JP7551787B2 - Wafer back grinding method and electronic device manufacturing method - Google Patents

Description

The present invention relates to a method for grinding the back surface of a wafer, among other methods for thinning a wafer having an uneven surface. More specifically, the present invention relates to a method for grinding the back surface of a wafer, which suppresses the effect of unevenness on the wafer surface by protecting the wafer surface with a protective layer and then flattening the surface of the protective layer that is not in contact with the wafer, and which improves handleability in a wide range of processing processes after the wafer is thinned.

In order to achieve high integration of semiconductor devices or to manufacture high-performance semiconductor devices, back grinding is widely used to grind wafers on which circuits have been formed to a uniform thickness and thinness. However, in the manufacturing process of electronic devices such as semiconductor devices, circuits and the like are formed on the surface of semiconductor wafers such as silicon or gallium arsenide in the so-called front-end process, or bump electrodes and the like can cause unevenness on the surface of the wafer. Among such electronic devices, power devices used in power converters such as inverters and converters in particular have unevenness on the surface of the wafer due to their characteristics, structure, and manufacturing process. If a protective layer such as a protective adhesive tape is created in the so-called back-end process and the back grinding is performed as is, the unevenness on the surface of the wafer is transferred to the back side of the wafer, and the unevenness is reflected in the finished thickness of the wafer, which affects the device characteristics, especially in power devices.

A method for grinding the backside of a wafer that suppresses the effects of unevenness on the surface of the wafer is known (Patent Document 1), in which the wafer is supported by adhesive tape, and then the base material of the tape is flattened by a surface planer to make the finished thickness of the backside of the wafer uniform. However, although this method can suppress variations in the finished thickness of the wafer, it has the problem of making the handling of the wafer, such as transportability, difficult after thinning.

On the other hand, a method for improving the handleability of thinned wafers is known in which a protective layer is used to temporarily fix the wafer and the supporting substrate to facilitate handling (Patent Document 2). However, with this method, there are cases where the unevenness of the wafer surface, which can cause unevenness in the application of the protective layer, etc., can result in insufficient suppression of variations in the finished thickness of the wafer.

JP 2009-43931 A JP 2004-64040 A

In view of the above technical background, the object of the present invention is to provide a method for grinding the backside of a wafer that can suppress the effects of unevenness on the surface of the wafer and improves the handleability of the wafer after thinning.

As a result of intensive research, the inventors have found that the above-mentioned problems can be solved by protecting the surface of the wafer with a protective layer prior to grinding the backside of the wafer, then flattening the surface of the protective layer that is not in contact with the wafer, and adhering the flattened surface of the protective layer that is not in contact with the wafer to a support via an adhesive layer, thereby completing the present invention.
That is, the present invention provides:
[1]
A method for grinding the backside of a wafer having an uneven surface, comprising the steps of:
A step (1) of forming a protective layer on the surface of the wafer;
A step (2) of flattening a surface of the protective layer not in contact with the wafer, and a step (3) of adhering the surface of the protective layer not in contact with the wafer to a support via an adhesive layer.
The present invention relates to a method for grinding the back surface of a wafer, comprising the steps of:

