TW202305914A - Protection processing method for devices on wafer for preventing devices from being contaminated from the beginning of a back grinding process until the completion of dicing step - Google Patents

Abstract

The invention is provided to consistently and reliably prevent devices from being contaminated from the beginning of a back grinding process of a wafer on which components are formed until the completion of dicing step. A protective processing method according to the invention includes: (1) forming devices on the surface of a wafer; (2) applying a coating agent to form a coating film; (3) attaching a BG tape for back grinding on the coating film; (4) fixing the surface side of the BG tape and grinding the back side to thin the wafer; (5) fixing the back surface of the wafer to the dicing tape attached on a wafer frame; (6) peeling off the BG tape; (7) performing a dicing process to separate each device until the step is completed; and (8) cleaning and washing away the coating film that consistently covers the surface of each device.

Description

Protection processing method for components on wafer

The present invention relates to an improved method for processing a wafer with several components formed on its surface.

Patterned wafers of large-scale integrated circuits (LSI), complementary metal-oxide semiconductors (CMOS), power devices, etc., which use compounds such as silicon or sapphire as substrates, are divided by vertical and horizontal dicing lines to form several Component (device, component wafer).

In order to make the wafer as thin as possible on a wafer with several devices formed on its surface, it is necessary to make the thickness of the state where the devices are stored thinner. Therefore, the surface of the protective device side is covered with an adhesive protective tape (back grinding (BG) tape), and the thickness of the wafer is adjusted by grinding the back side of the wafer after fixing the BG tape side. Thinning (back grinding) treatment for thinning.

The thinned wafer is adhered to the dicing tape attached to the wafer frame on the back side. After peeling off the BG tape on the surface, the high-speed rotating blade is used to cut along the dicing line to separate components. In addition, the dicing tape is irradiated with ultraviolet light (UV) to weaken its adhesive effect, and then the divided components are transferred to the sheet for shipment, washed with pure water, and the components are inspected before being transported to the next step. step.

In this conventional process, in the grinding (back grinding) process and the dividing (dicing) process of the back of the wafer, on the components formed on the surface of the wafer, fine particles such as abrasive sheets are often seen attached, making it polluted.

That is, in the grinding step of the backside of the wafer, due to the height difference between the surface of the wafer and the components formed on the surface, it is difficult for the BG tape to fully cover the surface of the components. In this way, grinding chips and the like are mixed between the wafer surface and the device to contaminate the device. Even, the adhesive of the BG tape can become a cause of contamination.

Furthermore, in the dividing step of the components, it is necessary to flow the processing liquid between the wafer and the rotating dicing blade, while cooling the cutting part, and reducing the frictional resistance during cutting, so as to cut smoothly. And, the chips generated by cutting are removed by washing with water (pure water). However, it is difficult to sufficiently remove the swarf, which may contaminate components.

When dicing the wafer, the back side of the wafer is attached to an adhesive dicing tape, and the dicing tape is fixed on the wafer frame for dicing. During the dicing process, the dicing knife cuts each element along the dicing lane of the wafer. At this time, the edge of the dicing knife enters the adhesive layer of the dicing tape attached to the wafer to cut.

At this time, the dicing knife will produce dicing chips of the wafer, and the blade of the dicing knife will bring up the adhesive of the adhesive layer of the dicing tape to form fine fragments and scatter. Since the fine fragments of such an adhesive are sticky, they will adhere to the surface of the component and cause contamination because they cannot be washed off.

Furthermore, the surface of the components formed on the wafer is covered by an oxide film. When each element is cut with the dicing blade, the oxide film is partially cracked and peeled off by the blade. It was observed that the peeled oxide film was scattered and damaged the surface of the device.

In particular, in the image sensing unit (image sensor) used in a camera, the lens (sensing pixel portion) on the surface of the element (chip) only needs to adhere to the above-mentioned chips or fine fragments of the adhesive, or damage the The pixel part, that is, lowers the performance of the element, and becomes an important cause of an increase in the defective rate. Therefore, in order to avoid such a phenomenon, further improvement is required.

Furthermore, the dicing process is completed and the divided components are transferred to the shipping sheet by the dicing tape, washed with pure water, and then inspected for shipping in the next step. Moreover, in such a process, due to the manufacturing environment and the presence of workers, dust that is difficult to remove adheres to the surface of components such as image sensing units, resulting in performance degradation.

Patent Document 1 is Japanese Unexamined Patent Application Publication No. 2003-94295.

