JP6308733B2 - Laser processing apparatus and manufacturing method - Google Patents

Description

  The present invention relates to a processing apparatus and a manufacturing method using laser light.

  Marking and the like are performed by irradiating a transparent material such as glass with a femtosecond laser. At this time, not only the surface of the glass but also the inside can be processed by adjusting the position so that the focal point of the laser beam is inside the glass.

JP2002-154845

  However, in order to perform the above-described processing using a femtosecond laser, a large output femtosecond laser is required.

  In addition, in order to change the depth of the processing site, physical position adjustment is necessary, so that there is a problem that adjustment is complicated or quick adjustment of the processing depth is difficult. It was.

  In addition, in the prior art described in Patent Document 1, although it has been disclosed that marking of various colors is performed by sequentially irradiating two types of laser beams, the above-described problems are not solved. It was.

  An object of this invention is to provide the apparatus and manufacturing method which process using the femtosecond laser of a small output.

(1) (6) A laser processing apparatus according to the present invention comprises an ultrashort light pulse laser irradiation means for irradiating an irradiation region of an object with an ultrashort light pulse laser, and an irradiation region of the object with an ultrashort light pulse laser. And a thermal effect laser irradiation means for irradiating the thermal effect laser in an overlapping manner.

  Therefore, even when processing is not possible or insufficient with only the ultrashort optical pulse laser, it can be appropriately processed.

(2) (7) The laser processing apparatus according to the present invention is characterized in that the ultrashort light pulse laser is a picosecond laser or a femtosecond laser.

(3) (8) The laser processing apparatus according to the present invention is characterized in that the thermal effect laser is a carbon dioxide gas laser or a YAG laser.

(4) (9) The laser processing apparatus according to the present invention is characterized in that the object has a property of transmitting the light of the ultrashort pulse laser.

  Therefore, internal processing can be performed.

(5) (10) The laser processing apparatus according to the present invention is characterized in that the processing depth is adjusted by adjusting the output of the thermal effect laser.

  Accordingly, since the processing depth and the like can be controlled by adjusting the output of the thermal effect laser without physically moving the focal point of the ultrashort optical pulse laser, rapid control is possible.

  In the present invention, the “ultrashort optical pulse laser” refers to a laser that emits light only in the picosecond or femtosecond order and is irradiated at certain intervals.

  “Thermal effect laser” refers to a laser capable of generating a thermal effect such as a thermal lens in the vicinity of an irradiation area of an object, and is any of a continuous wave laser and a pulsed laser as long as such an effect is generated. May be. The “continuous wave laser” refers to a laser beam that is continuously irradiated with a laser beam, and includes a concept in which a duty ratio is adjusted for output adjustment or the like. In the embodiment, a carbon dioxide laser corresponds to this.

It is a figure for demonstrating formation of the thermal lens by a carbon dioxide laser. It is a figure for demonstrating formation of the thermal lens by a carbon dioxide laser. It is a figure which shows the structure of an apparatus. It is an image which shows the effect of a thermal lens. FIG. 5A shows an image when surface ablation occurs (FIG. 5A) and FIG. 5B shows an image when refractive index change occurs inside. FIG. 6A shows an image when surface ablation occurs (FIG. 6A), an image when refractive index change occurs inside (FIG. 6B), and an image when both occur (FIG. 6C). It is a figure which shows the change of the processing state at the time of changing the energy of a femtosecond laser pulse, and the output of a carbon dioxide gas laser beam. It is a figure which shows the processing state (FIG. 8B) at the time of using together a processing state only with a femtosecond laser (FIG. 8A), and a carbon dioxide gas laser. FIG. 9A is a diagram illustrating the relationship between the pulse energy of a femtosecond laser and the size of a processing mark. FIG. 9B is a diagram showing the relationship between the output of the carbon dioxide laser and the size of the machining mark. It is a graph which shows the increase rate of the process trace at the time of using a carbon dioxide laser together. It is sectional drawing of a processing state. It is a figure which shows the relationship between the output of a carbon dioxide laser, and processing depth. It is a figure which shows the relationship between the output of a carbon dioxide laser, a scanning speed, and a processing state. It is a figure which shows the processing state by the femtosecond laser and a hybrid laser at the time of scanning. It is a figure which shows the relationship between a scanning speed and a process state. It is a figure which shows the relationship between a scanning speed and a process trace width. It is a figure which shows the processing state in the case of using together a carbon dioxide gas laser, and the processing state in the case of only a femtosecond laser.

