Substrate processing method and substrate processing apparatus

Abstract

A substrate processing method for processing a bonded substrate in which a first substrate and a second substrate are bonded together, the second substrate having a separation promotion layer and a laser absorption layer laminated in this order, the separation promotion layer and the laser absorption layer being formed on the second substrate, the processing method including: irradiating the laser absorption layer with a laser to form a separation modification layer and generate stress inside the laser absorption layer; and separating the second substrate from the first substrate along a boundary between the second substrate and the separation promotion layer.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a substrate processing method and a substrate processing apparatus. BACKGROUND

[0002] A method of manufacturing a semiconductor device is disclosed in Patent Literature 1. The method of manufacturing a semiconductor device includes a heating step of locally heating a separation oxide film by irradiating a CO2 laser from a back surface of a semiconductor substrate, and a transfer step of transferring a semiconductor element to a transfer target substrate by generating separation at the separation oxide film and / or an interface between the separation oxide film and the semiconductor substrate.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2007-220749 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] The technology according to the present disclosure appropriately separates a second substrate from a first substrate in a bonded substrate in which the first substrate and the second substrate are bonded.

[0008] SOLUTION TO PROBLEM

[0009] One embodiment of the present disclosure is a substrate processing method of processing a bonded substrate in which a first substrate and a second substrate are bonded, the second substrate having a separation promotion layer and a laser absorption layer laminated in this order, the separation promotion layer and the laser absorption layer being formed on the second substrate, the processing method including: irradiating a laser to the laser absorption layer to form a separation modification layer and generate stress inside the laser absorption layer; and separating the second substrate from the first substrate along a boundary of the second substrate and the separation promotion layer.

[0010] EFFECT OF THE INVENTION

[0011] According to the present disclosure, a second substrate can be appropriately separated from a first substrate in a bonded substrate in which the first substrate and the second substrate are bonded. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a side view showing an example of a bonded wafer processed by a wafer processing system.

[0013] Figure 2 is a plan view schematically showing an outline of a structure of a wafer processing system.

[0014] Figure 3 is a side view showing an outline of a structure of an interface laser irradiation apparatus.

[0015] Figure 4 This is a top view showing an outline of the structure of the laser irradiation device for the interface.

[0016] Figure 5 This is an explanatory diagram illustrating the formation of the peeling modification layer involved in this embodiment.

[0017] Figure 6 This is a top view showing an example of the formation of the peeling modified layer according to this embodiment.

[0018] Figure 7 This is an explanatory diagram illustrating the gas flow inside the overlapping wafer during wafer processing according to this embodiment.

[0019] Figure 8 This is a top view showing other examples of the formation of the peeling modified layer involved in this embodiment.

[0020] Figure 9 This is an explanatory diagram illustrating the peeling of the second wafer involved in this embodiment.

[0021] Figure 10 This is an explanatory diagram illustrating the peeling of the second wafer involved in this embodiment.

[0022] Figure 11 This is an explanatory diagram showing the pressing of the second wafer.

[0023] Figure 12 This is an explanatory diagram showing the pressing of the second wafer.

[0024] Figure 13 This is a side view illustrating the outline of the structure of the superimposed wafer in other embodiments.

[0025] Figure 14 This is an explanatory diagram illustrating the process of edge trimming involved in this embodiment. Detailed Implementation

[0026] In recent years, laser lift-off, a process known as laser stripping, has been used in LED manufacturing to peel GaN (gallium nitride) compound crystalline layers (material layers) from sapphire substrates. In this laser lift-off process, because the sapphire substrate is translucent to short-wavelength lasers (such as UV light), short-wavelength lasers with high absorption rates for the laser absorption layer can be used, and the range of lasers that can be selected is also wide.

[0027] On the other hand, in the manufacturing process of semiconductor devices, a device layer formed on the surface of one substrate (such as a silicon substrate) is transferred to another substrate. Generally, silicon substrates are transparent to NIR (near-infrared) lasers, but laser-absorbing layers are also transparent to NIR lasers, so the device layer may be damaged. Therefore, in the manufacturing process of semiconductor devices, lasers in the FIR (far-infrared) region are used for laser lift-off.

[0028] Generally, for example, a laser with an FIR wavelength can be used using a CO2 laser. In the method described in Patent Document 1 above, a CO2 laser is irradiated onto a release oxide film, which serves as a laser absorption layer, to generate a release at the interface between the release oxide film and the substrate.

[0029] However, after careful study, the inventors of this invention discovered that in the laser lift-off method, sometimes the peeling between the substrate and the laser absorption layer is not properly achieved, i.e., the transfer cannot be performed properly. Specifically, if there are areas on the surface of the laser absorption layer that have not been irradiated by the laser, and the bonding strength between the laser absorption layer and the substrate has not decreased, then if the wafer W is peeled off from the inside in these unirradiated areas, a portion of the wafer W (silicon wafer) may be transferred along with the device layer onto the surface of the laser absorption layer after the transfer process.

[0030] The technology disclosed herein involves appropriately peeling the second substrate from the first substrate in an overlapping substrate formed by bonding the first and second substrates. Hereinafter, a wafer processing system as a substrate processing apparatus and a wafer processing method as a substrate processing method according to this embodiment will be described with reference to the accompanying drawings. Furthermore, in this specification and the accompanying drawings, elements having substantially the same functional structure are labeled with the same reference numerals, thereby omitting repeated descriptions.

