JP5965194B2 - Method for forming fine structure - Google Patents

Description

  The present invention relates to a method for forming a fine structure using laser light.

  2. Description of the Related Art Conventionally, as a method for manufacturing a fine structure, a technique for processing by combining a photolithography method and an etching method is known. The photolithography method is a technique in which a region where a fine structure is not formed is covered with a resin or the like on the main surface of a substrate and masked. By etching the substrate on which such a mask is formed, an unmasked region is selectively etched, and a microstructure is formed in the depth direction from the main surface of the substrate. According to the above technique, a fine structure can be formed on the main surface of the substrate.

  On the other hand, linearly polarized laser light (linearly polarized laser light) with a pulse width on the order of picoseconds or less is condensed and irradiated on the inside of the substrate, and a structural modification part (modified part) is provided in the vicinity of the focused focal point. In recent years, attention has been paid to a method of forming a fine structure inside a substrate by forming and etching the modified portion. According to this method, a three-dimensional microstructure can be formed inside the substrate.

According to Patent Document 1, as shown in FIG. 10, when a quartz substrate 601 is focused and irradiated with a pulsed laser beam 602 having a pulse width equal to or less than the picosecond order of linearly polarized light, the focused irradiation is performed. The region is a structurally modified portion that is locally modified. The structural modification part is composed of a first modification part 603d and a second modification part 603c, and the size of each modification part in the direction parallel to the substrate main surface is about the wavelength of the irradiated laser beam. (Several hundreds [nm]). In the structural reforming portion, the first reforming portion 603d and the second reforming portion 603c are alternately arranged, and the direction in which they are arranged on the main surface of the quartz substrate 601 is the polarization direction of the laser beam 602. E and perpendicular. This is because the interaction is activated by the interference effect between the electron plasma wave and the incident light generated in the laser beam condensing part, and the structural modification of the substrate is induced by the periodic modulation of the electron plasma density. It is attributed to that. The quartz substrate 601 is in a state where oxygen is deficient in a region where the electron plasma wave and incident light are intensified, and is in an oxygen-rich state in a region where the electron beam is weakened.
The structural modification part formed in the condensing part of the laser beam 602 has weak etching resistance against a chemical solution such as a hydrofluoric acid aqueous solution. In particular, etching is more likely to proceed in the oxygen-deficient portion (oxygen-deficient portion) than in the oxygen-rich portion.

According to Patent Document 2, as the pulse energy of the laser beam 702 having a pulse width of the picosecond order or less is gradually weakened, the region to be modified becomes smaller, and finally the structure modification in which only one oxygen-deficient portion is formed. Become a quality department. The pulse energy of the laser beam 702 in which only one oxygen-deficient part is formed is a value defined for each material of the substrate, and is called a processing lower limit threshold for the substrate material. By performing an etching process on the oxygen-deficient portion formed by the laser beam 702 whose pulse energy is a processing lower limit threshold value, nano-level microfabrication can be performed.
Furthermore, as shown in FIG. 11, the laser beam 702 is condensed and irradiated with the pulse energy of the processing lower limit threshold, and scanning is performed while shifting the focal point, thereby forming a continuous oxygen-deficient portion formed for each pulse. Is done. By etching this, it is possible to form nano-sized micropores.
However, since the laser beam 702 of Patent Document 2 is a linearly polarized laser beam, the structural modification portion must be formed while keeping the polarization direction of the laser beam 702 and the scanning direction of the focus perpendicular to each other. When the polarization direction of the laser beam 702 and the scanning direction of the focal point are not perpendicular to each other, the oxygen-deficient portion formed for each pulse is not connected and formed, so that the formed structural modification portion extends over the entire length. In other words, the pores are not homogeneous and fine pores cannot be formed at a stable etching rate.

