TW201944157A - Laser beam focus position detection method capable of easily and reliably detecting a laser focus position for laser processing - Google Patents

Abstract

An object of the invention is to easily and reliably detect a laser focus position for laser processing. To achieve the object, an inspected wafer (TS) is irradiated with a pulsed laser beam with an absorptive wavelength. With the irradiation, a plurality of different laser spots (LS) are formed on condensing positions in the vertical direction, and a gap (S) is formed between adjacent laser spots. Thereafter, a photographing means (50) is provided to photograph each laser spot, and a control means (60) is provided to capture a contour of each laser spot from the photographed image of each laser spot, and calculate similarity thereof with a contour of an ideal laser spot shape stored in advance in a storage means (61). Then, the condensing position with the maximum similarity is determined to be the appropriate focus position.

Description

Method for detecting focus position of laser light

The invention relates to a method for detecting a focal position of a laser beam, which detects the focal position of the laser beam generated by oscillation of a laser beam oscillating means of a laser processing device and focused by a condenser.

In the semiconductor device manufacturing step, a plurality of regions are divided by a plurality of predetermined division lines formed in a grid shape on the front surface of a semiconductor wafer having a substantially circular plate shape, and elements such as ICs and LSIs are formed in the divided regions. . A method of dividing a semiconductor wafer along a predetermined division line is to form a pulse laser light having a wavelength absorptivity to the wafer by condensing at a desired position with a condenser, and irradiate along the predetermined division line to form a semiconductor wafer. Laser machined groove as the starting point of fracture. A method has been proposed in which cutting is performed by applying an external force along a predetermined dividing line in which a laser processing groove as a starting point of fracture is formed (for example, refer to Patent Document 1).

[Xizhi technical literature]
[Patent Literature]
[Patent Document 1] Japanese Patent Laid-Open No. 2006-294674

[Problems to be Solved by the Invention]
When the chuck table holding the semiconductor wafer is replaced, or the state of the optical system is changed due to the use of the laser processing device, the light collecting position may be changed. In order to cope with such a situation, a pulse laser mark may be formed by changing the light-condensing position on the inspection wafer, and the operator's visual judgment will determine which light-condensing position to sharpen the edge of the pulse laser-mark, and further Detect and correct the just-focus position. Therefore, it becomes a troublesome task involving the subjectivity of the operator, and there are problems in reliability and workability.

Therefore, an object of the present invention is to provide a focus position detection method for laser light, which can easily and reliably detect the focus position of laser light.

[Technical means to solve the problem]
According to the present invention, there is provided a method for detecting a focus position of a laser ray. The laser processing apparatus detects a focus position of the laser ray irradiated by the laser ray irradiating means. The laser processing apparatus includes: holding means, holding Workpiece; laser light irradiating means, including a condenser that irradiates laser light from the upper surface side of the workpiece held by the holding means to form a light collecting point; means for adjusting the position of the light collecting point to make the laser formed by the light collector The light-condensing point of the light beam moves in a direction perpendicular to the workpiece holding surface of the holding means; the processing feed means moves the holding means and the laser light irradiation means relatively in the processing feed direction; the camera means, photographing and holding An upper surface of the workpiece on the holding means; and a control means, wherein the focus detection method of the laser light includes a step of placing a wafer for inspection, and placing the inspection wafer having a flat front and a back on the retaining means; ; A laser spot forming step, after implementing the wafer mounting step for inspection, a predetermined range in a vertical direction to sandwich the upper surface position of the wafer for inspection; The laser beam is condensed by changing the condensing position of the laser beam multiple times and positioned, and the pulsed laser beam with a wavelength absorptive to the inspection wafer is continuously irradiated with a gap between adjacent laser points, and Forming a plurality of laser points at a plurality of condensing positions in a predetermined range; and a focus position determining step, after implementing the laser point forming step, photographing the laser points at each condensing position by the imaging means, and borrowing The control means captures the shape of the laser point from the captured laser point image, and calculates the similarity between each of the laser point shapes and the ideal laser point shape previously stored in the memory means according to the light collecting positions, condensing the maximum similarity. The position is determined as the focus position.

