Peeling method

Abstract

To reduce manufacturing costs and allow wafers to be easily separated from bonded wafers. [Solution] The present invention relates to a method for peeling a silicon wafer from a bonded wafer (23) which is formed by bonding a wafer (15) having a device (14) formed on its surface (12) with a silicon wafer (11) using a light-absorbing film 19 that serves as a bonding member. The silicon wafer is provided with a light-absorbing film (19). A laser beam (LB) with a wavelength that is transparent to the silicon wafer is irradiated from the silicon wafer side, causing the light-absorbing film to absorb the light and form a processed layer (26) on the light-absorbing film. After that, the silicon wafer is peeled from the wafer starting from the processed layer.

Description

Technical Field

[0001] The present invention relates to a peeling method for peeling one wafer from a bonded wafer.

Background Art

[0002] On the surface of a wafer on which a device is formed, there may be irregularities due to circuit formation, bump placement, etc. In order to thin such a wafer having irregularities, for example, as disclosed in Patent Document 1, a process of grinding the back surface of the wafer is performed.

[0003] In Patent Document 1, a liquid resin is applied to the element surface (front surface) of the wafer to form a resin layer, and a hard plate is attached before the resin of the resin layer is completely cured. Then, the hard plate and the resin layer form a protective member that protects the surface of the wafer. After the hard plate of the protective member is held by a chuck table, processing such as grinding or polishing the back surface of the wafer becomes possible.

[0004] Further, Patent Document 1 uses a glass plate for the hard plate. After performing processing such as grinding on the wafer, a processed layer is formed in the resin layer by irradiating laser light from the hard plate (glass plate) side, and the hard plate is peeled off from the wafer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] [[ID=4In Patent Document 1, a portion of the resin layer remains attached to the hard plate after peeling. Therefore, when a glass plate is used instead of a hard plate for peeling by laser irradiation, and the glass plate is reused, a process to remove the resin from the glass plate is required, and this removal process is time-consuming. Using quartz glass for the glass plate is expensive, and in practice, it is reused to reduce manufacturing costs.

[0007] This invention has been made in view of the above, and one of its objectives is to provide a peeling method that can reduce manufacturing costs and easily peel wafers from bonded wafers. [Means for solving the problem]

[0008] A peeling method according to one aspect of the present invention is a peeling method for peeling a silicon wafer from a bonded wafer, which is formed by bonding a wafer on which a device is formed on its surface with a bonding member, wherein the silicon wafer is equipped with a light-absorbing film, and the method comprises a laser processing step of irradiating the silicon wafer with a laser beam of a wavelength that is transparent to the silicon wafer from the silicon wafer side, causing the light-absorbing film to absorb the light and form a processed layer on the light-absorbing film, and a peeling step of peeling the silicon wafer from the wafer starting from the processed layer. [Effects of the Invention]

[0009] According to the present invention, since a silicon wafer is used as the support plate for the wafer having a device, it can be manufactured at a lower cost compared to the case where a glass plate made of quartz glass is used. As a result, even if the silicon wafer peeled off from the bonded wafer is discarded without being reused, the cost required to prepare multiple silicon wafers is minimal, and the process of removing resin from the conventional glass plate can be omitted, thereby reducing the overall manufacturing cost. Furthermore, since a processed layer is formed by absorbing a laser beam into the light-absorbing film before peeling the wafer from the bonded wafer, this peeling can be easily performed. [Brief explanation of the drawing]

[0010] [Figure 1] These are explanatory diagrams of each step in the first embodiment, with Figure 1A showing the preparation step, Figure 1B showing the bonding step, Figure 1C showing the laser processing step, and Figure 1D showing the peeling step. [Figure 2] These are explanatory diagrams of each step in the second embodiment, with Figure 2A being the preparation step, Figure 2B the bonding step, Figure 2C the laser processing step, and Figure 2D the peeling step. [Figure 3] These are explanatory diagrams of each step in the second embodiment, with Figure 3A being the mounting step and Figures 3B and 3C being the splitting steps. [Figure 4] Figures 4A and 4B are explanatory diagrams of the cleaning process in the second embodiment. [Modes for carrying out the invention]

