Method for improving bonding force between bump and bottom, and chip structure

Abstract

The present invention belongs to the field of chip packaging technology, and in particular, relates to a method for improving the bonding strength between a bump and a bottom, and a chip structure. The method comprises depositing a seed layer on a wafer substrate, coating a photoresist film on the seed layer, removing excess photoresist film, projecting a target pattern onto the photoresist film, developing, removing excess photoresist film, forming an RDL wiring pattern layer on the remaining photoresist film, depositing a metal layer, removing the photoresist film in the RDL wiring pattern layer, covering with an insulating layer, making a wiring opening, making a bump in the wiring opening, and removing excess insulating layer and seed layer; the seed layer is made of materials including Ti, Cu, and a thin film, the thin film is obtained by solidifying a nanocomposite liquid, and the raw materials of the nanocomposite liquid include silicon dioxide, dopamine, 3-mercaptopropyltriethoxysilane, copper sulfate, and PVP. The chip structure is prepared by the method. The present invention can improve the structural bonding strength between chip structures and improve the problem of poor bumps.

Description

Technical Field

[0001] The present invention belongs to the technical field of chip packaging, and in particular, relates to a method for improving the bonding force between a bump and a bottom, and a chip structure. Background Art

[0002] With the development of chip packaging technology, higher requirements are being placed on the number and position arrangement of bumps in chip packages. According to the position and function of bumps in chip packages, they are divided into active bumps and support bumps.

[0003] Support bumps are typically placed on the chip's surface passivation layer or passivation layer. They don't need to connect to the chip's pin pads, providing stress support for subsequent flip-chip or FC-BGA operations. The placement of support bumps requires consideration of factors such as the spacing between solder joints on the substrate and frame. This significantly limits the support bump's diameter, resulting in poor adhesion between the support bump and the substrate's passivation layer, making it prone to bump dropout or abnormalities. Summary of the Invention

[0004] In order to overcome the defects in the prior art, the present invention provides a method for improving the bonding force between a bump and a bottom, and a chip structure.

[0005] The technical solutions of the present invention include the following:

[0006] The present invention produces a chip structure, which is a chip-related structure and relates to a chip packaging structure. The chip structure includes a substrate, a seed layer covering the substrate, a metal layer covering the seed layer, and bumps covering the metal layer, wherein the seed layer partially or completely covers the substrate, and the bumps partially or completely cover the metal layer.

[0007] The chip structure is prepared according to a method for improving the bonding strength between the bump and the bottom, comprising the following steps:

[0008] A seed layer is deposited on the substrate of the wafer, a photoresist film is coated on the seed layer, excess photoresist film is removed, the target pattern is projected onto the photoresist film, developed, excess photoresist film is removed, an RDL wiring pattern layer is formed on the remaining photoresist film by the RDL method, a metal layer is deposited on the RDL wiring pattern, the photoresist film in the RDL wiring pattern layer is removed, an insulating layer is covered, a wiring opening is made on the insulating layer, a bump is made in the wiring opening, and excess insulating layer and seed layer are removed.

[0009] Furthermore, the seed layer is made of materials including Ti, Cu, and a thin film, the thin film is solidified by a nano-composite liquid, and the raw materials of the nano-composite liquid include silicon dioxide, dopamine, 3-mercaptopropyltriethoxysilane, copper sulfate, and PVP.

[0010] Furthermore, when depositing a seed layer on the substrate surface of the wafer, Ti and / or Cu are deposited on the substrate to obtain a base material, and the base material is soaked in ethanethiol solution and then coated with the nanocomposite liquid and cured to obtain a thin film.

[0011] Furthermore, the preparation method of the nanocomposite liquid includes the following steps:

[0012] Dopamine is added to the silica solution, the pH is adjusted, the solution is stirred, and the solution is centrifuged to obtain silica-polydopamine particles; the silica-polydopamine particles are dispersed in a solvent, 3-mercaptopropyltriethoxysilane is added, the solution is stirred, and the solution is centrifuged to obtain modified particles; the modified particles and PVP are added to a copper sulfate solution to obtain a nanocomposite solution.

