JP2013063446A - Periodic structure and method of forming the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a periodic structure with high periodicity.SOLUTION: A method of forming a periodic structure includes a step of forming a periodic uneven structure 58 on a surface of a workpiece 40 by irradiating a surface of the workpiece 40 with continuous wave laser beam 52, 54 in energy density or lower to cause ablation of the workpiece 40, in a condition that the workpiece 40 is relatively scanned to continuous wave laser lights 52, 54.

Description

  The present invention relates to a periodic structure and a method for forming the same, for example, a periodic structure formed by irradiating a laser beam and a method for forming the same.

  By applying a periodic structure having a fine period to a coating film such as DLC (Diamond Like Carbon), the slidability of a cutting machine or a processing machine can be improved. In addition, such a periodic structure can be applied to optical elements such as a non-reflective plate and the development of a structural color using color generation by light interference. Furthermore, it can also be used to form a liquid flow path by exhibiting water repellency with respect to a liquid having a periodic structure.

  As a method for forming a fine periodic structure, there are a method using photolithography which is a manufacturing process of a semiconductor device, a method using nanoimprint, and the like. However, these methods are performed in a special environment such as a clean room. Further, in order to perform these methods, a plurality of complicated apparatuses are used.

  Patent Document 1 describes a technique for forming a periodic structure using a femtosecond laser.

JP 2003-211400 A

  If a fine periodic structure can be formed by irradiating laser light as in Patent Document 1, the periodic structure can be formed without using a special environment such as a clean room or many devices.

  However, the method described in Patent Document 1 has poor periodicity. Further, the scanning speed of the laser beam is slow, and it takes time to form the periodic structure.

  This invention is made | formed in view of the said subject, and aims at forming a periodic structure with high periodicity.

  In the present invention, the workpiece is scanned at an energy density equal to or lower than an energy density at which the ablation of the workpiece is generated in a state where the workpiece is scanned relative to the continuous wave laser beam. A method for forming a periodic structure comprising the step of forming a periodic uneven structure on the surface of the workpiece by irradiating the surface of the workpiece. According to the present invention, a periodic structure with high periodicity can be formed.

  The said structure WHEREIN: The energy density of the said continuous wave laser beam can be set as the structure more than the energy density which the surface of the said workpiece melts.

  In the above configuration, the continuous wave laser beam may be a plurality of laser beams having different wavelengths.

  The said structure WHEREIN: The period of the said uneven structure can be set as the structure which is below the longest wavelength and more than the shortest wavelength among these laser beams.

  The said structure WHEREIN: The period of the said uneven structure can be set as the structure controlled by changing the energy density of these laser beams relatively.

  The said structure WHEREIN: The direction of the period of the said uneven structure can be set as the structure which is the polarization direction of the said continuous wave laser.

  In the above configuration, the polarization direction of the continuous wave laser may be the same as the scanning direction.

  In the above-described configuration, the period of the concavo-convex structure may be substantially equal to the wavelength of the continuous wave laser beam.

  The present invention is a periodic structure manufactured by the method for forming a periodic structure.

  According to the present invention, a periodic structure with high periodicity can be formed.

FIG. 1 is a block diagram illustrating a laser apparatus used in the method for manufacturing a periodic structure according to the first embodiment. FIG. 2A is a schematic diagram of the surface of the workpiece, and FIG. 2B is a schematic sectional view of the workpiece. FIG. 3A is a diagram schematically showing an SEM image from the upper surface of the concavo-convex structure, and FIG. 3B is a diagram schematically showing an SEM image obtained by obliquely viewing a cross section of the concavo-convex structure. FIG. 4 is a diagram illustrating the period L with respect to the energy density of the first laser beam.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram illustrating a laser apparatus used in the method for manufacturing a periodic structure according to the first embodiment. As shown in FIG. 1, the laser device 100 mainly includes a first laser device 10, a first optical system 12, a second laser device 20, a second optical system 22, a dichroic mirror 30, an imaging optical system 32, and a drive system. 36. The first laser device 10 emits a first laser beam 14 that is a continuous wave laser beam. The first optical system 12 shapes the intensity distribution and diameter of the first laser beam 14. The second laser device 20 emits a second laser beam 24 that is a continuous wave laser beam having a wavelength different from that of the first laser beam 14. The second optical system 22 shapes the intensity distribution and the diameter of the second laser light 24.

