JP2009283753A - Laser processing method and laser processing device for wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser processing method and a laser processing device for a wafer which have an altered layer formed inside along streets without causing abrasion even if a plurality of devices formed on a surface of the wafer have defective regions. <P>SOLUTION: The laser processing method includes a defective region detecting step of detecting the height position of the surface along the streets 21 of the wafer 20 and detecting a defective region 220 lowered blow a prescribed surface height position; and an altered layer forming step of forming the altered layer 201 in the interior of the wafer along the streets except the defective region by stopping irradiating the defective region with a laser light beam when the convergence point of the laser light beam is positioned in the interior of the wafer from the surface side to irradiate the wafer with the laser light beam along the streets. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention condenses a laser beam from a surface side of a wafer to a wafer in which a plurality of regions are partitioned by a plurality of streets arranged in a lattice pattern on the surface and a device is formed in the partitioned region. The present invention relates to a wafer laser processing method and a laser processing apparatus for locating a point and irradiating a laser beam along a street to form a deteriorated layer along the street inside the wafer.

  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, optical device wafers with gallium nitride compound semiconductors laminated on the surface of a sapphire substrate are also divided into individual optical devices such as light emitting diodes and laser diodes by cutting along the streets, and are widely used in electrical equipment. ing.

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

  Thus, a wafer formed with a device such as a micro electro mechanical system (MEMS) was depressed by a defective etching or the like in the device region where the device was formed, and was several μm to several tens μm lower than the normal surface. There may be defective areas. Since the surface of such a defect region is rough, even if a laser beam having a wavelength that is transmissive to the wafer is irradiated, ablation occurs on the rough surface and debris is generated. There is a problem that the quality of the device is deteriorated due to the adhesion.

  The present invention has been made in view of the above-mentioned facts, and the main technical problem thereof is that even if a defect region exists in a plurality of devices formed on the surface of the wafer, the inside of the wafer is not ablated and follows the street. It is an object of the present invention to provide a wafer laser processing method and a laser processing apparatus capable of forming a deteriorated layer.

In order to solve the main technical problem, according to the present invention, a wafer in which a plurality of regions are partitioned by a plurality of streets arranged in a lattice pattern on the surface and a device is formed in the partitioned regions, A wafer laser processing method in which a condensing point of a laser beam is positioned from the front surface side of a wafer to irradiate the laser beam along the street, and a plurality of altered layers are formed along the street inside the wafer. ,
A defect area detecting step for detecting a height position of the surface along the street of the wafer, and detecting a defect area that is lower than a predetermined surface height position;
When the laser beam is focused along the street from the front side of the wafer and the laser beam is focused, the defect area is removed from the interior of the wafer by stopping the irradiation of the laser beam. An altered layer forming step of forming an altered layer along the street,
A wafer laser processing method is provided.

In addition, according to the present invention, a chuck table having a holding surface for holding a wafer, a laser beam irradiation means having a condenser for irradiating a laser beam to the wafer held by the chuck table, and the laser beam irradiation A condensing point position adjusting means for displacing a condensing point position of a laser beam condensed by the concentrator of the means, a processing feeding means for moving the chuck table in the processing feeding direction (X-axis direction), Index feed means for moving the chuck table in an index feed direction (Y-axis direction) orthogonal to the machining feed direction, X-axis direction position detection means for detecting the machining feed position of the chuck table, Y-axis direction position detection means for detecting the index feed position and a height for detecting the upper surface height position of the wafer held by the chuck table Position detection means, height position detection means, X-axis direction position detection means, and Y-axis direction position detection means are input, and the laser beam irradiation means, focusing point position adjustment means, and processing feed means And a laser processing apparatus comprising a control means for outputting a control signal to the indexing and feeding means.
A plurality of regions are partitioned by a plurality of streets arranged in a lattice pattern on the surface, and a laser beam condensing point is positioned from the surface side of the wafer to the inside where a device is formed in the partitioned region. When the laser beam is irradiated along the street, and the altered layer is laminated along the street inside the wafer, the control means includes:
Based on detection signals from the height position detection means, the X-axis direction position detection means, and the Y-axis direction position detection means, a surface height position is detected along the street of the wafer, and a predetermined surface height position is detected. A defective area detecting step of detecting a defective area that has been further lowered and storing the coordinate value of the defective area in a storage means;
When the laser beam irradiating means is operated to position a laser beam condensing point from the front side of the wafer and irradiate the laser beam along the street, the defect area stored in the storage means is irradiated with the laser beam. By performing an altered layer forming step of forming an altered layer along the street excluding the defect region inside the wafer,
A laser processing apparatus is provided.