[0031] like Figure 1 As shown, in the wafer processing according to this embodiment, the overlapping wafer T, which serves as the overlapping substrate, is formed by bonding a first wafer W1, which serves as the first substrate, and a second wafer W2, which serves as the second substrate. Hereinafter, the side of the first wafer W1 that is bonded to the second wafer W2 is referred to as surface W1a, and the side opposite to surface W1a is referred to as back surface W1b. Similarly, the side of the second wafer W2 that is bonded to the first wafer W1 is referred to as surface W2a, and the side opposite to surface W2a is referred to as back surface W2b.

[0032] The first wafer W1 is, for example, a semiconductor wafer such as a silicon substrate. A device layer D1 comprising multiple devices is formed on the surface W1a of the first wafer W1. A surface film F1 is also formed on the device layer D1, through which the wafer W2 is bonded. Examples of surface films F1 include oxide films (SiO2 films, TEOS films), SiC films, SiCN films, or adhesives. Alternatively, sometimes neither the device layer D1 nor the surface film F1 is formed on the surface W1a.

[0033] The second wafer W2 is, for example, a semiconductor wafer such as a silicon substrate. On the surface W2a of the second wafer W2, starting from the surface W2a side, the release facilitator layer P2, the laser absorption layer P, the device layer D2, and the surface film F2 are stacked in the following order: release facilitator layer P2, laser absorption layer P, device layer D2, and surface film F2. The second wafer W2 is bonded to the first wafer W1 via the surface film F2. The device layer D2 and the surface film F2 are the same as the device layer D1 and surface film F1 of the first wafer W1, respectively. Examples of laser absorption layers P, such as oxide films (SiO2 films, TEOS films), which can absorb laser light (e.g., CO2 lasers), are given later. The release facilitator layer P2 is formed to facilitate the separation (transfer) of the second wafer W2 from the first wafer W1. This release facilitator layer P2 is formed of a material, such as silicon nitride (SiN), that provides a lower adhesion to the second wafer W2 (silicon) than to the laser absorption layer P. In addition, sometimes the release facilitator layer P2, the laser absorption layer P, the device layer D2, and the surface film F2 are not formed on the surface W2a. In this case, the release facilitator layer P2 and the laser absorption layer P are formed on the surface W1a of the first wafer W1 on which the device layer D1 and the surface film F1 are formed, and the device layer D1 is transferred to the side of the second wafer W2.

[0034] The peripheral portion We of the second wafer W2 is chamfered, and the thickness of the cross-section of the peripheral portion We decreases towards its leading edge. In semiconductor device manufacturing processes, the back side of the second wafer W2, formed in this way, is sometimes removed to thin it. During this thinning process, the peripheral portion We may become a sharp shape (a so-called blade shape). As a result, fragments are generated at the peripheral portion We of the second wafer W2, and the second wafer W2 may be damaged. Therefore, sometimes an edge trimming process, described later, is performed to remove the peripheral portion We of the second wafer W2 before this thinning process. The peripheral portion We is the part removed in this edge trimming, for example, a radial range of 0.5 mm to 3 mm from the outer end of the second wafer W2.

[0035] In the wafer processing system 1 described later in this embodiment, the aforementioned laser lift-off process, i.e., the transfer process of transferring the device layer D2 to the side of the first wafer W1, or the aforementioned edge trimming process, i.e., the removal process of removing the peripheral portion We of the second wafer W2, is performed as wafer processing.

[0036] like Figure 2 As shown, the wafer processing system 1 has a structure that connects the infeed / outfeed block G1, the conveyor block G2, and the processing block G3 into one unit. The infeed / outfeed block G1, the conveyor block G2, and the processing block G3 are arranged in the order described, starting from the negative X-axis direction.

[0037] The loading / unloading block G1 can, for example, load and unload boxes Ct, Cw1, and Cw2, respectively, with external components to accommodate multiple overlapping wafers T, multiple first wafers W1, and multiple second wafers W2. A box mounting stage 10 is provided on the loading / unloading block G1. In the illustrated example, multiple, for example, three boxes Ct, Cw1, and Cw2 are freely arranged in a row along the Y-axis on the box mounting stage 10. Furthermore, the number of boxes Ct, Cw1, and Cw2 mounted on the box mounting stage 10 is not limited to this embodiment and can be arbitrarily determined.

[0038] On the positive X-axis side of the transfer block G2 and the cassette stage 10, a wafer transfer device 20 is disposed adjacent to the cassette stage 10. The wafer transfer device 20 is configured to move freely on a transfer path 21 extending along the Y-axis direction. Furthermore, the wafer transfer device 20 has, for example, two transfer arms 22, 22 for holding and transferring overlapping wafers T, first wafer W1, and second wafer W2. Each transfer arm 22 is configured to move freely in the horizontal and vertical directions and about the horizontal and vertical axes. Moreover, the structure of the transfer arm 22 is not limited to this embodiment, and any structure can be adopted. Furthermore, the wafer transfer device 20 is configured to transfer overlapping wafers T, first wafer W1, and second wafer W2 to the cassettes Ct, Cw1, Cw2 of the cassette stage 10 and the transfer device 30 described later.

[0039] On the positive X-axis side of the transfer block G2 and the wafer transfer device 20, a transfer device 30 for transferring overlapping wafer T, first wafer W1 and second wafer W2 is provided adjacent to the wafer transfer device 20.

