WO2019223805A1 - Method and apparatus for surface texturing of semiconductor substrate - Google Patents

Method and apparatus for surface texturing of semiconductor substrate Download PDF

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Publication number
WO2019223805A1
WO2019223805A1 PCT/CN2019/088548 CN2019088548W WO2019223805A1 WO 2019223805 A1 WO2019223805 A1 WO 2019223805A1 CN 2019088548 W CN2019088548 W CN 2019088548W WO 2019223805 A1 WO2019223805 A1 WO 2019223805A1
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semiconductor substrate
liquid
rinsing
cleaning
process liquid
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PCT/CN2019/088548
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French (fr)
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Peter Fath
Ihor Melnyk
Wolfgang Jooss
Jan JUNG-KOENIG
Andreas TEPPPE
Sukumar MADUGULA
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Rct Solutions Gmbh
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67011—Apparatus for manufacture or treatment
    • H01L21/67017—Apparatus for fluid treatment
    • H01L21/67063—Apparatus for fluid treatment for etching
    • H01L21/67075—Apparatus for fluid treatment for etching for wet etching
    • H01L21/6708—Apparatus for fluid treatment for etching for wet etching using mainly spraying means, e.g. nozzles
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
    • H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
    • H01L21/30604—Chemical etching
    • H01L21/30608—Anisotropic liquid etching
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67011—Apparatus for manufacture or treatment
    • H01L21/67017—Apparatus for fluid treatment
    • H01L21/67063—Apparatus for fluid treatment for etching
    • H01L21/67075—Apparatus for fluid treatment for etching for wet etching
    • H01L21/67086—Apparatus for fluid treatment for etching for wet etching with the semiconductor substrates being dipped in baths or vessels
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67011—Apparatus for manufacture or treatment
    • H01L21/67155—Apparatus for manufacturing or treating in a plurality of work-stations
    • H01L21/67161—Apparatus for manufacturing or treating in a plurality of work-stations characterized by the layout of the process chambers
    • H01L21/67173—Apparatus for manufacturing or treating in a plurality of work-stations characterized by the layout of the process chambers in-line arrangement
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/677—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations
    • H01L21/67739—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for conveying, e.g. between different workstations into and out of processing chamber
    • H01L21/6776—Continuous loading and unloading into and out of a processing chamber, e.g. transporting belts within processing chambers
    • 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
    • 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
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic Table
    • 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
    • Y02E10/547—Monocrystalline silicon PV cells

Definitions

  • the present invention relates to an apparatus for surface texturing of a semiconductor substrate, and further relates to a method for surface texturing of a semiconductor substrate.
  • the efficiency of solar cells depends on the reflection losses.
  • semiconductor substrates are produced with a textured surface structure. If such semiconductor or silicon substrates are treated with particularly effective methods, these are referred to, for example, as “black silicon” .
  • black silicon In order to particularly effectively achieve a black silicon texturization, it is known to use a process of metal catalyst chemical etching (abbreviated as “MCCE” , also called a metal catalyst assisted chemical etching) .
  • MCCE metal catalyst chemical etching
  • Processes for texturing a single crystal silicon wafer known in the prior art for example use alkaline solution (KOH, NaOH, etc. ) and isopropanol or additives to generate randomly distributed upright pyramid-type surface structures. These processes typically require a long process time, for example, more than 15 minutes for the additives and more than 30 minutes for isopropanol, and accordingly such processes for texturing the single crystal silicon wafer are usually carried out in a batch apparatus.
  • the resulting pyramids have a size that typically can vary over a wide range of from less than 1 ⁇ m to more than 5 ⁇ m, and is typically about 1 ⁇ m.
  • these known processes are generally quite expensive, and their cost is mainly caused by the cost of the additives.
  • this solution is capable of reducing manufacturing cost, providing an apparatus having a higher throughput of e.g., larger than 8000 wafers/h, and thereby reducing the equipment size (with respect to wafer /h /equipment area) .
  • this solution is further capable of providing a better performance, e.g., reducing front surface reflectivity, or increase light trapping, especially for a thin wafer.
  • an inverted-pyramid-type surface structure can be used to replace the randomly distributed upright pyramid-type surface structure.
  • a process for preparation of the inverted-pyramid-type surface structure comprises: firstly forming, e.g. by lithography, a regular surface structure of an etching resist, followed by an alkaline etching treatment, in which an anisotropic etching behaviour occurs, to obtain the inverted-pyramid-type surface structure.
  • the semiconductor substrate can be textured in a one-step process by the MCCE method, in which metal Cu is used, to prepare an inverted-pyramid type surface structure.
  • a method of forming an inverted-pyramid-type porous surface nanotexture on polycrystalline silicon by the MCCE method is known from CN103456804A.
  • an inverted-pyramid-type surface texture Compared to a randomly distributed upright pyramid-type surface texture prepared by a standard alkaline texturing process for single crystal, an inverted-pyramid-type surface texture exhibits much better optical performances in terms of reflectivity and light trapping.
  • Better results of a randomly distributed inverted-pyramid-type surface texture obtained to date have been achieved by a Cu-based MCCE process using a HF: H 2 O 2 etching solution at a process temperature of 50°C.
  • a major disadvantage for this process is that the process time is about 15 minutes, and the use of the H 2 O 2 etching solution at 50°C will be accompanied by accelerated and uncontrolled volatilization of H 2 O 2 , thereby making it difficult to ensure a stable texturing process in industrial applications.
  • Cu-based etching MCCE solutions suffer from a limited acceptance in the manufacture of photovoltaic products.
  • the technical problem to be solved by the present invention is to overcome the drawbacks in the prior art, and to provide an improved apparatus and an improved method for surface texturing of a semiconductor substrate, which are capable of obtaining, in a simple and effective manner, an inverted-pyramid-type textured surface structure for the semiconductor substrate, so as to produce a solar cell with an extremely low reflectivity loss and a high efficiency.
  • the above-mentioned problem has been solved by an apparatus in accordance with the present invention, i.e., an apparatus for surface texturing of a semiconductor substrate.
  • the apparatus comprises: a first process tank configured to receive a first process liquid and, by means of said first process liquid, deposit silver (Ag) particles on the surface of the semiconductor substrate and form a large number of holes, in which said Ag particles are contained, on the surface of the semiconductor substrate by Ag-based metal catalyst chemical etching; a second process tank configured to receive a second process liquid and perform alkaline etching to said holes in the presence of said Ag particles by means of said second process liquid, in order to form an inverted-pyramid-type textured surface structure of the semiconductor substrate; and, a cleaning device configured to perform at least one cleaning of the inverted-pyramid-type textured surface structure by means of a cleaning liquid in order to remove said Ag particles.
  • the inventor has surprisingly found that, when the semiconductor substrate is subjected to an alkaline etching or alkaline texturing in the presence of Ag particles on the surface of a semiconductor substrate, and more accurately, within or in holes (or pores) of the surface of the semiconductor substrate, the resulting textured surface structure is not a randomly distributed upright pyramid-type textured surface structure, which would generally have formed under similar conditions, but a randomly distributed inverted-pyramid-type textured surface structure. Namely, during the alkaline etching or alkaline texturing, the presence of the Ag particles is essential to obtain the inverted-pyramid-type textured surface structure.
  • the apparatus according to the present invention further comprises a third process tank configured to receive a third process liquid and perform a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure in the absence of said Ag particles by means of the third process liquid in order to form the enlarged inverted-pyramid-type textured surface structure.
  • a third process tank configured to receive a third process liquid and perform a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure in the absence of said Ag particles by means of the third process liquid in order to form the enlarged inverted-pyramid-type textured surface structure.
  • the size of the inverted-pyramid-type textured surface structure is enabled to be further enlarged.
  • first process tank, “second” process tank, and “third” process tank are merely intended to distinguish the process tanks from each other, and should not be understood to be restrictive.
  • other tanks e.g., a cleaning tank and/or a rinsing tank may be disposed before, between, and/or behind the process tanks.
  • first process liquid, “second” process liquid, and “third” process liquid are merely intended to distinguish the process tanks from each other, and should not be understood to be restrictive.
  • the first process tank Ag particles are deposited on the surface of the semiconductor substrate by means of said first process liquid, and a large number of holes, in which said Ag particles are contained, are formed on the surface of the semiconductor substrate by Ag-based metal catalyst chemical etching.
  • the holes Preferably, the holes have a maximum dimension of between 50 nm and 300 nm, preferably between 100 nm and 200 nm.
  • the deposition of Ag particles and the hole drilling i.e., hole etching process
  • the deposition of Ag particles on the semiconductor substrate largely increases the rate of etching. In this process step, the surface of the semiconductor substrate remains hydrophilic, thereby rendering it to be wetted easily with the first process liquid.
  • the first process tank is configured to remove the sawn surface structure, preferably in the range of 0.5 to 4.0 ⁇ m/side, additionally by means of the first process liquid.
  • the first process tank contains a first process liquid, which is suitable both for removing e.g. the sawn surface structure, and for depositing Ag particles on the semiconductor substrate and generating a large number of holes by a metal catalyst chemical etching, a textured surface structure with a lower reflectivity loss and a high efficiency can be obtained in a simpler and more effective manner.
  • the first process liquid saw damages or sawn surface structures are removed, Ag particles are deposited on the semiconductor substrate, and a large number of holes are drilled out by the metal catalyst chemical etching. This takes place in particular exclusively in the first process tank or with the first process liquid, i.e., in a single process bath or process step.
  • a sawn surface structure or a saw-damaged surface structure caused by a Diamond Wire Saw process (DWS) is removed.
  • DWS Diamond Wire Saw process
  • the first process liquid contains hydrofluoric acid (HF) , nitric acid (HNO 3 ) , and silver nitrate (AgNO 3 ) .
  • the first process liquid is preferably comprised of an aqueous solution containing hydrofluoric acid (i.e. hydrogen fluoride) , nitric acid (i.e. hydrogen nitrate) and silver ions.
  • the aqueous solution preferably comprises distilled water as a matrix.
  • the silver ions are contained preferably in the form of hydrated silver ions, wherein silver is added into the aqueous solution in the form of silver nitrate.
  • silver is deposited on the surface and forms silver particles.
  • the first process liquid contains from 10 wt. %to 25 wt. %, preferably from 12 wt. %to 20 wt. %of hydrofluoric acid, from 12 wt. %to 25 wt. %, preferably from 15 wt. %to 22 wt. %of nitric acid, and from 0.0001 wt. %to 0.05 wt. %, preferably from 0.001 wt. %to 0.015 wt. %of silver nitrate.
  • the first process liquid contains less than 5 wt. %, especially less than 1 wt. %, and especially 0 wt. %of hydrogen peroxide.
  • Hydrogen peroxide affects the desired metal catalyst chemical etching.
  • the first process liquid preferably does not contain hydrogen peroxide. In this manner, the process duration and process stability are optimized, and the structure of the apparatus is simplified since less process chemical formulations, for example, are required for the operation of the apparatus.
  • the first process liquid has a temperature T1, which satisfies: 6°C ⁇ T1 ⁇ 40°C, preferably 8°C ⁇ T1 ⁇ 30°C.
  • T1 a desired metal deposition and a desired metal catalyst chemical etching can be achieved, and the process time is optimized.
  • the apparatus is configured to keep the semiconductor substrate in the third process liquid for 0.5 to 4 minutes.
  • a desired metal deposition and a desired metal catalyst chemical etching can be achieved.
  • an alkaline etching upon said holes by means of the second process liquid is carried out in the presence of the Ag particles, to form an inverted-pyramid-type textured surface structure of the semiconductor substrate.
  • the holes are etched anisotropically (undergo an anisotropic etching) , thereby forming an inverted-pyramid-type surface structure, wherein the Ag particles should function as a catalyst in the anisotropic etching process since a higher etching rate has been observed in the vicinity of the Ag particles.
  • the inverted pyramids may be “interconnected” or fused together.
  • the inverted-pyramid-type textured surface structure is formed by a first structure element, wherein at least 70%of the first structure elements have a maximum dimension of between 50 nm and 600 nm, preferably between 150 nm and 400 nm. Preferably, at least 80%, particularly at least 90%of the first structure elements have said maximum dimension.
  • said maximum dimension herein refers to a maximum width parallel to the plane of a substrate and/or a maximum length vertical to the plane of a substrate.
  • the second process liquid contains an alkaline liquid and, but not imperatively, a surface wetting agent.
  • the alkaline liquid contains in particular potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2 CO 3 /Na 2 CO 3 ) .
  • the surface wetting agent may be various surfactant solutions for improving wetting ability of a surface, which are, for example, commercially available from: Changzhou Shichuang Energy Technology Co., Ltd., Model Nos. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model Nos. Alka-Tex and Alka-Tex. 2+.
  • the second process liquid contains from 0.01 wt. %to 4 wt. %, in particular from 0.05 wt. %to 1.5 wt. %of potassium hydroxide or from 0.01 wt. %to 3 wt. %, in particular from 0.025 wt. %to 1.5 wt. %of sodium hydroxide, and contains from 0.1 wt. %to 5 wt. %, in particular from 0.2 wt. %to 2.5 wt. %of the surface wetting agent.
  • the second process liquid has a temperature T2, which satisfies: 50°C ⁇ T2 ⁇ 100°C, in particular 55°C ⁇ T2 ⁇ 95°C.
  • T2 a desired alkaline etching for texturing and the optimization of the process time can be achieved.
  • the apparatus is configured to keep the semiconductor substrate in the second process liquid for 0.2 to 2 minutes.
  • a desired alkaline etching for texturing can be achieved.
  • the cleaning device at least one cleaning of the inverted-pyramid-type textured surface structure is performed effectively and reliably by means of the cleaning liquid in order to remove Ag particles and silver ions located in the etched holes or on the substrate surface.
