JP2010052014A - Laser beam machining apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining apparatus which correctly performs machining from the surface of a workpiece to a prescribed depth position even if there is a variation in the thickness of the workpiece. <P>SOLUTION: The laser beam machining apparatus includes: a height position detection means 8 which irradiates the workpiece held on a chuck table with a laser beam for detection with wavelength different from the wavelength of a laser beam for machining through a condenser 7 and detects the upper face height position of the workpiece held on the chuck table based on reflected light reflected at the upper face of the workpiece; a first condensing point position adjustment means 82 which moves a laser beam irradiation means in a direction vertical to the held face of the workpiece and adjusts the condensing point position of the laser beam condensed by the condenser; a second condensing point position adjustment means 74 which comprises a piezo motor displacing the condensing point position of the laser beam by displacing the condensing lens of the condenser to a direction vertical to the held face of the workpiece; and a control means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laser processing apparatus that performs laser processing on a plate-like workpiece held on a chuck table along a predetermined processing line.

  In the semiconductor device manufacturing process, a plurality of regions are partitioned by dividing lines called streets arranged in a lattice pattern on the surface of a substantially wafer-shaped semiconductor wafer, and devices such as ICs, LSIs, etc. are partitioned in the partitioned regions. Form. Then, the semiconductor wafer is cut along the streets to divide the region where the circuit is formed to manufacture individual semiconductor chips. In addition, a semiconductor wafer in which a gallium nitride compound semiconductor or the like is laminated on the surface of a sapphire substrate is also divided into optical devices such as individual light emitting diodes and laser diodes by cutting along the street, and is widely used in electrical equipment. Yes.

In recent years, as a method of dividing a plate-like workpiece such as a semiconductor wafer, a pulsed laser beam having transparency to the workpiece is used, and the focused laser beam is aligned with the inside of the region to be divided. Laser processing methods for irradiation have also been attempted. The dividing method using this laser processing method irradiates a pulse laser beam having a wavelength (for example, 1064 nm) having transparency with respect to the work piece by aligning the condensing point from one side of the work piece to the inside. In this work, an altered layer is continuously formed along the street inside the workpiece, and the workpiece is divided by applying an external force along the street whose strength has been reduced by the formation of the altered layer. is there. (For example, refer to Patent Document 1.)
Japanese Patent No. 3408805

  However, a plate-like workpiece such as a semiconductor wafer has undulation, and if the thickness varies, a uniform alteration layer is formed at a predetermined depth due to the refractive index when irradiating a laser beam. I can't. Therefore, in order to uniformly form a deteriorated layer at a predetermined depth inside a semiconductor wafer or the like, it is necessary to detect irregularities in a region irradiated with a laser beam in advance and to process the irregularities by following the laser beam irradiation means. .

In order to solve the above-described problems, a chuck table having a workpiece holding surface for holding a workpiece, and processing for oscillating a processing laser beam for laser processing the workpiece held on the chuck table. Laser beam oscillating means, a condenser having a condenser lens for condensing the machining laser beam oscillated by the machining laser beam oscillating means, and a processing laser beam condensed by the condenser lens of the condenser A focusing point position adjusting means for moving the focusing point of the workpiece in a direction perpendicular to the workpiece holding surface, a height position detecting means for detecting the height position of the workpiece held on the chuck table, and the height There has been proposed a laser processing apparatus including a control means for controlling the condensing point position adjusting means based on the height position signal detected by the height position detecting means. (For example, see Patent Document 2.)
Japanese Patent Laid-Open No. 2008-12566

The height position detecting means in the laser processing apparatus disclosed in Patent Document 2 irradiates the surface of the workpiece held on the chuck table through the condenser lens with the detection laser beam, and based on the area of the reflected light. The height position of the workpiece held on the chuck table is detected.
However, the height position detection means disclosed in the above-mentioned Patent Document 2 has the focusing point of the processing laser beam coincident with the focusing point of the processing laser beam, so that the focusing point of the processing laser beam is held on the chuck table. When processing with the focal point positioned deep from the surface of the workpiece, the spot area of the detection laser beam irradiated onto the surface of the workpiece becomes very large. As a result, the amount of reflected light per unit area is reduced, so that the height position of the workpiece held on the chuck table cannot be accurately detected. Therefore, there is a problem that it is impossible to accurately process a predetermined depth position from the surface of the workpiece following the undulation of the workpiece.

The height position detecting means in the laser processing apparatus disclosed in Patent Document 2 irradiates the surface of the workpiece held on the chuck table through the condenser lens with the detection laser beam, and based on the area of the reflected light. The height position of the workpiece held on the chuck table is detected.
However, the focusing point position adjusting means for displacing the focusing point of the detection laser beam and the focusing point position of the processing laser beam of the height position detection unit disclosed in the above-mentioned Patent Document 2 uses a galvano scanner mechanism. Therefore, it is difficult to quickly follow the focal point position of the processing laser beam corresponding to the change in the height position of the workpiece detected by the height position detecting means.

  The present invention has been made in view of the above facts, and its main technical problem is that the focusing point of the laser beam for processing corresponds to the change in the height position of the workpiece detected by the height position detecting means. It is an object of the present invention to provide a laser processing apparatus capable of quickly following a position and accurately processing a predetermined depth position from the surface of the workpiece even if the thickness of the workpiece varies.

In order to solve the above main technical problem, according to the present invention, a chuck table having a workpiece holding surface for holding a workpiece, and processing for laser processing the workpiece held on the chuck table. Laser beam irradiating means having a processing laser beam oscillating means for oscillating a processing laser beam, a condenser having a condenser lens for condensing the processing laser beam oscillated by the laser beam oscillating means, the chuck table, and the laser beam irradiation Machining feed means for relatively moving the means in the machining feed direction (X-axis direction), and the chuck table and the laser beam irradiation means in an index feed direction (Y-axis direction) orthogonal to the machining feed direction (X-axis direction) In a laser processing apparatus comprising an indexing and feeding means for relatively moving,
The workpiece held on the chuck table is irradiated with a detection laser beam having a wavelength different from the wavelength of the machining laser beam through the condenser, and is reflected on the chuck table based on the reflected light reflected from the upper surface of the workpiece. Height position detecting means for detecting the upper surface height position of the workpiece to be held;
A first collection of adjusting the position of the condensing point of the laser beam for detection and the laser beam for processing collected by moving the laser beam irradiating means in a direction perpendicular to the workpiece holding surface. Light spot position adjusting means;
A second piezo-motor that displaces the condensing point position of the detection laser beam and the processing laser beam by displacing the condensing lens of the concentrator in a direction perpendicular to the workpiece holding surface; Focusing point position adjusting means;
A detection signal from the height position detection means is input, and the first focusing point position adjusting means, the second focusing point position adjusting means, the laser beam irradiation means, the processing feeding means, and the indexing feeding means are provided. Control means for controlling,
A laser processing apparatus is provided.

