JP5839383B2 - Wafer processing method - Google Patents

Description

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

  A wafer such as a silicon wafer or 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 electrical equipment 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 a metal or a resin at a high speed of about 30000 rpm. Divide into

  On the other hand, in recent years, a laser processing groove is formed by irradiating a wafer with a pulsed laser beam having a wavelength that absorbs the wafer, and an external force is applied to the wafer by a braking device along the laser processing groove. A method of cleaving a wafer and dividing it into individual devices has been proposed (see, for example, Japanese Patent Laid-Open No. 10-305420).

  The formation of the laser processing groove by the laser processing apparatus can increase the processing speed as compared with the dicing method using the dicer, and relatively easily processes even a wafer made of a material having high hardness such as sapphire or SiC. be able to. Further, since the processing groove can be made narrow, for example, 10 μm or less, the amount of devices taken per wafer can be increased as compared with the case of processing by the dicing method.

  In the processing of a wafer by a laser processing apparatus, the wafer is attached to a dicing tape whose outer peripheral portion is attached to an annular frame, and the wafer is supported by the annular frame via the dicing tape. Then, the laser beam is irradiated in a state where the wafer is sucked and held via the dicing tape on the chuck table of the laser processing apparatus.

  At the time of laser processing, the laser beam is also applied to the outer peripheral surplus area on the extension line of the planned division line so that the wafer is smoothly divided, thereby forming a laser processing groove (divided groove).

JP-A-10-305420 JP 2007-214266 A

  As described above, the laser beam is also irradiated to the outer peripheral surplus area on the extension line of the planned dividing line so that the wafer can be divided smoothly, and further, the processing feed of the chuck table cannot be stopped suddenly. The run laser beam is also applied to the dicing tape.

  When the laser beam overrunning the wafer is irradiated onto the dicing tape as described above, there is a problem that the dicing tape is melted and oxidized to damage the chucking surface of the chuck table.

  The present invention has been made in view of these points, and the object of the present invention is to provide a wafer that does not melt and oxidize the dicing tape even if the laser beam overruns the wafer during laser processing of the wafer. It is to provide a processing method.

According to the present invention, there is provided a wafer processing method comprising a device region formed by dividing a plurality of devices by division-scheduled lines and an outer peripheral surplus region surrounding the device region, wherein the wafer back surface has an outer periphery. A part of which is attached to a dicing tape attached to an annular frame and a wafer is supported by the annular frame through the dicing tape, and a wafer supported by the annular frame is chucked by the laser processing apparatus through the dicing tape. A holding step of sucking and holding the table, and a pulse laser beam having a wavelength that is absorptive with respect to the wafer having the first intensity is applied to the region corresponding to the division line to divide the wafer surface to the first depth. a dividing groove forming step of forming a groove, the irradiation position of the pulse laser beam of the boundary between the device region and the outer peripheral marginal area A pulsed laser beam having an absorption wavelength to the second intensity of the wafer to the peripheral marginal region of the extension of the dividing line does not melt the dicing tape lower than the intensity of the first upon reaching a target position And a guide groove forming step of forming a guide groove having a second depth shallower than the first depth for inducing division by irradiation.

  According to the wafer processing method of the present invention, a guide groove for inducing division by irradiating a laser beam having a relatively low intensity that does not melt the dicing tape is formed in the outer peripheral surplus area on the extension line of the planned division line. Since the wafer is smoothly divided and the dicing tape does not melt and oxidize even if the laser beam overruns the wafer, the problem of damaging the chucking surface of the chuck table can be solved.

It is a perspective view of a laser processing apparatus. It is a surface side perspective view of the wafer supported by the annular frame via the dicing tape. It is a block diagram of a laser beam irradiation unit. It is a perspective view explaining a division slot and a guide slot formation process. It is a partial cross section side view explaining a division groove and a guide groove formation process. It is a perspective view of the wafer supported by the annular frame via the dicing tape in the state where the laser processing method is completed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic configuration diagram of a laser processing apparatus 2 suitable for carrying out the wafer processing method of the present invention. The laser processing apparatus 2 includes a first slide block 6 mounted on a stationary base 4 so as to be movable in the X-axis direction.

  The first slide block 6 is moved along the pair of guide rails 14 in the machining feed direction, that is, the X-axis direction, by the machining feed means 12 including the ball screw 8 and the pulse motor 10.

  A second slide block 16 is mounted on the first slide block 6 so as to be movable in the Y-axis direction. That is, the second slide block 16 is moved in the indexing direction, that is, the Y-axis direction along the pair of guide rails 24 by the indexing feeding means 22 constituted by the ball screw 18 and the pulse motor 20.

  A chuck table 28 is mounted on the second slide block 16 via a cylindrical support member 26, and the chuck table 28 can be moved in the X-axis direction and the Y-axis direction by the processing feed means 12 and the index feed means 22. . The chuck table 28 is provided with a clamp 30 for clamping the wafer sucked and held by the chuck table 28.

