JP2019188424A - Focus position detection method of laser beam - Google Patents

Abstract

To easily and surely detect a laser focus position for laser processing.SOLUTION: A pulse laser beam of a wave length having absorptivity is radiated to an inspection wafer (TS). A plurality of laser spots (LS) different in a condensation position in the vertical direction are formed by this irradiation, and a clearance (S) is interposed between the adjacent laser spots. Afterwards, the respective laser spots are imaged by imaging means (50), and the contour of the respective laser spots is extracted from an image of the respective laser spots imaged by control means (60), and similarity with the contour of an ideal laser spot shape prestored in storage means (61) is calculated. A condensation position of the maximum similarity is determined as a just focus position.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a laser beam focal position detection method for inspecting the focal position of a laser beam that is oscillated from a laser beam oscillation means of a laser processing apparatus and collected by a condenser.

  In the semiconductor device manufacturing process, a plurality of regions are defined by division lines formed in a lattice shape on the surface of a substantially disc-shaped semiconductor wafer, and devices such as ICs and LSIs are formed in the partitioned regions. . As a method of dividing a semiconductor wafer along a planned dividing line, a pulse laser beam having a wavelength that absorbs the wafer is condensed at a desired position by a condenser and irradiated along the scheduled dividing line. A laser-processed groove serving as a starting point is formed. There has been proposed a method of cleaving by applying an external force along a planned division line in which a laser processing groove serving as a starting point of the fracture is formed (see, for example, Patent Document 1).

JP 2006-294673 A

  When the chuck table holding the semiconductor wafer is replaced or when the state of the optical system changes due to the use of the laser processing apparatus, the condensing position may change. In order to deal with such a case, the focus position is changed on the inspection wafer to form a pulse laser mark, and the operator visually determines at which focus position the edge of the pulse laser mark becomes clear. Thus, the just focus position is detected and corrected. Therefore, it is a cumbersome work that involves the subjectivity of the operator, and there are problems in reliability and workability.

  The present invention has been made in view of this point, and an object of the present invention is to provide a method for detecting the focal position of a laser beam that can easily and reliably detect the focal position of the laser beam.

  The present invention comprises a holding means for holding a workpiece, a laser beam irradiating means including a condenser for irradiating a laser beam from the upper surface side of the workpiece held by the holding means to generate a focusing point, The condensing point position adjusting means for moving the condensing point of the laser beam generated by the concentrator in the direction perpendicular to the workpiece holding surface of the holding means, and the holding means and the laser beam irradiating means in the processing feed direction. Irradiated by the laser beam irradiating means in a laser processing apparatus comprising: a processing feed means for relatively moving; an imaging means for imaging an upper surface of the workpiece held by the holding means; and a control means. A focus position detecting method for detecting a focus position of the laser beam, wherein an inspection wafer mounting step for mounting a front and back flat inspection wafer on the holding means, and the inspection wafer mounting step The laser beam condensing position is changed a plurality of times in a predetermined range in the vertical direction across the position of the upper surface of the inspection wafer, and a pulse laser beam having a wavelength that absorbs the inspection wafer. A laser spot forming step of forming a plurality of laser spots at a plurality of condensing positions within a predetermined range by performing continuous irradiation with a gap between adjacent laser spots and performing the laser spot forming step After that, the laser spot at each condensing position is imaged by the imaging means, the laser spot shape is extracted from the laser spot image taken by the control means, and the ideal laser spot shape recorded in advance on the recording means Is calculated for each condensing position, and the condensing position with the maximum similarity is the just focus position. A just focus position determination step of determining, characterized in that it is composed of.

  In the just focus position determination step, an approximate curve of similarity at each condensing position is calculated, and the condensing position of the maximum similarity in the approximate curve may be determined as the just focus position.

  According to the laser beam focal position detection method of the present invention, the laser spot formed at a plurality of different condensing positions on the inspection wafer is imaged by the imaging means, and the similarity to the ideal laser spot shape is calculated. Since the just focus position is detected, it is possible to automatically and reliably perform an inspection without requiring a special mechanism.

