KR20130125438A - Laser machine using ultra - short pulse laser by single photon absorption - Google Patents

Abstract

The present invention relates to a laser processing apparatus using the single photon absorption of an ultra-short pulse laser, wherein the laser processing apparatus forms a modified area due to the single photon absorption by irradiating an ultra-short pulse laser (1 x 10^-18 to 1 x 10^-12) beam to a local portion inside a workpiece (A), thereby easily performing a precise processing process, gaining a uniform processed section, and performing various pattern processing processes through a circular interpolation processing process. The laser processing apparatus according to the present invention comprises: a work stage on which the workpiece (A) is put and having a chuck table (111) of which the x- and y-axial movements are simultaneously controlled; a laser source (120) being installed at the work stage (110) and irradiating the ultra-short pulse laser beam to the surface of the workpiece (A); scanners (130) being respectively formed in the front and the rear side of a processing direction based on the laser beam irradiated to the surface of the workpiece and measuring the surface height variation of the workpiece (A) put on the chuck table (111); and a control part (140) receiving data corresponding to the surface height variation of the workpiece (A) from the scanners (130) and controlling the focal point of the laser source (120) in real time in order to form the modified area at a position which is separated from the surface of the workpiece (A) at a certain distance.

Description

Laser machine using ultra-short pulse laser by single photon absorption

The present invention is a modified area by a single photon absorption by irradiating an ultra short pulse laser (1x10 ^-18 ~ 1x10 ^-12 s) light to a local portion inside the workpiece (A) The present invention relates to a laser processing apparatus using single photon absorption of an ultra-short pulsed laser, which enables easy processing of precision and obtains a uniform processing cross section, and enables processing of various patterns through circular interpolation processing. .

Applications of the laser are diverse, such as cutting / dicing, welding, drilling, and the like.

Among them, for example, cutting of wafers (sapphire, quartz, silicon substrates, etc.), glass substrates such as LCD, (O) LED, ITO (Indium Tin Oxide), etc. are required for each chip unit or generation of cutting lines is required. After irradiating the laser light of the wavelength having the maximum absorption to the point where it is absorbed, and then performing the melt heating on the back side of the workpiece at the point where the cutting or cutting line is generated by the absorption of the laser light to cut or generate the cutting line The way to make it is representative.

However, in such a cutting method, since the region around the cut part of the workpiece is also heated by melting, the workpiece may be damaged in the case of a semiconductor wafer or a glass substrate. In addition, since the cutting method has a very large average energy input (incident averaged energy), the heat damage of the workpiece itself is large.

As one of methods for preventing melting of the surface of the workpiece, a laser processing method using multi-photon absorption disclosed in Korean Patent Publication No. 10-66746 and European Patent EP1338371 is known.

According to this processing method, in the case of a silicon substrate, as shown in FIG. 1, an ultra-short pulsed laser light B having a peak power density of 1 × 10 ⁸ W / cm 2 or more and a pulse width of 1 mW or less is focused inside. When irradiated, optical damage by multi-photon absorption occurs inside the work piece A, and the modified area 1 is formed inside the work piece A by the optical damage. A local crack area is created inside the. By making this crack area along the line to be cut, it is possible to divide or cut the work piece A with a small force after machining in principle.

Here, "multiphoton absorption" refers to the excitation state when two or more photons are absorbed at the same time when a strong laser light is irradiated to a material to be processed. It is a phenomenon that emits higher energy (photons) than the energy of and returns to the ground state. On the other hand, "single photon absorption" refers to a phenomenon in which only one photon is absorbed into an excited state and returns to the ground state while emitting photons of a unique laser wavelength.

In addition, the peak power density (W / cm 2) is obtained by (energy per pulse at the focus) ÷ (beam spot cross-sectional area × pulse width) .In the case of a silicon wafer, the peak power density is generally 1 × 10. ^It is reported that absorption by multiple photons occurs at ⁸ W / cm 2 or more.

