JP5942558B2 - Microcavity formation method - Google Patents

Description

  The present invention relates to a method for forming a microcavity communicating with the outside by using a pulsed laser beam, and in particular, by locally condensing a workpiece such as silica glass by focused laser beam irradiation. The present invention relates to a method of forming a minute cavity such as a minute hole, a minute groove, and a minute recess by forming a modified region and removing the modified region by etching.

  Conventionally, a glass material having a minute cavity communicating with the outside such as a minute hole, a minute groove, and a minute recess is expected to be used as a micro nozzle, a biochip, a chemistry chip, or the like. The technique of forming a microstructure on glass using pulsed laser light, particularly femtosecond laser, has the advantage that it can be processed into a three-dimensional structure.

  As a technique for forming a microstructure on glass using a femtosecond laser, for example, a technique disclosed in Patent Document 1 is known. This technology focuses and irradiates a work piece made of a transparent material such as silica glass with a pulse laser beam having a pulse duration of femtosecond to picosecond order. Scanning at least one location including a position on the surface of the work piece, so that a modified region modified by irradiation with a pulsed laser beam is formed from the surface to the inside of the work piece. The modified region is formed and removed by etching with the surface as a starting point, thereby forming a hole in the trace from which the modified region has been removed.

  By the way, in the prior art, since the progress of the etching proceeds from the surface of the workpiece to the inside, the hole diameter becomes larger than the back side, the burrs are generated at the hole edge, especially in the vicinity of the etching solution inlet, There is a risk of quality deterioration, such as the shape becoming unstable or the surroundings of the hole being altered. In addition, when the modified region is formed by laser processing so as to include the front or back surface of the workpiece, the modified laser light causes irregular reflection or refraction at the front or back surface of the workpiece. There is a risk that the processing accuracy of the region is lowered.

  Therefore, in the prior art described in Patent Document 2, a modified region is formed only inside a flat workpiece by irradiation with pulsed laser light, and thereafter, a modified region on the front and back surfaces of the workpiece. An etching protective film is formed so as to cover the other part by opening the part corresponding to the above, and then the work piece and the etching protective film are immersed in an etching solution, and the front and back surfaces facing each other across the modified region The material between the openings is removed to form a through hole.

However, according to the latter prior art, the etching protection film must be formed leaving the opening at a specific position corresponding to the modified region, and the formation of the opening and the etching protection film itself requires accuracy. , It takes man-hours.
In addition, when the diameters of the opening and the modified region do not coincide with each other or are shifted, there is a possibility that a step is formed in the completed through hole or the coaxiality varies.

JP 2002-210730 A JP 2004-351494 A

  This invention makes it an example of a subject to cope with the said conventional situation. That is, in the formation of a microcavity exposed to the outside, the object of the present invention is to form a microcavity having a stable shape with high dimensional accuracy, to prevent deterioration of the quality around the microcavity, and to improve productivity. It is.

One means for solving the above-mentioned problems is a laser processing step of performing focused irradiation of pulsed laser light on a workpiece to form a continuous modified region not exposed to the outside in the workpiece, A machining process for forming an exposed portion in the modified region by removing a part of the workpiece by machining, and an etching for removing the modified region by etching from the exposed portion to form a microcavity It is seen including a step, and in the machining process, and forming a communication hole communicating with the reforming area in the workpiece by machining.
According to this microcavity forming method, in the laser processing step, pulse laser light is not focused and irradiated on the front surface or back surface of the work piece, so that only the inside of the work piece has a stable shape with high dimensional accuracy. A quality region can be formed.
In the machining process, an exposed portion is formed in the modified region only by machining without requiring a step of forming an etching protective film or a step of etching a portion other than the modified region of the workpiece. Can do.
Next, in the etching step, the modified region is removed by etching with the exposed portion as a starting point, so that a microcavity having a stable shape with high dimensional accuracy can be obtained as a trace of the removal.
In addition, the said machining means the process which cuts off a part of workpiece from the outside using a tool or a machine tool, and this machining includes grinding, polishing, and cutting, but laser processing Etching is not included.
Further, with this means, since only the portion communicating with the modified region is drilled in the workpiece, machining allowance is small and speedy machining with a good yield is possible.

  Another means is characterized in that a through hole is formed as the microcavity. The through hole is useful as, for example, a micro nozzle.

