A bonding method for low-warpage bonding sheets

Abstract

The present invention discloses a bonding method for a low-warpage bonding pad, which relates to the field of semiconductor manufacturing and includes the following steps: forming first and second bonding materials on pre-bonding surfaces of an epitaxial layer and a silicon substrate, aligning and placing them on a graphite disk with a curved surface for bonding; heating the materials to a first temperature and applying a first pressure thereto for a first time to melt and fuse the bonding materials; decreasing the temperature from the first temperature to a preset temperature in an arithmetic progression according to temperature differences, while decreasing the pressure from the first pressure to a preset pressure in an arithmetic progression according to pressure differences, with each stage maintained for a predetermined time. The method of the present invention reduces stress in the bonding structure and reduces the warpage of the bonding structure, thereby obtaining a bonding pad with low warpage, by using a graphite disk with a curved surface for bonding, and controlling the temperature and pressure to decrease simultaneously in stages, with each stage maintained for a predetermined time.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing, and in particular to a bonding method for a low-warpage bonding sheet. Background Art

[0002] The manufacturing process of vertical LED chips requires a bonding process to transfer the epitaxial layer from the sapphire substrate to the silicon substrate. Figure 1 The schematic diagram of the existing bonding structure is shown, which includes a sapphire substrate 10, an epitaxial layer 20, a bonding layer 30 and a silicon substrate 40, wherein the thickness of the sapphire substrate 10 is 500-700 μm, and the thickness of the silicon substrate 40 is 450-550 μm, and the size of the two substrates is 2 inches or 4 inches; before bonding, metal materials need to be evaporated on the epitaxial layer 20 and the silicon substrate 40 as bonding materials, and then they are bonded together using a bonding machine with a flat graphite disk 100 (such as Figure 2 As shown), the bonding material forms a bonding layer 30.

[0003] However, due to the large difference in thermal expansion coefficients between the sapphire substrate 10 and the silicon substrate 40, relatively large internal stress will be generated during cooling after bonding, causing the bonding structure to warp with a warpage of more than 400um, which will make subsequent processing difficult. Moreover, if the warpage is too large, it will easily cause the silicon substrate 40 to crack. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art. The present invention provides a bonding method for low-warpage bonding sheets, which uses a graphite disk with a certain curved surface for bonding processing, and controls the temperature and pressure to be reduced in stages and maintained for a certain time in each stage, thereby reducing the stress in the bonding sheet and reducing the warpage of the bonding sheet.

[0005] The present invention provides a bonding method for a low-warpage bonding sheet, comprising the following steps:

[0006] Providing a silicon substrate and a sapphire substrate, wherein an epitaxial layer is grown on the sapphire substrate;

[0007] forming a first bonding material on the pre-bonding surface of the epitaxial layer and forming a second bonding material on the pre-bonding surface of the silicon substrate;

[0008] Aligning and laminating the first bonding material and the second bonding material to form a pre-bonded structure, and placing the pre-bonded structure in a graphite disk with a certain arc surface for bonding;

[0009] During the bonding process, heating the pre-bonded structure to a first temperature and applying a first pressure to the pre-bonded structure for a first time to allow the first bonding material and the second bonding material to melt and fuse to form a bonding layer;

[0010] After the bonding layer is formed, the temperature of the pre-bonded structure is gradually decreased from the first temperature to the preset temperature in the form of an arithmetic progression according to the temperature difference. At the same time, the pressure applied to the pre-bonded structure is gradually decreased from the first pressure to the preset pressure in the form of an arithmetic progression according to the pressure difference. Each stage is maintained for a period of time according to a preset time value to obtain a bonding structure.

[0011] Specifically, the thickness of the silicon substrate is H1, the thickness of the sapphire substrate is H2, and the relationship between H1 and H2 is: H1≥2H2.

[0012] Specifically, the thickness of the silicon substrate is 800-1500 um; the thickness of the sapphire substrate is 250-400 um.

