JP2015095497A - Laser processing method of wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing method of a wafer that can reduce a risk to wrongly detect a modified layer formed inside the wafer.SOLUTION: A laser processing method of a wafer includes: a first imaging step which detects a scheduled split line 13 and obtains a first captured image by infrared ray imaging means from a rear surface of the wafer; a modified layer formation step which, after the first imaging step, irradiates a laser beam of a wavelength having a transmissivity through the wafer from the rear surface side of the wafer with a light condensing point set in the inside near the surface of the wafer and forms a modified layer 21 in the inside near the wafer surface; a second imaging step which, after the modified layer is formed along at least a part of the scheduled split line, detects the scheduled split lines where the modified layers are formed, and obtains a second captured image by the infrared ray imaging means from the rear surface of the wafer; and a modified layer clarifying step which contrasts the first captured image with the second captured image, extracts a part which is not common, and clarifies the modified layers.

Description

  The present invention relates to a wafer laser processing method.

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

  A dicing method using a cutting device called a dicer 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 metal or resin at a high speed of about 30000 rpm. Into device chips.

  On the other hand, in recent years, as a method of dividing a semiconductor wafer or an optical device wafer into individual device chips, a laser beam having a wavelength that is transparent to the wafer is irradiated along the planned dividing line, and a modified layer is formed inside the wafer. Is used to provide a break starting point and to divide a wafer into device chips from the break starting point by applying an external force.

  However, the method of dividing the wafer into individual device chips by applying an external force after forming a modified layer inside the wafer may reduce the bending strength of the device chip. In response to the demand for improving the bending strength, a processing method in which a modified layer is formed inside the wafer and then the back surface is ground to thin the wafer and divide it into individual device chips has begun to be put into practical use.

  According to this method, the narrowing street by laser processing, the risk of breakage of the thinned wafer due to the absence of the division process after grinding, and the modified layer can be removed by grinding to improve the bending strength. There are various advantages.

JP 2009-289773 A

  However, when forming a modified layer by laser beam irradiation, when confirming whether the modified layer is positioned at an appropriate position (predetermined position with respect to the line to be divided) Since the thin linear modified layer is very similar, the modified layer formed inside the wafer may be erroneously detected.

  The present invention has been made in view of such points, and an object of the present invention is to provide a wafer laser processing method capable of reducing erroneous detection of a modified layer formed inside a wafer. It is to be.

  According to the present invention, there is provided a wafer laser processing method for processing a wafer having a device formed in each region partitioned by a plurality of division lines formed in a lattice shape on the surface with a laser beam, the back surface of the wafer A wafer holding step in which the wafer is held on the holding surface of the chuck table, and after the wafer holding step, the vicinity of the division line is imaged from the back surface of the wafer by infrared imaging means, and the division line is A first imaging step for detecting and acquiring a first captured image; and after the first imaging step, a laser beam having a wavelength that is transparent to the wafer is focused on the interior of the wafer near the surface. And irradiating along the planned dividing line from the back side of the wafer to form a modified layer inside the wafer near the surface Forming a modified layer along at least a portion of the planned dividing line, and then imaging the vicinity of the planned dividing line from the back surface of the wafer by the infrared imaging means. The second imaging step of detecting the planned division line formed and acquiring the second captured image is compared with the first captured image and the second captured image, and a non-common part is extracted. And a modified layer clarification step for clarifying the modified layer. A wafer laser processing method is provided.

  Preferably, the wafer laser processing method further includes a modified layer determination step for determining whether the position of the modified layer is appropriate or the formation state of the modified layer is appropriate after the modified layer clarification step. .

  In the wafer laser processing method of the present invention, two images are obtained by first obtaining a captured image in the vicinity of the planned division line before forming the modified layer and comparing it with a captured image at a similar position after forming the modified layer. Since the non-common part of the image is specified as the modified layer, it is possible to reduce the possibility of misrecognizing the pattern and the modified layer formed in advance on the wafer.

  In addition, since the captured image before forming the modified layer can be acquired during the alignment operation for detecting the modified layer along the planned division line, it can be acquired without increasing the number of operations separately.

It is a perspective view which shows a mode that a protective tape is stuck on the surface of a semiconductor wafer. It is a perspective view which shows a wafer holding | maintenance step. FIG. 3A is a perspective view showing the first imaging step, and FIG. 3B is an enlarged view showing the first captured image. It is a perspective view which shows a modified layer formation step. It is a block diagram of a laser beam generation unit. FIG. 6A is a perspective view illustrating the second imaging step, and FIG. 6B is an enlarged view illustrating the second captured image. It is a figure explaining a modified layer identification step. It is a figure which shows the captured image which clarified the non-common part.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a perspective view showing a state in which a protective tape 17 is attached to a surface 11 a of a semiconductor wafer (hereinafter sometimes simply referred to as a wafer) 11.