  The dichroic mirror 30 reflects the first laser beam 14 and transmits the second laser beam 24. Thereby, the first laser beam 14 and the second laser beam 24 are synthesized. The imaging optical system 32 is an imaging lens and collects and irradiates the first laser beam 14 and the second laser beam 24 on the workpiece 40. The workpiece 40 is disposed on the stage 34. The stage 34 and the first and second laser beams 14 and 24 are relatively scanned by the drive system 36.

In the first embodiment, the first laser device 10 emits the second harmonic of the YVO ₄ laser. The wavelength of the first laser beam 14 is about 532 nm. The second laser device 20 is a semiconductor laser, and the wavelength of the second laser light 24 is about 797 nm. The drive system 36 scans the stage 34 with the first and second laser beams 14 and 24 at a speed of 300 m / min or 360 m / min. As the workpiece 40, a single crystal silicon substrate into which phosphorus (P) is ion-implanted is used. The phosphorus implantation conditions are an implantation energy of 200 keV and a dose of 1 × 10 ¹³ cm ² .

FIG. 2A is a schematic diagram of the surface of the workpiece, and FIG. 2B is a schematic sectional view of the workpiece. As shown in FIG. 2A, the surface of the workpiece 40 is irradiated with the first laser beam 52 and the second laser beam 54. The first laser beam 52 has an energy density of 32 J / cm ² , the second laser beam 54 has an energy density of 32 J / cm ² , and the first laser beam 52 and the second laser beam 54 are processed objects. 40 is scanned in the scanning direction 50 at a speed of about 360 m / min. The polarization directions 56 of the first laser beam 52 and the second laser beam 54 substantially coincide with the scanning direction 50. A periodic uneven structure 58 is formed in the periodic direction 59 on the surface of the workpiece 40 irradiated with the first laser beam 52 and the second laser beam 54. The width W of the concavo-convex structure 58 is about 6 μm.

  As shown in FIG. 2B, in the concavo-convex structure 58, protrusions 62 having a period L are formed on the flat portion 60. The trench length T, which is the length of the flat portion 60, is about 200 nm. The height H of the protrusion 62 is about 20 nm. The uneven structure 58 was observed using an SEM (Scanning Electron Microscope).

  FIG. 3A is a diagram schematically showing an SEM image from the upper surface of the concavo-convex structure, and FIG. 3B is a diagram schematically showing an SEM image obtained by obliquely viewing a cross section of the concavo-convex structure. As shown in FIG. 3A, the concavo-convex structure 58 is formed so as to intersect the scanning direction 50. The scanning direction 50 and the extending direction of the protrusion 62 are substantially orthogonal. As shown in FIG. 3B, protrusions 62 are periodically formed on the flat portion 60.

The energy density of the second laser beam 54 is fixed at 32 J / cm ^2, the energy density of the first laser beam 52 is changed from 24J / cm ² to 36J / cm ^2, to produce an uneven structure 58. The scanning speed of the first laser beam 52 and the second laser beam 54 with respect to the workpiece 40 is about 300 m / min. Table 1 is a table showing the period L, height H, trench length T, and width W of the concavo-convex structure 58 with respect to the energy density of the second laser beam 54.

  FIG. 4 is a diagram showing the period L with respect to the energy density of the first laser beam 52. As shown in FIG. 4 and Table 1, when the energy density of the second laser beam 54 is small, the period L is about 770 nm, and when the energy density of the second laser beam 54 is increased, the period L is about 530 nm. Further, the height H of the protrusion 62 increases as the energy density of the first laser beam 52 increases. The trench length T increases as the energy density of the first laser beam 52 increases. The width W of the concavo-convex structure 58 increases as the energy density of the first laser beam 52 increases.

