after the separation step S40. For convenience, the protective tape 19a and the frame 19b are omitted from Figs. 14(A) and 14(B).

[0119] Incidentally, in the separation step S40, instead of applying an external force to the wafer 11 using a wedge portion 64 or the like, ultrasonic vibrations may be applied to the wafer 11 to connect the cracks 25b along the front surface 11a or the back surface 11b.

[0120] For example, a disk-shaped vibration member (not shown) having an ultrasonic vibrator is brought close to the back surface 11b of the wafer 11, the front surface 11a of which is held by suction. Then, a liquid such as pure water is supplied from a nozzle (not shown) to the back surface 11b at a predetermined flow rate, and ultrasonic vibration is applied to the wafer 11 from the vibration member via the liquid.

[0121] After the separation step S40, the separation surface (third surface) 31a side of the front surface side wafer 31 opposite to the front surface 11a is ground (grinding step S50). In the grinding step S50, a grinding device 72 is used (see FIG. 15).

[0122] The grinding device 72 has a disk-shaped chuck table 74. The chuck table 74 has a disk-shaped frame body made of non-porous ceramics. A disk-shaped recess (not shown) is formed in the center of the frame body.

[0123] A circular porous plate made of ceramic is fixed in this recess. There are 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.

[0124] The upper surface of the porous plate is conical, with the center slightly protruding compared to the outer periphery. The circular upper surface of the porous plate and the annular upper surface of the frame are substantially flush with each other, and function as a substantially flat holding surface for holding the wafer 11 by suction.

[0125] A circular, flat table base (not shown) that rotatably supports the chuck table 74 is provided below the chuck table 74. In addition, a tilt adjustment mechanism (not shown) that adjusts the tilt of the chuck table 74 is provided below the table base.

[0126] Furthermore, a rotary shaft 74a (shown by a dashed line in FIG. 15) is connected to the lower part of the chuck table 74. A rotary drive source (not shown) such as a motor is connected to the rotary shaft 74a via a pulley, a belt, etc. When the rotary drive source is operated, the chuck table 74 rotates around the rotary shaft 74a.

[0127] A grinding unit 76 is disposed above the chuck table 74. The grinding unit 76 has a cylindrical spindle housing (not shown) whose longitudinal portion is disposed substantially parallel to the vertical direction.

[0128] A ball screw type processing feed mechanism (not shown) that moves the grinding unit 76 in a predetermined direction (for example, the vertical direction) is connected to the spindle housing. Also, a part of a cylindrical spindle 78 is rotatably accommodated in the spindle housing.

[0129] A rotational drive source such as a motor is provided at the upper end of the spindle 78. A disk-shaped mount 80 is fixed to the lower end of the spindle 78. An annular grinding wheel 82 is attached to the lower surface of the mount 80.

[0130] The grinding wheel 82 has a base 84 made of an aluminum alloy. The upper surface of the base 84 is disposed so as to be in contact with the mount 80. On the lower surface of the base 84, a plurality of grinding stones 86 are disposed at approximately equal intervals along the circumferential direction of the base 84.

[0131] Each grinding wheel 86 has a binder such as metal, ceramic, or resin, and abrasive grains such as diamond, cBN (cubic boron nitride), etc. Abrasive grains with a relatively large average grain size are used for rough grinding wheels, and abrasive grains with a relatively small average grain size are used for finish grinding wheels.

[0132] When the spindle 78 is rotated, a circular grinding surface is formed by the locus of the lower surfaces of the multiple grinding wheels 86. The grinding surface is a plane perpendicular to the longitudinal direction of the spindle 78. Figure 15 is a diagram showing the grinding step S50. For convenience, the protective tape 19a and the frame 19b are omitted from Figure 15.

[0133] In the grinding step S50, first, the front surface 11a side of the front surface side wafer 31 is suction-held via the protective tape 19a on the holding surface of the chuck table 74. Next, the table base is tilted so that a part of the holding surface of the chuck table 74 is approximately parallel to the grinding surface of the grinding wheel 82.