It is a perspective view which shows an example of the laser processing apparatus of this Embodiment. It is a block block diagram of the laser beam irradiation means with which the said laser processing apparatus is equipped. It is the elements on larger scale of the wafer in which the laser spot formation step was implemented. It is a perspective view which shows the several laser spot from which the condensing position differs formed in the laser spot formation step in the focus position detection method of this Embodiment. It is a graph which shows the aspect of similarity determination with the image data of each laser spot, and reference | standard data.

  Hereinafter, a focal position detection method for a pulse laser beam according to the present embodiment will be described with reference to the accompanying drawings. FIG. 1 is a perspective view showing an example of a laser processing apparatus according to the present embodiment. Note that the laser processing apparatus used in the method for detecting the focal position of the pulsed laser beam according to the present embodiment is not limited to the configuration shown in FIG. 1, as long as the wafer can be processed as in the present embodiment. Any processing device may be used.

  As shown in FIG. 1, the laser processing apparatus 1 is provided with a disk-shaped wafer (workpiece) W held on a chuck table (holding means) 3 on a base 2 above the chuck table 3. The laser beam irradiation means 4 is used for processing. The wafer W is divided into a plurality of areas by a plurality of streets ST formed in a lattice pattern on the surface, and devices D such as IC and LSI are formed in the divided areas. A protective tape T made of a synthetic resin sheet is attached to the back surface of the wafer W, and the wafer W is mounted on the annular frame F via the protective tape T. Various wafers can be adopted as long as a laser spot is formed by a pulsed laser beam as will be described later. For example, it may be a semiconductor wafer in which a semiconductor device such as IC or LSI is formed on a semiconductor substrate such as silicon or gallium arsenide, or an optical device wafer in which an optical device such as LED is formed on an inorganic material substrate such as sapphire or silicon carbide. But you can.

  On the surface of the chuck table 3, a holding surface (workpiece holding surface) 3a for sucking and holding the wafer W from the back side is formed by a porous ceramic material. The holding surface 3 a is connected to a suction source (not shown) through a flow path in the chuck table 3. The chuck table 3 has a disk shape, and is provided so as to be rotatable about a disk center by a rotating means (not shown). A pair of clamps 9 are provided around the chuck table 3 via support arms. Each clamp 9 is driven by an air actuator, whereby the frame F around the wafer W is clamped and fixed from both sides in the X-axis direction.

  A cover 11 supported by the cylindrical member 10 is provided below the chuck table 3. The cylindrical member 10 is installed above the index feeding means 13. The index feeding means 13 includes a pair of guide rails 14 and a ball screw 15 that are parallel to the Y-axis direction, and a Y-axis table 16 that is slidably installed on the pair of guide rails 14. A nut portion (not shown) is formed on the back side of the Y-axis table 16, and a ball screw 15 is screwed into the nut portion. The drive motor 17 connected to one end of the ball screw 15 is rotationally driven, so that the Y-axis table 16 is moved along the guide rail 14 in the indexing and feeding direction (Y-axis direction).

  The index feed means 13 is provided on an X-axis table 21 that constitutes the machining feed means 20. The processing feed means 20 further includes a pair of guide rails 22 and a ball screw 23 arranged on the base 2 and parallel to the X-axis direction, and the X-axis table 21 is slidably installed on the pair of guide rails 22. . A nut portion (not shown) is formed on the back side of the X-axis table 21, and a ball screw 23 is screwed to the nut portion. Then, the drive motor 24 connected to one end of the ball screw 23 is rotationally driven, whereby the X-axis table 21 is moved along the guide rail 22 in the machining feed direction (X-axis direction).