Preferably, in the focus position determining step, an approximate curve of the similarity of each of the light-condensing positions is calculated, and the light-condensing position of the maximum similarity in the approximate curve is determined as the focus-focusing position.

[Inventive effect]
According to the method for detecting the focus position of the laser beam according to the present invention, the imaging point is used to image the laser spot formed at different multiple light-concentrating positions on the inspection wafer, and the similarity with the ideal laser spot shape is calculated. Since the focus position is detected, there is no need to provide a special mechanism, and the inspection can be performed easily and reliably automatically.

Hereinafter, a focus position detection method of the pulsed laser beam according to the present embodiment will be described with reference to the accompanying drawings. FIG. 1 is a perspective view of an example of a laser processing apparatus according to the present embodiment. In addition, the laser processing device used in the focus position detection method of the pulsed laser light according to the present embodiment is not limited to the configuration shown in FIG. 1, and may be a wafer that can be processed in the same manner as the present embodiment. Any processing device.

As shown in FIG. 1, the laser processing apparatus 1 is configured to pass a disk-shaped wafer (workpiece) W of a chuck table (holding means) 3 held on a base 2 to a disk wafer (workpiece) W provided above the chuck table 3. The laser light irradiation means 4 performs processing. The wafer W is divided into a plurality of regions on the front surface by a plurality of scribe lines ST formed in a grid pattern, and elements D such as ICs and LSIs are formed in the divided regions. A protective adhesive film T made of a synthetic resin sheet is adhered to the back surface of the wafer W, and the wafer W is mounted on the ring-shaped frame F through the protective adhesive film T. In addition, as long as the wafer W is within a range where a laser point is formed by pulsed laser light as described later, various wafers can be used. For example, it may be a semiconductor wafer in which semiconductor elements such as IC and LSI are formed on a semiconductor substrate such as silicon or gallium arsenide, or an optical element in which optical elements such as LEDs are formed on an inorganic material substrate such as sapphire or silicon carbide. Wafer.

A holding surface (work holding surface) 3 a is formed on the surface of the chuck table 3 by holding a wafer W 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 to be rotatable around a center of the disk by a rotation means (not shown). A pair of jigs 9 are provided around the chuck table 3 through a support arm. Each jig 9 is driven by an air actuator, thereby holding and fixing the frame F around the wafer W from both sides in the X-axis direction.

A cover plate 11 supported by a cylindrical member 10 is provided below the chuck table 3. The cylindrical member 10 is provided above the index feeding means 13. The indexing feeding means 13 includes a pair of guide rails 14 and a ball screw 15 parallel to the Y-axis direction, and a Y-axis table 16 slidably provided 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 the ball screw 15 is screwed to the nut portion. Then, the Y-axis table 16 is moved in the index feed direction (Y-axis direction) along the guide rail 14 by the drive of the drive motor 17 connected to one end of the ball screw 15.

The indexing feed means 13 is provided on an X-axis table 21 constituting the processing 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 provided 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 the 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 to move the X-axis table 21 along the guide rail 22 in the processing feed direction (X-axis direction).

The laser light 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 includes 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 provided on the pair of guide rails 28. The Y-axis table 29 is formed in a rectangular shape in plan view, and a side wall portion 30 is erected at one end portion in the X-axis direction.

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

The laser light irradiation means 4 includes a cylindrical case 40 that is cantilevered and supported by the Z-axis table 33 and a condenser 44 attached to the front end of the case 40. The laser light irradiation means 4 will be described below with reference to FIG. 2. FIG. 2 is a block configuration diagram of a laser ray irradiation means installed in the laser processing apparatus. As shown in FIG. 2, the laser light irradiation means 4 includes a laser light oscillation means 42 disposed in the housing 40 of FIG. 1, and an optical system 43 that oscillates a pulsed laser generated by the laser light oscillation means 42. The light is transmitted; the condenser 44 condenses the pulsed laser light transmitted by the optical system 43 and irradiates the wafer W held on the chuck table 3 to generate a condensing point; and the wavelength conversion mechanism 45 is provided. Between the optical system 43 and the condenser 44, the wavelength of the pulsed laser light generated by the laser light oscillation means 42 is converted into a short wavelength suitable for wafer W processing.