  A column 32 is erected on the stationary base 4, and a casing 35 for accommodating the laser beam irradiation unit 34 is attached to the column 32. As shown in FIG. 3, the laser beam irradiation unit 34 includes a laser oscillator 62 that oscillates a YAG laser or a YVO4 laser, a repetition frequency setting unit 64, a pulse width adjustment unit 66, and a power adjustment unit 68. .

  The pulse laser beam adjusted to a predetermined power by the power adjusting means 68 of the laser beam irradiation unit 34 is reflected by the mirror 70 of the condenser 36 attached to the tip of the casing 35 and further collected by the condenser objective lens 72. The wafer 11 is irradiated with light and applied to the chuck table 28.

  At the tip of the casing 35, an image pickup means 38 for detecting a processing region to be laser processed aligned with the condenser 36 in the X-axis direction is disposed. The image pickup means 38 includes an image pickup element such as a normal CCD that picks up an image of a processing region of a semiconductor wafer with visible light.

  The imaging unit 38 further includes an infrared irradiation unit that irradiates the semiconductor wafer with infrared rays, an optical system that captures the 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 imaging means composed of an infrared imaging element such as the above is included, and the captured image signal is transmitted to a controller (control means) 40.

  The controller 40 includes a central processing unit (CPU) 42 that performs arithmetic processing according to a control program, a read-only memory (ROM) 44 that stores a control program, and a random read / write that stores arithmetic results. An access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52 are provided.

  Reference numeral 56 denotes a processing feed amount detection means comprising a linear scale 54 disposed along the guide rail 14 and a read head (not shown) disposed on the first slide block 6. Is input to the input interface 50 of the controller 40.

  Reference numeral 60 denotes index feed amount detection means comprising a linear scale 58 disposed along the guide rail 24 and a read head (not shown) disposed on the second slide block 16. The detection signal is input to the input interface 50 of the controller 40.

  An image signal picked up by the image pickup means 38 is also input to the input interface 50 of the controller 40. On the other hand, a control signal is output from the output interface 52 of the controller 40 to the pulse motor 10, the pulse motor 20, the laser beam irradiation unit 34, and the like.

  As shown in FIG. 2, on the surface 11 a of the wafer 11 to be processed by the laser processing apparatus 2, a plurality of streets (division planned lines) 13 are formed orthogonally and are partitioned by the orthogonal streets 13. A device 15 is formed in each region. The wafer 11 includes a device region 17 in which a large number of devices 15 are formed, and an outer peripheral surplus region 19 surrounding the device region 17 on the surface 11a.

  The back surface 11 b of the wafer 11 is attached to a dicing tape T that is an adhesive tape, and the outer peripheral portion of the dicing tape T is attached to an annular frame F. As a result, the wafer 11 is supported by the annular frame F via the dicing tape T. During laser processing, the wafer 11 is sucked and held by the chuck table 28 via the dicing tape T, and the annular frame F is held by the clamp 30. Clamped and fixed.

  Next, a wafer processing method according to an embodiment of the present invention will be described in detail with reference to FIGS. First, a pattern for imaging the processing region of the wafer 11 with the imaging unit 38 and aligning the condenser 36 of the laser beam irradiation unit 34 that irradiates the laser beam with the street 13 extending in the first direction. Image processing such as matching is executed to align the laser beam irradiation position. Next, the chuck table 28 is rotated by 90 degrees, and the alignment between the street 13 extending in the second direction and the condenser 28 is performed.

  In addition, the entire image of the wafer 11 is picked up by the image pickup means 38, and the coordinates (X, Y coordinates) of the intersections of all the streets 13 extending in the first direction and the outer periphery of the wafer 11 are detected. It is stored in 40 RAMs 46. Next, the coordinates of the intersections of all the streets 13 extending in the second direction and the outer periphery of the wafer 11 are detected, and the coordinates are stored in the RAM 46 of the controller 40.

  Further, the coordinate position of the boundary line between the device area 17 and the outer peripheral surplus area 19 of the wafer 11 is also detected for each street 13, and these coordinate positions are stored in the RAM 46 of the controller 40.

  When the alignment and the detection of each coordinate position are completed, as shown in FIG. 4, a pulsed laser beam having a wavelength that is absorptive with respect to the wafer 11 with a first output is passed through the condenser 36 as shown in FIG. Irradiation is started from one end of the street 13 to be machined 11, the chuck table 28 is moved at a predetermined machining feed rate in the direction indicated by the arrow X 1, and the dividing groove 74 is formed along the street 13.

  When the irradiation position of the laser beam reaches the coordinate position of the boundary between the device region 17 and the outer peripheral surplus region 19, the output of the laser beam is lowered to a second output lower than the first output, and the predetermined processing described above is performed. When the chuck table 28 is moved in the X1 direction at the feeding speed to form the guide groove 76 that guides the division to the outer peripheral surplus area 19, and the irradiation position of the laser beam reaches the other end of the wafer on the extension line of the street 13, The irradiation of the pulse laser beam is stopped and the movement of the chuck table 28 is stopped.

