Method for processing wafers and apparatus for processing wafers

Abstract

To provide a processing method of a wafer capable of appropriately dividing the wafer into individual chips even if the wafer is thin, and a processing device of the wafer.SOLUTION: A method comprises steps of: irradiating a wafer 10 with a pulse laser beam LB having a wavelength having penetrability to the wafer while positioning a focal point of the laser beam at an inner part of a division schedule line; continuously forming a modified layer; and applying an external force to the wafer to divide it. The step of forming the modified layer comprises steps of: setting a position of a focal point S at a first depth d1 from a surface 10a irradiated with the laser beam and a second depth d2 shallower than the first depth; finding a speed that a thermal impulse generated by the formation of the modified layer in the first depth and a delivery time when the thermal impulse reaches the second depth by using the difference between the first depth and the second depth; calculating a total time by adding the delivery time to the time when the modified layer is formed at the second depth; and setting the time of the total time or more as a pulse width of a pulse laser beam.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer and a wafer processing apparatus.

Background Art

[0002] A wafer on which a plurality of devices such as ICs and LSIs are partitioned by a dicing line and formed on the surface is diced by a dicing apparatus and used in electric devices such as mobile phones and personal computers.

[0003] Also, a method has been proposed in which a condensing point of a pulsed laser beam having a wavelength that is transmissive to the wafer is positioned inside the dicing line and irradiated, and the wafer is processed and fed to continuously form a modified layer inside the dicing line, and then an external force is applied to divide the wafer into individual device chips, thereby narrowing the width of the dicing line and preventing the wafer from being contaminated with cutting chips (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in recent years, miniaturization of device chips has been progressing, and along with this, the thickness of wafers has been decreasing as well. In particular, when the thickness of the wafer becomes 100 μm or less, it becomes difficult to extend cracks in the vertical direction from the modified layer without applying an excessive load to the wafer, and there is a problem that it becomes difficult to appropriately divide the wafer into individual device chips.

[0006] The present invention has been made in view of the above facts, and its main technical problem is to provide a wafer processing method and a wafer processing apparatus that can properly divide a wafer into individual chips even when the wafer thickness is thin. [Means for solving the problem]

[0007] To solve the main technical problems described above, the present invention provides a wafer processing method comprising: a modified layer formation step in which a pulsed laser beam with a wavelength that is transparent to the wafer is positioned at the focal point inside the division line and irradiated, and the wafer is fed through the processing to continuously form a modified layer inside the division line; and a division step in which an external force is applied to the division line in which the modified layer has been formed to divide the wafer, wherein in the modified layer formation step, the focal point is positioned at a first depth and a second depth shallower than the first depth from the side on which the pulsed laser beam is irradiated. A wafer processing method is provided, which includes: a focusing point setting step; an arrival time calculation step, in which the arrival time for the thermal shock wave to reach the second depth is determined by using the speed at which the thermal shock wave generated when the modified layer is formed at the first depth as the denominator and the difference between the first depth and the second depth as the numerator; a total time calculation step, in which the arrival time is added to the time when the thermal shock wave reaches the second depth and the modified layer is formed at the second depth to determine the total time; and a pulse width setting step, in which the pulse width of the pulsed laser beam is set to a time equal to or greater than the total time.

[0008] In the focusing point setting step, it is preferable that the arrival time is set such that the arrival time falls within the time it takes for the thermal shock wave to be generated, attenuated, and disappear. Furthermore, when the propagation speed of the thermal shock wave in the wafer is 182 m / s and the time it takes for the thermal shock wave to be generated, attenuated, and disappear is 110 ns, it is preferable to set the focusing point such that the difference between the first depth and the second depth is 20 μm or less, and to set the pulse width to 200 to 500 ns in the pulse width setting step. In addition, it is preferable to set the pulse energy to 2.5 to 7.5 μJ in the modified layer formation process.

[0009] In the modified layer formation process, the pitch of the focal point, which is determined by using the feed rate for processing as the numerator and the repetition frequency of the pulsed laser beam as the denominator, is preferably set to 2.25 to 10.25 μm. Furthermore, the wafer is preferably a silicon wafer with a thickness of 100 μm or less.

