TW201350238A - Laser processing apparatus and laser processing method (I) - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provides a laser processing apparatus and a laser processing method capable of implementing a uniform laser treatment without being affected by the status of laser irradiated surface of a work-piece. SOLUTION: A laser processing apparatus for performing laser treatment on the work-piece is characterized by comprising: a chuck table for holding the work-piece; a laser beam irradiation means comprising a laser oscillator and a processing head provided with a condenser for condensing the laser beam oscillated by the laser oscillator; a reflected light amount detection means for detecting the reflected light amount of laser beam irradiated by the laser beam irradiation means on the work-piece held on the chuck table; an output adjusting means for adjusting the output of laser beam oscillated by the laser oscillator in accordance with the reflected light amount detected by the reflected light amount detection means.

Description

Laser processing device and laser processing method (1) Field of invention

The present invention relates to a laser processing apparatus and a laser processing method for performing laser processing on a workpiece such as a semiconductor wafer.

Background of the invention

A plurality of components such as ICs, LSIs, and LEDs are divided into wafers such as tantalum wafers and sapphire wafers formed on a surface by dividing a predetermined line, and are divided into individual elements by a processing device, and the divided components are widely used. Various electronic devices such as mobile phones and computers.

In the case of wafer division, a cutting method using a cutting device called a cutter is widely used. In the dicing method, a cutting insert having a thickness of about 30 μm is fixed by grinding a grain of diamond or the like with a metal or a resin, and is rotated at a high speed of about 30,000 rpm to cut into a wafer, thereby cutting the wafer and dividing it into individual element wafers.

On the other hand, in recent years, a method of dividing a wafer into individual element wafers using a laser beam has been developed and put into practical use. A method of dividing a wafer into individual element wafers using a laser beam is known as the first and second processing methods described below.

The first processing method is to have a wavelength that is transparent to the wafer (for example) The concentrating point of the laser beam, such as 1064 nm, is positioned inside the wafer corresponding to the predetermined dividing line, and the laser beam is irradiated along the dividing line to form a modified layer inside the wafer, and then the crystal is formed by the dividing device. A method of dividing a wafer into individual element wafers by using a modified layer as a starting point for the division and external force (for example, refer to Japanese Patent No. 3408805).

In the second processing method, a light-converging point of a laser beam having a wavelength (for example, 355 nm) having an absorptivity to a wafer is irradiated to a region corresponding to a predetermined dividing line, and a processing groove is formed by a grinding process, and then an external force is applied to The processing groove is a method of dividing the wafer into individual element wafers by dividing the starting point (for example, refer to Japanese Patent Laid-Open No. Hei 10-305420).

The processing method using the laser beam can speed up the processing speed compared to the cutting method using the cutter, and the wafer made of a material having high hardness such as sapphire or SiC is relatively easy to process.

Further, since the modified layer or the processing groove can be made to have a narrow width of, for example, 10 μm or less, it is advantageous in that the amount of component per wafer can be increased with respect to the processing by the dicing method.

Further, an oxide film or a nitride film remains on the inner surface of the semiconductor wafer before the inner surface polishing is performed by the polishing apparatus. Further, there are also a semiconductor wafer having a Low-k film formed on its surface or a wafer having a metal film formed on its inner surface.

When laser processing is performed by irradiating a laser beam with the processed object to which the film is attached, a part of the laser beam irradiated by the film is reflected. The reflectance varies depending on the type and thickness of the film, and the reflectance of each workpiece is different or the reflectance is not uniform in one workpiece.

Being processed at a wavelength that is transparent to the workpiece In the first processing method in which the modified layer is formed inside the material, and in the second processing method in which the workpiece is subjected to the sharpening process by the wavelength at which the workpiece is absorbing, the reflectance of the workpiece is also large. The amount of light that is transmitted or absorbed by the laser beam is reduced, so in order to perform the desired laser processing, the output of the irradiated laser beam must be increased.

Advanced technical literature Patent literature

[Patent Document 1] Japanese Patent No. 3408805

[Patent Document 2] Japanese Patent Laid-Open No. 10-305420

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2009-021476

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2010-245172

Summary of invention

When the reflectance of each workpiece is different, when a plurality of workpieces are subjected to laser processing under a single processing condition, the depth of the laser processing formed by irradiating the laser beam between the workpieces is not Both, and there is a problem of unevenness of the reforming layer formed by irradiating the laser beam.