[0011] [First Embodiment] The method for manufacturing a device chip, including the peeling method of the first embodiment, will be described below with reference to the attached drawings. Figure 1A shows the preparation step, Figure 1B shows the bonding step, Figure 1C shows the laser processing step, and Figure 1D shows the peeling step. Note that the steps shown in each figure in the first embodiment are merely examples and are not limited to this configuration.

[0012] [Preparation process] The preparation step is for forming the bonded wafer 23 (see Figure 1C), and as shown in Figure 1A, a disc-shaped silicon wafer 11 and a disc-shaped wafer 15 with a device 14 formed on its surface 12 are prepared.

[0013] The silicon wafer 11 is a dummy wafer that functions as a support plate. The silicon wafer 11 has an outer shape corresponding to the wafer 15. For example, the silicon wafer 11 is formed in a disc shape similar to that of the wafer 15. For example, the silicon wafer 11 can be the same as the wafer 15 before the device 14 is formed. However, the silicon wafer 11 is not limited to this.

[0014] The silicon wafer 11 comprises one surface 17 and the other surface 18 which are perpendicular to the thickness direction, with one surface 17 facing upward in Figure 1A and the other surface 18 facing downward in Figure 1A. Each surface 17 and 18 is formed by parallel and flat surfaces. The silicon wafer 11 has a light-absorbing film 19 on one surface 17.

[0015] The light-absorbing film 19 may be one of the following: a silicon oxide film (SiO2 film), a silicon carbide film (SiC film), a silicon nitride film (SiN film), or a nitrogen-doped silicon carbide film (SiCN film). The light-absorbing film 19 absorbs the laser beam LB (see Figure 1C) irradiated during the laser processing process. The top surface of the light-absorbing film 19 may be flattened by methods such as CMP (Chemical Mechanical Polishing), and flattening the light-absorbing film 19 can improve the flatness (TTV: Total Thickness Valuation) of the wafer 15 after grinding.

[0016] The wafer 15 is positioned with its front surface 12 facing upwards in Figure 1A and its back surface 13 facing downwards in Figure 1A. Multiple intersecting division lines 21 are set on the front surface 12 of the wafer 15, and devices 14 are formed in each region partitioned by the division lines 21 on the front surface 12.

[0017] Each of the multiple devices 14 includes, for example, elements for constituting an IC, semiconductor memory, or image sensor. Furthermore, for example, grid-like division lines 21 extend between the multiple devices 14, and by cutting the wafer 15 along the division lines 21, device chips, each containing a device 14, can be manufactured. Since the devices 14 are formed on the surface 12 of the wafer 15, the surface 12 is also the surface of the devices 14. Therefore, in the following, the surface 12 of the wafer 15 may be referred to as "the surface of the device 14."

[0018] In the preparation process, as preparation for the bonding process by plasma-activated bonding, preparation is carried out to enable bonding of the light absorption film 19 of the silicon wafer 11 to the surface of the device 14 on the wafer 15. In the preparation process, for example, the light absorption film 19 on one surface 17 side of the silicon wafer 11 is irradiated with plasma of a rare gas generated using a rare gas and high-frequency power to activate the surface of the light absorption film 19. Also, the surface of the device 14 on the wafer 15 is irradiated with plasma of a rare gas to activate the surface of an insulating film (not shown) on the surface of the device 14. As a result, in the bonding process, the light absorption film 19 of the silicon wafer 11 and the insulating film of the wafer 15 can function as a bonding member.

