Method for reusing support wafer

Abstract

To reduce processing costs and make a support wafer reusable.SOLUTION: A method for reusing a support substrate 40, which is a support wafer, includes peeling the support substrate 40 from a chip or a wafer attached to the support substrate 40 with an adhesive 41, and then removing the adhesive 41 from the support substrate 40. This reuse method also includes an adhesive removal step of applying a laser beam L to the adhesive 41 of the support substrate 40 that remains due to peeling of the chip or wafer from the adhesive 41, thereby removing the adhesive 41.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for reusing a support wafer. [Background technology]

[0002] A known method for manufacturing a stacked device involves bonding a temporary wafer, on which semiconductor device chips selected as non-defective products are bonded, to a semiconductor wafer to create a bonded wafer, and then peeling the support wafer that constitutes the temporary wafer from the bonded wafer (see Patent Documents 1 and 2). By creating a bonded wafer, the semiconductor devices on the temporary wafer and the semiconductor wafer are stacked in the thickness direction of the wafer.

[0003] The adhesive used to bond the semiconductor device chips remains on the support wafer that has been peeled off from the bonded wafer. In order to reuse the support wafer to create a new bonded wafer, it is desirable to remove the adhesive remaining on the support wafer. To remove the adhesive remaining on the support wafer, an organic solvent can be used, for example, as described in Patent Document 3. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-134231 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-233049 [Patent Document 3] Japanese Patent Application Publication No. 09-069509 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the use of organic solvents results in a problem of high wastewater treatment costs. The present invention has been made in view of the above circumstances, and aims to provide a technology that reduces treatment costs and enables the support wafer to be reused. [Means for solving the problem]

[0006] A method for reusing a support wafer according to one embodiment of the present invention is a method for reusing a support wafer in which the support wafer is peeled off from a chip or wafer attached to the support wafer with an adhesive, and then the adhesive is removed from the support wafer, and includes an adhesive removal step in which a laser beam is irradiated onto the adhesive on the support wafer that remains after the chip or wafer has been peeled off from the adhesive, thereby removing the adhesive. [Effects of the Invention]

[0007] According to the present invention, a technique can be provided that reduces processing costs and enables the support wafer to be reused. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic perspective view of a first semiconductor wafer and a second semiconductor wafer. [Figure 2] 1 is an explanatory diagram of a bonding process, showing a state at the start of the bonding process. [Figure 3] 10 is an explanatory diagram of the bonding process, showing the state when the bonding process is completed. FIG. [Figure 4] 10A to 10C are explanatory views of a support substrate peeling step. [Figure 5] FIG. [Figure 6] FIG. 10 is another explanatory view of the adhesive removing step. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. First, a first semiconductor wafer and a second semiconductor wafer used in manufacturing a stacked device will be described with reference to Fig. 1. Fig. 1 is a schematic perspective view of the first semiconductor wafer and the second semiconductor wafer.

[0010] 1, the first semiconductor wafer 10 includes a disk-shaped first base 11 having a front surface 11a and a back surface 11b, and a plurality of first planned dividing lines (streets) 12 that intersect in a grid pattern are set on the front surface 11a of the first base 11. The first semiconductor wafer 10 further includes a plurality of first semiconductor devices 13, such as LSIs, and each first semiconductor device 13 is disposed in a respective region of the front surface 11a that is partitioned by the first planned dividing lines 12.

[0011] The second semiconductor wafer 20 has a similar external configuration to the first semiconductor wafer 10, although the size, material, internal structure, etc. of the devices are different. Therefore, the explanation of the configuration of the second semiconductor wafer 20 will be omitted by changing the name of each component of the first semiconductor wafer 10 from "first" to "second" and changing the last two digits of the reference numerals from "1" to "2" and listing them together in parentheses in Figure 1.

[0012] Next, a method for manufacturing a stacked device according to this embodiment will be described with reference to Fig. 2 to Fig. 4. Fig. 2 and Fig. 3 are explanatory views of the bonding step. Fig. 2 shows the state at the start of the bonding step, and Fig. 3 shows the state at the completion of the bonding step. Fig. 4 is an explanatory view of the support substrate peeling step.

[0013] First, the first semiconductor wafer 10 is cut along the first planned dividing lines 12 (cutting step). The cutting step is performed using, for example, a dicer. As a result, the first semiconductor wafer 10 is divided into chips, and a plurality of first device chips 15, each including a first semiconductor device 13, are formed.

