JP2011216584A - Method of manufacturing semiconductor device - Google Patents

Abstract

In the electroless plating process for forming an under bump metal, while maintaining the handleability of a thin wafer, the wafer is prevented from being damaged during plating and the plating is prevented from adhering to the non-plated surface of the wafer. .
SOLUTION: Back grinding process 1 on the back side of the wafer, and then, step 2 of laminating and sticking one or more adhesive films having a releasable type adhesive on the back side of the wafer, Conducting an electroless plating process 3 for forming an under bump metal (UBM) on the wafer surface, and then a process 4 for peeling the adhesive film on the wafer having the adhesive film attached to the back surface. A method for manufacturing a semiconductor device.
[Selection figure] None

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a thin semiconductor device.

  In recent years, with the full-scale introduction of SIP (System In Package), IC (Integrated Circuit) cards, RFID (Radio Frequency IDentification) tags, etc., especially for mobile products, semiconductor devices with a chip thickness of 100 μm or less are practically used as products. It has become. Along with such a demand for thinning the final product, the importance of a technique for processing a thin wafer used therefor is also increasing.

  In general, semiconductor devices are manufactured by a plating process for forming an under bump metal for an electrode on a wafer as a device substrate, a back grinding process for thinning the wafer, and stable dicing. First, dicing tape and ring frame are prepared, the wafer is mounted in the ring frame with dicing tape (frame mounting process), and the wafer stabilized with dicing tape and ring frame is divided into individual chips by dicing. And the like.

As a method for manufacturing such a semiconductor device, the following is known.
1. Manufacturing method 1
The conventional manufacturing method 1 performs each process mentioned above in order of the following (1)-(7).
(1) Plating process for forming under bump metal (UBM) on the wafer surface (2) Wafer surface protective film (BG tape) affixing process (3) Wafer back grinding process (thinness by grinding the backside of the wafer) Process)
(4) Frame mounting process (5) Wafer surface protective film peeling process (6) Dicing process (7) Chip separation process

2. Manufacturing method 2
The conventional manufacturing method 2 performs each process mentioned above in order of the following (1)-(7).
(1) Plating process for forming under bump metal (UBM) on the wafer surface (2) Half-cut dicing process (3) Wafer surface protective film (BG tape) attaching process (4) Wafer back grinding process (5) Frame mounting process (6) Wafer surface protective film peeling process (7) Chip separation process

3. Manufacturing method 3
The conventional manufacturing method 3 performs each process mentioned above in order of the following (1)-(7).
(1) Half-cut dicing process (2) Plating process for forming under bump metal (UBM) on the wafer surface (3) Wafer surface protective film (BG tape) attaching process (4) Wafer back-grinding process (5) Frame mounting process (6) Wafer surface protective film peeling process (7) Chip separation process

  Semiconductor devices are manufactured in various orders as described above. After performing a plating process for forming electrode metal (UBM) on the wafer surface, a back grinding process is performed to reduce the thickness of the wafer. It is common. However, when the back grinding process is performed after the plating process is performed, if the plating film thickness is thick, the stress of the plating also increases and the wafer warps, which adversely affects the subsequent back grinding process. For this reason, the thickness of the plating formed on the wafer surface cannot be increased.

In order to solve such a problem, a method of performing the back grinding process before the plating process as described below has been studied.
4). Manufacturing method 4
The conventional manufacturing method 4 performs each process mentioned above in order of the following (1)-(8).
(1) Wafer surface protective film (BG tape) attaching process (2) Wafer back grinding process (3) Wafer surface protective film (BG tape) peeling process (4) Under bump metal (UBM) on the wafer surface Plating process for forming (5) Frame mounting process (6) Wafer surface protective film peeling process (7) Dicing process (8) Chip separation process

  However, in the manufacturing method 4 described above, since the back grinding process is performed before the plating process, there is a problem that the plating adheres to the back surface of the wafer and the wafer is damaged. For this reason, as disclosed in Patent Documents 1 to 3, the use of a plating jig prevents the plating from adhering to the back surface of the wafer.

JP 2002-339078 A JP 2002-339079 A JP 2002-343851 A

  However, when a special plating jig is used, particularly in the case of a thin wafer, the wafer is likely to warp when the jig is attached or detached. Further, the special plating jig deteriorates the handleability of the wafer, and furthermore, since a large space is required, it is difficult to plate many wafers at once.