However, in the laser processing method using the multi-photon absorption as described above, when the laser light (B) is irradiated to the local region inside the workpiece (A), the overlap due to any pulse collision or polarization state (random) As the polarization state increases, the temperature of the reformed region 1 rapidly increases, and nonlinear absorption occurs. Since the pulse repetition rate is very large, the previous pulse and the subsequent pulse overlap each other, so that the pulse region of the reformed region 1 As the temperature rises rapidly, nonlinear absorption occurs, and as a result, cracking or chipping due to stress occurs at the processing point.

In other words, when high energy is concentrated in a narrow space by using an ultra-short pulse laser, the photon of the preceding pulse and the following pulse randomly collides with each other, which causes an undesirable nonlinear phenomenon due to temperature rise. . In addition, the random pulse superimposition phenomenon becomes deeper as the moving speed of the laser is slower, the focal diameter of the laser light B is larger, and the pulse repetition rate is larger.

In addition, since the heat generated during the processing by the arbitrary pulse overlap is accumulated in the workpiece (A), while melting to the periphery beyond the target cutting line, the processing precision and characteristics are greatly deteriorated, which acts as a very disadvantageous factor in the precision processing.

On the other hand, as shown in Figure 2, the conventional laser processing method follows a discontinuous linear processing method.

That is, since the surface of the work piece A has a slight height deviation, the laser light B should always be focused within a predetermined distance. Therefore, when work is started, the work piece A is cut along one side of the cutting line. The scanner 130 measures the surface height deviation of the workpiece A while moving in the direction, and when the scanning process is completed, the laser light source operates and moves along the cutting schedule line, thereby processing is performed. The scanner returns to its original position after the machining is completed.

At this time, the control unit receives the surface height deviation data of the workpiece (A) from the scanner 130 to change the focus position of the laser in the vertical direction in accordance with the laser movement position while the laser light at a constant distance from the surface of the workpiece (A) Control to be processed.

In the conventional laser processing method, the processing section is limited to a straight line, and the scanning and laser processing processes are separately formed, so that the workpiece A reciprocates the processing section while repeatedly moving and stopping. As a ramping section in which the feed speed of the workpiece A is decelerated is generated, the machining speed is lowered and the interference of laser light is concentrated in the deceleration section.

The present invention has been made to solve the above problems, single-photon absorption of the ultra-short pulse laser that can perform a rapid and precise processing without generating cracks or chipping due to stress in the processing point through the continuous processing It is an object to provide a laser processing apparatus using.

In order to achieve the above object, the laser processing apparatus using the single photon absorption of the ultra-short pulse laser of the present invention, the work stage is provided with a chuck table on which the workpiece is placed and the movement in the x-axis, y-axis direction is controlled simultaneously; An ultra-short laser light source installed on the work stage to induce single photon absorption by increasing the pulse repetition rate on the surface of the workpiece in Mhz units; A scanner which is provided at the front and the rear in the processing direction on the basis of the laser light irradiated onto the surface of the workpiece to measure the surface height deviation of the workpiece placed on the chuck table; And a control unit which receives the surface height deviation data of the workpiece A from the scanner and controls the focal position of the laser light source in real time so that a modified region can be formed inside a predetermined distance from the surface of the workpiece. It features.

In addition, the scanner may be composed of a light to illuminate the surface of the workpiece, and the camera to monitor the surface state of the workpiece through the illumination.

In this case, the controller may compare the data photographed by the camera with the initial focus position of the laser light to correct the height of the condenser lens in real time so that the focus of the laser light is placed at the correct processing position.

In addition, in one direction of the work stage, it is preferable that a first transfer part on which workpieces are mounted, and a second transfer part on which processed objects are mounted.

In this case, between the first and second transfer parts and the chuck table, the operation of placing the workpiece mounted on the first transfer part on the chuck table and the operation of mounting the finished object placed on the chuck table on the chuck table are sequentially performed. The carrying robot can be installed.

And the transfer robot, the rotating body portion is installed to be rotatable; A transfer arm having a scalar arm structure installed on the rotating body part and rotating together with the rotating body part and moving forward and backward in a straight line by stretching; And an end effector formed at the tip of the transfer arm to hold the workpiece.