According to Patent Document 3, a region in which a fine structure is provided in a substrate is irradiated with laser light having a pulse width whose pulse time width is equal to or less than the picosecond order, and the focal point where the laser light is condensed is scanned to change the structure. Form a mass part. In Patent Document 1 and Patent Document 2, linearly polarized linearly polarized laser light is used, whereas in Patent Document 3, circularly polarized laser light is used. The structural reforming portion formed by the circularly polarized laser beam is a mixture of oxygen-deficient sites and oxygen-rich sites at random. That is, there is no regularity between the polarization direction of the laser light and the internal structure of the structural modification portion. Therefore, there is no need to change the scanning direction of the focus during the scanning or to adjust the polarizing filter in accordance with the scanning direction.
However, in the formation of the structural modification portion using the circularly polarized laser beam of Patent Document 3, mention is made of a technique for forming nano-level micropores of less than 1 μm, in which the size of the micropores is several μm to several tens of μm. It has not been. Therefore, in the processing method of Patent Document 3, as a result, it is difficult to form nano-level micropores.

International Publication No. 2011/096356 International Publication No. 2011/096353 JP 2011-222700 A

  The present invention has been made in consideration of the above-described problems. A laser beam having a pulse width of picosecond order or less is focused on the substrate, and the focal point is scanned to form a structurally modified portion. In this case, an object of the present invention is to provide a method for forming a fine structure capable of forming a structural modification portion having a nano-level (1 nm or more and less than 1000 nm) size that is etched at a stable etching rate.

According to a first aspect of the present invention, there is provided a method for forming a fine structure in which a laser beam having a pulse width emitted from a light source and having a picosecond order or less is irradiated to a substrate through a polarizing unit and a condensing unit, and the focal point where the laser beam is condensed is scanned. Thus, there is provided a method for forming a fine structure, comprising: a first step of forming a structural modification portion on the substrate; and a second step of forming a fine hole by etching the structural modification portion. Te, the output laser beam is the is converted into circularly polarized laser beam by the polarization means, the intensity of the circularly polarized laser light in the focal point, the linearly polarized laser beam which is linearly polarized the emitted laser beam to the base body It is characterized by being 1.3 times or more and 2 times or less with respect to the intensity required to form the structural modification portion by irradiation.

  According to the first aspect of the present invention, in the method for forming a microstructure according to the present invention, in the first step, a circularly polarized laser beam having a pulse width of the picosecond order or less is condensed and irradiated into the substrate, and the focal point thereof is focused. The structural modification part is formed by scanning. The structure modification portion formed by such a method has a random-like shape for each pulse according to the focused and irradiated laser beam, and the entire structure is uniform by scanning the focal point of the laser beam. It becomes the reforming section.

  Furthermore, when the intensity at the focal point is 1.3 times or more and 2 times or less than the intensity necessary for irradiating the linearly polarized laser beam in the substrate to form the structural modification portion, it is formed in the substrate. The structurally modified portion is nano-sized (less than 1 μm) and is in a modified state that can be etched. Therefore, it is possible to form a nano-sized structural modified portion that is etched at a stable etching rate, and it is possible to form a microstructure by etching the formed structural modified portion. .

Method of forming a fine structure according to claim 2, Oite to claim 1, the scanning direction of the focal point of the laser beam used for the first step is changed while scanning the focal point, characterized in that .

According to the second aspect , since the state of the structural reforming portion does not change before and after changing the scanning direction, the etching rate when etching the structural reforming portion extends over the entire length of the formed structural reforming portion. It becomes constant and a fine structure can be formed stably.

According to a third aspect of the present invention, there is provided the fine structure forming method according to the first or second aspect , wherein the scanning of the focal point of the circularly polarized laser beam is repeated a plurality of times.

According to the third aspect , since the scanning of the focus of the circularly polarized laser beam is repeated a plurality of times, a plurality of line-shaped structural modification portions are formed. Therefore, variation in the etching rate of each structural modification portion can be suppressed.

  In the fine structure forming method according to the present invention, in the first step, the structurally modified portion is formed by condensing and irradiating circularly polarized laser light into the substrate and scanning the focal point. The structure modification portion formed by such a method has a random-like shape for each pulse according to the focused and irradiated laser beam, and the entire structure is uniform by scanning the focal point of the laser beam. It becomes the reforming section.

