JP2010127920A - Edge detection apparatus and laser machining system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an edge detection apparatus which detects the edge position of an object to be detected with a high degree of accuracy regardless of the shape of the object to be detected, of which accuracy as a spatial filter is high, and which has a lot of flexibility in placement. <P>SOLUTION: The apparatus includes: a white light source 101 which sends white light including light having two or more wavelengths to a first optical path 109a; a chromatic aberration focusing lens 102 which forms two or more focuses on the optical axis towards a workpiece 1 (the object to be detected) for respective wavelengths contained in the white light sent to the first optical path 109a; an optical fiber 104 which brings the white light reflected by the workpiece 1 to a second optical path 109b different from the first optical path 109a; and a detector 103 which detects the intensity of the white light brought to the second optical path 109b by the optical fiber 104. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an edge detection device for detecting an edge of a detection object such as a semiconductor wafer, and a laser processing apparatus including the edge detection device.

  In the semiconductor device manufacturing process, a plurality of regions are defined by streets (cutting lines) arranged in a lattice pattern on the surface of a semiconductor wafer having a substantially disk shape, and circuits such as ICs and LSIs are formed in the partitioned regions. The formed semiconductor wafer is cut along the streets to divide the circuit into circuits to manufacture individual semiconductor chips. Cutting along the streets of a semiconductor wafer is usually performed by a cutting device called a dicer, but a processing method of cutting by irradiating a laser beam has also been attempted (see, for example, Patent Document 1).

  In order to perform laser processing on the semiconductor wafer, the chuck table and the laser beam irradiation unit are relatively moved in the processing feed direction while irradiating the laser beam from the laser beam irradiation unit while the semiconductor wafer is held on the chuck table. However, when the laser beam is irradiated beyond the outer peripheral edge of the semiconductor wafer, the chuck table holding the semiconductor wafer is irradiated with the laser beam, the workpiece holding area of the chuck table is damaged, and the surface accuracy is lowered. There is a problem.

  Further, when the semiconductor wafer is divided along the division line, the laser beam is irradiated along the division line while the semiconductor wafer is adhered to the dicing tape. However, as described above, when the laser beam is irradiated beyond the outer peripheral edge of the semiconductor wafer, the dicing tape is heated and melted and adheres to the workpiece holding region of the chuck table. There is a problem that a hole for sucking the vacuum formed in the workpiece holding area is clogged by the adhering dicing tape or the surface accuracy of the workpiece holding area is lowered. For this reason, it is necessary to scrape off the dicing tape adhering to the workpiece holding region with a grindstone, and in some cases, the chuck table must be replaced.

  In order to solve the above-described problem, there has been proposed a chuck table in which a work holding area is formed to be small and similar to the work, and a buffer groove is formed around the outside of the work holding area (see, for example, Patent Document 2). ).

  Further, white light including light of various wavelength components is converged and projected on the detection target via an optical system having axial chromatic aberration, and the reflected light is received by the spectroscope via a spatial filter. A confocal edge detection device using white light is also disclosed in Patent Document 3, for example. This is because an optical system having axial chromatic aberration has a different refractive index depending on the wavelength, and the imaging position of light passing therethrough also differs, so that only a specific wavelength component in white light is imaged on the detection target. While passing through the spatial filter and entering the spectroscope, light of other wavelength components hardly enters the spectroscope. Therefore, the spectroscope can detect the distance to the detection object by analyzing the wavelength of the light that is incident through the spatial filter.

JP-A-10-305420 JP 2005-262249 A JP 2007-178309 A

  However, the technique disclosed in Patent Document 2 requires a separate chuck table according to the shape of the workpiece, which is expensive and requires time for table replacement.

  Moreover, in the conventional confocal detection device as shown in Patent Document 3 or the like, as a spatial filter for guiding only light of a specific wavelength focused on a detection object in white light to a spectroscope. Although a pinhole mask is used, there is a problem that the accuracy as a spatial filter and the installation work of each optical component and the spectroscope are complicated and the degree of freedom of arrangement is limited.

  The present invention has been made in view of the above, and can detect the edge position of a detection target with high accuracy regardless of the shape of the detection target. An object of the present invention is to provide an edge detection device and a laser processing device having a high degree of freedom.