  • the alkaline etching is terminated and the texturing will not be further continued; on the other hand, decreased efficiency of a solar cell made of the semiconductor substrate due to the remained silver ions can be avoided.
  • the cleaning liquid comprises an aqueous solution containing nitric acid.
  • the aqueous solution preferably contains distilled water as a matrix.
  • the cleaning liquid comprises nitric acid, preferably from 10 wt. %to 70 wt. %, and more preferably from 20 wt. %to 70 wt. %of nitric acid.
  • the cleaning liquid has a temperature TR, which satisfies: 20°C ⁇ TR ⁇ 65°C, preferably 23°C ⁇ TR ⁇ 60°C.
  • the apparatus is configured to keep the semiconductor substrate in the cleaning liquid for 0.5-3 minutes. By means of this configuration, the Ag particles and the silver ions can be removed simply and effectively.
  • the cleaning device has a cleaning tank with a cleaning liquid, wherein the cleaning device has a plurality of successively arranged spray units for spraying the cleaning liquid onto the textured surface structure, said plurality of successively arranged spraying units preferably being arranged inside and/or above the cleaning tank respectively.
  • the Ag particles and the silver ions can be removed in a particularly simple and effective manner.
  • the apparatus further comprises at least one rinsing device disposed directly behind the first process tank, the second process tank and/or the cleaning device, and configured to use the rinsing liquid to rinse the semiconductor substrate output from the first process tank, the second process tank and/or the cleaning device; wherein the rinse liquid is preferably water, especially deionized water; and preferably, the rinse device is a spraying type device or an immersion type device.
  • the rinsing device comprises at least one spray unit for spraying the rinsing liquid onto the semiconductor substrate, and the at least one spray unit is preferably arranged inside and/or above at least one rinsing tank.
  • the rinsing liquid is configured to be circulated e.g. by a circulating pump or by compressed dry air bubbling.
  • the apparatus further comprises an acid bath tank, a rinsing device, and a drying device that are sequentially disposed behind the rinsing device of the cleaning device, wherein the acid bath tank is configured to post-treat the semiconductor substrate, which is output from the cleaning device and subsequently rinsed with the rinsing liquid, with an aqueous solution preferably consisting of hydrofluoric acid and nitric acid, the rinsing device is configured to rinse the post-treated semiconductor substrate with the rinsing liquid, and the drying device is configured to dry the semiconductor substrate.
  • the acid bath tank is configured to post-treat the semiconductor substrate, which is output from the cleaning device and subsequently rinsed with the rinsing liquid, with an aqueous solution preferably consisting of hydrofluoric acid and nitric acid
  • the rinsing device is configured to rinse the post-treated semiconductor substrate with the rinsing liquid
  • the drying device is configured to dry the semiconductor substrate.
  • a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure is performed in the absence of said Ag particles by means of the third process liquid in order to form an enlarged inverted-pyramid-type textured surface structure.
  • the enlarged inverted-pyramid-type textured surface structure is formed by a second structure element, wherein at least 70%of the second structure elements have a maximum dimension of 250 nm to 1200 nm, especially 400 nm to 1000 nm. More preferably, at least 80%, especially at least 90%of the second structure element has said maximum dimension.
  • Said maximum dimension herein refers to a maximum width parallel to the plane of a substrate and/or a maximum length vertical to the plane of a substrate.
  • the third process liquid comprises an alkaline liquid and not imperatively a surface wetting agent, wherein in particular, the alkaline liquid contains potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2 CO 3 /Na 2 CO 3 )
  • the surface wetting agent may be various surfactant solutions for improving wetting ability of a surface, e.g., available from: Changzhou Shichuang Energy TechnologyCo., Ltd., Model No. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model No. Alka-Tex and Alka-Tex. 2+.
  • the third process liquid comprises 0.1wt.
  • the third process liquid has a temperature T3, wherein: 50°C ⁇ T3 ⁇ 100°C, especially 60°C ⁇ T2 ⁇ 95°C.
  • the apparatus is configured to keep the semiconductor substrate in the third process liquid for 1-5 minutes.
  • the apparatus further comprises a rinsing device disposed directly after the third process tank, which is configured to rinse the semiconductor substrate output from the third process tank with rinsing liquid; preferably, the rinsing liquid is water, especially deionized water.
  • the apparatus further comprises an acid bath tank, a rinsing device, and a drying device that are sequentially disposed behind the rinsing device of the third process tank, wherein the acid bath tank is configured to post-treat the semiconductor substrate, which is output from the third process tank and subsequently rinsed with the rinsing liquid, with an aqueous solution preferably consisting of hydrofluoric acid and hydrochloric acid, the rinsing device is configured to rinse the post-treated semiconductor substrate with the rinsing liquid, and the drying device is configured to dry the semiconductor substrate.
  • the acid bath tank is configured to post-treat the semiconductor substrate, which is output from the third process tank and subsequently rinsed with the rinsing liquid, with an aqueous solution preferably consisting of hydrofluoric acid and hydrochloric acid
  • the rinsing device is configured to rinse the post-treated semiconductor substrate with the rinsing liquid
  • the drying device is configured to dry the semiconductor substrate.
  • the apparatus may be an inline type apparatus in which a conveying device for continuously conveying the semiconductor substrate is provided.
  • the apparatus preferably comprises at least one conveying device for continuously conveying the semiconductor substrate in a conveying direction.
  • the at least one conveying device extends at least from the first process tank to the second process tank, preferably from the first process tank to the cleaning device disposed behind the second process tank, and especially from the first process tank to the third process tank.
  • the at least one conveying device can achieve continuous parallel conveyance of the semiconductor substrates in the conveying direction.
  • the apparatus comprises one conveying device, which conveys, in a continuous and parallel manner, the semiconductor substrates from the first process tank to the third process tank.
  • the apparatus comprises two conveying devices, wherein the first conveying device conveys, in a continuous and parallel manner, the semiconductor substrates from the first process tank to the cleaning device disposed behind the second process tank, and the second conveying device conveys, in a continuous and parallel manner, the semiconductor substrates from the cleaning device to the third process tank. Between the first conveying device and the second conveying device, the semiconductor substrates are conveyed e.g., by hand or via a moving device.
  • the inline type apparatus further comprises a mechanical transfer unit disposed directly behind the rinsing device of said cleaning device or disposed directly behind said cleaning device in a conveying direction of said semiconductor substrate, wherein said mechanical transfer unit is configured to transfer the rinsed or non-rinsed semiconductor substrate after cleaning by means of the cleaning liquid in wet state directly to another inline type apparatus for post-treating.
  • a mechanical transfer unit disposed directly behind the rinsing device of said cleaning device or disposed directly behind said cleaning device in a conveying direction of said semiconductor substrate, wherein said mechanical transfer unit is configured to transfer the rinsed or non-rinsed semiconductor substrate after cleaning by means of the cleaning liquid in wet state directly to another inline type apparatus for post-treating.
  • the inline type apparatus further comprises a mechanical transfer unit disposed directly behind the rinsing device of said third process tank or disposed directly behind said third process tank in a conveying direction of said semiconductor substrate, wherein said mechanical transfer unit is configured to transfer the rinsed or non-rinsed semiconductor substrate after further alkaline etching by means of the third process liquid in a wet state directly to another apparatus for post-treating.
  • a mechanical transfer unit disposed directly behind the rinsing device of said third process tank or disposed directly behind said third process tank in a conveying direction of said semiconductor substrate, wherein said mechanical transfer unit is configured to transfer the rinsed or non-rinsed semiconductor substrate after further alkaline etching by means of the third process liquid in a wet state directly to another apparatus for post-treating.
  • the prior inline type apparatus for post-treating may comprise a tank for post-treating, e.g., an acid bath tank (HF and HNO 3 ) .
  • a treatment process that occurs in the prior inline type apparatus for post-treating comprises: inputting, spraying and rinsing with deionized water, acid bathing, another spraying and rinsing with deionized water, drying, and outputting.
  • the subsequent post-treatment with the liquid for post-treatment is only used for cleaning the resulting inverted-pyramid-type textured surface, during which no silicon is removed.
  • the mechanical transfer unit By means of the mechanical transfer unit, it is possible that the semiconductor substrates cleaned by the cleaning device is transferred in a wet state to the tank for post-treatment in the prior apparatus, thereby integrating the apparatus according to the present invention with the prior apparatus into a set of apparatuses, which means that it is unnecessary to perform the conventional unloading and loading of a semiconductor substrate between two previously separated apparatuses.
  • the semiconductor substrate cleaned via the cleaning device is not dried, but is transferred in a wet state between the two previously separated apparatuses.
  • the apparatus comprises a batch type apparatus in which a carrier device for carrying and conveying semiconductor substrates in batches is provided.
  • all the above process tanks, the cleaning device and the rinsing device can be configured as immersion type devices, wherein all the process liquids, the cleaning liquid and the rinsing liquid can be provided to be circulated e.g., by a circulating pump or by compressed dry air bubbling.
  • the batch type apparatus is configured to use the carrier device to transfer the rinsed or non-rinsed semiconductor substrate after cleaning with the cleaning liquid in a wet state directly to another batch type apparatus for post-treating.
  • the batch type apparatus further includes a drying device disposed behind the rinsing device of the cleaning device, and the drying device is configured to sufficiently dry the semiconductor substrate output from the cleaning device and then rinsed with a rinsing liquid so that the dried plurality of semiconductor substrates when stacked together would not be connected to each other due to residual moisture in the surface structure.
  • the semiconductor substrates stacked together are easy to be transferred, by hand or by means of a moving tool, to a position or place of the prior apparatus for post-treatment, so as to carry out a treatment, which, for example, comprises sequentially inputting, spraying and rinsing with deionized water, acid bathing, another spraying and rinsing with deionized water, drying, and outputting.
  • the apparatus is used to conduct a surface texturing on a polycrystalline or single crystalline semiconductor substrate, preferably a single crystalline semiconductor substrate, more preferably a single crystalline silicon substrate.
  • the present invention provides a method for surface texturing of a semiconductor substrate, which comprises the following steps: depositing Ag particles on the surface of a semiconductor substrate and form a large number of holes in which said Ag particles are contained, on the surface of the semiconductor substrate by Ag-based metal catalyst chemical etching, by means of a first process liquid; performing alkaline etching to said holes in the presence of said Ag particles by means of a second process liquid, in order to form an inverted-pyramid-type textured surface structure of the semiconductor substrate; and, performing at least one cleaning of the inverted-pyramid-type textured surface structure by means of a cleaning liquid in order to remove said Ag particles and/or Ag + ions.
  • Advantages of the method according to the present invention corresponds to those of the apparatus according to the present invention. Particularly, the method according to the present invention can also be improved in accordance with at least one feature of the apparatus according to the present invention.
  • the method according to the present invention further comprises performing a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure in the absence of said Ag particles by means of a third process liquid in order to form an enlarged inverted-pyramid-type textured surface structure.
  • the first process liquid comprises hydrofluoric acid, nitric acid and silver nitrate; preferably, the first process liquid comprises 10wt. %to 25wt. %, especially 12wt. %to 20wt. %of hydrofluoric acid, 12wt. %to 25wt. %, especially 15 wt. %to 22wt. %of nitric acid and 0.0001wt. %to 0.05wt. %, especially 0.001wt. %to 0.015wt. %of silver nitrate.
  • the first process liquid contains less than 5wt. %, especially less than 1wt. %, and especially 0wt. %of hydrogen peroxide.
  • the first process liquid has a temperature T1, where: 6°C ⁇ T1 ⁇ 40°C, especially 8°C ⁇ T1 ⁇ 30°C.
  • the semiconductor substrate is kept in the first process liquid for 0.5-4 minutes.
  • the holes formed by means of the first process liquid has a maximum dimension between 50 nm and 300 nm, preferably between 100 nm and 200 nm.
  • the semiconductor substrate has a sawn surface structure, wherein said sawn surface structure, preferably in the range of 0.5 to 4.0 ⁇ m/side, is meanwhile (or additionally) removed by means of the first process liquid.
  • the second process liquid comprises an alkaline liquid and a surface wetting agent, wherein the alkaline liquid comprises in particular, potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2 CO 3 /Na 2 CO 3 ) .
  • the surface wetting agent may comprise various surfactant solutions for improve wetting ability of a surface, which is, for example, available from: Changzhou Shichuang Energy Technology Co., Ltd., Model Nos. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model Nos. Alka-Tex and Alka-Tex. 2+.
  • said second process liquid contains 0.01wt.
  • the second process liquid has a temperature T2, wherein: 50°C ⁇ T2 ⁇ 100°C, especially 55°C ⁇ T2 ⁇ 95°C.
  • the semiconductor substrate is kept in the second process liquid for 0.2 to 2 minutes. Therefore, it can be ensured that an inverted-pyramid-type textured surface structure is formed effectively.
  • said inverted-pyramid-type textured surface structure is formed by a first structure element, wherein at least 70%of the first structure elements have a maximum dimension of 50 nm to 600 nm, especially 150 nm to 400 nm. Preferably, at least 80%, especially at least 90%of the first structure elements have said maximum dimension.
  • the maximum dimension refers to a maximum width parallel to the plane of a substrate and/or a maximum length vertical to the plane of a substrate.
  • the cleaning liquid contains nitric acid, in particular 10wt. %to 70wt. %, especially 20wt. %to 70wt. %of nitric acid.
  • the cleaning liquid in particular has a temperature TR, wherein: 20°C ⁇ TR ⁇ 65°C, especially 23°C ⁇ TR ⁇ 60°C.
  • the semiconductor substrate is kept in the cleaning liquid for 0.5-3 minutes. Thereby, it is ensured that the Ag particles and the silver ions can be removed effectively.
  • the method further comprises using a rinsing liquid to rinse the semiconductor substrate output from the first process liquid, the second process liquid and/or the cleaning liquid, wherein the rinse liquid is preferably water, especially deionized water; and preferably, the rinsing is a spraying type or an immersion type rinsing.