[0013] Furthermore, the material of the substrate includes silicon nitride and silicon dioxide.

[0014] Furthermore, the thickness of the metal layer is 1-5 μm.

[0015] Furthermore, the thickness of the insulating layer is 30-80 μm.

[0016] Furthermore, the material of the bump includes at least one of Cu, Sn, and a copper-tin alloy, and the material of the metal layer includes Cu.

[0017] Furthermore, when the bumps are formed in the wiring openings, the bumps are formed through electroplating and reflow processes, and the height of the bumps after reflow is 30-80 μm.

[0018] Furthermore, the thickness of the seed layer is 0.05-1 μm, and the thickness of the film is 10-20 nm.

[0019] According to the inventive concept of the present invention, the advantages and beneficial effects of the present invention are as follows:

[0020] The present invention provides a method for improving the bonding force between a bump and a bottom, and a chip structure. Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) In the prior art, the bonding strength between the supporting bump and the passivation layer of the substrate is very poor, and the bump is prone to falling off or abnormality. Therefore, the present invention constructs a seed layer and a metal layer between the bump and the substrate. The seed layer enhances the bonding strength between the substrate and the metal layer through chemical bonding, conductivity, and barrier effects. The metal layer enhances the bonding strength between the seed layer and the bump by improving the conductive path and interface compatibility. The multi-layer structure of the present application synergistically increases the bonding strength between the structures and also improves the bonding strength between the bump and the bottom material.

[0022] (2) Although the materials used in the seed layer of the present invention (e.g., Ti, Cu, or Ti / Cu laminates) have good conductivity, the bonding strength between the Ti seed layer and the substrate is limited, making it prone to peeling or cracking during subsequent processes. The Cu seed layer may experience performance degradation due to diffusion or oxidation over long-term use, especially when combined with subsequent electroplating layers, which are affected by interfacial stress. Ultimately, this affects the bonding between the structures.

[0023] Therefore, the present invention provides a novel method for preparing a seed layer: a nanocomposite liquid is prepared, which can be solidified into a thin film and combined with Ti and / or Cu to form a seed layer. Specifically, the following steps are performed: 1) Ti and / or Cu are deposited on a substrate to form a base material. Soaking the substrate in an ethanethiol solution enhances the substrate's surface activity, providing better interfacial conditions for the nanocomposite liquid to adhere. The thiol groups in the nanocomposite liquid further form chemical bonds with the ethanethiol-treated substrate, enhancing interfacial bonding. 2) The raw materials for the nanocomposite liquid include silica, dopamine, 3-mercaptopropyltriethoxysilane, and copper sulfate. Silica provides mechanical strength and chemical stability, dopamine enhances the adhesion and reactivity of the raw material particles, and 3-mercaptopropyltriethoxysilane achieves strong bonding with the substrate and modified particles through its thiol and siloxane groups. PVP improves the dispersibility of the raw material particles. Copper ions are evenly distributed in the film through coordination with the thiol groups and PVP, enhancing conductivity and interfacial compatibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 This is a schematic diagram of the structure of the present invention after gluing;

[0026] Figure 2 It is a schematic diagram of the structure after development of the present invention;

[0027] Figure 3 This is a schematic diagram of the structure after Cu electroplating of the present invention;

[0028] Figure 4 This is a schematic diagram of the structure of the re-covering adhesive layer of the present invention;

[0029] Figure 5 This is a schematic diagram of the structure after wiring opening of the present invention;

[0030] Figure 6 This is a schematic diagram of the structure after the bumps are prepared in the present invention;

[0031] The markings in the figure are: 1. substrate; 2. seed layer; 3. photoresist film; 4. RDL wiring pattern; 5. metal layer; 6. insulation layer; 7. wiring opening; 8. bump. DETAILED DESCRIPTION

[0032] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described below in conjunction with specific embodiments. The methods described are conventional methods unless otherwise specified, and the raw materials described can be obtained from public commercial channels unless otherwise specified.

