Laser processing device

Abstract

Laser processing device (1) with: a clamping table (36) for holding a workpiece (10); a laser beam application unit (4) with a processing head for applying a laser beam to the workpiece which is held by the clamping table; a movement mechanism for relative movement of the clamping table (36) and the laser beam application unit (4); an alignment unit for detecting an object surface of the workpiece that is held by the clamping table; a control unit (9) for controlling the laser beam application unit (4) and the movement mechanism; a control panel (90) for entering a desired processing result into the control unit (9); and a 3D imaging unit (7) for imaging a machined state of the workpiece, which is held by the clamping table, in order to form a three-dimensional image, wherein the control performs a processing state adjustment step to adjust processing states so that the desired processing result, which is entered by the control panel (90), is obtained, depending on the desired processing result and the three-dimensional image which was formed by the 3D imaging unit (7), and subsequently controls the laser beam application unit (4) and the movement mechanism depending on the processing states which were adjusted in the processing state adjustment step, wherein the processing state adjustment step comprises the control means: a fundamental numerical value setting step to set a fundamental numerical value of each machining factor from a plurality of machining factors depending on the desired machining result entered by the control panel (90), and a fundamental numerical range of each machining factor from the plurality of machining factors entered by the control panel (90); a fundamental machining execution step for controlling the laser beam application unit (4) and the movement mechanism depending on the fundamental numerical value of each machining factor that was set in the fundamental numerical value setting step in order to perform a fundamental machining of the workpiece (10) which is held by the clamping table (36); a 3D imaging step for operating the 3D imaging unit (7) to map the machined state of the workpiece (10) that was machined by the fundamental machining execution step, thereby forming a three-dimensional image; a diagram creation step for creating a diagram of the processing results in relation to each processing factor as a function of the three-dimensional image that was formed in the 3D mapping step; a Modified Numerical Range setting step to select the machining factor that affects the machining results by comparing the charts that correspond to the machining factors created in the chart creation step, and to subsequently set a modified numerical range for the machining factor that was previously selected; a Modified Numeric Value Setting Step to specify a modified numeric value for each processing factor depending on the modified numeric range specified in the Modified Numeric Range Setting Step; and a modified machining execution step for controlling the laser beam application unit (4) and the movement mechanism depending on the modified numerical value of each machining factor that was set in the modified numerical value setting step, thereby performing a modified machining of the workpiece held by the clamping table (36); wherein the 3D mapping step, the diagram creation step, the modified numerical range setting step, the modified numerical value setting step and the modified machining execution step are repeated until the actual machining result obtained by the modified machining falls within an acceptable range of the desired machining result.

Description

Technical area

[0001] The present invention relates to a laser processing apparatus for laser processing a workpiece such as a wafer. Description of the state of the art

[0002] In a semiconductor device manufacturing process, a plurality of intersecting dividing lines are formed on the front surface of a substantially disc-shaped semiconductor wafer, thereby defining a plurality of separate regions in which a plurality of semiconductor devices, such as ICs and LSIs, are respectively formed. The semiconductor wafer is divided along the dividing lines to thereby separate the regions where the semiconductor devices are formed, thereby obtaining a plurality of individual semiconductor device chips.

[0003] As a method for dividing a wafer, such as a semiconductor wafer, along the dividing lines, a method has been proposed which comprises applying a laser beam having an absorption wavelength to the wafer along the dividing lines to thereby form a laser-machined groove as a breaking start point along each dividing line by ablation, and then applying an external force to the wafer along each dividing line where the laser-machined groove is formed as the breaking start point, thereby breaking the wafer along each dividing line.

[0004] The laser processing mentioned above is performed using a laser processing device. The laser processing device includes a workpiece holding means for holding a workpiece, a laser beam application means having a processing head for applying a laser beam to the workpiece held by the workpiece holding means, a feeding means for relatively moving the workpiece holding means and the laser beam application means in a feeding direction (X direction), a moving means for relatively moving the workpiece holding means and the laser beam application means in a moving direction (Y direction) perpendicular to the feeding direction (X direction), and an alignment means for detecting an object surface of the workpiece to be processed (see, for example, JP 2006-289388 A).

[0005] The documents JP 2009- 928 A and JP 2011- 187 829 A disclose further prior art. PRESENTATION OF THE INVENTION

[0006] However, when forming a laser-machined groove with a predetermined depth (e.g., 10 µm) on a workpiece such as a wafer, it is necessary to appropriately adjust the numerical values ​​of various processing factors, such as energy, repetition frequency, pulse width, and focal spot diameter of the laser beam, as well as a processing feed speed, and determine the processing conditions through trial and error, such as measuring the depth of the laser-machined groove. As a result, productivity is reduced. In addition, the wafer as a workpiece differs in its characteristics depending on the type or manufacturer, so the processing conditions must be changed every time the wafer changes. Consequently, setting the processing conditions is time-consuming for the operator.

[0007] It is therefore an object of the present invention to provide a laser processing apparatus which can automatically determine the processing conditions for the workpiece by inputting required quantities.