  The control means operates the height position detection means and operates the machining feed means and the index feed means to detect the surface height position in the machining area of the workpiece held by the chuck table, and to detect the maximum value and the minimum value. A height position detecting step for obtaining a value, and a laser beam collected by the condenser by operating the first focusing point position adjusting means based on the highest value and the lowest value obtained by the height position detecting step. A focusing point position adjusting step for adjusting the focusing point position to an intermediate position between the highest value and the lowest value, and a workpiece detected by the height position detecting means while operating the laser beam irradiation means and the height position detecting means. A laser processing step for controlling the second light condensing point position adjusting means composed of a piezo motor corresponding to the height position is executed.

  A laser processing apparatus according to the present invention moves a height position detecting means for detecting a top surface height position of a workpiece held on a chuck table and a laser beam irradiation means in a direction perpendicular to the workpiece holding surface. A first condensing point position adjusting means for adjusting a condensing point position of the detection laser beam and the processing laser beam collected by the concentrator; and a condensing lens of the concentrator with respect to the workpiece holding surface. Since there is provided a second condensing point position adjusting means comprising a piezo motor for displacing the condensing point positions of the detection laser beam and the processing laser beam by displacing in the vertical direction, and a control means, the concentrator Is positioned at a predetermined reference position, the first condensing point position adjusting means comprising a ball screw mechanism or the like is actuated to collect the detection laser beam based on the detection signal from the height position detecting means. When allowed to displace the focal position of the processing laser beam and the point position controls the second focal position adjusting means for a response consists of fast piezoelectric motor. Accordingly, it is possible to quickly follow the condensing point position of the processing laser beam in response to the change in the height position of the workpiece detected by the height position detecting means, and there is a variation in the thickness of the workpiece. Even if it exists, it can be processed accurately at a predetermined depth position from the surface of the workpiece.

  Preferred embodiments of a laser processing apparatus configured according to the present invention will be described below in more detail with reference to the accompanying drawings.

  FIG. 1 is a perspective view of a laser processing apparatus constructed according to the present invention. A laser processing apparatus shown in FIG. 1 includes a stationary base 2, a chuck table mechanism 3 that is disposed on the stationary base 2 so as to be movable in a machining feed direction indicated by an arrow X, and holds a workpiece. 2, a laser beam irradiation unit support mechanism 4 movably disposed in an indexing feed direction (Y axis direction) indicated by an arrow Y perpendicular to the direction indicated by the arrow X (X axis direction), and the laser beam unit support mechanism 4 And a laser beam irradiation unit 5 disposed so as to be movable in a direction indicated by an arrow Z (Z-axis direction).

  The chuck table mechanism 3 includes a pair of guide rails 31, 31 arranged in parallel along the machining feed direction indicated by the arrow X on the stationary base 2, and the arrow X on the guide rails 31, 31. A first sliding block 32 disposed so as to be movable in the machining feed direction (X-axis direction), and disposed on the first sliding block 32 so as to be movable in the index feed direction (Y-axis direction) indicated by an arrow Y. A second sliding block 33 provided, a cover table 35 supported on the second sliding block 33 by a cylindrical member 34, and a chuck table 36 as a workpiece holding means are provided. The chuck table 36 includes a suction chuck 361 formed of a porous material, and a workpiece, for example, a disk-shaped semiconductor wafer as a workpiece is placed on a suction chuck 361 as a workpiece holding surface by suction means (not shown). It comes to hold. The chuck table 36 configured as described above is rotated by a pulse motor (not shown) disposed in the cylindrical member 34. The chuck table 36 is provided with a clamp 362 for fixing an annular frame described later.

  The first sliding block 32 is provided with a pair of guided grooves 321 and 321 fitted to the pair of guide rails 31 and 31 on the lower surface thereof, and in the index feed direction indicated by an arrow Y on the upper surface thereof. A pair of guide rails 322 and 322 formed in parallel with each other are provided. The first sliding block 32 configured in this way is processed by the arrow X along the pair of guide rails 31, 31 when the guided grooves 321, 321 are fitted into the pair of guide rails 31, 31. It is configured to be movable in the feed direction. The chuck table mechanism 3 in the illustrated embodiment includes a machining feed means 37 including a ball screw mechanism for moving the first sliding block 32 in the machining feed direction indicated by the arrow X along the pair of guide rails 31, 31. It has. The processing feed means 37 includes a male screw rod 371 disposed in parallel between the pair of guide rails 31 and 31, and a drive source such as a pulse motor 372 for rotationally driving the male screw rod 371. One end of the male screw rod 371 is rotatably supported by a bearing block 373 fixed to the stationary base 2, and the other end is connected to the output shaft of the pulse motor 372 by transmission. The male screw rod 371 is screwed into a penetrating female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the first sliding block 32. Accordingly, by driving the male screw rod 371 in the forward and reverse directions by the pulse motor 372, the first slide block 32 is moved along the guide rails 31 and 31 in the machining feed direction (X-axis direction) indicated by the arrow X. .