[0010] Furthermore, according to the present invention, a wafer processing apparatus includes a holding means for holding a wafer, a laser beam irradiation means for irradiating the wafer held by the holding means with a pulsed laser beam, and a processing feed means for relative processing feed of the holding means and the laser beam irradiation means, wherein the laser beam irradiation means includes an oscillator that emits a pulsed laser beam of a wavelength that is transparent to the wafer, a concentrator that focuses the pulsed laser beam emitted by the oscillator and positions a focal point inside the wafer held by the holding means, and a first depth and a depth greater than the first depth of the wafer held by the holding means The system includes a focusing point setting unit for setting the focusing point to a shallower second depth, and a control means, the control means including: an arrival time storage unit that calculates and stores the arrival time of the thermal shock wave when it reaches the second depth, using the speed at which the thermal shock wave propagates when the modified layer is formed at the first depth as the denominator and the difference between the first depth and the second depth as the numerator; a total time storage unit that stores the total time obtained by adding the arrival time to the time it takes for the thermal shock wave to reach the second depth and for the modified layer to be formed at the second depth; and a pulse width adjustment unit that sets the pulse width of the pulsed laser beam to be a time equal to or greater than the total time. The focusing point setting unit is a spatial light phase modulator or a mask that forms an elliptical beam. Wafer processing equipment is provided. [Effects of the Invention]

[0012] The wafer processing method of the present invention comprises: a modified layer formation step of positioning the focal point of a pulsed laser beam with a wavelength that is transparent to the wafer inside the line to be divided and irradiating it, and feeding the wafer to continuously form a modified layer inside the line to be divided; and a dividing step of applying an external force to the line to be divided in which the modified layer has been formed to divide it, wherein in the modified layer formation step, a focal point setting step is set so that the focal point is positioned at a first depth and a second depth shallower than the first depth from the side on which the pulsed laser beam is irradiated; and the difference between the first depth and the second depth is divided by the speed at which the thermal shock wave generated when the modified layer is formed at the first depth propagates. The process includes a step to calculate the arrival time for the thermal shock wave to reach the second depth, a step to calculate the total time by adding the arrival time to the time it takes for the thermal shock wave to reach the second depth and for a modified layer to be formed at that second depth, and a step to set the pulse width of the pulsed laser beam to be equal to or greater than the total time. As a result, even with a thin wafer, for example, less than 100 μm thick, multiple modified layers can be easily formed in the vertical direction with a single scan of the pulsed laser beam LB, and cracks that extend vertically can be formed in the modified layers, making it possible to properly divide the wafer into individual chips.

[0013] Furthermore, the wafer processing apparatus of the present invention includes a holding means for holding a wafer, a laser beam irradiation means for irradiating the wafer held by the holding means with a pulsed laser beam, and a processing feed means for relative processing feed of the holding means and the laser beam irradiation means, wherein the laser beam irradiation means includes an oscillator that emits a pulsed laser beam of a wavelength that is transparent to the wafer, a concentrator that focuses the pulsed laser beam emitted by the oscillator and positions a focal point inside the wafer held by the holding means, and a first depth and a second depth shallower than the first depth relative to the wafer held by the holding means. The system includes a focusing point setting unit for setting the focusing point to be located at two depths, and a control means, the control means including: an arrival time storage unit that calculates and stores the arrival time of the thermal shock wave when it reaches the second depth, using the velocity V at which the thermal shock wave propagates when the modified layer is formed at the first depth as the denominator and the difference between the first depth and the second depth as the numerator; a total time storage unit that stores the total time obtained by adding the arrival time to the time it takes for the thermal shock wave to reach the second depth and for the modified layer to be formed at the second depth; and a pulse width adjustment unit that sets the pulse width of the pulsed laser beam to be a time equal to or greater than the total time. Furthermore, the focusing point setting unit is a spatial light phase modulator or a mask that forms an elliptical beam. Therefore, even with thin wafers, for example, those less than 100 μm thick, multiple modified layers can be easily formed in the vertical direction with a single scan of the pulsed laser beam LB, and cracks extending in the vertical direction can be formed in these modified layers, making it possible to properly divide the wafer into individual chips. [Brief explanation of the drawing]