  Therefore, the present invention provides a method for manufacturing a semiconductor device including performing a back grinding process before a plating process for forming an under bump metal, and prevents the adhesion of plating to a non-plated surface of a wafer. It is an object of the present invention to provide a method capable of performing an electrolytic plating process while maintaining the handleability of a wafer.

  As a result of intensive studies, the inventors of the present invention, when performing electroless plating on a wafer, by attaching one or more adhesive films having a re-peelable adhesive on the non-plated surface to the non-plated surface, Plating adherence to the plating surface can be prevented, and it is not necessary to place the wafer on a special jig and perform electroless plating, and the wafer after the adhesive film is attached is substantially before the adhesive film is attached. It has been found that since it is the same size as this wafer, it is easy to handle and can be electrolessly plated in large quantities using a general-purpose wafer cassette.

  In one aspect, the present invention completed on the basis of the above knowledge is a back grinding process 1 on the back side of the wafer, and then one or more adhesive films having a re-peelable adhesive on the back side of the wafer. Step 2 of laminating and attaching, and then electroless plating treatment step 3 for forming under bump metal (UBM) on the wafer surface, followed by adhesion to the wafer with the adhesive film attached to the back surface It is a manufacturing method of the semiconductor device including implementing the process 4 which peels a film.

  In one embodiment of the method for producing a semiconductor device according to the present invention, in step 2, the Young's modulus per adhesive film is 2 to 5 GPa.

  In another embodiment of the method for manufacturing a semiconductor device according to the present invention, in step 2, two or more adhesive films are laminated and pasted.

  In still another embodiment of the method for producing a semiconductor device according to the present invention, the pressure-sensitive adhesive film has a pressure-sensitive adhesive whose adhesive force is reduced when the pressure-sensitive adhesive film is irradiated with ultraviolet rays.

  In still another embodiment of the method for manufacturing a semiconductor device according to the present invention, the thickness of the wafer after step 1 is 200 μm or less.

  In yet another embodiment of the semiconductor device manufacturing method according to the present invention, step 3 is performed by storing a plurality of wafers in a wafer cassette and immersing the wafer cassette in an electroless plating solution.

  According to the present invention, plating adhesion to the non-plated surface of the wafer can be prevented without sacrificing the handling property of the wafer during the electroless plating process for forming the under bump metal. In addition, since no special jig is required, electroless plating can be efficiently performed in large quantities simply by using a general-purpose wafer cassette.

<Step 1: Back grinding of wafer back>
In general, a wafer surface protective film is attached to the wafer before entering the back grinding process. This wafer surface protective film protects the wafer surface on which elements are formed in the backgrinding process, and prevents contamination of the wafer surface due to the ingress of grinding water, grinding scraps, and the like.

  Although not limited, the wafer is formed in a disk shape having a diameter of about 50 to 300 mm having a thickness of about 100 to 775 μm, for example, and is formed using a compound semiconductor such as silicon or GaAs. A plurality of semiconductor elements may be already formed on the wafer surface at this point.

  The wafer surface protective film is composed of a base film and an adhesive provided on the base film. As the base film, for example, a polyethylene film, a polypropylene film, a polyvinyl chloride film, a polyethylene terephthalate film, an ethylene-vinyl acetate copolymer film, an ionomer resin film or the like is used, and the thickness is preferably about 15 to 100 μm. . As the pressure-sensitive adhesive, acrylic resin, methacrylic resin, silicon resin, polyamide resin, polyester resin, polyurethane resin, EVA (copolymer of ethylene and vinyl acetate) resin, and the like can be used.

  After the surface protective film is attached to the wafer, a wafer back grinding process is performed. Any known apparatus can be used for backgridding. For example, a vacuum suction table for fixing the wafer, a rotating grindstone for grinding the wafer, and a grinding liquid (usually water) on the wafer during grinding. It consists of a grinding fluid supply unit to be supplied.

  A wafer whose surface is protected by a surface protective film is provided on a vacuum suction table of a back grinding apparatus with its back surface facing up. Next, in a state where the wafer is sucked and fixed by the vacuum suction table, the grinding liquid is supplied onto the wafer from the grinding liquid supply unit, and the wafer is ground to a predetermined thickness by a rotating grindstone. If necessary, after grinding with a rotating grindstone, finish grinding is subsequently performed to smoothly finish the ground surface of the wafer. As described above, the wafer can be thinned to a thickness of, for example, 50 to 400 μm, more preferably 50 to 150 μm. Since the effect of the present invention is particularly exerted on a thin wafer, the method according to the present invention is suitable for a wafer thinned to 200 μm or less. Furthermore, even a thin wafer having a thickness of 150 μm or less and 100 μm or less can be suitably used by selecting an appropriate adhesive film as described below.