  The second sliding block 33 is provided with a pair of guided grooves 331 and 331 which are fitted to a pair of guide rails 322 and 322 provided on the upper surface of the first sliding block 32 on the lower surface thereof. By fitting the guided grooves 331 and 331 to the pair of guide rails 322 and 322, the guided grooves 331 and 331 are configured to be movable in the indexing feed direction (Y-axis direction) indicated by the arrow Y. The chuck table mechanism 3 in the illustrated embodiment includes an index feed direction (Y-axis direction) indicated by an arrow Y along the pair of guide rails 322 and 322 provided on the first slide block 32. The first index feeding means 38 comprising a ball screw mechanism is provided. The first index feed means 38 includes a male screw rod 381 disposed in parallel between the pair of guide rails 322 and 322, and a drive source such as a pulse motor 382 for rotationally driving the male screw rod 381. It is out. One end of the male screw rod 381 is rotatably supported by a bearing block 383 fixed to the upper surface of the first sliding block 32, and the other end is connected to the output shaft of the pulse motor 382. The male screw rod 381 is screwed into a penetrating female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the second sliding block 33. Therefore, by driving the male screw rod 381 forward and backward by the pulse motor 382, the second slide block 33 is moved along the guide rails 322 and 322 in the indexing feed direction (Y-axis direction) indicated by the arrow Y. .

  The laser beam irradiation unit support mechanism 4 includes a pair of guide rails 41, 41 arranged in parallel along the indexing feed direction (Y-axis direction) indicated by an arrow Y on the stationary base 2, and the guide rails 41, 41, A movable support base 42 is provided on 41 so as to be movable in the direction indicated by arrow Y. The movable support base 42 includes a movement support portion 421 that is movably disposed on the guide rails 41, 41, and a mounting portion 422 that is attached to the movement support portion 421. The mounting portion 422 is provided with a pair of guide rails 423 and 423 extending in the direction indicated by the arrow Z on one side surface in parallel. The laser beam irradiation unit support mechanism 4 in the illustrated embodiment includes a ball screw mechanism for moving the movable support base 42 along the pair of guide rails 41 and 41 in the indexing feed direction (Y-axis direction) indicated by the arrow Y. The second index feed means 43 is provided. The second index feed means 43 includes a male screw rod 431 disposed in parallel between the pair of guide rails 41, 41, and a drive source such as a pulse motor 432 for rotationally driving the male screw rod 431. It is out. One end of the male screw rod 431 is rotatably supported by a bearing block (not shown) fixed to the stationary base 2, and the other end is connected to the output shaft of the pulse motor 432. The male screw rod 431 is screwed into a female screw hole formed in a female screw block (not shown) provided on the lower surface of the central portion of the moving support portion 421 constituting the movable support base 42. Therefore, the movable support base 42 is moved along the guide rails 41 and 41 in the indexing feed direction (Y-axis direction) indicated by the arrow Y by driving the male screw rod 431 forward and backward by the pulse motor 432. .

  The laser beam irradiation unit 5 in the illustrated embodiment includes a unit holder 51 and laser beam irradiation means 52 attached to the unit holder 51. The unit holder 51 is provided with a pair of guided grooves 511 and 511 that are slidably fitted to a pair of guide rails 423 and 423 provided in the mounting portion 422. By being fitted to the guide rails 423 and 423, the guide rails 423 and 423 are supported so as to be movable in the direction indicated by the arrow Z (Z-axis direction).

  The laser beam irradiation unit 5 in the illustrated embodiment includes a unit holder 51 along a pair of guide rails 423 and 423, and a focal position adjustment direction (Z) indicated by an arrow Z which is a direction perpendicular to the chuck table 36 workpiece holding surface. First focusing point position adjusting means 53 for moving in the axial direction is provided. The first condensing point position adjusting means 53 is composed of a ball screw mechanism, like the processing feeding means 37, the first index feeding means 38 and the second index feeding means 43. The first condensing point position adjusting means 53 includes a male screw rod (not shown) disposed between the pair of guide rails 423 and 423, and a pulse motor 532 for rotationally driving the male screw rod. The unit holder 51 and the laser beam irradiation means 52 are indicated by the arrow Z along the guide rails 423 and 423 by driving the male screw rod (not shown) in the normal direction and the reverse direction by the pulse motor 532. Move in the condensing point position adjustment direction (Z-axis direction). In the illustrated embodiment, the laser beam irradiation means 52 is moved upward by driving the pulse motor 532 forward, and the laser beam irradiation means 52 is moved downward by driving the pulse motor 532 in reverse. Yes.

  The illustrated laser beam application means 52 includes a cylindrical casing 521 arranged substantially horizontally. As shown in FIG. 2, a processing pulse laser beam oscillating means 6 is disposed in the casing 521, and a processing pulse laser beam oscillated by the processing pulse laser beam oscillating means 6 is provided at the tip of the casing 521. A condenser 7 for irradiating the workpiece held by 36 is disposed. The processing pulse laser beam oscillating means 6 oscillates a processing pulse laser beam LB1 having a wavelength that is transparent to the wafer that is the workpiece. As the processing pulse laser beam oscillation means 6, for example, a YVO4 pulse laser oscillator or a YAG pulse laser oscillator that oscillates a processing pulse laser beam LB1 having a wavelength of 1064 nm can be used.

  The condenser 7 has a direction changing mirror 71 that changes the direction of the processing pulse laser beam LB1 oscillated from the processing pulse laser beam oscillation means 6 downward in FIG. A condensing lens 72 that condenses the processing pulse laser beam LB1 and a case 73 that accommodates the condensing lens 72 in a direction perpendicular to the holding surface (upper surface) of the chuck table 36 (vertical direction in FIG. 2). An actuator 74 for moving is provided. In the illustrated embodiment, the actuator 74 is composed of a piezoelectric motor constituted by a piezoelectric element extending in the axial direction corresponding to the voltage value to be applied. Therefore, the actuator 74 composed of a piezo motor is controlled by a control means to be described later, and moves the condenser lens 72 in the vertical direction (direction perpendicular to the chuck table 36 workpiece holding surface) in FIG. It functions as a second focusing point position adjusting means for displacing the focusing point position.

  Continuing the description with reference to FIG. 2, the laser processing apparatus in the illustrated embodiment includes a height position detecting means 8 for detecting the upper surface height position of the workpiece held on the chuck table. Yes. The height position detection means 8 is arranged in a path between the inspection laser beam oscillation means 80 for oscillating the inspection laser beam and the processing pulse laser beam oscillation means 6 and the condenser 7. A dichroic mirror 81 that splits the oscillated inspection laser beam toward the condenser 7, and an inspection that is disposed between the dichroic mirror 81 and the inspection laser beam oscillation means 80 and oscillated by the inspection laser beam oscillation means 80. The position of the condensing point of the laser beam for condensing by the condensing lens 72 of the condenser 7 and the position of the condensing point of the processing laser beam for condensing by the condensing lens 72 of the condenser 7 are displaced. A condensing point position displacing means 82 and a condensing point position disposed between the condensing point position displacing means 82 and the dichroic mirror 81. And it comprises a first beam splitter 83 for guiding the detection laser beam passing through the displacement means 82 to the first path 83a directed to the dichroic mirror 81.