  In order to solve the above-described problems and achieve the object, an edge detection device according to the present invention emits white light including light of a plurality of wavelengths to a first optical path, and emits the white light to the first optical path. A chromatic aberration condensing lens that forms a plurality of focal points on the optical axis toward the detection target for each wavelength included in the white light, and the white light reflected by the detection target is the first optical path. Comprises an optical fiber that leads to a different second optical path, and a detector that detects the intensity of the white light guided to the second optical path by the optical fiber.

  The laser processing apparatus according to the present invention includes a holding unit having a holding surface for holding a workpiece, and a processing laser beam irradiation for irradiating the workpiece held on the holding surface with a processing laser beam. And an edge detection device according to the invention that detects an edge position of the workpiece as a detection target.

  According to the present invention, white light is irradiated onto the detection target with the chromatic aberration condenser lens, and the reflected light is received by the detector as white light and the light intensity is detected. Even if there are variations in the surface position of the object, the focus variation width in the height direction can be adjusted by forming multiple focal points on the optical axis, and the reflected light has a wavelength component that is focused at the edge position. By always including the detection target, the edge position of the detection target can be detected with high accuracy regardless of the shape of the detection target. At this time, the white light reflected by the detection target is detected by the optical fiber with the second optical path. Since it is guided to and incident on the detector, there is an effect that the configuration as a spatial filter is high and the degree of freedom in arrangement is high.

  Hereinafter, an edge detection apparatus and a laser processing apparatus including the edge detection apparatus which are the best mode for carrying out the present invention will be described with reference to the drawings. In this embodiment, an edge detection device that detects the edge position of a workpiece such as a semiconductor wafer in which devices are formed in a plurality of regions partitioned by a plurality of streets arranged in a lattice shape as a detection target. In addition, an example of application to a laser processing apparatus that performs laser processing by irradiating a workpiece with a processing laser beam along a street will be described.

  FIG. 1 is an external perspective view showing the main part of the laser processing apparatus of the present embodiment. The laser processing apparatus 20 according to the present embodiment includes a holding unit 21 having a holding surface 21a for holding the workpiece 1, and a workpiece 1 held on the holding surface 21a of the holding unit 21 for pulse-like machining. Laser beam irradiating means 22 for performing laser processing by irradiating a laser beam, and an edge detecting device 100 for detecting the edge position of the workpiece 1 held on the holding surface 21a of the holding means 21 as a detection target; The control means 200 is provided. The holding means 21 sucks and holds the workpiece 1 and is rotatably connected to a motor (not shown) in the cylindrical portion 24.

  The holding means 21 is mounted on two stages of sliding blocks 25 and 26. The holding means 21 is provided and mounted on the sliding block 25 so as to be movable in the X-axis direction, which is the horizontal direction, by a processing feed means 29 constituted by a ball screw 27, a nut (not shown), a pulse motor 28, and the like. The processed object 1 is processed and fed relative to the pulsed laser beam irradiated by the processing laser beam irradiation means 22. Similarly, the holding means 21 is provided so as to be movable in the Y-axis direction, which is the horizontal direction, by an index feeding means 32 constituted by a ball screw 30, a nut (not shown), a pulse motor 31 and the like with respect to the sliding block 26. The mounted workpiece 1 is indexed and fed relative to the pulsed laser beam irradiated by the processing laser beam irradiation means 22.

  Here, the processing feed means 29 is provided with a processing feed amount detection means 33 for detecting the processing feed amount of the holding means 21. The processing feed amount detection means 33 includes a linear scale 33a disposed along the X-axis direction, and a reading head (not shown) disposed along the linear scale 33a along with the sliding block 25. Yes. The machining feed amount detection means 33 sends a pulse signal of one pulse to the control means 200 for every 1 μm, for example, so that the control means 200 counts the input pulse signal and detects the machining feed amount of the holding means 21. To do.

