WO2011145131A1 - 光起電力装置の製造方法及び光起電力装置の製造装置 - Google Patents
光起電力装置の製造方法及び光起電力装置の製造装置 Download PDFInfo
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- WO2011145131A1 WO2011145131A1 PCT/JP2010/003303 JP2010003303W WO2011145131A1 WO 2011145131 A1 WO2011145131 A1 WO 2011145131A1 JP 2010003303 W JP2010003303 W JP 2010003303W WO 2011145131 A1 WO2011145131 A1 WO 2011145131A1
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- 238000004519 manufacturing process Methods 0.000 title claims description 26
- 238000005530 etching Methods 0.000 claims abstract description 76
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 24
- 239000010703 silicon Substances 0.000 claims abstract description 24
- 238000001039 wet etching Methods 0.000 claims abstract description 18
- 238000000059 patterning Methods 0.000 claims abstract description 15
- 239000000758 substrate Substances 0.000 claims description 55
- 229910021421 monocrystalline silicon Inorganic materials 0.000 claims description 37
- 238000000034 method Methods 0.000 claims description 35
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 23
- 230000000737 periodic effect Effects 0.000 claims description 5
- 238000012545 processing Methods 0.000 description 37
- 239000011295 pitch Substances 0.000 description 32
- 238000010586 diagram Methods 0.000 description 10
- 230000003287 optical effect Effects 0.000 description 10
- 230000000694 effects Effects 0.000 description 9
- 230000015572 biosynthetic process Effects 0.000 description 8
- 238000012546 transfer Methods 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 230000006866 deterioration Effects 0.000 description 5
- 238000007429 general method Methods 0.000 description 4
- 229910052581 Si3N4 Inorganic materials 0.000 description 3
- 239000003513 alkali Substances 0.000 description 3
- 229910021419 crystalline silicon Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 3
- 229910004298 SiO 2 Inorganic materials 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 229910052814 silicon oxide Inorganic materials 0.000 description 2
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 238000000347 anisotropic wet etching Methods 0.000 description 1
- 230000003667 anti-reflective effect Effects 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/02—Details
- H01L31/0236—Special surface textures
- H01L31/02363—Special surface textures of the semiconductor body itself, e.g. textured active layers
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
Definitions
- the present invention relates to a method and an apparatus for manufacturing a photovoltaic device using crystalline silicon.
- Patent Document 1 when forming a fine texture structure for reducing the reflectance of the photovoltaic manufacturing apparatus, one of the laser openings for the etching resistant film is used. One concave portion of the texture structure corresponds.
- the diameter of the laser aperture is enlarged or etching is performed for a long time.
- productivity of the laser aperture process is reduced and the laser aperture is reduced.
- Deterioration of texture size uniformity due to dispersion, and deterioration of characteristics due to damage remaining in the wafer caused by increased laser intensity are problems.
- productivity in the etching process is reduced and etching is performed for a long time.
- Variations in the texture size due to an increase in the influence of etching conditions such as temperature and liquid concentration that change to a problem arise.
- the photovoltaic device manufacturing method and manufacturing apparatus include: When forming an anti-reflective texture on the surface of a photovoltaic device using single crystal silicon by laser patterning and wet etching of the etching resistant film, the bottom surface of the desired pyramidal recess is formed using a pulse laser and laser beam branching means. A plurality of laser apertures are processed in the diagonal direction of the square, and the pitch of the laser apertures between the squares is formed from a plurality of laser apertures whose pitch is larger than the pitch on the diagonal line to form a concave portion of one texture structure The arrangement of the laser openings is formed by a pattern having at least two types of pitch sizes.
- the concave portion of one texture structure is formed from a plurality of relatively small laser apertures, the productivity of the laser aperture process is lowered, and the uniformity of the texture size due to variations in aperture shapes is reduced. While suppressing the deterioration, there is an unprecedented remarkable effect that a pyramidal texture can be formed without variation in size by etching in a short time.
- Embodiment 1 of this invention It is a figure for demonstrating another example of the formation process of the texture in Embodiment 1 of this invention. It is a schematic block diagram of the laser processing apparatus for forming the laser aperture pattern in Embodiment 1 of this invention. It is the schematic for demonstrating the laser beam branch pattern in Embodiment 1 of this invention. It is the schematic for demonstrating the laser beam branch pattern in Embodiment 2 of this invention. It is the schematic for demonstrating the laser beam branch pattern in Embodiment 3 of this invention. It is the schematic for demonstrating the timing of the laser pulse in Embodiment 3 of this invention. It is the schematic for demonstrating the surface orientation of the single crystal silicon substrate on the silicon substrate conveyance means in embodiment of this invention.