As shown in Table 1, the uneven structure 58 was not formed when the energy density of the first laser beam 52 was 24 J / cm ² . The molten state of the workpiece 40 (silicon) was calculated by the finite element method. As a result, it was found that when the energy density of the first laser beam 52 was 26 J / cm ² or more, the surface of the workpiece 40 was melted for 6 μsec or more. Thus, it was found that in order to form the concavo-convex structure 58, it is preferable that the surface of the workpiece 40 is melted for a predetermined time or more.

  As shown in FIG. 2A, the periodic direction 59 of the concavo-convex structure 58 substantially coincides with the polarization direction 56. Further, as shown in FIG. 4, when the energy density of the first laser beam 52 is increased, the period L substantially coincides with the wavelength of the first laser beam 52. When the energy density of the second laser beam 54 is increased, the period L is increased. It almost coincides with the wavelength of the laser beam 54. From these facts, in the state where the surface of the workpiece 40 is melted, the periodic concavo-convex structure 58 is related to the standing wave of the laser beam generated parallel to the polarization direction 56 on the surface of the workpiece 40. Presumed to be formed.

  From the above estimation, the continuous wave laser beam may be a laser beam having one wavelength. Further, the continuous wave laser beam may be a plurality of laser beams having different wavelengths. In a state where the workpiece 40 is scanned relative to the continuous wave laser beam, the surface of the workpiece is irradiated with the continuous wave laser beam. At this time, when the energy density of the laser beams 52 and 54 is higher than the energy density at which the ablation of the workpiece 40 is ablated, ablation occurs, and thus the concavo-convex structure 58 is not formed. Therefore, the surface of the workpiece 40 is irradiated with continuous wave laser light at an energy density equal to or lower than the energy density at which the ablation of the workpiece 40 occurs. Thereby, the periodic uneven structure 58 can be formed on the surface of the workpiece 40.

  Even when the energy density of the continuous wave laser beam is smaller than the energy density at which the workpiece 40 is melted, atomic rearrangement may occur, and a concavo-convex structure having periodicity may be formed. However, in order to form the concavo-convex structure 58 having periodicity more reliably, the energy density of the laser beams 52 and 54 is preferably equal to or higher than the energy density at which the surface of the workpiece 40 is melted. When the continuous wave laser beam is a plurality of laser beams, the energy density at which the workpiece 40 is ablated and the energy density at which the surface of the workpiece 40 is melted are the total energy density of the plurality of laser beams. .

  As shown in FIGS. 3A and 3B, the formed concavo-convex structure 58 has a high periodicity because the period is substantially the wavelength of the laser beam. On the other hand, in the method of Patent Document 1, only a fibrous concavo-convex structure can be formed, and a concavo-convex structure with high periodicity cannot be formed as shown in FIGS. 3 (a) and 3 (b). In addition, since the workpiece 40 can be scanned relative to the laser beams 52 and 54 at a high speed, the concavo-convex structure 58 can be formed at a high speed. Furthermore, the concavo-convex structure 58 can be easily formed as compared with a semiconductor device manufacturing process or a method using nanoimprint. For example, the concavo-convex structure 58 can be formed in the atmosphere.

  The scanning of the workpiece 40 with respect to the laser beams 52 and 54 may be performed by fixing the workpiece 40 and scanning the laser beams 52 and 54. Alternatively, the workpiece 40 may be scanned with the laser beams 52 and 54 fixed. Further, the laser beams 52 and 54 and the workpiece 40 may be scanned in different directions. The scanning speed can also be set arbitrarily.

  Further, as in Example 1, it is preferable to use a plurality of laser beams having different wavelengths as the continuous wave laser beam. Thereby, for example, the temperature of the surface of the workpiece 40 is increased by irradiating the second laser light 54, and the surface of the workpiece 40 is melted by irradiating the first laser light 52, so that the first An uneven structure 58 having a period of the wavelength of the laser light 52 can be formed.

