Method of manufacturing wafer

Abstract

To efficiently perform chamfering in manufacturing a wafer.SOLUTION: A method of manufacturing a wafer for manufacturing from a first wafer a second wafer which is smaller than the first wafer includes: a first protective film forming step S10 of forming a first protective film on a first face of the first wafer; a first protective film removing step S20 of removing the first protective film along a contour of the second wafer; a segmentation step S30 of segmenting the second wafer along the contour by means of plasma etching on a first condition from the side of the first face using the first protective film as a mask; and a chamfering step S40 of chamfering an outer edge of the second wafer by means of plasma etching on a second condition which is different from the first condition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, in order to improve productivity, the production of device chips using large wafers has become mainstream. On the other hand, methods for manufacturing smaller wafers from such wafers have also been proposed. Such techniques are described, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-091779 [Patent Document 2] International Publication No. 2020 / 081644 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-093865 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 describes cutting a plurality of small-diameter wafers from a wafer and chamfering the outer peripheries of the cut small-diameter wafers. Because the work of chamfering the outer peripheries of each cut wafer takes time, it is desirable to perform the chamfering efficiently to improve productivity.

[0005] The present invention has been made in view of the above points, and aims to provide a technique for efficiently performing chamfering in wafer manufacturing. [Means for solving the problem]

[0006] One aspect of the present invention provides a wafer manufacturing method for manufacturing a second wafer having a smaller diameter than a first wafer from a first wafer, the method comprising: a first protective film forming step for forming a first protective film on a first surface of the first wafer; a first protective film removing step for removing the first protective film along the contour of the second wafer; a cutting step for cutting the second wafer along the contour from the first surface side by plasma etching under first conditions using the first protective film as a mask; and a chamfering step for chamfering the outer edge of the second wafer by plasma etching under second conditions different from the first conditions. [Effects of the Invention]

[0007] According to the present invention, chamfering can be performed efficiently in wafer manufacturing. [Brief explanation of the drawings]

[0008] [Figure 1] 3 is a flowchart of a wafer manufacturing method according to the first embodiment. [Figure 2] 10A to 10C are diagrams illustrating a first protective film forming step. [Figure 3] 10A to 10C are diagrams illustrating a first protective film removing step. [Figure 4] FIG. 10 is another view illustrating the first protective film removing step. [Figure 5] FIG. 10 is a diagram illustrating a cutting step. [Figure 6] FIG. 10 is another diagram illustrating the cutting step. [Figure 7] 1 is a flowchart of the Bosch process. [Figure 8] FIG. 10 is a diagram illustrating a chamfering step. [Figure 9] 10 is a flowchart of a wafer manufacturing method according to a second embodiment. [Figure 10] 10 is a flowchart of a wafer manufacturing method according to a third embodiment. [Figure 11] 10 is a flowchart of a wafer manufacturing method according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] (First embodiment) 1 is a flowchart of a wafer manufacturing method according to this embodiment. The wafer manufacturing method according to this embodiment will be described below with reference to the accompanying drawings. The wafer manufacturing method according to this embodiment is a method for manufacturing a smaller wafer (second wafer) from an original wafer (first wafer).

[0010] In the wafer manufacturing method according to this embodiment, it is sufficient that one or more small wafers are manufactured from the original wafer. For example, one 6-inch wafer may be manufactured from an 8-inch wafer, or multiple 3-inch, 1-inch, 0.5-inch, or other wafers may be manufactured from an 8-inch wafer. Furthermore, the size of the wafers manufactured from the original wafer is not limited to one type. For example, a 6-inch wafer and a 3-inch wafer may be manufactured from a 12-inch wafer. Furthermore, the shapes of the original wafer and the wafers to be cut out are not limited to circular, and may be rectangular or polygonal, and any shape is acceptable.

[0011] The wafer manufacturing method according to this embodiment includes four steps (a first protective film forming step, a first protective film removing step, a cutting step, and a chamfering step) as shown in Fig. 1. Each step will be specifically described below.

[0012] 2 is a diagram illustrating the first protective film forming step. When the manufacturing process using the manufacturing method shown in FIG. 1 is started, the first protective film forming step is performed first (step S10). The first protective film forming step is performed by, for example, a protective film forming apparatus 10.

