Wafer fabrication methods

Abstract

[Problem] To laminate a wafer onto a support substrate and process the wafer in a manner that improves flatness. [Solution] A wafer processing method, the wafer having a front side and a back side facing the front side, the wafer processing method comprising: a preparation step of preparing a support substrate having a support surface supporting the wafer; a hydrophilication step of performing a hydrophilication treatment on one or both of the front side of the wafer and the support surface of the support substrate; a bonding step of bonding the front side of the wafer and the support surface of the support substrate facing each other and bonding them together after the hydrophilication step to form a bonded wafer; a first heating step of heating the bonded wafer to a first temperature; a processing step of processing the wafer contained 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; and a peeling step of peeling the wafer from the support substrate after the second heating step.

Description

Technical Field

[0001] The present invention relates to a wafer processing method, which comprises laminating a wafer having a plurality of elements formed on the front side to a supporting substrate, processing the wafer laminating to the supporting substrate, and peeling the processed wafer from the supporting substrate. Prior Art

[0002] Chips containing components such as ICs (Integrated Circuits) are essential components of various electronic devices, including mobile phones and personal computers. These chips are manufactured by, for example, grinding a wafer with multiple components formed on the front side to the desired thickness, then forming dividing grooves through the wafer along the boundaries between the components.

[0003] In recent years, a technology has been developed to achieve higher capacity and smaller chips, stacking and integrating multiple chips such as DRAM (Dynamic Random Access Memory). This technology requires pre-thinning each chip to a thickness of less than 10 μm, but handling the wafers after thinning to this thickness is challenging. Therefore, a method has been adopted in which the pre-thinned wafers are bonded to a supporting substrate using a later removable adhesive (see Patent Document 1).

[0004] Furthermore, as wafers become thinner, the thickness uniformity and flatness (TTV) of the thinned wafers are also required to be improved. Specifically, for wafers thinned to a thickness of 10μm, a flatness of less than 0.5μm is required. [Conventional technical literature] [Patent Document]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-153193 Summary of the Invention

[0006] [Problems to be Solved by the Invention] However, when bonding a wafer to a supporting substrate using an adhesive, in order to complete a wafer with high flatness, not only a supporting substrate with extremely high flatness is used, but also the adhesive layer formed must have extremely high flatness.

[0007] Support substrates with sufficiently high flatness are obtained by pre-processing them with a grinding machine. However, improving the flatness of adhesives applied to support substrates and other materials is not easy. For example, when UV light is irradiated to cure the adhesive after sandwiching it between the support substrate and the wafer, the adhesive shrinks unevenly. As a result, the resulting adhesive layer tends to have low flatness.

[0008] The present invention is completed in view of this problem, and its purpose is to provide a wafer processing method, which can process the wafer that has been attached to the supporting substrate in a manner that improves the flatness.

[0009] [Technical means to solve the problem] According to the present invention, a method for processing a wafer is provided, wherein the wafer has a front side and a back side opposite to the front side, and the method for processing the wafer is characterized in that it comprises: a preparation step, wherein a supporting substrate is prepared, wherein the supporting substrate has a supporting surface for supporting the wafer; a hydrophilization step, wherein one or both of the front side of the wafer or the supporting surface of the supporting substrate are subjected to hydrophilization treatment; a bonding step, wherein after the hydrophilization step, the front side of the wafer and the supporting surface of the supporting substrate are made to face each other and bonded to form a bonded wafer; a first heating step, wherein the bonded wafer is heated to a first temperature to increase the bonding strength between the wafer and the supporting substrate; a processing step, wherein after the first heating step, the wafer contained in the bonded wafer is processed from the back side; a second heating step, wherein after the processing step, the bonded wafer is heated to a second temperature higher than the first temperature to reduce the bonding strength between the wafer and the supporting substrate; and a peeling step, wherein after the second heating step, the wafer is peeled off from the supporting substrate.

[0010] Preferably, in the hydrophilization step, the contact angle between the hydrophilized front surface of the wafer or the supporting surface of the supporting substrate and the dropped pure water is greater than or equal to 10° and less than or equal to 50°.

[0011] Furthermore, preferably, in the hydrophilization step, the hydrophilization treatment is performed on the peripheral area of ​​one or both of the front surface of the wafer and the supporting surface of the supporting substrate, and the hydrophilization treatment is not performed on the area inside the peripheral area.

[0012] Furthermore, preferably, in the first heating step, the peripheral area of ​​the bonded wafer is heated.

[0013] Furthermore, preferably, in the second heating step, the peripheral region of the bonded wafer is heated.

[0014] Furthermore, preferably, the hydrophilization step is performed by bringing plasma generated under atmospheric pressure into contact with one or both of the front surface of the wafer and the supporting surface of the supporting substrate.

[0015] Furthermore, preferably, the supporting surface of the supporting substrate has an outer shape corresponding to the front surface of the wafer.

[0016] Furthermore, preferably, the first temperature is greater than or equal to 150° C. and less than or equal to 250° C., and the second temperature is greater than or equal to 250° C. and less than or equal to 350° C.

[0017] [Effects of the invention] In one aspect of the wafer processing method of the present invention, a hydrophilic treatment is performed on one or both of the front surface of the wafer and the supporting surface of the supporting substrate. The front surface of the wafer and the supporting surface of the supporting substrate are then brought into contact and bonded to form a bonded wafer. The wafers included in the bonded wafer are then processed from the back side, and the wafers are then peeled from the supporting substrate.