  On the surface 11 a of the semiconductor wafer 11, devices 15 such as ICs and LSIs are formed in each region partitioned by a plurality of division lines (streets) 13 formed in a lattice shape. The semiconductor wafer 11 is made of, for example, a silicon wafer and has a thickness of about 700 μm.

  In the wafer laser processing method of the embodiment of the present invention, as shown in FIG. 2, first, a wafer holding step is performed in which the back surface of the wafer 11 is exposed and the wafer 11 is held by the holding surface of the chuck table 10 of the laser processing apparatus. .

  After performing the wafer holding step, the first imaging step is performed in which the vicinity of the division line 13 is imaged by the infrared imaging means from the back surface 11b of the wafer 11 to detect the division line 13 and acquire the first captured image. To do.

  This first imaging step will be described with reference to FIG. FIG. 3A is a perspective view showing the first imaging step, and FIG. 3B is an enlarged view showing the first captured image acquired in the first imaging step.

  In FIG. 3A, reference numeral 12 denotes a laser beam irradiation unit (laser beam irradiation means), which includes a laser beam generation unit 16 accommodated in a casing 14 and a condenser (laser head) mounted at the tip of the casing 14. ) 18.

  An imaging unit (imaging means) 20 is attached to the casing 14, and the imaging unit 20 includes a microscope that images a processing region of the semiconductor wafer 11 with visible light and an imaging element such as a normal CCD.

  The imaging unit 20 further includes an infrared irradiation unit that irradiates the wafer 11 with infrared rays, an optical system that captures infrared rays irradiated by the infrared irradiation unit, and an infrared CCD that outputs an electrical signal corresponding to the infrared rays captured by the optical system. Infrared image pickup means composed of an infrared image pickup device such as the above is included, and the picked up image signal is transmitted to a controller (control means) (not shown) of the laser processing apparatus.

  As shown in FIG. 5, the laser beam generation unit 16 includes a laser oscillator 22 that oscillates a YAG pulse laser or a YVO4 pulse laser, a repetition frequency setting unit 24, a pulse width adjustment unit 26, and a power adjustment unit 28. It is out. Although not particularly illustrated, the laser oscillator 22 has a Brewster window, and the laser beam emitted from the laser oscillator 22 is a linearly polarized laser beam.

  The pulsed laser beam adjusted to a predetermined power by the power adjusting means 28 of the laser beam generating unit 16 is reflected by the mirror 30 of the condenser 18 and further condensed by the condenser objective lens 32 and held on the chuck table 10. The irradiated wafer 11 is irradiated to form a modified layer inside the wafer 11.

  Referring back to FIG. 3A, in the first imaging step, the vicinity of the division line 13 formed on the front surface 11a of the wafer 11 is imaged from the back surface 11b of the wafer 11 by the infrared imaging means of the imaging unit 20. While detecting the division | segmentation scheduled line 13, a 1st captured image is acquired.

  The first captured image is stored in the memory of the controller. This first imaging step can be performed at the same time in the alignment step of aligning the planned dividing line 13 on which the modified layer is to be formed with the condenser 18 in the processing feed direction.

  As shown in the enlarged view of FIG. 3B, for example, the first captured image acquired in the first imaging step is a TEG (Test Element) formed on the intersecting scheduled division line 13, the device 15, and the scheduled division line 13. Group) 19 is included.

  After carrying out the first imaging step, a laser beam having a wavelength that is transmissive to the wafer 11 is aligned along the planned division line 13 from the back surface 11b of the wafer 11 with the focal point aligned inside the wafer 11 near the front surface 11a. Then, a modified layer forming step for forming a modified layer inside the wafer 11 near the surface 11a is performed.

  This modified layer forming step will be described with reference to FIG. In the modified layer forming step, a condensing point of a laser beam having a wavelength (for example, 1064 nm) having transparency with respect to the wafer 11 is positioned inside the surface 11a of the wafer 11 corresponding to the planned division line 13 and the chuck table. While moving 10 in the direction of arrow X1 or arrow X2, a laser beam is irradiated from the back surface 11b of the wafer 11 along the planned dividing line 13 to form a modified layer 21 in the interior near the surface 11a of the wafer 11. .