[0013] In the first protective film forming step, the protective film forming apparatus 10 forms a protective film 4 on the first side 2 of the wafer 1. More specifically, the protective film forming apparatus 10 suction-holds the second side 3 of the wafer 1, which has been carried in as part of a frame unit, on a table (not shown) of the protective film forming apparatus 10 via tape T. The frame unit is formed by adhering the wafer 1 to tape T that covers the opening of an annular frame F. The tape T may be a tape consisting of an adhesive layer and a base layer, or a tape without an adhesive layer that is made of a thermoplastic resin base layer. The protective film forming apparatus 10 then forms a protective film 4 on the first side 2 of the wafer 1, opposite the second side 3 that has been suction-held.

[0014] Wafer 1 is a first wafer. Wafer 1 is not particularly limited, but may be, for example, a disk-shaped silicon wafer that is ground to a predetermined thickness and the surface on which devices are manufactured is polished to a mirror finish. However, the material, shape, processing state, size, etc. of wafer 1 are not limited to this example and are not particularly limited. First surface 2 of wafer 1 is, for example, the surface on which devices are manufactured and is a mirror-finished surface. Second surface 3 of wafer 1 is the surface opposite to first surface 2.

[0015] The protective film 4 is a film that protects the wafer 1 from plasma etching, and may be any film that is resistant to plasma etching. The protective film 4 is, for example, a negative photoresist designed to withstand plasma etching under predetermined conditions, which will be described later. In this case, the protective film 4 may be formed by exposing a negative photoresist that has been uniformly applied to the first surface 2 using a spin coater or the like. The protective film 4 may also be formed, for example, by spraying a liquid resin onto the first surface 2, or by placing a pre-formed sheet on the first surface 2. If the liquid resin is water-soluble, it can be washed with water without using chemicals, which simplifies the washing equipment and is therefore preferable.

[0016] 3 and 4 are diagrams illustrating the first protective film removing step. After the protective film 4 is formed, the first protective film removing step is then performed (step S20). The first protective film removing step is performed by, for example, a laser processing device 20.

[0017] In the first protective film removal step, the laser processing apparatus 20 removes the protective film 4 formed on the wafer 1 along the contour of a wafer 5 having a smaller diameter than the wafer 1 to be cut out from the wafer 1. More specifically, as shown in FIG. 3 , the laser processing apparatus 20 suction-holds the second surface 3 of the wafer 1 on a table (not shown) via tape T, and focuses the laser unit 21 so that the focal point of the laser beam LB is located on the protective film 4. At this time, as shown in FIG. 4 , the laser unit 21 is moved relative to the wafer 1 so that the focal point of the laser beam LB moves along the planned cutting line 6 on the protective film 4 that corresponds to the contour of the wafer 5. As a result, the protective film 4 is removed along the planned cutting line 6 irradiated by the laser beam LB.

[0018] 5 and 6 are diagrams for explaining the cutting step. Fig. 7 is a flowchart of the Bosch process. After the protective film 4 is removed along the cutting line 6, the cutting step is then performed (step S30). The cutting step is performed by, for example, a plasma generating device 30.

[0019] In the cutting step, the plasma generating device 30 cuts out the wafer 5 along its contour from the first surface 2 side by plasma etching under a first condition using the protective film 4 as a mask. More specifically, the frame unit is first transported into the chamber 31 of the plasma generating device 30 and placed on the table 32 in the chamber 31 with the tape T side facing the table 32. Then, the plasma generating device 30 supplies a predetermined gas into the chamber 31 from the gas head 39, while generating a plasma discharge between the gas head 39 and an electrode 33 installed inside the table 32 using power from the high-frequency power supply 34. This converts the gas in the chamber 31 into plasma, and the plasma PA plasma-etches the wafer 5 from the first surface 2 side. The plasma etching removes the contour portion of the wafer 5 where the first surface 2 is exposed, forming a groove 7 in the wafer 1. In the cutting step, plasma etching is performed until the groove 7 reaches the second surface 3, thereby cutting out small-diameter wafers 5 along their contour from the wafer 1.