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

The condenser 44 is provided with a direction conversion mirror 441 that oscillates from the laser light oscillating means 42 and is transmitted by the optical system 43 and converts the wavelength of the pulse laser light by the wavelength conversion mechanism 45 to be described later toward the card The disk table 3; and the condenser lens 442 condenses the pulsed laser light whose direction is changed by the direction conversion mirror 441 and irradiates the wafer W. The wavelength conversion mechanism 45 is disposed between the optical system 43 and the condenser 44. The wavelength conversion mechanism 45 converts, for example, a pulsed laser beam having a wavelength of 1064 nm through the optical system 43 into a pulsed laser beam having a wavelength of 532 nm or 266 nm.

Returning to FIG. 1, the imaging means 50 is disposed at the front end portion of the housing 40. The imaging means 50 is provided so as to be able to capture a front region of the wafer W which is magnified and projected by a microscope at a predetermined magnification. The imaging means 50 includes an imaging element (not shown) such as a CCD. The imaging element is composed of a plurality of pixels and can obtain an electric signal according to the amount of light received by each pixel. Therefore, the imaging means 50 can image and detect the scribe line ST by imaging the front side of the wafer W. The laser image irradiation means 4 and the wafer W are aligned based on a captured image by the imaging means 50.

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

Furthermore, the laser processing device 1 is provided with a memory means 61 that memorizes various parameters, programs, and the like. The memory means 61 is composed of a memory. The memory is composed of one or more memory media such as a ROM (Read Only Memory), a RAM (Random Access Memory), and the like according to the application. The memory means 61 stores data on a shape profile of an ideal laser point LS (see FIG. 3) described later, a threshold value of similarity described later on the profile, and the like.

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

In the processing method of this embodiment, a wafer mounting step is performed first. In the wafer mounting step, the wafer W supported by the annular frame F through the protective adhesive film T is placed on the chuck table 3 shown in FIG. 1 by a conveyance means (not shown) or the like. Then, the wafer W is sucked and held on the chuck table 3 through the protective adhesive film T by operating a suction means (not shown). The frame F is fixed by a jig 9.

After the wafer mounting step is performed, a laser spot forming step is performed. In the laser spot forming step, first, the chuck table 3 is positioned directly below the imaging means 50 by the processing feed means 20, and the wafer is inspected by the imaging means 50 and the control means 60. Laser processing should be performed Alignment of the area. In the alignment operation, in order to align the condenser 44 of the laser light irradiation means 4 with the wafer W, the control means 60 patterns the dicing track ST of the wafer W captured by the imaging means 50. Image processing such as matching.

Then, based on the calculation result by the control means 60, the movement and rotation of the chuck table 3 are controlled, and the wafer W is aligned so that any one of the orthogonal scribe lines ST is parallel to the X-axis direction and extends. Next, for the wafer W on the chuck table 3, the condenser 44 of the laser light irradiation means 4 is positioned at a scribe line ST parallel to the X-axis direction. The condensing point of the pulsed laser light emitted from the condenser 44 is positioned on the wafer W held on the chuck table 3. Then, while radiating a pulsed laser beam having a wavelength absorptive to the wafer W from the condenser 44, the chuck table 3 and the condenser 44 are aligned on the X axis, which is the processing feed direction, by the processing feed means 20. The directions move relatively.

Thereby, as shown in FIG. 3, a plurality of laser spots LS are formed on the wafer W along each dicing pitch of the pulse laser light wavelength along the scribe line ST. In other words, by the continuous irradiation of the pulsed laser light, a state in which the gap S is between the adjacent laser points LS is formed. FIG. 3 is a partially enlarged plan view of a wafer on which a laser spot forming step has been performed. In FIG. 3, the shape of the laser point LS is formed in a shape of a corner, an arc, a quadrangle, or a long hole. However, the shape is not limited to this, and various modifications such as a circle, a circle, and a rectangle (square) can be made.

After forming a plurality of laser points LS along the cutting path ST of the object, stop the irradiation of the pulsed laser light, and move the chuck table 3 and the condenser 44 in the Y-axis direction corresponding to the interval of the cutting path ST (indexing) Feed). Thereby, the condenser 44 can be aligned with the scribe line ST adjacent to the target scribe line ST. Next, a plurality of laser spots LS are similarly formed along the adjacent scribe lines ST. Repeat this operation to form a laser point LS along all the cutting paths ST extending in the X-axis direction, and then rotate the chuck table 3 by 90 ° about the rotation axis to form a laser along the cutting path ST extending in the Y-axis direction. Click LS.