[0134] In this state, the chuck table 74 is rotated around the rotary shaft 74a at a predetermined rotation speed (for example, 200 rpm), and the grinding wheel 82 is rotated at a predetermined rotation speed (for example, 3000 rpm).

[0135] 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 separation surface 31a, the grinding unit 76 is moved downward (i.e., processed) at a predetermined processing feed speed (e.g., 1.0 μm / s).

[0136] The grinding surface comes into contact with the separation surface 31a side, thereby grinding the separation surface 31a side. The separation surface 31a side is ground and flattened until the grinding surface reaches the above-mentioned division starting points 23, and the front surface side wafer 31 is divided into a plurality of device chips 35 (see FIG. 16). FIG. 16 is a perspective view showing a plurality of device chips 35.

[0137] In the grinding step S50 of this embodiment, the separation surface 31a side is roughly ground using one grinding unit 76 (i.e., a rough grinding unit) having a rough grinding wheel as the grinding wheel 86, and then the separation surface 31a side is finish-ground using another grinding unit 76 (i.e., a finish grinding unit) having a finish grinding wheel as the grinding wheel 86.

[0138] The separation layer 25 side of the front side wafer 31 (i.e., the separation surface 31 a By grinding the separation surface 31a side, the front surface wafer 31 can be divided into a plurality of device chips 35. Furthermore, after the finish grinding, the separation surface 31a side may be polished using a polishing unit (not shown).

[0139] The polishing unit has a spindle 78 and a polishing pad attached to one end of the spindle 78. By performing polishing in addition to rough grinding and finish grinding, the flexural strength of the device chip 35 can be improved compared to when polishing is not performed.

[0140] In this embodiment, since the separation layer 25 is formed closer to the front surface 11a than to the back surface 11b, the amount of grinding of the wafer 11 can be reduced compared to when the wafer 11 is ground from the back surface 11b. In addition, the back surface side wafer 33 can be reused as a new single crystal silicon wafer.

[0141] Incidentally, if the division starting point forming step S20 is performed after the separation layer forming step S30, the division starting point 23 will be formed on the front surface 11a after the separation layer 25 is formed on the back surface 11b.

[0142] In this case, the separation layer 25 on the rear surface 11b prevents the laser beam L A To prevent the particles from scattering, first, in a separation layer forming step S30, the front surface 11a side is suction-held by the holding surface 26a, and a separation layer 25 is formed on the back surface 11b side.

[0143] Then, in the subsequent division starting point forming step S20, it is necessary to hold the rear surface 11b side by suction with the holding surface 26a, and form the division starting point 23 on the front surface 11a side of the separation layer 25. For this purpose, after the separation layer forming step S30 and before the division starting point forming step S20, table Face 11 a Protective tape from side 19 a It is necessary to peel off the wafer 11 and flip it over.

[0144] In contrast to this, in this embodiment, the separation layer forming step S30 is performed after the division start point forming step S20, which has the advantage that processing can proceed up to the grinding step S50 using the protective tape 19a as it is.

[0145] In the above-mentioned processing method, the laser beam L split into linear regions along the crystal orientation

[0010] A By irradiating the laser beam with the light, a plurality of modified regions 25a are formed so as to be aligned in a direction perpendicular to the direction in which the linear regions extend in a plan view.

[0146] In this case, there are more cracks 25b extending from each of the multiple modified regions 25a along the crystal planes {N10} (N is a natural number equal to or less than 10, excluding 0) that are parallel to the crystal orientation

[0010] of the single crystal silicon.

[0147] As a result, in the above-described processing method, the laser beam L is directed along the crystal orientation

[0011] of the wafer 11. A As a result, when manufacturing device chips 35 from the wafer 11, the time required for laser processing can be shortened and the amount of single-crystal silicon removed by grinding or the like can be reduced.

[0148] The above-described method for processing the wafer 11 is one embodiment of the present invention, and the present invention is not limited to the above-described method. For example, the wafer 11 is not limited to those shown in Figures 1 and 2.