Meanwhile, a reflection mirror may be further provided between the beam expander and the condenser lens to convert the direction of the laser light output from the beam expander to the condenser lens side.

In addition, the chuck table is configured to be freely moved in the x-axis and y-axis through the x-axis feed unit and the y-axis feed unit, the x-axis feed unit and the y-axis feed unit to perform circular interpolation without stop and deceleration It is preferable to be controlled simultaneously in real time through the control unit.

The present invention configured as described above minimizes dispersion when the laser light is focused in the absence of a nonlinear phenomenon by increasing the pulse repetition rate of the ultra-short pulsed laser light source using single photon absorption in MHz units. The lens can be used to collect strong pulse intensity in small spot sizes. Therefore, the beam quality characteristics at the point where the focus is made is excellent, there is an effect that can greatly increase the processing speed and quality in the processing of the wafer or glass substrate.

In addition, the present invention is to control the x-axis and y-axis of the work stage at the same time to enable circular interpolation processing, while simultaneously mounting the scanner on both sides of the laser light source to move back and forth to measure the height deviation of the workpiece surface and laser processing at the same time Since it is configured to make, unlike the prior art it is possible not only to process a variety of patterns, but also to increase the processing speed greatly by the non-deceleration, non-stop processing, and linearly, linear absorption, etc., the processing accuracy is greatly increased.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the state in which the laser processing using general multi-photon absorption is performed.
2 is a diagram illustrating a process in which laser processing using a general multi-photon absorption is discontinuously straight;
Figure 3 is a perspective view of a laser processing apparatus using single photon absorption of the ultrashort pulse laser of the present invention.
Figure 4 is a side view of Figure 3;
Fig. 5 is a front view of Fig. 3; Fig.
6 is a view showing a process of performing circular interpolation and continuous processing through a laser processing apparatus using a single photon absorption of the ultra-short pulse laser of the present invention.

The features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments based on the accompanying drawings. Prior to this, terms and words used in the present specification and claims are to be interpreted in accordance with the technical idea of the present invention based on the principle that the inventor can properly define the concept of the term in order to explain his invention in the best way. It must be interpreted in terms of meaning and concept.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings, the same reference numerals are used for the same configuration, and only the different parts will be mainly described so as not to overlap for clarity.

As shown in Figures 3 to 5, the present invention is a work stage 110 having a chuck table 111 in which the workpiece (A) is placed and the movement in the x-axis, y-axis direction is controlled at the same time, and the work stage The laser light source 120 installed at 110 and irradiating the ultra-short laser light to the surface of the workpiece A and the chuck table are provided at the front and rear of the machining direction based on the laser light irradiated to the surface of the workpiece. Scanner 130 for measuring the surface height deviation of the workpiece (A) placed on the (111) and the surface height deviation data of the workpiece (A) in real time from the scanner 130 receives a predetermined distance from the surface of the workpiece (A) The controller 140 is configured to control the focus position of the laser light source 120 in real time so that a modified region may be formed at a remote location.

The work stage 110 is provided with a chuck table 111 to which the workpiece A is placed and fixed, and the chuck table 111 is x through the x-axis transfer unit 112 and the y-axis transfer unit 113. It is installed to move the axis and y axis freely. The x-axis conveying unit 112 and the y-axis conveying unit 113 are transfer devices such as an L guide or a ball screw installed in the lower part of the chuck table 111, and are installed to enable simultaneous control through the control unit 140. .

In this embodiment, the chuck table 111 is fixed to the upper portion of the y-axis transfer unit 113, the y-axis transfer unit 113 is installed on the x-axis transfer unit 112 and installed to be movable on the x-axis It was made.

As such, when simultaneous control of the x-axis feed unit 112 and the y-axis feed unit 113 becomes possible, the linear movement of the workpiece A placed on the chuck table 111 is possible as well as the curve movement, thereby performing circular interpolation. Pattern processing of various shapes is possible. In addition, since the chuck table 111 moves along the pattern without stopping, continuous processing is possible without deceleration section during processing.