  Although not specifically shown, the chuck table 10 is alternately processed and fed in the direction of the arrow X1 and the arrow X2 by the processing feed means, and is further indexed by the pitch of the planned dividing line 13 in the indexing feed direction orthogonal to the machining feed direction. While being fed, the modified layer 21 is formed one after another in the vicinity of the surface 11a of the wafer 11 along the planned division line 13 extending in the first direction. Next, after the chuck table 10 is rotated by 90 °, a similar modified layer 21 is formed inside the wafer 11 along the planned division line 13 extending in the second direction orthogonal to the first direction.

  The laser processing conditions in the modified layer forming step are, for example, as follows.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1064 nm
Average output: 1W
Pulse width: 40 ns
Condensing spot diameter: φ1μm
Repetition frequency: 100 kHz
Processing feed rate: 100 mm / s

  In the wafer laser processing method of this embodiment, after forming the modified layer 21 along at least a part of the division lines 13, as shown in FIG. 6A, infrared imaging means is applied from the back surface 11b of the wafer 11. In this way, the vicinity of the planned division line 13 where the modified layer 21 is formed is imaged to detect the planned divided line 13 where the modified layer 21 is formed, and a second captured image as shown in FIG. To get.

  This second captured image includes the scheduled division line 13, the device 15, the TEG 19, and the modified layer 21 that intersect each other. The second captured image is stored in the memory of the controller of the laser processing apparatus. The part of the planned division lines 13 described above can be set as appropriate with five or ten planned division lines 13.

  Here, the focus of the image pickup unit 20 at the time of image pickup is adjusted to the surface 11a of the wafer 11 at the time of first image pickup and to the height position of the modified layer 21 at the time of second image pickup. To do. Since the difference in height between when the first captured image is captured and when the second captured image is captured is approximately 30 to 100 μm, captured images with no significant difference can be obtained.

  After the second imaging step, the first captured image shown in FIG. 7A is compared with the second captured image shown in FIG. 7B, and the non-common part is shown as shown by the solid line in FIG. The modified layer clarification step is performed to clarify the modified layer 21 by extracting.

  Preferably, after the modified layer clarification step is performed, a modified layer determination step for determining whether the position of the modified layer 21 is appropriate or the formation state of the modified layer 21 is appropriate is performed. If it is determined to be appropriate, the modified layer forming step is continued along the scheduled division line 13 where the modified layer is not formed.

  When it is determined that the determination step is inappropriate, after the correction step is performed, the modified layer forming step is continued along the scheduled division line 13 where the modified layer is not formed. In this correction step, for example, the chuck table holding the wafer 11 is moved slightly in the indexing and feeding direction so that the laser beam irradiation position by the condenser 18 is positioned at the center of the scheduled division line 13 or by the power adjusting means 28. The power of the laser beam is adjusted so that an appropriate modified layer 21 can be formed.

  When the modified layer 21 is formed in the vicinity of the surface 11 a of the wafer 11 along all the planned dividing lines 13, many microcracks extending from the modified layer 21 to the surface 11 a of the wafer 11 are generated.

  Therefore, when the back surface 11b of the wafer 11 is ground to a thickness that removes the modified layer 21, the wafer 11 can be divided into individual device chips 15 by grinding pressure.

10 Chuck Table 11 Semiconductor Wafer 12 Laser Beam Irradiation Unit 13 Line to be Divided 15 Device 17 Protective Tape 18 Condenser 19 TEG
20 Imaging unit (imaging means)
21 Modified layer

Claims (2)

A wafer laser processing method for processing a wafer in which a device is formed in each region partitioned by a plurality of division lines formed in a lattice shape on a surface with a laser beam,
A wafer holding step for exposing the back surface of the wafer and holding the wafer on the holding surface of the chuck table;
After the wafer holding step, a first imaging step of imaging the vicinity of the planned division line from the back surface of the wafer by infrared imaging means, detecting the planned division line and acquiring a first captured image;
After the first imaging step, a laser beam having a wavelength that is transmissive to the wafer is irradiated along the planned division line from the back side of the wafer with the focusing point inside the wafer near the surface. And a modified layer forming step for forming a modified layer in the interior of the wafer close to the surface;
After the modified layer is formed along at least a part of the planned dividing line, the vicinity of the planned dividing line is imaged from the back surface of the wafer by the infrared imaging means, and the planned divided line on which the modified layer is formed A second imaging step of detecting a second captured image and detecting a second captured image;
A modified layer clarification step of comparing the first captured image with the second captured image, extracting a non-common part, and clarifying the modified layer;
A wafer laser processing method characterized by comprising:   2. The wafer according to claim 1, further comprising a modified layer determination step for determining whether the position of the modified layer is appropriate or the formation state of the modified layer is appropriate after the modified layer clarification step. Laser processing method.

Images