[0013] Specifically, the first bonding material is evaporated to form a thickness of 1 to 2 μm on the pre-bonding surface of the epitaxial layer; and the second bonding material is evaporated to form a thickness of 1 to 2 μm on the pre-bonding surface of the silicon substrate.

[0014] Specifically, the first bonding material is gold, nickel, tin, gold-tin or nickel-tin; the second bonding material is gold, nickel, tin, gold-tin or nickel-tin; when the first bonding material is gold or nickel, the second bonding material is tin; when the first bonding material is tin, the second bonding material is gold or nickel; when the first bonding material is gold-tin, the second bonding material is gold-tin; when the first bonding material is nickel-tin, the second bonding material is nickel-tin.

[0015] Specifically, the first bonding material and the second bonding material are aligned and bonded to form a pre-bonded structure, and placed in a graphite disk with a certain curved surface for bonding processing, including: contacting the silicon substrate with the upper convex disk of the graphite disk, and the central protrusion height of the upper convex disk is 50 to 100 μm; contacting the sapphire substrate with the lower concave disk of the graphite disk, and the central depression depth of the lower concave disk is 50 to 100 μm.

[0016] Specifically, the first temperature is 250-320°C.

[0017] Specifically, the first pressure is 2000-5000 kgf.

[0018] Specifically, the first time is 5 to 30 minutes.

[0019] Specifically, the preset temperature is 40-80° C., the preset pressure is 0 kgf, and the preset time is 5-20 minutes;

[0020] The step of gradually decreasing the temperature of the pre-bonded structure from the first temperature to the preset temperature in an arithmetic progression according to the temperature difference comprises: calculating the temperature difference and the temperature of each stage by a formula, wherein the formula is:

[0021] ɑ=(T0-T N ) / N;

[0022] T n =T0-nɑ;

[0023] Where: ɑ is the temperature difference, T0 is the first temperature, T N is the preset temperature, N is the total number of stages, N is a natural number and 4≤N≤6, n represents the nth stage in the total number of stages N, T n represents the temperature of the nth stage;

[0024] The pressure applied to the pre-bonded structure is gradually reduced from the first pressure to the preset pressure in the form of an arithmetic progression according to the pressure difference, comprising: calculating the pressure difference and the pressure at each stage by a formula, wherein the formula is:

[0025] β=(P0-P N ) / N;

[0026] P n =P0-nβ;

[0027] Where: β is the pressure difference, P0 is the first pressure, P N is the preset pressure, N is the total number of stages, N is a natural number and 4≤N≤6, n represents the nth stage in the total number of stages N, P n is the pressure at the nth stage.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] By adjusting the thickness of the silicon substrate and the sapphire substrate so that the thickness of the silicon substrate is ≥ 2 times the thickness of the sapphire substrate, the warpage of the bonding structure can be effectively reduced, and the risk of cracking of the silicon substrate can also be effectively reduced;

[0030] The pre-bonded structure is bonded in a graphite disk with a certain arc surface, so that the pre-bonded structure first forms a spherical curvature opposite to the warping direction, thereby pre-compensating the warping amount of the bonded structure and reducing the warping degree of the obtained bonded structure;

[0031] After the bonding layer is formed, the temperature and pressure are controlled to decrease simultaneously in stages in the form of an arithmetic progression according to a certain difference and each stage is maintained for a certain time, which can release and reduce the stress in the bonding structure, thereby reducing the warpage of the bonding structure;

[0032] The method of the present invention can reduce the warpage of the bonding structure, obtain a bonding sheet with low warpage, and facilitate subsequent processing such as peeling of the sapphire substrate and polishing and grinding of the silicon substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram of the existing bonding structure;

[0034] Figure 2 is a schematic diagram of the bonding process using a flat graphite disk;

[0035] Figure 3 This is a flow chart of a bonding method for a low-warpage bonding sheet according to an embodiment of the present invention;

[0036] Figure 4 is a schematic diagram of a bonding structure in an embodiment of the present invention;

[0037] Figure 5 Schematic diagram of the bonding process using a graphite disk with a certain curved surface in an embodiment of the present invention;

[0038] Figure 6 Schematic diagram of the time-temperature curve and time-pressure curve of the bonding process in an embodiment of the present invention.

