JP4402971B2 - Wafer division method - Google Patents

Description

  The present invention relates to a wafer in which a functional element is arranged in a region partitioned by a predetermined division line formed in a lattice pattern on the surface, and the wafer is divided along the predetermined division line to pick up the divided individual chips. It relates to the division method.

  In the semiconductor device manufacturing process, a plurality of regions are partitioned by dividing lines called streets arranged in a lattice pattern on the surface of a substantially disc-shaped semiconductor wafer, and circuits such as ICs, LSIs, etc. are partitioned in these partitioned regions. (Functional element) is formed. Then, by cutting the semiconductor wafer along the planned dividing line, the region where the circuit is formed is divided to manufacture individual semiconductor chips. In addition, an optical device wafer in which a light receiving element (functional element) such as a photodiode or a light emitting element (functional element) such as a laser diode is laminated on the surface of a sapphire substrate is cut along individual lines by dividing each photo. Divided into optical devices such as diodes and laser diodes, they are widely used in electrical equipment.

  The cutting along the division lines such as the semiconductor wafer and the optical device wafer described above is usually performed by a cutting apparatus called a dicer. This cutting apparatus includes a chuck table for holding a workpiece such as a semiconductor wafer or an optical device wafer, a cutting means for cutting the workpiece held on the chuck table, and a chuck table and the cutting means. And a cutting feed means for moving it. The cutting means includes a spindle unit having a rotary spindle, a cutting blade mounted on the spindle, and a drive mechanism for driving the rotary spindle to rotate. The cutting blade is composed of a disk-shaped base and an annular cutting edge mounted on the outer periphery of the side surface of the base. The cutting edge is fixed to the base by electroforming, for example, diamond abrasive grains having a particle size of about 3 μm. It is formed to a thickness of about 20 μm.

  However, since the cutting blade has a thickness of about 20 μm, the dividing line that divides the chip needs to have a width of about 50 μm, and the area ratio of the dividing line to the area of the wafer is large, resulting in poor productivity. There is. Moreover, since the sapphire substrate, the silicon carbide substrate, and the like have high Mohs hardness, cutting with the cutting blade is not always easy.

On the other hand, in recent years, as a method for dividing a plate-like workpiece such as a semiconductor wafer, a pulse laser beam that uses a pulsed laser beam that is transparent to the workpiece and aligns the condensing point inside the region to be divided is used. A laser processing method for irradiating the film has also been attempted. In the dividing method using this laser processing method, a pulse laser beam in an infrared light region having a light-transmitting property with respect to the work piece is irradiated from the one surface side of the work piece to the inside, and irradiated. The workpiece is divided by continuously forming a deteriorated layer along the planned division line inside the workpiece and applying external force along the planned division line whose strength has been reduced by the formation of this modified layer. To do. (For example, refer to Patent Document 1.)
Japanese Patent No. 3408805

  Thus, although a process for picking up the chips by cutting the wafer completely by cutting the wafer with the above-described cutting apparatus has been established, a pulse laser beam is used along the planned division line inside the wafer. Since the technology for forming an altered layer cannot completely divide the wafer, the production line has not been established and is in a trial and error state.

  The present invention has been made in view of the above-mentioned facts, and the main technical problem thereof is that a deteriorated layer is formed along the line to be divided inside the wafer by using a pulsed laser beam, and an individual layer is formed along this deteriorated layer. To provide a wafer dividing method capable of establishing a process of picking up divided chips while dividing the chips.

