GB2486883A - Method and apparatus for surface texture modification of silicon wafers for photovoltaic cell devices - Google Patents

Method and apparatus for surface texture modification of silicon wafers for photovoltaic cell devices Download PDF

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GB2486883A
GB2486883A GB1021693.5A GB201021693A GB2486883A GB 2486883 A GB2486883 A GB 2486883A GB 201021693 A GB201021693 A GB 201021693A GB 2486883 A GB2486883 A GB 2486883A
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substrate
gas
etchant
reactor
silicon
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GB201021693D0 (en
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Edward Duffy
Laurent Clochard
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Ultra High Vacuum Solutions Ltd
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Ultra High Vacuum Solutions Ltd
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Priority to GB1021693.5A priority Critical patent/GB2486883A/en
Publication of GB201021693D0 publication Critical patent/GB201021693D0/en
Priority to ES11724988.8T priority patent/ES2643645T3/en
Priority to PL11724988T priority patent/PL2569802T3/en
Priority to LTEP11724988.8T priority patent/LT2569802T/en
Priority to US13/696,730 priority patent/US9548224B2/en
Priority to EP11724988.8A priority patent/EP2569802B1/en
Priority to PCT/EP2011/057633 priority patent/WO2011141516A2/en
Priority to JP2013509564A priority patent/JP6012597B2/en
Publication of GB2486883A publication Critical patent/GB2486883A/en
Withdrawn legal-status Critical Current

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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
    • H01L21/67155—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
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    • 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
    • H01L21/02041—Cleaning
    • H01L21/02043—Cleaning before device manufacture, i.e. Begin-Of-Line process
    • H01L21/02046—Dry cleaning only
    • 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
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    • 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
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3105—After-treatment
    • H01L21/311—Etching the insulating layers by chemical or physical means
    • H01L21/31105—Etching inorganic layers
    • H01L21/31111—Etching inorganic layers by chemical means
    • H01L21/31116—Etching inorganic layers by chemical means by dry-etching
    • H—ELECTRICITY
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    • 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
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3105—After-treatment
    • H01L21/311—Etching the insulating layers by chemical or physical means
    • H01L21/31127—Etching organic layers
    • H01L21/31133—Etching organic layers by chemical means
    • H01L21/31138—Etching organic layers by chemical means by dry-etching
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    • 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
    • H01L21/67069—Apparatus for fluid treatment for etching for drying etching
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    • 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
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    • 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
    • H01L31/02002—Arrangements for conducting electric current to or from the device in operations
    • H01L31/02005—Arrangements for conducting electric current to or from the device in operations for device characterised by at least one potential jump barrier or surface barrier
    • H01L31/02008—Arrangements for conducting electric current to or from the device in operations for device characterised by at least one potential jump barrier or surface barrier for solar cells or solar cell modules
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
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    • H01L31/02—Details
    • H01L31/0216—Coatings
    • H01L31/02161—Coatings for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/02167—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H01L31/02168—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells the coatings being antireflective or having enhancing optical properties for the solar cells
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    • H01—ELECTRIC ELEMENTS
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    • 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
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    • 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
    • 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

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Abstract

A method or apparatus for modifying the surface structure of a silicon substrate or deposited layer which is suitable for etching silicon wafers or for making photovoltaic (PV) devices and capacitive sensing touch screens comprising disposing the substrate 30 or deposited layer on a moveable carrier e.g. conveyor belt 32, pre-heating the substrate 30 or deposited layer (e.g. using heater 24), continuously moving the substrate 30 or deposited layer through an atmospheric reactor 20 under an etchant delivering feature and etching the substrate 30 or deposited layer by applying at least one etchant in gas form under pressure e.g. atmospheric pressure. The etchant gas may be selected from the group comprising fluoride-containing gases e.g. tetrafluoromethane or elemental fluorine and chlorine-based compounds e.g. tetrachloromethane and may also comprise any other thermally activated silicon etching gas. The etchant gas may be thermally activated without using a plasma. The reaction region of the atmospheric reactor 20 may be sealed by purging gas curtains located outside a heating zone (fig. 4). Exhaust plenums 14, 15 funnel exhaust gases outside housing 2. Multiple lanes of substrate (30, fig. 3) or deposited layer may be placed on the conveyor belt (32, fig. 3).

