JP2010239025A - Processing method of semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide, in a process of making a semiconductor wafer ultra-thin and also separating to individual chips, a processing method of the semiconductor wafer which does not cause contamination by infiltrating grinding water by surely protecting the surface of the wafer and easily peels off a sheet after the grinding process. <P>SOLUTION: The processing method of the semiconductor wafer includes a step of pasting a surface protecting sheet 20 on a circuit surface 10S and forming half-cut grooves 10K by performing half-cut dicing of the wafer 10 from the surface protecting sheet 20 side, a step of pasting a grinding sheet 30 over the surface protecting sheet 20 and grinding the rear surface of the wafer 10, a step of hardening the surface protecting sheet 20 by irradiating ultraviolet ray from the sheet side after dividing the wafer 10 into individual chips 18 by this grinding, and further a step of peeling off the surface protecting sheet 20 after reducing the contact area to the individualized chip 18 by heat-shrinking. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for processing a semiconductor wafer, and more particularly to a method for processing a wafer to be extremely thinned.

  As information terminal devices are rapidly becoming smaller and more multifunctional, semiconductor devices mounted on them are required to be thinner and higher in density. In particular, in a memory chip, a silicon wafer is processed as thin as possible to increase the capacity by multilayering. Corresponding to the trend of such semiconductor devices, in the semiconductor processing process, the ultra-thin processing of the wafer is important, and various ultra-thin processing methods have been devised.

  As one of ultra-thin processing methods, a prior dicing process (DBG process, for example, Patent Document 1) is considered promising. In the DBG process, half-cut dicing is performed from the circuit surface side of the wafer prior to back surface grinding, and then the wafer is chipped simultaneously with grinding. In this DBG process for ultra-thin processing, it is generally necessary to deliberately reduce the peeling force of the surface protection sheet that protects the surface of the wafer, that is, the force necessary for peeling. This is to prevent the wafer from being damaged when the surface protection sheet is peeled off. In particular, since the wafer (chip) having a thickness of about 100 μm or less is very brittle, the surface protection sheet having a low peeling force. Is required.

  On the other hand, since the surface protection sheet is for protecting the circuit surface of the wafer from grinding water or the like used when grinding the back surface of the wafer, it is also required to be sufficiently adhered to the wafer during back surface grinding. As described above, in order to satisfy the contradictory performance requirements for the surface protection sheet, the energy ray curable surface protection sheet is widely used. This is because it has a sufficient adhesive force before irradiation with energy rays and can be easily peeled off by irradiation with energy rays.

JP 2001-127029 A

  With the recent increase in capacity of memory chips, the miniaturization and high density of the circuit surface of the wafer are progressing, so that the chips that are singulated often have many fine irregularities. Thus, since the actual surface area of the chip tends to be very large compared to the apparent surface area, even if the energy ray curable sheet is irradiated with energy rays, the peeling force may not be sufficiently reduced. . In this case, there may be a problem that the wafer (chip) is damaged when the surface protection sheet is peeled off. This problem is particularly remarkable in a thin wafer (chip).

  Therefore, when a surface protective sheet having a sufficiently low peel strength is used in advance, the surface protective sheet cannot have sufficient adhesiveness. As a result, the wafer is not sufficiently protected by the surface protection sheet. For example, when grinding the back surface of the wafer, there may be a problem that grinding water enters the circuit surface of the wafer and the circuit surface is contaminated.

  Therefore, the present invention provides a semiconductor wafer processing process that reliably protects the surface of the wafer and easily peels off the sheet after the grinding process even in the process of making the semiconductor wafer extremely thin and chip-divided. For the purpose.

  A method for processing a semiconductor wafer according to the present invention includes the following steps. That is, with the surface protection sheet attached to the circuit surface of the wafer, a dicing step of performing half-cut dicing of the wafer from the surface protection sheet side, an attaching step of attaching the grinding sheet to the surface protection sheet, and the wafer Grinding process for grinding the back surface of the wafer to divide the wafer into chips, a processing process for processing the surface protection sheet to reduce the contact area between the surface protection sheet and the circuit surface, and for the treated surface protection It is a peeling process which peels a sheet | seat and the sheet | seat for grinding. In the above grinding step, it is preferable to grind the wafer until the thickness becomes 50 μm or less.