- Embodiment 3 of this invention It is the schematic for demonstrating the pattern of the laser opening part in Embodiment 3 of this invention. It is the schematic for demonstrating the texture structure in Embodiment 3 of this invention. It is the schematic for demonstrating the pattern of the laser opening part in Embodiment 4 of this invention. It is the schematic for demonstrating the pattern of the laser opening part in Embodiment 5 of this invention. It is a schematic block diagram of the laser processing apparatus for forming the laser aperture pattern in Embodiment 5 of this invention. It is a figure for demonstrating the formation process of the texture in Embodiment 6 of this invention.
- Embodiments of a photovoltaic device manufacturing method and a photovoltaic device manufacturing apparatus according to the present invention will be described below in detail with reference to the drawings.
- Embodiment 1 FIG.
- the texture structure is a concavo-convex structure provided on the surface of the single crystal silicon substrate, and incident sunlight is absorbed while being reflected by the concavo-convex structure on the substrate surface, which is effective in suppressing reflected light. .
- reflected light on the surface can be suppressed and photoelectric conversion efficiency can be improved.
- FIGS. 1 to 3 are schematic diagrams for explaining a process for forming a texture structure of a general crystalline silicon solar cell.
- a in each figure is a top view as seen from the light incident surface
- b is a cross-sectional view when the light incident surface is facing up.
- the texture structure is formed by using a commonly used p-type or n-type single crystal silicon substrate, and its typical specification is that the specific resistance sliced along the (100) plane is 0.1 to The thickness is 10 ⁇ cm and the thickness is 200 to 400 ⁇ m.
- an etching resistant film 2 having resistance to wet etching is formed on the entire surface of the single crystal silicon substrate 1.
- a silicon nitride film Si 3 N 4 film
- the etching resistant film 2 (a in FIG. 1 and b) in FIG. 1).
- a silicon oxide film (SiO 2 film) or the like can be used as the etching resistant film 2 because it has sufficient etching selectivity between silicon and the film in alkaline etching. It is.
- an aligned laser opening 3 having a geometric periodic structure is formed in the etching resistant film 2 (FIG. 2).
- the laser openings 3 are formed on a square lattice with a pitch of 20 ⁇ m in a direction parallel to the (010) and (001) planes.
- the diameter of each laser opening 3 is about ⁇ 7 ⁇ m.
- the diameter of the laser opening 3 is determined by the intensity of the laser to be used and the focused diameter on the silicon substrate.
- the productivity in the etching process is improved.
- the laser condensing diameter may be increased.
- the laser condensing diameter is increased while keeping the laser intensity as it is, the intensity per unit area decreases. This is because when the laser intensity per unit area decreases, the temperature rise on the substrate surface due to laser irradiation becomes insufficient and an opening cannot be formed.
- a method for branching a laser beam and performing laser processing at multiple points simultaneously is one promising means for increasing the speed of laser processing.
- the diameter of the laser aperture was set to about ⁇ 7 ⁇ m as a result of the trade-off between these two factors.
- anisotropic wet etching is performed on the single crystal silicon substrate 1 through the laser opening 3 using an alkaline etchant such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) aqueous solution.
- KOH potassium hydroxide
- NaOH sodium hydroxide
- anisotropic etching is performed with an alkaline aqueous solution on a single crystal silicon substrate sliced in the (100) plane, the substrate is anisotropically etched along the (111) plane and oriented in the (111) plane.
- the four pyramid-shaped recesses 4 having a V-shaped cross section are obtained.
- anisotropic etching is performed through the laser opening 3 formed in the etching resistant film 2, the anisotropic etching proceeds with respect to the silicon exposed in the laser opening 3, so that the laser can be etched in a relatively short time.
- a pyramid-shaped recess formed by four walls oriented with the circumscribed square of the opening 3 as the bottom and oriented in the (111) plane is formed (FIG. 3).