[0014] [Figure 1] This is an overall perspective view of the laser processing apparatus of this embodiment. [Figure 2] Figure 1 is a schematic block diagram showing the optical system of the laser beam irradiation means to be mounted on the laser processing apparatus shown in Figure 1. [Figure 3] Figure 1 is a perspective view of a wafer processed by the laser processing apparatus shown. [Figure 4] This is a perspective view showing an embodiment of the modified layer formation process. [Figure 5]This is a partially enlarged cross-sectional view showing the first and second focal points formed in the modified layer formation process shown in Figure 4. [Figure 6] This is a partially enlarged cross-sectional view showing how the modified layer is formed during the modified layer formation process. [Modes for carrying out the invention]

[0015] Hereinafter, embodiments relating to a wafer processing method and a wafer processing apparatus constructed based on the present invention will be described in detail with reference to the attached drawings.

[0016] Figure 1 shows a laser processing apparatus 1, which is an example of a wafer processing apparatus according to the present invention. The laser processing apparatus 1 is an apparatus for performing laser processing on a wafer 10, for example, made of silicon (Si), which is held via a protective tape T on an annular frame F held by a holding means 3. The laser processing apparatus 1 is disposed on a base 2 and includes at least a laser beam irradiation means 7 that irradiates the surface 10a of the wafer 10 with a pulsed laser beam LB.

[0017] In addition to the holding means 3 and laser beam irradiation means 7 described above, the laser processing apparatus 1 is equipped with a processing feed means 4 that relatively feeds the holding means 3 and the laser beam irradiation means 7 for processing. The processing feed means 4 includes an X-axis moving means 4a that moves the holding means 3 in the X-axis direction and a Y-axis moving means 4b that moves the holding means 3 in the Y-axis direction. Furthermore, the laser processing apparatus 1 is equipped with a frame 5 consisting of a vertical wall portion 5a erected on the side of the X-axis moving means 4a and Y-axis moving means 4b on the base 2 and a horizontal wall portion 5b extending horizontally from the upper end of the vertical wall portion 5a, and a control means 100 that controls each operating part.

[0018] The holding means 3 includes a rectangular X-axis movable plate 31 mounted on the base 2 so as to be movable in the X-axis direction, a rectangular Y-axis movable plate 32 mounted on the X-axis movable plate 31 so as to be movable in the Y-axis direction, a cylindrical support column 33 fixed to the upper surface of the Y-axis movable plate 32, and a rectangular cover plate 34 fixed to the upper end of the support column 33. A chuck table 35 extending upward through a long hole formed on the cover plate 34 is disposed on the cover plate 34. The chuck table 35 is configured to be rotatable by a rotation driving means (not shown) housed in the support column 33. On the upper surface of the chuck table 35, a circular suction chuck 36 formed of a porous material having air permeability and having an XY plane specified by X coordinates and Y coordinates as a holding surface is disposed. The suction chuck 36 is connected to a suction means (not shown) by a flow path passing through the support column 33. Around the suction chuck 36, four clamps 37 for gripping and fixing the frame F when holding the wafer 10 on the chuck table 35 are arranged at equal intervals.

[0019] The X-axis moving means 4a converts the rotational motion of the motor 42a into a linear motion via a ball screw 42b and transmits it to the X-axis movable plate 31, and moves the X-axis movable plate 31 in the X-axis direction along a pair of guide rails 2A, 2A arranged along the X-axis direction on the base 2. The Y-axis moving means 4b converts the rotational motion of the motor 44a into a linear motion via a ball screw 44b and transmits it to the Y-axis movable plate 32, and moves the Y-axis movable plate 32 in the Y-axis direction along a pair of guide rails 31a, 31a arranged along the Y-axis direction on the X-axis movable plate 31.

[0020] Inside the horizontal wall portion 5b of the frame body 5, an optical system constituting the above-described laser beam irradiation means 7 and an alignment means 6 are accommodated. On the lower surface side of the tip of the horizontal wall portion 5b, a condenser 71 is disposed which constitutes a part of the laser beam irradiation means 7 and condenses the pulsed laser beam LB to irradiate the wafer 10. The alignment means 6 is an imaging means for imaging the wafer 10 held by the holding means 3 and detecting the position and orientation of the wafer 10, the position of the division planned line 14 irradiated with the pulsed laser beam LB, etc., and is disposed at a position adjacent in the X-axis direction shown by the arrow X in the figure with respect to the above-described condenser 71.