[0008] According to one aspect of the present invention, a laser machining apparatus is provided, comprising a workpiece holding means for holding a workpiece; a laser beam applying means having a machining head for applying a laser beam to the workpiece held by the workpiece holding means; a moving means for relatively moving the workpiece holding means and the laser beam applying means; an alignment means for detecting an object surface of the workpiece held by the workpiece holding means; a control means for controlling the laser beam applying means and the moving means; an input means for inputting a desired machining result to the control means.and a 3D imaging means for imaging a machined state of the workpiece held by the workpiece holding means to form a three-dimensional image; wherein the control means performs a machining state adjustment step for adjusting machining states so that the desired machining result inputted by the input means is achieved, the adjustment being performed depending on the desired machining result and the three-dimensional image formed by the 3D imaging means, and then controls the laser beam application means and the movement means depending on the machining states adjusted in the machining state adjustment step.

[0009] Further, according to the aspect of the present invention, the machining condition adjustment step by the control means includes a fundamental numerical value setting step of setting a fundamental numerical value of each machining factor from a plurality of machining factors depending on the target machining result inputted by the input means and a fundamental numerical range of each machining factor from the plurality of machining factors inputted by the input means; a fundamental machining execution step of controlling the laser beam application means and the movement means depending on the fundamental numerical value of each machining factor set in the fundamental numerical value setting step, thereby performing fundamental machining of the workpiece held by the workpiece holding means;a 3D imaging step for operating the 3D imaging means to image the machined state of the workpiece machined by the fundamental machining execution step, thereby forming a three-dimensional image; a graph creation step for creating a graph of the machining results in relation to each machining factor depending on the three-dimensional image formed in the 3D imaging step; a modified numerical range setting step for selecting the machining factor that has an influence on the machining results by comparing the graphs corresponding to the machining factors created in the graph creation step, and then setting a modified numerical range for the previously selected machining factor;a modified numerical value setting step for setting a modified numerical value of each machining factor depending on the modified numerical range set in the modified numerical range setting step; and a modified machining execution step for controlling the laser beam applying means and the moving means depending on the modified numerical value of each machining factor set in the modified numerical value setting step, thereby modifying the workpiece held by the workpiece holding means;wherein the 3D mapping step, the diagram creation step, the changed numerical range setting step, the changed numerical value setting step, and the changed machining execution step are repeated until the actual machining result achieved by the changed machining falls within an allowable range of the target machining result;

[0010] Preferably, the fundamental numerical value setting step, the diagram creation step and the modified numerical value setting step are carried out in one test setup.

[0011] The laser machining apparatus according to the present invention includes the 3D imaging means for imaging the machined state of the workpiece held by the workpiece holding means to form the three-dimensional image of this machined state. The control means performs the machining state adjustment step for adjusting the machining states so that the desired machining result inputted by the input means is obtained, depending on the desired machining result and the three-dimensional image formed by the 3D imaging means. Subsequently, the control means controls the laser beam application means and the movement means depending on the machining states adjusted in the machining state adjustment step.As a result, the machining conditions for the workpiece can be determined automatically by entering the required parameters through the input device. This eliminates the need for the operator to set the machining conditions by trial and error, thus improving productivity.

[0012] The above and other objects, features and advantages of the present invention and the mode for carrying them out, as well as the invention itself, will be best understood by studying the following description and accompanying claims with reference to the accompanying drawings which show a preferred embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a laser processing apparatus according to a preferred embodiment of the present invention. Fig. 2 is an exploded perspective view of a 3D imaging means used in the laser processing apparatus of Fig. 1 is included. Fig. 3 is a sectional view showing an essential part of an interference imaging mechanism which comprises the 3D imaging means of Fig. 2 designed. Fig. Fig. 4 is a schematic view for illustrating a focusing means and an interference light generating means used in the interference imaging mechanism of Fig. 3 are included. Fig. 5 is a block diagram of a control means used in the laser processing apparatus of Fig. 1 is included. Fig. 6 is a control diagram defining the relationship between a voltage applied to an actuator provided by a piezoelectric motor and an axial displacement of the piezoelectric motor. Fig. 7 is a perspective view of a semiconductor wafer as a workpiece in the state where the semiconductor wafer is attached to a saw band held by a ring frame. Fig. 8 is a table for showing a fundamental numerical range of each machining factor input to the control means. Fig. 9A and Fig. 9B are tables for representing a fundamental numerical value of each machining factor set in a fundamental numerical value setting step by the control means. Fig. 10 is a sectional view of laser-machined grooves #1 to #5 formed in a fundamental machining execution step by the control means. Fig. 11 is a perspective view for illustrating three-dimensional images of the laser-machined grooves #1 to #5 formed in a 3D imaging step by the control means. Fig. 12A to 12C are diagrams showing the relationship between machining factors and machining results created in a diagram creating step by the control means. Fig. 13 is a table for illustrating a changed numerical range of each machining factor set in a changed numerical range setting step by the control means. Fig. 14A and Fig. 14B are tables for illustrating a changed numerical value of each machining factor set in a changed numerical value setting step by the control means. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] A preferred embodiment of the laser processing apparatus according to the present invention will now be described with reference to the accompanying drawings. Fig. Fig. 1 is a perspective view of a laser processing apparatus 1 according to this preferred embodiment. The laser processing apparatus 1 shown in Fig. 1, comprises a stationary base 2, a workpiece holding mechanism 3 for holding a workpiece, the workpiece holding mechanism 3 being provided on the stationary base 2 so as to be movable in a feeding direction (X direction) shown by an arrow X, and a laser beam applying unit 4 provided on the stationary base 2, the laser beam applying unit 4 having a laser beam applying means which will be described below.