  In the present invention, the defect area is detected by detecting the height position of the surface along the street of the wafer, and the laser beam condensing point is positioned inside from the surface side of the wafer to irradiate the laser beam along the street. In this case, the defect area is stopped by irradiating the laser beam to form a deteriorated layer along the street except for the defect area inside the wafer. No ablation or debris. Therefore, it is possible to prevent debris generated due to ablation from adhering to the device by irradiating the defect region having a rough surface with the laser beam.

  Preferred embodiments of a wafer laser processing method and a laser processing apparatus constructed 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 irradiation unit support mechanism 4 includes 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 for moving the first sliding block 32 along the pair of guide rails 31 and 31 in the machining feed direction indicated by the arrow X. 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 laser processing apparatus in the illustrated embodiment includes X-axis direction position detection means 374 for detecting the X-axis direction position of the chuck table 36. The X-axis direction position detecting means 374 is a linear scale 374a disposed along the guide rail 31, and a reading that is disposed along the linear scale 374a together with the first sliding block 32 disposed along the first sliding block 32. It consists of a head 374b. In the illustrated embodiment, the read head 374b of the X-axis direction position detecting means 374 sends a pulse signal of one pulse every 1 μm to the control means described later. The control means described later detects the position of the chuck table 36 in the X-axis direction by counting the input pulse signals.

  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 for moving to the first position 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 processing apparatus in the illustrated embodiment includes Y-axis direction position detecting means 384 for detecting the Y-axis direction position of the second sliding block 33. The Y-axis direction position detecting means 384 is a linear scale 384a disposed along the guide rail 322, and a reading which is disposed along the linear scale 384a together with the second sliding block 33 disposed along the second sliding block 33. And a head 384b. In the illustrated embodiment, the reading head 384b of the Y-axis direction position detecting means 384 sends a pulse signal of one pulse every 1 μm to the control means described later. The control means described later detects the position of the chuck table 36 in the Y-axis direction by counting the input pulse signals.

  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 has a second index for moving the movable support base 42 along the pair of guide rails 41 and 41 in the index feed direction (Y-axis direction) indicated by the arrow Y. A feeding 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 has a condensing point position adjusting means 53 for moving the unit holder 51 along the pair of guide rails 423 and 423 in the focus position adjusting direction (Z-axis direction) indicated by the arrow Z. It has. The 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 drive source such as a pulse motor 532 for rotationally driving the male screw rod. The male screw rod (not shown) is driven to rotate forward and reverse by the pulse motor 532, so that the unit holder 51 and the laser beam irradiation means 52 are moved along the guide rails 423 and 423 along the focusing point position adjusting direction (Z Move it in the axial 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 laser beam irradiation unit 5 in the illustrated embodiment includes Z-axis direction position detection means 55 for detecting the position of the laser beam irradiation means 52 in the Z-axis direction. The Z-axis direction position detecting means 55 includes a linear scale 551 disposed in parallel with the guide rails 423 and 423, a reading head 552 attached to the unit holder 51 and moving along with the unit holder 51 along the linear scale 551. It is made up of. In the illustrated embodiment, the reading head 552 of the Z-axis direction position detecting means 55 sends a pulse signal of one pulse every 1 μm to the control means described later.

  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. The processing pulse laser beam oscillation means 6 can use a YVO4 pulse laser oscillator or a YAG pulse laser oscillator that oscillates a processing pulse laser beam LB1 having a wavelength (for example, 1064 nm) that is transparent to a workpiece to be described later. .

  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. And a condensing lens 72 that condenses the processing pulse laser beam LB1. The condensing lens 72 condenses the processing pulse laser beam LB1 whose direction has been changed by the direction changing mirror 71 at a condensing point P.