[0021] FIG. 2 shows a block diagram schematically showing the optical system of the above-described laser beam irradiation means 7. The laser beam irradiation means 7 of the present embodiment includes an oscillator 72 that oscillates a pulsed laser beam LB having a wavelength that is transmissive to the wafer 10, an attenuator 73 that adjusts the output of the pulsed laser beam LB, and a condenser point setting unit 74 that sets the condenser point of the pulsed laser beam LB to be positioned at a first depth d1 and a second depth d2 shallower than the first depth d1 with respect to the wafer 10, and a reflection mirror 75. The pulsed laser beam LB is condensed by the condenser lens 71a of the condenser 71 and irradiated to the wafer 10 held by the holding means 3. Note that the attenuator 73 and the reflection mirror 75 are set as necessary and can be omitted as appropriate.

[0022] The focusing point setting unit 74 will be described with reference to Figure 2. The focusing point setting unit 74 is composed of, for example, a spatial optical phase modulator (LCOS), and electrically controls the spatial distribution of the incident pulsed laser beam LB to position a first focusing point S1 at an arbitrary first depth d1 from the upper surface of the wafer 10 (in this embodiment, the surface 10a), and a second focusing point S2 at an arbitrary second depth d2 shallower than the first depth d1. As a specific setting method for setting the first focusing point S1 and the second focusing point S2 at arbitrary depth positions, as shown in Figure 2, the shape of the spot S of the pulsed laser beam LB is formed using the focusing point setting unit 74, and when viewed in the XY plane, it is set to be an elliptical beam extended in the scanning direction (X-axis direction) of the pulsed laser beam LB. In this way, by forming a spot S having a high-energy-density region Sc at its center and irradiating it from the surface 10a side of the wafer 10, it is possible to position the focal point at the first depth d1 and the second depth d2, respectively, as shown in the figure. In this embodiment, the spot S of the pulsed laser beam LB is set by the focal point setting unit 74 to be an approximately elliptical shape with a major axis dimension of 12 μm and a minor axis dimension of 2 μm, along the X axis direction in which the pulsed laser beam LB is scanned. As a result, the first depth d1 where the first focal point S1 is positioned is set to a depth of 60 μm from the surface 10a of the wafer 10, and the second depth d2 where the second focal point S2 is positioned is set to a depth of 48 μm from the surface 10a. As a result, the difference between the first depth d1 and the second depth d2 (d1-d2) is 12 μm.

[0023] Furthermore, the focusing point setting unit 74 of the present invention is not limited to being composed of the spatial optical phase modulator (LCOS) described above. In order to make the spot S of the pulsed laser beam LB an elliptical beam as described above, a mask having an elliptical gap can be placed at any position between the oscillator 72 and the focusing unit 71 instead of the spatial optical phase modulator to form a spot shape S of the shape described above. Furthermore, as a means of positioning a first focal point S1 at an arbitrary first depth d1 and a second focal point S2 at an arbitrary second depth d2 shallower than the first depth d1, the method is not limited to forming the spot shape into an elliptical shape as described above. The focal point setting unit 74 may be formed by two optical paths, the pulsed laser beam LB emitted from the oscillator 72 may be branched on the optical path of the optical system and passed through two different optical paths to form two types of pulsed laser beams adjusted so that the focal points are at different positions, and the focal points may be positioned at the first depth d1 and the second depth d2 by focusing these two types of pulsed laser beams with the condenser 71. Moreover, it is also possible to simulate the formation of these two types of pulsed laser beams using the spatial optical phase modulator described above, and the method is not necessarily limited to branching and forming them on the optical system of the laser beam irradiation means 7.