Description

Method and apparatus for surface texture modification of silicon wafers for photovoltaic cell devices
Field of the Invention
The invention relates to a method and apparatus for dry chemical texturing of silicon based photovoltaic (PV) devices. More particularly, the invention relates to a method and apparatus for inline, continuous pass-through dry chemical etching at atmospheric pressure without the use of a plasma.
ic2rQlinSIii th lQveiitiwi Solar cells are photovoltaic (PV) semiconductor devices that convert sunlight into electricity. Photons from the sunlight knock electrons loose from their atoms, generating a current through the material. These photovoltaic semiconductors may be made from; single crystal silicon (mono-crystalline), polycrystalline (multi-crystalline) silicon, amorphous silicon or other compound semiconductor materials.
In simple terms an electrical P-N junction is created in PY material or substrate i.e. silicon wafer. This material is then connected to an electrical circuit my means of the positive and negative electrode. When exposed to sunlight a current is generated in the PY material due to a photoelectric effect.
There are various processing methods used to manufacture a PY solar cell, and several manufacturing process steps are required. Of particular interest for this invention are the etching steps, where a controlled amount of material has to removed from the substrate and deposited layers; including wafer damage removal, cleaning, texturing, polishing, and by-products (PSO) removal.
One particular stcp of interest for this invention is the texturing of the substratc material; a light trapping pattern is formed on the sunny side of the wafer, leading to increase cell efficiency. Texturing the surface of the substrate will enlarge the surface area and lower the reflectivity of the base material therefore capturing more of the light that falls on the surface. A smooth surface tcxturing of the back-side of thc wafer is desirable as it leads to better passivation and increased overall cell efficiency.
Currently these steps is carried out via a wet chemical process where the silicon substrates are dipped in a heated Acidic or Alkaline solution for a period of time to fonn uneven patterns on the surface of the substrate.
The problems associated with wet chemical etching for crystalline solar cells production are: 1. Very large amounts of water and other chemicals are consumed during these wet chemical etch steps.
2. Wet etch process is not adequate for thinner wafers (clôOum).
3. Texturing by the traditional alkaline wet chemical etching of the cheaper multi-crystalline silicon solar cell does not give satisfactory antirefiective properties.
This is due to anisotropic nature of the multi-crystalline silicon substrate.
4. The process of record for multi-crystalline silicon solar cell manufacturing is to use an additional wet etch step using an acidic solution e.g. a mix of HF and HNO3. This "Isotexturing" results in lower reflection that the traditional anisotropic etching on multi-crystalline substrates. However, as outlined in point 1 it does not give the same results as traditional alkaline etching on mono-crystalline substrates. This leaves the overall cell conversion efficiencies of multi-crystalline silicon solar cells to lag behind the conversion efficiencies of the more expensive mono-crystalline silicon solar cells.
5. The wet etch equipment can be very large (in same case up to 17 m long) and has limited process throughput capability.
6. Wet etch efficiency is highly dependent the crystallographic structure of the wafer and requires different chemicals recipes for mono or multi-Si wafer.
7. Limited single sides of the wet process that does not provide for decoupled surface treatment.
8. Wet etch needs some defects in the wafer to work. It does not work from a smooth surface.
Dry etching plasma-less process have hcen recently used for vacuum chamber cleaning application. For example as described in US2008 142046 molecular Fluorine (F2) was used for the cleaning of Silicon Nitride (SiNx) in chemical vacuum deposition (CVD) chamber. Pre-diluted Fluorine in an inert gas is delivered into the vacuum chamber and S the fluorine is thermally dissociated by heating the chamber to a temperature between 230 to 565 deg C. The undesired silicon nitride is removed from the inner chamber's surfaces by chemical reaction. This vacuum chamber cleaning process is required in order to prevent cross process contamination.
US 6,500,356 (B2) describes a dry etching process that selectively etch Silicon on electronic devices, without etching Silicon oxide or silicon nitride. The specification is very much restricted to holding the substrate in the interior of a vacuum chamber and supplying the etch gas to the same chamber, at less than atmospheric pressure (260 millitorr (mT)).
In US 2008/0305643 an atniospheric plasma etching apparatus to remove the doped surface layers on the back faces of a crystalline solar wafer is described. Similarly, US 2010/0062608 describes an apparatus to selectively etch the phosphorus silicate glass (PSO) formed during the diffusion process using a plasma-based process.
Dry texturing of PY solar cells has been under development for some time. There have been numerous publications using traditional vacuum based plasma etching techniques.
The main problem with these methods is the PY material is damaged caused by the ions from the plasma during the etching process. Although some progress has been made in regard to this plasma damage issue, the commercialisation of such solutions is unlikely as the cost of the vacuum-based systems is prohibitive and the low throughput is not suitable for large-scale solar PY cell manufacturing.