[0014] The workpiece holding mechanism 3 includes a pair of guide rails 31 provided on the stationary base 2 so as to extend parallel to each other in the X direction, a first slide block 32 provided on the guide rails 31 so as to be movable in the X direction, a second slide block 33 provided on the first slide block 32 so as to be movable in a displacement direction (Y direction) shown by an arrow Y and perpendicular to the X direction, a cover table 35 supported by a cylindrical member 34 standing on the second slide block 33, and a chuck table 36 as a workpiece holding means. The chuck table 36 has a vacuum chuck 361 made of a porous material.A workpiece, such as a disk-shaped semiconductor wafer, is arranged to be held under suction on the upper surface of the vacuum chuck 361 as a holding surface by operating a suction means (not shown). The chuck table 36 is rotatable by a servo motor (not shown) provided in the cylindrical member 34. The chuck table 36 is provided with clamps 362 for fixing an annular frame supporting a semiconductor wafer as the workpiece through a protective tape.

[0015] The lower surface of the first slide block 32 is formed with a pair of guide grooves 321 for slidably engaging the pair of guide rails 31 mentioned above. A pair of guide rails 322 are provided on the upper surface of the first slide block 32 so as to extend parallel to each other in the Y direction. Thus, the first slide block 32 is movable in the X direction along the guide rails 31 by the slidable engagement of the guide grooves 321 with the guide rails 31. The workpiece holding mechanism 3 further includes an X-moving means 37 for moving the first slide block 32 in the X direction along the guide rails 31. The X-moving means 37 includes an externally threaded rod 371 extending parallel to the guide rails 31 so as to be interposed therebetween, and a servo motor 372 as a drive source for rotationally driving the externally threaded rod 371.The male screw rod 371 is rotatably supported at one end by a bearing block 373 fixed to the stationary base 2, and connected at the other end to an output shaft of the actuator motor 372 so as to receive the torque therefrom. The male screw rod 371 is engaged with a threaded through hole formed in a female screw block (not shown) protruding from the lower surface of the first slide block 32 at a central portion thereof. Thus, the first slide block 32 is moved in the X direction along the guide rails 31 by driving the actuator motor 372 to rotate the male screw rod 371 normally or reversely.

[0016] The laser processing apparatus 1 includes an X-position detecting means 374 for detecting the X-position of the chuck table 36. The X-position detecting means 374 includes a linear scale 374a extending along one of the guide rails 31, and a read head 374b provided on the first slide block 32 and movable along the linear scale 374a together with the first slide block 32. The read head 374b of the X-position detecting means 374 transmits a pulse signal of one pulse every 1 µm in this preferred embodiment to the control means, which will be described below. The control means counts the number of pulses as the pulse signal input by the read head 374b, thereby detecting the X-position of the chuck table 36.In the case where the pulse motor 372 is used as the drive source for the X-moving means 37, as in this preferred embodiment, the number of pulses as a drive signal output from the control means to the servo motor 372 can be counted by the control means, thereby detecting the X-position of the chuck table 36. In the case where a servo motor is used as the drive source for the X-moving means 37, a pulse signal output from an encoder for detecting the rotational speed of the servo motor can be sent to the control means, and the number of pulses as the pulse signal input to the control means by the encoder can be counted by the control means, thereby detecting the X-position of the chuck table 36.

[0017] The lower surface of the second slide block 33 is formed with a pair of guide grooves 331 for slidably engaging with the pair of guide rails 322 provided on the upper surface of the first slide block 32, as mentioned above. Thus, the second slide block 32 is movable in the Y direction along the guide rails 322 by the slidable engagement of the guide grooves 331 with the guide rails 322. The workpiece holding mechanism 3 further includes a Y-moving means 38 for moving the second slide block 33 in the Y direction along the guide rails 322. The Y-moving means 38 includes an externally threaded rod 381 extending parallel to the guide rails 322 so as to be interposed therebetween, and a servo motor 382 as a drive source for rotationally driving the externally threaded rod 381.The male threaded rod 381 is rotatably supported at one end thereof by a bearing block 383 fixed to an upper surface of the first slide block 32, and connected at the other end to an output shaft of the actuator 382 so as to receive the torque therefrom. The male threaded rod 381 is engaged with a threaded through hole formed in a female threaded block (not shown) protruding from the lower surface of the second slide block 33 at a central portion thereof. Thus, the second slide block 33 is moved in the Y direction along the guide rails 322 by driving the actuator 382 to rotate the male threaded rod 381 normally or reversely.

[0018] The laser processing apparatus 1 includes a Y-position detecting means 384 for detecting the Y-position of the chuck table 36. The Y-position detecting means 384 includes a linear scale 384a extending along one of the guide rails 322, and a read head 384b provided on the second slide block 33 and movable along the linear scale 384a together with the second slide block 33. The read head 384b of the Y-position detecting means 384 transmits a pulse signal of one pulse every 1 µm in this preferred embodiment to the control means described below. This control means counts the number of pulses as the pulse signal input from the read head 384b, thereby detecting the Y-position of the chuck table 36.In the case where the servo motor 382 is used as the drive source for the Y-moving means 38, as in this preferred embodiment, the number of pulses as a drive source output from the control means to the servo motor 382 can be counted by the control means to thereby detect the Y-position of the chuck table 36. In the case where a servo motor is used as the drive source for the Y-moving means 38, a pulse signal output from an encoder for detecting the rotational speed of the servo motor can be sent to the control means, and the number of pulses as the pulse signal input from the encoder to the control means can be counted by the control means to thereby detect the Y-position of the chuck table 36.