  That is, as shown in the partial cross-sectional side view of FIG. 5, in the split groove forming process indicated by arrow A, the split grooves 74 are formed by irradiating the first output laser beam along the streets 13 of the device region 17. In the guide groove forming step indicated by the arrow B, the guide groove 76 that guides the division by irradiating the outer peripheral surplus region 19 on the extension line of the street 13 with the laser beam having the second output lower than the first output is formed. .

  The movement of the chuck table 28 is controlled to stop at the end of the wafer 11 (the right end in FIG. 5). However, since the chuck table 28 cannot be stopped suddenly due to its inertia, the laser beam emitted from the condenser 36 is used. Irradiates the dicing tape T after slightly overrunning the wafer 11.

  In this embodiment, since the output of the laser beam irradiated in the guide groove forming process indicated by the arrow B is adjusted to a relatively low second output that does not melt the dicing tape T, the laser that overruns the wafer 11. Even if the beam is applied to the dicing tape T, the dicing tape T is not melted and oxidized.

  If the divided groove forming step and the guide groove forming step described above are performed along all the streets 13 extending in the first direction, the chuck table 28 is rotated by 90 degrees and then all extended in the second direction. The divided groove forming step and the guide groove forming step are performed along the street 13. FIG. 6 shows a perspective view of the wafer 11 in a state where the dividing groove forming step and the guide groove forming step are performed along all the streets 13 in this way.

  The first laser processing condition example is as follows.

(A) Split groove forming step:
Light source: YAG laser Wavelength: 355 nm (third harmonic of YAG laser)
Average output: 1.5W
Processing depth: 25 μm
Repetition frequency: 100 kHz
Spot diameter: 5 μm
Feeding speed: 150mm / s

(B) Guide groove forming step:
Light source: YAG laser Wavelength: 355 nm (third harmonic of YAG laser)
Average output: 0.5W
Processing depth: 10 μm
Repetition frequency: 100 kHz
Spot diameter: 5 μm
Feeding speed: 150mm / s

  In the first processing condition example described above, the average output of the laser beam in the guide groove forming step is reduced to 1/3 of the average output of the laser beam in the split groove forming step. All are the same.

  The second laser processing condition example is as follows.

(A) Split groove forming step:
Light source: YAG laser Wavelength: 355 nm (third harmonic of YAG laser)
Average output: 1.5W
Processing depth: 25 μm
Repetition frequency: 100 kHz
Spot diameter: 5 μm
Feeding speed: 150mm / s

(B) Guide groove forming step:
Light source: YAG laser Wavelength: 355 nm (third harmonic of YAG laser)
Average output: 1.5W
Processing depth: 10 μm
Repetition frequency: 100 kHz
Spot diameter: 5 μm
Feeding speed: 300mm / s

  In the second processing condition example described above, the average output of the guide groove forming process and the average output of the split groove forming process are maintained at the same output, and the feed speed of the guide groove forming process is twice the feed speed of the split groove forming process. The speed is increased.

  The intensity of the laser beam can also be reduced by increasing the feed speed in the guide groove forming process from the feed speed in the split groove forming process without changing the average output in this way. Even if the dicing tape T is irradiated with the overrun, the dicing tape T is not melted and oxidized. As a result, the problem of damaging the suction surface of the chuck table 28 can be solved.

  In short, in the wafer processing method of the present invention, it is important to control the intensity of the laser beam in the guide groove forming process to be lower than the intensity of the laser beam in the divided groove forming process. In order to control the intensity of the laser beam low, the laser beam output in the guide groove forming process is set lower than the laser beam output in the split groove forming process, or the laser beam having the same output is irradiated in both processes. The feed speed in the guide groove forming step may be controlled to be higher than the feed speed in the divided groove forming process.

T Dicing tape F Annular frame 2 Laser processing equipment 11 Wafer 13 Scheduled line (street)
15 Device 17 Device area 19 Peripheral surplus area 28 Chuck table 34 Laser beam irradiation unit 36 Concentrator 74 Dividing groove 76 Guide groove

Claims (1)

A wafer processing method comprising a device region formed by dividing a plurality of devices by division-scheduled lines and an outer peripheral surplus region surrounding the device region on the surface,
A supporting step of attaching the back surface of the wafer to a dicing tape whose outer peripheral portion is attached to an annular frame, and supporting the wafer with the annular frame via the dicing tape;
A holding step of sucking and holding the wafer supported by the annular frame with a chuck table of a laser processing apparatus via a dicing tape;
A split groove forming step of forming a split groove having a first depth on the surface of the wafer by irradiating a region corresponding to the planned split line with a pulse laser beam having a wavelength that is absorptive to the first intensity wafer ; ,
When the irradiation position of the pulse laser beam reaches the coordinate position of the boundary between the device region and the outer peripheral surplus region, the dicing tape is melted to be lower than the first intensity in the outer peripheral surplus region on the extension line of the planned division line. A guide groove forming step of forming a guide groove having a second depth shallower than the first depth for inducing division by irradiating a wafer having a second absorption intensity with a pulsed laser beam having an absorption wavelength . When,
A wafer processing method characterized by comprising:

Images