  The laser beam irradiation means 4 is provided so as to be movable in the Y-axis direction and the Z-axis direction (vertical direction) above the chuck table 3 by a support mechanism (condensing point position adjusting means) 27. The support mechanism 27 has a pair of guide rails 28 arranged on the base 2 and parallel to the Y-axis direction, and a motor-driven Y-axis table 29 slidably installed on the pair of guide rails 28. Yes. The Y-axis table 29 is formed in a rectangular shape when viewed from above, and a side wall 30 is erected at one end in the X-axis direction.

  The support mechanism 27 includes a pair of guide rails 32 (only one shown) installed on the wall surface of the side wall portion 30 and parallel to the Z-axis direction, and a Z-axis table slidably installed on the pair of guide rails 32. 33. Further, nut portions (not shown) are formed on the back sides of the Y-axis table 29 and the Z-axis table 33, and ball screws 34 and 35 are screwed to these nut portions. The drive motors 36 and 37 connected to one end of the ball screws 34 and 35 are rotationally driven, so that the laser beam irradiation means 4 is moved along the guide rails 28 and 32 in the Y-axis direction and the Z-axis direction. .

  The laser beam irradiation means 4 includes a cylindrical casing 40 that is cantilevered by the Z-axis table 33, and a condenser 44 attached to the tip of the casing 40. The laser beam irradiation means 4 will be described below with reference to FIG. FIG. 2 is a block diagram of the laser beam irradiation means provided in the laser processing apparatus. As shown in FIG. 2, the laser beam irradiating unit 4 includes a laser beam oscillating unit 42 disposed in the casing 40 of FIG. 1, an optical system 43 for transmitting a pulsed laser beam oscillated by the laser beam oscillating unit 42, and an optical system. The condensing unit 44 condenses the pulse laser beam transmitted by the unit 43 and irradiates the wafer W held on the chuck table 3 to generate a condensing point, and is arranged between the optical system 43 and the concentrating unit 44. And a wavelength conversion mechanism 45 for converting the wavelength of the pulse laser beam oscillated by the laser beam oscillation means 42 into a short wavelength suitable for processing the wafer W.

  The laser beam oscillation means 42 includes, for example, a pulse laser beam oscillator 421 that oscillates a pulse laser beam having a wavelength of 1064 nm, and a repetition frequency setting means 422 that sets a repetition frequency of the pulse laser beam oscillated by the pulse laser beam oscillator 421. The optical system 43 is disposed between the laser beam oscillation means 42 and the condenser 44. The optical system 43 includes a beam diameter adjuster 431 that adjusts the beam diameter of the pulse laser beam oscillated from the laser beam oscillating means 42, and an output adjusting means that adjusts the output of the pulse laser beam oscillated from the laser beam oscillating means 42 to a predetermined output. 432. The pulse laser beam oscillator 421 and the repetition frequency setting unit 422 of the laser beam oscillation unit 42 and the beam diameter adjuster 431 and the output adjustment unit 432 of the optical system 43 are controlled by the control unit 60 described later.

  The condenser 44 is a direction changing mirror 441 that oscillates from the laser beam oscillating means 42 and is transmitted by the optical system 43 and that changes the direction of the pulse laser beam wavelength-converted by the wavelength converting mechanism 45 described later toward the chuck table 3; A condensing lens 442 that condenses the pulse laser beam whose direction has been changed by the direction conversion mirror 441 and irradiates the wafer W is provided. The wavelength conversion mechanism 45 is disposed between the optical system 43 and the condenser 44. In the wavelength conversion mechanism 45, for example, a pulse laser beam having a wavelength of 1064 nm that has passed through the optical system 43 is converted into a pulse laser beam having a wavelength of 532 nm or 266 nm.

  Returning to FIG. 1, an imaging means 50 is disposed at the front end of the casing 40. The image pickup means 50 is provided so as to be able to pick up an image of the surface area of the wafer W projected with a microscope at a predetermined magnification. The image pickup means 50 includes an image pickup device (not shown) such as a CCD, and the image pickup device is composed of a plurality of pixels so that an electric signal corresponding to the amount of light received by each pixel can be obtained. Therefore, the imaging unit 50 can detect the street ST by imaging the surface of the wafer W. Based on the captured image of the imaging means 50, the laser beam irradiation means 4 and the wafer W are aligned.

