JP6494467B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a method for processing a wafer such as a semiconductor wafer or an optical device wafer.

  A wafer such as a silicon wafer or a sapphire wafer in which a plurality of devices such as IC, LSI, LED, etc. are partitioned by a dividing line and formed on the surface is divided into individual device chips by a processing apparatus. Widely used in various electronic devices such as mobile phones and personal computers.

  A dicing method using a cutting device called a dicing saw is widely used for dividing the wafer. In the dicing method, a wafer is cut by cutting a wafer into a wafer while rotating a cutting blade having a thickness of about 30 μm by solidifying abrasive grains such as diamond with a metal or a resin at a high speed of about 30000 rpm. Divide into chips.

  On the other hand, in recent years, a method of dividing a wafer into individual device chips using a laser beam has been developed and put into practical use. In particular, a method in which a wafer is irradiated with a laser beam so as to be focused inside the wafer, a modified layer is formed inside the wafer, an external force is applied, and the wafer is divided into device chips using the modified layer as a rupture starting point. Then, there is no generation of machining waste, and there are merits such as narrowing of the cut line and anhydrous machining as compared with dicing by a cutting blade that has been generally used conventionally.

  In addition, the dicing method by laser beam irradiation has an advantage that a wafer having a structure in which streets (division lines to be divided) represented by a projection wafer are discontinuous can be processed (for example, JP 2010-123723 A). reference). In the processing of a wafer in which the division lines are discontinuous, the laser beam output is turned ON / OFF according to the setting of the division lines.

JP 2010-123723 A JP 2009-184002 A

  However, in the vicinity of the intersection where the planned division line extending in the second direction hits the planned division line extending in the first direction, a part of the laser beam that processes the other division planned line in the modified layer already formed May cause reflection or scattering of the laser beam, and light leaks into the device region, which may damage the device.

  Therefore, a processing method is proposed in Patent Document 2 in which the output of the laser beam is reduced or stopped on the near side of the intersection and a non-processed portion is left in the vicinity of the intersection. However, in this processing method, since there is no modified layer in the non-processed portion, there is a problem that when the wafer is divided into device chips, oblique cracking of the chips may occur.

  The present invention has been made in view of such a point, and the object of the present invention is to perform laser processing on a wafer on which at least one of the planned division lines is discontinuously formed. Suppresses the laser beam from being applied to the modified layer already formed near the intersection where the end hits the other split line, prevents reflection or scattering of the laser beam at the modified layer, and damages the device It is an object of the present invention to provide a wafer processing method capable of preventing the above.

  According to the present invention, each divided by a plurality of first division planned lines formed in the first direction and a plurality of second division planned lines formed in the second direction intersecting the first direction. A device is formed in a region, and at least the second scheduled division line and the second scheduled division line at least the second scheduled division line are formed discontinuously, the first and first A wafer processing method for forming a modified layer along a line to be divided into two, and condensing a laser beam having a wavelength that is transmissive to the wafer along the first line to be divided into the wafer. Irradiating and forming a first modified layer forming step for forming a first modified layer along the first division planned line inside the wafer, and the first end of the extending direction abuts against the first division planned line Along the split line Formation of a second modified layer for condensing and irradiating the inside of the wafer with a laser beam having a wavelength that is transparent to the wafer, thereby forming a second modified layer along the second scheduled division line inside the wafer A spot shape of the laser beam irradiated on the wafer in the second modified layer forming step, the length in a direction parallel to the second planned division line is parallel to the first planned division line There is provided a method of processing a wafer characterized in that the wafer is shaped shorter than the length of the wafer.

  Preferably, in the second modified layer forming step, the laser beam is shaped by blocking both ends in the extending direction of the second scheduled division line by slits that pass before focusing. Alternatively, in the second modified layer forming step, the laser beam is shaped into an ellipse having a major axis in the extension direction of the first planned division line.

  Preferably, in the second modified layer forming step, the energy of the laser beam is reduced just before the intersection of the first scheduled division line and the second scheduled division line when viewed from the scanning direction of the laser beam. Is done.

  According to the wafer processing method of the present invention, the laser beam spot irradiated in the second modified layer forming step is shaped so as to block both ends in the extending direction of the second modified layer, thereby dividing the second division schedule. When processing the front side of the intersection where the end of the line hits the first division planned line, it is possible to prevent the first modified layer that has already been formed from being irradiated with a part of the laser beam. It is possible to prevent the laser beam from being reflected or scattered by one modified layer and damaging the device.

