JP5635151B2 - Periodic structure forming method - Google Patents

Description

  The present invention relates to a periodic structure forming method.

  Surface texturing is one of the methods for expressing various surface functions such as improvement of sliding characteristics. The laser processing method for forming a fine periodic structure in a self-organizing manner is an effective processing method for forming the surface texture.

  As the laser processing method, a linearly polarized laser beam is irradiated with an irradiation intensity in the vicinity of the processing threshold value, and scanning is performed while overlapping the irradiated portions to form a grating-like periodic structure in a self-organized manner.

  In other words, when a linearly polarized laser beam is irradiated onto the substrate at an energy density near the processing threshold, energy is emitted at a periodic interval that is approximately between the laser wavelength due to interference between the incident light and surface scattered light originating from defects on the substrate or plasma waves. A slight roughness occurs in the distribution. In a general processing method, the entire laser irradiation surface is processed, but a portion of high energy can be selectively processed by laser irradiation at an energy density near the processing threshold. As a result, a grating-like periodic structure is formed while performing laser irradiation with one optical axis. At this time, the longer the pulse width of the laser used for processing, the more disturbed the periodic structure is due to the influence of heat and the scattering of the laser due to the interaction with the processed evaporation.

  When the periodic structure is formed, the processed transpiration material becomes fine particles called debris and reattaches to the processed surface and its periphery. This debris tends to increase as the pulse width of the laser used for processing increases.

  Conventionally, there is a removal method for removing deposits attached to an object to be processed having a periodic structure by a cleaning device using a laser (Patent Document 1). In this Patent Document 1, a periodic structure is provided in a portion irradiated with laser light, and as a principle that an attached matter is easily peeled off, a meniscus force acting between two objects, electrostatic force and van der Worth force are used. The so-called adhesion force formation range becomes smaller, and the periodic structure formed on the surface of the object to be processed acts like a diffraction grating, that is, by repeatedly reflecting incident laser light without scattering it. It is described that the deposits and the periodic structure are irradiated.

  By the way, the thing of the said patent document 1 uses the nanosecond laser as a laser. Deposits larger than the pitch of the periodic structure can be removed by general laser cleaning using a nanosecond laser or the like. However, the fine debris trapped in the groove of the periodic structure is greatly influenced by the surface force, and the adhesion is higher than the portion where the periodic structure is not formed due to the anchor effect. For this reason, in normal laser cleaning, the laser output necessary for debris removal exceeds the damage threshold of the periodic structure, and the periodic structure is damaged.

  For this reason, the debris removal of the periodic structure is generally performed using an ultrasonic cleaning apparatus as shown in FIG. The ultrasonic cleaning apparatus shown in FIG. 11 includes a cleaning tank 51 containing a cleaning liquid, a vibrator 52 attached to the cleaning tank 51, an oscillator 53 that vibrates the vibrator 52, and a power source connected to the oscillator 53. 54 etc.

  That is, a workpiece (a substrate having a periodic structure formed thereon) is immersed in the cleaning tank 51, and in that state, the vibrator 52 is vibrated via the oscillator 53, thereby generating ultrasonic vibrations in the cleaning tank 51. Let

  Ultrasonic cleaning is performed by three synergistic effects: cavitation effect, acceleration, and straight flow. The cavitation effect is to remove the dirt from the workpiece using a shock wave generated by cavitation. The peeled dirt is peeled off by acceleration and dispersed and removed by a straight flow.

  That is, the cavitation effect is a cleaning method using a shock wave generated by rupturing a vacuum bubble generated in a liquid (cleaning liquid) by ultrasonic waves. When the liquid is irradiated with ultrasonic waves, the liquid is vigorously shaken, and a portion where the pressure is locally high and a portion where the pressure is low are formed. In the part where the pressure is low, a small vacuum cavity (cavitation) is formed in the liquid, and when the pressure becomes high again and the cavity is crushed, a shock wave is generated in the liquid. This shock wave peels off the dirt adhering to the solid surface.