However, the laser light emitted during laser processing is set to focus the wafer W in a predetermined position in the Z-axis direction (vertical direction) to form a laser point LS. When the laser processing apparatus 1 is shipped, the light condensing position of the laser light irradiated from the laser light irradiation means 4 is set as a design value. When the chuck table 3 is replaced, or when the state of the laser light irradiation means 4 changes (deformation or contamination of the lens, fine position deviation of the optical system, etc.) due to the use of the device, the concentration of the wafer W during the laser light irradiation The light position may change from the design value, so it is necessary to detect the actual laser light condensing position before processing.

This embodiment is a technique for automatically performing such a focus position detection of laser light under the control of the control means 60, and a detection method thereof will be described. In this inspection method, an inspection wafer is used instead of the wafer W described above. As the inspection wafer, as long as the laser point LS can be formed as described above, the same wafer as the wafer W used for manufacturing the product can be used, or a material different from the wafer W (different price) can be used. ) Wafer.

The laser beam focus position detection method of this embodiment is implemented in the order of a wafer mounting step, a laser spot formation step, and a focus position determination step.

In the method for detecting the focal position of the laser beam according to the present embodiment, the wafer W is changed to an inspection wafer for the above-mentioned processing method, and after the wafer mounting step is performed in the same manner as described above, a laser spot forming step is performed. Therefore, as the inspection wafer, parentheses are added and the symbol TS is described in the symbol of the wafer W in FIG. 1 and FIG. 3, and a detailed description of the wafer mounting procedure 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 shown while being held on the chuck table 3 during the wafer mounting step. Level. 4 shows a part of the inspection wafer TS in the X-axis direction and the Y-axis direction. The actual outer shape of the inspection wafer TS is different from that shown in FIG. 4.

In the laser spot forming step of the focus position detection method, similarly to the laser spot forming step of the above-mentioned processing method, a plurality of laser spots LS are formed on the inspection wafer TS by interposing a gap S in the X-axis direction. However, when these laser points LS are formed, as shown in FIG. 4, the laser light is focused within a predetermined range in the Z-axis direction (vertical direction) of the U position on the upper surface of the wafer inspection TS. Position changes are performed multiple times for alignment (to change the defocus amount), and laser points LS (LS1 to LS6) are formed at multiple positions with different Z-axis directions. In FIG. 4, the difference in the light-concentration positions in the Z-axis direction forming the laser points LS1 to LS6 is imaginarily represented 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. 4.

After performing the laser spot formation step in this manner, the focus position determination step is performed. In the focus position determination step, an imaging step, an acquisition step, a calculation step, and a determination step are performed.

In the imaging step, a plurality of laser points LS (FIG. 4) having different focusing positions (defocus amounts) formed in the previous laser point forming step are positioned directly below the imaging means 50 and are used as a processing feed. There are multiple X-directions in the direction, and each laser point LS is captured by the imaging means 50. The captured image data of the laser point LS at each light-condensing position is input to the control means 60.

After the image capturing step is implemented, a capturing step is performed. In the acquisition step, the control means 60 performs appropriate processing for extracting the outline of the laser point LS from the image data of the laser point LS at each light-condensing position. For example, image processing of linearly capturing the outline of the laser point LS from the image data of the laser point LS at each light-condensing position is performed by a predetermined algorithm. In order to obtain an appropriate calculation result in the next calculation step, the contour extraction processing in the acquisition step is performed on the image data of the laser point LS all at the light-concentrating position under the same conditions.

In the acquisition step, the contour extraction process is performed on the laser point LS captured by the imaging step with the two end portions E surrounded by the dotted frame in FIG. 3 as objects. Since the two end portions E of the laser point LS are not simple straight lines but include characteristic shapes, they are suitable for edge detection and can extract contours with high accuracy. In addition, in the case of a laser point LS that is not a corner-arc quadrangle as shown in FIG. 3, it is preferable to use both end portions in the longitudinal direction of the laser point as the object of contour extraction.