[0020] In the cutting step, the plasma generating device 30 preferably performs the so-called Bosch process as the first condition of plasma etching. The Bosch process is reactive ion etching for etching silicon with a high aspect ratio, and is a process in which a passivation step and an etching step are repeated in a relatively short cycle. In the etching step of the Bosch process, anisotropic etching and isotropic etching are performed by switching between them using power control. Therefore, as shown in FIG. 7, the Bosch process is composed of a passivation step (step S31), an anisotropic etching step (step S32), and an isotropic etching step (step S33).

[0021] In the passivation step of step S31, the plasma generating device 30 supplies C4F8 gas from the gas source 35 to the gas head 39 via the supply port 36, and generates C4F8 plasma in the chamber 31 by plasma discharge between the gas head 39 and the electrode 33. The resulting fluorine-based polymer is deposited in the groove 7, and the plasma generating device 30 forms a protective film on the surface of the groove 7 (the bottom and sidewalls of the groove 7).

[0022] In the etching step, which follows the passivation step, the plasma generator 30 supplies SF6 gas from the gas source 37 to the gas head 39 via the supply port 38, generating SF6 plasma in the chamber 31 by plasma discharge between the gas head 39 and the electrode 33. More specifically, the plasma generator 30 controls the high-frequency power supplied from the high-frequency power source 34 to the electrode 33 at a first power, which is higher than the high-frequency power supplied in the passivation step, at the beginning of the etching step. As a result, charged ions in the SF6 plasma are strongly attracted to the electrode 33 by a large electric field generated by the first power, accelerating them in the depth direction of the grooves 7. As a result, the accelerated ions collide with the bottom of the grooves 7, removing the protective film formed on the bottom of the grooves 7. Furthermore, the ion collisions and the reaction of fluorine radicals in the SF6 plasma with silicon combine to perform anisotropic etching, in which silicon is etched in the depth direction of the grooves (step S32). Thereafter, the plasma generating device 30 controls the high frequency power supplied to the electrode 33 to a second power lower than the first power. As a result, isotropic etching by fluorine radicals is performed in a state where the etching rate in the width direction is adjusted by suppressing the power (step S33).

[0023] In this way, in the etching step using the Bosch process, anisotropic etching is performed followed by isotropic etching. Therefore, in the cutting step, it is desirable to repeat the passivation step and etching step (anisotropic etching step, isotropic etching step) in a relatively short time to prevent the isotropic etching from progressing excessively. This makes it possible to proceed with etching in the depth direction while protecting the sidewalls of the trench 7 with a protective film. This allows etching to be performed with a high aspect ratio.

[0024] 8 is a diagram illustrating the chamfering step. After the wafer 5 is cut out from the wafer 1 in the cutting step, the chamfering step is then performed (step S40). The chamfering step is performed, for example, by the same plasma generating device 30 as in the cutting step.

[0025] In the chamfering step, the plasma generating device 30 chamfers the outer edge of the wafer 5 by plasma etching under second conditions different from the first conditions of the plasma etching in the cutting step. More specifically, the plasma generating device 30 supplies a predetermined gas from the gas head 39 into the chamber 31, while generating a plasma discharge between the gas head 39 and the electrode 33 using power from the high-frequency power supply 34. This converts the gas in the chamber 31 into plasma, and the plasma PB plasma-etches the wafer 5 from the first surface 2 side. In this way, with the high-aspect-ratio grooves 7 formed in the cutting step, plasma etching is further performed under the second conditions, thereby particularly chamfering the outer edge of the surface of the wafer 5 corresponding to the first surface 2 of the wafer 1 (i.e., the surface on the first surface 2 side), which is most exposed to the plasma. Furthermore, the plasma gas that enters and remains in the processed groove also promotes chamfering of the outer edge of the surface on the second surface 3 side. Therefore, in the chamfering step, the outer edges of both sides of the wafer 5 are chamfered.

