JP7285433B2 - LASER PROCESSING APPARATUS AND LASER PROCESSING METHOD - Google Patents

Description

The present invention relates to a laser processing apparatus and a laser processing method for processing a work using laser light.

As a conventional laser processing technology, a technology is known in which a laser beam for processing is condensed on the surface or inside of a work through a condenser lens while scanning the work. In such laser processing technology, in order to keep the height of the focal point of the processing laser beam (or processing depth) constant, the autofocus function is used to adjust the surface of the workpiece (laser beam irradiation surface). Feedback control is performed to adjust the position of the condenser lens so that the condenser lens follows the displacement (see Patent Documents 1 and 2, for example).

JP 2005-193284 A JP 2009-297773 A

When creating a workpiece, for example, a molding process is performed to reduce the thickness of the workpiece by back grinding. 9). During laser processing, when the distance between the converging point FP1 of the processing laser beam and the surface (upper surface) _W1U of the workpiece W1 is maintained at a desired distance by the autofocus function, the converging point FP1 of the processing laser beam and The distance between the back surface (lower surface) _W1B of the work W1 changes according to this thickness variation.

When processing a wafer on which semiconductor devices are formed, there is a case where the surface on which the semiconductor devices are formed faces downward and is irradiated with processing laser light from the front side (upper side). In this case, the distance between the focal point FP1 of the processing laser beam and the back surface _W1B of the work W has a significant effect on the quality of the semiconductor device. For example, if the distance between the focal point FP1 of the processing laser beam and the back surface _W1B of the workpiece W becomes too long, the crack will not extend sufficiently from the laser processing region P1 to the back surface _W1B , and the wafer will be broken. It will be torn apart when divided. When the wafer is torn, the peripheral edges and side surfaces of the semiconductor devices become meandering or rough, making the semiconductor devices more susceptible to damage. On the other hand, if the distance between the focal point of the processing laser beam and the rear surface _W1B of the work W is too close, the semiconductor device is likely to be thermally damaged by the processing laser beam.

The present invention has been made in view of such circumstances, and provides a laser processing apparatus and a laser processing method capable of appropriately adjusting the distance between the focal point of the laser beam for processing and the back surface of the work. intended to provide

In order to achieve the above objects, the following inventions are provided.

A laser processing apparatus according to a first aspect of the present invention includes a condensing lens that irradiates a processing laser beam from the surface side of a work, and a work thickness profile acquisition means that acquires a work thickness profile indicating the thickness of the work at the laser processing position. and control means for adjusting the position of the condensing lens based on the thickness profile of the work so that the distance from the back surface of the work to the focal point of the laser beam for processing is within a predetermined range.

According to the first aspect, it is possible to appropriately adjust the distance between the focal point of the processing laser beam and the back surface of the workpiece. As a result, the laser-processed region can be formed such that the crack sufficiently extends from the laser-processed region to the back side of the work. Furthermore, it is possible to suppress the conduction of laser light heat to the back side of the workpiece caused by the processing laser light. Moreover, in the first aspect, for example, the focal point of the processing laser beam can be set at a desired distance from the back surface of the workpiece. As a result, it is possible to prevent the laser beam for processing from reaching the back surface of the work and giving thermal damage to the semiconductor device formed on the back surface of the work.

According to a second aspect of the present invention, there is provided a laser processing apparatus according to the first aspect, wherein the control means keeps a constant distance from the rear surface of the work to the focal point of the laser beam for processing.

A laser processing apparatus according to a third aspect of the present invention is, in the first or second aspect, stage height profile acquisition means for acquiring a stage height profile indicating the height position of the surface of the stage on which the workpiece is held; , the workpiece held on the stage is irradiated with a detection laser beam through a condenser lens, and the height position of the workpiece surface is measured based on the reflected light from the surface of the workpiece. Work height profile acquisition means for acquiring a work height profile indicating the height position, and the work thickness profile acquisition means acquires the work thickness profile indicating the thickness of the work at the laser processing position. .