[0024] The control means 100 includes: an arrival time storage unit 110 that stores the arrival time t1 it takes for the thermal shock wave to reach the second depth d2, with the propagation speed V of the thermal shock wave generated when a modified layer is formed at the first depth d1 as the denominator and the difference between the first depth d1 and the second depth d2 (d1-d2) as the numerator; a total time storage unit 120 that stores the total time t3 obtained by adding the arrival time t1 to the time t2 it takes for the thermal shock wave to reach the second depth d2 and for a modified layer to be formed at the second depth d2; and a pulse width adjustment unit 130 that sets the pulse width Pw of the pulsed laser beam LB to be greater than or equal to the total time t3 and adjusts the pulse width of the pulsed laser beam LB emitted from the oscillator 72.

[0025] The laser processing apparatus 1 of this embodiment has a configuration that is generally as described above, and an embodiment of the wafer processing method of the present invention, which is carried out using the laser processing apparatus 1 described above, will be described below.

[0026] The wafer 10 processed by the wafer processing method of this embodiment is, for example, a silicon (Si) wafer with a thickness of 100 μm, and as shown in Figure 3, a plurality of devices 12 are partitioned by division lines 14 and formed on the surface 10a of the wafer. The wafer 10 is positioned in the center of the opening Fa of an annular frame F having an opening Fa capable of accommodating the wafer 10, and is held via protective tape T. In the embodiments described below, an example is described in which a pulsed laser beam LB is irradiated from the surface 10a side of the wafer 10 to form a modified layer along the interior of the division lines 14, but the present invention is not limited thereto and also includes the case in which a pulsed laser beam LB is irradiated from the back side of the wafer 10 to form a modified layer along the interior of the division lines 14.

[0027] Once the wafer 10 described above is prepared, as shown in Figure 4, a pulsed laser beam LB with a wavelength that is transparent to the wafer 10 is positioned at its focal point inside the division line 14 and irradiated, and the wafer 10 is processed and fed to perform a modified layer formation process in which a modified layer is continuously formed inside the division line 14.

[0028] In carrying out the modified layer formation process, first, a focusing point setting step is performed in which the focusing point is positioned at a first depth d1 and a second depth d2 that is shallower than the first depth d1 from the upper surface (surface 10a in this embodiment) irradiated with the pulsed laser beam LB. In the focusing point setting step of this embodiment, as described above, the first depth d1 where the first focusing point S1 is positioned is set to 60 μm, and the second depth d2 where the second focusing point S2 is positioned is set to 48 μm.

[0029] Next, a step is performed to calculate the arrival time t1 for the thermal shock wave to reach the second depth d2, using the propagation speed V of the thermal shock wave generated when the modified layer is formed at the first depth d1 as the denominator and the difference between the first depth d1 and the second depth d2 (d1-d2=12μm) as the numerator. In a silicon (Si) wafer 10, the propagation speed V of the thermal shock wave generated when the modified layer is formed is known to be 182 m / s. Arrival time t1=(d1-d2) / V=66ns The arrival time t1 calculated in this way is stored in the arrival time storage unit 110 of the control means 100 described above.

[0030] Next, a total time calculation step is performed to determine the total time t3 by adding the arrival time t1 to the time t2 required for the thermal shock wave to reach the second focal point S2 formed at the second depth d2 and for the modified layer to be formed at the second focal point S2 at the second depth d2. The time t2 required for the modified layer to be formed at this second focal point S2 has been confirmed by the inventors of the present invention, and in this embodiment, the time t2 required for the modified layer to be formed at the second focal point S2 was 100 ns, Total time t3 = t1 + t2 = 166 ns The total time t3 calculated by performing the above total time calculation step is stored in the total time storage unit 120 of the control means 100 described above.

[0031] Next, a pulse width setting step is performed in which the pulse width Pw (for example, 350 ns) of the pulsed laser beam LB is set to a time equal to or greater than the total time t3 calculated by the total time calculation step described above and stored in the total time storage unit 120. This is based on the fact that, as a condition for the proper formation of a modified layer at the second depth d2, it is necessary that the second focal point S2 is formed at the second depth d2 when the thermal shock wave generated when the modified layer is formed at the first focal point S1 reaches the second depth d2, and in addition, the pulse width Pw must be set to a time equal to or greater than the total time t3. By setting the pulse width Pw in this way, a modified layer is properly formed at the second depth d2.

