JP2004160493A - Laser machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser machining method for reducing energy losses by the reflection of laser beams and considerably reducing the energy consumption. <P>SOLUTION: The laser machining method to perform a predetermined machining by irradiating a workpiece with laser beams comprises a reflection preventive layer forming step of forming a reflection preventive layer at least in an area of the workpiece irradiated with laser beams, and a laser beam irradiating step of irradiating with laser beams through the reflection preventive layer. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing method for performing predetermined processing by irradiating a predetermined region of a workpiece with a laser beam.
[0002]
As is well known to those skilled in the art, in a semiconductor device manufacturing process, a plurality of regions are defined by streets (cutting lines) arranged in a lattice pattern on the surface of a substantially wafer-shaped semiconductor wafer. A circuit such as an IC or an LSI is formed. Then, the semiconductor wafer is cut along the streets to divide the region where the circuit is formed to manufacture individual semiconductor chips. Cutting along the streets of a semiconductor wafer is usually performed by a cutting device called a dicer. This cutting apparatus has a chuck table for holding a semiconductor wafer as a workpiece, a cutting means for cutting the semiconductor wafer held on the chuck table, and a movement for relatively moving the chuck table and the cutting means. Means. The cutting means includes a rotating spindle rotated at a high speed and a cutting blade mounted on the spindle. The cutting blade is composed of a disk-shaped base and an annular cutting edge mounted on the outer periphery of the side surface of the base. The cutting edge is fixed to the base by electroforming, for example, diamond abrasive grains having a particle size of about 3 μm. It is formed to a thickness of about 20 μm. When a semiconductor wafer is cut with such a cutting blade, chips and cracks are generated on the cut surface of the cut semiconductor chip. Therefore, the width of the street is formed to be about 50 μm in consideration of the effects of the chips and cracks. However, when the size of the semiconductor chip is reduced, the proportion of streets in the semiconductor chip increases, which causes a decrease in productivity. Further, in cutting with a cutting blade, there is a problem that the feed rate is limited and the semiconductor chip is contaminated by the generation of cutting waste.
[0003]
On the other hand, as a method for dividing a workpiece in recent years, a laser processing method in which a laser beam in an infrared light region (for example, 1064 nm) is irradiated with a condensing point inside the region to be divided has been tried. The semiconductor wafer dividing method using this laser processing method is to irradiate a laser beam in the infrared region along the street of the semiconductor wafer and irradiate a laser beam in the infrared region, and to alter the altered region along the street inside the semiconductor wafer. Are continuously formed to divide into individual semiconductor chips partitioned by streets. (For example, refer to Patent Document 1.)
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-192367
[Problems to be solved by the invention]
Thus, when a semiconductor wafer made of silicon or the like is irradiated with a laser beam in the infrared region, the semiconductor wafer is reflected with a reflectance of about 30% of the irradiated beam. Therefore, it is necessary to irradiate a high-power laser beam in view of energy loss due to this reflection, which is one of the causes of a large energy consumption in laser processing.
Further, even when a workpiece other than a semiconductor wafer is laser processed, energy loss due to reflection of the laser beam is inevitable.
[0006]
The present invention has been made in view of the above-mentioned facts, and its main technical problem is to provide a laser processing method capable of reducing energy loss due to reflection of a laser beam and greatly reducing energy consumption. It is.
[0007]
[Means for Solving the Problems]
In order to solve the main technical problem, according to the present invention, a laser processing method for performing predetermined processing by irradiating a workpiece with a laser beam,
An anti-reflection layer forming step of forming an anti-reflection layer in a region irradiated with at least a laser beam of the workpiece;
A laser beam irradiation step of irradiating a laser beam through the antireflection layer,
A laser processing method is provided.