In the laser processing apparatus according to the fourth aspect of the present invention, in the third aspect, the work thickness profile acquisition means is based on the height position of the work measured along at least one scan line and the stage height profile , the thickness of the workpiece along the scan line is calculated, and the thickness profile of the workpiece is calculated based on the symmetry of the shape of the workpiece.

According to the fourth aspect, by utilizing the symmetry of the workpiece, the number of scan lines for measuring the height position of the surface of the workpiece can be reduced, and the cost required for measurement can be reduced.

In the laser processing apparatus according to a fifth aspect of the present invention, in the fourth aspect, the work height profile acquisition means measures the height position of the work along a scan line passing through the center of symmetry of the work, and the stage height From the thickness profile, the thickness of the work along the scan line is calculated, and the work thickness profile is calculated based on the symmetry of the shape of the work.

According to the fifth aspect, by using the measurement result along the scan line passing through the center of symmetry of the work, it is possible to improve the calculation accuracy of the work thickness profile.

A laser processing method according to a sixth aspect of the present invention is a laser processing method in which a processing laser beam is irradiated from the surface side of a work using a condenser lens to form a laser processing region, wherein the laser processing position of the work obtaining a workpiece thickness profile indicating the thickness of the workpiece, and adjusting the position of the condenser lens so that the distance from the back surface of the workpiece of the laser beam for processing to the focusing point of the laser beam for processing is within a predetermined range based on the workpiece thickness profile and adjusting the

According to the present invention, it is possible to appropriately adjust the distance between the focal point of the processing laser beam and the back surface of the workpiece.

FIG. 1 is a configuration diagram showing an outline of a laser processing apparatus according to one embodiment of the present invention. FIG. 2 is a conceptual diagram for explaining a laser processing area formed in the vicinity of the focal point inside the work. FIG. 3 is a block diagram showing the configuration of the control device. FIG. 4 is a diagram for explaining a work thickness profile. FIG. 5 is a diagram for explaining the offset amount. FIG. 6 is a cross-sectional view showing the process of forming the laser-processed region P. As shown in FIG. FIG. 7 is a table showing the offset amount for each machining position of the workpiece W. FIG. FIG. 8 is a flow chart showing a laser processing method according to one embodiment of the present invention. FIG. 9 is a cross-sectional view showing an example in which laser processing is performed while maintaining the distance between the focal point of the processing laser beam and the surface of the work.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(laser processing equipment)
FIG. 1 is a configuration diagram showing an outline of a laser processing apparatus 10 according to one embodiment of the present invention. As shown in FIG. 1, the laser processing apparatus 10 of the present embodiment includes a stage 12 for moving a work W, a processing laser beam L1 for irradiating the work W, and a position of a focal point of the processing laser beam L1. An optical system device 20 for adjusting (processing depth) and a control device 50 for controlling each part of the laser processing device 10 are provided.

Although the work W is not particularly limited, for example, a semiconductor substrate such as a silicon wafer, a glass substrate, a piezoelectric ceramic substrate, a glass substrate, or the like can be applied.

The stage 12 is configured to be movable in XYZθ directions. In this embodiment, the stage 12 moves relative to the optical system device 20, but at least one of the optical system devices 20 may move, or both the stage 12 and the optical system device 20 may move. may move.

The stage 12 holds the workpiece W by suction. The workpiece W is placed on the stage 12 so that its surface W _U (laser beam irradiation surface) is opposite to the device surface.

In the example shown in FIG. 1, the three XYZ directions are orthogonal to each other, of which the X and Y directions are horizontal, and the Z direction is vertical. The θ direction is the direction of rotation about the vertical axis (Z axis).

The optical system device 20 is arranged at a position facing the work W, and irradiates the work W with a processing laser beam L1 for forming a laser processing region P inside the work W. As shown in FIG.

The optical system device 20 includes a laser light source 21 , a dichroic mirror 23 , a processing objective lens (collecting lens) 24 , an actuator 25 and an AF (Automatic Focus) sensor 30 .

The laser light source 21 emits a processing laser beam L1 for forming a laser processing region P inside the work W. As shown in FIG.