[0149] Specifically, in the present invention, a single crystal silicon wafer having an orientation flat formed on the outer periphery may be processed, or a single crystal silicon wafer having neither a notch 13 nor an orientation flat formed on the outer periphery may be processed.

[0150] Furthermore, the structure of the laser processing device used in the present invention is not limited to the structure of the above-described laser processing device 2. For example, the present invention may be implemented using a laser processing device provided with a horizontal movement mechanism that moves the irradiation head 52 of the laser beam irradiation unit 42 and the like along the X-axis direction and / or the Y-axis direction.

[0151] That is, in the present invention, the chuck table 26 that holds the wafer 11 and the laser beam L A The structure for this purpose is not limited as long as the irradiation head 52 that emits the light beam can move relatively along the X-axis direction and the Y-axis direction.

[0152] In the present invention, the laser beam L AThe linear region inside the wafer 11 onto which the laser beam is irradiated is not limited to a linear region along the crystal orientation

[0010] .

[0153] For example, in the present invention, a laser beam L is applied to a linear region along the crystal orientation

[0001] . A In this case, the crack 25b tends to propagate in the crystal planes shown in the following formulas 3 and 4.

[0154]

number

[0155]

number

[0156] Furthermore, in the present invention, the laser beam L is directed to a linear region along a direction slightly tilted from the crystal orientation

[0010] or the crystal orientation

[0001] in a plan view. A This point will be described with reference to FIG.

[0157] Figure 17 shows the laser beam L in linear regions, each aligned along a different crystal orientation. A 11 is a graph showing the width B (see FIG. 10) of the separation layer 25 formed inside the wafer 11 when irradiated with .beta.. The width B of the separation layer 25 is shown in FIG.

[0158] The horizontal axis of the graph indicates the angle between the direction in which a linear region (reference region) perpendicular to the crystal orientation

[0011] extends and the direction in which a linear region to be measured (measurement region) extends when viewed in a plane of the wafer 11.

[0159] That is, when the measurement target is a linear region along the crystal orientation

[0001] , the horizontal axis of this graph will be 45° (see 45° in Figure 2). Similarly, when the measurement target is a linear region along the crystal orientation

[0010] , the horizontal axis of this graph will be 135° (see 135° in Figure 2).

[0160] The vertical axis of the graph in Figure 17 is the laser beam L A The width B of the separation layer 25 formed in the measurement area by irradiating the laser beam L onto the reference area is measured. A The value is obtained by dividing the width B of the separation layer 25 formed in the reference region by irradiating the reference region with the laser beam.

[0161] As shown in Figure 17, the width B of the separation layer 25 in the measurement area is relatively wide when the angle between the direction in which the reference area extends and the direction in which the measurement area extends is 40° or more and 50° or less, or 130° or more and 140° or less.

[0162] That is, the width B of the separation layer 25 is set so that the laser beam L is directed not only to the crystal orientation

[0001] or the crystal orientation

[0010] but also to a linear region along a direction in which the acute angle formed with these crystal orientations is 5° or less. A It becomes relatively wide when irradiated.

[0163] Therefore, in the present invention, the laser beam L is directed to a linear area parallel to the crystal plane (100) and inclined at 5° or less from the crystal orientation

[0001] or the crystal orientation

[0010] . A may be irradiated.

[0164] Incidentally, in the separation layer formation step S30, the modified region formation step S32 and the indexing feed step S34 may be repeated to form a separation layer 25 from one end to the other end in the Y-axis direction inside the wafer 11, and then the separation layer 25 may be formed again from one end to the other end in the Y-axis direction at approximately the same depth position inside the wafer 11.

[0165] In this way, by performing the separation layer formation step S30 multiple times, the density of the modified regions 25a and the cracks 25b included in the separation layer 25 increases compared to when the separation layer formation step S30 is performed only once, which makes it easier to separate the front side wafer 31 and the back side wafer 33 in the separation step S40.