In order to solve the above-mentioned main technical problem, according to the present invention, a wafer in which a mechanism element is arranged in a region partitioned by a predetermined division line formed in a lattice shape on the surface is divided along the predetermined division line. A method of dividing a wafer,
A protective member attaching step for attaching a protective member to the surface of the wafer;
A polishing step of polishing the back surface of the wafer having a protective member attached to the surface;
A deteriorated layer forming step of irradiating a pulse laser beam having transparency to the wafer from the back side of the polished wafer along the planned dividing line and forming a modified layer along the planned dividing line inside the wafer;
A dividing step of applying an external force along the planned dividing line of the wafer in which the altered layer is formed along the planned dividing line, and dividing the wafer into individual chips along the planned dividing line;
A frame holding step of attaching the back surface of the wafer divided into individual chips to a dicing tape attached to an annular frame;
An expansion process for expanding the dicing tape to which the wafer divided into individual chips is attached and expanding the distance between the chips;
A pickup step for picking up each chip from the expanded dicing tape, only including,
In the deteriorated layer forming step, the deteriorated layer formed inside the wafer is formed to be exposed at least on the surface of the wafer.
A method of dividing a wafer is provided.

Since the wafer dividing method according to the present invention comprises the above steps, a pulsed laser beam having transparency to a wafer in which functional elements are disposed in regions partitioned by scheduled dividing lines formed in a lattice pattern on the surface. Is irradiated along the planned dividing line to form an altered layer at least on the surface of the wafer along the planned dividing line, and is divided into individual chips along the altered layer. A process for picking up the finished chip can be established.

  Preferred embodiments of a wafer dividing method according to the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 shows a perspective view of a semiconductor wafer as a wafer to be processed according to the present invention. A semiconductor wafer 2 shown in FIG. 1 is made of a silicon wafer, and a plurality of division lines 21 are formed in a lattice shape on the surface 2a, and in a plurality of regions partitioned by the plurality of division lines 21. A circuit 22 as a functional element is formed. As shown in FIG. 2, the protective member 3 is stuck to the surface 2a of the semiconductor wafer 2 configured as described above (protective member sticking step).

  When the protective member 3 is attached to the front surface 2a of the semiconductor wafer 2 by performing the protective member attaching step, a polishing step is performed in which the back surface 2b of the semiconductor wafer 2 is polished into a mirror surface. This polishing step is performed in order to prevent the infrared laser beam irradiated from the back surface 2b side of the semiconductor wafer 2 from being irregularly reflected. That is, in a wafer formed of silicon or the like, when an infrared laser beam is irradiated with a condensing point inside, if the surface roughness of the surface on which the infrared laser beam is irradiated is rough, it is irregularly reflected on the surface and is predetermined. This is because the laser beam does not reach the condensing point, and it is difficult to form a predetermined deteriorated layer inside. This polishing step is performed by a polishing apparatus in the embodiment shown in FIG. That is, in the polishing process, first, as shown in FIG. 3, the protective member 3 side of the semiconductor wafer 2 is placed on the chuck table 41 of the polishing apparatus 4 (therefore, the back surface 2b of the semiconductor wafer 2 is on the upper side). The semiconductor wafer 2 is sucked and held on the chuck table 41 by the suction means that does not. Then, while rotating the chuck table 41 at, for example, 300 rpm, a polishing tool 43 provided with a polishing grindstone 42 in which abrasive grains such as zirconia oxide are dispersed in a flexible member such as felt and fixed with an appropriate bonding agent is rotated at, for example, 6000 rpm. By contacting the back surface 2b of the semiconductor wafer 2, the back surface 2b of the semiconductor wafer 2 is mirror-finished. In this mirror surface processing step, the back surface 2b of the semiconductor wafer 2, which is a processed surface, has a surface roughness (Ra) specified by JIS B0601 of 0.05 μm or less (Ra ≦ 0.05 μm), preferably 0.02 μm or less (Ra ≦ 0.02 μm).

  Next, a pulsed laser beam having transparency to the wafer is irradiated along the planned division line from the back surface 2b side of the polished semiconductor wafer 2 to form a deteriorated layer along the planned division line inside the wafer. An altered layer forming step is performed. This deteriorated layer forming step is performed using a laser processing apparatus 5 shown in FIGS. A laser processing apparatus 5 shown in FIGS. 4 to 6 includes a chuck table 51 that holds a workpiece, laser beam irradiation means 52 that irradiates the workpiece held on the chuck table 51 with a laser beam, and a chuck table 51. An image pickup means 53 for picking up an image of the workpiece held thereon is provided. The chuck table 51 is configured to suck and hold a workpiece, and can be moved in a machining feed direction indicated by an arrow X and an index feed direction indicated by an arrow Y in FIG. Yes.