The dichroic mirror 23 transmits the processing laser beam L1 and reflects the detection laser beam L2 emitted from the AF sensor 30, which will be described later. In this embodiment, the optical axis of the detection laser beam L2 and the optical axis of the processing laser beam L1 are made coaxial by the dichroic mirror 23 and emitted.

The processing laser beam L1 emitted from the laser light source 21 passes through the dichroic mirror 23 and then is condensed inside the work W by the condensing lens 24 . The position (focus position) of the condensing point FP of the processing laser beam L1 is adjusted by slightly moving the condensing lens 24 in the Z direction by the actuator 25 .

FIG. 2 is a conceptual diagram explaining a laser processing area formed in the vicinity of the focal point inside the work W. As shown in FIG. 2A shows a state in which the processing laser beam L1 incident inside the workpiece W forms a laser processing region P at the focal point, and 2B in FIG. 2 shows an intermittent pulse-like processing laser beam L1. The workpiece W is horizontally moved under , and discontinuous laser processing regions P, P, . . . are formed side by side. 2C of FIG. 2 shows a state in which the laser processing region P is formed in multiple layers inside the workpiece W. FIG.

As shown in 2A of FIG. 2, when the focal point of the processing laser beam L1 incident from the surface of the work W is set inside the work W in the thickness direction, the processing laser light transmitted through the surface of the work W is The energy of the light L1 is concentrated at a condensing point inside the work W, and a laser processing area P is formed in the vicinity of the condensing point inside the work W. As shown in FIG. Here, the laser processing region P is a region where the physical properties such as density, refractive index, mechanical strength, etc. inside the work W become different from the surroundings due to the irradiation of the laser beam, and the strength is lower than the surroundings. includes, for example, crack regions.

As shown in 2B of FIG. 2, the workpiece W is irradiated with an intermittent pulsed processing laser beam L1 to divide a plurality of laser processing regions P, P, . , the work W loses the balance of the intermolecular forces, and is naturally cleaved starting from the laser processing regions P, P, . . . or cleaved by applying a slight external force.

In addition, in the case of a thick work W, it is difficult to cut a single layer of the laser processing area P, so as shown in 2C of FIG. By moving the light condensing point of L1, the laser processing region P is formed in multiple layers and cut.

In the examples shown in FIGS. 2B and 2C, the discontinuous laser processing regions P, P, . A continuous laser processing area P may be formed under the continuous wave of . When a discontinuous laser processing region P is formed, it is less likely to be broken than when a continuous laser processing region P is formed. It is appropriately selected whether to use a continuous wave or an intermittent wave.

Returning to FIG. 1, the AF sensor 30 detects a profile indicating the uneven shape information of the surface W _U (laser beam irradiation surface) of the workpiece W along the processing line when forming the laser processing region P along the processing line. provided to obtain. The surface _WU of the work W is an example of the "principal surface of the work" in the present invention.

The AF sensor 30 includes a detection light source (not shown) that emits a detection laser beam L2. The detection laser beam L2 has a wavelength different from that of the processing laser beam L1 and has a wavelength that can be reflected by the surface W _U (laser beam irradiation surface) of the workpiece W.

The detection laser beam L2 emitted from the AF sensor 30 is reflected by the dichroic mirror 23, condensed by the condensing lens 24, and irradiated onto the surface _WU of the workpiece W. As shown in FIG. The reflected light of the detection laser beam L2 reflected by the workpiece W passes through the condenser lens 24, is reflected by the dichroic mirror 23, and is received by the light receiving surface of the photodetector provided in the AF sensor 30. FIG. Based on the received reflected light, the AF sensor 30 detects a detection signal corresponding to the height of the surface _WU of the workpiece W and outputs it to the control device 50 .

Here, the distribution and light quantity of the reflected light of the detection laser beam _L2 reflected by the surface WU of the workpiece W are determined by the distance from the condenser lens 24 to the workpiece W, that is, the uneven shape of the surface _WU of the workpiece W ( surface displacement). Using this property, the AF sensor 30 obtains the position of the surface _WU of the workpiece _W based on the distribution of the reflected light of the detection laser beam L2 reflected by the surface WU of the workpiece W and changes in the amount of light. As a method for measuring the position of the surface _WU of the work W in the AF sensor 30, for example, an astigmatism method, a knife edge method, or the like can be preferably used. Since these methods are publicly known, detailed description thereof is omitted here.