  The laser beam irradiation unit 52 in the illustrated embodiment includes an optical axis changing unit 60 that deflects the optical axis of the processing pulse laser beam oscillated from the processing pulse laser beam oscillation unit 6. In the illustrated embodiment, the optical axis changing means 60 is applied to the acoustooptic element 61 and the acoustooptic element 61 disposed in the optical path of the machining pulse laser beam oscillated from the machining pulse laser beam oscillation means 6. An RF oscillator 62 that generates RF (radio frequency), an RF amplifier 63 that amplifies the RF power generated by the RF oscillator 62 and applies the amplified power to the acoustooptic device 61, and an RF frequency generated by the RF oscillator 62 A deflection angle adjusting means 64 for adjusting the angle is provided. The acoustooptic device 61 adjusts the angle at which the optical axis of the laser beam is deflected in accordance with the frequency of the applied RF. The deflection angle adjusting means 64 is controlled by a control means described later.

  Further, the optical axis changing means 60 in the illustrated embodiment absorbs the laser beam deflected by the acoustooptic device 61 as indicated by a broken line in FIG. 2 when RF of a predetermined frequency is applied to the acoustooptic device 61. A laser beam absorbing means 65 is provided.

The optical axis changing means 60 in the illustrated embodiment is configured as described above, and the operation thereof will be described below with reference to FIG.
For example, when a voltage of 0 V is applied to the deflection angle adjusting unit 64 constituting the optical axis changing unit 60 and an RF having a frequency corresponding to 0 V is applied to the acoustooptic device 61, the processing pulse laser beam oscillation unit 6 The oscillated processing pulse laser beam LB 1 has its optical axis directed to the direction changing mirror 71 of the condenser 7. On the other hand, when a voltage of 10 V, for example, is applied to the deflection angle adjusting means 64 and an RF having a frequency corresponding to 10 V is applied to the acoustooptic device 61, the processing pulse oscillated from the processing pulse laser beam oscillation means 6 is applied. The laser beam LB1 is guided to the laser beam absorbing means 65 as indicated by a broken line in FIG.

  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 detecting means 8 is arranged in the path between the inspection laser beam oscillation means 81 for oscillating the inspection laser beam, and the optical axis changing means 60 of the processing pulse laser beam oscillation means 6 and the condenser 7. The inspection laser beam oscillated from the inspection laser beam oscillation means 81 is dispersed between the dichroic mirror 82 for dispersing the inspection laser beam toward the condenser 7, and the inspection laser beam oscillation means 81 and the dichroic mirror 82. A first beam splitter 83 is provided for guiding the inspection laser beam oscillated from the means 81 to a first path 83 a that directs the dichroic mirror 82.

  As the inspection laser beam oscillation means 81, a He-Ne pulse laser oscillator that oscillates an inspection laser beam LB2 having a wavelength (for example, 635 nm) having reflectivity with respect to a workpiece to be described later 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 82 reflects the inspection laser beam LB2 oscillated from the inspection laser beam oscillation means 81 toward the condenser 7 though the processing pulse laser beam LB1 passes through. The first beam splitter 83 guides the inspection laser beam LB2 oscillated from the inspection laser beam oscillation means 81 to the first path 83a directed to the dichroic mirror 82 and is split by the dichroic mirror 82 to be described later. The reflected light is guided to the second path 83b.