  The inventors irradiate a femtosecond laser by irradiating a carbon dioxide gas laser (continuous wave laser whose duty ratio can be adjusted), which is a thermal effect laser, on a femtosecond laser in the processing part of the object or in the vicinity of the processing part. It was found that the machining capability by the improved. In other words, it was possible to perform processing even with a small output femtosecond laser.

  This is presumed to be because molecular bonds are easily broken by the femtosecond laser due to the vibration of the molecules by the carbon dioxide laser.

  It was also found that the processing depth and width can be controlled by changing the output of the carbon dioxide laser. This seems to be because a thermal lens is formed in the air and in the object by the carbon dioxide laser.

  FIG. 1 schematically shows a thermal lens formed by a carbon dioxide laser. As shown in Table 1, since air has a negative density change with a rise in temperature, when heated by a carbon dioxide laser, the density of the portion becomes lower than that of the surrounding area, and the concave lens 2 is formed. When the object is glass, the density change with respect to the temperature information is positive, so that the convex lens 4 is formed.

  Accordingly, as shown in FIG. 1, the femtosecond laser is normally focused as indicated by a solid line 6, but the focusing position is changed by a concave lens 2 and a convex lens 4 as indicated by a broken line 8. Since the refractive indexes of the concave lens 2 and the convex lens 4 vary depending on the output of the carbon dioxide laser, the processing position and range of the femtosecond laser can be controlled by controlling the output of the carbon dioxide laser.

  In the above, a femtosecond laser is used as an ultrashort optical pulse laser, but other ultrashort optical pulse lasers such as a picosecond laser can also be used. Further, instead of the carbon dioxide laser, a continuous wave laser such as a YAG laser may be used. Further, a pulse wave laser (preferably one having a pulse output period longer than μ seconds) may be used as the thermal effect laser.

1. Outline Ultrashort light pulses have a very short pulse width and a very high peak power, so they have great potential for applications such as processing of three-dimensional shapes. When an ultrashort light pulse is collected in a transparent material, the intensity in the vicinity of the focal point becomes very large, causing non-linear absorption phenomena such as multiphoton ionization and tunnel ionization, and further transparent locally by subsequent avalanche ionization. The molecular structure in the material can be changed. This structural change due to laser excitation is mostly caused by refractive index changes and scattering damage depending on the light collection conditions, the type of material to be processed, and the laser parameters (wavelength, pulse width, incident pulse energy, repetition frequency, etc.). ) And voids (voids, voids). In particular, if the refractive index changing region is formed one-, two-, or three-dimensionally inside the transparent material by a computer-controlled automatic stage, three-dimensional such as an optical waveguide, an optical coupler, a lens, or a diffraction grating is formed inside the transparent material. Optical devices can be made.

  For three-dimensional microfabrication inside transparent materials, a single ultrashort optical pulse laser has been used since Davis et al. Produced a waveguide using a refractive index change by laser excitation in 1996. . This single ultrashort optical pulse laser can output optical pulses with high pulse energy, various wavelengths and repetition frequencies, and can also convert the wavelength of the output ultrashort optical pulse later. Amplified mode-locked titanium / sapphire femtosecond lasers are commonly used. When this ultrashort light pulse having a repetition frequency of 1 kHz to 200 kHz is condensed and irradiated inside the glass, structural changes having different characteristics can be induced according to two threshold values. Between the first threshold value and the second threshold value, a refractive index change having a small refractive index change amount is induced. In a region exceeding the second threshold value, scattering damage occurs, and a structural change having a large refractive index change amount can be obtained. Moreover, if an ultrashort light pulse is condensed inside the transparent material by an objective lens having a high numerical aperture, a void can be generated. This void is said to have a shape in which a low density portion is surrounded by a high density shell.