[0039] In the accompanying drawings, 10 is a sapphire substrate; 11 is a thinned sapphire substrate; 20 is an epitaxial layer; 30 is a bonding layer; 40 is a silicon substrate; 41 is a thickened silicon substrate; 100 is a flat graphite disk; 200 is a graphite disk with a certain arc surface; 210 is an upper convex disk; and 220 is a lower concave disk. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0041] Example 1:

[0042] Figure 3 A flow chart of a bonding method for a low-warpage bonding sheet according to an embodiment of the present invention is shown, comprising the following steps:

[0043] S1. Providing a silicon substrate and a sapphire substrate, wherein an epitaxial layer is grown on the sapphire substrate;

[0044] S2. forming a first bonding material on the pre-bonding surface of the epitaxial layer, and forming a second bonding material on the pre-bonding surface of the silicon substrate;

[0045] S3, aligning and laminating the first bonding material and the second bonding material to form a pre-bonded structure, and placing the pre-bonded structure in a graphite disk with a certain arc surface for bonding;

[0046] S4. During the bonding process, heating the pre-bonded structure to a first temperature and applying a first pressure to the pre-bonded structure for a first time to allow the first bonding material and the second bonding material to melt and fuse to form a bonding layer;

[0047] S5. After the bonding layer is formed, the temperature of the pre-bonded structure is gradually decreased from the first temperature to the preset temperature in the form of an arithmetic progression according to the temperature difference. At the same time, the pressure applied to the pre-bonded structure is gradually decreased from the first pressure to the preset pressure in the form of an arithmetic progression according to the pressure difference. Each stage is maintained for a period of time according to a preset time value to obtain a bonding structure.

[0048] When using the bonding process to transfer the epitaxial layer from the sapphire substrate to the silicon substrate, the sapphire substrate and the silicon substrate are subjected to temperature changes from low to high and then from high to low. Due to the large difference in the thermal expansion coefficients of the two substrates, the deformation of the two substrates is also large. The two substrates are connected into a whole by the bonding layer in the expanded state. When the temperature changes from high to low, since the two substrates are connected as a whole by the bonding layer, they cannot shrink and deform freely, resulting in large stress inside the bonding structure. The sapphire substrate with large shrinkage deformation will pull the silicon substrate with small shrinkage deformation to its side, causing the entire bonding structure to bend toward the sapphire substrate side, that is, warping.

[0049] The pre-bonded structure is bonded in a graphite disk with a certain arc surface, so that the pre-bonded structure first forms a spherical curvature opposite to the warping direction, thereby pre-compensating the warping amount of the bonded structure and reducing the warping degree of the obtained bonded structure;

[0050] Furthermore, after the bonding layer is formed, the temperature and pressure are controlled to be reduced simultaneously in stages in the form of an arithmetic progression according to a certain difference and each stage is maintained for a certain time. On the one hand, the shrinkage deformation of the sapphire substrate and the silicon substrate can gradually tend to balance, thereby releasing stress; on the other hand, the strength of the sapphire substrate and the silicon substrate can be gradually restored to resist stress; on the other hand, the sapphire substrate and the silicon substrate can produce a certain plastic deformation, thereby reducing stress; ultimately, the stress in the bonding structure is reduced, thereby reducing the warping degree of the bonding structure, and obtaining a bonding sheet with low warping.

[0051] Example 2:

[0052] Figure 3 A flow chart of a bonding method for a low-warpage bonding sheet according to an embodiment of the present invention is shown, comprising the following steps:

[0053] S1. Providing a silicon substrate and a sapphire substrate, wherein an epitaxial layer is grown on the sapphire substrate;

[0054] Figure 4 A schematic diagram of a bonding structure in an embodiment of the present invention is shown. The embodiment of the present invention provides a thickened silicon substrate 41 and a thinned sapphire substrate 11. The thickness of the thickened silicon substrate 41 is H1, and the thickness of the thinned sapphire substrate 11 is H2. The relationship between H1 and H2 is: H1≥2H2.