[0014] After the first device chips 15 are formed, a temporary wafer 44 is subsequently fabricated (a temporary wafer fabrication process). In the temporary wafer fabrication process, a support substrate 40 made of, for example, sapphire, quartz glass, silicon, or SiC is first prepared. The support substrate 40 is an example of a supporting wafer that constitutes a temporary wafer. Next, an adhesive 41 is applied to the support substrate 40. The adhesive 41 is an adhesive used for temporary bonding. It is sufficient that the adhesive 41 adheres the support substrate 40 in a releasable manner in a subsequent process, and the type and curing mechanism are not important. The adhesive may be, for example, a polymer resin such as an acrylic resin, an epoxy resin, or a silicone resin, or may be an adhesive with any curing mechanism, such as an ultraviolet-curing type, a thermosetting type, or a volatile curing type. Then, the surface 15a of the first device chip 15, on which the first semiconductor devices 13 are exposed, is pressed against the adhesive 41 on the support substrate 40 to bond the first device chip 15 to the support substrate 40, completing the fabrication of the temporary wafer 44 shown in FIG. 2.

[0015] Alternatively, the first semiconductor wafer 10 may be thinned by forming a cutting groove along the first planned dividing line 12 in the first semiconductor wafer 10 that is not completely cut with a cutting blade, and then bonding the first semiconductor wafer 10 with the cutting groove formed therein to the support substrate 40, and then grinding the back surface 15b of the first semiconductor wafer 10, or by thinning the wafer to expose the cutting groove on the surface to be ground, a first device chip 15 may be formed to create a temporary wafer 44.

[0016] 2, in the temporary wafer production process, the multiple first device chips 15 are bonded to the support substrate 40 so that the position of each first device chip 15 on the support substrate 40 corresponds to the position of each second semiconductor device 23 on the second semiconductor wafer 20. The electrodes 24 shown in FIG. 2 are electrodes formed on the second semiconductor devices 23, and will be connected to electrodes (not shown) of the first semiconductor devices 13 in a process described later.

[0017] Once the temporary wafer 44 is created, it is bonded to the second semiconductor wafer 20 to create the bonded wafer 50 shown in FIG. 3 (bonded wafer creation process). In the bonded wafer creation process, first, an adhesive 46 is applied to the front surface 21a of the second semiconductor wafer 20 on which the second semiconductor devices 23 are formed. The adhesive 46 is a different adhesive from the adhesive 41 and has adhesive properties that ensure a bonded state even in subsequent processes and during use as a product. Next, in a vacuum, the back surface 15b of the first device chip 15 on the temporary wafer 44 is brought into contact with the front surface 21a (adhesive 46 side) of the second semiconductor wafer 20. Thereafter, the temporary wafer 44 and the second semiconductor wafer 20 are aligned to position the first device chip 15 and the second semiconductor devices 23 in a vertically aligned and corresponding state. Finally, the temporary wafer 44 and the second semiconductor wafer 20 are laminated together via an adhesive 46 to form a bonded wafer 50 shown in FIG.

[0018] Once the bonded wafer 50 is formed, the support substrate 40 is peeled from the bonded wafer 50 as shown in FIG. 4 (support substrate peeling process). In the support substrate peeling process, the adhesive 41 is subjected to a predetermined treatment to lose or reduce its adhesive strength, and then the support substrate 40 is peeled from the bonded wafer 50. The predetermined treatment is not particularly limited, but may be, for example, ultraviolet light irradiation. Specifically, first, for example, ultraviolet light from an ultraviolet light irradiation unit (not shown) is irradiated onto the adhesive 41 to lose or reduce the adhesive strength of the adhesive 41. Next, with the second semiconductor wafer 20 constituting the bonded wafer 50 held by a holding mechanism (not shown), the support substrate 40 constituting the bonded wafer 50 is suction-held by a holding table 60, and further, the support substrate 40 is lifted by a lifting mechanism 90. As a result, the bonded wafer 50 is separated at the adhesive 41, whose adhesive strength has been lost or reduced, and the support substrate 40 is peeled from the bonded wafer 50 as shown in FIG. 4.

[0019] In the above example, ultraviolet light is applied during peeling, but a laser beam may be applied to burn off the adhesive 41 and peel off the support substrate 40.