There is therefore a need to provide a process and apparatus for dry etching/texturing of crystalline silicon photovoltaic solar cells which overcomes the above-mentioned problems.
Summary of the invention
According to the present invention there is provided, as set out in the appended claims, a method to modify the surface structure of a silicon substrate or deposited silicon layer in a controllable manner using gas only for making photovoltaic (PV) devices, the method comprising the steps of: disposing the substrate or deposited layer on a moveable carrier; pre-heating the substrate or deposited layer; continuously moving the substrate or deposited layer for etching through an atmospheric reactor; and continuously moving the substrate under an etchant delivering feature inside the reactor by applying at least one etchant in gas form under pressure to the substrate or deposited layer in the reactor, wherein the at least one etchant gas is selected from the group comprising fluoride-containing gases and chlorine-based compounds.
The technical problem that has been solved is the provision of a high throughput dry etching method which does not require plasma to aid the etching process using fluoride-containing gases and chlorine-based compounds and which is performed at atmospheric pressure. The use of elemental fluorine, which has a significantly lower bonding energy than any of the other etchants used to date, allows for the use of much lower power energy source to crack the elemental fluorine in to its etching radicals. As the method can he run at atmospheric pressure, this allows the continuous movement of the work pieces through the etching zone and enables much higher throughput required by the PY industry. The use of elemental or molecular fluorine without the aid of plasma at atmospheric pressure for dry etching of substrates provides a simple effective process for texturing or etching a substrate or deposited layer.
In one embodiment the the etchant is activated thermally without the help of a plasma.
In one embodiment the process is carried out as a continuous pass through process.
In one embodiment the pressure is atmospheric pressure.
in one embodiment the reaction region of the reactor is sealed by purging gas curtains.
in one embodiment the pre-heating zone is located inside the purge gas curtains.
in onc embodiment the resulting substrate's surface texture is rough to reduce its reflectivity and increase the light absorbed.
in one embodiment the resulting substrate's surface texture is smooth.
in one embodiment the etchant gas is molecular or atomic Fluorine, or any other silicon etching gas with an energy bond value that allows for thermal activation.
in one embodiment the fluoride-containing gases may be selected from the group comprising tetrafluoromethane, trifluoromethane, carbonyl fluoride, sulphur bexafluoride, nitrogen trifluoride, xenon difluoride. and elemental fluorine.
in one embodiment, the chlorine-based compounds may be selected from the group comprising tetraehloromethane, a mixture of triehlorosilane and hydrogen, and hydrogen chloride.
Each etch gas may have its own method of etching radical formation.
in one embodiment the substrate for etching may be selected from the group comprising a photovoltaic solar cell, a silicon wafer, or a layer deposited on substrates such as, for example, glass, A1TiC (Aluminum Titanium Carbon), ITO (Indium tin oxide) and FR4 laminates (woven fibreglass cloth with an epoxy resin binder that is flame resistant).
in another embodiment this atmospheric dry etching technology may be used in conjunction with laser micromachining process. The laser machining/drilling damages a region of the material being cut and a dry etch may be performed after or during the machining/drill process to remove/repair the damaged regions.
in another embodiment, this method may he used in the manufacture of capacitive sensing touch screens, where a matrix of micro holes are etched into the ITO and FR4 fiberglass reinforced epoxy laminates and PCBs (printed circuit boards).
According to a further embodiment of the invention there is provided a apparatus to modify the surface structure of a silicon substrate or deposited silicon layer in a controllable manner using gas only, suitable for making photovoltaic (PV) devices, the S apparatus comprising: (i) a housing; (ii) an atmospheric reactor; (iii) at least one etchant gas exhaust plenum; (iv) means for disposing the substrate or deposited layer on a moveable carrier; (v) means for pre-heating the substrate or deposited layer; (vi) means for continuously moving the substrate or deposited layer for etching through the atmospheric reactor; and (vii) means for continuously moving the substrate under an etchant delivering feature inside the reactor by applying at least one etchant in gas form under pressure to the substrate or deposited layer in the reactor, wherein the at least one etchant gas is selected from the group comprising fluoride-containing gases and chlorine-based compounds.
According to another aspect of the present invention there is provided an apparatus for dry etching a substrate comprising: (i) a housing; (ii) an etchant gas delivery reactor; (iii) at least one etchant gas exhaust plenum; and (iv) a means for delivering etchant gas to the housing at atmospheric pressure.
In one embodiment the etchant gas in the delivery reactor may be heated to produce base radicals to perform the dry etching.
In one embodiment the delivery reactor may bc heated to a temperature of between about 100 and 300 deg C. in a further aspect of the present invention, there is provided a device comprising a substrate etched by the method described above.