[0018] According to this method, the wafer can be supported by the support substrate without using an adhesive. Therefore, the wafer supported by the support substrate can be processed without causing a decrease in the thickness uniformity or flatness of the adhesive layer.

[0019] Therefore, according to one aspect of the present invention, a wafer processing method is provided, which can process a wafer bonded to a supporting substrate in a manner that improves its flatness. Simple diagram description

[0020] FIG1(A) is a perspective view schematically showing a supporting substrate, and FIG1(B) is a perspective view schematically showing an example of a wafer. FIG2 is a perspective view schematically showing the hydrophilization step. FIG3(A) is a perspective view schematically showing a bonding step, and FIG3(B) is a perspective view schematically showing a bonded wafer. FIG4 is a perspective view schematically showing an example of the first heating step. FIG5(A) is a perspective view schematically showing a laser annealing unit and a holding table used in the first heating step of another example, and FIG5(B) is a perspective view schematically showing the first heating step of another example. FIG6 is a perspective view schematically showing a processing device. FIG7 is a perspective view schematically showing the processing steps. FIG8(A) is a perspective view schematically showing the second heating step of one example, and FIG8(B) is a perspective view schematically showing the second heating step of another example. FIG9 is a perspective view schematically showing the peeling step. FIG10 is a cross-sectional view schematically showing the peeling step. FIG. 11 is a graph showing an example of the relationship between hydrophilization treatment conditions and wettability. FIG12 is a flow chart showing the flow of a wafer processing method. Implementation Method

[0021] Embodiments of the present invention will be described with reference to the accompanying drawings. FIG1(B) schematically illustrates a perspective view of a wafer 1 processed using a wafer processing method according to this embodiment. Wafer 1 is formed into a circular plate shape using a semiconductor material such as silicon (Si). Multiple intersecting dividing lines 3 are defined on the front surface 1a of wafer 1. Components 5 are formed in each region of the front surface 1a of wafer 1 divided by the dividing lines 3.

[0022] The plurality of components 5 each include, for example, components used to form an IC, semiconductor memory, or image sensor. Furthermore, the boundaries between the plurality of components 5 extend, for example, in a grid pattern. Subsequently, by cutting the wafer 1 along the planned dividing lines 3, component wafers each including the components 5 can be produced.

[0023] Furthermore, there are no limitations on the material, shape, structure, or size of wafer 1. For example, wafer 1 can be made of semiconductor materials other than silicon (e.g., silicon carbide (SiC) or gallium nitride (GaN)). Similarly, there are no limitations on the type, quantity, shape, structure, size, or placement of elements 5.

[0024] Wafer 1 has a chamfered outer edge, meaning that a chamfered portion is formed on the outer edge of wafer 1. In other words, the side of wafer 1 is curved in a convex manner. Furthermore, the front surface 1a and the back surface 1b opposite the front surface 1a of wafer 1 are parallel, and local thickness variations are minimal.

[0025] Furthermore, an insulating film covering the device 5 may be provided on the front surface 1a of the wafer 1. The insulating film may be composed of, for example, a silicon oxide film (SiO2 film), a silicon nitride film (SiN film), a silicon oxynitride film (SiON film), a silicon carbonitride film (SiCN film), or an organic resin film. The top surface of the insulating film covering the device 5 may also be flattened using methods such as CMP (Chemical Mechanical Polishing). This flattening minimizes any unevenness on the front surface 1a of the wafer 1.

[0026] FIG1(A) is a perspective view schematically showing an example of a support substrate 11 attached to a wafer 1. In the processing method of wafer 1 of this embodiment, support substrate 11 is attached to the front surface 1a of wafer 1 to form a bonded wafer in order to protect components 5, etc., and wafer 1, contained within the bonded wafer, is processed.

[0027] The support substrate 11 will now be described. The support substrate 11 has a shape corresponding to the front surface 1a of the wafer 1. For example, the support substrate 11 is formed into a circular plate having the same shape as the wafer 1. For example, the support substrate 11 can be the same as the wafer 1 before forming the element 5. However, the support substrate 11 is not limited to this.

[0028] The support substrate 11 has a support surface 11a that supports the wafer 1 and a back surface 11b that faces the support surface 11a. By appropriately processing the wafer 1 supported by the support substrate 11, the support surface 11a and back surface 11b of the support substrate 11 have minimal unevenness and are equally flat as the front surface 1a and back surface 11b of the wafer 1. Furthermore, the support surface 11a and back surface 11b of the support substrate 11 are parallel to each other, and local variations in the thickness of the support substrate 11 are also minimal.

[0029] Conventionally, an adhesive is used to attach the support substrate 11 to the wafer 1. However, it is not easy to form a uniform thickness of the adhesive layer sandwiched between the wafer 1 and the support substrate 11. When the adhesive is irradiated with ultraviolet light to cure the adhesive after being sandwiched between the support substrate 11 and the wafer 1, the adhesive shrinks unevenly, which can lead to poor flatness of the resulting adhesive layer.