Hereinafter, [2] to [15] are each a preferred aspect or embodiment of the present invention.
[2]
The method for grinding the backside of a wafer according to [1], wherein the protective layer is a protective adhesive tape.
[3]
The method for grinding a wafer backside according to [2], wherein the base layer of the protective adhesive tape contains at least one resin selected from the group consisting of PET, PEN, PBT, LCP, PI, PA, PEEK, and PPS.
[4]
The method for grinding a backside of a wafer according to any one of [1] to [3], wherein the wafer having an uneven surface is a wafer having unevenness due to at least one of electrodes, circuit patterns, polyimide, defect marks, and bumps formed on the surface.
[5]
The method for grinding a backside of a wafer according to any one of [1] to [4], wherein the planarizing step is a step of planarizing by cutting, grinding, or polishing.
[6]
The method for grinding the back surface of a wafer according to [5], wherein the cutting is performed by a cutting tool.
[7]
The method for grinding a wafer backside according to any one of [1] to [6], wherein the adhesive layer is a liquid adhesive or an adhesive tape.
[8]
The method for grinding a backside of a wafer according to any one of [1] to [7], wherein the support is made of glass, silicon, ceramic, metal, resin, or a composite material thereof.
[9]
The method for grinding the backside of a wafer according to any one of [1] to [8], further comprising the step of forming the adhesive layer on a surface of the planarized protective layer not in contact with the wafer, on a surface of the support, or on both of the surface and the support, after the step (2) and before the step (3).
[10]
The method for grinding a wafer backside according to any one of [1] to [9], further comprising a backside treatment step of the wafer after grinding the backside of the wafer.
[11]
The method for grinding the back surface of a wafer according to [10], wherein the back surface treatment process of the wafer includes at least one of etching, electrode formation, ion implantation, and annealing.
[12]
The method for grinding the backside of a wafer according to any one of [1] to [11], wherein the thickness of the wafer after backside grinding is 200 μm or less.
[13]
A method for manufacturing an electronic device, comprising the method for grinding the backside of a wafer according to any one of [1] to [12] in a manufacturing process.
[14]
The method for producing an electronic device according to [13], wherein the electronic device is a device having an electrode also on the back surface side.
[15]
The method for producing an electronic device according to [14], wherein the electronic device is a power device.

According to the wafer back-grinding method of the present invention, it is possible to suppress the effects of unevenness on the wafer surface when grinding the wafer back, and the handleability of the wafer after thinning is improved, allowing the wafer to be stably processed in a wide range of processes after thinning. This prevents damage to circuits, etc. formed on the wafer, suppresses unintended effects on the characteristics of electronic devices such as semiconductor devices, and makes it possible to carry out multiple and/or wide-ranging processes on the wafer with high productivity and yield, greatly contributing to improving the productivity of electronic devices such as semiconductor devices.

Schematic diagrams for explaining steps in one embodiment of the present invention. (a) shows a wafer 1 whose back surface 12 is ground in the present invention. (b) shows a wafer 1 in which a protective adhesive tape 3 is attached to the front surface 11 of the wafer 1 by step (1) using a protective adhesive tape 3 as a protective layer. (c) shows a wafer 1 in which a base layer 31 of the protective adhesive tape 3 is flattened by step (2). (d) shows a wafer 1 in which a tacky adhesive layer 4 is formed on the flattened base layer 33 of the protective adhesive tape 3 obtained in step (2). (e) shows a wafer 1 in which a support 5 and the flattened base layer 33 of the protective adhesive tape 3 are bonded via a tacky adhesive layer 4 by step (3).

The present invention relates to
A method for grinding the backside of a wafer having an uneven surface, comprising the steps of:
A step (1) of forming a protective layer on the surface of the wafer;
A step (2) of flattening a surface of the protective layer not in contact with the wafer, and a step (3) of adhering the surface of the protective layer not in contact with the wafer to a support via an adhesive layer.
The method for grinding the back surface of a wafer is characterized by comprising the steps of:

Wafers having uneven surfaces Wafers that are back-ground by the method of the present invention have uneven surfaces. The unevenness on the surface of the wafer can be due to, for example, electrodes, circuit patterns, thick polyimide (5-20 μm) that is a protective film, defective marks (5-100 μm) for identifying defective chips, gold bumps (10-100 μm) and solder bumps (50-300 μm) for bump bonding instead of wire bonding, and the height of the unevenness can be 5-300 μm.

The wafer material is a material that is usually used in the manufacture of electronic devices, capable of forming electronic circuits, etc., and is expected to be thinned as a substrate to be ground. Examples include, but are not limited to, silicon wafers, compound semiconductor wafers such as SiC, AlSb, AlAs, AlN, AlP, BN, BP, BAs, GaSb, GaAs, GaN, GaP, InSb, InAs, InN, or InP, quartz wafers, sapphire, or glass. The silicon wafer or compound semiconductor wafer may be doped.

Examples of wafers with particularly uneven surfaces include power device wafers used in power converters such as inverters and converters in electronic devices.

Step (1)
Step (1) is a step of forming a protective layer on the surface of a wafer.