  • the method further comprises the following steps in sequence: post-treating the semiconductor substrate, which is output from the cleaning liquid and subsequently rinsed with the rinsing liquid, with an aqueous solution preferably consisting of hydrofluoric acid and nitric acid, rinsing the post-treated semiconductor substrate with a rinsing liquid, and drying the semiconductor substrate.
  • the method further comprises performing a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure in the absence of said Ag particles by means of a third process liquid in order to form an enlarged inverted- pyramid-type textured surface structure.
  • the enlarged inverted-pyramid-type textured surface structure is formed by a second structure element, wherein at least 70%of the second structure elements have a maximum dimension of 250 nm to 1200 nm, especially 400 nm to 1000 nm.
  • the third process liquid contains an alkaline liquid and a surface wetting agent, wherein the alkaline liquid comprises in particular potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2 CO 3 /Na 2 CO 3 ) , and the surface wetting agent may comprise various surfactant solutions for improving wetting ability of a surface, which is, for example, available from: Changzhou Shichuang Energy Technology Co., Ltd., Model Nos. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model Nos. Alka-Tex and Alka-Tex. 2+.
  • the third process liquid comprises 0.1wt.
  • the third process liquid has a temperature T3, wherein: 50°C ⁇ T3 ⁇ 100°C, especially 60°C ⁇ T2 ⁇ 95°C.
  • the semiconductor substrate is kept in the third process liquid for 1-5 minutes.
  • the method further comprises rinsing the semiconductor substrate output from the third process liquid with a rinsing liquid, wherein the rinsing liquid is water, in particular deionized water.
  • the method further comprises the following steps in sequence: post-treating the semiconductor substrate, which is output from the third process liquid and subsequently rinsed with the rinsing liquid, with an aqueous solution preferable consisting of hydrofluoric acid and nitric acid, rinsing the semiconductor substrate with a rinsing liquid, and drying the semiconductor substrate.
  • the method steps are carried out in an inline type apparatus, and the semiconductor substrates are continuously conveyed.
  • the rinsed or non-rinsed semiconductor substrate after cleaning by means of the cleaning liquid in said inline type apparatus is transferred in a wet state directly to another inline type apparatus for post-treating.
  • the rinsed or non-rinsed semiconductor substrate after further alkaline etching by means of the third process liquid in said inline type apparatus is transferred in a wet state directly to another inline type apparatus for post-treating.
  • the method steps are carried out in a batch type apparatus and the semiconductor substrate is conveyed in batch.
  • the rinsed or non-rinsed semiconductor substrate after cleaning with the cleaning liquid in the batch type apparatus is transferred in a wet state directly to another batch type device for post-treating.
  • the semiconductor substrate output from the cleaning device and then rinsed with a rinsing liquid is sufficiently dried so that the dried plurality of semiconductor substrates when stacked together would not be connected to each other due to residual moisture in the surface structure.
  • the semiconductor substrate is a single crystalline semiconductor substrate, in particular a single crystalline silicon substrate.
  • advantages of the apparatus and method of the present invention comprises:
  • FIG. 1 shows an embodiment of an inline type apparatus according to the present invention for surface texturing of a semiconductor substrate
  • FIG. 2 shows another embodiment of an inline type apparatus according to the present invention for surface texturing of a semiconductor substrate
  • FIG. 3 shows an embodiment of a batch type apparatus according to the present invention for surface texturing of a semiconductor substrate
  • FIG. 4 shows another embodiment of a batch type apparatus according to the present invention for surface texturing of a semiconductor substrate
  • FIG. 5 shows yet another embodiment of a batch type apparatus according to the present invention for surface texturing of a semiconductor substrate
  • FIG. 6 shows still yet another embodiment of a batch type apparatus according to the present invention for surface texturing of a semiconductor substrate
  • FIG. 7 are scanning electron microscope photographs showing the textured surface structure of the semiconductor substrate prepared in the inventive apparatus.
  • FIG. 8 shows a graph plotting optical reflectivity values as a function of wavelengths of the textured surface structure of the semiconductor substrate prepared in the inventive apparatus.
  • FIG. 9 shows a schematic diagram of one embodiment of the method according to the present invention for surface texturing of a semiconductor substrate.
  • FIG. 1 shows an embodiment of the inline type apparatus 1 according to the present invention for surface texturing of a semiconductor substrate 3, wherein the inline type apparatus 1 for wet chemical treatment of the semiconductor substrate 3 comprises a conveying device 4 for conveying the semiconductor substrate 3 in the conveying direction.
  • the conveying device 4 comprises a plurality of conveying rollers 4’ which are sequentially arranged in the conveying direction and are rotationally driven.
  • the apparatus 1 comprises the first process tank 11, the first rinsing device R 1 , the second process tank 12, the second rinsing device R 2 , the cleaning device 13, the third rinsing device R 3 , the third process tank 14, the fourth rinsing device R 4 , an acid bath tank 15, the fifth rinsing device R 5 , and a drying device D, which are sequentially arranged in the conveying direction.
  • the first process tank 11 is configured to receive a first process liquid, and is configured to remove, by means of the first process liquid, preferably 0.5 to 4.0 ⁇ m/side of sawn surface structures S 0 of the semiconductor substrate 3, and meanwhile to generate a surface structure S 1 having holes, which contain Ag particles, by Ag particle deposition and metal catalyst chemical etching.
  • the first process tank 11 is filled with the first process liquid.
  • the first process liquid is an aqueous solution in which distilled water is used as a matrix, and comprises hydrofluoric acid (HF) , nitric acid (HNO 3 ) and silver nitrate (AgNO 3 ) .
  • the first process liquid contains 10 wt. %to 25 wt. %, preferably 12 wt.
  • the first process liquid for example, contains 15 wt. %of hydrofluoric acid (HF) , 20 wt. %of nitric acid (HNO 3 ) and 0.005 wt. %of silver nitrate (AgNO 3 ) .
  • HF hydrofluoric acid
  • HNO 3 20 wt. %of nitric acid
  • AgNO 3 silver nitrate
  • the first process liquid contains no hydrogen peroxide (H 2 O 2 ) .
  • the first process liquid has a temperature T1, wherein: 6°C ⁇ T1 ⁇ 40°C, preferably 8°C ⁇ T1 ⁇ 30°C.
  • the above data are all in weight percent.
  • the first rinsing device R 1 is configured to use a rinsing liquid to rinse the semiconductor substrate 3 output from the first process tank 11.
  • the rinsing liquid is preferably water, especially deionized water.
  • the rinsing device is a spraying type device with a plurality of spray units R 1 ’ .
  • the second process tank 12 is configured to receive the second process liquid, and is configured to perform an alkaline etching to the holes, in the presence of the Ag particles within the holes, by means of the second process liquid, to form an inverted-pyramid-type textured surface structure of the semiconductor substrate 3.
  • the second process liquid comprises an alkaline liquid and, but not imperatively, a surface wetting agent, wherein the alkaline liquid, in particular, contains potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2 CO 3 /Na 2 CO 3 ) , and the surface wetting agent may be various surfactant solutions for improving wetting ability of a surface, which are, for example, available from: Changzhou Shichuang Energy Technology Co., Ltd., Model Nos. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model Nos. Alka-Tex and Alka-Tex. 2+.
  • the second process liquid contains 0.01 wt.
  • the second process liquid has a temperature T2, wherein: 50°C ⁇ T2 ⁇ 100°C, preferably 55°C ⁇ T2 ⁇ 95°C.
  • the second rinsing device R 2 is configured to use a rinsing liquid to rinse the semiconductor substrate 3 output from the second process tank 12.
  • the rinsing liquid preferably is water, and preferably is deionized water.
  • the rinsing device is a spraying type device with a plurality of spray units R 2 ’ .
  • the cleaning device 13 is configured to perform at least one cleaning to the inverted-pyramid-type textured surface structure by means of a cleaning liquid, to remove the Ag particles.
  • the cleaning liquid contains nitric acid, preferably 10 wt. %to 70 wt. %, and more preferably 20 wt. %to 70 wt. %of nitric acid.
  • the cleaning liquid has a temperature TR, wherein: 20°C ⁇ TR ⁇ 65°C, preferably 23°C ⁇ TR ⁇ 60°C.
  • the apparatus 1 is configured to keep the semiconductor substrate 3 in the cleaning liquid for 0.5 to 3 minutes.
  • the cleaning device has a cleaning tank holding the cleaning liquid, and a plurality of successively arranged spray units for spraying the cleaning liquid onto the textured surface structure, wherein said plurality of successively arranged spraying units preferably are arranged inside and/or above the cleaning tank.
  • the third rinsing device R 3 is configured to rinse the semiconductor substrate 3 output from the cleaning device 13 with a rinsing liquid.
  • the rinsing liquid preferably is water, and preferably is deionized water.
  • the rinsing device is a spraying type device with a plurality of spray units R 3 ’ .
  • the third process tank 14 is configured to receive the third process liquid, and is configured to perform, in the absence of the Ag particles, a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure by means of the third process liquid, to form an enlarged inverted-pyramid-type textured surface structure.
  • the third process liquid contains an alkaline liquid and, but not imperatively, a surface wetting agent, wherein the alkaline liquid preferably comprises potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2 CO 3 /Na 2 CO 3 ) , and the surface wetting agent may be various surfactant solutions for improving wetting ability of a surface, which are, for example, available from: Changzhou Shichuang Energy Technology Co., Ltd., Model Nos. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model Nos. Alka-Tex and Alka-Tex. 2+.
  • the third process liquid contains 0.1 wt.
  • the third process liquid has a temperature T3, wherein: 50°C ⁇ T3 ⁇ 100°C, preferably 60°C ⁇ T3 ⁇ 95°C.
  • the apparatus is configured to keep the semiconductor substrate 3 in the third process liquid for 1 to 5 minutes.
  • the fourth rinsing device R 4 is configured to rinse the semiconductor substrate 3 output from the third process tank 14 with a rinsing liquid.
  • the rinsing liquid preferably is water, and preferably is deionized water.
  • the rinsing device is a spraying type device with a plurality of spray units R 4 ’ .
  • An acid bath tank 15 is configured to treat the semiconductor substrate 3 with an aqueous solution containing HF and HCl. At this moment, the surface structure to be dried is hydrophobic, and it is relatively easy to dry the surface structure.
  • the fifth rinsing device R 5 is configured to rinse the semiconductor substrate 3 output from the acid bath tank 15 with a rinsing liquid.
  • the rinsing liquid preferably is water, and preferably is deionized water.
  • the rinsing device is a spraying type device with a plurality of spray units R 5 ’ .
  • the drying device D is arranged in a conventional manner of the art, wherein it comprises nozzles D’ for jetting dry air. After dried in the drying device D, the semiconductor substrate 3 is output.
  • the surface (S 0 ) of the semiconductor substrate 3 Before input into the apparatus 1 of the present invention, the surface (S 0 ) of the semiconductor substrate 3 has a sawn surface structure.
  • the surface (S 1 ) of the semiconductor substrate 3 obtained after treated in the first process tank 11 has a large number of holes, wherein the holes have a maximum dimension between 50 nm and 300 nm, and preferably between 100 nm and 200 nm.
  • the surface (S 2 ) of the semiconductor substrate 3 obtained after the MCCE treatment in the second process tank 12 has an inverted-pyramid-type textured surface structure formed by a first structure element, wherein at least 70%of the first structure elements have a maximum dimension between 50 nm and 600 nm, and preferably between 150 nm and 400 nm.
  • the Ag particles and the silver ions are removed from the surface (S 3 ) of the semiconductor substrate 3 obtained after performing at least one cleaning in the cleaning device.
  • the surface (S 4 ) of the semiconductor substrate 3 obtained after the treatment in the third process tank has an enlarged inverted-pyramid-type textured surface structure, which is formed by a second structure elements wherein at least 70%of the second structure elements have a maximum dimension between 250 nm and 1200 nm, and preferably between 400 nm and 1000 nm.
  • the surface (S 5 ) of the semiconductor substrate 3 is hydrophobic and can be dried easily.
  • FIG. 2 shows another embodiment of the inline type apparatus 1 according to the present invention for surface texturing of a semiconductor substrate 3. It differs from the apparatus 1 as shown in FIG. 1 in that in the apparatus 1 of FIG. 2, a mechanical transfer unit C is disposed behind the third process tank 14 and the fourth rinsing device R 4 disposed thereafter, wherein the mechanical transfer unit C is configured to transfer the rinsed semiconductor substrate 3 after cleaning with the cleaning liquid in a wet state directly to another inline type apparatus 2 for post-treating.
  • the another inline type apparatus 2 for post-treating may be an existing apparatus of an industrial supplier, in which an acid bath tank 21, a rinsing device 22 and a drying device D are provided.
  • FIG. 3 shows an embodiment of a batch type apparatus 1’ according to the present invention for surface texturing of a semiconductor substrate 3.
  • a carrier device 7 for carrying and conveying semiconductor substrates 3 in batches is provided in the batch type apparatus 1’ .
  • a plurality of semiconductor substrates, such as single crystalline silicon wafers, are loaded in the same carrier device 7, which is for example made from a polymer, e.g., PVDF, PTFE or the like.
  • the carrier device 7 is placed on an input unit 5 of the apparatus 1’ , wherein the input unit 5 may have a plurality of rollers 5’ .
  • the carrier device 7 bearing the substrates (e.g., 100 single crystalline silicon wafers) is placed from the input unit 5 to the first process tank 11, the first rinsing device R 1 , the second process tank 12, the second rinsing device R 2 , the cleaning device 13, the third rinsing device R 3 , the third process tank 14, the fourth rinsing device R 4 , the acid bath tank 15, the fifth rinsing device R 5 , the sixth rinsing device R 6 , and the drying device D sequentially, wherein all the process tanks, the cleaning device and the rinsing device are provided as immersion type devices.
