TW201343302A - Laser processing method - Google Patents

Abstract

The present invention aims to provide a laser processing method which can form a uniform modified layer within the processed workpiece without depending on the state of the irradiated surface of the workpiece irradiated by laser beam. The invention includes a reflectivity detection step, an antireflection film forming step, and a laser processing step. The reflectivity detection step detects the reflectivity of the laser beam irradiating on the irradiated surface of the processed workpiece. After the reflectivity detection step, the antireflection film forming step, according to the detected reflectivity, forms an antireflection film on the irradiated surface of the processed workpiece to make the reflectivity of the irradiated surface smaller than a predetermined value. After the antireflection film forming step, the laser processing step irradiates laser beam with penetrating wavelength onto the irradiated surface (surface of the antireflection film) of the processed workpiece so as to form a modified layer within the processed workpiece. Since the surface of antireflection film is used as the irradiated surface and laser beam is irradiated into the interior the processed workpiece, a uniform modified layer can be formed.

Description

Laser processing method Field of invention

The present invention relates to a laser processing method for forming a modified layer of a laser beam having a wavelength that is transparent to a thin plate-shaped workpiece such as a semiconductor wafer to form a modified layer inside the workpiece.

Background of the invention

For example, a semiconductor wafer is manufactured by a process in which a plurality of electronic circuits including ICs, LSIs, and the like are formed on a surface of a wafer made of a semiconductor such as germanium or gallium arsenide, and then the back surface of the wafer is polished. After thinning to a predetermined thickness, the wafer is divided into respective element regions in which electronic circuits are formed. In order to divide a thin plate-shaped workpiece such as a wafer, a wafer is usually cut by a cutting blade. In recent years, a laser processing method has also been adopted, which is a method of irradiating a workpiece to be penetrated. A laser beam having a wavelength of a wavelength forms a modified layer inside the workpiece, and an external force is applied to the wafer, and the wafer is cut by dividing the wafer with the modified layer as a starting point (Patent Document 1 and the like).

Advanced technical literature Patent literature

Patent Document 1 Japanese Patent Publication No. 3408805

Summary of invention

On the other hand, in the semiconductor wafer or the like, an oxide film or a nitride film remains on the back surface of the state before the back surface polishing. Further, in various wafers, a low dielectric constant insulator coating film (Low-k film) formed of an organic film such as polyimide or parylene or a metal film formed on the back surface is formed on the surface. By.

When the wafer having the film is irradiated from the film side as a workpiece, and laser processing is performed, a part of the irradiated laser beam is partially reflected on the film. The reflectance differs depending on the type or thickness of the film, and the reflectance of the surface varies depending on the workpiece, or the reflectance varies within one workpiece. When the reflectance differs depending on each workpiece, when a plurality of workpieces are subjected to laser processing under a single processing condition, variations occur in the reforming layer formed by irradiation of the laser beam. Further, when the reflectance varies in one workpiece, when the laser processing is performed under a single processing condition, the region having a different reflectance varies in the reforming layer. In addition, the deviation of the modified layer referred to herein means the depth of the modified layer formed from the irradiated surface of the irradiated laser beam or the thickness of the modified layer.

The present invention has been made in view of the above circumstances, and a main technical problem thereof is to provide a laser which forms a uniform modified layer in a workpiece without depending on a state in which the object to be irradiated of the laser beam can be irradiated. processing methods.

The laser processing method of the present invention is characterized in that a laser beam having a wavelength that is transparent to a workpiece is irradiated to form a modified layer on a workpiece, and the reflectance detecting step and the anti-reflection film forming step are included. And a laser processing step of detecting a reflectance of the laser beam irradiated by the irradiated surface of the laser beam irradiated with the workpiece; the anti-reflection film forming step is performed by performing the reflectance detection After the step, an anti-reflection film is formed on the irradiated surface of the workpiece according to the detected reflectance, and the irradiated surface is set to have a predetermined reflectance or less; and the laser processing step is performed to form the anti-reflection film. After the step, a laser beam having a penetrating wavelength is irradiated onto the irradiated surface of the workpiece to form a modified layer inside the workpiece.

