Adhesive sheet for back-grinding wafer

Abstract

The present invention discloses an adhesive sheet for back-grinding wafers. The adhesive sheet primarily includes a base layer, a pressure-sensitive adhesive layer

Description

[Technical Field]

[0001] The present invention relates to a wafer polishing tape, particularly a tape used in the wafer backside polishing process. [Previous Technology]

[0002] In semiconductor wafer manufacturing, wafers must be thinned before packaging or dicing, which involves a back-side polishing process. Before polishing, a protective film is applied to the wafer surface to prevent damage to bumps or circuits. This film is then removed after polishing.

[0003] Currently, the commonly used wafer polishing tape is the UV anti-tack tape. After polishing, UV light can be used to reduce or even remove the tack, allowing the tape to be removed from the wafer surface. The UV anti-tack tape mainly consists of a substrate layer and an adhesive layer. The substrate layer is usually made of polyolefin (PO) or polyethylene terephthalate (PET). The adhesive layer is usually made of polyacrylates, such as poly(methyl methacrylate) (PMMA), and may contain hardeners, UV light initiators, inhibitors, crosslinking agents, etc., as needed. During the application of the tape and the polishing of the wafer, due to the effects of elasticity and stress, damage, water seepage, or excessive flatness or sagging of the polished wafer may occur. Removing the tape after polishing also often causes damage to semiconductor components.

[0004] The known solutions mainly involve increasing the rigidity of the substrate layer to reduce the curvature of the wafer and suppress problems such as wafer breakage, water seepage, or excessive flatness of the wafer after grinding during the grinding process. However, this solution still carries practical risks; because increasing the thickness of the substrate makes it difficult for the tape to adhere and cover properly, and it is also not easy to remove it from the delicate wafer surface.

[0005] To address this problem, the present invention has developed a novel wafer polishing tape with a dual pressure-sensitive adhesive layer design. In this configuration, pressure-sensitive adhesive layer 1 is disposed on the substrate layer, while pressure-sensitive adhesive layer 2 is disposed on adhesive layer 1, thereby providing appropriate adhesion and flexibility. This structure effectively reduces wafer breakage without increasing the thickness of any substrate layer. The dual pressure-sensitive adhesive layer design not only effectively covers solder balls, copper pillars, and other related designs, preventing wafer breakage, water seepage, or excessive flatness of the polished wafer, but also facilitates adhesion and removal without affecting the effectiveness of the adhesive. [Summary of the Invention]

[0006] The purpose of this invention is to provide a wafer grinding tape that can effectively cover solder balls, copper pillars and other related designs during the back-side grinding process of the wafer, so as to avoid wafer damage, water seepage or excessive flatness of the wafer after grinding, while being easy to adhere and remove.

[0007] The wafer grinding tape of the present invention sequentially laminates a substrate layer, a pressure-sensitive adhesive layer 1 and a pressure-sensitive adhesive layer 2.

[0008] The thickness of the substrate layer is 30~100μm, and the material can be polyolefin (PO), polyethylene terephthalate (PET) or other suitable materials.

[0009] The thickness of the pressure-sensitive adhesive layer 1 is 50~200μm, preferably 100~170μm; it mainly includes polyurethane acrylate oligomer and hydroxyl-containing monomer.

[0010] The polyurethane acrylate oligomer is preferably aliphatic polyurethane diacrylate; accounting for 45 to 90% by weight of the pressure-sensitive adhesive layer 1, more preferably 55 to 80% by weight, and even more preferably 60 to 75% by weight.

[0011] The hydroxyl-containing monomer is preferably hydroxyethyl acrylate (HEA); accounting for 5 to 40% by weight of the pressure-sensitive adhesive layer 1, more preferably 10 to 30% by weight, and even more preferably 10 to 20% by weight.

[0012] The adhesion of the pressure-sensitive adhesive layer 1 is 400~2000gf / 25mm (180º, stretching speed 300mm / min, stainless steel surface), preferably 600~1000gf / 25mm.