As described above, the present invention consistently and reliably protects the components from the process of thinning (back grinding) of the back grinding of the wafer on which the components have been formed, to the completion of the division (cutting) of the components. Pollution caused by grinding dust or chips generated. In addition, the fine fragments of the adhesive produced by the adhesive layer of the dicing tape, which may have more adverse effects than the grinding dust or chips, can effectively prevent contamination of components. Furthermore, it is also possible to reliably prevent damage to elements caused by scattering of the oxide film.

The protection processing method of the components on the wafer according to the present invention starts from the back grinding step (back grinding) of the wafer on which the components have been formed on the surface before entering the thinning step (back grinding), goes through the back grinding step and completes the division step of the components. , consistently protect the components on the surface of the wafer with a coating film, and process while protecting the components on the wafer.

Furthermore, on the surface of the wafer on which the device has been formed, a coating film is formed with a coating agent, and a surface protection tape (BG tape) for back grinding is pasted on the coating film, and the surface side of the BG tape is fixed and ground ( backside grinding) back side to thin the wafer. Next, after fixing the back of the wafer to the dicing tape pasted on the wafer frame, the BG tape is peeled off, and the components are diced and separated. Until the dividing step is completed, the coating film covers the surface of each element consistently. The covering film after the separation step is washed and removed.

According to the present invention, before entering the thinning step of the backside of the wafer on which devices are formed on the surface, the device division step is completed, and the surface of the device is consistently covered with a coating film until it is transported to the next step. In this way, the components on the surface of the wafer will not be polluted during the various processing steps, and the functions as components can be reliably maintained.

Furthermore, the coating can prevent chips generated by dicing knives, or fine fragments of adhesives generated by dicing tape from adhering to the surface of the device, and can prevent partial peeling of the oxide film from scattering. The damage of the components can also prevent the adhesion of dust. Furthermore, the coating can be cleanly removed by washing after the consistent processing step, so that a divided component with a clean surface free from contamination can be obtained.

The step of forming devices on the surface of the wafer (1) is to grind the back of the wafer to thin the wafer. Such thinning of the wafer can reduce the thickness of the part where the device is mounted by reducing the thickness of the device as a whole. Furthermore, by reducing the volume occupied by the device, it is possible to form a bulky mount.

On the surface of the wafer, since several elements are formed through the vertical and horizontal dicing lines, the surface (2) of the wafer is covered with a coating agent before entering the thinning step on the back of the wafer.

Examples of substrates for such coating agents include rosins, wood rosins, rosin esters, hydrogenated rosins, hydrogenated rosin esters, polymerized rosins, polymerized rosin esters, maleate-modified rosins, and rosin-modified phenolic resins. kind. Furthermore, there are acrylic resins such as copolymers of (meth)acrylic acid and other copolymerizable monomolecules, polyacrylic acid, polymethacrylic acid, and polyacrylamide. Further, epoxy resins such as phenol novolac epoxy resin and cresol novolac epoxy resin are mentioned; others include terpene resin, phenol resin, polyester resin, polypropylene glycol and the like.

The base material of the coating agent is preferably used. Rosins, terpene resins, acrylic resins, epoxy resins, phenolic resins, polyester resins, polypropylene glycol, etc. are also mixed appropriately in order to meet the needs. The number average molecular weight of the acrylic resin is 1,000-100,000, preferably about 6,000-35,000.

As the substrate of the coating agent, as will be described later, a resin that can be removed by an alkaline cleaning solution such as an alkaline aqueous solution is particularly effective. As such, the resin includes, for example, rosin, alkali-soluble acrylic resin, epoxy resin, etc., or a mixture thereof.

The substrate of the coating agent can be added with polysaccharides, fatty acids, fatty acid esters and surfactants. These can be used individually or in combination appropriately. Such additives can improve the coating film forming property and cleaning removability of the coating agent.

Examples of such additional components include cellulose, starch, glycogen, and the like as polysaccharides. Examples of fatty acids include caproic acid, caprylic acid, palmitic acid, stearic acid, lauric acid and the like. Examples of fatty acid esters include methyl caproate, ethyl caproate, methyl caprylate, ethyl caproate, and the like. Surfactants include anionic, cationic, nonionic, and amphoteric surfactants.

The glass transition point (Tg) of the coating agent is not particularly limited, but it is preferably about 50-80°C. The coating agent, additives, etc. are appropriately prepared with an organic solvent, dissolved and dispersed uniformly by a known method, and usually can be used as a solution of about 10 to 40% by mass. Examples of such an organic solvent include alcohols, ethers, esters, ketones, aromatics, etc., which are dispersed in a uniform state as a whole. These can be used individually or in mixture of 2 or more types.

The coating agent is applied to the surface of the wafer on which the device has been formed by means of dipping, roll coating, spin coating, spraying, etc. (2). It is preferably applied by spin coating, and dried at about 80°C to 150°C to form a uniform coating film on the wafer surface. The film thickness of the coating film is about 1.50-7.50 μm, preferably about 2.00-4.50 μm.