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

[0031] FIG12 is a flow chart showing the flow of each step of the wafer processing method of this embodiment. In the wafer processing method of this embodiment shown in FIG12 , first, a preparation step S10 is performed to prepare a support substrate 11 having a support surface 11 a for supporting the wafer 1 .

[0032] For example, in preparation step S10, a wafer without devices 5 formed thereon is prepared as support substrate 11. This wafer can also be used to manufacture device wafers. Alternatively, support substrate 11 can be prepared by processing a wafer that has devices formed thereon but is defective for some reason to remove the devices and flatten the wafer. The method for obtaining support substrate 11 is not limited.

[0033] Furthermore, in the preparation step S10, the size of the formed unevenness, i.e., the flatness, of the support surface 11a and back surface 11b of the support substrate 11 can be evaluated. Furthermore, the degree of parallelism between the support surface 11a and back surface 11b of the support substrate 11, i.e., the thickness uniformity of the support substrate 11, can also be evaluated. Then, in the preparation step S10, the support substrate 11 can be subjected to a process such as CMP so that the flatness and thickness uniformity meet predetermined levels.

[0034] Here, an example of the required flatness of the support surface 11a of the support substrate 11 prepared in the preparation step S10 is specifically described. For example, the support surface 11a of the support substrate 11 desirably has a surface roughness (Rms) of 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 satisfactorily bonded to the front surface 1a of the wafer 1, as described below.

[0035] Furthermore, if the flatness of the front 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 in preparation step S10, the front surface 1a of the wafer 1 may be subjected to a process such as CMP to improve its flatness. More specifically, CMP may be performed on the front surface 1a of the wafer 1 to a thickness of approximately 50 nm using a slurry used in CMP for removing barrier metals from semiconductor devices. Alternatively, a wafer 1 that has already undergone such CMP may be prepared in preparation step S10.

[0036] Next, a hydrophilization step S20 is performed to prepare for bonding between wafer 1 and support substrate 11. This step S20 hydrophilizes one or both of the front surface 1a of wafer 1 and the support surface 11a of support substrate 11. This step S20 is performed by contacting one or both of the front surface 1a of wafer 1 and the support surface 11a of support substrate 11 with plasma generated at atmospheric pressure (atmospheric pressure plasma).

[0037] The following description uses the example of performing a hydrophilic treatment on the front surface 1a of wafer 1. FIG2 is a schematic perspective view of wafer 1 undergoing a hydrophilic treatment on the front surface 1a. FIG2 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 irradiates a wafer 1 placed on a rotating support 4 with plasma 10 under atmospheric pressure. The upper surface of the rotating support 4 serves as a holding surface 4a, which preferably holds the wafer 1 placed on the holding surface 4a. For example, the rotating support 4 applies negative pressure to the wafer 1 placed on the holding surface 4a, thereby attracting and holding the wafer 1.

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

[0040] Here, the configuration of the plasma irradiation unit 8 is described. For example, the plasma irradiation unit 8 can utilize the plasma generating device "CeraPlas (registered trademark)" manufactured by TDK Electronics AG. However, the plasma irradiation unit 8 is not limited to this device and any plasma generating device capable of generating plasma 10 under atmospheric pressure can be utilized.

[0041] In the hydrophilization step S20, for example, wafer 1 is placed on the holding surface 4a of the rotary support table 4 with its front surface 1a, which will become the bonding surface, facing upward. Wafer 1 is then held by suction by the rotary support table 4. Subsequently, plasma 10 is irradiated from the plasma irradiation unit 8 onto the front surface 1a of the wafer 1 under predetermined conditions while the rotary support table 4 rotates one or more revolutions about the table rotation axis 6. In this manner, the outer peripheral area 7 of the front surface 1a of the wafer 1 is hydrophilized.

[0042] Next, an example of plasma irradiation conditions in the hydrophilization step S20 is described. For example, plasma irradiation unit 8 generates plasma using air as the gas type and sprays plasma 10 at a flow rate of 50 sccm. The distance from the plasma irradiation unit 8's ejection port to the front surface 1a of wafer 1 is set to approximately 10 mm, and the plasma is irradiated onto an area of ​​approximately 10 mm in diameter on the front surface 1a of wafer 1. Then, with the outer periphery of the plasma irradiation area positioned at the outer periphery of the front surface 1a of wafer 1, the rotary support 4 is rotated at a rotation speed of 3° to 30° per minute.

[0043] Alternatively, the support surface 11a of the support substrate 11 may be subjected to a hydrophilic treatment instead of the front surface 1a of the wafer 1. Furthermore, the hydrophilic treatment may be applied to both the front surface 1a of the wafer 1 and the support surface 11a of the support substrate 11. The steps for hydrophilicizing the support surface 11a of the support substrate 11 are the same as those for the hydrophilic treatment of the front surface 1a of the wafer 1. The conditions for irradiating the support surface 11a of the support substrate 11 with plasma are preferably the same as those for irradiating the front surface 1a of the wafer 1.

[0044] However, the plasma irradiation conditions in the hydrophilization step S20 are not limited thereto. The plasma irradiation conditions can be varied within a range that achieves predetermined properties on the front surface 1a of the wafer 1 or the support surface 11a of the support substrate 11. Furthermore, when performing the hydrophilization treatment on both the front surface 1a of the wafer 1 and the support surface 11a of the support substrate 11, the conditions do not need to be identical.