  Next, if a high-repetition ultrashort optical pulse laser is used in which the ultrashort optical pulse irradiation pulse interval is shorter than the thermal diffusion time from the vicinity of the condensing point, the structural change caused by heat accumulation in the vicinity of the condensing point. Regions can be formed. The size of the structural change region depends on the number of applied pulses since the structural change mechanism is heat accumulation. Furthermore, since a high repetition ultrashort optical pulse laser can supply a large number of pulses in a single time, high-speed micromachining can be realized as compared with a low repetition ultrashort optical pulse laser. To date, there have been reports of structural changes into the glass using cavity-dumped titanium sapphire lasers with repetition rates higher than 5 MHz. Here, the cavity dumper outputs the light after the regenerative amplifier amplifies the light from the oscillator, whereas the spontaneous emission light generated in the crystal is amplified without the need for the light from the oscillator, This is taken out after amplification. Recently, optical waveguides have also been fabricated using picosecond or femtosecond high repetition rate fiber laser systems, which have superior reliability and stability compared to titanium sapphire laser systems and are highly useful. It has been broken.

These studies revealed the correlation between ultrashort light pulses from a single laser source and transparent materials, but the correlation between ultrashort light pulses from a single laser source and continuous wave lasers and transparent materials. Is not shown. Here, we investigate the laser-induced structural changes in BK7 glass when a femtosecond fiber laser with a high repetition frequency and a continuous-wave oscillation CO2 laser are applied to BK7 glass processing.

2. Principle of Micro Machining Using Femtosecond Laser and Carbon Dioxide Laser FIGS. 2A and 2B show the principle of laser micro machining using a femtosecond laser and a carbon dioxide gas laser system. When the ultrashort laser pulse is condensed on the surface of the transparent material, nonlinear absorption occurs near the focal point, photoionization occurs, and microplasma is formed. With this microplasma, the transparent material near the focal point can be locally processed. This time, since the focal point is the surface of the transparent material, ablation occurs on the material surface (see FIG. 2A). Next, when a carbon dioxide laser beam and a femtosecond laser pulse are simultaneously irradiated onto the material, a thermal lens effect is generated. The thermal lens effect, first reported by Gordon et al., Arises due to the temperature dependence of the refractive indices of the two media around the laser irradiation area. In general, the intensity distribution of a light beam in a plane perpendicular to the optical axis can be characterized as a Gaussian distribution. That is, when a Gaussian beam that is symmetrical in the radial direction along the laser beam path is absorbed by the material, the heat generated in the material also has a Gaussian distribution that is symmetrical in the radial direction. Also, many materials have a refractive index that decreases with increasing temperature. Therefore, the central part of the light irradiation part where the temperature is highest has the lowest refractive index.

As shown in Table 1 above, the temperature coefficient of glass is positive and the temperature coefficient of air is negative. Furthermore, the absolute value of the temperature coefficient of glass is greater than that of air. Thus, in the case of air and glass, the thermal lens will have a negative focal length and the focal position of the femtosecond laser pulse will move inward from the surface of the glass material (see FIG. 2B). This results in local structural changes inside the glass instead of ablation.

3. Apparatus FIG. 3 shows the configuration of the apparatus. The three-dimensional stage 10 is movable in the XYZ directions by computer control. An object 12 is placed on the three-dimensional stage 10. Laser light from the femtosecond laser 26 passes through the half-wave plate 28, the polarizing plate 30, and the shutter 32, is reflected by the dichroic mirror 20, and is irradiated onto the object 12 through the objective lens 18. Laser light from the carbon dioxide laser 14 is reflected by the mirror 16 and applied to the object 12. The dichroic mirror 20 can reflect femtosecond laser light and transmit visible light. Therefore, the camera 24 can image the surface or the inside of the object 12. That is, the situation of the object 12 can be monitored by the camera 24.