  In addition, the liquid molecules vibrate vigorously due to the amplitude of the ultrasonic waves. For this reason, the effect of peeling off the dirt peeled off by the cavitation effect is the acceleration effect. Due to the radiation pressure from the vibrator 52, a straight flow is generated when the input of ultrasonic waves is equal to or higher than a predetermined intensity (ultrasonic intensity), and a slight water flow is generated in the cleaning tank 51. The effect is a straight-ahead effect.

JP 2011-32559 A

  If an ultrasonic cleaning apparatus as shown in FIG. 11 is used, so-called batch processing is performed, and productivity is poor. That is, since the cleaning process time becomes long, batch processing is performed. Further, since the cleaning liquid is used, a large amount of the cleaning liquid including the removed deposits is produced, and management and processing of the cleaning liquid are necessary, resulting in an increase in cost. Furthermore, the washing tank has a disadvantage that it is increased in size in order to introduce a plurality of objects to be cleaned, and the entire apparatus is increased in size.

  In view of the above problems, the present invention provides a periodic structure forming method capable of forming a periodic structure with less debris adhesion by a so-called dry process without performing ultrasonic cleaning using a cleaning tank.

The periodic structure forming method of the present invention irradiates linearly polarized first-step pulse laser with an irradiation intensity in the vicinity of the processing threshold, scans the irradiated portions in an overlapping manner, and forms a grating-like periodic structure in a self-organized manner. And irradiation with a second step pulse laser having a wavelength within ± 10% of the first step pulse laser in the first step and a pulse width of 50 picoseconds or less. Irradiation energy per unit area is lower than that in the first step while overlapping portions, and the polarization direction of the laser in the second step is within ± 10 ° of the polarization direction of the laser in the first step. set as by irradiating the grating shape periodic structure formed in the first step, der that a second step of re-scanned by resonance the incident light and the surface electromagnetic wave .

  According to the periodic structure forming method of the present invention, first, a grating-like periodic structure can be formed on a workpiece (workpiece) in the first step. Then, by irradiating the periodic structure formed in the first step with the laser in the second step, the incident light and the surface electromagnetic wave resonate to process the extreme surface layer and remove debris with a small incident energy. Can do.

  By the way, after about 50 picoseconds (ps) elapses after the laser irradiation of the workpiece (workpiece), the influence of the interaction between the processed vaporized material and the laser becomes obvious. For this reason, when the pulse width of the laser used in the second step is 50 ps or less, debris can be removed without causing disturbance of the periodic structure even when the pulse width of the first step is shorter than the pulse width of the second step. On the other hand, if the pulse width of the first step is longer than the pulse width of the second step, the disturbance of the periodic structure can be corrected and debris can be removed if the pulse width of the second step is 50 picoseconds (ps) or less. it can. That is, the second step can also serve as a periodic structure finishing step.

  It is preferable to set the scanning area of the second step wider than the scanning area of the first step. Further, the irradiation energy per unit area of the second step is set to 5% to 30% of the irradiation energy per unit area of the first step, or the number of shots of laser irradiation to the same position in the second step is 1. 10 shots are preferable.

The rescanning in the second step can be performed a plurality of times. In this case, the total irradiation energy of the second step is 5% to 30% of the irradiation energy per unit area of the first step.
% Have it is preferable to set in.

  In the periodic structure forming method of the present invention, debris can be removed in the second step without causing disturbance of the periodic structure with respect to the periodic structure formed in the first step, and a product with a high-quality periodic structure formed can be provided. . Further, since the incident energy in the second step can be reduced, there is an advantage that a periodic structure with less disturbance and debris can be formed even for a semiconductor or ceramic having a laser penetration length longer than that of a metal. Further, when the pulse width of the first step is longer than the pulse width of the second step, the pulse width of the second step is 50 picoseconds (ps) or less, so that the disturbance of the periodic structure is corrected and debris is removed. Therefore, the second step can also serve as a periodic structure finishing step. In addition, the generation of new debris is suppressed by lowering the irradiation energy per unit area in the second step than in the first step in the previous period, which can contribute to the formation of a periodic structure with less disturbance and debris.

