TWI757482B - Processing method of workpiece - Google Patents

Abstract

[Problem] To provide a method for processing a workpiece which can improve productivity without lowering the flexural strength of a wafer. [Solution] A method for machining a workpiece with a plurality of intersecting predetermined scribe lines set on the surface, characterized by comprising: a holding step of holding the surface side of the workpiece by a table; A laser processing step in which the workpiece of the table is irradiated with a pulsed laser beam having a wavelength having transmissivity from the back side of the workpiece to form a plurality of shielding tunnels from the front side of the workpiece to the workpiece. The fine hole above the finishing thickness of the object and the amorphous or metamorphic layer surrounding the fine hole are formed; and after the laser processing step is performed, the back surface of the workpiece is ground to thin the workpiece into the fine hole. Grinding step for machining thickness.

Description

Processing method of workpiece

The present invention relates to a processing method of a workpiece, wherein a plurality of intersecting planned dividing lines are set on the surface of the workpiece.

A SAW filter (Surface Acoustic Wave Filter) that extracts electrical signals in a specific frequency band is used as an RF filter (Radio Frequency Filter) or an IF filter (Intermediate Frequency Filter) except for most mobile phones. , is also widely used in digital TV or GPS, wireless LAM (wireless local area network) and other filters.

In the SAW filter manufacturing process, single crystal ingots such as lithium niobate (LiNbO ₃ ) or lithium tantalate (LiTaO ₃ ) are grown by spin-up method or double crucible method, and then the ingot is sliced into wafers. , grinding is performed by a grinding device or a polishing device, and polishing is performed to make it flat (for example, refer to Japanese Patent Laid-Open No. 2001-332949).

On the flattened lithium niobate wafer or lithium tantalate wafer, a plurality of comb electrodes with a period of about 2 to 5 μm are formed from a thin film of aluminum or aluminum alloy using photolithography. SAW filter.

Lithium niobate wafers (LN wafers) or lithium tantalate wafers (LT wafers) with a plurality of SAW elements such as SAW filters formed on the surface have high Mohs hardness and are cut with a dicing blade It is difficult to increase the feed rate, and the productivity is extremely poor.

Therefore, in a lithium niobate wafer or a lithium tantalate wafer on which SAW elements are formed on the surface of a general thickness, after forming the starting point of division by laser processing, the wafer is divided into individual wafers by applying an external force to the wafer.

However, the ablation processing method of irradiating the LN wafer or LT wafer with a pulsed laser beam having an absorbing wavelength, or irradiating the LN wafer or LT wafer with a pulsed laser beam having a transmissive wavelength On the other hand, in the SD (stealth dicing) processing method in which a modified layer is formed inside the wafer, a pulsed laser beam must be irradiated several times to one planned dividing line, and further improvement in productivity is expected.

Here, Japanese Patent Laid-Open No. 2014-221483 describes that an object to be processed made of a single crystal substrate is irradiated with a pulsed laser beam that is transparent to the single crystal substrate using a condenser lens with a small numerical aperture, A processing method in which the workpiece is divided into individual wafers by applying an external force to the workpiece after forming a shield tunnel composed of pores and an amorphous material that shields the pores inside the workpiece.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2001-332949

[Patent Document 2] Japanese Patent Laid-Open No. 2014-221483

However, in the processing method described in Patent Document 2, the productivity can be improved compared with the SD processing method and the ablation processing method using a dicing blade or a pulsed laser beam, but compared with the dicing by the dicing blade, there is a resistance to bending of the wafer. The problem of strength deterioration.

The present invention has been made in view of this point, and an object of the present invention is to provide a method for processing a workpiece which can improve productivity without lowering the flexural strength of a wafer.