In another means, the machining is grinding, polishing or cutting as a processing method with particularly good productivity.
Here, the grinding includes lapping, surface grinding, honing, ultrasonic grinding and the like. The polishing process includes mechanical polishing, chemical mechanical polishing, barrel polishing, buff polishing, brush polishing, and the like. The cutting includes drill drilling, ultrasonic cutting, diamond cutting, milling, lathe processing, and the like.

In another means, in the machining step, the surface of the workpiece is removed with the same thickness by machining.
This means is particularly suitable for forming a straight hole as the microcavity.

In another means, after the laser processing step, the machining is performed only on one surface side of the workpiece to form the exposed portion in the modified region,
Next, the modified region is etched away by the etching process starting from the exposed portion to form the microcavity,
Next, the machining is performed on the other surface side of the workpiece to form the through hole.

  Since the present invention is configured as described above, the present invention includes forming a microcavity having a stable shape with high dimensional accuracy, preventing quality deterioration around the microcavity, improving productivity, etc. Can achieve the purpose.

It is a schematic diagram which shows an example of the microcavity formation method which concerns on this invention, (a) is the to-be-processed object before a process, (b) is the state which formed the modified area | region by laser processing, (c) is by machining A state in which the modified region is exposed, (d) shows a state in which a microcavity is formed. It is a schematic diagram which shows an example of a laser processing process. It is a schematic diagram which shows an example of an etching process. It is a schematic diagram which shows the other example of the microcavity formation method which concerns on this invention, (a) is the to-be-processed object before a process, (b) is the state which formed the modified area | region by laser processing, (c) is machining (D) shows a state in which a microcavity is formed. It is sectional drawing which shows an example which used the microcavity as the bottomed hole. It is sectional drawing which shows the other example which used the microcavity as the bottomed hole. It is a schematic diagram which shows the example of a change of the microcavity formation method of FIG. It is a schematic diagram which shows the example of a change of the microcavity formation method of FIG.

Hereinafter, particularly preferred embodiments of the present invention will be described in detail with reference to the drawings.
In the microcavity forming method of the present embodiment, as shown in FIGS. 1 to 3, a focused laser beam a emitted from a laser processing apparatus 20 is focused on the workpiece 10 and the workpiece 10 is irradiated with the focused laser beam. A laser processing step of forming a continuous modified region 11 not exposed to the outside, and a machining step of forming an exposed portion 11a in the modified region 11 by removing a part of the workpiece 10 by machining; And an etching step of forming the microcavity 12 by etching away the modified region 11 starting from the exposed portion 11a.

  The workpiece 10 is a flat transparent silica glass, and for example, a thin plate having a thickness of about several millimeters is used.

The laser processing apparatus 20 includes a light emitting source 21 that emits pulsed laser light a and a lens 22 that focuses the pulsed laser light a.
The pulsed laser light a needs to have a laser intensity that is equal to or higher than a processing threshold. Specifically, the pulse width of the pulse laser beam a can be 150 fs to 1 ps, a repetition period of 1 kHz to 300 kHz, a wavelength of 780 nm to 800 nm, and an average output of about 1 W can be used. In particular, in order to make the inner surface of the microcavity 12 smoother, it is preferable to increase the repetition period of the pulsed laser light a and to keep the laser intensity small.

As a more preferable pulse laser beam a, a pulse laser beam having a pulse width of 1 ps or less is used. This is because a laser with a short pulse width has a laser intensity of 10 TW / cm ² or more, and the silica glass absorbs a pulsed laser beam having the intensity to cause multiphoton absorption, thereby causing the silica glass to be modified. This is because it can. The multi-photon absorbed pulsed laser light hardly causes thermal diffusion, and can modify only the vicinity of the laser focused irradiation part, and is therefore very suitable for microfabrication like this embodiment.

  Further, in order to cause spatial modification selectively within the workpiece 10 (silica glass), it is preferable that the wavelength of the pulsed laser light a is a wavelength that transmits the workpiece 10. This is because when the pulse laser beam a is irradiated onto the workpiece 10, if the wavelength of the pulse laser beam a to be used is within the intrinsic absorption of the workpiece 10, the laser is absorbed on the surface of the workpiece 10. This is because the portion is modified and the portion is modified, which is likely to hinder the processing of the workpiece 10.