- the etching rate of the (111) plane is slow in anisotropic etching, so that the square shape that forms the bottom surface of the pyramid. The speed at which the size of the recess, which is typically represented by the length of the side and the height of the pyramid, increases.
- the interval between the pyramid-shaped recesses needs to be sufficiently narrow compared to the size of the pyramid.
- the size expansion rate of the pyramidal recesses by anisotropic etching is significantly reduced. Therefore, in order to sufficiently narrow the interval between the pyramid recesses, etching is performed for a long time or the laser aperture 3 It is necessary to enlarge the area.
- the productivity of the etching process is lowered.
- the etching conditions such as the temperature and concentration of the etching solution that fluctuates during the long-time etching.
- the size of the pyramidal recesses varies. As a result, in some areas of the substrate, the interval between the pyramid-shaped recesses remains wide, but in other areas, adjacent pyramid-shaped recesses are connected to flatten the ridgeline, reducing the reflectance reduction effect. The problem also arises.
- the pyramid due to the shape variation related to the opening diameter of the laser opening 3 is obtained.
- the size of the concave portion is nonuniform.
- the laser aperture 3 is ideally a perfect circle having a uniform size when viewed from the laser incident side of the silicon substrate, but in reality, aberrations peculiar to the optical system of the laser processing machine that performs the laser aperture and Due to the thickness variation of the wafer, the diameter may vary within a range of about 30% of the maximum diameter, or the perfect circular shape may become an ellipse.
- the laser aperture 3 composed of four apertures is taken as one unit, and the laser aperture 3 is formed as densely as possible on the substrate.
- a desired one pyramidal recess as shown in FIG. 8A is finally formed (FIG. 8A).
- the laser aperture 3 is formed on the diagonal of the square on the bottom surface of the pyramidal recess, and these diagonals are spaced apart from each other by a certain distance in parallel (see FIG. FIG. 6 a)).
- FIG. 4 is a diagram for explaining the pattern of the laser aperture in the first embodiment of the present invention.
- the four laser openings for forming one pyramidal recess are formed at a certain distance from the four laser openings 3 for forming neighboring pyramid recesses.
- the interval between the pyramid-shaped concave portions to be formed can be controlled. That is, the pattern of the laser aperture 3 is a relatively narrow pitch (6 ⁇ m pitch in the example of the present invention) that divides the diagonal line of the pyramid-shaped recess and a relatively wide pitch (determined according to the present invention). In the example, the pitch is 20 ⁇ m).
- a procedure for forming a texture structure by the pattern of the laser aperture will be described with reference to FIGS.
- a silicon nitride film (Si 3 N 4 film) or a silicon oxide film (SiO 2 ) is formed on the entire surface of the single crystal silicon substrate 1 as an etching resistant film 2 having resistance to wet etching. ) Is formed (FIG. 5).
- a laser opening 3 is formed in the etching resistant film 2 by a laser (FIG. 6).
- four directions are formed at a pitch of 6 ⁇ m on the (111) plane in the direction of 45 degrees with the (001) direction (the diagonal direction of the square that forms the bottom surface of the pyramidal recess formed in the later etching process).
- One opening is formed as a set, and the laser openings 3 are formed at a pitch of 20 ⁇ m between the sets in the direction of each side of the square that becomes the bottom surface of the pyramidal concave portion.
- the number of laser openings 3 formed per one silicon substrate increases four times.
- one of the four openings of the laser aperture 3 is formed.
- a typical value for the opening size is ⁇ 4 ⁇ m ⁇ 1 ⁇ m. Specific means for forming such a periodic pattern composed of two types of pitch will be described later.
- anisotropic etching is performed on the single crystal silicon substrate 1 through the laser opening 3 as in the case of a general method.
- a pyramidal recess having a circumscribed square circumscribing the circular shape of each laser opening 3 is formed by short-time etching (FIG. 7).
- the size increase of the pyramid-shaped recess proceeds very slowly.
- the etching rate is reduced, the pyramidal recesses formed by the four sets of laser openings 3 formed in the laser opening process are connected with a relatively short time of etching because the intervals are sufficiently narrow.
- the etching proceeds again at a high speed.
- the etching time is about 1/5 compared with the case where a general method is used, and a texture structure with a uniform pyramidal recess can be formed. After forming the texture structure, if necessary, etching for removing the etching resistant film 2 is performed.
- FIG. 9 shows a schematic configuration of a laser processing apparatus for forming a laser aperture pattern.