[0026] It is desirable that the plasma etching under the second condition sufficiently chamfers the outer edge of the surface of the wafer 5 on the first surface 2 side without excessively widening the grooves 7 already formed in the cutting step in the width direction. Therefore, it is desirable that the plasma etching under the second condition be anisotropic etching that suppresses the progression of etching in the width direction. Although not particularly limited, the plasma etching under the second condition may use, for example, SF6 gas or Ar gas. Furthermore, in order to sufficiently chamfer the outer edge of the wafer 5, it is desirable that the plasma etching under the second condition be performed for a time sufficiently longer than the time of each etching step repeatedly performed in the cutting step. Specifically, for example, the Bosch process cycle in the cutting step is about several seconds, and each segment of the anisotropic etching is performed for about several seconds, whereas the plasma etching in the chamfering step may continue for one minute or more (e.g., 1.5 minutes). As described above, in both isotropic etching and anisotropic etching in the Bosch process, a predetermined amount of high-frequency power is supplied to the lower electrode (electrode 33) and the upper electrode (gas head 39), and a plasma-like gas is supplied to the wafer. In the case of anisotropic etching, however, the high-frequency power supplied to the lower electrode (electrode 33) is higher than in the case of isotropic etching, so that ions in the plasma are attracted to the lower electrode (electrode 33), thereby achieving vertical processing. This is also true for the anisotropic etching in the chamfering step.

[0027] In this way, the chamfering step according to this embodiment actively utilizes the effect of chamfering the inlet edge, which is most exposed to plasma and which is considered undesirable in normal etching, and the effect of chamfering the bottom edge of the groove due to the accumulation of plasma gas that has entered the groove, thereby chamfering preferably both or at least one of the first surface 2 and the second surface 3. In particular, by performing anisotropic etching for a time that is sufficiently longer than the cycle of the Bosch process, chamfering can be performed without significantly increasing the overall width of the groove 7.

[0028] As described above, in the wafer manufacturing method according to this embodiment, chamfering of one or more wafers 5 cut out from the wafer 1 can be performed all at once. This allows for more efficient chamfering than when chamfering individual wafers 5 one by one. Furthermore, by performing cutting by plasma etching and then chamfering by the same plasma etching, the cutting step and the chamfering step can be performed consecutively in the same apparatus. This also contributes to improving work efficiency. Therefore, according to the wafer manufacturing method according to this embodiment, chamfering can be performed efficiently, and further, small wafers can be efficiently manufactured.

[0029] (Second embodiment) 9 is a flowchart of the wafer manufacturing method according to this embodiment. The wafer manufacturing method shown in FIG. 9 differs from the wafer manufacturing method according to the first embodiment in that a polishing step (step S50) is further performed after the chamfering step (step S40). The polishing step is performed, for example, by the same plasma generation apparatus 30 as the cutting step and the chamfering step.

[0030] In the polishing step, the plasma generator 30 polishes the side surface of the wafer 5 cut out from the wafer 1 by isotropic etching. More specifically, the plasma generator 30 supplies a predetermined gas from the gas head 39 into the chamber 31, while generating a plasma discharge between the gas head 39 and the electrode 33 using power from the high-frequency power supply 34. This converts the gas in the chamber 31 into plasma, and the plasma isotropically etches the wafer 5 from the first surface 2 side. In this way, with the grooves 7 having a high aspect ratio formed in the cutting step, further isotropic etching is performed, etching and polishing the sidewalls of the grooves 7, i.e., the side surfaces of the wafer 5. Note that the relationship between the isotropic etching in the polishing step and the anisotropic etching in the chamfering step preferably satisfies at least one of the following: the time for which the isotropic etching in the polishing step is performed is shorter than the time for which the anisotropic etching in the chamfering step is performed, and the high-frequency power supplied to the upper electrode and the lower electrode is lower than that for the anisotropic etching.

[0031] The isotropic etching performed in the polishing step may be any type that polishes the side surface of the wafer 5. Therefore, it is not necessarily limited to plasma etching, but plasma etching is preferable because it allows polishing to be performed in the same equipment as the cutting step and the chamfering step, thereby improving work efficiency. The gas used in the polishing step is not particularly limited, but it may be, for example, SF6 gas, the same as that used in the cutting step, or other gases may be used.