  By setting the scanning area of the second process wider than the scanning area of the first process, it is possible to remove debris adhering to the periodic structure non-formed part, and it is possible to maintain high quality even as the periodic structure non-formed part. . Further, by setting the irradiation energy per unit area in the second step as described above, it is possible to significantly reduce the disturbance of the periodic structure and the adhesion of debris. Furthermore, by setting the number of laser shots in the second step as described above, it is possible to efficiently form a periodic structure with less disturbance and debris by high-speed scanning. Debris adhesion can be minimized by repeating the rescanning of the second step a plurality of times. By making the polarization directions of the lasers used in the first step and the second step the same direction, resonance between incident light and surface electromagnetic waves occurs efficiently, and the irradiation energy in the second step can be further reduced, so that the disturbance of the periodic structure is suppressed. It is effective for improving finishing accuracy. Even when the polarization direction of the laser in the second step is within ± 10 ° of the polarization direction of the laser in the first step, it is possible to sufficiently exhibit the disturbance of the periodic structure and improve the finishing accuracy.

It is a block diagram of the periodic structure formation method which shows embodiment of this invention. It is a principal part expanded sectional view of the sliding surface structure which has the periodic structure part formed by the periodic structure formation method of this invention. FIG. 3 is a simplified view of a sliding surface having a periodic structure portion of the sliding surface structure shown in FIG. 2. It is an enlarged view of the periodic structure part formed in the said sliding surface. It is a simplified diagram of the laser surface processing apparatus used for the periodic structure forming method. It is a graph for demonstrating the definition of arithmetic mean roughness. It is an electron microscope figure which shows the boundary part of the periodic structure part after a 1st process, and an unformed part. It is an electron microscope figure which shows the boundary part of the periodic structure part after a 2nd process, and an unformed part. It is an electron microscope figure which shows the boundary part of a 1st process and a 2nd process. It is the graph which compared the friction coefficient of the invention which performed the 1st process and the 2nd process, and the conventional product which performed ultrasonic cleaning. It is a simplified diagram of an ultrasonic cleaning device.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram showing a periodic structure forming method according to the present invention, and FIG. 2 shows a sliding surface structure having a periodic structure portion formed by this periodic structure forming method. As shown in FIG. 2, this sliding surface structure is such that the sliding surface 1 a of the first member 1 and the sliding surface 2 a of the second member 2 slide relative to each other under the lubricant L. In this case, the first member 1 and the second member 2 may be carbon steel, copper, aluminum, platinum, cemented carbide, silicon ceramics such as silicon carbide or silicon nitride, engineer plastic, etc. It may be. Further, the lubricant L may be water or alcohol, or may be a lubricating oil such as engine oil. That is, various lubricants can be used depending on the material of the first and second members 1 and 2 and the environment in which they are used. Moreover, the 1st member 1 was made into the ring body as shown, for example in FIG. 3, and the 2nd member 2 was comprised by the disk shaped body, for example.

  The upper surface of the first member 1 becomes the sliding surface 1a, and the lower surface of the second member 2 becomes the sliding surface 2a. The sliding surface 1a of the first member 1 is provided with a periodic structure portion 3 having grating-like irregularities and a periodic structure non-formed portion 8 in which the periodic structure portion is not formed. That is, the spiral periodic structure portion 3 is formed on the outer diameter side of the sliding surface 1 a of the first member 1, and the periodic structure non-formed portion 8 is formed on the inner diameter side of the sliding surface 1 a of the first member 1. Is done.