  The inspection laser beam oscillating means 80 is different from the wavelength of the processing pulse laser beam oscillated from the processing pulse laser beam oscillating means 6 and has a wavelength that is reflective to the wafer being processed, for example, a wavelength of 635 nm. A He-Ne pulse laser oscillator that oscillates the laser beam LB2 can be used. Note that the output of the inspection laser beam LB2 oscillated from the inspection laser beam oscillation means 80 is set to 10 mW in the illustrated embodiment. The dichroic mirror 81 reflects the inspection laser beam oscillated from the inspection laser beam oscillation means 80 toward the condenser 7 though the processing pulse laser beam LB1 passes through. In the illustrated embodiment, the condensing point position displacing means 82 includes a pair of convex lenses 821 and 822 arranged in series at a predetermined interval along the optical axis of the inspection laser beam LB2, and the pair of convex lenses 821. , 822 for adjusting the interval 822, and the interval adjusting unit 823 is controlled by a control unit to be described later. The first beam splitter 83 guides the inspection laser beam LB2 that has passed through the interval adjusting means 823 to the first path 83a directed to the dichroic mirror 81, and reflects reflected light that will be described later reflected by the dichroic mirror 81. 2 path 83b.

  The height position detecting means 8 in the illustrated embodiment has a wavelength of the inspection laser beam LB2 (635 nm in the illustrated embodiment) of the reflected light that is disposed in the second path 83b and reflected by the first beam splitter 83. ) And a reflected light analyzing means 85 that analyzes the reflected light that has passed through the band pass filter 84 and sends the analysis result to a control means that will be described later. The reflected light analysis means 85 includes a second beam splitter 851 that splits the reflected light that has passed through the bandpass filter 84 into a third path 85a and a fourth path 85b, and a third beam splitter 851 that generates a third beam. A condensing lens 852 that condenses 100% of the reflected light split into the path 85a and a first light receiving element 853 that receives the reflected light collected by the condensing lens 852 are provided. The first light receiving element 853 sends a voltage signal corresponding to the received light quantity to the control means described later. The reflected light analyzing means 85 in the illustrated embodiment includes a second light receiving element 854 that receives the reflected light split into the fourth path 85b by the second beam splitter 851, and the second light receiving element 854. Is provided with light receiving area regulating means 855 for regulating the light receiving area of the reflected light received by. In the illustrated embodiment, the light receiving region restricting unit 855 includes a cylindrical lens 855a that condenses the reflected light split into the fourth path 85b by the second beam splitter 851 in a one-dimensional manner, and the cylindrical lens 855a. And a one-dimensional mask 855b for restricting the reflected light focused on the unit length. The second light receiving element 854 that receives the reflected light that has passed through the one-dimensional mask 855b sends a voltage signal corresponding to the received light amount to the control means described later.

The height position detecting means 8 in the embodiment shown in FIG. 2 is configured as described above, and the operation thereof will be described below.
The inspection laser beam LB2 composed of parallel light oscillated from the inspection laser beam oscillation means 80 changes the distance between the convex lenses 821 and 822 of the condensing point position displacing means 82 to change the condensing lens 72 of the condenser 7. The position of the condensing point collected by is changed. That is, as shown in FIG. 3A, when the focal position of the convex lens 821 and the focal position of the convex lens 822 are aligned, the inspection laser beam LB2 incident on the convex lens 821 is parallel from the convex lens 822. Is output as a light beam. On the other hand, when the distance between the convex lenses 821 and 822 is smaller than that shown in FIG. 3A as shown in FIG. 3B, the inspection laser beam LB2 incident on the convex lens 821 is divergent from the convex lens 822. Is output. 3C, when the distance between the convex lenses 821 and 822 is larger than that in FIG. 3A, the inspection laser beam LB2 incident on the convex lens 821 is constricted from the convex lens 822. Output as rays. As shown in FIG. 3A, the inspection laser beam LB2 output as a parallel light beam from the convex lens 822 of the condensing point position displacing means 82 is output from the condenser 7 as shown in FIG. The light is condensed at the condensing point position P1 by the condensing lens 72. This condensing point position P1 coincides with the condensing point position of the processing pulse laser beam LB1. On the other hand, as shown in FIG. 3B, the inspection laser beam LB2 output as a divergent beam from the convex lens 822 of the condensing point position displacing means 82 is collected as shown in FIG. 7 is condensed at a condensing point position P2 below the condensing point position P1. Further, as shown in FIG. 3 (c), the inspection laser beam LB2 output as a confined beam from the convex lens 822 of the condensing point position displacing means 82 is collected as shown in FIG. 4 (c). The light is condensed at a condensing point position P3 above the condensing point position P by the condensing lens 72 of the optical device 7.

Here, the focal point positions of the inspection laser beam LB2 and the processing pulse laser beam LB1 collected by the condenser 7 will be described with reference to FIG. In addition, the space | interval of the convex lenses 821 and 822 of the condensing point position displacement means 82 which comprises the condensing point position displacement means 82 uses the aspect shown to the said FIG.
The processing pulse laser beam LB1 is condensed at the condensing point position P by the condenser lens 72 of the condenser 7. On the other hand, the inspection laser beam LB2 is condensed at the condensing point position P3 above the condensing point position P by the condenser lens 72 of the condenser 7 as described above. The distance (L) between the condensing point position P of the processing pulse laser beam LB1 and the condensing point position P3 of the inspection laser beam LB2 is adjusted by adjusting the distance between the convex lenses 821 and 822 of the condensing point position displacement means 82. Can be changed. Note that the condensing point position where the inspection laser beam oscillated by the inspection laser beam oscillation means 80 is condensed by the condensing lens 72 of the concentrator 7 and the condensing lens of the concentrator 7 of the processing laser beam. The condensing point position displacing means 82 for displacing the condensing point position condensed by 72 may be disposed on the path from the processing pulse laser beam oscillation means 6 to the dichroic mirror 81.