[0013] The pressure-sensitive adhesive layer 1 may further include 2-ethyl hexyl acrylate (EHA), cyclic trimethylolpropane formal acrylate (CTFA), ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L), etc.

[0014] Preferably, the pressure-sensitive adhesive layer 1 is a radiation-cured pressure-sensitive adhesive.

[0015] The thickness of the pressure-sensitive adhesive layer 2 is 1~50μm, preferably 15~50μm, and mainly includes acrylate polymer and isocyanide crosslinker.

[0016] The adhesion of the pressure-sensitive adhesive layer 2 is 300~1500gf / 25mm (180º, stretching speed 300mm / min, stainless steel surface), preferably 400~1000gf / 25mm.

[0017] Preferably, the pressure-sensitive adhesive layer 2 is a radiation-induced tack-reducing pressure-sensitive adhesive.

Implementation Method

[0018] The following examples are only for illustrating the wafer grinding tape of the present invention, but should not be limited thereto.

[0019] The wafer grinding tape of the present invention having a double adhesive layer structure includes, in sequence, a substrate layer, a pressure-sensitive adhesive layer 1 and a pressure-sensitive adhesive layer 2.

[0020] The thickness of the substrate layer is 50μm, and the material is polyethylene terephthalate (PET), which can provide appropriate support for the wafer grinding tape.

[0021] The thickness of the pressure-sensitive adhesive layer 1 is typically between 50 and 200 μm, preferably between 100 and 170 μm. A thickness less than 50 μm may cause accidental damage to the fragile adhesive after grinding. In this embodiment, the thickness of the pressure-sensitive adhesive layer 1 is 100 μm.

[0022] The pressure-sensitive adhesive layer 1 is formed from a variety of monomers, functional groups, and additives to achieve optimal performance for semiconductor applications. These components enhance the mechanical strength and thermal stability of the adhesive, which is crucial for high-precision applications such as wafer fabrication. The main components are urethane acrylate oligomers and hydroxy-containing monomers.

[0023] Polyurethane acrylate oligomers can be combined with UV-curable oligomers to enhance the mechanical integrity and shape stability of adhesive layers through their low viscosity and excellent crosslinking properties. The UV-curable oligomers can be cyclic trimethylol-propane formal acrylate (CTFA) or polyester acrylates. Examples use aliphatic urethane diacrylate (Doublemer® 5500 or DM5500) from Double Bond Chemicals.

[0024] Hydroxyl-containing monomers help improve heat resistance and cohesive strength, ensuring the adhesive layer performs effectively under challenging processing conditions. The combination of hydroxyl-containing monomers, such as hydroxyethyl acrylate (HEA), with 2-ethyl hexyl acrylate (EHA) can effectively improve crosslinking efficiency and flexibility.

[0025] Multifunctional monomers HEA and EHA are mixed with oligomer CTFA and aliphatic polyurethane diacrylate (DM5500), and a UV polymerization and curing reaction is initiated by the photoinitiator ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L). This forms a dense cross-linked network, producing an adhesive layer with excellent elasticity, adhesion, and environmental resilience. UV curing offers several advantages, including faster polymerization rates, lower energy consumption, and the ability to obtain high molecular weight polymers with minimal thermal impact. By optimizing UV irradiation parameters and TPO-L concentration, a uniform cross-linked polymer network can be achieved to meet the specific application requirements of pressure-sensitive adhesive layer 1. This method ensures enhanced adhesion, thermal stability, and cohesive strength, making it suitable for high-precision semiconductor applications.

[0026] Tables 1 and 2 show the adhesion of the laminated pressure-sensitive adhesive layer 1 on the substrate layer with different formulations (100% solid content). The ultraviolet irradiation dose was 1100 MJ / cm2. The adhesion test conditions were 180º, tensile speed 300 mm / min, and the test was conducted on a stainless steel surface.