<Step 2: Adhesion of adhesive film to wafer back>
After step 1, one or more sheets are laminated and attached to the back surface of the wafer. The surface protective film attached in step 1 may be peeled off after the adhesive film is attached to the back surface of the wafer, or may be peeled off before the adhesive film is attached to the back surface of the wafer. Any method known to those skilled in the art may be employed as the method for peeling the surface protective film. For example, the surface protective film is provided on a predetermined stage with the surface of the wafer to which the surface protective film is attached facing upward. Subsequently, a peeling film is attached to the wafer surface protective film on the wafer surface, and the wafer surface protective tape is peeled off from the wafer together with the peeling tape.

  An adhesive film is comprised with the adhesive provided on the base film and the base film, for example. As a base film, it is preferable that it is a material which a plating solution and a plating pretreatment liquid do not permeate, and plating does not precipitate on the surface. Films that can be used as the base film, such as polyester film, polyethylene film, polypropylene film, polyvinyl chloride film, polyethylene terephthalate (PET) film, ethylene-vinyl acetate copolymer film, ionomer resin film, polyimide film, etc. are used. In view of securing rigidity, a PET film is preferable.

  Further, the adhesive film is preferably made of a material that is elastic enough to function as a support that prevents the wafer from being damaged by the influence of a liquid flow during plating. On the other hand, if the adhesive film is too hard, it cannot be rolled, so it is very difficult to peel off the adhesive film without breaking a thin wafer. Therefore, it is preferable to use an adhesive film having a Young's modulus of 2 to 5 GPa. When a plurality of adhesive films are laminated and pasted, although depending on the rigidity of the adhesive film, the total thickness is preferably 100 to 1000 μm, more preferably 100 to 300 μm.

  As the adhesive, it is preferable to have a tackiness that does not allow the plating solution or the plating pretreatment solution to permeate during use, for example, acrylic, silicone, polyamide, polyester, polyurethane, In addition, an EVA resin or the like can be used. Especially, it is preferable that it is a re-peeling type adhesive which adhesive strength falls by irritation | stimulation, such as light or a heat | fever so that it may peel easily after metal-plating process. Such pressure-sensitive adhesives are known per se, and include, for example, radiation-curable pressure-sensitive adhesives, ultraviolet-curable pressure-sensitive adhesives, and electron beam-curable pressure-sensitive adhesives, and particularly acrylic UV-curable pressure-sensitive adhesives. In order to peel off the tape without damaging the wafer, a pressure-sensitive adhesive whose adhesive strength is reduced by irradiating with ultraviolet rays is more preferable.

<Process 3: Electroless plating>
Next, an electroless plating process for forming under bump metal (UBM) on the wafer surface is performed on the wafer having the adhesive film attached to the back surface. Although the electroless plating method itself is known and can be carried out by any method known to those skilled in the art, a preferred embodiment will be described below.

  When performing the electroless plating process, first, as a process of the surface to be plated of the wafer, a cleaning process is usually performed. The cleaning process may be a dry process or a wet process. In the case of dry processing, ashing processing, UV processing, reactive ion etching processing, and the like are preferable. In the case of wet processing, either the dipping method or the spin coating method may be used, but it is more preferable that the dipping method is used because batch processing is possible. Examples of the wet treatment include ultrasonic cleaning in water, immersion in an alkali or acidic degreasing solution, immersion in a surfactant aqueous solution, and immersion in a soft etching solution. Examples of the wet treatment include treatment with a commercially available acid degreasing solution, alkaline degreasing solution, and soft etching solution, and the use of these is preferable in that the treatment becomes simple. These treatments may be used alone or in combination, and it is desirable to select an optimum treatment method depending on the degree of contamination of the wafer and the type of passivation.

  After the above-described cleaning, it is preferable to subsequently treat a metal compound having catalytic activity when depositing metal from the electroless plating solution onto the wafer surface. Examples of such a metal compound include a palladium compound and a zinc compound. With respect to the palladium compound, examples include palladium chlorides, hydroxides, oxides, sulfates, ammonium salts and the like that exhibit a catalytic effect. The palladium compound is used as an aqueous solution or an organic solvent solution. As the organic solvent, for example, methyl alcohol, ethyl alcohol, isopropanol, acetone, methyl ethyl ketone, toluene, ethylene glycol, polyethylene glycol, dimethylformamide, dimethyl sulfoxide, dioxane and the like, and mixtures thereof can be used. The palladium compound is more preferably used as an aqueous solution in view of a series of treatments. Moreover, a zinc compound is common as a zincate treatment, and a commercially available chemical can be used.