[0055] The thickened silicon substrate 41 has better strength and can effectively resist the pull from the thinned sapphire substrate 11 during the cooling process after bonding, avoiding being bent and cracked by the thinned sapphire substrate 11; accordingly, the strength of the thinned sapphire substrate 11 is weaker, thereby reducing its pulling force on the thickened silicon substrate 41 during the cooling process after bonding; by using the thickened silicon substrate 41 and the thinned sapphire substrate 11, the warping of the bonding structure can be effectively reduced, and the risk of the silicon substrate cracking can also be effectively reduced.

[0056] The thickened silicon substrate 41 is a standard part prefabricated according to the required thickness; the thinned sapphire substrate 11 can be a standard part prefabricated according to the required thickness, or a processed part formed by grinding and thinning the existing sapphire substrate 10.

[0057] Selecting appropriate thicknesses for the thickened silicon substrate 41 and the thinned sapphire substrate 11 can effectively control warpage. The thickness of the thickened silicon substrate 41 is 800 to 1500 um, and the thickness of the thinned sapphire substrate 11 is 250 to 400 um. Within the allowable range, a thicker thickened silicon substrate 41 and a thinner thinned sapphire substrate 11 should be selected as much as possible to reduce the influence of stress between the substrates on the warpage of the bonding wafer; preferably, the thickness of the thickened silicon substrate 41 is 1150 to 1500 um, and the thickness of the thinned sapphire substrate 11 is 250 to 325 um.

[0058] S2. forming a first bonding material on the pre-bonding surface of the epitaxial layer, and forming a second bonding material on the pre-bonding surface of the silicon substrate;

[0059] S3, aligning and laminating the first bonding material and the second bonding material to form a pre-bonded structure, and placing the pre-bonded structure in a graphite disk with a certain arc surface for bonding;

[0060] S4. During the bonding process, heating the pre-bonded structure to a first temperature and applying a first pressure to the pre-bonded structure for a first time to allow the first bonding material and the second bonding material to melt and fuse to form a bonding layer;

[0061] S5. After the bonding layer is formed, the temperature of the pre-bonded structure is gradually decreased from the first temperature to the preset temperature in the form of an arithmetic progression according to the temperature difference. At the same time, the pressure applied to the pre-bonded structure is gradually decreased from the first pressure to the preset pressure in the form of an arithmetic progression according to the pressure difference. Each stage is maintained for a period of time according to a preset time value to obtain a bonding structure.

[0062] By providing a thickened silicon substrate and a thinned sapphire substrate, the thickness of the silicon substrate is made ≥ 2 times the thickness of the sapphire substrate, which can effectively reduce the warpage of the bonding structure and the risk of silicon substrate cracking;

[0063] The pre-bonded structure is bonded in a graphite disk with a certain arc surface, so that the pre-bonded structure first forms a spherical curvature opposite to the warping direction, thereby pre-compensating the warping amount of the bonded structure and reducing the warping degree of the obtained bonded structure;

[0064] After the bonding layer is formed, the temperature and pressure are controlled to be reduced simultaneously in stages in the form of an arithmetic progression according to a certain difference and each stage is maintained for a certain time. This can release and reduce the stress in the bonding structure, thereby reducing the warping degree of the bonding structure; ultimately, a bonding sheet with low warping is obtained, which is convenient for subsequent processing such as peeling of the sapphire substrate and polishing and grinding of the silicon substrate.

