Protective sheet and method for processing wafers using the same

A protective sheet with a deformable liquid resin conforms to wafer irregularities, enabling efficient grinding and residue-free peeling, enhancing resource efficiency.

JP7886259B2Active Publication Date: 2026-07-07DISCO CORP
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Patent Information

Authority / Receiving Office
JP · JP
Patent Type
Patents
Current Assignee / Owner
DISCO CORP
Filing Date
2022-11-25
Publication Date
2026-07-07

AI Technical Summary

Technical Problem

Existing wafer grinding methods leave residual resin on the surface after processing, requiring additional peeling operations.

Method used

A protective sheet comprising a bag-shaped resin sheet filled with a liquid resin that conforms to wafer irregularities by heating and pressing, allowing easy peeling post-processing.

Benefits of technology

The protective sheet effectively flattens the wafer surface by conforming to irregularities and can be reliably peeled off without residue, facilitating reuse and reducing resource waste.

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Abstract

To provide a protective sheet and a wafer processing method using the same, which can make the surface of a wafer flat by following the irregularities of the surface of a wafer with good followability and can be reliably peeled off without remaining on the wafer after the wafer is processed.SOLUTION: A protective sheet 1, which protects the surface of a wafer W, which has an uneven surface, includes a bag-shaped resin sheet 2, and a liquid resin 3 filled inside the resin sheet 2. A processing method for the wafer W, which protects the surface of the wafer W with the protective sheet 1, includes a holding step of holding the back surface of the wafer W by a chuck table 10, and a fixing step of fixing the protective sheet 1 to the surface of the wafer W. The fixing step is performed by pressing the opposite side of one side of the resin sheet 2 to make the liquid resin 3 flow and make one side of the resin sheet 2 conform to the unevenness of the surface of the wafer W.SELECTED DRAWING: Figure 7
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Description

Technical Field

[0001] The present invention relates to a protective sheet for protecting the surface of a wafer having irregularities formed on its surface and a method for processing a wafer using the protective sheet.

Background Art

[0002] In recent years, as a technology for realizing miniaturization of semiconductor devices such as ICs and LSIs used in various electronic devices, a substrate mounting technology of a device has been put into practical use, in which a plurality of protruding electrodes called bumps are mounted on the surface of the device and these bumps are opposed to electrodes formed on a wiring substrate and the two are directly joined. Among wafers having bumps formed on their surfaces, some have large irregularities formed on their surfaces as a result of mounting bumps having a large thickness called high bumps.

[0003] By the way, as a grinding method for grinding the back surface of a wafer having large irregularities formed on its surface, the surface of the wafer is coated with an ultraviolet curable resin that is cured by irradiation with ultraviolet rays (UV) to make the surface a flat plane without irregularities, and the wafer is sucked and held on the holding surface of a chuck table with this surface facing down, and the back surface of the wafer is ground with a grinding wheel. This method has been proposed in Patent Document 1.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, according to the method proposed in Patent Document 1, when peeling the resin coating the surface of the wafer after grinding, a part of the resin remains on the wafer, and there is a problem that an operation of peeling off the remaining resin is required.

[0006] The present invention has been made in view of the above problems, and its object is to provide a protective sheet that can be fixed to a wafer so as to conform well to the irregularities on the wafer surface, making the wafer surface a flat plane, and that can be reliably peeled off without remaining on the wafer after processing, and a wafer processing method using the same. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides a protective sheet for protecting the surface of a wafer having irregularities formed on its surface, characterized by comprising a bag-shaped resin sheet and a liquid resin filled inside the resin sheet.

[0008] Furthermore, the present invention relates to a wafer processing method for protecting the surface of a wafer with the protective sheet, comprising a holding step of holding the back surface of the wafer with a chuck table, and a fixing step of fixing the protective sheet to the surface of the wafer, wherein the fixing step is characterized by pressing the opposite side of one side of the resin sheet to cause the liquid resin to flow and make one side of the resin sheet conform to the irregularities on the surface of the wafer. [Effects of the Invention]

[0009] According to the present invention, in the fixing step, the protective sheet is heated to turn the liquid resin into a liquid state (liquid phase), and the protective sheet is pressed onto the surface of the wafer. As a result, the flow of the liquid resin within the resin sheet causes the protective sheet to deform to conform to the irregularities on the wafer surface, and the protective sheet is pressed (thermally pressed) onto the wafer surface. After the protective sheet fixed to the wafer is cooled and solidified, a predetermined process such as grinding is performed on the wafer, and then the protective sheet is heated again. This softens the protective sheet, allowing the entire protective sheet to be easily and reliably peeled off the wafer. Therefore, the protective sheet can be fixed to conform well to the irregularities on the wafer surface, resulting in a flat wafer surface, and after processing such as grinding on the wafer is completed, the protective sheet can be reliably peeled off the wafer without leaving any residue. [Brief explanation of the drawing]