  According to the present invention, even in the process of thinning a semiconductor wafer into chips, the surface of the wafer is reliably protected so that defects such as chipping and chip breakage do not occur, and the sheet is formed after the grinding process. It is possible to realize a processing process of a semiconductor wafer that easily peels off.

It is sectional drawing which shows the state by which the sheet | seat for surface protection was affixed on the wafer by which the chip | tip was bonded to the circuit surface. It is sectional drawing which shows the dicing process which performs the half cut dicing of a wafer. It is sectional drawing which shows the sticking process which piles up and sticks the sheet | seat for grinding on the sheet | seat for surface protection. It is sectional drawing which shows the state which stuck the transfer tape on the grinding surface of the chip | tip separated into pieces. It is sectional drawing which shows the process process which heats and shrinks the surface protection sheet.

  The semiconductor wafer processing method in this embodiment will be described below. This processing method is a DBG process utilizing a surface protecting sheet and a grinding sheet. FIG. 1 is a cross-sectional view showing a state where a surface protection sheet is attached to a wafer. FIG. 2 is a cross-sectional view showing a dicing process for performing half-cut dicing of the wafer.

  A surface protection sheet 20 is attached to the circuit surface 10 </ b> S of the wafer 10.

  Half-cut dicing of the wafer 10 is performed from the surface protection sheet 20 side with the surface protection sheet 20 still attached to the circuit surface 10S (see FIG. 2, dicing process). Half-cut dicing is a dicing method in which a wafer is cut so as not to be cut completely. A plurality of half-cut grooves 10K are formed by this dicing process. The half cut groove 10K has an appropriate cutting depth with respect to the wafer 10, and does not reach the back surface 10R of the wafer 10. In the dicing process, the surface protection sheet 20 is cut when the wafer 10 is half-cut, but the surface protection sheet 20 prevents cutting water or the like from entering the circuit surface 10S.

  Next to the dicing step, the grinding sheet 30 is pasted to the cut surface protecting sheet 20 (see FIG. 3, pasting step).

  Thus, the back surface 10R of the wafer 10 is ground using a grinder in a state where the grinding sheet 30 and the surface protection sheet 20 are laminated. At the time of this grinding, the circuit surface 10S is protected from the intrusion of grinding water through the half cut groove 10K by the grinding sheet 30 laminated on the surface protection sheet 20.

  The grinder grinds the wafer 10 beyond the bottom surface of the half-cut groove 10K to a predetermined chip thickness, so that the wafer 10 is divided into a large number of chips separated by the half-cut groove 10K and separated into pieces (grinding). Process). For example, the wafer 10 is ground so that the thickness is as extremely thin as 50 μm or less. The chips thus separated are fixed by the grinding sheet 30 laminated on the surface protection sheet 20, so that the chips are not dissipated, and damage due to contact between the chips is prevented. .

  FIG. 4 is a cross-sectional view showing a state in which the transfer tape 16 is attached to the ground surface of the separated chip. FIG. 5 is a cross-sectional view illustrating a processing step in which the surface protecting sheet 20 is processed and contracted.

  After the surface protection sheet 20 is cured, the transfer tape 16 is attached to the back surface (ground surface) 18R side of the singulated chip 18. The transfer tape 16 holds the singulated chips 18 with appropriate adhesiveness. In this state, the surface protection sheet 20 is processed. When the treatment is performed by heating, the heating may be performed by a heating furnace, a heat plate, or the like. When using a heat plate, it may be performed from the grinding sheet 30 side or from the transfer tape 16 side. By this treatment (treatment step), the shrinkable surface protection sheet 20 is shrunk, and as shown in FIG. 5, the contact area between the surface protection sheet 20 and the surface of the singulated chip 18 is reduced. Further, the contracted end portion of the surface protecting sheet 20 is lifted from the surface of the individualized chip 18, and a slight gap can be formed between the surface of the individualized chip 18.