  The laser processing apparatus 1 is provided with a control means 60 that performs overall control of each component of the apparatus. The control means 60 is composed of a processor that executes various processes. In addition to the signal detected by the imaging means 50, detection results from various detectors (not shown) are input to the control means 60. A control signal is output from the control means 60 to the drive motors 17, 24, 36 and 37, the laser beam oscillation means 42 and the like.

  Further, the laser processing apparatus 1 is provided with a storage means 61 for storing various parameters, programs, and the like. The storage means 61 is constituted by a memory. The memory is composed of one or a plurality of storage media such as a ROM (Read Only Memory) and a RAM (Random Access Memory) depending on the application. The storage unit 61 stores data about the contour of the shape of an ideal laser spot LS (see FIG. 3), which will be described later, and a threshold value of similarity, which will be described later, for the contour.

  Next, a wafer processing method will be described. In the processing method using the laser processing apparatus of the present embodiment, a plurality of laser spots LS (see FIG. 3) are formed at predetermined intervals along the street ST of the wafer W.

  In the processing method of the present embodiment, first, a wafer placement step is performed. In the wafer placement step, the wafer W supported on the annular frame F via the protective tape T is placed on the chuck table 3 shown in FIG. Then, by operating a suction means (not shown), the wafer W is sucked and held on the chuck table 3 via the protective tape T. The frame F is fixed by a clamp 9.

  After the wafer placement step is performed, a laser spot forming step is performed. In the laser spot forming step, first, the chuck table 3 is positioned immediately below the imaging unit 50 by the processing feeding unit 20, and alignment for detecting the processing region of the wafer W to be laser processed is performed by the imaging unit 50 and the control unit 60. . In alignment, image processing such as pattern matching is performed on the street ST of the wafer W picked up by the image pickup means 50 by the control means 60 in order to align the condenser 44 of the laser beam irradiation means 4 and the wafer W. .

  Thereafter, the movement and rotation of the chuck table 3 are controlled based on the calculation result of the control means 60, and the wafer W is positioned so that any one of the orthogonal streets ST extends in parallel with the X-axis direction. Next, the condenser 44 of the laser beam application means 4 is positioned on the street ST parallel to the X-axis direction with respect to the wafer W on the chuck table 3. Further, the focal point of the pulse laser beam irradiated from the condenser 44 is positioned on the wafer W held on the chuck table 3. While the wafer W is irradiated with a pulsed laser beam having an absorptive wavelength from the condenser 44, the chuck table 3 and the condenser 44 are relatively moved in the X-axis direction, which is the machining feed direction, by the machining feed means 20. Moved.

  As a result, as shown in FIG. 3, a plurality of laser spots LS are formed on the wafer W along the street ST for each pulse pitch based on the wavelength of the pulse laser beam. In other words, the gap S is formed between adjacent laser spots LS by continuous irradiation with a pulsed laser beam. FIG. 3 is a partially enlarged view of the wafer subjected to the laser spot forming step. In FIG. 3, the shape of the laser spot LS is formed in a rounded square shape or a long hole shape, but is not limited to this, and various modifications such as a circular shape, an elliptical shape, and a rectangular shape (rectangular shape) are possible. is there.

  After forming a plurality of laser spots LS along the target street ST, the irradiation of the pulse laser beam is stopped, and the chuck table 3 and the condenser 44 are relatively moved in the Y-axis direction corresponding to the interval of the street ST. (Index feed). Thereby, the collector 44 can be adjusted to the street ST adjacent to the target street ST. Subsequently, a plurality of laser spots LS are similarly formed along the adjacent streets ST. By repeating this operation, laser spots LS are formed along all the streets ST extending in the X-axis direction, and then the chuck table 3 is rotated by 90 ° around the rotation axis, along the streets ST extending in the Y-axis direction. Thus, a laser spot LS is formed.

