Device and method for bonding sapphire epitaxial wafer and silicon wafer

Abstract

The invention relates to the technical field of semiconductor technologies, in particular to a device and a method for bonding a sapphire epitaxial wafer and a silicon wafer, the sapphire epitaxial wafer can be expanded towards the position of an arc-shaped concave cavity by arranging the arc-shaped concave cavity, and an arc-shaped convex part is arranged to abut against the silicon wafer stacked above the sapphire epitaxial wafer, so that the bonding effect of the sapphire epitaxial wafer and the silicon wafer is improved. The possibility of upward expansion of the sapphire epitaxial wafer can be effectively avoided, and the expansion size of the sapphire epitaxial wafer is limited in the arc-shaped concave cavity as much as possible, so that the warping degree after bonding of the sapphire epitaxial wafer and the silicon wafer is effectively reduced.

Description

Technical Field

[0001] The present application relates to the field of semiconductor process technology, and in particular, to a device and method for bonding a sapphire epitaxial wafer to a silicon wafer. Background Art

[0002] Wafer bonding technology uses the force of an external field to bond two homogeneous or heterogeneous wafers into a whole that meets the requirements. However, large warping is likely to occur during the bonding process. The warping will not only affect the yield of bonding, but will also have an adverse effect on the subsequent stripping process and photolithography alignment, which will directly affect the yield of the chip. When two warped silicon wafers are used for bonding, they can be flattened with a flat fixture (i.e., the pressing surface is flat). Since the thermal expansion coefficients of the two silicon wafers are the same, the warping after bonding can be reduced to a certain extent. However, in the bonding process of sapphire epitaxial wafers and silicon wafers, since the sapphire epitaxial wafer itself has a certain warping height, and the expansion coefficient of the sapphire epitaxial wafer is higher than that of the silicon wafer, large warping is likely to occur during the bonding process. In existing bonding technologies, bonding mainly uses a flat fixture, and the flat fixture has very limited improvement on the warping of the bonding of sapphire epitaxial wafers and silicon wafers, and cannot effectively reduce the warping after bonding.

[0003] There is currently no effective technical solution to the above problems. Summary of the invention

[0004] The purpose of the present application is to provide a device for bonding a sapphire epitaxial wafer and a silicon wafer, which can effectively reduce the warping of the sapphire epitaxial wafer and the silicon wafer after bonding.

[0005] In a first aspect, the present application provides a device for bonding a sapphire epitaxial wafer and a silicon wafer, comprising: a jig, wherein the jig comprises an upper jig and a lower jig; An arc-shaped concave cavity is provided at the upper end of the lower fixture, and the arc-shaped concave cavity is used to place the sapphire epitaxial wafer that is warped downward; The lower end of the upper fixture is provided with an arc-shaped protrusion, the arc-shaped protrusion is used to abut against the silicon wafer stacked on the sapphire epitaxial wafer, and the arc-shaped concave cavity is adapted to the arc-shaped protrusion; The upper jig and the lower jig are used to bond the sapphire epitaxial wafer and the silicon wafer by pressing each other.

[0006] Through the above-mentioned arrangement, the warping degree of the sapphire epitaxial wafer and the silicon wafer after bonding can be effectively reduced, so that the yield of the subsequent stripping process and photolithography alignment can be greatly improved.

[0007] Optionally, the maximum depth of the arc-shaped concave cavity is half of the warping height of the sapphire epitaxial wafer.

[0008] Through the above arrangement, the warping of the sapphire epitaxial wafer is effectively reduced.

[0009] Optionally, the linear width of the arc-shaped concave cavity is 5 mm-10 mm larger than the linear width of the sapphire epitaxial wafer.

[0010] Optionally, the upper fixture is made of graphite.

[0011] Through the above settings, graphite has high strength and rigidity, is light in weight, and can withstand the pressure when the sapphire epitaxial wafer and the silicon wafer are bonded.

[0012] Optionally, the material of the lower fixture is graphite.

[0013] Optionally, a graphite gasket is provided on the upper surface of the arc-shaped concave cavity.

[0014] Optionally, a graphite gasket is provided on the lower surface of the arc-shaped protrusion.