  Then, the actuator as the second focusing point position adjusting means so as to position the focusing point position P of the processing pulse laser beam LB1 at a position above the lower surface of the workpiece W held by the chuck table 36 by a predetermined amount. A predetermined voltage (for example, 5 V) is applied to 74. At this time, the distance between the convex lenses 821 and 822 of the condensing point position displacement means 82 is set so that the condensing point position P3 of the inspection laser beam LB2 is located below the upper surface of the workpiece W (downstream in the laser beam irradiation direction). adjust. Accordingly, the inspection laser beam LB2 is irradiated with the spot S on the upper surface of the workpiece W held on the chuck table 36, and is reflected by the size of the spot S (reflected light). In this way, the spot S of the inspection laser beam LB2 irradiated on the upper surface of the workpiece W held on the chuck table 36 is significantly more than the spot S0 when the focal point position coincides with the processing pulse laser beam LB1. Since it is small, the amount of reflected light per unit area increases. Therefore, the height position of the workpiece W held on the chuck table 36, which is obtained by the reflected light analyzing means 85 based on the amount of reflected light, becomes accurate.

  Thus, the reflected light of the spot S reflected by the upper surface of the workpiece W is bandpassed via the condenser lens 72, the direction changing mirror 71, the dichroic mirror 81, and the first beam splitter 83 as shown in FIG. The filter 84 is reached. The reflected light of the processing pulse laser beam LB1 also reaches the bandpass filter 84 via the path in the same manner as the inspection laser beam LB2. Since the band pass filter 84 is configured to pass only the reflected light corresponding to the frequency of the inspection laser beam LB2 as described above, the reflected light of the processing pulse laser beam LB1 is blocked by the band pass filter 84. Accordingly, only the reflected light of the inspection laser beam LB2 passes through the bandpass filter 84 and is split into the third path 85a and the fourth path 85b by the second beam splitter 851 constituting the reflected light analysis means 85. The reflected light of the inspection laser beam LB2 split into the third path 85a is condensed by 100% by the condenser lens 852 and received by the first light receiving element 853. Then, the first light receiving element 853 sends a voltage signal corresponding to the received light amount to the control means described later. On the other hand, the reflected light of the inspection laser beam LB2 split into 85b in the fourth path is condensed one-dimensionally by the cylindrical lens 855a of the light-receiving region restricting means 855, and restricted to a predetermined unit length by the one-dimensional mask 855b. Then, the light is received by the second light receiving element 854. Then, the second light receiving element 854 sends a voltage signal corresponding to the received light amount to the control means described later.

Here, the amount of the reflected light of the inspection laser beam LB2 received by the first light receiving element 853 and the second light receiving element 854 will be described.
The reflected light received by the first light receiving element 853 is condensed 100% by the condenser lens 852, so that the amount of received light is constant, and the voltage value (V1) output from the first light receiving element 853 is constant. (For example, 10V). On the other hand, the reflected light received by the second light receiving element 854 is focused one-dimensionally by the cylindrical lens 855a of the light-receiving area restricting means 855, and then restricted to a predetermined unit length by the one-dimensional mask 855b. 2 is received by the two light receiving elements 854, so that when the inspection laser beam LB2 is applied to the upper surface of the workpiece W, as shown in FIG. The amount of light received by the second light receiving element 854 varies depending on the distance to the upper surface, that is, the height position (thickness) of the workpiece W. Accordingly, the voltage value (V2) output from the second light receiving element 854 changes depending on the height position of the upper surface of the workpiece W irradiated with the inspection laser beam LB2.

  For example, as shown in FIG. 6 (a), the height position of the workpiece W is low (the thickness of the workpiece W is thin), from the condenser lens 72 of the condenser 7 to the upper surface of the workpiece W. When the distance (H) is large, the inspection laser beam LB2 is reflected by the spot S1 irradiated on the upper surface of the workpiece W. As described above, the reflected light is split into the third path 85a and the fourth path 85b by the second beam splitter 851, and the reflected light of the spot S1 split into the third path 85a is the condenser lens. Since 100% is condensed by 852, the entire light amount of the reflected light is received by the first light receiving element 853. On the other hand, the reflected light of the spot S1 split into the fourth path 85b by the second beam splitter 851 is condensed in a one-dimensional manner by the cylindrical lens 855a, so that the cross section is substantially rectangular. Since the reflected light whose cross section is narrowed to a substantially rectangular shape in this way is regulated to a predetermined unit length by the one-dimensional mask 855b, a part of the reflected light dispersed in the fourth path 85b is the second. Light is received by the light receiving element 854. Accordingly, the amount of reflected light received by the second light receiving element 854 is smaller than the amount of light received by the first light receiving element 853 described above.

  Next, as shown in FIG. 6B, the height position of the workpiece W is high (the thickness of the workpiece W is thick), from the condenser lens 72 of the condenser 7 to the upper surface of the workpiece W. When the distance (H) is small, the inspection laser beam LB2 is reflected by the spot S2 irradiated on the upper surface of the workpiece W. The annular spot S2 is larger than the spot S1. The reflected light of the spot S2 is split into the third path 85a and the fourth path 85b by the second beam splitter 851 as described above, but the reflected light of the spot S2 split into the third path 85a is Since 100% of the light is condensed by the condensing lens 852, all the reflected light is received by the first light receiving element 853. On the other hand, the reflected light of the spot S2 split into the fourth path 85b by the second beam splitter 851 is condensed in a one-dimensional manner by the cylindrical lens 855a, so that the cross section is substantially rectangular. The length of the long side of the substantially rectangular shape is longer than that of the spot S1 because the reflected light spot S2 is larger than the annular spot S1. In this way, the reflected light condensed in a substantially rectangular cross section is divided into a predetermined length by the one-dimensional mask 855 b and a part is received by the second light receiving element 854. Accordingly, the amount of light received by the second light receiving element 854 is less than that shown in FIG. Thus, the amount of reflected light received by the second light receiving element 854 is the distance (H) from the condenser lens 72 of the condenser 7 to the upper surface of the workpiece W, that is, the height of the workpiece W. The lower the position (the thinner the workpiece W is), the greater the distance (H) from the condenser lens 72 of the condenser 7 to the upper surface of the workpiece W, that is, the height position of the workpiece W is higher. It becomes smaller as the thickness of the workpiece W is thicker.