It is a perspective view which shows a mode that the wafer unit was hold | maintained at the chuck table of the laser processing apparatus. It is a block diagram of a laser beam generation unit. It is typical sectional drawing which shows a 1st modified layer formation step. It is typical sectional drawing which shows a 2nd modified layer formation step. FIG. 5A is a schematic enlarged sectional view showing a second modified layer forming step, and FIG. 5B is a schematic plan view of FIG. 6A is a schematic enlarged sectional view showing a conventional second modified layer forming step, and FIG. 6B is a schematic plan view of FIG. 6A. It is a partial cross section typical side view explaining the shaping method of the spot of the laser beam of 1st Embodiment. It is a typical side view explaining the shaping method of the spot of the laser beam of 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, a perspective view of a state in which a wafer unit 12 is held on a chuck table 10 of a laser processing apparatus is shown. The wafer unit 12 is configured by adhering a surface 11a of a semiconductor wafer (hereinafter sometimes simply referred to as a wafer) 11 to a dicing tape T which is an adhesive tape having an outer peripheral portion attached to an annular frame F. ing. In the state shown in FIG. 1, the back surface 11b of the wafer 11 is exposed upward.

  On the surface 11a of the wafer 11, a plurality of first division lines 13a formed continuously in the first direction and a plurality of second divisions formed discontinuously in a direction orthogonal to the first division lines 13a. A scheduled line 13b is formed, and a device 15 such as an LSI is formed in an area partitioned by the first scheduled division line 13a and the second scheduled division line 13b.

  Incidentally, the wafer 11 to be processed by the wafer processing method of the present invention is not limited to a semiconductor wafer, but an LED, a region divided by the first scheduled division line 13a and the second scheduled division line 13b, A wafer such as an optical device wafer on which an optical device such as an LD is formed is also included.

  In the wafer processing method of this embodiment, first, as shown in FIG. 1, a holding step is performed in which the wafer 11 of the wafer unit 12 is sucked and held via the dicing tape T by the chuck table 10 of the laser processing apparatus. Although not particularly illustrated, the annular frame F of the wafer unit 12 is clamped and fixed by a clamp (not shown).

  The wafer 11 held on the chuck table 10 in this way is irradiated with a laser beam LB having a wavelength that is transmissive to the wafer 11 by condensing the inside of the wafer by the condenser 14, and the first division planned line. A first modified layer or a second modified layer is formed inside the wafer along the line 13a or the second division line 13b.

  Referring to FIG. 2, a block diagram of the laser beam generating unit 16 is shown. The laser beam generating unit 16 repeatedly includes a laser oscillator 18 such as a YAG laser oscillator or a YVO4 laser oscillator that oscillates a pulse laser with a wavelength of 1064 nm, and the like. Frequency setting means 20, pulse width adjustment means 22, and power adjustment means 24 for adjusting the power of the pulse laser beam oscillated from the laser oscillator 18 are included.

  The laser beam LB adjusted to a predetermined power by the power adjusting means 24 of the laser beam generating unit 16 is condensed and irradiated inside the wafer 11 by the condenser 14 shown in FIG.

  Although not particularly shown, in the wafer processing method of the present invention, first, the wafer 11 sucked and held by the chuck table 10 is positioned immediately below an imaging unit (not shown) of the laser processing apparatus, and the wafer 11 is imaged by the imaging unit. The alignment which aligns the 1st division | segmentation scheduled line 13a with the collector 14 in the X-axis direction is implemented.

  Next, after the chuck table 10 is rotated by 90 °, the same alignment is performed on the second scheduled division line 13b extending in the direction orthogonal to the first scheduled division line 13a, and the alignment data is transferred to the controller of the laser processing apparatus. Stored in the RAM.

  Since the imaging unit of the laser processing apparatus normally includes an infrared camera, the infrared camera captures the first and second scheduled division lines 13a and 13b formed on the front surface 11a through the wafer 11 from the back surface 11b side of the wafer 11. Can be detected.

  After the alignment, a first modified layer forming step for forming the first modified layer 17 in the wafer 11 along the first division planned line 13a is performed. In this first modified layer forming step, as shown in FIG. 3, a condensing point having a wavelength (for example, 1064 nm) having transparency to the wafer is positioned inside the wafer 11 by the condenser 14, and the wafer 11 By irradiating the first division line 13a from the back surface 11b side of the wafer and processing and feeding the chuck table 10 in the direction of the arrow X1, the first modified layer 17 along the first division line 13a is formed inside the wafer 11. Form.