[0032] Incidentally, the first depth d1 and the second depth d2, which are set by the above-described focusing point setting step, are set taking into consideration the following conditions. First, when a modified layer is formed and a thermal shock wave is generated at the first depth d1, where higher energy is concentrated compared to the second depth d2, the thermal shock wave is attenuated as it propagates through the wafer 10. In the laser processing conditions for processing the silicon wafer 10 described above, it is known that the thermal shock wave generated at the first focusing point S1 is extinguished in a predetermined extinction time T = 110 ns. Therefore, the first depth d1 and the second depth d2 are set such that the time it takes for the thermal shock wave generated by the formation of the modified layer at the first depth d1 to reach the second depth d2 is at least within the above extinction time T (110 ns).

[0033] Furthermore, the first depth d1 and the second depth d2 set by the above-described focusing point setting step may be set to satisfy the following conditions. That is, if the velocity V (182 m / s) when a thermal shock wave propagates within the wafer 10 and the time until the thermal shock wave V attenuates and disappears is T (110 ns), the distance over which the thermal shock wave propagates can be calculated by V × T, d1-d2 < V×T (=20μm) The first depth d1 and the second depth d2 should be set to satisfy the condition, and in this embodiment, d1-d2 is set to 12 μm.

[0034] As described above, once the focusing point setting step, arrival time calculation step, total time calculation step, and pulse width setting step have been performed, the focusing point of the pulsed laser beam LB, which has a wavelength that is transparent to the wafer 10, is positioned inside the line to be divided, and the wafer is irradiated and processed to continuously form a modified layer inside the line to be divided.

[0035] Once the wafer 10 is placed on the chuck table 35 of the laser processing apparatus 1, it is sucked in by a suction means (not shown) and the frame F is gripped and fixed by a clamp 37. Next, the X-axis moving means 4a and Y-axis moving means 4b of the processing feed means 4 are activated to position it directly below the alignment means 6 shown in Figure 1. Then, the wafer 10 is photographed by the alignment means 6, and the chuck table 35 is rotated by a rotational drive means (not shown) to align the direction of the predetermined division line 14 in the X-axis direction, and align the division line 14 perpendicular to the division line 14 in the Y-axis direction. Furthermore, position information defined by the XY coordinates of the division line 14 to be processed is stored in the control means 100.

[0036] Based on the position information of the division line 14 to be processed detected by the alignment means 6 described above, the processing feed means 4 is activated to position the predetermined division line 14 formed on the wafer 10 directly below the focuser 71 of the laser beam irradiation means 7, as shown in Figure 4. Next, as shown in Figure 5, a first focusing point S1 is positioned on the wafer 10 at a first depth d1 (60 μm) of the pulsed laser beam LB, and a second focusing point S2 is positioned at a second depth d2 (48 μm) that is shallower than the first depth d1. In this embodiment, high-energy-density regions are formed at the first focusing point S1 and the second focusing point S2, and a low-energy-density region S3 is formed surrounding the first focusing point S1 and the second focusing point S2, so that more energy is supplied to the first focusing point S1 than to the second focusing point S2.

[0037] As described above, once the focal point of the pulsed laser beam LB is positioned inside the wafer 10, the X-axis moving means 4a is activated to move the wafer 10 in the X-axis direction, as shown in Figure 6, and the pulsed laser beam LB is irradiated along the interior of the division line 14, thereby continuously forming a modified layer 18 inside the division line 14. The modified layer 18 includes a first modified layer 16a formed at the first focal point S1 and a second modified layer 16b formed when a thermal shock wave generated from the first modified layer 16a reaches the second focal point S2. In this embodiment, it further includes a plurality of cracks 17 formed in the vertical direction (Z-axis direction) to connect the first modified layer 16a and the second modified layer 16b as they are formed substantially simultaneously.

[0038] The laser beam irradiation means 7, the X-axis moving means 4a, the Y-axis moving means 4b, and the rotational drive means of the chuck table 35 (not shown) are operated to continuously form the modified layer 18 along the inside of all the planned division lines 14 formed on the surface 10a of the wafer 10, thereby completing the modified layer formation process.