[0019] The laser beam application unit 4 includes a support member 41 provided on the stationary base 2, a unit case 42 supported by the support member 41 so as to extend substantially horizontally, a laser beam application means 5 provided on the unit case 42, and an imaging means 6 for detecting a surface to be laser processed. The laser beam application means 5 includes a pulsed laser beam oscillation means (not shown) provided in the unit case 42, and a machining head 51 for focusing a pulsed laser beam oscillated by the pulsed laser beam oscillation means and applying this pulsed laser beam to the workpiece held on the chuck table 36. The pulsed laser beam oscillation means includes a pulsed laser beam oscillator and a repetition frequency adjusting means.

[0020] The imaging means 6 is provided on the unit case 42 at a position spaced apart from the machining head 51 in the X direction by a predetermined distance. The imaging means 6 includes a conventional imaging device (CCD) for imaging the workpiece using visible light, an infrared light applying means for applying infrared light to the workpiece, an optical system for detecting the infrared light applied to the workpiece by the infrared light applying means, and an imaging device (infrared CCD) for outputting an electrical signal corresponding to the infrared light detected by the optical system. An imaging signal output by the imaging means 6 is sent to the control means, which will be described below.

[0021] The laser processing apparatus 1 includes a 3D imaging means 7 for imaging a processed state of the workpiece held on the chuck table 36 to form a three-dimensional image. The 3D imaging means 7 includes an interference imaging mechanism 70 provided on the unit case 42 for imaging the workpiece held on the chuck table 36 in three dimensions consisting of the X direction, the Y direction perpendicular to the X direction, and the Z direction perpendicular to both the X and Y directions, and then outputting an image signal obtained as described above. The interference imaging mechanism 70 is attached to a first Z-moving means 8 provided on the unit case 42 so that it is movable in the Z direction by the first Z-moving means 8.The interference imaging mechanism 70 and the first Z-moving means 8, which configure the 3D imaging means 7, will now be described in detail with reference to FIG. Fig. 2 to 4.

[0022] The interference imaging mechanism 70, which in Fig. 2 to 4 is a so-called Mirau interference imaging mechanism. As shown in Fig. 3 in detail, the interference imaging mechanism 70 includes a mechanism housing 71, an imaging device 72 provided at the upper portion of the mechanism housing 71, a focusing device 73 provided at the lower portion of the mechanism housing 71 so as to face the support surface (upper surface) of the chuck table 36, and a light applying device 74 for applying light through the focusing device 73 to the workpiece held on the support surface of the chuck table 36. The imaging device 72 includes a plurality of pixels arranged in the X direction and the Y direction and outputs an imaging signal to the control device, which will be described below.

[0023] The focusing means 73, which forms the interference imaging mechanism 70, comprises a unit case 731 and an objective lens 732 provided in the unit case 731. As shown in Fig. As shown in Figure 4, the objective lens 732 functions to focus the light from the light applying means 74 onto a focal point P (imaging position). In this preferred embodiment, the focal spot diameter at the focal point P is set to 100 µm. Furthermore, an interference light generating means 75 is provided in the unit case 731 of the focusing means 73. The interference light generating means 75 functions to generate interference light in response to return light reflected from the workpiece held on the holding surface of the chuck table 36. As shown in Fig. As shown in Figure 4, the interference light generating means 75 is formed of a glass plate 751 inserted between the objective lens 732 and the chuck table 36, and a first beam splitter 752 arranged between the glass plate 751 and the chuck table 36. The glass plate 751 is provided with a central microscope mirror 751a having a diameter of, for example, 0.5 mm. The first beam splitter 752 functions to partially transmit light applied by the light applying means 74 and focused by the objective lens 732, thereby applying the transmitted light to the workpiece held on the workpiece holding surface of the chuck table 36, and also to partially reflect the light applied by the light applying means 74 and focused by the objective lens 732, thereby directing the reflected light toward the mirror 751a of the glass plate 751.The transmitted light through the first beam splitter 752 is reflected at the focal point P (imaging position) to interfere with the reflected light from the first beam splitter 752 on the glass plate 751. Thus, the focusing means 73 and the interference light generating means 75 cooperate to generate interference light with high intensity and guide this interference light toward the imaging means 72.

[0024] As in Fig. 3, the mechanism housing 71 has a bottom wall 711 with a mounting hole 711a. The unit housing 731, which includes the objective lens 732 and the interference light generating means 75, is mounted on the mechanism housing 71 in such a way that it can be projected through the mounting hole 711a of the bottom wall 711 in one direction (vertical direction in Fig. 3), which is perpendicular to the holding surface (upper surface) of the chuck table 36. A flange portion 731a is provided at the upper end of the unit case 731, and an actuator 76 is provided between the bottom wall 711 of the mechanism housing 71 and the flange portion 731a of the unit case 731 of the focus means 73. The actuator 76 functions as a second Z-moving means for moving the unit case 731 in the vertical direction of Fig. 3. In this preferred embodiment, the actuator 76 is provided by a piezoelectric motor comprising a piezoelectric element configured to extend axially in response to an applied voltage. Accordingly, the actuator 76 provided by such a piezoelectric motor can move the unit case 731 in the vertical direction of Fig. 3 (the direction perpendicular to the support surface of the chuck table 36) in response to a voltage applied under the control of the control means described below. As a modification, a fast-response voice coil motor, such as a piezoelectric motor, may be used as the actuator 76.