- This laser processing apparatus includes a silicon substrate transfer unit 5, a laser oscillator 6, a laser beam intensity adjusting unit 7, a laser beam shape adjusting unit 8, one or more light guide mirrors 9, and a laser beam dividing unit. 10 and laser beam condensing means 11.
- the silicon substrate transfer means 5 holds the single crystal silicon substrate 1 having an etching resistant film (not shown) formed on the surface thereof with the surface to be processed facing upward, and collects the single crystal silicon substrate 1 with a laser beam. Move along the light surface.
- the laser oscillator 6 emits a laser beam.
- the laser oscillator 6 can use, for example, a double wave (wavelength: 532 nm) of a 40 kHz Q-switch LD-pumped Nd: YVO 4 laser as a typical repetition frequency.
- an ultraviolet laser such as a third harmonic or a fourth harmonic is used, since the absorption coefficient of the etching-resistant film and silicon is high, processing with a smaller diameter and higher quality is possible. The problem of deterioration of the optical element occurs due to the influence of impurities. An appropriate wavelength may be selected in view of merits and demerits.
- the laser beam intensity adjusting means 7 is means for attenuating the laser intensity automatically or manually to obtain a laser intensity suitable for processing.
- the laser beam shape adjusting means 8 includes a combination of a plurality of cylindrical lenses for making the shape of the laser beam a perfect circle and a combination of a plurality of spherical lenses for obtaining a desired beam diameter and beam divergence angle. .
- One light guide mirror 9 is arranged between the laser beam shape adjusting means 8 and the laser beam splitting means 10 in FIG. 9, but in order to guide the laser beam in accordance with the space of the laser processing machine.
- One or more sheets are arranged as appropriate.
- the laser beam splitting means 10 splits the laser beam into a laser beam branching pattern having a predetermined geometric periodic structure as shown in FIG.
- FIG. 10 is a schematic diagram showing a laser beam branching pattern.
- the laser beam branch pattern is a set of four branch patterns (indicated by “A” in FIG. 10) at a pitch of 6 ⁇ m, and a direction that forms an angle of 45 degrees with the alignment direction of the branch pattern of 6 ⁇ m pitch (in FIG. 10).
- 90 patterns are arranged at a pitch of 20 ⁇ m.
- a diffractive optical element can be used.
- a mask having a plurality of apertures can be used, but it is desirable to use a diffractive optical element from the viewpoint of the uniformity and efficiency of the beam.
- the laser beam split by the laser beam splitting means 10 is focused on the single crystal silicon substrate 1 by the laser beam focusing means 11.
- the laser oscillator 6 is pulse-oscillated at 40 kHz
- the single crystal silicon substrate transport means 5 moves the single crystal silicon substrate 1 at 800 mm / second in the direction indicated by the x direction in FIG.
- the y direction and the x direction in FIG. 9 are made to coincide with the X direction and the Y direction in FIG. 10, respectively.
- the single crystal silicon substrate 1 is moved by the single crystal silicon substrate transfer means 5.
- the F ⁇ lens as means, the same effect can be obtained by scanning the single crystal silicon substrate 1 with the laser beam divided by the laser beam dividing means.
- the laser beam scanning method can scan at a higher speed than moving the object to be processed by the conveying means, and the laser processing productivity can be improved by appropriately selecting the laser intensity and the repetition frequency. I can do it.
- Embodiment 2 The purpose of this embodiment is to reduce the reflectance of sunlight on the surface of the single crystal silicon solar cell by forming an etching resistant film on the surface of the single crystal silicon solar cell, laser opening of the etching resistant film, and wet etching. Although an inverted pyramid-shaped concavo-convex structure is formed, since only the laser processing step is different from that of the first embodiment, the laser processing step will be mainly described here.
- the narrowest pitch is set to 6 ⁇ m as shown in FIG.
- the condensing diameter of the laser beam on the single crystal silicon substrate 1 is set to ⁇ 4 ⁇ m.
- FIG. 11 shows a laser beam branching pattern in the present embodiment.
- the distance between the closest points is 10 ⁇ m.
- the condensing diameter of the laser beam on the single crystal silicon substrate 1 is ⁇ 4 ⁇ m, and the distance between the nearest points is more than twice, and the deterioration of the shape of the laser aperture due to interference does not matter.