[0008]
Moreover, according to the present invention, a laser processing method for generating a modified region by irradiating a laser beam having a wavelength in an infrared light region with a converging point inside the workpiece to perform a predetermined processing,
An anti-reflection layer forming step of forming an anti-reflection layer in a region irradiated with at least a laser beam of the workpiece;
And a laser beam irradiation step of irradiating a laser beam with a focusing point inside the workpiece through the antireflection layer,
A laser processing method is provided.
[0009]
Furthermore, in the present invention, the workpiece is a semiconductor wafer in which a plurality of streets are formed in a lattice shape on the surface and a circuit is formed in a plurality of regions partitioned by the plurality of streets. In the process, a laser processing method is provided in which the altered region is continuously formed along the street and the semiconductor wafer is divided into individual semiconductor chips. In the antireflection layer forming step, an antireflection layer is formed on the back surface of the semiconductor wafer, and in the laser beam irradiation step, a laser beam is irradiated along the street through the antireflection layer formed on the back surface of the semiconductor wafer. Irradiation is desirable.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the laser processing method according to the present invention will be described in more detail with reference to the accompanying drawings.
[0011]
FIG. 1 is a perspective view of a laser processing apparatus for carrying out the laser processing method according to the present invention. The laser processing apparatus shown in FIG. 1 includes a stationary base 2, a chuck table mechanism 3 that is disposed on the stationary base 2 so as to be movable in the direction indicated by an arrow X, and holds a workpiece. The laser beam irradiation unit support mechanism 4 is movably disposed in the direction indicated by the arrow Y perpendicular to the direction indicated by the arrow X in FIG. 2, and the laser beam unit support mechanism 4 is movably disposed in the direction indicated by the arrow Z. The laser beam irradiation unit 5 is provided.
[0012]
The chuck table mechanism 3 includes a pair of guide rails 31, 31 arranged in parallel along the direction indicated by the arrow X on the stationary base 2, and the direction indicated by the arrow X on the guide rails 31, 31. A first sliding block 32 movably disposed, a second sliding block 33 movably disposed on the first sliding block 32 in a direction indicated by an arrow Y, and the second sliding block A support table 35 supported by a cylindrical member 34 on a block 33 and a chuck table 36 as a workpiece holding means are provided. The chuck table 36 includes a suction chuck 361 formed of a porous material, and holds, for example, a disk-shaped semiconductor wafer, which is a workpiece, on the suction chuck 361 by suction means (not shown). . Further, the chuck table 36 is rotated by a pulse motor (not shown) disposed in the cylindrical member 34.
[0013]
The first sliding block 32 is provided with a pair of guided grooves 321 and 321 fitted to the pair of guide rails 31 and 31 on the lower surface thereof, and along the direction indicated by the arrow Y on the upper surface thereof. A pair of guide rails 322 and 322 formed in parallel are provided. The first sliding block 32 configured as described above has the guided grooves 321 and 321 fitted into the pair of guide rails 31 and 31, thereby the direction indicated by the arrow X along the pair of guide rails 31 and 31. It is configured to be movable. The chuck table mechanism 3 in the illustrated embodiment includes a moving means 37 for moving the first sliding block 32 in the direction indicated by the arrow X along the pair of guide rails 31, 31. The moving means 37 includes a male screw rod 371 disposed in parallel between the pair of guide rails 31 and 31 and a drive source such as a pulse motor 372 for rotationally driving the male screw rod 371. One end of the male screw rod 371 is rotatably supported by a bearing block 373 fixed to the stationary base 2, and the other end is connected to the output shaft of the pulse motor 372 via a reduction gear (not shown). ing. The male screw rod 371 is screwed into a penetrating female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the first sliding block 32. Therefore, the first slide block 32 is moved in the direction indicated by the arrow X along the guide rails 31 and 31 by driving the male screw rod 371 forward and backward by the pulse motor 372.