[0025] The light applying means 74 is configured from a light source 741, such as an LED, provided in a side protrusion 712 protruding from a side surface of the mechanism housing 71, and a second beam splitter 742 provided in the mechanism housing 741 at a position between the imaging means 72 and the focusing means 73. The second beam splitter 742 functions to direct light output from the light source 741 toward the focusing means 73 and further to direct the light reflected from the workpiece held on the holding surface of the chuck table 36 toward the imaging means 72.

[0026] The design of the first Z-movement means 8 will now be described in detail with reference to Fig. 2. The first Z-moving means is configured from a support case 81 for supporting the mechanism case 71 of the interference imaging mechanism 70 so that the mechanism case 71 is movable in the Z direction indicated by an arrow Z (in the direction perpendicular to the support surface of the chuck table 36), and a driving means 82 for moving the mechanism case 71 in the Z direction, which is supported on the support case 81. The support case 81 is configured from an upper wall 811, a lower wall 812, opposite side walls 813 and 814, and a rear wall (not shown). The opposite side walls 813 and 814 protrude toward the front to form a pair of guide rails 813a and 814a, respectively. The operating means 82 comprises an externally threaded rod 821 which extends parallel to the opposite side walls 813 and 814 of the support housing 81 so as to be arranged therebetween.The external threaded rod 821 is rotatably supported on the upper wall 811 and the lower wall 812. The driving means 82 further includes a servo motor 822 as a drive source provided on the upper wall 811 for rotationally driving the external threaded rod 821. A female threaded block 713 having a threaded through hole 713a is provided on the rear wall of the mechanism housing 71. The threaded through hole 713a of the female threaded block 713 is rotatably engaged with the external threaded rod 821 of the driving means 82. Thus, the mechanism housing 71 with the female threaded block 713 is moved along the guide rails 813a and 814a in the Z direction by driving the servo motor 822 to normally or reversely rotate the external threaded rod 821.

[0027] The 3D imaging means 7 further includes a Z-position detection means 80 for detecting the Z-position of the interference imaging mechanism 70, which is to be moved by the Z-moving means 8. The Z-position detection means 80 is configured from a linear scale 80a provided on the guide rail 813a and a read head 80b mounted on the mechanism housing 71 of the interference imaging mechanism 70 and movable along the linear scale 80a together with the mechanism housing 71. The read head 80b of the Z-position detection means 80 transmits a pulse signal of, for example, one pulse every 1 µm to the control means to be described below.

[0028] The laser processing device 1 comprises a control means 9 which is Fig. 5. The control means 9 functions to generate imaging information in response to an imaging signal output from the imaging means 72 of the interference imaging mechanism 70. The control means 9 controls not only the components of the 3D imaging means 7, but also all other components of the laser processing apparatus 1. The control means 9 is configured by a computer and includes a processor (CPU) 91 for executing operations in accordance with a control program, a read-only memory (ROM) 92 that previously stores the control program, a random access memory (RAM) 93 for storing calculation results, etc., an input interface 94, and an output interface 95.Detection signals of the X-position detecting means 374, the Y-position detecting means 384, the imaging means 6, the imaging device means 72 of the interference imaging mechanism 70, the read head 80b of the Z-position detecting means 80 for detecting the Z-position of the interference imaging mechanism 70, and an input means 90 are input to the input interface 94 of the control means 9. On the other hand, control signals are output from the output interface 95 of the control means 9 to the actuator 372 of the X-moving means 37, the actuator 382 of the Y-moving means 38, the laser beam applying means 5, the actuator 822 of the first Z-moving means 8, the actuator 76 provided by a piezoelectric motor and functioning as the second Z-moving means, the light source 741 of the light applying means 74, and an output means 900 such as a display means and a printer.The RAM 93 includes a memory area which previously stores a control plan which is in . Fig. 6, to define the relationship between a voltage applied to the actuator 76, which is provided by a piezoelectric motor, and an axial displacement of the piezoelectric motor. The RAM 93 also includes other memory areas.

[0029] The operation of the laser processing apparatus 1 configured as described above will now be described. Fig. Fig. 7 is a perspective view of a semiconductor wafer 10 as a workpiece to be processed by the laser processing apparatus 1 in the state where the semiconductor wafer 10 is attached to a dicing tape T supported by a ring frame F. The semiconductor wafer 10 shown in Fig. 7 is a silicon wafer. A plurality of intersecting dividing lines 101 are formed on the front side 10a of the semiconductor wafer 10 to define a plurality of individual regions where a plurality of devices 102, such as ICs and LSIs, are respectively formed.