In one embodiment the device may be selected from the group comprising a photovoltaic solar cell, a silicon wafer, a glass substrate, a layer deposited on a substrate (amoiphous silicon, SiNx, SiOx) In another embodiment there is provided a method for dry etching a substrate or deposited layer in order to modify its surface structure or remove a controlled thickness, comprising the steps of: (i) disposing the substrate for etching on a support substrate; (ii) pre-heating the substrate; (iii) delivering the substrate for etching to an etching chamber; and (iv) applying at least one etehant in gas form under pressure to the substrate in the chamber, wherein the at least one etchant gas is selected from the group comprising fluoride-containing gases and chlorine-based compounds. Preferably the pressure may be atmospheric pressure.
Brief Description of the Drawings
The invention will he more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:-Figure 1 is a flow diagram illustrating the dry etching process of the present invention; Figure 2 illustrates a section view of a dry etching apparatus of the present invention; Figure 3 illustrates a layout of the process of the present invention for continuous in-line processing of substrates at atmospheric pressure; and Figure 4 illustrates another section view of a dry etching apparatus according to another embodiment of the invention.
Detailed Description of the Drawints
The present invention uses a novel dry-etch chemistry where the etching is not limited by the crystalline structure of the surface to he etched. The etchants are delivered in gaseous form and are applied to the surface to be etched at atmospheric pressure. There is no requirement for the etching zone to be contained in a vacuum chamber.
Figure 1 illustrates a general flow diagram of the method of the present invention to modify the surface structure of a silicon substrate or deposited silicon layer in a controllable manner using gas only, suitable for making photovoltaic (PY) devices, described in more detail with respect to Figures 2 to 4.
As illustrated in Figures 2 and 3, there is provided an apparatus to carry out the method of the invention. The apparatus is referred to generally with reference numeral 1 according to one embodiment of the invention. The apparatus comprises a housing 2 having walls 4, a cover 6, and a support 8 opposite and in a parallel plane to the cover 6.
Within the housing 2 are located gas isolation seal modules 10, ii nestled close to walls 4 and resting on the support 8. Inside the modules 10, ii and positioned towards the centre of the housing 2 are etchant gas exhaust plenums 14, 15, which are juxtaposed the modules 10,11 respectively. The exhaust plenums 14, 15 are connected to each other via piping 17, 18 which funnels exhaust gases from inside the housing 2 to outside via a chute 19.
Situated between plenums 14, 15 is an etchant gas delivery reactor 20. The delivery reactor 20 emits a curtain of gas 22 from an aperture 24 at a base 26 of the reactor 20.
Sitting on top of the reactor 20 is a water cooling device 28. Etching gas is delivered to the water cooling device 28 which pumps the cooled gas into the delivery reactor 20 where it is heated to a suitable temperature. The heated gas is then emitted from the aperture 24 onto a substrate 30. Recycled purged etch gas or an etch gas mixture is pumped into the reactor 20 via piping 32.
In use, as illustrated in Figure 3, multiple lanes of the substrate 30 are placed on a conveyor belt 32 and delivered to a heating device 34. The substrate is pre-beated to a temperature of between about 300°C to about 400°C prior to passing into the apparatus 1. The substrate 30 is exposed to heated etchant gas in a chamber 40 of the apparatus 1.
Once the substrate 30 has been exposed to etehant gas for a predetermined period of time, the conveyor belt 32 moves the etched substrate 30 through the apparatus I and the next substrate to be etched is exposed to etchant gas.
it is the preferred embodiment of this invention to use elemental fluorine F2 gas that is cracked or energized by simple heating in the delivery reactor 20 to produce fluorine base radicals to perform the etching on the surface of the substrates 30. it is envisaged that other etching processes could also be performed in this way not only in the PV solar cell manufacturing area but also in the Semiconductor and iC packaging industry.
Referring to Figure 4 illustrates an atmospheric reactor adapted to perform the method of the invention. The substrate or deposited layer is placed on a moveable carrier for example a substrate conveyor that is adapted to move continuously to deliver the substrate to a heating zone. The heating zone can be in or outside the reaction area. The reaction area can he sealed off by purge curtains, or other suitable sealing means, at the entrance and the exit. The preheating zone can be positioned before or after the purge curtains. The substrate or deposited layer is preheated by a heater; and is subsequently delivered to the reactor zone by the continuous conveyor. The conveyor moves the substrate through the reaction area in a controlled manner such that under an etchant delivering feature inside the reactor at least one etchant in gas form is applied under pressure to the substrate or deposited layer in the reactor. The at least one etchant gas is selected from the group comprising fluoride-containing gases and chlorine-based compounds.
In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms "include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.
The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.