  Similarly, an index feed amount detection means 34 for detecting the index feed amount of the holding means 21 is attached to the index feed means 32. The index feed amount detection means 34 includes a linear scale 34a disposed along the Y-axis direction and a read head (not shown) disposed along the linear block 34a and disposed along the sliding block 26 along the linear scale 34a. Yes. For example, the indexing feed amount detection means 34 sends a pulse signal of one pulse every 1 μm to the control means 200, so that the control means 200 counts the input pulse signals and detects the indexing feed amount of the holding means 21. To do.

  Further, the processing laser beam irradiation means 22 includes a casing 35 arranged substantially horizontally, and can be moved in the Z-axis direction by a Z-axis moving means (not shown) via the casing 35 with respect to the support block 36. Is provided. The processing laser beam irradiating means 22 includes a laser beam oscillating means and a transmission optical system (not shown) provided in the casing 35, and a pulse-like processing oscillated by the laser beam oscillating means provided at the tip of the casing 35. A condenser 39 for irradiating the workpiece 1 held by the holding means 21 with a laser beam is provided. The laser beam oscillation means is constituted by a laser beam oscillator composed of a YAG laser oscillator or a YVO4 laser oscillator. This laser beam oscillator and the like are controlled by the control means 200.

  Further, the edge detection device 100 attached to the tip of the casing 35 precedes the processing laser beam irradiation means 22 on the street to be processed of the workpiece 1 held on the holding surface 21a of the holding means 21. Then, the detection light is irradiated to detect the edge position on the street. Information on the edge position detected by the edge detection apparatus 100 is sent to the control means 200, and is used for controlling the irradiation start position and irradiation end position of the processing laser beam on the workpiece 1 during laser processing of the street. .

  2 is a configuration diagram schematically showing the edge detection apparatus 100 of the present embodiment, FIG. 3 is a configuration diagram showing an enlarged portion A in FIG. 2, and FIG. 4 is a configuration diagram in FIG. It is a block diagram which expands and shows the B part. The edge detection apparatus 100 according to the present embodiment mainly includes a white light source 101, a chromatic aberration condensing lens 102, a detector 103, and an optical fiber 104.

  The white light source 101 is a light source that emits white light including light of a plurality of wavelengths, and a tungsten lamp, a halogen lamp, a white LED, or the like can be used. In this embodiment, for example, a halogen lamp is used. The chromatic aberration condensing lens 102 is for condensing and irradiating white light emitted from the white light source 101 toward the holding surface 21 a (workpiece 1) side of the holding means 21. Here, the chromatic aberration condensing lens 102 is a condensing lens that forms a plurality of focal points on the optical axis toward the workpiece 1 for each wavelength included in white light. That is, since the white light collected by the chromatic aberration condensing lens 102 has a different refractive index depending on the wavelength, the focal length differs depending on the wavelength. As such a chromatic aberration condensing lens 102, for example, an aspherical lens having a numerical aperture NA = 0.68 and a viewing angle WD = 1.56 mm is used. Further, the chromatic aberration condensing lens 102 is disposed so as to be positioned at a preceding position on the same processing line as the condenser 39 of the processing laser beam irradiation means 22.

  Here, between the white light source 101 and the chromatic aberration condensing lens 102, a collimating lens 105, a condensing lens 106, an irradiation side optical fiber 107, and a collimating lens 108 are arranged in this order. The irradiation side optical fiber 107 forms the first optical path 109a, and stably propagates only the white light necessary for the chromatic aberration condensing lens 102 with respect to the white light emitted from the white light source 101. Further, the collimating lens 105 and the condensing lens 106 are lenses for converting the white light emitted from the white light source 101 into a parallel beam and then condensing it so as to efficiently enter the incident end of the irradiation side optical fiber 107. In both cases, lenses without chromatic aberration are used. Further, a fiber coupler 110 that is integrated with the incident end side of the optical fiber 104 is provided on the emission end side of the irradiation side optical fiber 107, and is connected to the common optical fiber 111. The collimating lens 108 provided between the common optical fiber 111 and the chromatic aberration condensing lens 102 converts the white light emitted from the common optical fiber 111 through the irradiation side optical fiber 107 into a parallel beam, thereby converting the chromatic aberration condensing lens. The lens has no chromatic aberration to be guided to 102.

