Surface modification laser irradiation device, surface modification laser irradiation method, semiconductor member, and silicone solar cell

Abstract

To provide a surface modification laser irradiation device which can form a nano-dot structure without melting, without using chemicals that are difficult to be treated.SOLUTION: A surface modification laser irradiation device includes a light source device 70 including a laser light source for emitting a laser beam, and an optical system 20 for arranging the laser beam emitted from the laser light source in a previously set optical path toward a target 1 subjected to surface modification and guiding the laser beam, a storage part 50 for storing the target 1 together with a medium 7 which is liquid or gas having thermal conductivity higher than that of air, and a moving mechanism 40 for moving either or both of the target and the laser beam irradiation position, wherein the storage part has a supporting part 53 for supporting the target irradiated with the laser beam through the medium, and laser energy density in which the target in the medium is irradiated with the laser beam from the light source device is equal to or more a bulge start threshold of a second projection 5 formed on a conical side face of a first projection having a conical shape of the target, and is equal to or less than a melting threshold of the target in the medium.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a surface-modifying laser irradiation device and a surface-modifying laser irradiation method for modifying the surface of a semiconductor member used when performing photoelectric conversion, the semiconductor member, and a silicon solar cell. [Background technology]

[0002] There is a known technology for forming a micro-dot structure by irradiating a pulsed laser onto the surface of a semiconductor material such as silicon. This technology can improve the light-to-electricity conversion efficiency by forming minute protrusions on the surface of a silicon panel used in, for example, a solar cell. In particular, it is expected that by forming a pyramidal structure of several μm to a dozen μm as the protrusions and forming a nano-dot structure on the surface of the pyramidal structure, the reflection of light on the silicon panel can be suppressed and the efficiency of photoelectric conversion can be improved. As an example, there is a known report of the formation of a fine periodic structure on the surface of a silicon solar cell (see non-patent documents 1, 2, 3). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Fumitaka Nigo1 · Masaki Hashida2 · Masahiro Tsukamoto3 · Shuji Sakabe2 · Mitsuhiro Kusaba1 "Reflectance and crystallinity of silicon solar cells with LIPSS produced by XeCl excimer laser pulses" Received:14 October 2019 / Accepted:9 January 2020 Springer-Verlag GmbH Germany,part of Springer Nature 2020 [Non-Patent Document 2] Fumitaka Koji and Mitsuhiro Kusaba (Graduate School of Engineering, Osaka Sangyo University: 3-1-1 Nakagakiuchi, Daito-shi, Osaka), Masaki Hashida and Shuji Sakabe (Institute for Chemical Research, Kyoto University: Gokasho, Uji-shi, Kyoto), "Nano-fine structure formation on silicon solar cell surface by non-thermal processing with excimer laser," Laser Research: March 2019 issue, pp. 160-163 [Non-Patent Document 3] Fumitaka Kogo and Mitsuhiro Kusaba (Graduate School of Engineering, Osaka Sangyo University: 3-1-1 Nakagakiuchi, Daito, Osaka) Masaki Hashida and Shuji Sakabe (Institute for Chemical Research, Kyoto University: Gokasho, Uji, Kyoto) Masahiro Tsukamoto (Joining and Welding Research Institute, Osaka University: 11-1 Mihogaoka, Ibaraki, Osaka) "Surface roughness and crystal structure of silicon photovoltaic cells irradiated with ultraviolet femtosecond laser" Journal of the Society A (Basics, Materials, and Common Division Paper) Vol. 140 No. 8 pp. 401-406 DOI: 10.1541 / ieejfins.140.401 IEEJ Trans.FM, Vol. 140, No. 8, 2020 (Received October 24, 2019, Reaccepted December 14, 2019) Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional technology, the heat generated when the laser is irradiated causes a part of the nanodot structure to melt, and the effect of the nanodot structure cannot be achieved as desired. There is also a technology that uses chemicals to form a nanodot structure on the surface of the pyramid structure of several μ to several tens of μ, but the waste liquid disposal of the used chemicals is troublesome and expensive, and is not desirable at present.

[0005] Therefore, the present invention has been devised in consideration of the above-mentioned circumstances, and has an objective of providing a surface modification laser irradiation device, a surface modification laser irradiation method, a semiconductor component, and a silicon solar cell that can form a nanodot structure without melting, without using chemicals that are difficult to process. [Means for solving the problem]

[0006] In order to solve the above problem, the surface modification laser irradiation device according to the present invention includes a light source device including a laser light source that irradiates laser light, and an optical system that arranges and guides the laser light from the laser light source on a preset optical path toward a target to be surface modified, a storage unit that stores the target together with a medium that is a liquid or gas having a higher thermal conductivity than air, and a moving mechanism that moves either the target or the irradiation position of the laser light, or both. The storage unit also has a support unit that supports the target to be irradiated by the laser light through the medium. Furthermore, the laser energy density at which the laser light from the light source device is irradiated to the target in the medium is equal to or higher than the protuberance start threshold of the second convex portion formed on the cone side surface of the cone-shaped first convex portion of the target, and is equal to or lower than the melting threshold of the target in the medium.

[0007] In addition, in order to solve the above-mentioned problems, the surface modification laser irradiation method of the present invention includes the steps of preparing a target to be surface modified by storing it in a storage section filled with a medium, which is a liquid or gas having a thermal conductivity higher than that of air, irradiating the target in the prepared storage section with laser light from a laser light source through the medium by an optical system arranged in an optical path, and moving one or both of the target and the irradiation position of the laser light via a moving mechanism so that the laser light is irradiated over the entire area of ​​a predetermined irradiation area of ​​the target, wherein in the step of irradiating the laser light, the laser energy density at which the laser light is irradiated onto the target is equal to or higher than the protuberance start threshold of a second convex portion formed on the cone side surface of a cone-shaped first convex portion of the target, and equal to or lower than the melting threshold of the target in the medium.

[0008] Furthermore, in order to solve the above problems, the semiconductor member according to the present invention is a semiconductor member having a pyramidal convex portion on its surface for converting received light into electricity, the convex portion having a pyramidal first convex portion formed on the surface of the semiconductor member and a second convex portion on the pyramidal side surface of the first convex portion, the first convex portion having a size of 1 μm to 30 μm, the second convex portion having a size of 1 / 50 to 1 / 2 the wavelength of the irradiated laser light, and either or both of the ratio of the length of one side of the apex to the length of one side of the base is 1≦base / apex≦4, or the aspect ratio of the base to the height is 0.1≦base / height≦2.

[0009] In order to solve the above problems, the silicon solar cell of the present invention is a solar cell comprising a silicon panel used for photoelectric conversion, a first electrode arranged on the light-receiving surface side of the silicon panel, and a second electrode arranged on the other surface of the silicon panel opposite the light-receiving surface, wherein the silicon panel is configured as a semiconductor component having the above-described structure. Effect of the Invention

[0010] According to the surface modification laser irradiation device and the surface modification laser irradiation method of the present invention, it is possible to form a semiconductor member without using chemicals that are difficult to process and without melting the nanodot structure. Therefore, it is possible to improve the photoelectric conversion efficiency of the surface-modified semiconductor member and silicon solar cell. [Brief description of the drawings]