[0033] Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred over other embodiments. Although various aspects of the embodiments are presented in the drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0034] Method 1

[0035] The present invention provides a method for improving the bonding force between the bump and the bottom, referring to Figures 1-6 , the specific steps are as follows:

[0036] 1) Physical vapor deposition (PVD) is used to deposit a layer of metal on the surface of the wafer substrate 1, serving as the seed layer 2 for subsequent electroplating. Seed layer 2 can be made of Ti, Cu, or a combination of Ti and Cu. The thickness of seed layer 2 is 0.05-1 μm. When Ti is used alone, the thickness is 0.1 μm; when Cu is used alone, the thickness is 0.2 μm. Substrate 1 is made of a material that includes a passivation layer or has a passivating effect. Materials for substrate 1 include silicon nitride and silicon dioxide.

[0037] 2) After the metal seed layer 2 is deposited, Figure 1 As shown, a photoresist film 3 is applied to the surface of a metal seed layer 2 by spin coating from low to high speed. The thickness of the photoresist film 3 is approximately 2 μm. After coating, a chemical EBR method is used to spray a solvent at the edge of the wafer to remove excess photoresist film 3 to prevent accumulation of the photoresist film 3. The photoresist film 3 is formed of photoresist, and the spraying solvent can be a conventional EBR solvent, including PGMEA.

[0038] 3) After the coating is completed, the target pattern is projected onto the photoresist film 3 by a stepper exposure method, that is, using a stepper lithography machine, so that the photoresist film 3 is sensitive to light and undergoes chemical and physical changes; then the wet development method is used to dissolve the unnecessary photoresist film 3 with a chemical solution, and the remaining photoresist film 3 is composed of Figure 2The wiring width of the RDL wiring pattern layer 4 shown is not specifically limited and can be flexibly adjusted according to the specifications of the subsequent bump 8 pitch and bump 8 diameter. The chemical solution can be a conventional adhesive remover, including PGMEA.

[0039] 4) On the formed RDL wiring pattern 4, as shown in FIG. Figure 3 As shown, a thin Cu layer is electrolytically deposited using a full-surface electroplating process to deposit a uniform metal layer 5 with good bonding strength to fill the wiring pattern and serve as a conductive layer for the subsequent electroplated bump 8, wherein the thickness of the metal layer is 1-5um, and the preferred thickness of the metal layer 5 is about 2um.

[0040] 5) Remove the photoresist film 3 on the wafer surface where the RDL pattern has been formed by wet stripping, and re-cover it with an insulating layer 6 by spin coating. Figure 4 As shown in FIG. 4 , the insulating layer 6 can cover the metal layer 5 and the seed layer 2 on the wafer.

[0041] The insulating layer 6 may be made of a photoresist film 3 having insulating properties. The thickness of the insulating layer is 30-80 μm, preferably about 65 μm. However, if necessary, the thickness may be adjusted flexibly according to the specifications of the subsequent bump 8 height and bump 8 diameter.

[0042] 6) Using the exposure and development method of step 3), a wiring opening 7 required for subsequent support bumps (i.e., bumps 8) is made on the insulating layer 6. The manufacturing process can be completed by an etching process, such as Figure 5 This will expose the RDL pattern layer, making it easier to grow supporting bumps (i.e., bumps 8) on the metal layer 5.

[0043] 7) Bumps 8 are formed in wiring openings 7 through electroplating and reflow processes. Bumps 8 are made of Cu, Sn, or a copper-tin alloy. This allows for continuity between RDL layers and interconnection with underlying circuits. The height of the bumps after reflow is 30-80 μm, preferably about 65 μm. However, the height of the Cu and Sn layers can be adjusted flexibly based on process and design requirements.

[0044] 8) Remove the excess insulating layer 6 around the bump 8 with a wet chemical solution; then use an etching solution to remove the excess seed layer 2; Figure 6 As shown. This can achieve the combination of the bump 8 and the bottom material. The chemical solution can be a conventional adhesive remover, including PGMEA.