  • the carrier device loaded with the semiconductor substrates 3 is placed on an output unit 6 by means of a robot, wherein the output unit 6, for example, comprises a plurality of rollers 6’ .
  • FIG. 4 shows another embodiment of a batch type apparatus 1’ according to the present invention for surface texturing of a semiconductor substrate 3.
  • the apparatus 1’ in FIG. 4 differs from the apparatus 1’ as shown in FIG. 3 in that it only comprises the first process tank 11, the first rinsing device R 1 , the second process tank 12, the second rinsing device R 2 , the cleaning device 13 and the third rinsing device R 3 , which are arranged in sequence.
  • the carrier device 7 loaded with the semiconductor substrates 3 is transferred directly into another prior batch type apparatus 2, wherein the apparatus 2, for example, comprises an acid bath tank 21, a rinsing device 22, a hot water rinsing device 23, a drying device D and an output unit 8, and the output unit may have a plurality of rollers 8’ .
  • FIG. 5 shows yet another embodiment of a batch type apparatus 1’ according to the present invention for surface texturing of a semiconductor substrate 3.
  • the apparatus 1’ of FIG. 5 differs from the apparatus 1’ as shown in FIG. 4 in that it only comprises the first process tank 11, the first rinsing device R 1 , the second process tank 12, the second rinsing device R 2 , the cleaning device13, and the third rinsing device R 3 arranged sequentially.
  • the carrier device 7 loaded with the semiconductor substrates 3 is placed onto a mechanical transfer unit C, wherein the mechanical transfer unit C herein is an input unit of another prior batch type apparatus 2.
  • the carrier device 7 bearing the substrates is placed into an acid bath tank 21, a rinsing device 22, a hot water rinsing device 23 and a drying device D of the apparatus 2, and finally is placed on an output unit 8, wherein the output unit may have a plurality of rollers 8’ .
  • FIG. 6 shows still yet another embodiment of a batch type apparatus 1’ according to the present invention for surface texturing of a semiconductor substrate 3.
  • the apparatus 1’ of FIG. 6 differs from the apparatus 1’ as shown in FIG. 3 in that it only comprises the first process tank 11, the first rinsing device R 1 , the second process tank 12, the second rinsing device R 2 , the cleaning device 13, the third rinsing device R 3 and the drying device D, arranged sequentially.
  • FIG. 7 are scanning electron microscope photographs showing the textured surface structure of the semiconductor substrate 3 prepared in the inventive apparatus. The two photographs of FIG. 7 are taken respectively at different amplifications. It is clear from FIG. 7 that the semiconductor substrate 3 prepared in the apparatus 1, 1’ according to the present invention has an inverted-pyramid-type textured surface structure.
  • FIG. 8 shows a graph plotting optical reflectivity values as a function of wavelengths of the textured surface structure of the semiconductor substrate prepared in the inventive apparatus.
  • the semiconductor reference sample is obtained by a standard alkaline etching or alkaline single crystalline texturing process in the prior art, and has a randomly distributed upright pyramid-type surface structure.
  • the semiconductor substrates in the Examples 1 to 3 are prepared by using the apparatus 1, 1’ according to the present invention, and all have a randomly distributed inverted-pyramid-type textured surface structure.
  • the process parameters used in the examples are set forth in Table 1.
  • Textured surfaces of the semiconductor substrates obtained according to Example 1 to 3 of the present invention as well as that obtained according to the reference sample are compared in terms of etched depth, basic size of pyramids and reflectivity. Results are shown in Table 2.
  • the average reflectivity values in the Examples 1 to 3 are largely decreased compared to that in the reference sample, particularly at the wavelength range of 400 to 550 nm, in which a decreased reflectivity is very beneficial since this wavelength range is most effective for a shallow emitter or a selective emitter.
  • Reflectivity of the resulting textured single crystalline silicon wafer can be significantly decreased by changing the process parameters (e.g., concentration, temperature and/or time) .
  • the inverted-pyramid-type textured surface structure according to the Examples 1-3 of the present invention is more flexible in e.g., size or depth.
  • FIG. 9 schematically shows an embodiment of the method according to the present invention for surface texturing of a semiconductor substrate.
  • the method comprises the following steps: providing a semiconductor substrate (step 101) ; depositing Ag particles onto the surface of the semiconductor substrate by means of the first process liquid (step 102) , and forming a large number of holes, in which the Ag particles are contained, on the surface of the semiconductor substrate by Ag-based metal catalyst chemical etching (step 103) ; in the presence of the Ag particles, performing an alkaline etching to the holes by means of the second process liquid, to form an inverted-pyramid-type textured surface structure of the semiconductor substrate (step 104) ; performing at least one cleaning to the inverted-pyramid-type textured surface structure by means of the cleaning liquid, to remove the Ag particles (step 105) ; and, in the absence of the Ag particles, performing a further alkaline etching to the cleaned inverted-pyramid-type textured surface structure by means of the third process liquid, to form an enlarged inverted-pyramid

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Abstract

An apparatus (1) and a method for surface texturing of semiconductor substrate (3). The apparatus (1) comprises: a first process tank (11) configured to receive a first process liquid and, by means of said first process liquid, deposit Ag particles on the surface of the semiconductor substrate (3) and form a large number of holes, in which said Ag particles are contained, on the surface of the semiconductor substrate (3) by Ag-based metal catalyst chemical etching; a second process tank (12) configured to receive a second process liquid and perform alkaline etching to said holes in the presence of said Ag particles by means of said second process liquid, in order to form an inverted-pyramid-type textured surface structure of the semiconductor substrate (3); and a cleaning device (13) configured to perform at least one cleaning of the inverted-pyramid-type textured surface structure by means of a cleaning liquid in order to remove said Ag particles. The inverted-pyramid-type textured surface can be obtained in a simple and effective manner in order to manufacture a solar cell with extremely low reflection loss and high efficiency.

Description

METHOD AND APPARATUS FOR SURFACE TEXTURING OF SEMICONDUCTOR SUBSTRATE TECHNICAL FIELD
The present invention relates to an apparatus for surface texturing of a semiconductor substrate, and further relates to a method for surface texturing of a semiconductor substrate.
BACKGROUND
The efficiency of solar cells depends on the reflection losses. In order to minimize the reflection losses and to optimize the efficiency, semiconductor substrates are produced with a textured surface structure. If such semiconductor or silicon substrates are treated with particularly effective methods, these are referred to, for example, as "black silicon" . In order to particularly effectively achieve a black silicon texturization, it is known to use a process of metal catalyst chemical etching (abbreviated as “MCCE” , also called a metal catalyst assisted chemical etching) .
Processes for texturing a single crystal silicon wafer known in the prior art for example use alkaline solution (KOH, NaOH, etc. ) and isopropanol or additives to generate randomly distributed upright pyramid-type surface structures. These processes typically require a long process time, for example, more than 15 minutes for the additives and more than 30 minutes for isopropanol, and accordingly such processes for texturing the single crystal silicon wafer are usually carried out in a batch apparatus. The resulting pyramids have a size that typically can vary over a wide range of from less than 1μm to more than 5μm, and is typically about 1μm. In addition, these known processes are generally quite expensive, and their cost is mainly caused by the cost of the additives. 
Thus, it is necessary to seek for an alternative solution, which is capable of reducing manufacturing cost, providing an apparatus having a higher throughput of e.g., larger than 8000 wafers/h, and thereby reducing the equipment size (with respect to wafer /h /equipment area) . In addition, it is desired that this solution is further capable of providing a better performance, e.g., reducing front surface reflectivity, or increase light trapping, especially for a thin wafer.
It is known that an inverted-pyramid-type surface structure can be used to replace the randomly distributed upright pyramid-type surface structure. A process for preparation of the inverted-pyramid-type surface structure, for example, comprises: firstly forming, e.g. by lithography, a regular surface structure of an etching resist, followed by an alkaline etching treatment, in which an anisotropic etching behaviour occurs, to obtain the inverted-pyramid-type surface structure. It has also been demonstrated that the semiconductor substrate can be textured in a one-step process by the MCCE method, in which metal Cu is used, to prepare an inverted-pyramid type surface structure. Further, a method of forming an inverted-pyramid-type porous surface nanotexture on polycrystalline silicon by the MCCE method is known from CN103456804A.
Compared to a randomly distributed upright pyramid-type surface texture prepared by a standard alkaline texturing process for single crystal, an inverted-pyramid-type surface texture exhibits much better optical performances in terms of reflectivity and light trapping. Better results of a randomly distributed inverted-pyramid-type surface texture obtained to date have been achieved by a Cu-based MCCE process using a HF: H 2O 2 etching solution at a process temperature of 50℃. A major disadvantage for this process is that the process time is about 15 minutes, and the use of the H 2O 2 etching solution at 50℃ will be accompanied by accelerated and uncontrolled volatilization of H 2O 2, thereby making it difficult to ensure a stable texturing process in industrial applications. In addition, due to the risk of Cu pollution, Cu-based etching MCCE solutions suffer from a limited acceptance in the manufacture of photovoltaic products.
SUMMARY
The technical problem to be solved by the present invention is to overcome the drawbacks in the prior art, and to provide an improved apparatus and an improved method for surface texturing of a semiconductor substrate, which are capable of obtaining, in a simple and effective manner, an inverted-pyramid-type textured surface structure for the semiconductor substrate, so as to produce a solar cell with an extremely low reflectivity loss and a high efficiency.
The above-mentioned problem has been solved by an apparatus in accordance with the present invention, i.e., an apparatus for surface texturing of a semiconductor substrate.  The apparatus comprises: a first process tank configured to receive a first process liquid and, by means of said first process liquid, deposit silver (Ag) particles on the surface of the semiconductor substrate and form a large number of holes, in which said Ag particles are contained, on the surface of the semiconductor substrate by Ag-based metal catalyst chemical etching; a second process tank configured to receive a second process liquid and perform alkaline etching to said holes in the presence of said Ag particles by means of said second process liquid, in order to form an inverted-pyramid-type textured surface structure of the semiconductor substrate; and, a cleaning device configured to perform at least one cleaning of the inverted-pyramid-type textured surface structure by means of a cleaning liquid in order to remove said Ag particles.
The inventor has surprisingly found that, when the semiconductor substrate is subjected to an alkaline etching or alkaline texturing in the presence of Ag particles on the surface of a semiconductor substrate, and more accurately, within or in holes (or pores) of the surface of the semiconductor substrate, the resulting textured surface structure is not a randomly distributed upright pyramid-type textured surface structure, which would generally have formed under similar conditions, but a randomly distributed inverted-pyramid-type textured surface structure. Namely, during the alkaline etching or alkaline texturing, the presence of the Ag particles is essential to obtain the inverted-pyramid-type textured surface structure.
Preferably, the apparatus according to the present invention further comprises a third process tank configured to receive a third process liquid and perform a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure in the absence of said Ag particles by means of the third process liquid in order to form the enlarged inverted-pyramid-type textured surface structure. During this process, the size of the inverted-pyramid-type textured surface structure is enabled to be further enlarged.
The terms “first” process tank, “second” process tank, and “third” process tank are merely intended to distinguish the process tanks from each other, and should not be understood to be restrictive. Especially, other tanks, e.g., a cleaning tank and/or a rinsing tank may be disposed before, between, and/or behind the process tanks. Accordingly, the terms “first” process liquid, “second” process liquid, and “third”  process liquid are merely intended to distinguish the process tanks from each other, and should not be understood to be restrictive.
In the first process tank, Ag particles are deposited on the surface of the semiconductor substrate by means of said first process liquid, and a large number of holes, in which said Ag particles are contained, are formed on the surface of the semiconductor substrate by Ag-based metal catalyst chemical etching. Preferably, the holes have a maximum dimension of between 50 nm and 300 nm, preferably between 100 nm and 200 nm. Advantageously, the deposition of Ag particles and the hole drilling (i.e., hole etching process) are completed in the same process step. Moreover, the deposition of Ag particles on the semiconductor substrate largely increases the rate of etching. In this process step, the surface of the semiconductor substrate remains hydrophilic, thereby rendering it to be wetted easily with the first process liquid.
When the semiconductor substrate has e.g., a sawn surface structure, the first process tank is configured to remove the sawn surface structure, preferably in the range of 0.5 to 4.0 μm/side, additionally by means of the first process liquid. In accordance with the present invention, if the first process tank contains a first process liquid, which is suitable both for removing e.g. the sawn surface structure, and for depositing Ag particles on the semiconductor substrate and generating a large number of holes by a metal catalyst chemical etching, a textured surface structure with a lower reflectivity loss and a high efficiency can be obtained in a simpler and more effective manner. Therefore, by means of the first process liquid, saw damages or sawn surface structures are removed, Ag particles are deposited on the semiconductor substrate, and a large number of holes are drilled out by the metal catalyst chemical etching. This takes place in particular exclusively in the first process tank or with the first process liquid, i.e., in a single process bath or process step. In particular, by means of the first process liquid, a sawn surface structure or a saw-damaged surface structure caused by a Diamond Wire Saw process (DWS) is removed.
Preferably, the first process liquid contains hydrofluoric acid (HF) , nitric acid (HNO 3) , and silver nitrate (AgNO 3) . That is, the first process liquid is preferably comprised of an aqueous solution containing hydrofluoric acid (i.e. hydrogen fluoride) , nitric acid (i.e. hydrogen nitrate) and silver ions. The aqueous solution preferably comprises  distilled water as a matrix. In the first process liquid, the silver ions are contained preferably in the form of hydrated silver ions, wherein silver is added into the aqueous solution in the form of silver nitrate. In the first process liquid, silver is deposited on the surface and forms silver particles. These silver particles function as a catalyst and locally accelerates the wet chemical etching process. In this manner, etched pits or etched holes are formed in the region on the surface of the semiconductor substrate in which the silver metal particles exist. Preferably, the first process liquid contains from 10 wt. %to 25 wt. %, preferably from 12 wt. %to 20 wt. %of hydrofluoric acid, from 12 wt. %to 25 wt. %, preferably from 15 wt. %to 22 wt. %of nitric acid, and from 0.0001 wt. %to 0.05 wt. %, preferably from 0.001 wt. %to 0.015 wt. %of silver nitrate.