[0011] [Figure 1] 1 is a block diagram showing a surface modification laser irradiation device according to the present invention; [Diagram 2] 2 is a perspective view showing a schematic irradiation state of laser light irradiated from a cylindrical lens onto a target in the surface modification laser irradiation device of FIG. 1. FIG. [Figure 3A] 3 is a front view showing a schematic enlarged view of a part of a target irradiated with laser light in FIG. 2. [Figure 3B]3 is a front view showing a schematic view of the irradiation position of the laser light in FIG. 2 on a part of the target. [Figure 4A] FIG. 2 is a perspective view that typically shows a state in which second protrusions are formed on first protrusions of a semiconductor article according to the present invention. [Figure 4B] FIG. 4B is a plan view diagrammatically illustrating the state of FIG. 4A. [Figure 4C] 4B is a perspective view showing a schematic enlargement of a second protrusion portion of FIG. 4A. FIG. [Diagram 5] 2 is a flowchart showing a surface modification laser irradiation method according to the present invention. [Figure 6A] 4 is a schematic diagram for illustrating a state in which a second protrusion is formed on a conical side surface of a first protrusion of a semiconductor member in water. FIG. [Figure 6B] 4 is an explanatory diagram illustrating a state of a second protrusion formed on a conical side surface of a first protrusion of a semiconductor member in the atmosphere. FIG. [Figure 7A] 4 is a schematic diagram for explaining second convex portions formed on a first cone-shaped side surface and a third cone-shaped side surface of a first convex portion of a semiconductor member in the atmosphere. FIG. [Figure 7B] 4 is an explanatory diagram showing a schematic state of second convex portions formed on a first cone-shaped side surface and a third cone-shaped side surface of a first convex portion of a semiconductor member in water. FIG. [Figure 8A] FIG. 1 is a graph showing the relationship between the melting diameter [μm] and the laser energy density (Laser fluence) [J / cm2] when a silicon panel used in a silicon solar cell is irradiated with laser light in the atmosphere. [Figure 8B] FIG. 1 is a graph showing the relationship between the melting diameter [μm] and the laser energy density (Laser fluence) [J / cm2] when a silicon panel used in a silicon solar cell is irradiated with laser light in water. [Figure 9A] FIG. 2 is a block diagram showing a first modified example of the surface modification laser irradiation device according to the present invention. [Figure 9B] FIG. 11 is a block diagram showing a second modified example of the surface modification laser irradiation device according to the present invention. [Figure 10]1 is a schematic diagram showing the configuration of a first application example of a surface-modifying laser irradiation device according to the present invention; FIG. [Figure 11] FIG. 2 is a schematic diagram showing the configuration of a second application example of the surface modification laser irradiation device according to the present invention. [Figure 12A] FIG. 1 is a perspective view showing a schematic view of a portion of a silicon solar cell according to the present invention. [Figure 12B] FIG. 12B is an enlarged perspective view showing a schematic enlargement of a portion XVIIB in FIG. 12A. [Figure 12C] FIG. 12C is an enlarged schematic cross-sectional view of a portion XVIIC in FIG. 12B. [Figure 12D] FIG. 12D is an enlarged perspective view showing a schematic view of a portion XVIID in FIG. 12C. [Figure 12E] FIG. 12E is a plan view showing a schematic view of the protrusion shown in FIG. 12D as viewed from above. [Figure 13A] 4 is an enlarged photograph showing a first convex portion of a silicon panel of a silicon solar cell before being irradiated with laser light in an example of the present invention. [Figure 13B] 14 is a photograph showing a state in which second convex portions are formed by irradiating the first convex portions of FIG. 13 with 200 pulses of laser light at a laser energy density of 0.80 J / cm 2 . [Figure 13C] 14 is a photograph showing a state in which second convex portions are formed by irradiating the first convex portions of FIG. 13 with 200 pulses of laser light at a laser energy density of 0.60 J / cm 2 . [Figure 14A] 4 is an enlarged photograph showing a first convex portion of a silicon panel of a silicon solar cell before being irradiated with laser light in an example of the present invention. [Figure 14B] 15 is a photograph showing a state in which second convex portions are formed by irradiating the first convex portions of FIG. 14 with 200 pulses of laser light at a laser energy density of 0.50 J / cm 2 . [Figure 14C] 15 is a photograph showing a state in which second convex portions are formed by irradiating the first convex portions of FIG. 14 with 200 pulses of laser light at a laser energy density of 0.40 J / cm 2 . [Figure 15A] 14 is a photograph showing an enlarged view of the second protrusion in FIG. 13. [Figure 15B] 15 is a photograph showing an enlarged view of the second protrusion in FIG. 14. [Figure 16A] This is a 10,000x magnified image of a portion of a silicon panel used in silicon solar cells after it was irradiated in air with 200 pulses of 532 nm YAG laser light with a laser energy density of 0.40 J / cm2. [Figure 16B] 14B is a photograph showing a part of the silicon panel shown in FIG. 14A at 40,000 times magnification. [Figure 17A] This is a 10,000x magnified image of a portion of a silicon panel used in silicon solar cells after it was irradiated with 200 pulses of 532 nm YAG laser light at a laser energy density of 0.40 J / cm2 in water. [Figure 17B] 17B is a photograph showing a part of the silicon panel shown in FIG. 17A at 40,000 times magnification. [Figure 18A] 1 is a field emission scanning electron microscope (FE-SEM) photographic image of a convex portion of a silicon panel used in a silicon solar cell of the present invention after being irradiated with 600 pulses of 532 nm YAG laser light at a laser energy density of 0.40 J / cm2. [Figure 18B] This is a FE-SEM photo image of a convex portion of a silicon panel magnified 27,000 times. [Figure 18C] This is a FE-SEM photograph of a convex portion of a silicon panel magnified 40,000 times. [Figure 19A] 1 is a FE-SEM photograph of a convex portion of a silicon panel used in a silicon solar cell of the present invention, magnified by 10,000 times. [Figure 19B] This is a FE-SEM photo image of a convex portion of a silicon panel magnified 27,000 times. [Figure 19C] This is a FE-SEM photograph of a convex portion of a silicon panel magnified 40,000 times. [Figure 20A]This is a graph showing the relationship between the reflectance (%) on the surface of a silicon panel and the wavelength (nm) of the light on the surface of the silicon panel after irradiating the silicon panel with 200 pulses of 532 nm YAG laser light at a laser energy density of 0.40 J / cm2 in the atmosphere. [Figure 20B] This is a graph showing the relationship between the reflectance (%) on the surface of a silicon panel and the wavelength (nm) of the light on the surface of the silicon panel after irradiating the silicon panel with 200 pulses of 532 nm YAG laser light at a laser energy density of 0.40 J / cm2 in water. [Figure 21A] 16C is a graph showing the area ratio between the bottom surface (lower base) and the top surface (upper base) of the second convex portion formed in the atmosphere shown in FIG. 16B, and the frequency. [Figure 21B] 17C is a graph showing the area ratio between the bottom surface (lower base) and the top surface (upper base) of the second convex portion formed in water shown in FIG. 17B, and the frequency. [Figure 22A] 16C is a graph showing the ratio (aspect ratio) of the height to the bottom surface (lower base) of the second convex portion formed in the atmosphere shown in FIG. 16B, and the frequency. [Figure 22B] 17C is a graph showing the ratio (aspect ratio) of the height to the bottom surface (lower base) of the second convex portion formed in water shown in FIG. 17B, and the frequency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment described below. As shown in FIG. 1, the surface modification laser irradiation device 100 stores a target 1 in a storage section 50 and modifies the surface of the target 1 by irradiating laser light Ld through a medium 7, which is a liquid or gas having a higher thermal conductivity than air and is placed inside the storage section 50.

[0013] As shown in FIG. 1, the surface modification laser irradiation device 100 includes, as an example, a light source device 70 having a laser light source 10 and an optical system 20 arranged on a preset optical path to guide the laser light Ld from the laser light source 10 to the target 1, a storage unit 50 for storing the target 1 to be irradiated with the laser light Ld via the optical system 20 of the light source device 70, and a moving mechanism 40 for moving the target 1 so that the laser light Ld is irradiated to the entire area of ​​the preset irradiation area of ​​the target 1. In addition, the surface modification laser irradiation device 100 further includes a visible light laser light source 30 for confirming that the laser light Ld from the laser light source 10 is appropriately irradiated to the target 1, a CMOS camera 60 as an imaging camera used when adjusting the laser light Ld, and a photodetector 28 for detecting the intensity of the laser light Ld irradiated to the target 1, and can be used for optical adjustment before irradiation of the target. In addition, the camera and the photodetector are retracted during processing.

[0014] The surface modification laser irradiation device 100 includes a first optical path P1 along which the laser light Ld travels from the laser light source 10 to the target 1, and a second optical path P2 along which the visible laser light Ls travels from the visible light laser light source 30 to the target 1. The first optical path P1 and the second optical path P2 are configured to share a part of the optical path including the cylindrical lens 27 serving as an objective lens toward the target 1.

[0015] As an example, the first optical path P1 includes a first reflecting mirror 21a1 that reflects the laser light Ld from the laser light source 10, a half-wave plate 23a that rotates the polarization direction of the laser light Ld from the first reflecting mirror 21a1, a polarizing prism 24a that arbitrarily varies the transmission intensity of the s-polarized light that passes through the half-wave plate 23a and travels straight ahead according to the polarization direction, a second reflecting mirror 21a2 to a fourth reflecting mirror 21a4 that reflect the s-polarized laser light Ld from the polarizing prism 24a, a mirror 22 that reflects the laser light Ld from the fourth reflecting mirror 21a4, a fifth reflecting mirror 21a5 that reflects the laser light Ld from the mirror 22, and a cylindrical lens 27 that is an objective lens that collects the laser light Ld from the fifth reflecting mirror. The mirror 22 is a wavelength selection mirror that reflects the wavelength of the laser light Ld and transmits visible laser light Ls, which will be described later.