  As shown in FIG. 4, the periodic structure portion 3 is formed by alternately arranging minute concave portions 5 and minute convex portions 6 at a predetermined pitch. It is preferable that the irregular pitch of the periodic structure portion 3 is 10 μm or less and the depth of the concave portion 5 is 1 μm or less. In this case, the recess 5 of the periodic structure portion 3 communicates (opens) with the outer peripheral edge (sliding surface peripheral edge) 1 b of the first member 1, but does not open with the inner peripheral edge 1 c of the first member 1. . And the recessed part 5 of the periodic structure part 3 is curving in spiral shape.

  Then, when at least one of the first member 1 and the second member 2 rotates around its axis, the periodic structure portion 3 of the first member 1 is lubricated from the outer peripheral edge side of the sliding surface 1a. Is set to be introduced into the first member 1. In this case, since all the concave portions 5 of the periodic structure portion 3 are open to the outer peripheral edge 1b of the first member 1, the lubricant can be drawn from the entire peripheral edge of the sliding surface.

  As shown in FIG. 5, the periodic structure unit 3 uses a laser surface processing apparatus including a laser generator 11 and an optical system 10. As shown in FIG. 1, the periodic structure forming method of the present invention includes a first step 21 for forming a grating-like periodic structure, and debris attached to the periodic structure formed in the first step 21. The second step 22 to be removed is performed.

  In this laser surface processing apparatus, the laser generator 11 is folded back toward the processing material W by the mirror 12 and guided to the mechanical shutter 13. At the time of laser irradiation, the mechanical shutter 13 is opened, the laser irradiation intensity can be adjusted by the half-wave plate 14 and the polarization beam splitter 16, the polarization direction is adjusted by the half-wave plate 15, and the condenser lens 17 The surface of the work material W on the XYθ stage 19 is focused and irradiated.

  In the first step 21, a linearly polarized laser beam is irradiated with an irradiation intensity in the vicinity of the processing threshold, and the irradiated portion is scanned while overlapping to form a self-organized structure. That is, when a workpiece (working material) W is irradiated with a linearly polarized laser beam at a fluence near the ablation threshold, interference between the incident light and the scattered light or plasma wave along the surface of the processing material W is approximately the same as the laser wavelength. At periodic intervals, there is a slight roughness in the energy distribution. In a general processing method, the entire laser irradiation surface is processed, but a portion of high energy can be selectively processed by laser irradiation at an energy density near the processing threshold. As a result, a grating-like periodic structure is formed while performing laser irradiation with one optical axis. At this time, the longer the pulse width of the laser used for processing, the more disturbed the periodic structure is due to the influence of heat and the scattering of the laser due to the interaction with the processed evaporation.

  When the periodic structure is formed, the processed transpiration material becomes fine particles called debris and reattaches to the processed surface and its periphery. This debris tends to increase as the pulse width of the laser used for processing increases. Therefore, after the periodic structure is formed on the work in the first step 21, the second step 22 is performed to remove the debris, and the periodic structure as shown in FIG. Complete part 3.

  Also in the second step 22, irradiation with linearly polarized laser is performed, and scanning (rescanning) is performed while overlapping the irradiated portions. In this case, in the second step 22, the first step in the first step 21 is performed. The irradiation energy per unit area of the second process pulse laser with a wavelength within ± 10% of the pulse laser for use and having a pulse width of 50 picoseconds or less is overlapped with the first irradiation energy. Re-scanning is performed with setting to be lower than in step 21.

  In either the first step 21 or the second step 22, the laser scan may be performed by fixing the laser and moving the XYθ stage 19 that supports the workpiece W, or by fixing the XYθ stage 19 and moving the laser. May be moved. Alternatively, the laser and the XYθ stage 19 may be moved simultaneously.

  In this way, the periodic structure formed in the first step 21 is irradiated with the laser of the second step 22 having a wavelength within ± 10% with respect to the pulse laser for the first step. Surface electromagnetic waves resonate, and processing of the extreme surface layer and removal of debris can be performed with a small incident energy. That is, the debris can be removed in the second step 22 without causing disturbance of the periodic structure with respect to the periodic structure formed in the first step 21, and a product having a high-quality periodic structure can be provided.