[0019] [Bonding Process] After the preparation process is completed, as shown in FIG. 1B, the bonding process is carried out by plasma-activated bonding. In the bonding process, after the light absorption film 19 of the silicon wafer 11 is faced to the surface 12 of the wafer 15, the light absorption film 19 is pressed against the surface of the device 14 on the wafer 15. As a result, the light absorption film 19 functioning as a bonding member and the surface (insulating film surface) of the device 14 are joined, and a bonded wafer 23 in which the wafer 15 and the silicon wafer 11 are bonded is formed. In the bonded wafer 23, the wafer 15 is supported on one surface 17 side of the silicon wafer 11 via the light absorption film 19.

[0020] After the bonding process is completed, although not shown in the figure, for example, a processing step of grinding the back surface 13 of the wafer 15 with a grinding wheel to a predetermined thickness or polishing the back surface 13 is performed. In this step, the other surface 18 of the silicon wafer 11 in the bonded wafer 23 is held by a chuck table or the like.

[0021] <00...​​After the bonding process and the processing process are completed, as shown in FIG. 1C, a laser processing process is performed. In the laser processing process, a laser beam LB having a wavelength that is transmissive to the silicon wafer 11 is irradiated from the laser irradiation unit 25 onto the silicon wafer 11 side. The irradiated laser beam LB is condensed into the light absorption film 19 by a condenser lens (not shown) and absorbed by the light absorption film 19, so that a part of the light absorption film 19 is sublimated and ablated, and a processing layer 26 is formed on the light absorption film 19. At this time, a table (not shown) that holds the bonded wafer 23 is relatively moved in a zigzag manner along the horizontal direction with respect to the laser irradiation unit 25, and the laser beam LB is irradiated over the entire area of the light absorption film 19. By forming the processing layer 26 on the light absorption film 19, the bonding strength between the wafer 15 and the silicon wafer 11 is weakened.

[0022] The laser beam LB used in the laser processing process is set such that the wavelength λ is 2.7 μm or more and 2.9 μm or less, and more preferably, the wavelength λ is set to 2.8 μm. By setting the wavelength λ to such a value, while allowing the transmission of the laser beam LB in the silicon wafer 11, the energy of the laser beam LB can be efficiently absorbed by the light absorption film 19.

[0023] Here, Table 1 below shows various conditions of laser irradiation and the film thickness of the light absorption film 19 when the light absorption film 19 is made of SiO2, SiC, SiN, or SiCN.

[0024]

Table 1

[0025] By forming the light absorption film 19 to the film thickness in Table 1, it becomes possible to form the processing layer 26 while avoiding damage to the device 14 of the wafer 15. Among the three types of light absorption films 19 in Table 1, SiCN can form the processing layer 26 with the lowest laser energy, and therefore, the film thickness can be made the thinnest. When the light-absorbing film 19 is SiCN, the irradiation with the laser beam LB may be performed in two steps. For example, in the first step, the SiCN is irradiated with a laser energy of 30-50 μJ to carbonize the SiCN, and then in the second step, the SiCN is irradiated with a laser energy of 206 μJ to generate carbon (C) from the SiCN, followed by the generation of nitrogen (N2). Furthermore, the processing time can be shortened by setting the beam diameter (spot diameter) to 10 μm in the first step and to 30 μm in the second step.

[0026] [Peeling process] After the laser processing is completed, a delamination process is performed as shown in Figure 1D. In the delamination process, the other side 18 of the silicon wafer 11 is held by an adsorption pad 29 connected to a suction source 27, which generates negative pressure on the holding surface 28. Then, the adsorption pad 29 is raised via the lifting mechanism 32, applying a force to separate the silicon wafer 11 from the wafer 15. As a result, the silicon wafer 11 is separated from the wafer 15 in the bonded wafer 23, starting from the processed layer 26. When raising the adsorption pad 29, compressed air may be sprayed from the outer edge of the wafer 15 towards the center by an air nozzle 31.