- the same laser aperture pattern as in a) of FIG. 6 can be processed.
- the laser repetition frequency may be set to 40 kHz
- the moving speed of the single crystal silicon substrate 1 by the silicon substrate transfer means 5 may be set to 800 mm / second.
- a texture structure with pyramidal recesses as shown in FIG. 8 can be formed.
- the laser beam branch pattern is formed with two kinds of pitches as shown in FIGS.
- two types of pitches are mixed, whether or not to set a grating with the greatest common divisor and place the laser beam on the grating
- a 6 ⁇ m pitch lattice is set, and every other 12 ⁇ m pitch is expressed as an 18 ⁇ m pitch. If this pitch is fine, the pitch of the surface shape of the diffractive optical element is enlarged, so it is necessary to set a large laser incident beam to the diffractive optical element.
- the laser beam branch pattern, the laser pulse timing, and the plane orientation of the single crystal silicon substrate 1 on the silicon substrate transport means 5 are changed from those in the first and second embodiments.
- FIG. 12 is a schematic diagram for explaining a laser beam branching pattern according to the third embodiment of the present invention.
- this laser beam branching pattern 68 laser beams are arranged at a pitch of 28 ⁇ m in the Y direction, and two rows of laser beams arranged at a pitch of 14 ⁇ m in the X direction are shifted from each other by 14 ⁇ m in the Y direction.
- FIG. 13 shows a schematic diagram for explaining the timing of the laser pulse in the third embodiment.
- Laser pulses are generated at a pitch of 35 ⁇ sec from this set to obtain a laser pulse train with timing as shown in FIG.
- the plane orientation of the single crystal silicon substrate 1 on the silicon substrate transfer means 5 is arranged such that the (010) plane and the (001) plane are 45 degrees with respect to the four sides of the single crystal silicon substrate 1.
- FIG. 14 shows the plane orientation of the single crystal silicon substrate 1 on the silicon substrate transfer means 5 in the embodiment of the present invention.
- FIG. 15 shows a pattern of the laser opening 3 processed when the single crystal silicon substrate 1 is moved in the x direction at 800 mm / second as the laser pulse timing of FIG. 13 with the laser beam branching pattern of FIG.
- FIG. 15 is a schematic diagram for explaining the pattern of the laser aperture in the third embodiment of the present invention.
- the laser condensing diameter and the laser intensity on the silicon substrate are adjusted so that the diameter of the laser opening 3 is ⁇ 4 ⁇ m.
- FIG. 16 is a schematic diagram for explaining a texture structure according to Embodiment 3 of the present invention.
- FIG. 17 shows a laser aperture pattern in the fourth embodiment.
- the laser aperture is configured by a laser aperture formed on a square diagonal line that becomes the bottom surface of the quadrangular pyramid-shaped recess to be formed. In this way, by forming the laser aperture on one diagonal line, it is possible to obtain a recess connecting the diagonal lines of a desired texture shape by etching in a short time with a small area laser aperture.
- the laser processing speed is inversely proportional to the total area of the laser aperture, and therefore can be increased with a small area laser aperture.
- the etching time for enlarging the recess in the diagonal direction perpendicular to the diagonal line in which the laser aperture is formed requires a certain length. If the required tact time for etching is short and there is a margin of laser output relative to the required tact time for laser processing, the time for enlarging the recess can be increased by forming the laser aperture in a place other than the diagonal line as shown in FIG. Since it can be reduced, the etching time can be shortened.
- FIG. 18 shows a laser aperture pattern in the fifth embodiment.
- the shape of the laser aperture is a perfect circle.
- the shape of the laser aperture is set to be an ellipse.
- the area of the laser aperture can be reduced. Reducing the area of the laser aperture and improving the tact time of laser processing are almost equivalent. This is due to the following reason.
- the laser beam is focused and processed in a smaller area. Therefore, the laser energy density per unit area is increased at the same laser power and the same number of laser beam branches. I can do it. If the laser energy density required for processing the etching resistant film is the processing laser energy density, a larger number of laser beam branches can be obtained with the same laser power. By increasing the number of laser beam branches, the tact time of laser processing can be improved.
- FIG. 19 is a schematic configuration diagram of a laser processing apparatus for forming a laser aperture pattern in the fifth embodiment of the present invention.