[0166] Furthermore, when the separation layer formation step S30 is performed multiple times, the cracks 25b contained in the separation layer 25 extend further, and the width B of the separation layer 25 (see Figure 10) becomes wider than when the separation layer formation step S30 is performed once.

[0167] Therefore, when the separation layer formation step S30 is performed multiple times, the relative movement distance (index) between the irradiation head 52 and the chuck table 26 in the Y-axis direction in the indexing feed step S34 can be made longer than when the separation layer formation step S30 is performed once.

[0168] In addition, in the separation layer forming step S30, the modified region forming step S32 may be performed again after the modified region forming step S32 and before the indexing step S34. That is, the laser beam L is applied to the linear region where the separation layer 25 has already been formed so as to form the separation layer 25 again. A may be irradiated.

[0169] In this case as well, separation of the front side wafer 31 and the back side wafer 33 in the separation step S40 becomes easy, and the index in the indexing and feeding step S34 can be lengthened.

[0170] Next, second and third embodiments in which the dividing start point forming step S20 is performed by cutting will be described. For the cutting, a cutting device 90 shown in Fig. 18 is used. The cutting device 90 has a chuck table 92 in the shape of a disk.

[0171] The chuck table 92 has a holding surface 92a that suction-holds the wafer 11. The shape, structure, function, etc. of the chuck table 92 are the same as those of the chuck table 26 shown in Fig. 4, so detailed description thereof will be omitted.

[0172] A rotary drive source (not shown) such as a motor is connected to the bottom of the chuck table 92, and the chuck table 92 and the rotary drive source are supported by an X-axis moving plate (not shown) and can be moved along the X-axis direction by a ball screw type X-axis moving mechanism (not shown).

[0173] A cutting unit 94 is disposed above the chuck table 92. The cutting unit 94 has a cylindrical spindle housing 96 whose longitudinal portion is disposed along the Y-axis direction. The spindle housing 96 is movable along the Y-axis and Z-axis directions by ball screw-type Y-axis movement mechanisms and Z-axis movement mechanisms (neither of which is shown).

[0174] 4 is disposed on the side of the spindle housing 96. A part of a cylindrical spindle 98 is rotatably housed in the spindle housing 96.

[0175] The spindle 98 has a longitudinal portion arranged along the Y-axis direction. A rotation drive source (not shown), such as a motor, is provided at one end of the spindle 98. The other end of the spindle 98 protrudes from the spindle housing 96, and a cutting blade 100 is attached to the protruding tip.

[0176] The step S20 of forming division starting points by cutting is performed, for example, after the holding step S10 and before the step S30 of forming a separation layer (second embodiment). When performing the cutting, first, a wafer unit 41 is formed in which the back surface 11b side is supported by a frame 19b (not shown in FIG. 18) via a protective tape 19a.

[0177] Then, the back surface 11b side is suction-held by the holding surface 92a via the protective tape 19a so that the front surface 11a side is exposed upward. Next, the orientation of the chuck table 92 is adjusted so that one of the planned division lines 15 is approximately parallel to the X-axis direction.

[0178] Then, the cutting blade 100 is rotated at a predetermined rotation speed outside the holding surface 92a, and the bottom of the cutting blade 100 is positioned at a depth position corresponding to the finishing thickness 11c from the surface 11a.

[0179] In this state, the chuck table 92 is processed and fed at a predetermined processing feed rate along the X-axis direction to form a cutting groove 11e having a depth corresponding to the finishing thickness 11c from the surface 11a along one planned division line 15. This cutting groove 11e functions as a division starting point 23.

[0180] 18 is a partial cross-sectional side view showing how the front surface 11a side is cut. Note that the cut groove 11e is also called a half-cut groove, but it does not necessarily have a depth that is exactly half the thickness of the wafer 11.

[0181] The cut groove 11e in this embodiment has a depth that does not reach the back surface 11b, and is a shallow groove compared to the thickness of the wafer 11. During cutting, cutting water (not shown) such as pure water is supplied near the processing point at a predetermined flow rate. Processing conditions during cutting are set, for example, as follows.