[0032] As described above, in the wafer manufacturing method according to this embodiment, by further performing isotropic plasma etching after the chamfering step, side polishing of one or more wafers 5 cut out from the wafer 1 can be performed all at once. This allows side polishing to be performed more efficiently than when the side surfaces of individual wafers 5 are polished one by one in sequence. Furthermore, by performing cutting and chamfering by plasma etching and then polishing by the same plasma etching, the cutting step, chamfering step, and polishing step can be performed consecutively in the same apparatus. This also contributes to improving work efficiency. Therefore, according to the wafer manufacturing method according to this embodiment, smaller wafers can be manufactured more efficiently.

[0033] (Third embodiment) Fig. 10 is a flowchart of the wafer manufacturing method according to this embodiment. The wafer manufacturing method shown in Fig. 10 differs from the wafer manufacturing method according to the first embodiment in that the outer edges of both surfaces of the wafer 5 are chamfered. Note that the processes from step S10 to step S40 are the same as those in the wafer manufacturing method according to the first embodiment.

[0034] In the wafer manufacturing method according to this embodiment, after the outer edge of the surface of the wafer 5 corresponding to the first surface 2 is chamfered and the chamfering step (first chamfering step) is completed, a first protective film cleaning step is then performed (step S60). In the first protective film cleaning step, a spinner cleaning device cleans and removes the protective film 4 formed on the first surface 2 of the wafer 1 (wafer 5).

[0035] After the protective film 4 is removed, a second protective film forming step is performed (step S70). The second protective film forming step is performed, for example, by the protective film forming apparatus 10, similarly to the first protective film forming step. In the second protective film forming step, first, a new frame unit is created by attaching tape T to the first surface 2 side of the wafer 1, and the new frame unit is loaded into the protective film forming apparatus 10. Thereafter, the protective film forming apparatus 10 operates similarly to the second protective film forming step, except that the first surface 2 of the wafer 1 is suction-held to the table via tape T, thereby forming a protective film of the same type as the protective film 4 on the second surface 3. However, the protective film formed on the second surface 3 need only be a protective film that is resistant to plasma etching, which will be described later, and is not limited to being the same protective film as the protective film 4 formed on the first surface 2. In the second protective film forming step, a protective film different from the protective film 4 formed in the first protective film forming step may be formed.

[0036] Once the protective film is formed on the second surface 3, a second chamfering step is performed (step S80). The second chamfering step is a second chamfering step, and is performed, for example, in the plasma generation device 30, similarly to the first chamfering step. In the second chamfering step, first, the frame unit transported into the chamber 31 of the plasma generation device 30 is placed on the table 32 in the chamber 31 with the tape T side (first surface 2 side) facing the table 32. Then, while the same predetermined gas as in the first chamfering step is supplied into the chamber 31 from the gas head 39, a plasma discharge is generated between the gas head 39 and the electrode 33 by power from the high-frequency power supply 34. This converts the gas in the chamber 31 into plasma, and plasma etching is performed on the wafer 5 from the second surface 3 side by the plasma PB, which is the same as in the first chamfering step. As a result, the outer edge of the surface of the wafer 5 corresponding to the second surface 3 of the wafer 1 (the surface on the second surface 3 side) is particularly chamfered.

[0037] When the outer edge of the surface of the wafer 5 on the second side 3 side is chamfered and the second chamfering step is completed, a second protective film cleaning step is performed (step S90). The second protective film cleaning step is performed, for example, in a spinner cleaning device, similar to the first protective film cleaning step. The spinner cleaning device cleans and removes the protective film formed on the second side 3 of the wafer 1 (wafer 5).

[0038] As described above, in the wafer manufacturing method according to this embodiment, the outer edges of both the first surface 2 and the second surface 3 are more reliably chamfered after the slicing step. According to the wafer manufacturing method according to this embodiment, both surfaces of the wafer 5 can be chamfered efficiently. Therefore, small wafers can be efficiently manufactured.

[0039] (Fourth embodiment) 11 is a flowchart of a wafer manufacturing method according to this embodiment. The wafer manufacturing method according to this embodiment shown in FIG. 11 is similar to the wafer manufacturing method according to the third embodiment in that the outer edges of both surfaces of the wafer 5 are chamfered. However, the wafer manufacturing method according to this embodiment is similar to the wafer manufacturing method according to the third embodiment in that a protective film is formed on both surfaces (step S110) before the slicing step (step S30) and the protective film is removed from both surfaces along the contour of the wafer 5 (step S120), and in that after the slicing step, the outer edges of both surfaces of the wafer 5 are chamfered (step S140) and the protective film on both surfaces is cleaned (step S150).

