Wafer processing method

Abstract

To attach a wafer on a supporting substrate and increase flatness of the wafer.SOLUTION: A method for processing a wafer having a front surface and a back surface facing each other sequentially includes: a preparation step of preparing a supporting substrate having a supporting surface for supporting the wafer; a hydrophilic treatment step of performing hydrophilic treatment on at least one of the front surface of the wafer and the supporting surface of the supporting substrate; a joining step of joining the front surface of the wafer and the supporting surface of the supporting substrate to face each other and forming a joint wafer after the hydrophilic treatment; a first heating step of heating the joint wafer to a first temperature; a processing step of processing the wafer of the joint wafer from the back surface side after the first heating step; a second heating step of heating the joint wafer to a second temperature higher than the first temperature; and a separation step of separating the wafer from the supporting substrate, after the second heating step.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a wafer processing method in which a wafer having a plurality of devices formed on a surface side is bonded to a support substrate, the bonded wafer is processed, and the processed wafer is peeled off from the support substrate.

Background Art

[0002] Chips of devices such as ICs (Integrated Circuits) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by grinding a wafer having a plurality of devices formed on a surface side to a desired thickness and then forming a dicing groove that penetrates the wafer along the boundaries of the plurality of devices.

[0003] In recent years, in order to increase the capacity and miniaturize chips, a technology for stacking and integrating a plurality of chips such as DRAMs (Dynamic Random Access Memories) has been realized. In this technology, each of the stacked chips is required to be thinned to a thickness of 10 μm or less in advance, but it is not easy to handle the wafer after being thinned to such a thickness. Therefore, a method of bonding a support substrate to the wafer before thinning using an adhesive that can be peeled off later is used (see Patent Document 1).

[0004] In addition, with the deepening of wafer thinning, improvement in the thickness uniformity and flatness (TTV: Total Thickness Valuation) of the thinned wafer is also required. Specifically, for a wafer thinned to a thickness of 10 μm, a flatness of 0.5 μm or less is required.

Prior Art Documents

Patent Documents

[0005] [[ID=Z]] [[ID=A]]

Patent Document 1

Summary of the Invention

[0006] However, when bonding a wafer to a support substrate using adhesive, in order to produce a wafer with high flatness, it is necessary not only to use a support substrate with extremely high flatness, but also for the adhesive layer formed to be extremely flat.

[0007] A support substrate with sufficiently high flatness can be obtained by pre-processing the support substrate with a grinding device. In contrast, it is not easy to improve the flatness of adhesive applied to a support substrate. For example, when ultraviolet light is irradiated to cure the adhesive after it has been sandwiched between the support substrate and the wafer, uneven shrinkage of the adhesive occurs. As a result, the flatness of the formed adhesive layer tends to be low.

[0008] This invention has been made in view of the above problems, and its objective is to provide a wafer processing method that can process a wafer bonded to a support substrate to improve its flatness. [Means for solving the problem]

[0009] According to the present invention, a method for processing a wafer having a surface and a back surface facing the surface is provided, comprising: a preparation step of preparing a support substrate having a support surface for supporting the wafer; a hydrophilization step of performing a hydrophilization treatment on one or both of the surface of the wafer or the support surface of the support substrate; a bonding step of forming a bonded wafer by bonding the surface of the wafer and the support surface of the support substrate facing each other after the hydrophilization step; a first heating step of heating the bonded wafer to a first temperature to increase the bonding strength between the wafer and the support substrate; a processing step of processing the wafer included in the bonded wafer from the back side after the first heating step; a second heating step of heating the bonded wafer to a second temperature higher than the first temperature after the processing step to decrease the bonding strength between the wafer and the support substrate; and a peeling step of peeling the wafer from the support substrate after the second heating step.

[0010] Preferably, in the hydrophilization step, the contact angle between the surface of the hydrophilized wafer or the support surface of the support substrate and the dropped pure water is 10° or more and 50° or less.

[0011] Preferably, in the hydrophilization step, the hydrophilization treatment is performed on the outer peripheral region of either the surface of the wafer or the support surface of the support substrate, or both, but not on the area inside the outer peripheral region.

[0012] Furthermore, preferably, the first heating step involves heating the outer peripheral region of the bonded wafer.

[0013] Preferably, the second heating step involves heating the outer peripheral region of the bonded wafer.

[0014] Furthermore, preferably, the hydrophilization step involves bringing a plasma generated under atmospheric pressure into contact with either or both of the surface of the wafer or the support surface of the support substrate to perform the hydrophilization treatment.

[0015] Preferably, the support surface of the support substrate has an outer shape corresponding to the surface of the wafer.

[0016] Furthermore, preferably, the first temperature is 150°C or more and less than 250°C, and the second temperature is 250°C or more and 350°C or less. [Effects of the Invention]

[0017] In one aspect of the present invention, a wafer processing method is performed in advance on either the surface of the wafer or the support surface of the support substrate, or both. Then, the surface of the wafer and the support surface of the support substrate are brought facing each other and joined to form a bonded wafer. After processing the wafer contained in the bonded wafer from the back side, the wafer is peeled off the support substrate.

[0018] This method allows the wafer to be supported by a support substrate without the use of adhesive. Therefore, the wafer supported by the support substrate can be processed without the reduction in thickness uniformity or flatness caused by the adhesive layer.

[0019] Therefore, according to one aspect of the present invention, a wafer processing method is provided that can process a wafer bonded to a support substrate to improve its flatness. [Brief explanation of the drawing]

[0020] [Figure 1] Figure 1(A) is a schematic perspective view of a support substrate, and Figure 1(B) is a schematic cross-sectional view of an example of a wafer. [Figure 2] This is a schematic perspective view illustrating the hydrophilization step. [Figure 3] Figure 3(A) is a schematic perspective view showing the bonding step, and Figure 3(B) is a schematic perspective view showing the bonded wafer. [Figure 4] This is a schematic perspective view showing the first heating step in one example. [Figure 5]FIG. 5(A) is a perspective view schematically showing a laser annealing unit and a holding table used in a first heating step according to another example, and FIG. 5(B) is a perspective view schematically showing the first heating step according to another example. [Figure 6] It is a perspective view schematically showing a processing apparatus. [Figure 7] It is a perspective view schematically showing a processing step. [Figure 8] FIG. 8(A) is a perspective view schematically showing a second heating step according to an example, and FIG. 8(B) is a perspective view schematically showing the second heating step according to another example. [Figure 9] It is a perspective view schematically showing a peeling step. [Figure 10] It is a cross-sectional view schematically showing a peeling step. [Figure 11] It is a graph showing an example of the relationship between hydrophilic treatment conditions and wettability. [Figure 12] It is a flowchart showing the flow of a wafer processing method.