Protective layerThe protective layer is intended to prevent the electronic circuits, etc. on the front surface of the wafer from being damaged or contaminated by grinding debris, grinding water, etc., during grinding of the back surface of the wafer. In order to grind the back surface of the wafer, an in-feed grinding method is generally adopted in which the wafer is attracted to and held on a vacuum chuck table, and a grinding tool such as a grinding wheel is pressed against the back surface of the wafer while rotating the chuck table to rotate the wafer. When grinding the back surface of the wafer in this manner, the front surface of the wafer is covered with a protective layer to prevent the front surface of the wafer from coming into direct contact with the holding surface of the chuck table and damaging the electronic circuits, etc., on the front surface of the wafer.
In one embodiment, the protective layer may be, for example, a protective adhesive tape or a protective resin layer, and preferably, the protective layer is a protective adhesive tape.

The protective layer in the present invention has a thickness appropriate for protecting the surface of the wafer, and at the same time, is thick enough to withstand planarization in step (2) described below, i.e., has a thickness that is sufficient for the required cutting thickness.

It is preferable to use a protective adhesive tape as the protective layer. When the protective layer is a protective adhesive tape, step (1) is a step of applying the protective adhesive tape to the surface of the wafer. The application of the protective adhesive tape to the surface of the wafer may be performed by a conventional method known in the art, but is preferably performed using an automatic application device, and it is preferable to appropriately adjust the pressure, temperature, time, etc. depending on the material and type of the wafer and protective adhesive tape.

Protective Adhesive Tape The protective adhesive tape used as a preferred protective layer in the method of the present invention is not particularly limited as long as it has adhesion capable of withstanding planarization in step (2) described below, cutting processability, adhesion capable of withstanding back grinding described below, chemical resistance and heat resistance capable of withstanding the back treatment step described below, and finally, can be removed from the wafer with reduced contamination of the wafer surface. The protective adhesive tape may be preferably selected and used from those generally used as protective adhesive tapes for back grinding of semiconductor wafers.

Examples of materials for the base layer of the protective adhesive tape include high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), very low density polyethylene (VLDPE), linear low density polyethylene (L-LDPE), random copolymer polypropylene (random PP), block copolymer polypropylene (block PP), homopolypropylene (homo PP), polybutene (PB), polymethylpentene (PMP), ethylene-vinyl acetate copolymer (EVA), ethylene acrylic acid copolymer, ethylene methacrylic acid copolymer and their metal crosslinked bodies (ionomers), etc. Examples of the material include polyolefins, polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), and liquid crystal polymer (LCP), and further include polyurethane (PU), polycarbonate (PC), polyimide (PI), polyether ether ketone (PEEK), polyetherimide (PEI), polyamide (PA), wholly aromatic polyamide, polyphenyl sulfide (PPS), fluororesin, polyvinyl chloride, polyvinylidene chloride, and cellulose-based resin. The resin may be used alone as a single-layer substrate, or may be a blend of a plurality of the resins or a multi-layer structure of different resins. From the viewpoint of heat resistance, a substrate having a melting point or glass transition temperature of 100° C. or higher is preferred, and a substrate having a melting point or glass transition temperature of 150° C. or higher is particularly preferred.
In one embodiment, it is particularly preferable that the base layer of the protective adhesive tape contains PET, PEN, PBT, LCP, PI, PA, PEEK, or PPS, taking the following conditions into consideration.

Since the base layer of the protective adhesive tape must be able to withstand flattening, it is preferable that the thickness before flattening is 10 to 1000 μm, and particularly preferable that the thickness is 25 to 500 μm. If the thickness of the base layer of the protective adhesive tape is thin, the protective layer is thin and the amount that can be ground during flattening is limited, so the effect of flattening the protective layer tends to be small. Therefore, if the unevenness on the wafer surface is large, the wafer thickness accuracy after grinding may decrease due to this influence. On the other hand, if the protective layer before flattening is thick, the rigidity of the protective layer is high, the processability in the tape shape decreases, and the cutability when cutting the tape into the wafer shape tends to decrease. In addition, due to the rigidity, the protective adhesive tape is difficult to deform, so the peelability tends to decrease in the protective layer removal process after grinding the back surface of the wafer.