The hardness of the coating film formed as above is not too hard, but is preferably about B to 2H of pencil hardness. On the surface of the wafer coated with such a coating agent, a BG tape (3) used in the conventional thinning (back grinding) step is further pasted, and the BG tape is formed on the entire surface of the plastic sheet. There is an adhesive layer.

Then, fix the BG tape side covering the surface of the wafer, and grind (back grind) the back side of the wafer (4) to make the thickness of the wafer thinner. At this time, even if the abrasive sheet of the wafer enters through the gap between the BG tape and the surface of the wafer, since the components formed on the surface of the wafer are covered by the coating film, the components will not be polluted. After completing the thinning process, stick its back on the cutting tape and fix it (5), and install it on the cutting frame.

Next, the BG tape ( 6 ) is peeled off, and the thinned wafer covered with the coating film is transported to the next dividing step (dicing) ( 7 ). In the dividing step, for the fixed wafer, the components are divided by a cutting knife rotating at high speed along the dicing lines that separate the components formed on the surface of the wafer and run vertically and horizontally.

The cutting system supplies cutting water while the cutting knife moves along the cutting path, and the blade cuts each element. At this time, chips will be generated from the wafer due to cutting by the blade. Furthermore, at the same time, the front end of the blade will even cut into the adhesive layer of the dicing tape and the dicing tape substrate below it during cutting, making these become thin pieces and being taken up.

Such shavings or flaky adhesives are removed by cutting water, but they cannot be removed sufficiently and there will be residues. Although the shavings of the wafer are relatively easy to remove, the flakes generated by the adhesive layer still have adhesiveness, so they tend to adhere to the surface of the wafer. However, since the components on the surface side of the wafer as described above are covered by the coating film, the components can be protected from contamination.

Furthermore, the oxide film formed on the surface of the element is also covered by the coating film, so it can also effectively prevent the oxide film from being partially peeled off by the dicing knife (delamination, delamination) and the peeled oxide film pieces are scattered. to the surface of the component and cause damage.

After the cutting is completed, the coating agent (8) covering each element is washed and removed. As a cleaning agent for removing the coating film of the coating agent, cleaning using an alkaline cleaning solution such as an alkaline aqueous solution is particularly effective as described above. As such a cleaning agent, there is an alkaline aqueous solution composed of alkaline agents such as caustic soda, caustic potash, and ammonia. Furthermore, organic bases such as alkanolamines, pentanols, and water-soluble amines; water-soluble solutions of inorganic alkali salts such as silicates and carbonates, and the like can be used.

In this way, after removing the coating film that consistently covers the surface of the device, ultraviolet light (UV) (9) is irradiated to the adhesive layer of the dicing tape to weaken the adhesiveness of the adhesive layer. The divided components carried on the adhesive layer of the dicing tape having weakened adhesiveness are aligned and transferred onto a transfer sheet (10) to be transferred to the next step for transfer.

After being transferred to the sheet for conveyance, it is thoroughly washed with pure water (11) to obtain a dirt-free and clean element. After the components cleaned in this way pass the inspection step (12), those meeting the specifications can be sent to the next step. The above-mentioned removal of the covering film may vary depending on the case, and the divided elements may be transferred to a sheet for transportation, and even after that, they may be sufficiently washed with pure water.

<Example> In order to prepare Examples and Comparative Examples, the coating agents described below were prepared. Test piece 1: The resin solid content is 35% of acrylic resin with a molecular weight of 10,000 or more, 25% of an acrylic resin with a molecular weight of less than 10,000, 32% of abietyl alcohol, and 8% of a plasticizer. A coating agent with a number average molecular weight of 6,000 .

Test piece 2: Resin solid content is 47% of acrylic resin with a molecular weight of 10,000 or more, 33% of an acrylic resin with a molecular weight of less than 10,000, 10% of abietyl alcohol, and 10% of a plasticizer. A coating agent with a number average molecular weight of 8,000 . Test piece 3: Coating agent with a number average molecular weight of 20,000 with a resin solid content of 89% of acrylic resin with a molecular weight of 10,000 or more, 11% of acrylic resin with a molecular weight of less than 10,000, 0% of abietol, and 0% of a plasticizer .

Test piece 4: Resin solid content is 74% of acrylic resin with a molecular weight of 10,000 or more, 9% of acrylic resin with a molecular weight of less than 10,000, 9% of abietyl alcohol, and 8% of a plasticizer. A coating agent with a number average molecular weight of 25,000 . Test piece 5: Resin solid content is 89% acrylic resin with a molecular weight of 10,000 or more, 11% acrylic resin with a molecular weight of less than 10,000, a coating agent with a number average molecular weight of 35,000 with 0% abietol and 0% plasticizer .

