Method of processing a wafer

Abstract

The present invention provides a wafer processing method capable of suppressing clogging of a grinding tool when grinding a film on the back surface of a wafer before laser processing. The wafer processing method includes the following steps: a laser processing groove forming step of forming a laser processing groove that locally removes a film on the back surface of a wafer by laser light of a wavelength that is absorbed by the film or a substrate; a preliminary grinding step of grinding the back surface of the wafer to remove the film and the laser processing groove, thereby forming a wafer having a thickness of a predetermined thickness or more; a modification layer forming step of forming a modification layer along a division predetermined line in the inside of the substrate by irradiating laser light of a wavelength that is transmitted by the substrate from the back surface side of the wafer, the focal point of the laser light being positioned in the inside of the substrate; and a grinding step of grinding the wafer from the back surface side to thin the wafer to a finished thickness and dividing the wafer into chips along the modification layer.

Description

Technical Field

[0001] This invention relates to a method for processing wafers. Background Technology

[0002] As a method for manufacturing semiconductor device chips, it is known to use a cutting tool or a laser beam to cleave a wafer on the front side of a substrate in which a functional layer forming the device is stacked. Compared with cleaving based on a cutting tool, the method of cleaving by forming a modified layer inside the substrate as a fracture initiation point using a laser beam has the following advantages: it can make the predetermined cleaving line narrower and can greatly suppress the generation of cutting chips (see, for example, Patent Document 1).

[0003] In laser beam dicing, the laser beam needs to pass through the interior of the substrate. Therefore, the laser beam is irradiated from the back side of the wafer, which has a functional layer that does not obstruct the transmission of the laser beam. In this case, if a nitride film or oxide film with a specified reflectivity is formed on the back side of the wafer, the back side film needs to be removed by grinding beforehand.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2013-008831

[0005] However, in the grinding of the back film, to prevent the wafer from breaking during transport to the next laser processing step, the grinding amount is suppressed to maintain a certain thickness. Therefore, the proportion of film in the grinding volume increases, making the grinding wheel prone to clogging. This necessitates periodic dressing of the grinding wheel, resulting in increased dressing time and increased wear on the grinding wheel due to dressing. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a wafer processing method that can suppress the clogging of the grinding tool when grinding the film on the back side of the wafer before laser processing.

[0007] According to the present invention, a wafer processing method is provided, wherein a wafer having multiple devices formed by a functional layer stacked on the front side of a substrate and a film formed on the back side of the substrate is diced along multiple predetermined dividing lines that intersect to divide the devices. The wafer processing method includes the following steps: a protective member placement step, in which a protective member is placed on the front side of the wafer; a laser processing trench formation step, after the protective member placement step, in which laser light of a wavelength that absorbs the film or the substrate is irradiated onto the back side of the wafer to form a laser processing trench on the back side of the wafer to partially remove the film; and a pre-grinding step, in which grinding is performed... The grinding wheel grinds the back side of the wafer on which the laser processing groove is formed to remove the film and the laser processing groove, forming a wafer of a predetermined thickness or more; in the modification layer formation step, after the pre-grinding step, a focal point of a laser beam with a wavelength that is transparent to the substrate is positioned inside the substrate, and the wafer with the film removed is irradiated from the back side, forming a modification layer along the predetermined dividing line inside the substrate; and in the grinding step, the wafer on which the modification layer is formed is ground from the back side using a grinding wheel, thinning the wafer to the finished thickness, and dividing the wafer into individual chips along the modification layer.

[0008] According to the present invention, when grinding the film on the back side of a wafer before laser processing, clogging of the grinding tool can be suppressed. Attached Figure Description

[0009] Figure 1 This is a perspective view of an example of a wafer to be processed according to the wafer processing method of the embodiment.

[0010] Figure 2 This is a flowchart illustrating the wafer fabrication method of an embodiment.

[0011] Figure 3 It is shown Figure 2 A perspective view of an example of the steps for installing the protective component.

[0012] Figure 4 This is a perspective view of the chip after the protective component installation steps.

[0013] Figure 5 Shown using partial cross-sections Figure 2 A side view of an example of the laser processing groove formation process shown.

[0014] Figure 6 This is a three-dimensional view showing the wafer after the laser processing groove formation step.

[0015] Figure 7 Shown using partial cross-sections Figure 2 A side view of an example of the preparatory grinding steps shown.

[0016] Figure 8 Shown using partial cross-sections Figure 2 A side view of an example of the modified layer formation step shown.

[0017] Figure 9 Shown using partial cross-sections Figure 2 A side view of an example of the grinding process shown.