Embodiments for Carrying Out the Invention

[0021] Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1(B) is a perspective view schematically showing a wafer 1 processed by the wafer processing method according to the present embodiment. The wafer 1 is formed in a disk shape from a semiconductor material such as silicon (Si), for example. A plurality of division planned lines 3 intersecting each other are set on the surface 1a of the wafer 1, and devices 5 are formed in each region partitioned by the division planned lines 3 on the surface 1a of the wafer 1.

[0022] Each of the plurality of devices 5 includes, for example, elements for constituting an IC, a semiconductor memory, or an image sensor. Further, the boundaries of the plurality of devices 5 extend, for example, in a grid pattern. When the wafer 1 is cut along the division planned line 3, device chips each provided with a device 5 can be manufactured.

[0023] There are no restrictions on the material, shape, structure, or size of wafer 1. Wafer 1 may be made of a semiconductor material other than silicon (for example, silicon carbide (SiC) or gallium nitride (GaN)). Similarly, there are no restrictions on the type, quantity, shape, structure, size, or arrangement of device 5.

[0024] The outer edge of wafer 1 is chamfered; that is, a chamfered portion is formed on the outer edge of wafer 1. In other words, the side surface of wafer 1 is curved so as to be convex outwards. Furthermore, in wafer 1, the surface 1a and the back surface 1b opposite to surface 1a are parallel, and the local variation in thickness is extremely small.

[0025] Furthermore, an insulating film covering the device 5 may be provided on the surface 1a of the wafer 1. The insulating film is composed of, for example, a silicon oxide film (SiO2 film), a silicon nitride film (SiN film), a silicon oxynitride film (SiON film), a nitrogen-doped silicon carbide film (SiCN film), or an organic resin film. The upper surface of the insulating film covering the device 5 may be flattened by methods such as CMP (Chemical Mechanical Polishing). When the upper surface is flattened, the irregularities on the surface 1a of the wafer 1 become extremely small.

[0026] Figure 1(A) is a schematic perspective view showing an example of a support substrate 11 attached to wafer 1. In the wafer 1 processing method according to this embodiment, a support substrate 11 is attached to the surface 1a side of wafer 1 to protect the device 5, etc., to form a bonded wafer, and wafer 1 is processed while included in the bonded wafer.

[0027] The support substrate 11 will now be described. The support substrate 11 has an outer shape corresponding to the surface 1a of the wafer 1. For example, the support substrate 11 is formed in a disc shape similar to that of the wafer 1. For example, the support substrate 11 can be the same as the wafer 1 before the device 5 is formed. However, the support substrate 11 is not limited to this.

[0028] The support substrate 11 has a support surface 11a for supporting the wafer 1 and a back surface 11b facing the support surface 11a. To ensure that the wafer 1 supported by the support substrate 11 is properly processed, the support surface 11a and back surface 11b of the support substrate 11 have extremely small irregularities and are as flat as the front surface 1a and back surface 1b of the wafer 1. Furthermore, the support surface 11a and back surface 11b of the support substrate 11 are parallel to each other, and the support substrate 11 has extremely small local variations in thickness.

[0029] Conventionally, adhesive was used to attach the support substrate 11 to the wafer 1. However, it was not easy to form an adhesive layer of uniform thickness between the wafer 1 and the support substrate 11. When ultraviolet light was irradiated to cure the adhesive after it had been sandwiched between the support substrate 11 and the wafer 1, the adhesive may shrink unevenly, resulting in a low flatness of the formed adhesive layer.

[0030] Therefore, even if a bonded wafer is formed by bonding the wafer 1 and the support substrate 11 with an adhesive, and the wafer 1 in this bonded wafer state is processed, the wafer 1 cannot be processed with high precision due to the adhesive layer. Therefore, in the wafer processing method according to this embodiment, the wafer 1 and the support substrate 11 are bonded together without using an adhesive, and then the wafer 1 is processed. The wafer processing method according to this embodiment will be described in detail below.

[0031] Figure 12 is a flowchart showing the flow of each step in the wafer processing method according to this embodiment. In the wafer processing method according to this embodiment shown in Figure 12, first, a preparation step S10 is performed to prepare a support substrate 11 having a support surface 11a for supporting the wafer 1.

[0032] For example, in preparation step S10, a wafer that can also be used for manufacturing device chips, but on which the device 5 is not formed, is prepared as the support substrate 11. Alternatively, a wafer on which a device has been formed but which has become defective for some reason may be processed to remove the device and flatten it to prepare the support substrate 11. Thus, there are no restrictions on how the support substrate 11 is procured.

[0033] Furthermore, in preparation step S10, the size of the irregularities formed on the support surface 11a and the back surface 11b of the support substrate 11, i.e., the flatness, may be evaluated. Also, the degree of parallelism between the support surface 11a and the back surface 11b of the support substrate 11, i.e., the uniformity of the thickness of the support substrate 11, may be evaluated. In preparation step S10, processing such as CMP may be performed on the support substrate 11 so that the flatness and thickness uniformity meet predetermined levels.

[0034] Here, we will specifically describe an example of the flatness required for the support surface 11a of the support substrate 11 prepared in preparation step S10. For example, it is desirable that the surface roughness (Rms) of the support surface 11a of the support substrate 11 be 3 nm or less. If the surface roughness (Rms) of the support surface 11a is 3 nm or less, the support surface 11a of the support substrate 11 can be well bonded to the surface 1a of the wafer 1, as will be explained later.