Further, when the reflectance is not uniform in one workpiece, when the laser processing is performed under a single processing condition, the depth of the laser processing structure formed by irradiating the laser beam due to the region is uneven, and The modified layer formed by irradiating the laser beam produces a problem of unevenness.

The present invention has been made in view of the above, and an object thereof is to provide a uniformity that can be performed without being affected by the state of a laser irradiation surface of a workpiece. Laser processing equipment for laser processing and laser processing methods.

According to the invention of claim 1, there is provided a laser processing apparatus which is a laser processing apparatus for performing laser processing on a workpiece, comprising: a chuck table for holding a workpiece; and a laser The beam irradiation means includes a laser oscillator and a processing head having a condensing mirror that converges the laser beam oscillated by the laser oscillator; and the reflected light amount detecting means detects that the laser beam irradiation means is irradiated to remain The amount of reflected light of the laser beam of the workpiece of the chuck table; and the output adjusting means adjust the output of the laser beam oscillated by the laser oscillator based on the amount of reflected light detected by the reflected light amount detecting means.

Preferably, the laser processing apparatus further includes a number-of-segment calculation means for calculating a thickness direction of the workpiece by the laser beam irradiation means based on the amount of reflected light detected by the reflected light amount detecting means. The number of segments of the laser processing that perform multiple segments.

According to the invention of claim 3, there is provided a laser processing method which is a laser processing method for performing laser processing on a workpiece, which comprises the steps of: maintaining a step of holding the workpiece in the chuck a laser beam irradiation step for detecting the amount of reflected light, the laser beam irradiation means irradiates the laser beam with the workpiece held by the chuck table under the first condition; and the reflected light amount detecting step is for detecting the amount of the reflected light Detecting the amount of reflected light of the reflected light reflected from the laser beam irradiated onto the workpiece by the laser beam irradiation step; and performing a laser processing step according to the reflected light amount detecting step after performing the reflected light amount detecting step The amount of reflected light detected is set to the output of the laser beam irradiated by the laser beam irradiation means The laser beam irradiation means irradiates the laser beam to the workpiece held on the chuck table under the second condition, and performs laser processing on the workpiece.

Preferably, the laser processing method further includes a number-of-segment calculation step of calculating a laser beam subjected to a plurality of sections including a thickness direction of the workpiece according to the amount of reflected light detected by the reflected light amount detecting step. In the laser processing step, the number of stages calculated by the number of stages is calculated, and the laser processing of the plurality of stages is performed in the thickness direction of the workpiece.

The laser processing apparatus of the present invention has a reflected light amount detecting means for detecting the amount of reflected light reflected on the workpiece, and an output adjustment for adjusting the output of the laser beam to be optimal according to the detected amount of reflected light. The means is therefore not subject to the laser irradiation surface condition of the workpiece, and uniform laser processing can be performed.

In the laser processing method of the present invention, the laser beam irradiation step for detecting the amount of reflected light is detected, the reflected light amount detecting step of detecting the amount of reflected light, and the output of the laser beam is set based on the amount of reflected light detected in the reflected light amount detecting step, and Since the workpiece is subjected to a laser processing step of laser processing, it is possible to perform uniform laser processing on the workpiece without being affected by the state of the laser irradiation surface of the workpiece.