The calculation step is performed after the acquisition step is performed. At the stage before the calculation step is performed, the reference data that can be used as the shape of the laser spot LS to reach the ideal contour is stored in advance in the storage means 61 based on the irradiation conditions of the pulsed laser light and the like. The ideal shape referred to herein can be set by, for example, the shape of a mask for controlling the passage of laser light for forming the laser point LS.

In the calculation step, each image data (especially the contour image data of the E at both ends) of the laser point LS (FIG. 4) at each of the light-gathering positions acquired in the acquisition step is controlled by the control means 60 and the memory. The reference data in the memory means 61 are respectively compared, and the similarity of each image data with respect to the reference data is calculated by a predetermined image determination method such as pattern matching. The similarity is a way of indicating the deviation degree of the image data from the reference data. The larger the deviation degree is, the lower the similarity degree is; the smaller the deviation degree is, the higher the similarity degree is.

As shown in FIG. 4, the formation positions of the plurality of laser points LS1 to LS6 formed by different light-condensing positions in the Z-axis direction are also different. Therefore, due to the difference in the defocus amount, the contour sharpness (blurring amount) of each laser point LS1 to LS6 is different at the time of shooting in the imaging step. Based on the difference in sharpness, the image data acquired from the laser points LS1 to LS6 in the acquisition step are different. As a result, in the calculation step, the similarity of the image data of each laser point LS1 to LS6 with respect to the reference data will be different. That is, the similarity difference calculated in the calculation step corresponds to the difference in the light-condensing positions of the respective laser points LS1 to LS6.

The decision step is performed after the calculation step. In the determining step, the focus position of the laser point LS with the largest similarity with respect to the ideal contour is determined as the focal point among the similarity degrees of the image data of the plurality of laser point points LS in the calculating step. position.

FIG. 5 is a conceptual diagram showing similarity determination for a plurality of laser points LS (LS1 to LS6) having different focusing positions. In the example in FIG. 5, among the laser points LS1 to LS6, the similarity between the image data of the laser point LS4 and the reference data reaches the maximum. The first aspect of the determination step is to directly determine the focusing position of the laser point LS4 with the maximum similarity as the focal position.

The second aspect of the determination step is the relationship between the light-condensing position (defocus amount) of each laser point LS and the contour sharpness (similarity with reference data) of the image data of each laser point LS. An approximation curve AC (FIG. 5) of similarity is prepared, and the focusing position LS-V (FIG. 5) of the maximum similarity on the approximation curve AC is determined as the focal position. By making an approximate curve in this way, the focus position can be set even if the light-condensing position is not captured in the imaging step, so that a more accurate focus determination can be achieved.

The control means 60 uses the in-focus position determined through the above steps as a reference, and locates the light-condensing position of the laser light, and the above detection method ends. Next, based on the detected (corrected) light-condensing position, the position in the Z-axis direction of the laser light irradiation means 4 is controlled, and laser processing of the wafer W in the processing method described above is performed.

As described above, in the detection method of the present embodiment, based on the imaging results of the laser point LS, the control means 60 can be used to determine the laser condensing position belonging to the in-focus position. In this way, even without the operator's visual inspection, it is possible to prevent the situation where the detection accuracy becomes unstable due to the operator's proficiency, and to stably detect the focal position of the laser light with excellent accuracy. In addition, the processing time required for the determination can be shortened compared with the visual inspection of the operator, and the detection efficiency can be improved.

In addition, since the laser point LS can be detected using the imaging means 50 for the alignment of the wafer W, it is not necessary to add a sensor or a camera for such detection, so that the device configuration can be simplified.

In addition, a threshold value may be set for the reference data similarity determination of the determination step. When all the image data of the plurality of laser points LS obtained in the imaging step and the acquisition step are lower than the threshold (similarity is too low) in the similarity with respect to the reference data calculated in the calculation step, there may be There is a possibility that a certain error occurs in the laser irradiation in the laser beam irradiation means 4 or the holding state of the inspection wafer TS, and the laser spot is not properly formed. In this case, the control means 60 may not perform the focus position determination in the determination step, and may notify the operator of an error state using a notification means (not shown) such as display or sound.