  Further, since the incident energy in the second step 21 can be reduced, there is an advantage that a periodic structure with less disturbance and debris can be formed even for a semiconductor or ceramic having a laser penetration length longer than that of a metal. Furthermore, when the pulse width of the first step 21 is longer than the pulse width of the second step 22, the pulse width of the second step 22 is 50 ps or less, so that the disturbance of the periodic structure can be corrected and debris can be removed. Thus, the second step 22 can also serve as a periodic structure finishing step. Moreover, by making the irradiation energy per unit area in the second step 22 lower than that in the first step 21, the generation of new debris is suppressed, which can contribute to the formation of the periodic structure portion 3 with less disturbance and debris.

  By the way, in the second step 22, the debris adhering to the periodic structure formed in the first step 21 is removed. Therefore, the scanning region and the scanning region in the second step 22 are usually set to be the same. become. However, the scanning area of the second step 22 can be set wider than the scanning area of the first step 21. Thus, by widening the scanning region of the second step 22, debris adhering to the structure unformed portion 8 can be removed, and high quality can be maintained as the periodic structure unformed portion 8 as well.

  The irradiation energy per unit area in the second step 22 is preferably set to 5% to 30% of the irradiation energy per unit area in the first step 21. By setting in this way, disturbance of the periodic structure portion 3 and adhesion of debris can be significantly reduced. That is, if it is less than 5%, the effect of removing debris adhesion is not exhibited, and if it exceeds 30%, the periodic structure portion 3 may be disturbed.

  It is preferable that the number of shots of laser irradiation to the same position in the second step 22 is 1 to 10 shots. By setting in this way, it is possible to efficiently form the periodic structure part 3 with less disturbance and debris by high-speed scanning. The rescan in the second step 22 may be repeated a plurality of times. By repeating a plurality of times in this way, the adhesion of debris can be minimized. Even in the case of repeating a plurality of times, in order to prevent disturbance of the periodic structure portion 3 and adhesion of debris, the total irradiation energy of the second step 22 is 5 of the irradiation energy per unit area of the first step 21. It is preferable to set to 30% to 30%.

  Further, it is preferable that the polarization direction of the laser in the first step 21 is the same as the polarization direction of the laser in the second step. By making the polarization direction of the laser the same direction, the resonance of the incident light and the surface electromagnetic wave occurs efficiently, and the irradiation energy in the second step 22 can be further reduced, which is effective in suppressing the disturbance of the periodic structure and improving the finishing accuracy. In this case, the polarization direction of the laser in the second step 22 is set within ± 10 ° of the polarization direction of the laser in the first step 21. That is, it is the same when tilted within 10 ° clockwise and within 10 ° counterclockwise with respect to the completely coincident direction and the polarization direction of the laser in the first step 21. Is included. Thus, even if the polarization direction of the laser in the second step 22 is within ± 10 ° of the polarization direction of the laser in the first step 21, it is possible to sufficiently exhibit the disturbance of the periodic structure and improve the finishing accuracy.

  As mentioned above, although it demonstrated per embodiment of this invention, this invention is not limited to the said embodiment, A various deformation | transformation is possible, for example, in the said embodiment, the periodic structure part 3 is the 1st member 1 side. However, the periodic structure portion 3 may be formed on the second member 2 side or on both sides of the first member 1 and the second member 2. Further, the shapes of the first member 1 and the second member 2 are not limited to those in the illustrated example, and can be configured in other various shapes.

  Even if the relative sliding movement of the first member 1 and the second member 2 is such that the first member 1 is fixed and the second member 2 is slid (rotated), the second member 2 side is reversed. May be fixed, and the first member side may be slid (rotated). That is, the direction in which the periodic structure portion 3 is formed may be slid, or the direction in which the periodic structure portion 3 is not formed may be slid (rotated). Further, both the first member 1 and the second member 2 may be slid (rotated).