According to the present invention, there is provided a method for processing a workpiece, which is a method for processing a workpiece with a plurality of intersecting predetermined scribe lines set on the surface, which is characterized by comprising: The holding step of holding on the surface side of the table; for the workpiece held on the table, the position of the upper end of the condensing region of the pulsed laser beam having a transmissive wavelength is located at a position higher than that from the workpiece. A plurality of shielding tunnels are formed by irradiating the pulsed laser beam from the back side of the workpiece so that the surface of the object is farther from the position of the finish thickness of the workpiece and the position between the back surface of the workpiece. The laser processing step, the shielding tunnel is formed from the surface of the object to be processed by a fine hole longer than the finished thickness and shorter than the thickness of the workpiece, and an amorphous or and a grinding step of grinding the back surface of the workpiece to remove the upper end of the shielding tunnel and thinning the workpiece to the finishing thickness after the laser processing step is performed.

According to the processing method of the present invention, the laser processing can be completed in one pass, and the productivity can be improved compared with the conventional laser processing based on SD processing or ablation processing. In addition, the upper end portion of the shielding tunnel is removed by grinding and does not remain on the wafer, so that the flexural strength can be improved.

In addition, in the present invention, the back surface of the workpiece is ground after the laser processing, and the thickness of the workpiece is reduced by finishing the workpiece, and the grinding load can be locally divided into individual wafers. The output laser beam forms a shielding tunnel, which can improve the flexural strength of the wafer compared with the case where no grinding is performed after laser processing.

11: Lithium Niobate Wafer (LN Wafer)

12: Condenser

12a: Condenser lens

13: Split predetermined lines

15: SAW components

16: Grinding unit

17: Protective tape

19: Shielded Tunnel

21: Pore

22: Grinding Wheel

23: Amorphous

25: Component wafer

26: Grinding Grinding Stone

30: Expansion device

34: Keeping Components

38: Extension Roller

[Fig. 1] A perspective view showing how a protective tape is attached to the surface of a wafer.

[ Fig. 2 ] A cross-sectional view showing a holding step.

[ Fig. 3 ] A cross-sectional view showing a laser processing step.

4(A) shows a cross-sectional view of an embodiment in which shield tunnels are formed from the front surface of the wafer to the middle, and FIG. 4(B) shows an embodiment in which shield tunnels are formed from the front surface to the back surface of the wafer sectional view.

[ Fig. 5 ] A partial cross-sectional side view showing one of the grinding steps.

[Fig. 6] A perspective view showing the transfer step.

[ Fig. 7] Fig. 7 is a cross-sectional view showing a spacer forming step for forming a spacer between wafers.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing a state in which a protective tape 17 is attached to a surface 11 a of a lithium niobate (LiNbO ₃ ) wafer 11 . SAWs such as SAW filters are formed on the surface 11a of a lithium niobate wafer (called an LN wafer or simply a wafer) 11 in each region delimited by a plurality of planned division lines 13 formed in a lattice shape element 15. The SAW element 15 is formed by a thin film of aluminum or an aluminum alloy, for example, as a comb-shaped electrode with a period of about 2 to 5 μm.

The thickness of the LN wafer 11 is about 350 μm, and the processing method of the present embodiment includes a grinding step of grinding the back surface 11 b of the LN wafer 11 to a finish thickness of 130 μm.

In the processing method of the present embodiment, an example of using an LN wafer as the workpiece is described, but the workpiece is not limited to this, and lithium tantalate wafers (LiTaO ₃ wafers), SiC wafers, and sapphire crystals may also be used. Other processed objects such as circles, GaN wafers, Si wafers, glass wafers, etc.

After the protective tape 17 is attached to the surface 11 a of the LN wafer 11 , as shown in FIG. 2 , the LN wafer 11 is sucked and held by the table 10 of the laser processing apparatus with the protective tape 17 as the lower side, so that the LN wafer 11 is sucked and held. The back surface 11b of 11 is exposed.

Next, as shown in FIG. 3 , a laser processing step is performed, that is, the LN wafer 11 is irradiated with a pulsed laser beam LB of a wavelength having transmissivity from the condenser 12 having the condenser lens 12 a , and the A plurality of shield tunnels 19 are formed inside.

In the laser processing step of forming the shielding tunnel 19 inside the wafer 11 , the value obtained by dividing the numerical aperture (NA) of the condenser lens 12 a by the refractive index of the single crystal substrate, that is, the LN wafer 11 is set to a value of 0.05 to 0.35 within the range.