[0018] Figure 10 This is a three-dimensional view showing the wafer after the grinding process.

[0019] Label Explanation

[0020] 10: Wafer; 11: Substrate; 12: Front side; 13: Pre-defined dividing line; 14: Device; 15: Back side; 16: Functional layer; 17: Film; 18: Laser processing tank; 19: Modified layer; 20: Protective component; 30: Laser beam; 31: Focusing point; 93: Grinding tool. Detailed Implementation

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the contents described in the following embodiments. Furthermore, the structural elements described below include substantially the same elements that can be readily conceived by those skilled in the art. Furthermore, the structures described below can be appropriately combined. Additionally, various omissions, substitutions, or modifications to the structure can be made without departing from the spirit of the present invention.

[0022] The processing method of the wafer 10 according to an embodiment of the present invention will be described with reference to the accompanying drawings. First, the structure of the wafer 10, which is the object of processing in the embodiment, will be described. Figure 1 This is a perspective view of an example of a wafer 10 that is the object of processing according to the processing method of the wafer 10 of the embodiment.

[0023] like Figure 1 As shown, wafer 10 is a disc-shaped semiconductor wafer, optical device wafer, or other wafer with a substrate 11 made of silicon (Si), sapphire (Al2O3), gallium arsenide (GaAs), or silicon carbide (SiC). Wafer 10 has multiple predetermined dividing lines 13 formed on the front side 12 of the substrate 11 and devices 14 formed in regions divided by the intersecting multiple predetermined dividing lines 13 in a lattice pattern. The side of wafer 10 opposite to the front side 12 where the devices 14 are formed is designated as the back side 15. A film 17, such as a nitride film or an oxide film, with a specified or higher reflectivity is formed on the back side 15 of the substrate 11.

[0024] Device 14 is, for example, an integrated circuit such as IC (Integrated Circuit) or LSI (Large Scale Integration), an image sensor such as CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), or MEMS (Micro Electro Mechanical Systems).

[0025] A functional layer 16 is stacked on the front side 12 of the substrate 11. The functional layer 16 has a low-dielectric-constant insulating film (hereinafter referred to as a Low-k film) made of inorganic materials such as SiOF and BSG (SiOB) or organic materials such as polyimide and parylene as polymer films, and a conductive film made of a conductive metal. The Low-k film and the conductive film are stacked to form a device 14. The conductive film constitutes the circuit of the device 14. Therefore, the device 14 is composed of Low-k films stacked on top of each other and conductive films stacked between the Low-k films. In addition, the functional layer 16 that divides the predetermined lines 13 is composed of a Low-k film and does not have a conductive film.

[0026] Next, the processing method of the wafer 10 according to the embodiment will be described. Figure 2 This is a flowchart illustrating the processing method of wafer 10 according to an embodiment. The processing method of wafer 10 includes a protective component placement step 1, a laser processing trench formation step 2, a pre-grinding step 3, a modified layer formation step 4, and a grinding step 5.

[0027] (Protective component installation step 1)

[0028] Figure 3 It is shown Figure 2 The diagram shows a perspective view of an example of the protective component being installed in step 1. Figure 4 This is a perspective view of the wafer 10 after step 1 of the protective component placement. Step 1 of the protective component placement is the step of placing the protective component 20 on the front side 12 of the wafer 10.

[0029] Protective component 20 is attached to the laser processing apparatus 40 described later (see reference). Figure 5 ) or grinding device 70 (refer to) Figure 7The protective member 20 protects the device 14 on the front side 12 of the wafer 10 held by the chuck stages 50 and 80 from foreign matter adhesion or damage caused by contact. In an embodiment, the protective member 20 is a disc-shaped strip with a diameter larger than that of the wafer 10. The protective member 20 includes, for example, a substrate layer made of synthetic resin and an adhesive paste layer laminated on at least one of the front and back sides of the substrate layer.

[0030] like Figure 2 As shown, in step 1 of the protective component installation, firstly, the protective component 20 is attached to the back side of the frame 21. The frame 21 has an opening larger than the outer diameter of the wafer 10. Next, the wafer 10 is positioned at a predetermined position within the opening of the frame 21, and the back side 15 is attached to the protective component 20. Thus, as... Figure 3 As shown, the chip 10 is fixed to the protective component 20 and the frame 21.