- the elliptical optical system 13 for making the shape of the laser aperture an ellipse can use a cylindrical lens or a prism.
- Embodiment 6 Since this embodiment is different from the first embodiment only in the wet etching process, the wet etching process will be mainly described here.
- the wet etching is only anisotropic alkali etching.
- wet etching is divided into two or more steps. As a wet etching process, isotropic etching using a mixed acid or the like is first performed, and then anisotropic alkali etching is performed. In anisotropic etching, when the (111) plane comes out, the etching rate for enlarging the concave portion is remarkably reduced.
- the etching time is long until the small pyramid concave portion based on the adjacent laser aperture is connected after the (111) plane comes out. Take it.
- a concave portion is formed as shown in FIG. 20 a) and FIG. 20 b) without being affected by the crystal orientation, and adjacent laser apertures are formed in a comparatively short time.
- the concave part used as a base point can be connected.
- 20A is a view of the solar battery cell viewed from the light receiving surface side
- FIG. 20B is a cross-sectional view of the solar battery cell. Therefore, the etching time can be shortened.
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Abstract
Description
耐エッチング膜のレーザパターニングとウェットエッチングとで単結晶シリコンを使用した光起電力装置表面に反射防止テクスチャーを形成する際に、パルスレーザとレーザビーム分岐手段を用いて、所望のピラミッド状凹部の底面となる正方形の対角線方向に複数のレーザ開口を加工し、各正方形の間のレーザ開口のピッチは前記対角線上におけるピッチよりピッチを大きくする
複数のレーザ開口から一つのテクスチャー構造の凹部を形成するため、レーザ開口の配置を少なくとも2種類のピッチのサイズからなるパターンで形成することを特徴とする。
実施の形態1.
本実施の形態にかかる光起電力装置の製造方法及び製造装置において、単結晶シリコン太陽電池の表面(太陽光の入射側の面)にテクスチャー構造を形成するためのレーザ加工概要を説明する。ここで、テクスチャー構造とは単結晶シリコン基板の表面に設けた凹凸構造であり、入射した太陽光が基板表面の凹凸構造に多重反射しながら吸収されるため、反射光の抑制に効果的である。単結晶シリコン太陽電池の表面にテクスチャー構造を形成することで、表面での反射光を抑制でき、光電変換効率を向上することが可能である。
また、レーザで電極のパターン等をパターニング可能なため、単結晶シリコン基板1の表面の全面に、ウェットエッチングに対して耐性を有する耐エッチング膜2を形成する。耐エッチング膜2としては、例えばシリコン窒化膜(Si3N4膜)を用いる(図1のa)及び図1のb))。なお、耐エッチング膜2としては、シリコン窒化膜(Si3N4膜)の他にシリコン酸化膜(SiO2膜)などもアルカリエッチングでのシリコンと膜のエッチング選択性が十分にあり、使用可能である。