Preferably, the first process liquid contains less than 5 wt. %, especially less than 1 wt. %, and especially 0 wt. %of hydrogen peroxide. Hydrogen peroxide affects the desired metal catalyst chemical etching. The first process liquid preferably does not contain hydrogen peroxide. In this manner, the process duration and process stability are optimized, and the structure of the apparatus is simplified since less process chemical formulations, for example, are required for the operation of the apparatus.
Preferably, the first process liquid has a temperature T1, which satisfies: 6℃≤ T1 ≤ 40℃, preferably 8℃ ≤ T1 ≤ 30℃. By means of the temperature T1, a desired metal deposition and a desired metal catalyst chemical etching can be achieved, and the process time is optimized.
Preferably, the apparatus is configured to keep the semiconductor substrate in the third process liquid for 0.5 to 4 minutes. By means of this configuration, a desired metal deposition and a desired metal catalyst chemical etching can be achieved.
In the second process tank, an alkaline etching upon said holes by means of the second process liquid is carried out in the presence of the Ag particles, to form an inverted-pyramid-type textured surface structure of the semiconductor substrate. Under the alkaline conditions, the holes are etched anisotropically (undergo an anisotropic etching) , thereby forming an inverted-pyramid-type surface structure, wherein the Ag particles should function as a catalyst in the anisotropic etching process since a higher etching rate has been observed in the vicinity of the Ag particles. During growth of the  inverted-pyramid-type surface structure, the inverted pyramids may be “interconnected” or fused together. Preferably, the inverted-pyramid-type textured surface structure is formed by a first structure element, wherein at least 70%of the first structure elements have a maximum dimension of between 50 nm and 600 nm, preferably between 150 nm and 400 nm. Preferably, at least 80%, particularly at least 90%of the first structure elements have said maximum dimension. In particular, said maximum dimension herein refers to a maximum width parallel to the plane of a substrate and/or a maximum length vertical to the plane of a substrate.
Preferably, the second process liquid contains an alkaline liquid and, but not imperatively, a surface wetting agent. The alkaline liquid contains in particular potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2CO 3/Na 2CO 3) . The surface wetting agent may be various surfactant solutions for improving wetting ability of a surface, which are, for example, commercially available from: Changzhou Shichuang Energy Technology Co., Ltd., Model Nos. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model Nos. Alka-Tex and Alka-Tex. 2+. Preferably, the second process liquid contains from 0.01 wt. %to 4 wt. %, in particular from 0.05 wt. %to 1.5 wt. %of potassium hydroxide or from 0.01 wt. %to 3 wt. %, in particular from 0.025 wt. %to 1.5 wt. %of sodium hydroxide, and contains from 0.1 wt. %to 5 wt. %, in particular from 0.2 wt. %to 2.5 wt. %of the surface wetting agent.
Preferably, the second process liquid has a temperature T2, which satisfies: 50℃≤ T2 ≤ 100℃, in particular 55℃ ≤ T2 ≤ 95℃. By means of the temperature T2, a desired alkaline etching for texturing and the optimization of the process time can be achieved.
Preferably, the apparatus is configured to keep the semiconductor substrate in the second process liquid for 0.2 to 2 minutes. By means of this configuration, a desired alkaline etching for texturing can be achieved.
Next, in the cleaning device, at least one cleaning of the inverted-pyramid-type textured surface structure is performed effectively and reliably by means of the cleaning liquid in order to remove Ag particles and silver ions located in the etched holes or on the substrate surface. As a result, on one hand, the alkaline etching is terminated and the  texturing will not be further continued; on the other hand, decreased efficiency of a solar cell made of the semiconductor substrate due to the remained silver ions can be avoided.
Preferably, the cleaning liquid comprises an aqueous solution containing nitric acid. The aqueous solution preferably contains distilled water as a matrix. Preferably, the cleaning liquid comprises nitric acid, preferably from 10 wt. %to 70 wt. %, and more preferably from 20 wt. %to 70 wt. %of nitric acid. Preferably, the cleaning liquid has a temperature TR, which satisfies: 20℃ ≤ TR ≤ 65℃, preferably 23℃ ≤ TR ≤ 60℃. Preferably, the apparatus is configured to keep the semiconductor substrate in the cleaning liquid for 0.5-3 minutes. By means of this configuration, the Ag particles and the silver ions can be removed simply and effectively.
Preferably, the cleaning device has a cleaning tank with a cleaning liquid, wherein the cleaning device has a plurality of successively arranged spray units for spraying the cleaning liquid onto the textured surface structure, said plurality of successively arranged spraying units preferably being arranged inside and/or above the cleaning tank respectively. By means of this configuration, the Ag particles and the silver ions can be removed in a particularly simple and effective manner.
Preferably, the apparatus further comprises at least one rinsing device disposed directly behind the first process tank, the second process tank and/or the cleaning device, and configured to use the rinsing liquid to rinse the semiconductor substrate output from the first process tank, the second process tank and/or the cleaning device; wherein the rinse liquid is preferably water, especially deionized water; and preferably, the rinse device is a spraying type device or an immersion type device. Preferably, as to the spraying type device, the rinsing device comprises at least one spray unit for spraying the rinsing liquid onto the semiconductor substrate, and the at least one spray unit is preferably arranged inside and/or above at least one rinsing tank. As to the immersion type device, the rinsing liquid is configured to be circulated e.g. by a circulating pump or by compressed dry air bubbling.
Preferably, the apparatus further comprises an acid bath tank, a rinsing device, and a drying device that are sequentially disposed behind the rinsing device of the cleaning  device, wherein the acid bath tank is configured to post-treat the semiconductor substrate, which is output from the cleaning device and subsequently rinsed with the rinsing liquid, with an aqueous solution preferably consisting of hydrofluoric acid and nitric acid, the rinsing device is configured to rinse the post-treated semiconductor substrate with the rinsing liquid, and the drying device is configured to dry the semiconductor substrate.
In the third process tank, a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure is performed in the absence of said Ag particles by means of the third process liquid in order to form an enlarged inverted-pyramid-type textured surface structure. Preferably, the enlarged inverted-pyramid-type textured surface structure is formed by a second structure element, wherein at least 70%of the second structure elements have a maximum dimension of 250 nm to 1200 nm, especially 400 nm to 1000 nm. More preferably, at least 80%, especially at least 90%of the second structure element has said maximum dimension. Said maximum dimension herein refers to a maximum width parallel to the plane of a substrate and/or a maximum length vertical to the plane of a substrate. Thereby, a textured surface structure with an extremely low reflectivity loss can be ensured.
Preferably, the third process liquid comprises an alkaline liquid and not imperatively a surface wetting agent, wherein in particular, the alkaline liquid contains potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2CO 3/Na 2CO 3) , the surface wetting agent may be various surfactant solutions for improving wetting ability of a surface, e.g., available from: Changzhou Shichuang Energy TechnologyCo., Ltd., Model No. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model No. Alka-Tex and Alka-Tex. 2+. Preferably, the third process liquid comprises 0.1wt. %to 4wt. %, especially 0.5wt. %to 3.5wt. %of potassium hydroxide or 0.05wt. %to 3wt. %, especially 0.25wt. %to 2wt. %of sodium hydroxide and contains 0.1wt. %to 5wt. %, especially 0.3wt. %to 3.5wt. %of the surface wetting agent; preferably, the third process liquid has a temperature T3, wherein: 50℃ ≤ T3 ≤ 100℃, especially 60℃ ≤ T2 ≤ 95℃. Preferably, the apparatus is configured to keep the semiconductor substrate in the third process liquid for 1-5 minutes. By means of the above configuration, the size of the inverted pyramids can be  enlarged simply and effectively, so as to form an enlarged inverted-pyramid-type textured surface structure.
In another embodiment of the present invention, the apparatus further comprises a rinsing device disposed directly after the third process tank, which is configured to rinse the semiconductor substrate output from the third process tank with rinsing liquid; preferably, the rinsing liquid is water, especially deionized water.
In another embodiment of the present invention, the apparatus further comprises an acid bath tank, a rinsing device, and a drying device that are sequentially disposed behind the rinsing device of the third process tank, wherein the acid bath tank is configured to post-treat the semiconductor substrate, which is output from the third process tank and subsequently rinsed with the rinsing liquid, with an aqueous solution preferably consisting of hydrofluoric acid and hydrochloric acid, the rinsing device is configured to rinse the post-treated semiconductor substrate with the rinsing liquid, and the drying device is configured to dry the semiconductor substrate.
In one embodiment of the present invention, the apparatus may be an inline type apparatus in which a conveying device for continuously conveying the semiconductor substrate is provided. In this manner, a large number of the semiconductor substrates with a desired textured surface structure can be produced in a simple and effective way. The apparatus preferably comprises at least one conveying device for continuously conveying the semiconductor substrate in a conveying direction. The at least one conveying device extends at least from the first process tank to the second process tank, preferably from the first process tank to the cleaning device disposed behind the second process tank, and especially from the first process tank to the third process tank. The at least one conveying device can achieve continuous parallel conveyance of the semiconductor substrates in the conveying direction. In the first example, the apparatus comprises one conveying device, which conveys, in a continuous and parallel manner, the semiconductor substrates from the first process tank to the third process tank. In the second example, the apparatus comprises two conveying devices, wherein the first conveying device conveys, in a continuous and parallel manner, the semiconductor substrates from the first process tank to the cleaning device disposed behind the second process tank, and the second conveying device conveys, in a continuous and parallel  manner, the semiconductor substrates from the cleaning device to the third process tank. Between the first conveying device and the second conveying device, the semiconductor substrates are conveyed e.g., by hand or via a moving device.
Preferably, the inline type apparatus further comprises a mechanical transfer unit disposed directly behind the rinsing device of said cleaning device or disposed directly behind said cleaning device in a conveying direction of said semiconductor substrate, wherein said mechanical transfer unit is configured to transfer the rinsed or non-rinsed semiconductor substrate after cleaning by means of the cleaning liquid in wet state directly to another inline type apparatus for post-treating.
Preferably, the inline type apparatus further comprises a mechanical transfer unit disposed directly behind the rinsing device of said third process tank or disposed directly behind said third process tank in a conveying direction of said semiconductor substrate, wherein said mechanical transfer unit is configured to transfer the rinsed or non-rinsed semiconductor substrate after further alkaline etching by means of the third process liquid in a wet state directly to another apparatus for post-treating.
The prior inline type apparatus for post-treating may comprise a tank for post-treating, e.g., an acid bath tank (HF and HNO 3) . A treatment process that occurs in the prior inline type apparatus for post-treating, for example, comprises: inputting, spraying and rinsing with deionized water, acid bathing, another spraying and rinsing with deionized water, drying, and outputting. In the tank for post-treating, the subsequent post-treatment with the liquid for post-treatment is only used for cleaning the resulting inverted-pyramid-type textured surface, during which no silicon is removed. By means of the mechanical transfer unit, it is possible that the semiconductor substrates cleaned by the cleaning device is transferred in a wet state to the tank for post-treatment in the prior apparatus, thereby integrating the apparatus according to the present invention with the prior apparatus into a set of apparatuses, which means that it is unnecessary to perform the conventional unloading and loading of a semiconductor substrate between two previously separated apparatuses. In addition, the semiconductor substrate cleaned via the cleaning device is not dried, but is transferred in a wet state between the two previously separated apparatuses.
In one embodiment of the present invention, the apparatus comprises a batch type apparatus in which a carrier device for carrying and conveying semiconductor substrates in batches is provided. Here, all the above process tanks, the cleaning device and the rinsing device can be configured as immersion type devices, wherein all the process liquids, the cleaning liquid and the rinsing liquid can be provided to be circulated e.g., by a circulating pump or by compressed dry air bubbling. In an embodiment, the batch type apparatus is configured to use the carrier device to transfer the rinsed or non-rinsed semiconductor substrate after cleaning with the cleaning liquid in a wet state directly to another batch type apparatus for post-treating. In another embodiment, the batch type apparatus further includes a drying device disposed behind the rinsing device of the cleaning device, and the drying device is configured to sufficiently dry the semiconductor substrate output from the cleaning device and then rinsed with a rinsing liquid so that the dried plurality of semiconductor substrates when stacked together would not be connected to each other due to residual moisture in the surface structure. The semiconductor substrates stacked together are easy to be transferred, by hand or by means of a moving tool, to a position or place of the prior apparatus for post-treatment, so as to carry out a treatment, which, for example, comprises sequentially inputting, spraying and rinsing with deionized water, acid bathing, another spraying and rinsing with deionized water, drying, and outputting.
In a preferred embodiment of the present invention, the apparatus is used to conduct a surface texturing on a polycrystalline or single crystalline semiconductor substrate, preferably a single crystalline semiconductor substrate, more preferably a single crystalline silicon substrate.
On the other hand, the present invention provides a method for surface texturing of a semiconductor substrate, which comprises the following steps: depositing Ag particles on the surface of a semiconductor substrate and form a large number of holes in which said Ag particles are contained, on the surface of the semiconductor substrate by Ag-based metal catalyst chemical etching, by means of a first process liquid; performing alkaline etching to said holes in the presence of said Ag particles by means of a second process liquid, in order to form an inverted-pyramid-type textured surface structure of the semiconductor substrate; and, performing at least one cleaning of the inverted-pyramid-type textured surface structure by means of a cleaning liquid in order to  remove said Ag particles and/or Ag + ions. Advantages of the method according to the present invention corresponds to those of the apparatus according to the present invention. Particularly, the method according to the present invention can also be improved in accordance with at least one feature of the apparatus according to the present invention.