[0016] Furthermore, in the first optical path P1, a first ND filter 26a1 is disposed in an optical path between the polarizing prism 24a and the second reflecting mirror so as to be freely installable and retractable, and a second ND filter 26a2 is disposed in an optical path between the fourth reflecting mirror 21a4 and the mirror 22 so as to be freely installable and retractable. These first ND filter 26a1 and second ND filter 26a2 are used at the time of setting before performing the surface modification processing of the target 1, and are intended to attenuate the light intensity of the laser light Ld. In addition, in the first optical path P1, a first shutter 25a is disposed between the third reflecting mirror 21a3 and the fourth reflecting mirror 21a4. The first shutter 25a is used to control the passage and blocking of the laser light Ld, for example, at the time of setting the laser light Ld before performing the surface modification processing, or when ensuring safety.

[0017] As an example, the second optical path P2 includes a first visible light reflecting mirror 21b1 that reflects the visible laser light Ls from the visible light laser source 30, a second visible light reflecting mirror 21b2 that reflects the visible laser light Ls from the first visible light reflecting mirror 21b1, a half-wave plate 23b that rotates the polarization direction of the visible laser light Ls from the second visible light reflecting mirror 21b2, a polarizing prism 24b that treats the visible laser light Ls transmitted through the half-wave plate 23b as s-polarized light and arbitrarily varies the transmission intensity, a third visible light reflecting mirror 21b3 that reflects the visible laser light Ls transmitted through the polarizing prism 24b, a mirror 22 that transmits light from the third visible light reflecting mirror 21b3, a fifth reflecting mirror 21a5 that reflects the visible laser light Ls from the mirror 22, and a cylindrical lens 27 that collects the visible laser light Ls from the fifth reflecting mirror 21a5 and irradiates the visible laser light Ls onto the target 1.

[0018] In the second optical path P2, a second shutter 25b is disposed in the optical path between the polarizing prism 24b and the third visible light reflecting mirror 21b3 to control the blocking of the passage of the visible laser light Ls. In the surface modification laser irradiation device 100, the first optical path P1 and the second optical path P2 share a part of the optical path. As an example, the first optical path P1 and the second optical path P2 share the optical path from the mirror 22 to the objective lens. Further, in order to measure the light intensity of the laser light Ld on the first optical path P1, a photodetector 28 is provided between the cylindrical lens 27 and the target 1 so as to be freely installed and retracted. As an example, the photodetector 28 detects the light intensity of the laser light Ld and adjusts it so that it falls within a preset threshold range.

[0019] The laser light source 10 may be, for example, a CO2 laser, a fiber laser, a titanium sapphire laser, an excimer laser, or a YAG laser, and a YAG laser is used here. The laser light source 10 used here can output wavelengths such as a fundamental wavelength of 1064 nm, a second harmonic of 532 nm, and a third harmonic of 355 nm, and as an example, a laser light Ld of a second harmonic of 532 nm is used. This laser light source 10 irradiates the laser light Ld for surface modification of the target 1. The laser light source 10 operates so that the laser light Ld has a predetermined pulse number. As an example, the laser light source 10 operates so that the target 1 is irradiated with the laser light Ld in the range of 50 to 600 pulses. It is preferable that the wavelength band of the laser light Ld is within a range equal to or smaller than the interval between the first convex portions. This is because the intervals at which the second protrusions 5 are formed are close to the wavelength of the laser light Ld, so that, for example, when the size of the first protrusions 4 is 1 μm to 30 μm, in order to form a plurality of second protrusions 5 on the pyramidal side surface 3 of the first protrusions 4, the wavelength of the laser light Ld is preferably in the range of 266 nm to 10.6 μm. Furthermore, the laser energy density F irradiated from the laser light source 10 is equal to or higher than the protrusion start threshold of the second protrusions 5 and equal to or lower than the melting threshold, that is, F=0.40 to 0.55 J / cm. 2 The laser energy density F is in the range of 0.04 J / cm 2 In this case, the second convex portion 5 cannot be formed, and the laser energy density F is 0.55 J / cm 2 If the laser energy density F exceeds this value, the top side of the second convex portion 5 will melt. Note that the laser energy density F is measured between the storage portion 50 and the cylindrical lens 27, as an example.

[0020] For example, a He-Ne laser can be used as the visible light laser light source 30. The visible light laser light source 30 uses red visible laser light Ls, which is visible light that does not modify the surface of the target 1. By using this visible laser light, the operator can visually confirm the position where the visible laser light Ls is irradiated, and can confirm the irradiation position of the laser light Ld that modifies the surface of the target 1.

[0021] The optical system 20 disposed on the first optical path P1 includes, for example, a first reflecting mirror 21a1 to a fifth reflecting mirror 21a5, a mirror 22, a half-wave plate 23a, a polarizing prism 24a, and an objective lens 27. Note that here, the ND filters 26 (first ND filter 26a1, second ND filter 26a2) are disposed on the optical path in preparation for adjusting the laser light Ld, and are removed from the optical path when surface modification is performed.

[0022] The reflecting mirror 21a arranged on the first optical path P1 reflects the laser light Ld in the direction of a preset optical path. The reflecting mirror 21a includes a first reflecting mirror 21a1 to a fifth reflecting mirror 21a5, each of which reflects the laser light Ld in a predetermined angular direction and guides it to the target 1. The reflecting mirror 21a is configured to reflect the laser light Ld of a preset wavelength and pass light of other wavelengths. The visible light reflecting mirror arranged in the second optical path P2 reflects the visible laser light Ls in the direction of a preset optical path. The visible light reflecting mirrors are made up of the first visible light reflecting mirror 21b1 to the third visible light reflecting mirror 21b3, and are configured to reflect light of a preset wavelength and pass light of other wavelengths. Therefore, the fifth reflecting mirror 21a5 is configured to reflect the laser light Ld and the visible laser light Ls.

[0023] The half-wave plate 23a in the first optical path P1 is rotated to arbitrarily rotate the polarization direction of the laser light Ld irradiated from the laser light source 10 and reflected from the first reflecting mirror 21a1. The half-wave plate 23a in the first optical path P1 rotates the laser light Ld, and the polarization prism 24a changes the transmission intensity of the s-polarized light so that the s-polarized light is used as the laser light Ld for surface modification. As an example, a damper 29 that absorbs light that is not allowed to pass is disposed next to the polarization prism 24a at a position perpendicular to the laser light Ld passing through it.

[0024] The half-wave plate 23b of the second optical path P2 arbitrarily rotates the polarization direction of the visible laser light Ls irradiated from the visible laser light source 30 and reflected from the first visible light reflector 21b1. The half-wave plate 23a of the second optical path P2 rotates the visible laser light Ls, and the polarizing prism 24b changes the transmission intensity of the s-polarized light so that the s-polarized visible laser light Ls is irradiated onto the target 1 as a mark for surface modification. As an example, the visible laser light Ls uses a red wavelength, and the wavelength band is not limited as long as it is visible light that can be viewed with the light intensity of light that does not modify the surface.

[0025] The mirror 22 shared by the first optical path P1 and the second optical path P2 is set to reflect the laser light Ld on the first optical path P1 and transmit the visible laser light Ls on the second optical path P2. This mirror 22 is the starting point of the optical path shared by the first optical path P1 and the second optical path P2. The cylindrical lens 27 focuses the laser light Ld from the first optical path P1 or the visible laser light Ls from the second optical path P2 and irradiates the target 1. The cylindrical lens 27 focuses the laser light Ld so that the vertical width is small without changing the horizontal width, and irradiates the surface of the target 1 with light so that the focus is constant (see LA in FIG. 2). For example, a cylindrical lens 27 having a focal length f=300 mm is used. This cylindrical lens 27 is preferably arranged so as to be movable in the optical path direction, and the focus can be adjusted according to the position of the target 1. It is preferable that the cylindrical lens 27 is used in combination with an fθ lens, for example. By using an fθ lens together with the cylindrical lens, it becomes possible to irradiate the laser light Ld with a focus always kept constant with respect to the irradiation area, even if the target 1 or the laser light Ld moves. As an example, the light source device 70 accommodates the laser light source 10, the optical system 20, and the visible light laser light source 30 in a housing, and the cylindrical lens 27 is disposed so as to face the opening of the housing. The laser light Ld irradiated from the cylindrical lens 27 forms a horizontally elongated irradiation area LA as shown in Fig. 2 and Fig. 3A. This irradiation area LA is irradiated onto the surface of the target 1 with a vertical interval Hd, with a height indicated by WT and a width indicated by WD.

[0026] The storage unit 50 used in the surface modification laser irradiation device 100 stores the medium 7, which is a liquid or gas having a higher thermal conductivity than air, together with the target 1. The target 1 is placed in the storage unit 50 in which the medium 7 is placed. The target 1 is stored in the storage unit 50 via, for example, a support part 53 installed inside the storage unit 50 so that the position of the target 1 is fixed in the storage unit 50. The storage unit 50 has a light incidence surface 51 on which the laser light Ld is incident and a back surface 52 opposite the light incidence surface 51, which are formed of a material that transmits at least the laser light Ld. Note that, in this embodiment, the storage unit 50 has a surface formed of a material that transmits light in the direction in which the laser light Ld is incident, but the upper surface of the stored medium 7 may be the light incidence surface.

