JP2005014050A - Laser processing equipment - Google Patents

Abstract

A laser processing apparatus capable of positioning processing with very high quality and high accuracy is provided.
A table 12 on which a workpiece is placed, a laser oscillator 1 that outputs a pulsed laser beam 15, and an optical means 4 are provided, and the X-axis direction, the Y-axis direction, and the rotation direction in an orthogonal coordinate system are provided. The workpiece 13 is rotated by the signals from the driving means 6, 7, 8 for driving the table and the detection means 10, 11 for detecting the position of the workpiece, and the arrangement of the machining position and the X-axis direction or the Y-axis Control means 14 is provided for controlling the drive means 6, 7, and 8 so that the directions are matched and the laser light is relatively moved in this matched direction.
[Selection] Figure 1

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing apparatus using pulsed laser light.
[0002]
[Prior art]
A conventional laser processing apparatus will be described below.
[0003]
A conventional laser processing apparatus includes a laser oscillation device that outputs laser light, an optical unit that guides laser light output from the laser oscillation device to a workpiece, a detection unit that detects a target position of the workpiece, A worktable is placed on the X and Y axes and a table that can be moved is provided. During machining, both axes of the table are moved simultaneously, and laser beam is irradiated to the machining position by interpolation processing. (For example, see Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent No. 3257157 gazette
[Problems to be solved by the invention]
However, when processing with very high accuracy, when performing the interpolation process by moving the X axis and the Y axis at the same time, a processing error has occurred due to the interpolation resolution and the feed error of each axis.
[0006]
The present invention solves the above-mentioned conventional problems, and an object thereof is to provide means for realizing a required extremely high-quality and high-precision positioning process.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, a laser processing apparatus according to the present invention includes a table on which a workpiece is placed, a laser oscillator that outputs a pulsed laser beam, and an optical unit that guides the laser beam to the workpiece. A driving means for driving the table in the X-axis direction, the Y-axis direction, and the rotation direction in a Cartesian coordinate system, a detection means for detecting the position of the workpiece, and a workpiece from a signal from the detection means , The control means for controlling the driving means so that the arrangement of the processing position and the X-axis direction or the Y-axis direction coincide with each other and the laser light is relatively moved in the coincident direction, and the thickness of the workpiece With the configuration provided with the thickness detecting means for detecting the thickness, it is possible to provide means for realizing the required extremely high-quality and high-precision positioning processing.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0009]
FIG. 1 is a configuration diagram of a laser processing apparatus of the present invention.
[0010]
Reference numeral 1 denotes a laser oscillator that outputs pulsed laser light. The wavelength of the laser oscillator 1 is ultraviolet light of 400 nm or less, specifically, the third harmonic (wavelength 355 nm) and the fourth harmonic (wavelength 266 nm) of YAG. Further, there are YVO4 (vanadate) third harmonic and fourth harmonic as laser oscillators of the same wavelength, and YLF third harmonic and fourth harmonic of substantially the same wavelength can also be used. Lasers of this wavelength have high absorptance in many materials and can be processed. In addition, the use of ultraviolet light can suppress the thermal influence during processing, and it is possible to obtain good processing quality.
[0011]
The light output from the laser oscillator 1 is irradiated on the mask 3 after the beam diameter is converted by the collimator 2. The collimator 2 includes two lenses, and converts the beam diameter by adjusting the distance between the lenses. At the same time, combined with the mask 3, the amount of energy of the laser beam passing through the mask 3 can be controlled, and the energy of the processing point can be changed. Similar effects can be obtained by using a beam expander instead of the collimator.