In the microcavity forming method of the present embodiment, as a pre-process of the laser processing step, at least the laser irradiation side surface (more preferably the front and back surfaces) of the workpiece 10 is polished. This polishing process is for preventing the pulsed laser light a from being refracted or scattered due to the influence of irregularities on the surface of the silica glass.
The workpiece 10 is mounted on the mounting table 30 after the polishing in the previous step.

  In the laser processing step, as shown in FIGS. 1B and 2, the pulsed laser beam a that meets the above-described conditions is condensed by the lens 22 and irradiated onto the workpiece 10. The workpiece 10 in the vicinity of the focal point is modified. Then, the workpiece 10 is reformed while moving the mounting table by means of an XYZ stage or the like and scanning the focal point.

  Here, the modification by the pulsed laser beam a is performed in the processing region of the workpiece 10 when a minute cavity continuous in the thickness direction such as a through hole or a bottomed hole is formed in the workpiece 10. It is preferable that the focus is scanned toward the front side with the deepest position from the surface as the starting point a1. In other words, if the scanning is performed from the front side to the back side, contrary to the above, the irradiated pulse laser beam a may be refracted and scattered by the modified part of the workpiece 10 (silica glass). There is. Therefore, in this embodiment, scanning is performed as described above in order to prevent such a situation.

  By the laser processing step, a continuous modified region 11 that is not exposed to the outside is formed in the workpiece 10. According to the example shown in FIG. 1, the modified region 11 is formed in a substantially cylindrical shape that is continuous in the thickness direction of the workpiece 10.

Next, in the machining step, as shown in FIG. 1C, the surface layer portion 13 and the back layer portion 14 of the workpiece 10 are scraped off by polishing.
Here, the surface layer portion 13 and the back layer portion 14 are portions located on both sides so as to sandwich the modified region 11 in the thickness direction of the workpiece 10. The surface layer portion 13 includes a part of one end side (upper end side in the illustrated example) of the modified region 11 in the laser scanning direction. Similarly, the back layer portion 14 includes a portion of the modified region 11 on the other end side in the laser scanning direction.
Therefore, when the surface layer portion 13 and the back layer portion 14 are removed, exposed portions 11 a exposed to the outside are formed on both end sides of the modified region 11.

The polishing process includes mechanical polishing, chemical mechanical polishing, barrel polishing, buffing, brush polishing, and the like as preferable specific examples. In one example of FIG. 1, the surface and the back surface of the workpiece 10 are respectively The entire surface is scraped to approximately the same thickness.
Instead of the polishing process, the surface layer part 13 and the back layer part 14 may be scraped off by grinding, or the grinding process and the polishing process are combined, and the polishing process is performed after the grinding process. The back layer portion 14 may be scraped off. Preferable specific examples of grinding include surface grinding, honing, ultrasonic grinding, and the like.

Next, in the etching process, the workpiece 10 that has been subjected to the laser processing process and the machining process as described above is immersed in the etching tank 40, so that the modified region 11 is formed starting from the exposed portion 11a. Etching is removed to form the microcavity 12.
As an etchant 41 to be put in the etching tank 40, a potassium hydroxide aqueous solution is used. The concentration of the potassium hydroxide aqueous solution is applicable from 50 wt% to a dilute aqueous solution of 0.1 wt%. If an aqueous potassium hydroxide solution in this concentration range is used, the unmodified region of the workpiece 10 (silica glass) can be easily etched moderately, and the etched microcavity 12 (through-hole) can be formed by etching the unmodified region. ) Can be prevented from being tapered.

  The etchant 41 in the etching tank 40 is heated to an appropriate temperature by a heater 42 provided on the lower side of the etching tank 40. The liquid temperature of the etchant 41 is preferably in the range of 20 ° C. to 60 ° C., particularly in the range of 50 ° C. to 60 ° C. This is because if the liquid temperature is higher than 60 ° C., the unmodified region of the workpiece 10 (silica glass) may be excessively etched, and conversely if the liquid temperature is lower than 20 ° C., the depth of the microcavity 12 may be increased. This is because the etching in the vertical direction hardly proceeds.

  Then, the attached etchant 41 is removed from the workpiece 10 from which the modified region 11 has been removed by etching, by means such as cleaning. In this way, a straight through-hole-shaped microcavity 12 is formed in the workpiece 10.