2‧‧‧ Laser processing equipment

4‧‧‧Standing abutment

6‧‧‧1st sliding block

8‧‧‧Ball screws

10‧‧‧pulse motor

11‧‧‧Semiconductor wafer

11a‧‧‧ surface

11b‧‧‧ inside

12‧‧‧Processing means of feeding

13‧‧‧Division line

14‧‧‧ rails

15‧‧‧ components

16‧‧‧2nd sliding block

17‧‧‧Oxide film

18‧‧‧ Ball Screws

19‧‧‧Modified layer

20‧‧‧pulse motor

22‧‧‧Divided feeding means

24‧‧‧rail

26‧‧‧Support components

28‧‧‧ chuck table

30‧‧‧Clamp

32‧‧‧Cylinder

34‧‧‧Laser beam irradiation unit

35‧‧‧Shell

36‧‧‧Processing head

38‧‧‧ Shooting unit

40‧‧‧ Controller

42‧‧‧Central processing unit

44‧‧‧Read-only memory

46‧‧‧ Random access memory

48‧‧‧ counter

50‧‧‧Input interface

52‧‧‧Output interface

54‧‧‧linear scale

56‧‧‧Processing feed detection means

60‧‧‧Divided feed detection means

62‧‧‧Laser oscillation unit

64‧‧‧Laser oscillator

66‧‧‧Repetition frequency setting unit

68‧‧‧Output adjustment unit

69‧‧‧Laser beam

70‧‧‧shell

71‧‧‧ Reflected light

72‧‧‧Mirror

73‧‧‧ Related Relations

74‧‧‧Condenser

76‧‧‧Half mirror

78‧‧‧Reflected light detector

83‧‧‧ grinding wheel

84‧‧‧Rotary axis

86‧‧‧ wheel seat

88‧‧‧ grinding wheel

90‧‧‧ screws

92‧‧‧Circular abutments

94‧‧‧Martstone

96‧‧‧ chuck table

F‧‧‧Ring frame

T‧‧‧Adhesive tape

Figure 1 is a perspective view of a laser processing apparatus.

2 is a block diagram of an optical system of a laser beam irradiation unit.

3 is a perspective view of a surface side of a semiconductor wafer.

4 is an exploded perspective view showing a state in which a surface side of a semiconductor wafer is attached to an adhesive tape on which an outer peripheral portion is attached to an annular frame.

Figure 5 is a partial cross-sectional side view showing the holding step.

Fig. 6 is a partial cross-sectional side view showing a step of irradiating a laser beam for detecting reflected light amount.

Fig. 7 is a graph showing the correlation between the reflectance of the workpiece and the appropriate pulse energy.

Figure 8 is a partial cross-sectional side view showing a laser processing step of forming a modified layer inside a wafer.

Fig. 9 is a partial cross-sectional side view showing a step of irradiating a laser beam for detecting the amount of reflected light applied to the surface side of the wafer.

Fig. 10 is a partial cross-sectional side view showing an embodiment in which the amount of reflected light is detected and laser processing is performed.

Figure 11 is a perspective view showing the inner surface grinding step.

Detailed description of the preferred embodiment

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 is a perspective view showing the appearance of a laser processing apparatus according to an embodiment of the present invention. The laser processing apparatus 2 includes a first slider 6 that is mounted on the stationary base 4 so as to be movable in the X-axis direction.

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

The first slider 6 is mounted with a second slide that is movable in the Y-axis direction. Moving block 16. In other words, the second slider 16 is moved along the pair of guide rails 24 in the index feed direction, that is, the Y-axis direction by the index feed means 22 including the ball screw 18 and the pulse motor 20.

The chuck table 28 is mounted on the second slider 16 via the cylindrical support member 26, and the chuck table 28 can be oriented in the X-axis direction and the Y-axis by the machining feed means 12 and the index feeding means 22. Move in direction. The chuck table 28 is provided with a jig 30 for holding and holding the semiconductor wafer held by the chuck table 28.

The stationary base 4 is provided with a column 32 erected, and a laser beam irradiation unit 34 is mounted on the column 32. The laser beam irradiation unit 34 includes a laser oscillation unit 62 shown in FIG. 2 housed in the casing 35, and a machining head 36 attached to the front end of the casing 35.

The laser oscillation unit 62 is a laser oscillator 64 including an oscillating YAG laser or a YVO4 laser, and a repetition frequency setting unit 66 as shown in FIG. Although not specifically illustrated, the laser oscillator 64 has a Brewster window, and the laser beam emitted by the laser oscillator 64 is a linearly polarized laser beam.

At the front end of the casing 35, a machining head 36 and a photographing unit 38 arranged in the X-axis direction for detecting a processing region to be subjected to laser processing are disposed. The imaging unit 38 includes an imaging unit such as a general CCD that captures a processing area of the semiconductor wafer by visible light.

The imaging unit 38 further includes: an infrared ray irradiation means for irradiating the infrared ray to the semiconductor wafer; an optical system for capturing the infrared ray irradiated by the infrared ray irradiation means; and an infrared ray imaging means for outputting the infrared ray corresponding to the optical system Red signal of infrared CCD, etc. The external line imaging unit is configured to transmit an image signal to the controller (control means) 40.