In the present invention, before the laser processing is performed, the reflectance of the irradiated surface of the workpiece is detected, and an anti-reflection film is formed on the irradiated surface of the workpiece in accordance with the detected reflectance, so that it is scheduled Below the reflectance, the laser beam is irradiated onto the inside of the workpiece from the side of the antireflection film. Therefore, the laser beam can be made to reach the inside of the workpiece with good efficiency, and as a result, a uniform reforming layer can be formed in the workpiece without depending on the state of the surface to be irradiated.

According to the present invention, it is possible to provide a laser processing method for forming a uniform modified layer in a workpiece without depending on the state of the irradiated surface of the laser beam that can be irradiated to the workpiece.

1‧‧‧Processed objects

1b‧‧‧back

1c‧‧‧Modified layer

2‧‧‧ dividing line

3‧‧‧Component area

4‧‧‧ film

5‧‧‧Anti-reflection film

10‧‧‧Frame

11‧‧‧Adhesive tape

20‧‧‧ Laser processing equipment

21‧‧‧Abutment

22‧‧‧XY mobile station

23‧‧‧ column

30‧‧‧X-axis base

31,41‧‧‧Guided orbit

32, 42‧‧‧ motor

33,43‧‧‧Rolling screw

34‧‧‧X-axis drive equipment

40‧‧‧Y-axis base

44‧‧‧Y-axis drive equipment

50‧‧‧ chuck base

51‧‧‧ chuck table

52‧‧‧clip

53‧‧‧ pole

60‧‧‧Laser illumination

61‧‧‧Shell

62‧‧‧ Department of Irradiation

63‧‧‧Laser oscillation unit

64‧‧‧Output adjustment unit

65‧‧‧Reflected light detector

70‧‧‧calibration agency

71‧‧‧ camera

80‧‧‧film forming device

81‧‧‧ device box

P‧‧‧Resin

82‧‧‧Rotating table

83‧‧‧Resin supply nozzle

84‧‧‧Motor

85‧‧‧ drive shaft

86‧‧‧ centrifugal clamp

91‧‧‧ mandrel

92‧‧‧ grinding wheel

93‧‧‧磨石

621‧‧‧Mirror

622‧‧‧half mirror

623‧‧‧ Concentrating lens

631‧‧‧Laser oscillator

632‧‧‧Repetition frequency setting unit

811‧‧‧ box body

811a‧‧ hole

812‧‧‧ Cover

831‧‧‧ resin supply port

A, B‧‧‧ arrows

L‧‧‧Laser beam

1(a) and 1(b) show a mine according to an embodiment of the present invention. The shot processing method is a (a) perspective view and a (b) cross-sectional view of the laser processed workpiece being supported by the adhesive tape on the frame.

Fig. 2 is a perspective view of the entire laser processing apparatus suitable for implementing the laser processing method of the embodiment.

Fig. 3 is a view showing an optical system of a laser irradiation mechanism of the laser processing apparatus.

Fig. 4 is a cross-sectional view showing a film forming apparatus used in the anti-reflection film forming step of the laser processing method of the embodiment.

Fig. 5 is a side view showing a state in which a laser processing step of the laser processing method of one embodiment is performed.

Figure 6 is a cross-sectional view showing a detail of the laser processing step.

FIG. 7 is a perspective view showing a state in which the workpiece is divided into the elements by the grinding mechanism and the external force is applied to the back side of the workpiece after the laser processing step.

Form for implementing the invention

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

Reference numeral 1 in Fig. 1 shows a workpiece to be subjected to laser processing in the present embodiment, and Fig. 2 shows a laser processing apparatus 20 which performs laser processing on a workpiece.

(1) Workpiece

The workpiece 1 shown in FIG. 1 is a disk-shaped semiconductor wafer having a thickness of, for example, several hundreds of μm, and is supplied to the laser processing apparatus 20, and the surface side is attached to the adhesive tape attached to the annular frame 10. 11. On the surface of the workpiece 1 The lattice-shaped dividing line 2 is provided with a plurality of rectangular element regions 3, and an electronic circuit composed of, for example, an IC or an LSI is formed in the element regions 3. As shown in FIG. 1(b), a film 4 is formed on the entire surface of the back surface 1b of the workpiece 1. The film 4 is, for example, an oxide film, a nitride film, a metal film, or the like.