[0065] Example 3:

[0066] Figure 3 A flow chart of a bonding method for a low-warpage bonding sheet according to an embodiment of the present invention is shown, comprising the following steps:

[0067] S1. Providing a silicon substrate and a sapphire substrate, wherein an epitaxial layer is grown on the sapphire substrate;

[0068] Figure 4 A schematic diagram of a bonding structure in an embodiment of the present invention is shown. The embodiment of the present invention provides a thickened silicon substrate 41 and a thinned sapphire substrate 11. The thickness of the thickened silicon substrate 41 is H1, and the thickness of the thinned sapphire substrate 11 is H2. The relationship between H1 and H2 is: H1≥2H2.

[0069] The thickened silicon substrate 41 has better strength and can effectively resist the pull from the thinned sapphire substrate 11 during the cooling process after bonding, avoiding being bent and cracked by the thinned sapphire substrate 11; accordingly, the strength of the thinned sapphire substrate 11 is weaker, thereby reducing its pulling force on the thickened silicon substrate 41 during the cooling process after bonding; by using the thickened silicon substrate 41 and the thinned sapphire substrate 11, the warping of the bonding structure can be effectively reduced, and the risk of the silicon substrate cracking can also be effectively reduced.

[0070] The thickened silicon substrate 41 is a standard part prefabricated according to the required thickness; the thinned sapphire substrate 11 can be a standard part prefabricated according to the required thickness, or a processed part formed by grinding and thinning the existing sapphire substrate 10.

[0071] Selecting appropriate thicknesses for the thickened silicon substrate 41 and the thinned sapphire substrate 11 can effectively control warpage. The thickness of the thickened silicon substrate 41 is 800 to 1500 um, and the thickness of the thinned sapphire substrate 11 is 250 to 400 um. Within the allowable range, a thicker thickened silicon substrate 41 and a thinner thinned sapphire substrate 11 should be selected as much as possible to reduce the influence of stress between the substrates on the warpage of the bonding wafer; preferably, the thickness of the thickened silicon substrate 41 is 1150 to 1500 um, and the thickness of the thinned sapphire substrate 11 is 250 to 325 um.

[0072] S2. forming a first bonding material on the pre-bonding surface of the epitaxial layer, and forming a second bonding material on the pre-bonding surface of the silicon substrate;

[0073] The first bonding material is evaporated to form a thickness of 1 to 2 um on the pre-bonding surface of the epitaxial layer 20; the second bonding material is evaporated to form a thickness of 1 to 2 um on the pre-bonding surface of the silicon substrate 40; the first bonding material is gold, nickel, tin, gold-tin or nickel-tin; the second bonding material is gold, nickel, tin, gold-tin or nickel-tin; when the first bonding material is gold or nickel, the second bonding material is tin; when the first bonding material is tin, the second bonding material is gold or nickel; when the first bonding material is gold-tin, the second bonding material is gold-tin; when the first bonding material is nickel-tin, the second bonding material is nickel-tin.

[0074] The bonding material does not need to be too thick, 1 to 2 μm is more suitable. If it is too thin, insufficient molten liquid will be generated during bonding, which will cause voids in the bonding layer 30 and poor connection. If it is too thick, excessive molten liquid will overflow and flow to the non-bonding area during bonding, causing waste. The bonding material contains tin, which has a relatively low melting point and is easy to melt quickly during bonding. The molten liquid diffuses quickly and can well fuse gold or nickel, resulting in a good connection effect.

[0075] S3, aligning and laminating the first bonding material and the second bonding material to form a pre-bonded structure, and placing the pre-bonded structure in a graphite disk with a certain arc surface for bonding;

[0076] Figure 5A schematic diagram of the bonding process using a graphite disk with a certain curved surface in an embodiment of the present invention is shown, wherein the thickened silicon substrate 41 is brought into contact with the upper convex disk 210 of the graphite disk 200 with a certain curved surface, and the central protrusion height of the upper convex disk 210 is 50 to 100 μm; the thinned sapphire substrate 11 is brought into contact with the lower concave disk 220 of the graphite disk 200 with a certain curved surface, and the central depression depth of the lower concave disk 220 is 50 to 100 μm.