Preferably, the method according to the present invention further comprises performing a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure in the absence of said Ag particles by means of a third process liquid in order to form an enlarged inverted-pyramid-type textured surface structure.
The first process liquid comprises hydrofluoric acid, nitric acid and silver nitrate; preferably, the first process liquid comprises 10wt. %to 25wt. %, especially 12wt. %to 20wt. %of hydrofluoric acid, 12wt. %to 25wt. %, especially 15 wt. %to 22wt. %of nitric acid and 0.0001wt. %to 0.05wt. %, especially 0.001wt. %to 0.015wt. %of silver nitrate. Preferably, the first process liquid contains less than 5wt. %, especially less than 1wt. %, and especially 0wt. %of hydrogen peroxide. Preferably, the first process liquid has a temperature T1, where: 6℃ ≤ T1 ≤ 40℃, especially 8℃ ≤ T1 ≤ 30℃. Preferably, the semiconductor substrate is kept in the first process liquid for 0.5-4 minutes. Preferably, the holes formed by means of the first process liquid has a maximum dimension between 50 nm and 300 nm, preferably between 100 nm and 200 nm. In certain embodiments, the semiconductor substrate has a sawn surface structure, wherein said sawn surface structure, preferably in the range of 0.5 to 4.0 μm/side, is meanwhile (or additionally) removed by means of the first process liquid.
Preferably, the second process liquid comprises an alkaline liquid and a surface wetting agent, wherein the alkaline liquid comprises in particular, potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2CO 3/Na 2CO 3) . The surface wetting agent may comprise various surfactant solutions for improve wetting ability of a surface, which is, for example, available from: Changzhou Shichuang Energy Technology Co., Ltd., Model Nos. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model Nos. Alka-Tex and Alka-Tex. 2+. Preferably, said second process liquid contains 0.01wt. %to 4wt. %, especially 0.05wt. %to 1.5wt. %of potassium hydroxide or 0.01wt. %to 3wt. %, especially  0.025wt. %to 1.5wt. %of sodium hydroxide, and contains 0.1wt. %to 5wt. %, especially 0.2wt. %to 2.5wt. %of the surface wetting agent; preferably, the second process liquid has a temperature T2, wherein: 50℃ ≤ T2 ≤ 100℃, especially 55℃ ≤ T2 ≤ 95℃. The semiconductor substrate is kept in the second process liquid for 0.2 to 2 minutes. Therefore, it can be ensured that an inverted-pyramid-type textured surface structure is formed effectively. Preferably, said inverted-pyramid-type textured surface structure is formed by a first structure element, wherein at least 70%of the first structure elements have a maximum dimension of 50 nm to 600 nm, especially 150 nm to 400 nm. Preferably, at least 80%, especially at least 90%of the first structure elements have said maximum dimension. In particular, the maximum dimension refers to a maximum width parallel to the plane of a substrate and/or a maximum length vertical to the plane of a substrate.
Preferably, the cleaning liquid contains nitric acid, in particular 10wt. %to 70wt. %, especially 20wt. %to 70wt. %of nitric acid. Preferably, the cleaning liquid in particular has a temperature TR, wherein: 20℃ ≤ TR ≤ 65℃, especially 23℃ ≤ TR ≤ 60℃. Preferably, the semiconductor substrate is kept in the cleaning liquid for 0.5-3 minutes. Thereby, it is ensured that the Ag particles and the silver ions can be removed effectively.
Preferably, the method further comprises using a rinsing liquid to rinse the semiconductor substrate output from the first process liquid, the second process liquid and/or the cleaning liquid, wherein the rinse liquid is preferably water, especially deionized water; and preferably, the rinsing is a spraying type or an immersion type rinsing.
Preferably, the method further comprises the following steps in sequence: post-treating the semiconductor substrate, which is output from the cleaning liquid and subsequently rinsed with the rinsing liquid, with an aqueous solution preferably consisting of hydrofluoric acid and nitric acid, rinsing the post-treated semiconductor substrate with a rinsing liquid, and drying the semiconductor substrate.
Preferably, the method further comprises performing a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure in the absence of said Ag particles by means of a third process liquid in order to form an enlarged inverted- pyramid-type textured surface structure. Preferably, the enlarged inverted-pyramid-type textured surface structure is formed by a second structure element, wherein at least 70%of the second structure elements have a maximum dimension of 250 nm to 1200 nm, especially 400 nm to 1000 nm. Preferably, the third process liquid contains an alkaline liquid and a surface wetting agent, wherein the alkaline liquid comprises in particular potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2CO 3/Na 2CO 3) , and the surface wetting agent may comprise various surfactant solutions for improving wetting ability of a surface, which is, for example, available from: Changzhou Shichuang Energy Technology Co., Ltd., Model Nos. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model Nos. Alka-Tex and Alka-Tex. 2+. Preferably, the third process liquid comprises 0.1wt. %to 4wt. %, especially 0.5wt. %to 3.5wt. %of potassium hydroxide or 0.05wt. %to 3wt. %, especially 0.25wt. %to 2wt. %of sodium hydroxide and contains 0.1wt. %to 5wt. %, especially 0.3wt. %to 3.5wt. %of the surface wetting agent. Preferably, the third process liquid has a temperature T3, wherein: 50℃ ≤ T3 ≤ 100℃, especially 60℃ ≤ T2 ≤ 95℃. Preferably, the semiconductor substrate is kept in the third process liquid for 1-5 minutes. Preferably, the method further comprises rinsing the semiconductor substrate output from the third process liquid with a rinsing liquid, wherein the rinsing liquid is water, in particular deionized water. Preferably, the method further comprises the following steps in sequence: post-treating the semiconductor substrate, which is output from the third process liquid and subsequently rinsed with the rinsing liquid, with an aqueous solution preferable consisting of hydrofluoric acid and nitric acid, rinsing the semiconductor substrate with a rinsing liquid, and drying the semiconductor substrate.
Preferably, the method steps are carried out in an inline type apparatus, and the semiconductor substrates are continuously conveyed. In an embodiment, the rinsed or non-rinsed semiconductor substrate after cleaning by means of the cleaning liquid in said inline type apparatus is transferred in a wet state directly to another inline type apparatus for post-treating. In another embodiment, the rinsed or non-rinsed semiconductor substrate after further alkaline etching by means of the third process liquid in said inline type apparatus is transferred in a wet state directly to another inline type apparatus for post-treating.
In another embodiment, the method steps are carried out in a batch type apparatus and the semiconductor substrate is conveyed in batch. In another embodiment, the rinsed or non-rinsed semiconductor substrate after cleaning with the cleaning liquid in the batch type apparatus is transferred in a wet state directly to another batch type device for post-treating. In another embodiment, the semiconductor substrate output from the cleaning device and then rinsed with a rinsing liquid is sufficiently dried so that the dried plurality of semiconductor substrates when stacked together would not be connected to each other due to residual moisture in the surface structure.
Preferably, the semiconductor substrate is a single crystalline semiconductor substrate, in particular a single crystalline silicon substrate.
Compared to the prior art, advantages of the apparatus and method of the present invention comprises:
-adopting an Ag-based MCCE process, without a risk of Cu pollution;
-using an etching solution of HF/HNO 3 during MCCE, which contains no H 2O 2, wherein the use of said etching solution is well-known to be a stable process in industrial applications;
-less than 5 minutes of total duration of the etching, which is suitable for both inline-type and batch-type, high throughout apparatus;
-a process temperature of not higher than 70℃, reducing stress on hardware and improving control over the process; and,
-adjusting size and depth of pyramids by varying the process formulation, thereby resulting in different reflectivity and light trapping behaviours, which is, therefore, very suitable for different solar cell structures.
Undoubtedly, the features, which have been mentioned before or will be illustrated hereafter, can be used not only in the given combinations, but also in other combinations, as long as they are not departing from the scope of the present invention as outlined in the claims.
The advantages of the present invention will be illustrated according to the following examples and accompanied figures. The examples are preferable forms for carrying out the present invention, but the present invention should not be limited to them in any way. Furthermore, to facilitate a better understanding, the views in the figures are merely schematic and may not represent an actual situation. Just for the sake of illustration, the proportions shown in the figures may not coincide with their actual proportions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an embodiment of an inline type apparatus according to the present invention for surface texturing of a semiconductor substrate;
FIG. 2 shows another embodiment of an inline type apparatus according to the present invention for surface texturing of a semiconductor substrate;
FIG. 3 shows an embodiment of a batch type apparatus according to the present invention for surface texturing of a semiconductor substrate;
FIG. 4 shows another embodiment of a batch type apparatus according to the present invention for surface texturing of a semiconductor substrate;
FIG. 5 shows yet another embodiment of a batch type apparatus according to the present invention for surface texturing of a semiconductor substrate;
FIG. 6 shows still yet another embodiment of a batch type apparatus according to the present invention for surface texturing of a semiconductor substrate;
FIG. 7 are scanning electron microscope photographs showing the textured surface structure of the semiconductor substrate prepared in the inventive apparatus;
FIG. 8 shows a graph plotting optical reflectivity values as a function of wavelengths of the textured surface structure of the semiconductor substrate prepared in the inventive apparatus; and,
FIG. 9 shows a schematic diagram of one embodiment of the method according to the present invention for surface texturing of a semiconductor substrate.
DETAILED DESCRIPTION
FIG. 1 shows an embodiment of the inline type apparatus 1 according to the present invention for surface texturing of a semiconductor substrate 3, wherein the inline type apparatus 1 for wet chemical treatment of the semiconductor substrate 3 comprises a conveying device 4 for conveying the semiconductor substrate 3 in the conveying direction. The conveying device 4 comprises a plurality of conveying rollers 4’ which are sequentially arranged in the conveying direction and are rotationally driven.
The apparatus 1 comprises the first process tank 11, the first rinsing device R 1, the second process tank 12, the second rinsing device R 2, the cleaning device 13, the third rinsing device R 3, the third process tank 14, the fourth rinsing device R 4, an acid bath tank 15, the fifth rinsing device R 5, and a drying device D, which are sequentially arranged in the conveying direction.
The first process tank 11 is configured to receive a first process liquid, and is configured to remove, by means of the first process liquid, preferably 0.5 to 4.0 μm/side of sawn surface structures S 0 of the semiconductor substrate 3, and meanwhile to generate a surface structure S 1 having holes, which contain Ag particles, by Ag particle deposition and metal catalyst chemical etching. The first process tank 11 is filled with the first process liquid. The first process liquid is an aqueous solution in which distilled water is used as a matrix, and comprises hydrofluoric acid (HF) , nitric acid (HNO 3) and silver nitrate (AgNO 3) . The first process liquid contains 10 wt. %to 25 wt. %, preferably 12 wt. %to 20 wt. %of hydrofluoric acid, 12 wt. %to 25 wt. %, preferably 15 wt. %to 22 wt. %of nitric acid, and 0.0001 wt. %to 0.05 wt. %, preferably 0.001 wt. %to 0.015 wt. %of silver nitrate. The first process liquid, for example, contains 15 wt. %of hydrofluoric acid (HF) , 20 wt. %of nitric acid (HNO 3) and 0.005 wt. %of silver nitrate (AgNO 3) . The first process liquid contains no hydrogen peroxide (H 2O 2) . The first process liquid has a temperature T1, wherein: 6℃ ≤ T1 ≤ 40℃, preferably 8℃ ≤ T1 ≤ 30℃. The above data are all in weight percent.
The first rinsing device R 1 is configured to use a rinsing liquid to rinse the semiconductor substrate 3 output from the first process tank 11. The rinsing liquid is  preferably water, especially deionized water. Herein, the rinsing device is a spraying type device with a plurality of spray units R 1’ .
The second process tank 12 is configured to receive the second process liquid, and is configured to perform an alkaline etching to the holes, in the presence of the Ag particles within the holes, by means of the second process liquid, to form an inverted-pyramid-type textured surface structure of the semiconductor substrate 3. The second process liquid comprises an alkaline liquid and, but not imperatively, a surface wetting agent, wherein the alkaline liquid, in particular, contains potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2CO 3/Na 2CO 3) , and the surface wetting agent may be various surfactant solutions for improving wetting ability of a surface, which are, for example, available from: Changzhou Shichuang Energy Technology Co., Ltd., Model Nos. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model Nos. Alka-Tex and Alka-Tex. 2+. Preferably, the second process liquid contains 0.01 wt. %to 4 wt. %, preferably 0.05 wt. %to 1.5 wt. %of potassium hydroxide or 0.01 wt. %to 3 wt. %, preferably 0.025 wt. %to 1.5 wt. %of sodium hydroxide, and contains 0.1 wt. %to 5 wt. %, preferably 0.2 wt. %to 2.5 wt. %of the surface wetting agent. Preferably, the second process liquid has a temperature T2, wherein: 50℃ ≤ T2 ≤ 100℃, preferably 55℃ ≤ T2 ≤ 95℃.
The second rinsing device R 2 is configured to use a rinsing liquid to rinse the semiconductor substrate 3 output from the second process tank 12. The rinsing liquid preferably is water, and preferably is deionized water. Here, the rinsing device is a spraying type device with a plurality of spray units R 2’ .
The cleaning device 13 is configured to perform at least one cleaning to the inverted-pyramid-type textured surface structure by means of a cleaning liquid, to remove the Ag particles. The cleaning liquid contains nitric acid, preferably 10 wt. %to 70 wt. %, and more preferably 20 wt. %to 70 wt. %of nitric acid. Preferably, the cleaning liquid has a temperature TR, wherein: 20℃ ≤ TR ≤ 65℃, preferably 23℃ ≤ TR ≤ 60℃. The apparatus 1 is configured to keep the semiconductor substrate 3 in the cleaning liquid for 0.5 to 3 minutes. The cleaning device has a cleaning tank holding the cleaning liquid, and a plurality of successively arranged spray units for spraying the cleaning liquid onto  the textured surface structure, wherein said plurality of successively arranged spraying units preferably are arranged inside and/or above the cleaning tank.