  In this example, an Fianium FP1060S-PP-D was used as the femtosecond laser 26. This can output a femtosecond laser pulse with a wavelength of 1.06 μm. The pulse width is 250 fs. The maximum output pulse energy is 2 μJ. The pulse energy can be adjusted by rotating the half-wave plate 28 in front of the polarizing plate 30. Since the repetition frequency is 1 MHz, the effect of heat accumulation can be given to the BK7 glass. Here, S-BSL7 manufactured by OHARA Inc. was used as the BK7 glass. Details of the characteristics are shown in Table 2.

As the carbon dioxide laser 14, H48-1-28SW manufactured by Kantum Electronics was used. The carbon dioxide laser 14 outputs a continuous wave laser beam having a wavelength of 10.6 μm. The maximum output is 10 W. The laser output can be controlled by changing the duty ratio of an electric pulse signal applied to a driver device (not shown) for driving the carbon dioxide laser. The object 12 (using glass here) is cleaned and placed on a three-dimensional stage 10 controlled by a computer. A femtosecond laser pulse is condensed on the surface of the object 12 by an objective lens 18 (Olympus, LMPlan20 × IR) having a numerical aperture of 0.40 and 20 times. In order to obtain a linear structural change region on the object 12, the focal point of the femtosecond laser pulse is moved 1 mm along the X axis at a speed of 0.1 mm / s. In the structural change region by laser excitation, the XY plane of the object 12 can be observed by irradiating the object 12 with a white light source (not shown) and capturing the transmitted light with the camera 24. Further, by changing the position of the camera 24, the XZ plane of the object 12 can also be observed. Note that the camera 24 may not be provided when configured as a processing apparatus.

4). result
4.1 Effect of using carbon dioxide laser 14 together In order to confirm the effect of carbon dioxide laser 14, (i) when only femtosecond laser 26 is used, (ii) when both femtosecond laser and carbon dioxide laser are used (below) , Called a hybrid laser system), laser micromachining was performed on the object 12. The pulse energy of the femtosecond laser was set to 0.6 μJ. The output of the carbon dioxide laser was 3 W. FIG. 4 shows an image on the XY plane of the object 12 captured by the camera 24. FIG. 4A is an image of the object 12 when the carbon dioxide laser 14 is not irradiated. From FIG. 4A, the character “5” drawn on the surface of the object 12 can be clearly confirmed. FIG. 4B shows an image of the object 12 when the focal position of the camera 24 at this time is kept as it is and the carbon dioxide laser 14 is irradiated. It can be seen that the character “5” is blurred due to the thermal lens effect of the carbon dioxide laser 14.

  In FIG. 5, the image of the XY plane of the target object 12 after a process is shown. FIG. 5A shows the result when only the femtosecond laser 26 is used, and FIG. 5B shows the result when the hybrid system is used. In FIG. 5A, since irregular reflection occurs and it is black, it can be seen that when only the femtosecond laser 26 is used, ablation occurs on the surface. In the case of the hybrid system, the refractive index change region was formed inside without causing ablation on the surface. This is apparent from FIG. 5B, since the surface ablation has not occurred, and the region with the change in the refractive index is clearly displayed.

  FIG. 17 shows changes in the processing state when the energy of the femtosecond laser 26 is set to 0.525 μJ and the output of the carbon dioxide gas laser 14 is set to 0 W, 6 W, and 8 W. The focal point of the femtosecond laser 26 was adjusted so as to come to the surface of the object 12 in a state where the carbon dioxide laser 14 was not irradiated (a state where the output was 0 W).

  FIG. 17C shows the result when the carbon dioxide laser 14 is not used. The upper row is an image on the XY plane (lateral direction), and the lower row is an image on the XZ plane (depth direction). As is apparent from FIG. 17C, when the carbon dioxide laser 14 is not used together, a processing mark does not appear.