The controller 40 is composed of a computer, and includes a central processing unit (CPU) 42 that performs arithmetic processing according to a control program, a read-only memory (ROM) 44 for storing a control program, and the like, and a storage operation result. Read and write random access memory (RAM) 46, counter 48, and input interface 50, and output interface 52.

56 is a machining feed amount detecting means including a linear scale 54 disposed along the guide rail 14 and a reading head (not shown) disposed in the first slide block 6, and the machining feed amount detecting means 56 The detection signal is input to the input interface 50 of the controller 40.

Reference numeral 60 denotes an indexing amount detecting means constituted by a linear scale 58 disposed along the guide rail 24 and a reading head (not shown) disposed on the second slider 16, and the indexing amount detecting means 60 The detection signal is input to the input interface 50 of the controller 40.

The image signal captured by the imaging unit 38 is also input to the input interface 50 of the controller 40. On the other hand, the 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.

Referring to Fig. 2, an optical system of a laser beam irradiation unit 34 according to an embodiment of the present invention is shown. A mirror 76 and a condensing mirror 74 are housed in the casing 70 of the machining head 36. Further, a half mirror (beam splitter) 76 is disposed between the mirror 72 and the condensing mirror 74.

Oscillation by the laser beam oscillating unit 62 and output adjustment sheet The laser beam 69 adjusted to a predetermined power by the element 68 is reflected by the mirror 72 of the processing head 36, and a part thereof penetrates the half mirror 76 and is irradiated to the wafer 11 as a workpiece by the condensing mirror 74.

The reflected light 71 reflected on the wafer 11 is condensed by the condensing mirror 74, and a part thereof is reflected by the half mirror 76, and the amount of reflected light is detected by the reflected light amount detector 78 composed of a light receiving member such as a photodiode. Based on the amount of reflected light, the controller 40 controls the laser beam oscillating unit 62 and the output adjusting unit 68 as will be described in detail later.

The half mirror 76 may be disposed between the condensing mirror 74 and the workpiece (wafer) 11. However, since the half mirror 76 is disposed on the upstream side of the condensing mirror 74, only the reflected light reflected on the wafer 11 can be reflected. The condensing mirror 74 condenses light and enters the half mirror 76, so the detection of the amount of reflected light is preferably such a configuration.

Referring to Fig. 3, there is shown a front side perspective view of a semiconductor wafer 11 which is one of the workpieces of the laser processing method of the present invention. The semiconductor wafer 11 is formed of, for example, a silicon wafer having a thickness of 700 μm, and a lattice-shaped plurality of predetermined dividing lines 13 are formed on the surface 11a, and ICs, LSIs, and the like are formed in respective regions divided by the plurality of predetermined dividing lines 13. Element 15. As shown in FIG. 4, the inner surface 11b of the semiconductor wafer 11 is formed with an oxide film 17 made of SiO ₂ .

In the laser processing method of the present invention, the workpiece is not limited to the semiconductor wafer 11 shown in FIG. 3, and includes a film having an oxide film, a nitride film, a metal film, a Low-k film, or the like on the surface or the inner surface. The processed object.

In carrying out the laser processing method of the present invention, the surface 11a side of the semiconductor wafer 11 is as shown in Fig. 4, and the outer peripheral portion is attached to the adhesive tape T attached to the annular frame, and the inner surface 11b thereof is on the upper side.

Next, as shown in FIG. 5, the semiconductor wafer 11 is sucked and held by the chuck table 28 of the laser processing apparatus 2 via the adhesive tape T, and the annular frame F is pinched and fixed by the clamp 30.

Next, as shown in FIG. 6, a laser beam irradiation step for detecting the amount of reflected light is performed, and the laser beam 69 is irradiated to the chuck table 28 by the processing head 36 of the laser beam irradiation unit 34 under the first condition. Wafer 11.

Before the step of irradiating the reflected light amount detecting laser beam is performed, the calibration for detecting the predetermined dividing line 13 for laser processing is performed. In other words, the infrared camera of the imaging unit 38 takes the wafer 11 from the inner surface 11b side, and uses image processing such as pattern matching, which is widely known, to detect the predetermined dividing line 13 extending in the first direction and the first straight line with the first direction. The dividing line 13 is elongated in the 2 direction.