Claims (20)

  1. Claims 1. A method to modify the surface structure of a silicon substrate or deposited silicon layer in a controllable manner using gas only, suitable for making photovoltaic (PV) devices, the method comprising the steps of: disposing the substrate or deposited layer on a moveable carrier; pre-heating the substrate or deposited layer; continuously moving the substrate or deposited layer for etching through an atmospheric reactor; and continuously moving the substrate under an etchant delivering feature inside the reactor by applying at least one etchant in gas form under pressure to the substrate or deposited layer in the reactor, wherein the at least one etchant gas is selected from the group comprising fluoride-containing gases and chlorine-based compounds.
  2. 2. A method according to claim 1 wherein the etchant is activated thermally without the need of a plasma.
  3. 3. A method according to claim 1 wherein the process is carried out as a continuous pass through process.
  4. 4. A method according to any preceding claim wherein the pressure is atmospheric pressure.
  5. 5. A method according to any preceding claim wherein the reaction region of the reactor is sealed by purging gas curtains.
  6. 6. A method according to claim 5 wherein the pre-heating zone is located inside the purge gas curtains.
  7. 7. A method according to any preceding claim wherein the resulting substrate's surface texture is rough to reduce its reflectivity and increase the light absorbed.
  8. 8. A method according to any of claims 1 to 6 wherein the resulting substrate's surface texture is smooth.
  9. 9. A method according to any preceding claim, wherein the etchant gas is molecular or atomic Fluorine, or any other silicon etching gas with an energy bond value that allows for thermal activation.
  10. IO.A method according to any preceding claim, wherein the fluoride-containing gases are selected from the group comprising tetrafluoromethane, trifluoromethane, carbonyl fluoride, sulphur hexafluoride, nitrogen trifluoride, xenon difluoride, and elemental fluorine.
  11. I l.A method according to any preceding claim, wherein the chlorine-based compounds are selected from the group comprising tetrachioromethane, a mixture of trichlorosilane and hydrogen, and hydrogen chloride.
  12. 12.A method according to any preceding claim wherein oxygen or ozone is additionally provided to enhance the texturing process.
  13. 13.A method according to any preceding claim wherein the substrate for etching is selected from the group comprising a photovoltaic solar cell, a silicon waler, or a layer deposited on a substrate selected from the group comprising glass, AITiC, ITO, and FR4 laminates.
  14. I4.A method according to any preceding claims performed in the absence of plasma.
  15. 15.An apparatus to modify the surface structure of a silicon substrate or deposited silicon layer in a controllable manner using gas only, suitable for making photovoltaic (PV) devices, the apparatus comprising: (i) a housing; (ii) an atmospheric reactor; (iii) at least one etchant gas exhaust plenum; (iv) means for disposing the substrate or deposited layer on a moveable carrier; (v) means for pre-heating the substrate or deposited layer; (vi) a conveyor adapted for continuously moving the substrate or deposited layer for etching through the atmospheric reactor; and (vii) means for continuously moving the substrate using the conveyor under S an etchant delivering feature inside the reactor by applying at least one etchant in gas form under pressure to the substrate or deposited layer in the reactor, wherein the at least one etchant gas is selected from the group comprising fluoride-containing gases and chlorine-based compounds.
  16. 16.An apparatus according to Claim 115 wherein the etchant gas in the delivery reactor is heated to produce base radicals to perform the dry etching.
  17. l7.An apparatus according to Claim 115 or Claim 116 wherein the delivery reactor is heated to a temperature of between about 100°C and about 300°C.
  18. 18.A device comprising a substrate etched by the method of any of Claims 1 to 14.
  19. 19. A device according to Claim 18 selected from the group comprising a photovoltaic solar cell a silicon wafer, a glass substrate, or a layer deposited on a substrate (amorphous silicon, SiNx, SiOx).
  20. 20. A process to modify the surface structure of a silicon substrate or deposited silicon layer, as substantially hereinhefore described with reference to the accompanyingdescription and/or drawings.
GB1021693.5A 2010-05-11 2010-12-22 Method and apparatus for surface texture modification of silicon wafers for photovoltaic cell devices Withdrawn GB2486883A (en)

