A thermally reversible cross-linking wafer temporary bonding adhesive and a preparation method thereof

Abstract

The application discloses a kind of heat reversible crosslinking type wafer temporary bonding glue and preparation method thereof, specifically related to the field of semiconductor packaging and microelectronic manufacturing, including the following components by mass fraction: furan modified hydrogenated poly-alpha-methylstyrene 40-60 parts, bismaleimide 5-15 parts, hydrogenated rosin methyl ester 3-8 parts, electronic grade solvent 30-50 parts, silane coupling agent 0.5-2 parts, fluorine modified acrylate leveling agent 0.1-0.5 parts, multi-hindered phenol-phosphite compounded antioxidant 0.2-0.8 parts.The temporary bonding glue for wafer processing is a kind of heat reversible crosslinking, temperature resistance up to 300 DEG C or more, high bonding strength, easy to dissociate without residue, spin coating uniform temporary bonding glue, can be widely used in wafer thinning, etching and other downstream processing.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging and microelectronics manufacturing technology, and more specifically, to a thermally reversible crosslinked wafer temporary bonding adhesive and its preparation method. Background Technology

[0002] With the continuous improvement of semiconductor device integration, advanced packaging technologies such as wafer-level 3D stacking and system-in-package (SIIP) are widely used, placing higher demands on ultra-thin wafer processing. In this technological evolution, ultra-thin wafer processing (typically reducing thickness to 50μm or even less) has become an indispensable key step. However, ultra-thin wafers, due to their significantly reduced mechanical strength, are highly susceptible to warping, vibration, and even breakage during subsequent high-temperature, high-stress processing steps such as photolithography, etching, physical vapor deposition (PVD), and chemical mechanical polishing (CMP). To address this, temporary bonding / debonding technology has emerged. Its core principle is to reversibly fix the device wafer to a rigid carrier (such as a glass substrate or silicon wafer) using a layer of temporary bonding adhesive. After all subsequent processing is completed, the wafer is then separated non-destructively using specific methods.

[0003] As a core consumable in this technology, the performance of temporary bonding adhesive directly determines the processing yield and process reliability. An ideal temporary bonding adhesive must simultaneously meet multiple requirements, including high temperature resistance, adhesive strength, and ease of dissociation. For example, it must possess excellent thermal stability, able to withstand high-temperature processes of 250°C or even 300°C without thermal decomposition or excessive rheology; it must have sufficient adhesive strength at processing temperatures to prevent wafer slippage during high-speed rotation or chemical washing; and after processing, it must be able to be quickly debonded using gentle methods, and the adhesive layer must be completely dissolved in cleaning solvents without leaving any residue to avoid contaminating the device surface.

[0004] Currently, temporary bonding materials on the market are mainly divided into thermoplastic systems, thermosetting systems, and laser debonding systems. While thermoplastic materials are easy to debond, they have poor temperature resistance, typically softening around 200°C, which cannot meet the high-temperature process requirements of advanced nodes. Thermosetting materials have better temperature resistance, but after curing, they form a permanent cross-linked network that is insoluble and infusible. Debonding requires laser ablation or mechanical peeling, which is not only inefficient but also prone to leaving residue or causing stress damage to the wafer. Laser debonding systems can achieve rapid separation, but the equipment investment is high, and the optical uniformity of the adhesive layer is extremely important. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a thermally reversible crosslinked wafer temporary bonding adhesive and its preparation method. The technical problem to be solved by the present invention is that the existing temporary bonding adhesives are difficult to balance high-temperature stability and easy dissociation.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a thermally reversible crosslinking temporary bonding adhesive for wafers, comprising the following components in parts by weight: 40-60 parts of base resin, 5-15 parts of crosslinking agent, 3-8 parts of tackifying resin, 30-50 parts of electronic-grade solvent, 0.5-2 parts of coupling agent, 0.1-0.5 parts of wetting and leveling agent, and 0.2-0.8 parts of antioxidant;

[0007] The base resin is furan-modified hydrogenated poly(α-methylstyrene); the crosslinking agent is bismaleimide; the tackifying resin is hydrogenated rosin methyl ester; the coupling agent is silane coupling agent KH550; the wetting and leveling agent is fluorinated acrylate leveling agent; the antioxidant is a poly-hindered phenol-phosphite compound antioxidant; and the electronic-grade solvent is one or a compound of two of propylene glycol methyl ether acetate (PGMEA) and dimethylacetamide (DMAc).