[0045] Here, we will explain the phenomena that occur on the front surface 1a of wafer 1, etc., when irradiated with atmospheric pressure plasma. Before irradiation with atmospheric pressure plasma, a large number of organic molecules floating in the atmosphere adhere to the wafer 1, etc., which is placed in air. Subsequently, when atmospheric pressure plasma is irradiated on the front surface 1a of wafer 1, etc., the organic molecules are removed from the irradiated area, and water molecules from the atmosphere attach to them, or the organic molecules decompose, resulting in the front surface 1a of wafer 1 being capped with numerous hydroxyl groups (OH groups).

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

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

[0048] Alternatively, hydrophilization can be performed using other methods. For example, it can be performed by irradiating the front surface 1a of the wafer 1 with ultraviolet light under predetermined conditions. Even in this case, the ultraviolet light decomposes or removes organic molecules attached to the front surface 1a of the wafer 1, leaving hydroxyl groups on the front surface 1a of the wafer 1.

[0049] Furthermore, in the hydrophilization step S20, the entire front surface 1a of the wafer 1 may be hydrophilized. 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 processing of the wafer 1.

[0050] However, if the entire front surface 1a of the wafer 1 is hydrophilized, when the support surface 11a of the support substrate 11 is bonded to the front surface 1a of the wafer 1, the device region 9 of the wafer 1, where the device 5 is formed, may become firmly attached to the support substrate 11. In this case, when the support substrate 11 is finally peeled off from the wafer 1, there is a concern that an additional load may be applied to the device 5.

[0051] Therefore, in the hydrophilization step S20, it is also preferred to perform a hydrophilization treatment on the outer peripheral region 7 of the front surface 1a of the wafer 1 where the device 5 is not formed, and not perform a hydrophilization treatment on the area inside the outer peripheral region 7. Furthermore, when performing a hydrophilization treatment 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 of this embodiment, the bonding step S30 is performed after the hydrophilization step S20. Next, the bonding step S30 will be described. FIG3(A) is a perspective view schematically showing the bonding step S30, and FIG3(B) is a perspective view schematically showing the resulting bonded wafer 13.

[0053] In the bonding step S30, as shown in FIG3(A), the front surface 1a of the wafer 1 is brought into contact with the supporting surface 11a of the supporting substrate 11. FIG3(A) shows the wafer 1 positioned above the supporting substrate 11, but the supporting substrate 11 may also be positioned above the wafer 1. The wafer 1 and the supporting substrate 11 are then brought closer together, with the front surface 1a of the wafer 1 in contact with the supporting surface 11a of the supporting substrate 11.

[0054] In this case, hydrogen bonds are formed between the front surface 1a of the wafer 1 and the supporting surface 11a of the supporting substrate 11 through the hydroxyl groups formed on one or both of them during the hydrophilization step S20. The two are then bonded together to form a bonded wafer 13. The amount of hydrogen bonds formed between the front surface 1a and the supporting surface 11a varies depending on the amount of hydroxyl groups formed during the hydrophilization step S20. Therefore, the bond strength between the wafer 1 and the supporting substrate 11 varies depending on the intensity of the hydrophilization treatment performed during the hydrophilization step S20.

[0055] In particular, when both the front 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 more easily formed between the hydroxyl groups formed on the front surface 1a and the hydroxyl groups formed on the support surface 11a. Consequently, the bonding strength between the wafer 1 and the support substrate 11 is enhanced.

[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. FIG4 is a perspective view schematically illustrating an example of the first heating step S40. In the first heating step S40, for example, a heating device 12 having a heating holding stage 14 with a built-in heater is used.

[0057] The heating and holding stage 14 included in the heating device 12 comprises a porous member with a suction path formed therein. The porous member has a diameter equal to that of the bonded wafer 13 and is exposed on its upper surface. One end of the suction path is connected to the porous member, and the other end is connected to a suction source (not shown). The upper surface of the porous member serves as a holding surface 14a on which the bonded wafer 13 is placed and held by suction. Furthermore, a heater (not shown) composed of, for example, a heating wire is disposed within the heating and holding stage 14.

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

[0059] If one or both of wafer 1 and support substrate 11 are hydrophilized and hydrogen bonds are formed to form bonded wafer 13, heating bonded wafer 13 to a certain temperature improves the adhesion between wafer 1 and support substrate 11. This is due in part to the hydroxyl groups that form hydrogen bonds, which undergo a dehydration condensation reaction, forming a covalent bond between front surface 1a and support surface 11a via oxygen atoms. This bond is stronger than a hydrogen bond.

[0060] Therefore, performing the first heating step S40 improves the adhesion of the bonded wafer 13, making it difficult for the wafer 1 to separate from the support substrate 11 even when the wafer 1 is processed in the processing step S50 described below. Therefore, in the wafer processing method of this embodiment, the heating conditions for the bonded wafer 13 in the first heating step S40 must be appropriately determined along with the conditions for the hydrophilization treatment in the hydrophilization step S20. The hydrophilization treatment conditions and the preferred range of the first temperature will be described in detail later.

[0061] The first heating step S40 may also be performed using a method other than heating by the heating device 12 having the heating holding stage 14. Next, another example of the first heating step S40 will be described. FIG5(A) is a perspective view schematically showing the laser annealing unit 22 and holding stage 20 used in another example of the first heating step, and FIG5(B) is a perspective view schematically showing another example of the first heating step.