[0045] The processes or methods or agents or potions not described in detail above are conventional means in the field, which can be clearly known to those skilled in the art and are not key factors affecting the technical effects of this application, so they are not described in detail.

[0046] Finally, according to method 1, Figure 6 The structure shown:

[0047] The substrate 1 is covered with a seed layer 2 , the seed layer 2 is covered with a metal layer 5 , and the metal layer 5 is covered with bumps 8 .

[0048] The seed layer 2 may not completely cover the substrate 1 , and the seed layer 2 may be arranged in an array according to actual needs. The bumps 8 may not completely cover the metal layer 5 either.

[0049] It is worth noting that in the prior art, the bonding force between the supporting bump and the substrate passivation layer is very poor, and the bump is prone to falling off or abnormality.

[0050] The present application constructs a seed layer 2 and a metal layer 5 between the bump 8 and the substrate 1. The seed layer 2 enhances the bonding between the substrate 1 and the metal layer 5 through chemical bonding, conductivity, and barrier effects. The metal layer 5 enhances the bonding between the seed layer 2 and the bump 8 by improving the conductive path and interface compatibility. The multi-layer structure of the present application synergistically increases the bonding between the structures and also improves the bonding between the bump 8 and the underlying material.

[0051] Method 2:

[0052] In Method 1, while the material used for the seed layer 2 (e.g., Ti, Cu, or a Ti / Cu stack) has good conductivity, the Ti seed layer's bonding to the substrate 1 is limited, making it susceptible to delamination or cracking during subsequent processing. The Cu seed layer can degrade over time due to diffusion or oxidation, especially when combined with subsequent electroplated layers, which are affected by interfacial stress. Ultimately, these factors can affect the bonding between the structures.

[0053] The present invention further improves the preparation method of the seed layer 2 material, and the specific steps are as follows:

[0054] A 50nm thick layer of Ti was deposited on substrate 1 using a high-purity Ti target using PVD. A 50nm thick layer of Cu was then deposited using a high-purity Cu target. This produced a substrate. Substrate 1 was made of silicon dioxide.

[0055] Prepare a 0.01 M ethanethiol solution using ethanethiol and ethanol, immerse the substrate in the 0.01 M ethanethiol solution until it is fully submerged, and treat at room temperature for 5 minutes. Rinse the substrate with ethanol and blow dry with nitrogen gas.

[0056] Take 5 g of silica, disperse it in 100 mL of deionized water, ultrasonically disperse it for 30 minutes, add 0.2 g of 0.2 wt% dopamine, adjust the pH to 8.5 (Tris buffer can be used), stir for 12 hours, centrifuge at 8000 rpm for 10 minutes, wash it three times with deionized water, and dry it for later use to obtain silica polydopamine particles.

[0057] 2 g of silica polydopamine particles were dispersed in 100 mL of 1 wt% ethanol, ultrasonically dispersed for 30 minutes, 1.9 g of 0.1 M 3-mercaptopropyltriethoxysilane was added, stirred for 6 hours, centrifuged at 8000 rpm for 10 minutes, washed with ethanol three times, and dried for later use to obtain modified particles.

[0058] Prepare a 0.1-0.5M copper sulfate solution with copper sulfate and deionized water. Add 1g of modified particles and 0.5g of 0.5wt% PVP to 100mL of the 0.5M copper sulfate solution and disperse by ultrasonication to obtain a nanocomposite solution.

[0059] The nanocomposite liquid is spin-coated on a substrate and cured after coating to form a thin film on the substrate. The thickness of the film is about 10-20 nm, preferably about 15 nm. The curing can be thermal curing, UV curing, or a combination of the two.

[0060] The seed layer 2 is prepared in this way. The structure of the seed layer 2 includes a substrate and a film.

[0061] Among them, raw materials:

[0062] Silica: Silica nanoparticles, particle size 5-10 nm, available from Sigma-Aldrich;

[0063] Dopamine: dopamine hydrochloride, available from Sigma-Aldrich;

[0064] Copper sulfate: analytical grade;

[0065] PVP: polyvinylpyrrolidone, molecular weight 10,000, available from Sigma-Aldrich.