[0077] The pre-bonded structure is placed in a graphite disk 200 having a certain arc surface. The thickened silicon substrate 41 contacts the upper convex disk 210 at the top, and the thinned sapphire substrate 11 contacts the lower concave disk 220 at the bottom. When pressure is applied to the pre-bonded structure, the pre-bonded structure forms a spherical curvature in the opposite direction of the warping, pre-compensating for the warping of the bonded structure and reducing the warping degree of the bonded structure.

[0078] The spherical curvature of the pre-bonded structure should be appropriate. If the spherical curvature is too large, it will be over-compensated, causing the bonded structure to bend toward the thickened silicon substrate 41, or even cause the thickened silicon substrate 41 to crack. If the spherical curvature is too small, the warpage cannot be effectively compensated, and the purpose of reducing the warpage of the bonded structure cannot be achieved.

[0079] It is more appropriate to make the pre-bonded structure form a spherical curve with a height difference of 50 to 100 um between the center and the edge. This is achieved by setting the central protrusion height of the upper convex plate 210 to 50 to 100 um and the central depression depth of the lower concave plate 220 to 50 to 100 um. The upper convex plate 210 and the lower concave plate 220 must be completely matched, that is, the central protrusion height of the upper convex plate 210 must be consistent with the central depression depth of the lower concave plate 220. The protrusion height and the depression depth can be 50 um, 75 um, 100 um, and so on.

[0080] S4. During the bonding process, heating the pre-bonded structure to a first temperature and applying a first pressure to the pre-bonded structure for a first time to allow the first bonding material and the second bonding material to melt and fuse to form a bonding layer;

[0081] The first temperature is 250-320°C, which is the eutectic melting temperature, which melts the bonding material; the first pressure is 2000-5000kgf, which can promote the contact and fusion of the first bonding material and the second bonding material, and promote the molten bonding material to fully diffuse between the epitaxial layer 20 and the thickened silicon substrate 41, avoiding the generation of bonding voids; the first time is 5-30min, and maintaining it for 5-30min after reaching the eutectic melting temperature can make the bonding material fully melt. If the time is kept too short, the bonding material melting effect will be poor and bonding voids will be easily formed. If the time is kept too long, the molten liquid formed by the bonding material will overflow, which will also affect production efficiency.

[0082] S5. After the bonding layer is formed, the temperature of the pre-bonded structure is gradually decreased from the first temperature to the preset temperature in the form of an arithmetic progression according to the temperature difference. At the same time, the pressure applied to the pre-bonded structure is gradually decreased from the first pressure to the preset pressure in the form of an arithmetic progression according to the pressure difference. Each stage is maintained for a period of time according to a preset time value to obtain a bonding structure.

[0083] The preset temperature is 40°C to 80°C, the preset pressure is 0 kgf, the preset time is 5 to 20 minutes, and the cooling rate is 3 to 8°C / min;

[0084] Figure 6 A schematic diagram of a time-temperature curve and a time-pressure curve of a bonding process in an embodiment of the present invention is shown. The step of gradually decreasing the temperature of the pre-bonded structure from the first temperature to the preset temperature in an arithmetic progression according to the temperature difference includes calculating the temperature difference and the temperature of each stage by a formula, wherein the formula is:

[0085] ɑ=(T0-T N ) / N;

[0086] T n =T0-nɑ;

[0087] Where: ɑ is the temperature difference, T0 is the first temperature, T N is the preset temperature, N is the total number of stages, N is a natural number and 4≤N≤6, n represents the nth stage in the total number of stages N, T n represents the temperature of the nth stage;

[0088] The pressure applied to the pre-bonded structure is gradually reduced from the first pressure to the preset pressure in the form of an arithmetic progression according to the pressure difference, comprising: calculating the pressure difference and the pressure at each stage by a formula, wherein the formula is:

[0089] β=(P0-P N ) / N;

[0090] P n=P0-nβ;

[0091] Where: β is the pressure difference, P0 is the first pressure, P N is the preset pressure, N is the total number of stages, N is a natural number and 4≤N≤6, n represents the nth stage in the total number of stages N, P n is the pressure at the nth stage.