[0030] A setting procedure for the processing conditions for forming a laser-machined groove with a predetermined depth (for example, 10 µm) on the semiconductor wafer will now be described. First, the semiconductor wafer 10, which is supported on the ring frame F by the dicing tape T, is placed on the chuck table 36 of the laser processing apparatus 1 shown in Fig. 1, in the state where the dicing tape T is in contact with the upper surface of the chuck table 36. Subsequently, the suction means (not shown) is operated to hold the semiconductor wafer 10 on the chuck table 36 under suction by the dicing tape T. Thus, the semiconductor wafer 10 is held by the dicing tape T on the chuck table 36 in the state where the front surface 10a of the semiconductor wafer 10 is directed upward. Further, the ring frame F supporting the dicing tape T is fixed by the clamps 362 provided on the chuck table 36. Subsequently, the X-moving means 37 is operated to move the chuck table 36 holding the semiconductor wafer 10 to a position directly below the imaging means 6.

[0031] In the state where the chuck table 36 is disposed directly below the imaging means 6, an alignment operation is performed by the imaging means 6 and the control means 9 to detect a target surface of the semiconductor wafer 10 to be laser-processed. More specifically, the imaging means 6 and the control means 9 perform imaging processing, such as pattern matching, to align the dividing lines 101 extending in a first direction on the semiconductor wafer 10 and the processing head 51 of the laser beam application means 5, thereby performing alignment for the dividing lines 101 extending in the first direction. Similarly, this alignment is performed for the other dividing lines 101 extending in a second direction perpendicular to the first direction on the semiconductor wafer 10.

[0032] After performing this alignment operation for detecting the target surface of the semiconductor wafer 10 held on the chuck table 36, a processing condition adjustment step is performed by the control means 9 in such a manner that the processing conditions are adjusted so as to obtain a target processing result inputted through the input means 90, wherein the adjustment is performed depending on the target processing result and a three-dimensional image formed by the 3D imaging means 7. In this processing condition adjustment step, the operator first sets the target depth of the laser-machined groove (for example, 10 µm) as the target processing result and further sets the fundamental numerical ranges of the processing factors contained in Fig. 8. The target depth and the fundamental numerical ranges, which are set as above, are input from the input means 90 into the control means 9 by the operator. For example, the machining factors are defined as the repetition frequency of a pulsed laser beam, the energy of the pulsed laser beam, and the machining feed rate. The fundamental numerical range of each machining factor is determined by setting the maximum value and the minimum value of each machining factor. For example, as shown in Fig. 8, the maximum and minimum values ​​of the repetition frequency of the pulsed laser beam were set to 200 kHz and 40 kHz, respectively, the maximum and minimum values ​​of the energy of the pulsed laser beam were set to 2 W and 0.5 W, respectively, and the maximum and minimum values ​​of the machining feed speed were set to 200 mm / second and 50 mm / second, respectively.

[0033] After inputting the fundamental numerical range of each machining factor, the control means 9 performs a fundamental numerical value setting step of calculating, depending on the fundamental numerical range of each machining factor, using a test setup to thereby set a fundamental value of each machining factor. By performing this fundamental numerical value setting step, each fundamental numerical value of each machining factor is set as shown in Fig. 9A. For example, five test samples #1 to #5 are prepared as shown in Fig. 9A, the fundamental numerical values ​​for the repetition frequency, energy, and machining feed rate are set as the machining factors in each test sample, and the machining result (the depth of the laser-machined groove) is also set. The fundamental numerical values ​​set as described above are stored in the RAM 93.

[0034] After executing the fundamental numerical value setting step mentioned above, the control means 9 executes a fundamental machining execution step of controlling the laser beam application means 5 and the X-axis movement means 37 depending on the fundamental numerical values ​​set in the fundamental numerical value setting step, thereby performing fundamental machining of the semiconductor wafer 10 held on the chuck table 36. Specifically, the control means 9 moves the chuck table 36 so as to position one end of a predetermined one of the dividing lines 101 directly below the machining head 51 of the laser beam application means 5.Subsequently, the control means 9 operates the laser beam application means 5 and the X-movement means 37 using the fundamental numerical values ​​set in the test sample #1 (repetition frequency: 200 kHz, power: 2 W, machining feed speed: 200 mm / second), thereby applying a pulsed laser beam along the predetermined dividing line 101. The focal spot diameter of the pulsed laser beam to be focused by the machining head 51 is previously set to, for example, 2 µm. As a result, a laser-machined groove defined by #1 in . Fig. 10 is formed on the semiconductor wafer 10.

[0035] Subsequently, the control means 9 operates the Y-moving means 38 to move the chuck table 36 in the Y-direction by the pitch of the dividing lines 101, thereby locating one end of the next dividing line 101 directly below the machining head 51. Subsequently, the control means 9 similarly operates the laser beam applying means 5 and the X-moving means 37 using the fundamental numerical values ​​set in test sample #2 (repetition frequency: 40 kHz, power: 2 W, machining feed speed: 50 mm / second), thereby applying a pulsed laser beam along this next dividing line 101. As a result, a laser-machined groove defined by #2 in Fig. 10 is formed on the semiconductor wafer 10. Subsequently, laser processing is performed in a similar manner on the next dividing lines 101 using the fundamental numerical values ​​specified in the test samples #3, #4, and #5. As a result, laser-machined grooves indicated by #3, #4, and #5 are formed. Fig. 10 are formed on the semiconductor wafer 10.