[0040] The processing block G3 includes a wafer transport device 40, a peripheral removal device 50, a cleaning device 60, an internal laser irradiation device 70, and an interface laser irradiation device 80.

[0041] The wafer transport device 40 is configured to move freely along a transport path 41 extending along the X-axis. Furthermore, the wafer transport device 40 has, for example, two transport arms 42, 42 that hold and transport the overlapping wafer T, the first wafer W1, and the second wafer W2. Each transport arm 42 is configured to move freely in the horizontal and vertical directions and about the horizontal and vertical axes. Moreover, the structure of the transport arm 42 is not limited to this embodiment, and any structure can be adopted. Furthermore, the wafer transport device 40 is configured to transport the overlapping wafer T, the first wafer W1, and the second wafer W2 to the transport device 30, the peripheral removal device 50, the cleaning device 60, the internal laser irradiation device 70, and the interface laser irradiation device 80.

[0042] A peripheral removal device 50 is disposed on the positive Y-axis side of the wafer transport device 40 and is used to remove the peripheral portion We of the second wafer W2, i.e., edge trimming. A cleaning device 60 is disposed on the negative Y-axis side of the wafer transport device 40 and is used to clean the overlapping wafer T after peeling or after removing the peripheral portion We. An internal laser irradiation device 70, which serves as the second laser irradiation unit, is disposed on the positive Y-axis side of the wafer transport device 40 and is used to irradiate the interior of the second wafer W2 with a laser (internal laser, such as a YAG laser) to form a peripheral modification layer M2, which serves as the base point for peeling off the peripheral portion We. An interface laser irradiation device 80 is disposed on the negative Y-axis side of the wafer transport device 40 and is used to irradiate the laser absorption layer P formed on the surface W2a of the second wafer W2 with a laser (interface laser, such as a CO2 laser). The structure of the interface laser irradiation device 80 will be described later.

[0043] The wafer processing system 1 described above is equipped with a control device 90, which serves as a control unit. The control device 90 is, for example, a computer, and has a program storage unit (not shown). The program storage unit stores programs for controlling the processing of overlapping wafers T in the wafer processing system 1. Additionally, the program storage unit also stores programs for controlling the operation of the drive systems of the various processing devices, transport devices, etc., described above to implement the wafer processing described later in the wafer processing system 1. Furthermore, the above programs can be recorded in a computer-readable storage medium H and installed from that storage medium H into the control device 90.

[0044] The wafer processing system 1 is configured as described above. In the wafer processing system 1, the laser lift-off process of the overlapping wafer T described above, namely, the transfer process of the transfer device layer D2 on the first wafer W1 and the edge trimming process of the second wafer W2 described above, can be performed separately. Furthermore, for example, if the edge trimming process of the second wafer W2 is not performed in the wafer processing system 1, the peripheral removal device 50 and the internal laser irradiation device 70 can be omitted.

[0045] In addition, in this embodiment, the second wafer W2 is stripped from the first wafer W1 in the interface laser irradiation device 80 as described later, but a stripping device as a stripping part may also be provided in the wafer processing system 1.

[0046] Next, the interface described above will be explained using the laser irradiation device 80.

[0047] like Figure 3 and Figure 4 As shown, the interface laser irradiation device 80 has a chuck 100 that holds the overlapping wafer T through its upper surface. The chuck 100 adsorbs and holds a portion or the entire back surface W1b of the first wafer W1. A lifting pin (not shown) is provided in the chuck 100 for transferring the overlapping wafer T between itself and the transport arm 42. The lifting pin is configured to pass through a through hole (not shown) formed in the chuck 100 and move freely up and down, supporting the overlapping wafer T from below and allowing it to move up and down.

[0048] The suction cup 100 is supported on the sliding table 102 via an air bearing 101. A rotating mechanism 103 is provided on the lower surface of the sliding table 102. The rotating mechanism 103 may incorporate a motor as a drive source. The suction cup 100 is configured to rotate freely about the θ axis (vertical axis) via the air bearing 101 through the rotating mechanism 103. The sliding table 102 is configured to move freely along a guide rail 105 provided on its lower surface via a moving mechanism 104, which is provided on the base 106 and extends along the Y-axis. Furthermore, there is no particular limitation on the drive source of the moving mechanism 104; for example, a linear motor may be used.

[0049] A laser head 110, serving as a laser irradiation unit, is disposed above the chuck 100. The laser head 110 includes a lens 111. The lens 111 is a cylindrical component disposed on the lower surface of the laser head 110, used to irradiate the superimposed wafer T held in the chuck 100 with laser light. In this embodiment, the laser is a pulsed CO2 laser, and the laser emitted from the laser head 110 passes through the second wafer W2 and irradiates the laser absorption layer P. Furthermore, the wavelength of the CO2 laser is, for example, 8.9 μm to 11 μm. Additionally, the laser head 110 is configured to be freely raised and lowered via a lifting mechanism (not shown). Furthermore, the laser light source is disposed at a phase-separated position outside the laser head 110.