[0031] (Step 2 of forming the laser processing tank)

[0032] Figure 5 Shown using partial cross-sections Figure 2 The side view shown is an example of step 2 of forming the laser processing groove. Figure 6 This is a perspective view of the wafer 10 after laser processing trench formation step 2. Laser processing trench formation step 2 is a step of forming a laser processing trench 18 on the back surface 15 of the wafer 10 by irradiating the back surface 15 of the wafer 10 with laser light 30, thereby partially removing the film 17.

[0033] In step 2 of forming the laser processing groove, a laser processing groove 18 is formed on the back side 15 of the wafer 10 by ablation processing based on the laser processing apparatus 40. The laser beam 30 is a laser beam with a wavelength that is absorbed by the film 17 or the substrate 11. The laser processing apparatus 40 includes a chuck stage 50, a laser beam irradiation unit 60, a moving unit (not shown) that moves the chuck stage 50 and the laser beam irradiation unit 60 relative to each other, and an imaging unit (not shown) that images the wafer 10.

[0034] In step 2 of forming the laser processing groove, firstly, the front side 12 of the wafer 10 is attracted and held on the holding surface 51 of the chuck stage 50 through the protective member 20, and the outer edge of the frame 21 is fixed by the clamping part 52. Furthermore, at this time, the frame 21 is pressed down to a position lower than the front side 12 of the wafer 10 and then fixed, thereby fixing the front side 12 of the wafer 10 onto the holding surface 51 of the chuck stage 50.

[0035] In the laser processing groove forming step 2, the chuck stage 50 is then moved to the processing position by a moving unit (not shown), and the wafer 10 is photographed and aligned by an imaging unit (not shown), thereby positioning the irradiation part 61 of the laser beam irradiation unit 60 at the position where the laser processing groove 18 is formed on the wafer 10.

[0036] Furthermore, when the laser processing groove 18 is formed along the predetermined dividing line 13, the wafer 10 is photographed using an imaging unit (not shown), and alignment with the dividing line 13 is performed. Regardless of the location where the laser processing groove 18 is formed, for example, the positions of the outer edges of the wafer 10 at three or more locations can be detected, the coordinates of the outer edges can be calculated, and thus alignment with the position of the wafer 10 can be performed. Alternatively, if the wafer 10 can always be positioned in the same location when it is transferred to the chuck stage 50, the above alignment may not be necessary.

[0037] In step 2 of forming the laser processing groove, the chuck stage 50 is moved relative to the laser beam irradiation unit 60 while a laser beam 30 is irradiated toward the wafer 10 held on the holding surface 51 of the chuck stage 50. At this time, a pulsed laser beam 30 is irradiated from the back surface 15 side of the wafer 10 by positioning the focal point 31 on the film 17. By irradiating the back surface 15 of the wafer 10 with the laser beam 30 positioning the focal point 31 on the film 17, a laser processing groove 18 is formed on the back surface 15 of the wafer 10.

[0038] Furthermore, in this invention, the laser beam 30 can be a wavelength that is absorbed only by the substrate 11, a wavelength that is absorbed by the film 17, or a wavelength that is not absorbed by the film 17. Even if the laser beam 30 is a wavelength that is absorbed only by the substrate 11, the film 17 can still be removed by the laser beam 30.

[0039] The location and number of laser processing grooves 18 are not particularly limited, but the laser processing grooves 18 are preferably formed in a grid pattern, for example. Furthermore, the depth of the laser processing grooves 18 is not particularly limited, but the laser processing grooves 18 preferably penetrate the film 17 in the height direction. Additionally, if the film 17 is easily transmissible to the laser beam 30, laser processing can be performed after coating the front side of the film 17 with a water-soluble liquid resin containing a light-absorbing material such as an oxide or nitride that promotes the absorption of the laser beam 30. Therefore, even if the film 17 is easily transmissible to the laser beam 30, the removal of the film 17 based on laser processing can be promoted. In the laser processing groove formation step 2, when the laser processing grooves 18 are formed on the entire back side 15 of the wafer 10, the irradiation of the laser beam 30 is released, the chuck stage 50 is used to hold the wafer, and the process proceeds to the pre-grinding step 3.

[0040] (Preparatory grinding step 3)

[0041] Figure 7 Shown using partial cross-sections Figure 2 The side view shows an example of pre-grinding step 3. Pre-grinding step 3 is a step in which the film 17 and the laser processing groove 18 are removed by grinding the back side 15 of the wafer 10, which has the laser processing groove 18 formed, using a grinding tool 93, thereby forming a wafer 10 with a specified thickness or more.