  Furthermore, when the intensity at the focal point is 1.3 times or more and 2 times or less than the intensity necessary for irradiating the linearly polarized laser beam in the substrate to form the structural modification portion, it is formed in the substrate. The structurally modified portion is nano-sized (1 nm or more and less than 1000 nm) and is in a modified state that can be etched. Therefore, it is possible to form a nano-sized structural modified portion that is etched at a stable etching rate, and it is possible to form a microstructure by etching the formed structural modified portion. .

  In the first step, the fine structure forming method according to the present invention condenses and irradiates a circularly polarized laser beam onto a quartz glass substrate and scans the focal point thereof. The pulse energy at the focal point is 80 [nJ / pulse] or more and 125 [nJ / pulse] or less. As a result, a nano-sized structurally modified portion is formed on the quartz glass substrate so as to have a modified state that can be etched, and the formed structurally modified portion has a random-like oxygen-depleted portion at every pulse. It becomes the state distributed in. Therefore, in the second step of etching the quartz glass substrate, the structural modification portion is etched at a stable etching rate. Therefore, it is possible to provide a method for forming a fine structure that can form a structural modification portion having a nano-level size that is etched at a stable etching rate.

(A) It is a perspective view of the to-be-processed object in a 1st process among the formation methods of the microstructure of this invention. (B) It is the figure which showed typically about the control system of the pulse power of a laser beam. (C) It is a perspective view of the to-be-processed object in a 2nd process among the formation methods of the microstructure of this invention. It is the flow of the process performed at a 1st process among the formation methods of the microstructure of this invention. It is the figure which showed typically about the control system of the polarization state of a laser beam. (A)-(f) It is a SEM image which shows the shape of the longitudinal direction of the fine structure formed according to the irradiation conditions of the laser beam. (A)-(f) It is a SEM image which shows the shape of the fine structure in the cross section perpendicular | vertical to a longitudinal direction formed according to the irradiation conditions of the laser beam. (A) It is the graph which showed the relationship between the irradiation conditions of a laser beam, and the etching depth. (B) It is the graph which showed the relationship between the irradiation conditions of a laser beam, and the short axis in the cross section of the substantially elliptical shape of a fine structure. (A)-(c) It is a SEM image which shows the shape of the longitudinal direction of the fine structure formed according to the irradiation conditions of the laser beam. It is a SEM image which shows the shape of the fine structure in the cross section perpendicular | vertical to a longitudinal direction formed according to the irradiation conditions of the laser beam. (A), (b) It is a top view which shows the shape of the fine structure which can be formed by this invention. It is a figure which illustrates typically a mode that the structural modification part of a periodic pattern is formed in the substrate surface by laser beam irradiation of a prior art. It is a figure which illustrates typically the formation method of the fine structure by a prior art.

  Hereinafter, based on a preferred embodiment, the present invention will be described with reference to the drawings.

<First embodiment>

(Method for forming fine structure)
A method for forming a microstructure according to the first embodiment of the present invention will be described with reference to FIGS. The formation method of the microstructure is a method including at least two steps (first step and second step) described below in order.

  First, as shown in FIG. 1A, as a first step, laser light circularly polarized (circularly polarized laser light) in a region where a fine structure (micropore) is formed in the flat substrate 101. The structural modification part (modification part) 103 is formed by focusing and irradiating 102.

  A 1st process is performed through five steps (S1-S5) shown to the flow of FIG.

  That is, as the first step S1, a laser beam having a pulse width of picosecond order or less is emitted from a light source disposed in a space closed by a shutter or the like. In the present invention, the pulse width on the order of picoseconds means a pulse width of 1 nanosecond or less. In general laser light, laser light emitted from a light source is laser light whose polarization state is linearly polarized light.

  Next, in step S2 following step S1, laser light generated in the light source is converted into circularly polarized laser light 102 circularly polarized clockwise or counterclockwise. Adjustment of the polarization state of the laser light emitted from the light source is performed via a polarization means. The polarization means is constituted by a quarter-wave plate 22 that tilts the polarization plane of laser light by 45 degrees with respect to the fast axis (or slow axis), for example.