[0050] Additionally, a transfer pad 120 serving as a peeling section is provided above the suction cup 100. The transfer pad 120 has an adsorption surface on its lower surface for adsorbing and holding the back side W2b of the second wafer W2. The transfer pad 120 is configured to move freely up and down via a lifting mechanism (not shown). The transfer pad 120 transports the second wafer W2 between the suction cup 100 and the transfer arm 42. Specifically, after the suction cup 100 is moved below the transfer pad 120 (to the junction position with the transfer arm 42), the transfer pad 120 is lowered to adsorb and hold the back side W2b of the second wafer W2. Then, the transfer pad 120 is raised again to peel the second wafer W2 from the first wafer W1. The peeled second wafer W2 is transferred from the transfer pad 120 to the transfer arm 42 and removed from the interface laser irradiation device 80. Furthermore, the transfer pad 120 can be configured to flip the surface and back side of the wafer via a flipping mechanism (not shown).

[0051] Next, the wafer processing performed using the wafer processing system 1 configured as described above will be explained. Furthermore, the following description will explain the case where laser lift-off processing is performed in the wafer processing system 1, specifically the case where the device layer D2 of the second wafer W2 is transferred to the first wafer W1. In this embodiment, the first wafer W1 and the second wafer W2 are pre-bonded in a bonding device (not shown) outside the wafer processing system 1 to form an overlapping wafer T.

[0052] First, a cassette Ct containing multiple overlapping wafers T is placed on the cassette stage 10 of the transfer block G1. Next, the overlapping wafers T are removed from the cassette Ct by the wafer transfer device 20. The overlapping wafers T removed from the cassette Ct are transferred to the wafer transfer device 40 via the transfer device 30, and then transported to the interface laser irradiation device 80. In the interface laser irradiation device 80, the second wafer W2 is peeled off from the first wafer W1 (laser peeling process).

[0053] Specifically, firstly, the overlapping wafer T, which is held in place by the conveying arm 42 via the lifting pin, is moved to a processing position by the moving mechanism 104. This processing position is a position where laser light can be irradiated from the laser head 110 onto the overlapping wafer T (laser absorption layer P).

[0054] Next, as Figure 5 and Figure 6 As shown, laser L (CO2 laser) is pulsedly irradiated from laser head 110 toward the back surface W2b of the second wafer W2. At this time, laser L passes through the back surface W2b of the second wafer W2 and the lift-off promoting layer P2, and is absorbed by the laser absorption layer P. Furthermore, within the laser absorption layer P that absorbs the laser L, as... Figure 7As shown in (a), stress is generated. Hereinafter, the stress accumulation layer formed by laser irradiation, which serves as the base point for the peeling of the second wafer W2 (the base point for the transfer of device layer D2), is sometimes referred to as the "peeling modification layer M1". Furthermore, by forming the peeling modification layer M1, almost all the energy of the laser L irradiated on the laser absorption layer P is absorbed and does not reach device layer D2. Therefore, damage to device layer D2 can be suppressed.

[0055] Here, the output of the laser L irradiating the laser absorption layer P is controlled so that the peeling promotion layer P2 and the laser absorption layer P will not peel off due to the stress generated by irradiating the laser L.

[0056] In this way, by eliminating the stress release space generated in a manner that prevents the peeling-promoting layer P2 from peeling off from the laser-absorbing layer P due to laser irradiation L, stress is accumulated inside the laser-absorbing layer P, thereby forming the peeling-modified layer M1. More specifically, for example, by irradiating the laser-absorbing layer P with a laser to vaporize it, the gas release space generated is eliminated as described above, thereby accumulating compressive stress into the peeling-modified layer M1. Alternatively, for example, by absorbing laser light to generate heat in the laser-absorbing layer P, the difference in thermal expansion coefficients between the peeling-promoting layer P2 and the laser-absorbing layer P causes shear stress to accumulate into the peeling-modified layer M1.

[0057] The stress generated by irradiating the laser L typically remains at the irradiation site of the laser L (inside the laser absorption layer P), as described above, and forms a release modification layer M1. However, in this embodiment, a release promoting layer P2 is formed between the surface W2a of the second wafer W2 and the laser absorption layer P. The adhesion between the release promoting layer P2 and the second wafer W2 is less than the adhesion between the release promoting layer P2 and the laser absorption layer P. Therefore, as... Figure 7 As shown in (b), the stress generated inside the laser absorption layer P passes through the release facilitator layer P2 and accumulates at the interface between the release facilitator layer P2 and the second wafer W2. In other words, the stress generated by irradiating the laser L moves to the interface between the release facilitator layer P2 and the second wafer W2, where it can be more stably retained, and accumulates at that interface. Moreover, when stress accumulates at the interface between the release facilitator layer P2 and the second wafer W2 in this way, the bonding strength between the release facilitator layer P2 and the second wafer W2 decreases.

[0058] Furthermore, in this embodiment, the entire surface of the laser absorption layer P, viewed from above, is irradiated with laser L targeting the laser absorption layer P, i.e., the separation promoting layer P2 and the second wafer W2 are separated. Specifically, when irradiating the laser absorption layer P with laser L, the chuck 100 (overlapping wafer T) is rotated by the rotation mechanism 103, and the chuck 100 is moved along the Y-axis by the moving mechanism 104. Thus, laser L is irradiated onto the laser absorption layer P, for example, from the radially outer side towards the inner side, resulting in laser L being irradiated in a spiral pattern from the outer side towards the inner side across the entire surface of the laser absorption layer P. Furthermore, Figure 6 The black arrows indicate the rotation direction of the suction cup 100. Furthermore, the formation direction of the peeling modification layer M1 can also be from the radial inside to the outer side.