Examples 1-9 were produced using the said test piece. (Example 1) Prepare a coating agent that adds twice the amount (capacity) of solvent alcohol to test piece 1, and form the surface of an 8-inch wafer with a CMOS image sensor as an element on a silicon substrate. Coating was performed by spin coating to form a coating film with a film thickness of 4.08 μm.

(Examples 2-9) Using the test pieces 2 to 5 shown in Table 1, coating films having the film thicknesses shown in Table 1 were formed according to Example 1.

(comparative example 1) In Comparative Example 1, a coating agent was not used, and a coating film was not formed, and the others were the same as in Example 1.

(test) In Examples 1 to 9 and Comparative Example 1, the following tests were carried out in order to observe the performance when the coating film was formed from the coating agent.

(Test of Delamination Occurrence Ratio) Form the coating film, perform the above-mentioned series of wafer thinning and dicing treatments, and then use the cleaning agent to remove the coating film, and observe the state of peeling (delamination) on the oxide film on the surface of the device with the appearance inspection device . The delamination state of Comparative Example 1 in which no coating film was formed was taken as 100%, and the state of the examples was expressed as a numerical value (%) in the same manner.

(evaluation criteria) It shows that the smaller the value (%), the less the rate of delamination. (test results) The results of the test are shown in Table 1. In addition, in Table 1, the glass transition point (Tg) (degreeC) of the test pieces 1-5 of a coating agent, and the pencil hardness of the formed coating film are also described.

(discuss) In Examples 1 to 9, the occurrence rate of delamination of the oxide film on the surface of the element is 44 to 96%, which is less than 100% in Comparative Example 1, and it can be seen that the formation of the coating film due to the coating agent is The protection system of the components can work effectively.

Form 1 coating agent Number average molecular weight Tg film thickness pencil hardness Delamination rate Example 1 Test piece 1 6000 65 4.08 B 86 Example 2 Test piece 2 8000 76 2.06 HB 96 Example 3 Test piece 2 8000 76 3.01 HB 65 Example 4 Test piece 2 8000 76 3.93 HB 54 Example 5 Test piece 2 8000 76 7.00 HB 55 Example 6 Test piece 3 20000 54 3.18 2H 70 Example 7 Test piece 3 20000 54 3.98 2H 61 Example 8 Test piece 4 25000 53 4.04 h 44 Example 9 Test piece 5 35000 68 4.11 2H 58 Comparative example 1 none - - - 100

1: Wafer with components formed 2: Coating coating agent 3: Paste BG tape 4: Back grinding 5: Fixed on cutting tape 6: Peel off the BG tape 7: cutting 8: Remove the coating agent 9: UV irradiation 10: Transfer to the sheet for conveying 11: Wash with pure water 12: check

[Fig. 1] An explanatory diagram illustrating the outline of an embodiment of the protective treatment method of the present invention.

1: Wafer with components formed

2: Coating coating agent

3: Paste BG tape

4: Back grinding

5: Fixed on cutting tape

6: Peel off the BG tape

7: cutting

8: Remove the coating agent

9: UV irradiation

10: Transfer to the sheet for conveying

11: Wash with pure water

12: check

Claims (7)

A method for protecting and treating components on a wafer, which consists of going through the step of back grinding (back grinding) before entering the thinning step (back grinding) of the wafer on which the components have been formed on the surface, and until the step of dividing the components is completed. First, protect the components on the wafer surface with a coating film. A method for protecting and treating components on a wafer. On the surface of a wafer where components have been formed, a coating film is formed by a coating agent, and a surface protection tape (BG tape) for back grinding is pasted on the coating film. Fix the surface side of the BG tape and grind (back grind) the back side to make the wafer thinner, fix the back side of the wafer to the dicing tape attached to the wafer frame, peel off the BG tape, and complete the dicing and separation of each component The coating film covers the surface of the element consistently until processing (cutting), and the coating film is washed and removed. As in claim 1 or 2, the component protection treatment method, the coating agent is an acrylic resin-based surface coating agent. According to the device protection treatment method of claim 3, the number average molecular weight of the acrylic resin of the coating agent is 1,000-100,000, and the film thickness of the coating agent is 1.50-7.50 μm. According to the protection treatment method for components in claim 4, the film thickness of the coating agent is 2.00-4.50 μm. According to the protection treatment method of the device in claim 3, the pencil hardness of the coating film formed on the device by the coating agent is in the range of B to 2H. According to the protection treatment method of the device according to claim 4 or 5, the pencil hardness of the coating film formed on the device by the coating agent is B-2H.

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