[0027] In addition, it is preferable that the opening of the storage unit 50 is closed so that the medium 7 in the storage unit 50 does not spill out when the target 1 is stored and moved by the lid via the moving mechanism 40. In the figure, the storage unit 50 is shown as an example in which the target 1 is processed as a single-wafer type such as a silicon plate. In addition, when the lid side is the light incident surface, the bottom surface facing the lid is formed of a material that transmits light. When the storage unit 50 has a housing shape, all the surfaces of the housing may be formed of a material that transmits laser light. The surface of the storage unit 50 facing the placed target 1 or the entire surface is formed of a material that transmits laser light Ld and visible laser light Ls, such as glass.

[0028] For example, when the target 1 is in the shape of a plate, the support portion 53 includes linear guides 53a, 53a arranged in parallel so as to pass through both ends of the plate and slide the same. The linear guide 53a is installed on one storage surface side of the storage unit 50 and supports a portion of both ends of the target 1. A horizontal guide that supports a portion of the target may be installed together with the linear guides 53a, 53a. By installing the horizontal guide, a portion of the lower end of the target 1 is supported, so that the target 1 can be supported more stably. The support unit 53 supports the target 1 by sliding the target 1 from above to below on the linear guide 53a, and supports the target 1 in a fixed state within the medium 7. The support unit 53 is not particularly limited as long as it is configured so that the target 1 is fixed at a preset position within the medium 7 and does not cover the irradiation area.

[0029] The medium 7 stored in the storage unit 50 is a liquid having a higher thermal conductivity than air, such as water, methanol, ethanol, acetone, or oil, or a gas such as helium or hydrogen. Here, as an example, water is used as the medium 7, and it is more preferable to use pure water or ultrapure water. By using the medium 7, heat can be released from the target 1 when the target 1 is irradiated with the laser light Ld, and the surface of the target 1 can be appropriately modified. When pure water or ultrapure water is used in the storage unit 50, it is preferable to provide a configuration that prevents impurities from remaining mixed in the medium 7 stored in the storage unit 50. That is, it is more preferable that the storage unit 50 is configured to have a filter and a circulation device installed at a position that does not interfere with the irradiation of the laser light Ld, and to circulate the medium 7 through the filter by the circulation device to remove dirt from the medium 7. It is preferable to operate the circulation device when the target 1 is replaced with a new one.

[0030] In addition, the storage unit 50 is connected to a moving mechanism 40 so that the laser light Ld can be irradiated to the entire irradiation area of ​​the stored target 1 that is set in advance. The moving mechanism 40 is detachably connected to the storage unit 50 via an attachment unit 43, and the target 1 can be moved up, down, left, and right by moving the storage unit 50. As an example, the moving mechanism 40 includes a vertical guide mechanism 41 that moves the storage unit 50 in the vertical direction, and a horizontal guide mechanism 42 that supports the vertical guide mechanism 41 and moves the storage unit 50 together with the vertical guide mechanism 41 in the horizontal direction. The storage unit 50 is configured to move in the horizontal direction along the horizontal guide mechanism 42 and move in the vertical direction by the vertical guide mechanism 41, so that the laser light Ld can be irradiated to the entire irradiation area of ​​the target 1.

[0031] In addition, in the rear of the storage unit 50, which is opposite to the surface irradiated with the laser light Ld, a CMOS camera 60, which is an imaging camera, is arranged so as to be freely installed and removed when adjusting the laser light Ld. The CMOS camera 60 is arranged so as to be able to observe, for example, the state of the laser beam diameter of the laser light Ld using the first ND filter 26a1 and the second ND filter 26a2 arranged in the first optical path P1. The CMOS camera 60 is arranged so as to be able to move in the optical axis direction, and is used when adjusting the state of the laser beam diameter of the laser light Ld. The CMOS camera 60 is removed when performing surface modification of the target 1. In addition, a photodetector 28 is configured to be detachably disposed on the optical path between the fifth reflecting mirror 21a5 and the storage section 50. The photodetector 28 is used when measuring the amount of laser light Ld before performing surface modification. After being used in the preparation process, the photodetector 28 is removed from the optical path.

[0032] The target 1 is, for example, a semiconductor member, a silicon-based semiconductor or a compound-based semiconductor, and here, as an example, a silicon panel. The silicon panel is used as a solar cell, and a pyramidal first convex portion 4 is formed on the surface in advance. In this case, for example, as shown in FIG. 20A, the surface reflectance of the silicon panel is about 16% for light with a wavelength of 500 nm, which is lower than the reflectance of mirror silicon without the first convex portion, which is 40%. The reflection of light is determined by the refractive index difference at the material interface, but the presence of the convex portion 2 causes the apparent refractive index to gradually change, so that the surface reflectance can be reduced. Here, the convex portion 2 includes the first convex portion 4 formed in advance with a size of 1 μm to 30 μm, and the second convex portion 5 formed by irradiation with the laser light Ld with a size of 1 / 50 to 1 / 2 of the wavelength of the laser light Ld. The first convex portion 4 is formed in advance on the surface of the target 1, which is a silicon panel, and what is formed in the medium 7 by the laser light Ld from the light source device 70 is the second convex portion 5 disposed on the cone side surface 3 of the existing first convex portion 4. These additional processes can make the degree of refractive index change described above even smoother and widen the wavelength band that can contribute to reducing the reflectance.

[0033] As shown in Fig. 4A and Fig. 4B, the second convex portion 5 is formed in nano-order size on the pyramidal side surface 3 of the first convex portion 4 having a polygonal pyramidal shape (a quadrangular pyramidal shape in the figure) by irradiation with laser light Ld from the light source device 70. Note that Fig. 4A and Fig. 4B show an example of a configuration in which the second convex portion 5 is formed on the first convex side surface 3A1 to the fourth convex side surface 3A4 of the first convex portion 4, but it is sufficient that the second convex portion 5 is formed on at least one of the first convex side surface 3A1 to the fourth convex side surface 3A4 of the first convex portion 4. The second convex portion 5 arranged on the pyramidal side surface 3 of the first convex portion 4 is formed with a pointed tip as shown in Fig. 4C, and is formed so that the ratio (L1 / Sr1) of the length of one side of the apex (Sr1) to the length of one side of the bottom surface portion in contact with the pyramidal side surface 3 is 1≦bottom surface portion / apex ≦4. That is, the second protrusion 5 is formed in a pyramidal shape such as a cone shape or a pyramidal shape (polygonal pyramid shape) and the bottom surface of the protrusion does not expand but maintains a constant shape. For example, when the laser light Ld is 532 nm, the second protrusion 5 is formed to a height in the range of 10.64 nm to 266 nm.

[0034] In addition, the second convex portion 5 is preferably formed so that the aspect ratio of the base L1 to the height T1 is 0.1≦base / height≦2 in both the minute convex portion 5a and the small convex portion 5b. That is, as described above, the second convex portion 5 is preferably either such that the ratio of the length of the bottom surface portion (lower base) L1 (or L2) to the length of one side of the top surface portion (upper base), which is the area ratio, is in the range of 1≦L1 / Sr1≦4 (1≦bottom surface portion / top surface portion≦4), or the aspect ratio of the base L1 to the height T1 is 0.1≦base / height≦2). Of course, it does not matter if the above two conditions are satisfied. These can generally be designed by numerical simulation as the reflectance reduction effect of the convex portion shape. In addition, it is preferable to adopt the longest value of the length of each side including the diagonal line or the average length as the one side of the bottom surface portion. Similarly, it is preferable that the side of the apex is the longest value among the lengths of the sides including the diagonal or the average length.