[0059] Here, the formation interval of adjacent exfoliation modified layers M1, in other words, the pulse interval (frequency) of the laser L, is controlled to a distance such that exfoliation does not occur in adjacent exfoliation modified layers M1 due to the impact generated during the formation of the exfoliation modified layer M1. Specifically, for example, it is preferable that adjacent exfoliation modified layers M1 are formed in a manner that they do not overlap when viewed from above. In addition, it is preferable that adjacent exfoliation modified layers M1 are formed close to each other.

[0060] In addition, such as Figure 8 As shown, the laser L can be irradiated concentrically and in a ring shape within the laser absorption layer P. However, in this case, the rotation of the chuck 100 and the movement of the chuck 100 in the Y direction are performed alternately, so the irradiation time can be shortened and productivity increased by irradiating the laser L in a spiral shape as described above.

[0061] In this embodiment, when the laser L is irradiated onto the laser absorption layer P, the chuck 100 is rotated. However, the laser head 110 can also be moved to rotate relative to the chuck 100. Furthermore, the chuck 100 can be moved along the Y-axis, but the laser head 110 can also be moved along the Y-axis.

[0062] When laser L irradiates the entire surface of the laser absorption layer P, the suction cup 100 is then moved to the junction position below the transfer pad 120 by the moving mechanism 104. At the junction position, as... Figure 9 As shown in (a), the back surface W2b of the second wafer W2 is adsorbed and held by the transport pad 120, and then, as shown in (a), Figure 9As shown in (b), the transport pad 120 rises, thereby peeling the second wafer W2 from the release facilitator layer P2 (the first wafer W1). As a result, the device layer D2 formed on the surface of the second wafer W2 is transferred to the first wafer W1. At this time, as described above, stress generated by laser irradiation accumulates at the interface between the release facilitator layer P2 and the second wafer W2, reducing the bonding strength. Therefore, the second wafer W2 can be peeled from the release facilitator layer P2 without applying a large load.

[0063] Furthermore, as described above, the release modification layers M1 are formed in a non-overlapping manner. However, when the second wafer W2 peels off from the release promoting layer P2 at the location where the release modification layer M1 is formed, the stress accumulated during the formation of the release modification layer M1 is released to the outside. Moreover, in this embodiment, the release modification layers M1 are formed close to each other as described above. Therefore, when peeling occurs at the location where adjacent release modification layers M1 are formed, i.e., when stress is released to the outside at adjacent locations, a chain release occurs. That is, when a portion of the interface between the release promoting layer P2 and the second wafer W2 is peeled off by raising the transport pad 120, the entire surface of the second wafer W2 is chain-peeled off starting from that peeling location. In other words, the second wafer W2 can be peeled off from the release promoting layer P2 more appropriately without applying a large load.

[0064] Furthermore, sometimes regions (unpeeled regions) are formed where the laser absorption layer P is not irradiated with laser L due to factors such as the frequency of laser L and the rotation speed of the chuck 100, thus preventing the peeling of the release facilitator layer P2 from the second wafer W2. However, according to this embodiment, the release facilitator layer P2 is formed of a material with low adhesion to the second wafer W2 (silicon). Therefore, even when unpeeled regions are formed in this way, the peeling of the release facilitator layer P2 from the second wafer W2 can be easily performed. Moreover, since the release facilitator layer P2 is properly peeled from the second wafer W2 in this way, it is possible to appropriately suppress the transfer of a portion of the second wafer W2 (silicon wafer) onto the surface of the release facilitator layer P2 after the second wafer W2 has been peeled off. In addition, damage to the second wafer W2 after peeling can be suppressed.

[0065] Furthermore, when properly peeling at the interface between the peeling facilitator layer P2 and the second wafer W2, it is necessary to allow the stress generated by laser irradiation to pass through the peeling facilitator layer P2. Specifically, for example, when the laser absorption layer P is gasified, the generated gas needs to pass through the peeling facilitator layer P2. Additionally, for example, when peeling the peeling facilitator layer P2 and the second wafer W2 is performed using the difference in thermal expansion coefficients, it is necessary to properly transfer the heat generated by laser irradiation to the interface between the peeling facilitator layer P2 and the second wafer W2. However, when the thickness of the peeling facilitator layer P2 is large, the generated stress sometimes cannot properly pass through the peeling facilitator layer P2 and remains at the interface between the peeling facilitator layer P2 and the laser absorption layer P. Therefore, in order to properly peel at the interface between the peeling facilitator layer P2 and the second wafer W2, it is preferable that the thickness of the peeling facilitator layer P2 is thinner than that of the laser absorption layer P; specifically, for example, it is preferable that the thickness of the peeling facilitator layer P2 is about one-tenth the thickness of the laser absorption layer P. By reducing the thickness of the release facilitator layer P2 in this way, the generated stress can be properly transmitted through the release facilitator layer P2, thereby reducing the bonding strength between the second wafer W2 and the release facilitator layer P2. That is, the second wafer W2 can be properly peeled off from the release facilitator layer P2.

[0066] However, even if the stress generated by the large thickness of the release facilitator layer P2 does not properly pass through P2 and remains at the interface between P2 and the laser absorption layer P, P2 can still function as a protective film for the second wafer W2. That is, it can appropriately suppress the transfer of the silicon wafer and the device layer D2 together to the interface after the second wafer W2 is peeled off from the inside.