Measurement of the position of the surface _WU of the workpiece W by the AF sensor 30 as described above is continuously performed on a predetermined processing line. As a result, when forming the laser processing area P inside the workpiece W along the processing line, it is possible to control the condensing position of the processing laser beam L1 in real time based on the measurement result of the AF sensor 30. Become.

In this embodiment, the AF sensor 30 is provided in the optical system device 20, and the optical axis of the detection laser beam L2 is made coaxial with the optical axis of the processing laser beam L1 by the dichroic mirror 23, and is emitted. However, it is not limited to this configuration. For example, the AF sensor 30 may be provided independently of the optical system device 20 and adjacent thereto.

A control device 50 shown in FIG. 1 controls the operation of each part of the laser processing apparatus 10 and stores data necessary for processing.

The control device 50 can be implemented by, for example, a general-purpose computer such as a personal computer or microcomputer.

The control device 50 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input/output interface, and the like. In the control device 50, various programs, such as a control program stored in the ROM, are developed in the RAM, and the programs developed in the RAM are executed by the CPU, so that each unit in the control device 50 shown in FIG. Functions are realized, and various arithmetic processing and control processing are executed via an input/output interface.

FIG. 3 is a block diagram showing the configuration of the control device 50. As shown in FIG. As shown in FIG. 3, the control device 50 includes a control unit 52, a storage unit 54, a workpiece thickness information calculation unit 56, an offset data calculation unit 58, a focus shift amount calculation unit 60, a control data calculation unit 62, and an AF control unit 64. function as

The control unit 52 is a functional unit that controls each unit of the laser processing apparatus 10 in an integrated manner. For example, when forming the laser processing area P inside the work W, the control unit 52 moves the stage 12 so that the work W is scanned with the processing laser beam L1 along a predetermined processing line. control. The control unit 52 also controls the emission of the processing laser light L1, and controls, for example, the wavelength, pulse width, intensity, emission timing, repetition frequency, and the like of the processing laser light L1.

The work thickness information calculation unit 56 (work thickness profile acquisition means) calculates a work height profile P1 indicating the height of each position on the surface _WU of the work W and a stage height indicating the height of each position on the surface of the stage 12. Get profile P2. Then, the work thickness information calculation unit 56 calculates a work thickness profile P3 indicating the thickness of the work W at each laser processing position (i, j) from the work height profile P1 and the stage height profile P2 (see FIG. 4). .details later). A work thickness profile (work thickness information) P3 calculated by the work thickness information calculation unit 56 is stored in the storage unit 54 .

In this embodiment, the work thickness profile P3 is calculated from the work height profile P1 and the stage height profile P2 measured by the laser processing apparatus 10, but the present invention is not limited to this. For example, the work thickness profile P3 created by a device other than the laser processing device 10 may be obtained and used. Also, the same work thickness profile P3 may be used for works W of the same shape that are formed by the same device.

The storage unit 54 is a storage device that stores various data. As the storage unit 54, for example, a device including a magnetic disk such as a HDD (Hard Disk Drive), a device including a flash memory such as an eMMC (embedded Multi Media Card), an SSD (Solid State Drive), or the like can be used.

The offset data calculator 58 moves the condensing lens 24 based on the work thickness profile P3 so that the distance between the condensing point FP of the processing laser beam L1 and the back surface _WB of the work W becomes constant. Calculate the amount (offset amount). The distance between the focal point FP of the processing laser beam L1 and the back surface _WB of the work W can be determined by, for example, the material of the work W, the intensity of the processing laser beam L1, the irradiation time, and the size of the laser processing area P. Depending on the size, interval, number of layers, etc., the crack is sufficiently extended from the laser processing region P to the back surface _WB side of the work W, and the processing laser beam L1 is applied to the semiconductor device or the like formed on the back surface _WB . It is possible to determine experimentally within a range in which thermal damage does not occur due to

The defocus amount calculator 60 calculates the defocus amount (defocus amount) between the position of the focal point FP of the processing laser beam L1 and the target value based on the output from the AF sensor 30 .