  The height position detection means 8 in the illustrated embodiment analyzes the reflected light that is disposed in the second path 83b and is reflected by the first beam splitter 83, and transmits the analysis result to the control means that will be described later. 85. The reflected light analyzing means 85 includes a second beam splitter 851 that splits the reflected light reflected by the first beam splitter 83 into a third path 85a and a fourth path 85b, and the second beam splitter 851. A condensing lens 852 for condensing the reflected light split into the third path 85a by 100%, and a first light receiving element 853 for receiving the reflected light condensed by the condensing lens 852. . 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 oscillated from the inspection laser beam oscillation means 81 passes through the first beam splitter 83, reaches the dichroic mirror 82, and is reflected by the dichroic mirror 82 toward the direction changing mirror 71 of the condenser 7. Is done. The inspection laser beam LB2 reflected toward the direction conversion mirror 71 is collected by the condenser lens 72 in the same manner as the processing pulse laser beam LB1. The inspection laser beam LB2 collected in this way is reflected on the upper surface of the workpiece W held on the chuck table 36, and the reflected light is converted into a condensing lens 72 and changed in direction as indicated by a broken line in FIG. The light beam reaches the second beam splitter 851 of the reflected light analyzing means 85 through the mirror 71, the dichroic mirror 82, and the first beam splitter 83. The reflected light of the inspection laser beam LB2 reaching the second beam splitter 851 is split into the third path 85a and the fourth path 85b by the second beam splitter 851. 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. Since the light is received by the second light receiving element 854, when the inspection laser beam LB2 is applied to the upper surface of the workpiece W as shown in FIGS. The amount of light received by the second light receiving element 854 varies depending on the distance from the lens 72 to the upper surface of the workpiece W, 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. 3A, the height position of the workpiece W is low (the thickness of the workpiece W is thin), and the distance from the condenser lens 72 of the condenser 7 to the upper surface of the workpiece W is shown. 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. 3B, 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 smaller 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 is (the thinner the workpiece W is, the thinner the thickness (T)), 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 of the workpiece W. The higher the position (the thicker the workpiece W is, the smaller the thickness (T)), the smaller the position.

  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 thickness (T) of the workpiece W held on the chuck table 36 will be described with reference to the control map shown in FIG. In FIG. 4, the horizontal axis is 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, and the vertical axis is The distance (H) from the condenser lens 72 of the condenser 7 to the upper surface of the workpiece W is shown. The control map shown in FIG. 4 uses a condensing lens with a focal length of 30 mm, and the distance (H) from the condensing lens 72 of the condenser 7 to the upper surface of the workpiece W is 30 mm. 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 “1”, and the condenser 7 The ratio (V1 / V2) increases as the distance (H) from the condenser lens 72 to the upper surface of the workpiece W decreases, that is, as the thickness (T) of the workpiece W increases. 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. 4, the distance (H) from the condenser lens 72 of the condenser 7 to the upper surface of the workpiece W, that is, held on the chuck table 36. The thickness (T) of the processed workpiece W can be obtained. Note that the control map shown in FIG. 4 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. The input interface 104 of the control means 10 includes a reading head 374b of the X-axis direction position detecting means 374, a reading head 384b of the Y-axis direction position detecting means 384, a reading head 552 of the Z-axis direction position detecting means 55, a first head. Detection signals from the light receiving element 853, the second light receiving element 854, the imaging means 9, and the like are input. 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, the inspection laser beam oscillation means 81, and the optical axis changing means 60. A control signal is output to the deflection angle adjusting means 64. The random access memory (RAM) 103 as the storage means stores the first storage area 103a for storing the control map shown in FIG. 4 and the second design data for the workpiece to be described later. A storage area 103b, a third storage area 103c for storing the height position of the wafer 10 described later, and other storage areas are provided.

The laser processing apparatus in the illustrated embodiment is configured as described above, and the operation thereof will be described below.
FIG. 6A shows a perspective view of the wafer 20 as a workpiece to be laser processed, and FIG. 6B shows a cross-sectional view of the wafer 20.
A wafer 20 shown in FIGS. 6A and 6B is made of, for example, a silicon wafer having a diameter of 200 mm, and a plurality of areas are defined by a plurality of streets 21 arranged in a lattice pattern on the surface 20a. In addition, a micro electro mechanical system (MEMS) as the device 22 is formed in the partitioned area. A notch 23 indicating the crystal orientation of the silicon wafer is formed on the outer periphery of the wafer 2. It is assumed that a defect region 220 of a device exists in the wafer 20 formed in this way. The defect region 220 is depressed from the regular surface 20a of the wafer 20 as shown in FIG.

An embodiment of laser processing that uses the laser processing apparatus described above to irradiate a laser beam along the street 21 of the wafer 20 to form a deteriorated layer along the street 21 inside the wafer 20 will be described.
In order to perform the laser processing for forming the deteriorated layer along the street 21 inside the wafer 20 described above, the wafer 20 is attached to the adhesive tape T attached to the annular frame F as shown in FIG. To do. At this time, the wafer 20 is attached to the adhesive tape T with the back surface side facing up.