[0182] Spindle speed: 30,000 rpm Processing feed rate: 1.0mm / s or more and 20mm / s or less Cutting water flow rate: specified value between 0.5L / min and 1.5L / min

[0183] After forming the cutting groove 11e along one of the dividing lines 15, the cutting unit 94 is indexed and fed to similarly form cutting grooves 11e along other dividing lines 15 adjacent to the dividing line 15 on which the cutting groove 11e has been formed. In this way, cutting grooves 11e are formed along all of the dividing lines 15 along one direction.

[0184] Thereafter, the chuck table 92 is rotated by 90°. Then, cutting grooves 11e are formed in the same manner along all of the division lines 15 along the other direction perpendicular to the one direction. After the division start point forming step S20, a wafer unit 21 is formed with a protective tape 19a attached to the front surface 11a side.

[0185] Then, in the separation layer forming step S30, the laser beam L is directed to the rear surface 11b side from the bottom of the cut groove 11e.A The light condensing point is positioned to form the separation layer 25. In the separation layer forming step S30, a wafer unit 21 is formed with a protective tape 19a attached to the front surface 11a side.

[0186] Then, the laser beam L is directed toward the back surface 11b from the bottom of the cut groove 11e. A The focal point of the laser beam is positioned to form the separation layer 25. After the separation layer forming step S30, the separation step S40 and the grinding step S50 are performed in this order. Fig. 19(A) is a flow diagram of the processing method according to the second embodiment.

[0187] In contrast to this, in the third embodiment, after the holding step S10 and the separation layer forming step S30, a cutting process is performed to form division start points S35. Fig. 19(B) is a flow diagram of the processing method according to the third embodiment.

[0188] In the splitting start point forming step S35 of the third embodiment, the cut groove 11e is formed so that the bottom of the cut groove 11e is located closer to the front surface 11a than the separation layer 25. That is, the separation layer 25 is formed at a depth position corresponding to the rear surface 11b side of the splitting start point 23.

[0189] In the processing methods according to the second and third embodiments, by grinding the separation layer 25 side of the front surface side wafer 31 in the grinding step S50 after the separation step S40, the front surface side wafer 31 can be divided into a plurality of device chips 35. Therefore, the amount of grinding of the wafer 11 can be reduced compared to when the wafer 11 is ground from the back surface 11b of the wafer 11.

[0190] Next, fourth and fifth embodiments will be described in which the division start point forming step S20 is performed by ablation processing. A laser processing device 102 shown in FIG.

[0191] Compared to the laser processing apparatus 2 shown in FIG. 4, the laser processing apparatus 102 has a laser beam irradiation unit 104 that is different from the laser beam irradiation unit 42, but other than the laser beam irradiation unit 104, it is approximately the same as the laser processing apparatus 2.

[0192] The laser beam irradiation unit 104 has a laser oscillator 44 fixed to a base 4. The laser oscillator 44 has a rod-shaped laser medium made of Nd:YAG or Nd:YVO4.

[0193] The pulsed laser beam emitted from the laser oscillator 44 passes through a wavelength conversion unit (not shown), an attenuator 46, etc., and is then irradiated onto the holding surface 26a from the irradiation head 52. The wavelength conversion unit has, for example, a nonlinear optical crystal that generates harmonics of the laser beam.

[0194] The wavelength conversion unit converts the fundamental wavelength emitted from the laser oscillator 44 into A pulsed laser beam having , a pulsed laser beam L having a wavelength that is absorbed by the wafer 11 B For example, the wavelength conversion unit converts a fundamental wavelength of 1064 nm into a third harmonic (for example, 355 nm). The processing conditions for the ablation processing are set, for example, as follows.

[0195] Laser beam wavelength: 355nm Average output: 0.3W to 4.0W (specified value) Pulse repetition frequency: A specified value between 10 kHz and 200 kHz Processing feed rate: 1.0mm / s or more and 1000mm / s or less Number of passes: A predetermined number between 1 and 10

[0196] The laser beam irradiation unit 104 does not have a branching unit 48. B The light beams are not branched and converge to a single point. The step S20 of forming splitting start points by ablation is performed, for example, after the step S10 of holding and before the step S30 of forming a separation layer (fourth embodiment).