[0015] Optionally, the upper end surface of the lower fixture is provided with a fixing portion, and the lower end surface of the upper fixture is provided with a through hole adapted to the fixing portion, and the fixing portion is used to fix the sapphire epitaxial wafer and the silicon wafer in the arc-shaped concave cavity.

[0016] In a second aspect, the present application provides a method for bonding a sapphire epitaxial wafer to a silicon wafer, based on any of the above-mentioned devices for bonding a sapphire epitaxial wafer to a silicon wafer, the method for bonding a sapphire epitaxial wafer to a silicon wafer comprises the steps of: A1. placing a sapphire epitaxial wafer on the arc-shaped concave cavity of the lower fixture, and making the warping direction of the sapphire epitaxial wafer face downward; A2. Placing a silicon wafer on top of the sapphire epitaxial wafer; A3. Align the upper jig with the lower jig and place it into the cavity of the bonding device; A4. Evacuate the cavity of the bonding device to reach a preset vacuum degree; A5. Heat and pressurize the jig to bond the sapphire epitaxial wafer in the jig to the silicon wafer.

[0017] Optionally, step A5 includes: The jig was heated to 260° C. and a pressure of 5000 kgf was applied to the jig to bond the sapphire epitaxial wafer in the jig to the silicon wafer.

[0018] Beneficial effect: The present application provides a device and method for bonding a sapphire epitaxial wafer and a silicon wafer. By providing an arc-shaped concave cavity, the sapphire epitaxial wafer can be expanded toward the position of the arc-shaped concave cavity, and an arc-shaped protrusion is provided to abut against the silicon wafer stacked on the sapphire epitaxial wafer, which can effectively avoid the possibility of the sapphire epitaxial wafer expanding upward, and limit the size of the expansion of the sapphire epitaxial wafer to the extent possible within the arc-shaped concave cavity, thereby effectively reducing the warping of the sapphire epitaxial wafer and the silicon wafer after bonding. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the structure of the lower fixture provided in this application.

[0020] Figure 2 This is a schematic diagram of the structure of the upper fixture provided in this application.

[0021] Figure 3 This is a schematic diagram of the positions of the fixing part and the lower fixture provided in this application.

[0022] Figure 4 This is a schematic diagram of the positions of the through holes and the upper fixture provided in this application.

[0023] Figure 5 Schematic diagram of the effect of sapphire epitaxial wafer warping.

[0024] Explanation of reference numerals: 10, upper fixture; 11, arc-shaped protruding portion; 20, lower fixture; 21, arc-shaped concave cavity; 30, fixing portion; 40, through hole. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0026] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0027] Please refer to Figure 1-4As shown, in a first aspect, the present application provides a device for bonding a sapphire epitaxial wafer and a silicon wafer, comprising: a fixture, the fixture comprising an upper fixture 10 and a lower fixture 20; An arc-shaped concave cavity 21 is provided at the upper end of the lower fixture 20, and the arc-shaped concave cavity 21 is used to place the sapphire epitaxial wafer that is warped downward; The lower end of the upper fixture 10 is provided with an arc-shaped protrusion 11, which is used to abut against the silicon wafer stacked on the sapphire epitaxial wafer, and the arc-shaped concave cavity 21 is adapted to the arc-shaped protrusion 11; The upper fixture 10 and the lower fixture 20 are used to bond the sapphire epitaxial wafer and the silicon wafer by pressing each other.

[0028] The downward warping of the sapphire epitaxial wafer refers to the sapphire epitaxial wafer bending downward before bonding so that the height of the edge is lower than the height of the middle. Figure 5 Shown by the dashed line.

[0029] Specifically, since the thermal expansion coefficient of the sapphire epitaxial wafer is relatively high and the thermal expansion coefficient of the silicon wafer is relatively low, the two expand at different speeds during bonding. Since ordinary flat jigs do not reserve this space, the warping of the sapphire epitaxial wafer after bonding cannot be effectively reduced. Therefore, the present application provides an arc-shaped concave cavity 21 to allow the sapphire epitaxial wafer to expand toward the position of the arc-shaped concave cavity 21, and provides an arc-shaped protrusion 11 so that the arc-shaped protrusion 11 abuts against the silicon wafer stacked on the sapphire epitaxial wafer, which can effectively avoid the possibility of the sapphire epitaxial wafer expanding upward, and limit the size of the expansion of the sapphire epitaxial wafer to the arc-shaped concave cavity 21 as much as possible, thereby effectively reducing the warping of the sapphire epitaxial wafer and the silicon wafer after bonding.