[0036] After performing the fundamental processing execution step, the control means 9 performs a 3D imaging step for imaging the processed state of the semiconductor wafer 10 to generate a three-dimensional image. In this 3D imaging step, the control means 9 operates the X-moving means 37 to move the chuck table 36, which holds the semiconductor wafer 10 processed by the fundamental processing execution step, to a position directly below the focusing means 73 that configures the interference imaging mechanism 70 of the 3D imaging means 7. In this state, the laser-machined groove #1 formed on the semiconductor wafer 10 is located directly below the focusing means 73. Subsequently, the first Z-moving means 8 is operated to lower the interference imaging mechanism 70 from a predetermined rest position.Further, for example, a voltage of 60 V is applied to the actuator 76 provided by a piezoelectric motor as the second Z-moving means, whereby the actuator 76 moves by an amount of 60 µm as shown in FIG. Fig. 6, axially extended / displaced. In this extended / extended state, the focal point P (see Fig. 4) the light to be applied from the focusing means 73 of the interference imaging mechanism 70 is set near the front side 10a (upper surface) of the semiconductor wafer 10 held on the chuck table 36.

[0037] Subsequently, the control means 9 operates the imaging means 72 and the light source 741 of the light application means 74, which configures the interference imaging mechanism 70. Further, the voltage applied to the actuator 76 as a piezoelectric motor is reduced from 60 V in steps of 1 V. As a result, the actuator 76 as a piezoelectric motor is reduced in length in steps of 1 µm, as shown by Fig. 6, so that the focus means 73 is lowered in the Z direction in steps of 1 µm. At each time the focus means 73 is lowered in steps of 1 µm, the X-movement means 37 is operated by the control means 9, wherein the imaging device means 72 forms an image and transmits an image signal to the control means 9. The control means 9 inputs the image signal transmitted from the imaging device means 72 in steps of 100 µm for the movement of the chuck table 36 in the X direction in response to the detection signal from the X-position detection means 374, thereby forming a three-dimensional image of the laser-machined groove #1 as shown in Fig. 11. This 3D imaging step is carried out in a similar manner for the other laser-machined grooves #2 to #5, thereby forming three-dimensional images of the laser-machined grooves #2 to #5, as shown in Fig. 11. At the same time, the depths of the laser-machined grooves #1 to #5 are measured from the three-dimensional images of the laser-machined grooves #1 to #5. Then, the control means 9 stores the three-dimensional images of the laser-machined grooves #1 to #5 previously formed in the RAM 93 and further stores the depths of the laser-machined grooves #1 to #5 measured as previously in the groove depth (µm) column shown in Fig. 9A, which is previously stored with the fundamental numerical values ​​of the machining factors in the RAM 93. The depths (µm) of the laser-machined grooves #1 to #5 recorded as described above are shown in Fig. 9B shown.

[0038] When one of the depths (µm) of the laser-machined grooves #1 to #5 acquired as described above falls within an allowable range (9.5 µm to 10.5 µm) of the target machining result (10 µm as the target depth of the laser-machined groove), the control means 9 determines the machining conditions for forming this laser-machined groove having the depth falling within this allowable range as the target machining conditions.

[0039] Then, the control means 9 executes a diagram creation step for creating a diagram of the machining results in relation to each machining factor depending on the three-dimensional images formed in the 3D imaging step. More specifically, the control means 9 calculates, depending on the three-dimensional images formed in Fig. 11, using an experimental setup, and then shows the machining tendency for the depth of the laser-machined groove as a function of the repetition frequency of the pulsed laser beam, the energy of the pulsed laser beam and the machining feed speed, as shown in Fig. 12A to 12C. Subsequently, the control means 9 selects the machining factor which has an influence on the machining results by the diagrams shown in Fig. 12A to 12C. That is, as can be seen from the diagrams shown in Fig. 12A to 12C, it can be determined that the machining factor having the greatest influence on the target machining result (10 µm as the target depth of the first laser-machined groove) is the machining feed speed having a machining tendency with respect to the target depth of 10 µm (changed numerical range setting step). After determining that the machining factor having an influence on the target machining result is the machining feed speed, the control means 9 determines that the range of the machining feed speed having an influence on the target machining result in the diagram shown in Fig. 12C, is higher than 125 mm / second, which is a midpoint between 50 mm / second and 200 mm / second. Then, the control means 9 changes the minimum value of the machining feed speed as the machining factor of 50 mm / second (see Fig. 8) to 125 mm / second (see Fig. 13) and sets this changed numeric range (changed numeric range setting step).

[0040] After executing the changed numerical range setting step mentioned above, the control means executes a changed numerical value setting step of calculating, depending on the changed numerical range of the selected machining factor using a test setup, and changing the numerical value of each machining factor to set this changed numerical value. By executing this changed numerical value setting step, the changed numerical values ​​for each machining factor are set in all the test samples #1 to #5, as shown in Fig. 14A. The changed numerical values, which are determined as previously, are stored in RAM 93.

[0041] After executing the above-mentioned modified numerical value setting step, the control means 9 executes a modified machining execution step of controlling the laser beam application means 5 and the X-axis movement means 37 depending on the modified numerical value of each machining factor set in the modified numerical value setting step, thereby executing modified machining of the semiconductor wafer 10 held on the chuck table 36. This modified machining execution step is executed in a manner similar to the above-mentioned fundamental machining execution step.

