Processing method of wafer

Abstract

To provide a processing method of an adhering wafer that can reduce a possibility of causing a production defect.SOLUTION: A processing method of a wafer, comprises: a preparation step 101 of preparing an adhering wafer; a holding step 103 of holding a back surface side of a first wafer so as to be exposed; a division starting point formation step 105 of forming a modification layer inside a second wafer by radiating a laser beam along a division schedule line by positioning a focal point of the laser beam inside the second wafer from the back surface side of the first wafer; and a suppression layer formation step 104 of forming a suppression layer by radiating the laser beam along the division schedule line by positioning the focal point of the laser beam inside the first wafer from the back surface side of the first wafer. The suppression layer formation step 104 is performed prior to the division starting point formation step 105.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wafer processing method. [Background technology]

[0002] As a method for dividing a semiconductor wafer into device chips, a method is known in which a modified layer is formed inside the wafer by irradiating the wafer with a laser beam along the intended dividing line, and then dividing the wafer using this modified layer as the starting point (see, for example, Patent Document 1).

[0003] In the above-mentioned processing method, depending on the thickness and material of the wafer, a plurality of modified layers are formed in the thickness direction inside the wafer in order to improve divisibility.

[0004] Here, when forming a multi-layer modified layer, the focal point of the laser beam is generally first positioned at a depth position inside the wafer close to the surface opposite to the irradiated surface to which the laser beam is irradiated, and then moved in sequence to a depth position closer to the irradiated surface. This is because if a modified layer is first formed at a depth position close to the irradiated surface, the previously formed modified layer may prevent the laser beam from focusing when processing a depth position far from the irradiated surface later, making the formation of the modified layer unstable and decreasing the divisibility. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3408805 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, attention has been focused on three-dimensional mounting technology known as WoW (Wafer on wafer), which connects wafers vertically using penetrating electrodes, and technology for creating structures such as movable parts within a hollow structure by bonding a wafer with a cavity structure formed on its surface to a wafer with a structure formed on its surface.

[0007] It has been found that when the above-mentioned processing method is applied to such bonded wafers, when forming a modified layer inside the lower wafer, the laser beam is reflected at the bonded surface of the wafer, forming an unintended modified layer on the upper wafer, or the reflected light reaches the surface irradiated with the laser beam and forms ablation marks. The modified layer formed at an unintended position and the ablation marks formed on the irradiated surface may cause a decrease in splittability, a decrease in flexural strength, and the extension of cracks, which may result in a decrease in yield.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a processing method for a bonded wafer capable of reducing the possibility of causing product defects. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, a wafer processing method of the present invention is a wafer processing method, comprising: a preparation step of preparing a bonded wafer by bonding one surface of a first wafer and one surface of a second wafer; a holding step of holding the other surface side of the second wafer of the bonded wafer so that the other surface side of the first wafer is exposed by facing the holding surface of a holding unit; and a step of positioning a focal point of a laser beam inside the second wafer from the other surface side of the first wafer and irradiating the laser beam along a planned division line, thereby The method includes a splitting starting point forming step of forming a modified layer inside the second wafer, which serves as a splitting starting point, and an inhibition layer forming step of forming an inhibition layer that inhibits the other side of the first wafer from being processed by the laser beam reflected from one side of the first wafer in the splitting starting point forming step by positioning a focal point of a laser beam inside the first wafer from the other side of the first wafer and irradiating the laser beam along the planned split line of the bonded wafer, and the inhibition layer forming step is characterized in that the inhibition layer forming step is performed prior to the splitting starting point forming step.

[0010] In the wafer processing method, when a laser beam is irradiated from the other surface side of the first wafer and a focal point of the laser beam is positioned inside the second wafer, the method may further include a storage step of pre-storing a depth position at which the laser beam is reflected from one surface side of the first wafer and focused inside the first wafer, and in the suppression layer formation step, the focal point of the laser beam may be positioned at the depth position stored in the storage step.