  Moreover, in the said embodiment, in the periodic structure part 3 shown in FIG. 1 etc., the recessed part 5 is opened to the outer periphery 1b without opening to the inner periphery 1c of the 1st member 1, and it is made to open from an outer peripheral side to an inner peripheral side. The lubricant is drawn in, but conversely, the recess 5 may be opened in the inner peripheral edge 1c without opening in the outer peripheral edge 1b, and the lubricant may be drawn in from the inner peripheral side to the outer peripheral side.

  In the embodiment, the concave portion 5 of the periodic structure portion 3 is formed in a spiral shape over the entire circumference on the outer peripheral side. However, the plurality of periodic structure portions 3 are arranged at a predetermined pitch along the circumferential direction. Even if it exists, you may arrange | position in a concentric form, without making it curve in a spiral form. Moreover, as a sliding surface structure, in the said embodiment, although it was the relative rotation of the 1st member 1 and the 2nd member, you may comprise linear reciprocation.

  As the laser used in the first step 21, a pulse laser such as a femtosecond laser, a picosecond laser, and a nanosecond laser can be used.

  SiC was irradiated with linearly polarized laser (wavelength 1064 nm, pulse width 10 ps) at an irradiation intensity in the vicinity of the processing threshold, and scanning was performed while overlapping the irradiated portions to form a periodic structure (first step 21). FIG. 7 shows an electron microscope image of the boundary portion between the periodic structure portion 3 and the non-formed portion 8 after the first step 21 is completed. It can be confirmed that debris is attached not only to the periodic structure portion 3 but also to the unformed portion 8. In addition, many very small debris that cannot be recognized as particles at the magnification of FIG. 7 are attached, and the whole looks whitish.

  Next, the laser wavelength, the pulse width, and the polarization direction are made the same as those in the first step 21, and the laser pulse energy and the scanning speed are adjusted so that the irradiation energy per unit area becomes 1/6 of that in the first step 21. Re-scanning was performed including the periodic structure non-formed part 8 in which the adhesion was observed (second step 22). An electron microscope image of the boundary portion between the periodic structure portion 3 and the unformed portion 8 after the second step 22 is shown in FIG. It can be confirmed from FIG. 8 that the periodic structure portion 3 with less disturbance and debris is formed. In addition, very small debris is also removed, and the whole is changed to blackish as compared with FIG.

  The color tone of the periodic structure non-formed part 8 from which the debris was removed was almost the same as the original color tone of the SiC substrate. FIG. 9 shows an electron microscope image of the boundary portion between the first step 21 and the second step 22 when the second step 22 is stopped in the middle of the periodic structure portion 3. The change of the color tone by the 2nd process 22 can be confirmed clearly. The same phenomenon was confirmed when the irradiation energy per unit area of the second step 22 was 5% to 30% of the first step 21.

  If the laser wavelength in the second step 22 is ± 10% with respect to the first step 21, the incident light and the surface electromagnetic wave resonate when the periodic structure formed in the first step 21 is irradiated with the laser in the second step 22. In addition, it is possible to process the extreme surface layer and remove debris with a small incident energy. Since the incident energy can be reduced, it is possible to remove debris without disturbing the periodic structure even for semiconductors and ceramics having a laser penetration length longer than that of metal.

  When about 50 ps elapses after the laser irradiation, the influence of the interaction between the processed vaporized material and the laser becomes obvious. Therefore, the pulse width of the laser used in the second step 22 is desirably 50 ps or less. The pulse width of the laser used in the first step 21 is desirably a short pulse, but is not particularly limited to within 50 ps.

  When the pulse width of the first step 21 was shorter than the pulse width of the second step 22, debris could be removed without causing disturbance of the periodic structure if the pulse width of the second step 22 was 50 ps or less. When the pulse width of the first step 21 is longer than the pulse width of the second step 22, if the pulse width of the second step 22 is 5 Ops or less, the disturbance of the periodic structure can be corrected and debris can be removed. If the polarization direction of the laser used in the second step 22 is the same as the polarization direction of the first step 21, the resonance between the incident light and the surface electromagnetic wave occurs efficiently, which is effective for suppressing the disturbance of the periodic structure and improving the finishing accuracy.