On the other hand, when the output of the carbon dioxide laser 14 is 6 W or 8 W, machining traces appear. As described above, it has been clarified that even when the processing cannot be performed because the output of the femtosecond laser 26 is small, the processing can be performed by using the carbon dioxide gas laser 14 together.

4.2 Changes in processing width due to the output of the carbon dioxide laser beam and the energy of the femtosecond laser pulse The state of processing by laser excitation (surface ablation, internal processing, intermediate) by changing the output of the carbon dioxide laser 14 and the energy of the femtosecond laser 26 Changes in the state (transition state from surface ablation to internal machining) were observed. The energy of the femtosecond laser 26 was changed to 0.60 μJ, 0.65 μJ, 0.70 μJ, and 0.75 μJ. The output of the carbon dioxide laser 14 was changed to 1W, 2W, 3W, and 4W.

  FIG. 6 shows an image on the XY plane of the processed object 12. 6A shows a state in which surface ablation has occurred, FIG. 6B shows a state in which internal processing has been performed, and FIG. 6C shows a state in which both have occurred (intermediate state).

  FIG. 7 shows a machining state obtained when the pulse energy of the femtosecond laser or the output of the carbon dioxide gas laser is changed. The cross mark is the surface ablation of FIG. 6A, the round mark is the internal machining state of FIG. 6B, and the square mark is the intermediate state of FIG. 6C. As can be seen from FIG. 7, by setting the output of the carbon dioxide laser 14 to 2 W or more, the focal position is changed from the surface of the object 12 to the inside, and it is understood that internal processing is performed.

  FIG. 8A shows an image on the XY plane of the object 12 obtained by focusing and processing only the light pulse of the femtosecond laser 26 inside the object 12. FIG. 8B shows an image in the case where the carbon dioxide laser 14 is irradiated in an overlapping manner without changing the energy of the femtosecond laser 26. As is apparent from FIG. 8, it can be seen that the processing marks are larger in the hybrid laser system than in the case of the femtosecond laser 26 alone.

  FIG. 9A shows a change in the size of a processing mark when the pulse energy is changed in processing of the femtosecond laser 26 alone. It can be seen that as the energy increases, the diameter of the machining mark also increases. In addition, FIG. 9A also shows that stable machining is performed because the same machining characteristics are obtained in the first to third experiments performed under the same conditions. FIG. 9B shows a change in the size of the processing mark when the carbon dioxide laser 14 is used in combination. It is shown that the diameter of the machining mark is increased by using the carbon dioxide laser 14 together. It is also clear that the diameter of the machining mark increases by increasing the output of the carbon dioxide laser used together.

FIG. 10 shows the processing mark diameter when the pulse energy of the femtosecond laser 26 and the output of the carbon dioxide gas laser 14 are changed. The energy of the femtosecond laser 26 is 0.9 μJ and the output of the carbon dioxide laser 14 is 1 W. The magnification obtained by dividing by the machining mark diameter is shown. As is apparent from FIG. 10, it can be seen that by increasing the output of the carbon dioxide laser 14, it is possible to dramatically increase the diameter of the machining mark as compared with the machining with the femtosecond laser 26 alone.

4.3 Changes in processing depth due to carbon dioxide laser beam output and femtosecond laser pulse energy Next, changes in the processing depth were examined by changing the output of the carbon dioxide laser 14 and the energy of the femtosecond laser 26. The pulse energy of the femtosecond laser was changed to 0.60 μJ, 0.65 μJ, 0.70 μJ, and 0.75 μJ. The output of the carbon dioxide laser 14 was changed to 1W, 2W, 3W, and 4W.

  In FIG. 11, the image of the XZ plane of the process trace formed in the target object 12 is shown. It can be seen that a processing mark 42, which is a processing region having a different refractive index, is formed under the glass surface 40, that is, inside the glass surface 40. Here, the depth from the surface 40 of the object 12 to the lower end of the machining mark 42 was measured as the depth.