  By transmitting the linearly polarized laser beam generated in the light source 21 through the quarter-wave plate 22, the phase of two orthogonal polarization components is shifted by a quarter wavelength. Thereby, a laser beam polarized in the clockwise direction with respect to the traveling direction k is obtained on a plane (XZ plane) perpendicular to the traveling direction k (Y-axis direction) of the laser beam.

  Symbols A and B in FIG. 3 indicate the vibration directions of the electric field constituting the linearly polarized laser beam and the circularly polarized laser beam, respectively. Circularly polarized laser light also has a pulse width on the order of picoseconds or less, as before polarization. In FIG. 3, by rotating the polarization direction of the wave plate or the incident hole by 90 °, a laser beam that is circularly polarized counterclockwise with respect to the traveling direction k can be obtained.

  Next, as step S3 following step S2, the opening / closing means (shutter) of the closed space where the light source is arranged is opened, and the base 101 is irradiated with the circularly polarized laser beam 102. The circularly polarized laser beam 102 is condensed through a condensing unit. As the light condensing means, for example, a refractive objective lens is preferably used, but an objective lens such as a Fresnel type, a reflective type, an oil immersion type, or a water immersion type may be used. Further, by using, for example, a cylindrical lens as the lens 12, it is possible to irradiate a plurality of circularly polarized laser beams 102 over a wide range of the surface of the base 101.

  As the substrate 101, for example, an amorphous substrate made of quartz glass or the like excellent in workability, or a crystalline substrate made of silicon or sapphire is used. In this embodiment and an experimental example described later, an example in which a structural reforming portion and a micro hole described later are formed inside a flat substrate is shown. However, the structural reforming portion and the micro hole are formed inside. In doing so, the shape of the substrate is not limited.

  The pulse energy of the circularly polarized laser beam 102 is adjusted at this point. The adjustment of the pulse energy can be performed using a measurement system 10 as shown in FIG. The measurement system 10 includes an objective lens 11, a power meter (measuring unit) 12, a monitor (display unit) 13, and a wiring 14 that electrically connects the power meter 12 and the monitor 13.

  A procedure for adjusting the pulse energy of the circularly polarized laser beam by the measurement system 10 will be described. First, a laser beam 15a emitted from a light source (not shown) is received using a power meter 12 through a polarizing unit and a condensing unit. Next, the output of the condensed laser beam 15 b is measured by the power meter 12, and the measurement result is displayed on the monitor 13. Based on the display content of the monitor 13, the average output is adjusted using a neutral density filter or the like so that the laser beam 15 has a desired pulse energy.

  Next, as step S4 following step S3, the focused focal point 102f is scanned along the region where the microhole is formed. In order to scan the focal point 102f, the light source side may be moved, or the substrate 101 side may be moved.

  In step S5 subsequent to step S4, the shutter is closed and the irradiation of the laser beam 102 is interrupted. When another structural modification portion is formed on the base 101 subsequent to step S5, the process returns to step S3, the light source or the base 101 is moved to a place where another structural modification portion is formed, and the focal point 102f is again formed. Scan.

  By passing through the above five steps, the structure modification | reformation part 103 can be formed in the area | region which carried out the condensing irradiation of the laser beam 102 inside the base | substrate 101, and was scanned. The formed structural reforming portion 103 has weak etching resistance.

  Since the structural modification portion 103 is modified by the circularly polarized laser beam 102, the oxygen-deficient portion and the oxygen-rich portion are formed in a random manner. The structural modification portion 103 has weak etching resistance against a chemical solution such as a hydrofluoric acid aqueous solution, and the etching deficiency is reduced in a portion lacking oxygen compared to a portion in an oxygen-rich state.

  Next, as a second step, at least a part of the structural reforming portion 103 formed through the first step is exposed, and the structural reforming portion 103 is selectively etched, so that the inside of the substrate 101 is formed. Micropores are formed.

  For example, as shown in FIG. 1A, the structural modification unit 103 can be exposed by providing at least one end 103 a of the laser beam scanning path in the first step on the surface of the substrate 101. The structural modification unit 103 can also be exposed by removing the substrate 101 by polishing or the like from the surface to a position where the structural modification unit 103 is located.