The workpiece 1 is in a state in which the surface 1a side is attached to the adhesive tape 11 and the back surface 1b is exposed. The frame 10 is made of a rigid metal plate or the like such as stainless steel, and the workpiece 1 is conveyed to the laser processing apparatus 20 by the frame 10 and the adhesive tape 11.

In the laser processing of the present embodiment, a laser beam is irradiated along the dividing line 2 inside the workpiece 1 to form a reforming layer. The steps of the laser processing apparatus 20 and the laser processing method will be described below.

(2) Laser processing device

A laser processing apparatus 20 that performs laser processing on the workpiece 1 will be described with reference to Fig. 2 .

The laser processing apparatus 20 has a base 21, and the XY moving stage 22 is provided on the base 21 so as to be movable in the horizontal X-axis direction and the Y-axis direction. The XY moving table 22 is provided with a chuck table 51 that holds the workpiece 1. The illuminating unit 62 of the laser irradiation unit 60 that irradiates the laser to the workpiece 1 held by the chuck table 51 is disposed above the ram stage 51 in a state of being opposed to the ram stage 51.

The XY moving table 22 is configured by a combination of an X-axis base 30 that is movably provided on the base 21 in the X-axis direction and a Y-axis base 40 that is movably disposed on the X-axis base 30 in the Y-axis direction. . The X-axis base 30 is slidably mounted on a guide rail 31 fixed to the base 21 and extending in the X-axis direction by a pair of parallel guide rails 31, whereby the X-axis drive device 34 for actuating the ball screw 33 by the motor 32 is X Move in the direction of the axis. On the other hand, the Y-axis base 40 is slidably attached to a Y-axis drive device 44 that is fixed to the X-axis base 30 and extends in the Y-axis direction by a pair of parallel guide rails 41, whereby the motor 42 causes the ball screw 43 to actuate. Move in the Y-axis direction.

The cylindrical chuck base 50 is rotatably supported on the upper surface of the Y-axis base 40 in the Z-axis direction (vertical direction) as a rotation axis, and the chuck table 51 is fixed concentrically on the chuck base 50. The chuck table 51 is a vacuum chuck type which is generally known to suction and hold a workpiece by vacuum suction. The chuck table 51 is rotationally driven integrally with the chuck base 50 by a rotary drive mechanism (not shown). Around the chuck table 51, the frame 10 is held in a detachable manner, and the pair of clips 52 are disposed at positions separated from each other by 180 degrees. The clips 52 are attached to the collet base 50 by struts (see FIG. 5) 53.

In the XY moving table 22, when the X-axis base 30 moves in the X-axis direction, the laser beam is fed along the processing of the planned dividing line 2 of the workpiece 1. Then, the Y-axis base 40 is moved in the Y-axis direction to perform indexing feed of the division planned line 2 of the object to be irradiated with the laser beam. In addition, the machining feed direction and the index feed direction may be reversed, that is, the Y-axis direction is set to the machining feed direction, and the X-axis direction is set to the index feed direction, which is not limited.

The laser irradiation mechanism 60 has a rectangular parallelepiped casing 61 extending in the Y-axis direction above the chuck table 51, and the irradiation portion 62 is provided at the front end of the casing 61. The casing 61 is provided on the column 23 which is erected on the base 21 in a state of being vertically movable in the vertical direction (Z-axis direction), and the upper and lower drive mechanisms are not vertically moved in the figure which can be accommodated in the column 23.

The front end of the housing 61 is fixed in the vicinity of the illuminating portion 62. The calibration mechanism 70 that detects the planned dividing line 2 of the workpiece 1 is detected. The calibration mechanism 70 has a camera 71 that captures the workpiece 1, and the calibration mechanism 70 detects (calibrates) the division planned line 2 based on the image acquired by the camera 71.

Hereinafter, the laser irradiation mechanism 60 will be described.

As shown in FIG. 3, a laser oscillation unit 63 that oscillates a laser beam, an output adjustment unit 64, and a reflected light amount detector 65 are housed in the casing 61. The laser oscillation unit 63 has a laser oscillator 631 that oscillates a pulse laser such as YAG or YVO, and a repetition frequency setting unit 632 that sets the frequency of the laser beam oscillated by the laser oscillator 631. In the laser oscillator 631, a pulse laser having a wavelength set by the repetition frequency setting unit 632 is irradiated, and the laser beam is irradiated toward the irradiation unit 62.