  When a deteriorated layer is formed inside the wafer 20 by irradiating a laser beam from the surface side of the wafer 20 described above, the surface of the defect region 220 is rough, so that when the laser beam is irradiated, the wafer 20 is transmitted to the wafer. Even with a laser beam having a characteristic wavelength, ablation occurs and debris is generated. This debris adheres to the device 22 and degrades the quality of the device. Therefore, in the present invention, the irradiation of the laser beam in the defect area 220 is stopped. For this reason, before the laser processing, the height position of the wafer 20 held on the chuck table 36 is measured by the above-described height position detection device 8, and the wafer 20 is depressed and lowered from the regular surface 20a of the wafer 20. A defective area detecting step for detecting the defective area 220 is performed.

  In order to carry out the defect region detection step, first, the wafer 20 is placed on the chuck table 36 of the laser processing apparatus shown in FIG. 1 and the wafer 20 is sucked and held on the chuck table 36. At this time, the wafer 20 places the adhesive tape T side on the chuck table 36. Accordingly, the wafer 20 is held with the surface 20a facing upward. The annular frame F is fixed by a clamp 362 disposed on the chuck table 36. The chuck table 36 that sucks and holds the wafer 20 in this way is positioned immediately below the imaging means 9 by the processing feed means 37.

  When the chuck table 36 that sucks and holds the wafer 20 is positioned immediately 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 wafer 20. That is, the imaging unit 9 and the control unit 10 execute image processing such as pattern matching for aligning the plurality of streets 21 formed in the predetermined direction on the surface 21 a of the wafer 20 and the condenser 7. And perform alignment. Further, alignment is similarly performed on the street 21 formed in the direction orthogonal to the predetermined direction formed on the surface 21a of the wafer 20.

  When alignment is performed as described above, the wafer 20 on the chuck table 36 is positioned at the coordinate position shown in FIG. FIG. 8B shows a state in which the chuck table 36, that is, the wafer 20, is rotated 90 degrees from the state shown in FIG.

  It should be noted that the feed start position coordinate values (A1, A2, A3... An of each street 21 formed on the wafer 20 in the state positioned at the coordinate positions shown in (a) and (b) of FIG. ), Feed end position coordinate values (B1, B2, B3 ... Bn), feed start position coordinate values (C1, C2, C3 ... Cn) and feed end position coordinate values (D1, D2, D3 ... The design value of Dn) is stored in the second storage area 103 b of the random access memory (RAM) 103.

  As described above, when the street 21 formed on the wafer 20 held on the chuck table 36 is detected and alignment of the defect area detection position is performed, the chuck table 36 is moved to move to (a) of FIG. ), The uppermost street 21 is positioned directly below the condenser 7. Further, as shown in FIG. 9A, the feed start position coordinate value (A1) (see FIG. 8A) which is one end of the street 21 (the left end in FIG. 9A) is used as a condenser. Position directly under 7. Then, while operating the height position detecting means 8, the chuck table 36 is moved in the direction indicated by the arrow X1 in FIG. 9 and moved to the feed end position coordinate value (B1), whereby the surface (upper surface) of the wafer 20 is obtained. The height position is detected (defect area detection step). That is, the control unit 10 detects the detection signal from the X-axis direction position detection unit 374 and the Y-axis direction position detection unit 384, the voltage value (V1) output from the first light receiving element 853, and the second light reception. Based on the ratio (V1 / V2) to the voltage value (V2) output from the element 854, the height position along the street 21 is obtained from the control map shown in FIG. 4, and this value is obtained from the random access memory ( RAM) 103 in the third storage area 103c. In this way, the boundary position detection process is performed along all the streets 21 formed on the wafer 20, and the height position and the boundary position in each street 21 are stored in the third memory of the random access memory (RAM) 103. Store in area 103c.

  As described above, in the defect region detection step performed along each street 21 formed on the wafer 20, when there is no defect region, the voltage value (V1) output from the first light receiving element 853 and the first value Variation in the ratio (V1 / V2) to the voltage value (V2) output from the second light receiving element 854 is extremely small. For example, when the defect area detection step is performed with the distance (H) from the condenser lens 72 (having a focal length of 30 mm) of the condenser 7 to the surface 20a of the wafer 20 set to 29.5 mm, As shown in FIG. 9B, 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. Changes around “5” (see the control map shown in FIG. 4).