  The etching process may be performed using either a dry etching method or a wet etching method. When the wet etching method is used, as shown in FIG. 1C, the structural modification portion 103 is etched by immersing the substrate 101 that has undergone the first step in an etching solution 105 accommodated in a container 104. As the etchant, for example, an alkaline solution mainly containing hydrofluoric acid (HF) or potassium hydroxide (KOH), a hydrofluoric acid-based mixed acid solution in which an appropriate amount of nitric acid or the like is added to hydrofluoric acid, and the like can be used. Other chemicals can be used depending on the material constituting the.

  A fine structure can be formed on the substrate 101 through the first step (steps S1 to S5) and the second step.

  As described above, the fine structure forming method according to the first embodiment circularly polarizes the laser light used for forming the structural modification portion in the first step. The structural modification portion formed by the circularly polarized laser beam (circularly polarized laser beam) is in a state where oxygen-deficient sites are distributed in a random manner. Therefore, even if a plurality of structural reforming portions are formed, a uniform reforming state is achieved in any structural reforming portion, and an etching process in which variation in etching rate is reduced during the etching process is possible. In addition, even if the scanning direction is changed during the scanning of the focal point, it does not become a modified state depending on the relationship between the scanning direction and the polarization direction as in the case of forming using linearly polarized laser light. A uniform modified state is obtained over the entire length of the modified portion, and an etching process with a constant etching rate is possible when the etching process is performed.

  Hereinafter, the present invention will be described in more detail using Experimental Examples 1 to 3 to which the method for forming a microstructure according to the first embodiment is applied, but the experimental example to which the present invention is applicable is Experimental Example 1. It is not limited to ~ 3.

[Experiment 1]
(Pulse energy of circularly polarized laser light)
Experimental Example 1 is an example in which the irradiation power of the circularly polarized hole laser light to be irradiated is changed for the fine holes formed by the irradiation with the circularly polarized laser light and the etching process. The case where the main component of the etching solution used in the etching process in the second step is hydrofluoric acid (HF) will be described with reference to FIGS.

  4 (a) to 4 (f) show one surface 301b of the substrate where the substrates 301, 311, 321, 331, 341, and 351 that have undergone the first step and the second step are opposed to the light source in the first step, respectively. It is the top view seen from 311b, 321b, 331b, 341b, 351b side. After forming the structural modification portion in the first step, all the substrates are cut on one surface 301a, 311a, 321a, 331a, 341a, 351a perpendicular to the one surface 301b, 311b, 321b, 331b, 341b, 351b of the substrate. Then, the structural modification portion is exposed, and further, an etching process is performed in the subsequent second step. Thereby, the micropore formed through the first step and the second step is exposed in the cross section.

  4A to 4F show an example in which the pulse energy of the circularly polarized laser beam used in the first step is 60, 70, 80, 90, 100, and 125 [nJ / pulse], respectively. Yes. The pulse energy is defined as an amount obtained by multiplying the intensity W by the area S of the condensing portion of the circularly polarized laser beam and the pulse width (pulse time width) T, that is, pulse energy = W × S × T. . In the description of the present invention, the area S and the pulse width T of the collected portion are treated as being substantially constant. Therefore, controlling the pulse energy corresponds to controlling the intensity W.

  As the bases 301, 311, 321, 331, 341, and 351 shown in FIGS. 4A to 4F, all of them were flat and made of quartz glass. The etching process in the second step was performed using an etching solution mainly containing hydrofluoric acid (HF). The temperature of the etching solution was room temperature, and the etching time was 30 minutes.

As shown in FIGS. 4A and 4B, when the pulse energy of the circularly polarized laser beam is set to 60 and 70 [nJ / pulse], the structural modification portion is formed in the first step. Etching did not proceed in the second step, and no micropores were formed.
On the other hand, as shown in FIGS. 4C to 4F, when the pulse energy is set to 80 [nJ / pulse] or more, the inside of each substrate (side surface) 321a, 331a, 341a, 351a is introduced into the inside. Micropores 326, 336, 346, and 356 extending toward the surface were formed.