[0092] As an example, when the first temperature T0 is 250°C, the preset temperature T N is 50℃, the first pressure P0 is 2000kgf, the preset pressure P N When the temperature difference ɑ is 0 kgf, the total number of stages N is 4, and the preset time value is 5 minutes, the obtained temperature difference ɑ is 50°C, and the pressure difference β is 500 kgf; even if the temperature of the pre-bonded structure decreases from 250°C to the preset temperature of 50°C in 4 stages in the form of an arithmetic progression according to a temperature difference of 50°C, and at the same time, the pressure applied to the pre-bonded structure decreases from 2000 kgf to the preset pressure of 0 kgf in 4 stages in the form of an arithmetic progression according to a pressure difference of 500 kgf, and each stage is maintained for 5 minutes, a bonding structure is obtained.

[0093] Specifically, the temperature was lowered from 250°C to 200°C, and the pressure was simultaneously lowered from 2000 kgf to 1500 kgf, and maintained at 200°C and 1500 kgf for 5 minutes;

[0094] Then, the temperature was lowered from 200°C to 150°C, and the pressure was simultaneously lowered from 1500 kgf to 1000 kgf, and maintained at 150°C and 1000 kgf for 5 min.

[0095] Next, the temperature was lowered from 150°C to 100°C, and the pressure was simultaneously lowered from 1000 kgf to 500 kgf, and maintained at 100°C and 500 kgf for 5 minutes.

[0096] Finally, the temperature was lowered from 100°C to 50°C, while the pressure was reduced from 500kgf to 0kgf to complete the bonding and obtain a low-warpage bonded structure.

[0097] After the bonding layer is formed, the temperature and pressure are controlled to be reduced simultaneously in stages in the form of an arithmetic progression according to a certain difference and each stage is maintained for a certain time. On the one hand, the shrinkage deformation of the sapphire substrate and the silicon substrate can gradually tend to balance, releasing stress; on the other hand, the strength of the sapphire substrate and the silicon substrate can be gradually restored to resist stress; on the other hand, the sapphire substrate and the silicon substrate can produce a certain plastic deformation, reducing stress; ultimately reducing the stress in the bonding structure, thereby reducing the warping degree of the bonding structure and obtaining a bonding sheet with low warping.

[0098] In summary, the bonding method of a low-warpage bonding sheet provided in an embodiment of the present invention can effectively reduce the warpage of the bonding structure and the risk of silicon substrate breakage by providing a thickened silicon substrate and a thinned sapphire substrate so that the thickness of the silicon substrate is ≥2 times the thickness of the sapphire substrate; the pre-bonded structure is bonded in a graphite disk with a certain arc surface so that the pre-bonded structure first forms a spherical bend opposite to the warping direction, pre-compensates the warping amount of the bonding structure, and reduces the warping of the obtained bonding structure; after the bonding layer is formed, the temperature and pressure are controlled to be reduced in stages in the form of an arithmetic progression according to a certain difference and maintained for a certain time in each stage, which can release and reduce the stress in the bonding structure, thereby reducing the degree of warping of the bonding structure; the method of the present invention can reduce the warpage of the bonding structure and obtain a bonding sheet with low warpage, which is convenient for subsequent processing such as peeling of the sapphire substrate and polishing and grinding of the silicon substrate.