  The detector 103 is for detecting the intensity of the reflected white light reflected by the workpiece 1 or the holding surface 21a after being condensed by the chromatic aberration condensing lens 102, and is composed of a normal photodetector. The optical fiber 104 forms a second optical path 109b different from the first optical path 109a, and guides the reflected white light reflected by the workpiece 1 or the holding surface 21a to the detector 103. As the optical fibers 104, 107, and 111, a multimode fiber having a core and a clad, for example, having a core diameter of 50 μm is used.

  The control means 200 is composed of a computer having a CPU (not shown) and a RAM (not shown) that execute arithmetic processing according to a control program stored in a ROM (not shown). The control unit 200 determines the edge position of the workpiece 1 based on the light intensity information of the white light detected by the detector 103 of the edge detection apparatus 100 and acquires the edge position information. At this time, the X and Y coordinate values at the time of edge position detection are obtained from the machining feed amount detection means 33 and the index feed amount detection means 34, thereby specifying the X and Y coordinate values of the edge position. The control unit 200 controls the entire laser processing apparatus 20. In particular, the control unit 200 controls the processing laser beam irradiation unit 22 with reference to edge position information acquired from the edge detection apparatus 100.

  Next, the detection principle of the edge Ed of the workpiece 1 in the present embodiment will be described. First, the detection of the edge Ed is basically performed by holding the light collected by the chromatic aberration condensing lens 102 so that it is not focused on the holding surface 21a and is focused on the surface 1a of the workpiece 1. This is performed by irradiating toward the 21a side, receiving the reflected light by the detector 103, and detecting the magnitude change position of the received light intensity. The light intensity when receiving reflected light from the in-focus holding surface 21a is small, and the light intensity when receiving reflected light from the focused surface 1a is increased, and the edge of the workpiece 1 is increased. This is because the change is large at the position of Ed. Therefore, the edge Ed can be detected by using a predetermined threshold for the light intensity detected by the detector 103.

  Consider a case where single-wavelength light is used to detect such an edge Ed. In this case, if the focal position is slightly deviated from the height position of the surface 1a of the workpiece 1, the rising edge of the light intensity changes when approaching the edge Ed for each height. Ed position accuracy is degraded. If the height of the surface 1a of the workpiece 1 is too far from the focal position, the detection itself cannot be performed.

  In this respect, in the present embodiment, since the white light is condensed by the chromatic aberration condensing lens 102 and is irradiated toward the holding surface 21a side, the work piece is compared with the case where single wavelength light is used. Even if there is a variation in the height position of the surface 1a, the edge Ed can be detected reliably because the focus variation width in the height direction can be adjusted. Further, since there is a point where the peak power of the focal point always returns when the holding surface 21a changes to the surface 1a of the workpiece 1, the position of the edge Ed can be detected with high accuracy.

  This point will be described in more detail with reference to FIG. As described above, the white light emitted from the white light source 101 is irradiated toward the holding surface 21 a side of the holding unit 21 that holds the workpiece 1 through the chromatic aberration condenser lens 102. At this time, the chromatic aberration condensing lens 102 has a focal length at which the white light that has passed differs depending on the wavelength. That is, the chromatic aberration condenser lens 102 forms a plurality of focal points on the optical axis toward the workpiece 1 for each wavelength included in white light. Therefore, as shown in FIG. 3, an infinite number of focal points exist for each wavelength included in the white light in the range L immediately below the optical axis center of the chromatic aberration condensing lens 102. Therefore, if white light is irradiated so that the surface 1a of the workpiece 1 exists in this range L where innumerable focal points exist, regardless of variations in the height position of the surface 1a of the workpiece 1, There is always light reflected in focus, and the position of the edge Ed can be reliably detected.

  The range L indicating the variation in focus can be freely designed from several μm to several mm depending on the numerical aperture NA and material of the chromatic aberration condensing lens 102, or the use of a diffractive lens as the chromatic aberration condensing lens 102. It is.