[0008] In a preferred embodiment, the base resin furan-modified hydrogenated poly(α-methylstyrene) has a mass fraction of 45-55 parts. As a film-forming resin, it imparts excellent spin-coating film-forming properties and thermoplasticity to the adhesive. At the same time, the furan groups on the side chains provide key reactive sites for subsequent thermally reversible crosslinking.

[0009] In a preferred embodiment, the crosslinking agent bismaleimide has a mass fraction of 8 to 12 parts. The bismaleimide groups in its molecular structure can undergo an efficient Diels-Alder cycloaddition reaction with furan groups under heating conditions to construct a three-dimensional crosslinking network, thereby significantly improving the high-temperature creep resistance and cohesive strength of the adhesive layer.

[0010] In a preferred embodiment, the tackifying resin hydrogenated rosin methyl ester has a mass fraction of 4 to 6 parts, which can effectively reduce the interfacial tension between the adhesive layer and the inorganic wafer surface, and significantly improve the bonding strength through the interaction of polar groups.

[0011] In a preferred embodiment, the electronic-grade solvent is a mixture of PGMEA and DMAc in a volume ratio of 1:1. This mixed solvent combines excellent solubility for each component with a moderate evaporation rate, effectively avoiding defects such as poor leveling, bubble breakage, or impurities during spin coating.

[0012] In a preferred embodiment, the antioxidant is a compound of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite in a mass ratio of 1:2. This combination can synergistically inhibit the thermo-oxidative aging of the adhesive layer during high-temperature processing or long-term use, and maintain the long-term stability of the material properties.

[0013] This invention also includes a method for preparing a thermally reversible crosslinked temporary bonding adhesive for wafers, comprising the following steps:

[0014] S1: Add the prescribed amount of electronic-grade solvent to the reaction vessel and stir at 100-200 r / min for 10-20 min at room temperature to ensure the solvent system is mixed evenly.

[0015] S2: Add the formulated amount of base resin to the solvent, increase the stirring speed to 300-500 r / min, stir for 30-40 min until the resin is completely dissolved to form a homogeneous, transparent, viscous solution.

[0016] S3: Add the prescribed amount of crosslinking agent to the solution obtained in step S2, and stir at 300-500 r / min for 20-25 min to fully disperse the crosslinking agent powder into the system;

[0017] S4: Add the formulated amount of thickening resin to the dispersion obtained in step S3, and continue stirring at 300-500 r / min for 20-30 min until all solid components are completely dissolved to form a clear and transparent mixture.

[0018] S5: Add the formulated amount of coupling agent, wetting and leveling agent and antioxidant to the mixture obtained in step S4 in sequence, and continue stirring at 300-500 r / min for 10-15 min to make each trace additive achieve uniform dispersion at the molecular level in the system.

[0019] S6: After the adhesive solution obtained in step S5 is allowed to stand and cool to room temperature, it is placed in a vacuum degassing machine for vacuum degassing to remove air bubbles mixed in during the stirring process. Finally, the adhesive solution is transferred to a clean container and sealed for storage.