[0012]
The mask 3 cuts out a part of the laser beam passing therethrough, and the laser beam is shaped to have the same beam diameter as that of the mask 3. At this time, the beam to be cut out is desirably 80% or less in order to stabilize the processing. This beam is reduced by the ratio of the focal length of the condensing lens 5 and the distance from the mask 3 to the condensing lens 5 and becomes the beam diameter of the processing point. By using the mask 3, the beam shape on the mask can be transferred to the processing point, so that stable processing is possible. The mask 3 is provided with a plurality of holes for shaping the beam shape, and the diameters of the holes are different. By selecting a mask with a different hole diameter, it is possible to change the beam diameter of the processing point. In addition, when the hole diameter is sufficiently larger than the beam diameter of the laser beam passing therethrough, the beam is not cut out by the mask, so the beam diameter at the processing point condensed by the condenser lens is as follows: Become.
[0013]
R = (1.22 × λ × F) D
R: Diameter of the condensing point λ: Wavelength D: Beam diameter incident on the condensing lens F: When changing the processing beam diameter without using the focal length mask 3 of the condensing lens, based on the above formula Adjustment is possible by changing the beam diameter entering the condenser lens 5. Further, by shifting the focal position, the beam diameter can be adjusted within a range larger than the diameter obtained from the above formula.
[0014]
The laser beam that has passed through the mask 3 is guided to the vicinity of the processing point by the bend mirror 4, condensed by the condenser lens 5, and irradiated onto the workpiece 13. The workpiece 13 has an orthogonal coordinate system in the X and Y directions and a table 12 that is driven in the rotational direction. The table 12 is moved in the horizontal direction of the drawing by the X direction driving means 6. Further, the table 12 is moved in the direction from the back to the front of the drawing by the Y direction driving means 7. Further, the table 12 is rotated on the XY plane by the rotation direction drive 8. Further, the machining head unit 14 mounted with the condenser lens 5, the position detecting means 10, the thickness detecting means 11 and the like is moved by the Z direction driving means 9 in a direction perpendicular to the XY plane of the table 12, The focus of the processing focus and position detection means 10 can be adjusted. Even if the X-direction driving means 6, the Y-direction driving means 7 and the rotational direction driving means 8 are configured not to move the table but to move the laser beam side, the same effect is obtained. Further, even if the entire table 12 is driven by the Z direction driving means 9, the same effect is obtained.
[0015]
When the table 12 on which the workpiece 13 is placed is moved by the X direction driving means 6 or the Y direction driving means 7, the workpiece 13 is moved relative to the laser beam, thereby being determined by the mask 3. Processing of the width of the beam diameter at the processing point is performed.
[0016]
In order to ensure the processing position accuracy, the reference mark provided on the workpiece 13 is detected by the position detection means 10 using a CCD camera, and the workpiece 12 is rotated when the table 12 is rotated and processed in the X direction. The X axis of the table 12 and the X axis of the table 12 are made to coincide with each other, positioning in the Y direction is performed, and the beam condensing point and the workpiece 13 are moved relative to each other in the X axis direction for processing. When machining in the Y direction, similarly to machining in the X direction, the Y axis of the workpiece 13 and the Y axis of the table 12 are made to coincide with each other, positioning in the X direction is performed, and the beam condensing point and the object to be covered in the Y axis direction The workpiece 13 is moved relative to the workpiece.
[0017]
The thickness detector 11 measures the distance from the table 12 to the surface of the workpiece 13 in order to place the workpiece 13 at a focal position physically determined by the beam incident on the condenser lens 5. To do. FIG. 1 shows a contact type detection means. First, the position of the surface of the table 12 is contacted and detected by the thickness detecting means 11, and after the workpiece 13 is mounted on the table 5, the surface position of the workpiece 13 is detected by contact, and the difference is detected from the difference. The thickness of the workpiece 13 is detected. Since the workpiece 13 is adhered by the holding material 18, the thickness detector 11 measures not only the thickness variation of the workpiece 13 but also the thickness variation of the elastic holding material 18.
[0018]
As shown in FIG. 2, the workpiece 13 itself is composed of a silicon substrate 17 having a dielectric layer 16 on the surface and held by a holding material 18. The holding material 18 is held separately from the silicon substrate 17. A material frame 19 is disposed outside the silicon substrate 17, and in this laser processing apparatus, at least the dielectric layer 16 disposed on the surface is cut off by laser light.