[0035] The second convex portion 5 preferably includes a mixture of minute convex portions 5a of 30 nm or less, including 10 nm or less, and small convex portions 5b of 100 nm or more and 266 nm or less. The second convex portion 5 is preferably formed on at least one of the cone side surfaces 3 (any of the first cone side surface 3A1 to the fourth cone side surface 3A4) of the cone side surface 3 of the first convex portion 4. Here, the second convex portion 5 is formed on each of the cone side surfaces 3 (the first cone side surface 3A1 to the fourth cone side surface 3A4) of the first convex portion 4 as an example. This is because the above-mentioned convex portions of different sizes can widen the effective wavelength band. In addition, the density of the convex portions is most ideally so dense that there is no flat bottom, but in reality, the small convex portions 5b are preferably 10 or more on one cone side surface 3 of the first convex portion 4, for example, the first cone side surface 3A1, more preferably 15 or more, and even more preferably 20 or more. Moreover, the number of the minute convex portions 5a is preferably 10 or more, more preferably 15 or more, and even more preferably 20 or more on the first pyramidal side surface 3A1 where the small convex portions 5b are formed. The second convex portions 5 are formed at intervals close to the wavelength of the laser light Ld irradiated from the light source device 70, so that if the first convex portions are 30 μm, it is desirable that the wavelength be smaller than that. Here, as an example, the wavelength of the laser light Ld irradiated from the light source device 70 is in the range of 266 nm to 10.6 μm. Moreover, when the second convex portions 5 are formed, the laser energy density F of the laser light Ld is equal to or higher than the protuberance start threshold and equal to or lower than the melting threshold, F=0.40 J / cm. 2 More than 0.55J / cm 2 The irradiation is performed in the range of .

[0036] As described above, the surface modification laser irradiation device 100 can perform surface modification of the target 1 by irradiating the target 1 with laser light Ld from the laser light source 10 through the medium 7 stored in the storage section 50, thereby forming a second convex portion 5 on the conical side surface 3 of the first convex portion 4 of the target 1. When the target 1 is a silicon panel, by performing surface modification and providing a plurality of second convex portions 5, the surface reflectance for light having a wavelength band of 400 nm to 800 nm received on the surface of the silicon panel can be reduced by 3% or more compared to a silicon panel having only the first convex portions 4. And when the target 1 is a silicon panel, by providing a plurality of second convex portions 5, the surface reflectance for light having a wavelength of 500 nm ± 2 nm received on the surface of the silicon panel can be reduced by 3% or more compared to the surface reflectance of a silicon panel having only the first convex portions 4. Note that the value of 3% is an example, and the reflectance can be further reduced by providing a plurality of convex portions more densely as explained above.

[0037] Next, an example of a surface modification laser irradiation method will be described with reference to Fig. 5. Note that the same reference numerals are used for the configurations already described, and the description may be omitted as appropriate. Here, a case where the surface modification laser irradiation device 100 shown in Fig. 1 is used will be described. The surface modification laser irradiation method S10 includes a step S11 of preparing a target to be surface modified by storing it in a storage section filled with a medium, which is a liquid or gas having a thermal conductivity higher than that of air, a step S12 of irradiating the target in the prepared storage section with laser light from a laser light source via an optical system arranged in the light path, and a step S13 of moving one or both of the target and the irradiation position of the laser light via a moving mechanism so that the laser light is irradiated over the entire area of ​​a predetermined irradiation area of ​​the target.

[0038] In the preparation step S11, the target 1 to be surface modified is stored in the storage unit 50 filled with the medium 7 to prepare it. In the preparation step S11, when pure water is used as the medium 7, the target 1 is supported on the support part 53 of the storage unit 50 in a state where the storage unit 50 is filled with pure water, or the storage unit 50 is filled with the medium 7, that is, pure water, in a state where the target 1 is supported on the support part 53. The storage unit 50 is supported by the moving mechanism 40 and the focus of the laser light Ld is adjusted. As an example, the focus of the laser light Ld is adjusted as follows. In the surface modification laser irradiation device 100, the cylindrical lens 27 is once removed from the optical path, and further, a metal mesh is supported on the support part 53 of the storage unit 50 instead of the target 1.

[0039] Then, with the first ND filter 26a1 and the second ND filter 26a2 placed on the first optical path P1, the laser light source 10 irradiates the laser light Ld, and the position of the storage section 50 is adjusted so that the CMOS camera 60 focuses on the metal mesh. Furthermore, the photodetector 28 is placed just before the target and the light intensity is adjusted. Thereafter, the photodetector 28 is removed. Next, a cylindrical lens is placed on the optical path, and the cylindrical lens 27 is adjusted via the CMOS camera 60 to a position where the laser light Ld is focused. Furthermore, after adjustment of the laser light Ld from the laser light source 10 is completed, the metal mesh is removed, the target 1 is supported by the support portion 53, and the visible laser light Ls from the visible light laser light source 30 is irradiated through the second optical path P2 to check whether the visible laser light Ls is irradiated onto the irradiation area of ​​the target 1. After performing the adjustment process in this manner, the next process is performed.

[0040] In the step S12 of irradiating the laser light, the laser light Ld is irradiated from the laser light source 10 via the optical system 20 to the target 1 supported by the support part 53 in water, which is the medium 7 stored in the storage part 50 (see LA in FIG. 2). In this step S12 of irradiating the laser light, the laser light Ld is irradiated in a state in which the first ND filter 26a1 and the second ND filter 26a2 are removed from the first optical path P1. When irradiating the laser light Ld, the laser light Ld is irradiated to the irradiation area of ​​the target 1 by setting the range of 50 pulses to 600 pulses. When irradiating the target 1 with the laser light Ld, the laser energy density F is set to 0.40 J / cm, which is equal to or higher than the protrusion start threshold and equal to or lower than the melting threshold of the second convex part 5, in the wavelength range of 266 nm to 10.6 μm. 2 More than 0.55J / cm 2 In the step S12 of irradiating the laser light, the s-polarized laser light Ld is used. The laser light Ld may be circularly polarized.

[0041] The laser light Ld is irradiated to the target 1 at a temperature equal to or higher than the swelling threshold and lower than the melting threshold of the silicon panel as the target 1 in the water as the medium 7. Here, as shown in FIG. 8B, the laser energy density F of the laser light Ld is set to 0.40 J / cm 2 The limit is 0.40 J / cm 2 If the laser energy density is not more than 0.55 J / cm, the second protrusion 5 cannot be formed on the pyramidal side surface 3 of the first protrusion 4. The laser energy density at which the second protrusion 5 can start to protrude and form is defined as the damage threshold (protrusion start threshold). 2When the melting threshold is exceeded, the second convex portion 5 melts even in the medium 7. When the target 1 is irradiated with the laser light Ld in the medium 7, the second convex portion 5 is formed on the pyramidal side surface 3 of the first convex portion 4 without the tip side of the second convex portion 5 melting. The second convex portion 5 is formed on the pyramidal side surface 3 to a size (height) of 1 / 50 to 1 / 2 of the wavelength of 532 nm of the laser light Ld. The second convex portion 5 is formed in a plurality of forms, including minute convex portions 5a having a size (height) of 10 nm to 30 nm and small convex portions 5b having a size (height) of 100 nm to 266 nm.

[0042] As shown in FIG. 6A, when the second convex portion 5 is formed on the cone side surface 3 of the first convex portion 4, the second convex portion 5 forms a small bulge on the cone side surface 3 by irradiation with the laser light Ld in the water serving as the medium 7, and gradually grows larger as shown in (1) to (4) of FIG. 6A by being irradiated with the laser light Ld. Note that FIG. 6A shows a state in which one second convex portion 5 gradually increases in height as shown in (1) to (4). As already explained in FIG. 4A to FIG. 4C, the second convex portion is formed in either or both of the following states: the aspect ratio is 0.1≦base / height≦2, or the ratio of the length of one side (Sr1) of the top portion to the length of one side (L1) of the bottom portion is 1≦bottom / top portion≦41.

[0043] As shown in Fig. 7B, when the medium 7 is water (pure water, ultrapure water), the refractive index is 1 / 1.33 (1 / n) [n is the refractive index] compared to the refractive index n=1 in air, and the intervals between the second convex portions 5 formed on the cone side surface 3 are closer than in air. The second convex portions 5 are formed at intervals close to the wavelength of the irradiated laser light Ld, so for example, in the case of a 532 nm laser light Ld, they are approximately arranged at intervals in the range of 532 / 1.33=400 nm±10, taking into account the refractive index in water. Also, as shown in Fig. 8B, the laser energy density in water is 0.4 J / cm 2 If the laser energy density is less than 0.40 J / cm, the second protrusion 5 is not formed on the pyramidal side surface 3 of the first protrusion 4. In other words, the range of the laser energy density is 0.40 J / cm, which is equal to or higher than the protrusion start threshold at which the second protrusion 5 starts to be formed and equal to or lower than the melting threshold. 2 More than 0.55J / cm 2As already described, the measurement position of the laser energy density is between the storage unit 50 and the cylindrical lens, for example, a position equivalent to the light entrance surface 51 immediately before the storage unit 50.

[0044] In contrast, as shown in Fig. 6B, when the second convex portion Cov formed in the atmosphere is formed on the cone side surface 3 of the first convex portion 4, the top side of the second convex portion Cov formed in the atmosphere is melted by irradiation with the laser beam Ld, and the top of the second convex portion Cov formed in the atmosphere cannot be made higher. 2 If this is the case, the atmospherically-formed second convex portion Cov of the target 1 (see Figure 13B) will melt, making it impossible to secure the height, and the ratio of the length of one side of the bottom portion of the atmospherically-formed second convex portion Cov to the length of one side of the top portion (1≦bottom portion / top portion≦4) will become 4 or more, and the surface modification will not lead to a reduction in reflectance (see Figure 20A).