The laser beam irradiated from the laser oscillator 631 is adjusted and output by the output adjustment unit 64, and then irradiated to the mirror 621 disposed in the upper portion of the illuminating portion 62. A mirror 621, a half mirror 622, and a collecting lens 623 are housed in the irradiation unit 62 from above. The laser beam irradiated to the mirror 621 is reflected downward by the mirror 621, is incident on the condensing lens 623, and is incident on the workpiece 1 held by the chuck table 51.

Further, the laser beam irradiated onto the workpiece 1 is reflected on the surface to be irradiated on the upper surface of the workpiece 1 as indicated by a broken line in Fig. 3, and the reflected light is guided by the half mirror 622 to the reflected light amount detector 65. . The reflected light amount detector 65 detects the amount of reflected light on the illuminated surface. Then, the amount of reflected light and the amount of reflected light of the reference workpiece such as a mirror wafer that has been previously detected are compared, and the value as the reflectance is obtained. As will be described later, the laser beam for detecting reflectance and the laser beam for laser processing for forming a modified layer can be irradiated from the illuminating unit 62.

(3) Laser processing method

The above is the configuration of the laser processing apparatus 20. Next, the procedure of the laser processing method for forming a modified layer inside the workpiece 1 using the laser processing apparatus 20 will be described.

First, the workpiece 1 is placed on the chuck table 51 of the laser processing apparatus 20 by the adhesive tape 11, and is adsorbed and held by the chuck table 51 by vacuum suction. The workpiece 1 is held by the chuck table 51 in a state in which the film 1 is exposed on the side of the back surface 1b. Also, the frame 10 can be held by the clip 52.

Next, the X-axis base 30 and the Y-axis base 40 of the XY moving stage 22 are appropriately moved to position the workpiece 1 below the irradiation unit 62 of the laser irradiation unit 60, and the X-axis base 30 is placed. The laser beam for detecting the reflectance is irradiated onto the workpiece 1 from the irradiation unit 62, and the laser beam irradiated onto the surface to be irradiated (the surface of the film 4) is detected by the irradiation unit 62. Reflectance of the beam (reflectance detection step). The machining feed speed at which the workpiece 1 is moved together with the chuck table 51 is, for example, about 400 mm/s. Further, the laser beam output for reflectance detection is smaller than the output when the reforming layer is formed, and is, for example, a laser beam having the following conditions.

‧wavelength: 1064nm

‧Repetition frequency: 100kHz

‧ Average output: 0.1W

As shown in FIG. 3, the reflectance is guided by the half mirror 622 to the reflected light beam detector 65 to reflect the reflected light of the laser beam reflected on the surface of the object 1 (the surface of the film 4) to reflect Comparison of the amount of reflected light detected by the light amount detector 65 and the amount of reflected light of the reference object to be detected in advance Out.

When the reflectance of the surface to be irradiated of the workpiece 1 is obtained, the workpiece 1 is carried out from the laser processing apparatus 20, and an anti-reflection film is formed on the surface to be irradiated of the workpiece 1 based on the detected reflectance. On the other hand, the surface to be illuminated is equal to or lower than a predetermined reflectance (reflection preventing film forming step).

FIG. 4 is a film forming apparatus suitable for forming an anti-reflection film on the surface to be irradiated of the workpiece 1. In the film forming apparatus 80, the liquid resin P is dropped from the resin supply nozzle 83 to the upper surface of the workpiece 1 held on the disk-shaped rotary table 82 in the apparatus casing 81, that is, the surface of the film 4, and spin coating is performed. The form of the person.

The device case 81 is constituted by a cylindrical case body 811 having an opening 811a at the center and a cover 812 for closing the hole 811a of the case body 811, and a drive shaft 85 of the motor 84 is inserted through the cover 812 from below. The rotary table 82 is fixed at its center to the upper end of the drive shaft 85 projecting into the device casing 81 and is supported to be horizontally rotatable by the drive of the motor 84.

The workpiece 1 is placed on the upper surface of the rotary table 82 by the adhesive tape 11, and is adsorbed and held on the upper surface of the rotary table 82 by vacuum suction. A plurality of centrifugal clips 86 that are actuated to press the frame 10 from above when the centrifugal force is generated by the rotation of the rotary table 82 are attached to the peripheral portion of the rotary table 82, and the frame 10 is held by the centrifugal clamps 86.