[0035] Furthermore, in preparation step S10, if the flatness of the surface 1a (the upper surface of the insulating film covering the device 5) of the wafer 1 on which the device 5 is formed does not meet a predetermined level, processing such as CMP should be performed on the surface 1a of the wafer 1 to improve its flatness. More specifically, CMP should be performed on the surface 1a of the wafer 1 to a thickness of about 50 nm using a slurry used in CMP for removing barrier metal from semiconductor devices. Alternatively, in preparation step S10, a wafer 1 on which such CMP has been performed is prepared.

[0036] Next, in preparation for bonding the wafer 1 and the support substrate 11, a hydrophilization step S20 is performed, in which a hydrophilization treatment is carried out on either or both of the surface 1a of the wafer 1 or the support surface 11a of the support substrate 11. The hydrophilization step S20 is performed by bringing plasma generated under atmospheric pressure (atmospheric pressure plasma) into contact with either or both of the surface 1a of the wafer 1 or the support surface 11a of the support substrate 11.

[0037] The following explanation will use the case of performing a hydrophilic treatment on the surface 1a of wafer 1 as an example. Figure 2 is a schematic perspective view showing wafer 1 with a hydrophilic treatment performed on its surface 1a. Figure 2 shows an atmospheric pressure plasma irradiation apparatus 2 that performs atmospheric pressure plasma irradiation as an example of a hydrophilic treatment.

[0038] The atmospheric pressure plasma irradiation apparatus 2 includes a plasma irradiation unit 8 that can irradiate a wafer 1 placed on a rotating support table 4 with plasma 10 under atmospheric pressure. The upper surface of the rotating support table 4 is a holding surface 4a, and preferably, it can hold the wafer 1 placed on the holding surface 4a. For example, the rotating support table 4 holds the wafer 1 by suction by applying negative pressure to the wafer 1 placed on the holding surface 4a.

[0039] Furthermore, the rotary support table 4 is connected to a rotational drive source (not shown), such as a motor, and can rotate around a table rotation axis 6 that is approximately perpendicular to the holding surface 4a. The plasma irradiation unit 8 is positioned above one end of the holding surface 4a of the rotary support table 4 and has the function of irradiating the holding surface 4a with plasma 10.

[0040] The configuration of the plasma irradiation unit 8 will now be described. For example, the plasma generator "CeraPlas® element" from TDK Electronics AG can be used for the plasma irradiation unit 8. However, the plasma irradiation unit 8 is not limited to this, and any plasma generator capable of forming plasma 10 under atmospheric pressure can be used.

[0041] In the hydrophilization step S20, for example, the wafer 1 is placed on the holding surface 4a of the rotary support table 4 with the surface 1a that will be bonded facing upwards, and the wafer 1 is held in place by the rotary support table 4 through suction. Then, the rotary support table 4 is rotated one or more times around the table rotation axis 6 while the plasma 10 is irradiated onto the surface 1a of the wafer 1 from the plasma irradiation unit 8 under predetermined conditions. As a result, the outer peripheral region 7 of the surface 1a of the wafer 1 is hydrophilized.

[0042] Next, an example of plasma irradiation conditions in the hydrophilization step S20 will be described. For example, the plasma irradiation unit 8 generates a plasma with air as the gas species and ejects the plasma 10 at a flow rate of 50 sccm. The distance from the nozzle of the plasma irradiation unit 8 to the surface 1a of the wafer 1 is set to about 10 mm, and the plasma is irradiated to an area of ​​the surface 1a of the wafer 1 with a diameter of about 10 mm. Then, with the outer edge of the plasma irradiation area positioned at the outer edge of the surface 1a of the wafer 1, the rotary support table 4 is rotated at a rotation speed of 3° to 30° per minute.

[0043] The hydrophilization treatment may be performed on the support surface 11a of the support substrate 11 instead of the surface 1a of the wafer 1. Alternatively, the hydrophilization treatment may be performed on both the surface 1a of the wafer 1 and the support surface 11a of the support substrate 11. The procedure for performing the hydrophilization treatment on the support surface 11a of the support substrate 11 is the same as the procedure for performing the hydrophilization treatment on the surface 1a of the wafer 1 described above. The conditions for irradiating the support surface 11a of the support substrate 11 with plasma may also be the same as the conditions for irradiating the surface 1a of the wafer 1 with plasma.

[0044] However, the plasma irradiation conditions in the hydrophilization step S20 are not limited to these. The plasma irradiation conditions can be changed within a range in which the surface 1a of the wafer 1 or the support surface 11a of the support substrate 11 acquires the desired properties. Furthermore, when hydrophilization treatment is performed on both the surface 1a of the wafer 1 and the support surface 11a of the support substrate 11, the conditions do not need to be the same.

[0045] Here, we will explain the phenomena that occur on the surface 1a of wafer 1 due to irradiation with atmospheric pressure plasma. Before irradiation with atmospheric pressure plasma, wafer 1, which is placed in the air, has countless organic molecules floating in the atmosphere attached to it. When atmospheric pressure plasma is irradiated onto the surface 1a of wafer 1, the organic molecules are removed in the irradiated area, water molecules from the atmosphere adhere to it, or the organic molecules decompose, and the surface 1a of wafer 1 is terminated by countless hydroxyl groups (OH groups).

[0046] When hydroxyl groups are introduced to the surface 1a of wafer 1, the hydrophilicity of the surface 1a of wafer 1 improves. Therefore, the degree of modification of the surface 1a of wafer 1 by plasma irradiation can be evaluated by the degree of hydrophilicity (wettability) of the plasma-irradiated area, and can be expressed by the contact angle of water with the surface 1a of wafer 1 when water is dropped onto the irradiated area. The preferred range of the relationship between the plasma irradiation conditions and the water contact angle will be described in detail later.

[0047] Here, in order to actively introduce hydroxyl groups through hydrophilization treatment, organic molecules may be introduced in advance onto the surface 1a of wafer 1. For example, a liquid such as ethanol, acetone, or acetic acid may be pre-applied to the surface 1a of wafer 1.

[0048] The hydrophilization treatment may be carried out by other methods. For example, it may be carried out by irradiating the surface 1a of wafer 1 with ultraviolet light under predetermined conditions. In this case as well, the organic molecules attached to the surface 1a of wafer 1 are decomposed or removed by the irradiation of ultraviolet light, and hydroxyl groups remain on the surface 1a of wafer 1.