[0067] Specifically, the exfoliation modification layer M1 is formed by generating stress at the interface between the exfoliation promoting layer P2 and the laser absorption layer P, and stress remains at this interface, such as... Figure 10 As shown, the second wafer W2 is peeled off from the first wafer W1 with the peel-promoting layer P2 and the laser absorption layer P as the boundary. At this time, the second wafer W2 is peeled off from the laser absorption layer P through the peel-promoting layer P2, so no second wafer W2 remains at the peeling interface. That is, the surface W2a of the second wafer W2 can be protected, thereby suppressing damage to the peeling surface.

[0068] The second wafer W2, stripped from the first wafer W1, is transferred from the transfer pad 120 to the transfer arm 42 of the wafer transfer device 40 and then to the cassette Cw2 of the cassette stage 10. Furthermore, the surface W2a of the second wafer W2 can be cleaned in the cleaning device 60 before being transferred to the cassette Cw2 from the interface laser irradiation device 80.

[0069] On the other hand, the first wafer W1, held in the chuck 100, is transferred to the transfer arm 42 of the wafer transport device 40 via a lifting pin and then transported to the cleaning device 60. In the cleaning device 60, the surface of the release promoting layer P2, which serves as the release surface, is brushed. Furthermore, in the cleaning device 60, the back surface W1b of the first wafer W1 can be cleaned together with the surface of the release promoting layer P2.

[0070] Subsequently, the first wafer W1, after undergoing all the processing related to the transfer of device layer D2 to the first wafer W1, is transferred via the transfer device 30 to the cassette Cw1 of the cassette stage 1 by the wafer transfer device 20. In this way, a series of wafer processing steps in the wafer processing system 1 are completed.

[0071] According to the above embodiments, by forming a release facilitating layer P2 between the second wafer W2 and the laser absorption layer P, the second wafer W2 can be appropriately peeled from the first wafer W1, that is, the device layer D2 can be appropriately transferred. Specifically, the stress generated in the laser absorption layer P by irradiation with a laser moves to the boundary between the second wafer W2 and the release facilitating layer P2, thereby reducing the bonding strength at the boundary between the second wafer W2 and the release facilitating layer P2, and thus the second wafer W2 can be appropriately peeled from the release facilitating layer P2. In addition, since the release facilitating layer P2 is formed of a material with low adhesion to the second wafer W2 (e.g., SiN), the second wafer W2 can be more appropriately peeled off from the release facilitating layer P2.

[0072] Furthermore, in the above embodiment, a material with low adhesion to the second wafer W2 (silicon) is used as the release facilitator layer P2. However, the material used for the release facilitator layer P2 is not limited to this; for example, a material with a different coefficient of thermal expansion than that of the second wafer W2 (silicon) can also be used. In this case, since the amount of deformation caused by the heat generated by irradiating the laser absorption layer P with laser L is different between the second wafer W2 and the release facilitator layer P2, shear force is generated at the interface between the second wafer W2 and the release facilitator layer P2, enabling the second wafer W2 to be peeled off from the release facilitator layer P2. In particular, when shear stress is generated at the interface between the second wafer W2 and the release facilitator layer P2 as described above, and this shear stress accumulates into the release modification layer M1, by using a material with a different coefficient of thermal expansion as the release facilitator layer P2, the peeling of the second wafer W2 from the release facilitator layer P2 can be performed more appropriately.

[0073] Furthermore, in the above embodiments, the second wafer W2 is peeled from the peeling promotion layer P2 by irradiating the laser L. However, during the peeling of the second wafer W2, warping sometimes occurs in the overlapping wafer T. Moreover, when warping occurs in the overlapping wafer T, proper wafer processing in the wafer processing system 1 may not be possible. Therefore, in order to suppress the warping of the overlapping wafer T, the overlapping wafer T can be pressed down from above while the laser absorption layer P is irradiated with the laser L.

[0074] For example, in the case where the overlapping wafer T warps by deforming into a convex shape, such as Figure 11 As shown, the center portion of the superimposed wafer T can be pressed by the pressing member 200. Specifically, when peeling off the second wafer W2, firstly, a peeling modification layer M1 is pre-formed at the center portion of the laser absorption layer P, which is within the pressing range of the pressing member 200. There is no particular limitation on the radial formation direction of the peeling modification layer M1. When the peeling modification layer M1 is formed at the center portion of the laser absorption layer P, the center portion of the superimposed wafer T, where the peeling modification layer M1 is formed, is then pressed by the pressing member 200. Furthermore, while the center portion is pressed by the pressing member 200, the peeling modification layer M1 is formed at the outer periphery of the laser absorption layer P, and then the second wafer W2 is peeled off. At this time, since the center portion of the superimposed wafer T is pressed by the pressing member 200, warping of the superimposed wafer T can be suppressed during the formation of the peeling modification layer M1 at the outer periphery of the laser absorption layer P and the peeling off of the second wafer W2.

[0075] Furthermore, since the superimposed wafer T is rotated when the laser L is irradiated, it is desirable that the end of the pressing member 200 be configured to rotate together with the superimposed wafer T.