  FIG. 12 shows the relationship between the pulse energy of the femtosecond laser 26, the output of the carbon dioxide laser 14, and the depth of the processing mark. It can be seen that as the output of the carbon dioxide laser 14 increases, the depth of the processing trace also increases. Similarly, it can be seen that as the energy of the femtosecond laser 26 increases, the depth of the processing trace also increases. However, when surface ablation occurred, even if the pulse energy of the femtosecond laser 26 was increased, no significant change was observed in the depth of the processing mark.

As described above, the output of the carbon dioxide laser 14 and the energy of the light pulse from the femtosecond laser 26 have an influence on the depth. That is, it is considered that when the output of the carbon dioxide laser increases, the curvature of the thermal lens changes, the numerical aperture of the thermal lens decreases, and the processing depth increases.

4.4 Changes in scanning speed and machining conditions When the output of the carbon dioxide laser 14 is changed to 1 W, 2 W, and 3 W, and the moving speed of the three-dimensional stage 10 (that is, the moving speed of the object 12 with respect to the laser beam) is changed. The processing state is shown in FIG. It can be seen that if the moving speed is high, a large carbon dioxide laser output is required to move from surface ablation to internal processing. This seems to be because the thermal effect by the carbon dioxide laser is sufficiently given when the moving speed is slow.

  FIG. 14A shows an image on the XY plane of the object 12 when internal processing is performed only with the femtosecond laser 26. FIG. 14B shows an image on the XY plane of the object 12 when internal processing is performed by the hybrid laser system. Here, the scanning speed was 1.0 mm / s, the pulse energy of the femtosecond laser 26 was 1.0 μJ, the focal depth of the optical pulse from the surface of the object 12 was 200 μm, and the output of the carbon dioxide laser 14 was 3 W.

As apparent from FIG. 14, the processing width of the hybrid laser system is wider than that of processing using only the femtosecond laser 26. Next, FIG. 15 shows changes in the processing state when the scanning speed is changed under the same conditions using the hybrid laser system. From FIG. 15, it was found that the higher the scanning speed, the more uniformly the refractive index changes and the clean processing can be performed. Further, as shown in FIG. 16, the processing width becomes narrower as the scanning speed increases, but when the speed exceeds a certain speed (in FIG. 16, it exceeds 40 mm / s), the change in the descending width may disappear. It was revealed.

Claims (10)

An ultrashort optical pulse laser irradiation means for processing an object by irradiating an irradiation region of the object with an ultrashort optical pulse laser;
Thermal effect of superimposing a thermal effect laser on an output of the target so that a thermal lens is formed on the target in an irradiation region of the target and the focal position of the ultrashort optical pulse laser is deepened. Laser irradiation means;
A laser processing apparatus comprising: In the laser processing apparatus of Claim 1,
The ultrashort optical pulse laser is a picosecond laser or a femtosecond laser. In the laser processing apparatus of Claim 1 or 2,
The laser processing apparatus, wherein the thermal effect laser is a carbon dioxide laser or a YAG laser. In the laser processing apparatus in any one of Claims 1-3,
The laser processing apparatus, wherein the object has a property of transmitting light of an ultrashort pulse laser. In the laser processing apparatus of Claim 4,
A laser processing apparatus for adjusting a processing depth or a processing area by adjusting an output of the thermal effect laser. Irradiate the irradiation area of the object with an ultrashort pulse laser,
By irradiating the thermal effect laser in an overlapping manner with an output that causes a thermal lens to be generated in the target and the focal position of the ultrashort optical pulse laser becomes deeper in the irradiation region of the ultrashort optical pulse laser of the target The manufacturing method of the laser workpiece which processes a target object. In the manufacturing method of Claim 6,
The ultrashort light pulse laser is a femtosecond laser. In the manufacturing method of Claim 6 or 7,
The manufacturing method, wherein the thermal effect laser is a carbon dioxide laser or a YAG laser. In the manufacturing method in any one of Claims 6-8,
The method according to claim 1, wherein the object has a property of transmitting laser light. In the manufacturing method of Claim 9,
A manufacturing depth or a processing area is adjusted by adjusting an output of the thermal effect laser.