[0020] This invention also includes a method for using a thermally reversible crosslinked temporary wafer bonding adhesive in wafer back-end processing, comprising the following steps: uniformly coating the temporary bonding adhesive onto the surface of a carrier wafer using a spin coating process; after pre-baking at 90–110°C to remove most of the organic solvents; bonding the device wafer to be processed to the carrier wafer under vacuum; placing the bonded assembly in an oven or on a heating plate, heating to 120–130°C and holding at that temperature for 30–60 minutes. The process involves allowing the furan groups and bismaleimide groups in the adhesive layer to undergo a Diels-Alder cycloaddition reaction, forming a stable three-dimensional covalent cross-linked network in situ, thereby achieving a strong bond between the carrier wafer and the device wafer. After completing all subsequent processing steps such as wafer thinning and etching, the bond is heated to 240–260°C to trigger a reverse Diels-Alder reaction, causing the cross-linked network to dissociate into linear thermoplastic molecular chains, softening the adhesive layer and restoring its fluidity. Subsequently, the debonded wafer surface is rinsed with PGMEA solvent for 1–10 minutes to remove the residual adhesive layer.

[0021] The technical effects and advantages of this invention are as follows:

[0022] 1. This invention achieves a synergistic effect of high heat resistance and easy dissociation by constructing a thermally reversible crosslinking system based on the Diels-Alder cycloaddition reaction using furan-modified hydrogenated poly(α-methylstyrene) and bismaleimide. At a bonding temperature of 120–130°C, the furan groups react with bismaleimide to form a three-dimensional covalent crosslinking network, endowing the adhesive layer with excellent high-temperature creep resistance and high bonding strength. The dry film thermal decomposition temperature reaches above 350°C, which can withstand the 300°C high-temperature process in wafer back-end processing. At a debonding temperature of 250°C, the reverse Diels-Alder reaction triggers the dissociation of the crosslinking network, and the adhesive layer returns to a thermoplastic flow state. It can be dissolved and removed within minutes with PGMEA solvent without residue, solving the technical problem of the mutual restriction between the temperature resistance and dissociation of traditional temporary bonding adhesives.

[0023] 2. This invention, through the synergistic proportioning of components and the preparation process of stepwise stirring and vacuum degassing, produces a uniform and defect-free spin-coated film of bonding adhesive. The interfacial bonding strength is improved compared to the unbonded system, maintaining the bonding strength after processing at 300℃ and exhibiting excellent long-term storage stability. The entire bonding / debonding process can be completed with only conventional heating and PGMEA cleaning, reducing the overall cost of temporary wafer bonding processes. Attached Figure Description

[0024] Figure 1 This is a thermogravimetric curve of the temporary bonding adhesive coating in Embodiment 1 of the present invention.

[0025] Figure 2This is a thermogravimetric curve of the dry film coating of the temporary bonding adhesive in Example 2 of the present invention.

[0026] Figure 3 This is a viscosity-temperature curve of the temporary bonding adhesive after solvent removal in Example 2 of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1:

[0029] This invention provides a thermally reversible crosslinking temporary bonding adhesive for wafers, the specific formulation of which is as follows:

[0030] Base resin: furan-modified hydrogenated poly-α-methylstyrene, 50g;

[0031] Crosslinking agent: bismaleimide, 10g;

[0032] Tackifying resin: Hydrogenated rosin methyl ester, 5g;

[0033] Electronic grade solvent: PGMEA, 32g;

[0034] Coupling agent: Silane coupling agent KH550, 1g;

[0035] Wetting and leveling agent: Fluorine-modified acrylate leveling agent (model: BYK-381), 0.3 g;

[0036] Antioxidant: A compound of polyhedral hindered phenol (Irganox 1010) and phosphite (Irgafos 168) in a mass ratio of 1:2, 0.5g.

[0037] The temporary bonding adhesive in this embodiment is prepared according to the following steps:

[0038] S1: At room temperature, accurately add 32g of PGMEA solvent to a three-necked flask equipped with a mechanical stirrer and thermometer, start stirring, set the speed to 150 r / min, and stir for 15 min;

[0039] S2: Slowly add 50g of furan-modified hydrogenated poly-α-methylstyrene resin to the flask, increase the stirring speed to 400 r / min, and continue stirring for 35 min. Observe that the resin is completely dissolved and the solution is transparent and viscous.