  However, as shown in FIG. 10A, when there is a defect area 220 that is depressed on the surface 20a of the wafer 20, the defect area 220 has a low height and the condenser lens 72 (focal length) of the condenser 7. Since the distance (H) from the surface 20a of the wafer 20 becomes longer (but shorter than the focal length of the condenser lens 72), the voltage value (V1) output from the first light receiving element 853 changes. However, since the voltage value (V2) output from the second light receiving element 854 increases rapidly, the voltage value (V1) output from the first light receiving element 853 as shown in FIG. And the voltage value (V2) output from the second light receiving element 854 (V1 / V2) rapidly decreases in the defect region 220. Accordingly, the control means 10 determines that the area from the start point E1 to the end point E2 where the ratio (V1 / V2) has decreased rapidly is a defective area, and determines the coordinate values of the start point E1 and the end point E2 as the random access memory (RAM ) The third storage area 103c is stored together with the height position.

When the defect region detection step is performed along all the streets 21 formed on the wafer 20 as described above, laser processing for forming a deteriorated layer along the street 21 inside the wafer 20 is performed.
In order to carry out laser processing, first, the chuck table 36 is moved, and the uppermost street 21 is positioned directly below the condenser 7 in FIG. Further, as shown in FIG. 11A, the feed start position coordinate value (A1) (see FIG. 8A) which is one end of the street 21 (the left end in FIG. 11A) is used as a condenser. Position directly under 7. The control means 10 operates the condensing point position adjusting means 53 to bring the condensing point P of the processing pulse laser beam LB1 irradiated from the condenser 7 from the surface 20a (upper surface) of the wafer 20 to a predetermined depth position. Position. Next, the control unit 10 operates the processing pulse laser beam oscillation unit 6 of the processing pulse laser beam oscillation unit 6 and applies a voltage of, for example, 0 V to the deflection angle adjustment unit 64 constituting the optical axis changing unit 60. As a result, as described above, the processing pulse laser beam LB1 oscillated from the processing pulse laser beam oscillating means 6 is irradiated from the collector 7 with its optical axis directed toward the collector 7. Then, the control means 10 moves the chuck table 36 in the direction indicated by the arrow X1 at a predetermined processing feed rate (deformed layer forming step). When the defect area 220 does not exist, the irradiation of the processing pulse laser beam LB1 is continued along the street 21, and the irradiation position of the condenser 7 is the street as shown in FIG. When the feed end position coordinate value (B1) (see FIG. 8A) which is the other end of 21 (the right end in FIG. 11B) is reached, the control means 10 deflects to constitute the optical axis changing means 60. For example, a voltage of 10 V is applied to the angle adjusting means 64 and the movement of the chuck table 36 is stopped. As a result, the processing pulse laser beam LB1 oscillated from the processing pulse laser beam oscillation means 6 as described above is guided to the laser beam absorption means 65 as indicated by a broken line in FIG. By performing the deteriorated layer forming step in this manner, the deteriorated layer 201 is formed inside the wafer 20 as shown in FIG.

Note that the processing conditions in the deteriorated layer forming step are set as follows, for example.
Laser: YVO4 pulse laser Wavelength: 1064nm
Repetition frequency: 100 kHz
Pulse output: 2.5μJ
Condensing spot diameter: φ1μm
Processing feed rate: 100 mm / sec

  The thickness of the altered layer 201 formed under the above processing conditions is about 50 μm. Therefore, in order to easily divide the wafer 20 along the street 211, a plurality of altered layers are formed in the thickness direction of the wafer 20. There is a need to. In order to form a plurality of deteriorated layers in the thickness direction of the wafer 20, a process of irradiating from the condenser 7 by operating the condensing point position adjusting means 53 and sequentially raising the laser beam irradiation means 52 stepwise. The condensing point of the pulsed laser beam LB1 for use is gradually shifted upward in stages to carry out the above-mentioned deteriorated layer forming step, and a plurality of deteriorated layers 201 are laminated in the thickness direction of the wafer 20 as shown in FIG. To do.