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GB1021693.5A GB2486883A (en) 2010-12-22 2010-12-22 Method and apparatus for surface texture modification of silicon wafers for photovoltaic cell devices
ES11724988.8T ES2643645T3 (en) 2010-05-11 2011-05-11 Method to control the modification of the surface texture of silicon wafers for photovoltaic cell devices
PL11724988T PL2569802T3 (en) 2010-05-11 2011-05-11 Method to control surface texture modification of silicon wafers for photovoltaic cell devices
LTEP11724988.8T LT2569802T (en) 2010-05-11 2011-05-11 Method to control surface texture modification of silicon wafers for photovoltaic cell devices
US13/696,730 US9548224B2 (en) 2010-05-11 2011-05-11 Method and apparatus to control surface texture modification of silicon wafers for photovoltaic cell devices
EP11724988.8A EP2569802B1 (en) 2010-05-11 2011-05-11 Method to control surface texture modification of silicon wafers for photovoltaic cell devices
PCT/EP2011/057633 WO2011141516A2 (en) 2010-05-11 2011-05-11 Method and apparatus to control surface texture modification of silicon wafers for photovoltaic cell devices
JP2013509564A JP6012597B2 (en) 2010-05-11 2011-05-11 Method and apparatus for controlling surface texture modification of silicon wafers for photovoltaic cell devices

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