[0011] In the above-described wafer processing method, the bonded wafer may have a predetermined gap between the first wafer and the second wafer along the planned dividing line. Effect of the Invention

[0012] The present invention has an effect of reducing the possibility of causing product defects. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a flowchart showing the flow of the wafer processing method according to the first embodiment. [Diagram 2] FIG. 2 is a perspective view that typically shows a first wafer and a second wafer prepared in a preparation step of the wafer processing method shown in FIG. [Diagram 3] FIG. 3 is a perspective view that typically shows a bonded wafer formed in the preparation step of the wafer processing method shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view that typically shows the bonded wafer shown in FIG. [Diagram 5] FIG. 5 is a cross-sectional view that typically shows a storage step of the wafer processing method shown in FIG. [Figure 6] FIG. 6 is a side view, partially in section, typically showing the holding step of the wafer processing method shown in FIG. [Figure 7] FIG. 7 is a side view, partially in section, typically showing the suppression layer forming step of the wafer processing method shown in FIG. [Figure 8] FIG. 8 is a cross-sectional view of the bonded wafer after the inhibiting layer forming step in the wafer processing method shown in FIG. [Figure 9] FIG. 9 is a side view, partially in section, typically showing the dividing start point forming step of the wafer processing method shown in FIG. [Figure 10] FIG. 10 is a cross-sectional view of the bonded wafer after the dividing start point forming step of the wafer processing method shown in FIG. [Figure 11] FIG. 11 is a cross-sectional view that typically shows a modified example of the bonded wafer shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The form (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. Furthermore, the components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the configurations described below can be appropriately combined. Furthermore, various omissions, substitutions, or modifications of the configurations can be made without departing from the gist of the present invention.

[0015] [Embodiment 1] The processing method according to the first embodiment of the present invention will be described with reference to the drawings, in which: Fig. 1 is a flow chart showing the flow of the wafer processing method according to the first embodiment.

[0016] The wafer processing method according to the first embodiment includes a preparation step 101, a storage step 102, a holding step 103, an inhibition layer forming step 104, and a division starter forming step 105, as shown in FIG.

[0017] (Preparation step) Fig. 2 is a perspective view typically showing a first wafer and a second wafer prepared in a preparation step of the wafer processing method shown in Fig. 1. Fig. 3 is a perspective view typically showing a bonded wafer formed in the preparation step of the wafer processing method shown in Fig. 1. Fig. 4 is a cross-sectional view typically showing the bonded wafer shown in Fig. 3.

[0018] The preparation step 101 is a step of preparing a bonded wafer 20 shown in Figures 3 and 4, which is obtained by bonding together a front surface 2, which is one surface of a first wafer 1 shown in Figure 2, and a front surface 12, which is one surface of a second wafer 11. That is, the wafer processing method according to the first embodiment is a processing method for the wafers 1 and 11 shown in Figure 1.

[0019] The first wafer 1 is a wafer such as a disk-shaped semiconductor wafer or an optical device wafer, with silicon (Si), sapphire (Al2O3), gallium arsenide (GaAs), silicon carbide (SiC), or the like, as a substrate 3. The first wafer 1 has devices 5 formed in regions partitioned in a lattice pattern by a plurality of planned dividing lines 4 formed in a lattice pattern on a surface 2.

[0020] The device 5 is, for example, an integrated circuit such as an IC (Integrated Circuit) or an LSI (Large Scale Integration), an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), an optical element such as an LED (Light-Emitting Diode), a MEMS (Micro Electro Mechanical Systems), or a semiconductor memory (semiconductor memory device). In the first embodiment, the device 5 of the first wafer 1 is a MEMS.

[0021] The second wafer 11 is a disk-shaped substrate wafer having a substrate 13 made of silicon, glass, ceramics, etc., and having the same diameter as the first wafer 1 and no devices 5 formed on the surface 12. However, in the present invention, the second wafer 11 may also be a wafer having devices 5 formed on the surface 12, similar to the first wafer 1.

[0022] In the first embodiment, the thickness of the first wafer 1 and the second wafer 11 is not less than 50 μm and not more than 100 μm.

[0023] In the preparation step 101, first, the surface 2 of the first wafer 1 and the surface 12 of the second wafer 11 are opposed to each other with a gap therebetween, as shown in Fig. 2. Next, the surface 2 of the first wafer 1 and the surface 12 of the second wafer 11 are bonded together. This forms a bonded wafer 20 shown in Figs. 3 and 4.