[0049] Furthermore, in the hydrophilization step S20, the hydrophilization treatment may be performed on the entire surface 1a of the wafer 1. In this case, when the support substrate 11 is bonded to the wafer 1 as described later, the wafer 1 is firmly supported by the support substrate 11 during the processing of the wafer 1.

[0050] However, if the entire surface 1a of the wafer 1 is subjected to hydrophilic treatment, when the support surface 11a of the support substrate 11 is bonded to the surface 1a of the wafer 1, the wafer 1 may adhere firmly to the support substrate 11 in the device region 9 where the device 5 is formed. In this case, there is a risk that an unnecessary load will be placed on the device 5 when the support substrate 11 is finally peeled off from the wafer 1.

[0051] Therefore, in the hydrophilization step S20, it is preferable to perform the hydrophilization treatment on the outer peripheral region 7 on the surface 1a of the wafer 1 where the device 5 is not formed, and not perform the hydrophilization treatment inside the outer peripheral region 7. Furthermore, when the hydrophilization treatment is performed on the support surface 11a of the support substrate 11, it is preferable to perform the hydrophilization treatment on the outer peripheral region that does not overlap with the device region 9 of the wafer 1.

[0052] In the wafer processing method according to this embodiment, a bonding step S30 is performed after the hydrophilization step S20. Next, the bonding step S30 will be described. Figure 3(A) is a schematic perspective view showing the bonding step S30, and Figure 3(B) is a schematic perspective view showing the formed bonded wafer 13.

[0053] In bonding step S30, the surface 1a of the wafer 1 and the support surface 11a of the support substrate 11 are brought into contact, as shown in Figure 3(A). Although Figure 3(A) shows the case where the wafer 1 is placed above the support substrate 11, the support substrate 11 may also be placed above the wafer 1. Then, the wafer 1 and the support substrate 11 are brought closer together so that the surface 1a of the wafer 1 and the support surface 11a of the support substrate 11 come into contact.

[0054] In this case, hydrogen bonds are formed between the surface 1a of the wafer 1 and the support surface 11a of the support substrate 11 via hydroxyl groups formed on one or both of the surface 1a and the support surface 11a of the support substrate 11 during the hydrophilization step S20. As a result, the two are joined together to form a bonded wafer 13. The amount of hydrogen bonds formed between the surface 1a and the support surface 11a changes depending on the amount of hydroxyl groups formed in the hydrophilization step S20. Therefore, the bonding strength between the wafer 1 and the support substrate 11 changes depending on the intensity of the hydrophilization treatment performed in the hydrophilization step S20.

[0055] In particular, if both the surface 1a of the wafer 1 and the support surface 11a of the support substrate 11 are hydrophilized in the hydrophilization step S20, hydrogen bonds are formed relatively easily between the hydroxyl groups formed on the surface 1a and the hydroxyl groups formed on the support surface 11a. As a result, the bonding strength between the wafer 1 and the support substrate 11 is increased.

[0056] Next, a first heating step S40 is performed to heat the bonded wafer 13 to a first temperature to increase the bonding strength between the wafer 1 and the support substrate 11. Figure 4 is a schematic perspective view showing the first heating step S40 according to one example. In the first heating step S40, for example, a heating device 12 equipped with a heating and holding table 14 with a built-in heater is used.

[0057] The heating and holding table 14 of the heating device 12 has a diameter equal to that of the bonded wafer 13 and includes a porous member exposed on its upper surface. A suction passage is formed inside, with one end passing through the porous member and the other end passing through a suction source (not shown). The upper surface of the porous member becomes the holding surface 14a on which the bonded wafer 13, which is held by suction, rests. A heater (not shown), composed of an electric heating wire or the like, is also provided inside the heating and holding table 14.

[0058] In the first heating step S40, the bonded wafer 13 is placed on the holding surface 14a of the heating and holding table 14, and the suction source is activated to hold the bonded wafer 13 by suction on the heating and holding table 14. Next, the heater is activated to transfer heat to the bonded wafer 13, heating the bonded wafer 13 to a first temperature.

[0059] When one or both of the wafer 1 and the support substrate 11 are hydrophilized, and a bonded wafer 13 is formed by hydrogen bonding, the adhesion between the wafer 1 and the support substrate 11 improves when the bonded wafer 13 is heated to a certain temperature. This is partly because the hydroxyl groups that constitute the hydrogen bonds are involved in a dehydration condensation reaction, forming a covalent bond between the surface 1a and the support surface 11a via oxygen atoms. This bond is stronger than hydrogen bonding.

[0060] Therefore, when the first heating step S40 is performed, the adhesion of the bonded wafer 13 is improved, and even when the wafer 1 is processed in the processing step S50 described next, the wafer 1 is less likely to peel off from the support substrate 11. Thus, in the wafer processing method according to this embodiment, it is necessary to appropriately determine the heating conditions of the bonded wafer 13 in the first heating step S40, as well as the conditions for the hydrophilization treatment in the hydrophilization step S20. The preferred ranges for the conditions for the hydrophilization treatment and the first temperature will be described in detail later.

[0061] The first heating step S40 may be carried out by a method other than heating by a heating device 12 equipped with a heating and holding table 14. Next, another example of the first heating step S40 will be described. Figure 5(A) is a schematic perspective view showing the laser annealing unit 22 and holding table 20 used in the first heating step according to another example, and Figure 5(B) is a schematic perspective view showing the first heating step according to another example.

[0062] The holding table 20 shown in Figure 5(A) comprises a porous member exposed on its upper surface and a suction path (not shown) that serves as a path for supplying negative pressure to the porous member. The upper surface of this porous member becomes the holding surface 20a of the bonded wafer 13. When the bonded wafer 13 is placed on the holding surface 20a and negative pressure is applied to the bonded wafer 13 through the porous member, the holding table 20 can hold the bonded wafer 13 by suction.