[0099] The above is a detailed introduction to the bonding method of a low-warpage bonding sheet provided in an embodiment of the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A bonding method for a low-warpage bonding sheet, characterized in that: The following steps are involved: Providing a silicon substrate and a sapphire substrate, wherein an epitaxial layer is grown on the sapphire substrate; forming a first bonding material on the pre-bonding surface of the epitaxial layer and forming a second bonding material on the pre-bonding surface of the silicon substrate; Aligning and laminating the first bonding material and the second bonding material to form a pre-bonded structure, and placing the pre-bonded structure in a graphite disk with a certain arc surface for bonding; During the bonding process, heating the pre-bonded structure to a first temperature and applying a first pressure to the pre-bonded structure for a first time to allow the first bonding material and the second bonding material to melt and fuse to form a bonding layer; After the bonding layer is formed, the temperature of the pre-bonded structure is gradually decreased from the first temperature to the preset temperature in the form of an arithmetic progression according to the temperature difference. At the same time, the pressure applied to the pre-bonded structure is gradually decreased from the first pressure to the preset pressure in the form of an arithmetic progression according to the pressure difference. Each stage is maintained for a period of time according to a preset time value to obtain a bonding structure.

2. The bonding method of a low-warpage bonding sheet according to claim 1, wherein: The thickness of the silicon substrate is H1, the thickness of the sapphire substrate is H2, and the relationship between H1 and H2 is: H1≥2H2.

3. The bonding method of a low-warpage bonding sheet according to claim 1, wherein: The thickness of the silicon substrate is 800-1500 um; the thickness of the sapphire substrate is 250-400 um.

4. The bonding method of a low-warpage bonding sheet according to claim 1, wherein: The first bonding material is formed on the pre-bonding surface of the epitaxial layer by evaporation to form a thickness of 1 to 2 μm; and the second bonding material is formed on the pre-bonding surface of the silicon substrate by evaporation to form a thickness of 1 to 2 μm.

5. The bonding method of a low-warpage bonding sheet according to claim 1, wherein: The first bonding material is gold, nickel, tin, gold-tin or nickel-tin; the second bonding material is gold, nickel, tin, gold-tin or nickel-tin.

6. The bonding method of a low-warpage bonding sheet according to claim 5, wherein: When the first bonding material is gold or nickel, the second bonding material is tin; when the first bonding material is tin, the second bonding material is gold or nickel; when the first bonding material is gold-tin, the second bonding material is gold-tin; when the first bonding material is nickel-tin, the second bonding material is nickel-tin.

7. The bonding method of a low-warpage bonding sheet according to claim 1, wherein: The first bonding material and the second bonding material are aligned and bonded to form a pre-bonded structure, and placed in a graphite disk with a certain curved surface for bonding processing, including: contacting the silicon substrate with the upper convex disk of the graphite disk, and the central protrusion height of the upper convex disk is 50 to 100 μm; contacting the sapphire substrate with the lower concave disk of the graphite disk, and the central depression depth of the lower concave disk is 50 to 100 μm.

8. The bonding method of a low-warpage bonding sheet according to claim 1, wherein: The first temperature is 250-320° C., and the first pressure is 2000-5000 kgf.

9. The bonding method of a low-warpage bonding sheet according to claim 1, wherein: The first time is 5 to 30 minutes.

10. The bonding method of a low-warpage bonding sheet according to claim 1, wherein: The preset temperature is 40-80°C, the preset pressure is 0 kgf, and the preset time is 5-20 minutes; The step of gradually decreasing the temperature of the pre-bonded structure from the first temperature to the preset temperature in an arithmetic progression according to the temperature difference comprises: calculating the temperature difference and the temperature of each stage by a formula, wherein the formula is: ɑ=(T0-T N ) / N; T n =T0-nɑ; Where: ɑ is the temperature difference, T0 is the first temperature, T N is the preset temperature, N is the total number of stages, N is a natural number and 4≤N≤6, n represents the nth stage in the total number of stages N, T n represents the temperature of the nth stage; The pressure applied to the pre-bonded structure is gradually reduced from the first pressure to the preset pressure in the form of an arithmetic progression according to the pressure difference, comprising: calculating the pressure difference and the pressure at each stage by a formula, wherein the formula is: β=(P0-P N ) / N; P n =P0-nβ; Where: β is the pressure difference, P0 is the first pressure, P N is the preset pressure, N is the total number of stages, N is a natural number and 4≤N≤6, n represents the nth stage in the total number of stages N, P n is the pressure at the nth stage.

Images