The control data calculator 62 calculates the amount of movement of the condenser lens 24 by the actuator 25 based on the defocus amount and the offset amount, and calculates control data for controlling the actuator 25 .

The AF control unit 64 controls the amount of movement of the actuator 25 based on the control data calculated by the control data calculation unit 62, and performs AF control of the processing laser beam L1.

(Laser processing procedure)
Next, a laser processing procedure will be described with reference to FIGS. 4 to 6. FIG.

First, the work thickness profile P3 of the work W will be described. FIG. 4 is a diagram for explaining a work thickness profile. In FIG. 4, details of changes in the height positions of the surfaces of the workpiece W and the stage 12 are omitted.

First, the control unit 52 (stage height profile acquisition means) causes the AF sensor 30 to detect the height of the surface of the stage 12 at each position while moving the stage 12 along the scanning direction (main scanning direction, for example, the X direction). Measure the thickness (see FIG. 4(a)). The height of the surface of the stage 12 is measured by sucking and holding the calibration work having a known (for example, constant) thickness on the surface of the stage 12 and measuring the height position (Z coordinate) of the surface of the calibration work. I do. By subtracting the known thickness of the calibration work from the height position of the surface of the calibration work, the height position of the surface of the stage 12 can be calculated. Here, for the calibration work, it is preferable to use, for example, one having the same or larger planar shape as the work W to be processed.

When creating the stage height profile P2, the optical system device 20 is moved in a direction perpendicular to the scanning direction (the sub-scanning direction, for example, the Y direction), and the height of the stage 12 is changed at predetermined intervals in the sub-scanning direction. Repeat the position measurement. Then, by interpolating the measurement result of the height position of the stage 12, the stage height profile P2 can be created for the entire area of the stage 12 where the work W is sucked and held.

Although the calibration work is used in this embodiment, it is also possible to directly measure the height of the surface of the stage 12 without using the calibration work.

Next, the control unit 52 creates a stage height profile P2 representing the uneven shape of the surface of the stage 12 based on the height of each position on the surface of the stage 12 (see FIG. 4(c)). This stage height profile P2 is stored in the storage unit 54 and used to calculate the work height profile P3 when the work W is processed.

Each time the workpiece W is processed a predetermined number of times, each time the period of use of the laser processing apparatus 10 (stage 12) exceeds a predetermined period, or according to an operator's instruction, the height of each position on the surface of the stage 12 is changed. Measurements may be taken to update the stage height profile P2.

Next, the workpiece W to be processed is measured. The control unit 52 (work height profile acquisition means) moves the stage 12 along the processing line DLi extending in the main scanning direction while the work W is held by the stage 12 by suction. Measure the height for each location on the surface W _U of . Then, the optical system device 20 is moved in the sub-scanning direction, and the measurement of the height position of the surface of the work W is repeated. As a result, a workpiece height profile P1 representing the uneven shape of the surface _WU of the workpiece W on all the machining lines DLi is created (see FIG. 4(b)).

The work thickness information calculator 56 creates a work thickness profile P3 indicating the height of the work W at each position by subtracting the stage height profile P2 from the work height profile P1 (see FIG. 4(d)). . The work thickness profile P3 calculated by the work thickness information calculation section 56 is stored in the storage section 54 .

By the way, in general, when the workpiece W is a circular or rectangular wafer, the shape and thickness of the wafer are substantially point-symmetrical with respect to its center (the center during grinding) due to the grinding method in the wafer forming process. . In this case, the thickness of the wafer varies concentrically from its center and smoothly in the planar direction. Therefore, using the symmetry of this work W, it is also possible to create the work thickness profile P3.