  Here, the ratio between the voltage value (V 1) output from the first light receiving element 853 and the voltage value (V 2) output from the second light receiving element 854, and the condenser lens 72 of the condenser 7. The relationship between the distance (H) to the upper surface of the workpiece W, that is, the height position of the workpiece W will be described with reference to the control map shown in FIG. In FIG. 7, the horizontal axis represents the ratio (V1 / V2) between the voltage value (V1) output from the first light receiving element 853 and the voltage value (V2) output from the second light receiving element 854. The axis indicates the amount of displacement with respect to a predetermined distance (reference value) from the condenser lens 72 of the condenser 7 to the upper surface of the workpiece W. In the example shown in FIG. 7, the condenser lens of the condenser 7 is applied in the state where a predetermined voltage (for example, 5V) is applied to the actuator 74 as the second condenser point position adjusting means as described above. When the distance (H) from 72 to the upper surface of the workpiece W is 30.0 mm, the voltage value ratio (V1 / V2) is set to “5” with the reference value (0). When the height position of the workpiece W held on the chuck table is lower than the reference value (the workpiece W is thin), the workpiece W is removed from the condenser lens 72 of the condenser 7. Since the distance (H) to the upper surface of the electrode becomes longer, the voltage value ratio (V1 / V2) becomes larger than “5”. On the other hand, when the height position of the workpiece W held on the chuck table is higher than the reference value (the workpiece W is thick), the workpiece W is removed from the condenser lens 72 of the condenser 7. Since the distance (H) to the upper surface of the electrode becomes shorter, the voltage value ratio (V1 / V2) becomes smaller than “5”. Therefore, as described above, the ratio (V1 / V2) between the voltage value (V1) output from the first light receiving element 853 and the voltage value (V2) output from the second light receiving element 854 is obtained, and this voltage is obtained. By comparing the value ratio (V1 / V2) with the control map shown in FIG. 7, the distance (H) from the condenser lens 72 of the condenser 7 to the upper surface of the workpiece W, that is, from the above reference value. The amount of displacement can be determined. The control map shown in FIG. 7 is stored in the memory of the control means described later.

  Returning to FIG. 1, the description will be continued. At the front end portion of the casing 521 constituting the laser beam irradiation means 52, an imaging means 9 for detecting a processing region to be laser processed by the laser beam irradiation means 52 is disposed. The imaging means 9 includes an infrared illumination means for irradiating a workpiece with infrared rays, an optical system for capturing infrared rays emitted by the infrared illumination means, in addition to a normal imaging device (CCD) for imaging with visible light, An image sensor (infrared CCD) that outputs an electrical signal corresponding to the infrared rays captured by the optical system is used, and the captured image signal is sent to a control means to be described later.

  The laser processing apparatus in the illustrated embodiment includes a control means 10 shown in FIG. The control means 10 is constituted by a computer, and a central processing unit (CPU) 101 that performs arithmetic processing according to a control program, a read-only memory (ROM) 102 that stores a control program and the like, and a readable and writable data that stores arithmetic results and the like. A random access memory (RAM) 103, an input interface 104 and an output interface 105 are provided. Detection signals from the first light receiving element 853, the second light receiving element 854, the imaging means 9, and the like are input to the input interface 104 of the control means 10. From the output interface 105 of the control means 10, the pulse motor 372, the pulse motor 382, the pulse motor 432, the pulse motor 532, the processing pulse laser beam oscillation means 6, and the piezo motor as the second focusing point position adjusting means. A control signal is output to the actuator 74, the inspection laser beam oscillation means 80, and the like. The random access memory (RAM) 103 includes a first storage area 103a for storing the control map shown in FIG. 7 described above, and a voltage value output from the first light receiving element 853 as shown in FIG. V1) and the voltage value (V2) output from the second light receiving element 854 (V1 / V2), the voltage to be applied to the actuator 74 as the second focusing point position adjusting means is set. A second storage area 103b for storing the control map, a third storage area 103c for storing the maximum value and the minimum value of the height position detected by the height position detection process described later, and other storage areas are provided. . The control map shown in FIG. 9 is set to 5 V when the voltage value ratio (V1 / V2) is “5”. When the voltage value ratio (V1 / V2) is smaller than “5”, the voltage applied to the actuator 74 composed of a piezo motor to lower the condenser lens 72 is high, and the voltage value ratio (V1 / V2) Is larger than “5”, the voltage applied to the actuator 74 composed of a piezo motor to raise the condenser lens 72 is set to be low. Therefore, the voltage value (V1) output from the first light receiving element 853 of the height position detecting means 8 and the second voltage are controlled by controlling the voltage applied to the actuator 74 composed of a piezo motor according to the control map shown in FIG. The ratio (V1 / V2) to the voltage value (V2) output from the light receiving element 854 is controlled to be “5”. As a result, the distance (H) from the condenser lens 72 of the condenser 7 to the upper surface of the workpiece W is controlled to a constant value.

The laser processing apparatus in the illustrated embodiment is configured as described above, and the operation thereof will be described below.
FIG. 10 is a perspective view of a semiconductor wafer 20 as a workpiece to be laser processed. FIG. 10 is made of a silicon wafer, and a plurality of areas are defined by a plurality of streets 201 arranged in a lattice pattern on the surface 20a, and devices 202 such as IC and LSI are formed in the partitioned areas. Has been.

  In order to form a laser processing groove along the street 201 of the semiconductor wafer 20 described above, the semiconductor wafer 20 is attached to a dicing tape T mounted on an annular frame F as shown in FIG. At this time, the semiconductor wafer 20 is attached to the dicing tape T with the front surface 20a facing up and the back surface 20b side.