[0010] [Figure 1] This is a perspective view of the protective sheet and wafer according to the present invention. [Figure 2] This is a side cross-sectional view of the protective sheet according to the present invention. [Figure 3] This is an enlarged detail view of section A in Figure 2. [Figure 4] This is a flowchart showing the wafer processing method according to the present invention in step order. [Figure 5] This is a side view showing the holding step in the method of the present invention. [Figure 6] This is a fractured side view showing the pressing step in the method of the present invention. [Figure 7] This is a fractured side view showing the curing step in the method of the present invention. [Figure 8] This is a fractured side view showing the processing steps in the method of the present invention. [Figure 9] This is a fractured side view showing the softening step in the method of the present invention. [Figure 10] This is a fractured side view showing the peeling step in the method of the present invention. [Figure 11] It is a broken side view showing the state of the protective sheet after a series of steps of the method of the present invention.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

[0012] [Protective Sheet] First, the configuration of the protective sheet 1 according to the present invention will be described based on FIGS. 1 to 3.

[0013] As shown in FIG. 1, the protective sheet 1 according to the present invention protects the surface of a thin disk-shaped wafer W having a plurality of bumps (protrusion electrodes) B formed on its surface (the upper surface in FIG. 1). As shown in FIG. 2, it is configured by filling a liquid resin 3 that becomes liquid when heated to a temperature equal to or higher than the glass transition point or melting point into a circular planar bag-shaped resin sheet 2 having elastic deformable flexibility. And an adhesive layer 4 is formed on one surface (the lower surface in FIG. 2) of the resin sheet 2 as shown in FIG. 3.

[0014] In the present embodiment, as the liquid resin 3 filled inside the resin sheet 2, a thermoplastic resin that remains liquid when heated to a temperature equal to or higher than the glass transition point or melting point and becomes hard when cooled is used. Here, as the thermoplastic resin, polypropylene (PP), polyethylene (PE), acrylonitrile-butadiene-styrene (ABS), acrylic (PMMA), polyamide (PA), etc. are used.

[0015] By the way, the wafer W is composed of a single crystal silicon base material. As shown in FIG. 1, its surface (the upper surface in FIG. 1) is partitioned into a number of rectangular regions by a plurality of division planned lines L1, L2 that are orthogonal to each other and are called streets arranged in a grid pattern, and bumps (protrusion electrodes) B are mounted in each rectangular region.

[0016] [Method of Processing the Wafer] Next, a method for processing the wafer W using the protective sheet 1 configured as described above will be described based on FIGS. 4 to 11.

[0017] As shown in FIG. 4, the method for processing the wafer W according to the present invention is a method of grinding the back surface (the lower surface in FIG. 1) of the wafer W through the following steps in sequence: 1) holding step, 2) fixing step, 3) processing step, 4) softening step, and 5) peeling step. The fixing step in 2) includes a 2-1) pressing step and a 2-2) curing step. Hereinafter, each step will be described respectively.

[0018] 1) Holding step: As shown in FIG. 5, the holding step is a step of holding the wafer W having a plurality of bumps B mounted on its front surface (the upper surface in FIG. 5) with its back surface (the lower surface in FIG. 1) down on the holding surface (the upper surface) of the disk-shaped chuck table 10. Although not shown in FIG. 5, as shown in FIG. 8, the chuck table 10 has a porous member 11 made of porous ceramic or the like incorporated in the upper central portion thereof. By sucking the porous member 11 by a suction source (not shown) such as a vacuum pump, the wafer W is sucked and held on the holding surface of the chuck table 10.

[0019] 2) Fixing step: The fixing step is a step of fixing the protective sheet 1 to the front surface of the wafer W held on the holding surface of the chuck table 10 in the holding step. As described above, this includes the following 2-1) pressing step and 2-2) curing step.

[0020] 2-1) Pressing step: The pressing step involves heating the protective sheet 1 to a temperature above the glass transition point or melting point of the liquid resin 3 to make the liquid resin 3 liquid, and then pressing the protective sheet 1 onto the surface of the wafer W as shown in Figure 6. In this pressing step, the flow of the liquid resin 3 within the resin sheet 2 causes one side of the protective sheet 1 (the bottom side in Figure 6) to deform to conform to the irregularities caused by the multiple bumps B on the surface of the wafer W, and the protective sheet 1 is pressed (thermally pressed) onto the surface of the wafer W by the adhesive layer 4 (see Figure 3) formed on one side (the bottom side).