[0024] At this time, in the first embodiment, a convex portion 21 shown in FIG. 4 is formed around the device 5 of the first wafer 1, and the surface 2 of the first wafer 1 and the surface 12 of the second wafer 11 are bonded together via the convex portion 21 to form a bonded wafer 20. In the first embodiment, the bonded wafer 20 has a gap 22 formed between the surface 2 of the first wafer 1 and the surface 12 of the second wafer 11 by the convex portion 21, and the thickness 23 of the gap 22 is 1 μm or more and 20 μm or less. In this way, the bonded wafer 20 has a predetermined gap 22 between the first wafer 1 and the second wafer 11 on the division line 4, and the distance between the first wafer 1 and the second wafer 11 on the division line 4 is 1 μm or more and 20 μm or less.

[0025] (Memory step) Fig. 5 is a cross-sectional view that typically shows a storage step of the wafer processing method shown in Fig. 1. Storage step 102 is a step of storing in advance a depth position 34 (distance from the back surface 6) of a focal point 33 where the laser beam 31 is reflected by the front surface 2 side of the first wafer 1 and focused inside the first wafer 1 when the laser beam 31 is irradiated from the back surface 6 side, which is the other surface of the first wafer 1, and a focal point 32 of the laser beam 31 is positioned inside the second wafer 11.

[0026] In the first embodiment, in the storing step 102, a focal point 32 is set at a position set in the splitting starting point forming step 105 inside the second wafer 11 using well-known simulation software, as shown in Fig. 5, and a depth position 34 of a focal point 33 of the laser beam 31 reflected from the front surface 2 when the laser beam 31 used in the suppression layer forming step 104 and the splitting starting point forming step 105 is irradiated from the back surface 6 of the first wafer 1 of the bonded wafer 20 is calculated. Also, in the first embodiment, in the storing step 102, the processing conditions of the laser beam 31 are set to the same processing conditions as those in the splitting starting point forming step 105.

[0027] In the first embodiment, in the storage step 102, the depth position 34 of the focal point 33 of the reflected laser beam 31 is stored in a control unit of the laser processing device 30 (shown in FIG. 6) which performs the suppression layer forming step 104 and the division starting point forming step 105. In the first embodiment, the depth position 34 of the focal point 33 of the reflected laser beam 31 is calculated using well-known simulation software, but the back surface 16, which is the other surface of the second wafer 11 of the bonded wafer 20, may be held on the holding surface 36 of the holding unit 35 of the laser processing device 30 which performs the suppression layer forming step 104 and the division starting point forming step 105, and the back surface 6 of the first wafer 1 may be irradiated with the laser beam 31 to measure the depth position 34 of the focal point 33 of the reflected laser beam 31.

[0028] (holding step) 6 is a side view showing a schematic partial cross section of the holding step of the wafer processing method shown in FIG. 1. The holding step 103 is a step of holding the back surface 16 of the second wafer 11 of the bonded wafer 20 so as to face the holding surface 36 of the holding unit 35 and expose the back surface 6 of the first wafer 1. In the embodiment 1, in the holding step 103, the laser processing device 30 places the back surface 16 of the second wafer 11 of the bonded wafer 20 on the holding surface 36 of the holding unit 35. In the embodiment 1, in the holding step 103, the laser processing device 30 suction-holds the back surface 16 of the second wafer 11 of the bonded wafer 20 on the holding surface 36 of the holding unit 35 as shown in FIG. 6, exposing the back surface 6 of the first wafer 1.

[0029] (Inhibition layer formation step) Fig. 7 is a side view showing a schematic partial cross section of the suppression layer forming step of the wafer processing method shown in Fig. 1. Fig. 8 is a cross-sectional view of the bonded wafer after the suppression layer forming step of the wafer processing method shown in Fig. 1. The suppression layer forming step 104 is a step of forming the suppression layer 7 that suppresses the back surface 6 side of the first wafer 1 from being processed by the laser beam 31 reflected on the front surface 2 side of the first wafer 1 in the splitting start point forming step 105 by positioning the focal point 32 of the laser beam 31 inside the first wafer 1 from the back surface 6 side of the first wafer 1 and irradiating the laser beam 31 along the planned splitting line 4 of the bonded wafer 20.