[0039] Once the above-described modified layer formation process is carried out, a splitting process is performed to divide the wafer 10 into individual chips by applying an external force to the splitting line 14 on which the modified layer 18 has been formed. This splitting process can be carried out using well-known external force application means, which are not shown in the figures. These external force application means may be, for example, means of applying an external force to the splitting line 14 by pressing and rolling an elastic roller on the surface 10a of the wafer 10, or means of applying an external force to the splitting line 14 by radially expanding a protective tape T that holds the wafer 10, thereby dividing the wafer 10 into individual chips.

[0040] The inventors of the present invention conducted laser processing experiments to form the modified layer by changing the laser processing conditions within the following range in order to find the appropriate range of laser processing conditions for forming the modified layer 18 described above, and confirmed the range in which the appropriate modified layer 18 described above can be formed. Wavelength: 1080nm Repetition frequency: 80kHz Average output: 0.1~1.0W Pulse energy: 1.25~12.5 μJ Machining feed rate: 100~1000mm / s Pulse pitch: 1.25~12.5μm Pulse width Pw: 150~500ns

[0041] Regarding the pulse width Pw when irradiating with the pulsed laser beam LB, it was stated that it is necessary to set the pulse width Pw to a time equal to or greater than the total time t3 (166 ns) mentioned above. However, experiments conducted by changing the above laser processing conditions confirmed that a good modified layer 18 is formed, particularly when set to 200-500 ns. Furthermore, based on the results of the above experiments, it was estimated that setting the pulse width Pw to a value exceeding 500 ns would result in a failure to form a good modified layer at the second depth d2, and a decrease in the quality of the modified layer 18.

[0042] Furthermore, it was confirmed that a good modified layer 18 could be formed by setting the pulse energy when irradiating with the pulsed laser beam LB in the range of 2.5 to 7.5 μJ. In particular, it was confirmed that a good modified layer 18 could be formed by setting the pulse energy in the range of 3.5 to 7.5 μJ and the pulse width Pw in the range of 250 to 350 ns when performing the above modified layer formation process, including a first modified layer 16a, a second modified layer 16b, and cracks 17 extending in the vertical direction.

[0043] Furthermore, when forming the modified layer 18 described above, by irradiating with a pulsed laser beam LB and positioning the focal point along the planned division line 14 to perform laser processing, the pitch of the focal point (pulse pitch), which is obtained by calculating with the processing feed speed as the numerator and the repetition frequency of the pulsed laser beam as the denominator, can be set in the range of 2.25 to 10.25 μm, thereby forming the modified layer 18 at appropriate intervals along the planned division line 14, making it possible to divide the wafer 10 into individual chips more accurately.

[0044] In the embodiments described above, an example in which a wafer 10 made of silicon is used as the workpiece was explained. However, the present invention is not limited to wafers 10 made of silicon, and is applicable even if the wafer is made of other materials, for example, including cases where the wafer is made of gallium nitride (GaN) or silicon carbide (SiC). The propagation speed of the thermal shock wave generated when a modified layer is formed on the wafer, the time it takes for the thermal shock wave to be generated, attenuated and disappear, and the time it takes for the modified layer to be formed at the second depth d2 will depend on the material that makes up the wafer. Therefore, when a wafer made of other materials is used as the workpiece, the propagation speed of the thermal shock wave generated when a modified layer is formed at the first depth d1 of the wafer, the time it takes for the thermal shock wave to be generated, attenuated and disappear, and the time it takes for the modified layer to be formed at the second depth d2 will be measured according to the material that makes up the wafer, and applied to the present invention to carry out the wafer processing method described above.