[0027] The delamination method of the first embodiment is carried out by a laser processing step and a delamination step. As for the manufacturing method of the device chip of the first embodiment, after the delamination step is completed, although not particularly limited, examples include performing steps similar to the mounting step, splitting step, and cleaning step of the second embodiment described later.

[0028] According to the first embodiment described above, since the support plate in the bonded wafer 23 is a silicon wafer 11, when a glass plate made of quartz glass is used, the process is cheaper compared to the process of removing resin from the glass plate in order to reuse the glass plate. As a result, by discarding the silicon wafer 11 that has been peeled off from the bonded wafer 23 without reusing it, the increase in the cost required for the silicon wafer 11 can be suppressed by reducing the number of man-hours.

[0029] Furthermore, since a processed layer 26 can be formed on the light-absorbing film 19 by irradiating it with a laser beam LB that penetrates the silicon wafer 11, the silicon wafer 11 can be easily peeled off in the peeling process.

[0030] [Second Embodiment] Next, a second embodiment of the present invention will be described. In the following description, the same reference numerals may be used for components that are the same as or equivalent to those in the first embodiment, and their descriptions may be omitted or simplified.

[0031] A second embodiment of the present invention will be described with reference to Figures 2 to 4. Figures 2 to 4 are explanatory diagrams of the manufacturing method of the device chip according to the second embodiment. Figure 2A shows the preparation step, Figure 2B shows the bonding step, Figure 2C shows the laser processing step, and Figure 2D shows the peeling step. In the second embodiment, the bonding member is changed to a liquid resin 35 (see Figure 2B) compared to the first embodiment. It should be noted that the steps shown in each figure in the second embodiment are merely examples and the invention is not limited to this configuration.

[0032] [Preparation process] The preparation step is for forming the bonded wafer 23 (see Figure 2B), and, as in the first embodiment, a silicon wafer 11 and a disc-shaped wafer 15 on which the device 14 is formed are prepared (see Figure 2A).

[0033] [Bonding process] After the preparation process is complete, the bonding process is carried out as shown in Figure 2B. In the bonding process, a liquid resin that hardens when exposed to external stimuli such as ultraviolet light or heat is applied to the surface 12 of the wafer 15.

[0034] In the bonding process, the light-absorbing film 19 of the silicon wafer 11 is brought into contact with the liquid resin applied to the surface 12 of the wafer 15, and the light-absorbing film 19 is pressed against the upper surface of the liquid resin. Then, an external stimulus such as ultraviolet light or heat (in this embodiment, ultraviolet light) is applied to the liquid resin to cure it. As a result, the cured resin 35 functions as a bonding member, forming a bonded wafer 23 in which the wafer 15 and the silicon wafer 11 are bonded together by the resin 35. In the bonded wafer 23, the wafer 15 is supported on one side 17 of the silicon wafer 11 via the resin 35. After the bonding process is completed, a processing process is performed in the same manner as in the first embodiment.

[0035] [Laser processing process] After the bonding and processing steps are completed, a laser processing step is performed as shown in Figure 2C. In the laser processing step, similar to the first embodiment, a laser beam LB with a wavelength that is transparent to the silicon wafer 11 is irradiated from the silicon wafer 11 side, and the laser beam LB is absorbed by the light absorption film 19 to form a processed layer 26.

[0036] [Peeling process] After the laser processing step is completed, a peeling step is performed as shown in Figure 2D. In the peeling step, the silicon wafer 11 is peeled off from the wafer 15, starting from the processed layer 26, similar to the first embodiment. After the silicon wafer 11 is peeled off, the surface 12 of the wafer 15 will be laminated with the cured resin 35 and a portion of the light-absorbing film 19. The peeling method of the second embodiment is performed by the laser processing step and peeling step described above.