In addition, the base layer of the protective tape preferably has a tensile modulus of elasticity of 1×10 ⁷ Pa or more at 23° C. according to JIS K7113, and more preferably has a tensile modulus of elasticity of 5×10 ⁷ Pa or more. When the tensile modulus is low, the flattening of the base layer of the protective tape tends to be affected. Specifically, even after flattening, the wafer thickness accuracy after back grinding tends to decrease due to the influence of the unevenness of the wafer surface. On the other hand, the tensile modulus is preferably 1×10 ¹⁰ Pa or less, and more preferably 6×10 ⁹ Pa or less, from the viewpoints of the workability, cuttability, bendability, etc. of the base layer.

The adhesive layer of the protective adhesive tape can be a commonly used pressure-sensitive adhesive or a curing adhesive. In addition, the adhesive layer may generally be a single layer or multiple layers, and from the viewpoint of conforming to the unevenness of the wafer surface, it may be a multi-layer structure in which a flexible intermediate layer and a low-contamination adhesive layer are laminated.

Examples of the pressure-sensitive adhesive include acrylic adhesives, rubber adhesives, silicone adhesives, etc. Acrylic adhesives that use an acrylic polymer as the base polymer are preferred in terms of adhesion to the semiconductor wafer and base layer, and the ability to clean and wash the wafer with ultrapure water or organic solvents such as alcohol after the protective adhesive tape has been peeled off.

Examples of the curable adhesive include photocurable adhesives that crosslink and harden when irradiated with light, and thermosetting adhesives that crosslink and harden when heated. Examples of the photocurable adhesive include photocurable adhesives that contain a polymerizable polymer as the main component and a photopolymerization initiator. Examples of the thermocurable adhesive include thermocurable adhesives that contain a polymerizable polymer as the main component and a thermal polymerization initiator.

If the adhesive layer of the protective adhesive tape has a low peel adhesion, the adhesive strength to the wafer is insufficient against the shear force when flattening the base layer of the protective adhesive tape, and the protective adhesive tape peels off from the wafer. On the other hand, if the peel adhesion is high, it may be difficult to peel the protective adhesive tape from the wafer. Therefore, from the viewpoint of final peeling from the wafer, the thickness is preferably 5 to 500 μm, and more preferably 10 to 100 μm. Except for the case where the adherend is a silicon mirror wafer, the 180° peel adhesion (peel speed 300 mm/min) according to JIS Z0237 (2009) is preferably 0.3 to 10 N/25 mm, and more preferably 0.5 to 7 N/25 mm. Adjustments are made within this range as appropriate according to the process.

A protective resin layer can also be used as the protective layer. When the protective layer is a protective resin layer, the protective resin layer is formed by applying a raw resin dissolved in a solvent or the raw resin itself in liquid form (hereinafter referred to as a precursor resin liquid) by a known method such as spin coating, and then curing the applied layer by light irradiation, heating, drying, etc., to function as a solid protective layer. It may be formed in multiple layers.

The protective resin layer that can be used as the protective layer is not particularly limited as long as it has adhesiveness and cutting processability that can withstand planarization in the step (2) described later, adhesiveness that can withstand back grinding described later, chemical resistance and heat resistance that can withstand the back surface treatment step described later, and can finally be removed from the wafer with reduced contamination of the wafer surface, and can be preferably selected from known materials that temporarily fix the device wafer to the support and can be used. Examples of the precursor resin liquid include a rubber-based resin liquid in which rubber, elastomer, etc. are dissolved in a solvent, a one-liquid thermosetting resin liquid based on epoxy, urethane, etc., a two-liquid mixed reaction type resin liquid based on epoxy, urethane, acrylic, etc., a hot melt adhesive, an ultraviolet (UV) or electron beam curable resin liquid based on acrylic, epoxy, etc., and a water-dispersed resin liquid. A UV-curable resin liquid in which a photopolymerization initiator and, in some cases, an additive are added to an oligomer having a polymerizable vinyl group such as urethane acrylate, epoxy acrylate, or polyester acrylate, and/or an acrylic or methacrylic monomer is preferably used. The additives include a thickener, a plasticizer, a dispersant, a filler, a flame retardant, and a heat aging inhibitor, etc. The protective resin layer may be formed of a plurality of layers.