[0076] Additionally, for example, in the case where the overlapping wafer T warps by deforming into a convex shape, such as Figure 12 As shown, the periphery We of the overlapping wafer T can be pressed by the pressing member 200. Specifically, when peeling off the second wafer W2, firstly, a peeling modification layer M1 is pre-formed on the outer periphery of the laser absorption layer P, which is the pressing area of ​​the pressing member 200. When the peeling modification layer M1 is formed on the outer periphery of the laser absorption layer P, the outer periphery of the overlapping wafer T on which the peeling modification layer M1 is formed is then pressed by the pressing member 200. Furthermore, while the outer periphery is being pressed by the pressing member 200, the peeling modification layer M1 is formed at the center of the laser absorption layer P, and then the second wafer W2 is peeled off. At this time, since the outer periphery of the overlapping wafer T is pressed by the pressing member 200, warping of the overlapping wafer T can be suppressed when the peeling modification layer M1 is formed at the center of the laser absorption layer P and when the second wafer W2 is peeled off.

[0077] Furthermore, in the overlapping wafer T processed through the above embodiments, such as Figure 13 As shown, a reflective film R can be disposed between the laser absorption layer P and the device layer D2. That is, the reflective film R is formed on the side of the laser absorption layer P opposite to the incident surface of the laser L. A material with high reflectivity and high melting point for the laser L, such as a metal film, is used as the reflective film R. Furthermore, the device layer D2 is a functional layer, unlike the reflective film R.

[0078] In this case, the laser L emitted from the laser head 110 passes through the second wafer W2 and is almost completely absorbed in the laser absorption layer P. However, even if there is any unabsorbed laser L, it will be reflected by the reflective film R. As a result, the laser L will not reach the device layer D2, thus reliably suppressing damage to the device layer D2.

[0079] Furthermore, the laser L reflected by the reflective film R is absorbed in the laser absorption layer P. Therefore, the stripping efficiency of the second wafer W2 can be improved.

[0080] Furthermore, in the above embodiments, the laser lift-off process of the overlapping wafer T, i.e., the transfer process of the device layer D2 for the first wafer W1, was described in the wafer processing system 1. However, as described above, the edge trimming process of the second wafer W2 can be performed in the wafer processing system 1. The edge trimming process of the second wafer W2 in the wafer processing system 1 will be described below.

[0081] First, the overlapping wafer T is taken out from the cassette Ct of the cassette stage 10 placed on the transfer block G1 by the wafer transfer device 20, and then transferred to the wafer transfer device 40 via the transfer device 30, and then transferred to the internal laser irradiation device 70.

[0082] In the internal laser irradiation device 70, such as Figure 14 As shown in (a), a laser L2 (YAG laser) is irradiated into the interior of the second wafer W2 to form a peripheral modification layer M2, which serves as the base point for removing the peripheral portion We during edge trimming, as described later. A crack C2 extends from the peripheral modification layer M2 along the thickness direction of the second wafer W2. The upper and lower ends of the crack C2 reach, for example, the back surface W2b and the surface W2a of the second wafer W2, respectively. Next, the overlapping wafer T, with the peripheral modification layer M2 formed inside the second wafer W2, is transported by the wafer transport device 40 to the interface laser irradiation device 80.

[0083] In the interface laser irradiation apparatus 80, in the overlapping wafer T, the bonding strength between the peeling promoting layer P2 and the second wafer W2 at the peripheral portion We of the second wafer W2, which is the target of removal, decreases. Specifically, as Figure 14As shown in (b), when laser L (CO2 laser) is irradiated onto the laser absorption layer P, stress is generated inside the laser absorption layer P at a position further radially outward than the peripheral modification layer M2 formed by the internal laser irradiation device 70. Furthermore, the generated stress is as follows: Figure 14 As shown in (c), stress accumulates at the boundary between the second wafer W2 and the release-promoting layer P2 through the release-promoting layer P2.

[0084] Next, the overlapping wafer T, on which the peeling modification layer M1 and the peeling promotion layer P2 have been formed on the entire surface of the peripheral portion We, and whose bonding strength with the second wafer W2 has decreased, is transported to the peripheral removal device 50 by the wafer transport device 40.

[0085] In the peripheral removal device 50, in the overlapping wafer T, such as Figure 14 As shown in (d), the peripheral portion We of the second wafer W2 is removed (edge ​​trimming) using the peripheral modification layer M2 and the crack C2 as reference points. Furthermore, the edge trimming method of the peripheral removal apparatus 50 can be arbitrarily selected. In this case, when removing the peripheral portion We, the bonding strength between the second wafer W2 and the release promoting layer P2 is reduced by forming the release modification layer M1, thus making the removal of the peripheral portion We easier.

[0086] Next, the overlapping wafer T, with the peripheral portion We of the second wafer W2 removed, is transported to the cleaning unit 60 via the wafer transport device 40. In the cleaning unit 60, the overlapping wafer T is brushed. Afterward, the overlapping wafer T, having undergone all processing, is removed from the cleaning unit 60 by the wafer transport device 40 and transported to the cassette Ct of the cassette stage 10 via the wafer transport device 20 and the transfer device 30. In this way, the series of wafer processing steps in the wafer processing system 1 is completed.

[0087] As described above, according to the technology disclosed herein, the bonding strength between the second wafer W2 at the peripheral portion We and the peeling promotion layer P2 can be reduced in the interface laser irradiation apparatus 80, thereby enabling appropriate removal of the peripheral portion We, i.e., edge trimming, in the peripheral removal apparatus 50.