[0014]
The second sliding block 33 is provided with a pair of guided grooves 331 and 331 which are fitted to a pair of guide rails 322 and 322 provided on the upper surface of the first sliding block 32 on the lower surface thereof. By fitting the guided grooves 331 and 331 to the pair of guide rails 322 and 322, the guided grooves 331 and 331 are configured to be movable in the direction indicated by the arrow Y. The chuck table mechanism 3 in the illustrated embodiment has a moving means for moving the second slide block 33 along the pair of guide rails 322 and 322 provided in the first slide block 32 in the direction indicated by the arrow Y. 38. The moving means 38 includes a male screw rod 381 disposed in parallel between the pair of guide rails 322 and 322, and a drive source such as a pulse motor 382 for rotationally driving the male screw rod 381. One end of the male screw rod 381 is rotatably supported by a bearing block 383 fixed to the upper surface of the first sliding block 32, and the other end is connected to the output shaft of the pulse motor 382 via a reduction gear (not shown). Are connected. The male screw rod 381 is screwed into a penetrating female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the second sliding block 33. Therefore, by driving the male screw rod 381 forward and backward by the pulse motor 382, the second slide block 33 is moved along the guide rails 322 and 322 in the direction indicated by the arrow X.
[0015]
The laser beam irradiation unit support mechanism 4 includes a pair of guide rails 41, 41 arranged in parallel along the indexing feed direction indicated by the arrow Y on the stationary base 2, and the arrow Y on the guide rails 41, 41. The movable support base 42 is provided so as to be movable in the direction indicated by. The movable support base 42 includes a movement support portion 421 that is movably disposed on the guide rails 41, 41, and a mounting portion 422 that is attached to the movement support portion 421. The mounting portion 422 is provided with a pair of guide rails 423 and 423 extending in the direction indicated by the arrow Z on one side surface in parallel. The laser beam irradiation unit support mechanism 4 in the illustrated embodiment includes moving means 43 for moving the movable support base 42 along the pair of guide rails 41, 41 in the direction indicated by the arrow Y that is the indexing feed direction. ing. The moving means 43 includes a male screw rod 431 disposed in parallel between the pair of guide rails 41, 41, and a drive source such as a pulse motor 432 for rotationally driving the male screw rod 431. One end of the male screw rod 431 is rotatably supported by a bearing block (not shown) fixed to the stationary base 2 and the other end is connected to the output shaft of the pulse motor 432 via a reduction gear (not shown). Has been. The male screw rod 431 is screwed into a female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the moving support portion 421 constituting the movable support base 42. For this reason, when the male screw rod 431 is driven to rotate forward and backward by the pulse motor 432, the movable support base 42 is moved along the guide rails 41, 41 in the index feed direction indicated by the arrow Y.
[0016]
The laser beam irradiation unit 5 in the illustrated embodiment includes a unit holder 51 and laser beam irradiation means 52 attached to the unit holder 51. The unit holder 51 is provided with a pair of guided grooves 511 and 511 that are slidably fitted to a pair of guide rails 423 and 423 provided in the mounting portion 422. By being fitted to the guide rails 423 and 423, the guide rails 423 and 423 are supported so as to be movable in the direction indicated by the arrow Z.
[0017]
The illustrated laser beam application means 52 includes a cylindrical casing 521 that is fixed to the unit holder 51 and extends substantially horizontally. In the casing 521, as shown in FIG. 2, laser beam oscillation means 522 and laser beam modulation means 523 are arranged. As the laser beam oscillation means 522, a YAG laser oscillator or a YVO4 laser oscillator can be used. The laser beam modulation unit 523 includes a repetition frequency setting unit 523a, a laser beam pulse width setting unit 523b, and a laser beam wavelength setting unit 523c. The repetition frequency setting means 523a, laser beam pulse width setting means 523b and laser beam wavelength setting means 523c constituting the laser beam modulation means 523 may be of a form well known to those skilled in the art. It is omitted in the specification. A condenser 524, which may be in a known form, is attached to the tip of the casing 521.