[0045] In addition, the second convex portion 5 is easily formed on the first cone side 3A1 and the third cone side 3A3 of the first cone 4 by using the s-polarized laser light Ld. Therefore, the second cone 5 is less likely to be formed on the second cone side 3A2 and the fourth cone side 3A4 than on the first cone side 3A1 and the third cone side 3A3. Therefore, in order to form a large number of second cone 5 on any of the cone side surfaces from the first cone side 3A1 to the fourth cone side 3A4 of the first cone 4, it is preferable to irradiate the target 1 with the s-polarized laser light Ld while rotating the supporting direction of the target 1 by 90 degrees. In addition, it is preferable to use the circularly polarized laser light Ld.

[0046] Even when the target 1 is in the state of the second convex portion 5 formed by irradiating the s-polarized laser light Ld without rotating it by 90 degrees, the surface reflectance for light having a wavelength band of 400 nm to 800 nm received on the surface of the silicon panel as the target 1 can be reduced by 3% or more compared to a silicon panel having only the first convex portion 4. Furthermore, the surface reflectance for light having a wavelength of 500 nm ±2 nm received on the surface of the silicon panel can be reduced by 3% or more compared to the surface reflectance of a silicon panel having only the first convex portion 4.

[0047] Next, in the surface modification laser irradiation method S10, a step S13 of moving the target or the laser light irradiation position is performed. This step S13 is a step of moving one or both of the target 1 and the laser light irradiation position via a moving mechanism. In this step S13, as an example, the target 1 stored in the storage unit 50 is moved by moving the storage unit 50. When moving the target 1, for example, a moving mechanism configured to move the storage unit 50 as shown in FIG. 2 is used, and when moving the laser light irradiation position, for example, a moving mechanism configured like a galvano mirror 22B (see FIG. 9B) is used.

[0048] In this step S13, the moving mechanism 40 is set in advance, and the horizontal guide mechanism 42 moves the target 1 in the horizontal direction (see M1) so that the target 1 can be irradiated with the laser light Ld from the upper left to the upper right as shown in FIG. 3B (see LA in FIG. 3B). Then, the vertical guide mechanism 41 raises the target's irradiation area one step higher (see M2) and moves the target 1 in the horizontal direction from the right end to the left end. By repeating such movements, the entire irradiation area of ​​the target 1 is irradiated with the laser light Ld. It is preferable that this step S13 is set in advance so that the power supply of the laser light source 10 is cut off once, or the optical path is blocked by the shutter 25a, when the target 1 has been moved so that the laser light Ld irradiates the entire irradiation area. Then, the target 1 whose irradiation area has been irradiated with the laser light Ld is taken out of the storage unit 50, and a new target 1 is supported by the support unit 53 of the storage unit 50, and the same steps are repeated.

[0049] By carrying out the surface modification laser irradiation method S10, the semiconductor member serving as the target 1 can be surface modified. The target 1 is a silicon-based semiconductor or a compound-based semiconductor, and here, as an example, a silicon panel used in a solar cell is used. The silicon panel serving as the target 1 is provided with a first protrusion 4 on its surface in advance, and by surface modification, a second protrusion 5 is formed on the pyramidal side surface 3 of the first protrusion 4. The target 1 is, for example, a panel that is a sheet, but may be in a sheet-like state as described later. Furthermore, in the target 1, by forming the second convex portion 5, the surface reflectance for light in the wavelength band of 400 nm to 800 nm received on the surface of the target 1 is reduced by 3% or more compared to the surface reflectance of only the first convex portion 4. In particular, when the target 1 is a silicon panel, the surface reflectance for light with a wavelength of 500 nm±2 nm received on the surface of the target 1 is reduced by 3% or more compared to the surface reflectance of only the first convex portion 4 (see FIG. 20B).

[0050] The surface modification laser irradiation device 100 may be, for example, surface modification laser irradiation devices 100A and 100B having the configurations shown in Figures 9A and 9B. In addition, the surface modification laser irradiation method may use the surface modification laser irradiation devices 100 to 100B shown in Figures 9 to 9B. In Figures 9A and 9B, the configurations already described will be omitted and different configurations will be mainly described below. As shown in Fig. 9A, the surface modification laser irradiation device 100A uses circularly polarized laser light Ld, unlike the s-polarized light in Fig. 1. To obtain circularly polarized laser light Ld, a quarter-wave plate 23c is placed after the polarizing prism 24a to convert linearly polarized light into circularly polarized light. In addition, in order to set the same polarization conditions for the visible laser light Ls from the visible light laser source 30, a quarter-wave plate may be placed after the polarizing prism 24b.

[0051] In the surface modification laser irradiation device 100A, the target 1 is irradiated with circularly polarized laser light Ld. Therefore, the second convex portions 5 are easily formed on the first convex portion 4 of the target 1 from the first convex portion 3A1 to the fourth convex portion 3A4. The second convex portions 5 formed by the circularly polarized laser light Ld are more likely to be formed in a short time and in greater numbers than the second convex portions formed by the s-polarized laser light Ld.

[0052] As shown in FIG. 9B, the surface modification laser irradiation device 100B is configured to change the irradiation position of the laser light Ld as a moving mechanism. Note that FIG. 9B shows the configuration of an optical system using circularly polarized laser light Ld, but the optical system may use s-polarized laser light Ld. In the surface modification laser irradiation device 100B, a galvano mirror 22B is disposed as a moving mechanism at the position of the fifth reflecting mirror 21a5, and a light emission unit 27B including an fθ lens 27b1 and a diffractive optical element 27b2 is provided to input the laser light Ld from the galvano mirror 22B and emit it to the irradiation area of ​​the target 1. The galvano mirror 22B reflects the laser light Ld by changing the angle so that the laser light Ld is irradiated to the entire irradiation area of ​​the target 1. The light output unit 27B, which includes an fθ lens 27b1 and a diffractive optical element 27b2, scans the laser light Ld from the galvano mirror 22B at a constant speed on the focal plane. The storage unit 50 is supported by the moving mechanism 40B here, but when the target 1 is irradiated with the laser light Ld, the moving mechanism 40B may support the storage unit 50 at a predetermined position, or may move the storage unit 50 in conjunction with the galvano mirror 22B to move the target 1 together.

[0053] Also, the surface modification laser irradiation apparatus 100C, 100D may be configured as shown in FIG. 10 and FIG. 11. In FIG. 10, when the target 1C has a roll-to-roll configuration, the surface modification laser irradiation apparatus 100C further includes a conveying means 200. That is, the surface modification laser irradiation apparatus 100C includes a light source device 70A, a storage section 50C, and a moving mechanism 40C, and here, the moving mechanism 40C includes a conveying means 200 and a moving means 140. The target 1C is sheet-shaped, and irradiation areas are formed at regular intervals. The conveying means 200 includes a conveying roller arranged in a conveying section 201, a plurality of conveying rollers 202 that convey the target 1C into the storage section 50C, and a plurality of conveying rollers 203 arranged in a conveying section 204 that conveys the target 1C from the storage section 50C.

[0054] The storage unit 50C is disposed directly below the light source device 70A with water (pure water) stored therein as the medium 7C. The storage unit 50C includes a support roller serving as a support unit 53A for supporting the irradiation area of ​​the target 1. The light source device 70A includes the configuration already described, and irradiates the irradiation area of ​​the target 1 with the laser light Ld output from the cylindrical lens 27 serving as an objective lens. The moving means 140 moves the irradiation area of ​​the target 1C to a preset position in conjunction with the conveying means 200. When the irradiation of the irradiation area of ​​the target 1C with the laser light Ld is completed, the conveying means 200 moves the target 1C so that the next irradiation area is conveyed to the position of the support unit 53A. By repeating such an operation, the irradiation area of ​​the target 1C is irradiated with the laser light Ld. Instead of the light source device 70A, a light source device 70B for changing the irradiation position of the laser light Ld may be used.

[0055] 11, the surface modification laser irradiation device 100D includes the light source device 70B, the conveying means 300, and the storage unit 50D, and is configured to move the irradiation position of the laser light Ld to the light source device 70B side. The conveying means 300 includes a carry-in belt 301 that carries the target 1D into the storage unit 50D, a conveying support belt 302 that conveys the irradiation area of ​​the target 1 to the irradiation position of the laser light Ld and also functions as the support unit 53D, and an unloading belt 303 that receives the target 1D conveyed from the conveying support belt 302 and conveys it out of the storage unit 50D. The conveying means 300 moves the target 1D by rotating the endless belts arranged on both sides. Furthermore, the storage unit 50D stores therein a gas having a higher thermal conductivity than air as the medium 7D, such as helium, and is provided with opening / closing shutters 54D, 54D at the loading and unloading points of the target 1D in the storage unit 50D, and closing the loading and unloading points with the opening / closing shutters 54D, 54D minimizes the outflow of the medium 7D in the storage unit 50D.