In other embodiments, the holding surface of the chuck table 28 may be formed of a transparent member, and the wafer 11 may be imaged using a camera disposed under the chuck table 28 to perform calibration.

Further, in the present invention, before detecting the amount of reflected light of the wafer 11, one or a plurality of reference workpieces having a known reflectance are prepared in advance, and the amount of reflected light is detected in the reference workpiece, and the amount of reflected light at that time is used as a reference material. It is first stored in the RAM 46 of the controller 40.

In the laser beam irradiation step for detecting the amount of reflected light, as shown in FIG. 6, the chuck table 28 is processed and fed in the direction of the arrow mark X1, and the laser beam 69 is irradiated by the processing head 36 to the oxide film 17 is formed. The reflected light 71 is detected by the reflected light amount detector 78 on the inner surface 11b of the wafer 11.

For example, any predetermined dividing line 13 of the wafer 11 and a plurality of The division planned line 13 or all the division planned lines 13 illuminate the reflected light amount detecting laser beam, and then detect the amount of reflected light.

The irradiation conditions of the reflected light amount detecting laser beam when the reforming layer is formed inside the wafer 11 by the irradiation of the laser beam 69 are as follows, for example.

Light source: LD-induced Q conversion Nd: YVO4 pulse laser

Wavelength: 1064nm

Repeat frequency: 100kHz

Average output: 0.1W

Processing feed rate: 400mm/s

When the laser beam irradiation step of the reflected light amount detecting laser beam irradiates the laser beam 69 on the inner surface 11b of the wafer 11, the reflected light 71 reflected on the inner surface 11b on which the oxide film 17 is formed is collected in the condensing mirror 74 shown in FIG. The light is partially reflected by the half mirror 76 and incident on the reflected light amount detector 78 composed of the light receiving member, and detects the amount of reflected light reflected on the inner surface 11b of the wafer 11. The reflectance of the detected inner surface 11b of the wafer 11 is calculated from the amount of reflected light stored in the RAM 46 and the amount of reflected light from the known reference workpiece.

The ROM 44 of the controller 40 stores in advance a correlation diagram showing a correlation 73 between a plurality of reflectances and an appropriate pulse energy as shown in Fig. 7 depending on the type of the workpiece or the type of the film. Thus, the appropriate pulse energy relative to the reflectivity can be obtained from the correlation maps.

The average output and repetition frequency of the laser beam oscillated by the laser oscillator 64 are adjusted based on the appropriate pulse energy. For example, when the reflectance is 50%, the appropriate pulse energy is determined to be 20 μJ from the correlation diagram of FIG. because Thus, by pulse energy (J) = average output (W) / repetition frequency (Hz), for example, the repetition frequency is 100 kHz and the average output is 2 W.

Since the maximum power of the laser oscillator 64 is insufficient due to the reflectance, it is impossible to form a sufficient reforming layer inside the wafer 11 in the irradiation of the primary laser beam. Therefore, a modified layer including a plurality of segments is formed in the thickness direction of the wafer 11 in accordance with the amount of reflected light detected in the reflected light amount detecting step. The number-of-segment calculation means for calculating the necessary number of segments based on the amount of reflected light is first stored in the ROM 44 of the controller 40.

After the reflected light amount detecting step is performed, a laser processing step is performed which sets the output of the laser beam irradiated by the laser beam irradiating unit 34 based on the amount of reflected light detected in the reflected light amount detecting step, and is irradiated by the laser beam The processing head 36 of the unit 34 irradiates the laser beam 11 on the wafer 11 held by the chuck table 28 under the second condition, and forms the modified layer 19 inside the wafer 11.

In the laser processing step, as shown in FIG. 8, the chuck table 28 is machined in the direction of the arrow mark X1, and the processing head 36 of the laser beam irradiation unit 34 irradiates the laser beam 69 under the second condition. A modified layer 19 is then formed inside the wafer 11.

The chuck table 28 is indexed in the Y-axis direction, and the same modified layer 19 is sequentially formed inside the wafer 11 along the dividing line 13 which is elongated in the first direction. Next, the chuck table 28 is rotated by 90 degrees, and the same modified layer 19 is formed along the dividing line 13 which is elongated in the second direction.