[0066] It is worth mentioning that

[0067] Ti is deposited first, serving as an adhesion layer, followed by Cu, serving as a conductive layer. The substrate is immersed in an ethanethiol solution. The thiol groups in the ethanethiol molecules have strong coordination capabilities, forming stable chemical bonds on the substrate surface. For example, Cu-S can form on the substrate surface. This Cu-S chemical bond strengthens the adhesion between the substrate and the film while reducing Cu surface oxidation.

[0068] The silica core is coated with polydopamine. Thiol groups are introduced to the particle surface via 3-mercaptopropyltriethoxysilane. Furthermore, dopamine self-polymerizes to form polydopamine, giving the particles adhesive properties similar to mussel adhesive proteins. Furthermore, the particles possess a certain self-healing ability, mitigating the growth of microcracks. During the preparation of the nanocomposite solution, copper ions are introduced via a copper sulfate solution.

[0069] Therefore, the nanocomposite liquid is prepared layer by layer, dopamine can provide adhesion, silica provides mechanical strength, thiol groups form coordination bonds with copper ions to improve the uniformity of copper ion dispersion, and PVP can act as a dispersant and stabilizer to prevent copper ions from agglomerating.

[0070] After the substrate is treated with ethyl mercaptan, it cooperates with the nanocomposite liquid to enhance the interfacial bonding force through double thiol functionalization, form a physical barrier, reduce copper ion diffusion and oxidation, and also increase the compatibility of the film with the substrate and the metal layer 5 respectively.

[0071] In the following examples and comparative examples, the parameter ranges in Method 1 will affect the final test results. Therefore, to facilitate testing and comparison, the preferred point within the parameter ranges is used as the specific parameter. For example, the thickness of metal layer 5 is 2 μm, the thickness of insulating layer 6 is 65 μm, the height of bump 8 after reflow is 65 μm, and the thickness of the film is 15 nm.

[0072] Example 1

[0073] The sample was prepared according to the steps of Method 1. The seed layer 2 was also prepared according to the method of Method 1.

[0074] The substrate 1 is made of silicon dioxide.

[0075] Seed layer 2: A 60 nm thick Ti layer was deposited on substrate 1 using a high-purity Ti target by PVD, and a 60 nm thick Cu layer was deposited using a high-purity Cu target, thereby preparing a substrate.

[0076] Example 2

[0077] The sample was prepared according to the steps of Method 1, but the seed layer 2 was prepared according to the method of Method 2.

[0078] The substrate 1 is made of silicon dioxide.

[0079] Example 3

[0080] Different from Example 2, Ti is not deposited:

[0081] A 50 nm thick Cu layer was deposited on the substrate 1 using a high purity Cu target by PVD method, thereby preparing a base material.

[0082] The rest is the same as Example 2.

[0083] Comparative Example 1

[0084] Different from Example 1 and Example 2, the seed layer 2 is not prepared. The remaining steps of Method 1 are followed to prepare the sample.

[0085] That is, finally, the structure prepared according to method 1 is: the substrate 1 is covered with a metal layer 5 , and the metal layer 5 is covered with bumps 8 .

[0086] The samples prepared in Examples 1-3 and Comparative Example 1 were tested:

[0087] Pull-out test: Use the fixture of the Dage 4000 pull-out tester to fix the top of the sample protrusion 8 and apply a vertical upward pulling force until the sample structure separates or breaks.

[0088] Parameters: Pulling speed: 50um / min

[0089] The maximum pull-out force (breaking force) was recorded; the higher the pull-out force, the stronger the bonding strength.

[0090] The results are shown in Table 1:

[0091] Table 1

[0092]

[0093] Analysis: Comparing Examples 1-3 with Comparative Example 1, Comparative Example 1 has no seed layer, has the lowest average pull-out force, and has poor bonding strength between structures in the sample, indicating that the presence of the seed layer 2 significantly improves the bonding strength between structures.