[0197] When performing the ablation process, first, a wafer unit 41 is formed in which the back surface 11b side is supported by a frame 19b (not shown in FIG. 20) via a protective tape 19a. Then, a water-soluble resin film (not shown) of approximately uniform thickness is formed on the front surface 11a side.

[0198] Next, the back surface 11b side is suction-held by the holding surface 26a via the protective tape 19a so that the front surface 11a side is positioned upward. Next, the orientation of the chuck table 26 is adjusted so that one of the planned division lines 15 is approximately parallel to the X-axis direction.

[0199] And the laser beam L B The focal point of the beam is positioned at approximately the same height as the surface 11a, and the chuck table 26 is processed and fed at a predetermined processing feed rate along the X-axis direction, thereby forming a groove 11f having a depth corresponding to the finishing thickness 11c from the surface 11a along one of the planned division lines 15. This groove 11f functions as a division starting point 23.

[0200] 20 is a partial cross-sectional side view showing the state in which ablation processing is performed on the front surface 11a side. After forming a groove 11f along one of the dividing lines 15, the chuck table 26 is indexed and fed to similarly form grooves 11f along other dividing lines 15 adjacent to the dividing line 15 on which the groove 11f has been formed.

[0201] In this way, grooves 11f are formed along all of the division lines 15 extending in one direction. Thereafter, the chuck table 92 is rotated by 90°. Then, grooves 11f are similarly formed along all of the division lines 15 extending in another direction perpendicular to the one direction.

[0202] Next, the water-soluble resin film on the surface 11a side is removed by spin cleaning to remove processing debris that has adhered to the water-soluble resin film during the ablation process. Thereafter, the surface 11a side is dried, thereby completing the division starting point forming step S20.

[0203] After the division starting point forming step S20, a wafer unit 21 is formed with a protective tape 19a attached to the front surface 11a side. Then, in the separation layer forming step S30, a laser beam L is applied to the rear surface 11b side of the bottom of the groove 11f. A The light condensing point is positioned to form the separation layer 25 .

[0204] Thereafter, a separation step S40 and a grinding step S50 are performed in sequence. Fig. 21(A) is a flow diagram of the processing method according to the fourth embodiment. In contrast, in the fifth embodiment, after the holding step S10 and the separation layer forming step S30, a division start point forming step S35 by ablation processing is performed.

[0205] In the splitting start point forming step S35 of the fifth embodiment, the groove 11f is formed so that the bottom of the groove 11f is located closer to the front surface 11a than the separation layer 25. That is, the separation layer 25 is formed at a depth position corresponding to the rear surface 11b side of the splitting start point 23.

[0206] 21(B) is a flow diagram of the processing method according to the fifth embodiment. In the processing methods according to the fourth and fifth embodiments, the front surface side wafer 31 can be divided into a plurality of device chips 35 by grinding the separation layer 25 side of the front surface side wafer 31 in the grinding step S50 after the separation step S40.

[0207] Therefore, the amount of grinding of the wafer 11 can be reduced compared to when the wafer 11 is ground from the back surface 11b of the wafer 11. In addition, the structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of symbols]