  Thereafter, the surface protecting sheet 20 and the grinding sheet 30 are peeled off from the singulated chips 18 (peeling step). At this time, since the grinding sheet 30 is firmly bonded to the surface protection sheet 20, the cut surface protection sheet 20 can be peeled integrally with the grinding sheet 30. Further, the contact surface of the surface protection sheet 20 with the individualized chips 18 is reduced, and a slight gap is formed between the peripheral portion of the surface protective sheet 20 and the surface of the individualized chips 18. Therefore, even in an extremely thin chip having a thickness of 50 μm or less, in particular, a thickness of 25 μm or less, the surface protection sheet 20 is further easily peeled off.

Next, the surface protection sheet 20 used in this embodiment will be described.
The surface protecting sheet 20 in the present invention includes a base material 22 and an adhesive layer 24. The base material 22 is a film that shrinks when subjected to some treatment. As a process for shrinking the base material 22, a heat treatment is preferable.
Examples of the substrate 22 having such properties include polyolefins such as polyethylene, polypropylene, and polymethylpentene, polyethylene terephthalate, and polyvinyl chloride. In particular, a heat-shrinkable polyethylene film is preferable.
The shrinkage ratio R (%) of the base material 22 is calculated by the following equation (1). The shrinkage ratio R when the base material 22 is heated to 120 ° C. is preferably 10 to 90%, and more preferably 20 to 80%. When the shrinkage rate R of the base material 22 is low, it becomes difficult to peel off the surface protection sheet 20 from the singulated chips 18 (see FIGS. 4 and 5, etc.), and when the shrinkage rate R is high, the surface prior to the peeling step. This is because the protective sheet 20 can shrink unnecessarily.
R = (L ₁ −L ₂ ) / L ₁ × 100 (1)
(L ₁ (mm) is a dimension before contraction, L ₂ (mm) is a dimension after contraction by heating)
The thickness of the base material 22 is preferably 2 to 160 μm, more preferably 10 to 50 μm. This is because if the substrate 22 is too thin, the circuit surface 10S (see FIGS. 1 and 2) cannot be sufficiently protected, and if the thickness is too large, shrinkage due to heating may be insufficient.
Moreover, the base material 22 may be formed using the material which shrinks | contracts by irradiation of energy rays, such as an ultraviolet-ray and an electron beam, besides the type which heat-shrinks.
The pressure-sensitive adhesive layer 24 of the surface protecting sheet 20 includes, for example, an acrylic pressure-sensitive adhesive as a main component. Since the pressure-sensitive adhesive layer 24 is moderately soft, when it is affixed to the circuit surface 10S, it follows the minute irregularities on the surface of the chip 12. The pressure-sensitive adhesive layer 24 is preferably a layer made of an energy ray-curable pressure-sensitive adhesive that is cured by irradiation with energy rays such as ultraviolet rays and can be easily peeled off. The thickness of the pressure-sensitive adhesive layer 24 is preferably 2 to 200 μm, more preferably 5 to 60 μm.