[0063] The holding table 20 is supported by a table rotation shaft 18 connected to a rotation drive source (not shown), such as a motor. When this rotation drive source is activated, the holding table 20 can be rotated around the holding surface 20a. Furthermore, the holding table 20 may be equipped with an internal cooling water channel (not shown). The holding table 20 is maintained at a predetermined temperature by the flow of cooling water through the cooling water channel.

[0064] Furthermore, the diameter of the upper surface (holding surface 20a) of the holding table 20 is smaller than the diameter of the bonded wafer 13. Therefore, when the bonded wafer 13 is held by suction on the holding table 20, the outer peripheral region of the bonded wafer 13 extends beyond the holding surface 20a. When cooling water is flowed through the cooling water channel in this state, the temperature of the region of the bonded wafer 13 in contact with the holding surface 20a is easily kept constant.

[0065] The laser annealing unit 22 will now be described. The laser annealing unit 22 is located outside the holding table 20 and at a position lower than the holding surface 20a of the holding table 20. The laser annealing unit 22 is equipped with a laser oscillator, such as a CO2 laser oscillator or an Nd:YAG laser oscillator, and can emit a laser beam of a predetermined wavelength.

[0066] As shown in Figure 5(B), in the first heating step S40 of the modified example, the bonded wafer 13 is placed on the holding surface 20a of the holding table 20, and the bonded wafer 13 is held by suction with the holding table 20. At this time, the outer peripheral region of the bonded wafer extends beyond the outside of the holding surface 20a. In this state, the table rotation axis 18 is rotated to rotate the holding table 20, and a laser beam 24 is irradiated from the laser annealing unit 22 onto the outer peripheral region of the bonded wafer 13. This heats the outer peripheral region of the bonded wafer 13 to the first temperature.

[0067] If the hydrophilization treatment is performed only on the outer peripheral region 7 of the surface 1a of wafer 1 in the hydrophilization step S20, it is not necessary to heat the central region of the bonded wafer 13. Furthermore, depending on the structure formed on the surface 1a of wafer 1, heating the central region of wafer 1 to the first temperature may cause problems.

[0068] Therefore, if the holding table 20 is equipped with a cooling water channel through which cooling water flows, it is advisable to keep the cooling water flowing through the cooling water channel. In this case, the temperature of the bonded wafer 13 will not rise easily inside the area surrounded by the outer peripheral region of the bonded wafer 13.

[0069] In the wafer processing method according to this embodiment, after the first heating step S40, a processing step S50 is performed in which the wafer 1 included in the bonded wafer 13 is processed from the back surface 1b side. That is, in processing step S50, the wafer 1 supported by the support substrate 11 is processed.

[0070] There are no restrictions on the processing performed on wafer 1 in processing step S50. For example, in processing step S50, wafer 1 is thinned by grinding from the back surface 1b. Below, processing step S50 will be described using the example of grinding as the processing performed in processing step S50, but processing step S50 is not limited to this.

[0071] First, let's describe the processing apparatus for processing wafer 1. Figure 6 is a schematic perspective view of a processing apparatus (grinding apparatus) 26 for processing (grinding) the workpiece. The processing apparatus 26 includes a base 28 that supports each component. An opening 28a is formed on the upper surface of the base 28, oriented along the Y-axis.

[0072] The opening 28a is provided with a holding table 30 that can move along the Y-axis direction by a ball screw type moving mechanism, and a dustproof and splashproof cover 28b that covers the opening 28a while exposing the holding table 30.

[0073] The holding table 30 can hold a bonded wafer 13, including the wafer 1 to be ground, by suction. The holding table 30 has a frame 30c made of stainless steel or ceramic. A suction passage (not shown) is provided inside the frame 30c, and a suction source (not shown), such as an ejector, is connected to one end of this suction passage. The frame 30c has a recess on its upper side, which consists of a disc-shaped space. A substantially disc-shaped porous member 30a is housed and fixed in this recess.

[0074] The diameter of the porous member 30a is approximately the same as the diameter of the support substrate 11. The upper surface of the porous member 30a becomes the holding surface 30b. When the bonded wafer 13 is placed on the porous member 30a and the suction source is activated, negative pressure acts on the bonded wafer 13 through the suction passage and the porous member 30a, and the bonded wafer 13 is held in place by suction to the holding table 30.

[0075] The holding table 30 moves along the Y-axis direction by a Y-axis movement mechanism provided inside the opening 28a and covered by a dustproof and waterproof cover 28b. The Y-axis movement mechanism is, for example, a ball screw type movement mechanism having a ball screw that rotates with a rotational drive source such as a motor. The holding table 30 is also connected to a rotational drive source such as a motor (not shown) and can rotate around a table rotation axis 30d (see Figure 7) perpendicular to the holding surface 30b.

[0076] The processing apparatus 26 includes a processing unit (grinding unit) 34 for processing (grinding) the wafer 1 contained in the bonded wafer 13 held by the holding table 30, and a processing feed unit 36 ​​for raising and lowering the processing unit 34. A support section 32 is erected on the rear side of the processing apparatus 26, and the processing unit 34 is supported by this support section 32 via the processing feed unit 36. A pair of guide rails 38 are provided on the front of the support section 32, aligned in the Z-axis direction (vertical direction). A lifting plate 40 is slidably attached to each guide rail 38.

[0077] A nut (not shown) is provided on the back (rear) side of the lifting plate 40, and a ball screw 42 parallel to the guide rail 38 is screwed into this nut. A pulse motor 44 is connected to one end of the ball screw 42. When the pulse motor 44 rotates the ball screw 42, the lifting plate 40 moves along the guide rail 38 in the Z-axis direction.

[0078] A processing unit 34, which performs grinding of the wafer 1, is fixed to the front side of the lifting plate 40. By moving the lifting plate 40, the processing unit 34 can move in the Z-axis direction (grinding feed direction). The processing unit 34 has a cut cylindrical support 46. The support 46 is fixed to the front surface of the lifting plate 40 and forms the exterior of the processing unit 34.

[0079] Inside the support 46 is a spindle housing 48 supported by the support 46. A portion of the spindle 50 is housed in the spindle housing 48 in a manner that allows it to rotate. A rotational drive mechanism (not shown), such as a motor, is connected to the upper end of the spindle 50. When the rotational drive mechanism is activated, the spindle 50 rotates around the axis of rotation.