[0030] In the first embodiment, the suppression layer forming step 104 is performed prior to the splitting starting point forming step 105. In the first embodiment, in the suppression layer forming step 104, the laser processing device 30 positions the focal point 32 of the laser beam 31 having a wavelength that is transparent to the substrates 3, 13 of the wafers 1, 11 at the depth position 34 stored in the storage step 102, as shown in Fig. 7, and irradiates the bonded wafer 20 with the laser beam 31 from the back surface 6 side from the laser beam irradiation unit 37 while relatively moving the bonded wafer 20 and the laser beam irradiation unit 37 in the horizontal direction along the planned split line 4.

[0031] Then, since the wavelength of the laser beam 31 is a wavelength that is transparent to the substrates 3, 13 of the wafers 1, 11, an inhibition layer 7 is formed inside the substrate 3 of the first wafer 1 along the intended division line 4, as shown in Fig. 8. The inhibition layer 7 means a region in which the density, refractive index, mechanical strength, and other physical properties are different from those of the surrounding areas, and examples of the inhibition layer 7 include a melting treatment region, a crack region, a dielectric breakdown region, a refractive index change region, and a region in which these regions are mixed.

[0032] (Splitting point formation step) Fig. 9 is a side view, partially in cross section, that typically shows the splitting start point forming step of the wafer processing method shown in Fig. 1. Fig. 10 is a cross-sectional view of the bonded wafer after the splitting start point forming step of the wafer processing method shown in Fig. 1. The splitting start point forming step 105 is a step of forming a modified layer 17, which serves as a splitting start point, inside the second wafer 11 by positioning a focal point 32 of a laser beam 31 inside the second wafer 11 from the back surface 6 side of the first wafer 1 and irradiating the laser beam 31 along the intended split line 4.

[0033] In embodiment 1, in the splitting starting point formation step 105, the laser processing device 30 positions a focal point 32 of a laser beam 31 having a wavelength that is transparent to the substrates 3, 13 of the wafers 1, 11 inside the second wafer 11, as shown in FIG. 9, and irradiates the bonded wafer 20 from the back surface 6 side with the laser beam 31 from the laser beam irradiation unit 37 while moving the bonded wafer 20 and the laser beam irradiation unit 37 relatively in the horizontal direction along the planned split line 4.

[0034] Then, since the wavelength of the laser beam 31 is a wavelength that is transparent to the substrates 3, 13 of the wafers 1, 11, a modified layer 17 is formed inside the substrate 13 of the second wafer 11 along the intended division line 4, as shown in Fig. 10. The modified layer 17, like the suppression layer 7, means a region in which the density, refractive index, mechanical strength and other physical properties are different from those of the surrounding area, and examples of the modified layer 17 include a melting treatment region, a crack region, a dielectric breakdown region, a refractive index change region, and a region in which these regions are mixed.

[0035] Furthermore, in the splitting starting point forming step 105, since the suppression layer 7 is formed at the focal point 33 of the laser beam 31 reflected by the front surface 2 of the first wafer 1, it is possible to suppress the formation of a modified layer inside the first wafer 1 by the reflected laser beam 31. Furthermore, in the splitting starting point forming step 105, since the suppression layer 7 is formed at the focal point 33 of the laser beam 31 reflected by the front surface 2 of the first wafer 1, it is possible to suppress the reflected laser beam 31 from being scattered by the suppression layer 7 and reaching the back surface 6 of the first wafer 1.

[0036] The bonded wafer 20 on which the modified layer 17 is formed is divided at the modified layer 17 and the suppression layer 7 as starting points.