[0042] In the pre-grinding step 3, the film 17 and laser processing groove 18 on the back side 15 of the wafer 10 are removed by grinding through the grinding apparatus 70, forming a wafer 10 with a specified thickness or greater. The grinding apparatus 70 has a chuck table 80 and a grinding unit 90. The grinding unit 90 has a spindle 91 as a rotating axis component, a grinding wheel base 92 mounted on the lower end of the spindle 91, a grinding wheel 93 mounted on the lower surface of the grinding wheel base 92, and a grinding water supply nozzle 94. The grinding wheel base 92 rotates about a rotation axis parallel to the axis of the chuck table 80.

[0043] In the pre-grinding step 3, firstly, the front side 12 of the wafer 10 is attracted and held on the holding surface 81 of the chuck stage 80 through the protective member 20, and the outer edge of the frame 21 is fixed by the clamping part 82. Furthermore, at this time, the frame 21 is pressed down to a position lower than the front side 12 of the wafer 10 and then fixed, thereby fixing the front side 12 of the wafer 10 onto the holding surface 81 of the chuck stage 80.

[0044] In the pre-grinding step 3, while the chuck table 80 is rotating about its axis, the grinding wheel base 92 is also rotated about its axis. Grinding water 95 is supplied from the grinding water supply nozzle 94, and the grinding tool 93 mounted on the lower surface of the grinding wheel base 92 is brought close to the chuck table 80 at a predetermined feed rate, thereby grinding the wafer 10 from the back side 15 using the grinding tool 93.

[0045] In the pre-grinding step 3, the film 17 and the laser processing groove 18 on the back side 15 of the wafer 10 are removed. That is, the depth of the grinding is greater than that of the laser processing groove 18. At this time, a wafer 10 with a specified thickness or more is formed based on the thickness of the remaining wafer 10 after finishing. The thickness ground by the pre-grinding step 3 is, for example, 100 μm or less.

[0046] When grinding the film 17 on the back side 15 of the wafer 10 in the pre-grinding step 3, the volume of the film 17 relative to the grinding volume is reduced compared to the case without the laser processing groove 18, due to the formation of the laser processing groove 18. Furthermore, the unevenness of the laser processing groove 18 creates an impact when the grinding tool 93 collides with the protrusion, thereby expecting a dressing effect from the grinding tool 93. In the pre-grinding step 3, when the wafer 10 has reached a thickness of at least a predetermined thickness, the rotation of the chuck stage 80 and the grinding unit 90 is stopped, the suction holding of the chuck stage 80 is released, and the process proceeds to the modified layer formation step 4.

[0047] (Step 4 of the modified layer formation)

[0048] Figure 8 Shown using partial cross-sections Figure 2 The side view shows an example of the modified layer formation step 4. The modified layer formation step 4 is performed after the pre-grinding step 3. The modified layer formation step 4 is a step of forming a modified layer 19 along the predetermined dividing line 13 inside the substrate 11 by irradiating the back side 15 side of the wafer 10 from which the film 17 has been removed with laser light 30.

[0049] The modified layer 19 refers to a region whose density, refractive index, mechanical strength, or other physical properties differ from those of its surroundings. The modified layer 19 may be, for example, a melt-processed region, a cracked region, an insulation failure region, a region with a changing refractive index, or a region where these regions coexist. The mechanical strength of the modified layer 19 is lower than that of other parts of the wafer 10.

[0050] In step 4 of forming the modified layer, a modified layer 19 is formed inside the substrate 11 of the wafer 10 by stealth cutting based on the laser processing apparatus 40. The laser beam 30 is a laser beam with a wavelength that is transparent to the substrate 11. The laser processing apparatus 40 may also be the same apparatus used in step 2 of forming the laser processing tank.

[0051] In step 4 of forming the modified layer, firstly, similar to step 2 of forming the laser processing tank, the front side 12 of the wafer 10 is attracted and held on the holding surface 51 of the chuck stage 50 via the protective member 20, and the outer edge of the frame 21 is fixed by the clamping part 52. Next, the chuck stage 50 is moved to the processing position by a moving unit (not shown), and the wafer 10 is photographed and aligned by an imaging unit (not shown), thereby aligning the irradiation part 61 of the laser beam irradiation unit 60 with the predetermined dividing line 13 of the wafer 10.

[0052] In step 4 of the modified layer formation, while moving the chuck stage 50 relative to the laser beam irradiation unit 60, a pulsed laser beam 30 is irradiated from the back side 15 of the wafer 10 by positioning the focusing point 31 inside the substrate 11. By irradiating the laser beam 30, which positions the focusing point 31 inside the substrate 11, along the predetermined dividing lines 13, a modified layer 19 is formed inside the substrate 11 along the predetermined dividing lines 13. In step 4 of the modified layer formation, when the modified layer 19 has been formed along all the predetermined dividing lines 13, the irradiation of the laser beam 30 is released, the chuck stage 50 is stopped, and the grinding step 5 begins.