According to the above microcavity formation method, the front and back surfaces of the workpiece 10 are not focused and irradiated with the pulsed laser beam a, so that only unnecessary portions of the workpiece 10 are formed without forming unnecessary modified portions. The reformed region 11 having a stable shape with high dimensional accuracy can be formed.
Further, since the exposed portion 11a is formed in the modified region 11 only by machining, the portion other than the step of forming an etching protective film and the modified region of the work piece are etched as in the prior art. The processing equipment can be simplified and the processing speed is relatively fast without the need for processes.
In the etching step, etching is performed only on the modified region 11 without performing etching in a range extending from the unmodified region on the surface layer side of the workpiece to the modified region on the deep layer side as in the prior art. Therefore, the continuity of the inner surface of the microcavity 12 after removing the modified region 11 can be improved.
Therefore, quality deterioration around the microcavity 12 is small, a high-quality microcavity 12 having a stable shape with high dimensional accuracy can be obtained, and productivity can be improved with simple production equipment. .

Next, another example of the microcavity forming method according to the present invention will be described with reference to FIG.
In addition, since the other example of the microcavity formation method shown below changes a part of the said microcavity formation method, it mainly demonstrates the change location in detail and abbreviate | omits the overlapping detailed description.

The microcavity forming method shown in FIG. 4 is obtained by changing the machining step (see FIG. 4C) with respect to the microcavity forming method (see FIG. 1).
That is, in the machining process of this microcavity forming method, the communication hole 15 communicating with the modified region 11 is formed by machining on the workpiece 10 that has undergone the laser machining process.

The machining is cutting with a machine tool (for example, a drilling machine) using a drilling tool such as a drill, and is applied to both the front surface and the back surface of the workpiece 10.
Each communication hole 15 has a depth that reaches at least the end of the modified region 11 in the laser scanning direction. Therefore, when the communication holes 15 are formed on the front and back surfaces of the workpiece 10 by the machining, exposed portions 11a exposed to the outside are formed on both end sides of the modified region 11.

  Next, in the etching step, the workpiece 10 that has been subjected to the laser processing step and the machining step as described above is placed in the etching tank 40 in the same manner as the above-described microcavity formation method (see FIGS. 1 and 3). In this way, the modified region 11 is removed by etching with the exposed portion 11a as a starting point, and the microcavity 16 is obtained.

  The microcavity 16 is a space including a cylindrical portion 16a formed by etching away the modified region 11, and the communication holes 15 and 15 continuous at both ends of the cylindrical portion 16a. The workpiece 10 penetrates in the thickness direction and communicates with the outside of the workpiece 10.

  In the example shown in FIGS. 1 and 4, the microcavity is formed so as to penetrate the workpiece 10. However, as another example, a microcavity having a bottomed hole shape as shown in FIGS. 5 and 6 is used. 17 and 18 can also be formed.

  The microcavity 17 shown in FIG. 5 is formed by removing only the surface layer portion 13 from the workpiece 10 and machining the back layer portion 14 in the machining step (see FIG. 1C) in the microcavity forming method shown in FIG. I try not to cut. Therefore, after the modified region 11 is removed by etching in the next etching step, the bottomed hole-shaped microcavity 17 is formed.

  The microcavity 18 shown in FIG. 6 is formed by drilling only the surface side communication hole 15 in the workpiece 10 in the microcavity forming method shown in FIG. 4 in the machining step (see FIG. 4C). ing. Therefore, after the modified region 11 is removed by etching in the next etching step, the bottomed hole-like shape comprising the cylindrical portion 18a of the trace from which the modified region 11 has been removed and the communication hole 15 on the surface side is formed. A microcavity 18 is formed.

  Further, in the microcavities 16 and 18 shown in FIG. 4D and FIG. 6, the inner diameter of the communication hole 15 is made larger than that of the cylindrical portions 16a and 18a. It is also possible to make the inner diameter of the communication hole 15 smaller than the shaped portions 16a and 18a.

  Moreover, in the said form, although the elongate minute space was formed in the thickness direction of the to-be-processed object 10, as an other example, the minute space inclined with respect to the thickness direction of the to-be-processed object 10 or substantially orthogonal to the thickness direction It is also possible to make a minute space or the like.