[0037] [Mounting process] Figure 3A is an explanatory diagram of the mounting process. After the peeling process is completed, the mounting process is performed as shown in Figure 3A. In the mounting process, the back surface 13 of the wafer 15 from which the silicon wafer 11 has been peeled is attached to the upper surface of the dicing tape 37, so that the wafer 15 is held in place by the dicing tape 37. Although not shown, the outer circumference of the dicing tape 37 may be supported by a ring-shaped frame that is concentric with the wafer 15, and the frame, dicing tape 37, and wafer 15 may be integrated to form a workset.

[0038] [Dividing process] Figures 3B and 3C are explanatory diagrams of the splitting process. After the mounting process is completed, the splitting process is carried out as shown in Figure 3B. The splitting process manufactures individual device chips 42 (see Figure 3C) by splitting the wafer 15 along the planned splitting lines 21 of the wafer 15. In the splitting process, the wafer 15 is held in the chuck table of the cutting machine (neither shown) via the dicing tape 37, and then the wafer 15 is cut along the planned splitting lines 21 by a rotating cutting blade 38. As a result, as shown in Figure 3C, cutting grooves 41 are formed in the resin 35, along the entire thickness direction of the wafer 15, and midway through the thickness of the dicing tape 37, thereby splitting the wafer 15 and forming device chips 42, each containing one device 14.

[0039] [Washing process] Figures 4A and 4B are explanatory diagrams of the cleaning process. After the splitting process is completed, the cleaning process is carried out as shown in Figure 4A. In the cleaning process, hot water is supplied from a hot water supply nozzle 44 to the surface 12 of the wafer 15 that has been split by forming the cutting grooves 41. This supply of hot water reduces the adhesion of the resin 35 to the wafer 15, causing the resin 35 to be removed from the surface 12, and the light-absorbing film 19 laminated on the resin 35 is also removed. As a result, the surface 12 of the wafer 15 is cleaned, as shown in Figure 4B.

[0040] In the second embodiment, as in the first embodiment, a silicon wafer 11 can be used as the support plate, and the silicon wafer 11 can be easily peeled off by irradiating the light-absorbing film 19 with a laser beam LB that penetrates the silicon wafer 11.

[0041] Furthermore, the present invention is not limited to the embodiments described above, and can be implemented with various modifications. In the embodiments described above, the size, shape, etc., shown in the accompanying drawings are not limited thereto, and can be appropriately modified within the scope that allows the present invention to exert its effects. In addition, the present invention can be implemented with appropriate modifications as long as it does not deviate from the scope of its objectives.

[0042] In the second embodiment described above, the wafer 15 splitting process can be modified in various ways, such as splitting the wafer 15 using the modified layer formed inside the wafer 15 by laser irradiation as the splitting starting point, as long as the device chip 42 can be formed. [Industrial applicability]

[0043] As described above, the present invention has the effect of reducing manufacturing costs when performing the process of peeling wafers from bonded wafers and facilitating such peeling. [Explanation of Symbols]

[0044] 11: Silicon wafer 12: Surface 14: Device 15: Wafer 19: Light-absorbing film 23: Laminated wafer 26: Processing layer LB: Laser beam

Claims

1. A method for peeling a silicon wafer from a bonded wafer, which is formed by bonding a wafer on which a device is formed on the surface with a silicon wafer using a bonding member, The silicon wafer is equipped with a light-absorbing film, A laser processing step involves irradiating the silicon wafer with a laser beam of a wavelength that is transparent to the silicon wafer from the silicon wafer side, causing the light to be absorbed by the light-absorbing film, and forming a processed layer on the light-absorbing film. A peeling method comprising: a peeling step of peeling the silicon wafer from the wafer starting from the processed layer.

2. The peeling method according to claim 1, wherein the bonding member is the light-absorbing film.

3. The peeling method according to claim 1, wherein the bonding member is a liquid resin.

4. The stripping method according to claim 1, wherein the laser beam used in the laser processing step has a wavelength λ of 2.7 μm or more and 2.9 μm or less.

5. The light-absorbing film is made of SiO ２ The peeling method according to claim 1, wherein the material is one of SiC, SiCN, or SiN.

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