[0062] The holding table 20 shown in Figure 5(A) includes a porous member exposed on its upper surface and a suction path (not shown) that applies negative pressure to the porous member. The upper surface of the porous member serves as a holding surface 20a for 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 suction and hold the bonded wafer 13.

[0063] The holding table 20 is supported by a table rotation shaft 18 connected to a rotational drive source (not shown), such as a motor. Operating this rotational drive source rotates the holding table 20 about the table rotation shaft 18. Furthermore, the holding table 20 may include an internal cooling water channel (not shown). Cooling water flowing through the cooling water channel maintains the holding table 20 at a predetermined temperature.

[0064] Furthermore, the diameter of the upper surface (holding surface 20a) of the holding table 20 is smaller than that of the bonded wafer 13. Therefore, when the bonded wafer 13 is held by the holding table 20 under suction, the outer peripheral area of ​​the bonded wafer 13 is exposed outside the holding surface 20a. Flowing cooling water through the cooling water path in this state helps maintain a constant temperature in the area of ​​the bonded wafer 13 in contact with the holding surface 20a.

[0065] The laser annealing unit 22 is described below. The laser annealing unit 22 is disposed outside the holding table 20 at a position lower than the holding surface 20a of the holding table 20. The laser annealing unit 22 includes 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 FIG5(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 holding table 20 suction-holds the bonded wafer 13. At this point, the outer peripheral region of the bonded wafer 13 is exposed outside the holding surface 20a. In this state, while the table rotation shaft 18 rotates to rotate the holding table 20, the laser annealing unit 22 irradiates the outer peripheral region of the bonded wafer 13 with a laser beam 24. This heats the outer peripheral region of the bonded wafer 13 to a first temperature.

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

[0068] Therefore, if the holding table 20 has a cooling water channel for cooling water to flow, it is preferable to first flow cooling water in the cooling water channel. In this case, the temperature of the bonded wafer 13 becomes difficult to rise inside the outer peripheral area of ​​the bonded wafer 13.

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

[0070] The processing performed on wafer 1 in processing step S50 is not limited. For example, in processing step S50, wafer 1 is ground and thinned from the back side. Although processing step S50 is described below using grinding as an example, processing step S50 is not limited to this.

[0071] First, the processing device for processing wafer 1 will be described. Figure 6 is a schematic perspective view of a processing device (grinding device) 26 for processing (grinding) a workpiece. Processing device 26 includes a base 28 that supports various components. An opening 28a is formed on the top surface of base 28 along the Y-axis direction.

[0072] The opening 28a is provided with: a holding platform 30, which can be moved along the Y-axis direction by a ball screw type moving mechanism; and a dust and drip proof cover 28b, which exposes the holding platform 30 and covers the opening 28a at the same time.

[0073] The holding table 30 can hold the bonded wafer 13, including the ground wafer 1, by suction. The holding table 30 comprises a stainless steel or ceramic frame 30c. A suction path (not shown) is provided within the frame 30c, one end of which is connected to a suction source (not shown), such as an ejector. The frame 30c has a recessed portion on its upper surface, formed by a disc-shaped space. A substantially disc-shaped porous member 30a is housed and secured within this recessed portion.

[0074] The diameter of the porous member 30a is set to be approximately the same as the diameter of the support substrate 11. The upper surface of the porous member 30a serves as 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 path and the porous member 30a, and the bonded wafer 13 is sucked and held on the holding table 30.

[0075] The holding table 30 is moved along the Y-axis by a Y-axis movement mechanism located within the opening 28a and covered by a dust and drip proof cover 28b. The Y-axis movement mechanism is, for example, a ball screw-type movement mechanism having a ball screw that is rotated by a rotational drive source such as a motor. Furthermore, the holding table 30 is connected to a rotational drive source such as a motor (not shown) and is rotatable about a table rotation axis 30d (see FIG. 7 ) perpendicular to the holding surface 30b.

[0076] The processing device 26 includes a processing unit (grinding unit) 34 that processes (grinds) the wafer 1 included in the bonded wafer 13 held by the holding table 30, and a processing feed unit 36 ​​that raises and lowers the processing unit 34. A support portion 32 is provided on the rear side of the processing device 26, and the processing unit 34 is supported by this support portion 32 via the processing feed unit 36. A pair of guide rails 38 extending along the Z-axis (vertical direction) are provided on the front surface of the support portion 32. A lifting plate 40 is slidably mounted on each guide rail 38.

[0077] A nut (not shown) is provided on the back side (rear surface) of the lift plate 40. A ball screw 42 is threadedly engaged with the nut, running parallel to the guide rail 38. A pulse motor 44 is connected to one end of the ball screw 42. Rotating the ball screw 42 by the pulse motor 44 causes the lift plate 40 to move in the Z-axis direction along the guide rail 38.

[0078] A processing unit 34, which performs grinding on the wafer 1, is fixed to the front surface of the lift plate 40. Moving the lift plate 40 allows the processing unit 34 to move in the Z-axis direction (grinding feed direction). The processing unit 34 includes a cut cylindrical support 46. The support 46 is fixed to the front surface of the lift plate 40 and serves as the outer shell of the processing unit 34.