  Preferably, the concentrator 14 is moved upward in a stepwise manner, and a plurality of first modified layers 17, for example, three first modified layers, along the first division planned line 13 a inside the wafer 11. 17 is formed.

  The modified layer 17 is a region in which density, refractive index, mechanical strength, and other physical characteristics are different from the surroundings, and is formed as a melt-resolidified layer. The processing conditions in the first modified layer forming step are set as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1064 nm
Repetition frequency: 100 kHz
Pulse output: 10μJ
Condensing spot diameter: φ1μm
Processing feed rate: 500 mm / s

After performing the first modified layer forming step, the end portion in the extending direction (extension direction) is permeable to the wafer 11 along the second scheduled division line 13b that abuts on the first scheduled division line 13a. Formation of a second modified layer for condensing and irradiating a laser beam having a wavelength (for example, 1064 nm) inside the wafer 11 to form a second modified layer 19 along the second division planned line 13b inside the wafer 11 Perform the steps.

  In this second modified layer forming step, after completion of the first modified layer forming step, the chuck table 10 is rotated by 90 °, and then the laser beam LB is focused from the back surface 11b side of the wafer 11 as shown in FIG. By irradiating the point positioned inside the wafer 11 corresponding to the second scheduled division line 13b, and feeding the chuck table 10 in the direction of the arrow X1, the second along the second scheduled division line 13b is introduced into the wafer 11. 2 The modified layer 19 is formed. In the present embodiment, the second modified layer 19 having three layers is formed inside the wafer 11 by moving the condenser 10 upward stepwise.

  The wafer processing method of the present invention is characterized by this second modified layer forming step. First, the first feature is that when the second modified layer forming step is performed, the length of the beam spot parallel to the second scheduled division line 13b is set to be longer than the length of the beam spot parallel to the first scheduled division line 13a. Is to irradiate the wafer 11 with the laser beam LB shaped to be shorter.

  A first embodiment of the method of shaping the spot of the laser beam LB will be described with reference to FIG. In the spot shaping method of the first embodiment, a mask 26 having a long slit 28 is disposed between the laser beam generating unit 16 and the condenser 14.

  The spot shape of the laser beam LB emitted from the laser beam generating unit 16 is circular as indicated by reference numeral 34, but the spot shape of the laser beam LB after passing through the slit 28 is the upper end and lower end of the spot 34. The portion is blocked by the mask 26 and shaped into the shape indicated by the reference numeral 36.

  The laser beam LB having the spot 36 is reflected by the mirror 36 of the condenser 14 and then condensed by the condenser lens 32 inside the wafer 11 held on the chuck table 10.

  As shown in FIG. 5B, the spot shape of the laser beam LB when irradiating the wafer 11 has a length parallel to the second division planned line 13b and a length parallel to the first division planned line 13a. The shorter spot 36 is formed. In other words, the shape of the spot 36 is shaped so that the width in the direction parallel to the second planned division line 13b is narrower than the width in the direction parallel to the first planned division line 13a.

  As shown in FIG. 5A, when the second modified layer 19 is formed along the second division line 13b where the end in the extending direction (extension direction) abuts against the first division line 13a, At the end of the second modified layer 19, the irradiation of the laser beam LB emitted from the condenser 14 is stopped, and the formation of the second modified layer 19 is stopped before the first modified layer 17.

  At this time, since the laser beam LB irradiated to the wafer 11 has the spot shape as described above, a part of the laser beam LB is prevented from being irradiated to the first modified layer 17 already formed. It is possible to prevent the laser beam LB from being reflected or scattered by the modified layer 17 and damaging the device 15.

  The laser beam irradiation is stopped by, for example, inserting an unillustrated acousto-optic element (AOD: Acoustic-Optic Defector) between the laser beam generating unit 16 and the condenser 14, and selectively applying a voltage to the AOD. Can be achieved by diverting the optical path of the laser beam LB from the condenser 14.

  A second embodiment of a method for correcting the laser beam LB irradiated in the second modified layer forming step will be described with reference to FIG. In the second embodiment, a condenser 14A having a built-in cylindrical lens unit 38 is used.

  The cylindrical lens unit 38 is arranged so as to be movable in the vertical direction, and the spot shape of the laser beam after passing through the cylindrical lens unit 38 is shaped into an ellipse that is long in the Y-axis direction as indicated by reference numeral 40. Even when the second modified layer forming step is performed by irradiating the wafer 11 with the laser beam having the elliptical beam spot 40 as described above, the laser beam having the beam spot 36 of the first embodiment is the same as that described above. The effect can be achieved.