[0030] Among them, the applicant conducted comparative tests on the same sapphire epitaxial wafer and silicon wafer. The warping height after bonding using a conventional flat jig was 500μm, while using the upper jig 10 and the lower jig 20 of the present application, the warping height of the sapphire epitaxial wafer and the silicon wafer after bonding was only 100μm. Therefore, the device for bonding sapphire epitaxial wafers and silicon wafers of the present application can effectively reduce the warping of the sapphire epitaxial wafer and the silicon wafer after bonding, thereby greatly improving the yield of the subsequent stripping process and lithography alignment.

[0031] In the present application, only one jig is needed to effectively improve the warping problem of sapphire epitaxial wafers and silicon wafers after bonding, with low economic cost and great economic benefits.

[0032] In some embodiments, the maximum depth of the arc-shaped concave cavity 21 is half of the warping height of the sapphire epitaxial wafer.

[0033] Specifically, during the bonding process between the sapphire epitaxial wafer and the silicon wafer, the position where the sapphire epitaxial wafer is warped is mainly concentrated in the middle position, and the arc-shaped protrusion 11 of the upper fixture 10 abuts against the silicon wafer stacked on the sapphire epitaxial wafer, that is, the main force of the arc-shaped protrusion 11 is concentrated in the middle position of the silicon wafer, which can limit the height of the warping of the sapphire epitaxial wafer, and by setting the maximum depth of the arc-shaped concave cavity 21 (such as Figure 1 The H in the figure is half of the warping height of the sapphire epitaxial wafer, which effectively reduces the warping degree of the sapphire epitaxial wafer.

[0034] If the warping height of the sapphire epitaxial wafer before bonding is 80 μm, the maximum depth of the arc-shaped concave cavity 21 can be designed to be 40 μm, but is not limited thereto and can be specifically set according to the warping height of the sapphire epitaxial wafer.

[0035] In some embodiments, the linear width of the arc-shaped concave cavity 21 is 5 mm-10 mm greater than the linear width of the sapphire epitaxial wafer (referring to the linear distance between two opposite edges).

[0036] Specifically, in order to reasonably ensure that the fixture can accommodate the silicon substrate and the sapphire epitaxial wafer, the linear width of the arc-shaped concave cavity 21 (eg Figure 1 The L in the figure is 5mm-10mm larger than the straight width of the sapphire epitaxial wafer.

[0037] In some embodiments, the material of the upper jig 10 is graphite.

[0038] Specifically, graphite has high strength and rigidity, is lightweight, and can withstand the pressure when bonding sapphire epitaxial wafers to silicon wafers.

[0039] In some embodiments, the material of the lower jig 20 is graphite.

[0040] Specifically, in order to ensure that the hardness of the jig is large enough to withstand the pressure during bonding, the material of the lower jig 20 is also graphite.

[0041] In some embodiments, a graphite gasket is disposed on the upper surface of the arc-shaped concave cavity 21 .

[0042] Specifically, since the graphite gasket has good compression resilience and can rebound when subjected to pressure, and at the same time, it also has good strength and can withstand certain mechanical stress, a graphite gasket is provided on the upper surface of the arc-shaped concave cavity 21 to further release the uneven pressure during bonding, which is beneficial to improving the stability of the bonding.

[0043] In some embodiments, a graphite gasket is disposed on the lower surface of the arc-shaped protrusion 11 .

[0044] Specifically, by providing a graphite gasket, the uneven pressure during bonding is further released, which is beneficial to improving the stability of bonding.

[0045] In some embodiments, the upper end surface of the lower fixture 20 is provided with a fixing portion 30 , and the lower end surface of the upper fixture 10 is provided with a through hole 40 adapted to the fixing portion 30 , and the fixing portion 30 is used to fix the sapphire epitaxial wafer and the silicon wafer in the arc-shaped concave cavity 21 .