The laser light source 120 is installed on the upper end of the vertical support 114 installed on the working stage 110 to irradiate the laser light of the ultra-short pulse in the horizontal direction.

When the glass is processed assuming that the laser light source 120 is a picosecond laser, at least the pulse repetition rate is 1 to 20MHz, the energy is about 20 to 50μJ and the interval between successive pulse trains is less than 1/5 of the light source focal diameter. It is desirable to have a small value (overlap between pulse trains <95%).

In addition, the objective lens is suitable for the condenser lens 150, and when the thickness of the workpiece is 50 to 150 μm, the numerical aperture (NA) is 0.5 to 1 or less, and the magnification is 50 to 100 times or less. good. In this case, the resolution of the laser light capable of distinguishing two adjacent points is maximized to 0.25 μm or less, thereby obtaining the best processing result.

In this case, in the workpiece A, a modified area is formed by single photon absorption. The energy per pulse of single photon absorption is larger than that of multi-photon absorption and does not collide with other photons. Therefore, when focused on, it is possible to collect strong light of 1TW / cm 2 or more at a spot size of 10 μm or less without dispersion.

Therefore, while the melt heating is prevented to the processing peripheral region, in the case of a wafer, a glass substrate, etc., precise processing is performed without any damage of the workpiece A due to unnecessary cleavage.

Although not shown, the vertical support 114 has an attenuator for controlling the output intensity of the laser light generated from the ultra-short laser 120 and the size of the light is enlarged according to the magnification, and the enlarged laser light is lensed. A beam expander is installed which arbitrarily controls the size of the light in accordance with the processing size using a system or the like.

In addition, a light collecting lens 150 is further provided on the upper part spaced apart from the chuck table 111 by a predetermined distance. The condenser lens 150 condenses the laser light that has passed through the beam expander. In this case, the controller 140 controls the operations of the attenuator, the beam expander, and the condenser lens 150.

The condenser lens 150 is installed in the z-axis transfer unit 160 provided at the center of the vertical support 114 to move in the vertical direction. The light collecting lens 150 collects the laser light passing through the beam expander inside the work piece A placed on the chuck table 111 so that inner scribing is performed.

On the other hand, between the laser light source 120 and the condenser lens 150, a reflection mirror 170 for converting the direction of the laser beam passing through the beam expander toward the condenser lens 150 is installed at an angle of 45 degrees. The reflection mirror 170 rotates the direction of the laser light incident in the horizontal direction by 90 ° to irradiate vertically toward the chuck table 111.

In addition, the present invention is a control unit for controlling the operation of the light collecting lens 150 so that the modified region (I) is formed along the moving direction of the chuck table 111 at a position away from the surface of the workpiece (A) by a predetermined distance 140. The control unit 140 is installed in the z-axis transfer unit 160 is installed so that the height can be adjusted together with the scanner 130 and the condenser lens 150.

The controller 140 inputs the information of the workpiece A and the processing type, and sets the position of the chuck table 111, the numerical setting of the attenuator and the beam expander, and the condenser lens based on the information. All operations and values of the associated equipment, such as height, location of 150, are controlled in real time.

In addition, the present invention is a scanner 130 consisting of a CCD camera 132 for photographing the surface of the workpiece (A) placed on the chuck table 111 and the illumination 131 installed a predetermined distance away from the top of the chuck table 111 It is provided. The illumination 131 and the CCD camera 132 are respectively installed at the front and the rear in the processing direction based on the laser light irradiated to the workpiece A. FIG. The scanner 130 is also installed in the z-axis transfer unit 160 to be height-adjustable together with the condenser lens 150.

The illumination 131 illuminates the work A placed on the chuck table 111, and the CCD camera 132 monitors the work state of the work A through the illumination 131. Measure the height difference of the surface and transmits it immediately to the control unit 140.

The controller 140 compares the data captured by the CCD camera 132 with the initial focusing position of the laser light, and corrects the height of the condenser lens 150 in real time so that the focus of the laser light is placed at the correct processing position. do.