Since the refractive index of lithium niobate is 2.2, it is preferable to set the numerical aperture (NA) of the condenser lens 12a to 0.1 to 0.7. For example, a condenser lens having spherical aberration is used as the condenser lens 12a.

Alternatively, spherical aberration may be generated by arranging a lens on the upstream side or downstream side of the condenser lens, oscillating from a laser beam oscillator to generate a laser beam having a predetermined divergence angle, and passing through the laser beam oscillator. Condensing lenses may also be used for condensing light.

Therefore, the laser beam is irradiated to the wafer in a state where longitudinal aberration is generated in the laser beam condensed by the condenser lens, whereby the shielding tunnel 19 can be formed inside the wafer 11 .

In this laser processing step, the position of the upper end portion of the condensing region P of the pulsed laser beam LB controlled to a predetermined output is positioned at the position of the finishing thickness t1+α from the surface 11a of the wafer 11 , the pulsed laser beam LB is irradiated from the back surface 11 b side of the wafer 11 .

In this way, the shielding tunnel 19 is instantaneously formed as the irradiation of the pulsed laser beam LB proceeds from the position where the upper end portion of the light-converging region P is located toward the front surface 11 a of the wafer. The upper end of the shielded tunnel 19 formed The strength of the surrounding area is lower than that of other areas, so the flexural strength of the formed device wafer can be improved by grinding and removing this area by the subsequent grinding step.

Here, the term of the condensing region P of the laser beam LB is used because the condenser lens 12a has spherical aberration, and therefore the laser beam LB is adjusted based on the radial position of the laser beam LB passing through the condenser lens 12a. The condensed positions differ in the optical axis direction of the condensing lens 12 a, and therefore the condensing region P extends in the thickness direction of the wafer 11 .

In this way, the pulsed laser beam LB is irradiated from the back surface 11 b side of the wafer 11 so that the condensing region P extends into the inside of the wafer 11 , and the table 10 is moved along the arrow X-axis direction at a predetermined processing feed speed. The machining feed is performed, whereby a plurality of shield tunnels 19 having a length of finish thickness t1+α from the surface 11a of the wafer 11 are formed in the wafer 11 along the scribe line 13 to be divided. In the present embodiment, the finishing thickness t1 is set to 130 μm, and α is set to, for example, 10 to 15 μm.

The shielding tunnel 19 is formed of pores having a diameter of about 1 μm and amorphous that shields the pores. When the repetition frequency of the irradiated pulsed laser beam LB is set to 50 kHz, and the processing feed speed is set to 500 mm/s, shielding tunnels 19 are formed at intervals of 10 μm along the scribe lines 13 to be divided into the wafer 11 so as to be adjacent to each other. A state in which local cracks occur between pores.

The laser processing step of forming the shielding tunnels 19 in the inside of the wafer 11 is sequentially performed along the scribe lines to be divided extending in the first direction. All the planned division lines 13 extending in the second direction of the intersection are implemented.

The processing conditions of the laser processing step of forming the shield tunnel 19 inside the wafer 11 are, for example, as follows.

Wavelength: 1064nm

Average output: 0.2~0.5W

Repetition frequency: 20~50kHz

Pulse width: 10ps

Condenser spot diameter: 10μm

Processing feed rate: 100~600mm/s

When glass is used as the object to be processed, the glass is originally amorphous, so when the laser processing step is performed, a shielding tunnel formed of pores and an amorphous metamorphic layer shielding the pores is formed.

As shown in FIG. 4(A), the shielding tunnel 19 formed inside the LN wafer 11 is preferably the length of the finishing thickness t1+α, but as shown in FIG. 4(B), the laser beam may be increased The output of the LB, and the shielding tunnel 19 is formed from the front surface 11a of the wafer 11 to the back surface 11b. In this case, among the above-mentioned laser processing conditions, it is preferable to increase the average output to 2 to 4W.

In the thickness of the shield tunnel=finished thickness+α, α is preferably 10 to 15 μm, but may be set to this value or more. When +α is small, the flexural strength of the segmented element wafer can be improved, but when α is increased, as shown in FIG. 4(B), when the shielding tunnel 19 is formed from the front surface 11a to the back surface 11b, the LN wafer 11 can be improved. Divisibility.