[0079] A spindle housing 48 is provided inside the support body 46 and supported by the support body 46. A portion of the spindle 50 is rotatably housed within the spindle housing 48. A rotation drive mechanism (not shown), such as a motor, is connected to the upper end of the spindle 50. When the rotation drive mechanism is activated, the spindle 50 rotates about its axis of rotation.

[0080] The lower end of the spindle 50 is located below the bottom of the support 46. The upper surface of a disc-shaped wheel mount 52 is connected to the lower end of the spindle 50. A grinding wheel (processing tool) 54 is fixed to the wheel mount 52. FIG7 is a perspective view schematically showing a state in which the grinding wheel 54 fixed to the wheel mount 52 is processing (grinding) the wafer 1.

[0081] The grinding wheel (processing tool) 54 includes an annular wheel base 56. The wheel base 56 is formed of a metal such as aluminum and has a diameter corresponding to the diameter of the wafer 1. A plurality of grinding stones 58 are arranged in a ring on the outer periphery of the lower surface (bottom) of the wheel base 56. Each grinding stone 58 is formed by mixing abrasive grains such as diamond or cBN (cubic boron nitride) with a vitrified bond or a resin-based binder, and then sintering the resulting mixture.

[0082] The wheel mount 52 is provided with multiple grinding wheel fixing holes extending through the wheel mount 52, and the wheel base 56 is provided with locking holes for receiving a fixing tool 60, such as a bolt. Passing the fixing tool 60 through the grinding wheel fixing holes and locking it into the locking holes secures the grinding wheel 54 to the wheel mount 52. At this point, 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 held by suction by the holding table 30. At this time, the back surface 11b of the support substrate 11 faces the holding surface 30b, exposing the back surface 1b of the wafer 1 upward. Next, the holding table 30 is moved below the processing unit 34.

[0084] Then, the rotation drive source connected to the spindle 50 is operated to rotate the spindle 50 around the spindle rotation axis 50a. This causes the grinding wheel 54 to rotate, and the grinding stone 58 to move along the rotation track. Furthermore, the holding table 30 is rotated around the table rotation axis 30d.

[0085] Next, the processing feed unit 36 ​​is activated, lowering the processing unit 34. The bottom surface of the grinding stone 58, which is moving on a rotating track, comes into contact with the surface to be ground (back surface 1b) of the wafer 1. The wafer 1 is then ground, gradually becoming thinner. The thickness of the wafer 1 is monitored, and the lowering of the processing unit 34 is stopped when the wafer 1 reaches the desired thickness. Thus, a wafer 1 having the desired thickness is obtained.

[0086] In the wafer processing method of this embodiment, wafer 1 is supported by support substrate 11 without passing through the adhesive. Therefore, thickness variations in wafer 1 due to the adhesive layer are eliminated. Furthermore, because wafer 1 is supported by support substrate 11, it can be ground to an extremely thin thickness. The hydrophilization step S20 and the first heating step S40 enhance the adhesion between wafer 1 and support substrate 11, preventing wafer 1 from peeling off from support substrate 11 during processing.

[0087] In the wafer 1 processing method of this embodiment, the support substrate 11 is peeled from the processed wafer 1. In preparation for peeling the wafer 1, a second heating step S60 is performed after the processing step S50. This step heats the bonded wafer 13 to a second temperature, thereby reducing the bond strength between the wafer 1 and the support substrate 11. The second heating step S60 can be performed similarly to the first heating step S40. Therefore, the description of the second heating step S60 can be appropriately referred to the above description of the first heating step S40.

[0088] FIG8(A) is a perspective view schematically showing one example of the second heating step S60, and FIG8(B) is a perspective view schematically showing another example of the second heating step S60. In the second heating step S60, similar to the first heating step S40, the heating device 12 and the laser annealing unit 22 can be used.

[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 temperature, which is the target temperature for heating the bonded wafer 13 in the second heating step S60, is set higher than the first temperature, which is the 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 lower than 250°C, while the second temperature is preferably 250°C or higher and lower than 350°C.

[0090] As shown in FIG8(A), when the heating device 12 is used in the second heating step S60, the built-in heater is operated under conditions that can heat the bonded wafer 13 to the second temperature. Furthermore, when the laser annealing unit 22 is used in the second heating step S60, as shown in FIG8(B), the laser beam 24a is irradiated onto the bonded wafer 13 to heat the outer peripheral area of ​​the bonded wafer 13 to the second temperature.

[0091] Here, we will describe 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 (second temperature) higher than the first temperature at which the dehydration condensation reaction between the wafer 1 and the support substrate 11, as described in the first heating step S40, occurs, some of the organic molecules remaining between the wafer 1 and the support substrate 11 vaporize. Subsequently, bubbles form at the bond interface between the wafer 1 and the support substrate 11, reducing the bond strength between the wafer 1 and the support substrate 11. In other words, these bubbles can trigger delamination.

[0092] In turn, if the temperature of heating the joined wafer 13 in the first heating step S40 becomes too high, not only a dehydration condensation reaction but also an air bubble is generated in the joining interface between wafer 1 and the support substrate 11 . Therefore, there will be insufficient joint strength at the time point at the end of the first heating step S40.