[0021] 2-2) Curing Step In the curing step, the protective sheet 1, which was pressed onto the surface of the wafer W in the pressing step, is cooled to a temperature below the glass transition point or melting point of the liquid resin 3. As a result, as shown in Figure 7, the liquid resin 3 filled within the resin sheet 2 of the protective sheet 1 hardens, and the entire protective sheet 1 solidifies, making the other surface (the top surface in Figure 7) a flat plane.

[0022] 3) Processing step: The processing step involves grinding the back surface of the wafer W. In this processing step, as shown in Figure 8, the wafer W is held by suction on the holding surface of the chuck table 10 with the protective sheet 1 facing downwards. That is, when the porous member 11 incorporated into the chuck table 10 is evacuated by a suction source (not shown), negative pressure is generated in the porous member 11, and the wafer W is held by suction on the holding surface (upper surface) of the chuck table 10 by this negative pressure. At this time, since the other surface of the protective sheet 1 (the lower surface in Figure 8) is a flat plane as described above, the wafer W is reliably held by suction on the holding surface of the chuck table 10 with the protective sheet 1 in close contact with the holding surface of the chuck table 10.

[0023] As described above, when the wafer W is held by suction on the holding surface of the chuck table 10 with the protective sheet 1 facing downwards, the chuck table 10 and the wafer W held thereon move horizontally by a horizontal movement mechanism (not shown), and the chuck table 10 and wafer W are positioned below the grinding wheel 21 of the grinding unit 20.

[0024] Here, the grinding wheel 21 is detachably mounted on a disc-shaped mount 24 attached to the lower end of a vertical spindle 22, and consists of a disc-shaped wheel base 25a and a plurality of grinding wheels 25b, which are processing tools attached in an annular shape to the lower surface of the wheel base 25a. The grinding wheels 25b are rectangular block-shaped processing tools for grinding the wafer W, and the horizontal positional relationship between the grinding wheels 26b and the lower surface (processing surface) of the grinding wheels 26b is adjusted so that it passes through the center of the wafer W.

[0025] In this processing step, with the chuck table 10 and the grinding wheel 25 both rotated at a predetermined speed in the direction of the arrow, the grinding wheel 25 is lowered by a grinding feed mechanism (not shown), and the grinding wheel 25b of the grinding wheel 25 approaches the wafer W which is held and rotated on the chuck table 10. When the grinding wheel 25b contacts the back surface (top surface in Figure 8) of the wafer W which rotates with the chuck table 10, grinding of the back surface (top surface) of the wafer W by the grinding wheel 25b begins, and grinding is carried out until the thickness of the wafer W reaches a predetermined finish thickness. During this wafer W grinding process, grinding water such as pure water is supplied to the contact area (processing area) between the grinding wheel 21b and the wafer W.

[0026] 4) Softening step: In the processing step described above, once the back surface of the wafer W is ground to a predetermined finish thickness, in the next softening step, as shown in Figure 9, the wafer W is held on the chuck table 10 with its back surface (ground surface) facing downwards, and the protective sheet 1 attached to the surface (top surface in Figure 9) of the wafer W is heated. As a result, the liquid resin 3 filled in the resin sheet 2 of the protective sheet 1 softens, and the protective sheet 1 becomes more elastically deformable.

[0027] 5) Peeling step: In the peeling step, the protective sheet 1, which has been softened in the softening step, is peeled off from the surface of the wafer W. As shown in Figure 10, the protective sheet 1, which is easily elastically deformed by softening, can be easily peeled off from the surface of the wafer W by pulling up one end in the direction of the arrow. In this case, since the protective sheet 1 is easily elastically deformed by softening, even if it is peeled off from the wafer W, no part of it remains on the wafer W, and the entire protective sheet 1 can be reliably and easily peeled off from the wafer W as is.

[0028] After the series of steps described above, the grinding process on the back surface of the wafer W is completed. After this grinding process is finished, the protective sheet 1 is restored to the state shown in Figure 2, as shown in Figure 11, in order to maintain the liquid resin 3 filled inside the resin sheet 2 in a liquid state. Therefore, the protective sheet 1 can be used continuously for grinding multiple wafers W. In other words, the protective sheet 1 can be reused and used many times, thus achieving resource conservation and cost reduction.