[0040] S3: Continue to add 10g of bismaleimide crosslinking agent to the flask, and stir at 400 r / min for 22 min until the crosslinking agent powder is evenly dispersed and there are no obvious particles.

[0041] S4: Add 5g of hydrogenated rosin methyl ester tackifying resin to the system and continue stirring at 400 r / min for 25 min until the tackifying resin is completely dissolved and the system is clear and transparent again.

[0042] S5: Add 1g of KH550 coupling agent, 0.3g of fluorinated modified acrylate leveling agent and 0.5g of compound antioxidant to the flask in sequence, and continue stirring at 400 r / min for 12 min to ensure that the components are fully mixed.

[0043] S6: Stop stirring, allow the contents of the flask to cool to room temperature, then place it in a vacuum degasser and degas it at a vacuum of -0.08 MPa for 10 min to completely remove tiny air bubbles from the system. Finally, transfer the resulting gel to a clean brown reagent bottle, seal and store for later use.

[0044] Example 2:

[0045] This embodiment provides a thermally reversible crosslinking temporary wafer bonding adhesive, the specific formulation of which is as follows:

[0046] Base resin: furan-modified hydrogenated poly-α-methylstyrene, 45g;

[0047] Crosslinking agent: bismaleimide, 8g;

[0048] Tackifying resin: Hydrogenated rosin methyl ester, 6g;

[0049] Electronic grade solvent: a compound solvent composed of PGMEA and DMAc in a volume ratio of 1:1, 35g;

[0050] Coupling agent: Silane coupling agent KH550, 1.2g;

[0051] Wetting and leveling agent: Fluorine-modified acrylate leveling agent (model: BYK-381), 0.2g;

[0052] Antioxidant: Irganox 1010 and Irgafos 168 are compounded at a mass ratio of 1:2, 0.4g.

[0053] The preparation method of the temporary bonding adhesive in this embodiment is the same as that in Example 1, and a transparent, stable, particle-free homogeneous adhesive solution is finally obtained.

[0054] Example 3:

[0055] This embodiment provides a thermally reversible crosslinking temporary wafer bonding adhesive, the specific formulation of which is as follows:

[0056] Base resin: furan-modified hydrogenated poly-α-methylstyrene, 55g;

[0057] Crosslinking agent: bismaleimide, 12g;

[0058] Tackifying resin: Hydrogenated rosin methyl ester, 4g;

[0059] Electronic grade solvent: DMAc, 40g;

[0060] Coupling agent: Silane coupling agent KH550, 0.8g;

[0061] Wetting and leveling agent: Fluorine-modified acrylate leveling agent (model: BYK-388), 0.4g;

[0062] Antioxidant: Irganox 1010 and Irgafos 168 are compounded at a mass ratio of 1:2, 0.6g.

[0063] The preparation method of the temporary bonding adhesive in this embodiment is the same as that in Example 1.

[0064] The temporary bonding adhesives prepared in Examples 1-3 above were subjected to performance tests, and the specific test items and results are as follows:

[0065] The adhesive solutions from Examples 1-3 were applied to the surface of a 4-inch silicon wafer using a spin coater at a speed of 800 r / min for 30 s. Observations showed that all three adhesive solutions spread evenly during spin coating, with no pinholes, streaks, or other defects. The resulting coatings had smooth surfaces and uniform thickness. After baking at 100°C for 3 min to remove the solvent, all solutions formed transparent, colorless solid dry films.

[0066] Take 5-10 mg of each of the dry film samples pre-baked at 100°C from Examples 1 and 2, and heat them from room temperature to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere. Record their thermogravimetric curves (TGA), as shown below. Figure 1 and Figure 2As shown in the TGA curves, it is clear that the dry film samples of Examples 1 and 2 show almost no significant mass loss in the temperature range from room temperature to 350°C, and their thermal decomposition onset temperature (Td, defined as the temperature at which 5% mass loss occurs) is higher than 350°C. Within the 350°C to 450°C range, the samples exhibit the main thermal decomposition behavior, and the decomposition process is relatively concentrated. These results indicate that, thanks to the formation of the DA reversible crosslinking network and the design of the high-heat-resistant framework structure in this invention, the adhesive layer possesses extremely excellent high-temperature thermal stability, fully capable of withstanding short-term high-temperature shocks at 300°C levels during wafer back-end processing (such as rapid thermal annealing, chemical vapor deposition, etc.). During processing, no volatiles are generated due to thermal decomposition, thus effectively avoiding the risk of failure such as bonding interface bubbles, delamination, or wafer contamination.