An embodiment of laser processing in which the above-described laser processing apparatus is used to irradiate a laser beam along the division line 201 of the semiconductor wafer 20 to form a deteriorated layer along the street 201 inside the semiconductor wafer 20 will be described. In addition, when the altered layer is formed inside the semiconductor wafer 20, if the thickness of the semiconductor wafer 20 varies, the altered layer is uniformly formed at a predetermined depth due to the refractive index as described above. I can't. Therefore, before the laser processing, the height position of the semiconductor wafer 20 held on the chuck table 36 is measured by the height position detecting means 8 described above.
That is, first, the dicing tape T side on which the semiconductor wafer 20 is adhered is placed on the chuck table 36 of the laser processing apparatus shown in FIG. 1 and the semiconductor wafer 20 is placed on the chuck table 36 via the dicing tape T. Hold the suction. Accordingly, the surface 20a of the semiconductor wafer 20 sucked and held on the chuck table 36 via the dicing tape T is on the upper side. The chuck table 36 that sucks and holds the semiconductor wafer 20 in this way is positioned immediately below the imaging means 9 by the processing feed means 37.

  When the chuck table 36 is positioned directly below the image pickup means 9, the image pickup means 9 and the control means 10 execute an alignment operation for detecting a processing region to be laser processed on the semiconductor wafer 20. That is, the image pickup means 9 and the control means 10 collect the street 201 formed in a predetermined direction of the semiconductor wafer 20 and the light concentration of the height position detection means 8 that detects the height of the semiconductor wafer 20 along the street 201. Image processing such as pattern matching for alignment with the device 7 is executed to perform alignment. In addition, the alignment is similarly performed on the street 201 formed in the direction orthogonal to the predetermined direction formed in the semiconductor wafer 20.

  When the alignment is performed as described above, the chuck table 36 is moved as shown in FIG. 12, and the predetermined street 201 of the semiconductor wafer 20 held on the chuck table 36 is positioned immediately below the condenser 7. Further, as shown in FIG. 12, one end (the left end in FIG. 12) of the street 201 is positioned directly below the condenser 7. Next, the control means 10 operates the height position detection means 8 and also operates the processing feed means 37 to move the chuck table 36 in the direction indicated by the arrow X in FIG. 12 at the right end) until it reaches just below the condenser 7 (height position detection step). As a result, the height position of the semiconductor wafer 20 on the predetermined street 201 (distance (H) from the condenser lens 72 to the upper surface of the workpiece W) can be detected as described above. Then, the control means 10 stores the highest value and the lowest value of the detected height position in the third storage area 103 c of the random access memory (RAM) 103.

  When the height position detecting step is executed along all the streets 201 extending in the predetermined direction of the semiconductor wafer 20 as described above, the chuck table 36 is rotated by 90 degrees so as to be in the predetermined direction. The height position detecting step is executed along each street 201 extending in a direction perpendicular to the vertical direction. When the height position detecting process is performed along all the streets 201 formed on the semiconductor wafer 20 in this way, laser processing for forming a deteriorated layer along the street 201 inside the semiconductor wafer 20 is performed. .

  In the laser processing step, first, the chuck table 36 is moved to position one end of the predetermined street 201 (the left end in 13 (a)) directly below the condenser 7 as shown in FIG. Next, the control means 10 applies a predetermined voltage (for example, 5V) to the actuator 74 composed of a piezo motor as the second focusing point position adjusting means, and also adjusts the first focusing point position. The means 53 is operated to position the condenser 7 at a position based on the intermediate position between the highest value and the lowest value of the semiconductor wafer 20, and the focusing point position of the processing pulse laser beam LB1 and the inspection laser beam LB2 Is set to the state shown in FIG. As a result, the condensing point position P of the processing pulse laser beam LB1 is positioned at a predetermined depth position set from the surface of the semiconductor wafer 20.

  Next, the control means 10 operates the height position detection means 8 to irradiate the upper surface of the semiconductor wafer 20 held on the chuck table 36 with the inspection laser beam LB2, and the chuck table 36 is moved to the position shown in FIG. While moving in the direction shown by the arrow X1, the processing pulse laser beam oscillation means 6 is operated to irradiate the processing pulse laser beam LB1 (laser processing step). In this laser processing step, the control means 10 uses the voltage value (V1) output from the first light receiving element 853 of the height position detecting means 8 and the voltage value (V2) output from the second light receiving element 854. The ratio (V1 / V2) is calculated and applied to the actuator 74 composed of a piezo motor as the second focusing point position adjusting means from the control map shown in FIG. 9 based on the voltage ratio (V1 / V2). The obtained voltage is obtained, and this obtained voltage is applied to the actuator 74 composed of a piezo motor. That is, the control means 10 determines the ratio (V1) between the voltage value (V1) output from the first light receiving element 853 of the height position detecting means 8 and the voltage value (V2) output from the second light receiving element 854. The voltage applied to the actuator 74 composed of a piezo motor is controlled so that / V2) becomes “5”. Then, as shown in FIG. 13B, when the other end of the street 201 (the right end in 12B) reaches directly below the condenser 7, the height position detecting means 8 and the processing pulse laser beam oscillating means. 6 is stopped, and the movement of the chuck table 36 is stopped. As a result, the condenser lens 72 of the condenser 7 moves up and down corresponding to the irregularities of the semiconductor wafer 20, and the distance (H) from the condenser lens 72 of the condenser 7 to the upper surface of the semiconductor wafer 20 becomes a predetermined value. Be controlled. Therefore, the altered layer 210 is formed on the semiconductor wafer 20 at a uniform predetermined depth from the upper surface as shown in FIG. In this way, in the laser processing step, the voltage applied to the actuator 74 composed of a piezo motor having a quick response is controlled based on the detection signal from the height position detecting means 8, so that the semiconductor wafer detected by the height position detecting means 8 is controlled. The focusing point position of the processing laser beam can be quickly followed in response to the change in the height position of the semiconductor wafer 20, and even if the thickness of the semiconductor wafer 20 varies, a predetermined depth from the surface of the semiconductor wafer 20 can be obtained. The position can be processed accurately

In addition, the processing conditions in the said laser processing process are set as follows, for example.
Laser: YVO4 pulse laser Wavelength: 1064nm
Repetition frequency: 200 kHz
Average output: 1W
Condensing spot diameter: φ1μm
Processing feed rate: 300 mm / sec

When the semiconductor wafer 20 is thick and the deteriorated layer is formed in multiple layers, the interval adjusting means 823 of the condensing point position displacing means 82 is controlled to adjust the interval between the convex lenses 821 and 822, and the processing pulse laser beam. The laser processing step may be performed by changing the distance (L) between the condensing point position of LB1 and the condensing point position of the inspection laser beam LB2.
Further, the displacement amount of the surface position along the street 201 of the semiconductor wafer 20 detected by the height position detecting means 8 in the first laser processing step is stored in a read only memory (ROM) 102 of the control means 10. In the second laser processing step, the detection by the height position detecting means 8 may be stopped and the actuator 74 may be controlled based on the data stored in the read only memory (ROM) 102.