[0027]

[0028]

[0029] In Table 1, when the HEA content of formulation A is close to 100 wt%, the adhesion is only 141 gf / 25 mm. The HEA content of formulations B to H is reduced from 60 wt% and 40 wt% to 20 wt%, respectively, while DM5500, CTFA, and / or EHA are added. The results show that when the HEA content is 20 wt% and the DM5500 content is 80 wt%, the adhesion can be increased to 474 gf / 25 mm.

[0030] In Table 2, the HEA content of formulations I to O is maintained at 20wt%, the DM5500 content is 70wt% and 65wt%, and when CTFA and / or EHA are added appropriately, the adhesion is significantly improved to 525gf / 25mm~798gf / 25mm.

[0031] The composition and formulation in Table 2 not only provide the required adhesion and flexibility between the substrate layer and the pressure-sensitive adhesive layer 2, but also avoid excessive flow characteristics or tackiness. The HEA introduces hydroxyl groups that enhance hydrogen bonding, generating stronger adhesion between the substrate layer and the pressure-sensitive adhesive layer 2. In addition to balancing properties, the HEA increases flexibility, further improving compatibility and adhesion performance. The polyurethane functional groups of the DM5500 oligomer can perform crosslinking, thereby forming a highly durable and environmentally resistant intermediate layer. Furthermore, the formulation of this invention avoids monomer migration, ensuring a clean and stable adhesive interface, which is particularly useful in processes where contamination is unacceptable.

[0032] The shear modulus (25°C) of the pressure-sensitive adhesive layer 1 is lower than the instrument detection limit of 0.0001MPa, indicating that it has appropriate flexibility and is suitable for being sandwiched between the substrate layer and the pressure-sensitive adhesive layer 2, without causing the wafer to deform during processing or grinding.

[0033] The thickness of the pressure-sensitive adhesive layer 2 can be 1~50μm, preferably 5~30μm. When the thickness is less than 1μm, it may be brittle after grinding due to insufficient adhesion. When the thickness is greater than 50μm, it may lead to excessive stiffness, which is economically disadvantageous for material use; at the same time, it may inhibit the deformation of the wafer grinding tape, making it difficult to form a peeling start point. In this embodiment of the invention, the thickness is 20μm.

[0034] Pressure-sensitive adhesive layer 2 is an active energy radiation-cured adhesive, comprising a base polymer (such as an acrylic pressure-sensitive adhesive) and an active energy radiation-cured compound. Pressure-sensitive adhesive layer 2 exhibits high adhesion at room temperature, allowing for wafer grinding and polishing. When exposed to UV radiation, the photoinitiator in pressure-sensitive adhesive layer 2 initiates a cross-linking mechanism, reducing adhesion.

[0035] In the embodiments, the components used in the pressure-sensitive adhesive layer 2 include: Nanpao Resin Chemical's adhesive SD-488® (a mixture of ethyl acetate and acrylate polymer), Nanpao Resin Chemical's curing agent A-10T® (a mixture of modified polyisocyanate, N-butyl acetate, and xylene), photoinitiator diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), additive 2,4-Pentanedione, and solvent methyl ethyl ketone.

[0036] If the formulation consists of 100 parts by weight of adhesive SD-488®, then the curing agent A-10T® is 0.5 parts by weight, the photoinitiator TPO is 2 parts by weight, the additive 2,4-pentanedione is 2 parts by weight, the solvent methyl ethyl ketone is 5 parts by weight, and the solid content is 44.0%. The modified polyisocyanate in curing agent A-10T® has excellent adhesion and flexibility to the wafer surface. Under ultraviolet light irradiation, it can undergo a cross-linking reaction to form a robust three-dimensional network structure, reducing its adhesion and allowing the adhesive to be effectively separated.

[0037] Pressure-sensitive adhesive layer 2 was deposited on the substrate layer and its adhesion was tested. The test conditions were 180º, tensile speed 300 mm / min, and the test was conducted on a stainless steel surface. The adhesion was found to be 469 gf / 25 mm, indicating that it has good adhesion and can effectively protect the wafer during the polishing process. After UV irradiation, the adhesion of pressure-sensitive adhesive layer 2 decreased to 20 gf / 25 mm, and it can be easily peeled off without damaging the fragile wafer.