  5A to 5F are enlarged plan views of one surface 301a, 311a, 321a, 331a, 341a, and 351a of the base body shown in FIGS. 4A to 4F, respectively. As shown in FIGS. 5A and 5B, when the pulse energy is set to 60 and 70 [nJ / pulse], the structural reforming portion formed in the first step is subjected to the etching process in the second step. Even if it performed, it was not removed and the micropore was not formed. On the other hand, as shown in FIGS. 5C to 5F, when the pulse energy is set to 80 [nJ / pulse] or more, the fine holes 326 opened on the one surface 321a, 331a, 341a, and 351a of the substrate, respectively. 336, 346, 356 were formed.

  When the etching process is performed as the second step, the portions near the one surface 321b, 331b, 341b, and 351b of the base that is opposed to the light source are removed from the structural reforming portion formed in the first step, and the fine portions are respectively removed. A tendency to become holes 326, 336, 346, 356 was observed. At the same time, the portions far from the one surface 321b, 331b, 341b, 351b of the substrate were not removed, and there was a tendency to remain as the structural reforming portions 323c, 333c, 343c, 353c.

  4 (a) to 4 (f) and FIGS. 5 (a) to 5 (f), in the first step, a substrate made of quartz glass is irradiated with a circularly polarized laser beam to form a structural modification portion, and the second step. When performing etching using an etchant containing hydrofluoric acid as a main component, it is necessary to use laser light having a pulse energy of at least 80 [nJ / pulse] or more in the first step. Conceivable.

  FIG. 6A is a graph showing the results shown in FIGS. The horizontal axis of the graph indicates the pulse energy of the circularly polarized laser beam used in the first step. The vertical axis of the graph indicates the size (etching depth) of the micropores measured in the depth direction from one surface of the substrate.

  According to the graph of FIG. 6A, in the range where the pulse energy of the laser light is 100 [nJ / pulse] or less, the etching depth of the formed microholes is several [μm] as the pulse energy is increased. There was a tendency to increase in the order of.

  On the other hand, in the range where the pulse energy of the laser beam exceeds 100 [nJ / pulse], the etching depth when the formed etching depth is within the range of 100 [nJ / pulse] or less is 1 There was a tendency to exceed orders of magnitude.

  FIG. 6B is a graph showing the results shown in FIGS. The horizontal axis of the graph indicates the pulse energy of the circularly polarized laser beam used in the first step. The vertical axis of the graph represents an elliptical minor axis in a cross section perpendicular to the longitudinal direction of the micropore. It was found that when the pulse energy of the laser beam is in the range of 70 [nJ / pulse] or less, the minor diameter of the formed micropore is 0 [μm], and the micropore is not formed. In the range where the pulse energy exceeds 80 [nJ / pulse], the short diameter of the formed micropores tends to increase as the pulse energy is increased. When the pulse energy was 125 [nJ / pulse], the size of the minor axis was about 1 μm. From this result, it was found that nano-level (1 nm or more and less than 1000 nm) micropores were formed in the range of pulse energy of 80 [nJ / pulse] to 125 [nJ / pulse].

  In the case of forming nano-scale micropores by forming a structural modification part in a quartz glass substrate using linearly polarized laser light and etching the structural modification part, the pulse energy of linearly polarized laser light is as follows: , At least 60 [nJ / pulse] is required. Based on that value, the pulse energy of the laser beam irradiated when using the circularly polarized laser beam in forming the microhole is 1.3 to 2 times that when using the linearly polarized laser beam. Good.

[Experiment 2]
Experimental Example 2 is an example in which the shape of the micropore formed by applying the present invention is compared by changing the pulse energy and polarization state of the laser light used in the first step. The pulse energy is defined as an amount obtained by multiplying the intensity by the area of the condensing portion of the laser beam and the pulse width. In the present invention, since the area of the condensed portion and the pulse width are treated as being substantially constant, controlling the pulse energy corresponds to controlling the intensity. Experimental example 2 will be described with reference to FIGS. 7A to 7C and FIG.