[0019]
The table 12 is made highly rigid to ensure accuracy and is heavy. Therefore, it takes time to reach the optimum speed. Here, as shown in FIG. 3A, the table 12 is accelerated until the laser beam condensing position reaches a desired processing position of the workpiece 13, and the laser beam is kept at an optimum processing speed. Laser irradiation is performed at the stage where the condensing position has reached the desired processing position of the workpiece 13. Similarly, when the processing advances and the laser condensing point reaches the opposite side of the workpiece 13, the irradiation of the laser beam is stopped there, and the table 12 is decelerated. By irradiating the laser beam only on the workpiece 13, damage to the holding material 18 of the workpiece 13 due to the laser beam can be suppressed.
[0020]
As shown in FIG. 3B, a shielding means 20 that absorbs or reflects a laser beam is provided outside the desired processing range of the workpiece 13 on the frame 19 of the holding material. The table 12 is accelerated by irradiating the laser above until the focused position of the laser beam reaches the desired processing position of the workpiece 13, so that the moving speed of the table 12 reaches the optimum processing speed. When the table 12 is decelerated when it comes to the opposite side of the workpiece 13 and laser irradiation is stopped, damage to the holding material 18 of the workpiece 13 due to the laser beam can be similarly suppressed.
[0021]
Next, the processing speed will be described with reference to FIG. Assuming that the pulse output frequency of the laser oscillator is f, the laser beam diameter at the processing position is D, and the rate of overlap of the beam diameters is a, as shown in Equation 1, v = D × (1-a) × f By moving and moving the workpiece 13 relative to the laser condensing point at a speed, a groove having a width made up of the diameter of the laser beam at the condensing point can be performed as shown in FIG.
[0022]
5, 6, and 7 illustrate correction of a processing position for performing high-precision processing required for the semiconductor substrate that is the workpiece 13.
[0023]
The movement distance correction will be described with reference to FIG. The workpiece 13 and the table 12 both expand and contract slightly due to temperature changes. In order to correct this expansion and contraction, the positions of at least two reference marks arranged on the workpiece 13 are read. When there is a rotation error between the XY axis of the workpiece 13 and the XY axis of the table, both axes are matched by the rotation direction driving means 8. When the rotation is performed, the positions of at least two reference marks arranged on the workpiece 13 are read again. When the design value between the marks of the workpiece 13 and the measured mark interval are different as shown in FIG. 5, the workpiece 13 is expanded and contracted with reference to the movement on the apparatus side, position correction is performed, and X , Y drive means 6 and 7 are corrected and driven. By performing this correction separately for the X direction and the Y direction, correction with higher accuracy becomes possible. In FIG. 5, it is assumed that the design value is 100 mm and the actual measurement value is 101 mm. Here, it is assumed that the workpiece 13 has spread with reference to the axis of the apparatus, and the distance of the workpiece 13 and the movement distance of the apparatus are matched by moving the table 12 longer than the design value.
[0024]
The position correction of the condensing point of the laser beam will be described with reference to FIG. The laser beam emission direction changes slightly depending on temperature and aging. In addition, optical components such as mirrors, masks, and lenses also change slightly due to temperature stress. Even if the table 12 operates with high accuracy, if the condensing point of the laser beam is changed, the processing cannot be performed at a desired position. Therefore, the table 12 is moved so that the laser beam is positioned at a disposal location that is different from the processing position of the workpiece 13, and then a laser is irradiated to a predetermined location of the disposal location as a trial. The position detection means 10 detects the difference between the target position and the actual machining position as a deviation amount, and corrects the position based on the deviation amount so that the target value can be correctly irradiated with the laser during the original machining.