  In addition, the light reflected by the holding surface 21a and the surface 1a travels back in the optical path and enters the common optical fiber 111 (optical fiber 104). At this time, the light reflected by the out-of-focus holding surface 21a is difficult to recombine with the common optical fiber 111, and the amount of incident light is small, so that the light intensity detected by the detector 103 is small. On the other hand, among the white light, regardless of variations in the height position of the surface 1a of the workpiece 1, the light having a wavelength irradiated on the surface 1a in a focused state is a common optical fiber as shown in FIG. It recombines most strongly with the core 111a surrounded by the clad 111b. As a result, the light intensity that is guided to the second optical path 109b by the common optical fiber 111 (optical fiber 104) and detected by the detector 103 increases.

  For the detection of such an edge, for example, a confocal detection device as shown in Patent Document 3 is used, and only a specific wavelength light focused on the workpiece 1 in white light is spectroscope. Although it is possible to use a pinhole mask as a spatial filter for guiding the light to the surface, the accuracy as the spatial filter and the installation work of each optical component and spectrometer are complicated, and the degree of freedom of arrangement is limited. Problems arise. Also in this regard, according to the present embodiment, the white light reflected by the surface 1a of the workpiece 1 is guided to the detector 103 side by the common optical fiber 111 (optical fiber 104) having a core diameter of 50 μm, for example, and is incident. Therefore, the accuracy as a spatial filter is high, and the degree of freedom in arrangement is high. Moreover, it is sufficient to detect the light intensity using the detector 103 made of a photodetector without using a spectroscope, and a simple detection system is obtained.

  Next, a laser processing method for the workpiece 1 using such a laser processing apparatus 20 will be described. FIG. 5 is an external perspective view showing the workpiece 1. As shown in FIG. 5, a workpiece 1 to be processed is prepared with a surface 1a facing upward on a dicing tape 3 made of a synthetic resin sheet such as polyolefin mounted on an annular frame 2. Is done. The workpiece 1 is not particularly limited. For example, an adhesive member such as a wafer such as a semiconductor wafer, a DAF (Die Attach Film) provided on the back surface of the wafer for chip mounting, or a semiconductor product package, ceramic , Glass-based or silicon-based substrates, and various processed materials that require accuracy on the order of μm. The workpiece 1 of the present embodiment is based on a semiconductor wafer or the like, and has a plurality of rectangles partitioned by a plurality of first streets 4a and a plurality of second streets 4b arranged in a lattice pattern on the surface 1a. A region is formed, and the device 5 is formed in the plurality of rectangular regions.

  In processing, first, the workpiece 1 is placed on the holding surface 21a of the holding means 21 and sucked and held. The frame 2 is fixed by a clamp member 21b. Then, the holding means 21 that sucks and holds the workpiece 1 is positioned immediately below an imaging means (not shown), and an alignment operation for detecting a processing area of the workpiece 1 to be laser processed is executed. That is, pattern matching for aligning the first street 4a formed in a predetermined direction of the workpiece 1 and the condenser 39 and the chromatic aberration condenser lens 102 along the first street 4a. The image processing such as the above is executed to perform alignment. The same applies to the second street 4b.

  When alignment is performed in this manner, the workpiece 1 on the holding means 21 is positioned at a coordinate position as shown in FIG. FIG. 6 is an explanatory diagram showing the relationship with the coordinate position in a state where the workpiece 1 is held at a predetermined position of the holding means 21. FIG. 6B shows a state in which the holding means 21, that is, the workpiece 1 is rotated 90 degrees from the state shown in FIG.

  When the first street 4a formed on the workpiece 1 held by the holding means 21 is detected and the laser processing position is aligned, the control means 200 performs the workpiece in this way. The edge position detection and laser processing are performed along the first street 4a that is formed in 1 and to be processed. That is, the holding means 21 is moved so that the lowest first street 4 a in FIG. 6A is positioned directly below the condenser 39 and the chromatic aberration condenser lens 102. Then, the edge detection device 100 is operated, and the holding means 21 is moved in the machining feed direction in accordance with a predetermined machining feed speed. With this process, the edge position A1 that is the beam irradiation start position is first detected in advance for the lowest first street 4a.