  Although not particularly illustrated, it is preferable that the second modified layer 19 is also formed in a plurality of layers (for example, three layers) inside the wafer 11, similarly to the first modified layer 17. The laser processing conditions in the second modified layer forming step are the same as the processing conditions in the first modified layer forming step described above.

  Next, problems of the conventional method will be described with reference to FIG. In the conventional second modified layer forming step, the second modified layer forming step is performed using a laser beam having a circular spot 34.

  In this case, a part of the laser beam LB irradiated from the condenser 14 is irradiated to the already formed first modified layer 17, and the laser beam is reflected or scattered by the first modified layer 17. As shown in FIG. 5B, there is a problem that the device 15 formed on the surface 11a of the wafer 11 may be irradiated to damage the device 15. The present invention solves this problem by shaping the spot shape of the laser beam LB as described above.

  In the conventional second modified layer forming step, the output of the laser beam LB is stopped or reduced to some extent before the intersection of the first division planned line 13a and the second division planned line 13b, and the vicinity of the intersection is compared. Although there is an idea that the laser beam LB is not blocked by the first modified layer 17 by leaving a non-processed portion in a long region, the device 15 is prevented from being damaged. Since the second modified layer 19 is not formed, there is a problem that it is difficult to divide the wafer 11 into device chips or the divided device chips are broken obliquely. It is not desirable to take it.

  The second feature of the second modified layer forming step is that the energy of the irradiated laser beam is reduced on the front side of the intersection where the second scheduled division line 13b hits the first scheduled division line 13a.

  By controlling in this way, even when the spot shape of the laser beam is shaped as described above, in the unlikely event that a part of the laser beam LB is already irradiated to the first modified layer 17, Since the energy reflected or scattered by the first modified layer 17 is small, damage to the device 15 can be reduced.

  The control to reduce the energy of the laser beam irradiated in the second modified layer forming step only needs to be before the intersection where the end of the second scheduled division line 13b hits the first scheduled division line 13a. The energy of the laser beam LB does not need to be reduced at a point where the second scheduled division line 13b intersects the first scheduled division line 13a.

  In the wafer processing method according to the above-described embodiment, the example of shaping the spot shape of the laser beam irradiated in the second modified layer forming step as described above has been described. Even when the first modified layer 17 is formed, the laser beam shaped as described above may be irradiated.

DESCRIPTION OF SYMBOLS 11 Semiconductor wafer 12 Wafer unit 13a 1st division planned line 13b 2nd division planned line 14 Condenser 15 Device 16 Laser beam generating unit 17 1st modified layer 19 2nd modified layer 26 Mask 28 Slit 38 Cylindrical lens unit

Claims (4)

A device is formed in each region defined by a plurality of first division lines formed in the first direction and a plurality of second division lines formed in the second direction intersecting the first direction. And, with respect to a wafer in which at least the second division planned line is formed discontinuously among the first division planned line and the second division planned line, the first and second division planned lines are formed inside the wafer. A wafer processing method for forming a modified layer along the surface,
A laser beam having a wavelength that is transparent to the wafer along the first division line is condensed and irradiated inside the wafer, and the first modified layer along the first division line is irradiated inside the wafer. A first modified layer forming step of forming
A laser beam having a wavelength that is transmissive to the wafer is focused and irradiated along the second division line where the end in the extending direction hits the first division line. A second modified layer forming step for forming a second modified layer along the second division planned line inside,
The spot shape of the laser beam irradiated to the wafer in the second modified layer forming step is shaped so that the length in the direction parallel to the second planned division line is shorter than the length in the direction parallel to the first planned division line. A wafer processing method characterized by the above.   2. The wafer processing method according to claim 1, wherein, in the second modified layer forming step, the laser beam is shaped by blocking both ends in the extending direction of the second scheduled division line by slits that pass before focusing. 3. .   2. The wafer processing method according to claim 1, wherein, in the second modified layer forming step, the laser beam is shaped into an ellipse having a major axis in an extending direction of the first division line. 3.   In the second modified layer forming step, the energy of the laser beam is reduced before the intersection of the first scheduled division line and the second scheduled division line as viewed from the scanning direction of the laser beam. Item 4. A method for processing a wafer according to any one of Items 1 to 3.

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