[0025]
In this manner, by instructing the X direction driving means 6 and the Y direction driving means 7 during the processing and processing the correction amount, it is possible to correct the variation in the beam condensing position. The correction of the beam condensing point in the X and Y directions may be performed by a configuration in which the laser emission direction can be changed by a control device other than the X direction driving means 6 and the Y direction driving means 7, or a mirror or the like. A similar effect can be obtained even if the optical component is made movable and can be changed by the control device.
[0026]
Next, position correction will be described with reference to FIG. A plurality of marks are arranged on the workpiece 13, and the machining position correction and rotation correction are performed using the marks. First, assuming that the XY axis of the table 12 and the XY axis of the workpiece 13 are greatly deviated and the position is largely deviated, the mark is confirmed with a wide-field camera. However, the range of the wide field of view is determined from the range in which the adjacent mark is not recognized and the variation in the positioning accuracy of the workpiece. In this apparatus, it is 5 mm square. Two marks are recognized within this range, and the amount of rotational displacement between the table 12 and the workpiece 13 is obtained. The obtained rotation amount is rotated by the rotation direction driving means 8 and the X axis of the table 12 and the X axis of the workpiece 13 are combined. Next, the mark is recognized again with the wide-field camera, and the amount of deviation in the X and Y directions is obtained. Here, at least one mark is recognized, and the deviation of the mark is corrected by using the X direction driving means and the Y direction driving means. Now that the rough correction has been completed, the four-point mark is recognized using a narrow-field camera in order to perform the next fine correction. In order to process in the X direction, the X direction of the table and the X direction of the workpiece are matched. For this purpose, the rotation of the table 12 and the workpiece 13 from two sets of marks that are separated in the X direction of the four marks. The amount is obtained, and the average is taken as the amount of rotational displacement, and the table 12 is rotated by the rotation direction driving means 8 so that the X-axis direction of the table 12 and the workpiece 13 is matched. Next, the four marks are recognized again, the respective amounts of deviation in the X and Y directions are obtained and averaged, and the position is adjusted using the X direction driving means 6 and the Y direction driving means 7. Depending on the required accuracy, the number of marks to be recognized for rotation amount alignment and position alignment is increased or decreased.
[0027]
Here, machining in the X direction is performed, and the XY axis of the table 12 and the XY axis of the workpiece 13 are moved to the machining in the Y direction, and the correction method is that the axis whose rotation angle coincides with that in the X axis direction. The description is omitted because it is the same. At this time, the rotation angle is almost the same, so that coarse adjustment by the wide-field camera is not necessary, and the recognition can be performed from the narrow-field camera.
[0028]
Further, when the rotation amount is obtained in the above-mentioned wide-field and narrow-field cameras, the displacement amount in the XY directions can be obtained at the same time. It is also possible to obtain the amount of displacement of the mark center position by the following procedure. First, the rotation amount to be obtained is θ, the center of the workpiece and the center of rotation of the table are the origin (0, 0), the mark position on the workpiece is (Xo, Yo), and the measured mark position Is (Xm, Ym), and the shift movement amount to be obtained is (x, y), the shift movement amount is obtained by the following equation.
[0029]
X direction deviation = cos θ × Xm−sin θ × Ym−Xo
Y direction deviation = sin θ × Xm + cos θ × Ym−Yo
It is possible to reduce the movement time and the number of times of recognition by simultaneously moving the rotation amount θ by the rotation direction moving unit 8 and the obtained shift amount by the X direction moving unit 6 and the Y direction moving unit 7 at the same time.
[0030]
FIG. 8 is a diagram showing an arrangement in which an optical system 21 for splitting a beam into two is arranged between the mask 3 and the condenser lens 5 in FIG. For this branching, spectroscopy using a diffraction grating such as a diffractive optical element (DOE) is used. As a result, it is possible to provide two condensing points at the machining point, and two grooves can be machined by moving the table once in one direction.
[0031]
Further, by using a diffraction grating in the optical system 21, two or more branches can be easily performed. Further, in the case of using two spectrums, it is possible to change the beam interval by changing the angle of the DOE as shown in FIG. 9, and it is possible to cope with the change of the groove interval.