The third rinsing device R 3 is configured to rinse the semiconductor substrate 3 output from the cleaning device 13 with a rinsing liquid. The rinsing liquid preferably is water, and preferably is deionized water. Here, the rinsing device is a spraying type device with a plurality of spray units R 3’ .
The third process tank 14 is configured to receive the third process liquid, and is configured to perform, in the absence of the Ag particles, a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure by means of the third process liquid, to form an enlarged inverted-pyramid-type textured surface structure. The third process liquid contains an alkaline liquid and, but not imperatively, a surface wetting agent, wherein the alkaline liquid preferably comprises potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2CO 3/Na 2CO 3) , and the surface wetting agent may be various surfactant solutions for improving wetting ability of a surface, which are, for example, available from: Changzhou Shichuang Energy Technology Co., Ltd., Model Nos. TS 4 and TS 5; ICB Co., Ltd., Model No. CellTex; GP solar company, Model Nos. Alka-Tex and Alka-Tex. 2+. Preferably, the third process liquid contains 0.1 wt. %to 4 wt. %, preferably 0.5 wt. %to 3.5 wt. %of potassium hydroxide or 0.05 wt. %to 3 wt. %, preferably 0.25 wt. %to 2 wt. %of sodium hydroxide, and contains 0.1 wt. %to 5 wt. %, preferably 0.3 wt. %to 3.5 wt. %of the surface wetting agent. Preferably, the third process liquid has a temperature T3, wherein: 50℃ ≤ T3 ≤ 100℃, preferably 60℃ ≤ T3 ≤ 95℃. The apparatus is configured to keep the semiconductor substrate 3 in the third process liquid for 1 to 5 minutes.
The fourth rinsing device R 4 is configured to rinse the semiconductor substrate 3 output from the third process tank 14 with a rinsing liquid. The rinsing liquid preferably is water, and preferably is deionized water. Herein, the rinsing device is a spraying type device with a plurality of spray units R 4’ .
An acid bath tank 15 is configured to treat the semiconductor substrate 3 with an aqueous solution containing HF and HCl. At this moment, the surface structure to be  dried is hydrophobic, and it is relatively easy to dry the surface structure. The fifth rinsing device R 5 is configured to rinse the semiconductor substrate 3 output from the acid bath tank 15 with a rinsing liquid. The rinsing liquid preferably is water, and preferably is deionized water. Here, the rinsing device is a spraying type device with a plurality of spray units R 5’ . The drying device D is arranged in a conventional manner of the art, wherein it comprises nozzles D’ for jetting dry air. After dried in the drying device D, the semiconductor substrate 3 is output.
Before input into the apparatus 1 of the present invention, the surface (S 0) of the semiconductor substrate 3 has a sawn surface structure. The surface (S 1) of the semiconductor substrate 3 obtained after treated in the first process tank 11 has a large number of holes, wherein the holes have a maximum dimension between 50 nm and 300 nm, and preferably between 100 nm and 200 nm. The surface (S 2) of the semiconductor substrate 3 obtained after the MCCE treatment in the second process tank 12 has an inverted-pyramid-type textured surface structure formed by a first structure element, wherein at least 70%of the first structure elements have a maximum dimension between 50 nm and 600 nm, and preferably between 150 nm and 400 nm. The Ag particles and the silver ions are removed from the surface (S 3) of the semiconductor substrate 3 obtained after performing at least one cleaning in the cleaning device. The surface (S 4) of the semiconductor substrate 3 obtained after the treatment in the third process tank has an enlarged inverted-pyramid-type textured surface structure, which is formed by a second structure elements wherein at least 70%of the second structure elements have a maximum dimension between 250 nm and 1200 nm, and preferably between 400 nm and 1000 nm. After subjected to a treatment in the acid bath tank, the surface (S 5) of the semiconductor substrate 3 is hydrophobic and can be dried easily.
FIG. 2 shows another embodiment of the inline type apparatus 1 according to the present invention for surface texturing of a semiconductor substrate 3. It differs from the apparatus 1 as shown in FIG. 1 in that in the apparatus 1 of FIG. 2, a mechanical transfer unit C is disposed behind the third process tank 14 and the fourth rinsing device R 4 disposed thereafter, wherein the mechanical transfer unit C is configured to transfer the rinsed semiconductor substrate 3 after cleaning with the cleaning liquid in a wet state directly to another inline type apparatus 2 for post-treating. The another inline type  apparatus 2 for post-treating may be an existing apparatus of an industrial supplier, in which an acid bath tank 21, a rinsing device 22 and a drying device D are provided.
FIG. 3 shows an embodiment of a batch type apparatus 1’ according to the present invention for surface texturing of a semiconductor substrate 3. A carrier device 7 for carrying and conveying semiconductor substrates 3 in batches is provided in the batch type apparatus 1’ . A plurality of semiconductor substrates, such as single crystalline silicon wafers, are loaded in the same carrier device 7, which is for example made from a polymer, e.g., PVDF, PTFE or the like. The carrier device 7 is placed on an input unit 5 of the apparatus 1’ , wherein the input unit 5 may have a plurality of rollers 5’ . In the batch type apparatus 1’ , by means of a robot, the carrier device 7 bearing the substrates (e.g., 100 single crystalline silicon wafers) is placed from the input unit 5 to the first process tank 11, the first rinsing device R 1, the second process tank 12, the second rinsing device R 2, the cleaning device 13, the third rinsing device R 3, the third process tank 14, the fourth rinsing device R 4, the acid bath tank 15, the fifth rinsing device R 5, the sixth rinsing device R 6, and the drying device D sequentially, wherein all the process tanks, the cleaning device and the rinsing device are provided as immersion type devices. After the drying is completed in the drying device D, the carrier device loaded with the semiconductor substrates 3 is placed on an output unit 6 by means of a robot, wherein the output unit 6, for example, comprises a plurality of rollers 6’ .
FIG. 4 shows another embodiment of a batch type apparatus 1’ according to the present invention for surface texturing of a semiconductor substrate 3. The apparatus 1’ in FIG. 4 differs from the apparatus 1’ as shown in FIG. 3 in that it only comprises the first process tank 11, the first rinsing device R 1, the second process tank 12, the second rinsing device R 2, the cleaning device 13 and the third rinsing device R 3, which are arranged in sequence. After the third rinsing device R 3, the carrier device 7 loaded with the semiconductor substrates 3 is transferred directly into another prior batch type apparatus 2, wherein the apparatus 2, for example, comprises an acid bath tank 21, a rinsing device 22, a hot water rinsing device 23, a drying device D and an output unit 8, and the output unit may have a plurality of rollers 8’ .
FIG. 5 shows yet another embodiment of a batch type apparatus 1’ according to the present invention for surface texturing of a semiconductor substrate 3. The apparatus 1’  of FIG. 5 differs from the apparatus 1’ as shown in FIG. 4 in that it only comprises the first process tank 11, the first rinsing device R 1, the second process tank 12, the second rinsing device R 2, the cleaning device13, and the third rinsing device R 3 arranged sequentially. After the third rinsing device R 3, the carrier device 7 loaded with the semiconductor substrates 3 is placed onto a mechanical transfer unit C, wherein the mechanical transfer unit C herein is an input unit of another prior batch type apparatus 2. By means of a robot of the apparatus 2, the carrier device 7 bearing the substrates is placed into an acid bath tank 21, a rinsing device 22, a hot water rinsing device 23 and a drying device D of the apparatus 2, and finally is placed on an output unit 8, wherein the output unit may have a plurality of rollers 8’ .
FIG. 6 shows still yet another embodiment of a batch type apparatus 1’ according to the present invention for surface texturing of a semiconductor substrate 3. The apparatus 1’ of FIG. 6 differs from the apparatus 1’ as shown in FIG. 3 in that it only comprises the first process tank 11, the first rinsing device R 1, the second process tank 12, the second rinsing device R 2, the cleaning device 13, the third rinsing device R 3 and the drying device D, arranged sequentially.
FIG. 7 are scanning electron microscope photographs showing the textured surface structure of the semiconductor substrate 3 prepared in the inventive apparatus. The two photographs of FIG. 7 are taken respectively at different amplifications. It is clear from FIG. 7 that the semiconductor substrate 3 prepared in the apparatus 1, 1’ according to the present invention has an inverted-pyramid-type textured surface structure.
FIG. 8 shows a graph plotting optical reflectivity values as a function of wavelengths of the textured surface structure of the semiconductor substrate prepared in the inventive apparatus. In this figure, the Examples 1 to 3 and a reference sample are shown. The semiconductor reference sample is obtained by a standard alkaline etching or alkaline single crystalline texturing process in the prior art, and has a randomly distributed upright pyramid-type surface structure. The semiconductor substrates in the Examples 1 to 3 are prepared by using the apparatus 1, 1’ according to the present invention, and all have a randomly distributed inverted-pyramid-type textured surface structure. The process parameters used in the examples are set forth in Table 1.
Table 1
Figure PCTCN2019088548-appb-000001
Textured surfaces of the semiconductor substrates obtained according to Example 1 to 3 of the present invention as well as that obtained according to the reference sample are compared in terms of etched depth, basic size of pyramids and reflectivity. Results are shown in Table 2.
Table 2
Figure PCTCN2019088548-appb-000002
It can be seen from FIG. 8 and Table 2 that the average reflectivity values in the Examples 1 to 3 are largely decreased compared to that in the reference sample, particularly at the wavelength range of 400 to 550 nm, in which a decreased reflectivity is very beneficial since this wavelength range is most effective for a shallow emitter or a selective emitter. Reflectivity of the resulting textured single crystalline silicon wafer can be significantly decreased by changing the process parameters (e.g., concentration, temperature and/or time) . Contrary to the standard upright pyramid-type textured surface structure, the inverted-pyramid-type textured surface structure according to the Examples 1-3 of the present invention is more flexible in e.g., size or depth.
FIG. 9 schematically shows an embodiment of the method according to the present invention for surface texturing of a semiconductor substrate. The method comprises the following steps: providing a semiconductor substrate (step 101) ; depositing Ag particles onto the surface of the semiconductor substrate by means of the first process liquid (step 102) , and forming a large number of holes, in which the Ag particles are contained, on the surface of the semiconductor substrate by Ag-based metal catalyst chemical etching (step 103) ; in the presence of the Ag particles, performing an alkaline etching to the holes by means of the second process liquid, to form an inverted-pyramid-type textured surface structure of the semiconductor substrate (step 104) ; performing at least one cleaning to the inverted-pyramid-type textured surface structure by means of the cleaning liquid, to remove the Ag particles (step 105) ; and, in the absence of the Ag particles, performing a further alkaline etching to the cleaned inverted-pyramid-type textured surface structure by means of the third process liquid, to form an enlarged inverted-pyramid-type textured surface structure (step 106) .

Claims (48)

  1. An apparatus for surface texturing of semiconductor substrate, comprising:
    a first process tank configured to receive a first process liquid and, by means of said first process liquid, deposit Ag particles on the surface of the semiconductor substrate and form a large number of holes, in which said Ag particles are contained, on the surface of the semiconductor substrate by Ag-based metal catalyst chemical etching;
    a second process tank configured to receive a second process liquid and perform alkaline etching to said holes in the presence of said Ag particles by means of said second process liquid, in order to form an inverted-pyramid-type textured surface structure of the semiconductor substrate, and
    a cleaning device configured to perform at least one cleaning of the inverted-pyramid-type textured surface structure by means of a cleaning liquid in order to remove said Ag particles.
  2. The apparatus according to claim 1, wherein the first process liquid comprises hydrogen fluoride (HF) , hydrogen nitrate (HNO 3) and silver nitrate (AgNO 3) ; preferably, the first process liquid comprises 10wt. %to 25wt. %, especially 12wt. %to 20wt. %of hydrogen fluoride, 12 wt. %to 25wt. %, especially 15 wt. %to 22wt. %hydrogen nitrate and 0.0001wt. %to 0.05wt. %especially 0.001wt. %to 0.015wt. %silver nitrate; preferably, the first process liquid contains less than 5wt. %, especially less than 1wt. %, and especially 0wt. %of hydrogen peroxide; preferably, the first process liquid has a temperature T1, where: 6℃ ≤ T1 ≤ 40℃, especially 8℃ ≤ T1 ≤ 30℃; preferably, the hole has a maximum dimension of between 50nm and 300 nm, in particular between 100nm and 200 nm.
  3. The apparatus according to claim 1, wherein the apparatus is configured to keep the semiconductor substrate in the first process liquid for 0.5-4 minutes.
  4. The apparatus according to claim 1, wherein the semiconductor substrate has a sawn surface structure, and the first process tank is configured to remove the sawn surface structure, preferably in the range of 0.5 to 4.0 μm/side of the sawn surface structure additionally by means of the first process liquid.
  5. The apparatus according to claim 1, wherein the second process liquid comprises an alkaline liquid and, but not imperatively, a surface wetting agent, said alkaline liquid contains in particular potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2CO 3/Na 2CO 3) ; preferably, said second process liquid contains 0.01wt. %to 4wt. %, especially 0.05wt. %to 1.5wt. %of potassium hydroxide or 0.01wt. %to 3wt. %, especially 0.025wt. %to 1.5wt. %of sodium hydroxide and contains 0.1wt. %to 5wt. %, especially 0.2wt. %to 2.5wt. %of surface wetting agent; preferably, the second process liquid has a temperature T2, wherein: 50℃ ≤ T2 ≤ 100℃, especially 55℃ ≤ T2 ≤ 95℃; preferably, said inverted-pyramid-type textured surface structure is formed by a first structure element, wherein at least 70%of the first structure elements have a maximum dimension of 50 nm to 600 nm, especially 150 nm to 400 nm.