[0093] Therefore, it is desirable to heat the bonded wafer 13 to a temperature at which it is difficult to generate bubbles in the first heating step s40 . That is, in the first heating step S40, it is advisable to heat the joint wafer 13 at a lower first temperature than in the second heating step S60.

[0094] In the processing method of the wafer of this embodiment, after the second heating step S60, a stripping step S70 is implemented, which strips the wafer 1 from the support substrate 11 . 9 is a schematic representation of a three-dimensional view of the stripping step S70, and FIG. The stripping step S70 is, for example, implemented by resorting to the stripping device 62 schematically represented in FIGS.

[0095] The stripping device 62 has a retaining stage 64 of the attractive retaining junction wafer 13 . The upper surface of the holding stage 64 becomes the holding surface 64 a , which may attract the bonded wafer 13 that the holding stage is loaded on the holding surface 64 a . Furthermore, the holding table 64 is connected with an unillustrated rotational drive source such as a motor and is capable of rotating around an axis perpendicular to the holding surface 64a .

[0096] Also, a stripping blade 66 is used in the stripping device 62 , which is inserted from the peripheral side between wafer 1 and the supporting substrate 11 of the engaged wafer 13 held in the holding table 64 . The stripping blade 66 is a plate-like member that is thinned toward the leading edge and is a member formed of a resin material or a metal material.

[0097] In the stripping step S70, the engaged wafer 13 is held to suction with the holding stage 64 , and the leading edge of the stripping blade 66 is inserted between wafer 1 of the engaged wafer 13 and the supporting substrate 11 . Herein, wafer 1 is easily stripped from the support substrate 11 in the portion where the stripping blade 66 has been inserted because the bonding strength of wafer 1 and support substrate 11 is reduced by the second heating step S 60 .

[0098] In this state, if the holding table 64 is rotated about the table rotation axis 64b, the peeling blade 66 gradually expands the separation area between the wafer 1 and the support substrate 11. During this process, if the peeling blade 66 is slowly pushed toward the center of the bonded wafer 13, the entire front surface 1a of the wafer 1 is eventually released from the support surface 11a of the support substrate 11. This completes the separation of the wafer 1 from the support substrate 11, resulting in a processed wafer 1.

[0099] Performing the second heating step S60 reduces the bonding strength between wafer 1 and support substrate 11. Therefore, when performing the subsequent peeling step S70 to peel wafer 1 from support substrate 11, a large force is not required. Therefore, since a large force is not applied to wafer 1 during peeling, damage to wafer 1 caused by the peeling operation is less likely to occur.

[0100] As described above, in the wafer processing method of this embodiment, one or both of the front surface 1a of the wafer 1 and the supporting surface 11a of the supporting substrate 11 are preliminarily subjected to a hydrophilic treatment. The front surface 1a of the wafer 1 and the supporting surface 11a of the supporting substrate 11 are then brought into contact with each other and bonded together to form a bonded wafer 13. The wafer 1 included in the bonded wafer 13 is then processed from the back surface 1b side, and then the wafer 1 is peeled from the supporting substrate 11.

[0101] According to this method, the wafer 1 can be supported by the support substrate 11 without using an adhesive. Therefore, the wafer 1 supported by the support substrate 11 can be processed without causing a decrease in thickness uniformity or flatness due to the adhesive layer. Therefore, the wafer 1 bonded to the support substrate 11 can be processed with improved flatness.

[0102] Here, the relationship between the conditions of atmospheric pressure plasma irradiation in the hydrophilization step S20 and the hydrophilicity of the front surface 1a of the wafer 1 irradiated with atmospheric pressure plasma is described. Furthermore, the preferred range of the hydrophilicity of the front surface 1a of the wafer 1 is described.

[0103] If the intensity of the atmospheric pressure plasma irradiation in the hydrophilization step S20 is too high, excessively increasing the hydrophilicity of the front surface 1a of the wafer 1 and other surfaces, the bond strength between the wafer 1 and the support substrate 11 will become too strong even after the bonding step S30 and the first heating step S40 have been performed. In this case, even performing the second heating step S60 after the processing step S50 will not sufficiently reduce the bond strength, making it difficult to peel the wafer 1 from the support substrate 11 in the peeling step S70.

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

[0105] In other words, in the wafer processing method of this embodiment, by adjusting the atmospheric pressure plasma irradiation conditions performed as a hydrophilic treatment in the hydrophilicization step S20, it is possible to achieve optimal bonding strength between the wafer 1 and the supporting substrate 11. Here, an experiment examining the relationship between atmospheric pressure plasma irradiation conditions and the hydrophilicity (wettability) of the front surface 1a of the wafer 1 and the like will be described.

[0106] In this experiment, atmospheric pressure plasma was applied to a silicon wafer (which can be used as wafer 1 or support substrate 11) while varying the irradiation conditions. The wettability of the area irradiated with atmospheric pressure plasma was evaluated. Atmospheric pressure plasma irradiation was performed using the atmospheric pressure plasma irradiation apparatus 2 illustrated in Figure 2 . The irradiation conditions varied depending on the distance from the plasma irradiation unit 8 to the wafer 1, i.e., the irradiation distance, and the irradiation time. Hydrophilicity was evaluated by dropping pure water onto the irradiated area and measuring the contact angle between the pure water and the front surface of the silicon wafer.