[0032]
FIG. 10 shows the shape of the laser beam and the shape of the processed groove.
[0033]
When the Gaussian mode beam (a) is used, the wall surface can be tapered as shown in the figure. When a top hat beam having a uniform beam intensity and a steep surrounding beam is used in (b), the groove bottom can be widened and processing with less taper on the wall surface can be performed. When the cross-section of (c) is a mountain shape and a beam shape that is continuous in the depth direction with respect to the cross section is used, the beam depth direction is brought perpendicular to the relative movement direction of the laser condensing point and the workpiece, thereby increasing the width. Can be processed. Further, by rotating the beam depth direction with respect to the relative movement direction, the processing width can be varied.
[0034]
FIG. 11 illustrates a procedure for relative movement of the laser focusing point and the workpiece.
[0035]
The workpiece 13 is a semiconductor substrate, and chips called dies are arranged in a lattice pattern. As described above, when there are a plurality of positions to be processed in parallel, when the laser focusing point and the workpiece 13 are relatively moved in the X-axis direction, after the relative movement in the X direction (a direction), Moves the workpiece 13 in a different direction (b direction) and then moves the workpiece 13 in the opposite direction (c direction) to the relative movement direction of X that was moved first. By doing so, it is possible to shorten the dead time and to process one workpiece in a short time as compared with the case of processing from one direction.
[0036]
FIG. 12 shows the processing position of the workpiece. As described above, the workpiece 13 has chips arranged in a lattice pattern, and processes a street between the chips. When the laser processing width is wide, the entire street is processed at once, and when the laser processing width is narrow, both sides of the street are processed. This is performed as a pre-processing when the chip is separated after the laser processing. Thereby, the mechanical vibration at the time of cutting can be separated from the chip.
[0037]
【The invention's effect】
As described above, the present invention includes a table on which a workpiece is placed, a laser oscillator that outputs a pulsed laser beam, and an optical unit that guides the laser beam to the workpiece. A driving means for driving the table in the X-axis direction, the Y-axis direction, and the rotation direction, a detection means for detecting the position of the work piece, and a signal from the detection means, the work piece is rotated to change the machining position. Control means for controlling the driving means so that the arrangement and the X-axis direction or the Y-axis direction coincide with each other and the laser light is relatively moved in the matched direction, and thickness detection for detecting the thickness of the workpiece By providing the means, it is possible to provide means for realizing very high-quality and high-precision positioning processing required for a semiconductor substrate or the like.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an embodiment of the present invention. FIG. 2 is an explanatory diagram of a workpiece. FIG. 3 is an explanatory diagram of damage suppression of a holding material. FIG. 4 is an image of a processing width. FIG. 6 is a flowchart for correcting the position of the laser focusing point. FIG. 7 is an explanatory diagram for correcting the processing position. FIG. 8 is an explanatory diagram for laser light spectroscopy. FIG. 9 is an explanatory diagram for adjusting the processing width during laser spectroscopy. [Fig. 10] Beam mode and its cut shape diagram [Fig. 11] Explanatory diagram of relative movement procedure during machining [Fig. 12] Explanatory diagram of cutting after laser machining [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Collimator 3 Mask 4 Bend mirror 5 Condensing lens 6 X direction drive means 7 Y direction drive means 8 Rotation direction drive means 9 Z direction drive means 10 Position detection means 11 Thickness detection means 12 Table 13 Workpiece 14 Control device 15 Laser beam 16 Surface layer 17 including dielectric material Silicon substrate 18 Holding material 19 Holding material (frame)
20 Shielding means 21 DOE

Claims (21)

A table for placing a workpiece, a laser oscillator for outputting a pulsed laser beam, and optical means for guiding the laser beam to the workpiece, and rotating in an X-axis direction and a Y-axis direction in an orthogonal coordinate system A driving means for driving the table in the direction, a detecting means for detecting the position of the workpiece, and a signal from the detecting means to rotate the workpiece to arrange the processing position and the X-axis direction or the Y-axis. A laser processing apparatus provided with a control means for controlling the driving means so as to move the laser light relative to each other in the direction matched and a thickness detection means for detecting the thickness of the workpiece. The laser processing apparatus according to claim 1, wherein the wavelength of the laser beam is 400 nm or less. 3. The laser processing apparatus according to claim 1, wherein at least the dielectric layer of a semiconductor substrate having a dielectric layer formed on at least a surface thereof is processed as a workpiece. The laser processing apparatus according to claim 1, wherein the laser beam is irradiated only on the workpiece when the laser beam is relatively moved. 4. The laser processing apparatus according to claim 1, wherein a laser beam shielding means is provided outside the processing position of the workpiece. When the laser frequency of the laser beam is set to f, the beam diameter of the laser beam is set to D, and the overlapping ratio of the adjacent laser beams is set to a, the relative movement is performed at the relative moving speed v of the laser beam obtained from the relationship of (Equation 1) below. Item 6. The laser processing apparatus according to any one of Items 1 to 5.