  6. The apparatus according to claim 1, wherein the apparatus is configured to keep the semiconductor substrate in the second process liquid for 0.2-2 minutes.
  7. The apparatus according to claim 1, wherein the cleaning liquid comprises hydrogen nitrate, in particular 10wt. %to 70wt. %, especially 20wt. %to 70wt. %hydrogen nitrate; preferably, the cleaning liquid in particular has a temperature TR, where: 20℃ ≤ TR ≤ 65℃, especially 23℃ ≤ TR ≤ 60℃.
  8. The apparatus according to claim 1, wherein the apparatus is configured to keep the semiconductor substrate in the cleaning liquid for 0.5-3 minutes.
  9. The apparatus according to claim 1, wherein the cleaning device has a cleaning tank with cleaning liquid, wherein the cleaning device has a plurality of successively arranged spray units for spraying the cleaning liquid onto the textured surface structure,  said plurality of successively arranged spraying units particularly being arranged inside and/or above the cleaning tank.
  10. The apparatus according to claim 1, wherein the apparatus further comprises at least one rinsing device disposed directly behind the first process tank, the second process tank, and/or the cleaning device, and configured to use the rinsing liquid to rinse the semiconductor substrate output from the first process tank, the second process tank, and/or the cleaning device; wherein the rinse liquid is preferably water, especially deionized water; preferably, the rinse device is a spraying type device or an immersion type device.
  11. The apparatus according to claim 10, wherein the apparatus further comprises an acid bath tank, a rinsing device, and a drying device that are sequentially disposed behind the rinsing device of the cleaning device, wherein the acid bath tank is configured to post-treat the semiconductor substrate, which is output from the cleaning device and subsequently rinsed with the rinsing liquid, with an aqueous solution preferably consisting of hydrofluoric acid and nitric acid, the rinsing device is configured to rinse the post-treated semiconductor substrate with a rinsing liquid, and the drying device is configured to dry the semiconductor substrate.
  12. The apparatus according to claim 1, wherein the apparatus further comprises a third process tank configured to receive a third process liquid and perform a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure in the absence of said Ag particles by means of the third process liquid in order to form the enlarged inverted-pyramid-type textured surface structure.
  13. The apparatus according to claim 12, wherein the third process liquid comprises an alkaline liquid and a surface wetting agent, the alkaline liquid comprising in particular potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2CO 3/Na 2CO 3) ; preferably, the third process liquid contains 0.1wt. %to 4wt. %, especially 0.5wt. %to 3.5wt. %of potassium hydroxide or 0.05wt. %to 3wt. %, especially 0.25wt. %to 2wt. %of sodium hydroxide and  contains0.1wt. %to 5wt. %, especially 0.3wt. %to 3.5wt. %of surface wetting agent; preferably, the third process liquid has a temperature T3, wherein: 50℃ ≤ T3 ≤ 100℃, especially 60℃ ≤ T3 ≤ 95℃; preferably, the enlarged inverted-pyramid-type textured surface structure is formed by a second structure element, wherein at least 70%of the second structure elements have a maximum dimension of 250 nm to 1200 nm, especially 400 nm to 1000 nm.
  14. The apparatus according to claim 12, wherein the apparatus is configured to keep the semiconductor substrate in the third process liquid for 1 to 5 minutes.
  15. The apparatus according to claim 12, wherein said apparatus further comprises a rinsing device disposed directly after the third process tank, which is configured to rinse the semiconductor substrate output from the third process tank with rinsing liquid; preferably, the rinsing liquid is water, especially deionized water.
  16. The apparatus according to claim 15, wherein the apparatus further comprises an acid bath tank, a rinsing device, and a drying device that are sequentially disposed behind the rinsing device of the third process tank, wherein the acid bath tank is configured to post-treat the semiconductor substrate, which is output from the third process tank and subsequently rinsed with the rinsing liquid, with an aqueous solution preferable consisting of hydrofluoric acid and hydrochloric acid, the rinsing device is configured to rinse the post-treated semiconductor substrate with a rinsing liquid, and the drying device is configured to dry the semiconductor substrate.
  17. The apparatus according to one of claims 1 to 16, wherein the apparatus is an inline type apparatus in which a conveying device for continuously conveying the semiconductor substrate is provided.
  18. The apparatus according to claim 17, wherein said inline type apparatus further comprises a mechanical transfer unit disposed directly behind the rinsing device of said cleaning device or disposed directly behind said cleaning device in a conveying direction of said semiconductor substrate, said mechanical transfer unit is configured to  transfer the rinsed or non-rinsed semiconductor substrate after cleaning by means of the cleaning liquid in wet state directly to another inline type apparatus for post-treating.
  19. The apparatus according to claim 17, wherein said apparatus further comprises a mechanical transfer unit disposed directly behind the rinsing device of said third process tank or disposed directly behind said third process tank in a conveying direction of said semiconductor substrate, said mechanical transfer unit is configured to transfer the rinsed or non-rinsed semiconductor substrate after further alkaline etching by means of the third process liquid in wet state directly to another apparatus for post-treating.
  20. The apparatus according to one of claims 1-16, wherein the apparatus is a batch type apparatus in which a carrier device for carrying and conveying semiconductor substrates in batches is provided.
  21. The apparatus according to claim 20, wherein the batch type apparatus is configured to use the carrier device to transfer the rinsed or non-rinsed semiconductor substrate after cleaning with the cleaning liquid in a wet state directly to another batch type device for post-treating.
  22. The apparatus according to claim 20, wherein the batch type apparatus further includes a drying device disposed behind the rinsing device of the cleaning device, and the drying device is configured to sufficiently dry the semiconductor substrate output from the cleaning device and then rinsed with a rinsing liquid so that the dried plurality of semiconductor substrates when stacked together would not be connected to each other due to residual moisture in the surface structure.
  23. The apparatus according to one of claims 1 to 22, wherein the apparatus is used for surface texturing single crystalline semiconductor substrates, in particular single crystalline silicon substrates.
  24. A method for surface texturing of a semiconductor substrate, comprising the steps of:
    - depositing Ag particles on the surface of the semiconductor substrate and form a  large number of holes in which said Ag particles are contained, on the surface of the semiconductor substrate by Ag-based metal catalyst chemical etching, by means of a first process liquid,
    - performing alkaline etching to said holes in the presence of said Ag particles by means of a second process liquid, in order to form an inverted-pyramid-type textured surface structure of the semiconductor substrate, and
    - performing at least one cleaning of the inverted-pyramid-type textured surface structure by means of a cleaning liquid in order to remove said Ag particles and/or Ag +ions.
  25. The method according to claim 24, wherein the hole has a maximum dimension of between 50nm and 300 nm, in particular between 100nm and 200 nm.
  26. The method according to claim 24, wherein the first process liquid comprises hydrogen fluoride (HF) , hydrogen nitrate (HNO 3) and silver nitrate (AgNO 3) ; preferably, the first process liquid comprises 10wt. %to 25wt. %, especially 12wt. %to 20wt. %of hydrogen fluoride, 12wt. %to 25wt. %, especially 15 wt. %to 22wt. %of hydrogen nitrate and 0.0001wt. %to 0.05wt. %, especially 0.001wt. %to 0.015wt. %of silver nitrate; preferably, the first process liquid contains less than 5wt. %, especially less than 1wt. %, and especially 0wt. %of hydrogen peroxide; preferably, the first process liquid has a temperature T1, where: 6℃ ≤ T1 ≤ 40℃, especially 8℃ ≤ T1 ≤ 30℃.
  27. The method according to claim 24, wherein the semiconductor substrate is kept in the first process liquid for 0.5-4 minutes.
  28. The method according to claim 24, wherein the semiconductor substrate has a sawn surface structure, and said sawn surface structure, preferably in the range of 0.5 to 4.0 μm/side of the sawn surface structure is removed additionally by means of the first process liquid.
  29. The method according to claim 24, wherein said inverted-pyramid-type textured surface structure is formed by a first structure element, wherein at least 70% of the first structure elements have a maximum dimension of 50 nm to 600 nm, especially 150 nm to 400 nm.
  30. The method according to claim 24, wherein the second process liquid comprises an alkaline liquid and a surface wetting agent, in particular the alkaline liquid comprises potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2CO 3/Na 2CO 3) ; preferably, said second process liquid contains 0.01wt. %to 4wt. %, especially 0.05wt. %to 1.5wt. %of potassium hydroxide or 0.01wt. %to 3wt. %, especially 0.025wt. %to 1.5wt. % of sodium hydroxide and contains 0.1wt. %to 5wt. %, especially 0.2wt. %to 2.5wt. %of the surface wetting agent; preferably, the second process liquid has a temperature T2, wherein: 50℃ ≤ T2 ≤100℃, especially 55℃ ≤ T2 ≤ 95℃.
  31. The method according to claim 24, wherein the semiconductor substrate is kept in the second process liquid for 0.2-2 minutes.
  32. The method according to claim 24, wherein the cleaning liquid contains hydrogen nitrate, in particular 10wt. %to 70wt. %, especially 20wt. %to 70wt. %of hydrogen nitrate; preferably, the cleaning liquid in particular has a temperature TR, wherein: 20℃ ≤ TR ≤ 65℃, especially 23℃ ≤ TR ≤ 60℃.
  33. The method according to claim 24, wherein the semiconductor substrate is kept in the cleaning liquid for 0.5-3 minutes.
  34. The method according to claim 24, wherein the method further comprises using the rinsing liquid to rinse the semiconductor substrate output from the first process liquid, the second process liquid, and/or the cleaning liquid; wherein the rinse liquid is preferably water, especially deionized water; preferably, the rinsing is a spraying type or an immersion type rinsing.
  35. The method according to claim 24, wherein the method further comprises the following steps in sequence: post-treating the semiconductor substrate, which is output from the cleaning liquid and subsequently rinsed with the rinsing liquid, with an  aqueous solution preferably consisting of hydrofluoric acid and nitric acid, rinsing the post-treated semiconductor substrate with a rinsing liquid, and drying the semiconductor substrate.
  36. The method according to claim 24, wherein the method further comprises performing a further alkaline etching to the cleaned, inverted-pyramid-type textured surface structure in the absence of said Ag particles by means of a third process liquid in order to form a enlarged inverted-pyramid-type textured surface structure.
  37. The method according to claim 36, wherein the enlarged inverted-pyramid-type textured surface structure is formed by a second structure element, wherein at least 70%of the second structure elements have a maximum dimension of 250 nm to 1200 nm, especially 400 nm to 1000 nm.
  38. The method according to claim 36, wherein the third process liquid comprises an alkaline liquid and a surface wetting agent, in particular the alkaline liquid comprises potassium hydroxide (KOH) and/or sodium hydroxide (NaOH) and/or potassium/sodium carbonate (K 2CO 3/Na 2CO 3) ; preferably, the third process liquid comprises 0.1wt. %to 4wt. %, especially 0.5wt. %to 3.5wt. %of potassium hydroxide or 0.05wt. %to 3wt. %, especially 0.25wt. %to 2wt. %of sodium hydroxide and contains 0.1wt. %to 5wt. %, especially 0.3wt. %to 3.5wt. %of the surface wetting agent; preferably, the third process liquid has a temperature T3, wherein: 50℃ ≤ T3 ≤ 100℃, especially 60℃ ≤ T2 ≤ 95℃.
  39. The method according to claim 36, wherein the semiconductor substrate is kept in the third process liquid for 1-5 minutes.
  40. The method according to claim 36, wherein the method further comprises rinsing the semiconductor substrate output from the third process liquid with a rinsing liquid; preferably, the rinsing liquid is water, in particular deionized water.
  41. The method according to claim 40, wherein the method further comprises the following steps in sequence: post-treating the semiconductor substrate, which is output  from the third process liquid and subsequently rinsed with the rinsing liquid, with an aqueous solution preferable consisting of hydrofluoric acid and hydrochloric acid, rinsing the semiconductor substrate with a rinsing liquid, and drying the semiconductor substrate.
  42. The method according to one of claims 24 to 41, wherein the method steps are carried out in an inline type apparatus and the semiconductor substrate is continuously conveyed.
  43. The method according to claim 42, wherein the rinsed or non-rinsed semiconductor substrate after cleaning by means of the cleaning liquid in said inline type apparatus is transferred in wet state directly to another inline type apparatus for post-treating.
  44. The method according to claim 42, wherein the rinsed or non-rinsed semiconductor substrate after further alkaline etching by means of the third process liquid in said inline type apparatus is transferred in wet state directly to another inline type apparatus for post-treating.
  45. The method according to one of claims 24 to 41, wherein the method steps are carried out in a batch type apparatus and the semiconductor substrate is conveyed in batch.
  46. The method according to claim 45, wherein the rinsed or non-rinsed semiconductor substrate after cleaning with the cleaning liquid in the batch type apparatus is transferred in a wet state directly to another batch type device for post-treating.
  47. The method according to claim 45, wherein the semiconductor substrate output from the cleaning device and then rinsed with a rinsing liquid is sufficiently dried so that the dried plurality of semiconductor substrates when stacked together would not be connected to each other due to residual moisture in the surface structure.
  48. The method according to one of claims 24 to 47, wherein the semiconductor  substrate is single crystalline semiconductor substrate, in particular single crystalline silicon substrate.
PCT/CN2019/088548 2018-05-25 2019-05-27 Method and apparatus for surface texturing of semiconductor substrate WO2019223805A1 (en)

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CN102646758A (en) * 2012-05-05 2012-08-22 云南师范大学 Modification method of mono-crystalline silicon wafer surfaces for solar batteries
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