[0053] (Grinding step 5)

[0054] Figure 9 Shown using partial cross-sections Figure 2 A side view of an example of grinding step 5 shown. Figure 10 This is a perspective view showing the wafer 10 after grinding step 5. Grinding step 5 is a step in which the wafer 10 with the modified layer 19 formed is ground from the back side 15 using a grinding tool 93 to thin the wafer 10 to the finished thickness and form the wafer 10 divided along the modified layer 19.

[0055] In grinding step 5, the wafer 10 is thinned to the finished thickness by grinding from the back side 15 through grinding processing based on the grinding apparatus 70. The grinding apparatus 70 may also be the same apparatus used in the pre-grinding step 3.

[0056] In grinding step 5, firstly, similar to pre-grinding step 3, the front side 12 of the wafer 10 is attracted and held on the holding surface 81 of the chuck table 80 via the protective member 20, and the outer edge of the frame 21 is fixed by the clamping part 82. Next, while the chuck table 80 is rotating about its axis, the grinding wheel base 92 is rotated about its axis. Grinding water 95 is supplied from the grinding water supply nozzle 94, and the grinding tool 93 mounted on the lower surface of the grinding wheel base 92 is brought close to the chuck table 80 at a predetermined feed rate, thereby grinding the wafer 10 from the back side 15 using the grinding tool 93.

[0057] In grinding step 5, the wafer 10 is ground from the back side 15 until it reaches the finished thickness. Additionally, in grinding step 5, the wafer 10 is diced along the predetermined dividing line 13 into individual chips by the grinding stress acting from the grinding wheel base 92 of the grinding unit 90, with the modified layer 19 as the fracture origin. When the wafer 10 is ground to the finished thickness, the wafer 10 processing method of this embodiment concludes all processes.

[0058] As explained above, in the wafer 10 processing method of the embodiment, a laser processing groove 18 is formed on the back surface 15 of the wafer 10, and the film 17 is partially removed before the pre-grinding step 3. When grinding the film 17 on the back surface 15 side of the wafer 10 by the pre-grinding step 3, the volume of the film 17 relative to the grinding volume is reduced compared to the case without the laser processing groove 18 due to the formation of the laser processing groove 18. As a result, the clogging of the grinding tool 93 can be suppressed by the pre-grinding step 3. In addition, the unevenness of the laser processing groove 18 creates an impact when the grinding tool 93 collides with the protrusion, and the dressing effect of the grinding tool 93 can be expected.

[0059] Furthermore, the present invention is not limited to the embodiments described above. That is, it can be implemented in various modifications without departing from the spirit of the present invention. For example, in the laser processing trench forming step 2, pre-grinding step 3, modified layer forming step 4, and grinding step 5 of the embodiment, the wafer 10 is fixed to the frame 21. However, in the present invention, a protective member 20 with approximately the same diameter as the wafer 10 can be attached without using the frame 21 to perform each step. That is, in the laser processing trench forming step 2, pre-grinding step 3, modified layer forming step 4, and grinding step 5, it is sufficient to simply attach the protective member 20 to the wafer 10, or the frame 21 can be fixed without the protective member 20.

Claims

1. A method for processing a wafer, wherein a wafer having multiple devices formed on a functional layer stacked on the front side of a substrate and a film formed on the back side of the substrate is diced along multiple predetermined dicing lines that intersect to divide the devices, wherein, The wafer fabrication method comprises the following steps: The protective component installation step involves installing a protective component on the front side of the chip. In the laser processing groove forming step, after the protective component placement step, laser light of a wavelength that is absorbent to the film or the substrate is irradiated onto the back side of the wafer to form a laser processing groove on the back side of the wafer that locally removes the film. The preparatory grinding step involves using a grinding tool to grind the back side of the wafer on which the laser processing groove is formed, thereby removing the film and the laser processing groove, and forming the wafer with a specified thickness or more. In the modified layer formation step, after the pre-grinding step, a laser beam of wavelength that is transparent to the substrate is focused inside the substrate and irradiated from the back side of the wafer after the film has been removed, thereby forming a modified layer along the predetermined dividing line inside the substrate. as well as The grinding step involves using a grinding tool to grind the wafer with the modified layer formed on the back side, thinning the wafer to the finished thickness, and dividing the wafer into individual chips along the modified layer.

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