[0067] The dynamic viscosity of the temporary bonding adhesive (after solvent removal) from Example 1 was tested using a rotational rheometer. Under nitrogen protection, the temperature was increased from 80°C to 280°C at a rate of 2°C / min, and the complex viscosity was measured as a function of temperature. The results are as follows: Figure 3 As shown in the viscosity-temperature curve, the viscosity of the adhesive layer remains at a high level (above approximately 103 Pa·s) in the temperature range of 80℃ to approximately 120℃. This ensures the dimensional stability and creep resistance of the adhesive layer during low-temperature bonding and processing. As the temperature rises above 120℃, the viscosity increases further due to the intensification of the DA forward crosslinking reaction, marking the construction of the crosslinking network. When the temperature exceeds 200℃, especially close to 250℃, the reverse DA reaction gradually becomes dominant, the crosslinking network begins to dissociate, and the viscosity drops sharply to below approximately 102 Pa·s, restoring the fluidity of the adhesive layer. This viscosity change curve intuitively demonstrates that the adhesive possesses thermally reversible characteristics, that is, it can stably cure at the processing temperature window (approximately 120℃) and rapidly soften and flow at the debonding temperature (approximately 250℃), facilitating non-destructive separation of the wafer.

[0068] The adhesives from Examples 1-3 were used in bonding experiments between 4-inch silicon wafers and glass substrates. The bonding process was: curing at 120℃ for 1 hour. The bond shear strength at room temperature was measured using a shear force tester. The results showed that the bond strengths of Examples 1-3 reached 2.5 MPa, 2.2 MPa, and 2.8 MPa, respectively, all exceeding the industry benchmark requirement of 2.0 MPa. After heating the bonded samples to 250℃ on a heating stage and holding for 10 minutes, all samples could be easily separated manually. The separated wafers and glass substrates were immersed in PGMEA solvent and ultrasonically cleaned for 5 minutes. Inspection using an optical microscope and surface contact angle tester revealed no adhesive residue or surface contamination. The surface cleanliness of the wafers after cleaning met the VDA Class 1 standard. This fully demonstrates that the bonding adhesive of this invention possesses the dual advantages of high adhesion and easy dissociation without residue.

[0069] Based on the above test results, the key performance indicators of Examples 1-3 are summarized in Table 1. Compared with mainstream competing products in the market (typical thermoplastic system A and thermosetting system B), the present invention shows significant balanced advantages in core parameters such as heat resistance temperature, bond strength, debonding time and residual adhesive level, as detailed in Table 2.

[0070] Table 1 Summary of Key Performance Test Results for Examples 1-3

[0071]

[0072] Table 2. Comparison of the overall performance of Embodiment 1 of the present invention with representative products of the prior art.

[0073]

[0074] As shown in Table 2, although thermosetting system B has high bonding strength, its debonding process is cumbersome and easily damages the wafer; while thermoplastic system A, although easily dissociated, has severely insufficient temperature resistance. This solution achieves a breakthrough balance between heat resistance and dissociation through a unique DA reversible crosslinking molecular design, and has a wide overall process window, requiring neither special equipment nor toxic or harmful reagents, thus possessing extremely high industrial application value.