Step (2)
Step (2) is a step of planarizing the surface of the protective layer that is not in contact with the wafer.

For example, when the protective layer is a protective adhesive tape, this is a step of planarizing the base layer of the protective adhesive tape. In step (1), when the protective adhesive tape is attached to the surface of the wafer, the unevenness of the surface of the wafer is transferred to the base layer of the protective adhesive tape, and if the back grinding is performed as it is, the force of the back grinder is not uniformly applied, and the unevenness of the base layer of the protective adhesive tape is reflected, and the unevenness is also transferred to the back surface of the wafer. Even when the protective layer is formed from a protective resin layer, there are cases where the simple spin coating cannot achieve sufficient planarization, and unevenness is also generated on the surface of the protective layer, which may be transferred to the back surface of the wafer.
By flattening the base layer of the protective adhesive tape to which the irregularities have been transferred in this manner prior to backgrinding, the force of the back grinder can be applied evenly, preventing the irregularities from being transferred to the back surface of the wafer.

The planarization is not particularly limited as long as it can prevent the transfer of irregularities to the rear surface of the wafer. For example, it is preferable that the following conditions are satisfied.
The difference between the concave and convex portions of the surface of the protective layer not in contact with the wafer is preferably 5 μm or less, more preferably 3 μm or less, and particularly preferably 1 μm or less, over the entire cut surface.
In one embodiment, the planarization is performed by cutting, grinding, or polishing.

In one embodiment, the cutting is performed by cutting with a cutting tool. By cutting with a cutting tool, problems such as clogging of the grinding wheel during polishing can be eliminated and flattening can be easily performed, compared to flattening by polishing with a polishing machine. Cutting with a cutting tool may be performed by a surface planer.

Step (3)
Step (3) is a step of bonding the surface of the protective layer not in contact with the wafer to a support via an adhesive layer to form a laminate.

The adhesive layer is used to bond the surface of the protective layer that is not in contact with the wafer to the support. The adhesive layer may be a known temporary fixing material that can be used to temporarily fix the wafer to the support and easily separate the support after processing is completed, for example, by IR laser method, UV irradiation method, laser lift-off method, solvent peeling method, heat/UV foaming method, mechanical peeling method, etc., and may be a liquid adhesive (adhesive dissolved in a solvent, etc.) applied by spin coating or the like to form a viscous adhesive tape. The adhesive layer may be formed on the support, on the protective layer, or on both. The thickness variation of the adhesive layer is preferably 5 μm or less, more preferably 3 μm or less, and particularly preferably 1 μm or less.

The adhesive layer is at least one selected from acrylic, silicone, polyimide, and rubber. When the adhesive layer is an adhesive tape, the adhesive tape may be a single layer or a laminate of multiple layers, or may be a double-sided tape containing a base film in the layers.

The support preferably has sufficient strength and rigidity, and is excellent in heat resistance, chemical resistance, and thickness accuracy. By using such a support, even if the wafer is thinned after grinding, the wafer can be stably handled, and the wafer can be subjected to multiple and/or diverse processes without bending or the like.

Although known supports can be used as the support, preferred materials include silicon, sapphire, quartz, metals (e.g., aluminum, copper, steel, stainless steel), various glasses and ceramics, and resins (e.g., polyimide, polyamide, epoxy, phenol, polyphenylene ether, polyether ether ketone, polyetherimide, wholly aromatic polyamide, polyphenyl sulfide resin). The support may be made of a single material, but may also be made of multiple materials, and may contain other materials deposited on the substrate. For example, a silicon wafer may have a vapor deposition layer of silicon nitride or the like. Particularly preferably, the support is made of glass, silicon, ceramic, metal, resin, or a composite material thereof.