[0208] 2: Laser processing device, 4: Base, 6: X-axis and Y-axis movement mechanism, 8: Y-axis guide rail 10: Y-axis moving plate, 12: screw shaft, 14: motor, 16: X-axis guide rail 11: Wafer (single crystal silicon wafer) 11a: Front side (first side), 11b: Back side (second side) 11c: Finished thickness, 11d: Depth, 11e: Cutting groove, 11f: Processing groove 13: Notch, 15: Planned division line 17: device, 19a: protective tape, 19b: frame, 21: wafer unit 18: X-axis moving plate, 20: screw shaft, 22: motor, 24: table base 23: Splitting point, 23a: Modified area, 23b: Crack 25, 25-1, 25-2: Separation layer, 25a: Modified region, 25b: Crack 25c1, 25c2: Line 26: chuck table, 26a: holding surface, 26b: clamp unit 30: Support structure, 32: Z-axis movement mechanism, 34: Z-axis guide rail 31: front surface side wafer (first surface side wafer), 31a: separation surface (third surface) 33: Backside wafer (second side wafer), 35: Device chip 36: Z-axis moving plate, 38: motor, 40: support 41: Wafer unit 42: Laser beam irradiation unit, 44: Laser oscillator, 46: Attenuator 48: Branching unit, 50: Mirror, 52: Irradiation head, 54: Housing 56: Imaging unit, 58: Touch panel, 60: Separation device 62: chuck table, 62a: holding surface, 62b: rotation axis 64: wedge portion, 64a: one end portion, 66: suction unit, 68: housing 70: suction part, 70a: holding surface, 72: grinding device 74: chuck table, 74a: rotary shaft, 76: grinding unit, 78: spindle 80: Mount, 82: Grinding wheel, 84: Base, 86: Grinding stone 90: cutting device, 92: chuck table, 92a: holding surface, 94: cutting unit 96: Spindle housing, 98: Spindle, 100: Cutting blade 102: Laser processing device, 104: Laser beam irradiation unit A: Center, B: Width, C: Thickness, L A , L B :Laser beam P1, P2, P3, P4, P5: Focus point

Claims

1. A processing method for processing a single crystal silicon wafer having a first surface and a second surface located opposite to the first surface, each of which is formed so as to expose a specific crystal plane included in a crystal plane {100}, and in which devices are formed in each of a plurality of regions partitioned by a plurality of planned dividing lines set in a lattice pattern on the first surface, comprising: a dividing start point forming step of forming dividing start points for dividing the single crystal silicon wafer along each of the planned dividing lines to a depth corresponding to at least a finished thickness of device chips; a separation layer forming step of positioning a focal point of a pulsed laser beam having a wavelength that is transmitted through the single crystal silicon wafer inside the single crystal silicon wafer, and relatively moving the focal point and the single crystal silicon wafer along a first direction that is parallel to a crystal plane of the second surface and forms an acute angle with a crystal orientation <100> of 5° or less, thereby forming a separation layer along the crystal plane of the second surface at a depth corresponding to a position closer to the second surface than the splitting starting point; a separation step of separating the single crystal silicon wafer, after the splitting starting point forming step and the separation layer forming step, using the separation layer as a starting point, into a first surface side wafer including a plurality of devices formed on the first surface side and a second surface side wafer located on the second surface side and not including any devices, The separation layer forming step includes: a modified region forming step of forming a modified region by relatively moving the focal point of the laser beam and the single-crystal silicon wafer along the first direction; an indexing step of relatively indexing the focal point and the single crystal silicon wafer in a second direction that is parallel to a crystal plane of the second surface and perpendicular to the first direction, the separation layer includes the modified region and a crack extending from the modified region; the separation step applies an external force to the single crystal silicon wafer to extend a crack in the separation layer, and then separates the single crystal silicon wafer into the first surface side wafer and the second surface side wafer so as to separate the first surface side and the second surface side wafer.

2. 2. The processing method according to claim 1, further comprising a grinding step, after the separating step, of grinding a third surface side of the first surface side wafer located on the opposite side to the first surface, and dividing the first surface side wafer into a plurality of device chips.

3. A processing method as described in claim 1, characterized in that the first surface side wafer and the second surface side wafer separated in the separation step have the same diameter.

4. The processing method described in claim 1, characterized in that in the splitting starting point formation step, the splitting starting point is formed by forming a cutting groove in the single crystal silicon wafer with a cutting blade, or the splitting starting point is formed by forming a processed groove in the single crystal silicon wafer by ablation processing.

5. A processing method as described in claim 1, characterized in that in the separation layer formation step, the focal point of the laser beam is branched into multiple points and positioned inside the single crystal silicon wafer.

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