[0038] The pressure-sensitive adhesive layer 2 has a shear modulus of less than 0.2 MPa at 80°C, making it suitable for temporary bonding with the wafer. For compact wafer ball patterns, the flexibility of the pressure-sensitive adhesive layer 2 ensures that the adhesive can cover every corner of the ball without damaging the wafer.

[0039] To obtain a wafer grinding tape with a double-layer adhesive structure, pressure-sensitive adhesive layer 1 and pressure-sensitive adhesive layer 2 of formulations 1-1 to 1-0 were sequentially laminated on a substrate layer. Table 3 shows the results of the adhesion test; the test conditions were 180º, tensile speed 300 mm / min, and the test was conducted on a stainless steel surface.

[0040]

[0041] The results show that the dual-layer adhesive structure of the present invention not only provides superior flexibility and coverage, but also possesses appropriate adhesion. It offers better protection for dense wafer spherical patterns during the wafer backside polishing process.

[0042] Many factors affect the wafer polishing protection effect, such as the source and composition of raw materials, the thickness and hardness of each layer, the wafer surface conditions, and the bonding temperature, which will not be discussed in detail here. The above embodiments are only used to prove that the structure and composition of the present invention are indeed feasible as a wafer polishing tape and have industrial applicability.

Claims

1. A wafer grinding tape, wherein a pressure-sensitive adhesive layer 1 and a pressure-sensitive adhesive layer 2 are sequentially laminated on a substrate layer, wherein, The substrate layer has a thickness of 30-100 μm and is made of polyolefin or polyethylene terephthalate. The pressure-sensitive adhesive layer 1 has a thickness of 50-200 μm and includes aliphatic polyurethane diacrylate and hydroxyl-containing monomer. The aliphatic polyurethane diacrylate accounts for 60-90% by weight of the pressure-sensitive adhesive layer 1, and the hydroxyl-containing monomer accounts for 10-40% by weight of the pressure-sensitive adhesive layer 1. The adhesion of the pressure-sensitive adhesive layer 1 is 400-1000 gf / 25 mm (180º, tensile speed 300 mm / min, stainless steel surface). The pressure-sensitive adhesive layer 2 has a thickness of 1-50 μm and includes acrylate polymer and isocyanide crosslinker. The adhesion is 300-1000 gf / 25 mm (180º, tensile speed 300 mm / min, stainless steel surface).

2. The wafer grinding tape as requested in item 1, wherein, The thickness of the pressure-sensitive adhesive layer 1 is 100~170μm.

3. The wafer grinding tape as requested in item 1, wherein, The hydroxyl-containing monomer of the pressure-sensitive adhesive layer 1 is hydroxyethyl acrylate (HEA).

4. The wafer grinding tape as requested in item 1, wherein, The pressure-sensitive adhesive layer 1 also includes 2-ethyl hexyl acrylate (EHA).

5. The wafer grinding tape as requested in item 1, wherein, The pressure-sensitive adhesive layer 1 also includes cyclic trimethylol-propane formal acrylate (CTFA).

6. The wafer grinding tape as requested in item 1, wherein, The pressure-sensitive adhesive layer 1 further includes ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate (TPO-L).

7. The wafer grinding tape as requested in item 1, wherein, The adhesion of the pressure-sensitive adhesive layer 1 is 600~1000gf / 25mm (180º, tensile speed 300mm / min, stainless steel surface).

8. The wafer grinding tape as requested in item 1, wherein, The thickness of the pressure-sensitive adhesive layer 2 is 15~50μm.

9. The wafer grinding tape as requested in item 1, wherein, The pressure-sensitive adhesive layer 2 is a radiation-induced tack-reducing pressure-sensitive adhesive.

10. The wafer grinding tape as requested in item 1, wherein, The adhesion of the pressure-sensitive adhesive layer 2 is 400~1000gf / 25mm (180º, tensile speed 300mm / min, stainless steel surface).