[0080] The lower end of the spindle 50 is located below the bottom of the support 46. The upper side of a disc-shaped wheel mount 52 is connected to the lower end of the spindle 50. A grinding wheel (working tool) 54 is fixed to the wheel mount 52. Figure 7 is a schematic perspective view showing how the wafer 1 is processed (ground) by the grinding wheel 54 fixed to the wheel mount 52.

[0081] The grinding wheel (working tool) 54 has an annular wheel base 56. The wheel base 56 is made of a metal such as aluminum and has a diameter corresponding to the diameter of the wafer 1. Multiple grinding wheels 58 are arranged in an annular pattern on the outer circumference of the lower (bottom) side of the wheel base 56. Each grinding wheel 58 is formed by mixing abrasive grains such as diamond or cBN (cubic boron nitride) with a binder such as vitrified or resinoid, and sintering the mixture.

[0082] The wheel mount 52 is provided with multiple grinding wheel fixing holes that penetrate vertically, and the wheel base 56 has fastening holes into which fasteners 60 such as bolts are tightened. When the fasteners 60 are passed through the grinding wheel fixing holes and tightened into the fastening holes, the grinding wheel 54 is fixed to the wheel mount 52. At this time, the wheel mount 52 supports the grinding wheel 54 from above.

[0083] In processing step S50, the bonded wafer 13 is placed on the holding table 30, and the holding table 30 holds the bonded wafer 13 by suction. At this time, the back surface 11b of the support substrate 11 is brought facing the holding surface 30b, and the back surface 1b of the wafer 1 is exposed upwards. Next, the holding table 30 is moved below the processing unit 34.

[0084] Subsequently, the rotational drive source connected to the spindle 50 is activated to rotate the spindle 50 around the wheel rotation axis 50a. This causes the grinding wheel 54 to rotate and the grinding wheel 58 to move along its rotational trajectory. The holding table 30 is also rotated around the table rotation axis 30d.

[0085] Then, the processing feed unit 36 ​​is activated to lower the processing unit 34, bringing the bottom surface of the grinding wheel 58, which is moving along a rotating trajectory, into contact with the surface to be ground (back surface 1b) of the wafer 1. As a result, the wafer 1 is ground and gradually thins. At this time, the thickness of the wafer 1 is monitored, and when the wafer 1 reaches a predetermined thickness, the lowering of the processing unit 34 is stopped. As a result, a wafer 1 of the predetermined thickness is obtained.

[0086] In the wafer processing method according to this embodiment, the wafer 1 is supported on the support substrate 11 without an adhesive. Therefore, variations in thickness caused by the adhesive layer do not occur in the wafer 1. Also, because the wafer 1 is supported on the support substrate 11, the wafer 1 can be ground to an extremely thin thickness. Furthermore, since the hydrophilization step S20 and the first heating step S40 are performed and the adhesion between the wafer 1 and the support substrate 11 is increased, the wafer 1 does not peel off from the support substrate 11 during processing.

[0087] In the wafer processing method according to this embodiment, the support substrate 11 is peeled off from the processed wafer 1. As preparation for peeling off the wafer 1, after the processing step S50, a second heating step S60 is performed in which the bonded wafer 13 is heated to a second temperature to reduce the bonding strength between the wafer 1 and the support substrate 11. The second heating step S60 can be performed in the same manner as the first heating step S40. Therefore, the above description of the first heating step S40 can be appropriately referred to as a description of the second heating step S60.

[0088] Figure 8(A) is a schematic perspective view showing the second heating step S60 according to one example, and Figure 8(B) is a schematic perspective view showing the second heating step S60 according to another example. In the second heating step S60, the heating device 12 and the laser annealing unit 22 can be used, similar to the first heating step S40.

[0089] The main difference between the second heating step S60 and the first heating step S40 is the temperature at which the bonded wafer 13 is heated. Specifically, the second target temperature for heating the bonded wafer 13 in the second heating step S60 is set higher than the first target temperature for heating the bonded wafer 13 in the first heating step S40. More specifically, the first temperature is preferably 150°C or higher and less than 250°C, and the second temperature is preferably 250°C or higher and 350°C or lower.

[0090] As shown in Figure 8(A), when the heating device 12 is used in the second heating step S60, the built-in heater is activated under conditions that allow the bonded wafer 13 to be heated to the second temperature. Also, when the laser annealing unit 22 is used in the second heating step S60, as shown in Figure 8(B), a laser beam 24a capable of heating the outer peripheral region of the bonded wafer 13 to the second temperature is irradiated onto the bonded wafer 13.

[0091] Here, we will explain the phenomenon that occurs in the bonded wafer 13 during the second heating step S60. When the bonded wafer 13 is heated to a temperature even higher than the first temperature at which the dehydration condensation reaction described in the first heating step S40 occurs between the wafer 1 and the support substrate 11 (the second temperature), some of the organic molecules remaining between the wafer 1 and the support substrate 11 gasify. Then, when bubbles are generated at the bonding interface between the wafer 1 and the support substrate 11, the bonding strength between the wafer 1 and the support substrate 11 decreases. In other words, these bubbles trigger delamination.

[0092] Conversely, if the temperature at which the bonded wafer 13 is heated in the first heating step S40 becomes too high, not only will a dehydration condensation reaction occur at the bonding interface between the wafer 1 and the support substrate 11, but bubbles will also form. As a result, sufficient bonding strength may not be achieved when the first heating step S40 is completed.

[0093] Therefore, in the first heating step S40, it is preferable that the bonded wafer 13 be heated to a temperature at which bubbles are less likely to form, and in the second heating step S60, it is preferable that the bonded wafer 13 be heated to a temperature at which bubbles are more likely to form. In other words, in the first heating step S40, it is preferable that the bonded wafer 13 be heated to a first temperature lower than the second temperature, and in the second heating step S60, it is preferable that the bonded wafer 13 be heated to a second temperature higher than the first temperature.