  The laser beam irradiation means 52 includes a cylindrical casing 521 disposed substantially horizontally. In the casing 521, a pulse laser beam oscillation means 522 and a transmission optical system 523 are arranged as shown in FIG. The pulse laser beam oscillation means 522 is composed of a pulse laser beam oscillator 522a composed of a YAG laser oscillator or a YVO4 laser oscillator, and a repetition frequency setting means 522b attached thereto. The transmission optical system 523 includes an appropriate optical element such as a beam splitter. A condenser 524 containing a condenser lens (not shown) composed of a combination lens that may be in a known form is attached to the tip of the casing 521. The laser beam oscillated from the pulse laser beam oscillating means 522 reaches the condenser 524 through the transmission optical system 523, and a predetermined focused spot diameter is applied to the workpiece held on the chuck table 51 from the condenser 524. Irradiated with D. As shown in FIG. 6, the focused spot diameter D is D (μm) = 4 × λ × f / (π when a pulse laser beam having a Gaussian distribution is irradiated through the objective condenser lens 524 a of the condenser 524. × W), where λ is defined by the wavelength (μm) of the pulsed laser beam, W is the diameter (mm) of the pulsed laser beam incident on the objective lens 524a, and f is the focal length (mm) of the objective lens 524a.

  In the illustrated embodiment, the image pickup means 53 mounted on the tip of the casing 521 constituting the laser beam irradiation means 52 emits infrared rays to the workpiece in addition to a normal image pickup device (CCD) that picks up an image with visible light. Infrared illumination means for irradiating, an optical system for capturing infrared light emitted by the infrared illumination means, an image pickup device (infrared CCD) for outputting an electrical signal corresponding to the infrared light captured by the optical system, and the like Then, the captured image signal is sent to the control means described later.

The deteriorated layer forming step performed using the laser processing apparatus 5 described above will be described with reference to FIGS. 4, 7, and 8.
In this deteriorated layer forming step, first, the protective member 3 side of the semiconductor wafer 2 whose back surface 2b is polished is placed on the chuck table 51 of the laser processing apparatus 5 shown in FIG. The semiconductor wafer 2 is sucked and held on the chuck table 51 by suction means (not shown). The chuck table 51 that sucks and holds the semiconductor wafer 2 is positioned directly below the imaging means 53 by a moving mechanism (not shown).

  When the chuck table 51 is positioned immediately below the image pickup means 53, an alignment operation for detecting a processing region to be laser processed of the semiconductor wafer 2 is executed by the image pickup means 53 and a control means (not shown). That is, the image pickup means 53 and the control means (not shown) include the division line 21 formed in a predetermined direction of the semiconductor wafer 2, and the condenser 524 of the laser beam irradiation means 52 that irradiates the laser beam along the division line 21. Image processing such as pattern matching is performed to align the laser beam, and alignment of the laser beam irradiation position is performed. In addition, alignment of the laser beam irradiation position is similarly performed on the division line 21 formed on the semiconductor wafer 2 and extending at right angles to the predetermined direction. At this time, the surface 2a on which the division line 21 of the semiconductor wafer 2 is formed is positioned on the lower side. Since an image pickup unit configured with an image pickup device (infrared CCD) or the like that outputs an electric signal is provided, the division line 21 can be picked up through the back surface 2b.