In one embodiment, the adhesive layer may be formed on the base layer of the protective adhesive tape flattened in step (2), or on the surface of the support, or on both sides. Methods for forming the adhesive layer include, but are not limited to, spin coating when the adhesive layer is a liquid adhesive (such as an adhesive dissolved in a solvent), or laminating tapes when the adhesive layer is a tape.

Backside Grinding Process The backside grinding process is typically a process of grinding and polishing the wafer, but is not limited thereto and may also include singulation and the like.
When grinding or polishing a wafer having electrodes formed on its front surface, the surface on which the electrodes are not formed (back surface) is ground or polished. The thickness of the wafer after grinding or polishing the back surface varies depending on the electronic device in which the semiconductor device is used, but is preferably set to 200 μm or less, more preferably 50 μm or less. This allows the semiconductor device to be thinned, and the electronic device using the semiconductor device to be miniaturized.

When grinding or polishing the wafer, in step (3), the wafer is laminated with a rigid support via the adhesive layer to form a laminate with high thickness accuracy, which allows the wafer to be ground, etc. with better processing accuracy. After grinding, etc., the wafer can be subjected to the back surface processing step described below or easily separated from the support and adhesive layer without damaging the wafer.

In one embodiment, the method for grinding the backside of a wafer of the present invention may further include at least one of a wafer backside processing step, a support removal step, an adhesive layer removal step, or a protective adhesive tape removal step after grinding the backside of the wafer.

Backside Treatment Step The method for grinding the backside of a wafer of the present invention may further include a backside treatment step of subjecting the wafer to processing and/or chemical treatment after grinding the backside of the wafer.

Examples of the above processing include, but are not limited to, annealing, back electrode formation (sputtering), deposition, etching, chemical vapor deposition (CVD), physical vapor deposition (PVD), resist coating/patterning, reflow, and dopant ion implantation.

The above-mentioned chemical treatments are typically treatments using acids, alkalis or organic solvents, and examples thereof include plating processes such as electrolytic plating and electroless plating, wet etching processes using hydrofluoric acid, tetramethylammonium hydroxide aqueous solution (TMAH), etc., resist stripping processes using N-methyl-2-pyrrolidone, monoethanolamine, DMSO, etc., and cleaning processes using concentrated sulfuric acid, ammonia water, hydrogen peroxide water, etc., but are not limited to these.

In one embodiment, the back surface treatment includes at least one of etching, electrode formation, ion implantation, and annealing.

The support removing step is a step of removing the support from the laminate. Examples of the support removing method include, but are not limited to, an IR laser method, a UV irradiation method, a laser lift-off method, a solvent stripping method, a heat/UV foaming method, and a mechanical stripping method.

The protective layer and adhesive layer removing step is a step of removing the protective layer and the adhesive layer from the thinned wafer, and the protective layer and the adhesive layer may be removed simultaneously or sequentially. The removal method includes peeling, washing, etc.

In one aspect, a method for manufacturing an electronic device is provided that includes the wafer backgrinding method of the present invention in the manufacturing process. That is, a wafer ground by the wafer backgrinding method of the present invention can be subjected to further steps to manufacture a final product. When a circuit or the like is formed on the wafer, steps typically used in the manufacture of semiconductor devices or electronic devices, such as dicing, bonding, packaging, and sealing, can be carried out to manufacture a semiconductor device or electronic device as a product.

In one embodiment, the electronic device is a power device. As described above, power devices are used in power converters such as inverters and converters, and have unevenness on the surface of the wafer due to their characteristics, structure, manufacturing process, etc. The present invention makes it possible to suppress the influence of the unevenness on the device characteristics.
Furthermore, since the effect of unevenness can be suppressed and handling can be improved not only in grinding the back surface of a wafer but also in a wide range of processing processes, the present invention can also be applied to grinding electrodes (TSVs) that vertically penetrate a silicon substrate and bump wafers with large unevenness.

Below, the method for grinding the back surface of a wafer according to one embodiment of the present invention will be further described with reference to the drawings, but the present invention is not limited to these embodiments.