  As described above, when the laser processing step is executed along all the streets 201 extending in a predetermined direction of the semiconductor wafer 20, the chuck table 36 is rotated by 90 degrees so as to be in the predetermined direction. The laser processing is performed along each street 201 extending in the orthogonal direction. Thus, if the laser processing step is performed along all the streets 201 formed on the semiconductor wafer 20, the chuck table 36 holding the semiconductor wafer 20 first holds the semiconductor wafer 20 by suction. The semiconductor wafer 20 is released from the suction holding state. Then, the semiconductor wafer 20 is transferred to the dividing step by a transfer means (not shown).

The perspective view of the laser processing apparatus comprised according to this invention. The block diagram which shows the structure of the laser beam irradiation means with which the laser processing apparatus shown in FIG. 1 is equipped, and the height position detection means of the workpiece hold | maintained at the chuck table. Explanatory drawing which shows the aspect which changes the light beam of a laser beam by the condensing point position displacement means which comprises the height position detection means shown in FIG. Explanatory drawing which shows the condensing state which a collector condenses the laser beam for a test | inspection corresponding to each aspect of the condensing point position displacement means shown in FIG. Explanatory drawing which shows the condensing point position of the processing laser beam condensed by the condensing lens with which the laser processing apparatus shown in FIG. 1 is equipped, and the condensing point position of the laser beam for a test | inspection. FIG. 3 is an explanatory view showing a state in which an inspection laser beam is irradiated onto a workpiece having a different thickness held on a chuck table by the height position detection means shown in FIG. 2. The ratio between the voltage value (V1) output from the first light receiving element and the voltage value (V2) output from the second light receiving element constituting the height position detecting means shown in FIG. The control map which shows the relationship with the variation | mutation on the basis of the predetermined distance to the upper surface of a workpiece. The block diagram which shows the control means with which the laser processing apparatus shown in FIG. 1 is equipped. The ratio between the voltage value (V1) output from the first light receiving element and the voltage value (V2) output from the second light receiving element constituting the height position detecting means shown in FIG. The control map which shows the relationship with the voltage applied to the actuator which comprises. The perspective view of the semiconductor wafer as a to-be-processed object. The perspective view which shows the state which affixed the semiconductor wafer shown in FIG. 10 on the surface of the dicing tape with which the cyclic | annular flame | frame was mounted | worn. Explanatory drawing of the height position detection process which detects a height position along the street of the semiconductor wafer shown in FIG. 10 with the laser processing apparatus shown in FIG. Explanatory drawing of the laser processing process which implements a laser processing along the street of the semiconductor wafer shown in FIG. 10 with the laser processing apparatus shown in FIG.

Explanation of symbols

1: Laser processing device 2: Stationary base 3: Chuck table mechanism 36: Chuck table 37: Processing feed means 374: X-axis direction position detection means 38: First index feed means 384: Y-axis direction position detection means 4: Laser beam irradiation unit support mechanism 42: movable support base 43: second index feeding means 5: laser beam irradiation unit 6: processing pulse laser beam oscillation means 7: condenser 71: direction changing mirror 72: condenser lens 73: window Lens 74: Actuator 8: Height position detection means 80: Inspection laser beam oscillation means 81: Dichroic mirror 82: Focusing point position displacement means 821, 822: A pair of convex lenses 823: Spacing adjustment means 83: First beam splitter 84 : Band pass filter 85: Reflected light analysis means 851: No. Beam splitter 852: condenser lens 853: first light receiving element 854: second light receiving element 9: imaging unit 10: Control unit 20: semiconductor wafer

Claims (2)

A chuck table having a workpiece holding surface for holding a workpiece, a processing laser beam oscillation means for oscillating a processing laser beam for laser processing the workpiece held on the chuck table, and the laser beam oscillation means A laser beam irradiating means having a condenser having a condensing lens for condensing the processing laser beam oscillated by the laser beam, and relatively moving the chuck table and the laser beam irradiating means in the processing feed direction (X-axis direction) And a machining feed means for causing the chuck table and the laser beam irradiation means to move relative to an index feed direction (Y-axis direction) perpendicular to the machining feed direction (X-axis direction). In laser processing equipment,
The workpiece held on the chuck table is irradiated with a detection laser beam having a wavelength different from the wavelength of the machining laser beam through the condenser, and is reflected on the chuck table based on the reflected light reflected from the upper surface of the workpiece. Height position detecting means for detecting the upper surface height position of the workpiece to be held;
A first collection of adjusting the position of the condensing point of the laser beam for detection and the laser beam for processing collected by moving the laser beam irradiating means in a direction perpendicular to the workpiece holding surface. Light spot position adjusting means;
A second piezo-motor that displaces the condensing point position of the detection laser beam and the processing laser beam by displacing the condensing lens of the concentrator in a direction perpendicular to the workpiece holding surface; Focusing point position adjusting means;
A detection signal from the height position detection means is inputted, and the first focusing point position adjusting means, the second focusing point position adjusting means, the laser beam irradiation means, the processing feeding means, and the indexing feeding means are provided. Control means for controlling,
Laser processing equipment characterized by that.   The control means operates the height position detection means and operates the machining feed means and index feed means to detect the surface height position in the machining area of the workpiece held on the chuck table and A height position detecting step for obtaining a value and a minimum value, and operating the first condensing point position adjusting means based on the maximum value and the minimum value obtained by the height position detecting step to A condensing point position adjusting step for adjusting the condensing point position of the laser beam condensed by the detector to an intermediate position between the highest value and the lowest value, while operating the laser beam irradiating means and the height position detecting means 2. The laser according to claim 1, wherein a laser processing step of controlling the second focusing point position adjusting means comprising the piezo motor is executed corresponding to the height position of the workpiece detected by the height position detecting means. Processing equipment.

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