[0046] Specifically, Figure 3 and Figure 4 As shown, by providing the fixing portion 30, displacement of the sapphire epitaxial wafer and the silicon wafer during the bonding process can be avoided.

[0047] In a second aspect, the present application provides a method for bonding a sapphire epitaxial wafer to a silicon wafer. Based on any of the above-mentioned devices for bonding a sapphire epitaxial wafer to a silicon wafer, the method for bonding a sapphire epitaxial wafer to a silicon wafer comprises the steps of: A1. Place the sapphire epitaxial wafer on the arc-shaped concave cavity 21 of the lower fixture 20, and make the warping direction of the sapphire epitaxial wafer face downward; A2. Place the silicon wafer on top of the sapphire epitaxial wafer; A3. Align the upper fixture 10 and the lower fixture 20 and place them into the cavity of the bonding device; A4. Evacuate the cavity of the bonding equipment to reach a preset vacuum degree; A5. Heat and pressurize the jig to bond the sapphire epitaxial wafer in the jig to the silicon wafer.

[0048] Specifically, first, a sapphire epitaxial wafer is placed on the arc-shaped concave cavity 21 of the lower jig 20, and the warping direction of the sapphire epitaxial wafer is directed downward, that is, the downwardly bent side of the sapphire epitaxial wafer is adapted to the concave cavity in the arc-shaped concave cavity 21, and then a silicon wafer is placed on top of the sapphire epitaxial wafer, so that the bonding surface of the silicon wafer is aligned with the bonding surface of the sapphire epitaxial wafer, and then the upper jig 10 and the lower jig 20 are aligned and merged and placed in the cavity of a bonding device (which is a prior art and is not described in detail here), and then the cavity of the bonding device is evacuated to make the vacuum degree in the cavity of the bonding device reach a preset vacuum degree (which can be set according to actual needs and is not specifically limited here), and then the heating device and the pressurizing device in the bonding device are started to make the temperature in the cavity of the bonding device reach the bonding temperature, and pressure is applied to the upper jig 10 and the lower jig 20 to make them reach the pressure required for bonding, thereby achieving bonding of the sapphire epitaxial wafer in the jig with the silicon wafer.

[0049] In some embodiments, before step A1, the method further includes: placing a graphite gasket on the arc-shaped concave cavity 21 of the lower fixture 20, and after step A2 and before step A3, the method further includes: placing a graphite gasket on top of the silicon wafer.

[0050] Specifically, by first placing a graphite gasket on the arc-shaped concave cavity 21 of the lower fixture 20 and then placing a graphite gasket on top of the silicon wafer, the uneven pressure during bonding is further released, which is beneficial to improving the stability of bonding.

[0051] In some embodiments, step A5 comprises: The jig is heated to 260°C and a pressure of 5000kgf is applied to the jig to bond the sapphire epitaxial wafer in the jig to the silicon wafer.

[0052] Specifically, the heating device and the pressurizing device in the bonding device are started to make the temperature in the cavity of the bonding device reach the bonding temperature, that is, the jig is heated to 260°C and a pressure of 5000kgf is applied to the upper jig 10 and the lower jig 20, so as to achieve bonding between the sapphire epitaxial wafer and the silicon wafer in the jig.

[0053] Among them, since the thermal expansion coefficient of sapphire epitaxial wafers (5.3×10^-6 / K) is higher than that of silicon (2.6×10^-6 / K), during the heating process, sapphire epitaxial wafers will expand more than silicon wafers. Uneven or excessive thermal stress may cause cracks or deformation at the bonding interface. The appropriate bonding temperature (usually between 250-450°C) is crucial to improving the bonding effect. High temperature can promote the diffusion between atoms and enhance the bonding force. When the fixture is heated to 260°C, it can provide sufficient bonding strength and better interface integrity. When the fixture is heated to 300°C, the diffusion between atoms increases, which helps to form stronger chemical bonds, thereby improving the bonding strength. However, a more complex stress release design or a slower temperature change rate is required at this temperature. Therefore, in practical applications, the appropriate bonding temperature should be selected according to the actual process.

[0054] Among them, the temperature gradient bonding technology can be used in the heating process, that is, the temperature is gradually increased or decreased during the bonding process to reduce the stress caused by the difference in thermal expansion coefficient.