[0094] In the wafer processing method according to this embodiment, after the second heating step S60, a peeling step S70 is performed to peel the wafer 1 from the support substrate 11. Figure 9 is a schematic perspective view showing the peeling step S70, and Figure 10 is a schematic cross-sectional view showing the peeling step S70. The peeling step S70 is performed, for example, by a peeling apparatus 62 schematically shown in Figures 9 and 10.

[0095] The delamination apparatus 62 includes a holding table 64 for suction holding the bonded wafer 13. The upper surface of the holding table 64 is a holding surface 64a, and the holding table 64 can suction hold the bonded wafer 13 placed on the holding surface 64a. The holding table 64 is also connected to a rotational drive source (not shown), such as a motor, and is rotatable around an axis perpendicular to the holding surface 64a.

[0096] Furthermore, the peeling apparatus 62 uses a peeling blade 66 that is inserted from the outer periphery between the wafer 1 and the support substrate 11 of the bonded wafer 13 held on the holding table 64. The peeling blade 66 is a plate-shaped member that becomes thinner towards the tip and is made of a resin material or a metal material.

[0097] In the peeling step S70, the bonded wafer 13 is held by suction on the holding table 64, and the tip of the peeling blade 66 is inserted between the wafer 1 and the support substrate 11 of the bonded wafer 13. At this point, because the bonding strength between the wafer 1 and the support substrate 11 has decreased due to the second heating step S60, the wafer 1 easily peels away from the support substrate 11 at the portion where the peeling blade 66 is inserted.

[0098] In this state, when the holding table 64 is rotated around the table rotation axis 64b, the peeling blade 66 gradually expands the peeling area between the wafer 1 and the support substrate 11. In this process, as the peeling blade 66 is gradually pushed toward the center of the bonded wafer 13, the bond between the support substrate 11 and the support surface 11a of the wafer 1 is eventually released over the entire surface 1a of the wafer 1. In other words, the peeling of the wafer 1 from the support substrate 11 is completed, and the processed wafer 1 is obtained.

[0099] When the second heating step S60 is performed, the bonding strength between the wafer 1 and the support substrate 11 is reduced. Therefore, when the peeling step S70 is performed afterward to peel the wafer 1 from the support substrate 11, less force is required. As a result, since no large force is applied to the wafer 1 when it is peeled off, damage to the wafer 1 caused by the peeling process becomes extremely unlikely.

[0100] As described above, in the wafer processing method according to this embodiment, one or both of the surface 1a of the wafer 1 and the support surface 11a of the support substrate 11 are subjected to a hydrophilic treatment in advance, and then the surface 1a of the wafer 1 and the support surface 11a of the support substrate 11 are brought facing each other and joined to form a bonded wafer 13. Then, the wafer 1 included in the bonded wafer 13 is processed from the back surface 1b side, and then the wafer 1 is peeled off from the support substrate 11.

[0101] This method allows the wafer 1 to be supported by the support substrate 11 without the use of adhesive. Therefore, the wafer 1 supported by the support substrate 11 can be processed without the reduction in thickness uniformity or flatness caused by the adhesive layer. Consequently, the wafer 1 bonded to the support substrate 11 can be processed to have high flatness.

[0102] Here, we will explain the relationship between the conditions for atmospheric pressure plasma irradiation performed in the hydrophilization step S20 and the hydrophilicity of the surface 1a of wafer 1 irradiated with atmospheric pressure plasma. We will also explain the preferred range of hydrophilicity of the surface 1a of wafer 1.

[0103] In the hydrophilization step S20, if the intensity of the atmospheric pressure plasma irradiation is too high and the hydrophilicity of the surface 1a of the wafer 1 increases too much, the bonding strength between the wafer 1 and the support substrate 11 becomes too strong when the bonding step S30 and the first heating step S40 are performed. In this case, even if the second heating step S60 is performed after the processing step S50, the bonding strength cannot be sufficiently reduced, and the wafer 1 becomes difficult to peel off from the support substrate 11 in the peeling step S70.

[0104] Conversely, if the intensity of the atmospheric pressure plasma irradiation is too low in the hydrophilization step S20, and the hydrophilicity of the surface 1a of the wafer 1 does not increase, the bonding strength between the wafer 1 and the support substrate 11 may be insufficient even after performing the bonding step S30 and the first heating step S40. In this case, there is a risk that the wafer 1 will peel off from the support substrate 11 while the processing step S50 is being performed.

[0105] In other words, in the wafer processing method according to this embodiment, the optimal bonding strength between the wafer 1 and the support substrate 11 can be obtained by adjusting the irradiation conditions of the atmospheric pressure plasma performed as a hydrophilization treatment in the hydrophilization step S20. Here, we will describe an experiment concerning the relationship between the irradiation conditions of the atmospheric pressure plasma and the hydrophilicity (wettability) of the surface 1a of the wafer 1.

[0106] In this experiment, atmospheric pressure plasma was irradiated onto wafer 1 or a silicon wafer usable as a support substrate 11 under various irradiation conditions, and the wettability of the irradiated area was evaluated. Irradiation with atmospheric pressure plasma was performed using the atmospheric pressure plasma irradiation apparatus 2 described in Figure 2. The irradiation conditions that were changed were the distance from the plasma irradiation unit 8 to wafer 1, i.e., the irradiation distance, and the irradiation time of the atmospheric pressure plasma. Hydrophilicity was evaluated by dropping pure water onto the irradiated area and measuring the contact angle between the pure water and the silicon wafer surface.

[0107] In this experiment, the distance (Z) from the plasma irradiation unit 8 to wafer 1 was set to 5 mm, 10 mm, 20 mm, or 50 mm. The irradiation time with atmospheric pressure plasma was set to 3 seconds or 10 seconds. Figure 11 is a graph showing the relationship between the distance (Z) from the plasma irradiation unit 8 to wafer 1 and the water contact angle. The black circular plots on the graph represent an irradiation time of 3 seconds, and the white square plots represent an irradiation time of 10 seconds.