(Embodiment 1)
Reference numeral 1 in Fig. 1(a) denotes a semiconductor wafer (hereinafter referred to as wafer) to be thinned by back grinding. This wafer 1 is a silicon wafer or the like, and its thickness before processing is uniform, for example, 700 µm to 800 µm. A plurality of rectangular devices are partitioned on a surface 11 of the wafer 1 by grid-like division lines. Electrodes and the like are formed on the devices, which cause unevenness on the surface 11 of the wafer 1.

As shown in Figures 1(a) to 1(e), the method for grinding the backside of a wafer in this embodiment involves applying a protective adhesive tape 3 to the front side 11 of a wafer 1, then flattening the base layer 31 of the protective adhesive tape 3 by grinding with a tool, then bonding the flattened base layer 33 of the protective adhesive tape 3 to a support 5 via an adhesive layer 4, and then grinding the back side 12 of the wafer 1 to thin it to the desired thickness (e.g., 200 μm or less). The process is described in detail below.

As described above, in this embodiment, first, the protective adhesive tape 3 is applied to the surface 11 of the wafer 1. The application is performed using an automatic application device by reducing the pressure to 100 Pa or less and heating to 100° C. or less. As shown in FIG. 1(b), the unevenness on the surface 11 of the wafer 1 is transferred to the base layer 31 of the applied protective adhesive tape 3.

The wafer 1 with the protective adhesive tape 3 attached to its front surface 11 is then cut flat to have the base layer 31 of the protective adhesive tape 3 cut using a surface planer. With this surface planer, the back surface 12 of the wafer 1 is held by adsorption to the adsorption surface of a vacuum chuck table, and the base layer 31 of the protective adhesive tape 3 is cut flat by the bit of a rotating cutting tool of a cutting unit.

Next, a tacky adhesive layer 4 is formed on the flattened base layer 33 of the protective adhesive tape. To form this tacky adhesive layer 4, a spin coating method is preferably used in which the wafer 1 is placed and held on a rotating table so that the base layer 33 of the flattened protective adhesive tape is exposed and the center of the wafer 1 coincides with the rotation axis of the table, the table is rotated, liquid adhesive is dropped onto the center of the rotating wafer 1, and the tacky adhesive is spread over the entire surface of the base layer 33 of the flattened protective adhesive tape by centrifugal force to apply it. In this way, a tacky adhesive layer 4 is formed on the base layer 33 of the flattened protective adhesive tape as shown in FIG. 1(d).

Next, the support 5 is bonded to the adhesive layer 4 to obtain the laminate shown in Fig. 1 (e). The laminate thus obtained has no irregularities in the base layer 33 of the protective adhesive tape 3, so that the irregularities on the front surface 11 of the wafer 1 are not transferred when the back surface 12 of the wafer 1 is ground, and since the support 5 is retained, handling properties such as transportability are not lost in the subsequent processing process even if the wafer 1 is thinned by back surface grinding.

Next, the back surface 12 of the wafer 1 is ground to thin the wafer 1 to the desired thickness. A grinding device that performs in-feed grinding is preferably used to grind the back surface of the wafer 1. With this grinding device, the support 5 is adsorbed to the adsorption surface of a vacuum chuck table to hold the laminate, and rough grinding and finish grinding are sequentially performed on the back surface 12 of the wafer 1 by two grinding units (one for rough grinding and one for finish grinding).

In this case, to remove the thinned wafer 1, the support 5 is removed, and then the protective adhesive tape 3 is removed. The support 5 is removed by a mechanical peeling method in which a remover is inserted into the interface between the support 5 and the adhesive layer 4, and the support 5 is pulled up. The protective adhesive tape 3 is removed by peeling it off from the wafer 1. By using the protective adhesive tape 3, the wafer cleaning process after peeling is unnecessary or can be minimized, which provides excellent workability and makes it possible to reduce the manufacturing costs of semiconductor devices and electronic devices.