The resin supply nozzle 83 is rotatably supported at the bottom of the cartridge body 811, and can be wound around the resin supply port 831 of the front end directly above the center of the rotary table 82.

In the anti-reflection film forming step, the workpiece 1 is adhered by The tape 11 is held on the rotary table 82, and the rotary table 82 is rotationally driven to hold the frame 10 with the centrifugal clamp 86. Then, the resin P is dropped from the resin supply port 831 of the resin supply nozzle 83 to the upper surface of the workpiece 1 in the spinning state, that is, the center of the surface of the film 4. The resin P dropped onto the film 4 is spin-coated on the entire surface of the film 4 by centrifugal force, and the anti-reflection film 5 formed of the resin P is uniformly formed (see FIG. 5).

The resin P for forming the anti-reflection film 5 may be exemplified by polyimide, optical plastic, polyvinyl alcohol (PVA) or the like. Further, the material having the refractive index as described below is selected such that the difference between the refractive index of the refractive index-based anti-reflection film 5 and the refractive index of the film 4 is smaller than that of the laser beam irradiated to the workpiece 1 at the time of subsequent laser processing. The difference between the refractive index of the air of the wavelength and the refractive index of the surface of the film 4. This is because it is difficult to reflect the laser beam for laser processing by the reflection preventing film 5 at the time of laser processing, and the laser beam can efficiently penetrate into the inside of the workpiece 1.

Further, the thickness of the anti-reflection film 5 formed is in accordance with the reflectance detected in the reflectance detecting step. For example, when the reflectance is 30%, the thickness of the anti-reflection film 5 is 2 μm to 100 nm. It is preferable to adjust the reflectance of the surface to be irradiated of the workpiece 1 at the time of laser processing, that is, the surface of the anti-reflection film 5 to about 0 to 18%.

After the anti-reflection film 5 is formed on the surface to be irradiated of the workpiece 1, the workpiece 1 is carried out from the film forming apparatus 80, placed in the laser processing apparatus 50, and irradiated along the dividing line 2 to be transparent. The laser beam of the wavelength forms a modified layer along the predetermined dividing line inside the workpiece 1 (laser processing step).

Similarly to the reflectance detecting step, the workpiece 1 is held by the adhesive tape 11 on the chuck table 51, and the frame 10 is held by the clip 52. Then, after the position of the planned dividing line 2 is detected by the aligning mechanism 70, as shown in FIGS. 5 and 6, the laser beam for laser processing of the workpiece 1 is transmitted from the illuminating unit 62 of the laser irradiation unit 60. The beam L is positioned inside the workpiece 1 to be spotted along the detected dividing line 2 along the detected spot.

The laser beam L for laser processing output is larger than the laser beam when the reflectance is detected. For example, the laser beam is the following condition.

‧ Wavelength: 1064nm pulsed laser

‧Repetition frequency: 100kHz

‧ Average output: 1.5W

As shown in FIG. 6, the laser beam L at the time of laser processing is condensed in the workpiece 1 via the anti-reflection film 5 and the film 4, thereby forming a line along the division line 2 inside the workpiece 1. The modified layer 1c. The reforming layer 1c is formed at a certain thickness in a position at a certain depth from the surface 1a of the workpiece 1. The modified layer 1c has a lower strength than other portions in the workpiece 1.

The scanning of the laser beam along the dividing line 2 of the laser processing apparatus 20 is such that the dividing line 2 is set to be parallel to the machining feed by rotating the chuck table 51 so that the chuck table 51 is at the X The machining feed in the axial direction is performed. The arrow B of Fig. 5 is a moving direction of the chuck table 51 during laser processing, and the illuminating unit 62 is relatively processed and fed in the direction of the arrow A. The processing feed speed at this time is, for example, about 400 mm/s. Further, the conversion of the predetermined dividing line of the irradiated laser beam is performed by the indexing of the movement of the chuck table 51 in the Y-axis direction. Thereby, a change along the line 2 of all divisions is formed in the workpiece 1 Mass layer 1c.