大きなレーザ開口部3を得るためには、一つのレーザ開口へ照射するレーザ強度を上げると同時に、シリコン基板上の集光径を拡大すれば良い。レーザ加工径を拡大するためには、レーザ集光径を拡大すれば良いが、レーザ強度をそのままとして、レーザ集光径を拡大すると、単位面積当たりの強度は低下する。単位面積当たりのレーザ強度が低下すると、レーザ照射による基板表面の温度上昇が不十分となり開口を形成できないためである。
一般的な方法の場合と同様、単結晶シリコン基板1の表面の全面に、ウェットエッチングに対して耐性を有する耐エッチング膜2としてシリコン窒化膜(Si3N4膜)やシリコン酸化膜(SiO2)を形成する(図5)。
この時、図6のように、(111)面上に(001)方向と45度となる方向(後のエッチング工程で形成するピラミッド状凹部の底面となる正方形の対角線方向)に6μmピッチで四つの開口を一組として形成し、ピラミッド状凹部の底面となる正方形の各辺の方向に、各組間を20μmピッチでレーザ開口部3を形成する。
本実施の形態は、単結晶シリコン太陽電池の表面に、耐エッチング膜の形成、耐エッチング膜のレーザ開口、ウェットエッチングにより、単結晶シリコン太陽電池の表面に太陽光の反射率を低減する目的で、逆ピラミッド形状の凹凸構造を形成するものであるが、実施の形態1とレーザ加工の工程のみ異なるため、ここでは、レーザ加工の工程を中心に述べる。
本実施の形態は、実施の形態1とレーザ加工の工程のみ異なるため、ここでは、レーザ加工の工程を中心に述べる。
実施の形態1及び実施の形態2においては、レーザビーム分岐パターンは図10および図11に示したように二種類のピッチで形成されていた。レーザビーム分岐のための回折光学素子の設計・製造においては、二種類のピッチが混在する場合、その最大公約数となるピッチの格子を設定し、格子上にレーザビームを配置するか、しないかで二種類のピッチを表現する。例えば12μmピッチと、18μmピッチが混在する場合、6μmピッチの格子を設定し、一つおきとして12μmピッチを二つおきとして18μmピッチを表現することになる。このピッチが細かいと回折光学素子の表面形状のピッチが拡大するために、回折光学素子へのレーザ入射ビームを大きく設定する必要がある。
図12のレーザビーム分岐パターンで、図13のレーザパルスタイミングとして、x方向に800mm/秒で単結晶シリコン基板1を移動したときに、加工されるレーザ開口部3のパターンを図15に示す。図15は本発明の実施の形態3におけるレーザ開口部のパターンを説明するための概略図である。レーザ開口部3の径は、φ4μmとなるように、シリコン基板上のレーザ集光径とレーザ強度を調整する。
本実施の形態は、実施の形態1とレーザ加工の工程のみ異なるため、ここでは、レーザ加工の工程を中心に述べる。図17に実施の形態4におけるレーザ開口のパターンを示す。実施の形態1乃至実施の形態3においては、レーザ開口部は形成すべき四角錐状凹部の底面となる正方形の対角線上に形成したレーザ開口により構成した。このように、一本の対角線上にレーザ開口を形成することで、小面積のレーザ開口で短時間のエッチングにより、所望のテクスチャー形状の対角線上を結ぶ凹部を得ることが出来る。単純化して考えると、レーザ加工速度は、レーザ開口の総面積に反比例するため、小面積のレーザ開口では、速くできる。
本実施の形態は、実施の形態1とレーザ加工の工程のみ異なるため、ここでは、レーザ加工の工程を中心に述べる。図18に実施の形態5におけるレーザ開口のパターンを示す。実施の形態1乃至実施の形態4においては、レーザ開口の形状を真円としていた。それに対して本実施の形態では、レーザ開口の形状を楕円に設定する。レーザ開口の形状が真円である図4と比較すると明らかなように、レーザ開口の面積を低減可能である。レーザ開口の面積を低減することと、レーザ加工のタクトを向上させることはほぼ等価である。
これは以下の理由による。
本実施の形態は、実施の形態1とウェットエッチングの工程のみ異なるため、ここでは、ウェットエッチングの工程を中心に述べる。実施の形態1においては、ウェットエッチングは、異方性のアルカリエッチングのみであった。それに対して、本実施の形態では、ウェットエッチングを2段階以上の工程に分割する。ウェットエッチング工程としてまず混酸などによる等方的なエッチングを実施して、その後、異方性のアルカリエッチングを実施する。異方性エッチングは(111)面が出ると凹部を拡大するエッチング速度は著しく低下するため、(111)面が出てから隣接したレーザ開口を基点とした小さなピラミッド凹部がつながるまでにエッチング時間がかかる。それに対して、等方的エッチングにおいては、結晶方位の影響を受けず図20のa)及び図20のb)に示すようにおわん状の凹部が形成され、比較短時間で隣接したレーザ開口を基点とした凹部をつなげることが出来る。図20のa)は、太陽電池セルを受光面側より見た図、図20のb)は、太陽電池セルの断面図である。よってエッチング時間を短縮することが可能である。また、更に異方性のアルカリエッチング実施後にIPA等の添加材を入れたアルカリにてエッチングすることで、隣接したピラミッド状凹部がつながった時、ピラミッド状凹部の境界線がエッチングにより崩れることを防止することが出来る。