  If the division line 21 formed on the semiconductor wafer 2 held on the chuck table 51 is detected as described above and alignment of the laser beam irradiation position is performed, it is shown in FIG. In this way, the chuck table 51 is moved to the laser beam irradiation region where the condenser 524 of the laser beam irradiation means 52 for irradiating the laser beam is located, and one end (the left end in FIG. 7A) of the predetermined division line 21 is irradiated with the laser beam. Positioned just below the light collector 524 of the means 52. The chuck table 51, that is, the semiconductor wafer 2, is moved at a predetermined feed speed in the direction indicated by the arrow X1 in FIG. Then, as shown in FIG. 8B, when the irradiation position of the condenser 524 of the laser beam irradiation means 52 reaches the position of the other end of the division planned line 21, the irradiation of the pulse laser beam is stopped and the chuck table 51, that is, The movement of the semiconductor wafer 2 is stopped. In this deteriorated layer forming step, the condensing point P of the pulse laser beam is matched with the vicinity of the surface 2a (lower surface) of the semiconductor wafer 2, so that the deteriorated layer 210 is exposed to the surface 2a (lower surface) and from the surface 2a toward the inside. Is formed. This altered layer 210 is formed as a melt-resolidified layer. By forming the altered layer 210 so as to be exposed on the surface 2 a of the semiconductor wafer 2, division by applying an external force along the altered layer 210 is facilitated.

Note that the processing conditions in the deteriorated layer forming step are set as follows, for example.
Light source: LD excitation Q switch Nd: YVO4 laser wavelength: 1064 nm pulse laser Pulse output: 10 μJ
Condensing spot diameter: φ1μm
Pulse width; 40 ns
Peak power density at condensing point; 3.2 × 10 ¹⁰ W / cm ²
Repetition frequency: 100 kHz
Processing feed rate: 100 mm / sec

  When the thickness of the semiconductor wafer 2 is thick, the plurality of deteriorated layers 210 are formed by changing the condensing point P stepwise as shown in FIG. Form. Note that, since the thickness of the deteriorated layer formed at one time is about 50 μm under the above-described processing conditions, in the illustrated embodiment, six deteriorated layers are formed on the wafer 2 having a thickness of 300 μm. . As a result, the altered layer 210 formed inside the semiconductor wafer 2 is formed from the front surface 2a to the back surface 2b along the planned dividing line 21.

If the deteriorated layer 210 is formed along the planned division line 21 inside the semiconductor wafer 2 by the above-described deteriorated layer forming step, a division process for dividing the semiconductor wafer 2 along the planned division line 21 is performed.
An embodiment of the dividing step will be described with reference to FIG. The embodiment of the dividing step shown in FIG. 9 is performed using a laser processing apparatus 6 similar to the laser processing apparatus shown in FIGS. That is, as shown in FIG. 9, the protection member 3 side of the semiconductor wafer 2 in which the altered layer 210 is formed along the scheduled division line 21 is placed on the chuck table 61 of the laser processing apparatus 6 (accordingly, the semiconductor wafer 2). Is held by suction by a suction means (not shown). Next, the chuck table 61 is moved to the laser beam irradiation area where the condenser 63 of the laser beam application means is located, and one end (the left end in FIG. 9) of the predetermined division line 21 is positioned directly below the condenser 63. Then, while irradiating the semiconductor wafer 2 with a continuous wave laser beam having an absorptivity from the condenser 63, the chuck table 61, that is, the semiconductor wafer 2 is moved in the direction indicated by the arrow X1 in FIG. When the other end (the right end in FIG. 9) of the predetermined division line 21 reaches the irradiation position of the condenser 63, the irradiation of the laser beam is stopped and the movement of the chuck table 61, that is, the semiconductor wafer 2 is stopped. In this dividing step, the condensing point P of the continuous wave laser beam is aligned with the back surface 2b (upper surface) of the semiconductor wafer 2, and the dividing line 21 on which the altered layer 210 is formed is heated to generate thermal stress, Give a shock. As a result, the semiconductor wafer 2 is divided by being divided along the planned dividing line 21 where the altered layer 210 is formed. In addition, the laser beam irradiated along the planned dividing line 21 in which the altered layer 210 is formed in the dividing step is sufficient for the output to heat the semiconductor wafer 2 to give an appropriate temperature gradient (100 to 400 ° C.). Yes, it does not melt silicon.