[0108] As shown in the graph, with an irradiation time of 3 seconds, the contact angle was 3° at an irradiation distance of 5 mm, 18° at an irradiation distance of 10 mm, 34° at an irradiation distance of 20 mm, and 45° at an irradiation distance of 50 mm. Furthermore, with an irradiation time of 10 seconds, the contact angle was 3° at an irradiation distance of 5 mm, 3° at an irradiation distance of 10 mm, 42° at an irradiation distance of 20 mm, and 43° at an irradiation distance of 50 mm. In addition, the contact angle was 52° before irradiation with atmospheric pressure plasma.

[0109] As shown in this graph, it was confirmed that the contact angle of water changes significantly depending on the irradiation time and irradiation distance of atmospheric pressure plasma, and that the hydrophilicity of the irradiated area of ​​atmospheric pressure plasma changes significantly.

[0110] In this experiment, when the contact angle was 52°, forming a bonded wafer from the wafer used in the experiment did not result in sufficient bonding strength. Furthermore, when the contact angle was 3°, forming a bonded wafer from the same wafer resulted in excessively high bonding strength, making it difficult to delaminate even after heating the bonded wafer.

[0111] Therefore, when the irradiation time of atmospheric pressure plasma is 3 seconds, it is preferable that the irradiation distance of the atmospheric pressure plasma be 10 mm or more. Also, when the irradiation time of atmospheric pressure plasma is 10 seconds, it is preferable that the irradiation distance of the atmospheric pressure plasma be 20 mm or more. However, the irradiation time and irradiation distance of the atmospheric pressure plasma are not limited to these values.

[0112] From another perspective, it is preferable that the contact angle between the surface 1a of the hydrophilized wafer 1 or the support surface 11a of the support substrate 11 and the dropped pure water be 10° or more and 50° or less, and more preferably 18° or more and 45° or less.

[0113] It should be noted that the present invention is not limited to the embodiments described above and can be implemented with various modifications. For example, in the above embodiment, the case in which the wafer 1 of the bonded wafer 13 is ground from the back surface 1b side in processing step S50 was described, but one aspect of the present invention is not limited to this.

[0114] In processing step S50, for example, the wafer 1 supported on the support substrate 11 may be polished from the back surface 1b side. Alternatively, in processing step S50, the wafer 1 supported on the support substrate 11 may be divided along the planned division line 3 by methods such as cutting or laser processing.

[0115] Furthermore, in the above embodiment, the case in which the bonded wafer 13 is held by the holding table 64 of the peeling device 62 and the wafer 1 is peeled off the support substrate 11 in the peeling step S70 was described, but the present invention is not limited to this. For example, after the processing step S50 is completed, a tape with a diameter greater than or equal to the diameter of the wafer 1 may be attached to the back surface 1b of the wafer 1 of the bonded wafer 13, and the bonded wafer 13 may be supported by the tape before the wafer 1 is peeled off the support substrate 11.

[0116] In this case, even if the wafer 1 becomes extremely thin due to processing, the wafer 1, after being peeled from the support substrate 11, is supported by the tape, making it easy to handle the wafer 1. Furthermore, further processing can be easily performed on the wafer 1 supported by the tape.

[0117] Furthermore, the structures and methods of the embodiments described above can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0118] 1 wafer 1a surface 1b back side Planned division lines (3 divisions) 5 devices 7 Outer area 9. Device Formation Region 11 Support substrate 11a Support surface 11b Back side 13 Bonded wafer 2. Atmospheric pressure plasma irradiation device 4. Holding Table 4a Holding surface 6 Table rotation axis 8 Plasma irradiation unit 10 Plasma 12 Heating device 14 Heating and holding table 14a Holding surface 16 Heating device 18 rotation axes 20 Cooling and holding tables 20a Holding surface 22 Laser annealing section 24 laser beams 26 Processing equipment 28 base 30 Holding Tables 30a Holding surface 30b Porous member 30c frame 30d Table rotation axis 32 Support structure 34 Processing Units 36 Lifting Unit 38 Guide rails 40 Lifting Plate 42 Ball screw 44 motors 46 Support 48 Spindle Housing 50 spindles 50a Spindle rotation shaft 52 Wheel Mount 54. Machining Tools (Grinding Wheels) 56 Wheel base 58 Sharpening Stone Section 60 Fixtures 62 Peeling device 64 Rotating Table 66 Release plate

Claims

1. A method for processing a wafer having a surface and a back surface opposite to the surface, A preparation step of preparing a support substrate having a support surface for supporting the wafer, A hydrophilization step in which a hydrophilization treatment is performed on either or both the surface of the wafer or the support surface of the support substrate, After the hydrophilization step, the surface of the wafer and the support surface of the support substrate are brought facing each other and joined to form a bonded wafer. A first heating step involves heating the bonded wafer to a first temperature to increase the bonding strength between the wafer and the support substrate, After the first heating step, a processing step is performed to process the wafer included in the bonded wafer from the back side, A second heating step is performed after the processing step, in which the bonded wafer is heated to a second temperature higher than the first temperature to reduce the bonding strength between the wafer and the support substrate. A wafer processing method characterized by comprising a peeling step of peeling the wafer from the support substrate after the second heating step.

2. The wafer processing method according to claim 1, characterized in that, in the hydrophilization step, the contact angle between the surface of the hydrophilized wafer or the support surface of the support substrate and the dropped pure water is 10° or more and 50° or less.

3. The wafer processing method according to claim 1 or 2, characterized in that the hydrophilization step is performed on the outer peripheral region of the surface of the wafer or the support surface of the support substrate, or both, but not on the area inside the outer peripheral region.

4. The wafer processing method according to claim 1 or 2, characterized in that the first heating step involves heating the outer peripheral region of the bonded wafer.

5. The wafer processing method according to claim 4, characterized in that the second heating step involves heating the outer peripheral region of the bonded wafer.

6. The wafer processing method according to claim 1, characterized in that the hydrophilization step involves bringing a plasma generated under atmospheric pressure into contact with one or both of the surface of the wafer or the support surface of the support substrate to perform the hydrophilization treatment.

7. The wafer processing method according to claim 1, characterized in that the support surface of the support substrate has an outer shape corresponding to the surface of the wafer.

8. The first temperature is 150°C or higher and less than 250°C. The wafer processing method according to claim 1, characterized in that the second temperature is 250°C or more and 350°C or less.

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