[0018]
The laser beam oscillated by the laser beam oscillation means 522 reaches the condenser 524 via the laser beam modulation means 523. The repetition frequency setting means 523a in the laser beam modulation means 523 turns the laser beam into a pulse laser beam having a predetermined repetition frequency, the laser beam pulse width setting means 523b sets the pulse width of the pulse laser beam to a predetermined width, and the laser beam wavelength setting means 523c The wavelength is set to a predetermined value.
[0019]
An imaging unit 6 is disposed at a front end portion of the casing 521 constituting the laser beam irradiation unit 52. In the illustrated embodiment, the imaging unit 6 corresponds to an infrared illumination unit that irradiates a workpiece with infrared rays, an optical system that captures infrared rays irradiated by the infrared illumination unit, and infrared rays captured by the optical system. An image pickup device (infrared CCD) or the like that outputs the electrical signal is sent to the control means (not shown).
[0020]
The laser beam irradiation unit 5 in the illustrated embodiment includes a moving means 53 for moving the unit holder 51 along the pair of guide rails 423 and 423 in the direction indicated by the arrow Z. The moving means 53 includes a male screw rod (not shown) disposed between the pair of guide rails 423 and 423, and a drive source such as a pulse motor 532 for rotationally driving the male screw rod in the same manner as the above moving means. The unit holder 51 and the laser beam irradiation means 52 are moved in the direction indicated by the arrow Z along the guide rails 423 and 423 by driving the male screw rod (not shown) forward and backward by the pulse motor 532.
[0021]
Next, a processing method for dividing a semiconductor wafer into individual semiconductor chips using the laser processing apparatus described above will be described.
As shown in FIG. 3, the semiconductor wafer 10 is divided into a plurality of areas by a plurality of streets (cutting lines) 101 arranged in a lattice pattern on the surface 10a, and circuits 102 such as ICs and LSIs are formed in the divided areas. Is formed. In the semiconductor wafer 10 thus configured, an antireflection layer 103 is formed on the back surface 10b as shown in FIG. 4 (antireflection layer forming step). This antireflection layer 103 is formed by coating the other surface 10b of the semiconductor wafer 10 with an antireflection agent (trade name; MLAR (Y1)) provided by, for example, Sigma Koki Co., Ltd. Form. In addition, what is necessary is just to form the antireflection layer 103 in the area | region where a laser beam is irradiated in the laser beam irradiation process mentioned later.
[0022]
When the antireflection layer 103 is formed on the back surface 10b of the semiconductor wafer 10 as described above, the front surface 10a on which the circuit 102 is formed is pasted on the protective tape 12 mounted on the annular frame 11 as shown in FIG. To wear. The semiconductor wafer 10 supported on the annular frame 11 via the protective tape 12 (hereinafter simply referred to as the semiconductor wafer 10) is a chuck table 36 that constitutes the chuck table mechanism 3 by a workpiece transfer means (not shown). The anti-reflection layer 103 formed on the suction chuck 361 is conveyed with the back surface 10b facing upward, and is sucked and held by the suction chuck 361. The chuck table 36 that sucks and holds the semiconductor wafer 10 in this way is moved along the guide rails 31, 31 by the operation of the moving means 37, and is positioned immediately below the imaging means 6 disposed in the laser beam irradiation unit 5. .
[0023]
As described above, when the chuck table 36 is positioned immediately below the image pickup means 6, the first direction street formed on the semiconductor wafer 10 by the image pickup means 6 and a control means (not shown) and the laser beam are irradiated along the street. Image processing such as pattern matching for performing alignment with the condenser 524 of the laser beam irradiation unit 5 is performed, and alignment of the laser beam irradiation position is performed. In addition, the alignment of the laser beam irradiation position is similarly performed on the street in the second direction formed on the semiconductor wafer 10. At this time, the back surface 10a on which the street of the semiconductor wafer 10 is formed is located on the lower side. However, as described above, the imaging unit 6 transmits the infrared illumination unit, the optical system for capturing infrared rays, and the electrical signal corresponding to the infrared rays. Since it is composed of an output image sensor (infrared CCD) or the like, the street can be imaged through the back surface.