In addition, the processing conditions in the said division | segmentation process are set as follows, for example.
Light source: LD pumped Nd: YAG second harmonic laser (CW)
Wavelength: 532 nm
Output: 10W
Condensing spot diameter: φ0.5 mm (heats a relatively wide area including the altered layer 110)
Processing feed rate: 100 mm / sec

  When the division process is performed as described above, the chuck table 61, that is, the semiconductor wafer 2, is indexed and fed in the direction perpendicular to the paper surface in FIG. 9 by the interval of the division line 21 and the continuous wave laser beam is irradiated again as described above. While performing the process feed. When the processing feed and the indexing feed are performed along all the division lines 21 formed in the predetermined direction, the chuck table 61, that is, the semiconductor wafer 2 is rotated by 90 degrees to make the predetermined direction. By performing the processing feed and the index feed along the planned division line 21 formed at right angles, the cutting and division are performed along the planned division line 21 formed on the semiconductor wafer 2. The semiconductor wafer 2 is divided into individual chips by being cleaved along the division line 21, but the protective member 3 is attached to the back surface 2 b of the semiconductor wafer 2, so The wafer form is maintained.

  In addition, in the dividing process of dividing the semiconductor wafer 2 along the planned dividing line 21, in addition to the dividing method described above, for example, the semiconductor wafer 2 attached to a protective member is placed on a flexible rubber sheet, By pressing the upper surface with a roller, it is possible to use a method of cleaving the semiconductor wafer 2 along the planned dividing line 21 in which the deteriorated layer 210 is formed and the strength is reduced.

  If the dividing step described above is performed, a frame holding step is performed in which the semiconductor wafer 2 divided into individual semiconductor chips is attached to a dicing tape mounted on an annular frame. In the frame holding step, as shown in FIG. 10, the back surface 2b of the semiconductor wafer 2 is adhered to the surface of the expandable dicing tape 70 mounted on the annular frame 7. Then, the protective member 3 attached to the surface 2a of the semiconductor wafer 2 is peeled off. In the illustrated embodiment, the dicing tape 70 has an acrylic resin-based paste applied to the surface of a sheet base material made of polyvinyl chloride (PVC) having a thickness of 100 μm to a thickness of about 5 μm. This paste has a property that the adhesive strength is reduced by an external stimulus such as ultraviolet rays.

  If the above-described frame holding process is performed, an expansion process is performed in which the dicing tape to which the wafer divided into individual chips is attached is expanded to widen the interval between the chips. This expansion process is performed by the pickup device 8 shown in FIGS. Here, the pickup device 8 will be described. The illustrated pickup device 8 includes a cylindrical base 81 on which a mounting surface 81 a for mounting the frame 7 is formed, and a dicing tape 70 disposed concentrically within the base 81 and mounted on the frame 7. The expansion means 82 for pushing out is provided. The expansion means 82 includes a cylindrical expansion member 83 that supports a region 701 where the semiconductor wafer 2 exists in the dicing tape 70. The expansion member 83 is moved vertically between the reference position shown in (a) of FIG. 12 and the extended position shown in (b) of FIG. It is configured to be movable in the axial direction. In the illustrated embodiment, an ultraviolet irradiation lamp 84 is disposed in the expansion member 83.

The expansion process performed using the pickup device 8 described above will be described with reference to FIGS.
As described above, the frame 7 on which the dicing tape 70 to which the back surface 2b of the semiconductor wafer 2 divided into individual chips 20 is attached has a cylindrical base as shown in FIG. 11 and FIG. 81 is mounted on the mounting surface 81 a and is fixed to the base 81 by a clamp 85. Next, as shown in FIG. 12B, the expansion member 83 of the expansion means 82 supporting the region 701 where the semiconductor wafer 2 is present in the dicing tape 70 is moved to the reference position shown in FIG. To the extended position shown in FIG. As a result, the expandable dicing tape 70 is expanded, so that a gap is generated between the dicing tape 70 and the chip 20 to reduce the adhesion, so that the chip 20 can be easily detached from the dicing tape 70. A gap is formed between the individual semiconductor chips 20.