In this case, as shown in FIG. 4( a ), the work thickness information calculator 56 moves the optical system device 20 along the scan line DLc passing through the center C of the work W while measuring the surface W _U of the work W. The height position is measured to create a workpiece height profile P1c along the scan line DLc (see FIG. 4(b)). Then, based on the workpiece height profile P1c and the stage height profile P2c along the scan line DLc, a workpiece thickness profile P3c along the scan line DLc is created.

Next, the work thickness information calculator 56 creates a work thickness profile P3i along all the processing lines DLi based on the symmetry of the work W and the work thickness profile P3c along the scan line DLc (see FIG. 4 ( d) see). Specifically, the work thickness information calculation unit 56 assumes that the change in the shape and thickness of the work W is point symmetrical with respect to the center C, and calculates from the work thickness profile P3c along the scan line DLc to the processing line DLi. A work thickness profile P3i along the line is calculated. Thereby, it is possible to create the work thickness profile P3 along all the processing lines DLi.

When creating the work thickness profile P3 using the symmetry of the work W, the number of scan lines at the height position of the work can be reduced, and the time required for measurement can be shortened.

The work height profile P1i along the processing line DLi can be calculated by adding the work thickness profile P3i along the processing line DLi and the stage height profile P2i.

Also, the scan line in this case is not limited to one line DLc passing through the center C of the workpiece W. FIG. For example, the workpiece thickness profile P3 may be created based on the measurement results of a plurality of scan lines and the symmetry of the workpiece W shape.

Moreover, the shape of the work W is not limited to one having point symmetry. For calculating the workpiece thickness profile P3, for example, it is possible to use point symmetry or other shape symmetry that occurs according to the grinding process mode or the material of the workpiece W.

When utilizing the symmetry of the workpiece W, at least one of the scan lines preferably passes through the center of symmetry (point of symmetry). For example, if the workpiece W is axisymmetric, the scan lines preferably include a line of symmetry and a line that intersects the line of symmetry. By setting the scan lines as described above, it is possible to improve the calculation accuracy of the workpiece thickness profile P3.

Next, the offset amount will be described with reference to FIGS. 5 to 7. FIG. 5A and 5B are diagrams for explaining the amount of offset, and FIG. FIG. 7 is a table showing the offset amount for each machining position of the workpiece W. FIG.

The offset data calculator 58 calculates the height position of the back surface _WB of the work W at each laser processing position on the processing line DLi. The height position of the back surface _WB of the work W can be calculated, for example, by subtracting the work thickness profile P3 from the work height profile P1. Further, the height position of the back surface _WB of the work W can be calculated based on the stage height profile P2 when the back grind tape is not attached to the back surface _WB of the work W.

Based on the height position of the back surface _WB of the workpiece W, the offset data calculator 58 calculates the distance between the focal point FP of the processing laser beam L1 and the back surface _WB of the workpiece W so that the distance is constant. Then, the movement amount (offset amount) of the condenser lens 24 is calculated.

Here, the offset data calculation unit 58 calculates the difference between the uneven shape of the surface _WU of the work W (the amount of change from the reference point), the refractive index of the laser processing environment (for example, air), and the refractive index of the work W. The amount of offset is calculated based on As shown in FIG. 5, when the processing laser beam L1 passes through the surface _WU and enters the work W, the incident angle is θ, and the refraction angle (or the incident angle from the work W to the air side) is θn _. , the absolute refractive index of air (hereinafter simply referred to as the refractive index) is 1.0, and the refractive index of the work W is n, the following equation (1) is obtained from Snell's law.

sinθ=n・_sinθn (1)
By modifying the formula (1), the following formula (2) is obtained.

_θn = arcsin(sinθ/n) (2)
_{Let dn be} the distance from the surface _WU of the work W to the focal point FP, and d be the distance from the surface _WU of the work W to the focal point _FP0 when there is no refraction (θ= _θn ). , the following equation (3) is obtained.

tan θ・d=tan _θn・_dn (3)
By modifying the formula (3) and substituting the formula (2), the following formula (4) is obtained.