Next, a description will be given of a deteriorated layer forming step in the case where a defect region 220 that is depressed on the surface 20a of the wafer 20 exists as shown in FIG.
First, as in the embodiment shown in FIG. 11, the chuck table 36 is moved to position the predetermined street 21 directly below the light collector 7. Further, as shown in FIG. 13A, one end of the street 21 (the left end in FIG. 13A) is positioned directly below the condenser 7. The control means 10 operates the condensing point position adjusting means 53 to bring the condensing point P of the processing pulse laser beam LB1 irradiated from the condenser 7 from the surface 20a (upper surface) of the wafer 20 to a predetermined depth position. Position. Next, the control unit 10 operates the processing pulse laser beam oscillation unit 6 of the processing pulse laser beam oscillation unit 6 and applies a voltage of, for example, 0 V to the deflection angle adjustment unit 64 constituting the optical axis changing unit 60. As a result, as described above, the processing pulse laser beam LB1 oscillated from the processing pulse laser beam oscillating means 6 is irradiated from the collector 7 with its optical axis directed toward the collector 7. Further, the control means 10 moves the chuck table 36 in the direction indicated by the arrow X1 at a predetermined processing feed rate. When the coordinate value of the starting point E1 of the defect area 220 existing on the wafer 20 held on the chuck table 36 reaches just below the condenser 7, as shown in FIG. For example, a voltage of 10 V is applied to the deflection angle adjusting unit 64 constituting the changing unit 60, and the processing pulse laser beam LB1 oscillated from the processing pulse laser beam oscillation unit 6 is applied to the laser beam absorption unit 65 as indicated by a broken line in FIG. Control as led. Further, the chuck table 36 is moved in the direction indicated by the arrow X1, and the coordinate value of the end point E2 of the defect area 220 existing on the wafer 20 held by the chuck table 36 as shown in FIG. For example, a voltage of 0 V is applied to the deflection angle adjusting means 64 constituting the optical axis changing means 60 again. As a result, as described above, the processing pulse laser beam LB1 oscillated from the processing pulse laser beam oscillating means 6 is irradiated again from the condenser 7 with its optical axis directed to the condenser 7. When the irradiation position of the condenser 7 reaches the other end of the street 21 (the right end in FIG. 13D) as shown in FIG. 13D, the control means 10 constitutes the optical axis changing means 60. For example, a voltage of 10 V is applied to the deflection angle adjusting means 64, and the movement of the chuck table 36 is stopped. As a result, the processing pulse laser beam LB1 oscillated from the processing pulse laser beam oscillation means 6 as described above is guided to the laser beam absorption means 65 as indicated by a broken line in FIG. By performing the deteriorated layer forming step in this way, the deteriorated layer 201 is formed along the street 21 inside the wafer 20 except for the defect region 220 as shown in FIG.

  In order to form a plurality of deteriorated layers in the thickness direction of the wafer 20, the condensing unit 7 irradiates the laser beam irradiation unit 52 by operating the condensing point position adjusting unit 53 and sequentially raising the laser beam irradiation unit 52 stepwise. The condensing point of the processing pulse laser beam LB1 is gradually shifted upward stepwise to carry out the above-mentioned deteriorated layer forming step, and a plurality of deteriorated layers 201 are laminated in the thickness direction of the wafer 20 as shown in FIG. Form.

  In this way, in the present invention, the defect region 220 existing on the wafer 20 is stopped from being irradiated with the processing pulse laser beam LB1 and the rough surface defect region 220 is not irradiated with the laser beam, so ablation occurs and debris is generated. Without alteration, the altered layer 201 can be formed along the street 21 except for the defect region 220 inside the wafer 20.