[0037] In the wafer processing method according to the first embodiment described above, the suppression layer 7 is first formed on the upper first wafer 1 of the bonded wafers 20 in the suppression layer forming step 104, and then the modified layer 17 is formed on the lower second wafer 11 in the division starting point forming step 105. As a result, in the wafer processing method according to the first embodiment, when the modified layer 17 is formed on the second wafer 11 in the division starting point forming step 105, even if the laser beam 31 reflected by the surface 2 of the first wafer 1 of the bonded wafer 20 is focused inside the upper first wafer 1, the suppression layer 7 has already been formed, so that the formation of a new unintended modified layer is prevented.

[0038] Furthermore, in the wafer processing method according to embodiment 1, in the splitting starting point formation step 105, the laser beam 31 reflected from the front surface 2 is scattered by the already formed inhibition layer 7, thereby preventing the laser beam 31 reflected from the front surface 2 from reaching the back surface 6 of the upper first wafer 1, thereby contributing to reducing ablation scars on the back surface 6 of the first wafer 1.

[0039] As a result, the wafer processing method according to the first embodiment has the effect of reducing the possibility of causing product defects.

[0040] In addition, the wafer processing method according to embodiment 1 has the effect of making it possible to further reduce the possibility of causing product defects, since a bonded wafer 20 having a gap 22 between the wafers 1, 11 is more susceptible to ablation scars than a bonded wafer having no gap 22 in which the wafers 1, 11 are directly bonded.

[0041] The present invention is not limited to the above embodiment. That is, various modifications can be made without departing from the gist of the present invention. For example, in the present invention, in the preparation step 101, as shown in FIG. 11, the bonded wafer 20 is prepared by laminating a bonding layer 24 on one of the surface 2 of the first wafer 1 and the surface 12 of the second wafer 11, and then bonding the wafers 1 and 11 together via the bonding layer 24, so that the surfaces 2 and 12 of the wafers 1 and 11 are brought into close contact with each other, without forming a gap 22.

[0042] The bonding layer 24 may be a double-sided tape in which an adhesive layer is laminated on the front and back surfaces of a base layer, an oxide film, or a layer formed by applying an adhesive containing a resin or the like. The first wafer 1 and the second wafer 11 may be directly bonded together without using the bonding layer 24. FIG. 11 is a cross-sectional view that shows a schematic diagram of a modified example of the bonded wafer shown in FIG. 4. In FIG. 11, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. [Explanation of symbols]

[0043] 1. First Wafer 2 Surface (one side) 4. Planned division line 6 Back side (other side) 7 Inhibition layer 11 Second Wafer 12 Surface (one side) 16 Back side (other side) 17 Modification layer 20 Bonded wafer 22 void 31 Laser Beam 32 Focus point 34 Depth Position 35 Holding Unit 36 Holding surface 101 Preparation Steps 102 Memory Step 103 Retention Step 104 Inhibition layer formation step 105 Division origin formation step

Claims

1. A wafer processing method comprising the steps of: a preparation step of preparing a bonded wafer by bonding one surface of a first wafer and one surface of a second wafer together; a holding step of holding the other surface side of the second wafer of the bonded wafer so as to face a holding surface of a holding unit and expose the other surface side of the first wafer; a splitting starting point forming step of forming a modified layer serving as a splitting starting point within the second wafer by positioning a focusing point of a laser beam within the second wafer from the other surface side of the first wafer and irradiating the laser beam along a planned splitting line; and an inhibition layer forming step of forming an inhibition layer that inhibits the other surface side of the first wafer from being processed by the laser beam reflected by the one surface side of the first wafer in the division starting point forming step by positioning a focal point of a laser beam inside the first wafer from the other surface side of the first wafer and irradiating the laser beam along a planned division line of the bonded wafer, A wafer processing method, wherein the suppression layer forming step is performed prior to the division starting point forming step.

2. a storage step of storing in advance a depth position at which the laser beam is reflected by one surface side of the first wafer and focused inside the first wafer when a laser beam is irradiated from the other surface side of the first wafer and a focusing point of the laser beam is positioned inside the second wafer, In the suppression layer forming step, a focal point of the laser beam is positioned at the depth position stored in the storage step. The wafer processing method according to claim 1 .

3. The bonded wafer has a predetermined gap between the first wafer and the second wafer at a division line. The wafer processing method according to claim 1 or 2.

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