  Incidentally, the laser beam irradiated at the time of laser processing is set so as to focus on a predetermined position in the Z-axis direction (vertical direction) with respect to the wafer W to form a laser spot LS. At the time of shipment of the laser processing apparatus 1, the condensing position of the laser beam irradiated from the laser beam irradiation means 4 is set as a design value. Condensing position with respect to the wafer W when the laser beam is irradiated when the chuck table 3 is replaced or when the state of the laser beam irradiation means 4 changes due to use of the apparatus (deformation or contamination of the lens, minute positional deviation of the optical system, etc.) May change from the design value, so it is necessary to detect the actual condensing position of the laser beam before processing.

  In the present embodiment, the detection of the focal position of the laser beam is automatically performed under the control of the control means 60, and the detection method will be described. In this detection method, an inspection wafer is used instead of the wafer W. As the inspection wafer, as long as the laser spot LS can be formed in the same manner as described above, the same wafer W used for manufacturing the product may be used, or a different material (different price) from the wafer W. May be used.

  The focal position detection method of the laser beam in the present embodiment is performed in the order of the wafer placement step, the laser spot formation step, and the just focus position determination step.

  In the method of detecting the focal position of the laser beam in the present embodiment, the wafer W is changed to an inspection wafer with respect to the above processing method, and after the wafer placement step is performed as described above, the laser spot forming step is performed. The Therefore, as an inspection wafer, the reference numeral TS is written in parentheses to the reference numeral of the wafer W in FIGS. 1 and 3, and a detailed description of the wafer mounting step is omitted. As shown in FIG. 4, the front and back surfaces of the inspection wafer TS are flat, and the upper surface U (FIG. 4) of the inspection wafer TS is horizontal while being held on the chuck table 3 in the wafer placement step. FIG. 4 shows a part of the inspection wafer TS in the X-axis direction and the Y-axis direction, and the actual outer shape of the inspection wafer TS is different from that shown in FIG.

  In the laser spot forming step in the focus position detecting method, a plurality of laser spots LS are formed on the inspection wafer TS with the gaps S in the X-axis direction interposed in the same manner as the laser spot forming step in the processing method. However, when forming these laser spots LS, as shown in FIG. 4, a plurality of laser beam condensing positions within a predetermined range in the Z-axis direction (vertical direction) sandwiching the upper surface U position of the inspection wafer TS. Each laser spot LS (LS1 to LS6) is formed at a plurality of different positions in the Z-axis direction by changing the position (by changing the defocus amount). In FIG. 4, the difference in the condensing position in the Z-axis direction that forms the laser spots LS <b> 1 to LS <b> 6 is virtually indicated by a one-dot chain line M. The number of laser spots formed in the laser spot forming step is arbitrary and is not limited to the number shown in FIG.

  After the laser spot forming step is performed in this way, the just focus position determining step is performed. In the just focus position determination step, an imaging step, an extraction step, a calculation step, and a determination step are performed.

  In the imaging step, a plurality of laser spots LS (FIG. 4) with different condensing positions (defocus amounts) formed in the previous laser spot forming step are positioned immediately below the imaging means 50, and are in the processing feed direction X Each laser spot LS is imaged by the imaging means 50 at a plurality of locations in the axial direction. The captured image data of the laser spot LS at each condensing position is input to the control means 60.

  After the imaging step is performed, the extraction step is performed. In the extraction step, an appropriate process for extracting the contour of the laser spot LS from the captured image data of the laser spot LS at each condensing position is performed by the control means 60. For example, image processing for extracting the outline of the laser spot LS in a linear manner from the image data of the laser spot LS at each condensing position by a predetermined algorithm is performed. In order to obtain an appropriate calculation result in the next calculation step, the contour extraction process in the extraction step is performed under the same conditions on the image data of the laser spot LS at all the condensing positions.