[0042] After performing the modified processing execution step mentioned above, the control means 9 performs a second 3D imaging step of imaging the processed state of the semiconductor wafer 10 processed by the modified processing execution step and then forming a three-dimensional image. This second 3D imaging step is performed in a similar manner to the 3D imaging step of imaging the processed state of the semiconductor wafer 10 processed by the fundamental processing execution step mentioned above, using the 3D imaging means 7. In this manner, the control means 9 generates three-dimensional images of the laser-machined grooves #1 to #5 and measures the depth of the laser-machined grooves #1 to #5.Further, the control means 9 stores the three-dimensional images of the laser-machined grooves #1 to #5 in the RAM 93 and further stores the depths of the laser-machined grooves #1 to #5 previously measured in the groove depth (µm) column shown in . Fig. 14A, which was previously stored with the changed numerical values ​​of the machining factors in the RAM 93. The depths (µm) of the laser-machined grooves #1 to #5, as previously recorded, are shown in Fig. 14B. When one of the depths (µm) of the laser-machined grooves #1 to #5 recorded as above falls within the allowable range (9.5 µm to 10.5 µm) of the target machining result (10 µm as the target depth of the laser-machined groove), the control means 9 determines that the machining conditions for forming this laser-machined groove with the depth falling within the allowable range are the target machining conditions. In the case shown in Fig.As shown in Fig. 14B, the control means 9 determines the machining conditions for forming the laser-machined groove #3 with a depth of 10 µm, which falls within this allowable range, as the target machining conditions for forming the laser-machined groove with the target depth of 10 µm (repetition frequency: 200 kHz, power: 0.5 W, machining feed speed: 125 mm / second). Subsequently, the control means 9 outputs the determined machining conditions (repetition frequency: 200 kHz, power: 0.5 W, machining feed speed: 125 mm / second) to the output means 900, thereby displaying them on a display means such as a monitor or printing them out by a printer.

[0043] In the case where the depth of each laser-machined groove does not fall within the allowable range (9.5 µm to 10.5 µm) of the target machining result (10 µm as the target depth of the laser-machined groove) in the second 3D mapping step, the diagram creation step, the changed numerical range setting step, the changed numerical value setting step, the changed machining execution step, and the second 3D mapping step are repeated until the actual machining result obtained by the changed machining falls within this allowable range.

[0044] In the laser processing apparatus according to the present invention described above, the processing conditions for the workpiece can be automatically set by inputting the required parameters. Therefore, the operator does not need to set the processing conditions by trial and error, thus improving productivity.

[0045] Although the repetition frequency of the pulsed laser beam, the energy of the pulsed laser beam, and the machining feed speed are set as machining conditions in the above embodiment, it is preferable to set the pulse width of the pulsed laser beam and the focal spot diameter of the pulsed laser beam as machining conditions.

Claims

[1] Laser processing device (1) with: a clamping table (36) for holding a workpiece (10); a laser beam application unit (4) having a machining head for applying a laser beam to the workpiece held by the clamping table; a movement mechanism for relatively moving the clamping table (36) and the laser beam application unit (4); an alignment unit for detecting an object surface of the workpiece held by the clamping table; a controller (9) for controlling the laser beam application unit (4) and the movement mechanism; an operating panel (90) for inputting a desired machining result into the control (9); and a 3D imaging unit (7) for imaging a machined state of the workpiece held by the clamping table to form a three-dimensional image, wherein the controller executes a machining state adjustment step for adjusting machining states so that the desired machining result inputted through the operation panel (90) is obtained, depending on the desired machining result and the three-dimensional image formed by the 3D imaging unit (7), and then controls the laser beam application unit (4) and the moving mechanism depending on the machining states adjusted in the machining state adjustment step, wherein the machining state adjustment step by the control means comprises: a fundamental numerical value setting step for setting a fundamental numerical value of each machining factor from a plurality of machining factors depending on the desired machining result inputted through the operation panel (90) and a fundamental numerical range of each machining factor from the plurality of machining factors inputted through the operation panel (90); a fundamental machining execution step of controlling the laser beam application unit (4) and the moving mechanism depending on the fundamental numerical value of each machining factor set in the fundamental numerical value setting step, to thereby execute fundamental machining of the workpiece (10) held by the chuck table (36); a 3D imaging step of operating the 3D imaging unit (7) to image the machined state of the workpiece (10) machined by the fundamental machining execution step, thereby forming a three-dimensional image; a diagram creating step of creating a diagram of the machining results with respect to each machining factor depending on the three-dimensional image formed in the 3D imaging step; a changed numerical range setting step for selecting the machining factor having an influence on the machining results by comparing the diagrams each corresponding to the machining factors created in the diagram creating step, and then setting a changed numerical range for the machining factor previously selected; a modified numerical value setting step for setting a modified numerical value of each machining factor depending on the modified numerical range set in the modified numerical range setting step; and a modified machining execution step for controlling the laser beam application unit (4) and the moving mechanism in accordance with the modified numerical value of each machining factor set in the modified numerical value setting step, thereby executing modified machining of the workpiece held by the chuck table (36); wherein the 3D mapping step, the diagram creation step, the changed numerical range setting step, the changed numerical value setting step, and the changed machining execution step are repeated until the actual machining result obtained by the changed machining falls within an allowable range of the target machining result. [2] The laser processing apparatus (1) according to claim 1, wherein the fundamental numerical value setting step, the diagram applying step and the changed numerical value setting step are carried out according to an experimental arrangement.

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