The diameter of the microcavities 12, 16, 17, and 18 is 0.5 μm to 25 μm.
Moreover, although the substantially cylindrical microcavity was illustrated in the said form, the shape of this microcavity can be made into arbitrary shapes other than cylindrical shapes, such as square tube shape, groove shape, a recessed part, for example. is there.

  Moreover, in the said form, although the micro cavity was formed with respect to the flat plate-shaped to-be-processed object 10, as another example, it is the same micro as above with respect to solid shapes other than flat shape (for example, a cube, a rectangular parallelepiped, a sphere, etc.). It is possible to form a cavity.

  Moreover, in the said form, although the to-be-processed object 10 was made into silica glass, this to-be-processed object 10 is silica glass like borosilicate glass, soda-lime glass, sapphire, lithium tantalate, lithium niobate etc., for example. Other materials can be used.

  Moreover, in the said form, although potassium hydroxide aqueous solution was used as the etchant 41 in an etching process, as other examples of an etchant, mixing with a hydrofluoric acid, a buffered hydrofluoric acid, a hydrofluoric acid, a sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc. It is also possible to use a liquid or the like.

  Further, after the laser processing step, machining is performed only on one surface side of the workpiece 10 to form an exposed portion 11a in the modified region 11, and the modified region 11 is then etched by using the exposed portion 11a as a starting point. The microcavity forming method according to the present embodiment is formed so that the microcavity 12 or 16 is formed by etching and then machining is performed on the other surface side of the workpiece 10 to form a through hole. It may be changed. For example, FIG. 7 shows a modified example of the microcavity forming method of FIG. 1, and FIG. 8 shows a modified example of the microcavity forming method of FIG.

  The microcavity forming method in FIG. 7 differs from that in FIG. 1 in that only the surface layer portion 13 on one surface side of the workpiece 10 in FIG. 7 is first scraped off by polishing (see FIG. 7C), and the modified region 11 is formed with an exposed portion 11a, and then the modified region 11 is removed by etching to form a microcavity 12 (see FIG. 7D), and then the back layer portion on the other surface side of the workpiece 10 14 is scraped off by polishing (see FIG. 7E), and through holes are formed (see FIG. 7F). That is, it differs from FIG. 1 in that the polishing of the back layer portion 14 is performed after the etching process of the modified region 11. Therefore, the effect of the microcavity forming method of FIG. 1 also has the microcavity forming method of FIG.

  8 differs from FIG. 4 in that in FIG. 8, first, a communication hole 15 is drilled only on one surface side of the workpiece 10 by cutting using a drill or the like (FIG. 8C). Next, after the modified region 11 is removed by etching to form the microcavity 16 (see FIG. 8D), the communication hole 15 is formed on the other surface side of the workpiece 10 to penetrate therethrough. A hole is formed (see FIG. 8E). That is, it differs from FIG. 4 in that the cutting process for forming one communication hole 15 is performed after the etching process of the modified region 11. Therefore, the effect of the microcavity forming method of FIG. 4 is also the microcavity forming method of FIG.

10: Workpiece 11: Modified region 11a: Exposed portion 12, 16, 17, 18: Micro cavity 15: Communication hole a: Pulsed laser beam

Claims (5)

A laser processing step for forming a continuous modified region that is not exposed to the outside in the workpiece by performing focused laser beam irradiation on the workpiece, and removing a part of the workpiece by machining wherein the machining step of forming an exposed part to the reforming area, seen including an etching step, a forming microcavities removed by etching the modified region to the exposed portion to the starting point by,
In the machining step, the microcavity forming method is characterized in that a communication hole communicating with the modified region is formed in the workpiece by machining .   2. The method of forming a microcavity according to claim 1, wherein a through hole is formed as the microcavity.   The method for forming a microcavity according to claim 1 or 2, wherein the machining is grinding, polishing, or cutting.   4. The method for forming a microcavity according to claim 1, wherein in the machining step, at least one surface of the workpiece is removed by machining so as to have substantially the same thickness over the entire surface. 5. After the laser processing step, the machining is performed only on one surface side of the workpiece to form the exposed portion in the modified region,
  Next, the modified region is etched away by the etching process starting from the exposed portion to form the microcavity,
  5. The method for forming a microcavity according to claim 2, wherein the machining is performed on the other surface side of the workpiece to form the through hole.

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