_dn /d=tan θ/tan _θn
dn /d=tan θ/tan{arcsin(sin θ/n)} (4)
Z ₀ is the height position of the reference point (for example, the point with the maximum Z coordinate) on the surface W _U of the work W, and Z is the height position of the surface W _U of the laser processing position (i, j) on the processing line DLi Assuming _{that i,j} is the amount of change in thickness from the reference point of the workpiece W at the laser processing position (i,j) ΔZ (=|Z ₀ −Z _i,j |), the offset amount K _i,j is given by the following formula: (5).

K _i,j =ΔZ/(d _n /d) (5)
Thus, as shown in FIG. 7, the offset amount K _i,j (i=1, . . . , p, j=1, . . . , q) at the laser processing position (i, j) on the processing line DLi is obtained. .

Assuming that the workpiece W is a silicon wafer, the refractive index n is n≈3.5, and the numerical aperture (Numerical Aperture) of the condenser lens 24 is NA=1·sin θ=0.4, d _n /d is obtained by the following: .

_dn /d=tan θ/tan{arc sin(sin θ/n)}
_dn /d≈tan{arcsin(0.4)}/tan{arcsin(0.4/3.5)}
_dn /d≈3.8
As described above, when the workpiece W is a silicon wafer, the refractive index n of the workpiece W is larger than the refractive index of air, so the offset amount is about 1/3.8, which is smaller than the variation ΔZ of the thickness of the workpiece W. , the height position of the focal point FP is appropriately adjusted.

When laser processing is performed at each laser processing position (i, j), the defocus amount calculator 60 calculates the defocus amount based on the output from the AF sensor 30 at each laser processing position (i, j). calculate. Then, the control data calculation unit 62 calculates the amount of movement of the condenser lens 24 by the actuator 25 based on the defocus amount and the offset amount Ki _,j at the laser processing position (i,j). 25 control data is calculated.

The AF control unit 64 (control means) controls the amount of movement of the actuator 25 based on the control data calculated by the control data calculation unit 62, and performs AF control of the processing laser beam L1. Thereby, at each processing position (i, j) of the work W, the crack extending from the laser processing region P to the back surface _WB side of the work W can be used to cut the work W without tearing. Furthermore, the conduction of heat to the back surface _WB side of the work W can be suppressed. In addition, since the distance ZT between the condensing point of the processing laser beam L1 and the back surface _WB of the work W can be appropriately adjusted, for example, the distance _ZT for processing can be adjusted from the back surface _WB of the work W to a desired distance. The focal point of the laser beam L1 can be set, and the processing laser beam L1 can be prevented from reaching the back surface _WB of the workpiece W and causing thermal damage to the semiconductor device.

In FIG. 6, the distance _ZT between the laser processing region P _i,j and the back surface W _B of the work W is constant, but the present invention is not limited to this. In the laser processing region P _i,j , a crack sufficiently extends from the laser processing region P _i,j to the back surface _WB side of the workpiece W, and the processing laser beam L1 is applied to a semiconductor device or the like formed on the back surface _WB . _ZT may be different for each laser-processed region P _i,j as long as it is within a range in which thermal damage does not occur.

(laser processing method)
Next, a laser processing method will be described with reference to FIG. FIG. 8 is a flow chart showing a laser processing method according to one embodiment of the present invention.

First, the control unit 52 measures the work height profile P1 by the AF sensor 30 (step S10).

Next, the work thickness information calculation unit 56 acquires the table height profile P2 from the storage unit 54 (step S12), subtracts the table height profile P2 from the work height profile P1, and calculates the work thickness profile P3. (step S14). When calculating the work thickness profile P3, in step S10, the height position of the surface _WU of the work W is measured for all the processing lines DLi to create the work height profile P1. The work thickness profile P3 may be calculated using the profile P1. Also, the scan line (DLc) in step S10 may be limited and the symmetry of the work W may be used to calculate the work thickness height profile P3.

Next, the offset data calculator 58 calculates the offset amount K _i,j at each laser processing position for each processing line DLi (step S16).