[0088] Furthermore, the processing sequence of processing the overlapping wafer T by the internal laser irradiation device 70 and the interface laser irradiation device 80 is not limited to the above embodiment. After the peripheral portion We is peeled off by the interface laser irradiation device 80, the peripheral modification layer M2 can be formed by the internal laser irradiation device 70.

[0089] It should be considered that the embodiments disclosed herein are illustrative in all respects and not restrictive. The above embodiments may be omitted, substituted, or modified in various ways without departing from the appended claims and their spirit.

[0090] Explanation of reference numerals in the attached figures

[0091] D2: Device layer; L: Laser; P: Laser absorption layer; P2: Lifting promotion layer; T: Overlapping wafer; W1: First wafer; W2: Second wafer; W2a: Surface; W2b: Back side.

Claims

1. A substrate processing method of processing a bonded substrate in which a first substrate and a second substrate are bonded, the second substrate having a separation promotion layer and a laser absorption layer laminated in this order, the substrate processing method comprising: forming a separation modification layer by irradiating laser light to the laser absorption layer, and generating stress inside the laser absorption layer; and separating the second substrate from the first substrate along a boundary between the second substrate and the separation promotion layer, wherein the separation promotion layer is formed of a material having a smaller adhesive force to the second substrate than an adhesive force to the laser absorption layer.

2. The substrate processing method according to claim 1, wherein a thickness of the separation promotion layer is smaller than a thickness of the laser absorption layer.

3. The substrate processing method according to claim 2, wherein the thickness of the separation promotion layer is 1 / 10 of the thickness of the laser absorption layer.

4. The substrate processing method according to any one of claims 1 to 3, wherein, during formation of the separation modification layer, the stress generated inside the laser absorption layer is transmitted through the separation promotion layer and accumulated at the boundary between the second substrate and the separation promotion layer, to reduce the bonding strength of the separation promotion layer to the second substrate.

5. The substrate processing method according to any one of claims 1 to 3, wherein the separation promotion layer is formed of a material having a thermal expansion rate different from a thermal expansion rate of the second substrate.

6. The substrate processing method according to claim 1, wherein the material forming the separation promotion layer is SiN.

7. The substrate processing method according to any one of claims 1 to 3, wherein the separation of the second substrate is performed by releasing the stress generated inside the laser absorption layer and accumulated in a chain.

8. The substrate processing method according to any one of claims 1 to 3, further comprising forming a peripheral modification layer along a boundary between a peripheral portion of the second substrate as a removal target and a central portion of the second substrate, wherein the separation modification layer is formed at a position more radially outward than the peripheral modification layer.

9. The substrate processing method according to any one of claims 1 to 3, wherein a reflective film is formed on a surface of the laser absorption layer opposite to a surface on which the laser light is incident, the laser light not absorbed by the laser absorption layer among the laser light irradiated to the laser absorption layer is reflected by the reflective film, and the laser light reflected by the reflective film is absorbed by the laser absorption layer.

10. A substrate processing apparatus of processing a bonded substrate in which a first substrate and a second substrate are bonded, the second substrate having a separation promotion layer and a laser absorption layer laminated in this order, the substrate processing apparatus comprising: a laser light irradiation section that irradiates laser light to the laser absorption layer. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ a peeling section that peels the second substrate from the first substrate; and a control section that controls operations of the laser irradiation section and the peeling section, wherein the control section controls the operation of the laser irradiation section so that the second substrate can be peeled from the first substrate along a boundary of the second substrate and the peeling promotion layer after a stress is generated inside the laser absorption layer by forming the peeling modification layer by irradiating the laser, the peeling promotion layer is formed of a material that has a smaller adhesive force with the second substrate than with the laser absorption layer.

11. The substrate processing apparatus according to claim 10, wherein a thickness of the peeling promotion layer is smaller than a thickness of the laser absorption layer.

12. The substrate processing apparatus according to claim 11, wherein the thickness of the peeling promotion layer is 1 / 10 of the thickness of the laser absorption layer.

13. The substrate processing apparatus according to any one of claims 10 to 12, wherein the control section controls the operation of the laser irradiation section so that a stress generated by modification of the laser absorption layer is transmitted through the peeling promotion layer and accumulated at a boundary of the second substrate and the peeling promotion layer, to decrease a bonding strength of the peeling promotion layer and the second substrate.

14. The substrate processing apparatus according to any one of claims 10 to 12, wherein the peeling promotion layer is formed of a material that has a different thermal expansion rate from a thermal expansion rate of the second substrate.

15. The substrate processing apparatus according to claim 10, wherein a material that forms the peeling promotion layer is SiN.

16. The substrate processing apparatus according to any one of claims 10 to 12, wherein the control section controls the operations of the laser irradiation section and the peeling section so that peeling of the second substrate can be performed by releasing the stress generated inside the laser absorption layer and accumulated in a chain.

17. The substrate processing apparatus according to any one of claims 10 to 12, further comprising a second laser irradiation section for forming a peripheral modification layer along a boundary of a peripheral portion of the second substrate and a central portion of the second substrate, the control section controls the operation of the laser irradiation section so that the peeling modification layer is formed at a position more radially outward than the peripheral modification layer.

18. The substrate processing apparatus according to any one of claims 10 to 12, wherein a reflecting film is formed on a surface of the laser absorption layer opposite to a surface on which the laser is incident. ​

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