The thickness of the shielding tunnel (long (degree) is about 150 μm, and the thickness (length) of the shielding tunnel that can be formed at one time is about 250 μm if the flexural strength is not concerned.

After the laser processing step is performed, a grinding step of partially dividing the wafer 11 into individual wafers is performed while grinding the back surface 11b of the wafer 11 to reduce the thickness of the wafer 11 to the finishing thickness t.

In the grinding step, as shown in FIG. 6 , the back surface 11 b of the wafer 11 is exposed by sucking and holding the protective tape 17 side of the wafer 11 by the table 14 of the grinding device. The grinding unit 16 of the grinding device includes: a mandrel 18 rotatably driven by a motor; a wheel mount 20 fixed to the front end of the mandrel 18; way mounted grinding wheel 22. The grinding wheel 22 is composed of a ring-shaped wheel base 24 and a plurality of grinding stones 26 fixed to the outer peripheral portion of the lower end of the wheel base 24 .

In the grinding step, the grinding stone 26 of the grinding wheel 22 is brought into contact with the wafer 11 held by the table 14 by operating a grinding feeding mechanism (not shown), and the grinding wheel 22 is ground and fed at a predetermined grinding feed speed. The LN wafer 11 is ground while the table 14 is rotated in the direction indicated by the arrow a at, for example, 300 rpm, and the grinding wheel 22 is rotated in the direction indicated by the arrow b, for example, at 1500 to 2000 rpm.

Preferably, the grinding step is carried out in two stages of a rough grinding step and a finishing grinding step after the rough grinding step is carried out. In the rough grinding step, grinding was performed by rotating the grinding wheel 22 at 2000 rpm while rotating the table 14 at 300 rpm using a #1000 vitrified frit grinding stone 26 .

In the finishing grinding step after the rough grinding is completed, the grinding wheel 22 is rotated at 1500 rpm while the table 14 is rotated at 300 rpm using a vitrified frit grinding stone 26 of #3000 until the wafer 11 is ground. Thinning becomes the finishing thickness t1=50 μm.

In the grinding step consisting of the rough grinding step and the finishing grinding step, a predetermined grinding load is always applied to the back surface 11b of the wafer 11, and therefore the wafer 11 is caused to follow the planned dividing line 13 and shield the wafer 11 by the grinding load. The tunnel 19 is broken from the starting point, and is at least partially divided into individual element wafers.

In addition, in the grinding step, the wafer 11 may not be completely divided into the individual element wafers along the planned dividing line 13 with the shield tunnel 19 as the breaking point. Therefore, the wafer 11 after the grinding step is performed. It is preferable to apply an external force so that the wafer 11 is completely divided into individual wafers along the planned division scribe line 13 .

After the grinding step is completed, as shown in FIG. 7 , the back surface 11 b of the wafer 11 that has been divided into the individual element wafers is adhered to the outer peripheral portion of the expansion tape T with the annular frame F attached, and the front surface 11 a of the wafer 11 is protected. The transfer step in which the tape 17 is peeled off. It is preferable to use a UV-curable tape as the extension tape.

After the transfer step is performed, a dividing step of forming a space between the wafers while expanding the expansion tape T to completely divide the wafer 11 attached to the expansion tape T into each element wafer 25 is performed. An example of this dividing step is performed using the expansion device 30 shown in FIG. 7 .

The expansion device 30 includes a frame holder for holding the annular frame F means 32. The frame holding means 32 is constituted by an annular frame holding member 34 and a plurality of clips 36 as fixing means arranged on the outer periphery of the frame holding member 34 . The upper surface of the frame holding member 34 is formed as a placing surface 34a on which the annular frame F is placed, and the annular frame F is placed on the placing surface 34a.

The ring-shaped frame F placed on the placement surface 34 a is fixed to the holding member 34 by the jig 36 . At this time, the expansion tape T on which the wafer 11 is pasted is abutted against the upper end of the expansion roller 38 .

The holding table 46 is arranged inside the expansion drum 38 , and the suction holding part 46 a of the holding table 46 is selectively connected to the suction source 52 via the suction passage 48 and the electromagnetic switching valve 50 .