When the partitioning property is low due to the thickness or material of the wafer 11, a plurality of modified layers 19 are formed inside the wafer. Moreover, the reflectivity of the wafer 11 is high and the maximum power of the laser oscillator 64 is too low, and the laser beam is irradiated once. When a sufficient reforming layer 19 cannot be formed inside the wafer 11, a plurality of modified layers 19 are formed inside the wafer 11.

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

Light source: LD-induced Q conversion Nd: YVO4 pulse laser

Wavelength: 1064nm

Repeat frequency: 100kHz

Average output: 2.0W

Processing feed rate: 400mm/s

Referring to Fig. 9, there is shown a partial cross-sectional side view for explaining a step of irradiating a laser beam for detecting the amount of reflected light when the wafer 11 is subjected to a sharpening process. For example, when the Low-k film formed on the surface 11a of the wafer 11 is subjected to a sharpening process, the laser beam 69 is incident on the surface 11a side of the wafer 11. Next, the amount of light reflected by the reflected light 71 reflected on the surface 11a is detected by the reflected light amount detector 78.

In the same manner as the above-described reforming layer forming process, the laser beam for detecting the amount of reflected light is irradiated onto the arbitrary dividing line 13 of the wafer 11, the predetermined dividing line 13 or all the dividing lines 13 to be detected. The amount of reflected light.

The laser beam irradiation conditions during the sharpening process are set as follows.

Light source: LD-induced Q conversion Nd: YVO4 pulse laser

Wavelength: 355nm (the third harmonic of the YV04 pulsed laser)

Repeat frequency: 200kHz

Average output: 0.1W

Processing feed rate: 200mm/s

In the shaving processing, after the reflected light amount detecting step is performed, a laser processing step is performed in which the output of the laser beam irradiated by the laser beam irradiating unit 34 is set based on the amount of reflected light detected in the reflected light amount detecting step, The condition is that the processing head 36 of the laser beam irradiation unit 34 irradiates the laser beam on the surface 11a of the wafer 11 held by the chuck table 28, and performs a sharpening process on the dividing line 13 of the wafer 11 to form a laser processing. ditch.

The laser processing conditions in this sharpening process are set as follows.

Light source: LD-induced Q conversion Nd: YVO4 pulse laser

Wavelength: 355nm (the third harmonic of the YVO4 pulsed laser)

Repeat frequency: 200kHz

Average output: 1W

Processing feed rate: 200mm/s

In the film cutting process, the condensing point of the condensing mirror 74 can be changed in the thickness direction of the wafer 11 according to the reflectance of the surface 11a of the wafer 11 and the maximum power of the laser oscillator 64 to form a plurality of laser processing grooves. The number of segments at this time is calculated by the number of segments stored in the ROM in accordance with the reflectance detected in the reflectance detecting step.

In the second embodiment of the laser processing method of the present invention, the laser processing step may be performed while performing the reflected light amount detecting step. That is, as shown in Fig. 10, the chuck table 28 is fed in the direction of the arrow mark X1, and the laser beam 69 is irradiated by the processing head 36 of the laser beam irradiation unit 34, and the crystal beam is detected using the reflected light amount detector 78. The amount of reflected light reflected by the reflected light 71 reflected by the inner surface 11b of the circle 11.

Based on the amount of reflected light, the controller 40 performs feedback control on the output adjustment unit 68, and forms the modified layer 19 inside the wafer 11 by using the laser beam 69 which is the most appropriate output of the amount of reflected light.

In the sharpening process, the output adjustment unit 68 can also be controlled in response to the amount of reflected light, and the laser beam 69 of the most appropriate power is irradiated by the processing head 36 to perform a sharpening process. After the modified layer 19 or the laser processing groove is formed on the wafer 11, a dividing step of applying an external force to the wafer 11 and dividing into individual wafers is performed.

In the present embodiment, after the modified layer 19 is formed inside the wafer 11 along all the planned dividing lines 13, the inner surface polishing step of polishing the inner surface 11b of the wafer 11 is performed. In the inner surface polishing step, as shown in FIG. 11, the inner surface 11b of the wafer 11 held by the chuck table 96 of the polishing apparatus is polished by the grindstone 94, and the wafer 11 is divided by the pressing force in the polishing. Into each wafer.