(Embodiment 2)
Instead of the protective adhesive tape 3 of the first embodiment, a protective resin layer can be used to protect the surface 11 of the wafer 1. In this case, the wafer 1 is placed and held on a rotating table so that the surface 11 of the wafer 1 is exposed and the center of the wafer 1 coincides with the rotation axis of the table, the table is rotated, and a precursor resin liquid is dropped onto the center of the rotating wafer 1, and the precursor resin liquid is spread over the entire surface of the surface 11 of the wafer 1 by centrifugal force to apply the precursor resin liquid. The coating film after spin coating is placed on a hot plate and dried, and the solvent in the film is completely removed to form a protective layer. The other steps are the same as those of the first embodiment.

In this case, instead of peeling off the protective adhesive tape 3 as in the first embodiment, the protective layer is removed by a cleaning process. In the cleaning process, the wafer 1 is fixed onto a rotating table with the protective layer facing up, the cleaning solvent is sprayed, the cleaning solvent is placed on the wafer and allowed to stand, the cleaning solvent is discarded, and new cleaning solvent is placed on the wafer in the same manner and allowed to stand. This procedure is repeated twice, and the wafer 1 is then rinsed by spraying isopropyl alcohol (IPA) on the wafer while rotating.

The wafer back grinding method of the present invention can suppress the effects of unevenness on the wafer surface and improve handleability in a wide range of processing processes after wafer thinning, making a significant contribution to improving the productivity of semiconductor devices, electronic devices, etc., and has high applicability in various industrial fields, including the semiconductor process industry, the electronic components industry, the electrical and electronics industry that uses electronic components, the transportation machinery industry, the information and communications industry, and the precision machinery industry.

REFERENCE SIGNS LIST 1 Semiconductor wafer 11 Surface of wafer 12 Back surface of wafer 3 Protective adhesive tape 31 Base layer of protective adhesive tape 32 Adhesive layer of protective adhesive tape 33 Flattened base layer of protective adhesive tape 4 Adhesive layer 5 Support

Claims (14)

A method for grinding the backside of a wafer having an uneven surface, comprising the steps of:
A step (1) of forming a protective layer on the surface of the wafer;
A step (2) of flattening a surface of the protective layer not in contact with the wafer, and a step (3) of adhering the surface of the protective layer not in contact with the wafer to a support via an adhesive layer.
A method for grinding the back surface of a wafer, comprising :
However, the protective layer is a protective adhesive tape . 2. The method for grinding a wafer backside according to claim 1 , wherein the base layer of the protective adhesive tape contains at least one resin selected from the group consisting of PET, PEN, PBT, LCP, PI, PA, PEEK, and PPS. 3. The method for grinding the back surface of a wafer according to claim 1, wherein the wafer having an uneven surface is a wafer having unevenness due to at least one of electrodes, circuit patterns, polyimide, defect marks, and bumps formed on the surface. 4. The method for grinding a back surface of a wafer according to claim 1 , wherein the planarizing step is a step of planarizing by cutting, grinding, or polishing. 5. The method for grinding the back surface of a wafer according to claim 4 , wherein the cutting is performed by a cutting tool. The method for grinding a wafer backside according to any one of claims 1 to 5 , wherein the adhesive layer is a liquid adhesive or an adhesive tape. 7. The method for grinding a wafer backside according to claim 1 , wherein the support is made of glass, silicon, ceramic, metal, resin or a composite material thereof. The method for grinding a wafer backside according to any one of claims 1 to 7, further comprising the step of forming the adhesive layer on a surface of the planarized protection layer not in contact with the wafer, on a surface of the support, or on both of the surfaces, after the step (2) and before the step (3) . The method for grinding the backside of a wafer according to any one of claims 1 to 8 , further comprising a backside treatment step for the wafer after grinding the backside of the wafer. 10. The method for grinding the back surface of a wafer according to claim 9 , wherein the back surface processing step of the wafer includes at least one of etching, electrode formation, ion implantation, and annealing. The method for grinding the backside of a wafer according to any one of claims 1 to 10 , wherein the thickness of the wafer after backside grinding is 200 µm or less. A method for manufacturing an electronic device, comprising the method for grinding the backside of a wafer according to any one of claims 1 to 11 in the manufacturing process. The method for producing an electronic device according to claim 12 , wherein the electronic device is a device having an electrode also on the back side. The method for producing an electronic device according to claim 13 , wherein the electronic device is a power device.

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