A drive means 40 for moving the annular frame holding member 32 in the vertical direction is disposed outside the expansion drum 38 . The driving means 40 is constituted by a plurality of cylinders 42 , and piston rods 44 of the cylinders 42 are connected to the lower surface of the holding member 34 .

The driving means 40 constituted by a plurality of cylinders 42 makes the annular frame holding member 34 a reference position on the mounting surface 34a of the ring-shaped frame holding member 34 which is substantially the same height as the upper end of the expansion drum 38, and is lower than the upper end of the expansion drum 38 by a predetermined amount. It moves in the up and down direction between the extended positions on the lower side of the volume.

In the dividing step using the expansion device 30 configured in this way, the annular frame F supporting the wafer 11 through the expansion tape T is placed on the placement surface 34a of the frame holding member 34, It is fixed to the frame holding member 34 . At this time, the position of the frame holding member 34 is a reference position at which the mounting surface 34a of the frame holding member 34 becomes substantially the same height as the upper end of the expansion drum 38 .

Next, the drive cylinder 42 pulls down the frame holding member 34 to the expanded position shown in FIG. 7(B). As a result, the annular frame F fixed on the mounting surface 34 of the frame holding member 34 is also pulled down, so that the expansion tape T adhered to the annular frame F abuts on the upper end edge of the expansion drum 38 mainly along the radius direction expansion.

As a result, while the wafer 11 is completely divided into the individual element wafers 25 along the planned division scribe lines 13 , spaces are formed between the adjacent element wafers 25 . After the expansion belt T is expanded, the electromagnetic switching valve 50 is switched to the communication position, the negative pressure of the suction source 52 is applied to the suction holding portion 46 a of the holding table 46 , and the wafer 11 is separated from the wafer 25 in a state where the gap is formed. Keep.

After the dividing step is performed, the extension tape T is irradiated with ultraviolet rays in a state in which the extension tape T is adsorbed and held by the holding table 46 to reduce the adhesive force of the extension tape T, and then the element wafer 25 is picked up from the extension tape T by a pick-up device. .

According to the above-described embodiment, since the backside grinding of the wafer 11 is performed after the laser processing, the wafer 11 is at least partially divided into individual wafers by the grinding load. Therefore, compared with the case where no grinding is performed, even by low-output laser processing, it can be divided into wafers, so that the flexural strength of the element wafer can be improved compared with the case where no grinding is performed after the laser processing. In addition, the upper end portion of the shielding tunnel is removed by grinding and does not remain on the wafer, so that the flexural strength of the element wafer can be improved.

10‧‧‧Workbench

11‧‧‧Lithium Niobate Wafer (LN Wafer)

11a‧‧‧Surface

11b‧‧‧Back

12‧‧‧Concentrator

12a‧‧‧Condenser lens

15‧‧‧SAW components

17‧‧‧Protective tape

19‧‧‧Shielded Tunnel

LB‧‧‧Laser Beam

P‧‧‧Concentrating area

tI‧‧‧Finishing thickness

Claims (2)

A method for processing a workpiece, which is a method for processing a workpiece with a plurality of intersecting predetermined scribe lines set on the surface, characterized by comprising: a holding step of holding the surface side of the workpiece by a table; With respect to the workpiece held on the table, the position of the upper end of the condensing region of the pulsed laser beam having a transmissive wavelength is located more precisely than the surface of the workpiece away from the workpiece. A laser processing step in which a plurality of shielding tunnels are formed by irradiating the pulsed laser beam from the backside side of the workpiece in such a manner that the position between the position where the thickness is further away and the backside of the workpiece is processed. It consists of pores formed from the surface of the workpiece which are longer than the finishing thickness and shorter than the thickness of the workpiece, and an amorphous or metamorphic layer surrounding the pores; and in the implementation of the laser After the processing step, the back surface of the workpiece is ground to remove the upper end portion of the shielding tunnel and the workpiece is thinned to the finishing thickness. The processing method of the workpiece as claimed in claim 1, further comprising: a dividing step of applying an external force to the workpiece to divide the workpiece into individual wafers after the grinding step is performed.

Images