  When the deteriorated layer forming step is executed along all the streets 21 extending in the predetermined direction of the wafer 20 as described above, the chuck table 36 is rotated 90 degrees to The altered layer forming step is executed along each street 21 extending at a right angle. In this way, when the above processing steps are executed along all the streets 21 formed on the wafer 20, the chuck table 36 holding the wafer 20 returns to the position where the wafer 20 is first sucked and held. At this point, the suction holding of the wafer 20 is released. The wafer 20 is transported to the dividing step by a transport 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. FIG. 3 is an explanatory diagram showing a state in which an inspection laser beam is irradiated to a workpiece having a different thickness held on a chuck table by the height position detection device 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 predetermined distance (H) 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. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view and an enlarged cross-sectional view of a wafer laser processed by the wafer laser processing method according to the present invention. The perspective view which shows the state which affixed the wafer shown in FIG. 6 on the surface of the adhesive tape with which the cyclic | annular flame | frame was mounted | worn. FIG. 7 is an explanatory diagram showing a relationship with coordinate positions in a state where the wafer shown in FIG. 6 is held at a predetermined position of the chuck table of the laser processing apparatus shown in FIG. 1. Explanatory drawing of the defect area | region detection process (when a defect area | region does not exist) in the laser processing method of the wafer by this invention. Explanatory drawing of the defect area | region detection process (when a defect area | region exists) in the laser processing method of the wafer by this invention. Explanatory drawing of the deteriorated layer formation process (when a defect area | region does not exist) in the laser processing method of the wafer by this invention. Explanatory drawing which shows the state formed by laminating | stacking a deteriorated layer inside a wafer in the deteriorated layer formation process shown in FIG. Explanatory drawing of the deteriorated layer formation process (when a defect area | region exists) in the laser processing method of the wafer by this invention. Explanatory drawing which shows the state formed by laminating | stacking an alteration layer inside a wafer in the alteration layer formation process shown in FIG.

Explanation of symbols

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 indexing and feeding means 5: Laser beam irradiation unit 55: Z-axis direction position detecting means 6: Pulsed laser beam oscillation means for processing 60: Optical axis changing means 7: Condenser 71: Direction conversion Mirror 72: Condensing lens 8: Height position detection device 81: Inspection laser beam oscillation means 82: Dichroic mirror 83: First beam splitter 85: Reflected light analysis means 9: Imaging means 10: Control means 20: Wafer

Claims (2)

A plurality of regions are partitioned by a plurality of streets arranged in a lattice pattern on the surface, and a laser beam condensing point is positioned from the surface side of the wafer to the inside where a device is formed in the partitioned region. A wafer laser processing method for irradiating a laser beam along the street and forming a plurality of altered layers along the street inside the wafer,
A defect area detecting step for detecting a height position of the surface along the street of the wafer, and detecting a defect area that is lower than a predetermined surface height position;
When the laser beam is focused along the street from the front side of the wafer and the laser beam is focused, the defect area is removed from the interior of the wafer by stopping the irradiation of the laser beam. An altered layer forming step of forming an altered layer along the street,
A wafer laser processing method characterized by the above. A chuck table having a holding surface for holding a wafer, a laser beam irradiation means having a condenser for irradiating a wafer held by the chuck table with a laser beam, and a collector of the laser beam irradiation means Focusing point position adjusting means for displacing the focusing point position of the laser beam to be emitted, processing feeding means for moving the chuck table in the processing feed direction (X-axis direction), and the chuck table in the processing feed direction Index feed means for moving in the perpendicular index feed direction (Y-axis direction), X-axis direction position detection means for detecting the machining feed position of the chuck table, and Y axis for detecting the index feed position of the chuck table Direction position detecting means, height position detecting means for detecting the height position of the upper surface of the wafer held by the chuck table, and the height Detection signals from the position detection means, the X-axis direction position detection means, and the Y-axis direction position detection means are input, and control signals are sent to the laser beam irradiation means, the focal point position adjustment means, the processing feed means, and the index feed means. In a laser processing apparatus comprising a control means for outputting,
A plurality of regions are partitioned by a plurality of streets arranged in a lattice pattern on the surface, and a laser beam condensing point is positioned from the surface side of the wafer to the inside where a device is formed in the partitioned region. When irradiating a laser beam along the street and forming a deteriorated layer along the street inside the wafer, the control means includes:
Based on detection signals from the height position detection means, the X-axis direction position detection means, and the Y-axis direction position detection means, a surface height position is detected along the street of the wafer, and a predetermined surface height position is detected. A defective area detecting step of detecting a defective area that has been further lowered and storing the coordinate value of the defective area in a storage means;
When the laser beam irradiating means is operated to position a laser beam condensing point from the front side of the wafer and irradiate the laser beam along the street, the defect area stored in the storage means is irradiated with the laser beam. By performing an altered layer forming step of forming an altered layer along the street excluding the defect region inside the wafer,
Laser processing equipment characterized by that.

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