  In the extraction step, contour extraction processing is performed for each end portion E surrounded by a broken-line frame in FIG. 3 among the laser spots LS imaged in the imaging step. Since both end portions E of the laser spot LS include not a simple straight line but a characteristic shape, they are suitable for edge detection, and the contour can be extracted with high accuracy. Even when the laser spot LS is not a rounded quadrangular laser spot as shown in FIG. 3, it is preferable that both ends of the laser spot in the longitudinal direction are extracted.

  After the extraction step is performed, the calculation step is performed. Prior to the execution of the calculation step, the reference data of the contour that is ideal as the shape of the laser spot LS is stored in the storage unit 61 in advance based on the irradiation condition of the pulse laser beam. The ideal shape here can be set from, for example, a mask shape for controlling the passage of a laser beam for forming the laser spot LS.

  In the calculation step, the individual image data of the laser spot LS (FIG. 4) at each condensing position extracted in the extraction step (particularly the image data of the contours of both end portions E), the reference data stored in the storage means 61, and Are respectively compared by the control means 60, and the degree of similarity of the individual image data with respect to the reference data is calculated by a predetermined image determination method such as pattern matching. The similarity indicates the shift of the image data with respect to the reference data, and the similarity decreases as the shift increases, and increases when the shift is small.

  As shown in FIG. 4, the plurality of laser spots LS <b> 1 to LS <b> 6 formed with different condensing positions are different from each other in the Z-axis direction. For this reason, the sharpness (blur amount) of the contours of the laser spots LS1 to LS6 at the time of imaging in the imaging step varies depending on the difference in defocus amount. Based on the difference in definition, the image data extracted from the individual laser spots LS1 to LS6 in the extraction step is different. As a result, in the calculation step, a difference occurs in the similarity of the image data of the laser spots LS1 to LS6 with respect to the reference data. That is, the difference in similarity calculated in the calculation step corresponds to the difference in the condensing positions of the individual laser spots LS1 to LS6.

  After the calculation step is performed, the determination step is performed. In the determining step, the condensing position of the laser spot LS having the maximum similarity to the ideal contour among the similarities calculated in the calculating step for the image data of the plurality of laser spots LS is determined as the just focus position. .

  FIG. 5 shows the concept of similarity determination for a plurality of laser spots LS (LS1 to LS6) having different condensing positions. In the example of FIG. 5, among the laser spots LS1 to LS6, the image data of the laser spot LS4 has the maximum similarity to the reference data. As a first aspect of the determination step, the condensing position of the laser spot LS4 having the maximum similarity is directly determined as the just focus position.

  As a second aspect of the determination step, similarity is obtained from the relationship between the condensing position (defocus amount) of each laser spot LS and the sharpness (similarity with reference data) of the contour of the image data of each laser spot LS. An approximate curve AC (FIG. 5) of the degree is created, and the condensing position LS-V (FIG. 5) having the maximum similarity in the approximate curve AC is determined as the just focus position. By creating the approximate curve in this way, it is possible to set the just focus position even at the light collection position where the image is not captured in the imaging step, and it is possible to realize a more accurate just focus determination.

  The control means 60 positions the condensing position of the laser beam with reference to the just focus position determined through the above steps, and completes the detection method. Then, based on the condensing position after detection (after correction), the position of the laser beam irradiation means 4 in the Z-axis direction is controlled to perform laser processing on the wafer W by the above processing method.

  As described above, in the detection method of the present embodiment, the control unit 60 can determine the laser focusing position, which is the just focus position, based on the imaging result of the laser spot LS. This eliminates the need for visual observation by the operator, prevents the detection accuracy from becoming unstable due to the skill level of the operator, and allows the focal position of the laser beam to be detected accurately and stably. Further, the processing time required for the determination can be shortened compared with the visual observation by the operator, and the detection efficiency can be improved.

  In addition, the laser spot LS can be detected using the imaging means 50 used for the alignment of the wafer W, and it is not necessary to increase the number of sensors and imaging equipment for such detection, so that the apparatus configuration can be simplified.