[0029] As described above, in this embodiment, in the pressing step of the fixing step, the protective sheet 1 is heated to a temperature above the glass transition point or melting point of the liquid resin 3 to make the liquid resin 3 liquid, and the protective sheet 1 is pressed onto the surface of the wafer W. As a result, the flow of the liquid resin 3 within the resin sheet 2 causes the protective sheet 1 to deform to conform to the unevenness caused by the multiple bumps B on the surface of the wafer W, and the protective sheet 1 is pressed (thermally pressed) onto the surface of the wafer W by the adhesive layer 4 (see Figure 3) formed on one side (bottom surface) of the protective sheet 1. Then, in the subsequent curing step, the protective sheet 1 pressed onto the surface of the wafer W is cooled to cure the liquid resin 3, so that the entire protective sheet 1 solidifies, and the solidified protective sheet 1 conforms well to the unevenness on the surface of the wafer W and is fixed to the wafer W.

[0030] Next, in the processing step, with the wafer W held on the chuck table 10 with the hardened protective sheet 1 facing downwards, the back surface of the wafer W (the side opposite to the side to which the protective sheet 1 is fixed) is ground. Then, in the following softening step, the protective sheet 1 is heated to soften it, and this softened protective sheet 1 is peeled off from the surface of the wafer W. As the protective sheet 1 is easily elastically deformed by softening, it can be easily peeled off from the surface of the wafer W. In this case, because the protective sheet 1 is easily elastically deformed by softening, even if it is peeled off from the wafer W, no part of it remains on the wafer W, and the entire protective sheet 1 can be reliably and easily peeled off from the wafer W as is.

[0031] Therefore, according to this embodiment, the protective sheet 1 can be fixed to the wafer W surface in a manner that conforms well to the irregularities, the wafer surface can be made flat by the protective sheet 1, and after processing the wafer W, the protective sheet 1 can be easily and reliably peeled off and removed without leaving any residue on the wafer W. Furthermore, the protective sheet 1 can be repeatedly used for grinding multiple wafers W, thereby enjoying resource conservation and economic benefits.

[0032] In the above embodiments, a thermoplastic resin was used as the liquid resin 3 filled into the resin sheet 2 of the protective sheet 1. However, as the liquid resin 3, thermosetting resins such as phenolic resin (PF) and epoxy resin (EP) that harden by heating, ultraviolet-curing resins that harden by ultraviolet (UV) irradiation, and magnetic resins that harden by magnetization can be used. However, if a thermoplastic resin that repeatedly liquefies and solidifies is used as the liquid resin 3, it can be used repeatedly.

[0033] Furthermore, while the above explanation used grinding of wafer W as an example of a processing method for wafer W, processing methods also include cutting and polishing of wafer W.

[0034] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the technical idea described in the claims, specification, and drawings. [Explanation of Symbols]

[0035] 1: Protective sheet, 2: Resin sheet, 3: Liquid resin, 4: Adhesive layer 10: Chuck table, 11: Porous material, 20: Cutting unit, 21: Grinding wheel, 21a: Wheel base, 21b: Grinding wheel, 22: Spindle, 23: Mount, B: Bump, L1, L2: Planned splitting lines, W: Wafer

Claims

1. A protective sheet for protecting the surface of a wafer having irregularities formed on its surface, A bag-shaped resin sheet, The liquid resin filled inside the resin sheet, A protective sheet characterized by having the following features.

2. The protective sheet according to claim 1, characterized in that the liquid resin is a thermoplastic resin or a thermosetting resin.

3. The protective sheet according to claim 1, characterized in that the liquid resin is an ultraviolet-curing resin.

4. The protective sheet according to claim 1, characterized in that the liquid resin is a magnetic resin.

5. The protective sheet according to claim 1, characterized in that an adhesive layer is formed on one surface of the resin sheet.

6. A wafer processing method comprising protecting the surface of a wafer with a protective sheet according to any one of claims 1 to 5, A holding step of holding the back side of the wafer with a chuck table, A fixing step of fixing a protective sheet to the surface of the wafer, Equipped with, The fixing step is characterized by pressing the opposite side of one side of the resin sheet to cause the liquid resin to flow, thereby making one side of the resin sheet conform to the irregularities on the surface of the wafer.

7. The wafer processing method according to claim 6, characterized in that the fixing step involves heating the resin sheet and fixing the protective sheet to the surface of the wafer by thermocompression bonding.

8. The wafer processing method according to claim 6, characterized in that the fixing step involves fixing the protective sheet to the wafer by an adhesive layer formed on one side of the resin sheet.

9. The fixing step is, A pressing step of pressing one side of the resin sheet, A curing step for curing the liquid resin, The wafer processing method according to claim 6, characterized by comprising the following:

10. After the fixing step, The wafer processing method according to claim 6, further comprising a processing step of processing the back surface of the wafer.

11. After the processing step, The wafer processing method according to claim 10, further comprising a softening step of softening the liquid resin.

12. After the processing step, or after the softening step, The wafer processing method according to claim 11, further comprising a peeling step of peeling the protective sheet from the wafer.