7. The laser processing according to claim 1, wherein a difference between a distance set on the workpiece and a moving distance of the table is detected based on a signal from the detection means, and the driving means is controlled using the difference as a correction value. apparatus. When there are a plurality of processing positions arranged in parallel, the processing laser light is moved relative to each other, the workpiece is moved in a direction different from the direction in the X-axis direction or the Y-axis direction, and the processing laser light is moved relative to each other. The laser processing apparatus according to claim 1, wherein the laser processing apparatus is relatively moved in a direction opposite to the direction of. 9. The laser processing apparatus according to claim 1, wherein the optical means is provided with branching means for branching the laser light guided to the workpiece into a plurality of parts. The laser processing apparatus according to claim 1, wherein the beam mode of the laser beam is a Gaussian mode. The laser processing apparatus according to claim 1, wherein the beam mode of the laser beam is a top hat mode. The laser processing apparatus according to any one of claims 1 to 9, wherein the beam mode of the laser beam has a mountain-shaped cross section and is continuous in the depth direction with respect to the cross section. The laser processing according to any one of claims 1 to 12, wherein the processing position of the workpiece is provided between a plurality of desired regions of the workpiece and at a position where the desired region is separated after processing by laser light. apparatus. The mark according to any one of claims 1 to 13, wherein a plurality of marks indicating a reference position are provided at a predetermined position of the workpiece, the arrangement of the machining positions is detected from at least two of the plurality of marks, and the amount of rotation of the workpiece is determined. A laser processing apparatus according to claim 1. The image recognition means is used as the detection means, the position of the workpiece is obtained by detection in a visual field range in which at least two of the plurality of marks can be detected, and each mark is detected according to the position. Laser processing equipment. The laser processing apparatus according to claim 1, wherein a plurality of marks indicating reference positions are provided at predetermined positions of the workpiece, and a center position of the workpiece is detected from at least two of the plurality of marks. A plurality of marks indicating a reference position are provided at a predetermined position of the workpiece, the arrangement of the machining positions is detected from the plurality of marks, and the rotation amount of the workpiece and the correction amounts in the X-axis direction and the Y-axis direction are determined. Item 17. The laser processing apparatus according to any one of Items 1 to 16. The laser processing apparatus according to claim 1, wherein the optical means has a mask provided with a hole for shaping laser light into a desired beam shape. 19. The laser processing apparatus according to claim 18, wherein a plurality of holes for shaping into a desired beam shape are provided in the mask, and the plurality of holes are switched as necessary. The laser processing apparatus according to claim 18 or 19, wherein a collimator is provided between the laser oscillator and the mask, and the collimator is moved in the laser beam direction between the laser oscillator and the mask. The laser processing is performed on a portion different from the processing position of the workpiece, and the processing state is detected by the detecting means, and at least one of the laser oscillator, the optical means, and the driving means is controlled. Laser processing equipment.

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