After the above-described metal compound treatment, the wafer is immersed in an electroless plating solution to perform an electroless plating treatment. When performing electroless plating, in order to increase production efficiency, a plurality of wafers are stored in, for example, a three-point support type or four-point support type wafer cassette, and the wafer cassette is immersed in an electroless plating solution. Is advantageous. Electroless plating may be by substitution or by reduction. The electroless plating solution contains a metal ion source for forming a desired plating in the form of, for example, a sulfate or a chloride. In addition, electroless plating solutions include reducing agents such as formaldehyde, hydrazine, sodium hypophosphite, sodium borohydride, ascorbic acid, glyoxylic acid, sodium acetate, EDTA, tartaric acid, malic acid, citric acid, glycine, etc. A complexing agent, a precipitation controlling agent and the like may be contained.
The electroless plating solution can be a commonly used pH adjusting agent such as sodium hydroxide or potassium hydroxide, but it is necessary to avoid alkali metals such as sodium and potassium in semiconductor applications. Is preferably tetramethylammonium hydroxide.
By the above-described steps, the electroless plating process can be performed on the wafer surface, and for example, a Ni / Au, Ni / Pd, Ni / Pd / Au coating or the like can be formed on the wafer surface.

<Process 4: Dicing>
After step 3, the adhesive film attached during the electroless plating process in step 3 is peeled off. For example, a remover (a piece of another adhesive film) is attached to one end of the adhesive film, the adhesive film attached to the back surface of the wafer is held with the remover, and pulled and peeled in the opposite direction of 180 °. At this time, care should be taken not to break the wafer. In the case of a pressure-sensitive adhesive film using a pressure-sensitive adhesive whose adhesive strength is reduced by stimulation such as heat, it should be peeled off after the adhesive strength is reduced.

  Next, dicing is performed. This process itself is publicly known, and an arbitrary method known to those skilled in the art may be adopted, and is exemplified below. A dicing table provided with a suction unit and a dicing apparatus provided with a dicing saw and the like are prepared. The dicing saw is composed of, for example, an extremely thin circular blade with diamond fine particles attached thereto. Note that the wafer may be cut using a laser instead of the dicing saw.

Subsequently, the wafer attached to the dicing tape together with the ring frame and plated on the surface as described above is placed on the dicing table of the dicing apparatus with the surface facing upward, and the vacuum suction of the suction portion To fix.
Next, the wafer in the ring frame is cut vertically and horizontally from the surface side by a dicing saw to obtain individual chips. Since the individual chips after being cut are fixed by a dicing tape, they are kept in an aligned state.

  After the dicing process, a predetermined inspection is performed as appropriate, and then the process proceeds to a chip separation process. Each separated chip is mounted at a predetermined position on the circuit board, and each chip is connected to the metal wiring of the circuit board. Thus, a desired semiconductor device is manufactured.

  EXAMPLES Examples of the present invention will be described below, but these are provided for better understanding of the present invention and are not intended to limit the present invention.

(1) The Young's modulus of the adhesive film was measured by performing a tensile test using AG-100KNG manufactured by Shimadzu Corporation according to JIS K7127.
(2) The thickness of the plating film was measured with a fluorescent X-ray film thickness measuring device (SFT 9550 manufactured by SII).
(3) The thickness of the adhesive film was measured with a micrometer (293-666 MDQ-30M manufactured by Mitutoyo Corporation).
(4) The thickness of the wafer was measured with a micrometer (293-666 MDQ-30M manufactured by Mitutoyo Corporation).