  The control means 200 further continues the processing feed of the holding means 21, and when the condenser 39 reaches the edge position A1, the processing laser beam irradiation means 22 is driven to process the workpiece 1. The laser beam irradiation is started. At this time, for example, laser processing is performed to form a processing groove along the first street 4a by irradiating the condensing point of the processing laser beam with the surface 1a of the workpiece 1 by means of a condenser 39, for example. To do. In parallel with this processing, the control means 200 continues the edge position detection operation by the edge detection device 100, and precedes the edge position B1 that is the beam irradiation end position with respect to the lowest first street 4a. To detect.

  Then, the control means 200 continues the processing feed of the holding means 21, and stops the driving of the processing laser beam irradiation means 22 when the condenser 39 reaches the edge position B1, whereby the workpiece is processed. Irradiation of the processing laser beam to one street 4a is terminated.

  In this way, when the edge detection process and the laser machining process related to the lowest first street 4a are completed, the control unit 200 moves the holding unit 21 to the original position side, and further feeds it by dividing it by one line. Thus, the next first street 4a from the lowest position in FIG. 6A is positioned immediately below the condenser 39 and the chromatic aberration condenser lens 102, and the above-mentioned processing is performed for the next first street 4a. In the same manner, edge positions A2 and B2 are detected.

  Thereafter, the edge detection process and the laser processing process are repeatedly performed as parallel processes in the same manner for the subsequent first street 4a. When the edge detection process and the laser processing process for all the first streets 4a are executed, the holding means 21 is rotated 90 degrees so as to be positioned as shown in FIG. 6B, and the second street 4b. Similarly, edge detection processing and laser processing are executed for all of the above. With respect to the edge detection process, the edge positions C1, D1, C2, D2,. When all the processes are completed, the holding means 21 holding the workpiece 1 is first returned to the position where the workpiece 1 is sucked and held, and the suction holding of the workpiece 1 is released here. And the to-be-processed object 1 is conveyed by the division process by the conveyance means which is not shown in figure.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the present embodiment, a laser processing example in which a processing groove is formed by irradiating a processing laser beam having a wavelength that is absorbed by the workpiece 1 has been described. Even in the case of laser processing in which a modified layer is formed by irradiating a laser beam for use, the same can be applied.

  In this embodiment, the example of the workpiece 1 using the dicing tape 3 has been described. However, the workpiece 1 is directly held on the holding surface 21 a of the holding means 21 without using the dicing tape 3. Even if it is of the type to be made, it can be similarly applied. In this case, it is possible to avoid a problem that the processing laser beam is irradiated onto the holding surface 21a that holds the workpiece 1 by detecting the edge position with high accuracy.

  Further, the edge position detected by the edge detection apparatus 100 is not limited to the case where the workpiece 1 used for laser processing is set as a detection target, and the same is true even when another member is set as the detection target. It is applicable to.

It is an external appearance perspective view which shows the principal part of the laser processing apparatus of embodiment of this invention. It is a block diagram which shows schematically the edge detection apparatus of this Embodiment. It is a block diagram which expands and shows the A section in FIG. It is a block diagram which expands and shows the B section in FIG. It is an external appearance perspective view which shows a to-be-processed object. It is explanatory drawing which shows the relationship with the coordinate position in the state by which the to-be-processed object was hold | maintained at the predetermined position of the holding means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Workpiece 20 Laser processing apparatus 21 Holding means 21a Holding surface 22 Laser beam irradiation means for processing 100 Edge detection apparatus 101 White light source 102 Chromatic aberration condensing lens 103 Detector 104 Optical fiber 109a First optical path 109b Second optical path

Claims (2)

A white light source that emits white light including light of a plurality of wavelengths to the first optical path;
A chromatic aberration condensing lens that forms a plurality of focal points on the optical axis toward the detection object for each wavelength included in the white light emitted in the first optical path;
An optical fiber that guides the white light reflected by the detection object to a second optical path different from the first optical path;
A detector for detecting the intensity of the white light guided to the second optical path by the optical fiber;
An edge detection apparatus comprising: Holding means having a holding surface for holding the workpiece;
A processing laser beam irradiation means for irradiating the workpiece held on the holding surface with a processing laser beam;
The edge detection apparatus according to claim 1, wherein the edge position is detected using the workpiece as a detection target;
A laser processing apparatus comprising:

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