Claims (10)
- 単結晶シリコン基板を使用し、耐エッチング膜のレーザパターニングとウェットエッチングとを用いて光起電力装置表面に反射防止テクスチャーを形成する光起電力装置の製造方法において、
前記レーザパターニングによって、複数の開口からなるレーザ開口部を形成する第一の工程と、
ウェットエッチングによって、前記各開口を基に正方形状底面を有し、前記シリコン基板表面からみて逆ピラミット状となる上記開口と同数の四角錐状凹部を形成した後、
上記開口と同数の四角錐状凹部を全て含み、当該四角錐状凹部の正方形状底面の複数の四角錐状凹部の数とほぼ同数倍のサイズの四角錐状凹部を形成する第二の工程と、
からなることを特徴とする光起電力装置の製造方法。 - 単結晶シリコン基板を使用し、耐エッチング膜のレーザパターニングとウェットエッチングとを用いて光起電力装置表面に反射防止テクスチャーを形成する光起電力装置の製造方法において、
前記レーザパターニングによって、複数の開口からなるレーザ開口部を形成する第一の工程と、
ウェットエッチングによって、前記各開口を基に正方形状底面を有し、前記シリコン基板表面からみて逆ピラミット状となる上記開口と同数の四角錐状凹部を形成した後、
上記開口と同数の四角錐状凹部を全て含み、当該四角錐状凹部の正方形状底面の対角線方向のうち全四角錐状凹部が一直線状に繋がる方向に、前記複数の四角錐状凹部の数とほぼ同数倍のサイズの四角錐状凹部を形成する第二の工程と、
からなることを特徴とする光起電力装置の製造方法。 - 前記レーザパターニングに用いるレーザビームはパルスレーザであり、
当該レーザパターニングは、
前記パルスレーザと、
前記レーザビームを既定の幾何学的な周期構造を有するレーザビーム分岐パターンへ分岐するレーザビーム分割手段と、を用いて形成されたものであって、
複数のレーザ開口からなるレーザ開口部を形成するとともに、
前記レーザ開口部の各開口部間の最短のピッチは、前記レーザ開口部に属する任意の2個のレーザ開口間の最短のピッチより大きくしたものであることを特徴とする請求項2に記載の光起電力装置の製造方法。 - 前記レーザビーム分岐パターンにおいて、近接するレーザビームの間の距離をレーザビーム集光径の2倍以上に設定することを特徴とする請求項3に記載の光起電力装置の製造方法。
- 前記レーザビーム分岐パターンのピッチを一種類とし、レーザパルスのタイミングの調整によりレーザパターニングを行なうことを特徴とする請求項3に記載の光起電力装置の製造方法。
- 前記レーザ開口部の各レーザ開口間のピッチは、少なくとも2個からなる等ピッチで1組の開口を、少なくとも1組含むことを特徴とする請求項3に記載の光起電力装置の製造方法。
- 前記レーザ開口部の各レーザ開口の形状が、サイズの大きい方向とサイズの小さい方向とを含む細長い形状であることを特徴とする請求項1から請求項3に記載の光起電力装置の製造方法。
- 前記ウェットエッチングが、エッチング液の組成を変えた2種類以上のエッチングにより構成されることを特徴とする請求項1から7に記載の光起電力装置の製造方法。
- 単結晶シリコン基板を使用し、耐エッチング膜のレーザパターニングとウェットエッチングとを用いて光起電力装置表面に反射防止テクスチャーを形成する光起電力装置の製造装置において、
前記レーザパターニングによって複数の開口からなるレーザ開口部を形成するとともに、
ウェットエッチングによって、
前記各開口を基に正方形状底面を有し、前記シリコン基板表面からみて逆ピラミット状となる上記開口と同数の四角錐状凹部を形成した後、
上記開口と同数の四角錐状凹部を全て含み、当該四角錐状凹部の正方形状底面の対角線方向のうち全四角錐状凹部が一直線状に繋がる方向に、前記複数の四角錐状凹部の数とほぼ同数倍のサイズの四角錐状凹部を形成することを特徴とする光起電力装置の製造装置。 - 前記レーザパターニングに用いるレーザビームはパルスレーザであり、
当該レーザパターニングは、
前記パルスレーザと、
前記レーザビームを既定の幾何学的な周期構造を有するレーザビーム分岐パターンへ分岐するレーザビーム分割手段と、を用いて形成されたものであって、
複数のレーザ開口からなるレーザ開口部を形成するとともに、
前記レーザ開口部の各開口部間の最短のピッチは、前記レーザ開口部に属する任意の2個のレーザ開口間の最短のピッチより大きくしたものであることを特徴とする請求項9に記載の光起電力装置の製造装置。
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