(Example 1: Comparative example)
A back grinding tape was applied to the surface of a 150 mm diameter Si wafer, and the back surface of the wafer was back ground until the wafer thickness shown in Table 1 was reached. Next, after peeling off the backgrinding tape, an adhesive film using a glue that has a Young's modulus of about 4 GPa, a thickness of 100 μm, and does not change its adhesive strength by stimulation so as to cover the entire back surface of the wafer (the film base is PET) I stuck one. When attaching the film, a “back grinding tape application machine” (RADTEC RAD-3500m / 12DBS) was used to prevent bubbles and sagging of the film from occurring between the wafer and the film.
In this way, a single wafer wafer having an adhesive film attached to the entire polishing surface is prepared, and a wafer cassette case designed to accommodate a plurality of wafers is immersed in a plating solution to remove Ni / Au. Electrolytic plating treatment was performed. As a procedure of electroless plating treatment, alkaline degreasing → soft etching → zincate treatment → electroless Ni plating (film thickness: about 1 μm) → electroless Au plating (film thickness: about 0.07 μm) were performed.
Thus, five sheets were tested under each condition, and the following evaluation was performed.

(1) Film peeling This was defined as “none” when film peeling did not occur during plating. Table 1 shows the ratio at which film peeling was “none”.
(2) Plating solution soaking into backside This means that when there was no soaking between the wafer and the tape, plating soaking into the backside was “None”. In Table 1, the ratio that the plating soaking into the back surface was “none” is shown.
(3) Wafer cracking during plating This means that the wafer cracking during plating was “none” when the wafer did not crack during plating. Table 1 lists the percentage of wafer cracking during plating that was “none”.
(4) Film peeling after plating When the wafer did not break during film peeling, the film peeling after plating was regarded as “success”. Table 1 lists the percentage of successful film peeling after plating.

The results are shown in Table 1.

(Example 2: Comparative example)
A back grinding tape was applied to the surface of a Si wafer having a diameter of 150 mm, and the back surface of the wafer was back ground until the wafer thickness shown in Table 2 was reached. Next, the back grinding tape was peeled off.
The wafer was housed in a wafer cassette designed to accommodate a plurality of wafers, and the wafer cassette case was immersed in a plating solution and subjected to the same electroless plating treatment as in Example 1. Thus, five sheets were tested under each condition, and the same evaluation as in Example 1 was performed.

The results are shown in Table 2.

(Example 3: Example)
As an adhesive film, an electroless plating treatment was performed in the same procedure as in Example 1 except that an adhesive film (ADWILL-D210 manufactured by Lintec Co., Ltd.) using adhesive whose adhesive strength was reduced by UV irradiation was used. Evaluation similar to 1 was performed.

The results are shown in Table 3.

(Example 4: Example)
The electroless plating is performed in the same procedure as in Example 1 except that an adhesive film using a paste whose adhesive strength is reduced by UV irradiation is used as the adhesive film, and two adhesive films are laminated. Processing was performed and the same evaluation as in Example 1 was performed.

The results are shown in Table 4.

(Example 5: Example)
As the adhesive film, an adhesive film (ADWILL-D203 manufactured by Lintec Co., Ltd.) using glue whose adhesive strength is reduced by UV irradiation is used. The thickness of the adhesive film is 50 μm per sheet, and 4 adhesive films are used. The electroless plating treatment was performed in the same procedure as in Example 1 except that the layers were used in a stacked manner, and the same evaluation as in Example 1 was performed.

The results are shown in Table 5.

(Example 6: Example)
The same as Example 1 except that an adhesive film (ADWILL-D210 manufactured by Lintec Co., Ltd.) using glue whose adhesive strength is reduced by UV irradiation is used as the adhesive film, and four adhesive films are laminated and used. The electroless plating process was performed according to the procedure described above, and the same evaluation as in Example 1 was performed.

The results are shown in Table 6.

Claims (6)

  Back grinding process 1 on the back side of the wafer, then, step 2 on the back side of the wafer and affixing one or more adhesive films having a releasable adhesive on the adhesive side, and then attaching the adhesive film to the back side An electroless plating process 3 for forming an under bump metal (UBM) on the wafer surface and a process 4 for peeling the adhesive film are performed on the wafer attached to the semiconductor device. Production method.   In the process 2, the Young's modulus per adhesive film is 2-5 GPa, The manufacturing method of Claim 1.   The manufacturing method according to claim 1 or 2, wherein in step 2, two or more adhesive films are laminated and pasted.   The manufacturing method as described in any one of Claims 1-3 which has an adhesive in which adhesive force falls by an adhesive film irradiating an ultraviolet-ray in an adhesive surface.   The manufacturing method according to claim 1, wherein the thickness of the wafer after step 1 is 200 μm or less.   Process 3 is a manufacturing method as described in any one of Claims 1-5 performed by accommodating a several wafer in a wafer cassette and immersing this wafer cassette in an electroless-plating liquid.