Next, the grinding sheet 30 used in this embodiment will be described.
The grinding sheet 30 includes a base material 32 and an adhesive layer 34.
The substrate 32 is, for example, polyethylene, polypropylene, polybutene, polybutadiene, polymethylpentene, polyvinyl chloride, vinyl chloride copolymer, polyethylene terephthalate, polybutylene terephthalate, polyurethane, ethylene vinyl acetate copolymer, ionomer resin, ethylene It is formed of a film made of a (meth) acrylic acid copolymer, an ethylene / (meth) acrylic acid ester copolymer, polystyrene, polycarbonate, a fluororesin, and a water additive or a modified product thereof. These crosslinked films are also used. The above-mentioned substrate may be one kind alone, or may be a composite film in which two or more kinds are combined.
The Young's modulus of the substrate 32 is preferably in the range of 3.0 × 10 ^{7 to} 5.0 × 10 ⁹ Pa, and the product of the Young's modulus and the thickness of the substrate 32 is 1.0 × 10 ^3. It is preferable that it exists in the range of -1.0 * 10 < ⁷ > N / m. If the value of Young's modulus or the product of Young's modulus and thickness is less than the above range, the grinding sheet 30 becomes too soft, and the wafer may be cracked during grinding, or problems such as chipping may occur. In addition, the shape of the grinding sheet 30 is not maintained due to the thermal contraction of the surface protection sheet 20, which causes problems such as warping of the sheet. On the other hand, if the value of Young's modulus or the like exceeds the above range, the grinding sheet 30 that is too hard cannot follow the surface protection sheet 20 and may be peeled off from the surface protection sheet 20.
The thickness of the base material 32 becomes like this. Preferably it is 10-200 micrometers, More preferably, it is 50-150 micrometers.
The pressure-sensitive adhesive layer 34 includes, for example, an acrylic pressure-sensitive adhesive as a main component. As the pressure-sensitive adhesive layer 34, a strong pressure-sensitive adhesive that has strong adhesiveness that prevents the grinding sheet 30 from peeling off from the contracted surface protecting sheet 20 is selected. The thickness of the pressure-sensitive adhesive layer 34 is preferably 5 to 100 μm, more preferably 10 to 50 μm.

  Hereinafter, components and manufacturing methods of Examples of the surface protecting sheet 20 and the grinding sheet 30 in the present embodiment will be described.

  First, the formulation of the surface protecting sheet 20 in Example 1 will be described. Each compounding quantity shows the value of solid content conversion. A copolymer of 70 parts by weight of n-butyl acrylate, 10 parts by weight of methyl methacrylate and 20 parts by weight of 2-hydroxyethyl acrylate was prepared, and methacryloyloxyethyl isocyanate was 80% of the hydroxyl groups of 2-hydroxyethyl acrylate. Nart was added to make an acrylic adhesive. 0.185 parts by weight of an isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Co., Ltd., Coronate L) is added to 100 parts by weight of this acrylic pressure-sensitive adhesive, and the composition of the pressure-sensitive adhesive layer 24 in the surface protection sheet 20 of Example 1 is added. Manufactured.

  This pressure-sensitive adhesive layer composition was applied on a 38 μm-thick polyethylene terephthalate film that had been subjected to a release treatment so as to have a thickness of 20 μm, and heated at 100 ° C. for 1 minute. The pressure-sensitive adhesive layer 24 thus formed was bonded and transferred to a shrinkable polyethylene film for forming the base material 22 to obtain the surface protecting sheet 20 of Example 1.

  The shrinkable polyethylene film on which the substrate 22 was formed had a thickness of 35 μm, and the shrinkage rate when heated to 120 ° C. was 50%.

The shrinkage ratio R (%) was calculated by the following equation (1) from the dimension L ₁ (mm) before shrinkage in the polyethylene film and the dimension L ₂ (mm) after shrinkage due to heating.
R = (L ₁ −L ₂ ) / L ₁ × 100 (1)

  As the grinding sheet 30 of Example 1, an acrylic strong adhesive film having a pressure-sensitive adhesive layer 34 having a thickness of 40 μm was used. In this grinding sheet 30, the substrate 32 had a Young's modulus of 4600 MPa and a thickness of 100 μm, and the product of the Young's modulus and the thickness was 460,000 N / m.

  In Example 2, the base material 22 of the surface protecting sheet 20 was formed using shrinkable polyethylene having a shrinkage ratio of 70% when heated at 120 ° C., and the same surface protecting sheet 20 and grinding as in Example 1 were performed. The sheet 30 for use was used. In Example 3, the same surface protecting sheet 20 and grinding sheet 30 as in Examples 1 and 2 were used in addition to the use of shrinkable polyethylene having a shrinkage rate of 30% when heated at 120 ° C. as the base material 22. .

  Next, evaluation tests and results of the surface protecting sheet 20 and the grinding sheet 30 of Examples 1 to 3 will be described.