[0107] In this experiment, the distance (Z) from the plasma irradiation unit 8 to the wafer 1 was set to 5 mm, 10 mm, 20 mm, or 50 mm. Furthermore, the atmospheric pressure plasma irradiation time 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 the wafer 1 and the contact angle of water. The black circles in the graph represent an irradiation time of 3 seconds, while the hollow squares represent an irradiation time of 10 seconds.

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

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

[0110] Here, at a contact angle of 52°, even when a bonded wafer was formed from the wafer used in the experiment, the bond strength was insufficient. Furthermore, at a contact angle of 3°, when a bonded wafer was formed from the wafer used in the experiment, the bond strength was too high, making it difficult to separate the bonded wafer even after heating.

[0111] Therefore, when the atmospheric pressure plasma irradiation time is set to 3 seconds, the atmospheric pressure plasma irradiation distance is preferably 10 mm or greater. Furthermore, when the atmospheric pressure plasma irradiation time is set to 10 seconds, the atmospheric pressure plasma irradiation distance is preferably 20 mm or greater. However, the atmospheric pressure plasma irradiation time and irradiation distance are not limited to these.

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

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

[0114] In the processing step S50, for example, the wafer 1 supported by the support substrate 11 may be ground from the back surface 1b side. Furthermore, in the processing step S50, the wafer 1 supported by the support substrate 11 may be divided along the planned dividing lines 3 by dicing or laser processing.

[0115] Furthermore, in the above embodiment, while the peeling step S70 describes a case where the bonded wafer 13 is held by the holding table 64 of the peeling device 62 and the wafer 1 is peeled from the support substrate 11, one aspect of the present invention is not limited thereto. For example, after the processing step S50 is completed, an adhesive film having a diameter greater than the diameter of the wafer 1 may be attached to the back surface 1b of the bonded wafer 13, and after the bonded wafer 13 is supported by the adhesive film, the wafer 1 may be peeled from the support substrate 11.

[0116] In this case, even if the wafer 1 is processed to be extremely thin, the wafer 1 peeled from the support substrate 11 is supported by the adhesive film, making it easy to handle the wafer 1. Further processing can then be easily performed on the wafer 1 supported by the adhesive film.

[0117] In addition, the structures and methods of the above-mentioned embodiments can be appropriately modified and implemented without departing from the scope of the purpose of the present invention.

[0118] 1: Wafer 1a: Front 1b: Back 3: Split the predetermined line 5: Components 7: Peripheral area 9: Component area 11: Support substrate 11a: Support surface 11b: Back 13: Bonding wafers 2: Atmospheric pressure plasma irradiation device 4: Holding table 4a: Holding surface 6: Worktable rotation axis 8: Plasma irradiation unit 10: Plasma 12: Heating device 14: Heating holding table 14a: Keeping surface 16: Heating device 18: Rotation axis 20: Holding table 20a: Keep the surface 22: Laser annealing unit 24: Laser beam 26: Processing device 28:Abutment 30: Holding table 30a: porous component 30b: Keep surface 30c: frame 30d: Worktable rotation axis 32: Supporting part 34: Processing unit 36: Processing feed unit 38: Guide rail 40:Lifting plate 42: Ball Screw 44: Motor 46: support body 48: Spindle housing 50: spindle 50a: spindle rotation axis 52: Wheel mounting parts 54: Processing tools (grinding wheels) 56: Wheel base 58:Grinding stone 60:Fixing tools 62: Peeling device 64:Holding table 66: Peeling Blade

Claims

1. A method for processing a wafer, the wafer having a front side and a back side facing the front side, the method comprising: a preparation step of preparing a support substrate having a support surface supporting the wafer; a hydrophilication step of performing a hydrophilication treatment on one or both of the front side of the wafer and the support surface of the support substrate; a bonding step of, after the hydrophilication step, bonding the front side of the wafer to the support surface of the support substrate to form a bonded wafer; 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, after the first heating step, processing the wafer contained in the bonded wafer from the back side; a second heating step of, after the processing step, heating the bonded wafer to a second temperature higher than the first temperature to reduce 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.

2. The wafer fabrication method as described in claim 1, wherein, In this hydrophilization step, the contact angle between the front side of the wafer or the support surface of the support substrate after hydrophilization treatment and the dripped pure water is 10° or more and 50° or less.

3. The wafer processing method as described in claim 1 or 2, wherein, In this hydrophilization step, the hydrophilization treatment is performed on the outer peripheral area of ​​one or both of the front side of the wafer or the support surface of the support substrate, and not on the inner side beyond the outer peripheral area.

4. The wafer fabrication method as described in claim 1 or 2, wherein, In this first heating step, the outer peripheral region of the bonding wafer is heated.

5. The wafer fabrication method as described in claim 4, wherein, In the second heating step, the outer peripheral region of the bonding wafer is heated.

6. The wafer fabrication method as described in claim 1, wherein, The hydrophilization step is performed by bringing plasma generated under atmospheric pressure into contact with one or both of the front side of the wafer or the support surface of the support substrate.

7. The wafer fabrication method as described in claim 1, wherein, The supporting surface of the supporting substrate has an outer shape corresponding to the front side of the wafer.

8. The wafer fabrication method as described in claim 1, wherein, The first temperature is above 150°C and below 250°C, and the second temperature is above 250°C and below 350°C.

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