Meanwhile, one side of the work stage 110 may further include a first transfer part 200 on which the workpieces A are mounted, and a second transfer part 300 on which the processed objects are mounted.

Between the first and second transfer parts 200 and 300 and the chuck table 111, the operation of placing the workpiece A mounted on the first transfer part 200 on the chuck table 111 and the finished workpiece A are completed. The transport robot 400 may be further installed to sequentially perform the operation of mounting the to the second transfer unit 300.

In this case, the transfer robot 400 is installed on the rotating main body 410 to be rotatable, and installed on the rotating main body 410 to rotate together with the rotating main body 410 and stretch in a straight line by stretching, It is preferable that the transfer arm 420 has a scalar arm structure that moves backward, and an end effector 430 formed at the tip of the transfer arm 420 to hold the workpiece A.

The present invention configured as described above is processed through the following process.

First, the transfer robot 400 draws out the workpiece A supplied through the first transfer unit 200 and places the drawn workpiece A on the chuck table 111. When the workpiece A is placed on the chuck table 111, the control unit 140 adjusts the attenuator, beam expander, condenser lens 150, and x-axis feed according to the conditions such as the thickness and processing depth of the workpiece A previously input. The operation of the unit 112, the y-axis transfer unit 113, and the like are overall controlled.

That is, the control unit 140 transmits a processing signal including a processing value calculated according to a previously input program toward the attenuator, the beam expander, and the condenser lens 150. The attenuator receiving the processing signal from the controller 140 adjusts the output intensity of the laser light, the beam expander adjusts the laser light irradiation range, and the condenser lens 150 is set to an appropriate height.

In addition, when the work A placed on the chuck table 111 is illuminated while the illumination 131 installed under the chuck table 111 is turned on, the CCD camera 132 is operated. The CCD camera 132 monitors the processing state of the workpiece A through the illumination 131.

When the preparation for processing is completed in this way, the laser light is irradiated horizontally from the laser light source 120. The laser light is passed through the attenuator and the beam expander, and the light emitted from the 45 ° reflecting mirror is turned to 90 °, and then the workpiece A on the chuck table 111 is passed through the condenser lens 150 positioned at the bottom of the reflecting mirror. Is irradiated perpendicularly).

In this case, assuming that the laser light irradiated to the workpiece A is a picosecond laser, the maximum peak density is 1TW / cm ² or more, and the pulse train interval is greater than 1/5 of the light source focal diameter, having a frequency of at least 1 MHz. Try to have a small value (pulse overlap <90%).

In this case, the laser light is irradiated to the workpiece A through the condenser lens 150 to focus the laser light within a predetermined distance from the surface of the workpiece A, and at this point, an ultra-short laser pulse is induced. Since single photon absorption occurs, the modified region is easily formed without increasing the temperature of the peripheral portion, thereby obtaining a fast and precise machining cross section.

In addition, the control unit 140 may freely move the chuck table 111 in the x-axis direction and the y-axis direction according to the previously input processing form, thereby expanding the reformed region according to the previously input processing pattern. Such processing is performed through simultaneous control of the x-axis transfer unit 112 and the y-axis transfer unit 113, so that circular interpolation processing is possible, thereby implementing various processing patterns and processing speed improvements.

In addition, when processing is started, the CCD camera 132 installed in the front of the processing direction with respect to the laser light source 120 measures the height deviation of the surface of the workpiece A and immediately transmits it to the controller 140, and the controller 140. ) Compares the data photographed by the CCD camera 132 with the initial focusing position of the laser light to appropriately change the height of the condensing lens 150 to correct the focus of the laser light at the correct processing position.

As shown in FIG. 6A, the present invention provides a surface scan of the processing section by the scanner 130 and laser processing by the laser light B passing through the condenser lens 150 simultaneously with the movement of the chuck table 111. Since it is made together, the movement path of the chuck table 111 is significantly shorter as compared to the conventional operation speed is made very quickly.