  First, the heat-shrinkable surface protective sheet 20 described above was attached to the circuit surface of a dummy wafer having a diameter of 8 inches and a thickness of 725 μm using a laminator (RAD-3510F / 12 manufactured by Lintec Corporation). Next, using a dicing apparatus (DFD 6361, manufactured by DISCO Corporation), half-cut dicing of the wafer was performed on the circuit surface together with the surface protection sheet 20 to form a lattice-like groove having a width of 35 μm and a depth of 50 μm. .

  Next, the grinding sheet 30 was pasted on the surface protection sheet 20 using a laminator (RAD-3510F / 12, manufactured by Lintec Corporation). Then, ultrathin grinding was performed until the thickness of the dummy wafer became 20 μm with a backside polishing apparatus (DGP 8760, manufactured by Disco Corporation), and at the same time, individualized chips 18 (12 mm × 12 mm) were separated.

  Thereafter, ultraviolet rays were irradiated from the sheet surface side using a tape mounter with an ultraviolet irradiation unit (RAD-2700F / 12, manufactured by Lintec Corporation), and the transfer tape 16 was attached to the grinding surface side of the singulated chips 18. Then, the surface protection sheet 20 was heated and shrunk by allowing to stand for 30 seconds so that the surface of the transfer tape 16 was in contact with an 80 ° C. hot plate. The surface protective sheet 20 and the grinding sheet 30 thus contracted were peeled off from the singulated chips 18 held by the transfer tape 16.

After the surface protecting sheet 20 and the grinding sheet 30 were peeled off, the penetration of grinding water into the surface of the singulated chip 18 and the presence or absence of contamination were observed and evaluated. Further, it was evaluated whether all the chips were transferred to the transfer sheet without damaging the chips.
Table 1 shows the results of the evaluation tests of the examples.

  As is clear from the results in Table 1, in the examples of the present invention, neither infiltration of grinding water nor surface contamination of the singulated chips 18 was observed. Further, all chips were transferred to the transfer sheet without being damaged, and no peeling failure occurred. As is apparent from the above, in the embodiment of the present invention, the surface protection sheet 20 reliably protects the wafer 10 in the dicing step, and the grinding water is prevented from entering the wafer surface. No. 30 reliably prevents the surface protection sheet 20 and the grinding sheet 30 from being peeled off from an extremely thin chip without any problem.

  As described above, according to the present embodiment, the surface of the wafer 10 is reliably protected even in the back surface grinding for making the wafer 10 extremely thin by the DBG process using the surface protecting sheet 20 and the grinding sheet 30 in combination. Thus, it is possible to prevent contamination due to the ingress of grinding water and to peel the sheet without damaging the chip.

  This is because the surface protection sheet 20 with sufficient adhesiveness is affixed to the wafer 10 and the circuit surface 10S is reliably protected by performing half-cut dicing together with the surface protection sheet 20 (see FIG. 2 and the like) This is because the back surface of the wafer is ground in a state where the grinding sheets 30 are stacked (see FIG. 4 and the like), so that the surface of the singulated chips can be protected by the grinding sheet 30. Further, the surface-protecting sheet 20 having such a high adhesion is heated and contracted after finishing the role of protecting the wafer 10 and the surface of the chip (see FIG. 5 and the like), so that peeling can be easily performed. This is because.

DESCRIPTION OF SYMBOLS 10 Wafer 10K Half cut groove 10R Back surface 10S Circuit surface 16 Transfer tape 18 Divided chip 20 Surface protection sheet 22 Base material 24 Adhesive layer 30 Grinding sheet 32 Base material 34 Adhesive layer

Claims (2)

A dicing step of performing half-cut dicing of the wafer from the surface protection sheet side with the surface protection sheet attached to the circuit surface of the wafer;
An attaching step of attaching a grinding sheet to the surface protecting sheet;
Grinding the back surface of the wafer to separate the wafer into chips;
A treatment step of treating the surface protection sheet to reduce a contact area between the surface protection sheet and the circuit surface;
A method for processing a semiconductor wafer, comprising: a peeling step of peeling the treated surface protecting sheet and the grinding sheet.   2. The semiconductor wafer processing method according to claim 1, wherein, in the grinding step, the wafer is ground until the thickness becomes 50 [mu] m or less.

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