  Note that a threshold may be set for similarity determination with reference data in the determination step. When all of the image data of the plurality of laser spots LS acquired in the imaging step and the extraction step are below the threshold in the similarity to the reference data calculated in the calculation step (similarity is too low), the laser beam irradiation means 4 There is a possibility that some kind of error occurs in the laser irradiation or the holding state of the inspection wafer TS and the laser spot is not properly formed. In such a case, the control unit 60 may not determine the just focus position in the determination step, and may notify the operator of an error state using a notification unit (not shown) such as a display or sound. .

  The embodiments of the present invention are not limited to the above-described embodiments, and various changes, substitutions, and modifications may be made without departing from the spirit of the technical idea of the present invention. Furthermore, if the technical idea of the present invention can be realized in another way by technological advancement or another derived technique, the method may be used. Accordingly, the claims cover all embodiments that can be included within the scope of the technical idea of the present invention.

  In the above embodiment, the similarity with the ideal laser spot shape is calculated using pattern matching in the calculation step, but the method of calculating the similarity between the two laser spot shapes can calculate the degree of correlation between them. As long as it is not limited, various methods can be adopted.

  Moreover, although the case where the imaging means 50 is used for both the detection of the laser spot LS and the alignment of the wafer W has been described, it does not preclude providing a dedicated imaging means for each.

  As described above, the present invention has an effect that the focal position of a laser beam can be easily and reliably determined, and is useful when a workpiece is irradiated with a laser beam to form a laser spot and processed.

1: Laser processing device 3: Chuck table (holding means)
3a: Holding surface (workpiece holding surface)
4: Laser beam irradiation means 13: Index feed means 16: Y-axis table 20: Processing feed means 21: X-axis table 27: Support mechanism (focusing point position adjusting means)
29: Y-axis table 33: Z-axis table 42: Laser beam oscillation means 43: Optical system 44: Condenser 45: Wavelength conversion mechanism 50: Imaging means 60: Control means 61: Storage means AC: Approximation curve LS: Laser spot LS -V: Condensing position TS of the maximum similarity on the approximate curve: Wafer for inspection W: Wafer (workpiece)

Claims (2)

A holding means for holding the workpiece, a laser beam irradiation means including a condenser for irradiating a laser beam from the upper surface side of the workpiece held by the holding means to generate a condensing point, and the condenser The focusing point position adjusting means for moving the focusing point of the generated laser beam in a direction perpendicular to the workpiece holding surface of the holding means, and the holding means and the laser beam irradiating means are relatively moved in the processing feed direction. In a laser processing apparatus comprising a processing feed means for performing imaging, an imaging means for imaging the upper surface of the workpiece held by the holding means, and a control means, the laser beam irradiated by the laser beam irradiation means A focal position detection method for detecting a focal position,
An inspection wafer mounting step of mounting a front and back flat inspection wafer on the holding means;
After performing the inspection wafer mounting step, the laser beam condensing position is positioned by changing the laser beam condensing position a plurality of times within a predetermined range in the vertical direction across the inspection wafer upper surface position. A laser spot forming step of irradiating a pulsed laser beam having a wavelength and continuously irradiating with a gap between adjacent laser spots to form a plurality of laser spots at a plurality of condensing positions within a predetermined range;
After performing the laser spot forming step, the laser spot at each condensing position is picked up by the image pickup means, the laser spot shape is extracted from the laser spot image picked up by the control means, and recorded in the recording means in advance. Just focus position determination step for calculating the degree of similarity with the ideal laser spot shape for each condensing position and determining that the condensing position with the maximum similarity is the just focus position;
A method for detecting a focal position of a laser beam, comprising:   The step of determining the just focus position calculates an approximate curve of the similarity at each condensing position, and determines that the condensing position of the maximum similarity in the approximate curve is the just focus position. Item 2. A method for detecting a focal position of a laser beam according to Item 1.

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