  The friction coefficient of the test piece having the periodic structure portion 3 formed by performing the first step 21 and the second step 22 and the test piece subjected to ultrasonic cleaning after the first step 21 were compared.

  Experiments were performed using a ring-on-disk test apparatus. The ring test piece was used as the rotation side test piece (Sic), and the disk test piece (alumina) was used as the fixed side test piece. The surface roughness (arithmetic average roughness) of each test piece was Ra 0.02 μm or less. All the disk test pieces were mirror surfaces, and a spiral periodic structure portion (periodic structure for the purpose of generating dynamic pressure) as shown in FIG. 3 was formed on the ring test pieces (outer diameter 16 mm, inner diameter 10 mm).

As shown in FIG. 6, the arithmetic average roughness Ra is obtained by extracting only the reference length from the roughness curve in the direction of the average line, the X axis in the direction of the average line m of the extracted portion, and the direction of the vertical magnification. When the Y-axis is taken and the roughness curve is represented by y = f (x), the value obtained by the following equation 1 is represented by micrometers (μm).

  The ring test piece is formed by the conventional method (first step 21 + ultrasonic cleaning) (conventional product) and the periodic structure part 3 and the present method (first step 21 + second step 22) (product of the present invention). The periodic structure portion 3 was formed in two types. The same laser (wavelength 1064 nm, pulse width 10 ps) was used in the first step 21 and the second step 22. The irradiation energy per unit area in the second step 22 was set to 1/6 that of the first step 21. The inclination angle of the periodic structure with respect to the sliding direction was θ = 45 °. The pitch of the periodic structure was about 950 nm and the depth was about 250 nm. In order to evaluate basic lubrication characteristics, PAO4 (18.82 cP @ 37 ° C.) having no polarity and being thermally and chemically stable was used as the lubricant. The load was 20 N (0.16 Ma), and the average friction coefficient for 5 min at each sliding speed was measured while the sliding speed was gradually reduced from 81.5 mm / s to 3.3 mm / s.

  FIG. 10 shows a comparison of the coefficient of friction of the ring test piece in which a spiral periodic structure is formed by the conventional method and the present method. The friction coefficient of the method of the present application was slightly higher at the time of high-speed sliding than that of the conventional method and slightly lower at the time of low-speed sliding, but these are in the category of experimental error, and it can be determined that there is no significant difference between the two. That is, according to the method of the present application, it is possible to eliminate the ultrasonic cleaning process that requires batch processing and waste liquid processing, and to form a periodic structure with less disturbance and debris in a complete dry process.

21 1st process 22 2nd process

Claims (5)

A first step of irradiating a linearly polarized first-stage pulse laser with an irradiation intensity in the vicinity of a processing threshold, scanning the overlapping portions to overlap, and forming a grating-like periodic structure in a self-organized manner; Per unit area while overlapping the irradiated portion with the second step pulse laser having a wavelength within ± 10% of the first step pulse laser in the first step and having a pulse width of 50 picoseconds or less. In the first step, the irradiation energy of the second step is set to be lower than that of the first step and the polarization direction of the laser in the second step is within ± 10 ° of the polarization direction of the laser in the first step A periodic structure forming method comprising: a second step of re-scanning by resonating the incident light and surface electromagnetic waves by irradiating the formed grating-like periodic structure .   2. The method for forming a periodic structure according to claim 1, wherein the scanning region in the second step is set wider than the scanning region in the first step.   3. The periodic structure forming method according to claim 1, wherein the irradiation energy per unit area of the second step is set to 5% to 30% of the irradiation energy per unit area of the first step. 4. .   The periodic structure forming method according to claim 1, wherein the number of shots of laser irradiation to the same position in the second step is 1 to 10 shots.   The periodic structure forming method according to claim 1, wherein rescanning in the second step is performed a plurality of times.