[0094] Both Examples 2 and 3 used Method 2 to prepare the seed layer 2, and Example 3 did not deposit Cu; their pull-out forces were significantly higher than those of Example 1 and Comparative Example 1, indicating that Method 2 for preparing the seed layer 2 helps improve the bonding strength between structures.

[0095] Comparing Example 2 with Example 3, the average pull-out force of Example 2 is higher, indicating that when Ti and Cu are deposited simultaneously, the bonding strength between the structures can be further improved.

[0096] In summary, the above specific embodiments and comparative examples are only for the purpose of clearly illustrating the present invention and are not to be construed as limiting the present invention. It should be understood by those skilled in the art that, without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications, changes or improvements may be made to the technical solutions of the present invention and their implementations, and that these changes or improvements are all within the scope of the present invention. The scope of protection of the present invention shall be subject to the appended claims.

Claims

1. A method for improving the bonding strength between a bump and a bottom, characterized in that: The steps include: Depositing a seed layer on a wafer substrate, coating a photoresist film on the seed layer, removing excess photoresist film, projecting a target pattern onto the photoresist film, developing, removing excess photoresist film, forming an RDL wiring pattern layer on the remaining photoresist film by an RDL method, depositing a metal layer on the RDL wiring pattern, removing the photoresist film in the RDL wiring pattern layer, covering with an insulating layer, making a wiring opening on the insulating layer, making a bump in the wiring opening, and removing excess insulating layer and seed layer; The seed layer is made of Ti and / or Cu and a thin film, the thin film is solidified by a nanocomposite liquid, and the raw materials of the nanocomposite liquid include silicon dioxide, dopamine, 3-mercaptopropyltriethoxysilane, copper sulfate, and PVP.

2. The method for improving the bonding strength between a bump and a bottom according to claim 1, wherein: When a seed layer is deposited on the substrate surface of the wafer, Ti and / or Cu are deposited on the substrate to obtain a base material. The base material is soaked in an ethanethiol solution and then coated with a nanocomposite liquid and cured to obtain a thin film.

3. The method for improving the bonding strength between a bump and a bottom according to claim 1, wherein: The preparation method of the nanocomposite liquid comprises the following steps: Dopamine is added to the silica solution, the pH is adjusted, the solution is stirred, and the solution is centrifuged to obtain silica-polydopamine particles; the silica-polydopamine particles are dispersed in a solvent, 3-mercaptopropyltriethoxysilane is added, the solution is stirred, and the solution is centrifuged to obtain modified particles; the modified particles and PVP are added to a copper sulfate solution to obtain a nanocomposite solution.

4. The method for improving the bonding strength between a bump and a base according to claim 1, wherein: The substrate is made of silicon nitride or silicon dioxide.

5. The method for improving the bonding strength between a bump and a base according to claim 1, wherein: The thickness of the metal layer is 1-5um.

6. The method for improving the bonding strength between a bump and a base according to claim 1, wherein: The thickness of the insulation layer is 30-80um.

7. The method for improving the bonding strength between a bump and a base according to claim 1, wherein: The material of the bump includes at least one of Cu, Sn, and a copper-tin alloy, and the material of the metal layer includes Cu.

8. The method for improving the bonding strength between a bump and a base according to claim 1, wherein: When making bumps in wiring openings, the bumps are made through electroplating and reflow processes, and the height of the bumps after reflow is 30-80um.

9. The method for improving the bonding strength between a bump and a base according to claim 1, wherein: The thickness of the seed layer is 0.05-1 μm, and the thickness of the film is 10-20 nm.

10. A chip structure, the chip structure being prepared according to the method for improving the bonding force between a bump and a bottom according to any one of claims 1 to 9, characterized in that: The chip structure includes a substrate, a seed layer covered on the substrate, a metal layer covered on the seed layer, and bumps covered on the metal layer. The seed layer partially or completely covers the substrate, and the bumps partially or completely cover the metal layer.

Images