[0020] 4 is a suction check table that generates negative pressure on a holding surface 62, which is the surface of a porous plate 61, when a suction source 70 is operated. The holding table 60 is configured to be rotatable around the Z axis, movable in horizontal directions (e.g., X-axis direction, Y-axis direction), and movable in vertical directions (Z-axis direction) by a spindle 63, a horizontal movement mechanism 80, and an elevation mechanism 90, respectively.

[0021] After the support substrate 40 is peeled off, the exposed first device chips 15 are coated with resin (resin coating process). In the resin coating process, the spaces between the first device chips 15 and the surfaces 15a of the first device chips 15 are coated with resin such as epoxy resin, and then the surface of the resin is ground with a grinding device. As a result, all of the first device chips 15 are coated with a flattened upper surface of the resin.

[0022] Once the first device chip 15 is covered with resin, the electrodes of the first device chip 15 are connected to the electrodes 24 of the second semiconductor device 23 (electrode connecting process). In the electrode connecting process, for example, through holes are formed from the upper surface of the resin to the electrodes of the first device chip 15, and through holes are formed from the upper surface of the resin to the electrodes 24 of the second semiconductor device 23. Thereafter, copper is filled into each through hole from the upper surface side of the resin so that copper that overflows from each through hole comes into contact with the upper surface of the resin, thereby forming through electrodes that electrically connect the first device chip 15 and the second semiconductor device 23.

[0023] After the through electrodes are formed, the back surface 21b of the second semiconductor wafer 20 is ground and polished, and then the second semiconductor wafer 20 is divided into individual laminated devices (dividing step). The dividing step is performed, for example, with a dicer. In the dividing step, the second semiconductor wafer 20 is cut along the second planned dividing lines 22 to divide it into individual laminated devices, thereby obtaining a plurality of laminated devices. Each laminated device includes a first device chip 15 and a second semiconductor device 23 electrically connected by a through electrode.

[0024] A method for reusing a support wafer according to this embodiment will be described with reference to FIG. 5. FIG. 5 is an explanatory diagram of an adhesive removal step. As described above, in the method for manufacturing a laminated device, the support substrate 40, which is the support wafer, is peeled off from the bonded wafer 50. More specifically, the support substrate 40, which is the support wafer, is peeled off from the first device chip 15 or the second semiconductor wafer 20, which is attached to the support substrate 40 by an adhesive 41 in the bonded wafer 50. At this time, as shown in FIG. 4, some or all of the adhesive 41 remains on the support substrate 40. In order to form a new bonded wafer 50 using the support substrate 40, it is desirable to remove the adhesive 41 remaining on the support substrate 40.

[0025] In the method for reusing a support wafer according to this embodiment, the adhesive 41 remaining on the support substrate 40 after peeling is removed by irradiating the adhesive 41 with a laser beam (adhesive removing step). In the adhesive removing step, the adhesive 41 is removed by scanning the entire lower surface of the support substrate 40 while the laser beam is focused at a position slightly defocused from the lower surface of the support substrate 40 where the adhesive 41 remains. Specifically, first, as shown in FIG. 5 , the support substrate 40 held on the holding table 60 and peeled from the bonded wafer 50 is positioned above the laser unit 30 using the horizontal movement mechanism 80 and the lifting mechanism 90. Thereafter, the laser beam L focused by the condenser 31 of the laser unit 30 shown in FIG. 5 is focused on the adhesive 41 remaining on the lower surface of the support substrate 40, and the laser spot formed by the laser beam L is moved relative to the support substrate 40 to scan the lower surface of the support substrate 40 with the laser beam L. As a result, the adhesive 41 irradiated with the laser beam L is removed from the lower surface of the support substrate 40, and therefore the adhesive 41 is removed from the entire lower surface of the support substrate 40.

[0026] 5, which operates as a laser processing device as described above, the laser unit 30 preferably pulses a short-wavelength laser beam, for example, emitting UV light of 266 nm or less. Photoablation using UV light can remove the adhesive 41 while minimizing the heat-affected zone (HAZ), which is subject to thermal influence. Therefore, the adhesive 41 remaining on the underside of the adhesive 41 can be accurately removed while minimizing damage to the support substrate 40.