[0045] According to the present invention, even with thin wafers having a thickness of 100 μm or less, it is possible to easily form multiple modified layers in the vertical direction with a single scan of a pulsed laser beam LB, and since cracks extending in the vertical direction can be formed in these modified layers, it becomes possible to properly divide the wafer into individual chips. [Explanation of symbols]

[0046] 1: Laser processing equipment 2: Base 3: Holding means 31:X-axis movable plate 32: Y-axis movable plate 33: Post 34: Cover board 35: Chuck Table 36: Suction Chuck 37: Clamp 4: Processing feed means 4a:X-axis movement means 4b: Y-axis movement means 5:Frame body 5a: Vertical wall 5b:Horizontal wall part 6: Alignment means 7: Laser beam irradiation means 71: Light concentrator 71a: Focusing lens 72: Oscillator 73: Attenuator 74: Focusing point setting unit 75: Reflective mirror 10: Wafer 10a: surface 12: Devices 14: Planned division line 16a: First modified layer 16b: Second modification layer 17: Crack 18: Modified layer 100: Control means 110: Arrival time storage unit 120: Total time memory unit 130: Pulse width adjustment section d1: First depth d2: Second depth S: Spot S1: First focusing point S2; Second focusing point S3: Low energy density region Sc: central area

Claims

1. A method for processing wafers, A modified layer formation step involves positioning the focal point of a pulsed laser beam with a wavelength that is transparent to the wafer within the line to be divided and irradiating it, while simultaneously feeding the wafer through the process to continuously form a modified layer within the line to be divided, The process includes a splitting step of applying an external force to the splitting line on which the modified layer has been formed to split it, In the modified layer formation process, A focusing point setting step, which sets the focusing point to be located at a first depth and a second depth shallower than the first depth from the side on which the pulsed laser beam is irradiated, A step to calculate arrival time, in which the arrival time for the thermal shock wave to reach the second depth is determined by using the speed at which the thermal shock wave propagates when a modified layer is formed at the first depth as the denominator and the difference between the first depth and the second depth as the numerator, A total time calculation step involves adding the arrival time to the time when the thermal shock wave reaches the second depth and the modified layer is formed at the second depth, in order to obtain the total time. A pulse width setting step in which the pulse width of the pulsed laser beam is set to a time equal to or greater than the total time, A method for processing wafers including [a specific component].

2. In the light-gathering point setting step, The wafer processing method according to claim 1, wherein the first depth and the second depth are set such that the arrival time falls within the time it takes for the thermal shock wave to be generated, attenuated, and disappear.

3. A wafer processing method according to claim 2, wherein, when the speed at which a thermal shock wave propagates in the wafer is 182 m / s and the time it takes for the thermal shock wave to be generated, attenuated, and disappear is 110 ns, the focusing point is set such that the difference between the first depth and the second depth is 20 μm or less, and in the pulse width setting step, the pulse width is set to 200 to 500 ns.

4. In the modified layer formation process, The wafer processing method according to claim 1, wherein the pulse energy is set to 2.5 to 7.5 μJ.

5. In the modified layer formation process, The wafer processing method according to claim 1, wherein the pitch of the focal point, which is determined by using the feed rate for processing as the numerator and the repetition frequency of the pulsed laser beam as the denominator, is set to 2.25 to 10.25 μm.

6. The wafer processing method according to any one of claims 3 to 5, wherein the wafer is a silicon wafer and has a thickness of 100 μm or less.

7. A wafer processing apparatus, The system includes a holding means for holding a wafer, a laser beam irradiation means for irradiating the wafer held by the holding means with a pulsed laser beam, and a processing feed means for relative processing feed between the holding means and the laser beam irradiation means. The laser beam irradiation means comprises an oscillator that emits a pulsed laser beam of a wavelength that is penetrating to a wafer, a concentrator that focuses the pulsed laser beam emitted by the oscillator and holds it in the holding means to position a focal point inside the wafer, a focal point setting unit that sets the focal point to be positioned at a first depth and a second depth shallower than the first depth with respect to the wafer held in the holding means, and a control means. The control means is, An arrival time storage unit calculates and stores the arrival time of the thermal shock wave when it reaches the second depth, using the speed at which the thermal shock wave propagates when the modified layer is formed at the first depth as the denominator and the difference between the first depth and the second depth as the numerator. A total time storage unit stores the total time obtained by adding the arrival time to the time when the thermal shock wave reaches the second depth and a modified layer is formed at the second depth, A pulse width adjustment unit sets the pulse width of the pulsed laser beam to a time equal to or greater than the total time, Includes, The focusing point setting unit is a spatial light phase modulator or a mask for forming an elliptical beam, in a wafer processing apparatus.

Images