[0056] In addition, the position of the storage section 50D facing the light emission section 27B of the light source device 70B is formed of a light-transmitting member that transmits the laser light Ld. Furthermore, a positioning mechanism 53D1 is disposed between the transport support belts 302. The positioning mechanism 53D1 has a contact portion that contacts the end face of the target 1D and is installed so as to be freely stretchable, and is equipped with a moving portion that moves the contact portion so as to contact and separate from the end face of the target 1. Therefore, when the target 1D is transported to a predetermined position in the storage section 50D by the transport support belts 302, the contact portion of the positioning mechanism 53D1 extends, and the contact portion presses the end face of the target 1 by the moving portion, thereby positioning the target 1D at the irradiation position of the laser light Ld. Note that, when the positioning of the target 1D is completed, the positioning mechanism 53D1 lowers the contact portion to the same height as the target so as not to interfere with the transport of the target 1D, and stores the target 1D in preparation for the positioning work of the next target 1D.

[0057] In the surface modification laser irradiation device 100D, when the target 1D is placed on the carry-in belt 301, the opening / closing shutter 54D of the carry-in section opens, and the target 1D is transferred from the carry-in belt 301 to the conveying support belt 302. The opening / closing shutter 54D of the carry-in section is closed, and the conveying support belt 302 that has received the target 1D conveys the target 1D to a preset position and stops it. Then, the contact portion of the positioning mechanism 53D1 is extended, and the end face of the target 1D is pushed and moved, thereby moving the target 1D to the irradiation position of the laser light Ld. The positioning mechanism 53D1 stores the contact portion and returns to the original position. When the positioning of the target 1D is completed, the laser light Ld is irradiated from the light source device 70B, and the laser light Ld reflected at a different angle by the galvano mirror 22B (see FIG. 9B) is irradiated to the irradiation area of ​​the target 1D, thereby modifying the surface of the target 1D. When the irradiation of the laser light Ld is completed, the opening / closing shutter 54D of the discharge section is opened, and the target 1D is discharged to the discharge belt 303 by the transport support belt 302. When the target 1D is handed over to the discharge belt 303, the opening / closing shutter 54D of the discharge section is closed, thereby completing the surface modification of one target 1D. By repeating the above operations, the surface modification of the next target 1D can be performed. The surface modification laser irradiation apparatuses 100A to 100D can achieve the same effects as those described for the surface modification laser irradiation apparatus 100.

[0058] Next, as shown in Fig. 12A to Fig. 12E, a silicon solar cell 500 will be described. The silicon solar cell 500 includes a panel unit 80P used for photoelectric conversion and a frame 501 surrounding the panel unit 80P, and a plurality of frames 501 surrounding the panel unit 80P are arranged adjacent to each other. The panel unit 80P includes a silicon panel 1P, a first electrode 82 arranged on the light receiving surface side of the silicon panel 1P, and a second electrode 83 arranged on the other surface opposite to the light receiving surface of the silicon panel 1P. The silicon panel 1P is a semiconductor member having a pyramidal convex portion 2 on its surface and converting received light into electricity, and the convex portion 2 includes a pyramidal first convex portion 4 formed on the surface of the semiconductor member, and a second convex portion 5 on the pyramidal side surface 3 of the first convex portion 4. The first convex portion 4 has a size of 1 μm or more and 30 μm or less. In addition, the second convex portion 5 has a size of 1 / 50 or more and 1 / 2 or less of the wavelength of the laser light, and the aspect ratio of the base to the height is 0.1≦base / height≦2, or the ratio of the length of one side of the base to one side of the top is in the range of 1≦base / top≦4.

[0059] As shown in FIG. 12A, the silicon solar cell 500 is configured such that a plurality of panel units 80P are arranged in a frame 501, and each panel unit 80P is electrically connected. As shown in FIG. 12B and FIG. 12C, the first electrode 82 of the silicon panel 1P is arranged on the light receiving surface side of the silicon panel 1P, and the second electrode 83 is arranged on the other surface side of the silicon panel 1P. The silicon panel 1P is formed by stacking n-type silicon 1Pa and p-type silicon 1Pb, and a first convex portion 4 and a second convex portion 5 are formed on the surface of the n-type silicon 1Pa. That is, as shown in FIG. 12D and FIG. 12E, the silicon panel 1P has a convex portion 2 on the n-type silicon on the light receiving surface side, the convex portion 2 has a first convex portion 4 and a second convex portion 5, and the cone side surface 3 of the first convex portion 4 has a second convex portion 5. The first convex portion 4 and the second convex portion 5 have the same configuration as that already described. Furthermore, the silicon panel 1P also has a second protrusion having a size of 10 nm or less. By providing the first protrusion 4 with a second protrusion having a size of 10 nm or less, the quantum effect of the quantum dots becomes prominent, and light absorption occurs via a quantum level that does not exist in bulk Si, improving the conversion efficiency.

[0060] Therefore, in the silicon solar cell 500, by modifying the surface of the silicon panel (i.e., by providing the second convex portion 5), the surface reflectance for light in the wavelength band of 400 nm to 800 nm received at the surface is reduced by 3% or more compared to the surface reflectance of only the first convex portion. Furthermore, the surface reflectance for light of a wavelength of 500 nm±2 nm, which is highly absorbed by silicon and received at the surface, is reduced by 3% or more compared to the surface reflectance of only the first convex portion (see FIG. 20B).

[0061] Next, an embodiment of the present invention will be described below. The surface modification laser irradiation device used was the one shown in FIG. 1. In a configuration according to the prior art, the target 1 was supported by the support part 53 so that it was in the air without water (pure water) serving as the medium 7 being placed in the storage part 50, and the laser light Ld was irradiated. On the other hand, in a configuration according to an embodiment of the present invention, the target 1 was supported by the support part 53 and the laser light Ld was irradiated with water (pure water) serving as the medium 7 placed in the storage part 50. The laser light source 10 used was a YAG laser 532 (nm), with a pulse width of 10 ns, a repetition rate of 10 Hz, and a laser spot size (FWe -1 M) is X=9.1mm, Y=18μm, and the laser energy density (Laser fluence) is 0.4-0.8J / cm 2 The number of pulses was 200 pulses, the hatching distance was 18 μm, and the number of scans was 3.

[0062] A cylindrical lens with f=300 mm was used as the objective lens. The size of the target 1 was a silicon plate with a length and width of 20 mm x 20 mm. In the following, the laser energy density is expressed as F=J / cm. 2 The storage unit 50 used here is, as an example, a bottomed rectangular cylindrical container made of quartz glass. The size of the container as the storage unit 50 is 30 mm wide, 30 mm deep, and 50 mm high, and quartz with a thickness of 2 mm and surface accuracy of λ / 4 is used. The medium stored in the storage unit 50 is water (pure water). The target 1 is fixed to the quartz glass surface that is one side of the container, and the laser light Ld is irradiated onto the surface of the target 1 after passing through 2 mm of quartz glass and approximately 27 mm of water.

[0063] As shown in FIGS. 13A and 14A, the first convex portion 4 is formed in advance on the silicon plate serving as the target 1 before being irradiated with the laser beam Ld. FIG. 13B shows the laser light Ld at F=0.80 J / cm 2 FIG. 13C shows the result of irradiating a silicon plate with a laser beam Ld of F=0.60 J / cm. 2 FIG. 14B shows the results of irradiation of a silicon plate with F=0.50 J / cm. 2 FIG. 14C shows the results of irradiation of a silicon plate with F=0.40 J / cm. 2 The results of irradiation onto a silicon plate are shown. Laser light Ld is 0.60 J / cm 2 , 0.80J / cm 2 In the case of (2), the tip side of the second convex portion 5 (Cov) was melted and was not in a state where the surface reflectance could be reduced. On the other hand, the laser light Ld is 0.40 J / cm 2 , 0.50J / cm 2 In this case, as shown in Figures 15A and 15B, which show the second convex portions 5 (micro convex portions 5a, small convex portions 5b) enlarged, it was confirmed that the ratio of the length of one side of the base portion of the second convex portion 5 to the length of one side of the top portion is 1≦(bottom portion / top portion)≦4, or the aspect ratio of the base portion to the height is 0.1≦base portion / height≦2.