[0027] 5 desirably operates under the following laser processing conditions: The reference surface for the defocus amount is the lower surface of the support substrate 40. Wavelength: 257.5nm Output: 0.5~1.5W Repetition frequency: 100-200kHz Laser overlap: 50% or more Laser spot size: 20~60μm Defocus amount: -2mm That is, the focal point of the laser beam L is positioned 2 mm below the lower surface of the support substrate 40 .

[0028] The relative movement of the laser beam L performed by the laser processing device may be performed by a horizontal movement mechanism 80 moving the support substrate 40, or by a laser scanner (polygon mirror, galvanometer scanner) (not shown) placed on the optical path of the laser beam L deflecting the laser beam.

[0029] On the underside of the support substrate 40 scanned with the laser beam L, some of the adhesive 41 may be altered by absorbing the energy of the laser beam L, specifically, some of the adhesive 41 may be carbonized. For this reason, the adhesive removal step may further include a step of removing the altered material from the underside of the support substrate 40 after irradiating with the laser beam L. Specifically, it is desirable to perform, for example, two-fluid cleaning, CMP polishing, or wet etching following the irradiation with the laser beam.

[0030] The support substrate 40 from which the adhesive 41 has been removed in the adhesive removing step is then used again to create temporary wafers and bonded wafers, and is repeatedly used in the manufacture of laminated devices.

[0031] As described above, according to the method for reusing a support wafer according to this embodiment, the remaining adhesive 41 on the support substrate 40 can be removed by using a laser beam without using an organic solvent. This makes it possible to omit the waste liquid treatment that is required when using an organic solvent, and the support wafer can be regenerated and reused while reducing processing costs.

[0032] Furthermore, according to the method for reusing a support wafer according to this embodiment, by using UV light, the adhesive 41 can be removed while minimizing the heat-affected zone (HAZ). This makes it possible to precisely control the removal area and reliably remove the adhesive 41 from the support substrate 40. Furthermore, it is possible to suppress adverse effects on the support substrate 40, allowing the support substrate 40 to be reused for a long period of time.

[0033] The embodiments of the present invention are not limited to the above-described embodiments, and may be variously modified, substituted, or altered without departing from the spirit and scope of the technical idea of ​​the present invention. Furthermore, if the technical idea of ​​the present invention can be realized in a different way due to technological advances or other derived technologies, it may be implemented using that method. Therefore, the claims cover all embodiments that may fall within the scope of the technical idea of ​​the present invention.

[0034] In the above-described embodiment, an example has been shown in which the adhesive 41 is removed by irradiating the support substrate 40 with the laser beam L from vertically below while the surface on which the adhesive 41 is applied faces vertically downward, but the laser processing apparatus may have a laser unit 130 above the support substrate 40, and a holding table 160, a suction source 170, an X-axis movement mechanism 180, and a Y-axis movement mechanism 190 below the support substrate 40, as shown in Fig. 6. Furthermore, the laser processing apparatus shown in Fig. 6 may be used to remove the adhesive 41 by irradiating the support substrate 40 with the laser beam L from vertically above while the surface on which the adhesive 41 is applied faces vertically upward. [Industrial Applicability]

[0035] As described above, the method for reusing a support wafer of the present invention makes it possible to regenerate a support wafer by removing the adhesive without using an organic solvent, and makes the regenerated support wafer reusable, which is useful in the manufacture of stacked devices in which support wafers are used. [Explanation of symbols]

[0036] 10: first semiconductor wafer, 11: first base, 11a, 15a, 21a: front surface, 11b, 15b, 21b: back surface, 12: first planned division line, 13: first semiconductor device, 15: first device chip, 20: second semiconductor wafer, 22: second planned division line, 23: second semiconductor device, 24: electrode, 30, 130: laser unit, 31: condenser, 40: support substrate, 41: adhesive, 44: temporary wafer, 46: permanent adhesive, 50: bonded wafer, 60, 160: holding table, 61: porous plate, 62: holding surface, 63: spindle, 70, 170: suction source, 80, 180: horizontal movement mechanism, 90, 190: lifting mechanism, L: laser beam

Claims

[Claim 1] A method for reusing a support wafer, comprising: peeling the support wafer from a chip or wafer attached to the support wafer by an adhesive, and then removing the adhesive from the support wafer, the method comprising: an adhesive removal step of irradiating the adhesive of the support wafer remaining after peeling the chip or the wafer from the adhesive with a laser beam to remove the adhesive; A method for reusing a support wafer, comprising:

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