Then, based on the offset amount Ki _,j calculated in step S16 and the amount of defocus at each laser processing position (i,j), laser processing is repeated for each processing line DLi (step S18). Then, when the laser processing for all the processing lines DLi is completed (Yes in step S20), the laser processing for the workpiece W is completed.

According to this embodiment, at each processing position (i, j) of the work W, the distance _ZT between the laser processing region P _{i, j} and the back surface W _B of the work W is adjusted, and the laser processing region P Cracks can be sufficiently extended from _{i and j} to the back surface _WB side of the work W, and a semiconductor device or the like formed on the back surface _WB can be set to a range in which the processing laser beam L1 does not cause thermal damage. As a result, the crack extending from the laser processing region P _i,j toward the back surface _WB of the work W can be used to cut the work W without splitting it. Furthermore, the conduction of heat to the back surface _WB side of the work W can be suppressed. Further, according to the present embodiment, the distance _ZT between the focal point _of the processing laser beam L1 and the back surface _WB of the work W can be adjusted appropriately. It is possible to set the condensing point of the processing laser beam L1 at a desired distance from the surface of the workpiece W, thereby suppressing the processing laser beam L1 from reaching the back surface _WB of the work W and causing thermal damage to the semiconductor device. can.

DESCRIPTION OF SYMBOLS 10... Laser processing apparatus, 12... Stage, 14... Stage encoder, 20... Optical system apparatus, 21... Laser light source, 23... Dichroic mirror, 24... Objective lens for processing (collecting lens), 25... Actuator, 30... AF Sensor, 50... Control device, 52... Control unit, 54... Storage unit, 56... Work thickness information calculation unit, 58... Offset data calculation unit, 60... Focus shift amount calculation unit, 62... Control data calculation unit, 64... AF Control unit, L1... laser beam for processing, L2... laser beam for detection

Claims (3)

a condensing lens that irradiates the processing laser beam from the surface side of the workpiece;
stage height profile acquisition means for acquiring a stage height profile indicating the height position of the surface of the stage on which the workpiece is held;
Through the condenser lens, the workpiece held on the stage is irradiated with a detection laser beam, and based on the reflected light from the surface of the workpiece, a plurality of laser beams, at least one of which passes through the center of symmetry of the workpiece. Work height profile acquisition means for measuring the height position of the surface of the work along a scan line and acquiring a work height profile indicating the height position of the surface of the work;
creating a workpiece thickness profile along the plurality of scan lines from the workpiece height profile and the stage height profile along the plurality of scan lines, and determining symmetry of the workpiece and the workpiece along the plurality of scan lines; a workpiece thickness profile acquisition means for creating a workpiece thickness profile indicating the thickness of the workpiece at each position along all machining lines, based on the thickness profile;
Based on the work thickness profile indicating the thickness of the work at each position along all the processing lines , the distance from the back surface of the work to the converging point of the processing laser beam is within a predetermined range. , a control means for adjusting the position of the condenser lens;
A laser processing device with a The control means maintains a constant distance from the back surface of the workpiece to the focal point of the processing laser beam.
The laser processing apparatus according to claim 1. A laser processing method in which a laser processing area is formed by irradiating a processing laser beam from the surface side of a work using a condenser lens,
obtaining a stage height profile indicating the height position of the surface of the stage on which the workpiece is held;
Through the condenser lens, the workpiece held on the stage is irradiated with a detection laser beam, and based on the reflected light from the surface of the workpiece, a plurality of laser beams, at least one of which passes through the center of symmetry of the workpiece. measuring the height position of the surface of the workpiece along a scan line to obtain a workpiece height profile indicating the height position of the surface of the workpiece;
creating a workpiece thickness profile along the plurality of scan lines from the workpiece height profile and the stage height profile along the plurality of scan lines, and determining symmetry of the workpiece and the workpiece along the plurality of scan lines; creating a workpiece thickness profile indicating the thickness of the workpiece at each position along all processing lines, based on the thickness profile;
Based on the work thickness profile indicating the thickness of the work at each position along all the processing lines , the distance from the back surface of the work to the converging point of the processing laser beam is within a predetermined range. , adjusting the position of the condenser lens;
A laser processing method comprising:

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