In addition, the embodiments of the present invention are not limited to the above-mentioned embodiments, and various changes, substitutions, and modifications may be made without departing from the gist of the technical idea of the present invention. Even with the advancement of technology or other technologies derived from it, as long as the technical idea of the present invention can be realized by other methods, this method can also be implemented. Therefore, the scope of application for a patent covers all implementation forms that can be included within the scope of the technical idea of the present invention.

In the above embodiment, although the pattern matching is used to calculate the similarity with the ideal laser point shape in the calculation step, the similarity of the two laser point shapes is calculated as long as the degree of correlation between them can be calculated. Various methods can be used without particular limitation.

In addition, although the imaging means 50 is described as being used for both the detection of the laser point LS and the alignment of the wafer W, it is also possible to provide a dedicated imaging means separately.

As described above, the present invention has the effect of easily and surely determining the focal position of the laser light, and is useful when the workpiece is irradiated with the laser light to form a laser point for processing.

1‧‧‧laser processing device

3‧‧‧ chuck table (holding means)

3a‧‧‧ holding surface (workpiece holding surface)

4‧‧‧Laser light irradiation means

13‧‧‧ indexing feeding means

16‧‧‧Y-axis table

20‧‧‧ Processing feed means

21‧‧‧X-axis table

27‧‧‧Supporting mechanism (means for adjusting the position of the light spot)

29‧‧‧Y-axis table

33‧‧‧Z axis table

42‧‧‧ Laser Oscillation Means

43‧‧‧ Optical System

44‧‧‧ Concentrator

45‧‧‧wavelength conversion mechanism

50‧‧‧ camera means

60‧‧‧Control means

61‧‧‧means of memory

AC‧‧‧Approximation curve

LS‧‧‧Laser Point

LS－V‧‧‧ the most similar degree of light spot on the approximate curve

TS‧‧‧ Inspection Wafer

W‧‧‧ Wafer (workpiece)

FIG. 1 is a perspective view showing an example of a laser processing apparatus according to this embodiment.

FIG. 2 is a block configuration diagram of a laser ray irradiation means installed in the laser processing apparatus.

FIG. 3 is a partially enlarged plan view of a wafer subjected to a laser spot forming step.

FIG. 4 is a perspective view of a plurality of laser points with different focusing positions formed in the laser point forming step in the focus position detection method of the embodiment.

FIG. 5 is a graph showing the similarity determination mode of the image data of each laser point and the reference data.

Claims (2)

A method for detecting a focus position of a laser ray, detecting the focus position of the laser ray irradiated by the laser ray irradiation means in a laser processing device, the laser processing device includes: Holding means The laser light irradiation means includes a condenser that irradiates the laser light from the upper surface side of the workpiece held by the holding means and forms a condensing point; Condensing point position adjusting means, so that the condensing point of the laser light formed by the concentrator moves in a direction perpendicular to the workpiece holding surface of the holding means; A processing feed means to relatively move the holding means and the laser light irradiation means in the processing feed direction; An imaging means for photographing an upper surface of a workpiece held by the holding means; and Means of control, The focus detection method of the laser light includes: An inspection wafer mounting step, placing inspection wafers having flat front and back surfaces on the holding means; A laser spot forming step, after performing the wafer mounting step for inspection, changing the laser beam focusing position multiple times within a predetermined range in a vertical direction sandwiching the upper surface position of the wafer for inspection and positioning Continuously irradiating the pulsed laser light having a wavelength absorptive to the wafer for inspection with a gap between adjacent laser points, and forming a plurality of laser points at a plurality of condensing positions within a predetermined range; as well as The focus position determining step. After implementing the laser point forming step, the laser points of each light collecting position are captured by the imaging means, and the laser points are captured from the captured laser point image by the control means. For the shape, the similarity between each shape and the ideal laser point shape memorized in the memory means is calculated according to the respective condensing positions, and the condensing position with the maximum similarity is determined as the focus position. The method for detecting a focal position of a laser ray according to item 1 of the scope of patent application, wherein: In the focus position determining step, an approximation curve of the similarity degree of each condensing position is calculated, and a condensing position of a maximum similarity degree in the approximation curve is determined as the focus position.