[0064] In contrast, as shown in FIGS. 16A and 16B, the laser light Ld is irradiated in the atmosphere with F=0.40 J / cm 2As a result of irradiation with 200 pulses, the atmospherically formed second convex portion Cov formed on the first convex portion 4 that received the laser light Ld in the atmosphere has a melted tip side and an aspect ratio of less than 2. In addition, the ratio of the length of one side of the bottom surface portion of the atmospherically formed second convex portion Cov to the length of one side of the top surface is out of the range of 1≦bottom surface portion / top surface portion≦4 (see FIG. 21A). In addition, the aspect ratio of the bottom surface portion to the height is out of the range of 0.1≦bottom surface portion / height≦2 (see FIG. 22A). Therefore, as shown in FIG. 20A, the surface reflectance of the surface-modified silicon solar cell on which the atmospherically formed second convex portion Cov is formed is higher than the surface reflectance of the silicon solar cell (a silicon panel having only the first convex portion).

[0065] On the other hand, as shown in Fig. 17A, Fig. 17B, Fig. 18A to Fig. 18C, and Fig. 19A to Fig. 19C, in a silicon solar cell in which the laser light Ld is irradiated underwater to form the second convex portion 5 on the first convex portion, as shown in Fig. 20B, it is found that the surface reflectance of the silicon solar cell having only the first convex portion is reduced by 3% or more. In particular, it is found that the surface reflectance of the light of 500 nm ± 2 nm, which has a high absorption rate as silicon, is reduced by 3% or more compared to a silicon solar cell having only the first convex portion. As an example, when the second convex portion 5 in the state shown in Fig. 17B is analyzed as shown in Fig. 21B and Fig. 22B, the ratio of the length of one side of the bottom surface portion to one side of the top surface is in the range of 1 ≦ bottom surface portion / top surface ≦ 4 (see Fig. 21B). In addition, the aspect ratio of the bottom surface portion to the height is in the range of 0.1 ≦ base side / height ≦ 2 (see Fig. 22B).

[0066] In addition, the second convex portion Cov shown in FIG. 16A is 107.1 μm 2 The number of particles is 52, and the unit area (μm 2 ) 0.48 particles / μm 2 As shown in FIG. 16B, the second convex portion Cov on one pyramid side surface was 7.29 μm 2 21 particles are formed per unit area (μm 2 ) 2.88 particles / μm 2 It was. On the other hand, the second protrusion 5 shown in FIG. 17A is 107.1 μm 2 The number of particles in the unit area (μm 2 ) 1.98 particles / μm 2 As shown in FIG. 17B, the second protrusion 5 on one pyramidal side surface was 7.29 μm 2 37 particles are formed per unit area (μm 2 ) 5.07 particles / μm 2 It was.

[0067] That is, in the surface modification laser irradiation device and method according to the present invention, the laser light Ld is irradiated through the medium 7 at a laser energy density that is equal to or higher than the protrusion start threshold of the second protrusion 5 and equal to or lower than the melting threshold, for example, 0.4 J / cm 2 More than 0.55J / cm 2 In the following, by irradiating 50 to 600 pulses in the wavelength range of 266 nm to 10.6 μm, it is possible to realize a semiconductor component such as a silicon panel or a silicon solar cell in which the surface reflectance for light in the wavelength range of 400 nm to 800 nm received on the surface is reduced by 3% or more compared to the surface reflectance of only the first convex portion. Note that the protuberance start threshold and dissolution threshold differ depending on the type and configuration of the target 1 and the medium 7, and are within the above-mentioned 0.4 J / cm 2 More than 0.55J / cm 2 The values ​​shown below are merely examples and are not limiting. In particular, the surface reflectance for light of 500 nm±2 nm, which is highly absorbed by silicon and received on the target surface, is reduced by 3% or more compared to the surface reflectance of only the first convex portion (see FIG. 20B). Therefore, by using the target 1, which is a semiconductor member having the second convex portion 5, in the silicon solar cell 500, it is possible to improve the photoelectric conversion efficiency.

[0068] Although an example of a silicon-based semiconductor member has been described above using a silicon panel as an example of a target, for example, even if the compound semiconductor is GaAs / InGaP / AlGaAs on a GaAs substrate or InGaP / InGaAs on a Ge substrate, by forming a second convex portion on the first convex portion, the surface reflectance can be reduced compared to that of a substrate having only the first convex portion. When the compound semiconductor is formed into a panel, it has a polygonal pyramidal first convex portion on its surface, and the second convex portion can be formed on the side surface of the first convex portion in the same manner as a silicon panel. [Explanation of symbols]

[0069] 1. Target (semiconductor material) 2 Convex 3 Cone side 3A1 1st cone side 3A2 2nd cone side 3A3 3rd pyramid side 3A4 4th cone side 4 First protrusion 5 Second protrusion 5a Micro-projection 5b Small convex part 7 Medium (water, pure water, ultrapure water) 10 Laser light source 20 Optical system 21 Reflector 22. Mirror 23 Half-wave plate 24 Polarizing Prism 25 Shutter 26 ND Filters 27 Cylindrical lens (objective lens) 30 Visible light laser source 40 Moving mechanism 50 Storage section 53 Support part 60 CMOS camera (imaging camera) 70 Light source device 100, 100A-100D Surface modification laser irradiation equipment 500 Silicon solar cell S10 Surface modification laser irradiation method S11 Preparation process S12 A step of irradiating the medium with laser light. S13 Moving process

Claims

1. A light source device including a laser light source that irradiates laser light and an optical system that guides the laser light from the laser light source along a preset optical path toward a target to be surface modified; a storage section for storing the target together with a medium, which is a liquid or gas having a thermal conductivity higher than that of air; a moving mechanism for moving either the target or the irradiation position of the laser light, or both of the target and the laser light; the storage unit has a support unit that supports the target to be irradiated by the laser light through the medium, A surface modification laser irradiation device in which the laser energy density at which laser light is irradiated from the light source device to the target in the medium is greater than or equal to the threshold at which the second convex portion formed on the cone-shaped side surface of the first convex portion of the target begins to rise, and is less than the melting threshold of the target in the medium.

2. 2. The surface modification laser irradiation device according to claim 1, wherein the medium is any one of a liquid such as water, methanol, ethanol, acetone, and oil, or a gas such as helium and hydrogen.

3. A step of preparing a target to be surface modified by storing it in a storage unit filled with a medium that is a liquid or gas having a thermal conductivity higher than that of air; a step of irradiating a laser beam from a laser light source onto a target in a prepared storage section through the medium by an optical system arranged in a light path; and moving one or both of the target and the irradiation position of the laser light via a moving mechanism so that the laser light is irradiated over the entire area of ​​a preset irradiation area of ​​the target, A surface modification laser irradiation method, in which in the process of irradiating the laser light, the laser energy density at which the laser light is irradiated to the target is equal to or higher than the protrusion start threshold of a second convex portion formed on the cone side surface of a cone-shaped first convex portion of the target, and is equal to or lower than the melting threshold of the target in the medium.

4. 6. The surface modification laser irradiation method according to claim 5, wherein the laser light has a wavelength in the range of 266 nm to 10.6 μm and has a pulse length of 50 to 600 pulses.

5. A semiconductor member having a cone-shaped convex portion on its surface and converting received light into electricity, The convex portion includes a first convex portion having a pyramidal shape formed on the surface of the semiconductor member, and a second convex portion on a pyramidal side surface of the first convex portion, The first convex portion has a size of 1 μm or more and 30 μm or less, The second convex portion is a semiconductor component having a size of 1 / 50 or more and 1 / 2 or less of the wavelength of the irradiated laser light, and the ratio of the length of one side of the top portion to the length of one side of the bottom portion is 1≦bottom portion / top portion≦4, or the aspect ratio of the base portion to the height is 0.1≦base portion / height≦2, or both.

6. The semiconductor member according to claim 5, wherein the surface reflectance for light having a wavelength of 500 nm ± 2 nm received on a surface having the first convex portion and the second convex portion is reduced by 3% or more compared to the surface reflectance for light received on a surface having only the first convex portion.

7. The semiconductor member according to claim 5, wherein the surface reflectance for light in the wavelength band of 400 nm to 800 nm received on a surface having the first convex portion and the second convex portion is reduced by 3% or more compared to the surface reflectance for light received on a surface of only the first convex portion.

8. A solar cell comprising: a silicon panel used for photoelectric conversion; a first electrode disposed on a light-receiving surface side of the silicon panel; and a second electrode disposed on another surface of the silicon panel opposite to the light-receiving surface, The silicon panel is a silicon solar cell which is a semiconductor member according to any one of claims 5 to 7.

9. The silicon solar cell according to claim 8 , wherein the silicon panel includes a second protrusion having a size of 10 nm or less.

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