  FIG. 7A is a plane photograph of the flat substrate 201 having the micro holes 206 formed therein, as viewed from the one surface 201b side, through the first step and the second step. The laser beam was condensed on the substrate 201, and the focal point was scanned 10 times to form ten structurally modified portions extending in a line shape. Thereafter, the base body 201 was divided so as to cross the structural modified portion extending in a line shape, and the structural modified portion was exposed in the divided cross section after the division. Then, the structure 201 was etched by immersing the base body 201 in an etching solution. By performing an etching process, nano-level micropores were formed. FIG. 7A shows an example in which linearly polarized laser light having a pulse energy of 60 [nJ / pulse] is used in the first step.

  FIG. 7C is a plan view of the flat substrate 221 having the fine holes 226 formed therein, as viewed from the one surface 221b side of the substrate 221, which has undergone the first step and the second step. The laser beam was condensed on the substrate 221 and the focal point was scanned 10 times to form ten structurally modified portions extending in a line shape. Thereafter, the base body 221 was divided so as to cross the structurally modified portion extending in a line shape, and the structurally modified portion was exposed in the divided cross section after being divided. Then, the substrate 221 was immersed in an etching solution to perform an etching process on the structural modification portion. By performing an etching process, nano-level micropores were formed. FIG. 7C shows an example of using a circularly polarized laser beam having a pulse energy of 100 [nJ / pulse] in the first step.

  As the base 201 and the base 221, a flat plate made of quartz glass (quartz glass substrate) was used. In the first step, the laser light focused and irradiated on the base 201 and the base 221 was modified so as to be the same except for pulse energy and polarization. The etching process in the second step was performed using a dilute hydrofluoric acid (HF) solution. The temperature of the etching solution was normal temperature and the etching time was 30 minutes.

  From the substrate on which the micropores shown in FIG. 7C and FIG. 7A are formed, the micropores are formed using a circularly polarized laser beam, and the micropores are formed using a linearly polarized laser beam. The case was compared. Specifically, the length of the fine holes was measured with a length measuring microscope, calculated as an etching rate, and compared.

  First, the average length of the micropores shown in FIG. 7C was 11.8 μm, the maximum value was 15.4 μm, and the minimum value was 8.1 μm. When the etching rate was calculated from this result, the average value of the etching rate was 0.39 μm / min, the maximum value was 0.51 μm / min, and the minimum value was 0.27 μm / min. The index indicating the degree of variation in the etching rate, that is, the value of (maximum value−minimum value) ÷ (maximum value + minimum value) was 31.18.

On the other hand, the average length of the micropores shown in FIG. 7A was 52.0 μm, the maximum value was 67.5 μm, and the minimum value was 27.3 μm. When the etching rate was calculated from this result, the average value of the etching rate was 1.73 μm / min, the maximum value was 2.25 μm / min, and the minimum value was 0.91 μm / min. The index indicating the degree of variation in the etching rate, that is, the value of (maximum value−minimum value) ÷ (maximum value + minimum value) is 42.40, which is a larger value than when circularly polarized laser light is used. .
As described above, the structure modified portion formed using the circularly polarized laser beam has less variation in the etching rate than the structure modified portion formed using the linearly polarized laser beam, and stable etching is possible. It became clear.

  FIG. 8 is an enlarged plan view of one surface 221a of the base shown in FIG. As shown in FIG. 8, each fine hole 226 formed was opened on one surface 221a of the substrate. The opening surface of the fine hole 226 was substantially elliptical. When the etching process is performed as the second step, the portion close to the one surface 221b of the substrate is removed from the structural modification portion formed in the first step to form the fine hole 226, and the portion far from the one surface 221b is not removed. There was a tendency that the structural reforming part 223a remained.

  After the etching process in the second step, a fine hole 106 is formed at a predetermined position inside the substrate 101. Note that the laser light used in the first step can be modified by scanning a minute region smaller than a micron order. Therefore, it is possible to form the micropore 106 having a minimum dimension in the nano order. The cross-section of the formed fine hole 106 is substantially elliptical. Depending on the state of the etching process, the cross section may have a shape close to a rectangle.