[0055] In some embodiments, step A5 further includes: Step A6. Annealing the sapphire epitaxial wafer and silicon wafer bonded in the fixture at a temperature of 250° C. to 450° C. for 5 to 12 hours.

[0056] In order to improve the bonding quality, the bonded sapphire epitaxial wafer and silicon wafer are annealed, and the annealing temperature is maintained at 250°C-450°C for 5-12 hours. Thermal stress can be released at a higher annealing temperature. The specific annealing temperature and holding time can be selected according to the actual process and are not specifically limited here.

[0057] In this document, relational terms such as first and second, etc. are used merely to distinguish one entity or operation from another entity or operation, but do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0058] The above are only embodiments of the present application and are not intended to limit the scope of protection of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A device for bonding a sapphire epitaxial wafer to a silicon wafer, characterized in that: include: A fixture, which includes an upper fixture (10) and a lower fixture (20); An arc-shaped concave cavity (21) is provided at the upper end of the lower fixture (20), and the arc-shaped concave cavity (21) is used to place a sapphire epitaxial wafer that is warped downward; The lower end of the upper fixture (10) is provided with an arc-shaped protrusion (11), the arc-shaped protrusion (11) is used to abut against a silicon wafer stacked on the sapphire epitaxial wafer, and the arc-shaped concave cavity (21) is adapted to fit the arc-shaped protrusion (11); The upper jig (10) and the lower jig (20) are used to bond the sapphire epitaxial wafer and the silicon wafer by pressing each other.

2. The device for bonding a sapphire epitaxial wafer to a silicon wafer according to claim 1, characterized in that: The maximum depth of the arc-shaped concave cavity (21) is half the warping height of the sapphire epitaxial wafer.

3. The device for bonding a sapphire epitaxial wafer to a silicon wafer according to claim 2, characterized in that: The linear width of the arc-shaped concave cavity (21) is 5 mm to 10 mm greater than the linear width of the sapphire epitaxial wafer.

4. The device for bonding a sapphire epitaxial wafer to a silicon wafer according to claim 1, characterized in that: The material of the upper fixture (10) is graphite.

5. The device for bonding a sapphire epitaxial wafer to a silicon wafer according to claim 1, characterized in that: The material of the lower fixture (20) is graphite.

6. The device for bonding a sapphire epitaxial wafer to a silicon wafer according to claim 1, characterized in that: A graphite gasket is provided on the upper surface of the arc-shaped concave cavity (21).

7. The device for bonding a sapphire epitaxial wafer to a silicon wafer according to claim 1, characterized in that: A graphite gasket is provided on the lower surface of the arc-shaped raised portion (11).

8. The device for bonding a sapphire epitaxial wafer to a silicon wafer according to claim 1, characterized in that: The upper end surface of the lower fixture (20) is provided with a fixing portion (30), and the lower end surface of the upper fixture (10) is provided with a through hole (40) adapted to the fixing portion (30), and the fixing portion (30) is used to fix the sapphire epitaxial wafer and the silicon wafer in the arc-shaped concave cavity (21).

9. A method for bonding a sapphire epitaxial wafer to a silicon wafer, characterized in that: Based on the device for bonding a sapphire epitaxial wafer to a silicon wafer according to any one of claims 1 to 8, the method for bonding a sapphire epitaxial wafer to a silicon wafer comprises the steps of: A1. placing a sapphire epitaxial wafer on the arc-shaped concave cavity (21) of the lower fixture (20), and making the warping direction of the sapphire epitaxial wafer face downward; A2. Placing a silicon wafer on top of the sapphire epitaxial wafer; A3. Align the upper jig (10) and the lower jig (20) and place them into the cavity of the bonding device; A4. Evacuate the cavity of the bonding device to reach a preset vacuum degree; A5. Heat and pressurize the jig to bond the sapphire epitaxial wafer in the jig to the silicon wafer.

10. The method for bonding a sapphire epitaxial wafer to a silicon wafer according to claim 9, characterized in that: Step A5 includes: The jig was heated to 260° C. and a pressure of 5000 kgf was applied to the jig to bond the sapphire epitaxial wafer in the jig to the silicon wafer.

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