[0075] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A thermally reversible crosslinking temporary bonding adhesive for wafers, characterized in that, The product comprises the following components in parts by weight: 40-60 parts of furan-modified hydrogenated poly-α-methylstyrene, 5-15 parts of bismaleimide, 3-8 parts of hydrogenated rosin methyl ester, 30-50 parts of electronic-grade solvent, 0.5-2 parts of γ-aminopropyltriethoxysilane, 0.1-0.5 parts of fluorine-modified acrylate leveling agent, and 0.2-0.8 parts of poly-hindered phenol-phosphite compound antioxidant.

2. The thermally reversible crosslinking temporary bonding adhesive for wafers according to claim 1, characterized in that: The furan-modified hydrogenated poly(α-methylstyrene) has a mass fraction of 45-55 parts, which serves as a base resin to provide film-forming and thermoplastic properties, and its side chain furan groups provide reactive sites for thermally reversible crosslinking.

3. The thermally reversible crosslinking temporary bonding adhesive for wafers according to claim 1, characterized in that: The bismaleimide has a mass fraction of 8 to 12 parts, and it acts as a crosslinking agent to form a three-dimensional covalent crosslinked network with the furan groups in furan-modified hydrogenated poly(α-methylstyrene) through a Diels-Alder cycloaddition reaction.

4. The thermally reversible crosslinking temporary bonding adhesive for wafers according to claim 1, characterized in that: The hydrogenated rosin methyl ester is present in a mass fraction of 4 to 6 parts, and is used as a tackifying resin to improve the interfacial adhesion performance between the bonding adhesive and the wafer surface.

5. The thermally reversible crosslinking temporary bonding adhesive for wafers according to claim 1, characterized in that: The electronic-grade solvent is one or a mixture of two of propylene glycol methyl ether acetate and dimethylacetamide in any proportion, and the amount of electronic-grade solvent used is 35 to 40 parts by mass.

6. The thermally reversible crosslinking temporary bonding adhesive for wafers according to claim 1, characterized in that: The γ-aminopropyltriethoxysilane is present in a mass fraction of 0.8 to 1.2 parts and is used to enhance the interfacial bonding force between the adhesive layer and the inorganic substrate.

7. The thermally reversible crosslinking temporary bonding adhesive for wafers according to claim 1, characterized in that: The multi-component hindered phenol-phosphite compound antioxidant is composed of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl)phosphite in a mass ratio of 1:1.5 to 1:2.5, and is used to improve the antioxidant stability of the adhesive layer during high-temperature processing.

8. A method for preparing the thermally reversible crosslinking temporary wafer bonding adhesive according to any one of claims 1-7, characterized in that, Specifically, the processing steps include the following: S1. Add electronic-grade solvent to the reaction vessel and stir at room temperature for 10-20 min at a speed of 100-200 r / min. S2. Add furan-modified hydrogenated poly-α-methylstyrene and stir at 300-500 r / min for 30-40 min until completely dissolved; S3. Add bismaleimide and stir at 300-500 r / min for 20-25 min until uniformly dispersed; S4. Add hydrogenated rosin methyl ester and stir at 300-500 r / min for 20-30 min until a clear and transparent liquid is formed; S5. Add silane coupling agent, fluorinated acrylate leveling agent and poly-hindered phenol-phosphite compound antioxidant, and stir at 300-500 r / min for 10-15 min. S6. After cooling, perform vacuum degassing and store in a sealed container.

9. The method for preparing a thermally reversible crosslinked wafer temporary bonding adhesive according to claim 8, characterized in that: In step S6, the vacuum degassing process has a gauge pressure of -0.06 to -0.09 MPa and a processing time of 5 to 15 minutes to remove air bubbles from the adhesive.

10. A method for post-processing of wafer thinning, etching, or three-dimensional stacking, characterized in that... The thermally reversible crosslinked temporary wafer bonding adhesive according to any one of claims 1-7 is characterized in that: the bonding adhesive is cured by heating to 120-130°C to form a crosslinked layer to achieve wafer bonding, and debonding is achieved by heating to 240-260°C to trigger a reverse Diels-Alder reaction, and the residual adhesive layer after debonding is removed by rinsing with PGMEA solvent.

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