The laser processing of the workpiece 1 is completed as described above. Thereafter, the workpiece 1 is subjected to an external force, and the modified layer 1c having a reduced strength is used as a starting point to be divided into the element regions 3 to form a wafer-shaped element. A method of imparting an external force to the workpiece 1 is exemplified by a method in which the plurality of grindstones 93 of the grinding wheel 92 that is rotationally driven by the mandrel 91 are pressed against the workpiece to be ground as shown in FIG. The polishing mechanism 90 of the form polishes the back side 1b side of the workpiece 1. The workpiece 1 is held by the rotatable holding mechanism 94 in a state where the back surface 1b side, that is, the side of the anti-reflection film 5 is exposed.

When the force is applied in this way, the anti-reflection film 5 and the film 4 can be removed, and the workpiece 1 can be thinned to a predetermined thickness and divided into a plurality of elements. Further, the method of imparting an external force to the workpiece 1 is not limited to grinding, and for example, the adhesive tape 11 may be expanded.

Further, there is a case where the back surface 1b side is not polished after the reforming layer 1c is formed. In this case, the liquid resin forming the anti-reflection film 5 is selected to be water-soluble, and the water is washed and reflected after the reforming layer 1c is formed. It is only necessary to prevent the film 5 from being removed. At this time, the water-soluble anti-reflection film 5 can be removed by using the film forming apparatus 80 shown in FIG. 4 by replacing the liquid resin with water. Further, as the water-soluble liquid resin, a water-soluble resist such as polyvinyl alcohol (PVA), polyethylene glycol (PEG) or polyethylene oxide (PEO) is preferably used.

Further, in the above-described laser processing step, the workpiece 1 is directly supported by the adhesive tape 11 while being supported by the frame 10, and the workpiece 1 may be peeled off from the adhesive tape 11 as it is. The processed material 1 is directly held in the state of the chuck table 51, and the modified layer 1c is formed.

According to the laser processing method of the above embodiment, the reflectance of the surface to be irradiated (the surface of the film 4) of the workpiece 1 is detected before the laser processing is performed, and the object 1 is processed in accordance with the detected reflectance. The irradiation preventing surface 5 is formed to have a predetermined thickness of the anti-reflection film 5, and after the predetermined reflectance is equal to or lower than the predetermined reflectance, the laser beam is irradiated from the side of the anti-reflection film 5 to form the modified layer 1c in the workpiece 1. In other words, the surface to be irradiated of the laser beam when the reforming layer 1c is formed is not formed in advance on the surface of the film 4 on the back surface 1b of the workpiece 1, but is changed to an antireflection film having a predetermined thickness and a predetermined reflectance or less. 5. Therefore, under the condition that the state of the film 4 is not affected, the laser beam can reach the inside of the workpiece 1 with good efficiency. As a result, the uniform modified layer 1c can be formed in the workpiece 1 without depending on the surface state of the film 4.

Further, when the film 4 formed on the surface 1a of the workpiece 1 is different in advance, in the reflectance detecting step, the reflectance of the entire surface of the surface 1a having the deviation is detected, and the state of the deviation of the reflectance is detected, which corresponds to the deviation. In the state, it is preferable to set the thickness of the anti-reflection film 5 formed in the anti-reflection film forming step.

1‧‧‧Processed objects

1c‧‧‧Modified layer

4‧‧‧ film

5‧‧‧Anti-reflection film

10‧‧‧Frame

11‧‧‧Adhesive tape

51‧‧‧ chuck table

52‧‧‧clip

53‧‧‧ pole

62‧‧‧ Department of Irradiation

A, B‧‧‧ arrows

L‧‧‧Laser beam

Claims (1)

A laser processing method for irradiating a laser beam having a wavelength that is transparent to a workpiece to form a modified layer on a workpiece, and comprising: a reflectance detecting step for detecting a workpiece The reflectance of the laser beam irradiated by the irradiated surface of the irradiated laser beam; the anti-reflection film forming step is performed on the object to be processed according to the detected reflectance after performing the reflectance detecting step Forming an anti-reflection film on the surface to be irradiated, and setting the surface to be irradiated to a predetermined reflectance or lower; and performing a laser processing step on the laser beam having a penetrating wavelength after the step of forming the anti-reflection film The irradiated surface of the workpiece is formed into a modified layer inside the workpiece.