[0024]
As described above, when the street formed on the semiconductor wafer 10 held on the chuck table 36 is detected and the alignment of the laser beam irradiation position is performed, the laser beam irradiation for irradiating the chuck table 36 with the laser beam is performed. It moves to the laser beam irradiation region where the condenser 524 of the unit 5 is located, and the laser beam is irradiated from the collector 524 of the laser beam irradiation unit 5 along the street of the semiconductor wafer 10 in the laser beam irradiation region (laser beam irradiation step).
[0025]
Here, the laser beam irradiation process will be described.
In the laser beam irradiation step, a pulse laser beam is irradiated from the condenser 524 of the laser beam irradiation unit 5 that irradiates the laser beam toward a predetermined street of the semiconductor wafer 10, and the chuck table 36, and thus the semiconductor wafer held on the chuck table 36 is held. 10 is moved in a direction indicated by an arrow X at a predetermined feed rate (for example, 100 mm / second). In the laser beam irradiation step, for example, the following laser beam is irradiated as the laser beam.
Light source: YAG laser or YVO4 laser wavelength: 1064 nm (external infrared laser beam)
Output: 3.5W
Repeat frequency: 100 kHz
Pulse width: 20 ns
Condensing spot diameter: φ1μm
[0026]
As the laser beam irradiated in the laser beam irradiation step described above, a laser beam in the infrared light region having a long wavelength is used, and condensed inside through the antireflection layer 103 formed on the back surface 10b of the semiconductor wafer 10 as shown in FIG. Irradiate with matching points. The reason why the laser beam in the infrared region is used in this laser beam irradiation step is that the laser beam in the ultraviolet region having a short wavelength is reflected by the surface and does not enter the semiconductor wafer 10. In this way, by moving the semiconductor wafer 10 in the direction indicated by the arrow X while aligning the condensing point inside the semiconductor wafer 10 and irradiating the laser beam, the altered region continues along the street inside the semiconductor wafer 10. Formed. As a result, the semiconductor wafer 10 can be divided along a continuously formed altered region, that is, a street. In the laser beam irradiation step described above, the laser beam is irradiated through the antireflection layer 103 formed on the back surface 10b of the semiconductor wafer 10, so that the reflectance of the laser beam is reduced and energy loss due to the reflection of the laser beam is reduced. Therefore, energy close to 100% of the irradiated laser beam can be contributed to the processing, so that energy consumption can be greatly reduced. Further, in the illustrated embodiment, the antireflection layer 103 is formed on the back surface 10b where the circuit 102 of the semiconductor wafer 10 is not formed, and the laser beam is irradiated from the back surface 10b side where the antireflection layer 103 is formed. Therefore, it can be divided into individual semiconductor chips without damaging the circuit 102.
[0027]
When the laser beam irradiation process described above is executed along all the streets formed in the first direction of the semiconductor wafer 10, the chuck table 36 is rotated by 90 degrees. The semiconductor wafer 10 is divided into individual semiconductor chips by performing the above-described laser beam irradiation process on all the streets formed in the second direction of the semiconductor wafer 10.
[0028]
In the illustrated embodiment described above, the semiconductor wafer 10 held on the chuck table 36 is moved when performing the laser beam irradiation step. However, the laser beam irradiation unit 5 may be moved. In the illustrated embodiment, the semiconductor wafer 10 held on the chuck table 36 is indexed and moved in the arrow Y direction. However, the laser beam irradiation unit 5 can be indexed and moved in the arrow Y direction. . However, when the laser beam irradiation means 524 is moved, the accuracy may be deteriorated due to vibration or the like. Therefore, the laser beam irradiation unit 5 is kept stationary and the chuck table 36 and thus the semiconductor wafer held by the laser beam irradiation unit 5 are moved. It is preferable to move 10 appropriately.