[0040] In the wafer manufacturing method according to this embodiment, the outer edges of both the first surface 2 and the second surface 3 are chamfered after the slicing step, so that both surfaces of the wafer 5 can be chamfered efficiently, similarly to the wafer manufacturing method according to the third embodiment. Therefore, small wafers can be manufactured efficiently.

[0041] 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.

[0042] The processing order of the steps described in the above embodiment is not limited to this example and can be changed within a range that does not cause inconsistencies. For example, in the above embodiment, the chamfering step is performed after the cutting step, but the chamfering step may be performed during the cutting step.

[0043] In the above-described embodiment, an example has been shown in which a small wafer is manufactured from a wafer having a mirror-finished surface on which devices are manufactured, but a small wafer may also be manufactured from a wafer having a mirror-finished surface on both sides, or a small wafer may be manufactured from a wafer that has not been mirror-finished, and then the small wafer may be mirror-finished.

[0044] In the above-described embodiment, an example has been shown in which small wafers are cut out from a wafer by plasma etching performed from the side on which devices are manufactured, but the plasma etching for cutting out small wafers is not limited to being performed from the side on which devices are manufactured, and may also be performed from the side opposite to the side on which devices are manufactured.

[0045] In the above-described embodiment, the wafer is made of silicon, but the wafer material is not limited to silicon and may be made of other materials. Furthermore, in the above-described embodiment, an example is shown in which SF6 gas and C4F8 gas are used in the cutting step, but other gases may be used in addition to or instead of these gases. Furthermore, in the above-described embodiment, an example is shown in which SF6 gas is used in the chamfering step, but other gases may be used in addition to or instead of SF6 gas. Furthermore, in the above-described embodiment, an example is shown in which SF6 gas is used in the polishing step, but other gases may be used in addition to or instead of SF6 gas. [Industrial Applicability]

[0046] As described above, according to the wafer manufacturing method of the present invention, the chamfering of small wafers can be efficiently performed, thereby improving the efficiency of manufacturing small wafers. Therefore, the method is useful for manufacturing small wafers. [Explanation of symbols]

[0047] 1.5 wafers 2 Front page 3 Second side 4 Protective film 6 Planned cutting line 7 grooves 10 Protective film forming device 20 Laser processing equipment 21 Laser unit 30 Plasma generator 31 Chamber 32 tables 33 electrode 34 High frequency power supply 35, 37 Gas source 36, 38 Supply port 39 Gas Head F Frame LB laser beam PA, PB plasma T-tape

Claims

1. A wafer manufacturing method for manufacturing a second wafer smaller than a first wafer from the first wafer, comprising: a first protective film forming step of forming a first protective film on a first surface of the first wafer; a first protective film removing step of removing the first protective film along the contour of the second wafer; a cutting step of cutting the second wafer along the contour by plasma etching under first conditions from the first surface side using the first protective film as a mask; and a chamfering step of chamfering the outer edge of the second wafer by plasma etching under second conditions different from the first conditions. Wafer manufacturing method.

2. The chamfering step is performed after the cutting step. The method for manufacturing a wafer according to claim 1 .

3. The second condition of plasma etching is anisotropic etching. The method for manufacturing a wafer according to claim 1 .

4. The chamfering step includes: a first chamfering step of chamfering an outer edge of a surface of the second wafer corresponding to the first surface while holding a second surface of the first wafer opposite the first surface; a second chamfering step of chamfering an outer edge of a surface of the second wafer corresponding to the second surface of the first wafer while the first surface side is held. The method for manufacturing a wafer according to claim 1 .

5. Before the second chamfering step, The method further includes a second protective film forming step of forming a second protective film on the second surface. The method for producing a wafer according to claim 4.

6. After the chamfering step, a polishing step of polishing the side surface of the second wafer by isotropic etching is further included. The method for manufacturing a wafer according to claim 1 .

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