  Furthermore, as shown in FIG. 4, when a plurality of laser beams 52 and 54 are used, the period of the concavo-convex structure 58 can be set to the longest wavelength or shorter and the shortest wavelength or longer among the plurality of laser beams 52 and 54. . At this time, the period L of the concavo-convex structure 58 can be controlled to relatively change the energy density of the plurality of laser beams 52 and 54. Simply, the period L of the concavo-convex structure 58 can be controlled by the ratio of the energy densities of the plurality of laser beams 52 and 54. However, strictly speaking, the period L of the concavo-convex structure 58 and the ratio of the energy densities of the plurality of laser beams 52 and 54 do not change linearly.

  As in the first embodiment, the periodic direction 59 of the concavo-convex structure 58 is the polarization direction 56 of the continuous wave laser beams 52 and 54. For this reason, by making the polarization direction 56 of the continuous wave laser beams 52 and 54 substantially the same as the scanning direction 50, the periodic uneven structure 58 can be formed continuously in the scanning direction 50. Note that the polarization direction 56 and the scanning direction 50 can also intersect. For example, the concavo-convex structure 58 oblique to the scanning direction 50 can be formed by obliquely intersecting the polarization direction 56 and the scanning direction 50.

  In the first embodiment, light having a wavelength of the first laser beam 52 of 532 nm and a wavelength of the second laser beam 54 of 797 nm is used. However, the wavelength of the laser beam is appropriately selected according to the period of the uneven structure 58 to be formed. Can do. Moreover, when irradiating the plurality of laser beams 52 and 54, the example in which the plurality of laser beams 52 and 54 are simultaneously irradiated to the same position of the workpiece 40 as shown in FIG. 2A has been described. A plurality of laser beams 52 and 54 may be irradiated with a time difference at the same position of the object 40. For example, the first laser beam 52 is irradiated while the second laser beam 54 is irradiated to a certain position on the workpiece 40 and the effect of the second laser beam 54 remains (for example, before the temperature of the workpiece 40 decreases). The same position may be irradiated.

  Furthermore, although the silicon substrate has been described as an example of the workpiece 40, a semiconductor other than silicon, a metal such as stainless steel, an inorganic compound such as ceramic, an organic compound, or the like can also be used.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 10 1st laser apparatus 14,52 1st laser beam 20 2nd laser apparatus 24,54 2nd laser beam 40 Work piece 50 Scanning direction 56 Polarization direction 58 Uneven structure 59 Period direction

Claims (9)

  In a state where the workpiece is scanned relative to the continuous wave laser beam, the continuous wave laser beam is irradiated on the surface of the workpiece with an energy density equal to or lower than an energy density at which the ablation of the workpiece is generated. A method for forming a periodic structure, comprising: forming a periodic concavo-convex structure on the surface of the workpiece.   2. The method for forming a periodic structure according to claim 1, wherein an energy density of the continuous wave laser beam is equal to or higher than an energy density at which a surface of the workpiece is melted.   3. The method for forming a periodic structure according to claim 1, wherein the continuous wave laser beam is a plurality of laser beams having different wavelengths.   4. The method for forming a periodic structure according to claim 3, wherein a period of the concavo-convex structure is not longer than a longest wavelength and not shorter than a shortest wavelength among the plurality of laser beams.   5. The method for forming a periodic structure according to claim 4, wherein the period of the concavo-convex structure is controlled by relatively changing the energy density of the plurality of laser beams.   6. The method of forming a periodic structure according to claim 1, wherein the direction of the period of the concavo-convex structure is a polarization direction of the continuous wave laser.   The method for forming a periodic structure according to claim 6, wherein the polarization direction of the continuous wave laser is the same as the scanning direction.   2. The method for forming a periodic structure according to claim 1, wherein a period of the concavo-convex structure is substantially equal to a wavelength of the continuous wave laser beam.   A periodic structure manufactured by the method for forming a periodic structure according to claim 1.

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