In Fig. 11, the polishing unit 32 is composed of a rotary shaft 84, a wheel base 86 fixed to the front end of the rotary shaft 84, and a grinding wheel 83 detachably attached to the wheel base 86 by a plurality of screws 90. The grinding wheel 83 is configured by fixing a plurality of grindstones 94 to the outer periphery of the lower end portion of the annular base 92.

In the inner surface grinding step, the chuck table 96 is rotated in the direction of the arrow mark a at, for example, 300 rpm, and the grinding wheel 88 is rotated in the direction of the arrow mark b at, for example, 6000 rpm, and the grinding unit conveying mechanism is actuated to cause the grinding stone 94. Contact with the inner surface 11b of the wafer 11.

Next, the polishing wheel 88 is ground and fed downward at a predetermined polishing feed rate, and the inner surface 11b of the wafer 11 is polished. The thickness of the wafer 11 is measured in a contact or non-contact thickness gauge, and the wafer 11 is finally processed to a desired thickness, for example, 50 μm.

In the middle of the polishing, since the reforming layer 19 is formed along the dividing line 13 inside the wafer 11, the wafer 11 is divided into individual wafers by using the reforming layer 19 as a dividing starting point by the pressing force during polishing. .

Here, in the case of a workpiece having a low degree of division, a step of dividing the external force into the workpiece and dividing it is performed before the inner surface polishing is performed. Alternatively, after the inner surface polishing is performed, a dividing step of dividing the workpiece with an external force is performed.

In the above embodiment, after the modified layer 19 is formed on a wafer having a thick thickness (700 μm), the inner surface 11b of the wafer 11 is polished to thin the wafer, and the pressing force at the time of polishing is The modified layer 19 is divided into individual wafers by dividing the starting point, but the modified layer 19 or the laser processing groove may be formed by the wafer 11 which is thinned in advance on the polished inner surface 11b. Further, the wafer 11 may be irradiated with a laser beam having an absorptive wavelength to completely cut the wafer 11.

11‧‧‧Semiconductor wafer

34‧‧‧Laser beam irradiation unit

36‧‧‧Processing head

40‧‧‧ Controller

62‧‧‧Laser oscillation unit

64‧‧‧Laser oscillator

66‧‧‧Repetition frequency setting unit

68‧‧‧Output adjustment unit

69‧‧‧Laser beam

70‧‧‧shell

71‧‧‧ Reflected light

72‧‧‧Mirror

74‧‧‧Condenser

76‧‧‧Half mirror

Claims (4)

A laser processing apparatus is a laser processing apparatus for performing laser processing on a workpiece, which comprises: a chuck table for holding a workpiece; and a laser beam irradiation means including a laser oscillator and a processing head having a condensing mirror that converges a laser beam oscillated by the laser oscillator; and the reflected light amount detecting means detects a ray irradiated to the workpiece held by the cradle by the laser beam irradiation means The amount of reflected light of the beam; and the output adjusting means adjust the output of the laser beam oscillated by the laser oscillator based on the amount of reflected light detected by the reflected light amount detecting means. The laser processing apparatus according to claim 1, further comprising a number-of-segment calculation means for calculating, based on the amount of reflected light detected by the reflected light amount detecting means, the laser beam irradiation means The number of segments of the laser processing in the thickness direction of the processed object. A laser processing method is a laser processing method for performing laser processing on a workpiece, which comprises the steps of: maintaining a step of holding a workpiece at a chuck table; and detecting a reflected light amount by a laser beam a step of irradiating the laser beam to the workpiece held by the chuck table under the first condition by the laser beam irradiation means; and detecting the amount of reflected light for detecting the amount of the reflected light a laser beam irradiation step irradiates the amount of reflected light of the reflected light reflected by the laser beam of the workpiece onto the workpiece; and a laser processing step is performed according to the reflected light amount detecting step after performing the reflected light amount detecting step The amount of reflected light is set to the output of the laser beam irradiated by the laser beam irradiation means, and the laser beam irradiation means irradiates the laser beam to the workpiece held by the chuck table under the second condition, and the processed object is processed. The object is subjected to laser processing. The laser processing method of claim 3, further comprising a number-of-segment calculation step of calculating a thickness direction of the workpiece according to the amount of reflected light detected by the reflected light amount detecting step The number of segments of the laser processing in the plurality of stages, in the laser processing step, the number of segments calculated according to the number of steps is calculated, and the laser processing of the plurality of segments is performed in the thickness direction of the workpiece.