[Experiment 3]
FIGS. 9A and 9B show an experimental example 3 regarding the shape of the micropores that can be formed by applying the present invention. A substrate 501 shown in FIG. 9A includes circular fine holes 506 therein. A base 511 shown in FIG. 9B includes a sine curve-shaped fine hole 516 therein. About the base | substrate 501 and the base | substrate 511, about the structure except the shape of the micropore, all are the same as that of the structure of the base | substrate 101 shown as 1st embodiment. As the etching solution used in the second step, an alkaline solution containing potassium hydroxide (KOH) as a main component, which is considered to easily form high aspect ratio micropores, was used.

  In the method for forming a fine structure according to the present invention, a structurally modified portion is formed inside a substrate using a circularly polarized laser beam. The structurally modified portion formed using the circularly polarized laser beam has oxygen-deficient sites randomly formed therein. Therefore, a uniform structural modification portion is formed regardless of the direction in which the circularly polarized laser beam is scanned.

  Therefore, it is possible to form a structurally modified portion having a uniform etching rate along the desired direction scanned with the laser light inside the bases 501 and 511. Then, by performing an etching process on the formed structural modification portion, for example, a circular closed fine hole as shown in FIG. 9A or a plurality of places as shown in FIG. 9B bends. Micropores can be formed.

  In FIGS. 9A and 9B, the shape of the micropores included in one plane and made of a smooth curve is taken as an example. However, by applying the present invention, the micropores are formed. Further, it may be formed so as to form a structure in which a part is bent or branched, or a three-dimensional structure arranged perpendicularly or obliquely to one surface of the substrate.

  The present invention can be widely applied to technical fields such as a microstructure forming method and a substrate having a microstructure, such as a microchannel, a microwell, an optical component, and an electronic component.

DESCRIPTION OF SYMBOLS 10, 20 ... Control system, 11 ... Objective lens, 12 ... Power meter (measuring means), 13 ... Monitor (display means), 14 ... Wiring, 15, 15a, 15b ...・ Laser light,
21 ... Light source, 22 ... 1/4 wavelength plate,
101, 111, 121, 201, 211, 221 ... base,
301, 311, 321, 331, 341, 351,...
401, 411, 421, 431, 441, 501, 511 ... substrate,
101a, 201a, 221a ... one side,
401a, 411a, 421a, 431a, 441a, 451a ... one side,
101b, 201b, 211b, 221b ... one side,
301b, 311b, 321b, 331b, 341b, 351b ... one side,
102: Circularly polarized laser beam, 102f: Focus,
103, 103c, 113, 123 ... structural reforming part,
103a... One end, 103b.
303c, 313c, 323c, 333c, 343c, 353c ... structural modification part,
403c, 413c, 423c, 433c, 443c, 453c ... structural reforming section,
104 ... Container, 105 ... Etching solution,
106, 206, 226 ... micropores,
326, 336, 346, 356 ... micropores,
426, 436, 446, 456 ... fine holes,
107, 207 ... external space,
307, 317, 327, 337, 347, 357 ... external space,
407, 417, 427, 437, 447, 457 ... external space,
A, B: vibration direction, E: polarization direction, k: optical axis direction, S: scanning direction,
S1-S5... Step.

Claims (3)

A laser beam with a pulse width emitted from a light source of the order of picoseconds or less is irradiated onto the substrate through the polarizing means and the condensing means, and the structural focus is formed on the substrate by scanning the focal point where the laser light is collected. The first step;
A second step of forming micropores by etching the structural modification portion, and a method for forming a microstructural body,
The output laser beam is the converted by the polarization means to circularly polarized laser beam, the intensity pulse power of the circularly polarized laser light in the focal point, the linearly polarized laser beam which is linearly polarized the emitted laser beam to the base body A method for forming a microstructure, which is 1.3 times or more and 2 times or less the strength necessary for forming a structurally modified portion by irradiation. Wherein the scanning direction of the focal point of the laser beam used in the first step, method of forming a fine structure according to claim 1, characterized in that to change while scanning the focal point. 3. The method for forming a fine structure according to claim 1, wherein scanning of the focal point of the circularly polarized laser beam is repeated a plurality of times.