[0029]
As mentioned above, although this invention was demonstrated based on embodiment of illustration, this invention is not limited to embodiment mentioned above. That is, in the illustrated embodiment, the antireflection layer 103 is formed on the back surface 10b where the circuit 102 of the semiconductor wafer 10 is not formed, and the laser beam is irradiated from the back surface 10b side where the antireflection layer 103 is formed. As an example, the antireflection layer 103 may be formed along the street (cutting line) 101 on the surface 10a, and laser light may be emitted from the surface 10a side through the antireflection layer 103. In the illustrated embodiment, the semiconductor wafer 10 is divided into individual semiconductor chips. However, the present invention can be widely applied to various processes using a laser beam.
[0030]
【The invention's effect】
According to the laser processing method of the present invention, after forming the antireflection layer in the region of the workpiece to be irradiated with the laser beam, the laser beam is irradiated through the antireflection layer, so that the reflectance of the laser beam is reduced, Energy loss due to reflection of the laser beam is reduced. Therefore, energy close to 100% of the irradiated laser beam can be contributed to the processing, so that energy consumption can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a perspective view of a laser processing apparatus for carrying out a laser processing method according to the present invention.
FIG. 2 is a block diagram schematically showing a configuration of laser beam processing means provided in the laser processing apparatus shown in FIG.
FIG. 3 is a perspective view of a semiconductor wafer as a workpiece to be divided and processed by the laser processing method according to the present invention.
4 shows a state in which an antireflection layer is formed on the back surface of the semiconductor wafer as the workpiece shown in FIG. 2 by the antireflection layer forming step in the laser processing method according to the present invention, and a part thereof is broken away. Perspective view.
5 is a perspective view showing a state in which the front surface of the semiconductor wafer having an antireflection layer formed on the back surface shown in FIG. 4 is attached to a protective tape attached to an annular frame.
FIG. 6 is an explanatory view showing a laser beam irradiation step in the laser processing method according to the present invention.
[Explanation of symbols]
2: stationary base 3: chuck table mechanism 31: guide rail 32: first sliding block 33: second sliding block 36: chuck table 37: moving means 38: moving means 4: laser beam irradiation unit support mechanism 41: guidance Rail 42: Movable support base 43: Moving means 5: Laser beam irradiation unit 51: Unit holder 52: Laser beam processing means 522: Laser beam oscillation means 523: Laser beam modulating means 524: Condenser 53: Moving means 6: Imaging Means 10: semiconductor wafer 101: street 102: circuit 103: antireflection layer 11: annular frame 12: protective tape

Claims (4)

A laser processing method for performing predetermined processing by irradiating a workpiece with a laser beam,
An anti-reflection layer forming step of forming an anti-reflection layer in a region irradiated with at least a laser beam of the workpiece;
A laser beam irradiation step of irradiating a laser beam through the antireflection layer,
A laser processing method characterized by the above. A laser processing method for generating a modified region by irradiating a laser beam having a wavelength in the infrared region with a focusing point inside the workpiece, and performing a predetermined processing,
An anti-reflection layer forming step of forming an anti-reflection layer in a region irradiated with at least a laser beam of the workpiece;
And a laser beam irradiation step of irradiating a laser beam with a focusing point inside the workpiece through the antireflection layer,
A laser processing method characterized by the above. The workpiece is a semiconductor wafer in which a plurality of streets are formed in a lattice shape on the surface and a circuit is formed in a plurality of regions partitioned by the plurality of streets. 3. The laser processing method according to claim 2, wherein the semiconductor wafer is formed continuously along the street and the semiconductor wafer is divided into individual semiconductor chips. The antireflection layer forming step forms the antireflection layer on the back surface of the semiconductor wafer, and the laser beam irradiation step aligns the condensing point along the street through the antireflection layer formed on the back surface of the semiconductor wafer. The laser processing method of Claim 3 which irradiates a laser beam.

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