6B, when the processing direction is reversed, the opposite CCD camera 132 becomes the CCD camera 132 installed in front of the processing direction with respect to the laser light source 120. 132 measures and transmits the height deviation of the surface of the workpiece A toward the control unit 140. As described above, in the present invention, the CCD camera 132 is provided in the front and rear of the processing progress direction with respect to the condensing lens 150 and can be processed continuously without stopping the workpiece A. FIG.

6A and 6B, the dotted lines show the laser processing paths as expected lines and the solid lines show the lines on which the processing is completed.

On the other hand, the CCD camera 132 photographs whether the modified region is formed into a pre-input form and outputs the monitor in real time. And if the reformed area to be formed is out of a predetermined range from the pre-entered machining type by outputting a warning message to the manager.

After the process as described above, the workpiece A is processed in a state in which cracking is possible by refraction along the modified region, and the finished workpiece A is transferred from the chuck table 111 through the transfer robot 400 to the second transfer part. It is mounted on the (300) in turn and transferred to the subsequent process.

110 working stage 111 ... chuck table
112 ... x axis feed unit 113 ... y axis feed unit
114 Vertical support 120 Laser light source
130 ... scanner 131 ... lighting
132 CCD camera 140 Control unit
150 ... condensing lens 170 ... reflective mirror
160 ... z-axis transfer unit 200 ... 1st transfer unit
300 ... 2nd transfer part 400 ... transfer robot
410 ... rotating body 420 ... transfer arm
430 End Effector A Workpiece
B ... laser light

Claims (8)

A work stage having a chuck table on which a workpiece is placed and which movement in the x- and y-axis directions is simultaneously controlled;
An ultra-short laser light source installed on the work stage to induce single photon absorption by increasing a pulse repetition rate on a surface of a workpiece in MHz units;
A scanner which is provided at the front and the rear in the processing direction on the basis of the laser light irradiated onto the surface of the workpiece to measure the surface height deviation of the workpiece placed on the chuck table; And
And a controller for controlling the focus position of the laser light source in real time to receive the surface height deviation data of the workpiece from the scanner so that a modified region can be formed within a predetermined distance from the surface of the workpiece. Laser processing apparatus using single photon absorption of short pulse laser. The method of claim 1,
The scanner is laser processing apparatus using a single-photon absorption of the ultra-short pulse laser, characterized in that consisting of a light to illuminate the surface of the workpiece, and the camera to monitor the surface state of the workpiece through the illumination. The method of claim 2,
The control unit compares the data captured by the camera with the initial focus position of the laser light to correct the height of the condenser lens in real time so that the focus of the laser light is positioned at the correct processing position. Laser processing equipment. The method of claim 1,
One side of the work stage is a laser processing apparatus using a single photon absorption of ultra-short pulsed laser, characterized in that the first transfer portion on which the workpieces are mounted, and the second transfer portion on which the processed objects are mounted. 5. The method of claim 4,
Transfer between the first and second transfer unit and the chuck table sequentially performing the operation of placing the workpiece mounted on the first transfer unit on the chuck table and the operation of mounting the finished object placed on the chuck table to the second transfer unit Laser processing apparatus using a single photon absorption of ultra-short pulsed laser, characterized in that the robot is installed. 6. The method of claim 5,
The transfer robot,
Rotating body portion is installed to be rotatable;
A transfer arm having a scalar arm structure installed on the rotating body part and rotating together with the rotating main body part and moving forward and backward in a straight line by stretching; And
Laser processing apparatus using an ultra-short pulse laser, characterized in that the end effector formed on the tip of the transfer arm to hold the workpiece (A). The method of claim 1,
Laser processing apparatus using a single-photon absorption of the ultra-short pulse laser, characterized in that provided between the beam expander and the condenser lens for changing the direction of the laser light output from the beam expander toward the condenser lens side . The method of claim 1,
The chuck table is configured to freely move the x-axis and y-axis through the x-axis transfer unit and the y-axis transfer unit,
The x-axis transfer unit and the y-axis transfer unit is a laser processing apparatus using a single photon absorption of ultra-short pulsed laser, characterized in that simultaneously controlled in real time through a control unit to perform circular interpolation processing without stop and deceleration.

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