  Next, as shown in FIG. 11, the pickup collet 86 disposed above the pickup device 8 is operated to separate the individual chips 20 from the upper surface of the dicing tape 70 and convey them to a tray (not shown). . At this time, the ultraviolet irradiation lamp 84 disposed in the expansion member 83 is turned on to irradiate the dicing tape 70 with ultraviolet rays, so that the adhesive strength of the dicing tape 70 is reduced, so that it can be detached more easily.

The perspective view of the semiconductor wafer divided | segmented by the division | segmentation method of the wafer by this invention. The perspective view which shows the state which affixed the protection member on the surface of the semiconductor wafer shown in FIG. Explanatory drawing of the grinding | polishing process in the division | segmentation method of the wafer by this invention. The principal part perspective view of the laser processing apparatus which implements the deteriorated layer formation process in the division | segmentation method of the wafer by this invention. The block diagram which shows simply the structure of the laser beam irradiation means with which the laser processing apparatus shown in FIG. 4 is equipped. The simplification figure for demonstrating the condensing spot diameter of a pulse laser beam. Explanatory drawing of the altered layer formation process in the division | segmentation method of the wafer by this invention. Explanatory drawing which shows the state formed by laminating | stacking a deteriorated layer inside a wafer in the deteriorated layer formation process shown in FIG. Explanatory drawing of the division | segmentation process in the division | segmentation method of the wafer by this invention. The perspective view which shows the state which affixed the back surface of the wafer divided | segmented into each semiconductor chip on the dicing tape with which the cyclic | annular flame | frame was mounted | worn. The perspective view of the pick-up apparatus which implements the expansion process and pick-up process in the division | segmentation method of the wafer by this invention. Explanatory drawing which shows the expansion process in the division | segmentation method of the wafer by this invention.

Explanation of symbols

2: Semiconductor wafer 20: Semiconductor chip 21: Planned division line 22: Circuit 210: Altered layer 3: Protection member 4: Polishing device 41: Chuck table of polishing device 43: Polishing tool 5: Laser processing device 51: Laser processing device Chuck table 51: Laser beam irradiation means 53: Imaging means 6: Laser processing apparatus 61: Chuck table of laser processing apparatus 7: Annular frame 70: Dicing tape 8: Pickup device 81: Cylindrical base 82: Expansion means 84: Ultraviolet light Irradiation lamp 86: Pickup collet

Claims (1)

A wafer dividing method for dividing a wafer in which a mechanism element is arranged in a region partitioned by a planned dividing line formed in a lattice shape on the surface, along the planned dividing line,
A protective member attaching step for attaching a protective member to the surface of the wafer;
A polishing step of polishing the back surface of the wafer having a protective member attached to the surface;
A deteriorated layer forming step of irradiating a pulse laser beam having transparency to the wafer from the back side of the polished wafer along the planned dividing line and forming a modified layer along the planned dividing line inside the wafer;
A dividing step of applying an external force along the planned dividing line of the wafer in which the altered layer is formed along the planned dividing line, and dividing the wafer into individual chips along the planned dividing line;
A frame holding step of attaching the back surface of the wafer divided into individual chips to a dicing tape attached to an annular frame;
An expansion process for expanding the dicing tape to which the wafer divided into individual chips is attached and expanding the distance between the chips;
A pickup step for picking up each chip from the expanded dicing tape, only including,
In the deteriorated layer forming step, the deteriorated layer formed inside the wafer is formed to be exposed at least on the surface of the wafer.
A wafer dividing method characterized by the above.

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